来源：http://www.jnmcd.com 发布时间：2019-01-29 浏览：次
直流无刷电机是同步电机的一种，也就是说电机转子的转速受电机定子旋转磁场的速度及转子极数(P)影响：N=120．f / P。在转子极数固定情况下，改变定子旋转磁场的频率就可以改变转子的转速。直流无刷电机即是将同步电机加上电子式操控(驱动器)，操控定子旋转磁场的频率并将电机转子的转速回授至操控中心反复校对，以期达到接近直流电机特性的方式。也就是说直流无刷电机可以在额定负载范围内当负载改变时仍可以操控电机转子保持必定的转速。 直流无刷驱动器包含电源部及操控部如图 (1) ：电源部供给三相电源给电机，操控部则依需求转化输入电源频率。
Brushless DC motor is a kind of synchronous motor, that is to say, the speed of motor rotor is affected by the speed of stator rotating magnetic field and the number of rotor poles (P): N = 120.f/P. When the poles of the rotor are fixed, the speed of the rotor can be changed by changing the frequency of the stator rotating magnetic field. Brushless DC motor is a synchronous motor with electronic control (driver), which controls the frequency of stator rotating magnetic field and feeds the speed of motor rotor back to the control center for repeated proofreading, in order to achieve close to the characteristics of DC motor. That is to say, the brushless DC motor can control the motor rotor to maintain a certain speed when the load changes in the rated load range. The DC brushless driver includes power supply and control unit as shown in Figure (1): The power supply unit supplies three-phase power to the motor, while the control unit converts the input power frequency according to the demand.
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电源部可以直接以直流电输入(一般为24V)或以交流电输入(110V/220 V)，如果输入是交流电就得先经转化器(converter)转成直流。不论是直流电输入或交流电输入要转入电机线圈前须先将直流电压由换流器(inverter)转成3相电压来驱动电机。换流器(inverter)一般由6个功率晶体管(Q1～Q6)分为上臂(Q1、Q3、Q5)/下臂(Q2、Q4、Q6)衔接电机作为操控流经电机线圈的开关。操控部则供给PWM(脉冲宽度调制)决议功率晶体管开关频度及换流器(inverter)换相的时机。直流无刷电机一般期望使用在当负载改变时速度可以稳定于设定值而不会改变太大的速度操控，所以电机内部装有能感应磁场的霍尔传感器(hall-sensor)，做为速度之闭回路操控，同时也做为相序操控的依据。但这只是用来做为速度操控并不能拿来做为定位操控 。
The power supply can be directly input by direct current (usually 24V) or alternating current (110V/220 V). If the input is alternating current, it must be converted to direct current by converter. Whether DC or AC input is to be converted into motor coil, the DC voltage must be converted from a converter (inverter) to a three-phase voltage to drive the motor. Converter (Inverter) generally consists of six power transistors (Q1-Q6) which are divided into upper arm (Q1, Q3, Q5) / lower arm (Q2, Q4, Q6) connected motor as a switch to control the flow through the motor coil. The control unit provides PWM (pulse width modulation) to determine the switching frequency of power transistors and the timing of commutation of converters. DC brushless motor generally expects that the speed can be stabilized at the set value without changing too much speed control when the load changes, so the motor is equipped with Hall-sensor which can induce magnetic field, as a closed-loop control of speed, but also as a basis for phase sequence control. But this is only used as speed control, not positioning control.
Control Principle of DC Brushless Motor
In order to make the motor roll, the control unit must first base on the current orientation of the motor rotor induced by hall-sensor, then open (or close) the power transistors in the converter according to the stator winding resolution, AH, BH, CH (these are called upper arm power transistors) and AL, BL, CL (these are called lower arm power transistors) in inverter, so that the current flows through the motor in sequence. The coil produces a forward (or reverse) rotating magnetic field and interacts with the magnet of the rotor, so that the motor can roll clockwise/counter-clockwise. When the motor rotor rolls to the Hall-sensor to sense the orientation of another set of signals, the control unit opens the next set of power transistors, so that the circulating motor can continue to roll in the same direction until the control unit decides to stop the motor rotor, then the closed power transistor (or only open the lower arm power transistor); if the motor rotor is reversed, the power transistor opens in reverse order.
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Basically, the open method of power transistors can be illustrated as follows:
AH, BL group AH, CL group BH, CL group BH, AL group CH, AL group CH, BL group, but must not be opened into AH, AL or BH, BL or CH, CL. In addition, because the electronic parts always have the response time of the switch, the power transistor should take the response time of the part into account when interleaving with the open. Otherwise, when the upper arm (or lower arm) has not been completely closed, the lower arm (or upper arm) has been opened, resulting in the short circuit between the upper arm and the lower arm, which causes the power transistor to burn.
When the motor rolls up, the control unit compares (or calculates by software) the speed of the Hall-sensor signal with the command (Command) composed of the speed set by the driver and the acceleration/deceleration rate, and then decides whether the next group (AH, BL or AH, CL or BH, CL or... (2) Switching on, and the length of the turning on time. If the speed is not enough, it will be longer, but if the speed is too high, it will be shorter. This part of the work will be completed by PWM. PWM is the way that decides the speed of motor fast or slow. How to generate such PWM is the core to achieve more accurate speed control. High speed speed control must consider whether the CLOCK resolution of the system is enough to grasp the processing time of software instructions. In addition, the data access mode of Hall-sensor signal changes also affects the processor's efficiency, correctness and real-time performance.
As for the low speed speed control, especially the low speed start, the Hall-sensor signal is changed more slowly. It is very important how to pick up the signal mode, the processing time and the appropriate equipment control parameters according to the characteristics of the motor. Or the speed return change refers to the encoder change to increase the signal resolution in order to get better control. The motor can work smoothly and respond well, and the proper operation of P.I.D. can not be ignored. As mentioned earlier, brushless DC motor is closed-loop control, so the feedback signal is equivalent to telling the control unit how far the motor speed is from the target speed, which is Error. Knowing the error will naturally be compensated by traditional engineering manipulation such as P.I.D. manipulation.
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