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Design of Instantaneous High Power Supply System with power distribution management for portable military devices
Journal of Power Sources 288 (2015) 328e336
Contents lists available at ScienceDirect
Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour
Design of Instantaneous High Power Supply System with power distribution management for portable military devices Kiho Kwak*, Dongmin Kwak, Joohong Yoon Agency for Defense Development, South Korea
h i g h l i g h t s A power board supplying instantaneous high power to pulse loads. A hybrid battery consisted of a D-size spiral type Li-SOCL2 and supercapacitors. A variable current limiting and 2-step supercapacitor charging methodology.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 26 December 2014 Received in revised form 27 February 2015 Accepted 12 April 2015 Available online
A design of an Instantaneous High Power Supply System (IHPSS) with a power distribution management (PDM) for portable military devices is newly addressed. The system includes a power board and a hybrid battery that can not only supply instantaneous high power but also maintain stable operation at critical low temperature (30 C). The power leakage and battery overcharge are effectively prevented by the optimal PDM. The performance of the proposed system under the required pulse loads and the operating conditions of a Korean Advanced Combat Rifle employed in the battlefield is modeled with simulations and verified experimentally. The system with the IHPSS charged the fuse setter with 1.7 times higher voltage (8.6 V) than the one without (5.4 V) under the pulse discharging rate (1 A at 0.5 duty, 1 ms) for 500 ms. © 2015 Elsevier B.V. All rights reserved.
Keywords: Instantaneous High Power Supply System Hybrid battery Supercapacitor Power distribution management Portable military device
1. Introduction In recent years, digitization of the battlefield leads to increased demand for portable military equipment powered by batteries. The most challenging but crucial problem with these portable military devices is the development of a stable system with long operation time and minimal power consumption. Size, weight, and power are the most important elements in portable military device design because a soldier should be able to carry and to operate without being overburdened. Well-designed power supply system can greatly simplify the portable military device design because the power consumption directly impacts the size of the required batteries, and larger batteries comprise the size of and weight constraints of portable devices. A battery has been a big design constraint for small military devices since the operation time and power consumption is
* Corresponding author. E-mail address: [email protected] (K. Kwak). http://dx.doi.org/10.1016/j.jpowsour.2015.04.061 0378-7753/© 2015 Elsevier B.V. All rights reserved.
proportional to the number, size and capacity of the batteries. Most commercial portable electric devices are rarely operated at temperatures lower than 0 C or higher than 50 C. Small and slim rechargeable battery packs or lower price alkaline nonrechargeable cells are sufficient for such devices. However, a battery for military devices should be more robust than commercial products, because the military devices should be able to maintain high performance under more extreme environment (40 Ce65 C) even when capacity and performance of batteries drops at lower temperature [1,2]. Moreover, it is very difficult to supply different types of power to various loads requiring instantaneous high power with a single battery. The battery may break down or cause the system to malfunction if the battery is designed to supply constant power and instantaneous pulsed current for a few hundred millisecond at the same time. Ordinary systems do not require constant monitoring of power supply and real time power distribution because they are designed to operate with marginal battery capacity. However, portable military equipment with minimal size, weight and limited
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power source should be able to control power output according to the operation status and supply instant power exceeding the maximum power output to the systems [3]. A hybrid power source with a combination of a battery and supercapacitors (SC) takes advantage of the energy density of the primary battery for long operational time and the power density of the secondary SC for pulse power requirement. Generally, a battery has higher energy density but lower power density than an SC and vice versa [4,5]. The hybrid power sources can meet the pulse power requirements with higher specific power and efficiency than batteries alone. Moreover, an SC is able to reduce the stress on a battery and extend the operational life of the battery [6]. Furthermore, in order to enhance the performance of the hybrid power source and to ensure charge balance and robustness of the system power, it is necessary to adopt power distribution management (PDM). The PDM is used to schedule the allocation of available power and energy to electric loads on a subsystem or component level. Effectively, it ensures the controlled function delivery of individual electric features by prioritization. By setting the electric feature priorities, the PDM keeps the system voltage stability under pulse loads, minimizes the power loss of the system, and extends the operational life of the battery [6]. This paper proposes an Instantaneous High Power Supply System (IHPSS) for portable military devices. The IHPSS consists of a set of a power board and a hybrid battery that supplies instantaneous high power and maintains stable operation over large operating temperature range (40 Ce65 C). The IHPSS is able to supply continuous power and instantaneous high power simultaneously and prevent power leakage and battery overcharge through optimal power distribution management. The performance of the proposed system is verified through several experiments. The IHPSS has been used for the fire control system of the Korean Advanced Combat Rifle, K11 employed in the battlefield [7,8]. The contributions of this paper are threefold: (i) design of a power board supplying instantaneous high power to pulse loads, (ii) design of a hybrid battery consisted of a D-size spiral type Lithium-Thionyl-Chloride battery (Li-SOCL2) and SCs, and (iii) the development of a variable current limiting and 2-step SC charging methodology using an optimal power distribution algorithm based on precise status information about our system.
329
Fig. 2. Overall power requirement of K11 FCS. The power board supply various types of voltages for each electric components (blue). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
and 5.56 mm NATO ammunition with automatic electro-optical Fire Control System (FCS) to defeat targets at extended ranges as shown in Fig. 1. K11 is able to strike point targets and especially hidden target in a fox hole with 20 mm air bursting ammunition. K11 maximizes combat effectiveness with a new concept and technology, such as precise air bursting against defilade targets, FCS at day and night, and lightweight dual barrel rifle [8]. The K11 FCS is a small and complex system that has functionalities of the FCS of an armored vehicle such as a tank or an infantry vehicle into a small firearms, such as day and night target detection, range finding, ballistic trajectory computation, and wireless energy charging and signal transmission. For these functionalities, the K11 FCS consists of complex optical modules with a thermal detector, a Laser Range Finder (LRF), a ballistic computer, a IHPSS, and a fuse setter. The K11 FCS should operate at day and night under all weather conditions. The FCS provides the electronic aiming reticle after measuring the distance and computing the ballistic trajectory to the target, and programs and charge the air-burst ammo through the fuse setter. The air-burst ammo is set to explode at specific range above of the target.
2. Overview of Korean Advanced Combat Rifle (K11)
3. Instantaneous High Power Supply System (IHPSS) design
K11, a dual barrel air burst weapon, has been employed in Korea army since 2010 [9]. K11 combines the 20 mm air burst ammunition
The portable military system such as the K11 FCS should be able to operate under more extreme conditions than commercial
Fig. 1. Overview of Korean Advanced Combat Rifle, K11.
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systems. If the system should maintain stable operation at low temperature and then supply instantaneous high power with only a single battery, a new approaches to design the optimal power supply for the system is required. To design the optimal power supply, thorough analysis on the load and operation condition of the system is required. In the case of the K11 FCS that needs various types of power sources (see Fig. 2), it should supply instantaneous high power to the LRF module and the fuse setter and compensate the battery response time under all temperature conditions required for portable military devices. In this paper, the IHPSS for the K11 FCS that guarantees stable operation under all temperature and load conditions is presented. The power supply system consists of two main components: (i) a power board that compensates a battery response time and supplies instantaneous high power to the loads and (ii) a D-size hybrid battery with a spiral type Li-SOCL2 and SCs that compensates poor discharging characteristic under low temperature. The performance of the proposed system is verified with simulations and experiments under required pulse loads and operating conditions. 3.1. Power board design The power board supplies instantaneous high power to the pulse loads such as an LRF module and a fuse setter. In order to design the power board, the capacitance of the SC installed on the board that supplies high power to the load instead of the primary power source as a battery is calculated. The capacitance is determined by first inspect which load needs the highest power during operation. The K11 FCS requires instantaneous high power when we measure a distance using the LRF module and charge energy into the fuse setter. Then the capacitance of the SC is calculated in consideration of energy required for both the LRF module and the fuse setter. In the K11 FCS, the power board supplies energy into the fuse setter for 500 ms. Given the average voltage and current, and the minimum voltage, the energy Efuse for the fuse setter is estimated as follows:
VMax ¼ 7:2V: Maximum storage voltage VMin ¼ 6:0V: Minimum operating voltage Vfuse ¼ 6:4V: Average voltage for fuse setter charging Ifuse ¼ 1:0A: Average current for fuse setter charging Tfuse ¼ 0:5sec: Fuse setter charging time
Efuse ¼ Pfuse Tfuse ¼ ðVfuse Ifuse Þ Tfuse ¼ ð6:4V 1:0AÞ 0:5sec ¼ 3:2J
(1)
The capacitance Cfuse of the SC is derived using the following equation:
Cfuse ¼
2Efuse 2 2 VMax VMin
¼ 0:4F
(2)
Although energy charging for the fuse setter and LRF firing do not occur at the same time we should estimate the capacitance of the SC considering the LRF module. The system supplies energy to the fuse setter with a time delay (250e300 ms) after measuring the distance to a target object with the LRF. However, these sequential event does not mean that the capacitance 0.4 F is enough to supply power for both processes. It is not possible to fully charge the 0.4 F SC with limited current within 300 ms because the LRF module requires the maximum 3 J energy. The total capacitance of the SC is calculated taken into account the maximum capacitance for the LRF
Fig. 3. Circuit of an SC in parallel with a battery.
operation and the rechargeable capacitance within 300 ms. As the result, the system needs more than 0.8 F SC which includes extra added 0.4 F. The charging and discharging characteristics of the SC are obtained from a simulation based on the measured capacitance. The basic circuit considered in this analysis is shown in Fig. 3 [6]. The SC is modeled by a nominal capacitance CC (1 F/7.5 V) and equivalent series resistance RC (0.25 U), and the battery by an ideal voltage source VB and an internal resistance RB (0.5 U). For the performance analysis of the SC on the power board, the battery supply voltage is set to 7.2 V which is equivalent to the voltage requirement for the LRF operation and the energy charging for the fuse setter. The equivalent load condition for charging the real fuse setter was used. The input current is limited to 1.5 A and the maximum voltage for the SC is set to 7.2 V as in the real system. Fig. 4 shows the discharge current and the voltage drop patterns of the battery and the SC installed on the power board during the fuse setter charging. Stable power is supplied to the system as the SC compensates the slow discharge characteristics of battery in the first 500 ms of initial charging. The result shows that five second is required to fully charge the capacitor after first discharging. A power board capable of supplying instantaneous high power to loads is designed based on the simulation result. Fig. 5 shows the voltage and current patterns of the battery and the SC on the designed power board. The procedure was as follows: (i) distance is measured with LRF, (ii) after 250 ms, the fuse setter first charges, and (iii) thereafter, energy is retransmitted to the fuse setter for 500 ms every 5 s. It is confirmed that supplying instantaneous high power is feasible with a power board equipped with SCs and a D-size LiSOCL2 battery. However, as shown in the experiment, the maximum voltage drop of the SC is 10 times higher than the voltage drop in the simulation. The maximum voltage drop of the battery is 0.6 V during the LRF operation the fuse setter charging, which is lower than the minimum system input voltage 2.4 V. The K11 FCS should not only be able to supply instantaneous high power to the LRF module and the fuse setter, but also supply continuous power to other loads such as the main control board and the IR module and operate at as low temperature as 30 C. Since the experiment results were collected at room temperature, it is difficult to maintain stable operation of the system at low temperature due to poor discharging characteristic. 3.2. Hybrid battery design A spiral type Li-SOCL2 battery used for the main power source of K11 FCS is robust against instantaneous current discharge compared to other commercial batteries. However, the discharging performance of Li-SOCL2 battery deteriorates at low temperature and instantaneous power supply (See Fig. 6) [10]. To solve the
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Fig. 4. Simulation result of the discharge current and the voltage drop. Vcap (dark blue) and Vout (pink) are the voltage of the SC and the pulse load respectively. iC (blue) and iB (red) are the current of the SC and the battery respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 5. Discharge current and voltage drop by using the proposed power board. Blue is the voltage of the SC on the power board. Red and yellow are the current and voltage of the battery. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
problem, we built a hybrid battery consisted of a D-size Li-SOCL2 battery and SCs to minimize the battery voltage drop at instantaneous high power supply and performance deterioration at low temperature. The performance of the hybrid battery is verified through a simulation under the K11 operation scenario at the night mode (See Fig. 7). An equivalent circuit shown in Fig. 3 is used for this analysis. The parameters of the Li-SOCL2 and SC for the simulation is calibrated at 30 C temperature condition on their data sheets. The simulation was run in night mode where the system requires 15 times instantaneous high power in the total duration of 48 s. Fig. 8 (a) shows the response current of the hybrid battery and the SC when we apply the pulse load condition. We notice from the
result that about 50% of the discharge current required by the load is supplied by the SC instead of Li-SOCL2 battery. Fig. 8 (b) shows the voltage drop of the hybrid battery at 30 C. The battery voltage does not drop below 2.5 V even at extreme condition. This result indicates the system can operate at 30 C. The evaluation of the performance of our hybrid battery under the extreme operating condition (night mode at 30 C) is presented in this section. For this analysis, The batteries are stored for 3 h at each temperature condition and tested the batteries with the pulse load condition as Fig. 7. Fig. 9 shows the voltage drops of the Li-SOCL2 battery alone and the hybrid battery. At 30 C, the LiSOCL2 battery did not operate but the hybrid battery worked with better performance than the Li-SOCL2 at 20 C.
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Fig. 6. Voltage drop pattern of Li-SOCL2. The discharging patterns are obtained in the day mode, in which the IR module does not operate.
Fig. 7. Pulse load condition for the simulation. In the night mode, the average continuous current is 1.2 A, and the instantaneous high currents for the LRF and the fuse setter are 1.9 and 2.9 A respectively.
3.3. Power distribution management At power-on, the K11-FCS should be able to supply power to the main control board and the IR module and charge the SC (1 F/7.5 V) on the power board simultaneously. Charging the SC requires instantaneous high power and it is challenging to supply the other electric boards with the limited power source. Therefore, A new methodology that can optimally distribute power and prevent over-discharging of the hybrid battery by maintaining the discharge current within the maximum continuous current of the hybrid battery is needed. In order to enhance the performance of the hybrid power source and to ensure charge balance and robustness of the system power, the power distribution
Fig. 9. Voltage drop pattern of Li-SOCL2 and Hybrid battery at Night mode.
management (PDM) is adopted by setting the electric feature priorities. The PDM is based on a variable current limit and a 2-step SC charging technique. The K11 FCS system consumes more power at the initial (at power-on) than the stable operation state. Compared to the stable state, the system requires 35% more power at the initial state due to the SC charging. A new circuit is designed that can implement 2step SC charging and variable current limit value based on an optimal power control algorithm. The variable current limit technique is able to control current supplied to the power board at the initial state by using two current limiting ICs with different maximum current. The 2-step SC charging technique charges the SC in 2-step to minimize inrush current at initial charging (see Fig. 10) and maximize charge efficiency of the SC on the power board. Fig. 11 shows the conceptual diagram of our circuit with optimal power control algorithm based on the variable current limit and the 2-step capacitor charging techniques. When power is supplied from the hybrid battery, the power control microprocessor of the power supply device turns on the low current limit part #1 (1 A), and keeps the high current limit part #2 (1.5 A), a step-up DCeDC boost converter #1, and a step-up DCeDC boost converter #2 turned off. At this point, the current that has passed through the low current limit part #1 charges the SC through the Zener diode. The power
Fig. 8. Simulation result of the discharge current and the voltage drop of the battery and the SC. (a) Discharge current patterns of the battery, the SC, and the pulse load. (b) Voltage drop pattern of the battery.
K. Kwak et al. / Journal of Power Sources 288 (2015) 328e336
333
Fig. 10. Inrush Current during the SC charging. Yellow is the SC voltage pattern for charging. Green is a current pattern of the hybrid battery. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
control microprocessor checks the charging voltage in real-time. If the SC is charged up to the same voltage level as that of the battery 1, the power control microprocessor turns on the step-up converter #1 and charges the SC up to a final voltage, and subsequently discharges the charged voltage when the load requires an instantaneous high power. Furthermore, in order to minimize the leakage current, the stepup converter #2 is only turned on when we drives the LRF module. If the SC is fully charged and other electronic boards are stabilized after power is first supplied to the system, current consumed by
corresponding electronic boards is reduced significantly. For example, the K11 FCS consumes 400 mA less current at stable state compared to the initial state. The power control microprocessor that checks the power state of the system in real-time turns off the low current limit part #1 and turns on the high current limit part #2 in order to return this current to the other electric boards. Thus, power required by respective units of the system can be used efficiently within a limited power capacity of the battery. Fig. 12 shows is the result of the SC charging at the stable state when the high current limit part is turned on. The initial current
Fig. 11. Conceptual diagram of our proposed power board. Red dash describes the power board. Blue arrows mean the control signal of each component on the power board. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Fig. 12. SC charging result with variable current limit and 2-step SC charging technique. Blue is the SC voltage pattern for charging and pink is a current pattern of the hybrid battery. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
limit spikes to 1.7 A due to the chip error (about 20%). The switching pattern in the graph occurs when the power control processor triggers every 200 ms to correctly measure the voltage of the SC. 4. Experimental results of IHPSS The overall performance of our IHPSS with the hybrid battery and the power board is tested such as shown in Fig. 13. In this experiment, A prototype K11 is used, which is assembled with the FCS, the dual barrel system. In order to evaluate the energy transmission performance of the fuse setter, the system voltage of the programmable fuse in the air-burst ammo and the charging current of the fuse setter are measured directly. The power supplying pattern of the IHPSS using the newest PDM algorithm are also tested. The system voltages of the programmable fuse in the air-burst ammo are measured for both when the IHPSS is applied to the K11 FCS or not. Table 1 shows the system voltage of the fuse. The energy is supplied from the FCS as a pulse current (1 A at 0.5 duty, 1 ms) for 300, 500, 1000 ms. Without the IHPSS, the system voltage
Table 1 System voltage of programmable fuse. Power source
Without IHPSS With IHPSS
Supplying period 300 ms
500 ms
1000 ms
4.0 V 8.2 V
5.2 V 8.6 V
5.4 V 8.6 V
of the fuse did not reach the minimum voltage (8.0 V) required for the fuse activation regardless of the energy supplying time. With the IHPSS, the system voltage was over the minimum voltage level at 300 ms and reached the maximum voltage level over 500 ms. Fig. 14 shows the charging current of the fuse setter when the energy is supplied for 500 ms. Without the IHPSS (see Fig. 14 (a)), the average charging current supplying from the FCS was about 500 mA. However, with the IHPSS (see Fig. 14 (b)), the average charging current was about 920 mA. In the average charging current, the current loss of 80 mA due to the inefficiency of the step-up
Fig. 13. Design of IHPSS with a power board (left) and a hybrid battery (right). The black part on the power board is the SC package (1 F/7.5 V). The hybrid battery is packed with an Li-SOCL2 and two SCs (1 F/5 V).
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Fig. 14. Charging current of the fuse setter. (a) Without IHPSS. (b) With IHPSS.
Fig. 15. Voltage and current pattern of hybrid battery. Green (1 V/div) is the battery voltage and red (500 mA/div) is the battery current. Time axis represents 1 s/div. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
DCeDC boosting converter caused. It did not disrupt the activation of the programmable fuse. Fig. 15 shows the voltage and current patterns of the hybrid battery during LRF module operation and the energy transmission of the fuse setter. In this experiment, we used the newest PDM algorithm that is optimized with our operating scenario. The procedure is as follows: (i) distance is measured with LRF, (ii) after 200 ms, the fuse setter first charges for 250 ms twice within 750 ms, and (iii) thereafter, energy is retransmitted to the fuse setter for 70 ms every 2 s. The minimum voltage drop of the battery was 2.8 V for the initial state and the voltage of the programmable fuse continued over 8.6 V. 5. Conclusion A new Instantaneous High Power Supply System (IHPSS) that
consists of a set of a power board and a hybrid battery is proposed for portable military devices. To achieve the goal, we developed a power board supplying instantaneous high power to pulse loads, designed a hybrid battery consisted of a D-size spiral type Li-SOCL2 and SCs, and developed a variable current limiting and 2-step SC charging methodology using the optimal power distribution algorithm based on precise status information of the K11 FCS. The performance of the IHPSS is modeled with simulation and verified by the real experiments. The hybrid batty under critical operation temperature (30 C) supplied stable power for 5 h under 3 A pulse load (minimum operating voltage 2.5 V), when an existing D-size spiral type Li-SOCL2 fails to operate. The FCS with IHPSS charged the fuse setter under the pulse discharging rate (1 A at 0.5 duty, 1 ms) for 500 ms. The board design and power management techniques of the IHPSS can improve the battery life cycle and energy efficiency of the commercial and military systems that
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require instantaneous high power and maintain stable operation over large operating temperature range (40 Ce65 C). References [1] T.B. Atwater, P.J. Cygan, F.C. Leung, Man portable power needs of the 21st century: I. Applications for the dismounted soldier. II. Enhanced capabilities through the use of hybrid power sources, J. Power Sources 91 (1) (2000) 27e36. [2] L. Jarvis, P. Cygan, M. Roberts, Hybrid power source for manportable applications, Aerosp. Electron. Syst. Mag. IEEE 18 (1) (2003) 13e16. [3] L. Jarvis, T. Atwater, P. Cygan, Hybrid power sources for Land Warrior scenario, Aerosp. Electron. Syst. Mag. IEEE 15 (9) (2000) 37e41. [4] C. Holland, J. Weidner, R. Dougal, R. White, Experimental characterization of hybrid power systems under pulse current loads, J. Power Sources 109 (1)
(2002) 32e37. [5] G. Sikha, B.N. Popov, Performance optimization of a battery-capacitor hybrid system, J. Power Sources 134 (2004) 130e138. [6] R. Dougal, S. Liu, R. White, Power and life extension of battery-ultracapacitor hybrids, Compon. Packag. Technol. IEEE Trans. 25 (1) (2002) 120e131. [7] Kwak K, Ko J, Yoon J, Device and methods for supplying instant high power to small arms fire control system, uS Patent App. 11/944,869, 2010. [8] E. Choe, Technical overview of the K11 Dual-Barrel Air-Burst Weapon, in: Exhibition & Firing Demonstration, 2012 Joint Armaments Conference, 14002, 2012. [9] A. Cordesman, A. Hess, The Evolving Military Balance in the Korean Peninsula and Northeast Asia: Conventional Balance, Asymmetric Forces, and U.S. Forces, CSIS Reports, Center for Strategic & International Studies, 2013. [10] M. Jain, G. Nagasubramanian, R.G. Jungst, J.W. Weidner, Analysis of a lithium thionyl chloride battery under moderate? Rate discharge, J. Electrochem. Soc. 146 (11) (1999) 4023e4030.
Contents lists available at ScienceDirect
Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour
Design of Instantaneous High Power Supply System with power distribution management for portable military devices Kiho Kwak*, Dongmin Kwak, Joohong Yoon Agency for Defense Development, South Korea
h i g h l i g h t s A power board supplying instantaneous high power to pulse loads. A hybrid battery consisted of a D-size spiral type Li-SOCL2 and supercapacitors. A variable current limiting and 2-step supercapacitor charging methodology.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 26 December 2014 Received in revised form 27 February 2015 Accepted 12 April 2015 Available online
A design of an Instantaneous High Power Supply System (IHPSS) with a power distribution management (PDM) for portable military devices is newly addressed. The system includes a power board and a hybrid battery that can not only supply instantaneous high power but also maintain stable operation at critical low temperature (30 C). The power leakage and battery overcharge are effectively prevented by the optimal PDM. The performance of the proposed system under the required pulse loads and the operating conditions of a Korean Advanced Combat Rifle employed in the battlefield is modeled with simulations and verified experimentally. The system with the IHPSS charged the fuse setter with 1.7 times higher voltage (8.6 V) than the one without (5.4 V) under the pulse discharging rate (1 A at 0.5 duty, 1 ms) for 500 ms. © 2015 Elsevier B.V. All rights reserved.
Keywords: Instantaneous High Power Supply System Hybrid battery Supercapacitor Power distribution management Portable military device
1. Introduction In recent years, digitization of the battlefield leads to increased demand for portable military equipment powered by batteries. The most challenging but crucial problem with these portable military devices is the development of a stable system with long operation time and minimal power consumption. Size, weight, and power are the most important elements in portable military device design because a soldier should be able to carry and to operate without being overburdened. Well-designed power supply system can greatly simplify the portable military device design because the power consumption directly impacts the size of the required batteries, and larger batteries comprise the size of and weight constraints of portable devices. A battery has been a big design constraint for small military devices since the operation time and power consumption is
* Corresponding author. E-mail address: [email protected] (K. Kwak). http://dx.doi.org/10.1016/j.jpowsour.2015.04.061 0378-7753/© 2015 Elsevier B.V. All rights reserved.
proportional to the number, size and capacity of the batteries. Most commercial portable electric devices are rarely operated at temperatures lower than 0 C or higher than 50 C. Small and slim rechargeable battery packs or lower price alkaline nonrechargeable cells are sufficient for such devices. However, a battery for military devices should be more robust than commercial products, because the military devices should be able to maintain high performance under more extreme environment (40 Ce65 C) even when capacity and performance of batteries drops at lower temperature [1,2]. Moreover, it is very difficult to supply different types of power to various loads requiring instantaneous high power with a single battery. The battery may break down or cause the system to malfunction if the battery is designed to supply constant power and instantaneous pulsed current for a few hundred millisecond at the same time. Ordinary systems do not require constant monitoring of power supply and real time power distribution because they are designed to operate with marginal battery capacity. However, portable military equipment with minimal size, weight and limited
K. Kwak et al. / Journal of Power Sources 288 (2015) 328e336
power source should be able to control power output according to the operation status and supply instant power exceeding the maximum power output to the systems [3]. A hybrid power source with a combination of a battery and supercapacitors (SC) takes advantage of the energy density of the primary battery for long operational time and the power density of the secondary SC for pulse power requirement. Generally, a battery has higher energy density but lower power density than an SC and vice versa [4,5]. The hybrid power sources can meet the pulse power requirements with higher specific power and efficiency than batteries alone. Moreover, an SC is able to reduce the stress on a battery and extend the operational life of the battery [6]. Furthermore, in order to enhance the performance of the hybrid power source and to ensure charge balance and robustness of the system power, it is necessary to adopt power distribution management (PDM). The PDM is used to schedule the allocation of available power and energy to electric loads on a subsystem or component level. Effectively, it ensures the controlled function delivery of individual electric features by prioritization. By setting the electric feature priorities, the PDM keeps the system voltage stability under pulse loads, minimizes the power loss of the system, and extends the operational life of the battery [6]. This paper proposes an Instantaneous High Power Supply System (IHPSS) for portable military devices. The IHPSS consists of a set of a power board and a hybrid battery that supplies instantaneous high power and maintains stable operation over large operating temperature range (40 Ce65 C). The IHPSS is able to supply continuous power and instantaneous high power simultaneously and prevent power leakage and battery overcharge through optimal power distribution management. The performance of the proposed system is verified through several experiments. The IHPSS has been used for the fire control system of the Korean Advanced Combat Rifle, K11 employed in the battlefield [7,8]. The contributions of this paper are threefold: (i) design of a power board supplying instantaneous high power to pulse loads, (ii) design of a hybrid battery consisted of a D-size spiral type Lithium-Thionyl-Chloride battery (Li-SOCL2) and SCs, and (iii) the development of a variable current limiting and 2-step SC charging methodology using an optimal power distribution algorithm based on precise status information about our system.
329
Fig. 2. Overall power requirement of K11 FCS. The power board supply various types of voltages for each electric components (blue). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
and 5.56 mm NATO ammunition with automatic electro-optical Fire Control System (FCS) to defeat targets at extended ranges as shown in Fig. 1. K11 is able to strike point targets and especially hidden target in a fox hole with 20 mm air bursting ammunition. K11 maximizes combat effectiveness with a new concept and technology, such as precise air bursting against defilade targets, FCS at day and night, and lightweight dual barrel rifle [8]. The K11 FCS is a small and complex system that has functionalities of the FCS of an armored vehicle such as a tank or an infantry vehicle into a small firearms, such as day and night target detection, range finding, ballistic trajectory computation, and wireless energy charging and signal transmission. For these functionalities, the K11 FCS consists of complex optical modules with a thermal detector, a Laser Range Finder (LRF), a ballistic computer, a IHPSS, and a fuse setter. The K11 FCS should operate at day and night under all weather conditions. The FCS provides the electronic aiming reticle after measuring the distance and computing the ballistic trajectory to the target, and programs and charge the air-burst ammo through the fuse setter. The air-burst ammo is set to explode at specific range above of the target.
2. Overview of Korean Advanced Combat Rifle (K11)
3. Instantaneous High Power Supply System (IHPSS) design
K11, a dual barrel air burst weapon, has been employed in Korea army since 2010 [9]. K11 combines the 20 mm air burst ammunition
The portable military system such as the K11 FCS should be able to operate under more extreme conditions than commercial
Fig. 1. Overview of Korean Advanced Combat Rifle, K11.
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systems. If the system should maintain stable operation at low temperature and then supply instantaneous high power with only a single battery, a new approaches to design the optimal power supply for the system is required. To design the optimal power supply, thorough analysis on the load and operation condition of the system is required. In the case of the K11 FCS that needs various types of power sources (see Fig. 2), it should supply instantaneous high power to the LRF module and the fuse setter and compensate the battery response time under all temperature conditions required for portable military devices. In this paper, the IHPSS for the K11 FCS that guarantees stable operation under all temperature and load conditions is presented. The power supply system consists of two main components: (i) a power board that compensates a battery response time and supplies instantaneous high power to the loads and (ii) a D-size hybrid battery with a spiral type Li-SOCL2 and SCs that compensates poor discharging characteristic under low temperature. The performance of the proposed system is verified with simulations and experiments under required pulse loads and operating conditions. 3.1. Power board design The power board supplies instantaneous high power to the pulse loads such as an LRF module and a fuse setter. In order to design the power board, the capacitance of the SC installed on the board that supplies high power to the load instead of the primary power source as a battery is calculated. The capacitance is determined by first inspect which load needs the highest power during operation. The K11 FCS requires instantaneous high power when we measure a distance using the LRF module and charge energy into the fuse setter. Then the capacitance of the SC is calculated in consideration of energy required for both the LRF module and the fuse setter. In the K11 FCS, the power board supplies energy into the fuse setter for 500 ms. Given the average voltage and current, and the minimum voltage, the energy Efuse for the fuse setter is estimated as follows:
VMax ¼ 7:2V: Maximum storage voltage VMin ¼ 6:0V: Minimum operating voltage Vfuse ¼ 6:4V: Average voltage for fuse setter charging Ifuse ¼ 1:0A: Average current for fuse setter charging Tfuse ¼ 0:5sec: Fuse setter charging time
Efuse ¼ Pfuse Tfuse ¼ ðVfuse Ifuse Þ Tfuse ¼ ð6:4V 1:0AÞ 0:5sec ¼ 3:2J
(1)
The capacitance Cfuse of the SC is derived using the following equation:
Cfuse ¼
2Efuse 2 2 VMax VMin
¼ 0:4F
(2)
Although energy charging for the fuse setter and LRF firing do not occur at the same time we should estimate the capacitance of the SC considering the LRF module. The system supplies energy to the fuse setter with a time delay (250e300 ms) after measuring the distance to a target object with the LRF. However, these sequential event does not mean that the capacitance 0.4 F is enough to supply power for both processes. It is not possible to fully charge the 0.4 F SC with limited current within 300 ms because the LRF module requires the maximum 3 J energy. The total capacitance of the SC is calculated taken into account the maximum capacitance for the LRF
Fig. 3. Circuit of an SC in parallel with a battery.
operation and the rechargeable capacitance within 300 ms. As the result, the system needs more than 0.8 F SC which includes extra added 0.4 F. The charging and discharging characteristics of the SC are obtained from a simulation based on the measured capacitance. The basic circuit considered in this analysis is shown in Fig. 3 [6]. The SC is modeled by a nominal capacitance CC (1 F/7.5 V) and equivalent series resistance RC (0.25 U), and the battery by an ideal voltage source VB and an internal resistance RB (0.5 U). For the performance analysis of the SC on the power board, the battery supply voltage is set to 7.2 V which is equivalent to the voltage requirement for the LRF operation and the energy charging for the fuse setter. The equivalent load condition for charging the real fuse setter was used. The input current is limited to 1.5 A and the maximum voltage for the SC is set to 7.2 V as in the real system. Fig. 4 shows the discharge current and the voltage drop patterns of the battery and the SC installed on the power board during the fuse setter charging. Stable power is supplied to the system as the SC compensates the slow discharge characteristics of battery in the first 500 ms of initial charging. The result shows that five second is required to fully charge the capacitor after first discharging. A power board capable of supplying instantaneous high power to loads is designed based on the simulation result. Fig. 5 shows the voltage and current patterns of the battery and the SC on the designed power board. The procedure was as follows: (i) distance is measured with LRF, (ii) after 250 ms, the fuse setter first charges, and (iii) thereafter, energy is retransmitted to the fuse setter for 500 ms every 5 s. It is confirmed that supplying instantaneous high power is feasible with a power board equipped with SCs and a D-size LiSOCL2 battery. However, as shown in the experiment, the maximum voltage drop of the SC is 10 times higher than the voltage drop in the simulation. The maximum voltage drop of the battery is 0.6 V during the LRF operation the fuse setter charging, which is lower than the minimum system input voltage 2.4 V. The K11 FCS should not only be able to supply instantaneous high power to the LRF module and the fuse setter, but also supply continuous power to other loads such as the main control board and the IR module and operate at as low temperature as 30 C. Since the experiment results were collected at room temperature, it is difficult to maintain stable operation of the system at low temperature due to poor discharging characteristic. 3.2. Hybrid battery design A spiral type Li-SOCL2 battery used for the main power source of K11 FCS is robust against instantaneous current discharge compared to other commercial batteries. However, the discharging performance of Li-SOCL2 battery deteriorates at low temperature and instantaneous power supply (See Fig. 6) [10]. To solve the
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Fig. 4. Simulation result of the discharge current and the voltage drop. Vcap (dark blue) and Vout (pink) are the voltage of the SC and the pulse load respectively. iC (blue) and iB (red) are the current of the SC and the battery respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 5. Discharge current and voltage drop by using the proposed power board. Blue is the voltage of the SC on the power board. Red and yellow are the current and voltage of the battery. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
problem, we built a hybrid battery consisted of a D-size Li-SOCL2 battery and SCs to minimize the battery voltage drop at instantaneous high power supply and performance deterioration at low temperature. The performance of the hybrid battery is verified through a simulation under the K11 operation scenario at the night mode (See Fig. 7). An equivalent circuit shown in Fig. 3 is used for this analysis. The parameters of the Li-SOCL2 and SC for the simulation is calibrated at 30 C temperature condition on their data sheets. The simulation was run in night mode where the system requires 15 times instantaneous high power in the total duration of 48 s. Fig. 8 (a) shows the response current of the hybrid battery and the SC when we apply the pulse load condition. We notice from the
result that about 50% of the discharge current required by the load is supplied by the SC instead of Li-SOCL2 battery. Fig. 8 (b) shows the voltage drop of the hybrid battery at 30 C. The battery voltage does not drop below 2.5 V even at extreme condition. This result indicates the system can operate at 30 C. The evaluation of the performance of our hybrid battery under the extreme operating condition (night mode at 30 C) is presented in this section. For this analysis, The batteries are stored for 3 h at each temperature condition and tested the batteries with the pulse load condition as Fig. 7. Fig. 9 shows the voltage drops of the Li-SOCL2 battery alone and the hybrid battery. At 30 C, the LiSOCL2 battery did not operate but the hybrid battery worked with better performance than the Li-SOCL2 at 20 C.
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Fig. 6. Voltage drop pattern of Li-SOCL2. The discharging patterns are obtained in the day mode, in which the IR module does not operate.
Fig. 7. Pulse load condition for the simulation. In the night mode, the average continuous current is 1.2 A, and the instantaneous high currents for the LRF and the fuse setter are 1.9 and 2.9 A respectively.
3.3. Power distribution management At power-on, the K11-FCS should be able to supply power to the main control board and the IR module and charge the SC (1 F/7.5 V) on the power board simultaneously. Charging the SC requires instantaneous high power and it is challenging to supply the other electric boards with the limited power source. Therefore, A new methodology that can optimally distribute power and prevent over-discharging of the hybrid battery by maintaining the discharge current within the maximum continuous current of the hybrid battery is needed. In order to enhance the performance of the hybrid power source and to ensure charge balance and robustness of the system power, the power distribution
Fig. 9. Voltage drop pattern of Li-SOCL2 and Hybrid battery at Night mode.
management (PDM) is adopted by setting the electric feature priorities. The PDM is based on a variable current limit and a 2-step SC charging technique. The K11 FCS system consumes more power at the initial (at power-on) than the stable operation state. Compared to the stable state, the system requires 35% more power at the initial state due to the SC charging. A new circuit is designed that can implement 2step SC charging and variable current limit value based on an optimal power control algorithm. The variable current limit technique is able to control current supplied to the power board at the initial state by using two current limiting ICs with different maximum current. The 2-step SC charging technique charges the SC in 2-step to minimize inrush current at initial charging (see Fig. 10) and maximize charge efficiency of the SC on the power board. Fig. 11 shows the conceptual diagram of our circuit with optimal power control algorithm based on the variable current limit and the 2-step capacitor charging techniques. When power is supplied from the hybrid battery, the power control microprocessor of the power supply device turns on the low current limit part #1 (1 A), and keeps the high current limit part #2 (1.5 A), a step-up DCeDC boost converter #1, and a step-up DCeDC boost converter #2 turned off. At this point, the current that has passed through the low current limit part #1 charges the SC through the Zener diode. The power
Fig. 8. Simulation result of the discharge current and the voltage drop of the battery and the SC. (a) Discharge current patterns of the battery, the SC, and the pulse load. (b) Voltage drop pattern of the battery.
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Fig. 10. Inrush Current during the SC charging. Yellow is the SC voltage pattern for charging. Green is a current pattern of the hybrid battery. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
control microprocessor checks the charging voltage in real-time. If the SC is charged up to the same voltage level as that of the battery 1, the power control microprocessor turns on the step-up converter #1 and charges the SC up to a final voltage, and subsequently discharges the charged voltage when the load requires an instantaneous high power. Furthermore, in order to minimize the leakage current, the stepup converter #2 is only turned on when we drives the LRF module. If the SC is fully charged and other electronic boards are stabilized after power is first supplied to the system, current consumed by
corresponding electronic boards is reduced significantly. For example, the K11 FCS consumes 400 mA less current at stable state compared to the initial state. The power control microprocessor that checks the power state of the system in real-time turns off the low current limit part #1 and turns on the high current limit part #2 in order to return this current to the other electric boards. Thus, power required by respective units of the system can be used efficiently within a limited power capacity of the battery. Fig. 12 shows is the result of the SC charging at the stable state when the high current limit part is turned on. The initial current
Fig. 11. Conceptual diagram of our proposed power board. Red dash describes the power board. Blue arrows mean the control signal of each component on the power board. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Fig. 12. SC charging result with variable current limit and 2-step SC charging technique. Blue is the SC voltage pattern for charging and pink is a current pattern of the hybrid battery. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
limit spikes to 1.7 A due to the chip error (about 20%). The switching pattern in the graph occurs when the power control processor triggers every 200 ms to correctly measure the voltage of the SC. 4. Experimental results of IHPSS The overall performance of our IHPSS with the hybrid battery and the power board is tested such as shown in Fig. 13. In this experiment, A prototype K11 is used, which is assembled with the FCS, the dual barrel system. In order to evaluate the energy transmission performance of the fuse setter, the system voltage of the programmable fuse in the air-burst ammo and the charging current of the fuse setter are measured directly. The power supplying pattern of the IHPSS using the newest PDM algorithm are also tested. The system voltages of the programmable fuse in the air-burst ammo are measured for both when the IHPSS is applied to the K11 FCS or not. Table 1 shows the system voltage of the fuse. The energy is supplied from the FCS as a pulse current (1 A at 0.5 duty, 1 ms) for 300, 500, 1000 ms. Without the IHPSS, the system voltage
Table 1 System voltage of programmable fuse. Power source
Without IHPSS With IHPSS
Supplying period 300 ms
500 ms
1000 ms
4.0 V 8.2 V
5.2 V 8.6 V
5.4 V 8.6 V
of the fuse did not reach the minimum voltage (8.0 V) required for the fuse activation regardless of the energy supplying time. With the IHPSS, the system voltage was over the minimum voltage level at 300 ms and reached the maximum voltage level over 500 ms. Fig. 14 shows the charging current of the fuse setter when the energy is supplied for 500 ms. Without the IHPSS (see Fig. 14 (a)), the average charging current supplying from the FCS was about 500 mA. However, with the IHPSS (see Fig. 14 (b)), the average charging current was about 920 mA. In the average charging current, the current loss of 80 mA due to the inefficiency of the step-up
Fig. 13. Design of IHPSS with a power board (left) and a hybrid battery (right). The black part on the power board is the SC package (1 F/7.5 V). The hybrid battery is packed with an Li-SOCL2 and two SCs (1 F/5 V).
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Fig. 14. Charging current of the fuse setter. (a) Without IHPSS. (b) With IHPSS.
Fig. 15. Voltage and current pattern of hybrid battery. Green (1 V/div) is the battery voltage and red (500 mA/div) is the battery current. Time axis represents 1 s/div. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
DCeDC boosting converter caused. It did not disrupt the activation of the programmable fuse. Fig. 15 shows the voltage and current patterns of the hybrid battery during LRF module operation and the energy transmission of the fuse setter. In this experiment, we used the newest PDM algorithm that is optimized with our operating scenario. The procedure is as follows: (i) distance is measured with LRF, (ii) after 200 ms, the fuse setter first charges for 250 ms twice within 750 ms, and (iii) thereafter, energy is retransmitted to the fuse setter for 70 ms every 2 s. The minimum voltage drop of the battery was 2.8 V for the initial state and the voltage of the programmable fuse continued over 8.6 V. 5. Conclusion A new Instantaneous High Power Supply System (IHPSS) that
consists of a set of a power board and a hybrid battery is proposed for portable military devices. To achieve the goal, we developed a power board supplying instantaneous high power to pulse loads, designed a hybrid battery consisted of a D-size spiral type Li-SOCL2 and SCs, and developed a variable current limiting and 2-step SC charging methodology using the optimal power distribution algorithm based on precise status information of the K11 FCS. The performance of the IHPSS is modeled with simulation and verified by the real experiments. The hybrid batty under critical operation temperature (30 C) supplied stable power for 5 h under 3 A pulse load (minimum operating voltage 2.5 V), when an existing D-size spiral type Li-SOCL2 fails to operate. The FCS with IHPSS charged the fuse setter under the pulse discharging rate (1 A at 0.5 duty, 1 ms) for 500 ms. The board design and power management techniques of the IHPSS can improve the battery life cycle and energy efficiency of the commercial and military systems that
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require instantaneous high power and maintain stable operation over large operating temperature range (40 Ce65 C). References [1] T.B. Atwater, P.J. Cygan, F.C. Leung, Man portable power needs of the 21st century: I. Applications for the dismounted soldier. II. Enhanced capabilities through the use of hybrid power sources, J. Power Sources 91 (1) (2000) 27e36. [2] L. Jarvis, P. Cygan, M. Roberts, Hybrid power source for manportable applications, Aerosp. Electron. Syst. Mag. IEEE 18 (1) (2003) 13e16. [3] L. Jarvis, T. Atwater, P. Cygan, Hybrid power sources for Land Warrior scenario, Aerosp. Electron. Syst. Mag. IEEE 15 (9) (2000) 37e41. [4] C. Holland, J. Weidner, R. Dougal, R. White, Experimental characterization of hybrid power systems under pulse current loads, J. Power Sources 109 (1)
(2002) 32e37. [5] G. Sikha, B.N. Popov, Performance optimization of a battery-capacitor hybrid system, J. Power Sources 134 (2004) 130e138. [6] R. Dougal, S. Liu, R. White, Power and life extension of battery-ultracapacitor hybrids, Compon. Packag. Technol. IEEE Trans. 25 (1) (2002) 120e131. [7] Kwak K, Ko J, Yoon J, Device and methods for supplying instant high power to small arms fire control system, uS Patent App. 11/944,869, 2010. [8] E. Choe, Technical overview of the K11 Dual-Barrel Air-Burst Weapon, in: Exhibition & Firing Demonstration, 2012 Joint Armaments Conference, 14002, 2012. [9] A. Cordesman, A. Hess, The Evolving Military Balance in the Korean Peninsula and Northeast Asia: Conventional Balance, Asymmetric Forces, and U.S. Forces, CSIS Reports, Center for Strategic & International Studies, 2013. [10] M. Jain, G. Nagasubramanian, R.G. Jungst, J.W. Weidner, Analysis of a lithium thionyl chloride battery under moderate? Rate discharge, J. Electrochem. Soc. 146 (11) (1999) 4023e4030.