KR20170004178A - Discontinuous voltage modulation based grid connected power inverter and method for the same - Google Patents

Abstract

Provided are a grid connected power inverter based on a discontinuous voltage modulation and a method thereof. The grid connected power inverter based on a discontinuous voltage modulation includes: an offset voltage generator for generating a DC voltage output from a DC power source, and a first offset voltage based on a phase voltage command output from a current controller; a high-frequency generator electrically connected to a phase fixing loop to generate a high frequency of n orders, wherein n is an integer, based on a phase angle of a system; and a signal control unit for generating a new second offset voltage by introducing the high frequency of n orders into the first offset voltage, and for outputting a PWM signal for controlling an inverter circuit based on a terminal voltage command generated by adding the second offset voltage to the phase voltage command.

Description

TECHNICAL FIELD [0001] The present invention relates to a grid-connected power conversion apparatus and method based on a discontinuous voltage modulation method,

Embodiments of the present invention relate to a grid-based power conversion apparatus and method based on a discrete voltage modulation scheme.

The grid-connected inverter is an essential module for the control of the renewable energy generation system and the energy storage system which are not only the conventional power control system but also the recent environmental problem.

Recently, a high efficiency inverter has been required to operate an efficient power conversion device, and a discontinuous voltage modulation control method capable of achieving high efficiency due to a limitation of a topology and a performance limit of a switching device is widely used.

When a discontinuous voltage modulation method is applied to an inverter using an LC filter or an LCL filter, there arises a problem that a resonance current is generated in the output current and adversely affects the quality of the current. Therefore, there is a need for inverter control techniques capable of high efficiency and improving current quality.

On the other hand, the conventional method for reducing the resonance problem of the output current is divided into the passive damping method and the active damping method.

The passive damping technique can be constructed by connecting a damping resistor to the filter capacitor. This method can reduce the resonance of the current, but there is a continuous loss in the damping resistance and an additional heat dissipation system is required.

The active damping technique can be configured through software using a digital filter. Since the resonance of the current generated when the discontinuous voltage modulation method is used occurs at the moment when the modulation signal is discontinuously changed, the resonance problem of the current can not be solved by the active damping technique in which the resonance current should be extracted and controlled.

Related Prior Art Korean Patent Registration No. 10-1027937 entitled " Power Transducer in a Transformer-Type Grid-Connect Photovoltaic System ", Registered on Apr. 1, 2011) is available.

In an embodiment of the present invention, harmonic waves generated in an output voltage are reduced by injecting an n-th order harmonic such as a sixth harmonic wave or a twelfth harmonic wave into an offset voltage of a discontinuous voltage modulation method to reduce a resonance current generated in an output current A grid-connected power conversion apparatus and method based on a discontinuous voltage modulation method are provided.

The problems to be solved by the present invention are not limited to the above-mentioned problem (s), and another problem (s) not mentioned can be clearly understood by those skilled in the art from the following description.

The grid-connected power conversion apparatus based on the discontinuous voltage modulation method according to an embodiment of the present invention includes a DC voltage output from the DC power supply and an offset voltage for generating a first offset voltage based on a phase voltage command output from the current controller generator; A harmonic generator that is electrically connected to the phase locked loop and generates an nth-order harmonic (where n is an integer) based on a phase angle of the system output from the phase locked loop; And a control circuit for controlling the inverter circuit based on a polarity voltage command generated by adding the n-th order harmonic to the first offset voltage to generate a new second offset voltage and adding the second offset voltage to the phase voltage command And a signal controller for outputting a PWM signal.

The harmonic generator may estimate the phase angle of the system from the phase locked loop based on the three-phase system voltage of the inverter circuit and generate the n-th harmonic based on the phase angle of the system.

The harmonic generator may generate a phase angle of sixth harmonic by six times the phase angle of the system.

The signal control unit generates the second offset voltage by injecting the sixth harmonic in the first and last 15-degree intervals of the 60-degree interval in which the pole voltage command is fixed to the DC bus (+ DC bus or -DC-bus) can do.

The magnitude of the sixth harmonic may be a difference between a voltage magnitude of the DC bus and a magnitude of a voltage of the phase voltage command.

The harmonic generator may generate a twelfth harmonic phase angle by twelve times the phase angle of the system.

The signal control unit generates the second offset voltage by injecting the twelfth harmonic in the first and the last 7.5 degree intervals of the 60 degree interval in which the pole voltage command is fixed to the DC bus (+ DC bus or -DC bus) can do.

The size of the 12th harmonic may be a difference between a voltage magnitude of the DC bus and a magnitude of a voltage of the phase voltage command.

The signal control unit adds the second offset voltage to the phase voltage command to fix the pole voltage command to the DC bus (+ DC bus or -DC-bus), so that the disc voltage command is discontinuous Can be changed to a continuously varying voltage section to reduce the resonance current generated in the output current of the inverter circuit.

Wherein the inverter circuit includes: a plurality of switching elements for converting the direct-current voltage input from the direct-current voltage into an alternating-current voltage through the switching of an ON or OFF state based on the PWM signal; And a system interconnection filter having an inverter and a system side inductor and a filter capacitor and removing a high frequency component due to the switching of the on or off state of the plurality of switching elements from the AC voltage, It is possible to maintain either the ON state or the OFF state by not performing the switching operation for switching the on or off state during a 60-degree interval in which the voltage magnitude is greatest during one period of the voltage.

A method of controlling a grid-connected power conversion apparatus based on a discontinuous voltage modulation method according to an embodiment of the present invention includes a DC voltage output from a DC power supply and a DC voltage output from a current controller Generating a first offset voltage based on the phase voltage command; Generating, in the harmonic generator of the grid-connected power converter, an n-th order harmonic (n is an integer) based on a phase angle of the system output from the phase locked loop; Generating a second offset voltage by injecting the n-th order harmonic into the first offset voltage in the signal controller of the grid-connected power converter; And outputting a PWM signal for controlling the inverter circuit based on a polarity voltage command generated by adding the second offset voltage to the phase voltage command in the signal controller.

Wherein generating the n-th harmonic comprises: estimating a phase angle of the system from the phase locked loop based on a three-phase system voltage of the inverter circuit; And generating the n-th order harmonic based on the phase angle of the system.

Generating the n-th harmonic based on the phase angle of the system comprises: generating a sixth harmonic phase angle by six times the phase angle of the system; Or 12 times the phase angle of the system to generate a phase angle of the 12th harmonic.

The step of generating the second offset voltage may include injecting the sixth harmonic into the first and the last 15-degree intervals of the 60-degree interval in which the polar voltage command is fixed to the DC bus (+ DC bus or -DC-bus) And generating a second offset voltage.

The generating of the second offset voltage may include injecting the twelfth harmonic into the first and the last 7.5 degree intervals of the 60 degree interval in which the polar voltage command is fixed to the DC bus (+ DC bus or-DC bus) And generating a second offset voltage.

The details of other embodiments are included in the detailed description and the accompanying drawings.

According to an embodiment of the present invention, an n-order harmonic such as a sixth harmonic or a twelfth harmonic is injected into an offset voltage of a discontinuous voltage modulation method to reduce a harmonic generated in an output voltage, thereby reducing a resonant current generated in an output current can do.

According to one embodiment of the present invention, the efficiency of the grid-connected power converter can be improved by reducing the resonance current generated in the output current, and further, the quality of the output current can be improved.

FIG. 1 is a block diagram illustrating a grid-based power conversion apparatus based on a discontinuous voltage modulation method according to an embodiment of the present invention. Referring to FIG.
2 is a circuit diagram showing a detailed configuration of the inverter circuit of Fig.
3 is a circuit diagram showing a detailed configuration of the control circuit of FIG.
4 is a diagram showing an equivalent circuit of an LCL filter used as a grid interconnect filter in an embodiment of the present invention.
5 is a diagram illustrating a method of injecting a sixth harmonic into a first offset voltage to generate a new second offset in an embodiment of the present invention.
6 is a waveform diagram showing a modulation signal (polarity voltage command, second offset voltage) and an output current in the time domain in an embodiment of the present invention.
FIG. 7 is a diagram illustrating a comparison between a conventional 60-degree discontinuous voltage modulation method and a THD result of an output current according to an embodiment of the present invention.
8 is a flowchart illustrating a method of controlling a grid-connected power conversion apparatus based on a discontinuous voltage modulation method according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and / or features of the present invention, and how to accomplish them, will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

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

FIG. 1 is a block diagram illustrating a grid-based power conversion apparatus based on a discontinuous voltage modulation method according to an embodiment of the present invention. FIG. 2 shows a detailed configuration of the inverter circuit 120 of FIG. 1 3 is a circuit diagram showing the detailed configuration of the control circuit 130 of FIG.

Referring to FIGS. 1 to 3, the discontinuous voltage modulation type grid-connected power inverter 100 according to an embodiment of the present invention includes a DC power source 110, an inverter circuit 120, and a control circuit 130 ). ≪ / RTI >

The DC power source 110 may be a power source for outputting DC power and may include a renewable energy generation device such as a solar cell. In the case of the foregoing example, the solar cell can generate the direct current power by converting solar energy into electric energy.

The DC power supply 110 outputs the generated DC power to the inverter circuit 122. Also, the DC power supply 110 is not limited to generating the DC power by the solar cell. For example, the DC power may be generated by a fuel cell, a storage battery, an electric double layer condenser, a lithium ion battery, or the like.

Also, the DC power source 110 may generate the DC power by converting the AC power generated by the diesel engine generator, the micro gas turbine generator, the wind turbine generator, or the like into DC power and outputting the DC power.

The inverter circuit 120 may include a plurality of switching devices 210 and a grid interconnect filter 220 as shown in FIG.

The plurality of switching devices 210 may be switched on or off based on a PWM (Pulse Width Modulation) signal for controlling the inverter circuit 120 so that the direct current The voltage can be converted into an AC voltage.

In one embodiment of the present invention, the plurality of switching elements 210 do not perform a switching operation for switching the on or off state during a maximum period of 60 degrees during one period of a phase voltage, Or the OFF state of the second transistor.

In other words, the plurality of switching elements 210 may not switch only one of the three phases during the 60-degree interval, thereby maintaining the state of the corresponding one of the switching elements 210 on or off.

In an embodiment of the present invention, the power conversion apparatus 100 is operated based on the discontinuous voltage modulation scheme through the switching operation control described above, and the offset voltage is continuously changed through the control circuit 130 The resonance problem of the output current of the inverter circuit 120 can be solved. The control circuit 130 will be described later with reference to Fig.

The grid coupling filter 220 may include an inverter and a system side inductor L _i , L _g and a filter capacitor C _f . That is, the grid link filter 220 may be implemented as an LCL filter. Alternatively, the grid coupling filter 220 may be implemented as an LC filter.

The equivalent circuit of the LCL filter used as the grid interconnect filter 220 is shown in FIG. That is, the LCL filter may be represented by an inverter and a system side inductor (L _i , L _g ) and a filter capacitor (C _f ). When the LCL filter is used, a resonance phenomenon occurs by L and C, and a resonance band is formed around the resonance frequency (f _resonant ).

If the harmonic frequency generated by the discontinuous voltage modulation method applied to the embodiment of the present invention is overlapped with the resonance band, a problem that the output current of the inverter circuit 120 resonates may occur. Therefore, in one embodiment of the present invention, as described above, the offset voltage is continuously changed through the control circuit 130, which will be described later, to solve the resonance problem of the output current of the inverter circuit 120 .

The resonance frequency can be expressed by Equation (1) below.

[Equation 1]

Where f _resonant is the resonant frequency, L _i is the inverter side inductor, L _g is the system side inductor, and C _f is the filter capacitor.

The grid coupling filter 220 can remove high frequency components due to the switching of the on / off states of the plurality of switching elements 210 from the AC voltage.

The control circuit 130 may include an offset voltage generator 310, a harmonic generator 320, and a signal controller 330, as shown in FIG. In addition, the control circuit 130 may further include a current controller 301 and a phase locked loop (PPL) 302.

The offset voltage generator 310 generates a first offset voltage based on the DC voltage V _dc output from the DC power supply 110 and the phase voltage command V ^* _abcs output from the current controller 301 do.

Here, the phase voltage command is a sinusoidal (sinusoidal) signal. In addition, the first offset voltage V _offset may have a waveform as shown on the left side of FIG. That is, the first offset voltage V _offset may have a discontinuous waveform.

The harmonic generator 320 is electrically connected to the phase locked loop 302 and is connected to the phase locked loop 302 based on the phase angle? Of the system (three phase power system) order harmonic (n is an integer).

That is, the harmonic generator 320 estimates the phase angle? Of the system 101 from the phase locked loop 302 based on the three-phase system voltage V _abc of the inverter circuit 120, The n-th order harmonic can be generated based on the phase angle [theta] of the system 101. [

In one embodiment, the harmonic generator 320 may generate a phase angle of the sixth harmonic by six times the phase angle? Of the system 101.

In another embodiment, the harmonic generator 320 may generate a twelfth order harmonic phase angle by twelve times the phase angle? Of the system 101.

The signal controller 330 generates the second offset voltage by injecting the n-th harmonic into the first offset voltage, and generates a second offset voltage based on the polarity voltage command, A signal can be output.

Here, the pole voltage commands V ^* _an , V ^* _bn , and V ^* _cn may be obtained by _multiplying the phase voltage commands V ^* _as , V ^* _bs , and V ^* _cs by the second offset voltage (V _offset ).

&Quot; (2) "

V ^* _an , V ^* _bn , and V ^* _cn represent the polarity voltage command, V ^* _as , V ^* _bs , V ^* _cs represent the phase voltage command, and V _offset represents the second offset voltage, respectively.

At this time, the n-th harmonic wave may be generated as a sixth harmonic wave by the harmonic generator 320. In this case, as shown in the right part of FIG. 5, the signal controller 330 sets the polarity voltage command V ^* _abcn to the DC bus (DC bus or -DC-bus) And the sixth offset voltage V _{new_offset} may be generated by injecting the sixth harmonic in the first and last 15 degrees intervals.

Here, the magnitude of the sixth harmonic may be a difference between a voltage magnitude of the DC bus and a magnitude of a voltage of the phase voltage command (V ^* _abcs ).

Further, unlike the second offset voltage (V _{new _offset)} is the first offset voltage (V _offset) according to the injection of the sixth-order harmonics, varied discontinuously, and can have a waveform that changes continuously. The second offset voltage (V _{new _offset)} can be expressed as Equation (3).

&Quot; (3) "

Here, V _{new _offset} a second offset voltage, V _dc is the DC voltage, V ^* _{as, bs} ^* V is the voltage command, ₃₆₀ ω is the angular speed of 360Hz, t represents the time, respectively.

Therefore, according to the embodiment of the present invention, it is possible to reduce harmonics of a large number of voltages generated at the instant when the first offset voltage V _offset is discontinuously changed, thereby reducing the resonance current generated in the output current .

Note that, in one embodiment of the invention, such as the pole voltage command (V ^* _abcn) is said second offset voltage (V _{new _offset)} is ii of Figure 6, it can appear as i) in Fig. 6) And the output current of the inverter circuit 120 may be represented as iii) in FIG. In particular, in the clamping moment of FIG. 6, a harmonic is generated due to a discontinuous change of the offset voltage in the prior art, and a resonance problem of the output current occurs. However, according to the embodiment of the present invention, the offset voltage (V _{new _offset)} may be due to change continuously confirmed that the generation of harmonics reduced, and can solve the problem of the output resonant current of the inverter circuit 120 through it.

The n-th order harmonic may be generated by the harmonic generator 320 in the twelfth order harmonic. In this case, the signal controller 330 sets the 12- _th order voltage _Vc ^* in the first and the last 7.5-degree intervals of the 60-degree interval in which the pole voltage command V ^* _abcn is fixed to the DC bus (+ DC bus or _-DC- It can be injected into the harmonic generating the second offset voltage (V _{new _offset).}

Here, the size of the twelfth harmonic may be a difference between the voltage magnitude of the DC bus and the largest voltage magnitude of the phase voltage command.

Further, unlike the second offset voltage (V _{new _offset)} is the first offset voltage (V _offset) according to the injection of the 12 th harmonic, changes discontinuously, and can have a waveform that changes continuously. The case where the the 12th-order harmonic injection, the second offset voltage in the equation 3, "ω ₃₆₀ t" a "ω ₇₂₀ t" in, "π / 12, 3π / 12, 4π / 12" and " π / 24, 3π / 24, 4π / 24 ", and the like.

Therefore, according to the embodiment of the present invention, it is possible to reduce harmonics of a large number of voltages generated at the instant when the first offset voltage V _offset is discontinuously changed, thereby reducing the resonance current generated in the output current .

To this end, the signal controller 330 adds the second offset voltage to the phase voltage command so that the pole voltage command V ^* _abcs is fixed to the DC bus (-DC bus or -DC-bus) It is possible to reduce the resonance current generated in the output current of the inverter circuit 120 by varying the voltage section that varies discontinuously for every predetermined angle (60 degrees) by the discontinuous voltage modulation method to a continuously varying voltage section.

The conventional 60-degree discontinuous voltage modulation method and THD (Total Harmonic Distortion) of the output current according to an embodiment of the present invention are shown in FIG. That is, as shown in FIG. 7, the THD of the output current according to an embodiment of the present invention is smaller than the THD of the output current using the conventional 60-degree discontinuous voltage modulation method, .

8 is a flowchart illustrating a method of controlling a grid-connected power conversion apparatus based on a discontinuous voltage modulation method according to an embodiment of the present invention.

3 and 8, in step 810, the offset voltage generator 310 generates a DC voltage V _dc of the DC power source and a phase voltage command V ^* _abcs output from the current controller 301, And generates a first offset voltage V _offset based on the first offset voltage V _offset .

Next, in step 820, the harmonic generator 320 generates an n-th order harmonic based on the phase angle? Of the system output from the phase locked loop 302.

At this time, the harmonic generator 320 estimates the phase angle? Of the system from the phase locked loop 302 based on the three-phase system voltage of the inverter circuit, Thereby generating the n-th order harmonic.

For example, the harmonic generator 320 can generate a phase angle of the sixth harmonic by six times the phase angle of the system. Alternatively, the harmonic generator 320 may twiddle the phase angle &thetas; It may also generate a phase angle of harmonics.

Next, the signal control unit 330 in step 830 generates a new second offset voltage (V _{new _offset)} is injected into the n-th harmonic to said first offset voltage (V _offset).

At this time, the signal controller 330 sets the _{sixth harmonic} ( _Vdd ) in the first and last 15 degree intervals of the 60 degree interval in which the pole voltage command V ^* _abcn is fixed to the DC bus (+ DC bus _or- So as to generate the second offset voltage.

Alternatively, the signal controller 330 may control the polarity of the 12-th (n + ₁ ) -th cycle in the first and the last 7.5-degree intervals of the 60-degree interval in which the pole voltage command V ^* _abcn is fixed to the DC- And the second offset voltage may be generated by injecting harmonics.

Next, based upon the signal control unit 330 is the pole voltage command (V ^* _abcn) is generated by adding the second offset voltage (V _{new _offset)} to the phase voltage command (V ^* _abcs) in step 840, And outputs a PWM signal for controlling the inverter circuit.

Embodiments of the present invention include computer readable media including program instructions for performing various computer implemented operations. The computer-readable medium may include program instructions, local data files, local data structures, etc., alone or in combination. The media may be those specially designed and constructed for the present invention or may be those known to those skilled in the computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape, optical recording media such as CD-ROMs and DVDs, magneto-optical media such as floppy disks, and ROMs, And hardware devices specifically configured to store and execute the same program instructions. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by the scope of the appended claims and equivalents thereof.

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, Modification is possible. Accordingly, the spirit of the present invention should be understood only in accordance with the following claims, and all equivalents or equivalent variations thereof are included in the scope of the present invention.

101: Three phase power system
110: DC power source
120: inverter circuit
130: control circuit
210: a plurality of switching elements
220: Grid filter
301: Current controller
302: phase locked loop
310: Offset voltage generator
320: Harmonic generator
330: Signal control section

Claims (15)

An offset voltage generator for generating a first offset voltage based on a DC voltage output from the DC power supply and a phase voltage command output from the current controller;
A harmonic generator that is electrically connected to the phase locked loop and generates an nth-order harmonic (where n is an integer) based on a phase angle of the system output from the phase locked loop; And
A second offset voltage is generated by adding the n-th harmonic to the first offset voltage, and a second offset voltage is generated by adding the second offset voltage to the phase voltage command to generate a PWM A signal control unit
And a second power supply connected between the first power supply and the second power supply.
The method according to claim 1,
The harmonic generator
Estimating a phase angle of the system from the phase locked loop based on the three-phase system voltage of the inverter circuit, and generating the n-th harmonic based on the phase angle of the system. Grid - connected power converter.
3. The method of claim 2,
The harmonic generator
And a phase angle of a sixth harmonic is generated by six times the phase angle of the system.
The method of claim 3,
The signal control unit
And the sixth offset voltage is generated by injecting the sixth harmonic in the first and last 15-degree intervals of the 60-degree interval in which the pole voltage command is fixed to the DC bus (+ DC bus or -DC-bus) Based on a discrete voltage modulation scheme.
5. The method of claim 4,
The size of the sixth harmonic is
Wherein the difference between the voltage magnitude of the DC bus and the maximum voltage magnitude of the phase voltage command is a difference value between the voltage magnitude of the DC bus and the phase voltage command.
3. The method of claim 2,
The harmonic generator
And a twelfth-order harmonic phase angle is generated by 12 times the phase angle of the system.
The method according to claim 6,
The signal control unit
And the 12th-order harmonic is injected into the first and the last 7.5-degree intervals of the 60-degree interval in which the polar voltage command is fixed to the DC bus (+ DC bus or -DC-bus), thereby generating the second offset voltage Based on a discrete voltage modulation scheme.
8. The method of claim 7,
The size of the twelfth order harmonic
Wherein the difference between the voltage magnitude of the DC bus and the maximum voltage magnitude of the phase voltage command is a difference value between the voltage magnitude of the DC bus and the phase voltage command.
The method according to claim 1,
The signal control unit
And the second offset voltage is added to the phase voltage command so that the pole voltage command is fixed to the DC bus (+ DC bus or -DC-bus), whereby the voltage section discontinuously changing at every predetermined angle by the discontinuous voltage modulation method To a continuously varying voltage section to reduce the resonance current generated in the output current of the inverter circuit, based on the discontinuous voltage modulation method.
The method according to claim 1,
The inverter circuit
A plurality of switching elements for converting the direct-current voltage input from the direct-current voltage into an alternating-current voltage through the switching of the on or off state based on the PWM signal; And
An inductor and a system side inductor and a filter capacitor, and a grid interconnect filter for removing high frequency components due to the switching of the on / off states of the plurality of switching elements from the AC voltage,
Lt; / RTI >
The plurality of switching elements
Wherein the switching operation for switching the on state or the off state is not performed during one cycle of the phase voltage during the maximum 60 degree interval so that either the on state or the off state is maintained. A system - based grid - connected power converter.
Generating a first offset voltage based on a DC voltage output from a DC power supply and a phase voltage command output from a current controller in an offset voltage generator of a grid-connected power conversion apparatus;
Generating, in the harmonic generator of the grid-connected power converter, an n-th order harmonic (n is an integer) based on a phase angle of the system output from the phase locked loop;
Generating a second offset voltage by injecting the n-th order harmonic into the first offset voltage in the signal controller of the grid-connected power converter; And
Outputting a PWM signal for controlling the inverter circuit based on a polarity voltage command generated by adding the second offset voltage to the phase voltage command in the signal control section
And a control unit for controlling the power of the grid-connected power conversion apparatus based on the discontinuous voltage modulation method.
The method according to claim 1,
The step of generating the n-
Estimating a phase angle of the system from the phase locked loop based on a three-phase system voltage of the inverter circuit; And
Generating the n-th order harmonic based on the phase angle of the system
And a control unit for controlling the power of the grid-connected power conversion apparatus based on the discontinuous voltage modulation method.
13. The method of claim 12,
The step of generating the n-th order harmonic based on the phase angle of the system
Generating a sixth harmonic phase angle by multiplying the phase angle of the system by six; or
Generating a twelfth harmonic phase angle by twelve times the phase angle of the system
And a control unit for controlling the power of the grid-connected power conversion apparatus based on the discontinuous voltage modulation method.
14. The method of claim 13,
The step of generating the second offset voltage
Generating the second offset voltage by injecting the sixth harmonic in the first and last 15-degree intervals of the 60-degree interval in which the polar voltage command is fixed to the DC bus (+ DC bus or -DC-bus)
And a control unit for controlling the power of the grid-connected power conversion apparatus based on the discontinuous voltage modulation method.
14. The method of claim 13,
The step of generating the second offset voltage
Generating the second offset voltage by injecting the twelfth order harmonic into the first and the last 7.5 degree intervals of the 60 degree interval in which the pole voltage command is fixed to the DC bus (+ DC bus or -DC-bus)
And a control unit for controlling the power of the grid-connected power conversion apparatus based on the discontinuous voltage modulation method.

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