JP2001231262A - Controller for direct current motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC motor controller which improves a power factor stably at all times, and reduces higher harmonics, even when power voltage, etc., vary. SOLUTION: This is a DC motor controller which controls the rotational speed of a DC motor 16 by varying DC output voltage detected by a DC voltage detector 10. The controller has a control circuit 15 provided with a first control means which controls the on-duty of a switching element 7 so that the instantaneous value of a current value detected by a current detector 6 may be current value of a target power factor; and a second control means which sets an upper limit value and a lower limit value for the minimum value of the DC output voltage, sets the minimum value of the DC output voltage varying it in accordance with rectified voltage detected by a rectified voltage detector 4, so that the minimum value of the DC output voltage may be in the range between the upper limit value and the lower limit value, and controls the on-duty of the switching element 7 in accordance with the set value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a DC motor, and more particularly to a control device for boosting a DC voltage supplied to an inverter circuit of the DC motor control device.

[0002]

2. Description of the Related Art In a conventional DC motor control, first, an AC power supply is boosted by a boost converter and converted into a DC voltage, which is supplied to a power supply terminal of an inverter device. 100% duty of PWM signal of inverter device
During this time, the DC output voltage value from the boost converter is set to a predetermined fixed minimum output voltage value, and the duty of the PWM signal of the inverter device is varied to control the rotation speed of the DC motor. After the duty of the PWM signal becomes 100%, the rotation speed of the DC motor is controlled by varying the DC output voltage value.

In the boost converter, not only boosting but also control for improving a power factor by controlling an input AC current waveform to be a sine wave and reducing harmonic current is performed.
The power factor improvement control is performed by the power factor improvement control IC and its peripheral circuits.The full-wave rectified voltage waveform, DC output voltage, and current waveform are input and the input AC current waveform is boosted to become a sine wave. Controls the drive signal of the switching element of the converter. As a conventional technique of power factor improvement control, for example, there is one disclosed in Japanese Patent Application Laid-Open No. 10-52050.

[0004]

The boosting by the boosting converter is performed by the on / off operation of the switching element. In the drive control of the switching element by the PWM control, the on-duty of the switching element is changed according to the rectified voltage waveform as shown in FIG. That is, since the rectified voltage value is small near the zero cross point of the rectified voltage waveform and the difference from the predetermined output voltage value is large, the on-duty is increased, and the rectified voltage value is large near the peak point of the rectified voltage waveform. Since the difference from the output voltage value is small, the on-duty is reduced.

The boost amount can be adjusted by an average value of the on-duty in the PWM cycle. When the average on-duty is reduced, the boost amount is also reduced. On the other hand, the switching element in the boost converter also performs power factor improvement for improving the input current waveform to a sine wave at the same time as boosting.

When the boosting amount is small, it is necessary to reduce the average on-duty in the PWM cycle, and in order to reduce the average on-duty, the maximum duty must also be reduced. Therefore, when the boosting amount is small, the change amount of the duty from the minimum duty to the maximum duty is small, and the range of the selectable duty value is limited, so that the input current waveform is shaped into the same phase as the rectified voltage waveform. It becomes difficult and the power factor decreases.

In the prior art, since the minimum value of the DC output voltage is fixed, if the power supply voltage rises due to, for example, fluctuations in the power supply voltage, the amount of boost must be reduced accordingly. In some cases, the power factor at the time of voltage was reduced.

Further, since the control of the DC motor and the control of the boost converter are performed by separate control devices, there is a problem that the circuit configuration becomes complicated and the cost increases.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a DC motor control device capable of stably improving a power factor and reducing harmonics even with a difference in a used power supply or a fluctuation in a power supply voltage. I do. Another object of the present invention is to provide a DC motor control device that can be realized with a simple circuit configuration by performing control of a boost converter and operation control of a DC motor in parallel by a single control device.

[0010]

In order to achieve the above object, the present invention rectifies an AC power supply voltage, boosts the rectified voltage with a reactor and a switching element, smoothes the rectified voltage with a capacitor, and obtains a DC output voltage. In the DC motor control device, the DC output voltage is supplied as a power supply voltage of an inverter for driving the DC motor, and the rotation speed of the DC motor can be controlled by changing the DC output voltage value. Current detection means for detecting an instantaneous value of an input current; first control means for controlling on-duty of the switching element such that the detected instantaneous value of the current value becomes a current value of a target power factor; An upper limit value and a lower limit value are provided for the minimum value of the output voltage, and the DC output voltage is set so that the minimum value of the DC output falls within the range between the upper limit value and the lower limit value. Variably set in accordance with the minimum value to the rectified voltage, and a second control means for controlling the on-duty of the switching element in accordance with the set value, comprising: a.

[0011]

According to such a configuration, even if the rectified voltage becomes high due to, for example, fluctuations in the power supply voltage, the minimum DC output voltage has a width, so that the upper limit value of the minimum DC output voltage is sufficiently larger than the rectified voltage. If it is high, a sufficient boosting amount will be secured. That the amount of boost is sufficiently secured,
That is, the variable width of the ON duty of the switching element is wide, and the duty adjustment for improving the power factor can be sufficiently performed.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. FIG. 2 is a circuit block diagram of a DC motor control device according to an embodiment of the present invention. In the figure,
Reference numeral 1 denotes a commercial AC power supply of AC 100 V, and reference numeral 2 denotes a boost converter that rectifies and boosts the AC power supply voltage and supplies a DC voltage to the inverter 11 that controls the DC motor 16 at a variable speed.

The step-up converter section 2 includes a rectifier circuit 3 connected to the AC power supply 1, a reactor 5 connected to the rectifier circuit 3, and a switching element for controlling the accumulation and release of energy to and from the reactor 5 by an on / off operation. 7, a smoothing capacitor 9 provided on the output side of the switching element 7, a diode 8 for preventing a reverse current, a rectified voltage detection circuit 4 for detecting a rectified voltage value, and a boost converter section. It comprises a DC voltage detection circuit 10 for detecting a DC output voltage value from the input device, and an input current detection circuit 6 for detecting an instantaneous value of the input current.

Rectified voltage detection circuit 4 and DC voltage detection circuit 1
0 and the input current detection circuit 6 are connected to the A / D conversion terminal of the control circuit 15. The control circuit 15 switches the switching element 7 so that the DC output voltage becomes a predetermined voltage value from the A / D input value and the input current waveform becomes a sine wave having the same phase as the input voltage waveform. The duty of the motor.

When the DC motor 16 is controlled by the 120 ° conduction method, it is necessary to detect the position of the rotor. Therefore, the position signal is obtained from the induced voltage generated at the winding terminal of the DC motor 16 by the position detection circuit 14. Create and control circuit 1
Enter 5 The control circuit 15 controls the rotation of the DC motor 16 by switching the drive signal for driving the inverter 11 according to the input position signal.

FIG. 3 is a circuit diagram showing a configuration of inverter 11. The inverter 11 has six switching elements Q
1 to Q6 and six diodes D1 to D6 for protecting the switching elements. Terminal T1 and terminal T2 are
Connected to the output side of converter unit 2. Terminals K1 to K6
Are connected to the drive circuit 13, and drive signals (PWM signals) from the drive circuit 13 are switched by the switching elements Q1 to Q
6 base. The terminals L <b> 1 to L <b> 3 are connected to the position detection circuit 14, and input an induced voltage generated at a winding terminal of the DC motor 16 to the position detection circuit 14.

When the DC motor 16 is started, the DC voltage output from the boost converter 2 has a minimum voltage value.
FIG. 4 shows a procedure for determining the minimum output voltage value. The control circuit (microcomputer) 15 first proceeds to step #
In step 5, the maximum value of the A / D value input from the rectified voltage detection circuit 4 is obtained. Next, in step # 10, a predetermined minimum boost value is added to the maximum value. And
In the next step # 15, it is determined whether or not the added value is larger than a predetermined lower limit. If the added value is smaller than the lower limit value, the lower limit value is set to the minimum output voltage value (step # 25). If the added value is larger than the predetermined lower limit value, the process proceeds to step # 20. Is larger than a predetermined upper limit. If the sum is larger than the upper limit, the upper limit is set to the minimum output voltage (step # 30). If the sum is smaller than the upper limit (that is, if the sum falls within the range between the lower limit and the upper limit),
The flow ends without doing anything (while keeping the added value at the minimum output voltage value).

For example, assume that the minimum boost value is 20 V, the lower limit is 160 V, and the upper limit is 170 V. When the AC power supply voltage drops to 85 V due to fluctuations in the power supply voltage or the like, the maximum value of the rectified voltage value becomes 120 V (= 85 V × √2).
However, since this is smaller than the lower limit value of 160 V, the minimum output voltage value is determined to be 160 V. Also, when the AC power supply voltage rises to 115 V, the maximum value of the rectified voltage value becomes 162 V (= 115 V × 、 2). Is smaller than 170V, the minimum output voltage value is 1
It is determined to be 70V. When the AC power supply voltage is 100 V, the maximum value of the rectified voltage value is 141 V (= 100 V × √
2), the minimum boosted value of 20 V is added to the voltage, and the voltage becomes 161 V. Since the voltage falls within the range between the lower limit and the upper limit, the minimum output voltage value is determined to be 161 V, and the voltage is necessarily boosted to some extent.

The rotation speed of the DC motor 16 is controlled by fixing the DC output voltage to the minimum output voltage described above while the duty of the PWM signal of the inverter 11 is less than 100%. After the duty of the PWM signal of the inverter 11 reaches 100%, the DC output voltage of the boost converter 2 is adjusted to adjust the DC motor 1.
6 is controlled. FIG. 5 shows the relationship among the rotation speed of the DC motor 16, the DC output voltage, and the duty of the PWM signal of the inverter 11.

Next, a PWM for controlling the switching element 7 of the boost converter 2 to boost the DC output voltage
A method for determining the signal duty will be described. The AC power supply voltage is full-wave rectified by the rectifier circuit 3. The rectified voltage is divided into resistors by the rectified voltage detection circuit 4, and the rectified voltage value is detected by the A / D converter of the control circuit 15.
FIG. 6 is an example of sampling of a rectified voltage value. The sampled rectified voltage value is handled as a normalized decimal value of 1.0 or less in the control circuit 15. The switching element 7 of the boost converter unit 2 is switched at a PWM cycle sufficiently faster than the AC power supply cycle. When the switching element 7 is turned on, energy is stored in the reactor 5, and when the switching element 7 is turned off, the stored energy is released and charged in the smoothing capacitor 9.

By appropriately performing the on / off operation, the DC output voltage is boosted. At this time, the on-duty of the switching element 7 is changed according to the rectified voltage waveform. That is, since the rectified voltage value is small near the zero cross point of the rectified voltage waveform and the difference from the predetermined output voltage value is large, the on-duty is increased, and the rectified voltage value is large near the peak point of the rectified voltage waveform. Since the difference from the output voltage value is small, the on-duty is reduced.

When the area where the on-duty changes in the PWM signal in accordance with the detected value of the rectified voltage (the maximum duty value in the ON period) is TM, and the detected value of the rectified voltage is represented by AD, the duty of the PWM signal is 1) It is obtained by calculation of the equation.

Basic on-duty = TM−TM × AD (1)

At this time, the initial value of TM is set to 0%, and by increasing this value, the area where the on-duty changes in the PWM signal in accordance with the detected value of the rectified voltage becomes large. Accordingly, the average value of the on-duty in the PWM cycle also increases, the boosting amount increases, and the DC output voltage value also increases, so that the detection value from the DC voltage detection circuit 10 becomes the target DC voltage value. Adjust the value of TM.

If the output voltage cannot be increased to the target value even if the value of TM is increased to the maximum value within the adjustment range, a small value of 1.0 or less is added to the detected rectified voltage value AD in equation (1). The output voltage can be further boosted by multiplying and increasing the on-duty of the PWM signal by proportionally reducing the detected rectified voltage value. Assuming that a coefficient for reducing the magnitude of the detected value AD of the rectified voltage proportionally is denoted by K, the duty of the PWM signal at this time can be obtained by the following equation (2).

Basic on-duty = TM-TM × AD × K (2)

At this time, the value of TM is fixed to the maximum value, and the initial value of K is set to 1.0. When the value of K is reduced, the magnitude of the detected value AD of the rectified voltage is reduced proportionally as is apparent from the equation (2), and the on-duty near the peak point of the rectified voltage increases accordingly. As a result, the energy stored in the reactor 5 increases,
Since the DC output voltage increases, the value of K is adjusted so that the detection value from the DC voltage detection circuit 10 becomes the target DC voltage value.

Next, a method of adjusting the duty of the PWM signal for controlling the switching element 7 of the boost converter section 2 in order to improve the power factor will be described. In order to improve the power factor, the input current waveform needs to be a sine wave having the same phase as the input voltage. Therefore, first, a target instantaneous value of the input current waveform is determined. The maximum value of the input current value detected by the input current detection circuit 6 is obtained every half cycle of the power supply. When the maximum value of the input current value obtained in the immediately preceding power supply half cycle is multiplied by the rectified voltage value detected by the rectified voltage detection circuit 4 as a normalized decimal value of 1.0 or less, the value becomes a peak value. Is equal to the maximum value of the input current value in the immediately preceding power supply half cycle, and the input current waveform has the same phase as the input voltage. Therefore, this value is set as the instantaneous value of the target input current waveform. The detected value of the rectified voltage is A
When expressed as D, the target instantaneous value of the input current can be expressed as in equation (3). FIG. 7 shows a conceptual diagram.

The instantaneous value of the target input current = the maximum value of the input current value in the immediately preceding power supply half cycle × AD (3)

In this case, the crest value of the target current waveform is equal to the crest value of the input current waveform in the immediately preceding half cycle of the power supply. The target current waveform may be obtained by multiplying the maximum value of the input current in the power supply half cycle. If a decimal value for suppressing the peak value is expressed as S, the instantaneous value of the target input current can be expressed as in equation (4).

The instantaneous value of the target input current = the maximum value of the input current value in the immediately preceding power supply half cycle × S × AD (4)

For example, when it is desired to suppress the peak value of the target current waveform to 90% of the peak value of the input current waveform in the immediately preceding power supply half cycle, the value of S may be set to 0.9.

The current flowing when the switching element 7 is switched at the on-duty determined by the equation (1) or (2) is detected by the input current detection circuit 6. The difference between the detected instantaneous value of the input current and the target instantaneous value of the input current obtained by the equation (3) or (4) is obtained,
Adjust the on-duty. If the detected instantaneous value of the input current is smaller than the target value, the on-duty is increased, and if the detected instantaneous value of the input current is larger than the target value, the on-duty is reduced. When the on-duty adjustment method is expressed using two constants A and B, for example,
It can be expressed as in equation (5).

On-duty = Basic on-duty × A + (Target current value−Detected current value) × B × Basic on-duty (5)

The basic on-duty is the on-duty obtained by the equation (1) or (2), and the constant A is a constant for determining the ratio of the basic on-duty to the finally obtained on-duty. The constant B is a constant for determining a ratio in which a difference from the target current value is reflected on the finally determined on-duty.

As is apparent from equation (5), when the detected current value is smaller than the target current value, the difference acts to increase the on-duty, and when the detected current value is larger than the target current value. , The difference acts to reduce the on-duty. As described above, by adjusting the on-duty according to the difference between the instantaneous value of the target input current and the instantaneous value of the detected input current, the detected current waveform becomes equal to the target current waveform, and the input current waveform becomes Since the sine wave has the same phase as the input voltage, the power factor is improved.

[0037]

According to the present invention, the minimum value of the DC output voltage of the boost converter is variably set in accordance with the rectified voltage. Does not decrease, the power factor can be constantly and stably improved, and the harmonic current can be reduced. Further, since the minimum voltage value is always set within the range between the upper limit value and the lower limit value, it is possible to secure a wide range of change in the DC output voltage of the boost converter, and as a result, the control efficiency of the DC motor is improved. There is an effect that it becomes better.

Further, according to the present invention, the duty of the PWM signal for controlling the switching element of the step-up converter is changed in accordance with the rectified voltage value within a half cycle of the power supply, so that the ripple of the output DC voltage value is reduced. The output DC voltage value is suppressed to be stable, and the power factor is improved because the input current waveform approaches a sine wave having the same phase as the input voltage.

According to the present invention, the amount of change in the duty of the PWM signal is adjusted by changing the magnitude of the maximum duty value during the ON period in the PWM cycle, and the magnitude of the DC voltage is adjusted. Even when the input power is small, the DC output voltage can be finely adjusted while improving the power factor.

Further, according to the present invention, the on-duty of the PWM signal is adjusted by multiplying the detected rectified voltage value by a decimal value of 1.0 or less to proportionally reduce the detected rectified voltage value, and Since the magnitude of the voltage is adjusted, it is possible to finely adjust the DC output voltage while improving the power factor even when the input power to the DC motor is large.

According to the present invention, the on-duty of the switching element is adjusted in accordance with the difference between the target current value obtained by a predetermined method and the actually detected current value, so that the input current waveform is the same as the input voltage waveform. The phase becomes a sine wave, and the power factor is improved.

Further, according to the present invention, the multiplied value of the input current waveform of the immediately preceding power supply half cycle and the rectified voltage value is used as the target instantaneous value of the input current. The sine wave can be in phase with the waveform, and the power factor is improved.

Further, according to the present invention, the product of the maximum value of the input current waveform of the immediately preceding power supply half cycle multiplied by a decimal value of 1.0 or less and the rectified voltage value is used as the target instantaneous value of the input current. Therefore, the peak value of the target current waveform can be suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining boosting by PWM control in a boost converter.

FIG. 2 is a circuit block diagram of a DC motor control device according to the present invention.

FIG. 3 is a diagram showing an inverter configuration in the DC motor control device of the present invention.

FIG. 4 is a diagram showing a procedure for determining a minimum DC output voltage value by the control circuit of FIG. 2;

FIG. 5 is a diagram illustrating a relationship among a rotation speed of a DC motor, a DC output voltage, and a duty of a PWM signal of an inverter device.

FIG. 6 is a diagram showing sampling of a rectified voltage value.

FIG. 7 is a conceptual diagram of a method of obtaining a target current waveform.

[Explanation of symbols]

 1. AC power supply 2. 2. Boost converter section Rectifier circuit 4. Rectified voltage detection circuit Reactor 6. 6. Input current detection circuit Switching element 8. Diode 9. Smoothing capacitor 10. DC voltage detection circuit 16. DC motor D1 to D6. Diodes K1 to K6. Terminals L1 to L3. Terminals connected to position detection circuit 14 Q1 to Q6. Switching elements T1, T2. Terminal connected to converter unit 2

Claims (7)

[Claims] An AC power supply voltage is rectified, the rectified voltage is boosted by a reactor and a switching element, and then smoothed by a capacitor to obtain a DC output voltage. The DC output voltage is used as a power supply voltage of an inverter for driving a DC motor. Current control means for detecting the instantaneous value of the input current in a DC motor control device which is capable of controlling the rotation speed of the DC motor by making the DC output voltage value variable. First control means for controlling the on-duty of the switching element so that the instantaneous value of the current value becomes the current value of the target power factor; and providing an upper limit value and a lower limit value to the minimum value of the DC output voltage, The minimum value of the DC output voltage is variably set according to the rectified voltage so that the minimum value of the output voltage falls within the range between the upper limit value and the lower limit value. Control device for a DC motor, characterized in that it comprises a second control means for controlling the on-duty of the switching element in accordance with the set value. 2. An AC power supply voltage is rectified, the rectified voltage is boosted by a reactor and a switching element, and then smoothed by a capacitor to obtain a DC output voltage. The DC output voltage is used as a power supply voltage of an inverter for driving a DC motor. Current control means for detecting the instantaneous value of the input current in a DC motor control device which is capable of controlling the rotation speed of the DC motor by making the DC output voltage value variable. First control means for controlling the on-duty of the switching element so that the instantaneous value of the current value becomes the current value of the target power factor; and normalizing the rectified voltage value to a decimal value of 1.0 or less, and driving the switching element. Of the rectified voltage value and a predetermined value that is the maximum duty value during the ON period in one cycle of the PWM signal for controlling the A second control means for controlling the switching element by using a value obtained by subtracting the multiplied value from a predetermined value serving as a duty value as an on-duty of the PWM signal for controlling the driving of the switching element. Motor control device. 3. The control device for a DC motor according to claim 2, wherein the predetermined value that becomes the maximum duty value is variable. 4. The DC motor control device according to claim 2, wherein the rectified voltage value is proportionally reduced by multiplying the rectified voltage value by a decimal value of 1.0 or less. 5. An AC power supply voltage is rectified, the rectified voltage is boosted by a reactor and a switching element, and then smoothed by a capacitor to obtain a DC output voltage. The DC output voltage is used as a power supply voltage of an inverter for driving a DC motor. Current control means for detecting the instantaneous value of the input current in a DC motor control device which is capable of controlling the rotation speed of the DC motor by making the DC output voltage value variable. First control means for obtaining a value obtained by subtracting the instantaneous value of the current value from the target current value, and controlling the on-duty of the switching element according to the subtraction value; and the switching according to the set value of the DC output voltage. And a second control means for controlling the on-duty of the element. 6. The target current value is a value obtained by multiplying a maximum value of the rectified current and the rectified voltage value in a power supply half cycle before a power supply half cycle to which the rectified current belongs. The control device for a DC motor according to claim 5, wherein 7. The maximum value of the rectified current in a power supply half cycle immediately before a power supply half cycle to which the rectified current belongs is 1.0.
6. The DC motor control device according to claim 5, wherein a value obtained by multiplying a value obtained by multiplying the following decimal number by the rectified voltage value is set as the target current value.