CN113725895A - Independent active support type photovoltaic inverter with unbalanced load - Google Patents
Independent active support type photovoltaic inverter with unbalanced load Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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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
- H02M1/12—Arrangements for reducing harmonics from ac input or output
- H02M1/126—Arrangements for reducing harmonics from ac input or output using passive filters
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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
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
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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
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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
- H02M7/53—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 using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
- H02M7/53871—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
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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
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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Abstract
The invention provides an active support type photovoltaic inverter with an unbalanced load independently. This independent active support type photovoltaic inverter with unbalanced load includes: the photovoltaic junction, the load junction, the preceding converter and the subsequent inverter; the photovoltaic contact is used for connecting an external photovoltaic, and the load contact is used for connecting an external load; the first end of the preceding-stage converter is connected with the photovoltaic contact, and the second end of the preceding-stage converter is connected with the first end of the rear-stage inverter; and the second end of the rear-stage inverter is connected with the load contact. The invention can separate the positive sequence from the negative sequence of the voltage and the current when the independent load runs, independently control the positive sequence component and the negative sequence component, control the positive sequence component to maintain the voltage and the frequency of the bus by adopting a constant voltage and constant frequency control strategy, introduce the negative sequence double-loop control to inhibit the negative sequence component, eliminate the power fluctuation, ensure the stable running of the system and improve the running reliability.
Description
Technical Field
The invention relates to the technical field of new energy power generation, in particular to an active support type photovoltaic inverter with an unbalanced load independently.
Background
With the rapid development of human society, traditional energy sources such as natural gas and oil are gradually consumed, the resource shortage and the environmental problems caused by the traditional energy sources are not neglected, the development and the utilization of new energy sources go to the historical stage and become important issues which are not neglected in the global energy source field, and a photovoltaic power supply is taken as one of the main ways of supplying power by the new energy sources, and the development of the photovoltaic power supply is emphasized in various countries in the world. After the distributed energy is merged into the power grid, a fixation effect is generated on the power grid, efficient grid connection can be achieved through a reasonable control strategy, the active supporting effect on the power grid is achieved, and the operation stability is improved.
When the power grid side breaks down, the distributed photovoltaic system needs to be separated from the power grid to carry out independent loading, so that stable operation of the system is maintained, and reliability is improved. When an actual power grid runs, an asymmetric three-phase load often exists, a negative sequence component is generated in an inverter system, power fluctuation is generated, the output waveform of the inverter is seriously influenced, meanwhile, a certain negative sequence voltage drop is generated in line impedance by negative sequence current, and the power quality is reduced. The photovoltaic inverter can be provided with the capability of independently carrying three-phase unbalanced loads, has high quality and stably provides the voltage required by the load operation. When the photovoltaic inverter is independently loaded, a voltage type control strategy is generally adopted, and when three-phase loads are inconsistent, unbalanced current can be generated, so that the output voltage is unbalanced, and therefore the negative voltage is reacted to cause adverse effects on the safe use of the loads.
However, the photovoltaic inverter has a problem of poor electric energy quality when the photovoltaic inverter operates independently under a load.
Disclosure of Invention
The embodiment of the invention provides an active support type photovoltaic inverter with an unbalanced load independently, and aims to solve the problem that the photovoltaic inverter has poor electric energy quality when the photovoltaic inverter operates with the load independently.
The embodiment of the invention provides an independent active support type photovoltaic inverter with unbalanced load, which comprises:
the photovoltaic junction, the load junction, the preceding converter and the subsequent inverter;
the photovoltaic contact is connected with an external photovoltaic, the load contact is connected with an external load, the first end of the preceding-stage converter is connected with the photovoltaic contact, the second end of the preceding-stage converter is connected with the first end of the rear-stage inverter, and the second end of the rear-stage inverter is connected with the load contact;
the pre-stage converter is used for maintaining the constant direct-current voltage of the external photovoltaic;
and the rear-stage inverter is used for carrying out positive-negative sequence separation on the voltage and the current and independently controlling the positive sequence and the negative sequence so as to eliminate negative sequence unbalanced voltage.
In one possible implementation, the pre-converter is a Boost converter;
the modulation signal of a Boost switching tube corresponding to the single closed-loop control of the direct-current side capacitor voltage by the Boost converter is as follows:
wherein u isdc_gFor modulating signals for Boost switching tubes, kp_dcIs the value of the proportional controller of the PI regulator, ki_dcIntegrating the value of the controller for the PI regulator, udcrefFor a given value of the DC-side capacitor voltage udcIs the measured dc side capacitance voltage.
In one possible implementation, the rear stage inverter includes: the device comprises a positive and negative sequence separation module, an A/D conversion module, a positive sequence component control module, a negative sequence component control module and a D/A conversion module.
In one possible implementation, the calculation formula of the output value of the a/D conversion module is as follows:
wherein ia、ib、icThree-phase currents, i, respectively output by invertersd、iqFor the value of the output three-phase current in the Dq synchronous rotation coordinate system, ua、ub、ucThree-phase voltages, u, respectively output by invertersd、uqIs the value of the output three-phase voltage in a Dq synchronous rotation coordinate system, theta1Is the included angle of the d-axis and the phase reference axis.
In one possible implementation, the calculation formula of the output value of the D/a conversion module is as follows:
wherein ia、ib、icThree-phase currents, i, respectively output by invertersd、iqFor the value of the output three-phase current in the Dq synchronous rotation coordinate system, ua、ub、ucThree-phase voltages, u, respectively output by invertersd、uqIs the value of the output three-phase voltage in a Dq synchronous rotation coordinate system, theta1Is the included angle of the d-axis and the phase reference axis.
In a possible implementation manner, the positive-negative sequence separation module adopts a time domain detection algorithm based on trigonometric function orthogonal transformation to separate positive-negative sequence components of voltage and current, and expresses the voltage as a combination of a positive sequence component and a negative sequence component by utilizing the orthogonality of a sine function and a cosine function, and the calculation formula is as follows:
wherein, a1Is a voltage positive sequence total component coefficient, a2Is the coefficient of the voltage negative-sequence sinusoidal component, b2Is the coefficient of the negative sequence cosine component of voltage, omega is the angular frequency of voltage, phi1Is the initial phase angle of the positive sequence component of the voltage.
In one possible implementation, the positive sequence component control module controls the positive sequence component using a voltage-current dual-loop, and the negative sequence component control module includes: the first voltage outer ring control module and the first current inner ring control module;
the negative sequence component control module adopts constant voltage constant frequency to control the negative sequence component, and the positive sequence component control module includes: the device comprises a capacitor voltage equipartition control module, a second voltage outer ring control module, a second current inner ring control module and a voltage feedforward module.
In one possible implementation manner, the calculation formula for the first voltage outer loop control module to generate the command value of the current inner loop control module is as follows:
wherein, Ud_nref＝0,U q_nref0; in the formula id_nrefIs a negative sequence d-axis current command value, iq_nrefIs a negative-sequence q-axis current command value, kp_nduThe value, k, of the proportional controller of the outer loop PI regulator for the negative sequence d-axis voltagei_nduIntegrating the value of the proportional controller, k, for a negative sequence d-axis voltage outer loop PI regulatorp_nquIs the value, k, of the proportional controller of the negative sequence q-axis voltage outer loop PI regulatori_nquIntegrating the value of the controller for the outer loop PI regulator for negative sequence q-axis voltages, Ud_nrefIs a negative sequence d-axis voltage command value, Uq_nrefIs a negative sequence q-axis voltage command value, Ud_nAnd Uq_nThe values of the negative sequence voltage on the d-axis and the q-axis, respectively;
the calculation formula of the first current inner loop control module for generating the modulation signal is as follows:
wherein m isd_nAnd mq_nRespectively d-axis negative sequence modulation quantity of inverter output voltage and q-axis negative sequence modulation quantity, k of inverter output voltagep_ndi、ki_ndiThe value of the proportional controller and the value of the integral controller of the negative sequence d-axis voltage outer loop PI regulator are respectivelyp_nqi、ki_nqiThe value of the proportional controller and the value of the integral controller, I, of the negative sequence q-axis voltage outer loop PI regulator are respectivelyd_nrefIs a negative sequence d-axis current command value, Iq_nrefFor negative sequence q-axis current command values, id_nAnd iq_nThe values of the negative-sequence current on the d-axis and q-axis, respectively.
In one possible implementation manner, the calculation formula for the second voltage outer loop control module to generate the command value of the current inner loop control module is as follows:
Ud_pref＝311,Uq_pref＝0
wherein, Id_prefIs a positive sequence d-axis current command value, Iq_prefIs a positive sequence q-axis current command value, kp_pduThe value, k, of the proportional controller of the outer loop PI regulator for positive sequence d-axis voltagesi_pduIntegrating the value of the proportional controller, k, for the positive sequence d-axis voltage outer loop PI regulatorp_pquOuter loop PI regulator proportional controller value, k, for positive sequence q-axis voltagei_pquIntegrating the value of the controller for the outer loop PI regulator for the positive sequence q-axis voltage, Ud_prefFor positive sequence d-axis voltage command value, Uq_prefFor positive sequence q-axis voltage command values, Ud_pAnd Uq_pThe values of the positive sequence voltage on the d-axis and the q-axis, respectively;
the calculation formula of the second current inner loop control module for generating the modulation signal is as follows:
wherein m isd_p1And mq_p1Respectively generating a modulation instruction value for a positive sequence d-axis current inner ring and a modulation instruction value, k, for a positive sequence q-axis current inner ringp_pdi、ki_pdiThe value of the proportional controller and the value of the integral controller, k, of the outer ring PI regulator of the positive sequence d-axis voltage respectivelyp_pqi、ki_pqiThe value of the proportional controller and the value of the integral controller, I, of the outer loop PI regulator of the positive sequence q-axis voltaged_prefIs a positive sequence d-axis current command value, Iq_prefFor positive-sequence q-axis current command value, id_pAnd iq_pThe values of the positive sequence current on the d-axis and the q-axis respectively, K is the proportionality coefficient of the feedforward signal, Ud_pAnd Uq_pThe values of the positive sequence voltage on the d-axis and q-axis, respectively.
In one possible implementation manner, the method further includes: and the load contact is connected with the first end of the filter, and the second end of the filter is connected with an external load.
The embodiment of the invention provides an independent active support type photovoltaic inverter with an unbalanced load, which comprises a photovoltaic contact, a load contact, a preceding-stage converter and a subsequent-stage inverter; the photovoltaic contact is used for connecting an external photovoltaic, and the load contact is used for connecting an external load; the first end of the preceding-stage converter is connected with the photovoltaic contact, and the second end of the preceding-stage converter is connected with the first end of the rear-stage inverter; the second end of the rear-stage inverter is connected with the load contact; when the independent load-carrying operation is carried out, positive and negative sequence separation is carried out on voltage and current, a positive sequence component and a negative sequence component are independently controlled, the positive sequence component is controlled by adopting a constant-voltage constant-frequency control strategy to maintain the voltage and the frequency of a bus, negative sequence double-loop control is introduced to inhibit the negative sequence component, power fluctuation is eliminated, the stable operation of a system is ensured, and the operation reliability and the electric energy quality are improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the embodiments or drawings used in the prior art description, and obviously, 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 these drawings without creative efforts.
Fig. 1 is a block diagram illustrating a two-stage photovoltaic independent-band unbalanced load operation control provided in an embodiment of the present invention;
fig. 2 is a structure diagram of a piconet in parallel and off-grid switching according to an embodiment of the present invention;
FIG. 3 is a block diagram of negative sequence component voltage current dual loop control provided by an embodiment of the present invention;
fig. 4 is a block diagram of positive sequence component constant voltage and constant frequency control provided in the embodiment of the present invention;
fig. 5 is a block diagram of voltage-sharing control of capacitors on the dc side of the inverter according to the embodiment of the present invention;
fig. 6 is a waveform diagram of the output voltage of the photovoltaic inverter without the power quality management function according to the embodiment of the present invention;
fig. 7 is a voltage waveform diagram of positive and negative output sequences of an active-support photovoltaic inverter without power quality management function according to an embodiment of the present invention;
fig. 8 is a waveform diagram of the output voltage imbalance of the active-support photovoltaic inverter without the power quality management function according to the embodiment of the present invention;
fig. 9 is a graph of output voltage waveforms of an independent actively-supported photovoltaic inverter with unbalanced loads according to an embodiment of the present invention;
fig. 10 is a graph of output positive and negative sequence voltage waveforms of an independent active support type photovoltaic inverter with unbalanced load according to an embodiment of the present invention;
fig. 11 is a waveform diagram of an output voltage imbalance of an independent unbalanced-load actively-supported photovoltaic inverter according to an embodiment of the present invention.
Detailed Description
In order to make the technical solution better understood by those skilled in the art, the technical solution in the embodiment of the present invention will be clearly described below with reference to the drawings in the embodiment of the present invention, and it is obvious that the described embodiment is a part of the embodiment of the present invention, and not a whole embodiment. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present disclosure without any creative effort shall fall within the protection scope of the present disclosure.
The terms "include" and any other variations in the description and claims of this document and the above-described figures, mean "include but not limited to", and are intended to cover non-exclusive inclusions and not limited to the examples listed herein. Furthermore, the terms "first" and "second," etc. are used to distinguish between different objects and are not used to describe a particular order.
The following detailed description of implementations of the invention refers to the accompanying drawings in which:
fig. 1 is a schematic structural diagram of an independent active-support photovoltaic inverter with unbalanced load according to an embodiment of the present invention. Referring to fig. 1, the independent unbalanced-load actively-supported photovoltaic inverter includes:
the photovoltaic junction, the load junction, the preceding converter and the subsequent inverter;
the photovoltaic contact is connected with an external photovoltaic, the load contact is connected with an external load, the first end of the preceding-stage converter is connected with the photovoltaic contact, the second end of the preceding-stage converter is connected with the first end of the rear-stage inverter, and the second end of the rear-stage inverter is connected with the load contact;
the pre-stage converter is used for maintaining the constant direct-current voltage of the external photovoltaic;
and the rear-stage inverter is used for separating positive and negative sequences of the voltage and the current and independently controlling the positive and negative sequences so as to eliminate negative sequence unbalanced voltage and ensure that the positive sequence voltage supplies power to an off-grid external load and the photovoltaic inverter outputs constant-frequency voltage.
The independent active support type photovoltaic inverter with the unbalanced load specifically comprises the following control steps:
step 1: the voltage of the direct current capacitor is controlled by the preceding stage Boost converter.
Step 1-1: the Boost converter outputs the capacitor voltage udcAnd a given DC capacitor voltage reference udc_refAnd (3) making a difference, sending the generated difference signal into a PI (proportional-integral) regulator, and generating a PWM (pulse-width modulation) wave, wherein the calculation formula is as follows:
in the formula udc_pFor modulating signals for Boost switching tubes, kp_dcIs the value of the proportional controller of the PI regulator, ki_dcIntegrating the value of the controller for the PI regulator, udcrefFor a given value of the DC-side capacitor voltage udcIs the measured dc side capacitance voltage.
Step 1-2: the on-off of the switching tube in the boost circuit is controlled by the generated duty ratio signal.
Step 2: and the later-stage inverter part controls the photovoltaic inverter to output stable voltage to maintain the constant frequency of the bus voltage.
Step 2-1: the system bus voltage uabcAnd output inductor current iabcPositive and negative sequence components U are obtained through conversiond_n、Uq_nAnd id_n、iq_n. The voltage (flow) is represented as a combination of positive and negative sequence components:
wherein, subscript 1 represents the positive sequence component, and subscript 2 represents the negative sequence component, for the convenience of calculation, the positive sequence component is represented as the sum of the sine component and the cosine component, and the orthogonality of the sine function and the cosine function can be used for calculating the positive and negative sequence components:
step 2-2: the negative sequence component is controlled by using a voltage-current double loop, and the control block diagram is shown in FIG. 3:
step 2-2-1: and generating a current inner ring command value by using the voltage outer ring, wherein the calculation formula is as follows:
in the formula Id_nrefIs a negative sequence d-axis current command value, Iq_nrefIs a negative sequence q-axis current command value, kp_nduThe value, k, of the proportional controller of the outer loop PI regulator for the negative sequence d-axis voltagei_nduIntegrating the value of the proportional controller, k, for a negative sequence d-axis voltage outer loop PI regulatorp_nquThe value, k, of the proportional controller of the outer loop PI regulator for negative sequence q-axis voltagesi_nquIntegrating the value of the controller for the outer loop PI regulator for negative sequence q-axis voltages, Ud_nrefIs a negative sequence d-axis voltage command value, Uq_nrefIs a negative sequence q-axis voltage command value, Ud_nAnd Uq_nThe values of the negative sequence voltage on the d-axis and q-axis, respectively.
Wherein,
Ud_nref＝0,Uq_nref＝0 (5)
step 2-2-2: the current inner loop control module generates a modulation signal, and the calculation formula is as follows:
in the formula md_nAnd mq_nThe d-axis negative sequence modulation quantity and the q-axis negative sequence modulation quantity, k of the output voltage of the inverter arep_ndi、ki_ndiThe value of the proportional controller and the value of the integral controller of the negative sequence d-axis voltage outer loop PI regulator are respectivelyp_nqi、ki_nqiThe value of the proportional controller and the value of the integral controller, I, of the negative sequence q-axis voltage outer loop PI regulator are respectivelyd_nrefIs a negative sequence d-axis current command value, Iq_nrefIs a negative sequence q-axis current command value, id_nAnd iq_nThe values of the negative-sequence current on the d-axis and q-axis, respectively.
And step 3: the positive sequence component is controlled by adopting a constant-voltage constant-frequency control strategy to provide voltage frequency support required by normal operation for off-grid loads, and a control block diagram is shown in fig. 4:
step 3-1: the zero sequence current injection method is used for controlling the voltage equalizing of the capacitor on the direct current side of the inverter, and the control block diagram is shown in fig. 5. And (3) making a difference between the direct current side capacitor voltage and the voltage difference value, sending the voltage difference value to a PI (proportional integral) regulator, and making a difference between the voltage difference value and a zero sequence current component to generate an instruction signal:
in the formula, mp0Respectively, the generated modulation signals u1、u2Respectively, the DC side upper and lower capacitor voltages, kp_pdc、 ki_pdcRespectively the value of the proportional controller and the value of the integral controller, I, of the PI regulator0Is the current zero sequence component.
Step 3-2: and generating a current inner ring command value by using the voltage outer ring, wherein the calculation formula is as follows:
wherein:
Ud_pref＝311,Uq_pref＝0 (9)
in the formula Id_prefIs a positive sequence d-axis current command value, Iq_prefIs a positive sequence q-axis current command value, kp_pduThe value, k, of the proportional controller of the outer loop PI regulator for positive sequence d-axis voltagesi_pduIntegrating the value of the proportional controller, k, for the positive sequence d-axis voltage outer loop PI regulatorp_pquOuter loop PI regulator proportional controller value, k, for positive sequence q-axis voltagei_pquIntegrating the value of the controller for the outer loop PI regulator for the positive sequence q-axis voltage, Ud_prefFor positive sequence d-axis voltage command value, Uq_prefFor positive sequence q-axis voltage command values, Ud_pAnd Uq_pThe values of the positive sequence voltage on the d-axis and q-axis, respectively.
Step 3-3: the current inner loop control module is used for generating a modulation signal, and the calculation formula is as follows:
in the formula, md_p1And mq_p1Generating a modulation command value for the positive sequence d-axis current inner loop and a modulation command value, k, for the positive sequence q-axis current inner loopp_pdi、ki_pdiThe value of the proportional controller and the value of the integral controller, k, of the outer ring PI regulator of the positive sequence d-axis voltage respectivelyp_pqi、ki_pqiThe values of the proportional controller and the integral controller of the outer loop PI regulator of the positive sequence q-axis voltage are respectivelyd_prefIs a positive sequence d-axis current command value, Iq_prefFor positive-sequence q-axis current command value, id_pAnd iq_pThe values of the positive sequence current on the d-axis and the q-axis respectively, K is the proportionality coefficient of the feedforward signal, Ud_pAnd Uq_pThe values of the positive sequence voltage on the d-axis and q-axis, respectively.
Step 3-4: m is to bed_p1And mq_p1Carrying out dq/abc inverse transformation to generate a driving PWM signal, and adding a DC offset modulation signal mp0And generating a positive sequence PWM signal. A/D (i.e., abc/dq) and D/A (i.e., dq/abc) refer to the switching of digital and analog circuits, which shall be referred to herein as hardware circuits, and dq refers to the software component.
Step 3-5: and superposing the positive-sequence PWM signal and the negative-sequence PWM signal to obtain the inverter switching tube driving PWM wave.
In order to test the invention, a simulation model of an independent active support type photovoltaic inverter with unbalanced load is built in MATLAB/Simulink.
Fig. 6, 7, and 8 show waveforms of the photovoltaic inverter without the power quality control function with a three-phase unbalanced load. Fig. 6 is a voltage waveform diagram of the output voltage of the photovoltaic inverter without the function of managing the power quality, fig. 7 is a waveform diagram of the positive and negative sequence components of the output voltage, and fig. 8 is a waveform diagram of the imbalance degree of the output voltage. It can be seen from the comparison of the three oscillograms that the negative sequence component contained in the output voltage of the photovoltaic inverter without the function of managing the electric energy quality is larger when the three-phase load is unbalanced, the voltage unbalance degree is higher, and the stable operation of the system is not facilitated.
Fig. 9, 10 and 11 show waveforms of independent unbalanced-load active-support photovoltaic inverters with three-phase unbalanced loads. Fig. 9 is a waveform diagram of an output voltage of an independent active support type photovoltaic inverter with an unbalanced load, fig. 10 is a waveform diagram of positive and negative sequence components of the output voltage, and fig. 11 is a waveform diagram of an unbalanced degree of the output voltage. As can be seen from the figure, through the control strategy, the negative sequence component of the output voltage of the photovoltaic inverter is greatly reduced, the unbalance degree of the three phases of the voltage is very low, the electric energy quality of the load voltage is guaranteed, and the reliability and the stability of the active supporting power supply of the photovoltaic inverter are improved.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; 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; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. An active support type photovoltaic inverter with an unbalanced load, comprising:
the photovoltaic junction, the load junction, the preceding converter and the subsequent inverter;
the photovoltaic contact is connected with an external photovoltaic, the load contact is connected with an external load, the first end of the preceding-stage converter is connected with the photovoltaic contact, the second end of the preceding-stage converter is connected with the first end of the rear-stage inverter, and the second end of the rear-stage inverter is connected with the load contact;
the pre-stage converter is used for maintaining the direct-current voltage of the external photovoltaic to be constant;
and the rear-stage inverter is used for carrying out positive-negative sequence separation on the voltage and the current and independently controlling positive and negative sequences so as to eliminate negative sequence unbalanced voltage.
2. The active support type photovoltaic inverter with unbalanced load as recited in claim 1, wherein the pre-converter is a Boost converter;
the calculation formula of the modulation signal of the Boost switching tube corresponding to the single closed-loop control of the direct-current side capacitor voltage by the Boost converter is as follows:
wherein u isdc_gFor modulating signals for Boost switching tubes, kp_dcIs the value of the proportional controller of the PI regulator, ki_dcIntegrating the value of the controller for the PI regulator, udcrefFor a given value of the DC-side capacitor voltage udcIs the measured dc side capacitance voltage.
3. The isolated unbalanced load actively supported photovoltaic inverter of claim 1, wherein the back-stage inverter comprises: the device comprises a positive and negative sequence separation module, an A/D conversion module, a positive sequence component control module, a negative sequence component control module and a D/A conversion module.
4. The isolated unbalanced-load actively-supported photovoltaic inverter as recited in claim 3, wherein the output of the A/D converter module is calculated as follows:
wherein ia、ib、icThree-phase currents, i, respectively output by invertersd、iqFor the value of the output three-phase current in the Dq synchronous rotation coordinate system, ua、ub、ucThree-phase voltages, u, respectively output by invertersd、uqIs the value of the output three-phase voltage in a Dq synchronous rotation coordinate system, theta1Is the angle between the d-axis and the phase reference axis.
5. The isolated unbalanced-load actively-supported photovoltaic inverter as recited in claim 3, wherein the D/a conversion module output value is calculated as follows:
wherein ia、ib、icThree-phase currents, i, respectively output by invertersd、iqFor the value of the output three-phase current in the Dq synchronous rotation coordinate system, ua、ub、ucThree-phase voltages, u, respectively output by invertersd、uqIs the value of the output three-phase voltage in a Dq synchronous rotation coordinate system, theta1Is the angle between the d-axis and the phase reference axis.
6. The active-support photovoltaic inverter with unbalanced load as recited in claim 3, wherein the positive-negative sequence separation module separates the positive-negative sequence component of the voltage and the current by using a time domain detection algorithm based on trigonometric function orthogonal transformation, and expresses the voltage as a combination of the positive-sequence component and the negative-sequence component by using orthogonality of a sine function and a cosine function, and the calculation formula is as follows:
wherein, a1Is a voltage positive sequence total component coefficient, a2Is the coefficient of the voltage negative-sequence sinusoidal component, b2Is the coefficient of the negative sequence cosine component of voltage, omega is the angular frequency of voltage, phi1Is the initial phase angle of the positive sequence component of the voltage.
7. The isolated unbalanced-load actively-supported photovoltaic inverter of claim 3, wherein the positive sequence component control module controls the positive sequence component with dual voltage-current loops, and the negative sequence component control module comprises: the first voltage outer ring control module and the first current inner ring control module;
negative sequence component control module adopts constant voltage constant frequency to control negative sequence component, positive sequence component control module includes: the device comprises a capacitor voltage equalization control module, a second voltage outer ring control module, a second current inner ring control module and a voltage feedforward module.
8. The isolated unbalanced load actively supported photovoltaic inverter of claim 7, wherein the first voltage outer loop control module generates the current inner loop control module command value by the following equation:
wherein, Ud_nref＝0,Uq_nref0; in the formula id_nrefIs a negative sequence d-axis current command value, iq_nrefIs a negative sequence q-axis current command value, kp_nduProportional control of external ring PI regulator for negative sequence d-axis voltageValue of the system, ki_nduIntegrating the value of the proportional controller, k, for a negative sequence d-axis voltage outer loop PI regulatorp_nquThe value, k, of the proportional controller of the outer loop PI regulator for negative sequence q-axis voltagesi_nquIntegrating the value of the controller for the outer loop PI regulator for negative sequence q-axis voltages, Ud_nrefIs a negative sequence d-axis voltage command value, Uq_nrefIs a negative sequence q-axis voltage command value, Ud_nAnd Uq_nThe values of the negative sequence voltage on the d-axis and the q-axis, respectively;
the calculation formula of the first current inner loop control module for generating the modulation signal is as follows:
wherein m isd_nAnd mq_nRespectively d-axis negative sequence modulation quantity of inverter output voltage and q-axis negative sequence modulation quantity, k of inverter output voltagep_ndi、ki_ndiThe value of the proportional controller and the value of the integral controller of the negative sequence d-axis voltage outer loop PI regulator are respectivelyp_nqi、ki_nqiThe value of the proportional controller and the value of the integral controller, I, of the negative sequence q-axis voltage outer loop PI regulator are respectivelyd_nrefIs a negative sequence d-axis current command value, Iq_nrefIs a negative sequence q-axis current command value, id_nAnd iq_nThe values of the negative-sequence current on the d-axis and q-axis, respectively.
9. The isolated unbalanced-load actively-supported photovoltaic inverter of claim 7, wherein the second voltage outer loop control module generates the current inner loop control module command value by the following equation:
Ud_pref＝311,Uq_pref＝0
wherein, Id_prefIs a positive sequence d-axis current command value, Iq_prefIs in positive orderq-axis current command value, kp_pduThe value, k, of the proportional controller of the outer loop PI regulator for positive sequence d-axis voltagesi_pduIntegrating the value of the proportional controller, k, for the positive sequence d-axis voltage outer loop PI regulatorp_pquOuter loop PI regulator proportional controller value, k, for positive sequence q-axis voltagei_pquIntegrating the value of the controller for the outer loop PI regulator for the positive sequence q-axis voltage, Ud_prefFor positive sequence d-axis voltage command value, Uq_prefFor positive sequence q-axis voltage command values, Ud_pAnd Uq_pThe values of the positive sequence voltage on the d-axis and the q-axis, respectively;
the calculation formula of the second current inner loop control module for generating the modulation signal is as follows:
wherein m isd_p1And mq_p1Respectively generating a modulation instruction value for a positive sequence d-axis current inner ring and a modulation instruction value, k, for a positive sequence q-axis current inner ringp_pdi、ki_pdiThe value of the proportional controller and the value of the integral controller, k, of the outer ring PI regulator of the positive sequence d-axis voltage respectivelyp_pqi、ki_pqiThe value of the proportional controller and the value of the integral controller, I, of the outer loop PI regulator of the positive sequence q-axis voltaged_prefIs a positive sequence d-axis current command value, Iq_prefFor positive-sequence q-axis current command value, id_pAnd iq_pThe values of the positive sequence current on the d-axis and the q-axis respectively, K is the proportionality coefficient of the feedforward signal, Ud_pAnd Uq_pThe values of the positive sequence voltage on the d-axis and q-axis, respectively.
10. The actively-supported, independently unbalanced-loaded photovoltaic inverter as recited in any one of claims 1 to 9, further comprising: a filter, the load contact being connected to a first end of the filter, a second end of the filter being connected to the external load.
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