JP2005102443A - Output voltage detecting method of power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect, as quick as possible, an output voltage of a power converter such as an inverter, while maintaining insulation performance. <P>SOLUTION: Resistors R11-R23 are connected parallel to, for example, semiconductor switch elements Q11-Q23 of IGBT or the like constituting a power converter (inverter) Conv of three-phase bridge configuration. Detectors CT1-CT3 are provided to a common line that connects the semiconductor switch elements and the resistors, for detecting a current. An output voltage is indirectly acquired from the current value, for the high-speed detection of a voltage with no delay in detection while easily attaining insulation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an output voltage detection method for a power conversion device constituted by semiconductor elements, and more particularly to an output voltage detection method capable of detecting an element failure together with its part.

FIG. 13 shows this type of conventional example. This shows a power converter that supplies arbitrary AC power to a load L connected to an output terminal by configuring a semiconductor element arbitrarily in series or parallel and connecting it to a DC power supply Ed, that is, an inverter. is there.
In FIG. 13, as a means for detecting the output voltage of the power converter, a voltage detection circuit Vsen is provided for each phase as shown, and an inverter output voltage command estimated from an on / off signal output from the control device. In general, the value is compared with the actual output voltage value detected by the voltage detection circuit Vsen, and the output voltage amount is corrected by the control device.
Examples of such a voltage detection circuit are shown in Patent Documents 1 and 2 and the like. As shown in Patent Document 1, as shown in FIG. 14, a high frequency component of an output voltage of an inverter is removed by a filter such as a resistor and a capacitor, and input through an insulation amplifier or the like.

  By the way, it is ideal that, for example, the U-phase output voltage is output from the inverter as shown in FIG. 15B by the ON / OFF signal as shown in FIG. 15A from the control device shown in FIG. It is. However, actually, as shown in FIG. 16D, on / off signals are input to a gate drive circuit GA that drives an IGBT (insulated gate bipolar transistor) as a semiconductor element, and from this GA to the gate of the IGBT. After the signal is transmitted, there is a delay of td1 and td2, as shown in FIG. Due to this delay, a deviation occurs between the output voltage command from the control device and the actual inverter output voltage. Therefore, it is necessary to detect the actual output voltage value in order to supply the load with high accuracy.

  In Patent Document 2, the AC output voltage Vac is input to the comparator CP. However, detection power sources E1 and E2 for driving the comparator CP are required. That is, the detection power supplies E1 and E2 must be newly provided, and these must be insulated from the main circuit. Furthermore, not only a means for isolating the output of the comparator CP by the photocoupler PC and transmitting it to the control device is required, but also a high-speed response of the comparator and the photocoupler is required for high-speed detection.

Japanese Patent Laid-Open No. 08-107700 (page 3, FIG. 1) Japanese Patent Laid-Open No. 06-121544 (page 3, FIG. 1)

In the above-mentioned Patent Document 1, a filter composed of a resistor, a capacitor or the like is required to remove a high frequency component from the AC output voltage of the inverter. When the time constant of the filter is reduced, there is a trade-off relationship that the detection becomes faster but the noise becomes weaker.
Therefore, an object of the present invention is to insulate the output voltage of the inverter so that it can be detected at high speed.

  In order to solve such a problem, in the invention of claim 1, in a power conversion device including one or more semiconductor elements driven by an on / off signal provided per bridge-structured arm, A resistor is connected in parallel to each other, and a detecting means for detecting a current value and a direction flowing through a common line connecting the resistors and the semiconductor elements is provided, and the detecting device can detect an AC output voltage of the power converter. It is characterized by detecting.

  According to the first aspect of the present invention, the failure of the semiconductor element can be detected together with the portion thereof by combining the on / off signal in the direction and the direction of the current flowing through the common line (the second aspect of the invention). In the invention of claim 1 or 2, when the current flowing through the common line is smaller than a predetermined value, the on / off signal can be turned off to stop the operation of the power converter. Invention).

  According to the present invention, since the AC output voltage is detected indirectly by detecting the current, the detection delay can be eliminated. In addition, by using a type of current detector that is inserted into an electric wire, such as a current transformer, it is possible to easily insulate, and because it is arranged in a separate part from the main current of the power converter, The current measurable range can be limited to a very small current range, and the size and cost can be reduced.

  FIG. 1 is a circuit diagram showing a first embodiment of the present invention, and one phase portion is shown in FIGS. FIG. 2 shows an example in which resistors R1n and R2n are connected in parallel to the devices IGBTQ1n and Q2n, respectively. When these resistors R1n and R2n are connected to the connection point Vac of the devices IGBTQ1n and Q2n, the common line (thick line) shown in FIG. 1), and when the current detector CTn is inserted into the common thick line, the result is as shown in FIG.

  The operation of FIG. 1 will be described with reference to FIGS. 4 and 5 using the circuit for one phase shown in FIG. 4A to 4D show circuit states when the power converter is operating. FIG. 4A shows a current flow through the IGBT Q1n, and FIG. 4B shows an antiparallel connection to the IGBT Q1n. 4 (c) shows the current flowing through the IGBT Q2n, and FIG. 4 (d) shows the current flowing through the FWD connected in reverse parallel to the IGBT Q2n. Show.

  That is, when the power converter is in operation, one of the states shown in FIGS. 4A to 4D is taken, and the AC output terminals output voltages of Ed, Ed, 0, 0, respectively. That is, the current detector CTn detects currents of Ed / R2n, Ed / R2n, Ed / R1n, and Ed / R1n, respectively. FIG. 5 shows these operations. As shown in the figure, the output voltage of the power converter is proportional to the value detected by the current detector CTn. From this, the output voltage of the power converter is detected by the current detector CTn. Can be detected.

  At this time, since the current detector CTn only needs to detect the current flowing through the resistor, not the main current of the power conversion device, the current detector CTn can be a small current detector. Furthermore, since the current detector CTn is insulated from the power converter, the output signal of the current detector CTn can be directly taken into the control device.

FIG. 6 is an explanatory diagram for explaining a second embodiment of the present invention, and a circuit diagram thereof is the same as FIG.
In FIG. 6A, it is assumed that the IGBT Q2n is destroyed due to some failure. In this state, when an on signal is input to the IGBT Q1n and turned on, a short circuit occurs. At this time, IGBTQ1n and IGBTQ2n each divide DC voltage Ed. When IGBTQ1n and IGBTQ2n equally divide DC voltage Ed, a voltage of Ed / 2 is generated at the output terminal. Since the connection point between the resistors R1n and R2n is also Ed / 2, no current flows through CTn.

Further, even when the voltage is not equally divided between the IGBT Q1n and the IGBT Q2n, the resistance values of the resistors R1n and R2n are
R1n = R2n = R
Then, the current Is flowing through the current detector CTn is
-Ed / R <Is <Ed / R
Therefore, it is possible to detect an element failure by setting the current value in this range as a failure. Moreover, when an element failure is detected, it is desirable to turn off all on / off signals to the element and stop the operation of the power converter.

Further, even when the element Q1n has the full DC voltage Ed, the element failure can be detected from the relationship between the direction of the current (current polarity) flowing through the current detector CTn and the on / off signal. For example, when the ON signal ON2 is given to the element Q2n in FIG. 7, it is determined that the direction of the current flowing in CTn is normal if it is FIG. 8 (a), and abnormal if it is FIG. 8 (b).
As shown in FIG. 6B, the same applies when the element Q1n is destroyed. In this case, when the element Q2n is turned on by an ON signal, a short circuit occurs. A) By detecting Is, the destruction of the element Q1n can be detected in the same manner.

  FIG. 9 is an explanatory diagram for explaining a second embodiment of the present invention. This shows two examples as an example of connecting a plurality of switching elements in series. That is, the resistors R11n, R12n, R21n, and R22n are connected in parallel to the IGBTs Q11n, Q12n, Q21n, and Q22n, respectively. Current detectors CT1n, CT2n, and CT12n are inserted into lines common to the resistors connected in parallel to the IGBTs. The operation principle of FIG. 9 is shown in FIGS.

9 and 10 correspond to FIGS. 4 and 5, respectively. Therefore, the current value Is detected by the current detector CT12n is the same as in FIGS.
Is = 2Ed / (R21n + R22n) in the case of FIGS. 9A and 9B = 2Ed / (R11n + R12n) In the case of FIGS. 9C and 9D. Here, to simplify the calculation,
R11n, R12n, R21n, R22n = R
Then, Is = 2Ed / (2R) = Ed / R
And
It is clear that detection can be performed in exactly the same manner as in FIG.

FIG. 11 shows an example in the case of a failure.
In the states of FIGS. 9A, 9B, 9C, and 9D, the currents detected by the current detectors CT1n and CT2n are all “0”. In FIG. 11, for example, if Q22n is destroyed, a current of 2 Ed / R is detected in CT2n. Thereby, it becomes possible to detect an element failure together with the part. FIG. 12 shows the relationship between the current (magnitude) and direction (polarity) of the current detector when each part fails. This is the case of FIG. 9 (a). Similarly, in each of the cases of FIGS. 9 (b), (c), and (d), an element failure is detected together with its location from the current and direction of the current detector. It becomes possible to detect.

Circuit diagram showing an embodiment of the present invention 1 is an explanatory diagram of a connection mode of resistors connected in parallel to the semiconductor element for one phase in FIG. Circuit diagram showing the case where the current detector is connected in FIG. Transition diagram of the operation state of FIG. FIG. 1 is an explanatory diagram of the operation. Short-circuit current path explanatory diagram of FIG. Operation explanatory diagram at the time of failure of FIG. Operational explanation diagram at the time of device failure of FIG. Transition diagram of operating state when each arm is composed of multiple elements Operation explanatory diagram when each arm is composed of multiple elements Explanation of operation when one phase has failed Explanatory diagram of relationship between faulty element and detected value Configuration diagram showing a conventional example of a power converter Circuit diagram showing a specific example of a conventional voltage detection circuit FIG. 13 is a diagram for explaining the operation. Explanatory drawing explaining the subject of a prior art example

Explanation of symbols

Q11, Q12, Q13, Q21, Q22, Q23, Q1n, Q2n ... IGBT (insulated gate bipolar transistor), CT1, CT2, CT3, CTn, CT1n, CT2n, CT12n ... current detector, R11, R12, R21, R22 , R13, R23, R1n, R2n, R11n, R12n, R21n, R22n ... resistors, Ed ... DC power supply.

Claims (3)

In the power conversion device comprising one or more semiconductor elements driven by an on / off signal, provided at least one arm in a bridge configuration,
A resistor is connected in parallel with each of the semiconductor elements, and a detecting means for detecting a current value flowing in a common line connecting the resistors and between the semiconductor elements and a direction thereof are provided, and a power conversion device is provided by the detecting means. The output voltage detection method of the power converter device which detects the alternating current output voltage of this.   2. The output voltage detection of the power converter according to claim 1, wherein a failure of the semiconductor element is detected together with a portion thereof by combining the on / off signal in the direction and the current value flowing through the common line. Method. 3. The power conversion device according to claim 1, wherein when the value of a current flowing through the common line is smaller than a predetermined value, the operation of the power conversion device is stopped by turning off all of the on / off signals. Output voltage detection method.

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