CN106816876B - voltage compensation method and circuit for eliminating influence of DVR (digital video recorder) on adjacent load - Google Patents

voltage compensation method and circuit for eliminating influence of DVR (digital video recorder) on adjacent load Download PDF

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Publication number
CN106816876B
CN106816876B CN201710008929.2A CN201710008929A CN106816876B CN 106816876 B CN106816876 B CN 106816876B CN 201710008929 A CN201710008929 A CN 201710008929A CN 106816876 B CN106816876 B CN 106816876B
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voltage
load
dvr
sensitive load
phase angle
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CN106816876A (en
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杜兆斌
戴观权
管霖
刘嘉林
周保荣
洪潮
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South China University of Technology SCUT
Research Institute of Southern Power Grid Co Ltd
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South China University of Technology SCUT
Research Institute of Southern Power Grid Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load

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Abstract

The invention discloses a voltage compensation method for eliminating influence of a DVR (digital video recorder) on an adjacent load, which comprises the following steps that after system voltage is temporarily reduced, the current amplitude of a sensitive load and the current amplitude of an adjacent non-sensitive load are reduced to x 1, the phase angle change value is beta, the phase shift is carried out to enable the beta to be beta set, the end point meeting is exactly positioned on a primary event current circle, the amplitude of the phase angle of minus the beta set and the amplitude of are combined to be a target voltage phasor standard voltage phasor minus the target voltage phasor to obtain , and a PWM driving signal is obtained through a hysteresis comparator, the PWM driving signal drives an inversion unit, and a signal output by the inversion unit generates an ideal compensation voltage after passing through a filtering unit.

Description

Voltage compensation method and circuit for eliminating influence of DVR (digital video recorder) on adjacent load
Technical Field
The invention relates to the field of power supply of a power grid, in particular to a voltage compensation method and a voltage compensation circuit for eliminating the influence of a DVR (digital video recorder) on an adjacent load.
Background
The Dynamic Voltage Restorer (DVR) is a novel series voltage compensation device which is connected in series between a system power grid and a sensitive user load, can effectively eliminate voltage fluctuation, voltage flicker, asymmetries of each phase voltage of sister and short-time power supply interruption and other faults, and has the advantages of good dynamic performance, low economic cost, good compensation benefit and the like.
the Dynamic Voltage Restorer (DVR) can be equivalent to a controlled voltage source, and has the function of energy output, and can input energy to the power grid system in the working state, and the installation configuration of the dynamic voltage restorer in the power system is shown in fig. 1.
the working principle of the Dynamic Voltage Restorer (DVR):
As shown in fig. 1, when the system power grid supplies power normally, the bypass switch is in a closed state, the Dynamic Voltage Restorer (DVR) is in a standby state, and the dynamic voltage restorer is not connected to the power grid system, and does not affect the power grid system or sensitive loads. When the voltage of the system power grid drops, the bypass switch is switched to an off state from a closed state within a short time (several milliseconds), the Dynamic Voltage Restorer (DVR) is immediately connected to the power grid system, compensation voltage is injected between the system power grid and the sensitive load to compensate the voltage drop of the power grid, so that the sensitive load can hardly feel the influence of the voltage drop of the system power grid, the voltage drop can be always kept to work under a normal voltage level, and the problem of the voltage drop can be effectively solved.
A Dynamic Voltage Restorer (DVR) is a user voltage compensation device which is used by sensitive load users to solve the problem of power grid dynamic power quality and reduce the investment and installation of the influence of system power grid voltage drop on self sensitive loads, and is installed between a system power grid and a sensitive load branch in series. Three basic voltage droop compensation strategies are currently in common use: the compensation goals of the three compensation strategies are based on satisfying that the self-contained sensitive load keeps working under a normal voltage level and neglecting the change condition of the voltage of the adjacent load, so that the access of a Dynamic Voltage Restorer (DVR) inevitably causes certain influence on the adjacent load.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a voltage compensation method for eliminating the influence of a DVR on an adjacent load, thereby effectively solving the problems of the benefit of the DVR and the energy exchange among users.
It is another object of the present invention to provide a voltage compensation circuit that eliminates the effect of the DVR on the adjacent load.
The purpose of the invention is realized by the following technical scheme:
A voltage compensation method for eliminating the influence of DVR to adjacent load, comprising the steps of:
S1, setting equivalent impedance of the sensitive load and the non-sensitive load to be the same, so that the normal current of the sensitive load and the normal current of the adjacent non-sensitive load are equal in magnitude and same in phase, and the amplitude of the normal current of the sensitive load and the amplitude of the normal current of the adjacent non-sensitive load are both 1; after the system voltage is temporarily reduced, the current amplitude of the sensitive load and the current amplitude of the adjacent non-sensitive load are reduced to x1The phase angle is changed to beta, and the phase shift makes beta equal to betasetsatisfy the following requirementsFalls exactly on the primary event current circle, where β1＜βset＜β2；
Wherein:
Beta isAndphase angle therebetween orAndThe phase angle therebetween;
the compensation current flows through the sensitive load when the DVR acts independently after the voltage sag;
for system voltage after voltage sagWhen acting alone, the current flows through a sensitive load;
The compensation current flows through the adjacent non-sensitive load when the DVR acts alone after the voltage sag;
For system voltage after voltage sagWhen acting alone, current flows through the adjacent non-sensitive load;
β1Is composed ofWhen the end point is within the primary event current circleAndThe phase angle therebetween;
β2Is composed ofwhen the end point of (1) is outside the primary event current circleandthe phase angle therebetween;
βsetis composed ofWhen the end point of (a) falls exactly on the primary event current circleandthe phase angle therebetween;
At system voltage for adjacent non-sensitive loadsAnd compensation voltageunder the combined action of;
Before the voltage of the power grid drops temporarily, the current flows through a sensitive load;
Before the voltage of the power grid drops temporarily, current of non-sensitive load flows;
S2, mixingPhase angle of (1) minus betasetAndIn combination with the synthesized target voltage phasorWherein the target voltage phasorHas a phase angle ofPhase angle of (1) minus betasetAmplitude of isThe amplitude of (d);
Wherein:
before the voltage of the power grid drops temporarily, the voltages at two ends of a sensitive load are detected;
For system voltage after voltage sagWhen acting alone, the voltage at the two ends of the sensitive load;
s3 standard voltage phasorSubtracting target voltage phasorTo obtainObtaining a PWM driving signal through a hysteresis comparator;
s4, driving the inversion unit by the PWM driving signal, generating ideal compensation voltage after the signal output by the inversion unit passes through the filtering unit
in step S1, the betasetThe acquisition mode is as follows:
Is provided withHas an amplitude of x2Then is atAndThe phasor triangle satisfies the cosine theorem:
Note the bookIn thatAndin the phasor triangle of (1), wherein ZLThe common bus B supplies power for a sensitive load configured with a DVR and an adjacent non-sensitive load respectively for the impedance of a main line between a system and the bus B; z2Is the equivalent impedance of the adjacent non-sensitive load; x is the number of3Is ZLAnd ZL+Z2The amplitude ratio of (a); alpha isAnd-The phase angle therebetween;
due to the fact thatAnd isAndThe formed phasor triangle is an isosceles triangle, and then the following conditions are met:
WhereinPhi isand-The phase angle therebetween;
The above equation thus becomes:
in the formula (1), x1Is obtained by the DVR detection module and is a known quantity; x is the number of3and α is the system parameter and its formulaFound, also known quantity; beta is aset、x2Is a quantity to be calculated;
The formula (2) is simplified and known, and the formula (2) is related to the unknown quantity x2 2Quadratic equation of one unit
a·(x2 2)2+b·x2 2+c＝0；
wherein the content of the first and second substances,
It is easier to find the unknown quantity
Thus, find out
Will find x2Can determine beta by substituting the value of (1)setan angle of magnitude such thatFalls on the primary event current circle.
The DVR is switched in, so that the phase of the current of the non-sensitive load is changed, and the amplitude is not changed, namely the active power consumed by the non-sensitive load is not changed.
In step S2, thethe phase angle of (a) is obtained by the FFT module,the amplitude of (a) is also obtained by the FFT module; the FFT module is a fast Fourier transform module.
The other purpose of the invention is realized by the following technical scheme:
a voltage compensation circuit for eliminating influence of DVR on adjacent load comprises a measuring module, a first FFT module, a second FFT module, a first adder, a synthesized target voltage phasor module and a second adderTwo summators, a hysteresis comparator, an inversion unit and a filtering unit, wherein the measurement module respectively measures the voltages at two ends of a sensitive load before the voltage of the power grid drops temporarilyAnd system voltage after voltage sagvoltage across a sensitive load when acting aloneMeasured by the first FFT modulethe phase angle of (a) is,Phase angle of (1) is subtracted by beta via the first addersetFinally, a synthetic target voltage phasor module is reached;measured by the second FFT moduleThe amplitude of the voltage is finally reached to a synthesized target voltage phasor module; target voltage phasor synthesis module target voltage phasor synthesisWherein the target voltage phasorHas a phase angle ofphase angle of (1) minus betasetAmplitude of isThe amplitude of (d); phasor of standard voltageSubtracting the target voltage phasor by a second adderTo obtainobtaining a PWM driving signal through a hysteresis comparator; the PWM driving signal is subjected to inversion unit to obtain a sine wave signal; the filtering unit filters multiple harmonics in the sine wave signal to obtain ideal compensation voltage
the impact of the access of the Dynamic Voltage Restorer (DVR) on the neighboring load is analyzed as follows:
referring to fig. 2, the common bus B supplies power to a sensitive load equipped with DVR and other (non-sensitive) loads, respectively, and the system voltage isThe impedance of the trunk line from the system to the bus B is ZLThe corresponding line impedance with DVR installed in the outlet line of the public bus and the connected sensitive load impedance are equivalent to Z1The other outgoing lines except the DVR line and the connected load are temporarily equivalent to a non-sensitive load, and the corresponding impedance is Z2。
When a voltage dip of a system is disturbed, the DVR is instantly put into the power grid to work and is connected between the system and a sensitive load in series, and the DVR can be equivalent to a controlled series voltage sourceAfter the voltage sag, the system voltage, the DVR voltage, provides the appropriate voltage level to the load. The following was studied separately using the superposition theoremAndThe effect on the load.
In FIG. 3-1, the system voltage after the voltage sagWhen acting alone, flows through a sensitive load Z1current ofThe current flowing through the insensitive load isthe current flowing through the mains of the power supply isIn FIG. 3-2, DVR alone is acting to flow through the sensitive load Z1With a compensation current ofThe compensating current flowing through the insensitive load isThe compensation current flowing through the main line of the power supply isThe direction of the positive direction is defined as the direction of the arrow in figures 3-1 and 3-2.
the insensitive load branch current obtained by using the current splitting principle according to the graph of fig. 3-2 has the following relation:
Wherein:
Line impedance ZLAnd load equivalent impedance Z1、Z2all are inductive impedance, and generally, the line impedance is much smaller than the load equivalent impedance, and the line impedance angle is much larger than the load equivalent impedance angle, so as to facilitate analysis, assume that the sensitive load impedance Z is1With adjacent non-sensitive load impedance Z2The impedance mode and the impedance angle of (2) are equal, so that the universality of an analysis result is not influenced. Thus, according to the positive direction of current in FIG. 3-2, then AndThe phasor relationship of the four is shown in FIG. 4 (where α depends on)。
according to the working principle of DVR, when the system voltage is distorted (amplitude is reduced and phase angle is changed), the voltage amplitude of sensitive load is reduced and the phase angle is reduced, the DVR is put into operation in a short time, and a compensation voltage is injected between the sensitive load and the systemAnd maintaining a normal voltage level for the sensitive load within a certain time and normally working. When the sensitive load voltage recovers, as shown in the left half of FIG. 5, atUnder the action of (2), generating a compensation currentthe current of the sensitive load branch is restored to a normal level. While flowing through the adjacent non-sensitive load according to the shunting principle and the compensated current phasor diagram of fig. 4The magnitude and phase angle of (a) are also shown in the left half of fig. 5. As shown in the right half of fig. 5, the proximity of the non-sensitive load is at the system voltageAnd compensation voltageUnder the combined action of the two electrodes, the current becomesThe current is shown as the current adjacent the load after DVR has been placed into use and its magnitude and phase angle are shown in the right half of fig. 5. Adjacent load current under independent action of system voltage after voltage sagA circle is made for the radius, which is referred to herein as the primary event current circle.
When in useIs a controlled quantity, varying its amplitude and phase will be directed to the adjacent load currentDifferent effects will also be created, which will also relate to the benefits of the DVR and the problem of energy exchange between users.
①Falls within the primary event current circle.
as shown in fig. 5, whenAndPhase angle β between them1When the adjacent load current is reduced due to the system voltageBecome intoAn additional current is generated due to the connection of DVRso that the current becomesIs obviously presentAssuming that the power factor of the adjacent load remains unchanged, the current amplitude of the voltage drops twice during the period when the voltage drops to the DVR access system, so that the active power of the DVR drops twice. Under the condition, the behavior of the DVR action for increasing the operating voltage of the sensitive load after disturbance causes the power of the adjacent load to be more seriously reduced, and the objective influence can cause the electricity utilization dispute between the sensitive user and the non-sensitive user.
②Falls outside the primary event current circle.
as shown in fig. 6, when the phase angle β is β2＞β1In time, similar to the analysis of (i), a voltage sag occurs in the system causing adjacent load currents to changeThe switching on of the DVR instead causes this current magnitude to rise,thus, the active power of the nearby load is boosted by the normal droop that occurs after the voltage sag event, with the increased active power being shared by the system and the DVR. Under such conditions, there is a potential for the DVR to transfer stored energy to a nearby load, and such a situation will result in increased DVR energy consumption, which is typically invested by sensitive load users, and further may result in a grid, sensitive load usersThe coordination problem of the investment responsibility and the resource right of the user and the adjacent user is solved.
③Falls on the primary event current circle.
As shown in fig. 7, when the phase angle β is βsetIn which is beta1＜βset＜β2Similarly to the analysis of (i), when a voltage sag occurs in the system, the current of the adjacent load changesthereafter, the DVR is switched on to generate an additional currentSo that the adjacent load current becomesFalls on the primary event current circle, i.e.It is precisely the case that the access of the DVR does not affect the current of the adjacent load. In the process of system change, the active power of the adjacent load only changes along with the change of system voltage, and has no obvious relation with the access of the DVR.
In summary, one can conclude that: for the period of system voltage drop after disturbance, if the current phase angle of the sensitive load branch of the system changes to beta, betasetthen, the compensation voltage of DVRthe access of the load does not influence the active power of the adjacent load (namely the situation (c)); if β ≠ βsetThen the compensation voltage of DVRWill cause the active power of the adjacent load to go upEither up (case ii) or down (case i) will have some effect on the adjacent load.
compared with the prior art, the invention has the following advantages and beneficial effects:
The voltage compensation method for eliminating the influence of the DVR on the adjacent load can effectively eliminate the influence of the DVR on the adjacent load without influencing the normal work of the DVR.
Drawings
Fig. 1 is a circuit diagram of a Dynamic Voltage Restorer (DVR) and a connection to a power grid.
fig. 2 is an equivalent circuit diagram of a typical low-voltage distribution network.
Fig. 3-1 is a circuit diagram of the system power supply acting alone.
Fig. 3-2 is a circuit diagram of the DVR functioning alone.
Fig. 4 is a diagram of the compensated current phasors.
Fig. 5 is a load current compensation phasor diagram (inside the circle) where the left half of the diagram is relevant for a sensitive load and the right half is relevant for an adjacent non-sensitive load.
fig. 6 is a load current compensation phasor diagram (out of circle) where the left half of the diagram is relevant for a sensitive load and the right half is relevant for an adjacent non-sensitive load.
Fig. 7 is a load current compensation phasor diagram (circle) where the left half of the diagram is relevant for a sensitive load and the right half is relevant for an adjacent non-sensitive load.
FIG. 8 is a flowchart of a voltage compensation method for eliminating the influence of DVR on neighboring loads according to the invention.
Fig. 9 is a circuit diagram of a target voltage phasor synthesis section.
fig. 10 is a circuit diagram of the PWM drive signal generating section.
fig. 11 is a circuit diagram of the compensation voltage generating portion.
Fig. 12 is a circuit diagram of a voltage compensation circuit for eliminating the influence of DVR on a neighboring load according to the present invention.
Fig. 13 is a system simulation diagram.
fig. 14 is a waveform diagram of a sensitive load voltage wave before and after DVR compensation.
fig. 15-1 is a diagram illustrating the simulation result of active power in the conventional DVR compensation method when the phase angle is changed to 30 °.
Fig. 15-2 is a diagram illustrating the simulation result of the active power of the conventional DVR compensation method when the phase angle is changed to-30 °.
fig. 16 is a schematic diagram of an active power simulation result of the DVR compensation method according to the present invention.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.
Example one
A voltage compensation method for eliminating the influence of DVR to adjacent load, comprising the steps of:
step 1: beta is asetComputing
determining beta for simplicity of illustrationsetThe principle of the magnitude is consistent with the assumption that the equivalent impedance of the sensitive load is the same as that of the non-sensitive load, so that the normal current of the sensitive load is equal to the normal current of the adjacent non-sensitive load in magnitude and the phase is the same, and the amplitude of the normal current of the sensitive load and the amplitude of the normal current of the adjacent non-sensitive load are both set to be 1; after the system voltage drops, the current amplitude of the two drops to x1The phase angle is changed to beta, and the phase shift makes beta equal to betasetsatisfy the following requirementsFalls exactly on the primary event current circle as shown in fig. 7, whenHas an amplitude of x2Then is atAndThe phasor triangle satisfies the cosine theorem:
note the bookIn thatAndIn the phasor triangle, as shown in FIG. 7, sinceAnd isAndThe formed phasor triangle is an isosceles triangle, and then the following conditions are met:
Wherein
The above equation thus becomes:
combining equations (1) and (2) to obtain the following system of equations
In the formula (1), x1is obtained by the DVR detection module and is a known quantity, x3And alpha is the system parameter and its publicFormula (II)The obtained value is also a known value. Beta is aset、x2Is the amount to be requested.
The formula (2) is simplified and known, and the formula (2) is related to the unknown quantity x2 22 order equation of unity
a·(x2 2)2+b·x2 2+c＝0
Wherein the content of the first and second substances,
It is easier to find the unknown quantity
thus, find out
Will find x2Can determine beta by substituting the value of (1)setAn angle of magnitude such thatThe phase of the current of the insensitive load is changed without changing the amplitude, namely, the active power consumed by the insensitive load is not changed.
Step 2: target voltage phasor synthesis
Refer to FIG. 7, whereinAndIn response to this, the mobile terminal is allowed to,AndCorrespond to, can proveAndphase angle difference of equal toAndphase angle difference of (2). As shown in fig. 9, obtained from the measurement moduleobtained through an FFT modulethe phase angle of (d); also obtained from the measuring moduleObtained through an FFT moduleThe amplitude of (d); at last handlePhase angle of (1) minus betasetAndIn combination with the synthesized target voltage phasor
and step 3: PWM drive signal
as shown in fig. 10, the target voltage phasors synthesized in step 2Phasor with standard voltageby comparison, obtainAnd obtaining a PWM driving signal through a hysteresis comparator.
and 4, step 4: compensating voltage
as shown in fig. 11, the PWM driving signal generated in step 3 is used to drive the inverter unit, and then the ideal compensation voltage is generated through the filtering unit.
Referring to fig. 12, a voltage compensation circuit for eliminating the influence of DVR on the adjacent load includes a measurement module, a first FFT module, a second FFT module, a first adder, a synthesized target voltage phasor module, a second adder, a hysteresis comparator, an inversion unit, and a filtering unit, where the measurement module measures the voltages at the two ends of the sensitive load before the network voltage sagAnd system voltage after voltage sagVoltage across a sensitive load when acting aloneMeasured by the first FFT moduleThe phase angle of (a) is,phase angle of (1) is subtracted by beta via the first addersetFinally, a synthetic target voltage phasor module is reached;Measured by the second FFT moduleThe amplitude of the voltage is finally reached to a synthesized target voltage phasor module; target voltage phasor synthesis module target voltage phasor synthesisWherein the target voltage phasorHas a phase angle ofPhase angle of (1) minus betasetAmplitude of isThe amplitude of (d); phasor of standard voltageSubtracting the target voltage phasor by a second adderTo obtainObtaining a PWM driving signal through a hysteresis comparator; the PWM driving signal is subjected to inversion unit to obtain a sine wave signal; the filtering unit filters multiple harmonics in the sine wave signal to obtain ideal compensation voltage
Example two
the DVR is used as a voltage compensation device for providing a stable and reasonable voltage working environment for sensitive loads, is generally used in a medium and low voltage distribution network more frequently, and the medium and low voltage distribution network is a three-phase four-wire system, and aiming at the three-phase four-wire system, the technical scheme adopts a three-single-phase full-bridge structure as a simulation model. The energy storage device is a super capacitor, the voltage level is not high due to a low-voltage distribution network, the coupling type is simpler capacitive coupling, and the filter is composed of a reactance and a coupling capacitor.
The three-phase output voltages are assumed to be independent and not mutually interfered, so that the single-phase DVR compensation circuit can be simulated, and the corresponding compensation effect of the single-phase DVR compensation circuit can be analyzed and researched. A distribution network terminal system is arranged and consists of a single-phase power supply, line equivalent impedance, two equivalent load impedances (sensitive load equivalent impedance and adjacent load equivalent impedance) and DVR. The DVR is connected with the sensitive load branch in series. A simulation system was built under Matlab2014a/Simulink, as shown in FIG. 13.
The DVR in the simulation example of the embodiment adopts a hysteresis control comparison mode, is a rapid real-time PWM tracking technology, has rapid response of compensation quantity, simple circuit, no carrier wave, almost no harmonic component with specific frequency in the voltage output of the inverter, ideal compensation voltage waveform and good compensation effect. Load parameter Z1＝Z27.26+3.5162i, parameter Z of the lineL0.264+0.738 i. The control strategy adopts an active management strategy which is provided by the technical scheme and is used for eliminating the DVR aggravating the active reduction of the adjacent load and avoiding the DVR from transferring the adjacent load.
The simulation system generates a voltage sag event in 0.06 second, the system generates voltage sag, the amplitude of the power supply voltage sag is 20%, the phase angle is ± 30 °, after 0.14 second, the voltage sag is over, and the system voltage returns to the normal level, as shown in fig. 14 (only the compensation effect of the amplitude of the power supply voltage sag being 20% and the phase angle being 30 ° is shown). Simulation results show that the DVR compensation strategy designed by the technical scheme has good capacity of compensating sensitive loads.
the following is to compare and analyze the active power influence of the traditional DVR compensation mode and the compensation mode designed by the technical scheme on the adjacent load.
As can be seen from fig. 15-1 and 15-2, with conventional backoff strategies, access to the DVR will always cause the active power of nearby non-sensitive loads to increase or decrease. As shown in fig. 15-1, when the phase change is 30 °, the access of the DVR causes the active power of the adjacent non-sensitive load to decrease, which is the adverse effect of the adjacent non-sensitive load causing the power decrease; as shown in fig. 15-2, when the phase change is-30 °, the accessing of the DVR causes the active power of the neighboring non-sensitive load to increase, which means that the neighboring non-sensitive load absorbs a certain amount of active power from the DVR, increasing the energy investment of the DVR.
When the technical scheme is adopted to design the DVR control strategy for compensation, as shown in figure 16, firstly, the system parameter is utilized to calculate betasetAngle size, then willThrough a phase shift module to becomeSo that beta is equal to betasetAnd injecting compensation voltage between the sensitive load and the system to restore the voltage and the current of the sensitive load to normal levels, wherein the injected compensation voltage does not influence the active power of the adjacent load. Fig. 16 is a diagram showing an active power simulation result of the DVR compensation method designed by the technical scheme. The compensation results of the two DVR compensation modes are shown in table 1.
TABLE 1
The same results can be obtained for other voltage drop conditions (amplitude drops of 5%, 10%, 15%, 25% and 30%, respectively, and phase angle change of 10 °), and the compensation results for two DVR compensation methods for other voltage drop conditions are shown in Table 2
TABLE 2
As can be seen from table 2, for other voltage drop conditions, the DVR adopting the novel compensation strategy of the technical scheme hardly affects the active power of the adjacent non-sensitive load, and at this time, the DVR only works for the sensitive load; the DVR adopting the conventional compensation method always causes the active power of the adjacent non-sensitive load to increase or decrease, and at this time, the DVR always has a certain influence on the adjacent non-sensitive load.
Aiming at the problems possibly brought by the influence, the technical scheme provides a novel DVR control strategy, and the partial compensation capacity of the DVR for a sensitive load phase angle is sacrificed in a mode of rotating a load reference voltage, so that the DVR does not influence the active power consumption of an adjacent load when compensating for the sensitive load.
The simulation real example proves that the DVR compensation scheme designed by the technical scheme has good compensation sensitive load capacity, can well eliminate the influence on the active power of the adjacent load, and is a compensation scheme with practical value.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims (4)

1. a voltage compensation method for eliminating the influence of a DVR to a neighboring load, comprising the steps of:
S1, setting equivalent impedance of the sensitive load and the non-sensitive load to be the same, so that the normal current of the sensitive load and the normal current of the adjacent non-sensitive load are equal in magnitude and same in phase, and the amplitude of the normal current of the sensitive load and the amplitude of the normal current of the adjacent non-sensitive load are both 1; after the system voltage is temporarily reduced, the current amplitude of the sensitive load and the current amplitude of the adjacent non-sensitive load are reduced to x1The phase angle is changed to beta, and the phase shift makes beta equal to betasetSatisfy the following requirementsFalls exactly on the one-time event current circleWherein β is1＜βset＜β2；
Wherein:
Beta isAndphase angle therebetween orAndThe phase angle therebetween;
The compensation current flows through the sensitive load when the DVR acts independently after the voltage sag;
For system voltage after voltage sagWhen acting alone, the current flows through a sensitive load;
The compensation current flows through the adjacent non-sensitive load when the DVR acts alone after the voltage sag;
For system voltage after voltage sagwhen acting alone, flowCurrent in the over-proximity of the non-sensitive load;
β1Is composed ofwhen the end point is within the primary event current circleAndThe phase angle therebetween;
β2Is composed ofWhen the end point of (1) is outside the primary event current circleAndthe phase angle therebetween;
βsetIs composed ofwhen the end point of (a) falls exactly on the primary event current circleAndThe phase angle therebetween;
At system voltage for adjacent non-sensitive loadsand compensation voltageunder the combined action of;
Before the voltage of the power grid drops temporarily, the current flows through a sensitive load;
Before the voltage sag, the current flows through the non-sensitive load;
S2, mixingPhase angle of (1) minus betasetandIn combination with the synthesized target voltage phasorWherein the target voltage phasorHas a phase angle ofPhase angle of (1) minus betasetAmplitude of isthe amplitude of (d);
wherein:
before the voltage of the power grid drops temporarily, the voltages at two ends of a sensitive load are detected;
for system voltage after voltage sagWhen acting alone, the voltage at the two ends of the sensitive load;
S3 standard voltage phasorsubtracting target voltage phasorTo obtainObtaining a PWM driving signal through a hysteresis comparator;
S4, driving the inversion unit by the PWM driving signal, generating ideal compensation voltage after the signal output by the inversion unit passes through the filtering unit
2. The method of claim 1, wherein in step S1, β is defined as a function of a voltage level of the DVR caused by a nearby loadsetThe acquisition mode is as follows:
Is provided withhas an amplitude of x2Then is atandThe phasor triangle satisfies the cosine theorem:
Note the bookIn thatAndIn the phasor triangle of (1), wherein ZLThe common bus B supplies power for a sensitive load configured with a DVR and an adjacent non-sensitive load respectively for the impedance of a main line between a system and the bus B; z2is the equivalent impedance of the adjacent non-sensitive load; x is the number of3Is ZLAnd ZL+Z2The amplitude ratio of (a); alpha isAndThe phase angle therebetween;
Due to the fact thatand is Andthe formed phasor triangle is an isosceles triangle, and then the following conditions are met:
whereinPhi isAndThe phase angle therebetween;
the above equation thus becomes:
In the formula (1), x1Is obtained by the DVR detection module and is a known quantity; x is the number of3And α is the system parameter and its formulafound, also known quantity; beta is aset、x2Is a quantity to be calculated;
The formula (2) is simplified and known, and the formula (2) is related to the unknown quantity x2 2quadratic equation of one unit
a·(x2 2)2+b·x2 2+c＝0；
wherein the content of the first and second substances,
It is easier to find the unknown quantity
Thus, find out
will find x2Can determine beta by substituting the value of (1)setAn angle of magnitude such thatfalls on the primary event current circle.
3. The method of claim 1, wherein in step S2, the DVR is configured to compensate for voltage effects on nearby loadsThe phase angle of (a) is obtained by the FFT module,The amplitude of (a) is also obtained by the FFT module; the FFT module is a fast Fourier transform module.
4. a voltage compensation circuit for eliminating the influence of a DVR on an adjacent load based on the voltage compensation method for eliminating the influence of the DVR on the adjacent load as claimed in any one of claims 1 to 3 comprises a measuring module, a first FFT module, a second FFT module, a first adder, a synthesized target voltage phasor module, a second adder, a hysteresis comparator, an inversion unit and a filtering unit, wherein the measuring module respectively measures the voltage at two ends of a sensitive load before the voltage of a power grid is temporarily droppedAnd system voltage after voltage sagVoltage across a sensitive load when acting aloneMeasured by the first FFT moduleThe phase angle of (a) is,Phase angle of (1) is subtracted by beta via the first addersetFinally, a synthetic target voltage phasor module is reached;Measured by the second FFT moduleThe amplitude of the voltage is finally reached to a synthesized target voltage phasor module; target voltage phasor synthesis module target voltage phasor synthesisWherein the target voltage phasorHas a phase angle ofPhase angle of (1) minus betasetAmplitude of isThe amplitude of (d); phasor of standard voltageSubtracting the target voltage phasor by a second adderTo obtainObtaining a PWM driving signal through a hysteresis comparator; the PWM driving signal is subjected to inversion unit to obtain a sine wave signal; the filtering unit filters out more of the sine wave signalsSub-harmonic to obtain ideal compensation voltage
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