基于自适应虚拟阻抗与缓启升压协同的交流微电网黑启动控制方法OA

When the natural disasters cause the outage of power grid,the islanded AC microgrids are started to feed the loads fast.However,due to the lack of the communication links,it is difficult to share information among paralleled inverters interfacing distributed energy sources in the islanded AC microgrids and acknowledge the load information for each inverter.Thus,the inverters need to equip black-start capability.Overcurrent suppression is the key for a successful black-start.To improve the overcurrent suppression capability of the inverters in the black-start,this paper proposed a black-start control method for AC microgrids based on coordination between adaptive virtual impedance and slow-voltage-rising.In the proposed method,the surge current and overload current are suppressed by the slow-voltage-rising strategy.Additionally,when the inverter is connected to the point of the common coupling,the impulse current caused by the difference on the voltage amplitude and the asynchronization on the voltage phase,is suppressed by introducing the adaptive virtual impedance. Specifically,the proposed method has four modes.In the initial mode,the virtual impedance is set as zero while the slow-voltage-rising control is activated;in the overcurrent suppression mode,the virtual impedance is regulated by a proportional controller to suppress the impulse current while the slow-voltage-rising control is inactivated;in the transition mode,the virtual impedance maintains constant while the slow-voltage-rising control is inactivated;in the virtual impedance slow-removal mode,the virtual impedance is removed step by step with the set virtual impedance step-length to eliminate the oscillation of the virtual impedance,while the slow-voltage-rising control is activated.Under the proposed method,the inverter with overcurrent first works on the overcurrent suppression mode,and then works on the switching between transition mode and virtual impedance slow-removal mode until initial mode;other inverters without overcurrent work on the initial mode all along.Meanwhile,to guide the design of the overcurrent suppression mode,an overall small-signal model of the virtual impedance loop consisting of inner voltage loop is built,which indicates that the inner voltage loop obviously deteriorates the stability of the virtual impedance loop.Additionally,the constrain of the current increase serves as the sufficient condition to design the virtual impedance removal-step length. Simulation and experimental results which are inducted on the voltage amplitude difference and voltage phase asynchronization,both show that the proposed method can suppress overcurrent while achieving the smooth virtual impedance variation.Additionally,the special load,i.e.,motor load and the stability analysis,is also verified by the simulation and experimental results,respectively. The following conclusions can be drawn.Firstly,the proposed method suppresses the surge current and overload current by the slow-voltage-rising strategy,and the impulse current is suppressed by introducing the adaptive virtual impedance while the virtual impedance oscillation is also eliminated by the proposed transition mode and the virtual impedance slow-removal mode.Secondly,by building the small-signal model of the virtual impedance loop consisting of the inner voltage loop,the stability of the proposed method is analyzed and the overcurrent suppression mode is designed.Meanwhile,the virtual impedance removal-step length is also designed based on the constrain of the current increase.