KR101248593B1 - Photoelectric cell system with compensating wattless power and operating method of it - Google Patents

Abstract

PURPOSE: A photovoltaic power generation system with a reactive power compensation function and an operation method thereof are provided to implement small size and light weight by generating photovoltaic maximum power, compensating reactive power and improving power quality without an additional apparatus. CONSTITUTION: A photovoltaic module(110) converts optical energy into electric energy. An inverter(160) converts DC voltage inputted from the photovoltaic module into AC voltage. A filter unit removes a noise component in the output of the inverter. The filter unit transfers the output of the inverter in which the noise component is removed to an output end. A PLL(Phase Locked Loop) control unit(200) PWM controls the operation of the inverter in a PLL technique with respect to the measured value of the output end.

Description

Photoelectric Cell System with Compensating Wattless Power and Operating Method of it}

The present invention relates to a photovoltaic power generation system having a function of compensating reactive power in conjunction with a grid, and a method of operating the same.

In the past decades, the demand for renewable energy has increased significantly due to the shortcomings of fossil fuels and the greenhouse effect. Of the various types of renewable energy sources, solar and wind energy have become the most promising and attractive due to advances in power electronic technology. Photovoltaic (PV) power supplies are currently used in a variety of applications with the advantage of no maintenance and contamination. In particular, the field of solar energy power has grown consistently over the last few years due to increased efficiency of solar cells, improved manufacturing technology and economies of scale. Increasingly, PV modules have been connected to and will be connected to utility systems in many countries. The world's largest PV power plant is now larger than 100 MW.

However, the output of the PV array depends on solar irradiation and weather conditions. More importantly, the high initial cost and limited lifetime of PV panels are required to extract as much power from them as possible. Therefore, a maximum power point tracking (MPPT) technique must be implemented to achieve maximum efficiency of the PV array in the DC / DC converter. Several algorithms have been developed to achieve MPPT technology.

Due to the capacity of the PV system to grow significantly, the influence of PV modules on the power grid cannot be ignored. They cause problems with the system, such as flickering and increasing harmonics, and worsen the stability of the power system. Both the capacity increase of PV arrays and the maintenance of power quality are necessary to comply with the technical requirements for PV systems such as function and harmonic current regulation. Especially when large PV modules are connected to the grid, there is a possibility that the effects on the grid will certainly be severe. Therefore, when PV modules are connected to the power grid, the requirements for system operation and system stability under fault conditions will be strengthened.

The increasing use of electrostatic source converters, such as rectifiers and switched mode power supplies, causes the injection of harmonic currents into the distributed system. Current harmonics cause voltage distortion, current distortion and unstable operation of the power system. Harmonic mitigation measures therefore play an important role in grid-connected PV systems. In addition to the active power supply, the PV inverter can be controlled to provide the harmonic current required by the nonlinear load, allowing the current on the grid side to be close to the sine wave.

In general, a grid-connected photovoltaic power generation system is composed of a solar cell, an MPPT converter, and an inverter for supplying power generated from the solar cell to the grid. The existing system simply supplies the electricity generated from the solar power to the system by the MPPT control of the converter (or inverter) and can be used only in the daytime with insolation, so that the utilization rate (5-6 hours / day) is high compared to the high installation cost. In addition to the very low power, when applied to non-linear and power factor loads such as homes and office buildings, the power factor of the system is rather deteriorated due to the active power support by solar power generation.

In general, when a power factor occurs in a system, the supply power requirement of the system increases because the same active power demand must be supplied considering reactive power. It is not a big problem for the system because of the small size of the currently installed system, but as mentioned above, in view of the fact that the prevalence is greatly expanded, there may be a problem due to the grid connection. In addition, the proliferation of non-linear loads, such as computers and modern electronic devices, leads to problems such as power quality of the system, such as increased harmonics and reduced power factor, as well as malfunction of electrical equipment and increased rated capacity of the power converter.

1. Prior Document 1: Korean Patent Publication No. 2009-0124515 (2009.12.03) 2. Prior Document 2: Republic of Korea Publication No. 2009-0015391 (2009.02.12)

The present invention is to provide a photovoltaic power generation system that provides an effective function as a system even in a non-power generation period such as night.

More specifically, the photovoltaic power generation system is composed of a solar cell that generates power by using sunlight as an energy source and a current controlled voltage source inverter (CCVSI) that supplies the generated power to the grid, and operates in day mode and night mode. In night mode, it performs reactive power compensation functions such as harmonic reduction and power factor improvement of the system.In daylight mode with solar radiation, the solar power generation system which performs MPPT control and reactive power compensation function simultaneously to obtain maximum output from solar cells To provide.

Photovoltaic power generation system according to an aspect of the present invention, a photovoltaic module for converting light energy into electrical energy; An inverter for converting a DC voltage input from the photovoltaic module into an AC voltage; A filter unit for transmitting the output of the inverter to an output terminal by removing a noise component; And a PLL controller configured to PWM control the operation of the inverter by the PLL method for the output stage measured value.

Here, the PLL control unit may perform a reactive power compensation function of harmonic reduction and power factor improvement of a system in a non-power generation period, and control to perform a reactive power compensation function of a power generation during a power generation period.

Here, the PLL controller may turn off the switching elements of the inverter while the output terminal is connected to the grid during the non-power generation period of the photovoltaic module.

The PLL controller may include: a PWM driver for driving the inverter in a PWM manner; A PLL detector for detecting an electrical signal of the three-phase output terminal; An abc / dq signal generator configured to apply a phase detection value (θ) of the PLL detector to perform a dq conversion of a three-phase variable; A dq-frame controller for generating a drive signal of the PWM driver using a dp current signal determined from the converted dq and a dp voltage signal generated by the PLL detector; and generating a drive signal of the dq-frame controller. It may include a reference signal generator for providing the necessary reference signal.

The apparatus may further include a boost converter for boosting the voltage produced by the photovoltaic module and transferring the voltage to the inverter.

Here, the filter unit may include a reactor for limiting a current at the output terminal and a capacitor for blocking high frequency components.

According to another aspect of the present invention, there is provided a method of operating a solar power generation system, the method comprising: converting light energy into electrical energy in a photovoltaic module; Converting a DC voltage into an AC voltage in an inverter input from the photovoltaic module; Transmitting an output of the inverter to an output stage by removing a noise component from a filter unit; PWM controlling the operation of the inverter by the PLL method for the output stage measured value,

During the non-power generation period, blocking the photovoltaic module; Performing a reactive power compensation function of the connected grid power may be performed.

Here, in the blocking of the photovoltaic module, the switching elements of the inverter may be turned off.

The controlling of the PWM may include detecting a potential difference between two phases and a three-phase current value among the three phases of the output terminal; Generating an abc / dq signal by performing dq conversion of a three-phase variable by applying the detection values and the phase detection value θ; Generating a reference signal; And generating the PWM driving signal using the dp current signal determined from the converted dq, the dp voltage signal generated by the PLL detector, and the reference signal.

The blocking of the photovoltaic module may be performed using the inverter, and the performing of the reactive power compensation function of the connected grid power may be performed using the filter unit.

When implementing the solar power generation system of the present invention according to the above configuration, there is an advantage to provide an effective function as a system even in a non-power generation period such as night.

For example, the proposed system can improve the power quality of the system by using only one CCVSI, which can receive power in both directions, as well as the maximum power production of photovoltaic power generation as well as power factor improvement and harmonic reduction. This can maximize the utilization rate (24 / day) compared to the existing system that operates only during the day, and can perform maximum solar power generation, reactive power compensation, and power quality improvement simultaneously without additional equipment, thereby improving efficiency and miniaturization. Can be achieved.

1 is a block diagram showing a solar power system according to an embodiment of the present invention.
FIG. 2 is a detailed block diagram illustrating an associated portion of a boost converter, an inverter, and a filter unit in the solar power generation system of FIG. 1.
3 is a detailed block diagram of a PWM driver provided in the PLL control unit of the solar power generation system of FIG.
4 is a graph showing I / V and P / V characteristics of PV module output, respectively.
5 is a flow diagram illustrating a method in accordance with an incremental conductance algorithm.
6 is a detailed block diagram illustrating the boost converter and MPPT control circuit portion of FIG.
FIG. 7 is a detailed block diagram illustrating an embodiment of the PLL detector of FIG. 1. FIG.
FIG. 8 is a detailed block diagram illustrating an embodiment of the dq-frame controller of FIG. 1. FIG.
9 is a block diagram illustrating the solar power generation system of FIG. 1 connected to various grid loads.
10 is a flowchart illustrating a method of operating a photovoltaic power generation system according to an embodiment of the present invention.
11 is a simulation graph showing inverter current, nonlinear load current and grid current with harmonic compensation.
12 is a simulation graph showing a harmonic order diagram according to total harmonic distortion.

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

Photovoltaic power generation system according to an embodiment of the present invention shown in Figure 1, a photovoltaic module 110 for converting light energy into electrical energy; An inverter (160) for converting a DC voltage input from the photovoltaic module into an AC voltage; A filter unit for transmitting the output of the inverter 160 to an output terminal by removing a noise component; And a PLL controller 200 for PWM controlling the operation of the inverter in a PLL manner with respect to the output stage measured value.

In addition, the photovoltaic power generation system may further include a booster converter 120 for boosting the voltage produced by the photovoltaic module and transferring the voltage to the inverter.

The PLL control unit 200 may be operated to perform reactive power compensation for reducing harmonics and improving power factor of the system during non-power generation periods such as nighttime or bad weather, and to perform reactive power compensation for generation power during the daytime generation period. have. To this end, in the above-described photovoltaic power generation system of the present embodiment, only a component capable of compensating for reactive power can be connected to the grid in a non-power generation period, and the photovoltaic module can be disconnected from the grid. As the component that performs the function of compensating the reactive power, the filter unit having a relatively large amount of inductor or capacitor component is representative.

Although separate switch elements may be provided for grid connection of the filter unit and grid shutdown of the photovoltaic module during the non-power generation period, a switch element belonging to the inverter (inverter generally includes a switch element for converting direct current into alternating current). It has the advantage of cost reduction.

In this case, the PLL controller 200 may turn off all switching elements (switching transistors) for DC-AC conversion of the inverter 160 while the output terminal is connected to the grid during the non-power generation period of the photovoltaic module. The control of the method can be performed.

The photovoltaic power generation system (PV system) shown in FIG. 1 is in a state of being connected to a distributed network, and the figure illustrates a schematic diagram of disconnection of the system.

In the case of grid-connected PV systems, the photovoltaic (PV) array 110 is connected to the grid via a power electronic inverter that converts DC power to AC power. Many other topologies have been developed and used over the last few decades. Dual-string topologies are the most common type of PV installation in the past.

Some strings connect voltage boost with their own DC / DC converters and are connected to the DC bus. At that time, a common DC / AC inverter is used for integration with the utility. The advantage of this topology is the fact that it has independent control of the power supply, better protection, safer during installation and maintenance, lower cost and so on.

Maximum power point tracking (MPPT) technology is implemented in the DC / DC converter to achieve maximum efficiency of the PV modules. DC / DC converter topology commonly used by boost and chuck converters. However, boost converters offer advantages over chuck converters because of blocking diodes that can prevent reverse currents in PV arrays. Incremental conductance (IncCond) method is used for boost converter control.

The output of boost converter 120 is connected to central inverter 160 via a DC transmission line. DC transmission lines are considered to be short circuits at the same distance from both boost converters. Multi-string PV arrays are connected together at certain points. The DC common bus is then connected to the dc end of the dc connection capacitor C and the dc side of a three phase voltage source inverter (VSI). The DC-connected capacitor tries to regulate the voltage on the DC side of the inverter. And the capacity depends on the ripple requirement of the capacitor. Based on the sinusoidal-triangle modulation strategy, the VSC is controlled. The connection resistor connects a point of common coupling (PCC) to the distributed end of the VSC's AC side. The connection resistor includes the resistance of the IGBT. Filter capacitor C _f provides a low impedance path to the current harmonics produced by the inverter.

A distributed network is just an example of simplifying a real distributed network. The distribution network comprises a transformer T _r1 , a load, two distribution lines and a capacitor C ₁ . T _r1 steps the network voltage down to an appropriate level for the PV system. The high voltage side of T _{r1 has} a Y-shaped connection and is firmly grounded. In addition, three-phase loads are connected by lines at locations between the PCC and the system. The inductor and resistance of the distributed line between the PCC and the load are represented by L ₁ and R ₁ , respectively. Similarly, R ₂ and L ₂ represent the inductor and resistance of the line between the load and the grid, respectively. Capacitor C ₁ is used to improve the load power factor and always provide it to the load.

An overview of a multi-string grid-connected photovoltaic (PV) system with the function of harmonic compensation is illustrated in FIG. 2. However, transformers are not represented in hardware configurations because of the fact that large transformers are not needed at low voltage levels. However, a variable transformer is needed to bring down the voltage to the commercial voltage. Moreover, the transmission line is not taken into account because the resistor and inductor are included in both the LC filter and the connecting line in this machine. Since the PV array is not available in the laboratory, a controllable DC power source is used instead to mimic the characteristics of the PV array. In parallel with the three-phase R load, the three-phase diode rectifier is connected with a nonlinear load.

FIG. 2 illustrates in detail the associated part of the boost converter, the inverter, and the filter unit in the solar power generation system of FIG. 1. The filter unit may include a reactor L1 for limiting a current at the output terminal and an output capacitor C0 for removing high frequency noise. In addition, according to a viewpoint, the capacitor C1 connected to the input terminal of the inverter 160 of FIG. 1 may also be defined to be included as a filter in its function.

3 illustrates a detailed structure of the PWM driver included in the PLL controller of the solar power generation system of FIG. 1. The illustrated PWM driver operates as a sinusoidal-triangular modulation control block. The switching operation of the switching transistors of the inverter of FIG. 2 may be controlled in a PWM manner by signals output from the PWM driver of FIG. 2.

Next, we will look at the maximum power point tracking and PLL control algorithm of the photovoltaic power generation system.

Performance and reliability are of paramount importance in PV systems with significant power devices and voltage levels. Therefore, proper modeling and control design allows the progress of hardware execution. The entire PV system can be divided into several subsystems to facilitate control individually. First, in a multi-string grid-connected photovoltaic (PV) system, an equivalent circuit is made to represent the PV array.

Maximum power point tracking (MPPT) control is implemented to ensure high efficiency of distributed generation in the boost converter. MPPT algorithm and block model are discussed. Three-phase inverters convert DC power to distributed networks and harmonic AC power. Inverter current control is so critical because it determines how well harmonics are compensated. This section deals with voltage power inverter (VSI) control. For the purpose of analysis and control, the VSI pulse width modulation and control is synchronized with a phase locked loop (PLL) to the distributed network voltage. Three-phase AC voltages and currents are then converted into dq-axis counterparts to make design and control easier. In this regard, harmonic components of the nonlinear load are detected. We present and explain a time-domain harmonic extraction method. System differential equations and eigenvalues are derived to analyze the stability of the system. Determine system parameters that affect system stability.

Next, we will look at the control method using the maximum power point tracking, and in particular, the incremental conductance algorithm. PV arrays exhibit nonlinear characteristics. 4 shows the I / V and P / V characteristics of the PV module output, respectively. The power conversion ratio of PV panels is not so high yet. Therefore, it is important to extract as much power as possible from PV panels.

Many kinds of MPPT algorithms have been developed and put into application. The most widespread is the incremental conductance method (IncCond) of constant voltage tracking (CVT), perturbation and observation method (P & O). The dual incremental conductance method has advantages over others, such as high tracking accuracy and no vibration around the MPP. A flowchart of the method according to the incremental conductance algorithm is shown in FIG. 5.

As can be seen in the flowchart shown, the MPP can be tracked by comparing the instantaneous conductance (I / V) with the incremental conductance (ΔI / ΔV). V _ref is the reference voltage and is equal to V _MPP in _MPP . Once the MPP is reached, the operation of the PV array is maintained at that point unless there is a change in ΔI indicating a change in solar irradiation or weather conditions. The algorithm decreases or increases V _ref to track the new MPP.

6 is a schematic diagram of a boost converter MPPT control circuit, and the MPPT execution process will be described with reference to this drawing.

The control algorithm is executed in the boost converter to provide the DC voltage to the voltage source inverter. The boost converter topology has advantages over buck converters for MPPT applications for the following reasons. First, the effective current through the inductor is less than that of a buck converter. For power IGBT and driver selection, the current rating is lower in the boost converter than in the buck converter. The capacity of a solar power system depends on light. At night, current can flow back into the photovoltaic cell from the grid, where leakage losses can cause massive damage. Reverse current blocking diodes are effective to prevent reverse currents in the boost converter, and diodes help to avoid reverse currents with reverse current blocking diodes. Compared to natural frequencies that do not attenuate, boost transducers exhibit better dynamics than buck transducers. In general, it offers advantages in terms of wider bandwidth and smaller resonance because of the small input capacitance of the boost converter.

Next, a control process according to a phase-locked loop will be described.

The PLL controller 200 of FIG. 1 includes a PWM driver 220 for driving the inverter in a PWM manner; A PLL detector 230 for detecting an electrical signal of the three-phase output terminal; An abc / dq signal generator 240 for applying a phase detection value θ of the PLL detector 230 to perform dq conversion of a three-phase variable; A dq-frame controller 280 for generating a drive signal of the PWM driver using the dp current signal determined from the converted dq and the dp voltage signal generated by the PLL detector: and driving of the dq-frame controller It may include a reference signal generator 270 for providing a reference signal required for signal generation.

Phase locked loop technology is a common method of synthesizing the phase and frequency information of an electrical device, especially when connected to power electronics. A simple way to obtain phase information is to detect the zero crossing of a commercial voltage. However, since zero crossings can only be detected in each half period of commercial frequency, phase tracking is not possible between detection points, and fast dynamic performance cannot be obtained. We present an improved method using the integration of the input waveforms. In a three-phase system, the dq transform of the three-phase variable has the same characteristics, and the pLL system can be executed using the dq transform.

The PLL detector 230 may include a potential sensor 315 for detecting a potential between any two lines of the three-phase output lines of the inverter (the redundant sensing is not performed because the potential between the other two lines is substantially the same) and the Three-phase current sensors 311, 312, and 313 for sensing the current of each three-phase output line may be included.

7 is a block diagram illustrating an embodiment of the PLL detector 230 that calculates v _d , v _q, and θ from the above-described sensed values. In FIG. 7, Van, Vbn, and Vcn may be obtained by calculating sensing values of the three-phase current sensors 311, 312, and 313 of FIG. 1 and sensing values of the potential sensor 315.

Here, the three-phase system voltage may be expressed in a synchronous reference frame. The transformation matrix T _S (θ) may be expressed by Equation 1 below.

The three-phase voltage is converted into two DC quantities on the dq axis. The amount v _sq of the next q-axis is compared with a reference value of 0 and produces an error signal. In the steady state, the reference value of the q-axis is set to "0". Thus, only the d-axis component exists to represent the amount of AC while each frequency is equal to the system frequency. Error passes through the loop filter to each frequency. The phase transition θ is induced by the integration of each frequency. By properly designing the loop filter K _i (s), the PLL frequencies ω and phase θ can be accurately tracked.

There are various ways to design loop filters. The second order loop is commonly used as a good tradeoff between filter performance and system stability. The proportional-integral (PI) filter for the second order loop is given by Equation 2 below.

Where K _p and τ represent the gain and time constant of the PI filter, respectively. Dynamic performance is considered in the design of PI filters that satisfy fast tracking and good filtering characteristics.

Next, we will look at the VSC current control process.

The voltage and current in the PV modules are measured and used to calculate the active power output of the generated PV modules. For a two string PV system, the actual power is calculated as in Equation 3 below.

The reactive power Q _ref introduced into the distributed network is set to "0". This allows the power factor of the distributed network to be adjusted. The current reference on the dq axis is derived as shown in Equation 4 below.

Where V _sd and V _sq represent the voltage on the dq axis at the point of common coupling (PCC). The current control algorithm is designed based on Equations 5 and 6 below.

Where i _d and i _q are the currents flowing to the PCC, respectively, and R and L are the resistors and inductors of the LC filter connected to the VSC and the dispersion network, respectively. m _d and m _q are the modulation indices on the dq axis. The current i _d and i _q combine due to the Lω factor. In order to separate the operation of the current, Equations 5 and 6 are given as Equations 7 and 8 below.

Where u _d and u _q are the two new inputs. By substituting m _d and m _q in Equations 7 and 8 into Equations 5 and 6, Equations 9 and 10 can be obtained.

Equations 9 and 10 express two linear systems in which i _d and i _q can be controlled by u _d and u _q . FIG. 8 is a block diagram illustrating an outline of dq axis current control of the dq-frame controller of FIG. 1.

를 처리하는 보정장치의 출력K_d(s) 임을 보여준다. 마찬가지로, u_q는 오차신호

를 처리하는 보정장치의 출력 K_q(s) 이다. 변조 신호 m_d와 m_q를 생성하기 위해서는,

는 DC 연결 전압 v_dc에서 그리고 i_q를 분리하는 feed-forward 신호로 채택된다. feed-forward 보상은 PV 시스템 안정성을 강화하기 위하여 시스템의 나머지에서 PV 어레이를 분리한다. PWM 변조 신호는 m_a, m_b, m_c로 m_d와 m_q의 변환에 의해 일어난다. 전압원 인버터를 위한 펄스는 정현 삼각형 변조를 사용해서 점화된다.
In FIG. 8, the control signal u _d is an error signal.

It shows that the output K _d (s) of the compensator. Similarly, u _q is the error signal

The output K _q (s) of the compensator that processes. To generate modulated signals m _d and m _q ,

Is adopted as the feed-forward signal at the _dc connection voltage v _dc and for separating i _q . Feed-forward compensation separates the PV array from the rest of the system to enhance PV system stability. The PWM modulated signal is generated by the conversion of m _d and m _q into m _a , m _b and m _c . The pulses for the voltage source inverter are ignited using sinusoidal modulation.

Next, a process of compensating harmonics of the photovoltaic power generation system having the above-described configuration will be described.

9 shows the solar power generation system of FIG. 1 in a state connected to various grid loads. The PV system in the illustrated state not only supplies active power to the power system but can also compensate for harmonics generated by nonlinear loads.

The grid voltage is assumed to be balanced and simulated with the ideal voltage source. Solar arrays and systems are powering diode rectifiers in parallel with resistive loads. There are many harmonics in the load current, and the inverter is controlled to provide harmonic compensation.

The DC-connected capacitor controls the DC input voltage for the voltage source inverter (VSI). The value of the capacitor depends on the power variation on the three phase side, since all power comes from the PV array through the DC-connected capacitor. The LC filter is always present with a voltage source inverter (VSI) used to eliminate higher voltage harmonics. However, the LC filter cannot be eliminated due to the fact that it determines the output voltage waveform of the VSI, which is important on the AC side. It outputs a sinusoidal waveform from a pulse based on another modulation algorithm. Yet, LC filters limit the amount of harmonics that can be compensated for. Since it is a low pass filter, the higher order current harmonics fall outside the function of compensation. Fortunately, higher harmonics are much smaller compared to lower harmonics.

As described above, the operation method of the photovoltaic power generation system according to the present embodiment performing harmonic compensation of a system in a non-power generation period according to the spirit of the present invention is as shown in FIG. 10.

The operating method of the photovoltaic power generation system of this embodiment shown in FIG. 10 includes the steps of converting light energy into electrical energy in a photovoltaic module during a power generation period (S220); Converting DC power into AC power in the inverter input from the photovoltaic module (S240); Transmitting an output of the inverter to an output terminal by removing a noise component from a filter unit (S260); And PWM controlling the operation of the inverter by the PLL method for the output stage measured value (S280).

In a non-power generation period, blocking the photovoltaic module (S310); And performing a reactive power compensation function of grid power to the filter unit (S350).

Here, in detail the step of controlling the PWM (S280), detecting the potential difference between the two phases and the three-phase current value of the three phases of the output stage; Generating an abc / dq signal by performing dq conversion of a three-phase variable by applying the detection values and the phase detection value θ; Generating a reference signal; And generating the PWM driving signal using the dp current signal determined from the converted dq, the dp voltage signal generated by the PLL detector, and the reference signal.

In the illustrated process, the steps S240, S310, and S390 may be performed using the inverter 160 (more specifically, a switching transistor belonging to the inverter) of FIG. 1, which is the same component, or the steps S260 and Step S350 may be performed using the filter unit of the system of FIG. 1, which is the same component.

That is, in an implementation of preventing cost increase due to additional switching elements for shutting down the grid, in the step of blocking the photovoltaic module (S310), the switching elements (switching transistors) of the inverter may be turned off.

11 and 12 are simulation results for evaluating harmonic compensation effects, and FIG. 11 shows inverter currents, nonlinear load currents and grid currents with harmonic compensation, and FIG. 12 shows harmonic order charts according to total harmonic distortion. have.

In the figure, I _sa : grid current, I _La : nonlinear load current, and I _a : inverter current.

As shown in Fig. 11, it can be seen that the current on the inverter side is filled with harmonics compared to it before compensating. However, the current on the grid side is close to the sinusoid after compensating with the inverter current.

Meanwhile, in FIG. 12, it can be seen that the lower harmonic component generated by the non-sinusoidal load current is compensated for the reactive power by the inverter current, and the lower harmonic component of the grid current is attenuated. Current distortion is greatly reduced after harmonic compensation.

It should be noted that the above embodiment is for the purpose of illustration and not for the purpose of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

110: photovoltaic module 120: booster converter
160: inverter 200: PLL control unit
220: PWM driver 230: PLL detector
240: abc / dq signal generator 270: reference signal generator
280: dq-frame control unit

Claims (7)

A photovoltaic module for converting light energy into electrical energy;
An inverter for converting a DC voltage input from the photovoltaic module into an AC voltage;
A filter unit for transmitting the output of the inverter to an output terminal by removing a noise component; And
It includes a PLL control unit for PWM control the operation of the inverter in a PLL method for the measured value of the output stage,
The PLL control unit,
A PWM driver for driving the inverter in a PWM manner;
A PLL detector for detecting an electrical signal at the output terminal;
An abc / dq signal generator configured to apply a phase detection value (θ) of the PLL detector to perform a dq conversion of a three-phase variable;
A dq-frame controller configured to generate a driving signal of the PWM driver using a dp current signal determined from the converted dq and a dp voltage signal generated by the PLL detector; and
Including a reference signal generator for providing a reference signal for generating a drive signal of the dq-frame control unit,
In the non-power generation period, the system performs reactive power compensation function to reduce harmonics and power factor improvement of the system.
The PLL control unit, in the non-power generation period of the photovoltaic module, with the output terminal connected to the grid, switching off the switching elements of the inverter,
The reference signal is provided by the following formula (1).
[Equation 1]

Where I _dref and I _qref are reference signals,
V _sd , V _sq is the voltage on the dq axis at the joint,
P _ref is the actual power, Q _ref is the reactive power.
delete The method of claim 1,
And a boost converter for boosting the voltage produced by the photovoltaic module and transferring the voltage to the inverter.
The method of claim 1,
The filter unit includes:
A photovoltaic power generation system comprising a reactor for limiting current at an output stage and a capacitor for blocking high frequency components.
In the developing period,
Converting light energy into electrical energy in the photovoltaic module;
Converting a DC voltage into an AC voltage in an inverter input from the photovoltaic module;
Transmitting an output of the inverter to an output stage by removing a noise component from a filter unit;
PWM controlling the operation of the inverter by the PLL method for the measured value of the output stage;
In the non-development period,
Blocking the photovoltaic module;
Perform reactive power compensation of the connected grid power,
The PWM control step,
Detecting a potential difference, a three-phase current value, and a phase θ of two phases of the three phases of the output terminal;
Generating an abc / dq signal by performing dq conversion of the three-phase variable by applying the detected potential difference, the current value, and the phase θ;
Generating a reference signal;
Generating a PWM driving signal for controlling the operation of the inverter by using the dp current signal determined from the converted dq, the dp voltage signal detected at the output terminal, and the reference signal;
In the blocking of the photovoltaic module, the switching elements of the inverter are turned off,
Performing a reactive power compensation function of the connected grid power is performed using the filter unit,
The reference signal is generated by the following [Equation 2] operating method of the photovoltaic power generation system.
[Equation 2]

Where I _dref and I _qref are reference signals,
V _sd , V _sq is the voltage on the dq axis at the joint,
P _ref is the actual power, Q _ref is the reactive power. delete delete

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