EPE Association: EPE 2003 - Topic 04a: Converter Control Sets and Modulation Strategies

EPE 2003 - Topic 04a: Converter Control Sets and Modulation Strategies
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2003 - Conference > EPE 2003 - Topic 04: MODULATION STRATEGIES AND SPECIFIC CONTROL METHODS FOR STATIC CONVERTER > EPE 2003 - Topic 04a: Converter Control Sets and Modulation Strategies

   [return to parent folder]

   Analytical investigation of a new space-vector PWM strategy for improved induction motor drive reliability
By J. Klima [View]
[Download]

Abstract: Three-phase voltage source (VSI) induction motor drives are prone to different inverter faults that cause the drive system to shut down. This paper investigate by the analytical model the utilization of a simplified topology that permits the fault tolerance operation of a three-phase induction machine fed from the voltage source inverter when one of the inverter leg is lost. In that case, the machine phase with a lost inverter leg is connected to a zero DC voltage point to maintain balanced operation. The space-vector modulation strategy which is proposed has the same symmetry as for the B6 inverter and is simple without significant increase in switching frequency. It is also shown that derived time portions allocated to the proposed modulation strategy in the B4 connection are similar to that time portions derived for the classical B6 inverter. From the mathematical model we can derive both the steady-state and transient characteristics of the motor. Finally, analytical model is verified experimentally and close agreement between analytical and measured waveforms is found.

   A generalized reduced order sampled-data dynamic model of a robust controller using extended describing function method for series-parallel resonant converter
By M. Z. Youssef; H. Pinheiro; P. K. Jain [View]
[Download]

Abstract: In this paper, a novel analytical reduced-order sampled-data model for the series parallel resonant converter under self-sustained oscillation control (SOC) is proposed. The proposed model is based on Extended Describing Function (EDF) technique to derive the steady state characteristics, which allows converter design optimization. Then, simple low order small-signal and large-signal models are derived. The model accounts for effects of realtime element value uncertainty. Also, a conventional variable frequency controller is presented for performance comparison. Finally, the proposed dynamic model is verified by online experimental results. The findings match the outcomes of a detailed numerical solution, simulation results of the converter to prove the dynamic model validity.

   Three-level space vector modulation - An application to a space vector controlled unidirectional three-phase/level/switch VIENNA I rectifier
By T. Viitanen, H. Tuusa [View]
[Download]

Abstract: This paper examines a novel three-level space vector modulation method applied to a vector controlled VIENNA I rectifier. The principle modulation algorithm operation, basic assumptions and restrictions due to the main circuit are analysed. On the basis of the key equations derived from the system examined, the vector control system is realised. The theoretical analysis of the proposed modulation technique and vector control system is verified by Simplorer and Matlab Simulink simulations, taking into consideration the total harmonic line current distortion, the losses in the active and passive components, delays and switching transients of the semiconductor devices. The rectifier system is designed to operate at a nominal DC link output power of 50kW, DC link voltage 650V and applied switching frequency 3.5kHz. The L filter is designed so that the total harmonic line current distortion is 4%.

   Reduction of bearing currents by using asymmetric, space-vector-based switching patterns
By J. Zitzelsberger; W. Hofmann [View]
[Download]

Abstract: The phenomena of bearing currents is known for a long period. Especially those which are caused by magnetic asymmetries have been investigated since the beginning of the 20th century. Nowadays new kinds of bearing currents can be observed in inverter fed induction drives. Investigations done on these effects show that the switched operational mode – especially of voltage source inverters – causes a high frequency common mode voltage (CMV). This voltage supplies the common mode circuit of an electrical machine in which the bearings are a part of. Therefore, to reduce the occurrence of bearing currents it is necessary to avoid or - at least - to minimise the common mode voltage in drive applications fed by voltage source inverters. A novel principle for such a purpose is the space vector based modulation with sequentially positioned pulses (SPP). With this modulation it is possible to reduce both the number of edges within the CMV and its amplitude to a great extent without influencing the modulation index. The present paper summarises the ideas which stand behind the principle of SPP and gives an overview over the major dependence's from characteristics of the drive system. Moreover, the functionality and the compatibility to standard inverter fed drives is shown by means of simulations and measurements.

   A resonant voltage controller for fast regulation of a three-phase voltage source
By J.C. Le Claire; R. Moreau; N. Ginot [View]
[Download]

Abstract: Some recent papers describe a Resonant Current Controller well suited for voltage supply inverter's current control. Here, we study the three-phase Resonant Voltage Controller involving a single feedback loop per phase. It controls the VSI added low-pass filter output voltages. Theoretical results and experimental measurements involving a 1kW-power converter demonstrate its excellent behaviour.

   Multi-phase system supplied by PWM VSI. A new technique to compute the duty cycles
By X. Kestelyn; E. Semail; J.P Hautier. [View]
[Download]

Abstract: When multi-phase machines with magnetic couplings between phases are supplied by triangle intersection PWM, there are parasitic currents. To solve the problem, it’s necessary to use Space Vector Modulation. We propose a SVM extended to systems with arbitrary number of phases and with optimization of time computation and consideration of switching constraints.

   Innovative control technique of a high-power AC-DC converter for particle accelerator
By M. Incurvati; F. Caricchi; C. Sanelli; F. Guilii Capponi [View]
[Download]

Abstract: Feasible solutions for a power supply for dipole magnets of medical particle accelerator are invvestigated. Switching and thyristor converters are compared. Physical constraints dictate converter ratings being in the range 0-1500V, 0-3000A, 2 seconds cycle, maximum current error less then 1A. A thyristor solution, with particular care in the design of the feedback is proposed, and benefits and drawbacks are analyzed. A non-conventional control technique for thyristor converters is also investigated which uses multilevel approach to control thyristor bridges. Simulmation are presented showing the feasibility of the new control technique.

   A new partly unsymmetrical PWM technique for harmonic compensation
By H. Zhang; M. Braun [View]
[Download]

Abstract: A new partly unsymmetrical PWM technique for FACTS is proposed. The exact switching angles are calculated off-line by optimizing the pulse patterns. The proposed strategy has the advantage of enabling the inverter to control the fundamental component and some specific order harmonics. The validity is verified by FFT analysis.

   Examination of dead-time eliminination strategies using the error voltage phasor theory
By F. Herty [View]
[Download]

Abstract: In this paper, the two most important effects distorting the output voltage of a tree-phase voltage source inverter are analyzed. The effects are the forward voltage of the freewheeling diode as well as the on-voltage of the power switch and the insertion of dead-time intervals by the inverter control circuitry. Although these effects are different, a common description is provided by the presented theory. The distortions are modeled by a so-called error voltage, which is superposed with the reference voltage.

   Stability analysis of a constant-power inverter
By E. Godoy; S. Tebbani; Y. Louvain; K. Sauterau [View]
[Download]

Abstract: This paper deals with the study of a constant-power inverter and its controllability analysis. This process is used in train air-conditioning power supply. Because of the load at constant power, in the absence of specific control law, this system is characterized by an unstable behaviour. This problem can be solved by adding a passive device, however this solution leads to losses of power. An alternative and more interesting solution is to introduce an active solution by means of closed loop regulation, however some internal variables of this system have a small degree of commandability, which makes difficult the achievement of this solution. First, the system is studied: modelling, stability and controllability analysis, study of passive stabilisation. Then the active control law developed is presented. More precisely, a methodology is described for the design of a control law, which permits on one hand to stabilize the inverter without adding any complementary passive device, and on the other hand to let the output voltage track a sinusoidal reference signal. Finally, some numerical results are given to show the efficiency of such a law.

   Synchronization of the inverter voltage supply in order to reduce the residual output ripple
By S. Tebbani; E. Godoy; K. Sauterau; Y. Louvain [View]
[Download]

Abstract: This paper deals with the study of an inverter system, used in train supply application. This system has been modelized and a control law has been determined so that the imposed specifications are respected [1]. However, when using an AC rectified inverter supply, it has been noticed residual low-frequency ripple on the output voltage of the machine. This ripple appears especially when the output inverter frequency is close to that of the AC supply. This paper shows that this phenomenon can be restricted by the synchronization of the frequencies of the inverter and of the voltage supply. The supply voltage characteristics will be estimated using Kalman filter. This strategy was tested on the real system and has been found very efficient. Some numerical results will illustrate the efficiency of this strategy. Keywords: Inverter, output low-frequency ripple, Kalman filter, inverter frequency synchronization. The considered system is used in the train air-conditioning supply. It consists in converting a onephase high-voltage supply into a three-phase lower-level voltage supply. This system is composed of: • The system is supplied with an AC supply which modulus and frequency are known approximately and depend on the electrical supply network dealt with (frequency of about 50Hz for the French network, and about 2 16Hz 3 for the German one),

   Mutual compensation of harmonic distortion in a PDM multi-converters system used in induction heating
By A. Sandali; P. Sicard; A. Chériti [View]
[Download]

Abstract: The application of Pulse Density Modulation (PDM) control to a rectifier - series resonant inverter set makes it possible to implement an ac/ac converter with good performances (size and efficiency). However its power factor decreases when the load power decreases. We propose a PDM control strategy adapted to a set of identical ac/ac converters, to obtain mutual compensation of the harmonic distortion among the ac/ac converters. The set presents a power factor close to 1 for power levels ranging between 100/G % and 100 % of the full power, where G is the number of ac/ac converters in the system.

   Coordinate PWM control strategy of the direct frequency converter
By R.T. Shreiner; V.K. Krivovyaz; A.I. Kalygin [View]
[Download]

Abstract: The paper presents a coordinate pwm strategy for the power switches control of a matrix and two-stage direct frequency converter (DFC). An algorithm of the modulating functions synthesis which assures network currents and output voltages equal to their reference values under the condition of no intermediate dc smoothing filter was worked out. The simulation results of the DFC operating with an equivalent RLE-load and induction motor are presented.

   A novel topology of delta modulator for static PWM inverter
By C.Choochuan; V. Tipsuwanporn; V. Pirajnanchai [View]
[Download]

Abstract: This paper presents a new topologies of delta modulator (DM) for static PWM inverter application and an improved inverter waveform of delta modulation. The tuned and the multi-integrator DM are the two schemes proposed for PWM waveform synthesis so far[2]. The methods were found useful for variable speed PWM inverter-fed ac drives and minimization of harmonic in delta modulated inverters. However it was observed that during tuning and filtering process, fundamental output voltage of the inverter reduced. With an aim to overcome this effect, a new topologies of delta modulator which combines the advantageous features of both the variable slope of integrator and variable hysteresis window DM in one modulator is proposed. Pulse-width modulation (PWM) signals are synthesized by using R-C multivibrator base. Therefore, the proposed DM consisted a few component and another achieved objective are minimized of control circuit complexity. The topologies has the capability to maintain a constant fundamental voltage of the output waveform of the inverters and the PWM switching frequency to be near constant for all PWM pulses at any amplitude reference signal. The performance and cost of this modulator is better than other DM topologies so far reported. Experimental results confirming the feasibility of the proposed modulator.

   Switching strategy without dead time for the voltage source inverter supplying the sensorless controlled induction motor
By K. Zbigniew; L. Arkadiusz [View]
[Download]

Abstract: To avoid a problem of inverter output voltage distortion during zero crossing by the inverter output current a new algorithm of switching control was developed. Special patterns were applied in which nonzero amplitudes of passive vectors are compensated for. The algorithm ensures smooth sinusoidal inverter output current and is suitable for a control system based on speed observer of the induction motor. Multiscalar model of the induction motor and nonlinear feedback were used in the control system. Experimental results are presented.

   Vector control of induction machine based on smart modulation algorithm
By M. S. Carmeli; F. Castelli-Dezza; G. Superti-Furga [View]
[Download]

Abstract: This paper focuses on a new vector control algorithm, which is realized through smart modulation technique. The presented algorithm is based on direct current control: it allows constant switching frequency, ripple control and can be easily extended to multiconverter power systems. The application to an induction motor drive allows reduced regulator complexity, good dynamic response and accurate harmonic control. The proposed strategy has been validated through simulation and laboratory tests.

   Fast current controllers using FPGAs
By K. Ljøkelsøy; O. Mo [View]
[Download]

Abstract: This paper describes a FPGA (Field Programmable Grid Array) based PI controller and Pulse Width Modulator for a three-phase inverter. The signal processing circuitry is designed as a distributed pipelined architecture, consisting of several small building blocks. It is designed to be functionally equivalent to an analog PI-controller/modulator circuit. By using a high sampling rate, 1,5 MHz, the effects of sampling and delay in the feedback loop are small compared to the process time scale. The signal processing can be considered to be approximated quite closely as a continuous process, in contrast to common processor based digital implementations that have sample rates of one or two times the switching frequency. This allows for higher feedback loop gain, and shorter time constants. This gives better performance in applications like active filters, where response time is important.

   A simple and high-performance control strategy for three-phase PFC rectifier
By D. Yazdani; A.R. Bakhshai; M. Saeedifard [View]
[Download]

Abstract: Performance criteria of three-phase boost rectifiers improve significantly with increasing the switching frequency, and highly depend on the control strategy used. This paper introduces a modified vector classification SVM-based control strategy for three-phase boost rectifiers. By means of the proposed technique abc-dq and dq-áâ transformation carried out in conventional SVM-based strategies are avoided. Therefore current regulators in d-q frame and also control difficulties associated with them are removed. In addition, the proposed technique maintains the advantages of other schemes. Simulation results provided, confirm the validity of the analytical work.

   New control strategy of current source inverter asynchronous drives
By S.H. Shahalami; S. Saadate; A. Cherifi [View]
[Download]

Abstract: This paper presents a novel control approach of a current suorce inverter drive system using an induction motor. A variant of hysteresis-band current control adapted to the current source inverter circuit topology is proposed. The current control strategy is based on the correction of the two out of three large errors of the instantaneous real currents of motor with respect to their references. The well known GTO current source inverter in which an auxiary branch of inverter is added in order to ensure the continuity of DC link current in special conditions. The indirect motor flux-orientated vector control of induction motor gives the reference motor's currents. In order to suppress the inherent instability of current fed induction motor, a coefficient of derivative of real motor's current is added to the reference ones. The simulation results of steady state and dynamic operations of the novel control asynchronos drive are shown and the advantages of this technique are discussed.

   Modeling and design of a flux regulator to three-phase PWM inverters with constant switching frequency
By B. Shi; G. Venkataramanan; M.C. Chandorkar [View]
[Download]

Abstract: Abstract Three phase PWM inverters employing flux regulators have been shown to be a superior means of control for distributed UPS systems and other applications. However, in most manifestations, they have the drawback of variable switching frequency. In this paper, a flux regulator operating at constant switching frequency is presented. The regulator operates in the synchronously rotating d-q frame of reference, and uses a proportional controller with decoupling between D and Q axis quantities. The flux regulator is used as a basis for output voltage of a sinusoidal inverter system. Analytical results with computer simulations verified using an experiment prototype inverter are presented in the paper.

EPE 2003 - Topic 04a: Converter Control Sets and Modulation Strategies
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2003 - Conference > EPE 2003 - Topic 04: MODULATION STRATEGIES AND SPECIFIC CONTROL METHODS FOR STATIC CONVERTER > EPE 2003 - Topic 04a: Converter Control Sets and Modulation Strategies
	[return to parent folder]

	Analytical investigation of a new space-vector PWM strategy for improved induction motor drive reliability By J. Klima	[View] [Download]
Abstract: Three-phase voltage source (VSI) induction motor drives are prone to different inverter faults that cause the drive system to shut down. This paper investigate by the analytical model the utilization of a simplified topology that permits the fault tolerance operation of a three-phase induction machine fed from the voltage source inverter when one of the inverter leg is lost. In that case, the machine phase with a lost inverter leg is connected to a zero DC voltage point to maintain balanced operation. The space-vector modulation strategy which is proposed has the same symmetry as for the B6 inverter and is simple without significant increase in switching frequency. It is also shown that derived time portions allocated to the proposed modulation strategy in the B4 connection are similar to that time portions derived for the classical B6 inverter. From the mathematical model we can derive both the steady-state and transient characteristics of the motor. Finally, analytical model is verified experimentally and close agreement between analytical and measured waveforms is found.

	A generalized reduced order sampled-data dynamic model of a robust controller using extended describing function method for series-parallel resonant converter By M. Z. Youssef; H. Pinheiro; P. K. Jain	[View] [Download]
Abstract: In this paper, a novel analytical reduced-order sampled-data model for the series parallel resonant converter under self-sustained oscillation control (SOC) is proposed. The proposed model is based on Extended Describing Function (EDF) technique to derive the steady state characteristics, which allows converter design optimization. Then, simple low order small-signal and large-signal models are derived. The model accounts for effects of realtime element value uncertainty. Also, a conventional variable frequency controller is presented for performance comparison. Finally, the proposed dynamic model is verified by online experimental results. The findings match the outcomes of a detailed numerical solution, simulation results of the converter to prove the dynamic model validity.

	Three-level space vector modulation - An application to a space vector controlled unidirectional three-phase/level/switch VIENNA I rectifier By T. Viitanen, H. Tuusa	[View] [Download]
Abstract: This paper examines a novel three-level space vector modulation method applied to a vector controlled VIENNA I rectifier. The principle modulation algorithm operation, basic assumptions and restrictions due to the main circuit are analysed. On the basis of the key equations derived from the system examined, the vector control system is realised. The theoretical analysis of the proposed modulation technique and vector control system is verified by Simplorer and Matlab Simulink simulations, taking into consideration the total harmonic line current distortion, the losses in the active and passive components, delays and switching transients of the semiconductor devices. The rectifier system is designed to operate at a nominal DC link output power of 50kW, DC link voltage 650V and applied switching frequency 3.5kHz. The L filter is designed so that the total harmonic line current distortion is 4%.

	Reduction of bearing currents by using asymmetric, space-vector-based switching patterns By J. Zitzelsberger; W. Hofmann	[View] [Download]
Abstract: The phenomena of bearing currents is known for a long period. Especially those which are caused by magnetic asymmetries have been investigated since the beginning of the 20th century. Nowadays new kinds of bearing currents can be observed in inverter fed induction drives. Investigations done on these effects show that the switched operational mode – especially of voltage source inverters – causes a high frequency common mode voltage (CMV). This voltage supplies the common mode circuit of an electrical machine in which the bearings are a part of. Therefore, to reduce the occurrence of bearing currents it is necessary to avoid or - at least - to minimise the common mode voltage in drive applications fed by voltage source inverters. A novel principle for such a purpose is the space vector based modulation with sequentially positioned pulses (SPP). With this modulation it is possible to reduce both the number of edges within the CMV and its amplitude to a great extent without influencing the modulation index. The present paper summarises the ideas which stand behind the principle of SPP and gives an overview over the major dependence's from characteristics of the drive system. Moreover, the functionality and the compatibility to standard inverter fed drives is shown by means of simulations and measurements.

	A resonant voltage controller for fast regulation of a three-phase voltage source By J.C. Le Claire; R. Moreau; N. Ginot	[View] [Download]
Abstract: Some recent papers describe a Resonant Current Controller well suited for voltage supply inverter's current control. Here, we study the three-phase Resonant Voltage Controller involving a single feedback loop per phase. It controls the VSI added low-pass filter output voltages. Theoretical results and experimental measurements involving a 1kW-power converter demonstrate its excellent behaviour.

	Multi-phase system supplied by PWM VSI. A new technique to compute the duty cycles By X. Kestelyn; E. Semail; J.P Hautier.	[View] [Download]
Abstract: When multi-phase machines with magnetic couplings between phases are supplied by triangle intersection PWM, there are parasitic currents. To solve the problem, it’s necessary to use Space Vector Modulation. We propose a SVM extended to systems with arbitrary number of phases and with optimization of time computation and consideration of switching constraints.

	Innovative control technique of a high-power AC-DC converter for particle accelerator By M. Incurvati; F. Caricchi; C. Sanelli; F. Guilii Capponi	[View] [Download]
Abstract: Feasible solutions for a power supply for dipole magnets of medical particle accelerator are invvestigated. Switching and thyristor converters are compared. Physical constraints dictate converter ratings being in the range 0-1500V, 0-3000A, 2 seconds cycle, maximum current error less then 1A. A thyristor solution, with particular care in the design of the feedback is proposed, and benefits and drawbacks are analyzed. A non-conventional control technique for thyristor converters is also investigated which uses multilevel approach to control thyristor bridges. Simulmation are presented showing the feasibility of the new control technique.

	A new partly unsymmetrical PWM technique for harmonic compensation By H. Zhang; M. Braun	[View] [Download]
Abstract: A new partly unsymmetrical PWM technique for FACTS is proposed. The exact switching angles are calculated off-line by optimizing the pulse patterns. The proposed strategy has the advantage of enabling the inverter to control the fundamental component and some specific order harmonics. The validity is verified by FFT analysis.

	Examination of dead-time eliminination strategies using the error voltage phasor theory By F. Herty	[View] [Download]
Abstract: In this paper, the two most important effects distorting the output voltage of a tree-phase voltage source inverter are analyzed. The effects are the forward voltage of the freewheeling diode as well as the on-voltage of the power switch and the insertion of dead-time intervals by the inverter control circuitry. Although these effects are different, a common description is provided by the presented theory. The distortions are modeled by a so-called error voltage, which is superposed with the reference voltage.

	Stability analysis of a constant-power inverter By E. Godoy; S. Tebbani; Y. Louvain; K. Sauterau	[View] [Download]
Abstract: This paper deals with the study of a constant-power inverter and its controllability analysis. This process is used in train air-conditioning power supply. Because of the load at constant power, in the absence of specific control law, this system is characterized by an unstable behaviour. This problem can be solved by adding a passive device, however this solution leads to losses of power. An alternative and more interesting solution is to introduce an active solution by means of closed loop regulation, however some internal variables of this system have a small degree of commandability, which makes difficult the achievement of this solution. First, the system is studied: modelling, stability and controllability analysis, study of passive stabilisation. Then the active control law developed is presented. More precisely, a methodology is described for the design of a control law, which permits on one hand to stabilize the inverter without adding any complementary passive device, and on the other hand to let the output voltage track a sinusoidal reference signal. Finally, some numerical results are given to show the efficiency of such a law.

	Synchronization of the inverter voltage supply in order to reduce the residual output ripple By S. Tebbani; E. Godoy; K. Sauterau; Y. Louvain	[View] [Download]
Abstract: This paper deals with the study of an inverter system, used in train supply application. This system has been modelized and a control law has been determined so that the imposed specifications are respected [1]. However, when using an AC rectified inverter supply, it has been noticed residual low-frequency ripple on the output voltage of the machine. This ripple appears especially when the output inverter frequency is close to that of the AC supply. This paper shows that this phenomenon can be restricted by the synchronization of the frequencies of the inverter and of the voltage supply. The supply voltage characteristics will be estimated using Kalman filter. This strategy was tested on the real system and has been found very efficient. Some numerical results will illustrate the efficiency of this strategy. Keywords: Inverter, output low-frequency ripple, Kalman filter, inverter frequency synchronization. The considered system is used in the train air-conditioning supply. It consists in converting a onephase high-voltage supply into a three-phase lower-level voltage supply. This system is composed of: • The system is supplied with an AC supply which modulus and frequency are known approximately and depend on the electrical supply network dealt with (frequency of about 50Hz for the French network, and about 2 16Hz 3 for the German one),

	Mutual compensation of harmonic distortion in a PDM multi-converters system used in induction heating By A. Sandali; P. Sicard; A. Chériti	[View] [Download]
Abstract: The application of Pulse Density Modulation (PDM) control to a rectifier - series resonant inverter set makes it possible to implement an ac/ac converter with good performances (size and efficiency). However its power factor decreases when the load power decreases. We propose a PDM control strategy adapted to a set of identical ac/ac converters, to obtain mutual compensation of the harmonic distortion among the ac/ac converters. The set presents a power factor close to 1 for power levels ranging between 100/G % and 100 % of the full power, where G is the number of ac/ac converters in the system.

	Coordinate PWM control strategy of the direct frequency converter By R.T. Shreiner; V.K. Krivovyaz; A.I. Kalygin	[View] [Download]
Abstract: The paper presents a coordinate pwm strategy for the power switches control of a matrix and two-stage direct frequency converter (DFC). An algorithm of the modulating functions synthesis which assures network currents and output voltages equal to their reference values under the condition of no intermediate dc smoothing filter was worked out. The simulation results of the DFC operating with an equivalent RLE-load and induction motor are presented.

	A novel topology of delta modulator for static PWM inverter By C.Choochuan; V. Tipsuwanporn; V. Pirajnanchai	[View] [Download]
Abstract: This paper presents a new topologies of delta modulator (DM) for static PWM inverter application and an improved inverter waveform of delta modulation. The tuned and the multi-integrator DM are the two schemes proposed for PWM waveform synthesis so far[2]. The methods were found useful for variable speed PWM inverter-fed ac drives and minimization of harmonic in delta modulated inverters. However it was observed that during tuning and filtering process, fundamental output voltage of the inverter reduced. With an aim to overcome this effect, a new topologies of delta modulator which combines the advantageous features of both the variable slope of integrator and variable hysteresis window DM in one modulator is proposed. Pulse-width modulation (PWM) signals are synthesized by using R-C multivibrator base. Therefore, the proposed DM consisted a few component and another achieved objective are minimized of control circuit complexity. The topologies has the capability to maintain a constant fundamental voltage of the output waveform of the inverters and the PWM switching frequency to be near constant for all PWM pulses at any amplitude reference signal. The performance and cost of this modulator is better than other DM topologies so far reported. Experimental results confirming the feasibility of the proposed modulator.

	Switching strategy without dead time for the voltage source inverter supplying the sensorless controlled induction motor By K. Zbigniew; L. Arkadiusz	[View] [Download]
Abstract: To avoid a problem of inverter output voltage distortion during zero crossing by the inverter output current a new algorithm of switching control was developed. Special patterns were applied in which nonzero amplitudes of passive vectors are compensated for. The algorithm ensures smooth sinusoidal inverter output current and is suitable for a control system based on speed observer of the induction motor. Multiscalar model of the induction motor and nonlinear feedback were used in the control system. Experimental results are presented.

	Vector control of induction machine based on smart modulation algorithm By M. S. Carmeli; F. Castelli-Dezza; G. Superti-Furga	[View] [Download]
Abstract: This paper focuses on a new vector control algorithm, which is realized through smart modulation technique. The presented algorithm is based on direct current control: it allows constant switching frequency, ripple control and can be easily extended to multiconverter power systems. The application to an induction motor drive allows reduced regulator complexity, good dynamic response and accurate harmonic control. The proposed strategy has been validated through simulation and laboratory tests.

	Fast current controllers using FPGAs By K. Ljøkelsøy; O. Mo	[View] [Download]
Abstract: This paper describes a FPGA (Field Programmable Grid Array) based PI controller and Pulse Width Modulator for a three-phase inverter. The signal processing circuitry is designed as a distributed pipelined architecture, consisting of several small building blocks. It is designed to be functionally equivalent to an analog PI-controller/modulator circuit. By using a high sampling rate, 1,5 MHz, the effects of sampling and delay in the feedback loop are small compared to the process time scale. The signal processing can be considered to be approximated quite closely as a continuous process, in contrast to common processor based digital implementations that have sample rates of one or two times the switching frequency. This allows for higher feedback loop gain, and shorter time constants. This gives better performance in applications like active filters, where response time is important.

	A simple and high-performance control strategy for three-phase PFC rectifier By D. Yazdani; A.R. Bakhshai; M. Saeedifard	[View] [Download]
Abstract: Performance criteria of three-phase boost rectifiers improve significantly with increasing the switching frequency, and highly depend on the control strategy used. This paper introduces a modified vector classification SVM-based control strategy for three-phase boost rectifiers. By means of the proposed technique abc-dq and dq-áâ transformation carried out in conventional SVM-based strategies are avoided. Therefore current regulators in d-q frame and also control difficulties associated with them are removed. In addition, the proposed technique maintains the advantages of other schemes. Simulation results provided, confirm the validity of the analytical work.

	New control strategy of current source inverter asynchronous drives By S.H. Shahalami; S. Saadate; A. Cherifi	[View] [Download]
Abstract: This paper presents a novel control approach of a current suorce inverter drive system using an induction motor. A variant of hysteresis-band current control adapted to the current source inverter circuit topology is proposed. The current control strategy is based on the correction of the two out of three large errors of the instantaneous real currents of motor with respect to their references. The well known GTO current source inverter in which an auxiary branch of inverter is added in order to ensure the continuity of DC link current in special conditions. The indirect motor flux-orientated vector control of induction motor gives the reference motor's currents. In order to suppress the inherent instability of current fed induction motor, a coefficient of derivative of real motor's current is added to the reference ones. The simulation results of steady state and dynamic operations of the novel control asynchronos drive are shown and the advantages of this technique are discussed.

	Modeling and design of a flux regulator to three-phase PWM inverters with constant switching frequency By B. Shi; G. Venkataramanan; M.C. Chandorkar	[View] [Download]
Abstract: Abstract Three phase PWM inverters employing flux regulators have been shown to be a superior means of control for distributed UPS systems and other applications. However, in most manifestations, they have the drawback of variable switching frequency. In this paper, a flux regulator operating at constant switching frequency is presented. The regulator operates in the synchronously rotating d-q frame of reference, and uses a proportional controller with decoupling between D and Q axis quantities. The flux regulator is used as a basis for output voltage of a sinusoidal inverter system. Analytical results with computer simulations verified using an experiment prototype inverter are presented in the paper.