TW201304389A - Motor frequency conversion apparatus - Google Patents

Abstract

A motor frequency conversion apparatus includes a motor and a driving device. The driving device is suitable for driving the motor, and is inclusive of a drive voltage generating circuit and a control circuit. The drive voltage generating circuit is controlled by a plurality of switching signals to output multi-phase drive voltage. The control circuit comprises a processor electrically connected to the drive voltage generating circuit, and is stored with a predetermined speed value to receive a feedback speed value related to the motor rotation speed and generate a plurality of control signals. The control signal is modulated with pulse width, generates the switching signal, and compares whether feedback speed value is less than predetermined speed value, in order to determine whether the plurality of control signals are set to a staircase wave individually. The staircase wave is used for reducing the harmonic of the drive voltage.

Description

Motor frequency conversion equipment

The invention relates to a frequency conversion device, in particular to a motor frequency conversion device.

In recent years, due to the needs of the industry, the speed of the motor has been rapidly increased to more than 300,000 rpm. Conventionally, for a high speed motor, a switching signal in the form of a square wave is used to control a switch of a power transistor module to output a driving voltage. Taking a three-phase motor as an example, the power transistor module has six power transistors, each of which is turned on for half a cycle, so that the voltage of each phase of the motor is in the form of a six-step square wave. Each cycle provides six discrete voltage vectors in the stator coil of the motor, which contain many harmonic components. If used to drive the motor, it will cause torque pulsation of the motor, which is more obvious at low speed. Therefore, it is not suitable for low speed operation.

Accordingly, it is an object of the present invention to provide a high speed motor frequency conversion apparatus that suppresses harmonics.

Thus, the motor frequency conversion device of the present invention comprises a motor and a driving device.

The driving device is adapted to drive the motor and includes a driving voltage generating circuit and a control circuit.

The driving voltage generating circuit is controlled by a plurality of switching signals to output the multi-phase driving voltage.

The control circuit has a processor electrically connected to the driving voltage generating circuit, pre-stores a preset speed value, and receives a feedback speed value related to the motor speed to generate a plurality of control signals, and then The control signal is modulated by the pulse width to generate the switching signals, wherein the processor compares whether the feedback speed value is lower than a preset speed value, and when the feedback speed value is less than the preset speed value, The control signals are respectively set to a trapezoidal wave, and when the feedback speed value is greater than the preset speed value, the control signals are respectively set to a square wave.

The present invention utilizes trapezoidal waves to reduce harmonics of the driving voltage, enabling the motor to operate at high speed and stable operation.

The above and other technical contents, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments.

Referring to Figure 1, a preferred embodiment of the motor frequency conversion apparatus of the present invention includes a motor 3 and a drive unit 4.

In the preferred embodiment, the motor 3 is a three-phase induction motor that is driven by a multi-phase drive voltage to produce a motor speed. In this embodiment, the driving voltage is three-phase, and includes three phase voltages V _a , V _{b ,} and V _c .

The driving device 4 is adapted to drive the motor 3 and includes a driving voltage generating circuit 2 and a control circuit 1.

The control circuit 1 has a processor 18 and a detector 17. The detector 17 is electrically connected to the three-phase input terminals of the motor 3 to obtain the phase voltages V _a , V _b and V _c , and the motor speed is estimated according to the driving voltage frequency to generate and output a feedback speed value. The feedback speed value can also be generated by a speed sensing device (not shown) mounted on the shaft of the motor 3, and the speed sensing device is electrically connected to the control circuit to output the feedback speed value.

The processor 18 receives an input speed command and electrically connects the detector to receive the feedback speed value, and generates six control signals V ₁ , V ₂ , V ₃ , V ₄ , V ₅ according to the control law. And V ₆ (not shown), and then the control signals V ₁ VV ₆ are modulated by the pulse width to generate six switching signals 11, 12, 13, 14, 15, and 16.

The driving voltage generating circuit 2 is electrically connected to the processor 18 to receive the switching signals 11-16, and is controlled by the switching signals 11-16 to output the phase voltages V _a , V _b and V _c for driving the High speed motor 3. The driving voltage generating circuit 2 includes a rectifying unit 22, a voltage adjusting unit 23 and a power transistor module 24.

The rectifying unit 22 is electrically connected to an AC power source 21 to receive an AC power and rectify it to output a first DC power.

The voltage regulating unit 23 is electrically connected to the rectifying unit 22 to receive the first direct current, electrically connected to the processor 18 and controlled by the processor 18 to output a second direct current having a predetermined voltage value. The voltage adjusting unit can adopt a Buck converter to convert the first direct current of the high voltage into the second direct current of the lower voltage by means of the pulse width modulation.

The power transistor module 24 has a plurality of switch units 241 connected in parallel to each other and electrically connected to the step-down unit 23. Each switch unit 241 has a first power transistor and a second power transistor connected in series. The two power transistors are electrically connected to the processor 18 and controlled by the switching signals 11-16 to be turned on or off, so that the second DC power is outputted or not between the two power transistors as the phase voltage. V _a , V _b and V _{c are used} to drive the high speed motor 3 to rotate.

In the preferred embodiment, the voltage adjustment unit 23 adjusts the amplitudes of the phase voltages V _a , V _{b ,} and V _c , and the power transistor module 24 adjusts the frequencies of the phase voltages V _a , V _{b ,} and V _c . . However, the voltage adjustment unit 23 may be omitted, and the amplitude and frequency of the phase voltages V _a , V _{b ,} and V _c may be directly adjusted by switching of the power transistor module 24 .

The mode of pulse width modulation is: comparing each control signal with a triangular carrier, and using the difference between the two, when the control signal is larger than the triangular carrier, a "on" switching signal is generated; when the control signal is smaller than the triangular carrier , generating a "non-conducting" switching signal.

Limited to the current power crystal characteristics and loss of motor magnetic materials, the general carrier frequency is at most 10~15 kHz. However, in order to maintain the quality of the output voltage of the driving device, the carrier frequency must be at least 19 times the frequency of the sine wave control signal, so the conventional driving device is mostly used for systems with lower output frequencies such as DC to 600 Hz. To drive a high-speed motor of 300,000 rpm, the sine wave control signal frequency needs to be 5 kHz, and the carrier frequency will be as high as 95 kHz. Currently, the power crystal cannot be supported, and the resulting switching power loss is too large.

Therefore, at a high rotational speed, the motor 3 is driven by a six-step square wave method, and the control signals are square waves having a duty-conducting ratio of one-half, and the switching signals are 11 to 16 after being modulated by the pulse width. The waveform is the same as the control signals V ₁ VV ₆ , and the timing is as shown in FIG. 2 .

In order to solve the harmonic problem generated by the square wave, at low speeds, the control signals V ₁ VV ₆ generated by the control circuit 1 are composed of periodic sine waves. In the preferred embodiment, the periodic sine wave has a fundamental frequency component and a triple frequency component. The frequency of the triple frequency component is three times the fundamental frequency component, and the amplitude is one sixth of the fundamental frequency component.

The voltage phases of the three control signals V ₁ , V ₂ , and V ₃ are one-third of a cycle apart, and the expression is as follows:

The other three control signals V ₄ , V ₅ , and V ₆ are inverted from V ₁ , V ₂ , and V ₃ , respectively, and the timings of the control signals V ₁ VV ₆ are as shown in FIG. 3 . The switching signals 11, 12, 13 provided to the first power transistors and the switching signals 14, 15, 16 of the second power transistors are respectively controlled by the control signals V ₁ , V ₂ , V ₃ , V ₄ V ₅ and V ₆ are converted by pulse width modulation.

Referring to FIG. 4, after the fundamental frequency and the triple frequency component are superimposed, a trapezoidal wave with a waveform resembling a trapezoidal wave is formed. The preferred embodiment can use trapezoidal waves or trapezoidal waves, both of which have similar effects. Compared with sinusoidal waves, trapezoidal waves or trapezoidal waves are flat at the peaks and have the characteristics of square waves. Pulse width modulation can be performed using carriers with lower frequencies. Figure 5 takes a trapezoidal wave as an example to compare the trapezoidal wave control signal, the triangular carrier, and the corresponding switching signal. It can be seen from FIG. 5 that for the power transistor module 24, the switching signal of the last one-third period is the maximum value, and the other one-third period is the minimum value. The first power transistor is continuously turned on for one-third of the time, and the second power transistor is continuously turned on for another one-third of the time. Compared with the sine wave, the trapezoidal wave can effectively reduce the number of switching of the power transistor. Reduce switching loss.

At the same time, since the trapezoidal wave is composed of a sine wave, the curve is smoother and the harmonics are less, and the torque ripple of the motor can be reduced with respect to the square wave. The magnitude of the harmonics can be known by measuring the three-phase voltage of the motor.

The following table compares the total harmonic distortion at each speed when the control signal is a square wave and a trapezoidal wave:

Since the three-phase coil of the motor has an inductance, it can be regarded as a low-pass filter. Therefore, as the rotational speed increases, the frequency of the control signal increases. Even after a certain frequency is exceeded, even a square wave can be filtered out of higher harmonics to have a performance close to the sine wave. As can be seen from the above table, the trapezoidal wave performs better at low speeds, and the square wave performs better at high speeds. Depending on the motor 3 and the driving device 4, a speed preset value is taken between 110,000 and 140,000 rpm, and when the feedback speed value is less than the preset speed value, the control signals V ₁ ~ V ₆ uses trapezoidal waves. When the feedback speed value is greater than the preset speed value, the control signals V ₁ VV ₆ are in the form of a periodic square wave.

In summary, the above embodiment has the following advantages:

1. Use a trapezoidal control signal to reduce harmonics for low speed operation.

2. At the same time, the motor 3 is driven in different ways at low speed and high speed, so that the motor 3 can maintain stable operation in its operating range.

The above is only the preferred embodiment of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent changes and modifications made by the scope of the invention and the description of the invention are All remain within the scope of the invention patent.

1‧‧‧Control circuit

11‧‧‧Switch signal

12‧‧‧Switch signal

13‧‧‧Switch signal

14‧‧‧Switch signal

15‧‧‧Switch signal

16‧‧‧Switch signal

17‧‧‧Detector

18‧‧‧ processor

2‧‧‧Drive voltage generation circuit

21‧‧‧Power supply

22‧‧‧Rectifier unit

23‧‧‧Voltage adjustment unit

24‧‧‧Power transistor module

241‧‧‧Switch unit

3‧‧‧Motor

4‧‧‧ drive

V ₁ ‧‧‧ control signal

V ₂ ‧‧‧ control signal

V ₃ ‧‧‧ control signal

V ₄ ‧‧‧ control signal

V ₅ ‧‧‧ control signal

V ₆ ‧‧‧ control signal

V _a ‧‧‧ phase voltage

V _b ‧‧‧ phase voltage

V _c ‧‧‧ phase voltage

1 is a circuit diagram of a preferred embodiment of a motor frequency conversion device of the present invention; FIG. 2 is a timing diagram of control signals in the form of six square waves of the preferred embodiment; and FIG. 3 is a six trapezoidal wave form of the preferred embodiment. FIG. 4 is a waveform diagram of a trapezoidal wave, a type of trapezoidal wave, and a sine wave of the preferred embodiment; and FIG. 5 is a trapezoidal wave control signal, a triangular carrier, and a preferred embodiment of the present invention. Waveform diagram of the switching signal.

1‧‧‧Control circuit

11‧‧‧Switch signal

12‧‧‧Switch signal

13‧‧‧Switch signal

14‧‧‧Switch signal

15‧‧‧Switch signal

16‧‧‧Switch signal

17‧‧‧Detector

18‧‧‧ processor

2‧‧‧Drive voltage generation road

21‧‧‧Power supply

22‧‧‧Rectifier unit

23‧‧‧Voltage adjustment unit

24‧‧‧Power transistor module

241‧‧‧Switch unit

3‧‧‧Motor

4‧‧‧ drive

V _a ‧‧‧ phase voltage

V _b ‧‧‧ phase voltage

V _c ‧‧‧ phase voltage

Claims (10)

A motor frequency conversion device comprising: a motor driven by a driving voltage to generate a motor speed; and a driving device adapted to drive the motor, and comprising: a driving voltage generating circuit controlled by the plurality of switching signals to output the a multi-phase driving voltage; and a control circuit having a processor electrically connected to the driving voltage generating circuit, pre-storing a preset speed value, and receiving a feedback speed value related to the motor speed to generate a plurality of Controlling the signals, and then modifying the control signals by the pulse width to generate the switching signals, wherein the processor compares whether the feedback speed value is lower than a preset speed value, and when the feedback speed value is less than the preset When the speed value is set, the control signals are respectively set to a trapezoidal wave, and when the feedback speed value is greater than the preset speed value, the control signals are respectively set to a square wave. The motor frequency conversion device according to claim 1, wherein the trapezoidal wave has: a fundamental frequency component; and a triple frequency component having a frequency three times the fundamental frequency component and an amplitude of the fundamental frequency component one-sixth. The motor frequency conversion device according to claim 1, wherein the driving voltage generating circuit comprises: a rectifying unit that receives the alternating voltage and rectifies to output a a first DC power; a voltage adjusting unit electrically connected to the rectifying unit to receive the first direct current, electrically connected to the microprocessor and controlled by the microprocessor to output a second direct current; and a power transistor module having a plurality of switch units connected in parallel to each other and electrically connected to the step-down unit, each switch unit having a first power transistor and a second power transistor connected in series, the two power transistors being electrically connected to the microprocessor and respectively The switching signals are controlled to be turned on or off, such that the second direct current is output or not output between the two power transistors to drive the motor to rotate. The motor frequency conversion device according to claim 1, wherein the preset speed value is between 110,000 and 140,000 rpm. A driving device for driving a motor, comprising: a driving voltage generating circuit controlled by a plurality of switching signals to output a driving voltage in a multi-phase; and a control circuit having: a processor electrically connected to the driving The voltage generating circuit prestores a preset speed value, and receives a feedback speed value related to the motor speed, generates a plurality of control signals, and then modulates the control signals by a pulse width to generate the switching signals. The processor compares whether the feedback speed value is lower than a preset speed value. When the feedback speed value is less than the preset speed value, the control signals are respectively set to a trapezoidal wave, when the feedback speed is When the value is greater than the preset speed value, the control signals are respectively set to one-wave. The driving device according to claim 5, wherein the trapezoidal wave has: a fundamental frequency component; and a triple frequency component having a frequency three times that of the fundamental frequency component, and the vibration is the fundamental frequency component one-sixth. The driving device according to claim 5, wherein the driving voltage generating circuit comprises: a rectifying unit that receives the alternating voltage and rectifies to output a first direct current; and a voltage adjusting unit electrically connects the rectifying unit Receiving the first direct current, electrically connecting the microprocessor and being controlled by the microprocessor to output a second direct current; and a power transistor module having a plurality of switch units connected in parallel and electrically connected to the buck unit Each switching unit has a first power transistor and a second power transistor connected in series, and the two power transistors are electrically connected to the microprocessor and controlled by the switching signals to be turned on or off, so that the two The second direct current is output or not output between the power transistors to drive the motor to rotate. The driving device according to claim 5, wherein the preset speed value is between 110,000 and 140,000 rpm. A control circuit is applied to a driving voltage generating circuit, and the driving voltage generating circuit is controlled by a plurality of switching signals to output a driving voltage of a plurality of phases for driving a motor, the control circuit comprising: a detector, the electric Connecting the motor to obtain the driving voltages, The driving voltage frequency estimates a motor speed to generate and output a feedback speed value related to the motor speed; and a processor electrically connected to the driving voltage generating circuit, pre-stores a preset speed value, and is electrically connected to the detecting The detector receives the feedback speed value, generates a plurality of control signals, and then modulates the control signals with a pulse width to generate the switching signals, wherein the processor compares whether the feedback speed value is lower than a preset value Setting a speed value, when the feedback speed value is less than the preset speed value, respectively setting the control signals as a trapezoidal wave, and when the feedback speed value is greater than the preset speed value, respectively, the control signals are respectively Set to one wave. The control circuit of claim 9, wherein the preset speed value is between 110,000 and 140,000 rpm.