JPH0614589A - Shading motor inverter control circuit - Google Patents

Abstract

PURPOSE:To realize variable control of power supply voltage and frequency freely without requiring significant modification of specification of commercial power supply motor. CONSTITUTION:A voltage control means 42 delivers a driving pulse signal, corresponding to an output voltage set value from a variable output voltage setting means 41, to a switching element and converts the output voltage from a full-wave rectifier 25 into a duty factor thus controlling the voltage. Output voltage Vi from the full-wave rectifier 25 is then compared with a target output voltage set value Vf from the variable output voltage setting means 41. A driving pulse signal having increased pulse delay time is delivered to a switching element 18 if Vi>Vf whereas a driving pulse signal having decreased pulse delay time is delivered to the switching element 18 if Vi<Vf thus performing control of power supply voltage. On the other hand, a frequency control means 44 delivers a trigger pulse signal having preset frequency corresponding to the output voltage set value from the variable output setting means 41 to two thyristors 8, 9 thus performing frequency control depending on the output voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shunting motor inverter control circuit, and more particularly to a rotation speed control by voltage and frequency control of a shunting induction motor (hereinafter referred to as "squirting motor").

[0002]

2. Description of the Related Art Conventionally, the rotational speed control technology by controlling the voltage and frequency of a shading motor has not been put to practical use at present. This is because the problem is that the performance of the bear motor is expensive relative to the performance due to the cost-performance problem, but as a conventional bear motor inverter control circuit, a textbook technique as shown in FIG. 11 is known. (Mc
umurray-Badford Inverte
r).

In FIG. 11, 1 is a DC 24V power source, 2
Is a variable frequency setting device, for which a multivibrator or the like is used. Reference numeral 3 is a shunting motor, 4 is a voltage conversion transformer, and primary windings 5 and 6 and secondary winding 7 are provided, and the primary windings 5 and 6 are connected in opposite polarities. 8, 9
Is a thyristor which is a switching element, and 10 is a commutation capacitor.

Since the conventional shading motor inverter control circuit is configured as described above, the trigger pulse signal 12 for triggering the thyristor 9 is generated from the multivibrator circuit 2 as well as the trigger pulse signal 11 for triggering the thyristor 8. They occur alternately at equal intervals (see FIG. 12). The thyristors 8 and 9 are alternately turned on by the trigger pulse signals 11 and 12, current flows through the primary windings 5 and 6 of the voltage conversion transformer 4 each time, and the primary winding 5 when the thyristor 8 is turned on. Is 14 and the voltage of the primary winding 6 when the thyristor 9 is conducting is converted into an alternating current as shown by 13 (see FIG. 12).

On the other hand, generally, the motor 3 is a commercial 100V.
Since it is manufactured for use, the winding number ratio of the secondary winding 7 is appropriately set and driven at 100V. The commutation capacitor 10 serves to prevent the energization of the conducting thyristor 8 or 9.

[0006]

SUMMARY OF THE INVENTION In the conventional bear motor inverter control circuit as described above, the commercial AC power supply 1 is used.
The DC 24V power supply 1 required a voltage conversion transformer for the inexpensive motor 3 of 00V specification. Then, the inductance value of the winding of the voltage conversion transformer changes depending on the frequency, and the impedance represented by Z = 2πfL increases as the frequency increases, and the winding current decreases and torque becomes insufficient. As the frequency decreases, the value decreases, the winding current increases, the temperature of the winding rises, and the insulation temperature limit may be exceeded.

Therefore, the power supply potential must be changed as the frequency is changed. For that purpose, if a transformer having a variable frequency is used, the voltage conversion transformer is expensive because it has various voltage taps. Further, there is a problem that tap switching requires a proper switching means, the configuration is complicated, and the cost is further increased. Further, it is necessary to constantly monitor the presence or absence of oscillation, which is the control status of the motor 3, and the current value to perform control, but conventionally, no meaningful proposal has been made regarding this point.

The present invention has been made to solve the above problems, and voltage and frequency can be freely changed without drastically changing the specifications of a commercial power supply type motor used in the conventional example. It is an object of the present invention to provide a bear motor inverter control circuit that can be controlled.

[0009]

SUMMARY OF THE INVENTION A bear-wound motor inverter control circuit according to the present invention is provided between a full-wave rectifier for full-wave rectifying an AC voltage of an AC power supply, and an AC power supply and a full-wave rectifier. A switch element for controlling the flow rate, a smoothing capacitor for smoothing the output voltage of the full-wave rectifier, and a bear motor having two primary windings to which the output voltages of the smoothing capacitors are respectively applied via thyristors, Variable output voltage setting means for setting the initial output voltage set value to the target output voltage set value by gradually increasing the value, and a drive pulse signal having a pulse delay time according to the output voltage set value of the variable output voltage setting means. Is output to the switching element, the target output voltage set value of the variable output voltage setting means is compared with the output voltage of the smoothing capacitor, and the output voltage is compared. When the output voltage is larger than the target output voltage setting value, a drive pulse signal having a pulse delay time that is longer than the pulse delay time corresponding to the target output voltage setting value is output, and the output voltage is smaller than the target output voltage setting value. In this case, voltage control means for outputting to the switching element a drive pulse signal having a pulse delay time shorter than the pulse delay time corresponding to the target output voltage setting value, and the output voltage setting value of the variable output voltage setting means A frequency control means for outputting a trigger pulse signal having a correspondingly preset frequency to the thyristor is configured.

[0010]

According to the present invention, the voltage control means is provided with a driving pulse signal having a pulse delay time corresponding to the output voltage setting value set by the variable output voltage setting means, provided between the AC power supply and the full-wave rectifier. The output voltage of the smoothing capacitor that is output to the element and connected to the full-wave rectifier is controlled by changing the conduction ratio, and the target output voltage setting value of the variable output voltage setting means and the output voltage of the smoothing capacitor are compared. When the output voltage is higher than the target output voltage set value, a drive pulse signal with a pulse delay time that is longer than the pulse delay time according to the target output voltage set value is output, and the output voltage is higher than the target output voltage set value. When it is smaller, a drive pulse signal having a pulse delay time that is shorter than the pulse delay time corresponding to the target output voltage setting value is output to the switching element. Unishi controls the power supply voltage Te.

Further, the frequency control means provides a trigger pulse signal having a frequency preset corresponding to the output voltage set value of the variable output voltage setting means between the smoothing capacitor and the two primary windings of the bear picking motor. The thyristor is triggered by the frequency corresponding to the output voltage by outputting it to the two controlled thyristors to control the frequency.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an essential part of an embodiment of the present invention, FIG. 2 is a circuit diagram showing the same embodiment, and FIG. 3 shows a coil of a shading motor of the embodiment. Perspective view,
FIG. 4 is a waveform diagram showing the waveform of each part of the embodiment.

In the figure, reference numerals 5 and 6 denote primary windings of the shunting motor, which are divided into two and are connected to each other with opposite polarities so that pseudo alternating current is conducted. The details are as shown in the actual wiring of FIG. 8 and 9 are primary windings 5 and 6 of the bear motor
A thyristor, which is a switching element for controlling the electric current flowing to the device, 10 is a commutation capacitor connected between the anodes of the thyristors 8 and 9, 15 is a microcomputer for controlling the present invention, and 16 and 17 are thyristors 8 and 9. An output port 18 for supplying a trigger pulse signal to the gate, 18 is a triac, which is a switching element that is provided between an AC power supply and a full-wave rectifier to be described later and controls the conduction ratio, 1
Reference numeral 9 is a phototriac coupler for controlling the drive pulse signal flowing to the triac 18, 20 is a light emitting diode in the phototriac coupler 19, 21 is a microcomputer output port for supplying a current to the light emitting diode 20, 22
Is a transistor, and 23 is a microcomputer input port for receiving the signal of the transistor 22.

Reference numeral 25 is a full-wave rectifier for full-wave rectifying the AC voltage of the AC power source, 26 is a smoothing capacitor for smoothing the rectified voltage of the full-wave rectifier 25, and 27 and 28 are resistors for dividing the rectified voltage of the smoothing capacitor 26. Reference numeral 29 is an input port for inputting the divided voltage values of the resistors 27 and 28 into the microcomputer 15, 30 is a shunt resistor for monitoring the winding current of the primary windings 5 and 6, 31 is a smoothing capacitor, and 32 is the primary winding 5 ，
An input port for reading the current value of 6 as a voltage, 33 is a dropper rectifier, 34 is a dropper resistor, 35 is a smoothing capacitor, and 36 is a constant voltage IC that gives the microcomputer 15 a potential of 5V.

Reference numeral 41 is a variable output voltage setting device for setting the voltage applied to the primary winding of the shading motor, and 42 is a pulse delay time corresponding to the output voltage setting value set by the variable output voltage setting device 41. Triac 1 for driving pulse signal
8, voltage control means for controlling the conduction ratio, and 43 for voltage-frequency memory for storing a preset frequency corresponding to the output voltage set value set by the variable output voltage setting means 41, and 44 for variable Based on the output voltage setting value of the output voltage setting means 41, the frequency corresponding to this is read from the voltage-versus-frequency program 43, and the trigger pulse signal of that frequency is output to the thyristors 8 and 9. The microcomputer 15 is an output voltage variable setting device 4
1, a voltage control means 42, a voltage-versus-frequency memory 43, and a frequency control means 44.

Next, an outline of the operation of the above embodiment will be described. The circuit of the present invention connected to an AC voltage which is a commercial power source reduces the duty factor in the triac 18, and as a result, the voltage is suppressed to a low potential and becomes a rectified voltage rectified by the full-wave rectifier 25 and smoothed. The ripple is reduced by the capacitor 26, and the ripple is supplied to the primary windings 5 and 6 of the bear motor of the load. At this time, the microcomputer 15 controls the duty ratio. Until the microcomputer 15 starts controlling the triac 18, several tens of milliamperes are supplied as an operating current of the microcomputer 15 by the dropper rectifier 33, the dropper resistor 34 and the smoothing capacitor 35, and the circuit is activated. The wattage of this dropper resistor 34 is 4.5k
Ω, about 2 W is sufficient.

First, the power supply voltage control of the shading motor will be described. In this embodiment, the purpose is to function as a DC power supply of about 40V. The transistor 22 slices the full-wave rectified waveform 37 of the rectified voltage shown in FIG. 4 of the full-wave rectifier 25 with its base-emitter potential of 0.8 V (indicated by 38 in the figure) to generate a collector voltage waveform 39, which is It is introduced to the input port 32 of FIG. 2 as a timing signal for phase control. On the other hand, smoothing capacitor 2
The rectified voltage of the full-wave rectifier 25 smoothed by 6 is divided by the dividing resistors 27 and 28 and introduced into the analog processing port 27 of the microcomputer 15 as a divided voltage.

The voltage control means 42 of the microcomputer 15 initially sets the transistor 22 based on the initial output voltage setting value set by the variable output voltage setting means 41 at the start-up.
The collector voltage of is set to a potential necessary for control, and the timing signal 39, which is the collector voltage, is set for a predetermined time (40 in the figure).
Td) The delayed drive pulse signal is output from the output port 21 to trigger the triac 18. In the circuit shown in FIG. 2, the trigger of the triac 18 is the light emitting diode 20 in the phototriac coupler 19.
In addition, a current of about 10 mA is drawn into the output port 21.

After the start of activation, the variable output voltage setting means 41 gradually increases the set value from the initial output voltage set value to the target output voltage set value, and accordingly, the voltage control means 42 outputs. By gradually reducing the delay time of the drive pulse signal to increase the conduction ratio, finally, a drive pulse signal having a pulse delay time according to the target output voltage setting value is output, The output voltage of the smoothing capacitor 26 is soft-start controlled so as to reach the target output set value. Incidentally, when the output voltage of the smoothing capacitor 26 (that is, the applied voltage 46 of the primary windings 5 and 6) is 40 V and 1 A as shown in FIG. 4, the delay time T _d is 8 ms.

After that, the voltage control means 42 compares the target output voltage value V _f set by the variable output voltage setting means 41 with the output voltage V _i of the smoothing capacitor 26, and when they match each other, the target output voltage is kept as it is. A drive pulse signal having a pulse delay time according to the set value is output. When the two do not match and the output voltage V _i is large, the pulse delay time of the drive pulse signal is increased, and when the output voltage V _{i is} small, the pulse delay time of the drive pulse signal is decreased to reduce the output voltage. Voltage control is performed so that V _i becomes the target output voltage value V _f .

Next, frequency control of the shading motor will be described. The thyristors 8 and 9 are alternately triggered at a predetermined frequency, and the control range is 60 to 100 Hz in this embodiment. The inductance of the primary windings 5 and 6 is Z =
Since it is 2πfL, L is 30 μH and 11.3Ω
It changes to 18Ω, and the energizing current also changes. As for the specifications of the bear motor, a polyurethane coating wire having a diameter of 0.35 mm is used as the primary windings 5 and 6, and a secondary winding is provided, so that the winding configuration is about 400 turns. As a result,
The electric potential required to generate a predetermined torque is 30V at 60Hz,
It was set as 45 V at 100 Hz.

The frequency control of the bear motor is the frequency that alternately triggers the thyristors 8 and 9, but as described above, the variable output voltage setting device 41
The frequency corresponding to the set output voltage setting value is determined as shown in the graph of FIG. 9 and stored in the voltage vs. frequency memory 43. Therefore, in the frequency control means 44, the frequency corresponding to the output voltage setting value set by the variable output voltage setting device 41 is read from the voltage vs. frequency memory 43, and the trigger pulse signal of that frequency is output to the thyristors 8 and 9. By alternately triggering the thyristors 8 and 9, frequency control corresponding to the output voltage is performed.

It should be noted that the shunt resistor 30 monitors the value of the current flowing through the thyristors 8 and 9 at the analog processing port 32 of the microcomputer 15, for example, the thyristors 8 and 9.
It is detected that the current to the port 32 is doubled due to the two thyristors 8 and 9 being conducted together due to the commutation trouble, and the abnormal oscillation and the abnormal oscillation determining means 45 are detected.
When the judgment is made, a signal for stopping the output of the drive pulse signal is outputted to the voltage control means 42 to control the power off. It should be noted that the output voltage is 0.5 when the soft start gradually increases the conduction ratio of the triac 18 at the time of startup.
It is increased by 4 V every second, while the frequency is increased by 10 Hz every 0.5 seconds as shown in the graph of FIG.

Further, the operation of the above embodiment will be described in detail with reference to the flowcharts of FIGS. In the flowchart of FIG. 5, the zero-cross signal 23 of the power supply frequency (50/60 Hz) output from the full-wave rectifier 25 is read (step S1) and used as a reference signal for phase control.
Although the circuit drive is initially started at 60 Hz, the voltage control means 42 sets the output voltage set value (set to 1/10 of the actual output voltage) corresponding to 50 Hz set by the variable output voltage setting means 41. Based on this, the driving pulse signal for phase control (40 in FIG. 4) is set with the pulse delay time T ₀ (9.5 ms at 50 Hz) from the zero-cross reference point, and driving is started (step S2). The oscillation abnormality determining means 45 determines 1V as a threshold value for the voltage drop of the resistor 30 (see FIG. 2) provided in the motor current circuit (step S3), and if the voltage drop is 1V or more, it is abnormal. And the retry process is performed three times (step S
4) If the voltage drop does not exceed 1 V, proceed to the DC voltage determination step. At this time, the output voltage of the smoothing capacitor 26 reaches a substantially predetermined voltage by setting the delay time T ₀ .

FIG. 6 is a flowchart showing a subroutine of the retry processing 4 of three times. When the oscillation abnormality determining means 45 determines that there is an abnormality in the three retry processes 4,
Once the output of the drive pulse signal from the voltage control means 42 is prohibited (step S5), the energization of the triac 18 is blocked to cut off the voltage, the retry counter is advanced by one in step S6, and the counter is set in step S7. While monitoring, reset the pulse delay time T ₀ in step S8,
In step S9, the oscillation monitoring is performed in the same manner as in steps S2 and S3, and when the counter has reached 3 times in step S7, "although it does not start even if it is tried three times", an alarm is issued simultaneously with the stop processing. It is a notification.

As described above, when the pulse delay time T ₀ is set and the driving starts normally, the output voltage setting value V _f of the variable output voltage setting means 41 is changed stepwise until it reaches 2V, and Correspondingly, the pulse delay time T _n is reduced by 0.1 ms for each step (this pulse delay time is defined by T _n , and is sequentially advanced from n = 0) to sequentially energize. The rate is increased and the voltage is increased to 2V. The relationship between the output voltage and the drive frequency of the bear motor at this time is as shown in the graph of FIG.
Remembered in. Therefore, in the frequency control means 44,
The trigger pulse signal having a frequency corresponding to the output voltage set value set by the variable output voltage setting means 41 is supplied to the thyristor 8,
By alternately outputting to 9 and triggering, frequency control corresponding to the output voltage is performed. That is, the output voltage 2
Thyristors 8 and 9 with a driving frequency of 60 Hz for V
Is triggered.

In this way, when the output voltage of the smoothing capacitor 26 reaches 2V, the voltage control means 42 determines the DC voltage. That is, the output voltage set value V _f (2 V) set by the variable output voltage setting means 41 and the smoothing capacitor 2
The DC voltage signal V _i (which is a voltage obtained by dividing the actual output voltage by 1/10) which is the output voltage of No. 6 is compared (step S12), and the DC voltage signal V _i indicates the output voltage set value V _i.
If it is larger than _f , the variable voltage setting means 41 is set to 2 V so as to reduce the DC voltage signal V _i . The pulse delay time T _n corresponding to the output voltage setting value set to 2 V is 0.1 m.
The pulse delay time increasing process for resetting the pulse delay time of T _n +0.1 ms increased by s is performed (step S1).
3). Further, if the DC voltage signal V _i is smaller than the output voltage set value V _f, the pulse delay corresponding to the output voltage set value set by the variable output voltage setting means 41 as 2 V so as to increase the DC voltage signal V _i. 0.1 from time T _n
The pulse delay time of T _n -0.1 ms reduced by ms is reset and the control for increasing the voltage is started (step S14). Thereafter, the output voltage setting value V _f by comparing the DC voltage signal V _i again (step S15), and the DC voltage signal V _i is smaller than the output voltage setting value V _f, to increase the DC voltage signal V _i As described above, the pulse delay time reduction processing for resetting the pulse delay time which is 0.2 ms less than the pulse delay time T _n -0.1 ms is performed (step S16). Further, if the DC voltage signal V _i is larger than the DC voltage setting value V _f, so as to reduce the DC voltage signal V _i, the pulse delay time T _n -0.1ms than zero.
The pulse delay time increased by 1 ms is set again, and the control is started to decrease the duty ratio and decrease the voltage (step S17).

After that, the oscillation abnormality judging means 45 judges that the voltage drop of the shunt resistor 3 is 1V (step S18), and if the voltage drop is 1V or more,
It is determined to be abnormal, the output of the drive pulse signal from the voltage control means 42 is prohibited (step S19), the alarm generation process is performed simultaneously with the stop process (step S20), and the standby state is entered. If the voltage drop does not exceed 1V, step S
Return to 3.

FIG. 7 is a flowchart showing a subroutine of the pulse delay time increasing process 13, which is a process for gradually decreasing the voltage. The pulse delay time increase process, T _n
Is set (step S61), the output voltage setting value V _f is fetched (step S62), and the DC voltage signal V _i is compared with the output voltage setting value V _f plus 0.5 V (step S63). If the DC voltage signal V _i is small, the pulse delay time increasing process for resetting the pulse delay time of T _n +0.2 ms, which is 0.2 ms longer than the pulse delay time T _n , is performed, and the voltage comparison is repeated. As a result, the DC voltage signal V
_{When i} becomes large, the pulse delay time T _n is reset to the pulse delay time T _na of T _n +0.1 ms in which the increase width of the pulse delay time T _n is halved, and the change is delayed to improve the controllability. FIG. 5 is connected before step S12 of the main routine.

Further, FIG. 8 shows pulse delay time reduction processing 16
In the flowchart shown in the sub-routine, the voltage is gradually increased. The pulse delay time reduction processing is T _na
Is set (step S71), the output voltage set value V _f is fetched (step S72), and the DC voltage signal V _i is compared with the output voltage set value V _f minus 0.5 V (step S73). performs pulse delay time reducing process to reset the pulse delay time of T _na -1ms DC voltage value V _i is the reduced 0.1ms than if the pulse delay time T _na small, repeated voltage comparison. As a result, when the DC voltage signal V _i becomes large, the pulse delay time T _n is reset to T _na −0.2 ms, which is 0.2 ms smaller than T _na , and the change is accelerated to increase the voltage. The speed at which the
It is inserted before step S15 of the main routine shown in FIG.

FIG. 9 shows the relationship between the motor drive frequency and the output voltage, where 81 is V _f on the vertical axis, 82 is the drive frequency on the horizontal axis, and 83 is the function thereof. An arbitrary function may be stored in the voltage-versus-frequency memory 43 instead of the linear function as in the example. Also,
FIG. 10 is an example of a function of gradually increasing the drive frequency on the horizontal axis of 82, 84 is the motor drive frequency on the vertical axis, and 85 is
Is a time transition on the horizontal axis, and 86 is a function thereof.

[0032]

As described above, according to the present invention, the voltage control means outputs the drive pulse signal having the pulse delay time corresponding to the output voltage setting value set by the variable output voltage setting means between the AC power supply and the full-wave rectifier. The output voltage of the smoothing capacitor connected to the full-wave rectifier is controlled by changing the conduction ratio of the output voltage of the smoothing capacitor and the target output voltage setting value of the variable output voltage setting means and the output voltage of the smoothing capacitor. When the output voltage is higher than the target output voltage set value, the drive pulse signal having a pulse delay time that is longer than the pulse delay time corresponding to the target output voltage set value is output, and the output signal is the target When it is smaller than the output voltage setting value, the drive pulse signal having the pulse delay time which is shorter than the pulse delay time corresponding to the target output voltage setting value is switched. Since to output the element has the effect that the control of the low cost power supply voltage transformer enables freely performed, yet can control the output voltage reaches quickly the target output voltage.

Further, the frequency control means provides a trigger pulse signal having a frequency preset corresponding to the output voltage set value of the variable output voltage setting means between the smoothing capacitor and the two primary windings of the bear picking motor. Since the thyristor is triggered by the frequency corresponding to the output voltage by outputting to the two thyristors, the frequency control can be freely performed without cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main part abbreviated as a part of an embodiment of the present invention.

FIG. 2 is a circuit diagram showing the same embodiment.

FIG. 3 is a perspective view showing a coil of the shading motor of the embodiment.

FIG. 4 is a waveform diagram showing a waveform of each part of the embodiment.

FIG. 5 is a flowchart showing a main routine of operation of the embodiment.

FIG. 6 is a flowchart showing a subroutine of retry processing of three times.

FIG. 7 is a flowchart showing a subroutine of pulse delay time increasing processing.

FIG. 8 is a flowchart showing a subroutine of pulse delay time reduction processing.

FIG. 9 is a graph showing the relationship between output voltage and drive frequency.

FIG. 10 is a graph showing a relationship between drive frequency and transition of time.

FIG. 11 is a circuit diagram of a conventional shaded motor inverter control circuit.

FIG. 12 is a waveform diagram showing a waveform of each part of the control circuit.

[Explanation of symbols]

 5,6 Bear winding motor primary winding 8,9 Thyristor 18 Triac (switching element) 25 Full-wave rectifier 26 Smoothing capacitor 41 Variable output voltage setting means 42 Voltage control means 43 Frequency control means

Claims (1)

[Claims] 1. A full-wave rectifier for full-wave rectifying the AC voltage of an AC power supply, a switching element provided between the AC power supply and the full-wave rectifier, for controlling the conduction ratio, and an output voltage of the full-wave rectifier. A smoothing capacitor for smoothing, a bear motor having two primary windings to which the output voltage of the smoothing capacitor is respectively applied via thyristors, and a stepwise process from the initial output voltage setting value to the target output voltage setting value. A variable output voltage setting means for variably increasing and setting, and a drive pulse signal having a pulse delay time corresponding to the output voltage setting value of the variable output voltage setting means are output to the switching element, and at the same time, the variable output voltage setting means Compare the target output voltage setting value with the output voltage of the smoothing capacitor, and if the output voltage is greater than the target output voltage setting value, respond to the target output voltage setting value. Output a drive pulse signal having a pulse delay time that is greater than the pulse delay time, and when the output voltage is less than the target output voltage setting value, it is less than the pulse delay time corresponding to the target output voltage setting value. A voltage control means for outputting a drive pulse signal having a pulse delay time to the switching element, and a frequency for outputting to the thyristor a trigger pulse signal having a frequency preset corresponding to the output voltage setting value of the variable output voltage setting means. A dark circle motor inverter control circuit comprising: a control means.