Control device for power conversion device and control method for power conversion device

Abstract

To provide a control device that suppresses continuous overload current flow to a switching element of a power conversion device.SOLUTION: In a control method for a power conversion device 1 using a switching element Q1 that applies a pulse width modulation voltage having a predetermined amplitude of a first control voltage Vg1 to a control electrode of the switching element Q1 and generates an operational signal Vc based on an element current Id flowing to a main electrode of the switching element Q1, if the operational signal Vc reaches a first reference value Vc1, the element current Id is suppressed by limiting the amplitude to a second control voltage Vg2 smaller than the first control voltage Vg1, and if the operational signal Vc reaches a second reference value Vc2 greater than the first reference value Vc1 before a predetermined suppress time ΔT1 after limiting to the second control voltage Vg2 elapses, the element current is further suppressed by limiting the amplitude to a third control voltage Vg3 smaller than the second control voltage Vg2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a control device for a power conversion device and a control method for a power conversion device. [Background technology]

[0002] Patent Document 1 describes a protection circuit for a power conversion device that detects a short circuit in a switching element and turns off the switching element to protect the switching element. The protection circuit for the power conversion device in Patent Document 1 reduces the gate voltage of the switching element when an overcurrent occurs in the switching element and measures the duration of the overcurrent state of the switching element using a timer. To prevent erroneous determination, the protection circuit for the power conversion device determines that a short circuit has occurred if the overcurrent state of the switching element has continued for a certain period of time and turns off the switching element. On the other hand, if the overcurrent state of the switching element no longer continues within the certain period of time, the protection circuit for the power conversion device increases the gate voltage to its original value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-012755 Summary of the Invention [Problem to be solved by the invention]

[0004] In the protection device for a power conversion device described in Patent Document 1, in order to prevent erroneous judgment, if an overcurrent state of a switching element continues for a certain period of time, it is judged to be a short circuit and the switching element is turned off. Therefore, there is a problem in that an overcurrent continues to flow through the switching element for the certain period of time, which may cause damage to the switching element.

[0005] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a control device for a power conversion device and a control method for a power conversion device that can suppress the continuous flow of overcurrent through the switching elements of the power conversion device. [Means for solving the problem]

[0006] A control method for a power conversion device according to one aspect of the present invention applies a pulse-width modulated voltage having a predetermined amplitude of a first control voltage to a control electrode of a switching element, and generates an operating signal based on an element current flowing through a main electrode of the switching element. When the operating signal reaches a first reference value, the amplitude is limited to a second control voltage smaller than the first control voltage to suppress the element current. If the operating signal reaches a second reference value larger than the first reference value before a predetermined suppression time has elapsed since limiting the operating signal to the second control voltage, the amplitude is limited to a third control voltage smaller than the second control voltage to further suppress the element current. [Effects of the Invention]

[0007] According to the control device for a power converter and the control method for a power converter of the present invention, it is possible to prevent an overcurrent from continuously flowing through a switching element of the power converter. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a circuit diagram showing an example of a power conversion device to which a control device according to an embodiment is applied. [Figure 2] FIG. 2 is a circuit diagram illustrating an example of a control voltage suppression unit of the control device according to the embodiment. [Figure 3] FIG. 3 is a time chart illustrating a first operation of the control device according to the embodiment. [Figure 4] FIG. 4 is a time chart illustrating a second operation of the control device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] A protection device for a power conversion device according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same parts are given the same reference numerals and the description thereof will be omitted.

[0010] An example of a power conversion device to which a control device according to an embodiment is applied will be described with reference to FIGS.

[0011] The power conversion device 1 is mounted on, for example, an electric vehicle and performs power conversion between a DC power source 2 and a three-phase motor M, which is an AC load. The power conversion device 1 will be described using a bidirectional three-phase inverter circuit equipped with multiple switching elements Q1-Q6. However, the present invention is not limited to this, and the power conversion device 1 may be, for example, a unidirectional single-phase inverter equipped with multiple switching elements. The AC load is not limited to a motor, and any AC load can be used. In the embodiment, N-channel MOSFETs are used as the switching elements Q1-Q6, but the present invention is not limited to this, and power semiconductor elements such as IGBTs can be used.

[0012] The power conversion device 1 converts DC power supplied from a DC power source 2 into AC power to drive a three-phase motor M, and also converts AC power supplied from the three-phase motor M into DC power to charge the DC power source 2. The DC power source 2 may be, for example, a lithium-ion battery, which is a rechargeable secondary battery. The DC voltage V0 output from the DC power source 2 is, for example, 400 V. The three-phase AC voltage of the three-phase motor M has an effective value of, for example, 100 V and a low frequency of, for example, 50 Hz.

[0013] The power conversion device 1 includes a smoothing capacitor C0, a first upper and lower arm S1, a second upper and lower arm S2, and a third upper and lower arm S3, each connected in parallel to a DC power supply 2. The first upper and lower arm S1 includes a switching element Q1 as an upper arm element and a switching element Q2 as a lower arm element connected in series, with the junction of the switching elements Q1 and Q2 forming a U-phase electrode U of three-phase AC. The second upper and lower arm S2 includes a switching element Q3 as an upper arm element and a switching element Q4 as a lower arm element connected in series, with the junction of the switching elements Q3 and Q4 forming a V-phase electrode V of three-phase AC. The third upper and lower arm S3 includes a switching element Q5 as an upper arm element and a switching element Q6 as a lower arm element connected in series, with the junction of the switching elements Q5 and Q6 forming a W-phase electrode W of three-phase AC. The U-phase electrode U, V-phase electrode V, and W-phase electrode W of the three-phase AC are connected to power supply terminals of a three-phase motor M, which serves as an AC load.

[0014] A control device 4 for controlling the switching elements Q1-Q6 is connected to the gate electrode G, which is the control electrode of each of the switching elements Q1-Q6. In order to avoid complicating the circuit diagram, Fig. 1 shows the state in which the control device 4 is connected only to the gate electrode G of the switching element Q1, and the configuration of the switching elements Q2-Q6 is omitted. In the following, an example in which the control device 4 controls the switching element Q1 will be described, but the switching elements Q2-Q6 are configured in a similar manner.

[0015] The control device 4 includes a drive circuit unit 5, an overcurrent detection unit 6, a control voltage suppression unit 7, and an overcurrent determination unit 8. The drive circuit unit 5 applies a high-frequency pulse-width modulated voltage having a predetermined amplitude of a first control voltage Vg1, generated based on a high-frequency carrier voltage of, for example, several hundred kHz, to the gate electrode G of the switching element Q1 as a control voltage, i.e., a gate voltage Vg. The predetermined first control voltage Vg1 is a value sufficient to fully turn on the switching element Q1, e.g., 18.0 V. This allows the switching element Q1 to perform an operation suitable for DC-AC power conversion for supplying power from a DC power source 2 to a three-phase motor M or from the three-phase motor M to the DC power source 2. The basic operation of a bidirectional three-phase inverter circuit including multiple switching elements Q1-Q6 is well known, and therefore a detailed description thereof will be omitted here.

[0016] The overcurrent detection unit 6 generates an operation signal Vc based on the drain current Id, which is the element current flowing through the drain electrode D, which is the first main electrode of the switching element Q1. The operation signal Vc is transmitted to the inputs of the control voltage suppression unit 7 and the overcurrent determination unit 8.

[0017] The control voltage suppression unit 7 is turned on when the operating signal Vc reaches the first reference value Vc1 and limits the amplitude of the pulse-width modulated voltage applied to the gate electrode of the switching element Q1 to a second control voltage Vg2, which is smaller than the first control voltage Vg1, for a predetermined suppression time ΔT1. The second control voltage Vg2 is adjusted so that the switching element Q1 is not completely turned off. By limiting the second control voltage Vg2 to a value smaller than the first control voltage Vg1, an increase in the drain current Id of the switching element Q1 is suppressed, and heat generation by the switching element Q1 is also suppressed. If the operating signal Vc does not reach the second reference value Vc2, which is larger than the first reference value Vc1, during the suppression time ΔT1, the control voltage suppression unit 7 is turned off, and the amplitude of the pulse-width modulated voltage applied by the drive circuit unit 5 to the gate electrode of the switching element Q1 returns to the first control voltage Vg1.

[0018] When the operating signal Vc reaches the second reference value Vc2 within the suppression time ΔT1, the overcurrent determination unit 8 determines that an overcurrent is occurring and limits the amplitude of the pulse-width modulated voltage applied to the gate electrode of the switching element Q1 to a third control voltage Vg3, which is lower than the second control voltage Vg2. For example, if the overcurrent determination unit 8 sets the amplitude of the pulse-width modulated voltage applied to the gate electrode of the switching element Q1 by the drive circuit unit 5 to the third control voltage Vg3=0, the operation of the switching element Q1 is turned off and the drain current Id becomes zero. Furthermore, for example, when the operating signal Vc becomes smaller than the first reference value Vc1, the overcurrent determination unit 8 turns off and the amplitude of the pulse-width modulated voltage applied to the gate electrode of the switching element Q1 by the drive circuit unit 5 returns to the first control voltage Vg1.

[0019] Next, the configuration of the overcurrent detection unit 6 in the control device 4 according to the embodiment will be described in more detail. The overcurrent detection unit 6 includes a diode D1, a resistor R1, a capacitor C1, and a constant current source .

[0020] The cathode of diode D1 is connected to the drain electrode, which is the first main electrode, of switching element Q1. Resistor R1 has a first end connected to the anode of diode D1 and a second end connected to the inputs of control voltage suppression unit 7 and overcurrent determination unit 8. Capacitor C1 is connected between the connection point of the second end of resistor R1 and the inputs of control voltage suppression unit 7 and overcurrent determination unit 8 and ground potential. Constant current source 10 is connected between the connection point of the second end of resistor R1 and the inputs of control voltage suppression unit 7 and overcurrent determination unit 8 and ground potential, and outputs DC current I1.

[0021] When no drain current Id flows through the switching element Q1, the DC current I1 from the constant current source 10 flows through the resistor R1 and the diode D1 to the drain electrode of the switching element Q1. Therefore, the operation signal Vc, which is the input voltage of the control voltage suppression unit 7 and the overcurrent detection unit 8, is zero. The potential V1 at the junction of the resistor R1 and the diode D1 is I1·R1, which is the product of the DC current I1 and the resistance R1 of the resistor R1. When the switching element Q1 is turned on and the drain current Id flows, a drain potential Vd is generated. When the drain potential Vd exceeds the potential V1 at the junction of the resistor R1 and the diode D1, the DC current I1 from the constant current source 10 no longer flows beyond the diode D1, and the capacitor C1 is charged by the DC current I1. Therefore, the operation signal Vc increases over time depending on the DC current I1 and the capacitance C1 of the capacitor C1. Furthermore, as the drain current Id decreases, the drain potential Vd becomes smaller than the potential V1 at the junction between the resistor R1 and the diode D1. This causes the DC current I1 to flow through the resistor R1 and the diode D1 to the drain electrode of the switching element Q1. As a result, the operating signal Vc becomes zero again. In the overcurrent detection unit 6 configured as above, the time ΔT2 until the operating signal Vc reaches the second reference value Vc2 is set according to the DC current I1 and the capacitance C1 of the capacitor C1. This time ΔT2 should be set to a time shorter than the suppression time ΔT1 and long enough to prevent the switching element Q1 from being damaged by the overcurrent.

[0022] However, the configuration of the overcurrent detection unit 6 is not limited to this. For example, the same operation can be achieved even if the constant current source 10 is replaced with a constant voltage source. Also, for example, any one of the drain current Id, drain potential Vd, and drain-source voltage Vds of the switching element Q1 may be measured, and a voltage proportional to the measured value may be output as the operation signal Vc.

[0023] Next, the configuration of the control voltage suppression unit 7 in the control device 4 according to the embodiment will be described in more detail. The control voltage suppression unit 7 includes a suppression start determination unit 11, a suppression time adjustment unit 12, and a suppression voltage generation unit 13.

[0024] The suppression start determination unit 11 includes a comparator CP and a series circuit of resistors Ra and Rb connected between a DC potential Ve and a source electrode S, which is a second main electrode of the switching element Q1. The positive input terminal + of the comparator CP serves as an input to the control voltage suppression unit 7 and receives an operation signal Vc. The negative input terminal − of the comparator CP is connected to the junction of the resistors Ra and Rb and receives a first reference value Vc1, which is set by the DC potential Ve, the resistance value Ra of the resistor Ra, and the resistance value Rb of the resistor Rb. The output of the comparator CP is an L signal (e.g., 0 V) when the operation signal Vc is smaller than the first reference value Vc1, and is an H signal (e.g., 18 V) when the operation signal Vc is equal to or greater than the first reference value Vc1. The output of the comparator CP is connected to the input of the suppression time adjustment unit 12.

[0025] The suppression time adjustment unit 12 includes a circuit configured with a capacitor C2 and a resistor R2. The capacitor C2 is connected between the output of the comparator CP and the input of the suppression voltage generation unit 13. The resistor R2 is connected between the connection point of the capacitor C2 and the input of the suppression voltage generation unit 13 and the source electrode of the switching element Q1. The suppression time adjustment unit 12 sets a predetermined suppression time ΔT1 based on the time constant of the circuit configured with the capacitor C2 and the resistor R2. Note that the suppression time adjustment unit 12 may be a circuit using a general-purpose IC or a timer circuit. However, by using only the capacitor C2 and the resistor R2 as shown in FIG. 2, the circuit size can be reduced compared to using a general-purpose IC or a timer circuit.

[0026] The suppression voltage generator 13 includes a series circuit of a constant voltage diode Dz, a resistor R3, and a switching element Q7. In this embodiment, the switching element Q7 is an N-channel MOSFET, but this is not limited to this. A power semiconductor element such as an IGBT can also be used. The cathode of the constant voltage diode Dz is connected to the connection point between the output of the drive circuit 5 and the gate electrode G of the switching element Q1. The resistor R3 is connected to the anode of the constant voltage diode Dz and the drain electrode of the switching element Q7. The source electrode of the switching element Q7 is connected to the source electrode S of the switching element Q1. The gate electrode of the switching element Q7 serves as the input to the suppression voltage generator 13. The constant voltage Vz of the constant voltage diode Dz sets the second control voltage Vg2. Using a low-resistance resistor R3 allows for rapid discharge of charge accumulated between the gate and source of the switching element Q1, making it possible to rapidly limit the gate voltage Vg of the switching element Q1 from the first control voltage Vg1 to the second control voltage Vg2 with a small circuit scale. When the gate voltage input to the gate electrode of switching element Q7 switches from an L signal to an H signal, switching element Q7 turns on and becomes conductive, causing the amplitude of the output pulse voltage of drive circuit unit 5 connected to the gate electrode of switching element Q1 to rapidly decrease from the first control voltage Vg1 and be limited to the second control voltage Vg2 set by constant voltage diode Dz.

[0027] When the operating signal Vc reaches the first reference value Vc1, the control voltage suppression unit 7 can quickly reduce the amplitude applied to the gate electrode of the switching element Q1 to a second control voltage Vg2 that is smaller than the first control voltage Vg1, and limit it for a predetermined suppression time ΔT1.

[0028] Next, a first operation of the control device 4 will be described with reference to FIG.

[0029] The output of the drive circuit unit 5 switches the gate voltage Vg of the switching element Q1 from 0V to the first control voltage Vg1 at time 0. This causes a drain current Id to flow through the switching element Q1. When the drain current Id reaches a predetermined value Id1 at time t1, the overcurrent detection unit 6 turns on and generates the operation signal Vc. When the operation signal Vc reaches a first reference value Vc1 at time t2, the control voltage suppression unit 7 turns on, limiting the gate voltage Vg of the switching element Q1 from the first control voltage Vg1 to a second control voltage Vg2, thereby reducing the value of the drain current Id. Furthermore, when the operation signal Vc reaches a second reference value Vc2 at time t3 before the predetermined suppression time ΔT1 has elapsed from time t2, the overcurrent determination unit 8 turns on, causing the output of the drive circuit unit 5 to switch to a third control voltage Vg3 (0V), which is lower than the second control voltage Vg2. Then, the gate voltage Vg of the switching element Q1 becomes the third control voltage Vg3=0 V, turning off the switching element Q1 and causing the drain current Id to become 0 A, thereby protecting the switching element Q1 from damage due to overcurrent. At this time, the operation signal Vc becomes equal to or less than the first reference value Vc1 at time t4, causing the DC current I1 of the constant current source 10 to flow to the drain electrode of the switching element Q1 via the resistor R1 and diode D1, turning off the overcurrent detection unit 6 and causing the operation signal Vc to become 0.

[0030] Thus, in the first operation of the control device 4, when the operating signal Vc reaches the first reference value Vc1, the gate voltage Vg of the switching element Q1 is limited from the first control voltage Vg1 to the second control voltage Vg2, thereby suppressing the drain current Id. Furthermore, when the operating signal Vc reaches the second reference value Vc2 from the first reference value Vc1 before the suppression time ΔT1 has elapsed, the switching element Q1 is turned off, and the drain current Id becomes zero. With this configuration, the continuous flow of an overcurrent through the switching element Q1 of the power conversion device 1 is suppressed, and the switching element Q1 is protected from damage due to the overcurrent.

[0031] Next, a second operation of the control device 4 will be described with reference to FIG.

[0032] In the second operation of the control device 4, the gate voltage Vg of the switching element Q1 is switched from 0 V to the first control voltage Vg1 at time t0 by the output of the drive circuit unit 5. Then, a drain current Id begins to flow through the switching element Q1, but because the drain current Id does not reach the predetermined value Id1, the operation signal Vc output by the overcurrent detection unit 6 remains at 0. However, because noise is present in the operation signal Vc output by the overcurrent detection unit 6, the noise level of the operation signal Vc reaches the first reference value Vc1 at time t5. Then, the control voltage suppression unit 7 operates to limit the gate voltage Vg of the switching element Q1 from the first control voltage Vg1 to the second control voltage Vg2, thereby reducing the value of the drain current Id. Because the drain current Id remains below the predetermined value Id1, the operation signal Vc does not reach the second reference value Vc2 even at time t6, which is the predetermined suppression time ΔT1 after time t5. As a result, the control voltage suppression unit 7 is turned off, and the gate voltage Vg of the switching element Q1 returns from the second control voltage Vg2 to the first control voltage Vg1.

[0033] By making the second reference value Vc2 of the overcurrent determination unit 8 larger than the first reference value Vc1 of the control voltage suppression unit 7, even if noise intermittently flows into the operation signal Vc, which is the output of the overcurrent detection unit 6, it is possible to prevent the switching element Q1 from being turned off due to an erroneous judgment caused by noise.

[0034] Although the embodiments of the present invention have been described above, the descriptions and drawings that form part of this disclosure should not be understood to limit the present invention. Various alternative embodiments, examples, and operating techniques will become apparent to those skilled in the art from this disclosure. [Explanation of symbols]

[0035] 1 Power conversion device 2 DC power supply 4. Control device 5. Drive circuit section 6 Overcurrent detection section 7 Control voltage suppression section 8 Overcurrent judgment section 10 Constant current source 11 Suppression start determination section 12 Suppression time adjustment section 13 Suppression voltage generation unit C0 smoothing capacitor Id Device current (drain current) M Three-phase motor Q1-Q6 switching elements S1 First upper and lower arm S2 Second upper and lower arm S3 3rd upper and lower arm Vc operating signal Vc1 First reference value Vc2 Second reference value Vd Drain potential Vg Control voltage (gate voltage) Vg1 First control voltage Vg2 Second control voltage Vg3 Third control voltage ΔT1 suppression time

Claims

1. A control method for a power conversion device using a switching element, applying a pulse width modulated voltage having a predetermined amplitude of a first control voltage to a control electrode of the switching element; generating an operating signal based on an element current flowing through a main electrode of the switching element; When the operating signal reaches a first reference value, the amplitude is limited to a second control voltage that is smaller than the first control voltage to suppress the device current; If the operating signal reaches a second reference value greater than the first reference value before a predetermined suppression time has elapsed since the amplitude was limited to the second control voltage, the amplitude is limited to a third control voltage smaller than the second control voltage to further suppress the element current. A method for controlling a power conversion device.

2. 2. The control method for a power conversion device according to claim 1, wherein, if the operation signal does not reach a second reference value even after the suppression time has elapsed since the amplitude was limited to the second control voltage, the amplitude is returned from the second control voltage to the first control voltage.

3. A control device for a power conversion device using a switching element, a drive circuit section that applies a pulse width modulated voltage having a predetermined amplitude of a first control voltage to a control electrode of the switching element; an overcurrent detection unit that generates an operation signal based on an element current flowing through a main electrode of the switching element; a control voltage suppression unit that, when the operation signal reaches a first reference value, limits the amplitude to a second control voltage that is smaller than the first control voltage; an overcurrent determination unit that limits the amplitude to a third control voltage that is smaller than the second control voltage when the operation signal reaches a second reference value that is larger than the first reference value before a predetermined suppression time has elapsed since the operation signal was limited to the second control voltage; A control device for a power conversion device comprising:

4. 4. The control device for a power conversion device according to claim 3, wherein the control voltage suppression unit returns the amplitude from the second control voltage to the first control voltage when the operation signal does not reach a second reference value even after the suppression time has elapsed since the amplitude was limited to the second control voltage.

5. 5. The control device for a power conversion device according to claim 3, wherein the control voltage suppression unit includes a suppression start determination unit that sets the first reference value, a suppression time adjustment unit that sets the suppression time, and a suppression voltage generation unit that sets the second control voltage.

6. the suppression time adjustment unit includes a circuit configured with a resistor and a capacitor, The suppression time is set by the time constant of the circuit. The control device for a power conversion device according to claim 5 .

7. the suppression voltage generating unit includes a series circuit of a constant voltage diode and a resistor, the second control voltage is set by the value of the constant voltage of the constant voltage diode; The control device for a power conversion device according to claim 5 .

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