WO2022027722A1 - 一种基于pi和mpr的光伏lcl并网逆变器谐波抑制方法 - Google Patents

一种基于pi和mpr的光伏lcl并网逆变器谐波抑制方法 Download PDF

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WO2022027722A1
WO2022027722A1 PCT/CN2020/109108 CN2020109108W WO2022027722A1 WO 2022027722 A1 WO2022027722 A1 WO 2022027722A1 CN 2020109108 W CN2020109108 W CN 2020109108W WO 2022027722 A1 WO2022027722 A1 WO 2022027722A1
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proportional
grid
lcl
controller
photovoltaic
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PCT/CN2020/109108
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English (en)
French (fr)
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冯仰敏
王恩南
谭光道
杨沛豪
杨明伟
张宝锋
李楠
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西安热工研究院有限公司
中国华能集团有限公司贵州分公司
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Publication of WO2022027722A1 publication Critical patent/WO2022027722A1/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
    • 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
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • 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
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • 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
    • 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
    • Y02B10/00—Integration of renewable energy sources in buildings
    • Y02B10/10—Photovoltaic [PV]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40—Arrangements for reducing harmonics

Definitions

  • the invention belongs to the technical field of photovoltaic power generation, and in particular relates to a harmonic suppression method for photovoltaic LCL grid-connected inverters based on PI and MPR.
  • Harmonic pollution is a problem that must be solved when photovoltaic power generation is connected to the grid.
  • the distortion of the grid-connected voltage and current waveforms will cause electromagnetic interference along the lines, increase the operating burden of the load, and in severe cases will cause serious damage to the safe and reliable operation of the power grid. Therefore, it is very important to accurately detect and effectively suppress the harmonic current of photovoltaic power generation grid-connected.
  • one method is to transform the hardware circuit topology of the inverter, and apply the second-order high-pass filter to the photovoltaic inverter grid connection.
  • Resistor selection although this method has better filtering characteristics, it increases the system volume and cost.
  • Another method is to establish a grid-connected model based on an LC-type virtual synchronous generator. In order to effectively suppress the resonance caused by harmonics, a virtual impedance is introduced. Although this method has a good control effect, the design is complicated and is not suitable for practical applications.
  • the technical problem to be solved by the present invention is to provide a method that can achieve harmonic suppression by improving the control algorithm without modifying the hardware circuit topology of the photovoltaic LCL grid-connected inverter. Specifically, on the basis of PI control, an improved MPR is used. control.
  • the present invention adopts the following technical solutions to realize:
  • a harmonic suppression method for photovoltaic LCL grid-connected inverter based on PI and MPR comprising the following steps:
  • Step 1 establish the current feedback closed-loop control model of the LCL type three-phase grid-connected inverter
  • Step 2 in the LCL type three-phase grid-connected inverter current feedback closed-loop control model established in step 1, apply proportional-resonance control, and analyze its transfer function;
  • Step 3 improve the proportional-resonance control in step 2, obtain an improved proportional-resonant controller, and analyze the transfer function;
  • Step 4 compare the amplitude-frequency characteristic curves of the proportional-resonant control in step 2 and the improved proportional-resonant controller in step 3, compare the gain and phase angle, and verify the superiority of the improved proportional-resonant controller in step 3 ;
  • Step 5 in order to suppress the 5th and 7th specific harmonics in the grid-connected current, construct a multiple proportional controller
  • Step 6 the multiple proportional controllers in step 5 are introduced into the improved proportional-resonance controller in step 3, and the transfer function is analyzed;
  • Step 7 The improved proportional-resonance controller with multiple proportional controllers obtained in step 6 is mostly applied to the current PI control of the photovoltaic LCL grid-connected inverter, and under the premise of ensuring error-free tracking of the reference current, the The 5th, 7th and other low-order harmonics existing in the output current are effectively suppressed.
  • a further improvement of the present invention is that, in step 1, an LCL type three-phase grid-connected inverter current feedback closed-loop control model is established, including: G c (s) transfer function of grid-connected inverter current closed-loop control; K PWM inverter Circuit magnification; H is the current feedback coefficient.
  • a further improvement of the present invention is that, in step 2, in the current feedback closed-loop control model of the LCL type three-phase grid-connected inverter established in step 1, proportional-resonance control is applied, and the transfer function is analyzed as follows: Where: K P is the proportional coefficient; K R is the resonance coefficient; ⁇ c is the cutoff frequency; ⁇ 0 is the resonance frequency; s is the differential operator.
  • a further improvement of the present invention is that, in step 3, the proportional-resonance control in step 2 is improved to obtain an improved proportional-resonance controller, and the transfer function is analyzed:
  • a further improvement of the present invention is that, in step 4, the amplitude-frequency characteristic curves of the proportional-resonance control in step 2 and the improved proportional-resonance controller in step 3 are compared, and the gain and phase angle are compared to verify the improved type in step 3.
  • the superiority of the proportional-resonant controller when the parameters K P , K R , ⁇ c and ⁇ 0 are exactly the same, the amplitude gain of the transfer function G PR1 and the transfer function G PR2 at the resonant frequency are compared, and the phase angle range is verified.
  • the progressive proportional-resonant controller can achieve accurate tracking of specific sub-frequency signals.
  • a further improvement of the present invention is that, in step 5, in order to suppress the 5th and 7th specific harmonics in the grid-connected current, a multiple proportional controller is constructed: Where: ⁇ i is the specific resonant frequency.
  • step 6 the multiple proportional controller in step 5 is introduced into the improved proportional-resonance controller in step 3, and the transfer function is analyzed:
  • a further improvement of the present invention is that, in step 7, the improved proportional-resonance controller with multiple proportional controllers obtained in step 6 is mostly applied to the current PI control of the photovoltaic LCL grid-connected inverter, so as to ensure that the reference current is stable to the reference current. Under the premise of error-free tracking, it can effectively suppress the 5th, 7th and other low-order harmonics existing in the output current.
  • the present invention has the following beneficial effects:
  • the invention adopts PI and MPR in the photovoltaic LCL grid-connected inverter control system, which can suppress the harmonics in the grid-side current while ensuring the dynamic response of the grid-connected current.
  • the present invention adopts PI control to realize error-free tracking of the DC reference current, and MPR control can effectively suppress the 5th, 7th and other low-order harmonics in the grid-connected current.
  • MPR control can effectively suppress the 5th, 7th and other low-order harmonics in the grid-connected current.
  • the dynamic responses of the two controllers are completely consistent, and the steady-state operation of the grid-connected inverter system can be guaranteed without compensating for the phase angle.
  • Figure 1 is a topology diagram of an LCL type three-phase grid-connected inverter circuit
  • Figure 2 is a schematic diagram of the current feedback closed-loop control model of the LCL type three-phase grid-connected inverter
  • Fig. 3 is the traditional PR and the improved PR amplitude-frequency characteristic curve
  • Fig. 4 is the phase-frequency characteristic curve of traditional PR and improved PR
  • Fig. 5 is the structural block diagram of MPR control algorithm
  • Fig. 6 is the inverter control structure diagram of PI and MPR control algorithm
  • Fig. 7 is the Nyquist waveform diagram of the transfer function of the PI and MPR controllers
  • Figure 8 is the simulation waveform of the grid-connected current under the PI control scheme
  • Fig. 9 is the THD analysis diagram of the grid-connected current under the PI control scheme.
  • Figure 10 is the simulation waveform of grid-connected current under the PI and MPR control schemes
  • Figure 11 is the THD analysis diagram of the grid-connected current under the PI and MPR control schemes.
  • a layer/element when referred to as being "on" another layer/element, it can be directly on the other layer/element or intervening layers/elements may be present therebetween. element.
  • a layer/element when a layer/element is “on” another layer/element in one orientation, then when the orientation is reversed, the layer/element can be "under” the other layer/element.
  • the present invention provides a method for suppressing harmonics of photovoltaic LCL grid-connected inverter based on PI and MPR, comprising the following steps:
  • Step 1 establish the current feedback closed-loop control model of the LCL type three-phase grid-connected inverter
  • Step 2 in the LCL type three-phase grid-connected inverter current feedback closed-loop control model established in step 1, apply proportional-resonance control, and analyze its transfer function;
  • Step 3 improve the proportional-resonance control in step 2, obtain an improved proportional-resonant controller, and analyze the transfer function;
  • Step 4 compare the amplitude-frequency characteristic curves of the proportional-resonant control in step 2 and the improved proportional-resonant controller in step 3, compare the gain and phase angle, and verify the superiority of the improved proportional-resonant controller in step 3 .
  • Step 5 In order to suppress the 5th and 7th specific harmonics in the grid-connected current, a multiple proportional controller is constructed.
  • step 6 the multiple proportional controller in step 5 is introduced into the improved proportional-resonant controller in step 3, and the transfer function is analyzed.
  • Step 7 The improved proportional-resonance controller with multiple proportional controllers obtained in step 6 is mostly applied to the current PI control of the photovoltaic LCL grid-connected inverter, and under the premise of ensuring error-free tracking of the reference current, the The 5th, 7th and other low-order harmonics existing in the output current are effectively suppressed.
  • U dc is the DC bus voltage
  • C dc is the DC voltage regulator capacitor
  • u is the inverter output voltage
  • uc is the voltage across the capacitor
  • ug is the grid side voltage
  • i 1 is the inverter output Current
  • ic is the current flowing through the capacitor
  • i2 is the grid-side current
  • L1 is the inverter - side inductance
  • R1 is the inverter - side inductor series equivalent resistance
  • L2 is the grid - side inductance
  • R2 is the grid - side inductance Equivalent resistance in series with side inductance.
  • G c (s) is the transfer function of the grid-connected inverter current closed-loop control
  • K PWM is the amplification factor of the inverter circuit
  • H is the current feedback coefficient.
  • the traditional proportional-resonance control can cause resonance at a specific frequency, increase the gain amplitude at this frequency, and is suitable for controlling AC signals. It has good harmonic suppression capability in the controller control system.
  • K P is the proportional coefficient
  • K R is the resonance coefficient
  • ⁇ c is the cut-off frequency.
  • the conventional proportional-resonance control has the largest amplitude gain at the resonant frequency ⁇ c , where the phase is 0, but the amplitude gain at a specific sub-frequency is not very large.
  • the present invention improves the traditional proportional-resonance control, and obtains an improved proportional resonant controller whose transfer function can be written as:
  • parameters K P , K R , ⁇ c are defined in accordance with the traditional proportional-resonance control parameters, and ⁇ 0 is the resonance frequency.
  • the transfer function G PR2 has a larger amplitude gain at the resonant frequency and a wider phase angle range, which can be used for a specific order. Accurate tracking of frequency signals.
  • ⁇ i is a specific sub-resonant frequency.
  • G PI (s) is the transfer function of PI control
  • the error of the sinusoidal three-phase AC signal can be written as e ⁇ (t) and e ⁇ (t) in the ⁇ two-phase stationary coordinate system.
  • the output signal in the dq two-phase rotating coordinate system can be obtained, and then controlled by PI.
  • d JO and q JO are equivalent expressions of decoupling items, and their expressions can be written as:
  • ugd and ugq are the components of the grid side voltage under the dq axis
  • I 1d and I 1q are the components of the inverter side current under the dq axis
  • I 2d and I 2q are the grid side currents under the dq axis components
  • u Cd and u Cq are the components of the capacitor voltage under the dq axis
  • DC given value G(s) is the mathematical model of the inverter transfer function, which can be written as:

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Abstract

一种基于PI和MPR的光伏LCL并网逆变器谐波抑制方法，包括：建立LCL型三相并网逆变器电流反馈闭环控制模型；应用比例-谐振控制，并分析其传递函数；对比例-谐振控制进行改进，得出改进型比例-谐振控制器；对比比例-谐振控制和改进型比例-谐振控制器的幅频特性曲线，对比增益、相角，验证改进型比例-谐振控制器的优越性；为了抑制并网电流中的5次、7次特定次谐波，构建多重比例控制器；将多重比例控制器引入改进型比例-谐振控制器中，分析传递函数；将含有多重比例控制器的改进型比例-谐振控制器应用于光伏LCL并网逆变器电流PI控制中，在保证对参考电流的无误差跟踪前提下，实现对输出电流中存在的5次、7次等低次谐波进行有效抑制。

Description

一种基于PI和MPR的光伏LCL并网逆变器谐波抑制方法 【技术领域】
本发明属于光伏发电技术领域，具体涉及一种基于PI和MPR的光伏LCL并网逆变器谐波抑制方法。
【背景技术】
太阳能作为一种新兴的分布式发电单元，由于自身的局限性，相比于传统发电行业，具有孤岛效应、谐波污染等问题。
谐波污染是光伏发电并网必须要解决的问题。并网电压、电流波形的畸变会对沿途线路造成电磁干扰，增加负载的运行负担，严重时会对电网的安全、可靠运行造成严重损害。因此，对光伏发电并网的谐波电流进行准确检测，并且有效抑制是至关重要的。
目前在光伏发电并网逆变器谐波抑制方面，一种方法是改造逆变器硬件电路拓扑，将二阶高通滤波器应用到光伏逆变并网中，对滤波器元器件即电容、电感、电阻进行选型，该方法虽然滤波特性较好，但增加了系统体积和成本。另一种方法是建立基于LC型虚拟同步发电机并网模型，为了有效抑制谐波引起的谐振，引入虚拟阻抗，该方法虽然控制效果较好，但设计复杂，不适合实际应用。
【发明内容】
本发明所要解决的技术问题是提供一种在不改造光伏LCL并网逆变器硬件电路拓基础上，可以通过控制算法改进达到谐波抑制的方法，具体是在PI控制的基础上采用改进MPR控制。
为达到上述目的，本发明采用以下技术方案予以实现：
一种基于PI和MPR的光伏LCL并网逆变器谐波抑制方法，包括以下步骤：
步骤1，建立LCL型三相并网逆变器电流反馈闭环控制模型；
步骤2，在步骤1建立的LCL型三相并网逆变器电流反馈闭环控制模型中，应用比例-谐振控制，并分析其传递函数；
步骤3，对步骤2中的比例-谐振控制进行改进，得出改进型比例-谐振控制器，分析传递函数；
步骤4，对比步骤2中的比例-谐振控制和步骤3中的改进型比例-谐振控制器的幅频特性曲线，对比增益、相角，验证步骤3中改进型比例-谐振控制器的优越性；
步骤5，为了抑制并网电流中的5次、7次特定次谐波，构建多重比例控制器；
步骤6，将步骤5中多重比例控制器引入步骤3中的改进型比例-谐振控制器中，分析传递函数；
步骤7，将步骤6得到的含有多重比例控制器的改进型比例-谐振控制器多应用于光伏LCL并网逆变器电流PI控制中，在保证对参考电流的无误差跟踪前提下，实现对输出电流中存在的5次、7次等低次谐波进行有效抑制。
本发明进一步的改进在于，步骤1中，建立LCL型三相并网逆变器电流反馈闭环控制模型，包括：G c(s)并网逆变器电流闭环控制的传递函数；K PWM逆变电路放大倍数；H为电流反馈系数。
本发明进一步的改进在于，步骤2中，在步骤1建立的LCL型三相并网逆变器电流反馈闭环控制模型中，应用比例-谐振控制，分析其传递函数为：
Figure PCTCN2020109108-appb-000001
其中：K P是比例系数；K R是谐振系数；ω c是截止频率；ω 0是谐振频率；s为微分算子。
本发明进一步的改进在于，步骤3中，对步骤2中的比例-谐振控制进行改进，得出改进型比例-谐振控制器，分析传递函数：
Figure PCTCN2020109108-appb-000002
本发明进一步的改进在于，步骤4中，对比步骤2中的比例-谐振控制和步骤3中的改进型比例-谐振控制器的幅频特性曲线，对比增益、相角，验证步骤3中改进型比例-谐振控制器的优越性；在参数K P、K R、ω c和ω 0完全相同时，对比传递函数G PR1，传递函数G PR2在谐振频率处的幅值增益，相角范围，验证进型比例-谐振控制器能够实现对特定次频率信号的准确跟踪。
本发明进一步的改进在于，步骤5中，为了抑制并网电流中的5次、7次特定次谐波，构建多重比例控制器：
Figure PCTCN2020109108-appb-000003
其中：ω i为特定次谐振频率。
本发明进一步的改进在于，步骤6中，将步骤5中多重比例控制器引入步骤3中的改进型比例-谐振控制器中，分析传递函数：
Figure PCTCN2020109108-appb-000004
本发明进一步的改进在于，步骤7中，将步骤6得到的含有多重比例控制器的改进型比例-谐振控制器多应用于光伏LCL并网逆变器电流PI控制中，在保证对参考电流的无误差跟踪前提下，实现对输出电流中存在的5次、7次等低次谐波进行有效抑制。
与现有技术相比，本发明具有以下有益效果：
本发明采用PI和MPR在光伏LCL并网逆变器控制系统中，在保证并网电流动态响应的同时，能够抑制网侧电流中的谐波。
进一步，本发明采用PI控制能够实现对直流参考电流的无误差跟踪，MPR控制可以对并网电流中5次、7次等低次谐波进行有效抑制。同时，两个控制器的动态响应完全一致，不用对相角补偿就可以保证并网逆变器系统的稳态运行。
【附图说明】
图1为LCL型三相并网逆变电路拓扑结构图；
图2为LCL型三相并网逆变器电流反馈闭环控制模型原理图；
图3为传统PR和改进PR幅频特性曲线；
图4为传统PR和改进PR相频特性曲线；
图5为MPR控制算法结构框图；
图6为PI和MPR控制算法的逆变器控制结构图；
图7为PI和MPR控制器传递函数的Nyquist波形图；
图8为PI控制方案下的并网电流仿真波形；
图9为PI控制方案下的并网电流THD分析图；
图10为PI和MPR控制方案下的并网电流仿真波形；
图11为PI和MPR控制方案下的并网电流THD分析图。
【具体实施方式】
为了使本技术领域的人员更好地理解本发明方案，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，所描述的实施例仅仅是本发明一部分的实施例，不是全部的实施例，而并非要限制本发明公开的范围。此外，在以下说明中，省略了对公知结构和技术的描述，以避免不必要的混淆本发明公开的概念。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都应当属于本发明保护的范围。
在附图中示出了根据本发明公开实施例的各种结构示意图。这些图并非是按比例绘制的，其中为了清楚表达的目的，放大了某些细节，并且可能省略了某些细节。图中所示出的各种区域、层的形状及它们之间的相对大小、位置关系仅是示例性的，实际中可能由于制造公差或技术限制而有所偏差，并且本领域技术人员根据实际所需可以另外设计具有不同形状、大小、相对位置的区域/层。
本发明公开的上下文中，当将一层/元件称作位于另一层/元件“上”时，该层/元件可以直接位于该另一层/元件上，或者它们之间可以存在居中层/元件。另外，如果在一种朝向中一层/元件位于另一层/元件“上”，那么当调转朝向时，该层/元件可以位于该另一层/元件“下”。
需要说明的是，本发明的说明书和权利要求书及上述附图中的术语“第一”、“第二”等是用于区别类似的对象，而不必用于描述特定的顺序或先后次序。应该理解这样使用的数据在适当情况下可以互换，以便这里描述的本发明的实施例能够以除了在这里图示或描述的那些以外的顺序实施。此外，术语“包括”和“具有”以及他们的任何变形，意图在于覆盖不排他的包含，例如，包含了一系列步骤或单元的过程、方法、系统、产品或设备不必限于清楚地列出的那些步骤或单元，而是可包括没有清楚地列出的或对于这些过程、方法、产品或设备固有的其它步骤或单元。
下面结合附图对本发明做进一步详细描述：
本发明提供的一种基于PI和MPR的光伏LCL并网逆变器谐波抑制方法，包括以下步骤：
步骤1，建立LCL型三相并网逆变器电流反馈闭环控制模型；
步骤2，在步骤1建立的LCL型三相并网逆变器电流反馈闭环控制模型中， 应用比例-谐振控制，并分析其传递函数；
步骤3，对步骤2中的比例-谐振控制进行改进，得出改进型比例-谐振控制器，分析传递函数；
步骤4，对比步骤2中的比例-谐振控制和步骤3中的改进型比例-谐振控制器的幅频特性曲线，对比增益、相角，验证步骤3中改进型比例-谐振控制器的优越性。
步骤5，为了抑制并网电流中的5次、7次特定次谐波，构建多重比例控制器。
步骤6，将步骤5中多重比例控制器引入步骤3中的改进型比例-谐振控制器中，分析传递函数。
步骤7，将步骤6得到的含有多重比例控制器的改进型比例-谐振控制器多应用于光伏LCL并网逆变器电流PI控制中，在保证对参考电流的无误差跟踪前提下，实现对输出电流中存在的5次、7次等低次谐波进行有效抑制。
在图1中，U dc为直流母线电压、C dc为直流稳压电容；u为逆变器输出电压、u c为电容两端电压、u g为网侧电压；i 1为逆变器输出电流、i c为流经电容电流、i 2为网侧电流；L 1为逆变器侧电感、R 1为逆变器侧电感串联等效电阻；L 2为网侧电感、R 2为网侧电感串联等效电阻。
图2中，忽略电感侧串联等效电阻的影响，G c(s)为并网逆变器电流闭环控制的传递函数；K PWM为逆变电路放大倍数；H为电流反馈系数。
在图3中，在图4中，传统比例-谐振控制(Proportional Resonance，PR)，能够引起特定次频率的谐振，增大该频率处的增益幅值，适合控制交流信号，在并网逆变器控制系统中具有良好的谐波抑制能力。
传统PR控制器的传递函数公式可以写成：
Figure PCTCN2020109108-appb-000005
所述传统PR控制器的传递函数中：K P是比例系数；K R是谐振系数；ω c是截止频率。所述传统比例-谐振控制在谐振频率ω c处的幅值增益最大，该频率处的相位为0，但在特定次频率处的幅值增益并不是很大。本发明对传统比例-谐振控制进行改进，得到一种改进型比例谐振控制器，其传递函数可以写成：
Figure PCTCN2020109108-appb-000006
所述改进型比例谐振控制传递函数中：参数K P、K R、ω c与所述传统比例-谐振控制参数定义一致，ω 0是谐振频率。当参数K P、K R、ω c和ω 0完全相同时，相比于传递函数G PR1，传递函数G PR2在谐振频率处的幅值增益较大，相角范围更宽，能够对特定次频率信号的准确跟踪。
在图5中，对光伏LCL并网逆变器输出电流含量最多的5次、7次特定次谐波进行抑制，得到多重比例谐振传递函数：
Figure PCTCN2020109108-appb-000007
所述多重比例谐振传递函数中：ω i为特定次谐振频率。
在图6中，G PI(s)为PI控制的传递函数，
Figure PCTCN2020109108-appb-000008
正弦三相交流信号的误差在αβ两相静止坐标系下可以写成e α(t)、e β(t)，经过Park变换后可以得到dq两相旋转坐标系下的输出信号，之后通过PI控制器，最后经过Park逆变换，最后变换到αβ两相静止坐标系下的输出信号u α(t)、u β(t)。d JO、q JO为等效之后的解耦项表达式，其表达式可以写成：
Figure PCTCN2020109108-appb-000009
其中：u gd、u gq为网侧电压在dq轴下的分量；I 1d、I 1q为逆变器侧电流在dq轴下的分量；I 2d、I 2q为网侧电流在dq轴下的分量；u Cd、u Cq为电容电压在dq 轴下的分量；
Figure PCTCN2020109108-appb-000010
直流给定值；G(s)为逆变器传递函数的数学模型，可以写成：
Figure PCTCN2020109108-appb-000011
为了验证所提出方法的有效性，在Matlab/Simulink搭建了LCL三相并网逆变器仿真实验平台，设开关频率为10KHz、直流母线电压U dc＝80V、直流母线侧电容C dc＝4700μF、逆变器测电容C f＝20μF、L 1＝5mH、L 2＝0.5mH，为了验证所提方法的谐波抑制能力，在仿真中加入3％的5次谐波和3％的7次谐波，此时并网电流中的总谐波畸变率为7.23％。
在图7中，为了验证PI和MPR控制系统的稳定性，对PI和MPR控制器的传递函数进行Nyquist分析，灰色圆形曲线为稳定区间，当控制器传递函数的Nyquist曲线在稳定区间内部时，系统稳定，因此，可以得出PI和MPR控制系统为一个稳定的控制系统的结论。
对比图8和图10，当向并网逆变器控制系统中注入5次、7次谐波时，PI和MPR控制系统下的并网电流波形光滑，正弦特性明显优于传统PI控制系统下的并网电流波形。
对比图9和图11，当向并网逆变器控制系统中注入5次、7次谐波时，PI控制系统下的a相并网电流THD＝7.71％，不能满足并网要求；而PI和MPR控制系统下的THD＝2.03％，满足并网要求，且5次、7次谐波明显降低。
以上内容仅为说明本发明的技术思想，不能以此限定本发明的保护范围，凡是按照本发明提出的技术思想，在技术方案基础上所做的任何改动，均落入本发明权利要求书的保护范围之内。

Claims (8)

  1. 一种基于PI和MPR的光伏LCL并网逆变器谐波抑制方法，其特征在于，包括以下步骤：
    步骤1，建立LCL型三相并网逆变器电流反馈闭环控制模型；
    步骤2，在步骤1建立的LCL型三相并网逆变器电流反馈闭环控制模型中，应用比例-谐振控制，并分析其传递函数；
    步骤3，对步骤2中的比例-谐振控制进行改进，得出改进型比例-谐振控制器，分析传递函数；
    步骤4，对比步骤2中的比例-谐振控制和步骤3中的改进型比例-谐振控制器的幅频特性曲线，对比增益、相角，验证步骤3中改进型比例-谐振控制器的优越性；
    步骤5，为了抑制并网电流中的5次、7次特定次谐波，构建多重比例控制器；
    步骤6，将步骤5中多重比例控制器引入步骤3中的改进型比例-谐振控制器中，分析传递函数；
    步骤7，将步骤6得到的含有多重比例控制器的改进型比例-谐振控制器多应用于光伏LCL并网逆变器电流PI控制中，在保证对参考电流的无误差跟踪前提下，实现对输出电流中存在的5次、7次等低次谐波进行有效抑制。
  2. 根据权利要求1所述的一种基于PI和MPR的光伏LCL并网逆变器谐波抑制方法，其特征在于，步骤1中，建立LCL型三相并网逆变器电流反馈闭环控制模型，包括：G c(s)并网逆变器电流闭环控制的传递函数；K PWM逆变电路放大倍数；H为电流反馈系数。
  3. 根据权利要求1所述的一种基于PI和MPR的光伏LCL并网逆变器谐波抑制方法，其特征在于，步骤2中，在步骤1建立的LCL型三相并网逆变器电 流反馈闭环控制模型中，应用比例-谐振控制，分析其传递函数为：
    Figure PCTCN2020109108-appb-100001
    其中：K P是比例系数；K R是谐振系数；ω c是截止频率；ω 0是谐振频率；s为微分算子。
  4. 根据权利要求3所述的一种基于PI和MPR的光伏LCL并网逆变器谐波抑制方法，其特征在于，步骤3中，对步骤2中的比例-谐振控制进行改进，得出改进型比例-谐振控制器，分析传递函数：
    Figure PCTCN2020109108-appb-100002
  5. 根据权利要求4所述的一种基于PI和MPR的光伏LCL并网逆变器谐波抑制方法，其特征在于，步骤4中，对比步骤2中的比例-谐振控制和步骤3中的改进型比例-谐振控制器的幅频特性曲线，对比增益、相角，验证步骤3中改进型比例-谐振控制器的优越性；在参数K P、K R、ω c和ω 0完全相同时，对比传递函数G PR1，传递函数G PR2在谐振频率处的幅值增益，相角范围，验证进型比例-谐振控制器能够实现对特定次频率信号的准确跟踪。
  6. 根据权利要求5所述的一种基于PI和MPR的光伏LCL并网逆变器谐波抑制方法，其特征在于，步骤5中，为了抑制并网电流中的5次、7次特定次谐波，构建多重比例控制器：
    Figure PCTCN2020109108-appb-100003
    其中：ω i为特定次谐振频率。
  7. 根据权利要求6所述的一种基于PI和MPR的光伏LCL并网逆变器谐波抑制方法，其特征在于，步骤6中，将步骤5中多重比例控制器引入步骤3中的改进型比例-谐振控制器中，分析传递函数：
    Figure PCTCN2020109108-appb-100004
  8. 根据权利要求7所述的一种基于PI和MPR的光伏LCL并网逆变器谐波抑制方法，其特征在于，步骤7中，将步骤6得到的含有多重比例控制器的改 进型比例-谐振控制器多应用于光伏LCL并网逆变器电流PI控制中，在保证对参考电流的无误差跟踪前提下，实现对输出电流中存在的5次、7次等低次谐波进行有效抑制。
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