Research On Power Converting And Control Technology Of Dual Mode Photovoltaic Energy Storage Hybrid Generation System

With the development of society and the gradual depletion of traditional energy, the solar energy, as the representative of the clean energy, has been paid more and more attention, and many countries have vigorously developed photovoltaic generation technology. In this paper, a dual mode photovoltaic energy storage hybrid generation system is designed. The operation modes of the system include grid connection and off grid. The designed scheme of power convert system and the corresponding control technology are mainly studied. The related simulation and physical test are proposed in detail.According to the mathematical model of photovoltaic cell, the output characteristic curves are studied. Aiming at the shortcoming of the traditional maximum power point tracking (MPPT) algorithm, a new MPPT algorithm called the improved perturbation and observation method is proposed. The new method has better performance in fast response and high precision, while it can also avoid the occurrence of oscillation. According to the off-grid mode with small load and full charged battery, photovoltaic limited power mode is designed. And the switching between MPPT and photovoltaic limited power mode is completed. The photovoltaic DC/DC converter is designed, and according to the operation mode, a control strategy based on duty cycle feedforward control and double loop control is proposed in this paper. The photovoltaic DC/DC converter using this control strategy has the characteristic of good dynamic performance and high precision, which can be in continuous operation under various conditions.According to the characteristics of the energy storage battery, the battery pack scheme is developed, and the energy storage DC/DC converter structure of the bidirectional Buck-Boost circuit is designed. Aiming at the control strategies of single current loop and voltage current dual loop, comparative analysis of the control effect of unipolar and bipolar PWM, single loop and dual loop control strategies of bipolar PWM is developed. The method has the advantages of current commutation stability and small overshoot.Based on the working principle of the dual mode inverter, the mathematical models of grid connection and off grid are established. Voltage oriented control and V/f control are selected to be the control strategies of the grid connected mode and the off-grid mode respectively. In view of the possible island problem, a simple and reliable active angular frequency perturbation method based on d-q phase locked loop, which has little effect on the stability of the system, is proposed to detect the islanding condition. The active damping control used in the dual mode inverter is carried out for the LCL filter circuit which can suppress the resonant current effectively and simply.The overall structure and control strategy of the dual mode photovoltaic energy storage hybrid generation system are designed. Finally, specific experiments were carried out by the experimental platform, and the results verified the feasibility and practicability of system design and control technology.