Cheng Shukang

Comparison and Evaluation of Charge Equalization Technique for Series Connected Batteries

Charging and discharging of series connected batteries as a whole is associated with charge imbalance problems, which will result in damage to battery cells and reduction of battery life. Various circuits for charge/discharge equalization have been proposed. But so far there is no criterion for comparison and evaluation. In this paper, all the circuits are divided into four groups according to the structure, and each of them is qualitative analyzed and marked with 5-degree marking system. The results are helpful for people to select suitable charge/discharge equalization method. Furthermore, based on experimental results a novel evaluation method with two parameters is proposed, which is very convenient for estimating the equalization effects in static and dynamic equalization. All the results can be used for further study on charging equalization technique.

Design characteristics of the induction motor used for hybrid electric vehicle

Design characteristics of the induction motor used for HEV (hybrid electric vehicle) are discussed. Equivalent circuits corresponding to the starting, operating performance and harmonics are given. The selecting rules of the starting voltage and frequency are got. The relations between the iron core and copper loss vs. frequency are analyzed and compared. The influence of harmonics on the induction motor is analyzed. The design principles of the induction motor used for HEV are given considering the impacts of the starting, operating performance and harmonics.

Flux-Weakening-Characteristic Analysis of a New Permanent-Magnet Synchronous Motor Used for Electric Vehicles

The permanent-magnet (PM) synchronous motor (PMSM) takes advantages of small capacity, high efficiency, and high power density and have become commonplace in electric-vehicle driving systems. However, the excitation of PMSM cannot be adjusted, which restrains the PMSM from widening the speed range above its base speed. A PMSM with a variable magnetic reluctance field adjustment is presented in this paper. A new structure of the rotor is introduced, and flux-weakening (FW) principle is formulated. Analysis is discussed, including the force on the main PM, the movement process of the PM in the PM slot, the characteristics of the movement of the PM, and the FW performance of the new PMSM used for electric vehicles. The emulation analysis coincides with the test result, which verifies the availability and feasibility of the FW method for this kind of PMSM used for electric vehicles.

Double-Stator Permanent Magnet Synchronous In-Wheel Motor For Hybrid Electric Drive System

For modern wheeled vehicles, hybrid electric drive system (HEDS) technology can effectively improve their performance, and hence attracts wide attention. As a core part, the in-wheel motor directly affects the capability of the whole system. In order to improve the overload ability of the in-wheel motor, this paper introduces a type of double-stator permanent magnet synchronous motor (DSPMSM). Then, from the view of electric load, theoretical deduction and simulation experiments are done to analyze the torque characteristics of this motor. Results show that by adjusting the outer-inner winding turns ratio properly, DSPMSM has higher torque and power density, in comparison to traditional single-stator motors. This helps to improve the performance of HEDS.

Magnetization analysis of the brushless DC motor used for hybrid electric vehicle

Component magnetization and post-assembly magnetization are compared for the brushless DC motors used for hybrid electric vehicles through theoretical analysis, FEM calculation and experiment. Provided with enough magnetizing MMF, the permanent magnets can be fully magnetized both by component magnetization and post-assembly magnetization. The tested rotor surface flux densities of the component magnetization and post-assembly magnetization are consistent, and they are in good agreement with the FEM calculated values. By contrast, we prefer the post-assembly magnetization in order to overcome the problem of magnetic forces and ferrous debris during the assembly process.

Study of Bidirectional DC-DC Converter for Power Management in Electric Bus with Supercapacitors

Electric bus with supercapacitors (SCs) as the only on-board power source could realize fast and effective recuperation of energy in frequent braking and deceleration in city. However, its a very challenging task to design a bi-directional DC-DC converter because of wide voltage range and high current order of SCs. This paper presents an analysis and comparative study of several non-isolated bi-directional DC-DC converters. As a compromise of power density, cost and reliability, buck/boost converter is adopted as the final choice. Furthermore, a soft-switching circuit with snubber is designed and realized to reduce EMI and losses in switching devices. Experimental results show its high continuous-running efficiency and reliability, which could satisfy the requirements of this power-management application

Advantages of electrostatic micromotor and its application to medical instruments

In this paper, electrostatic micromotor and conventional electromagnetic micromotor are compared. According to their different operation principles, the paper firstly analyzes the scaling effect of driving forces. Characteristic dimension L represents the linear scale of the micromotors. Electromagnetic driving force is proportional to high-order power of characteristic dimension L whereas electrostatic driving force is not. So, in micro domain, the effect of electrostatic force is larger than that of electromagnetic force, which makes electrostatic micromotor more competitive against electromagnetic alternative in MEMS. In assessing the performance of the micromotor, the power per unit volume and efficiency are the two most important criteria. Hence, the paper further compares the two kinds of micromotors from these two aspects. The results indicate that electrostatic micromotor has higher power per unit volume and efficiency, moreover, its structure is simple, it can be made sufficiently small. For those advantages of electrostatic micromotor, the paper finally discusses its application to medical instruments.

The Performance Research of Starter-Generator Based on Reluctance Torque Used in HEV

The objective of this paper is to describe the role that reluctance plays in interior permanent magnet (IPM) starter-generator (SG) analytically. 4-pole and 6-pole models of SG including the radial and tangential flux are analyzed. For increasing the value of q -axis reactance, several possible factors are considered. The stationary torque versus control angle was predicted by finite element analysis (FEA). The permanent magnet and the reluctance components of the torque were analyzed and computed. The results show that the rotor shape, magnet length, magnet thickness and the amount of poles etc., will observably affect the component of the reluctance. One working prototype of the SG-1 was built and fully tested. The motoring torque within 1700 rpm and the generating power within 6000 rpm were measured. The motoring power can supply 8 kW at 1700 rpm and the torque can keep constantly with 45 Nm; Generating results have proven that the ISG is capable of meeting the specification for output power 4 kW up to 6000 rpm and the maximal speed can reach to 7927 rpm. In addition, the efficiency contour maps of motoring and generating are obtained by experiment. The results show that the prototype has wide high efficiency region. The FEA prediction and experiment results were proved well. The improved prototype SG-2 was simulated by FEA. SG-2 is a radial-flux structure machine, and its utilization of permanent magnet and the saliency ratio are both higher than SG-1. The results show that no matter constant torque ability or the constant power range, compared with SG-1, SG-2 both has an improvement to a large extent.

A new flux weakening method of permanent magnet synchronous machine

As traditional permanent magnet synchronous machines (PMSM) are deficient in flux weakening operation, a new method of automatic flux weakening with the rotor speed is presented. The flux weakening principle of permanent magnet synchronous motor (PMSM) is introduced. The flux weakening speed range is investigated and the forces on magnetic conductor which for adjusting the leakage reluctance of the rotor are analyzed in detail. Results from the finite element field emulation analysis are presented to verify the validity and feasibility.

Thermal analysis of solid rotor in PMSM used for EV

A solid rotor permanent magnet synchronous motor (PMSM) is developed for the electric propulsion part in electric vehicles (EV). The rotor in this kind of motor is composed of splits solid bodies, interior permanent magnets and starting bars. Wedges and bars are shot circuited by end rings that promote the generation of starting torque jointly. While PMSM used in EV, it may need to start frequently at different load, which would cause eddy losses in rotor and related to thermal demagnetization of permanent magnet directly. In this paper, a prototype of 30kW solid rotor PMSM is proposed, and numerical calculation models for thermal analysis are established. The 2D electromagnetic fields were calculated by using finite element method (FEM) first and motor losses in rotor were determined. From the analysis of fluid analysis of air in airgap, an effective coefficient of heat transfer is proposed to deal with the complex heat exchanges between rotor and stator. Then steady thermal field is analyzed, and influences of motor fan, loads and stray loss on rotor temperature distribution were studied. Some associate test work has been done with results in a good agreement with the analysis data. Some reasonable conclusions were obtained, which can provide some help for the design of this kind of PMSM and its application in EV.