Applications in Control of the Hybrid Power Systems

Abstract

This chapter analyses the control of the Hybrid Power Sources (HPS) based on some applications performed. Usually, a HPS combines two or more energy sources that work together with the Energy Storage Devices (ESD) to deliver power continuously to the DC load or to the AC load via the inverter system. In the automotive applications, the ESD stack can be charged from the regenerative braking power flow or from other power sources like the thermoelectric generator or the renewable source. The last may have a daily variable power flow such as the photovoltaic panels integrated into a car’s body or into buildings. In the first section, an efficient fuel cell/battery HPS topology is proposed for high power applications to obtain both performances in energy conversion efficiency and fuel cell ripple mitigation. This topology uses an inverter system directly powered from the appropriate Polymer Electrolyte Membrane Fuel Cell (PEMFC) stack that is the main power source and a buck Controlled Current Source (buck CCS) supplied by a batteries stack, which is the low power auxiliary source. The buck CCS is connected in parallel with the main power source, the PEMFC stack. Usually, the FC HPS supply inverter systems and PMFC current ripple normally appear in operation of the inverter system that is grid connected or supply the AC motors in vehicle applications. The Low Frequency (LF) ripple mitigation is based on the active nonlinear control placed in the tracking control loop of the fuel cell current ripple shape. So the buck CCS will generate an anti-ripple current that tracks the FC current shape. This anti-ripple current is injected into the output node of the HPS to mitigate the inverter current ripple. Consequently, the buck CCS must be designed in order to assure the dynamic requested in the control loop. The ripple mitigation performances are evaluated by some indicators related to the LF harmonics mitigation. It is shown that good performances are also obtained with the hysteretic current—mode control, but the nonlinear control has better performances. The nonlinear control of the buck CCS is implemented based on a piecewise linear control law. This control law is simply designed based on the inverse gain that is computed to give a constant answer for all levels of the LF current ripple. The control performances are shown by the simulations performed. Finally, the designed control law will be validated using a Fuzzy Logic Controller (FLC). In the second and the third section is proposed and analysed a nonlinear control for FC HPS based on bi-buck topology that further improves FC performance and its durability in use in the low and medium power applications. The nonlinear voltage control is analysed and designed in the second section using a systematic approach. The design goal is to stabilise the HPS output voltage. This voltage must have a low voltage ripple. Additionally, the power spectrum of this ripple must be spread in a wide frequencies band using an anti-chaos control. All the results have been validated with several simulations.