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

Time delay caused by digital control may significantly degrade the controllability of electric vehicle traction motor controller in high-speed applications. This paper proposes a method to reduce the side impact of digital delay on the motor current control. The complex vector current regulator considering delay and hold is modelled in d-q frame. Double-sided frequency response function is applied to analyze the stability, dynamic response and decoupling. State feedback control with phase compensation is used to enhance the stability, bandwidth and decoupling effect. The feasibility and effectiveness of this method is verified by simulation results.

Modified Current Regulator for High-Power Traction Motor with Low Sampling Frequency to Operating Frequency Ratio

This paper proposes a modified dc fault protection scheme for multi-terminal HVDC grid based on hybrid fault current limiters(HFCLs). To release the pressure of dc circuit breakers(DCCBs), HFCLs are applied to limit the fault current in advance. During the interrupting process, a coordinating method of DCCB and HFCL by utilizing the charged capacitor in HFCL is proposed so that the fault current could be interrupted more quickly, thus accelerating the protecting process. $\mathrm{A}\pm 500\text{kV}$ 4-terminal HVDC grid is built in PSCAD/EMTDC and the performance of proposed and other protection schemes are compared. The simulation results verify that the proposed modified protection scheme could effectively limit the fault current, shorten the protecting time and reduce the energy dissipation in DCCB.

A modified DC fault protection scheme for multi-terminal HVDC grid based on fault current limiters

The synchronous rectification (SR) is an effective method to further improve the efficiency of the CLLC bidirectional resonant converters However, the SR driving signals are hard to generate This paper proposed a novel SR scheme based on resonant inductor voltage sensing The inductor voltage is sensed by a voltage sensing winding integrated in the inductor, and is then integrated to obtain the resonant current The resonant current direction is used to generate SR driving signals, and a widely applicable control strategy is proposed to cover all operation conditions The proposed method does not need any loss, costly and bulky current sensors, while maintaining the benefits of current sensing based SR methods Finally, the proposed SR scheme is verified on a 380V/270V CLLC bidirectional resonant converter

A Synchronous Rectification Scheme based on Inductor Voltage Sensing for CLLC Bidirectional Resonant Converter

In this paper, an adaptive control strategy is presented for automotive HID lamps. Based on the HID lamps' model, a method of identifying cold and hot lamp is mentioned. And then the proposed warm-up current reference and DC operation time are designed during the warm-up stage based on the lamp's initial temperature. Compared with the traditional method, this control strategy could reduce the loss of the lamp's electrodes and extend the lamp life. Experimental results are presented to show the performance of this proposed control strategy.

An adaptive control strategy for automotive HID lamps based on lamp temperature

The invention discloses a model predictive control strategy of a modular multilevel converter. At present, the control strategies for MMC are generally PI control and PR control, and the control effect is not good. By controlling the working state of each phase sub-module, the invention enables the modular multi-level converter to output the rated reference value, thus ensuring that the conductionangles of the upper and lower switching power devices in each sub-module are complementary and not conductive at the same time. Ensuring that the number of sub-modules put into operation in the upperand lower bridge arms at each time of each phase is N; The switching state of each phase sub-module changes optimally each time. The invention adds the prediction period to compensate and corrects the prediction value, realizes the effective control of the modular multi-level converter, reduces the error caused by sampling and calculation, and is a high-reliability and practical control strategy.At the same time, considering the weight of all kinds of factors, the optimal working state of the sub-module is selected.

Min Chen

Papers

Modified Current Regulator for High-Power Traction Motor with Low Sampling Frequency to Operating Frequency Ratio

A modified DC fault protection scheme for multi-terminal HVDC grid based on fault current limiters

A Synchronous Rectification Scheme based on Inductor Voltage Sensing for CLLC Bidirectional Resonant Converter

An adaptive control strategy for automotive HID lamps based on lamp temperature

Model predictive control strategy for modular multilevel converters