An Improved Charging Method of IPMSM-integrated Boost Converter for Electric Vehicles

Abstract

As electric vehicles’ (EVs) driving range increases, there’s a simultaneous rise in battery capacity and charger power ratings. However, the allowable charging current is limited by some factors such as the weight and volume of the charging cable and conductors. To accommodate higher charging power, EVs are now being equipped with high-voltage batteries, surpassing 800V. Many existing charging stations are designed for 400V batteries. An addi- tional boost on-board charger (400V to 800V) is required for charging at existing charging stations. However, the weight and volume of the additional boost con- verter capable of fast charging places a significant burden on EVs. To solve these problems, methods of charging batteries using EV motors and inverters have recently been studied. This integrated charger facilitates high-power charg- ing without necessitating an additional DC-DC converter, reducing the weight and volume of power conversion devices within EVs. When employing an Interior Permanent Magnet Synchronous Machine (IPMSM) as three-phase boost inductors, phase current ripple tends to be larger than dur- ing propulsion operation. Large phase current ripple limits the charging capacity of motors and inverters below their rated power levels. Furthermore, due to the complex nature of the IPMSM’s phase current waveform, accurately measuring its average using existing sampling methods is challenging. This inaccuracy in averaging contributes to motor rotational torque, raising safety concerns during charging. In this study, a complete analysis of phase currents was derived using IPMSM’s matrix inductance model, and current ripple was expressed as a function of rotor angle and switching duty. Based on this analysis, the maximum charging current and power were derived and the specific rotor angles that allow for maximum power charging were calculated. Additionally, challenges in measuring average current when sensing coupled phase currents of the IPMSM through single or double sampling methods were addressed. An average compensation algorithm for phase currents was proposed, ensuring zero torque charging conditions by equalizing the phase currents. Furthermore, an algorithm was introduced to estimate the motor angle and diagnose potential malfunctions in the motor position sensor during EV charg- ing. This algorithm estimates angular information based on the ripple equations which are the sinusoidal functions of the rotor angle. The proposed angle estima- tion algorithm, utilizing the Phase-Locked Loop (PLL) technique, can accurately estimate the precise rotor angle, regardless of motor and system parameters. The derived equations and algorithms were verified through simulations and experiments.