CN117728522A - Grid-connected system, converter and voltage fault ride-through reactive power compensation method thereof - Google Patents
Grid-connected system, converter and voltage fault ride-through reactive power compensation method thereof Download PDFInfo
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Abstract
The utility model provides a grid-connected system, a converter and a voltage fault ride-through reactive power compensation method thereof, wherein the voltage fault ride-through reactive power compensation method is used for obtaining grid-connected side port voltage and inversion output current of the converter, and then calculating to obtain a PCC voltage estimated value according to the grid-connected side port voltage, the inversion output current and equivalent impedance between the grid-connected side of the converter and PCC; then, when voltage fault ride-through occurs, calculating to obtain a reactive current instruction value according to the PCC voltage estimated value; and the reactive current command value is input into a current loop to control the reactive current output by the converter, so as to realize reactive compensation. Because the reactive current command value of the input current loop is calculated according to the PCC voltage estimated value, the problem that the scene requirement for judging the reactive compensation effect according to the PCC voltage cannot be met when reactive compensation is carried out based on the port voltage of the grid-connected side of the converter in the prior art can be avoided.
Description
Technical Field
The application relates to the technical field of power electronics, in particular to a grid-connected system, a converter and a voltage fault ride-through reactive power compensation method.
Background
With the increase of the permeability of new energy represented by photovoltaic power generation, the power grid will gradually develop into a novel power system mainly composed of a power electronic converter, and the power grid side has higher requirements on the reactive power supporting capability of converter equipment such as an inverter during voltage faults.
At present, converter equipment such as an inverter and the like basically calculates and obtains reactive power instructions according to port voltages of grid-connected sides of the converter equipment according to requirements of power grid standards. However, in an actual photovoltaic power station application scenario, for some countries, the evaluation standard of the power grid guide is to refer to the voltage of the PCC (Point of Coupled Connection, public grid connection point) to determine whether the power station has injected enough reactive power; at this time, reactive compensation is performed only according to the grid-connected port voltage of the converter device, and the requirements of the application scenes cannot be met.
Disclosure of Invention
In view of this, the present application provides a grid-connected system, a converter and a voltage fault ride through reactive power compensation method thereof, so as to perform reactive power compensation according to the estimated PCC voltage, and meet the scenario requirement of determining the reactive power compensation effect according to the PCC voltage.
In order to achieve the above purpose, the present application provides the following technical solutions:
the first aspect of the application provides a voltage fault ride-through reactive power compensation method of a converter, wherein a grid-connected side of the converter is connected into a public grid-connected point PCC through at least one transformer; the voltage fault ride-through reactive compensation method comprises the following steps:
acquiring port voltage and inversion output current of a grid-connected side of the converter;
calculating to obtain a PCC voltage estimated value according to the grid-connected side port voltage, the inversion output current and the equivalent impedance between the grid-connected side of the converter and the PCC;
when voltage fault ride-through occurs, calculating to obtain a reactive current instruction value according to the PCC voltage estimated value;
and inputting the reactive current command value into a current loop to control the reactive current output by the converter.
Optionally, the source of the equivalent impedance is: pre-input, or automatic detection.
Optionally, calculating to obtain a PCC voltage estimated value according to the grid-connected side port voltage, the inversion output current, and an equivalent impedance between the grid-connected side of the converter and the PCC, including:
calculating to obtain active current and reactive current according to the grid-connected side port voltage and the inversion output current;
according to the active current, the reactive current and the equivalent impedance, calculating to obtain the partial pressure on the equivalent impedance;
and taking the difference value obtained by subtracting the partial pressure from the grid-connected side port voltage as the PCC voltage estimated value.
Optionally, calculating a reactive current command value according to the PCC voltage estimation value includes:
and taking the product of the difference value obtained by subtracting the PCC voltage estimated value from the voltage fault ride-through threshold value and a preset reactive compensation coefficient as the reactive current command value.
Optionally, the method further comprises:
obtaining a PCC voltage detection value through communication;
and in a reactive compensation steady-state stage, replacing the PCC voltage estimated value with the PCC voltage detected value, calculating the reactive current command value, and throwing the reactive current command value obtained currently into the current loop to control the reactive current output by the converter.
A second aspect of the present application provides a current transformer, comprising: the device comprises a control unit, a main circuit, a filter, a current sampling module and a voltage sampling module; wherein,
the alternating current side of the main circuit is connected with one end of the filter and is provided with the current sampling module;
the other end of the filter is used as a grid-connected side of the converter and is provided with the voltage sampling module;
the current sampling module outputs inversion output current to the control unit, and the voltage sampling module outputs grid-connected side port voltage to the control unit;
the main circuit is controlled by the control unit;
the control unit is configured to perform the voltage fault ride through reactive compensation method of the converter according to any one of the first aspect.
Optionally, the main circuit includes: a DC/AC conversion circuit;
the alternating current side of the DC/AC conversion circuit is used as the alternating current side of the main circuit;
the direct current side of the DC/AC conversion circuit is used for connecting a direct current source.
Optionally, the main circuit further includes: at least one DC/DC conversion circuit;
the DC/DC conversion circuit is connected between the DC source and a DC side of the DC/AC conversion circuit.
A third aspect of the present application provides a grid-tie system, comprising: at least one transformer, at least one current transformer as described in any of the second aspects above and the direct current source to which it is connected; wherein,
the grid-connected side of the converter is connected with the PCC through at least one transformer;
when the number of the converters is greater than 1, grid-connected sides of the converters are connected in parallel, corresponding transformers are respectively arranged between parallel connection points and the grid-connected sides of the converters, and/or corresponding transformers are arranged between the parallel connection points and the PCCs.
Optionally, corresponding transformers are respectively arranged between the parallel connection point and the grid-connected side of each converter and between the parallel connection point and the PCC.
Optionally, the method further comprises: and the system controller is in communication connection with the control units in the converters and is used for acquiring the PCC voltage detection value and sending the PCC voltage detection value to the control units.
Optionally, the system controller is: a photovoltaic power plant controller PPC or an energy management system EMS.
Optionally, the direct current source is: at least one string of photovoltaic groups, or at least one cluster of cells.
According to the voltage fault ride-through reactive power compensation method for the converter, after grid-connected side port voltage and inversion output current of the converter are obtained, a PCC voltage estimated value is obtained through calculation according to the grid-connected side port voltage, the inversion output current and equivalent impedance between the grid-connected side of the converter and PCC; then, when voltage fault ride-through occurs, calculating to obtain a reactive current instruction value according to the PCC voltage estimated value; and the reactive current command value is input into a current loop to control the reactive current output by the converter, so as to realize reactive compensation. Because the reactive current command value of the input current loop is calculated according to the PCC voltage estimated value, the problem that the scene requirement for judging the reactive compensation effect according to the PCC voltage cannot be met when reactive compensation is carried out based on the port voltage of the grid-connected side of the converter in the prior art can be avoided.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following description will briefly explain the embodiments or the drawings to be used in the description of the prior art, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic structural diagram of a grid-connected system according to an embodiment of the present application;
fig. 2 is a flowchart of a voltage fault ride-through reactive power compensation method of a converter according to an embodiment of the present application;
fig. 3 is a simplified equivalent schematic diagram between a converter and a power grid according to an embodiment of the present application;
fig. 4 is a partial flowchart of a voltage fault ride-through reactive power compensation method of a converter according to an embodiment of the present application;
fig. 5 is a schematic flow chart of a voltage fault ride-through reactive compensation method of a converter according to an embodiment of the present application.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In this application, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises an element.
In practical application, the grid-connected side of the converter needs to be connected into the PCC through at least one transformer; for large new energy power stations, as shown in fig. 1, a plurality of converters are generally included, and two-stage transformers (such as T1 and T2 shown in fig. 1) are configured for the converters in a general station to be connected to the PCC. Because the two-stage transformer and the power transmission line are arranged between the grid-connected side port of the converter and the PCC, the voltage of the grid-connected side port of the converter cannot fully reflect the voltage at the PCC during the voltage fault period; therefore, when the new energy station judges whether the reactive power injection requirement can be met or not according to the PCC voltage during the fault period, if the reactive power injection is still carried out according to the grid-connected side port voltage of the converter, the requirement is difficult to meet.
The application provides a voltage fault ride-through reactive power compensation method of a converter, which is used for carrying out reactive power compensation according to estimated PCC voltage and meeting the scene requirement of judging reactive power compensation effect according to the PCC voltage.
Referring to fig. 2, the voltage fault ride through reactive compensation method of the current transformer includes:
s101, acquiring grid-connected side port voltage and inversion output current of the converter.
As shown in fig. 1, in the converter, a corresponding current sampling module (CT as shown in the figure) is arranged between the ac side of the main circuit and the filter, and is used for collecting the inversion output current; a corresponding voltage sampling module (VT shown in the figure) is arranged between the filter and the grid-connected side of the converter and is used for collecting the port voltage of the grid-connected side; the control unit receives the inversion output current output by the current sampling module and the grid-connected port voltage output by the voltage sampling module, so that two signals are obtained.
S102, calculating to obtain a PCC voltage estimated value according to the grid-connected side port voltage, the inversion output current and the equivalent impedance between the grid-connected side of the converter and the PCC.
The equivalent impedance between the grid-connected side of the converter and the PCC specifically refers to the sum of the leakage reactance and the line impedance of the transformer between the grid-connected side of the converter and the PCC; fig. 3 shows a simplified equivalent principle between a current transformer and a power grid, where Xt is the equivalent impedance and Xg is the equivalent impedance of a transmission cable between PCC and the power grid.
In practical applications, the specific source of the equivalent impedance between the grid-connected side of the converter and the PCC may be input in advance, or may be detected automatically, which is not limited herein. When the equivalent impedance is derived from the data input in advance, the equivalent impedance can be realized by manually setting operation and maintenance personnel after carrying out unified folding calculation according to the actual parameter values of the transformer and the line to obtain corresponding values. When the equivalent impedance is automatically detected, the equivalent impedance can be obtained by controlling the voltage and the current on the grid-connected side of the converter to change through software, combining the acquired data of the voltage and the current and then calculating according to the change quantity of the voltage and the current.
S103, judging whether voltage fault crossing occurs.
The voltage fault ride through may specifically be referred to as LVRT (Low Voltage Ride Through ). The specific process of determining whether voltage fault ride through occurs may be referred to the prior art, and will not be described herein.
If voltage fault ride-through occurs, S104 is performed. If the voltage fault crossing does not occur, the normal operation is performed.
S104, calculating to obtain a reactive current instruction value according to the PCC voltage estimation value.
The process specifically can be as follows: and (3) calculating a difference value obtained by subtracting the PCC voltage estimated value Upc_1 from the voltage fault crossing threshold U0, and taking the product of the difference value and a preset reactive compensation coefficient Kf as the reactive current command value iqr.
That is, when the voltage fault crossing moment occurs in the converter, the control unit calculates the reactive current command value iqr, that is, a given value when reactive current compensation is performed, according to the calculated PCC voltage estimated value upcc_1 and according to a compensation formula iqr= (U0-upc_1) ×kf.
The voltage fault ride-through threshold U0 may refer to a voltage threshold when entering the LVRT, and a specific value of the voltage fault ride-through threshold U0 may be set according to an actual application scenario, which is not limited herein. In addition, the specific value of the preset reactive compensation coefficient Kf may be set according to the actual application scenario, which is not limited herein.
S105, inputting a current loop with a reactive current command value, and controlling reactive current output by the converter.
The specific process of inputting the reactive current command value iqr into the current loop can be referred to in the prior art, and will not be described herein again; based on the reactive current command value iqr, the converter can realize the output of reactive current through a current loop.
It should be noted that, each step may be performed in real time or periodically; further, S103 may be executed after S102, or the PCC voltage estimation value upcc_1 may be calculated after determining that the voltage fault ride through has occurred in S103; or, S102 and S103 may be executed simultaneously, depending on the specific application environment; as long as S104 is executed according to the PCC voltage estimation value upcc_1 obtained by the last calculation after determining that the voltage fault ride through occurs, the flow shown in fig. 2 is only an example, and all the above cases are within the protection scope of the present application.
According to the voltage fault ride-through reactive power compensation method for the converter, reactive power compensation can be achieved through the principle; moreover, since the reactive current command value iqr of the input current loop is calculated according to the PCC voltage estimation value upcc_1 in the embodiment, the problem that the scenario requirement for judging the reactive compensation effect according to the PCC voltage cannot be met when reactive compensation is performed based on the port voltage of the grid-connected side of the converter in the prior art can be avoided.
Based on the above embodiment, the present embodiment provides some examples for a specific implementation process of S102 in the voltage fault ride through reactive power compensation method of the current transformer, for example, the process of calculating a PCC voltage estimated value according to the port voltage on the grid-connected side, the inverted output current, and the equivalent impedance between the grid-connected side of the current transformer and the PCC in S102 may specifically include the steps shown in fig. 4:
s201, calculating to obtain active current and reactive current according to grid-connected side port voltage and inversion output current.
After the inversion output current and the grid-connected side port voltage are obtained, the control unit in the converter can obtain active current Ip and reactive current Iq by converting three-phase electric parameters of the inversion output current and the grid-connected side port voltage into an abc/dq coordinate system.
S202, calculating partial pressure on the equivalent impedance according to the active current, the reactive current and the equivalent impedance.
When the partial pressure Ux on the equivalent impedance Xt is calculated according to the active current Ip, the reactive current Iq and the equivalent impedance Xt, a specific calculation formula is as follows: ux= jXt (ip+ jIq).
S203, subtracting the partial pressure from the grid-connected side port voltage to obtain a difference value serving as a PCC voltage estimated value.
In fig. 3, ut is the grid-connected port voltage of the converter, upcc is the voltage at PCC, and the difference between the two voltages is the partial voltage Ux on the equivalent impedance Xt, that is: ut-upccj1= jXt (ip+ jIq); therefore, when estimating the voltage at the PCC by the grid-side port voltage Ut, the calculation formula upcc_1=ut-jXt (ip+ jIq) may be used to obtain the PCC voltage estimation value upcc_1.
Then, a reactive current command value iqr can be calculated according to the PCC voltage estimated value Upc_1, and the reactive current command value iqr is put into a current loop to realize the output control of the reactive current of the converter.
In addition, another embodiment of the present application provides a more preferable voltage fault ride through reactive compensation method, which further includes, based on the above embodiment: obtaining a PCC voltage detection value through communication; and in the reactive compensation steady-state stage, replacing the PCC voltage estimated value with the PCC voltage detected value, calculating a reactive current command value, and throwing the reactive current command value into a current loop to control the reactive current output by the converter.
At this time, the complete process of the voltage fault ride through reactive compensation method of the current transformer can be seen in fig. 5:
(1) The inversion output current is collected through a current sampling module (such as CT shown in figure 1), and the grid-connected side port voltage is collected through a voltage sampling module (such as VT shown in figure).
(2) After the control unit obtains the inversion output current and the grid-connected side port voltage, the active current Ip and the reactive current Iq are calculated. And the control unit also obtains the equivalent impedance Xt from the grid-connected side port of the converter to the PCC through a manual setting or automatic detection mode. Then, in combination with the grid-connected side port voltage Ut of the converter, an estimated PCC voltage value mcc_1 is estimated using the configuration of upccj1=ut-jXt (ip+ jIq). Meanwhile, a system controller in communication connection with the control units in the converters transmits a PCC voltage detection value Upcc_2 obtained by collecting the voltage at the PCC to the control units through communication.
(3) And judging whether voltage fault crossing occurs.
(4) When the voltage fault crossing moment occurs to the converter, the control unit calculates reactive compensation current according to the calculated PCC voltage estimated value Upc_1 and iqr= (U0-Upc_1) Kf to obtain the reactive current command value iqr.
(5) Entering a reactive compensation steady-state stage, for example, when the reactive current output by the converter is in the fluctuation range of the reactive current instruction value iqr, replacing the PCC voltage estimation value Upc_1 with the PCC voltage detection value Upc_2, calculating the reactive current instruction value iqr according to iqr= (U0-Upc_2) Kf, and throwing the reactive current output by the converter into a current loop according to the reactive current instruction value iqr, so that the reactive current output by the converter is controlled, and accurate calculation and accurate compensation of the PCC reactive current can be realized.
It should be noted that, if the voltage at the PCC is directly collected by the system controller after the voltage fault ride-through occurs, then the collected PCC voltage detection value upcc_2 is sent to all converters in the power station by a communication manner, and then the converters successfully receive the PCC voltage detection value upcc_2 to perform reactive current compensation, the requirement of rapid reactive current support in the grid-connected guide rule is difficult to be met due to the limitation of the communication rate between the system controller and the converters in the station, for example, reactive current cannot be adjusted to the reactive current command value iqr in the reactive current request response time of 30 ms.
Therefore, the embodiment estimates the PCC voltage based on the active current Ip, the reactive current Iq, the equivalent impedance Xt of the transformer and the transmission line, and the port voltage Ut at the grid-connected side of the converter, and performs reactive current compensation by using the estimated PCC voltage estimation value upcc_1 in the dynamic process of reactive compensation, thereby meeting the fast reactive power demand; and after the reactive compensation enters a steady state stage, the system controller is utilized to acquire the PCC voltage to obtain a PCC voltage detection value UpcC_2, so as to correct the reactive current compensation of the PCC and ensure the accurate compensation after the steady state.
Another embodiment of the present application further provides a current transformer, as shown in fig. 1, which specifically includes: a control unit 103, a main circuit 101, a filter 102, a current sampling module (CT as shown in the figure) and a voltage sampling module (VT as shown in the figure); wherein:
an alternating current side of the main circuit 101 is connected with one end of the filter 102 and is provided with a current sampling module; the other end of the filter 102 is provided with a voltage sampling module as the grid-connected side of the converter 10. The other side of the main circuit 101 is used to connect to a power source, such as a photovoltaic string or a battery cluster, for example.
The current sampling module outputs an inversion output current to the control unit 103, and the voltage sampling module outputs a grid-connected side port voltage to the control unit 103.
In practical applications, the main circuit 101 may include only: a DC/AC conversion circuit; the AC side of the DC/AC conversion circuit is the AC side of the main circuit 101; the direct current side of the DC/AC conversion circuit is used for connecting a direct current source.
Alternatively, the main circuit 101 may further include: at least one DC/DC conversion circuit; the DC/DC conversion circuit is connected between the DC source and the DC side of the DC/AC conversion circuit.
The dc source may be at least one photovoltaic string, or at least one battery cluster, which is not limited herein, and may be within the scope of the present application, depending on the specific application environment.
The main circuit 101 is controlled by a control unit 103; the control principle of the control unit 103 for the main circuit 101 may refer to the prior art, for example, performing abc/dq coordinate system conversion and power calculation on the collected inversion output current and the output grid-connected side port voltage, then performing double-loop control on the voltage loop and the current loop to obtain a modulation voltage, and then generating a control signal for the main circuit 101 by the dq/abc coordinate system conversion and the PWM module. Unlike the prior art, the control unit 103 is further configured to perform the voltage-fault-ride-through reactive compensation method of the converter 10 according to any of the embodiments described above. The specific process and principle of the voltage fault ride-through reactive compensation method can be seen in the above embodiments, and will not be described in detail herein.
The control unit 103 performs a voltage fault ride-through reactive compensation method, and can perform rapid dynamic reactive current compensation based on the equivalent impedance after estimating the equivalent impedance from the grid-connected side port of the converter 10 to the PCC by adopting a manual setting or automatic detection mode, thereby meeting the requirement of rapid reactive current injection of the PCC; then, in the reactive power compensation steady-state stage, the PCC voltage collected by the system controller 20 is obtained by the converter 10 based on a communication manner, and accurate compensation for reactive power current after steady-state is ensured by using the accurately collected PCC voltage.
Another embodiment of the present application further provides a grid-connected system, as shown in fig. 1, including: at least one transformer, at least one current transformer 10 as described in the above embodiments and the direct current source to which it is connected; wherein:
the dc source may be at least one photovoltaic string, or at least one battery cluster, which is not limited herein, and may be within the scope of the present application, depending on the specific application environment.
The grid-connected side of the converter 10 is connected to the PCC via at least one transformer (shown in fig. 1 as two transformers T1 and T2).
When the number of the converters 10 is greater than 1, the grid-connected sides of the converters 10 are connected in parallel, and a corresponding transformer (T1 shown in the figure) is respectively disposed between the parallel connection point and the grid-connected side of each converter 10, and/or a corresponding transformer (T2 shown in the figure) is disposed between the parallel connection point and the PCC.
In one example, as shown in fig. 1, corresponding transformers are respectively disposed between the parallel connection point and the grid-connected side of each converter 10, and between the parallel connection point and the PCC, so as to implement a corresponding boosting function.
In order to improve the compensation precision of the reactive compensation steady-state stage, the grid-connected system further comprises: the system controller 20 is communicatively connected to the control units 103 in each converter 10, and is configured to obtain the PCC voltage detection value and send the PCC voltage detection value to each control unit 103.
In practical applications, the system controller 20 may specifically be a PPC (powerplant controller, photovoltaic power station controller) or an EMS (Energy Management System ), depending on the specific application environment, and all are within the scope of the present application.
According to the grid-connected system, the equivalent impedance from the grid-connected side port of the converter 10 to the PCC can be estimated through manual setting or automatic detection, and quick dynamic reactive current compensation is performed based on the equivalent impedance, so that the requirement of PCC on quick reactive current injection is met; then, in the reactive power compensation steady-state stage, the PCC voltage collected by the system controller 20 is obtained by the converter 10 based on a communication manner, and accurate compensation for reactive power current after steady-state is ensured by using the accurately collected PCC voltage.
The same and similar parts of the embodiments in this specification are all mutually referred to, and each embodiment focuses on the differences from the other embodiments. In particular, for a system or system embodiment, since it is substantially similar to a method embodiment, the description is relatively simple, with reference to the description of the method embodiment being made in part. The systems and system embodiments described above are merely illustrative, wherein the elements illustrated as separate elements may or may not be physically separate, and the elements shown as elements may or may not be physical elements, may be located in one place, or may be distributed over a plurality of network elements. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art will understand and implement the present invention without undue burden.
Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative elements and steps are described above generally in terms of functionality in order to clearly illustrate the interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The features described in the various embodiments of the present disclosure may be interchanged or combined with one another in the description of the disclosed embodiments to enable those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (13)
1. The voltage fault ride-through reactive compensation method of the converter is characterized in that a grid-connected side of the converter is connected into a public grid-connected point PCC through at least one transformer; the voltage fault ride-through reactive compensation method comprises the following steps:
acquiring port voltage and inversion output current of a grid-connected side of the converter;
calculating to obtain a PCC voltage estimated value according to the grid-connected side port voltage, the inversion output current and the equivalent impedance between the grid-connected side of the converter and the PCC;
when voltage fault ride-through occurs, calculating to obtain a reactive current instruction value according to the PCC voltage estimated value;
and inputting the reactive current command value into a current loop to control the reactive current output by the converter.
2. The method for voltage-fault-ride-through reactive compensation of a converter according to claim 1, wherein the source of the equivalent impedance is: pre-input, or automatic detection.
3. The voltage fault ride-through reactive compensation method of the converter according to claim 1, wherein calculating a PCC voltage estimate based on the grid-side port voltage, the inverted output current, and an equivalent impedance between a grid-side of the converter and a PCC comprises:
calculating to obtain active current and reactive current according to the grid-connected side port voltage and the inversion output current;
according to the active current, the reactive current and the equivalent impedance, calculating to obtain the partial pressure on the equivalent impedance;
and taking the difference value obtained by subtracting the partial pressure from the grid-connected side port voltage as the PCC voltage estimated value.
4. The voltage fault ride-through reactive compensation method of a converter according to claim 1, wherein calculating a reactive current command value from the PCC voltage estimate comprises:
and taking the product of the difference value obtained by subtracting the PCC voltage estimated value from the voltage fault ride-through threshold value and a preset reactive compensation coefficient as the reactive current command value.
5. The voltage-fault-ride-through reactive compensation method of a converter according to any one of claims 1 to 4, further comprising:
obtaining a PCC voltage detection value through communication;
and in a reactive compensation steady-state stage, replacing the PCC voltage estimated value with the PCC voltage detected value, calculating the reactive current command value, and throwing the reactive current command value obtained currently into the current loop to control the reactive current output by the converter.
6. A current transformer, comprising: the device comprises a control unit, a main circuit, a filter, a current sampling module and a voltage sampling module; wherein,
the alternating current side of the main circuit is connected with one end of the filter and is provided with the current sampling module;
the other end of the filter is used as a grid-connected side of the converter and is provided with the voltage sampling module;
the current sampling module outputs inversion output current to the control unit, and the voltage sampling module outputs grid-connected side port voltage to the control unit;
the main circuit is controlled by the control unit;
the control unit is configured to perform a voltage-fault-ride-through reactive compensation method of a converter according to any one of claims 1 to 5.
7. The current transformer of claim 6, wherein the main circuit comprises: a DC/AC conversion circuit;
the alternating current side of the DC/AC conversion circuit is used as the alternating current side of the main circuit;
the direct current side of the DC/AC conversion circuit is used for connecting a direct current source.
8. The current transformer of claim 7, wherein the main circuit further comprises: at least one DC/DC conversion circuit;
the DC/DC conversion circuit is connected between the DC source and a DC side of the DC/AC conversion circuit.
9. A grid-tie system, comprising: at least one transformer, at least one current transformer according to any one of claims 6 to 8 and a direct current source connected thereto; wherein,
the grid-connected side of the converter is connected with the PCC through at least one transformer;
when the number of the converters is greater than 1, grid-connected sides of the converters are connected in parallel, corresponding transformers are respectively arranged between parallel connection points and the grid-connected sides of the converters, and/or corresponding transformers are arranged between the parallel connection points and the PCCs.
10. The grid-tie system according to claim 9, wherein the transformers are respectively provided between the parallel connection point and the grid-tie side of each converter and between the parallel connection point and the PCC.
11. The grid-tie system according to claim 9 or 10, further comprising: and the system controller is in communication connection with the control units in the converters and is used for acquiring the PCC voltage detection value and sending the PCC voltage detection value to the control units.
12. The grid-tie system of claim 11, wherein the system controller is: a photovoltaic power plant controller PPC or an energy management system EMS.
13. The grid-tie system according to claim 9 or 10, wherein the dc source is: at least one string of photovoltaic groups, or at least one cluster of cells.
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