Voltage equalizer is essential for mitigating the inconsistencies of series-connected lithium-ion batteries in electric vehicles to ensure operation life and work safety. To keep voltage balancing, voltage equalizers are widely adopted in the battery string application. However, traditional voltage equalizers have high circuit costs and large sizes due to the need for a large number of MOSFETs and isolated gate drivers. Moreover, as the voltage difference between the batteries in the series decreases towards the end of the equalization process, the equalization current also decreases, which can affect the speed of voltage equalization. To overcome these problems, an isolated multiple half-bridge converter with a multiport transformer is proposed. The balancing circuit has two power transfer paths, allowing for energy transfer among multiple cells simultaneously, which could achieve a significant equalization current even when the voltage difference is close to zero. In the proposed equalizer, only one MOSFET is needed for one cell and two cells can share one transformer winding. Hence, it is more applicable for a large number of battery stacks, such as electric vehicles. Finally, to improve the equalization speed and efficiency, three equalization control strategies, i.e., average voltage, predicted voltage, and boundary voltage control strategies are introduced and verified by a 100 kHz 24-cell voltage equalization prototype.

The single-phase unified power quality conditioner (UPQC) is widely used to improve the power quality of sensitive end-users. However, the inherent instantaneous power difference between parallel and series converter will generate a significant low-frequency dc-link voltage ripple and degrade the compensation performance of UPQC. The generation mechanism of dc-link voltage ripple and its influences on compensation voltage and current are analyzed in this paper. To suppress the influence, a control strategy is proposed for the single-phase UPQC. For parallel converter, a notch filter is introduced in the outer voltage loop to prevent the ripple from entering the control loop, the specific order harmonic compensation is proposed in the inner current loop to reduce the grid current harmonics. For series converter, the dc-link voltage feedback is adopted to suppress the influence of voltage ripple on the compensation performance. Simulation and experimental results show that the grid current total harmonic distortion (THD) can be reduced effectively with the fixed dc-link capacitance compared with the traditional control strategy. The load voltage THD has also been reduced by more than half by the dc-link voltage feedback control. Moreover, with the smaller dc-link capacitance, single-phase UPQC can maintain better performance under the proposed control strategy.

A single-phase isolated ac-dc-dc converter with low total harmonic distortion (THD) and high power factor (PF) usually suffers from a significant ripple power at double line frequency. The inherent ripple power brings a significant low-frequency voltage ripple on the dc-link capacitor. To reduce the voltage ripple, bulky electrolytic capacitors and hardware low-pass filter are widely adopted. However, the converter becomes bulky because of large capacitor. In order to reduce the dc-link capacitance, optimal control strategies are proposed for ac-dc and dc-dc converter respectively in this paper. Firstly, the notch filter with current disturbance feedforward strategy (NF-CDFS) are proposed to minimize input harmonic current of ac-dc converter. Secondly, the feedback linearization with voltage disturbance feedforward strategy (FLVDFS) is designed to suppress the output voltage ripple of dc-dc converter based on generalized state space averaging model. With the proposed NF-CDFS plus FLVDFS control strategy, low input harmonic current and low output voltage ripple are achieved. In addition, more than about 85% of dc-link capacitance is reduced compared to conventional methods.

The harmonic suppression performance of active power filter (APF) under model predictive current control is obviously reduced, when the parameter exists a mismatch between the actual value in system and the nominal value adopted in the control. To suppress the influence of parameter mismatching, a model predictive control based on parameter identification with forgetting factor recursive least square (FFRLS) method is proposed for APF. The digital processing procedure of the FFRLS-based APF controller is detailed analyzed and designed. The identification error of inductance between identification value and the actual value is less to 6%, and the total harmonic distortion of grid current is significantly improved, especially a lower value of actual inductance. Simulation and experimental results show that the proposed method can not only effectively eliminate the influence of parameter mismatch on the control, but also result in better steady-state performance while retaining fast dynamic response.

The dual active bridge (DAB) converters offer high-power density and bidirectional transfer capabilities. The input series output parallel (ISOP) modular DAB converters are commonly used for isolated medium/high to low voltage conversion. To address the power unbalance problem caused by the differences among modules in the ISOP-DAB converter, this article proposed a sensorless power balance control method based on parameters estimation (SPBCM-PE) that does not require additional voltage/current sensors, additional auxiliary circuits, or specific system parameters. Compared to existing power balance methods for ISOP-DAB, the proposed load-independent method is compatible with multimodule converters and does not require load parameters, eliminating the need for real-time dynamic estimation. It is considered the balance of both the modules’ input voltage and output current. To validate the proposed SPBCM-PE, this article designed a 220 V–24 V ISOP-DAB experimental platform with a neutral point clamped half bridge–full bridge topology and significant differences between modules. In the power range of 10–435 W, the experiments showed that the proposed method significantly improved input voltage and output current balance compared to the traditional method with system efficiency ranging between 87.2% and 94.3%. Overall, the proposed balance method offers an effective solution for achieving power dynamic balance in the full power range.

The dual active bridge (DAB) converter is widely used in renewable energy power generation systems with wide input voltage characteristics. An inappropriate duty cycle will lead to a larger inductor root-mean-square (RMS) current and low efficiency. In this article, an efficiency-oriented optimized triple-phase-shift (OTPS) scheme is proposed for the DAB converter that can reduce the inductor rms current for a wide input voltage and realize zero-voltage switching (ZVS). The ZVS condition contains the direction and amplitude of the inductor current to make the ZVS area more accurate. In addition, the OTPS scheme also has the capability of voltage balancing without additional voltage equalizers under unbalanced load. The influence of deadtime on voltage balance is analyzed and a voltage balancing scheme with compensation of the duty cycle is proposed. To reduce resource occupation and operation time, an online implementation scheme of variable parameter control based on field-programable gate array (FPGA) is proposed. Without a look-up table, the sum of the operation time of the control module and modulation module is only 0.66 $\mu$ s, and the required memory bits are only 459 k. Both operation time and memory bits are reduced by more than 90% compared to the existing literature. Finally, the whole proposed process is verified by the experimental results.