JP2003348880A - Motor control device and control method thereof - Google Patents

Abstract

(57) [Problem] To reduce the size of a drive circuit by reducing the capacity of a bootstrap capacitor in a motor control device. When a DC voltage of a main power supply is switched by an inverter circuit and applied to a motor, switching devices Ua, Va and Wa of an upper arm are controlled via a bootstrap drive circuit and
The switching elements X, Y, and Z of the lower arm are controlled via a drive circuit 2 using a bootstrap method. At this time, the switching elements Ua, Va, and Wa are PWM-controlled to drive the motor 3, but when the PWM control is off, the lower-arm switching elements are turned on to change the bootstrap capacitor 10 of the power supply circuit of the live circuit 2 for a predetermined period. A refresh circuit for charging each time is formed, and the bootstrap capacitor 10 is used as a constant voltage source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for driving a motor (for example, a brushless DC motor) by inverter control, and more specifically, a technique for reducing the size of a control device (drive circuit) so as to be built in the motor. It is about.

[0002]

2. Description of the Related Art For example, a general configuration of an inverter control device for a brushless DC motor is shown in FIG. According to this, the motor control device includes six transistors Ua, V
The inverter circuit 1 includes a, Wa, X, Y, and Z connected to a three-phase bridge. Each transistor Ua, Va,
For Wa, X, Y, and Z, a transistor (for example, IGBT) capable of high-speed switching is used from the viewpoint of the carrier frequency of the inverter and low motor noise. Each drive circuit 2 for driving the inverter circuit 1 employs a bootstrap method.

Each drive circuit 2 includes a shift circuit 2a for adjusting the level of a signal (including, for example, a PWM waveform signal) from a control circuit (microcomputer) 4 for controlling the brushless DC motor 3, and a level-shifted circuit. And a buffer circuit 2b for driving the IGBT by a signal. Regarding the drive circuit 2, a high-side gate drive circuit is used for the upper arm IGBT and a low-side gate drive circuit is used for the lower arm IGBT in many cases.

A power supply (for example, 15
To explain the (V voltage) 5, the 15 V voltage is directly supplied to the low side gate drive circuit.
The high side gate drive circuit charges the bootstrap capacitor 8 with the 15V voltage via the charging current limiting resistor 6 and the bootstrap diode 7, and the voltage generated at both ends of the bootstrap capacitor 8 is used as a voltage source. .

The ground of the low-side gate drive circuit is at the ground level of the power supply 5, and the ground of the high-side gate drive circuit is at the emitter terminal level of the transistor (IGBT) of the upper arm.

In the high side gate drive circuit using the bootstrap circuit, the lower arm IGBT
Is turned on, the current of the power supply 5 is changed from the bootstrap diode 7 to the bootstrap capacitor 8 to the lower arm I
The voltage flows through the GBT path, a voltage is generated across the bootstrap capacitor 8, and the voltage is used as a voltage source.

For example, as shown in FIG. 5 (f), when the GZ signal is on, the bootstrap capacitor 2 for supplying to the transistor Wa is charged.
The inverter circuit 1 is supplied with power from a main power supply (DC power supply) 9.

As described above, by employing a transistor inverter configuration having a high-side gate drive circuit and a low-side gate drive circuit by the bootstrap circuit, the drive circuit does not require a photocoupler or the like, and the drive circuit can be simplified. . Also, the drive circuits of the upper arm IGBT and the lower arm IGBT need only have one power supply, and the power supply can be simplified.

In the control device having the above configuration, when rotating the three-phase motor 3, the control circuit 4 switches the IGBT of the inverter circuit 1 to a three-phase rectangular wave voltage, which is applied to the three-phase motor 3. I do. If two phases are energized out of three phases, for example, U-phase to W-phase energization is switched to V-phase to W-phase energization, a PWM waveform is generated and a signal including the PWM waveform is generated. Output (see FIG. 5).

For example, the transistor Ua is turned on and off at a predetermined duty ratio by the GUa signal (see FIG. 5).
(A)), the transistor Z is turned on by the GZ signal (see FIG. 5 (f)), and then the transistor Va is turned on and off at a predetermined duty ratio by the GVa signal (see FIG. 5 (b)). The signal transistor Z is kept on (see FIG. 5F). Note that the other transistors are off (see FIG. 5). Thus, by sequentially switching the three-phase winding energization and generating a rotating magnetic field, a rotating force is generated in the motor 3.

[0011]

In the above motor control device, the voltage of the bootstrap capacitor 8 decreases due to the operation of the transistors Ua, Va and Wa. The capacitor 8 is charged to obtain the operating voltages of the transistors Ua, Va, Wa.

Therefore, a large bootstrap capacitor 8 has to be used because the bootstrap capacitor 8 requires a certain capacity or more. Conventionally, this has been an obstacle in reducing the size and cost of the drive circuit.

For example, when the motor 3 is applied to a fan motor of an air conditioner (air conditioner), it is difficult to incorporate a control device into the motor, and at least the bootstrap capacitor 8 is externally mounted.

Therefore, a first object of the present invention is to reduce the capacity of a bootstrap capacitor to reduce the size of a drive circuit, and to enable the drive circuit to be built in a motor. A second object of the present invention is to protect the control device from regenerative energy generated when the motor is forcibly rotated by an external force for some reason.

[0015]

In order to solve the above-mentioned first problem, the present invention provides a method for applying a DC voltage to a motor by switching the DC voltage with an inverter comprising switching elements of an upper arm and a lower arm and applying the switching to a motor. The switching element of the arm is controlled via a high-side gate drive circuit of a bootstrap method, and the switching element of the lower arm is controlled via a low-side gate drive circuit of a bootstrap method, while at least the switching element of the upper arm is controlled. In the motor control device for driving the motor by PWM control, a refresh circuit for charging a bootstrap capacitor constituting a power supply circuit of the high-side gate drive circuit at regular intervals is provided.

According to this configuration, since the capacity of the bootstrap capacitor can be reduced, the size of the entire control device can be reduced. Therefore, the control device itself can be incorporated in the motor.

Further, in order to solve the second problem,
In the present invention, the motor is a fan motor of an air conditioner, and the main power supply (DC voltage source) of the inverter is forcibly rotated by an external force when the refresh circuit is formed. It is characterized by having a discharge resistor that consumes regenerative energy returned to the main power supply due to the generated short-circuit brake current. In this case, the control device is built in the motor except for the discharge resistor.

Further, in order to solve the first problem,
The method of controlling a motor according to the present invention is characterized in that when a DC voltage is switched by an inverter including switching elements of an upper arm and a lower arm and applied to the motor, a high-side gate drive circuit using a bootstrap method is used for the switching elements of the upper arm. And the switching element of the lower arm is controlled via a low side gate drive circuit of a bootstrap method, while at least the switching element of the upper arm is controlled by PW
In driving the motor under M control, when the PWM of the switching element of the upper arm is turned off, the switching element of the lower arm is turned on, and the bootstrap capacitor constituting the power supply circuit of the high side gate drive circuit is switched at regular intervals. A refresh circuit for charging the battery is formed.

Further, in order to solve the second problem,
The method of controlling a motor according to the present invention is characterized in that when a DC voltage is switched by an inverter including switching elements of an upper arm and a lower arm and applied to the motor, a high-side gate drive circuit using a bootstrap method is used for the switching elements of the upper arm. And the switching element of the lower arm is controlled via a low side gate drive circuit of a bootstrap method, while at least the switching element of the upper arm is controlled by PW
In driving the motor under M control, the main power supply circuit of the inverter has a discharge resistor in parallel, and when the PWM of the switching element of the upper arm is off, the switching element of the lower arm is turned on, and While forming a refresh circuit for charging the bootstrap capacitor constituting the power supply circuit of the side gate drive circuit at regular intervals, when the refresh circuit is formed, the motor is forcibly rotated by an external force. The regenerative energy returned to the main power supply by the short-circuit brake current is consumed by the discharge resistor.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described in detail with reference to FIGS. In FIG. 1, the same parts as those in FIG. 4 are denoted by the same reference numerals, and redundant description will be omitted.

In the present invention, an inverter transistor (I) having a drive circuit of a bootstrap method is used.
GBT), when the upper arm transistor is under PWM control, when the PWM is off, the lower arm IG
By forming a refresh circuit that turns on the BT and charges the bootstrap capacitor at regular intervals and uses the bootstrap capacitor as a constant voltage source,
The bootstrap capacitor is intended to have a smaller capacity than before.

For this purpose, as shown in FIG. 1, the motor control device of the present invention includes a small-capacity bootstrap capacitor 10 used in place of the bootstrap capacitor 8 shown in FIG. When the IGBT of the upper arm for performing duty ratio control) is turned off, the IGBT of the lower arm corresponding to the IGBT is turned on, and the current of the power supply 5 flows to the bootstrap diode 7 and the bootstrap capacitor 10, and the power supply 5 is supplied at regular intervals. A refresh circuit for charging the bootstrap capacitor 10 is formed, and a control circuit 11 using the voltage across the bootstrap capacitor 10 as a constant voltage source, a DC voltage source similar to the conventional one, and a control circuit 11 in parallel with both ends of the DC voltage source. Power supply 12 having discharge resistor 12a and capacitor 12b connected to
And

The operation of the control device having the above configuration will be described with reference to the time chart of FIG. 2A to 2F correspond to FIGS. 5A to 5F. First, the control circuit 11 performs GUa, GVa, GWa, X,
Outputs Y and Z signals and outputs IGB of upper arm and lower arm
T is switched in a predetermined manner, and the winding energization of the motor 3 is switched.

At this time, for example, in order to conduct current from the U phase to the W phase, the upper arm transistor Ua is PWM-controlled and the lower arm transistor Z is turned on, while the off state of the transistor Ua is used. The pulse is superimposed on the GX signal (off signal) of the lower arm transistor X (see FIG. 2D). Note that the width (ON width) of the superposed pulse is smaller than the OFF width of the PWM control.

Subsequently, in order to energize from the V phase to the W phase,
While controlling the upper arm transistor Va by PWM,
While the lower-arm transistor Z is turned on, a pulse is superimposed on the GY signal (off-signal) of the lower-arm transistor Y using the off-state of the transistor Va (FIG. 2).
(E)).

In the same manner, since the energization of each phase is switched in the same manner, a refresh circuit for flowing the current of the power supply 5 to the bootstrap diode 7 and the bootstrap capacitor 10 for each energization is synchronized with the PWM waveform at a constant period. It is formed.

Thus, the bootstrap capacitor 10 is charged not only by the same charge as in the conventional example but also by the formation of the refresh circuit of the present invention, that is, the voltage across the bootstrap capacitor 10 is always a constant voltage. Source can be maintained.

Therefore, even if the capacity of the bootstrap capacitor 10 is smaller than that of the conventional bootstrap capacitor 8, the drive circuit 2 can be driven reliably and the drive circuit can be downsized.

The above bootstrap capacitor 1
0 means that the conventional bootstrap capacitor 8 is 1
In the case of 00 μF, about 1 μF is sufficient. Further, for example, when the motor 3 is a fan motor of an air conditioner, the control device can be incorporated in the fan motor. further,
By reducing the capacity of the bootstrap capacitor 10, the cost of the control device can be reduced.

By the way, if any external force is applied during the operation of the refresh circuit and the motor 3 is forcibly rotated, the motor 3 forms an equivalent circuit shown in FIG. Generates an induced voltage.

Due to the generation of the induced voltage, a short-circuit brake current (short-circuit current) is generated. When the current is switched, a regenerative current is generated toward the main power supply 12. That is, for example, the transistor X in the lower arm is turned on when the PWM is turned off when the U-phase → W-phase is energized (see FIG. 2D), and the transistor Y is turned on when the PWM is turned off when the V-phase → W-phase is energized. (See FIG. 2E).

Then, the voltage of the main power supply 12 increases, and in the worst case, a problem may occur that the breakdown voltage of the IGBT or the capacitor is exceeded. That is, the voltage rise depends on the short-circuit current value before switching, and the short-circuit current depends on the speed of forced rotation. The larger the external force or the like, the larger the voltage rise.

For example, if the motor is forcibly rotated by an external force and a short-circuit current is generated, a regenerative energy E expressed by the following equation (1) is obtained every time the short-circuit current is switched.
Is returned to the main power supply 12.

[0034] In ^{E = L × I 2/2} ...... formula (1) Same formula (1), L winding inductance, I of the motor 3 is a short-circuit current at the time of switching.

The regenerative energy E is consumed by a discharge resistor 12a connected in parallel with the power supply of the main power supply 12. Therefore, the resistance value R of the discharge resistor 12a may be determined by the following equation (2).

R ≦ (2 × V ² ) / (L × I ² × f) Equation (2) In the equation (2), V is the breakdown voltage of the IGBT, and f is the short-circuit current switching frequency.

As described above, the discharge resistor 12a is connected to the main power source 12
In this case, it is possible to solve the problem caused by forming the refresh circuit, that is, the overvoltage of the IGBT and the capacitor due to the increase in the power supply voltage of the inverter circuit 1. Further, as described above, when the control device is built in the fan motor, the discharge resistor 12a may be externally provided.

[0038]

As described above, according to the present invention,
In a motor control device that rotates a motor by PWM controlling an inverter transistor, a switching element of an upper arm is controlled through a high-side gate drive circuit of a bootstrap method, and a switching element of a lower arm is controlled by a bootstrap method of a low side. A refresh circuit that charges a bootstrap capacitor constituting a power supply circuit of a high-side gate drive circuit at regular intervals when driving the motor by controlling at least a switching element of the upper arm by PWM while controlling the gate drive circuit. Since the bootstrap capacitor is charged even when the refresh circuit is formed, the capacity of the bootstrap capacitor can be small and the drive circuit can be downsized. Can, thus the control device is a motor that can be built compact, also has the effect of cost reduction can be achieved.

Further, according to the motor control method of the present invention, the main power supply circuit of the inverter has a discharge resistor in parallel, and when the PWM of the switching element of the upper arm is turned off, the switching element of the lower arm is turned on. Then, while forming a refresh circuit that charges the bootstrap capacitor constituting the power supply circuit of the high-side gate drive circuit for driving the upper arm at regular intervals, while the refresh circuit is being formed, the motor is driven by external force. Since the regenerative energy returned to the main power supply by the short-circuit brake current generated by forcible rotation can be consumed by the discharge resistor, in addition to the same effect as described above, there is a problem when the motor is forcibly rotated by external force. Can be eliminated.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing an embodiment of a motor control device according to the present invention.

FIG. 2 is a schematic time chart for explaining the operation of the embodiment.

FIG. 3 is a schematic equivalent circuit diagram of a motor for explaining the operation of the embodiment.

FIG. 4 is a schematic block diagram for explaining a conventional motor control device.

FIG. 5 is a schematic time chart for explaining the operation of the conventional control device.

[Explanation of symbols]

1 Inverter circuit 2 Drive circuit (drive circuit) 2a Shift circuit (level) 2b buffer circuit 3 Motor 4,11 control circuit (microcomputer) 5 Power supply 6 Charge current limiting resistor 7 Bootstrap diode 8,10 Bootstrap capacitor 9,12 Main power supply 12a Discharge resistance 12b capacitor

Claims (5)

[Claims] When a DC voltage is switched by an inverter including switching elements of an upper arm and a lower arm and applied to a motor, the switching element of the upper arm is controlled via a high-side gate drive circuit of a bootstrap method. A control device for controlling the switching element of the lower arm through a low-side gate drive circuit based on a bootstrap method, and at least controlling the switching element of the upper arm by PWM to drive the motor; A motor control device comprising a refresh circuit for charging a bootstrap capacitor constituting a power supply circuit of a drive circuit at regular intervals. 2. The motor control device according to claim 1, wherein the control device itself can be built in the motor. 3. The motor is a fan motor of an air conditioner, and a main power supply (DC voltage source) of the inverter is forcibly rotated by an external force when the refresh circuit is formed. 2. The motor control device according to claim 1, further comprising a discharge resistor that consumes regenerative energy returned to the main power supply due to the short-circuit brake current generated, and excluding the discharge resistor, the control device is built in the motor. 3. 4. When a DC voltage is switched by an inverter including switching elements of an upper arm and a lower arm and applied to a motor, the switching element of the upper arm is controlled via a high-side gate drive circuit of a bootstrap system. And controlling the switching element of the lower arm through a low-side gate drive circuit based on a bootstrap method, and at least controlling the switching element of the upper arm by PWM to drive the motor. When the PWM of the switching element is off, a switching circuit of the lower arm is turned on to form a refresh circuit for charging a bootstrap capacitor constituting a power supply circuit of the high side gate drive circuit at regular intervals. A motor control method according to claim. 5. When a DC voltage is switched by an inverter including upper and lower switching elements and applied to a motor, the switching element of the upper arm is controlled via a high-side gate drive circuit of a bootstrap method. And controlling the switching element of the lower arm through a low-side gate drive circuit based on a bootstrap method, and controlling the motor by driving at least the PWM control of the switching element of the upper arm. The power supply circuit has a discharge resistor in parallel. When the PWM of the switching element of the upper arm is turned off, the switching element of the lower arm is turned on, and a bootstrap capacitor constituting a power supply circuit of the high side gate drive circuit is provided. Constant While forming the refresh circuit for charging every period, when the refresh circuit is formed, the regenerative energy returned to the main power supply by the short-circuit brake current generated when the motor is forcibly rotated by an external force is used. A method for controlling a motor, wherein the motor is consumed by a discharge resistor.