WO2015096586A1 - 一种微电网系统无缝切换的方法及系统 - Google Patents

一种微电网系统无缝切换的方法及系统 Download PDF

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WO2015096586A1
WO2015096586A1 PCT/CN2014/092365 CN2014092365W WO2015096586A1 WO 2015096586 A1 WO2015096586 A1 WO 2015096586A1 CN 2014092365 W CN2014092365 W CN 2014092365W WO 2015096586 A1 WO2015096586 A1 WO 2015096586A1
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value
voltage
grid
microgrid
phase
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PCT/CN2014/092365
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English (en)
French (fr)
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刘志强
张东升
苏位峰
卫三民
苟锐锋
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中国西电电气股份有限公司
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Priority to BR112015029845A priority Critical patent/BR112015029845A2/pt
Priority to RU2015151610A priority patent/RU2629747C2/ru
Publication of WO2015096586A1 publication Critical patent/WO2015096586A1/zh

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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
    • H02J9/00—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting
    • H02J9/04—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source
    • H02J9/06—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source with automatic change-over, e.g. UPS systems
    • 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
    • H02J3/40—Synchronising a generator for connection to a network or to another generator
    • H02J3/44—Synchronising a generator for connection to a network or to another generator with means for ensuring correct phase sequence
    • 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
    • H02J3/40—Synchronising a generator for connection to a network or to another generator
    • H02J3/42—Synchronising a generator for connection to a network or to another generator with automatic parallel connection when synchronisation is achieved
    • 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
    • H02J2310/00—The network for supplying or distributing electric power characterised by its spatial reach or by the load
    • H02J2310/10—The network having a local or delimited stationary reach
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/30—Systems integrating technologies related to power network operation and communication or information technologies for improving the carbon footprint of the management of residential or tertiary loads, i.e. smart grids as climate change mitigation technology in the buildings sector, including also the last stages of power distribution and the control, monitoring or operating management systems at local level
    • 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
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S20/00—Management or operation of end-user stationary applications or the last stages of power distribution; Controlling, monitoring or operating thereof
    • Y04S20/20—End-user application control systems

Definitions

  • the invention relates to the field of power switching control, in particular to a method and system for seamless switching of a micro grid system.
  • a piconet system is connected to the grid via a switching device.
  • the switching device includes a controller and a PCS (Power Conversion System) device.
  • PCS Power Conversion System
  • the microgrid system needs to timely switch the power supply of the load device from the power grid to the micro network, and provide power to the load device through the power of the micro network.
  • the current handover process includes:
  • the controller When the power grid fails and the detected electrical signal is less than the threshold, the controller sends a notification to the PCS, and the PCS sends an electrical signal before the grid fault to the microgrid, and turns off the PCC switch;
  • the microgrid synchronizes voltage, amplitude, etc. according to the electrical signal and provides power.
  • V/F switching control algorithms for grid-connected to off-grid.
  • the first is for amplitude ramp start and PI regulation control, and the second is for direct given nominal amplitude and PI regulation control.
  • the control block diagram is shown in Figure 2.
  • the first method has a slower control speed, which causes the distributed generation power supply to report the undervoltage and underfrequency faults on the grid side and stops working.
  • the second method of voltage amplitude given method will cause current impact during the switching process, resulting in PCS energy storage. The streamer reported an overcurrent fault and the PCS stopped working.
  • the present invention provides a method and system for seamlessly switching a microgrid system to solve the problem of slow speed or large current impact during the above switching process.
  • the present invention provides a method for seamlessly switching a microgrid system, including:
  • the first voltage collecting module collects phase voltage values of the grid side; the first voltage collecting module is connected to the grid side;
  • the PCS determines, according to the voltage values of the respective phases collected by the first voltage collecting module, a power loss ratio of a current voltage value of each phase voltage with respect to a standard value, and counts a number of times that the power loss ratio value of each phase voltage is lower than a predetermined value. a sum; the standard value is a known amount;
  • the V/F switching is performed, and the PCC switch between the grid and the microgrid connected thereto is triggered to be disconnected.
  • the power loss ratio is:
  • the current voltage value is deviated from the standard value, and the ratio of the difference value to the standard value is used as the power loss ratio value;
  • the predetermined value is between 12% and 18%, and the number of times is between 4 and 8.
  • the predetermined value is 15% and the number of times is 5.
  • the method further comprises: switching the piconet system to the grid, comprising:
  • the first voltage collecting module collects the voltage value, the frequency value and the phase value of the connected grid side; the second voltage collecting module collects the voltage value, the frequency value and the phase value of the connected microgrid side;
  • the PCS regulates the voltage on the microgrid side according to the grid side voltage value, and adjusts the frequency of the microgrid side according to the grid side frequency value;
  • PCS compares the absolute value of the phase difference between the grid side and the microgrid side
  • the piconet system is switched to the grid.
  • the embodiment of the invention further provides a system for seamlessly switching a microgrid system, comprising:
  • a first collecting unit configured to collect, by using the first voltage collecting module, voltage values of respective phases of the connected grid side
  • a comparison unit configured to determine, by the PCS, a power loss ratio of a current voltage value of each phase voltage with respect to a standard value, and count a sum of times of the power loss ratio values of the phase voltages being lower than a predetermined value
  • the first control unit is configured to determine, by the PCS, that the value of the sum is greater than a threshold, perform V/F switching, and trigger a disconnection of a PCC switch between the connected grid and the microgrid.
  • the method further comprises:
  • a second collecting unit configured to collect a voltage by using a second voltage collecting module connected to the microgrid side
  • the second control unit is configured to control the PCS to trigger the connection of the PCC switch according to the electrical signal acquisition value of the first voltage collection module and the second voltage collection module.
  • the method and system of the invention realizes the disconnection or closing of the PCC switch between the power grid and the microgrid by comparing the voltage on the grid side, and has the characteristics of high speed and small impact.
  • FIG. 1 is a schematic diagram of a network structure of a prior art large power grid and a micro power grid;
  • FIG. 2 is a block diagram of a control algorithm of a prior art large power grid when failing over to a microgrid
  • FIG. 3 is a schematic structural diagram of a network in the embodiment
  • FIG. 4 is a schematic structural diagram of a voltage collecting module in the embodiment
  • FIG. 5 is a schematic structural diagram of an intelligent PCS energy storage converter according to the embodiment.
  • FIG. 7 is a flowchart of a control algorithm of a grid-to-off network in the embodiment.
  • FIG. 8 is a block diagram of a control algorithm of a grid-to-off network in the embodiment.
  • FIG. 9 is a simulation diagram of a grid-to-off-network handover according to the embodiment.
  • FIG. 11 is a flowchart of a control algorithm for off-grid to grid-connected in the embodiment.
  • the structure of the microgrid system in the embodiment of the present invention includes: an intelligent PCS energy storage converter, a PCC switch, a voltage acquisition module V1, and a voltage acquisition module V2.
  • the PCC switch is between the main power grid and the micro grid.
  • the voltage acquisition module V1 is connected between the main power grid and the intelligent PCS energy storage converter.
  • the voltage acquisition module V2 is connected between the micro grid and the intelligent PCS energy storage converter. .
  • the intelligent PCS energy storage converter detects the voltage of the large power grid line in real time through the voltage acquisition module V1, calculates the voltage amplitude Ugrid, phase ⁇ minigrid and frequency fgrid of the large power grid in real time; detects the voltage of the micro network line in real time through the voltage acquisition module V2, and calculates the microgrid in real time. Voltage amplitude Uminigrid, phase ⁇ minigrid and frequency fminigrid.
  • the intelligent PCS energy storage converter controls the PCC switch based on the collected data of the above voltage and frequency.
  • the voltage acquisition module is implemented by the hardware structure as shown in FIG. 4 .
  • the voltage acquisition module V1 and the voltage acquisition module V2 have the same internal structure, and are composed of the resistors R1 and R2 and the voltage sensor 1 and the voltage sensor 2 .
  • the intelligent PCS energy storage converter is implemented by the structure shown in FIG. 5, including a smart PCS energy storage converter central processor (for example: DSP) and a three-phase rectifier/inverter circuit module, wherein the smart PCS
  • the central processing unit of the energy storage converter includes a data acquisition module, a grid voltage detection controller, a phase difference detection controller, a PCC switch controller, and a battery management system.
  • the method of the present invention implements the grid-connected and off-grid process between the piconet and the grid through the microgrid systems of Figures 3, 4, and 5 above.
  • the first voltage collecting module collects the voltage values of the phases of the connected grid side; the first voltage collecting module is the voltage collecting module V1 in FIG. 3;
  • the PCS determines a power loss ratio of a current voltage value of each phase voltage with respect to a standard value, and counts a sum of times of the power loss ratio values of the phase voltages below a predetermined value;
  • the PCS determines that the value of the sum of the times is greater than the threshold, and then switches to the voltage V/F mode, that is, the voltage amplitude and the frequency are used as control targets; and simultaneously triggers the PCC switch between the connected grid and the microgrid Disconnected to achieve off-grid between the piconet and the grid.
  • the method of the embodiment of the present invention calculates the PWM output duty by directly giving a modulation wave ratio. It can ensure that the intelligent PCS energy storage converter quickly establishes the reference voltage amplitude and frequency of the micro-network during V/F control during the process of grid-to-off-network switching to ensure the normal operation of the distributed power supply of the micro-network system.
  • the flow-to-network flow diagram includes the following steps:
  • the first voltage collecting module collects the voltage values of the phases of the connected grid side
  • the PCS determines a power-off ratio of the current voltage value of each phase voltage with respect to the standard value, and counts the sum of the times that the power-off ratio of each phase voltage is lower than a predetermined value;
  • the PCS determines that the value of the sum is greater than the first threshold, then performs V/F switching while triggering the PCC switch between the grid and the piconet to which it is connected to be disconnected.
  • the power loss ratio is a difference between a current voltage value and the standard value, and a ratio of the difference value to the standard value is used as the power loss ratio value;
  • the predetermined value is between 12% and 18%, and the number of times is between 4 and 8.
  • the predetermined value is 15% and the number of times is 5.
  • N>5 first threshold
  • the intelligent PCS energy storage converter performs grid-to-off-network switching control, starts V/F control, and simultaneously outputs a PCC switch opening control signal to implement grid-connected to off-grid. Seamless switching control. If N ⁇ 5, the intelligent PCS energy storage converter does not perform grid-to-off-network switching and keeps the grid running. If the voltage amplitudes of the three phases of UA, UB, and UC do not drop by 15%, the detection is restarted.
  • setting the threshold value too low will increase the sensitivity of the system, but will reduce the stability of the system; setting the threshold value too high will mention the stability of the system, but will reduce the dynamics of the system. response.
  • the microgrid system is very sensitive to detecting changes in the three-phase voltage UA, UB or UC of the grid, and the grid voltage is caused by other factors such as load increase and capacitor equipment startup. Recovery after a transient decline, which will result in a microgrid system and off-grid switching frequency Switching, the resulting load power is abnormal, reducing the system's fault tolerance technology and reducing the stability of the microgrid system.
  • the threshold is set higher than 18%, although the stability of the microgrid system increases, it will not be sensitive enough to the system parameter changes, resulting in the system not being able to detect the change of the grid voltage in time, resulting in the microgrid system.
  • the inverter of the device is faulty and the microgrid system is faulty.
  • the predetermined value is set to 15%, which can meet the sensitivity of the microgrid system to parameter changes, and can dynamically respond to parameter changes, and at the same time ensure the stability of the microgrid system.
  • the grid-to-off-network switching control calculates the PWM output duty ratio by directly giving a modulated wave, and can be connected to the network.
  • the intelligent PCS energy storage converter ensures that the micro-network reference voltage amplitude and frequency are quickly established during V/F control to ensure that the distributed power supply of the micro-network system works normally.
  • FIG. 9 the simulation diagram of the grid-to-off-network switching in this embodiment can be seen through the simulation experiment, and the switching at the zero-crossing point can be seen, the current impact is small, and the smooth switching from the grid to the off-network can be realized.
  • the handover process of the piconet system from the network to the grid includes:
  • the first voltage collecting module collects the voltage value, the frequency value and the phase value of the connected grid side; the second voltage collecting module collects the voltage value, the frequency value and the phase value of the connected microgrid side;
  • phase value appearing above refers to the phase value of the voltage.
  • the PCS adjusts the voltage on the microgrid side according to the grid side voltage value, and adjusts the frequency of the microgrid side according to the grid side frequency value;
  • S106 Switch the microgrid system to the grid until it is determined that the absolute value is not greater than the third threshold.
  • the invention realizes fast adjustment of the phase, amplitude and frequency adjustment of the microgrid grid, and realizes the switching of the microgrid system from the off-network state to the grid-connected state.
  • the off-grid to the grid-connected switch further includes: the second voltage collecting module V2 collecting the voltage value and the frequency value of the micro-grid side; the PCS comparing the voltage of the grid side and the micro-grid side Whether the difference between the value and the frequency value is less than the threshold, and if it is less, the operation from off-grid to the grid is performed.
  • the micro-network intelligent PCS energy storage converter is in the V/F voltage source control mode when the micro-network system is in an off-grid operation state.
  • the micro-network intelligent PCS energy storage converter can detect the micro-network voltage amplitude Uminigrid, phase ⁇ minigrid and frequency fminigrid in real time through the voltage acquisition module V2; if the large grid loses power to restore power supply, the intelligent PCS energy storage converter passes voltage collection.
  • Module V1 detects the magnitude Ugrid, phase grid and frequency fgrid of the large grid.
  • the voltage and frequency control of the microgrid system can be directly performed.
  • the microgrid intelligent PCS is stored.
  • the microgrid system voltage frequency fminigrid fgrid; because the intelligent PCS energy storage converter controls the phase error of the output microgrid grid voltage phase and the large grid, it is necessary to adjust the phase of the microgrid system.
  • the second threshold is 0.5235
  • the first adjustment range is between 0.1 and 0.2
  • the second adjustment range is between 0.01 and 0.02.
  • the process of switching from the network to the grid includes: determining that the absolute value meets the requirement, and the process of switching the micro network system to the grid comprises: determining that the absolute value is less than a third threshold of 0.087, and sending a control signal to the PCC switch, A PCC switch closes the grid and the piconet.
  • phase difference ⁇ between the microgrid system and the large power grid. If ⁇ is greater than 0, it means that the microgrid system lags behind the large grid, and the intelligent PCS energy storage converter will reduce the ⁇ minigrid value; if ⁇ is less than 0 , indicating that the microgrid system is ahead of the large grid, and the intelligent PCS energy storage converter will increase the ⁇ minigrid value. Since the ⁇ error value may be large, directly changing the ⁇ minigrid value may cause an impact of current.
  • the second threshold is 0.5235
  • the first adjustment range is between 0.1 and 0.2
  • the second range is between 0.01 and 0.02.
  • the search step In the off-grid to grid-connected mode, if the search step is set too high, the accuracy of the system will be lowered, but the response speed of the system will be increased. If the search step is set too low, the response speed of the system will be reduced. But it will improve the accuracy of the system.
  • the search step size ⁇ 1 is used (0.1 to 0.2) (corresponding to an angle of 5.7° to 11.4°).
  • the phase difference is greater than 30 degrees, the system's fast response speed is guaranteed. If the value of ⁇ 1 is less than 0.1, the phase difference reduction speed decreases, and the corresponding microgrid tracks the phase velocity of the large power grid, thereby reducing the corresponding speed of the microgrid system; if the value of ⁇ 1 is greater than 0.2, the phase difference decreasing speed is improved.
  • the corresponding micro-grid tracks the phase speed of the large power grid, thereby reducing the response speed of the micro-grid system, but the tracking accuracy is reduced, and it is easy to exceed the threshold range, causing the system to oscillate.
  • the purpose is to ensure the tracking accuracy of the system.
  • the value of ⁇ 2 is greater than 0.02, the phase difference reduction speed is increased, and the corresponding microgrid tracks the phase speed of the large power grid, thereby increasing the corresponding speed of the microgrid system.
  • the tracking accuracy is reduced; if the value of ⁇ 2 is less than 0.01, the phase difference decreasing speed is reduced, and the phase speed of the corresponding microgrid tracking large grid is reduced, but the accuracy of the system tracking is improved to ensure stable operation of the system.
  • the threshold value of the predetermined value is set to 0.5235.
  • the range of ⁇ 1 (0.1 to 0.2) and the range of ⁇ 2 (0.01 to 0.02) can satisfy the microgrid system.
  • the sensitivity of the parameter changes, while being able to dynamically respond to changes in parameters, while also ensuring the stability requirements of the microgrid system.
  • the PCS triggers the PCC switch to be turned off according to the number of times the phase voltage loss ratio of each phase of the grid side collected by the first voltage collecting module.
  • the invention also provides a system for seamless switching of a microgrid system, comprising:
  • a first collecting unit configured to collect, by using the first voltage collecting module, voltage values of respective phases of the connected grid side
  • a comparison unit for determining, by the PCS, a loss of a current voltage value of each phase voltage from a standard value The electrical ratio, the sum of the times when the power loss ratio of each phase voltage is lower than a predetermined value;
  • a first control unit configured to determine, by the PCS, that the value of the sum is greater than a threshold, perform V/F switching, and trigger a disconnection of a PCC switch between the grid and the microgrid to which the connection is triggered.
  • the method further comprises:
  • a second collecting unit configured to collect a voltage by using a second voltage collecting module connected to the microgrid side
  • the second control unit is configured to control the PCS to trigger the connection of the PCC switch according to the electrical signal acquisition value of the first voltage collection module and the second voltage collection module.
  • the method and system of the invention realizes the disconnection or closing of the PCC switch between the power grid and the microgrid by comparing the voltage on the grid side, and has the characteristics of high speed and small impact.

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  • Business, Economics & Management (AREA)
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Abstract

一种微电网系统无缝切换的方法及系统，方法包括：第一电压采集模块采集其连接的电网侧的各相电压值；PCS确定每相电压的当前电压值相对于标准值的失电比值，统计各相电压的所述失电比值低于预定值的次数总和；PCS判断所述总和的数值大于阈值，则执行V/F切换，同时触发其连接的所述电网和微网之间的PCC开关断开。采用上述并网到离网的切换方式，电流冲击很小，能够实现并网到离网的平滑切换。

Description

一种微电网系统无缝切换的方法及系统
本申请要求于2013年12月24日提交中国专利局、申请号为201310722452.6、发明名称为“一种微电网系统无缝切换的方法及系统”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本发明涉及电力切换控制领域，特别是指一种微电网系统无缝切换的方法及系统。
背景技术
在智能电网中，微网系统通过切换设备与电网相连接。切换设备包括控制器和PCS(能量转换系统，Power Conversion System)装置。
在运行过程中，当电网出现问题后，微网系统需要及时将负载设备的电力供应从电网切换到微网上，通过微网的电源为负载设备提供电力。
参见图1所示的现有的网络结构示意图，目前的切换过程包括：
通过微网系统控制器检测电网的电信号；
当电网故障，检测的电信号小于阈值，则控制器向PCS发送通知，PCS向微网发送电网故障前的电信号，同时关闭PCC开关；
微网按照该电信号同步电压、幅值等，并提供电力。
切换过程中，并网到离网V/F切换控制算法一般为两种，第一种为幅值斜坡启动和PI调节控制实现，第二种为直接给定额定幅值和PI调节控制实现，控制框图如图2所示。第一种方法控制速度较慢，会导致分布式发电电源报电网侧欠压和欠频故障而停止工作；第二种方法电压幅值给定法会导致切换过程中电流冲击，导致PCS储能变流器报过流故障，PCS停止工作。
发明内容
有鉴于此，本发明在于提供一种微电网系统无缝切换的方法及系统，以解决上述切换过程中速度慢或电流冲击大的问题。
为解决上述问题，本发明提供一种微电网系统无缝切换的方法，包括：
第一电压采集模块采集电网侧的各相电压值；所述第一电压采集模块与电网侧连接；
PCS根据所述第一电压采集模块采集的所述各相电压值确定每相电压的当前电压值相对于标准值的失电比值，统计各相电压的所述失电比值低于预定值的次数总和；所述标准值为已知量；
所述PCS判断所述次数总和的数值大于第一阈值，则执行V/F切换，同时触发与其连接的所述电网和微网之间的PCC开关断开。
优选地，所述失电比值为：
当前电压值与所述标准值求差值，该差值与所述标准值的比值作为所述失电比值；
所述预定值为12％～18％之间，所述次数为4～8之间。
优选地，所述预定值为15％，所述次数为5。
优选地，还包括将微网系统切换到并网，包括：
第一电压采集模块采集连接的电网侧的电压值、频率值和相位值；第二电压采集模块采集连接的微网侧的电压值、频率值和相位值；
PCS按照所述电网侧电压值调控所述微网侧的电压、按照所述电网侧频率值调控所述微网侧的频率；
PCS比较电网侧与微网侧的相位差的绝对值；
如果判断到绝对值大于第二阈值，则控制所述微网侧的相位按照第一调节范围值超前或滞后相应角度；
如果判断到绝对值不大于第二阈值，则控制所述微网侧的相位按照第二调节范围值超前或滞后相应角度；
直到判断到所述绝对值不大于第三阈值，将微网系统切换到并网。
本发明实施例还提供一种微电网系统无缝切换的系统，包括：
第一采集单元，用于通过第一电压采集模块采集其连接的电网侧的各相电压值；
比较单元，用于通过PCS确定每相电压的当前电压值相对于标准值的失电比值，统计各相电压的所述失电比值低于预定值的次数总和；
第一控制单元，用于通过PCS判断所述总和的数值大于阈值，则执行V/F切换，同时触发其连接的电网和微网之间的PCC开关断开。
优选地，还包括：
第二采集单元，用于通过与微网侧连接的第二电压采集模块采集电压；
第二控制单元，用于控制所述PCS根据所述第一电压采集模块和第二电压采集模块的电信号采集值，触发其连接的所述PCC开关闭合。
本发明的方法和系统，通过比较电网侧的电压，实现电网和微网之间的PCC开关断开或闭合，具有速度快、冲击小的特点。
附图说明
图1为现有技术的大电网和微电网的网络结构示意图；
图2为现有技术大电网故障切换到微电网时的控制算法框图；
图3为本实施例中网络结构示意图；
图4为本实施例中电压采集模块的结构示意图；
图5为本实施例中智能PCS储能变流器的结构示意图；
图6为本实施例中离网过程的流程图；
图7为本实施例中并网到离网的控制算法流程图；
图8为本实施例并网到离网的控制算法框图；
图9为本实施例并网到离网切换的仿真图；
图10为本实施例离网到并网的切换过程；
图11为本实施例离网到并网的控制算法流程图。
具体实施方式
为使本发明的上述目的、特征和优点能够更加明显易懂，下面结合附图对 本发明的具体实施方式做详细的说明。
本发明实施例中的微网系统的结构，参见图3，包括：智能PCS储能变流器、PCC开关、电压采集模块V1和电压采集模块V2。
PCC开关在市电大电网和微电网之间，电压采集模块V1连接在市电大电网与智能PCS储能变流器之间；电压采集模块V2连接在微电网与智能PCS储能变流器之间。
智能PCS储能变流器通过电压采集模块V1实时检测大电网线电压，实时计算大电网电压幅值Ugrid、相位φminigrid和频率fgrid；通过电压采集模块V2实时检测微网线电压，实时计算出微网电压幅值Uminigrid、相位φminigrid和频率fminigrid。
智能PCS储能变流器根据采集的上述电压和频率的数据控制PCC开关。
其中，电压采集模块采用如图4所示的硬件结构实现，参见图4，电压采集模块V1和电压采集模块V2内部结构一样，均由电阻R1、R2和电压传感器1、电压传感器2组成。
参见图5，智能PCS储能变流器采用如图5所示的结构实现，包括智能PCS储能变流器中央处理器(例如：DSP)和三相整流/逆变电路模块，其中智能PCS储能变流器中央处理器包括数据采集模块、电网电压检测控制器、相位差检测控制器、PCC开关控制器、电池管理系统。
本发明的方法通过上述图3、4、5的微网系统实现微网与电网之间的并网和离网过程。
下面首先说明微网与大电网之间的离网过程，参见图6，包括：
S61：第一电压采集模块采集其连接的电网侧的各相电压值；第一电压采集模块即图3中的电压采集模块V1；
S62：PCS确定每相电压的当前电压值相对于标准值的失电比值，统计各相电压的所述失电比值低于预定值的次数总和；
S63：PCS判断所述次数总和的数值大于阈值，则切换到压频V/F模式，即以电压幅值和频率为控制目标；同时触发其连接的所述电网和微网之间的PCC开关断开，从而实现微网与电网之间的离网。
本发明的实施例的方法，通过直接给定调制波的方式计算PWM输出占空 比。能够在并网到离网切换过程中，保证智能PCS储能变流器在V/F控制时快速建立微网参考电压幅值和频率，保证微网系统分布式电源正常工作。
参见图7所示的流程图，并网到离网的流程图，包括以下步骤：
第一电压采集模块采集其连接的电网侧的各相电压值；
PCS确定每相电压的当前电压值相对于标准值的失电比值，统计各相电压的所述失电比值低于预定值的次数总和；
PCS判断所述总和的数值大于第一阈值，则执行V/F切换，同时触发其连接的所述电网和微网之间的PCC开关断开。
所述失电比值为当前电压值与所述标准值求差值，该差值与所述标准值的比值作为所述失电比值；
优选地：所述预定值为12％～18％之间，所述次数为4～8之间。
优选地：所述预定值为15％，所述次数为5。
具体操作过程为：
S11：第一电压采集模块V1实时采集大电网的线电压，此时计数值N＝0；
S12：实时计算大电网的有效电压值UA，UB，UC；
S13：比较UA，UB或UC三相任意一相电压幅值是否低落幅度超过15％，如果UA，UB或UC任意一相电压幅值跌落15％，此时计数值N进行步长为1的累加计算。
S14：如果N>5(第一阈值)，则智能PCS储能变流器进行并网到离网切换控制，启动V/F控制，同时输出PCC开关分闸控制信号，实现并网到离网的无缝切换控制。如果N<5，则智能PCS储能变流器不进行并网到离网切换，保持并网运行。如果UA，UB，UC三相的电压幅值都没有跌落15％，则重新开始检测。
在并网至离网切换中，预定值阈值设置过低会提高系统的敏感度，但是会降低系统的稳定性；预定值阈值设置过高会提到系统的稳定性，但是会降低系统的动态响应。
在实验过程中，当设置阈值低于为12％时，微网系统对检测电网三相电压UA，UB或UC参数变化非常敏感，在电网电压因负载增加、电容设备启动等其他原因导致电网电压短暂性下降后恢复，此时会导致微网系统并离网开关频 繁切换，导致的负载用电出现异常，降低系统的容错技术，降低微网系统稳定性。
在实验室过程中，当设置阈值高于为18％时，微网系统虽然稳定性增加，但是会导致对系统参数变化不够敏感，导致系统不能及时检测出电网电压的变化，导致微网系统各设备逆变器出现故障，微网系统出现故障异常。
因此，经过实验数据和综合分析，将预定值设置为15％，能够满足微网系统对参数变化的敏感度，同时能够对参数变化做出动态反应，同时，也能保证微网系统能够稳定性要求。
参见图8，为本实施例中并网到离网的控制算法框图，通过上述实施例，并网到离网切换控制通过直接给定调制波的方式计算PWM输出占空比，能够在并网到离网切换过程中，保证智能PCS储能变流器在V/F控制时快速建立微网参考电压幅值和频率，保证微网系统分布式电源正常工作。参见图9，本实施例并网到离网切换的仿真图，通过仿真实验，可以看到在过零点的切换，电流冲击很小，能够实现并网到离网的平滑切换。
上面的实施例详细说明了并网到离网的切换过程，下面通过实施例说明离网到并网的切换过程，参见图10，微网系统离网到并网的切换过程，包括：
S101：第一电压采集模块采集连接的电网侧的电压值、频率值和相位值；第二电压采集模块采集连接的微网侧的电压值、频率值和相位值；
需要说明的是，以上出现的相位值指的是电压的相位值。
S102：PCS按照所述电网侧电压值调控所述微网侧的电压、按照所述电网侧频率值调控所述微网侧的频率；
S103：PCS比较电网侧与微网侧的相位差的绝对值；
S104：如果判断到绝对值大于第二阈值，则控制所述微网侧的相位按照第一调节范围值超前或滞后相应角度；
S105：如果判断到绝对值不大于第二阈值，则控制所述微网侧的相位按照第二调节范围值超前或滞后相应角度；
S106：直到判断到所述绝对值不大于第三阈值，将微网系统切换到并网。
通过上述的调节步骤之后，实现离网到并网的平滑切换。下面通过具体的实例详细说明上述过程。参加图11，包括：
在离网状态切换到并网状态时，必须保证微网交流母线和大电网交流母线幅值、相位和频率一致。本发明实现快速调节微网电网相位、幅值、频率调节，实现微网系统从离网状态到并网状态的切换。
所述离网到并网的切换之前还包括：所述第二电压采集模块V2采集所述微网侧的电压值和频率值；所述PCS比较所述电网侧和所述微网侧的电压值的差值、频率值的差值是否小于阈值，如果小于，则执行离网到并网的操作。具体为：在微网系统处于离网运行状态，微网智能PCS储能变流器处于V/F电压源控制模式。微网智能PCS储能变流器可通过电压采集模块V2实时检测微网电压幅值Uminigrid、相位φminigrid和频率fminigrid；如果大电网从失电到恢复供电，智能PCS储能变流器通过电压采集模块V1检测大电网的幅值Ugrid、相位grid和频率fgrid。
由于智能PCS储能变流器控制输出微网电网电压幅值和频率与大电网的幅值误差和频率误差较小，可直接进行微网系统电压和频率控制，首先将微网智能PCS储能变流器V/F控制的电压参考值Uref＝Ugrid，控制微网系统电压幅值Uminigrid＝Ugrid；然后将微网智能PCS储能变流器V/F控制的电压参考值fref＝fgrid，控制微网系统电压频率fminigrid＝fgrid；由于智能PCS储能变流器控制输出微网电网电压相位与大电网的相位误差较大，需要对微网系统的相位进行调节。
优选地，所述第二阈值为0.5235，所述第一调节范围值为，0.1～0.2之间；所述第二调节范围值为0.01～0.02之间。
离网到并网的切换过程还包括，判断所述绝对值符合要求，将微网系统切换到并网的过程包括：判断所述绝对值小于第三阈值0.087，则向PCC开关发出控制信号，PCC开关闭合所述电网和所述微网。
具体为：首先计算出微网系统与大电网相位差△φ，如果△φ大于0，则表示微网系统滞后大电网，智能PCS储能变流器将减小φminigrid值；如果△φ小于0，则表示微网系统超前大电网，智能PCS储能变流器将增加φminigrid值。由于△φ误差值可能较大，直接改变φminigrid值可能造成电流的冲击。如果|△φ|大于0.5235(角度为30度)，对应微网系统φminigrid±γ1|△φ|，如果|△φ|小于0.5235(角度为30度)，对应微网系统φminigrid±γ2|△φ|，其中，γ1>γ2，一般γ1取值范 围(0.1～0.2)，一般γ2取值范围(0.01～0.02)]，此时如果△φ小于0.087(角度为5度)，则不进行相位调节，然后智能PCS储能变流器输出PCC开关合闸控制信号，实现微网系统从离网到并网控制。
优选地，所述第二阈值为0.5235，所述第一调节范围值为，0.1～0.2之间；所述第二调范围值为0.01～0.02之间。
在离网至并网切换中，在低于阈值范围内，搜索步长设置过高会降低系统的精确度，但是会提高系统的响应速度；搜索步长设置过低会降低系统的响应速度，但是会提高系统的精确度。
在实验过程中，当相位差大于第二阈值0.5235(对应角度30度)时，采用搜索步长γ1取值范围(0.1～0.2)(对应角度5.7°～11.4°)。在相位差大于30度时，保证系统的快速响应速度。如果γ1取值小于0.1时，相位差减小速度降低，相应微网跟踪大电网相位速度降低，从而降低微网系统的相应速度；如果γ1取值大于0.2时，相位差减小速度提高，相应微网跟踪大电网相位速度提高，从而降低微网系统的响应速度，但是跟踪精度降低，容易超出阈值范围，引起系统的震荡。在相位差小于30度时，目的是保证系统跟踪精度，如果γ2取值大于0.02时，相位差减小速度提高，相应微网跟踪大电网相位速度提高，从而提高微网系统的相应速度但是降低了跟踪精度；如果γ2取值小于0.01时，相位差减小速度降低，相应微网跟踪大电网相位速度降低，但是提高系统跟踪的精度，保证系统的稳定运行。
因此，经过实验数据和综合分析，将预定值阈值设置为0.5235，在大于0.5235时，γ1取值范围(0.1～0.2)，γ2取值范围(0.01～0.02)，能够满足微网系统对参数变化的敏感度，同时能够对参数变化做出动态反应，同时，也能保证微网系统能够稳定性要求。
所述PCS根据所述第一电压采集模块采集的电网侧的各相电压失值比的次数，触发所述PCC开关断开。
本发明还提供一种微电网系统无缝切换的系统，包括：
第一采集单元，用于通过第一电压采集模块采集其连接的电网侧的各相电压值；
比较单元，用于通过PCS确定每相电压的当前电压值相对于标准值的失 电比值，统计各相电压的所述失电比值低于预定值的次数总和；
第一控制单元，用于通过PCS判断所述总和的数值大于阈值，则执行V/F切换，同时触发其连接的所述电网和微网之间的PCC开关断开。
优选地，还包括：
第二采集单元，用于通过与微网侧连接的第二电压采集模块采集电压；
第二控制单元，用于控制所述PCS根据所述第一电压采集模块和第二电压采集模块的电信号采集值，触发其连接的所述PCC开关闭合。
本发明的方法和系统，通过比较电网侧的电压，实现电网和微网之间的PCC开关断开或闭合，具有速度快、冲击小的特点。
以上所述，仅是本发明的较佳实施例而已，并非对本发明作任何形式上的限制。虽然本发明已以较佳实施例揭露如上，然而并非用以限定本发明。任何熟悉本领域的技术人员，在不脱离本发明技术方案范围情况下，都可利用上述揭示的方法和技术内容对本发明技术方案做出许多可能的变动和修饰，或修改为等同变化的等效实施例。因此，凡是未脱离本发明技术方案的内容，依据本发明的技术实质对以上实施例所做的任何简单修改、等同变化及修饰，均仍属于本发明技术方案保护的范围内。

Claims (6)

  1. 一种微电网系统无缝切换的方法，其特征在于，包括：
    第一电压采集模块采集电网侧的各相电压值；所述第一电压采集模块与电网侧连接；
    PCS根据所述第一电压采集模块采集的所述各相电压值确定每相电压的当前电压值相对于标准值的失电比值，统计各相电压的所述失电比值低于预定值的次数总和；所述标准值为已知量；
    所述PCS判断所述次数总和的数值大于第一阈值，则执行V/F切换，同时触发与其连接的所述电网和微网之间的PCC开关断开。
  2. 根据权利要求1所述的方法，其特征在于，所述失电比值为：
    当前电压值与所述标准值求差值，该差值与所述标准值的比值作为所述失电比值；
    所述预定值为12％～18％之间，所述次数为4～8之间。
  3. 根据权利要求2所述的方法，其特征在于，所述预定值为15％，所述次数为5。
  4. 根据权利要求1所述的方法，其特征在于，还包括将微网系统切换到并网，包括：
    第一电压采集模块采集连接的电网侧的电压值、频率值和相位值；第二电压采集模块采集连接的微网侧的电压值、频率值和相位值；
    PCS按照所述电网侧电压值调控所述微网侧的电压、按照所述电网侧频率值调控所述微网侧的频率；
    PCS比较电网侧与微网侧的相位差的绝对值；
    如果判断到绝对值大于第二阈值，则控制所述微网侧的相位按照第一调节范围值超前或滞后相应角度；
    如果判断到绝对值不大于第二阈值，则控制所述微网侧的相位按照第二调节范围值超前或滞后相应角度；
    直到判断到所述绝对值不大于第三阈值，将微网系统切换到并网。
  5. 一种微电网系统无缝切换的系统，其特征在于，包括：
    第一采集单元，用于通过第一电压采集模块采集其连接的电网侧的各相电压值；
    比较单元，用于通过PCS确定每相电压的当前电压值相对于标准值的失电比值，统计各相电压的所述失电比值低于预定值的次数总和；
    第一控制单元，用于通过PCS判断所述总和的数值大于阈值，则执行V/F切换，同时触发其连接的电网和微网之间的PCC开关断开。
  6. 根据权利要求4所述的切换系统，其特征在于，还包括：
    第二采集单元，用于通过与微网侧连接的第二电压采集模块采集电压；
    第二控制单元，用于控制所述PCS根据所述第一电压采集模块和第二电压采集模块的电信号采集值，触发其连接的所述PCC开关闭合。
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