Phase closed loop control direct current motor speed regulating method

Abstract

The invention relates to a phase closed loop control direct current motor speed regulating method, which comprises the following steps: a voltage-phase converter is adopted to convert the voltage drop at the two ends of a TRIAC which is in series with the direct current motor, the rotating speed signals of the direct current motor are obtained through measuring the phase pulse width, the negative feedback closed-loop control can be realized by a time-delay control algorithm of fixed length which is synchronous to a phase falling edge or by a time-delay control algorithm of variable length which is synchronous to a zero crossing point. The speed regulating method provided by the invention is applicable to the speed regulating for small and medium power direct current motors, such as body massage machine, blood circulation machine and the like, thus having the advantages of low cost, flexible control, stable and reliable rotating speed control.

Description

technical field [0001] The invention relates to a speed regulating method of a direct current motor, in particular to a speed regulating method of a direct current motor using a bidirectional thyristor TRIAC as a switch element and controlled by a phase closed-loop under a load changing state. Background technique [0002] With the development of power electronics technology, the methods of driving DC motors are becoming more and more abundant. Among them, the power control circuit using bidirectional thyristor TRIAC has the advantages of simple structure, reliable performance and low price, and has been widely used in medium and small power motor drives. Wide range of applications. [0003] Because the DC motor drive circuit using bidirectional thyristor TRIAC is mostly used in low-cost occasions, such as low-power human body massage machines, blood circulation machines, etc., the open-loop control method is generally used, that is, by adjusting the bidirectional thyristor ...

AI Technical Summary

Problems solved by technology

Because the voltage signal sampling is simple and reliable, the VZC synchronization method is mostly used in most simple applications; and in consideration of better matching the requirements of the turn-off sequence of the bidirectional thyristor TRIAC components, the performance will be better by using the CZC synchronization method , but due to the difficulty of current sampling, it will increase the hardware cost

However, regardless of the VZC synchronization method or the CZC synchronization method, the feedback signal does not come directly from the speed signal, and the conduction angle and phase are fixed in the circuit in advance, so these two methods are used in applications with constant loads (such as soybean milk machines). There will be no unstable speed, but in applications with changing loads (such as human body massage machines), there will be problems with unstable speed

[0005] The key to the speed closed-loop control method is the sampling of the speed feedback signal. There are currently two methods: one is to directly measure the speed physically, such as using a photoelectric encoder, a Hall sensor, or a DC tachogenerator. The advantage of this method is to directly measure the mechanical speed of the motor, with high measurement accuracy and fast feedback speed. The disadvantage is that the system cost needs to be increased; the second is to measure the speed indirectly. Since the speed of the DC motor is linear with the voltage at both ends, it can be measured The voltage at both ends is used to estimate the speed. Similarly, the speed can also be estimated by measuring the load current of the DC motor. This method has low measurement accuracy, and the driving part of the DC motor is high voltage relative to the control part, so the sampling signal needs to be electrically converted. And electrical isolation before it can be sent to the low-voltage control part

[0006] For some low-cost variable load applications, such as human body massage machines, the resistance torque that reacts on the human body massage machine changes according to the body weight and physique, as well as the position and force of the human body. If the open-loop control method is used, the greater the resistance torque, the higher the speed. On the contrary, the smaller it is, the problem that it can't achieve the massage effect; and for the application of human body massage machine, it does not need precise speed control, and the closed-loop method needs to increase the hardware cost, which is not cost-effective.

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