KR20100132696A - Apparatus and method for controlling pos mppt in solar power generation system - Google Patents

Abstract

PURPOSE: A POS MPPT control device and a control method thereof are provided to obtain an optimum speed and stable maximum power by feeding back one among a current component flowing to the load of a DC-DC converter. CONSTITUTION: A DC-DC converter(120) converts a current outputted from a solar array(110) into a DC current. A load(125) receives a current outputted from the DC-DC converter. A POS MPPT control part(210) executes a control process in order to get maximum power from the DC-DC converter by feeding back the duty ratio of the DC-DC converter and a current flowing into the load.

Description

APOS MPP Control System and Control Method of Solar Power System {APPARATUS AND METHOD FOR CONTROLLING POS MPPT IN SOLAR POWER GENERATION SYSTEM}

The present invention relates to an MPPT control technology of a photovoltaic power generation system. More specifically, the DC-DC converter is configured to feedback-adjust the current flowing into the load and the duty ratio of the DC-DC converter. The present invention relates to a POS (MPPT) control device and a control method of a photovoltaic power generation system for controlling power output.

The photovoltaic system is a mechanism for producing electrical energy using clean, pollution-free energy, infinite energy sources, and solar, which is environmentally friendly. There are basically two types of photovoltaic power generation technologies. There are a stand-alone type in which a battery is connected to a power conversion unit and an associated type associated with a power system.

The output characteristics of the photovoltaic power generation system are not constant between solar radiation, surface temperature, and solar cell manufacturer, and change every moment, so it is necessary to control MPP (Maximum Power Point Tracking) to get the maximum output from the solar cell at all times. .

Among conventional MPPT control methods, there is a power comparison method (Perturb and Observe (P & O)), which feeds back both the output voltage and the output current of a solar cell and follows the maximum point of power to always maximize the output. Following the way.

However, the conventional power comparison method (Perturb and Observe, P & O) requires at least two voltage and current sensors on the photovoltaic side, and due to the complexity of the control algorithm, there is a risk of failing the maximum output point following control. have.

The technical problem to be solved by the present invention, by applying a photo-voltatic output sensorless (POS) MPPT control technology to the DC-DC converter constituting the photovoltaic power generation system The present invention provides a POS (MPPT) control device and a control method for outputting an optimum speed and a stable maximum power reaching a maximum power point (MPP) according to the size.

POS MPP control apparatus of the solar system according to the present invention for achieving the above technical problem is a solar array; A DC-DC converter converting current output from the solar array into direct current; A load into which the current output from the DC-DC converter flows; And feedback-adjusting the current flowing into the load and the duty ratio of the DC-DC converter to control the DC-DC converter to output the maximum power. .

According to an aspect of the present invention, a method for controlling POS MPP of a solar power generation system includes: (a) detecting and storing a current current NC and a previous current OC flowing into a load; (b) detecting and storing a duty ratio ND currently used in the PWM signal generator and a duty ratio OD previously used; (c) comparing the magnitudes of the current duty ratio ND and the previous duty ratio OD; (d) comparing the current current NC and the previous current OC when the comparison result of step (c) determines that the current duty ratio ND is greater than the previous duty ratio OD; (e) comparing the current current NC and the previous current OC when the comparison result of step (c) determines that the current duty ratio ND is not greater than the previous duty ratio OD; (f) As a result of comparing and comparing the steps (c) and (d), the current duty ratio ND is greater than the previous duty ratio OD (ND> OD), and the current current NC is Greater than previous current OC (NC> OC) or the current duty ratio ND is less than the previous duty ratio OD (ND <OD), and the current current NC is equal to the previous current OC Adding (ND + ΔD) a duty ratio change rate (ΔD) to the current duty ratio (ND) when smaller (NC <OC); (g) As a result of comparing and comparing the steps (c) and (e), the current duty ratio ND is greater than the previous duty ratio OD (ND> OD), and the current current NC is Less than previous current OC (NC <OC) or the current duty ratio ND is less than the previous duty ratio OD (ND <OD), and the current current NC is the previous current OC Subtracting the duty ratio change rate ΔD from the current duty ratio ND if greater than (NC> OC) (ND−ΔD); (h) generating a new duty ratio in response to the results of steps (f) and (g); (i) generating a PWM signal in response to the new duty ratio of step (h); And (j) controlling the DC-DC converter by outputting the PWM signal to a DC-DC converter.

The present invention feeds back only the output current of the DC-DC converter, i.e., the current component flowing into the load, thereby providing the optimum speed and stable maximum power reaching the maximum power point (MPP) according to the duty ratio increase and decrease. There is an advantage to providing.

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

1 illustrates a general configuration of a grid-connected photovoltaic power generation system to which the POS MPMP control technology of the present invention is applied.

Referring to FIG. 1, the grid-connected photovoltaic power generation system 100 includes a photovoltaic array (PV array) 110, a DC-DC converter 120, a DC-AC converter 130, and a power grid. Grid 140 is provided.

The photovoltaic array 110 is a conventional solar cell that generates direct current power using sunlight.

The DC-DC converter 120 is a part for adjusting the non-constant solar power output from the solar array 110 to always be maximum, and the PIO of the present invention with respect to the DC-DC converter 120 part. POS (MPOS) control technology was applied.

The DC-AC converter 130 converts a direct current (DC) into an alternating current (AC) in order to connect with the power grid 140.

2 shows a circuit constituting a POS (MPPT) control device of the present invention applied to a DC-DC converter of a grid-tied photovoltaic power generation system.

Referring to FIG. 2, the Photo-voltatic Output Sensorless (POS) Maximum Power Point Tracking (MPPT) control apparatus 200 of the present invention includes a solar array 110 and a DC-DC converter 120. And a load 125 and a POS MPMP controller 210.

The POS MPMP controller 210 detects and stores a current current NC and a previous current OC flowing into a load, and then feeds back the current comparator 240. A duty ratio detection and comparison unit 230 for detecting and comparing a current duty ratio ND and a previous duty ratio OD of the feedback unit 220, the DC-DC converter 120, and the current duty ratio ( ND) and a current comparator 240 for comparing the current current NC and the previous current OC according to a comparison result value of the previous duty OD, the current current NC, and the previous current ( The DC-type PWM signal modulating the pulse width of the control signal in response to the duty ratio calculator 250 that adds or subtracts the duty ratio according to the comparison result of OC) and the duty ratio calculated by the duty ratio calculator. A PWM signal generator 260 for outputting to the DC converter 120 is provided.

The current feedback unit 220 includes a current transformer 221, an analog to digital converter 223, and current and previous current detectors 225. The current transformer 221 detects the output current of the DC-DC converter 120 which converts the output current of the solar array 110 into a direct current (DC-DC) and flows it into the load 125. The analog-to-digital converter 223 converts the load current output from the current transformer 125 as an analog signal into a digital signal. The current and previous current detection unit 225 may be a current input to the load 125 from a current value output from the analog-digital converter 223 (New Input Current, hereinafter referred to as NC) and a previous current (Old Input Current, OC) is then detected and stored, respectively.

The duty ratio detection and comparison unit 230 includes a current duty ratio (ND) detector 231, an old duty ratio (OD) detector 233, a current duty ratio (ND), and the like. The previous duty (OD) comparator 235 is included. The current duty ratio ND detector 231 receives the output signals of the duty ratio adder 251 and the duty ratio subtractor 253 to detect and store the current duty ratio ND. The previous duty ratio detector 233 receives the output signal of the PWM signal generator 260 and detects and stores the previous duty ratio OD. The current duty ratio (ND) and the previous duty (OD) comparator 235 receive the output signals of the current duty ratio (ND) detector 231 and the previous duty ratio (OD) detector 233, respectively, and compare them with each other. Function

The current comparator 240 includes a first current current (NC) and an old current (OC) comparator 241, a second current current (NC) and a previous current (OC) comparator 243. ). The first current current NC and the previous current OC comparator 241 and the second current current NC and the previous current OC comparator 243 have a current duty ratio ND and a previous duty OD. ) The current duty ratio ND is compared to the previous duty ratio OD by receiving the comparison result of the comparator 235 and the current current NC and the previous current OC output from the current and previous current detectors 225, respectively. In the large state (ND> OD) or the small state (ND <OD), the current current NC and the previous current OC are compared with each other, and an output value corresponding to the result is the duty ratio adder 251 and the duty ratio subtractor ( 253), respectively, as shown in FIGS. 2 and 3.

The duty ratio calculator 250 includes a duty ratio adder 251 and a duty ratio subtractor 253. The duty ratio adder 251 outputs a duty to a current duty ratio ND when a predetermined output signal is input from the first current and previous current comparator 241 and the second current and previous current comparator 243, respectively. A new duty ratio is calculated by adding the ratio change amount D. The duty ratio subtractor 253 outputs a duty to a current duty ratio ND when a predetermined output signal is input from the first current and previous current comparator 241 and the second current and previous current comparator 243, respectively. The new duty ratio is calculated by subtracting the ratio change ΔD. (See Figures 2 and 3)

The PWM signal generator 260 is configured to increase or decrease the current duty ratio ND in response to the new duty ratio output from the duty ratio adder 251 and the duty ratio subtractor 253 through the current duty ratio detector 231. When input, the PWM signal modulating the pulse width of the control signal (PWM) is output to the previous duty ratio detector 233 and the DC-DC converter 120 in response to the duty ratio.

As described above, the output voltage from the photovoltaic array 110 is increased or decreased by feedback of the current flowing into the load 125. In this case, DC is increased or decreased by the duty ratio inputted as a control signal of the DC-DC converter 120. It can be seen that the input terminal voltage of the DC converter 120 is increased or decreased.

That is, when the on time of the PWM signal output from the PWM signal generator 260 is large, the voltage at the input terminal of the DC-DC converter 120 decreases and the current flowing therein increases. On the other hand, when the On time of the PWM signal output from the PWM signal generator 260 is short, the voltage at the input terminal of the DC-DC converter 120 increases and the current flowing therein decreases. Therefore, the output voltage of the photovoltaic array 110 output through the DC-DC converter 120 controlled by the PWM signal generator 260 may be always supplied to the load 125 in an optimal state.

In summary, since the power output from the photovoltaic array is constant, as the duty ratio increases (high switching), the voltage decreases and the current increases. On the other hand, as the duty ratio decreases (less switching), the voltage increases and the current decreases.

According to the present invention, the POS MPMP control technology of the present invention provides a basic physical principle that the output power is also maximized when the power flowing into the input of the power converter becomes the maximum regardless of the load. Applicable to the system. That is, if the power flowing into the load increases in proportion to the power supply, the load power (P) is equal to the product of the voltage (V) and the current (I), so the current (I) flowing into the load also increases, thereby increasing the load power (P). The component of and the component of the current (I) can be identified. Therefore, when the output of the solar array is the maximum, the load current (I) also becomes the maximum.

3 is a flowchart illustrating a method for controlling a POS MPMP of the present invention applied to a DC-DC converter of a grid-connected photovoltaic power generation system.

Hereinafter, with reference to FIGS. 2 and 3, a method of controlling a POS (MPPT) of the present invention will be described.

In a first step, the current and previous current detector 225 connected to the current transformer 221 has a step (S10) of detecting and storing the current flowing into the load 125.

The current duty ratio detector 231 and the previous duty ratio detector 233 respectively detect and store the duty ratio ND currently used and the duty ratio OD previously used in the PWM signal generator 260 (S20). Has

Comparing the magnitude of the current duty ratio (ND) with the previous duty ratio (OD) (S31).

When it is determined that the current duty ratio ND is greater than the previous duty ratio OD as a result of performing the step S31, the step S33 is compared with the magnitude of the current current NC and the previous current OC.

When it is determined that the current duty ratio ND is not greater than the previous duty ratio OD as a result of performing step S31, the method compares the magnitude of the current current NC and the previous current OC (S35).

As a result of the comparison between the steps S31 and S33, the current duty ratio ND is greater than the previous duty ratio OD (ND> OD) and the current current NC is greater than the previous current OC (NC> OC). Alternatively, if the current duty ratio ND is smaller than the previous duty ratio OD (ND <OD) and the current current is smaller than the previous current (NC <OC), the duty ratio change rate ΔD is applied to the current duty ratio ND. A step S41 of adding (ND + ΔD) and generating a new duty ratio based on the result of the step S41 are included.

As a result of comparing and determining in steps S31 and S33, the current duty ratio ND is greater than the previous previous duty ratio OD (ND> OD), and the current current NC is smaller than the previous current OC (NC <OC). ) Or if the current duty ratio (ND) is less than the previous duty ratio (OD) (ND <OD) and the current current (NC) is greater than the previous current (OC) (NC> OC) A step S43 of subtracting the duty ratio change ratio DELTA D is performed (S43) and a step S50 of generating a new duty ratio based on the result of the step S43.

Generating a PWM signal corresponding to the new duty ratio by the PWM signal generator 260 (S60) and controlling the DC-DC converter 120 by the PWM signal (S70).

After the step S70, the operation of repeating steps S10 to S70 is performed until the target MPPT control is performed, but the program ends when the target MPPT control is performed. .

4 illustrates a power-voltage characteristic curve implemented by the POS and MPPT control apparatus and method of the present invention.

Table 1 below shows the duty ratio (D), the load current (I) and the duty ratio change ratio (ΔD) according to each track in the power-voltage characteristic curve.

Table 1

Track Duty ratio (D) Load current (I) Duty ratio change rate (△ D) 1 (V _{0 →} V ₁ ) (-) (+) (-) 2 (V _{1 →} V ₂ ) (-) (-) (+) 3 (V _{2 →} V ₃ ) (+) (+) (+) 4 (V _{3 →} V ₁ ) (+) (-) (-)

Referring to FIG. 4 and Table 1, if the duty ratio D decreases (-) in the track 1, the load current I increases (+) and the sign of the duty increase / decrease rate (ΔD) is negative (−). This means that the duty ratio D in track 2 decreases (-).

When the duty ratio D decreases (-) in the track 2, the load current I decreases (-), and the duty change rate DELTA D becomes positive. Then, the duty ratio (D) of track 3 increases (+), and if the duty ratio (D) increases in track 3, the load current (I) also increases (+) and the duty change rate (ΔD) is positive (+). Becomes As a result, the duty ratio D of the track 4 increases (+).

When the process of tracks 1 to 4 is repeated, it always operates above the maximum power point (MPP).

The duty ratio (D) is adjusted by the PWM signal generator. If the duty ratio change rate (ΔD) is known in the PWM signal generator, there is no need to feedback the increase or decrease of the voltage (V) component separately, and thus the load current ( I) By receiving only one feedback, the output power of the solar array 110 can be controlled to the maximum.

Figure 5a shows the waveform of duty ratio, current and voltage over time when the POS (MPPT) control of the present invention is applied, Figure 5b is a conventional power comparison method (P & O) MPPT (MPPT) Shows the waveform of duty ratio, current and voltage over time when the control technique is applied.

5A and 5B, the present invention feeds back only one output component of the DC-DC converter 120, that is, a current component flowing into the load 125. The output voltage of the DC-DC converter 120 is constant. Has a value. As a result, it can be seen that the optimum speed and stable power value reaching the maximum power point (MPP) is determined according to the duty ratio increase and decrease.

On the other hand, conventional power comparison (P & O) MPPT control technology has to feed back both the output voltage and the output current of the solar array, and the output voltage has a floating value. As a result, the speed of reaching the maximum power point (MPP) is slow depending on the size of the duty ratio increase and decrease, and the power also has an unstable value.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope of the present invention.

1 illustrates a general configuration of a grid-connected photovoltaic power generation system to which the POS MPMP control technology of the present invention is applied.

2 shows a circuit constituting a POS (MPPT) control device of the present invention applied to a DC-DC converter of a grid-tied photovoltaic power generation system.

3 is a flowchart illustrating a method for controlling a POS MPMP of the present invention applied to a DC-DC converter of a grid-connected photovoltaic power generation system.

4 illustrates a power-voltage characteristic curve implemented by the POS and MPPT control apparatus and method of the present invention.

5A illustrates waveforms of duty ratio, current, and voltage over time when the POS MPMP control of the present invention is applied.

Figure 5b shows the waveform of duty ratio, current and voltage over time when the conventional power comparison method (P & O) MPPT control technique is applied.

Claims (7)

In the MPPT control device applied to a solar power system,  Solar arrays; A DC-DC converter converting current output from the solar array into direct current;  A load into which the current output from the DC-DC converter flows; And And a feedback control (POS) MPPT controller for controlling the DC-DC converter to output the maximum power by feedback-adjusting the current flowing into the load and the duty ratio of the DC-DC converter. A POS system MPPT control device of a photovoltaic system. The method of claim 1, wherein the POS (MPPT) control unit  A current feedback unit which detects and stores a current current NC and a previous current OC flowing into the load and feeds it back to a current comparing unit; A duty ratio detection and comparison unit for detecting a current duty ratio ND and a previous duty ratio OD of the DC-DC converter and comparing them with each other;  A current comparing unit comparing the current current NC and the previous current OC according to a comparison result value of the current duty ratio ND and the previous duty OD; A duty ratio calculator for adding or subtracting a duty ratio according to a comparison result of the current current NC and the previous current OC; And POS of the solar power generation system characterized in that it comprises a PWM signal generator for outputting the PWM signal modulated the pulse width of the control signal to the DC-DC converter in response to the duty ratio calculated by the duty ratio calculator ( POS) MPPT control device. The method of claim 2, wherein the current feedback unit A current transformer for detecting current flowing into the load; An analog-digital converter for converting an analog signal output from the current transformer into a digital signal; And The current and previous current detection unit for detecting the current (NC) and the current (OC) output from the analog-to-digital converter, respectively, characterized in that the POS (MP) MPP (MPPT) of the photovoltaic system A) control device. The method of claim 2, wherein the duty ratio detection and comparison unit A current duty ratio (ND) detector for detecting a current duty ratio (ND) of the DC-DC converter; A previous duty ratio detector (OD) for detecting a previous duty ratio (OD) of the DC-DC converter; And  POS of the photovoltaic system, characterized in that it comprises a current duty ratio (ND) and a previous duty (OD) comparator for comparing the size of the current duty ratio (ND) and the previous duty ratio (OD). ) MPPT control device. The method of claim 2, wherein the current comparison unit A first current current NC and a previous current OC comparator comparing the current current NC and the previous current OC when the current duty ratio ND is greater than the previous duty ratio OD; And And having a second current current NC and a previous current OC comparator comparing the current current NC and the previous current OC when the current duty ratio ND is smaller than the previous duty ratio OD. A POS system MPPT control device of a photovoltaic system. The method of claim 2, wherein the duty ratio calculation unit  The current duty ratio (ND) is greater than the previous duty ratio (OD) (ND> OD) and the current current (NC) is greater than the previous current (OC) (NC> OC) or the current duty ratio (ND) is the previous duty ratio. A duty ratio adder that adds (ND + ΔD) the duty ratio change rate ΔD to the current duty ratio ND if less than (OD) (ND <OD) and the current current is less than the previous current (NC <OC); And  The current duty ratio (ND) is greater than the previous duty ratio (OD) (ND> OD), the current current (NC) is less than the previous current (OC) (NC <OC), or the current duty ratio (ND) is transferred If the duty ratio (OD) is less than (ND <OD) and the current current (NC) is greater than the previous current (OC) (NC> OC), the duty ratio change ratio (ΔD) is subtracted from the current duty ratio (ND) (ND- (POS) MPPT control device of a photovoltaic system, characterized by comprising a duty ratio subtractor (DELTA) D. In the method for controlling MPPT applied to the solar power system, (a) detecting and storing a current current NC and a previous current OC flowing into the load; (b) detecting and storing a duty ratio ND currently used in the PWM signal generator and a duty ratio OD previously used; (c) comparing the magnitudes of the current duty ratio ND and the previous duty ratio OD; (d) comparing the current current NC and the previous current OC when the comparison result of step (c) determines that the current duty ratio ND is greater than the previous duty ratio OD; (e) comparing the current current NC and the previous current OC when the comparison result of step (c) determines that the current duty ratio ND is not greater than the previous duty ratio OD; (f) As a result of the comparison judgment of steps (c) and (d), the current duty ratio ND is greater than the previous duty ratio OD (ND> OD), and the current current NC is Greater than previous current OC (NC> OC) or the current duty ratio ND is less than the previous duty ratio OD (ND <OD), and the current current NC is equal to the previous current OC Adding (ND + ΔD) a duty ratio change rate (ΔD) to the current duty ratio (ND) when smaller (NC <OC);  (g) As a result of the comparison determination of the steps (c) and (e), the current duty ratio ND is greater than the previous duty ratio OD (ND> OD), and the current current NC is Less than previous current OC (NC <OC) or the current duty ratio ND is less than the previous duty ratio OD (ND <OD) and the current current NC is the previous current OC Subtracting the duty ratio change rate ΔD from the current duty ratio ND if greater than (NC> OC); (h) generating a new duty ratio in response to the results of steps (f) and (g); (i) generating a PWM signal in response to the new duty ratio of step (h); And (j) controlling the DC-DC converter by outputting the PWM signal to a DC-DC converter.

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