This paper develops a 6.78 MHz multiple-receiver wireless power transfer system driven by a Class E power amplifier. Constant output voltage is achieved for each receiver with optimized overall efficiency. A novel one-receiver model is built to analyze the overall power-efficiency characteristics. The loads and input voltage are then designed as two control variables. Through tuning the loads, constant output voltage is achieved by independent controllers at the receiver side. Then, the efficiency is optimized by tuning the input voltage at the transmitter side. Finally, the theoretical analysis and control scheme are validated using a three-receiver system. It shows that different constant output voltages, 5, 9, and 12 V can be achieved independently for different receivers. When the load resistance, real coupling, and number of receivers change, the voltage can be quickly regulated, and the overall optimum system efficiency is 66.6%.

This paper proposes a new battery cell voltage equalization approach using multiple-receiver wireless power transfer (WPT) working at megahertz (MHz). Compared with existing multiwinding transformer, the MHz multiple-receiver WPT system is advantageous in terms of saved weight and space, ease of implementation, and improved safety. In this paper, the unique operating principle of the WPT-based equalization is first explained, through which equalization currents are naturally determined by the battery cell voltage distribution. The currents are also analytically derived. This facilitates the discussion on power amplifier (PA) design. Performance analysis is then provided to investigate the influences of system parameters on the efficiency and equalization ability of the proposed WPT-based equalization system, and thus guide following design and implementation. Considering the uncertainty in PA load due to the random cell voltage distribution, a current-model Class E PA is designed that enables approximately constant PA output current. Experimental results show that the proposed multiple-receiver WPT-based battery cell equalization system can achieve high overall system efficiency (above 71%) when equalizing six lithium-ion battery cells under loosely coupling (k = 0.065). A good match between the experimental and calculation results also validates the correctness of the theoretical discussion.

The dual active bridge (DAB) converter operating with a relatively high switching frequency is well suited for deriving a high-power density electric vehicle (EV) charger. In this case, safeguarding the realization of zero voltage switching (ZVS) for a wide operating range becomes crucial to ensure a good performance in terms of efficiency and control reliability. Unfortunately, most modulation schemes available today in the literature require a detrimental compromise in the achievable ZVS range, particularly the ones working mainly toward the minimization of the current stress. Due to the fact a public EV charger will work with multiple vehicles having quite different charging profiles, i.e., with wide operational voltage and currents ratings, the ZVS operation may be prone to fail to undermine the whole cycle charging efficiency. To relieve the issues, this article proposes a new modulation scheme for the DAB converter featuring a maximized ZVS range and a quasi-optimal inductor rms current. Herein, the concept of dynamic settings of the required modulator's ZVS-current is utilized and a straightforward implementation with seamless circuit mode transition is achieved. With the above characteristics, the dynamic and static losses of the component circuits can be reduced together. By adopting the dynamic ZVS-current settings strategy, the turning- on currents of the DAB switches are adjusted in real-time guaranteeing the ZVS operation under various operating conditions. With the seamless transition, the inductor current can be smoothly regulated to ensure system stability. The proposed modulation scheme is introduced, analyzed, validated, and benchmarked in a 4.5 kW/100 kHz SiC-based DAB prototype, whose peak efficiency can reach 96.3% when operated at partial load.

With the increasing penetration of voltage source converters (VSC) in the modern power grid, the transient stability of grid-following converters has attracted extensive attention. During grid faults, instabilities of the grid-following converter might happen which mainly originates from the phase-locked loop (PLL) being not synchronized with the grid. In the existing research, current dynamics is considered to be very fast and its effect on the transient synchronization stability can be ignored. However, in the case of high-power converters used for large wind turbines, the bandwidth of the current loop cannot be designed too high due to low switching frequency. Neglecting the coupling effect on the synchronization stability will lead to wrong conclusions. This article firstly proposes an improved equal-area criterion to show that the current dynamics change the accelerating and decelerating area and might deteriorate the stability, which reveals that the coupling effect of current and PLL is non-negligible. Accordingly, a refined fourth-order nonlinear model is proposed to describe the coupling effect of the current loop and PLL, which is utilized to give the bandwidth boundary whether the current dynamics can be ignored. Simulations and experiments are performed to verify the correctness of the proposed nonlinear model.

During the deregulation of retail power market, multiple stakeholders are gradually involved in distribution network to invest distributed resources and participate in power transactions, bringing great uncertainty to grid operation. This paper proposes a novel robust coordination expansion planning method that considers non-network solutions in a deregulated retail market, including the closed-loop demand response and other controllable strategies. A double-nested game model is constructed to simulate the bi-directional interaction between distribution system operator and stakeholders. Given that this model cannot be solved directly, a tri-layer decomposition algorithm is presented to enable a distributed optimization of the coupled problem. Furthermore, the case study is implemented on an IEEE 33-bus distribution system and an IEEE 123-bus distribution system, which demonstrates the efficiency and practicability of the proposed method and highlights its merits on enhancing flexibility and postponing unnecessary investments.

The advancement in modulation strategies brings emergent solutions to suppress the leakage current in three-phase two-level transformerless grid-connected voltage source inverters (VSIs). However, most of the techniques are analyzed based on reduced common-mode voltage pulse width modulation in motor drivers but fail to satisfy the specific requirement of grid-connected applications such as wider power factor operation and lesser current distortion. To overcome such substantial drawbacks, this paper proposes a novel scalar PWM method for transformerless grid-connected VSIs. Firstly, presented through a generalized scalar approach with unified zero-sequence voltage generation, the method is simple to implement and favored in practice. Besides, systematic and comprehensive mathematical analysis is illustrated to exhibit the validity of implemented method in reducing leakage current and shows its advantages over whole power factor range in terms of DC-link current harmonic, output current quality, and switching losses. Finally, simulations and experimental results are carried out to verify the effectiveness and superiority of the proposed method.