Research On The Power Converter Of Flywheel Energy Storage System

As an electromechanical conversion and storage device, flywheel energy storage system has many advantages including high efficiency, large energy storage density, fast dynamic response, no pollution and etc. It can be used in power systems in order to balance the grid energy fluctuations and optimize the power supply. The flywheel energy storage power converter for power peak adjustion is composed of two parts which are motor-side converter and grid-side converter. This paper investigates the overall topology of power converter, the control of motor-side converter, and the control of grid-side converter and the parallel of flywheel energy storage systems.The back-to-back double PWM converter which can be controlled flexibly in motor-side and grid-side is adopted through the comparison of advantages and disadvantages of the topology and the control strategy of power converter. According to the control system objective, the control strategy for the power output controlled by the motor-side converter and the balance of energy transfer controlled by grid-side converter is given after the topology was established.The double closed-loop control strategies in motor-side and grid-side converter are adopted. The control strategy of motor-side converter is composed of inner current-loop and external power-loop. It realizes the energy transmission control that the motor winding current is controlled by output of power-loop. The double closed-loop control strategy of grid-side converter is composed of inner current-loop and external voltage-loop. It realizes the energy passing balance between motor-side and grid-side with the aid of stabilizing the bus voltage. For the motor-side control, the drive control mode and the influence of different Pulse Width Modulation (PWM) are analyzed. In order to assure the grid-side converter running safely and reliably, an improved phase-locked loop method used for obtaining the grid voltage phase quickly and accurately is proposed, when the grid voltage is unbalance and distortion.The energy store of single flywheel system is limited. In order to achieve parallel operation of multi-flywheel system, the power distribution and current-sharing strategy control of parallel operation are analyzed respectively. The carrier phase-shifting technique is adopted in order to reduce the current harmonics of grid-side, when multiple systems operating in parallel. The improved carrier phase-shifting technique is presented in this paper to solve the problem that the effect of traditional carrier phase-shifting techniques is poor when the modulation ratio is small. The simulation models are established by Simulink including motor-side converter, grid-side converter and multi-flywheel system in parallel and the above mentioned problems are also investigated.At last, in order to verify the validity of the control strategy and topology of power converter, the complete test platform is developed, and the results of simulation and experiment are in good agreement.