CN110365025B - Series capacitance coupling type dynamic voltage restorer and control method thereof - Google Patents
Series capacitance coupling type dynamic voltage restorer and control method thereof Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
- H02J3/1807—Arrangements for adjusting, eliminating or compensating reactive power in networks using series compensators
- H02J3/1814—Arrangements for adjusting, eliminating or compensating reactive power in networks using series compensators wherein al least one reactive element is actively controlled by a bridge converter, e.g. unified power flow controllers [UPFC]
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Abstract
The invention provides a series capacitance coupling type dynamic voltage restorer and a control method thereof, wherein the restorer comprises a PWM inverter and a direct current side energy storage capacitor C, wherein the PWM inverter is composed of full-control devices dc The LC output filter, the series transformer T and the series coupling capacitor C; the series coupling capacitor C is arranged in series on the filter capacitor C f And a series transformer T; when the minimum energy compensation strategy is adopted, the minimum active output can be realized on the basis of not changing the filtering effect, and the output voltage of the inverter can be obviously reduced, so that the capacity of the inverter and the voltage level of a direct current side are effectively reduced, and the equipment cost and the system loss are reduced; in order to ensure a safe and stable operation of the device in the event of load fluctuations during the compensation, the angle adjustment method according to the invention is provided, if appropriate with regard to the load voltage U l An adjustment of the angle delta is performed.
Description
Technical Field
The invention belongs to the technical field of power electronic control, and relates to a series capacitance coupling type dynamic voltage restorer and a control method thereof.
Background
With the rapid development of micro-grids and the widespread use of a large number of precision instruments and sensitive devices, more and more power quality problems are gradually highlighted, and the voltage drop problem is one of the most important problems affecting the stable operation of power loads. A Dynamic Voltage Restorer (DVR) is a most economical and effective dynamic compensation device for solving the problem of voltage drop in an electric power system at present by virtue of its advantages of high operating efficiency, high reliability, good rapidity, and the like. When the voltage of the power grid is dropped, the output voltage of the dynamic voltage restorer is related to the whole capacity of the PWM inverter, namely the larger the compensation voltage to be output is, the larger the capacity of the PWM inverter needs to be, and further the running cost and the power loss of equipment are increased. The voltage compensation strategy of the dynamic voltage restorer mainly comprises three kinds of in-phase voltage compensation, complete voltage compensation and minimum energy compensation, in order to achieve minimization of active power injection of the dynamic voltage restorer, direct-current side energy storage equipment is fully and effectively utilized, compensation time is prolonged, and a minimum energy compensation method is paid extensive attention. Although the active demand can be reduced to a certain extent, the compensation time is prolonged, and the compensation capability is increased when the minimum energy compensation strategy is adopted by the dynamic voltage restorer, the problem of the amplitude increase of the output voltage of the dynamic voltage restorer is inevitably brought. How to reduce the output voltage grade while reducing the active power requirement in the compensation process so as to effectively reduce the whole capacity of the device is worth deeply researching and discussing.
Disclosure of Invention
In order to achieve the above object, the present invention provides a series capacitance coupling type dynamic voltage restorer, which solves the problem of the prior art that the amplitude of the output voltage of the dynamic voltage restorer is increased when the dynamic voltage restorer adopts a minimum energy compensation strategy.
Another object of the present invention is to provide a control method of the above dynamic voltage restorer.
In order to solve the technical problem, the invention adopts the technical scheme that the series capacitor coupling type dynamic voltage restorer is characterized in that a PWM inverter and a direct current side energy storage capacitor C are formed by full-control devices dc LC output filter, series transformer T and series coupling capacitor C.
Further, the LC output filter is composed of a filter inductor L f And a filter capacitor C f And (4) forming.
Further, the PWM inverter is composed of 4 full-control type devices IGBT and 4 free-wheeling diodes.
Further, the dc side energy storage capacitor C dc The LC output filter is arranged on the DC side of the PWM inverter, and the LC output filter is arranged on the AC side of the PWM inverter; DC side energy storage capacitor C dc The positive electrode is connected with the collector electrode of the 1 st IGBT, and the direct current side energy storage capacitor C dc The negative pole is connected with the emitter of the 3 rd IGBT, one end of the LC output filter is connected with the emitter of the 1 st IGBT, and the other end of the LC output filter is connected with the collector of the 4 th IGBT.
Furthermore, the series coupling capacitor C is arranged in series on the filter capacitor C f And a series transformer T.
Further, the series transformer T connects the series capacitive coupling type dynamic voltage restorer to a power grid, and a bypass switch K is connected in parallel to the primary side of the series transformer T.
The other technical scheme of the invention is that the control method of the series capacitance coupling type dynamic voltage restorer comprises the following steps: detecting the network voltage U s If d is sag ≥0.9，d sag If the voltage drop factor is a power grid voltage drop factor, voltage compensation is not needed, the bypass switch K is closed, and the series capacitor coupling type dynamic voltage restorer works in a standby state; if d is sag If the voltage of the power grid is less than 0.9, voltage compensation is needed when the voltage of the power grid drops, the bypass switch K is switched off, the series capacitance coupling type dynamic voltage restorer works normally, and corresponding compensation voltage is injected into the power grid to maintain the stability of the voltage amplitude of the load side.
Further, the compensation voltage is determined according to the following method:
s1, after the voltage of the power grid is detected to drop, the command voltage calculation link of the series capacitance coupling type dynamic voltage restorer can calculate a command value U of compensation voltage which needs to be injected into the power grid by the series capacitance coupling type dynamic voltage restorer * dvr ；
S2, performing voltage and current double closed-loop control on the compensation voltage output by the series capacitor coupling type dynamic voltage restorer: compensating the reference voltage command value U * dvr Injection compensation voltage U coupled with series capacitor type dynamic voltage restorer dvr Making a difference, and sending the difference to a voltage outer ring PI controller to obtain a proportional-integral parameter K of the voltage outer ring PI controller P1 And K I1 Operated to obtain an adjustment signal I r Then, the adjusting signal I obtained by the voltage outer loop PI controller is used r Reference instruction signal and filter inductor L used as current inner loop PI controller f Filter inductance current I Lf Making difference, inputting the obtained difference value into a current inner loop PI controller, and obtaining a proportional integral parameter K of the current inner loop PI controller P2 And K I2 Calculating to obtain a corresponding adjusting signal;
and S3, sending the obtained regulating signal to a driving circuit to generate a corresponding driving signal to control a PWM inverter, so that the series capacitance coupling type dynamic voltage restorer generates the required compensation voltage.
Furthermore, during the period of outputting the compensation voltage by the series capacitance coupling type dynamic voltage restorer, in order to ensure that the output voltage of the PWM inverter does not exceed the output limit voltage value U when the load fluctuates inv-max Detection of the output voltage U of the PWM inverter inv Size of (2), if U inv ≤U inv-max If the output voltage of the PWM inverter does not exceed the output limit voltage value, the series capacitance coupling type dynamic voltage restorer can safely and stably operate without angle adjustment to obtain the command value U of the compensation voltage * dvr ＝U dvr (ii) a If U is inv ＞U inv-max Indicating that the output voltage of the PWM inverter exceeds the output limit voltage value thereof, for ensuring the deviceSafe and stable operation, and need to be controlled by load voltage U l Adjusting the angle delta to change the compensation voltage and phase, and adjusting and calculating to obtain the command value U of the compensation voltage * dvr ＝U dvr′ ，U dvr′ The injection compensation voltage of the series capacitance coupling type dynamic voltage restorer is adjusted, so that the output voltage of the PWM inverter finally meets the limit voltage requirement.
Further, the method for changing the magnitude and the phase of the compensation voltage by adjusting the magnitude of the angle δ is as follows:
here, the PWM inverter outputs a voltage U inv Satisfies the conditions
U inv ≤M·U dc (1)
Therefore, the limit voltage value U which can be output by the PWM inverter can be obtained inv-max ＝M·U dc ；
According to
And
the relationship between δ can be derived from the following formula
U LCC ＝(1/ωC-ωL f )·I l (2)
After the adjustment angle delta is determined, the injection compensation voltage of the adjusted dynamic voltage restorer can be obtained to be
Further, can obtain
And
is an angle of
It can be obtained that the adjusted compensation voltage has a phase of
Wherein C in the formula (3) is a capacitance value, M is a modulation ratio, and U is dc Is the DC side voltage of the PWM inverter,
For the grid voltage during a fault,
Is a load voltage,
For the regulated load voltage, I l Is the current on the series coupling capacitor C, omega =2 pi f, f is the fundamental frequency equal to 50Hz, omega is the angular velocity,
For coupling the voltage on the capacitor C in series
And a filter inductor L f Upper voltage of
Sum (i.e.
Representative vectors with dots on the head, here
And
all represent vectors), U LCC Representing a vector
Of amplitude a is
And
the vector included angle alpha' is the phase of the adjusted compensation voltage,
Is power factor angle, gamma is
And
the included angle of,
Injecting compensation voltage for the dynamic voltage restorer,
And injecting compensation voltage for the adjusted dynamic voltage restorer.
The beneficial effects of the invention are: under the environment of the same system parameters, due to the existence of the series coupling capacitor C, the voltage on the series coupling capacitor C is reasonably designed
Can reduce the output voltage of the PWM inverter
And because the output voltage of the PWM inverter is reduced, the capacity of the PWM inverter and the voltage level of a direct current side can be reduced after the coupling capacitor C is connected in series, and the equipment cost and the system loss are reduced. Under the same working condition, when the minimum energy compensation strategy is adopted, the fundamental wave effective value of the output voltage of the PWM inverter of the series capacitance coupling type dynamic voltage restorer is much lower than that of the traditional dynamic voltage restorer, and is also lower than that of the traditional dynamic voltage restorer adopting the in-phase compensation strategy. By adjusting the angle, the magnitude and the phase of the compensation voltage can be changed, so that the output voltage of the PWM inverter finally meets the requirement of the limit voltage of the PWM inverter.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a topological structure diagram of a series capacitance coupling type dynamic voltage restorer;
fig. 2 is a system equivalent circuit diagram of a series capacitance coupling type dynamic voltage restorer;
fig. 3a is a working vector diagram of the series capacitance coupling type dynamic voltage restorer adopting a pure reactive compensation strategy;
fig. 3b is a working vector diagram of the series capacitance coupling type dynamic voltage restorer adopting a critical compensation strategy;
fig. 3c is a diagram of a working vector when the series capacitance coupling type dynamic voltage restorer adopts a minimum active power compensation strategy;
FIG. 4 is a comparison graph of PWM inverter output voltages under different operating conditions;
FIG. 5a is a diagram of the operation vector of the series capacitor coupling type dynamic voltage restorer when the load current is reduced;
FIG. 5b is a diagram of the working vector of the series capacitive coupling type dynamic voltage restorer when the power factor angle changes;
fig. 6 is a system control block diagram of the series capacitive coupling type dynamic voltage restorer.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
Example 1
A series capacitor coupling type dynamic voltage restorer comprises a PWM inverter composed of full-control devices, and a DC side energy storage capacitor C dc LC output filter, series transformer T and series coupling capacitor C.
The LC output filter is composed of a filter inductor L f And a filter capacitor C f And (4) forming. The PWM inverter is composed of 4 full-control type devices IGBT and 4 freewheeling diodes. The DC side energy storage capacitor C dc The LC output filter is arranged on the DC side of the PWM inverter, and the LC output filter is arranged on the AC side of the PWM inverter; DC side energy storage capacitor C dc The positive electrode of the positive electrode is connected with the collector electrode of the 1 st IGBT, and the direct current side energy storage capacitor C dc The negative pole is connected with the emitter of the 3 rd IGBT, one end of the LC output filter is connected with the emitter of the 1 st IGBT, and the other end of the LC output filter is connected with the collector of the 4 th IGBT. The series coupling capacitor C is arranged in series on the filter capacitor C f And a series transformer T. The series transformer T connects the series capacitance coupling type dynamic voltage restorer with a power grid, and a bypass switch K is connected with the primary side of the series transformer T in parallel.
A control method of a series capacitance coupling type dynamic voltage restorer is controlled according to the following method: detecting the network voltage U s If d is sag ≥0.9，d sag The power grid voltage drop factor is not needed to be compensated, the bypass switch K is closed, and the series capacitance coupling type dynamic voltage restorer is connected in seriesWorking in a standby state; if d is sag If the voltage of the power grid drops, voltage compensation is needed, the bypass switch K is disconnected, the series capacitor coupling type dynamic voltage restorer works normally, and corresponding compensation voltage is injected into the power grid to maintain the stability of the voltage amplitude of the load side.
The compensation voltage is determined as follows:
s1, after the voltage of the power grid is detected to drop, the command voltage calculation link of the series capacitance coupling type dynamic voltage restorer can calculate a command value U of compensation voltage which needs to be injected into the power grid by the series capacitance coupling type dynamic voltage restorer * dvr ；
S2, performing voltage and current double closed-loop control on the compensation voltage output by the series capacitor coupling type dynamic voltage restorer: compensating the reference voltage command value U * dvr Injection compensation voltage U coupled with series capacitor type dynamic voltage restorer dvr Making a difference, sending the difference to a voltage outer loop PI controller, and comparing the difference with an outer loop proportional integral parameter K P1 And K I1 Operating to obtain an adjustment signal I r Then, the adjusting signal I obtained by the voltage outer loop PI controller is used r Reference instruction signal and filter inductor L used as current inner loop PI controller f Filter inductance current I Lf Making difference, inputting the obtained difference value into a current inner loop PI controller, and obtaining a proportional integral parameter K of the current inner loop PI controller P2 And K I2 Calculating to obtain a corresponding adjusting signal; the voltage outer loop controller and the current inner loop controller are not part of an actual circuit structure, but are a special term for introducing a control strategy, belong to the prior art and are not described in detail;
and S3, sending the obtained regulating signal to a driving circuit to generate a corresponding driving signal to control the PWM inverter, so that the series capacitance coupling type dynamic voltage restorer generates required compensation voltage.
During the period of outputting compensation voltage by the series capacitance coupling type dynamic voltage restorer, in order to ensure that the output voltage of the PWM inverter does not exceed the output limit voltage value U when the load fluctuates inv-max Detection of the output voltage U of the PWM inverter inv Size of (1), if U inv ≤U inv-max If the output voltage of the PWM inverter does not exceed the output limit voltage value, the series capacitance coupling type dynamic voltage restorer can safely and stably operate without angle adjustment to obtain the command value U of the compensation voltage * dvr ＝U dvr ，U dvr Injecting compensation voltage for the series capacitance coupling type dynamic voltage restorer; if U is present inv ＞U inv-max If the output voltage of the PWM inverter exceeds the output limit voltage value, the load voltage U is required to ensure the safe and stable operation of the device l Adjusting the angle delta to change the magnitude and phase of the compensation voltage, and adjusting and calculating to obtain the command value U of the compensation voltage * dvr ＝U dvr′ ，U dvr′ The injection compensation voltage of the series capacitance coupling type dynamic voltage restorer is adjusted, so that the output voltage of the PWM inverter finally meets the limit voltage requirement.
The method for changing the magnitude and the phase of the compensation voltage by adjusting the magnitude of the angle delta comprises the following steps:
here, the PWM inverter outputs a voltage U inv Satisfy the condition
U inv ≤M·U dc (1)
Therefore, the limit voltage value U which can be output by the PWM inverter can be obtained inv-max ＝M·U dc ；
According to
And
the relationship between δ can be derived from the following formula
U LCC ＝(1/ωC-ωL f )·I l (2)
After the adjustment angle delta is determined, the injection compensation voltage of the adjusted dynamic voltage restorer can be obtained to be
Further, can obtain
And
is an angle of
It can be derived that the adjusted compensation voltage has a phase of
As can be seen from equations (5) and (6), the magnitude and phase of the compensation voltage can be changed by adjusting the magnitude of the angle δ, so that the output voltage of the PWM inverter finally satisfies the limit voltage requirement.
Fig. 1 shows a series capacitive coupling dynamic voltage restorer according to the present invention. The structure comprises a PWM inverter composed of full-control devices and a DC side energy storage capacitor C dc LC output filter, series transformer T and series coupling capacitor C. DC side energy storage capacitor C dc Providing energy support for compensation voltage of the series capacitance coupling type dynamic voltage restorer; the LC output filter filters the output of the PWM inverter, so that the harmonic content of the compensation voltage meets the requirement; the series coupling capacitor C is arranged in series on the filter capacitor C f And a series transformer T capable of supplying a voltage U increased by a hysteresis load current by 90 DEG C So as to connect the capacitors in seriesWhen the coupling type dynamic voltage restorer adopts a minimum energy compensation strategy, the coupling type dynamic voltage restorer can remarkably reduce the output voltage of the PWM inverter, so that the capacity and the direct-current side voltage level of the PWM inverter are effectively reduced, and part of capacitive reactive power can be borne, the coupling type dynamic voltage restorer is essentially different from the structure in the patent CN201410499807.4, and the function of remarkably reducing the output voltage of the PWM inverter when the minimum energy compensation strategy is adopted cannot be realized; and the series transformer T couples the compensation voltage output by the series capacitance coupling type dynamic voltage restorer into a power grid.
Wherein: the LC output filter is composed of a filter inductor L f And a filter capacitor C f The design of the series coupling capacitor C does not influence the filtering effect of the series coupling capacitor C, and the attenuation capacity of high-frequency resonance can be increased, so that the output of the PWM inverter can be better filtered, and the quality of the electric energy of the compensation voltage output by the series coupling capacitor type dynamic voltage restorer meets the requirement; the PWM inverter consists of 4 full-control type devices IGBT and 4 freewheeling diodes, inverts the direct-current side voltage into the required alternating-current voltage, and can select smaller capacity and direct-current side voltage when the series capacitance coupling type dynamic voltage restorer adopts a minimum energy compensation strategy due to the addition of the series coupling capacitance C; DC side energy storage capacitor C dc The PWM inverter is arranged on the direct current side of the PWM inverter, provides energy support for compensating voltage of the series capacitance coupling type dynamic voltage restorer and supports normal work of the series capacitance coupling type dynamic voltage restorer; the series transformer T connects the series capacitance coupling type dynamic voltage restorer with a power grid, and couples the compensation voltage output by the series capacitance coupling type dynamic voltage restorer into the power grid.
In FIG. 2, U L For filtering the voltage across the inductor, U C Is the voltage over a series coupling capacitor C, Z l Is the load equivalent impedance.
In fig. 3, according to the difference of the grid voltage drop depth, the series capacitance coupling type dynamic voltage restorer works in three different modes, including: pure reactive compensation figure 3a, critical compensation figure 3b and minimum active compensation figure 3c.
Wherein the content of the first and second substances,
in order to be the voltage of the load,
in order to be the load current,
for the purpose of the grid voltage during a fault,
a compensation voltage is injected for the dynamic voltage restorer,
is the voltage over the series-coupled capacitor C,
is a filter inductance L f The voltage of the voltage across the capacitor is,
a PWM inverter output voltage of a series capacitive coupling type dynamic voltage restorer,
is a power factor angle, alpha is
And
angle theta is
And
beta is
And
the included angle of (a).
Rated network voltage is set as U sref The grid voltage drop factor is:
d sag ＝U s /U sref (1-1)
the grid voltage during the fault is then:
U s ＝d sag U sref (1-2)
the magnitude and the angle of the injection compensation voltage of the series capacitance coupling type dynamic voltage restorer are respectively as follows:
wherein the content of the first and second substances,
thus, the output voltage of the PWM inverter of the series capacitance coupling type dynamic voltage restorer is
Where ω =2 π f, f is the fundamental frequency equal to 50Hz, and ω is the angular velocity.
As can be seen from the formulas (1-5), under the environment of the same system parameters, due to the existence of the series coupling capacitor C, through reasonable design
Can reduce the output voltage of the PWM inverter
And because the output voltage of the PWM inverter is reduced, the capacity of the PWM inverter and the voltage level of a direct current side can be reduced after the PWM inverter is connected with the coupling capacitor C in series, and meanwhile, the equipment cost and the system loss are reduced.
In fig. 4, a broken line with a triangle indicates the PWM inverter output voltage when the conventional dynamic voltage restorer adopts the minimum energy compensation strategy, a broken line with a dot indicates the PWM inverter output voltage when the conventional dynamic voltage restorer adopts the in-phase compensation strategy, and a broken line with a square indicates the PWM inverter output voltage when the series capacitive coupling type dynamic voltage restorer adopts the minimum energy compensation strategy. The fundamental wave effective values of the output voltage of the PWM inverter under the three conditions are respectively given when the amplitude of the power grid voltage drops by 10% to 50%. It can be seen by comparison that under the same working condition, when the minimum energy compensation strategy is adopted, the fundamental wave effective value of the output voltage of the PWM inverter of the series capacitance coupling type dynamic voltage restorer is much lower than that of the traditional dynamic voltage restorer, and is also lower than that of the traditional dynamic voltage restorer when the in-phase compensation strategy is adopted, so that the superiority of the series capacitance coupling type dynamic voltage restorer provided by the invention is directly verified.
In fig. 5a and 5b, delta is the adjustment angle,
for coupling voltages on capacitors C in series
And a filter inductor L f Upper voltage of
The sum of the total weight of the components,
in order to achieve the adjusted load voltage,
injecting a compensation voltage of alpha 'into the regulated dynamic voltage restorer'For the adjusted compensation voltage phase, gamma is
And
is/are as follows the included angle is formed by the angle of inclination,
is the limit value of the PWM inverter output voltage.
The load fluctuation may cause the output voltage of the PWM inverter to exceed its output limit voltage value, and at this time, corresponding angle adjustment is required to ensure that the output voltage of the PWM inverter is within its limit range, and the series capacitance coupling type dynamic voltage restorer is enabled to work in a minimum energy compensation state within the output capability range.
Here, the PWM inverter outputs a voltage U inv Satisfies the conditions
U inv ≤M·U dc (1)
In the formula (1), M is a modulation ratio, U dc Is the dc side voltage of the PWM inverter. Therefore, the limit voltage value U which can be output by the PWM inverter can be obtained inv-ma x＝M·U dc 。
According to
And
the relationship between δ can be derived from the following formula
U LCC ＝(1/ωC-ωL f )·I l (2)
After the adjustment angle δ is determined, an adjusted compensation voltage of magnitude
Further, can obtain
And
is an angle of
It can be derived that the adjusted compensation voltage has a phase of
As can be seen from equations (5) and (6), by adjusting the magnitude of the angle δ, the magnitude and phase of the compensation voltage can be changed, so that the PWM inverter output voltage finally satisfies the limit voltage requirement.
In FIG. 6, I l Is the current on the series coupling capacitor C; k PWM For equivalent gain of the PWM inverter, K is taken here for simplicity of analysis PWM 1,s represents a differentiation operation in the frequency domain, and 1/s represents an integration operation in the frequency domain.
The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.
Claims (5)
1. The series capacitance coupling type dynamic voltage restorer is characterized in that a PWM inverter and a direct current side energy storage capacitor C are formed by full-control devices dc The LC output filter, the series transformer T and the series coupling capacitor C;
the LC output filter is composed of a filter circuitFeeling L f And a filter capacitor C f Forming;
the PWM inverter consists of 4 full-control type devices IGBT and 4 freewheeling diodes;
the DC side energy storage capacitor C dc The LC output filter is arranged on the DC side of the PWM inverter, and the LC output filter is arranged on the AC side of the PWM inverter; DC side energy storage capacitor C dc The positive electrode of the positive electrode is connected with the collector electrode of the 1 st IGBT, and the direct current side energy storage capacitor C dc The negative electrode of the LC output filter is connected with the emitter of the 3 rd IGBT, one end of the LC output filter is connected with the emitter of the 1 st IGBT, and the other end of the LC output filter is connected with the collector of the 4 th IGBT;
the series coupling capacitor C is arranged in series on the filter capacitor C f And a series transformer T;
the series transformer T connects the series capacitance coupling type dynamic voltage restorer with a power grid, and a bypass switch K is connected with the primary side of the series transformer T in parallel.
2. A control method of a series capacitance coupling type dynamic voltage restorer, which is applied to the series capacitance coupling type dynamic voltage restorer as claimed in claim 1, and is characterized in that a power grid voltage U is detected s If d is sag ≥0.9，d sag If the voltage drop factor is a power grid voltage drop factor, voltage compensation is not needed, the bypass switch K is closed, and the series capacitance coupling type dynamic voltage restorer works in a standby state; if d is sag If the voltage of the power grid drops, voltage compensation is needed, the bypass switch K is disconnected, the series capacitor coupling type dynamic voltage restorer works normally, and corresponding compensation voltage is injected into the power grid to maintain the stability of the voltage amplitude of the load side.
3. The method according to claim 2, wherein the compensation voltage is determined by the following method:
step S1, after the voltage of the power grid is detected to drop, the command voltage calculation link of the series capacitance coupling type dynamic voltage restorer can calculateInstruction value U of compensation voltage required to be injected into power grid by series capacitance coupling type dynamic voltage restorer * dvr ；
S2, performing voltage and current double closed-loop control on the compensation voltage output by the series capacitor coupling type dynamic voltage restorer: compensating the reference voltage command value U * dvr Injection compensation voltage U coupled with series capacitor type dynamic voltage restorer dvr Making a difference, sending the difference to a voltage outer loop PI controller, and comparing the difference with an outer loop proportional integral parameter K P1 And K I1 Operating to obtain an adjustment signal I r Then, the adjusting signal I obtained by the voltage outer loop PI controller is used r Reference instruction signal and filter inductor L used as current inner loop PI controller f Filter inductance current I Lf Making difference, inputting the obtained difference value into a current inner loop PI controller, and obtaining a proportional integral parameter K of the current inner loop PI controller P2 And K I2 Calculating to obtain a corresponding adjusting signal;
and S3, sending the obtained regulating signal to a driving circuit to generate a corresponding driving signal to control the PWM inverter, so that the series capacitance coupling type dynamic voltage restorer generates required compensation voltage.
4. The method according to claim 3, wherein the PWM inverter output voltage does not exceed the output limit voltage value UpVQ during the period of outputting the compensation voltage during the load fluctuation inv-max Detection of the output voltage U of the PWM inverter inv Size of (2), if U inv ≤U inv-max If the output voltage of the PWM inverter does not exceed the output limit voltage value, the series capacitance coupling type dynamic voltage restorer can safely and stably operate without angle adjustment to obtain the command value U of the compensation voltage * dvr ＝U dvr (ii) a If U is inv ＞U inv-max If the output voltage of the PWM inverter exceeds the output limit voltage value, the load voltage U is required to ensure the safe and stable operation of the device l To carry outAdjusting the angle delta to change the magnitude and phase of the compensation voltage, and adjusting and calculating to obtain the command value U of the compensation voltage * dvr ＝U dvr' ，U dvr' The injection compensation voltage of the series capacitance coupling type dynamic voltage restorer is adjusted, so that the output voltage of the PWM inverter finally meets the limit voltage requirement.
5. The method for controlling a dynamic voltage restorer of the series capacitive coupling type according to claim 4, wherein the compensation voltage and the phase can be changed by adjusting the magnitude of the angle δ by:
here, the PWM inverter outputs a voltage U inv Satisfies the conditions
U inv ≤M·U dc (1)
Therefore, the limit voltage value U which can be output by the PWM inverter can be obtained inv-max ＝M·U dc ；
According to
And
the relationship between δ can be derived from the following formula
U LCC ＝(1/ωC-ωL f )·I l (2)
After the adjustment angle delta is determined, the injection compensation voltage of the adjusted dynamic voltage restorer can be obtained to be
Further, can obtain
And
is an angle of
It can be obtained that the adjusted compensation voltage has a phase of
Wherein M is a modulation ratio, U dc Is the DC side voltage of the PWM inverter,
For the grid voltage during a fault,
Is a load voltage,
For the regulated load voltage, U s Is composed of
Magnitude of amplitude, U l ' is a
Magnitude of amplitude of (I) l Is the current on the series coupling capacitor C, omega =2 pi f, f is the fundamental frequency equal to 50Hz, omega is the angular velocity,
For coupling voltages on capacitors C in series
And a filter inductor L f Upper voltage of
Sum, U LCC Representing a vector
Of amplitude a is
And
the included angle of the vector alpha' is the phase of the adjusted compensation voltage,
Is power factor angle, gamma is
And
the included angle of,
Injecting compensation voltage for dynamic voltage restorer,
And injecting a compensation voltage for the adjusted dynamic voltage restorer.
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| CN111884235B (en) * | 2020-08-05 | 2021-12-07 | 珠海万力达电气自动化有限公司 | Control method of dynamic voltage restorer |
| CN113315133A (en) * | 2021-05-31 | 2021-08-27 | 广东电网有限责任公司广州供电局 | Control method and device of voltage sag treatment device and electronic equipment |
| CN113872218A (en) * | 2021-10-10 | 2021-12-31 | 费籁电气(上海)有限公司 | Method for analyzing running characteristic of series capacitance coupling type dynamic voltage restorer |
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