Realization of class – A chopper using dSPACE

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www.elsevier.com/locate/pr International Conference on Computer Computational Intelligence (ICCIDS 2018) Procedia Science 132 (2018) 563–571and Data Science International Conference on Computational Intelligence and Data Science ocedia(ICCIDS 2018)

Realization of class – A chopper using dSPACE

Realization ofComputational class – AIntelligence chopper dSPACE International Conference on andusing Data Science (ICCIDS 2018) a

Realization

Akshat Jaina,* , Dheeraj Joshiaa a,* Dheeraj Joshi ofAkshat classJain – A, chopper using

dSPACE

Electrical Engineering Department, Delhi Technological University, Shahabad Daulatpur, New Delhi-110042, India a Electrical Engineering Department, Delhi Technological New Delhi-110042, India a,* University, Shahabad Daulatpur, a

Akshat Jain , Dheeraj Joshi

Abstract aElectrical Engineering Department, Delhi Technological University, Shahabad Daulatpur, New Delhi-110042, India Abstract This paper describes the designing and analysis of a class – A Chopper in open loop as well as closed loop control. This paper This the designing analysis of a as class – A Chopper in open as well as closed This paper aims paper to put describes up the results based on and software as well hardware simulation. DC loop chopper is realized by loop usingcontrol. dSPACE DS1104 Abstract aimsopen to put upoperation the resultsofbased software well resistive as hardware DC computed chopper isvalues realized using dSPACE DS1104 for loop classon –A chopperaswith load.simulation. In this paper, arebycompared with measured for openand loop operation error of class – A chopper resistive load. Inofthis paper, voltage computed valuesstrategy are compared with measured values accordingly is calculated. In with closed loop control chopper, control is implemented using This paper describes the designing and analysis of a class – A Chopper in open loop as well as closed loop control. This paper values and2016a. accordingly errorresults is calculated. In closed loop control of loop chopper, voltage control strategy is implemented using MATLAB Improved illustrate the effectiveness of closed control strategy. aims to put up the results based on software as well as hardware simulation. DC chopper is realized by using dSPACE DS1104 MATLAB 2016a. Improved results illustrate the effectiveness of closed loop control strategy. for open loop operation of class – A chopper with resistive load. In this paper, computed values are compared with measured values error isby calculated. In closed loop control of chopper, voltage control strategy is implemented using © 2018and Theaccordingly Authors. Published Elsevier B.V. MATLAB Improved results illustrateB.V. the effectiveness of closed loop control strategy. © 2018 The2016a. Authors. Published by Elsevier Peer-review under responsibility of the scientific committee of the International Conference on Computational © 2018 The Authors. Published by Elsevier Ltd. under responsibility of the scientific committee of the International Conference on Computational This is anPeer-review open accessand article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/3.0/) Intelligence Data Science (ICCIDS 2018). © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the (ICCIDS scientific 2018). committee of the International Conference on Computational Intelligence and Intelligence and Data Science Data Science (ICCIDS 2018). Keywords: Peer-review Class – A DC Chopper; dSPACE 1104; of Ripple RMS committee voltage; Output Voltage; Voltage Control on Computational under responsibility the Factor; scientific of Average the International Conference Keywords: Class – A DC Chopper; dSPACE 1104; Ripple Factor; RMS voltage; Output Average Voltage; Voltage Control

Intelligence and Data Science (ICCIDS 2018).

1. Introduction Keywords: Class – A DC Chopper; dSPACE 1104; Ripple Factor; RMS voltage; Output Average Voltage; Voltage Control 1. Introduction Digital Signal Processing (DSP) has entangled its root in almost all parts of world. It has become an integral Signal Processing (DSP) root inpractice almost all parts of world. It has becomeschemes an integral part Digital of various developments acrosshas theentangled world. Initsearlier there were a lot of switching for 1. Introduction part of various the world. was In earlier practiceinthere a lot schemes. of switching schemes for switching of fastdevelopments devices. Lot across of commutations implemented thosewere switching These switching switching of fast devices. Lot of commutations was implemented in those switching schemes. These switching schemes can be made much easier by using the applications of Digital Signal Processing. Implementation of Digital Digital Signal Processing (DSP) has entangled its root in almost all parts of world. It has become an integral schemes can be made muchreplacing easier by the using the applications ofpractice Digital Signal Processing. Implementation of Digital SignalofProcessing is slowly switching schemes of power part various developments across theconventional world. In earlier there were adevices. lot of switching schemes for Signal Processing is slowly replacing the conventional switching schemes of power devices. switching of fast devices. Lot of commutations was implemented in those switching schemes. These switching schemes can be made much easier by using the applications of Digital Signal Processing. Implementation of Digital Signal Processing is slowly replacing the conventional switching schemes of power devices.

*

Telephone: +91-9729038102 address: [email protected] Telephone: +91-9729038102 Email address: [email protected]

*Email

*

Telephone:©+91-9729038102 1877-0509 2018 The Authors. Published by Elsevier Ltd. Email This isaddress: an [email protected] access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/3.0/) Peer-review under responsibility of the scientific committee of the International Conference on Computational Intelligence and Data Science (ICCIDS 2018). 10.1016/j.procs.2018.05.010

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There are many researches that are done on DC choppers and their closed loop control. In 1980, Takahiko Iida and group used the thyristor based DC chopper for DC motor control [3]. In 2004, ripple of DC converters was analysis [5]. In 2007, Huangsheng Xu, used DC chopper to control speed and current of universal motors using microcontroller [8]. In 2012, Anupam Agarwal designed a DC chopper to minimize the voltage ripple [1]. Then in 2014, Shun Takeuchi used current control technique for closed loop DC chopper. Then in 2017, Yifan Lang and group implemented the closed loop buck chopper with more refined outputs by triggering again by microcontroller 8052. This paper includes the interfacing of MATLAB Simulink with dSPACE DS1104 R&D Controller Board, analyzing its applications and further using these applications for the switching of different converters. In this paper, author will implement Class – A DC Chopper by triggering it through dSPACE. Operation of Class – A DC chopper is done both in open loop as well as in closed loop, and finally the error is compared and calculated at different values. 2.

Block diagram and circuit diagram

Operation of a Class – A DC chopper is generally based on the operation of a single power electronic switch like MOSFET, IGBT, Thyristor, GTO, BJT, etc. One needs to select the switch from the available choices depending upon the circuit requirement. For example, IGBTs are used for high power requirement devices and MOSFETs are used in circuits where high switching frequency is required. Thyristor can also be used in such a condition, but implementation of a thyristor controlled converter is a complex and tedious process as it requires a commutation circuit and thyristor operation support circuit for its operation. Instead of using such a tedious circuit, best practice is to use a single switch instead. Here as high frequency carrier wave is used for PWM signal generation as well as the circuit is operating with low power requirement, so MOSFET is used as a switch in the chopper. 2.1 Open Loop Class – A DC Chopper Main objective of DC Chopper is to change the DC voltage level, either by stepping up the voltage or by stepping down the voltage. Class – A chopper is used to step down the DC voltage and is the most basic type of choppers used. It operates in first quadrant of V-I plane, which means both voltage as well as current will remain positive throughout the operation.

dSPACE DSP Output

Driver Circuit

DC Chopper

Figure 1: Block Diagram of open loop DC Chopper

Fig. 1 shows the block diagram of DC chopper operated in open loop mode. A constant input DC power supply is connected to the switch and then the output is obtained from the switch. For getting the desired output one needs to change the operating state of that switch as per the requirement, so accordingly switch has to be triggered by using some external medium. This external medium can be – microcontroller output, DSP kit output, dSPACE output, bistable or monostable operation of 555 IC, PWM generation ICs (LM5045, SG3525 and UC3843), etc. Here for this paper author has used dSPACE 1104 as the triggering medium as it has many advantages as compared to other triggering mediums. dSPACE 1104 have many PWM outputs, ADC inputs, DAC outputs and Digital input/output. It also provides the user with serial communication port (RS232 and RS485). Above all, it facilitates



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the user with real time simulation and control of converter unlike other triggering mediums. It is required to connect a driver circuit between the output of dSPACE and the gate terminal of switch in order to isolate the dSPACE from hardware circuit such that any residual current may not damage the dSPACE. Driver circuit is also responsible for bringing the input voltage at gate to desired voltage level.

Figure 2: Schematic Diagram of open loop DC Chopper

As seen in figure 2, input DC voltage is connected at Drain terminal of MOSFET and load is connected at source terminal of MOSFET and to reference ground. A DC voltmeter is connected across the load to measure the average output voltage across the load. Gate terminal of MOSFET is receiving triggering signal. For convenience, instead of dSPACE block, a pulse generator block is used with exactly the same parameters defined as dSPACE block does not work in the absence of hardware circuit that is to be attached.

Figure 3: DC Chopper Circuit A: Driver Cicuit; B: MOSFET IRF640N

Figure 3 shows the circuit of DC Chopper made on a general purpose PCB where details of A and B are shown in Appendix. In this circuit, a part of circuit is enclosed in a green box which is indicating the driver circuit. In this driver circuit, left IC is an optocoupler which is used for isolating the dSPACE from chopper circuit to prevent any reverse flow of current. It gives an output of magnitude between 3volts – 5volts and 1800 out of phase. But to drive the given MOSFET at least 10V is recommended, so the output of optocoupler is fed to an OPAMP connected as an

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inverting amplifier. This will not only amplify the voltage but also will bring the final output in phase of the dSPACE output. 2.2 Closed Loop Class – A DC Chopper With Voltage Control Open loop DC chopper does not gives required error correction, so one needs to give error as feedback to input, forming a closed loop control strategy. Here, instead of taking a PWM signal for gate triggering, feedback signal is used for gate triggering. A voltage sensor is used to measure the output voltage of DC chopper. This measured value is then compared with some reference value to calculate error. This error is then fed back to the input through some appropriate controller, in order to minimize that error and finally obtaining the most accurate output possible. Block diagram of closed loop operation of class – A chopper is shown in figure 4.

Figure 4: Block Diagram of Closed Loop DC Chopper

This chopper circuit is receiving some DC input through Drain terminal of MOSFET. Output of chopper is measured across the load by connecting a voltage sensor between Source terminal of MOSFET and reference ground. This output is now compared with some reference signal by using a comparator which will be the error in output. Now, the error signal is fed back to the gate terminal of MOSFET through a PI controller. Controller parameters are adjusted for optimum performance parameters. Output of PI controller is compared with a triangular wave of high frequency, so that number of samples increases in order to provide further better output.

Figure 5: Schematic Diagram of Closed Loop DC Chopper



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While implementing the schematic diagram (as shown in figure 5) on hardware, the same open loop DC chopper circuit (as shown in figure 3) can be used along with a voltage sensor connected across load. Output of voltage sensor is now fed to dSPACE through either its ADC terminal or Digital Input terminal. Further task of error calculation, PI control implementation and finally sampling is done through computer. In short dSPACE is not only facilitating an individual to trigger the switch but it is also reducing the complexity of the circuit by minimizing the hardware. It is also providing an inbuilt PI controller due to which need of external PI controller and its manual tuning has been eliminated. Output of the relational operator can be taken out of dSPACE through DAC terminal or Digital Output terminal of dSPACE workbox. This signal is further fed to Gate terminal of MOSFET for its triggering. Hardware implementation of closed loop control will be done later when closed loop control strategy will be finalized. 3. Results and calculations 3.1 Calculations Mean value of a DC chopper is taken as output because the output obtained is a DC and for DC voltage, mean voltage is considered. So below are the necessary calculations that are done to calculate the error. Duty cycle (D)

=

50% (1) (2) (3) (4)

Here is the error calculation for Open Loop DC Chopper, Table 1: Error calculation for open loop DC chopper

Sr.No.

Actual Value (V)

Measured Value (V)

Relative Error (V)

Percentage Error (%)

1.

12

11.170

-0.830

-6.917

2.

11

10.240

-0.760

-6.909

3.

10

9.306

-0.694

-6.940

4.

9

8.375

-0.625

-6.944

5.

8

7.445

-0.555

-6.938

6.

7

6.514

-0.486

-6.943

7.

6

5.584

-0.416

-6.933

8.

5

4.653

-0.347

-6.940

As we can see in table 1, percentage error at all values lies from -6.905% to -6.945%. Generally, error should lie in ±5% tolerance but this error is more than the specified range. Negative sign signifies that measured value is less than the calculated value. Error calculation for closed loop control of DC chopper with voltage control strategy is tabulated below.

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Table 2: Error calculation for closed loop DC chopper

Sr.No.

Actual Value (V)

Measured Value (V)

Relative Error (V)

Percentage Error (%)

1.

12

12.010

0.010

0.083

2.

11

11.030

0.030

0.273

3.

10

10.070

0.070

0.700

4.

9

9.074

0.074

0.822

5.

8

8.093

0.093

1.163

6.

7

7.111

0.111

1.586

7.

6

6.130

0.130

2.167

8.

5

5.150

0.150

3.000

After applying closed loop control to DC – chopper, it can be observe from table 2 that the percentage error has reduced to great extent and lies between 0.083% and 3%. It can be observed that as the reference voltage is getting decreased, percentage error is getting increased. It is also lying in ±5% tolerance band, which is acceptable. 3.2 Results On running the simulation of open loop class – A DC chopper, one should obtain a waveform such that the amplitude should be positive and must be equal to DC input voltage (Vin) when switch is ON and output should be zero when the switch is OFF. Here, duty cycle (D) is 50%, so switch will be ON for half cycle and OFF another half.

Figure 6: Output of open loop DC chopper

As it can be clearly seen from the output waveform of open loop DC chopper in (figure 6), when switch is ON output is +12V which is exactly equal to Vin and when switch is OFF output is slightly more than zero. Duty cycle is also 50% as observed from the waveform.



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Figure 7: Output of hardware of open loop DC chopper

For an input of 18V, output should be 9V and it can be seen in figure 7, 9.05V is obtained as mean voltage. This value is very near to 9V as a result 0.555% error only. Spikes seen in the waveform are switching transients which will be removed by connecting some adequate filter later.

Figure 8: Output of closed loop DC chopper

As it can be seen from the waveform in figure 8, amplitude is of 24V. This is because input DC voltage of chopper is 24V itself but as reference value of 6V is taken, so the mean output obtained will be approximately 6V. Varying duty cycle is observed in this waveform, because PI controller is bringing the output close to 6V cycle by cycle.

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Figure 9: Comparison of open loop and closed loop errors

In figure 9, author has compared the percentage error obtained in open loop class – A chopper with percentage error obtained in closed loop class – A chopper. Blue line denotes the percentage error from open loop chopper while red shows the percentage error shown in closed loop chopper. 4.

Conclusion

After analyzing all the calculations and results, it can be seen that percentage error in open loop DC chopper is out of ±5% tolerance range. Now in order to reduce the error, closed loop control of DC chopper was employed whose output must have lied in ±5% tolerance range. After analyzing the results of closed loop chopper, it can be seen that it is actually fulfilling the criteria. Hence, it can be concluded that closed loop control is efficient in reducing the error in output. After going through the error waveform it can also be seen that open loop error is more or less constant but closed loop error is varying with change in values because in closed loop output is continuously monitored and better output is achieved. Chopper is generally a single switch circuit. As the author is able to analyze the single switch based convertor using dSPACE, some multi-switch convertor (like single phase inverters, 3-phase inverter, multi-level inverters etc.) circuits can also be implemented using the same with different switching strategies. In future, author will try to implement other control strategies for chopper to further reduce the error. Researcher will also implement single phase as well as 3-phase inverters using dSPACE and further will choose the best control strategy for inverters after implementing various voltage as well as current control strategies. References [1] Agarwal Anupam and Dheeraj Joshi. (2012) “Design of Class-A Chopper for Minimizing Load Voltage Ripple.” in 5th India International Conference on Power Electronics. Delhi, India, 6-8 Dec. 2012: IEEE [2] Bimal K. Bose, “Power Electronics and AC Drives”, Prentice-Hall,’’ NJ, USA, 2002. [3] Iida Takahiko, Hideo Iwamoto, Hisao Oka and Shigeru Funakawa (1980) “New DC Chopper Circuits Using Fast-Switching Reverse- Conducting Thyristors for Low-Voltage DC Motor Control.” in IEEE Transactions on Industry Applications (Volume: IA-16, Issue: 1, Jan. 1980). Jan. 1980: IEEE; 111 - 118. [4] Lang Yifan, Xin Ge, Runan Gu and Yuanyuan Zhang (2017) “The Closed-Loop Design for Buck Chopper Circuit.” in 2017 International Conference on Circuits, Devices and Systems. Chengdu, China, 5-8 Sept. 2017: IEEE; 38-43. [5] Mihajlovic Zoric, Brad Lehman and Chunxiao Sun. (2004) “Output Ripple Analysis of Switching DC-DC Converters.” in IEEE Transactions on Circuits and Systems I: Regular Papers (Volume: 51, Issue: 8, Aug. 2004), 16 August 2004: IEEE; 1596 - 1611.



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[6] Muhammad H. Rashid, “Power electronics circuits, devices and applications”, 2nd ed, Prentice-Hall, 1993. [7] Takeuchi Shun and Keiji Wada. (2014) “Experimental Verification of Noiseless Sampling for Buck Chopper Circuit with Current Control.” in Power Electronics Conference (IPEC-Hiroshima 2014 - ECCE-ASIA). Hiroshima, Japan, 18-21 May 2014: IEEE; 3646 - 3651. [8] Xu Huangsheng, Kevin King and Yashvant Jani. (2007) “High Performance DC Chopper Speed and Current Control of Universal Motors Using a Microcontroller.” in Industry Applications Conference, 2007. 42nd IAS Annual Meeting. Conference Record of the 2007 IEEE. New Orleans, LA, USA, 23-27 Sept. 2007: IEEE; 701 705. Appendix A. Driver circuit It has an optocoupler (6N137) and an OPAMP (uA741). Output of 6N137 is cascaded to inverting input of uA741 as shown in figure 10.

Figure 10: Circuit diagram of driver circuit





6N137 have following features: o Enable input voltage o Enable input current o Output voltage o Output current uA741 have following features: o Supply voltage o Operating temperature

= = = =

Vcc + 0.5V 5mA 7V 50mA

= =

-18V to 18V 00C to 700C

B. MOSFET MOSFET used here is IRF640N and its features are: o o o o o o o

Gate-to-source voltage = = Power dissipation at 250C Turn-ON delay time = Rise time = Turn-ON delay time = Fall time = Drain-to-source breakdown voltage =

±20V 150W 10ns 19ns 23ns 5.5ns 200V