Research On Influence Of Distributed Photovoltaic Power Generation System For Power Quality In Distribution Network

With the increased penetration of distributed photovoltaic(PV) power in distribution network, the influence of distributed PV on the stability and power quality of distribution network keeps rising.Distributed PV has changed the way of radial power flow power mode in traditional distribution network. In distribution network with high PV penetration especially weak radial low voltage distribution network, reverse power is likely to occur when the load is light, which may result in over-voltage. The PV output volatility caused by passing clouds obscured may lead to voltage sags, flicker and even system stability. Faced with the above-mentioned power quality problems caused by the access of distributed PV, the traditional voltage regulation method such as OLTC and power capacitors will fail because of slow response speed.Firstly, the paper summarizes the typical power quality problems in distribution network with distributed PV. The network voltage variation mechanism is analyzed, and distributed PV systems typically topology is established.Secondly, to solve overvoltage problem caused by the access of distributed PV under the premise of not changing the distribution network structure and device configuration, an active and reactive power integrated control strategy is proposed. When the network has overvoltage risk, the active power limit will be set in real time. At the same time the remaining capacity of the inverter will be used to absorb inductive reactive power to further reduce the voltage while avoiding unnecessary active cuts. On this basis, multiple power coordination control scheme is designed to enhance the capacity of the distribution network voltage regulation. Simulation results show that the proposed control scheme can effectively solve the distribution network overvoltage problem caused by access of distributed PV.Then, to explore the potential of distributed PV in distribution network voltage quality regulation, active/reactive power-voltage regulation operation strategy is put forward based on the typical structure of distributed PV systems previously mentioned. Dead zone with Schmitt circuit characteristics is set in active power control loop to ensure the priority of reactive power control. Dead zone control may cause frequent voltage shake near the threshold voltage value due to high sensitivity of active power regulation. Different positive/negative threshold voltage in Schmitt circuit can effectively eliminate shake. Simulation results show that the proposed scheme can effectively deal with voltage problems associated with sudden changes in solar power output, high capacity load switching and distribution network disturbances.Finally, to take full advantage of distributed PV's potential in distribution network power quality regulation, double-level control strategy which includes a central control and a local control for photovoltaic is established. The proposed control strategy can make the distributed PV system participate in frequency modulation, grid scheduling as well as energy state adjustment of energy storage element, at the same time, the stability of DC bus voltage is guaranteed.