An ideal inverter should have sinusoidal voltage and current outputs. Generally, output voltages of a voltage‐source PWM inverter contain high‐level switching frequency harmonies due to the PWM operation, while output currents are kept nearly sinusoidal. High‐level harmonics contained in output voltages of a voltage‐source inverter cause acoustic noises, iron losses and electromagnetic interferences. An LC filter was used to suppress the switching frequency harmonics; however, there is a danger of resonance in the LC filter. Accordingly, to remove harmonics of the LC filter resonance frequency, the authors add a voltage feedback loop. A conventional system can operate without difficulty within 50 Hz. However, with accompanying increases in the output frequency, output voltages are largely delayed and reduced by a high‐pass filter inserted in the feedback loop. These problems are caused by a high‐pass filter inserted in the feedback loop. Accompanied by the inverter output frequency, a high‐pass filter cannot remove the fundamental component perfectly. As a result, a small fundamental component is fed back, which causes a delay and decrease in output voltage. This paper proposes the application of coordinate transformation to a high‐pass filter inserted in the feedback loop. As a result, the proposed system realizes an ideal filter which can suppress fundamental frequency components perfectly, and improves the characteristics of the inverter with sinusoidal voltage outputs greatly. Theoretical analyses, simulations and experiments showed satisfactory results. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 118 (4): 94–102, 1997
A capacitor input type rectifier is spreading widely by reason that its circuit configuration is simple and low cost. However, the rectifier includes many harmonics in an input current, and an input power factor is low. Hence, the input current harmonics cause voltage waveform distortion of an input power source, and the low power factor causes efficiency decline.Many sinusoidal rectifiers have been proposed to solve these problems. However, most of them have any complicated control such as a pulse width modulation (PWM) or a feed back control. Therefore, the authors have been proposed a twin converter which is composed of a full bridge diode rectifier, a pair of capacitors, a pair of reactors, and a pair of switching devices. The twin converter has simple configuration and simple control strategy. And excellent performance of the twin converter is revealed. However, the design method of the twin converter is not established firmly.Therefore, this paper studies on design method of the twin converter. And the design method is shown in detail in order to derive optimum values of the pair of reactors and the pair of capacitors. Moreover, experiments are carried out to verify the feasibility of the proposed design method of the twin converter.
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