JPH07298677A - Fan motor - Google Patents

Abstract

PURPOSE:To reduce the electromagnetic noise from a motor by holding down the maximum value of conduction current of an inverter section which drives the fan motor and reducing other frequency components than a specified one. CONSTITUTION:Comparing a current command value 6a corresponding to a difference between a rotating speed command 5 and an actual rotating speed of a motor 3 with a triangular signal 11a from an oscillation circuit 11, a PWM signal generating circuit 12 generates a PWM signal 12a which has a duty ratio corresponding to the current command value 6a. The current command value 6a is so set that the maximum duty ratio of the PWM signal 12a may be 100% or smaller. When the conduction current I of an inverter section 2 reaches the current limit value IL, a current limiting circuit 10 generates current limiting signals 10a, 10b. A cycle of the PWM signal 12a is held down by the current limiting signal 10a in a composite circuit 7 and the duty ratio of the PWM signal 12a is made smaller by making the duration of the current limiting signal 10a and the current command value 6a smaller in a calculating and controlling circuit 6. The thus generated signal 7a is a driving signal of the inverter section 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fan motor used in an air conditioner and other devices, and more particularly to suppressing the maximum value of the current flowing through the inverter section, downsizing the semiconductor element, and The present invention relates to a fan motor that reduces electromagnetic noise.

[0002]

2. Description of the Related Art An example of a conventional fan motor is, for example,
It is described in JP-A-63-031487. This will be described with reference to FIG. However, 2 is an inverter unit, 3
Is an electric motor, 4 is a position detection circuit, 5 is an input terminal for an external speed command, 6 is a calculation / control circuit, 7 is a synthesis circuit, 8 is a drive circuit, 9 is a current detector, 13 is a commercial power supply, and 14 is a rectifier. Circuit.

In the figure, the AC voltage from the commercial power supply 13 is rectified by the rectifier circuit 14 to be converted into DC, and supplied to the inverter unit 2. The actual rotation speed of the electric motor 3 is detected by the position detection circuit 4, and the calculation / control circuit 6 increases or decreases the duty ratio according to the difference between the detected rotation speed and the external rotation speed command from the input terminal 5. Wave) signal 6a is generated. Further, the current I flowing through the inverter unit 2 is the current detector 9
When the energization current I becomes equal to or more than a predetermined current value (current limit value) I _L , the detection signal 9a is detected in the cycle of the PWM signal 6a when the current limiting circuit operates and it occurs.
Is output.

The PWM signal 6a and the detection signal 9a are logically ANDed by the synthesizing circuit 7, and the PWM wave drive in which the cycle in which it is detected that the energizing current I becomes the current limit value _IL or more is suppressed is suppressed. The signal 7a is generated. The drive circuit 8 drives the inverter unit 2 with this drive signal 7a. When the period of this detection signal 9a has passed,
When the drive signal 7a is supplied to the inverter unit 2 again and the energizing current I becomes equal to or more than the current limit value I _L again, the above operation is repeated.

In this way, although the rotation speed of the electric motor 3 is reduced, the duty ratio of the PWM signal 6a is changed and the energized current is controlled so as not to exceed the current limit value I _L.

[0006]

In the above-mentioned prior art, P
Rotation speed control by increasing / decreasing the duty ratio of the WM signal 6a,
It is used together with the current control for limiting the energizing current I with the above current limiting value I _L , and is suitable for peak cutting of the energizing current I.

However, when the duty ratio of the PWM signal 6a is large and the pulse width is wide, when it is detected that the conduction current I exceeds the current limit value I _L at the beginning of the cycle, as shown in FIG. As shown in (1), it becomes substantially equivalent to the suppression of the entire cycle, and the duty ratio of the drive signal 7a at that time is largely changed to cause PW.
A portion having a cycle T2 that is twice the cycle T1 of the M signal 6a occurs. Therefore, a frequency component that is 1/2 times the switching frequency of the inverter unit 2 is generated. Therefore, even if the switching frequency is set to 20 KHz, which is higher than the audible frequency, in such a state, it becomes 1 within the audible frequency band.
A component of 0 KHz is generated, which causes a problem that electromagnetic noise is generated from the electric motor 3.

[0008] Then, almost 100% duty ratio of the PWM signal 6a (i.e., the PWM signal 6a DC) when it is, the energization current I becomes equal to or larger than the predetermined current value I _L, the period of the detection signal is a PWM signal 6a N times T1 (n =
, 1, 2, 3, ...) and therefore the period T
Drive signal 7a which is intermittently suppressed at a cycle of n times 1
Is generated. Therefore, a frequency component 1 / n times the switching frequency of the inverter unit 2 is generated, and electromagnetic noise is generated from the electric motor 3, which is a problem.

In particular, when the DC voltage applied to the inverter section 2 is high, the current limiting circuit is likely to operate and the above problems are likely to occur.

This problem of electromagnetic noise does not occur if the current limit value I _L is increased, but in that case, the inverter section 2
There is a problem in that the capacity of the semiconductor element as the switching element must be increased.

An object of the present invention is to solve such a problem, to suppress the maximum limit value of the current flowing through the inverter section, to make the semiconductor element compact, and to reduce the frequency components other than the predetermined frequency of the drive signal. Another object of the present invention is to provide a fan motor capable of reducing electromagnetic noise of an electric motor.

[0012]

In order to achieve the above object, the present invention outputs a current command value and an oscillation circuit according to a difference between a designated rotation speed of an electric motor and an actual rotation speed of the electric motor. A PWM signal is generated by the level comparison with the periodic signal, and the drive signal of the inverter unit is formed based on this PWM signal. However, in order to make the maximum duty ratio of this PWM signal less than 100%, Limit the current command value.

Further, according to the present invention, when the current limiting circuit detects that the current flowing through the inverter reaches the current limiting value, the current command value is lowered for a predetermined period and the duty ratio of the PWM signal is reduced.

Further, according to the present invention, when the DC power supply voltage applied to the inverter section becomes equal to or higher than a predetermined limit voltage, the current command value is reduced for a predetermined period and the duty ratio of the PWM signal is reduced.

[0015]

The actual rotation speed of the electric motor is detected by the position detection circuit, and the current command value is created according to the difference from the rotation speed command. A PWM signal of this cycle is generated by comparing this current command value with a triangular wave signal of a predetermined cycle output from the oscillation circuit. Here, by setting the level of the current command value to be compared with the triangular wave signal to be smaller than the maximum amplitude of the triangular wave signal, the maximum duty ratio of the PWM signal becomes less than 100%. As a result, frequency components other than the frequency of the triangular wave signal set by the oscillator circuit are not generated, and electromagnetic noise from the electric motor is reduced.

Further, when the current limiting circuit detects that the current passed through the inverter reaches the current limiting value, the current command value is lowered for a predetermined period to lower the duty ratio of the PWM signal. As a result, the energized current during this period becomes small, and the current limit value is not reached. Therefore, there is no frequency component other than the frequency of the output signal of the oscillation circuit, and electromagnetic noise is reduced.

Electromagnetic noise from the electric motor is likely to occur when the DC power supply voltage applied to the inverter section is high. Therefore, the DC power supply voltage applied to the inverter section is detected, and this DC power supply voltage exceeds a predetermined limit voltage. Then, by reducing the current limit value during that period, frequency components other than the frequency of the output signal of the oscillation circuit do not occur, and electromagnetic noise is reduced.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a block diagram showing an embodiment of a fan motor according to the present invention, in which 1 is a DC voltage source, 2 is an inverter unit,
3 is an electric motor, 4 is a position detection circuit, 5 is an external rotation speed command source, 6 is a calculation / control unit, 7 is a combination circuit, 8 is a drive circuit, 9 is a current detector, 10 is a current limiting circuit, and 11 is an oscillation. The circuit, 12 is a PWM signal generating circuit.

FIG. 2 is a waveform diagram showing the signals of the respective parts of FIG. 1, and the signals corresponding to those of FIG.

In FIGS. 1 and 2, the actual rotation speed of the electric motor 3 is detected by the position detection circuit 4, and the difference between this detected rotation speed and the external rotation speed command indicating the rotation speed of the electric motor 3 from the command source 5. Is calculated by the calculation / control unit 6 and a current command value 6a corresponding to the difference is generated. In addition, from the oscillation circuit 11, a constant frequency higher than the audible frequency (for example, 20 k
The triangular wave signal 11a having a constant amplitude is output at a frequency of (Hz), and the PWM signal generating circuit 12 outputs the triangular wave signal 11a.
And the current command value 6a are compared in level, and the current command value 6a
A PWM signal 12a having a duty ratio according to a is obtained.

On the other hand, the current detector 9 detects the energizing current I of the inverter section 2 and the DC power source voltage E of the DC voltage source 1, and the energizing current I is set to a preset current limit value I _L. When the DC power supply voltage E increases abnormally or when the DC power supply voltage E exceeds a preset predetermined voltage value (voltage limit value) E _L , the current limit signal 10b is output for a predetermined period and the PWM at that time is output. The "L" (low level) current limit signal 10a is also output within the cycle of the signal 12a.

This will be described more specifically.
The control circuit 6 detects the commutation timing of the motor current of the electric motor 3 from the detection output of the position detection circuit 4, and generates the release signal 6b at this timing. When the current detection circuit 9 receives the release signal 6b and the energizing current I of the inverter unit 2 rises to reach the current limit value I _L , the period from this detection time to the time when the next release signal 6b is received (that is, , The current limiting signal 10b for the predetermined period) is output. Also, P
If one cycle of the PWM signal 12a generated by the WM signal generation circuit 12 is a period from its rising edge to the next rising edge, the PWM signal generation circuit 12 releases at the timing of the falling edge of each cycle of the PWM signal 12a. Generate signal 12b. The current limiting circuit 10 outputs the current limiting signal 10a during the period from the time of this detection to the time of receiving the next release signal 12b when the current I flowing through the inverter unit 2 rises and reaches the current limiting value I _L. .

The current limiting circuit 10 includes a DC voltage source 1
When the DC power supply voltage E of exceeds the voltage limit value E _L ,
During that period, the current limiting signal 10b is output.

The current limiting signal 10b is supplied to the arithmetic / control section 6, and the current command value 6 is supplied during the period of the current limiting signal 10b.
a is reduced. As a result, the PWM signal generation circuit 12
The duty ratio of the PWM signal 12a output from is low.

The "L" (low level) current limiting signal 10a output from the current limiting circuit 10 is generated by the synthesizing circuit 7.
Are supplied to the PWM signal generating circuit 12 and are subjected to logical product operation processing with the PWM signal 12a from the PWM signal generating circuit 12. As a result, the combining circuit 7 obtains the PWM-wave drive signal 7a in which the cycle is suppressed when the energizing current I of the inverter unit 2 exceeds the current limit value I _L, and is supplied to the inverter unit 2. . As a result, the electric motor 3 is driven.

FIG. 3 shows the arithmetic / control unit 6, the synthesizing circuit 7, the current limiting circuit 10 and the PWM signal generating circuit 12 shown in FIG.
It is a circuit diagram which shows one specific example, 13-20 is an input terminal, 21-25 is a comparator, 26 is an output terminal, 27
Is an input terminal, R1 to R4 are resistors, C1 is a capacitor, T
r1 to Tr3 are transistors, and signals corresponding to those in FIGS. 1 and 2 are designated by the same reference numerals.

In the figure, the resistors R1 to R4 and the capacitor C1 constitute the arithmetic / control section 6 in FIG. 1, and the comparator 21 comprises the PWM signal generating circuit 12 in FIG.
Comparators 22 and 23 and transistors Tr2 and Tr
3 is the current limiting circuit 10 in FIG.
Respectively configure the synthesizing circuit 7 in FIG.

The operation of this specific example will be described below with reference to FIG.

A current command value 6a corresponding to the difference between the actual speed of the electric motor 3 detected by the position detection circuit 4 and the external speed command.
Is smoothed by the voltage dividing resistors R1 and R2 and the capacitor C1 to be a DC voltage, which is supplied to the comparator 21 and compared in level with the triangular wave signal 11a from the oscillation circuit 11. As a result, the PWM signal 12a having the duty ratio corresponding to the current command value 6a is generated.

Here, the DC voltage level of the current command value 6a when input from the input terminal 13 is the PWM signal 12
The duty ratio of a is set to be equal to the maximum amplitude of the PWM signal 12a so that the duty ratio of a becomes 100%.
1 and R2, and is set to be smaller than the maximum amplitude of the triangular wave signal 11a. Therefore, the PWM signal 12
The maximum duty ratio of a is less than 100%. As a result, the problem that occurs in the above-described conventional technique when the duty ratio of the PWM signal 12a becomes 100% is solved,
Frequency components other than the frequency of the triangular wave signal 11a set by the oscillation circuit 11 are eliminated, and electromagnetic noise is reduced.

The current detection value of the energizing current I of the current detection circuit 9 from the input terminal 15 and the current limit value I from the input terminal 16
It is compared with _L by the comparator 22, and when the energized current I becomes the current limit value I _L or more, the "H" (high level) current limit signal 10a is generated. This comparator 22 has a hysteresis characteristic, and its output signal is once "H".
Then, "H" is held as it is. This "H" current limiting signal 10a turns on the transistor Tr1 and blocks the PWM signal 12a from the comparator 21. The comparator 25 compares the current command value 6a and the triangular wave signal 11a in level, and the comparator 2
The same PWM signal as 1 is output. The "L" period of this PWM signal becomes the release signal 12b. This release signal 12
b is the output terminal of the comparator 22 and the transistor Tr1
The signal is supplied to the connection point with the, and the comparator 22 is returned to the initial state by the release signal 12b of "L", and the transistor Tr1 is turned off.

In this way, Tr1 is the comparator 2
After it is detected that the energizing current I has reached the current limit value I _L in 2, the comparator 25 releases the signal 12b of “L”.
Therefore, the PWM signal 12a output from the comparator 21 is suppressed by the cycle when the energization current I reaches the current limit value I _L , and is missing. In this way, the cycle is suppressed P
The WM signal 12a is the drive signal 7a.

The current detection circuit 9 from the input terminal 17
The current detection value of the energizing current I of the current and the current limit value I _L from the input terminal 18 are compared by the comparator 23, and the energizing current I
When the current limit value I _L is equal to or higher than the current limit value I _L , an “H” output signal is generated. This comparator 23 also has a hysteresis characteristic, and once its output signal becomes "H", it holds "H" as it is. This "H" output signal turns on the transistor Tr2, and the "L" current limiting signal 10
b occurs and activates resistor R3. This resistance R3
And the resistors R1 and R2 change the voltage division ratio of the current command value 6a input from the input terminal 13.
The value a is reduced and supplied to the comparators 21 and 25. Therefore, the PWM output from the comparator 21
The duty ratio of the signal 12a becomes smaller.

On the other hand, the operation / control section 6 is connected to the input terminal 27.
Is inputted with the release signal 6b of "L" which coincides with the commutation timing of the motor current. The release signal 6b is supplied to the connection point between the output terminal of the comparator 23 and the transistor Tr2.
Returns to the initial state, and the transistor Tr2 is turned off.

In this way, Tr2 is the comparator 2
3 is ON for a period from when it is detected that the energizing current I has reached the current limit value I _L until the release signal 6b of “L” is supplied from the input terminal 27, and the duty ratio of the drive signal 7a during this period is Get smaller.

When the energizing current I reaches the current limit value I _L by the above operation, the cycle of the drive signal 7a at that time is omitted, so that the energizing current I does not exceed the current limit value I _L. At the same time, the transistor Tr2 is turned on to reduce the duty ratio of the drive signal 7a, and even if the transistor Tr1 is turned on and the drive signal 7a is supplied to the inverter unit 2 again, the energizing current I is equal to or more than the current limit value I _L. Do not become As a result, the transistor Tr1 does not turn on continuously,
The cycle of the drive signal 7a is always equal to the cycle of the PWM signal 12a. Therefore, by setting the frequency of the PWM signal 12a outside the audible frequency range such as 20 kHz, the switching frequency in the inverter unit 2 is always outside the audible frequency range, and the electromagnetic noise is not generated from the electric motor 3. In addition, since the energizing current I is always maintained at the current limit value _IL or less, a small switching element in the inverter unit 2 can be used.

When the electric motor 3 is started or when the load changes, the energizing current increases rapidly, but the above operation is repeated until the rotational speed of the electric motor 3 stabilizes at the specified rotational speed. It does not exceed the current limit value,
Also, no electromagnetic noise is generated.

Further, the voltage detection value of the DC power supply voltage E of the current detection circuit 9 from the input terminal 19 and the voltage limit value E _L from the input terminal 20 are compared by the comparator 24, and the DC power supply voltage E is the voltage limit value. When it exceeds E _L, an output signal of “H” is generated. This "H" output signal turns on the transistor Tr3 and activates the resistor R4.
By the resistor R4 and the resistors R1 and R2, the input terminal 13
The voltage division ratio of the current command value 6a input from the controller changes, and the current command value 6a becomes smaller, so that the comparators 21, 25
Is supplied to. Therefore, the duty ratio of the PWM signal 12a output from the comparator 21 becomes small. The period during which the DC power supply voltage E is equal to or higher than the voltage limit value E _L ,
This state continues.

In this way, when the DC power supply voltage E fluctuates and becomes equal to or higher than the voltage limit value E _L , the duty ratio of the drive signal 7a becomes small and the energizing current I becomes the current limit value I _L.
I try not to exceed.

[0040]

As described above, according to the present invention,
Since the semiconductor element can be downsized while suppressing the maximum value of the current flowing through the inverter, the frequency of the PWM signal becomes constant and the fluctuation of the duty ratio becomes small, the frequency components other than the predetermined frequency are reduced, and The electromagnetic noise of can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a fan motor according to the present invention.

FIG. 2 is a waveform diagram showing signals of respective parts in FIG.

3 is a circuit diagram showing a specific example of a calculation / control circuit, a combination circuit, a current limiting circuit, and a PWM signal generation circuit in FIG.

FIG. 4 is a configuration diagram showing an example of a conventional fan motor.

FIG. 5 is a waveform chart showing signals of respective parts of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC voltage source 2 Inverter section 3 Motor 4 Position detection circuit 5 External rotation speed command source 6 Calculation / control section 7 Combined circuit 8 Drive circuit 9 Current detector 10 Current limiting circuit 11 Oscillation circuit 12 PWM signal generation circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toru Kitayama 800 Tomita, Ohira-cho, Shimotsuga-gun, Tochigi Prefecture Living Equipment Division, Hitachi, Ltd.

Claims (4)

[Claims] 1. An inverter section formed by connecting a plurality of semiconductor elements in a bridge connection, a current detector for detecting a current flowing through an electric motor, a periodic signal of an oscillation circuit and a current command value.
A fan motor including a PWM signal generating circuit for generating a WM signal and a current limiting circuit for limiting the maximum value of a motor current is provided with a means for inhibiting the duty ratio of the PWM signal from becoming 100%. Characteristic fan motor. 2. The fan motor according to claim 1, wherein a maximum value of the current command value is defined, and an off section is provided in the PWM signal. 3. The fan motor according to claim 1, wherein the current command value is lowered when the current limiting circuit operates. 4. The DC voltage applied to the inverter unit according to claim 1, the current command value is lowered, the maximum value of the current command value is defined, and an OFF section is added to the PWM signal. A fan motor characterized by being provided.