Design and development of a traction motor emulator using a three-phase bidirectional buck-boost AC-DC converter

Abstract

An industrial drive testing, with a ‘real-machine’ can pave way, for some serious issues to test-bench, motor, and the operator. A slight disturbance in control logic amid testing, can damage the physical machine or drive. Such dangerous testing conditions can be avoided by supplanting real motor with a power electronic converter based ‘Motor Emulator’ (ME) test-bench system. The conventional ME comprises of two-stage three-phase AC-DC-AC conversion with first-stage AC-DC as emulator and second-stage DC-AC as regenerating unit. This two-stage power conversion, require independent control algorithm, burdening control complexity as well as the number of power electronic switches are quite significant. Therefore, to economize and downsize conventional multistage ME system, this research work experimentally validates a common-DC-bus-configured ME system with only the AC-DC regenerative emulator stage. A bidirectional three-phase AC-DC converter is proposed as the regenerative emulator converter in a common-DC-Bus-configured ME system. The Proposed converter’s operating principle along with mathematical design and control strategy are also presented. To validate the operation of the proposed converter as a common DC-bus-configured emulator, two permanent magnet synchronous motors (PMSM) of 7.5 kW and 2.0 kW are emulated and their simulation and experimental results are presented here. The proposed bi-directional converter inspired from classical buck-boost operation, requires just ten unidirectional IGBT switches preventing any circulating current in the system. The proposed converter also eliminates the regenerative converter stage in classical ME system. Also, the proposed common-DC-bus-configured ME system requires a single stage control unlike independent control in existing ME system. The proposed converter provides four-quadrant operation and emulation of motor under study. The dynamic model of PMSM motor is simulated on the MATLAB simulation platform and the Simulation results are compared with experimental results. From the simulation and experimental results, it is concluded that, with the presented control scheme, the proposed ME converter can be made to draw the same current as a real machine would have drawn, had it been driven by the same DUT. Since, the output current of proposed converter is fed back to DC bus, the input power source requirement is reduced, making the overall ME system more energy efficient.