Integrated drive using motor windings for electric vehicle application
Creators: name: Niakinezhad, Mehdi
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400907
subject: Industrial electronics

description: Recent trends in Electric Vehicle (EV) technology have attempted to integrate the motor drive and on-board battery charger into a single circuit and minimize the weight and volume of the overall system. This technology is referred to as an integrated drive. The objectives of designing an integrated drive include maximizing efficiency, fault tolerance, Power Factor Correction (PFC) capability, galvanic isolation, battery voltage equalization, Constant Current-Constant Voltage (CCCV), fast charging capability and multi-power source support. New research attempt to utilize the motor windings as the inductive elements in the battery charging process. Thereby it can eliminate the use of additional heavy inductors in charging circuitry. This requires zero torque production during the charging process.

This research investigates integrated drive topologies for Switched Reluctance Motors (SRMs). During the research project, three new power electronic topologies are proposed and simulated via extensive simulations in finite element modelling software (Maxwell) and MATLAB/Simulink.

The first topology is based on a modular asymmetrical half-bridge integrated drive designed for a 12/8 SRM. The drive can be utilized in driving and charging modes and does not require any circuit reconfiguration to switch between two modes. However, this circuit requires the SRM windings to be split and tapped at the centre. In addition to high degree of fault tolerance, voltage equalization of the battery packs can be achieved with ease in both idle and charging modes. A power factor correction strategy is applied to shape the grid side current. Simulations have been conducted based on 100kW 12/8 SRM with 400V rated voltage. The simulation shows that despite different SoC levels (e.g., test case of SOCB1=30%, SOCB2=45%, SOCB3=60%, SOCB4=10%, SOCB5=25%, SOCB6=40%) all the batteries reach to the same SoC after 4 hours. Also, the input inductance from AC grid point of view is almost constant with negligible fluctuation. Therefore, the DC-DC converter operation is not affected by variation of the SRM inductance with rotor position at standstill. In addition, FFT analysis of the input current shows total harmonic distortion (THD) less than 4% with unity power factor.

The second topology presented in this thesis is a multiport integrated drive for an SRM with an additional relay placed strategically to switch the winding to the AC grid for charging mode. The proposed circuit achieves CCCV charging of the on-board battery. In addition, unity power factor on the AC side is achieved without using any additional circuitry. In order to assess the performance of the proposed circuit and control strategy for this integrated multi-level converter, simulations have been performed for a 60kW, three phase 6/4 SRM in MATLAB/Simulink. It was shown that the dc-link voltage ripple in driving mode is reasonably low (around 4V) around 0.6% of the nominal dc-link voltage. This is in line with the contribution of this topology in driving mode. It is also proven that the charger can achieve 3.4% and 3.57% input current THDs for minimum and maximum input inductances, respectively. Also, the dc-link voltage ripple is around 30Vpp while its voltage level is set to 600V. CCCV charging process for a 120Ah battery with initial 25% SoC is also simulated. The control circuit is able to conduct CC initially till the SoC level reaches around 80% with set-point current of 30A and then transits to 220V CV charging.

The third circuit topology proposed in this research is based on a form of Split-rail asymmetric half bridge converter as an SRM drive and enables hybrid power source integration. The proposed charger has the ability to charge the on-board battery pack with AC power as well as with a secondary DC source, e.g., a Photo-voltaic (PV) array as considered in this thesis. The PV power is extracted using Maximum Power Point Tracking (MPPT) algorithm and the charging of battery is performed with CCCV strategy. The control is designed in a way that the PV array is treated as the priority power source and the deficit power is supplied by the AC grid to fulfil the output power requirement. Extensive simulation results are provided to illustrate the performance of the proposed integrated charger circuit a 16 panel PV array. The irradiance of the PV array changes between 350 to 1000 W/m2 and the MPPT controller is able to extract the maximum power from the solar panels. The dc-link voltage is maintained at 400V with a ripple of 10Vpp. The distribution of power is achieved in such a way that the PV array is treated as the priority power source while only the surplus power is delivered by the AC grid. Simulation results shows the input THD of around 2.7%. Since the input current is phase locked with the input voltage PFC is guaranteed.