CN111856144A - Ground insulation impedance detection circuit and method of photovoltaic inverter - Google Patents
Ground insulation impedance detection circuit and method of photovoltaic inverter Download PDFInfo
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- CN111856144A CN111856144A CN202010918973.9A CN202010918973A CN111856144A CN 111856144 A CN111856144 A CN 111856144A CN 202010918973 A CN202010918973 A CN 202010918973A CN 111856144 A CN111856144 A CN 111856144A
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- 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
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- 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
- G01R27/20—Measuring earth resistance; Measuring contact resistance, e.g. of earth connections, e.g. plates
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Abstract
The invention discloses a ground insulation impedance detection circuit and method of a photovoltaic inverter. The ground insulation impedance detection circuit further comprises a disturbance resistor and a voltage sampling device, a bridge arm of the inverter bridge, which is closest to the bus capacitor, comprises a first switch and a second switch which are connected in series, one end of the first switch is connected to the positive direct-current bus, one end of the second switch is connected to the negative direct-current bus, the first end of the disturbance resistor is grounded, the second end of the disturbance resistor is connected to the middle point of the first switch and the second switch, and the voltage sampling device is connected between the positive direct-current bus and the disturbance resistor. The detection method comprises the following steps: all switches of the driving inverter bridge are switched off, and the sampling voltage Vpe1 in the state is recorded; driving the first switch to close, keeping the other switches open, and recording the sampling voltage Vpe2 in the state; calculating to obtain the insulation resistance to the ground
And R is the resistance value of the disturbance resistor. The invention can quickly solveThe size of the insulation resistance is large, and the hardware cost is low.
Description
Technical Field
The invention belongs to the field of insulation impedance detection of photovoltaic inverters, and relates to a circuit and a method for detecting insulation impedance to ground of a photovoltaic inverter.
Background
In a photovoltaic inverter system, protection of a photovoltaic inverter against ground insulation impedance is important. All regions or countries have clear regulations, and the input end can be used by the standard that the insulation resistance of the earth (the shell) is smaller than the specified threshold value. Insulation impedance detection methods are also various, most of the insulation impedance detection methods are obtained by solving based on kirchhoff's law, and the methods also involve solutions with equivalent infinite sizes and are complex. And the circuit design adopts the signal quantity of the panel input side, so that the hardware cost is higher.
Chinese patent CN105548719B discloses a circuit and a method for detecting insulation resistance to ground, which detect insulation resistance of a photovoltaic inverter based on the circuit for detecting insulation resistance to ground shown in fig. 1. The resistors R01 and R02 are equivalent resistors of the insulation resistance to the ground of the device to be detected, and the resistors R30, R40, R50, R60 and the switch Q10 form a topological structure of the detection circuit. The detection circuit solves the resistance value of the resistors R01 and R02 by introducing resistance disturbance and according to kirchhoff's law. However, in the insulation impedance detection circuit and method, the ground insulation impedance is obtained by solving the equivalent calculation formula, at least one switch needs to be assisted on hardware, the equivalent formula is solved by switching on and off the switch and the input side voltage, devices such as the switch are added on the original circuit of the photovoltaic inverter, the hardware cost is high, the algorithm is complex, and the calculation amount is large.
Disclosure of Invention
In view of the above technical problems, the present invention provides an improved circuit and method for detecting insulation resistance to ground of a photovoltaic inverter.
The invention provides a ground insulation impedance detection circuit of a photovoltaic inverter, which comprises a positive direct current bus, a negative direct current bus, a bus capacitor and an inverter bridge, wherein the bus capacitor and the inverter bridge are electrically connected between the positive direct current bus and the negative direct current bus, the inverter bridge at least comprises a first bridge arm closest to the bus capacitor, the first bridge arm comprises a first switch and a second switch which are connected in series, one end of the first switch is electrically connected to the positive direct current bus, one end of the second switch is electrically connected to the negative direct current bus, the ground insulation impedance detection circuit also comprises a disturbance resistor and a voltage sampling device, wherein the first end of the disturbance resistor is grounded, the second end of the disturbance resistor is electrically connected to the middle point of the first switch and the second switch, the voltage sampling device is electrically connected between the positive direct current bus and the disturbance resistor; the ground isolation impedance detection circuit further comprises a controller for driving all switches of the inverter bridge to be open in a first state and driving the first switch to be closed while the other switches remain open in a second state.
Preferably, the controller is configured to calculate the ground insulation impedance Xiso of the photovoltaic inverter according to the following formula
Wherein R is a resistance value of the disturbance resistance, and Vpe1 and Vpe2 are sampling voltages in the first state and the second state, respectively.
Preferably, the controller is used for receiving the sampling voltage acquired by the voltage sampling device in real time or in timing.
Optionally, the inverter bridge includes, but is not limited to: the first inverter bridge is an H4 inverter bridge or an electric bridge of the H6 inverter bridge closest to the input ends of the positive direct-current bus and the negative direct-current bus.
In a specific embodiment, the inverter bridge further includes a second bridge arm, the second bridge arm and the first bridge arm are connected in parallel, the second bridge arm includes a third switch and a fourth switch that are connected in series, one end of the third switch is electrically connected to the positive dc bus, one end of the fourth switch is electrically connected to the negative dc bus, and the second switch, the third switch and the fourth switch are kept off in the first state and the second state.
Further, the output of the first bridge arm is electrically connected to the positive electrode of the alternating current output end through a connecting wire provided with a first inductor, and the output of the second bridge arm is electrically connected to the negative electrode of the alternating current output end through a connecting wire provided with a second inductor.
Preferably, the controller is electrically connected with the voltage sampling device.
Preferably, the controller is electrically connected to each switch of the inverter bridge.
Another aspect of the present invention provides a method for detecting insulation resistance to ground of a photovoltaic inverter, which employs the circuit for detecting insulation resistance to ground as described above, and the method includes the following steps:
A. all switches of the inverter bridge are driven to be switched off, and the sampling voltage Vpe1 acquired by the voltage sampling device in the state is recorded;
B. driving the first switch to be closed, keeping other switches to be opened, and recording the sampling voltage Vpe2 acquired by the voltage sampling device in the state;
C. calculating the ground insulation impedance Xiso of the photovoltaic inverter according to the following formula
Wherein R is the resistance value of the disturbance resistor.
Preferably, the ground insulation resistance detection method further comprises the following steps: and sending the sampling voltage obtained by the voltage sampling device into the controller, and updating the sampling voltage once by the controller at regular time.
Preferably, the ground insulation resistance detection method further comprises the following steps: when the ground insulation impedance Xiso is smaller than a set threshold value, the photovoltaic inverter enters the next state detection; when the insulation resistance to ground Xiso is greater than or equal to a set threshold value, the photovoltaic inverter self-tests again.
Compared with the prior art, the invention has the following advantages by adopting the scheme:
the ground insulation impedance detection circuit and the ground insulation impedance detection method of the photovoltaic inverter are based on the existing hardware inversion topological structure, do not need to add other switches such as relays and the like, can quickly solve the size of insulation impedance, and have lower hardware cost.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
Fig. 1 is a hardware topology of a photovoltaic inverter ground insulation resistance detection circuit in the prior art;
FIG. 2 is a hardware topology of a ground isolation impedance detection circuit according to an embodiment of the present invention;
fig. 3 is a flowchart of a method for detecting insulation resistance to ground according to an embodiment of the present invention.
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings so that the advantages and features of the invention may be more readily understood by those skilled in the art. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The ground insulation resistance detection circuit and the ground insulation resistance detection method of the photovoltaic inverter according to the embodiment of the present invention will be described in detail by taking the H4 inverter shown in fig. 2 as an example. The hardware topology of the photovoltaic inverter can be expanded to any form, such as an H6 inverter bridge and the like.
Referring to fig. 2, the ground insulation resistance detection circuit of the photovoltaic inverter includes: a positive direct current bus Vbus +, a negative direct current bus Vbus-, a bus capacitor C and an inverter bridge. The positive direct current bus Vbus + and the negative direct current bus Vbus-are respectively provided with an input end positioned on the direct current side of the photovoltaic inverter and used for being electrically connected with the photovoltaic panel. The bus capacitor C is also located on the dc side of the photovoltaic inverter, and a first end of the bus capacitor C is electrically connected to the positive dc bus Vbus +, and a second end is electrically connected to the negative dc bus Vbus-. The inverter bridge comprises a first bridge arm 1 and a second bridge arm 2 which are connected in parallel, wherein the first bridge arm 1 is closest to a bus capacitor C, namely closest to input ends of a positive direct current bus Vbus + and a negative direct current bus Vbus-. The first bridge arm 1 comprises a first switch K1 and a second switch K3 which are connected in series, wherein one end of the first switch K1 is electrically connected to the positive direct current bus Vbus +, and one end of the second switch K3 is electrically connected to the negative direct current bus Vbus-. The second bridge arm 2 comprises a third switch K4 and a fourth switch K2 which are connected in series, wherein one end of the third switch K4 is electrically connected to the positive direct current bus Vbus +, and one end of the fourth switch K2 is electrically connected to the negative direct current bus Vbus-. The outputs of the first bridge arm 1 and the second bridge arm 2 are respectively and electrically connected to the positive electrode of the alternating current output end and the negative electrode of the alternating current output end of the photovoltaic inverter, the positive electrode of the alternating current output end and the negative electrode of the alternating current output end can be electrically connected to a power grid, and alternating current converted by the inverter bridge is fed into the power grid AC. Specifically, the middle point of the first switch K1 and the second switch K3 is electrically connected to the positive electrode of the alternating current output end of the photovoltaic inverter through a connecting wire provided with a first inductor L1; the middle point of the third switch K4 and the fourth switch K2 is electrically connected to the negative electrode of the ac output terminal through a connecting wire with a second inductor L2. The first switch K1, the second switch K3, the third switch K4 and the fourth switch K2 are respectively connected in parallel with a rectifying diode.
Further, the ground insulation resistance detection circuit further comprises a disturbance resistor R and a voltage sampling device Vpe. The first end of the disturbance resistor R is grounded, and the second end of the disturbance resistor R is electrically connected to the middle point of the first switch K1 and the second switch K3. The voltage sampling device Vpe is electrically connected between the positive direct current bus Vbus + and the disturbance resistor R, and is used for collecting the voltage of the positive direct current bus Vbus + to the ground PE. The voltage sampling device Vpe may be a voltage sampling circuit including an operational amplifier or the like, and samples an analog voltage signal of the positive dc bus Vbus + to ground, and converts the analog voltage signal into a digital signal that can be recognized by the MCU. The disturbance resistor R and the voltage sampling device Vpe are both arranged between the bus capacitor C and the first bridge arm 1 of the inverter bridge.
Further, the ground insulation resistance detection circuit also comprises a controller, and the controller is used for driving all switches of the inverter bridge to be opened in the first state and driving the first switch K1 to be closed and other switches to be kept opened in the second state. The controller may specifically comprise an MCU.
The controller is electrically connected with the voltage sampling device Vpe and is used for receiving the sampling voltage acquired by the voltage sampling device Vpe in real time or at regular time.
The switches (including the first switch K1, the second switch K3, the third switch K4 and the fourth switch K2) of the controller and the inverter are electrically connected. When the controller outputs a low level driving signal to the switch, the switch is turned off. When the controller outputs a high level driving signal to the switch, the switch is closed.
The detection principle of the ground insulation resistance detection circuit is as follows:
firstly, the controller controls the switches K1-K4 of all inverter bridge arms of the inverter bridge to be switched off, so that the photovoltaic inverter is in a first state, and the value of the sampling voltage of the direct-current bus voltage to the ground in the state can be expressed as an expression (1):
optimizing the formula (1) into the formula (2)
Vpe1*X1+Vpe1*X2＝X2*Vbus (2)
Further optimized as formula (3)
Then, the controller controls the first switch K1 to close, so that the photovoltaic inverter is in the second state, and the value of the sampling voltage of the direct current bus voltage to the ground in the state can be expressed as formula (4)
Substituting formula (3) for formula (4) to obtain formula (5)
Further optimization to obtain formula (6)
Further optimization to obtain the formula (7)
Vpe2*(Vpe1*X2+R*Vbus)＝Vpe1*R*Vbus (7)
Can obtain the formula (8)
From the principle of hardware, the total insulation resistance Xiso ═ X1// X2 can be obtained, and in combination with formula (3), formula (9) can be obtained
Then pass through
Can finally obtain the formula (10)
In the derivation process, X1 is the equivalent insulation resistance of the positive dc bus Vbus + to ground PE, X2 is the equivalent insulation resistance of the negative dc bus Vbus-to ground PE, R is the disturbance resistance, and Vbus is the dc bus voltage.
Thus, the controller can calculate the ground insulation impedance Xiso of the photovoltaic inverter according to the following formula
Wherein, R is a resistance value of the disturbance resistance, and Vpe1 and Vpe are sampling voltages sampled by the voltage sampling device in the first state and the second state.
Referring to fig. 3, the method for detecting insulation resistance to ground of the photovoltaic inverter of the present embodiment includes the steps of:
s1, sending the sampling voltage Vpe obtained by the voltage sampling device to the MCU, and updating the sampling voltage by the MCU every 20 ms;
s2, the inverter enters a wait self-checking mode, the MCU controls the driving of the switches K1-K4, waits for the time delay of T1, pulls down the driving signal, the switches K1-K4 are all disconnected, and at the moment, the sampling voltage Vpe1 obtained by the voltage sampling device in the state is recorded;
s3, waiting for T2 time delay, setting the driving signal of the first switch K1 to be high, at the moment, closing the first switch K1, and opening the other three switches, at the moment, recording the sampling voltage Vpe2 acquired by the voltage sampling device in the state;
s4, waiting for T3 time delay according to a formula
Finally, calculating the ground insulation impedance Xiso of the photovoltaic inverter;
s5, determination condition: when the Xiso is smaller than the preset threshold value Xset of the software, the machine enters the function detection of the next state; when the Xiso is larger than or equal to the software preset threshold value Xset, the inverter reports the error of the insulation resistance to the ground, and the inverter performs self-checking again.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and are preferred embodiments, which are intended to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (10)
1. A ground insulation impedance detection circuit of a photovoltaic inverter comprises a positive direct-current bus, a negative direct-current bus, a bus capacitor and an inverter bridge, wherein the bus capacitor is electrically connected between the positive direct-current bus and the negative direct-current bus, the inverter bridge at least comprises a first bridge arm closest to the bus capacitor, the first bridge arm comprises a first switch and a second switch which are connected in series, one end of the first switch is electrically connected to the positive direct-current bus, and one end of the second switch is electrically connected to the negative direct-current bus, and the ground insulation impedance detection circuit is characterized in that: the ground insulation impedance detection circuit further comprises a disturbance resistor and a voltage sampling device, wherein a first end of the disturbance resistor is grounded, a second end of the disturbance resistor is electrically connected to a middle point of the first switch and the second switch, and the voltage sampling device is electrically connected between the positive direct current bus and the disturbance resistor; the ground isolation impedance detection circuit further comprises a controller for driving all switches of the inverter bridge to be open in a first state and driving the first switch to be closed while the other switches remain open in a second state.
2. The ground insulation resistance detection circuit according to claim 1, wherein: the controller is used for calculating the ground insulation impedance Xiso of the photovoltaic inverter according to the following formula
Wherein R is a resistance value of the disturbance resistance, and Vpe1 and Vpe2 are sampling voltages in the first state and the second state, respectively.
3. The ground insulation resistance detection circuit according to claim 1 or 2, characterized in that: the controller is used for receiving the sampling voltage acquired by the voltage sampling device in real time or in a timing mode.
4. The ground insulation detection circuit according to claim 1, wherein: the inverter bridge further comprises a second bridge arm, the second bridge arm and the first bridge arm are connected in parallel, the second bridge arm comprises a third switch and a fourth switch which are connected in series, one end of the third switch is electrically connected to the positive direct-current bus, one end of the fourth switch is electrically connected to the negative direct-current bus, and the second switch, the third switch and the fourth switch are all kept disconnected in the first state and the second state.
5. The ground insulation detection circuit according to claim 4, wherein: the output of the first bridge arm is electrically connected to the anode of the alternating current output end through a connecting wire provided with a first inductor, and the output of the second bridge arm is electrically connected to the cathode of the alternating current output end through a connecting wire provided with a second inductor.
6. The ground insulation resistance detection circuit according to claim 1, wherein: the controller is electrically connected with the voltage sampling device.
7. The ground insulation resistance detection circuit according to claim 1, wherein: and the controller is electrically connected with each switch of the inverter bridge.
8. A method for detecting insulation resistance to ground of a photovoltaic inverter, wherein the circuit for detecting insulation resistance to ground of any one of claims 1 to 7 is used, the method comprising the steps of:
A. all switches of the inverter bridge are driven to be switched off, and the sampling voltage Vpe1 acquired by the voltage sampling device in the state is recorded;
B. driving the first switch to be closed, keeping other switches to be opened, and recording the sampling voltage Vpe2 acquired by the voltage sampling device in the state;
C. calculating the ground insulation impedance Xiso of the photovoltaic inverter according to the following formula
Wherein R is the resistance value of the disturbance resistor.
9. The ground insulation resistance detection method according to claim 1, further comprising the steps of: and sending the sampling voltage obtained by the voltage sampling device into the controller, and updating the sampling voltage once by the controller at regular time.
10. The ground insulation resistance detection method according to claim 1, further comprising the steps of: when the ground insulation impedance Xiso is smaller than a set threshold value, the photovoltaic inverter enters the next state detection; when the insulation resistance to ground Xiso is greater than or equal to a set threshold value, the photovoltaic inverter self-tests again.
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| CN112327055A (en) * | 2020-11-09 | 2021-02-05 | 爱士惟新能源技术(扬中)有限公司 | Insulation impedance detection circuit and method for photovoltaic inverter |
| CN112345904A (en) * | 2020-11-02 | 2021-02-09 | 深圳威迈斯新能源股份有限公司 | Insulation detection circuit and detection method thereof |
| CN112540231A (en) * | 2020-12-02 | 2021-03-23 | 爱士惟新能源技术(扬中)有限公司 | Insulation impedance detection circuit and method of photovoltaic inverter |
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| CN114019242A (en) * | 2022-01-06 | 2022-02-08 | 杭州禾迈电力电子股份有限公司 | Method and device for detecting insulation impedance of direct current side of photovoltaic inverter |
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| CN115356540A (en) * | 2022-10-17 | 2022-11-18 | 阳光电源股份有限公司 | Alternating current-direct current ground insulation impedance monitoring device of inverter and self-checking method thereof |
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