This paper concerns the effect of symmetric supply voltage harmonics in a space-vector modulated three-phase indirect matrix converter (IMC). The IMC is modulated using indirect space-vector modulation. The effect of symmetric supply harmonics on load voltages and currents is analyzed using space-vector presentation. The measurement and simulation results with distorted supply voltages are compared to the results with pure sinusoidal supply voltage. Four simple control methods of IMC are tested in simulations and measurements: 1) open-loop control without measurements (Method I); 2) calculation of modulation index using measured supply voltages (Method II); 3) closed-loop control of output currents (Method III); and 4) combination of Methods II and III, i.e., closed-loop output current control with supply voltage measurement (Method IV). All the methods are easy to implement and do not require complicated computing. It is noted that Methods II and IV, where modulation index is calculated using measured supply voltage magnitudes, can produce more sinusoidal load currents than Methods I and III, which suppose ideal supply conditions

Comparison of Simple Control Strategies of Space-Vector Modulated Indirect Matrix Converter Under Distorted Supply Voltage

Until now, direct control methods have been mainly investigated and used in conjunction with voltage source converters. In this paper, the authors develop a direct current control method for matrix converters. There are two objectives for the direct current control: the desired current has to be impressed into the load, and the current, drawn from the mains, should be in phase with the voltage and should be (nearly) sinusoidal. This implies active damping of the 400 Hz resonance or the line filter. The method is implemented on a DSP and tested on a 10 kVA matrix converter.

A direct control method for matrix converters

Due to the nonexistence of natural free-wheeling paths the commutation in matrix converters is more complicated than in voltage source converters. For bidirectional switches where the current flow is controllable separately for both directions this paper proposes new commutation strategies. Based on the measurement of the current direction and the signs of the line to line input voltages commutation in one step is enabled. Compared to multistepped proposals this strategy presents a much smaller deadtime near the switching time.

New one-step commutation strategies in matrix converters

The paper proposes an implementation of a two steps commutated matrix converter. Switching patterns are presented which guarantee safe control of bidirectional switches during a change of the sign of a line to line input voltage. A simple control of the output current is possible without adding any additional snubber circuit.

http://ieeexplore.ieee.org/iel5/6364/17081/00788999.pdf

Implementation of a two steps commutated matrix converter

A Direct Frequency Changer with Control of Input Reactive Power

The thesis is concerned with static frequency changers, using solid-state switching devices, capable of directly (i.e. without an intermediate dc link) converting polyphase ac power of a given frequency to single or polyphase power of a chosen frequency. The thesis consists of two parts. The first part, comprising five chapters, is devoted to the study of ideal frequency changers operated from ac Sources having zero internal impedance. The second part, comprising two chapters, considers sources with finite internal impedances . Chapter 1 introduces the basic concepts of static frequency conversion, outlines the basic mathematical models representing static frequency changers and defines the output and input performance indicators. Chapter 2 presents a detailed investigation of that class of three-pulse frequency changers which will be studied in the thesis. A large portion of the chapter is devoted to the study of output waveform generation. The mathematical tools of the investigation, existence matrices and modulating functions, are introduced and defined. Analytical expressions for output waveforms corresponding to various practical modulating functions are derived and the related performance indicators are computed. Assuming a given desired output performance, criteria for an optimal modulating function are established. It is proved that only one system can generate an output waveform conforming to the postulated prerequisites. This system is termed the "Unrestricted" Frequency Changer. Expressions for the input current waves are also derived in this chapter and the corresponding input performance indicators are determined . The concept of a new frequency changer having the unique property of providing unity input power factor, regardless of the load, is introduced. This system is termed the "Unity Power Factor" Frequency Changer. In Chapter 3 the previous results are extended to systems having pulse numbers which are integral multiples of three. Chapter 4 is devoted to the study of output voltage control. Three basic methods are analysed and detailed quantitative data for output voltage and input current waves, and the related performance indicators, are presented in graphical form. In Chapter 5 special aspects of static frequency changing are investigated. It is shown that the input displacement factor is variable. The concept of the "Controlled Displacement Factor" Frequency Changer is introduced It is proven that the naturally commutated cycloconvertor is theoretically equivalent to a particular "Controlled Displacement Factor" Frequency Changer. Chapter 6 presents a detailed analysis of the "Unrestricted" Frequency Changer, operated from an ac source with finite internal impedance. The basic conditions are defined and an outline is given of the techniques of symmetrical components used for the analysis. The input current, input terminal voltage and output voltage waveforms are expressed in terms of the input terminal impedance and the positive, negative and zero sequence components of the output currents. The equivalent sequence impedances and the output impedance matrix are derived . The output voltage unbalance is computed under various conditions and presented in graphical form. The relationships between the amplitudes of the unwanted components in the output waveform and the resonant frequency of the input terminal circuit are also graphically presented. The results obtained are verified by computer simulations. In Chapter 7 a similar analysis of the "Unity Power Factor" Frequency Changer is carried out . The computed data are also graphically presented. Again, the results are verified by appropriate computer simulations.

L Gyugyi

Papers

Generalized theory of static power frequency changers