To study the conducted common-mode (CM) electromagnetic interference (EMI) characteristics of a single-switch forward converter and reduce its CM noise, the analysis of the transmission mechanism of conducted CM noise in the single-switch forward converter is necessary. On this basis, a CM noise transmission path model is established, and a calculation method is proposed to determine the specific external capacitance to reduce the CM noise. In addition, aimed at the defects of the traditional calculation model of induced charge on the secondary side, an improved calculation model is put forward, and simulation results show that the accuracy of the improved model is higher under ideal conditions. Afterwards, the balanced winding method was used to reduce the CM noise flowing through the transformer, and a prototype of single-switch forward converter power supply was used for experimental verification. Results show that the method of calculating the external capacitance was effective, and the accuracy of charge calculated by the improved calculation model was higher when the windings were close or when the number of turns per unit length was relatively large.

The control system for hybrid distributed energy storage virtual synchronous generator (VSG) composed of a battery and a supercapacitor is improved. A principle for the power allocation of hybrid energy storage is proposed, and a frequency division sliding filter method is designed according to different frequency bands. In view of the power fluctuations of different frequencies, the virtual moment of inertia is piecewise improved to achieve the coordination between the battery and the supercapacitor. Aimed that the problem that the traditional VSG cannot suppress the frequency oscillations, the virtual damping coefficient is modified, and adaptive virtual damping is used to improve the regulation capability of the control system when the frequency oscillations occur. MATLAB is used to verify the proposed control strategy through simulations. Results show that the hybrid energy storage VSG can be controlled in terms of frequency, i.e., when the load fluctuates irregularly, the supercapacitor responds to the high-frequency power fluctuation in time while the battery suppresses the low-frequency power, thus realizing the coordination between the battery and the supercapacitor. When faced with a sudden decrease or increase of 10 kW load, adaptive virtual damping can be used to deal with the frequency oscillations of active output caused by load power fluctuations of hybrid energy storage, and the frequency overshoot is controlled within 0.06 Hz. As a result, the proposed control strategy can adjust the small deviation of frequency regardless of the sudden increase or decrease of power.

A fast and accurate estimation of the state-of-charge (SOC) of lithium batteries is critical for the battery management system. Aimed at the problem that the Kalman filter algorithm lacks reasonable constraints on the resistance-capacitance (RC) parameters when estimating the SOC of lithium batteries, an optimization method of RC parameters filtering is proposed, and it is combined with unscented Kalman filter (UKF) to achieve the fast and accurate convergence of lithium battery SOC estimation. First, an equivalent circuit model of lithium battery is established by combing the polynomial equation. Then, forgetting factor recursive least squares is used to obtain the time-varying and time-invariant model RC parameters. The expression of RC parameters filtering relationship is established by setting the Kalman gain threshold, and an RC optimization UKF algorithm is proposed for lithium battery SOC estimation. Finally, hybrid pulse-power characteristic experiment, intermittent constant-current discharge experiment and dynamic stress test experiment were designed to verify the convergence and robustness of the proposed algorithm. The maximum estimation error of SOC was less than 1.0%, and the reference range of gain threshold was also given.

In an energy storage system, the current-fed dual-active-bridge converter has a large current stress and the corresponding soft-switching range is limited, which limits the converter’s efficiency and power density. To solve these problems, combined with the coupled inductor technology, a current-fed dual-active-bridge converter with a low current ripple on the energy storage side and a wide soft-switching range is proposed. Two current-fed full bridges are connected in parallel on the energy storage side, thus effectively reducing the current stress of switches therein. By adjusting the phase shift angle between the two parallel full bridges on the energy storage side, the current ripple is reduced. By reasonably designing the coupling filter inductance, the obtained mutual inductance current is large enough to satisfy the soft-switching conditions for switches. The working principle and steady-state analysis of the converter were given in detail, and a 400 W experimental prototype was designed to verify the superiority and feasibility of the proposed converter.

The switching speed and switching frequency of converters keep increasing, and higher requirements are also imposed on the DC-side decoupling capacitors. To solve the problems of overvoltage spikes and decoupling capacitor losses caused by voltage and current oscillations during the switch-off process, a transient circuit model considering the system’s stray parameters is established, and the evolution of overvoltage and decoupling capacitor current oscillation is analyzed. On this basis, a loss model considering the parasitic parameters of the main circuit and the equivalent series resistance of the decoupling capacitor is proposed. The limiting factors for the selection of decoupling capacitors in practical engineering are quantitatively analyzed, and an optimal selection method for the decoupling capacitance and loss limit condition is obtained. Finally, the proposed model and analysis method were verified by simulation and experimental results.

The flying capacitor clamped three-level converter has many advantages, e.g., it can reduce the voltage stress of a switch and the volume of a filter inductor. Under its operation, it is necessary to stabilize the flying capacitor voltage at half of the high-voltage side voltage, so a control strategy of adjusting the duty cycle is often used. However, this method has the problem of coupling control between flying capacitor voltage and output voltage, resulting significant fluctuations of inductance current in the process of flying capacitor voltage regulation. To solve this problem, the advantages of using the phase-shifting control strategy to realize the decoupling control of flying capacitor voltage and output volt-age are analyzed, and the corresponding control characteristics are also studied. Through the establishment of a harmonic model of flying capacitor voltage, the relationship between flying capacitor voltage and phase-shifting angle is given. A low-order harmonic function relationship is constructed, which indicates that the flying capacitor voltage is affected by the switch duty cycle D and phase-shifting angle ∆φ. The effective duty cycle interval of phase-shifting control and the duty cycle that optimizes the performance of phase-shifting control are delimited by combining with a time-domain model. A simulation model was established, and an experimental prototype with 3.6 kW was built. The control strategies of adjusting flying capacitor voltage based on phase-shifting angle and duty cycle are compared to verify the decoupling advantages and control characteristics of phase-shifting control.

Aimed at the problems of unbalanced capacitor neutral-point voltage and high common-mode voltage in a permanent magnet synchronous motor drive system powered by a T-type three-level inverter, a model predictive instantaneous torque control (MPITC) strategy based on finite voltage vector set optimization is proposed. First, in view of the influence of voltage vectors on the neutral-point voltage, only zero, small and large vectors are selected to participate in MPITC. Second, according to the relationship between the switching states and common-mode voltage, it is confirmed that 13 low common-mode voltage vectors participate in the control. To improve the operation performance of the motor, the long vector synthetic virtual voltage vector is used to replace the medium vector to participate in the model predictive control. Finally, according to the neutral-point potential and the motor current direction, the voltage vector which is favorable for maintaining the neutral-point voltage balance is selected from 19 voltage vectors as the preselected vector set. Experimental results show that the proposed control strategy can effectively reduce the electromagnetic torque, flux linkage pulsation and common-mode voltage amplitude, and the neutral-point voltage achieves balanced control.

To ensure the motor drive performance while saving cost in the field of electric industrial vehicles, low-precision encoders are often adopted. Although these encoders can measure the rotor’s accurate mechanical position, they introduce a long delay and large errors to the measured speed information. Therefore, the traditional load torque observers cannot obtain the accurate load torque information, and when the inaccurate information is used as feedforward of the current loop, the motor speed fluctuation cannot be effectively suppressed. To solve this problem, a second-order sliding-mode load torque observer based on a low-precision encoder is proposed, which can obtain the accurate load torque information based on the rotor position information and thus improve the anti-interference performance of the system. Finally, the correctness and effectiveness of the proposed method was verified by simulation and experimental results.

Aimed at the problems such as voltage sag/surge resulting from strong fluctuations of high-permeability renewable energy, which cannot be dealt with by using the existing transformers, a novel hybrid distribution transformer (HDT) based on a three-bridge arm power converter is proposed. This method is realized by adding a series three-bridge arm power converter to the primary side of the existing distribution transformer. The proposed novel HDT has two advantages, i.e., it can reduce the rated power of the power converter, and it can improve the transformer’s degree of freedom by adding an additional current loop. In addition, to further improve the power quality of the transformer, the proposed method integrates the voltage vector, which can compensate the adverse effects of voltage sag/surge and grid voltage harmonics on the transformer. Therefore, it improves the power factor of power grid, as well as the transmission efficiency of the distribution network. Finally, the configuration and control strategy for the proposed HDT are discussed, and the effectiveness and superiority of the proposed method are verified by simulation analysis.

Electric vehicle fast charging piles are prone to overheating of power devices under high-power operation, causing potential safety hazards. However, the existing cooling strategy adopts a rule-based forced air cooling method, and the cooling fan rotates at a high speed and generates large environmental noise. To protect the thermal safety of core components in the module while optimizing the cooling regulation strategy, an optimal thermal management method for electric vehicle fast charging module based on data-driven model predictive control (MPC) is proposed. This method adopts a data-driven method to construct a prediction model of module temperature distribution based on the long short-term memory neural network, and it combines MPC to control the fan speed, thus optimizing the thermal management strategy for the fast charging module and reducing the fan noise. Through experimental tests, it was verified that this method can effectively reduce the average fan speed by 1 293 rpm and reduce the average noise by 4.99 dB while ensuring that the key components are not overheated, which ensures the thermal safety of core components and the durability of the cooling fan.