JP2001309693A - Motor control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that the fluctuation of direct current voltage influences the rotation state of a motor if the direct current voltage is not directed in an electric power circuit when the electrostatic capacity of the capacitor of an intermediate direct current part for small size and low cost is lessened in the three-phase motor drive circuit of single phase alternating current input. SOLUTION: The frequency and phase of the single phase alternating current input are detected, a regulation parameter group corresponding to the period of the half of a cycle is provided, the regulation parameter equivalent to an input voltage phase is minutely corrected when the voltage and current phase difference detection timing of the motor out of the regulation parameter group is obtained so that the phase difference between the current phase detection means of the motor and motor application voltage is equal to a set value, and the regulation parameter is used for the motor application voltage generation as a direct current voltage estimation value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a control device capable of driving a three-phase motor at a variable speed from a single-phase AC power supply.

[0002]

2. Description of the Related Art FIG. 7 is a circuit diagram showing a basic structure of a conventional motor drive circuit. The single-phase AC 2 is rectified by rectifier diodes 3u, 3v, 3x, 3y, smoothed by a capacitor 5, and three-phase bridge inverters 4u, 4v, 4w,
The three-phase motor 1 is driven by 4x, 4y, 4z and the three-phase PWM control signal from the control circuit 6.

Here, the capacitor 5 is for smoothing a single-phase AC power ripple in an intermediate DC portion, and generally uses a capacitor having a capacitance of a certain level or more. However, increasing the capacitance of the capacitor 5 causes problems such as an increase in volume or an increase in the cost of components.

[0004] For this reason, when a capacitor having a large capacitance is not used in the intermediate DC portion, the effect of the power ripple remains as a voltage ripple.
Thus, the duty correction is performed so that the motor applied voltage does not fluctuate according to the fluctuation of the intermediate DC voltage.

[0005]

As described in the prior art, when a capacitor having a large capacitance is not used in the intermediate DC portion, it is necessary to directly detect the intermediate DC voltage. Are connected at the same potential, so that they are susceptible to noise generated in the power circuit. There is also a method of transmitting voltage information detected on the power circuit side to the control circuit side by an insulating amplifier. However, a precise insulating amplifier is required, and there remains a problem in miniaturization and cost.

[0006]

According to the present invention, there is provided a voltage polarity detecting means connected to an AC power supply, and a fluctuation period is measured from a detection result of the voltage polarity detecting means to determine a power supply frequency, and Is detected. An adjustment parameter group corresponding to a half period of the detected AC power supply cycle is provided,
The adjustment parameter corresponding to the input voltage phase when the motor voltage and current phase detection timing is obtained from the adjustment parameter group is finely corrected so that the phase difference between the motor applied voltage and the motor current becomes equal to the set value. By not directly detecting the intermediate DC voltage and using the adjustment parameter as a DC voltage estimation value for the motor applied voltage, even when a capacitor having a large capacitance is not used in the intermediate DC portion, the power can be reduced. The three-phase PWM duty can be corrected so that the motor applied voltage does not fluctuate in accordance with the fluctuation ripple of the intermediate DC voltage without using an accurate isolation amplifier, etc. It is.

[0007]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing the configuration of a voltage polarity detecting means according to an embodiment of the present invention;
And the phase of the AC power supply is detected, and an adjustment parameter group is provided according to a half period of the detected AC power supply cycle, and the adjustment parameter group is set so that a phase difference between the motor applied voltage and the motor current becomes equal to a set value. Among them, the adjustment parameter corresponding to the input voltage phase when the timing of detecting the voltage and the current phase difference of the motor is obtained is slightly corrected, and the adjustment parameter is used as the DC voltage estimated value for generating the motor applied voltage.

[Embodiment] An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an embodiment of a three-phase motor drive in a single-phase AC input of the present invention, FIG. 2 is a waveform of each part with respect to a single-phase AC input voltage waveform, FIG. 3 is a phase difference of an input voltage current due to a capacitance of a smoothing capacitor, FIG.
FIG. 5 is a block diagram showing the relationship between the voltage and the current phase in the induction motor, FIG. 5 is a block diagram showing the relationship between the voltage and the current phase in the synchronous motor, and FIG. 6 is a block diagram showing that the DC voltage is estimated using the adjustment parameters.

First, in FIG. 1, a single-phase AC 2 is rectified by rectifier diodes 3u, 3v, 3x, 3y, smoothed by a capacitor 5, and converted into three-phase bridge inverters 4u, 4v,
4w, 4x, 4y, 4z and three-phase PWM from the control circuit 6
The three-phase motor 1 is driven by the control signal.

Here, the capacitor 5 is for smoothing the power ripple of the single-phase AC input in the intermediate DC portion. Therefore, it is common to use a capacitor having a certain level of capacitance or more.However, in order to reduce the size and cost of the drive circuit, if a capacitor having a sufficiently large capacitance is not used in this intermediate DC portion, Since the influence of the power ripple having a cycle of half of the AC input voltage cycle remains as the voltage ripple, the intermediate DC voltage fluctuates. In order to prevent the three-phase PWM output from being disturbed by the fluctuation, the control circuit 6 needs to correct the three-phase PWM output duty in accordance with the fluctuation of the intermediate DC voltage.

However, when a directly varying intermediate DC voltage is detected, the control circuit and the power circuit are connected at the same potential, so that the control side is more susceptible to the noise generated in the power circuit. Have. In order to cope with this, in this embodiment, the intermediate DC voltage is estimated directly based on the detection values from the detection circuit 7 and the current sensor 11 instead of directly detecting the intermediate DC voltage, and the three-phase PWM output duty is corrected. Do. From the AC input voltage cycle and phase, the intermediate DC voltage value is estimated from the cycle and phase of the intermediate DC voltage and the phase difference between the motor applied voltage and the motor current, and the three-phase PWM output duty is corrected.

First, FIGS. 2 (a) and 2 (e) show the cycle and phase of the intermediate DC voltage fluctuation with respect to the single-phase AC input voltage. The intermediate DC voltage is affected by the input power ripple, and its fluctuation cycle is half of the AC input voltage cycle. The cycle of the AC input voltage is the same as the cycle of the waveform detected as shown in FIG. 2B by the detection circuit 7 including the capacitor 9 and the photocoupler 8 of the threshold voltage Vth in FIG. The period of the intermediate DC voltage can be estimated from this detection result.

At this time, the maximum value of the AC input voltage is detected by detecting the timing when the threshold voltage Vth is exceeded and the photocoupler 8 switches to the active state as t ₁ , and the timing when the photocoupler 8 switches below the threshold voltage Vth to the OFF state as t _3. Phase information at each point such as a point t ₂ (middle point of the active period), a minimum value point t ₅ (middle point of the OFF period), and a zero cross point t ₄ (middle point of the maximum and minimum value points) can be obtained. It is also possible to continuously estimate the phase in each section.

The intermediate DC voltage has a certain phase difference depending on the load state with respect to the estimated AC input voltage phase. When the smoothing capacitor 5 is sufficiently large, the intermediate DC voltage ripple becomes small and has a phase delayed by approximately 90 ° with respect to the input power waveform as shown in FIG. Conversely, when the smoothing capacitor 5 is small and a large voltage ripple occurs, the phase delay with respect to the input power waveform becomes smaller than 90 ° as shown in FIG. However,
The phase difference for the AC input voltage cannot be directly estimated.

In order to enable estimation, it is necessary to use a current sensor in combination with the detection circuit 7 in FIG. The signal detected by this current sensor is shown in FIG. Assuming that the maximum value point of the current sensor signal is t ₆ and the minimum value point is t ₇ , the difference between the above-described AC voltage maximum value point t ₂ and the maximum value point t ₆ of the current sensor signal is the magnitude of the AC input voltage and the current. It becomes a difference. This makes it possible to detect the phase difference of the current with respect to the AC input voltage whose continuous phase has been estimated, and it is possible to continuously estimate the phase of the intermediate DC voltage affected by the input power ripple. As described above, it is possible to estimate both the period and the phase of the intermediate DC voltage based on the result detected using the detection circuit 7.

Next, the estimation of the intermediate DC voltage value will be described. The relationship between the voltage applied to the motor and the phase of the motor current in the induction motor and the synchronous motor is as shown in FIGS. In the case of an induction motor, it is generally known that the phase delay of the motor current with respect to the motor applied voltage increases as the motor applied voltage increases, and the phase delay of the motor current decreases as the motor applied voltage decreases. However, the phases of the motor applied voltage and the motor current are not reversed by the load.

Next, in the case of the synchronous motor, the phase difference between the motor applied voltage and the motor current changes according to the motor applied voltage value as in the case of the induction motor, but depending on the load condition, the phases of both motors are reversed. It is generally known that by advancing the PWM duty output timing, the motor current phase with respect to the motor applied voltage can be advanced.

The process up to estimating the intermediate DC voltage value from the respective detection results using the relationship between the phase difference between the motor applied voltage and the motor current, the motor applied voltage value, and the three-phase PWM output timing will be described with reference to FIG. I do.

When the motor to be used is an induction motor,
The phase of the motor current with respect to the motor applied voltage detected using the current sensor 11 in FIG. 1 is compared with a preset value. When the delay is behind the set value, the input voltage phase when the motor voltage and current phase detection timing is obtained from the adjustment parameter group corresponding to a half period of the cycle detected by the single-phase AC input cycle detection means. Is slightly corrected in the direction in which the DC voltage estimated value decreases, and when the phase is advanced, the parameter is adjusted in the opposite direction.

When the motor to be used is a synchronous motor, the phase of the motor current with respect to the motor applied voltage detected using the current sensor 11 is compared with a preset value. When the delay is behind the set value, the input voltage phase when the motor voltage and current phase detection timing is obtained from the adjustment parameter group corresponding to a half period of the cycle detected by the single-phase AC input cycle detection means. The parameter corresponding to is slightly corrected in the direction in which the DC voltage estimated value decreases, or the adjustment parameter is slightly corrected so as to advance the output timing of the three-phase PWM output duty. Adjust in the opposite direction.

According to the above method, a three-phase P
In a control device capable of driving the WM motor at a variable speed, the intermediate DC voltage value is estimated, and even when an intermediate DC voltage ripple occurs due to insufficient capacitance of the smoothing capacitor 5, the estimated fluctuation of the intermediate DC voltage is obtained. It is possible to output a three-phase PWM duty corrected in accordance with.

[0022]

The present invention is embodied in the form described above, and has the following effects. Even when a voltage ripple occurs in the intermediate DC voltage portion in a device that drives a three-phase PWM motor at a variable speed from a single-phase AC power supply, the device can be driven without being affected by the ripple.

Further, by suppressing the capacitance of the capacitor for smoothing the intermediate DC voltage, the size and cost of the inverter circuit can be reduced, and the intermediate DC voltage can be directly detected with respect to the correction of the ripple of the intermediate DC voltage. Rather than inferring the noise from the power circuit, it is inferred from the AC input voltage cycle, the phase and the phase relationship between the motor applied voltage and the motor current. In addition, since a highly accurate insulating amplifier is not required, reliability and accuracy are improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a three-phase motor drive circuit according to one embodiment of the present invention.

FIG. 2 is a time chart showing a relationship between a cycle and a phase of each waveform with respect to an AC input voltage.

FIG. 3 is a vector diagram showing a phase difference due to the capacitance of a smoothing capacitor.

FIG. 4 is a time chart showing a phase relationship between a motor voltage and a current in the induction motor.

FIG. 5 is a time chart showing a phase relationship between a motor voltage and a current in the synchronous motor.

FIG. 6 is a block diagram showing DC voltage estimation using adjustment parameters.

FIG. 7 is a basic circuit configuration diagram of a conventional three-phase motor drive circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Three-phase motor 2 Single-phase AC power supply 3 Rectifier diode 4 Three-phase bridge inverter 5 Smoothing capacitor 6 Microcomputer 7 Input power cycle and phase detection device 8 Photocoupler 9 Capacitor 10 Resistance 11 Current sensor 12 DC power supply 13 Resistance

Claims (4)

[Claims] 1. Detecting the frequency and phase of a single-phase AC input,
An adjustment parameter group corresponding to a half period of the cycle is provided,
In order to make the phase difference between the motor applied voltage and the motor current equal to the set value, the adjustment parameter corresponding to the input voltage phase at the time of obtaining the motor voltage and current phase difference detection timing in the adjustment parameter group is very small. A motor control device, wherein the corrected DC voltage estimated value calculated using the adjustment parameter is used for generating the motor applied voltage. 2. The motor control device according to claim 1, wherein the adjustment parameter group is adjusted so as to smoothly change in a time series, and then used as an estimated DC voltage value for generating the motor applied voltage. . 3. When the motor to be used is an induction motor, and when the phase of the current with respect to the AC input voltage is delayed, the adjustment parameter is adjusted so that the estimated DC voltage value decreases in order to match a predetermined power factor value. Is slightly modified,
3. The motor control device according to claim 1, wherein when the phase is advanced, the phase is adjusted in the opposite direction. 4. When the motor to be used is a synchronous motor, and when the phase of the current with respect to the input voltage is delayed, the DC voltage estimation value is decreased in order to match a predetermined power factor value, or 3. The motor control device according to claim 1, wherein the adjustment parameter relating to the output timing of the three-phase PWM duty is finely corrected so as to reduce the phase difference, and when the current phase is advanced, the adjustment is performed in the opposite direction. .