【作者】 周扬忠；

【导师】 胡育文；

【作者基本信息】 南京航空航天大学 ， 电力电子与电力传动， 2007， 博士

【摘要】 电励磁同步电机(ESM)具有功率因数可调、效率高等优点,无论在航空工业还是地面工业大功率场合均获得了广泛应用,所以研究和开发高性能的ESM驱动系统具有重大的经济价值和社会效应。目前开发高性能ESM驱动系统所采用的控制方案主要有两种:一种是磁场定向矢量控制(FOC);另一种是直接转矩控制(DTC)。FOC ESM系统动态性能明显较标量控制系统性能提高了很多,但ESM转子凸极结构和较大的转子回路时间常数使得ESM FOC系统无法实现真正意义上的解耦控制。DTC思想把电机和逆变器作为一个整体,在定子静止坐标系中利用逆变器输出电压矢量直接控制定子磁链和转矩,获得了快速的转矩响应。若在ESM上采用DTC恰恰可以弥补FOC的缺陷,达到转矩的直接而快速控制。在国外,1998年前后瑞士ABB公司和芬兰拉彭兰塔理工大学合作研究了ESM DTC的部分内容。出于商业保密考虑,他们没有详细给出实现的细节,甚至没有给出最优开关表的具体构成。从他们所公开的不完整资料中我们无法获知ESM DTC的完整理论构架。在国内,1997年至2001年南京航空航天大学针对无阻尼绕组ESM DTC也开展了初步的理论研究,但没有进行详细的实践研究。因此,无论在国内还是在国外,ESM DTC系统的研究还缺乏全面深入的理论研究,还没有建造起ESM DTC系统的理论体系构架。本文的主要任务和目的就是比较全面和深入地完成这一理论构架,为以后更深入地、广泛地研究ESM DTC技术,打好一个坚实的理论基础。本论文主要内容如下:对交流电机低转矩磁链脉动型DTC策略进行了综述,指出低转矩磁链脉动型DTC控制策略有:运用空间矢量调制(SVM)技术输出多个电压矢量、采用新型逆变器输出多个电压矢量、用多相逆变器控制多相电机、引入现代控制理论等。对交流同步电机无位置速度传感器运行及转子初始位置估计技术进行了综述,结果指出目前无位置速度传感器技术主要有两大类:基于基波量的检测法和基于外加信号激励法。对于初始转子位置估计法有:基于定子电感检测法、高频交替磁化法、高频信号注入法、基于磁路饱和特性等,电励磁同步电机转子初始位置估计研究还很少。分析研究了有阻尼绕组电励磁同步电机气隙磁链性质,结果指出气隙磁链为一个时间常数较大的惯性环节,ESM DTC正是基于此,利用定子侧的电压矢量迅速控制定子磁链矢量的模、旋转方向及旋转角度,迅速改变定子磁链矢量和气隙磁链矢量之间的夹角(定义为转矩角),实现对电磁转矩的迅速控制。仿真和实验证明了上述分析的正确性。从转矩角控制转矩入手,详细推导并分析了有阻尼绕组ESM电磁转矩。运用仿真手段研究了DTC控制ESM中直/交轴阻尼绕组对电机动态行为的影响,研究结果表明:交轴阻尼绕组有利于电机动态性能的改善;直轴方向上定子绕组、阻尼绕组及转子励磁绕组相互耦合,会形成振荡,导致直轴阻尼绕组对电机动态性能的改善不明显,甚至有危害;对于电动运行的ESM不宜采用直轴阻尼绕组;主转矩角与主转矩在主转矩角零点附近变化趋势始终一致。分析了ESM DTC系统弱磁控制原理,从提高ESM DTC系统全速度范围内综合指标出发,针对DTC控制ESM提出一种全速度范围内转子励磁电流控制策略。指出在恒转矩区宜采用转子电流内控法,实现电机内功率因数等于1;在弱磁恒功率区宜采用转子电流外控法,实现电机外功率因数等于1;转子电流内控法和外控法在额定转速点处直接转换,不需要插入过渡区。仿真和实验结果表明无论恒转矩区或弱磁恒功率区,电机功率因数均较高;由恒转矩区到弱磁恒功率区过渡很平滑。针对ESM提出一种基于定子磁链误差矢量补偿的SVM-DTC结构。运用仿真和实验手段对基本DTC和SVM-DTC两种ESM驱动系统进行了详细对比研究,结果表明:SVM-DTC具有基本DTC系统简洁结构的同时大幅度减小了转矩、磁链、电流的脉动;降低了起动电流的冲击幅度;功率管开关频率基本恒定;弱磁方法依然适用。针对无阻尼绕组ESM SVM-DTC系统转矩角控制转矩特点,提出并设计了一种变比例系数转矩PI调节器,旨在实现SVM-DTC系统转矩的快速而准确控制。仿真及实验结果表明系统起动转矩快速而准确地跟踪上给定值,系统稳态运行平稳。这种变比例系数的调节方法对永磁电机也特别适用。一般ESM DTC系统中没有直接检测定子端电压传感器,但有定子绕组和转子励磁绕组电流传感器。本文基于转子励磁绕组通入直流脉动电流,在三相短路的定子绕组中感应出电流的原理,提出基于定子感应电流和转子励磁电流检测的两种初始转子位置估计方法-闭环法和开环法。实验结果表明转子初始位置机械角度估计误差在±2度范围内;SVM-DTC系统能够以给定的最大转矩顺利起动。分析研究了基于两电平逆变器供电ESM基本DTC和SVM-DTC中影响起动冲击电流的因数。基于基本DTC结构提出一种约束矢量作用时间的改进型基本DTC,基于补偿定子磁链误差矢量的SVM-DTC结构提出一种电流主动控制的SVM-DTC。仿真和实验结果证明了上述两种新型DTC系统对降低起动冲击电流幅度的有效性。仿真研究了基于多电平逆变器供电ESM SVM-DTC系统对起动冲击电流的抑制效果,结果表明,由于多电平逆变器输出电压矢量幅值能随电机转速自动调整,因而有效地抑制了起动冲击电流幅度。更多还原

【Abstract】 Electrically excited synchronous motor (ESM) has been widely applied in industry because of its advantages of adjustable power factor and high efficiency, and so it deserves researching high performance ESM drives. Recently, there are mainly two control schemes used by developing performance ESM drive systems: one is field orientation control (FOC), and the other is direct torque control (DTC). Although the ESM drive systems controlled by FOC have many advantages over the scalar controlled ESM systems in dynamic performance, the decoupling control in FOC ESM could not come true because of the salient pole of rotor structure and the large time constant of rotor winding circuit. The DTC considers the motor and inverter as a whole, and controls the stator flux linkage vector and electromagnetic torque directly by applying an optimal space voltage vector during each sampling period in the stator reference frame. If the DTC is implemented on ESM, the response time of torque can be much shorter. Although the ESM DTC was partly researched by ABB and Lappeenranta University of Switzerland in about 1998, the whole theory structure of ESM DTC could not be obtained from their few published papers. At home, the no-damper windings ESM DTC had been investigated by Nanjing University of Aeronautics and Astronautics partly from 1997 to 2001. So the ESM DTC lacks full and in-depth study, and the theory for ESM DTC has not been constructed. The main purpose of this thesis is to build up the theory construction as follows:After reviewing the DTC scheme with low torque and low flux linkage ripples for AC motors, the control methods of reducing the torque and flux linkage ripples are given as: improving the output of voltage vector in software, applying new inverter with multi-vector output, applying multi-phase motor, and applying modern control theory et. After reviewing the sensorless schemes of AC synchronous motors, the sensorless technologies are grouped under two kinds. One is based on the fundamental variables, and the other is based on external exciting signal. The estimation method of the initial rotor position can be classified as: basing on the calculation of stator inductance, alternative magnetize using high signal, high frequency signal injection, and the saturate effect of motor magnetic circuit et. There are few papers investigating the ESM initial rotor position estimation.The feature of air-gap flux linkage in ESM with damper windings has been analyzed, and the results show that the time constant of air-gap flux linkage is very large. The quick response of torque in ESM DTC can be gained by controlling the torque angular between the stator flux linkage vector and the air-gap flux linkage vector using the optimal space voltage vectors. The results of simulation and experiment show that the above analysis is correct.In this thesis the relationship between torque and torque angle in ESM of DTC has been deduced in detail, and the effect of damper windings on the dynamic performance of ESM based on DTC has been presented by digital simulation. The results of simulation show that the derivative of the main torque near the zero cross is positive with respect to the main torque angle. The q-axis damper winding can reduce the oscillation amplitude of the torque and speed significantly, and the d-axis damper winding improves the dynamic performance of the motor slightly and decreases the system’s stability. So the d-axis damper winding of ESM operating at motor is unnecessary.The weakening control principle of ESM DTC systems has been analyzed and an optimal excitation control method for DTC-controlled ESM drives in the whole speed rang has been investigated in this thesis. The inner control method for excitation should been applied in the constant torque range, and the unit inner power factor is gained. The outer control method for excitation should been applied in the weakening range, and the unit outer power factor is achieved. The conversation between the two excitation methods can directly happens at the rated speed without transition. The results of simulation and experiment show the power factor of ESM is very high both in constant torque range and in field weakening range, and the conversation between the two excitation control methods is very smooth. A DTC scheme with space vector modulation (SVM) for ESM has been investigated in this thesis. It is based on the compensation of the stator flux linkage vector error using the space vector modulation in order to decrease the torque and flux linkage ripples. Compared with the basic DTC, the results of simulation and experiment show that the torque and flux linkage ripples are all much reduced, the maximum current value is decreased during the startup and the current distortion of steady state is much small in the SVM-DTC system. The SVM-DTC system is also simple and the switching frequency of inverter is approximately constant. The field-weakening control is incorporated into the SVM-DTC successfully.In this work, a proportional-plus-integral (PI) torque controller with variable proportion for direct torque controlled ESM drive based on the torque angle controlling the torque is proposed in order to ensure exact and quick control of torque. The experimental results verify the feasibility and effectiveness of the proposed PI torque controller. This PI torque controller is also suitable for the permanent synchronous motor drive system based on DTC.This thesis has proposed two methods of the initial rotor position estimation, i.e. closed loop estimation and open loop estimation, for ESM drives based on DTC without stator voltage sensors. The stator currents and rotor excitation current should be sensed under the condition of three-phase short-circuit and AC rotor current or DC pulsation rotor current in the two strategies. The results of simulation and experiment show that the estimated value error of initial rotor mechanical angle is less than±20, and SVM-DTC system can start up with given torque smoothly with the estimated initial rotor position.The effect of DC-link voltage, sampling period, and inductance of stator on the maximum start-up current has been analyzed on conventional DTC(CDTC) and SVM-DTC drive based on the two-level inverter. A modified CDTC scheme with time-controlled vectors has been proposed using torque and stator flux linkage hysteresis controller and switching table. A stator current-controlled SVM-DTC has been proposed based on the principle of stator flux linkage vector error compensation. The results of simulation and experiment show that the two proposed DTC schemes are effective to reduce the start-up current. The effect of multi-level inverter on decreasing the start-up current of ESM SVM-DTC has been researched by means of simulation. The results of simulation show that multi-level inverter can reduce the value of start-up current effectively because the magnitude of output voltage vector in multi-level inverter can be changed automatically according to the rotor speed.更多还原