CN209982435U - Photovoltaic system prevent PID device and photovoltaic system - Google Patents
Photovoltaic system prevent PID device and photovoltaic system Download PDFInfo
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- CN209982435U CN209982435U CN201920654556.0U CN201920654556U CN209982435U CN 209982435 U CN209982435 U CN 209982435U CN 201920654556 U CN201920654556 U CN 201920654556U CN 209982435 U CN209982435 U CN 209982435U
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Abstract
The utility model discloses a photovoltaic system and a PID prevention device thereof, which comprises an adjustable voltage source, an equivalent neutral point circuit, a switch array and a controller; the adjustable voltage source is connected with the equivalent neutral point circuit through the switch array, and the equivalent neutral point circuit is used for constructing an equivalent neutral point on an alternating current side, which is equivalent to a neutral point on a direct current side, in the photovoltaic system. The PID prevention device adjusts the voltage value of the equivalent neutral point at the alternating current side to the ground voltage by controlling the switch state in the switch array and the output voltage of the adjustable voltage source through the controller, so that the voltage value of the anode or the cathode of the inverter to the ground voltage is adjusted, and the PID effect of the photovoltaic module is restrained. Namely, the PID prevention device can be used for adjusting the voltage to ground of the anode of the inverter and the voltage to ground of the cathode of the inverter.
Description
Technical Field
The utility model relates to a photovoltaic power generation technical field especially relates to photovoltaic system prevents PID device and photovoltaic system.
Background
The photovoltaic power generation system is a power generation system comprising photovoltaic components, an inverter, cables, a transformer and other equipment, and can realize conversion from solar energy to available electric energy in a high-voltage state.
If the photovoltaic module works in a humid and high-temperature environment for a long time and is in a high-voltage state, a large amount of charges are collected on the surface of a cell, leakage current is generated between a glass substrate and an encapsulating material of the photovoltaic module, and the surface of the photovoltaic module can generate a polarization phenomenon, so that the filling factor of the photovoltaic module is reduced, the short-circuit current density and the open-circuit voltage are reduced, and the performance of the photovoltaic module is lower than the design standard, namely, the Potential Induced Degradation (PID) effect is generated.
The PID effect of the photovoltaic module causes the power attenuation of the photovoltaic module to become a non-negligible problem in the photovoltaic field. Photovoltaic modules are further classified into P-type photovoltaic modules and N-type photovoltaic modules according to the doped elements. Due to the fact that the polarity of the P-type photovoltaic assembly is different from that of the N-type photovoltaic assembly, the PID prevention device cannot be used universally.
At present, most of PID prevention schemes of a photovoltaic system are directed at a P-type photovoltaic module, and few PID prevention schemes are directed at an N-type photovoltaic module. With the technical development of the N-type photovoltaic module, the N-type photovoltaic module is applied more and more, and the PID effect of the N-type photovoltaic module is more obvious. With the increasing application of N-type photovoltaic modules, it may happen that the same photovoltaic power station uses both P-type and N-type photovoltaic modules, and if a PID prevention device is configured for each type of module in such an application scenario, the system cost and the later maintenance cost are inevitably increased.
SUMMERY OF THE UTILITY MODEL
In view of this, the utility model provides a photovoltaic system prevents PID device and photovoltaic system to solve P type photovoltaic module and N type photovoltaic module prevent that PID device can't general technical problem. The specific technical scheme is as follows:
in a first aspect, the utility model provides a photovoltaic system prevents PID device, photovoltaic system includes the parallelly connected dc-to-ac converter of N side of exchanging, every a photovoltaic array is all connected to the direct current side of dc-to-ac converter, and every the positive pole and the negative pole of inverter are all not ground connection, prevent that the PID device includes: the circuit comprises an adjustable voltage source, an equivalent neutral point circuit, a switch array and a controller, wherein the switch array comprises a first switch, a second switch, a third switch and a fourth switch;
a first switch branch circuit is connected between the positive pole and the negative pole of the adjustable voltage source in parallel, wherein the first switch branch circuit is obtained by connecting the second switch and the third switch in series, and the common connection point of the second switch and the third switch is connected with a ground terminal;
the anode of the adjustable voltage source is also connected with the equivalent neutral point circuit through the first switch, and the cathode of the adjustable voltage source is also connected with the equivalent neutral point circuit through the fourth switch;
the other end of the equivalent neutral point circuit is connected with the alternating current side of the inverter, and the equivalent neutral point circuit is used for constructing an equivalent neutral point on the alternating current side;
the controller is used for controlling different switch combinations in the switch array to be switched on or switched off and controlling the output voltage of the adjustable voltage source so as to enable the equivalent neutral point on the alternating current side to be raised or lowered to the ground voltage.
Optionally, the photovoltaic module types include P-type and N-type;
the switches matched with the P-type photovoltaic module are the first switch and the third switch;
and the switches matched with the N-type photovoltaic module are the second switch and the fourth switch.
Optionally, the equivalent neutral point circuit comprises a three-phase transformer and a three-phase diode rectification circuit;
the primary winding of the three-phase transformer is connected with the alternating current side of the inverter, and the secondary winding of the three-phase transformer is connected with the alternating current end of the three-phase diode rectifying circuit;
the positive pole of the three-phase diode rectifying circuit is connected with the fourth switch, and the negative pole of the three-phase diode rectifying circuit is connected with the first switch.
Optionally, the apparatus further comprises: a first sampling resistor;
the first sampling resistor is connected between the anode of the adjustable voltage source and the first switch in series;
and the controller calculates the ground insulation impedance of the photovoltaic system according to the obtained first direct-current component of the ground voltage of the three-phase power grid, the voltage at two ends of the first sampling resistor and the resistance value of the first sampling resistor.
Optionally, the apparatus further comprises: a second sampling resistor and a fifth switch;
the second sampling resistor is connected with the fifth switch in series and then connected with two ends of the first sampling resistor in parallel;
the controller calculates and obtains the ground insulation impedance of the photovoltaic system according to the obtained first direct current component and second direct current component of the voltage to ground of the three-phase power grid, the resistance value of the first sampling resistor and the resistance value of the second sampling resistor;
wherein the first direct current component is a direct current component of the three-phase grid voltage to ground obtained when the fifth switch is opened, and the second direct current component is a direct current component of the three-phase grid voltage to ground obtained when the fifth switch is closed.
Optionally, the equivalent neutral point circuit is formed by connecting three impedances with the same resistance value in a star structure, a common connection point of the three impedances is the equivalent neutral point, the equivalent neutral point is respectively connected with the first switch and the fourth switch, and the other ends of the three impedances are respectively connected with a phase with different alternating current sides of the inverter.
Optionally, the three impedances are any combination of resistors, inductors, capacitors, and diodes.
In a second aspect, the utility model provides a photovoltaic system prevents PID device, photovoltaic system includes a N dc-to-ac converter, connects three phase transformer's primary winding after the interchange side of a N dc-to-ac converter is parallelly connected, three phase transformer's secondary winding connects the three-phase electric wire netting, and a photovoltaic array is all connected to the direct current side of every dc-to-ac converter, and the positive pole and the negative pole of every dc-to-ac converter are all ungrounded, three primary winding of three phase transformer is star type connection and three primary winding's tie point is the equivalent neutral point of interchange side, prevent the PID device and include: the system comprises an adjustable voltage source, a switch array and a controller, wherein the switch array comprises a first switch, a second switch, a third switch and a fourth switch;
a first switch branch circuit is connected between the positive pole and the negative pole of the adjustable voltage source in parallel, wherein the first switch branch circuit is obtained by connecting the second switch and the third switch in series, and the common connection point of the second switch and the third switch is connected with a ground terminal;
the anode of the adjustable voltage source is also connected with the equivalent neutral point on the alternating current side through the first switch, and the cathode of the adjustable voltage source is also connected with the equivalent neutral point on the alternating current side through the fourth switch.
A third aspect, the present invention also provides a photovoltaic system, including: n photovoltaic arrays, N inverters, a transformer and the PID prevention device according to any one of the implementation manners of the first aspect;
the alternating current sides of the N inverters are connected with the primary winding of the transformer in parallel, and the secondary winding of the transformer is connected with a three-phase power grid;
and the controller obtains the target voltage value according to the voltage-to-ground of the positive electrodes or the voltage-to-ground of the negative electrodes of the N inverters.
In a fourth aspect, the present invention also provides a photovoltaic system, including: the three-phase transformer comprises N photovoltaic arrays, N inverters, a three-phase transformer and a PID (proportion integration differentiation) prevention device, wherein three primary windings of the three-phase transformer are in star connection, and a common connection point of the three primary windings is an equivalent neutral point of an alternating current side;
the direct current side of each inverter is connected with a photovoltaic array, the alternating current sides of the N inverters are connected in parallel and then connected with the primary side winding of the three-phase transformer, and the secondary side winding of the three-phase transformer is connected with a three-phase power grid;
and the controller obtains the target voltage value according to the voltage-to-ground of the positive electrodes or the voltage-to-ground of the negative electrodes of the N inverters.
The utility model provides a photovoltaic system prevents PID device, including adjustable voltage source, equivalent neutral point circuit, switch array and controller; the adjustable voltage source is connected with the equivalent neutral point circuit through the switch array, and the equivalent neutral point circuit is used for constructing an equivalent neutral point on an alternating current side, which is equivalent to a neutral point on a direct current side, in the photovoltaic system. The PID prevention device adjusts the equivalent neutral point-to-ground voltage of the alternating current side by controlling the switch state in the switch array and the output voltage of the adjustable voltage source, so that the voltage-to-ground voltage of the anode or the cathode of the inverter is adjusted, and the PID effect of the photovoltaic module is restrained. Namely, the PID prevention device can be used for adjusting the voltage to ground of the anode of the inverter and the voltage to ground of the cathode of the inverter, so that the PID prevention device is suitable for both a P-type photovoltaic module and an N-type photovoltaic module.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be 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 embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a PID prevention apparatus of a photovoltaic system disclosed in the present application;
fig. 2 is an equivalent circuit diagram of a photovoltaic system using a P-type photovoltaic module as disclosed herein;
FIG. 3 is an equivalent circuit diagram of a photovoltaic system using an N-type photovoltaic module as disclosed herein;
FIG. 4 is a schematic structural diagram of another photovoltaic system PID prevention device disclosed herein;
FIG. 5 is a schematic structural diagram of yet another photovoltaic system PID prevention device disclosed herein;
fig. 6 is a schematic structural diagram of another photovoltaic system PID prevention apparatus disclosed in the present application.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. 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.
Please refer to fig. 1, which is a schematic structural diagram of a PID prevention apparatus of a photovoltaic system according to an embodiment of the present disclosure, in which a positive electrode and a negative electrode of the photovoltaic system are not grounded, that is, the positive electrode and the negative electrode of an inverter are not grounded.
As shown in fig. 1, the PID prevention apparatus includes: an adjustable voltage source 101, an equivalent neutral point circuit 102, a switch array 103 and a controller 104, wherein the switch array 103 comprises a first switch K1, a second switch K2, a third switch K3 and a fourth switch K4;
a first switching branch is connected in parallel between the positive pole and the negative pole of the adjustable voltage source 101. The first switch branch is formed by connecting the second switch K2 and the third switch K3 in series, and the common connection point of the second switch K2 and the third switch K3 is connected with the ground terminal PE.
The anode of the adjustable voltage source 101 is further connected to the equivalent neutral point circuit 102 through a first switch K1, and the cathode of the adjustable voltage source 101 is further connected to the equivalent neutral point circuit 102 through a fourth switch K4.
It should be noted that the adjustable voltage source 101 may be configured as a Boost type switching power supply circuit, a Buck-Boost type switching power supply circuit, a constant voltage source, and other circuits that can directly provide a dc voltage.
The other end of the equivalent neutral point circuit 102 is connected to the ac side of the inverter, and the equivalent neutral point circuit 102 is used to construct an ac side equivalent neutral point.
The number of the inverters is N, where N is an integer equal to or greater than 1. The direct current side of each inverter is connected with a photovoltaic array, wherein the photovoltaic array is composed of a plurality of photovoltaic components.
A first input end of the controller 104 inputs a target voltage value, a first output end of the controller 104 is connected with the adjustable voltage source 101, and a second output end is connected with the switch array 103; the controller 104 controls the switches in the switch array 103, which are matched with the current photovoltaic module type, to be turned on according to the current photovoltaic module type and the target voltage value, controls the adjustable voltage source 101 to output voltage so that the voltage of the equivalent neutral point on the alternating current side of the inverter changes to the target voltage value relative to the voltage of the ground terminal, and then adjusts the voltage according to the change of the voltage to the ground of the anode or the cathode of the inverter
The types of the photovoltaic modules comprise a P-type photovoltaic module and an N-type photovoltaic module. The P-type photovoltaic module is a solar cell with an N/P type structure formed by diffusing boron on a P-type semiconductor material. The N-type photovoltaic module is a solar cell with an N/P type structure formed by diffusing phosphorus element on an N-type semiconductor material.
In one embodiment of the present application, the switches matched with the P-type photovoltaic module are a first switch K1 and a third switch K3. The switches matched with the N-type photovoltaic module are a second switch K2 and a fourth switch K4.
If the current photovoltaic module is a P-type photovoltaic module, the target voltage value is the voltage value to ground of the negative electrode of the inverter to be lifted; if the current photovoltaic module is an N-type photovoltaic module, the target voltage value is the voltage value of the anode of the inverter to ground, which needs to be lowered. In this specification, "ground" means the earth.
Wherein the target voltage value is a maximum value among absolute values of voltages to ground of cathodes (or anodes) of the respective inverters.
In one embodiment of the present application, the voltage to ground of the negative electrode (or positive electrode) of each inverter may be collected by the data collection module and the voltage value with the largest absolute value may be determined as the target voltage value and transmitted to the controller 104. Alternatively, the data acquisition module may directly provide the acquired negative (or positive) voltage to ground of each inverter to the controller 104.
In another embodiment of the present application, the voltage to ground of the negative electrode (or positive electrode) itself may be directly collected by the inverter and transmitted to the controller 104, and the controller 104 determines the voltage value with the largest absolute value as the target voltage value.
Because the voltage to ground of the direct current side neutral point (namely, the neutral point of the direct current bus) of the inverter and the voltage to ground of the alternating current side equivalent neutral point are always approximately equal, and because the voltage of the neutral point of the direct current bus relative to the positive bus and the negative bus is clamped to a certain value in the grid-connected operation process of the inverter, the voltage to ground of the alternating current side equivalent neutral point increases or decreases a target voltage value, the voltage to ground of the negative pole of the inverter is inevitably increased or decreased by the target voltage value (or the voltage to ground of the positive pole of the inverter is decreased by the target voltage value), and therefore, the voltage to ground of the negative pole of the inverter is larger than 0 (or the. That is, the inverter positive or negative voltage-to-ground is controlled by controlling the ac-side equivalent neutral point-to-ground voltage.
In this application, when the type of the photovoltaic module is a P-type photovoltaic module, the controller 104 controls the first switch K1 and the third switch K3 in the switch array 103 to be closed, and controls the output voltage of the adjustable voltage source 101 according to a target voltage value, so that the voltage of the equivalent neutral point on the ac side with respect to the ground terminal is raised by the target voltage value.
Wherein the output voltage of the adjustable voltage source 101 is determined by the target voltage value and the equivalent output voltage of the equivalent neutral point circuit 102.
Please refer to fig. 2, which is an equivalent circuit diagram of a photovoltaic system of a P-type photovoltaic module, wherein U isgridFor the direct component of the voltage to earth of a three-phase network, UXThe equivalent output voltage of the equivalent neutral point circuit 102 is Uo, which is the rated output voltage of the adjustable voltage source, and the point N is the equivalent neutral point on the alternating current side. Wherein Rs is the current limiting resistor of the PID prevention device.
If the target voltage value is U0, the voltage of the negative terminal of the inverter needs to be raised by U0, and therefore, the voltage of the N point to ground (PE ground) needs to be raised by U0, as can be seen from fig. 2, the voltage of the N point to PE ground is about UX+ Uo ≈ U0, thus controlling the adjustable voltage source 101 outputFixed voltage Uo is approximately equal to U0-UX。
In one embodiment of the present application, the controller 104 may directly control the output voltage of the adjustable voltage source 101 to be U0-U due to the measurement errorXThen further regulated according to the negative voltage to ground of the inverter until the negative voltage to ground of the inverter increases by U0. In another embodiment of the present application, the controller 104 may adjust the output voltage of the adjustable voltage source 101 according to a preset voltage step, and the specific control process is as follows:
1) if the target voltage value is U0 and U0 is greater than 0, controlling the adjustable voltage source 101 to output a preset voltage U1; the preset voltage U1 is a preset voltage step, the value of U1 can be selected according to actual needs, and U1 is much smaller than U0, for example, U0 is 50V, and U1 can take 10V.
2) After a period of time delay, the voltage to ground of the negative electrode of each inverter is obtained again, and the magnitude of the voltage to ground of the negative electrode of the photovoltaic system needing to be lifted at the moment is calculated again to be U01.
3) If U01 is greater than 0, controlling the adjustable voltage source to output 2U 1; and if the U01 is equal to 0, controlling the output U1 of the adjustable voltage source to be unchanged.
And analogizing in sequence, the output voltage of the adjustable voltage source is not controlled to increase until the voltage of the cathode to ground which needs to be raised according to the currently obtained photovoltaic system is 0, and the last output voltage is kept unchanged.
When the type of the photovoltaic module is an N-type photovoltaic module, the second switch K2 and the fourth switch K4 in the switch array 103 are controlled to be closed, and the output voltage of the adjustable voltage source 101 is controlled according to a target voltage value, so that the voltage of the equivalent neutral point on the alternating current side relative to the ground terminal is reduced by the target voltage value.
Similar to fig. 2, as shown in fig. 3, which is an equivalent circuit diagram of a photovoltaic system of an N-type photovoltaic module, if the target voltage value is U0, it is necessary to lower the voltage of the positive electrode of the inverter to the ground voltage U0, and therefore, it is necessary to control the voltage of the N-point to the ground voltage to lower U0, and it can be known from fig. 3 that the adjustable voltage source 101 needs to be controlled to output a fixed voltage U0-UX。
For the photovoltaic system of the N-type photovoltaic module, the adjustment process of the output voltage of the adjustable voltage source 101 is the same as the above process, and is not described herein again.
The PID prevention device of the photovoltaic system comprises an adjustable voltage source, an equivalent neutral point circuit, a switch array and a controller; the adjustable voltage source is connected with the equivalent neutral point circuit through the switch array, wherein the equivalent neutral point circuit is used for constructing an equivalent neutral point on an alternating current side, which is equivalent to a neutral point on a direct current side, in the photovoltaic system. The PID prevention device adjusts the voltage of the equivalent neutral point at the alternating current side to the ground voltage by controlling the switch state in the switch array and the output voltage of the adjustable voltage source, and further realizes the adjustment of the voltage of the anode or the cathode of the inverter to the ground voltage. Thereby suppressing the PID effect of the photovoltaic module. Namely, the PID prevention device can be used for adjusting the voltage to ground of the anode of the inverter and the voltage to ground of the cathode of the inverter, so that the PID prevention device is suitable for both a P-type photovoltaic module and an N-type photovoltaic module.
Referring to fig. 4, a schematic structural diagram of another PID prevention apparatus for a photovoltaic system provided in an embodiment of the present application is shown, where the equivalent neutral circuit 102 in the embodiment includes a three-phase transformer T1 and a three-phase diode rectification circuit 201.
As shown in fig. 4, the three-phase transformer T1 is an autotransformer, and the secondary winding of the autotransformer is a part of the primary winding; three windings of the autotransformer are in a star connection mode, and a common connection point of the three windings is an equivalent neutral point on an alternating current side.
Of course, in other embodiments, the three-phase transformer T1 may also be another type of transformer, such as an isolation transformer.
Each phase of the three-phase diode rectifying circuit 201 comprises two rectifying branches obtained by connecting two diodes in series in the same direction, the common connection point of the two diodes in each rectifying branch is an alternating current end, and the cathodes of the three rectifying branches are connected and then used as the anode Vin + of the three-phase diode rectifying circuit 201; the anodes of the three rectifying branches are connected and then used as the cathode Vin-.
The primary winding of the three-phase transformer T1 is connected to the ac side of the inverter, and the secondary winding is connected to the ac side of the three-phase diode rectifier circuit 201.
The positive electrode Vin + of the three-phase diode rectifying circuit 201 is connected with one end of a fourth switch K4, and the other end of the fourth switch K4 is connected with the negative electrode of the adjustable voltage source 101; the negative electrode Vin-of the three-phase diode rectifying circuit 201 is connected with one end of a first switch K1, and the other end of the first switch K1 is connected with the positive electrode of the adjustable voltage source 101.
In this embodiment, the process of adjusting the ac-equivalent neutral point to ground voltage is the same as the process of adjusting the ac-equivalent neutral point to ground voltage in the embodiment shown in fig. 1, and is not described herein again.
The unqualified insulation resistance to the ground at the alternating current side of the photovoltaic system seriously threatens equipment and personal safety, and along with the higher and higher requirements on the safety of the photovoltaic system, the photovoltaic system has more and more requirements on increasing the alternating current insulation monitoring function, so that the monitoring on the ground insulation condition of a power grid at the alternating current side of the photovoltaic system is realized. Adding ac insulation monitoring devices alone necessarily increases system cost and also increases system complexity. The PID prevention device has the alternating-current insulation monitoring function on the premise of not increasing the system cost and the system complexity. After the output voltage of the adjustable voltage source is stable, the PID prevention device can be utilized to perform an alternating current insulation monitoring function.
In an embodiment of the present application, the PID prevention apparatus shown in fig. 4 further includes a first sampling resistor R1, and the first sampling resistor R1 is connected in series between the positive electrode of the adjustable voltage source 101 and the first switch K1.
Referring to the equivalent circuit of the photovoltaic system shown in fig. 2 or fig. 3, wherein the resistance of R1 is known as Rs 1, the voltage U across the first sampling resistor R1 is collectedRAnd a first direct-current component U of the voltage to ground of the three-phase networkgridAnd calculating to obtain the ground insulation impedance of the three-phase power grid, namely the ground insulation impedance of the photovoltaic system.
Wherein a first direct-current component U of a three-phase network voltage to groundgridThe method can be obtained after the three-phase voltage of the three-phase power grid is obtained through sampling and the alternating current component is filtered.
As can be seen from the equivalent circuit shown in figure 2 or figure 3,
therefore, equation 1 for the insulation resistance of the three-phase network to ground is as follows:
in formula 1, RgridFor the impedance of the three-phase network to ground, i.e. the impedance value, U, to which the AC insulation impedance of the photovoltaic system should be broughtgridIs a first DC component, URIs the voltage across the first sampling resistor R1, and R1 is the resistance of the first sampling resistor.
After the three-phase grid ground insulation impedance is calculated, the inverter can monitor whether the ac insulation impedance of the photovoltaic system is qualified according to the value, for example, if the three-phase grid ground insulation impedance is detected to be smaller than the ac insulation impedance of the photovoltaic system, it is determined that the ac insulation of the photovoltaic system is abnormal, and the inverter should be stopped for inspection or warning.
In this embodiment, the first sampling resistor R1 is required to be arranged on the circuit structure, and a device for acquiring the dc component of the voltage to ground of the three-phase power grid and a device for acquiring the voltage across the first sampling resistor R1 are required to be arranged.
In another embodiment of the present application, as shown in fig. 4, the PID prevention apparatus further includes: a second sampling resistor R2 and a fifth switch K5.
The second sampling resistor R2 is connected in series with the fifth switch K5 and then connected in parallel with two ends of the first sampling resistor R1.
In this embodiment, when the fifth switch K5 is turned off, Rs in the equivalent circuit shown in fig. 2 or 3 is R1, and at this time, the controller obtains the first dc component of the three-phase grid voltage to ground as Ugrid1From ohm's law, there is a relationship as shown in the following equation 2:
in equation 2, Uo is the output voltage of the adjustable voltage source, UXIs the equivalent output voltage of the equivalent neutral point circuit.
When the fifth switch K5 is closed, Rs in the equivalent circuit shown in fig. 2 or fig. 3 is equal to the parallel resistance value of R1 and R2, that is, Rs is R1// R2, and at this time, the controller obtains the second direct-current component of the voltage to ground of the three-phase power grid as Ugrid2From ohm's law, there is a relationship as shown in the following equation 3:
in the formula 3, R1// R2 refers to the resistance value of the first sampling resistor R1 and the second sampling resistor R2 after being connected in parallel.
By combining formula 2 and formula 3, the ground insulation resistance R of the three-phase power grid can be obtained through calculationgridThe calculation formula of (a) is as follows:
this embodiment requires a second sampling resistor R2 and a fifth switch K5 in terms of circuit configuration, and requires a device for collecting the dc component of the three-phase grid voltage to ground.
It should be noted that R can be set and obtained according to actual requirementsgridThe method (1).
In other embodiments of the present application, the equivalent neutral point circuit may also employ other circuit configurations than the circuit shown in fig. 4.
Referring to fig. 5, a schematic structural diagram of another photovoltaic system PID prevention apparatus provided in the embodiment of the present application is shown, in which an equivalent neutral point circuit is implemented by using three impedances with equal resistance values.
As shown in fig. 5, the equivalent neutral point circuit 102 is formed by connecting three impedances having the same resistance in a star configuration, and the common connection point of the three impedances is an ac-side equivalent neutral point. The equivalent neutral point on the alternating current side is respectively connected with a first switch K1 and a fourth switch K4; the other ends of the three impedances are respectively connected with the alternating current side of the inverter, namely, the three-phase power grid on the alternating current side.
Wherein, the three impedances are any combination of a resistor, an inductor, a capacitor and a diode.
It should be noted that the operation principle of other parts and the PID prevention device is the same as the embodiment shown in fig. 4, and the description thereof is omitted.
In addition, the PID device also has an ac insulation monitoring function, specifically, three impedances in the equivalent neutral point circuit 102 are used as sampling resistors, and the equivalent resistance value of the sampling resistor is a parallel impedance value of the three impedances; the calculation process of the insulation resistance of the three-phase power grid to the ground is the same as that in fig. 4, and the details are not repeated here.
Referring to fig. 6, a schematic structural diagram of another PID prevention apparatus for a photovoltaic system according to an embodiment of the present disclosure is provided, in which an equivalent neutral point on an ac side is generated by a three-phase transformer T2 between a three-phase grid and an inverter.
The primary winding of the three-phase transformer T2 is connected with the alternating current side of the inverter, the secondary winding of the three-phase transformer T2 is connected with a three-phase power grid, the three primary windings of the three-phase transformer T2 are in a star connection mode, and the three secondary windings can be in a star connection mode or a triangular connection mode.
The common connection point of the three primary windings of the three-phase transformer T2 is an AC side equivalent neutral point, and the AC side equivalent neutral point is respectively connected with the first switch K1 and the fourth switch K4.
In this embodiment, the controller 104 may receive the target voltage value determined by the data acquisition module; alternatively, the controller 104 directly receives the positive (or negative) voltage-to-ground of each inverter and determines the target voltage value according to the positive (or negative) voltage-to-ground of each inverter.
The working principle of the PID prevention device of the photovoltaic system is the same as the working process of the PID prevention device, and the detailed description is omitted here. In addition, a third sampling resistor R3 may be connected in series between T2 and the switch array 103, and the ground insulation resistance of the three-phase power grid is calculated by detecting the voltage across R3, where the calculation process of the ground insulation resistance is the same as that in the embodiment shown in fig. 4, and is not described here again.
On the other hand, the present application also provides a photovoltaic system including the PID prevention apparatus provided in the above embodiment, the photovoltaic system further includes, in addition to the PID prevention apparatus shown in fig. 1, 4, 5 and 6: n inverters, N photovoltaic modules and a three-phase transformer. The connection between these parts and the PID device is described above and will not be described herein.
It should be noted that a data acquisition module independent from the inverters may be provided, and the data acquisition module acquires the voltages to ground of the positive electrode or the negative electrode of each inverter and provides the voltages to the controller in the PID prevention device. Or the voltage of the anode or the cathode of the inverter is directly collected by the inverter and is supplied to a controller in the PID prevention device.
The photovoltaic system comprises N photovoltaic assemblies, N inverters, a data acquisition module, a transformer and a photovoltaic system PID (proportion integration differentiation) prevention device; the direct current side of each inverter is connected with a photovoltaic array; the alternating current sides of the N inverters are connected with a primary winding of a transformer in parallel, and a secondary winding of the transformer is connected with a three-phase power grid; the controller in the PID prevention device acquires the voltage to ground of the positive electrodes or the voltage to ground of the negative electrodes of the N inverters, controls the state of the switches in the switch array, controls the voltage output by the adjustable voltage source, adjusts the voltage to ground of the equivalent neutral point at the alternating current side, realizes adjustment of the voltage to ground of the positive electrodes or the negative electrodes of the inverters, and finally realizes suppression of the PID effect of the photovoltaic module.
The embodiments of the present invention are described in a progressive manner, each embodiment is mainly described as different from other embodiments, and the same similar parts between the embodiments are 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 previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. The utility model provides a photovoltaic system prevent PID device, photovoltaic system includes N parallelly connected inverters of interchange side, every a photovoltaic array is all connected to the direct current side of inverter, and every positive pole and the negative pole of inverter all do not all ground connection, its characterized in that, prevent PID device includes: the circuit comprises an adjustable voltage source, an equivalent neutral point circuit, a switch array and a controller, wherein the switch array comprises a first switch, a second switch, a third switch and a fourth switch;
a first switch branch circuit is connected between the positive pole and the negative pole of the adjustable voltage source in parallel, wherein the first switch branch circuit is obtained by connecting the second switch and the third switch in series, and the common connection point of the second switch and the third switch is connected with a ground terminal;
the anode of the adjustable voltage source is also connected with the equivalent neutral point circuit through the first switch, and the cathode of the adjustable voltage source is also connected with the equivalent neutral point circuit through the fourth switch;
the other end of the equivalent neutral point circuit is connected with the alternating current side of the inverter, and the equivalent neutral point circuit is used for constructing an equivalent neutral point on the alternating current side;
the controller is used for controlling different switch combinations in the switch array to be switched on or switched off and controlling the output voltage of the adjustable voltage source so as to enable the equivalent neutral point on the alternating current side to be raised or lowered to the ground voltage.
2. The PID prevention device of claim 1, wherein the photovoltaic module types include P-type and N-type;
the switches matched with the P-type photovoltaic module are the first switch and the third switch;
and the switches matched with the N-type photovoltaic module are the second switch and the fourth switch.
3. The PID prevention device according to claim 1 or 2, wherein the equivalent neutral point circuit includes a three-phase transformer and a three-phase diode rectification circuit;
the primary winding of the three-phase transformer is connected with the alternating current side of the inverter, and the secondary winding of the three-phase transformer is connected with the alternating current end of the three-phase diode rectifying circuit;
the positive pole of the three-phase diode rectifying circuit is connected with the fourth switch, and the negative pole of the three-phase diode rectifying circuit is connected with the first switch.
4. The PID prevention device of claim 3, further comprising: a first sampling resistor;
the first sampling resistor is connected between the anode of the adjustable voltage source and the first switch in series;
and the controller calculates the ground insulation impedance of the photovoltaic system according to the obtained first direct-current component of the ground voltage of the three-phase power grid, the voltage at two ends of the first sampling resistor and the resistance value of the first sampling resistor.
5. The PID prevention device of claim 4, further comprising: a second sampling resistor and a fifth switch;
the second sampling resistor is connected with the fifth switch in series and then connected with two ends of the first sampling resistor in parallel;
the controller calculates and obtains the ground insulation impedance of the photovoltaic system according to the obtained first direct current component and second direct current component of the voltage to ground of the three-phase power grid, the resistance value of the first sampling resistor and the resistance value of the second sampling resistor;
wherein the first direct current component is a direct current component of the three-phase grid voltage to ground obtained when the fifth switch is opened, and the second direct current component is a direct current component of the three-phase grid voltage to ground obtained when the fifth switch is closed.
6. The PID prevention device according to claim 1 or 2, wherein the equivalent neutral point circuit is formed by connecting three impedances having the same resistance in a star configuration, a common connection point of the three impedances is the equivalent neutral point, the equivalent neutral point is connected to the first switch and the fourth switch, respectively, and the other ends of the three impedances are connected to a phase having an ac side different from the ac side of the inverter, respectively.
7. The PID prevention device of claim 6, wherein the three impedances are any combination of resistors, inductors, capacitors, and diodes.
8. The utility model provides a photovoltaic system prevents PID device, photovoltaic system includes N dc-to-ac converter, the primary winding of connecting three-phase transformer after the interchange side of N dc-to-ac converter connects in parallel, three-phase electric wire netting is connected to the secondary winding of three-phase transformer, the direct current side of every dc-to-ac converter all connects a photovoltaic array, and the positive pole and the negative pole of every dc-to-ac converter all are ungrounded, three primary winding of three-phase transformer are star type connection and the public connection point of three primary winding is the equivalent neutral point of interchange side, its characterized in that, prevent PID device includes: the system comprises an adjustable voltage source, a switch array and a controller, wherein the switch array comprises a first switch, a second switch, a third switch and a fourth switch;
a first switch branch circuit is connected between the positive pole and the negative pole of the adjustable voltage source in parallel, wherein the first switch branch circuit is obtained by connecting the second switch and the third switch in series, and the common connection point of the second switch and the third switch is connected with a ground terminal;
the anode of the adjustable voltage source is also connected with the equivalent neutral point on the alternating current side through the first switch, and the cathode of the adjustable voltage source is also connected with the equivalent neutral point on the alternating current side through the fourth switch.
9. A photovoltaic system, comprising: n photovoltaic arrays, N inverters, transformers and the PID prevention apparatus of any one of claims 1 to 7;
the alternating current sides of the N inverters are connected with the primary winding of the transformer in parallel, and the secondary winding of the transformer is connected with a three-phase power grid.
10. A photovoltaic system, comprising: the apparatus comprises N photovoltaic arrays, N inverters, a three-phase transformer, and the PID prevention device of claim 8, wherein three primary windings of the three-phase transformer are in star connection and a common connection point of the three primary windings is an equivalent neutral point of an alternating current side;
the direct current side of each inverter is connected with a photovoltaic array, the alternating current sides of the N inverters are connected in parallel and then connected with the primary side winding of the three-phase transformer, and the secondary side winding of the three-phase transformer is connected with a three-phase power grid.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113852129A (en) * | 2021-11-04 | 2021-12-28 | 阳光电源股份有限公司 | Photovoltaic power generation system and control method thereof |
| EP4270710A1 (en) * | 2022-04-20 | 2023-11-01 | Sungrow Power Supply Co., Ltd. | Insulation monitoring on both sides of an inverter supplied by renewable energy |
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2019
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113852129A (en) * | 2021-11-04 | 2021-12-28 | 阳光电源股份有限公司 | Photovoltaic power generation system and control method thereof |
| CN113852129B (en) * | 2021-11-04 | 2024-05-14 | 阳光电源股份有限公司 | Photovoltaic power generation system and control method thereof |
| EP4270710A1 (en) * | 2022-04-20 | 2023-11-01 | Sungrow Power Supply Co., Ltd. | Insulation monitoring on both sides of an inverter supplied by renewable energy |
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