Showing papers by "Geza Joos published in 1991"
TL;DR: In this paper, a closed-loop active current wave-shaping technique was proposed for input power factor correction, where nearly sinusoidal input currents are obtained at constant switching frequencies.
Abstract: A novel input power factor correction method that uses a closed-loop active current waveshaping technique is presented. The novel feature of the method is that nearly sinusoidal input currents are obtained at constant switching frequencies. Moreover, the method exhibits instantaneous current control, which results in very fast response and increased switch reliability. Selected predicted system performance and design methods were verified experimentally on a 1 kVA laboratory prototype. >
180 citations
TL;DR: The performance of a three-phase solid-state reactive power compensator with fast dynamic response is analyzed and a mathematical model for the compensator connected across a variable power factor load is derived.
Abstract: The performance of a three-phase solid-state reactive power compensator with fast dynamic response is analyzed. The compensator consists of a three-phase pulse-width modulated voltage-source inverter connected to a self-controlled DC bus. The principal advantage of this scheme is that it can maintain a near-unity source power factor without sensing and computation of the associated reactive power component. A mathematical model for the compensator connected across a variable power factor load is derived. The frequency response is obtained for open-loop operation. This allows the design of the controller. Predicted results are verified experimentally for both open and closed-loop responses. >
101 citations
TL;DR: In this article, the effect of voltage unbalance on the rectifier output voltage is examined, and a specific practical solution for the elimination of the triplen input current harmonics is proposed.
Abstract: The authors analyze the effect of input voltage unbalances on the rectifier input current and on the filter kilovoltampere rating. The effect of voltage unbalance on the rectifier output voltage is examined, and a specific practical solution for the elimination of the triplen input current harmonics is proposed. The authors conclusively demonstrate that the elimination of these noncharacteristic harmonics can be accomplished by using a firing scheme that results in equal and equally spaced thyristor conduction periods, irrespective of the degree of unbalance in input voltages. However, the scheme has a drawback: the amplification of the ripple voltage at the rectifier output. These conclusions are verified experimentally using a 5 kVA setup. >
38 citations
24 Jun 1991
TL;DR: In this article, the authors proposed a class of compact regenerative SFCs, which do not require a DC filter, are insensitive to input unbalances, and have a very rugged power and control circuit structure.
Abstract: Static frequency changers (SFCs) typically use a rectifier-inverter combination with a passive LC filter as the intermediate DC link. This class of SFCs does not allow sustained regeneration and requires a bulky DC filter. A recently proposed alternative, based on the synchronous energy transfer principles, has successfully solved the problems of power regeneration, but still requires a DC side filter. Moreover, it is very susceptible to input AC line unbalances. A class of compact regenerative SFCs, which do not require a DC filter, are insensitive to input unbalances, and have a very rugged power and control circuit structure. PWM pattern generation on the inverter side is based on output current control. Design and implementation considerations are discussed. Simulation and experimental results confirm the feasibility and predicted performance of the proposed class of converter circuits. >
32 citations
24 Jun 1991
TL;DR: A modified PWM (pulse width modulated) current source inverter (CSI) that can operate with varying modulation indices (including low modulation indices) is presented in this paper.
Abstract: A modified PWM (pulse width modulated) current source inverter (CSI) that can operate with varying modulation indices (including low modulation indices) is presented. Any standard VSI (voltage source inverter) PWM pattern can be used with this inverter. This feature is obtained without compromising the converter system efficiency and power factor, and at the cost of only one auxiliary switch. The added degree of freedom obtained through modulation index control allows instantaneous control of output current and results in a high-performance inverter system. Inverter steady-state performance equations have been derived, as well as design equations and guidelines. The feasibility and performance of the CSI are verified by simulation and experimental implementation on a 5 kVA system. >
30 citations
28 Sep 1991
TL;DR: In this paper, a DC-side commutated zero voltage switching (ZVS) PWM 3-/spl Phi/VSI topology is discussed, which consists of a typical six-switch bridge with the addition of a simple DC bus commutating subcircuit which can provide, on demand, the necessary soft switching zero-volts interval across the inverter DC bus.
Abstract: The introduction of soft switching features in medium power static converters promises improved semiconductor utilization and higher switching frequencies. In this paper a DC-side commutated zero voltage switching (ZVS) PWM 3-/spl Phi/ VSI topology is discussed. This topology consists of a typical six-switch bridge with the addition of a simple DC bus commutating subcircuit which can provide, on demand, the necessary soft switching zero-volts interval across the inverter DC bus. The objective of this paper is to identify a specific PWM technique which, in combination with the proposed ZVS scheme, can provide optimum overall converter switching performance. Moreover, the combination of the inverter topology and the modulation strategy proposed here yields a soft switching environment at the lowest possible switching frequency. Reduction in switching losses is further enhanced by increasing the effective and reducing the actual switching frequency. Finally, this paper includes a detailed analysis and design procedure for the proposed notch commutated inverter topology. Simulation and experimental results are also presented to verify key predicted results. >
25 citations
TL;DR: In this paper, a stand alone, three-phase, delta-modulated, current-source PWM rectifier has been built and has been shown to be capable of operating with near sinusoidal current waveforms, unity power factor and good DC current regulation.
Abstract: A stand alone, three-phase, delta-modulated, current-source PWM rectifier has been built and has been shown to be capable of operating with near sinusoidal current waveforms, unity power factor. and good DC current regulation. A mathematical model that has been justified against experimental measurements and results from digital simulations is presented. The current waveform distortion limit and the asymptotic stability limit are established. It is shown that the rectifier can operate safely within these limits in the entire range of its power ratings. >
19 citations
24 Jun 1991
TL;DR: A novel three-phase ZVS PWM VSI topology employing a simple DC bus active snubber subcircuit that provides soft switching commutations is proposed and simulation and experimental results are presented to verify the principles of operation of the proposed power inverter scheme.
Abstract: Switching losses limit the inverter switching frequency and decrease the overall conversion efficiency. Minimizing switching losses can be effectively achieved by employing soft switching techniques. Specifically, zero voltage switching (ZVS) for a three-phase voltage source inverter (VSI) can be obtained by reducing the switch voltage to zero before main transistor turn-on (switch antiparallel diode conduction) and by keeping the switch voltage to zero during turn-off (purely capacitive snubber). A novel three-phase ZVS PWM VSI topology employing a simple DC bus active snubber subcircuit that provides soft switching commutations is proposed. The main advantage of the proposed inverter commutation scheme is that the DC bus snubber subcircuit is activated only when required, that is when dictated by the respective pulsewidth modulator. Detailed analysis and design procedures are provided and simulation and experimental results are presented to verify the principles of operation of the proposed power inverter scheme. >
9 citations
24 Jun 1991
TL;DR: In this paper, a DC bus snubber subcircuit for high-frequency high-power half-bridge forward PWM DC-to-DC converters is presented, which consists of a dc bus interrupt switch and a capacitor connected across the converter.
Abstract: A novel DC bus snubber subcircuit for high-frequency high-power half-bridge forward PWM DC-to-DC converters is presented. This snubber consists of a DC bus interrupt switch and a capacitor connected across the converter. The effective use of these components yields zero voltage switching conditions for both the DC switch and the high-frequency inverter. Additionally, the DC bus switch can be utilized to isolate the inverter under abnormal operating conditions. Complete circuit analysis, design procedures, and a simulated verified design example are included. >
6 citations
28 Oct 1991
TL;DR: In this paper, the input characteristics of a modified CSI with improved performance characteristics have been investigated, and the quality of the input AC line currents is analyzed, and a design procedure for the input filters is given.
Abstract: The input characteristics of a modified CSI (current source inverter) with improved performance characteristics have been investigated. The quality of the input AC line currents is analyzed, and a design procedure for the input filters is given. Equations describing the steady-state operating characteristics are derived. These have been used to compare the input characteristics of the modified CSI with those of other CSI control schemes also using a phase-controlled front and rectifier. These comparisons have shown that the advanced features of the modified CSI are obtained without any penalty on input power factor and system efficiency. In particular, the combined displacement and distortion power factor for unity modulation index is only slightly lower than that of a six-step inverter and other CSIs also using pulse width modulation. The input characteristics of the modified CSI have been verified on an experimental 5 kVA unit and confirm the predicted results. >
28 Oct 1991
TL;DR: It is shown that it is possible to reduce and stabilize the switching frequency of three-phase delta- modulated PWM (pulse-width-modulated) inverters, while improving performance, by exploiting the characteristics ofThree-phase systems.
Abstract: It is shown that it is possible to reduce and stabilize the switching frequency of three-phase delta-modulated PWM (pulse-width-modulated) inverters, while improving performance. This has been achieved by exploiting the characteristics of three-phase systems. The proposed modulator is based on controlling only two inverter legs at any given time, and forcing the switches in the other leg to remain permanently on or off for specified time intervals. The scheme imposes no penalty on the transient performance and the quality of the output waveform does not suffer. The resulting voltage gain of the inverter is also increased to the level of optimized techniques. Implementation of the technique is simple, requiring no additional computation or circuits. Experimental results on a 5 kVA unit confirm the feasibility of the proposed modulator. >
10 Mar 1991
TL;DR: In this article, the authors proposed a full bridge PWM converter with a DC bus switch and a lossless DC bus snubber circuit, comprising an inductor and two capacitors.
Abstract: The full bridge pulse-width-modulated (PWM) converter proposed has functions under nearly zero-current-zero-voltage switching conditions, thus minimizing switching losses. This is achieved by using a DC bus switch and a lossless DC bus snubber circuit, comprising an inductor and two capacitors. The DC bus switch can also be used to isolate the inverter under adverse system operation conditions. A complete circuit analysis and a design procedure are presented. Theoretical results have been verified experimentally on a 1 kW 20 kHz laboratory prototype. >
TL;DR: In this paper, three phase PWM pattern generators that are simple to implement with low cost circuitry, particularly with analog components, are presented, where the current in the built-in load model is forced to follow a reference by means of hysteresis control.
Abstract: Optimized PWM techniques have been developed and used with good results for voltage source inverters. However, implementation frequently requires complex electronic circuits, usually microprocessor-based, that cannot be justified in low cost applications. The paper examines three phase PWM pattern generators that are simple to implement with low cost circuitry, particularly with analog components. These modulation techniques are based on the model reference adaptive (MRA) technique. They exhibit intrinsic constant Volts/Hertz operation, and do not require frequency synchronization and frequency jumping, making them ideal for low cost inverter driven variable speed ac motor drives. The PWM patterns are generated by forcing the current in the built-in load model to follow a reference, by means of hysteresis control, also known as the delta modulation technique, or error triangulation control. Unlike delta modulation, the latter technique exhibits constant switching frequency and has an output voltage spectr...
10 Mar 1991
TL;DR: The single-phase full-bridge mode pulse-width modulated (PWM) DC-DC converter topology discussed minimizes switching losses and resulting stresses through the effective use of one DC bus inductor and two snubber capacitors.
Abstract: The single-phase full-bridge mode pulse-width modulated (PWM) DC-DC converter topology discussed minimizes switching losses and resulting stresses through the effective use of one DC bus inductor and two snubber capacitors. The inductor provides zero current turn-on and the capacitors are alternately connected across each switch, thus providing zero voltage turn-off. After turn-off, capacitor energy is transferred to the load through a low loss path. A simple active energy recovery network that increases the overall converter efficiency is also proposed. The authors include a complete circuit analysis and design procedure. Predicted results are verified experimentally on a 5 kW, 10 kHz laboratory prototype. >
28 Oct 1991
TL;DR: Simulated and experimental results confirm the theoretical concept and feasibility of the proposed voltage compensator system and show that the compensation can be achieved with low-kVA inverters and that harmonic injection is reduced to a minimum.
Abstract: Voltage unbalance typically present a three-phase AC supply systems adversely affects power system components, static converters, electric drive systems, electric machines, etc. connected to the system. The authors describe a method to eliminate this unbalance by means of a voltage compensator connected in series with the supply through transformers. The technique is based on extracting the negative sequence voltage component of the supply and canceling it in order to obtain balanced voltages. The positive sequence component is then adjusted to achieve voltage regulation. It is shown that the compensation can be achieved with low-kVA inverters and that harmonic injection is reduced to a minimum. Implementation principles, design equations, and a design example are presented. Simulated and experimental results confirm the theoretical concept and feasibility of the proposed system. >