We performed a theoretical and experimental study of low-frequency oscillation in a Hall thruster. The oscillation phenomenon depends on various external control parameters. However, we found that such dependence can be observed very clearly using certain expressions, which are combinations of external control parameters. Using these expressions, one can observe the oscillation strength and oscillation mode for a given set of external control parameters. We considered that low-frequency oscillation can be essentially suppressed by a method of determining parameter sets. The method of determining the parameter sets is very important for Hall thruster design and control; in particular, it makes it easy to manage electromagnetic compatibility with the other equipments in a satellite, using a power supply control.
Recent increase of semiconductor power converter systems brings about harmonic problems. In a single phase power converter, a capacitor-filtered rectifier is used to derive DC voltage from an AC commercial power source. This converter generates harmonic currents and its power factor is very low. In order to reduce harmonic currents and compensate the input power factor, we propose a novel switching method, called the simple partial switching method (SPSM), for a single phase AC to DC converter. A control device of the converter switches once in every half cycle of an AC commercial power source by this SPSM. The switching timing is decided by the input power factor and by the odd order harmonic estima tion function of the input current. The estimation function is defined as the harmonics ratio compared with the harmonic currents standard. Experimental results clarify that our SPSM converter reduces harmonic currents and compensates the input power factor.
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