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How to control brushless motor?

Views: 241     Author: Site Editor     Publish Time: 2022-06-27      Origin: Site

不同的电机类型


当今有几种可用的电机控制拓扑结构:有刷、无刷直流 (BLDC)、步进和电感。BLDC 和永磁同步电机 (PMSM) 是两种最密切相关的无刷电机类型。


无刷电机无需使用电机电刷,因而广泛用于当今的许多应用中。这些 BLDC 拓扑结构使用换向逻辑来移动转子,从而提高电机的效率和可靠性。我们来详细介绍一下。


了解 BLDC 和 PMSM 类型的电机


BLDC 和 PMSM 电机的工作原理与同步电机相同。转子在每次换向时都会继续跟随定子转动,所以电机能够持续运转。然而,这两种直流电机的定子绕组采用不同的几何形状,因此可产生不同的反电动势 (BEMF) 响应。BLDC BEFM 为梯形。PMSM 电机的 BEMF 则为正弦曲线形,因此线圈绕组以正弦方式缠绕。为最大限度地提高性能,这些电极通常采用正弦波换向。


BLDC 和 PMSM 电机(图 1)在运行时通过其绕组产生电动势。在任何电机中,由于运动,产生的 EMF 称为反电动势 (BEMF),这是因为电机中感应的电动势与发电机的电动势相反。

brushless motor 1

图 1:BLDC 和 PMSM 电机通常使用正弦波换向。


磁场定向控制说明


为实现控制 PMSM 电机的正弦波形,需要使用磁场定向控制 (FOC) 算法。FOC 通常用于最大限度地提高 PMSM 三相电机的效率。与 BLDC 的梯形控制器相比,PMSM 的正弦控制器更为复杂,成本也更高。然而,成本的增加也带来了一些优势,如减少了电流波形中的噪声和谐波。BLDC 的主要优势是更易于控制。最后,最好根据应用需求来选择电机。


带传感器和不带传感器的 BLDC 和 PMSM 电机


BLDC 和 PMSM 电机可带传感器,也可不带传感器。带传感器的电机(图 2)适用于需要在负载条件下起动电机的应用。这些电机使用霍尔传感器,传感器嵌入电极定子中。从本质上说,传感器就是一种开关,其数字输出等同于检测到的磁场极性。电机的每个相都需要使用一个单独的霍尔传感器。三相电机需要三个霍尔传感器。不带传感器的电机需要将电机用作传感器,采用算法来运行。它们依赖于 BEMF 信息。通过对 BEMF 进行采样,可推断出转子的位置,从而无需使用基于硬件的传感器。无论电机的拓扑结构如何,控制这些电机需要了解转子位置,这样电机才能有效换向。


brushless motor 2

图 2:BLDC 和 PMSM 电机示意图。


电机控制软件算法


如今,计算机程序之类的软件算法(为执行具体任务而设计的一组指令)开始用于控制 BLDC 和 PMSM 电机。这些软件算法通过监控电机运行来提高电机效率,降低运行成本。算法中的一些主要功能包括电机初始化、霍尔传感器位置检测以及用于提高或降低电流基准的开关信号检查。

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控制器如何处理电机传感器信息


三相 BLDC 电机具有 6 种状态。如图 3 所示,三位代码可表示 1 至 6 之间的操作码编号。传感器用于通过 8 个操作码中的 6 个操作码(1 至 6)提供三位数据输出。该信息非常有用,因为控制器可确定何时发出了非法操作码,并根据合法操作码(1 至 6)执行操作。算法获取霍尔传感器操作码,并对其进行解码。当霍尔传感器操作码值发生变化时,控制器就会改变送电方案,以实现换向。微控制器使用操作码从查找表中提取送电信息。在使用新的扇区命令给三相逆变器送电后,磁场转移至新位置,同时推动着转子沿着移动方向运动。电机运转时会不断重复此过程。

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图 3:三位代码可用于表示 1 至 6 之间的操作码编号。




Rising consumer demands for power, reliability, functionality, and performance are driving rapid growth in electronic devices, including lawnmowers, refrigerators, vacuum cleaners, automobiles, and more. Manufacturers want full-scale delivery. Motor control plays a major role in delivering on these promises, and understanding the fundamentals is the first step toward that goal.


different motor types

There are several motor control topologies available today: brushed, brushless DC (BLDC), stepper, and inductive. BLDC and permanent magnet synchronous motor (PMSM) are the two most closely related types of brushless motors.

Brushless motors eliminate the need for motor brushes and are used in many applications today. These BLDC topologies use commutation logic to move the rotor, increasing the efficiency and reliability of the motor. Let's go into details.


Learn about BLDC and PMSM type motors

BLDC and PMSM motors work on the same principle as synchronous motors. The rotor continues to follow the stator with each commutation, so the motor can continue to run. However, the stator windings of the two DC motors have different geometries, which can result in different back electromotive force (BEMF) responses. BLDC BEFM is trapezoidal. The BEMF of a PMSM motor is sinusoidal, so the coil windings are wound sinusoidally. To maximize performance, these electrodes are typically sinusoidally commutated.


BLDC and PMSM motors (Figure 1) generate electromotive force through their windings during operation. In any electric machine, due to motion, the resulting EMF is called back electromotive force (BEMF) because the electromotive force induced in the electric machine is opposite to the electromotive force of the generator.

brushless motor 1

Figure 1: BLDC and PMSM motors typically use sine wave commutation.


Field Oriented Control Description

To achieve a sinusoidal waveform to control a PMSM motor, a Field Oriented Control (FOC) algorithm is required. FOC is often used to maximize the efficiency of PMSM three-phase motors. Compared with BLDC's ladder controller, PMSM's sinusoidal controller is more complex and more expensive. However, the increased cost also brings some advantages, such as reducing noise and harmonics in the current waveform. The main advantage of BLDC is easier control. In the end, it is best to choose a motor based on the application needs.


Sensored and Unsensored BLDC and PMSM Motors

BLDC and PMSM motors are available with or without sensors. Motors with sensors (Figure 2) are suitable for applications that need to start the motor under load. These motors use Hall sensors, which are embedded in the electrode stator. Essentially, a sensor is a switch whose digital output is equivalent to the detected polarity of the magnetic field. A separate Hall sensor is required for each phase of the motor. Three-phase motors require three Hall sensors. Motors without sensors require an algorithm to operate using the motor as a sensor. They rely on BEMF information. By sampling the BEMF, the position of the rotor can be inferred, eliminating the need for hardware-based sensors. Regardless of the motor topology, controlling these motors requires knowledge of the rotor position so that the motor can commutate effectively.


brushless motor 2

Figure 2: Schematic diagram of BLDC and PMSM motors.


Motor Control Software Algorithms

Today, software algorithms such as computer programs (a set of instructions designed to perform a specific task) are beginning to be used to control BLDC and PMSM motors. These software algorithms improve motor efficiency and reduce operating costs by monitoring motor operation. Some of the main functions in the algorithm include motor initialization, Hall sensor position detection, and switch signal checking for raising or lowering the current reference.


brushless motor 3


How the Controller Processes Motor Sensor Information

A three-phase BLDC motor has 6 states. As shown in Figure 3, the three-digit code can represent an opcode number between 1 and 6. The sensor is used to provide a three-bit data output via 6 of the 8 opcodes (1 to 6). This information is useful because the controller can determine when an illegal opcode has been issued and take action based on the legal opcodes (1 through 6). The algorithm takes the Hall sensor opcode and decodes it. When the Hall sensor opcode value changes, the controller changes the power delivery scheme to achieve commutation. The microcontroller uses the opcode to extract the power delivery information from the lookup table. After powering the three-phase inverter with the new sector command, the magnetic field shifts to the new position, pushing the rotor in the direction of movement. This process is repeated continuously while the motor is running.


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Figure 3: Three-digit codes can be used to represent opcode numbers between 1 and 6.