Dusan Borojevic

Interleaved PWM with discontinuous space-vector modulation

This paper describes the effect of interleaved discontinuous space-vector modulation (SVM) in paralleled three-phase systems using three-phase pulsewidth modulation (PWM) rectifiers as an example. At the discontinuous point of the SVM, the phase shift between the switching signals of the paralleled modules generates a zero-sequence excitation to the system. Because the conventional control in a balanced three-phase system with only dq channels cannot reject this disturbance, a beat-frequency circulating current will develop on the zero axis. Based on this observation, a SVM without using zero vectors is used to eliminate the cause of pure zero-sequence current for parallel operation. Using this SVM, the circulating current is observable in dq channels. It can be suppressed dynamically by strong current loops of power-factor-correction (PFC) circuits. The concept is verified experimentally on a breadboard system.

A comprehensive study of neutral-point voltage balancing problem in three-level neutral-point-clamped voltage source PWM inverters

This paper explores the fundamental limitations of neutral-point voltage balancing problem for different loading conditions of three level voltage source inverters. A new model in DQ coordinate frame utilizing current switching functions is developed, as a means to investigate theoretical limitations and lend more intuitive insight into the problem. The low frequency ripple of the neutral point caused by certain loading conditions is observed and quantified.

Individual load impedance specification for a stable DC distributed power system

This paper continues the effort to define load impedance specification for a stable DC distributed power system. To improve the existing load impedance specification, an alternative forbidden region for Z/sub 0//Z/sub i/ is proposed, based on which individual impedance specification for each load is defined. Theoretical verification, accompanied with simulation results, shows that the proposed impedance specification is a sufficient condition for small signal system stability. Finally, conservativeness in load impedance specification is discussed.

A new control algorithm for three-phase PWM buck rectifier with input displacement factor compensation

A new control algorithm for the three-phase buck rectifier with an input filter is developed. The algorithm employs a separate control loop for compensation of the input current displacement factor in steady-state, in addition to the standard output voltage regulation loop. The algorithm allows separate design of the input filter and of closed loop output voltage control. The design procedure is explained and illustrated on an example. The algorithm is verified experimentally on an 1-kW, 100-kHz, three-phase isolated buck power converter. >

Space vector modulated, zero-voltage transition three-phase to DC bidirectional converter

Operation and implementation of the novel, space vector modulated, zero-voltage transition, three phase voltage source inverter/boost rectifier is presented. The converter is intended for high performance, medium power applications requiring bidirectional power flow. The proposed modified space-vector modulation allows all switches to be operated with soft-switching and constant frequency. The modulation algorithm also eliminates any low frequency distortion caused by the zero-voltage transitions and can be applied to any soft switching PWM three-phase converters. A simple, digital signal processor based implementation of the modulator and current regulators, operating with 30 /spl mu/s sampling time, is described. Measured efficiency of the 30 kHz, IGBT prototype is around 95%, and distortion of the three-phase currents is extremely small.<<ETX>>

A new zero-voltage transition, three-phase PWM rectifier/inverter circuit

A switching rectifier/inverter technique that combines the conventional three-phase, six-stepped pulse-width modulated (PWM) rectifier/inverter with a simple commutation circuit to provide zero-voltage turn-on for the switches and soft turn-off for the diodes is presented. The commutation circuit is active only during a short period of the switching cycle, thus it consumes minimum power and does not impair the normal constant frequency PWM control. The addition of the commutation circuit does not result in increased component current and voltage stresses compared to the conventional PWM converter.<<ETX>>

Digital-signal-processor-based control of three-phase space vector modulated converters

The paper presents the implementation of a DSP-based controller for three-phase, space-vector modulated converters. The implementation is illustrated for the control of a 2 kW, ZVS matrix power converter-based three-phase PWM rectifier. The controller features very high data processing speed (converter switching frequency of 100 kHz), and provides high-quality, low-distortion power converter input currents and output voltages. The controller can be implemented using only a few standard integrated circuits, providing high reliability and low cost. >

Input filter design for power factor correction circuits

The issues involved in the design of power factor correction circuit input filters are significantly different than those involved in the design of input filters for DC-DC power converters. So far, there exist no guidelines for high-frequency AC power converter input filter design. This paper addresses these issues and proposes the use of a high order, actively damped filter to achieve the required EMI attenuation and power factor requirements. The new filter topology typically provides 50% filter size reduction over the standard filter designs, and simultaneously minimizes the filter-converter interaction.<<ETX>>

Analysis and design of a zero-voltage switched, three-phase PWM rectifier with power factor correction

A three-phase, single-stage, isolated PWM rectifier capable of power factor correction and low harmonic current distortion and at the same time realizing zero voltage switching for all power semiconductor devices is proposed. The circuit is thoroughly analyzed. Design equations and tradeoffs are provided. The performance of the circuit is demonstrated through the implementation of a 2 kW, 91 kHz, digital signal processor controlled prototype. The isolated DC output voltage is regulated at 50 V. The conversion efficiency is around 93%.<<ETX>>

An active bus conditioner for a distributed power system

In a distributed power system with many power converters on the DC bus, there is always the concern of the possible interactions between the system building blocks, which are designed at the individual box level. This paper presents a novel concept, the DC bus conditioner, which compensates the harmonic and reactive current on the DC bus and actively damps the oscillations in a DC power system. With a certain amount of extra energy storage, the bus conditioner can provide the large signal variable frequency ripple current as required by the load and actively shape the small signal impedance characteristics of the DC bus interface at the mid-frequency range to increase the system stability margin. The breadboard experimental results are presented.