CN111130372B - Three-level grid-connected inverter bus midpoint potential adjusting method and terminal equipment - Google Patents
Three-level grid-connected inverter bus midpoint potential adjusting method and terminal equipment Download PDFInfo
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- CN111130372B CN111130372B CN202010003024.8A CN202010003024A CN111130372B CN 111130372 B CN111130372 B CN 111130372B CN 202010003024 A CN202010003024 A CN 202010003024A CN 111130372 B CN111130372 B CN 111130372B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
- H02M7/487—Neutral point clamped inverters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/0048—Circuits or arrangements for reducing losses
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
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Abstract
The invention is suitable for the technical field of grid-connected power generation, and provides a method for adjusting the neutral point potential of a bus of a three-level grid-connected inverter and terminal equipment, wherein the method comprises the following steps: determining a first given value corresponding to a voltage control loop through the voltage of the power grid; determining a given value of a current control loop according to the output of the voltage control loop, and determining three-phase inductive current as a feedback value of the current control loop; determining a second given value and a feedback value corresponding to the midpoint control loop; obtaining three-phase inductive current after low-pass filtering; obtaining a first three-phase modulation wave through a current control loop; carrying out proportional regulation and integral regulation on the second given value and the feedback value of the midpoint control loop through the midpoint control loop to obtain an output quantity; and regulating the voltage of the middle point of the bus of the three-level three-phase grid-connected inverter through the three-phase inductive current after low-pass filtering, the first three-phase modulation wave and the output quantity. The invention can reduce the cost and the self loss of the three-level grid-connected inverter and improve the generating capacity of the three-level grid-connected inverter.
Description
Technical Field
The invention belongs to the technical field of grid-connected power generation, and particularly relates to a method for adjusting a neutral point potential of a bus of a three-level grid-connected inverter and terminal equipment.
Background
In recent years, renewable energy sources such as wind energy and solar energy have been widely used to cope with problems such as energy crisis and environmental pollution. The grid-connected inverter is becoming a hot point for researchers at home and abroad as an interface between a distributed renewable power generation unit and a power grid.
The traditional two-level inverter has low efficiency, high output current harmonic and easy generation of leakage current, and is gradually replaced by a three-level inverter. In the grid-connected process of the three-level grid-connected inverter, the following working condition exists: due to the fact that the middle points of the buses are unbalanced for some special reasons, large deviation occurs between the positive buses and the negative buses, and the inverter is protected in a power failure mode. If the grid connection is continuously tried under the condition that the pressure difference between the positive bus and the negative bus is large, the following problems are caused: first, power device stress increases; secondly, the harmonic distortion rate of the output current is increased, so that the quality of the output electric energy of the grid-connected inverter is influenced; third, the possible presence of half bus overmodulation will exacerbate bus midpoint imbalance.
When the above problems occur, the prior art processes are as follows: when the positive and negative bus voltages generate large deviation, the inverter stops grid connection, and after the positive and negative bus capacitors eliminate the positive and negative bus voltage difference through self-discharging and other modes, grid connection is carried out again. However, there are many disadvantages to this method of adjusting the bus voltage through a hardware circuit, such as: the extra discharge circuit increases the cost of the whole machine; the loss of the inverter is increased, and the generated energy of the grid-connected inverter is reduced; the time for adjusting the midpoint voltage of the bus is difficult to control, and the like.
Therefore, the prior art lacks a method for adjusting the neutral point potential of the bus of the three-level grid-connected inverter, so as to solve various problems caused by adjusting the bus voltage through a hardware circuit in the prior art.
Disclosure of Invention
In view of this, the invention provides a method for adjusting a midpoint potential of a bus of a three-level grid-connected inverter and a terminal device, which can reduce the cost and the loss of the three-level grid-connected inverter and improve the power generation capacity of the three-level grid-connected inverter.
The first aspect of the embodiment of the invention provides a method for adjusting a neutral point potential of a bus of a three-level grid-connected inverter, which is applied to the three-level three-phase grid-connected inverter and comprises the following steps:
switching the three-level three-phase grid-connected inverter to a preset control loop, wherein the preset control loop comprises a current control loop, a voltage control loop and a middle point control loop;
determining a first given value corresponding to the voltage control loop through the voltage of the power grid;
determining a given value of the current control loop according to the output of the voltage control loop, and determining a three-phase inductive current of the three-level three-phase grid-connected inverter as a feedback value of the current control loop;
determining a second given value corresponding to the midpoint control loop and determining a feedback value of the midpoint control loop according to the positive bus voltage and the negative bus voltage of the direct-current side of the three-level three-phase grid-connected inverter;
carrying out low-pass filtering on the three-phase inductive current to obtain the three-phase inductive current after low-pass filtering;
obtaining a first three-phase modulation wave through the current control loop;
carrying out proportional regulation and integral regulation on the second given value and the feedback value of the midpoint control loop through the midpoint control loop to obtain an output quantity;
and regulating the voltage of the midpoint of the bus of the three-level three-phase grid-connected inverter through the three-phase inductive current after low-pass filtering, the first three-phase modulation wave and the output quantity.
A second aspect of the embodiments of the present invention provides a terminal, including a memory, a processor, and a computer program stored in the memory and executable on the processor, where the processor implements the steps of any one of the methods for adjusting a midpoint potential of a bus of a three-level grid-connected inverter when executing the computer program.
A third aspect of embodiments of the present invention provides a computer-readable storage medium, where a computer program is stored, and when the computer program is executed by a processor, the computer program implements the steps of any one of the three-level grid-connected inverter bus midpoint potential adjusting methods.
Compared with the prior art, the invention has the following beneficial effects: the method comprises the steps of determining a first given value corresponding to a voltage control loop through the voltage of a power grid; determining a given value of a current control loop according to the output of the voltage control loop, and determining three-phase inductive current as a feedback value of the current control loop; determining a second given value and a feedback value corresponding to the midpoint control loop; obtaining three-phase inductive current after low-pass filtering; obtaining a first three-phase modulation wave through a current control loop; carrying out proportional regulation and integral regulation on the second given value and the feedback value of the midpoint control loop through the midpoint control loop to obtain an output quantity; and regulating the voltage of the middle point of the bus of the three-level three-phase grid-connected inverter through the three-phase inductive current after low-pass filtering, the first three-phase modulation wave and the output quantity. The invention can reduce the cost and the self loss of the three-level grid-connected inverter and improve the generating capacity of the three-level grid-connected inverter.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.
Fig. 1 is a flowchart of an implementation of a method for adjusting a midpoint potential of a bus of a three-level grid-connected inverter according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a topology structure of a three-level three-phase grid-connected inverter according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a default control loop according to an embodiment of the present invention;
fig. 4 is a flowchart of implementing another method for adjusting a midpoint potential of a bus of a three-level grid-connected inverter according to an embodiment of the present invention;
fig. 5 is a flowchart illustrating an implementation of a method for adjusting a midpoint potential of a bus of a three-level grid-connected inverter according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of another exemplary default control loop provided in accordance with an embodiment of the present invention;
fig. 7 is a schematic structural diagram of a neutral point potential adjusting device in a bus of a three-level grid-connected inverter according to an embodiment of the present invention;
fig. 8 is a schematic diagram of a terminal according to an embodiment of the present invention.
Detailed Description
In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular system structures, techniques, etc. in order to provide a thorough understanding of the embodiments of the invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the following description is made by way of specific embodiments with reference to the accompanying drawings.
Referring to fig. 1, it shows an implementation flowchart of a method for adjusting a midpoint potential of a bus of a three-level grid-connected inverter according to an embodiment of the present invention, which is detailed as follows:
s101, switching the three-level three-phase grid-connected inverter to a preset control loop, wherein the preset control loop comprises a current control loop, a voltage control loop and a middle point control loop.
As shown in fig. 2, an exemplary three-level three-phase grid-connected inverter topology is shown, a direct current side of the three-level three-phase grid-connected inverter includes two sets of capacitors of a positive bus and a negative bus, the direct current is converted into an alternating current through a three-level inverter bridge, a filter adopts an LC structure, and then the filter passes through an alternating current contactor and is connected to a power grid.
It should be noted that the three-level three-phase grid-connected inverter shown in fig. 2 is only used as an exemplary grid-connected inverter to which the present invention is applicable, and the method provided by the embodiment of the present invention is not only applied to this grid-connected inverter, but also applicable to grid-connected inverters with other topology structures, and the implementation of the present invention is not limited thereto.
When the three-level three-phase grid-connected inverter is normally connected to the grid, the voltage difference of the direct-current positive and negative bus voltages is larger than a certain value due to some reasons, for example, the voltage difference is larger than a preset threshold value, and the three-level three-phase grid-connected inverter is subjected to off-grid protection. In order to ensure the reliability and stability of the detection of the neutral point imbalance of the positive bus and the negative bus, the detection return difference is increased, namely, the three-level three-phase grid-connected inverter is allowed to be connected with the grid again only when the differential pressure of the positive bus and the negative bus is reduced to be lower than a preset threshold value.
Based on this, before step S101, the method provided in the embodiment of the present invention further includes a step of performing state detection on the three-level three-phase grid-connected inverter, including:
judging whether the three-level three-phase grid-connected inverter is in a preset off-grid state; and if the three-level three-phase grid-connected inverter is in a preset off-grid state, disconnecting an alternating current contactor connected with a power grid in the three-level three-phase grid-connected inverter.
Specifically, the step of judging whether the three-level three-phase grid-connected inverter is in a preset off-grid state includes:
calculating the difference value of the positive bus voltage and the negative bus voltage of the direct-current side of the three-level three-phase grid-connected inverter; and if the difference value is larger than a preset value, judging that the three-level three-phase grid-connected inverter is in a preset off-grid state.
When the three-level three-phase grid-connected inverter is determined to be in the preset off-grid state, in order to shorten the time for the voltage difference of the positive bus and the negative bus of the three-level three-phase grid-connected inverter to fall back, reduce the cost and the loss of the three-level grid-connected inverter and improve the generating capacity of the three-level grid-connected inverter, the embodiment of the invention provides a method for adjusting the neutral point potential of the bus of the three-level grid-connected inverter, and the method is realized by relying on a preset control ring shown in fig. 3, wherein the preset control ring comprises a current control ring, a voltage control ring and a neutral point control ring.
Specifically, the symbols of the preset control loop shown in fig. 3 are described as follows:
ia/ib/ic: three-phase inductive current;
LPF: low-pass filtering;
i'a/ib'/i'c: the three-phase inductive current after low-pass filtering;
sign: calculating a sign;
ubus_p: the voltage of the positive bus to the bus midpoint N;
ubus_n: the midpoint N of the bus is opposite to the voltage of the negative bus;
uref: a voltage loop set value;
ua/ub/uc: current loop output, in the practice of the inventionIn the example, the first three-phase modulation wave is corresponded;
u'a/u'b/u'c: the modulated wave corresponds to a second three-phase modulated wave in the embodiment of the present invention.
S102, determining a first given value corresponding to the voltage control loop through the voltage of a power grid, determining a given value of the current control loop according to the output of the voltage control loop, determining a three-phase inductive current of the three-level three-phase grid-connected inverter as a feedback value of the current control loop, determining a second given value corresponding to the midpoint control loop, and determining the feedback value of the midpoint control loop according to a positive bus voltage and a negative bus voltage on the direct current side of the three-level three-phase grid-connected inverter.
Optionally, the voltage control loop is controlled before the current control loop, and optionally, the given value of the voltage control loop, that is, the first given value, is obtained by performing Clark and Park conversion on the grid voltage.
The given value of the current control loop is the output of the voltage control loop, and the three-phase inductive current of the three-level three-phase grid-connected inverter is the feedback value of the current control loop;
optionally, a given value of the midpoint control loop, that is, a second given value, is set to 0, and the feedback value is a difference value between a positive bus voltage and a negative bus voltage at the direct current side of the three-level three-phase grid-connected inverter;
further, it is also necessary to limit the given value of the voltage control loop, that is, the amplitude of the first given value, specifically, the amplitude of the first given value is limited by a preset formula, where the preset formula is:
wherein u isd_refIs said first given value, ubus_pIs the voltage u of the middle point of the positive bus to the bus in the three-level three-phase grid-connected inverterbus nAnd the voltage of the negative bus at the midpoint of the bus in the three-phase three-level grid-connected inverter is obtained.
To voltage controlThe reason why the amplitude of the given value of the loop is limited is to prevent the half bus from overmodulation, and specifically, as can be seen from the principle of Space Vector Pulse Width Modulation (SVPWM), the amplitude of the phase voltage of the undistorted sinusoidal voltage that can be output by the inverter is the amplitude of the phase voltage
Therefore, when the DC voltage is UdcIn order to ensure that the voltage of the inverter capacitor is not distorted, the given value u of the voltage control loop is setd_refThe following conditions need to be satisfied:
when the positive and negative bus voltages have larger voltage difference, the total bus voltage UdcThe condition of the above formula is satisfied, and the voltage of the inverter capacitor cannot be guaranteed not to be distorted because of ubus_pAnd ubus_nOne of them will be less than 0.5UdcIf the given value of the voltage control loop is limited according to the formula, half bus overmodulation may occur, and bus midpoint imbalance is aggravated. For this reason, should be based on ubus_pAnd ubus_nThe smaller one of the voltage control loop set value u is used for obtaining the preset off-line state process of the voltage sourced_refThe limiting values of (a) and (b) are satisfied:
and S103, carrying out low-pass filtering on the three-phase inductive current to obtain the three-phase inductive current after low-pass filtering.
Optionally, the three-phase induction current is low-pass filtered by a filter with an LC structure to obtain the three-phase induction current after low-pass filtering, and the three-phase induction current may also be low-pass filtered by a filter with another structure, which is not limited in the embodiment of the present invention.
And S104, obtaining a first three-phase modulation wave through the current control loop.
As shown in FIG. 3, ua/ub/ucNamely the first three-phase modulation wave, namely the output of the current control loop is the first three-phase modulation wave.
And S105, carrying out proportional adjustment and integral adjustment on the second given value and the feedback value of the midpoint control loop through the midpoint control loop to obtain an output quantity.
As shown in fig. 3, the midpoint control loop includes a PI (proportional integral controller) controller, which is a linear controller, and forms a control deviation according to a given value and an actual output value, and linearly combines the proportion and the integral of the deviation to form a control quantity, so as to control the controlled object.
And carrying out proportional regulation and integral regulation on the second given value and the feedback value through a midpoint control loop to obtain an output quantity.
And S106, regulating the voltage of the middle point of the bus of the three-level three-phase grid-connected inverter through the three-phase inductive current after low-pass filtering, the first three-phase modulation wave and the output quantity.
Optionally, each switching tube of the three-level three-phase grid-connected inverter is driven to act, and the voltage of the midpoint of the bus is adjusted.
And when the pressure difference between the positive bus and the negative bus is less than or equal to a preset value, stopping the off-grid state of the grid-connected inverter, and re-connecting the grid-connected inverter.
Therefore, the three-level grid-connected inverter enters the off-grid state when the voltage difference of the positive bus voltage and the negative bus voltage is larger than the preset value, and the bus midpoint voltage which is originally greatly deviated is adjusted through the preset control ring.
Optionally, as shown in fig. 4, an embodiment of the present invention provides another method for adjusting a bus midpoint potential of a three-level grid-connected inverter, where the method specifically embodies how to adjust a bus midpoint voltage of the three-level three-phase grid-connected inverter through a three-phase inductive current after low-pass filtering, a first three-phase modulation wave, and the output quantity, and includes:
and S401, multiplying the three-phase induction current after low-pass filtering by the corresponding phase in the first three-phase modulation wave to obtain a first control quantity.
S402, calculating a sign bit of the first controlled variable, and multiplying the sign bit and the output quantity to obtain a second controlled variable.
And S403, superposing the first three-phase modulation wave and the second control quantity to obtain a second three-phase modulation wave.
S404, performing square wave pulse width modulation on the second three-phase modulation wave to obtain a duty ratio.
S405, regulating the voltage of the midpoint of the bus of the three-level three-phase grid-connected inverter through the duty ratio, so that the difference value between the positive bus voltage and the negative bus voltage of the direct-current side of the three-level three-phase grid-connected inverter is smaller than or equal to a preset value.
Therefore, the bus midpoint voltage of the three-level three-phase grid-connected inverter which is greatly deviated originally is adjusted through the preset control loop, compared with a mode of adjusting by adopting a hardware circuit, the cost and the loss of the three-level grid-connected inverter are reduced, and the power generation amount of the three-level grid-connected inverter is improved.
Fig. 5 shows a flowchart of an implementation of a method for adjusting a midpoint potential of a bus of a three-level grid-connected inverter, which is applied to a process of processing a three-phase inductor current in a current control loop, and the method includes:
s501, converting the three-phase inductive current to a DQ axis coordinate system through Clark conversion and Park conversion.
The embodiment of the invention is applied to the control as shown in FIG. 6Ring in which id/iqThe value of the inductive current on the DQ axis coordinate system.
And S502, performing low-pass filtering on the three-phase inductive current through the current control loop.
And S503, transforming the three-phase inductive current after low-pass filtering to a three-phase static coordinate system through Clark inverse transformation and Park inverse transformation.
The sign of the midpoint voltage control quantity is determined by the signs of the modulation wave and the inductive current. Because the inversion current is small when the grid-connected inverter operates in the off-grid mode and is influenced by factors such as inductive current ripples, high-frequency interference, sampling time and the like, sampling is easy to generate deviation and influences the symbol judgment of the inversion current. Therefore, the filter processing can be carried out on the inductive current. However, if the low-pass filtering is directly performed on the inductive current at power frequency, the phase shift generated by the low-pass filter at power frequency will delay the inductive current and ultimately affect the symbol judgment. Therefore, the three-phase inductive current can be firstly converted to a DQ axis coordinate system through Clark and Park, and the inductive current i isdAnd iqBecomes a DC quantity, then for idAnd iqAnd (4) performing low-pass filtering, and performing Clark and Park inverse transformation on the filtered value to return to the three-phase stationary coordinate system. The influence of the low-pass filtering on the phase of the inductive current can be eliminated because the low-pass filter has no phase shift at 0 Hz.
In the embodiment of the invention, the three-phase inductive current is converted into a DQ axis coordinate system through Clark and Park, so that the inductive current idAnd iqBecomes a DC quantity, then for idAnd iqAnd performing low-pass filtering, and performing Clark and Park inverse transformation on the filtering value to return to a three-phase static coordinate system, wherein the low-pass filter has no phase shift at 0Hz, so that the influence of the low-pass filtering on the phase of the inductive current is eliminated. The precision of the neutral point potential adjustment of the three-level grid-connected inverter bus is further improved.
It should be understood that, the sequence numbers of the steps in the foregoing embodiments do not imply an execution sequence, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.
The following are embodiments of the apparatus of the invention, reference being made to the corresponding method embodiments described above for details which are not described in detail therein.
Fig. 7 is a schematic structural diagram of a neutral point potential adjusting device in a three-level grid-connected inverter bus according to an embodiment of the present invention, and for convenience of description, only the parts related to the embodiment of the present invention are shown, and details are as follows:
as shown in fig. 7, the three-level grid-connected inverter bus midpoint potential adjusting device 7 includes:
a switching unit 71, a determination unit 72, a control unit 73, and an adjustment unit 74;
the switching unit 71 is configured to switch the three-level three-phase grid-connected inverter to a preset control loop, where the preset control loop includes a current control loop, a voltage control loop, and a midpoint control loop;
the determining unit 72 is configured to determine a first given value corresponding to the voltage control loop through a grid voltage, determine a given value of the current control loop according to an output of the voltage control loop, determine a three-phase inductive current of the three-level three-phase grid-connected inverter as a feedback value of the current control loop, determine a second given value corresponding to the midpoint control loop, and determine a feedback value of the midpoint control loop according to a positive bus voltage and a negative bus voltage on a direct current side of the three-level three-phase grid-connected inverter;
the control unit 73 is configured to perform low-pass filtering on the three-phase inductive current to obtain a low-pass filtered three-phase inductive current; obtaining a first three-phase modulation wave through the current control loop; carrying out proportional regulation and integral regulation on the second given value and the feedback value of the midpoint control loop through the midpoint control loop to obtain an output quantity;
and an adjusting unit 74, configured to adjust a voltage at a midpoint of a bus of the three-level three-phase grid-connected inverter through the low-pass filtered three-phase inductive current, the first three-phase modulation wave, and the output quantity.
Optionally, the adjusting unit 74 is configured to:
multiplying the three-phase inductive current after low-pass filtering with the corresponding phase in the first three-phase modulation wave to obtain a first control quantity;
calculating a sign bit of the first control quantity, and multiplying the sign bit by the output quantity to obtain a second control quantity;
superposing the first three-phase modulation wave and the second control quantity to obtain a second three-phase modulation wave;
carrying out square wave pulse width modulation on the second three-phase modulation wave to obtain a duty ratio;
and regulating the voltage of the midpoint of the bus of the three-level three-phase grid-connected inverter through the duty ratio so that the difference value between the positive bus voltage and the negative bus voltage at the direct current side of the three-level three-phase grid-connected inverter is smaller than or equal to a preset value.
Optionally, the apparatus further includes a determining unit 75, configured to:
judging whether the three-level three-phase grid-connected inverter is in a preset off-grid state;
and if the three-level three-phase grid-connected inverter is in a preset off-grid state, disconnecting an alternating current contactor connected with a power grid in the three-level three-phase grid-connected inverter.
Optionally, the determining unit 75 is configured to:
calculating the difference value of the positive bus voltage and the negative bus voltage of the direct-current side of the three-level three-phase grid-connected inverter;
and if the difference value is larger than a preset value, judging that the three-level three-phase grid-connected inverter is in a preset off-grid state.
Optionally, the determining unit 72 is configured to:
and obtaining the first given value by carrying out Clark and Park conversion on the power grid voltage.
Optionally, the determining unit 72 is further configured to:
limiting the amplitude of the first given value through a preset formula, wherein the preset formula is as follows:
wherein u isd_refIs said first given value, ubus_pIs the voltage u of the middle point of the positive bus to the bus in the three-level three-phase grid-connected inverterbus nAnd the voltage of the negative bus at the midpoint of the bus in the three-phase three-level grid-connected inverter is obtained.
Optionally, the determining unit 72 is further configured to:
and the second given value is set to be 0, and the feedback value is the difference value of the positive bus voltage and the negative bus voltage of the direct current side of the three-level three-phase grid-connected inverter.
Optionally, the control unit 73 is further configured to:
converting the three-phase inductive current to a DQ axis coordinate system through Clark conversion and Park conversion;
after low pass filtering the three phase inductor currents through the current control loop, the method further comprises:
and transforming the three-phase inductive current subjected to low-pass filtering into a three-phase static coordinate system through Clark inverse transformation and Park inverse transformation.
Therefore, the device provided by the invention can enable the three-level grid-connected inverter to enter the off-line state when the voltage difference of the positive bus voltage and the negative bus voltage is greater than the preset value, and adjust the bus midpoint voltage which is originally greatly deviated through the preset control loop.
Fig. 8 is a schematic diagram of a terminal according to an embodiment of the present invention. As shown in fig. 8, the terminal 8 of this embodiment includes: a processor 80, a memory 81 and a computer program 82 stored in said memory 81 and executable on said processor 80. The processor 80, when executing the computer program 82, implements the steps in each of the above-described embodiments of the method for adjusting a midpoint potential in a bus of a three-level grid-connected inverter, such as the steps 101 to 106 shown in fig. 1. Alternatively, the processor 80, when executing the computer program 82, implements the functions of the modules/units in the above-described device embodiments, such as the functions of the units 71 to 75 shown in fig. 7.
Illustratively, the computer program 82 may be partitioned into one or more modules/units that are stored in the memory 81 and executed by the processor 80 to implement the present invention. The one or more modules/units may be a series of computer program instruction segments capable of performing specific functions, which are used to describe the execution of the computer program 82 in the terminal 8.
The terminal 8 may be a desktop computer, a notebook, a palm computer, a cloud server, or other computing devices. The terminal may include, but is not limited to, a processor 80, a memory 81. It will be appreciated by those skilled in the art that fig. 8 is only an example of a terminal 8 and does not constitute a limitation of the terminal 8, and that it may comprise more or less components than those shown, or some components may be combined, or different components, for example the terminal may further comprise input output devices, network access devices, buses, etc.
The Processor 80 may be a Central Processing Unit (CPU), other general purpose Processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other Programmable logic device, discrete Gate or transistor logic, discrete hardware components, etc. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like.
The memory 81 may be an internal storage unit of the terminal 8, such as a hard disk or a memory of the terminal 8. The memory 81 may also be an external storage device of the terminal 8, such as a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash memory Card (Flash Card) and the like provided on the terminal 8. Further, the memory 81 may also include both an internal storage unit and an external storage device of the terminal 8. The memory 81 is used for storing the computer program and other programs and data required by the terminal. The memory 81 may also be used to temporarily store data that has been output or is to be output.
It will be apparent to those skilled in the art that, for convenience and brevity of description, only the above-mentioned division of the functional units and modules is illustrated, and in practical applications, the above-mentioned function distribution may be performed by different functional units and modules according to needs, that is, the internal structure of the apparatus is divided into different functional units or modules to perform all or part of the above-mentioned functions. Each functional unit and module in the embodiments may be integrated in one processing unit, or each unit may exist alone physically, or two or more units are integrated in one unit, and the integrated unit may be implemented in a form of hardware, or in a form of software functional unit. In addition, specific names of the functional units and modules are only for convenience of distinguishing from each other, and are not used for limiting the protection scope of the present application. The specific working processes of the units and modules in the system may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.
In the above embodiments, the descriptions of the respective embodiments have respective emphasis, and reference may be made to the related descriptions of other embodiments for parts that are not described or illustrated in a certain embodiment.
Those of ordinary skill in the art will appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. 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.
In the embodiments provided in the present invention, it should be understood that the disclosed apparatus/terminal and method may be implemented in other ways. For example, the above-described apparatus/terminal embodiments are merely illustrative, and for example, the division of the modules or units is only one logical division, and there may be other divisions when actually implemented, for example, a plurality of units or components may be combined or may be integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.
The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.
In addition, functional units in the embodiments of the present invention may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.
The integrated modules/units, if implemented in the form of software functional units and sold or used as separate products, may be stored in a computer readable storage medium. Based on such understanding, all or part of the flow of the method according to the embodiments of the present invention may also be implemented by a computer program, which may be stored in a computer-readable storage medium, and when the computer program is executed by a processor, the steps of the method embodiments may be implemented. Wherein the computer program comprises computer program code, which may be in the form of source code, object code, an executable file or some intermediate form, etc. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, usb disk, removable hard disk, magnetic disk, optical disk, computer Memory, Read-Only Memory (ROM), Random Access Memory (RAM), electrical carrier wave signals, telecommunications signals, software distribution medium, and the like. It should be noted that the computer readable medium may contain other components which may be suitably increased or decreased as required by legislation and patent practice in jurisdictions, for example, in some jurisdictions, computer readable media which may not include electrical carrier signals and telecommunications signals in accordance with legislation and patent practice.
The above-mentioned embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present invention, and are intended to be included within the scope of the present invention.
Claims (9)
1. A method for adjusting neutral point potential of a bus of a three-level grid-connected inverter is characterized by being applied to the three-level three-phase grid-connected inverter and comprising the following steps:
switching the three-level three-phase grid-connected inverter to a preset control loop, wherein the preset control loop comprises a current control loop, a voltage control loop and a middle point control loop;
determining a first given value corresponding to the voltage control loop through the voltage of a power grid, determining a given value of the current control loop according to the output of the voltage control loop, determining a three-phase inductive current of the three-level three-phase grid-connected inverter as a feedback value of the current control loop, determining a second given value corresponding to the midpoint control loop, and determining a feedback value of the midpoint control loop according to a positive bus voltage and a negative bus voltage on the direct current side of the three-level three-phase grid-connected inverter;
carrying out low-pass filtering on the three-phase inductive current to obtain the three-phase inductive current after low-pass filtering;
obtaining a first three-phase modulation wave through the current control loop;
carrying out proportional regulation and integral regulation on the second given value and the feedback value of the midpoint control loop through the midpoint control loop to obtain an output quantity;
the voltage of the middle point of a bus of the three-level three-phase grid-connected inverter is regulated through the three-phase inductive current after low-pass filtering, the first three-phase modulation wave and the output quantity; the method comprises the following steps: multiplying the three-phase inductive current after low-pass filtering with the corresponding phase in the first three-phase modulation wave to obtain a first control quantity; calculating a sign bit of the first control quantity, and multiplying the sign bit by the output quantity to obtain a second control quantity; superposing the first three-phase modulation wave and the second control quantity to obtain a second three-phase modulation wave; carrying out square wave pulse width modulation on the second three-phase modulation wave to obtain a duty ratio; and regulating the voltage of the midpoint of the bus of the three-level three-phase grid-connected inverter through the duty ratio so that the difference value between the positive bus voltage and the negative bus voltage at the direct current side of the three-level three-phase grid-connected inverter is smaller than or equal to a preset value.
2. The method for adjusting the neutral point potential of the three-level grid-connected inverter bus according to claim 1, wherein before switching the three-level three-phase grid-connected inverter to a preset control loop, the method further comprises:
judging whether the three-level three-phase grid-connected inverter is in a preset off-grid state;
and if the three-level three-phase grid-connected inverter is in a preset off-grid state, disconnecting an alternating current contactor connected with a power grid in the three-level three-phase grid-connected inverter.
3. The method for adjusting the neutral point potential of the three-level grid-connected inverter bus according to claim 2, wherein the step of judging whether the three-level three-phase grid-connected inverter is in a preset off-grid state comprises the steps of:
calculating the difference value of the positive bus voltage and the negative bus voltage of the direct-current side of the three-level three-phase grid-connected inverter;
and if the difference value is larger than a preset value, judging that the three-level three-phase grid-connected inverter is in a preset off-grid state.
4. The method for adjusting the neutral point potential of the three-level grid-connected inverter bus according to any one of claims 1 to 3, wherein the determining the first given value corresponding to the voltage control loop through the grid voltage comprises:
and obtaining the first given value by carrying out Clark and Park conversion on the power grid voltage.
5. The method for adjusting the neutral point potential of the three-level grid-connected inverter bus according to claim 4, further comprising the following steps:
limiting the amplitude of the first given value through a preset formula, wherein the preset formula is as follows:
wherein u isd_refIs said first given value, ubus_pIs the voltage u of the middle point of the positive bus to the bus in the three-level three-phase grid-connected inverterbus_nAnd the voltage of the negative bus at the midpoint of the bus in the three-phase three-level grid-connected inverter is obtained.
6. The method for adjusting the neutral point potential of the three-level grid-connected inverter bus according to any one of claims 1 to 3, wherein the determining a second given value corresponding to the neutral point control loop and the feedback value of the neutral point control loop according to the positive bus voltage and the negative bus voltage of the three-level three-phase grid-connected inverter on the direct current side comprises:
and the second given value is set to be 0, and the feedback value is the difference value of the positive bus voltage and the negative bus voltage of the direct current side of the three-level three-phase grid-connected inverter.
7. The method for adjusting the neutral point potential of the three-level grid-connected inverter bus according to any one of claims 1 to 3, wherein before the low-pass filtering of the three-phase inductor current by the current control loop, the method further comprises:
converting the three-phase inductive current to a DQ axis coordinate system through Clark conversion and Park conversion;
after low pass filtering the three phase inductor currents through the current control loop, the method further comprises:
and transforming the three-phase inductive current subjected to low-pass filtering into a three-phase static coordinate system through Clark inverse transformation and Park inverse transformation.
8. A terminal comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor when executing the computer program implements the steps of the method for adjusting neutral point potential in a bus of a three-level grid-connected inverter according to any of claims 1 to 7.
9. A computer-readable storage medium storing a computer program, wherein the computer program when executed by a processor implements the steps of the method for adjusting a midpoint potential of a bus of a tri-level grid-connected inverter as claimed in any one of claims 1 to 7.
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| CN112181009B (en) * | 2020-09-14 | 2022-07-05 | 科华恒盛股份有限公司 | Hotspot tracking control method and device and terminal equipment |
| CN112953270B (en) * | 2021-02-07 | 2022-09-06 | 石家庄通合电子科技股份有限公司 | Three-phase three-level rectifier neutral point balance control method and device and terminal equipment |
| CN114944773A (en) * | 2021-02-10 | 2022-08-26 | 华为数字能源技术有限公司 | Voltage control method, inverter and voltage control device |
| CN114629224A (en) * | 2022-03-24 | 2022-06-14 | 漳州科华电气技术有限公司 | Neutral point balance control method for direct current bus voltage of UPS system and inverter |
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| CN108964119A (en) * | 2018-06-21 | 2018-12-07 | 西安理工大学 | A kind of three level grid-connected inverter common-mode voltage predictor method of T-type |
| CN110061646A (en) * | 2019-05-22 | 2019-07-26 | 深圳市德力电气技术有限公司 | A kind of method, equipment and the storage medium of three-level inverter neutral balance |
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| CN101976968A (en) * | 2010-09-25 | 2011-02-16 | 西安交通大学 | Method for controlling midpoint potential of direct-current bus of three-level inverter |
| CN108964119A (en) * | 2018-06-21 | 2018-12-07 | 西安理工大学 | A kind of three level grid-connected inverter common-mode voltage predictor method of T-type |
| CN110061646A (en) * | 2019-05-22 | 2019-07-26 | 深圳市德力电气技术有限公司 | A kind of method, equipment and the storage medium of three-level inverter neutral balance |
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