Research on variable frequency operation mode of t

Research on variable-frequency operation mode of brushless synchronous motor

Abstract: brushless synchronous motor is widely used in chemical industry, coal mine and other places with explosive environment because it has no slip ring, carbon brush and other links that may produce sparks. In recent years, with the popularization of energy-saving concept, a large number of brushless synchronous motors will face frequency conversion transformation. This paper briefly introduces the structure, principle and operation mode of brushless synchronous motor, analyzes in detail the excitation, step-by-step, excitation regulation and other problems encountered in the frequency conversion operation of brushless synchronous motor, and puts forward the frequency conversion operation mode of brushless synchronous motor, so that under this mode, the frequency converter can drive the brushless synchronous motor to regulate speed reliably and economically

key words 4. The interface on the plug-in controller must turn off the power supply of the controller: brushless synchronous motor, frequency conversion, speed regulation, operation mode

I. preface

brushless synchronous motor is widely used in places with explosive environment such as chemical industry and coal mine because it has no slip rings, carbon brushes and other links that may produce sparks. In addition, because the carbon brush and other vulnerable components are removed, the overall reliability of the motor is greatly improved. It is also used in some occasions that require long-term and high reliability operation. In recent years, with the popularization of energy-saving concept, a large number of brushless synchronous motors will face frequency conversion transformation

due to the inherent technical characteristics of brushless synchronous motor, the problems encountered by synchronous motor, such as weak field excitation, motor leading phase operation, frequency converter exciter collaborative control, have always restricted the frequency conversion application of brushless synchronous motor

based on the structure and principle of brushless synchronous motor, this paper makes a detailed analysis of various problems encountered in the frequency conversion operation of brushless synchronous motor, and puts forward appropriate solutions to these problems according to the results of theoretical analysis and simulation test, so that the frequency converter can drive the brushless synchronous motor reliably and economically

II. Structure and power frequency operation process of brushless synchronous motor

1 Structure of brushless synchronous motor

the structure of brushless synchronous motor is shown in Figure 1:

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Figure 1 brushless synchronous motor structure

in the figure: 1 is sliding bearing, 2 is brushless synchronous motor winding, 3 is cooler, 4 is rotating rectifier, 5 is excitation generator.

2. Brushless synchronous motor excitation system structure

brushless synchronous motor excitation system structure is shown in Figure 2, in which the excitation generator and synchronous motor rotate coaxially.

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Figure 2 brushless synchronous motor excitation system structure

among them, the rotating rectifier is responsible for the de excitation and excitation logic during the motor starting process, and its internal structure is shown in Figure 3. When the motor starts, the rotating rectifier controls the deexcitation thyristor T4 to connect the deexcitation resistance RF to the rotor excitation winding of the brushless synchronous motor to provide a large starting torque and reduce the voltage at the end of the excitation winding. At this time, the rectifier thyristor T1 ~ T3 is cut off; When the motor reaches the subsynchronous speed and meets the quasi angle conditions, the controller triggers the rectifier thyristor T1 ~ T3, rectifies the armature voltage of the excitation generator and adds it to the excitation winding of the synchronous motor, which is a synchronous motor event. 8. Irregular deviation of the indicated value; The generator provides continuous excitation current and turns off the de excitation thyristor T4 at the same time. At this time, the rotating rectifier is equivalent to a three-phase diode uncontrolled rectifier

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Figure 3 rotating rectifier structure

3. power frequency steady-state operation of brushless synchronous motor

when the brushless synchronous motor operates at power frequency steady-state, the exciter applies appropriate excitation current to the stator excitation winding of the excitation generator, induces three-phase AC voltage at the end of the rotor armature winding of the excitation generator, and the rotating rectifier (equivalent to diode rectifier) Rectified into DC voltage, which is applied to the rotor excitation winding of brushless synchronous motor to provide continuous excitation current

according to the physical characteristics of the excitation generator, the output armature voltage is approximately proportional to the product of the motor speed and the excitation current of the excitation generator. Therefore, the exciter can adjust the stator excitation current of the excitation generator by adjusting the trigger angle of the thyristor, so as to achieve the purpose of adjusting the rotor excitation current of the brushless synchronous motor

4. The power frequency starting and excitation process of brushless synchronous motor

the power frequency starting and excitation process of brushless synchronous motor is shown in Figure 4:

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Figure 4 power frequency starting process of brushless synchronous motor

when power frequency starting, first the high-voltage circuit breaker is closed, the de excitation part circuit of the rotating rectifier connects the de excitation resistance to the excitation winding of the synchronous motor according to the induced voltage on the excitation winding of the synchronous motor, and the synchronous motor gradually accelerates.

after the high-voltage circuit breaker is closed, the exciter triggers the thyristor to connect to the stator excitation winding of the excitation generator With a certain excitation current. With the increase of motor speed, the voltage of the rotor armature winding of the excitation generator gradually increases. When it is higher than the minimum working voltage of the rotating rectifier, the rotating rectifier controller powered by it is powered on, and the rotating rectifier monitors the induced voltage on the excitation winding of the synchronous motor. When its cycle is greater than the preset value (indicating that the synchronous motor has reached sub synchronous speed) and reaches the reverse zero crossing point, the rectifier thyristor is triggered, Turn off the de excitation thyristor, rectify the rotor armature voltage of the excitation generator and apply it to the excitation winding of the synchronous motor to complete the excitation

the motor enters a stable synchronous operation after a short whole step process