JPH089681A - Pwm motor drive apparatus - Google Patents

Abstract

PURPOSE:To obtain a PWM motor drive apparatus whose control accuracy is increased by a method wherein a mean current in a DC motor driven according to a PWM system is detected with high accuracy. CONSTITUTION:When a CPU 3 closes and drives a transistor Q3 or Q4 by PWM pulses, a sample-and-hold circuit 13 detects the voltage-converted value of an means current in a DC motor 2 to feed back to the CPU 3. The rotation of the DC motor 2 by a triangular wave shaped current can be PWM controlled on the basis of a means current Im which is equal to the arithmetic means value of the highest value and the lowest value of the triangular wave shaped current. Thereby, a high accuracy motor drive operation can be performed irrespective of the pulse width of the PWM pulses which changes dynamically according to a control deviation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PWM type motor driving device for detecting the average current flowing through a DC motor driven by the PWM type with high accuracy and enhancing the control accuracy.

[0002]

2. Description of the Related Art Four-wheel steering (4W) for steering front and rear wheels of a vehicle
The S) mechanism generally changes the steering angle of the rear wheels directly or indirectly by using a DC motor as a power source. In order to suppress consumption of battery power, the DC motor is subjected to pulse width modulation control (PW).
Many of the structures are driven by the M) method. A conventional PWM type motor drive device 1 shown in FIG. 5 drives a DC motor 2 for varying the rear wheel steering angle according to the PWM system so that a target steering angle can be obtained, and is arranged in a power supply path of the DC motor 2. The CPU 3 performs on / off control of the switching element by a PWM pulse, and supplies a motor drive current according to the deviation from the target steering angle to the DC motor 2.

Since the DC motor 2 steers the rear wheels to the left and right, it is premised that the DC motor 2 can be rotated forward and backward, and is driven by being supplied with a triangular wave current of a required polarity by a bridge circuit 4 connected in an H shape. The DC motor 2 has an equivalent resistance Rm.
And an inductance Lm can be regarded as a series circuit,
The electrical rising time constant when a pulse current is applied is Lm / Rm. Further, it is known that a considerable amount of electromagnetic energy is stored in the inductance Lm, so that a current called a flywheel current continues to flow to the DC motor 2 even after the energization of the pulse current is cut off. The bridge circuit 4 is connected to the battery power source 5 via the current detection resistor Rd.
Two transistors Q1, Q3 and Q2, Q4 are connected as a switching element for controlling energization of a motor drive current to a pair of lines connected in parallel with each other, and a connection point of the transistors Q1, Q3 and a transistor Q2 are connected. , Q4
The DC motor 2 bridges the connection points of. In addition, in the bridge circuit 4, in consideration of the energization path of the flywheel current, any of the transistors Q1 to Q4 has a diode D1 in the direction opposite to the energization direction of the motor drive current.
~ D4 are connected in parallel. In the case of the present example, the four transistors Q1 to Q4 employ a control method in which the transistors located in diagonal positions corresponding to the rotation direction of the DC motor 2, that is, the polarity of voltage application to the DC motor 2 are electrically connected in pairs. Therefore, here, the transistors Q1 and Q4 form a conducting pair for leftward steering, and the transistors Q2 and Q3 form a conducting pair for rightward steering.

The CPU 3, which is the main body of PWM control, must monitor the current flowing through the DC motor 2, and here, the current detection resistor Rd interposed in the line connecting the battery power source 5 and the power feeding end of the bridge circuit 4 is used. The terminal voltage generated at both ends is amplified by the amplifier 6a forming the current-voltage converter 6 together with the current detection resistor Rd, and the voltage-converted current is taken into the AD conversion input port of the CPU 3 via the peak hold circuit 7. I am doing it. The CPU 3 changes the duty ratio of the PWM pulse so that the motor drive current converted into digital data by AD conversion matches a predetermined current corresponding to the deviation between the target steering angle and the current steering angle, and the transistor Q3 or Q4. Control on and off.

For example, when the rear wheels are steered to the left, the transistor Q1 of the transistors Q1 and Q4 forming a current-carrying pair is kept conductive during the left-hand steering period, whereas the transistor Q4 is turned on. On / off control is performed by the PWM pulse output from the CPU 3. Figure 6
As shown in (A) to (D), when the transistor Q4 conducts during the ON period of the PWM pulse, the motor drive current is supplied from the battery power source 5 to the DC motor 2 through the current detection resistor Rd and the transistor Q1. This motor drive current flows through the transistor Q4. On the other hand, PW
When the transistor Q4 becomes non-conductive during the off period of the M pulse, the flywheel current flows through the closed loop connecting the diode D2, the transistor Q1 and the DC motor 2 due to the electromagnetic energy stored in the inductance Lm of the DC motor 2. For this reason, the DC motor 2
Is a triangular wave current in which a motor drive current that linearly increases during the ON period of the PWM pulse and a flywheel current that linearly decreases during the OFF period of the PWM pulse are connected, and the peak value of this triangular wave current is the PWM pulse It changes according to the duty ratio of. It should be noted that here, a PWM pulse for turning on / off the transistor Q4 and a high-level pulse for keeping the transistor Q1 conductive or a transistor Q2 which is a non-conductive pair.
It is called a control pulse including a low level pulse for keeping Q4 non-conductive.

[0006]

The conventional PWM type motor drive device 1 detects the maximum value (peak current Ip) of the motor drive current flowing through the DC motor 2 as a voltage conversion value by the peak hold circuit 7 and causes the CPU 3 to do so. Although being fed back, the peak current Ip held by the peak hold circuit 7 is different from the average current Im which is the average value of the motor drive current. That is, as apparent from FIG. 6B, the peak current Ip and the average current I flowing through the DC motor 2
There is always an error of 1/2 the crest value of the triangular wave current between m and m, and the duty ratio of the PWM pulse is 50.
This error, which takes the maximum value near%, varies depending on the duty ratio. Therefore, the conventional PWM type motor drive device 1 has the peak current I from the average current Im.
There is a problem that the error is superimposed on the feedback information to the CPU 3, which is the PWM control circuit, by the deviation of p, and the accuracy of the PWM control is likely to decrease accordingly.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems and provides a direct current motor driven in forward and reverse directions according to the polarity of an applied voltage and a pair of parallel lines connected to a direct current power source. A bridge circuit in which two switching elements are connected in series and each connection point of the two switching elements is bridged by the DC motor, and at least two of the four switching elements forming the bridge circuit Flywheel diodes respectively connected in parallel to the four switching elements, and the four switching elements are opened / closed by a control pulse including a PWM pulse so that a voltage having a polarity corresponding to a rotation direction is applied to the DC motor, During the ON period of the PWM pulse, the DC motor is rotationally driven by the motor drive current from the DC power source, During the off period, a pulse width modulation control circuit for rotationally driving the DC motor with a flywheel current flowing through the flywheel diode, and detecting an average current of the motor driving current flowing through the DC motor and the flywheel current, An average current detecting means for feeding back to the pulse width modulation control circuit is provided.

Further, according to the present invention, the average current detecting means generates a sampling pulse which lasts for approximately ½ of the ON period of the PWM pulse from the beginning of the ON period of the PWM pulse, A current-voltage converter that converts the motor drive current into a voltage; and a sample-hold circuit that holds the output of the current-voltage converter by the sampling pulse and obtains the voltage-converted average current, or A current-voltage converter that converts the motor drive current into a voltage, a peak hold circuit that holds the output of the current-voltage converter at the highest value, and a bottom hold that holds the output of the current-voltage converter at the lowest value. Circuit, and the outputs of the bottom hold circuit and the peak hold circuit are arithmetically averaged to obtain the voltage-converted average current. Is characterized in that the and a pressure averaging circuit or the like.

[0009]

Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is a circuit configuration diagram showing an embodiment of a PWM type motor drive device of the present invention, and FIG.
FIG. 2 is a signal waveform diagram of each part of the circuit shown in FIG. 1.

A PWM type motor drive device 11 shown in FIG.
Is an average current flowing through the DC motor 2,
A sampling pulse generation circuit 12 that generates a sampling pulse that continues from the rising edge of the WM pulse to the midpoint is externally connected to the CPU 3, and a sample hold circuit 13 that holds the motor drive current by the sampling pulse that the sampling pulse generation circuit 12 generates. It is configured by being connected to the amplifier 6a in the current-voltage converter 6. The sampling pulse generation circuit 12 is triggered by the rising edge of the PWM pulse and outputs a pulse having a pulse width ½ of the PWM pulse as a sampling pulse.
The sample hold circuit 13 replaces the conventional peak hold circuit 7, and includes a sampling switch 13 a that is closed by a sampling pulse supplied from the sampling pulse generation circuit 12 and the sampling switch 1.
It comprises a hold capacitor 13b which holds the output voltage of the amplifier 6a when 3a is closed. Since the motor drive current increases during the sampling pulse period, the voltage held by the hold capacitor 13b corresponds to the motor drive current Im at the falling point of the sampling pulse, that is, the midpoint of the PWM pulse.

That is, as shown in FIGS. 2A to 2E, the motor drive current, which is conventionally detected as the peak current Ip which is the maximum value of the triangular wave current by the peak hold, is set to the midpoint of the PWM pulse. Therefore, the detected motor drive current becomes the average current Im itself flowing through the DC motor 2 every control cycle. The average current Im is equal to (Ip + Ib) / 2 obtained by arithmetically averaging the highest value Ip and the lowest value Ib of the motor drive current, which is (Ip-
Ib) / 2 is different. Therefore, it can be said that the detection accuracy of the average current Im is increased by this difference.

As described above, in the PWM type motor drive device 11, the CPU 3 drives the DC motor 2 energized by the four transistors Q1 to Q4 and the flywheel diodes D1 and D2 which form the bridge circuit 4, and the CPU 3 drives the transistor Q3. , Q4 is closed and driven by the PWM pulse, the average current flowing through the DC motor 2 is detected and CP is detected.
Since it is configured to feed back to U3, the motor drive current flowing through the transistors Q1, Q4 or Q2, Q3 during the ON period of the PWM pulse and the flywheel current flowing through the diode D2 or D1 during the OFF period of the PWM pulse form a triangular wave. The rotation of the DC motor 2 that is flowing can be PWM-controlled based on the average current Im that is equal to the arithmetic average of the maximum value Ip and the minimum value Ib of the triangular wave, whereby the maximum value Ip of the triangular wave is fed back to the PWM control. PWM that dynamically changes according to the control deviation compared to the conventional method
It is possible to drive the motor with high accuracy regardless of the pulse width of the pulse.

Further, since the sample hold circuit 13 is configured to hold the motor drive current to the average current Im by the sampling pulse which continues from the rise of the PWM pulse to the middle point, the current supplied to the DC motor 2 as a triangular wave. The midpoint of the motor drive current forming the rising hypotenuse can be sampled and held in synchronization with the midpoint of the PWM pulse, and the minimum value Ib of the motor drive current can be obtained.
Since it is possible to detect the current value just in the middle of the maximum value Ip as the average current Im, it is possible to improve the detection accuracy of the average current Im and at the same time improve the accuracy of the PWM control.

In the above embodiment, the sampling pulse generating circuit 12 is incorporated in the CPU 3,
The arithmetic processing function of the CPU 3 itself may generate the sampling pulse based on the PWM pulse,
In that case, the CPU 3 serves as both the pulse width modulation control circuit and the sampling pulse generation circuit.

Further, in the above embodiment, the average current detecting means is constituted by the sampling pulse generating circuit 12 and the sample hold circuit 13, but the average current detecting means is peak-held as in the PWM type motor drive device 21 shown in FIG. The circuit 22, the bottom hold circuit 23, and the arithmetic mean circuit 24 can also be used.

The peak hold circuit 22 holds the output of the amplifier 6a at a voltage conversion value corresponding to the maximum value Ip, and the bottom hold circuit 22 converts the output of the amplifier 6a into a voltage conversion value corresponding to the minimum value Ib. It is held as a value. Therefore, by adding the output of the peak hold circuit 22 and the output of the bottom hold circuit 23 and dividing by 2, the average current shown in FIG. 4D can be obtained. In the case of this embodiment, the bottom hold circuit 23 and the arithmetic mean circuit 24 are required in addition to the peak hold circuit 22, but it is easy to entrust the CPU 3 with the arithmetic mean function of the arithmetic mean circuit 24, for example. Further, by doing so, the entire circuit can be simplified.

In both of the above-mentioned embodiments, among the four transistors Q1 to Q4, for the transistors Q3 and Q4 which are on / off controlled by the PWM pulse, the flywheel diodes D3 and D4 in parallel with the transistors Q3 and Q4 generate the flywheel current. Does not contribute and can therefore be omitted. Similarly, four transistors Q1
It is also possible to control ON / OFF of the transistors Q1 and Q2 among the Q4 through PWM pulses, in which case the flywheel diodes D3 and D4 in parallel with the transistors Q3 and Q4 contribute to the passage of flywheel current,
Instead, the flywheel diodes D1 and D2 in parallel with the transistors Q1 and Q2 do not contribute to the conduction of the flywheel current and can be omitted. Also, P
A driving method in which a WM pulse is applied simultaneously to the transistors Q1 and Q4 or Q2 and Q3 in the diagonal position of the bridge circuit 4 is also possible. In that case, the transistor on the side where the PWM pulse is not applied (however, is not used for the entire period) Since the flywheel current flows through the flywheel diode in parallel with (conduction), the flywheel diodes D1 to D4 are all indispensable constituent elements. Therefore, in view of these points, all four transistors Q1 to Q4 are indispensable for driving the DC motor 2 by the PWM method, but at least two flywheel diodes are required.

[0018]

As described above, according to the present invention, when the pulse width modulation control circuit drives the switching element by closing the switching element by the PWM pulse, the pulse width modulation control is performed by detecting the average current flowing through the DC motor. Since it is configured to be fed back to the circuit, the rotation of the DC motor that flows as a triangular wave of the motor drive current flowing through the switching element during the ON period of the PWM pulse and the flywheel current flowing through the diode during the OFF period of the PWM pulse, PWM control can be performed based on the average current that is equal to the arithmetic average value of the maximum value and the minimum value of the triangular wave. As a result, the maximum value of the triangular wave is fed back to the PWM control, depending on the control deviation. The excellent effect that the motor can be driven with high precision, regardless of the pulse width of the PWM pulse that dynamically changes with time.

Further, according to the present invention, the sample-hold circuit holds the motor drive current and sets it as the average current by the sampling pulse which lasts ½ of the pulse width of the PWM pulse from the rising edge of the PWM pulse. , PW is the midpoint of the motor drive current that forms the rising hypotenuse of the current that is supplied to the DC motor as a triangular wave.
Since the sample and hold can be performed in synchronization with the midpoint of the M pulse, and a current value just between the minimum value and the maximum value of the motor drive current can be detected as the average current,
There is an effect that the accuracy of the average current can be increased and the accuracy of the PWM control can be improved at the same time.

Furthermore, according to the present invention, the motor drive current is held at both the maximum value and the minimum value by the peak hold circuit and the bottom hold circuit, and the average current is obtained as the arithmetic average value of both. There is an effect that the average value of the motor drive current can be obtained from the minimum value and the maximum value of the triangular wave motor drive current itself without using the PWM pulse, and the average value can be used for the PWM control.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a motor drive device of the present invention.

FIG. 2 is a signal waveform diagram of each part of the circuit shown in FIG.

FIG. 3 is a circuit configuration diagram showing another embodiment of the motor drive device of the present invention.

FIG. 4 is a signal waveform diagram of each part of the circuit shown in FIG.

FIG. 5 is a circuit configuration diagram showing an example of a conventional motor drive device.

6 is a signal waveform diagram of each part of the circuit shown in FIG.

[Explanation of symbols]

11, 21 PWM type motor drive device 2 DC motor 3 Pulse width modulation control circuit (CPU) 4 Bridge circuit 6 Current-voltage converter 12 Average current detection means (sampling pulse generation circuit) 13 Average current detection means (sample hold circuit) 13a Sampling switch 13b Hold capacitor 22 Average current detection means (peak hold circuit) 23 Average current detection means (bottom hold circuit) 24 Average current detection means (arithmetic averaging circuit) Q1 to Q4 Switching elements (transistors) D1 to D4 Flywheel diode

Claims (3)

[Claims] 1. A direct current motor driven in a forward and reverse direction according to the polarity of an applied voltage, and two switching elements connected in series to a pair of parallel lines connected to a direct current power source, and the two switching elements are connected in series. A bridge circuit whose connection points are bridged by the DC motor, flywheel diodes respectively connected in parallel to at least two switching elements of the four switching elements forming the bridge circuit, and the DC motor The four switching elements are opened and closed by a control pulse including a PWM pulse so that a voltage having a polarity corresponding to the rotation direction is applied to the switching element, and the motor drive current from the DC power supply is used during the ON period of the PWM pulse. Rotate and drive the DC motor,
A pulse width modulation control circuit that rotationally drives the DC motor with a flywheel current flowing through the flywheel diode during an off period of the PWM pulse, and an average current of the motor driving current and the flywheel current flowing through the DC motor. And a mean current detecting means for detecting the current and returning it to the pulse width modulation control circuit. 2. A sampling pulse generation circuit that generates a sampling pulse that lasts for approximately 1/2 of the ON period of the PWM pulse from the beginning of the ON period of the PWM pulse, and a current-voltage that converts the motor drive current into a voltage. It is constituted by the average current detecting means including a converter and a sample hold circuit which holds the output of the current-voltage converter by the sampling pulse and obtains the voltage-converted average current. P according to claim 1
WM type motor drive device. 3. A current-voltage converter for converting the motor drive current into a voltage, a peak hold circuit for holding the output of the current-voltage converter at a maximum value, and a minimum output for the current-voltage converter. And an average current detecting means including a bottom hold circuit for holding the output of the bottom hold circuit and an average of the outputs of the bottom hold circuit and the peak hold circuit to obtain the voltage converted average current. The PWM type motor drive device according to claim 1, wherein