Comparison of Direct Digital Control and <i>DQ</i>-Based Control for a Three-Phase Three-Wire Inverter With <i>LCL</i> Filter

This research compares the performances of direct digital control (DDC) and DQ-axis control for a 12-kW three-phase three-wire (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\Phi 3$ </tex-math></inline-formula>W) LCL grid-connected inverter, with a focus on practical applications. The experiment involves using an inverter with LCL filters and adopting direct digital, and DQ-axis control. The objective is to evaluate the control capability of the system, including transient responses, steady-state responses, grid distortion responses, and unbalanced responses. It employs the division-summation (D–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Sigma $ </tex-math></inline-formula>) process to decouple the three-phase system, a practical approach that can be applied in real-world scenarios. It incorporates system parameters into the controller, saving CPU computation time around 40% compared to the DQ-axis control. On the other hand, the DQ-axis control simplifies the three-phase system by using the DQ domain with Park transformation. The system model is constructed through mathematical derivation, providing practical insights into the system’s behavior. The controller of the system is designed according to the model. We compare the results with simulation and experiment to analyze the effects of these filters with these controllers. Experimental tests include transient state, steady state, and distorted grid voltage with harmonic component conditions, providing practical implications for real-world applications.