KR20190036914A - High Efficiency Photovoltaic System Using DC-DC Voltage Regulator - Google Patents

Abstract

The objective of the present invention is to provide a high efficiency photovoltaic power system for using a DC-DC voltage regulator. The high efficiency photovoltaic power system comprises: each of strings (string one to string m) which is configured to be series connection of a plurality of photovoltaic modules (module one to module n); each of DC-DC voltage regulators (100) which is connected to output of each of the strings (string one to string m) to follow a maximum power point of photovoltaic power through maximum power point tracking (MPPT) control and prevent separation from a three-phase system connected inverter (200) through constant voltage control; and a three-phase system connected inverter (200) connected to output of each of the DC-DC voltage regulators (100).

Description

TECHNICAL FIELD [0001] The present invention relates to a high efficiency photovoltaic system using a DC-DC voltage regulator,

The present invention relates to a high efficiency solar power system using a DC-DC voltage regulator.

With the use of limited fossil fuel energy, socioeconomic problems and global environmental problems are becoming a major issue, and as an alternative, technology development and dissemination of new and renewable energy are being actively promoted around the world. Especially, solar energy is the most research and development and commercialized, and it is regarded as the most abundant resource of renewable energy.

Typical power loss factors of PV power can be classified into maintenance loss and environmental loss. Loss due to maintenance can be solved through periodic maintenance due to unbalance of serial parallel connection, MPPT (Maximum Power Point Tracking) mismatch loss, and power loss due to power conversion equipment. On the other hand, losses due to environmental factors include losses due to solar radiation variations, efficiency fluctuations due to temperature changes, loss due to shading, pollution and loss due to aging. Such environmental factors are difficult to control by the operator, It is necessary to improve the solar power control method.

In particular, in some solar power sources, installation efficiency is deteriorated due to shading due to buildings or trees installed without consideration of the surrounding environment. That is, in the conventional solar power control method, since a string (composed of a series connection of a plurality of solar modules) is connected to a three-phase (three-phase) grid-connected inverter, The voltage of the string becomes less than the operating voltage of the grid-connected inverter, so that the string is dropped at the inverter and the overall operation efficiency of the solar power source is considerably lowered.

FIG. 1 is a view showing a conventional solar power system.

In FIG. 1, a plurality of solar modules are connected in series to form one string, and a plurality of strings are connected in parallel to constitute a solar power source. In the conventional solar power control method, several strings are connected to a three-phase inverter. Therefore, if the voltage of the string decreases due to the shadow generated in the solar module, the string is dropped from the inverter by the reverse voltage diode, and the overall operation efficiency of the solar power source is lowered.

Related Prior Art Document Information: Registered Patent Publication No. 10-1454197 (October 24, 2014) "High Efficiency Power Transmission Device for Solar Power"

SUMMARY OF THE INVENTION The present invention has been conceived in order to solve the above-mentioned problems, and it is an object of the present invention to provide a DC-DC voltage regulator having an MPPT control and a constant voltage control function for each string output formed by series connection of a plurality of solar modules, And an object of the present invention is to provide a high efficiency solar power system using a DC-DC voltage regulator for connecting a three-phase grid-connected inverter to an output of a voltage regulator.

In order to achieve this object,

According to an aspect of the present invention,

Each string (string 1 to string m) consisting of a series connection of a plurality of solar modules (modules 1 to n);

And each DCP connected to each string (string 1 through string m) output to follow the maximum power point of the solar power source through MPPT control and preventing dropout from the three-phase grid-connected inverter 200 through constant voltage control A DC voltage regulator 100; And

A three-phase grid-connected inverter (200) connected to an output of each DC-DC voltage regulator (100);

And a control unit.

A stabilizing circuit including a capacitor is further provided between an output terminal of each of the DC-DC voltage regulators 100 and the input terminal of the three-phase grid-connected inverter 200, So that the ripple component is removed at the output of each DC-DC voltage regulator 100. [0034]

The three-phase grid interconnected inverter 200 is characterized in that it follows the phase of the system through phase locked loop (PLL) control and transmits the power output from each DC-DC voltage regulator 100 to the system .

The present invention relates to a DC-DC voltage regulator (100) having MPPT control and constant voltage control function for each string (string 1 to string m) output consisting of a series connection of a plurality of solar modules (modules 1 to n) Phase grid-connected inverter 200 is connected to the output of each DC-DC voltage regulator 100 to connect some of the plurality of solar modules (modules 1 to n) When the output voltage of a corresponding one of the strings (string 1 to string m) becomes lower than the operating voltage of the three-phase grid interconnected inverter 200 due to the power consumption (irradiation amount, temperature, etc.) There is an advantage that the problem that the inverter is eliminated or the worst case is eliminated is solved.

Also, since the output of the three-phase grid-connected inverter 200 is reduced only as much as the output of the module in which the shading occurs among the plurality of solar modules (modules 1 to n), the operation efficiency of the solar power source is improved.

FIG. 1 is a view showing a conventional solar power system.
FIG. 2 is a view showing an embodiment of a high efficiency solar power system using a DC-DC voltage regulator according to the present invention.
3 is a diagram for explaining the P & O (Perturbation & Observation) algorithm.
FIG. 4 is a flowchart showing the P & O algorithm described in FIG.
5 is a flowchart of constant voltage control.
6 is a diagram showing PLL control of a three-phase grid interconnected inverter.

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

FIG. 2 is a view showing an embodiment of a high-efficiency solar power system using a DC-DC voltage regulator according to the present invention, in which each string (string 1 to string m), each of the DC-DC voltage regulators 100 and the three-phase grid-connected inverter 200. Here, 1 to n and 1 to m mean plural numbers.

The present invention thus constructed will be described in detail with reference to FIGS. 3 to 6. FIG.

FIG. 3 is a diagram for explaining the P & O algorithm, FIG. 4 is a flowchart of the P & O algorithm described in FIG. 3, FIG. 5 is a flowchart of constant voltage control, PLL control.

First, in Fig. 2, each string (string 1 to string m) consists of a series connection of a plurality of solar modules (modules 1 to n).

Each of the DC-DC voltage regulators 100 is connected to each string (string 1 to string m) output to follow the maximum power point of the solar power source through MPPT control and controls the three-phase grid- 200 from being detached.

The three-phase grid-connected inverter 200 is connected to the output of each DC-DC voltage regulator 100.

A stabilizing circuit composed of a capacitor is provided between the output terminal of each DC-DC voltage regulator 100 and the input terminal of the three-phase grid-connected inverter 200 to maintain the boosted voltage of each DC-DC voltage regulator 100 And allows the ripple component to be removed at the output of each DC-DC voltage regulator 100.

The three-phase grid interconnected inverter 200 follows the phase of the system through the PLL control and delivers the power output from each DC-DC voltage regulator 100 to the system.

The maximum power point of the solar power source changes constantly due to environmental factors such as solar radiation and temperature change, so MPPT control is required to track the voltage and current value that can produce the maximum output of the solar power source at every moment.

The reason for performing the MPPT control in the DC-DC voltage regulator 100 is that when the environmental factors are different for each string (string 1 to string m) and the output is different, in the three-phase grid-connected inverter 200, The power point can not be found.

As the MPPT control method, P & O method, InCond (Incremental Conductance) method and differential element control method are generally used.

In the present invention, the most commonly used P & O method is applied to the output control method of the DC-DC voltage regulator 100.

The P & O method operates by a method of periodically increasing or decreasing the operating voltage of the solar cell, and by continuously comparing the previous output power of the solar cell with the current output power during the previous control period And finding the maximum power point.

) 및 전압변동분(

)을 계산한다. 만약

가 0이면 현재 출력을 최대전력점이라고 판단하여 제어 루프를 빠져나오고, 그렇지 않으면 다음 단계로

가 0보다 큰지 판단한다. 만약

가 0보다 크다면 이는 전력의 증가를 의미하며 그 다음으로

가 0보다 큰지 판단한다. 만약

가 0보다 크면 ①과 같이 기준전압(

)을 증가시키며, 이는 앞에서

가 0보다 크기 때문에

의 증가로 출력전력의 증가를 기대하기 때문이다. 즉, 전력-전압 곡선에서 현재 동작점이 최대전력점의 좌측에 있음을 의미한다. 반면,

가 0보다 작다면 ②와 같이

를 감소시키며, 이는 전력-전압 곡선에서 현재 동작점이 최대전력점의 우측에 있음을 의미한다. 한편,

가 0보다 작다면 이는 전력의 감소를 의미하며 마찬가지로

가 0보다 큰지 판단한다. 만약

가 0보다 크면 ③과 같이

를 감소시키는데, 이는 앞에서

가 0보다 작기 때문에

의 감소로 출력전력의 증가를 기대하기 때문이다. 즉, 전력-전압 곡선에서 현재 동작점이 최대전력점의 우측에 있음을 의미한다. 반면,

가 0보다 작다면 ④와 같이

를 증가시킨다. 이때는 전력-전압 곡선에서 현재 동작점이 최대전력점의 좌측에 있음을 의미한다.FIG. 3 is a diagram for explaining the P & O algorithm. The P & O method is applied to the output control method of the DC-DC voltage regulator 100 to follow the maximum power point. First, the voltage and current of the string (string 1 to string m) are measured through the sensor to determine the power variation

) And voltage variation (

). if

Is 0, it is judged that the present output is the maximum power point and the control loop is exited. Otherwise, the next step

Is greater than zero. if

Is greater than 0, this means an increase in power, and then

Is greater than zero. if

Is larger than 0, the reference voltage (

), Which increases

Is greater than zero

The output power is expected to increase. That is, it means that the current operating point is on the left of the maximum power point in the power-voltage curve. On the other hand,

Is less than 0,

Which means that the current operating point in the power-voltage curve is to the right of the maximum power point. Meanwhile,

Is less than 0, this means a decrease in power, and

Is greater than zero. if

Is greater than 0,

, Which is the

Is less than zero

The output power is expected to increase. That is, the current operating point in the power-voltage curve is to the right of the maximum power point. On the other hand,

Is less than 0,

. This means that the current operating point in the power-voltage curve is to the left of the maximum power point.

를 계산하고, 이전 전력과 현재 전력을 비교(

)하여 최대전력점을 추종한다. 여기서,

,

,

는 각각 현재의 스트링 전압, 전류, 전력을 의미하며,

는 측정시간 간격을 나타낸다.FIG. 4 is a flowchart showing the P & O algorithm described in FIG. 3,

And comparing the previous power with the current power (

) To follow the maximum power point. here,

,

,

Current < / RTI > voltage, current, and power, respectively,

Represents the measurement time interval.

When the voltage of the string is reduced to less than the operating voltage range of the three-phase grid-connected inverter 200 due to shading in a part of the solar module (module 1 to module n), the reverse- The grid interconnected inverter 200 is disconnected and the overall operation efficiency of the solar power source is lowered. Therefore, it is necessary to control the constant voltage of the DC-DC voltage regulator 100 to prevent the strings (string 1 to string m) from falling off from the three-phase grid interconnected inverter 200.

The constant voltage control of the DC-DC voltage regulator 100 means that the output voltage is held at the target voltage by taking the voltage of the string (string 1 to string m) as the input voltage. After setting the target output voltage, PI control is performed on the error between the voltage and the target voltage. Finally, a signal output from the control circuit is compared with a triangular wave to calculate a duty ratio for a constant voltage output, and a control signal output to the MOSFET device is applied.

)을 설정하고, 현재 출력전압(

)과 비교하여, 오차분(

)이 허용범위 이내이면 정전압 제어가 정상적으로 이루어진다고 판단하여 기존의 듀티비를 유지한다(단계 1).5 is a flow chart of constant voltage control in which the target output voltage of the DC-DC voltage regulator 100

), And the current output voltage (

), The error amount (

) Is within the permissible range, it is determined that the constant voltage control is normally performed, and the conventional duty ratio is maintained (step 1).

가 허용범위를 벗어나면, 오차분에 대한 PI 제어를 수행한다(단계 2). 여기서, 목표전압과 DC-DC 전압 레귤레이터(100)의 출력전압 사이의

는 수학식 1과 같이 계산되고, 오차분에 대하여 PI 제어는 수학식 2와 같다.By comparing the target voltage with the current output voltage

The PI control for the error is performed (step 2). Here, between the target voltage and the output voltage of the DC-DC voltage regulator 100

Is calculated as shown in Equation (1), and the PI control for the error is expressed by Equation (2).

는 전압 오차분에 대한 비례적분 제어 계산값,

는 비례이득,

는 적분이득,

는 시간이다.here,

Is the proportional integral control calculation value for the voltage error,

Is proportional gain,

Is an integral gain,

Is time.

)는 삼각파와 비교되어 듀티비가 결정되고, MOSFET 소자에 인가되어 DC-DC 전압 레귤레이터(100)의 출력전압이 결정된다(단계 3).The signal output in step 2 (

Is compared with the triangular wave to determine the duty ratio and applied to the MOSFET device to determine the output voltage of the DC-DC voltage regulator 100 (step 3).

The stabilization circuit is necessary for maintaining the boosted voltage in the DC-DC voltage regulator 100 and reducing the output voltage ripple. That is, the stabilization circuit estimates the appropriate reactance and capacitance for normal operation. First, boost control of the DC-DC voltage regulator 100 is performed through a MOSFET switching operation, which stores or discharges energy in the inductor. The minimum capacity of the inductor is given by Equation (3) under the condition that the minimum current of the inductor must be greater than zero in order to maintain the boosted voltage.

는 인덕터의 최소용량[H],

은 부하저항[Ω],

는 듀티비,

는 스위칭 주기[s]이다.here,

Is the minimum capacity [H] of the inductor,

Is the load resistance [Ω],

Lt; / RTI >

Is the switching period [s].

) 범위를 유지하기 위한 적정 커패시터의 용량은 수학식 4와 같이 나타낼 수 있다.Further, the target output ripple voltage (

) Can be expressed by Equation (4). &Quot; (4) "

는 커패시터의 용량[F],

는 DC-DC 전압 레귤레이터(100)의 입력전압[V],

는 DC-DC 전압 레귤레이터(100)의 출력 리플전압[V]이다.here,

Is the capacity [F] of the capacitor,

Is the input voltage [V] of the DC-DC voltage regulator 100,

Is the output ripple voltage [V] of the DC-DC voltage regulator 100.

The three-phase grid interconnected inverter 200 requires PLL control in order to accurately follow the phase of the system even if the input voltage and current change due to solar radiation variation or shading.

) 및 q축 전압(

)을 수학식 5, 6과 같이 산정한다.6 shows a PLL control of the three-phase grid interconnected inverter 200. In order to control the PLL, first, a d-axis voltage (a voltage obtained by converting the three-phase line voltage of the system into a two-

) And the q-axis voltage

) Is calculated as shown in Equations (5) and (6).

는 d-q 정지좌표계의 d축 전압[V],

는 d-q 정지좌표계의 q축 전압[V],

는 상전압 피크값[V],

는 계통 각속도[rad/s],

는 계통전압의 위상[rad],

: 인버터 출력전압의 위상[rad],

: 각속도 변화량[rad/s]here,

Is the d-axis voltage [V] of the dq stationary coordinate system,

Is the q-axis voltage [V] of the dq stationary coordinate system,

Is the phase voltage peak value [V],

Is the system angular velocity [rad / s],

Is the phase [rad] of the grid voltage,

: Phase [rad] of the inverter output voltage,

: Angular velocity variation [rad / s]

에 궤환신호

를

에 궤환신호

를 각각 곱한 후 각속도 변화량(

)을 계산하고,

의 비례제어 값과 기준 주파수(

, 60Hz)의 차에 대한 적분제어를 통해 3상 계통연계형 인버터(200) 출력전압의 위상(

)을 결정한다. 그리고

와 계통전압의 위상(

)의 차가 작다고 가정하면, 수학식 7과 같이 근사화 될 수 있으며,

와

가 일치하면 최종적으로 PLL 제어가 이루어진다.For feedback

The feedback signal

To

The feedback signal

And then the angular velocity variation (

),

And the reference frequency (

, 60 Hz), the phase of the output voltage of the three-phase grid-connected inverter 200

). And

And the phase of the grid voltage (

) Is small, it can be approximated as in Equation (7)

Wow

The PLL control is finally performed.

The present invention is applicable to each of DC-DC voltage regulators (MP1 to MPn) having MPPT control and constant voltage control function for each string (string 1 to string m) output composed of series connection of a plurality of solar modules (modules 1 to n) Phase grid-connected inverter 200 is connected to the output of each DC-DC voltage regulator 100. In this way, a plurality of photovoltaic modules (modules 1 to n) When the output voltage of the corresponding string among the strings (strings 1 to m) becomes lower than the operating voltage of the three-phase grid-connected inverter 200 due to a change (irradiation amount, temperature, etc.), the corresponding string does not operate, And the problem that the inverter is eliminated in the worst case is solved.

Also, since the output of the three-phase grid-connected inverter 200 is reduced only as much as the output of the module in which the shading occurs among the plurality of solar modules (modules 1 to n), the operation efficiency of the solar power source is improved.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. In addition, it is a matter of course that various modifications and variations are possible without departing from the scope of the technical idea of the present invention by anyone having ordinary skill in the art.

Claims (3)

Each string (string 1 to string m) consisting of a series connection of a plurality of solar modules (modules 1 to n);
And each DCP connected to each string (string 1 through string m) output to follow the maximum power point of the solar power source through MPPT control and preventing dropout from the three-phase grid-connected inverter 200 through constant voltage control A DC voltage regulator 100; And
A three-phase grid-connected inverter (200) connected to an output of each DC-DC voltage regulator (100);
Wherein the DC-DC voltage regulator comprises a DC-DC voltage regulator.
The method according to claim 1,
A stabilizing circuit including a capacitor is further provided between an output terminal of each of the DC-DC voltage regulators 100 and the input terminal of the three-phase grid-connected inverter 200, DC voltage regulator (100), wherein the ripple component is removed from the output of each DC-DC voltage regulator (100). The method according to claim 1,
The three-phase system grid inverter (200) follows the phase of the system through PLL control and transfers the power output from each DC-DC voltage regulator (100) to the system. High efficiency solar power system using.

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