WO2017025022A1 - 一种供电系统及供电方法 - Google Patents

一种供电系统及供电方法 Download PDF

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Publication number
WO2017025022A1
WO2017025022A1 PCT/CN2016/094228 CN2016094228W WO2017025022A1 WO 2017025022 A1 WO2017025022 A1 WO 2017025022A1 CN 2016094228 W CN2016094228 W CN 2016094228W WO 2017025022 A1 WO2017025022 A1 WO 2017025022A1
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WIPO (PCT)
Prior art keywords
voltage
grid
low voltage
unit
inverter
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PCT/CN2016/094228
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English (en)
French (fr)
Inventor
辛凯
郭海滨
高拥兵
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华为技术有限公司
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Priority to EP16834646.8A priority Critical patent/EP3324509A4/en
Publication of WO2017025022A1 publication Critical patent/WO2017025022A1/zh
Priority to US15/893,125 priority patent/US20180166883A1/en

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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
    • 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
    • H02J3/001—Methods to deal with contingencies, e.g. abnormalities, faults or failures
    • H02J3/0012—Contingency detection
    • 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
    • H02J3/001—Methods to deal with contingencies, e.g. abnormalities, faults or failures
    • H02J3/00125—Transmission line or load transient problems, e.g. overvoltage, resonance or self-excitation of inductive loads
    • 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
    • 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
    • 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
    • H02M7/539—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 with automatic control of output wave form or frequency
    • H02M7/5395—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 with automatic control of output wave form or frequency by pulse-width modulation
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S40/00—Components or accessories in combination with PV modules, not provided for in groups H02S10/00 - H02S30/00
    • H02S40/30—Electrical components
    • H02S40/32—Electrical components comprising DC/AC inverter means associated with the PV module itself, e.g. AC modules
    • 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

Definitions

  • the invention relates to the field of electric power, and in particular to a multi-machine grid-connected power converter low voltage ride through control system and method.
  • Low Voltage Ride Through refers to a PV power station in a certain voltage drop range and time interval when a power system accident or disturbance, such as a short circuit in the power system or a sudden change in load power, causes a voltage drop at the grid point of the PV power plant.
  • the invention provides a low voltage ride through control method for a multi-machine grid-connected power converter, which can overcome the instability of the power converter caused by the easy triggering bus voltage protection or device damage existing in the prior art, and requires a large bus bar.
  • the problem of increased system cost caused by capacitance capacitance can effectively reduce the capacitance of the bus capacitance and enhance the stability of low voltage ride through.
  • the first aspect provides a multi-machine grid-connected power converter low voltage ride-through control system, including: a photovoltaic array and an inverter, the inverter including a DC/DC conversion unit and an output end of the DC/DC conversion unit Connected DC/AC inverter unit, the DC/DC conversion unit input end is connected to the PV array output end, and the inverter is connected to the power grid at a grid connection point, and the grid connection point is a photovoltaic power station and a power grid Connection point, characterized in that
  • the inverter further includes a low voltage traversing detecting unit and a low voltage traversing control unit;
  • the low voltage traversing detecting unit is configured to detect a magnitude of a grid voltage of the grid-connected point to determine whether to trigger a low voltage traversal;
  • the low voltage traversing control unit is connected to the low voltage traverse detecting unit, and is configured to reduce an input voltage of the DC/DC converting unit in a case where the low voltage traversing detecting unit determines to trigger the low voltage traversing And reducing the output voltage of the photovoltaic array such that the output voltage of the photovoltaic array is less than the voltage tracked by the maximum power point during steady state operation of the inverter.
  • the low voltage traversing control unit is further configured to reduce the DC/DC conversion in a case where the low voltage traversal detecting unit determines to trigger the low voltage traversal
  • the output voltage of the unit to reduce the bus voltage caused by the instantaneous rise of the grid voltage during recovery of the low voltage crossing Raising a value to protect the busbar device or to avoid triggering busbar overvoltage protection
  • the busbar is for connecting the DC/DC converter unit to the DC/AC inverter unit, the busbar device being connected in series on the busbar Device.
  • the low voltage traversal control unit is further configured to reduce the DC/ in a case where the low voltage traversal detecting unit determines to trigger the low voltage traversal
  • the output voltage of the DC conversion unit is specifically used to:
  • the input voltage of the DC/DC conversion unit is lowered, thereby reducing the output voltage of the DC/DC conversion unit.
  • the low voltage traversal control unit is further configured to reduce an output of the DC/DC conversion unit a voltage to reduce an increase in a bus voltage caused by an instantaneous rise in the grid voltage during recovery to protect the busbar device or to avoid triggering busbar overvoltage protection, the busbar being used to connect the DC/DC converter unit with The DC/AC inverter unit is specifically used for:
  • the low voltage traversing detection unit is configured to be used for the The magnitude of the grid voltage is tested to detect whether low voltage ride through is triggered, specifically for:
  • the amplitude of the grid voltage is detected, and when the amplitude changes exceed a preset interval, low voltage crossing is triggered.
  • the second aspect provides a low voltage ride through control method for a multi-machine grid-connected power converter, which is characterized by comprising:
  • connection point is the connection point between the photovoltaic power station and the power grid;
  • the output voltage of the DC/DC conversion unit is decreased to reduce the instantaneous rise of the grid voltage during the recovery of the low voltage crossing in the case of determining that the low voltage ride through is triggered.
  • a height-induced increase in the bus voltage to protect the busbar device or to avoid triggering overvoltage protection, the busbar being used to connect the DC/DC converter unit to the DC/AC inverter unit, the busbar device being A device connected in series on the bus.
  • the reducing an output voltage of the DC/DC conversion unit includes:
  • the input voltage of the DC/DC conversion unit is lowered, thereby reducing the output voltage of the DC/DC conversion unit.
  • the reducing the output voltage of the DC/DC conversion unit to reduce The low voltage crossing increases the value of the bus voltage caused by the instantaneous rise of the grid voltage to protect the busbar device or to avoid triggering busbar overvoltage protection
  • the busbar is used to connect the DC/DC converter unit with the DC
  • the /AC inverter unit the busbar device is a device connected in series on the busbar, and specifically includes:
  • the detecting a magnitude of a grid voltage of the grid-connected point is detected, To determine Whether to trigger low voltage traversal, including:
  • the amplitude of the grid voltage of the grid-connected point is detected, and when the amplitude changes exceed a preset interval, low voltage crossing is triggered.
  • the invention provides a multi-machine grid-connected power converter low voltage ride-through control system, which reduces the output voltage and output power of the photovoltaic array by reducing the input voltage of the DC/DC converter unit, through the photovoltaic array
  • the output voltage and the input and output voltage of the inverter are adjusted to enable the inverter to achieve low voltage ride through and balance the power between the photovoltaic array, the inverter, and the grid interconnection point.
  • the power converter instability problem caused by the easy triggering bus voltage protection or busbar device damage in the prior art, and the system cost increase caused by the need for a large bus capacitance value, the method can effectively reduce the bus capacitance Value and enhance the stability of low voltage ride through.
  • FIG. 1 is a structural diagram of a low voltage ride through control system for a multi-machine grid-connected power converter according to an embodiment of the present invention
  • Figure 2 is a schematic diagram of the requirements for low voltage ride through in the Chinese grid-connected standard
  • FIG. 3 is a schematic diagram showing changes in current, voltage, and power of a photovoltaic array when the photovoltaic array is low voltage traversing according to the present invention
  • FIG. 4 is a circuit diagram of a low voltage ride through control system for a multi-machine grid-connected power converter according to an embodiment of the present invention
  • FIG. 5 is a control diagram of a low voltage ride through control system for a multi-machine grid-connected power converter according to an embodiment of the present invention
  • FIG. 6 is a flowchart of a low voltage ride through control method for a multi-machine grid-connected power converter according to an embodiment of the present invention
  • FIG. 7 is a flowchart of another low-voltage ride-through control method for a multi-machine grid-connected power converter according to an embodiment of the present invention.
  • a structural diagram of a low voltage ride through control system for a multi-machine grid-connected power converter includes:
  • the photovoltaic array 11 and the inverter 12, the inverter 12 includes a DC/DC conversion unit 13 and a DC/AC inverter unit 14 connected to the output of the DC/DC conversion unit 13, the inverter 12
  • the DC/DC conversion unit 13 is connected to the output end of the photovoltaic array 11, and the inverter 12 is connected to the power grid at a grid connection point, and the grid connection point is a connection point between the photovoltaic power station and the power grid.
  • the grid-connected point refers to a high-voltage side busbar or node of a boosting station for a photovoltaic power station having a boosting station, and an output summary point of a photovoltaic power station for a photovoltaic power station without a boosting station.
  • the inverter 12 further includes a low voltage traversing detecting unit 15 and a low voltage traversing control unit 16;
  • the low voltage traversing detecting unit 15 is configured to detect a magnitude of a grid voltage of the grid-connected point to determine whether to trigger a low voltage traversal; specifically, a sine wave converted according to an instantaneous value of an external grid voltage
  • the magnitude of the grid voltage is used to determine whether to trigger low voltage traversal; or, the amplitude or phase value of the latest grid voltage stored in the inverter chip can be directly called to determine.
  • the low voltage traversing control unit 16 is connected to the low voltage traverse detecting unit 15 and is configured to reduce the DC/DC converting unit in a case where the low voltage traversing detecting unit determines to trigger the low voltage traversing.
  • a voltage is input to reduce the output voltage of the photovoltaic array 11 such that the output voltage of the photovoltaic array 11 is less than the maximum power point of the inverter during steady state operation tracking the voltage of the MPPT.
  • the maximum power point tracking refers to detecting the power generation voltage of the solar panel of the photovoltaic array in real time, and tracking the highest voltage current value, so that the solar panel of the photovoltaic array operates at the maximum output power.
  • the method is to reduce the output voltage of the photovoltaic array 11 in order to reduce the output power, so that the output power is smaller than the output power when the inverter is in steady state operation.
  • the reducing the output voltage of the photovoltaic array 11 includes calling a control module of the DC/DC conversion unit by the digital signal processing chip DSP, thereby reducing an input voltage of the DC/DC conversion unit, thereby reducing the photovoltaic column
  • the output voltage of the array, the DSP integrates devices such as a processor and a memory.
  • the DC/DC conversion unit includes a BOOST circuit for boosting a DC voltage input to the DC/DC converter unit. Take the zero voltage crossing, that is, the voltage amplitude of the three-phase grid drops to 0%.
  • the output power of the inverter is 0kW due to the grid voltage being 0V.
  • the power of the PV side will be from steady state operation.
  • the Pmax is reduced to approximately 0 kW, causing the inverter input voltage to rise from Vmp to near Voc, as shown in Figure 3, which is a schematic diagram of PV array power and voltage variation at low voltage ride through.
  • the output power of the photovoltaic array is the output power PMAX of the steady-state operating point shown in FIG.
  • the output voltage of the photovoltaic array is raised from the voltage value Vmp corresponding to the output power Pmax point to the voltage value Voc, and the grid voltage approaches 0, at this time, the output power of the photovoltaic array will be reduced from Pmax in steady state operation to nearly 0 kW, so that the inverter input voltage is raised from Vmp to near the voltage value Voc, in which case the The output power of the photovoltaic array simultaneously increases the output voltage of the photovoltaic array.
  • the output voltage of the photovoltaic array is lowered by the low voltage traversing control module, so that the output voltage of the photovoltaic array is less than the maximum power of the inverter during steady state operation.
  • the point-tracked voltage Vmp reduces the output power of the photovoltaic array.
  • a multi-machine grid-connected power converter low voltage ride-through control system provided by the embodiment provides a low voltage ride through the inverter by adjusting the output voltage of the photovoltaic array and the input and output voltage of the inverter. Moreover, it can overcome the problem of power converter instability caused by easy triggering bus voltage protection or device damage existing in the prior art, and the problem of increasing system cost caused by a large bus capacitance value, which can effectively reduce the bus bar. Capacitance capacitance and enhance the stability of low voltage ride through.
  • the low voltage traversing control unit 16 is further configured to reduce an output voltage of the DC/DC converting unit 13 in a situation where the low voltage traversing detecting unit determines to trigger the low voltage traversing to reduce the Determining an increase in the bus voltage caused by an instantaneous rise in the grid voltage during recovery of the low voltage to protect the busbar device or to avoid triggering overvoltage protection, the busbar being used to connect the DC/DC converter unit to the DC/ An AC inverter unit, the busbar device being a device connected in series on the busbar.
  • the low voltage control unit invokes a control module of the DC/AC inverter unit to reduce the DC/ A control module of the input voltage of the AC inverter unit to reduce the increase in the output voltage of the DC/DC, thereby controlling the rise of the bus voltage for connecting the DC/DC converter unit and the DC/AC inverter unit.
  • the low voltage traversing control unit is further configured to reduce an output voltage of the DC/DC conversion unit to reduce an increase in a bus voltage caused by an instantaneous rise of a grid voltage during recovery of the low voltage ride through.
  • the busbar is used for connecting the DC/DC conversion unit and the DC/AC inverter unit, specifically for: reducing the DC/DC conversion unit The voltage is input to reduce the output voltage of the DC/DC converter unit.
  • the low voltage traversing control unit is further configured to reduce an output voltage of the DC/DC conversion unit to reduce an increase in a bus voltage caused by an instantaneous rise of a grid voltage during recovery of the low voltage ride through.
  • the busbar is used for connecting the DC/DC conversion unit and the DC/AC inverter unit, specifically for:
  • the low voltage traversing detecting unit is configured to detect a magnitude of a voltage of a grid connection point of the power grid to detect whether a low voltage traversing is triggered, and specifically: detecting a magnitude of a grid voltage, Low voltage crossing is triggered when the amplitude changes exceed a preset interval, or when the amplitude and phase changes exceed a predetermined interval.
  • Figure 2 is a schematic diagram of the requirements for low voltage ride through in the Chinese grid-connected standard
  • the vertical axis is a grid voltage standard value axis, and the grid voltage standard value is a current actual value of the grid voltage/rated grid voltage value; and is used to identify a drop of the grid voltage when the low voltage crossing occurs;
  • the horizontal axis is a time axis, which identifies the time that the inverter needs to maintain a normal grid connection when the grid voltage drops.
  • FIG. 3 is a schematic diagram showing changes in current, voltage, and power of a photovoltaic array at low voltage crossing
  • the output power of the photovoltaic array is the output power PMAX of the steady-state operating point shown in FIG.
  • the output voltage of the photovoltaic array is raised from the voltage value Vmp corresponding to the output power Pmax point to the voltage value Voc, and the grid voltage approaches 0, at this time, the output power of the photovoltaic array will be reduced from Pmax in steady state operation to nearly 0 kW, so that the inverter input voltage is raised from Vmp to near the voltage value Voc, in which case the The output power of the photovoltaic array simultaneously increases the output voltage of the photovoltaic array.
  • the output voltage of the photovoltaic array is lowered by a low voltage ride through control module such that the output voltage of the photovoltaic array is less than the maximum power point of the inverter during steady state operation.
  • the tracked voltage Vmp reduces the output power of the photovoltaic array.
  • FIG. 4 is a circuit diagram of a low voltage ride through control system for a multi-machine grid-connected power converter according to an embodiment of the present invention, including:
  • the inverter comprising a DC/DC conversion unit and a DC/AC inverter unit, the DC/DC conversion unit being connected to the output of the photovoltaic array, the inverter being at a grid connection point Connected to the grid.
  • the DC/DC conversion unit includes a capacitor C pv , a switch tube T, and an inductor L.
  • the BUS is a bus line connecting a DC/DC conversion unit and a DC/AC inverter unit.
  • a busbar device can be connected to the busbar, and the busbar device can be a capacitor.
  • the inverter further includes a low voltage traversing detecting unit and a low voltage traversing control unit, and the low voltage traversing detecting unit and the low voltage traversing control unit store and operate in the inverter chip, and on the circuit topology diagram Not marked.
  • the low voltage traversing detecting unit is configured to detect a magnitude or a phase of a grid voltage of the grid-connected point to determine whether to trigger a low voltage traversal;
  • the low voltage traversing control unit is connected to the low voltage traversing detecting unit, and is configured to reduce an output voltage of the photovoltaic array in a case where the low voltage traverse detecting unit determines to trigger the low voltage traversing, so that The output voltage of the photovoltaic array is less than the voltage tracked by the maximum power point when the inverter is in steady state operation; the low voltage traversing control unit is further configured to reduce the output voltage of the DC/DC conversion unit to reduce the Determining an increase in the bus voltage caused by an instantaneous rise in the grid voltage during recovery of the low voltage to protect the busbar device or to avoid triggering overvoltage protection, the busbar being used to connect the DC/DC converter unit to the DC/ An AC inverter unit, the busbar device being a device connected in series on the busbar.
  • the above-mentioned control performed by the low voltage traversing detecting unit and the low voltage traversing control unit does not change the working principle of each device of the circuit when the original grid voltage is normal, but only controls the output voltage of the photovoltaic array and the input of the inverter. Voltage and output voltage for low voltage ride through and protection of bus and busbar containers from normal operation.
  • Figure 4 shows the T-type three-level inverter topology. By controlling the turn-on and turn-off of the switch tube, the energy conversion from the solar cell DC to the grid AC is realized. It is a very promising topology in the solar photovoltaic system. .
  • the invention is applicable to a single inverter system or a multi-inverter parallel system; applicable to a three-phase T-type, I-type three-level inverter, and is also applicable to a three-phase T-type, I-type multi-level inverter Suitable for parallel systems with different architectures such as modular and tower cranes.
  • a control block diagram of a low voltage ride through control system for a multi-machine grid-connected power converter includes:
  • the three-phase AC information such as the grid voltage (e a , e b , e c ) and the grid-connected current (i a , i b , i c ) is first obtained by analog-to-digital conversion AD sampling.
  • the coordinate transformation and the grid phase lock phase obtain the grid voltage phase angle ⁇ and the components i d and i q of the grid-connected current in the dq coordinate axis, which are used as the active and reactive current feedback values in the grid-connected current control to participate in the grid-connected control. .
  • the low voltage ride through includes an LVRT detection unit and an LVRT control unit.
  • the LVRT detection unit performs real-time calculation on the magnitude and phase state of the grid voltage obtained by the AD sampling, and enters the fast detection through the positive and negative sequence separation algorithm to determine whether Trigger low voltage ride through. Specifically, judging according to the amplitude or phase value of the corresponding grid voltage converted by the sine wave of the instantaneous value of the external grid voltage to determine whether to trigger the low voltage traversal; or, the inverter may be directly invoked
  • the magnitude or phase value of the latest grid voltage stored in the chip is used to determine whether to trigger low voltage ride through.
  • the low voltage crossing is triggered; or when the amplitude is less than a value specified by the standard, and The low voltage crossing is triggered when the phase asymmetry exceeds a certain preset interval.
  • the amplitude changes; when the two phases fall, the amplitude and phase all change.
  • the digital signal processing chip DSP a control module of the DC/DC conversion unit to reduce an input voltage of the DC/DC conversion unit to reduce an output voltage of the photovoltaic array, thereby reducing the photovoltaic array
  • the output power is such that the output power is less than the output power of the inverter during steady state operation.
  • the DSP integrates devices such as a processor and a memory.
  • the low voltage control unit invokes the control module of the DC/AC inverter unit to reduce the DC/AC inverter unit
  • the input voltage is used to reduce the increase in the output voltage of the DC/DC, thereby controlling the rise of the bus voltage for connecting the DC/DC converter unit to the DC/AC inverter unit.
  • the LVRT control unit performs the calculation of the active reactive current command value according to the current grid voltage drop depth by the detection result of the LVRT detecting unit, and controls the working state of the inverter by controlling the switching time of the switch tube, thereby achieving low voltage crossing. Control of active and reactive currents in the process.
  • FIG. 6 is a flowchart of a low voltage ride through control method for a multi-machine grid-connected power converter according to an embodiment of the present invention, where the method includes:
  • Step S601 detecting a magnitude of a grid voltage of the grid-connected point to determine whether to trigger a low-voltage ride-through, where the grid-connecting point is a connection point between the photovoltaic power station and the grid.
  • the grid-connected point refers to a high-voltage side busbar or node of a boosting station for a photovoltaic power station having a boosting station, and an output summary point of a photovoltaic power station for a photovoltaic power station without a boosting station.
  • Detecting a magnitude of a grid voltage of the grid-connected point to determine whether to trigger a low voltage ride-through including: determining a magnitude of a corresponding grid voltage converted from a sine wave of an instantaneous value of the external grid voltage, to Decide whether to trigger low voltage traversal; alternatively, you can directly call the amplitude or phase value of the latest grid voltage stored in the inverter chip to determine whether to trigger low voltage traversal. Triggering low voltage crossing when the amplitude is less than the value specified by the standard; or triggering low voltage when the amplitude is less than the value specified by the standard, and when the asymmetry of the phase exceeds a certain preset interval Crossing. In the case of a three-phase symmetrical drop or a single relative drop, the amplitude changes; when the two phases fall, the amplitude and phase all change.
  • Step S602 in the case of determining that the low voltage ride through is triggered, reducing the output voltage of the photovoltaic array by reducing the input voltage of the DC/DCDC/DC conversion unit, so that the output voltage of the photovoltaic array is smaller than the inverter.
  • the voltage at which the maximum power point is tracked during steady state operation; specifically, the maximum power point tracking that is, The power generation voltage of the solar panel of the photovoltaic array is detected in real time, and the highest voltage current value is tracked, so that the solar panel of the photovoltaic array operates at the maximum output power.
  • the method is to reduce the output voltage of the photovoltaic array 11 in order to reduce the output power, so that the output power is smaller than the output power when the inverter is in steady state operation.
  • the reducing the output voltage of the photovoltaic array 11 includes calling a control module of the DC/DC conversion unit by the digital signal processing chip DSP, thereby reducing an input voltage of the DC/DC conversion unit, thereby reducing the photovoltaic column
  • the output voltage of the array, the DSP integrates devices such as a processor and a memory.
  • the DC/DC conversion unit includes a BOOST circuit for boosting a DC voltage input to the DC/DC converter unit.
  • the low voltage ride through control method for a multi-machine grid-connected power converter provided by the embodiment provides a low voltage ride through the inverter by adjusting the output voltage of the photovoltaic array and the input and output voltage of the inverter.
  • the power converter instability problem caused by the easy triggering bus voltage protection or device damage existing in the prior art can be overcome, and the method can effectively reduce the bus capacitance value and enhance the stability of the low voltage ride through.
  • step S603 the output voltage of the DC/DC conversion unit is decreased to reduce an increase value of a bus voltage caused by an instantaneous rise of the grid voltage during the recovery of the low voltage to protect the bus device or to avoid triggering.
  • Busbar overvoltage protection the busbar is used to connect the DC/DC conversion unit and the DC/AC inverter unit, and the busbar device is a device connected in series on the busbar, and specifically includes:
  • the busbar is for connecting the DC/DC converter unit to the DC/AC inverter unit, the busbar device being a device connected in series on the busbar.
  • step S604 the output voltage of the DC/DC conversion unit is decreased to reduce an increase value of a bus voltage caused by an instantaneous rise of the grid voltage during the recovery of the low voltage to protect the bus device or avoid triggering.
  • Busbar overvoltage protection the busbar is used to connect the DC/DC conversion unit and the DC/AC inverter unit, and the busbar device is a device connected in series on the busbar, and specifically includes:
  • step S605 the detecting the amplitude of the voltage of the grid-connected point of the power grid to determine whether to trigger the low-voltage traversal comprises: detecting the amplitude of the voltage of the grid-connected point of the power grid, where the amplitude is Low voltage crossing is triggered when the change exceeds the preset interval, or when the amplitude and phase changes exceed a preset interval.
  • FIG. 7 is a flowchart of another low-voltage ride-through control method for a multi-machine grid-connected power converter according to an embodiment of the present invention, where the method includes:
  • Step S701 detecting a magnitude of a grid voltage of the grid-connected point to determine whether to trigger a low-voltage ride-through, where the grid-connected point is a high-voltage side busbar or node of the photovoltaic power station booster station, or is the photovoltaic power station Output summary points.
  • the grid-connected point refers to a high-voltage side busbar or node of a boosting station for a photovoltaic power station having a boosting station, and an output summary point of a photovoltaic power station for a photovoltaic power station without a boosting station.
  • Detecting a magnitude of a grid voltage of the grid-connected point to determine whether to trigger a low voltage ride-through including: determining a magnitude of a corresponding grid voltage converted from a sine wave of an instantaneous value of the external grid voltage, to Decide whether to trigger low voltage traversal; alternatively, you can directly call the amplitude or phase value of the latest grid voltage stored in the inverter chip to determine whether to trigger low voltage traversal. Triggering low voltage crossing when the amplitude is less than the value specified by the standard; or triggering low voltage when the amplitude is less than the value specified by the standard, and when the asymmetry of the phase exceeds a certain preset interval Crossing. In the case of a three-phase symmetrical drop or a single relative drop, the amplitude changes; when the two phases fall, the amplitude and phase all change.
  • Step 702 in the case of determining that the low voltage ride through is triggered, reducing an output voltage of the photovoltaic array by reducing an input voltage of the DC/DCDC/DC conversion unit, so that an output voltage of the photovoltaic array is smaller than the inverter
  • the voltage of the maximum power point tracking during steady state operation specifically, the maximum power point tracking refers to real-time detection of the power generation voltage of the solar panel of the photovoltaic array, and tracking the highest voltage current value, so that the solar energy of the photovoltaic array
  • the board operates at maximum output power.
  • the method is to reduce the output voltage of the photovoltaic array 11 in order to reduce the output power, so that the output power is smaller than the output power when the inverter is in steady state operation.
  • the module is configured to reduce the input voltage of the DC/DC converter unit, thereby reducing the output voltage of the photovoltaic array, and the DSP integrates devices such as a processor and a memory.
  • the DC/DC conversion unit includes a BOOST circuit for boosting a DC voltage input to the DC/DC converter unit.
  • Step 703 reducing an output voltage of the DC/DC conversion unit to reduce an increase in a bus voltage caused by an instantaneous rise in the grid voltage during the recovery of the low voltage to protect the bus device or avoid triggering overvoltage protection.
  • the bus bar is used to connect the DC/DC conversion unit and the DC/AC inverter unit, and the bus bar device is a device connected in series on the bus bar.
  • the low voltage control unit invokes a control module of the DC/AC inverter unit, a control module for reducing an input voltage of the DC/AC inverter unit to reduce an increase in an output voltage of the DC/DCDC/DC conversion unit, thereby controlling connection between the DC/DC conversion unit and The bus voltage of the DC/AC inverter unit increases.
  • the low voltage ride through control method for a multi-machine grid-connected power converter provided by the embodiment provides a low voltage ride through the inverter by adjusting the output voltage of the inverter and can overcome the prior art
  • the power converter instability problem caused by easy to trigger bus voltage protection or device damage, and the increase in system cost caused by large bus capacitance value, the method can effectively reduce the bus capacitance value and enhance the low Stability of voltage ride through.
  • the output voltage of the DC/DC conversion unit is decreased to reduce an increase value of a bus voltage caused by an instantaneous rise of a grid voltage during the recovery of the low voltage to protect the bus device or avoid the trigger bus Overvoltage protection
  • the busbar is used to connect the DC/DC conversion unit and the DC/AC inverter unit
  • the busbar device is a device connected in series on the busbar, and specifically includes:
  • the busbar is for connecting the DC/DC converter unit to the DC/AC inverter unit, the busbar device being a device connected in series on the busbar.
  • step S705 the output voltage of the DC/DC conversion unit is decreased to reduce an increase value of a bus voltage caused by an instantaneous rise of a grid voltage during the recovery of the low voltage to protect the bus device or to avoid triggering.
  • Busbar overvoltage protection the busbar is used to connect the DC/DC conversion unit and the DC/AC inverter unit, and the busbar device is a device connected in series on the busbar, and specifically includes:
  • step S706 the amplitude of the voltage of the grid-connected point of the power grid is detected to determine whether to trigger the low voltage traversal, and specifically includes: detecting a magnitude of a voltage of a grid-connected point of the power grid, where the amplitude is The low voltage ride through is triggered when the change exceeds the preset interval, or when the change in the amplitude and phase exceeds the preset interval.
  • the low voltage ride through control method for a multi-machine grid-connected power converter provided by the embodiment provides a low voltage ride through the inverter by adjusting the output voltage of the inverter and can overcome the prior art
  • the power converter instability problem caused by easy to trigger bus voltage protection or device damage, and the increase in system cost caused by large bus capacitance value, the method can effectively reduce the bus capacitance value and enhance the low Stability of voltage ride through.
  • the present invention can be implemented by various embodiments, and the embodiments of the present invention can be implemented by specific software and hardware components, and those skilled in the art can think that various software or hardware combinations can also be applied to implement the embodiments of the present invention.
  • the above specific operations performed by hardware can also be implemented by software.

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Abstract

一种多机并网功率变换器低电压穿越控制系统和方法，包括光伏阵列（11）以及逆变器（12），逆变器包括DC/DC变换单元（13）和与DC/DC变换单元输出端相连的DC/AC逆变单元（14），DC/DC变换单元输入端与光伏阵列输出端相连，逆变器在并网点与电网相连，逆变器还包括低电压穿越检测单元（15）与低电压穿越控制单元（16）；低电压穿越检测单元用于对并网点的电网电压的幅值进行检测，以确定是否触发低电压穿越；低电压穿越控制单元在确定触发低电压穿越的情形下，用于降低DC/DC变换单元的输入电压，以降低光伏阵列的输出电压，以使光伏阵列的输出电压小于逆变器稳态运行时最大功率点跟踪的电压。该系统和方法能够有效降低母线电容值且增强低电压穿越的稳定性。

Description

一种供电系统及供电方法 技术领域
本发明涉及电力领域，尤其涉及一种多机并网功率变换器低电压穿越控制系统及方法。
背景技术
随着光伏发电的推广，建立起越来越多的大规模光伏电站，由于现场环境等各方面因素使得对光伏电站的并网特性要求越来越高。作为保障电网运行的一项重要指标，光伏逆变器的低电压穿越能力越来越被重视，各国并网标准中对低电压穿越均有严格的要求。低电压穿越(LVRT)：是指当电力系统事故或扰动，如发生电力系统短路或、负载功率的突变等引起光伏电站并网点的电压跌落时，在一定电压跌落范围和时间间隔内，光伏电站能够保证不脱网连续运行，避免电网故障的扩大化，同时光伏并网逆变器有正常的电压工作范围，电压太低时逆变器会关机，因此标准中提出低电压穿越，要求逆变器在低电压下继续工作一段时间，需要能够发出一定的有功和无功功率，以支撑电网恢复，从而穿越这个低电压时间区域。说明书附图中图2为中国并网标准中对低电压穿越的要求。当低电压穿越发生时，母线电压升高到光伏电池板的开路电压Voc，低穿恢复冲击即电网电压突然提升导致有功电流或无功电流突变的时候易触发母线电压保护，导致电容电压太高导致开启保护或器件损坏。
而且，在低电压穿越过程中，在较高的母线电压下，要求功率变换器器发出较 大的无功电流，需要较大的母线电容容值，以保证低穿稳态能够正常运行，较大的母线电容增加了系统成本。
发明内容
本发明提供一种多机并网功率变换器低电压穿越控制方法，能够克服现有技术中存在的易触发母线电压保护或器件损坏的导致的功率变换器不稳定问题，以及需要较大的母线电容容值导致的系统成本增加的问题，该方法能够有效降低母线电容容值且增强低电压穿越的稳定性。
第一方面提供一种多机并网功率变换器低电压穿越控制系统，包括：光伏阵列以及逆变器，所述逆变器包括DC/DC变换单元和与所述DC/DC变换单元输出端相连的DC/AC逆变单元，所述DC/DC变换单元输入端与所述光伏阵列输出端相连，所述逆变器在并网点与电网相连，所述并网点为光伏发电站与电网的连接点，其特征在于，
所述逆变器，还包括低电压穿越检测单元与低电压穿越控制单元；
所述低电压穿越检测单元，用于对所述并网点的电网电压的幅值进行检测，以确定是否触发低电压穿越；
所述低电压穿越控制单元，与所述低电压穿越检测单元相连,在所述低电压穿越检测单元确定触发所述低电压穿越的情形下，用于降低所述DC/DC变换单元的输入电压，以降低所述光伏阵列的输出电压，以使所述光伏阵列的输出电压小于所述逆变器稳态运行时最大功率点跟踪的电压。
在第一方面第一种可能的实现方式中，所述低电压穿越控制单元，在所述低电压穿越检测单元确定触发所述低电压穿越的情形下，还用于降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间升高引起的母线电压的 升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元，所述母线器件为串联在所述母线上的器件。
结合第一方面，在第二种可能的实现方式中，所述低电压穿越控制单元，在所述低电压穿越检测单元确定触发所述低电压穿越的情形下，还用于降低所述DC/DC变换单元的输出电压，具体用于：
降低所述DC/DC变换单元的输入电压，从而降低所述DC/DC变换单元的输出电压。
结合第一方面第一种或第二种可能的实现方式，在第三种可能的实现方式中，所述低电压穿越控制单元，在所述还用于降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间提升引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元方面，具体用于：
根据所述逆变器稳态运行时最大功率点跟踪的电压以及电网电压信息设置所述母线正常运行时的电压区间，将升高后的所述母线电压控制在所述母线正常运行时的电压区间。
结合第一方面至第一方面第三种可能的实现方式中任一种可能的实现方式，在第四种可能的实现方式中，所述低电压穿越检测单元，用于对所述并网点的电网电压的幅值进行检测，以检测是否触发低电压穿越方面，具体用于:
对电网电压的幅值进行检测，在所述幅值的变化超过预设区间时，触发低电压穿越。
第二方面提供一种多机并网功率变换器低电压穿越控制方法，其特征在于，包括：
对电网并网点的电压的幅值或相位进行检测，以确定是否触发低电压穿越，所 述并网点为光伏发电站与电网的连接点；
在确定触发所述低电压穿越的情形下，降低DC/DC变换单元的输入电压，以降低光伏阵列的输出电压，以使所述光伏阵列的输出电压小于所述逆变器稳态运行时最大功率点跟踪的电压。
在第二方面第一种可能的实现方式中，在确定触发所述低电压穿越的情形下，降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间升高引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元，所述母线器件为串联在所述母线上的器件。
结合第二方面，第二种可能的实现方式中，所述降低所述DC/DC变换单元的输出电压，具体包括：
降低所述DC/DC变换单元的输入电压，从而降低所述DC/DC变换单元的输出电压。
结合第二方面至第二方面第二种可能的实现方式中任一种可能的实现方式，在第三种可能的实现方式中，所述降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间升高引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元，所述母线器件为串联在所述母线上的器件，具体包括：
根据所述逆变器稳态运行时最大功率点跟踪的电压以及电网电压信息设置所述母线正常运行时的电压区间，将所述母线电压控制在所述母线正常运行时的电压区间。
结合第二方面至第二方面第三种可能的实现方式中任一种可能的实现方式，在第四种可能的实现方式中，所述对所述并网点的电网电压的幅值进行检测，以确定 是否触发低电压穿越，具体包括：
对并网点的电网电压的幅值进行检测，在所述幅值的变化超过预设区间时，触发低电压穿越。
本发明提供的一种多机并网功率变换器低电压穿越控制系统，通过降低所述DC/DC变换单元的输入电压，降低了所述光伏阵列的输出电压及输出功率，通过对光伏阵列的输出电压和逆变器的输入输出电压进行调节，在将所述光伏阵列、逆变器及电网并网点之间的功率平衡了的同时，使所述逆变器能够实现低电压穿越且能够克服现有技术中存在的易触发母线电压保护或母线器件损坏的导致的功率变换器不稳定问题，以及需要较大的母线电容容值导致的系统成本增加的问题，该方法能够有效降低母线电容容值且增强低电压穿越的稳定性。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作一简单地介绍，显而易见地，下面描述中的附图是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动性的前提下，还可以根据这些附图获得其他的附图。
图1为本发明实施例提供的一种多机并网功率变换器低电压穿越控制系统的结构图；
图2为中国并网标准中对低电压穿越的要求的示意图；
图3为本发明光伏阵列为低电压穿越时光伏阵列电流、电压及功率变化的示意图；
图4为本发明实施例提供的一种多机并网功率变换器低电压穿越控制系统的电路图；
图5为本发明实施例提供的一种多机并网功率变换器低电压穿越控制系统的控制图；
图6为本发明实施例提供的一种多机并网功率变换器低电压穿越控制方法的流程图；
图7为本发明实施例提供的另一种多机并网功率变换器低电压穿越控制方法的流程图；
具体实施方式
为使本发明实施例的目的、技术方案和优点更加清楚，下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
如图1所示，本发明实施例提供的一种多机并网功率变换器低电压穿越控制系统的结构图，包括：
光伏阵列11以及逆变器12，所述逆变器12包括DC/DC变换单元13和与所述DC/DC变换单元13输出端相连的DC/AC逆变单元14，所述逆变器12的所述DC/DC变换单元13与所述光伏阵列11输出端相连，所述逆变器12在并网点与电网相连，所述并网点为光伏发电站与电网的连接点。具体地，所述并网点对于有升压站的光伏发电站，指升压站高压侧母线或节点，对于无升压站的光伏发电站，指光伏发电站的输出汇总点。
所述逆变器12，还包括低电压穿越检测单元15与低电压穿越控制单元16；
所述低电压穿越检测单元15，用于对所述并网点的电网电压的幅值进行检测，以确定是否触发低电压穿越；具体地，根据外部电网电压的瞬时值的正弦波转化出的相应的电网电压的幅值值来进行判断，以决定是否触发低电压穿越；或者，也可以直接调用所述逆变器芯片中存储的最新的电网电压的幅值或相位值来进行判断， 以决定是否触发低电压穿越。当所述幅值小于标准规定的值的时候，触发低电压穿越；或者在当所述幅值小于标准规定的值的时候，且当相位的不对称超过一定预设区间的时候，触发低电压穿越。在三相对称跌落或在单相对地跌落的情形下，幅值发生变化；在两相相间跌落的时候，幅值与相位全都发生变化。
所述低电压穿越控制单元16，与所述低电压穿越检测单元15相连，在所述低电压穿越检测单元确定触发所述低电压穿越的情形下，用于降低所述DC/DC变换单元的输入电压，以降低所述光伏阵列11的输出电压，以使所述光伏阵列11的输出电压小于所述逆变器稳态运行时最大功率点跟踪MPPT的电压。具体地，所述最大功率点跟踪，即是指实时侦测光伏阵列的太阳能板的发电电压，并追踪最高电压电流值，使所述光伏阵列的太阳能板以最大的输出功率进行工作。所述以降低所述光伏列阵11的输出电压，是为了降低输出功率，使输出功率小于逆变器稳态工作时的输出功率。所述降低所述光伏列阵11的输出电压，包括由数字信号处理芯片DSP调用DC/DC变换单元的控制模块，从而降低所述DC/DC变换单元的输入电压，从而降低了所述光伏列阵的输出电压，所述DSP集成了处理器和存储器等器件。所述DC/DC变换单元，包括BOOST电路，用于升高输入所述DC/DC变换单元的直流电压。以零电压穿越即三相电网电压幅值跌落至0％为例，零电压穿越发生时，由于电网电压为0V，导致逆变器输出功率为0kW，此时PV侧的功率将由稳态运行时的Pmax降低到接近0kW，使得逆变器输入电压由Vmp升高至接近Voc，如图3所示，为低电压穿越时光伏阵列功率及电压变化示意图。在电网电压正常时，光伏阵列的输出功率为图3中所示的稳态运行点的输出功率PMAX。低电压穿越发生时，根据所述光伏阵列的功率与电压的关系的特性，光伏阵列的输出电压由输出功率Pmax点对应的电压值Vmp升高至接近电压值Voc，此时电网电压趋近于0，此时所述光伏阵列的输出功率将由稳态运行时的Pmax降低到接近0kW，使得逆变器输入电压由Vmp升高至接近电压值Voc，在这种情形下，只是降低了所述光伏阵列的输出功率，同时升高了所述光伏阵列的输出电压。在本实施例中，当低电压穿越发生时，通过低电压穿越控制模块降低所述光伏列阵的输出电压，以使所述光伏阵列的输出电压小于所述逆变器稳态运行时最大功率点跟踪的电压Vmp，同时降低了所述光伏阵列的输出功率。
有益效果:本实施例提供的一种多机并网功率变换器低电压穿越控制系统，通过对光伏阵列的输出电压和逆变器的输入输出电压进行调节，使逆变器能够实现低电压穿越且能够克服现有技术中存在的易触发母线电压保护或器件损坏的导致的功率变换器不稳定问题，以及需要较大的母线电容容值导致的系统成本增加的问题，该方法能够有效降低母线电容容值且增强低电压穿越的稳定性。
进一步地，所述低电压穿越控制单元16，在所述低电压穿越检测单元确定触发所述低电压穿越的情形下，还用于降低所述DC/DC变换单元13的输出电压，以降低所述低电压穿越恢复时电网电压瞬间升高引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元，所述母线器件为串联在所述母线上的器件。具体地，电网电压突然升高引起DC/AC逆变单元与DC/DC变换单元的电压升高时，所述低电压控制单元调用DC/AC逆变单元的控制模块，以降低所述DC/AC逆变单元的的输入电压的控制模块，以降低DC/DC的输出电压的升高幅度，从而控制用于连接DC/DC变换单元与DC/AC逆变单元的母线电压升高。
进一步地，所述低电压穿越控制单元，在所述还用于降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间提升引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元方面，具体用于：降低所述DC/DC变换单元的输入电压，从而降低所述DC/DC变换单元的输出电压。
进一步地，所述低电压穿越控制单元，在所述还用于降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间提升引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元方面，具体用于：
根据所述逆变器稳态运行时最大功率点跟踪的电压以及电网电压信息设置所述母线正常运行时的电压区间，将升高后的所述母线电压控制在所述母线正常运行时的电压区间。
进一步地，所述低电压穿越检测单元，用于对所述电网的并网点的电压的幅值进行检测，以检测是否触发低电压穿越方面，具体用于:对电网电压的幅值进行检测，在所述幅值变化超过预设区间时，或在所述幅值与相位的变化均超过预设区间时，触发低电压穿越。
图2为中国并网标准中对低电压穿越的要求的示意图；
所述纵轴为电网电压标玄值轴，所述电网电压标玄值为电网电压当前实际值/额定电网电压值；用于标识低电压穿越发生时电网电压的跌落情况；
所述横轴为时间轴，标识电网电压跌落时逆变器需要维持正常并网的时间。
图3为低电压穿越时光伏阵列电流、电压及功率变化的示意图；
在电网电压正常时，光伏阵列的输出功率为图3中所示的稳态运行点的输出功率PMAX。低电压穿越发生时，根据所述光伏阵列的功率与电压的关系的特性，光伏阵列的输出电压由输出功率Pmax点对应的电压值Vmp升高至接近电压值Voc，此时电网电压趋近于0，此时所述光伏阵列的输出功率将由稳态运行时的Pmax降低到接近0kW，使得逆变器输入电压由Vmp升高至接近电压值Voc，在这种情形下，只是降低了所述光伏阵列的输出功率，同时升高了所述光伏阵列的输出电压。
在本发明中，当低电压穿越发生时，通过低电压穿越控制模块降低所述光伏列阵的输出电压，以使所述光伏阵列的输出电压小于所述逆变器稳态运行时最大功率点跟踪的电压Vmp，同时降低了所述光伏阵列的输出功率。
图4为本发明实施例提供的一种多机并网功率变换器低电压穿越控制系统的电路图，包括：
光伏阵列以及逆变器，所述逆变器包括DC/DC变换单元和DC/AC逆变单元，所述DC/DC变换单元与所述光伏阵列输出端相连，所述逆变器在并网点与电网相连。所述DC/DC变换单元包括电容Cpv、开关管T及电感L。所述BUS为母线，连接DC/DC变换单元和DC/AC逆变单元。母线上可以连接母线器件，所述母线器件可以为电容。所述逆变器，还包括低电压穿越检测单元与低电压穿越控制单元，所述低电压穿越检测单元与低电压穿越控制单元存储并运行于逆变器芯片内，在此电路拓扑图上并未标示。
所述低电压穿越检测单元，用于对所述并网点的电网电压的幅值或相位进行检测，以确定是否触发低电压穿越；
所述低电压穿越控制单元，与所述低电压穿越检测单元相连,在所述低电压穿越检测单元确定触发所述低电压穿越的情形下，用于降低所述光伏阵列的输出电压，以使所述光伏阵列的输出电压小于所述逆变器稳态运行时最大功率点跟踪的电压；所述低电压穿越控制单元，还用于降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间升高引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元，所述母线器件为串联在所述母线上的器件。
所述低电压穿越检测单元与低电压穿越控制单元进行的上述控制，并未改变原有电网电压正常时此电路的各个器件的工作原理，只是通过控制光伏阵列的输出电压及逆变器的输入电压与输出电压来实现低电压穿越，并保护母线及母线容器正常工作。
图4为T型三电平逆变器拓扑，通过控制其开关管的开通、关断，实现从太阳能电池DC到电网AC的能量转换，是在太阳能光伏发电系统中非常有应用前景的拓扑结构。
本发明适用于单逆变器系统或多逆变器并机系统；适用于三相T型、I型三电平逆变器，还适用于三相T型、I型多电平逆变器；适用于模块化、塔式机等不同的架构形式的并机系统。
如图5所示，本发明实施例提供的一种多机并网功率变换器低电压穿越控制系统的控制框图，包括：
在逆变器并网控制中，首先通过模数转换AD采样获取电网电压(ea、eb、ec)、并网电流(ia、ib、ic)等三相交流信息，通过坐标变换和电网相位锁相获取电网电压相位角γ和并网电流在dq坐标轴下的分量id和iq，以此作为并网电流控制中的有功、无功电流反馈值参与并网控制。
低电压穿越(LVRT)包含LVRT检测单元和LVRT控制单元，LVRT检测单元实现对AD采样所获取的电网电压幅值和相位状态进行实时运算，通过正负序分离算法后进入快速检测，以判断是否触发低电压穿越。具体地，根据外部电网电压的瞬时值的正弦波转化出的相应的电网电压的幅值或相位值来进行判断，以决定是否触发所述低电压穿越；或者，也可以直接调用所述逆变器芯片中存储的最新的电网电压的幅值或相位值来进行判断，以决定是否触发低电压穿越。当所述幅值小于标准规定的值的时候，或者当相位的不对称超过一定预设区间的时候，触发所述低电压穿越；或者在当所述幅值小于标准规定的值的时候，且当相位的不对称超过一定预设区间的时候，触发所述低电压穿越。在三相对称跌落或在单相对地跌落的情形下，幅值发生变化；在两相相间跌落的时候，幅值与相位全都发生变化。
在发生低电压穿越时，在电网的输入功率降低，光伏列阵11的输出功率相对较高，导致逆变器电压升高，连接DC/DC变换单元与DC/AC逆变单元的母线电压升高。由数字信号处理芯片DSP调用所述DC/DC变换单元的控制模块，降低所述DC/DC变换单元的输入电压，以降低所述光伏列阵的输出电压，从而降低了所述光伏列阵的 输出功率，使所述输出功率小于逆变器稳态工作时的输出功率。所述DSP集成了处理器和存储器等器件。电网电压恢复时，电压突然升高，光伏阵列处于低电压穿越时的功率输出状态，此时所述光伏阵列的输出功率较低，电网侧功率较高，功率不匹配，引起逆变器电压升高，母线电容充电，因此在电网电压恢复前的低电压穿越的情形下，所述低电压控制单元调用所述DC/AC逆变单元的控制模块，以降低所述DC/AC逆变单元的的输入电压，以降低所述DC/DC的输出电压的升高幅度，从而控制用于连接所述DC/DC变换单元与DC/AC逆变单元的母线电压升高。具体地，LVRT控制单元通过LVRT检测单元的检测结果，根据当前电网电压跌落深度进行有功无功电流指令值计算，通过控制开关管的开关时间以控制逆变器的工作状态，从而实现低电压穿越过程中对有功、无功电流的控制。
图6为本发明实施例提供的一种多机并网功率变换器低电压穿越控制方法的流程图，所述方法包括：
步骤S601，对所述并网点的电网电压的幅值进行检测，以确定是否触发低电压穿越，所述并网点为光伏发电站与所述电网的连接点。具体地，所述并网点对于有升压站的光伏发电站，指升压站高压侧母线或节点，对于无升压站的光伏发电站，指光伏发电站的输出汇总点。对所述并网点的电网电压的幅值进行检测，以确定是否触发低电压穿越，包括：根据外部电网电压的瞬时值的正弦波转化出的相应的电网电压的幅值值来进行判断，以决定是否触发低电压穿越；或者，也可以直接调用所述逆变器芯片中存储的最新的电网电压的幅值或相位值来进行判断，以决定是否触发低电压穿越。当所述幅值小于标准规定的值的时候，触发低电压穿越；或者在当所述幅值小于标准规定的值的时候，且当相位的不对称超过一定预设区间的时候，触发低电压穿越。在三相对称跌落或在单相对地跌落的情形下，幅值发生变化；在两相相间跌落的时候，幅值与相位全都发生变化。
步骤S602，在确定触发所述低电压穿越的情形下，通过降低DC/DCDC/DC变换单元的输入电压以降低光伏阵列的输出电压，以使所述光伏阵列的输出电压小于所述逆变器稳态运行时最大功率点跟踪的电压；具体地，所述最大功率点跟踪，即是指 实时侦测光伏阵列的太阳能板的发电电压，并追踪最高电压电流值，使所述光伏阵列的太阳能板以最大的输出功率进行工作。所述以降低所述光伏列阵11的输出电压，是为了降低输出功率，使输出功率小于逆变器稳态工作时的输出功率。所述降低所述光伏列阵11的输出电压，包括由数字信号处理芯片DSP调用DC/DC变换单元的控制模块，从而降低所述DC/DC变换单元的输入电压，从而降低了所述光伏列阵的输出电压，所述DSP集成了处理器和存储器等器件。所述DC/DC变换单元，包括BOOST电路，用于升高输入所述DC/DC变换单元的直流电压。
有益效果:本实施例提供的一种多机并网功率变换器低电压穿越控制方法，通过对光伏阵列的输出电压和逆变器的输入输出电压进行调节，使逆变器能够实现低电压穿越且能够克服现有技术中存在的易触发母线电压保护或器件损坏的导致的功率变换器不稳定问题，该方法能够有效降低母线电容容值且增强低电压穿越的稳定性。
进一步地,步骤S603，所述降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间升高引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元，所述母线器件为串联在所述母线上的器件，具体包括：
降低所述DC/DC变换单元的输入电压，从而降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间升高引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元，所述母线器件为串联在所述母线上的器件。
进一步地，步骤S604，所述降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间升高引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元，所述母线器件为串联在所述母线上的器件，具体包括：
根据所述逆变器稳态运行时最大功率点跟踪的电压以及电网电压信息设置所述母线正常运行时的电压区间，将升高后的所述母线电压控制在所述母线正常运行时 的电压区间。
进一步地，步骤S605，所述对电网的并网点的电压的幅值进行检测，以确定是否触发低电压穿越，具体包括：对电网的并网点的电压的幅值进行检测，在所述幅值的变化超过预设区间时，或所述幅值与相位的变化超过预设区间时，触发低电压穿越。
图7为本发明实施例提供的另一种多机并网功率变换器低电压穿越控制方法的流程图，所述方法包括：
步骤S701，对所述并网点的电网电压的幅值进行检测，以确定是否触发低电压穿越，所述并网点为光伏发电站升压站高压侧母线或节点，或为所述光伏发电站的输出汇总点。具体地，所述并网点对于有升压站的光伏发电站，指升压站高压侧母线或节点，对于无升压站的光伏发电站，指光伏发电站的输出汇总点。对所述并网点的电网电压的幅值进行检测，以确定是否触发低电压穿越，包括：根据外部电网电压的瞬时值的正弦波转化出的相应的电网电压的幅值值来进行判断，以决定是否触发低电压穿越；或者，也可以直接调用所述逆变器芯片中存储的最新的电网电压的幅值或相位值来进行判断，以决定是否触发低电压穿越。当所述幅值小于标准规定的值的时候，触发低电压穿越；或者在当所述幅值小于标准规定的值的时候，且当相位的不对称超过一定预设区间的时候，触发低电压穿越。在三相对称跌落或在单相对地跌落的情形下，幅值发生变化；在两相相间跌落的时候，幅值与相位全都发生变化。
步骤702，在确定触发所述低电压穿越的情形下，通过降低DC/DCDC/DC变换单元的输入电压以降低光伏阵列的输出电压，以使所述光伏阵列的输出电压小于所述逆变器稳态运行时最大功率点跟踪的电压；具体地，所述最大功率点跟踪，即是指实时侦测光伏阵列的太阳能板的发电电压，并追踪最高电压电流值，使所述光伏阵列的太阳能板以最大的输出功率进行工作。所述以降低所述光伏列阵11的输出电压，是为了降低输出功率，使输出功率小于逆变器稳态工作时的输出功率。所述降低所述光伏列阵11的输出电压，包括由数字信号处理芯片DSP调用DC/DC变换单元的控 制模块，从而降低所述DC/DC变换单元的输入电压，从而降低了所述光伏列阵的输出电压，所述DSP集成了处理器和存储器等器件。所述DC/DC变换单元，包括BOOST电路，用于升高输入所述DC/DC变换单元的直流电压。
步骤703，降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间升高引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元，所述母线器件为串联在所述母线上的器件。具体地，电网电压突然升高引起所述DC/AC逆变单元与所述DC/DC变换单元的电压升高时，所述低电压控制单元调用所述DC/AC逆变单元的控制模块，以降低所述DC/AC逆变单元的的输入电压的控制模块，以降低所述DC/DCDC/DC变换单元的输出电压的升高幅度，从而控制用于连接所述DC/DC变换单元与所述DC/AC逆变单元的母线电压升高。
有益效果:本实施例提供的一种多机并网功率变换器低电压穿越控制方法，通过对逆变器输出电压进行调节，使所述逆变器能够实现低电压穿越且能够克服现有技术中存在的易触发母线电压保护或器件损坏的导致的功率变换器不稳定问题，以及需要较大的母线电容容值导致的系统成本增加的问题，该方法能够有效降低母线电容容值且增强低电压穿越的稳定性。
进一步地,S704，所述降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间升高引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元，所述母线器件为串联在所述母线上的器件，具体包括：
降低所述DC/DC变换单元的输入电压，从而降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间升高引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元，所述母线器件为串联在所述母线上的器件。
进一步地，步骤S705，所述降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间升高引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元，所述母线器件为串联在所述母线上的器件，具体包括：
根据所述逆变器稳态运行时最大功率点跟踪的电压以及电网电压信息设置所述母线正常运行时的电压区间，将升高后的所述母线电压控制在所述母线正常运行时的电压区间。
进一步地，步骤S706，所述对电网的并网点的电压的幅值进行检测，以确定是否触发低电压穿越，具体包括：对电网的并网点的电压的幅值进行检测，在所述幅值变化超过预设区间时，或在所述幅值和相位的变化超过预设区间时，触发低电压穿越。
有益效果:本实施例提供的一种多机并网功率变换器低电压穿越控制方法，通过对逆变器输出电压进行调节，使所述逆变器能够实现低电压穿越且能够克服现有技术中存在的易触发母线电压保护或器件损坏的导致的功率变换器不稳定问题，以及需要较大的母线电容容值导致的系统成本增加的问题，该方法能够有效降低母线电容容值且增强低电压穿越的稳定性。
本发明可以通过多种实施方式来实现，本发明实施例可以由特定软硬件组件进行执行，那些本领域技术人员认为各种不同的软件或硬件的组合也可以被应用来执行本发明实施例，上述被硬件执行的特定操作也可以被软件来实施。
最后应说明的是：以上各实施例仅用以说明本发明的技术方案，而非对其限制；尽管参照前述各实施例对本发明进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分或者全部技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本发明各实施例技术方案的范围。

Claims (10)

  1. 一种多机并网功率变换器低电压穿越控制系统，包括：光伏阵列以及逆变器，所述逆变器包括DC/DC变换单元和与所述DC/DC变换单元输出端相连的DC/AC逆变单元，所述DC/DC变换单元输入端与所述光伏阵列输出端相连，所述逆变器在并网点与电网相连，所述并网点为光伏发电站与所述电网的连接点，其特征在于，
    所述逆变器，还包括低电压穿越检测单元与低电压穿越控制单元；
    所述低电压穿越检测单元，用于对所述并网点的电网电压的幅值进行检测，以确定是否触发低电压穿越；
    所述低电压穿越控制单元，与所述低电压穿越检测单元相连,在所述低电压穿越检测单元确定触发所述低电压穿越的情形下，用于降低所述DC/DC变换单元的输入电压，以降低所述光伏阵列的输出电压，以使所述光伏阵列的输出电压小于所述逆变器稳态运行时最大功率点跟踪的电压。
  2. 根据权利要求1所述的系统，其特征在于，所述低电压穿越控制单元，在所述低电压穿越检测单元确定触发所述低电压穿越的情形下，还用于降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间升高引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元，所述母线器件为串联在所述母线上的器件。
  3. 根据权利要求2所述的系统，其特征在于，所述低电压穿越控制单元，在所述低电压穿越检测单元确定触发所述低电压穿越的情形下，还用于降低所述DC/DC变换单元的输出电压，具体用于：
    降低所述DC/DC变换单元的输入电压，从而降低所述DC/DC变换单元的输出电压。
  4. 根据权利要求2或3所述的系统，其特征在于，所述低电压穿越控制单元，在所述还用于降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间提升引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护， 所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元方面，具体用于：
    根据所述逆变器稳态运行时最大功率点跟踪的电压以及电网电压信息设置所述母线正常运行时的电压区间，将升高后的所述母线电压控制在所述母线正常运行时的电压区间。
  5. 根据权利要求1至4任一所述的系统，其特征在于，所述低电压穿越检测单元，用于对所述并网点的电网电压的幅值进行检测，以检测是否触发低电压穿越方面，具体用于:
    对电网电压的幅值进行检测，在所述幅值的变化超过预设区间时，触发低电压穿越。
  6. 一种多机并网功率变换器低电压穿越控制方法，其特征在于，包括：
    对电网并网点的电压的幅值或相位进行检测，以确定是否触发低电压穿越，所述并网点为光伏发电站与所述电网的连接点；
    在确定触发所述低电压穿越的情形下，降低DC/DC变换单元的输入电压，以降低光伏阵列的输出电压，以使所述光伏阵列的输出电压小于所述逆变器稳态运行时最大功率点跟踪的电压。
  7. 根据权利要求6所述的方法，其特征在于，还包括：
    在确定触发所述低电压穿越的情形下，降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间升高引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元，所述母线器件为串联在所述母线上的器件。
  8. 根据权利要求7所述的方法，其特征在于，所述降低所述DC/DC变换单元的输出电压，具体包括：
    降低所述DC/DC变换单元的输入电压，从而降低所述DC/DC变换单元的输出电压。
  9. 根据权利要求7或8所述的方法，其特征在于，所述降低所述DC/DC变换单元的输出电压，以降低所述低电压穿越恢复时电网电压瞬间升高引起的母线电压的升高值，以保护母线器件或避免触发母线过压保护，所述母线用于连接所述DC/DC变换单元与所述DC/AC逆变单元，所述母线器件为串联在所述母线上的器件，具体包括：
    根据所述逆变器稳态运行时最大功率点跟踪的电压以及电网电压信息设置所述母线正常运行时的电压区间，将所述母线电压控制在所述母线正常运行时的电压区间。
  10. 根据权利要求6-9任一所述的方法，其特征在于，所述对所述并网点的电网电压的幅值进行检测，以确定是否触发低电压穿越，具体包括：
    对并网点的电网电压的幅值进行检测，在所述幅值的变化超过预设区间时，触发低电压穿越。
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