A switched power filtter compensator scheme for ac motorized electrical loads

The paper presents a novel device for energy conservation, power quality enhancement using switched power filter and compensator device for three phase motorized electric loads. The modulated power filter and compensator (MPFC) was developed by the first author to vary the shunt power filter equivalent admittance, modify the reactive power flow to the motorized electric load, improve electrical utilization and power factor. The filter dynamic switching is achieved using two complementary switching pulses generated by a PWM- pulse width modulation strategy and controlled by a tri-loop dynamic controller comprising three regulating time decoupled control loops, a reference power factor tracking loop, a minimum RMS source current dynamic loop and a dynamic minimum-derivative type active power search loop. The aggregate error signal is input to the proportional plus integral control block that controls the input control signal to the PWM activation/ triggering block. The degree of reactive compensation is controlled by the duty ratio of the PWM switching. PWM switching technique provides switching at frequency much higher than the power line frequency and consequently does not result in any low-frequency offending harmonics.