Effects of Fundamental Component Output Voltage on the Active Filter Rating of Shunt Hybrid Power Filters

Non-linear loads increase the harmonic pollution of power systems and have undesired effects on the system and customer equipment. Passive filters have been conventionally used for mitigating harmonic distortion in industrial power systems. However, they have inherent drawbacks such as high dependency of their performance on the system impedance. Active power filters do not have the drawbacks of passive filters. They inject harmonics with appropriate magnitude and phase angle into the system, thereby canceling out harmonics of nonlinear loads. However, disadvantages such as high initial cost limit their wide usage. To overcome the above limitations imposed by passive and active filters, hybrid power filters have been introduced. They consist of two or more active and passive power filters in different configurations. This paper presents a control scheme enabling the shunt hybrid power filter to generate and inject a fundamental component voltage, in addition to the harmonic component, to the filter branch. The effect of an existing fundamental component in-phase with the system voltage is investigated on the output voltage of the active filter. This control system includes two main loops; one for generating harmonic component of the active filter reference voltage and one is used for generating a fundamental component voltage for the reactive power compensation. Computer simulations have been carried out for a typical power distribution system including a three-phase thyristor controlled rectifier as the nonlinear load and a shunt hybrid power filter. The results validate the presented mathematical analysis and performance of the proposed control scheme.