CN114759538A - Method for preventing switch overvoltage during reverse connection of photovoltaic group strings - Google Patents

Abstract

The invention relates to a method for preventing switch overvoltage when a photovoltaic string is reversely connected. Each panel component is connected to a photovoltaic inverter circuit through different controllable tripping DC switches; a photovoltaic inverter controller controls each controllable DC switch. After the on-off of the tripping DC switch detects the connection failure of the solar panel components, the solar panel components are turned on and connected to the circuit loop of the photovoltaic inverter. The power-on sequence of the controllable tripping DC switch is used to limit the power-on sequence. After power-on, it is detected whether the PV voltage of each channel is normal and reverse connection occurs. Through the controllable switch signal, the wrongly connected line DC switch is locked to avoid switching in the case of reverse connection. There is a risk of overvoltage and overcurrent when the switch is closed. It can avoid that the switch bears twice the PV voltage after reverse connection, and at the same time, when the string is reversely connected, there is no need to add additional fuses or anti-reverse diodes in the connection circuit of each group of solar panel components, and the method is effective and low in cost.

Description

Applicable to the method of preventing switch overvoltage when PV strings are connected in reverse

technical field

The invention relates to a new energy grid-connected power generation technology, in particular to a method for preventing switch overvoltage when a photovoltaic group string is reversely connected.

Background technique

Solar photovoltaic grid-connected power generation system is one of the important means to effectively utilize new energy. Solar grid-connected power generation has received more and more attention, and this power generation method has become more and more common in practical applications.

At present, there are a variety of mainstream specifications of photovoltaic panel components on the market. With the continuous improvement of power levels, photovoltaic inverters need to be compatible with various types of photovoltaic panel components, which puts forward higher requirements for the input part of photovoltaic inverter strings. However, the boost module of mainstream manufacturers has a limited processing power level of each channel, rashly increasing the type of modules or increasing the level of the boost module, the cost will also increase significantly, so the inverter manufacturers will maximize the use of the selected boost Modules, choose different numbers of parallel channels according to different component specifications. The common way is to input 2 channels, 3 channels or multiple channels in parallel to a boost channel.

In the case of multi-channel parallel input, one of them is reversely connected and the battery board is short-circuited. For the reverse connection of the battery board, the inverter needs to detect the reverse connection fault and stop, and at the same time, it can safely cut off the short-circuit and overcurrent of the battery string to the inverter. At present, the mainstream adopts fuse or anti-reverse device, and the new multi-channel direct current (DC) isolating switch with tripping function is gradually entering the market. Using the controllable function of the DC isolating switch can effectively realize the faulty battery pack. String separation to reduce power loss.

The inverter is compatible with different panel components, and its string input part will also be different. There are several common string input methods:

One is that the two sinks and one are connected in parallel and then input to the booster part (BOOST for short) through the DC switch K1, as shown in Figure 1. This method is not compatible with various types of battery board components, and the selection of the battery board is single;

The second is that the three-way-one is connected in parallel, and the DC switch K ₁ is used to input it to a BOOST, as shown in Figure 2. If the three-way-one is used, it is necessary to add a fuse, because if the battery is connected in series reversely, twice the short-circuit current will flow into the reverse direction. If the connected road is not disconnected in time, the battery string will be damaged by overcurrent, so it is generally considered to add fuse protection;

Similar 4-way or multi-way parallel input needs to consider adding protection devices such as fuses and diodes, and the operating current of the switch is also increased accordingly, which puts forward more stringent requirements for the selection of the switch.

The third is to connect N two-way and one in parallel at the back end of the switch to realize multi-channel parallel input, as shown in Figure 3. If PV(2N) is not connected, odd-numbered series connection is realized. The connection mode of each group is flexible and can be It is very suitable for various types of components, and the switch K _N is the Nth DC switch. By using a new type of multi-channel direct current (DC) isolation switch with tripping function, this solution can eliminate the need for protection devices such as fuses or diodes. Reduced system cost.

In order to save cost and space, photovoltaic inverters generally adopt the design of multiple switches, that is, a switch body contains multiple sets of contacts, and multiple inputs are turned on or off at the same time. As shown in Figure 4, one 4-level switch is usually connected to two-way two-way one photovoltaic string. If switch K ₁ and K ₂ or K _N in Figure 3 are on the same switch body, then one or more sets of contacts will bear twice the PV voltage when the switch body is closed or opened (for 1500V photovoltaic system, it is 3kV). Take N as ₂ as an example, assuming that PV4 is not connected, switch K1 and K2 are _on the same switch body, if PV3 is reversed, as shown in Figure 5, the four _- level contact of switch K1 is open or closed. It will withstand twice the PV voltage, which puts forward higher requirements for switch performance and safety. Once the switch cannot be broken normally, from the perspective of functional safety, fuses or anti-reverse devices need to be added, and the corresponding cost will also increase.

SUMMARY OF THE INVENTION

Aiming at the problems existing in the practical application of the new type of multi-channel direct current (DC) isolating switch with tripping function, a method for preventing switch overvoltage when the photovoltaic strings are reversed is proposed to ensure that different two-way direct current (DC) isolation switches or single The strings are connected through different controllable trip DC switches, and the power-on sequence of the controllable trip DC switches is used to limit the power-on sequence. Incorrectly connect the DC switch of the line to avoid the risk of overvoltage and overcurrent caused by the switch closing in the case of reverse connection.

The technical scheme of the present invention is as follows: a method suitable for preventing switch overvoltage when photovoltaic strings are reversely connected. The solar panel components are connected to the photovoltaic inverter through different DC switches in turn in a two-to-one string mode, and the photovoltaic inverter is connected to the photovoltaic inverter. Each channel of BOOST in the device is connected to the DC of the battery board assembly with no more than 2 sets of DC switches.

Further, each channel of BOOST allows no more than 4 channels of photovoltaic strings to be connected.

Further, when the number of the solar panel components is an odd number, the last odd number of solar panel components is connected to the photovoltaic inverter through a DC switch alone.

Further, the DC switch is a multi-channel DC isolation switch with tripping.

Further, the battery board assembly is a two-to-one group string. For example, one of the battery components is reversely connected, the group string is output by a constant current source to the outside, and the terminal voltage only has a diode voltage drop. The two-to-one battery board assembly is at the front end of the switch. Short-circuit, the short-circuit current does not pass through the DC switch, and the photovoltaic inverter controller judges the reverse connection or abnormality of the panel components according to the internal sampling, so as to locate the fault.

Further, the battery board assembly is connected to the inverter separately, and it is determined whether it is reversely connected by sampling the voltage or current of the battery board assembly at the front end of the DC switch. Switch command, the control command will be cancelled after the reverse connection fault is eliminated, and the switch will be connected normally after manual reset.

Further, the solar panel assembly has two-to-one strings without twice the short-circuit current sinking into the corresponding DC switches, and the DC switches are configured according to the rated current of the connected strings.

Further, there is no fuse or anti-reverse diode in the connection circuit of the battery board assembly.

Further, the photovoltaic inverter controller controls the power-on sequence of the DC switch to limit, and after power-on, detects whether the voltage of each string is normal. Overvoltage and overcurrent occur in reverse connection.

Further, the locked DC switch can only be reset manually.

The beneficial effects of the present invention are: the present invention is applicable to the method for preventing switch overvoltage when the photovoltaic string is reversely connected, which can prevent the switch from being subjected to twice the PV voltage after the reverse connection of the components, and at the same time does not require an additional increase in the connection circuit of each group of solar panel components. Fuse or anti-reverse diode, the method is effective and low cost.

Description of drawings

FIG. 1 is a schematic diagram of a first embodiment of the connection between an existing inverter and different battery panel assemblies;

FIG. 2 is a schematic diagram of the second embodiment of the connection between the existing inverter and different battery panel assemblies;

FIG. 3 is a schematic diagram of Embodiment 3 of the connection between the existing inverter and different battery panel assemblies;

Figure 4 is a schematic diagram of a 4-pole switch connected to two two-way one photovoltaic strings;

Fig. 5 is the schematic diagram after the failure of the embodiment of Fig. 3;

FIG. 6 is a circuit connection diagram of the method for preventing switch overvoltage in reverse connection of photovoltaic strings according to the present invention;

7 is a schematic diagram of Embodiment 1 of the method of the present invention;

8 is a schematic diagram of a short-circuit situation in the implementation of the method of the present invention;

FIG. 9 is a schematic diagram of two short-circuit situations in which the method of the present invention is implemented;

10 is a circuit implementation diagram of Embodiment 1 of the present invention;

FIG. 11 is a schematic diagram of the control flow of the method of the present invention.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and provides a detailed implementation manner and a specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

As shown in Figure 6, the circuit connection diagram of the method suitable for the reverse connection of photovoltaic strings to prevent switch overvoltage is to connect the first group of two-to-one strings (PV1/PV2) to BOOST ₁ through DC switch K ₁ , and the second group The two-to-one string (PV3/PV4) is connected to BOOST ₂ through another DC switch K ₂ (not on the same body as K ₁ ), and the PV strings are connected in sequence according to this. Similarly, connect the 2N-1 The two-to-one string (PV(4N-3)/PV(4N-2)) is connected to BOOST _N through a DC switch K _2N-1 , and the 2N group of two-to-one string (PV(4N- 1)/PV(4N)) is connected to BOOST _N through a DC switch K _2N , and at the same time ensure that the DC switch with odd number and the DC switch with even number are not on the same switch body, that is, the two are controlled separately. Only odd-numbered switches or even-numbered switches are allowed to be closed at the same time, and odd-numbered switches and even-numbered switches are not allowed to be closed at the same time. Each BOOST can allow no more than 4 PV strings to be connected. The specific number can be flexibly configured according to the module specifications and field applications. Here, the two-to-one string can also be connected to a single string, which can be better compatible with various types of modules. Serial input, and no need to add fuses or anti-reverse devices, theoretically only need 2 independently controlled DC switch bodies.

The following takes 1 channel BOOST as an example. When the reserved PV4 is not connected, as shown in Figure 7, PV1/2 and PV3 are connected by different control switches K ₁ and K _2. Considering the reverse short-circuit output of each battery string, and corresponding solutions.

Case 1: If PV1 or PV2 is reversely connected, similar to the short circuit shown in Figure 8, the photovoltaic panel can be equivalent to a current source and a diode connected in parallel (ignoring the influence of line impedance and leakage current impedance). A certain photocurrent, part of which is used to offset the junction current, and the other part is supplied to the load output. After a short circuit, the battery board shows a constant current source output to the outside, and the port voltage only has a diode voltage drop. Since the two strings of battery boards are short-circuited at the front of the switch, The short-circuit current is the sum of the short-circuit currents of the two strings of battery panels, but the short-circuit current does not pass through the DC switch. After the switch K1 is closed, the internal power supply _of the inverter is established (usually, there are multiple BOOST units inside the inverter, and any BOOST If there is voltage, the internal power supply will be established. Even if there are individual boosters connected to the string reversely, it will not affect the establishment of the internal power supply.) The control unit can judge the reverse connection or abnormality of the battery board according to the internal sampling (each booster inside the inverter Units have voltage/current sampling) to locate faults.

Case 2: If a single PV3 is reversely connected, it is similar to the short circuit shown in Figure 9, compared to Figure 5. If the DC switches K ₁ and K ₂ are closed at the same time, the 4-level contact will bear twice the PV voltage and double the short circuit at the same time. The current is poured into PV3 and needs to be protected by a fuse. However, Figure 9 uses two independent DC switches K ₁ and K ₂ , and the power-on sequence is limited to only close K _{1 first} . After K ₁ is closed, the inverter is powered on. After the power supply is established, check whether the PV3 voltage/current is normal. If it is not normal, lock K ₂ through the switch control signal. After confirming that the PV3 wiring is normal, K ₂ can be closed after manual reset, so there will be no short-circuit current flowing into PV3.

The present invention proposes a simple and effective solution for adapting each panel component to the photovoltaic inverter string input mode. The power-on sequence of the controllable tripping DC switch is used to limit the power-on sequence, and after power-on, it is detected whether the PV voltage of each channel is normal or not. In case of reverse connection, etc., through the controllable switch signal, the DC switch of the wrong connection line is locked to avoid the risk of overvoltage and overcurrent caused by the switch closing in the case of reverse connection.

Take 1 channel of BOOST as an example to illustrate the implementation of the specific solution. As shown in Figure 10, first close the switch K ₁ of the first PV string connected to one channel of BOOST. Usually, there are multiple BOOST units inside the inverter. If the boost voltage is present, the internal power supply will be established. Even if some BOOST is connected to the string in reverse, it will not affect the establishment of the internal power supply. After the internal power supply is established, first judge whether PV1/PV2 is reversed. If it is reversed, perform troubleshooting. If it is normal, the inverter can judge whether PV3 is reversed through the sampling voltage/current of PV3. Corresponding to the front end (closer to the component side ₎ of the switch K2, a voltage or current sampling branch can be added. If the polarity of PV3 voltage sampling is opposite, it is judged to be reversed, and the inverter internal controller issues a trip command to lock _{K 2 .}

The relevant control logic flow is shown in Figure 11. The controller CTR adopts the MCU control chip inside the inverter. After the internal power supply of the inverter is established, the voltage and current of each string can be detected. The string detection circuit can be used at the front end of the DC switch. detection.

The above-mentioned embodiments only represent several embodiments of the present invention, and the descriptions thereof are specific and detailed, but should not be construed as a limitation on the scope of the invention patent. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can also be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims (10)

1. A method for preventing switch overvoltage when photovoltaic strings are reversely connected, characterized in that the solar panel components are connected to the photovoltaic inverter through different DC switches in a two-to-one string manner, and the photovoltaic inverter is connected to the photovoltaic inverter. Each channel of BOOST is connected to a battery board assembly with no more than 2 sets of DC switches. 2 . The method for preventing switch overvoltage when a photovoltaic string is reversely connected according to claim 1 , wherein each channel of BOOST allows no more than 4 photovoltaic strings to be connected. 3 . 3. The method for preventing switch overvoltage when the photovoltaic string is reversely connected according to claim 1, wherein when the number of the solar panel components is an odd number, the last odd number of solar panel components is connected through a DC switch alone. PV inverter. 4. The method for preventing switch overvoltage when a photovoltaic string is reversely connected according to claim 1, 2 or 3, wherein the DC switch is a multi-channel DC isolation switch with tripping. 5 . The method of claim 4 , which is suitable for preventing switch overvoltage when a photovoltaic string is reversely connected, wherein the solar panel components are two-to-one strings. For example, if one battery component is reversely connected, the string Externally, it is a constant current source output, and the port voltage only has a diode voltage drop. The two solar panel components of two-to-one are short-circuited at the front end of the switch, and the short-circuit current does not pass through the DC switch. The photovoltaic inverter controller judges the solar panel components according to internal sampling. exception to locate the fault. 6 . The method for preventing switch overvoltage when photovoltaic strings are reversely connected according to claim 3 , wherein the solar panel assembly is connected to the inverter separately, and the voltage of the solar panel assembly at the front end of the DC switch is sampled by sampling the voltage of the solar panel assembly. 7 . Or current to determine whether it is reversed, if it is determined to be reversed, the inverter controller will issue a lock corresponding DC switch command, and the control command will be cancelled after the reversed fault is eliminated, and it will be normally closed and connected after manual reset. 7 . The method for preventing switch overvoltage when photovoltaic strings are reversely connected according to claim 5 , wherein the solar panel assembly does not have twice the short-circuit current in the two-to-one string to the corresponding DC. 8 . Switches, the DC switches are configured according to the rated current of the connected strings. 8 . The method for preventing switch overvoltage when a photovoltaic string is reversely connected according to any one of claims 1 , 2 , 3 , 5 , 6 and 7 , wherein there is no circuit in the connection circuit of the solar panel assembly. Fuse or anti-reverse diode. 9 . The method for preventing switch overvoltage when a photovoltaic string is reversely connected according to claim 7 , wherein the photovoltaic inverter controller controls the power-on sequence of the DC switch to limit the power-on sequence, and detects each circuit after power-on. 10 . Check whether the string voltage is normal. If reverse connection occurs, control the switch signal to lock the DC switch of the wrong connection line to avoid overvoltage and overcurrent in reverse connection. 10 . The method for preventing switch overvoltage when a photovoltaic string is reversely connected according to claim 8 , wherein the locked DC switch can only be reset manually. 11 .

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