The modular multilevel converter (MMC) has been a subject of increasing importance for medium/high-power energy conversion systems. Over the past few years, significant research has been done to address the technical challenges associated with the operation and control of the MMC. In this paper, a general overview of the basics of operation of the MMC along with its control challenges are discussed, and a review of state-of-the-art control strategies and trends is presented. Finally, the applications of the MMC and their challenges are highlighted.

Operation, Control, and Applications of the Modular Multilevel Converter: A Review

Due to increasing concerns about global warming, greenhouse gas emissions, and the depletion of fossil fuels, the electric vehicles (EVs) receive massive popularity due to their performances and efficiencies in recent decades. EVs have already been widely accepted in the automotive industries considering the most promising replacements in reducing CO2 emissions and global environmental issues. Lithium-ion batteries have attained huge attention in EVs application due to their lucrative features such as lightweight, fast charging, high energy density, low self-discharge and long lifespan. This paper comprehensively reviews the lithium-ion battery state of charge (SOC) estimation and its management system towards the sustainable future EV applications. The significance of battery management system (BMS) employing lithium-ion batteries is presented, which can guarantee a reliable and safe operation and assess the battery SOC. The review identifies that the SOC is a crucial parameter as it signifies the remaining available energy in a battery that provides an idea about charging/discharging strategies and protect the battery from overcharging/over discharging. It is also observed that the SOC of the existing lithium-ion batteries have a good contribution to run the EVs safely and efficiently with their charging/discharging capabilities. However, they still have some challenges due to their complex electro-chemical reactions, performance degradation and lack of accuracy towards the enhancement of battery performance and life. The classification of the estimation methodologies to estimate SOC focusing with the estimation model/algorithm, benefits, drawbacks and estimation error are extensively reviewed. The review highlights many factors and challenges with possible recommendations for the development of BMS and estimation of SOC in next-generation EV applications. All the highlighted insights of this review will widen the increasing efforts towards the development of the advanced SOC estimation method and energy management system of lithium-ion battery for the future high-tech EV applications.

A review of lithium-ion battery state of charge estimation and management system in electric vehicle applications: Challenges and recommendations

This paper investigates the characteristics of the active and reactive power sharing in a parallel inverters system under different system impedance conditions. The analyses conclude that the conventional droop method cannot achieve efficient power sharing for the case of a system with complex impedance condition. To achieve the proper power balance and minimize the circulating current in the different impedance situations, a novel droop controller that considers the impact of complex impedance is proposed in this paper. This controller can simplify the coupled active and reactive power relationships, which are caused by the complex impedance in the parallel system. In addition, a virtual complex impedance loop is included in the proposed controller to minimize the fundamental and harmonic circulating current that flows in the parallel system. Compared to the other methods, the proposed controller can achieve accurate power sharing, offers efficient dynamic performance, and is more adaptive to different line impedance situations. Simulation and experimental results are presented to prove the validity and the improvements achieved by the proposed controller.

Design and Analysis of the Droop Control Method for Parallel Inverters Considering the Impact of the Complex Impedance on the Power Sharing

With the rapidly evolving technology of the smart grid and electric vehicles (EVs), the battery has emerged as the most prominent energy storage device, attracting a significant amount of attention. The very recent discussions about the performance of lithium-ion (Li-ion) batteries in the Boeing 787 have confirmed so far that, while battery technology is growing very quickly, developing cells with higher power and energy densities, it is equally important to improve the performance of the battery management system (BMS) to make the battery a safe, reliable, and cost-efficient solution. The specific characteristics and needs of the smart grid and EVs, such as deep charge/discharge protection and accurate state-of-charge (SOC) and state-of-health (SOH) estimation, intensify the need for a more efficient BMS. The BMS should contain accurate algorithms to measure and estimate the functional status of the battery and, at the same time, be equipped with state-of-the-art mechanisms to protect the battery from hazardous and inefficient operating conditions.

Battery Management System: An Overview of Its Application in the Smart Grid and Electric Vehicles

A comprehensive review of lithium-ion batteries used in hybrid and electric vehicles at cold temperatures

The Wind Turbine Systems (WTS) are required to ride through recurring grid faults in some countries. In this paper, the capability of Doubly Fed Induction Generator (DFIG) WTS to ride through recurring asymmetrical grid faults is evaluated and compared with the ride through capability under single asymmetrical grid fault. A mathematical model of the DFIG under recurring asymmetrical grid faults is represented. The analysis are verified by simulations on a 1.5MW DFIG model and by experiments on a reduced-scale DFIG test system.

Capability of DFIG WTS to ride through recurring asymmetrical grid faults

To press-pack devices, higher packaging resistance results in higher conduction losses. In this paper, compositions of the packing resistance are studied for a press-pack SiC MOSFET. Firstly an estimation method of body resistance of conducting layers in the press-pack SiC MOSFET with ANSYS Q3D is investigated, which is verified by the experiment. Since the Q3D resistance estimation method is unable to obtain contact resistances between different layers in the press-pack, the contact resistances estimation method is proposed. Finally all resistances in the press-pack are obtained. It is concluded that the contact resistance is critical to the static loss of the press-pack. It is useful to the press-pack structure improvement in the future.

Analysis of Press-Pack SiC MOEFET’S Parasitic Resistance

In a hybrid IGBT module with SiC diodes as free-wheeling diodes, high frequency oscillation occurs during turn-on, which will cause higher EMI noise due to the larger capacitance of SiC diode To evaluate the influence of gate drive parameters on turn-on oscillation, different gate voltages and gate charge currents are used It is found that by changing gate drive parameters alone cannot reduce the settling time of the oscillation significantly Then an oscillation suppression method with damping circuits is proposed According to the analytical and experimental results, the damping circuits are able to effectively accelerate the damping of turn-on oscillation without significant increase in current overshoot and turn-on energy loss Finally to suppress the turn-on current overshoot, active gate driver method is also used without large increase in the turn-on energy loss The combination of damping circuit and active gate driver may be an optimized choice to achieve the lowest EMI noise

Switching noise suppression for hybrid IGBT modules

Active power decoupling (APD) techniques prove to be efficient in cutting passive component size for single-phase AC/DC converter, usually against bulky electrolytic capacitors (E-Cap) on DC side. Generally, no adding extra switches is expected to realize E-Capless function as well as original power factor correction (PFC). This paper proposes a multiplexing modulation strategy with optimized power-decoupling reference algorithm, employing a small LC branch as power decoupling circuit to replace large electrolytic capacitors, which could further reduce dc-link capacitance. Both simulation and experimental results for a lkW prototype are presented in this paper to validate the performance of proposed method.

A Multiplexing Modulation Strategy Based on Single-phase AC/DC Converter with Optimized E-Capless Function

Active power filter (APF) with digital control is widely used to solve harmonic problems. But inherent delay time introduced by digital control significantly affects the performance of APF. Here, we introduce an improved harmonic detection method by using phase-shifting. In order to shorten the computation time of harmonics reference, we use the data calculated in the last sample period. So the delay time is shortened, and the performance of APF is improved. The whole algorithm is based on generalized instantaneous reactive power theory. This method is easy to realize and useful for industrial application. A 50 kVA three-phase four-wire shunt active power filter is implemented. The controllers with two types of TI digital signal processors (TMS320LF240 and TMS320F2812) are compared. Experiment result shows good performance employing the new algorithm for APF.

Min Chen

Papers

Capability of DFIG WTS to ride through recurring asymmetrical grid faults

Analysis of Press-Pack SiC MOEFET’S Parasitic Resistance

Switching noise suppression for hybrid IGBT modules

A Multiplexing Modulation Strategy Based on Single-phase AC/DC Converter with Optimized E-Capless Function

An improved harmonic detection based on lead compensation for active power filter