【作者】 刘子建；

【导师】 吴敏；

【作者基本信息】 中南大学 ， 控制理论与控制工程， 2010， 博士

【摘要】 四象限级联型多电平逆变器采用电压型PWM整流器取代传统级联型多电平逆变器中的二极管整流器,从而能够实现能量的双向流动,克服传统级联型多电平逆变器不能再生运行的局限性,扩展级联型多电平逆变器的应用范围。它通过多个功率单元的串联来实现高压输出,每个功率单元由网侧电压型PWM整流器、直流电容和电机侧H桥逆变器组成。每个网侧电压型PWM整流器需要单独控制,所有的H桥逆变器能够统一调制。四象限级联型多电平逆变器主要应用于高压大功率交流电机变频调速领域。本文针对四象限级联型多电平逆变器,从网侧电压型PWM整流器的控制、电机侧H桥逆变器的调制和级联型多电平逆变器在高压大功率交流电机调速系统中的应用等三个方面展开研究,通过仿真分析验证了所提的所有控制策略和调制方法的有效性,取得的研究成果主要包括以下几个方面。(1)网侧电压型PWM整流器的非线性控制策略针对三相电压型PWM整流器,提出了2种非线性控制策略。在第1种控制策略中,电流内环采用滑模控制,根据趋近律算法设计滑模控制器,提高了系统对参数扰动的鲁棒性,具有设计过程简单,易于实现的优点。电压外环采用负载电流前馈控制和输出直流电压反馈控制相结合的方法,既充分发挥了前馈控制作用及时的优点,又保持了反馈控制能克服多个扰动和具有对被调量实现反馈检验的长处。在第2种控制策略中,采用自抗扰控制技术设计了电压和电流控制器,控制系统对负载扰动和参数扰动具有很强的鲁棒性。(2)电机侧H桥逆变器的PWM方法将空间矢量控制技术分别应用到采用5电平H桥逆变器的级联型多电平逆变器和非对称级联型多电平逆变器的调制中,这种调制方式能够使级联型多电平逆变器以较低的开关频率输出接近正弦波的电压且只有很低的共模电压,从而有效地降低了开关损耗,提高了转换效率(3)级联型多电平逆变器在异步电机调速系统中的应用提出了一种级联型多电平逆变器供电的异步电机矢量控制方案,该方案采用自抗扰控制技术设计速度控制器,利用载波移相脉宽调制方法生成级联型多电平逆变器的开关信号,通过自适应观测器来观测转子磁链。仿真结果表明,系统具有良好的动态和静态性能。提出了一种级联型多电平逆变器供电的异步电机直接转矩控制方案,该方案采用圆形磁链轨迹的直接转矩控制技术得到参考电压矢量,利用载波移相脉宽调制技术生成级联型多电平逆变器的开关信号,通过自适应观测器来观测定子磁链。仿真结果表明,在整个速度范围内,转矩的脉动都比较小。(4)级联型多电平逆变器在永磁同步电机调速系统中的应用提出了一种永磁同步电机矢量控制方案,该方案通过滑模控制技术和自抗扰控制技术来实现永磁同步电机的高性能控制,永磁同步电机既可以采用两电平逆变器供电,也可以采用级联型多电平逆变器供电。仿真结果表明,系统具有良好的动态和静态性能。提出了一种永磁同步电机直接转矩控制方案。在该方案中,设计了一种自适应定子磁链观测器,该观测器能快速准确地估计定子磁链和定子电阻；采用自抗扰控制技术设计了速度控制器,该控制器能对负载扰动进行估计和补偿；采用了基于负载角控制的直接转矩控制技术得到参考电压矢量,利用载波移相脉宽调制技术生成级联型多电平逆变器的开关信号。仿真结果表明,在整个速度范围内,转矩的脉动都比较小。(5)中点箝位式三电平逆变器的空间矢量脉宽调制提出了一种具有中点电位平衡控制的中点箝位式三电平逆变器空间矢量PWM方法,该方法只需检测中点电流方向和电容电压,通过调整冗余小电压矢量对的作用时间来控制中点电位,具有控制算法简单,易于实现的优点。当网侧电压型PWM整流器采用中点箝位式三电平PWM整流器,就可以采用该空间矢量PWM方法。更多还原

【Abstract】 Compared with a conventional cascaded multilevel inverter (CMI) using the diode rectifiers and limiting regeneration operation, a four-quadrant CMI using the voltage source PWM rectifiers enables a bidirectional power flow and finds wider application fields than the classical one. A CMI synthesizes a high-voltage output based on series connection of power cells, each consisting of a voltage source PWM rectifier at the line side, a dc capacitor, and a H-bridge inverter at the motor side. Each voltage source PWM rectifier at the line side needs to be individually controlled, while all the H-bridge inverters are subject to unified modulation. The four-quadrant CMIs are mainly applied in variable frequency speed control field of high-voltage high-power ac electric machines.This dissertation studies the four-quadrant CMI from three aspects: the control of the voltage source PWM rectifiers at the line side, the modulation of the H-bridge inverters at the motor side, and its application in the speed control systems of high-voltage high-power ac electric machines. All the control strategies and modulation methods presented here are verified to be valid by simulation analysis. The main research fields and results are as follows.(1) The nonlinear control strategy for the voltage source PWM rectifier at the line sideTwo nonlinear control strategies for the three phase voltage source PWM rectifier are put forward. For the first strategy, the sliding mode control was applied to the inner current control loop, and a sliding mode controller was designed according to the reaching law algorithm, which raised the robustness of the system rejecting the disturbance of the parameters. The advantages of the first strategy lie in the simple design and the easy implementation. The control of the outer voltage loop combines the feed-forward control of the load current and the feedback control of the output dc voltage. This combination brings the advantage into full play of the timely operation of the feed-forward control, while keeps the other advantage of the feedback control rejecting other disturbances and checking the feedback of the controlled variables. For the second strategy, a voltage controller and a current controller were designed by the active disturbance rejection control (ADRC) technique, and the corresponding control system manifests high robustness in rejecting disturbances from the load and some other parameters. (2) The PWM technique for the H-bridge inverters at the motor sideSpace vector control technique was respectively applied to modulating a CMI using five-level H-bridge inverters and an asymmetric CMI. This modulation method enables a CMI to generate almost sinusoidal voltage at low switching frequency and low common-mode voltage, thus effectively reducing switching losses, and raising conversion efficiency.(3) The application of the CMI in the speed control system of an asynchronous machineA vector control scheme was put forward for an asynchronous machine driven by a CMI. The scheme involves the design of a speed controller by an ADRC technique, the generation of the switching signals by the carrier phase-shifted PWM method, and the using of an adaptive observer for the rotor flux. The simulation results have shown that the system has good dynamic and static performance.A direct torque control scheme was presented for an asynchronous machine driven by a CMI. The reference voltage vector was obtained by the direct torque control based on the radial flux trajectory, the switching signals for the CMI were generated by the carrier phase-shifted PWM method, and the stator flux was observed by an adaptive observer. The simulation results have shown that at any speed within the limit, the pulsation of the torque is small.(4) The application of CMI in the speed control system of a permanent magnet synchronous machineA vector control scheme was put forward for a permanent magnet synchronous machine. The scheme uses the sliding mode control technique and the ADRC technique to realize the high performance control of a permanent magnet synchronous machine driven by two-level inverter or CMI. The simulation results have shown that the system has good dynamic and static performance.A direct torque control scheme was designed for the permanent magnet synchronous machine. In this scheme, an adaptive stator flux observer was presented that can quickly and exactly estimate both the stator flux and the stator resistance. A speed controller was designed based on the ADRC technique that estimates and compensates the load disturbance. The reference voltage vector was obtained by a direct torque control technique based on the control of the load angle. The switching signals for the CMI were generated by the earner phase-shifted PWM method. The simulation results have shown that at any speed within the limit, the pulsation of the torque is small.(5) The space vector PWM of a neutral-point-clamped three level inverterA space vector PWM method was presented for a neutral-point-clamped three level inverter with the balancing control of the neutral-point potential. The method only needs to check the direction of the neutral-point current and the capacitor voltage. The neutral-point potential is controlled by rearranging the time distribution of the redundant small voltage vectors. The method only involves some simple calculations. This space vector PWM method can be easily applied as long as the PWM rectifiers at the line side are neutral-point-clamped three level ones.更多还原