JP4225862B2 - Motor control device - Google Patents

Description

  The present invention relates to a motor control device that controls an electric motor in accordance with a switching operation of a switching element.

  Many motors are used in automobiles. However, when the electromagnetic noise generated when switching control of the most commonly used DC motor is large, there is a problem that noise enters a radio or the like. is there. Recently, it has been demanded to install a radio antenna that has been installed outside the rear glass or outside of the passenger compartment in the passenger compartment, particularly in the front seat. In this case, a drive circuit or motor that becomes a noise source and the radio antenna are required. Since the distance between and becomes closer, the influence of electromagnetic noise increases.

On the other hand, conventionally, in order to reduce the electromagnetic noise generated from the motor, there are measures such as adding an electromagnetic shield to the motor's power supply line or adding an electromagnetic noise absorbing element such as a choke coil or bypass capacitor. (See Patent Document 1).
JP-A-7-2839797

However, conventional electromagnetic noise countermeasures increase the cost to add an electromagnetic shield, an electromagnetic noise absorbing element, etc., and require a space for installing an electromagnetic shield, an electromagnetic noise absorbing element, etc. There was a problem that mountability deteriorated.
The present invention has been made based on the above circumstances, and an object of the present invention is to provide a motor control device that can suppress an increase in cost and can reduce the generation of electromagnetic noise without deteriorating mountability on a vehicle. There is.

(Invention of Claim 1 )
In the present invention, when a control signal is output from the switching control device to the first and second switching elements at the same timing, a time lag occurs in the switching operation of the first switching element and the second switching element. The switching control device generates a voltage applied to the first or second switching element in accordance with a time lag in switching operation between the first switching element and the second switching element. It is characterized by changing.
For example, by reducing the voltage applied to the first switching element, the operation timing of the first switching element can be delayed, thereby making the operation timings of the first and second switching elements substantially coincide. Is possible.

(Invention of Claim 2 )
In the present invention, when a control signal is output from the switching control device to the first and second switching elements at the same timing, a time lag occurs in the switching operation of the first switching element and the second switching element. The switching control device has a positive side terminal voltage of the electric motor to which the first switching element is connected and a negative side terminal voltage of the electric motor to which the second switching element is connected. The output timing or output voltage of the control signal for the first or second switching element is controlled so that the average voltage falls within a predetermined voltage range.
According to the above configuration, the common mode voltage causing the electromagnetic noise, that is, the average voltage of the positive terminal voltage and the negative terminal voltage of the electric motor can be kept within a predetermined voltage range. Electromagnetic noise generated during switching can be reduced.

  The best mode for carrying out the present invention will be described in detail by the following examples.

FIG. 2 is an electric circuit diagram of the motor control device 1.
The motor control device 1 performs PWM control of the motor 2 and includes a motor drive circuit 3, motor current detection means 4, and a switching control device 5 described below.

The motor 2 is a well-known DC motor that generates a rotational force in the armature 2c when a motor current flows through the armature 2c via a commutator (not shown) with which the brushes 2a and 2b are in sliding contact. Is connected to the motor terminal M1, and the other brush 2b is connected to the motor terminal M2.
The motor drive circuit 3 includes four switching elements (MOS-FETs in this embodiment) Q1, Q2, Q3, and Q4 forming an H-bridge circuit, and four switching elements Q1 to Q4 connected in parallel. Diodes D1, D2, D3 and D4 (parasitic diodes of MOS-FETs in this embodiment).

In the H bridge circuit, the connection point between the switching element Q1 and the switching element Q3 is connected to the DC power source VD, and the connection point between the switching element Q2 and the switching element Q4 is grounded. The connection point between the switching element Q1 and the switching element Q2 is connected to the motor terminal M1, and the connection point between the switching element Q3 and the switching element Q4 is connected to the motor terminal M2.
The motor current detection unit 4 detects the current I flowing through the motor 2 by a shunt resistor connected between the DC power supply VD and the motor drive circuit 3, for example, and outputs it to the switching control device 5.

The switching control device 5 outputs a control signal (referred to as a gate signal) to the gates of the switching elements Q1 to Q4 to control the switching operation of the switching elements Q1 to Q4.
Specifically, the gate signals G1 and G4 for the switching elements Q1 and Q4 are turned ON, and the gate signals G2 and G3 for the switching elements Q2 and Q3 are turned OFF, so that the motor 2 is rotationally driven in one direction. The motor 2 is driven to rotate in the other direction by turning on G2 and G3 and turning off the gate signals G1 and G4.

  Here, when the gate signals G1 and G4 for the switching elements simultaneously controlled to be switched, for example, the switching element Q1 and the switching element Q4 are turned ON, the DC power source VD → switching element Q1 → motor terminal M1 → motor 2 → switching element Q4 → GND. Current flows into the. At this time, the gate signals G2 and G3 are OFF. When the gate signals G1 and G4 are turned OFF, the reflux current flows from the motor terminal M2, the diode D3, the DC power supply VD, the GND, the diode D2, and the motor terminal M1 due to the inductance of the motor 2. At this time, the gate signals G2 and G3 are OFF.

  When the switching element Q1 is turned on, the voltage (referred to as M1 voltage) generated at the motor terminal M1 becomes the VD potential (hereinafter, the voltage drop of the diode is ignored). When the switching element Q4 is turned on, the voltage generated at the motor terminal M2 (referred to as the M2 voltage) becomes the GND potential. Therefore, the common mode voltage (the average voltage of the M1 voltage and the M2 voltage) that is a source of electromagnetic noise is a potential that is half of VD in a steady state. Further, at the time of switching, if the operation timings of the switching element Q1 and the switching element Q4 coincide (ON timing and OFF timing), the voltage waveform generated at the motor terminal M1 and the voltage waveform generated at the motor terminal M2 Is canceled out and becomes half the potential of VD.

However, in reality, a delay occurs in the timing when the switching elements Q1, Q4 are turned ON and OFF with respect to the gate signals G1, G4, and the delay time is different between the switching elements Q1, Q4. .
For example, as shown in FIG. 3, with respect to the time t1 when the gate signals G1 and G4 fall, the time t2 when the switching element Q1 is turned off and the M1 voltage falls, and the time t3 when the switching element Q4 is turned off and the M2 voltage rises And a delay Toff (t3-t2) occurs between the delay times of the two. Similarly, with respect to the time t4 when the gate signals G1 and G4 rise, there is a delay between the time t5 when the switching element Q1 is turned on and the M1 voltage rises, and the time t6 when the switching element Q4 is turned on and the M2 voltage falls, There is a shift Ton (t6-t5) in the delay time between the two.

  The cause of this delay may be that the gate resistance or input capacitance of the MOS-FET used for the switching element is different, or the gate threshold voltage at which the MOS-FET is turned on / off is different. In this way, when the switching element Q1 and the switching element Q4 are turned on and off at different timings with respect to the gate signals G1 and G4, the common mode voltage changes during switching, and electromagnetic noise is generated.

On the other hand, the switching control device 5 of this embodiment adjusts the output timing of the gate signals G1 and G4 so that the common mode voltage does not change.
For example, as shown in FIG. 3, when a delay occurs between the operation timing of the switching element Q1 with respect to the gate signal G1 and the operation timing of the switching element Q4 with respect to the gate signal G4, The output timing of the gate signal G1 is delayed by the shift time. As shown in FIG. 1A, the difference in the operation timing of the gate signal is that the gate signal G1 is delayed by an ON delay time Ton when ON and by an OFF delay time Toff when OFF, respectively. .

As a result, the time t10 when the gate signal G1 falls is delayed from the time t1 shown in FIG. 3 by the shift time Toff (t3−t2), so that the switching element Q1 is turned OFF and the voltage M1 is reduced. The falling time and the time t3 when the switching element Q4 is turned OFF and the M2 voltage rises substantially coincide.
Also, the time t11 at which the gate signal G1 rises is delayed by the shift time Ton (t6-t5) with respect to the time t4 shown in FIG. 3, so the time at which the switching element Q1 is turned on and the M1 voltage rises. And the time t6 when the switching element Q4 is turned on and the voltage M2 falls substantially coincides.

  According to the above method, since the operation timings of the switching elements Q1 and Q4 are substantially the same, as shown in FIG. 1B, the common mode voltage at the time of switching is the voltage waveform generated at the motor terminal M1 and the motor terminal. The voltage waveform generated at M2 is canceled out to a potential half of VD, and no noise component is generated. Actually, when the operation timing (ON timing) of the switching elements Q1 and Q4 is compared before and after the change, as shown in FIG. 4, (b) the timing compared with (a) before the timing change. It can be seen that the noise component of the common mode voltage becomes smaller after the change, and the noise of 1 to 6 MHz is reduced as shown in FIG.

  Further, the motor control device 1 of the present embodiment only needs to change the output timings of the gate signals G1 and G4 output from the switching control device 5 in order to match the operation timings of the switching elements Q1 and Q4. In this method, as explained in the prior art, since it is not necessary to add an electromagnetic shield or an electromagnetic noise absorbing element to the power supply line of the motor 2, the generation of electromagnetic noise can be suppressed at a low cost and the electromagnetic shield can be suppressed. In addition, a space for adding an electromagnetic noise absorbing element or the like is not necessary, so that the mounting property on a vehicle is not deteriorated.

(Modification)
In the above embodiment, when the motor 2 is rotated in one direction, that is, when the switching elements Q1 and Q4 are PWM-controlled, the method of matching the operation timings of both the switching elements Q1 and Q4 has been described. When rotating in the other direction, that is, when the switching elements Q2 and Q3 are PWM-controlled, the operation timings of both the switching elements Q2 and Q3 can be made substantially coincident with each other by the same method as in the above embodiment.
Further, the method described in the first embodiment can be applied to the case where the motor 2 is rotationally driven only in one direction as shown in FIG.

Since the delay value of the gate signal G1 varies depending on the current flowing through the motor 2, the output timing of the gate signal G1 may be adjusted based on the current value detected by the motor current detection means 4. When the variation due to temperature is large, the optimum value of the delay time may be changed according to the temperature.
Further, instead of delaying the gate signal G1, the output timing of the gate signal G4 may be advanced by the delay time of the switching element Q4 with respect to the gate signal G4.

In the first embodiment, the output timing of the gate signals G1 and G4 is changed in order to match the operation timing of the switching elements Q1 and Q4. However, the output timing of the gate signals G1 and G4 is not changed. The voltage values (gate voltages) of the gate signals G1 and G4 may be changed.
For example, by reducing the gate voltage of the switching element Q1, the operation timing of the first switching element can be delayed, thereby making it possible to substantially match the operation timings of the first and second switching elements. is there.

FIG. 7 is an electric circuit diagram of the motor control device 1 according to the third embodiment.
The motor control device 1 of the present embodiment is an example of feedback control of the gate signal so that the average voltage of the M1 voltage and the M2 voltage falls within a predetermined voltage range. The motor drive circuit 3 described in the first embodiment, In addition to the switching control device 5, as shown in FIG. 7, a capacitor 6 that extracts a noise component of the M1 voltage, a capacitor 7 that extracts a noise component of the M2 voltage, and an average value of both extracted noise components (referred to as a detection voltage VC). ) Is compared with the common mode lower limit voltage value VL, and a comparator circuit 9 is provided that compares the detection voltage VC with the common mode upper limit voltage value VH.

The switching control device 5 controls the output timing of the gate signal or the gate voltage so that the VC becomes larger than VL when VC becomes smaller than VL, and when VC becomes larger than VH, the VC becomes VC. The output timing of the gate signal or the gate voltage is controlled so that becomes smaller than VH. Thereby, VC can be kept within a predetermined voltage range (VL ≦ VC ≦ VH), and electromagnetic noise generated during switching can be reduced.
In the third embodiment, it is possible to easily adapt a change in a gate signal due to a load current, variations among products, and circuits of other specifications.

(Example 1) which is a time chart of the motor terminal voltage and common mode voltage corresponding to a gate signal. FIG. 2 is an electric circuit diagram of the motor control device shown in the first embodiment. It is a time chart of the motor terminal voltage corresponding to a gate signal, and a common mode voltage (when the operation timing of a switching element is delayed with respect to a gate signal). It is a graph which shows the result of having measured the noise component of the common mode voltage. It is the graph which compared the generated noise before and after changing the operation timing of a switching element. It is an electric circuit diagram of a motor control device (modification example of Example 1). FIG. 6 is an electric circuit diagram of a motor control device shown in Embodiment 3.

Explanation of symbols

1 Motor control device 2 Motor (electric motor)
DESCRIPTION OF SYMBOLS 3 Motor drive circuit 4 Motor current detection means 5 Switching control apparatus Q1 Switching element (1st switching element)
Q2 switching element (second switching element)
Q3 switching element (first switching element)
Q4 switching element (second switching element)

Claims (2)

A motor drive circuit having a first switching element connected to a high potential side line of a power supply line for supplying electric power from a DC power supply to an electric motor and a second switching element connected to a low potential side line of the power supply line When,
A switching control device that outputs a control signal for instructing a switching operation to the first and second switching elements and controls a switching operation of the first and second switching elements;
When the control signal is output from the switching control device to the first and second switching elements at the same timing, the switching operation between the first switching element and the second switching element is time-consuming. A motor control device in which deviation occurs,
The switching control device changes a voltage applied to the first or second switching element according to a time lag of a switching operation between the first switching element and the second switching element. A motor control device. A motor drive circuit having a first switching element connected to a high potential side line of a power supply line for supplying electric power from a DC power supply to an electric motor and a second switching element connected to a low potential side line of the power supply line When,
A switching control device that outputs a control signal for instructing a switching operation to the first and second switching elements and controls a switching operation of the first and second switching elements;
When the control signal is output from the switching control device to the first and second switching elements at the same timing, the switching operation between the first switching element and the second switching element is time-consuming. A motor control device in which deviation occurs,
In the switching control device, an average voltage between a positive terminal voltage of the electric motor to which the first switching element is connected and a negative terminal voltage of the electric motor to which the second switching element is connected is predetermined. A motor control device that controls an output timing or an output voltage of the control signal to the first or second switching element so as to fall within the voltage range .

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