Variable resistance circuit and control circuit

Abstract

To provide a variable resistance circuit capable of taking at least three resistance values by means of a novel circuit design.SOLUTION: The variable resistance circuit includes: a first resistor having a first input terminal and a first output terminal; a second resistor having a second input terminal and a second output terminal; a first switch for connecting between the first input terminal and the second input terminal; a second switch for connecting between the first output terminal and the second output terminal; and a third switch for connecting between the first output terminal and the second input terminal. The first input terminal is connected to a drive signal generation circuit for generating a drive signal for driving a main switching element, and the second output terminal is connected to a control terminal of the main switching element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to variable resistance circuits and control circuits. [Background technology]

[0002] Switching elements include bipolar transistors, field-effect transistors, thyristors, IGBTs (Insulated-Gate Bipolar Transistors), MOS (Metal Oxide Semiconductor) transistors, and other semiconductor elements with switching functions. Generally, a switching element has two main terminals called a collector and an emitter (or a source and a drain) and a control terminal called a gate (or a base). Based on a drive signal input to the control terminal, the switching element can selectively take a connected state in which the two main terminals are electrically connected and a disconnected state in which the two main terminals are electrically disconnected.

[0003] The voltage between the two main terminals of a switching element (hereinafter referred to as "terminal voltage") rises at a certain rate during the transition period from a connected state to a disconnected state (hereinafter referred to as the "transition period"). When the terminal voltage changes, a surge voltage occurs in which the terminal voltage during the transition period momentarily increases from the steady state. If the rate of change of the terminal voltage is large, this will result in an increase in the surge voltage. If this rate of change is small, this will result in increased power loss in the switching element. Generally, the rate of change of the terminal voltage can be adjusted by a resistor connected between the control terminal of the switching element and the drive signal generation circuit.

[0004] Patent Document 1 discloses a gate drive circuit including such a resistor. Specifically, the gate drive circuit includes a first resistor connected between a pulse generator and a gate output terminal of a switching element, and a second resistor connected in parallel to the first resistor. The second resistor has a higher resistance value than the first resistor. The gate drive circuit further includes a circuit that detects the rate of change of the voltage between the terminals of the switching element during a transition period, and a selector switch that connects one of the first resistor and the second resistor to the pulse generator in accordance with the rate of change. The selector switch first connects the first resistor, and if the rate of change of the voltage between the terminals during the transition period is less than a threshold, continues to connect the first resistor. If the rate of change of the voltage between the terminals during the transition period is equal to or greater than the threshold, connects the second resistor. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2017-220861 Summary of the Invention [Problem to be solved by the invention]

[0006] The gate drive circuit of Patent Document 1 includes a variable resistance circuit that selectively connects a first resistor and a second resistor connected in parallel. However, Patent Document 1 does not propose a variable resistance circuit that can take three or more resistance values. According to the circuit design of Patent Document 1, in order to take three or more resistance values, the variable resistance circuit would simply include three resistors connected in parallel and three switches. One objective of the present disclosure is to provide a variable resistance circuit that can take three or more resistance values ​​using a circuit design that differs from such conventional circuit designs.

[0007] Furthermore, switching elements must be designed so that the terminal voltage does not exceed the breakdown voltage of the switching element even when a surge voltage occurs. While reducing the rate of change of the terminal voltage is one possible solution, reducing the rate of change of the terminal voltage increases power loss in the switching element. Furthermore, because switching elements are sometimes used in applications where the current flowing between two main terminals varies depending on the situation, it is preferable to provide a control circuit for the switching element that can adapt to surge voltages that vary depending on the situation. Another object of the present disclosure is to provide a control circuit that adapts to variable surge voltages and suppresses power loss in the switching element while preventing the terminal voltage from exceeding the breakdown voltage of the switching element. [Means for solving the problem]

[0008] A variable resistance circuit according to one embodiment of the present disclosure includes a first resistor having a first input terminal and a first output terminal, a second resistor having a second input terminal and a second output terminal, a first switch connected between the first input terminal and the second input terminal, a second switch connected between the first output terminal and the second output terminal, and a third switch connected between the first output terminal and the second input terminal. The first input terminal is connected to a drive signal generating circuit that generates a drive signal for driving a main switching element. The second output terminal is connected to a control terminal of the main switching element.

[0009] A control circuit according to another aspect of the present disclosure changes the inter-terminal voltage of the main switching element at a first rate of change during a first period within a transition period during which the main switching element transitions from a connected state in which the two main terminals of the main switching element are electrically connected to a disconnected state in which the two main terminals of the main switching element are electrically disconnected, and changes the inter-terminal voltage of the main switching element at a second rate of change different from the first rate of change during a second period following the first period within the transition period. The second rate of change is controlled to be equal to or less than the first rate of change. The control circuit identifies a surge voltage included in the inter-terminal voltage, and adjusts the second rate of change to a smaller value as the surge voltage increases. [Effects of the Invention]

[0010] According to one aspect of the present disclosure, a variable resistance circuit capable of taking three or more resistance values ​​using a novel circuit design can be provided. According to another aspect of the present disclosure, a control circuit capable of adapting to variable surge voltages can be provided. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a circuit diagram illustrating a driving circuit for a switching element according to an embodiment of the present disclosure. [Figure 2] 5 is a flowchart showing control of switching elements according to a first control example of the present disclosure. [Figure 3] 6 is a timing chart showing the voltage between terminals of a switching element according to a first control example of the present disclosure. [Figure 4] 10 is a flowchart showing control of switching elements according to a second control example of the present disclosure. [Figure 5] 10 is a timing chart showing the voltage between terminals of a switching element according to a second control example of the present disclosure. [Figure 6] 10 is a flowchart showing control of switching elements according to a third control example of the present disclosure. [Figure 7] 10 is a timing chart showing the voltage between terminals of a switching element according to a third control example of the present disclosure. [Figure 8] 10 is a map showing the relationship between the rotational torque of the motor, the rotation speed of the motor, and the current of the motor according to a fourth control example of the present disclosure. [Figure 9] 10 is a flowchart showing control of switching elements according to a fourth control example of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] (Circuit configuration)

[0014] 1, the main switching element 14 has a first main terminal 14a, a second main terminal 14b, and a control terminal 14c. The first main terminal 14a is connected to a power supply terminal 11 via a load 13. The second main terminal 14b is connected to a ground terminal. The control terminal 14c is connected to a drive circuit 10 that drives the main switching element 14.

[0015] The drive circuit 10 includes a drive signal generating circuit 15 and a variable resistance circuit 16 connected between the drive signal generating circuit 15 and a control terminal 14c of the main switching element 14.

[0016] The drive signal generation circuit 15 generates a drive signal that specifies the connection state or disconnection state of the main switching element 14. The drive signal is, for example, a pulse signal that includes a high level that puts the main switching element 14 in the connection state and a low level that puts the main switching element 14 in the disconnection state.

[0017] The variable resistance circuit 16 is provided between the drive signal generating circuit 15 and the control terminal 14c of the main switching element 14 (drive signal path), and includes a first resistor 17 having a first input terminal N11 and a first output terminal N12, and a second resistor 18 having a second input terminal N21 and a second output terminal N22. The second resistor 18 may have the same resistance value as the first resistor 17, but preferably has a different resistance value. In this embodiment, the second resistor 18 has a higher resistance value than the first resistor 17.

[0018] The variable resistance circuit 16 further includes a first switch 19 connected between the first input terminal N11 and the second input terminal N21, a second switch 20 connected between the first output terminal N12 and the second output terminal N22, and a third switch 21 connected between the first output terminal N12 and the second input terminal N21. The first switch 19, the second switch 20, and the third switch 21 may be configured using, for example, transistors. The first input terminal N11 is connected to the drive signal generating circuit 15. The second output terminal N22 is connected to the control terminal 14c of the main switching element 14. It is desirable that the first switch 19 transitions from a connected state to a disconnected state (or from a disconnected state to a connected state) in a transition period shorter than that of the main switching element 14. The same applies to the second switch 20 and the third switch 21.

[0019] The variable resistance circuit 16 can take the following four states regarding the resistance value.

[0020] (1) Lowest resistance state: The first resistor 17 and the second resistor 18 are connected in parallel to each other in the drive signal path. At this time, the first switch 19 is on, the second switch 20 is on, and the third switch 21 is off.

[0021] (2) Low resistance state: Only the first resistor 17 is inserted in the drive signal path. At this time, the first switch 19 is off, the second switch 20 is on, and the third switch 21 is off.

[0022] (3) High resistance state: Only the second resistor 18 is inserted in the drive signal path. At this time, the first switch 19 is on, the second switch 20 is off, and the third switch 21 is off.

[0023] (4) Highest resistance state: The first resistor 17 and the second resistor 18 are serially inserted in the drive signal path. At this time, the first switch 19 is off, the second switch 20 is off, and the third switch 21 is on.

[0024] The drive circuit 10 further includes a control circuit 22 that generates a resistance control signal S2 for controlling the resistance state of the variable resistance circuit 16. As described above, the main switching element 14 transitions from a connected state to a disconnected state within a transition period. The control circuit 22 may control the variable resistance circuit 16 to assume a plurality of different resistance states within the transition period of the main switching element 14.

[0025] The control circuit 22 may receive a surge voltage signal S1 indicating the surge voltage of the main switching element 14, identify the surge voltage based on the surge voltage signal S1, and generate a resistance control signal S2 based on this surge voltage. The surge voltage signal S1 may be generated based on a measured value of the voltage across the main switching element 14, or may be generated based on a predicted value of the voltage across the main switching element 14.

[0026] The drive circuit 10 may further include a temperature sensor 23 that detects the temperature of the main switching element 14 and generates a temperature signal S3 indicating the temperature of the main switching element. The temperature sensor 23 is attached, for example, to the housing of the main switching element 14. The control circuit 22 may receive the temperature signal S3 from the temperature sensor 23, identify the temperature based on the temperature signal S3, and generate the resistance control signal S2 based on this temperature. The control circuit 22 may also generate the resistance control signal S2 based on a combination of the surge voltage and temperature of the main switching element 14.

[0027] The following describes specific operations (first to fourth control examples) of the control circuit 22. Note that from the second control example onwards, explanations of overlapping matters will be avoided.

[0028] (First control example)

[0029] 2, the control circuit 22 identifies the surge voltage of the main switching element 14 (step 101). For example, the control circuit 22 may receive a surge voltage signal S1 at a fixed sampling period and identify the surge voltage based on this surge voltage signal S1.

[0030] If the surge voltage is equal to or lower than the threshold (step 102, YES), the control circuit 22 executes two-stage switching control (low resistance → high resistance) (step 103), and if the surge voltage exceeds the threshold (step 102, NO), the control circuit 22 executes two-stage switching control (low resistance → highest resistance) (step 104). The transition period of the main switching element 14 includes a first period and a second period following the first period. The lengths of the first period and the second period may be predetermined.

[0031] In the two-stage switching control (low resistance → high resistance) of step 103, the control circuit 22 sets the variable resistance circuit 16 to a low resistance state during the first period and to a high resistance state during the second period. As a result, as shown in FIG. 3(a), during the first period (t1 to t2), the rate of change (first rate of change) of the voltage across the terminals of the main switching element 14 is a rate of change V1a, and during the second period (t2 to t3), the rate of change (second rate of change) of the voltage across the terminals of the main switching element 14 is a rate of change V2a, which is smaller than the rate of change V1a. The rate of change V1a is less effective at suppressing surge voltages than the rate of change V2a. However, because the surge voltage is originally below the threshold, the surge voltage is less likely to exceed the withstand voltage of the main switching element 14. On the other hand, the rate of change V1a enables a reduction in power loss in the main switching element 14 compared to the rate of change V2a.

[0032] On the other hand, in the two-stage switching control (low resistance → highest resistance) of step 104, the control circuit 22 sets the variable resistance circuit 16 to the low resistance state in the first period and sets the variable resistance circuit 16 to the highest resistance state in the second period. As a result, as shown in Fig. 3(b), in the first period (t1 to t2), the rate of change of the voltage between the terminals of the main switching element 14 is a rate of change V1a, and in the second period (t2 to t3), the rate of change of the voltage between the terminals of the main switching element 14 is a rate of change V2b, which is smaller than the rate of change V2a.

[0033] In this control example, the inter-terminal voltage during the first period is fixed at a rate of change V1a, and the inter-terminal voltage during the second period can have a rate of change V2a or V2b. However, this is not limiting, and the control circuit 22 may adjust the rate of change of the inter-terminal voltage during the first period and fix the rate of change of the inter-terminal voltage during the second period. Alternatively, the control circuit 22 may adjust both the rate of change of the inter-terminal voltage during the first period and the rate of change of the inter-terminal voltage during the second period. In these cases, the larger the surge voltage, the larger the resistance value selected.

[0034] In this way, the control circuit 22 adjusts the rate of change of the inter-terminal voltage during the first period and the rate of change of the inter-terminal voltage during the second period in response to the surge voltage. In this embodiment, the control circuit 22 adjusts the rate of change of the inter-terminal voltage by controlling the resistance value of the variable resistance circuit 16. The rate of change can be three different rates: rate of change V1a during the first period, and two rates of change V2a and V2b during the second period. In other words, three different resistance values ​​are required for the variable resistance circuit 16. In this case, while a conventional variable resistance circuit 16 would need to be provided with three resistors, the variable resistance circuit 16 of this embodiment can switch between up to four different resistance values ​​using two resistors.

[0035] (Second control example)

[0036] 4, the control circuit 22 determines the surge voltage and temperature of the main switching element 14 (step 201). For example, the control circuit 22 may receive a surge voltage signal S1 at a fixed sampling period and determine the surge voltage based on this surge voltage signal S1. The control circuit 22 may receive a temperature signal S3 at a fixed sampling period and determine the temperature of the main switching element 14 based on this temperature signal S3.

[0037] When the surge voltage exceeds the threshold value (step 202, NO), the control circuit 22 executes two-stage switching control (low resistance → high resistance) in the same manner as in the first control example (step 203).

[0038] If the surge voltage is equal to or lower than the threshold (step 202, YES) and the temperature exceeds the threshold (step 204, NO), the control circuit 22 executes two-stage switching control (minimum resistance → low resistance) (step 205). In the two-stage switching control (minimum resistance → low resistance) of step 205, the control circuit 22 sets the variable resistance circuit 16 to the minimum resistance state in the first period and to the low resistance state in the second period. As a result, as shown in FIG. 5(c), the voltage across the main switching element 14 has a rate of change V1b in the first period (t1 to t2), and a rate of change V1a, which is smaller than the rate of change V1b, in the second period (t2 to t3). The rate of change V1b enables the temperature rise of the main switching element 14 to be suppressed more effectively than the rate of change V1a. At this time, by setting the rate of change of the inter-terminal voltage of the main switching element 14 to rate of change V1a in the second period, the surge voltage can be prevented from exceeding the withstand voltage of the main switching element 14.

[0039] If the surge voltage exceeds the threshold (step 202, NO) and the temperature is equal to or lower than the threshold (step 204, YES), the control circuit 22 does not perform switching control (step 206). That is, in this embodiment, the rate of change in the first period and the rate of change in the second period can be the same value.

[0040] (Third Modification)

[0041] As shown in FIG. 6, the control circuit 22 identifies the surge voltage included in the inter-terminal voltage of the main switching element 14 and the temperature of the main switching element 14 (step 301).

[0042] If the surge voltage is equal to or lower than the threshold (step 302, YES), the control circuit 22 does not perform switching control (step 303). In this control example, the control circuit 22 sets the variable resistance circuit 16 to a low resistance state over the entire range of the transition period. As a result, the voltage across the main switching element 14 changes at a rate of V1a, as shown in FIG. 7(a).

[0043] If the surge voltage exceeds the threshold value (step 302, NO) and the temperature is equal to or lower than the threshold value (step 304, YES), the control circuit 22 executes two-stage switching control (step 305). In the two-stage switching control of step 305, the control circuit 22 sets the variable resistance circuit 16 to a low resistance state in a first period and sets the variable resistance circuit 16 to a high resistance state in a second period. As a result, as shown in FIG. 7(b), the voltage across the main switching element 14 has a rate of change of V1a in the first period (t1 to t2b), and a rate of change of V2a in the second period (t2b to t3).

[0044] If the surge voltage exceeds the threshold (step 302, NO) and the temperature exceeds the threshold (step 304, NO), the control circuit 22 executes two-stage switching control and timing control (step 306). In the timing control of step 306, the control circuit 22 lengthens the first period and shortens the second period. In the two-stage switching control of step 306, the control circuit 22 sets the variable resistance circuit 16 to a low resistance state in the first period and a high resistance state in the second period. As a result, as shown in FIG. 7(c), the voltage across the main switching element 14 has a rate of change V1a in the first period (t1 to t2c), and a rate of change V2a in the second period (t2c to t3). The timing control in step 306 prolongs the state in which the rate of change of the terminal voltage of main switching element 14 is large, and therefore can reduce power loss in main switching element 14 and reduce the temperature rise of main switching element 14 compared to the two-stage switching control in step 305. Therefore, if the temperature exceeds the threshold value, the first period is lengthened to suppress any further temperature rise.

[0045] Note that extending the first period and shortening the second period makes it easier for the surge voltage to exceed the breakdown voltage of the main switching element 14. Therefore, when extending the first period and shortening the second period, it is preferable to reduce the rate of change of the voltage across the main switching element 14 during the second period. For example, if the surge voltage exceeds the threshold (NO in step 302) and the temperature is equal to or lower than the threshold (YES in step 304), the control circuit 22 sets the variable resistance circuit 16 to a low resistance state during the first period and a high resistance state during the second period. On the other hand, if the surge voltage exceeds the threshold (NO in step 302) and the temperature exceeds the threshold (NO in step 304), the control circuit 22 extends the first period and shortens the second period, and sets the variable resistance circuit 16 to a low resistance state during the first period and a highest resistance state during the second period. As a result, when the temperature exceeds the threshold value, the first period is longer and the second period is shorter than when the temperature is equal to or lower than the threshold value, and the rate of change in the voltage between the terminals of the main switching element 14 during the second period is smaller. This makes it possible to prevent the surge voltage from exceeding the withstand voltage of the main switching element 14.

[0046] (Fourth control example)

[0047] In this control example, the surge voltage signal S1 is a motor control command indicating the rotational torque and rotation speed required of the motor. The main switching element 14 may be connected to a motor. In this embodiment, the main switching element 14 is connected to a traction motor of an electric vehicle. For example, the main switching element 14 is built into a three-phase inverter connected between a DC power source and a three-phase AC motor. The three-phase inverter includes a three-phase bridge consisting of six main switching elements 14 and a control circuit 22. The control circuit 22 receives the motor control command, determines an AC frequency and a current value based on the motor control command, and pulse-width controls the six main switching elements 14 to generate a three-phase AC current having the AC frequency and current value.

[0048] The control circuit 22 may include a map correlating rotational torque, rotation speed, and current value, as shown in Fig. 8. The control circuit 22 may determine the target rotational torque and target rotation speed based on the motor control command, and determine the current value based on the combination of the target rotational torque and target rotation speed. If the motor is a traction motor for an electric vehicle, the target rotational torque and target rotation speed are determined based on the required torque and vehicle speed of the electric vehicle.

[0049] The larger the current flowing through the three-phase AC motor, the larger the surge voltage that is likely to be included in the voltage between the terminals of the main switching element 14. Therefore, the control circuit 22 may determine the current value based on a combination of the rotational torque and the rotational speed, and then determine the surge voltage based on this current value.

[0050] As shown in FIG. 9, the control circuit 22 receives a motor control command (step 401), and identifies a surge voltage based on the motor control command (step 402).

[0051] If the surge voltage is equal to or lower than the threshold (step 403, YES), the control circuit 22 does not perform switching control (step 404). In this control example, the control circuit 22 keeps the variable resistance circuit 16 in the low resistance state over the entire range of the transition period.

[0052] If the surge voltage exceeds the threshold value (step 403, NO), the control circuit 22 executes two-stage switching control (step 405). In the two-stage switching control of step 405, the control circuit 22 sets the variable resistance circuit 16 to a low resistance state in a first period and sets the variable resistance circuit 16 to a high resistance state in a second period.

[0053] In this way, the control circuit 22 may determine the surge voltage based on the combination of the rotational torque and rotational speed required of the motor.

[0054] In this control example, the variable resistance circuit 16 need only be capable of selectively taking on two different resistance values, and does not necessarily need to have the circuit configuration shown in FIG.

[0055] The motor drive device may include a variable resistance circuit 16 connected between a control terminal of a main switching element 14 and a drive signal generating circuit 15, the variable resistance circuit 16 being capable of selectively taking on a first resistance value or a second resistance value greater than the first resistance value, and a control circuit 22 connected to the variable resistance circuit 16. The control circuit 22 receives a command indicating a rotational torque and rotation speed required of the motor. The control circuit 22 determines the rotational torque and rotation speed based on the command. The control circuit 22 determines a surge voltage contained in the voltage between the two main terminals of the main switching element 14 based on the combination of the rotational torque and rotation speed. If the surge voltage is equal to or less than a threshold, the control circuit 22 controls the variable resistance circuit 16 to select the first resistance value. If the surge voltage exceeds the threshold, the control circuit 22 controls the variable resistance circuit 16 to select the second resistance value.

[0056] The method of identifying a surge voltage in the fourth control example is also applicable to the first to third control examples.

[0057] The DC power supply, motor, and inverter may be implemented in, for example, an electric vehicle and a plug-in hybrid electric vehicle (PHEV). FIG. 8 shows classification of current into a small current region A1, a medium current region A2, and a large current region A3 according to the magnitude of the current. The small current region A1 corresponds to, for example, driving in a city. The medium current region A2 corresponds to, for example, driving in a suburban area. The large current region A3 corresponds to, for example, driving on a highway.

[0058] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications are possible within the scope of the gist of the invention. In particular, the multiple modifications described in this specification can be combined as needed. [Explanation of symbols]

[0059] 10: drive circuit, 14: main switching element, 14c: control terminal, 15: drive signal generating circuit, 16: variable resistance circuit, 17: first resistor, 18: second resistor, 19: first switch, 20: second switch, 21: third switch, 22: control circuit, 23: temperature sensor

Claims

1. a first resistor having a first input terminal and a first output terminal; a second resistor having a second input terminal and a second output terminal; a first switch connected between the first input terminal and the second input terminal; a second switch connected between the first output terminal and the second output terminal; a third switch connected between the first output terminal and the second input terminal; the first input terminal is connected to a drive signal generating circuit that generates a drive signal for driving the main switching element; the second output terminal is connected to a control terminal of the main switching element; Variable resistor circuit.

2. a control circuit that changes a voltage across the terminals of a main switching element at a first rate of change during a first period within a transition period during which a transition occurs from a connection state in which two main terminals of the main switching element are electrically connected to a disconnection state in which the two main terminals of the main switching element are electrically disconnected, and that changes the voltage across the terminals of the main switching element at a second rate of change during a second period subsequent to the first period within the transition period, the second rate of change is controlled to be equal to or less than the first rate of change; Identifying a surge voltage included in the terminal voltage; The larger the surge voltage, the smaller the second rate of change is adjusted to be. Control circuit.

3. The control circuit further comprises: Identifying the temperature of the main switching element; The second rate of change is adjusted to a smaller value as the surge voltage increases, and the first rate of change is adjusted to a larger value as the temperature of the main switching element increases.

3. The control circuit of claim 2.

4. The control circuit further comprises: Identifying the temperature of the main switching element; The higher the temperature of the main switching element, the longer the length of the first period.

3. The control circuit of claim 2.

5. The control circuit further comprises: When the temperature of the main switching element is equal to or higher than a predetermined value, the length of the first period is increased and the second rate of change in the second period is decreased.

5. The control circuit of claim 4.

6. The control circuit further comprises: obtaining a command indicating a target rotational torque and a target rotational speed required for a motor connected to the main switching element; specifying the magnitude of the surge voltage in accordance with a combination of the target rotational torque and the target rotational speed; 3. The control circuit of claim 2.

7. a variable resistance circuit connected between a drive signal generating circuit that generates a drive signal for driving the main switching element and a control terminal of the main switching element; the control circuit adjusts the second rate of change by adjusting the resistance value of the variable resistance circuit. The control circuit according to any one of claims 2 to 5.

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