Photovoltaic power stations cover a large area, use a large amount of DC bus cables, and have a lot of line power loss, and the line voltage drop is seriously inconsistent. In a photovoltaic power generation system, multiple photovoltaic modules are connected in series to form the smallest unit with the required DC output voltage. The current of the PV strings connected in series is the working current of a single PV module, and the current is relatively small. In order to facilitate the centralized transmission of current and reduce the power loss during the transmission process, the PV strings need to be connected locally.
At present, the junction box of photovoltaic modules adopts the method of one module and one junction box. The junction box of photovoltaic modules is designed according to the cross section of the connecting line of 4mm², and the junction boxes of photovoltaic modules are all equipped with 4mm² photovoltaic special cables. Separately laid 4mm² photovoltaic special cables lead to the photovoltaic array DC lightning protection combiner box. Under normal circumstances, the connection cable of photovoltaic modules is long, and the nearby connection will cause the cable to become entangled, and the resistance loss of the wire will be large, which will reduce the output power of the module.
There are two common ways to connect PV modules:
(1) The single-row direct connection method as shown in Figure 1. This wiring is the most common way of connecting modules in series. About 40 photovoltaic modules are arranged on each photovoltaic support, which is divided into upper and lower layers, with 20 pieces per layer. According to the arrangement of the components, the positive and negative lead-out wires that come with the components are used to connect the adjacent components in an orderly series according to the positive and negative polarities. The positive and negative ends of each group of strings are on both sides of the string, and each polar end is led to the combiner box through a 4mm² single-core cable. The upper and lower rows of modules installed on the same photovoltaic support are wired in this way. The advantage of this method is that the wiring is simple and clear, and it is not easy to make mistakes; the disadvantage is that the positive and negative lead wires are located at both ends of the string and the distance is more than 20m. In order to introduce into the combiner box, there must be an extra cable of more than 20m, which not only increases the amount of cables, but also increases the workload of cable laying.
(2) The double-row paired serial connection method as shown in Figure 2. According to the arrangement of the modules, the positive and negative lead-out wires of the modules are used to connect the adjacent modules in sequence according to the positive and negative polarities, and the upper and lower rows installed on the same photovoltaic support are connected in series to form a group string. , the positive and negative poles of each string are located on the same side of the string, and each polar end is led to the combiner box through a 4mm² single-core cable. The advantage of this method is that the positive and negative lead wires are located at the same end of the string, and the two cables can be led to the combiner box through the same path, which reduces the workload of cable laying. Therefore, the positive and negative directions of the photovoltaic module junction boxes in the upper and lower rows are inconsistent, and the construction personnel are easy to connect them in the opposite direction, which poses a safety hazard.
Based on work experience, combined with the characteristics of photovoltaic modules and cable connection technology, a self-distributed cable connection structure for modules with positive and negative outgoing wires on the same side without winding is proposed. The connection method of the module across the line, so that the connection cable is not tangled, and the positive and negative outgoing cables of the PV module string are drawn from the same side of the PV module string, which can not only meet the output efficiency of the PV module series, but also reduce the PV module series The amount of primary bus cable engineering to the combiner box reduces the power loss of the line (Figure 3).
The self-matching cable connection structure of the photovoltaic module string with the positive and negative poles directly connected to the same side includes a photovoltaic module string composed of even-numbered rows of photovoltaic modules, and a junction box is located on the photovoltaic module. The junction box includes the positive pole of the junction box and the negative pole of the junction box, and the self-distributed cable is led out from the terminal box. The negative outgoing wire of the string and the positive outgoing wire of the module string are drawn out on the same side. Even rows of photovoltaic modules are arranged in the same direction. The negative outgoing wire of the module string and the positive outgoing wire of the module string used are self-configured cables.
The direct connection line scheme of the positive and negative poles on the same side has the following three advantages:
1) All photovoltaic modules are placed in the same direction, and the positive and negative outgoing wires on the junction boxes of all modules are in the same direction, which reduces the probability of workers making mistakes during construction;
2) With this wiring scheme, the interconnection between the two adjacent photovoltaic modules in the same row and the photovoltaic modules in the same row, the upper and lower rows can all use the self-contained photovoltaic module cables, and there is no need to add other cables;
3) The positive and negative outgoing wires of a PV module string are on the same side of the PV module string, so the positive and negative outgoing wires of the PV module string can be connected to the combiner box through the same path, which is convenient for optimizing the arrangement of the PV module string and the combiner box in the design. , reducing the extra cable usage when the positive and negative outgoing wires are on both sides. For photovoltaic power stations with tens of thousands of photovoltaic module strings, more than ten kilometers of photovoltaic cables can be saved.