KR101382946B1 - Photovoltaic power generation system and control method thereof - Google Patents

Abstract

Photovoltaic power generation system according to an embodiment of the present invention is a solar cell; A converter connected to the output terminal of the solar cell; An inverter connected to an output terminal of the converter; And a controller configured to control the inverter by detecting an output signal of the inverter and adjusting a current within a predetermined range.

Description

Photovoltaic power generation system and control method

The present invention relates to a photovoltaic power generation system and a control method thereof, and more particularly, to a photovoltaic device and a method of controlling the output current of an inverter during photovoltaic power generation, which can be easily achieved at high speed and have improved reliability. It is about.

Recently, as the problem of depletion of natural resources and the environment and stability of nuclear power generation and nuclear power generation have been raised, studies on solar energy and wind power, which are representative green green energy, are actively underway. In particular, photovoltaic power generation is widely used in the fields of automobiles, toys, residential power generation and street lamps, as well as unmanned lighthouses, clock towers, and communication devices, which are separated from system lines and distant places.

Such a solar cell transforms the light energy of the sun into electric energy, and a typical solar cell has electric characteristics which are considerably different from those of an electric energy source. Since the conventional electric energy has the characteristics of a linear voltage source, it maintains a constant voltage and operates stably at all times even if a linear or nonlinear load is applied to the load end. Also, since it has only one operating point, it always operates as a stable device under any input / output conditions. That is, when using an electric energy source having a linear voltage source, desired operating conditions can be obtained regardless of the load conditions.

However, the solar cells are classified into nonlinear sources, and the power generated from the solar cells changes in size depending on load conditions and incident sunlight. As shown in FIG. 1, the power generation voltage Vs of the solar cell 10 increases due to climate change, thereby increasing the voltage Vd input to the inverter 30. However, the output current of the inverter 30 has a problem that the system is unstable because the system voltage is greatly affected by the change.

An object of the present invention is to prevent the output current of the inverter is affected by the fluctuation of the grid voltage, the system becomes unstable, and further the system stops.

In addition, when operating at the maximum power point and out of it, it aims to reduce the time required to follow the maximum power point.

Photovoltaic device according to an embodiment of the present invention is a solar cell; A converter connected to the output terminal of the solar cell; An inverter connected to an output terminal of the converter; And an output current controller for controlling the output current of the inverter.

According to the embodiment of the present invention, it is possible to control the fluctuation of the grid voltage of the solar cell, thereby improving the reliability of the device.

In addition, a simple forward feed forward loop can be added to reduce the time required to follow the maximum power point.

1 is a block diagram of a solar cell apparatus according to the prior art.
2 is a configuration diagram of a photovoltaic device according to an embodiment of the present invention.
3 is a diagram illustrating a configuration of an output current controller according to an embodiment of the present invention.
4 is a circuit diagram of a photovoltaic power generation system including an output current controller according to an embodiment of the invention.
5 is a graph of current-voltage characteristics and power-voltage characteristics of a solar cell.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The details of other embodiments are included in the detailed description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and how to accomplish them, will become apparent by reference to the embodiments described in detail below with reference to the accompanying drawings. Like reference numerals refer to like elements throughout the specification.

2 is a configuration diagram of a photovoltaic device according to an embodiment of the present invention. As shown in FIG. 2, the photovoltaic device is connected to a solar cell 100 for converting light energy into electrical energy by using a photovoltaic effect and an output terminal of the solar cell 100. A converter 200 for converting DC power generated in the solar cell 100 into an arbitrary DC voltage, an inverter 300 connected to an output terminal of the converter 200, and an output terminal of the inverter 300, A commercial power source 400 capable of detecting a voltage Vgrid, and a controller 500 for detecting a current of the inverter 300 and adjusting a current within a predetermined range.

The solar cell 100 converts light energy supplied from the sun into electrical energy using a photovoltaic effect. Such solar cells may be implemented with amorphous silicon, crystalline silicon, compound semiconductors, or the like. In addition, the solar cell 100 may be configured in the form of an array in which a plurality of solar cells are combined in series and in parallel in order to obtain the power Po required by a load.

The load may be, for example, a power means requiring high power, such as an electric heater or an electric motor or a commercial AC power system. It may also be a load operated at low power, such as a Ubiquitous Sensor Network (USN) system.

The converter 200 may include an inductor, a semiconductor switch, and a diode, and serves to boost the voltage output from the solar cell 100 to a specific voltage.

The first driver 210 may be connected to a switch of the converter 200 and may control an output voltage of the converter 200 by adjusting on and off duty.

The inverter 300 may be configured as a single-phase full bridge or three-phase inverter, and the second driver 310 drives the semiconductor switch of the inverter 300.

The grid voltage Vgrid may be detected in the grid of the commercial power supply 400.

The controller 500 may include a voltage controller 510, an output current controller 520, an MPPT (maximum power point tracking unit 530), and an output power controller 540.

The voltage controller 510 included in the controller 500 detects an output voltage of the converter 200 and transmits a control signal of the voltage to the first driver 210, and the first driver 210 transmits the control signal. By transmitting to the switch included in the converter 200 to control the output voltage of the converter 200.

The output current controller 520 included in the controller 500 detects the output current of the inverter 300 and transmits a control signal of the current to the second driver 310, and the second driver 310 The control signal is transmitted to the switch included in the inverter 300 to control the output voltage of the inverter 300. The specific signal flow of the output current controller 520 will be described later.

The maximum power point tracking (MPPT) 530 included in the controller 500 is an output power of the solar cell 100 based on the output current and the output voltage of the solar cell 100 detected by the current detector and the voltage detector. Calculate and extract the maximum power point of the solar cell 100 by following the calculated power. For example, the MPPT 530 compares the difference between the previous operating point power and the current operating point power while varying the operating voltage of the solar cell 100 using a Hill-Climbing method that follows the maximum power point. The maximum power point of the solar cell 100 is extracted.

The output power controller 540 included in the controller 500 is connected to the MPPT 530. The output power controller 540 compares the output power of the solar cell 100 and the inverter 300 and outputs a specific DC current value Ioref. The target value of the output current control system is generated by integrating the Ioref and the system voltage value.

3 is a diagram illustrating a configuration of an output current controller according to an embodiment of the present invention. 4 is a circuit diagram of a photovoltaic power generation system including an output current controller according to an embodiment of the invention.

As shown in FIG. 3, the output current controller 520 includes a voltage proportioner 521, a multiplier 522, a subtractor 523, a compensator 524, an adder 525, a gate signal generator 526, and a current. A proportioner 527.

As shown in FIG. 3, the output voltage Vcs of the inverter 300 is input to the voltage proportionalizer 521. The output voltage Vcs input to the voltage proportionalizer 521 is multiplied by 1 / Kvsense, which is a proportional constant of the voltage proportionalizer 521. The signal is input to a multiplier 522. The multiplier multiplies the Vcs / Kvsense and the DC current value Ioref.

The signal output from the voltage proportionalizer 521 is input to the multiplier 522 to generate a target value of the output current of the inverter 300. In Fig. 3, Ioref is a direct current signal, and by integrating this and a commercial voltage which is an alternating current signal, the target value of the output current of the inverter 300 is generated. The other signal output from the voltage proportionalizer 521 is input to the adder 525 as a feed forward signal of the output voltage.

The multiplier 522 receives a DC current value Ioref output from the output power controller 540 and a reference current Iref output from the voltage proportionalizer 521 and multiplies the output value to the subtractor 523. To pass.

The subtractor 523 receives an output value of the multiplier 522 and a signal of the current proportioner 527, calculates an error, and transmits the calculated error to the compensator 524.

The compensator 524 receives the current error signal from the subtractor 532 to compensate for the current error by a predetermined algorithm, and outputs a corresponding signal to the adder 525.

The adder 525 receives an output signal of the compensator 524 and an output signal of the voltage proportionalizer 521, calculates an error, and transmits the calculated error to the gate signal generator 526.

The gate signal generator 526 generates a signal for driving a switch element (eg, MPDFET, IGBT, etc.) included in the inverter 300 based on the output of the adder 525. In general, a PWM signal is generated by comparing the output of the adder 525 with the carrier (triangular waveform, saw blade waveform). Since the gate signal becomes an input signal of the second driver 310 to drive the switch element, a signal amplified to a predetermined voltage value is output from the second driver 310 and input to the inverter 300 to generate a current. Controlled.

In the above series of processes, it can be seen that the overall transfer function of the system shown in FIGS. 3 and 4 has uniformity by simple calculation according to the mathematical expression of the components represented by the blocks. That is, the current feed forward control system of FIGS. 3 and 4 can improve the tracking response of the current control.

4 is a circuit diagram of a photovoltaic power generation system including an output current controller according to an embodiment of the invention.

As shown in FIG. 4, the output terminal of the inverter 300 may include a filter 350. In addition, the voltage from the filter 350 may be transferred to the commercial power supply 400.

In FIG. 4, iout and iL are not strictly the same, but may be considered to be the same if the switching frequency is sufficiently lower than the cut-off frequency of the filter 350 (eg, 10 to 20 times). . The relation between voltage and current is as follows.

Equation 1

인버터(300)의 출력 역률이 1로 동작하는 것으로 가정하고 계통전압 Vcs를,

Assuming that the output power factor of the inverter 300 operates at 1, the grid voltage Vcs,

Equation 2

로 설정하면,

Is set to "

Equation 3

가 성립된다. 이에 따라 하기의 수학식이 성립한다.

. Accordingly, the following equation holds.

Equation 4

If the commercial voltage (system voltage) changes without the feed forward of Vcs, the predetermined output current value cannot be obtained unless V _B changes significantly. The feed forward improves the tracking performance of the control system without significantly changing V _B.

As can be seen in Equation 4, the voltage can be effectively controlled by feedforwarding Vcs.

5 is a graph of current-voltage characteristics and power-voltage characteristics of a solar cell. Referring to FIG. 5, the current-voltage characteristic from the solar cell maintains a constant current even when the voltage is increased, and rapidly decreases the current when the voltage is higher than a specific voltage. Comparing this with the power-voltage characteristic graph from the solar panel, the power increases as the voltage increases, and the characteristic that the power decreases sharply above the maximum power point Pmax occurs. The MPPT 550 generates a target power value of maximum power, and adjusts the power value to output the maximum power in consideration of the current-voltage characteristic of the solar cell.

The features, structures, effects and the like described in the embodiments are included in at least one embodiment of the present invention and are not necessarily limited to only one embodiment. Furthermore, the features, structures, effects and the like illustrated in the embodiments can be combined and modified by other persons skilled in the art to which the embodiments belong. Therefore, it should be understood that the present invention is not limited to these combinations and modifications.

Claims (6)

Solar cell;
A converter connected to the output terminal of the solar cell;
An inverter connected to an output terminal of the converter; And
A control unit for detecting the output signal of the inverter and controlling the inverter by adjusting a current within a predetermined range,
Wherein,
A voltage controller connected to the converter to control the converter;
An output current controller connected to the inverter to control the inverter;
An MPPT connected to the solar cell to follow the maximum power point of the solar cell; And
An output power control unit connected to the MPPT and the output current control unit;
The output current control unit,
A voltage proportioner configured to calculate and output a proportional constant to the output voltage of the inverter;
A current proportioner for calculating and outputting a proportional constant to the output current of the inverter;
A multiplier for multiplying the output value of the voltage proportionr by the output value of the output power controller;
A subtractor for subtracting the output value of the multiplier and the output value of the current proportioner;
A compensator receiving the output value of the subtractor to compensate for the current error by a predetermined algorithm and outputting a signal corresponding thereto;
An adder for adding an output value of the compensator and an output value of the voltage proportional unit;
And a gate signal generator configured to receive an output value of the adder and output a control signal of the inverter. delete The method of claim 1,
The inverter is a solar power generation system consisting of a single-phase full bridge or three-phase inverter. delete The method of claim 1,
And a second driver connected to the gate signal generator and driving a semiconductor device constituting the inverter by using a switching signal output from the gate signal generator. The method of claim 1,
And a first driver connected to the converter and the voltage controller and driving the semiconductor device constituting the converter by using a switching signal output from the voltage controller.

Images