CN101409449B - Circuit structure of a photovoltaic power generation system - Google Patents

Abstract

The invention discloses a circuit structure of a photovoltaic power generation system. The negative output terminal of the first DC power unit is connected to the positive output terminal of the adjacent DC power unit, and the positive output terminal of the first DC power unit is shared with the AC power unit. The positive input voltage terminal of the DC bus is connected, the negative output terminal of the last DC power unit is connected to the negative input voltage terminal of the common DC bus of the AC power units, and the negative output terminals of all parallel AC power units are connected to the common DC of the AC power unit. The negative input voltage terminals of the busbars are connected, and the positive output terminals of all parallel-connected AC power units are connected with the positive input voltage terminals of the common DC busbar of the AC power units. Adopting such a structure solves other new problems caused by existing photovoltaic power generation systems while solving the maximum power point tracking problem of branches affected by shadows.

Description

Circuit structure of a photovoltaic power generation system

technical field

The invention belongs to the technical field of solar power generation, and in particular relates to a circuit structure of a photovoltaic power generation system.

Background technique

With global warming and the continuous consumption of natural energy, the world is facing unprecedented energy crisis and challenges. Therefore, renewable new energy such as solar energy has been paid more and more attention by people. For large-scale photovoltaic power generation systems, the centralized photovoltaic power generation system has a very large advantage considering the hardware cost. However, since the photovoltaic array is directly connected in series and parallel, the partial shadow caused by clouds and tall buildings will cause the overall output power of the photovoltaic array to drop, and the photovoltaic cells affected by the shadow will also have hot spots. Overcoming the partial shadow problem has become one of the hotspots of people's research.

Literature [1] proposed a branch structure directly composed of photovoltaic panels in series, and literature [2] proposed a multi-branch structure. Both of them can only solve the problem of maximum power point tracking without shadow affecting branches, but cannot solve The maximum power point tracking problem for branches affected by shadows. Literature [3] proposed the circuit idea of AC Module, which can fundamentally solve the shadow problem, but since each photovoltaic panel has an independent power inverter, each power inverter must work in real time, so for For high power systems, not only the cost is very high, but the overall efficiency is not high. Literature [4] proposes a DC Module circuit, each photovoltaic panel has an independent DC/DC converter, and then multiple DC Module circuits are connected in series to share an inverter device. This circuit can also solve the problem of partial shading, but each DC Module circuit also works in real time, and the circuit itself must have power loss, so the efficiency of the entire system is reduced. At the same time, if the DC Module circuit fails, the photovoltaic panel cannot work properly, may cause overall system performance to degrade. Literature [5] proposes a bypass DC/DC module integrated converter structure based on the branch circuit structure. Only when the shadow appears, the corresponding bypass DC/DC conversion circuit starts to work, which can solve the problem of literature [4]. In ], the power loss caused by the real-time operation of the DC Module circuit itself, but due to the mutual influence between the bypass DC/DC conversion circuits, the maximum power point tracking speed is relatively slow, and the control algorithm is also relatively complicated, and the circuit also has post-fault effects Overall system performance issues.

For the inverter circuit device, it is usually designed for the maximum power of the photovoltaic array. If the output power of the photovoltaic array is very large, a single inverter circuit device is used to realize it, and the rated capacity of the power components of the main circuit must be very large. However, when the light intensity becomes weak, the output power of the photovoltaic array itself is not large, which causes the overall efficiency to be low. At the same time, from the perspective of safety and reliability, once a single inverter circuit device fails, the entire photovoltaic power generation system must stop running, which is very dangerous for important occasions. Literature [6] proposes a master-slave circuit structure based on inverter power units. One master inverter power unit controls whether other slave inverter power units are put into operation according to the actual power, which can solve the problem of overall efficiency and safety reliability. Unite. However, since the master inverter power unit is always put into operation, there is a problem that the service life of the master inverter power unit is shorter than that of other slave inverter power units.

Literature [1] B.Verhoeven et al., Utility aspects of grid connected photovoltaic power systems (1998). International energy agency photovoltaic power systems, IEA PVPS T5-01:1998. [online]. Available: www.iea-pvps.org .

Literature [2] M.Meinhardt and G.Cramer, "Past, present and future of gridconnected photovoltaic-and hybrid-power-systems," in Proc.IEEE-PES Summermeeting, vol.2, 2000, pp.1283-1288.

Literature [3] Gross M.A., Martin S.O., Pearsall N.M., "Estimation of outputenhancement of a partially shaded BIPV array by the use of AC modules," Photovoltaic Specialists Conference, Conference Record of the Twenty-sixth IEEE, pp.13481, 2-1 Sept.-3 Oct.1997.

Literature [4] G.R.Walker and P.C.Sernia, "Cascaded DC-DC converterconnection of photovoltaic modules," IEEE Transactions on Power Electronics, vol.19, no.4, pp.1130-1139, July 2004.

Literature [5] G.R.Walker, J.K.Xue and P.C.Sernia, "PV string per-modulemaximum power point enabling converters," Australasian Universities PowerEngineering Conference (AUPEC'03), vol.1, University of Canterbury, Christchurch, New Zealand, pp .1-6, available: www.itee.uq.edu.au/~aupec/.

Literature [6] M. Meinhardt, G. Cramer, F. Greizer, Technische innovationenimboomenden markt der PV Systemtechnik, 18 Symposium Photovoltaische Sonnenenergie, Staffelstein, Germany, 2003.

Contents of the invention

The purpose of the present invention is to provide a circuit structure of a photovoltaic power generation system, which not only solves the problem of maximum power point tracking affected by shadows, but also solves other problems caused by existing photovoltaic power generation systems when dealing with partial shadows, reducing It eliminates the power loss caused by the usual DC/DC conversion circuit working all the time, makes the DC/DC conversion circuits independent of each other, improves the performance and safety reliability of the system, reduces the cost of hardware, and improves the efficiency of the system.

The technical solution adopted in the present invention is a circuit structure of a photovoltaic power generation system, including at least two DC power units connected in series and at least two AC power units connected in parallel, and all DC power units communicate through a common serial The bus is connected to the serial communication network, all AC power units are connected to the serial communication network through a common serial communication bus, and the negative output terminal of the first DC power unit is connected to the positive output terminal of the adjacent DC power unit , the positive output terminal of the first DC power unit is connected to the positive input voltage terminal of the common DC bus of the AC power unit, the negative output terminal of the last DC power unit is connected to the negative input voltage terminal of the common DC bus of the AC power unit, The negative output terminals of all the parallel connected AC power units are connected to the negative input voltage terminals of the common DC bus of the AC power units, and the positive output terminals of all the parallel connected AC power units are connected to the positive input voltage terminals of the common DC bus of the AC power units.

The present invention is also characterized in that:

The structure of the DC power unit is: at least two photovoltaic panels are connected in parallel, and then connected in parallel with a DC/DC conversion circuit. Reverse charging power diode, the negative voltage output terminal of the photovoltaic cell panel is connected to the negative voltage output terminal of the DC/DC conversion circuit, and the negative voltage output terminal of the photovoltaic cell panel is at the same potential as the negative voltage output terminal of the DC/DC conversion circuit .

The AC power unit consists of a single-phase or three-phase inverter circuit.

The beneficial effect of the present invention is,

Connect several photovoltaic panels in parallel, and then connect them in parallel with a DC/DC conversion circuit, and then connect a power diode to prevent reverse charging between the positive voltage output terminal of the photovoltaic panel and the positive voltage output terminal of the DC/DC conversion circuit, constitutes a DC power unit. Then several DC power units are connected in series, and then connected with several parallel AC power units. Adopting such a structure solves other new problems caused by the existing photovoltaic power generation system while solving the maximum power point tracking problem of the branch affected by the shadow, and reduces the power caused by the usual DC/DC conversion circuit working all the time. Loss, so that the DC/DC conversion circuits do not affect each other, improve the performance and safety reliability of the system, reduce the cost of hardware, and improve the efficiency of the system.

Description of drawings

Fig. 1 is a schematic diagram of the circuit structure of the present invention;

Fig. 2 is a schematic diagram of the DC power unit structure in the circuit structure of the present invention;

Fig. 3 is a schematic diagram of the structure of the AC power unit in the circuit structure of the present invention.

In the figure, 1. Power diode, 2. Photovoltaic panel, 3. DC/DC conversion circuit, 4. AC power unit, 5. DC power unit, 6. Serial communication network.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

FIG. 1 is a schematic diagram of a circuit structure of an embodiment of the present invention. The negative output terminal of a DC power unit 5 is connected to the positive output terminal of an adjacent DC power unit 5, and so on, so that k DC power units 5 are connected in series. The positive output terminal of the first DC power unit 5 is connected to the positive input voltage terminal of the common DC bus of the AC power unit 4, and the negative output terminal of the kth DC power unit 5 is connected to the negative input of the common DC bus of the AC power unit 4 voltage terminal. The negative output terminals of the m AC power units 4 are connected in parallel to the negative input voltage terminal of the common DC bus, and the positive output terminals of the m AC power units 4 are connected in parallel to the positive input voltage terminal of the common DC bus.

All DC power units 5 and AC power units 4 have serial communication interface circuits, and the above-mentioned units are connected by a common serial communication bus. The circuit structure of the present invention communicates all DC power units 5 and 4 through a serial communication network 6. The power information in the AC power unit 4 is exchanged.

The output voltage of k DC power units 5 in series is used as the common DC bus voltage of m AC power units 4, so that the output voltage of k DC power units 5 in series reaches a higher DC voltage level to meet the requirements of the inverter voltage Require. Except for one AC power unit 4 as the master control unit, all other DC power units 5 and AC power units 4 are slave control units. The main control unit collects information such as output power, and directs whether the slave control unit is put into work. Each DC power unit 5 and AC power unit 4 has a maximum power point tracking function, which can solve the partial shadow problem. All the AC power units 4 constitute an inverter device as AC inverter units. According to the output power of all the DC power units 5 and the running time of each AC power unit 4, the operation and stop of the AC power units 4 are controlled through the serial network control technology. The serial network control technology can solve the problem of coordination between all the AC power units 4 and the DC power units 5, and at the same time increase the average service life of the AC inverter units.

The structure of the DC power unit 5 is shown in Figure 2. N photovoltaic cell panels 2 are connected in parallel, and then connected in parallel with a DC/DC conversion circuit 3. The positive voltage output terminal of the photovoltaic cell panel 2 is connected to the positive A power diode 1 to prevent reverse charging is connected between the voltage output terminals, the negative voltage output terminal of the photovoltaic cell panel 2 is connected to the negative voltage output terminal of the DC/DC conversion circuit 3, and the negative voltage output terminal of the photovoltaic cell panel 2 is connected to the negative voltage output terminal of the photovoltaic cell panel 2. The negative voltage output terminals of the DC/DC conversion circuit 3 are at the same potential.

When the light intensity is the same, all photovoltaic panels 2 output the same power through the power diode 1 that prevents reverse charging. At this time, because all DC/DC conversion circuits 3 are not working, all DC power units 5 have no power loss. When a partial shadow appears, the DC/DC conversion circuit 3 corresponding to the affected photovoltaic cell panel 2 will work, track the maximum power point, and prevent the reversely charged power diode 1 from automatically stopping current flow due to back pressure. The DC power unit 5 without shadow influence outputs power as usual through the power diode 1 which prevents reverse charging. When the partial shadow does not exist, the originally working DC/DC conversion circuit 3 stops working, and continues to output power through the corresponding reverse charging preventing power diode 1 . In this way, the problem of self-circuit loss caused by the continuous operation of the DC/DC conversion circuit 3 can be solved, and at the same time, the problem that the DC power unit cannot work due to the failure of the DC/DC conversion circuit can be avoided, and the safety and reliability of the system can be improved. sex.

The AC power unit 4 is composed of a single-phase or three-phase inverter circuit, as shown in Figure 3, the output end of the AC power unit 4 is connected to the power grid or an AC load, and the input end is respectively connected to the positive input voltage end of the common DC bus and the positive input voltage end of the common DC bus. Negative input voltage terminal. It can be used for both grid-connected operation and off-grid independent operation.

Since photovoltaic panels 2 of the same type have the same volt-ampere characteristics, and when photovoltaic panels 2 are connected in parallel, even if some of the panels are affected by shadows, the total power of the parallel connection is approximately equal to each The principle of the sum of the maximum power of the photovoltaic panels 2 is that as long as the DC/DC conversion circuit 3 realizes the maximum power point tracking, all the parallel connected photovoltaic panels 2 are approximately at the maximum power point. Therefore, the connection method of the photovoltaic cell panels 2 is to first connect N photovoltaic cell panels 2 in parallel, and then connect them in parallel with a DC/DC conversion circuit 3 to form a DC power unit 5 . K DC power units 5 are connected in series to form the input DC bus of the whole system. Adopting such a connection method can greatly reduce the number of DC/DC conversion circuits 3 , which can not only solve the problem of hardware cost, but also solve the problem of partial shading.

In the start-up phase, all DC power units 5 are not working, and all AC power units 4 are put into operation. After waiting for a few minutes, the system enters the normal working stage. At this time, the main control unit determines whether the shadow exists according to the output power of each DC power unit 5 . The basis for judging is that if the difference between the output power of a few DC power units 5 and the output power of most DC power units 5 exceeds the set range, for example, 10W, the corresponding few DC power units 5 are put into operation to track the maximum power point, and Other DC power units 5 still do not work. At the same time, the main control unit instructs some AC power units 4 to stop running according to the overall output power and the working time of each AC power unit 4 . When it is determined that there is no shadow, the main control unit instructs the working DC power unit 5 to stop working, and instructs each AC power unit 4 to run and stop. When the light intensity is very weak for a period of time, the main control unit instructs all DC power units 5 and AC power units 4 to stop working and no longer transmit energy to the grid or loads. When the light intensity becomes stronger for a period of time, re-enter the start-up phase.

The circuit structure of the present invention can not only solve the partial shadow problem of the photovoltaic array, but also reduce the power loss caused by the operation of the switching circuit itself, improve the system efficiency, and improve the reliability of the whole system at the same time. It adopts modular design, so it has very good advantages in terms of safety redundancy and installation and maintenance compared with the previous circuit structure. The circuit structure of the present invention can be used in photovoltaic power generation grid-connected systems or off-grid systems, suitable for both single-phase AC systems and three-phase AC systems, and has very good practical value in the field of large and medium power photovoltaic power generation.

Claims (2)

1. the circuit structure of a photovoltaic generating system, it is characterized in that, comprise at least two direct current power unit (5) that are in series and at least two AC power unit (4) that are in parallel, the above-mentioned direct current power unit (5) that is in series is connected with serial communication network (6) by public serial communication bus, the above-mentioned AC power unit (4) that is in parallel is connected with serial communication network (6) by public serial communication bus, the negative output terminal of first direct current power unit (5) is connected with the positive output end of adjacent direct current power cell (5), the positive output end of first direct current power unit (5) is connected with the positive input voltage end of AC power unit (4) common DC bus, the negative output terminal of last direct current power unit (5) is connected with the negative Input voltage terminal of AC power unit (4) common DC bus, the negative output terminal of the AC power unit (4) that all are in parallel is connected with the negative Input voltage terminal of AC power unit (4) common DC bus, and the positive output end of the AC power unit (4) that all are in parallel is connected with the positive input voltage end of AC power unit (4) common DC bus;

The structure of wherein said direct current power unit (5) is: at least two photovoltaic battery panels (2) parallel connection, in parallel with a DC/DC translation circuit (3) again, be connected with a power diode (1) that prevents reverse charging between the positive voltage output end of the positive voltage output end of photovoltaic battery panel (2) and DC/DC translation circuit (3), the negative voltage output of photovoltaic battery panel (2) is connected with the negative voltage output of DC/DC translation circuit (3), and the negative voltage output of the negative voltage output of photovoltaic battery panel (2) and DC/DC translation circuit (3) is a same potential.

2. according to the described circuit structure of claim 1, it is characterized in that described AC power unit (4) is made up of single-phase or three-phase inverting circuit.

Images