To acquire high efficiency and reduce EMI in wireless high power charging for EVs, it is of great importance to realize accurate zero voltage switching angle (ZVSA) control of inverter. However, traditional zero crossing detection cannot be applied in high power because of considerable noise and poor accuracy in wide power range applications. In this paper, to suppress the noise in high power, a current hysteresis comparator is adopted, and an enhanced phase detection methodology (EPDM) is proposed to measure the phase of resonant current by using a reference signal produced by processor. Meanwhile, to improve the accuracy of ZVSA, a uniform time delay compensation method (UTDCM) by considering the whole time delays synthetically is proposed, and a uniform time delay equation (UTDE) can be obtained to guarantee the high accuracy of phase detection especially in the wide power range. Finally, a novel control strategy with the ZVSA loop based on UTDCM is proposed for battery charging in wireless high power transfer system. A 500W WPT prototype is built to verify the accuracy of ZVSA based on UTDCM and the system efficiency can achieve 94.17% with k=0.22.

Charging electric vehicles wirelessly is promising because of its convenience as well as saving of charging cables. However, the existing wireless power transfer systems suffer from high resonant peaks and poor efficiency. Therefore, zero voltage switching (ZVS) operation of inverter should be achieved especially in high transfer power. Based on the variable frequency phase shift control strategy (VFPSC), this paper presents an optimal operation frequency range (OOFR) where the wireless power transfer (WPT) system can realize the required output and ZVS operation of inverter simultaneously without extra dc–dc converters. Meanwhile, based on OOFR, an optimized electrical parameter design method based on VFPSC is proposed with the multiple boundary conditions. Moreover, a novel three-loop control strategy (TLCS) is proposed to make the system operate at any points of OOFR. Especially, an implementation method of the TLCS is proposed, which can dynamically adjust frequency and phase shift to make the system always operate at the preset ZVS angle and realize the required output simultaneously. Finally, a 500-W WPT system is built to verify the correctness of theoretical analysis. The experimental results show that a very high overall efficiency is achieved in the whole charging process and the maximum efficiency can achieve 94.9% with $k$ = 0.2.

Except for the benefits of mimicking synchronous generators, virtual synchronous generators (VSGs) still face particular small- and large-disturbance stability problems in practical applications. Therein, the large-disturbance stability is a much more dramatic and intractable problem, such as a short circuit or line tripping. Accordingly, this article explores this challenging problem from the perspective of output impedance optimization for VSGs. First, focusing on the potential risk of overcurrent during the electromagnetic process, the dynamic performances of different virtual impedance control structures used in VSGs are comparatively analyzed, and the output impedance boundary for suppressing the transient current is derived. Then, the output impedance boundaries for maintaining electromechanical transient stability are discussed in depth by using Lyapunov stability theory, which provides novel virtual impedance optimal design guidelines exclusively for the large-disturbance stability. Furthermore, a large-disturbance stability enhancement strategy based on adaptive virtual impedance control is proposed, which can limit the electromagnetic transient current and improves the electromechanical transient stability simultaneously. Finally, experiments validate the accuracy of the theoretical analysis and the effectiveness of the proposed strategy.

Damping control plays an important role in suppressing the oscillation modes of virtual synchronous generators (VSGs). The most widely used damping control method through a frequency deviation feedback path is confronted with multiple challenging inherent contradictions among the different control objectives, resulting in seriously degraded control performance of VSGs. To resolve these contradictions fundamentally, this article proposes a novel phase feedforward damping (PFD) control method for VSG from the perspective of restructuring the damping controller. It replaces the traditional frequency deviation feedback path with a novel damping controller utilizing a phase feedforward path. Then, considering the grid-connected and islanding operation modes, respectively, a detailed comparative study of the traditional damping-based VSG (Tra-VSG) and the PFD-based VSG (PFD-VSG) is conducted. Both the theoretical and experimental results demonstrate convincingly that the proposed PFD control method can reconcile the different control objects of VSG, and thus, compared with Tra-VSG, PFD-VSG exhibits vastly superior response performance of the active power and the frequency in both grid-connected and islanding operation modes.

In wireless power transfer system (WPTS), the control technique of the active rectifier (AR) is vital for improving the transfer efficiency of resonant network, expanding operating range of load and increasing power density. An indispensable component of such control technique is the accurate and reliable phase-locked method for the resonant current. However, the traditional phase-locked method based on DSP controller tends to lose driver pulses, which might cause damage to the safe operation of WPTS. This paper illustrates the essential reason why the driver pulses lose and proposes a phase-locked loop combined with the chained trigger mode (PLL-CTM) which can lock the phase of resonant current accurately and produce the driver pulses reliably. With the proposed PLL-CTM applied, the reliability of WPTS can be enhanced tremendously. Furthermore, based on PLL-CTM, this paper also presents a double-side phase shift control (DPSC) strategy to achieve CC/CV charging and minimize the power loss of resonant network simultaneously. Finally, a 500W WPT prototype is built to verify the feasibility of DPSC with PLL-CTM. Benefiting from DPSC with PLL-CTM, the WPTS not only obtains a high accuracy in steady state, but also achieves a good dynamic performance with the step change of $R_\text{L}$ and $R_\text{Eref}$ .

Tight voltage regulation and high efficiency are fundamental objectives of wireless power transfer systems (WPTSs) as power supplies. Although the well-established impedance matching control attempts to achieve high efficiency, the associated extra dc-dc converters or hard switching of converters in WPTSs reduce the overall system efficiency, particularly for high-power applications. In this paper, under ZVS conditions, the minimum power loss point is derived and proved in detail with different ZVS angles. Moreover, a joint control with variable ZVS angles (JC-VZA) is proposed to ensure ZVS of all switches and achieve the required output, simultaneously. This control scheme is implemented by use of controllers in both sides of WPTSs, which adjust their respective ZVS angles for dynamic efficiency optimization. Under ZVS conditions, the proposed JC-VZA features an optimal amount of reactive power that achieves the minimum total power loss by significantly reducing the switching loss. As a result, the experimental results obtained from our WPTS prototype verify its superiority. With a coupling coefficient $k$ of 0.2 or 0.15, the maximum efficiency reaches 96.8% or 95.0% under the power rating of 288W (rated load) as well as 92.4% or 88.7% in the case of light load (9% of 288W).