JP2010154595A - Power conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power conversion device wherein when a short circuit current is generated immediately after the occurrence of abnormal conditions, such as overheating, it is prevented to interrupt the short circuit current passed through a switching element before short circuit protection processing is carried out and appropriate protection is provided against excessive surge voltage. <P>SOLUTION: The power conversion device 1 includes: a drive circuit 11 that drives a switching element Q; a current detecting means 13 for detecting a current passed through the switching element Q; and a short circuit protection means 14 that, when short-circuiting is detected, limits the current passed through the switching element Q to within a predetermined range and continues driving for a predetermined time. When detecting abnormal conditions in which the switching element Q should be stopped, the drive circuit 11 stops driving of the switching element Q. If the short-circuiting is detected after detection of the abnormal conditions and before driving is stopped based on the abnormal conditions, the short circuit protection processing based on the short circuit protection means 14 is carried out in priority to stoppage of driving based on the abnormal conditions. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power conversion device that performs a protection operation when an excessive current flows.

  In power converters using IGBTs, MOSFETs, and the like as switching elements, a drive circuit is provided with a protection function that stops driving of the switching elements when an abnormal state such as overheating or gate voltage drop occurs in order to prevent damage to the switching elements. It has been. When driving of the switching element is stopped, a surge voltage corresponding to L × dI / dt is generated due to the current I and the floating inductance L flowing through the switching element. Therefore, the drive circuit sets the turn-off time so that the surge voltage is smaller than the withstand voltage of the switching element.

  However, when driving of the switching element is stopped during a normal turn-off time in a short circuit state, an excessive current flows through the switching element, so that a surge voltage exceeding the breakdown voltage of the switching element is generated and the switching element is damaged.

Therefore, when a short-circuit current is detected, a short-circuit protection circuit that first limits the current flowing through the switching element to a predetermined range is provided. The technique to do is disclosed (for example, refer patent document 1).
JP-A-5-218836

  However, for example, if a short-circuit current flows to the switching element immediately after detecting an abnormal state of overheating of the switching element, the overheat protection function of the drive circuit is activated and the switching current is limited before the current flowing to the switching element is limited. The short-circuit current flowing through the element is cut off. As a result, the short-circuit current flowing through the switching element is interrupted without limiting the current flowing through the switching element, an excessive surge voltage is generated in the switching element, and the element may be destroyed.

  The present invention has been made in view of the above problems, and it is an object of the present invention to provide a power conversion device that can protect a switching element when a short circuit occurs.

  The invention described in claim 1 is a switching element, a drive circuit for driving the switching element, a current detection means for detecting a current flowing through the switching element, and a current flowing through the switching element when a short circuit state is detected by the current detection means. A short circuit protection means for continuing the driving for a predetermined time by limiting the power to a predetermined range, and in a power conversion device in which the driving circuit stops driving the switching element when an abnormal state in which the switching element should be stopped is detected If a short-circuit state is detected after an abnormal state is detected and before a drive stop based on the abnormal state is executed, priority is given to the short-circuit protection process based on the short-circuit protection means over the drive stop based on the abnormal state. It is characterized by executing.

  According to the above configuration, when the short circuit state is detected before the drive stop based on the abnormal state is performed, the short circuit protection process based on the short circuit protection unit is preferentially executed. As a result, it is possible to prevent a situation in which the short-circuit current flowing through the switching element is interrupted before performing the short-circuit protection process, and it is possible to appropriately protect the switching element from an excessive surge voltage.

  In the invention according to claim 2, the current detected by the current detection means is smaller than the short-circuit threshold of the current for detecting the short-circuit state and exceeds a reference value set to be equal to or higher than the over-current threshold for detecting the over-current normal state. Sometimes, the drive stop execution process based on the abnormal state other than the short circuit state and the overcurrent state is not performed.

  According to the above configuration, by making the reference value smaller than the short circuit threshold value, it is possible to start the process of not performing the drive stop execution process based on the abnormal state other than the short circuit state and the overcurrent state at an early stage. .

  In addition, by switching the reference value larger than the overcurrent threshold and removing the overcurrent abnormality and the short circuit abnormality from the abnormal state in which the drive stop execution process is not performed, the switching element It is possible to prevent a situation where the drive stop is not performed.

  As a result, as a result of the time difference between the detection of the short circuit state and the short circuit protection processing, it is possible to prevent the drive stop based on the abnormal state other than the short circuit state and the overcurrent state.

  Further, as described in claims 3 to 5, when the current detected by the current detecting means falls below a predetermined value, the current flowing through the switching element by the short-circuit protecting means falls within a predetermined range. After being limited, or after a predetermined time has elapsed since the detection of the short circuit state, the drive stop execution process based on the abnormal state other than the short circuit state and the overcurrent state is made executable.

  By making the execution process executable at the timing of the above configuration, the shutdown based on the previously detected abnormal state is performed, and the shutdown process due to short circuit protection and the shutdown process due to the abnormal state are quickly shut down. Processing is possible.

  The invention according to claim 6 includes a switching element, a drive circuit for driving the switching element, and current detection means for detecting a current flowing through the switching element, and when an abnormal state in which the switching element is to be stopped is detected In addition, in the power conversion device that switches the turn-off time required to turn off the switching element from on to off according to the abnormal state and stops driving the switching element, after the first abnormal state is detected, If a second abnormal state having a turn-off time longer than that of the first abnormal state is detected before the drive stop based on the first abnormal state is executed, the second stop state based on the first abnormal state is detected. The drive stop based on the abnormal state 2 is executed with priority.

  As a result of executing the drive stop based on the second abnormal state in preference to the drive stop based on the first abnormal state, for example, even if an overcurrent abnormality is detected immediately after the overheat abnormality is detected, the turn-off is performed. The drive stop based on the first abnormal state with a short time is not performed, and the drive stop based on the second abnormal state with a long turn-off time, that is, the soft shut-off is performed, thus effectively preventing the suppression of the surge voltage. can do.

(Overall structure)
FIG. 1 shows an overall configuration diagram of a power conversion apparatus according to an embodiment of the present invention, and FIG. 2 shows a main configuration of the power conversion apparatus according to an embodiment of the present invention.

  The power conversion device 1 is short-circuited by the switching elements Q1 to Q6, the drive circuit 11 that drives the switching elements Q1 to Q6, the current detection means 13 that detects the current flowing through the switching elements Q1 to Q6, and the current detection means 13. And short-circuit protection means 14 that limits the current flowing through the switching elements Q1 to Q6 to a predetermined range and continues driving for a predetermined time. The power conversion device 1 converts the power supplied from the battery 2 into desired power and outputs it to the motor 3 that is a load.

Switching elements Q1 to Q6 are each driven by drive circuit 11. Switching elements Q1, Q3, Q5 are connected to the positive terminal of battery 2, and switching elements Q2, Q4, Q6 are connected to the negative terminal of battery 2. Free wheel diodes (FWD) D1 to D6 are connected in parallel to switching elements Q1 to Q6. The capacitor C connected in parallel with the battery 2 is used for smoothing the voltage of the power supply line to which power from the battery 2 is supplied. Switching element Q1 and switching element Q2, switching element Q3 and switching element Q4, and switching element Q5 and switching element Q6 are each connected as a pair of serial bodies. The midpoint of each pair of series connection is connected to the U phase, V phase and W phase of the motor 3.
(Drive circuit)
The drive circuit 11 is a circuit that drives the switching element Q by applying a voltage to the control terminal of the switching element Q, and stops driving the switching element Q when an abnormal state in which the switching element Q should be stopped is detected.

  The drive circuit 11 is connected to the MOSFET 31 and the MOSEFT 32, and drives the switching element Q by intermittently applying the voltage of the gate drive power supply 35. When the drive circuit 11 drives the switching element Q, the MOSFET 31 is turned on, the MOSFET 32 is turned off, and the voltage of the gate drive power supply 35 is applied to the gate terminal of the switching element Q. On the other hand, when the drive circuit 11 cuts off the switching element Q, the MOFFET 31 is turned off, the MOSFET 32 is turned on, and the voltage of the gate drive power supply 35 is cut off. When a voltage is applied to the switching element Q, the collector and the emitter are energized and power can be supplied to the load.

  When detecting an abnormal state in which the switching element Q should be stopped, the drive circuit 11 cuts off the gate voltage applied to the switching element Q to protect the switching element Q from the abnormal state.

Examples of the abnormal state in which the switching element Q should be stopped include abnormal states such as overheating of the switching element Q, disconnection of the temperature sensitive diode, reduction in gate voltage applied to the switching element Q, short circuit abnormality, and overcurrent abnormality. When a short circuit abnormality occurs, the drive circuit 11 cuts off the gate voltage after the current flowing through the switching element Q is limited to a predetermined range by the short circuit protection means 14 to prevent the generation of an excessive surge voltage. The short circuit protection means 14 will be described later.
(Temperature sensor)
The temperature sensor 12 detects the temperature of the switching elements Q1 to Q6. In this embodiment, a temperature sensitive diode is used as the temperature sensitive element. The temperature sensor 12 detects the temperature of the switching elements Q1 to Q6 based on the voltage drop of the temperature sensitive diode. When the temperature detected by the temperature sensor 12 exceeds the temperature at which the switching elements Q1 to Q6 are expected to malfunction, the drive circuit 11 cuts off the gate voltage applied to the switching elements and drives the switching elements Q1 to Q6. Is stopped to protect the switching elements Q1 to Q6. Even when the temperature sensitive diode is disconnected, the drive circuit 11 stops driving the switching elements Q1 to Q6.

(Current detection means)
The current detection means 13 is a means for detecting a current flowing through the switching elements Q1 to Q6, and includes a sense terminal 34, a voltage dividing resistor 41, and a voltage dividing resistor 42. The sense terminal 34 is a terminal included in the switching elements Q1 to Q6. Between the collector terminal and the sense terminal 34, a sense of hundreds to thousands of the main current flowing between the collector terminal and the emitter terminal is sensed. Current can flow.

  A voltage dividing resistor 41 and a voltage dividing resistor 42 are connected in series to the sense terminal 34. The voltage dividing resistor 41 and the voltage dividing resistor 42 detect a minute current proportional to the current flowing through the switching elements Q1 to Q6. To do. A midpoint 43 of the voltage dividing resistor 41 and the voltage dividing resistor 42 is connected to the gate terminal of the MOSFET 33 and the drive circuit 11, and the voltage of the midpoint 43 is transmitted to each of the gate terminal of the MOSFET 33 and the drive circuit 11. .

  When the voltage at the midpoint 43 is input to the drive circuit 11, the drive circuit 11 determines an overcurrent or a short circuit by comparing it with a reference voltage using a comparator (not shown) included therein.

(Short-circuit protection means)
The short-circuit protection means 14 includes a MOSFET 33 and a Zener diode DI, and the gate terminal of the MOSFET 33 is connected between the voltage dividing resistor 41 and the voltage dividing resistor 42. When a short-circuit current flows through the switching element Q, the voltage drop due to the voltage dividing resistor 42 exceeds the voltage required to turn on the MOSFET 33, and the MOSFET 33 is turned on. As a result, a reverse current flows through the Zener diode, and the drive voltage applied to the switching element Q decreases to the Zener voltage. As a result, the gate voltage decreases, the current flowing through the switching element Q decreases, and the switching element Q can be protected from being destroyed by a short-circuit current.

(Protection treatment when a short-circuit current occurs)
A protection process when a short circuit current is generated will be described with reference to FIG. 3 using the gate voltage, collector current, and collector-emitter voltage of the switching element when a short circuit condition occurs. FIG. 3 is a diagram showing the FAIL output when the gate-emitter voltage, collector current, collector-emitter voltage, and abnormal state of the switching element Q are detected from above.

  When a short-circuit current flows through the switching element Q, the voltage applied to the MOSFET 33 of the short-circuit protection unit 14 via the current detection unit 13 increases. As a result, the MOSFET 33 is turned on, the gate voltage VGE (gate-emitter voltage) applied to the switching element Q is lowered, and the collector current is limited to a predetermined range (corresponding to the cutoff A in FIG. 3). The short-circuit protection means 14 limits the current flowing through the switching element Q without going through the drive circuit 11, and thus can quickly protect the switching element Q from the short-circuit current.

  On the other hand, the FAIL output changes from HIGH to LOW several seconds after the current detected by the current detection means 13 exceeds the short-circuit threshold. The drive circuit 11 that has detected that the FAIL output becomes the LOW level cuts off the gate voltage of the switching element Q. In this way, by interrupting the current flowing through the switching element Q by the two-stage process, it is possible to suppress the occurrence of an excessive surge voltage.

  Next, a protection process of the drive circuit 11 when a short-circuit current flows through the switching element Q immediately after an abnormal state due to overheating is detected will be described using FIG. FIG. 4 is a diagram illustrating a voltage waveform, a current waveform, and the like when a short-circuit current is generated after occurrence of an overheat abnormality in the power conversion device 1 according to the embodiment of the present invention. FIG. 4 shows the voltage waveform of the gate-emitter voltage, the collector current, the gate-emitter voltage, and the FAIL output in the drive circuit 11 from the top.

  When the short circuit state is detected after the abnormal state due to overheating is detected and before the drive stop based on the abnormal state is executed, the power converter 1 detects the short circuit protection means 14 rather than the drive stop based on the abnormal state. Priority is given to short-circuit protection processing based on the above.

  That is, normally, when an abnormal state due to overheating is detected by the drive circuit 11, the FAIL output changes from HIGH level to LOW level several seconds after detection of the abnormal state due to overheating, and the gate voltage of the switching element is cut off. However, if it is detected that the current detected by the current detection means 13 exceeds the reference value after the abnormal state due to overheating is detected and before the drive stop based on the abnormal state is executed, the short circuit state is detected. In addition, a mask process that prevents the drive from being stopped based on an abnormal state other than an overcurrent state acts on the drive circuit 11. When the mask process is performed, the drive circuit 11 does not detect a FAIL output related to an abnormal state due to overheating, so that the switching element is not suddenly interrupted in a situation where a short-circuit current flows through the switching element, and an excessive surge voltage is generated. This can be prevented.

  Thereafter, when the current detected by the current detection unit 13 exceeds the short-circuit threshold, the current flowing through the switching element is limited to a predetermined range by the short-circuit protection unit 14. As described above, when the current detected by the current detection means 13 exceeds the reference value, the drive is not stopped based on the abnormal state due to overheating. Therefore, the current is limited to a predetermined range after the short-circuit state is detected. In the meantime, it is possible to prevent an excessive surge voltage from being generated by stopping the driving based on an abnormal state due to overheating.

  In FIG. 4, the reference value is set equal to the overcurrent threshold, but the reference value is smaller than the short-circuit threshold of the current for detecting the short-circuit state and is equal to or greater than the over-current threshold for detecting the overcurrent normal state. Setting to is sufficient.

  Next, processing when the current detected by the current detection unit 13 exceeds the reference value but has not reached the short-circuit threshold will be described with reference to FIGS. 5 and 6. As shown in CASE 1 in FIG. 5, when the current detected by the current detection means 13 exceeds the reference value (step 001), a protection process is performed in which the drive stop based on the abnormal state other than the overcurrent state and the short circuit state is not performed. Work (step 002). Thereafter, when the current detected by the current detection means 13 becomes equal to or less than a predetermined value set as a reference value or the like (step S003), the drive stop execution process based on the abnormal state other than the short-circuit state and the overcurrent state can be executed again. A state is set (step 004). If the abnormal state due to overheating still continues after the drive stop execution process becomes executable again, the drive stop execution process is performed based on the abnormal state due to overheating.

  On the other hand, as shown in CASE 2 in FIG. 5, when the current detected by the current detection unit exceeds the reference value, the current value positioned between the reference value and the short-circuit threshold is maintained as it is. Based on this, the driving of the switching element is stopped. Therefore, even if the drive stop based on the abnormal state due to overheating is not performed, the drive stop based on the overcurrent state is performed, so that the switching element can be appropriately protected.

  In FIG. 5, when the current detected by the current detection means 13 becomes a predetermined value or less, the drive stop execution process based on the abnormal state other than the short-circuit state and the overcurrent state is made executable, but the short-circuit protection After the current flowing through the switching element is limited to a predetermined range by the means 14, or after a predetermined time has elapsed since the detection of the short circuit state, the drive stop execution process based on the abnormal state other than the short circuit state and the overcurrent state is performed. It may be in an executable state.

By making the execution process executable at the timing of the above configuration, the shutdown based on the previously detected abnormal state is performed, and the shutdown process due to short circuit protection and the shutdown process due to the abnormal state are quickly shut down. Processing is possible.
(Measures when changing the turn-off time)
Next, referring to FIG. 7, when the abnormal condition occurs between the first abnormal condition such as overheating, gate voltage drop, and temperature-sensitive diode disconnection and the second abnormal condition such as overcurrent and short circuit, A case where the turn-off time required for turning from on to off is switched will be described.

  When the turn-off time is the same, the magnitude of the surge voltage generated is different when overheating occurs and when overcurrent occurs. Therefore, soft shut-off is performed so that the turn-off time when the second abnormal state occurs is longer than the turn-off time when the first abnormal state occurs in order to suppress the surge voltage.

  In the power conversion device 1 according to the embodiment of the present invention, after the first abnormal state is detected and before the drive stop based on the first abnormal state is executed, the first abnormal state. However, when the second abnormal state with a long turn-off time is detected, the drive stop based on the second abnormal state is executed with priority over the drive stop based on the first abnormal state.

  As a result of prioritizing the drive stop based on the second abnormal state over the drive stop based on the first abnormal state, for example, even if an overcurrent abnormality is detected immediately after the overheat abnormality is detected, The drive stop based on the abnormality (first abnormal state) is not performed, and the drive stop based on the overcurrent abnormality (second abnormal state) with a long turn-off time (ie, the second abnormal state) is performed. Can be effectively prevented.

Furthermore, since the turn-off time when the second abnormal condition does not occur and the first abnormal condition occurs is shorter than the turn-off time when the second abnormal condition occurs, when the first abnormal condition occurs A rapid switching element protection process can be performed.
(Description of conventional method)
FIG. 8 shows a voltage waveform and a current waveform when a short-circuit current flows through the switching element immediately after the occurrence of overheating in the conventional power conversion device 1.

  Normally, when a short-circuit current flows through the switching element, as indicated by a cut-off A, the gate voltage is limited by the short-circuit protection means 14 to limit the current flowing through the switching element to a predetermined range and then applied to the switching element. Completely cut off the gate voltage. Thus, since the gate voltage is lowered in two stages, it is possible to prevent an excessive surge voltage from occurring.

  However, when a short-circuit state is detected immediately after overheating of the switching element is detected, the switching element is stopped based on an abnormal state due to overheating despite the short-circuit current flowing. For this reason, as shown in interruption | blocking B, the drive of a switching element is stopped in the state in which the short circuit current is flowing, without restrict | limiting the electric current by the short circuit protection means 14. FIG. As a result, an excessive surge voltage is caused in the switching element.

It is a figure which shows the whole structure of the power converter device which concerns on embodiment of this invention. It is the schematic which shows the principal part structure of the power converter device which concerns on embodiment of this invention. In the power converter device which concerns on embodiment of this invention, it is a figure which shows a voltage waveform, a current waveform, etc. when a short circuit current generate | occur | produces. In a power converter concerning an embodiment of the present invention, it is a figure showing a voltage waveform, a current waveform, etc. when a short circuit current occurs after an overheating abnormal state occurs. In the power converter device concerning the embodiment of the present invention, it is a figure showing the case where the short circuit threshold is not exceeded after the current value exceeds the reference value. It is a figure which shows the flowchart of the mask process in a drive circuit in the power converter device which concerns on embodiment of this invention. In a power converter concerning an embodiment of the present invention, it is a figure showing a voltage waveform, a current waveform, etc. when overcurrent occurs after overheating abnormality occurs. It is a figure which shows a voltage waveform, a current waveform, etc. when a short circuit current generate | occur | produces after generation | occurrence | production of an overheating abnormal state in the conventional power converter device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power converter 11 Drive circuit 13 Current detection means 14 Short-circuit protection means Q, Q1-Q6 Switching element

Claims (6)

A switching element;
A drive circuit for driving the switching element;
Current detecting means for detecting a current flowing through the switching element;
When a short circuit state is detected by the current detection unit, a short circuit protection unit that limits the current flowing through the switching element to a predetermined range and continues driving for a predetermined time;
With
In the power conversion device in which the drive circuit stops driving the switching element when an abnormal state to stop the switching element is detected,
When the short circuit state is detected after the abnormal state is detected and before the drive stop based on the abnormal state is executed,
The power conversion device is characterized in that a short-circuit protection process based on the short-circuit protection means is prioritized and executed over a drive stop based on the abnormal state. When the current detected by the current detection means is smaller than the short-circuit threshold of the current for detecting the short-circuit state and exceeds a reference value set to be equal to or higher than the over-current threshold for detecting the over-current normal state,
The power conversion device according to claim 1, wherein a drive stop execution process based on an abnormal state other than the short circuit state and the overcurrent state is not performed.   3. The drive stop based on an abnormal state other than the short-circuit state and the overcurrent state is made possible when the current detected by the current detection unit becomes a predetermined value or less. Power conversion device.   2. The drive stop based on an abnormal state other than the short circuit state and the overcurrent state is made possible after the current flowing through the switching element is limited to a predetermined range by the short circuit protection unit. 2. The power conversion device according to 2.   The drive stop execution process based on an abnormal state other than the short circuit state and the overcurrent state is made executable after a predetermined time has elapsed since the short circuit state was detected. Power conversion device.   A switching circuit; a driving circuit that drives the switching element; and a current detection unit that detects a current flowing through the switching element. When an abnormal state in which the switching element is to be stopped is detected, the switching element In the power conversion device that switches the turn-off time required to turn off from on to off according to the abnormal state and stops driving the switching element, after the first abnormal state is detected, the first If the second abnormal state having a longer turn-off time than the first abnormal state is detected before the driving stop based on the abnormal state is executed, the driving stop based on the first abnormal state is detected. Also, the power conversion device is characterized by preferentially executing the drive stop based on the second abnormal state.

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