JP2014150719A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power converter which generates a predetermined brake torque for decelerating an AC motor both during high speed rotation and low speed rotation of the AC motor being driven by a multiple inverter not having a power regeneration function, and allows for energy saving and cost reduction.SOLUTION: In a power converter including a multiwinding transformer 4 generating a plurality of power supply voltages from a system power supply, and a plurality of multiple inverters 1-3 consisting of a series connection of a plurality of single phase inverter units, generating a single phase voltage from the power supply voltage, and driving an AC motor 5 by these multiple inverters 1-3, a power regeneration device 9 is connected between the AC motor 5 and the system power supply via a step-down transformer 7. Furthermore, other power regeneration device 12 is connected, as required, between the non-output side terminals of the multiple inverters 1-3 and the system power supply.

Description

  The present invention relates to a power conversion device including multiple inverters. In particular, the present invention has a function of electrically assisting the stop or deceleration of the AC motor when the AC motor is driven by a multiple inverter formed by connecting a plurality of single-phase inverter units having no power regeneration function in series. The present invention relates to a power conversion device provided.

  The output side of multiple single-phase inverter units is connected in series as a high-voltage, large-capacity power converter that drives a multi-phase AC motor with a rated voltage of 3.3 [kV] or 6.6 [kV]. A multi-phase inverter for one phase is configured, and a multi-phase AC motor is driven by using this multi-inverter for the number of phases.

FIG. 4 is a configuration diagram of this type of power conversion device.
In FIG. 4, reference numerals 1, 2, and 3 denote multiple inverters, which are constituted by single-phase inverter units 11 and 12, single-phase inverter units 21 and 22, and single-phase inverter units 31 and 32, respectively. For example, the multi-inverter 1 connects each one end of two single-phase inverter units 11 and 12 in series and the other end on the output side of one single-phase inverter unit 11 to a three-phase AC motor 5 as a load device. The other end on the output side of the other single-phase inverter unit 12 is connected to a common connection point (neutral point of multiple inverter) N0. The connection state of the single-phase inverter units 11 and 12 described above is the same for the single-phase inverter units 21, 22 and 31 and 32 in the other multiple inverters 2 and 3.
Note that the configurations of the multiple inverters 1 to 3 are merely examples, and there are cases where one multiple inverter is configured by directly connecting three or more single-phase inverter units.

  Here, in order to connect a plurality of single-phase inverter units in series in the multiple inverter, it is necessary to electrically insulate the input side of each single-phase inverter unit. For this reason, the input sides of the single-phase inverter units 11, 12, 21, 22, 31, 32 are connected to the secondary winding 4 b of the multi-winding transformer 4. The primary winding 4a of the multi-winding transformer 4 is connected to a three-phase AC power supply (system power supply) not shown, and generates a single-phase power supply voltage from a plurality of secondary windings 4b. It is.

FIG. 5 shows a configuration example of the single-phase inverter unit 11 in FIG. 4, for example. The other single-phase inverter units 12, 21, 22, 31, 32 also have the same configuration.
The single-phase inverter unit 11 includes a diode rectifier 101 that converts three-phase AC power to DC power, an IGBT inverter 102 that converts DC power to single-phase AC power, and a capacitor that is connected to a DC intermediate circuit and smoothes the DC voltage. 103.

  Since the single-phase inverter unit 11 shown in FIG. 5 uses the diode rectifier 101 for AC-DC conversion, the DC power supply side of the diode rectifier 101 from the DC intermediate circuit (the secondary winding 4b of the multi-winding transformer 4). Power) cannot be regenerated. Therefore, if the IGBT inverter 102 regenerates power from the single-phase AC side to the DC intermediate circuit side, the voltage of the DC intermediate circuit rises abnormally, and in the worst case, the single-phase inverter unit 11 is destroyed by overvoltage. Will be.

In general, when an AC motor is to be rapidly decelerated by electric means, the AC motor is operated as a generator to regenerate power. However, as described above, when a diode rectifier is used for the single-phase inverter unit, power cannot be regenerated to the system power supply side via the single-phase inverter unit.
When power regeneration cannot be performed in this way, a very long time is required for the deceleration of the AC motor, so that there is a problem that a desired acceleration / deceleration characteristic cannot be obtained.
Therefore, in the modular multi-phase adjustable power source disclosed in Patent Document 1, a power converter using an IGBT capable of power regeneration is used instead of the diode rectifier in the single-phase inverter unit. Electricity can be regenerated.

  On the other hand, in applications where a certain degree of deceleration effect can be obtained by the load torque, it may be sufficient to add an auxiliary power regeneration function or a power consumption function using a braking resistor. As power converters having such a function, conventional techniques described in Patent Documents 2 to 5 are known.

That is, in the inverter device shown in Patent Document 2, a three-phase inverter is connected in series to a multiplex inverter, and a DC voltage detection circuit and a discharge circuit are provided in the three-phase inverter. In this inverter device, a DC voltage increase during power regeneration is detected by a DC voltage detection circuit, and the regenerative power is consumed by a resistor in the discharge circuit.
Patent Document 3 discloses a multiple power conversion device in which a specific single-phase inverter unit or a three-phase inverter connected in series to a multiple inverter has a function of consuming regenerative power.

In Patent Document 4, a resistor is connected between the neutral point of the multiple power converter and the neutral point of the induction motor, and the output voltage zero phase component of the multiple power converter is controlled, whereby the regenerative power is A technique for consuming by resistance is described. Patent Document 4 also discloses that a neutral point is taken out from a step-down transformer connected to the input side of the induction motor when it is difficult to take out the neutral point.
Further, Patent Document 4 discloses a technology in which a regenerative power converter is connected instead of the resistor, and power is regenerated to the system power supply side by the regenerative power converter.

Patent Document 5 discloses a power conversion device shown in FIG. In FIG. 6, the same components as those in FIG. 4 are denoted by the same reference numerals.
In FIG. 6, a power consumption circuit 6 including a switch 61 and a resistor 62 is connected to input terminals 5 u, 5 v, 5 w of an AC motor 5 connected to the output side of multiple inverters 1, 2, 3. When the switch 61 is turned on, each end of the star-connected resistor 62 is connected to the input terminals 5u, 5v, and 5w. This switch 61 is normally turned off, and is turned on when the AC motor 5 is decelerated (when braking torque is generated).

  That is, when the switch 61 is turned on, if a voltage is generated between its input terminals, a current flows through the resistor 62 and power is consumed. This power consumption can be supplied only from the multiple inverters 1 to 3 or from the AC motor 5, and can also be supplied from both the multiple inverters 1 to 3 and the AC motor 5. Next, each of these cases will be specifically described.

There are three cases as described above as cases where predetermined power is consumed by the resistor 62.
Case 1 is a case where the AC motor 5 is operating without load, and in this case, all the power consumed by the resistor 62 is supplied from the multiple inverters 1 to 3. Case 2 is a case in which the AC motor 5 operates as a generator and outputs power equal to the power consumption of the resistor 62. In this case, all of the power consumed by the resistor 62 is supplied from the AC motor 5. The Case 3 is a case where the power generated by the AC motor 5 is less than the power consumed by the resistor 62. In this case, the power consumed by the resistor 62 is supplied from both the multiple inverters 1 to 3 and the AC motor 5. .

  In the case 2 and case 3, the AC motor 5 is decelerated by its own generated power. Accordingly, by turning on the switch 61 and consuming electric power at the resistor 62, if the generated electric power of the AC motor 5 is a deceleration rate that satisfies the conditions of Case 2 and Case 3, the electric power is supplied to the multiple inverters 1 to 3 side. The AC motor 5 can be decelerated without regenerating. That is, in this case, the overvoltage breakdown of the single-phase inverter unit as described above does not occur.

  In this prior art, the case 2 is a condition for generating the largest braking torque without power regeneration in the multiple inverters 1 to 3. That is, when the power consumed by the resistor 62 is all covered by the power generated by the AC motor 5, the largest braking torque can be obtained.

Usually, the power consumption of the resistor 62 is proportional to the square of the voltage. On the other hand, in order to keep the magnetic flux of the AC motor 5 constant, it is necessary to make the terminal voltage V of the AC motor 5 and the frequency f substantially proportional, and the well-known V / f constant control is generally used. ing. Therefore, assuming this constant V / f control, the power consumption by the resistor 62 is proportional to the square of the frequency f. For these reasons, in an AC motor in which the frequency f and the rotation speed are approximately proportional, the power consumption by the resistor 62 is approximately proportional to the square of the rotation speed, as shown by the solid line in FIG.
On the other hand, the upper limit of the braking torque can be obtained by dividing the power consumption by the rotational angular speed of the motor, so that the characteristic is proportional to the speed as shown by the broken line in FIG.

Japanese Patent Laid-Open No. 2001-103766 (paragraphs [0018] to [0026], FIG. 1, FIG. 2, etc.) JP 2000-50643 A (paragraphs [0031] to [0035], FIG. 7 etc.) JP 2001-238455 A (paragraphs [0006] to [0009], FIG. 1, FIG. 4 etc.) Japanese Patent Laying-Open No. 2005-33903 (paragraphs [0009] to [0022], FIGS. 1, 4, 5, etc.) Japanese Unexamined Patent Publication No. 2000-50636 (paragraphs [0052] to [0057], FIG. 8, etc.)

According to the prior art according to Patent Document 1, it is possible to rapidly decelerate the AC motor. However, in applications that do not necessarily require a large torque as a braking torque for decelerating the electric motor, the specification becomes excessive and the size and cost of the device increases.
In the prior arts related to Patent Documents 2 and 3, since the magnetic flux of the AC motor is greatly weakened at a high speed, the control stability is deteriorated.
The prior art according to Patent Document 4 is not applicable to an AC motor that cannot extract a neutral point. Further, when an equivalent neutral point is generated using a step-down transformer, a zero-phase current flows through the step-down transformer, so that the capacity of the step-down transformer is increased.
In addition, the related arts disclosed in Patent Documents 2 to 4 have a common drawback that the braking torque during the high speed rotation of the AC motor is small.

In the prior art according to Patent Document 5 shown in FIG. 6 and FIG. 7, as is clear from FIG. 7, a large braking torque can be obtained when the AC motor rotates at high speed, but the braking torque decreases at low speed.
For example, when the braking torque of 10% of the rating is to be obtained at the rated speed of the AC motor, the current flowing through the resistor 62 in FIG. 6 is 10% of the rated current. In this case, as the switch 61 in the power consumption circuit 6, a mechanical switch or a semiconductor switch such as GTO or IGBT can be used. However, since high voltage / small current special specifications are required, the cost increases. Cause.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a predetermined braking for decelerating the AC motor in both cases of high-speed rotation and low-speed rotation of the AC motor in the power conversion device composed of multiple inverters having no power regeneration function. It is to generate torque.
Another object of the present invention is to provide a power converter capable of saving energy and reducing costs.

In order to solve the above problem, the invention according to claim 1 is a series of a multi-winding transformer that generates a plurality of power supply voltages from a system power supply and a plurality of single-phase inverter units that generate a single-phase voltage from the power supply voltage. A plurality of multiple inverters connected to the power converter, and a power converter for driving an AC motor by the multiple multiple inverters, wherein the multiple inverters do not have a power regeneration function for the system power supply. In the conversion device,
A power regeneration device is connected between the AC motor and the system power supply via a step-down transformer.

  The invention according to claim 2 is the power conversion device according to claim 1, wherein another power regeneration device is connected between the non-output side terminal of the multiple inverter and the system power supply. .

According to the invention which concerns on Claim 1, the braking torque which consumes the electric power generated by the AC motor and decelerates the AC motor can be generated by the power regeneration device.
According to the invention which concerns on Claim 2, the braking torque which decelerates an AC motor can be generated over the full speed range of an AC motor, without regenerating electric power via a multiple inverter.

It is a block diagram of 1st Embodiment of this invention. It is a block diagram of the electric power regeneration apparatus in FIG. It is a block diagram of 2nd Embodiment of this invention. It is a block diagram which shows the prior art of a power converter device. It is a block diagram of the single phase inverter in FIG. It is a block diagram of the prior art described in patent document 5. FIG. It is a figure which shows the relationship between the rotational speed of an alternating current motor, power consumption, and a braking torque upper limit in the prior art shown in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram showing a first embodiment of the present invention, and corresponds to the invention according to claim 1. 1, the same components as those in FIG. 4 are denoted by the same reference numerals.

In FIG. 1, the multiple inverters 1, 2, 3 are constituted by single-phase inverter units 11, 12, single-phase inverter units 21, 22, and single-phase inverter units 31, 32, respectively. For example, the multiple inverter 1 has one end on the output side of two single-phase inverter units 11 and 12 connected in series and the other end on the output side of one single-phase inverter unit 11 connected to the three-phase AC motor 5. And the other end of the output side of the other single-phase inverter unit 12 is connected to a neutral point N0. The connection state of the single-phase inverter units 11 and 12 described above is the same for the single-phase inverter units 21 and 22 and 31 and 32 in the other multiple inverters 2 and 3. Here, it is assumed that the AC motor 5 has no neutral point.
The number of single-phase inverter units constituting each of the multiple inverters 1, 2, 3 may be three or more.

The input sides of the single-phase inverter units 11, 12, 21, 22, 31, 32 are connected to a plurality of secondary windings 4 b of the multi-winding transformer 4. The primary winding 4a of the multi-winding transformer 4 is connected to a three-phase AC power supply (system power supply) not shown. The multi-winding transformer 4 generates a single-phase power supply voltage from a plurality of secondary windings 4b.
Here, the single-phase inverter units 11, 12, 21, 22, 31, and 32 are configured by the diode rectifier 101 and the IGBT inverter 102, for example, as shown in FIG. 5 described above, and regenerate power to the system power supply side. It has no function.

  A power regeneration device 9 is connected to the input terminals 5 u, 5 v, 5 w of the AC motor 5 connected to the multiple inverters 1 to 3 via a step-down transformer 7. Thus, since the step-down transformer 7 is connected between the input terminals 5u, 5v, 5w and the power regeneration device 9, the power regeneration device 9 has, for example, an AC voltage rating of 440 [V] class. Standard power converters can be used. The power regeneration device 9 includes a power conversion unit 90 and a transformer 94.

  FIG. 2 shows a configuration example of the power regeneration device 9. In FIG. 2, a power conversion unit 90 is generally known and includes power converters 91 and 92 for performing AC-DC-AC conversion and a capacitor 93 of a DC intermediate circuit. In this embodiment, by operating the power regeneration device 9 when the AC motor 5 is decelerated, the power absorbed from the input terminals 5u, 5v, 5w can be regenerated to the system power supply side, and the braking torque can be obtained.

Next, FIG. 3 shows a second embodiment of the present invention and corresponds to the invention according to claim 2.
1 and FIG. 2 is different from the first embodiment in that a power regeneration device 12 is added between the non-output side of the multiple inverters 1 to 3 and the system power supply.
Similar to the power regeneration device 9 shown in FIGS. 1 and 2, the power regeneration device 12 includes a power conversion unit 120 having a DC intermediate circuit, and a transformer connected between the power conversion unit 120 and the system power supply. 124. The configuration of the power conversion unit 120 is the same as that of the power conversion unit 90 of FIG. 2, and includes two power converters (corresponding to the power converters 91 and 92 of FIG. 2) and capacitors (also corresponding to the capacitor 93). Shall be.

Here, the characteristic features of the power regeneration device 12 will be described.
Assuming that two power converters in the power conversion unit 120 have a standard AC voltage rating of 440 [V]. The AC motor 5 is assumed to be an induction motor having a rated voltage of 3.3 [kV]. Since the general excitation current of an induction motor is about 30 [%] of the motor rated current, the current during deceleration is 30 [%] of the motor rated current.

At this time, the power that can be regenerated by the power regeneration device 12 is such that the ratio of the rated voltage of the power converter in the power conversion unit 120 to the rated voltage of the AC motor 5 is 13.3 [%] (= 440/3300). Since the ratio of the current during deceleration to the rated current is 30 [%], when these 13.3 [%] and 30 [%] are multiplied, 4 [%] of the rated capacity is obtained.
If the AC motor 5 is operated at the rated speed, a braking torque of 4 [%] of the rated torque can be obtained. If the AC motor 5 is operated at the speed of 50 [%] of the rated speed, the speed is increased. A braking torque of 8% of the rated torque can be obtained in inverse proportion to.

  Therefore, in the present embodiment, by combining the power regeneration device 9 that can obtain a large braking torque at a high speed and the power regeneration device 12 that can obtain a large braking torque at a low speed, the power regeneration devices 9 and 12 are configured as components. A standard low voltage power converter can be used to obtain sufficient braking torque over the entire speed range.

  Instead of the power regeneration device 9, a power consuming circuit having a simple configuration including a switch and a resistor may be used. In this case, since the electric power is regenerated only by the electric power regeneration device 12, the energy saving effect is reduced, but the effect that a sufficient braking torque is obtained in the entire speed range is maintained.

1, 2, 3: Multiple inverters 11, 12, 21, 22, 31, 32: Single phase inverter unit 4: Multi-winding transformer 4a: Primary winding 4b: Secondary winding 5: Three-phase AC motor 5u, 5v, 5w: Input terminal 7: Step-down transformer 9, 12: Power regeneration device 90, 120: Power conversion unit 91, 92: Power converter 93: Capacitor 94, 124: Transformer N0: Neutral point

Claims (2)

A multi-winding transformer that generates a plurality of power supply voltages from a system power supply, and a plurality of multiple inverters in which a plurality of single-phase inverter units that generate a single-phase voltage from the power supply voltage are connected in series. In a power conversion device for driving an AC motor by multiple multiplex inverters, the multiplex inverter does not have a power regeneration function to the system power supply,
A power converter, wherein a power regeneration device is connected between the AC motor and the system power supply via a step-down transformer. In the power converter device according to claim 1,
Another power regeneration device is connected between the non-output side terminal of the multiple inverter and the system power supply.

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