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Direct AC/AC converters have been investigated for miniaturization, high efficiency and harmonics reduction of mains current. These converters are classified into direct switch AC/AC converter (matrix converter) and PWM rectifier-inverter AC/AC converter in view of each circuit configuration.Firstly, this paper proposes averaged DC link voltage control of direct AC/AC converters, and details of the control method are described. In this method, averaged DC link voltage is derived from two selecting phase-to-phase mains voltages and the duty ratio of these selecting voltages for each modulation period. The averaged DC link voltage is used for the calculation of modulation index at each output phase.Secondly, this paper discusses a compensation method of output voltage error from commutation in case of applying the averaged DC link voltage control. Generally, the output voltage error occurs in direct AC/AC converters from commutation sequence consisting of two or four steps. And the compensation method reduces the error by analyzing commutation pattern created by the averaged DC link voltage control.Finally, experimental results are demonstrated, and it is confirmed that the harmonic distortion of the output current is efficiently reduced with the proposed compensation method.

A newly proposed energy-compensating active control is implemented to reduce the return current noise which is caused by inverter-driven electric car systems. The energy-compensating active control detects the energy charged at the filter capacitor, and reduces the energy and current of the noise frequency component by simple feedback loop incorporated with the conventional motor torque controller. No additional sensors or circuit arrangements are necessary; therefore, the return current can be attenuated effectively without any further cost. The return current with an inverter system is measured using a current probe and an FFT analyzer, and it is shown that the 25-Hz noise current is reduced by up to 10 dB with the control. The results reveal that the low-frequency return current noise can be attenuated with the simple control scheme, which would expectedly reduce the size of filter reactors and capacitors to meet the current limit level of the signaling system's track relays. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(4): 84–91, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20615