基于变开关频率的IGBT功率模块结温控制

发布时间：2018-12-24 11:12

【摘要】：由于风电变流器运行工况越来越复杂,使得对风电系统可靠性要求也越来越高。功率器件结温的波动是引起器件故障的主要因素,而器件结温的波动是随着风机输出功率变化而变化。因此,跟随风机输出功率的变化,实时的调节器件结温显得十分有必要。目前,主要的结温控制方式包括:以外部散热或冷却的方式来调节功率器件结温的外部结温控制和以控制功率器件损耗为基础的内部结温控制。前者主要是调节器件的平均结温,对器件结温的波动情况调节效果较差。由于开关频率对功率器件的损耗影响较大,因此本文采用变开关频率的内部结温控制方式,来实现风机中功率器件结温的调节来开展研究工作。为分析开关频率对IGBT功率模块损耗和结温的影响情况,本文首先对三相并网逆变器IGBT功率模块损耗进行了分析。针对传统的三相逆变器功率器件损耗模型局限于SPWM调制策略、对器件结温对损耗影响的分析不足等问题,本文推导了SVPWM调制下的三相并网逆变器功率器件损耗计算公式,该公式中引入了结温反馈量,并根据功率器件用户使用参数,采用曲线拟合的方式对IGBT功率器件损耗进行计算,并分析了开关频率对IGBT功率模块损耗的影响,为变开关频率调节结温提供了理论依据。其次,由于开关频率是影响IGBT功率模块损耗的重要因素,为实现IGBT功率模块结温的有效控制,本文提出了一种实时变开关频率的IGBT功率模块结温控制方法,通过建立风电变流器结温预测模型提取变开关频率结温控制参数,获得了流过IGBT的电流、开关频率、IGBT功率模块结温波动值的函数关系式,并通过仿真验证了运用该函数关系式对IGBT功率模块结温进行控制的可行性。然后,为在数字电路中实现三相并网逆变器变开关频率控制,本文提出了一种基于FPGA的变开关频率实现方法,该方法根据FPGA自上而下的设计思路以及并行运行的特点,将整个控制模块划分为多个子模块,每个子模块相对独立并行运行,通过VHDL语言编写SVPWM算法模块、Cordic算法模块、三相锁相环等子模块的逻辑行为,并通过Modelsim软件仿真验证模块的算法逻辑,从而验证了SVPWM调制下三相逆变器变开关频率的可行性。最后,搭建三相逆变器变开关结温控制实验平台,以DSP作为采样部分,FPGA作为控制核心,实现输出电流变化时,开关频率的变化情况对比。从而验证了提出变开关频率结温控制方法的合理性以及可行性。
[Abstract]:Because of the more and more complex operating conditions of wind power converter, the reliability requirement of wind power system is becoming more and more high. The fluctuation of junction temperature of power device is the main factor that causes device fault, and the fluctuation of device junction temperature changes with the change of fan output power. Therefore, following the change of fan output power, it is necessary to adjust the device junction temperature in real time. At present, the main control methods of junction temperature include the external junction temperature control based on external heat dissipation or cooling and the internal junction temperature control based on the control of power device loss. The former mainly adjusts the average junction temperature of the device, and the effect on the fluctuation of the device junction temperature is poor. Because the switching frequency has a great influence on the loss of power devices, the internal junction temperature control mode with variable switching frequency is adopted in this paper to realize the adjustment of junction temperature of power devices in the fan to carry out the research work. In order to analyze the influence of switching frequency on the loss and junction temperature of IGBT power module, the loss of IGBT power module of three-phase grid-connected inverter is analyzed in this paper. Aiming at the problem that the traditional power device loss model of three-phase inverter is limited to SPWM modulation strategy, and the influence of device junction temperature on loss is insufficient, this paper deduces the formula for calculating power device loss of three-phase grid-connected inverter under SVPWM modulation. According to the user parameters of power devices, the loss of IGBT power devices is calculated by curve fitting, and the influence of switching frequency on the loss of IGBT power modules is analyzed. It provides a theoretical basis for changing switching frequency to adjust junction temperature. Secondly, because switching frequency is an important factor that affects the loss of IGBT power module, in order to realize the effective control of the junction temperature of IGBT power module, this paper presents a real-time switching frequency control method for IGBT power module junction temperature. Through the establishment of wind power converter junction temperature prediction model to extract the variable switching frequency junction temperature control parameters, obtained the current, switching frequency, IGBT power module junction temperature fluctuation value of the functional expression. The feasibility of using the function relation to control the junction temperature of IGBT power module is verified by simulation. Then, in order to realize the variable switching frequency control of three-phase grid-connected inverter in digital circuit, this paper presents a method of realizing variable switching frequency based on FPGA. The method is based on the top-down design idea of FPGA and the characteristics of parallel operation. The whole control module is divided into several sub-modules, each module running independently and in parallel. The logic behavior of SVPWM algorithm module, Cordic algorithm module and three-phase phase-locked loop sub-module are programmed by VHDL language. The algorithm logic of the module is verified by Modelsim software simulation, which verifies the feasibility of variable switching frequency of three-phase inverter under SVPWM modulation. Finally, a three-phase inverter variable switch junction temperature control experimental platform is built, with DSP as the sampling part and FPGA as the control core, the switching frequency changes are compared when the output current changes. The rationality and feasibility of the proposed method are verified.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN322.8;TM464

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