WO2023032426A1

WO2023032426A1 - Power conversion device

Info

Publication number: WO2023032426A1
Application number: PCT/JP2022/024860
Authority: WO
Inventors: 卓郎新井; 洋平久保田; 元紀西尾; 正樹金森; 慶一加藤; 健太山本
Original assignee: 東芝キヤリア株式会社
Priority date: 2021-09-02
Filing date: 2022-06-22
Publication date: 2023-03-09
Also published as: JPWO2023032426A1

Abstract

The present invention provides a power conversion device that is connected in parallel with an air conditioner to a plurality of power supply lines of an AC power system to which the air conditioner is connected with a breaker interposed. The power conversion device has a plurality of unit converters including a plurality of switch elements and a capacitor connected to an output terminal via these switch elements, DC voltage of a plurality of levels is outputted from the output terminal by turning on and off each switch element, and a multilevel converter formed by serially connecting these unit converters is provided at the downstream side from the breaker in each of the power supply lines.

Description

power converter

An embodiment of the present invention relates to a power converter that is connected in parallel with an air conditioner to a power line of an AC power supply system to which an air conditioner is connected via a breaker.

An active filter that is connected to a power line to which an air conditioner equipped with an inverter device that easily generates harmonics is connected and that supplies AC voltage to the power line to suppress harmonics generated by the air conditioner. Are known. A power converter such as a two-level converter is used as such an active filter.

In addition, a breaker for overcurrent cutoff is placed on the power line to which the air conditioner is connected. The breaker operates to cut off the power line when an excessive current flows in the power line. For example, when a system short-circuit current flows from the power supply line to the air conditioner due to an inverter, motor, or the like in the air conditioner, the breaker operates to prevent damage to the power system from spreading.

JP-A-1-227630

When a short-circuit failure occurs in a switch element of a two-level converter, which is a power conversion device, a system short-circuit current flows from the power line to the power conversion device, the breaker of the power line is activated, and the operation of the air conditioner stops. .

Therefore, an object of the embodiments of the present invention is to provide a power converter that can suppress harmonics in an air conditioner and avoid unnecessary shutdown of the air conditioner.

The power conversion device of the embodiment is connected to a plurality of power lines of an AC power supply system to which an air conditioner is connected via a breaker in parallel with the air conditioner, and a plurality of switch elements and these switch elements are connected to each other. a plurality of unit converters each including a capacitor connected to the output terminal via an on/off switching element for outputting a plurality of levels of DC voltage from the output terminal; A connected multi-level converter was provided downstream of the breaker in each of the power supply lines.

1 is a block diagram showing the configuration of an embodiment; FIG. The figure which shows the structure of each unit converter in one Embodiment. The figure which shows the switching pattern of each unit converter in one Embodiment. The figure which shows the structure of the principal part of the control part in one embodiment. FIG. 5 is a diagram showing the configuration of a voltage command value calculation unit in FIG. 4; FIG. 4 is a diagram showing waveforms of voltage and current of each part in one embodiment; FIG. 5 is a diagram showing the configuration of a cell failure detection unit in FIG. 4; The figure which shows the path|route of the short circuit fault of a switch element, and a system short circuit current in one Embodiment. FIG. 4 is a diagram showing changes in load current and cell output voltage before and after a short circuit fault in one embodiment; The figure which shows the change of the load current before and behind the short circuit failure in the modification of one embodiment, and a cell output voltage. The figure which shows the path|route of the short-circuit fault of a switch element, and a system|strain short-circuit current in the modification of one Embodiment. The figure which shows the state of the short circuit failure of a switch element, and a bypass switch in the modification of one Embodiment. The block diagram which shows the structure of the modification of one Embodiment.

An embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, U-phase, V-phase, and W-phase power lines (first, second, and third power lines) Lu, Lv, and Lw of a three-phase AC system (including an electric power system and a distribution system) 1 have An air conditioner 2 is connected via a breaker B for overcurrent interruption. The air conditioner 2 includes a rectifier circuit 3 that rectifies the system voltages (three-phase AC voltages) Eu, Ev, and Ew of the power lines Lu, Lv, and Lw by bridge-connected diodes 3a to 3f, and the output voltage of the rectifier circuit 3 is A DC capacitor 5 applied through a DC reactor 4, an inverter 6 converting the voltage of the DC capacitor 5 into an AC voltage of a predetermined frequency and outputting it, a compressor motor 7 operated by the output of the inverter 6, and the compressor It includes a current detector 8 that detects a current (motor current) flowing through the motor 7, and a controller 9 that controls the inverter 6 according to the detection result of the current detector 8 and a command from a control section 15, which will be described later.

A power conversion device 10 of the present embodiment is connected in parallel with the air conditioner 2 between the breaker B and the air conditioner 2 on the power lines Lu, Lv, and Lw. An electric device 30 such as another air conditioner is connected to the power lines Lu, Lv, and Lw between the breaker B and the upstream side of the connecting position of the power converter 10 .

The power conversion device 10 includes switch contacts (for example, normally closed relay contacts) Su, Sv, and Sw,

buffer reactors

11u, 11v, and 11w, these switch contacts Su, Sv, and Sw, and the

buffer reactors

11u, 11v, and 11w. Multilevel converters (first, second and third multilevel converters) 12u having one end connected to the downstream side of the breaker B in the power supply lines Lu, Lv and Lw via and the other end interconnected (star connection) , 12v, 12w, and the power supply lines Lu, Lv, Lw, the system voltages Eu, Ev, Ew and the current flowing through the air conditioner 2 are arranged at positions closer to the air conditioner 2 than the connection positions of the switch contacts Su, Sv, Sw. Detectors 13 for detecting ILu, ILv, and ILw (referred to as load currents) are arranged in current paths between the

buffer reactors

11u, 11v, and 11w and the

multilevel converters

12u, 12v, and 12w, and the

multilevel converters

12u, 12v, and 12w. A detector 14 for detecting compensation currents (also referred to as output currents) Icu, Icv and Icw supplied from 12v and 12w to power supply lines Lu, Lv and Lw, multi-level conversion according to the detection results of these

detectors

13 and 14 It includes a control section 15 for controlling the

devices

12u, 12v, and 12w, and a control power supply section 16 for outputting a DC voltage (referred to as operating voltage) Vdd necessary for the operation of the control section 15. FIG. The operating voltage Vdd is, for example, 5V or 15V, and is also used as an operating voltage for voltage detectors 34, 44, 54 (described later) in the

multilevel converters

12u, 12v, 12w.

The switch contacts Su, Sv, and Sw are controlled to be opened and closed by the control unit 15, and are normally in a closed state, and are opened in an emergency such as the occurrence of a short circuit.
A terminal of the potential G serving as a reference for the output voltage of the control power supply section 16 is connected to, for example, a neutral point K which is an interconnection point of the other ends of the

multilevel converters

12u, 12v, and 12w. This potential G terminal may be connected to the negative side terminal of the DC capacitor 5 for fixing the potential.

A multi-level converter 12u connected to a power supply line Lu includes a plurality of

unit converters

21u, 22u, and 23u, each of which selectively generates and outputs a plurality of levels (multi-levels) of DC voltages by switching, connected in series (cascaded). connected), and the output voltages (cell output voltages) Vcu1, Vcu2, and Vcu3 of the

unit converters

21u, 22u, and 23u are added to form a sine wave for reducing harmonics. An AC voltage Vcu0 with a similar waveform is generated and output.

The multi-level converter 12v connected to the power supply line Lv is a so-called multi-serial converter formed by connecting in series a plurality of

unit converters

21v, 22v, and 23v, each of which selectively generates and outputs a plurality of levels of DC voltage by switching. The output voltages (cell output voltages) Vcv1, Vcv2, and Vcv3 of the

unit converters

21v, 22v, and 23v, which are converter clusters, are added to generate an AC voltage Vcv0 with a waveform close to a sine wave for reducing harmonics. output.

A multilevel converter 12w connected to a power supply line Lw includes a plurality of unit converters (third unit converters) 21w, 22w, and 23w each selectively generating and outputting a plurality of levels of DC voltages by switching. It is a so-called multi-serial converter cluster formed by connecting, and the output voltages (cell output voltages) Vcw1, Vcw2, and Vcw3 of the

unit converters

21w, 22w, and 23w are added to form a near sine wave for reducing harmonics. A waveform AC voltage Vcw0 is generated and output. Although the number of unit converters 21, 22, and 23 included in each multilevel converter 12 is three here, any number of unit converters 21, 22, and 23 may be used as long as the number is two or more.

In order to make the load currents ILu, ILv, ILw as close as possible to sinusoidal waves synchronized with the system voltages Eu, Ev, Ew, the control unit 15 controls compensation currents Icu, Icv, Icw to be added to the load currents ILu, ILv, ILw. are calculated respectively. Further, the control unit 15 calculates AC voltages Vcu0, Vcv0, Vcw0 required to supply the calculated compensation currents Icu, Icv, Icw, and

unit converters

21u, 22u, 23u for obtaining the AC voltages Vcu0. to determine the output voltages Vcu1, Vcu2 and Vcu3. Then, the control section 15 controls the operation of each unit converter in the

multilevel converters

12u, 12v, 12w so as to obtain the determined output voltages Vcu1, Vcu2, Vcu3.

AC voltages Vcu0, Vcv0, Vcw0 are supplied from the

multilevel converters

12u, 12v, 12w to the power supply lines Lu, Lv, Lw, thereby compensating and suppressing harmonics contained in the load currents ILu, ILv, ILw. be able to. That is, the power converter 10 operates as a so-called active filter.

FIG. 2 shows the circuit configuration of the

unit converters

21u, 22u, and 23u in the multilevel converter 12u.
The unit converter 21u has output terminals P1 and N1, a first switch element leg formed by connecting in series switch elements Q1a and Q1b each having a parasitic diode D, and switch elements Q1c and Q1d each having a parasitic diode D connected in series. A second switch element leg connected in parallel to the first switch element leg, a capacitor C1 connected to the output terminals P1 and N1 through these switch elements Q1a to Q1d, and a switch according to a drive signal from the control unit 15. A drive section (gate amplifier) 31 that drives the elements Q1a and Q1b on and off, a drive section 32 that drives the switch elements Q1c and Q1d on and off according to the drive signal from the control section 15, the voltage of the capacitor C1 (capacitor voltage ) is converted into a DC voltage (referred to as an operating voltage) required for the operation of the

drive units

31 and 32, and the operation voltage Vdd output from the control power supply unit 16 operates to convert the capacitor voltage Vc1 to A voltage detection unit 34 that detects and notifies the control unit 15, a shunt resistor 35 provided in the current path to the capacitor C1, detects the voltage generated in the shunt resistor 35, and notifies the control unit 15 of the detected result of the capacitor current. Including a buffer circuit 36 and a bypass switch (for example, a bidirectional semiconductor switch) 37 connected to the output terminals P1 and N1, selectively forming a plurality of conducting paths by turning on and off (opening and closing) the switch elements Q1a to Q1d. generates and outputs a DC voltage Vcu1 of multiple levels (positive level, zero level, negative level).

The unit converter 22u has output terminals P2 and N2, a first switch element leg formed by connecting in series switch elements Q2a and Q2b each having a parasitic diode D, and switch elements Q2c and Q2d each having a parasitic diode D connected in series. A second switch element leg connected in parallel to the first switch element leg, a capacitor C2 connected to the output terminals P2 and N2 through these switch elements Q2a to Q2d, and a switch according to a drive signal from the control unit 15. A drive section (gate amplifier) 41 that drives the elements Q2a and Q2b on and off, a drive section 42 that drives the switch elements Q2c and Q2d on and off according to the drive signal from the control section 15, the voltage of the capacitor C2 (capacitor voltage ) is converted into a DC voltage (referred to as operating voltage) necessary for the operation of the

drive units

41 and 42, and the operating voltage Vdd output from the control power supply unit 16 operates to convert the capacitor voltage Vc2 into A voltage detection unit 44 that detects and notifies the control unit 15, a shunt resistor 45 provided in the current path to the capacitor C2, detects the voltage generated in the shunt resistor 45, and notifies the control unit 15 of the detected result of the capacitor current. A buffer circuit 46 includes a bypass switch (for example, a bidirectional semiconductor switch) 47 connected to the output terminals P2 and N2. It generates and outputs a DC voltage Vcu2 of (positive level/zero level/negative level).

The unit converter 23u has output terminals P3 and N3, a first switch element leg formed by connecting in series switch elements Q3a and Q3b each having a parasitic diode D, and switch elements Q3c and Q3d each having a parasitic diode D connected in series. A second switch element leg connected in parallel to the first switch element leg, a capacitor C3 connected to the output terminals P3 and N3 via these switch elements Q3a to Q3d, and a switch according to a drive signal from the control unit 15. A drive section (gate amplifier) 51 that drives the elements Q3a and Q3b on and off, a drive section 52 that drives the switch elements Q3c and Q3d on and off according to the drive signal from the control section 15, the voltage of the capacitor C3 (capacitor voltage ) Vc3 into a DC voltage (referred to as an operating voltage) required for the operation of the

drive units

51 and 52, and the operating voltage Vdd output from the control power supply unit 16 operates to convert the capacitor voltage Vc3 into A voltage detection unit 54 that detects and notifies the control unit 15, a shunt resistor 55 provided in the current path to the capacitor C3, detects the voltage generated in the shunt resistor 55, and notifies the control unit 15 of the detected result of the capacitor current. A buffer circuit 56 includes a bypass switch (for example, a bidirectional semiconductor switch) 57 connected to the output terminals P3 and N3. It generates and outputs a DC voltage Vcu3 of (positive level/zero level/negative level).

The switching elements Q1a to Q3d of the

unit converters

21u, 22u, and 23u are semiconductor switching elements such as MOSFETs and IGBTs. The bypass switches 37, 47, and 57 are controlled to be turned on and off by the control unit 15, and are normally in an off (open) state, and are turned on (closed) in an emergency such as when a short circuit occurs.

There are a first, a second, a third, and a fourth energization paths as the plurality of energization paths formed by turning on and off the switch elements Q1a to Q1d in the unit converter 21u. Similarly, there are first to fourth conducting paths as a plurality of conducting paths formed by turning on and off the switching elements Q2a to Q2d in the unit converter 22u. Similarly, there are first to fourth energizing paths as the plurality of energizing paths formed by turning off.

For example, as shown in the unit converter 21u in FIG. 2, during the positive level period of the system voltage Eu, the switching elements Q1b and Q1d are turned on and the switching elements Q1a and Q1c are turned off, so that the output terminals P1 and N1 are mutually connected. A first conduction path is formed as shown by a solid arrow to conduct between and bypass the capacitor C1, and a zero level cell output voltage Vcu1 (=0) is generated between the output terminals P1 and N1.

As shown in the unit converter 22u in FIG. 2, the switching elements Q2a and Q2c are turned on and the switching elements Q2b and Q2d are turned off during the positive level period of the system voltage Eu. A fourth conducting path is formed between them to bypass the capacitor C2 as indicated by the solid line arrow, and a zero level cell output voltage Vcu2 (=0) is generated between the output terminals P2 and N2. Either the operation shown in the unit converter 21u or the operation shown in the unit converter 22u may be used for the zero-level cell output voltage.

As indicated by the solid line arrow in the unit converter 23u in FIG. 2, during the positive level period of the system voltage Eu, the switching elements Q3a and Q3d are turned on and the switching elements Q3b and Q3c are turned off. A second conducting path is formed which conducts one end of the output terminal N3 and the other end of the capacitor C3, and a positive level cell output voltage Vcu3 (=+Vc) based on the capacitor voltage Vc3 is applied to the output terminals P3 and N3. occur between

As indicated by the dashed arrow in the unit converter 23u in FIG. 2 as well, during the positive level period of the system voltage Eu, the switching elements Q3a and Q3d are turned on and the switching elements Q3b and Q3c are turned off. A third conducting path is formed which conducts one end of C3 and the output terminal P3 and the other end of the capacitor C3, and a negative level cell output voltage Vcu3 (=-Vc) based on the capacitor voltage Vc3 is applied to the output terminal P3. , N3.

The output terminal P1 of the unit converter 21u is connected to the power supply line Lu via the switch contacts Su, Sv, Sw and the buffer reactor 11u as one end of the multilevel converter 12u, and the output terminal N1 of the unit converter 21u is used for unit conversion. The output terminal P2 of the unit converter 22u is connected, the output terminal P3 of the unit converter 23u is connected to the output terminal N2 of the unit converter 22u, and the output terminal N3 of the unit converter 23u serves as the other end of the multilevel converter 12u. It is interconnected (star connection) with the other ends of the

multilevel converters

12v and 12w. By serial connection (cascade connection) of these

unit converters

21u, 22u and 23u, a voltage Vcu0 obtained by adding together the cell output voltages Vcu1, Vcu2 and Vcu3 of the

unit converters

21u, 22u and 23u is supplied to the power supply line Lu. In the example of FIG. 2, Vcu0=“0”+“0”+“+Vc”=+Vc.

FIG. 3 shows the relationship between the ON/OFF pattern of the switch elements Q1a to Q1d for obtaining the cell output voltage Vcu1 of multiple levels (positive level, zero level, negative level) from the unit converter 21u and the cell output voltage Vcu1. In order to obtain a desired level, pulse width modulation control (PWM control) may be performed using a triangular modulated wave and a command value signal that indicates a target output voltage.

A state in which all of the switch elements Q1a to Q1d in the unit converter 21u are turned off is called a gate block (GB) state. In this case, conduction paths are formed between the output terminals P1, N1 and the capacitor C1 through the parasitic diodes D of the switch elements Q1a to Q1d, respectively. When all of the switch elements Q1a-Q1d are turned on, the capacitor C1 is short-circuited through the switch elements Q1a-Q1d.
Although the operation of the unit converter 21u has been mainly described so far, the operation is the same for the

unit converters

22u and 23u.

The voltage detection unit 34 of the unit converter 21u has an inverting input terminal (-) connected to one end of the capacitor C1 via the first voltage dividing resistor R1, and the other end of the capacitor C1 to the second voltage dividing resistor R2. A non-inverting input terminal (+) connected to a common potential G through a third voltage dividing resistor R3, and connected to the inverting input terminal (-) through a fourth voltage dividing resistor R4. The difference between the potential of the inverting input terminal (-) and the potential of the non-inverting input terminal (+), that is, the voltage across the capacitor C1 (capacitor voltage) Vc1 It is a differential amplifier circuit that outputs a voltage Vx1 of a corresponding level from an operational amplifier A. FIG.

Similarly, the voltage detection section 44 of the unit converter 22u and the voltage detection section 54 of the unit converter 23u also detect voltages Vx2 and Vx3 at levels corresponding to the voltages (capacitor voltages) Vc2 and Vc3 across the capacitors C2 and C3, respectively. Output from each operational amplifier A.

Each of the operational amplifiers A of the

unit converters

21u, 22u, and 23u has a positive power supply terminal to which a positive voltage +Vdd based on the operating voltage Vdd output from the control power supply section 16 shown in FIG. and a negative power supply terminal to which a negative voltage -Vdd is applied. If an offset circuit is provided to remove fluctuations in the potential of the negative power supply terminal, only the positive voltage +Vdd may be applied to the operational amplifier A as the operating voltage.
Although the configuration and operation of the multilevel converter 12u have been described so far, the configuration and operation are the same for the

multilevel converters

12v and 12w.

[Control unit 15]
As shown in FIG. 4, the control unit 15 includes a voltage command value calculation unit 61 and a PWM control unit 62 as control means for each unit converter of the

multilevel converters

12u, 12v, and 12w. , 12v, and 12w includes a cell failure detection section 63 as detection means for detecting a short circuit failure of each switch element. An inverter circuit 64 and an AND circuit 65 are included as control means for turning off all switch elements Q1a to Q3d of each unit converter in the

multilevel converters

12u, 12v, 12w.

[Voltage command value calculator 61]
A voltage command value calculator 61 calculates voltage command values Vcu sinθ and Vcv sin(θ−2π/ 3), Vcw sin (θ+2π/3) is set, and as shown in FIG. 74 included.

A compensating current command unit 71 computes the load currents ILu, ILv, and ILw in rotational coordinates and removes low frequency components from the computation results, thereby obtaining a d-axis compensating current command value Id_comp and a q-axis compensating current command value for harmonic suppression. Iq_comp is obtained, and the d-axis compensation current command value Id_comp is added with the current command value Id_avr for controlling the capacitor voltage average value and the d-axis negative-phase current command value Id_inv for suppressing the imbalance of the capacitor voltage average value. Thus, the d-axis current command value Id_ref is obtained, and the q-axis negative-phase current command value Iq_inv for suppressing the imbalance between the phases of the capacitor voltage average value is added to the q-axis compensation current command value Iq_comp obtained above. Obtain the q-axis current command value Id_ref. A method of calculating the d-axis negative-phase current command value Id_inv and the q-axis negative-phase current command value Iq_inv will be described later.
Id_ref = Id_comp + Id_avr + Id_inv
Iq_ref = Iq_comp + Iq_inv

The capacitor voltage average value command unit 72 calculates a proportional integral (PI) gain for the deviation between the cell voltage command value for each unit converter and the capacitor voltage average values Vcux, Vcvx, and Vcwx in the

multilevel converters

12u, 12v, and 12w. to obtain the current command value Id_avr.

The capacitor voltage average value balance command unit 73 converts the capacitor voltage average values Vcux, Vcvx, and Vcwx in the

multilevel converters

12u, 12v, and 12w into three phases and two phases according to the following equations.

By this three-phase to two-phase conversion, the interphase deviations of the capacitor voltage average values Vcux, Vcvx, and Vcwx can be converted into the a-axis capacitor voltage Vca and the b-axis capacitor voltage Vcb. By controlling the a-axis capacitor voltage Vca and the b-axis capacitor voltage Vcb to be zero, it is possible to suppress interphase imbalance of the capacitor voltage average values Vcux, Vcvx, and Vcwx.

The capacitor voltage average value balance command unit 73 multiplies the a-axis capacitor voltage Vca and the b-axis capacitor voltage Vcb by a proportional integral gain, and converts the multiplication result into a rotating coordinate at a double angular frequency as shown in the following equation. , the d-axis negative-phase current command value Id_inv and the q-axis negative-phase current command value Iq_inv for suppressing the imbalance of the capacitor voltage average values Vcux, Vcvx, and Vcwx are obtained.

Based on the d-axis current command value Id_ref and the q-axis current command value Id_ref obtained by the compensation current command unit 71, the compensation current control unit 74 converts AC voltages having substantially the same waveforms as the system voltages Eu, Ev, and Ew to the multilevel converter. 12u, 12v, 12w and the negative phase current of the system frequency (the frequency of the AC voltage of the three-phase AC system 1) that suppresses the unbalance of the capacitor voltage average values Vcux, Vcvx, Vcwx when it occurs Power supply line Sets and outputs voltage command values Vcu sinθ, Vcv sin(θ−2π/3), and Vcw sin(θ+2π/3) for flowing through power supply lines Lu, Lv, and Lw. FIG. 6 shows waveforms of currents including the voltage of each part at this time and the d-axis reversed-phase current command value Id_inv and the q-axis reversed-phase current command value Iq_inv.

[PWM controller 62]
The PWM control unit 62 controls the voltage level of the triangular carrier signal and the voltage levels of the voltage command values Vcu sinθ, Vcv sin(θ−2π/3), and Vcw sin(θ+2π/3) from the voltage command value calculation unit 61. is generated by pulse width modulation that compares . The generated gate signal is supplied to each unit converter of the

multilevel converters

12u, 12v and 12w via one input terminal of the AND circuit 65. FIG.

[Cell failure detector 63]
A cell failure detection unit 63 detects a failure of each unit converter based on the voltage of all the capacitors C1 to C3 and the current flowing through all the capacitors C1 to C3 in each unit converter of the

multilevel converters

12u, 12v, and 12w. It detects a failure and outputs a logic "1" cell failure signal when there is a failure, and includes comparison/

determination units

81, 82, 83 and an OR circuit 84 as shown in FIG. The generated cell failure signal is supplied to the other input terminal of the AND circuit 65 with its logic inverted by the inverting circuit 64 and supplied to the controller 9 of the air conditioner 2 .

If any of the voltages Vc1 to Vc3 of all the capacitors C1 to C3 in each unit converter of the

multilevel converters

12u, 12v, and 12w is smaller than the first threshold, the comparison determination unit 81 determines that the capacitor with the smaller voltage exists. It is determined that there is a short-circuit fault in the switching element of the unit converter. For example, when the voltage of the capacitor C1 of the unit converter 21u (detected voltage of the voltage detector 34) Vc1 becomes smaller than the first threshold value, the comparison and determination unit 81 selects one of the switch elements Q1a to Q1d of the unit converter 21u. determines that there is a short circuit fault, and issues a logic "1" cell fault signal.

multilevel converters

12u, 12v, and 12w is greater than the second threshold (>first threshold), the comparison determination unit 82 Determine that there is some fault in the unit converter where the large voltage capacitor resides. For example, when the voltage of the capacitor C2 of the unit converter 21v (detected voltage of the voltage detector 44) Vc2 is greater than the second threshold (>first threshold), the comparison determination unit 82 determines that the unit converter 21v has some kind of failure. and issues a logic "1" cell failure signal.

If the current flowing through any one of the capacitors C1 to C3 in each unit converter of the

multilevel converters

12u, 12v, and 12w is equal to or greater than a threshold, the comparison determination unit 83 determines the unit in which the capacitor through which the current equal to or greater than the threshold exists. It is determined that there is a short-circuit fault in the switch element of the converter. For example, when the current flowing through the capacitor C2 of the unit converter 21v (the current detected via the shunt resistor 45) abnormally rises above the threshold value, the comparison determination unit 83 determines whether the switch elements Q1a to Q1d of the unit converter 21v It determines that there is a short circuit fault in either of them, and issues a logic "1" cell fault signal.

The cell failure signals generated from the comparison/

determination units

81 , 82 , 83 are supplied to the inverting circuit 64 through an OR circuit 84 and to the controller 9 of the air conditioner 2 .
That is, when the cell failure detection unit 63 does not detect a failure, the AND condition of the AND circuit 65 is established, so the gate signals output from the PWM control unit 62 are passed through the AND circuit 65 to the

multilevel converters

12u, 12v, and 12w. Supplied to each unit converter. As a result, all the switch elements Q1a to Q3d in each unit converter of the

multilevel converters

12u, 12v, 12w are repeatedly turned on and off.

When the cell failure detection unit 63 detects a failure, the AND condition of the AND circuit 65 is not established, so the gate signal output from the PWM control unit 62 is interrupted by the AND circuit 65 and the

multilevel converters

12u, 12v, Not supplied to each 12w unit converter. As a result, all the switch elements Q1a to Q3d in each unit converter are turned off (opened) and the off state is maintained.

[Example of short circuit failure]
As shown in FIG. 8, when a short-circuit failure (marked with x in the drawing) occurs in the switch elements Q1a and Q1b in the unit converter 21u of the multilevel converter 12u, both ends of the capacitor C1 are short-circuited through the switch elements Q1a and Q1b. A cell short-circuit current due to the discharge of the capacitor C1 flows as indicated by the dashed line in the drawing.

When a short-circuit fault occurs, the voltage Vc1 of the capacitor C1 instantly drops below the first threshold value, so that the comparison determination section 81 of the cell fault detection section 63 issues a cell fault signal of logic "1". Also, if the cell short-circuit current is equal to or greater than the threshold, the cell failure signal of logic "1" is issued from the comparison/determination unit 83 of the cell failure detection unit 63 . When a logic "1" cell failure signal is issued, all the switch elements Q1a to Q3d in each unit converter of the

multilevel converters

12u, 12v, 12w are turned off (opened) and the off state is maintained. In this case, control is performed to turn off all the switch elements Q1a to Q3d, but the switch elements Q1a and Q1b of the unit converter 21u in which the short-circuit failure has occurred remain short-circuited and do not operate.

In the unit converter 22u without a short circuit fault, all the switch elements Q1a to Q3d are turned off, and the output terminals P2 and N2 and the capacitor C2 are connected to the paths passing through the parasitic diodes D of the switch elements Q1a to Q3d, respectively. An electric path is formed. Similarly, in the unit converter 23u without a short circuit fault, all the switch elements Q1a to Q3d are turned off, and the output terminals P3, N3 and the capacitor C3 are connected to the output terminals P3, N3 and the capacitor C3 through the paths passing through the parasitic diodes D of the switch elements Q1a to Q3d, respectively. An electric path is formed to connect the

Looking at the multi-level converter 12u with a short-circuit fault and the multi-level converter 12v without a short-circuit fault, the system short-circuit current based on the line voltage Euv of the power supply lines Lu and Lv flows along the path indicated by the thick arrow in FIG. try That is, through the parasitic diodes D and all the capacitors C1, C2 and C3 of all the switch elements Q1a to Q3d in the

unit converters

21v, 22v and 23v, the parasitic power of all the switch elements Q1a to Q3d in the

unit converters

22u and 23u The system short-circuits through a path that passes through the diode D and the capacitors C2 and C3, through one of the short-circuited switch elements Q1a and Q1b in the unit converter 21u, and through the parasitic diode D of the switch elements Q1c and Q1d in the unit converter 21u. current tries to flow.

However, the path through which the system short-circuit current is to flow includes capacitors C1, C2, and C3 of

unit converters

21v, 22v, and 23v, excluding capacitor C1 of unit converter 21u. 23u capacitors C2 and C3 are interposed. If the sum of the voltages Vc1, Vc2, Vc3, Vc2, and Vc3 of these five intervening capacitors is higher than the line voltage Euv, no short-circuit current will flow.
Euv<(Vc1+Vc2+Vc3+Vc2+Vc3)

Looking at the multi-level converter 12w with a short-circuit fault and the multi-level converter 12u with no short-circuit fault, there is a unit conversion Except for the capacitor C1 of the unit 21u, the capacitors C1, C2 and C3 of the

unit converters

21w, 22w and 23w are interposed, and the capacitors C2 and C3 of the

unit converters

22u and 23u are interposed. If the sum of the voltages Vc1, Vc2, Vc3, Vc2 and Vc3 of these intervening five capacitors is higher than the line voltage Ewu, no short-circuit current will flow.
Ewu<(Vc1+Vc2+Vc3+Vc2+Vc3)

Looking at the

multilevel converters

12v and 12w with no short-circuit failure, the path through which the system short-circuit current based on the line voltage Evw of the power supply lines Lv and Lw tries to flow includes the capacitors C1 of the

unit converters

21v, 22v and 23v. , C2 and C3 are interposed, and further capacitors C1, C2 and C3 of

unit converters

22w, 22w and 23w are interposed. If the sum of the voltages Vc1, Vc2, Vc3, Vc1, Vc2, Vc3 of these intervening six capacitors is higher than the line voltage Evw, no short-circuit current will flow.
Evw<(Vc1+Vc2+Vc3+Vc1+Vc2+Vc3)

As described above, even if a short-circuit fault occurs in any of the switch elements in the unit converters of the

multilevel converters

12u, 12v, and 12w, the power supply lines Lu, Lv, and Lw are connected to the

multilevel converters

12u, 12v, and 12v. No system short-circuit current flows through 12w. Since the system short-circuit current does not flow, the breakers B of the power supply lines Lu, Lv, and Lw do not operate, and the air conditioner 2 can continue to operate. Furthermore, since the breaker B does not operate, the other electrical equipment 30 (see FIG. 1) connected in parallel with the air conditioner 2 can also continue to operate.

FIG. 9 shows changes in the load currents ILu, ILv, ILw and the cell output voltages Vcu1, Vcu2, Vcu3 of the

unit converters

21u, 22u, 23u before and after the occurrence of the short-circuit fault. Although the cell output voltage Vcu1 of the unit converter 21u drops due to the short-circuit fault, there is no problem such as a sudden increase in the load currents ILu, ILv, and ILw, and the waveform is simply in a state where harmonics are not suppressed. ing.

[Modification 1]
When a short-circuit fault occurs, the controller 9 supplied with the logic "1" cell fault signal gradually reduces the output frequency of the inverter 6. FIG.
By gradually decreasing the output frequency of the inverter 6, the rotational speed of the compressor motor 7 is gradually decreased as shown in FIG. Thereby, harmonics flowing out from the air conditioner 2 to the power supply lines Lu, Lv, Lw can be reduced.

[Modification 2]
As a modification of the cell failure detection unit 63 in the control unit 15, the comparison determination unit 81 determines whether any of the voltages Vc1 to Vc3 of all the capacitors C1 to C3 in each unit converter of the

multilevel converters

12u, 12v, and 12w is The difference between the voltage smaller than the first threshold and the average value of the voltages Vc1, Vc2, and Vc3 of each capacitor in each unit converter of the

multilevel converters

12u, 12v, and 12w is the second threshold ( >first threshold), it is determined that there is a short-circuit fault in the switch element of the unit converter having a capacitor with a voltage lower than the first threshold.
It is possible to prevent erroneous detection of a short-circuit failure, such as at startup when the voltages Vc1, Vc2, and Vc3 of the capacitors have not sufficiently increased.

[Modification 3]
When detecting a short-circuit fault, the control unit 15 turns off all the switch elements Q1a to Q3d in each unit converter of the

multilevel converters

12u, 12v, 12w, and then opens the switch contacts Su, Sv, Sw. By opening the switch contacts Su, Sv, and Sw, the

multilevel converters

12u, 12v, and 12w are separated from the power lines Lu, Lv, and Lw.

For example, in the multi-level converter 12u having the unit converter 21u in which the switch elements Q1a and Q1b are short-circuited, the capacitors C2 and C3 in the

unit converters

21v and 21w are turned off as all the switch elements Q1a to Q3d are turned off. The supply voltage will be applied to the two, and overvoltage may be applied to these capacitors C2 and C3. Also, by opening the switch contacts Su, Sv, and Sw, this overvoltage problem can be resolved, and the power converter 10 can be stopped safely.

[Modification 4]
In the above embodiment, when a short-circuit fault is detected, all the switch elements Q1a to Q3d in each unit converter of the

multilevel converters

12u, 12v, and 12w are turned off, but the unit converter of the multilevel converter 12u 21u, 22u, and 23u, all the switch elements Q1a to Q3d in the

unit converters

21u, 22u, and 23u of the multilevel converter 12u are turned off when a short circuit fault is detected in any one of the switch elements Q1a to Q3d in the

multilevel converter

21u, 22u, and 23u. When a short circuit fault of any of the switch elements Q1a to Q3d in the

unit converters

21v, 22v, and 23v of the converter 12v is detected, all the switch elements Q1a to in the

unit converters

21v, 22v, and 23v of the multilevel converter 12v When Q3d is turned off and a short-circuit failure in any of the switch elements Q1a to Q3d in the

unit converters

21w, 22w, and 23w of the multilevel converter 12w is detected, the

unit converters

21w, 22w, and 23w of the multilevel converter 12w may be configured to turn off all the switch elements Q1a to Q3d.

For example, as shown in FIG. 11, when a short-circuit fault occurs in the switch elements Q1a and Q1b in the unit converter 21u of the multilevel converter 12u, the controller 15 controls all the unit converters 21u of the multilevel converter 12u. switch elements Q1a to Q3d are turned off.

Looking at the multi-level converter 12u with a short-circuit fault and the multi-level converter 12v without a short-circuit fault, the system short-circuit current based on the line-to-line voltage Euv of the power supply lines Lu and Lv flows along the path indicated by the thick arrow in FIG. try That is, through the

unit converters

21v, 22v, 23v, through the parasitic diodes D and capacitors C2, C3 of all the switch elements Q1a to Q3d in the

unit converters

22u, 23u, the short-circuited switch element Q1a in the unit converter 21u , Q1b and the parasitic diode D of the switch elements Q1c and Q1d in the unit converter 21u.

However, at least the capacitors C2 and C3 of the

unit converters

22u and 23u intervene in the path through which the system short-circuit current flows, except for the capacitor C1 of the unit converter 21u. If the sum of the voltages Vc2 and Vc3 of the two intervening capacitors is higher than the system voltage Eu (=Euv-Ev), no short-circuit current will flow.
Eu<(Vc2+Vc3)
Only the

unit converters

22u and 23u function in the multilevel converter 12u, and the number of functioning unit converters is reduced. can continue.

[Modification 5]
When a short-circuit fault is detected, the control unit 15 turns off all the switch elements Q1a to Q3d in each unit converter of the

multilevel converters

12u, 12v, and 12w, and then detects a short-circuit fault as shown in FIG. The bypass switch 37 of the unit converter 21u having the switch elements Q1a and Q1b is turned on (closed).

By turning on the bypass switch 37, the unit converter 21u enters the bypass state within the multilevel converter 12u, and only the

unit converters

22u and 23u function within the multilevel converter 12u. Although the number of functioning unit transducers is reduced, harmonic suppression can continue with the remaining

unit transducers

22u, 23u.

[Modification 6]
In the above-described embodiment, the power conversion apparatus having a configuration in which the other ends of the

multilevel converters

12u, 12v, and 12w are interconnected (star connection) has been described. A so-called delta-connected power converter in which 12v and 12w are connected between power supply lines Lu, Lv, and Lw can also be implemented in the same manner.

In addition, the above embodiments and modifications are presented as examples and are not intended to limit the scope of the invention. These embodiments and modifications can be implemented in various other forms, and various omissions, rewrites, and modifications can be made without departing from the scope of the invention. These embodiments and modifications are included in the scope of the invention, and are included in the scope of the invention described in the claims and their equivalents.

DESCRIPTION OF SYMBOLS 1... Three-phase AC power supply, Lu, Lv, Lw... Power supply line (1st, 2nd, 3rd power supply line), 3... Air conditioner, 10... Power converter, 12u, 12v, 12w... Multilevel converter , 15... control section, 21u, 22u, 23u... unit converters, 21v, 22v, 23v... unit converters, 21w, 22w, 23w... unit converters, Q1a to Q3d... switch elements, C1, C2, C3... capacitors

Claims

A power conversion device connected in parallel with an air conditioner to a plurality of power lines of an AC power supply system to which the air conditioner is connected via a breaker,
a plurality of unit converters each including a plurality of switch elements and a capacitor connected to the output terminal through these switch elements, each of which outputs a plurality of levels of DC voltage from the output terminal by turning on and off the switch elements; and a multi-level converter formed by connecting these unit converters in series, provided on the downstream side of the breaker in each of the power supply lines.
detection means for detecting a short circuit failure of each of the switch elements in each of the unit converters of each of the multilevel converters;
control means for turning off all the switch elements in each unit converter of each multilevel converter when the detection means detects the short circuit fault;
The power converter according to claim 1, comprising:
The power lines are first, second, and third power lines of a three-phase AC system,
the multilevel converters are first, second and third multilevel converters connected to the first, second and third power supply lines;
The detection means detects each unit of the first, second and third multilevel converters based on the voltage of each capacitor in each unit converter of the first, second and third multilevel converters. detecting a short-circuit failure of each switch element in the converter;
The control means turns off all the switch elements in the unit converters of the first, second, and third multilevel converters when the detection means detects the short circuit fault.
The power converter according to claim 2.
The power lines are first, second, and third power lines of a three-phase AC system,
the multilevel converters are first, second and third multilevel converters connected to the first, second and third power supply lines;
The detection means detects each unit of the first, second and third multilevel converters based on the voltage of each capacitor in each unit converter of the first, second and third multilevel converters. detecting a short-circuit failure of each switch element in the converter;
The control means controls the unit conversion of the first multilevel converter when the detection means detects a short-circuit failure of any one of the switch elements in the unit converter of the first multilevel converter. turning off all the switch elements in the unit converter, and when the detection means detects a short circuit fault in any one of the switch elements in the unit converters of the second multilevel converter, the second multilevel converter When all the switch elements in the unit converters of the third multilevel converter are turned off, and the detection means detects a short circuit fault in any one of the switch elements in the unit converters of the third multilevel converter turning off all the switch elements in each of the unit converters of the third multilevel converter;
The power converter according to claim 2.
When any of the voltages of the capacitors in the unit converters of the multi-level converters is smaller than a threshold, the detecting means short-circuits the switch element of the unit converter having a capacitor with a voltage smaller than the threshold. determine that there is a fault,
The power converter according to claim 3.
When any of the voltages of the capacitors in the unit converters of the multi-level converters is smaller than a threshold, the detecting means short-circuits the switch element of the unit converter having a capacitor with a voltage smaller than the threshold. determine that there is a fault,
The power converter according to claim 4.
The detection means detects that any of the voltages of the capacitors in the unit converters of the multilevel converters is smaller than a first threshold and the voltage smaller than the first threshold and the voltage of the multilevel converters When the difference from the average value of the voltage of each capacitor in each unit converter is larger than a second threshold (> first threshold), the switch element of the unit converter having a capacitor with a voltage smaller than the first threshold is short-circuited. determine that there is a fault,
The power converter according to claim 3.
The detection means detects that any of the voltages of the capacitors in the unit converters of the multilevel converters is smaller than a first threshold and the voltage smaller than the first threshold and the voltage of the multilevel converters When the difference from the average value of the voltage of each capacitor in each unit converter is larger than a second threshold (> first threshold), the switch element of the unit converter having a capacitor with a voltage smaller than the first threshold is short-circuited. determine that there is a fault,
The power converter according to claim 4.
A switch provided between each line of the power supply line and each multilevel converter;
with
the control means opens the switch after turning off the switch element;
The power converter according to any one of claims 1 to 8.
each unit converter of each multi-level converter includes a bypass switch connected to each of the output terminals;
After turning off the switch element, the control means turns on the bypass switch of the unit converter having the switch element with the short circuit failure.
The power converter according to any one of claims 1 to 8.
The air conditioner includes a rectifier circuit that rectifies the voltage of the power supply line, an inverter that converts the output voltage of the rectifier circuit into an AC voltage of a predetermined frequency, and a compressor motor that operates with the output of the inverter.
The power converter according to claim 1.
Each multi-level converter generates an AC voltage having a waveform close to a sine wave by adding the output voltages of the unit converters of each multi-level converter and supplies it to the power supply line.
The power converter according to claim 1.
Each of the multi-level converters supplies a negative-phase current of a system frequency to the power supply line for suppressing an imbalance between phases of average capacitor voltage values.
The power converter according to claim 12.
Each of the multi-level converters has one end connected to the power supply line via a buffer reactor, and the other ends interconnected.
The power converter according to claim 1.
each of the multilevel converters is connected between the power supply lines via a buffer reactor, respectively;
The power converter according to claim 1.