【作者】 高吉磊；

【导师】 郑琼林；

【作者基本信息】 北京交通大学 ， 电力电子与电力传动， 2012， 博士

【摘要】 摘要：单相PWM整流器以高功率因数、低谐波含量以及能量可以双向流动等优点,广泛应用于新能源发电以及交流传动等领域。尽管与二极管整流相比,PWM整流器电网电流中的谐波含量大大降低,然而并不能完全消除,并受到各种因素的影响。随着PWM整流器的广泛应用,对提高其注入电网电流质量的研究受到越来越多的关注。首先建立了单相PWM整流器的数学模型,分析了直流电压脉动、电压谐波、电网电流预测误差以及电网参数对电网电流的影响。对于直流电压脉动引起的谐波电流,可以通过设置直流电压采样陷波器的方法,滤除进入控制环路中的二次脉动分量,抑制对电流环的影响。PWM脉宽调制及死区产生的谐波和电网电压谐波,均可以通过加入重复控制器或者谐振控制器的方法,提高PWM整流器在谐波频率处的输入阻抗,减小电网电流中的谐波含量。在光伏发电领域,单相PWM整流器主要用于小功率光伏并网逆变器,功率等级通常在5kW以下,开关频率在10kHz-20kHz之间,控制周期较短。针对单相光伏并网逆变器电流环具有较宽的带宽,以及重复控制数据运算量较小的特点,提出了采用无差拍控制和重复控制相结合的方法抑制电压谐波对电网电流的影响。分析了重复控制器参数对电流环鲁棒性以及动态性能的影响,给出了重复控制器参数的设计方法。研究表明较小的重复控制器增益系数有利于提高电流环的鲁棒性,并减小电网电流幅值阶跃变化时的畸变,但基波电流跟踪速度较慢。交流传动电力机车辅助供电系统中,单相PWM整流器的功率为上百千瓦,开关频率通常为2kHz-5kHz。开关频率的下降使电流环带宽变窄,但是控制周期变长,因而可采用带谐波补偿器的比例谐振控制,提高PWM整流器在谐波频率处的输入阻抗。由于基波和谐波谐振控制器具有不同的系数,提出了分别设置基波和谐波谐振控制器系数的方法,得到快速的基波电流动态响应,并达到稳态时抑制谐波电流的目的。目前谐波补偿器多采用并联式,即多个谐波频率处谐振控制器相加的形式。然而并联式谐波补偿器的设计方法难以直观的配置电流环零极点在z平面的位置,提出了级联式谐波补偿器基于z域的根轨迹设计方法,能够灵活配置电流环的零极点分布。从而保证稳态工作时谐波比例谐振控制器对谐波电压的抑制作用,动态响应时不会导致电网电流畸变,同时使基波电流能够快速跟踪指令值。交流传动电力机车的主牵引系统中,单相PWM整流器的功率为兆瓦级,两电平单相PWM整流器开关频率通常不到1kHz,使电流环的带宽进一步减小。并且由于数字控制系统存在控制延时,导致电流环性能变差。为了提高电流环的动态响应速度,通常采用预测电流控制。分析了传统的开环电流预测误差对电网电流谐波的影响,而电网电流预测误差导致的电网谐波电流无法通过电流环前向通道中加入内模进行抑制。针对这一问题,提出了采用重复观测器对电网电流进行预测的闭环电流预测算法,通过提高电网电流预测的精度,从而减小电网电流谐波含量。给出了电网电流重复观测器的设计方法,分析了重复观测器以及整个电流环的稳定性。电气化铁路的牵引网专门为交流传动电力机车供电,电网与电力机车网侧PWM整流器形成级联系统。尽管单相PWM整流器设计时,能够保证电流环稳定,然而电网短路阻抗以及分布电容等参数将对PWM整流器的稳定性产生影响,导致电网电流振荡,产生大量的谐波。提出了采用电网等效输出阻抗和PWM整流器输入阻抗的阻抗比分析电网参数对电流环稳定性的影响。并分别对单台和多台并联运行时,PWM整流器电流环控制器参数设计进行了分析,避免电网与PWM整流器之间谐振现象的产生。讨论了电流环内模加入对PWM整流器输入阻抗的影响。最后通过仿真和实验验证了理论分析的正确性。更多还原

【Abstract】 ABSTRACT:Single-phase PWM rectifier has been widely used in the fields of ac electric drives and renewable energy distribution generations with the advantages of high power factor, low current harmonics and bidirectional energy flowing. Although the grid current harmonics are much lower using PWM rectifier than that using diode rectifier, they can not be eliminated completely and are affected by many factors. More and more attentions have been paid on improving grid current quality with PWM rectifiers widely used.Mathematical model of single-phase PWM rectifier was established first. Impact on grid current made by dc-link voltage ripple, voltage harmonics, grid current predictive error and grid parameters was analyzed. The dc-link voltage ripple can be filtered by notch filter in the sample loop to eliminate its affect on grid current. PWM rectifier input impedance can be increased by adding repetitive or resonant controller into current-loop to reduce grid current harmonics caused by both grid voltage harmonics and PWM modulation.In the field of photovoltaic power generation, single-phase PWM rectifier is mainly used for low-power photovoltaic inverter, usually in5kW power level below. Its switching frequency is often10kHz-20kHz and the control cycle is short. Single-phase photovoltaic inverter current-loop has a wide-bandwidth and computation consumption of repetitive control is small. For these reasons, dead-beat control combined with repetitive control was proposed to eliminate grid current harmonic. Impact on current-loop robustness and dynamic performance by repetitive controller was analyzed. Design method of repetitive controller and current harmonic elimination performance was discussed. It is shown that smaller repetitive controller gain can improve current-loop robust and reduce grid current distortion when grid current amplitude reference steps. However, fundamental current tracking speed will slow down at the same time.In ac electric locomotive auxiliary power supply system, single-phase PWM rectifier’s power is hundreds of kilowatts and its switching frequency is typically2kHz-5kHz. Low switching frequency will decrease current-loop dynamic performance. Because of the long control cycle, harmonic compensator based on resonant control is proposed to improve PWM rectifier input impedance at harmonic frequency. The design method setting different fundamental and harmonic resonant controller coefficients was proposed to obtain high static and dynamic current-loop performance. Paralleled harmonic compensator by adding multiple harmonic resonant controllers is often used and discussed in references. However, its design method is difficult to visually configure zeros and poles in z plane. Root locus design method of cascaded harmonic compensator in z domain was proposed with the flexibility to configure the distribution of current-loop poles and zeros. In this method, it is can be make sure that current-loop has ability to eliminate harmonic voltage in steady-state and rapid fundamental current tracking without current distortion in dynamic-state.In ac electric locomotive main traction system, single-phase PWM rectifier’s power is megawatt and switching frequency is typically less than1kHz. The current-loop bandwidth is further reduced. Control delay will also result in deterioration of current-loop performance. Predictive current controller is often used to obtain high dynamic performance. Grid current predictive error using traditional open-loop current predictive method will distort grid current which can not be eliminated by adding internal model into current-loop. The current predictive algorithm based on repetitive control observer was proposed to improve grid current predictive precision. Design method of grid current observer was given and the observer stability and current-loop stability were both discussed.Traction network and locomotive grid-side PWM rectifier can be regarded as a cascaded system while traction network is specifically supplying for electric locomotive. PWM rectifier current-loop can be designed to guarantee stability. However, grids short-circuit impedance and distributed capacitance will affect the stability of PWM rectifier leading to grid current oscillation and a large amount of harmonics. Impedance ratio was used to analyze the influence on the stability of the current-loop by network parameters. Current-loop controller parameters design was analyzed respectively for single and multiple paralleled operations to avoid resonance between the grid and PWM rectifier. PWM rectifier input impedance was discussed when repetitive and resonant internal model was introduced. Finally, simulation and experimental results verified that theoretical analysis is correct.更多还原