2023 年 7 月 27 日

    Field-Oriented Control of BLDC and PSMS Motors Draft 4_fmedit

    超越传统有刷电机

    无刷直流(BLDC)电机和永磁同步电机(PMSM)摆脱了电刷及换向器,相比有刷电机带来更高的效率和更长的寿命,因而在许多应用中越来越受到欢迎。为消除电刷和换向器,这些电机利用电子产生的旋转磁场,并通过外部电路来调节相电压及电流来实现。

    此类电路固然增加了一些复杂性,但与传统有刷电机相比,BLDC和PMSM具备很大优势——对比以相同速度运行的有刷电机,其电子换向方案可将能效提升20%至30%,而且更耐用、更小、更轻、更安静。

    磁场定向控制(FOC)是一种用于PMSM的控制技术,在最大限度减少转矩纹波和扩大速度工作范围方面性能优越。目前,这一技术正变得越来越流行,并开始出现在成本更高、性能更强的电动工具和白色家电中。在微控制器(MCU)上进行嵌入式编程是实现FOC相关特性和功能的常见选择,同时还能在优化整体解决方案的同时满足每个应用的要求。

    本篇博文概述了Qorvo设计峰会相关网络研讨会的内容。该研讨会探讨了基于FOC的BLDC/PMSM电机设计,包括如何对微控制器芯片编程以访问并管理电机运行的示例。

    深入探讨

    参与设计峰会系列,与Qorvo技术专家一起更深入地探讨这一主题。该系列网络研讨会聚焦将引爆革命性突破的下一代技术进展。

    Fundamentals of Field-Oriented Control

    In any discussion of brushless motors, terms such as sinusoidal, trapezoidal and field-oriented control commonly appear. Understanding these terms is the first step to mastering the underlying concepts. The Design Summit video offers an overview of this topic, summarized briefly in this section. In a typical motor drive system with a battery or other DC source of power, a power stage delivers a three-phase AC current. As shown in Figure 1, the current driving of a BLDC or PMSM motor can be based on six-step trapezoidal control or field-oriented control.

    Accurately determining the rotor position affects how efficiently the motor speed and torque can be controlled. The rotor position is determined by hardware sensors via a module that detects the motor angle and speed. In some designs, current and voltage values can also be used to determine motor position through microcontroller functions.

     

    Figure 1. Difference between Trapezoidal and FOC

    In designs that use trapezoidal control, the current is conducted only during two phases. During a floating phase, sensor readings are obtained. At this time, the values of the back electro-motive force (BEMF) can be monitored to deduce the rotor position. While BLDC motor designs typically have high torque ripple, this approach is simpler and less expensive to implement.

    FOC implementations for PMSM motors conduct current in each of the three phases; each phase’s current, voltage and power is offset 120 degrees from the others’. This minimizes the torque ripple. Motor angle updates are continuous. This sinusoidal control primarily used for PMSM motors requires more elaborate electronic monitoring control circuitry. Control of an AC motor is essentially equivalent to controlling a DC motor using FOC.

    As shown in Figure 2, torque is monitored and controlled by a Current Control Loop. Feedback from a tri-phase inverter is fed to a current-sensing circuit and relayed to the control loop to maintain precise torque levels. A Motor Position Module samples voltage and current values to provide angle and speed levels of the motor through a series of transform operations.

     

     

    Figure 2. Fundamental components in a FOC-based implementation.

    Other Key Takeaways

    After the previous overview of FOC fundamentals, you should have a solid framework to better understand how firmware can be used to configure individual features. The Design Summit video offers a more detailed explanation of the typical process. It provides:

    • A list of Qorvo’s FOC solutions, available IPs and a deeper dive into some of the features
    • Step-by-step instructions for how to run a motor, including:
      • Hardware set up
      • Firmware Preparation
      • Motor Parameters Identification – Auto-tuning
      • Operating a motor from GUI or with a tuned motor parameter file (.xml)
      • Debugging tools and more

    The significant advances in motor control technology offer an array of opportunities for innovative product designs that capitalize on the efficiency, power handling and manageability of BLDC/PMSM motors. To learn more, go to Qorvo Online Design Summit: Field-Oriented Control for Tri-Phase BLDC/PMSM Motor Application.