Marcus Menne

Control of switched reluctance drives for electric vehicle applications

Dynamic controllers of switched reluctance drives adjust at least three variables, i.e., current amplitude, turn-on, and turn-off angles. In electric vehicle (EV) applications high efficiency of the drive over a wide speed range, wide torque bandwidth, and low torque ripple under varying DC-bus voltage conditions are important design goals. Hence, controllers of switched reluctance drives for EVs usually have a complex structure. In this paper, the demands on control accuracy of switched reluctance machine traction drives and the traction controller sampling frequency, which are necessary to take advantage of the switched reluctance machine dynamic capabilities, are discussed. To integrate the traction drive, the control commands need to be actualized with a sampling frequency of at least 100 Hz to meet the high-dynamic requirements of modern vehicle control systems, e.g., active cruise control, antislip control, and active damping of mechanical drivetrain oscillations. It is found that the switching angles have to be adjusted within one-tenth of a mechanical degree. This study shows that switched reluctance drives can fulfill all requirements needed for electric propulsion using standard microcontrollers or digital signal processors.

High-dynamic four-quadrant switched reluctance drive based on DITC

This paper presents the development of a four-quadrant switched reluctance machine (SRM) drive for high dynamic applications. Comprehensive fundamentals and analysis for operating switched reluctance machines in four quadrants are presented. The drive is designed based on a high dynamic control strategy called Direct Instantaneous Torque Control (DITC). The functionality of DITC is discussed in detail for both motoring and generating operation. A methodology to generate switching functions directly by the hysteresis torque controllers for SRMs is proposed. The proposed controller was prototyped and tested on a digital signal processor/field-programmable gate array development platform. High dynamic operation in both motoring and generating mode and the transition between these modes are validated by experimental results presented at the end of this paper.

Optimizing performance in switched-reluctance drives

This article discusses the requirements of electric vehicle traction drives and the consequences to the control strategies of a switched reluctance motor drive. The selection of these control strategies for different operating regions in the torque-speed diagram is also discussed. To test different control strategies, a specialized simulation program was constructed. The simulation results and the implementation of the optimization strategies are discussed. Finally, the measurement methods and the test results are presented.

Critical states in generating mode of switched reluctance machines

When switched reluctance drives operate in generator mode, overcurrents can occur due to high back EMF voltages. These overcurrents produce large torque pulsations. Moreover, they can become excessive, creating a thermal overload for the power converter. These phenomena have not been discussed in detail before and are analyzed in this paper. Two overcurrent limits have to be distinguished. A so-called critical factor is defined to assess the risk of overcurrents leading to torque pulsations. In addition, an absolute maximum overcurrent is calculated to specify converter device ratings, preventing converter overload or failure. To protect the drive against uncontrollable overcurrents and the resulting torque pulsations, an adaptation of the drive control to avoid such failure states is suggested.

Optimizing performance in switched reluctance drives

It is demonstrated how the overall performance of a switched reluctance drive can be improved by using different control strategies for different regions of the torque-speed diagram. For a 4-phase 30 kW machine these strategies are fitted by connecting different optimizing routines with a simulation program. The importance of a correct tuning of the control parameters like turn-on angle, turn-off angle, reference current and size of the hysteresis band is demonstrated for a current controlled drive. Furthermore, the test bench and the measurement procedure for the experimental verification and comparison to the simulation are presented.

High performance four-quadrant switched reluctance traction drive based on DITC

This work presents the development of a four-quadrant switched reluctance drive for traction applications, in which high performance over a wide operation range in all quadrants is required. Comprehensive fundamentals and analysis for operating switched reluctance machines in four quadrants are presented. The drive is designed based on a high dynamic control strategy called direct instantaneous torque control (DITC). The functionality of DITC will be discussed in detail for both motoring and generating operation. A methodology to design switching pattern for the hysteresis torque controllers for switched reluctance machines is proposed. A controller was prototyped and tested on a DSP/FPGA development platform. A high performance operation in both motoring and generating mode is validated by experimental results presented at the end of this paper.

Generator Operation of Switched Reluctance Machine Drives for Electric Vehicles

Abstract This contribution deals with the stringent control requirements of switched reluctance generators for electric vehicle (EV) applications. In EV applications, switched reluctance machines have to operate in generating mode over a wide torque-speed range, i.e. in the current controlled chopping mode at low speed as well as in the voltage controlled single-pulse operation at high speed. In addition, the d.c.-bus voltage varies with the load as a function of the energy source. This voltage variation requires continuous variable adaptation when a wide speed range is required. Furthermore, a novel control strategy to implement a three-level hysteresis current regulator for generating mode is presented. This technique improves drive efficiency up to 8% over a wide operating area. In addition, the problem of uncontrollable overcurrents due to excessive back-EMF voltage during generating mode is discussed. Therefore, the variables, which are necessary to control the switched reluctance drive, and the resulting efficiency characteristics are presented.