Intention of an inimitable sensorless control for BLDC motor drive

Abstract:

This drudgery suggests an enriched methodology, a position sensorless control scheme for Brushless dc (BLDC) motor drive. The sensorless control techniques based on a latent start-up method with a high starting torque are recommended. For some applications it is imperative to reduce the manufacturing cost of the drive. Cost reduction is generally accomplished by eradication of the drive components such as sensors. The rotor position is aligned at standstill for maximum starting torque without an extra sensor and any statistics of motor parameters. With an identified initial rotor position and a specified commutation logic, an open-loop control system is then applied to accelerate the motor from a standstill. The viability of the recommended sensorless control arrangement is authenticated by MATLAB/SIMULINK results.

Introduction

BRUSHLESS DC motor has a rotor with permanent magnets and a stator with windings. It is fundamentally a DC motor curved inside out. The brushes and commutator have been eradicated and the windings are coupled to the superintendent electronics. The superintendent electronics swap the function of the commutator and energize the appropriate winding. The motor has fewer inertia, therefore easier to start and stop. BLDC motors are possibly cleanser, quicker, more effective, fewer noisy and more consistent. In order to obtain an accurate and ripple-free instantaneous torque of BLDC motor, the rotor position info for stator current commutation important be known, which can be attained using hall sensors attached on a rotor . This results in a high costs as well as poor reliability. To cope with the above mentioned restriction, many position sensorless algorithms have been considered as potential solutions. The position information is extracted by integrating the back-EMF of the silent phase and . This method has an error accumulation problem at low speed. The sensorless control techniques using the phase-locked loop (PLL) and the third-harmonic back-EMF are suggested . Access to the motor neutral point is essential, which will obfuscate the motor construction and upturn the price. Some approaches use the zero crossing points of three-phase line-to-line voltages, so that they coincide to six commutation points . Therefore, a specific start-up process in sensorless drive scheme is needed. The general elucidation to the difficult is the open-loop start-up system termed lsquo;align and gorsquo; . The procedure is to excite two phases of the three-phase windings for a predetermined time. The permanent magnet rotor at that moment rotate to align to an exact position. With a known maiden rotor position and a specified commutation logic, an open-loop control system is then applied to accelerate the motor from a standstill. The sensorless rotor position system detects the zero crossing points of Back-EMF induced in the stator windings. The three phase stator Back-EMF Zero Crossing points are detected while one of the three phase windings is not energized. The attained info is processed in order to commutate energized phase pair and control the phase voltage, using Pulse Width Modulation . This application note provides a fundamental mathematical method for modeling, torque calculation and control concept of the offered drive. The drive was established in order to report simple applications (e.g. pumps, compressors, fans hellip;) within certain ranges of speed in addition load. Outcomes from simulation display the drive performance at different elucidate the drive scheme .

Back Emf Sensing

In PM brushless DC machines, the magnitude of the back EMF is a function of the instantaneous rotor position and has trapezoidal variation with 120° flat span. However, in practice, it is problematic to measure the back EMF, for the reason that of the quickly changing currents in machine windings and induced voltages due to phase switching. The back EMF is not adequate enough at starting until the rotor reaches some speed. Therefore, it is a normal practice to make the preliminary acceleration under open-loop control using a ramped frequency signal so that the back-EMF is computable for the controller to lock in.

One of the widespread starting methods is “align and go”, in which the rotor is line up to the definite position by energizing any two phases of the stator and then the rotor is accelerated to the desired speed according to the given commutation sequences. The “align and go” method agonizes demagnetization of permanent magnets due to large instantaneous peak currents at initial. The zero crossing points of the back EMF in each phase may be an elegant feature to use for detecting, for the reason that these points are sovereign of speed and occur at rotor positions where the phase winding is not energized. Though, these points do not relate to the commutation moments. So, the signals need to be phase shifted by 90° electrical formerly they can be utilized for commutation. The discovery of the third harmonic element in back EMF, direct current control procedure and phase locked loops have been suggested to overwhelmed the phase-shifting difficult.

Start-Up Technique

When the motor is at standstill or very low speed, the back-EMF is too small to estimate a precise rotor position. Therefore, a precise start-up process in sensorless drive systems is required.

A. Alignment of Rotor Position

In the BLDC motor, only two phases of the three-phase stator windings are excited at any time by utilizing alternative six excited voltage vectors . That is why the current can flow into only two of the three windings and commutated every 60° of electrical angle. At standstill, the initial rotor position is aligned into one of six positions that are determined by the six excited voltage vectors to energize two phases of the BLDC motor . As

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无刷直流电机无传感器控制的意图

摘要：

这一枯燥的工作说明了一种丰富的方法，一种无刷直流(BLDC)电机驱动的无位置传感器控制方案。它介绍了一种基于高起动转矩潜启动方法的无位置传感器控制技术.对于某些应用程序，降低驱动器的制造成本是必要的。降低成本通常是通过消除驱动部件，如传感器。转子位置在静止状态下对齐，以获得最大起动转矩，而不需要额外的传感器和任何电机参数统计。在给定的初始转子位置和指定的换相逻辑的情况下，应用开环控制系统将电机从静止状态下加速。

介绍

无刷直流电动机有一个带永磁体的转子和一个带绕组的定子。从根本上说，它是一种向外弯曲的直流电机。电刷和换向器已被消除，绕组连接到主管电子。电子总监更换换向器的功能，并激活应用程序。 旋转缠绕。电机的惯性较小，因此更容易启动和停止。无刷直流电机可能是清洁剂，更快，更有效，更少噪音和更一致。为了获得一个交流 对无刷直流电机的瞬时转矩进行修正和无纹波，了解定子电流换向的转子位置信息，可以通过安装在转子上的霍尔传感器获得转子位置信息。这导致高成本和低可靠性。为了应对上述限制，许多无位置传感器算法被认为是潜在的解决方案。的位置信息是通过集成反电动势来提取的。 安静的相位和。该方法存在低速误差积累问题。提出了采用锁相环(PLL)和三次谐波反电势的无位置传感器控制技术.进入电机中性点是必不可少的，这将混淆电机的结构和提高价格。有些方法使用三相线对线电压的过零点，所以 与六个换乘点重合。因此，在无传感器驱动方案中需要一个具体的启动过程.对开环启动系统的一般解释称为“对齐和转”。该程序是在预定的时间内激发三相绕组的两个相位.永久磁铁转子在那一刻旋转，以对齐一个准确的位置。有一个已知的少女转子p 然后应用开环控制系统和指定的换相逻辑来加速电机停止运转。无位置传感器转子位置检测系统 在定子绕组中感应的反电动势。三相定子反电势过零点检测，三相绕组之一不通电。所获得的信息被处理，以交换能量相位对和 控制相位电压，采用脉宽调制。本应用说明为所提供的传动的建模、转矩计算和控制概念提供了一种基本的数学方法。建立驱动器是为了报告简单的应用程序。 在一定的速度范围内附加负载。仿真结果显示了不同驱动方案下的驱动性能。

反电势传感

在永磁无刷直流电机中，反电动势的大小是瞬时转子位置的函数，具有梯形变化，具有120°的平距。然而，在实践中，这是有问题的。 测量反电势，是由于电机绕组电流变化过快和由于相位切换而产生的感应电压。反电动势在启动之前还不够充分。 转子达到一定的速度。因此，通常的做法是在开环控制下，利用脉冲频率信号进行初始加速，这样就可以计算出反电势 。

一种普遍的起动方法是“对齐和转”，在这种方法中，转子通过给定子的任意两个相位供电，从而使转子加速到定位置。 根据给定的换相序列确定速度。“对齐和转去”方法因初始瞬时峰值电流大而使永磁体退磁痛苦。过零 每个相位的反电势点可能是用于检测的一个优雅的特征，因为这些点与速度无关，并且发生在没有相位绕组的转子位置。 被激活了。然而，这些点与换向矩无关。因此，信号需要通过90°电相移，才能用于换向。这个发现提出了反电势中的三次谐波元件、直流控制程序和锁相环等克服移相困难的方法。

启动技术

当电机处于停顿状态或非常低速时，反电动势太小，无法估计精确的转子位置。因此，在无传感器驱动系统中需要一个精确的启动过程.

1. 转子位置对准

在无刷直流电机中，三相定子绕组在任何时候都只有两相励磁，利用六种不同的激励电压矢量。这就是为什么电流只能流入两个 这三个绕组和换向每60°的电气角度。在静止状态下，初始转子位置被排列成由六个激励电压矢量t决定的六个位置中的一个。 给无刷直流电机的两个阶段供电。众所周知，这些电压矢量的偏差是电角度的每60°。如果采用传统的对准方法，定子磁链与永磁体在起始点处产生的转子磁链不正交。因此，初始电机转矩此时无法获得最大值。此外，定子绕组通过固定的直流电源和电机参数产生很高的不可控电流。

1. 启动过程

在调整转子位置的过程中，考虑了起动过程，使无位置传感器的无位置传感器方案不能实现电机的自启动，从而使无位置传感器的无位置传感器电机从静止状态提高到一定的速度。 应该启动，并能以一定的速度检测到反电动势的过零点。随着频率的逐渐增大，转子转速也随之增大。参考电压的大小与转子转速成正比。相位角可由整数求出。 转子转速和选通信号的脉宽随参考电压的大小而调制。在不需要任何转子位置信息的情况下，产生6个相位位移为60°的PWM信号与相位角相对应。当转子转速达到2500 rpm时，可感应反电动势以提供转子位置信息，并将系统切换到无传感器控制。

控制器

速度调节采用PI控制器实现。通过增加速度调节器的比例增益，提高了调节器的灵敏度，使其在较小的速度下具有更快的反应速度 调节故障。这允许通过速度调节器发出的电流基准的快速反应，对速度方向进行更好的初始跟踪。这种改进的灵敏度也降低了 速度过快了。电枢电流降低更快，一旦达到预期的速度。

积分增益的增加将使电机的速度在采样期间更快地赶上速度参考坡道。这将确实允许对小速度错误作出更快的反应。 或当信号在坡道之后被调节时发生的积分项。产生加速坡道时，调整器将响应，通过产生一个稍高的加速扭矩，更快地减少误差积分。另一方面，过高的比例增益和积分增益会导致不稳定，控制器变得不敏感。过高的增益也可能导致饱和。调谐过程采用试差法，比例常数为0.1，积分常数为0.03。

结论

本文提出了一种无位置传感器的无位置传感器控制方案。它展示出，该方法提供了一个扩大版本的反电动势。只有三台电动机 终端电压需要测量，从而消除对电机中性电压的需求。本文利用创新的过零点检测算法，对机器在无位置传感器模式下的运行进行了预测。为了实现最大初始转矩，永磁无刷直流电机从静止状态到标称速度，对转子位置进行调整。通过改变特定开关器件的脉宽，可以毫不费力地控制用于调整转子位置的定子电流的大小。电机起动平稳。 即使在有负载和负载瞬变的情况下也没有传感器。

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