RU2817404C1 - Device for protection of photovoltaic modules against atmospheric overvoltage - Google Patents

Abstract

FIELD: solar engineering; electric power industry.

SUBSTANCE: invention is intended to provide protection of photovoltaic modules against atmospheric overvoltage at objects of industrial, agricultural and individual purpose. Surge protection device, consisting of two series-connected varistors, protection circuit additionally includes three self-recovering fuses connected in series by protective Schottky diodes, protection module is built into the terminal part of the photoelectric module and all semiconductor radioelectronic components are compactly located on a common textolite printed circuit board, common point of grounding bus of varistors is connected to metal frame of photovoltaic module frame.

EFFECT: device provides protection of both photoelectric elements and semiconductor diodes from thunderstorm electromagnetic disturbances; components of the protection device do not require periodic maintenance.

1 cl, 3 dwg

Description

The invention relates to the field of solar engineering and electric power engineering, and is also intended to provide protection of photovoltaic modules from atmospheric overvoltages at industrial, agricultural and individual facilities.

A device for protection against surge voltages is known, containing a varistor module, while one device combines the function of opening emergency alarm contacts in the power supply circuit, and the function of turning off the varistor, which are performed simultaneously in a single process of actuation of a charged spring mechanism when melting low-melting solder (Slovenian patent No. 20781, IPC N02N 7/09, publication 1995).

The disadvantage of this design is that the presence of mechanical contacts in the known device reduces its reliability and increases the cost of production.

There are known methods for protecting semiconductor electrical equipment from switching overvoltages, based on the absorption of overvoltage energy using damping capacitors and resistors; zinc oxide nonlinear limiters; arresters; diode limiters (see books: 1. Bickford J.P. et al. Fundamentals of the theory of overvoltages in electrical networks: Translated from English / V.V. Bazutkin; Edited by A.A. Obukh. - M.: Energoizdat , 1981, pp. 147-158; 2. Glukh E.M., Zelenov V.E. Protection of semiconductor converters. - M.: Energoizdat, p. 142-146; technology: Translated from German / I.P. Kuzhekin, edited by B.K. Maksimov.

There are known methods of protection against pulse overvoltages, consisting of a parallel-connected varistor and a symmetrical protective diode, separated by inductance, while a series-connected diode and a second varistor are inserted into the device, and the diode is connected opposite to the supply voltage, and the series-connected diode and the second varistor are included parallel to the symmetrical protective diode (RF patent for utility model No. 42921, IPC N02N 9/04).

The disadvantage of these methods and the devices that implement them is the impossibility with their help to achieve an effective, with a factor of less than two with technically acceptable parameters of damping elements, reduction of overvoltages in direct current networks that have a significant amount of distributed inductance with energy that determines the level of switching overvoltages of thousands of joules.

The closest to the declared utility model (prototype) [Schwab A. Electromagnetic compatibility. - M.: Energoatomizdat, 1995, pp. 183, fig. 4.24] is a surge protection device consisting of a varistor and a surge arrester connected in parallel. When an overvoltage pulse appears at the input of the device, the varistor, which has a higher operating speed compared to the arrester, starts working first. Under the influence of the residual voltage of the varistor, after the statistical delay time has elapsed, the spark gap breaks through, limiting the overvoltage pulse to an arc voltage in the spark gap of 20-30 V.

The disadvantage of this device is the impossibility of using it in low-resistance circuits, in DC circuits, due to the high accompanying current through the spark gap, which thermally destroys it. Triggering of the arrester leads to a significant decrease in voltage across the protected load, which may be unacceptable for the protected load.

The main problem is pulse overvoltages, which lead to breakdown of the p-n junction of shunt semiconductor Schottky diodes in photovoltaic modules.

This problem is widespread because... when a leader channel appears, which was mentioned earlier in the conductors connecting the photovoltaic modules, an induced pulse current appears, and the potential also increases, which reaches a value higher than the constant forward voltage of the diode or the pulsed reverse voltage, and as a result, in the entire chain of series-connected modules, shunt diodes are faulty. This damage is of a purely hidden nature, because it is almost impossible to quickly identify this defect; the defect manifests itself during the operation of the solar power plant (SPP). At extremely high ambient temperatures and massive shading, the process of large-scale overheating of photocells begins, the temperature reaches values of up to 100°C. These overheatings lead to an accelerated process of degradation (wear) and massive underproduction of electrical energy, and the fault can only be identified through a detailed comparative analysis of the output of each chain of photovoltaic modules connected in series separately or during television monitoring (TVM). The process of replacing photovoltaic modules (PVMs) due to damaged diodes is expensive, and the process of finding and replacing damaged diodes is very labor-intensive, practically consuming a large amount of time and human resources. Existing PV module circuits only use protection diodes, which provide protection against shading as a shunt; as discussed earlier, with lightning impulses, semiconductor diodes inevitably fail.

The objective of the technical solution is that to eliminate the influence of atmospheric overvoltages, photovoltaic modules provide additional protection, namely each module separately, regardless of their total number at the solar power plant facility.

The protection device components do not require periodic maintenance and have a service life similar to that of the photovoltaic module. The protection circuit is relatively simple and, with the correct selection of components, has virtually no failures.

The problem is solved by the fact that the surge protection device consists of two series-connected varistors, three self-restoring fuses are additionally introduced into the protection circuit, connected in series with semiconductor Schottky diodes, the protection module is built into the terminal part of the photovoltaic module and all semiconductor radio-electronic components are compactly located on a common textolite printed circuit board, the common point of the varistor grounding bus is connected to the metal frame of the photovoltaic module frame. The device allows for protection of both photovoltaic elements and semiconductor diodes from lightning electromagnetic disturbances; the components of the protection device do not require periodic maintenance.

Features common to the prototype:

- two series-connected varistors.

Features:

- three self-restoring fuses connected in series with semiconductor Schottky diodes,

- the protection module is built into the terminal part of the photovoltaic module,

- all semiconductor radio-electronic components are compactly located on a common textolite printed circuit board,

- the common point of the varistor grounding bus is connected to the metal frame of the photovoltaic module frame.

The combination of features of the invention and the achievement of particularly good properties ensures that the technical solution meets the criterion of “inventive step”

In FIG. 1 shows a diagram of the device.

In FIG. Figure 2 shows the sequence of operation of the protection.

In FIG. Figure 3 shows the phase state of the polymer from crystalline to amorphous.

The circuit includes a PEM supply conductor of negative polarity (1) (Fig. 1), a grounding bus (2) (Fig. 1), a PEM supply conductor of positive polarity (3) (Fig. 1), self-restoring fuses (4) (Fig. 1), photovoltaic module 5, semiconductor diodes (6) (Fig. 1), ground loop (7) (Fig. 1), varistors (8) (Fig. 1), contact connection point of the FEM ground loop bus (9) (Fig. 1), with FEM frame (5) (Fig. 1). The positive voltage of the photovoltaic module (PV) (5) is connected to terminal (3) (Fig. 1), and the negative voltage to terminal (1). Between the positive (3) and negative (1) terminals, varistors RU 2 and RU 1 (8) are connected (Fig. 1). The midpoint between the varistors RU 2 and RU 1 is connected to the grounding bus (2) (Fig. 1), and the grounding bus (2) (Fig. 1) is connected to the ground loop (7) (Fig. 1). Between the positive voltage - terminal (3) (Fig. 1) and the negative voltage - terminal (1) of the photovoltaic module (PVM), semiconductor diodes D1, D2, D3 (6) and self-restoring fuses (4) (Fig. 1) are connected with reverse polarity. , which protect the FEM (5) (Fig. 1) from breakdown.

The device works as follows.

When a lightning discharge hits the grounding bus (2) (Fig. 2), within a radius of more than 150 m, an induced potential arises in the conductors providing electrical power to photovoltaic modules and inverters, as a result of which single, double or complex pulses are formed, with different amplitudes . In order to provide protective functions, two varistors (8) are placed in the terminal box of the photovoltaic module, connected in series between the positive (3) and negative (1) output contact of the photovoltaic module (5); a grounding bus (2) is connected to the middle point between the varistors (8) , having direct contact with the metal protective frame of the photovoltaic module (5), where the mounting posts of the photovoltaic module (5) are pre-connected to the ground loop (7).

In normal operation of the device, the positive and negative poles of the module (5) are galvanically isolated from the ground loop (7), due to the fact that the resistance of the varistors RU 1 and RU 2 (8) have a high impedance. A varistor is a volume-type semiconductor resistor, the resistance of which changes with a change in the voltage applied to it according to a linear law, because The current-voltage characteristic of a varistor is symmetrical; it can be used in DC and AC circuits. When the voltage increases above the threshold value on the supply conductors of the module, the varistors sharply reduce their impedance from several thousand megaohms (MΩ) to tens of ohms. In the proposed circuit, varistors (8) are selected with an operating voltage close to the no-load voltage of the photovoltaic module (5) for correct operation in terms of voltage. Varistors (8) are connected in parallel to the terminals of the photovoltaic module (5) and when the input voltage surges, the main pulse current flows through them to the ground loop, bypassing the low-current protected elements of the photovoltaic module (5). The operation of varistor protection will be ensured at a high speed of about 10-25 ns. when a pulse occurs in both the negative and positive pole conductor, providing a short period of time with a shunt between the positive and negative poles, as well as providing a direct electrical connection with the ground electrode (7), if the pulse occurs again, this process will be repeated cyclically. One of the main characteristics of the component in question is the maximum pulse current and the maximum energy in Joules that the varistor can absorb in one pulse. If these characteristics are incorrectly selected, thermal destruction or breakdown of the varistors will occur, which will lead to undesirable consequences - shunting of the photovoltaic module and, as a result, a short circuit (short circuit). When choosing varistors 8, it is necessary to use only components with the same characteristics when connected in series to the circuit, for subsequent correct operation of the device when performing protective functions. When an induced pulse appears directly in the circuit of elements of the photovoltaic module, because the latter may also be in the zone of induced potential, the operation of high-speed self-recovering fuses (4) (Fig. 2) Fu 1-Fu 3, which prevents the flow of unacceptable current values in the forward and reverse directions through shunt semiconductor diodes (6) (Fig. 2) . After stabilization of the voltage parameters and the magnitude of the electric current, the resistance of the varistors (8) (Fig. 2) increases to the original value, and the conductivity of the fuses (4) (Fig. 2) Fu 1-Fu is restored independently as the temperature decreases. This device circuit will protect module elements from damage and reduce the influence of pulse overvoltages and currents I _pulse (Fig. 2) on the rest of the photovoltaic module connected in series in the circuit. The sequence of protection operation is shown in (Fig. 2), where the movement of pulse currents I _pulse (Fig. 2) occurs from the photovoltaic module (5) through varistors (8) along the ground bus (2), towards the ground loop (7). Pulse currents in the circuit of semiconductor diodes (6) do not flow due to a break in the electrical circuit, due to the activated state of the self-restoring fuses (4).

The self-resetting fuse (4) in the circuit represents a PTC thermistor. PTC (Positive temperature coefficient device) - polymer devices with a positive temperature coefficient of resistance. The characteristics of the device were first discovered and described by Bell Labs in 1939.

The operation of the PTC fuse in the proposed circuit lies in the ability of the polymer to change its conductive structure when heated. At a temperature of 25°C, the polymer has a crystalline structure, so that the movement of charged particles occurs in an orderly manner and the current in the circuit is determined by the operating value of the load resistance RL (12) (Fig. 2) of the subsequent cascade (inverter). In the event of lightning-induced currents, the current in the electrical circuit increases sharply, heating the polymer in the thermistor. When the threshold temperature is reached, the fuse is triggered, namely, the phase state of the polymer changes from crystalline to amorphous, shown in (Fig. 3). As a result, the thermistor resistance increases sharply, and the current in the circuit is now determined by the thermistor resistance value.

Let us consider in more detail in (Fig. 3) the state of the PEM. At a temperature of 25°C, the FEM is in a crystalline state; between terminals (3) and (1) (Fig. 1) there are continuous graphite conductive bonds. As a result, the resistance of the self-resetting fuse (4) turns out to be low point (a) (Fig. 3). With increasing temperature, for example, due to an increase in current through the RTS, a slight increase in resistance is observed, caused by thermal processes, point (b) (Fig. 3). With a further increase in current and heating of the RTS structure, the temperature can rise to a limiting value at which the polymer begins to transition from the crystalline state to the amorphous one. This transition is accompanied by significant expansion. As a result, the graphite bonds are broken and the resistance increases, point (c) (Fig. 3). The process has an abrupt nature, that is, even when the limit temperature is slightly exceeded, a sharp increase in the resistance of the self-resetting fuse is observed. An increase in resistance leads to current limitation. Moreover, if the current value does not decrease, then the RTS continues to dissipate significant power and remains in a heated high-resistance state, point (d) (Fig. 3). After the fault is eliminated, the RTS cools down and returns to its original conducting state.

The developed circuit will provide protection directly to photovoltaic modules from the effects of pulse overvoltages, as well as protection of semiconductor elements (Schottky diodes) that are included in the module circuit. An important aspect is that when implementing this scheme, the risk factor of failure from pulse overvoltages of module elements that are not in the zone of electromagnetic radiation, but have an electrical connection with them, is reduced.

The device is supposed to provide protection for both photovoltaic elements and semiconductor diodes from lightning electromagnetic disturbances.

Claims (1)

A device for protecting a photovoltaic module from surge voltages, consisting of two varistors connected in series, characterized in that the photovoltaic module contains positive and negative terminals, between which a circuit of series-connected varistors is connected; three are introduced in series in the protection device between the positive and negative terminals of the photovoltaic module connected circuits, each of which is connected to the corresponding element of the photovoltaic module and consists of a self-restoring fuse with an anti-series connected semiconductor Schottky diode, the protection device is built into the terminal part of the photovoltaic module, all semiconductor components of the protection device are located on a common textolite printed circuit board, a common connection point varistors are interconnected with a grounding bus and connected to the metal frame of the photovoltaic module frame.