Cascade Control Solution for Traction Motor for Hybrid Electric Vehicles

In this paper a hybrid electric vehicle is considered, which contains both an internal combustion engine and an electric motor (EM). Without focusing on the other components of the vehicle, the EM is treated in detail, both regarding modelling aspects and control solutions. After a brief modelling of the plant, two cascade speed control solutions are presented: first a classical PI+PI cascade control solution is presented. The control systems related to traction electric motors (used in vehicle traction) must be able to cope with different requests, such as variation of the reference signal, load disturbances which depend on the transport conditions and parametric disturbances regarding changes in the total mass of the vehicle. For this purpose, in the design of the speed controller (external loop) a specific methodology based on extension of the symmetrical optimum method is presented. The controllers are developed using the Modulus–Optimum method for the inner loop, and the Extended Symmetrical Optimum Method, corrected based on the 2p-SO-method, for the outer loop (for a more efficient disturbance rejection). In order to force the behaviour of the system regarding the reference input, a correction term is introduced as a non-homogenous structured PI controller solution. Simulations were performed using numerical values taken from a real application consisting in a hybrid vehicle prototype, showing satisfactory behaviour.