【作者】 张健；

【导师】 郑宏；

【作者基本信息】 江苏大学 ， 电力电子与电力传动， 2010， 硕士

【摘要】 随着全球能源危机和环境污染的日益严重,太阳能的开发和利用受到世界各国的普遍关注。光伏并网发电是太阳能光伏利用的主要发展趋势,必将得到快速的发展。在此背景下,本文对光伏并网逆变器的拓扑结构和并网控制方案进行了重点研究。传统的两电平并网逆变器开关损耗大,直流电压利用低,输出电流谐波高,无法实现高压高质量的并网要求。本文采用了三电平NPC光伏并网逆变主电路,分析了其工作原理,着重研究了空间矢量PWM调制方法。针对三电平逆变器直流侧中点电位不平衡问题,从空间矢量PWM调制方法的角度出发,本文采用了一种只需检测各相电流和中点电压波动的方向,动态调整正负小矢量作用时间实现中点电位平衡控制方法。仿真结果验证了方法的有效性。建立了三电平并网逆变器在静止ABC坐标系下的数学模型,通过坐标变换,推导了同步旋转dq坐标系下的数学模型。为了实现并网电流的跟踪控制,本文在旋转dq坐标系下提出了电流重复预测无差拍控制方案。构造状态观测器,对逆变器下一拍输出电流进行预报,补偿数字控制系统存在时间上的延时;同时,构造重复预测观测器,对下一时刻指令电流进行预测,在相同的采样频率下提供更为精确的并网电流预测值。整个方案消除了延时对控制系统的影响,实现无静差跟踪指令电流,动态响应快,降低了并网输出电流畸变率,改善了系统的控制性能。仿真结果表明了该方案的有效性和可行性。更多还原

【Abstract】 With the situation of global energy crisis and environment pollution becoming more and more serious, the whole world pays more attention on exploiting and utilizing the solar energy. The PV grid-connected system is the main utilization of the solar energy, so it will be developed rapidly. Under this background, the topology and control strategies of the PV grid-connected inverter are researched deeply in this paper.Traditional two-level inverter has disadvantages of large switching loss, low DC voltage utilization rate and high output current harmonics, so it couldn’t fulfill high quality of the gird-connect system. Three-level NPC inverter is introduced for the gird-connect system in this paper. SVPWM modulation scheme of Three-level inverter is introduced in detail. Neutral-point potential unbalance is an inherent problem of three-level NPC inverter, so a neutral-point control method which is based on directions of the three-phase output current and the neutral-point voltage to regulate the action times of positive and negative small vector is adopted. Availability of the method is testified by the simulation results.The mathematic model in ABC three-phase static coordinate of the three-level inverter is set up. Using coordinate transformation, the mathematic model in dq two-phase rotating coordinate is established. To actualize the gird-connected current tracking control, this paper presents a deadbeat repetitive predictive current control scheme in dq two-phase rotating coordinate. The state observer is designed to obtain the predictive output current value and compensate the time delay of digital control system. At the same time, the current repetitive predictor is adopted to achieve better prediction of the grid-connected current with the same sampling frequency. This scheme has merits of reducing output current harmonics, improving the effect of time delay and the overall performance of the system. The feasibility and correctness of the proposed control strategy are verified by simulation results.更多还原