KR101749270B1 - Photovoltaic system for grid connected with power-factor improvement - Google Patents

Abstract

In accordance with the present invention, the maximum power supply condition of the solar power generation system is tracked in conjunction with the power system, the power is supplied to the output power of the solar power generation system according to the tracked maximum power point, To a grid-connected photovoltaic power generation system having a power factor improvement function capable of maintaining optimal power quality by preventing deterioration of power quality due to voltage drop.
In order to solve the above problems, the grid-connected photovoltaic generation system having the power factor improving function according to the present invention collects the direct current produced from the solar cell array 1, (2) is connected to the solar cell array (1) by AC power so that the DC power input from the solar cell array (1) can be used as commercial power A solar inverter 100 for converting and outputting the solar light; An MPPT controller 200 receiving the output voltage of the solar cell array and the inverter and outputting the maximum solar output power and the reference voltage through maximum power point tracking; A current converter 300 for converting the load current from the abc coordinate system to the alpha co-ordinate system; A voltage converter 400 for converting the power system voltage from the abc coordinate system to the alpha co-ordinate system; A reactive power control unit (500) for controlling reactive power output from the inverter with the current and voltage converted by the current converting unit and the voltage converting unit; A PQ control unit 600 for calculating a reference current based on the solar active power output from the MPPT control unit 200 and the reactive power output from the reactive power control unit; A power converter 700 for converting the reference current output from the PQ controller 600 into an abc coordinate system; And a PWM control unit 800 for compensating the inverter current output from the inverter 100 using the reference current output from the PQ control unit 600.

Description

[0001] PHOTOVOLTAIC SYSTEM FOR GRID CONNECTED WITH POWER-FACTOR IMPROVEMENT [0002]

The present invention relates to a grid-connected photovoltaic power generation system having a power factor improving function, and more particularly, to a grid-connected photovoltaic power generation system having a power factor improving function, A grid-connected photovoltaic power generation system having a power factor improving function capable of supplying power with the output power of the power generation system and preventing the degradation of the power quality due to the voltage drop due to the supply of the reactive power to the power system, ≪ / RTI >

Generally, the photovoltaic power generation (Photovolatics) has a disadvantage that the power generation efficiency is lower than the high power generation cost. However, as environmental demands such as reduction of fossil energy and pollution have increased, much research is currently underway to improve the efficiency of solar power generation. The proportion of electrical energy that can convert the energy received from the sun through solar cells is only about 15-20% of the total solar energy.

The photovoltaic power generation system is a power generation system that converts light directly into electric energy using a solar cell without the aid of a generator, and is a power generation system configured to meet actual demand loads using solar cells.

Specifically, since the output of a solar cell that generates solar power is very small, a plurality of solar cells are connected in series to form a solar cell module (PV Module, PhotoVoltanic Module) The solar array (PV array) is constructed by connecting the battery modules again in series or in parallel. Here, since the maximum power point (MPP) varies depending on the solar radiation amount, operation voltage, temperature, etc., the output characteristic of the solar cell changes in order to maximize the efficiency of the solar power generation. It is necessary to control Maximum Power Point Tracking (MPPT).

MPPT is a control method for producing the maximum power according to the solar radiation change in the inverter. When the solar radiation amount is changed, the DC voltage is changed in size, and the efficiency of the inverter due to the voltage increase or decrease is decreased. Accordingly, various methods of MPPT algorithm for tracking the maximum power point of the solar light have been developed.

On the other hand, Japanese Patent Application Laid-Open No. 10-1256433 discloses a solar power generation system of maximum power point tracking using PV current.

The technique includes a photovoltaic panel for converting light energy into electrical energy; A symmetrical step-up converter for stepping up the output voltage of the photovoltaic panel; An A / D converter for converting an output voltage and an output current of the photovoltaic panel into a digital optical output voltage and a digital optical output current; Wherein the digital optical output power is calculated based on the digital optical output voltage and the digital optical output current from the A / D converter, and a comparison between the digital optical output power and a previous digital optical output power, A maximum power point tracking unit for performing a comparison of previous digital light output currents and generating any one of a constant decrease and an increase compensation amount according to a result of the comparison; A reference current regulator for regulating a reference current using the compensation amount from the maximum power point follower; An impact coefficient adjuster for adjusting an impact coefficient based on the adjusted reference current from the reference current adjuster and the digital optical output current from the A / D converter; A peak current controller for controlling operation of the maximum power point follower based on the digital optical output current from the A / D converter and the adjusted reference current from the reference current adjuster; And a PWM controller that generates a PWM control signal having a pulse width corresponding to the adjusted impact coefficient from the impact coefficient adjusting unit and controls a switching period of the symmetric step-up converter using the PWM control signal .

Although the above technology has the advantage of being able to follow the MPP quickly in the MPPT type solar photovoltaic system and improve the response speed, the photovoltaic power generation system is installed and operated in a region where the distance from the power grid is considerably large There is a disadvantage in that it can not be expected to cope with the voltage drop due to the line, the compensation of the voltage and the frequency against the sudden change of the load power, and the decrease in the power quality due to the accident or failure of the adjacent line.

KR 10-1256433 B1 (Registered on Apr. 12, 2013)

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems of the prior art and it is an object of the present invention to provide a solar power generation system capable of supplying a maximum power to a solar power generation system It is possible to distribute the power to the power system by distributing the power into the active power and the reactive power and to improve the power quality by supplying reactive power to the AC grid through the solar inverter in the case of the nighttime in which there is no power generated from the solar power generation system And to provide a grid-connected solar power generation system having a power factor improving function.

In order to solve the above problems, the grid-connected photovoltaic generation system having the power factor improving function according to the present invention collects the direct current produced from the solar cell array 1, (2) for converting the DC power received from the solar cell array (1) into AC power for use as commercial power and outputting the converted AC power to the solar cell An optical inverter (100); An MPPT controller 200 receiving the output voltage of the solar cell array and the inverter and outputting the maximum solar output power and the reference voltage through maximum power point tracking; A current converter 300 for converting the load current from the abc coordinate system to the alpha co-ordinate system; A voltage converter 400 for converting the power system voltage from the abc coordinate system to the alpha co-ordinate system; A reactive power control unit (500) for controlling reactive power output from the inverter with the current and voltage converted by the current converting unit and the voltage converting unit; A PQ control unit 600 for calculating a reference current based on the solar active power output from the MPPT control unit 200 and the reactive power output from the reactive power control unit; A power converter 700 for converting the reference current output from the PQ controller 600 into an abc coordinate system; And a PWM control unit 800 for compensating the inverter current output from the inverter 100 using the reference current output from the PQ control unit 600.

The PQ control unit 600 calculates a reference current based on the reactive power output from the reactive power control unit when there is no solar active power output from the MPPT control unit 200. [

In addition, the MPPT controller 200 performs maximum output point tracking by incremental conductance (IncCond, Incremental Conductance) method.

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The PWM control unit 800 is a hysteresis current control method for controlling the inverter current outputted from the inverter 100 within the range of the set bandwidth H with respect to the reference current output from the PQ control unit 600 And the inverter current is controlled.

According to the present invention, it is possible to satisfy the maximum power supply condition of the photovoltaic generation system in conjunction with the power system. In the night when the power is not outputted in the photovoltaic power generation system, reactive power is supplied to the power system, So that the optimum power quality can be maintained.

In addition, since the voltage and frequency can be compensated for in response to the abrupt load power of the local load with respect to the instantaneous power, there is an advantage that the burden on the consumer due to the improvement of the power factor can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a grid-connected photovoltaic power generation system having a power factor improving function according to the present invention; FIG.
BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a grid-connected photovoltaic generation system having a power factor improving function.
3 is a three-phase wiring diagram of a grid-connected photovoltaic generation system having a power factor improving function according to the present invention.
4 is a flowchart illustrating a process of tracking a maximum output point in a grid-connected solar power generation system having a power factor improving function according to the present invention.
5 is a block diagram for calculating active power in a grid-connected solar power generation system having a power factor improving function according to the present invention.
6 is a block diagram according to a hysteresis current control method in a grid-connected solar power generation system having a power factor improving function according to the present invention.
FIG. 7 is a graph showing current phases applied to a grid-connected photovoltaic power generation system having a power factor improving function according to the present invention.
FIG. 8 is a graph showing active power using a grid-connected solar power generation system having a power factor improving function according to the present invention.
FIG. 9 is a graph showing the effective power in the grid-connected photovoltaic generation system having the power factor improving function according to the present invention in the absence of photovoltaic power generation by solar radiation.
10 is a graph showing the relation between the solar power generation power Ppv, the grid active power Pgrid and the load effective power PI for solar radiation (a) in the grid-connected solar power generation system having the power factor improving function according to the present invention The graph shown.
11 is a graph showing the reactive power when the solar power generation system according to the present invention is applied and the reactive power when excluded, in the grid-connected solar power generation system having the power factor improving function according to the present invention.

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

In accordance with the present invention, the maximum power supply condition of the solar power generation system is tracked in conjunction with the power system, the power is supplied to the output power of the solar power generation system according to the tracked maximum power point, To a grid-connected photovoltaic power generation system having a power factor improvement function capable of maintaining optimal power quality by preventing deterioration of power quality due to voltage drop.

FIG. 1 is a schematic diagram of a grid-connected photovoltaic power generation system having a power factor improving function according to the present invention.

1, a grid-connected photovoltaic power generation system having a power factor improving function according to the present invention includes a solar cell array 1, a solar light connection panel 2, an AC grid 3, and a load .

The solar cell array 1 is for generating electricity by collecting sunlight incident from the outside, and silicon and a composite material are usually used mainly. Specifically, the solar cell array 1 uses a p-type semiconductor and an n-type semiconductor bonded together, and utilizes a photoelectric effect to generate electricity by receiving sunlight.

Most of the solar cell arrays 1 are formed of large-area P-N junction diodes, and the electromotive force generated at the opposite ends of the P-N junction diode is connected to an external circuit. The minimum unit of the solar cell array 1 is called a cell, and actually, a plurality of cells are used for the solar cell. In other words, since the required voltage used in the home is several tens to several hundreds of volts or more, the voltage from one cell is very small, about 0.5 V, so that a plurality of unit solar cells can be connected in series or parallel . In addition, when the solar cell array 1 is used outdoors, it is exposed to various harsh environments. Therefore, a plurality of cells are used as a package in order to protect a plurality of cells connected with a necessary unit capacity in a harsh environment.

The photovoltaic connection panel 2 is a device for collecting the direct current produced from the solar cell array 1 and outputting power by the inverter. The photovoltaic panel 2 receives the direct current power generated from the solar cell array 1, A main circuit device consisting of switchgear for output and switchgear (or molded case circuit breaker (MCCB)), busbar (or terminal block), magnetic switch, diode, power fuse and lightning protection device (SPD, ZNR) Not shown). In addition, the photovoltaic connection panel 2 may be provided with an output terminal switch for insulation resistance measurement or periodic short-circuit current confirmation.

The solar cell connection unit 2 tracks the maximum power supply condition generated and output from the photovoltaic solar cell array 1, and supplies the maximum output power of the photovoltaic power generation system on the basis thereof, And is configured to maintain the power quality by supplying reactive power.

The power output from the solar cell connecting unit 2 is supplied to the load in conjunction with the AC grid 3. [

FIG. 2 is a block diagram of a grid-connected photovoltaic power generation system having a power factor improving function according to the present invention, and FIG. 3 is a schematic diagram of a grid-connected photovoltaic power generation system having a power factor improving function according to the present invention. Fig.

2 and 3, the solar power generation system according to the present invention includes a solar light connecting panel 2, an AC grid 3 and a load, and the solar light connecting panel 2 is provided with a solar inverter The power conversion unit 700, the PWM control unit 800, the power control unit 800, the MPPT control unit 200, the current conversion unit 300, the voltage conversion unit 400, the reactive power control unit 500, the PQ control unit 600, .

The inverter 100 integrates the DC power received from the solar cell array 1 into one DC power and converts it into AC power for use as commercial power. The AC power output from the inverter 100 is supplied to the AC grid 3 and supplied to the load of the customer.

The MPPT control unit 200 is configured to supply active power and reactive power to the AC grid 3 in cooperation with a PQ control unit 600 to be described later through a maximum power point tracking, It is configured not to operate at nighttime.

Here, P & O (Perturb and Observe) and Incremental Conductance (IncCond, Incremental Conductance) are mainly used for the maximum output point tracking performed by the MPPT controller 200.

The P & O method is a method of periodically increasing or decreasing the output voltage of the solar cell array and comparing the previous output power with the current output power to find the maximum power operating point. The incremental conductance method is a method in which the conductance of the solar cell output and the incremental conductance And finds the maximum power operating point.

Accordingly, the maximum power point tracking performed by the MPPT controller 200 may be configured by adopting one selected from P & O or incremental conductance. However, in the P & O method, the tracking speed of the MPP increases However, the variation of the output voltage is widened. On the contrary, in the section where the voltage fluctuation is small, the tracking speed of the MPP is slowed, but the variation of the output voltage is narrowed.

The maximum output point tracking performed by the MPPT controller 200 is configured by applying an incremental conductance method (IncCond).

Before describing the incremental conductance, the current and voltage characteristics output from the solar cell array 1 will be described first.

The power output from the solar array is affected by solar radiation and ambient temperature. Therefore, the photocurrent according to the change value of the temperature is represented by the following equation (1).

(1)

Where I _ph is the photocurrent, I _{ph (ref)} is the nominal photocurrent, G is the solar radiation, G _ref is the nominal solar radiation, and I _{sc (ref)} is the nominal short-circuit current.

The output current of the solar cell output from the solar cell array using Equation (1) is expressed by the following equation (2).

(2)

Here, I _pv is (hereinafter referred to as "PV current"), the output current of the solar cell, p is the parallel connection number of the solar cell, s is a series connection number of the solar cell, I _o is the diode saturation current, V _pv is a solar cell , I _ph is the photocurrent, Rs is the series resistance of the solar cell, and V _T is the column voltage.

The solar cell output voltage (PV voltage) output from the solar cell array is expressed by the following equation (3).

(3)

Where V _ph is the PV voltage, p is the number of parallel connections of the solar cells, s is the number of series connections of the solar cells, I _o is the diode saturation current, I _ph is the photocurrent, V _T is the column voltage, Series resistance.

The output power of the solar cell according to Equation (2) and Equation (3) is defined by the following equation (4).

(4)

Where P _pv is the PV power, V _pv is the PV voltage, and I _pv is the PV current.

The maximum output point tracking process using the incremental conductance method of the present invention will be described with reference to Equations 1 to 3 above.

4 is a flowchart illustrating a process of tracking a maximum output point in a grid-connected solar power generation system having a power factor improving function according to the present invention.

The maximum output point tracking first detects (S10) the PV voltage (V (k)) and the PV current I (k) of the current period.

Next, the PV voltage increase amount dV, the PV current increase amount dI, and the PV power increase amount dP are calculated using the detected PV voltage V (k) and the PV current I (k) (S20).

If the PV voltage increase amount dV changes as a result of the determination, the incremental conductance and the detection conductance of the current cycle are compared with each other (S40) )do.

At this time, the detection conductance (-I / V) of the current period is compared with the incremental conductance (dI / dV). If the result of comparison between the incremental conductance and the detection conductance value is the same, the output power of the current period is determined as the maximum output point . The PV voltage Ppv and the reference voltage Vref are output (S50), and the PV voltage V (k-1) of the previous period and the PV The current I (k-1) is updated to the PV voltage V (k) and PV current I (k) of the current cycle (S60).

The incremental conductance (dI / dV) is compared with the detection conductance (-I / V) by comparing the detection conductance (-I / V) of the current period with the incremental conductance (Step S45).

If the incremental conductance dI / dV is larger than the detection conductance -I / V as a result of the determination S45, the reference voltage Vref increases the PV voltage increase amount dV to the reference voltage Vref at step S46. And if the incremental conductance dI / dV is smaller than the detection conductance -I / V, the reference voltage Vref decreases the PV voltage increase amount dV to the reference voltage Vref (S47).

(DI = I (k) -I (k-1)) if there is no change in the PV voltage increase amount dV as a result of the judgment of the PV voltage increase amount dV (S70).

If the PV current increment dI is 0 as a result of the determination S70, the reference voltage Vref is not adjusted and the current reference voltage Vref is maintained. If the PV power Ppv and the reference voltage Vref are maintained, (S50).

If it is determined in step S70 that there is PV increment (dI = I (k) -I (k-1)), it is determined in step S75 whether the incremented value is larger or smaller than 0 in step S75.

If it is determined that the PV current increment is positive as a result of the determination (75), the reference voltage (Vref) increases the PV voltage increment (dV) to the reference voltage (Vref) (S76). If it is determined that the PV current increment is negative as a result of the determination (75), the reference voltage Vref decreases the PV voltage increment dV to the reference voltage Vref (S77).

That is, if the PV current increment is positive, the reference voltage Vref is increased, and if the PV current increment is negative, the reference voltage Vref is reduced.

The maximum output point tracking using the incremental conductance method tracks the maximum output point (MPP) even when the external conditions such as the solar radiation amount and the temperature change suddenly change.

Next, a configuration for supplying reactive power will be described.

At this time, the reactive power parameters include the output power Ppv output from the MPPT controller 200, the voltage Vdc of the capacitor, the voltages usa, usb, and usc of the power system, the output currents ic, icb, icc) and the load current (i _La , i _Lb , i _Lc ) supplied to the load.

The current converting unit 300 and the voltage converting unit 400 are for converting the voltage and the load current of the AC grid from the abc coordinate system to the a [beta] coordinate system based on the instantaneous power and inputting them as variable values to the reactive power control unit 500 .

The current transformer 300 can convert the abc coordinate system of the load current (i _La , i _Lb , i _Lc ) input to the current transformer 300 into the αβ coordinate system, and the transformation of the coordinate system can be expressed by the following equation (5).

Equation (5)

If the power system voltage (ua, usb, usc) input to the voltage conversion unit 400 is converted from the abc coordinate system to the a [beta] coordinate system, it can be expressed by the following equation (6).

(6)

I _{L, αβ} is the load current _{(i La, i Lb, i} Lc) current, and i _{L, abc} of the αβ coordinate system is a load current _{(i La, i Lb, i} Lc) of the above in Equation 5, and 6 respectively, ≪ / RTI > Further, M is a matrix of Clarke transform, and M and M ^-1 are expressed by the following equation (7).

Equation (7)

The voltages of the load current and the power system are converted from the abc coordinate system to the a [beta] coordinate system and input to the reactive power control unit 500 according to Equations (5) to (7).

The reactive power control unit 500 controls the reactive power output from the inverter based on the load current and the voltage of the power system. The reactive power control unit 500 calculates the reactive power based on the load current and the voltage of the power system, Thereby outputting the reactive power.

The reactive power can be calculated by calculating the instantaneous reactive power q, and the instantaneous reactive power is defined by the following equation (8).

(8)

Here, q is the instantaneous reactive power, u _sα and u _sβ the voltage of the αβ coordinate system, i _Lα i _L? is the current in the? P coordinate system.

The PQ control unit 600 calculates the reference current based on the solar active power and the reactive power output from the MPPT control unit 200.

At this time, the PQ controller 600 calculates the reference current based on the reactive power at the nighttime when there is no active power output from the solar cell array 1.

Here, the PQ controller 600 calculates the reference current in the? P coordinate system based on the p-q theory. The calculation of the reference current is defined by the following equation (9).

Equation (9)

Here, i _{c * α} and i _{c * β} are the reference currents in the αβ coordinate system, u _sα and u _sβ are the voltages of the αβ coordinate system, P _pv is the output power output from the MPPT controller 200, and P _LOS is the proportional integral gain Is the loss power in the circuit.

The loss power (P _LOS ) in the above circuit will be described.

The MPPT control unit 200 provides the maximum output point of the solar cell array 1 and the corresponding solar cell maximum output power Ppv at this time. At this time, the MPPT control unit 200 performs automatic switching to convert the DC power of the solar inverter into the AC power Accordingly, a power loss occurs in the circuit.

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FIG. 5 is a block diagram for calculating the active power in the grid-connected solar power generation system having the power factor improving function according to the present invention.

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The loss power P _LOS calculated by the proportional integral gain unit 900 is added to the PV power P _PV output from the MPPT control unit 200 and input to the PQ control unit 600.

The reference currents i _{c * a} and i _{c * b} calculated by the PQ controller 600 correspond to the reference currents in the a _? Coordinate system, and the calculated reference currents i _{c * a} and i _{c *} The process of inverse transformation must be accompanied.

The inverse transformation is performed in the power conversion unit 700, and the calculation in the power conversion unit is defined by the following Equation (10).

(10)

Where i _{c * a} , i _{c * b} and i _{c * c} are the reference currents on phase a and phase b, respectively, and i _{c * α} and i _{c * β} are the reference currents in αβ coordinate system, respectively.

The PWM control unit 800 performs a function of compensating the inverter currents ic, icb, and icc output from the inverter 100 with the reference currents output from the PQ control unit 600, A hysteresis current control method can be used.

At this time, the PWM controller 800 includes an IGBT (insulated gate bipolar mode transistor) stack, which is a switching device.

6 is a block diagram illustrating a hysteresis current control method in a grid-connected solar power generation system having a power factor improving function according to the present invention.

6, the hysteresis current control adjusts the output current within the range of the bandwidth H set for the reference current. When the reference current is set to 0 and the output current is set to the set bandwidth H, Of the switching element is controlled so as to be output within a range of That is, when the output current reaches the upper band value (+ H / 2), the voltage is applied to lower the current, and when the output current reaches the lower band value (-H / 2), the + .

In the above configuration, if the band width H is set to be narrow, an output current close to the reference current can be obtained. However, the number of times of switching of the switching elements is increased, and thus much heat is generated in the switching elements.

Accordingly, in the present invention, when the output current reaches the upper band value (+ H / 2), the zero voltage is applied to gradually decrease the current. When the output current reaches the lower band value (-H / 2) Thereby gradually increasing the current.

That is, the output current is output in the form of a triangle wave between the upper band and the lower band centering on the reference current. When the output current reaches the upper band or the lower band, when the 0 voltage is applied, Access time or access time from lower band to upper band can be increased. In this way, as the time for the output current to reach the upper band and the lower band is increased, the number of switching operations is reduced to prevent the heat generation of the IGBT stack, which is a switching device.

As described above, in the grid-connected solar power generation system having the power factor improving function according to the present invention, the solar inverter applied to the present invention is invalid based on the voltage (u _s ) of the grid and the current (i _L ) And calculates the solar power (Ppv), the reference voltage (Vref) output through the calculated reactive power, the maximum power point tracking, and the loss power in the circuit according to the actual power (V _DC ) of the solar inverter P _LOS ) is calculated based on the pq theory, and the output current is controlled by a hysteresis current control method so that the output current (i _c ) of the solar inverter is brought close to the calculated reference current. Accordingly, the reactive power can be appropriately supplied according to the supply of the active power, so that there is an advantage that the power factor can be improved.

Further, at night without solar radiation, the reference current is calculated based on the pq theoretical loss power (P _LOS ) in the circuit according to the actual power (V _DC ) of the solar inverter, and the output current i _c is controlled to be close to the calculated reference current so that the power factor can be improved by appropriately supplying the reactive power to the nighttime as well as during the daytime.

FIG. 7 is a graph showing current phases using a grid-connected solar power generation system having a power factor improving function according to the present invention.

Referring to FIG. 7, it can be seen that the sum of the output current (i _ca ) of the inverter and the output current (i _sa ) of the power system coincides with the phase characteristic of the load current (i _La ).

FIG. 8 is a graph showing active power using a grid-connected solar power generation system having a power factor improving function according to the present invention.

Referring to FIG. 8, the photovoltaic power generation system follows the maximum power so as to operate at the maximum power point through the maximum output point tracking to supply the active power, and supplies the remaining active power to the load in the power system.

FIG. 9 is a graph showing the effective power in the grid-connected solar power generation system having the power factor improving function according to the present invention in the absence of solar photovoltaic power generated by solar radiation.

9A is a graph showing the output of the load current (a1), the grid current (isa), and the inverter current (ic) in the process of reducing the solar photovoltaic power, (isa) is increased as the ica of the solar radiation decreases, so that the supply of the active power and the reactive power according to the solar radiation is normally performed. In addition, it has been shown that the power of the solar inverter can be maintained by varying the grid current to the output and being supplied to the load.

9 (b) is a graph showing the active power output in the state of Fig. 9 (a) (when the current output of the solar inverter is decreasing), wherein the system power Pgrid and the output (Ppv) is equal to the load power, and the reactive load current in this case is also derived.

10 is a graph showing the relationship between the solar power generation active power Ppv, the grid active power Pgrid, and the load effective power PI for the solar radiation a in the grid-connected solar power generation system having the power factor improving function according to the present invention. Fig.

Referring to the attached drawings, the active power (Ppv) of the photovoltaic power generation according to the present invention can be supplied in excess of the grid active power (Pgrid) supplied from the grid-connected grid, It was derived that it can reduce the burden of electric power.

11 is a graph showing the reactive power when the solar power generation system according to the present invention is applied and the reactive power when excluded in the grid-connected solar power generation system having the power factor improving function according to the present invention.

11, the reactive power in the case where the photovoltaic power generation system according to the present invention is excluded is about 3.6 KVar. However, in the case where the photovoltaic power generation system according to the present invention is applied, the reactive power is approximated to 0 KVar Respectively. That is, by applying the solar power generation system according to the present invention, it is possible to provide a power generation system in which the power factor can approach 1 by supplying the reactive power.

According to the present invention, it is possible to satisfy the maximum power supply condition of the photovoltaic generation system in conjunction with the power system. In the night when the power is not outputted in the photovoltaic power generation system, reactive power is supplied to the power system, And it is also possible to compensate the voltage and the frequency corresponding to the abrupt load power of the local load with respect to the instantaneous power so that the burden on the consumer due to the improvement of the power factor can be reduced There are advantages.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

1: Photovoltaic array 2: Photovoltaic module
3: AC grid
100: solar inverter 200: MPPT control unit
300: current conversion unit 400: voltage conversion unit
500: reactive power control unit 600: PQ control unit
700: power conversion unit 800: PWM control unit
900: Proportional integral gain unit

Claims (5)

A photovoltaic power generation system comprising a photovoltaic panel (2) for collecting a direct current produced from a solar cell array (1) and outputting power by a photovoltaic inverter (100)
The photovoltaic panel (2)
A solar inverter 100 for converting AC power received from the solar cell array 1 into AC power for use as commercial power and outputting the AC power;
An MPPT controller 200 receiving the output voltage of the solar cell array and the inverter and outputting the maximum solar output power and the reference voltage through maximum power point tracking;
A current converter 300 for converting the load current from the abc coordinate system to the alpha co-ordinate system;
A voltage converter 400 for converting the power system voltage from the abc coordinate system to the alpha co-ordinate system;
A reactive power control unit (500) for controlling reactive power output from the inverter with the current and voltage converted by the current converting unit and the voltage converting unit;
A PQ control unit 600 for calculating a reference current based on the solar active power output from the MPPT control unit 200 and the reactive power output from the reactive power control unit;
A power converter 700 for converting the reference current output from the PQ controller 600 into an abc coordinate system; And
A PWM controller 800 for compensating an inverter current output from the inverter 100 with a reference current output from the PQ controller 600;
, ≪ / RTI >
The PWM control unit (800)
The inverter current is controlled by a hysteresis current control method in which an inverter current outputted from the inverter 100 is controlled within a range of a set bandwidth H with respect to a reference current outputted from the PQ controller 600,
When the inverter current outputted from the inverter 100 reaches the upper band value (+ H / 2), a voltage of 0 is applied to gradually decrease the current. When the inverter current outputted from the inverter 100 is lower than the lower band value (-H / 2), the zero voltage is applied to gradually increase the current, so that the inverter current outputted from the inverter 100 can increase the time for approaching the upper band value and the lower band value,
The maximum output point tracking performed by the MPPT controller 200 is an incremental conductance method using the following equations (1) to (3)
Wherein the maximum output point tracking comprises:
Current PV voltage (V _PV) of the period and the PV current (I _PV) of the detection and the detected PV voltage (V _PV) and PV voltage incremental amount (dV) by the PV current (I _PV), PV current increase (DV) of the PV voltage increase amount (dV) is calculated from the calculated values after calculating the quantity (dI) and the PV power increase amount (dP) And comparing the conductance (dI / dV) of the current period with the detection conductance of the current period, and determining the output power of the current period as the maximum output point if the comparison result of the incremental conductance and the detected conductance value is the same Grid - connected photovoltaic power generation system.
(1)

Where I _ph is the photocurrent, I _{ph (ref)} is the nominal photocurrent, G is the solar radiation, G _ref is the nominal solar radiation, and I _{sc (ref)} is the nominal short-circuit current.
(2)

Here, I _pv is (hereinafter referred to as "PV current"), the output current of the solar cell, p is the parallel connection number of the solar cell, s is a series connection number of the solar cell, I _o is the diode saturation current, V _pv is a solar cell I _ph is the photocurrent, R s is the solar cell's series resistance, and V _T is the thermal voltage.
(3)

Where V _ph is the PV voltage, p is the number of parallel connections of the solar cells, s is the number of series connections of the solar cells, I _o is the diode saturation current, I _ph is the photocurrent, V _T is the column voltage, Series resistance.
The method according to claim 1,
The PQ control unit 600,
And the reference current is calculated on the basis of the reactive power output from the reactive power control unit when there is no solar effective power output from the MPPT control unit (200). The grid-connected solar power generation system .
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