【作者】 章勇高；

【导师】 康勇； 张凯；

【作者基本信息】 华中科技大学 ， 电力电子与电力传动， 2007， 博士

【摘要】 高速功率开关器件的应用大大加快了电力电子装置的动态响应过程,降低了装置的体积与重量。然而功率器件的高速开关动作所引起电压与电流瞬变将会带来严重的电磁干扰(EMI)问题,其中共模EMI在变换器中占主要地位。国内外现已提出的共模EMI抑制方案大体分为改进PWM策略型、无源滤波型和有源/无源对消型三大类。针对目前共模EMI抑制中存在的问题,本文提出了采用全数字化并联有源共模EMI抑制技术,进行了以下六个方面的工作。第一,以单相全桥逆变器为例,对多桥臂开关变换器的共模EMI产生机理进行了研究,讨论了共模EMI噪声源和传播路径,指出基于噪声源串联等效电路的不足,提出了一种基于噪声源并联等效的单相全桥逆变器共模EMI等效电路。从时域和频域的角度,分析了单相全桥逆变器产生的共模电流波形与频谱特征,仿真与实验结果证明了并联等效电路的正确性。说明该等效电路适用叠加原理,能够更清晰地反映多桥臂电路中共模电流的传播机理。此外,该等效电路中每个桥臂中点的对地电容以及噪声源幅值都可以是不同的,为并联有源共模EMI抑制技术提供了理论基础,为补偿电路参数设计提供依据。第二,分析了单极倍频和双极性调制下单相全桥逆变器的共模电磁干扰,指出双极性SPWM调制下,单相全桥逆变器共模EMI理论上为0。但在实际装置中,由于驱动电路的传输延时不一致,导致两桥臂对角开关管驱动脉冲不能严格同步,从而使逆变器共模干扰变大。实验验证了预调整驱动脉冲沿能够有效的降低共模EMI水平,并提出了自调整驱动脉冲沿思路。对于不存在两个互补对称共模噪声源的场合,提出可以外加专门的补偿电路,实现并联有源共模EMI抑制。分析了并联有源共模EMI抑制中当补偿电流与噪声源共模电流大小相等方向相反时,补偿电路与被补偿桥臂的驱动信号延时不一致将影响共模电流抑制效果,与双极性调制下驱动脉冲延时不一致的问题具有相似性,指出共模噪声评估技术和脉冲沿闭环调整是系统中需要解决的两个主要技术。第三,针对数字化闭环控制系统中只需知道共模电流总体水平的变化趋势,并不需共模电流的详细频谱的情况,提出了以共模电流能量作为共模噪声的评估指标。研究了共模电流能量与全桥逆变器两桥臂对管的驱动信号延时之间的关系,结果表明共模电流能量在整个驱动信号延时时间内呈“V”字型对称衰减振荡,共模电流能量存在多个极小值。针对共模电流的检测问题,提出了两种方案:一是基于FPGA的共模电流检测系统,FPGA专门采样共模电流并计算共模电流能量,DSP实现变换器的控制并从FPGA读取共模电流能量,作为抑制控制系统中的反馈量;二是基于整流滤波后求能量的共模电流检测方法,通过分析整流滤波前后共模电流能量的关系说明了这种方法的可行性和有效性。此时,DSP既要控制变换器,又采集共模电流和计算共模电流能量。第四,根据共模电流能量与驱动信号延时之间的关系,针对大多情况下信号延时时间在±T/2(T为共模电流的振荡周期)范围内,关系曲线呈“V”型对称,提出基于局部最优搜索算法的共模电流能量搜索,同时指出当关系曲线中存在多个极小值时容易陷入局部最小值的缺陷。考虑DSP控制器中的编程实现,本文提出采用模拟退火搜索算法寻找共模电流能量的全局最小值。研究了模拟退火算法在共模电流能量和驱动脉冲延时关系曲线上的搜索过程,提出采用一种在搜索过程中保留中间最优解的改进模拟退火算法,通过仿真说明改进的模拟退火算法在搜索速度和搜索精度上的提高。第五,论述了数字化闭环控制的并联型共模电磁干扰抑制技术基本结构,讨论了直接并联补偿电路和间接并联补偿电路两种形式,即直接由逆变器直流母线提供以及外置低压直流电源。利用基于噪声源并联等效的共模电流模型讨论了补偿电路的输出电容和耦合电容的计算。通过实验验证了补偿电路输出电压的dv/dt以及输出电容影响着补偿电流的最大值和振荡频率。最后,建立了基于F2812数字化并联有源共模EMI抑制的单相半桥逆变器实验平台,通过高精密的全波整流滤波电路处理高频EMI电流,获取共模电流能量的评估指标,采用改进模拟退火搜索算法调整补偿电路驱动信号脉冲沿,实现共模电流最小能量的搜索,从而抑制EMI水平。实验结果表明了本文提出的基于模拟退火算法的数字化并联有源共模EMI抑制技术的正确性和有效性。更多还原

【Abstract】 With the application of high-speed high-power switch devices, the dynamic performance of power electronic products has been improved and the volumes and weight have become small. However, severe electromagnetic interference (EMI) is produced due to high dv/dt and high di/dt caused by high speed switching of power devices. There are basically two types of EMI in power electronics, namely common mode EMI and differential mode EMI. Common mode EMI usually constitutes a major part in total EMI. Recently, many efficient CM EMI suppression methods have been presented. They can be categorized into three classes: modified PWM strategies, passive filters and active/passive compensatory filters. To address the problem existed in the reported common mode EMI suppression technique, a novel active common mode EMI suppression method with digital closed-loop control is proposed in this dissertation. The six main researches are listed as following:Firstly, common mode conducted EMI in single-phase full-bridge converter is analyzed in this dissertation, it discuss the noise source and the flowing path of common mode current. Appoint the shortcoming of common mode current equivalent circuit based on noise source in series, and propose a novel equivalent cirvuit of common mode EMI based on noise source in parallel. Conducted EMI in single-phase full-bridge is analysize and identified in time domain and frequency domain. Simulation and experimental results prove the validity of proposed common mode EMI equivalent circuit. It is conclusion the proposed equivalent model can be the same with superposition principle, can make clear the radiate mechanism of common mode current in multi-bridge converter. Moreover, the equivalent parasitic capacitance and the magnitude of noise source voltage in proposed equivalent circuit can be different. The poposed equivalent circuit based on noise source in parallel is the basis of the active common mode EMI suppression method and the design of compensating circuit.Secondly, compared the conducted common mode EMI in full-bridge circuit with bipolar SPWM and unipolar SPWM modulate technique. It is conclusion that the conducted common mode current with bipolar SPWM modulation technique is theoretically zero because the two legs provide perfect CM current compensation for each other. However, different transmission delays of two drive signals in bipolar SPWM modulation technique always produce large CM current in real case. Experimental results validate fine-tunning driving signals before they are transmitted can suppression the common mode EMI in full-bridge converter efficiently, then an idea of fine-tunning driving signals technique with close-loop control system is proposed.Aim at the conditions without two complementary common mode noise sources, an active compensatory common mode EMI suppression technique with an external compensating circuit is proposed. In active compensatory common mode EMI suppression, when the compensating current and noise source common mode current are the same maginidute and anti-phase, whether driving signals transimmission delay of compensating circuit and main bridge are the same or not will impact the effect of common mode current suppression. It is conclusion the problem of anti-phase alignment and different transmission delays of two drive signals in bipolar SPWM modulation technique are similar, whose resolving method is the same. The two key techniques in fine-tuning system of the drive signals are common mode noise evaluation index and close-loop control stratery.Thirdly, Due to the change direction of common mode current level is needed in digitalized close-loop control system, and not the detailed current spectrum. A common mode noise evaluation index of the‘energy’of the common mode current is adopted here. The relationship between the common mode current energy and the delay time of the drive signals on the cross of two legs is studied. The result indicates that common mode current energy has several minimum values in the range of available time delay and the curve is symmetrical damp surge in‘V’figure.Aim at the detecting technique of common mode current, two schemes are put forward, they are as follows: one is common mode current detecting system based on FPGA. FPGA collect the common mode current and figure out the energy specially. The main controller DSP performs the converter control and picks up the common mode current energy values from FPGA, which considered as the feedback of digitalized close-loop control system. The other detecting technique is common mode current is treated by full wave rectifier and filter circuit firstly, then figure out the energy. This scheme is proved feasibility and validity in theory. At the time, DSP not only perform the converter control but also collect common mode current and calculate its energy.Fourthly, there are more than one local minimums of the common mode current energy in the relationship between the energy of common mode current the delay time of drive signals. In most cases the delay time of driving signals is in the range of±T/2, in which T the oscillating period of common mode current. It is proposed a local searching algorithm to search the minimum energy of CM current in the range of±T/2 when the curve is symmetrical damp surge in‘V’figure. At the same time it is explained the local searching algorithm is easy to get trapped at local minimums when there are more than one minimums energy of CM current in the curve. Considering of the fact that searching algorithm is preformed in DSP, this dissertation adopt simulated annealing algorithm to avoid getting trapped at local minimums. Application of simulated annealing algorithm (SAA) in find the global optimal energy value of common mode current is studied, and an improved SAA is proposed. In improved SAA, the ending criterion of annealing process and sampling process is modified in order to reserve the state of‘Best So Far’and improve the searching efficient. Simulation results show that the improved SAA has been increased in searching speed and searching precision.Fifthly, the basic configuration of digitalized close-loop control common mode EMI suppression technique is illustrated. Two kind of push-pull compensating circuit where the DC biased voltage source is provided by DC bus voltage of converter or external electric supply is discussed. The calculating process of output capacitor and coupling capacitor in active compensating circuit by using the common mode current equivalent mode based on noise source in parrellel. Experimental results verified the dv/dt of output voltage and output capacitance in active compensating circuit affects the peal value and the osicillation frequency of compensating current.At last, an experimental bench of single-phase half-bridge converter consists of digitalized active EMI suppression system based on F2812. High frequency common mode current is treated by high precision full-wave rectifier and filter circuit. Driving signals of compensating circuit are pre-adjusted by close-loop control system based on improved SAA. Experimental results show that Closed-loop control system with improved SAA can regulate the delay time of compensating current and suppress the common mode current noise level effectively.更多还原