Design Of Permanent Magnet Synchronous Generator Hydropower Grid-connected System Based On Dual PWM Converter

Small hydropower,as an important distributed energy in our country,plays an important role in flood prevention,ecology protection,promoting the construction of rural electrification and speeding up the economic development of poor areas.But the traditional small hydropower station adopts grid-connected directly hydraulic generator system structure,so the hydroturbine can only run at the rated speed.When the river flow or working water head of hydropower station changes,water power conversion efficiency of hydroturbine will decrease.Considering the above problems,this paper applies the structure of permanent magnet synchronous generator with dual PWM converter to the hydraulic power generation system to realize hydropower generation at the way of variable speed and constant frequency and improve the efficiency of hydropower generationFirstly,the structure of the hydropower grid-connected system of the permanent magnet synchronous generator is introduced.And the basic working principle and output power characteristics of the turbine are analyzed.The relationship between the output power of the hydroturbine and the opening of the guide vanes and speed is deduced.Based on the principle of vector transformation,a vector mathematical model of a permanent magnet synchronous generator,a dual PWM converter and the power grid is established Then the control principle of the grid-side converter and motor-side converter is analyzed.Secondly,the structure block diagram of the hydropower grid-connected control system is given.The maximum efficiency tracking control model of the hydroturbine is established based on the relationship between the output power of the hydroturbine and the opening of the guide vane and the speed.Considering the relationship of the output power of PMSG and the DC bus voltage and the speed,the unit power factor control is adopted to achieve power output when the load is small,switching to flux weakening control to improve the load capacity of PMSG by reasonably distributing the flux weakening current when the output power exceeds the DC bus voltage limit.And based on the flux weakening control principle and the traditional voltage feedback flux weakening control method,combined with the SVPWM modulation principle,a flux weakening control method based on non-zero voltage vector action time feedback is proposed to further increase the range of the voltage vector and decrease stator current.The synchronization control method of the power grid is introduced.Based on this,a grid-side power control model was established to achieve direct control of active and reactive power on the grid.Then the entire system was simulated and modeled using Simulink simulation softwareFinally,a 200kW hydropower grid-connected system platform is designed The hardware resource allocation of the system and the hardware circuit design of the dual PWM controller are introduced in detail.And the design ideas and design principles of some circuits are analyzed.Then the control software structure of the hardware platform,the implementation process of the host computer software and online programming software required for system debugging are introduced in detail.Ultimatly the original hydrogenerator system directly connected to the grid is replaced by the system in a hydropower station in Chenzhou,Hunan Province.The comparative experiment result shows that adopting variable speed and constant frequency power generation technology to adjust the speed of the hydroturbine can maintain the maximum hydropower conversion efficiency of the hydroturbine and significantly improve the utilization of water resources.And the advantages of power generation under low flow and low water head conditions are more obvious.