WO2013163778A1

WO2013163778A1 - Novel photovoltaic system

Info

Publication number: WO2013163778A1
Application number: PCT/CN2012/000593
Authority: WO
Inventors: 高峰
Original assignee: 上海康威特吉能源技术有限公司
Priority date: 2012-05-02
Filing date: 2012-05-02
Publication date: 2013-11-07

Abstract

A novel photovoltaic system. The photovoltaic system comprises a plurality of photovoltaic module series and a direct current/alternating current converter. The photovoltaic module series control photovoltaic modules to operate at a maximum power point. Outputs of the plurality of photovoltaic module series are parallel-connected and are coupled to an input of the direct current/alternating current converter, thus allowing the photovoltaic module series to be provided with consistent maximum power points, facilitating tracking and control of the maximum power of the photovoltaic system, and allowing for reduced costs and reduced losses.

Description

A new type of photovoltaic system

The present invention relates to a power generation system for a distributed power source, and more particularly to a photovoltaic system having a lumped compensation module. Background technique

Recently, renewable energy has received increasing attention, and research on distributed power sources (such as photovoltaic (PV) batteries, fuel cells, vehicle batteries, etc.) has increased. Considering many factors (such as voltage/current requirements, operating conditions, reliability, safety, cost, etc.), quite a number of topologies have been proposed to connect these distributed power supplies to the load. Most of these distributed DC power supplies can only provide low voltage output. In general, a cell can only provide a few volts, and a module that is connected in series by multiple cells can be used for tens of volts. Therefore, they need to be connected in series to achieve the desired operating voltage. However, a module (ie, a series of cells in series, typically 60 cells) does not provide the required current, so multiple modules need to be connected in parallel to provide the required current.

Furthermore, since the amount of power generated per distributed power source varies depending on process conditions, operating conditions, and environmental conditions. For example, many inconsistencies in the manufacturing process will result in two identical power supplies having different output characteristics. Similarly, two identical power supplies can react differently (affected) due to different operating conditions and/or environmental conditions (eg, load, temperature...h). In actual equipment, different power supplies may also suffer differently. Environmental conditions. For example, in photovoltaic power generation equipment, some photovoltaic panels will be completely exposed to sunlight, while the other part will be shielded, which will produce different output power. In some cases, some batteries will have different degrees of aging, which will result in different output power.

Referring to Figure 1, there is shown a voltage characteristic curve and a current characteristic curve of a photovoltaic (PV) battery. For each photovoltaic cell, the output current decreases as the output voltage increases. The output power of a photovoltaic cell is equal to the product of the output current and the output voltage (ie, P = lx V) and will vary with the output voltage obtained by the photovoltaic cell. Photovoltaic cells have different output currents and output voltages under different illumination conditions. At a certain output voltage, its output power will reach a maximum power point MPP (ie the most power-voltage curve) Great value). The photovoltaic cell is preferably operable at the maximum power point MPP, and the so-called maximum power point tracking (MPPT) is aimed at finding this point and operating the system above the maximum power point MPP in order to Maximum output power is achieved in photovoltaic cells. However, in the real world, it is very difficult to operate each photovoltaic cell at its maximum power point.

Referring to Figure 2, there is shown a related art for the principle of maximum power point tracking of photovoltaic system 200. As shown, a photovoltaic panel (consisting of a plurality of photovoltaic modules) 210 is coupled to a DC-DC converter 220 by a positive output 211 and a negative output 212. The DC-DC converter 220 is used to supply power/power to a load 230. In the photovoltaic system 200, the voltage sensor 222 coupled to the positive output terminal 211 is used to sample the input voltage of the DC-DC converter 220 (ie, the output voltage of the photovoltaic panel 210), and the current sensor coupled to the negative output terminal 212. 223 is used to sample the input current of the DC-DC converter 220 (ie, the output current of the photovoltaic panel 210). The multiplier 224 is operative to multiply the input current signal sensed by the current sensor 223 and the input voltage signal sensed by the voltage sensor 222 to produce a power signal. The maximum power point tracking controller 221 is configured to operate the photovoltaic system 200 below the maximum power point based on the power signal.

Referring to Figure 3, there is shown a related art of a centralized solar system with maximum power point tracking control. As shown in the figure, since the voltage provided by each photovoltaic module 310 is very low, a plurality of photovoltaic modules 310 need to be serially connected into one module serial 320. For a large device, when a larger current is required, a plurality of module series 320 are connected in parallel to form a front stage 350 (i.e., power stage or photovoltaic panel) of the entire photovoltaic system 300. These photovoltaic modules 310 can be placed outdoors and connected to a maximum power tracking (MPPT) module 330, which is then coupled to a DC-to-AC converter 340. In general, the maximum power tracking module 330 can be integrated into a portion of the DC-to-AC converter 340. The DC-AC converter 340 is configured to receive the energy obtained by the photovoltaic module 310 and convert the fluctuating DC voltage into an AC voltage having a desired voltage and a desired frequency. For example, the AC voltage can be an AC voltage of 110V or 220V and 60Hz, or an AC voltage of 220V and 50Hz. It should be noted that even in the United States, there are still many converters that generate 220V AC voltage, but then divide into two 110V supply boxes. The AC current generated by the DC-AC converter 340 can be used to operate an electrical product or to be supplied to a power network. If the photovoltaic system 300 is not connected to the power network, the energy generated by the DC-AC converter 340 can also be transferred to a conversion and charge/discharge circuit (conversion) And charge/discharge circuit), used to charge the extra power/energy into the battery. In a battery-type application, the DC-AC converter 340 can also be omitted, and the DC output of the maximum power tracking module 330 can be directly supplied to the charging/discharging circuit.

As described above, each photovoltaic module 310 can only provide relatively small voltages and currents, so the designer of the photovoltaic cell array (or photovoltaic panel) has a problem of how to provide the small voltage and current provided by the photovoltaic module 310. A standard AC output with a rms value of 110V or 220V is synthesized. In general, a DC-AC converter (such as DC-AC converter 340) will have the highest input efficiency when the input voltage is slightly higher than the rms voltage of the output. Therefore, in order to achieve the required voltage or current, multiple DC power sources (e.g., photovoltaic modules 310) are combined in many applications. The most common way is to connect multiple DC power supplies in series to get the required voltage, or to connect multiple DC power supplies in parallel to get the required current. As shown, a plurality of photovoltaic modules 310 are connected in series to form a module string 320, and a plurality of module series 320 are connected in parallel with the DC-AC converter 340. The plurality of photovoltaic modules 310 are connected in series to obtain a minimum voltage required for the DC-AC converter 340. The plurality of module series 320 are connected in parallel for supplying a larger current to provide a higher current. Output power. Similarly, a connector with a bypass diode can be attached to each of the photovoltaic modules 310 for protection, but the connector is not shown in FIG.

The benefits of this architecture are low cost and simple architecture, but still have many shortcomings. One of the shortcomings is that each photovoltaic module 310 cannot be operated at optimum power, which results in an unsatisfactory efficiency of this architecture. As mentioned above, the output of the photovoltaic module 310 is affected by various factors, so in order to obtain the maximum power from each photovoltaic module, the combination of voltage and current obtained needs to be changed as the case arises. Summary of the invention

The present invention is directed to the problem that the photovoltaic modules in the existing photovoltaic system are not allowed to operate at the optimum power when the photovoltaic modules are shaded, resulting in an unsatisfactory efficiency of the architecture, and providing a novel photovoltaic system. The system enables all PV modules to operate at optimum operating points.

In order to achieve the above object, the present invention adopts the following technical solution - a novel photovoltaic system, the photovoltaic system includes a photovoltaic module series, a DC-AC converter, and the photovoltaic module series includes a plurality of photovoltaic modules Group, the output of the photovoltaic module In series, the photovoltaic module series is coupled to an input of the DC-AC converter, and the photovoltaic system includes a lumped compensation module.

In a preferred embodiment of the present invention, the lumped compensation module is configured to operate a plurality of photovoltaic modules in the series of photovoltaic modules at an optimum efficiency point.

Further, the lumped compensation module is coupled to the plurality of photovoltaic modules, and the optical module is compensated to operate at a maximum power point.

Further, the two input ends of the lumped compensation module are coupled to the two output ends of the series of photovoltaic modules to receive energy for compensation.

Further, the two input ends of the lumped compensation module are coupled to an external energy source. In another preferred embodiment of the present invention, the photovoltaic system further includes a second photovoltaic module series, and the two photovoltaic modules are serially connected in parallel.

Further, the photovoltaic system is further provided with a second lumped compensation module, and the second lumped compensation module is coupled to the plurality of photovoltaic modules in the second photovoltaic module series, The PV module is compensated for operation at the maximum power point.

Further, the two input ends of the second lumped compensation module are coupled to the two output ends of the second photovoltaic module string to receive energy for compensation.

Further, the two input ends of the second lumped compensation module are coupled to an external energy source. In still another preferred embodiment of the present invention, the photovoltaic system further includes a maximum power tracking DC-DC conversion module, and the input of the maximum power tracking DC-DC conversion module and the output coupling of the photovoltaic module series The output of the maximum power tracking DC-DC conversion module is coupled to the input of the DC-AC converter.

The invention formed according to the above solution provides a lumped compensation module for current compensation of a shaded photovoltaic module in a series of photovoltaic modules, such that the photovoltaic module has a consistent maximum power point. It facilitates the maximum power tracking control of the photovoltaic system with low cost and low loss. DRAWINGS

The invention is further described below in conjunction with the drawings and specific embodiments.

Figure 1 shows the voltage characteristic curve and current characteristic curve of a photovoltaic cell.

Figure 2 is a schematic diagram of the maximum power point tracking of the existing photovoltaic system.

Figure 3 is a system block diagram of a conventional centralized photovoltaic system with maximum power point tracking control. Figure 4 is a diagram of a photovoltaic system architecture for distributed maximum power tracking.

5A is a system block diagram of an embodiment of a photovoltaic system having a lumped compensation module of the present invention. Figure 5B is a block diagram of another embodiment of a photovoltaic system having a lumped compensation module of the present invention.

6A is a block diagram of another embodiment of a photovoltaic system having a lumped compensation module of the present invention.

6B is a system block diagram of another embodiment of a photovoltaic system having a lumped compensation module of the present invention. detailed description

In order to make the technical means, the authoring features, the achievement of the object and the effect of the present invention easy to understand, the present invention will be further described below in conjunction with the specific drawings.

The photovoltaic system provided by the invention comprises a photovoltaic module serial and a DC-AC exchanger, wherein the photovoltaic module series can control the operation of the photovoltaic module at the maximum power point, and the output of the photovoltaic module and the DC-AC exchange The input of the device is coupled. The photovoltaic module series can also have a plurality of serials, and the outputs of the plurality of photovoltaic module series are connected in parallel.

Based on the above principles, the specific implementation of the present invention is as follows:

Example 1

In general, the preferred method is to connect the DC power supply (especially the equipment of the photovoltaic module) in series. Referring to FIG. 4, the photovoltaic module serial 440 in the photovoltaic system 400 provided by the embodiment is composed of a plurality of photovoltaic modules 410 and a plurality of DC-DC converters 420 having a maximum power tracking control mechanism.

Each photovoltaic module 410 is coupled to a DC-DC converter 420 having a maximum power tracking control mechanism via a connector having a bypass diode (not shown), and the outputs of these DC-DC converters 420 are Connected in series to form an output of the photovoltaic module string and connected to the DC-AC converter 430.

The DC-DC converter 420 senses the output voltage and output current of the photovoltaic module 410 (i.e., the input voltage and input current of the DC-DC converter 420) for operating the photovoltaic module 410 at the maximum power point.

Coupling DC-DC with maximum power tracking control mechanism behind each photovoltaic module 410 The converter 420, the DC-DC converter 420 senses the output voltage and the output current of the photovoltaic module 410, and multiplies the output voltage by the output current to obtain power for maximum power tracking control. In this way, all of the photovoltaic modules in the photovoltaic system 400 can be operated at their optimum operating point, regardless of whether all of the photovoltaic modules receive the same intensity of sunlight. However, the DC-DC converter 420 of all of the maximum power tracking control mechanisms of the photovoltaic system 400 always has a certain loss, resulting in a decrease in the efficiency of the system 400. Therefore, there is still a need for an effective architecture to address this drawback.

Example 2

This embodiment provides a photovoltaic system having a lumped compensation module for the problems of the photovoltaic system provided by Embodiment 1.

Referring to FIG. 5A, the photovoltaic system 500 provided in this embodiment includes a photovoltaic module series 510, 520, which are respectively composed of a plurality of photovoltaic modules 5101, 5102...510N; 5201, 5202...520N And lumped compensation module 540, 5402.

Several of the photovoltaic modules 5101, 5102...510N; 5201, 5202...520N are connected in series. The two series of outputs are connected in parallel and coupled to the input of a DC-to-AC converter 530 having a maximum power tracking function.

For the photovoltaic module string 510, there is a lumped compensation module 540 corresponding thereto, and the lumped compensation module 540 is coupled to all the photovoltaic modules 5101, 5102, ... 510N in the photovoltaic module series 510. The lumped compensation module 540 compensates for the shaded photovoltaic module, for example, compensating the current, so that the occlusion is blocked when a photovoltaic module such as 5102 in the photovoltaic module string 510 is shaded. The shaded photovoltaic modules continue to operate at substantially the same maximum power point as other unshaded photovoltaic modules.

For the photovoltaic module serial 520, there may be another lumped compensation module 5402 corresponding thereto, or the lumped compensation module 540 may be shared with the photovoltaic module serial 510. For the photovoltaic module series 520, there may be only one photovoltaic module string 510 and one lumped compensation module 540.

Example 3

Referring to FIG. 5B, the photovoltaic system 500 provided by the embodiment has a maximum power tracking DC-DC conversion module 550, and the input and parallel connection of the maximum power tracking DC-DC conversion module 550, compared with the photovoltaic system provided in Embodiment 2. The output of the photovoltaic module series 510, 520 is coupled, and its output is coupled to the input of the DC-AC converter 530. The maximum power tracking DC-DC conversion module 550 is used to operate the system in a maximum power state, and the DC-AC converter 530 is not required. Maximum power tracking function.

Example 4

Referring to FIG. 6A, the photovoltaic system 600 provided in this embodiment is different from the photovoltaic system provided in the second embodiment in that the two input terminals of the lumped compensation modules 640 and 6402 are coupled to the photovoltaic module series 610 and 620. The two outputs are compensated by the energy received, i.e., the energy on the DC BUS is used to provide an energy source for the lumped compensation modules 640, 6402. Because of the high voltage on the DC BUS, the lumped compensation modules 640, 6402 operate at high voltages with low losses. Compared to other distributed maximum power tracking PV systems, the system is less costly and requires only one total maximum power tracking module to achieve maximum power tracking control.

Example 5

Referring to FIG. 6B, the photovoltaic system 600 of the embodiment is different from the embodiment 4 in that the two input terminals of the lumped compensation modules 640 and 6402 are coupled to an external energy source such as a power module 650, which may also be a UPS. .

In summary, the present invention provides a lumped compensation module for current compensation of a shaded photovoltaic module in a series of photovoltaic modules, such that the photovoltaic module has a consistent maximum power point. It facilitates the maximum power tracking control of the photovoltaic system with low cost and low loss.

The basic principles, main features and advantages of the present invention are shown and described above. It should be understood by those skilled in the art that the present invention is not limited by the foregoing embodiments, and that the present invention is only described in the foregoing embodiments and the description of the present invention, without departing from the spirit and scope of the invention. Various changes and modifications are intended to fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and their equivalents.

Claims

Rights request

A photovoltaic system comprising a photovoltaic module series and a DC-AC converter, wherein the photovoltaic module series comprises a plurality of photovoltaic modules, and the outputs of the photovoltaic modules are connected in series. The photovoltaic module series is coupled to the input of the DC-AC converter, wherein the photovoltaic system comprises a lumped compensation module.

2. A novel photovoltaic system according to claim 1, wherein the lumped compensation module is configured to operate a plurality of photovoltaic modules in the series of photovoltaic modules at an optimum efficiency point.

3. A novel photovoltaic system according to claim 2, wherein the lumped compensation module is coupled to the plurality of photovoltaic modules, and the photovoltaic module is compensated for operation At the maximum power point.

A novel photovoltaic system according to any one of claims 1 to 3, wherein two input ends of the lumped compensation module are coupled to two of the photovoltaic module series The outputs are compensated by the energy received.

A novel photovoltaic system according to any one of claims 1 to 3, wherein the two input terminals of the lumped compensation module are coupled to an external energy source.

6. A novel photovoltaic system according to claim 1, wherein the photovoltaic system further comprises a second photovoltaic module series, and the two photovoltaic modules are connected in series with each other.

7. The novel photovoltaic system according to claim 6, wherein the photovoltaic system further comprises a second lumped compensation module, the second lumped compensation module and the second A plurality of photovoltaic modules are coupled in the series of photovoltaic modules, and the photovoltaic modules are compensated to operate at a maximum power point.

8. A novel photovoltaic system according to claim 7, wherein two input ends of the second lumped compensation module are coupled to two outputs of the second photovoltaic module string The end compensates by receiving energy.

9. A novel photovoltaic system according to claim 7, wherein the two input ends of the second lumped compensation module are coupled to an external energy source.

10. A novel photovoltaic system according to claim 1 or claim 6, wherein the photovoltaic system further comprises a maximum power tracking DC-DC conversion module, the maximum power The input of the tracking DC-DC conversion module is coupled to the output of the series of photovoltaic modules, and the output of the maximum power tracking DC-DC conversion module is coupled to the input of the DC-AC converter.