Research On Design And Control Of Permanent Magnet Synchronous Motor Based Mechanical Elastic Energy Storage System

Energy storage technology is a key and core technology in peak shaving, frequency regulation, smart grid construction, and intermittent energy interconnected into the grid safeguard. It can be of enormous significance in four links of generation, transmission, distribution and utilization for power system. A new type of mechanical elastic energy storage based on spiral torsion spring is proposed in the paper. Its overall technological scheme, system design, model and control method are researched. The main work of the paper are as follows:(1) A new spiral torsion spring based mechanical elastic energy storage technology is presented. Selection of permanent magnet synchronous motor as the actuator, permanent magnet synchronous motor based mechanical elastic energy storage system is constructed. The technological realization scheme of the system is designed. Technological feasibility of the system is demonstrated and the key technologies involved in the system are analyzed.(2) Technological indexes of mechanical elastic energy storage are established. A differential evolution based structure optimum design method for spiral spring is proposed and a novel linkage type energy storage box with hand-in-hand structure is devised. Based on the technological indexes, energy storage characteristics of three common materials are discussed and energy storage characteristics of mechanical elastic energy storage technology are compared with those of other mainstream energy storage technologies. Based on physical design of spiral spring through conventional empirical formula method, the differential evolution algorithm utilized to optimize the structure of spiral spring is proposed with the optimization objective functions of maximum energy capacity and maximum energy density. The results show that technological indexes have comparative advantages in many aspects such as power density, self-discharge rate, operating temperature, and the optimized shape of spindle diameter, thickness and intensity coefficient for the spiral spring under different objective functions basically keeps the same; increasing of the thickness is one of the effective methods to enhance the energy capacity and energy density. For the issue of low energy storage capacity in single spring box, a novel linkage type energy storage box structure is devised. Through serial connection of multiple spiral spring boxes and design of a simple and exquisite structure, the linkage type of energy storage box increases the energy storage capacity and smooths the output characteristic of torque with no change of maximum output torque of energy storage box.(3) The whole system mathematical model for mechanical elastic energy storage is established. A general calculation method based on divisions of stage and state for variable moment of inertia is put forward. The curve of the relation between the torque of spiral spring and the working turns is built; and the torsional deformation characteristic of spiral spring in energy storage process is analyzed. In terms of the state changes and the corresponding stage divisions of spring coils in energy storage, the moment of inertia of real-time variation is calculated. The results show that the spiral spring continues to contract from internal wall of external housing to inner shaft or spindle in energy storage, which makes its torque unceasingly increase and moment of inertia gradually decrease. Based on this, the whole system mathematical model for permanent magnet synchronous motor based mechanical elastic energy storage system is constructed and this model expresses a nonlinearity in high order, multivariable and strong coupling.(4) In allusion to the simultaneous change of spring torque and moment of inertia and low speed demand for the system operating in energy storage process, and on consideration of the characteristic of model nonlinearity for permanent magnet synchronous motor, an improved nonlinear backstepping control scheme combining least squares identification with a forgetting factor and differential evolution optimization is presented. By means of least squares method with a forgetting factor simultaneously estimating the energy storage system's torque and moment of inertia, the estimations of torque and moment of inertia are inputted into the designed backstepping controller, and control parameters are optimized through adaptive differential evolution algorithm. The simulation results show that the proposed control scheme is able to inhibit the simultaneous change of spiral spring's torque and moment of inertia, makes the mechanical elastic energy storage system store energy stably under a given low speed, and lets the stator current output the expected values.(5) Aiming at the simultaneous change of external power supply's torque and moment of inertia for the system operating in power generation process, and taking structural parameters uncertainties for permanent magnet synchronous generator into account, a high gain observer based L2 robust backstepping control scheme is proposed. The changes of external power source features and internal structural parameters are expressed as the comprehensive disturbances in state space of motor model, and high gain observers are utilized to estimate the comprehensive disturbances. Then, by integrating the theory of L2 gain with backstepping control, a L2 robust backstepping controller is designed. The simulation results show that high gain observers enable to estimate the external and internal disturbances accurately, and the proposed control scheme not only suppresses the external and internal disturbances, but also guarantees the output current and operating speed of permanent magnet synchronous generator to track the respective references and realizes the system to generate electricity securely and efficiently.(6) On the basis of the above research work, the spiral spring and linkage type of energy storage box based on spring steel are developed, a small-sized principle prototype of permanent magnet synchronous motor based mechanical elastic energy storage system is implemented. Through experiments of energy storage and power generation operation in principle prototype, the correctness and effectiveness of the proposed design scheme, model and control method are validated.