Implementation of Emergency Protections for the Electric Drive of Small-Capacity Fans

Abstract

The paper deals with the design of an inverter supplying power to the drive of fans cooling the subway car brake resistors and the traction electric drive power converter’s heat sink fins. Since this fan drive is a low-capacity one, it was decided to make the inverter for it with the minimal possible cost. To achieve the desired objective, it was decided to exclude protections from certain very unlikely emergency modes. It was proposed to use cheap IC chips of transistor switch drivers and to implement short-circuit protection using current transformers. The current transformers have a very large bandwidth and can be used in the application in question not only to protect the motor, but also to protect the inverter transistor switches. The current transformer signals are rectified by a low-capacity rectifier, thus making it possible to eliminate separate processing of the phase current positive and negative half-waves. The rectified signals are fed to the input of the protection circuit implemented on operational amplifiers. The total time of short-circuit protection system response to the input signal is about 1 μs. In measuring the current transformers’ output signals, it is possible to obtain a sufficient amount of data for making overload protection, phase open-circuit fault protection, load imbalance protection, and thermal protection. Emergency modes detection algorithms for implementing them in the scope of the electric drive microprocessor control system are presented. The proposed solutions were investigated on a mathematical model and on the inverter mockup prototype, and the obtained results have demonstrated their efficiency.