| Abstract |
The three-phase voltage source inverter (VSI) can be operated in grid-connected and/or stand-alone mode where the VSI is connected to the grid and/or critical loads at the point of common coupling (PCC). Proper voltage control is needed for the output voltage regulation in stand-alone operation and current control is needed for the grid current control. This paper presents a step-by-step design procedure, an extensive system stability analysis, and methods of discretization for the current control of three-phase power converters in the synchronous (dq) and stationary reference frame (SRF). A proportional-integral multi-resonant (PI-MR) controller in the synchronous reference frame (SynRF) is implemented for the regulation of the inner current loop. Moreover, the inverter inductor current controller in a stationary frame is proposed to provide active damping, and improve transients, and steady-state performance. The traditional PI-MR controller is compared for different load conditions with the modified practical proportional multi-resonant (PMR) controller in parallel with the harmonic compensators of orders 5th, 7th, 11th, and 13th to reduce low-order load current harmonics. The PMR controller shows superior performance with lower total harmonic distortion (THD) than the conventional PI and PI-MR controllers for highly non-linear load conditions. Moreover, the modified PMR controller has almost zero steady-state error, improved tracking of the reference signal, and better disturbance rejection compared to the conventional PI-MR control. A comprehensive design guideline of the proposed controller with a wider range of system stability margin is analyzed with harmonic damping of the three-phase VSI. Proper discretization methods for each controller have been outlined. The system is simulated in MATLAB/Simulink environment and experimentally implemented on a TMS320F28335 floating-point digital signal processor (DSP) for a 7.5 kW inverter to validate the performance of the controllers. |
