Direct power control of voltage source inverter in a virtual synchronous reference frame during frequency variation and network unbalance

Abstract

This study proposes a direct power control (DPC) scheme for grid-connected voltage source inverter (VSI) in a virtual synchronous reference frame during frequency variations and network unbalances. The proposed DPC scheme applies a virtual phase angle instead of the voltage phase angle acquired by the phase-locked loop (PLL) for coordinated transformations. This approach can eliminate the PLL and its low-frequency-oscillatory behaviours during the frequency variations. Meanwhile, two available control targets, that is, smooth active power and smooth reactive power, are defined for the VSI operation during network unbalance. In the proposed DPC scheme, the reduced-order vector integrator is employed to directly regulate the power pulsations caused by the voltage unbalances. Consequently, it can eliminate both the sequential separations of the voltages/currents and the complex calculations of the power compensating components. Then, based on the mathematical model of the VSI control system, the control performance, including the steady-state power errors and the system stability, is fully analysed. Finally, both the simulation and experimental results are provided to confirm the effectiveness of the proposed DPC scheme.

A Modified Self-Synchronized Synchronverter in Unbalanced Power Grids with Balanced Currents and Restrained Power Ripples

“…The grid voltage and current have both the negative and positive sequence components when the grid voltage becomes unbalanced, which will cause double frequency ripple components in the reactive and active powers [20]. Power control of conventional synchronverter has limited bandwidth.…”

“…To analyze the characteristics of the proposed strategy, the small signal model of synchronverter needs to be expanded considering two extra resonant controllers. According to (20), the following equations can be obtained: Equation 23can also be expressed as follows:…”

“…Resonant controllers have been widely adopted in the improved control strategies under unbalanced power grid conditions to deal with the negative sequence components and proven to be an effective way to deal with this problem. Different kinds of resonant controllers are combined with the vector control (VC) and direct power control (DPC), i.e., second-order generalized integrator (SOGI) [18] reduced-order generalized integrator (ROGI) [19] and reduced-order vector integrator (ROVI) [20]. Theoretical analyses and experimental studies have verified the effectiveness of the resonant based strategies in unbalanced power grid.…”

Vector Current Control Derived from Direct Power Control for Grid-Connected Inverters

“…However, it may incur additional computational burden. In addition, Cheng and Nian proposed a virtual synchronous reference frame based DPC for VSI in [44] and extended it to doubly fed induction generator system with consideration of unbalance grid voltage and harmonically distorted voltage conditions [45], [46]. They used a virtual phase angle instead of the voltage phase angle acquired by PLL for coordinate transformations, and apply the reduced-order vector integrators to directly regulate the power pulsations.…”

A three‐vector‐based direct power control strategy for three‐phase voltage source PWM converters

“…A zero vector and a non‐zero vector are then selected to control the instantaneous active and reactive power . This control principle is also suitable for the three‐phase voltage source PWM rectifiers and for the single‐phase three‐level pulse rectifiers . Although the predictive deadbeat direct power control of the PWM rectifier is simple in structure and the control performance is improved, it is still not perfect for the control of ripples in the reactive power.…”