【作者】 汪洪亮；

【导师】 康勇； 裴雪军；

【作者基本信息】 华中科技大学 ， 电气工程， 2011， 博士

【摘要】 大功率的用电领域,柔性交流输电、高压直流输电、等都离不开大功率的电力电子装置。提高装置容量的有效途径是多台并联运行,死区对逆变器输出电压波形质量影响、逆变器并联系统特性影响和逆变器并联系统的限流保护(尤其短路)都是比较关键的问题。电感电流纹波较大场合下死区在某些特定区域不产生死区电压,以往的基于电流极性的2段式死区平均电压分析方法难以解释该现象。针对该问题,在2段式死区电压分析的基础上,本文提出了通用7段式死区电压分析方法,该方法根据电感电流的基波成分、纹波成分和零电流成分将电感电流划分为7种状态,并对双极性SPWM调制和单极性SPWM调制下7种状态的死区平均效应分别深入分析发现,单极性SPWM调制还与调制波的正负息息相关。带LC滤波器的逆变电源中,死区效应除了与直流电压、死区时间所占开关周期的百分比的定量关系,还与很多因素有关。为研究死区效应具体与哪些因素有关,文中提出了一种空载下的死区效应评估方法,并分别建立了双极性SPWM调制和单极性SPWM调制下的死区效应评估函数,给出了参数变化的死区效应强弱曲线。研究了死区效应与LC滤波器的谐振频率、开关频率等的关系。直接根据7段式死区效应进行死区补偿需要检测准确检测零电流钳位现象的时间,实现上较为困难。针对该问题,文中借鉴估算电感电流的方法,提出了一种基于间接电感电流的3段式死区补偿方法。该方法避免了直接检测电感电流7种状态,而是检测接近正弦的负载电流,计算出电感电流的3个区域,并进行死区补偿,实现上较为容易,仿真和实验验证了所提方法的有效性。无死区的逆变器并联系统中认为有功功率、无功功率与电压幅值、电压相位呈现线性关系、存在一个常系数矩阵对功率进行解耦。但带死区的空载逆变器并联系统中(以两台为例),以电压瞬时值为分析手段,初步得到存在一个以平衡点为圆心,死区电压峰值为半径的不敏感区域,位于该圆域外,环流有功、环流无功随电压幅值、电压相位的变化较为明显,且靠近该区域时曲线发生扭曲,环流有功、环流无功与电压幅值、电压相位构成的三维图近似为平面(线性关系)。位于该圆域内环流较小,环流有功、环流无功受滤波电容的影响较大。为研究组合式三相逆变器并联系统的限流保护,本文首先给出了组合式三相逆变器的数学模型,并介绍了正常情况下电压控制模式和异常情况下电流控制模式两种数学模型,在电压控制模式下引入重复控制改善了输出电压波形质量。两种模式的相互平稳切换是一大难点,短路故障时,采用硬件和软件相结合的限流方式很好地保证了单台独立运行和多台并联运行平稳地由电压控制模式切换到电流控制模式,短路故障消除后,利用同步信号保证了多台并联逆变器在同一时刻由电流控制模式切换到电压控制模式,避免了功率倒灌现象、直流电压泵升等一系列问题。2台400KVA组合式三相逆变器并联系统进行实验验证。更多还原

【Abstract】 With the development of the Power Electrical technology, the applications of high power devices in power field such as FACTS、HVDC are more important than before. It is usually used that several inverters operate in parallel operation for increasing capability. Dead time influence to improve the output voltage distortion and current limit protection (such as short circuit) for system safety are more and more attention.On the occasion of the large inductor current ripple, the dead-time effect is eliminated at most zero-crossing zone of the inductor current, which is hard to explain using the conventional average dead time analysis. For this problem, a usual analysis metod based on seven situations of inductor current according to zero current clamping phenomenon is proposed. This method breaks inductor current into 7 situations using fundamental value、current ripple and zero current clamping phenomenon. The analyses of dead time effect using in unipolar and bipolar SPWM are obtained.For the inverter with output LC filter, the dead time effect is is not only relative DC voltage, dead time, switching cycle, but also relative modulation method, filter frequency, load current and so on. Thus, an estimating method for dead time effect is proposed for the inverter working in no load, and the dead time effect estimating functions are built for biopolar SPWM and unipolar SPWM. the curves is obtained to visually express the relation between LC filer frequency、switching frequency and dead time effect.The proposed dead-time compensation method is based on adjusting promptly the compensation voltage in accordance with the seven situations of inductor current in theory. However, it is difficulties to determine seven situations around the zero current clamping (ZCC), as the seven situations of inductor current are variable with change of the load current, DC voltage. Thus, an improved inductor current detecting method with high precision is presented, which estimates the inductor current by detecting load current instead of inductor current. Therefore, the proposed dead-time compensation method is based on compensation voltage according to the three zones (positive zone, zero-crossing zone, and negative zone) of estimated inductor current in practice. The simulation and experiment results show the validity of the analysis and the effectiveness of the proposed dead-time compensation.For parallel inverters system without dead time, the active power and reactive power are connected with voltage amplitude, voltage phase. The 3D figure is the flat, which means that it is possible to decouple between active power and reactive power using a constant coefficient matrix. However, there is a no sensitive area once adding the dead time. The change of active power, reactive power is large with change of voltage amplitude and phase without in this area. On the contrary, the power change is not obvious with the varying of voltage amplitude and phase.For analysis of current limit protection technique in the parallel inverters system. Controlling the output voltage in normal operation constantly is named the voltage control mode (VCM), and controlling the output current constantly in abnormal operation conditions (such as short circuit) is named the current control mode (CCM). A hybrid control strategy is proposed. On the one hand, the PID control and the repetitive control are used in VCM to obtain the fast dynamic responses and low harmonic distortions. On the other hand, the state feedback control is used in CCM. Pole assignment has been employed in designing parameter of the PID controller and state feedback, and the repetitive control design process is given.For ensuring reliable operation of high power inverter happening in load shocking (such as short circuit), the switching model between VCM and CCM becomes one of key technologies. However, it is possible to yield large shock between several parallel inverters when switching from CCM to VCM isn’t in same time for parallel inverters. Thus, the large circulating current results in power flooding inversely, even more stoping inverters. An improved switching model technique is proposed only according to the synchronizing signals for ensuring the same time from CCM to VCM. Experimental results validate the proposed control strategy using two 400KVA parallel inverters.更多还原