JP2008067566A - Three-level inverter system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a three-level inverter system which prevents overvoltages of dc capacitors and is constituted so as not to make the availability factor of the system deteriorated, when a short circuit fault is caused. <P>SOLUTION: The inverter system is constituted of a dc power supply 1, three sets of switching legs 2U, 2V and 2W, and a breaker 5, where the dc power supply includes positive and negative voltage-dividing capacitors 1P, 1N on the output side, and has a three-level potential, the switching legs are connected in parallel with the power supply 1; and the breaker is provided at a midpoint between the dc power supply 1 and each of the switching legs 2U, 2V and 2W. Positive-side fuses F1 are connected in series with switching elements Q1, Q2. Q3, and Q4 in positive-side arms of each of the switching legs 2U, 2V and 2W; while negative-side fuses F2 are connected in series with these switching elements in the negative-side arms, with these switching elements are connected in series, respectively. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a three-level inverter device that converts a direct current having three levels of potentials of positive, negative, and neutral points into alternating current.

  For example, in a converter / inverter device that converts AC power to DC power, converts it back to AC power, and feeds it to a load, it has three levels for the purpose of reducing the breakdown voltage of the switching elements of the main circuit and reducing output harmonics. A semiconductor power converter is used.

  The three-level semiconductor power conversion device is a device that performs power conversion between a three-phase alternating current and a direct current having a three-level potential. The switching element of each phase conversion arm in a converter / inverter device having a normal bridge configuration is divided into two. A series configuration is adopted in which the potential between the switching elements of each conversion arm is clamped to zero potential via a clamp diode. In addition, a fuse is provided in series in each conversion arm, and when a short circuit current flows without turning off when each switching element should be turned off due to a failure or a gate circuit abnormality, an accidental ripple is prevented.

  For example, in the three-level converter, consider a case where a short circuit failure has occurred in the switching element outside the U-phase positive side conversion arm. At this time, a short-circuit current flows through the U-phase conversion arm, and the fuse on the U-phase positive side is blown.

  However, after the U-phase positive fuse is blown, the elements inside the U-phase negative conversion arm, the U-phase negative clamp diode, the negative DC capacitor, and the anti-parallel diode of the V-phase negative conversion arm are connected from the AC power supply. A charging path is formed to return to the AC power source. by this. A short-circuit current flows through the negative DC capacitor, and the negative DC capacitor is charged up to √2 times the AC power supply voltage. Since the negative side DC capacitor is charged up to √2 times the AC voltage during normal operation, it may be charged up to about twice the AC voltage when the short circuit accident occurs.

On the other hand, when the above occurs, a proposal has been made to insert a fuse into a conceivable charging loop so as not to charge a positive or negative capacitor with an AC power supply (see, for example, Patent Document 1). .
JP 2004-248479 A (page 5, FIG. 1)

  The method disclosed in Patent Document 1 is an example in the case where the power converter is a three-level converter. In the case of a three-level converter, since a short-circuit current always flows in the above-described charging mode, the fuse is blown. However, when the power converter is a three-level inverter and the load is an electric motor, the value of the charging current varies depending on the operating conditions.

  When a short-circuit current flows and the fuse is blown, it is necessary to replace the fuse in the recovery operation, which deteriorates the operating rate of the apparatus.

  The present invention has been made in view of the above problems, and provides a three-level inverter device that prevents a DC capacitor from becoming overvoltage when a short-circuit failure occurs and does not deteriorate the operating rate of the device. The purpose is to do.

  In order to achieve the above object, a three-level inverter device of the present invention comprises positive and negative DC voltage dividing capacitors on the output side, a DC power source having a three-level potential, and a 3 connected in parallel to the DC power source. A pair of switching legs; and a midpoint of the DC power supply and a circuit breaker provided between the midpoints of the switching legs of each set. Each switching leg has one end on the positive side of the DC power supply. A positive fuse connected, a positive electrode connected to the other end of the positive fuse, a first switching element having a first diode connected in reverse parallel, and a positive electrode connected to the negative electrode of the first switching element A second switching element connected in reverse parallel connection with the second diode, and a third switching element in which the positive electrode is connected to the negative electrode of the second switching element and the third diode is connected in reverse parallel connection. An element, a positive electrode connected to the negative electrode of the third switching element, a fourth switching element having a fourth diode connected in reverse parallel, one end connected to the negative electrode of the fourth switching element, and the other end A negative fuse connected to the negative side of the DC power supply; a positive clamp diode having an anode connected to the midpoint of the switching leg; a cathode connected to the negative electrode of the first switching element; and the switching leg. And a negative clamp diode having a cathode connected to the negative electrode of the third switching element, and an AC output is obtained from the negative electrode of the second switching element to supply power to the AC motor. It is characterized by that.

  According to the present invention, it is possible to provide a three-level inverter device that prevents a DC capacitor from becoming an overvoltage when a short circuit failure occurs, and does not deteriorate the operating rate of the device.

  Embodiments of the present invention will be described below with reference to the drawings.

  A three-level inverter device according to Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is a circuit configuration diagram of a three-level inverter device according to Embodiment 1 of the present invention.

  The DC power supply unit 1 supplies a DC voltage obtained from the DC power supply 1 to a series circuit composed of DC voltage dividing capacitors 1P and 1N. The DC power supply unit 1 has a voltage of 2E. Therefore, if the positive potential of the DC voltage dividing capacitor 1P is + E, the potential at the midpoint of the DC voltage dividing capacitors 1P and 1N is 0, and the negative potential of the DC voltage dividing capacitor 1N is -E.

  The DC voltage having the three-level potential obtained in this way is supplied to the switching legs 2U, 2V and 2W. In FIG. 1, the internal structure of the switching leg 2U is shown with reference numerals. Since the internal configurations of the other switching legs 2V and 2W are basically the same as those of the switching leg 2U, their reference numerals and descriptions are omitted.

  The switching leg 2U includes a positive side fuse F1 having one end connected to the positive side of the DC power supply unit 1, and a switching element Q1 having a positive electrode connected to the other end of the positive side fuse F1 and a flywheel diode D1 connected in reverse parallel. A switching element Q2 in which the positive electrode is connected to the negative electrode of the switching element Q1 and the flywheel diode D2 is connected in antiparallel, and a switching element Q3 in which the positive electrode is connected to the negative electrode of the switching element Q2 and the flywheel diode D3 is connected in antiparallel. The switching element Q4 is connected to the negative electrode of the switching element Q3, the flywheel diode D4 is connected in reverse parallel, one end is connected to the negative electrode of the switching element Q4, and the other end is connected to the negative side of the DC power supply unit 1. The negative fuse F2 and the anode at the midpoint of the switching leg 2U A positive-side clamp diode DP having a cathode connected to the negative electrode of the element Q1, the anode to the midpoint of the switching leg 2U is constructed from a negative side clamp diode DN whose cathode is connected to the negative electrode of the switching element Q3. A circuit breaker 5 is provided between the midpoint of the switching leg 2U and the midpoint of the DC power supply unit 1.

  A gate pulse is applied to the control poles of the switching elements Q1, Q2, Q3 and Q4 constituting the switching leg 2U from a control unit (not shown). The switching elements Q1, Q2, Q3, and Q4 output a desired U-phase output voltage to the midpoint of the switching elements Q2 and Q3 by PWM control, for example. This U-phase output voltage is supplied to the primary winding of the AC motor 4 as a load via the switch 3. Similarly, the V-phase output voltage and the W-phase output voltage are supplied from the switching legs 2V and 2W to the primary winding of the AC motor 4, respectively.

  With this circuit configuration, when the switching elements Q1 and Q2 are turned on, the voltage of + E from the positive electrode of the DC power supply unit 1 is switched. When the switching elements Q3 and Q4 are turned on, the voltage of -E is switched from the negative electrode of the DC power supply unit 1. When the elements Q2 and Q3 or the switching elements Q3 and Q4 are turned on, zero voltage is supplied from the midpoint of the DC power supply unit 1.

  Here, when the switching elements Q2, Q3, and Q4 are simultaneously turned on, a short-circuit current flows from the midpoint of the DC power supply unit 1 through the clamp diode DP, the switching elements Q2, Q3, and Q4 to the negative electrode of the DC power supply unit 1. End up. Such a gate pulse is called a forbidden gate, but when the switching element Q4 is short-circuited for some reason, when the switching elements Q2 and Q3 are turned on to output a zero voltage, a DC short circuit similar to the above is caused. appear. When this short circuit occurs, a short circuit current flows through the fuse F2, so that the fuse F2 is melted.

  Consider a case where the switching element Q2 also has a short-circuit fault in the above state. The operation at this time will be described below with reference to FIG.

  FIG. 2 shows a circuit configuration in which the circuit breaker 5 is on and the switch 3 is on. Since the electromagnetic contactor with a slow response is normally used for the switch 3, it may be considered that the switch 3 is kept on in the following description.

  Even if the current is not supplied between the primary winding terminals of the AC motor 4 due to the blow of the fuse F2, a voltage slightly lower than that during the operation is maintained by the residual induced voltage. If the W-phase voltage is higher than the U-phase voltage in FIG. 2, as shown by the broken line, the positive arm of the switching leg 2W from the W-phase primary winding terminal, the DC voltage dividing capacitor 1P, the clamp diode DP, and the switching A short-circuit current that goes around the U-phase primary winding terminal flows through the element Q2, and the voltage applied to the DC voltage dividing capacitor 1P increases by the residual induced voltage between W and U of the AC motor 4.

  Similarly, although the current route is not shown in FIG. 2, if the V-phase voltage is higher than the U-phase voltage, the positive arm of the switching leg 2V from the V-phase primary winding terminal, the DC voltage dividing capacitor 1P , A short-circuit current that goes around to the U-phase primary winding terminal flows through the clamp diode DP and the switching element Q2, and the voltage applied to the DC voltage dividing capacitor 1P increases by the residual induced voltage between U and V of the AC motor 4 To do. Such a voltage increase threatens not only the DC voltage dividing capacitor 1P but also the withstand voltage of the switching element of the positive arm of each phase switching leg.

  According to the first embodiment, since the short-circuit current flows through the circuit breaker 5 shown in FIG. 1, the circuit breaker 5 can be quickly interrupted by the action of the overcurrent interruption.

  The circuit breaker 5 is not limited to a normal contact type circuit breaker, and for example, a contactless circuit breaker using a semiconductor element may be applied.

  FIG. 3 is a circuit configuration diagram of the three-level inverter device according to the second embodiment of the present invention. In the second embodiment, the same parts as those in the circuit configuration diagram of the three-level inverter device according to the first embodiment shown in FIG. The second embodiment is different from the first embodiment in that voltage detectors 1B and 1C for detecting voltages of the DC voltage dividing capacitors 1P and 1N are provided, and detection voltages supplied from the voltage detectors 1B and 1C. Is provided, and a determination circuit 6 for providing a trip signal to the circuit breaker 5 is provided.

  The determination circuit 6 is configured to give a trip signal to the circuit breaker 5 when the detection voltage of any one of the voltage detectors 1B and 1C exceeds a predetermined value. The overcurrent trip level of the circuit breaker 5 is set higher than the overcurrent trip level in the first embodiment.

  According to the second embodiment, since the circuit breaker 5 is tripped when the voltage of each of the direct-current voltage dividing capacitors 1P and 1N reaches a problematic voltage, an unnecessary trip of the circuit breaker 5 is prevented. As a result, the operating rate of the apparatus can be further improved.

  FIG. 4 is a circuit configuration diagram of the three-level inverter device according to the third embodiment of the present invention. Regarding the respective parts of the third embodiment, the same parts as those of the circuit configuration diagram of the three-level inverter device according to the first embodiment of FIG. The third embodiment differs from the first embodiment in that a voltage detector 7 for detecting the terminal voltage of the AC motor 4 is provided, a signal that the detected voltage of the voltage detector 7 exceeds a predetermined value, and each switching leg. This is that a determination circuit 6A having a function of giving a trip signal to the circuit breaker 5 under an AND condition of a signal in which any one of the fuses is blown is provided.

  The fuse blow signal is obtained from, for example, the OR condition of the auxiliary contact attached to each fuse. In the third embodiment, the overcurrent trip level of the circuit breaker 5 is set higher than the overcurrent trip level in the first embodiment.

  If the operating speed of the AC motor 4 is low, the residual induced voltage is low. Therefore, even if the fuse is blown by a short circuit failure and a short circuit as shown in FIG. 2 is formed, the voltage rise of the DC voltage dividing capacitor is small and does not cause a problem. Therefore, according to the third embodiment, as in the second embodiment, unnecessary tripping of the circuit breaker 5 can be prevented, and the operating rate of the apparatus can be further improved.

The circuit block diagram of the 3 level inverter apparatus which concerns on Example 1 of this invention. FIG. 3 is an operation explanatory diagram of the first embodiment. The circuit block diagram of the 3 level inverter apparatus which concerns on Example 2 of this invention. The circuit block diagram of the 3 level inverter apparatus which concerns on Example 3 of this invention.

Explanation of symbols

1 DC power supply 1A DC power supply 1P, 1N DC voltage dividing capacitor 1B, 1C Voltage detector 2U, 2V, 2W Switching legs Q1, Q2, Q3, Q4 Switching elements D1, D2, D3, D4 Flywheel diode DP, DN Clamp Diode F1, F2 Fuse 3 Switch 4 AC motor 5 Circuit breaker 6, 6A Judgment circuit 7 Voltage detector

Claims (3)

DC power supply having positive and negative DC voltage dividing capacitors on the output side and having a three-level potential;
Three sets of switching legs connected in parallel to the DC power supply;
It consists of a circuit breaker provided between the midpoint of the DC power supply and the midpoint of each set of switching legs,
Each of the switching legs is
A positive fuse having one end connected to the positive side of the DC power supply;
A first switching element having a positive electrode connected to the other end of the positive fuse and having a first diode connected in reverse parallel;
A second switching element having a positive electrode connected to the negative electrode of the first switching element and a second diode connected in antiparallel;
A third switching element having a positive electrode connected to the negative electrode of the second switching element and a third diode connected in reverse parallel;
A fourth switching element having a positive electrode connected to the negative electrode of the third switching element and an antiparallel connection of a fourth diode;
A negative fuse having one end connected to the negative electrode of the fourth switching element and the other end connected to the negative side of the DC power supply;
A positive-side clamp diode having an anode connected to the midpoint of the switching leg and a cathode connected to the negative electrode of the first switching element;
An anode at the midpoint of the switching leg, and a negative clamp diode having a cathode connected to the negative electrode of the third switching element,
An AC output is obtained from the negative electrode of the second switching element to supply power to the AC motor.   2. The three-level inverter device according to claim 1, wherein when the voltage of one of the positive and negative DC voltage dividing capacitors exceeds a first predetermined value, the circuit breaker is tripped. 3.   The circuit breaker is tripped when either the positive side fuse or the negative side fuse trips and the terminal voltage of the AC motor exceeds a second predetermined value. The three-level inverter device according to claim 1.

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