CN107748292B - Alternating current insulation detection circuit, system and method - Google Patents
Alternating current insulation detection circuit, system and method Download PDFInfo
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- CN107748292B CN107748292B CN201711267345.3A CN201711267345A CN107748292B CN 107748292 B CN107748292 B CN 107748292B CN 201711267345 A CN201711267345 A CN 201711267345A CN 107748292 B CN107748292 B CN 107748292B
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Abstract
The invention provides an alternating current insulation detection circuit, a system and a method, wherein the alternating current insulation detection circuit is formed by connecting a rectifier bridge, a current-limiting resistor, a controllable switch and a switching power supply module in series between a power grid and the ground, so that the current-limiting resistor and the alternating current power grid ground insulation impedance form a voltage division circuit to realize the calculation of the alternating current power grid ground insulation impedance; meanwhile, a three-phase virtual impedance unit realized by adopting a resistor in the prior art is replaced by the rectifier bridge, so that the problems of large system self-loss and heat dissipation in the prior art are solved.
Description
Technical Field
The invention relates to the technical field of photovoltaic power generation control, in particular to an alternating current insulation detection circuit, system and method.
Background
In order to ensure reliable operation of a high-power three-phase isolation transformer and a photovoltaic power station, a photovoltaic power generation system and a power grid side insulation impedance detection device thereof exist in the prior art, a three-phase virtual impedance unit is realized by adopting a resistor and an inductor, three-phase impedance in the three-phase virtual impedance unit can generate a virtual zero line with the same potential as an actual zero line, and then the virtual zero line is matched with a control unit to calculate, so that power grid side insulation impedance detection is realized.
However, in order to improve the power density of the inverter and the system power generation efficiency, the photovoltaic side direct current input voltage is increased from 1000V to 1500V, and the inverter alternating current side voltage is also increased from 400V, and can be increased to 800V at most. The resistance power is proportional to the square of the voltage, and as the voltage increases, the self-loss of the system is multiplied, and heat dissipation is needed, which affects the service life of the device.
Therefore, the scheme of realizing the three-phase virtual impedance unit through the resistor and further detecting the insulation impedance of the power grid in the prior art is not applicable any more.
Disclosure of Invention
The invention provides an alternating current insulation detection circuit, a system and a method, which aim to solve the problems of large system self-loss and heat dissipation requirement in the prior art.
In order to achieve the purpose, the technical scheme provided by the application is as follows:
an ac insulation detection circuit comprising: the circuit comprises a rectifier bridge, a current-limiting resistor, a controllable switch and a switching power supply module; wherein:
the current limiting resistor and the controllable switch are connected in series between the input end of the rectifier bridge and the high potential end of the switching power supply module;
the output end of the rectifier bridge is connected with a power grid;
and the low potential end of the switching power supply module is grounded.
Preferably, when the power grid is a single-phase power grid, the rectifier bridge is a diode; the anode of the diode is the input end of the rectifier bridge, and the cathode of the diode is the output end of the rectifier bridge.
Preferably, when the power grid is a three-phase power grid, the rectifier bridge includes: two diodes connected in parallel;
the anodes of the two diodes are connected, and the connection point is the input end of the rectifier bridge;
the cathodes of the two diodes are output ends of the rectifier bridge and are respectively connected with any two phases of the power grid in a one-to-one correspondence manner;
alternatively, the rectifier bridge comprises: three diodes connected in parallel;
the anodes of the three diodes are connected, and the connection point is the input end of the rectifier bridge;
and the cathodes of the three diodes are output ends of the rectifier bridge and are respectively connected with the three phases of the power grid in a one-to-one correspondence mode.
Preferably, the switching power supply module is: any one of BUCK topology, BOOST topology, BUCK-BOOST topology, CUK topology, forward topology, flyback topology, half-bridge topology, full-bridge topology and push-pull topology.
An ac insulation detection system comprising: the device comprises a voltage sampling module, a control unit and an alternating current insulation detection circuit; wherein:
the input end of the voltage sampling module is connected with the power grid;
the output end of the voltage sampling module is connected with the input end of the control unit;
the output end of the control unit is connected with the control end of a controllable switch in the alternating current insulation detection circuit;
the control unit is used for: the controllable switch is controlled to be switched off, and a phase voltage peak value is calculated according to the power grid phase voltage detected by the voltage sampling module; controlling the controllable switch to be closed, and calculating a phase voltage-to-average value according to the power grid phase voltage detected by the voltage sampling module; calculating to obtain the earth insulation impedance of the alternating current power grid according to ohm's law; and judging whether the insulation impedance of the alternating current power grid to the ground is smaller than a preset impedance reference, and if the insulation impedance of the alternating current power grid to the ground is smaller than the preset impedance reference, outputting an alarm signal.
Preferably, when the power grid is a three-phase power grid, the control unit calculates a phase voltage peak value according to the power grid phase voltage detected by the voltage sampling module, and an adopted formula is as follows:
Ua＝Ub＝Uc＝Umsinωt；
the method comprises the following steps of obtaining a three-phase grid phase voltage, obtaining a phase voltage peak value, obtaining an angular frequency, and obtaining time.
Preferably, when the power grid is a three-phase power grid, the control unit calculates the ground insulation impedance of the alternating-current power grid according to ohm's law, and the formula is as follows:
wherein, UZFor the grid-to-ground voltage, U1 is the output voltage of the switching power supply module, UEIs the direct current component of the input end of the rectifier bridge to the center line N, an
RZR1 is the resistance of the current limiting resistor, which is the insulation resistance of the ac grid to ground.
Preferably, the method further comprises the following steps: the input end of the data collector is connected with each inverter, and the output end of the data collector is connected with the input end of the control unit;
the output end of the control unit is also connected with the control end of a switch power supply module in the alternating current insulation detection circuit;
and the control unit is also used for adjusting the output of the switching power supply module according to the information obtained by the data acquisition unit so as to reduce the PID effect of the photovoltaic cell panel.
An alternating current insulation detection method is applied to a control unit in an alternating current insulation detection system, and the alternating current insulation detection system further comprises: a voltage sampling module and an alternating current insulation detection circuit as described in any of the above; the input end of the voltage sampling module is connected with the power grid; the output end of the voltage sampling module is connected with the input end of the control unit; the output end of the control unit is connected with the control end of a controllable switch in the alternating current insulation detection circuit;
the alternating current insulation detection method comprises the following steps:
controlling the controllable switch to be switched off;
calculating to obtain a phase voltage peak value according to the power grid phase voltage detected by the voltage sampling module;
controlling the controllable switch to close;
calculating to obtain a phase voltage-to-average value according to the power grid phase voltage detected by the voltage sampling module;
calculating to obtain the earth insulation impedance of the alternating current power grid according to ohm's law;
judging whether the insulation impedance of the alternating current power grid to the ground is smaller than a preset impedance reference or not;
and if the insulation impedance of the alternating current power grid to the ground is smaller than the preset impedance reference, outputting an alarm signal.
Preferably, when the power grid is a three-phase power grid, the calculating according to the grid phase voltage detected by the voltage sampling module to obtain the phase voltage peak value includes:
according to the grid phase voltage Ua, Ub or Uc of any phase detected by the voltage sampling module, calculating to obtain the phase voltage peak value Um through a formula Ua ═ Ub ═ Uc ═ Umsit;
where ω is the angular frequency and t is time.
Preferably, when the power grid is a three-phase power grid, the calculating according to ohm's law to obtain the insulation impedance of the alternating current power grid to the ground includes:
according to ohm's law, by the formula
Calculating to obtain the earth insulation impedance of the alternating current power grid;
wherein, UZFor the grid-to-ground voltage, U1 is the output voltage of the switching power supply module, UEIs the direct current component of the input end of the rectifier bridge to the center line N, an
RZR1 is the resistance of the current limiting resistor, which is the insulation resistance of the ac grid to ground.
The alternating current insulation detection circuit provided by the invention is characterized in that a rectifier bridge, a current-limiting resistor, a controllable switch and a switch power supply module are connected in series between a power grid and the ground, so that the current-limiting resistor and the alternating current power grid ground insulation impedance form a voltage division circuit, and the alternating current power grid ground insulation impedance is calculated; meanwhile, a three-phase virtual impedance unit realized by adopting a resistor in the prior art is replaced by the rectifier bridge, so that the problems of large system self-loss and heat dissipation in the prior art are solved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic circuit diagram of an AC insulation detection system according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a single-phase AC insulation detection circuit provided by an embodiment of the present invention;
FIG. 3 is an equivalent circuit diagram of a three-phase AC insulation detection circuit according to an embodiment of the present invention;
FIG. 4 is an equivalent circuit diagram of another three-phase AC insulation detection circuit provided by an embodiment of the present invention;
FIG. 5 is a schematic diagram of a rectified waveform of point A relative to a neutral line N according to an embodiment of the present invention;
FIG. 6 is another equivalent circuit diagram of a three-phase AC insulation detection circuit provided by an embodiment of the present invention;
fig. 7 is a schematic diagram of a three-phase ac insulation detection method according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. 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 application.
The invention provides an alternating current insulation detection circuit, which aims to solve the problems of large system self-loss and heat dissipation requirement in the prior art.
Specifically, referring to fig. 1, the ac insulation detection circuit includes: a rectifier bridge 101, a current limiting resistor R1, a controllable switch K1 and a switching power supply module 102; wherein:
the current limiting resistor R1 and the controllable switch K1 are connected in series between the input end of the rectifier bridge 101 and the high potential end of the switching power supply module 102;
the output end of the rectifier bridge 101 is connected with a power grid;
the low potential terminal of the switching power supply module 102 is grounded.
In a specific practical application, the connection sequence of the current limiting resistor R1 and the controllable switch K1 in series is not limited to the form shown in fig. 1, and fig. 1 is only an example, and may be determined according to the specific application environment, and is within the protection scope of the present application.
And fig. 1 shows a three-phase power grid as an example, when the power grid is a single-phase power grid, the rectifier bridge 101 may be a diode, and as shown in fig. 2, an anode of the diode is an input end of the rectifier bridge 101, and a cathode of the diode is an output end of the rectifier bridge 101.
When the grid is a three-phase grid, the rectifier bridge 101 may be of the form shown in fig. 1, including: three diodes connected in parallel; the anodes of the three diodes are connected, and the connection point is the input end of the rectifier bridge 101; the cathodes of the three diodes are the output terminals of the rectifier bridge 101, and are connected to the three phases of the power grid in a one-to-one correspondence manner.
Alternatively, when the grid is a three-phase grid, the rectifier bridge 101 may be of the form shown in fig. 3, including: two diodes connected in parallel; the anodes of the two diodes are connected, and the connection point is the input end of the rectifier bridge 101; the cathodes of the two diodes are the output ends of the rectifier bridge 101 and are respectively connected with any two phases of the power grid in a one-to-one correspondence manner;
in the following description, with reference to fig. 1 as an example, Ra, Rb and Rc are the ground impedances of each phase of the three-phase ac network, RZThe value of the insulation impedance to the ground of the alternating current power grid, which is to be calculated, namely the equivalent impedance to the ground of the three-phase alternating current power grid is obtained by connecting Ra, Rb and Rc in parallel; the resistance of the current limiting resistor R1 is known and not only plays a role of current limiting, but also participates in the calculation of the grid impedance, so the current limiting resistor R1 should select a resistor with higher precision. The controllable switch K1 may be a contactor, a relay or a semiconductor controllable component, and is not limited herein, depending on the application environment, and is within the scope of the present application. The output voltage of the switching power supply module 102 is U1, and its amplitude is controllable.
Referring to fig. 4, which is an equivalent circuit diagram of the ac insulation detection circuit shown in fig. 1, a phase voltage peak value Um may be calculated from the power grid phase voltage Ua, Ub, or Uc of any one phase, where Ua ═ Ub ═ Uc ═ Umsin ω t; where ω is the angular frequency and t is time.
FIG. 5 shows a rectified waveform of point A relative to the center line N in FIGS. 1 and 4, wherein only the DC component is considered in the present application, and therefore the AC component is removed from the rectified waveform to obtain a DC component UEThe approximate values are:
as can be seen from fig. 4, since the dc components of the three-phase grid phase voltages Ua, Ub and Uc are zero, the influence of the three-phase grid voltages on the topology shown in fig. 4 can be eliminated, and the equivalent diagram can be further simplified as shown in fig. 6. Here, it can be derived from ohm's law:
wherein, UZThe voltage of the power grid to the ground is equal to the average value of the voltage of the power grid to the ground.
In a specific detection process, because the grid phase voltages Ua, Ub or Uc need to be known, if the switching power supply module 102 is directly connected to a circuit, the waveforms of the grid phase voltages Ua, Ub, Uc to the ground voltage are affected, so the controllable switch K1 should be turned off first, and the grid phase voltages Ua, Ub or Uc are detected; then the controllable switch K1 is closed, and the average value U is calculated according to the detection values of the network phase voltages Ua, Ub and UcZ. Then, the voltage U is grounded in the power gridZOutput voltage U1 of switching power supply module 102, and direct-current component U of input end of rectifier bridge 101 to center line NEUnder the condition that the resistance value R1 of the current limiting resistor R1 is known, the earth insulation resistance R of the alternating current power grid can be obtained according to the ohm law calculation formulaZ。
The alternating current insulation detection circuit provided by the embodiment is characterized in that a rectifier bridge 101, a current limiting resistor R1, a controllable switch K1 and a switching power supply module 102 are connected in series between a power grid and the ground, so that the current limiting resistor R1 and the alternating current power grid ground insulation impedance form a voltage division circuit, and the alternating current power grid ground insulation impedance is calculated; meanwhile, the rectifier bridge 101 with low loss replaces a three-phase virtual impedance unit realized by adopting a resistor in the prior art, so that the problems of high system self-loss and heat dissipation in the prior art are solved.
It should be noted that the switching power supply module 102 may be: any one of a BUCK topology, a BOOST topology, a BUCK-BOOST topology, a CUK topology, a forward topology, a flyback topology, a half-bridge topology, a full-bridge topology, and a push-pull topology, which is not specifically limited herein, is within the protection scope of the present application depending on the specific application environment.
Another embodiment of the present invention further provides an ac insulation detection system, referring to fig. 1, including: the device comprises a voltage sampling module 104, a control unit 103 and an alternating current insulation detection circuit; wherein:
the input end of the voltage sampling module 104 is connected with a power grid;
the output end of the voltage sampling module 104 is connected with the input end of the control unit 103;
the output end of the control unit 103 is connected with the control end of a controllable switch K1 in the alternating current insulation detection circuit;
the control unit 103 is configured to: the controllable switch K1 is controlled to be switched off, and a phase voltage peak value is obtained through calculation according to the power grid phase voltage detected by the voltage sampling module 104; controlling the controllable switch K1 to be closed, and calculating to obtain a phase voltage-to-average value according to the power grid phase voltage detected by the voltage sampling module 104; calculating to obtain the earth insulation impedance of the alternating current power grid according to ohm's law; and judging whether the insulation impedance of the alternating current power grid to the ground is smaller than a preset impedance reference, and if the insulation impedance of the alternating current power grid to the ground is smaller than the preset impedance reference, outputting an alarm signal.
Further, the ac insulation detection circuit includes: a rectifier bridge 101, a current limiting resistor R1, a controllable switch K1 and a switching power supply module 102; wherein:
the current limiting resistor R1 and the controllable switch K1 are connected in series between the input end of the rectifier bridge 101 and the high potential end of the switching power supply module 102;
the output end of the rectifier bridge 101 is connected with a power grid;
the low potential terminal of the switching power supply module 102 is grounded.
In a specific practical application, the connection sequence of the current limiting resistor R1 and the controllable switch K1 in series is not limited to the form shown in fig. 1, and fig. 1 is only an example, and may be determined according to the specific application environment, and is within the protection scope of the present application.
In addition, when the power grid is a single-phase power grid, the rectifier bridge 101 may be a diode, and as shown in fig. 2, an anode of the diode is an input end of the rectifier bridge 101, and a cathode of the diode is an output end of the rectifier bridge 101. When the grid is a three-phase grid, the rectifier bridge 101 may be of the form shown in fig. 1, including: three diodes connected in parallel; the anodes of the three diodes are connected, and the connection point is the input end of the rectifier bridge 101; the cathodes of the three diodes are the output terminals of the rectifier bridge 101, and are connected to the three phases of the power grid in a one-to-one correspondence manner. Alternatively, when the grid is a three-phase grid, the rectifier bridge 101 may be of the form shown in fig. 3, including: two diodes connected in parallel; the anodes of the two diodes are connected, and the connection point is the input end of the rectifier bridge 101; the cathodes of the two diodes are the output ends of the rectifier bridge 101 and are respectively connected with any two phases of the power grid in a one-to-one correspondence manner;
optionally, the switching power supply module 102 may be: any one of a BUCK topology, a BOOST topology, a BUCK-BOOST topology, a CUK topology, a forward topology, a flyback topology, a half-bridge topology, a full-bridge topology, and a push-pull topology, which is not specifically limited herein, is within the protection scope of the present application depending on the specific application environment.
Preferably, when the power grid is a three-phase power grid, the control unit 103 calculates a phase voltage peak value according to the power grid phase voltage detected by the voltage sampling module 104, and the formula adopted is as follows:
Ua＝Ub＝Uc＝Umsinωt；
the system comprises a power grid phase voltage generator, a phase voltage peak value, an angular frequency generator, a phase voltage generator and a phase voltage generator, wherein Ua, Ub and Uc are three-phase power grid phase voltages.
Preferably, when the power grid is a three-phase power grid, the control unit 103 calculates the insulation impedance of the alternating-current power grid to ground according to ohm's law, and the formula adopted is as follows:
wherein, UZFor the grid-to-ground voltage, equal to the average value of the grid-to-phase voltages, U1 is the output voltage of the switching power supply module 102, UEIs the direct current component of the input end of the rectifier bridge 101 to the center line N, and
RZr1 is the resistance of the current limiting resistor R1, which is the ac grid to ground isolation resistance.
According to the analysis of the above embodiment, it can be known that the detection values of the grid phase voltages Ua, Ub, or Uc need to be obtained in the calculation process, which needs to be realized by the voltage sampling module 104; since the on and off of the controllable switch K1 needs to be controlled to detect the grid phase voltages Ua, Ub, or Uc before and after the on, the corresponding control of the control unit 103 is neededPreparing; in addition, the corresponding calculation process in the above embodiment may also be implemented by the control unit 103. And when the control unit 103 calculates the insulation resistance R of the alternating current network to the groundZLess than a built-in predetermined impedance reference RTAnd an alarm should be given.
The control unit 103 may be an overall controller in the system, or may be an individual controller, which is not specifically limited herein, and may be determined according to the specific application environment, and all of them are within the protection scope of the present application.
The specific working principle is the same as that of the above embodiment, and is not described in detail here.
Preferably, referring to fig. 1, the ac insulation detection system further includes: the input end of the data acquisition unit 105 is connected with each inverter, and the output end of the data acquisition unit 105 is connected with the input end of the control unit 103;
the output end of the control unit 103 is also connected with the control end of the switching power supply module 102 in the alternating current insulation detection circuit;
the control unit 103 is further configured to adjust the output of the switching power supply module 102 according to the information obtained by the data collector 105, so as to reduce the PID effect of the photovoltaic cell panel.
The voltage sampling module 104 and the controllable switch K1 are matched with the control unit 103 to realize the detection and calculation of the insulation impedance of the alternating current power grid to the ground; meanwhile, the data acquisition unit 105 transmits the obtained information of each photovoltaic inverter to the control unit 103, so that the control unit 103 can adjust the output of the switching power supply module 102 according to the received information, thereby reducing the PID effect of the photovoltaic cell panel.
Another embodiment of the present invention further provides an ac insulation detection method, which is applied to the control unit 103 of the ac insulation detection system in the above embodiment, and the structure and principle of the ac insulation detection system are the same as those of the above embodiment, and are not described herein again.
Referring to fig. 7, the ac insulation detection method includes:
s101, controlling the controllable switch to be switched off;
s102, calculating to obtain a phase voltage peak value according to the power grid phase voltage detected by the voltage sampling module;
s103, controlling the controllable switch to be closed;
s104, calculating to obtain a phase voltage-to-average value according to the power grid phase voltage detected by the voltage sampling module;
s105, calculating to obtain the earth insulation impedance of the alternating current power grid according to ohm law;
s106, judging whether the insulation impedance of the alternating current power grid to the ground is smaller than a preset impedance reference;
if the insulation impedance of the alternating current power grid to the ground is smaller than the preset impedance reference, executing step S107;
and S107, outputting an alarm signal.
Preferably, when the power grid is a three-phase power grid, step S102 includes:
according to the grid phase voltage Ua, Ub or Uc of any phase detected by the voltage sampling module 104, the phase voltage peak value Um is calculated by the formula Ua ═ Ub ═ Uc ═ Umsin ω t;
where ω is the angular frequency and t is time.
Preferably, when the power grid is a three-phase power grid, step S105 includes:
according to ohm's law, by the formula
Calculating to obtain the earth insulation impedance of the alternating current power grid;
wherein, UZFor the grid-to-ground voltage, U1 is the output voltage of the switching power supply module 102, UEIs the direct current component of the input end of the rectifier bridge 101 to the center line N, and
RZr1 is the resistance of the current limiting resistor R1, which is the ac grid to ground isolation resistance.
The specific principle is the same as the above embodiments, and is not described in detail here.
The embodiments of the invention are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments can be referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
The foregoing is merely a preferred embodiment of the invention and is not intended to limit the invention in any manner. Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make numerous possible variations and modifications to the present teachings, or modify equivalent embodiments to equivalent variations, without departing from the scope of the present teachings, using the methods and techniques disclosed above. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.
Claims (11)
1. An alternating current insulation detection circuit, comprising: the circuit comprises a rectifier bridge, a current-limiting resistor, a controllable switch and a switching power supply module; wherein:
the current limiting resistor and the controllable switch are connected in series between the input end of the rectifier bridge and the high potential end of the switching power supply module;
the output end of the rectifier bridge is connected with a power grid;
and the low potential end of the switching power supply module is grounded.
2. The ac insulation detection circuit of claim 1, wherein when the grid is a single-phase grid, the rectifier bridge is a diode; the anode of the diode is the input end of the rectifier bridge, and the cathode of the diode is the output end of the rectifier bridge.
3. The ac insulation detection circuit of claim 1, wherein when the grid is a three-phase grid, the rectifier bridge comprises: two diodes connected in parallel;
the anodes of the two diodes are connected, and the connection point is the input end of the rectifier bridge;
the cathodes of the two diodes are output ends of the rectifier bridge and are respectively connected with any two phases of the power grid in a one-to-one correspondence manner;
alternatively, the rectifier bridge comprises: three diodes connected in parallel;
the anodes of the three diodes are connected, and the connection point is the input end of the rectifier bridge;
and the cathodes of the three diodes are output ends of the rectifier bridge and are respectively connected with the three phases of the power grid in a one-to-one correspondence mode.
4. An ac insulation detection circuit according to any one of claims 1 to 3, wherein the switching power supply module is: any one of BUCK topology, BOOST topology, BUCK-BOOST topology, CUK topology, forward topology, flyback topology, half-bridge topology, full-bridge topology and push-pull topology.
5. An alternating current insulation detection system, comprising: a voltage sampling module, a control unit and an alternating current insulation detection circuit according to any one of claims 1 to 4; wherein:
the input end of the voltage sampling module is connected with the power grid;
the output end of the voltage sampling module is connected with the input end of the control unit;
the output end of the control unit is connected with the control end of a controllable switch in the alternating current insulation detection circuit;
the control unit is used for: the controllable switch is controlled to be switched off, and a phase voltage peak value is calculated according to the power grid phase voltage detected by the voltage sampling module; controlling the controllable switch to be closed, and calculating to obtain an average value according to the power grid phase voltage detected by the voltage sampling module to be used as the voltage to ground of the power grid; calculating to obtain the earth insulation impedance of the alternating current power grid according to ohm's law; and judging whether the insulation impedance of the alternating current power grid to the ground is smaller than a preset impedance reference, and if the insulation impedance of the alternating current power grid to the ground is smaller than the preset impedance reference, outputting an alarm signal.
6. The alternating current insulation detection system according to claim 5, wherein when the power grid is a three-phase power grid, the control unit calculates a phase voltage peak value according to the power grid phase voltage detected by the voltage sampling module, and the formula is as follows:
Ua＝Ub＝Uc＝Umsinωt；
the method comprises the following steps of obtaining a three-phase grid phase voltage, obtaining a phase voltage peak value, obtaining an angular frequency, and obtaining time.
7. The AC insulation detection system according to claim 6, wherein when said power grid is a three-phase power grid, said control unit calculates the insulation resistance of the AC power grid to ground according to ohm's law, using the formula:
wherein, UZFor the network voltage to ground, U1 is the output voltage of the switching power supply module, UEIs the direct current component of the input end of the rectifier bridge to the center line N, an
RZR1 is the resistance of the current limiting resistor, which is the insulation resistance of the ac grid to ground.
8. The ac insulation detection system of claim 5, further comprising: the input end of the data collector is connected with each inverter, and the output end of the data collector is connected with the input end of the control unit;
the output end of the control unit is also connected with the control end of a switch power supply module in the alternating current insulation detection circuit;
and the control unit is also used for adjusting the output of the switching power supply module according to the information obtained by the data acquisition unit so as to reduce the PID effect of the photovoltaic cell panel.
9. An ac insulation detection method, applied to a control unit in an ac insulation detection system, the ac insulation detection system further comprising: a voltage sampling module and an ac insulation detection circuit as claimed in any one of claims 1 to 4; the input end of the voltage sampling module is connected with the power grid; the output end of the voltage sampling module is connected with the input end of the control unit; the output end of the control unit is connected with the control end of a controllable switch in the alternating current insulation detection circuit;
the alternating current insulation detection method comprises the following steps:
controlling the controllable switch to be switched off;
calculating to obtain a phase voltage peak value according to the power grid phase voltage detected by the voltage sampling module;
controlling the controllable switch to close;
calculating to obtain an average value according to the power grid phase voltage detected by the voltage sampling module, and using the average value as the voltage to ground of the power grid;
calculating to obtain the earth insulation impedance of the alternating current power grid according to ohm's law;
judging whether the insulation impedance of the alternating current power grid to the ground is smaller than a preset impedance reference or not;
and if the insulation impedance of the alternating current power grid to the ground is smaller than the preset impedance reference, outputting an alarm signal.
10. The alternating current insulation detection method according to claim 9, wherein when the power grid is a three-phase power grid, calculating a phase voltage peak value according to the grid phase voltage detected by the voltage sampling module includes:
according to the grid phase voltage Ua, Ub or Uc of any phase detected by the voltage sampling module, calculating to obtain the phase voltage peak value Um through a formula Ua ═ Ub ═ Uc ═ Umsit;
where ω is the angular frequency and t is time.
11. The ac insulation detection method according to claim 10, wherein when the grid is a three-phase grid, the calculating an ac grid ground insulation impedance according to ohm's law includes:
according to ohm's law, by the formula
Calculating to obtain the earth insulation impedance of the alternating current power grid;
wherein, UZFor the network voltage to ground, U1 is the output voltage of the switching power supply module, UEIs the direct current component of the input end of the rectifier bridge to the center line N, an
RZR1 is the resistance of the current limiting resistor, which is the insulation resistance of the ac grid to ground.
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| CN109633276B (en) * | 2018-12-28 | 2021-04-13 | 蜂巢能源科技有限公司 | Insulation resistance detection method and device based on full-bridge insulation detection circuit |
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| CN114204594B (en) * | 2021-12-07 | 2024-05-14 | 阳光电源股份有限公司 | Grid-connected system and insulation resistance detection method |
| CN114236244B (en) * | 2021-12-17 | 2024-05-14 | 阳光电源股份有限公司 | Ground impedance detection method and inversion system |
| CN115009060B (en) * | 2022-06-30 | 2023-05-09 | 珠海英搏尔电气股份有限公司 | Insulation detection circuit, detection method and vehicle-mounted charger |
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