基于电压补偿的下垂控制变换器功率解耦策略OA

Grid-forming technologies such as droop control are the key to improving the stability of the modern power system.However,for independent control of active and reactive power,the equivalent impedance of transmission lines must be purely inductive,and the power angle should be small.In low/medium-voltage grids with distributed renewable energy integration,the line resistance cannot be ignored,and the power angle may vary over a more extensive range,leading to significant power coupling issues.Power coupling will increase steady-state reactive power deviation,reduce system stability margin,and even trigger oscillatory instability. A small-signal model of the grid-connected system with power coupling is first established.Root locus analysis indicates that power coupling reduces the system stability margin,and the larger the R/X ratio,the lower the system stability margin.Further amplitude-phase analysis shows that the negative damping in the active power loop due to power coupling is the primary cause of the reduced system stability margin.The steady-state power coupling coefficient reveals that power coupling increases the steady-state reactive power deviation,and the larger the R/X ratio,the greater the steady-state reactive power deviation. To address these issues,a power decoupling strategy based on voltage compensation principles is proposed:(1)An angular frequency deviation compensation term is introduced into the voltage loop to reduce the negative damping effect of power coupling and improve the system stability margin.(2)The ideal decoupled voltage when the steady-state reactive power deviation is zero is calculated,and the difference between the actual output voltage and the ideal decoupled voltage is used for active power feedforward compensation,thereby reducing the steady-state reactive power deviation. Experiments are carried out in a three-phase droop control converter grid-connected system.Under the conditions of R/X=0.32 and 0.53,the proposed decoupling method reduces the minimum reactive power during the dynamic process from-0.46(pu)and-0.59(pu)to 0.001(pu)and 0.008(pu),respectively.The steady-state reactive power deviation also decreases from-0.231(pu)and-0.342(pu)to-0.003(pu)and-0.007(pu),respectively.Furthermore,under the R/X=0.32 condition,the power response time using the proposed decoupling method is 120 ms,which is essentially the same as without the decoupling method.In contrast,with the virtualinductor(VI)decoupling method,the power response time increases to 360 ms,and the steady-state reactive power deviation is-0.131(pu).Therefore,the VI decoupling method not only slows down the response speed but also fails to eliminate steady-state power coupling. Experimental results show that:(1)The proposed decoupling method can suppress power oscillations during the dynamic process under various R/X conditions and improve the system stability margin.(2)The proposed decoupling method reduces steady-state reactive power deviation,and changes in the reactive power setpoint do not affect active power control accuracy.(3)Compared to the VI decoupling method,the proposed decoupling method does not slow down the converter's response speed and demonstrates better steady-state decoupling capability,helping to improve the dynamic and steady-state performance of droop-controlled converters in distributed renewable energy generation systems.