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New self-excited variable speed constant frequency generator for wind power systems
Energy Conversion & Management 41 (2000) 1405±1417
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New self-excited variable speed constant frequency generator for wind power systems Hamid M.B. Metwally* Electrical Power Engineering Department, Faculty of Engineering, Zagazig University, Zagazig, Egypt Received 3 May 1999; accepted 29 October 1999
Abstract In this work, the possibility of using a new single-phase commutator machine as a stand alone selfexcited generator is investigated. The performance of this generator is tested under variable speed operation to simulate the practical case of variable wind turbine speed. The generator is self-excited through a resonance capacitor. The eect of varying the capacitance of this capacitor on the generated voltage and its frequency is studied. Load tests under a wide range of operating conditions are conducted to explore the capability of this type of generator. It has been found that this machine can operate as a variable speed constant frequency generator simply by varying the capacitance of the excitation capacitor. This important property makes this type of generator suitable for use in wind driven power systems. Finally, a mathematical model for the generator is obtained and a simulation program is developed to predict the performance of the generator. Close agreement between the simulation and the experimental results is obtained. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Renewable energy sources; Wind energy; Constant frequency generator; ac commutator machines
1. Introduction Wind energy is one of the most important and promising forms of renewable energy sources. Its use is becoming more and more popular nowadays. This is because the price of fossil fuels is continuously increasing and because this source is a clean and inexhaustible energy source. Thus, wind energy electric systems have been built in many places around the world [1,2]. In * Tel.: +20-55-622-411; fax: +20-55-324-987. 0196-8904/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 1 9 6 - 8 9 0 4 ( 9 9 ) 0 0 1 7 0 - 3
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rural and isolated areas, stand alone power systems are used. When conventional machines are used as generators in these isolated systems, the output voltage will be of variable magnitude and frequency. Electronic converters are then necessary to obtain a constant frequency supply. The initial and maintenance costs of these converters are high. Synchronous and induction generators are widely used in wind energy systems [3±6]. Each type of these machines has its own advantages and disadvantages and also has its own method of control. This control, whether mechanical or electrical, is necessary to obtain a voltage of constant magnitude and frequency which can be connected to the grid. On the other hand, ac commutator machines have proved to be better competitors than conventional ac machines, synchronous and induction, when used as generators in wind power plants. This is because these machines generate a constant frequency voltage irrespective of their shaft speeds when excited from a constant frequency supply. This eliminates the need for electronic converters, which must be used with conventional machines. Thus, ac commutator machines, 3-phase and 1-phase, are used as generators in wind energy systems [7±9]. In a previous work [10], the author has thoroughly studied the performance of this type of generator when connected to the grid. In this paper, the potential capability of the single phase commutator machine as a self-excited stand alone generator for wind energy systems is theoretically and experimentally investigated. This machine is well known and is normally used as a universal motor. Its magnetic circuit is built from silicon steel laminations to be suitable for ac supply. 2. No load characteristics An extensive program of experimental work was conducted to explore the potential capabilities of this type of generator. The laboratory set-up is shown in Fig. 1a, and the speci®cations of the generator are given in Appendix B. It is connected as a single phase self-
Fig. 1. The experimental system.
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excited commutator generator. At no load, the excitation capacitor (C ) is connected in series with the ®eld coil. This capacitor allows only ac current to circulate through the circuit. 2.1. Voltage variation With a given value of capacitance (C ), the generator is driven at variable speed while switch S1 is open. The capacitor voltage, current and the armature voltage are recorded over a wide range of speeds. This is then repeated for six dierent values of capacitance (C ) from 25 to 400 mF. These voltage characteristics are shown in Figs. 2 and 3. As can be seen, the generated voltage increases as the speed is increased at a given value of capacitance. Also, as the capacitance is increased, the voltage decreases at all speeds. It is found that there is a critical speed for each value of capacitance. The generator does not build up any voltage when the speed is lower than this critical speed. This critical speed decreases as the capacitance is increased. This means that for this type of generator to develop voltage at low speeds, a high value of capacitance must be used. 2.2. Current variation The variation of excitation current with speed at dierent values of capacitance (C ) is shown in Fig. 4. The current increases as the speed is increased. Also, as the capacitance is increased the current increases at all speeds. At a given speed, the rate of increase of current with increase in capacitance is higher at low values of capacitance than that at high capacitance values.
Fig. 2. No load capacitor voltage.
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Fig. 3. No load armature voltage.
Fig. 4. No load capacitor current.
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2.3. Frequency variation The frequency characteristics of the generator are shown in Fig. 5. At a given value of capacitance (C ), the frequency increases as the speed is increased. The rate of increase of frequency with speed is higher at lower speeds. As the value of capacitance is increased, the frequency decreases at all speeds. At very high values of capacitance, the frequency becomes almost constant with speed but its value is low. The above characteristics show that this type of generator can operate as a variable speed constant frequency generator simply by changing the capacitance of the excitation capacitor. For example, by changing the capacitance in the range from 25 to 50 mF, a frequency of 50 Hz can be obtained over the speed range from about 1700 to 3500 rpm. Also, it can be seen that at C 400 mF the frequency is almost constant over the whole range of speed from 1000 to 3500 rpm. 3. Load characteristics 3.1. Method of loading As can be seen from Fig. 1, it is possible to load this generator by one of three methods. The load can be connected across the excitation capacitor (C ) or across the armature or the ®eld windings. Load tests were conducted at C 100 mF and 2500 rpm speed with the three possible methods of connection to establish which method is the best one. Fig. 6 shows that the obtainable voltage across the capacitor is the highest one. It is almost double the voltage across either the armature or the ®eld windings. Also, Fig. 7 shows that higher output power
Fig. 5. No load frequency.
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Fig. 6. Load voltage characteristics (at C 100 mF, speed 2500 rpm).
at lower load current is obtainable when the loading is across the capacitor. This proved that loading the generator across the capacitor is better because it produces higher voltage and higher output power at lower load current. This method of connection is used to obtain the generator performance in section 3.2.
Fig. 7. Output power characteristics (at C 100 mF, speed 2500 rpm).
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Fig. 8. Load voltage characteristics.
Fig. 9. Frequency characteristics (resistive load).
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Fig. 10. Output power characteristics.
Fig. 11. Eciency characteristics.
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3.2. Output power Load tests were conducted at a given value of load resistance and at dierent values of capacitance (C ). Only part of the obtained results is presented in Figs. 8±11. The variation of load voltage with speed and capacitance is depicted in Fig. 8. The same trend of variation as in the no load case is found. Fig. 9 shows that the frequency is almost constant at high values of capacitance. The output power and the generator eciency are shown in Figs. 10 and 11. The output power is increased with the increase in speed and is decreased with the increase in capacitance. The eciency is almost constant over the whole range of speeds at a given value of capacitance, but it is greatly increased as the capacitance is decreased. 4. Modeling and simulation 4.1. Armature and ®eld resistances The dc resistances of the armature and the ®eld windings are measured. Both cold and hot resistances are given in Appendix A. 4.2. Field winding inductance The ®eld winding is excited by a variable ac voltage. The applied voltage was varied and both voltage and current are recorded. The voltage was varied over a wide range so that the current changes from 0.1 to 3.2 A, which is a wide range covering about 170% of the
Fig. 12. Armature, ®eld and total inductances.
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operating range of the generator. For each point, the ®eld winding inductance is calculated. Fig. 12 shows how the ®eld winding inductance varies with the ®eld current. The least squares error method for curve ®tting was then used to ®t a polynomial representing the ®eld inductance as function of the ®eld current. It has been found that a polynomial of order six (seven coecients) is accurate enough to represent these measured inductance data. The coecients of this polynomial are given in Appendix A. 4.3. Armature winding inductance The above procedure is repeated here to measure and then ®t a sixth order polynomial to represent the armature winding inductance as a function of the armature current. The variation of the measured armature winding inductance with armature current is shown in Fig. 12. The obtained coecients of the polynomial are given in Appendix A 4.4. model The equivalent circuit of the generator under steady-state operation is shown in Fig. 1b. This equivalent circuit represents the generator whether it is loaded or unloaded, where: E is the generated emf (V), R is the equivalent series resistance of the circuit (O), XL is the equivalent series inductive reactance of the circuit (O), XC is the equivalent series capacitive reactance of the circuit (O). Since there is no external source in the circuit, current and, hence, voltage can be built up only at resonance. This means that the equivalent circuit is at resonance under all steady-state operating conditions. This is con®rmed by plotting the measured inductive and capacitive
Fig. 13. Variation of XL and Xc with speed.
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reactances (XL and XC) in Fig. 13. This ®gure shows that XL is equal to XC at dierent values of excitation capacitance and over a wide range of operating speeds. For each value of capacitance, there is a speed under which the two reactances are not equal, and hence, resonance can not be obtained. This is expected because at very low frequency, XC tends to in®nity while XL tends to zero. This property is exploited to predict the steady-state performance of the generator. First, the generator parameters are obtained, and then a computer program is developed to determine the generator performance under any steady-state operating condition. This will be explained in the following subsections. 4.5. Simulation A computer program is developed to obtain the performance of the generator under dierent operating conditions. At any operating condition, i.e. a given speed and capacitance, the program searches for the operating current. The procedure can be summarised in the following steps: 1. At any operating condition, i.e. a given speed and capacitance value, the program searches for a value of XC from the measured tabulated data. Cubic spline interpolation in two dimensions is used to calculate the intermediate values of XC. 2. Using this value of XC and the known value of capacitance, the operating frequency is calculated from f 1=2pCXc : 3. The inductance is then calculated using the formula L Xc =2pf: It should be noted that XL Xc because the circuit is at resonance. 4. The circulating current is then calculated using the ®tted polynomial of the inductance.
Fig. 14. Measured and calculated armature current.
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Under no load conditions, this current is the only current in the circuit. Under load conditions, this current is divided between the load and the capacitor. The load voltage is then obtained by multiplying the load current by the load resistance. 5. Finally, the output power and eciency are calculated at this operating point. The above simulation program is used to calculate the performance of the generator under dierent operating conditions. Fig. 14 shows a comparison between the measured and calculated current. Close agreement between the measured and predicted values is evident. 5. Conclusions This paper presents an experimental and mathematical investigation of the performance characteristics of a new self-excited variable speed constant frequency generator. Tests were conducted at a wide range of operating conditions. The results obtained showed that: 1. The magnitude and frequency of the generated voltage depend on both the speed and the capacitance of the excitation capacitor. 2. For each value of capacitance, there is a critical speed under which the generator fails to build up voltage. This critical speed decreases as the capacitance is increased. 3. At high values of excitation capacitance, the frequency becomes almost constant over the whole range of speeds. 4. It is possible to obtain constant frequency voltage simply by changing the capacitance value with speed. 5. It is better to load this generator across its excitation capacitor rather than across its armature. 6. There is no need for a separate constant frequency source to excite the generator .The above points showed that this machine is suitable for use as a generator with wind driven turbines in rural and isolated areas.
Appendix A. Generator parameters See Tables 1 and 2.
Table 1 Armature and ®eld resistances Winding
Armature (O)
Field (O)
Cold Hot
10.23 13.0
4.9 5.76
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Table 2 Coecients of ®eld inductance and armature inductance polynomials
A0 A1 A2 A3 A4 A5 A6
Field
Armature
0.1505 0.120544 ÿ0.04990 ÿ0.00578 ÿ0.00339 0.004292 ÿ0.00073
0.092223 0.083678 ÿ0.12264 0.091752 ÿ0.03891 0.008462 ÿ0.00073
Appendix B. Generator ratings The experimental system consists of two machines: the universal motor and the dc motor. The universal motor was reconnected to operate as a single phase self-excited generator. The dc motor was used to drive the generator at controllable speed. The ratings of the generator are: power 0.333 hp, current 1.9 A, voltage 220 V, frequency 50 Hz, speed 5000 rpm. References [1] Warne DF, Calnan PG. Generation of electricity from the wind. IEE Proc 1977;124(11R):963±85. [2] Musgrove PJ. Wind energy conversion: an introduction. IEE Proc 1983;130(9):506±16 [pt. A]. [3] Weh H. Directly-driven permanent magnet excited synchronous generator for variable speed operation. In: Proc. of the 1988 European Community Wind Energy Conference, Herning, Denmark. Herning, 1988. p. 566± 72. [4] Spooner E, Williamson AC. Permanent magnet generators for wind power applications. In: Proc. of the 1992 International Conf. on Electrical Machines, Manchester, UK, 1992. p. 1048±52. [5] Daly SA, de Paor AM, Simpson RJ. Modeling and control of a wind-driven induction generator for water storage heating. IEE Proc A 1983;130(9):596±603. [6] Yegha SS, Johnny VJ. Contributions to the steady-state analysis of wind turbine driven self-excited induction generator. IEEE Trans Energ Convers 1986;EC-1(1):169±76. [7] Abul Masrur MD, El-Jamous SG, Ayoub AK. The polyphase commutator machine as a wind generator. IEEE Trans PAS 1984;PAS-103(10):2838±43. [8] Ghoneem GA, Abdel-Kader FE, Holmes PG. The polyphase ac Commutator machine as a variable-speed constant-frequency generator. 23rd UPEC, 22±24 September, 1988, Nottingham, UK. [9] Abdel-Kader FE, Morsi AH, Hassan SA, Ghoneem GA. The single phase commutator generator in the wind energy plant. Int. Symposium on Electric Energy Conversion in Power Systems, May 25±27, 1989, Capri, Italy. [10] Metwally HMB. Operation of new variable-speed constant-voltage and frequency generator connected to the grid. In preparation.
www.elsevier.com/locate/enconman
New self-excited variable speed constant frequency generator for wind power systems Hamid M.B. Metwally* Electrical Power Engineering Department, Faculty of Engineering, Zagazig University, Zagazig, Egypt Received 3 May 1999; accepted 29 October 1999
Abstract In this work, the possibility of using a new single-phase commutator machine as a stand alone selfexcited generator is investigated. The performance of this generator is tested under variable speed operation to simulate the practical case of variable wind turbine speed. The generator is self-excited through a resonance capacitor. The eect of varying the capacitance of this capacitor on the generated voltage and its frequency is studied. Load tests under a wide range of operating conditions are conducted to explore the capability of this type of generator. It has been found that this machine can operate as a variable speed constant frequency generator simply by varying the capacitance of the excitation capacitor. This important property makes this type of generator suitable for use in wind driven power systems. Finally, a mathematical model for the generator is obtained and a simulation program is developed to predict the performance of the generator. Close agreement between the simulation and the experimental results is obtained. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Renewable energy sources; Wind energy; Constant frequency generator; ac commutator machines
1. Introduction Wind energy is one of the most important and promising forms of renewable energy sources. Its use is becoming more and more popular nowadays. This is because the price of fossil fuels is continuously increasing and because this source is a clean and inexhaustible energy source. Thus, wind energy electric systems have been built in many places around the world [1,2]. In * Tel.: +20-55-622-411; fax: +20-55-324-987. 0196-8904/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 1 9 6 - 8 9 0 4 ( 9 9 ) 0 0 1 7 0 - 3
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rural and isolated areas, stand alone power systems are used. When conventional machines are used as generators in these isolated systems, the output voltage will be of variable magnitude and frequency. Electronic converters are then necessary to obtain a constant frequency supply. The initial and maintenance costs of these converters are high. Synchronous and induction generators are widely used in wind energy systems [3±6]. Each type of these machines has its own advantages and disadvantages and also has its own method of control. This control, whether mechanical or electrical, is necessary to obtain a voltage of constant magnitude and frequency which can be connected to the grid. On the other hand, ac commutator machines have proved to be better competitors than conventional ac machines, synchronous and induction, when used as generators in wind power plants. This is because these machines generate a constant frequency voltage irrespective of their shaft speeds when excited from a constant frequency supply. This eliminates the need for electronic converters, which must be used with conventional machines. Thus, ac commutator machines, 3-phase and 1-phase, are used as generators in wind energy systems [7±9]. In a previous work [10], the author has thoroughly studied the performance of this type of generator when connected to the grid. In this paper, the potential capability of the single phase commutator machine as a self-excited stand alone generator for wind energy systems is theoretically and experimentally investigated. This machine is well known and is normally used as a universal motor. Its magnetic circuit is built from silicon steel laminations to be suitable for ac supply. 2. No load characteristics An extensive program of experimental work was conducted to explore the potential capabilities of this type of generator. The laboratory set-up is shown in Fig. 1a, and the speci®cations of the generator are given in Appendix B. It is connected as a single phase self-
Fig. 1. The experimental system.
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excited commutator generator. At no load, the excitation capacitor (C ) is connected in series with the ®eld coil. This capacitor allows only ac current to circulate through the circuit. 2.1. Voltage variation With a given value of capacitance (C ), the generator is driven at variable speed while switch S1 is open. The capacitor voltage, current and the armature voltage are recorded over a wide range of speeds. This is then repeated for six dierent values of capacitance (C ) from 25 to 400 mF. These voltage characteristics are shown in Figs. 2 and 3. As can be seen, the generated voltage increases as the speed is increased at a given value of capacitance. Also, as the capacitance is increased, the voltage decreases at all speeds. It is found that there is a critical speed for each value of capacitance. The generator does not build up any voltage when the speed is lower than this critical speed. This critical speed decreases as the capacitance is increased. This means that for this type of generator to develop voltage at low speeds, a high value of capacitance must be used. 2.2. Current variation The variation of excitation current with speed at dierent values of capacitance (C ) is shown in Fig. 4. The current increases as the speed is increased. Also, as the capacitance is increased the current increases at all speeds. At a given speed, the rate of increase of current with increase in capacitance is higher at low values of capacitance than that at high capacitance values.
Fig. 2. No load capacitor voltage.
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Fig. 3. No load armature voltage.
Fig. 4. No load capacitor current.
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2.3. Frequency variation The frequency characteristics of the generator are shown in Fig. 5. At a given value of capacitance (C ), the frequency increases as the speed is increased. The rate of increase of frequency with speed is higher at lower speeds. As the value of capacitance is increased, the frequency decreases at all speeds. At very high values of capacitance, the frequency becomes almost constant with speed but its value is low. The above characteristics show that this type of generator can operate as a variable speed constant frequency generator simply by changing the capacitance of the excitation capacitor. For example, by changing the capacitance in the range from 25 to 50 mF, a frequency of 50 Hz can be obtained over the speed range from about 1700 to 3500 rpm. Also, it can be seen that at C 400 mF the frequency is almost constant over the whole range of speed from 1000 to 3500 rpm. 3. Load characteristics 3.1. Method of loading As can be seen from Fig. 1, it is possible to load this generator by one of three methods. The load can be connected across the excitation capacitor (C ) or across the armature or the ®eld windings. Load tests were conducted at C 100 mF and 2500 rpm speed with the three possible methods of connection to establish which method is the best one. Fig. 6 shows that the obtainable voltage across the capacitor is the highest one. It is almost double the voltage across either the armature or the ®eld windings. Also, Fig. 7 shows that higher output power
Fig. 5. No load frequency.
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Fig. 6. Load voltage characteristics (at C 100 mF, speed 2500 rpm).
at lower load current is obtainable when the loading is across the capacitor. This proved that loading the generator across the capacitor is better because it produces higher voltage and higher output power at lower load current. This method of connection is used to obtain the generator performance in section 3.2.
Fig. 7. Output power characteristics (at C 100 mF, speed 2500 rpm).
H.M.B. Metwally / Energy Conversion & Management 41 (2000) 1405±1417
Fig. 8. Load voltage characteristics.
Fig. 9. Frequency characteristics (resistive load).
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Fig. 10. Output power characteristics.
Fig. 11. Eciency characteristics.
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3.2. Output power Load tests were conducted at a given value of load resistance and at dierent values of capacitance (C ). Only part of the obtained results is presented in Figs. 8±11. The variation of load voltage with speed and capacitance is depicted in Fig. 8. The same trend of variation as in the no load case is found. Fig. 9 shows that the frequency is almost constant at high values of capacitance. The output power and the generator eciency are shown in Figs. 10 and 11. The output power is increased with the increase in speed and is decreased with the increase in capacitance. The eciency is almost constant over the whole range of speeds at a given value of capacitance, but it is greatly increased as the capacitance is decreased. 4. Modeling and simulation 4.1. Armature and ®eld resistances The dc resistances of the armature and the ®eld windings are measured. Both cold and hot resistances are given in Appendix A. 4.2. Field winding inductance The ®eld winding is excited by a variable ac voltage. The applied voltage was varied and both voltage and current are recorded. The voltage was varied over a wide range so that the current changes from 0.1 to 3.2 A, which is a wide range covering about 170% of the
Fig. 12. Armature, ®eld and total inductances.
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operating range of the generator. For each point, the ®eld winding inductance is calculated. Fig. 12 shows how the ®eld winding inductance varies with the ®eld current. The least squares error method for curve ®tting was then used to ®t a polynomial representing the ®eld inductance as function of the ®eld current. It has been found that a polynomial of order six (seven coecients) is accurate enough to represent these measured inductance data. The coecients of this polynomial are given in Appendix A. 4.3. Armature winding inductance The above procedure is repeated here to measure and then ®t a sixth order polynomial to represent the armature winding inductance as a function of the armature current. The variation of the measured armature winding inductance with armature current is shown in Fig. 12. The obtained coecients of the polynomial are given in Appendix A 4.4. model The equivalent circuit of the generator under steady-state operation is shown in Fig. 1b. This equivalent circuit represents the generator whether it is loaded or unloaded, where: E is the generated emf (V), R is the equivalent series resistance of the circuit (O), XL is the equivalent series inductive reactance of the circuit (O), XC is the equivalent series capacitive reactance of the circuit (O). Since there is no external source in the circuit, current and, hence, voltage can be built up only at resonance. This means that the equivalent circuit is at resonance under all steady-state operating conditions. This is con®rmed by plotting the measured inductive and capacitive
Fig. 13. Variation of XL and Xc with speed.
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reactances (XL and XC) in Fig. 13. This ®gure shows that XL is equal to XC at dierent values of excitation capacitance and over a wide range of operating speeds. For each value of capacitance, there is a speed under which the two reactances are not equal, and hence, resonance can not be obtained. This is expected because at very low frequency, XC tends to in®nity while XL tends to zero. This property is exploited to predict the steady-state performance of the generator. First, the generator parameters are obtained, and then a computer program is developed to determine the generator performance under any steady-state operating condition. This will be explained in the following subsections. 4.5. Simulation A computer program is developed to obtain the performance of the generator under dierent operating conditions. At any operating condition, i.e. a given speed and capacitance, the program searches for the operating current. The procedure can be summarised in the following steps: 1. At any operating condition, i.e. a given speed and capacitance value, the program searches for a value of XC from the measured tabulated data. Cubic spline interpolation in two dimensions is used to calculate the intermediate values of XC. 2. Using this value of XC and the known value of capacitance, the operating frequency is calculated from f 1=2pCXc : 3. The inductance is then calculated using the formula L Xc =2pf: It should be noted that XL Xc because the circuit is at resonance. 4. The circulating current is then calculated using the ®tted polynomial of the inductance.
Fig. 14. Measured and calculated armature current.
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Under no load conditions, this current is the only current in the circuit. Under load conditions, this current is divided between the load and the capacitor. The load voltage is then obtained by multiplying the load current by the load resistance. 5. Finally, the output power and eciency are calculated at this operating point. The above simulation program is used to calculate the performance of the generator under dierent operating conditions. Fig. 14 shows a comparison between the measured and calculated current. Close agreement between the measured and predicted values is evident. 5. Conclusions This paper presents an experimental and mathematical investigation of the performance characteristics of a new self-excited variable speed constant frequency generator. Tests were conducted at a wide range of operating conditions. The results obtained showed that: 1. The magnitude and frequency of the generated voltage depend on both the speed and the capacitance of the excitation capacitor. 2. For each value of capacitance, there is a critical speed under which the generator fails to build up voltage. This critical speed decreases as the capacitance is increased. 3. At high values of excitation capacitance, the frequency becomes almost constant over the whole range of speeds. 4. It is possible to obtain constant frequency voltage simply by changing the capacitance value with speed. 5. It is better to load this generator across its excitation capacitor rather than across its armature. 6. There is no need for a separate constant frequency source to excite the generator .The above points showed that this machine is suitable for use as a generator with wind driven turbines in rural and isolated areas.
Appendix A. Generator parameters See Tables 1 and 2.
Table 1 Armature and ®eld resistances Winding
Armature (O)
Field (O)
Cold Hot
10.23 13.0
4.9 5.76
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Table 2 Coecients of ®eld inductance and armature inductance polynomials
A0 A1 A2 A3 A4 A5 A6
Field
Armature
0.1505 0.120544 ÿ0.04990 ÿ0.00578 ÿ0.00339 0.004292 ÿ0.00073
0.092223 0.083678 ÿ0.12264 0.091752 ÿ0.03891 0.008462 ÿ0.00073
Appendix B. Generator ratings The experimental system consists of two machines: the universal motor and the dc motor. The universal motor was reconnected to operate as a single phase self-excited generator. The dc motor was used to drive the generator at controllable speed. The ratings of the generator are: power 0.333 hp, current 1.9 A, voltage 220 V, frequency 50 Hz, speed 5000 rpm. References [1] Warne DF, Calnan PG. Generation of electricity from the wind. IEE Proc 1977;124(11R):963±85. [2] Musgrove PJ. Wind energy conversion: an introduction. IEE Proc 1983;130(9):506±16 [pt. A]. [3] Weh H. Directly-driven permanent magnet excited synchronous generator for variable speed operation. In: Proc. of the 1988 European Community Wind Energy Conference, Herning, Denmark. Herning, 1988. p. 566± 72. [4] Spooner E, Williamson AC. Permanent magnet generators for wind power applications. In: Proc. of the 1992 International Conf. on Electrical Machines, Manchester, UK, 1992. p. 1048±52. [5] Daly SA, de Paor AM, Simpson RJ. Modeling and control of a wind-driven induction generator for water storage heating. IEE Proc A 1983;130(9):596±603. [6] Yegha SS, Johnny VJ. Contributions to the steady-state analysis of wind turbine driven self-excited induction generator. IEEE Trans Energ Convers 1986;EC-1(1):169±76. [7] Abul Masrur MD, El-Jamous SG, Ayoub AK. The polyphase commutator machine as a wind generator. IEEE Trans PAS 1984;PAS-103(10):2838±43. [8] Ghoneem GA, Abdel-Kader FE, Holmes PG. The polyphase ac Commutator machine as a variable-speed constant-frequency generator. 23rd UPEC, 22±24 September, 1988, Nottingham, UK. [9] Abdel-Kader FE, Morsi AH, Hassan SA, Ghoneem GA. The single phase commutator generator in the wind energy plant. Int. Symposium on Electric Energy Conversion in Power Systems, May 25±27, 1989, Capri, Italy. [10] Metwally HMB. Operation of new variable-speed constant-voltage and frequency generator connected to the grid. In preparation.