JPS6034333B2 - Three-phase reactive power regulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a three-phase reactive power adjustment device that multiplexes bridge interference to suppress the generation of harmonics, reduce response delay, and simplify the circuit configuration.

In electric power systems, it is customary to supply reactive power in parallel with loads in order to improve the power factor of the system.

For example, in a three-phase power system 1, FIG.
The DC current flowing through the smoothing IJ factor 5 provided on the next side is adjusted. In addition, in Fig. 2, a self-excited inverter 7 (A type 1 main-900) is connected in parallel to the load 6 and takes the power factor.
The reactive power of the system is adjusted by adjusting the DC current flowing through the smoothing IJ vector 8 provided on the secondary side. In these examples, the reactive power that the inverter devices 4 and 7 receive from the grid is proportional to the DC current IDc flowing through the smoothing reactors 5 and 8, so the desired reactive power can be obtained by controlling the phase of the inverter device. However, in order to do this, smooth reactors are required that do not cause intermittent current over the entire power flow range, and these reactors must consume only a small amount of active power, so their structure and dimensions are quite large. becomes.

In addition, in the example shown in FIG. 2, the current taken by the load 6 is 1
L, if the current taken by the self-excited inverter 7 is lc, then the current 1 taken by the system is 1 = IL + lc, and the current and voltage waveforms are when the reactive current of the load is controlled to be canceled by the reactive current taken by the self-excited inverter. is as shown in FIG. 3 (only one of the three phases is shown). In this case, the fundamental wave reactive power of the current 1 taken from the grid is zero, but since the compensation current lc is a square wave, it contains considerable harmonic components, and a large-scale filter device is required to absorb this. Is required. The above-mentioned disadvantages can be solved by multiplexing the inverters as shown in FIG.

In the figure, N bridge inverters 10a, 10b...10n are connected in series to the smoothing reactor 9.
Each AC side is connected through N transformers 11a, 11b, . power supply system 12
is linked to. Figure 5 shows N=8 in the example of Figure 4.
The current and voltage waveforms are shown for the case where the compensation current l is
c is quite close to a sine wave, and the current 1 taken from the power supply system 12 is also in phase with the power supply voltage, and the waveform is close to a sine wave. Therefore, the filter should also absorb high-order harmonics. 4. Can be made lighter in size. In addition, when performing multiplexing in this way, the ripple component of the DC voltage is also reduced to 1/N compared to when multiplexing is not performed, so the inductance of each smoothing reactor can be reduced, and the inductance of the inverter DC current changes when the inverter DC current command changes. The responsiveness of the DC current is also very good, since the number of commutations is N times greater. By the way, single-phase reactive power is obtained by integrating the product of a current and a waveform whose phase is shifted by 900 degrees from the voltage over a certain period, and averaging the results.

That is, voltage e, current i, voltage e that is 900 deviated from voltage e.
If the voltage ee = 2 V sinwt i = 2 1 sin (wt-A blood 7) e': 2 V coswt and the period T, then the reactive power Q is Q = 2 V coswt. 'jdt=-VISin (positive Q indicates leading phase reactive power, and negative Q indicates lagging reactive power).

In the case of three phases, perform the same calculation as above for each phase,
Reactive power can be found by summing them, but if you try to detect reactive power in an actual circuit according to the above definition, it will be necessary to sample and hold the integral value, which will complicate the circuit configuration. On top of that, 1-1
A delay of /2 cycles occurs, and the detected values also become discontinuous, resulting in the inconvenience that it is not possible to follow sudden changes in the reactive power of the load.

The present invention has been made in order to eliminate the above-mentioned disadvantages in conventional devices, and the product of each phase voltage and phase current that is deviated by 900 from the power supply voltage is added for three phases, and is directly converted into instantaneous fundamental wave reactive power. It is an object of the present invention to provide a three-phase reactive power adjustment device that can detect rapid changes in reactive power without delay by detecting the detection and flowing an inverter DC current proportional to the detected current.

Hereinafter, details of the present invention will be explained with reference to the embodiments shown in FIG. 6 and subsequent figures.

In FIG. 6, a reactive power source 15 for absorbing reactive power Qc is connected in parallel near a load 14 connected to a three-phase power supply 13.

This reactive power source consists of N bridge inverters 16a to 16n connected in series on the DC side, as in FIG.
, a self-excited multiplex bridge inverter 18 consisting of N transformers 17a to 17n inserted between each of these AC terminals and the power supply 13, and a smoothing reactor 19 connected to the DC side thereof. ing. In addition, the power supply circuit 13
includes a filter 20 for absorbing harmonic current QF,
A reactive power detection device 21 for detecting reactive power Qs on the power source side is connected. The reactive power Qs is compared with the reactive power command value QR on the power supply side (zero if the input power factor is set to 1), and the deviation value is multiplied by the reactive power control transfer function Go in block 22 to obtain a direct current. The command becomes loR. This DC current command loR is the DC current value 1 of the smoothing reactor 19. The deviation value is multiplied by the DC current control transfer function C in block 23, and then input into the control mode of each inverter 16a to 16n to control their firing phase (A6CI knee 90o). In the above, the reactive power detection device 21 is configured as shown in FIG.

In the same figure, the system voltage VR of the three-phase power supply system R, S, T
, Vs, and VT are detected by the transformer 24, and some of them are inverted by the operational multipliers 25R, 25s, and 25T, resulting in one VR, one Vs, and one VT. These inverted outputs, along with the original signals VR, , Vs, and VT, are combined two by two so that they rotate in opposite directions to each other and are sent to the adjacent operational amplifier 26R.
, 26s, 26T, 90o from the original signal
−VR′, −Vs′ with delayed phase and reversed polarity
, -VT' is calculated. The relationship between these signals and the original signal can be expressed mathematically as follows: VR' = (Vs - VT
)/ノ3Vs'=(VT-VR)/ノ3V? '=(VR-Vs)Nono3 Also, if shown (only for one phase), it is as shown in FIG.

On the other hand, the currents iR, ls, and iT are detected by the current transformers 27 connected to the power supply systems R, S, and T, and these and the above-mentioned signals -
VR', -Vs'-VT' are combined with the same appendixes and guided to multipliers 28R, 28s, 28T, respectively, to obtain -V
R'IR, -Vs'ls, and -VT'IT are calculated, and these calculated values are passed through an arithmetic intensifier 29, where they are added together and the sign is inverted to obtain VR'iR+Vs'is+VT'iT. The instantaneous fundamental wave reactive power Qs detected by the reactive power detection device 21 in this way is compared with the reactive power command value QR on the power supply side as described in FIG. bridge invar
18 to control their firing phase. As described above, according to the embodiments of the present invention shown in FIGS. 6 and 7, it is possible to continuously output reactive power without delay, and it is possible to respond to sudden changes in reactive power without delay.

By the way, the control system shown in FIG. 6 can be expressed as shown in FIG.

Here, G and c are transfer functions from DC current command loR to DC current lo, and K is a conversion constant from DC current to reactive power (other symbols are as described above). Here, the multiplexed bridge inverter DC current lo and its input fundamental wave reactive power QC are Qci-KI.

There is a relationship between

As can be seen from this block diagram, in the control system of Fig. 6, the reactive power QL of the load acts as a disturbance and has a large influence on the control system, so the deviation signal A of QR-Qs is caused by changes in the reactive power QL. It changes greatly, worsening the transient characteristics. In addition, the DC current control transfer function G,c is generally 1/(
10ToS), the response time is long. However, these inconveniences can be avoided by partially changing the circuit configuration as shown in FIG.

That is, in the modified example of the present invention shown in FIG. /K, and the obtained loRL is the inverter DC current command value 1. DC current command 1 by adding it to Rs. I'm looking for R. This makes the control system unaffected by disturbances caused by load fluctuations. Also,
In the circuit of FIG. 10, a differentiation circuit 33 is added to the control system, and the sum of the DC current command loR and its differential value is used as the DC current command. R
'. By making the differential coefficient of the differentiating circuit 33 approximately equal to To of the first-order delay 1/(10T.S) of the DC current control system, it is possible to compensate for the delay of the DC current control loop and improve response performance. . In addition, in Figure 10,
Identical components in FIG. 6 are indicated by the same symbols.
Further, a block diagram of the control system in FIG. 10 is as shown in FIG. 11. In this way, in the present invention, 90
The three-phase sum of the products of voltage and current that are shifted to 0 is directly detected as instantaneous fundamental wave reactive power, and an inverter direct current proportional to this is passed, so the circuit does not become too complicated and the load In addition, when detecting load fluctuations and performing disturbance compensation or differentially compensating delays in current response, transient characteristics and response characteristics can be further improved.

In the above description, the details of the present invention have been explained with reference to an example using a separately excited multiplexing bridge inverter.
The present invention can be similarly applied to a three-phase reactive power adjustment device that combines a coil and a capacitor.

[Brief explanation of drawings]

Figures 1 and 2 are circuit diagrams illustrating conventional reactive power adjustment devices, Figure 3 is a current and voltage waveform diagram of each part in the circuit of Figure 2, and Figure 4 illustrates the basic configuration of a multiplexed inverter. 5 is a current and voltage waveform diagram of each part in the circuit of FIG. 4, FIG. 6 is a circuit diagram showing an example of the device of the present invention,
FIG. 7 is a circuit diagram showing a configuration example of a reactive power detection device used in the device of the present invention, FIG. 8 is a vector diagram showing the voltage relationship in the circuit of FIG. 7, and FIG. 9 is a circuit diagram showing the voltage relationship in the circuit of FIG. FIG. 10 is a block diagram showing an embodiment of the present invention, and FIG. 11 is a block diagram showing a control system in the circuit of FIG. 10. ~1, 12, 13... Three-phase power system, 2, 6, 14, 30... Load, 3... Power condenser, 4... Separately excited inverter, 5, 8, 9, 19
...Smoothing reactor, 7...Self-excited isoverter, 10a~
I0n, 16a to 16n...Bridge inverter, 11a
〜11n, 17a〜17n, 24...Transformer, 15...
Reactive power source, 20... Filter, 21, 31... Reactive power detection device, 25R, 25s, 25T... Arithmetic intensifier, 26R, 26s, 26... Arithmetic intensifier, 27
．． ．． ．． Current transformer, 28R, 28s, 28T...multiplier,
29... Arithmetic multiplier. Younger brother J figure 3 younger brother 4 figure 8 figure 3 younger brother Z figure Tsutomu 5 figure 6 younger brother K figure younger brother JO figure younger brother JJ figure

Claims (1)

[Claims] 1 A multiplexed bridge inverter is constructed by connecting three-phase bridge circuits of each of N transformers whose secondary phases are sequentially shifted by 60°/(N-1), and connecting their respective DC sides in series. In a device connected to a system in which a smoothing reactor is connected to the DC side, there is a means for detecting the voltage of each phase of the three-phase power supply system, and a voltage of 90° from each phase system through the output of the voltage detection means. means for forming a three-phase signal representing shifted phase voltages; means for detecting instantaneous values of phase currents flowing through the three-phase load and forming three-phase signals representing the instantaneous values of the phase currents; Means for obtaining an instantaneous fundamental wave reactive power value by calculating and adding the products for each phase with the phase signal, and means for controlling the DC current of the multiplexed bridge inverter based on this instantaneous fundamental wave reactive power value. A three-phase reactive power adjustment device characterized by comprising: