Design Of Controller For Photovoltaic Generation System Based On CAN Bus

With shortage of coal, natural gas, other traditional energy and global climate changes, the development of new energy resource represented by wind energy, solar energy has been an inevitable trend. Photovoltaic generation is a hotspot of the whole world develops among various applications of solar. Controller is the core of photovoltaic generation system, responsible for control of battery charge, discharge and system protection. The controller for stand-alone photovoltaic generation most adopt one-unit control model with a fixed capacity disadvantage. In order to meet the demand of various capacities photovoltaic generation, controller adopts two-stage control architecture. Power module is controlled by main-control module. Charging and discharging circuit is controlled by power module. Controller extends capacity of system in modularized way was achieved. As the CAN-bus with characteristics of high real-time, more nodes, CAN bus is used as the data transferring channels in control system. The main works of the thesis include the following five aspects:1) Strategy of charging with the N+1 redundancy mode was established. Controller controls charging array throw-in and cut-out according to the gradient-voltage. Gradient-voltage automatically adapt to changes in the number of charging array. The charging strategy made that charging curve is more stable, working life of battery is extend, good power supply of the load is achieved.2) To achieve data exchange through CAN bus between main-control module and power module, the structure of CAN bus message, the bit timing of CAN bus and the communication mode of CAN bus are discussed. With the CAN2.0B specification, the communication protocol of system is established.3) Hardware circuit was designed which applies the high performance AT90CAN128 as the main-control chip. Multiple parallel MOSFET driven by the transistor is applied in the charging and discharging control circuit. The design not only improves the circuit reliability, but also prevents the damage of reverse charging. The designed of double constant current source 3-wire platinum resistance temperature compensation circuit eliminates the error of leading wire and makes the temperature more accurate.4) System software of controller is designed in the GCC platform The software functions is achieved, which contains the control of the charging and discharging of storage battery, over-voltage/low-voltage protection, voltage acquisition of the storage battery and solar array, current acquisition of the charging and discharging process, communication through CAN bus, compensation of temperature and display of running dada.5) Base on the 48V stand-alone photovoltaic generation system, controller prototype has been tested. The result of test proves that the design of modular controller is feasible. The design has some guiding significance for engineering applications.