Research On Grid-Connected Control Method For Flywheel Energy Storage System

Flywheel energy storage system is a kind of energy storage device that uses highspeed rotating flywheel for energy storage,it is widely used in new energy generation,peak load and frequency regulation of power grid,vehicle regenerative braking,UPS power supply and other fields because of its advantages of high efficiency,long life and no pollution.In this paper,flywheel energy storage system is studied,including sensorless control technology of flywheel motor and grid-connected control method of flywheel energy storage system.Firstly,by comparing different types of motors,a PMSM is selected as the flywheel drive motor.The mathematical models of PMSM in ABC natural coordinate system,in ?? stationary coordinate system and in dq synchronous rotation coordinate system are established,which provide theoretical reference for the control of PMSM.The common control method of PMSM is introduced.Secondly,sensorless control technology of PMSM for FESS is studied.In order to overcome the chattering and phase delay of the traditional sliding mode observer,the current observer and the low-pass filter are improved respectively.The I/F control strategy is adopted in startup and low speeds operation stage of the flywheel motor to overcome the defects of too small reverse potential in start-up stage and the inability of sliding mode observer to accurately estimate rotor speed and position.The flywheel motor sensorless control at the whole speed range is realized.Simulation results validate the effctiveness of the improved sensorless motor control technology.Finally,the quasi-proportional resonance control and capacitive current feedback control are studied and applied to grid-connected control of FESS.A grid-connected control method for FESS is proposed.The control process includes charge,stand-by and grid-connected stages.At charge stage,the control of grid-side converter works on an outer voltage loop,while the flywheel-side converter adopts an outer speed loop.At standby and grid-connected stage,the control of grid-side converter adopts direct power control strategy based on a grid-side current loop cascaded with an inner capacitor current loop;the control of flywheel-side converter is based on an outer DC-bus voltage loop cascaded with an internal current loop,and maintains the DC-bus voltage.The parameters of the grid side controller are designed by the generalized root locus method.The grid connection model of the flywheel energy storage system is established,which verifies the good control performance of quasi-proportional resonance control and capacitor current control.