JP2002315350A - Controller for power converter connected in parallel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress cross current which is produced, when a direct current-to- alternating current converter, such as an inverter, is in parallel operation, through a simple constitution. SOLUTION: The direct-current voltage of a power converter, such as inverter, in parallel operation is detected; if the detected direct-current voltage 1 of the converter is increased (decreased), the output of the converter is considered too low (too high); the output 7 of a regulator 5 is subjected to addition (subtraction) at an adder 8 to increase (decrease) an alternating-current voltage amplitude command 6 and is corrected, and then turn-on and -off of switching elements (not shown) are controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for converting a direct current into an alternating current, such as a photovoltaic power generation inverter or an uninterruptible power supply (UPS), which is used in parallel with a plurality of common buses. The present invention relates to a control device for a power converter that enables suppression control of a cross current exchanged between power converters.

[0002]

2. Description of the Related Art When a plurality of power converters are connected to the same bus and operated in parallel, an unbalance occurs in the output due to variations in circuit elements used in the converters, which are unnecessary converters. Power exchange (cross current) may occur. Therefore, control for suppressing the cross flow is required.

As shown in FIG. 3, this type of converter is usually connected to a bus via reactors 14, 15 or a circuit element having a reactance such as a transformer.
Reference numeral 10 denotes a converter, 11 denotes a DC voltage detector, 1
2 and 16 are capacitors, and 13 is a DC voltage. Considering the fundamental relationship of the AC theory between the amplitude and phase of voltage and the power exchanged, two
When two power supplies are connected, active power is mainly transmitted and received due to the phase difference, and reactive power is transmitted and received due to the voltage difference. Has been thought to be able to be effectively suppressed. Regarding this method, for example, a paper No. In 803, the cross flow control is realized by correcting the phase.

[0004]

However, in an actual device, it is easy to adjust the voltage phase between converters using a synchronization signal or a PLL (phase locked loop). The imbalance of voltage amplitude is often the main cause of cross current. If an attempt is made to suppress the cross current by correcting the phase with respect to such imbalance of the voltage amplitude, indirect cross current suppression control is performed, and there is a problem that it is difficult to improve the control performance. Therefore, an object of the present invention is to suppress cross flow between converters without lowering control performance.

[0005]

In order to solve such a problem, the invention according to claim 1 has an energy storage element on the DC side, and is used by connecting a plurality of units in parallel to convert DC into AC. DC power detecting means for detecting the DC voltage of the energy storage element, calculating means for calculating a deviation between the detected detected DC voltage and the DC voltage command value, and inputting the deviation to each power converter. Adjusting means, a correcting means for correcting an AC voltage amplitude command according to the output of the adjusting means, and a control means for controlling the power converter with the corrected AC voltage amplitude command. I do.

In the first aspect of the present invention, a dead zone element is provided on the output side of the arithmetic means so that the deviation within a certain range is not output. In the invention according to claim 2, a limiter or a limiter with a dead zone is provided in place of the dead zone element, and the deviation is output only when the detected detected DC voltage rises above its DC voltage command value. (Invention of claim 3) or a limiter or a limiter with a dead zone is provided in place of the dead zone element, and the deviation is output only when the detected detected DC voltage falls below the DC voltage command value. (The invention of claim 4).

According to a fifth aspect of the present invention, the DC voltage of the energy storage element is provided to each power converter which has an energy storage element on the DC side and is used in parallel with each other to convert DC into AC. DC voltage detecting means for detecting, DC voltage change rate detecting means for detecting the rate of change of the detected detected DC voltage, adjusting means for inputting the DC voltage changing rate, and AC in accordance with the output of the adjusting means. A correction means for correcting a voltage amplitude command and a control means for controlling the power converter based on the corrected AC voltage amplitude command are provided.

According to the fifth aspect of the present invention, a dead zone element is provided on the output side of the DC voltage change rate detecting means so that the DC voltage change rate within a certain range is not output. invention). Further, in the invention according to claim 6, a limiter or a limiter with a dead zone is provided in place of the dead zone element, and this can be output only when the detected DC voltage change rate is positive (increase). (Invention of claim 7) Alternatively, a limiter or a limiter with a dead zone is provided in place of the dead zone element, and this can be output only when the detected DC voltage change rate is negative (falling) (claim 8). Invention).

The reactor and the transformer connected to the output side of the converter do not actually consist of only ideal reactances, but always include a resistance component. Assuming that two converters are connected in parallel and paying attention to this resistance, the power is low from the converter side where the AC side voltage is high (the amplitude is large) and the power side is the low AC side voltage (the amplitude is large). (Low amplitude) towards the transducer. As a result, since the converter itself has no energy storage capability, power flows into the energy storage element, such as a capacitor, which is normally connected to the DC side of the converter, on the side where the power has flowed. As a result, as a result, the DC voltage of the converter having the lower AC side voltage increases. Therefore, according to the present invention, the DC current is detected, and when the DC voltage rises, there is an inflow of power, that is, it is determined that the AC voltage amplitude is small, and the cross current is corrected by correcting the AC voltage amplitude in a direction to increase. When the DC voltage drops, there is an outflow of power, that is, it is determined that the AC voltage amplitude is large, and the cross current is suppressed by correcting the AC voltage amplitude in a direction to decrease it. . This relationship is
The same applies when three or more converters are connected in parallel.

[0010]

FIG. 1 is a block diagram showing a first embodiment of the present invention. When a plurality of power supply units are connected to the same bus 17 as shown in FIG. The main part (invention part) of the device is shown. Reference numeral 10 in FIG. 2 indicates a converter (power supply device). In the case of a three-phase inverter, for example, the inverter having the configuration shown in FIG. 15 is used.
Inverters having the configurations shown in FIG. The difference between the DC voltage 1 detected by the DC voltage detector 11 and the DC voltage command 2 is obtained by the subtractor 3 and input to the controller 5. As the adjuster 5, for example, a proportional-integral adjuster or an integral adjuster is used.

The output 7 of the controller 5 is added to an AC voltage amplitude command 6 in an adder 8, and when the DC voltage 1 increases, the output 7 is corrected so that the AC voltage amplitude command 6 increases. When the voltage 1 becomes smaller, the correction is made so that the AC voltage amplitude command 6 becomes smaller. Then, based on the corrected AC voltage amplitude command 9, for example, FIG.
A gate drive signal for the inverter is generated using a control device as shown in FIG.

FIG. 18 shows an example of a commonly used voltage control system, which will be briefly described. Here, an AC output voltage 33 detected by a voltage detector for detecting an output voltage of the converter is converted into an effective value by an effective value calculation circuit 34, and an AC voltage amplitude command 32, which is separately input, is used.
Is obtained by a subtracter 36, and the voltage deviation 37 is supplied to a controller 38 to perform a predetermined control operation. The output of the controller 37 is multiplied by a multiplier 40 with a reference sine wave 39 generated by a PLL or a synchronization signal. The result is pulse width modulated by a pulse width modulator 41 and sent to a gate drive unit (GDU) 42 for generating a gate drive signal. This gate drive signal is input to the gate of the switching element 24 (FIG. 16 shows an example of an IGBT) in FIGS. 15 and 16, and the switching operation is performed by the switching element.

When the input side of the inverter shown in FIGS. 15 and 16 fluctuates in voltage on the input side like a solar cell, it is further connected to the battery side of the DC side capacitor of each power supply device, for example, as shown in FIG. In some cases, a chopper circuit as shown is arranged to make the DC voltage 31 a voltage convenient for the operation of the inverter. The DC voltage command 2 is not a command value for controlling the DC voltage 13 shown in FIG. 2 to be constant, but a voltage level for detecting that the DC voltage has deviated from a specified value.

FIG. 4 shows a second embodiment of the present invention. The difference from FIG. 1 is that a dead band element 18 is provided on the output side of the DC voltage deviation calculating means 3 and when the DC voltage deviation 4 is small (within a certain range), the output (input of the controller) of the dead band element 18 is set to zero. The point is to be. In this way, when the deviation 4 exceeds a certain value and becomes excessively large or small, the cross current suppression control can be activated, and when the DC voltage fluctuates due to a factor different from the cross current. For example, the influence of the other factors can be eliminated.

FIG. 5 shows a third embodiment of the present invention. The difference from FIG. 1 is that the output of the DC voltage deviation calculating means 3 is output only on the (+) side using the limiter 19, so that the AC voltage amplitude command 6 is output only when the DC voltage 1 rises.
In other words, a limiter 19 is used in place of the dead zone element 18 in FIG. By doing so, it becomes possible to raise the AC output voltage only of the power supply device whose DC voltage has risen, balance the entire voltage, and suppress the cross current. FIG. 6 shows a modification of FIG. A feature is that a limiter 20 with a dead zone is provided instead of the limiter 19 in FIG. Thereby, the AC voltage amplitude command 6 is corrected only when the DC voltage 1 rises by a certain fixed value or more, and the other parts are the same as those in FIG.

FIG. 7 shows a fourth embodiment of the present invention. The difference from FIG. 1 is that the output of the DC voltage deviation calculating means 3 is output only to the (−) side using the limiter 21, so that the AC voltage amplitude command 6 is corrected only when the DC voltage 1 drops (−). It is something to do. By doing so, it becomes possible to lower the AC output voltage only in the power supply device in which the DC voltage has decreased, balance the entire voltage, and suppress the cross current. FIG. 8 shows a modification of FIG. A feature is that a limiter 22 with a dead zone is provided instead of the limiter 21 of FIG. Thus, the AC voltage amplitude command 6 is corrected only when the DC voltage 1 drops by a certain fixed value or more, and the rest is the same as FIG.

FIG. 9 shows a fifth embodiment of the present invention. The difference from FIG. 1 is that instead of using the deviation between the DC voltage and the DC voltage command as the input of the controller 5, the rate of change 43 of the DC voltage is used. Note that a differentiating circuit 44 is used here to obtain the rate of change 43. When the DC voltage change rate 43 increases (positive), the AC voltage amplitude command 6 is corrected so as to increase, and when the DC voltage change rate 43 decreases (negative), the AC voltage amplitude command 6 decreases. 6 is reduced so that the controller 6 performs a control operation based on the correction result.

FIG. 10 shows a sixth embodiment of the present invention. The difference from FIG. 9 is that the dead band element 18 is provided on the output side of the differentiating circuit 44 so that the output (input of the controller) of the dead band element 18 becomes zero when the detected DC voltage change rate 43 is small. It is in.

FIG. 11 shows a seventh embodiment of the present invention. The difference from FIG. 9 is that the output of the differentiating circuit 44 is
9 to output only the (+) side, so that the AC voltage amplitude command 6 is corrected only when the detected DC voltage change rate 43 is increased (positive). FIG. 12 shows a modification of FIG. The feature is that a limiter 20 with a dead zone is provided instead of the limiter 19 in FIG.
Thus, the AC voltage amplitude command 6 is corrected only when the DC voltage change rate 43 increases (positive) by a certain fixed value or more.

FIG. 13 shows an eighth embodiment of the present invention. The difference from FIG. 9 is that the output of the differentiating circuit 44 is
1 to output only the (−) side, so that the AC voltage amplitude command 6 is corrected only when the DC voltage change rate 43 decreases (−). FIG. 14 shows a modification of FIG. The feature is that a limiter 22 with a dead zone is provided instead of the limiter 21 of FIG. As a result, the AC voltage amplitude command 6 is corrected only when the DC voltage change rate 43 drops (-) by a certain fixed value or more.

[0021]

According to the present invention, even when the constants and the like of the power supply units connected in parallel have minute variations,
Since the cross flow of electric power can be suppressed only by adding a simple device, there is an advantage that the parallel operation of the power supply devices becomes easy.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing an example in which a plurality of power supply devices are connected to the same bus.

FIG. 3 is a configuration diagram illustrating an example of one power supply device.

FIG. 4 is a configuration diagram showing a second embodiment of the present invention.

FIG. 5 is a configuration diagram showing a third embodiment of the present invention.

FIG. 6 is a configuration diagram showing a modification of FIG. 5;

FIG. 7 is a configuration diagram showing a fourth embodiment of the present invention.

FIG. 8 is a configuration diagram showing a modification of FIG. 7;

FIG. 9 is a configuration diagram showing a fifth embodiment of the present invention.

FIG. 10 is a configuration diagram showing a sixth embodiment of the present invention.

FIG. 11 is a configuration diagram showing a seventh embodiment of the present invention.

FIG. 12 is a configuration diagram showing a modification of FIG. 11;

FIG. 13 is a configuration diagram showing an eighth embodiment of the present invention.

FIG. 14 is a configuration diagram showing a modified example of FIG.

FIG. 15 is a main circuit configuration diagram showing an example of a three-phase inverter.

FIG. 16 is a main circuit configuration diagram showing an example of a single-phase inverter.

FIG. 17 is a circuit configuration diagram showing an example of a chopper circuit.

FIG. 18 is a block diagram illustrating an example of a converter control unit.

[Explanation of symbols]

1: DC voltage detection, 2: DC voltage command, 3, 36: subtractor, 4: DC voltage deviation, 5, 38: controller, 6, 32 ...
AC voltage amplitude command, 7 ... output of controller, 8 ... adder, 9 ...
Corrected AC voltage amplitude command, 10 ... converter, 11 ... DC voltage detector, 12, 16, 26, 31 ... capacitor control unit, 13 ... DC voltage, 14, 15, 25 ... reactor, 17 ... common bus, 18 ... dead zone elements, 19, 21 ...
Limiters, 20, 22 ... Limiter with dead zone, 21: Dead zone element, 22: Limiter, 24, 29 ... Switching element, 27 ... Battery, 30 ... Reflux diode, 33 ... AC output voltage, 34 ... Effective value calculation circuit, 35 ... AC voltage effective value, 37 voltage deviation, 39 reference sine wave, 40 multiplier, 41 pulse width modulator, 42 gate drive unit (GDU), 43 change rate of DC voltage, 44 differentiation circuit.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H007 AA07 BB07 CA01 CB05 CC05 DA05 DB01 DC05 FA03

Claims (8)

[Claims] 1. A DC voltage detector for detecting a DC voltage of an energy storage element in each power converter having an energy storage element on a DC side and being used in parallel with a plurality of power converters for converting DC into AC. Means, a calculating means for calculating a deviation between the detected DC voltage and the DC voltage command value, an adjusting means to which the difference is inputted, and an AC voltage amplitude command being corrected according to the output of the adjusting means. A control device for a parallel-connected power converter, comprising: a correction unit; and a control unit that controls the power converter based on the corrected AC voltage amplitude command. 2. The control device for a parallel-connected power converter according to claim 1, wherein a dead band element is provided on an output side of the arithmetic unit, and the deviation within a certain range is not output. 3. The apparatus according to claim 1, wherein a limiter or a limiter with a dead zone is provided in place of said dead zone element, and said deviation is output only when said detected DC voltage rises above its DC voltage command value. 3. The control device for a parallel-connected power converter according to 2. 4. The apparatus according to claim 1, wherein a limiter or a limiter with a dead zone is provided instead of the dead zone element, and the deviation is output only when the detected DC voltage falls below the DC voltage command value. 3. The control device for a parallel-connected power converter according to 2. 5. A DC voltage detector for detecting a DC voltage of the energy storage element in each of the power converters having an energy storage element on the DC side and being used in parallel and converting DC into AC. Means, DC voltage change rate detecting means for detecting the detected change rate of the detected DC voltage, adjusting means for inputting the DC voltage change rate, and correcting the AC voltage amplitude command according to the output of the adjusting means. And a control unit for controlling the power converter based on the corrected AC voltage amplitude command. 6. The control of a parallel-connected power converter according to claim 5, wherein a dead zone element is provided on an output side of the DC voltage change rate detecting means, and a DC voltage change rate within a certain range is not output. apparatus. 7. The apparatus according to claim 6, wherein a limiter or a limiter with a dead zone is provided in place of the dead zone element, and this is output only when the detected DC voltage change rate is positive (increase). Control device for parallel connected power converter. 8. The apparatus according to claim 6, wherein a limiter or a limiter with a dead zone is provided in place of the dead zone element, and this is output only when the detected DC voltage change rate is negative (falling). Control device for parallel connected power converter.