KR101065786B1 - PV system and its operation method - Google Patents

Abstract

The present invention relates to a photovoltaic power generation system and its operation method, comprising: a solar cell module in which a plurality of solar cells absorbing sunlight are connected in series / parallel; A plurality of power converters connected in parallel with the terminals of the solar cell module; And a controller for controlling the power converter, wherein each of the plurality of power converters has a different rated capacity.

When providing the present invention as described above, through a simple configuration and operation method of the power converter, not only to provide a photovoltaic power generation system having a high efficiency corresponding to a wide range of load, but also according to the conventional switching signal difference By preventing accidents exceeding the rated capacity of the device in advance, it provides a stable, high efficiency solar power generation system and its power generation operation method.

Solar Cell, Power Inverter, PCS, IGBT

Description

Solar power plant system and its operating method

The present invention relates to a photovoltaic power generation system and a method of operating the same, and more particularly, to a photovoltaic power generation system having a high efficiency corresponding to a wide range of loads through a simple configuration and operation method of a power converter, and a provision thereof. The invention relates to a method.

Currently, the world's most energy-dependent coal and nuclear power plants continue to increase their interest in alternative energy due to resource depletion, environmental and stability issues. Among them, photovoltaic power generation has almost no maintenance cost, receives considerable attention from the viewpoint of infinite clean energy, and many studies have been made even now.

Currently, solar power is used in a wide range of applications such as battery chargers, pumps, home power supplies, street lights, and satellite power systems. However, the photovoltaic power generation system is somewhat limited in the spread of practical use due to the high price of the system including the solar cell module.

As a result, recent efforts have been made to reduce the manufacturing cost or improve the efficiency, and to research the lower cost and higher efficiency of peripheral devices such as inverters.

As solar cells have low conversion efficiency, an alternative to reducing the cost of the entire system is to increase the efficiency of power conversion devices and control them to generate maximum energy from solar cells.

DC / DC converter is applied to convert to voltage, and it is in the form of boost, buck, and buck-boost according to the condition of input and output voltage.

The converter applies a PWM switching technique to maintain a constant output voltage or output current at the same time as maximum power point tracking (MPPT). High frequency switching is advantageous from the point of view of reducing the ripple of the output voltage, but it is necessary to consider the problems such as the reduction of the efficiency of the entire system due to the switching loss and the EMI noise.

As a method of increasing the output of the photovoltaic power generation system, a method of increasing the total output by connecting the converter modules in parallel is widely used. However, if several converters have the same input and output stages and are driven by the same switching signal, the current of each converter is likely to be unbalanced. The parameters of the converters connected in parallel cannot be exactly the same in reality, resulting in a slight difference in the ratio of the switching signals.

Therefore, even if the same signal is given as the control signal of each converter switch, there is a slight difference in the gate signal of each switch, so that the converter having the largest conduction ratio operates in the continuous current mode and the other converters It will operate discontinuously. After increasing the load, the converter operating in the continuous current mode will increase the current more and more, out of the switch's current rating.

In addition, in general, the power conversion device for photovoltaic power generation can obtain a desired efficiency only when a certain load is higher than a predetermined load, and the efficiency decreases rapidly when the load falls below a specific value.

1 is a diagram illustrating a simplified block diagram of a conventional photovoltaic power generation system. As shown in FIG. 1, a photovoltaic power generation system includes a solar cell module in which a plurality of solar cells are connected in series / parallel to absorb sunlight and convert it into electrical energy, and receive power from the module to supply power to a load. It is composed of a control unit for controlling the power conversion device, the power conversion device for converting into an AC for.

In the conventional photovoltaic system, a single power converter is used to convert the available power. Generally, the power converter generates maximum power only at a specific load value (eg, 30% of the rated capacity). Since the power conversion efficiency drops below a certain load value, there is a problem in applying elastically to a low load, and there is a limit in providing a high efficiency system suitable for various environments and changes.

Therefore, in the case of a large-capacity photovoltaic power plant, it is common to configure and operate a parallel system using a plurality of power converters. For example, in the case of a 1MW power plant, four 250kW class systems are constructed and operated in parallel. As mentioned earlier, under certain loads, the efficiency of the power converter drops sharply. Therefore, to increase the efficiency at low loads, the power converter is operated sequentially according to the input power to maximize the system efficiency. (Not shown)

For example, in the case of a photovoltaic power generation system consisting of two power converters, if two units are operated simultaneously regardless of the load, they operate according to the load while exhibiting characteristics equivalent to the inherent efficiency curve of the power converter. On the other hand, when the output is low, such as in the morning or on a dark day, the output of the solar panel is driven to one system to generate power. The efficiency can be increased. This is called team driving.

2 is a graph illustrating an example of a characteristic curve of a general power converter. As shown in FIG. 2, assuming that the characteristic curve of the power conversion device is significantly lowered at 30%, when operating as one in the general common sense, since one power conversion device is half the load of the power generation system, the power conversion device is half the load. As a result, the efficiency can be improved from about 15% or more of the load. If the total system is 100kW, if 50kW is configured per unit, if the total system output is 15kW, the load ratio of the total power generation system capacity is 15%.

As such, using a plurality of power converters having the same capacity has the advantage of increasing the capacity, and using a team operation method can increase the efficiency of the entire system by increasing the efficiency in the low load region. However, as described above, in the case of the same capacity, since the difference in the switching signal appears, the converter having the largest conduction ratio operates in the current continuous mode and the remaining converters operate in the current discontinuity. After increasing the load, the converter operating in the continuous current mode has the disadvantage that the current increases more and more than the current rating of the switch, and a large number of power converters are required to improve the efficiency characteristic curve according to the load. The disadvantage is that.

The problem to solve the above-mentioned problem is to provide a photovoltaic power generation system having a high efficiency for a wide range of load, through a simple configuration and operation method of the power converter, and according to the difference in the switching signal It is to provide a stable, high efficiency photovoltaic power generation system and its power generation operation method by preventing the accident of exceeding the conventional rated capacity in advance.

A first aspect of the present invention for solving the above problems is a solar cell module connected to a plurality of solar cells that absorb the sunlight in series / parallel; A plurality of power converters connected in parallel with the terminals of the solar cell module; An energy storage device connected to the power converter to store solar energy; And a control unit for controlling the power converter and the energy storage device, wherein each of the plurality of power converters has a different rated capacity.

Here, the power converter preferably includes a DC / DC converter, a DC / AC inverter, and a sine filter, and the control unit preferably includes an IGBT element and a microprocessor.

In addition, a second aspect of the present invention provides a solar cell module including a plurality of solar cell arrays; Claims [1] A photovoltaic power generation system comprising a power conversion unit and a control unit including a power conversion device having a plurality of different rated capacities, the method comprising: measuring input power generated from the solar cell module; Comparing the measured input power with the power converter by the controller; And controlling the input power closest to the determined input power and the capacity of each power converter by the control unit.

The comparing may include measuring an input power by measuring a voltage and a current from the solar cell module; And comparing the measured input power with the capacity of each power converter.

In addition, when the input power exceeds the capacity of any one of the power converter, it may be to add at least one power converter of the remaining power converter in parallel operation.

When providing the present invention as described above, through a simple configuration and operation method of the power converter, not only to provide a photovoltaic power generation system having a high efficiency to meet a wide range of load, but also according to the conventional switching signal difference By preventing accidents exceeding the rated capacity of the device in advance, it provides a stable, high efficiency solar power generation system and its power generation operation method.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a diagram illustrating a configuration of a photovoltaic power generation system according to the present invention. As shown in FIG. 3, the photovoltaic power generation system includes a solar cell module 100 and a solar cell module 100 in which a plurality of solar cells 110 are connected in series / parallel to absorb sunlight and convert it into electrical energy. It is configured to include a control unit 300 for converting the AC power available to receive DC power from the power conversion unit consisting of a plurality of power converters (200, 210) having a different rated capacity and a power converter. do.

The photovoltaic power generation system includes a solar cell module 100 that generates power, and the power is converted into power in a state suitable for the load 400 by the power converter. The power of the conversion result is supplied to the load 400.

Here, the solar cell module 100 is configured in an array to combine a plurality of solar cells 110 using amorphous silicon, crystalline silicon, or compound semiconductors in series and in parallel to obtain a desired output voltage and current. The power conversion unit is a self turn-off switching device such as a power transistor, a power MOSFET, Insulated Gatebipolar Transistors (IGBT), or a gate turn-off thyristors (GTO). May be a DC / DC converter or a voltage-fed self-excited inverter.

The output (power, voltage, frequency, etc.) of the power converter can be controlled by changing the on / off duty (hereinafter also referred to as "duty ratio") of the gate pulse supplied to the switching device of the power converter.

An example of the load 400 is an electric heater or an electric motor or a commercial AC power system. If the load 400 is a commercial AC power system, i.e. a grid connection photovoltaic system, the power of the photovoltaic system that can be put into the commercial AC power system is not limited, and thus this configuration Is extremely desirable when taking more power from the solar cell module 100.

The control unit 300 is configured such that the output voltage and the output current of the solar cell include a voltage detecting means and a controller (not shown). The voltage detecting means digitally outputs a voltage signal indicating the output voltage of the solar cell module 100. Output as data. The voltage signal is input to the voltage setting means and the controller. The current detecting means outputs a current signal indicating the output current of the solar cell as digital data. This signal is input to the voltage setting means.

In the large-capacity photovoltaic power generation system of the present invention, the detection of voltage and current is preferably made of IGBT elements. An insulated gate bipolar transistor (IGBT) is a junction transistor in which a metal oxide semiconductor field effect transistor (MOSFET) is incorporated in a gate part. This is because the semiconductor device is a self-extinguishing type in which the voltage between the gate and the emitter is driven to be turned on and off by the input signal.

The voltage setting means determines the voltage setting value based on the voltage signal and the current signal applied thereto. The voltage setting means may be implemented by a microprocessor for control and is composed of a CPU, a RAM, a ROM, an input / output device, and the like. The controller adjusts the duty ratio described above so that the output voltage of the solar cell module 100 becomes the voltage set value determined by the voltage setting means, and generates a PWM pulse based on the duty ratio. This PWM pulse is a gate pulse which drives the gate of the switching device of a power conversion part. One way to adjust the duty ratio is a feedback control system based on proportional integration (PI) control.

As the PWM pulse generation method, there are a triangular wave comparator 2 method and a hysteresis comparator method. The controller of the controller 300 may be configured of an analog circuit or a digital circuit. In the case where the controller is a digital circuit, the controller is composed of a CPU or a DSP and can be implemented by one controlling microcomputer with a voltage setting means. Therefore, the output voltage of the solar cell module 100 is controlled by controlling the output of the power conversion means.

In the case of a general PV CONDITIONING SYSTEM (PCS) including a power conversion unit and a control unit 300, a power conversion unit having a rated capacity is configured as a single unit as shown in FIG. . In this case, as described above, when the load 400 is generally low, the efficiency is drastically reduced, so the light load 400 and the heavy load 400 have the characteristic of always moving back and forth. In PCS, this is a disadvantage.

The present invention proposes a configuration of a new photovoltaic power generation system having a feature that can have high efficiency even at such a light load 400. The proposed power conversion system (PCS) is composed of two power converters with different capacities unlike general products, and as described above, the low capacity is achieved by driving a low capacity power converter at light load 400 compared to the PCS rated capacity. Operating the power converter at the heavy load 400 can increase the efficiency of the entire PCS.

In addition, the efficiency of the PCS for photovoltaic power generation is important in addition to the European efficiency of introducing a weight according to the load 400 in addition to the highest efficiency. This is because in the case of photovoltaic power generation because all the load 400 region is used in one day, the amount of power generated by the device having higher European efficiency than the highest efficiency. In other words, the European efficiency is good at light load 400, the overall European efficiency is improved. When the PCS is configured in the manner proposed by the present invention, the efficiency becomes very good at the light load 400, and thus the amount of photovoltaic power generation can be further increased than the conventional PCS.

4 is a diagram illustrating a flowchart of a method of operating a photovoltaic power generation system according to the present invention. As shown in Figure 4, a plurality of solar cells are connected in series / parallel to measure the input power from the solar cell module 100 (S100), a plurality of power having a different rated capacity through the control unit 300 Comparing with the input power measured in the converter (S200), and the step of operating a power converter having a rated capacity closest to the input power through the compared data (S300) is configured.

Measuring the input power is measured from the solar cell module 100 through the voltage detection means and the current detection means included in the control unit 300 (S100), the measured input power data is different from the rated capacity through the controller Compared with the power capacity of the plurality of power converters (200, 210) having a (S200), the controller operates the power converter having the rated capacity closest to the input power (S300). The two power converters have the advantage of being able to increase efficiency by arranging devices having different rated capacities and driving the power converter having the closest capacity according to the input power according to the load 400.

And, while operating the power generation system through any one of the power converter, if the input power increases according to the load 400, the system (team) operating system that takes a method of operating in parallel with the power converter having a different capacity Operate. Thus, through the team operation method proposed in the present invention it is possible to achieve efficient solar power generation according to a wide range from light load 400 to high load 400.

5 is a graph comparing the efficiency of the system when using the photovoltaic power generation system and its operation method according to the present invention. The present invention is a method of configuring the power generation system with different capacities without configuring the power converter in the same capacity in parallel operation. For example, when the entire power generation system is configured as 100kW as described above, if 30kW and 70kW are configured, the 30kW power converter also has a characteristic curve as shown in FIG. The point is about 30% x 30kW = 9kW. That is, high efficiency can be obtained from the point where the output of the entire system becomes 9kW or more, which means that the efficiency can be improved from the 9% load 400 compared to the overall system.

In addition, if the system is further divided into three pieces, if a 9kW system, which is 30% of the small capacity power converter, is additionally configured, high efficiency can be obtained at 2.7% load (400) of 30% or more thereof. This comes out. In this way, the more finely sliced the characteristic curve is, the more vertical the characteristic curve can be obtained.

While the invention has been shown and described with respect to the specific embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. Anyone with it will know easily.

1 is a diagram illustrating a simplified block diagram of a conventional photovoltaic power generation system;

2 is a graph showing an example of a characteristic curve of a general power converter;

3 is a view illustrating a configuration diagram of a photovoltaic power generation system according to the present invention;

4 is a diagram illustrating a flowchart of a method of operating a photovoltaic power generation system according to the present invention.

Claims (8)

A solar cell module in which a plurality of solar cells absorbing sunlight are connected in series / parallel; A power converter including a plurality of power converters connected in parallel with the terminals of the solar cell module; And Including a control unit for controlling the power conversion unit, The solar cell module generates an input power according to the system load, The plurality of power converters have different rated capacity, The control unit compares the input power input from the solar cell module and the rated capacity of the power converter to drive at least one power converter having a rated capacity closest to the input power. . The method of claim 1, Each of the plurality of power converters includes a DC / DC converter and a DC / AC inverter. The method of claim 1, The control unit includes a voltage detection means for measuring the voltage output from the solar cell module; Current detection means for measuring a current output from the solar cell module; And Solar power generation system comprising a controller for controlling the power converter. The method of claim 3, And said voltage detecting means and current detecting means comprise an IGBT element. A solar cell module constituting a plurality of solar cell arrays; In the solar power generation system comprising a power conversion unit and a control unit consisting of a power conversion device having a plurality of different rated capacity, Measuring an input power variably generated according to a system load from the solar cell module; Comparing the measured input power with rated capacity of each of the plurality of power converters by the controller; And selecting and driving one or more power converters having a rated capacity closest to the input power according to the comparing step in the control unit. The method of claim 5, The comparing step further includes the step of measuring the input power by detecting the voltage and current from the solar cell module in the control unit; And And the control unit compares the measured input power with the rated capacity of each of the power converters. The method of claim 5, If the input power exceeds the rated capacity of the at least one selected power converter, And the control unit adds at least one of the remaining power converters to the selected one or more power converters to operate in parallel. The method of claim 5, The power converter selection step, And selecting, by the controller, one or more power converters of the plurality of power converters according to the light load of the system load.

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