WO2020253876A1 - 光伏阵列对地绝缘阻抗的检测电路、方法和光伏逆变器 - Google Patents

光伏阵列对地绝缘阻抗的检测电路、方法和光伏逆变器 Download PDF

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WO2020253876A1
WO2020253876A1 PCT/CN2020/097483 CN2020097483W WO2020253876A1 WO 2020253876 A1 WO2020253876 A1 WO 2020253876A1 CN 2020097483 W CN2020097483 W CN 2020097483W WO 2020253876 A1 WO2020253876 A1 WO 2020253876A1
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insulation resistance
ground
photovoltaic array
circuit
detection
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PCT/CN2020/097483
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English (en)
French (fr)
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刘松
黄敏
方刚
卢进军
蒋峰
袁鸿
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江苏固德威电源科技股份有限公司
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Priority to EP20827895.2A priority Critical patent/EP3988947A4/en
Publication of WO2020253876A1 publication Critical patent/WO2020253876A1/zh

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    • 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
    • H02S50/00—Monitoring or testing of PV systems, e.g. load balancing or fault identification
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/025—Measuring very high resistances, e.g. isolation resistances, i.e. megohm-meters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/16—Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line
    • G01R27/18—Measuring resistance to earth, i.e. line to ground
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/52—Testing for short-circuits, leakage current or ground faults
    • 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

Definitions

  • the invention belongs to the technical field of power electronics, and in particular relates to a detection circuit and method for the insulation resistance of a photovoltaic array to the ground, and a photovoltaic inverter based thereon.
  • non-isolated inverters do not have a transformer, while simplifying the circuit structure and saving costs, it also reduces the loss caused by the transformer and greatly improves the conversion efficiency. So it is widely promoted in photovoltaic power generation system.
  • the common method to detect the insulation resistance of photovoltaic arrays to ground is: connect the detection circuit to the input end of the inverter (when multiple inputs are connected, the same effect can be obtained by connecting to the bus capacitor), and by controlling the detection circuit
  • the relay changes the connection of the detection resistance to form an unbalanced bridge, and calculates the voltage on the divider resistance to calculate the insulation resistance.
  • One of the detection circuits is shown in Figure 1. Based on this detection circuit, the detection method is:
  • Step 1 Set the constant voltage of the photovoltaic array to U unchanged.
  • U ad U1 is measured:
  • Step 2 Set the constant voltage of the photovoltaic array to U unchanged.
  • U ad U2 is measured:
  • the current detection circuit requires relays and related drive circuits to be implemented, which will increase the volume and complexity of the inverter, thereby increasing the cost of the inverter. Especially in the current situation that the PV input voltage is getting higher and higher, the higher the specifications of the relay are required, which greatly increases the cost and complexity of the inverter;
  • Multi-channel input requires multiple relays to control the realization. At the same time, the amount of calculation will double, occupying control chip resources;
  • the purpose of the present invention is to provide a detection circuit for the insulation resistance of the photovoltaic array to the ground, which does not require a relay, has a lower complexity, a lower cost, simple calculation and guarantees the function of the inverter.
  • a detection circuit for the insulation resistance of a photovoltaic array to the ground comprising a first switching tube and a second switching tube, two detection resistors and an operational amplifier in an inverter circuit connected to the photovoltaic array.
  • the midpoint of the second switch tube is connected to the inverting input terminal of the operational amplifier via one of the detection resistors, the non-inverting input terminal of the operational amplifier is connected to the protective ground via the other detection resistor, and the operational amplifier
  • the output terminal forms the voltage detection terminal.
  • the detection circuit further includes two matching capacitors and two matching resistors.
  • One of the matching capacitors and one of the matching resistors are connected in parallel between the shield ground and the non-inverting input terminal of the operational amplifier, and the other The matching capacitor and the other matching resistance are connected in parallel between the inverting input terminal and the output terminal of the operational amplifier.
  • the detection circuit for the insulation resistance of the photovoltaic array to the ground further includes a circuit for controlling the first switching tube and the second switching tube, and connecting with the voltage detection terminal for voltage detection and calculating the photovoltaic array Chip with insulation resistance to ground.
  • the detection method adopted by the detection circuit for the insulation resistance of the photovoltaic array to the ground includes the following steps:
  • Step 1 Turn off the first switching tube and turn on the second switching tube, detect the first voltage of the voltage detection terminal and list the first formula
  • Step 2 Turn on the first switch tube and turn off the second switch tube, detect the second voltage at the voltage detection terminal, and list a second formula
  • Step 3 Solve the insulation resistance value of the photovoltaic array to the ground according to the first formula and the second formula.
  • the present invention also provides a photovoltaic inverter with simple structure, low cost, and reliable performance.
  • the photovoltaic inverter includes an inverter circuit, a detection circuit for the insulation resistance of the photovoltaic array to the ground, and an inverter control chip;
  • the variable circuit includes a first switching tube, a second switching tube, a third switching tube, and a fourth switching tube;
  • the detection circuit for the insulation resistance of the photovoltaic array to the ground includes the first switching tube, the second switching tube, Two detection resistors and operational amplifiers, the midpoint of the first switch tube and the second switch tube is connected to the inverting input terminal of the operational amplifier via the detection resistor, and the non-inverting input terminal of the operational amplifier Connected to the protective ground via the other detection resistor, the output terminal of the operational amplifier forms a voltage detection terminal;
  • the inverter control chip is used to control the first switching tube, the second switching tube, and the first switching tube.
  • the present invention has the following advantages compared with the prior art:
  • the present invention uses the original switch tube and drive circuit of the inverter to replace the relay and drive circuit, without additional components, and greatly saves machinery. Space and cost, while reducing the failure probability introduced by components such as relays.
  • the calculation formula based on the detection circuit is more concise, and the calculation amount of the control chip of the inverter can be reduced.
  • Fig. 1 is a circuit diagram of a detection circuit for the insulation resistance of a photovoltaic array to ground in the prior art
  • FIG. 2 is a circuit diagram of a detection circuit for the insulation resistance of a photovoltaic array to ground provided by an embodiment of the present invention
  • Fig. 3 is an equivalent circuit diagram of the detection circuit for the insulation resistance of the photovoltaic array to ground in Fig. 2.
  • Embodiment 1 As shown in Figure 2, the photovoltaic inverter includes an inverter circuit connected to the photovoltaic array.
  • the inverter circuit is a single-phase full-bridge inverter circuit as an example.
  • the inverter circuit includes a first The switching tube Q1, the second switching tube Q2, the third switching tube Q3, and the fourth switching tube Q4.
  • the first switching tube Q1 and the second switching tube Q2 are connected to form a bridge arm, and the third switching tube Q3 and the fourth switching tube Q4 are connected to form another bridge arm.
  • the photovoltaic inverter is applied to a photovoltaic array, and the photovoltaic inverter also includes a detection circuit for the insulation resistance of the photovoltaic array to the ground, an inverter control chip, and other functional circuits, such as a Boost circuit.
  • the detection circuit for the insulation resistance of the photovoltaic array to the ground includes a first resistor R1, a second resistor R2, and an operational amplifier.
  • One end of the first resistor R1 is connected to the non-inverting input terminal of the operational amplifier, and the other of the first resistor R1 is One end is connected to the ground end of the insulation impedance to be measured, one end of the second resistor R2 is connected to the inverting input end of the operational amplifier, and the other end of the second resistor R2 is connected to the inverter circuit connected to the photovoltaic array.
  • connection is as follows: the other end of the second resistor R2 is connected to the middle connecting end of the two switch tubes on the same bridge arm of the inverter circuit, that is, the first switch tube Q1 and the second switch
  • the connection end of the tube Q2 is connected to the other end of the second resistor R2, or the connection end of the third switch tube Q3 and the fourth switch tube Q4 is connected to the other end of the second resistor R2,
  • the connection methods are essentially the same.
  • the former is described as an example, see Figure 2:
  • the first switching tube Q1 and the second switching tube Q2 located on one bridge arm in the inverter circuit also include two detection resistors R1 and an operational amplifier.
  • the midpoint ie, the two switching tubes Q1 and the second switching tube Q2
  • the connection point of the operational amplifier is connected to the inverting input terminal of the operational amplifier via a detection resistor (ie, the second resistor R2), and the non-inverting input terminal of the operational amplifier is connected to the protective ground (ie, the first resistor R1) via another detection resistor (ie, the first resistor R1).
  • a detection resistor ie, the second resistor R2
  • the non-inverting input terminal of the operational amplifier is connected to the protective ground (ie, the first resistor R1) via another detection resistor (ie, the first resistor R1).
  • the output end of the operational amplifier forms a voltage detection end, that is, the insulation resistance of the photovoltaic array to the ground can be detected by detecting the voltage at the output end of the operational amplifier.
  • the detection circuit also includes two matching capacitors (ie, a first capacitor C1 and a second capacitor C2), two matching resistors (ie, a third resistor R3 and a fourth resistor R4), the first capacitor C1 and the third capacitor C1
  • the matching resistor R3 is connected in parallel between the shield ground and the non-inverting input end of the operational amplifier, that is, the first capacitor and the third resistor are connected in parallel to form a first parallel circuit, and one end of the first parallel circuit is connected to the operational amplifier.
  • the non-inverting input terminal is connected, and the other end of the first parallel circuit is connected to the shielding ground terminal; the second capacitor C2 and the fourth resistor R4 are connected in parallel between the inverting input terminal and the output terminal of the operational amplifier.
  • the second capacitor and the fourth resistor are connected in parallel to form a second parallel circuit, one end of the second parallel circuit is connected to the inverting input terminal of the operational amplifier, and the other end of the second parallel circuit is connected to the operational amplifier.
  • the output terminal is connected.
  • the first switching tube Q1 and the second switching tube Q2 in the inverter circuit can also be replaced by the third switching tube Q3 and the fourth switching tube Q4 on the other bridge arm.
  • the shielding ground terminal is the digital ground of the control board, and the PE terminal of the ground terminal is the ground, and there is a difference between the two.
  • the resistance values of the first resistor R1 and the second resistor R2 are equal, the resistance values of the third resistor R3 and the fourth resistor R4 are equal, and the capacitance values of the first capacitor C1 and the second capacitor C2 are equal, This realizes the symmetrical balance of the operational amplifier. It should be noted that even if the above resistance values are not equal or the capacitance values are not equal, the technical solution of the present invention can still be implemented, which only affects the accuracy of the detection circuit of the photovoltaic array's insulation resistance to ground in the embodiment of the present invention.
  • the inverter control chip is used to control the first switching tube Q1, the second switching tube Q2, the third switching tube Q3, and the fourth switching tube Q4 to turn on or off, and is also connected to the voltage detection terminal for controlling the The output terminal of the operational amplifier performs voltage detection to obtain the output voltage U ad .
  • the technical solution of the present invention can also be implemented: the three-phase full-bridge inverter circuit includes a first switch tube on a first bridge arm Q1 and the second switching tube Q2, the third switching tube Q3 and the fourth switching tube Q4 on the second bridge arm, the fifth switching tube Q5 and the sixth switching tube Q6 on the third bridge arm (the fifth switching tube Q5 and The sixth switch tube Q6 is not shown).
  • FIG. 2 only shows an embodiment in which the second resistor R2 is connected to the middle connection ends of the first switch tube Q1 and the second switch tube Q2 of the first bridge arm. .
  • the second resistor R2 is connected to the intermediate connecting ends of the third switch transistor Q3 and the fourth switch transistor Q4 of the second bridge arm, or the second resistor R2 is connected to the third bridge arm (not shown)
  • the connection of the intermediate connection ends of the fifth switch tube Q5 (not shown) and the sixth switch tube Q6 (not shown) is only a simple equivalent transformation, which also falls within the protection scope of the present invention; the photovoltaic array pair
  • the working principle of the detection circuit of ground insulation resistance is as above, so I will not repeat it.
  • the above-mentioned inverter control chip is used to control the first switching tube Q1, the second switching tube Q2, the third switching tube Q3, the fourth switching tube Q4, the fifth switching tube Q5 and the The six-switch tube Q6 is turned on or off.
  • the above-mentioned detection circuit for the insulation resistance of the photovoltaic array to the ground is moved from the PV terminal in the traditional detection circuit to the inverter circuit, using a switch tube instead of a relay to switch, and using the characteristics of the operational amplifier to form a new unbalanced circuit, thereby calculating Insulation resistance to ground.
  • the first switching tube Q1 and the second switching tube Q2 in Figure 2 can be equivalent to a single-pole double-throw switch S; on the other hand, according to the characteristics of the virtual short and virtual disconnection of the operational amplifier, its pins 5 and 6
  • the number pins can be directly shorted together, so that the first resistor R1 and the second resistor R2 are connected in series, and because one end of the first resistor R1 is connected to the PE end, that is, the middle of the two insulation resistances to ground R P and R N to be measured To the ground end PE end, the equivalent circuit obtained is shown in Figure 3.
  • the equivalent single-pole double-throw switch S turns on the circuit on the side where the second switching tube Q2 (the lower side in FIG. 3) is located;
  • the equivalent single-pole double-throw switch S turns on the side (the upper side of FIG. 3) where the first switching tube Q1 is located ( This state is not shown).
  • the detection method adopted by the detection circuit for the insulation resistance of the photovoltaic array to the ground includes the following steps:
  • the first switching device When the first switching device is turned off and the second switching device is turned on, the first voltage value at the output terminal of the operational amplifier is measured; the first switching device is controlled to turn on and the second switching device is turned off , The second voltage value of the output terminal of the operational amplifier is measured; and then according to the output voltage of the photovoltaic array, the first resistance, the second resistance, the first voltage value and the second voltage value, the insulation resistance to ground is calculated Impedance value. details as follows:
  • Step 1 Turn off the first switch Q1 and turn on the second switch Q2, which is equivalent to the single-pole double-throw switch S is switched to PV-, and the detection resistance is measured (that is, the first resistance R1 and the second resistance in series are equivalent R2)
  • the voltage at both ends, the first voltage Uad at the detection voltage detection terminal Uad U1 assuming that the photovoltaic array voltage U is constant, the first formula is listed at this time:
  • U1 is the first voltage value
  • U is the output voltage of the photovoltaic array
  • R1 is the first resistance value
  • R2 is the second resistance value
  • R P is the first insulation resistance value
  • RN is the second insulation resistance value .
  • the second formula is listed:
  • U2 is the second voltage value
  • U is the output voltage of the photovoltaic array
  • R1 is the first resistance value
  • R2 is the second resistance value
  • R P is the first insulation resistance value
  • RN is the second insulation resistance value .
  • Step 3 According to formula (5) and formula (6) to solve the insulation resistance value of photovoltaic array to ground, you can get:
  • R P and R N are the insulation resistance of the photovoltaic array to be tested to the ground.
  • the insulation resistance between the directly electrically connected photovoltaic array and the public grid can be detected in time, which can effectively avoid electrical safety accidents and improve the application of non-isolated inverters.
  • the invention uses the inverter circuit in the photovoltaic array to build a detection circuit for ground insulation impedance, which eliminates the need for relays and reduces costs; and the equivalent circuit further simplifies the impedance calculation formula and reduces the calculation amount of the inverter control chip. Greatly reduce the failure probability of the inverter and ensure the stable output of the photovoltaic network.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)
  • Measurement Of Resistance Or Impedance (AREA)
  • Inverter Devices (AREA)

Abstract

一种光伏阵列对地绝缘阻抗的检测电路，包括与光伏阵列相连接的逆变电路中的第一开关管Q1和第二开关管Q2、两个检测电阻R1、R2和运放，第一开关管Q1和第二开关管Q2的中点经检测电阻R2连接至运放的反相输入端，运放的同相输入端经检测电阻R1连接至对地端PE端，运放的输出端形成电压检测端。检测电路采用的检测方法包括以下步骤：步骤1：令第一开关管Q1截止、第二开关管Q2导通，列出第一公式；步骤2：令第一开关管Q1导通、第二开关管Q2截止，列出第二公式；步骤3：根据第一公式和第二公式求解光伏阵列对地绝缘阻抗值。一种光伏逆变器包括逆变电路、检测电路和逆变控制芯片。检测电路能够节省逆变器的空间和成本，降低逆变器的失效概率，减小逆变控制芯片的运算量。

Description

光伏阵列对地绝缘阻抗的检测电路、方法和光伏逆变器 技术领域
本发明属于电力电子技术领域，具体涉及一种光伏阵列对地绝缘阻抗的检测电路、方法和基于其的光伏逆变器。
背景技术
目前，非隔离型逆变器因为没有变压器，在简化电路结构、节省成本的同时，降低因变压器带来的损耗，极大提升转换效率。从而在光伏发电系统中被大量推广。
但是，从电气安全角度考虑，使用非隔离型逆变器会导致光伏阵列与公共电网为直接的电气连接。因此，需要及时检测出光伏阵列与公共电网间的绝缘阻抗，避免因长时间的日晒、水淋等原因导致光伏阵列的绝缘电阻过小，进而导致并网安全事故，造成人身、财产的损失。
目前，检测光伏阵列对地绝缘阻抗的常用方法是：将检测电路并接到逆变器的输入端(多路输入时，并接在母线电容上也可获得相同效果)，通过控制检测电路中的继电器改变检测电阻的连接，形成不平衡电桥，并计算分压电阻上的电压来计算绝缘阻抗。适当改变继电器和检测电阻的位置，可得到不同的检测电路和算法。其中一种检测电路如图1所示。基于此检测电路，检测方法为：
步骤1，设光伏阵列电压恒定为U不变，当继电器K截止时，测得U ad＝U1：
Figure PCTCN2020097483-appb-000001
步骤2，设光伏阵列电压恒定为U不变，当继电器K导通时，测得U ad＝U2：
Figure PCTCN2020097483-appb-000002
由公式(1)和(2)就可以求解出RP和RN。
上述现有技术存在以下问题：
1、当前的检测电路需要继电器以及相关的驱动电路才能实现，从而会增加逆变器的体积和复杂度，进而增加逆变器的成本。特别是在当前PV输入电压越来越高的情况下，对继电器的规格要求越高，大幅度增加逆变器的成本和复杂程度；
2、计算公式较复杂，增加逆变器的控制芯片运算量；
3、多路输入需要多个继电器来控制实现，同时，计算量也会成倍增加，占用控制芯片资源；
4、在增加元器件的同时，逆变器失效概率增加。
发明内容
本发明的目的是提供一种无需继电器，从而复杂程度较低、成本较低、计算简便且保证逆变器功能的光伏阵列对地绝缘阻抗的检测电路。
为达到上述目的，本发明采用的技术方案是：
一种光伏阵列对地绝缘阻抗的检测电路，包括与光伏阵列相连接的逆变电路中的第一开关管和第二开关管、两个检测电阻和运放，所述第一开关管和所述第二开关管的中点经一个所述检测电阻连接至所述运放的反相输入端，所述运放的同相输入端经另一个所述检测电阻连接至保护接地，所述运放的输出端形成电压检测端。
优选的，所述检测电路还包括两个匹配电容、两个匹配电阻，一个所述匹配电容和一个所述匹配电阻并联后连接在屏蔽接地与所述运放的同相输入端之间，另一个所述匹配电容和所述另一个所述匹配电阻并联后连接在所述运放的反相输入端与输出端之间。
优选的，所述光伏阵列对地绝缘阻抗的检测电路还包括用于控制所述第一开关管和所述第二开关管、与所述电压检测端相连接而进行电压检测并计算得到光伏阵列对地绝缘阻抗值的芯片。
上述光伏阵列对地绝缘阻抗的检测电路采用的检测方法包括以下步骤：
步骤1：令所述第一开关管截止、所述第二开关管导通，检测所述电压检测端的第一电压并列出第一公式；
步骤2：令所述第一开关管导通、所述第二开关管截止，检测所述电压检测 端的第二电压并列出第二公式；
步骤3：根据所述第一公式和所述第二公式求解光伏阵列对地绝缘阻抗值。
本发明还提供一种结构简单、成本较低的、性能可靠的光伏逆变器，该光伏逆变器包括逆变电路、光伏阵列对地绝缘阻抗的检测电路和逆变控制芯片；所述逆变电路包括第一开关管、第二开关管、第三开关管和第四开关管；所述光伏阵列对地绝缘阻抗的检测电路包括所述的第一开关管、所述第二开关管、两个检测电阻和运放，所述第一开关管和所述第二开关管的中点经一个所述检测电阻连接至所述运放的反相输入端，所述运放的同相输入端经另一个所述检测电阻连接至保护接地，所述运放的输出端形成电压检测端；所述逆变控制芯片用于控制所述第一开关管、所述第二开关管、所述第三开关管、所述第四开关管，所述逆变控制芯片还与所述电压检测端相连接而用于进行电压检测并计算得到光伏阵列对地绝缘阻抗值。
由于上述技术方案运用，本发明与现有技术相比具有下列优点：本发明使用逆变器原有的开关管及驱动电路替换继电器及驱动电路，未额外新增元器件，极大的节省机器空间和成本，同时降低了由继电器等元器件引入的失效概率。基于该检测电路的计算公式更加简洁，可以减小逆变器的控制芯片运算量。
附图说明
为了更清楚地说明本发明实施例中的技术方案，下面将对实施例描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅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的前提下，还可以根据这些附图获得其他的附图。
图1为现有技术中的一种光伏阵列对地绝缘阻抗的检测电路电路图；
图2为本发明实施例提供的光伏阵列对地绝缘阻抗的检测电路的电路图；
图3为图2中光伏阵列对地绝缘阻抗的检测电路的等效电路图。
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，更清楚地了解本发明的目的、技术方案及其优点，以下结合具体实施例并参照附图对本发明实施例中 的技术方案进行清楚、完整地描述。需要说明的是，附图中未绘示或描述的实现方式，为所属技术领域中普通技术人员所知的形式。另外，虽然本文可提供包含特定值的参数的示范，但应了解，参数无需确切等于相应的值，而是可在可接受的误差容限或设计约束内近似于相应的值。显然，所描述的实施例仅仅是本发明一部分的实施例，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。除此，本发明的说明书和权利要求书中的术语“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、装置、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。还需要说明的是，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。
下面结合附图所示的实施例对本发明作进一步描述。
实施例一：如附图2所示，光伏逆变器包括与光伏阵列相连接的逆变电路，所述逆变电路以单相全桥逆变电路为例，所述逆变电路包括第一开关管Q1、第二开关管Q2、第三开关管Q3和第四开关管Q4。第一开关管Q1和第二开关管Q2相连接够成一条桥臂，第三开关管Q3和第四开关管Q4相连接够成另一条桥臂。
该光伏逆变器应用于光伏阵列，所述光伏逆变器还包括光伏阵列对地绝缘阻抗的检测电路和逆变控制芯片以及其他功能电路，如Boost升压电路等。
光伏阵列对地绝缘阻抗的检测电路包括第一电阻R1、第二电阻R2和运算放大器，所述第一电阻R1的一端与所述运算放大器的同相输入端连接，所述第一电阻R1的另一端与待测绝缘阻抗的对地端连接，所述第二电阻R2的一端与所述运算放大器的反相输入端连接，所述第二电阻R2的另一端与连接光伏阵列的逆变电路通过如下方式连接：所述第二电阻R2的另一端与所述逆变电路的同一条桥臂上的两个开关管的中间连接端连接，即可以是所述第一开关管Q1与第二开关管Q2的连接端与所述第二电阻R2的另一端连接，也可以是所述第三开关管Q3与第四开关管Q4的连接端与所述第二电阻R2的另一端连接，以上两 种连接方式实质相同，以下以前者为例作出说明，参见图2：
逆变电路中位于一条桥臂上的第一开关管Q1和第二开关管Q2，还包括两个检测电阻R1和运算放大器，第一开关管Q1和第二开关管Q2的中点(即两者的连接点)经一个检测电阻(即第二电阻R2)连接至运算放大器的反相输入端，运算放大器的同相输入端经另一个检测电阻(即第一电阻R1)连接至保护接地(即图2中待测绝缘阻抗的对地端PE端)，运算放大器的输出端形成电压检测端，即可以通过检测所述运算放大器输出端的电压来检测光伏阵列对地绝缘阻抗。此外，该检测电路还包括两个匹配电容(即第一电容C1和第二电容C2)、两个匹配电阻(即第三电阻R3和第四电阻R4)，所述第一电容C1和第三匹配电阻R3并联后连接在屏蔽接地与运算放大器的同相输入端之间，即所述第一电容与第三电阻并联形成第一并联电路，所述第一并联电路的一端与所述运算放大器的同相输入端连接，所述第一并联电路的另一端与屏蔽接地端连接；所述第二电容C2和第四电阻R4并联后连接在运算放大器的反相输入端与输出端之间，即所述第二电容与第四电阻并联形成第二并联电路，所述第二并联电路的一端与所述运算放大器的反相输入端连接，所述第二并联电路的另一端与所述运算放大器的输出端连接。该方案中，采用逆变电路中的第一开关管Q1和第二开关管Q2也可以由另一条桥臂上的第三开关管Q3和第四开关管Q4替代。需要说明的是，所述屏蔽接地端为控制板的数字地，对地端PE端为大地，两者是有区别的。
在本发明的一个优选实施例中，以上第一电阻R1和第二电阻R2阻值相等，第三电阻R3和第四电阻R4阻值相等，第一电容C1和第二电容C2容值相等，这样实现运算放大器的对称平衡。需要说明的是，即使以上电阻值不相等或电容值不相等，依然可以实施本发明的技术方案，其仅仅影响本发明实施例的光伏阵列对地绝缘阻抗的检测电路的准确度。以上R1＝R2，R3＝R4，C1＝C2仅为提高所述检测电路的检测准确度的优选实施例，而不作为本发明所要求保护范围的限定条件。
所述逆变控制芯片用于控制第一开关管Q1、第二开关管Q2、第三开关管Q3、第四开关管Q4导通或截止，还与电压检测端相连接而用于对所述运算放大器的输出端进行电压检测获得输出电压U ad，最后根据光伏阵列的输出电压、 所述第一电阻、第二电阻、电压值U ad，计算得到光伏阵列对地绝缘阻抗值。
需要说明的是，对于上述逆变电路为三相全桥逆变电路的情况，同样可以实现本发明的技术方案：所述三相全桥逆变电路包括第一桥臂上的第一开关管Q1和第二开关管Q2、第二桥臂上的第三开关管Q3和第四开关管Q4、第三桥臂上的第五开关管Q5和第六开关管Q6(第五开关管Q5和第六开关管Q6未图示)。与上述单相全桥逆变电路一样，所述第二电阻R2的一端与所述运算放大器的反相输入端连接，所述第二电阻R2的另一端与所述逆变电路的任意一条桥臂上的两个开关管的中间连接端连接，图2仅示出了所述第二电阻R2与第一桥臂的第一开关管Q1和第二开关管Q2的中间连接端连接的实施例。显然，将所述第二电阻R2与第二桥臂的第三开关管Q3和第四开关管Q4的中间连接端连接、或者将所述第二电阻R2与第三桥臂(未图示)的第五开关管Q5(未图示)和第六开关管Q6(未图示)的中间连接端连接仅是简单的等效变换，同样落入本发明要求的保护范围；所述光伏阵列对地绝缘阻抗的检测电路的工作原理如上，不再赘述。
对于三相全桥逆变电路的情况，上述逆变控制芯片用于控制第一开关管Q1、第二开关管Q2、第三开关管Q3、第四开关管Q4、第五开关管Q5和第六开关管Q6导通或截止。
上述光伏阵列对地绝缘阻抗的检测电路由传统检测电路中位于PV端处移动到逆变电路上，使用开关管替代继电器进行切换，并利用运算放大器的特性形成新的不平衡电路，从而计算出对地绝缘阻抗。
计算对地绝缘阻抗之前，首先对图2中的检测电路转化为图3的等效电路，等效的原理如下：
一方面，图2中的第一开关管Q1和第二开关管Q2能够等效为单刀双掷开关S；另一方面，根据运算放大器虚短和虚断的特性，其5号引脚和6号引脚能够直接短在一起，使得第一电阻R1和第二电阻R2串联，并且由于第一电阻R1的一端与PE端连接，即两个待测对地绝缘阻抗R P和R N的中间对地端PE端，得到的等效电路如附图3所示。当所述第一开关管Q1截止、第二开关管Q2导通时，等效的单刀双掷开关S即导通所述第二开关管Q2所在的一侧(图3下方一侧)电路；当所述第一开关管Q1导通、第二开关管Q2截止时，等效的单刀双 掷开关S即导通所述第一开关管Q1所在的一侧(图3上方一侧)电路(此状态未示出)。
上述光伏阵列对地绝缘阻抗的检测电路采用的检测方法包括以下步骤：
控制所述第一开关器件截止、所述第二开关器件导通的，测得所述运算放大器的输出端的第一电压值；控制所述第一开关器件导通、所述第二开关器件截止，测得所述运算放大器的输出端的第二电压值；再根据光伏阵列的输出电压、所述第一电阻、第二电阻、第一电压值和第二电压值，计算得到对地绝缘阻抗的阻抗值。具体如下：
步骤1：令第一开关管Q1截止、第二开关管Q2导通，相当于单刀双掷开关S切换到PV-，测得检测电阻(即等效为串联的第一电阻R1和第二电阻R2)两端的电压，检测电压检测端的第一电压Uad＝U1，设光伏阵列电压U恒定不变，此时列出第一公式：
Figure PCTCN2020097483-appb-000003
其中，U1为第一电压值，U为光伏阵列的输出电压，R1为第一电阻阻值，R2为第二电阻阻值，R P为第一绝缘阻抗值，R N为第二绝缘阻抗值。
步骤2：令第一开关管Q1导通、第二开关管Q2截止，相当于单刀双掷开关S切换到PV+，测得检测电阻(即等效为串联的第一电阻R1和第二电阻R2)两端的电压，检测电压检测端的第二电压Uad＝U2，设光伏阵列电压U恒定不变，此时列出第二公式：
Figure PCTCN2020097483-appb-000004
其中，U2为第二电压值，U为光伏阵列的输出电压，R1为第一电阻阻值，R2为第二电阻阻值，R P为第一绝缘阻抗值，R N为第二绝缘阻抗值。
以上步骤1和步骤2可以互换顺序。
在优选实施例中，所述第一电阻的阻值与第二电阻的阻值相等，即R1+R2＝2*R1代入以上式(3)和式(4)，进一步简化计算公式如下：
Figure PCTCN2020097483-appb-000005
Figure PCTCN2020097483-appb-000006
步骤3：根据公式(5)和公式(6)求解光伏阵列对地绝缘阻抗值，即可得到：
Figure PCTCN2020097483-appb-000007
Figure PCTCN2020097483-appb-000008
R P、R N即为待检测的光伏阵列对地绝缘阻抗，及时检测出直接电气连接的光伏阵列与公共电网之间的绝缘阻抗，能够有效避免电气安全事故，提升非隔离型逆变器应用的广泛性。
本发明利用光伏阵列中的逆变电路搭建对地绝缘阻抗的检测电路，摆脱了继电器的需求，降低成本；并通过等效电路进一步简化阻抗计算公式，降低逆变器的控制芯片的运算量，大大降低逆变器的失效概率，确保光伏网络的稳定输出。
上述实施例只为说明本发明的技术构思及特点，其目的在于让熟悉此项技术的人士能够了解本发明的内容并据以实施，并不能以此限制本发明的保护范围。凡根据本发明精神实质所作的等效变化或修饰，都应涵盖在本发明的保护范围之内。

Claims (19)

  1. 一种光伏阵列对地绝缘阻抗的检测电路，其特征在于：所述光伏阵列对地绝缘阻抗的检测电路包括与光伏阵列相连接的逆变电路中的第一开关管和第二开关管、两个检测电阻和运放，所述第一开关管和所述第二开关管的中点经一个所述检测电阻连接至所述运放的反相输入端，所述运放的同相输入端经另一个所述检测电阻连接至保护接地，所述运放的输出端形成电压检测端。
  2. 根据权利要求1所述的光伏阵列对地绝缘阻抗的检测电路，其特征在于：所述检测电路还包括两个匹配电容、两个匹配电阻，一个所述匹配电容和一个所述匹配电阻并联后连接在屏蔽接地与所述运放的同相输入端之间，另一个所述匹配电容和所述另一个所述匹配电阻并联后连接在所述运放的反相输入端与输出端之间。
  3. 根据权利要求1或2所述的光伏阵列对地绝缘阻抗的检测电路，其特征在于：所述光伏阵列对地绝缘阻抗的检测电路还包括用于控制所述第一开关管和所述第二开关管、与所述电压检测端相连接而进行电压检测并计算得到光伏阵列对地绝缘阻抗值的芯片。
  4. 一种如权利要求1所述的光伏阵列对地绝缘阻抗的检测电路采用的检测方法，其特征在于：所述检测方法包括以下步骤：
    步骤1：令所述第一开关管截止、所述第二开关管导通，检测所述电压检测端的第一电压并列出第一公式；
    步骤2：令所述第一开关管导通、所述第二开关管截止，检测所述电压检测端的第二电压并列出第二公式；
    步骤3：根据所述第一公式和所述第二公式求解光伏阵列对地绝缘阻抗值。
  5. 一种光伏逆变器，包括逆变电路，所述逆变电路包括第一开关管、第二开关管、第三开关管和第四开关管，其特征在于：所述光伏逆变器还包括：
    光伏阵列对地绝缘阻抗的检测电路，所述光伏阵列对地绝缘阻抗的检测电路包括所述的第一开关管、所述第二开关管、两个检测电阻和运放，所述第一开关管和所述第二开关管的中点经一个所述检测电阻连接至所述运放的反相输入端，所述运放的同相输入端经另一个所述检测电阻连接至保护接地，所述运放的输出端形成电压检测端；
    逆变控制芯片，所述逆变控制芯片用于控制所述第一开关管、所述第二开关管、所述第三开关管、所述第四开关管，所述逆变控制芯片还与所述电压检测端相连接而用于进行电压检测并计算得到光伏阵列对地绝缘阻抗值。
  6. 一种光伏阵列对地绝缘阻抗的检测电路，其特征在于，所述检测电路包括第一电阻、第二电阻和运算放大器，所述第一电阻的一端与所述运算放大器的同相输入端连接，所述第一电阻的另一端与待测绝缘阻抗的对地端连接，所述第二电阻的一端与所述运算放大器的反相输入端连接，所述第二电阻的另一端与连接光伏阵列的逆变电路通过如下方式连接：所述逆变电路包括串联的第一开关器件和第二开关器件，所述第二电阻的另一端与所述第一开关器件和第二开关器件的中间连接端连接；
    通过检测所述运算放大器的输出端的电压值，并根据第一电阻、第二电阻的阻值，得到对地绝缘阻抗的阻抗值。
  7. 根据权利要求6所述的光伏阵列对地绝缘阻抗的检测电路，其特征在于，所述第一电阻与第二电阻阻值相等。
  8. 根据权利要求6所述的光伏阵列对地绝缘阻抗的检测电路，其特征在于，所述检测电路还包括第一电容、第二电容、第三电阻和第四电阻，所述第一电容与第三电阻并联形成第一并联电路，所述第一并联电路的一端与所述运算放大器的同相输入端连接，所述第一并联电路的另一端与屏蔽接地端连接；
    所述第二电容与第四电阻并联形成第二并联电路，所述第二并联电路的一端与所述运算放大器的反相输入端连接，所述第二并联电路的另一端与所述运算放大器的输出端连接。
  9. 根据权利要求8所述的光伏阵列对地绝缘阻抗的检测电路，其特征在于，所述第三电阻与第四电阻阻值相等，所述第一电容与第二电容的容值相等。
  10. 根据权利要求6所述的光伏阵列对地绝缘阻抗的检测电路，其特征在于，所述第一开关器件和第二开关器件为单相全桥逆变电路的任意一个桥臂上的两个开关管。
  11. 根据权利要求6所述的光伏阵列对地绝缘阻抗的检测电路，其特征在于，所述第一开关器件和第二开关器件为三相全桥逆变电路的任意一个桥臂上的两个开关管。
  12. 根据权利要求6所述的光伏阵列对地绝缘阻抗的检测电路，其特征在于，所述检测电路还包括用于控制所述第一开关器件和所述第二开关器件导通或截止的芯片，所述芯片还用于根据所述运算放大器的输出端电压值，计算得到对地绝缘阻抗的阻抗值。
  13. 一种基于权利要求6-12中任意一项所述的光伏阵列对地绝缘阻抗的检测电路的对地绝缘阻抗检测方法，其特征在于，包括以下步骤：
    S1：控制所述第一开关器件截止、所述第二开关器件导通的，测得所述运算放大器的输出端的第一电压值；控制所述第一开关器件导通、所述第二开关器件截止，测得所述运算放大器的输出端的第二电压值；
    S2：根据光伏阵列的输出电压、所述第一电阻、第二电阻、第一电压值和第二电压值，计算得到对地绝缘阻抗的阻抗值。
  14. 根据权利要求13所述的对地绝缘阻抗检测方法，其特征在于，待测绝缘阻抗包括第一绝缘阻抗和第二绝缘阻抗，所述S2包括通过以下公式计算所述对地绝缘阻抗的阻抗值：
    Figure PCTCN2020097483-appb-100001
    其中，U1为第一电压值，U2为第二电压值，U为光伏阵列的输出电压，R1为第一电阻阻值，R2为第二电阻阻值，R P为第一绝缘阻抗值，R N为第二绝缘阻抗值。
  15. 根据权利要求13所述的对地绝缘阻抗检测方法，其特征在于，设置第一电阻与第二电阻阻值相等，则所述S2包括通过以下公式计算所述对地绝缘阻抗的阻抗值：
    Figure PCTCN2020097483-appb-100002
    其中，U1为第一电压值，U2为第二电压值，U为光伏阵列的输出电压，R1为第一电阻阻值，R P为第一绝缘阻抗值，R N为第二绝缘阻抗值。
  16. 一种光伏逆变器，应用于光伏阵列，所述光伏逆变器包括全桥逆变电路，所述全桥逆变电路为单相全桥逆变电路或三相全桥逆变电路，其特征在于，所述光伏逆变器还包括如权利要求6-12中任意一项所述的光伏阵列对地绝缘阻抗的检测电路。
  17. 根据权利要求16所述的光伏逆变器，其特征在于，还包括逆变控制芯片，所述逆变控制芯片用于控制所述全桥逆变电路中的开关管导通或截止，所述逆变控制芯片还用于根据检测电路中第一电阻的阻值、第二电阻的阻值、运算放大器的输出端的电压值来计算光伏阵列对地绝缘阻抗值。
  18. 一种具有对地绝缘阻抗检测功能的光伏系统，包括光伏阵列及与其连接的逆变电路，所述逆变电路为单相全桥逆变电路或三相全桥逆变电路，其特征在于，所述光伏系统还包括如权利要求1-3中任意一项或6-12中任意一项所述的光伏阵列对地绝缘阻抗的检测电路。
  19. 一种具有对地绝缘阻抗检测功能的光伏系统，及与其连接的逆变电路，其特征在于，包括光伏阵列及如权利要求5或16或17所述的光伏逆变器。
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