CN212255492U - Ground insulation impedance detection circuit of photovoltaic inverter - Google Patents
Ground insulation impedance detection circuit of photovoltaic inverter Download PDFInfo
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- CN212255492U CN212255492U CN202021920587.5U CN202021920587U CN212255492U CN 212255492 U CN212255492 U CN 212255492U CN 202021920587 U CN202021920587 U CN 202021920587U CN 212255492 U CN212255492 U CN 212255492U
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Abstract
The utility model discloses a modified photovoltaic inverter's insulating impedance detection circuitry to ground. The ground insulation impedance detection circuit also comprises a disturbance resistor and a voltage sampling device, wherein 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 mutually 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 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, and the voltage sampling device is electrically connected between the positive direct current bus and the disturbance resistor; the ground insulation impedance detection circuit further comprises a controller, and the controller is used for driving the switches of the inverter bridge to be opened or closed. The utility model discloses a hardware cost to ground insulation resistance detection circuitry is lower.
Description
Technical Field
The utility model belongs to photovoltaic inverter insulation impedance detection area relates to a photovoltaic inverter's insulation impedance detection circuitry to ground.
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.
SUMMERY OF THE UTILITY MODEL
To the technical problem, the utility model provides a modified photovoltaic inverter's insulating impedance detection circuitry to ground.
The utility model 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 which 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 insulation impedance detection circuit further comprises a controller, and the controller is used for driving the switches of the inverter bridge to be opened or closed.
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 connected in series, one end of the third switch is electrically connected to the positive dc bus, and one end of the fourth switch is electrically connected to the negative dc bus.
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.
The utility model adopts the above scheme, compare prior art and have following advantage:
the utility model discloses a photovoltaic inverter's insulating impedance detection circuitry to ground based on current hardware contravariant topological structure, need not increase switches such as other relays, and the hardware cost is lower, just can solve out insulating impedance size fast through setting up disturbance resistance moreover.
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 are 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 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 flow chart of the method for detecting the insulation resistance to ground of the detection circuit shown in fig. 2.
Detailed Description
The following detailed description of the preferred embodiments of the invention, taken in conjunction with the accompanying drawings, enables the advantages and features of the invention to 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. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work belong to the protection scope of the present invention.
The ground insulation resistance detection circuit of a photovoltaic inverter according to an embodiment of the present invention will be described in detail by taking an 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 X ═ 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 resistor, and Vpe1 and Vpe2 are sampling voltages sampled by the voltage sampling device in the first state and the second state, respectively.
Referring to fig. 3, the detection method of the ground insulation resistance detection circuit of the photovoltaic inverter includes the following steps:
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 only for illustrating the technical concept and features of the present invention, and are preferred embodiments, which are intended to enable persons skilled in the art to understand the contents of the present invention and to implement the present invention, and thus, the protection scope of the present invention cannot be limited thereby. 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 (5)
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 insulation impedance detection circuit further comprises a controller, and the controller is used for driving the switches of the inverter bridge to be opened or closed.
2. The ground insulation resistance 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, and one end of the fourth switch is electrically connected to the negative direct-current bus.
3. The ground insulation resistance detection circuit according to claim 2, 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.
4. The ground insulation resistance detection circuit according to claim 1, wherein: the controller is electrically connected with the voltage sampling device.
5. The ground insulation resistance detection circuit according to claim 1, wherein: and the controller is electrically connected with each switch of the inverter bridge.
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| CN202021920587.5U CN212255492U (en) | 2020-09-04 | 2020-09-04 | Ground insulation impedance detection circuit of photovoltaic inverter |
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| CN202021920587.5U CN212255492U (en) | 2020-09-04 | 2020-09-04 | Ground insulation impedance detection circuit of photovoltaic inverter |
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