WO2019037428A1 - 双层优化全局同步脉冲宽度调制系统及方法 - Google Patents
双层优化全局同步脉冲宽度调制系统及方法 Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/40—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
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
- H02M1/126—Arrangements for reducing harmonics from ac input or output using passive filters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
- H02M1/123—Suppression of common mode voltage or current
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
Definitions
- the present invention relates to a two-layer optimized global synchronization pulse width modulation system and method.
- SPMW sine wave modulation
- the traditional three-phase inverter mostly adopts sine wave modulation (SPMW) technology, and the SPWM can make the output voltage and current of the three-phase inverter sinusoidal, ensuring that the new energy grid-connected power generation system is safely and stably connected to the power grid, which is a new energy source.
- SPWM technology will make the inverter's output voltage contain a lot of high-frequency components.
- the output voltage of the inverter can be divided into differential mode voltage and common mode voltage. The differential mode voltage ensures that the grid-connected inverter injects energy into the grid.
- the common mode voltage is the grounding point of the grid and the spurious parameters of the grid-connected power generation system. Wait for a common mode loop. SPWM will cause a large amount of high frequency components in the common mode voltage and form a large common mode current in the common mode loop. The presence of common mode current will not affect the grid-connected inverter to inject energy into the grid, but will increase the inverter. The loss of the device seriously affects the power conversion efficiency of the grid-connected power generation system, and also causes severe electromagnetic interference to peripheral equipment. According to China's new energy grid-connected system standard, the maximum value of common mode current should not exceed 400mA, so the common mode voltage and common mode current of the grid-connected inverter should be strictly controlled.
- Passive suppression includes common mode inductors, common mode rejection transformers, common mode filters, and common mode choke coils. These methods all require increased hardware cost; active suppression mainly suppresses common mode voltage from the inverter's control algorithm, but It will increase the control difficulty of the grid-connected inverter. There is an urgent need for a low cost method of suppressing common mode currents.
- the Chinese invention patent "Global Synchronous Pulse Width Modulation System and Method for Distributed Grid-Connected Inverter System” discloses a global synchronous pulse width modulation system for distributed grid-connected inverter system, which determines the basic structure of the global pulse width modulation system, including a main control unit (global synchronization unit) and a plurality of grid-connected inverters located in different geographical locations, each of which is connected to a distributed power source, and each grid-connected inverter passes through a common grid-connected point Connected to the power grid, the main control unit communicates with all the grid-connected inverters, and the main control unit receives the information of each grid-connected inverter, and after determining the global synchronization strategy, respectively, the global synchronization signals including the global synchronization strategy are respectively Sent to each grid-connected inverter, each grid-connected inverter uses its global synchronization signal to adjust its pulse-width modulated wave phase to achieve the phase difference between the pulse-width modulated waves of each grid
- the Chinese invention patent "Global Synchronous Pulse Width Phase and Frequency Dynamic Adjustment Method for Distributed Grid-Connected Inverter System” discloses a global synchronous pulse width phase and frequency dynamic adjustment method for distributed grid-connected inverter system. During the normal operation of the inverter, reducing the switching frequency of each inverter under the premise of meeting the requirements of grid-connected current harmonics can improve the operating efficiency of the entire system.
- the Chinese invention patent "a global synchronous pulse width modulation self-synchronization method under the condition of communication failure” proposes a global synchronous pulse width modulation self-synchronization method under the communication failure state.
- the inverter can maintain the global synchronous operation state in the case of communication failure, and the state of each inverter does not need to be changed, and the advantages of the global synchronous pulse width modulation method are fully utilized.
- the present invention proposes a two-layer optimized global synchronous pulse width modulation system and method.
- the invention can effectively avoid the common mode circulating current problem in a large-scale photovoltaic power station and improve the conversion efficiency of the photovoltaic grid-connected inverter.
- a two-layer optimized global synchronous pulse width modulation system comprising a central global synchronization unit, a plurality of global synchronization units and a photovoltaic grid-connected inverter connected to each photovoltaic panel, and the grid-connected inverter is divided into several groups, each group The inverter is connected to a common grid connection point through an isolation transformer, wherein each inverter group contains a global synchronization unit;
- the global synchronization unit is configured to receive operating parameters of the inverters of the group, and calculate a phase difference that allows all inverter common mode currents to meet the required phase, and each transformer is injected into the grid current at a high level. harmonic;
- the central global synchronization unit is configured to receive the total current harmonic information of the inverter group transmitted by each global synchronization unit, and calculate a phase difference that minimizes the content of higher harmonics in the grid current injected into the grid point, and The optimal phase difference that each PV grid-tied inverter needs to perform.
- the central global synchronization unit is configured with a total current ripple optimization calculation program.
- the global synchronization unit is configured with a common mode loop optimization calculation program for the group of inverters.
- a two-layer optimized global synchronization pulse width modulation method based on the above system includes the following steps:
- Receiving parameters sent by each inverter including output power of the inverter, filtering parameters, and equivalent capacitance parameters between the photovoltaic panel and the earth;
- the output power of the inverter can be obtained by the controller of the inverter, and the filter parameter is considered to be a fixed value, which is pre-stored in the controller of the inverter, and the equivalent capacitance parameter is obtained by measurement in advance and stored. In the controller of the inverter.
- steps of calculating the mathematical model of the common mode current include:
- a mathematical model for calculating the effective value of the common mode current of each inverter by using the particle swarm optimization algorithm is optimized to calculate a phase difference that enables the common mode leakage current to meet the requirements.
- the output current of each transformer is expressed as the sum of the harmonic currents of the respective frequencies, and the harmonic current of each frequency of the total current is expressed as the sum of the harmonic currents of the plurality of transformer output response frequencies, and the harmonics of the total current
- the current is represented as a superposition of multiple frequency harmonic currents, which in turn gives the harmonic current rms value of the total current.
- the optimum phase difference for each inverter is the sum of the phase difference that minimizes the total harmonic content of the total grid-connected current and the phase difference that allows the common-mode leakage current to meet the required phase.
- the method of the invention can effectively avoid the common mode circulation problem in a large-scale photovoltaic power station and improve the conversion efficiency of the photovoltaic grid-connected inverter.
- the method proposed by the invention can effectively reduce the harmonic content in the total grid-connected current of the photovoltaic power station while avoiding the common mode circulation problem, and improve the output power quality of the photovoltaic power station.
- the method of eliminating the common mode circulating current by adding an isolation transformer or an additional semiconductor device can reduce the requirement that the common mode circulating current of the inverter meets the requirements.
- the cost of the inverter increases the competitive advantage of the inverter.
- Figure 2 is a schematic diagram of a common mode current calculation circuit
- Figure 3 is a flow chart of a two-layer optimized global synchronous pulse width modulation method.
- orientation or positional relationship is based on the orientation or positional relationship shown in the drawings, and is merely a relative relationship for the purpose of describing the structural relationship of the components or components of the present invention, and is not specifically referring to any component or component of the present invention, and may not be construed as a Limitations of the invention.
- the grid-connected inverter is divided into several groups, and each group of inverters is connected to a common grid-connecting point through an isolating transformer, wherein each inverter group contains a global synchronization unit GSU, and the GSU receives the group inverse The operating parameters of the transformer, and calculate the phase difference that allows all inverter common mode currents to meet the requirements. And the higher harmonics of each transformer injected into the grid current at this phase difference.
- a two-layer optimized global synchronous pulse width modulation system including:
- the Central-GSU communicates with all GSUs, and the GSU communicates with all inverters in the group.
- the Central-GSU and GSU can be separate controllers or some of the functions that exist within an inverter controller.
- the total current ripple optimization calculation program is added to the Central-GSU, and the common mode circulating current optimization calculation program for the inverters of the group is added to the GSU.
- the two-layer optimized global synchronous pulse width modulation method includes the following steps:
- Step (1) The GSU receives parameters sent by each inverter, including an output power of the inverter, a filtering parameter, and an equivalent capacitance parameter between the photovoltaic panel and the ground.
- Step (2) The GSU calculates a mathematical model of the common mode leakage current according to the parameters received in the step (1).
- Step (3) GSU uses an intelligent optimization algorithm to calculate a phase difference that allows the common mode leakage current to meet the requirements.
- Step (4) Calculate each harmonic value i TQh of the total current i TQ injected into the common grid point of each transformer and send it to the Central-GSU.
- Step (5) The Central-GSU receives the i TQh sent by each GSU and calculates a mathematical model of the total current ripple.
- Step (6) Calculate the phase difference that can minimize the total grid-connected current THD
- Step (7) Calculate the optimal phase difference of each inverter as And sent to each inverter.
- Step (8) The Central-GSU sends a synchronization signal to each GSU, and the GSU forwards the synchronization signal to each inverter in the group.
- the output power of the inverter in step (1) can be obtained by the controller of the inverter.
- the filter parameters are considered to be fixed values and can be pre-stored in the controller of the inverter.
- the equivalent capacitance parameter can be obtained in advance by measurement and stored in the controller of the inverter.
- step (2) The steps of calculating the common mode current mathematical model in step (2) are as follows:
- u M0h is the output common mode harmonic voltage of the inverter M.
- u Mah , u Mbh , and u Mch are the three-phase output voltage harmonics of inverters a, b, and c, respectively.
- u M0hf is the component of the frequency f of the output common mode harmonic voltage of the inverter M.
- a phasor representation of the rms leakage current of the common mode of the inverter is output for the inverter M. Indicates the admittance relationship between the common mode leakage current of the inverter i and the output common mode voltage of the inverter j when the frequency is f.
- I MLRMS represents the effective value of the common mode leakage current of the inverter M.
- step (3) the GSU uses the intelligent optimization algorithm to calculate the phase difference that enables the common mode leakage current to meet the required phase difference as follows:
- the particle model algorithm is used to calculate the following mathematical model for optimization.
- the mathematical expression of the optimization model is:
- Step (4) calculates the specific formula of i TQh as:
- i TQh represents the total output harmonic current of the inverter group Q.
- the step of calculating the total current harmonic RMS value in the step (5) is:
- Step (5-1) Express the output current of each transformer as the sum of the harmonic currents of the respective frequencies:
- i TQhf represents the component of the frequency f of the total output harmonic current effective value of the inverter group Q.
- i sumhf represents the component of the frequency f of the output harmonic current of the entire photovoltaic power plant.
- Step (5-3) Express the harmonic current of the total current as a superposition of multiple frequency harmonic currents:
- i sumh represents the output harmonic current of the entire photovoltaic power station.
- Step (5-4) Indicates the rms value of the total current harmonic current:
- I sumh the effective value of the total harmonic current.
- Step (6) calculation The mathematical model is:
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Abstract
一种双层优化全局同步脉冲宽度调制系统及方法。该系统包括中央全局同步单元、若干个全局同步单元和与各个光伏电池板相连的光伏并网逆变器，并网逆变器划分成若干组，每组逆变器通过隔离变压器与公共并网点相连，其中每个逆变器组中含有一个全局同步单元；全局同步单元，被配置为接收本组逆变器的运行参数，并计算出让所有逆变器共模电流满足要求的相位差，在此相位差下每个变压器注入电网电流中的高次谐波；中央全局同步单元，被配置为接收各个全局同步单元传送的本逆变器组总电流高次谐波信息，并计算让公共并网点注入电网电流中高次谐波含量最小的相位差，以及各个光伏并网逆变器需要执行的最佳相位差。该系统能有效避免大规模光伏电站中共模环流问题，提高光伏并网逆变器的转化效率。
Description
本发明涉及一种双层优化全局同步脉冲宽度调制系统及方法。
随着电力电子技术的发展，并网逆变器广泛应用于新能源并网发电系统中。传统的三相逆变器多采用正弦波调制(SPMW)技术，SPWM可以使三相逆变器的输出电压电流为正弦波，保证了新能源并网发电系统安全稳定接入电网，是新能源并网发电系统中的重要技术，但同时，SPWM技术会使逆变器的输出电压中含有大量的高频成分。逆变器的输出电压可以分为差模电压和共模电压部分，差模电压保证并网逆变器向电网注入电能，共模电压则与电网的接地点、并网发电系统的杂散参数等形成共模回路。SPWM会使共模电压中含有大量高频成分，并在共模回路中形成较大的共模电流，共模电流的存在不会影响并网逆变器向电网注入能量，但会增加逆变器的损耗，严重影响并网发电系统的电能转化效率，同时还会对周边设备产生严重的电磁干扰。根据我国的新能源并网系统标准，共模电流的最大值不得超过400mA，因此并网逆变器的共模电压、共模电流需得到严格的控制。
传统的抑制共模电压的方法主要有主动抑制和被动抑制。被动抑制包括采用共模电感、共模抑制变压器、共模滤波器和共模扼流线圈等，这些方法均需要增加硬件成本；主动抑制主要从逆变器的控制算法入手抑制共模电压，但会增加并网逆变器的控制难度。急需一种低成本的抑制共模电流的方法。
中国发明专利《分布式并网逆变系统全局同步脉宽调制系统及方法》公开了一种分布式并网逆变系统全局同步脉宽调制系统，确定了全局脉宽调制系统的基本结构，包括主控单元(全局同步单元)和位于不同地理位置的若干个并网逆变器，每个所述并网逆变器均与分布式电源连接，每个并网逆变器均通过公共并网点与电网连接，所述主控单元与所有的并网逆变器通信，所述主控单元接收各个并网逆变器的信息，确定全局同步策略后，将包含全局同步策略的全局同步信号分别发送给各个并网逆变器，各个并网逆变器利用全局同步信号调整自己的脉宽调制波相位，以达到各个并网逆变器脉宽调制波之间能够满足谐波抵消的相位差，从而抵消各个并网逆变器注入电网的谐波电流。
中国发明专利《分布式并网逆变系统全局同步脉宽相位、频率动态调整方法》在上述专利基础上，公开了一种分布式并网逆变系统全局同步脉宽相位、频率动态调整方法，逆变器正常运行过程中，在满足并网电流谐波要求的前提下降低每个逆变器开关频率，能够提高整个系统的运行效率。
中国发明专利《一种通讯故障状态下的全局同步脉宽调制自同步方法》提出一种通讯故障状态下的全局同步脉宽调制自同步方法。能让逆变器在通讯故障的情况下依然保持全局同步运行状态，各逆变器的状态也无需改变，充分发挥全局同步脉宽调制方法的优势。
但现有专利和文献没有提出如何利用全局同步脉冲宽度调制方法降低多并联逆变器系统中的共模电流。
发明内容
本发明为了解决上述问题，提出了一种双层优化全局同步脉冲宽度调制系 统及方法，本发明能有效避免大规模光伏电站中共模环流问题，提高光伏并网逆变器的转化效率。
为了实现上述目的，本发明采用如下技术方案：
一种双层优化全局同步脉冲宽度调制系统，包括中央全局同步单元、若干个全局同步单元和与各个光伏电池板相连的光伏并网逆变器，并网逆变器划分成若干组，每组逆变器通过隔离变压器与公共并网点相连，其中每个逆变器组中含有一个全局同步单元；
所述全局同步单元，被配置为接收本组逆变器的运行参数，并计算出让所有逆变器共模电流满足要求的相位差，在此相位差下每个变压器注入电网电流中的高次谐波；
所述中央全局同步单元，被配置为接收各个全局同步单元传送的本逆变器组总电流高次谐波信息，并计算让公共并网点注入电网电流中高次谐波含量最小的相位差，以及各个光伏并网逆变器需要执行的最佳相位差。
进一步的，所述中央全局同步单元配置有总电流纹波优化计算程序。
进一步的，所述全局同步单元配置有针对本组逆变器的共模环流优化计算程序。
基于上述系统的双层优化全局同步脉冲宽度调制方法，包括以下步骤：
接收各个逆变器发送的参数，包括逆变器的输出功率、滤波参数以及光伏板与大地间的等效电容参数；
根据接收的参数计算出共模漏电流的数学模型，利用智能优化算法计算出能够让共模漏电流满足要求的相位差；
计算出每个变压器注入公共并网点总电流的各次谐波值；
根据总电流的各次谐波值计算总电流纹波的数学模型，以及让总并网电流高次谐波含量最小的相位差，每个逆变器的最佳相位差并反馈给各个逆变器，进行各个逆变器的同步。
进一步的，逆变器的输出功率可通过逆变器的控制器测量获得，滤波器参数认为是固定值，预先储存在逆变器的控制器中，等效电容参数预先通过测量获得，并存储在逆变器的控制器中。
进一步的，计算共模电流数学模型的步骤包括：
计算逆变器输出的纹波共模电压，将纹波共模电压表示不同频率的纹波电压和，在不同频率纹波电压单独作用下，根据多逆变器并联系统的共模等效电路计算流经各个逆变器的纹波电流，获得每个逆变器的共模电流有效值。
进一步的，利用粒子群算法计算每个逆变器的共模电流有效值的数学模型进行优化，以计算出能够让共模漏电流满足要求的相位差。
进一步的，将每个变压器的输出电流表示为各个频率的谐波电流之和，将总电流各个频率的谐波电流表示为多个变压器输出响应频率谐波电流之和，将总电流的谐波电流表示为多个频率谐波电流的叠加，进而得到总电流的谐波电流有效值。
每个逆变器的最佳相位差为能够让总并网电流高次谐波含量最小的相位差与让共模漏电流满足要求的相位差之和。
与现有技术相比，本发明的有益效果为：
(1)本发明所提方法能有效避免大规模光伏电站中共模环流问题，提高光 伏并网逆变器的转化效率。
(2)本发明所提方法在避免共模环流问题的同时，能够有效降低光伏电站输出总并网电流中的谐波含量，提高光伏电站的输出电能质量。
(3)相较于传统并网逆变器通过加装隔离变压器或额外半导体器件来消除共模环流的方法，本发明所提方法能够在保证逆变器共模环流满足要求的前提下，降低逆变器的成本，增加逆变器的竞争优势。
构成本申请的一部分的说明书附图用来提供对本申请的进一步理解，本申请的示意性实施例及其说明用于解释本申请，并不构成对本申请的不当限定。
图1双层优化全局同步脉冲宽度调制系统；
图2共模电流计算电路示意图；
图3双层优化全局同步脉冲宽度调制方法流程图。
下面结合附图与实施例对本发明作进一步说明。
应该指出，以下详细说明都是例示性的，旨在对本申请提供进一步的说明。除非另有指明，本文使用的所有技术和科学术语具有与本申请所属技术领域的普通技术人员通常理解的相同含义。
需要注意的是，这里所使用的术语仅是为了描述具体实施方式，而非意图限制根据本申请的示例性实施方式。如在这里所使用的，除非上下文另外明确指出，否则单数形式也意图包括复数形式，此外，还应当理解的是，当在本说明书中使用术语“包含”和/或“包括”时，其指明存在特征、步骤、操作、器件、组件和/或它们的组合。
在本发明中，术语如“上”、“下”、“左”、“右”、“前”、“后”、“竖直”、“水平”、“侧”、“底”等指示的方位或位置关系为基于附图所示的方位或位置关系，只是为了便于叙述本发明各部件或元件结构关系而确定的关系词，并非特指本发明中任一部件或元件，不能理解为对本发明的限制。
本发明中，术语如“固接”、“相连”、“连接”等应做广义理解，表示可以是固定连接，也可以是一体地连接或可拆卸连接；可以是直接相连，也可以通过中间媒介间接相连。对于本领域的相关科研或技术人员，可以根据具体情况确定上述术语在本发明中的具体含义，不能理解为对本发明的限制。
正如背景技术所介绍的，现有技术中存在抑制共模电压的方法主要有主动抑制和被动抑制。被动抑制包括采用共模电感、共模抑制变压器、共模滤波器和共模扼流线圈等，这些方法均需要增加硬件成本；主动抑制主要从逆变器的控制算法入手抑制共模电压，但会增加并网逆变器的控制难度的不足，为了解决如上的技术问题，本申请提出了一种双层优化全局同步脉冲宽度调制系统及方法。在光伏电站中，将并网逆变器划分成若干组，每组逆变器通过隔离变压器与公共并网点相连，其中每个逆变器组中含有一个全局同步单元GSU，GSU接收本组逆变器的运行参数，并计算出让所有逆变器共模电流满足要求的相位差
以及在此相位差下每个变压器注入电网电流中的高次谐波。中央全局同步单元Central-GSU接收GSU传送的本逆变器组总电流高次谐波信息，并计算出让公共并网点注入电网电流中高次谐波含量最小的相位差
(Q＝1,…,Q
max)。对于单个逆变器而言，其需要执行的最佳相位差为
该方法能够保证每个逆变器组中的共模电流满足要求，同时让公共并网点注入 电网的电流中含有最少的高次谐波。
如图1所示，双层优化全局同步脉冲宽度调制系统，包括：
中央全局同步单元Central-GSU，若干个全局同步单元GSU，大量的光伏并网逆变器。每个光伏并网逆变器与光伏电池板相连。大量的光伏并网逆变器被分成多个组，如图1所示，设组的数量Q
max，每个组的编号记为Q，其中Q＝1,…,Q
max。每个组中的多个光伏并网逆变器并联并通过隔离升压变压器接入公共并网点，每个组中光伏并网逆变器的数量定为N，逆变器的编号定为M(M＝1,…,N)。Central-GSU与所有GSU进行通讯，GSU与本组内的所有逆变器进行通讯。Central-GSU和GSU可以是单独的控制器，也可以是存在于某个逆变器控制器内的部分功能。Central-GSU中加入总电流纹波优化计算程序，GSU中加入针对本组逆变器的共模环流优化计算程序。
如图3所示，双层优化全局同步脉冲宽度调制方法，包括以下步骤：
步骤(1)：GSU接收各个逆变器发送的参数，包括逆变器的输出功率、滤波参数、光伏板与大地间的等效电容参数等。
步骤(2)：GSU根据步骤(1)接收的参数计算出共模漏电流的数学模型。
步骤(3)：GSU利用智能优化算法计算出能够让共模漏电流满足要求的相位差
步骤(4)：计算出每个变压器注入公共并网点总电流i
TQ的各次谐波值i
TQh并发送给Central-GSU。
步骤(5)：Central-GSU接收到每个GSU发送的i
TQh并计算出总电流纹波的数学模型。
步骤(6)：计算出能够让总并网电流THD最小的相位差
步骤(7)：计算出每个逆变器的最佳相位差为
并发送给各个逆变器。
步骤(8)：Central-GSU向每个GSU发送同步信号，GSU将同步信号转发给本组内的各个逆变器。
步骤(1)中逆变器的输出功率可通过逆变器的控制器测量获得。滤波器参数认为是固定值，可预先储存在逆变器的控制器中。等效电容参数可以预先通过测量获得，并存储在逆变器的控制器中。
步骤(2)中计算共模电流数学模型的步骤如下：
(2-1)计算出逆变器输出的纹波共模电压：
其中，u
M0h为逆变器M的输出共模谐波电压。u
Mah、u
Mbh、u
Mch分别为逆变器a、b、c三相输出电压谐波。
(2-2)将纹波共模电压表示不同频率的纹波电压和：
其中，u
M0hf为逆变器M的输出共模谐波电压中的频率为f的分量。
(2-3)在不同频率纹波电压单独作用下，根据图2多逆变器并联系统的共模等效电路计算流经各个逆变器的纹波电流：
其中，
为逆变器的M的共模漏电流有效值的相量表示形式。
为逆变器M输出谐波电压中频率为f的电压相量。
表示在频率为f时，逆变器i的共模漏电流与逆变器j的输出共模电压之间的导纳关系。
(2-4)获得每个逆变器的共模电流有效值表达式：
其中，I
MLRMS表示逆变器M的共模漏电流有效值。
步骤(3)中GSU利用智能优化算法计算出能够让共模漏电流满足要求的相位差的步骤如下：
利用粒子群算法计算以下数学模型进行优化，优化模型的数学表达为：
步骤(4)计算i
TQh的具体公式为：
其中i
TQh表示逆变器组Q的总输出谐波电流。
所述步骤(5)计算总电流谐波有效值的步骤为：
步骤(5-1)：将每个变压器的输出电流表示为各个频率的谐波电流之和：
其中，i
TQhf表示逆变器组Q的总输出谐波电流有效值中的频率为f的成分。
步骤(5-2)：将总电流各个频率的谐波电流表示为多个变压器输出响应频率谐波电流之和：
其中，i
sumhf表示整个光伏电站输出谐波电流中频率为f的成分。
步骤(5-3)：将总电流的谐波电流表示为多个频率谐波电流的叠加：
其中，i
sumh表示整个光伏电站输出谐波电流。
步骤(5-4)：表示出总电流的谐波电流有效值：
其中，I
sumh表示总谐波电流的有效值。
步骤(6)计算
的数学模型为：
以上所述仅为本申请的优选实施例而已，并不用于限制本申请，对于本领域的技术人员来说，本申请可以有各种更改和变化。凡在本申请的精神和原则之内，所作的任何修改、等同替换、改进等，均应包含在本申请的保护范围之内。
上述虽然结合附图对本发明的具体实施方式进行了描述，但并非对本发明保护范围的限制，所属领域技术人员应该明白，在本发明的技术方案的基础上，本领域技术人员不需要付出创造性劳动即可做出的各种修改或变形仍在本发明的保护范围以内。
Claims (9)
- 一种双层优化全局同步脉冲宽度调制系统，其特征是：包括中央全局同步单元、若干个全局同步单元和与各个光伏电池板相连的光伏并网逆变器，并网逆变器划分成若干组，每组逆变器通过隔离变压器与公共并网点相连，其中每个逆变器组中含有一个全局同步单元；所述全局同步单元，被配置为接收本组逆变器的运行参数，并计算出让所有逆变器共模电流满足要求的相位差，在此相位差下每个变压器注入电网电流中的高次谐波；所述中央全局同步单元，被配置为接收各个全局同步单元传送的本逆变器组总电流高次谐波信息，并计算让公共并网点注入电网电流中高次谐波含量最小的相位差，以及各个光伏并网逆变器需要执行的最佳相位差。
- 如权利要求1所述的一种双层优化全局同步脉冲宽度调制系统，其特征是：中央全局同步单元配置有总电流纹波优化计算程序。
- 如权利要求1所述的一种双层优化全局同步脉冲宽度调制系统，其特征是：所述全局同步单元配置有针对本组逆变器的共模环流优化计算程序。
- 基于如权利要求1-3中任一项所述的系统的双层优化全局同步脉冲宽度调制方法，其特征是：包括以下步骤：接收各个逆变器发送的参数，包括逆变器的输出功率、滤波参数以及光伏板与大地间的等效电容参数；根据接收的参数计算出共模漏电流的数学模型，利用智能优化算法计算出能够让共模漏电流满足要求的相位差；计算出每个变压器注入公共并网点总电流的各次谐波值；根据总电流的各次谐波值计算总电流纹波的数学模型，以及让总并网电流高次谐波含量最小的相位差，每个逆变器的最佳相位差并反馈给各个逆变器，进行各个逆变器的同步。
- 如权利要求4所述的调制方法，其特征是：逆变器的输出功率可通过逆变器的控制器测量获得，滤波器参数认为是固定值，预先储存在逆变器的控制器中，等效电容参数预先通过测量获得，并存储在逆变器的控制器中。
- 如权利要求4所述的调制方法，其特征是：计算共模电流数学模型的步骤包括：计算逆变器输出的纹波共模电压，将纹波共模电压表示不同频率的纹波电压和，在不同频率纹波电压单独作用下，根据多逆变器并联系统的共模等效电路计算流经各个逆变器的纹波电流，获得每个逆变器的共模电流有效值。
- 如权利要求4所述的调制方法，其特征是：利用粒子群算法计算每个逆变器的共模电流有效值的数学模型进行优化，以计算出能够让共模漏电流满足要求的相位差。
- 如权利要求4所述的调制方法，其特征是：将每个变压器的输出电流表示为各个频率的谐波电流之和，将总电流各个频率的谐波电流表示为多个变压器输出响应频率谐波电流之和，将总电流的谐波电流表示为多个频率谐波电流的叠加，进而得到总电流的谐波电流有效值。
- 如权利要求4所述的调制方法，其特征是：每个逆变器的最佳相位差为能够让总并网电流高次谐波含量最小的相位差与让共模漏电流满足要求的相位差之和。
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