Three-Phase Grid-Connected Inverter PQ Control Model Analysis

Analysis of the Three-Phase Grid-Connected Inverter PQ Control Model

In modern power systems, grid-connected control of three-phase inverters is critically important. The PQ control strategy has gained significant attention due to its ability to achieve precise active power (P) and reactive power (Q) regulation. This control model utilizes an LCL filter to achieve high-quality filtering of grid currents, ensuring system stability and power quality.

The core of PQ control lies in achieving decoupled control of active and reactive power on the grid side. The control system typically adopts a dual-loop structure: the outer power control loop generates current reference values based on given power commands, while the inner current control loop rapidly tracks these current references. By employing Park transformations to convert three-phase AC quantities into DC quantities in a rotating reference frame, the control process becomes more straightforward and efficient. From an implementation perspective, the Clarke and Park transformations are essential mathematical operations to convert abc-phase quantities into dq0 rotating frame quantities, enabling independent control of active and reactive power components.

The integration of LCL filters effectively suppresses high-frequency switching harmonics. Their design must consider factors such as resonant frequency and damping characteristics to avoid system oscillations. Control algorithms typically incorporate resonance suppression strategies or active damping methods to maintain stability even when grid impedance changes occur. In practical implementations, active damping techniques can be realized through virtual impedance methods or filter-based approaches in the control algorithm to mitigate resonance issues without additional hardware components.

This model achieves the goal of constant power output, maintaining set active and reactive power levels even under grid voltage fluctuations or load variations. This control approach is particularly suitable for grid-connected applications requiring precise power control, such as photovoltaic power generation and wind power generation systems. The control algorithm typically involves power calculation blocks, PI controllers for power regulation, current controllers with anti-windup features, and PWM generation modules to drive the inverter switches effectively.