JP7023357B2 - Motor control device - Google Patents

Description

The present invention relates to a motor control device that drives and controls a motor.

The three-phase inverter control circuit that realizes the motor control device that controls the three-phase motor consisted of six switching elements for switching, their drive circuits, and a resistor called a shunt resistor for detecting the bus current. (See, for example, Patent Document 1). In recent years, six switching elements for switching and their drive circuits have been integrated into a module called an inverter power module.

Japanese Unexamined Patent Publication No. 2011-234428

The shunt resistance of the motor control device is installed outside the inverter power module, and when a large current flows through the shunt resistance, heat is generated. Has been dealt with by implementing multiple parallels. However, the cement resistance for high power is large in size, and the inductance component parasitic on the wiring pattern and the resistance increases, which may cause a malfunction. Further, by mounting a plurality of chip resistors in parallel, the pattern area per circuit is expanded, and there are restrictions on the board size and the design of the board pattern.

The present invention has been made in view of the above, and an object of the present invention is to obtain a motor control device capable of detecting a bus current while suppressing the circuit scale.

In order to solve the above-mentioned problems and achieve the object, the present invention has an upper arm and a lower arm switching element for converting a DC voltage into an AC voltage and outputting it to a motor, and a drive circuit for driving the switching element. An inverter power module including a current detecting element connected to the switching element and for detecting a bus current flowing through the switching element. Further, the present invention includes an arithmetic unit that outputs a signal for the drive circuit to control the switching element to the drive circuit based on the detection value of the current detection element . The current detection element includes a first switching element, a second switching element connected in parallel to the first switching element, and a changeover switch. When the first switching element is selected, the voltage across the current detection element becomes smaller than the first voltage value, which is the lower limit voltage value at which the SN ratio can be tolerated, when the bus current is smaller than the first current value. When the bus current is larger than the first current value and smaller than the second current value, the loss of the first switching element is smaller than the loss of the second switching element, and the bus current is larger than the second current value. The loss of the first switching element is larger than the loss of the second switching element. The changeover switch selects the second switching element when the bus current is smaller than the first current value, and the first switch when the bus current is larger than the first current value and smaller than the second current value. A switching element is selected, and when the bus current is larger than the second current value, the second switching element is selected.

The motor control device according to the present invention has an effect that the circuit scale can be suppressed and the bus current can be detected.

The block diagram which shows the structure of the motor control device which concerns on Embodiment 1 of this invention. A time chart illustrating the operation of the motor control device according to the first embodiment. A block diagram showing a configuration of a motor control device according to a second embodiment of the present invention. A time chart illustrating the operation of the motor control device according to the second embodiment. A block diagram showing a configuration of a motor control device according to a third embodiment of the present invention. A graph showing the relationship between the loss of the current detection element and the bus current according to the third embodiment. A graph showing the relationship between the loss of the current detection element and the potential difference between both ends and the bus current according to the third embodiment. A block diagram showing the configuration of the MCU according to the first to third embodiments.

Hereinafter, the motor control device according to the embodiment of the present invention will be described in detail with reference to the drawings. The present invention is not limited to this embodiment.

Embodiment 1.
FIG. 1 is a block diagram showing a configuration of a motor control device 101 according to a first embodiment of the present invention. The motor control device 101 includes a bridge diode 2, a main circuit capacitor 3, a changeover switch 14 for switching a cutoff set value, an inverter power module 4, and an arithmetic unit 8 which is an MCU (Micro Controller Unit). .. The AC power supply 1 is connected to the bridge diode 2, and the inverter power module 4 drives the motor 5. The inverter power module 4 includes switching elements 4a to 4f and a control IC 4g which is a drive circuit for driving the switching elements 4a to 4f. The switching elements 4a to 4f are composed of switching elements 4a to 4c of the upper arm and switching elements 4d to 4f of the lower arm. Each of the switching elements 4a to 4f includes a bootstrap capacitor and a backflow prevention diode.

In FIG. 1, the voltage from the AC power supply 1 is rectified by the bridge diode 2 to charge the main circuit capacitor 3. As a result, the voltage after rectification is smoothed, and a bus voltage of the DC voltage with reference to the main circuit GND (ground) 6 is generated. The bus voltage is the voltage of the bus voltage terminal 7 with reference to the main circuit GND6. The power supply voltage 13a is the power supply voltage of the control IC 4g.

When the inverter operation is executed, the arithmetic unit 8 outputs signals 9a to 9f, which are various signal patterns for instructing on or off, to the control IC 4g of the inverter power module 4. The control IC 4g generates drive signals for driving the switching elements 4a to 4f based on the signals 9a to 9f which are switching signals for inverter control, and applies the generated drive signals to the switching elements 4a to 4f. That is, according to the signals 9a to 9f, the switching elements 4a to 4f are controlled by the control IC 4g so as to be on or off in an appropriate time width by the power supply voltage 13a and the gate voltage determined by the control GND15. .. As a result, an appropriate voltage is applied to the motor 5 based on the bus voltage, and an appropriate current flows in. In order to apply an appropriate voltage to the motor 5 and allow an appropriate current to flow in, it is necessary to detect the rotational state of the motor 5.

In the motor control device 101 according to the first embodiment, the current detection element 4h is installed inside the inverter power module 4. The current detection element 4h according to the first embodiment is not composed of only a resistance element. A specific example of the current detection element 4h is a current detection element that detects a current by using a magnetic flux such as DCCT (Direct Current Current Trans). In the motor control device 101, the current detection element 4h detects the bus current 12, thereby grasping the rotational state of the motor 5. The bus current 12 flows from the main circuit capacitor 3 via the bus voltage terminal 7, through the switching elements 4a to 4f and the motor 5, and finally passes through the terminal on the main circuit GND6 side of the main circuit capacitor 3. It returns to the circuit capacitor 3. When the current detection element 4h detects the value of the bus current 12, it notifies the control IC 4g of a signal 4j indicating the current value which is the detected value. The signal 4j, which is a current detection signal, is notified to the arithmetic unit 8 as a signal 4p amplified by the amplifier 4t in the control IC 4g. Further, the signal 4j may be notified to the arithmetic unit 8 as it is. The control IC 4g also notifies the arithmetic unit 8 of a cutoff signal 4k indicating that the operation of the switching elements 4a to 4f, which is the stop of the inverter operation, is cut off.

The changeover switch 14 selects one of a voltage from the signal 11 which is a cutoff setting signal from the arithmetic unit 8 and a voltage from the power supply voltage 13b and applies the voltage to the control IC 4g to obtain a drive signal from the control IC 4g. A cutoff setting value of 4n, which is a current threshold value for stopping the output, is set. The cutoff set value 4n is a current threshold value for stopping the inverter operation of the switching elements 4a to 4f in order to prevent the bus current 12 from becoming an overcurrent, and varies depending on the voltage value given by the changeover switch 14. That is, the cutoff setting value 4n is held in the control IC 4g and is a variable setting value depending on the power supply voltage 13b or the signal 11. The cutoff setting value 4n is a threshold value for the signal 4j indicating the current value of the bus current 12, but may be a threshold value for the signal 4p amplified by the amplifier 4t.

Further, in FIG. 1, the changeover switch 14 is installed outside the inverter power module 4, but may be installed inside. The power supply voltage 13b may be the same voltage as the power supply voltage 13a or may be a different voltage.

Next, the operation of the motor control device 101 will be described. If the motor 5 is overloaded or the lines of the motor 5 are short-circuited during the operation of the inverter, the bus current 12 increases. The current detection element 4h detects the increased bus current 12, and when the signal 4j indicating the detected current value reaches the cutoff set value 4n, the control IC 4g stops all or some of the switching elements 4a to 4f. , The cutoff signal 4k is output to the arithmetic unit 8. Upon receiving the cutoff signal 4k, the arithmetic unit 8 stops outputting the signals 9a to 9f to the control IC 4g.

FIG. 2 is a time chart illustrating the operation of the motor control device 101 according to the first embodiment. According to the motor control device 101, the following operations are possible.

The control IC 4g of the inverter power module 4 performs power-on reset, which is an initialization operation based on a reset signal internally generated when the power is turned on. At time t1 after the power-on reset, the cutoff set value 4n is set to a low value in the control IC 4g. After that, at the time t2 immediately before starting the switching elements 4a to 4f, the cutoff set value 4n is set to a value desired to be set at the time of starting. Further, when the connection of the motor 5 is switched from the Y connection to the Δ connection while the switching elements 4a to 4f are in operation, the cutoff setting value 4n is switched to a higher set value corresponding to the Δ connection at time t3. Then, at the time t4 when the switching elements 4a to 4f are stopped due to the overcurrent generated in the bus current 12, the cutoff set value 4n is set to a low value again.

According to the motor control device 101 according to the first embodiment, since the current detection element 4h is incorporated inside the inverter power module 4, the cutoff set value 4n can also be held inside the inverter power module 4. This makes it possible to perform signal processing for stopping the operation of the switching elements 4a to 4f inside the inverter power module 4. As a result, the distance between the control IC 4g and the current detection element 4h can be shortened, and the length of the signal line of the signal 4j can be shortened. Therefore, the pattern design of the control board becomes easy, the number of parts around the inverter power module 4 can be reduced, and the board size can be reduced. That is, the development load and cost can be reduced. Further, the resistance component, the inductance component and the capacitor component generated in the wiring pattern are reduced, and the operation of the motor control device 101 can be stabilized.

Embodiment 2.
FIG. 3 is a block diagram showing the configuration of the motor control device 102 according to the second embodiment of the present invention. In the motor control device 102, the current detection element 4h of the motor control device 101 according to the first embodiment is replaced with the current detection element 4q which is a switching element. A specific example of the current detection element 4q is a MOS-FET (Metal Oxide Semiconductor-Field Effect Transistor) having a higher withstand voltage and a lower loss than the switching elements 4a to 4f. The control IC 4g detects the value of the bus current 12 by causing the control IC 4g to detect the voltage value generated by the resistance value between the drain and the source as a signal 4j when the current flows through the current detection element 4q. The on or off of the current detection element 4q is controlled by changing the gate voltage of the signal 4l from the control IC 4g.

If there is a problem that some or all of the switching elements 4a to 4f are short-circuited after the inverter power module 4 is mounted on the control board, the bus current 12 from the main circuit capacitor 3 The current value rises. When the current detection element 4h is used as in the first embodiment, it is necessary to coordinate design between the fuse 10 and the inverter power module 4 in order to prevent heat generation due to the line resistance of each wiring until the fuse 10 is blown. On the other hand, in the second embodiment, since the current detection element 4q, which is a switching element, is used, it is possible to cut off the bus current 12 by turning off the current detection element 4q. That is, since the bus 10 is provided with a means for cutting off the bus current 12, the fuse 10 and the inverter power module 4 do not need to be coordinated with each other.

FIG. 4 is a time chart illustrating the operation of the motor control device 102 according to the second embodiment. According to the motor control device 102, the following operations are possible.

The start-up sequence of the inverter power module 4 will be described with reference to FIG. The voltage from the AC power supply 1 is rectified by the bridge diode 2 to charge the main circuit capacitor 3. As a result, the voltage after rectification is smoothed, and a bus voltage, which is a DC voltage of the bus voltage terminal 7 with reference to the main circuit GND6, is generated. The power supply voltage 13a may be generated and reach the maximum value before the bus voltage reaches the maximum value. After that, when the signal 16 from the arithmetic unit 8 switches from the Low level to the High level at time t2, the state of the protection register (not shown) provided inside the control IC 4g changes from the High level to the Low level. When the state of the protection register transitions to the Low level, the control IC 4g changes the gate voltage of the current detection element 4q by changing the signal 4l so as to turn on the current detection element 4q at time t5. The signal 4l is a signal instructing the on state or the off state of the current detection element 4q. Further, the control IC 4g notifies the arithmetic unit 8 that the inverter operation is possible by switching the cutoff signal 4k from the Low level indicating the cutoff state to the High level indicating the non-cutoff state at time t5. The arithmetic unit 8 notified that the inverter operation is possible sends a signal pattern indicating the inverter operation to the control IC 4g using the signals 9a to 9f. In this way, the activation sequence of the inverter power module 4 is executed.

During the inverter operation started in this way, when the current value of the bus current 12 rises due to a short circuit failure of the switching elements 4a to 4f and the signal 4j indicating the current value reaches the cutoff set value 4n, the control IC 4g Outputs a cutoff signal 4k indicating a cutoff state to the arithmetic unit 8 and changes the signal 4l. The control IC 4g changes the gate voltage of the current detection element 4q by changing the signal 4l, and controls the current detection element 4q to the off state. By turning off the current detection element 4q, it is possible to prevent the excessive bus current 12 from continuing to flow.

Embodiment 3.
FIG. 5 is a block diagram showing the configuration of the motor control device 103 according to the third embodiment of the present invention. In the motor control device 103, the current detection element 4q of the motor control device 102 according to the second embodiment is replaced with the current detection element 4s. The current detection element 4s has a configuration in which switching elements having different characteristics of the loss generated with respect to the current are connected in parallel. Specifically, the current detection element 4s has a configuration in which a MOS-FET 41 and an IGBT (Insulated Gate Bipolar Transistor) 42 are connected in parallel. The control IC 4g detects the value of the bus current 12 by causing the control IC 4g to detect the voltage value generated at both ends of the parallel connection as the signal 4j when the current flows through the current detection element 4s. Further, a changeover switch 4r connected to the gate electrode of the MOS-FET 41 and the base of the IGBT 42 is installed in the inverter power module 4. The changeover switch 4r can switch whether to turn on the MOS-FET 41 or the IGBT 42 based on the signal 4l from the control IC 4g. Further, the changeover switch 4r can also turn on both the MOS-FET 41 and the IGBT 42 based on the signal 4l from the control IC 4g.

FIG. 6 is a graph showing the relationship between the loss of the current detection element 4s and the bus current 12 according to the third embodiment. The loss generated between the drain and the source of the MOS-FET 41 is the value obtained by multiplying the resistance value between the drain and the source by the square of the value of the bus current 12. Therefore, when the bus current 12 flowing through the current detection element 4s flows into the MOS-FET 41 by the changeover switch 4r, the relationship between the bus current 12 and the loss of the current detection element 4s changes in a quadratic function.

On the other hand, the loss due to the IGBT 42 is a value obtained by multiplying the saturation voltage Vce_sat generated between the collector and the emitter of the IGBT 42 and the value of the bus current 12. Therefore, when the bus current 12 flowing through the current detection element 4s flows into the IGBT 42 by the changeover switch 4r, the relationship between the bus current 12 and the loss of the current detection element 4s changes linearly.

Then, in FIG. 6, there exists a value i1 of the bus current 12 in which the magnitude relationship of the loss value is reversed due to the difference between the behavior of the linear function and the behavior of the quadratic function. Therefore, switching elements having different loss characteristics such as the current detection element 4s are arranged in parallel, and a changeover switch 4r is further provided to switch the element used when the bus current 12 reaches the value i1 to the one with the smaller loss. As a result, the occurrence of loss can be effectively suppressed. The changeover switch 4r may be controlled by either the control IC 4g or the arithmetic unit 8.

FIG. 7 is a graph showing the relationship between the loss of the current detection element 4s and the potential difference between both ends and the bus current 12 according to the third embodiment. The vertical axis of FIG. 7 shows the loss of the current detection element 4s and also shows the potential difference generated at both ends of the path of the bus current 12 of the current detection element 4s.

When the occurrence of the loss of the current detection element 4s is made smaller, the potential difference generated at both ends of the path of the bus current 12 of the current detection element 4s becomes smaller. In FIG. 7, in addition to the relationship between the loss of the current detection element 4s and the bus current 12, the saturation voltage Vce_sat generated between the collector and the emitter of the IGBT 42 and the resistance between the drain and the source of the MOS-FET 41, which are the potential differences, cause the potential difference. The relationship between the generated voltage Vds_r_on and the bus current 12 is also shown.

When the potential difference generated at both ends of the current detection element 4s becomes small, the signal 4j for the control IC 4g to detect and the signal 4p for which the signal 4j is amplified by the amplifier 4t also become small. As a result, the SN ratio with respect to the noise around the signal 4j and the signal 4p deteriorates, and the controllability of the arithmetic unit 8 becomes unstable. In that case, by utilizing the fact that elements having different loss characteristics are used, the changeover switch 4r is used to switch so that the element whose potential difference generated at both ends of the current detection element 4s is smaller than the SN ratio allowable value is not used. .. That is, in the region of a minute potential difference in which the SN ratio deteriorates, the changeover switch 4r is used to switch to use the element whose potential difference is equal to or larger than the SN ratio allowable value.

Specifically, in FIG. 7, when the bus current 12 becomes smaller than the value i0, the voltage Vds_r_on generated by the resistance between the drain and the source of the MOS-FET 41 becomes smaller than the SN ratio allowable value. Therefore, when the bus current 12 becomes smaller than the value i0, the changeover switch 4r switches to use the IGBT 42. As a result, when the value of the bus current 12 is small and the voltage Vds_r_on generated between the drain and the source of the MOS-FET 41 is small, the MOS-FET 41 is not used. That is, it becomes difficult to grasp an appropriate value of the bus current 12 due to the deterioration of the SN ratio, and it is possible to prevent the controllability of the arithmetic unit 8 from becoming unstable.

As described above, in the current detection element 4s of the motor control device 103 according to the third embodiment, the IGBT 42 is used when the bus current 12 is smaller than the value i0 and larger than the value i1, and in other cases. Uses MOS-FET 41. As a result, it is possible to suppress the occurrence of loss of the current detection element 4s, save power, and secure the controllability stability of the arithmetic unit 8.

FIG. 8 is a block diagram showing the configuration of the MCU 30 according to the first to third embodiments. The arithmetic unit 8 is realized by the MCU 30. The MCU 30 includes a CPU (Central Processing Unit) 31 that executes arithmetic and control, a RAM (Random Access Memory) 32 that the CPU 31 uses for a work area, a ROM (Read Only Memory) 33 that stores programs and data, and an external device. It includes an I / O (Input / Output) 34, which is hardware for exchanging signals, and a peripheral device 35 including an oscillator that generates a clock. The control executed by the arithmetic unit 8 described in the first to third embodiments is realized by the CPU 31 executing a program which is software stored in the ROM 33. The ROM 33 may be a non-volatile memory such as a rewritable flash memory.

The configuration shown in the above-described embodiment shows an example of the content of the present invention, can be combined with another known technique, and is one of the configurations as long as it does not deviate from the gist of the present invention. It is also possible to omit or change the part.

1 AC power supply, 2 bridge diode, 3 main circuit capacitor, 4 inverter power module, 4a-4f switching element, 4g control IC, 4h, 4q, 4s current detection element, 4j, 4p, 9a-9f, 11,16 signal, 4k cutoff signal, 4r, 14 changeover switch, 5 motor, 6 main circuit GND, 7 bus voltage terminal, 8 calculator, 10 fuse, 12 bus current, 13a, 13b power supply voltage, 15 control GND, 30 MCU, 31 CPU, 32 RAM, 33 ROM, 34 I / O, 35 peripheral device, 41 MOS-FET, 42 IGBT, 101-103 motor control device.

Claims (3)

Upper arm and lower arm switching elements for converting DC voltage to AC voltage and outputting to a motor, a drive circuit for driving the switching element, and a bus current connected to the switching element and flowing through the switching element. An inverter power module having a current detection element for detection, and
An arithmetic unit that outputs a signal for the drive circuit to control the switching element to the drive circuit based on the detection value of the current detection element.
Equipped with
The current detection element is
The first switching element and
A second switching element connected in parallel to the first switching element,
Changeover switch and
Equipped with
The voltage across the current detection element when the first switching element is selected is a first voltage value which is a lower limit voltage value at which the SN ratio can be tolerated when the bus current is smaller than the first current value. Smaller,
When the bus current is smaller than the second current value larger than the first current value, the loss of the first switching element is smaller than the loss of the second switching element, and the bus current is the second current. When it is larger than the value, the loss of the first switching element is larger than the loss of the second switching element.
The changeover switch is
When the bus current is smaller than the first current value, the second switching element is selected.
When the generatrix current is larger than the first current value and smaller than the second current value, the first switching element is selected.
A motor control device that selects the second switching element when the generatrix current is larger than the second current value . The motor control device according to claim 1, wherein the first switching element is a MOS-FET, and the second switching element is an IGBT. The motor control device according to claim 1 or 2 , wherein the changeover switch switches between the first switching element and the second switching element based on a signal from the drive circuit or the arithmetic unit.

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