JP2017192297A - Multilevel power conversion device and method for controlling multilevel power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilevel power conversion device capable of evenly charging initial voltages of a plurality of smoothing capacitors at low cost.SOLUTION: A multilevel power conversion device includes a converter 210 converting AC power into DC power, an inverter 220 converting DC power of the converter unit 210 into AC power; and a plurality of smoothing capacitors C1-C4 connected in series to the converter 210 and a DC link of the inverter 220, and outputs a multi-level voltage. The multilevel power conversion device further includes: a Scotto transformer 700 to which three-phase AC from a three-phase AC power supply is input and from which two sets of single phase AC with a phase difference of 90 degrees is output; and a diode rectifier 900 performing half-wave rectification to the current output from a secondary side of the Scotto transformer 700 by diodes D1-D4 that are provided corresponding to the plurality of smoothing capacitors C1-C4, respectively, and guiding the half-wave rectified current to each of the smoothing capacitors C1-C4.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a multi-level power converter, and relates to precharging a smoothing capacitor in a DC link unit.

  A power converter having a smoothing capacitor in the DC link portion needs a precharge circuit for suppressing an inrush current flowing through the smoothing capacitor when the power is turned on. As a prior art of a power converter having a precharge circuit, for example, there is one described in Patent Document 1 (FIG. 1 of Patent Document 1 and paragraph numbers “0022” to “0048”).

  This patent document 1 discloses an auxiliary inverter device driven and controlled by a control signal for charging a smoothing capacitor in a main inverter device with a constant current before starting the main inverter device, an AC reactor, a step-up transformer, It is described that precharging (preliminary charging) is performed on a smoothing capacitor via a rectifier.

Japanese Patent Laid-Open No. 10-66388 Japanese Patent Laid-Open No. 7-79574 JP 2003-169480 A

"Transistor Technology", CQ Publisher, pp. 100-101, April 2016 issue

  Patent Document 1 described above does not consider the case of a multi-level power conversion device in which the number of output voltage levels is 3 or more, that is, the case where there are a plurality of smoothing capacitors.

  Here, FIG. 4 shows a configuration in a case where the technique of Patent Document 1 is applied to a five-level power converter. In FIG. 4, a high-voltage power supply (not shown) is connected to a load, for example, an electric motor 300 via a high-voltage circuit breaker 100 (first circuit breaker) and a five-level power converter 200.

  210 of the five-level power converter 200 is a converter unit that converts the input AC power of the high-voltage power source into DC power, 220 is an inverter unit that converts the DC output of the converter unit 210 into AC power, and C4 is a smoothing capacitor connected in series to divide the DC voltage of the DC link section of the converter section 210 and the inverter section 220.

  The plurality of semiconductor switching elements constituting the converter unit 210 and the inverter unit 220 are ON / OFF controlled by a control unit (not shown), and thereby the inverter unit 220 uses energy stored in the smoothing capacitors C1 to C4. An AC output having a five level potential corresponding to the four partial pressures is generated.

  A three-phase AC output of a low-voltage three-phase power supply (not shown) is connected to the AC input side of the rectifier 830 via a circuit breaker 400 (second circuit breaker), an auxiliary inverter 810, an AC reactor 820, and a step-up transformer 600. The positive output terminal of the rectifier 830 is connected to the positive electrode of the smoothing capacitor C1, and the negative output terminal is connected to the negative electrode of the smoothing capacitor C4.

  Before starting the five-level power conversion device 200, the control unit turns on the circuit breaker 400, and gives a drive signal to the auxiliary inverter device 810 to drive the smoothing capacitors C1 to C4 with a constant current. The smoothing capacitors C1 to C4 are charged (preliminarily charged) by the DC output of the rectifier 830.

  In this case, the smoothing capacitors C1 to C4 are charged with a voltage divided by the internal resistance values of the respective smoothing capacitors, and the internal resistance values are not uniform because they vary. If the voltage variation of the smoothing capacitors C1 to C4 increases, an excessive voltage is applied to some of the smoothing capacitors and the semiconductor switching elements connected to the smoothing capacitors, leading to overvoltage breakdown of the semiconductor switching elements.

  It also affects the AC voltage waveform (output voltage waveform) of the five-level power converter 200 and causes waveform distortion of the AC current (output current).

  Various methods for controlling and equalizing the voltage of the smoothing capacitor in the multilevel power conversion device have been proposed. For example, these methods are disclosed in Patent Documents 2 and 3. However, these methods control the voltage of the smoothing capacitor by a method such as adding a compensation value to the AC output voltage command after starting up the power conversion device (that is, after generating the output voltage by the ON / OFF operation of the semiconductor switching element). This is a technique, and the initial voltage of the smoothing capacitor before starting the power converter cannot be controlled. Therefore, these proposals cannot solve the problem of causing waveform distortion of the output current immediately after the power conversion device is started.

  Further, in the five-level power conversion device 200 configured in the same manner as in FIG. 4, voltage dispersion of the smoothing capacitors C1 to C4 is achieved by connecting balance resistors R1 to R4 in parallel with the smoothing capacitors C1 to C4 as shown in FIG. There is a method to alleviate this. However, even with this method, the voltages of the smoothing capacitors C1 to C4 are affected by variations in the resistance values of the balance resistors R1 to R4. Moreover, since these balance resistors R1 to R4 always consume power as long as a voltage is applied to the DC link portion of the five-level power converter 200, there is a problem that the loss of the power converter increases.

  In addition, when the technology of Patent Document 1 is applied and each smoothing capacitor of the multilevel power converter is charged one by one, the auxiliary inverter device 810, the AC reactor 820, and the step-up transformer 600 shown in FIGS. Is required for the number of smoothing capacitors.

Therefore, in the prior art,
If it is not connected in parallel to each smoothing capacitor, it is difficult to charge the initial voltage of the smoothing capacitor of the multi-level power converter evenly.

  ・ Connecting a balancing resistor in parallel to each smoothing capacitor can alleviate voltage variations, but it is affected by variations in resistance values of the balancing resistors. In addition, power loss due to the balance resistance also increases. Furthermore, the installation of the balance resistor increases the cost of the power conversion device and the manufacturing time.

  If a charging circuit is connected to each smoothing capacitor, an expensive AC reactor or step-up transformer is used for the number of smoothing capacitors, which increases the cost of the entire power converter.

  In the above case, since AC reactors and step-up transformers having a large volume and weight are used as many as the number of smoothing capacitors, the volume and weight of the power converter increases and the structural members that support them become expensive. This increases the cost of the power conversion device. Furthermore, the wiring work is increased when the power converter is manufactured.

  There was a problem.

  The present invention solves the above-described problems, and an object of the present invention is to provide a multilevel power conversion device and a control method therefor that can uniformly charge initial voltages of a plurality of smoothing capacitors at low cost.

The multilevel power conversion device according to claim 1 for solving the above-described problem is a converter unit that converts AC power from a first AC power source into DC power, and converts DC power of the converter unit into AC power. A multi-level power converter that has an inverter unit and a plurality of smoothing capacitors connected in series to the DC link unit of the converter unit and the inverter unit, and outputs a plurality of levels of voltage,
A single-phase alternating current is introduced from a second alternating-current power source, and individual charging current supply means for individually supplying a charging current to each of the plurality of smoothing capacitors by the single-phase alternating current is provided. .

  A multi-level power converter according to claim 2 is characterized in that, in claim 1, the first AC power supply and the second AC power supply are shared.

The multilevel power conversion device according to claim 3 is the multilevel power conversion device according to claim 1 or 2,
The individual charging current supply means includes
A Scott transformer that receives three-phase alternating current from a three-phase alternating current power supply and outputs two sets of single-phase alternating current with a phase difference of 90 degrees;
A diode rectifier that half-wave rectifies the current output from the secondary side of the Scott transformer with a diode provided corresponding to the plurality of smoothing capacitors and guides the current to each smoothing capacitor; Yes.

A multi-level power conversion device according to claim 4 is characterized in that in claim 3,
The multi-level power converter is a 5-level power converter that has first to fourth smoothing capacitors connected in series and outputs a 5-level voltage,
The Scott transformer has a main seat primary coil on the primary side and a T seat primary coil connected to the midpoint thereof, and a main seat secondary coil and a T seat secondary insulated from each other on the secondary side. Has a coil,
The diode rectifier is
The first to fourth diodes corresponding to the first to fourth smoothing capacitors are provided, and one end of the main secondary coil of the Scott transformer is connected to the first diode via the anode and cathode of the first diode. Connect to the positive electrode of the smoothing capacitor, connect the common connection point of the first smoothing capacitor and the second smoothing capacitor to the other end of the main secondary coil of the Scott transformer, and connect the negative electrode of the second smoothing capacitor to the second Is connected to one end of the main seat secondary coil via the anode and cathode of the diode, and one end of the T seat secondary coil of the Scott transformer is connected to the third smoothing capacitor via the anode and cathode of the third diode. Connect to the positive electrode, connect the common connection point of the third smoothing capacitor and the fourth smoothing capacitor to the other end of the T-seat secondary coil, and connect the negative electrode of the fourth smoothing capacitor to the fourth Wherein the diode anode of, through the cathode is constituted by connecting one end of the T locus secondary coil.

Further, the multilevel power conversion device according to claim 5 is characterized in that in claim 1 or 2,
The individual charging current supply means includes
A unit boosting rectifier circuit having a single-phase alternating current from the second alternating-current power supply as an input, connected to each of the plurality of smoothing capacitors via a third circuit breaker, and comprising the smoothing capacitors as respective output-side capacitors; And a Cockcroft-Walton circuit section connected in series with the same number as the smoothing capacitor.

A multi-level power conversion device according to claim 6 is characterized in that, in claim 5,
The multi-level power converter is a 5-level power converter that has first to fourth smoothing capacitors connected in series and outputs a 5-level voltage,
The Cockcroft-Walton circuit section is
A first input-side capacitor and a fifth anode having an anode connected to one end of the first input-side capacitor and a cathode connected to the positive electrode of the first smoothing capacitor via the first contact of the third circuit breaker; The diode and the cathode are connected to one end of the first input side capacitor, and the anode is connected to the common connection point of the first smoothing capacitor and the second smoothing capacitor via the second contact of the third circuit breaker. A first unit boost rectifier circuit having a sixth diode;
A second input side capacitor having one end connected to the other end of the first input side capacitor, an anode connected to one end of the second input side capacitor, and a cathode serving as the second contact of the third circuit breaker. A seventh diode connected to the common connection point of the first smoothing capacitor and the second smoothing capacitor, a cathode connected to one end of the second input-side capacitor, and an anode connected to the third of the third circuit breaker An eighth diode connected to a common connection point of the second smoothing capacitor and the third smoothing capacitor through the contact of the second unit boosting rectifier circuit,
A third input-side capacitor having one end connected to the other end of the second input-side capacitor, an anode connected to one end of the third input-side capacitor, and a cathode serving as the third contact of the third circuit breaker A ninth diode connected to the common connection point of the second smoothing capacitor and the third smoothing capacitor via the first input terminal, a cathode connected to one end of the third input side capacitor, and an anode connected to the fourth of the third circuit breaker. A third unit boost rectifier circuit having a tenth diode connected to a common connection point of the third smoothing capacitor and the fourth smoothing capacitor via the contact of
One end is connected to the other end of the third input side capacitor, the other end is connected to one end of the second AC power source, and the anode is connected to one end of the fourth input side capacitor. An eleventh diode whose cathode is connected to a common connection point of the third smoothing capacitor and the fourth smoothing capacitor via a fourth contact of the third circuit breaker, and a cathode of the fourth input side capacitor. A fourth diode having one end connected to one end and an anode connected to the negative electrode of the fourth smoothing capacitor and the other end of the second AC power source via the fifth contact of the third circuit breaker; Unit boost rectifier circuit,
It is characterized by having.

The control method of the multilevel power conversion device according to claim 7 is:
A converter unit that converts AC power from the first AC power source into DC power, an inverter unit that converts DC power of the converter unit into AC power, and a plurality of units connected in series to the DC link unit of the converter unit and the inverter unit In a device that has a smoothing capacitor and outputs a plurality of levels of voltage,
Individual charging current supply means for introducing a single-phase alternating current from a second alternating-current power supply and individually supplying a charging current to each of the plurality of smoothing capacitors by the single-phase alternating current; and the first alternating-current power supply And a first circuit breaker provided between the converter unit and a second circuit breaker provided between the second AC power source and the individual charging current supply means. A control method,
The control unit
Controlling the closing of the second circuit breaker when the first and second circuit breakers are off;
When the terminal voltage of each of the smoothing capacitors reaches the target voltage, opening the second circuit breaker, and then turning on the first circuit breaker;
Starting the converter unit and the inverter unit;
It is characterized by having.

A control method of a multilevel power conversion device according to claim 8 is the method according to claim 7,
The first AC power supply and the second AC power supply are shared, the first circuit breaker is provided between the shared AC power supply and the converter unit, and the second circuit breaker is It is provided between the common AC power supply and the individual charging current supply means.

A control method for a multilevel power conversion device according to claim 9 is the method according to claim 7 or 8,
The individual charging current supply means includes
A unit boosting rectifier circuit having a single-phase alternating current from the second alternating-current power supply as an input, connected to each of the plurality of smoothing capacitors via a third circuit breaker, and comprising the smoothing capacitors as respective output-side capacitors; The same number of the smoothing capacitor connected in series with the Cockcroft-Walton circuit unit,
The control unit
Controlling the closing of the second and third circuit breakers when the first, second and third circuit breakers are off;
When the terminal voltage of each smoothing capacitor reaches the target voltage, opening the second and third circuit breakers, and then turning on the first circuit breaker;
Starting the converter unit and the inverter unit;
It is characterized by having.

(1) According to the first to eighth aspects of the invention, when precharging the plurality of smoothing capacitors before starting the multilevel power converter, the initial voltages of the plurality of smoothing capacitors can be charged uniformly. . For this reason, an excessive voltage is not applied to the smoothing capacitor, the switching element of the converter part, and the inverter part, and the switching element is prevented from being destroyed by overvoltage.

  In addition, since the initial voltages of the plurality of smoothing capacitors can be charged uniformly, waveform distortion of the AC side current of the multilevel power converter can be suppressed.

In addition, since a plurality of smoothing capacitor precharge circuits are formed with a simple configuration, the cost of the entire multilevel power conversion device can be reduced.
(2) According to the second and eighth aspects of the present invention, there is no need to provide a dedicated AC power source for precharging a plurality of smoothing capacitors.
(3) According to the inventions of claims 4 and 6, when precharging the first to fourth smoothing capacitors before starting the five-level power converter, the initial voltages of the first to fourth smoothing capacitors Can be charged evenly, so that an excessive voltage is not applied to the smoothing capacitor, the switching element of the converter part, and the inverter part, and the switching element is prevented from being destroyed by overvoltage.
(4) According to the inventions of claims 5 and 6, since the Cockcroft-Walton circuit is used as the individual charging current supply means, the direct current is twice the peak value of the voltage on the input side of the Cockcroft-Walton circuit. Each smoothing capacitor can be charged with a voltage.

For this reason, the output voltage of the transformer for introducing a single-phase alternating current into the Cockcroft-Walton circuit may be a low voltage value, and the transformer can be miniaturized. Thereby, the cost of the entire multilevel power conversion device can be reduced.
(5) According to the inventions described in claims 7 and 8, the multilevel power conversion device can be started after the initial voltages of the plurality of smoothing capacitors are charged uniformly. For this reason, an excessive voltage is not applied to the smoothing capacitor, the switching element of the converter part, and the inverter part, and the switching element is prevented from being destroyed by overvoltage.

  In addition, since the initial voltages of the plurality of smoothing capacitors can be charged uniformly, waveform distortion of the AC side current of the multilevel power converter can be suppressed.

The block diagram of the 5 level power converter device by Example 1 of this invention. The block diagram of the 5 level power converter device by Example 2 of this invention. The Cockcroft-Walton circuit of a nonpatent literature 1 is represented, (a) is a circuit diagram, (b) is a voltage waveform figure of each point of the output side of Fig.3 (a). The block diagram of the 5 level power converter device to which the technique of patent document 1 is applied. The block diagram of the 5 level power converter device which applied the method of relieving the voltage variation of a smoothing capacitor to the apparatus of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments.

  FIG. 1 shows a configuration of a first embodiment in which the present invention is applied to a five-level power converter, and the same parts as those in FIG. 4 are denoted by the same reference numerals.

  In the DC link unit that connects the converter unit 210 and the inverter unit 220 of the five-level power converter 200, voltage detecting units 231 to 234 that detect the voltage of each smoothing capacitor are connected in parallel to the smoothing capacitors C1 to C4, respectively. Yes.

  The other end of the circuit breaker 400 whose one end is connected to a low-voltage three-phase power supply (not shown) is connected to the primary side of the step-up transformer 600 via a current limiting resistor 500. The secondary side of the step-up transformer 600 is input to the primary side of the Scott transformer 700 which receives a three-phase alternating current (U, V, W) and outputs a two-phase single-phase alternating current (u, v) having a phase difference of 90 degrees. It is connected.

  One end of the main seat primary coil 711 in the Scott transformer 700 is connected to the U-phase terminal, the other end is connected to the W-phase terminal, and the middle point is connected to one end of the T-seat primary coil 721. The other end of the T seat primary coil 721 is connected to the V phase terminal.

  One end of the main secondary coil 712 in the Scott transformer 700 is connected to the u terminal, and the other end is connected to the 0u terminal. In the Scott transformer 700, one end of the T seat secondary coil 722 insulated from the main seat secondary coil 712 is connected to the 0v terminal, and the other end is connected to the v terminal.

  The secondary side of the Scott transformer 700 is connected to the DC link unit of the five-level power converter 200 via a rectifier unit 900 having diodes D1 to D4 that function as half-wave diode rectifiers that convert AC voltage into DC voltage. Has been.

  That is, the u terminal at one end of the main seat secondary coil 712 is connected to the positive electrode of the smoothing capacitor C1 via the anode and cathode of the diode D1, and the 0 u terminal at the other end of the main seat secondary coil 712 is connected to the smoothing capacitors C1 and C2. Connected to the common connection point.

  The 0v terminal at one end of the T-seat secondary coil 722 is connected to the anode of the diode D2 and the common connection point of the smoothing capacitors C2 and C3 via the anode and cathode of the diode D3. The cathode of the diode D2 is connected to the u terminal and the anode of the diode D1. The v terminal at the other end of the T seat secondary coil 722 is connected to a common connection point of the smoothing capacitors C3 and C4.

  The negative electrode of the smoothing capacitor C4 is connected to the 0v terminal and the anode of the diode D3 via the anode and cathode of the diode D4.

  In the first embodiment, the Scott transformer 700 and the rectifying unit 900 constitute the individual charging current supply means of the present invention.

  The control unit 240 in the five-level power conversion device 200 has a function for ON / OFF control (switching control) of each semiconductor switching element of the converter unit 210 and the inverter unit 220, and voltage detection detected by the voltage detection units 231 to 234. A function of taking in values, and a function of giving ON / OFF commands to the high-voltage circuit breaker 100 and the circuit breaker 400 to perform ON / OFF switching control and confirming the ON / OFF state thereof are provided.

  Next, the operation of the 5-level power conversion device configured as described above will be described. When starting up the electric motor 300, the control part 240 confirms first that the high voltage circuit breaker 100 and the circuit breaker 400 are OFF. Next, the control unit 240 instructs the circuit breaker 400 to be turned on, and turns on the circuit breaker 400.

  When the circuit breaker 400 is turned on, the three-phase AC power from the low-voltage three-phase power source becomes high-voltage three-phase AC power via the current limiting resistor 500 and the step-up transformer 600 and is input to the Scott transformer 700. The three-phase AC power input to the Scott transformer 700 becomes two-phase isolated single-phase AC power of u-0u and 0v-v.

  When the 0u terminal potential is used as a reference, when the voltage between u and 0u is positive, current flows through a path of u terminal → diode D1 → smoothing capacitor C1 → 0u terminal, and charges the smoothing capacitor C1. When the voltage between u-0u is negative, the current flows through the path of 0u terminal → smoothing capacitor C2 → diode D2 → u terminal, and charges the smoothing capacitor C2.

  Similarly, when the voltage at the v terminal is used as a reference, when the voltage between 0 v and v is positive, the current flows through a path of 0 v terminal → diode D3 → smoothing capacitor C3 → v terminal, and charges the smoothing capacitor C3. When the voltage between 0v and v is negative, the current flows through the path of v terminal → smoothing capacitor C4 → diode D4 → 0v terminal, and charges the smoothing capacitor C4.

  Detection values detected by the voltage detection units 231 to 234 in the five-level power conversion device 200 are input to the control unit 240, and the preliminary charging is completed when the voltages of the smoothing capacitors C1 to C4 reach the target voltage.

  When the preliminary charging is completed, the control unit 240 instructs opening of the circuit breaker 400 and turns off the circuit breaker 400.

  Thereafter, the control unit 240 instructs the high voltage circuit breaker 100 to be turned on and turns on the high voltage circuit breaker 100.

  Next, the operation of the converter unit 210 and the inverter unit 220 is started by starting the ON / OFF operation of the semiconductor switching elements of the converter unit 210 and the inverter unit 220 in the five-level power converter 200.

  Each semiconductor switching element in the inverter unit 220 is ON / OFF controlled by a predetermined ON / OFF pattern, and assuming that each voltage of the smoothing capacitors C1 to C4 is E, 2E, E, 0, -E,- 5E voltage of 2E is output.

  Since the inverter unit 220 applies the output voltage to the electric motor 300, the electric motor 300 starts to start.

  In addition, after the converter part 210 and the inverter part 220 start operation, the voltage of each of the smoothing capacitors C1 to C4 is controlled to be a constant value by the ON / OFF operation of the semiconductor switching element. Therefore, the balance resistors (R1 to R4) described in FIG. 3 are not required even in the operation after the start of operation.

  The current limiting resistor 500 is installed to suppress an excessive charging current during charging of the smoothing capacitors C1 to C4. However, the charging current is excessive due to the impedance of the step-up transformer 600 and the Scott transformer 700. If not, it can be omitted.

  In FIG. 1, a low-voltage three-phase power source is used as a pre-charging power source for the smoothing capacitor. However, it is also possible to pre-charge from the high-voltage three-phase power source via the circuit breaker 400, and thus configured. This has the advantage that it is not necessary to prepare a low-voltage three-phase power source.

  In the above description, the preliminary charging is finished when the detection voltage of the voltage detectors 231 to 234 reaches the target voltage, but the preliminary charging time to reach the target voltage during the test run of the converter can be measured. For example, the voltage detectors 231 to 234 can be controlled to shut off the circuit breaker 400 when the precharge time measured in the trial operation has elapsed without measuring the voltage. In this case, there is an advantage that the voltage detection units 231 to 234 are unnecessary.

  In FIG. 1, the five-level power conversion device has been described. However, by preparing n (n = natural number) Scott transformers 700 and rectification units 900, a multi-level power conversion device having (4n + 1) levels is similarly applied. It is obvious that it can be configured.

  That is, n Scott transformers and rectifiers 900 connected thereto are arranged in parallel on the output side of the step-up transformer 600 in FIG. 1, and each rectified output side of the n rectifiers 900 is (4n + 1) as in FIG. ) Are respectively connected to the DC link part of the multi-level power converter having a level.

  As described above, according to the first embodiment, the following effects can be obtained.

  (1) During preliminary charging, the initial voltage of a plurality of smoothing capacitors can be charged evenly, and an excessive voltage is applied to each semiconductor switching element in the smoothing capacitor, converter section, and inverter section, causing the semiconductor switching element to be overvoltage destroyed. Is prevented.

  (2) By uniformly charging the initial voltage of the smoothing capacitor, the waveform distortion of the AC side current of the multilevel power converter is suppressed.

  (3) A balance resistor for reducing variations in the smoothing capacitor voltage is not necessary, and the power loss consumed by the balance resistor can be reduced. Furthermore, the cost of the balance resistor can be reduced, and the work time required for connecting the balance resistor can be reduced.

  (4) It is not necessary to use an expensive AC reactor, and since an expensive step-up transformer is used only in a number smaller than the number of smoothing capacitors, the cost of the entire power converter can be reduced.

  (5) It is not necessary to use an AC reactor having a large volume and weight, and since the step-up transformer having a large volume and weight is smaller than the number of smoothing capacitors, the volume and weight of the power converter can be reduced.

  (6) Since the volume and weight of the power conversion device can be reduced for the above reason, the structural member that supports the power conversion device is inexpensive, and the cost of the entire power conversion device can be reduced.

  (7) There is no need to use an AC reactor, and since only a number of step-up transformers less than the number of smoothing capacitors are used, the structure can be simplified and the working time required for wiring can be reduced.

  (8) When the AC power source on the input side of the converter unit and the three-phase AC power source on the input side of the Scott transformer are shared, there is no need to provide a dedicated AC power source for precharging a plurality of smoothing capacitors. .

  FIG. 2 shows a configuration of a second embodiment in which the present invention is applied to a five-level power converter, and the same parts as those in FIG. 2 differs from FIG. 1 in that a low-voltage single-phase power supply is provided instead of the low-voltage three-phase power supply, the secondary winding of the step-up transformer 600 is a single-phase winding, and the Scott transformer 700 and the rectifying unit 900 are Instead, the cockcroft-Walton circuit unit 1000 and the circuit breaker 1100 (third circuit breaker) are provided, and the other parts are the same as those in FIG. That is, in the second embodiment, the Cockcroft-Walton circuit unit 1000 and the circuit breaker 1100 constitute the individual charging current supply means of the present invention.

  The Cockcroft-Walton circuit unit 1000 includes the same number of first to fourth unit boosting rectifier circuits 1011 to 1014 via the circuit breaker 1100 with respect to the smoothing capacitors C1 to C4, and each of the smoothing capacitors C1 to C4 is a unit. The boost rectifier circuits 1011 to 1014 are connected to be output side capacitors.

  That is, the first unit boost rectifier circuit 1011 has an input side capacitor C11, an anode connected to one end of the input side capacitor C11, and a cathode connected to a smoothing capacitor via the contact 11 (first contact) of the circuit breaker 1100. The smoothing capacitors C1 and C2 are connected to the diode D11 (fifth diode) connected to the positive electrode of C1, the cathode is connected to one end of the input side capacitor C11, and the anode is connected to the circuit breaker 1100 via the contact 12 (second contact). And a diode D12 (sixth diode) connected to the common connection point.

  The second unit boost rectifier circuit 1012 has one end connected to the input side capacitor C12 connected to the other end of the input side capacitor C11, the anode connected to the common connection point of the input side capacitors C11 and C12, and the cathode connected to the contact 12. The diode D13 (seventh diode) connected to the common connection point of the smoothing capacitors C1 and C2 via the cathode, the cathode is connected to the common connection point of the input side capacitors C11 and C12, and the anode is the contact 13 of the circuit breaker 1100. And a diode D14 (eighth diode) connected to the common connection point of the smoothing capacitors C2 and C3 via the (third contact).

  The third unit boost rectifier circuit 1013 has one end connected to the input side capacitor C13 connected to the other end of the input side capacitor C12, the anode connected to the common connection point of the input side capacitors C12 and C13, and the cathode connected to the contact 13 The diode D15 (the ninth diode) connected to the common connection point of the smoothing capacitors C2 and C3 through the cathode, the cathode is connected to the common connection point of the input side capacitors C12 and C13, and the anode is the contact 14 of the circuit breaker 1100. And a diode D16 (tenth diode) connected to the common connection point of the smoothing capacitors C3 and C4 via the (fourth contact).

  The fourth unit boost rectifier circuit 1014 has one end connected to the other end of the input-side capacitor C13 and the other end connected to one end of the secondary-side single-phase winding of the step-up transformer 600; A diode D17 (11th diode) whose anode is connected to the common connection point of the input side capacitors C13 and C14 and whose cathode is connected to the common connection point of the smoothing capacitors C3 and C4 via the contact 14, and the cathode is input Is connected to the common connection point of the side capacitors C13 and C14, the anode is connected to the other end of the secondary single-phase winding of the step-up transformer 600, and via the contact 15 (fifth contact) of the circuit breaker 1100 And a diode D18 (a twelfth diode) connected to the negative electrode of the smoothing capacitor C4.

  The Cockcroft-Walton circuit unit 1000 applies a voltage twice as large as the input voltage Vin (single-phase AC output voltage of the step-up transformer 600) to the smoothing capacitors C1 to C4 that serve as output side capacitors of the unit step-up rectifier circuits 1011 to 1014. Each of these circuits can output the same signal as the Cockcroft-Walton circuit disclosed in Non-Patent Document 1 shown in FIG.

In FIG. 3A, the unit booster circuit (1) includes, for example, an input side capacitor C1 connected in series between both ends of a single-phase AC power source that outputs 500 V _PEAK and 10 kHz, a diode D1 of the illustrated polarity, and a diode D1. The diode D2 and the output-side capacitor C2 are connected in series between the cathode and the anode.

  The unit booster circuits configured in this way are connected in 10 stages (unit booster circuits (1) to (10)), and the output voltage Vout is output from the final stage.

  When the input voltage Vin of the unit booster circuit (1) is positive, the output side capacitor C2 is charged through the diode D2, and when the input voltage Vin is negative, the input side capacitor C1 is charged through the diode D1 and the output The operation of holding the charging voltage is repeated for the side capacitor C2.

  As a result, the voltage at the indicated point P1 of the capacitor C1 becomes a sine wave of ± 500V centered on 500V, and the voltage at the indicated point O1 of the output side capacitor C2 is a DC voltage of 1000V (twice the peak value of the input voltage Vin). It becomes.

  Therefore, the output voltage Vout at the final stage becomes 10 kV as shown in FIG. 3B showing the voltage change at each point (O1 to O9) and the output terminal (the output voltage Vout of the Cockcroft-Walton circuit is a unit booster circuit). If the number of stages is N, it is 2 · N times the peak value of the input voltage Vin).

  3, it can be seen that the output side capacitors C2, C4,... C20 of the unit booster circuits (1) to (10) are charged with an equal voltage.

  The operation similar to the operation of the Cockcroft-Walton circuit of FIG. 3 is performed in the Cockcroft-Walton circuit unit 1000 of FIG. 2, and the operation of the second embodiment will be described below.

  When starting up the electric motor 300, the control part 240 confirms first that the high voltage circuit breaker 100 and the circuit breakers 400 and 1100 are OFF. Next, the control unit 240 turns on the circuit breakers 400 and 1100.

  When the circuit breakers 400, 1100 (respective contacts 11 to 15) are turned ON, power from the low-voltage single-phase power supply is input to the Cockcroft-Walton circuit unit 1000 via the current limiting resistor 500 and the step-up transformer 600. . The smoothing capacitors C1 to C4 are charged with a DC voltage by the operation of the Cockcroft-Walton circuit unit 1000.

  That is, when the input voltage Vin (secondary voltage of the step-up transformer 600) of the first unit step-up rectifier circuit 1011 is a positive voltage, the step-up transformer 600 → the input side capacitor C14 → the diode D17 → the contact 14 → the smoothing capacitor C4 → A current flows through the path of the contact 15 → the step-up transformer 600, and the smoothing capacitor C4 is charged.

  Further, current flows through a path of step-up transformer 600 → input side capacitor C14 → input side capacitor C13 → diode D15 → contact 13 → smoothing capacitor C3 → smoothing capacitor C4 → contact 15 → step-up transformer 600, and smoothing capacitors C3 and C4 are charged. Is done.

  Further, the current flows through the step-up transformer 600 → input side capacitor C14 → input side capacitor C13 → input side capacitor C12 → diode D13 → contact 12 → smoothing capacitor C2 → smoothing capacitor C3 → smoothing capacitor C4 → contact 15 → step up transformer 600. The smoothing capacitors C2, C3, C4 are charged.

  Step-up transformer 600 → input side capacitor C14 → input side capacitor C13 → input side capacitor C12 → input side capacitor C11 → diode D11 → contact 11 → smoothing capacitor C1 → smoothing capacitor C2 → smoothing capacitor C3 → smoothing capacitor C4 → contact 15 → Current flows through the path of the step-up transformer 600, and the smoothing capacitors C1, C2, C3, and C4 are charged.

  When the input voltage Vin is negative, the step-up transformer 600 → contact 15 → smoothing capacitor C4 → smoothing capacitor C3 → smoothing capacitor C2 → contact 12 → diode D12 → input side capacitor C11 → input side capacitor C12 → input side A current flows through the path of the capacitor C13 → the input side capacitor C14 → the step-up transformer 600, and the smoothing capacitors C4, C3, and C2 are discharged.

  Further, a current flows through a path of the step-up transformer 600 → the contact 15 → the smoothing capacitor C4 → the smoothing capacitor C3 → the contact 13 → the diode D14 → the input side capacitor C12 → the input side capacitor C13 → the input side capacitor C14 → the step-up transformer 600. C4 and C3 are discharged.

Further, a current flows through a path of step-up transformer 600 → contact 15 → smoothing capacitor C4 → contact 14 → diode D16 → input side capacitor C13 → input side capacitor C14 → step-up transformer 600, and smoothing capacitor C4 is discharged.
Further, a current flows through a path of the step-up transformer 600 → the diode D 18 → the step-up transformer 600.

  By repeating the operation when the input voltage Vin is positive and the operation when Vin is negative, the smoothing capacitors C1 to C4 are charged to a DC voltage twice the peak value of the voltage of Vin, respectively. Is done. That is, the smoothing capacitors C1 to C4 are charged to a uniform voltage.

  Detection values detected by the voltage detection units 231 to 234 in the five-level power conversion device 200 are input to the control unit 240, and the preliminary charging is completed when the voltages of the smoothing capacitors C1 to C4 reach the target voltage.

  When the preliminary charging is completed, the control unit 240 instructs opening of the circuit breakers 400 and 1100, and turns off the circuit breakers 400 and 1100.

  Thereafter, the control unit 240 instructs the high voltage circuit breaker 100 to be turned on and turns on the high voltage circuit breaker 100.

  Next, the operation of the converter unit 210 and the inverter unit 220 is started by starting the ON / OFF operation of the semiconductor switching elements of the converter unit 210 and the inverter unit 220 in the five-level power converter 200.

  Each semiconductor switching element in the inverter unit 220 is ON / OFF controlled by a predetermined ON / OFF pattern, and assuming that each voltage of the smoothing capacitors C1 to C4 is E, 2E, E, 0, -E,- 5E voltage of 2E is output.

  Since the inverter unit 220 applies the output voltage to the electric motor 300, the electric motor 300 starts to start.

  In addition, after the converter part 210 and the inverter part 220 start operation, the voltage of each of the smoothing capacitors C1 to C4 is controlled to be a constant value by the ON / OFF operation of the semiconductor switching element. Therefore, the balance resistors (R1 to R4) described in FIG. 5 are not required even in the operation after the start of operation.

  In the above description, the preliminary charging is finished when the detection voltage of the voltage detectors 231 to 234 reaches the target voltage, but the preliminary charging time for reaching the target voltage during the test run of the converter can be measured. For example, it is possible to control the circuit breakers 400 and 1100 to be disconnected when the precharge time measured in the trial operation has elapsed without measuring the voltage with the voltage detection units 231 to 234. In this case, there is an advantage that the voltage detection units 231 to 234 are unnecessary.

  In the above description, the low-voltage single-phase power supply is used as the pre-charging power supply for the smoothing capacitor, but it is cut off from the two phases (for example, R phase and S phase) of the three-phase high-voltage power input to the five-level power converter 200. It is also possible to perform preliminary charging via the battery 400, and this configuration has the advantage that it is not necessary to prepare a low-voltage single-phase power source.

  FIG. 2 illustrates the five-level power converter (200) in which four smoothing capacitors are connected in series. However, the unit boost rectifier circuit (for example, 1011) of the Cockcroft-Walton circuit unit 1000 includes n stages (n = even number). It is self-evident that the (n + 1) level power conversion device in which n smoothing capacitors are connected in series can be configured in the same manner.

  As described above, according to the second embodiment, the following effects can be obtained.

  (1) During preliminary charging, the initial voltage of a plurality of smoothing capacitors can be charged evenly, and an excessive voltage is applied to each semiconductor switching element in the smoothing capacitor, converter section, and inverter section, causing the semiconductor switching element to be overvoltage destroyed. Is prevented.

  (2) By uniformly charging the initial voltage of the smoothing capacitor, the waveform distortion of the AC side current of the multilevel power converter is suppressed.

  (3) A balance resistor for reducing variations in the smoothing capacitor voltage is not necessary, and the power loss consumed by the balance resistor can be reduced. Furthermore, the cost of the balance resistor can be reduced, and the work time required for connecting the balance resistor can be reduced.

  (4) It is not necessary to use an expensive AC reactor, and since an expensive step-up transformer is used only in a number smaller than the number of smoothing capacitors, the cost of the entire power converter can be reduced.

  (5) It is not necessary to use an AC reactor having a large volume and weight, and since the step-up transformer having a large volume and weight is smaller than the number of smoothing capacitors, the volume and weight of the power converter can be reduced.

  (6) Since the volume and weight of the power conversion device can be reduced for the above reason, the structural member that supports the power conversion device is inexpensive, and the cost of the entire power conversion device can be reduced.

  (7) There is no need to use an AC reactor, and since only a number of step-up transformers less than the number of smoothing capacitors are used, the structure can be simplified and the working time required for wiring can be reduced.

  (8) Since the Cockcroft-Walton circuit is used, the smoothing capacitors C1 to C4 each have a DC voltage that is twice the output voltage of the step-up transformer 600, that is, the peak value of the input voltage Vin of the Cockcroft-Walton circuit unit 1000. Charged. For this reason, the output voltage (Vin) of the step-up transformer 600 of FIG. 2 may be a voltage value lower than the output voltage of the step-up transformer 600 of FIGS.

  Therefore, in the second embodiment, since the output voltage of the step-up transformer 600 is reduced, the withstand voltage specification of the step-up transformer 600 is also reduced. This leads to downsizing and cost reduction of the step-up transformer 600, and further downsizing and cost reduction of the power converter. Further, since the Scott transformer 700 is not used as compared with the configuration of FIG. 1 according to the first embodiment, the size, weight, and cost can be reduced.

DESCRIPTION OF SYMBOLS 11-15 ... Contact 100 ... High voltage circuit breaker 200 ... 5-level power converter 210 ... Converter part 220 ... Inverter part 231-234 ... Voltage detection part 240 ... Control part 300 ... Motor 400, 1100 ... Circuit breaker 500 ... Current limiting resistance Unit 600 ... Step-up transformer 700 ... Scott transformer 900 ... Rectifier unit 1000 ... Cockcroft-Walton circuit unit 1011-1014 ... Unit step-up rectifier circuit C1-C4 ... Smoothing capacitor C11-C14 ... Input side capacitor D1-D4, D11-D18 ... Diode

Claims (9)

A converter unit that converts AC power from the first AC power source into DC power, an inverter unit that converts DC power of the converter unit into AC power, and a plurality of units connected in series to the DC link unit of the converter unit and the inverter unit A multi-level power converter that has a smoothing capacitor and outputs a plurality of levels of voltage,
A single charge current supply means is provided for introducing a single phase alternating current from a second alternating current power supply and individually supplying a charging current to each of the plurality of smoothing capacitors by the single phase alternating current. Multi-level power converter.   The multilevel power converter according to claim 1, wherein the first AC power supply and the second AC power supply are shared. The individual charging current supply means includes
A Scott transformer that receives three-phase alternating current from a three-phase alternating current power supply and outputs two sets of single-phase alternating current with a phase difference of 90 degrees;
A diode rectifying unit that half-wave rectifies the current output from the secondary side of the Scott transformer by a diode provided corresponding to the plurality of smoothing capacitors and leads the current to each smoothing capacitor;
The multilevel power conversion device according to claim 1 or 2, further comprising: The multi-level power converter is a 5-level power converter that has first to fourth smoothing capacitors connected in series and outputs a 5-level voltage,
The Scott transformer has a main seat primary coil on the primary side and a T seat primary coil connected to the midpoint thereof, and a main seat secondary coil and a T seat secondary insulated from each other on the secondary side. Has a coil,
The diode rectifier is
The first to fourth diodes corresponding to the first to fourth smoothing capacitors are provided, and one end of the main secondary coil of the Scott transformer is connected to the first diode via the anode and cathode of the first diode. Connect to the positive electrode of the smoothing capacitor, connect the common connection point of the first smoothing capacitor and the second smoothing capacitor to the other end of the main secondary coil of the Scott transformer, and connect the negative electrode of the second smoothing capacitor to the second Is connected to one end of the main seat secondary coil via the anode and cathode of the diode, and one end of the T seat secondary coil of the Scott transformer is connected to the third smoothing capacitor via the anode and cathode of the third diode. Connect to the positive electrode, connect the common connection point of the third smoothing capacitor and the fourth smoothing capacitor to the other end of the T-seat secondary coil, and connect the negative electrode of the fourth smoothing capacitor to the fourth Aether anode, a multi-level power converter according to claim 3, characterized in that through the cathode is constituted by connecting one end of the T locus secondary coil. The individual charging current supply means includes
A unit boosting rectifier circuit having a single-phase alternating current from the second alternating-current power supply as an input, connected to each of the plurality of smoothing capacitors via a third circuit breaker, and comprising the smoothing capacitors as respective output-side capacitors; The multilevel power conversion device according to claim 1, further comprising a Cockcroft-Walton circuit unit connected in series with the same number as the smoothing capacitor. The multi-level power converter is a 5-level power converter that has first to fourth smoothing capacitors connected in series and outputs a 5-level voltage,
The Cockcroft-Walton circuit section is
A first input-side capacitor and a fifth anode having an anode connected to one end of the first input-side capacitor and a cathode connected to the positive electrode of the first smoothing capacitor via the first contact of the third circuit breaker; The diode and the cathode are connected to one end of the first input side capacitor, and the anode is connected to the common connection point of the first smoothing capacitor and the second smoothing capacitor via the second contact of the third circuit breaker. A first unit boost rectifier circuit having a sixth diode;
A second input side capacitor having one end connected to the other end of the first input side capacitor, an anode connected to one end of the second input side capacitor, and a cathode serving as the second contact of the third circuit breaker. A seventh diode connected to the common connection point of the first smoothing capacitor and the second smoothing capacitor, a cathode connected to one end of the second input-side capacitor, and an anode connected to the third of the third circuit breaker An eighth diode connected to a common connection point of the second smoothing capacitor and the third smoothing capacitor through the contact of the second unit boosting rectifier circuit,
A third input-side capacitor having one end connected to the other end of the second input-side capacitor, an anode connected to one end of the third input-side capacitor, and a cathode serving as the third contact of the third circuit breaker A ninth diode connected to the common connection point of the second smoothing capacitor and the third smoothing capacitor via the first input terminal, a cathode connected to one end of the third input side capacitor, and an anode connected to the fourth of the third circuit breaker. A third unit boost rectifier circuit having a tenth diode connected to a common connection point of the third smoothing capacitor and the fourth smoothing capacitor via the contact of
One end is connected to the other end of the third input side capacitor, the other end is connected to one end of the second AC power source, and the anode is connected to one end of the fourth input side capacitor. An eleventh diode whose cathode is connected to a common connection point of the third smoothing capacitor and the fourth smoothing capacitor via a fourth contact of the third circuit breaker, and a cathode of the fourth input side capacitor. A fourth diode having one end connected to one end and an anode connected to the negative electrode of the fourth smoothing capacitor and the other end of the second AC power source via the fifth contact of the third circuit breaker; Unit boost rectifier circuit,
The multilevel power conversion device according to claim 5, comprising: A converter unit that converts AC power from the first AC power source into DC power, an inverter unit that converts DC power of the converter unit into AC power, and a plurality of units connected in series to the DC link unit of the converter unit and the inverter unit In a device that has a smoothing capacitor and outputs a plurality of levels of voltage,
Individual charging current supply means for introducing a single-phase alternating current from a second alternating-current power supply and individually supplying a charging current to each of the plurality of smoothing capacitors by the single-phase alternating current; and the first alternating-current power supply And a first circuit breaker provided between the converter unit and a second circuit breaker provided between the second AC power source and the individual charging current supply means. A control method,
The control unit
Controlling the closing of the second circuit breaker when the first and second circuit breakers are off;
When the terminal voltage of each of the smoothing capacitors reaches the target voltage, opening the second circuit breaker, and then turning on the first circuit breaker;
Starting the converter unit and the inverter unit;
A control method for a multi-level power conversion device, comprising:   The first AC power supply and the second AC power supply are shared, the first circuit breaker is provided between the shared AC power supply and the converter unit, and the second circuit breaker is 8. The control method for a multilevel power conversion device according to claim 7, wherein the control method is provided between a common AC power supply and the individual charging current supply means. The individual charging current supply means includes
A unit boosting rectifier circuit having a single-phase alternating current from the second alternating-current power supply as an input, connected to each of the plurality of smoothing capacitors via a third circuit breaker, and comprising the smoothing capacitors as respective output-side capacitors; The same number of the smoothing capacitor connected in series with the Cockcroft-Walton circuit unit,
The control unit
Controlling the closing of the second and third circuit breakers when the first, second and third circuit breakers are off;
When the terminal voltage of each smoothing capacitor reaches the target voltage, opening the second and third circuit breakers, and then turning on the first circuit breaker;
Starting the converter unit and the inverter unit;
The control method of the multilevel power converter device of Claim 7 or 8 characterized by the above-mentioned.

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