A grid-connected inverter (GCI) with LCL filters is widely used in photovoltaic grid-connected systems. While introducing active damping methods can improve the quality of grid-connected current (GCC), the influence of grid voltage disturbances can still significantly impact the quality of GCC, leading to stability degradation, especially in weak grid conditions. This paper proposes a grid-voltage-weighted feedforward control scheme based on the quasi-proportional resonance (QPR) controller. This scheme introduces compensatory terms with different proportional coefficients in the voltage feedforward, controlled by the QPR controller. Through a series of analyses, reasonable inverter parameters are first designed. Then, the proposed system model is built in Matlab Simulink. Through simulation experiments and comparisons with various types of operating conditions, the effectiveness of the proposed system scheme is validated. It minimizes the impact of grid voltage disturbances, suppresses the influence of grid harmonics on the control system, improves current quality, and enhances the stability of the GCI system.

This paper introduces a digital control strategy for an inverter with an LCL filter that can be used in weak power grids. Due to the effects of digital control delays and the influence of grid voltage and impedance in a weak power grid (WPG) on the inverter system, it is easy for the system to oscillate, distort the output current, or even become unstable. By introducing grid voltage weighted feedforward (GVWF) based on the feedback of the filter capacitor current and using a Quasi-Proportional Resonance (QPR) current controller along with proper design, the system can achieve stable performance and high-quality, high-precision current output under various conditions, including WPG. The effectiveness of the proposed strategy was validated through hardware design and experimental tests. A comparative analysis was conducted under different control schemes with grid impedances of 0.5 mH, 6 mH, and 12 mH. The results demonstrated that the proposed strategy is a more suitable digital control method for LCL-type grid-connected inverter.

Retrofitting an internal combustion engine (ICE) dynamometer test bench for electric motor testing introduces significant measurement and control challenges. The two modes differ fundamentally in torque dynamics, communication protocols, and energy flow characteristics. This study presents a dual-mode measurement and control system for a retrofitted 250 kW test bench. The system retains ICE testing capability while adding motor testing through a shared LabVIEW interface. Three key technical problems are addressed: (i) a cross-mode PID controller with gain scheduling and bumpless mode switching; (ii) a wavelet-based dual-sensor torque fusion method using complementary filtering at a 50 Hz crossover frequency; and (iii) active front end (AFE) energy feedback optimization with quadrant-dependent DC bus voltage setpoints. Validation was performed on an 80 kW (240 kW peak) interior permanent magnet synchronous motor (IPMSM) across 823 operating points. The system achieved a peak system efficiency of 94.88%. Energy recovery efficiency improved from 58% to 82% through AFE parameter optimization. The proposed methodology offers a cost-effective template for extending existing ICE test infrastructure to support electric vehicle powertrain development.

With the increasing penetration of renewable energy sources, variations in grid impedance and background voltage harmonics have become major challenges to the operational stability and power quality of grid-connected inverters. Although conventional grid-voltage proportional feedforward (GVPF) effectively suppresses grid-voltage disturbances, its frequency-domain phase characteristics are highly sensitive to grid impedance variations, leading to reduced stability margins and even system instability under weak-grid conditions. To address this issue, this paper proposes a Frequency-Domain Phase-Shaping-Based Multi-Quasi-Proportional Resonant (FDPS-MQPR-PGVF) Control Strategy. Based on the established system impedance model, the phase characteristics at critical harmonic frequencies are systematically reshaped according to the impedance-based stability criterion (IBSC), enabling a systematic controller parameter design that simultaneously enhances weak-grid stability and background harmonic suppression. Simulation and experimental results demonstrate that the proposed strategy maintains stable operation under weak-grid conditions while significantly improving harmonic suppression performance. The proposed method provides an effective frequency-domain phase-shaping framework for enhancing the stability and harmonic performance of grid-connected inverters operating in weak grids.