CN218866068U - Detection circuit for insulation resistance to ground of grid-connected photovoltaic power supply - Google Patents
Detection circuit for insulation resistance to ground of grid-connected photovoltaic power supply Download PDFInfo
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- CN218866068U CN218866068U CN202223133234.2U CN202223133234U CN218866068U CN 218866068 U CN218866068 U CN 218866068U CN 202223133234 U CN202223133234 U CN 202223133234U CN 218866068 U CN218866068 U CN 218866068U
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Abstract
The utility model provides a detection circuitry of grid-connected photovoltaic power supply insulation resistance to ground, this detection circuitry includes first positive direct current input, the positive direct current input of second, negative direct current input, contravariant module, first resistance, second resistance and voltage detection module, contravariant module respectively with first positive direct current input, the positive direct current input of second and negative direct current input connection, contravariant module includes first bridge arm and the second bridge arm that connects in parallel each other, first bridge arm includes first switch tube and the second switch tube of mutual series connection, the second bridge arm includes third switch tube and the fourth switch tube of mutual series connection; the first end of the first resistor is connected to the connection point of the first switch tube and the second switch tube, and the second end of the first resistor is used for being connected with a live wire or a ground zero wire of a power grid; the third end of the second resistor is connected to the connection point of the third switching tube and the fourth switching tube, and the fourth end of the second resistor is connected with the second end of the fourth switching tube; the first detection end of the voltage detection module is connected to the first end or the third end, and the second detection end is connected to the second end.
Description
Technical Field
The utility model relates to a circuit detection technology field especially relates to a detection circuitry of grid-connected photovoltaic power supply insulation resistance to ground.
Background
At present, in order to meet the requirement of high-power output, a photovoltaic system is generally connected in series with a plurality of battery assemblies to form a photovoltaic power supply so as to improve voltage, realize connection with a power grid and transmit electric energy to the power grid, and in the photovoltaic system, because the output of a grid-connected photovoltaic power supply has earth impedance to the ground, the insulation impedance is the total equivalent resistance of the output end of the grid-connected photovoltaic power supply to the ground. When the insulation resistance is lower than a specific value, the inverter cannot be used, so that the damage to the whole photovoltaic system caused by the fact that the insulation resistance to the ground is too low is avoided. Therefore, before the photovoltaic inverter is connected to the grid, the photovoltaic power generation system needs to detect and calculate the insulation impedance of the grid-connected photovoltaic power supply to the ground.
In the related art, the grounding of an inverter shell is required for the ground insulation impedance of a grid-connected photovoltaic power supply, measurement and calculation are performed by controlling the on-off of a relay based on an unbalanced bridge principle, and the ground insulation impedance of the grid-connected photovoltaic power supply is difficult to accurately measure under the condition that the inverter shell cannot be grounded or is poor in grounding, and in addition, the ground insulation impedance of the grid-connected photovoltaic power supply cannot be measured and calculated due to the fact that contact failure is easily caused by oxidation of a relay contact. Therefore, how to stably measure the insulation resistance to ground of the grid-connected photovoltaic power supply becomes a problem which needs to be solved urgently.
SUMMERY OF THE UTILITY MODEL
The utility model discloses aim at solving one of the technical problem that exists among the prior art at least. Therefore, the utility model provides a detection circuitry of grid-connected photovoltaic power to insulation resistance to ground can improve the reliability to grid-connected photovoltaic power to insulation resistance to ground measurement.
In a first aspect, an embodiment of the present invention provides a detection circuit for insulation resistance to ground of a grid-connected photovoltaic power supply, including:
a first positive direct current input;
a second positive DC input;
a negative DC input, said negative DC input being grounded;
the positive end of the inversion module is connected with the first positive direct current input and the second positive direct current input respectively, the negative end of the inversion module is connected with the negative direct current input, the inversion module comprises a first bridge arm and a second bridge arm which are connected in parallel, the first bridge arm comprises a first switching tube and a second switching tube which are connected in series, and the second bridge arm comprises a third switching tube and a fourth switching tube which are connected in series;
the first resistor comprises a first end and a second end, the first end is connected to a connection point of the first switch tube and the second switch tube, and the second end is used for being connected with a live wire or a ground zero wire of a power grid;
the second resistor comprises a third end and a fourth end, the third end is connected to a connection point of the third switching tube and the fourth switching tube, and the fourth end is connected with the second end;
the voltage detection module comprises a first detection end and a second detection end, the first detection end is connected to the first end or the third end, the second detection end is connected to the second end, and the voltage detection module is used for detecting voltage between the first detection end and the second detection end.
According to the utility model discloses grid-connected photovoltaic power supply to ground insulation resistance's detection circuitry has following beneficial effect at least: under the condition that a plurality of common-ground grid-connected photovoltaic power supplies are connected to a power grid, the inverter module is respectively connected with each positive direct current input and each negative direct current input, a connection point between two switching tubes in the first bridge arm is connected with a first resistor, and a connection point between two switching tubes in the second bridge arm is connected with a second resistor. The fourth end of second resistance is connected to the second end, and the second end of first resistance is used for being connected with the live wire or the ground connection zero line of electric wire netting, consequently, through the condition of switching on of each switch tube in adjusting the contravariant module, forms different detection circuitry, changes the voltage of loading in first resistance and second resistance two to utilize voltage detection module to detect the voltage of first resistance or second resistance under different circumstances, and then can accurately calculate each positive negative direct current input to ground insulation impedance. Because the resistance disturbance is controlled by using a switching tube of the inverter circuit without depending on an additional relay or an isolation device, the insulation impedance of the grid-connected photovoltaic power supply to the ground is calculated, the cost of devices such as the relay is reduced, the problem that the relay cannot be measured due to poor contact is avoided, and the reliability of the detection circuit is improved.
In the above detection circuit, the voltage detection module includes an operational amplifier, a first capacitor and a feedback resistor, the operational amplifier includes a first input end, a second input end and a voltage output end, the first input end is connected to the first end or the third end, the second input end is connected to the second end, and the first input end is connected to the voltage output end through the feedback resistor; the first capacitor is connected with the feedback resistor in parallel.
Through mutual cooperation of the operational amplifier, the first capacitor and the feedback resistor, under the condition that the first input end is connected to the first end, the voltage at two ends of the first resistor can be measured, and under the condition that the first input end is connected to the third end, the voltage at two ends of the second resistor can be measured, so that the voltage signal of the first resistor or the second resistor can be acquired.
In the detection circuit, the detection circuit further includes a third resistor, the inverter module further includes a third bridge arm connected in parallel with the first bridge arm and the second bridge arm, respectively, the third bridge arm includes a fifth switching tube and a sixth switching tube connected in series, one end of the third resistor is connected between the fifth switching tube and the sixth switching tube, and the other end of the third resistor is connected with the second end.
The third resistor and the third bridge arm are added in the inversion module, namely, the number of the switching tubes of the inversion module is correspondingly increased, so that different conduction conditions of the switching tubes in the inversion module are increased, more detection circuits with different conditions can be formed, and then more grid-connected photovoltaic power supplies, namely the insulation resistance to the ground of positive direct current input can be measured and calculated.
In the above detection circuit, the inverter module includes a first detection state, and when the inverter module is in the first detection state, the first switch tube and the third switch tube are both in a conducting state, and the second switch tube and the fourth switch tube are both in a disconnecting state.
Through the condition of switching on of adjusting first switch tube, second switch tube, third switch tube and fourth switch tube, form first detection circuitry to can obtain the voltage condition of first resistance or second resistance under the contravariant module is in first detection state through the measurement of voltage detection module, and then can calculate the insulating impedance to ground that reachs each direct current input through the voltage condition under the different detection states.
In the above detection circuit, the inverter module includes a second detection state, and when the inverter module is in the second detection state, the first switching tube and the third switching tube are both in an open state, and the second switching tube and the fourth switching tube are both in a closed state.
Through the condition of switching on of adjusting first switch tube, second switch tube, third switch tube and fourth switch tube, form second detection circuitry to can measure through voltage detection module and obtain the voltage condition that first resistance or second resistance are in the second detection state at the contravariant module, and then can calculate through the voltage condition under the different detection states and obtain each direct current input's insulating impedance to ground.
In the above detection circuit, the inverter module includes a third detection state, when the inverter module is in the third detection state, the first switch tube and the fourth switch tube are both in a conducting state, and the second switch tube and the third switch tube are both in a disconnecting state.
Through the condition of switching on of adjusting first switch tube, second switch tube, third switch tube and fourth switch tube, form third detection circuitry to can obtain the voltage condition of first resistance or second resistance under the contravariant module is in the third detection state through the measurement of voltage detection module, and then can calculate the insulating impedance to ground that reachs each direct current input through the voltage condition under the different detection states.
In the above detection circuit, the inverter module includes a fourth detection state, when the inverter module is in the fourth detection state, the first switch tube and the fourth switch tube are both in an open state, and the second switch tube and the third switch tube are both in a closed state.
Through the condition of switching on of adjusting first switch tube, second switch tube, third switch tube and fourth switch tube, form fourth detection circuitry to can obtain the voltage condition of first resistance or second resistance under the contravariant module is in the fourth detection state through the measurement of voltage detection module, and then can calculate the insulating impedance to ground that reachs each direct current input through the voltage condition under the different detection states.
In the above detection circuit, the detection circuit further comprises a bus capacitor, and the bus capacitor is connected in parallel with the inverter module.
The one end of bus capacitor is connected with first positive direct current input and the positive direct current input of second respectively, and the other end is connected with negative direct current input, and bus capacitor is located between direct current input and the contravariant module to bus capacitor can carry out the energy storage, provides input current to the contravariant module, and the protection contravariant module avoids instantaneous peak value to strike.
In the above detection circuit, the detection circuit further includes a plurality of Power factor correction modules, and the first positive dc input and the second positive dc input are respectively connected to the inverter module through each Maximum Power Point Tracking (MPPT) module.
The first positive direct current input and the second positive direct current input are respectively connected with each MPPT module in a one-to-one correspondence mode, so that the MPPT modules can stabilize the output voltage of a photovoltaic power supply and provide stable voltage for the inversion modules.
In the detection circuit, the MPPT module includes a first inductor, a first diode, a second diode, and a correction switching tube, the first inductor is connected in series with the second diode, the first diode is connected in parallel to the first inductor and the second diode, a collector of the correction switching tube is connected to a connection point of the first inductor and the second diode, and an emitter of the correction switching tube is grounded.
When the correction switch tube is switched on, the first inductor stores energy, and when the correction switch tube is switched off, the two ends of the first inductor release electric energy to maintain the current direction and supply power to the inversion module. The second diode can carry out the rectification to the electric current that flows through, and first diode can drive contravariant module fast.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
The present invention will be further described with reference to the accompanying drawings and examples;
fig. 1 is a schematic structural diagram of a detection circuit of a grid-connected photovoltaic power supply insulation resistance to ground provided by an embodiment of the present invention;
fig. 2 is a schematic circuit connection diagram of a detection circuit of a grid-connected photovoltaic power supply to ground insulation resistance provided by the embodiment of the present invention when an inverter module is in a first detection state;
fig. 3 is a schematic circuit connection diagram of the detection circuit of the insulation resistance to ground of the grid-connected photovoltaic power supply provided by the embodiment of the present invention when the inverter module is in the second detection state;
fig. 4 is a schematic circuit connection diagram of a detection circuit of the ground insulation resistance of the grid-connected photovoltaic power supply provided by the embodiment of the present invention when the inverter module is in a third detection state;
fig. 5 is a schematic circuit connection diagram of a detection circuit of insulation resistance to ground of a grid-connected photovoltaic power supply according to another embodiment of the present invention.
Detailed Description
This section will describe in detail the embodiments of the present invention, the preferred embodiments of which are shown in the attached drawings, which are used to supplement the description of the text part of the specification with figures, so that one can visually and vividly understand each technical feature and the whole technical solution of the present invention, but it cannot be understood as a limitation to the scope of the present invention.
It should be understood that in the description of the embodiments of the present invention, if there is any description of "first", "second", etc., it is only for the purpose of distinguishing technical features, and it is not to be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or implicitly indicating the precedence of the indicated technical features. "at least one" means one or more, "a plurality" means two or more. "at least one of the following" and similar expressions refer to any combination of these items, including any combination of singular or plural items.
Furthermore, unless expressly stated or limited otherwise, the term "coupled" is to be construed broadly, and may include, for example, fixed or movable connections, removable or non-removable connections, or integral connections; may be mechanically, electrically or may be in communication with each other; may be directly connected or indirectly connected through an intermediate.
In the description of embodiments of the present disclosure, reference to the terms "one embodiment/implementation," "another embodiment/implementation," or "certain embodiments/implementations," "in the above examples/implementations," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least two embodiments or implementations of the present disclosure. In the present disclosure, a schematic representation of the above terms does not necessarily refer to the same exemplary embodiment or implementation. It should be noted that, although a logical order is illustrated in the flowcharts, in some cases, the steps illustrated or described may be performed in an order different from that in the flowcharts.
It should be noted that the technical features related to the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The embodiment of the utility model provides a detection circuitry of grid-connected photovoltaic power supply insulation resistance to ground, under a plurality of grid-connected photovoltaic power supply that are altogether inserts the electric wire netting the condition, the contravariant module is connected with each positive direct current input and burden direct current input respectively, and the tie point between two switch tubes in first bridge arm is connected first resistance to second resistance is connected to the tie point between two switch tubes in the second bridge arm. The fourth end of second resistance is connected to the second end, and the second end of first resistance is used for being connected with the live wire or the ground connection zero line of electric wire netting, consequently, through the condition of switching on of each switch tube in adjusting the contravariant module, forms different detection circuitry, changes the voltage of loading in first resistance and second resistance two to utilize voltage detection module to detect the voltage of first resistance or second resistance under different circumstances, and then can accurately calculate each positive negative direct current input to ground insulation impedance. Because the resistance disturbance is controlled by using a switching tube of the inverter circuit without depending on an additional relay or an isolation device, the insulation impedance of the grid-connected photovoltaic power supply to the ground is calculated, the cost of devices such as the relay is reduced, the problem that the relay cannot be measured due to poor contact is avoided, and the reliability of the detection circuit is improved.
The embodiments of the present invention will be further explained with reference to the drawings.
Referring to fig. 1, fig. 1 is a schematic structural diagram of a detection circuit of a grid-connected photovoltaic power supply insulation resistance to ground according to an embodiment of the present invention.
Wherein R1 is a first resistor, R2 is a second resistor, BUS + Is the inversion positive voltage of the inversion module positive terminal, BUS - The voltage of the negative electrode of the inverter module is an inverted negative electrode voltage of the negative electrode end of the inverter module, PV1 is a grid-connected photovoltaic power supply connected with a first positive direct current input, PV2 is a grid-connected photovoltaic power supply connected with a second positive direct current input, RZ1 is an equivalent earth impedance of the first positive direct current input, RZ2 is an equivalent earth impedance of the second positive direct current input, RZ3 is an equivalent earth impedance of the negative direct current input, Q1 is a first switching tube in the inverter module, Q2 is a second switching tube in the inverter module, Q3 is a third switching tube in the inverter module, Q4 is a fourth switching tube in the inverter module, R0 is an equivalent earth impedance accessed to a power grid, and the resistance value of R0 is 0 under the condition that a zero line accessed to the power grid is grounded.
It can be understood that, in the case of a photovoltaic system having a plurality of grid-connected photovoltaic power supplies, each grid-connected photovoltaic power supply has an insulation impedance to ground, wherein each grid-connected photovoltaic power supply is grounded through a negative dc input and is connected to the inverter module through a respective positive dc input for performing conversion output, that is, there is an equivalent impedance between each positive dc input and the grounded negative dc input and the ground. In the case of two grid-connected photovoltaic power supplies in a photovoltaic system, the detection circuit has a first positive direct current input, a second positive direct current input and a negative direct current input, so that the three direct current inputs have three impedance to ground, which need to be measured and calculated, wherein the equivalent impedance to ground of the first positive direct current input is a first impedance to ground, the equivalent impedance to ground of the second positive direct current input is a second impedance to ground, and the equivalent impedance to ground of the negative direct current input is a third impedance to ground. In addition, the first positive direct current input and the second positive direct current input in the detection circuit can be increased according to the actual number of the grid-connected photovoltaic power supplies, so that the ground insulation impedance of each grid-connected photovoltaic power supply is calculated.
The detection circuit also comprises an inversion module, a first resistor, a second resistor and a voltage detection module. The inversion module comprises a positive end and a negative end, the first positive direct current input and the second positive direct current input are respectively connected to the positive end of the inversion module, and the negative direct current input is connected to the negative end of the inversion module, so that each grid-connected photovoltaic power supply is input to a power grid after being subjected to inversion processing by the inversion module. The inversion module comprises a first bridge arm and a second bridge arm, the first bridge arm and the second bridge arm are connected in parallel, the first bridge arm comprises a first switch tube and a second switch tube, and the second bridge arm comprises a third switch tube and a fourth switch tube. The collector of the first switch tube is connected with the first positive direct current input, the second positive direct current input and the collector of the third switch tube respectively, the emitter of the first switch tube is connected with the collector of the second switch tube, the emitter of the third switch tube is connected with the collector of the fourth switch tube, and the emitter of the second switch tube and the emitter of the fourth switch tube are connected with the negative direct current input respectively and connected to the ground.
The first resistor comprises a first end and a second end, the first end is connected to a connection point where an emitting electrode of the first switch tube is connected with a collector electrode of the second switch tube, and the second end can be connected with a live wire connected into a power grid or connected with a grounding zero wire connected into the power grid. The second resistor comprises a third end and a fourth end, the third end is connected to a connection point where an emitting electrode of the third switching tube is connected with a collecting electrode of the fourth switching tube, the fourth end is connected with the second end, namely, under the condition that the second end is connected with a live wire of an access power grid, the fourth end can be connected with the live wire of the access power grid, and under the condition that the second end is connected with a grounding zero line of the access power grid, the fourth end can be connected with the grounding zero line of the access power grid.
In addition, the voltage detection module comprises a first detection end and a second detection end, wherein the first detection end can be connected to the first end and also can be connected to the third end, and the second detection end is connected to the second end, so that under the condition that the first detection end is connected to the first end, the voltage detection module is connected with the first resistor in parallel, and the voltage detection module can measure the voltage at the two ends of the first resistor. Under the condition that the first detection end is connected to the third end, the voltage detection module is connected with the second resistor in parallel, so that the voltage detection module can measure the voltage at two ends of the second resistor. The voltage detection module can be further provided with a plurality of voltage detection modules which are respectively connected with the first resistor and the second resistor in parallel and used for simultaneously measuring the voltage of the first resistor and the voltage of the second resistor. The voltage detection module may measure the voltage of the first resistor or the second resistor through a voltage dividing resistor circuit, a linear operational amplifier circuit, or a voltmeter, and the voltage detection module may detect the voltage between the first detection end and the second detection end, that is, the voltage of the first resistor or the second resistor.
Therefore, the first resistor and the second resistor divide the voltage output to the access power grid by the inverter module, so that the output current can be obtained by measuring the voltage of the first resistor and/or the second resistor. The first switch tube, the second switch tube, the third switch tube and the fourth switch tube in the inversion module are respectively in different conduction states, so that different detection circuits can be formed. The input voltages of the inverter modules in the detection circuits in different states are the same, and the voltages of the first resistor and the second resistor are different, so that the equivalent ground impedance of each direct current input can be calculated through the current-voltage relationship of the detection circuits in a plurality of states, namely through the relationship among the currents flowing through the first resistor, the first ground impedance, the second ground impedance and the third ground impedance, and the ground insulation impedance of each grid-connected photovoltaic power supply can be determined. Compared with the scheme that the unbalanced bridge is generated to measure under the condition that the inverter shell is grounded in the related technology, the detection circuit of the grid-connected photovoltaic power supply to the ground insulation resistance does not need an additional relay or an isolation element, but utilizes the switch tube of the inverter module to control resistance disturbance, calculates the insulation impedance of the grid-connected photovoltaic power supply to the ground, avoids the condition that the inverter shell is not grounded or grounded badly and cannot be measured, avoids the condition that the contact of the relay is oxidized to cause bad contact and further cannot be measured, and achieves the effects of reducing the circuit cost and improving the reliability of the detection circuit.
It should be noted that, since the ac voltage of the live wire to the ground zero line connected to the power grid is 220 v, the dc voltage measured by the voltage detection module when the second end is connected to the live wire connected to the power grid is superimposed with a fundamental component on the basis of the dc voltage measured when the second end is connected to the zero line connected to the power grid. Therefore, under the condition that the second end is connected to the power grid live wire, the complete fundamental wave period value of the direct current voltage measured by the voltage detection module is counted, and the counted numerical value is subjected to average processing, so that the alternating current fundamental wave component can be eliminated, and the direct current voltage measured by the voltage detection module under the condition that the second end is connected to the power grid zero line is obtained.
Referring to fig. 2, fig. 2 is a schematic circuit connection diagram of the detection circuit of the insulation resistance to ground of the grid-connected photovoltaic power supply provided by the embodiment of the present invention when the inverter module is in the first detection state.
It can be understood that, under the condition that the inverter module is in the first detection state, the first switching tube and the third switching tube are both in the on state, and the second switching tube and the fourth switching tube are both in the off state. Under the condition that the voltage detection module is connected to the first resistor in parallel, the voltage at two ends of the first resistor is measured to be the first voltage. And calculating the input earth current flowing into the power grid according to the first voltage, the resistance value of the first resistor and the resistance value of the second resistor after the first resistor and the second resistor are connected in parallel. The voltage to ground can be determined by the difference between the voltage of the inverting anode of the inverting module and the first voltage. The first ground current may be derived from a difference between a first access voltage of the first positive dc input and the ground voltage, and the first ground impedance. The second ground current can be obtained by the difference between the second access voltage of the second positive direct current input and the ground voltage and the second ground impedance. The third ground current may be determined from the voltage to ground and the third ground impedance. Therefore, by inputting the relationship among the ground current, the first ground current, the second ground current and the third ground current, the proportional relationship among the first ground impedance, the second ground impedance and the third ground impedance can be determined.
Wherein R1 is the resistance of the first resistor, R2 is the resistance of the second resistor, BUS + For inverting positive voltage, BUS, of the positive terminal of the inverting module - For the inversion negative voltage at the negative terminal of the inversion module, PV1 is the first access voltage from the first positive DC input to the inversion module, PV2 is the second access voltage from the second positive DC input to the inversion module, V R1 Is a first voltage across the first resistor,PE is the difference value of the inversion positive voltage and the first voltage, namely the voltage to ground, RZ1 is the resistance value of the first ground impedance, RZ2 is the resistance value of the second ground impedance, RZ3 is the resistance value of the third ground impedance, Q2 is the second switch tube in the inversion module, Q4 is the fourth switch tube in the inversion module, R0 is the equivalent ground resistance accessed to the power grid, and under the condition that the zero line accessed to the power grid is grounded, the resistance value of R0 is 0. On the BUS - When the voltage is zero, that is, when the negative terminal potential of the inverter module is the reference potential, the relationship among the input ground current, the first ground current, the second ground current, and the third ground current is as shown in the following equation (1).
Because of R1, R2 and BUS + PV1, PV2 and V R1 Can all be obtained by direct measurement, and PE can pass through BUS + And V R1 And (3) determining to obtain the formula (1) and obtaining the formula (2) equivalently.
The K1, the K2, the K3 and the K4 are known constants, so that the relationship among the first ground impedance, the second ground impedance and the third ground impedance can be determined by inputting the relationship among the ground current, the first ground current, the second ground current and the third ground current, and further, the specific numerical values of the first ground impedance, the second ground impedance and the third ground impedance can be simultaneously solved by the detection circuits in different states.
Referring to fig. 3, fig. 3 is a schematic circuit connection diagram of the detection circuit of the insulation resistance to ground of the grid-connected photovoltaic power supply provided by the embodiment of the present invention when the inverter module is in the second detection state.
It can be understood that, when the inverter module is in the second detection state, the first switching tube and the third switching tube are both in the cut-off state, and the second switching tube and the fourth switching tube are both in the conducting state. Under the condition that the voltage detection module is connected to the first resistor in parallel, the voltage at two ends of the first resistor is measured to be the first voltage.
And calculating the input earth current flowing into the power grid according to the first voltage, the resistance value of the first resistor and the resistance value of the second resistor after the first resistor and the second resistor are connected in parallel. And the voltage to ground can be determined by the negative value of the first voltage. The first ground current may be derived from a difference between a first access voltage of the first positive dc input and the ground voltage, and the first ground impedance. The second ground current may be derived from a difference between a second access voltage of the second positive dc input and the ground voltage, and the second ground impedance. By means of the voltage to ground and the third impedance to ground, a third current to ground can be determined. Therefore, by inputting the relationship among the ground current, the first ground current, the second ground current, and the third ground current, the proportional relationship among the first ground impedance, the second ground impedance, and the third ground impedance can be determined.
Wherein R1 is the resistance of the first resistor, R2 is the resistance of the second resistor, BUS + For inverting positive voltage, BUS, of the positive terminal of the inverting module - For the inversion negative voltage at the negative terminal of the inversion module, PV1 is the first access voltage from the first positive DC input to the inversion module, PV2 is the second access voltage from the second positive DC input to the inversion module, V R1 The resistance value of the resistor is equal to the first voltage at two ends of the first resistor, PE is the negative value of the first voltage, namely the voltage to ground, RZ1 is the resistance value of the first ground impedance, RZ2 is the resistance value of the second ground impedance, RZ3 is the resistance value of the third ground impedance, Q1 is a first switch tube in the inverter module, Q3 is a third switch tube in the inverter module, R0 is an equivalent ground resistor accessed to a power grid, and the resistance value of R0 is 0 under the condition that a zero line accessed to the power grid is grounded. On the BUS - When the voltage is zero, that is, when the negative terminal potential of the inverter module is the reference potential, the relationship among the input ground current, the first ground current, the second ground current, and the third ground current is as shown in the following equation (3).
Due to R1, R2, PV1, PV2 and V R1 Can be derived by direct measurement, while PE can be derived by V R1 Is determined to result in, wherein V R1 The detection circuits in different states are different, and therefore, equation (3) can equivalently obtain equation (4).
The K5, the K6, the K7 and the K8 are all known constants, so that the relationship among the first ground impedance, the second ground impedance and the third ground impedance can be determined by inputting the relationship among the ground current, the first ground current, the second ground current and the third ground current, and further, the specific numerical values of the first ground impedance, the second ground impedance and the third ground impedance can be simultaneously solved through the detection circuits in different states.
Referring to fig. 4, fig. 4 is a schematic circuit connection diagram of the detection circuit of the insulation resistance to ground of the grid-connected photovoltaic power supply provided by the embodiment of the present invention when the inverter module is in the third detection state.
It can be understood that, when the inverter module is in the third detection state, the first switching tube and the fourth switching tube are both in the on state, and the second switching tube and the third switching tube are both in the off state. Under the condition that the voltage detection module is connected to the first resistor in parallel, the voltage at two ends of the first resistor is measured to be the first voltage. A first input current flowing into the power grid is calculated through the first voltage and the first resistor. The voltage to ground can be determined by the difference between the inversion positive voltage of the inversion module and the first voltage. And calculating a second input current flowing into the power grid through the voltage to ground and the second resistor. The first ground current can be obtained by the difference between the first access voltage of the first positive direct current input and the ground voltage and the first ground impedance. The second ground current can be obtained by the difference between the second access voltage of the second positive direct current input and the ground voltage and the second ground impedance. The third ground current may be determined from the voltage to ground and the third ground impedance. Therefore, the proportional relationship among the first ground impedance, the second ground impedance and the third ground impedance can be determined through the relationship among the first input current, the second input current, the first ground current, the second ground current and the third ground current.
Wherein R1 is the resistance of the first resistor, R2 is the resistance of the second resistor, BUS + For inverting positive voltage, BUS, of the positive terminal of the inverting module - The negative inversion voltage at the negative end of the inversion module is PV1, the first positive DC input is input to the inversion module, the second positive DC input is input to the inversion module, PV2, and V R1 The first voltage at two ends of the first resistor is PE, the difference value between the inversion positive voltage and the first voltage is namely the voltage to ground, RZ1 is the resistance value of a first impedance to ground, RZ2 is the resistance value of a second impedance to ground, RZ3 is the resistance value of a third impedance to ground, Q2 is a second switching tube in the inversion module, Q3 is a third switching tube in the inversion module, R0 is an equivalent resistance to ground connected to a power grid, and under the condition that a zero line connected to the power grid is grounded, the resistance value of R0 is 0. On the BUS - When the voltage is zero, that is, the negative terminal potential of the inverter module is the reference potential, the relationship among the first input current, the second input current, the first ground-to-ground current, the second ground-to-ground current, and the third ground-to-ground current is as shown in the following equation (5).
Because R1, R2 and BUS + PV1, PV2 and V R1 Can all be obtained by direct measurement, and PE can be obtained by BUS + And V R1 It is determined that, therefore, equation (5) can equivalently yield equation (6).
Since K9, K10, K11, K12, and K13 are known constants, the relationship among the first input current, the second input current, the first ground-to-ground current, the second ground-to-ground impedance, and the third ground-to-ground impedance can be determined, and further, the specific values of the first ground-to-ground impedance, the second ground-to-ground impedance, and the third ground-to-ground impedance can be solved simultaneously by the detection circuits in different states, for example, the equations (2), (4), and (6) in the above embodiment are combined to construct an equation set, that is, the specific values of the first ground-to-ground impedance, the second ground-to-ground impedance, and the third ground-to-ground impedance can be calculated.
It can be understood that, the inverter module includes a fourth detection state, and under the condition that the inverter module is in the fourth detection state, the first switching tube and the fourth switching tube are both in the cut-off state, and the second switching tube and the third switching tube are both in the conduction state. Under the condition that the voltage detection module is connected to the first resistor in parallel, the voltage at two ends of the first resistor is measured to be the first voltage. A first input current flowing into the power grid is calculated through the first voltage and the first resistor. Meanwhile, the voltage to ground can be determined by the first voltage. And calculating a second input current flowing into the power grid through the voltage to ground and the second resistor. The first ground current may be derived from a difference between a first access voltage of the first positive dc input and the ground voltage, and the first ground impedance. The second ground current may be derived from a difference between a second access voltage of the second positive dc input and the ground voltage, and the second ground impedance. The third ground current may be determined from the voltage to ground and the third ground impedance. Therefore, the proportional relationship among the first ground impedance, the second ground impedance and the third ground impedance can be determined through the relationship among the first input current, the second input current, the first ground current, the second ground current and the third ground current, wherein the proportional relationship exists among the sum of the first ground impedance, the second ground impedance and the second input current and the sum of the first input current and the third ground current.
It can be understood that when three equivalent ground impedances exist in the detection circuit, that is, the respective ground impedances of the first positive direct current input, the second positive direct current input and the negative direct current input need to be measured, the specific resistance values of the three equivalent ground impedances can be determined through the proportional relationship of the three equivalent ground impedances formed by the inverter module in three different detection states.
When four equivalent ground impedances exist in the detection circuit, namely the respective ground impedance of three positive direct current inputs and one negative direct current input needs to be measured, the specific resistance values of the four equivalent ground impedances can be determined through the proportional relation of the four equivalent ground impedances formed by the inverter module in four different detection states.
It should be noted that, as the proportional relationship formed when the inverter modules are in different detection states is increased, the amount of the ground impedance of the grid-connected photovoltaic power supply can be detected.
It can be understood that the detection circuit may further include a third resistor, the inverter module includes a third bridge arm, the third bridge arm is connected in parallel with the first bridge arm and the second bridge arm, the third bridge arm includes a fifth switching tube and a sixth switching tube, a collector of the fifth switching tube is connected to each positive dc input, an emitter of the fifth switching tube is connected to a collector of the sixth switching tube, and an emitter of the sixth switching tube is connected to the negative dc input. One end of the third resistor is connected between the fifth switching tube and the sixth switching tube, and the other end of the third resistor is connected with the second end. Therefore, the voltage output to the access power grid by the inverter module is divided by adding the third resistor, and more different detection circuits are generated by increasing the number of the switching tubes in the inverter module, so that the current-voltage relation of the detection circuits in different states can be increased, and more equivalent earth impedance of direct current input can be calculated.
In addition, the first detection end of the voltage detection module can be connected to the connection point of the fifth switching tube and the sixth switching tube, and the second detection end is connected to the second end, so that the voltage detection module can measure the voltage at the two ends of the third resistor.
It should be noted that, according to the actual relationship among the ground impedances of the respective dc inputs, the numbers of the first resistor, the second resistor, and the third resistor may be adjusted, and the number of the switching tubes in the inverter module may also be adjusted, so that the ground impedance of each dc input can be determined through the current conservation relationship between the ground current flowing through the ground impedance of each dc input and the input current flowing through the first resistor, the second resistor, and the third resistor.
Referring to fig. 5, fig. 5 is a schematic circuit connection diagram of a detection circuit of insulation resistance to ground of a grid-connected photovoltaic power supply according to another embodiment of the present invention.
Wherein R1 is a first resistor, R2 is a second resistor, BUS + For inverting positive voltage, BUS, of the positive terminal of the inverting module - The voltage of the negative electrode of the inversion module is the inversion negative voltage of the negative end of the inversion module, PV1 is a grid-connected photovoltaic power supply connected with a first positive direct current input, PV2 is a grid-connected photovoltaic power supply connected with a second positive direct current input, RZ1 is an equivalent earth impedance of the first positive direct current input, RZ2 is an equivalent earth impedance of the second positive direct current input, RZ3 is an equivalent earth impedance of the negative direct current input, Q1 is a first switch tube in the inversion module, Q2 is a second switch tube in the inversion module, Q3 is a third switch tube in the inversion module, Q4 is a fourth switch tube in the inversion module, R0 is an equivalent earth impedance accessed to a power grid, and the resistance value of R0 is 0 under the condition that the zero line accessed to the power grid is grounded.
It is understood that the voltage detection module includes an operational amplifier, a first capacitor and a feedback resistor, wherein the operational amplifier includes a first input terminal, a second input terminal and a voltage output terminal. The feedback resistor is respectively connected to the first input end and the voltage output end, and the first capacitor is also respectively connected to the first input end and the voltage output end, namely the first capacitor and the feedback resistor are mutually connected in parallel. In a case where the first detection terminal of the voltage detection module is connected to the first terminal, the first input terminal is connected to the first terminal, and the second input terminal is connected to the second terminal, so that the voltage across the first resistor can be output from the voltage output terminal through a differential operation or a non-differential operation of the operational amplifier. Under the condition that the first detection end of the voltage detection module is connected to the third end, the first input end is connected to the third end, and the second input end is connected to the second end, so that the voltage output end can output the voltage at two ends of the second resistor.
It should be noted that the voltage detection module further includes a first auxiliary resistor, a second auxiliary resistor, a third auxiliary resistor, and a second capacitor, where the first input terminal is connected to the first terminal through the first auxiliary resistor, or the first input terminal is connected to the third terminal through the first auxiliary resistor, and the second input terminal is connected to the second terminal through the second auxiliary resistor. The second input end is grounded through a third auxiliary resistor, and the second capacitor is connected with the third auxiliary resistor in parallel. C1 is a first capacitor in the voltage detection module, C2 is a second capacitor in the voltage detection module, R5 is a feedback resistor in the voltage detection module, R3 is a first auxiliary resistor in the voltage detection module, R4 is a second auxiliary resistor in the voltage detection module, R6 is a third auxiliary resistor in the voltage detection module, and V R1 Is the voltage output end of the operational amplifier in the voltage detection module.
It can be understood that the detection circuit further comprises a bus capacitor, wherein C0 is the bus capacitor in the detection circuit, the bus capacitor is connected in parallel with the inversion module, one end of the bus capacitor is connected with the first positive direct current input and the second positive direct current input respectively, the other end of the bus capacitor is connected with the negative direct current input, the bus capacitor is located between the direct current input and the inversion module, and therefore the bus capacitor can store energy, provide input current for the inversion module, and protect the inversion module from transient peak impact.
It can be understood that still including a plurality of MPPT modules among the detection circuitry, wherein, MPPT module's quantity is corresponding with positive DC input's quantity, and first positive DC input and second positive DC input are connected with an MPPT module respectively to be connected with the contravariant module through the MPPT module, thereby, the voltage of the photovoltaic input power that is incorporated into the power networks can provide stable input voltage to the contravariant module in the steady voltage effect through the MPPT module. The MPPT module can detect the voltage and the current of the positive direct current input, calculate the power of the positive direct current input, realize the tracking of the maximum power point and stabilize the voltage input to the inversion module.
It is understood that the MPPT module includes a first inductor, a first diode, a second diode, and a correction switch. In addition, the positive end of the first diode is connected to the positive direct current input, the negative end of the first diode is connected to the positive end of the inverter module, namely a branch formed by the series connection of the first inductor and the second diode is connected in parallel with the first diode. The collector of the correction switch tube is connected to the connection point of the first inductor and the second diode, namely the positive terminal of the second diode, and the emitter of the correction switch tube is grounded. When the correction switching tube is switched on, the first inductor stores energy, and when the correction switching tube is switched off, electric energy is released from two ends of the first inductor to maintain the current direction and supply power to the inverter module. The second diode can carry out the rectification to the electric current that flows through, and first diode can drive contravariant module fast. Therefore, the output voltage of the grid-connected photovoltaic power supply can be stabilized by adjusting the on-time of the correction switch tube. Wherein, D1 and D2 are the first diode in the MPPT module, and D3 and D4 are the second diode in the MPPT module, and L1 and L2 are the first inductance in the MPPT module, and Q5 and Q6 are the correction switch tube in the MPPT module.
The embodiments of the present invention have been described in detail with reference to the drawings, but the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art.
Claims (10)
1. A detection circuit for insulation resistance to ground of a grid-connected photovoltaic power supply is characterized by comprising:
a first positive direct current input;
a second positive DC input;
a negative DC input, said negative DC input being grounded;
the first bridge arm comprises a first switch tube and a second switch tube which are connected in series, and the second bridge arm comprises a third switch tube and a fourth switch tube which are connected in series;
the first resistor comprises a first end and a second end, the first end is connected to a connection point of the first switch tube and the second switch tube, and the second end is used for being connected with a live wire or a ground zero wire of a power grid;
the second resistor comprises a third end and a fourth end, the third end is connected to a connection point of the third switching tube and the fourth switching tube, and the fourth end is connected with the second end;
the voltage detection module comprises a first detection end and a second detection end, the first detection end is connected to the first end or the third end, the second detection end is connected to the second end, and the voltage detection module is used for detecting voltage between the first detection end and the second detection end.
2. The detection circuit according to claim 1, wherein the voltage detection module comprises an operational amplifier, a first capacitor and a feedback resistor, the operational amplifier comprises a first input terminal, a second input terminal and a voltage output terminal, the first input terminal is connected to the first terminal or the third terminal, the second input terminal is connected to the second terminal, and the first input terminal is connected to the voltage output terminal through the feedback resistor; the first capacitor is connected in parallel with the feedback resistor.
3. The detection circuit according to claim 1, wherein the detection circuit further includes a third resistor, the inverter module further includes a third bridge arm connected in parallel to the first bridge arm and the second bridge arm, respectively, the third bridge arm includes a fifth switching tube and a sixth switching tube connected in series, one end of the third resistor is connected to a connection point between the fifth switching tube and the sixth switching tube, and the other end of the third resistor is connected to the second end.
4. The detection circuit according to claim 1, wherein the inverter module includes a first detection state, and when the inverter module is in the first detection state, the first switching tube and the third switching tube are both in an on state, and the second switching tube and the fourth switching tube are both in an off state.
5. The detection circuit according to claim 1, wherein the inverter module includes a second detection state, and when the inverter module is in the second detection state, the first switch tube and the third switch tube are both in an open state, and the second switch tube and the fourth switch tube are both in a closed state.
6. The detection circuit according to claim 1, wherein the inverter module includes a third detection state, and when the inverter module is in the third detection state, the first switch tube and the fourth switch tube are both in a conducting state, and the second switch tube and the third switch tube are both in a disconnecting state.
7. The detection circuit according to claim 1, wherein the inverter module includes a fourth detection state, and when the inverter module is in the fourth detection state, the first switch tube and the fourth switch tube are both in an open state, and the second switch tube and the third switch tube are both in a closed state.
8. The detection circuit of claim 1, further comprising a bus capacitor connected in parallel with the inverter module.
9. The detection circuit of claim 1, further comprising a plurality of power factor correction modules, wherein the first positive dc input and the second positive dc input are respectively connected to the inverter module through respective MPPT modules.
10. The detection circuit of claim 9, wherein the MPPT module comprises a first inductor, a first diode, a second diode, and a correction switch, the first inductor is connected in series with the second diode, the first diode is connected in parallel with the first inductor and the second diode, a collector of the correction switch is connected to a connection point of the first inductor and the second diode, and an emitter of the correction switch is grounded.
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| CN202223133234.2U CN218866068U (en) | 2022-11-24 | 2022-11-24 | Detection circuit for insulation resistance to ground of grid-connected photovoltaic power supply |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202223133234.2U CN218866068U (en) | 2022-11-24 | 2022-11-24 | Detection circuit for insulation resistance to ground of grid-connected photovoltaic power supply |
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