JPH07108111B2 - Brushless motor drive circuit - Google Patents

Description

The present invention relates to a drive circuit for a three-phase brushless motor.

(B) Conventional technology In a brushless motor drive circuit that regulates the DC voltage supplied to a three-phase brushless motor to control the rotation speed of the motor, an overcurrent flows when the motor is locked or overloaded, and the power supply A current control circuit is provided to prevent damage to the circuits and switching elements.

FIG. 5 shows a conventional example of such a brushless motor drive circuit. In the figure, the three-phase matrix control circuit 1 is
The magnetic pole position of the rotor of the three-phase brushless motor (hereinafter, simply abbreviated as motor) 2 is detected by the Hall elements 2a, 2b, 2c,
It outputs three drive signals with different phases by 120 °. The switching circuits 3 to 5 energize the windings 2u, 2v, 2w according to their respective drive signals. The supply voltage V _M supplied to the switching circuits 3 to 5 for this energization is the power supply voltage.
Vcc is PWM-modulated by the PWM control circuit 6 and obtained through the smoothing circuit 7. The modulation factor in the PWM control circuit 6 is set by the speed setting signal vb, and the supply voltage
The value of V _M is adjusted.

For the resistor Rx, switching circuits 3 to 5 and windings 2u, 2v, 2w
The electric current I flowing through is applied. The comparator 8 compares the voltage generated in the resistor Rx with the reference voltage e ₁ .

When the motor 2 is operated in this circuit and the load, which is the drive torque, gradually increases, the current I increases as shown in FIG. 6 (a). However, the load To
If the voltage generated in the resistor Rx becomes equal to or higher than the reference voltage e ₁ at, the comparator 8 outputs the current limiting signal S _L.

When the current limiting signal S _L is input, the three-phase matrix control circuit 1 lowers the signal level of the drive signal to the switching circuits 3 to 5 and outputs it. As a result, the switching circuits 3 to 5 operate to keep the current I at a constant value even when the load increases to To or higher.

For this reason, the rotation speed N of the motor 2 decreases as the load increases when it exceeds the load To, as shown in FIG.
The counter electromotive voltage E generated in the windings 2u, 2v, 2w also decreases in proportion to the rotation speed N as shown in FIG.

Here, the value obtained by multiplying the difference voltage between the supply voltage V _M and the voltage applied to the windings 2u, 2v, 2w by the current I is the power loss P, but the power loss P is P = {V _M It can be expressed as − (E + I−rm)} × I (where E is a counter electromotive voltage and rm is a winding resistance). Then, when the load increases, the rotation speed decreases, and the counter electromotive voltage E decreases, the power loss P increases, so that the power loss P becomes as shown in FIG. Will be dissipated.

(C) Problems to be Solved by the Invention Therefore, in such a conventional brushless motor drive circuit, a current loss occurs when the current is limited by the switching circuit, and the switching circuit 3 including a transistor or the like is also generated. There is a problem that a large heat dissipation plate must be attached in order to protect Nos. 5 to 5 from heat generation due to the power loss.

It is therefore an object of the present invention to solve the above problems and provide a brushless motor drive circuit that can reduce the power loss and downsize the heat sink.

(D) Means for Solving the Problems For this reason, the present invention generates a drive signal having a voltage value corresponding to the target speed based on the detection signal from the rotor position detection element arranged in the three-phase brushless motor. In the brushless motor drive circuit including a voltage adjusting circuit and a switching circuit that applies the drive signal to the windings of each phase of the three-phase brushless motor at a predetermined timing, windings of each phase of the three-phase brushless motor are provided. Current detection means for detecting the current flowing in the, and the detection value of the current detection means is compared with a predetermined value corresponding to the overload state, and when the detection value is larger than the predetermined value, a predetermined voltage value On the other hand, while outputting the voltage signal, a comparison circuit that outputs a zero level voltage signal when the detected value is less than or equal to the predetermined value, and a voltage output from the comparison circuit. A bias circuit for adding a filter circuit for extracting a DC component of the signal smoothing to, the speed setting signal corresponding to the output signal and the target speed of the three-phase brushless motor of the filter circuit,
A pulse signal generator that compares the output signal of the bias circuit with a predetermined triangular wave signal to generate a pulse signal, a transistor circuit that performs pulse width modulation of a reference power supply voltage based on the pulse signal, and an output of the transistor circuit A smoothing circuit for smoothing a signal and supplying it as a driving power source for the switching circuit is provided.

(E) Action When the overload condition occurs, a voltage signal of a predetermined level is output from the comparison circuit, the DC component of this voltage signal is added to the speed setting signal, and the state of pulse width modulation of the transistor circuit changes. Since the voltage of the smoothed driving power supply output from the smoothing circuit decreases, it is possible to suppress an increase in power loss in the switching circuit.

(F) Example Hereinafter, an example of the present invention will be described in detail.

FIG. 1 is a circuit configuration diagram showing a brushless motor drive circuit according to an embodiment of the present invention. In the figure, the three-phase matrix control circuit 1 inputs the detection signals of the Hall elements 2a, 2b, 2c attached to the three-phase brushless motor (hereinafter, simply referred to as a motor) 2, detects the magnetic pole position of the rotor 2r, and detects them respectively. It outputs three drive signals Su, Sv, Sw with different phases by 120 °.

On the other hand, the PWM control circuit 6 PWM-modulates the power supply voltage Vcc, and the smoothing circuit 7 including the choke coil L and the capacitor Cm smooths the modulated voltage to stable DC. The smoothed DC voltage is a supply voltage V _M to be supplied to the switching circuit 3-5.

The switching circuits 3 to 5 energize the windings 2u, 2v, 2w of the motor 2 according to the drive signals Su, Sv, Sw. The ground side terminals of the switching circuits 3 to 5 are grounded via the resistor Rx, and the current I due to the energization flows through the resistor Rx.

The comparator 8 inputs the voltage V ₁ generated at one end of the resistor Rx and the reference voltage e ₂ , and when the voltage V ₁ > e ₂ , the current limiting signal.
Output S _L. Further, the comparator 9 inputs the voltage V ₁ and the reference voltage e ₃ and outputs a signal V ₂ which becomes a constant voltage when the voltage V ₁ > e ₃ . Here, reference voltage e ₂ > reference voltage e ₃ is set.

The filter circuit 10 is composed of a resistor Rf and a capacitor Cf, takes out a DC component voltage from the signal V ₂ output as an on / off signal, and outputs a signal V ₃ indicating the voltage. The PWM control circuit 6 operates to change the modulation factor in the PWM modulation according to this signal V ₃ .

FIG. 2 (a) shows each voltage waveform when the load of the motor 2 is in a steady operation at a certain value or less. The voltage V ₁ generated at one end of the resistor Rx by the current I is output as shown in (a) of the figure, and the reference voltages e ₂ and e ₃ are set higher than the voltage V ₁ in the steady operation. Therefore, the current limiting signal S _L which is the output of the comparator 8 is off, and the output signal V ₂ of the comparator 9 is also at the zero level. Therefore, the output signal V ₃ of the filter circuit 10 becomes 0V as shown in FIG.

The speed setting signal vb input to the bias circuit 6a of the PWM control circuit 6 is a voltage for setting the rotation speed of the motor 2. Bias circuit 6a intended for adding the voltage level of the signal V ₃ and the signal vb inputted, now signal V ₃ is so 0V, the output signal V ₄ at this time is V ₄ = vb.

The triangular wave generation circuit 6b outputs a triangular wave signal Vs as shown in FIG. The comparator 6c compares the voltage level of this signal Vs with the voltage level of the above signal V _4, and as shown in FIG.
Outputs signal V ₅ when Vs> V ₄ . Transistor 6d is turning on and off the power supply voltage Vcc in accordance with the signal V _5. The turned-on voltage is input to the smoothing circuit 7 and smoothed as shown in FIG.
It becomes V _M.

Therefore, by changing the voltage level of the speed setting signal vb, can be arbitrarily varied modulation in the PWM modulation of the power supply voltage Vcc, by which the rotational speed of the motor 2 by adjusting the value of the supply voltage V _M Be in control.

On the other hand, when the load on the motor 2 gradually increases during operation at a constant speed, the current I increases according to the load as shown in FIG. 3 (a). As a result, the voltage V ₁ of the resistor Rx is
Rises. Now, as shown in (a) of FIG. 2 (b), if this voltage V ₁ rises, the comparator 9 outputs a signal V ₂ that is a constant voltage during the period of voltage V ₁ > reference voltage e _3. To do. The filter circuit 10 is, as shown in FIG.
The DC component of the signal V ₂ is extracted and the signal V ₃ is output.

The bias circuit 6a adds the voltage levels of the signal V ₃ and the speed setting signal vb to obtain a signal of a level as shown in FIG.
Output V ₄ . Comparator 6c compares the said as well as the triangular wave signal Vs and the signal V _4, and outputs a signal V ₅ as shown in FIG. (D). Since the transistor 6d is turned on / off by the signal V ₅ , the supply voltage V _M becomes lower as compared with the case shown in FIG. 2A as shown in FIG. This decrease in voltage is proportional to the period in which the voltage V ₁ > the reference voltage e ₃ .

That is, when the load of the motor 2 exceeds the constant load T ₁ in FIG. 3, assuming that the voltage V ₁ > the reference voltage e ₃ as described above, then the supply voltage V _M becomes the same as the load increases. As shown in FIG. 6 (c), it becomes lower. This allows
The current I, which is the amount of electricity supplied to the windings 2u, 2v, 2w of the motor 2, is the third
As shown in FIG. 7A, it does not increase when the load T ₁ is exceeded. When the energization amount is limited in this way, FIG.
As shown in (c), the rotation speed of the motor 2 decreases as the load increases, and the counter electromotive voltage E also decreases accordingly.

Power loss P generated inside the switching circuit 3-5, the winding 2u, 2v, neglecting losses caused by resistance components and the resistance Rx of 2w, the supply voltage V _M, the following equation from the back electromotive voltage E and current I Shown.

P = (V _M −E) × I However, in this case, as shown in FIG.
When the T ₁ obtaining electromotive, the difference (V _M -E) and the current I of the voltage is almost constant, the power loss P is not increased nearly as shown in FIG. (D).

Therefore, heat generation corresponding to the power loss is also reduced, so that the heat radiation plate attached to the switching elements such as the transistors forming the switching circuits 3 to 5 can be made small. At the time of lock, such as failure of startup or load of the motor 2, the current I is therefore maximized, operates to reduce the power supply V _M as described above. However,
There is a delay time from the flow of the current I to the decrease of the processing power supply V _M. Therefore, in order to prevent an excessive current I from flowing within this time, the comparator 8 compares the voltage V ₁ of the resistor Rx with the reference voltage e _2, and when V ₁ > e ₂ , the current limiting signal S _L Is output. At this time, the three-phase matrix circuit 1 and the switching circuits 3 to 5 operate in the same manner as described with reference to FIG.

In the present embodiment, the current limitation may be performed as described above only in a special case such as a locked state, so that the reference voltage e ₂ is set to the fifth value.
It is possible to set e ₂ > e ₁ with respect to the reference voltage e _{1 in the} figure.

Further, in the above operation, the signal V ₂ extracted by the comparator 9 is input to the PWM control circuit 6 through the filter circuit 10, so that stable operation can be performed. That is, FIG. 4 shows the operation when the signal V ₂ is directly input to the bias circuit 6a without providing the filter circuit 10.

When the load of the motor 2 exceeds a certain value, the comparator 9 outputs a signal as shown in FIG. 4 (b) as in FIG. 2 (b).
V ₂ is output. When this signal V ₂ is input to the bias circuit, the bias circuit 6a adds the voltage levels of the signal V ₂ and the speed setting signal vb and outputs the signal V ₄ .

Comparator 6c the figure (c), as shown in (d), and comparing the signal V ₄ and the triangular wave signal Vs, the voltage is Vs> V ₄
A signal V ₅ that becomes a constant voltage at the time of is output. Then, this signal V ₅ becomes an unstable burst signal as shown in the figure. Then, when the transistor 6d is turned on / off by this signal V ₅ , the smoothing circuit 7 cannot stabilize the voltage,
Supply voltage with large ripple component as shown in (e)
It will output V _M. Such a phenomenon occurs not only when the load is excessive as described above, but also when the load is started or when the load is locked.

With the supply voltage V _M having such a large ripple component, the motor 2
When driving, the casing of the motor 2 vibrates or generates abnormal noise, and stable operation cannot be performed. In order to solve this problem, the filter circuit 10 is provided so that the DC component signal V ₃ is extracted from the signal V ₂ .

As described above, in this embodiment, the load on the motor 2 increases,
When the energizing current I exceeds a certain value, the switching circuit 3 to
Since the supply voltage V _M to the switch 5 is lowered in accordance with the increase of the current I, the power loss generated inside the switching circuits 3 to 5 is reduced. As a result, the switching circuits 3 to
Since the amount of heat generated in the semiconductor element such as the transistor constituting the element 5 is reduced, the heat sink attached to the element can be downsized.

Further, when such a brushless motor drive circuit is packaged by an IC circuit, the treatment for heat dissipation can be simplified and the manufacturing cost is reduced.

(G) Effect of the Invention As described above, according to the present invention, when the three-phase brushless motor is overloaded, a voltage signal of a predetermined level is output from the comparison circuit, and the DC component of this voltage signal becomes the speed setting signal. As a result, the pulse width modulation state of the transistor circuit is changed, and as a result, the voltage of the smoothed driving power supply output from the smoothing circuit is reduced, so that an increase in power loss in the switching circuit can be suppressed. .

Further, since the output of the filter circuit becomes a signal of the same level, it is possible to obtain a pulse width modulation signal of the same period and the same width by turning on / off the transistor circuit at the same period. The output drive power source has a stable DC level, and thus, the switching circuit can be stably driven, and the vibration and noise of the three-phase brushless motor can be suppressed.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a brushless motor drive circuit according to an embodiment of the present invention, FIGS. 2 (a) and 2 (b) are waveform diagrams showing voltages and waveforms of respective portions of the circuit, and FIG. FIG. 4 is an explanatory diagram showing operating characteristics of a three-phase brushless motor in an example, FIG. 4 is a waveform diagram showing voltages and signals of respective parts of the above circuit when a filter circuit is not provided, and FIG. 5 is a circuit of a conventional brushless motor drive circuit. FIG. 6 is an explanatory diagram showing the operating characteristics of a conventional three-phase brushless motor. 1 ... 3-phase matrix control circuit, 2 ... 3-phase brushless motor, 3-5 ... switching circuit, 6 ... PWM control circuit, 6a ... Bias circuit, 6b ... Triangular wave generation circuit, 6
c, 8,9 …… Comparator, 6d …… Transistor, 7 ……
Smoothing circuit, 10 ... Filter circuit, Rx, Rf ... Resistance, e ₁ , e
₂ , e ₃ …… Reference voltage.

Front page continuation (72) Inventor Hiromitsu Nakano 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-60-51490 (JP, A)

Claims (1)

[Claims] 1. A voltage adjusting circuit for generating a drive signal having a voltage value corresponding to a target speed based on a detection signal from a rotor position detecting element arranged in a three-phase brushless motor, and the three-phase brushless motor. In a brushless motor drive circuit provided with a switching circuit for applying the drive signal to each phase winding at a predetermined timing, current detection means for detecting a current flowing in each phase winding of the three-phase brushless motor; The detected value of the current detection means is compared with a predetermined value corresponding to the overload state, and when the detected value is larger than the predetermined value, a voltage signal of a predetermined voltage value is output, while the detected value is A comparator circuit that outputs a zero-level voltage signal when it is below a predetermined value, and a DC component that is obtained by smoothing the voltage signal output from the comparator circuit. A filter circuit, a bias circuit for adding the output signal of the filter circuit and a speed setting signal corresponding to the target speed of the three-phase brushless motor, and a pulse comparing the output signal of the bias circuit with a predetermined triangular wave signal. A pulse signal generator that generates a signal, a transistor circuit that pulse-width modulates a reference power supply voltage based on the pulse signal, and a smoothing circuit that smoothes an output signal of the transistor circuit and supplies it as a driving power supply of the switching circuit A brushless motor drive circuit characterized by the above.