JP3112386B2 - Reactive power generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactive power generator for suppressing a voltage flicker in a power system due to a variation in a reactive current generated by a DC electric furnace or the like.

[0002]

Description of the Prior Art FIG. 4, Mitsubishi Electric Technical Report VO1.62. N
o. FIG. 1988 is a circuit diagram showing a configuration of this type of conventional active filter device disclosed in P15 to P20 and connection with a power supply system to be controlled.

In FIG . 4 , reference numeral 1 denotes a system power supply for supplying power to a load 2 to be compensated, and 2 denotes a load to be compensated connected to the system power supply 1 and a harmonic source 3 such as an inverter for generating harmonics. And a capacitive load 4 such as a phase capacitor. 5a is a load current IL flowing into the load 2 to be compensated.
, A compensation current I, which is the same as the harmonic current component of the load current IL, based on the output of the current transformer 5a.
This is an active filter device that outputs c.

[0004] active filter device 6 is composed of elements in the frame of one-dot chain line in FIG. 4. In the above frame of the figure, 5b is a current transformer for detecting the compensation current Ic,
Reference numeral 7 denotes an inverter transformer for inflowing a compensation current Ic from a power supply system composed of a system power supply 1 and a load to be compensated 2. Reference numeral 8 comprises a plurality of inverter units, and applies a voltage to the inverter transformer 7 for a DC voltage source. A self-excited inverter for converting the DC voltage charged in the capacitor 9 into an AC voltage, a compensation current detection circuit 10 for detecting a compensation current reference Ic ^* based on the load current IL (described in detail later), and a compensation current reference 11 Ic ^* and output Ic of the current transformer 5b ^- obtaining a difference ΔI between the adder-subtractor, 12 is the ΔI
And a current control circuit that calculates a voltage reference V ^* based on the output of the capacitor voltage control circuit 13, a capacitor voltage control circuit 13 that controls the voltage of the DC voltage source capacitor 9,
Reference numeral 14 denotes a PWM (Pulse Width Modulation) control circuit that drives the self-excited inverter 8 based on the output of the current control circuit 12.

Further, the compensation current detecting circuit 10 shown in FIG.
Is comprised of the elements within the dotted frame. In the above frame of the drawing, 10a is a PLL circuit for detecting an angular velocity θ (frequency of a fundamental wave) synchronized with a system power supply, and 10b is a three-phase signal (iLa, iLb,
iLc) is a 3φ / 2φ conversion circuit for converting an AC component into a DC component two-phase signal (id, iq) based on the angular velocity θ.
0c is a two-phase signal (i) output from the 3φ / 2φ conversion circuit 10b.
d, iq), a filter circuit for extracting a specific signal from the filter circuit 10d converts the two-phase signal (id ', iq') filtered by the filter circuit 10c into a three-phase signal based on the angular velocity .theta. ^This is a 2φ / 3φ conversion circuit that outputs as ^* . Note that the numeral (3) displayed on the signal line in the figure indicates that the signal line is a signal line for a three-phase signal.

Next, the operation will be described. The active filter device 6 is connected in parallel with the load 2 to be compensated, detects a fault current component such as a harmonic current included in the load current IL, and supplies a compensation current Ic having a phase opposite to that of the fault current component to the active filter device 6. This acts to cancel the fault current component on the power supply side. When the load current IL is supplied from the system power supply I to the load 2 to be compensated, first, the compensation current detection circuit 10
, A current for compensating this, that is, a compensation current reference Ic
^* Is determined (details will be described later).

The difference ΔI between the compensation current reference Ic ^* and the component Ic− of the current Ic (compensation current) flowing into the inverter transformer 7 is obtained by the adder / subtractor 11 and output to the current control circuit 12. The current control circuit 12 calculates a voltage reference V ^* based on ΔI and the output of the capacitor voltage control circuit 13. The PWM control circuit 14 compares the voltage reference V ^* with a triangular wave carrier signal for pulse width modulation (PWM) of the voltage reference V ^*, and modulates the self-excited inverter 8 so as to reduce ΔI by modulating the voltage reference V ^*. Drive and control its output voltage. Here, the output waveform (average) of the inverter unit becomes a sine wave by performing modulation using the triangular wave carrier signal.

The self-excited inverter 8 which is the center of the active filter device is composed of a plurality of inverter units, each of which is connected in series via an inverter transformer 7. Each inverter unit is controlled by a PWM control circuit 14 and generates a voltage required to supply a compensation current Ic to the inverter transformer 7. As described above, the inverter 8 plays a role of converting the DC voltage charged in the DC voltage source capacitor 9 into an AC voltage, and serves as a voltage source for generating the AC voltage Ed.

The compensation current detection circuit 10 is a circuit for determining a compensation current from the load current IL, that is, a circuit for detecting a compensation current reference Ic ^* . Next, the operation will be described in detail. The PLL circuit 10a detects an angular velocity θ (fundamental frequency) synchronized with the system voltage. The 3φ / 2φ conversion circuit 10b converts the load current IL detected by the current transformer 5a into a two-phase signal (id,
iq). id = (2/3) [iLa ・ sin θ + iLb ・ si
n (θ- (2/3) π) + iLc · sin (θ- (4/3) π)] iq = (2/3) [i
La ・ cos θ + iLb ・ cos (θ- (2/3) π) + iLc ・ cos (θ- (4 /
3) π)] The d-axis means a phase difference component from the reference θ,
The q-axis means an in-phase component with θ.

Here, the dq conversion is for obtaining a DC component of the angular velocity θ. That is, the above equation decomposes the three-phase AC into each AC component, converts the AC component into a two-phase AC, and further converts the angular velocity θ
Is used to convert the stationary coordinates into the rotating coordinates based on. This will be described with reference to FIG . The three-phase alternating current i (iu, iv, iw) at the three-phase fixed coordinates uvw shown in FIG.
Is converted into a two-phase alternating current i (iα, iβ) at the two-phase fixed coordinates αβ shown in FIG. This two-phase fixed coordinate α
In β, the two-phase alternating current i is rotating. Therefore, by converting the two-phase fixed coordinates αβ to the two-phase rotation coordinates dq shown in FIG. 3C, the two-phase alternating current i can be stopped at the two-phase coordinates dq. That is, id and iq are DC signals.

The outputs id, i of the 3φ / 2φ conversion circuit 10b
In q, id corresponds to the phase difference with respect to the signal of the angular velocity θ. On the other hand, iq corresponds to the in-phase component. At this time, assuming that θ is the reference of the rotation coordinate conversion and the phase difference φ between the vectors (id, iq) is as shown in FIG .

The filter 10c outputs the two-phase signal (id,
iq) is a circuit for extracting a specific signal from the iq), and a harmonic component other than the fundamental wave can be extracted by using a high-pass filter (HPF). And the filter 10
2φ / 3φ conversion circuit 10d based on the output of c and the angular velocity θ
Converts to a three-phase signal. ica ^* = id · cos θ + iq · sin θ icb ^* = id · cos (θ-2/3 · π) + iq · sin (θ-2/3 · π) ic ^* = id · cos (θ-4 / 3 · π) + iq · sin (θ-4 / 3 · π)

In this manner, the compensation current detection circuit 10 outputs the compensation current reference ic ^* (compensation amount corresponding to a harmonic component). Based on the compensation current reference ic ^* , the compensation current i
Generate c.

Next, a specific waveform will be described as an example. FIG. 5 shows operation waveforms when a rectifier load is assumed. The load current IL shown in FIG. 5A is detected by the transformer 5a. By the way, the load current IL can be separated into a fundamental wave component IL (a dotted waveform in the figure) and a harmonic component (a hatched portion in the figure), and the harmonic component becomes a waveform IH shown in FIG . In order to remove the harmonic component IH, the active filter device 6 detects the harmonic component IH by the compensation current detection circuit 10 (compensation current reference ic ^* ) and outputs the harmonic component IH.
And the opposite phase current Ic of FIG. 5 (c), by operating the self-excited inverter 8 so as to flow from the power supply system, the current IH is offset by the current Ic, Fig of the power supply side
5 As shown in (d), the sine wave current Is of only the fundamental wave component
Becomes

In the above, the harmonic compensation has been described as an example.
By appropriately setting the cut-off frequency of the filter 10c or appropriately changing the configuration of the filter circuit, a reactive power generation device (mainly, a device for compensating for the variation in the leading and lagging portions of the reactive current (id)) SVG device).

[0016]

A conventional SVG device is:
It is configured as described above, and it is possible to take out the fluctuation of the reactive power from the load current and compensate for it. However, if the compensation operation of the SVG device is utilized before the AC circuit breaker for the DC electric furnace is turned on, the When the AC circuit breaker for the electric furnace is turned on, the transformer rush current flowing from the power system to the electric furnace transformer is detected, and the SVG device attempts to compensate for the rush current.
The device attempts to generate an unbalanced current to counteract the inrush current, resulting in the SVG device transformer being demagnetized,
The overcurrent protection device for the inverter output current of the SVG device operates, the AC circuit breaker for the SVG device trips, and it becomes impossible to reduce the power system voltage rise by compensating the capacitor leading capacity of the harmonic filter .

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to obtain an SVG device that reduces an increase in power system voltage by adjusting an output operation point of the SVG device. Aim.

[0018]

(1) A reactive power generating apparatus according to the present invention has a power factor improving capacitive element connected in parallel with a load supplied from a system power supply to a load. For the system, a compensation current reference is derived according to the reactive current component of the load current, a compensation current is generated based on the compensation current reference, sent to the system, and a reactive power generation for adjusting the reactive power of the system. In the device, a combined value of a variable bias reference for varying a bias according to the load reactive current and a fixed Bais reference for setting to output a predetermined delayed reactive current is used as a bias reference, and the capacitance element A bias reference determining means for switching the fixed bias reference on and off in accordance with the switching on and off of the system, and a correcting means for correcting the compensation current reference based on the bias reference. A.

(2) Compensating the power supply from the system power supply to the load and the system having a power factor improving capacitance element connected in parallel to the load in accordance with the reactive current component of the load current. A reactive power generator that derives a current reference, generates a compensation current based on the compensation current reference, sends the compensation current to the system, and adjusts the reactive power of the system, varies a bias according to the load reactive current. The bias reference is a composite value of a variable bias reference and a fixed bais reference that is set to output a predetermined delayed reactive current, and the fixed bias reference is set according to the on / off state of the capacitance element. Bias reference determining means for turning on and off, correction means for correcting the compensation current reference based on the bias reference, and suppression of the compensation current reference for a predetermined time from when the load is turned on. Monodea that includes a suppressing means for
You.

[0020]

(1) The bias reference determining means sets a bias reference based on a composite value of a variable bias reference for varying a bias in accordance with a load reactive current and a fixed bais reference for setting a predetermined delayed reactive current. At the same time, the fixed bias reference is switched on and off in accordance with the switching of the capacitance element into and out of the system, and the compensation current reference is corrected by the correction unit by the correction means.

(2) The bias reference determining means sets a bias reference based on a composite value of a variable bias reference for changing a bias in accordance with a load reactive current and a fixed bais reference for setting a predetermined delayed reactive current to be output. In addition, the fixed bias reference is switched on and off in response to the switching of the capacitance element into and out of the system, the compensation current reference is corrected by the bias reference by the correction unit, and the suppression unit is controlled for a predetermined time after the load is turned on. The compensation current reference is suppressed during
You.

[0022]

[Embodiment 1 ] FIG. 1 shows an SVG device according to the present invention. The same functions as those of the prior art are denoted by the same reference numerals, and description thereof will be omitted.

In the drawing, reference numeral 2 denotes a compensation target, which comprises a DC electric furnace 3 and a harmonic filter 4 which also serves as a power factor improving capacitor 4. Numeral 15 indicates the transmission line impedance (Xs) of the power system, 52SVG is an AC circuit breaker for an SVG device (hereinafter, 52SVC), 52DC is an AC circuit breaker for a DC electric furnace (hereinafter, 52DC), and 52F is a harmonic. Breaker for wave filter (hereinafter referred to as 52F), 17
Is a limiter that limits the output signal of the filter 10c in accordance with the open / close state of the 52DC, 18 is an on-delay circuit that detects the open state of the 52DC, and 19 is a gain that determines the amount of compensation for fluctuations in the reactive current of the load.

Reference numeral 20 denotes a bias reference determining circuit for determining a bias reference, the details of which are shown in FIG. The compensation current Ic ^* is determined by subtracting the compensation amount for the load fluctuation and the bias compensation amount obtained by converting the bias reference by 2/3/3. FIG.
, 21a is a filter for smoothing the load reactive current signal (ido) (this output becomes a variable bias reference),
21b is a delay reactive current reference, 21c is a switch for turning on and off the 21b by 52F (this output signal becomes a fixed bias reference), 21d is a subtractor for subtracting a variable bias reference from the fixed bias reference, and 21e is the signal , And this output is used as a bias reference.

The compensation current detection circuit 10 shown in FIG. 1 detects the variation of the load reactive current. When the DC 52 is open, the compensation current detection circuit 10 is limited to a zero signal by the limiter 17. Next, even if 52DC is turned on, the signal is limited to a zero signal by the limiter 17 for a certain time by the on-delay circuit 18 and
It is possible not to compensate for the inrush current at the time of closing.

On the other hand, the bias reference determination circuit 20 shown in FIG.
Is set to 5 in advance.
Switch on and off with switch 21c according to the open / closed state of 2F,
When the harmonic filter is turned on, the switch 21
c is closed, a fixed bias reference is created, and a variable reactive reference is created from the load reactive current signal via the smoothing filter 21a. The bias reference is calculated via 21e.

The above operation will be described with reference to FIG. When the load is not applied and only the harmonic filter 4 is applied to the system, the SVG device outputs a constant delayed reactive current based on a fixed bias reference, and after the load is applied, continues during the on-delay time. It is possible to smoothly limit the SVG device delay current output by outputting a constant delay reactive current based on a fixed bias reference or limiting the bias reference according to the amount of load reactive current after the on-delay time. it can.

The compensation current reference Ic ^* is determined by subtracting the compensation signal determined from the variation of the load reactive current from the bias reference calculated as described above, and is sent to the power system to reduce the voltage rise.

In the above description, the load 3 is turned on after only the harmonic filter 4 has been connected (turned on) to the system. May be provided .

[0030]

As described above, the present invention has the following effects. (1) Providing variable bias means and fixed bias means,
The fixed bias means is turned on and off when the capacitance element enters and exits the system, so that the output of the reactive power generator is continuously delayed by decreasing the bias reference according to the increase in the load reactive current. This has the effect of limiting the reactive current and reducing voltage fluctuations in the power system.

(2) Further, a variable bias means and a fixed bias means are provided, and the fixed bias reference is turned on and off in accordance with the on / off operation of the capacitance element into and out of the system. As described above, the output of the reactive power generator is reduced in accordance with the increase of the load reactive current, the bias reference is reduced, the lag reactive current is continuously limited, and the voltage fluctuation of the power system can be reduced. This has the effect of not compensating for inrush current .

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a reactive power generation device according to a first embodiment of the present invention .

FIG. 2 is a configuration diagram of a bias reference determination circuit according to the first embodiment of the present invention.

FIG. 3 is an operation explanatory diagram of the first embodiment of the present invention.

FIG. 4 shows a configuration diagram of a conventional active filter device.
You.

FIG. 5 is an operation waveform diagram of a conventional active filter device.
Is shown.

FIG. 6 illustrates the operation principle of a conventional active filter device.
It is a figure for explaining.

FIG. 7 illustrates the operation principle of a conventional active filter device.
It is a figure for explaining.

[Explanation of symbols]

1 system power supply, 2 load, 3 harmonic source, 4 capacitive load, 5a, 5b current transformer, 6 active filter device, 7 inverter transformer, 8 self-excited inverter, 9 DC power supply capacitor, 10 compensation current detection circuit, 10a PLL circuit, 10b 3 phase / 2 phase (3φ / 2
φ) conversion circuit, 10c filter, 11 adder / subtracter, 17 limiter, 18 on-delay circuit, 19 gain, 20 bias reference determination circuit, 21a filter, 21b delay reactive current reference, 21c
Switch, 21d adder / subtractor, 21e filter, 52SVG AC circuit breaker for SVG device , 52DC AC circuit breaker for DC electric furnace, 52F Circuit breaker for high frequency filter.

Claims (2)

(57) [Claims] 1. A system comprising: a power supply from a system power supply to a load; and a system having a power factor improving capacitance element connected in parallel to the load, a compensation current reference according to a reactive current component of a load current. A reactive power generation device that derives and generates a compensation current based on the compensation current reference, sends the compensation current to the system, and adjusts the reactive power of the system, comprising: a variable bias reference that varies a bias according to the load reactive current. And a bias value based on a combined value of a fixed bais reference and a fixed bais reference that is set to output a predetermined delayed reactive current, and a bias that switches the fixed bias reference on and off when the capacitance element enters and exits the system. Reference determining means, and correcting means for correcting the compensation current reference based on the bias reference.
A reactive power generation device characterized in that a load is applied . 2. A system having a power supply from a system power supply to a load, and a power factor improving capacitance element connected in parallel to the load, a compensation current reference according to a reactive current component of the load current. A reactive power generation device that derives and generates a compensation current based on the compensation current reference, sends the compensation current to the system, and adjusts the reactive power of the system, comprising: a variable bias reference that varies a bias according to the load reactive current. And a bias value based on a combined value of a fixed bais reference and a fixed bais reference that is set to output a predetermined delayed reactive current, and a bias that switches the fixed bias reference on and off when the capacitance element enters and exits the system. Reference determination means, correction means for correcting the compensation current reference with the bias reference, and a suppressing means for suppressing the compensation current reference for a predetermined time from the time when the load is turned on. With the door, the fixed bias
A reactive power generation device characterized in that the above-mentioned load is turned on when the power is turned on.