Abstract
This paper proposes a fast phase capture (FPC) scheme and applies it to the control strategy of grid-tied inverters under imbalanced voltage. Firstly, a method for quickly extracting sequence components of power signals is derived through the symmetrical component method, and a real-time phase calculation method is proposed based on the rotating reference frame, thus avoiding the phase-locked loop (PLL) closed-loop adjustment process. Secondly, the grid-tied inverter suppresses the negative sequence current or power fluctuations through the direct resonance controller, so there is no need to separate the dynamically changing sequence current components. Finally, the experimental comparison with the PLL control strategy is carried out based on the RT-LAB platform. Compared with the previous phase-locking scheme, the FPC scheme has a faster phase-locking speed. Therefore, the fault ride-through capability of the grid-tied inverter is improved.
Highlights
Three-phase voltage imbalance is a common power system operating conditions, which will seriously interfere with the grid-tied inverter output power quality
In [8], An improved phase-locked loop (PLL) scheme is proposed to enhance the robustness of the power grid in the case of weak power grids
To further shorten the time that the grid-tied inverter bears malfunction, this paper proposes a fast phase capture (FPC) scheme for inverter systems
Summary
Three-phase voltage imbalance is a common power system operating conditions, which will seriously interfere with the grid-tied inverter output power quality. The dynamic and static response capabilities of the inverter are not considered Since these less-PLL solutions do not capture the grid voltage phase, the inverter cannot achieve decoupling control, which increases the operating burden of the DSP. The main factors affecting the transient response capability of the inverter are the digital delay process, the control parameter design of the current loop, and the phase lock speed of the PLL. A direct resonance controller is employed to ensure current balance or active power stability This method does not need to separate the positive and negative sequence components of the line current. This strategy avoids the problems of PLL closed-loop adjustment and parameter design difficulties, so that the negative sequence current compensation and power response ability of the inverter can be improved.
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