JP2013240238A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device that economically prevents switching elements and others from breaking down in the event of an open failure of a main switch.SOLUTION: The power conversion device includes: a switching circuit for converting DC power and AC power to each other between a battery and a motor for vehicle travel; a switch 5 for connecting the battery and the switching circuit during such conversion; a current sensor 6 for outputting a current value of a current flowing through the switch 5; a sampling section 14 for sampling the output of the current sensor 6 at a frequency higher than a carrier frequency; an open failure detection section 15 for detecting an open failure in the switch 5 in real time on the basis of the sampling value; and an operation stop section 16 for stopping the operation of the switching circuit in response to such detection.

Description

  The present invention relates to a power conversion device that converts power supplied from or supplied to a DC power supply.

  Conventionally, such a power converter performs conversion of frequency, voltage, etc., and conversion between DC power and AC power. For example, in a hybrid vehicle or an electric vehicle, a power conversion device that converts DC power and AC power between a battery and a motor is used.

  As such a power converter, the one described in Patent Document 1 opens and closes an inverter as a switching circuit that converts power between a DC power source and an AC motor by a switching element, and a connection between the DC power source and the inverter. A switch; a current sensor that outputs a current value of a current flowing between the DC power source and the inverter; and a drive unit that applies a pulse width modulation signal to drive the switching element of the inverter.

  In this power converter, a series circuit of another switch and a resistor is provided in parallel to the main switch that connects the DC power supply to the inverter. Further, a smoothing capacitor for stabilizing the DC voltage is provided between the DC power supply and the inverter.

  When connecting the DC power source to the inverter, in order to avoid an inrush current that is a large current that flows instantaneously to the inverter, first, the smoothing capacitor is charged by closing the switch of the series circuit. After charging is complete, the main switch is closed and the series circuit switch is opened.

  Therefore, the series circuit does not function normally and cannot avoid an inrush current when an open failure occurs in which the switch cannot be closed. For this reason, when connecting the DC power source to the inverter, the presence or absence of an open failure in the series circuit switch is detected prior to filling the smoothing capacitor.

  This detection is performed based on whether or not a predetermined current flows by applying a relatively small voltage to the series circuit. When it is determined that an open failure has not occurred, the DC power source is connected to the inverter by the above-described procedure.

JP 2007-59138 A

  However, in the technique of the above-mentioned Patent Document 1, no countermeasure is taken for an open failure in the main switch. For this reason, when a DC power source is connected to the inverter by the main switch, if an open-circuit failure occurs during the strong regeneration in which large regenerative power is regenerated from the AC motor to the DC power source, the subsequent inverter The voltage in the inverter rises due to switching surges caused by the operation of.

  If the increased voltage exceeds an allowable withstand voltage value such as a smoothing capacitor between the DC power source and the inverter or a switching element in the inverter, these elements may be damaged. In order to avoid this, it is necessary to use a switching element having a high allowable withstand voltage value or to increase the capacity of the smoothing capacitor. This increases the cost, weight and size of the device.

  An object of the present invention is to provide a power conversion device that can economically prevent damage to elements due to an open failure of a main switch, in view of the problems of the prior art.

  The power conversion device of the present invention includes a switching circuit that performs power conversion by switching operation of a switching element for power supplied from a DC power source to a vehicle driving motor or regenerated from the driving motor to the DC power source, and the power A switch for connecting the DC power supply and the switching circuit at the time of conversion, a current sensor for outputting a current value of a current flowing between the DC power supply and the switching circuit, and a predetermined carrier for driving the switching element A PWM control unit that generates a pulse width modulation signal of a frequency, a sampling unit that samples a current value output from the current sensor at a frequency higher than the carrier frequency, and a switch based on a sampling value by the sampling unit. An open fault detector that detects open faults in real time and the open fault detector Ri opening failure is characterized by comprising an operation stopping unit for stopping the operation of the switching circuit in response to being detected.

  Here, when the above open failure occurs while the vehicle is traveling, the regenerative power that is generated at any time during the traveling of the vehicle cannot be regenerated to the DC power source. At this time, if a large amount of regenerative power is generated and the operation of the switching circuit is continued, the voltage of the switching circuit may rise abnormally and the switching element or the like may be damaged.

  In this regard, according to the present invention, the current value of the current flowing between the DC power supply and the switching circuit is sampled at a frequency higher than the carrier frequency, and the open-circuit failure of the switch is detected in real time based on the sampled value. Therefore, when an open failure of the switch occurs, the open failure is detected in a time shorter than the switching cycle of the switching element, and the operation of the switching circuit can be stopped immediately.

  In other words, even when an open failure occurs and the regenerative power cannot be regenerated to the DC power supply, this can be detected at the earliest possible timing to predict a failure that may occur in the switching circuit and stop the switching circuit. It is possible to prevent the elements and the like from being damaged.

  This eliminates the need to use a switching element having a high allowable withstand voltage value. As the current sensor, a conventional sensor for measuring regenerative power or the like can be used as it is. Furthermore, the sampling unit can be configured only by changing the program. Therefore, damage to the switching element and the like can be prevented economically with an inexpensive configuration.

  In the present invention, the detection of an open failure by the open failure detection unit may be performed based on whether a predetermined large time change has occurred in a sampling value by the sampling unit.

  Here, when an open failure of the switch occurs, the current value of the current flowing between the DC power supply and the switching circuit decreases rapidly, so that the sampling value of this current also changes abruptly. Therefore, it is possible to easily detect an open failure of the switch based on whether or not a predetermined large time change has occurred in the sampling value.

  In the present invention, the detection of the open failure by the open failure detection unit may be performed by sequentially comparing the sampling value by the sampling unit with a predetermined value.

  As described above, when an open failure of the switch occurs, the current value of the current flowing between the DC power supply and the switching circuit is rapidly reduced. At this time, the current value decreases beyond the normal minimum value. Therefore, by sequentially comparing the sampling value with an appropriate predetermined value, it can be determined that an open failure has occurred when the sampling value becomes equal to or less than the predetermined value.

It is a block diagram which shows the structure of the motor drive device which concerns on one Embodiment of this invention. It is a block diagram which shows the structure of the control part in the motor drive device of FIG. It is a flowchart which shows the process by the control part of the motor drive device of FIG. It is a wave form diagram of the electric current value which the current sensor of the motor drive device of FIG. 1 outputs.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a motor drive device to which a power conversion device according to an embodiment of the present invention is applied. As shown in FIG. 1, the motor drive device includes a battery 1 as a DC power source, a motor 2 that is supplied with power from the battery 1 or regenerates power to the battery 1, and power between the battery 1 and the motor 2. And a power conversion device 3 that performs conversion. The motor 2 is a three-phase AC motor for driving the vehicle, and drives the driving wheels of the vehicle.

  The power conversion device 3 includes an inverter 4 as a switching circuit that converts power supplied from the battery 1 or regenerated to the battery 1, and a main switch as a switch that connects the battery 1 and the inverter 4 during power conversion by the inverter 4. A contactor 5, a current sensor 6 that outputs a current value of a current flowing between the battery 1 and the inverter 4, a pre-driver 7 that drives the inverter 4, and a control unit 8 that controls each part of the apparatus are provided.

  The inverter 4 is configured by a switching element such as an IGBT and performs power conversion by an opening / closing operation of the switching element. That is, the inverter 4 has a function of converting the direct current supplied from the battery 1 into alternating current power and supplying it to the motor 2, or converting the alternating current power regenerated from the motor 2 into direct current power and supplying it to the battery 1. Prepare.

  A smoothing capacitor 9 is connected between the positive and negative power lines between the inverter 4 and the main contactor 5. A series circuit of a precharge contactor 10 and a resistor 11 is provided in parallel to the main contactor 5.

  FIG. 2 is a block diagram showing a configuration of the control unit 8. As shown in FIG. 2, the control unit 8 includes a contactor control unit 12 that controls the main contactor 5 and the precharge contactor 10, a PWM control unit 13 that supplies a pulse width modulation signal having a predetermined carrier frequency to the predriver 7, And a sampling unit 14 that samples a current value output from the current sensor 6 at a frequency higher than the carrier frequency.

  The control unit 8 includes a microcomputer and a logic circuit. The pre-driver 7 drives the inverter 4 based on the pulse width modulation signal from the PWM control unit 13.

  Further, the control unit 8 responds to the detection of the open failure by the open failure detection unit 15 and the open failure detection unit 15 that detects the open failure of the main contactor 5 in real time based on the sampling value by the sampling unit 14. And an operation stop unit 16 for stopping the operation of the inverter 4. The operation of the inverter 4 is stopped by stopping the supply of the pulse width modulation signal from the PWM control unit 13.

  FIG. 3 is a flowchart showing a part of processing by the control unit 8. The control unit 8 starts the control of FIG. 3 when the motor driving device is activated. In detail, the control part 8 precharges the smoothing capacitor 9 by the contactor control part 12, and connects the battery 1 and the inverter 4 (step S1-S4).

  That is, when the precharge contactor 10 is closed (ON) (step S1), precharging of the smoothing capacitor 9 is started. When the precharge is completed (step S2), the main contactor 5 is closed (ON) (step S3), and the precharge contactor 10 is opened (OFF) (step S4).

  Next, the control unit 8 causes the PWM control unit 13 to start sending a pulse width modulation signal having a predetermined carrier frequency to the pre-driver 7. Thereby, the supply of the opening / closing signal to each switching element of the inverter 4 by the pre-driver 7 is started. That is, power conversion by driving the inverter 4 is started (step S5).

  After the drive of the inverter 4 is started, the control unit 8 monitors the presence or absence of an open failure of the main contactor 5 (steps S6 to S9). This monitoring is performed based on the current flowing through the main contactor 5.

  That is, the control unit 8 samples the current value output by the current sensor 6 (step S7) every time the sampling timing comes periodically (step S6). The sampling period is set to a value sufficiently shorter than the period of the carrier frequency of the pulse width modulation signal output from the PWM control unit 13.

  Each time this sampling is performed, the control unit 8 uses the open failure detection unit 15 to acquire the difference between the sampling value obtained this time and the sampling value obtained last time (step S8), and the obtained difference is predetermined. It is determined whether or not the value is greater than or equal to the value (step S9). If it is determined that it is not equal to or greater than the predetermined value, it is assumed that no open failure has occurred in the main contactor 5, and the process returns to step S5 to repeat the processes of steps S6 to S9.

  On the other hand, when it is determined that the obtained difference is equal to or greater than the predetermined value (step S9), it is considered that an open failure has occurred in the main contactor 5, and the operation stop unit 16 causes the PWM control unit 13 to perform pulse width modulation. Stop sending signals. In this case, the operations of the pre-driver 7 and the inverter 4 are stopped (step S10). Thereby, the process of FIG. 3 is completed.

  According to the process of FIG. 3, even if an open failure of the main contactor 5 occurs when strong regenerative power from the motor 2 is input to the inverter 4, the operation of the inverter 4 is performed almost simultaneously with the occurrence of the open failure. Stop. Thereby, it is avoided that the voltage of the circuit in the inverter 4 rises abnormally due to the boost or surge voltage due to the switching element of the inverter 4 continuing the opening / closing operation even after the open failure. Therefore, damage to the switching element of the inverter 4 and the smoothing capacitor 9 due to application of a voltage exceeding the allowable withstand voltage is prevented.

  FIG. 4 shows a waveform of a current value output from the current sensor 6 when the inverter 4 is driven. FIG. 4A shows a normal waveform when no open failure occurs in the main contactor 5. FIG. 4B shows a waveform when the main contactor 5 has an open failure in the middle.

  As shown in FIG. 4A, in the normal state, the waveform of the current value repeats substantially the same waveform with a period T corresponding to the switching frequency (switching frequency) of the switching elements constituting the inverter 4. The switching frequency usually matches the carrier frequency and never becomes higher than the carrier frequency.

  If such a current value is sampled at a period sufficiently smaller than the period of the carrier frequency, for example, at the time t1 to t6 shown in FIG. 4A, the difference between the adjacent sampling values is the end of the waveform. The difference between the sampling values at time t5 and t6 in the section is the largest value.

  On the other hand, as shown in FIG. 4B, if the main contactor 5 has an open failure immediately before the time point t1, the current value decreases abruptly immediately after that, and therefore, as shown in FIG. When the difference between adjacent sampling values is calculated for sampling values at times t1 to t6 immediately after the failure, at least the difference between the sampling values at the first time t1 after the occurrence of the open failure and the next time t2 is the open failure. It becomes a value corresponding to a substantially constant time gradient when the current value decreases after generation.

  Therefore, the predetermined value compared with the difference between the sampling values in the determination in step S9 in FIG. 3 is larger than the maximum difference between the adjacent sampling values at normal time, and the difference between the adjacent sampling values immediately after the occurrence of the open failure. By setting an appropriate value smaller than that, it is possible to appropriately determine the occurrence of an open failure in step S9.

  As described above, according to the present embodiment, the current value of the current flowing between the battery 1 and the inverter 4 is sampled at a frequency higher than the carrier frequency, and the open failure of the main contactor 5 is based on the sampled value. Is detected in real time (steps S6 to S9), and when an open failure of the main contactor 5 occurs, the open failure can be detected in a time shorter than the switching cycle of the switching element.

  Since the operation of the pre-driver 7 is stopped in response to the detection of the open failure (step S10), the main contactor 5 is opened when strong regenerative power from the motor 2 is input to the inverter 4. Even if a failure occurs, the operation of the inverter 4 can be stopped almost simultaneously with the occurrence of the open failure.

  That is, even when an open failure occurs and the regenerative power cannot be regenerated in the battery 1, this is detected at the earliest possible timing to predict a failure that may occur in the inverter 4, and the inverter 4 is stopped. It is possible to prevent a situation in which the voltage of the inverter 4 exceeds the allowable withstand voltage value of the switching element or the like and damages these elements after the failure occurs.

  This eliminates the need to use a switching element of the inverter 4 having a high allowable withstand voltage value. Further, as the current sensor 6, a conventional sensor for measuring regenerative power or the like can be used as it is. Furthermore, the sampling unit 14 can be easily configured simply by changing the program. Therefore, damage to the switching element and the like can be prevented economically with an inexpensive configuration.

  Moreover, since the open failure detection by the open failure detection unit 15 is performed based on whether a predetermined large time change has occurred in the sampling value by the sampling unit 14, an open failure of the main contactor 5 is easily detected. be able to.

  Although the embodiment has been described above, the present invention is not limited to this. For example, the power conversion device may include a DC-DC converter as a switching circuit that boosts the power supplied from the battery 1 to the inverter 4 and steps down the regenerative power to the battery 1 in addition to the inverter 4 described above. .

  Further, the detection of the open failure by the open failure detection unit 15 is performed by comparing the difference between adjacent sampling values with respect to the current value of the current sensor 6 with a predetermined value. May be performed by comparing a value obtained by processing with a predetermined differential filter with a predetermined value.

  Moreover, in the said embodiment, although the main contactor 5 is used as a switch, it may replace with this and may use a relay.

  Further, the detection of the open failure by the open failure detection unit 15 is performed by sequentially comparing the sampling values by the sampling unit 14 with a predetermined value, and determining that an open failure has occurred when the sampling value is equal to or less than the predetermined value. You may do it.

  That is, when an open failure of the main contactor 5 occurs, the current value of the current flowing between the battery 1 and the inverter 4 is rapidly reduced as shown in FIG. At this time, the current value decreases beyond the minimum value of the current value at the normal time shown in FIG. Therefore, by sequentially comparing the sampling value with an appropriate predetermined value, it can be determined that an open failure has occurred when the sampling value becomes equal to or less than the predetermined value.

  DESCRIPTION OF SYMBOLS 1 ... Battery (DC power supply), 2 ... Motor, 4 ... Inverter (switching circuit), 5 ... Main contactor (switch), 6 ... Current sensor, 8 ... Control part, 13 ... PWM control part, 14 ... Sampling part, 15 ... Open failure detection unit, 16 ... Operation stop unit.

Claims (3)

A switching circuit that performs power conversion by switching operation of a switching element for power supplied from a DC power source to a vehicle driving motor or regenerated from the driving motor to the DC power source;
A switch for connecting the DC power source and the switching circuit during the power conversion;
A current sensor that outputs a current value of a current flowing between the DC power source and the switching circuit;
A PWM controller that generates a pulse width modulation signal of a predetermined carrier frequency for driving the switching element;
A sampling unit that samples a current value output by the current sensor at a frequency higher than the carrier frequency;
An open failure detection unit that detects an open failure of the switch in real time based on a sampling value by the sampling unit;
An electric power conversion apparatus comprising: an operation stop unit that stops the operation of the switching circuit in response to detection of an open fault by the open fault detection unit.   The power converter according to claim 1, wherein the detection of an open failure by the open failure detection unit is performed based on whether a predetermined large time change has occurred in a sampling value by the sampling unit.   The power converter according to claim 1, wherein the detection of an open failure by the open failure detection unit is performed by sequentially comparing a sampling value by the sampling unit with a predetermined value.

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