Design, Implementation and Validation of EV Powertrain and Safety Systems

Abstract

For reliable energy storage in the mid-voltage EV powertrain, correct sizing of the cells alone is not enough. The accumulator system must provide dependable electrical output throughout all system operational states, which include system initiation, operation, and shutdown, especially during fault-related equipment failures. This paper describes the development and verification of a 96V class modular lithium-ion accumulator configured in the 18p24s arrangement providing 88.8V and 100.8V nominal and maximum voltages correspondingly, with an approximate total usable energy storage of 6.5kWh.

The busbar system consists of two materials, where nickel is used for connections in parallel, while aluminium is used for connections in series. Such a configuration ensures balanced currents at the 200A operational rating. There are three protection devices employed and verified: a pre-charge circuit preventing high inrush current to the motor controller; a passive discharge path, which decreases the DC-link bus voltage to under 10V after the relay disconnection; a hardware-based Brake System Plausibility Device (BSPD) that triggers the disconnection of isolation relays when both brake and throttle switches are activated simultaneously without requiring software implementation.

 A 24s1p mini-accumulator was built to test its performance at the complete system voltage. This method prevented repeated fault tests on the entire 432-cell assembly. The precharge circuit needs about 3 seconds to reach 96 percent of the relay closure point according to the recorded data. The discharge circuit successfully reaches the 10 V requirement within the calculated time, while the BSPD functioned to the requirements completing relay isolation in less than one second. The analytical predictions are similar to the hardware measurements with high accuracy, which proves that lumped-parameter RC analysis is an effective method for designing protection circuits in the chosen voltage and capacitance range.