KR20090096080A - System for Improving Power Factor of Dispersed Generation Grid-Connected Inverter - Google Patents

Abstract

A system for improving power factor of a dispersed generation grid-connected inverter is provided to reduce THD(Total Harmonic Distortion) of an output current by regularly maintaining output power factor of an inverter. A dispersed power detecting part(101) detects an output of a dispersed power. A grid power measuring part(102) measures a phase and a frequency of a grid power. A phase control part(103) and a frequency control part(104) perform synchronization with the grid power. An inverter converts a DC power of the dispersed power into an AC power according to a control of an inverter control part(105). An output filter(106) supplies the AC power to a grid(107). A power factor controller(108) calculates a reactive power and an active power in order to control a power factor of the output power. An active power generating part(109) and a reactive power generating part(110) output the active power and the reactive power to the inverter control part.

Description

Power Factor Correction System for Distributed Power Grid Connected Inverter {System for Improving Power Factor of Dispersed Generation Grid-Connected Inverter}

The present invention relates to a power factor improvement system for a distributed power grid-connected inverter, and more particularly, to a control for improving power factor of the inverter to supply high-quality power to the system.

Among the distributed power sources, DC power generation includes photovoltaic power generation, fuel cell power generation, and wind power generation.The system that supplies AC power to the system by inverting DC power into AC power by receiving this DC power is connected to the grid-type inverter. It is called.

That is, the grid-connected inverter converts a DC power obtained from a solar cell or a fuel cell using solar, which is a representative alternative energy source, into an AC power source using a semiconductor switch device, and then converts AC into a predetermined power system. Refers to a power converter for supplying the.

If the generation power of the alternative energy source is less than that consumed in the home (load), if the shortage is supplied from the grid power supply (commercial power) and the alternative energy generation power exceeds the power consumed in the home (load), It is a system that increases the overall operating efficiency by supplying the surplus power to the system power supply side.

1 is a block diagram of a conventional grid-connected inverter used in a distributed power source, a distributed power supply input unit 10, an inverted converter 20, a filter 30, a commercial frequency transformer 40 for grid insulation, an inverter output unit ( 50).

The distributed power supply input unit 10 receives DC power such as a solar cell, a fuel cell, and wind power generation, and the reverse converter 20 receives the DC power of the distributed power source and inverts the AC power into the AC power to calculate the phase and frequency of the system. Synchronize with the system by

The power converted by the inverse transform unit 20 becomes a sine wave through the filter 30, and the sine wave is transmitted to the commercial frequency transformer 40 for the system and the insulation, and the commercial frequency transformer 40 supplies the system and the inverter. After electrically insulating and boosting or stepping down the voltage, the AC power is boosted or stepped down through the inverter output unit 50.

FIG. 2 is a control block diagram of a conventional grid-connected inverter. The distributed power supply detecting unit 1 detects the output of the distributed power supply, and the grid power measuring unit 2 measures the power supply of the grid. Synchronization with the grid power supply is made via the control unit (4).

Inverter control unit 5 operates the inverter to invert the DC power of the distributed power supply to the AC power in synchronization, and the inverted power is transferred to system 7 via output filter 6.

The characteristics of such distributed power grid-connected inverters are that they are grid-linked, that the range of DC input voltage must be very wide, and the output power is always changing.

Among the grid-connected inverters, the distributed power source using solar power has an output during the day but no output at night, and the distributed power source using wind power varies according to the amount of wind, and the fuel cell depends on the amount of hydrogen. The output power is determined.

In other words, the grid-connected inverter for distributed power supplies must always be different in output power and be capable of generating power from zero to magnetic capacity.

Conventional grid-connected inverter for distributed power supply operates the power factor of the output power to almost 1, but the power factor is poor when the output power amount is small.

The cause of the power factor deterioration is due to the excitation current of the commercial frequency transformer 40 used to insulate the capacitor used as the filter 30 and the system 7.

In more detail, the power factor decreases when the output power amount is small. The grid-connected inverter produces only the active power of the output power, and the excitation current of the capacitor used as the filter 30 and the commercial frequency transformer 40 is used. (excite current) uses reactive power.

The power factor is calculated by Equation 1 below.

In Equation 1, the reactive power is determined by the capacity of the capacitor used as the filter 30 and the excitation current of the commercial frequency transformer 40, but the active power, which is the output of the inverter, varies according to the type of distributed power supply. do.

Therefore, when the output power is large, the power factor is improved because the active power is larger than the reactive power, but when the effective power is reduced, the power factor becomes worse because the reactive power is constant regardless of the output amount of the inverter.

In addition, even when the active power is operating at maximum, the power factor is operated close to 1, but even when the active power is maximum, the power factor does not become 1 because reactive power is always present.

The present invention has been made to solve the above-described problems, the output power factor of the grid-connected inverter used for distributed power supply is controlled to be 1 regardless of the output power amount, thereby minimizing the reactive power input to the inverter from the system The purpose is to provide a power factor improvement system for distributed power grid-connected inverters that can minimize the effects of reactive power and improve the output current quality.

The power factor improvement system of the distributed power grid-connected inverter according to the present invention for achieving the above object includes a distributed power detector for sensing the output of the distributed power supply, a grid power measurement unit for measuring the phase and frequency of the grid power; A phase controller and a frequency controller for synchronizing with the system power according to the phase and frequency of the system power, an inverter controller for operating the inverter to inversely convert the DC power of the distributed power supply into the AC power synchronized with the AC power, and the converted AC A control system of a distributed power grid-connected inverter comprising an output filter for supplying electric power to a grid;

A power factor controller that monitors the power factor of the output power output from the output filter to the system and calculates the reactive power and the active power as a command value to control the power factor of the output power to 1, and the active power and the invalid value according to the command value; It consists of an active power generation unit and a reactive power generation unit for producing power and outputting to the inverter control unit, the inverter control unit is characterized in that the output and the active power switching by switching the active power and reactive power so that the output power does not exceed the forward power factor. do.

According to the above-described problem solving means has a very excellent effect in the power generation of the inverter output power to always operate by 1 by generating the reactive power as necessary in the grid-connected inverter.

In addition, the power factor of a grid-connected inverter used for distributed power is always maintained at 1, which minimizes the effect on the grid and lowers the total harmonic distortion (THD) of the output current.

Hereinafter, the configuration and operation of the present invention will be described with reference to the accompanying drawings.

3 is a block diagram of a power factor improvement system according to the present invention.

As shown, distributed power supply sensing unit 101, system power measuring unit 102, phase control unit 103, frequency control unit 104, inverter control unit 105, output filter 106, system 107, power factor The controller 108, an active power generator 109, and a reactive power generator 110 are configured.

The distributed power detector 101 detects the output of the distributed power, and measures the phase and the frequency of the grid power in the grid power measurement unit 102, and the system 107 through the phase controller 103 and the frequency controller 104. ) Synchronize with power.

The inverter controller 105 operates the inverter to reversely convert the DC power of the distributed power supply to the synchronized AC power, and the converted power supplies power to the system 107 via the output filter 106.

The power factor controller 108 monitors the power factor of the output power output from the output filter 106 to the grid 107 and calculates the reactive power amount and the active power amount to control the power factor of the output power to 1 to generate the active power generation unit ( 109 and the reactive power generator 110.

When the reactive power is supplied more than necessary, the power of the phase power factor is supplied to the system 107 so that the power factor is lowered.

At this time, the required reactive power calculation method is as follows.

Where VA is the reactive power of the capacitor used as the output filter, C is the capacitance of the capacitor {캐}, E is the output voltage of the inverter [V], and f is the frequency of the inverter.

Equation 2 can be used to calculate the reactive power required by obtaining the capacitance of the filter capacitor, and the current value required for control can be obtained using Equation 3 below.

Since the capacitor used as the output filter 106 is a capacitive load, the current to be supplied to the capacitor becomes a true component.

The excitation current of a commercial frequency transformer depends on the capacity of the transformer, the material of the core used, and the winding, so it can be calculated by the formula, but many variables must be considered.

Therefore, the power factor controller 108 monitors the output power factor to control the output power factor of the inverter to 1 so that the command value (effective power amount and reactive power amount) is supplied to the active power generation unit 109 and the reactive power generation unit 110 such that the power factor becomes 1. ) To produce active and reactive power.

The produced active power and reactive power are sent to the inverter controller 105, and the inverter controller 105 switches the input active power and reactive power and outputs them to the output filter side.

At this time, the reactive power generation unit 110 produces only reactive power as required by the inverter, and if the reactive power is generated more than that, the power factor is advanced and the power factor is lowered. Adjust if possible.

That is, the present invention does not supply the reactive power of the output filter 106 from the system 107, calculates the capacity of the capacitor used as the output filter 106 in the inverter itself, and supplies the reactive power, and output power factor. Drive to 1, but do not control to advance to the advance power factor.

1 is a block diagram of a conventional grid-connected inverter used for distributed power supplies,

2 is a control block diagram of a conventional grid-connected inverter,

3 is a block diagram of a power factor improvement system according to the present invention.

<Description of the symbols for the main parts of the drawings>

101: distributed power detection unit 102: grid power measurement unit

103: phase control unit 104: frequency control unit

105: inverter control unit 106: output filter

107: system 108: power factor controller

109: active power generation unit 110: reactive power generation unit

Claims (3)

A distributed power detector for detecting the output of the distributed power supply, a system power measuring unit for measuring the phase and frequency of the system power, a phase controller and a frequency controller for synchronizing with the system power by matching the phase and frequency of the system power; A control system for a distributed power system-linked inverter comprising an inverter control unit for operating an inverter to inversely convert DC power of a distributed power source into AC power in synchronization with an output filter for supplying the converted AC power to a system; A power factor controller that monitors the power factor of the output power output from the output filter to the system and calculates the reactive power and the active power as a command value to control the power factor of the output power to 1, and the active power and the invalid value according to the command value; It consists of an active power generating unit and a reactive power generating unit for producing power and outputting to the inverter control unit, the inverter control unit is characterized in that the output and the active power switching by switching the active power and reactive power so that the output power does not exceed the forward power factor Power factor improvement system for distributed power grid inverters. The method of claim 1, The power factor controller calculates a reactive power of a capacitor used as an output filter by Equation 4.

Where VA is the reactive power of the capacitor used as the output filter, C is the capacitance of the capacitor, E is the output voltage of the inverter, and f is the frequency of the inverter. The method of claim 2, The power factor improvement system of the distributed power grid-connected inverter, characterized in that the current required for the control of the reactive power is calculated by the equation (5).

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