In this paper, a generalized droop control (GDC) is proposed for a grid-supporting inverter based on a comparison between traditional droop control and virtual synchronous generator (VSG) control. Both the traditional droop control and VSG control have their own advantages, but neither traditional droop control nor VSG control can meet the demand for different dynamic characteristics in grid-connected (GC) and stand-alone (SA) modes at the same time. Rather than using a proportional controller with a low pass filter, as in a traditional droop control, or fully mimicking the conventional synchronous generator (SG) parameters in a VSG control, the active power control loop of the GDC can be designed flexibly to adapt to different requirements. With a well-designed controller, the GDC can achieve satisfactory control performance; unlike a traditional droop control, it can provide virtual inertia and damping properties in stand-alone mode; unlike a VSG control, the output active power of an inverter with GDC can follow changing references quickly and accurately, without large overshoot or oscillation in the grid-connected mode. Moreover, given specific controller parameters, the GDC can function as both a traditional droop control and a VSG control. The GDC's controller parameter design are more intuitive and flexible, and this paper provides a distinct design process. Finally, the effectiveness of the proposed control method is validated by the simulation and experimental results.

The traditional fault-tolerant procedure usually comprises fault detection and fault tolerance. Fault detection is adopted to locate the specific fault, which increases the complexity and misdiagnosis risk of fault-tolerant systems. This article introduced an adaptive fault-tolerant control for open-phase faults and open-switch faults in dual three-phase permanent magnetic synchronous machine (PMSM) drives. The proposed fault-tolerant scheme is fulfilled by going through three operation states: healthy operation, transient xy open-loop faulty operation, and fault-tolerant operation. The angle of fault-tolerant reference currents on xy plane is obtained from the transient xy open-loop faulty operation. Unified fault-tolerant reference currents of open-circuit faults are built up by using the above reference angle. After the open-circuit faults occur, the unified fault-tolerant reference currents are directly applied to the drive system without fault localization. Experimental results demonstrate a very smooth switching capability of the developed adaptive fault-tolerant control from the faulty operation to the fault-tolerant operation without extra hardware.

This letter proposes a novel three-phase hybrid rectifier topology and control method for high power electrolytic hydrogen production application. It is composed of a primary rectifier, i.e., a six-pulse silicon controlled rectifier (SCR) and an auxiliary converter, including a pulsewidth modulation (PWM) voltage source converter and a phase-shift-full-bridge converter. SCR undertakes most of the power consumed by electrolysis cell, and the auxiliary converter can compensate dc current ripples and absorb ac current harmonics of primary rectifier simultaneously. Compared with high power PWM rectifier, the proposed hybrid rectifier can keep the main benefits of PWM rectifier, such as the low dc current ripple to realize improved efficiency of electrolytic hydrogen production and high grid current quality at ac side while significantly reducing the cost. The effectiveness of the proposed hybrid rectifier is verified by the simulation as well as experimental results.

A universal controller is proposed in this article to operate parallel inverters in both grid-connected (GC) state and standalone (SA) state and ensure seamless transfer between them without reconfiguring the control structure. The universal controller is mainly composed of frequency-locked-loop and three cascaded control loops: a grid current loop, capacitor voltage loop, and inductor current loop. A proportional-integral regulator is adopted in the grid current loop, and a limiter is inserted after the integrator. In the GC state, the proposed controller accurately regulates the grid current of an individual inverter. When islanding occurs, the proposed controller can automatically convert from grid current control to v _C -i _g -based droop control; critical islanding detection is not needed. This universal controller has several advantages. First, it can realize seamless transfer of parallel inverters; microgrid reliability can be guaranteed in the SA state, and power sharing can be achieved among parallel inverters without communication lines. Second, compared with droop control, it can regulate the grid current accurately and output constant power when the grid voltage fluctuates in the GC state. Third, the grid current harmonics in the GC state and capacitor voltage harmonics in the SA state can be mitigated. Simulation and experimental results verify the effectiveness of the controller.

Although many auxiliary circuits based fault-tolerant solutions have been developed for three-phase motor drives, the standard three-phase motor drive without any auxiliary circuits still dominates the market. It is important to improve the fault-tolerant capability of standard motor drive. In this paper, a predictive current control based fault-tolerant control scheme is proposed to optimize the fault-tolerant performance of standard PMSM drives under open-phase fault and open-switch fault. In the proposed scheme for open-phase fault, the fault-tolerant current references considering reluctance torque and overcurrent endurance of motor drive are derived. On this basis, the fault-tolerant current references are further optimized to reduce the copper loss without increasing the torque ripple. Besides, a fundamental period based speed calculation method is proposed to eliminate the negative impact of speed fluctuation. In the proposed scheme for open-switch fault, a two-mode current control based fault-tolerant control is designed to reduce the copper loss and torque ripple by fully utilizing the remaining healthy switch in the faulty inverter leg. The validity of the proposed scheme is verified by experiments.

This study proposed a universal model predictive control (MPC) strategy for dual inverters fed open-winding permanent magnet synchronous motor (OW-PMSM) drives where two isolated buses have arbitrary DC voltages. Diverse and unordered space vector distribution caused by different voltage ratios of DC buses that greatly increases the calculation burden for the conventional MPC algorithm is analyzed in detail. Based on this, a novel MPC strategy that is universally applicable to any voltage ratio is put forward, which could decrease the number of candidate vectors from 49 to less than 15 in every cycle. Although the computational burden is reduced, the output power quality is unaffected owing to the effective simplification of the vectors. Besides, an optimized switching algorithm is designed to adapt to the situation when the voltage ratio changes during the operation state. The experimental results are presented to verify the effectiveness of the proposed method.