JP5115730B2 - PWM converter device - Google Patents

Description

The present invention relates to a PWM converter control system that changes from AC to DC by using a three-phase four-wire AC power supply as an input, and in particular, eliminates the influence of common mode current when obtaining a sinusoidal waveform with less harmonic components as AC input current. The present invention relates to a highly stable control method.

FIG. 3 shows an example of the main circuit configuration of a PWM (pulse width modulation) converter using a three-phase four-wire AC power supply as an input. The power converter is connected to the AC power source 1 via a transformer 2 whose secondary winding is a star connection. The AC input of the converter 5 is connected to the filter 3 through the AC reactor 4, and the filter 3 is connected to the R-phase, S-phase, and T-phase terminals of the transformer 2 and the transformer neutral point N terminal. Further, the N terminal is connected to a capacitor series connection point of a series circuit of a capacitor 6a and a capacitor 6b connected between the positive electrode and the negative electrode of the DC output of the converter 5. Note that the load 13 of the converter 5 is a DC load. In some cases, AC power is supplied to the load after an inverter is connected and converted to AC.
In order to control the converter 5, the AC voltage detectors 16a, 16b, 16c, the AC current detectors 14a, 14b, 14c, and the DC voltage detector 7 are used, and each detection amount is input to the control device 23a, and from the control device A gate signal of each element used in the converter 5 is output.
Inside the control device 23a, control is performed to keep the voltages of the DC intermediate capacitors 6a and 6b constant. First, a difference in detection amount between the voltage command generator 17 and the DC voltage detector 7 is calculated by the DC voltage controller shown in FIG. 6 and input to the DC voltage regulator 18. By multiplying this output by the AC voltage detection amounts 16a, 16b, and 16c, current commands for the R phase, the S phase, and the T phase are calculated. As shown in FIG. 5, the deviation between these current commands and the detection amounts of the current detectors 14a, 14b, 14c is input to the normal current regulators 19a, 19b, 19c.

For example, in the control device disclosed in Patent Document 1, the adder 32 calculates three sums of detection amounts of the AC current detectors 14a, 14b, and 14c in order to suppress the zero-phase current flowing from the converter to the system. It is input to the zero-phase current regulator 20, and its output is subtracted from the outputs of the normal current regulators 19a, 19b and 19c by the adders 34a, 34b and 34c, respectively, and further the outputs of the AC voltage detectors 16a, 16b and 16c. Are respectively subtracted from each other and input to a gate signal generator 21 for calculating a gate pulse. The gate signal generator 21 compares this signal with the output of the carrier signal generator 22 to generate a gate on / off signal for the converter switching element.
FIG. 4 shows a configuration example in the case where a dedicated current detector 15 is used for zero-phase current detection. In FIG. 3, the zero-phase current detection amount is obtained as the sum of the output amounts of the AC current detectors 14a, 14b, and 14c. However, the control device 23b having the configuration shown in FIG. 4 is used inside the control device 23a shown in FIG. The adder 32 is unnecessary. Other configurations and operation principles are the same as those in the configuration example of FIG.
JP-A-2005-33895

As described above, in Patent Document 1, a three-phase phase current including a zero-phase current is used as a feedback amount as shown in FIG. 5, and the calculated or detected zero-phase current is also used as a feedback amount. The phase current is compensated twice, and an appropriate gain cannot be set. As a result, current control becomes unstable, leading to an increase in input harmonics and a serious failure due to DC overvoltage.
Accordingly, an object of the present invention is to construct a current control system capable of reducing input harmonics and stably performing DC voltage control in a PWM converter having a three-phase four-wire AC power supply as an input.

In order to solve the above-described problem, in the first invention, the input current of each of the three phases of the PWM converter that receives a three-phase four-wire AC power source is detected, and the sum thereof is calculated as a zero-phase component. In the control device that uses it as the feedback amount of the zero-phase current regulator, the zero-phase component is deleted from the two detected amounts of the input current detection value of each of the three phases to become the normal component, and operates as the feedback amount Control is performed using two normal component current regulators and one current regulator that operates using the zero-phase current component as a feedback amount.
In the second invention, the input current of each of the three phases and the N-phase current of the PWM converter that receives the three-phase four-wire AC power source is detected, and the N-phase current is fed back to the zero-phase current regulator. In the control device used as two current component current regulators that operate as a feedback amount by deleting the N-phase current component from the two detection amounts of the input current detection values of each of the three phases; And a single current regulator that operates using the N-phase current component as a feedback amount.
In the third invention, each of the output amounts of the current regulators of the two normal components and the current regulator output amounts of the remaining phases calculated from the output amounts of the current regulators of the two normal components Is added to or subtracted from the output amount of the zero-phase current regulator.
In a fourth aspect of the invention, the N-phase current is obtained by connecting a series connection point of a capacitor series circuit connected between a positive electrode and a negative electrode of a PWM converter DC output and a neutral point (N of the three-phase four-wire AC power source). And a current detector provided between the two points.
In the fifth invention, the N-phase current is detected by a current detector provided in a three-phase package of the PWM converter AC input line.

In the present invention, as a PWM converter control device using a three-phase four-wire AC power supply as an input, a method for detecting the input current of each of the three phases and calculating the sum of them as a zero-phase current component, or a zero-phase current A method of detecting with a dedicated current detector, obtaining a zero-phase current component, deleting this zero-phase current component from the AC input current and controlling the current as a normal current, and controlling only the zero-phase current component Since the current regulators are individually provided, it is possible to individually set the normal current control gain and the zero-phase current control gain. As a result, it is possible to set an appropriate gain, to reduce the input harmonics, and to construct a current control system capable of stable DC voltage control.

The gist of the present invention is a control device for a PWM converter that receives a three-phase four-wire AC power supply as an input, and detects the input current of each of the three phases and calculates the sum of them as a zero-phase current component, or zero-phase By detecting the current with a dedicated current detector, the zero-phase current component is obtained, and this zero-phase current component is deleted from the AC input current to control the current as a normal current and only the zero-phase current component. The current regulator to be controlled is provided individually.

FIG. 1 shows a first embodiment of the present invention. The same functions as those in the conventional example are assigned the same numbers, and explanations are omitted. In this embodiment, two current regulators for adjusting the R-phase current and the T-phase current and a current regulator for adjusting the zero-phase current (N-phase current) are used. It goes without saying that the current regulator that regulates the current of the two phases can be selected in either phase.
The sum of the output amounts of the current detectors 14a, 14b, and 14c is multiplied by 1/3 by the multiplier 33, and the zero-phase current component originally included in the phase current is calculated. The zero-phase current is subtracted by adders 31a and 31c from the R-phase current detected by the current detector 14a and the T-phase current detected by the current detector 14c, for example, as a normal component, and similarly to the conventional example. The difference from the current command is calculated by the adders 30a and 30c and input to the normal current regulators 19a and 19c, respectively. The outputs (for the R phase and T phase) of the two normal current regulators 19a and 19c are calculated by the adder 36 and become the control signal for the S phase.
From these outputs, the output of the zero-phase current regulator is subtracted by adders 34a, 34b, and 34c, and added to the voltage detection amount in the same manner as in the conventional example to obtain a voltage command signal. These voltage command signals are input to the gate signal generator 21 and compared with the carrier signal of the carrier signal generator 22, and then a converter switching element gate signal is generated via a pulse distribution circuit or the like.

FIG. 2 shows a second embodiment of the present invention. The difference from the first embodiment is how to obtain the zero-phase current. In the first embodiment, the AC input current of the converter is detected by the AC current detectors 14a, 14b, and 14c, and a value obtained by multiplying these added values by 1/3 is used as the zero-phase current. In the example, the detected value from the zero-phase current detector 15 is the zero-phase current. Therefore, the adder 32 and the multiplier 33 used in the first embodiment are not necessary. Other configurations and operations are the same as those in the first embodiment.
Here, as shown in FIG. 4, the zero-phase current detector 15 includes a series connection point of a series circuit of capacitors 6a and 6b provided between a positive electrode and a negative electrode of the DC output of the converter 5 and an N point ( However, a current detector for detecting the current of the AC input lines of the converter 5 may be provided.

The present invention is a control system for stably controlling a converter (here, a PWM converter) in which a zero-phase current (common mode current) flows. It can be applied not only to a converter but also to an inverse conversion circuit, and can also be applied to an uninterruptible power supply, a variable speed inverter, and the like.

1 is a block diagram of a control circuit showing a first embodiment of the present invention. The control circuit block diagram which shows the 2nd Example of this invention is shown. 1 shows a first configuration example of a conventional PWM converter device. The 2nd structural example of the conventional PWM converter apparatus is shown. An example of a current control circuit block diagram of a conventional PWM converter device is shown. An example of a current command generation control circuit block diagram of a conventional PWM converter device is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... AC power source 2 ... Transformer 3 ... Filter capacitor 4 ... Reactor 5 ... Converter 6a, 6b ... Capacitor 7 ... DC voltage detector 13 ... Load 14a, 14b , 14c ... AC current detector 15 ... Zero phase current detector 16a, 16b, 16c ... AC voltage detector 17 ... DC voltage command generator 18 ... DC voltage regulator 19a, 19b 19c: Normal current regulator 20: Zero-phase current regulator 21 ... Gate signal generator 22 ... Carrier generator 23a, 23b ... Control circuits 30a, 30b, 30c, 31a, 31c 32, 34a, 34b, 34c, 35a, 35b, 35c, 36... Adders 33, 37a, 37b, 37c.

Claims (5)

  A control device that detects the input current of each of the three phases of the PWM converter that receives a three-phase four-wire AC power source, calculates the sum of them as a zero-phase component, and uses this as the feedback amount of the zero-phase current regulator In the three-phase input current detection values, the zero-phase component is deleted from two detection amounts to obtain a normal component, and two normal-component current regulators that operate as feedback amounts, and the zero-phase current A PWM converter device controlled by using one current regulator that operates using a component as a feedback amount.   In a control device that detects an input current and an N-phase current of each of the three phases of a PWM converter that receives a three-phase four-wire AC power source and uses the N-phase current as a feedback amount of a zero-phase current regulator. Two normal component current regulators operating as a normal component by removing the N phase current component from the two detected amounts of the input current detection values of each of the three phases, and the N phase current component A PWM converter device controlled by using one current regulator operated as a feedback amount.   The zero-phase current regulator for each of the output amounts of the two normal component current regulators and the current regulator output amount of the remaining phase calculated from the output quantities of the two normal component current regulators The PWM converter device according to claim 1, wherein the output amount is added or subtracted.   The N-phase current is provided between the series connection point of the capacitor series circuit connected between the positive and negative electrodes of the PWM converter DC output and the neutral point (N point) of the three-phase four-wire AC power supply. 3. The PWM converter device according to claim 2, wherein the current is detected by a current detector. 3. The PWM converter device according to claim 2, wherein the N-phase current is detected by a current detector provided in a three-phase package of the PWM converter AC input line.

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