Wide-scale adoption and projected growth of electric vehicles (EVs) necessitate research and development of power electronic converters to achieve high power, low-cost, and reliable charging solutions for the EV battery. This paper presents a comprehensive review of EV off-board chargers that consist of ac-dc and dc-dc power stages from the power network to the EV battery. Although EV chargers are categorized into two types, namely, on-board and off-board chargers, it is essential to utilize off-board chargers for dc fast and ultra-fast charging so that volume and weight of EV can be reduced significantly. Here, we discuss the state-of-the-art topologies and control methods of both ac-dc and dc-dc power stages for off-board chargers, focusing on technical details, ongoing progress, and challenges. In addition, most of the recent multiport EV chargers integrating PV, energy storage, EV, and grid are presented. Moreover, comparative analysis has been carried out for the topologies and the control schemes of ac-dc rectifiers, dc-dc converters, and multiport converters in terms of architecture, power and voltage levels, efficiency, bidirectionality, control variables, advantages, and disadvantages which can be used as a guideline for future research directions in EV charging solutions. 

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A Comprehensive Review of Power Converter Topologies and Control Methods for Electric Vehicle Fast Charging Applications

Inductive power transfer (IPT) technologies have gained a wide acceptance in onboard battery charging applications due to some significant advantages over traditional plug-in systems. An IPT battery charger is expected to provide a configurable charging profile consisting of an initial constant current (CC) and a subsequent constant voltage (CV) efficiently. With a wide load range during the charging process, two sets of IPT topologies with the inherent load-independent CC and CV at the same zero-phase angle (ZPA) frequency are commonly combined into a hybrid topology to avoid sophisticated control schemes, while maintaining nearly unity power factor and soft switching of power switches simultaneously. However, the load-independent CC and CV are usually constrained by parameters of a loosely coupled transformer (LCT), making the LCT hard to design. To solve it, this paper systematically presents a method to derive such effective hybrid IPT converters, which starts from some existing topologies having the configurable CC or CV output and cascades a general T network for mode transition. Design principles with fewer mode switches and compensation components are proposed and some available hybrid topologies regardless of the constraint of LCT parameters are given in this paper. Control logic and sensitivities of compensation parameters to the input impedance and the load-independent output are also discussed. Finally, a 1 kW hybrid IPT battery charger prototype based on LCC-LCC and LCC-S topologies is built to verify the theoretical analysis.

Hybrid Inductive-Power-Transfer Battery Chargers for Electric Vehicle Onboard Charging With Configurable Charging Profile

Wide-scale adoption and projected growth of electric vehicles (EVs) necessitate research and development of power electronic converters to achieve high power, low-cost, and reliable charging solutions for the EV battery. This paper presents a comprehensive review of EV off-board chargers that consist of ac-dc and dc-dc power stages from the power network to the EV battery. Although EV chargers are categorized into two types, namely, on-board and off-board chargers, it is essential to utilize off-board chargers for dc fast and ultra-fast charging so that volume and weight of EV can be reduced significantly. Here, we discuss the state-of-the-art topologies and control methods of both ac-dc and dc-dc power stages for off-board chargers, focusing on technical details, ongoing progress, and challenges. In addition, most of the recent multiport EV chargers integrating PV, energy storage, EV, and grid are presented. Moreover, comparative analysis has been carried out for the topologies and the control schemes of ac-dc rectifiers, dc-dc converters, and multiport converters in terms of architecture, power and voltage levels, efficiency, bidirectionality, control variables, advantages, and disadvantages which can be used as a guideline for future research directions in EV charging solutions.

https://ieeexplore.ieee.org/ielx7/6287639/6514899/09755960.pdf

For decades high voltage alternating current (HVAC) was considered as most economical solution to transmit and deliver electric power. With the recent developments in power electronic devices, high voltage direct current (HVDC) system becomes most prominent technology. Multi-terminal direct current (MTDC) based system as a promising technology for future power system is the major focus area for researchers and industries these days. A number of MTDC systems have been implemented physically. The major motivation to construct such MTDC systems is the integration of large-scale offshore power sources such as wind turbines and solar systems. This article discusses the most critical challenges and issues related to operation, control and protection schemes for integration of modular multi-level converter (MMC) based MTDC systems. At first detailed literature survey has been presented to show the challenges for MMC based MTDC systems, then an analysis related to those challenges for operation, control and protection schemes for existing MMC based MTDC systems has been provided. Finally, a road map to tackle such challenges has been suggested.

MMC Based MTDC Grids: A Detailed Review on Issues and Challenges for Operation, Control and Protection Schemes

Power electronic transformer (PET) is a key apparatus in smart grid system, due to the advantages of power controllability and ac/dc grids interconnection. The four-stage PETs have multiple output ports, good controllability, and flexibility, but are limited by multiple power conversion stages, complex structure, and low efficiency. Therefore, a novel modular multilevel converter (MMC)-based PET topology with mixed-frequency modulation is proposed to reduce the power conversion stage. The power decoupling circuits are designed to realize multiple output ports, including medium voltage ac (MVAC) port, medium voltage dc (MVDC) port, and low voltage dc (LVDC) port. The equivalent circuit and controllability of proposed PET are analyzed. The proposed PET topology provides the same multiple output ports by only three power conversion stages, therefore, the PET structure is simplified. In addition, simulation results are provided to verify the effectiveness of proposed PET.

A Multiport Power Electronic Transformer Based on Modular Multilevel Converter and Mixed-Frequency Modulation

Inductive power transfer (IPT) systems have many unique benefits compared to conventional plugged-in systems. The coupling pads in IPT systems are inevitably misaligned in many practical applications, thus leading to variations of the transferred power and efficiency that necessitate the use of complicated control for output regulation. A common solution is to use two IPT converters with opposite trends of output to pad misalignment, so that the total output voltage or current could be kept near constant for large coupling variations. However, methods for deriving effective configurations for such hybrid IPT converters and their achievable tolerance to the misalignment are still missing. This article constructs a family of hybrid IPT topologies, including input-parallel–output-parallel, input-parallel–output-series, input-series–output-parallel (ISOP), and input-series–output-series for delivering a constant current (CC) or a constant voltage (CV). Design principles and characteristics for all the hybrid systems with near load-independent output and high tolerance to pad misalignment are derived and discussed in detail. Based on this family of configurations, this article also combines some existing IPT topologies and derives multiple hybrid converters for CC or CV output by using a simple duty cycle control. Finally, a 3.5-kW hybrid IPT prototype converter based on the ISOP structure is built to verify the theoretical analysis.

A Family of Hybrid IPT Topologies With Near Load-Independent Output and High Tolerance to Pad Misalignment

The half bridge sub-module (HBSM)-based modular multilevel converter (MMC) is widely used in high voltage direct current (HVDC) transmission systems. However, it cannot block the dc fault current due to the uncontrolled freewheeling diodes in IGBT modules. The existing sub-modules with inherent dc fault current blocking capability still suffer from large power device amounts and complex control schemes. To solve these issues, this brief proposed a novel double reverse blocking sub-module (DRBSM), which has the fewer power devices than the existing sub-modules. With the same output voltage level, DRBSM has the same dc fault current blocking capability as full bridge sub-module (FBSM) and the same control logic circuit as HBSM. In order to further reduce the amount of power devices, a hybrid MMC based on HBSM and DRBSM is also proposed and the design principle is given in detail. Two study cases are built in simulation to verify the proposed DRBSM-based MMC and hybrid MMC well.

A Modular Multilevel Converter With Novel Double Reverse Blocking Sub-Modules for DC Fault Current Blocking Capability

The motion performance of the robot largely depends on the PMSM control performance for the electrically driven robot. During the long-term operation of the robot, the motor temperature will rise. At this time, the motor resistance and flux linkage will change with the increase of temperature. When the robot runs, the working current of the motor increases sharply, and the flux linkage and inductance of the motor will be affected by magnetic circuit saturation. The change of motor parameters lead the motor control system performance to be worse. It is necessary to identify the motor parameters on-line to achieve high-performance control in the process of robot motion. A method based on a combination of forgetting factor recursive least squares algorithm (FFRLS) and model reference adaptive system (MRAS) is proposed in this paper, which can accurately identify the motor parameters of robot on-line, and improve the identification speed. The PI controller parameters of the motor's current loop are self-tuning on-line to realize the high-performance based on the identification values of the motor resistance and inductance.

On-line parameter identification and self-tuning PI controller for permanent magnet synchronous motor

The robot joint is one of the key components of robots. With the wide application of robot joints, the demand for joint torque is becoming higher and higher. However, at present, most high-torque robot joints are generally large in weight and size, which creates problems for some applications. For this purpose, a high-torque and high-torque-density robot joint is proposed. To improve the joints’ torque density, the lightweight motor and reducer with a large reduction ratio are selected, and the mechanical structure design is based on weight reduction, miniaturization, and heat dissipation. The maximum torque of the proposed robot joint can reach up to 182Nm, and its mass is only 1.8kg. Besides, an embedded control system is designed to control the robot joint. Many experiments were conducted to measure the robot joint’s characteristics, such as torque, speed, and control features. And the designed robot joints are successfully applied to a biped robot. The results verify the performance of the designed robot joint and its control system.

Yunchang Yao

Papers

A Family of Hybrid IPT Topologies With Near Load-Independent Output and High Tolerance to Pad Misalignment

Hybrid Inductive-Power-Transfer Battery Chargers for Electric Vehicle Onboard Charging With Configurable Charging Profile

A Modular Multilevel Converter With Novel Double Reverse Blocking Sub-Modules for DC Fault Current Blocking Capability

On-line parameter identification and self-tuning PI controller for permanent magnet synchronous motor

Design of a High-torque Robot Joint and Its Control System