A study for active filter using operating amplifier without harmonics of switching frequency

The active filter (AF) is a good solution for eliminating harmonics from switching devices. But, many types of AF are composed of switching devices. Still more, in order to compensate harmonics with AF sufficiently, we need to increase switching frequency of the inverter. This increases the switching losses of devices. In addition, this may cause new harmonics or EMI to the AC line. In this paper we propose a new type AF. This AF consists of power operating amplifier with resonant circuit and partial-switching-type AF. The power operating amplifier has an advantage of generating no harmonics, but a disadvantage at the point of efficiency. Therefore, we use a resonant circuit for reducing the capacity of operating amplifier. Furthermore, we combine this with partial-switching-type AF for further decreasing the capacity. As this type of AF has very low switching frequency (2 times switching in one source voltage period in this case), the conversion efficiency of this system is very high. But, as this type of AF has been developed for specific load such as home electronic applications, the control method of applying for various load has not been established. Therefore, we propose a method for adapting these loads in this paper. By using simulation and experimental results, we show that this system can be practical.