EPE Association: EPE 1991 - 28 - Session 3.6: PWM TECHNIQUES AND CURRENT CONTROLLERS

EPE 1991 - 28 - Session 3.6: PWM TECHNIQUES AND CURRENT CONTROLLERS
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 1991 - Conference > EPE 1991 - 28 - Session 3.6: PWM TECHNIQUES AND CURRENT CONTROLLERS

   [return to parent folder]

   APPLICATION OF STATE-PLANE AVERAGE METHOD TO CONVERTERS WITH FAST VARYING VARIABLES
By B. Margaritis; H. Grotstollen [View]
[Download]

Abstract: A new approach enables to consider fast and heavily varying state variables when applying state-space average method and is performed stepwise: At first an approximate dc model is calculated by use of the genuine method. Using the results, the fast variables appearing during short intervals within the switching period are investigated: The mean values of these variables during each short interval and the durations of these intervals are calculated. At last state-space averaging is repeated under consideration of the short intervals during which the fast varying variables are replaced by their mean values. The improvement which is achieved by the method is demonstrated at an example.

   A NEW CONTROL METHOD FOR CURRENT-SOURCE INVERTERS WITH SELF-EXTINCTION DEVICES, COMBINING LOW DISTORTION OF VOLTAGE AND CURRENT WITH FAST DYNAMIC RESPONSE
By G. Amler [View]
[Download]

Abstract: Self-extinction devices such as GTO thyristors provide the possibility to set up current-source inverters with sinusoidal inputs and outputs. For a high quality drive the resonant circuit made up with the capacitors at the inverter terminals and the machine inductances has to be kept under control. With an on-line calculation of the PWM switching times, not only the voltage but also the current is kept very close to the reference value, although the switching frequency is limited to a low maximum value. Measurements show the practicability of the suggested control scheme with the results of a low noise but high dynamic drive.

   CONTROL STRATEGIES FOR THE DISCONTINUOUS CURRENT MODE OF AC DRIVES WITH PWM INVERTERS
By Y. Wang; H. Grotstollen [View]
[Download]

Abstract: In ac drives, complicated error voltages are caused by the discontinuous current mode of PWM inverters. The static and dynamic performance of the drives can, therefore, not be assured to be satisfying by the conventional current controllers. This paper describes, after summarizing the discontinuous current mode with the experimental results, control measures to compensate the error voltages. The digital voltage control and the model reference adaptive control are suggested and investigated.

   A NOVEL PWM TECHNIQUE TO DECREASE LOWER HARMONICS
By Tsuneo Kume; Sumitoshi Sonoda; Hidetoshi Ryu; Eiji Watanabe [View]
[Download]

Abstract: Two-phase pulse-width modulation is widely used for the constant V/f type three-phase motor drives. Here, the intervals between 60 to 120 degrees and 240 to 300 degrees, in each phase, are not modulated and the remaining two phases are modulated. In this manner, the switching in one cycle is decreased and a higher maximum voltage is obtained. However, the dominant harmonic components are the sidebands around the carrier frequency which cause current ripple and audible noise. A new PWM method is proposed in this paper. A rectangular wave which has the frequency of three times the fundamental frequency is superimposed to the line voltages. The optimal magnitude of this signal is chosen so that the sideband components around the carrier frequency are minimized.

   STUDY OF 2 AND 3-LEVEL PRECALCULATED MODULATIONS
By B. Velaerts; P. Mathys; Z. F. Zendaoui [View]
[Download]

Abstract: This paper presents a comparative study of 2 and 3-level pulse-width modulated precalculated waveforms, applied to voltage source inverters. Two aspects have been investigated: global optimization of the loss factor o (up to 7 angles per quarter of cycle) and selective harmonic elimination (up to 5 angles per quarter of cycle) are taken into account. This research is intended to modulators implementing both sinusoidal and precalculated modulations together in a same strategy. The harmonics rejected in the DC link are analyzed through a newly defined rejection factor p, as well as the effect of PWM on the current going through the DC-side capacitors of the 3-level inverter. A whole strategy of modulation, which is implemented in C language on a 8097 microcontroller, is presented, completed by practical measurements on a 8 kW 3-level inverter.

   A NEW GENERALIZED MULTILEVEL THREE-PHASE STRUCTURE CONTROLLED BY PWM
By A. Campagna; G. Carrara; D. Casini; R. Salutari [View]
[Download]

Abstract: This paper presents a new three-phase generalized multilevel structure for a Voltage Source lnverter. A conversion system based on a five level realization of the structure employing DMOSFETs and controlled by high frequency multilevel subharmonic PWM is shown. Experimental results are presented. Improvements in the harmonic contents with respect to a conventional bipolar inverter are pointed out.

   NEW REGULAR-SAMPLED HARMONIC ELIMINATION PWM TECHNIQUES FOR DRIVES AND STATIC-POWER CONVERTERS
By Sidney Robert Bowes [View]
[Download]

Abstract: New Harmonic Elimination and Harmonic Minimisation PWM strategies for voltage-source and current-source inverters have recently been developed using modified Regular-Sampling techniques. These new PWM techniques can be applied to Drives, Unincerruptible Power Supplies and Static Frequency Changers. These new PWM strategies can be generated on-line in real-time using a simple microprocessor software algorithm, without resorting to the usual off-line time-consuming and complex mainframe computer Harmonic Elimination numerical techniques. The microprocessor implementation and generation of these new PWM techniques can be achieved using two-timer and single-timer microprocessor implementations. Experimental results are presented to demonstrate the special features of these new microprocessor-based Regular Sampled Harmonic Elimination / Minimisation PWM techniques.

   OVERSHOOT AND LIMIT CYCLE FREE CURRENT CONTROL METHOD FOR PWM INVERTERS
By Samir Salama; Sarah Lennon [View]
[Download]

Abstract: The tolerance-band (hysteresis) current control method is widely used in the control of high dynamic speed-controlled drives fed from voltage-source PWM-inverters. In this paper a new current controller, which completely removes the problems associated with this traditional method, will be presented. A comparison of the new controller with the hysteresis current controller shows a considerable reduction of the switching frequency of the inverter while eliminating the overshoot in the current deviation. Analytical and experimental investigations on a current regulated induction motor drive confirm the predicted advantages of the new current controller.

   ACOUSTIC NOISE REDUCED PWM CONVERTER AND INVERTER USING BJTs AND IGBTs
By Katsunori Taniguchi; Yoji Tomiyama; Tsuyoshi Iwatani; Hisaichi Irie [View]
[Download]

Abstract: Acoustic noise reduced converter and inverter suitable for use with bipolar junction transistor (BJT) and insulated gate bipolar transistor (IGBT) is described. A modulating signal for the three-phase PWM system is obtained by modifying the specific trapezoidal wave. The heating of the devices is reduced because the PWM system stops the switching operation during two-thirds period. Storage time of the BJT and IGBT is compensated by the new PWM technique. In the PWM converter, the input current is converted into a sinusoidal waveform and the power factor of the input power can be adjusted to arbitrary values. In the PWM inverter, torque ripple of the induction motor can be reduced by the new PWM technique. In both systems, sidebands of carrier frequency exist in over audible range.

   PULSE POSITION MODULATION FOR INVERTER-FED AC DRIVES
By X. Gao; J. Richardson [View]
[Download]

Abstract: Pulse position modulation (PPM) is a new technique which complements existing PWM strategies. PPM has the advantage of ease of pulse generation and control without complex circuitry. This development outlines the theoretica] development and practical implementation of the technique for a 3-phase inverter-fed a.c. induction drive system. The scheme is shown to be somewhat simpler and more flexible than that of near-optimal PWM control. No extensive arithmetic operations are required to produce the inverter gate triggering trains. The attraction of slightly reduced pulse widths in PPM control enables higher switching frequencies. Spectrum analyses of PPM waveforms are obtained numerically and compared with practical results. The disadvantage of a somewhat higher total harmonic distortion with PPM is not considered detrimental for a.c. drives.

   ANALYSIS OF THE HARMONICS IN VOLTAGE FED INVERTER DRIVES CAUSED BY PWM SCHEMES WITH DISCONTINUOUS SWITCHING OPERATION
By Heinz van der Broeck [View]
[Download]

Abstract: This paper deals with the pulse width modulation (PWM) for three phase voltage fed inverter drives. A review is made on established PWM strategies with continuous and discontinuous switching operation. Although PWM schemes with discontinuous switching operation generate higher harmonics than the optimum space vector PWM they are of special interest because of their lower switching losses. A new PWM scheme is presented which leaves the outputs of the inverter legs one after another on the negative rail of the DC supply voltage for 120° intervals. The mean squared value of the harmonic content of the current caused by this PWM scheme in a three phase load as well as the relative reduction of the switching losses are determined. The analysis is based on the characteristic drive parameters resulting in pure analytical equations for general use. A comparison is made to the corresponding currents of established PWM schemes. In a final evaluation application areas for the different PWM schemes with continuous and discontinuous switching operation are shown.

   The Optimal Switching Frequency for PWM Driven DC Motors by Simulation
By D.K.W. Cheng; C.K. Lee [View]
[Download]

Abstract: A more realistic simulation of a PWM driven DC motor switching at different frequencies is performed, and the corresponding switching current spikes, inductive current ripples, rms power delivered to the motor, and harmonic power loss are calculated. The optimal chopping frequency can then be selected based on the above results with the criteria of minimum current spikes, minimum current ripples, minimum harmonic power loss and maximum rms power delivered to the motor. It is found that the faster the rise and fall times of the PWM, the higher the switching current spikes and this determines the highest switching frequency. A more realistic model of the DC motor with high frequency effects is used [1] in the simulation. The equivalent circuit of the armature winding is obtained by the curve fitting method using the software package MATLAB. The software used for simulation is PSPICE which is a circuit simulation tool.

   OPTIMIZATION OF THREE PHASE PULSE PATTERN BY VARIABLE ZERO SEQUENCE COMPONENT
By L. Abraham; R. Blümel [View]
[Download]

Abstract: Approaching the desired output voltage curve of a power electronic inverter by pulse width modulation the pulse pattern of every individual sampling step may be investigated off-line deducing algorithms for optimized modulation procedure. For single phase inverters symmetrical switching points are best. ln three phase inverters it is possible to add a freely set zero sequence component to the desired voltage without changing the modulation factor but varying the harmonics produced by pulse width modulation. This degree of freedom may be used for optimization of pulse pattern in each sampling interval. This method is demonstrated and investigated, Theoretical and practical results are presented.

   CONTROL OF THE NEUTRAL POINT OF A THREE-LEVEL-INVERTER
By H. L. Klaver [View]
[Download]

Abstract: Since many years several types of inverters are used for the drive of squirrel cage induction machines. The upper limit in power is shifted over the 1 MW since the introduotion of three-level inverters and the availability of large GTO-switches. This type of inverter ia also called Neutral-point-clamped inverter. This inverter is a voltage source inverter in which the dc link capacitor is split into two to create a third level. One of the key items in controlling a three-level inverter is keeping the neutral point (= zero level) at a constant value of half the overall voltage. For that reason an extra control loop shall be integrated in the PWM of a three-level inverter. Simulations of the PWM with the extra control loop have been carried out for different operating points and gave good results. Tests on a prototype of 3 MVA are planned for the summer of 1991.

   NEW PWM METHOD BASED ON FLUX-LINKAGE TRAJECTORY CONTROL
By Zheng-Tang Yang; Guo-Hai Liu [View]
[Download]

Abstract: Based on flux-linkage trajectory control principle, a new pulse-width modulation (PWM) switching strategy is presented. By using modes of the "180-degree-on" and "120-degree-on" alternately, it has 12 voltage vectors, double of the conventional one. It is shown that this strategy makes the flux amplitude error between the practical flux-linkage trajectory and the ideal one much smaller. By spliting zero voltage vectors and scattering them in the non-zero voltage period, the more accurate control of rotating speed of the flux-linkage vectors can be achieved. Simulation results have demonstrated that the PWM strategy presented is superior to the conventional one.

   CONTROL ALGORITHM OF A THREE PHASE VOLTAGE SOURCED REVERSIBLE RECTIFIER
By I. Nagy [View]
[Download]

Abstract: The paper discusses a three phase voltage sourced reversible rectifier known from the literature. It achieves bidirectional power flow between a 3 phase a.c. supply and a d.c. bus. The sinusoidal currents drawn from the network are forced by hysteresis current control. The device operates at unity power factor. The novelty of the paper is the mathematical analysis of the configuration using Park vectors and the determination of sophisticated control algorithm of the switching sequences of the controlled switches tied to the instantaneous states of the circuit. The results provide a solid basis for simulation and for microprocessor control software. Computer simulation results presented support the theory.

   DESIGN OF A WIDE RANGE VARIABLE VOLTAGE VARIABLE FREQUENCY INVERTER MODULATOR USING THE COUNTER NUMBER METHOD
By Maria Isabel Gimenez de Guzman; Victor Manuel Guzman; Peter Bowler [View]
[Download]

Abstract: This paper presents the design of a very simple and economical Microcontrolled lnverter Modulator, based on the INTEL 8031, able to drive a three-phase induction motor over a wide frequency range (0.1 to 100 Hz), allowing an independent selection of the normalized fundamental voltage demand, output frequency and sense of rotation. Both Subharmonic PWM technique and Precalculated Switching Angle patterns, quantized using the Twelfth Mode and processed using the new Counter Number Method, developed by the authors, are employed in the implementation. Two Programmable Analog Pulse Generators are presented and their advantages and disadvantages are discussed.

   A PWM 3-phase on-line controller for A.C. drives
By J. Richardson; G. Bezanov [View]
[Download]

Abstract: The laws governing the commutation angles of optimal PWM strategies invariably describe a non-linear relationship to the fundamental component magnitude. For this reason these strategies cannot be realised using natural sampling techniques and are therefore entirely software-based. A considerable disadvantage of software based optimal strategies is that they cannot be described by an analytical expression which can be executed in real-time. In this investigation an analytic expression is defined which describes the modulation process of the harmonic elimination strategy. This modulation process is reduced to a fast algorithm for on-line calculation of the required pulse widths for eliminating the first four non-triplen harmonics and controlling the fundamental component. Results shown include the harmonic content of the waveforms supplied to a three phase induction motor load at selected operating frequencies. Also shown are selected open loop responses to sudden changes in supply frequency.

   PULSE-WITH-CODE MODULATION IN VOLTAGE SOURCE INVERTERS WITH VARIABLE OUTPUT FREQUENCY
By Valentin T. Oleschuk [View]
[Download]

Abstract: The algorithms of nonstandard pulse-width-code modulation, which provides smooth shockless inverter ratio changing, have been considered. This comparatively simple and easy digitisation control principle is based on the continuously step-by-step coding (identification) the widths of pulses and pauses of output voltage formed at clock points with the one of the main range of output pulses, connected directly with the output frequency. The basic methods of the pulse-width-code modulation for three-phase thyristor inverters with control both inside and in border of clock intervals have been developped for the standard and nonstandard performance modes. The analytical description of the rational control laws for ac inverter drives has been done for the instances when average frequency of inverter with commutation vary according to different linear and nonlinear correlations. The analysis of the harmonic composition of the various versions of inverter output voltage has been carried out and technique of its improvement has been considered.

   CONSTANT CURRENT MODE FOR PARALLEL LOADED RESONANCE CIRCUIT INVERTER: AC AND DC APPLICATIONS
By M. I. Mahmoud; J. Barbaroux; R. Perret [View]
[Download]

Abstract: Power electronic inverter with parallel loaded resonance circuit in the constant current mode of operation is investigated in order to obtain a true constant current source CCS. The implementation of this circuit with the power electronic inverter have been carried out for a high power constant current source inverter CCSI. The suitable inverter design for DC and three phase AC applications has been investigated. Two proposed control schemes for DC motor fed by a CCSI and three phase induction motor through a three phase CCSI have been realized. Theoretical and simulation studies have been made to obtain the form of the electrical variables for the CCSI in each case study.

   A SUBOPTIMAL PREDICTIVE CURRENT CONTROLLER FOR VSI-PWM INVERTERS
By Wilfried Hofmann [View]
[Download]

Abstract: A novel current controller for ac-drives fed by VSI inverter is proposed. It is explained the analytical relation between the current error phasor and its gradient based on a linear prediction. The selection of the output voltage phasor is realised result from the off-line computation of the inequations for the seven inverter output voltages and its error gradients by control options for small and large signal operations. The existence of approximated ranges for the error and motor voltage sectors gives the possibility to use geometrical features dependent on speed ranges. It results in a simple signal-processing for the current controller with a higher sampling rate and lead to a good control behaviour near to the optimum.

EPE 1991 - 28 - Session 3.6: PWM TECHNIQUES AND CURRENT CONTROLLERS
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 1991 - Conference > EPE 1991 - 28 - Session 3.6: PWM TECHNIQUES AND CURRENT CONTROLLERS
	[return to parent folder]

	APPLICATION OF STATE-PLANE AVERAGE METHOD TO CONVERTERS WITH FAST VARYING VARIABLES By B. Margaritis; H. Grotstollen	[View] [Download]
Abstract: A new approach enables to consider fast and heavily varying state variables when applying state-space average method and is performed stepwise: At first an approximate dc model is calculated by use of the genuine method. Using the results, the fast variables appearing during short intervals within the switching period are investigated: The mean values of these variables during each short interval and the durations of these intervals are calculated. At last state-space averaging is repeated under consideration of the short intervals during which the fast varying variables are replaced by their mean values. The improvement which is achieved by the method is demonstrated at an example.

	A NEW CONTROL METHOD FOR CURRENT-SOURCE INVERTERS WITH SELF-EXTINCTION DEVICES, COMBINING LOW DISTORTION OF VOLTAGE AND CURRENT WITH FAST DYNAMIC RESPONSE By G. Amler	[View] [Download]
Abstract: Self-extinction devices such as GTO thyristors provide the possibility to set up current-source inverters with sinusoidal inputs and outputs. For a high quality drive the resonant circuit made up with the capacitors at the inverter terminals and the machine inductances has to be kept under control. With an on-line calculation of the PWM switching times, not only the voltage but also the current is kept very close to the reference value, although the switching frequency is limited to a low maximum value. Measurements show the practicability of the suggested control scheme with the results of a low noise but high dynamic drive.

	CONTROL STRATEGIES FOR THE DISCONTINUOUS CURRENT MODE OF AC DRIVES WITH PWM INVERTERS By Y. Wang; H. Grotstollen	[View] [Download]
Abstract: In ac drives, complicated error voltages are caused by the discontinuous current mode of PWM inverters. The static and dynamic performance of the drives can, therefore, not be assured to be satisfying by the conventional current controllers. This paper describes, after summarizing the discontinuous current mode with the experimental results, control measures to compensate the error voltages. The digital voltage control and the model reference adaptive control are suggested and investigated.

	A NOVEL PWM TECHNIQUE TO DECREASE LOWER HARMONICS By Tsuneo Kume; Sumitoshi Sonoda; Hidetoshi Ryu; Eiji Watanabe	[View] [Download]
Abstract: Two-phase pulse-width modulation is widely used for the constant V/f type three-phase motor drives. Here, the intervals between 60 to 120 degrees and 240 to 300 degrees, in each phase, are not modulated and the remaining two phases are modulated. In this manner, the switching in one cycle is decreased and a higher maximum voltage is obtained. However, the dominant harmonic components are the sidebands around the carrier frequency which cause current ripple and audible noise. A new PWM method is proposed in this paper. A rectangular wave which has the frequency of three times the fundamental frequency is superimposed to the line voltages. The optimal magnitude of this signal is chosen so that the sideband components around the carrier frequency are minimized.

	STUDY OF 2 AND 3-LEVEL PRECALCULATED MODULATIONS By B. Velaerts; P. Mathys; Z. F. Zendaoui	[View] [Download]
Abstract: This paper presents a comparative study of 2 and 3-level pulse-width modulated precalculated waveforms, applied to voltage source inverters. Two aspects have been investigated: global optimization of the loss factor o (up to 7 angles per quarter of cycle) and selective harmonic elimination (up to 5 angles per quarter of cycle) are taken into account. This research is intended to modulators implementing both sinusoidal and precalculated modulations together in a same strategy. The harmonics rejected in the DC link are analyzed through a newly defined rejection factor p, as well as the effect of PWM on the current going through the DC-side capacitors of the 3-level inverter. A whole strategy of modulation, which is implemented in C language on a 8097 microcontroller, is presented, completed by practical measurements on a 8 kW 3-level inverter.

	A NEW GENERALIZED MULTILEVEL THREE-PHASE STRUCTURE CONTROLLED BY PWM By A. Campagna; G. Carrara; D. Casini; R. Salutari	[View] [Download]
Abstract: This paper presents a new three-phase generalized multilevel structure for a Voltage Source lnverter. A conversion system based on a five level realization of the structure employing DMOSFETs and controlled by high frequency multilevel subharmonic PWM is shown. Experimental results are presented. Improvements in the harmonic contents with respect to a conventional bipolar inverter are pointed out.

	NEW REGULAR-SAMPLED HARMONIC ELIMINATION PWM TECHNIQUES FOR DRIVES AND STATIC-POWER CONVERTERS By Sidney Robert Bowes	[View] [Download]
Abstract: New Harmonic Elimination and Harmonic Minimisation PWM strategies for voltage-source and current-source inverters have recently been developed using modified Regular-Sampling techniques. These new PWM techniques can be applied to Drives, Unincerruptible Power Supplies and Static Frequency Changers. These new PWM strategies can be generated on-line in real-time using a simple microprocessor software algorithm, without resorting to the usual off-line time-consuming and complex mainframe computer Harmonic Elimination numerical techniques. The microprocessor implementation and generation of these new PWM techniques can be achieved using two-timer and single-timer microprocessor implementations. Experimental results are presented to demonstrate the special features of these new microprocessor-based Regular Sampled Harmonic Elimination / Minimisation PWM techniques.

	OVERSHOOT AND LIMIT CYCLE FREE CURRENT CONTROL METHOD FOR PWM INVERTERS By Samir Salama; Sarah Lennon	[View] [Download]
Abstract: The tolerance-band (hysteresis) current control method is widely used in the control of high dynamic speed-controlled drives fed from voltage-source PWM-inverters. In this paper a new current controller, which completely removes the problems associated with this traditional method, will be presented. A comparison of the new controller with the hysteresis current controller shows a considerable reduction of the switching frequency of the inverter while eliminating the overshoot in the current deviation. Analytical and experimental investigations on a current regulated induction motor drive confirm the predicted advantages of the new current controller.

	ACOUSTIC NOISE REDUCED PWM CONVERTER AND INVERTER USING BJTs AND IGBTs By Katsunori Taniguchi; Yoji Tomiyama; Tsuyoshi Iwatani; Hisaichi Irie	[View] [Download]
Abstract: Acoustic noise reduced converter and inverter suitable for use with bipolar junction transistor (BJT) and insulated gate bipolar transistor (IGBT) is described. A modulating signal for the three-phase PWM system is obtained by modifying the specific trapezoidal wave. The heating of the devices is reduced because the PWM system stops the switching operation during two-thirds period. Storage time of the BJT and IGBT is compensated by the new PWM technique. In the PWM converter, the input current is converted into a sinusoidal waveform and the power factor of the input power can be adjusted to arbitrary values. In the PWM inverter, torque ripple of the induction motor can be reduced by the new PWM technique. In both systems, sidebands of carrier frequency exist in over audible range.

	PULSE POSITION MODULATION FOR INVERTER-FED AC DRIVES By X. Gao; J. Richardson	[View] [Download]
Abstract: Pulse position modulation (PPM) is a new technique which complements existing PWM strategies. PPM has the advantage of ease of pulse generation and control without complex circuitry. This development outlines the theoretica] development and practical implementation of the technique for a 3-phase inverter-fed a.c. induction drive system. The scheme is shown to be somewhat simpler and more flexible than that of near-optimal PWM control. No extensive arithmetic operations are required to produce the inverter gate triggering trains. The attraction of slightly reduced pulse widths in PPM control enables higher switching frequencies. Spectrum analyses of PPM waveforms are obtained numerically and compared with practical results. The disadvantage of a somewhat higher total harmonic distortion with PPM is not considered detrimental for a.c. drives.

	ANALYSIS OF THE HARMONICS IN VOLTAGE FED INVERTER DRIVES CAUSED BY PWM SCHEMES WITH DISCONTINUOUS SWITCHING OPERATION By Heinz van der Broeck	[View] [Download]
Abstract: This paper deals with the pulse width modulation (PWM) for three phase voltage fed inverter drives. A review is made on established PWM strategies with continuous and discontinuous switching operation. Although PWM schemes with discontinuous switching operation generate higher harmonics than the optimum space vector PWM they are of special interest because of their lower switching losses. A new PWM scheme is presented which leaves the outputs of the inverter legs one after another on the negative rail of the DC supply voltage for 120° intervals. The mean squared value of the harmonic content of the current caused by this PWM scheme in a three phase load as well as the relative reduction of the switching losses are determined. The analysis is based on the characteristic drive parameters resulting in pure analytical equations for general use. A comparison is made to the corresponding currents of established PWM schemes. In a final evaluation application areas for the different PWM schemes with continuous and discontinuous switching operation are shown.

	The Optimal Switching Frequency for PWM Driven DC Motors by Simulation By D.K.W. Cheng; C.K. Lee	[View] [Download]
Abstract: A more realistic simulation of a PWM driven DC motor switching at different frequencies is performed, and the corresponding switching current spikes, inductive current ripples, rms power delivered to the motor, and harmonic power loss are calculated. The optimal chopping frequency can then be selected based on the above results with the criteria of minimum current spikes, minimum current ripples, minimum harmonic power loss and maximum rms power delivered to the motor. It is found that the faster the rise and fall times of the PWM, the higher the switching current spikes and this determines the highest switching frequency. A more realistic model of the DC motor with high frequency effects is used [1] in the simulation. The equivalent circuit of the armature winding is obtained by the curve fitting method using the software package MATLAB. The software used for simulation is PSPICE which is a circuit simulation tool.

	OPTIMIZATION OF THREE PHASE PULSE PATTERN BY VARIABLE ZERO SEQUENCE COMPONENT By L. Abraham; R. Blümel	[View] [Download]
Abstract: Approaching the desired output voltage curve of a power electronic inverter by pulse width modulation the pulse pattern of every individual sampling step may be investigated off-line deducing algorithms for optimized modulation procedure. For single phase inverters symmetrical switching points are best. ln three phase inverters it is possible to add a freely set zero sequence component to the desired voltage without changing the modulation factor but varying the harmonics produced by pulse width modulation. This degree of freedom may be used for optimization of pulse pattern in each sampling interval. This method is demonstrated and investigated, Theoretical and practical results are presented.

	CONTROL OF THE NEUTRAL POINT OF A THREE-LEVEL-INVERTER By H. L. Klaver	[View] [Download]
Abstract: Since many years several types of inverters are used for the drive of squirrel cage induction machines. The upper limit in power is shifted over the 1 MW since the introduotion of three-level inverters and the availability of large GTO-switches. This type of inverter ia also called Neutral-point-clamped inverter. This inverter is a voltage source inverter in which the dc link capacitor is split into two to create a third level. One of the key items in controlling a three-level inverter is keeping the neutral point (= zero level) at a constant value of half the overall voltage. For that reason an extra control loop shall be integrated in the PWM of a three-level inverter. Simulations of the PWM with the extra control loop have been carried out for different operating points and gave good results. Tests on a prototype of 3 MVA are planned for the summer of 1991.

	NEW PWM METHOD BASED ON FLUX-LINKAGE TRAJECTORY CONTROL By Zheng-Tang Yang; Guo-Hai Liu	[View] [Download]
Abstract: Based on flux-linkage trajectory control principle, a new pulse-width modulation (PWM) switching strategy is presented. By using modes of the "180-degree-on" and "120-degree-on" alternately, it has 12 voltage vectors, double of the conventional one. It is shown that this strategy makes the flux amplitude error between the practical flux-linkage trajectory and the ideal one much smaller. By spliting zero voltage vectors and scattering them in the non-zero voltage period, the more accurate control of rotating speed of the flux-linkage vectors can be achieved. Simulation results have demonstrated that the PWM strategy presented is superior to the conventional one.

	CONTROL ALGORITHM OF A THREE PHASE VOLTAGE SOURCED REVERSIBLE RECTIFIER By I. Nagy	[View] [Download]
Abstract: The paper discusses a three phase voltage sourced reversible rectifier known from the literature. It achieves bidirectional power flow between a 3 phase a.c. supply and a d.c. bus. The sinusoidal currents drawn from the network are forced by hysteresis current control. The device operates at unity power factor. The novelty of the paper is the mathematical analysis of the configuration using Park vectors and the determination of sophisticated control algorithm of the switching sequences of the controlled switches tied to the instantaneous states of the circuit. The results provide a solid basis for simulation and for microprocessor control software. Computer simulation results presented support the theory.

	DESIGN OF A WIDE RANGE VARIABLE VOLTAGE VARIABLE FREQUENCY INVERTER MODULATOR USING THE COUNTER NUMBER METHOD By Maria Isabel Gimenez de Guzman; Victor Manuel Guzman; Peter Bowler	[View] [Download]
Abstract: This paper presents the design of a very simple and economical Microcontrolled lnverter Modulator, based on the INTEL 8031, able to drive a three-phase induction motor over a wide frequency range (0.1 to 100 Hz), allowing an independent selection of the normalized fundamental voltage demand, output frequency and sense of rotation. Both Subharmonic PWM technique and Precalculated Switching Angle patterns, quantized using the Twelfth Mode and processed using the new Counter Number Method, developed by the authors, are employed in the implementation. Two Programmable Analog Pulse Generators are presented and their advantages and disadvantages are discussed.

	A PWM 3-phase on-line controller for A.C. drives By J. Richardson; G. Bezanov	[View] [Download]
Abstract: The laws governing the commutation angles of optimal PWM strategies invariably describe a non-linear relationship to the fundamental component magnitude. For this reason these strategies cannot be realised using natural sampling techniques and are therefore entirely software-based. A considerable disadvantage of software based optimal strategies is that they cannot be described by an analytical expression which can be executed in real-time. In this investigation an analytic expression is defined which describes the modulation process of the harmonic elimination strategy. This modulation process is reduced to a fast algorithm for on-line calculation of the required pulse widths for eliminating the first four non-triplen harmonics and controlling the fundamental component. Results shown include the harmonic content of the waveforms supplied to a three phase induction motor load at selected operating frequencies. Also shown are selected open loop responses to sudden changes in supply frequency.

	PULSE-WITH-CODE MODULATION IN VOLTAGE SOURCE INVERTERS WITH VARIABLE OUTPUT FREQUENCY By Valentin T. Oleschuk	[View] [Download]
Abstract: The algorithms of nonstandard pulse-width-code modulation, which provides smooth shockless inverter ratio changing, have been considered. This comparatively simple and easy digitisation control principle is based on the continuously step-by-step coding (identification) the widths of pulses and pauses of output voltage formed at clock points with the one of the main range of output pulses, connected directly with the output frequency. The basic methods of the pulse-width-code modulation for three-phase thyristor inverters with control both inside and in border of clock intervals have been developped for the standard and nonstandard performance modes. The analytical description of the rational control laws for ac inverter drives has been done for the instances when average frequency of inverter with commutation vary according to different linear and nonlinear correlations. The analysis of the harmonic composition of the various versions of inverter output voltage has been carried out and technique of its improvement has been considered.

	CONSTANT CURRENT MODE FOR PARALLEL LOADED RESONANCE CIRCUIT INVERTER: AC AND DC APPLICATIONS By M. I. Mahmoud; J. Barbaroux; R. Perret	[View] [Download]
Abstract: Power electronic inverter with parallel loaded resonance circuit in the constant current mode of operation is investigated in order to obtain a true constant current source CCS. The implementation of this circuit with the power electronic inverter have been carried out for a high power constant current source inverter CCSI. The suitable inverter design for DC and three phase AC applications has been investigated. Two proposed control schemes for DC motor fed by a CCSI and three phase induction motor through a three phase CCSI have been realized. Theoretical and simulation studies have been made to obtain the form of the electrical variables for the CCSI in each case study.

	A SUBOPTIMAL PREDICTIVE CURRENT CONTROLLER FOR VSI-PWM INVERTERS By Wilfried Hofmann	[View] [Download]
Abstract: A novel current controller for ac-drives fed by VSI inverter is proposed. It is explained the analytical relation between the current error phasor and its gradient based on a linear prediction. The selection of the output voltage phasor is realised result from the off-line computation of the inequations for the seven inverter output voltages and its error gradients by control options for small and large signal operations. The existence of approximated ranges for the error and motor voltage sectors gives the possibility to use geometrical features dependent on speed ranges. It results in a simple signal-processing for the current controller with a higher sampling rate and lead to a good control behaviour near to the optimum.