COMPARISON OF CONTROL STRATEGIES FOR UNIFIED POWER QUALITY CONDITIONERS FOR VOLTAGE STABILIZATION AT THE DISTRIBUTION NETWORK LOAD BUS

Abstract

The paper presents a comparison of three control strategies for a Unified Power Quality Conditioner (UPQC) with a left-shunt configuration (parallel compensator connected on the source side) aimed at mitigating voltage fluctuations caused by supply voltage instability. The first strategy (Q-type UPQC) ensures that the regulator injects a voltage in quadrature with the load current. The second strategy (P-type UPQC) involves generating a voltage that is in phase with the load current. The third control strategy is employed in S-type conditioners, which generate a voltage with a phase angle relative to the load current ranging between 0 and π/2. Control laws were derived as dependencies of the series and shunt compensator EMFs on the supply voltage for Q-, P-, and S-type UPQCs to maintain a stable voltage at the load node. The voltage stabilization process at the load connection point was analyzed under supply voltage variations within the range of 10.5–10.0 kV, utilizing a corresponding UPQC control law based on informative parameters such as the current and base source EMF values and network parameters. Simulations were conducted for Q-, P-, and S-type UPQCs under two conditions: maximum reactive power compensation by the shunt compensator, and minimum reactive power compensation by both the shunt and series compensators. It is shown that the advantage of the Q-type UPQC compared to the S-type and P-type is the capability for a significant load voltage boost. In P-type and S-type UPQCs, such an increase is difficult to implement due to the non-identity of the active power consumption and generation dependencies of the shunt and series compensators. It is demonstrated that for voltage variations within 10.5–10.0 kV, the S-type UPQC exhibits lower active power, whereas for variations within 10.5–10.3 kV, the P-type UPQC has lower active power.