David Drury

Comparison of passive cell balancing and active cell balancing for automotive batteries

This paper presents a quantitative performance analysis of a conventional passive cell balancing method and a proposed active cell balancing method for automotive batteries. The proposed active cell balancing method was designed to perform continuous cell balancing during charge and discharge with high balancing current. An experimentally validated model was used to simulate the balancing process of both balancing circuits for a high capacity battery module. The results suggest that the proposed method can improve the power loss and extend the discharge time of a battery module. Hence, a higher energy output can be yielded.

Sensorless starting of a wound-field synchronous starter/generator for aerospace applications

The present paper describes an angle and speed estimation algorithm suitable for the control of a wound-field synchronous starter/generator (S/G) without position sensors for aircraft engine starting applications. The proposed control strategy is based on the injection of a high-frequency voltage signal and the subsequent demodulation of the resulting high-frequency stator current components. The coupling due to high-speed operation that degrades the estimation accuracy of similar algorithms based on signal injection is taken into account. Modeling of the machine response to a high-frequency voltage signal injected into the estimated d-axis is presented, also considering the influence of damping circuits both on the d- and q-axis. Local asymptotic stability of the proposed observer is also demonstrated. Through extensive experimental results, the proposed control technique is shown capable of guaranteeing full-torque sensorless operation at zero speed and sustained operation up to engine ignition speed.

Compensation of Inverter Nonlinear Distortion Effects for Signal-Injection-Based Sensorless Control

A simple analytical technique, which uses readily available datasheet parameters, is developed to model the low-current switching characteristics of insulated-gate bipolar transistors (IGBTs). Simulation and experimental results obtained using three differently rated inverters are presented to demonstrate the accuracy of the technique. The model is applied to compensate the nonlinear distortion, introduced by IGBT switching action in a three-phase inverter, of high-frequency injected voltage and current signals used in sensorless control of a permanent-magnet brushless ac machine. Experimental results show that the compensation technique improves rotor position estimation by up to 20° electrical.

Development of a Hardware-in-the-Loop Simulation System for Testing Cell Balancing Circuits

This paper presents the development of a hardware-in-the-loop (HIL) simulation system that facilitates the experimental testing of cell balancing circuits by emulating energy storage components. The system is developed with four cell simulators, each of which can emulate the battery voltage with the capabilities of sourcing and sinking current for the cell balancing circuit being tested. The cell simulator can also operate in battery testing mode for characterizing the behavior of a battery. One Li-polymer cell has been characterized using the cell simulator and a battery model has been built by the extracted parameters from the measurements. An active cell balancing experiment was conducted with a real 4-cell Li-polymer module followed by the same experiment using the HIL simulation system to emulate the Li-polymer cells based upon the method described in this paper. With the real battery module having a 9.4% SOC deviation initially, the final SOC deviation is reduced to 1.0% and the balancing time is 51.4 min. The HIL simulation gives very close results where the final SOC deviation and the balancing time are 1.2% and 52.0 min, respectively. The results demonstrate that the system can provide representative results for testing cell-balancing circuits with minimum resources and time.

An integrated design of active balancing and redundancy at module level for Electric Vehicle batteries

This paper proposes an integrated design of active balancing and battery redundancy at module level to maximize the performance and the reliability of the battery packs of Electric Vehicles (EVs) economically. Through the bidirectional flyback converter and the selection switches, the charge from the battery pack can be transferred to the selected module or vice versa to perform balancing. The design allows disconnection of faulty modules whilst maintaining the power supplied to the vehicle to avoid the risks of immediate power cut-off. Analytical studies and experimental results from the laboratory prototype are presented to verify the performance of the proposed design.

An Improved Substructuring Control Strategy based on the Adaptive Minimal Control Synthesis Control Algorithm

Abstract The use of the minimal control synthesis (MCS) adaptive control algorithm in substructuring experiments is examined in this paper. Substructuring is a method of dynamically testing a system by splitting it into two parts, one of which contains the region of particular interest and is tested experimentally. The rest of the system is contained in the second part and is modelled numerically. These two parts interact in real-time to emulate the complete system. For an accurate representation of the whole system, control of the displacements imposed on the experimental test specimen is crucial. In this paper, the performance of the MCS algorithm at controlling an actuator used to impose the displacement on the experimental specimen is examined for a one-degree-of-freedom system. Based on these results, an improvement to the MCS control strategy is proposed and tested. Finally, a comparison between the modified MCS-based control strategy and a linear controller is conducted to demonstrate the potential advantage of this adaptive strategy.

Computationally efficient modelling of permanent magnet synchronous motor drives for real-time Hardware-in-the-Loop simulation

Hardware-in-the-Loop testing allows the development and performance evaluation of a controller for a physical system in a realistic environment where the system under test is emulated in an accurate real-time simulation. The paper proposes the use of a computationally efficient, yet accurate approach for a real-time modeling of permanent magnet synchronous machines drive system. The proposed method is based on a synchronous reference frame approach where higher harmonics of the stator winding distribution and rotor magnet flux are fully represented up to a specified order. A procedure for extracting parameter from a set of Finite Element calculations is also reported. The real-time model is coded on a commercially available FPGA based platform. The proposed approach is verified on an interior permanent magnet synchronous motor designed for traction applications. Comparison of real-time implementation and experimental measurements on the actual motor are used to validate the proposed modeling.

Experiment informed methodology for thermal design of PM machines

The common approach used in the thermal design of electrical machines is calibrating thermal models based on the designers previous experience, or hardware tests on a prototype machine. This allows for various manufacture and assembly nuances to be accounted for in the design process, assuring accurate and computationally efficient predictions of the machine thermal behaviour. The post-manufacture calibration of thermal models from tests on a complete machine has limited use in development of machine topologies, where no previous experience or machine hardware exist. In this context, an experiment informed design technique that makes use of reduced order machine sub-assemblies presents an attractive alternative. In particular, the hardware manufacture cost and time is significantly reduced compared to the prototyping of the complete machine assembly. This allows for numerous hardware samples to be constructed and tested, to inform the machine design process. The use of the machine sub-assembly testing is focused, but not limited to identifying and quantifying various power loss and heat transfer phenomena. This paper reviews the applicability of the sub-assembly testing in a broader context of the machine design. The aim of the research focuses on formulating a basis for sub-assembly based, experiment informed methodology for the thermal design of electrical machines.

Hardware in the loop emulation of synchronous generators for aircraft power systems

Testing a piece of equipment under realistic operating conditions typical of a complex power system such as those for more electric aircraft application requires a significant effort in terms of costs and complexity of the experimental test rig. Significant advantages can be achieved by using the Power Hardware in-the-Loop (HIL) concept whereby the performances of a device under test are evaluated in an emulated environment of the remaining components of a complete system. This paper describes the application of the Power HIL concept to the emulation of a wound field synchronous generator of the type used in aircraft power systems. Modeling assumptions are detailed in the paper together with an experimental procedure for parameter extraction. The emulation is realized by a bespoke three phase MOSFET based inverter with appropriate output filters controlled by an FPGA based solution used for real time emulation.

Experimentally calibrated thermal stator modelling of AC machines for short-duty transient operation

This paper presents an approach to the thermal design of an AC machine where the application requires a low-duty transient operation. To provide accurate temperature predictions the design process has been informed with experimental data from tests on a stator-winding sector (motorette). These have been shown to be a time and cost-effective means of calibrating the thermal model of a full machine assembly, prior to manufacture of the final design. Such an approach is usually adopted in design analysis of machines with a concentrated winding topology. Here, the motorette testing has been extended to machines with distributed windings. In the interest of improving heat transfer from the winding body into the machine periphery, several alternative slot liner and impregnating materials have been compared. A total of nine stator section samples have been manufactured and evaluated. The performance trade-offs between the various combinations are discussed in detail alongside their ability to satisfy the design requirements. Based upon these experimental results three stator segment samples have been selected for transient duty analysis. A lumped parameter thermal model has been used and calibrated to match the performance of the experimental samples. This is turn has been used to predict the transient thermal performance of the full machine assembly, for the design specification. The most promising motorette variant has been selected for machine prototyping.