KR20180108534A - Photovoltaic Power Generation System - Google Patents

Abstract

Disclosed is a photovoltaic power generation system which comprises: a distributed maximum output point tracker; a plurality of solar cell modules each having the distributed maximum output point tracker; a string in which the plurality of solar cell modules are connected in series; an array formed by connecting the strings in parallel; and a photovoltaic inverter connected to the array. The distributed maximum output point tracker can track the maximum output point of the solar cell module, thereby maintaining an input voltage of the photovoltaic inverter higher than a voltage of the maximum output point of the array.

Description

[0001] The present invention relates to a photovoltaic power generation system,

Disclosure of the present invention relates to a distributed maximum output point tracking device and a solar inverter and a control method thereof for performing maximum power point tracking (MPPT) in each solar cell module, To a solar cell power generation system capable of harvesting a maximum power by minimizing a power mismatch loss due to an electrical characteristic difference such as a maximum output point voltage and a maximum output point current.

Herein, the background art relating to the present invention is provided, and they are not necessarily referred to as known arts.

Generally, a photovoltaic power generation system is a device for converting solar energy into electric energy using a photovoltaic cell and transferring it to a commercial power system. In this process, environmental pollution does not occur and it can be used semi-permanently .

Various types of solar cells used for solar cell power generation, such as inorganic solar cells, dye-sensitized solar cells, and organic solar cells, have been developed. These solar cells have a low output voltage and a relatively high current. In contrast, since the output voltage is high and the current is relatively low, a plurality of solar cells are commonly connected to form a single module. This solar cell module is called a solar cell module, and a plurality of the solar cell modules are connected in series ), And a plurality of the strings connected in parallel is called an array.

Generally, a solar power generation system is a solar power generation system in which the string or the array is connected to a solar inverter, and a solar power inverter having a maximum power point tracking (MPPT) The module's maximum output point tracking is achieved.

In other words, the conventional PV system can track the maximum output point of a plurality of solar modules connected in series or in parallel by using one maximum output point tracking device built in the solar inverter, The maximum output point of all the solar cell modules connected to the maximum output point tracking device of the present invention is tracked.

First, the currents flowing in the same string must be the same. In other words, the maximum power point current (Imp) of all the solar cell modules constituting it must match.

However, the deviation of the maximum power point current of the solar cell module during the manufacturing process necessarily occurs, and even in the solar power generation process, the deviation of the maximum power point current between the solar cell modules becomes larger due to environmental factors such as solar radiation amount and temperature shadow, There is a large power mismatch loss due to mismatch of the maximum output point current between the battery modules.

The voltages between the strings connected in parallel must be the same. That is, the maximum power point voltage Vmp of all the solar cell modules constituting the solar cell module.

However, the deviation of the maximum power point voltage of the solar cell module occurs in the manufacturing process, and even in the solar power generation process, the deviation of the maximum power point voltage between the solar cell modules becomes larger due to environmental factors such as solar radiation amount and temperature shadow, There is a large power mismatch loss due to inconsistency of the maximum output point voltage between the battery modules.

Therefore, the conventional solar power generation system has a structure to perform maximum power point tracking of a plurality of solar cell modules connected in series and in parallel using a single maximum power point tracking device built in a solar inverter, There is a problem of difficulty in harvesting the maximum electric power due to the occurrence of power mismatch loss due to the difference.

1. Korean Patent Publication No. 10-2011-0020002 2. Korean Patent Publication No. 10-2007-070685 3. Korean Patent Publication No. 10-2013-0025286

Disclosure of the Invention Disclosure is directed to a distributed maximum output point tracking device for minimizing power mismatch loss due to difference in electric characteristics such as a maximum output point voltage Vmp and a maximum output point current Imp in a solar cell module, Optical inverter, and control method thereof.

The present invention is not intended to be exhaustive or to limit the scope of the present invention to the full scope of the present invention. of its features).

In order to solve the above problems, a solar power generation system according to one aspect of the present invention includes a distributed maximum output point tracker; A plurality of solar cell modules each having a distributed maximum output point tracker; A string in which the plurality of solar cell modules are connected in series; An array in which the strings are connected in parallel; And a photovoltaic inverter coupled to the array, wherein the distributed maximum output point tracker is operable to convert the input voltage of the solar inverter to a maximum output point of the array, Voltage is maintained at a level higher than the voltage.

In a solar power generation system according to an aspect of the present invention, the distributed maximum output point tracker includes a Half bridge DC-DC converter having an output impedance variable according to a duty change, The maximum output point of the solar cell module is tracked by changing the duty in a direction of increasing the output by comparing the output change due to the duty change of the Half Bridge DC-DC converter connected in parallel with the solar cell module .

In the photovoltaic generation system according to an aspect of the present invention, the distributed maximum output point tracker includes: a Half bridge DC-DC converter having an output impedance variable according to a duty change; A first analog circuit and a second analog circuit for measuring voltage / current; A controller for measuring a voltage / current transmitted from the first analog circuit and the second analog circuit to compare a current power with a power of a changed duty to perform a maximum output point tracking algorithm; And a power supply for supplying power required for the controller and the half bridge DC-DC converter, wherein the duty ratio of the half bridge DC-DC converter To perform maximum output point tracking of the solar cell module.

In a solar power generation system according to an aspect of the present invention, the Half bridge DC-DC converter includes: a plurality of MOSFETs; a plurality of capacitors; and an inductor; And a High and Low Side Driver.

In a solar power generation system according to an aspect of the present invention, the distributed maximum output point tracker comprises: an initialization step (S710); Confirming the operation of the solar inverter (S720); (S725) while waiting for the solar inverter to maintain the initial duty while measuring the maximum output point voltage of the string; Measuring power P1 in the current duty D (S730); (S740), after increasing the duty (D = D +? D), measuring the power P2 and decreasing the duty (D = D -? D); A step (S750) of comparing the current duty power P1 with the duty-changed power P2; If P2 is larger than P1, the duty is increased (D = D +? D) and a certain time is delayed (S760); And a step (S770) of decreasing the duty (D = D -? D) and delaying a predetermined time when P1 is larger than P2; and repeating steps S730 to 770 in order to maximize the output point of the solar cell module Is performed.

According to the present invention, since the maximum output point of each solar cell module is tracked by the distributed maximum output point tracker, the difference in electrical characteristics such as the maximum output point voltage (Vmp) and the maximum output point current (Imp) It is possible to minimize the power mismatch loss and improve the efficiency of the photovoltaic power generation system.

In addition, even when the power mismatch due to environmental factors such as shadows is severe, there is an excellent effect of improving the efficiency of the photovoltaic power generation system by minimizing the loss.

1 is a block diagram showing a structure of a solar power generation system.
2 is a block diagram showing the structure of a solar cell module.
3 is a block diagram showing a structure of a string.
4 is a block diagram illustrating a distributed maximum output point tracker.
FIG. 5 is a flow chart showing an example of a control method performed by the distributed maximum output point tracker 400. FIG.
6 is a graph showing output characteristics of the solar cell module.
7 is a block diagram showing a solar inverter;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a solar power generation system according to the present invention will be described in detail with reference to the drawings.

It is to be understood, however, that the scope of the present invention is not limited to the embodiments described below, and those skilled in the art of the present invention, other than the scope of the present invention, It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention.

In addition, the terms used below are selected for convenience of explanation. Therefore, the technical meaning of the present invention should not be limited to the prior meaning, but should be properly interpreted in accordance with the technical idea of the present invention.

Before explaining the solar power generation system according to the present invention, the power mismatch of the solar cell module in the conventional solar power generation system will be analyzed.

The currents flowing in all the solar cell modules constituting the same string must be the same. Therefore, the maximum output point current of all solar cell modules must match. However, the deviation of the maximum output point current between the solar cell modules becomes larger due to the electrical variation due to the environmental variation such as the electric characteristic deviation of the solar cell module itself, the temperature, the solar radiation, etc., resulting in a power mismatch loss.

Further, in an array structure in which one or more strings are connected in parallel to one solar inverter, the voltage of each string must be the same. Therefore, the maximum output point voltage of all the solar cell modules must match.

However, the deviation of the maximum output point voltage between the solar cell modules becomes larger due to the electrical variation caused by the environmental variation such as the electric characteristic deviation of the solar cell module itself, the temperature, the solar radiation, etc., resulting in a large power mismatch loss.

Hereinafter, a photovoltaic power generation system according to an embodiment of the present invention will be described in detail with reference to Figs. 1 to 7. Fig.

<Solar power generation system>

1 is a block diagram showing the structure of a photovoltaic power generation system.

Referring to FIG. 1, a solar power generation system 100 includes N strings 500, a solar inverter 200, and a reverse current prevention diode 110.

In the solar power generation system 100, the string 500 and the backflow prevention diode 110 are connected in series, connected to the solar inverter 200, and connected in parallel between the strings 500.

The number of the solar cell modules 300 constituting the string 500 is preferably determined in consideration of the allowable range of the input voltage of the solar inverter 200.

<Structure of Solar Cell Module>

2 is a block diagram showing the structure of a solar cell module.

Referring to FIG. 2, the solar cell module 300 includes a plurality of solar cells 310 and a junction box 320, and serves to convert solar energy into electrical energy.

<String structure>

3 is a block diagram showing a structure of a string.

Referring to FIG. 3, the string 500 includes N solar cell modules 300 and a distributed maximum output point tracker 400 provided in each solar cell module 300.

The input terminal 470 of the distributed maximum output point tracker 400 is connected in parallel with the solar cell module 300 and the output terminal 480 is connected in series with each other.

It is preferable that the number of the solar cell modules 300 constituting the string 500 be the same.

<Distributed Maximum Output Point Tracker>

4 is a block diagram showing a distributed maximum output point tracker.

4, the distributed maximum output point tracker 400 includes a half bridge DC-DC converter 410, a controller 420, a power supply 430, a first analog circuit 440, A diode 450, a diode 460, an input terminal 470, and an output terminal 480.

The distributed maximum output point tracker 400 performs the function of tracking the maximum output point of the solar cell module 300 individually.

First, the half bridge DC-DC converter 410 includes a plurality of MOSFETs 411 (Metal Oxide Silicon Field Effect Transistor), an inductor 412 (Inductor), a plurality of capacitors 413 (Capacitor) Power generated in the solar cell module 300 using the fact that the output impedance Impedance is varied according to the duty ratio of the switching ON / OFF time of the MOSFET 411 including the side driver 414, To the solar inverter (200).

The MOSFET (411) includes a first MOSFET (411-1) and a second MOSFET (411-2).

The first MOSFET 411-1 is connected in series with the inductor 412.

One side of the second MOSFET 411-2 is connected between the inductor 412 and the first MOSFET 411-1 and the other side is connected to the ground GND.

The MOSFET 411 controls the current flow as a semiconductor switching element to store and discharge the magnetic field energy in the inductor 412 and to store and discharge the electric field energy in the capacitor 413.

A second MOSFET (411-2) is used instead of a diode to reduce power loss due to reflux.

Also, in order to minimize the power loss, the ON resistance of the MOSFET 411 is preferably small, preferably 10 mohm or less.

The inductor 412 has one side connected to the input and the other side connected to the first MOSFET 411-1 to store and discharge the magnetic field energy under the control of the current flow of the MOSFET 411.

The capacitor 413 has one side connected to the first MOSFET 411-1 and the other side connected to the ground and an output connected between the first MOSFET 411-1 and the capacitor 413.

The capacitor 413 serves to store and discharge the electric field energy according to the control of the current flow of the MOSFET 411.

The high and low side driver 414 is connected to the side of the high side driver for the first MOSFET 411-1 and connected to the side of the low side driver for the second MOSFET 411-2, (Duty) signal to the MOSFET 411 to control the current flow.

In addition, it generates two PWM signals by using one PWM signal input, and generates a high side driver signal by using a level shift.

Next, the controller 420 includes a PWM circuit 421 (Pulse Width Modulation), a plurality of ADC circuits 422 (ADC) and an algorithm processor 423, and a Half bridge DC- DC converter 410 to control the tracking of the maximum output point of the solar cell module 300.

The duty of the half bridge DC-DC converter 410 is controlled in a direction in which the electric power generated by the solar cell module 300 is always increased to the solar inverter 200.

For this purpose, a device such as an MCU (Micro Controller Unit) can be used.

The PWM circuit 421 is connected to the high and low side driver 414 and converts the duty determined by the algorithm processor 423 into an analog signal through a pulse width modulation circuit and sends the analog signal to the high and low side driver 414 .

The ADC circuit 422 includes a first ADC circuit 422-1 and a second ADC circuit 422-2 and serves to convert the analog data into digital data that can be processed by the controller 420 .

The algorithm processor 423 functions as a microprocessor that processes a maximum output point tracking algorithm and changes the duty of the Half bridge DC-DC converter 410 so that the maximum output point of the solar cell module 300 As well.

Next, the first analog circuit 440 serves to provide an analog circuit for measuring the voltage / current of the solar cell module 300, and the voltage measurement is performed using the first ADC circuit 422- 1), and the size of the distribution resistor should be at least 10 Kohm to reduce power consumption.

The current is preferably measured using a circuit such as a Hall sensor.

Next, the second analog circuit 450 serves to provide an analog circuit for measuring the output voltage / current of the half bridge DC-DC converter 410, and the voltage measurement is performed using a distribution resistor circuit, It is preferable to lower the voltage within the measurable range in the circuit 422-2, and the size of the distribution resistor is preferably 10 Kohm or more in order to reduce the power consumption.

Again, the current is preferably measured using a circuit such as a Hall sensor.

Next, the power supply 430 supplies power to the high and low side driver 414 and the controller 420 by using a voltage reduction circuit supplied with power from the solar cell module 300.

Next, the diode 460 serves as a bypass when an abnormality occurs in the power transmission due to a problem of the half bridge DC-DC converter 410 or the like.

Next, the input terminal 470 facilitates electrical connection between the solar cell module 300 and the dispersed maximum output point tracker 400. In order to increase the ease of connection, the input terminal 470 is formed as a connector .

Next, the output terminal 480 facilitates electrical connection between the distributed maximum output point tracker 400 and the distributed maximum output point tracker 400. In order to increase the ease of connection, a connector ). &Lt; / RTI &gt;

First, the controller 420 measures the current voltage / current using the ADC circuit 422 and calculates the current power (P = voltage x current) using the measured voltage / current. The changed duty is changed to the PWM signal through the PWM circuit 421 and transmitted to the High and Low side driver 414. [

Thus, the duty of the MOSFET 411 is changed, and the electric power generated by the solar cell module 300 is also changed to the solar light inverter 200.

And performs a function of tracking the maximum output point of the solar cell module 300 by changing the duty in a direction in which the power is always increased by comparing the current power and the changed power.

Hereinafter, a control method performed by the distributed maximum output point tracker 400 will be described in more detail.

<Distributed Maximum Output Point Tracking Control Flow>

FIG. 5 is a flow chart showing an example of a control method performed by the distributed maximum output point tracker 400. FIG.

5, the distributed maximum output point tracker 400 may be configured to perform the steps of initializing S710, confirming the operation of the solar inverter 200 S720, waiting S725, measuring the current duty P1 (Step S730), duty increase (D = D +? D) & power P2 measurement and duty reduction (D = D-? D) step S740, power comparison P1? P2 step S750, D +? D) & time delay step S760 and duty reduction (D = D-? D) & time delay step S770; and repeating step S730 to step S770, Of the maximum output point.

In step S710, which is the first step, variables such as initial duty, duty increase / decrease width d, delay time t and open circuit voltage (Voc) required for tracking the maximum output point are initialized.

The analog data of the first analog circuit 440 and the second analog circuit 450 is converted into the converted voltage / current through the ADC circuit 422 by the step of checking the operation of the solar inverter 200 in step S720. If the current value is higher than the open-circuit voltage of the solar cell module 300 or less than the reference current, step S710 is repeated to wait until the solar inverter 200 operates normally.

In the opposite case, the solar inverter 200 checks the open voltage of the string 500, determines that the normal operation has started, and proceeds to step S725.

Then, in step S725, the distributed maximum output point tracker 400 waits for a certain time while maintaining the initial duty while confirming the maximum output point voltage of the string 500 in the solar inverter 200, and then proceeds to step S730 do.

Next, in step S730, the voltage / current value is measured through the ADC circuit 422 as the step of measuring the power in the current duty to calculate the current power P1 (= voltage x current), and the process proceeds to step S740.

Next, in step S740, the algorithm processor 423 changes the current duty D to the duty (D = D + [Delta] d) by increasing the increase / decrease width [Delta] d And transmits it to the PWM circuit 421.

The modified PWM signal is transmitted to the high and low side drivers 414 and the switching duty of the MOSFET 411 is changed from D to D + Δd to change the output impedance.

Thus, the power transmitted from the solar cell module 300 to the solar inverter 200 is changed.

At this time, after calculating the power P2 according to the duty change by measuring the changed voltage / current value through the ADC 422 circuit, the duty D + d is subtracted by the increase / decrease width d (D = D + - DELTA d) and returns to the original duty D and proceeds to step S750.

Next, in step S750, it is determined whether or not the current output point of the solar cell module 300 is on the left or right side of the maximum output point, do.

If the current power P1 is less than the power P2 after the duty change, the current output point is located to the right of the maximum output point, and the duty can be increased to send the current output point to the maximum output point. The process proceeds to step S760.

In the opposite case, if the current power P1 is larger than the power P2 after the duty change, the current output point is located to the left of the maximum output point, and the duty is reduced to send the current output point to the maximum output point. The process proceeds to step S770.

Next, in step S760, the current output is increased and moved to the maximum output point direction by increasing the current duty by the duty increment / decrement? D, and the algorithm processor 423 multiplies the duty D by the duty increment / (D = D +? D), and transfers the PWM signal to the High and Low side driver 414 through the PWM circuit 421. [

As a result, the switching duty of the MOSFET 411 is increased, and the electric power generated by the solar cell module 300 is transmitted to the solar inverter 200 and transmitted.

In order to reduce the measurement distortion of the power due to the duty change of the other solar cell modules 300 constituting the same string 500, the process waits for a predetermined time and then proceeds to step S730.

Next, in step S770, if the current duty is decreased by the duty increasing / decreasing width d, the current output moves up to the maximum output point direction, and the algorithm processor 423 changes the duty D to the duty increase / (D = D -? D), and transmits the PWM signal to the High and Low side driver 414 through the PWM circuit 421. [

As a result, the switching duty of the MOSFET 411 is reduced, and the electric power produced by the solar cell module 300 is transmitted to the solar inverter 200 and transmitted.

In order to reduce the measurement distortion of the power due to the duty change of another solar cell module 300 constituting the same string 500, the process waits for a predetermined time and then proceeds to the next step S730.

The distributed maximum output point tracker 400 performs the maximum output point tracking of the solar cell module 300 by repeatedly performing step S730 to step S770.

Thus, the solar power generation system 100 can harvest the maximum output.

6 is a graph showing output characteristics of the solar cell module.

6, the maximum output point Pmax of the solar cell module 300 is determined by the maximum output current Imp and the maximum output voltage Vmp. On the basis of the maximum output point Pmax, The current is transmitted to the solar inverter 200 higher than the output current Imp and deviates from the maximum output point. On the contrary, the current is transmitted to the solar inverter 200 lower than the maximum output current Imp, Out of the point.

Fig. 7 is a block diagram showing a solar inverter; Fig.

7, the solar inverter 200 includes a DC-DC converter 210, a DC-AC inverter 220, an inverter controller 230, a third analog circuit 240, a fourth analog circuit 250, An output device 260 and a power supply device 270. The power supply device 270 converts the DC voltage supplied from the solar cell module 300 into an AC voltage and provides the AC voltage to the system.

The distributed maximum output point tracker 400 can keep track of the maximum output point of the solar cell module 300 by keeping the input voltage of the solar inverter 200 higher than the maximum output point voltage of the string 500 .

It is desirable to keep the input voltage 8% to 20% higher than the maximum output point voltage of the string 500.

First, the DC-DC converter 210 is connected to the string 500 and uses an impedance varying characteristic according to the duty to maintain the input voltage at 8% to 20% higher than the maximum output point voltage of the string 500 It plays a role. In addition, the other side is connected to the DC-AC inverter 220.

Next, the DC-AC inverter 220 converts the DC voltage received from the DC-DC converter 210 into an AC voltage and transmits it to the system.

Next, the controller 230 includes a third ADC circuit 231-1, a fourth ADC circuit 231-2, and an instruction processor 232, and the third analog circuit 240 and the fourth analog circuit 250 are converted into digital data using the third ADC circuit 231-1 and the fourth ADC circuit 231-2.

Using the converted data, the command processor 232 maintains the input voltage of the DC-DC converter 210 from 8% to 20% higher than the maximum output point voltage of the string 500.

In addition, it plays a role of displaying necessary information to the user in the output device 260.

Next, the third analog circuit 240 serves to provide an analog circuit for measuring the input voltage / current of the solar inverter 200.

The solar inverter 200 and the plurality of strings 300 are connected in parallel so that the voltages between the strings 300 are the same.

It is preferable that the voltage measurement is lowered to a voltage range measurable by the third ADC circuit 231-1 using a distribution resistance circuit, and the size of the distribution resistor is preferably 10 Kohm or more in order to minimize power loss.

Further, the current measurement can use a circuit such as a Hall sensor in which the currents of the plurality of strings 500 can be summed to measure a high current.

Next, the fourth analog circuit 250 serves to provide an analog circuit for measuring the output voltage / current of the DC-DC converter 210.

It is preferable that the voltage measurement is performed within a voltage range measurable by the fourth ADC circuit 231-2 using a distribution resistance circuit, and the size of the distribution resistor is preferably 10 Kohm or more in order to minimize power loss.

In addition, the current measurement can use a circuit such as a Hall sensor capable of measuring a high current.

Next, the output device 260 serves to provide necessary information to the user.

(Voltage / current) generated at the present solar cell module 300, power (voltage / current) transmitted to the system, and operation state of the solar inverter 200.

Next, the power supply device 270 serves to supply the high voltage of the string 500 with power necessary for the controller 230 and the like by using a voltage reducing circuit.

A distributed maximum output point tracker having a boost DC-DC converter connected in parallel with the output of the solar cell module, a solar inverter having a DC-DC converter and a DC-AC inverter connected in series with a distributed maximum output point tracker When the input voltage of the DC-DC converter of the solar inverter is kept constant higher than the maximum power point voltage of the string in the solar cell power generation system, all the solar cell modules in the string are lower than the maximum output point current, The point will be out.

If the duty of the boost DC-DC converter of the distributed maximum output point tracker is increased, the output voltage is increased and the input voltage (= output voltage of the solar cell module) is shifted toward the maximum output point voltage. By increasing the duty until the duty of the boost DC-DC converter reaches the maximum output point voltage, all the solar cell modules can operate at the maximum power point and learn the maximum output.

 Second, a distributed maximum output point tracker with a buck DC-DC converter connected in parallel with the output of the solar cell module, a DC-DC converter connected in series with a distributed maximum output point tracker, and a DC- When the input voltage of the DC-DC converter of the solar inverter is kept constant lower than the maximum power point voltage of the string in the solar cell power generation system equipped with the optical inverter, all the solar cell modules in the string are lower than the maximum output point voltage And is out of the maximum output point.

When the duty of the buck DC-DC converter of the distributed maximum output point tracker is reduced, the output voltage is reduced so that the input voltage (= the output voltage of the solar cell module) is shifted toward the maximum output point.

By decreasing the duty cycle of the DC-DC converter until it reaches the maximum output point, all the solar cell modules can operate at the maximum power point and learn the maximum output.

Claims (1)

Distributed Maximum Output Point Tracker;
A plurality of solar cell modules each having a distributed maximum output point tracker;
A string in which the plurality of solar cell modules are connected in series;
An array in which the strings are connected in parallel; And
And a solar inverter connected to the array,
Wherein the distributed maximum output point tracker maintains the input voltage of the solar inverter higher than the maximum output point voltage of the array so that it can perform maximum output point tracking of the solar cell module. .

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