THREE-PHASE FOUR-WIRE ACTIVE POWER FILTER CONTROL APPARATUS CAPABLE OF REMOVING NEUTRAL LINE CURRENT AND COMPENSATING REACTIVE POWER

摘要

PURPOSE: A three-phase four-wire active power filter control apparatus is provided to remove neutral line current produced from an imbalance of phase, and compensate a reactive power. CONSTITUTION: A three-phase four-wire active power filter control apparatus comprises an --0 converter(51), a power calculator(52), a LPF(53), a subtracter(54), a subtracter(55), an - current fundamental wave arithmetic operator(56), an --0 inverter(57), a subtracter(58), and an inverter PWM logic(59). The --0 converter obtains normal phase, reversed phase, and zero phase components based on the current signal received from a current transformer(CT1) of each phase and the fundamental frequency obtained from an PLL circuit(31) of a normal phase voltage detector(21) connected to a potential transformer(PT). The power calculator obtains an active power and a reactive power by using currents of normal phase, reversed phase, and zero phase components obtained from the --0 converter and instantaneous value voltages obtained from the normal phase voltage detector. The LPF obtains only a DC component of active power from the reactive power obtained from the power calculator. The subtracter(54) calculates a DC component of active power, and the - current fundamental wave arithmetic operator obtains normal phase and reverse phase currents by using a final compensated active power harmonic component calculated by the subtracter(55) and a reactive power component obtained from the power calculator. The --0 inverter obtains a compensated current waveform by using normal phase current and reversed phase current obtained from the operator(56) and the zero phase current obtained from the --0 converter. The subtracter(58) minimizes errors between the output current of an active power filter obtained from a current transformer(CT2) and the calculated compensated current waveform. The inverter PWM logic converts the final control current value into a pulse signal to be transmitted to a power element of the active power filter.