Asymmetric cascaded H-bridge (ACHB) converters with unequal DC-link voltages offer a promising solution to mitigate the substantial increase in power devices, energy storage components, and overall inverter volume that typically accompanies conventional cascaded H-bridge converters with a large number of output levels. However, existing modulation techniques often result in output power imbalance and current backflow among cascaded cells, and are typically limited to specific numbers of cascaded cells. To address these challenges, this paper first proposes a generalized ACHB converter topology scalable to an arbitrary number of cascaded cells, consisting of a main power cell and multiple switching cells. A robust hybrid modulation strategy is then developed, integrating dynamically adjusted staircase modulation for the main power cell and unipolar carrier phase-shifted modulation for the switching cells, enabling coordinated output power control across all cells. Simulation and experimental results validate the effectiveness of the proposed method in achieving balanced output power allocation and avoiding current backflow in multi-cell ACHB converters.

This paper presents a feed-forward decoupling control method to enhance the stability of a photovoltaic (PV) inverter connected to a weak grid. As the grid weakens, the point of common coupling (PCC) voltage becomes sensitive to the active power. This increases the coupling effects between control loops, Phase-Locked Loop (PLL) and grid dynamics, which deteriorate system stability. Therefore, in this paper, a decoupling control method is proposed in which the reference active current obtained by regulating the DC-link voltage to its reference value is feed-forwarded to modulate the reactive current reference generated by regulating the PCC voltage to its predefined value. As result, the robust performance of the PV inverter connected to a weak grid has been yielded, where the inverter stability is maintained for both wider PLL bandwidth and high grid impedance. Based on open-loop bode plot and closed-loop eigenvalues of the DC-link voltage control (DVC) loop, a stability analysis of the proposed control method and the conventional vector control method has been performed. Then, the proposed method is verified through simulation results obtained by PLECS.

Most of the microgrid inverters are based on PI-based voltage and current double-loop control structure to achieve control target, but the controller parameter setting is complicated and the dynamic response speed is slow. The paper adopt Predictive Models Control (MPC) replace traditional voltage and current double-loop and modulation to improve the dynamic response speed and parameters tuning. In order to maintain the damping character of microgrid and overcome droop control frequency change rate, this paper adopts the strategy of Virtual Synchronous Generator (VSG) in the power loop to make the system have inertia and enhance stability. The simulation comparison verifies the proposed control strategy is effective and the faster response speed.

In order to ensure good power quality, the grid-connected inverter mostly uses phase-locked loop (PLL) to maintain synchronization with large power grid. But the PLL will cause a negative-impact on the stability of grid-connected inverter under weak grids. The paper analyzes the equivalent impedance of the PLL under the weak grid firstly. Then the paper proposed a self-synchronization strategy using DC bus voltage and reactive power control to synchronize the frequency and amplitude with the grid-connected inverter instead of the applying PLL. Applying the proposed method to the on/off grid switching condition, a pre-synchronization control strategy based on virtual power is proposed to achieve seamless switching of the grid-connected inverter. At last, the designed self-synchronization control strategy and pre-synchronization strategy are verified on the Plecs simulation platform.

This paper mainly solves the problem of on/off-grid switching for Energy Router grid-connected inverters on the AC side. A control strategy based on sliding mode disturbance observer is proposed to suppress the disturbance of the output current to the output voltage. At the same time, the improved pre-synchronization method is used to achieve fast synchronization of voltage amplitude and phase. An improved frequency shift method is proposed for islanding detection for droop control grid-connected inverters. Finally, the proposed methods are verified by simulation in MATLAB/Simulink.

New studies on grid-connected voltage-source inverters (VSIs) show that sequence-admittance-based stability analysis model cannot be simply simplified as decoupled positive-sequence and negative-sequence impedance ratio because of sequence-couplings resulting from the outer asymmetric power control loops, such as the phase locked loop (PLL) and direct voltage control. Additionally, compared with single grid-connected VSI system, parallel-connected VSIs have stronger circuit-couplings via grid impedance. To get accurate stability conclusions in wider frequency range, both couplings are considered in this paper, and this paper firstly derives a sequence-admittance-based stability analysis model to capture resonances in parallel-connected VSIs. The proposed model is described as open-loop model and closed-loop model, to which Nyquist stability criterion is effectively applied instead of the complicated generalized Nyquist stability criterion. Take the PLL-induced low-frequency resonance for example, stability analysis of the studied cases is successfully conducted. Finally, time-domain simulations verify the accuracy and simplicity of the proposed model.

The paper firstly establishes a passivity-based control (PBC) of a double-fed inductor generator (DFIG). A new control method of the DFIG is proposed with the outer speed loop controlled by a full-order terminal sliding mode (TSM) controller to undertake maximum wind power point tracking (MPPT), while the inner current control loop is a PBC designed to manage the three-phase PWM rectifier. Simulation results show that the controller design is effective and that the system exhibits satisfactory performance.

The paper firstly establishes a port-controlled Hamiltonian dissipation (PCHD) based model of a direct-drive permanent magnet synchronous generator (D-PMSG). A new double loop control of the D-PMSG is proposed with the outer speed loop controlled by a non-singular higher-order terminal sliding mode (NHTSM) controller to undertake maximum wind power point tracking (MPPT). In the inner current control loop is a passivity-based controller (PBC) designed to manage the three-phase PWM rectifier. Simulation results show that the controller design is effective and that the system exhibits satisfactory performance.