JP2017123723A - Voltage converter - Google Patents

Abstract

A technology for suppressing heat generation in a voltage converter including an RC-IGBT is provided. A voltage converter has two RC-IGBTs connected in series with each other, and one end connected to the midpoint of the series connection of the two RC-IGBTs, and the other end connected to a battery 81 side. And a controller 10 that switches between conduction and non-conduction of the IGBTs of the two RC-IGBTs. In the step-down operation, the controller switches the IGBT between conduction and non-conduction at the first frequency when the limit value of the regenerative power sent from the inverter is set to the first limit value. When the absolute value of the limit value of the regenerative power to be generated is set to a second limit value that is larger than the absolute value of the first limit value, the conduction and non-conduction of the IGBT is a second frequency smaller than the first frequency. Switch with. [Selection] Figure 1

Description

  The present invention relates to a voltage converter mounted on an automobile. In particular, the present invention relates to a voltage converter that performs a step-up operation that boosts the voltage of a battery and supplies it to an inverter, and a step-down operation that generates a voltage from a traveling motor and steps down the regenerative power sent from the inverter. The “automobile” in this specification includes an electric vehicle that includes a motor for traveling but does not include an engine, a hybrid vehicle that includes both a motor and an engine, and a fuel cell vehicle.

  The automobile includes an inverter that converts the DC voltage of the battery into AC power and supplies the AC power to the traveling motor. Some automobiles include a voltage converter that connects a battery and an inverter. That is, an automobile in which a voltage converter and an inverter are connected in series between a battery and a motor is known. The voltage converter performs a step-up operation for boosting the voltage of the battery and supplying the boosted voltage to the inverter, and a step-down operation for stepping down the regenerative power generated by the traveling motor and supplied from the inverter to the battery.

  The voltage converter (also referred to as a step-up / down converter) includes two switching elements, two diodes, and a reactor. The two switching elements are connected in series. One of the two switching elements is connected in antiparallel with one of the two diodes. Similarly, the other switching element is connected in antiparallel with the other switching element. One end of the reactor is connected to the midpoint of two switching elements connected in series, and the other end of the reactor is connected to a high potential end on the battery side. In this configuration, a current flows through one switching element and the other diode in the boosting operation. Therefore, in the boosting operation, one switching element and the other diode generate heat. In the step-down operation, current flows through the other switching element and one diode. Therefore, in the step-down operation, one switching element and the other diode generate heat.

  In Patent Document 1, as a switching element and a diode, an RC-IGBT (abbreviation of reverse conducting diode IGBT), IGBT is an abbreviation of Insulated Gate Bipolar Transistor. A voltage converter is disclosed. In the RC-IGBT, an IGBT, which is a switching element, and a diode are mounted on one substrate and are connected in antiparallel.

Japanese Patent Laying-Open No. 2015-177635

  Since a motor for driving an automobile has a high output, the voltage converter generates a large amount of heat. In particular, in a voltage converter including an RC-IGBT, one of the IGBT and the diode of the RC-IGBT generates heat during the step-up operation, and the other of the IGBT and the diode of the RC-IGBT generates heat during the step-down operation. That is, since the RC-IGBT generates heat in both the step-up operation and the step-down operation, the cycle of heat generation and heat dissipation increases as compared with the case where the IGBT and the diode are arranged separately. As a result, solder used for RC-IGBT and grease for heat dissipation are likely to deteriorate.

  In particular, in a situation where the regenerative power is to be actively supplied to the battery, for example, when the remaining battery level is low, the limit value is increased in an automobile that temporarily expands the regenerative power limit value from the normal limit value. The current flowing through the RC-IGBT increases. Thereby, heat_generation | fever of RC-IGBT increases.

  The present specification provides a technique for suppressing heat generation in a voltage converter including an RC-IGBT.

  The present specification discloses a voltage converter. The voltage converter performs a step-up operation for boosting the voltage of the battery and supplying the boosted voltage to the inverter, and a step-down operation for stepping down the regenerative power generated by the traveling motor and supplied from the inverter to the battery. The voltage converter has two RC-IGBTs connected in series with each other and one end connected to the midpoint of the series connection of the two RC-IGBTs, and the other end connected to the high potential end on the battery side. And a controller that switches between conduction and non-conduction of each IGBT of the two RC-IGBTs. In the step-down operation, the controller switches the IGBT between conduction and non-conduction at the first frequency when the limit value of the regenerative power sent from the inverter is set to the first limit value. When the absolute value of the limit value of the regenerative power to be generated is set to a second limit value that is larger than the absolute value of the first limit value, the conduction and non-conduction of the IGBT is a second frequency smaller than the first frequency. Switch with.

  In this configuration, when the power limit value is increased during the step-down operation, the IGBT switching frequency is set lower than the switching frequency when the limit value is not increased. According to this configuration, the amount of heat generated by the RC-IGBT while the power limit value is expanded can be suppressed.

  Details and further improvements of the technology disclosed in this specification will be described in the following “DETAILED DESCRIPTION”.

It is a block diagram of the electric power system of the motor vehicle containing the power converter device of an Example. It is a time chart which shows the relationship between the switching frequency of RC-IGBT element at the time of the normal time of regenerative power restriction | limiting, and expansion, and temperature.

  FIG. 1 shows a block diagram of a power system of the automobile 100. The automobile 100 includes two motors 83 a and 83 b and the power conversion device 2. The outputs of the two motors 83a and 83b are combined / distributed by the power distribution mechanism 85 and transmitted to the axle 86 (that is, drive wheels). That is, the automobile 100 is driven by the two motors 83a and 83b. Note that the automobile 100 may have a driving engine in addition to the motor.

  The power conversion device 2 is connected to a battery 81 via a system main relay 82. The power conversion device 2 includes a voltage converter 12 and two sets of inverters 13a and 13b.

  The voltage converter 12 boosts the voltage of the battery 81 and supplies the boosted voltage to the inverters 13a and 13b. The voltage converter 12 steps down the regenerative power generated by the 83a and 83b and sent from the power generators 13a and 13b. Is a step-up / step-down voltage converter. The circuit of the voltage converter 12 includes two switching elements 8a and 9a, two diodes 8b and 9b, a reactor 7, and a capacitor 5. The two switching elements 8a and 9a are connected in series. Diodes 8b and 9b are connected to each switching element in antiparallel. Reactor 7 has one end connected to the midpoint of series connection of two switching elements 8a and 9a, and the other end connected to a high potential end on the battery side. The capacitor 5 is connected in parallel to the input end on the battery side.

  A hardware configuration of the switching elements 8a and 9a and the diodes 8b and 9b will be described. The switching elements 8a and 9a are IGBTs. The switching element 8a and the diode 8b connected in antiparallel are mounted on a single substrate and formed into one chip, and constitute an RC-IGBT8. Similarly, the switching element 9a and the diode 9b connected in antiparallel are mounted on a single substrate and formed into one chip to constitute the RC-IGBT 9. In RC-IGBTs 8 and 9, solder is used to attach each element. Moreover, RC-IGBT8, 9 is arrange | positioned at the cooling device through the thermal radiation grease. A temperature sensor is also mounted on the substrate of each chip. These temperature sensors measure the temperature of the chip (the temperature of the substrate). The series circuit of RC-IGBTs 8 and 9 has a terminal connected to the high potential side P electrode and a terminal connected to the low potential side N electrode.

  The inverter 13a has a configuration in which three sets of series circuits of two switching elements are connected in parallel (T1 and T4, T2 and T5, T3 and T6). A diode is connected in antiparallel to each switching element. In FIG. 1, each set of two switching elements and diodes of each switching element is surrounded by a broken line. The high potential side of the three sets of series circuits is connected to the output terminal on the high potential side P of the voltage converter 12, and the low potential side N of the three sets of series circuits is connected to the output terminal on the low potential side of the voltage converter 12. Has been. Three-phase alternating current (U-phase, V-phase, W-phase) is output from the midpoint of the three sets of series circuits.

  Since the configuration of the inverter 13b is the same as that of the inverter 13a, a specific circuit is not shown in FIG. 1. Like the inverter 13a, a series circuit of two switching elements and a set of diodes of each switching element are indicated by broken lines. Show. Similarly to the inverter 13a, the inverter 13b has a configuration in which three sets of series circuits of switching elements are connected in parallel.

  The smoothing capacitor 6 is connected in parallel to the input terminals of the inverters 13a and 13b. In other words, the smoothing capacitor 6 is connected in parallel to the output terminal of the voltage converter 12. Smoothing capacitor 6 removes noise (current pulsation associated with switching operation) superimposed on the output current of voltage converter 12.

  The switching elements T1 to T6 are transistors, typically IGBTs, but may be other transistors such as MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). Note that in the inverters 13a and 13b, one switching element and a diode connected in reverse parallel thereto may be an RC-IGBT.

  The automobile 100 supplies the power of the battery 81 to the motors 83a and 83b, the power running state in which the axle 86 is rotated by the motors 83a and 83b, and the regenerative state in which the power generated by the motors 83a and 83b is supplied to the battery 81. Can be migrated. In the power running state, voltage converter 12 boosts the voltage of battery 81 and supplies it to inverters 13a and 13b. The inverters 13a and 13b convert the boosted DC power into AC power and supply it to the traveling motors 83a and 83b. Thereby, the motors 83a and 83b are driven by the electric power of the battery 81 to rotate the axle 86. On the other hand, in the regenerative state, the automobile 100 rotates the motors 83a and 83b using kinetic energy. When the motors 83a and 83b rotate, the motors 83a and 83b generate electric power, and the AC power is converted into DC power by the inverters 13a and 13b. The converted DC power is stepped down by the voltage converter 12 and supplied to the battery 81.

  The voltage converter 12 and the inverters 13a and 13b are controlled by the controller 10. The controller 10 includes a CPU and a memory such as a ROM and a RAM. The controller 10 receives a command from a host controller that determines the target output of the motors 83a and 83b from the vehicle speed, the accelerator opening, the remaining battery level, and the like, and determines the target output of the inverters 13a and 13b. The controller 10 generates and supplies a PWM signal to be given to each switching element of the inverters 13a and 13b and a PWM signal to be given to each switching element 8a and 9a of the voltage converter 12 so that the target output is realized.

  The controller 10 stores in advance two types of limit values, a first limit value and a second limit value, as limit values for the regenerative power supplied to the battery 81 in the regenerative state. In this embodiment, the line power is expressed as a negative value. The absolute value of the second limit value is greater than the absolute value of the first limit value. As will be described later, the controller 10 sets one of the first limit value and the second limit value according to the remaining amount of the battery 81. The controller 10 determines the target output of the inverters 13a and 13b so as not to exceed the set limit value in the regenerative state, and controls the inverters 13a and 13b and the switching elements of the voltage converter 12.

  In the initial state, the first limit value having a relatively small absolute value is set. When the remaining amount of the battery 81 is less than a predetermined threshold, the controller 10 changes the limit value of the regenerative power from the first limit value at the normal time to the second limit value, and sets the limit value of the line power. Enlarge temporarily. Thereby, when the remaining amount of the battery 81 is small, the battery 81 can be charged early. FIG. 2 shows (a) a change in the regenerative power limit value, (b) a change in the actual regenerative power, (c) a change in the switching frequency of the switching elements 8 a and 9 a of the voltage converter 12, and (d) the voltage converter 12. The time chart which shows the change of the temperature of RC-IGBT8 of 9 is shown.

  When the remaining amount of the battery 81 becomes less than the threshold, the controller 10 sets an enlargement flag. Then, when the enlargement flag is set, the controller 10 determines whether or not the automobile 100 is shifted to the regenerative state depending on, for example, whether or not the accelerator pedal is operated. When the expansion flag is set, for example, when it is determined that the accelerator pedal is not operated and the automobile 100 is shifted to the regenerative state (time T1 in FIG. 2), the controller 10 sets the limit value of the regenerative power to the first value. The limit value is changed to the second limit value and enlarged from the normal time. Actually, the controller 10 increases the frequency of each switching element of the inverters 13a and 13b. Further, at time T1, the controller 10 decreases the switching frequency of the switching elements 8a and 9a of the voltage converter 12 from the first frequency to the second frequency when the voltage converter 12 performs the step-down operation. In FIGS. 2A and 2B, since the regenerative power is expressed as a negative value, the absolute value of the regenerative power is larger as it goes downward.

  The controller 10 controls the regenerative power when the remaining amount of the battery 81 is equal to or greater than the threshold value, or when, for example, the accelerator pedal is operated and the automobile 100 is shifted to the power running state (time T2 in FIG. 2). The value is returned from the second limit value to the first limit value. Actually, the controller 10 returns the frequency of each switching element of the inverters 13a and 13b to the value before increasing. Further, at time T2, the controller 10 increases the switching frequency of the switching elements 8a and 9a of the voltage converter 12 from the second frequency to the first frequency. In the modification, the timing for changing the limit value of the regenerative power and the timing for changing the switching frequency of the switching elements 8a and 9a may not be the same timing, for example, after the limit value of the regenerative power is changed. The switching frequency may be changed at a predetermined timing. In the modification, the limit value of the regenerative power and the switching frequency of the switching elements 8a and 9a may be switched according to the remaining amount of the battery 81, for example, and may not be determined by the accelerator pedal.

  As shown at time T3, when the remaining amount of the battery 81 is equal to or greater than the threshold, the controller 10 maintains the regenerative power limit value at the first limit value even when the automobile 100 is shifted to the regenerative state. Thus, the switching frequency of the switching elements 8a and 9a of the voltage converter 12 is not changed from the first frequency. Then, as shown at time T4, the controller 10 sets the regenerative power limit value and the switching frequency of the switching elements 8a and 9a of the voltage converter 12 from the first frequency even when the automobile 100 is shifted from the regenerative state to the power running state. Do not change.

  Since the remaining amount of the battery 81 is less than the threshold and the remaining amount of the battery 81 is less than the threshold during the period from time T5 to T6 in which the controller 81 is in the regenerative state, the controller 10 shifts to the regenerative state. The limit value is expanded and the switching frequency of the switching elements 8a and 9a of the voltage converter 12 is decreased.

  Since the motors 83a and 83b of the automobile 100 have high output, the current flowing through the voltage converter 12 is large and the amount of heat generated by the RC-IGBTs 8 and 9 is large. In the RC-IGBT 8, current flows through the diode 8b in the step-up operation to generate heat, and current flows through the IGBT 8a in the step-down operation to generate heat. When a current is passed through the IGBT 8a by switching the IGBT 8a in the boost operation, the IGBT 8a also generates heat in the boost operation. In the RC-IGBT 9, on the contrary, current flows through the IGBT 9a in the step-up operation to generate heat, and current flows through the diode 9b in the step-down operation to generate heat. That is, the RC-IGBTs 8 and 9 generate heat in both the step-up operation and the step-down operation.

  In voltage converter 12, in the regenerative state in which the limit value of regenerative power is expanded from the normal limit value, the current flowing through RC-IGBTs 8 and 9 increases. At this time, the switching frequency of the IGBTs 8a and 9a is made smaller than the switching frequency when the limit value is not expanded. According to this configuration, as shown by the temperature change line L1 in FIG. 2D, compared to the case where the switching frequency is not reduced (in the case indicated by the temperature change line L2 in FIG. 2D), the RC− The amount of heat generated by the IGBTs 8 and 9 can be suppressed. Thereby, deterioration of the solder used for RC-IGBT and the thermal radiation grease can be suppressed by the thermal cycle.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

2: Power converter 8: RC-IGBT
8a: Switching element 8b: Diode 9: RC-IGBT
9a: Switching element 9b: Diode 10: Controller 12: Voltage converter 13a: Inverter 13b: Inverter 81: Battery 83a: Motor 83b: Motor

Claims (1)

A voltage converter that performs a step-up operation that boosts the voltage of the battery and supplies the same to the inverter, and a step-down operation that generates power by the traveling motor and steps down the regenerative power sent from the inverter and supplies the battery to the battery,
Two RC-IGBTs connected in series with each other;
A reactor having one end connected to the midpoint of the series connection of the two RC-IGBTs and the other end connected to a high potential end on the battery side;
A controller that switches between conduction and non-conduction of each IGBT of the two RC-IGBTs,
The controller
In the step-down operation, when the limit value of the regenerative power sent from the inverter is set to the first limit value, the IGBT is switched between conduction and non-conduction at the first frequency,
In the step-down operation, when the absolute value of the limit value of the regenerative power sent from the inverter is set to a second limit value that is larger than the first limit value, the IGBT is turned on and off. Is switched at a second frequency smaller than the first frequency.

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