This article proposes a common-mode (CM) voltage reduction method using an active power filter (APF) and common-mode transformer (CMT) for a grid-connected three-phase three-level neutral-point-clamped (NPC) AC-DC pulsewidth modulation (PWM) converter. The CM voltage can be caused by switching operations of converters and the CM voltage should be reduced because it is one of the main causes of electromagnetic interference (EMI) noises. In this article, the CM voltage of the three-phase converter with the proposed APF is analyzed to explain the CM voltage reduction using the proposed APF. Based on this analysis, the application of a specific PWM method to the three-phase converter for an optimal reduction of the CM voltage is described. Besides, the APF circuit design and its switching method are proposed considering practical problems such as the self-resonance of inductors and the effect of the dead-time on the CM voltage. To prove the effectiveness of the proposed APF on the CM voltage reduction, experimental results for the CM voltage and current are presented in this article. Furthermore, EMI noise measurement results are shown to verify the performance of the noise reduction capability of the proposed APF.

This paper proposes a fault diagnosis and tolerant control methods for an open-switch fault caused in a three-phase three-level neutral-point-clamped (NPC) pulse-width modulation (PWM) active rectifier. The open-switch fault in the three-level NPC active rectifier causes a distortion in the input phase current and a ripple in the DC-link capacitor voltage. Therefore, proper fault diagnosis and tolerant control methods are required to prevent additional failures and performance degradation in the rectifier system. This paper conducted a detailed analysis of the effect of the single open-switch fault on the NPC PWM active rectifier and proposed a fault diagnosis method utilizing the DC link voltage and the phase angle of the input grid voltage. Furthermore, this paper proposes a fault-tolerant control method to reduce the effect of the open-switch fault by compensating a distorted reference voltage. The effectiveness of the proposed fault diagnosis and tolerant control methods are verified through experimental results.

This paper proposes a pulse-width-modulation (PWM) control strategy for the efficient operation of the three-phase three-level neutral-point-clamped (NPC) inverters with a bootstrap gate drive circuit. The bootstrap circuit used in the three-level NPC inverter has advantages in terms of the cost reduction and the compact circuit design. However, the bootstrap circuit has a drawback due to the low gate-emitter voltage during the low-frequency and variable load condition of the inverter system. This problem leads to lower efficiency and reliability of the inverter. Therefore, this paper analyzes the causes of the voltage decrease in bootstrap capacitors and proposed PWM control strategy to increase the voltage level of bootstrap capacitors for the efficient operation of the inverter. The proposed PWM control strategy provides efficient and stable operation of the inverter system by selecting the unipolar, dipolar or partial-dipolar modulation methods according to the fundamental output frequency and load current of the inverter system. Furthermore, this paper proposes a design method of the size of bootstrap capacitors for the optimal circuit design. The effectiveness of the proposed PWM control strategy is verified using the experimental results.

This paper proposes a novel modulation strategy with an active power filter (APF) for reducing conducted electromagnetic interference (EMI) in three-level neutral-point-clamped AC/DC PWM converters. Common-mode (CM) voltage is identified as one of the main causes of EMI in power electronics systems driven by pulse-width modulation (PWM) converters. To address this issue, the paper proposes a CM voltage reduction strategy using a fourth-leg APF with shunt capacitors, which overcomes the limitations of existing methods. The proposed strategy allows for the complete elimination of CM voltage, and compensation is proposed to eliminate residual CM voltages due to the dead time effect. Additionally, the paper presents a design procedure for the APF circuit to obtain a proper reduction performance. Simulation and experimental results demonstrate the effectiveness of the proposed strategy in reducing both CM voltage and current, as well as conducted EMI.

In recent years, electric propulsion systems have become widely, used and these systems have strict limits in volume and weight. Therefore, it is necessary to reduce the weight of the inverter-motor drive system. In a typical $n$ inverter-motor drive system, at least $2n$ phase current sensors are required. In order to reduce the number of phase current sensors, this paper proposes a method for measuring phase current using $n$DC link current sensors in a $2n$ inverter-motor drive system. Two phase currents per inverter-motor system are measured during one period of the switching frequency using the pulse width modulation (PWM) shift method. However, since the measured phase current contains an error component in the average current, the error component was compensated for in order to obtain a current similar to the actual phase current by using the slope and dwell time of the phase current. The effectiveness of the proposed method is verified through experiments.

The increasing adoption of electric vehicles (EVs) and battery energy storage systems (BESS) makes battery management systems (BMS) crucial for effectively managing battery cells, such as state of charge (SOC) and cell temperature. Significant imbalances in these parameters can degrade battery performance and reduce reliability. Although active balancing strategies offer greater control flexibility compared to passive methods, they typically face challenges in implementing complex control algorithms, particularly for multi-objective balancing tasks. To overcome these challenges, this paper proposes an enhanced active BMS employing reinforcement learning (RL) to simultaneously minimize deviations in SOC and cell temperature. Specifically, a proximal policy optimization (PPO)-based RL agent is trained within a simulation environment and subsequently deployed in a real-world experimental setup. Experimental results demonstrate that the proposed approach can quickly and effectively balance both SOC and cell temperature while efficiently managing the auxiliary power source (APS). This study validates the feasibility of intelligent multi-objective battery state balancing with RL.