JP3051754B2 - Motor drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a motor drive device that drives a motor so that its rotation speed can be changed.

(Prior Art) Conventionally, when a motor is operated at a variable speed using a DC power supply, as shown in FIG. 4, a voltage of a DC power supply 1 is converted into an AC voltage of an arbitrary frequency by an inverter main circuit 2. The motor 3 is driven by the inverter main circuit 2. In this case, the inverter main circuit 2 is controlled by the inverter control circuit 4. The inverter control circuit 4 performs PWM control on the inverter main circuit 2 so as to obtain a voltage (V / f = constant) corresponding to the output frequency of the inverter main circuit 2.
Controlled by control. The use of the PWM control type inverter is more advantageous in terms of efficiency than the case of the PAM control type inverter.

An example of such a motor drive device is an electric vehicle. In this case, the voltage of the DC power supply is
96V, when this is converted to AC by the inverter output circuit, the maximum value of the fundamental wave component of the output voltage is almost 75V It is.

(Problems to be Solved by the Invention) As described above, when the motor is operated at a variable speed by the PWM control type inverter, the DC power supply voltage is restricted although the PWM control type inverter is efficient. Under such circumstances, the output voltage of the inverter main circuit also becomes low, and as a result, a low-voltage high-current type motor must be designed. However, a low-voltage high-current type motor requires the use of a copper wire having a large wire diameter for the motor winding, so that the motor cost is high, and the wire area ratio is reduced to deteriorate the motor characteristics. Further, when the motor is driven at a low rotation speed by the PWM control type inverter, as shown in FIG. 5, the amplitude Aa of the sine wave control signal is changed with respect to the amplitude Aa of the carrier signal in order to obtain an output voltage corresponding thereto. Lower the PW
The pulse width of the M signal is reduced, but when the amplitude ratio, that is, the PWM control ratio (Ab / Aa) decreases, the harmonics increase, and the efficiency decreases.

The present invention has been made in view of the above circumstances, and has as its object not only the fact that an efficient PWM control type inverter can operate a motor at a variable speed, but also that a high-voltage type motor can be used as a motor. It is an object of the present invention to provide a motor drive device capable of reducing the diameter of a winding, improving a line factor and improving motor characteristics, and suppressing generation of harmonics in an inverter.

[Structure of the Invention] (Means for Solving the Problems) A motor drive device according to the present invention drives a motor so that the rotation speed can be changed. A DC voltage conversion circuit for stepping down, an inverter main circuit connected to the DC voltage conversion circuit, and a PWM control for the inverter main circuit, wherein the amplitude of the carrier signal is set to “A1” and the amplitude of the motor drive control signal is set to “A1”. When the ratio is “A2”, the ratio (A2 / A1) is 1
It is characterized by comprising an inverter control circuit fixed to the above value, and control means for controlling the output voltage of the DC voltage conversion circuit according to the output frequency of the inverter main circuit.

(Operation) According to the above means, since the DC power supply voltage is boosted by the DC voltage conversion circuit and the DC voltage is applied to the inverter main circuit, the output voltage of the inverter main circuit also increases,
A high-voltage low-current type motor can be used as the motor, and the diameter of the motor winding can be reduced.In addition, the line factor is improved, the motor characteristics are improved, and the DC power supply voltage is increased. , Even when rotating the motor at low speed,
It is only necessary to reduce the step-up width to reduce the output voltage of the inverter main circuit, so that the PWM control ratio does not need to be so small, and thus the control ratio can be fixed to a value of 1 or more.
By doing so, it is possible to suppress an increase in harmonics in the output voltage of the inverter main circuit, and to prevent a decrease in efficiency due to this.

(Embodiment) FIGS. 1 and 2 show a first embodiment of the present invention.
This will be described with reference to the drawings.

FIG. 1 shows the electrical configuration. The voltage of the DC power supply 11 is boosted by the DC voltage conversion circuit 12, and can be stepped down within the boosted range.
This DC voltage conversion circuit 12 is configured by connecting diodes 13, 14, a step-up NPN transistor 15, a reactor 16, a step-down NPN transistor 17 and a capacitor 18 to the DC power supply 11 as shown in FIG. The transistors 15 and 17 are switched by the base drive circuit 19. Thus, the DC voltage conversion circuit 12 reacts by turning on the transistor 15 intermittently while the transistor 17 is conducting.
The energy stored in 16 is supplied to the load side during the off period to boost the voltage E of the DC power supply 11 and the boosted voltage can be changed by changing the duty ratio of the transistor 15. That is, the voltage can be reduced within the range of the voltage increase.

An inverter main circuit 20 is connected to an output side of the DC voltage conversion circuit 12, and the inverter main circuit 20 is configured by a three-phase bridge circuit including a power transistor 20a. The motor 21 is controlled by the inverter main circuit 20.
Are driven so that the rotation speed can be changed. This motor 21
Consists of a 100V / 60Hz three-phase induction motor. The inverter main circuit 20 is PWM-controlled by an inverter control circuit 22.
Is a microcomputer 23 and a PWM signal generation circuit 24
And a base drive circuit 25.
In the signal generating circuit 24, as shown in FIG. 2, a PWM signal Sp is generated based on a triangular carrier signal Sc and a sine wave control signal Ss as a motor drive control signal, and the inverter main circuit is generated based on the PWM signal. Drive control of the twenty transistors 20a is performed. In this case, the control ratio (A2 / A1) between the amplitude A1 of the carrier signal Sc and the amplitude A2 of the sine wave control signal Ss is “1”.
It is fixed to.

The microcomputer 23 is a DC voltage conversion circuit.
The control means for controlling 12 is also used as the speed command.
When Sn is given, the output frequency of the inverter main circuit 20 is determined accordingly, and the boost voltage value in the DC voltage conversion circuit 12 is determined according to the output frequency, and the voltage value is output. The base drive circuit 19 is controlled.

Thus, in the above configuration, when the motor 21 of the 100 V / 60 Hz specification is operated at 120 Hz, the control means in the microcomputer 23 controls the DC voltage conversion circuit 12 so that the output voltage thereof is 256 Vac (the following (See equation).

In this case, as shown in FIG. 2, the inverter control circuit 22 has a control ratio (A2 / A1) of the amplitude A1 of the carrier signal Sc and the amplitude A2 of the sine wave control signal Ss at "1". The inverter main circuit 20 has a boosted voltage 25 by the DC voltage conversion circuit 12.
Since 6 V is applied, the motor 21 is applied with a voltage of 120 V at 200 Vac.

When the rotation speed of the motor 21 is reduced, the output voltage of the DC voltage conversion circuit 12 is reduced from 256 V by the microcomputer 23 while the control ratio of the inverter control circuit 22 remains “1”.

When the motor 21 is driven by the output voltage of the inverter main circuit 20 of 30 Hz, 50 Vac is required as the output voltage of the inverter main circuit 20.
Is reduced to approximately 65 V by the DC voltage conversion circuit 12. At this time, the DC voltage conversion circuit 12
Reference numeral 15 designates a non-conducting state, and controls only the conduction time ratio of the transistor 17.

According to this embodiment, since the DC power supply voltage 11 is boosted by the DC voltage conversion circuit 12 and the DC voltage is applied to the inverter main circuit 20, the output voltage of the inverter main circuit 20 also increases, and the motor 21 As a result, a high-voltage low-current type motor can be used, the diameter of the motor winding can be reduced, and the linearity factor is improved to improve the motor characteristics. Since the DC power supply voltage is stepped up, even when the motor 21 is rotated at a low speed, the output voltage of the inverter main circuit 20 can be lowered by reducing the stepped-up width, so that the PWM control ratio does not need to be reduced so much. Therefore, it is possible to fix the control ratio to a value of 1 or more. Thus, in this embodiment,
Since the control ratio is fixed to "1", it is possible to suppress an increase in harmonics in the output voltage of the inverter main circuit 20, and
This can eliminate the reduction in efficiency.

The PWM control ratio may be "1" or more. For example, as shown in FIG. 3 as a second embodiment of the present invention, the amplitude A1 of the carrier signal Sc and the amplitude A2 of the sine wave control signal Ss are different from each other. Control ratio (A2 / A1) may be fixed to “1.2”.

Also, the motor 21 need not be an induction motor,
For example, the present invention may be applied to driving of a DC brushless motor controlled by a rectangular wave-shaped motor drive control signal in a medium to high speed range, or may be a single-phase motor. Furthermore, the DC voltage conversion circuit 12 may be at least a step-up type, and a step-down function may be provided as needed.

In addition, the present invention is not limited to the above embodiments, and can be implemented with various modifications without departing from the scope of the invention.

[Effects of the Invention] As is apparent from the above description, the present invention relates to a motor that drives a motor so that its rotation speed can be changed. Circuit, an inverter main circuit connected to the DC voltage conversion circuit, and a PWM
An inverter control circuit for controlling an amplitude of a carrier signal to be “A1” and an amplitude of a motor drive control signal to be “A2” and fixing a ratio (A2 / A1) thereof to a value of 1 or more; Control means for controlling the output voltage of the DC voltage conversion circuit in accordance with the output frequency of the main circuit, so that the motor can be operated at a variable speed by an efficient PWM control type inverter. A high-voltage low-current type motor can be used as the motor, the motor winding can be reduced in diameter, the line factor can be improved, the motor characteristics can be improved, and harmonics in the inverter can be improved. This is an excellent effect that the increase in the density can be suppressed.

[Brief description of the drawings]

FIGS. 1 and 2 show a first embodiment of the present invention. FIG. 1 is an electric circuit diagram including some blocks, and FIG.
FIG. 3 is a waveform diagram showing a PWM control ratio, and FIG. 3 is a diagram corresponding to FIG. 2 showing a second embodiment. 4 and 5 show a conventional example, FIG. 4 is a block diagram of an electric configuration, and FIG. 5 is a diagram corresponding to FIG. In the drawings, 11 is a DC power supply, 12 is a DC voltage conversion circuit, 20 is an inverter main circuit, 21 is a motor, 22 is an inverter control circuit, and 23 is a microcomputer (control means).

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02P 7/63 H02M 7/48

Claims (2)

(57) [Claims] 1. A DC voltage conversion circuit for driving a motor so that its rotation speed can be changed, wherein the DC voltage conversion circuit raises a DC power supply voltage and drops the voltage within the range of the voltage increase, and is connected to the DC voltage conversion circuit. Inverter main circuit and PWM control of the inverter main circuit, wherein the ratio (A2 / A1) is 1 or more when the amplitude of the carrier signal is "A1" and the amplitude of the motor drive control signal is "A2". A motor drive device comprising: an inverter control circuit fixed to a value; and control means for controlling an output voltage of the DC voltage conversion circuit according to an output frequency of the inverter main circuit. 2. The motor drive device according to claim 1, wherein the motor drive control signal is a sinusoidal control signal.