The brushless DC motor is developed on the basis of the brushed DC motor. It has the advantages of stepless speed regulation, wide speed regulation range, strong overload capacity, good linearity, long life, small size, light weight and large output. It solves a series of problems existing in brushed motors and is widely used in various fields such as industrial equipment, instrumentation, household appliances, robots, and medical equipment. Since brushless motors do not have brushes for automatic commutation, an electronic commutator is required for commutation. The brushless DC motor driver realizes the function of this electronic commutator.
At present, there are three main control methods of BLDC motors: FOC (also known as vector frequency conversion, magnetic field vector oriented control), square wave control (also known as trapezoidal wave control, 120° control, 6-step commutation control) and sine wave control. So what are the advantages and disadvantages of each of these three control methods?
1.Square wave control
The square wave control uses the Hall sensor or the sensorless estimation algorithm to obtain the position of the motor rotor, and then commutates 6 times (one commutation every 60°) within the electrical cycle of 360° according to the position of the rotor. Each commutation position motor outputs a force in a specific direction, so it can be said that the position accuracy of the square wave control is electrical 60°. Because the phase current waveform of the motor is close to the square wave under the control in this way, it is called the square wave control.
The advantage of the square wave control method is that the control algorithm is simple, the hardware cost is low, and a higher motor speed can be obtained by using a controller with ordinary performance; the disadvantage is that the torque fluctuation is large, there is a certain current noise, and the efficiency cannot reach the maximum value. . Square wave control is suitable for occasions that do not require high motor rotation performance.
2.Sine wave control
The sine wave control method uses the SVPWM wave, the output is a 3-phase sine wave voltage, and the corresponding current is also a sine wave current. This method does not have the concept of square wave controlled commutation, or considers an infinite number of commutations in an electrical cycle. Obviously, compared with square wave control, sine wave control has smaller torque fluctuation and less current harmonics, and the control feels more “fine”, but the performance requirements of the controller are slightly higher than that of square wave control, and the motor efficiency cannot be exerted. maximum value.
3.FOC control
The sine wave control realizes the control of the voltage vector, and indirectly realizes the control of the current size, but cannot control the direction of the current. The FOC control method can be considered as an upgraded version of the sine wave control, which realizes the control of the current vector, that is, the vector control of the motor stator magnetic field.
Since the direction of the stator magnetic field of the motor is controlled, the stator magnetic field and the rotor magnetic field of the motor can be kept at 90° at all times to achieve the maximum torque output under a certain current. The advantages of the FOC control method are: small torque fluctuation, high efficiency, low noise, and fast dynamic response; the disadvantages are: high hardware cost, high requirements for controller performance, and matching motor parameters. Due to the obvious advantages of FOC, it has gradually replaced traditional control methods in many applications, and is favored in the motion control industry.
Shenzhen Zhongling Technology Co., Ltd. is an enterprise specializing in the production, manufacture and development of in-wheel motors that provides in-wheel motor products and other accessories for robots for a long time. in a leading position. And has always adhered to the concept of continuous innovation to bring customers the best products, a complete sales research and development system, to provide customers with the best buying experience. I hope we can accompany the rapid development of the robot industry.
Post time: Feb-22-2023