JP2003324986A - Control method for three-phase brushless dc motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control method for three-phase DC motor using MOS transistors, wherein power loss and heat generation are reduced; cooling operation is simplified; and thus the enhancement of reliability is accomplished. <P>SOLUTION: The upper arm-side MOS transistors 5a to 5c of a three-phase inverter circuit 5 which supplies the three-phase brushless DC motor 3 with power are successively provided with predetermined PWM control phase periods different from one another and thereby PWM-controlled. At this time, a lower arm-side MOS transistor 5d in the same phase as an upper arm-side MOS transistor (e.g. 5a) PWM-controlled is caused to operate complementarily to the MOS transistor 5a. Great power loss and heat generation caused by a flywheel current being passed through the parasitic diode 5k of the MOS transistor 5a are reduced or prevented. Thus, the enhancement of efficiency and the lightening of cooling load can be accomplished. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a three-phase brushless D
The present invention relates to a control method for a C motor.

[0002]

2. Description of the Related Art In the case of controlling a three-phase brushless DC motor by an inverter, each upper arm side switching element and each lower arm side switching element of a three-phase inverter circuit are switching-driven to convert DC power into three-phase AC power. . As one of the inverter energization control methods, a 120-degree energization method in which the ON period of each switching element is an electrical angle of 2π / 3 and a 180-degree energization method in which the ON period of each switching element is an electrical angle of π are known. There is. The electric torque of the three-phase brushless DC motor is controlled by PWM control of the switching element of the three-phase inverter circuit.

In the conventional method for controlling a three-phase brushless DC motor described above, since the three-phase brushless DC motor has a large inductance, the upper arm side switching element (or the lower arm side switching element) of a predetermined phase is PW.
When shutting off for M control, the magnetic energy stored in the inductance of the three-phase brushless DC motor tries to flow continuously when it is turned off.

In order to deal with this, a flywheel diode is connected in antiparallel with each switching element, and the magnetic energy stored in the inductance is deenergized through the flywheel diode. In addition,
When a MOS transistor is used as the switching element, a parasitic diode of the MOS transistor is often used as the flywheel diode.

[0005]

However, since the flywheel diode has a forward voltage drop of about 0.7V as is well known, the flywheel diode is used when a three-phase brushless DC motor is operated at a large current. However, there was a problem that the power loss and the heat generation were large. In particular,
When the switching element of the three-phase inverter circuit is composed of MOS transistors and this flywheel diode is composed of parasitic diodes of MOS transistors,
Since the above-mentioned heat generation of the parasitic diode and the heat generation due to the channel current of the MOS transistor itself occur in the same chip, the temperature rise of the MOS transistor becomes more serious.

The present invention has been made in view of the above problems, and provides a three-phase brushless DC motor using a MOS transistor capable of realizing reduction of power loss, heat generation, simplification of cooling, and improvement of reliability. Its purpose is to provide a control method.

[0007]

A control method for a three-phase brushless DC motor according to a first aspect of the invention is a predetermined PWM control which is different for each upper arm side switching element of a three-phase inverter circuit for supplying power to the three-phase brushless DC motor. Phase periods are given in order, each upper arm side switching element is turned on during each pulse width period within each pulse period in the PWM control phase period of its own, and each pulse width period is modulated, thereby the three-phase brushless In a control method of a three-phase brushless DC motor for PWM controlling a DC motor, each lower arm side switching element of the three phase inverter circuit is composed of a MOS transistor, and the PWM control phase period of the upper arm side switching element of a predetermined phase Each pulse interval period that is a period excluding each of the pulse width periods in each of the pulse periods in To, it is characterized in that to conduct the lower arm switching element of the predetermined phase.

That is, according to the present invention, when the switching element on the upper arm side of a certain phase is PWM-controlled, the switching element on the lower arm side of the same phase is made to have a substantially complementary operation (substantially reverse operation).

With this configuration, since the switching element on the lower arm side of the same phase is turned on immediately after turning off a certain switching element on the upper arm side by PWM control, immediately after the switching element on the upper arm side of this phase is turned off. The current that flows into the coil and deactivates the inductance of the three-phase brushless DC motor can flow through the switching element on the lower arm side, and thus flows through the flywheel diode connected in anti-parallel with the switching element on the lower arm side. Since the current can be reduced to 0 or significantly, the power loss and heat generation of the MOS transistor that constitutes the switching element on the lower arm side are reduced, the cooling load of the three-phase inverter circuit is reduced, and the reliability is improved. be able to.

In a preferred mode, the switching elements on the upper arm side are sequentially connected to the P elements at an electrical angle of 2π / 3.
A WM control phase period is given, and during the PWM control phase period of the upper arm side switching element of a predetermined phase, at least one of the lower arm side switching elements of the remaining two phases other than the predetermined phase is always conductive. . That is,
In this mode, the PW
Since the MOS transistors forming the M-controlled upper-arm switching element and the lower-arm switching element in the same phase are operated in a complementary manner, the control can be simplified.

In a preferred mode, during the PWM control phase period, between a conduction period of the upper arm side switching element of a predetermined phase, that is, a pulse width period, and a conduction period of the lower arm side switching element of the predetermined phase. A predetermined dead time period. As a result, it is possible to prevent the problem that a large DC current flows due to overlapping of the conduction periods of the switching elements of the upper and lower arms of the same phase due to the influence of noise or the like. It is preferable that the dead time period ends at least before a large current of a predetermined value or more starts to flow in the flywheel diode connected in antiparallel with the switching element on the lower arm side.

According to a fourth aspect of the present invention, there is provided a method for controlling a three-phase brushless DC motor, wherein the lower arm side switching elements of a three-phase inverter circuit feeding the three-phase brushless DC motor are sequentially provided with different predetermined PWM control phase periods. , Each of the lower arm side switching elements is conducted in each pulse width period within each pulse period in the PWM control phase period of its own, and PWM control of the three-phase brushless DC motor is performed by modulating each pulse width period. In a method for controlling a three-phase brushless DC motor, each upper arm side switching element of the three phase inverter circuit is composed of a MOS transistor, and each pulse cycle during the PWM control phase period of the lower arm side switching element of a predetermined phase. Within each pulse interval period that is a period excluding each pulse width period in It is characterized in that to conduct the upper arm switching element.

That is, in the present invention, when the switching element on the lower arm side of a certain phase is PWM-controlled, the switching element on the upper arm side of the same phase is made to have a substantially complementary operation (generally reverse operation).

With this configuration, the switching element on the upper arm side of the same phase is turned on immediately after the switching element on the lower arm side is turned off by the PWM control. Therefore, immediately after the switching element on the lower arm side of this phase is turned off. The current that flows into the inductor to deactivate the inductance of the three-phase brushless DC motor can flow through the switching element on the upper arm side, and thus flows through the flywheel diode connected in anti-parallel with the switching element on the upper arm side. Since the current can be reduced to 0 or significantly, the power loss and heat generation of the MOS transistor that constitutes the switching element on the upper arm side are reduced, the cooling load of the three-phase inverter circuit is reduced, and the reliability is improved. be able to.

In a preferred mode, the switching elements on the lower arm side are sequentially provided with the P elements at an electrical angle of 2π / 3.
A WM control phase period is given, and during the PWM control phase period of the lower arm side switching element of a predetermined phase, at least one of the remaining two phases other than the predetermined phase is constantly brought into conduction on the upper arm side switching element. . That is,
In this mode, the PW
Since the MOS transistor forming the switching element on the lower arm side which is M-controlled and the switching element on the upper arm side in the same phase are operated complementarily, control can be simplified.

In a preferred mode, during the PWM control phase period, between a conduction period of the lower arm side switching element of a predetermined phase, that is, a pulse width period, and a conduction period of the upper arm side switching element of the predetermined phase. A predetermined dead time period. As a result, it is possible to prevent the problem that a large DC current flows due to overlapping of the conduction periods of the switching elements of the upper and lower arms of the same phase due to the influence of noise or the like. It is preferable that the dead time period ends at least before a large current of a predetermined value or more begins to flow in the flywheel diode connected in antiparallel with the switching element on the upper arm side.

In a preferred aspect of the method for controlling a three-phase brushless DC motor according to any one of claims 1 to 6, a flywheel diode connected in anti-parallel to each switching element of the three-phase inverter circuit is connected to the MOS transistor. It is composed of a parasitic diode. This allows
Since it is not necessary to provide an independent flywheel diode, it is possible to simplify the circuit configuration of the three-phase inverter circuit, reduce the loss and heat generation of each MOS transistor, and simplify the cooling.

The present invention takes advantage of the fact that a MOS transistor connected in parallel with a flywheel diode for deactivating the magnetic energy stored in an inductance of a three-phase brushless DC motor can conduct electricity in both directions. , The switching element on the reverse arm side, namely P
The WM-controlled switching element may be a one-way conduction type switching element other than a MOS transistor.

Further, the present invention can be carried out not only by the 120-degree energization method but also by the 180-degree energization method.

[0020]

Preferred embodiments of the present invention will be specifically described with reference to the following examples. In the following embodiments, the energization phase control side arm is also referred to, and the PWM control side arm is also referred to as the PWM control side arm.

[0021]

EXAMPLE An example will be described below with reference to FIG. FIG. 1 shows a three-phase brushless D for engine starting and power generation.
The circuit diagram of a C motor drive circuit is shown.

(Circuit configuration) 1 is a battery, 2 is a motor control circuit, and 3 is a three-phase brushless DC motor comprising a permanent magnet type synchronous machine.

The motor control circuit 2 comprises a smoothing capacitor 4, a three-phase inverter circuit 5 and a gate controller 6.

The battery 1 applies a voltage between the pair of DC power supply terminals of the three-phase inverter circuit 5 and the smoothing capacitor 4.

The three-phase brushless DC motor 3 has U-phase windings, V-phase windings, and W-phase windings star-connected (or delta-connected), and the rotor is equipped with a predetermined number of field magnets. There is.

The three-phase inverter circuit 5 converts the applied DC power supply voltage into a three-phase AC voltage to generate a three-phase brushless DC voltage.
This is an orthogonal transformation circuit that outputs to the motor 3, and has MOS transistors 5a to 5f that form a switching element. 5g to 5m are parasitic diodes of the MOS transistors 5a to 5f. 5a is a switching element on the upper arm side of the U phase, 5b is a switching element on the upper arm side of the V phase, and 5c is a switching element on the upper arm side of the W phase. Similarly, 5d is a switching element on the lower arm side of the U phase, 5e is a switching element on the lower arm side of the V phase, and 5f is a switching element on the lower arm side of the W phase. Since the circuit configuration itself of the three-phase inverter circuit 5 is well known, further description will be omitted.

The gate controller 6 is a control circuit for applying a control voltage to the gate electrodes of the MOS transistors 5a to 5f to control the three-phase brushless DC motor 3 by 120-degree conduction PWM. Since the gate controller 6 itself is already well known, its explanation is omitted.

The gate controller 6 preferably switches the energization of the MOS transistors 5a to 5f of each phase according to the rotation angle of the three-phase brushless DC motor 3. Therefore, the three-phase brushless DC motor 3 is based on the three-phase AC voltage or current output by the three-phase inverter circuit 5.
The rotation angle of the three-phase brushless D
The C motor 3 is provided with a rotation angle sensor such as a resolver and the energization phase switching control is performed based on the output signal thereof.

Further, the gate controller 6 is a three-phase brushless D based on a torque command input from the outside.
It is preferable to perform torque control that matches the torque generated by the C motor 3 with it. To this end, for example, the three-phase AC current output from the three-phase inverter circuit 5 is detected, and each MOS forming the switching element on the upper arm side is arranged so that the detected current matches the target current corresponding to the torque command.
PWM the transistors 5a-5c at every electrical angle of 2π / 3
Control.

(Explanation of Operation) In this embodiment, the 120-degree conduction PWM control operation executed by the gate controller 6 will be described below with reference to the timing chart shown in FIG.

Each of the MOS transistors 5a to 5c has a PWM control period of electrical angle 2π / 3 in order.

The PWM control period is divided into pulse periods which are the reciprocal of a predetermined carrier frequency, and the MOS transistors 5a to 5c forming the switching elements on the upper arm side are divided by a predetermined pulse width period set in each pulse period. The MOS transistors 5a to 5c forming the switching element on the upper arm side are turned off for the pulse interval period which is the remaining period set in each pulse period, and the PWM control is performed by adjusting the pulse width period. .

To further explain, the MOS transistor 5a on the upper arm side is PWM-controlled at the time points t0 to t2 (PWM
It has a control period) and at the next time point t2 to t4
The OS transistor 5b is PWM-controlled (has a PWM control period), and the MOS transistor 5c on the upper arm side is PWM-controlled (has a PWM control period) at the next time points t4 to t6. Further, from time t6 to t1, the MOS transistor 5e on the lower arm side is constantly energized (has a constant energization period),
At the next time point t1 to t3, the MOS transistor 5 on the lower arm side
f is constantly energized (has a constant energization period), and next time t3
The MOS transistor 5d on the lower arm side is always energized at ~ t5 (always energized).

A particularly important point in the PWM control of this embodiment is that during the PWM control period, the MOS transistors 5b to 5f forming the switching elements on the lower arm side.
Is turned on during the off period of the MOS transistors 5a to 5c forming the switching element on the upper arm side in the same phase as those, that is, during the pulse interval period, and turned off during the pulse width period. That is, in this embodiment, the upper-arm side MOS transistor and the lower-arm side MOS transistor of the same phase perform complementary operations during the PWM control period.

The current flow will be described below with reference to FIGS. 3 and 4.

FIG. 3 shows the MOS during the time t0 to t1.
This is the case when the transistor 5a is on. The current flowing from the MOS transistor 5a to the three-phase brushless DC motor 3 returns to the battery 1 through the MOS transistor 5e, and at this time, magnetic energy is stored in the stator winding of the three-phase brushless DC motor 3.

FIG. 4 shows the MOS during the time t0 to t1.
This is the case when the transistor 5a is off. Due to the magnetic energy accumulated in the stator windings of the three-phase brushless DC motor 3, the flywheel current circulates from the MOS transistor 5a through the three-phase brushless DC motor 3 and the MOS transistor 5e.

As a result, the conventional MOS transistor 5
Since the flywheel current flowing through the parasitic diode 5k of d flows through the channel region of the MOS transistor 5d, power loss due to the forward voltage drop of the parasitic diode 5k and heat generation due to it can be eliminated or significantly reduced. Therefore, the efficiency of the three-phase inverter circuit 5 can be improved and the cooling can be simplified. Of course, at this time, the channel resistance of the MOS transistor 5d is set so that the channel voltage drop of the MOS transistor 5d becomes equal to or lower than the forward voltage drop of the parasitic diode 5k.

Also, in the above description, only the PWM control period of the U phase has been described, but it is natural that the remaining two phases are the same, and the description thereof will be omitted.

Further, in FIG. 2, the MOS transistors 5a and 5d of the same phase may be turned on after their counterparts are completely or almost turned off during their own PWM control period. By doing so, even if the on-timing of the MOS transistor is accelerated or the off-timing is delayed due to some factor such as electromagnetic noise, the direct current flowing through the pair of MOS transistors of the upper and lower arms of the same phase can be suppressed. You can Note that, in FIG. 2, TPWM-U, TPWM-V, and TPWM-W indicate the PWM control period of each phase.

(Modification) FIG. 5 is a circuit diagram of FIG. 1 in which the lower arm side MOS transistors 5d to 5f are PWM-controlled in order for every 120 electrical degrees, and the upper arm side M transistor is controlled.
The case where the OS transistors 5a to 5c are constantly energized at every 120 electrical degrees is shown.

(Modification) FIG. 6 shows that the PWM control is performed in the first half of the PWM control period and the constant energization period which are sequentially set by the electrical angle of 2π / 3 in FIG. 2, and the constant energization is performed in the latter half. , Each MOS transistor 5
The switching losses of a to 5f are evenly distributed. Also in this case, naturally, in the substantial PWM control period, the switching element of the opposite arm having the same phase as that of the PWM controlled switching element is complementarily operated, and as a result, the same effect as in the case of FIGS. Can be played.

FIG. 7 is a circuit diagram of FIG.
The WM control period is opposite, and even in this case, the same effect as in the case of FIG. 6 can be obtained.

In each of the embodiments described above, 120
Although the one-time energization type PWM control system has been described, the same effect can be obtained also in the 180-degree energization system by performing the same complementary operation.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a three-phase brushless DC motor drive circuit.

FIG. 2 is a timing chart showing the operation of the circuit of FIG.

FIG. 3 is a circuit diagram for explaining a current flow in the operation of FIG.

FIG. 4 is a circuit diagram for explaining a current flow in the operation of FIG.

FIG. 5 is a timing chart showing a modified mode.

FIG. 6 is a timing chart showing a modified mode.

FIG. 7 is a timing chart showing a modified mode.

[Explanation of symbols]

1 battery 2 Motor control circuit 3 three-phase brushless DC motor 4 Smoothing capacitor 5 three-phase inverter circuit 6 Gate controller 5a-5f MOS transistor (switching element)

Claims (7)

[Claims] 1. A PWM control phase period different from each other is sequentially given to each upper arm side switching element of a three phase inverter circuit for supplying power to a three phase brushless DC motor, and each upper arm side switching element is provided with its own PWM.
A control method for a three-phase brushless DC motor, wherein the three-phase brushless DC motor is PWM-controlled by conducting each pulse width period in each pulse period in a control phase period and modulating each pulse width period. Each lower arm side switching element of the inverter circuit is configured by a MOS transistor, and the PWM of the upper arm side switching element of a predetermined phase is provided.
In a three-phase brushless DC motor, the lower arm side switching element of the predetermined phase is made conductive during each pulse interval period which is a period excluding the pulse width period in each pulse period in the control phase period. Control method. 2. The control method for a three-phase brushless DC motor according to claim 1, wherein the switching element on each of the upper arms has an electrical angle of 2π / 3.
The PWM control phase period is given in sequence for each of the above, and the PWM of the upper arm side switching element of a predetermined phase is provided.
A control method for a three-phase brushless DC motor, characterized in that during a control phase period, at least one of the remaining two phases other than the predetermined phase is constantly brought into conduction with the switching element on the lower arm side. 3. The three-phase brushless DC according to claim 1 or 2.
In the motor control method, during the PWM control phase period, a conduction period, that is, a pulse width period of the upper arm side switching element of a predetermined phase,
A method for controlling a three-phase brushless DC motor, wherein a predetermined dead time period is provided between the predetermined phase and a conduction period of the lower arm side switching element. 4. A predetermined PWM control phase period different from each other is sequentially given to each lower arm side switching element of a three phase inverter circuit for supplying power to a three phase brushless DC motor, and each lower arm side switching element is provided with its own PWM.
A control method for a three-phase brushless DC motor, wherein the three-phase brushless DC motor is PWM-controlled by conducting each pulse width period in each pulse period in a control phase period and modulating each pulse width period. Each upper arm side switching element of the inverter circuit is composed of a MOS transistor, and the PWM of the lower arm side switching element of a predetermined phase is provided.
In the three-phase brushless DC motor, the upper arm side switching element of the predetermined phase is made conductive during each pulse interval period which is a period excluding the pulse width period in each pulse period in the control phase period. Control method. 5. The method for controlling a three-phase brushless DC motor according to claim 4, wherein the switching element on each of the lower arms has an electrical angle of 2π / 3.
The PWM control phase period is given in sequence for each of the above, and the PWM of the lower arm side switching element of a predetermined phase is provided.
A control method for a three-phase brushless DC motor, characterized in that during the control phase period, at least one of the remaining two phases other than the predetermined phase is constantly turned on on the upper arm side. 6. The three-phase brushless DC according to claim 4 or 5.
In the motor control method, during the PWM control phase period, a conduction period, that is, a pulse width period of the lower arm side switching element of a predetermined phase,
A method of controlling a three-phase brushless DC motor, wherein a predetermined dead time period is provided between the predetermined phase and a conduction period of the upper arm side switching element. 7. The method for controlling a three-phase brushless DC motor according to claim 1, wherein a flywheel diode connected in antiparallel to each switching element of the three-phase inverter circuit is a parasitic of the MOS transistor. The MOS transistor is formed of a diode, and in the stable conduction state, the MOS transistor has a source voltage smaller than a forward voltage drop of its own parasitic diode.
A method for controlling a three-phase brushless DC motor, which has a drain-to-drain voltage drop.