JPH09140182A - Drive circuit for brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a brushless motor in which both the circuit efficiency and motor efffciency are satisfied and the leakage current from motor is reduced while sustaining the power factor of AC power supply at 1. SOLUTION: Output of a rectifier circuit 6 is short-circuited through a switching element 5 and a reactor 4 which is short-circuited through a capacitor 2 and a diode 3 connected, on the cathode side, with one end of the reactor 4 closer to the positive output of rectifier circuit 6. The capacitor 2 is connected across a three-phase bridge type switching element group 1 reversely to the direction of current flowing through the rectifier diode 3. The switching element group 1 is connected, on the output, with a brushless motor 14 and a circuit 13, receiving the output voltage waveform and current waveform from the rectifier diode 3 and the voltage across the capacitor 2, controls the output current from the rectifier diode 3 to have a waveform similar to the voltage and the voltage across the capacitor 2 represents a voltage being applied to the brushless motor 14. Means 12 conducts the switching element group 1 selectively depending on the rotational phase of brushless motor 14 connected with the output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit of a brushless motor, which uses a permanent magnet as a rotor and switches a stator rotating magnetic field in synchronization with the rotation thereof.

[0002]

2. Description of the Related Art It is known that a brushless motor having a permanent magnet mounted on a rotor has higher efficiency than an induction motor. In recent years, by detecting the induced voltage, it has become possible to detect rotation information of the rotor without using a rotation sensor. As this specific driving method, for example, the 120-degree constant-width PWM method is known, which is described in p241 to p242 of "Introduction to Power Electronics" by Yamamura and Ohno.
That is, during the energization period of 120 degrees, a constant voltage is applied by the pulse width modulation output having the same width.

In recent years, there has been a demand for measures for preventing generation of higher harmonic currents in AC power supply equipment, and as a method therefor, a circuit using a boost converter has been proposed. The method using the boost converter simultaneously controls the output voltage to be constant while controlling the current waveform to match the rectified pulsating voltage waveform. In order to satisfy this condition, the output voltage becomes higher than the pulsating current voltage.

Therefore, in a device that drives a brushless motor based on an AC power supply, a DC conversion circuit using this step-up converter and a three-phase distribution circuit that energizes 120 degrees from the obtained DC are used. FIG. 3 shows a block diagram thereof. In FIG. 3, the voltage Vrip, which has a pulsating waveform due to passing through the rectifying diode bridge 6 from the AC power supply 7, is input to the power supply harmonics control means 63 by the voltage detection means 9. Positive side of pulsating voltage is reactor 5
4 and the other end of the reactor 54 is connected to the anode terminal of the diode 53 and the switching element 55. The other end of the switching element 55 is connected to the negative side of the rectifying diode bridge 6. The cathode of the diode 53 is connected to the positive side of the capacitor 2 and the positive side of the three-phase switching element group 1, and the negative side of the capacitor 2 and the three-phase switching element group 1 is connected to the negative side of the rectifying diode bridge 6. There is. The current sensor 10 includes a switching element 5
The current Irip between the diode 5 and the rectifying diode bridge 10 is detected and input to the power supply harmonic control means 63. Similarly, the voltage detecting means 58 detects the voltage of the capacitor 2 and inputs it to the power source harmonic control means 63.

Next, the operating principle of the power source harmonic control means 63 will be described. The power supply harmonic control means 63 controls the waveform of the current Irip to have the same shape as the pulsating current voltage Vrip, and controls the magnitude of the current Irip so that the voltage Vdc of the DC portion has a predetermined value. To do. That is, an error between the predetermined DC voltage and the current DC voltage Vdc is obtained, and the amplitude of the waveform of the pulsating current voltage Vrpi is adjusted based on the error. An error between the adjusted pulsating current voltage and the current waveform Irip is obtained, the error is pulse-width modulated, and the switching element 55 is turned on.
/ OFF control. When the switching element 55 is ON, current is accumulated in the reactor 54, and when the switching element 55 is OFF, the current accumulated in the reactor 54 charges the capacitor 2 via the diode 53.

Next, the motor drive circuit portion in the subsequent stage will be briefly described. Since the rotor of the brushless motor 14 is composed of a permanent magnet, an induced voltage corresponding to the rotation phase is generated. Energize the motor for 120 degrees and turn it off for 60 degrees.
In the case of the 120-degree energization method of FF, the induced voltage phase detection means 11 can detect the induced voltage during the OFF period, and obtain the timing signal to be used for switching other phases during this period. You can The timing signal thus obtained is input to the three-phase distribution control circuit 62 to selectively switch the switching elements of the three-phase bridge type switching element group 1. When the rotation speed of the brushless motor 14 is high, a high voltage is required for the motor 14, and an appropriate applied voltage can be given by selectively applying the boosted DC voltage Vdc (edited by Yamamura and Ohno). "Introduction to Power Electronics"
Pp. 241 to 242. )

[0007]

However, when the rotation speed of the brushless motor 14 is low, it is proper to apply a low voltage to the motor. However, according to the configuration described in FIG. 3, the DC voltage Vdc is used. It is difficult to make the voltage low. That is, the power supply harmonic control operation needs to be a voltage in which the DC voltage Vdc is higher than the input voltage Vrip. If the DC voltage Vdc is lower, regardless of whether the switching element 55 is ON or OFF, the reactor 5
The current flows through 4 and the diode 53, and Vri
This is because it is impossible to make the voltage lower than p and the current cannot be controlled.

Therefore, in order to drive the brushless motor 14 with a low applied voltage, the three-phase distribution control means 62 turns on the three-phase bridge type switching element group 1 by pulse width modulation to average the motor applied voltage. Value is DC voltage V
It is necessary to control so that the voltage becomes smaller than dc.

However, when the motor is driven by pulse width modulation, there is a problem that the current fluctuation of the remaining pulse width modulation component causes a decrease in motor efficiency and the generation of electromagnetic noise. There is also a problem that current fluctuation of the pulse width modulation component leaks through the electrostatic capacitance in the air gap of the motor.

Another method is to connect a step-down converter to the output of the step-up converter and selectively switch the three-phase bridge type switching element group with the output voltage. The two are connected in series, and there is a problem that the loss of the converter is doubled.

An object of the present invention is to solve such a conventional problem.

[0012]

In order to solve the above-mentioned problems, the present invention short-circuits the output of a rectifier circuit with a switching element and a reactor so that both ends of the reactor are closer to the positive side output of the rectifier circuit. Connect the diode connected to the cathode side at one end so as to be short-circuited by the capacitor, and connect the three-phase bridge type switching element group so that both ends of the capacitor are opposite to the current direction of the rectifying diode, and the three-phase bridge type A brushless motor is connected to the output of the switching element group, the rectifier diode output voltage waveform, the current waveform, and the voltage across the capacitor are input, and the output current of the rectifier diode becomes similar to the rectifier diode voltage waveform, and, The control circuit for controlling the voltage across the capacitor to be the voltage required for applying the brushless motor, and the three-phase Comprising means for selectively conductive in accordance with the ridge type switching element group to the rotational phase of the brushless motor connected to its output.

When the switching element is turned on, current is accumulated in the reactor. When the switching element is turned off, the current accumulated in the reactor charges the capacitor through the diode. Therefore, the voltage across the capacitor has a polarity opposite to that of the output of the rectifying diode bridge. The amount of current that can be stored also changes according to the length of the ON period of the switching element, the voltage across the capacitor also changes, and it is possible to generate an arbitrary voltage whose polarity is opposite to that of the pulsating current voltage.

On the other hand, due to the existence of the control system in which the rectifier diode output voltage and the rectifier diode output current are similar systems, the power supply current waveform becomes equal to the voltage waveform, and the power supply harmonic current does not occur.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings.

According to the first aspect of the present invention, the output of the rectifier circuit is short-circuited by the switching element and the reactor, and both ends of the reactor are connected to one end of the reactor closer to the positive side output of the rectifier circuit with the cathode side. The three-phase bridge type switching element group is connected in such a manner that the diode and the capacitor are short-circuited, and the both ends of the capacitor are connected so that the current direction of the rectifying diode is opposite to that of the three-phase bridge type switching element group. A brushless motor is connected to the output of the rectifier diode, and the rectifier diode output voltage waveform, the current waveform, and the voltage across the capacitor are input, and the output current of the rectifier diode becomes similar to the rectifier diode voltage waveform. In addition, the voltage across the capacitor is controlled to be the voltage required to apply the brushless motor. And a circuit, wherein the control apparatus for a brushless motor, characterized in that a means for selectively conductive in response to the three-phase bridge type switching element group to the rotational phase of the brushless motor connected to its output.

FIG. 1 is a circuit block diagram showing the configuration of an embodiment of the present invention. The AC power supply 7 has a pulsating voltage waveform through the rectifying diode bridge 6. A circuit is configured from the positive output of the rectifying diode bridge 6 to the negative output through the switching element 5 and the reactor 4. A circuit is composed of the diode 3 and the capacitor 2 at both ends of the reactor 4. These constitute an inverting DC converter circuit. Further, both ends of the capacitor 2 are connected to the brushless motor 14 by the three-phase bridge type switching element 1, and at the same time, the terminals of the motor are connected to the induced voltage phase detecting means 11. The output of the induced voltage phase detection means 11 is sent to the three-phase distribution control circuit 12 to send a distribution control command to the three-phase bridge type switching element 1. The three-phase distribution control method by detecting the induced voltage phase of the brushless motor is implemented by a known method.

In FIG. 1, the output voltage detection circuit includes a Zener diode 21, resistors 22 and 24, and an LED 2.
The output voltage is detected as the magnitude of the current flowing through the LED 23. The light generated in the LED 23 is transmitted to the phototransistor 8 and is transmitted to the control circuit 13 side.

In the control of the inverting type DC converter circuit, in the power source harmonic control means 13, the pulsating current voltage Vrip is detected by the voltage detecting means 9 and the pulsating current Ir is detected by the current detecting means 10.
ip is realized by inputting the capacitor voltage Vdc by the voltage detecting means 8 and performing pulse width modulation on the switching element 5. FIG. 2 is a block diagram showing information processing inside the power source harmonic control means 13. Induced voltage phase detection means 1
The error between the rotation speed and the rotation command obtained in 1 and the output voltage Vdc are compared by the comparison means 31, and the result is sent to the compensation means 32. In the compensating means 32, the comparison error is subjected to control compensation calculation such as proportional-plus-integral calculation and the result is multiplied by the multiplier 33
Send to The multiplier 33 multiplies the pulsating current voltage Vrip by the information based on the rotation error, and sends the result to the comparing means 34.
The comparison means 34 compares it with the pulsating current Irip and sends the result to the compensation means 35. The compensating means 35 performs control compensation calculation on the comparison error by proportional-plus-integral calculation or the like and sends the result to the comparing means 36. The comparing means 36 compares the output of the oscillating means 37 and sends the result as a switching command to the switching element to perform the switching operation. That is, the comparison means 36 and the oscillation means 37 constitute a pulse width modulation means. By controlling the pulse width modulation of the switching element 5 by comparing the output of the multiplier via the pulsating current voltage Vrip with the current Irip, a control system in which the current waveform and the voltage waveform have the same shape is configured, and it corresponds to the load. The control system for adjusting the power supply current amount is configured by controlling the pulse width modulation of the switching element 5 via the DC voltage Vdc, the comparison means 31, and the compensation means 32.

In the embodiment of the present invention, the switching element is connected to the positive output side of the rectifier circuit, but the switching element is connected to the negative output side of the rectifier circuit. It goes without saying that the present invention can be implemented in the same manner as long as it is an inverting DC converter.

Also, the output voltage detection circuit has been described using a simple circuit configuration, but the output voltage value is turned ON / O.
It goes without saying that it is possible to use a voltage information transmission method by another method such as a method of pulse-width modulating the FF information and driving the LED to transmit.

[0022]

As described above, the present invention has the effects that the power supply harmonic current is not generated, the motor efficiency is not lowered, and the leakage current from the motor is reduced.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of power supply harmonics control means in the present embodiment.

FIG. 3 is a circuit block diagram of a conventional example.

[Explanation of symbols]

 1 Three-Phase Bridge Type Switching Element Group 2 Capacitors 3, 53 Diodes 4, 54 Reactor 5, 55 Switching Elements 13 Power Harmonic Control Means 14 Brushless Motor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsukaharu Yoshioka 1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] 1. A diode in which the output of a rectifying circuit by a rectifying diode is short-circuited with a switching element and a reactor, and both ends of the reactor are connected to one end of the reactor closer to the positive output of the rectifying circuit on the cathode side. And a capacitor so that they are short-circuited, and the three-phase bridge type switching element group is connected so that both ends of the capacitor are opposite to the direction of the current of the rectifying diode, and the output of the three-phase bridge type switching element group. Is connected to a brushless motor, further, the rectifier diode output voltage waveform, the current waveform, and the voltage across the capacitor are input, the output current of the rectifier diode becomes similar to the rectifier diode voltage waveform, and, The voltage is controlled so that the voltage across the capacitor becomes the voltage required to apply the brushless motor. When the driving circuit of the brushless motor is characterized in that a means for selectively conductive in response to the three-phase bridge-type switching element group connected to rotation phase of the brushless motor at its output.