Development of control strategy of DC-DC converter for optimal operation of PV powered Electrolyser

Abstract

With the current need of implementing renewable energy sources to combat climate change, significant developments are being done into storage options for these intermittent energy sources. Green Hydrogen can be produced by the connection of a renewable energy source to an electrolyser which produces hydrogen, in this project the Photovoltaic (PV) System is indirectly connected to the electrolyser as this gives the ability to control the different systems and flexibility in sizing the different systems. Several different dc/dc converters are simulated in Matlab Simulink and compared to each other while also taking into account the project requirements. First, an overview of the project is presented after which the main idea of the thesis is presented in which the dc/dc converters are selected for optimal operation of the system. Two converters are selected based on simulations and mathematical calculations (Component sizes, Voltage ripple & Current ripple), for the Maximum Power Tracking converter (Connected to the PV system) the buck-boost converter was selected. This was because of its ability to fully track the Current-Voltage curve of a PV system. And for the connection to the Electrolyser system a 3-level Interleaved Buck converter was selected, because of its increased reliability to be able to continue working after a power electronic switch failure. With the PV system maximum power point being between 580-582 V (depending on the irradiance) and a Electrolyser voltage range between 210 - 260 V, the voltage needed to be reduced. After selecting the different converters, a control system was modelled and simulated, this is to optimize and control the working points of the PV-Electrolyser system. This control system works on the idea of matching the electrolyser load working point to the available PV power from the input. This control algorithm selects the right reference voltage which then goes into a voltage controller to ensure the correct voltage is at the output for the electrolyser load. This control algorithm was modelled and simulated in Matlab simulink and tested against different changing inputs (Changing the irradiance & electrolyser temperature). Furthermore, the controller was checked for several different stepsizes and time delays (accounting for external effects) and the optimal combination was found to be a stepsize of 0.1V and timedelay of 1ms which gave an Converter+algorithm efficiency of 98.42%. The results demonstrate the controller’s ability to correctly follow the irradiance pattern and electrolyser temperature changes.