Research On Load Virtual Synchronous Machine Control Strategy Under Unbalanced Voltage Conditions

The three-phase voltage source rectifier with load virtual synchronous machine control strategy can simulate the inertia and damping of synchronous motor in the distribution network,help the active frequency modulation and reactive voltage regulation of the power grid,and play a role in stabilizing the power grid,so it has received widespread attention.In practical applications,there is always a certain degree of voltage imbalance in the power grid,and the load virtual synchronous machine system may experience uncontrollable second harmonic power fluctuations.This paper mainly conducts research on the control scheme and algorithm improvement of the load virtual synchronous machine under the condition of voltage imbalance in the power grid.Firstly,a mathematical model of the load virtual synchronous machine was presented,demonstrating that it has inertia,damping,and electrical characteristics similar to synchronous motors.To address the issue of second harmonic power fluctuations when the voltage of the power grid is unbalanced,based on αβ The new instantaneous power definition derived from the voltage,current,and their 1/4 cycle delay under the axis proposes a new control scheme that does not require current positive and negative sequence extraction and voltage negative sequence extraction.Compared with the traditional scheme that requires positive and negative sequence decomposition,the control scheme proposed in this article utilizes a new instantaneous power definition to carry the information of grid voltage imbalance,without the need for separate positive and negative sequence current control channels,and the composition of the control system is more concise.At the same time,the proposed control scheme introduces the switching system theory,establishes the affine model of the switching system of the three-phase voltage source rectifier,derives the switching law based on Lyapunov stability theorem,designs the current inner loop switching controller,and simplifies the switching law in combination with the specific characteristics of the three-phase voltage source rectifier to facilitate digital implementation.Finally,a comparative simulation verification was conducted between the proposed control scheme and the traditional control scheme under balanced current,constant active power,and constant reactive power operating modes.Furthermore,comparative experimental research was conducted on an experimental platform with TMS320F28335 DSP as the control circuit core.The simulation and experimental results show that the proposed control scheme has similar performance in suppressing active or reactive power fluctuations,but the system robustness of the proposed scheme is better,the control of the algorithm is more concise,and the algorithm running time is shorter.