Electric vehicles interconnect and interact with the grid bidirectionally through a vehicle-to-grid (V2G) system. In V2G, the output power on the ac side pulsates at twice the grid frequency 2 f _o , which leads to the presence of a second harmonic current (SHC) on the dc side and reduces the reliability of the system. A bandstop filter with a center frequency of 2 f _o is introduced in the voltage sampling loop to suppress the SHC. A digital implementation of the BSF is proposed to apply at arbitrary frequencies, which avoids the cost increase and provides high simplicity and flexibility. An adaptive PI control method is further proposed to improve the dynamic performance, which adjusts the PI parameters in real-time according to the inductor current. A 3.5 kW V2G experimental prototype is built and tested to verify the feasibility and stability of the proposed strategies. The prototype offers an excellent dynamic and steady-state response in stand-alone and grid-tie modes.

A switching mode power supply (SMPS)-based lithium-ion (Li-ion) battery test system (BTS) is proposed to meet the increasing demands of tests in battery research. To improve the flexibility, while building the BTS with low cost and high reliability, an SMPS is employed as a charger/discharger, combined with a digital-to-analog hybrid control system to regulate its output voltage and current. Based on the BTS, two dc internal resistance (DCIR) measurement methods are designed, and a battery state classification method based on the DCIR cluster analysis with similarity as the judgment basis is proposed. An experimental prototype is developed to verify the feasibility of the proposed BTS and methods. The results show that the BTS possesses excellent voltage and current regulation capabilities for charging, discharging, and grid energy recovery. The internal parameter extraction method enables obtaining DCIR and other parameters with high accuracy. The online measurement method allows automatic acquisition of real-time DCIR and its variation trend without affecting the charging, which greatly improves the measurement efficiency. The proposed hierarchical clustering method based on DCIR effectively achieves the classification of battery states with excellent practicality and robustness.

The droop control strategy, known for its communication-free nature, is widely adopted for the parallel operation of inverter units. However, in microgrids, mismatches in line impedances and various measurement inaccuracies often lead to imbalanced reactive power sharing among inverters and significant circulating current. To address these challenges, this paper proposes an adaptive droop control method that relies solely on local measurements from each inverter, eliminating the need for communication. The proposed approach integrates the deviation between the ratio of reactive power to output voltage and its reference value to generate an Adaptive Virtual Impedance Droop Control (AVIDC) mechanism. This enables a dynamic balance between reactive power output and voltage drop. The simulation and experimental results validate the effectiveness of the proposed control strategy, demonstrating a significant improvement in the accuracy of reactive power sharing.

In PV grid-connected applications, a grid-connected converter is usually used to connect with the grid to realize dc/ac conversion and power flow control. How to improve the quality of grid-connected current of power equipment so that the harmonic content injected into the grid is as little as possible has become a hot research topic in the field of PV grid-connected applications. By analyzing the causes of grid-connected harmonic currents during the grid-connection process, a two-segment high-performance grid-connected inverter topology is proposed. This structure makes the main inverter basically equal to the grid voltage through the simplest closed-loop control. Since the voltage sensitivity of the auxiliary inverter is low, utilizing the auxiliary inverter for the compensation of grid-connected voltage and grid-connected control of power flow will lead to an improvement in the quality of grid-connected current. A 3.3 kW grid-connected inverter system prototype is fabricated and tested, and the experimental results verify the stability and effectiveness of the theoretical analysis and the proposed control scheme.

In this article, an adaptive fast charging strategy for lithium-ion batteries considering the variation of dc internal resistance (DCIR) is proposed, which applies to mobile applications. The experiments prove that the DCIR obeys the Gaussian distribution during the normal charging stage. However, the DCIR no longer obeys Gaussian distribution once the battery is fully charged. The proposed strategy employs the maximum-likelihood method to estimate the expectation and variance of the Gaussian distribution. The charging mode switches from constant current (CC) to constant voltage (CV) immediately when the DCIR deviates significantly from the expectation. Under the premise of satisfying the high accuracy for the parameter estimates, a constrained optimization problem is established to determine the DCIR minimum number of measurements ( n _min ), and the constraints are transformed into hypothesis testing for solving. The CC operating time is maximized based on n _min and the adaptive control of the transition point. The experiments verify the validity of the proposed method. The results show that compared with the CC-CV method, the proposed strategy saves 52.2%, 41.57%, and 29.72% of the charging time at 1C, 0.75C, and 0.5C, respectively, which effectively improves the charging speed and prevents overcharging.

When the three-phase grid voltage is distorted, the grid current total harmonic distortion (THD) will deteriorate accordingly in VIENNA rectifier. This paper proposes a current harmonic suppression strategy based on real-time discrete Fourier transform (DFT). The DFT is employed to extract the sine and cosine components of the grid current high-order harmonics, which are applied to the feedback loop of the dq rotating coordinate system. Independent control loops for high-order harmonic currents are introduced, and the references are set as 0 to suppress the corresponding harmonic currents. The difference between the control strategies of positive and negative sequence components is discussed. The proposed control method can be extended to other orders. To verify the validity of the proposed strategy, a 50 kW VIENNA rectifier prototype is designed and built. The experimental results show that the current THD is improved under grid voltage distortion over the entire load range.