Design of dc Voltage Controller for UPQC by Using its Small Signal Model

For UPQC, its series compensator and parallel compensator can be regarded as two dc voltage inverter. Therefore, maintaining a constant value for dc voltage is necessary for UPQC to performance normally. The constant dc voltage is related to the power balance between UPQC and sources, namely when the input active power of UPQC is equivalent to its consumption theoretically. So the controlling of dc voltage involves in the active current of sources. If the input signal of the controller is the error of dc voltage, its output signal should be the active current of sources. Under this circumstance, to get a mathematical model of its closed loop controller, finding the dc voltages expressed as a function of the active current of sources is critical. This paper proposed a method of design the dc voltage controller by using the small signal model of UPQC, with which mathematical relationship between dc voltages and the active current of sources is deduced. Based on that the mathematical model of closed loop of dc voltage is promoted. Parameters of the controller is calculated with it. A example is proposed in the last. The simulation results show that the dc control system has good stability margin and close-loop bandwidth, which verified the effectivity.