JP6718141B2 - Power converter - Google Patents

Description

The technology disclosed in this specification relates to a power converter.

The switching element is required for various applications, and is used, for example, in a voltage converter device that transforms a DC voltage and an inverter device that converts between a DC voltage and an AC voltage. A switching element having an insulated gate is known as an example of the switching element. This type of switching element is configured to switch on and off by charging and discharging the insulated gate. An example of this type of switching element is a power semiconductor element including an IGBT (Insulated Gate Bipolar Transistor) and a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).

The switching element is required to switch from the off state to the on state within a short time. That is, high operating speed is required. Higher operating speeds can reduce switching losses. At the same time, the power switching element is required to control power on/off so as not to generate an excessive surge voltage. If the surge voltage generated by the on/off control of electric power is high, the breakdown voltage required for the switching element will be high.
Increasing the operating speed of the switching element and suppressing the surge voltage have a trade-off relationship, and generally, increasing the operating speed has a relationship of increasing the surge voltage. It is difficult to suppress surge voltage while increasing operating speed.

In the power converter described in Patent Document 1, when the switching element starts the turn-off operation and the collector current of the switching element sharply decreases, the main current flowing in the switching element up to that time commutates to the snubber capacitor. That is, the snubber capacitor absorbs the surge energy generated during the turn-off operation of the switching element. Therefore, by suppressing the surge voltage by the action of the snubber capacitor, the operating speed of the switching element can be increased and the switching loss can be reduced.

JP, 2006-230168, A

The surge energy absorbed in the snubber capacitor during the turn-off operation of the switching element will be consumed by the resistor and switching element in the circuit until the charge of the snubber capacitor becomes zero when the switching element turns on. .. Therefore, in the power converter described in Patent Document 1, the snubber circuit causes a circuit loss.

The present invention provides a power converter that reduces circuit loss while suppressing surge during switching.

The power converter of the present invention includes a switching element and a snubber circuit including a capacitor that absorbs a transient high voltage generated when the switching element is turned off, and further, an element temperature acquisition that acquires the temperature of the switching element. Means, a changeover switch for connecting/disconnecting the electrical connection between the snubber circuit and the switching element, and an electrical connection between the snubber circuit and the switching element when the temperature of the switching element acquired by the element temperature acquisition means is equal to or lower than a threshold value. And a controller for controlling the changeover switch so as to disconnect the electrical connection between the snubber circuit and the switching element when the temperature of the switching element exceeds a threshold value.

As for the switching element, the lower the element temperature, the higher di/dt until the current becomes zero. Since the surge voltage generated at turn-off is the product of the wiring inductance value, the higher di/dt, the higher the surge voltage.
According to the above configuration, when the element temperature is equal to or lower than the threshold value, the snubber capacitor absorbs the surge energy generated at the time of switching, thereby suppressing the generation of an excessive surge voltage and keeping the switching element at a predetermined level. Operate within the range of withstand voltage.
On the other hand, when the element temperature exceeds the threshold value, since the surge voltage is low, the switching element can be operated within a predetermined withstand voltage range without using a snubber capacitor. Further, since the snubber capacitor is not used, surge energy is not absorbed by the snubber capacitor, and the absorbed surge energy does not have to be consumed by the resistor or switching element on the circuit, and the circuit loss can be reduced. ..

It is a description of the power converter 10 according to the first embodiment. It is a figure explaining the switching parts T7 and T8 of the voltage converter circuit 12 in the power converter 10 which concerns on 1st Embodiment. It is a figure explaining the switching parts T1-T6 of the inverter circuit 16 in the power converter 10 which concerns on 1st Embodiment. It is an example of a routine executed by the control device 15 according to the first embodiment. It is a figure explaining the power converter 20 which concerns on 2nd Embodiment. It is a figure explaining the switching parts T7 and T8 of the voltage converter circuit 12 in the power converter 20 which concerns on 2nd Embodiment. It is a figure explaining the switching parts T1-T6 of the inverter circuit 16 in the power converter 10 which concerns on 2nd Embodiment. It is an example of a routine executed by the control device 15 according to the second embodiment.

(First embodiment)
The power converter 10 according to the first embodiment disclosed in this specification will be described.
As shown in FIG. 1, the power converter 10 according to the first embodiment is connected to a battery 14. The power converter 10 includes a voltage converter circuit 12 that boosts the battery voltage, and an inverter circuit 16 that converts the boosted DC power into AC.

The circuit configuration of the voltage converter circuit 12 will be described. The reactor 2 and the switching element T7a are connected between the output side and the input side of the high potential side line of the voltage converter circuit 12. The line on the low potential side directly connects the input side and the output side of the voltage converter circuit 12. The line on the low potential side corresponds to the ground line. That is, a line that directly connects the low potential end on the input side (battery 14 side) of the voltage converter circuit 12 and the low potential end on the output side (side of the inverter circuit 16) corresponds to the ground line.

One end of the reactor 2 is connected to the high potential end on the input side (battery 14 side), and the switching element T7a (see FIG. 2) is connected to the other end (output side). Further, another switching element T8a (see FIG. 2) is connected between the other end of the reactor 2 (the low potential end of the switching section T7) and the ground line. That is, the voltage converter circuit 12 includes a series circuit of two switching elements (T7a, T8a), and the reactor 2 is connected to the midpoint thereof.

A filter capacitor 3 is connected between the midpoint line side of the reactor 2 and the ground line. On the other hand, the smoothing capacitor 4 is connected between the high potential side line on the inverter circuit side of the voltage converter circuit 12 and the ground line. The filter capacitor 3 is a device that temporarily stores electric energy during the step-up/step-down operation of the voltage converter circuit 12, and the smoothing capacitor 4 is a device that suppresses the pulsation of the current input to the inverter circuit 16. is there.

As shown in FIG. 2, each switching element (T7a, T8a) has two main electrodes and one control electrode. A pulse signal is sent from the control device 15 to the control electrode to control ON/OFF of each switching element (T7a, T8a). Further, diodes (D7a, D8a) are connected in antiparallel to the switching elements (T7a, T8a), respectively.

A snubber capacitor (C7, C8) is connected between the two main electrodes of each switching element (T7a, T8a) so as to be in parallel with each switching element (T7a, T8a). Further, changeover switches (T7b, T8b) for connecting or disconnecting the connection between each switching element (T7a, T8a) and the snubber capacitor (C7, C8) are provided. Diodes (D7b, D8b) are connected in antiparallel to the respective changeover switches (T7b, T8b). Below, each switching element (T7a, T8a), diode (D7a, D8a), changeover switch (T7b, T8b), diode (D7b, D8b), snubber capacitor (C7, C8) are generically referred to, and a switching part (T7, Call T8). A circuit including the snubber capacitor C7, the changeover switch T7b and the diode D7b (the snubber capacitor C8, the changeover switch T8b and the diode D8b) is called a snubber circuit.

The circuit configuration of the inverter circuit 16 will be described. As shown in FIG. 3, the inverter circuit 16 has a configuration in which three sets of series circuits of two switching elements are connected in parallel (T1a and T4a, T2a and T5a, T3a and T6a). The high potential side of the three sets of series circuits is connected to the high potential side input end of the inverter circuit 16, and the low potential side of the three sets of series circuits is connected to the low potential side input end of the inverter circuit 16.

Each switching element (T1a to T6a) has two main electrodes and one control electrode. A pulse signal is sent from the control device 15 to the control electrode to control ON/OFF of each switching element (T1a to T6a). As a result, three-phase alternating current is output from the midpoint of the three sets of series circuits. Further, diodes D1a to D6a are connected in antiparallel to the switching elements (T1a to T6a), respectively.

As shown in FIG. 3, snubber capacitors (C1 to C6) are connected between the two main electrodes of each switching element (T1a to T6a) in parallel with each switching element (T1a to T6a). ing. Further, changeover switches (T1b to T6b) for connecting or disconnecting the connection between the switching elements (T1a to T6a) and the snubber capacitors (C1 to C6) are provided. Diodes (D1b to D6b) are connected in antiparallel to the respective changeover switches (T1b to T6b). Hereinafter, the switching elements (T1a to T6a), the diodes (D1 to D6), the changeover switches (T1b to T6b), the diodes (D1b to D6b), and the snubber capacitors (C1 to C6) are collectively referred to as a switching unit (T1 to T6a). T)6. Further, like the voltage converter circuit 12, a circuit including snubber capacitors (C1 to C6), changeover switches (T1a to T6a) and diodes (D1b to D6b) is referred to as a snubber circuit.

As shown in FIGS. 2 and 3, the power converter 10 has element temperature acquisition means (S1 to S8) in order to detect the temperature of each switching element (T1 to T8). The element temperature acquisition means (S1 to S8) detects the temperature of the chip of the switching element (for example, a sense diode) and the temperature of the heat radiation medium (cooling water or heat radiation fin) of the switching element ( For example, a thermistor or a thermocouple).

The operation of each switching unit (T1 to T8) included in the voltage converter circuit 12 and the inverter circuit 16 will be described. Hereinafter, the switching unit T8 of the voltage converter circuit 12 will be described as an example, but the same applies to the other switching units (T1 to T7).

FIG. 4 is an example of a routine executed by the control device 15. The controller 15 regularly monitors whether the temperature of the switching element T8a acquired by the element temperature acquisition means S8 is equal to or lower than the threshold value Tth (step 11). When the temperature of the switching element T8a exceeds the threshold value Tth, the control device 15 controls the changeover switch T8b so that the connection between the switching element T8a and the snubber capacitor C8 is cut off (step 12).

On the other hand, when the temperature of the switching element T8a is equal to or lower than the threshold value Tth, the control device 15 controls the changeover switch T8b so that the connection between the switching element T8a and the snubber capacitor C8 becomes conductive. (Step 13) When the switching element T8a starts the OFF operation, the potential of the terminal on the reactor side 2 of the switching element T8a rises from the ground potential to the potential of the battery 14. At this time, electric charge flows into the snubber capacitor C8 and the surge energy is absorbed, so that the surge voltage of the switching element T8a can be suppressed. After that, when the switching element T8a starts the ON operation, charges flow from the snubber capacitor C8 to the switching element T8a, and the potential of the reactor side terminal of the switching element T8a drops to the ground potential.

The switching element T8a has a higher di/dt until the current becomes zero as the element temperature becomes lower. Since the surge voltage generated at turn-off is the product of the wiring inductance value, the higher di/dt, the higher the surge voltage. In addition, the breakdown voltage of the switching element becomes low at low temperature. Therefore, it is necessary to set the operating speed (driving speed) of the switching element so that the surge voltage at low temperature does not exceed the breakdown voltage at low temperature (lower than that at normal temperature). There were limits to reducing losses.
Further, the surge energy absorbed by the snubber capacitor C8 during the off operation of the switching element T8a, when the switching element subsequently starts the on operation, the resistance on the circuit and the switching element until the electric charge of the snubber capacitor C8 becomes zero. Therefore, the snubber circuit causes a circuit loss.

According to the first embodiment, when the temperature of the switching element T8a is equal to or lower than the threshold value Tth, the snubber capacitor C8 absorbs the surge energy generated at the time of switching, thereby operating speed (driving speed) of the switching element. Even if the switching loss is reduced earlier, the generation of an excessive surge voltage can be suppressed and the switching element T8a can be operated within a predetermined withstand voltage range.
On the other hand, when the temperature of the switching element T8a exceeds the threshold value Tth, the withstand voltage of the switching element T8a is relatively high and the surge voltage is low, so that the switching element T8a can be operated without using the snubber capacitor C8. It can be operated within a predetermined withstand voltage range. Further, since the snubber capacitor C8 is not used, surge energy is not absorbed by the snubber capacitor C8, and it is not necessary to consume the absorbed surge energy in the switching element T8a, which suppresses the occurrence of circuit loss by the snubber circuit. be able to.
As described above, in the first embodiment, attention is paid to the magnitude of the surge voltage that changes with temperature and the breakdown voltage of the switching element that changes with temperature, and when the temperature of the switching element is equal to or lower than the threshold Tth, the snubber circuit and the switching element are changed. When the temperature of the switching element exceeds the threshold value Tth, the electrical connection between the snubber circuit and the switching element is cut off. This threshold Tth can be set by, for example, an experiment so that the surge voltage generated when the snubber circuit is cut off does not exceed the breakdown voltage of the element at the element temperature exceeding the threshold Tth.

(Second embodiment)
A power converter 20 according to a second embodiment disclosed in this specification will be described.
FIG. 4 is a circuit diagram of the power converter according to the second embodiment of the present invention. In FIG. 4, the same or equivalent components as those in FIG. 1 are designated by the same reference numerals.
In the first embodiment, in the voltage converter circuit 12 and the inverter 16 circuit, the snubber circuit is connected in parallel to both the switching elements of the upper and lower arms, whereas in the second embodiment, of the upper and lower arms, The difference is that a snubber circuit is connected to either one of the switching elements. In FIG. 4, the snubber capacitors (C1 to C3, C7) are connected only to the switching elements (T1a to T3a, T7a) of the upper arm.

As in the first embodiment, as shown in FIGS. 5 and 6, the power converter 20 detects the temperature of each switching element (1 to T8) to obtain the element temperature acquisition means (S1 to S8). have. The element temperature acquisition means (S1 to S8) detects the temperature of the chip of the switching element (for example, a sense diode) and the temperature of the heat radiation medium (cooling water or heat radiation fin) of the switching element ( For example, a thermistor or a thermocouple).

The operation of each switching unit (T1 to T8) included in the voltage converter circuit 12 and the inverter circuit 16 will be described. In the switching unit (T1 to T3, T7) having the snubber capacitors, the snubber capacitors (C1 to C3, C7) are used to change the surge voltage of the switching elements (T1a to T3a, T7a) as in the first embodiment. Suppress. In the switching units (T4 to T6, T8) having no snubber capacitors, the snubber capacitors (C1 to C3, C7) of the opposing arms are used to suppress the surge voltage of the switching elements (T4a to T6a, T8a). Hereinafter, the switching section (T7/T8) of the voltage converter circuit 12 will be described as an example, but the same applies to the other switching sections (T1/T4, T2/T5, T3/T6).

FIG. 8 is an example of a routine executed by the control device 15. The control device 15 regularly monitors whether or not the temperature of the switching elements (T7a, T8a) acquired by the element temperature acquisition means (S7, S8) is equal to or lower than the threshold value Tth (step 21, step 23). When the temperature of both switching elements (S7, S8) exceeds the threshold value Tth, the control device 15 controls the changeover switch T7b so that the connection between the switching element T7a and the snubber capacitor C7 is cut off (step 25).

On the other hand, when the temperature of at least one of the switching elements (S7, S8) is equal to or lower than the threshold value Tth, the control device 15 controls the changeover switch T7b so that the connection between the switching element T7a and the snubber capacitor C7 becomes conductive. (Steps 22 and 23)

The OFF operation of each switching element (T7a, T8a) when the temperature of at least one of the switching elements (S7, S8) is less than or equal to the threshold value Tth will be described.
The OFF operation of the switching element T7a is the same as in the first embodiment. When the switching element T7a starts the off operation, the potential of the terminal on the reactor side 2 of the switching element T7a decreases from the potential of the battery 14 to the ground potential. At this time, the electric charge flows into the snubber capacitor C7 and the surge energy is absorbed, so that the surge voltage of the switching element T7a can be suppressed. After that, when the switching element T7a starts the ON operation, electric charge flows from the snubber capacitor C7 to the switching element T7a, and the potential of the reactor side terminal of the switching element T7a rises to the potential of the battery 14.

Next, the OFF operation of the switching element T8a will be described. When the switching element T8a starts the OFF operation, the potential of the reactor side terminal of the switching element T8a rises from the ground potential to the potential of the battery 14. At this time, the electric charge flows into the snubber capacitor C7 and the surge energy is absorbed, so that the surge voltage of the switching element T8a can be suppressed. After that, when the switching element T8a starts the ON operation, electric charges flow from the snubber capacitor C7 to the switching element T8a, and the potential of the reactor side terminal of the switching element T8a drops to the ground potential.

According to the second embodiment, as in the first embodiment, when the temperature of at least one of the switching elements (T7a, T8a) is equal to or lower than the threshold value Tth, the surge energy generated at the time of switching is changed to the snubber capacitor. By absorbing in C7, the operating speed (driving speed) of the switching element is accelerated, and even if the switching loss is reduced, generation of an excessive surge voltage is suppressed, and the switching element (T7a, T8a) is kept at a predetermined level. It can be operated within the withstand voltage range.
On the other hand, when both the temperatures of the switching elements (T7a, T8a) exceed the threshold value Tth, the withstand voltage of the switching elements (T7a, T8a) is relatively high and the surge voltage is low, so that the snubber capacitor C7 is used. The switching elements (T7a, T8a) can be operated within a predetermined withstand voltage range without using them. Further, since the snubber capacitor C7 is not used, the surge energy is not absorbed by the snubber capacitor C7, and the absorbed surge energy does not have to be consumed by the switching elements (T7a, T8a), and the circuit loss due to the snubber circuit is reduced. Occurrence can be suppressed.

In the first embodiment and the second embodiment, the case where the snubber capacitors (C1 to C8) and the changeover switches (T1a to T8a) are connected in series as the snubber circuit has been described. A snubber resistor may be connected in series with (C1 to C8) and the changeover switches (T1a to T8a). According to this, the surge energy absorbed by the snubber capacitors (C1 to C8) is also consumed by the snubber resistor, and the heat generated when the surge energy is consumed can be dispersed.

In 1st Embodiment and 2nd Embodiment, although the case where the snubber circuit was connected in parallel to each switching element (T1a-T8a) was demonstrated, two switching elements (T1a*T4a, T2a*T5a, A snubber circuit (collective snubber) may be connected in parallel with the series circuit of T3a/T6a, T7a/T8a). According to this, the circuit can be simplified.

Specific examples of the present invention have been described above in detail, but these are merely examples and do not limit the scope of the claims. The invention described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in the present specification or the drawings exert technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Further, the configurations illustrated in the present specification or the drawings can achieve a plurality of objects at the same time, and achieving the one object among them has technical utility.

2: Reactor 3: Filter capacitor 4: Smoothing capacitors 10, 20: Power converter 12: Voltage converter circuit 14: Battery 15: Control device 16: Inverter circuits S1 to S8: Element temperature acquisition means T1 to T8: Switching unit T1a -T8a: Switching elements T1b-T8b: Changeover switches C1-C8: Snubber capacitors D1a-D8a, D1b-D8b: Diodes

Claims (1)

A switching element,
A snubber circuit including a capacitor that absorbs a transient high voltage generated when the switching element is turned off,
In a power converter equipped with
Element temperature acquisition means for acquiring the temperature of the switching element,
A changeover switch for electrically connecting and disconnecting the electrical connection between the snubber circuit and the switching element,
When the temperature of the switching element acquired by the element temperature acquisition means is equal to or lower than a threshold value, the electrical connection between the snubber circuit and the switching element is conducted, and when the temperature of the switching element exceeds the threshold value, the snubber circuit and A control device for controlling the changeover switch so as to cut off the electrical connection of the switching element,
Power converter provided with.

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