Research On Active And Reactive Power Support For PV Network

With more and more new energy generation connected to the public grid, intermittently and volatility of its output power has brought new challenges to the grid such as security and stability operation, regulation of peak and frequency, new energy absorptive. To ensure the economy of users and security of the grid, this paper proposes an energy management and control method to participate the grid regulation of active and reactive power by using multi-functional photovoltaic (PV)-battery system. The scheme can improve the security and stability of the grid, make PV-battery generation systems economic and grid-friendly, and enhance the value of the high cost of PV, thus promoting the development of distributed PV.The main work is as follows:Firstly, a multi-functional PV-battery power topology is designed, and a novel control strategy is proposed to improve the power factor at the point of common coupling (PCC) using the multi-functional PV-battery generation system. By considering the rated capacity of the inverter, PV output power changes with solar radiation intensity and simultaneous fluctuations of load power, different operation modes of PV-battery generation system are analyzed and a hierarchical control strategy is employed. A central controller is designed to select the correct operation modes and achieve the smooth switch between different operation modes, to select the local controllers, to calculate and give the references of local controllers, and to decide the charge or discharge states of the battery. The local controller includes maximum power point tracking (MPPT) controller, active and reactive power (PQ) controller of the PV-inverter, and battery charge/discharge controllers. The presented control strategy can achieve that one operation mode is switched to another seamlessly and PV-inverter can feeds active power to public grid meanwhile provides the reactive power compensation to dynamically improve the power factor at the PCC. When the output apparent power of the PV-inverter reaches the rated capacity, the PV-inverter has to decrease its output active power to output more reactive power. A method that makes the remaining PV power save to the battery as much as possible is proposed to improve the utilization of PV and reduce the disposable light. In low-light condition or at night, the battery discharges to maintain the DC bus voltage, ensuring that the inverter can continue to provide reactive power for the main grid, and the PV is closed automatically without any hardware breaker.Secondly, thanks to grid-connected inverter instantaneous power response capability, a strategy is proposed to participate in auxiliary second frequency regulation of the power grid by using the multi-functional PV-battery system. When the grid frequency is abnormal, multiple operation modes of the PV-battery generation systems participating in the auxiliary second frequency regulation were analyzed and a hierarchical coordinated control strategy was presented considering the rated capacity of grid-connected inverter, solar radiation conditions, battery charge and discharge status, and etc. A central controller can achieve system operation mode selection and switching, the local controller selection, the controller reference value calculation and battery charge and discharge management according to the instructions of AGC (Automatic Generation Control) and the grid frequency of real-time detection. The hierarchical coordinated control strategy achieves a rapid recovery of grid frequency while little disposable light under different operation modes, and delivery PV energy to the grid as much as possible when the grid frequency is normal. When the grid frequency of abnormal time exceeds a certain value, PV-battery generation system can provide local load uninterruptible power supply (UPS) function.