KR101226104B1 - Power system of dc grid-connected photovoltaic pcs - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power system of a solar system for DC grid connection. The controller is configured to control the output power of the power circuit unit and the power circuit unit by controlling the output power by configuring an inductor between the power circuit output voltage and the grid voltage. The purpose is to provide a power system of the solar system for DC grid connection.
The present invention for achieving this object, the switch including a diode and a first capacitor for supplying the direct current power generated from the solar cell in one direction, connected in parallel with the first capacitor to perform switching for each phase, 1 A power circuit portion connected to the switch side and including a diode portion for generating an output voltage on a secondary side, a transformer portion connected to a second capacitor, and an inductor; And a control unit controlling output power of the power circuit unit. .

Description

Power system of solar PS for direct current grid connection {POWER SYSTEM OF DC GRID-CONNECTED PHOTOVOLTAIC PCS}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power system of a solar system for DC grid connection, and more particularly, to an electric power circuit unit and an output power of a solar process in consideration of electrical stability and functionality for a solar power conversion system (PCS). It relates to a power system of the solar system for DC grid connection configured to control the control.

Recently, DC loads such as computers, LED lighting, and IDC (Internet Data Center) are increasing. In order to drive such a DC load, a two-stage conversion from AC to DC to DC or AC is required, which converts a commercial AC input into a DC and then converts it into a DC power supply that meets specifications.

Therefore, the form in which the output of a power source having a direct current output such as a solar cell and a fuel cell is used is generally converted to AC, connected to a commercial AC system, and then converted to DC again as shown in [Table 1]. Since it is converted to a suitable DC power supply, basically three steps of conversion process are required.

In the case of 3 [kW] class photovoltaic power generation PCS, the output of distributed power is converted to AC through DC / DC conversion. In this case, a total of 4 steps of energy conversion are performed.

 Therefore, after constructing DC bus using AC / DC converter under the background of recent increase in DC load and increase in use of DC output type distributed power supply (representative example: solar, fuel cell), DC load is directly used by DC load. There has been an increased interest in direct current feeding systems.

In case of using the DC power supply system, the individual AC / DC conversion process of the DC load is omitted, thereby simplifying the load individual system configuration, increasing the efficiency of the load itself, and reducing heat generation. In addition, in case of DC output type distributed power supply (representative example: solar, fuel cell), DC / AC conversion process can be omitted because it can be directly connected to the DC bus. The conversion process reached is shortened from 3 steps (or 4 steps) to 2 steps, which has the advantage of more efficient power usage.

Process of output of DC type distributed power source reaching DC load division process General procedure for DC output to reach DC load in AC power supply system

→상용AC→DC(계통)→용도에 맞게 재 변환된 DC

: 채용되는 경우도 있음(예:3[kW] 계통연계 PCS)DC (distributed power supply) → (DC)

→ Commercial AC → DC (System) → DC reconverted to fit

Sometimes employed (e.g. 3 [kW] On-grid PCS) General procedure for DC output to reach DC load in DC feeding system DC (distributed power supply) → DC (system) → DC reconverted to suit the purpose

In order to generate the output of the solar cell in the DC system, a DC / DC converter having a power control function is required as an intermediary device between the solar cell and the DC system.

Conventional technology that converts the output of DC distributed power sources such as solar power into direct current is used for the purpose of boosting the power when the PCS for DC / AC conversion is difficult to use immediately because the output of the distributed power supply is low. In most cases, it is used for the purpose of stepping down. However, since the DCS PCS is connected to the DC system, the system voltage is fixed, and if the variation of the solar cell is large, it is necessary to have both the step-up and step-down functions.

In addition, it is necessary to configure the control system in such a way that the output power is freely controlled when the output of the PCS is changed according to the output of the solar cell or when the DC system voltage is changed. However, in general DC / DC conversion circuit, the circuit is configured to easily control the output voltage, and the control system design method is also proposed accordingly. Therefore, in order to construct the solar PCS for DC linkage, it is appropriate to use the existing DC / DC conversion circuit. Modifications and new control system configurations are needed.

In addition, since a DC power distribution system is likely to be constructed around a building, consideration thereof is necessary. In the case of a building power supply, a load that is sensitive to power quality such as a computer may be a majority, and thus, a power circuit needs to be configured in consideration of electrical stability when configuring a PCS for linkage.

The present invention has been made in view of the above problems, by configuring an inductor between the power circuit output voltage and the system voltage, a direct current system comprising a power circuit section for easy output power control and a control unit for controlling the output power of the power circuit section The purpose is to provide a power system of the solar PV C for connection.

The present invention for achieving the technical problem relates to a power system of the solar system for DC grid connection, comprising a diode and a first capacitor for supplying the direct current power generated from the solar cell in one direction, the first capacitor A switch unit 130 connected in parallel with each other to perform switching for each phase, a primary side connected to the switch unit, a diode unit for generating an output voltage to the secondary side, and a transformer unit connected to a second capacitor and an inductor. Power circuit section; And a control unit controlling output power of the power circuit unit. It includes.

In addition, the inductor is connected between the power circuit output voltage Vo and the grid voltage Vuti, and the potential difference Vlf between the power circuit output voltage Vo and the grid voltage Vuti is applied to both ends of the inductor. It features.

The controller may control a tracking value of the DC voltage based on the current isol supplied from the solar cell and the switching signal Vdc supplied from the switch unit.

)를 생성하며, 생성된 상기 출력 전류 기준신호(

)를 이용하여 출력 전류(

)를 제어하며, PWM의 제어신호로 전송함으로써 상기 스위치부의 전류 제어를 수행하는 것을 특징으로 한다. The controller generates a power reference signal and divides the generated power reference signal by an output voltage Vo to output an output current reference signal (

) And the generated output current reference signal (

Output current (

), And by controlling the current of the switch unit by transmitting a PWM control signal.

According to the present invention as described above, the inductor is configured between the power circuit output voltage and the grid voltage, it is easy to control the output power. That is, since the potential difference between the power circuit output voltage and the grid voltage is applied to both ends of the inductor, it serves to satisfy Kirchhoff's voltage law and filter high frequency components between the two voltage sources.

1 is an exemplary view showing a power circuit and a PWM operation waveform of a constant voltage output type isolated fixed frequency series resonant converter generally used.
2 is an exemplary view of an AC equivalent circuit of a fixed frequency series resonance circuit.
3 is an exemplary view showing a voltage gain curve.
Figure 4 is an exemplary view showing a conventional output voltage controlled system control system.
Figure 5 is an example for showing the power control concept of the PS for DC grid connection.
Figure 6 is a block diagram of a power system of the solar system for DC grid connection in accordance with an embodiment of the present invention.

Specific features and advantages of the present invention will become more apparent from the following detailed description based on the accompanying drawings. It is to be noted that the detailed description of known functions and constructions related to the present invention is omitted when it is determined that the gist of the present invention may be unnecessarily blurred.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings.

Referring to Figures 1 to 7 with respect to the power system of the solar system for DC grid connection according to an embodiment of the present invention.

Circuits that can be used in a DC-linked type include an isolated flyback converter, a full-bridge ZVZCS converter, a series resonant converter, and the like. In the present invention, a DC-linked PCS is configured using a fixed frequency series resonant converter.

1 shows a power circuit and a PWM operating waveform of a constant voltage output type isolated fixed frequency series resonant converter which is generally used. In addition, an AC equivalent circuit for analyzing the output characteristics of the series resonant converter of FIG. 1 is as shown in FIG. 2.

In FIG. 2 and the AC circuit, the voltage gain M (the magnitude of the output voltage / the magnitude of the input voltage) is as shown in Equation 1 below.

[Equation 1]

To solve this, the voltage gain M is expressed in the form of a frequency function as shown in Equation 2 below.

[Equation 2]

here,

)가 20[kHz]일 경우, 전압이득 곡선을 보이는 일예시도이다. 3 is the resonant frequency (

If) is 20 [kHz], it is an example showing the voltage gain curve.

As shown in FIG. 3, it can be seen that the frequency of the input voltage exhibits the largest gain near the resonance frequency. Therefore, when the switching frequency of the power circuit is fixed, it can be seen that the output voltage can be controlled by controlling the duty ratio (corresponding to D in FIG. 1).

The general control purpose of the system as shown in FIG. 1 is to constantly control the output voltage Vo, and a control system is generally configured as shown in FIG.

In order to use the fixed frequency series resonant circuit as shown in FIG. 1 as a PCS for DC system linkage, the output power control type for instantaneously balancing the power generated to the grid side according to the fluctuating output of the solar cell as shown in FIG. 5. Power circuits and control systems should be constructed.

In FIG. 5, Psol (t) is solar cell output power, Pout (t) is generated power to a DC system, and S (ωt) is switching signals Q1, Q2, Q3, and Q4.

6 is a configuration diagram of a power system of the solar system for DC grid connection according to an embodiment of the present invention.

FIG. 6A is an exemplary view illustrating a power circuit unit of an output power control type fixed frequency series resonant converter for a DC grid-connected photovoltaic PCS.

As shown, the power circuit unit 100 includes a diode 110 and a first capacitor 120 for supplying the DC power generated from the solar cell 10 in one direction.

In addition, the switch unit 130 connected in parallel with the first capacitor 120 to perform switching for each phase, the primary side is connected to the switch unit 130 with a predetermined winding ratio, and the secondary side is a diode unit ( A transformer 170 is connected to the 140, a diode unit 140 for generating an output voltage to the secondary side, a second capacitor 150, and an inductor 160.
In this case, the diode unit 140 is connected in parallel with the inductor 160, and is connected to the secondary side of the transformer unit 170.

Specifically, the inductor 160 is connected between the voltage (Vo) of the second capacitor 150 and the grid voltage (Vuti).

Since the potential difference Vlf between the voltage Vo at both ends of the second capacitor 150 and the system voltage Vuti is applied to both ends of the inductor 160, the voltage law of Kirchhoff is satisfied between the two voltage sources. And filtering for high frequency components.

6B is an exemplary view of the controller 200 for controlling the power circuit unit 100 according to an embodiment of the present invention.

At this time, the control unit 200, as shown in FIG. 5, power balance control between the solar cell output and the power generation to the system through the control of the output current (io) and tracking the maximum output operating point of the solar cell (Maximum Power Point Tracking: configured for MPPT.

)를 생성하며, 생성된 상기 출력 전류 기준신호(

)와 센싱된 출력 전류(

)의 차이를 이용하여 출력 전류(

)를 제어하기 위한 스위치부(130)의 듀티비(D)를 결정하며, 상기 듀티비(D)를 PWM의 제어신호로 전송함으로써, 스위치부(130)의 PWM 제어를 통해 출력 전류(

)의 제어를 수행한다.
Specifically, as shown in FIG. 6, the solar cell output current isol and the input DC voltage Vdc of the switch 130 are sensed to generate a maximum power point reference signal Vdc *, and the maximum power The system output power reference signal Po * is generated by using the difference between the point reference signal Vdc * and the voltage Vdc across the first capacitor 120, and the generated power reference signal Po * is generated. 2 divided by the voltage (Vo) of the capacitor 150, the output current reference signal (

) And the generated output current reference signal (

) And sensed output current (

Output current (

) Determines the duty ratio (D) of the switch unit 130 to control, and transmits the duty ratio (D) as a control signal of the PWM, the output current (PWM) through the PWM control of the switch unit (130)

) Control.

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While the present invention has been particularly shown and described with reference to preferred embodiments thereof, 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. It will be appreciated by those skilled in the art that numerous changes and modifications may be made without departing from the invention. Accordingly, all such appropriate modifications and changes, and equivalents thereof, should be regarded as within the scope of the present invention.

100: power circuit section 110: diode
120: first capacitor 130: switch unit
140: diode 150: second capacitor
160: inductor 200: control unit

Claims (4)

Switch including a diode 110 and a first capacitor 120 for supplying the DC power generated from the solar cell 10 in one direction, connected in parallel with the first capacitor 120 to perform switching for each phase 130, a transformer portion having a predetermined winding ratio, the primary side is connected to the switch unit 130, the secondary side is connected to the diode unit 140, the diode unit for generating an output voltage to the secondary side A power circuit unit 100 including a 140, a second capacitor 150, and an inductor 160; And
A control unit 200 for controlling the output power of the power circuit unit 100; Including but not limited to:
The diode unit 140 is connected in parallel with the inductor 160, characterized in that connected to the secondary side of the transformer 170,
The control unit (200)
The solar cell output current isol and the input DC voltage Vdc of the switch unit 130 are sensed to generate the maximum power point reference signal Vdc *, and the maximum power point reference signal Vdc * and the first capacitor. The system output power reference signal Po * is generated by using the difference between the voltages Vdc at 120, and the generated power reference signal Po * is output at both ends of the second capacitor 150. Divided by the output current reference signal (

) And the generated output current reference signal (

) And sensed output current (

Output current (

) Determines the duty ratio (D) of the switch unit 130 to control, and transmits the duty ratio (D) as a control signal of the PWM, the output current (PWM) through the PWM control of the switch unit (130)

Power system of the solar system for DC grid connection, characterized in that the control of).
The method of claim 1,
The inductor 160,
It is connected between the voltage (Vo) and the system voltage (Vuti) of both ends of the second capacitor 150,
The electric power of the DC solar cell of the DC grid connection, characterized in that the potential difference (Vlf) between the voltage (Vo) and the system voltage (Vuti) of both ends of the second capacitor 150 is applied to both ends of the inductor (160). system.
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