EPE Association: EPE 1993 - 32 - Dialogue Session DS1.8: CONTROL: HARMONIC REDUCTION

EPE 1993 - 32 - Dialogue Session DS1.8: CONTROL: HARMONIC REDUCTION
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   REDUCTION OF CURRENT AND FLUX DISTORTIONS OF VSI- FED INDUCTION MOTORS WITH DIRECT SELF-CONTROL
By A. M. Walczyna [View]
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Abstract: Direct self-control (DSC) of an inverter-fed induction machine is a signal processing technique based on two-level hysteresis controllers of the machine flux and torque. The attractiveness of DSC is its simplicity and high dynamic performance even using high power, low switching frequency converters . One disadvantage of DSC, however, is that the output inverter current is not sinusoidal, containing harmonic components typical of those in six-pulse, square wave inverters. In the previous works of the author two different techniques which allow reduction of the above distortions have been published. This reduction was achieved by: flux trajectory corner folding or by partial replacement of zero vectors. In the paper an alternative method is proposed which is based on processing a stator flux trajectory. The method offers possibility of flux self-compensation at low speed. It is shown that this method can be easily extended to drives with a discrete PWM which don't use zero vectors. It is also shown that by dividing a stator flux trajectory into two areas, in which different hysteresis width of a torque controller ls applied, reduction of motor current active distortions at speed close to nominal can be achieved.

   MODELLING AND CONTROL OF SINUSOIDAL PWM RECTIFIERS
By S. Fukuda; Y. Iwaji; T. Aoyama [View]
[Download]

Abstract: PWM rectifiers are promising because they can supply DC power while keaping a sinusoidal AC current with unity in the fundamental power factor. There are two types, a voltage-fed rectifier and a current-fed rectifier. The former is required to simultaneously control both the fundamental power factor and DC voltage, while the latter does so for both the fundamental power factor and DC current. State feedback control is essentially suited for multi-input and multi-output systems such as those. Here a discrete-time optimal regulator is applied to their control because it provides a microprocessor-based robust feedback system without steady-state errors in response to a step reference and/or disturbance change. To obtain a mathematical model, oniy the fundamental component of the rectifier switching function is considered. The obtained nonlinear equations are linearized and then modified in the form that the regulator requires. Finally, the regulator is implemented using a digital-signal-processor. Experimental results demonstrate the validity.

   LOW PWM INVERTER LOSSES AND LOW CURRENT DISTORTION - TWO CONFLICTING CLAIMS SETTLED BY BELLMAN'S DYNAMIC PROGRAMMING
By R. Blümel [View]
[Download]

Abstract: PWM techniques as applied to voltage source inverter-fed induction machines are well established. Even so it can be shown that strictly cutting down the pulse inverters turn-on and turn-off counts during a sampling period does not always lead to minimal switching losses as formerly alleged. Taking care of every single switching and conduction loss whilst maintaining a desired rms current deviation ends up in a nonlinear extreme value problem. To be more specific: Minimizing the expenditure of inverter losses to achieve a desired rms current deviation is the main objective of this paper. Therefore a CAD program utilizing Bellman's Dynamic Programming was developed which solves this problem and returns the optimal current trajectory. A novel model follower is employed to track the system along any given pre-calculated trajectory.

   LARGE SIGNAL MODELS AND CONTROL DESIGN FOR HIGH POWER-FACTOR PRECONDITIONERS
By S. R. Wall; R. D. Jackson [View]
[Download]

Abstract: Large signal models are derived for a boost converter operating as a single-phase high power-factor preconditioner. A design procedure is presented for a pwm system with nested control loops for input current and output voltage. The inner (current) loop model is found to be linear in the large, consisting of the often used small signal model and a distortion term. The switching effects are accounted for by the insertion of a pwm describing function biode in the feedback path. It is shown that careful controller design is required to avoid input current distortion or subharmonic oscillation. Controllers for the voltage loop are evaluated by analysis of the linearized plant and simulation of the full nonlinear model. The effect of input voltage feedforward with finite response time filters is investigated. Experimental results are used to corroborate the majority of the analysis.

   DEVELOPMENT OF AN INTEGRATED HIGH VOLTAGE 3-LEVEL CONVERTER-INVERTER SYSTEM WITH SINUSOIDAL INPUT-OUTPUT FOR FEEDING 3-PHASE INDUCTION MOTORS
By A. Mahfouz; J. Holtz; A. El-Tobshy [View]
[Download]

Abstract: This paper describes an integrated high voltage 3-level converter-inverter system . The system is characterized by a capacitor DC link voltage and a current controller based on space vector modulation (SVM) . Current drawn from the supply as well as current supplied by the inverter are sinusoidal with reduced harmonics. Through the current controller at the converter side, the system is forced to operate at unity power factor while the DC link voltage is observed dynamically and kept constant. Moreover the modulation at the inverter side is implemented using a singlechip 16-bit microcontroller (80196).

   THE MINIMISATION OF DISTURBANCES ON THE ELECTRICITY SUPPLY NETWORK WHEN CONTROLLING INDUSTRIAL, RESISTIVE LOADS
By M. J. Carabok [View]
[Download]

Abstract: Unacceptable disturbances can arise on the electricity supply network, in certain situations, when either burst firing or phase angle, thyristor load control is used. In order to combat situations where the disturbances created by either of these control methods exceed the recommended limits an investigation has been conducted into an operating mode which involves both phase angle and burst firing control. This mode is called soft-start, soft-finish, burst firing and incorporates a phase angle component on the leading and trailing edge of each burst fire. Consequently, this operational mode is modelled for the control of industrial, resistive loads. To construct this model several series of experimental data were required to supplement the derived algorithms. The model, which computes the voltage and current harmonics and voltage fluctuation disturbances, is then incorporated in a computer program. This program compares the disturbances with the acceptable limits and postulates the optimal ramp length for operation such that the disturbances on the electricity supply network will be minimised. The computer program also permits closer examination of the disturbances, should a reduction in a particular order of harmonic be desirable.

EPE 1993 - 32 - Dialogue Session DS1.8: CONTROL: HARMONIC REDUCTION
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 1993 - Conference > EPE 1993 - 32 - Dialogue Session DS1.8: CONTROL: HARMONIC REDUCTION
	[return to parent folder]

	REDUCTION OF CURRENT AND FLUX DISTORTIONS OF VSI- FED INDUCTION MOTORS WITH DIRECT SELF-CONTROL By A. M. Walczyna	[View] [Download]
Abstract: Direct self-control (DSC) of an inverter-fed induction machine is a signal processing technique based on two-level hysteresis controllers of the machine flux and torque. The attractiveness of DSC is its simplicity and high dynamic performance even using high power, low switching frequency converters . One disadvantage of DSC, however, is that the output inverter current is not sinusoidal, containing harmonic components typical of those in six-pulse, square wave inverters. In the previous works of the author two different techniques which allow reduction of the above distortions have been published. This reduction was achieved by: flux trajectory corner folding or by partial replacement of zero vectors. In the paper an alternative method is proposed which is based on processing a stator flux trajectory. The method offers possibility of flux self-compensation at low speed. It is shown that this method can be easily extended to drives with a discrete PWM which don't use zero vectors. It is also shown that by dividing a stator flux trajectory into two areas, in which different hysteresis width of a torque controller ls applied, reduction of motor current active distortions at speed close to nominal can be achieved.

	MODELLING AND CONTROL OF SINUSOIDAL PWM RECTIFIERS By S. Fukuda; Y. Iwaji; T. Aoyama	[View] [Download]
Abstract: PWM rectifiers are promising because they can supply DC power while keaping a sinusoidal AC current with unity in the fundamental power factor. There are two types, a voltage-fed rectifier and a current-fed rectifier. The former is required to simultaneously control both the fundamental power factor and DC voltage, while the latter does so for both the fundamental power factor and DC current. State feedback control is essentially suited for multi-input and multi-output systems such as those. Here a discrete-time optimal regulator is applied to their control because it provides a microprocessor-based robust feedback system without steady-state errors in response to a step reference and/or disturbance change. To obtain a mathematical model, oniy the fundamental component of the rectifier switching function is considered. The obtained nonlinear equations are linearized and then modified in the form that the regulator requires. Finally, the regulator is implemented using a digital-signal-processor. Experimental results demonstrate the validity.

	LOW PWM INVERTER LOSSES AND LOW CURRENT DISTORTION - TWO CONFLICTING CLAIMS SETTLED BY BELLMAN'S DYNAMIC PROGRAMMING By R. Blümel	[View] [Download]
Abstract: PWM techniques as applied to voltage source inverter-fed induction machines are well established. Even so it can be shown that strictly cutting down the pulse inverters turn-on and turn-off counts during a sampling period does not always lead to minimal switching losses as formerly alleged. Taking care of every single switching and conduction loss whilst maintaining a desired rms current deviation ends up in a nonlinear extreme value problem. To be more specific: Minimizing the expenditure of inverter losses to achieve a desired rms current deviation is the main objective of this paper. Therefore a CAD program utilizing Bellman's Dynamic Programming was developed which solves this problem and returns the optimal current trajectory. A novel model follower is employed to track the system along any given pre-calculated trajectory.

	LARGE SIGNAL MODELS AND CONTROL DESIGN FOR HIGH POWER-FACTOR PRECONDITIONERS By S. R. Wall; R. D. Jackson	[View] [Download]
Abstract: Large signal models are derived for a boost converter operating as a single-phase high power-factor preconditioner. A design procedure is presented for a pwm system with nested control loops for input current and output voltage. The inner (current) loop model is found to be linear in the large, consisting of the often used small signal model and a distortion term. The switching effects are accounted for by the insertion of a pwm describing function biode in the feedback path. It is shown that careful controller design is required to avoid input current distortion or subharmonic oscillation. Controllers for the voltage loop are evaluated by analysis of the linearized plant and simulation of the full nonlinear model. The effect of input voltage feedforward with finite response time filters is investigated. Experimental results are used to corroborate the majority of the analysis.

	DEVELOPMENT OF AN INTEGRATED HIGH VOLTAGE 3-LEVEL CONVERTER-INVERTER SYSTEM WITH SINUSOIDAL INPUT-OUTPUT FOR FEEDING 3-PHASE INDUCTION MOTORS By A. Mahfouz; J. Holtz; A. El-Tobshy	[View] [Download]
Abstract: This paper describes an integrated high voltage 3-level converter-inverter system . The system is characterized by a capacitor DC link voltage and a current controller based on space vector modulation (SVM) . Current drawn from the supply as well as current supplied by the inverter are sinusoidal with reduced harmonics. Through the current controller at the converter side, the system is forced to operate at unity power factor while the DC link voltage is observed dynamically and kept constant. Moreover the modulation at the inverter side is implemented using a singlechip 16-bit microcontroller (80196).

	THE MINIMISATION OF DISTURBANCES ON THE ELECTRICITY SUPPLY NETWORK WHEN CONTROLLING INDUSTRIAL, RESISTIVE LOADS By M. J. Carabok	[View] [Download]
Abstract: Unacceptable disturbances can arise on the electricity supply network, in certain situations, when either burst firing or phase angle, thyristor load control is used. In order to combat situations where the disturbances created by either of these control methods exceed the recommended limits an investigation has been conducted into an operating mode which involves both phase angle and burst firing control. This mode is called soft-start, soft-finish, burst firing and incorporates a phase angle component on the leading and trailing edge of each burst fire. Consequently, this operational mode is modelled for the control of industrial, resistive loads. To construct this model several series of experimental data were required to supplement the derived algorithms. The model, which computes the voltage and current harmonics and voltage fluctuation disturbances, is then incorporated in a computer program. This program compares the disturbances with the acceptable limits and postulates the optimal ramp length for operation such that the disturbances on the electricity supply network will be minimised. The computer program also permits closer examination of the disturbances, should a reduction in a particular order of harmonic be desirable.