JPS6051339B2 - power regulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power adjustment device capable of improving the power factor and achieving polyphase balancing for a polyphase unbalanced low power factor load, and also compensating for harmonic ripples of the load.

For multiphase AC power supplies, the current value of each phase is equally balanced with respect to the load, and there is no harmonic ripple.
At the same time, it is desirable that the phase difference between current and voltage be zero, that is, the power factor be 1.

If the above requirements are not met, this will lead to a significant increase in the power equipment capacity and a decrease in the power utilization rate. However, polyphase unbalanced low power factor loads such as arc furnace equipment and cycloconverter equipment have a large amount of reactive power, and furthermore, their fluctuations have the problem of adversely affecting other loads connected to the same power supply system. . Furthermore, in recent years, loads such as static Leonard devices using thyristors have emitted harmonic components other than the power supply frequency, causing induction disturbances and increasing harmonic loss. Therefore, in the past, for example, Japanese Patent Application Laid-Open No. 52-876
A power adjustment device that balances three-phase power and compensates for harmonic ripples has been proposed in Japanese Patent No. 50 and the like.

The device has a schematic configuration, for example, as shown in FIG.
The voltages VLU, VLV, and VLW are detected for each phase U, V, and W, and instantaneous power calculation circuit B calculates the instantaneous power P.
Find u■: iLu°VLU Pv: iLv0VLV PW=iLw, VLW.

Then, calculate the time average of 116 cycles from the above instantaneous power, sample this at the timing of zero cross point detection of each phase, and calculate the average power value F of the three phases as ) Find dt.

This value is regarded as the amplitude value of the effective current when balanced, and multiplier C multiplies it by the unitized detection voltage of each phase, i
SUR:ISRISinωt iSVR ■ISR゜sin (ω -2π13) iswR
(2) A balanced effective current command value is obtained by setting IsR, sin (ω to -4 (rI3)).

The compensation current command value is obtained by subtracting the load current from these power command values, and the compensation current 1 actually supplied from the inverter D is calculated.
The inverter D is controlled using the deviation from cu, icv, and icw. As a result, the unbalanced active current is compensated for by the compensation current from the inverter D, and the power supply only needs to supply balanced current. Of course, in the case of the device with the above configuration, it is necessary to calculate the balanced active power (active current) by calculating the instantaneous power, so calculation circuit B, zero cross point detector E, and sample hold circuit F are required. This necessitates a large-scale circuit configuration such as the following, which poses a problem of complicating the control and complicating the configuration.

For this reason, it has poor reliability and is economically disadvantageous, so there have been problems in putting it into practical use. Furthermore, in order to compensate for harmonic ripples, it was necessary to set the operating speed (response speed) of the device itself to be sufficiently high, which posed many technical difficulties. The present invention was made in consideration of the above circumstances, and
The purpose of this is to perform effective power compensation using simple arithmetic control to achieve multiphase balancing and improve the power factor of power supplies that drive multiphase unbalanced low power factor loads. It is an object of the present invention to provide a power regulating device having a simple and highly practical configuration that can also compensate for harmonic current.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a schematic configuration diagram, in which a three-phase unbalanced low power factor load 1 such as an arc furnace equipment consists of a U phase, a V phase, and a W phase. It is connected to a power source (not shown) via a three-phase AC power supply line 2, and is driven by electric power.

Further, the output of a PWM (pulse width modulation) inverter 4 connected to a DC power supply (capacitor) 3 is supplied to the load 1 via an AC reactor 5 for each phase. the above! P
WM inverter 4 has multiple SCRs with self commutation function.
(Sl, ~, S6) and a feedback diode (Dl,
, D6), and the output V of the DC power supply 3 under ignition control by a gate control circuit to be described later.
It modulates the pulse width and outputs a three-phase AC voltage of arbitrary magnitude, size, and phase. In addition, the output V of the DC power supply 3. is set larger than the maximum value Vm of the three-phase AC voltage V. Accordingly, a compensation current 1 is supplied from the PWM inverter 4 to the load 1 via the AC reactor 5. is determined by the output of the PWM inverter 4 and the voltage of the three-phase AC power supply, that is, the load voltage. Also, this compensation current 1. The value of is detected by an AC current transformer (CT) 6 for each phase. Also load 1
At the input terminal of the transformer (PT) 7, the load voltage V
, is detected, and the load current is detected for each phase by an AC current transformer (CT) 8. These detected components are used as compensation current control information for each phase. By the way, the DC power supply V.

The value of is V. The set value V is detected by the detector 9 and guided to the comparator 10. The deviation from R is calculated.

This deviation ε1 is the compensation element G1 of the control system by the integrator 11.
(S) to inverter control circuits 12a, 12b, and 12c corresponding to each phase, respectively. The control element Gl, $) is generally given as a proportional element K1 when performing proportional control, but an integral element is used when controlling by reducing the deviation ε1. Also, a differential element may be used to improve the response of the control system.
Now, the inverter control circuits 12a, 12b, and 12c input the deviation ε1 via the compensation element G1(S), and guide it to the multiplier 13.

This multiplier 13 normalizes and inputs the load voltage s detected by the transformer (PT) 7 via a coefficient unit 14 to the other side. That is, the coefficient multiplier 14 multiplies the detected load voltage ■ by the coefficient value, and therefore the multiplier 13
The output of is as follows. The currents 1SUR, i, VR, and 1SWR obtained in this way correspond to the command value of the three-phase balanced effective current, and are led to the comparator 15 and then passed through the AC current transformer (CT) 8. The detected load currents 1Lu, 1LV, and iLW of each phase are compared and determined.
The comparative judgment value, ie, the command value of the compensation current, is obtained as follows.

In other words, the current indicated by the above command value is the compensation current 1. Therefore, it is sufficient to supply the load 1 from the inverter 4 as follows. Therefore, the command value of the compensation current 10゛UR, iCVR
, iCml is guided by the comparator 16 to the AC current transformer 6
It is compared with the actual compensation current value detected by , and its deviation ε2 is determined. This deviation ε2 is passed through a compensation element G2 ($) of a control system consisting of an integrator 17, and a comparator 18 compares and determines an inverter carrier wave consisting of, for example, a 600 Hz triangular wave signal output from a triangular wave oscillator 19. Based on the result of this comparison, the gate circuit 20 is driven to control the firing of the SCR of the inverter 4 for each phase to make the deviation E2 zero, thereby balancing the power. It becomes possible. In this way, this device uses the output voltage V of the DC power supply 3.

and its setting value V. The command value for the three-phase balanced current is determined based on the deviation from R. In this respect, unlike conventional devices, the three-phase balanced active power is not calculated by complicated calculations from the instantaneous value of the load power, so the device can be configured very easily. Now, when the PWM inverter 4 starts to start, all the SCRs are in the off state, and the voltage of the DC power supply 3 is V.

is charged through the diode to the maximum voltage of the AC power supply. Therefore, the DC voltage command value VOR is set to 1.
Set to 5XVm. Therefore, the deviation ε1 is 0.5×V
．． ．． Therefore, the command value of the three-phase balanced effective current is given as follows. Therefore, the load current 1LU, iLV, i
The command value of the compensation current when LW is not flowing is,
Accordingly, the compensation current becomes equal to the above command value.
The WM inverter 4 is controlled.

In this case, the actual compensation current 1cu, icv, icw consists only of the effective current component flowing from the power supply to the PWM inverter 4, and the energy is stored in the AC reactor 5 and then in the DC power supply 3. . This energy E has the capacity of the DC power supply 3 as C. This is shown as the case where

Therefore, the capacity C. If is constant, the voltage V. Energy is stored as a result of the rise in . Therefore, the power supply voltage V. is the set value 1.5Vn. When the difference E1 becomes equal to , the deviation E1 becomes zero and charging to the power source 3 stops. Next, we will discuss the third case where the three-phase unbalanced low power factor load 1 operates from the above initial state.
This will be explained with reference to the figures.

FIG. 3 shows the vector relationship of three-phase voltages and currents, where Vu, Vv, and Vw indicate the voltage vectors of the U-phase, V-phase, and W-phase. In addition, the voltage vector Vu, ■V
, ■w, ILU, iLV, iLV, are load current vectors Hu, hv, hw are power supply current vectors, and Icu, icv, ici are compensation current vectors from the inverter 4. As shown in this vector relationship, if the three-phase balanced effective currents 1su, isv, hw are to be supplied from the power supply to the three-phase unbalanced load currents 1LU, iLV, iLW, the broken lines in the figure indicate The inverter 4 may be controlled so as to provide a compensation current of such a vector. In this way, all of the active power required for the load 1 is supplied from the power supply, and the supply ratio of the active power supplied from the inverter 4 to the load 1 is as follows, and the sum can be made zero.

Therefore, the output voltage V of the DC power supply 3. will always be held constant. By the way, the process of reaching such an equilibrium state is shown as follows.

That is, at the initial stage, both the deviation E1 and the effective current command value are zero, and the load current h is directly given as the compensation current command value 1CR. Therefore, the inverter control is performed so that the current flows, and as a result, Output voltage V of DC power supply 3.

decreases. As a result, the deviation ε1 increases (positive), and the effective current command value 1SR increases. Therefore, the actual compensation current 10 is determined by the compensation current command value 1cR (=IO-15R).
decreases, and the effective current 1s (=1, R) from the power supply side decreases accordingly.
will be supplied. And finally, the deviation ε1
The current 1 s from the power supply increases until becomes zero (sa0), and the vector relationship shown in FIG. 3 is reached and balanced. In this case, in the case of proportional control in which the compensation element Gl, S) is K1, the deviation E1 will maintain a small value, but in the case of a control element with an integral element added, the above deviation ε
1, that is, the steady-state deviation can be made zero. Furthermore, according to this device, when there is a change in the load current 1, the compensation current 10 changes in response to this, and the energy temporarily stored in the DC power supply (capacitor) 3 changes, so that the power is removed from the power supply. The three-phase balanced active current supplied will change and stabilize to another steady state, or equilibrium state.

Therefore, the inverter 4 normally acts as a three-phase reactive power source, but when the load 1 suddenly changes, it transiently uses the energy of the DC power supply 3 to act as an active and reactive power source. Therefore, a buffering effect is provided against sudden changes in load power, making it possible to suppress adverse effects on other loads connected to the same power supply system. As explained above, according to this device, the three-phase balanced active power can be supplied from the power source without the need for complex calculation processing of the three-phase balanced active power based on the instantaneous value of the load power, which has traditionally been required for power adjustment. It is possible to balance the current.

Furthermore, it is possible to improve the power factor. ! Therefore, by simplifying the installed capacity of the power supply, various problems associated with three-phase unbalanced current can be effectively solved. In addition, when the load 1 is a cycloconverter device etc., the load current contains harmonic components, but since the inverter 4 can supply the above harmonic components as part of the compensation current, the power supply current is always smoothed. Only the fundamental wave component can be used. That is, the command value of the three-phase balancing current is ε1 as described above.
・Since it is indicated by the product of G1 ($) and the unit voltage, if the power supply voltage is a sine wave, only its fundamental wave component is present.Therefore, ICUR=I and -1SUR etc. are harmonic components. Therefore, it is possible to eliminate induction disturbances due to harmonics and harmonic losses in power supply equipment.The present invention is not limited to the above embodiments.For example Inverter 4 as shown in Figure 4
A plurality of inverter carrier waves may be configured in parallel, and the inverter carrier wave may be inverted by the inverter 22 on one side to generate two carrier waves with different phases, and the two inverters 4 may be driven with different phases. In this way, the operating frequency for the load 1 from the inverter 4 side can be substantially doubled, so that it is possible to easily compensate for harmonic ripples sufficiently. It goes without saying that three or more inverters 4 may be configured in parallel to perform drive control with different phases to further increase the actual operating frequency. It goes without saying that transistors may be used instead of SCRs to configure the inverter 4, and the inverter 4 is not limited to three-phase AC, but also two-phase, six-phase, one-phase
It is possible to apply it to power sources such as Xiang. In short, the present invention can be implemented with various modifications without departing from the gist thereof.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing an example of a conventional device, Fig. 2 is a schematic configuration diagram not showing an embodiment of the present invention, and Fig. 3 is a vector showing the relationship between voltage and current showing the action of the present invention. 4 are schematic configuration diagrams showing other embodiments of the present invention. 1... Unbalanced low power factor load, 3... DC power supply, 4... PWM inverter, 5... AC reactor, 6, 8...・AC current transformer (CT)
, 7...Transformer (P1'), 9...V
O detector, 10, 15, 16, 18... Comparator, 12a, 12b, 12c... Inverter control circuit, 13... Multiplier, 19...・Triangular wave oscillator.

Claims (1)

[Claims] 1. A voltage-type PWM inverter connected in parallel to a load connected to an AC power source via an AC reactor, a capacitor connected to the DC side of this inverter, and the deviation between the detected value and set value of the voltage across this capacitor. is determined as a deviation value, this determined deviation value is used as a command value for the multiphase balanced active current via a compensation element, and a value obtained by subtracting this command value from the load current detection value is supplied from the voltage source PWM inverter. and an inverter control circuit that controls the value of the compensation current.