变频器控制.docx

1.设计一交流调速系统，对恒转矩负载进行开环调速控制。三相交流电动机参数：P=15kW，U=380V1）设计交-直-交变频主电路。（绘制主电路、主要元件参数计算及型号选定）。2）利用单片机实现控制（起动、制动等）电路设计。（设定输入 输出节点、控制电路简要设计、控制软件流程图）。（1）如下所示 交-直-交变频器内部主电路主电路参数计算及型号选定整流采用三相桥式不可控整流器，组成滤波电路，三个元件和 一起构成尖峰电压吸收电路（又称直流侧阻容吸收电路），用以削弱因逆变器换流而引起的尖峰电压，采用的是GRT三相桥式PWM逆变器。（2） 参数计算和元件选择1) 大功率开关管 SPWM正弦脉宽调制方法的直流利用率为0.866，即。为了使逆变器输出380V的线电压，要求直流侧的电源电压： 考虑到大功率的晶体管的管压降等，取则大功率晶体管的参数为，U(BR)CBO=(23)Ud=9001350V。2） 三相整流桥 整流桥输入侧电压为：取电动机的效率为0.82，则电动机的输入功率为P1=15000/0.8218.3KW。取逆变器的效率为0.93，则 直流侧的功率为： Pd=P1/0.9319.7 KW，故直流侧电流： Id= Pd/ Ud=19700/45043.8A。整流二极管最高反压：。基于以上数据，选用MDS型三相整流桥模块，其最大输出电流为50A，最高耐压为1000V。（3） LC滤波器 取，其最大耐压。选择两只2200uF，耐压在500V以上的电容器并联使用。滤波电感在这里主要用来限制电流脉动（PWM变频调速系统不存在电流不连续问题）和短路电流上升率，按照晶体管三相桥式整流电路限制电流脉动的电感量算式估计如下。（取）=mH18.61 mH考虑到电动机和整流变压器存在一定的电感量，取实际的串联电感为20mH。选择两台电感量各为10mH，额定电流不小于43.8A的电抗器串联。（2）驱动三相逆变桥系统主程序框图：2.英语翻译Vector control, also calledfield-oriented control(FOC), is avariable-frequency drive(VFD) control method in which thestatorcurrents of a three-phaseAC electric motorare identified as two orthogonal components that can be visualized with a vector. One component defines the magnetic flux of the motor, the other the torque. The control system of the drive calculates the corresponding current component references from the flux and torque references given by the drives speed control. Typicallyproportional-integral (PI) controllersare used to keep the measured current components at their reference values. Thepulse-width modulationof the variable-frequency drive defines thetransistorswitching according to the stator voltage references that are the output of the PI current controllers. FOC is used to controlACsynchronousandinduction motors.It was originally developed for high-performance motor applications that are required to operate smoothly over the fullspeedrange, generate fulltorqueat zero speed, and have high dynamic performance including fastaccelerationand deceleration. However, it is becoming increasingly attractive for lower performance applications as well due to FOCs motor size, cost andpower consumptionreduction superiority.It is expected that with increasing computational power of the microprocessors it will eventually nearly universally displace single-variablescalarvolts-per-Hertz(V/f) control.While the analysis of AC drive controls can be technically quite involved, such analysis invariably starts with modeling of the drive-motor circuit involved along the lines of accompanyingsignal flow graphand equations.In vector control, an AC induction or synchronous motor is controlled under all operating conditions like a separatelyexcitedDC motor.That is, the AC motor behaves like a DC motor in which thefield flux linkageandarmatureflux linkage created by the respective field and armature (or torque component) currents areorthogonallyaligned such that, when torque is controlled, the field flux linkage is not affected, hence enabling dynamic torque response.Vector control accordingly generates a three-phasePWMmotor voltage output derived from a complexvoltage vector to control a complex current vector derived from motors three-phase stator current input throughprojectionsorrotationsback and forth between the three-phase speed and time dependent system and these vectors rotating reference-frame two-coordinate time invariant system.Such complexstatorcurrent space vector can be defined in a (d,q) coordinate system with orthogonal components along d (direct) and q (quadrature) axes such that field flux linkage component of current is aligned along the d axis and torque component of current is aligned along the q axis.The induction motors (d,q) coordinate system can be superimposed to the motors instantaneous (a,b,c) three-phasesinusoidalsystem as shown in accompanying image (phases b & c not shown for clarity). Components of the (d,q) system current vector, allow conventional control such as proportional and integral, orPI, control, as with a DC motor.While (d,q) coordinate system rotation can arbitrarily be set to any speed, there are three preferred speeds or reference frames:l Stationary reference frame where (d,q) coordinate system does not rotate;l Synchronously rotating reference frame where (d,q) coordinate system rotates at synchronous speed;l Rotor reference frame where (d,q) coordinate system rotates at rotor speed.Decoupledtorque and field currents can thus be derived from raw stator current inputs for control algorithm developmenWhereas magnetic field and torque components in DC motors can be operated relatively simply by separately controlling the respective field and armature currents, economical control of AC motors in variable speed application has required development of microprocessor-based controlswith all AC drives now using powerful DSP (digital signal processing) technology.Inverters can be implemented as eitheropen-loopsensorless or closed-loop FOC, the key limitation of open-loop operation being mimimum speed possible at 100% torque, namely, about 0.8Hz compared to standstill for closed-loop operation.2.译文 矢量控制、矢量控制(FOC),也称为变频驱动器(VFD)控制方法中,定子电流的三相交流电动机被确定为两个正交组件,可以用一个向量。一个组件定义了电动机的磁通,另一个扭矩。驱动器的控制系统计算磁通和转矩的对应当前组件引用引用由驱动器的速度控制。通常比例积分(PI)控制器是用来衡量现有的组件参考价值。脉宽调制变频驱动定义了晶体管的开关根据定子电压引用的输出电流控制器。矢量控制是用来控制交流同步和感应电动机的控制。它最初开发高性能电机中顺利运营所需的应用程序在全速范围内,生成完整的转矩为零速度和高动态性能包括快速加速和减速。然而,它正变得越来越有吸引力较低性能的应用程序由于FOC的马达尺寸,减少成本和功耗优势。预计,随着微处理器的计算能力将最终变量几乎普遍取代标量volts-per-Hertz(V/f)控制。虽然交流传动控制的分析技术可以完全参与,这样的分析总是开始于建模驱动电动机的电路涉及附带的信号流图和方程。在矢量控制交流感应或同步电动机控制在所有操作条件下像他励直流电机。即交流电动机像一个直流电机的磁链和电枢磁链由