WO2014173002A1 - 光伏并网逆变器的低压穿越控制方法及装置 - Google Patents

光伏并网逆变器的低压穿越控制方法及装置 Download PDF

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Publication number
WO2014173002A1
WO2014173002A1 PCT/CN2013/078208 CN2013078208W WO2014173002A1 WO 2014173002 A1 WO2014173002 A1 WO 2014173002A1 CN 2013078208 W CN2013078208 W CN 2013078208W WO 2014173002 A1 WO2014173002 A1 WO 2014173002A1
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Prior art keywords
value
voltage value
inverter
low
current value
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PCT/CN2013/078208
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English (en)
French (fr)
Inventor
郑平
宋行宾
韩晓艳
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京东方科技集团股份有限公司
北京京东方能源科技有限公司
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Priority to US14/366,221 priority Critical patent/US9385582B2/en
Publication of WO2014173002A1 publication Critical patent/WO2014173002A1/zh

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Classifications

    • 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
    • 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
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H02J3/1807—Arrangements for adjusting, eliminating or compensating reactive power in networks using series compensators
    • H02J3/1814—Arrangements for adjusting, eliminating or compensating reactive power in networks using series compensators wherein al least one reactive element is actively controlled by a bridge converter, e.g. unified power flow controllers [UPFC]
    • 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
    • H02M1/36—Means for starting or stopping converters
    • 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
    • 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
    • H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
    • 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
    • H02M1/0003—Details of control, feedback or regulation circuits
    • 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
    • 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
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/10—Flexible AC transmission systems [FACTS]

Definitions

  • the present disclosure relates to the field of power control, and in particular, to a photovoltaic grid-connected inverter control method and apparatus. Background technique
  • Photovoltaic grid-connecting refers to a power grid that integrates solar arrays or photovoltaic power plants into the grid to supply electricity.
  • Low Voltage Ride Through means that when a voltage sag occurs in a photovoltaic grid-connected power network, the DC side, such as a PV power plant, can maintain a connection with the AC side power grid, and the DC voltage of the DC side is converted into an inverter by the inverter. The AC voltage of the AC side power grid is restored to the grid fault recovery, thereby traversing the voltage drop time to avoid causing the power grid fault to expand and improve the power supply reliability.
  • Voltage sag refers to an emergency in which the effective value of the bus voltage drops rapidly and the duration is extremely short.
  • the PV power plant or solar cell array has a large power supply ratio and high permeability in the power grid
  • the PV power plant adopts the passive protection method that is immediately removed from the power supply network during the voltage sag, it will lead to a large reduction in the output of the active power.
  • the recovery of the power supply system is difficult, and may even cause the disengagement of other units, resulting in large-scale power outages and expansion of faults. In this case, low voltage ride through capability is a must.
  • the present disclosure aims to provide a low-voltage traverse control method and device for a photovoltaic grid-connected inverter with small current fluctuation, low-voltage traversal capability, high system stability and high reliability during photovoltaic sag DC-side output. .
  • an embodiment of the present disclosure provides a low-voltage traverse control method for a photovoltaic grid-connected inverter, comprising the following steps: determining whether an effective voltage value of the power grid is less than an upper limit of a low-voltage value; determining that an effective voltage value of the power grid is not less than When the upper limit of the low voltage is reached, the inverter is controlled to operate normally; When the effective voltage value of the broken grid is less than the upper limit of the low voltage value, determine whether the grid voltage value is less than the lower limit of the low voltage value.
  • the control inverter stops working, and when the effective voltage of the grid is judged When the value is not less than the lower limit of the low voltage value, the active current value of the control inverter output is equal to the target active current value and the output reactive current value is equal to the target reactive current value, wherein the inverter outputs in the low pressure crossing state.
  • the difference between the total current and the current output in the normal state is less than the preset value.
  • the low-voltage traverse control method of the photovoltaic grid-connected inverter further includes: when determining that the effective voltage value of the power grid is less than the upper limit of the low-voltage value, timing the effective voltage value of the power grid not less than the lower limit of the low-voltage value, And determining whether the effective voltage value of the power grid is equal to the lower limit of the low voltage value; when determining that the effective voltage value of the power grid is equal to the lower limit of the low voltage value, determining whether the duration reaches the preset time T1, and when the determination duration reaches the preset time T1, controlling the inverter The device stops working.
  • the active current value of the control inverter is equal to the target active current value and the output reactive current value is equal to the target reactive current value; and when the determination of the grid is valid
  • the control inverter stops working, and when the judgment duration does not reach the preset time T2, the control is performed.
  • the active current value of the inverter output is equal to the target active current value and the output reactive current value Equal to the target reactive power threshold.
  • the low voltage ride-through control method of the photovoltaic grid-connected inverter further includes: collecting a voltage signal on the DC side, a current signal, and collecting voltage and current signals of the AC side power grid.
  • the active current value of the normal output of the control inverter is equal to the normal target current value obtained by the MPPT algorithm and the voltage PI control according to the collected signal and controlling the inverter The output current of the device is zero.
  • an embodiment of the present disclosure further provides a low-voltage traverse control device for a photovoltaic grid-connected inverter, including a control unit; the control unit determines whether an effective voltage value of the power grid is less than an upper limit of a low-voltage value; when determining an effective voltage value of the power grid When not lower than the upper limit of the low voltage value, the control unit controls the normal operation of the inverter; and when it is determined that the effective voltage value of the power grid is less than the upper limit of the low voltage value, the control unit determines whether the grid voltage value is less than the lower limit of the low voltage value, when determining the grid The effective voltage value is lower than the low voltage value
  • the control unit controls the inverter to stop working, and when it is determined that the effective voltage value of the power grid is not less than the lower limit of the low voltage value, the control unit controls the active current value output by the inverter to be equal to the target active current value and the output is absent.
  • the working current value is equal to the target reactive current value, where
  • the low voltage ride-through control device of the photovoltaic grid-connected inverter further includes a timing unit
  • the timing unit counts the duration that the effective voltage value of the power grid is not less than the lower limit of the low voltage value, and the control unit determines whether the effective voltage value of the power grid is equal to the lower limit of the low voltage value;
  • the control unit determines whether the duration reaches the preset time T1, and when the determination duration reaches the preset time T1, the control inverter stops working, when the determination duration is not
  • the preset time T1 is reached, the active current value of the control inverter is equal to the target active current value and the output reactive current value is equal to the target reactive current value; and when it is determined that the effective voltage value of the power grid is not equal to the lower limit of the low voltage value,
  • the control unit determines whether the duration reaches the preset time T2.
  • the control inverter stops working.
  • the output of the inverter is controlled.
  • the active current value is equal to the target active current value and the output reactive current value is equal to the target ZX reactive power value.
  • the low-voltage traverse control device of the photovoltaic grid-connected inverter further includes a sampling unit; the sampling unit includes a DC sampling module for collecting a voltage signal and a current signal on the DC side, and collecting a voltage of the AC-side power grid.
  • An AC sampling module for signal and current signals; wherein the control unit includes a normal control module, and when the effective voltage value of the power grid is not less than the upper limit of the low voltage value, the normal control module controls the normal output active current value of the inverter to be equal to The signal collected by the sampling unit controls the normal target current calculated by the MPPT algorithm and the voltage PI and controls the reactive current value of the normal output of the inverter to be zero.
  • control unit further includes a low-voltage traversal state control module for acquiring a target active current value and a target reactive current value in a low-voltage crossing state, wherein the target active current value i* d is a preset power grid.
  • FIG. 1 is a diagram showing a specification of a photovoltaic grid-connected inverter certification detection standard
  • FIG. 3 is a diagram illustrating a solution of a normal target active current value in a normal state according to an embodiment of the present disclosure
  • a connection structure diagram
  • Embodiment 1 is a diagrammatic representation of Embodiment 1:
  • step S1 it is determined whether the effective voltage value of the power grid is less than the upper limit of the low voltage value.
  • the upper limit of the low voltage value can be selected to be 0.9 times the rated voltage.
  • step S1 When it is judged in step S1 that the effective voltage value of the grid is not less than the upper limit of the low voltage value, the inverter is normally operated. If the effective voltage value of the power grid is greater than or equal to the upper limit of the low voltage value, it means that the photovoltaic grid connection does not have a voltage sag at this time but is in a normal working state, so the inverter can be normally operated.
  • the low-voltage traverse control method of the photovoltaic grid-connected inverter proceeds to a step S2.
  • step S2 it is determined whether the effective voltage value of the power grid is less than the lower limit of the low voltage value.
  • the lower limit of the low voltage value can be selected to be 0.2 times the rated voltage.
  • step S2 When it is judged in step S2 that the effective voltage value of the power grid is less than the lower limit of the low voltage value, the inverter is controlled to stop operating. Usually, if the effective voltage value on the grid side is too low, for example, lower than the lower limit of the low voltage value, the inverter is stopped, and the photovoltaic power station is decomposed from the power network. Usually the inverter stops working The method is to directly disconnect the corresponding circuit through the circuit breaker, so that the inverter and the photovoltaic power station or the solar battery are separated from the power grid.
  • step S2 When it is judged in step S2 that the effective voltage value of the power grid is not less than the lower limit of the low voltage value, the active current value of the control inverter output is equal to the target active current value and the output reactive current value is equal to the target reactive current value.
  • the value of the target active current value and the reactive current value varies according to the network parameters of different photovoltaic power grids and the operating conditions under normal conditions. By appropriately selecting the target active current value and the reactive current value, the difference between the total current output by the inverter in the low-voltage crossing state and the current output in the normal state is d, which is a preset value.
  • the transformer of the low voltage transit time is usually neglected.
  • the output current waveform and the amplitude are maintained, and in the low-voltage traverse control method of the photovoltaic grid-connected inverter of the embodiment, the inverter outputs the active current value and the reactive current value, and in the case of low power, the method is adopted.
  • the reactive power is compensated, so as to maintain the waveform distortion of the output current of the inverter during the low-voltage transit time, and the amplitude variation is small, thereby ensuring the power quality, improving the stability and reliability of the photovoltaic grid connection, and preventing the photovoltaic power supply in the photovoltaic grid connection. Partial disassociation leads to large-scale power outages and the problem of expanding faults.
  • Embodiment 2 is a diagrammatic representation of Embodiment 1:
  • the photovoltaic grid-connected inverter certification test standard "Technical requirements and test methods for grid-connected photovoltaic power generation inverters" CGC:2010 stipulates that medium- and high-voltage inverters are specially adapted for large-scale photovoltaic power plants. Should have a certain ability to withstand abnormal voltage, to avoid detachment when the grid voltage is abnormal, causing instability of the grid power supply, and made the following requirements;
  • ⁇ ⁇ is the upper limit of the low pressure value for normal operation
  • u u is the lower limit of the low pressure value that needs to be tolerated
  • T1 is the time required to maintain the grid when the voltage drops to u u ;
  • the U u , Tl, ⁇ 2 values must be determined in consideration of the actual situation such as protection and reclosing action time, usually 1 ⁇ . Take 0.9 times the rated voltage, U u is taken as 0.2 times rated voltage, T1 is set to is, T2 is set to 2S.
  • step S3 is added.
  • step S1 it is determined whether the effective voltage value of the grid is less than the upper limit U M of the low pressure value.
  • the inverter is normally operated.
  • the low-voltage traverse control method of the photovoltaic grid-connected inverter proceeds to a step S2.
  • step S2 it is determined whether the effective voltage value of the power grid is less than the lower limit value U u of the low voltage value.
  • step S2 When it is judged in step S2 that the effective voltage value of the grid is less than the lower limit of the low voltage value, the inverter is controlled to stop operating.
  • step S2 When it is judged in step S2 that the effective voltage value of the power grid is not less than the lower limit of the low voltage value, the active current value of the control inverter output is equal to the target active current value and the output reactive current value is equal to the target reactive current value.
  • step S3 when the effective voltage of the grid is less than the low pressure upper limit ⁇ ⁇ , the effective voltage value of the grid is not less than the low pressure value of the lower limit of the duration U u timing and determines the effective voltage value of the grid is equal to a low pressure lower limit u u .
  • the inverter When it is determined that the effective voltage value of the power grid is equal to the lower limit u u of the low voltage value, it is determined whether the duration reaches T1.
  • the value of T1 is as shown in FIG. 1 , which is usually 1 second (1S ).
  • the inverter is controlled to stop working.
  • the grid voltage value is equal to the lower limit of the low voltage value Uli , the duration reaches 1S, and the inverter is removed from the network through a device such as a circuit breaker. Therefore, the photovoltaic power supply part of the photovoltaic grid connection is separated from the power grid.
  • the active current value outputted by the inverter is controlled to be equal to the target active current value and the output reactive current value is equal to the target reactive current value, and the process returns to step S1. That is, if the duration is less than 1 S, the determination and timing operation are repeated from step S1.
  • T2 is as shown in FIG. 1 , which is usually 2S.
  • the crossing time T2 may be 2S; if the duration has reached 2S, the control inverter stops working; if the duration is less than 2S, Then, the active current value of the inverter output is controlled to be equal to the target active current value and the output reactive current value is equal to the target reactive current value, and the process returns to step S1, that is, the determination and timing operation are repeated from step S1.
  • the comparison difference between the total current outputted by the inverter in the low-voltage crossing state and the current outputted in the normal state is less than a preset value.
  • the power output quality is high, but also the voltage sag phenomenon is timed, so that the photovoltaic power supply part of the photovoltaic grid and the power grid of the AC side can be timely Detach and reduce waste.
  • Embodiment 3 is a diagrammatic representation of Embodiment 3
  • the low-voltage traverse control method of the photovoltaic grid-connected inverter further includes collecting a voltage signal, a current signal on the DC side, and collecting a voltage signal and a current signal of the AC side power grid. The steps of so.
  • the active current value of the normal output of the control inverter is equal to the maximum power tracking according to the signal collected according to the step so.
  • the Maximum Power Point Tracking (MPPT) algorithm and the voltage proportional integral (PI) control the normal target current, and the reactive current value that controls the normal output of the inverter is zero. That is, the inverter is controlled to operate normally.
  • MPPT Maximum Power Point Tracking
  • PI voltage proportional integral
  • the control program or controller calculates the normal target voltage value during normal operation of the inverter according to the DC voltage and the DC current signal collected by the step SO through the MPPT algorithm, and passes the deviation signal between the normal target voltage value and the collected DC voltage.
  • the PI of the voltage loop is adjusted to obtain the normal target current value. Since the grid is in normal operation state, no reactive power compensation is needed. Therefore, the power factor at this time is 1, and the active current output from the control inverter is the normal target current value. The reactive current is zero.
  • the solution for solving the target value of the active current value in the normal state of the network is connected by a three-phase alternating current grid and a photovoltaic power station.
  • step 1 the DC side current Idc and the DC side voltage Vdc are input to the inverter control device, and the DC side voltage reference value Vdc* is given by the MPPT algorithm.
  • step 2 the deviation signal between the DC side voltage reference value Vdc* and the DC side voltage Vdc is adjusted via a voltage loop (outer loop) PI to obtain a reference value id* of the current d-axis component (ie, active current), that is, the target Active current value.
  • step 3 the deviation between the d-axis current reference value id* and id (the current i[ia ib ic] from the sampled AC side is obtained by dark) is performed by current loop (inner loop) PI regulation. And the cross decoupling control obtains the d-axis target voltage ud*.
  • step 4 when the grid is in a normal state, the inverter output power factor is 1, so the control reactive current iq* is 0, and also passes through the actual iq (sampling i provided by the acquisition signal of the AC side in step SO)
  • the deviation between [ia ib ic] and the dark transform is performed by current loop PI adjustment and cross decoupling control to obtain the q-axis target voltage uq*.
  • ud*, uq* are vector space pulse width modulated SVPWM (Space Vector Pulse
  • Width Modulation Controls the output PWM control waveform, which is input to the switching device of the DC/AC inverter to control the DC/AC inverter output normal target active current value (ie i: ).
  • e d is the equivalent component of the active voltage (d-axis voltage) obtained by the dark conversion of the grid voltage of the AC side of the acquisition
  • e q is the reactive voltage obtained by the dark conversion of the grid voltage of the AC side of the acquisition ( The equivalent component of the q-axis voltage).
  • an accurate and convenient MPPT algorithm and voltage PI control are preferably controlled, and the cylinder is controlled.
  • the low-voltage traverse control method of the photovoltaic grid-connected inverter of the embodiment further includes: acquiring the target active current value and the target reactive current value in the low-voltage crossing state.
  • n is the preset amplitude of the total output current of the inverter.
  • the value of n can be set according to the actual grid operation needs, usually n is set to 1.1, so when the voltage sag occurs, the amplitude of the current output by the inverter is controlled at plus or minus ten percent relative to the traditional In the low-voltage ride-through control method, the current distortion control is neglected, the current output waveform is good, the amplitude variation is small, and the power output quality is high.
  • the control of the inverter is normally performed by combining the MPPT algorithm and the voltage PI control, and when the voltage sag occurs, the active power is compensated for the reactive power to make the output current.
  • the control method with small waveform distortion adopts two different control modes before and after the voltage sag, so that the total current of the output does not change much, which plays a good supporting role for the power grid, and prevents the passive solution of the photovoltaic power supply part in the power grid.
  • the low-voltage traverse control method of the photovoltaic grid-connected inverter described in this embodiment is applicable to the control of any photovoltaic grid-connected low-voltage traverse, especially for large-scale Photovoltaic grid connection, a network with high penetration rate of photovoltaic power supply.
  • the low-voltage ride-through control device of the photovoltaic grid-connected inverter includes a control unit.
  • the control unit determines whether the effective voltage value of the power grid is less than the upper limit of the low voltage value; when determining that the effective voltage value of the power grid is not less than the upper limit of the low voltage value, the inverter is controlled to operate normally, and when the effective voltage value of the power grid is determined to be less than the upper limit of the low pressure value , to determine whether the effective voltage value of the power grid is less than the lower limit of the low voltage value; when determining that the effective voltage value of the power grid is less than the lower limit of the low voltage value, the control inverter stops working, and when it is determined that the effective voltage value of the power grid is not less than the lower limit of the low voltage value, the control inverse
  • the active current value of the converter output is equal to the target active current value and the output reactive current value is equal to the target reactive current value.
  • the difference between the total current output by the inverter in the low-voltage crossing state and the current outputted in the normal state is less than a preset value.
  • the control of the active current and the reactive current of the inverter is realized when a voltage dip occurs, which not only enables the inverter and the photovoltaic power supply part located on the DC side of the inverter.
  • Part of the large-scale power outages caused by the disengagement of other units and the phenomenon of grid collapse have a good supporting effect on the operation of the grid.
  • control unit may be a value inside the DSP control unit, the MCU control unit, or the unit, or may be an amount input from the outside according to a specific need, or a value calculated by a preset calculation model. .
  • the low-voltage traverse control device of the photovoltaic grid-connected inverter may further include a timing unit.
  • the timing unit is configured to time the duration that the effective voltage value of the power grid is not less than the lower limit of the low voltage value
  • the control unit is configured to determine whether the effective voltage value of the power grid is equal to the low voltage.
  • the lower limit of the value is configured to determine whether the effective voltage value of the power grid is equal to the low voltage.
  • control unit determines whether the effective voltage value of the power grid is equal to the lower limit of the low voltage value. When the judgment duration reaches T1, the control inverter stops working.
  • control unit determines that the effective voltage value of the power grid is not equal to the lower limit of the low voltage value, it is determined whether the duration reaches ⁇ 2. When the judgment duration reaches ⁇ 2, the control inverter stops working.
  • the timing unit Through the setting of the timing unit, it is beneficial to the statistics of the low-voltage crossing time, and the inverter and the photovoltaic power supply part are separated from the grid on the AC side in time to protect the photovoltaic power supply part, and also meet the requirements.
  • Embodiment 6 A schematic diagram of a connection structure; wherein the photovoltaic grid connection comprises a photovoltaic power supply part on a DC side, an inverter that converts a DC of a photovoltaic power supply part into an AC, and a power grid connected to the AC side of the inverter through a filter circuit and Its load.
  • the low-voltage traverse control device of the photovoltaic grid-connected inverter of the embodiment includes a sampling unit, a control unit and a timing unit;
  • the sampling unit includes a DC sampling module for collecting voltage and current signals on the DC side and an AC sampling module for collecting voltage and current signals of the AC side network; wherein, the DC sampling module collects the voltage signal Vpv as shown in FIG.
  • the current signal Ipv the AC sampling module collects the voltage signal and the current signal I of the AC side power grid.
  • the AC side grid described in Figure 4 is a three-phase AC grid, so the AC side voltage samples include three phase voltage signals Ea, Eb, and Ec, and the AC side current samples include three phase current signals Ia, lb, and Ic.
  • the control unit determines whether the effective voltage value of the power grid is less than the upper limit of the low pressure value. When it is judged that the effective voltage value of the power grid is not less than the upper limit of the low voltage value, the control unit controls the normal operation of the inverter.
  • the control unit determines whether the effective voltage value of the power grid is less than the lower limit of the low voltage value, and when the effective voltage value of the power grid is determined to be less than the lower limit of the low voltage value, the control unit controls the inverter When the effective voltage value of the power grid is not less than the lower limit of the low voltage value, the control unit controls the active current value output by the inverter to be equal to the target active current value and the output reactive current value is equal to the target reactive current value.
  • the timing unit counts the duration that the effective value voltage value of the power grid is not less than the lower limit of the low voltage value, and the control unit determines whether the effective voltage value of the power grid is equal to the lower limit of the low voltage value.
  • the control unit determines whether the duration reaches T1, and controls the inverter to stop operating when it is determined that the duration reaches T1.
  • the control unit determines whether the duration reaches T2, and controls the inverter to stop operating when it is determined that the duration reaches T2.
  • the control unit includes a normal control module and a low-voltage traversing state control module, and controls the operation of the inverter through the PWM control waveform.
  • the control unit controls the inverter in various manners, and in this embodiment, A PWM control waveform for controlling the cartridge and realizing the cartridge is preferred. Control.
  • the normal control module controls the normal output current value of the inverter to be equal to the normal target current obtained by the MPPT algorithm and the voltage PI control according to the signal collected by the sampling unit. And the reactive current value that controls the normal output of the inverter is zero.
  • the control signal from the normal control module is shown in the solid arrow from the control unit to the inverter in Figure 4.
  • the control unit further includes a low-voltage traverse state control module for acquiring a target active current value and a target reactive current value in a low-voltage traverse state.
  • Active current target value i d * for the inverter preset normal time grid active current output value i d; reactive current target value i * q is ⁇ (n 2 - 1) X i d, wherein, ⁇
  • the active current value may be a value preset in the internal storage unit of the control device, or may be a value collected by the sampling unit, or may be a value solved by statistical data, and the target reactive current value is according to the need of compensation.
  • the size of ⁇ can be confirmed according to the needs of the power grid and the range allowed by the waveform distortion. Usually, the value of ⁇ is 1.1; preferably, ⁇ is greater than or equal to 0.8 and less than 1.2.
  • the control is divided into normal control and low-voltage traverse control. By adopting two different control methods, the waveform of the output of the inverter and the current output by the inverter under normal state are guaranteed.
  • the control device described in the embodiment of the present disclosure adopts the method of reactive power compensation to ensure that the waveform of the total current output and the amplitude change position of the inverter are within a preset range, so as to achieve stable power grid. Purpose, good effect, and realization of the tube.

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Abstract

一种光伏并网逆变器的低压穿越控制方法及装置。该控制方法包括：判断电网电压值是否小于低压值上限并且是否不大于低压值下限，当判断电网的有效电压值小于低压值上限并且大于低压值下限时，控制逆变器输出的有功电流值等于目标有功电流值且输出的无功电流值等于目标无功电流值，使得逆变器在低压穿越状态下输出的总电流与在常态下输出的电流的比较差值小于预设值。该方法及装置解决了逆变器低压穿越控制时忽略的电流波形及幅度控制而导致的稳定性差等问题，使得电压暂降前后的总电流变化小，从而支撑、稳定电网。

Description

光伏并网逆变器的低压穿越控制方法及装置 技术领域
本公开涉及电力控制领域， 尤其涉及一种光伏并网逆变器控制方法及装 置。 背景技术
光伏并网是指将太阳能电池方阵或光伏电站并入电网实现供电的电力网 络。 低压穿越 ( LVRT: Low Voltage Ride Through )是指在光伏并网电力网络 发生电压暂降时， 直流侧如光伏电站能够保持与交流侧电网的连接， 通过逆 变器将直流侧的直流电压转换成交流侧电网的交流电压， 支撑到电网故障恢 复， 从而穿越电压跌落时间， 以避免引起电网故障扩大化， 提高供电可靠性。 电压暂降是指母线电压有效值大幅快速下降且持续时间极短的突发事件。
当光伏发电站或太阳能电池方阵在电网中供电比重大、 渗透率高时， 若 光伏电站在电压暂降时采取立即从供电网络切除的被动保护方式解列， 将导 致有功出力的大量减少， 供电系统的恢复难， 甚至可能引起其他机组的解列， 导致大规模停电， 扩大故障。 在这种情况下， 低电压穿越能力就是必须的。
在目前的光伏并网逆变器的低电压穿越控制方法及装置中， 忽略了对逆 变器输出电流的控制，导致在电压大幅度跌落时出现电流波动失真状况严重、 输出电能质量受到严重影响的问题， 因此光伏并网逆变器的低电压穿越控制 方法及控制装置均需要进一步优化改进。 发明内容
(一）发明目的
本公开旨在提供一种在电压暂降时光伏并网直流侧输出的电流波动小、 低压穿越能力强、 系统稳定性高、 可靠性高的光伏并网逆变器的低压穿越控 制方法及装置。
(二）技术方案
为达上述目的， 本公开实施例提供了一种光伏并网逆变器的低压穿越控 制方法， 包括以下步骤： 判断电网的有效电压值是否小于低压值上限； 当判 断电网的有效电压值不小于低压值上限时， 控制逆变器正常运行； 以及当判 断电网的有效电压值小于低压值上限时， 判断电网电压值是否小于低压值下 限， 当判断电网的有效电压值小于低压值下限时， 控制逆变器停止工作， 而 当判断电网的有效电压值不小于低压值下限时， 控制逆变器输出的有功电流 值等于目标有功电流值且输出的无功电流值等于目标无功电流值， 其中， 所 述逆变器在低压穿越状态下输出的总电流与在常态下输出的电流的比较差值 小于预设值。
在一个示例中， 所述光伏并网逆变器的低压穿越控制方法还包括： 当判 断电网的有效电压值小于低压值上限时， 对电网的有效电压值不小于低压值 下限的持续时间计时， 并判断电网的有效电压值是否等于低压值下限； 当判 断电网的有效电压值等于低压值下限时，判断持续时间是否达到预设时间 T1 , 当判断持续时间达到预设时间 T1时， 控制逆变器停止工作， 当判断持续时间 未达到预设时间 T1时， 控制逆变器输出的有功电流值等于目标有功电流值且 输出的无功电流值等于目标无功电流值； 以及当判断电网的有效电压值不等 于低压值下限时， 判断持续时间是否达到预设时间 T2, 当判断持续时间达到 预设时间 T2时，控制逆变器停止工作， 当判断持续时间未达到预设时间 T2时, 控制逆变器输出的有功电流值等于目标有功电流值且输出的无功电流值等于 目标无功电巟值。
在一个示例中， 所述光伏并网逆变器的低压穿越控制方法还包括： 采集 直流侧的电压信号、 电流信号以及采集交流侧电网的电压、 电流信号。
其中， 当判断电网的有效电压值不小于低压值上限时， 控制逆变器正常 输出的有功电流值等于根据所采集的信号经由 MPPT算法及电压 PI控制得出 的常态目标电流值并且控制逆变器输出的无功电流值为零。
在一个示例中， 所述光伏并网逆变器的低压穿越控制方法还包括： 在低 压穿越状态下获取目标有功电流值以及目标无功电流值， 所述目标有功电流 值 i*d为预设的电网正常时刻逆变器输出的有功电流值 id； 所述目标无功电流 值 i为 i = (n2 _l) xid , 其中， n为预设的逆变器输出总电流的变化幅度。
此外，本公开实施例还提供了一种光伏并网逆变器的低压穿越控制装置 , 包括控制单元； 所述控制单元判断电网的有效电压值是否小于低压值上限； 当判断电网的有效电压值不小于低压值上限时， 所述控制单元控制逆变器正 常运行； 以及当判断电网的有效电压值小于低压值上限时， 所述控制单元判 断电网电压值是否小于低压值下限， 当判断电网的有效电压值小于低压值下 限时， 所述控制单元控制逆变器停止工作， 而当判断电网的有效电压值不小 于低压值下限时， 所述控制单元控制逆变器输出的有功电流值等于目标有功 电流值且输出的无功电流值等于目标无功电流值， 其中， 所述逆变器在低压 穿越状态下输出的总电流与在常态下输出的电流的比较差值 d、于预设值。
在一个示例中， 所述光伏并网逆变器的低压穿越控制装置还包括计时单 元；
当判断电网的有效电压值小于低压值上限时， 所述计时单元对电网的有 效电压值不小于低压值下限的持续时间计时， 并且所述控制单元判断电网的 有效电压值是否等于低压值下限； 当判断电网的有效电压值等于低压值下限 时， 所述控制单元判断持续时间是否达到预设时间 T1 , 当判断持续时间达到 预设时间 T1时，控制逆变器停止工作， 当判断持续时间未达到预设时间 T1时， 控制逆变器输出的有功电流值等于目标有功电流值且输出的无功电流值等于 目标无功电流值； 以及当判断电网的有效电压值不等于低压值下限时， 所述 控制单元判断持续时间是否达到预设时间 T2 , 当判断持续时间达到预设时间 T2时， 控制逆变器停止工作， 当判断持续时间未达到预设时间 T2时， 控制逆 变器输出的有功电流值等于目标有功电流值且输出的无功电流值等于目标无 功电巟值。
在一个示例中， 所述光伏并网逆变器的低压穿越控制装置还包括采样单 元； 所述采样单元包括用以采集直流侧的电压信号和电流信号的直流采样模 块以及采集交流侧电网的电压信号和电流信号的交流采样模块； 其中， 所述 控制单元包括常态控制模块， 当电网的有效电压值不小于低压值上限时， 所 述常态控制模块控制逆变器正常输出的有功电流值等于根据所述采样单元采 集的信号经由 MPPT算法及电压 PI控制计算得出的常态目标电流并且控制逆 变器正常输出的无功电流值为零。
在一个示例中， 所述控制单元还包括用以在低压穿越状态下获取目标有 功电流值以及目标无功电流值的低压穿越状态控制模块， 所述目标有功电流 值 i*d为预设的电网正常时刻逆变器输出的有功电流值 id； 所述目标无功电流 值 为 i = (n2 -l) xid；其中， n为预设的逆变器输出总电流的变化幅度。
(三）本公开实施例的光伏并网逆变器的低压穿越控制方法及装置的有 益效果： 现电压暂降时， 采用无功电流补偿的方式， 使得逆变器输出的总电流接近常 态时输出的电流， 从而电流波动小且失真小， 从而提高了光伏并网直流侧的 低压穿越能力， 使得电网的稳定性、 可靠性均得到提高， 且防止了因电压暂 降导致的光伏供电部分自动解列而引起的其他机组的解列所造成大规模停
附图说明
图 1为光伏并网逆变器认证检测标准规定的图示； 图 3为本公开实施例的常态下的常态目标有功电流值的求解图示； 以及 的连接结构示意图。 具体实施方式
下面结合说明书附图以及实施例对光伏并网逆变器低压穿越控制方法及 装置做进一步的说明。
实施例一：
下面， 将描述根据本实施例的光伏并网逆变器的低压穿越控制方法。 首先， 在步骤 S1 , 判断电网的有效电压值是否小于低压值上限。 通常， 可以将所述低压值上限选择为额定电压的 0.9倍。
当在步骤 S1中判断电网的有效电压值不小于低压值上限时， 则控制逆变 器正常运行。 若电网的有效电压值为大于或等于低压值上限， 则表示此时的 光伏并网没有出现电压暂降的现象而是处于正常工作状态， 故所述逆变器正 常运行即可。
当在步骤 S1中判断电网的有效电压值小于低压值上限时， 则根据本实施 例的光伏并网逆变器的低压穿越控制方法进入步骤 S2。
在步骤 S2中， 判断电网的有效电压值是否小于低压值下限。 通常， 可以 将所述低压值下限选择为额定电压的 0.2倍。
当在步骤 S2中判断电网的有效电压值小于低压值下限时， 则控制逆变器 停止工作。 通常， 若电网侧的有效电压值过低， 例如低于低压值下限， 则将 逆变器停止工作， 光伏电站从电力网络中解列。 通常使逆变器停止工作的方 法是通过断路器将相应的电路直接断开， 从而逆变器以及光伏电站或太阳能 电池从电力网给中脱离。
当在步骤 S2中判断电网的有效电压值不小于低压值下限时，则控制逆变 器输出的有功电流值等于目标有功电流值且输出的无功电流值等于目标无功 电流值。 目标有功电流值以及无功电流值的取值， 根据不同的光伏电网的网 络参数以及常态下的运行状况的不同而不同。 通过适当地选择目标有功电流 值以及无功电流值， 使得逆变器在低压穿越状态下输出的总电流与在常态下 输出的电流的比较差值 d、于预设值即可。
当电网的有效电压值小于低压值上限且大于或等于低压值下限时， 需要 保持光伏电站或太阳能电池方阵穿越该段低压时间， 在传统的控制方法中， 通常忽视了对低压穿越时间内变压器输出的电流波形以及幅度的保持， 而在 本实施例的光伏并网逆变器的低压穿越控制方法中， 控制逆变器输出有功电 流值以及无功电流值， 在功率低的情况下， 采用无功功率进行补偿， 从而达 到保持在低压穿越时间内逆变器输出电流波形失真小、 幅度变化小， 从而保 证电能质量， 提高光伏并网的稳定性、 可靠性， 防止光伏并网中光伏供电部 分的解列导致大规模停电并扩大故障的问题。
实施例二：
如图 1所示， 光伏并网逆变器认证检测标准《并网光伏发电专用逆变器 技术要求和试验方法》 CGC:2010中规定，对专门适用于大型光伏电站的中高 压型逆变器应具备一定的耐受异常电压的能力，避免在电网电压异常时脱离， 引起电网电源的不稳定， 做出了如下要求；
其中， υΜ为正常运行的低压值上限；
uu为需要耐受的低压值下限；
T1为电压跌落到 uu时需要保持并网的时间；
2为电压跌落到 υΜ时需要保持并网的时间。
Uu、 Tl、 Τ2数值的确定需考虑保护和重合闸动作时间等实际情况， 通常 1^。取0.9倍额定电压， Uu取为 0.2倍额定电压， T1设定为 is, T2设 定为 2S。
根据上述要求， 根据本实施例的光伏并网逆变器的低压穿越控制方法在 实施例一的基础上， 增加了步骤 S3。
将参考图 2来描述根据本实施例的光伏并网逆变器的低压穿越控制方 法。
首先， 在步骤 S1中， 判断电网的有效电压值是否小于低压值上限 UM。 当在步骤 SI中判断电网的有效电压值不小于低压值上限时， 则控制逆变 器正常运行。
当在步骤 S1中判断电网的有效电压值小于低压值上限时， 则根据本实施 例的光伏并网逆变器的低压穿越控制方法进入步骤 S2。
在步骤 S2中， 判断电网的有效电压值是否小于低压值下限 Uu。
当在步骤 S2中判断电网的有效电压值小于低压值下限时， 则控制逆变器 停止工作。
当在步骤 S2中判断电网的有效电压值不小于低压值下限时， 则控制逆变 器输出的有功电流值等于目标有功电流值且输出的无功电流值等于目标无功 电流值。
在步骤 S3中， 当电网的有效电压值小于低压值上限 υΜ时， 对电网的有 效电压值不小于低压值下限 Uu的持续时间计时并判断电网的有效电压值是 否等于低压值下限 uu。
在判断电网的有效电压值等于低压值下限 uu时， 则判断持续时间是否 达到 T1 , 本实施例中 T1取值如图 1所示， 通常为 1秒（1S )。 在判断持续时间 达到 T1时， 则控制逆变器停止工作， 在本实施例中如果电网电压值等于低压 值下限 Uli的持续时间达到 1S , 则通过断路器等设备将逆变器从网络中切除, 从而使光伏并网的光伏供电部分与电网脱离。 在判断持续时间未达到 T1时， 则控制逆变器输出的有功电流值等于目标有功电流值且输出的无功电流值等 于目标无功电流值， 并且返回步骤 Sl。 即， 如果持续时间不到 1S, 则从步骤 S1重复判定与计时操作。
在判断电网的有效电压值不等于低压值下限 Uu时， 则判断持续时间是 否达到 T2, 本实施例中 T2取值如图 1所示， 通常为 2S。 即， 如果电网的有效 电压值低于低压值上限且高于低压值下限， 则穿越时间 T2可以为 2S; 如果持 续时间已经达到 2S, 则控制逆变器停止工作； 如果持续的时间小于 2S, 则控 制逆变器输出的有功电流值等于目标有功电流值且输出的无功电流值等于目 标无功电流值， 并且返回步骤 S1 , 即从步骤 S1重复判定与计时操作。 在根据本实施例的光伏并网逆变器的低压穿越控制方法中， 所述逆变器 在低压穿越状态下输出的总电流与在常态下输出的电流的比较差值小于预设 值。
在本实施例中， 不仅实现了在低压穿越时保证电流失真小、 电能输出质 量高， 而且还对电压暂降现象进行计时， 从而能及时的将光伏并网的光伏供 电部分与交流侧的电网进行脱离， 减少浪费现象。
实施例三：
本实施例在上述两实施例其中之一的基础上， 所述光伏并网逆变器的低 压穿越控制方法还包括采集直流侧的电压信号、 电流信号以及采集交流侧电 网的电压信号、 电流信号的步骤 so。
在所述步骤 SI中电网的有效电压值不小于低压值上限时，控制逆变器正 常输出的有功电流值等于根据步骤 so采集的信号经由最大功率跟踪
( Maximum Power Point Tracking - MPPT )算法及电压比例积分（ PI )控制得 出的常态目标电流， 并且控制逆变器正常输出的无功电流值为零。 即， 控制 逆变器正常运行。
控制程序或控制器通过 MPPT算法 根据步骤 SO采集的直流电压、 直流 电流信号计算出逆变器正常工作时的常态目标电压值， 将该常态目标电压值 与采集的直流电压之间的偏差信号通过电压环的 PI调节，得到常态目标电流 值， 由于此时电网处于正常运行状态不需要进行无功补偿， 故此时的功率因 素为 1 , 控制逆变器输出的有功电流值为常态目标电流值， 无功电流则为零。 网中常态下有功电流值目标值的求解实施方案， 该光伏并网由三相交流电网 与光伏电站连接而成。
在步骤 1中，向逆变器控制装置输入直流侧电流 Idc以及直流侧电压 Vdc, 通过 MPPT算法计算给出直流侧电压参考值 Vdc*。
在步骤 2中，将直流侧电压参考值 Vdc*与直流侧电压 Vdc之间的偏差信 号经由电压环（外环） PI调节得到电流 d轴分量（即有功电流）的参考值 id* , 即目标有功电流值。
在步骤 3中， d轴电流参考值 id*与 id (由采样得到的交流侧的电流 i[ia ib ic]经过 dark (克拉克）变换得到）之间的偏差进行电流环（内环） PI调节 以及交叉解耦控制得到 d轴目标电压 ud*。 在步骤 4中， 在电网处于常态时， 逆变器输出功率因数为 1 , 故控制无 功电流 iq*为 0, 同样经过与实际 iq (由步骤 SO中的交流侧的采集信号提供 的采样 i[ia ib ic] , 经过 dark变换得到）之间的偏差进行电流环 PI调节以及 交叉解耦控制得到 q轴目标电压 uq*。
在步骤 5中， ud*、 uq*经矢量空间脉宽调制 SVPWM ( Space Vector Pulse
Width Modulation )控制输出 PWM控制波形， 输入到 DC/AC逆变器的开关 器件， 控制 DC/AC逆变器输出常态目标有功电流值（即 i： )。 其中， ed为采 集的交流侧的电网电压经 dark变换后得到的有功电压（d轴电压） 的等效分 量； eq为采集的交流侧的电网电压经 dark变换后得到的无功电压（ q轴电压） 的等效分量。
电网正常时， 逆变器的输出的控制方式有多种， 在本实施例中优选了控 制精确、 方便的 MPPT算法以及电压 PI控制， 且控制筒便。
作为本实施例的进一步的改进， 本实施例光伏并网逆变器的低压穿越控 制方法还包括： 在低压穿越状态下， 获取目标有功电流值以及目标无功电流 值。
所述目标有功电流值 i:为预设的电网正常时刻的逆变器输出的有功电流 值 id ; 故无功功率电流的目标无功电流值满足 id 2 +rq 2 = (nid )2 从而所述目标无 功电流值 i*q为
Figure imgf000010_0001
；
其中， n为预设的逆变器输出总电流的变化幅度。 n的取值可以根据实际 电网运行的需要来设定， 通常 n设定为 1.1 , 这样当出现电压暂降时， 逆变器 输出的电流的幅度控制在正负百分之十相对于传统的低压穿越控制方法中， 忽略电流失真的控制， 电流输出波形好， 幅度变化小， 电能输出质量高。
在本实施例中，对逆变器的控制正常是采用的 MPPT算法与电压 PI控制 相结合的方式进行， 而出现电压暂降时， 采用则是以无功功率补偿有功功率 以使输出电流的波形失真小的控制方式， 在电压暂降的前后采用两种不同的 控制方式， 使得输出的总电流变化不大， 对电网起到了很好的支撑作用， 防 止了电网中的光伏供电部分被动式解列， 导致加剧了电网的故障， 致使电网 完全瘫痪的问题， 本实施例所述的光伏并网逆变器的低压穿越控制方法， 适 用于任何光伏并网低压穿越的控制， 尤其适用于大型的光伏并网， 光伏供电 部分渗透率高的网络。
实施例五： 根据本实施例的光伏并网逆变器的低压穿越控制装置包括控制单元。 所述控制单元判断电网的有效电压值是否小于低压值上限； 在判断电网 的有效电压值不小于低压值上限时， 控制逆变器正常运行， 而在判断电网的 有效电压值小于低压值上限时，判断电网的有效电压值是否小于低压值下限； 在判断电网的有效电压值小于低压值下限时， 控制逆变器停止工作， 而在判 断电网的有效电压值不小于低压值下限时， 控制逆变器输出的有功电流值等 于目标有功电流值且输出的无功电流值等于目标无功电流值。
其中， 所述逆变器在低压穿越状态下输出的总电流与常态下输出的电流 的比较差值小于预设值。
在本实施例中， 通过控制单元的设置， 在出现电压突降时实现对逆变器 输出有功电流以及无功电流的控制， 不仅使逆变器以及位于逆变器直流侧的 光伏供电部分能顺利的实现低压穿越， 同时保证逆变器输出的电流失真小、 幅度变化小， 以使输出的电能质量好， 从而提高了电网的稳定性、 可靠性， 防止电网系统电压短暂的跌落造成光伏供电部分以及其他机组的解列所形成 的大面积停电、 电网瘫痪的现象， 对电网的运行有 ^艮好的支撑作用。
在本实施例中， 所述控制单元可以为 DSP控制单元、 MCU控制单元或 单元内部的值， 也可以是根据具体的需要从外部输入的量， 或是通过预设的 计算模型计算出的值。
优选地， 根据本实施例的光伏并网逆变器的低压穿越控制装置还可以包 括计时单元。
当电网的有效电压值小于低压值上限时， 所述计时单元用以对电网的有 效电压值不小于低压值下限的持续时间计时， 并且所述控制单元用以判断电 网的有效电压值是否等于低压值下限。
在所述控制单元判断电网的有效电压值等于低压值下限时， 则所述控制 单元判断持续时间是否达到 Tl。 在判断持续时间达到 T1时， 控制逆变器停止 工作。
在所述控制单元判断电网的有效电压值不等于低压值下限时， 判断持续 时间是否达到 Τ2。 在判断持续时间达到 Τ2时， 控制逆变器停止工作。
通过计时单元的设置， 有利于对低压穿越时间的统计， 并使逆变器以及 光伏供电部分及时地与交流侧的电网脱离， 保护光伏供电部分， 同时也满足 了行业对光伏并网中逆变器的规范。
实施例六： 的连接结构示意图； 其中所述光伏并网包括直流侧的光伏供电部分、 将光伏 供电部分的直流转化成交流的逆变器、 通过滤波电路连接在逆变器交流侧的 电网及其负载。
本实施例光伏并网逆变器的低压穿越控制装置， 包括采样单元、 控制单 元以及计时单元；
所述采样单元包括用以采集直流侧的电压和电流信号的直流采样模块以 及采集交流侧电网的电压和电流信号的交流采样模块； 其中， 直流采样模块 采集如图 4中所示的电压信号 Vpv、 电流信号 Ipv, 交流采样模块采集交流侧 电网的电压信号 、 电流信号 I。 图 4中所述的交流侧电网是三相交流电网， 故交流侧电压采样值包括三相电压信号 Ea、 Eb以及 Ec, 交流侧电流采样值 包括三相电流信号 Ia、 lb以及 Ic。
所述控制单元判断电网的有效电压值是否小于低压值上限。 当判断电网 的有效电压值不小于低压值上限时， 所述控制单元控制逆变器正常运行。 当 判断电网的有效电压值小于低压值上限时， 所述控制单元判断电网的有效电 压值是否小于低压值下限， 当判断电网的有效电压值小于低压值下限时， 所 述控制单元控制逆变器停止工作； 而当判断电网的有效电压值不小于低压值 下限时， 所述控制单元控制逆变器输出的有功电流值等于目标有功电流值且 输出的无功电流值等于目标无功电流值。
当电网的有效电压值小于低压值上限时， 所述计时单元对电网的有效值 电压值不小于低压值下限的持续时间计时， 并且所述控制单元判断电网的有 效电压值是否等于低压值下限。 在所述控制单元判断电网的有效电压值等于 低压值下限时， 所述控制单元判断持续时间是否达到 T1 , 并且在判断持续时 间达到 T1时控制逆变器停止工作。 在所述控制单元判断电网的有效电压值不 等于低压值下限时， 所述控制单元判断持续时间是否达到 T2, 并且在判断持 续时间达到 T2时控制逆变器停止工作。
所述控制单元包括常态控制模块以及低压穿越状态控制模块，通过 PWM 控制波形控制逆变器的工作， 在具体的实施过程中， 控制单元控制逆变器的 方法有多种， 而在本实施例中优选一种控制筒单、 实现筒便的 PWM控制波形 控制。
当电网的有效电压值不小于低压值上限时， 所述常态控制模块控制逆变 器正常输出的有功电流值等于根据所述采样单元采集的信号经由 MPPT算法 及电压 PI控制得出的常态目标电流， 并且控制逆变器正常输出的无功电流值 为零。常态控制模块发出的控制信号如图 4中从控制单元至逆变器的实线箭头 所示。
所述控制单元还包括用以在低压穿越状态下获取目标有功电流值以及目 标无功电流值的低压穿越状态控制模块。
目标有功电流值 id*为预设的电网正常时刻的逆变器输出的有功电流值 id； 目标无功电流值 i*q为 = ^(n2 - 1) X id , 其中， η为预设的逆变器输出总电流的 变化幅度；低压穿越状态控制模块发出的控制信号如图 4中从控制单元至逆变 器的虚线箭头所示。
所述有功电流值可以是预设在控制装置内部存储单元的值， 也可以是通 过采样单元采集的值， 还可以是通过统计数据求解的值， 而目标无功电流值 则是根据补偿的需要进行求解的值。 η的大小可以根据电网的需要以及波形失 真允许的范围进行确认， 通常 η的取值为 1.1; 优选的为 η大于等于 0.8, 小于等 于 1.2。 的控制划分为常态下的控制以及低压穿越状态下的控制， 通过采用两种不同 的控制方式保证了在低压穿越状态下逆变器输出的电流与在常态下逆变器输 出的电流的波形和幅度不会相差太大， 从而提供低压穿越状态下电网的稳定 性和可靠性。 尤其是在低压穿越状态下， 本公开实施例中所述的控制装置采 用无功补偿的方式保证逆变器输出的总电流的波形和幅度变化位置在预设的 范围内， 以达到稳定电网的目的， 效果佳、 实现筒便。
以上实施方式仅用于说明本公开， 而并非对本公开的限制， 有关技术领 域的普通技术人员， 在不脱离本公开的精神和范围的情况下， 还可以做出各 种变化和变型， 因此所有等同的技术方案也属于本公开的范畴， 本公开的专 利保护范围应由权利要求限定。

Claims

权 利 要 求 书
1、 一种光伏并网逆变器的低压穿越控制方法， 包括以下步骤：
判断电网的有效电压值是否小于低压值上限；
当判断电网的有效电压值不小于低压值上限时， 控制逆变器正常运行； 以及
当判断电网的有效电压值小于低压值上限时， 判断电网电压值是否小于 低压值下限， 当判断电网的有效电压值小于低压值下限时， 控制逆变器停止 工作， 而当判断电网的有效电压值不小于低压值下限时， 控制逆变器输出的 有功电流值等于目标有功电流值且输出的无功电流值等于目标无功电流值， 其中， 所述逆变器在低压穿越状态下输出的总电流与在常态下输出的电流的 比较差值小于预设值。
2、根据权利要求 1所述的光伏并网逆变器的低压穿越控制方法， 还包括： 当判断电网的有效电压值小于低压值上限时， 对电网的有效电压值不小 于低压值下限的持续时间计时， 并判断电网的有效电压值是否等于低压值下 限；
当判断电网的有效电压值等于低压值下限时， 判断持续时间是否达到预 设时间 T1 , 当判断持续时间达到预设时间 T1时， 控制逆变器停止工作， 当判 断持续时间未达到预设时间 T1时， 控制逆变器输出的有功电流值等于目标有 功电流值且输出的无功电流值等于目标无功电流值； 以及
当判断电网的有效电压值不等于低压值下限时， 判断持续时间是否达到 预设时间 T2, 当判断持续时间达到预设时间 T2时， 控制逆变器停止工作， 当 判断持续时间未达到预设时间 T2时， 控制逆变器输出的有功电流值等于目标 有功电流值且输出的无功电流值等于目标无功电流值。
3、根据权利要求 1或 2所述的光伏并网逆变器的低压穿越控制方法， 还 包括采集直流侧的电压信号、 电流信号以及采集交流侧电网的电压信号、 电 流信号，
其中， 当判断电网的有效电压值不小于低压值上限时， 控制逆变器正常 输出的有功电流值等于根据所采集的信号经由 MPPT算法及电压 PI控制得出 的常态目标电流值并且控制逆变器输出的无功电流值为零。
4、根据权利要求 1或 2所述的光伏并网逆变器的低压穿越控制方法， 还 包括： 在低压穿越状态下， 获取目标有功电流值以及目标无功电流值， 其中， 所述目标有功电流值 i:为预设的电网正常时刻的逆变器输出的有 功电巟值 id；
所述目标无功电流值 1；为 = (n2 -1) χ id；
其中， n为预设的逆变器输出总电流的变化幅度。
5、 一种光伏并网逆变器的低压穿越控制装置， 包括控制单元； 所述控制单元判断电网的有效电压值是否小于低压值上限；
当判断电网的有效电压值不小于低压值上限时， 所述控制单元控制逆变 器正常运行； 以及
当判断电网的有效电压值小于低压值上限时， 所述控制单元判断电网电 压值是否小于低压值下限， 当判断电网的有效电压值小于低压值下限时， 所 述控制单元控制逆变器停止工作， 而当判断电网的有效电压值不小于低压值 下限时， 所述控制单元控制逆变器输出的有功电流值等于目标有功电流值且 输出的无功电流值等于目标无功电流值， 其中， 所述逆变器在低压穿越状态 下输出的总电流与在常态下输出的电流的比较差值小于预设值。
6、 根据权利要求 5所述的光伏并网逆变器的低压穿越控制装置， 还包括 计时单元；
当判断电网的有效电压值小于低压值上限时， 所述计时单元对电网的有 效电压值不小于低压值下限的持续时间计时， 并且所述控制单元判断电网的 有效电压值是否等于低压值下限，
当判断电网的有效电压值等于低压值下限时， 所述控制单元判断持续时 间是否达到预设时间 T1 , 当判断持续时间达到预设时间 T1时， 控制逆变器停 止工作， 当判断持续时间未达到预设时间 T1时， 控制逆变器输出的有功电流 值等于目标有功电流值且输出的无功电流值等于目标无功电流值； 以及
当判断电网的有效电压值不等于低压值下限时， 所述控制单元判断持续 时间是否达到预设时间 T2, 当判断持续时间达到预设时间 T2时， 控制逆变器 停止工作， 当判断持续时间未达到预设时间 T2时， 控制逆变器输出的有功电 流值等于目标有功电流值且输出的无功电流值等于目标无功电流值。
7、根据权利要求 5或 6所述的光伏并网逆变器的低压穿越控制装置，还包 括采样单元；
所述采样单元包括用以采集直流侧的电压信号和电流信号的直流采样模 块以及采集交流侧电网的电压信号和电流信号的交流采样模块； 其中， 所述控制单元包括常态控制模块， 当电网的有效电压值不小于低 压值上限时， 所述常态控制模块控制逆变器正常输出的有功电流值等于根据 所述采样单元采集的信号经由 MPPT算法及电压 PI控制计算得出的常态目标 电流并且控制逆变器正常输出的无功电流值为零。
8、根据权利要求 5或 6所述的光伏并网逆变器的低压穿越控制装置，还包 括用以在低压穿越状态下获取目标有功电流值以及目标无功电流值的低压穿 越状态控制模块，
所述目标有功电流值 i:为预设的电网正常时刻逆变器输出的有功电流值 所述目标无功电流值 1；为 = (n2 -1) χ id；
其中， n为预设的逆变器输出总电流的变化幅度。
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