Joachim Bocker

Active damping of drive train oscillations for an electrically driven vehicle

A problem encountered with electrically driven vehicles are resonances in the drive train caused by elasticity and gear play. Disadvantageous effects caused by this are noticeable vibrations and high mechanical stresses due to torque oscillations. The oscillations can be damped using a control structure consisting of a nonlinear observer to estimate the torque in the gear and a controller, which computes a damping torque signal that is added to the drivers demand. The control algorithm was implemented in the existing motor control unit without any additional hardware cost. The controller was successfully tested in a test vehicle. The resonances can essentially be eliminated. The controller copes satisfactorily with the backlash problem.

Optimum Control for Interior Permanent Magnet Synchronous Motors (IPMSM) in Constant Torque and Flux Weakening Range

Interior Permanent Magnet Synchronous Motors (IPMSM) gain importance due to their high torque per volume ratio particularly for hybrid electrical vehicles. However, unlike to standard control theory, the torque control strategy for these motors is not apparently due to their reluctance torque, which is typical with interior magnet design. In this contribution, a control strategy is presented, which enables optimal torque control both in the lower speed range as well in the full flux weakening range. Operation during flux weakening, however, causes stress to the magnets of the motor with the risk of permanent demagnetization. The relations between the crucial design parameters are shown.

Optimal energy management for a hybrid energy storage system combining batteries and double layer capacitors

Many mobile vehicular applications like hybridelectrical cars and autonomous rail vehicles require an onboard energy storage for operation. High demands concerning power and energy density, small volume and weight at the same time cannot be satisfied solely by batteries or double layer capacitors. A suitable approach is to combine storage technologies with complementary characteristics as a hybrid energy storage system. Thus, long term storage like batteries featuring high energy density can be combined with short term storage like double layer capacitors offering high power density and high cycliability. To control the power flows of the system, we propose the use of self-optimization methods involving multi-objective and discrete optimization to design an operating strategy which is able to adapt the system behavior to different conditions not only by adapting its parameters but also its objectives, offering an optimal operation in different situations.

State of the Art of Induction Motor Control

The induction motor is well known as the workhorse of industry. The development of variable speed induction motor drives has a long history of more than four decades. Todays sophisticated industrial drives are the result of the extensive research and development during the last decades. In this paper the historical and recent developments and major milestones in control of induction motors are pointed out first and second how research results were translated into todays industrial standards, and third at last, what are the current trends in research and industry are summarized.

Optimal energy management for a hybrid energy storage system for electric vehicles based on Stochastic Dynamic Programming

For electric and hybrid electric cars, commonly nickel-metal hydride and lithium-ion batteries are used as energy storage. The size of the battery depends not only on the driving range, but also on the power demands for accelerating and braking and life-time considerations. This becomes even more apparent with short driving ranges, e.g. in commuter traffic. By hybridization of the storage, adding double layer capacitors, the battery can be relieved from the stress of peak power and even downsized to the energy demands instead of power demands. The dimensioning of the storage is performed by a parametric study via Deterministic Dynamic Programming. To determine an energy management to control the power flows to the storage online during operation which considers the stochastic influences of traffic and the driver, Stochastic Dynamic Programming is investigated and compared to the optimal strategy found during the dimensioning.

Analysis and design of improved isolated full-bridge bidirectional DC-DC converter

A novel isolated full-bridge DC-DC converter with bidirectional power flow is proposed in this paper. By adding auxiliary active clamping circuits to both bridges, zero-voltage and zero-current-switching are achieved to improve the performance of the bidirectional PWM converter. The switches are controlled by phase shifted PWM signals with a variable duty cycle. The principle of operation is analyzed and simulated. Experimental results of a 3 kW 50 kHz prototype are presented.

Linear switched reluctance motor as a high efficiency propulsion system for railway vehicles

A linear and a rotational switched reluctance drive with a large airgap are developed and manufactured for a test track of autonomous railway vehicles. The motor design, a coupled model and the results of finite-element-simulations are presented, along with the test bed structure and measurements. The design and control objectives are to maximize the efficiency and to minimize the acoustic noise at the given motor dimensions and the output power.

Adaptive digital slope compensation for peak current mode control

Peak current mode control as well as digital control offers a number of benefits. Therefore it is an interesting approach to combine these two techniques in one control structure. Based on microcontrollers with on-chip comparators, this combination is realizable with very low effort. In order to eliminate the drawbacks of peak current mode control, a slope compensation has to be added. This paper presents such a slope compensation implemented on a microcontroller not using an analog ramp signal but instead pre-calculating the desired comparator switch-off threshold. In contrast to conventional analog control, adaptive algorithms can be used to maintain optimal slope compensation over a wide operating range. Problems that occur in practice due to reverse recovery current spike and computing time can be handled with simple measures. The effectiveness of the proposed digital slope compensation is verified by experimental results.

Observer for the rotor temperature of IPMSM

In this paper an observer for the rotor temperature of an IPMSM, as commonly used in automotive applications, is presented. The observer is based on a flux observer utilizing the fact that the permanent magnet flux is temperature-dependent. Simulation and experimental results show good performance.

Analytical and Offline Approach to Select Optimal Hysteresis Bands of DTC for PMSM

The switching frequency of an inverter under direct torque control is mainly decided by the flux- and torque-controller output switching counts. It is known that, with fixed hysteresis bands, the switching frequency varies as the operating point changes. It is possible, however, to keep the switching frequency constant by the adaptation of hysteresis bands. The switching frequency is a function of both torque and flux bands. Different combinations of flux and torque bands can be used to achieve a desired switching frequency. However, for optimal control, one among the many available combinations has to be chosen. In this contribution, it is proposed to select the hysteresis bands based on the criterion of the minimum harmonic distortion in the motor currents for the required switching frequency. An analytical procedure is presented to calculate these optimal bands for the permanent-magnet synchronous motor. The analytical results were cross checked with simulation studies and validated by detailed experimentation. In order not to degrade the control performance by computational delay, a field-programmable-gate-array-based control platform is being used for implementation.