JP6954010B2 - Electronic control device - Google Patents

Description

The present invention relates to an electronic control device that drives a brushless DC motor by PWM drive on one side by position sensorless control.

Conventionally, as one of the methods for driving a brushless DC motor, the high side switch among the upper and lower switches constituting the drive circuit is driven by PWM (Pulse Width Modulation), and the low side switch is driven by continuously turning on the so-called. There is a one-sided PWM drive system. Further, when the motor is driven by the position sensorless method, the position information is often acquired by detecting the zero cross point of the counter electromotive force and the induced voltage generated in the winding of the motor.

FIG. 8 shows a circuit for driving a motor mounted on a vehicle by a conventional position sensorless method. The inverter circuit 1 is configured by connecting a P-channel MOSFET 2 which is a high-side switch and an N-channel MOSFET 3 which is a low-side switch in a three-phase bridge connection. The voltage VB of the battery power supply of the vehicle is supplied to the source of the FET 2, and the source of the FET 3 is connected to the ground. Each phase output terminal of the inverter circuit 1 is connected to one end of each phase winding of the three-phase brushless DC motor 4.

The counter electromotive force detection unit 5 includes comparators 6U, 6V, and 6W corresponding to each phase. The non-inverting input terminals of the comparator 6 are connected to one end of each phase winding of the motor 4 via a protection resistor R0. One end of the adder resistor R is commonly connected, and the other end is connected to one end of each phase winding. The inverting input terminal of the comparator 6 is commonly connected to the one end of the adder resistor R. As a result, the reference voltage for comparison applied to the comparator 6 becomes the virtual neutral point potential of the motor 4. The counter electromotive force detection unit 5 detects the counter electromotive force of the motor 4, that is, the zero crossing point of the induced voltage generated in the winding by the comparator 6.

FIG. 9 is a diagram showing an input waveform of the comparator 6. The solid line represents the comparative input voltage of the non-energized phase, and the broken line represents the reference voltage. The motor terminal voltage of the phase in which the low-side switch is continuously on is 0V, and the motor terminal voltage of the phase in which the high-side switch is PWM-driven is the power supply voltage VB during the switch-on period and -VF during the PWM switch-off period. Become. VF is the forward voltage of the body diode of the FET. Then, the back electromotive force VE of the motor becomes ± 0V at the zero crossing point. Therefore, the comparative input voltage and the reference voltage at the zero cross point are VB / 2 during the switch-on period and -VF / 2 during the switch-off period. On the other hand, before and after the zero cross point, the counter electromotive force ± VE is added to the comparison input voltage, and ± VE / 3 is added to the reference voltage.

In such a conventional technique, the input of the comparator 6 becomes a negative voltage and the output becomes unstable during the switch-off period in the PWM drive. Therefore, during this period, the control circuit and the microcomputer into which the output signal of the comparator 6 is input Mask processing is performed to prohibit the detection of zero cross points. In addition, since the voltage becomes unstable immediately after switching is turned on and off, detection of the zero crossing point is prohibited. Therefore, if the duty ratio of the PWM signal is small, the period for prohibiting the detection of the zero cross point becomes long, and the possibility that the zero cross point arrives during that period increases, so that the timing for inspecting the zero cross point tends to be deviated.

For example, as shown in Patent Document 1, this problem can be solved by inverting the counter electromotive force signal only when the duty ratio is 50% or less and enabling zero cross detection during the switch-off period in PWM drive.

Japanese Unexamined Patent Publication No. 2014-220987

However, in the configuration of Patent Document 1, the zero cross point cannot be detected during the switch-on period in the PWM drive by inverting the counter electromotive force signal. In particular, when the duty ratio is around 50%, the detectable period becomes short, so that accurate detection becomes impossible.

Further, when performing so-called balanced PWM drive in which both the high-side switch and the low-side switch are PWM-driven to drive the motor, a zero cross point can be detected in both the switch-on period and the switch-off period. However, in the balanced PWM drive, the current ripple and the switching loss are larger than those in the one-side PWM drive.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electronic control device capable of detecting a zero cross point in both a switch-on period and a switch-off period when performing one-sided PWM drive. be.

According to the electronic control device according to claim 1, the PWM signal output unit generates a PWM signal and outputs it to a high-side switch of a drive circuit, outputs a continuous on signal to a low-side switch, and is brushless with three or more phases. The DC motor is PWM-driven on one side by position sensorless control. The zero cross point detector has a pull-up resistor with one end commonly connected to the power supply terminal and a protective resistor with one end connected to the other end of the pull-up resistor and the other end connected to each phase winding of the motor. Be prepared. Then, the zero cross point detection unit detects the zero cross point of the induced voltage generated in the winding of the motor when its signal input terminal is connected to the common connection point of the pull-up resistor and the protection resistor.

With this configuration, the potential of the signal input terminal of the zero cross point detection unit is superimposed on the potential obtained by dividing the power supply voltage by the pull-up resistor and the protection resistor. As a result, even if the motor terminal voltage becomes a negative potential when the PWM drive switch is turned off, the potential of the signal input terminal is shifted to a positive potential. Therefore, the zero cross point detection unit can detect the zero cross point of the induced voltage even when the switch is off when the motor is PWM-driven on one side, and the position sensorless control can be performed with high accuracy.

The figure which shows 1st Embodiment and shows the structure of the electronic control apparatus with the main part. Diagram showing voltage at each node The figure which shows the waveform of the comparative input voltage and the reference voltage applied to a comparator Flowchart showing the process of detecting the zero crossing point of the induced voltage The figure which shows the A / D converter which is 2nd Embodiment and is used instead of a comparator. Flowchart showing the process of detecting the zero crossing point of the induced voltage FIG. 3 is a diagram showing a configuration in which a reference voltage obtained by dividing the power supply voltage VB is applied according to the third embodiment. The figure which shows an example of the configuration which drives a conventional motor by position sensorless control The figure which shows the waveform of the comparative input voltage and the reference voltage applied to a comparator

(First Embodiment)
Hereinafter, the first embodiment will be described with reference to FIGS. 1 to 4. The same parts as those in FIG. 8 are designated by the same reference numerals, the description thereof will be omitted, and different parts will be described. The protection resistor R0 is replaced with the protection resistor R2. The inverting input terminal of the comparator 6 is pulled up to the power supply VB via the pull-up resistor R1. Further, the comparator 6 is supplied with a battery voltage VB as an operating power source. The terminal of the battery voltage VB corresponds to the power supply terminal. The above constitutes the counter electromotive force detection unit 11. The output terminals of the comparators 6U to 6W are connected to the input terminals of the microcomputer 12 (hereinafter, abbreviated as the microcomputer 12).

The microcomputer 12 obtains the rotor rotation position of the motor 4 every 60 degrees of the electric angle from the zero crossing point of the induced voltage obtained for each phase. Based on this, position sensorless drive is performed by generating a PWM signal that energizes the motor 4. The PWM signal output unit 13 built in the microcomputer 12 generates three-phase PWM signals U +, U-, V +, V-, W +, and W-, and outputs them to the gates of FETs 2 and 3 constituting the inverter circuit 1, respectively. do. The inverter circuit 1 corresponds to a drive circuit. Further, the FET 2 corresponds to a high side switch, and the FET 3 corresponds to a low side switch. The counter electromotive force detection unit 11 and the microcomputer 12 correspond to the zero cross point detection unit.

FIG. 2 shows the potential at each node. Further, FIG. 3 shows an input waveform of the comparator 6 in this embodiment. Similar to FIG. 9, the solid line shows the comparative input voltage of the non-energized phase, and the broken line shows the reference voltage. Similar to the description in FIG. 9, the motor terminal voltage in the non-energized phase at the zero cross point is VB / 2 during the switch-on period in PWM drive and −VF / 2 during the switch-off period. Therefore, the comparative input voltage and reference voltage at the zero cross point are
Switch-on period: (R2 / VB + R1 / VB / 2) / (R1 + R2)
Switch-off period: (R2, VB-R1, VF / 2) / (R1 + R2)
Will be. Before and after the zero cross point, on the other hand, the comparative input voltage and the reference voltage are the comparative input voltage: ± R1 · VE / (R1 + R2), respectively.
Reference voltage: ± R1 ・ VE / {3 (R1 + R2)}
Is applied.

From the above, (R2 / VB-R1 / VF / 2) / (R1 + R2) ≥ 0
That is, if the voltage division ratio R1 / R2 is set to 2 VB / VF or less, the comparative input voltage and the reference voltage at the zero cross point are always 0 V or more regardless of the size of the switch on / off and the battery voltage VB in the PWM drive. And the voltage is VB or less.

Therefore, if the battery voltage VB is used as the power supply voltage of the comparator 6, zero-cross detection can always be performed except immediately after the switch is turned on and off when the voltage fluctuates. Regardless, the deviation of zero cross detection is less likely to occur. At that time, by setting the prohibition period of zero cross detection to different lengths immediately after on and immediately after turning off, each can be set to an optimum value, and the detection prohibition period can be minimized.

In the actual design, the counter electromotive force is added to the comparative input voltage and the reference voltage before and after the zero crossing point. Further, the inputtable range of a general comparator is further smaller than the range of 0V to the power supply voltage. In consideration of these, the voltage division ratios R1 / R2 are appropriately set so that the comparison input voltage and the reference voltage are always within the inputtable range of the comparator.

In the process of detecting the zero crossing point of the induced voltage shown in FIG. 4, the microcomputer 12 first waits until the first edge of the PWM signal generated and output by the PWM signal output unit 13 is detected (S0; NO). When the first edge is detected (YES), if it is a rising edge (S2; YES), the process proceeds to step S3, and if it is a falling edge (S2; NO), the process proceeds to step S4.

In step S3, the elapse of the first predetermined time is waited (NO), and when the first predetermined time elapses (YES), it is determined whether or not the output level of the non-energized phase comparator 6 at that time is reversed. (S5). If the output level is not inverted, the process returns to (NO) step S1. Further, in step S4, the process proceeds to step S5 after waiting for the elapse of the second predetermined time (NO) and (YES) when the second predetermined time elapses. For example, as shown in FIG. 3, the second predetermined time is set longer than the first predetermined time.

That is, after the rising edge is detected, the output level of the comparator 6 is not referred to until the first predetermined time elapses, and the reference is started when the first predetermined time elapses. Then, the loops of steps S1 and S5 are repeatedly executed until (YES) the zero crossing point of the induced voltage is detected by inverting the output level in step S5 (S6). When the rising edge is detected, the same process as described above is performed when the second predetermined time elapses. The first and second predetermined times correspond to the prohibited period. When the zero cross point is detected and the process is completed, the status of "first edge detection" in step S0 is reset.

As described above, according to the present embodiment, the PWM signal output unit 13 of the microcomputer 12 generates a PWM signal and outputs it to the high-side FET 2 of the inverter circuit 1, and outputs a continuous on signal to the low-side FET 3. , The motor 4 is PWM-driven on one side by position sensorless control. The zero cross point detector has a pull-up resistor R1 whose one end is commonly connected to the power supply terminal and a protective resistor whose one end is connected to the other end of the pull-up resistor R1 and the other end is connected to each phase winding of the motor. It has R2. Then, the counter electromotive force detection unit 11 detects the zero crossing point of the induced voltage generated in the winding of the motor 4 when its signal input terminal is connected to the common connection point of the pull-up resistor R1 and the protection resistor R2.

With this configuration, the potential of the signal input terminal of the counter electromotive force detection unit 11 is superposed with the potential obtained by dividing the power supply voltage VB by the pull-up resistor R1 and the protection resistor R2. As a result, even if the motor terminal voltage becomes a negative potential when the PWM drive switch is turned off, the potential of the signal input terminal is shifted to a positive potential. Therefore, the counter electromotive force detection unit 11 can detect the zero crossing point of the induced voltage even when the switch is off when the motor 4 is PWM-driven on one side, and the position sensorless control can be performed with high accuracy. ..

Further, since the counter electromotive force detection unit 11 includes a comparator 6 in which the voltage VB of the battery power supply of the vehicle that supplies the drive power supply to the inverter circuit 1 is supplied as the operating power supply, comparison is performed regardless of the level of the voltage VB. The vessel 6 can always keep the voltage of the input signal within the input range. Therefore, even if the voltage VB fluctuates, the zero cross point of the induced voltage can be detected both when the switch is turned on and when the switch is turned off in the PWM drive.

Further, since the potential of the virtual neutral point generated by adding the voltages given to the signal input terminals of each phase is applied to the comparator 6 as the reference voltage for comparison, the switch is turned on and off in the PWM drive. Regardless, the reference voltage becomes equal to the neutral point voltage of the motor 4. Therefore, unlike the configuration in which the reference voltage obtained by dividing the battery voltage VB is applied, it is not necessary to switch the reference voltage in synchronization with the PWM signal. Further, it is not necessary to consider the variation in the forward voltage VF of the freewheeling diodes connected in parallel to the FETs 2 and 3.

Further, since the microcomputer 12 sets a period for prohibiting the detection of the zero cross point immediately after the inverter circuit 1 switches based on the PWM signal, the zero cross occurs during the period when the motor terminal voltage becomes unstable immediately after the switching. It is possible to prevent erroneous detection of points. Further, the microcomputer 12 individually sets the length of the prohibition period at the turn-on time and the turn-off time of the switching, and sets each as the first predetermined time and the second predetermined time, respectively. As a result, even if the length of the period during which the motor terminal voltage becomes unstable differs between immediately after the turn-on and immediately after the turn-off, the prohibition period can be set as short as possible so as to be optimum for each.

(Second Embodiment)
Hereinafter, the same parts as those in the first embodiment are designated by the same reference numerals, description thereof will be omitted, and different parts will be described. In the second embodiment, as shown in FIG. 5, the A / D converter 14 is used instead of the comparator 6. The A / D converter 14 may be built in the microcomputer 12 or may be externally attached. The A / D converter 14 is provided with analog signal input terminals corresponding to each phase of U, V, and W, and switches them in a time division manner to perform A / D conversion and digital data such as 8-bit or 12-bit. Convert to and output. Similar to the comparator 6 of the first embodiment, the signal input terminal is connected to one end of each phase winding of the motor 4 via the protection resistor R2, and is pulled up to the power supply voltage VB by the pull-up resistor R1. Has been done.

In FIG. 6, which is a diagram corresponding to FIG. 4, the microcomputer 12 executes step S7 instead of step S5. Here, assuming that the voltage data of the non-energized phase is V1 and the voltage data of the energized phase is V2 and V3, it is determined whether or not the sign of the voltage {V1- (V1 + V2 + V3) / 3} is reversed. That is, the voltage (V1 + V2 + V3) / 3 is equal to the virtual neutral point voltage of the motor 4.

According to the second embodiment configured as described above, the microcomputer 12 uses the voltage converted into digital data by the A / D converter 14 as the virtual neutral point voltage of the motor 4, that is, the reference voltage by software processing. The zero cross point of the induced voltage is detected by comparison. In this case, for example, a digital filter can be used to remove the noise component superimposed on the input voltage.

(Third Embodiment)
In the third embodiment shown in FIG. 7, the comparator 6 is used as in the first embodiment. A series circuit of resistors R1, R2 and R3 is connected between the power supply terminal and the ground, and an N-channel MOSFET 15 is connected in parallel to the resistor R3. The resistance value of the resistor R3 is set to (R1 + R2). The inverting input terminal of the comparator 6 is connected to the common connection point of the resistors R1 and R2. The gate of the FET 15 is provided with a gate signal obtained by inverting the logic of the PWM signal.

In the third embodiment, the divided battery voltage VB is applied as the reference voltage of the comparator 6. In this case, the reference voltage is as follows between the switch-on period and the switch-off period in the PWM drive.
Switch-on period: (R2 / VB + R1 / VB / 2) / (R1 + R2)
Switch-off period: (R2 / VB) / (R1 + R2)

According to the third embodiment configured as described above, the reference voltage can be finely adjusted by setting the resistance values of the voltage dividing resistors R1 to R3. However, since the reference voltage during the switch-off period deviates from the theoretical value by {(R1 · VF / 2) / (R1 + R2)}, the detection timing of the zero cross point deviates by that amount.

(Other embodiments)
The operating power source of the comparator 6 does not necessarily have to be a battery power source.
The length of the first predetermined time and the second predetermined time may be set in reverse.
The zero cross point detection prohibition period may be set to the same length at the time of turn-on and at the time of turn-off. Further, the detection prohibition period may be set as necessary.
An N-channel MOSFET may be used for the high-side switch. In addition, an IGBT, a power transistor, or the like may be used as the switch.

Although the present disclosure has been described in accordance with the examples, it is understood that the present disclosure is not limited to the examples and structures. The present disclosure also includes various modifications and modifications within a uniform range. In addition, various combinations and forms, as well as other combinations and forms that include only one element, more, or less, are also within the scope of the present disclosure.

In the drawing, 1 is an inverter circuit, 2 is a P-channel MOSFET, 3 is an N-channel MOSFET, 4 is a brushless DC motor, 6 is a comparator, 11 is a counter electromotive force detector, 12 is a microcomputer, and 13 is a PWM signal output unit. , R1 indicates a pull-up resistance, and R2 indicates a protection resistance.

Claims (5)

Since a brushless DC motor (4) having three or more phases is PWM-driven on one side by position sensorless control, a PWM signal is generated and output to the high-side switch (2) of the drive circuit (1), and the low-side switch (3) is used. A PWM signal output unit (13) that outputs a continuous on signal,
It is provided with a zero cross point detection unit (11, 12) for detecting the zero cross point of the induced voltage generated in the winding of the motor.
One end of the zero cross point detector is connected to a pull-up resistor (R1) commonly connected to the power supply terminal, and one end is connected to the other end of the pull-up resistor, and the other end is connected to each phase winding of the motor. With a protection resistor (R2)
The signal input terminal of the zero cross point detection unit is an electronic control device connected to a common connection point between the pull-up resistor and the protection resistor. The power supply terminal supplies a drive power source to the drive circuit from a battery power source.
The electronic control device according to claim 1, wherein the zero cross point detection unit includes a comparator (6) to which an operating power supply is supplied via the power supply terminal. The electronic control device according to claim 2, wherein a potential of a virtual neutral point generated by adding a voltage given to a signal input terminal of each phase is applied to the comparator as a reference voltage for comparison. The electron according to any one of claims 1 to 3, wherein the zero cross point detection unit sets a prohibition period for prohibiting detection of the zero cross point immediately after the drive circuit switches based on the PWM signal. Control device. The electronic control device according to claim 4, wherein the zero cross point detection unit can individually set the length of the prohibition period at the turn-on time and the turn-off time of the switching.

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