KR20150025977A - Method for tracking maximum power point in phtovoltaic power generating system and system using the same - Google Patents

Abstract

Disclosed is a method of tracking a maximum power point of a photovoltaic power generating system. The method according to the present invention comprises: setting an initial reference voltage corresponding to a predetermined ratio of an open voltage of a photovoltaic power generating array and a predetermined power variation amount; receiving an output voltage and an output current from the photovoltaic power generating array to track a maximum power point using a variable inspection; and setting a disturbance to the open voltage to a predetermined ratio to track the maximum power point, when a variation of power outputted to a load is greater than the set power variation amount.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for tracking a maximum power point of a photovoltaic power generation system, and a photovoltaic power generation system using the same.

The present invention relates to a method for tracking a maximum power point of a solar power generation system and a solar power generation system using the same.

Generally, a photovoltaic system forms an array by serially or parallelly connecting one or more solar cell modules to convert solar energy into electrical energy. Such a photovoltaic power generation system includes an inverter or the like as a power conversion device for converting DC power generated from a solar cell module into AC power suitable for a load or a system.

In the stand-alone solar inverter system, the operating point of the output power is determined by the capacity of the load. However, in the grid-connected solar inverter system, the system load can be viewed as infinitely variable load. Therefore, It requires a maximum power point tracking (MPPT) method that can maximize the generated power.

The most known maximum power follow-up control algorithm to date is the Perturbation and Observation Method. This is because the operating voltage of the solar array continuously fluctuates (disturbance), and the position of the PV array on the voltage / current characteristic curve is compared by comparing the sampled previous power value with the current power value to determine the maximum power point It is the way to go.

However, such a variation observation method has a problem in that, when the solar radiation rapidly changes or shadows occur, that is, when two or more maximum power points appear, the maximum power point can not be traced according to the magnitude of the disturbance.

In order to solve such a problem, there are various control methods for tracking the maximum power point in a rapidly changing environmental condition. However, since a high CPU is required due to a large amount of computation, the price of the system increases, There is a problem that it takes a lot of time.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a solar cell module in which the maximum power point of a solar cell module is traced even when a solar radiation rapidly changes or a shadow is generated in the solar cell module, A method for tracking a maximum power point of a photovoltaic power generation system.

According to an aspect of the present invention, there is provided a maximum power point tracking method comprising: setting an initial reference voltage corresponding to a predetermined ratio of an open-circuit voltage of a solar array and a predetermined power variation; Receiving an output voltage and an output current of the solar array; Tracking the maximum power point by a variation observation; And tracking the maximum power point by setting a disturbance with respect to the open-circuit voltage at a predetermined ratio when the variation amount of the power output to the load is larger than the set power variation amount.

The maximum power point tracking method of an embodiment of the present invention may further include storing power and voltage at the maximum power point when a maximum power point is determined by variation observation.

In one embodiment of the present invention, the step of tracing by the variation observation includes the steps of: determining an output power using an output voltage and an output current of the solar array; Setting a reference voltage by moving a predetermined voltage in the same direction as the current tracking direction when the current output power is higher than the previous output power; And setting the reference voltage by moving a predetermined voltage in a direction opposite to the current tracking direction when the current output power is lower than the previous output power.

In one embodiment of the present invention, the initial reference voltage may be determined to be 85% of the open-circuit voltage of the solar array.

The maximum power point tracking method of an embodiment of the present invention may further comprise setting a flag that determines the direction of the reference voltage.

In one embodiment of the present invention, the step of tracking the maximum power point further comprises the steps of: measuring a voltage at an optimum power point determined by the variation observation and a reference voltage through a disturbance corresponding to a predetermined ratio of the flag and the open- Resetting; Calculating a slope of a power variation amount with respect to a voltage variation amount; And setting the reference voltage by shifting by a predetermined voltage in the same direction as the current tracking direction when the slope is positive.

In one embodiment of the present invention, the reference voltage to be reset can be determined by the following equation.

(Where Vmpp is a voltage at a maximum power point, Flag is a flag, and? Vbig is a disturbance corresponding to a predetermined ratio of an open-circuit voltage)

In one embodiment of the present invention, the predetermined ratio may be 50 to 70% of the open-circuit voltage.

In one embodiment of the present invention, the step of tracking the maximum power point further comprises returning to the step of tracking the maximum power point by the variation observation if the variation amount of the power output to the load is smaller than the set power variation amount .

According to another aspect of the present invention, there is provided a solar photovoltaic system including: a solar array; A voltage measuring unit for measuring an output voltage of the solar array; A current measuring unit for measuring an output current of the solar array; A boost converter for converting a DC power generated by the solar array and outputting the DC power to an inverter for driving a load; And when the variation amount of the power output to the load is larger than the set power variation amount, the disturbance with respect to the open voltage is set at a predetermined ratio to track the maximum power point, and when the variation amount of the power output to the load is smaller than the set power variation amount And a control unit for tracking the maximum power point by the variation observation.

In one embodiment of the present invention, the control section may set an initial reference voltage corresponding to a predetermined ratio of the open-circuit voltage of the solar array and a predetermined amount of power variation.

In one embodiment of the present invention, the control section may set the initial reference voltage to 85% of the open circuit voltage of the solar array.

In one embodiment of the present invention, the control unit determines the output power using the output voltage and the output current of the solar array, and when the current output power is higher than the previous output power, And sets the reference voltage by shifting by a predetermined voltage in the direction opposite to the current tracking direction to track the maximum power point by the fluctuation observation when the present output power is lower than the previous output power .

In one embodiment of the present invention, the control unit sets the reference voltage through a disturbance corresponding to a predetermined ratio of the voltage at the optimum power point determined by the variation observation, the flag, and the open-circuit voltage, The slope of the power change amount is calculated and if the slope is positive, the reference voltage is set by shifting by a predetermined voltage in the same direction as the current tracking direction to set the disturbance to the open voltage at a predetermined ratio to track the maximum power point have.

The present invention as described above enables the inverter to operate at the maximum power point of the solar cell module even when the solar radiation is rapidly changed or the solar array has a shadow effect. Further, since the present invention can be used in a tracking method and a hybrid method by the conventional variation observation method, the method is simple and easy to implement, and it is effective in realizing cost reduction in terms of unit cost of the system.

In addition, by setting the initial reference voltage to 85% of the solar cell open-circuit voltage at the maximum power point tracking, the maximum power point tracking time can be shortened and this method can be used in the P & O control method and the hybrid method. It is very easy and it is possible to realize cost reduction in terms of the unit price of the system.

Also, in tracking the maximum power point, it is possible to reduce the maximum power point tracking time by setting the initial optimum voltage to 85% of the solar cell open-circuit voltage, thereby increasing the utility of the entire system.

1 is a configuration diagram of a solar power generation system to which the present invention is applied.
2 is an example of a power characteristic curve of the solar array.
3 is a flowchart illustrating a method of tracking a maximum power point according to an embodiment of the present invention.
FIG. 4 is a flowchart of an embodiment for explaining a method of estimating a maximum power point by variation observation in FIG.
FIG. 5 is a flowchart illustrating a method of tracking a maximum power point by the shadow track of FIG. 3. Referring to FIG.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

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

1 is a configuration diagram of a solar power generation system to which the present invention is applied.

As shown in the figure, the system to which the present invention is applied includes a solar array 10, a boost converter 20, an inverter 30, a load 40, a current measuring unit 50, a voltage measuring unit 60 And a control unit 70. [0031]

The solar array 10 may be composed of a plurality of solar cell modules, and a solar cell module including semiconductor / compound semiconductor such as microcrystalline silicon, crystalline silicon, single crystal silicon, and amorphous silicon may be used. Battery modules may be arranged in an array so as to obtain an output voltage and an output current by combining them in series or in parallel.

The voltage measuring unit 60 measures the output voltage Vpv of the solar array 10. The voltage measuring unit 60 may be formed of a voltage divider using two resistors, but is not limited thereto.

The current measuring unit 50 measures the output current Ipv of the solar array 10. The current measuring unit 50 may include a plurality of measuring resistors having a low resistance value, an operational amplifier, a junction type transistor (BJT), and the like, but the present invention is not limited thereto.

The outputs of the voltage measurement unit 60 and the current measurement unit 50 are input to the control unit 70 so that the control unit 70 digitally converts the output voltage Vpv and the output current Ipv of the solar array 10 It can be used to derive the maximum power point by sampling.

A boost converter (20) converts the DC power generated by the solar array (10) into electric power and outputs the converted power, thereby adjusting the operating point of the solar array (10). In general, the boost converter is for converting a certain range of input power into fixed output power. In the present invention, the input power connected to the solar array 10 can be controlled and output.

The inverter 30 converts the voltage received from the boost converter 20 and supplies the converted voltage to the load 40.

The control unit 70 changes the output voltage of the solar array 10 from the open voltage Voc to a predetermined voltage and scans the power characteristic curve to derive the maximum power point P _MAX , Controls the boost converter 20 such that the solar array 10 is operated at a point. The control unit 70 of the present invention tracks the maximum power point according to the conventional variation observation method when the solar radiation amount is constant and performs sub control when the solar radiation amount suddenly changes or the solar battery module of the solar array 10 has a shadow effect Thereby tracking the maximum power point.

First, the power characteristic curve of the solar array 10 will be described.

Fig. 2 is an example of a power characteristic curve of the solar array, showing a case where the irradiation dose is constant and a case where the irradiation dose is rapidly changed.

As shown in the figure, when the maximum power point is one, the irradiation amount is constant (A), and when the maximum power point is two or more, the irradiation amount is rapidly changed (B). The inverter 30 must always operate at the maximum power point of the solar cell module of the solar array 10 in order to increase utilization and utility of the solar power generation.

In general, the method by which the control unit 70 tracks the maximum power point traces as it moves from right to left of the P-V curve. That is, it starts at the open voltage of the solar array 10.

When the solar radiation amount is constant, if the maximum power point is normally tracked, the operating point of the inverter 30 is located at MPP_1 in FIG. At this time, when the environment change condition occurs in the solar array 10 and the bypass diode of some solar cell module becomes conductive, the output curve of the solar array changes and the operating point moves to MPP_2. When the bypass diode is in a conduction state due to environmental change conditions, several maximum power points appear on the P-V characteristic curve. In FIG. 2, MPP_2 is one of them and MPP_3 is an actual maximum power point.

According to the conventional variation observation method, the output voltage periodically fluctuates based on the nonlinear characteristic in the P-V characteristic of the solar array, and the maximum power point is tracked by comparing the magnitude of the corresponding output power with the previous period.

That is, if the current output power obtained from the voltage and current of the present solar array 10 is compared with the previous output power, and the current output has increased from the previous output, the output voltage command proceeds in the same direction as the latest command In contrast, if the current output has decreased from the previous output, the output voltage command is changed in the opposite direction to the latest command.

However, according to the conventional variation observation method under the condition of environmental change, the maximum power point is determined while varying the voltage reference value from MPP_2. In this case, as shown in FIG. 2, since the power of the point in the voltage range of ± ΔV based on the MPP_2 point is lower than MPP_2, it is determined that MPP_2 is the maximum power point and the MPP_2 is vibrated. Therefore, according to the variation observation method, there is a case where the maximum power point tracking due to such environment change fails.

In order to solve such a problem, the present invention performs the maximum power point tracking of the hybrid system by performing the sub control routine in the environmental change condition with the conventional variation observation as the main control routine.

FIG. 3 is a flowchart illustrating a method of tracking a maximum power point according to an embodiment of the present invention, and shows a control operation of the controller 70 of FIG.

As shown in the figure, the control unit 70 sets the initial reference voltage Vref to the predetermined value of the open-circuit voltage Voc of the solar cell array 10 of the solar array 10 , And sets a predetermined power variation amount DELTA Pset (S31). At this time, the predetermined ratio may be, for example, 85%, but the present invention is not limited thereto, and the user can set it in consideration of the situation in order to quickly estimate the maximum power point.

Thereafter, the control unit 70 receives the current Ipv and the voltage Vpv of the solar array 10 from the current measuring unit 50 and the voltage measuring unit 60 (S32) (S33).

FIG. 4 is a flowchart of an embodiment for explaining a method of estimating a maximum power point by variation observation in FIG.

As shown in the figure, the method S33 of estimating the maximum power point by the variation observation is performed in such a manner that the voltage Vpv received from the voltage measuring unit 60 in S32 and the current Vpv received from the current measuring unit 50 The power Ppv at the current period k can be obtained by using the following equation (S41).

Thereafter, the control unit 70 compares the power fluctuation amount? Ppv (k), which is the difference between the power Ppv (k) in the current cycle and the power Ppv (k-1) in the previous cycle, (Vpv (k)), which is the difference between the voltage Vpv (k) and the voltage Vpv (k-1) in the previous period (S42), and determines whether the current power is greater than the previous power (S43) .

That is, when the current power is larger than the previous power (? Ppv (k)> 0) (S43) and the current voltage is smaller than the previous voltage (? Vpv (Vref = Vpv (k) +? V) (S45). If the current power is greater than the previous power (? Ppv (k) > 0) (S43) and the current voltage is not smaller than the previous voltage (S44), the controller 70 sets the reference voltage Vref to the left (Vref = Vpv (k) -? V) (S46).

On the other hand, when the current power is not greater than the previous power (S43) and the current voltage is greater than the previous voltage (? Vpv (k)> 0) (S47), the controller 70 sets the reference voltage Vref to the left (Vref = Vpv (k) -? V) (S48). If the current power is not greater than the previous power (S43) and the current voltage is not greater than the previous voltage, the controller 70 moves the reference voltage Vref to the right of the current voltage (Vref = Vpv (k) + DELTA V) (S49).

That is, when the current output power is higher than the previous output power, the control unit 70 moves the output voltage command in the same direction as the latest command, and when the current output power is lower than the previous output power, So as to track the maximum power point.

When the maximum power point is determined (S34), the flag is set to 1 (S35), and the maximum power point is set to 1 when the maximum power point is determined (Pmpp, Vmpp) at step S36.

Thereafter, the control unit 70 confirms the fluctuation amount AP of the power output to the load (S37), and when the fluctuation amount of the power is smaller than the fluctuation amount DELTA Pset set in S31, the maximum power point tracking is continued .

However, when the variation amount of the electric power is larger than the variation amount? Pset set in S31, it is determined that the irradiation amount has changed, and the sub control routine is executed. Hereinafter, in the case where it is determined that the amount of solar radiation has changed, the tracking of the maximum power point will be referred to as " maximum power point tracking by the shadow track ". That is, when the variation amount of the power is larger than the setting, the control unit 70 performs the maximum power point tracking by the shadow track (S39).

FIG. 5 is a flowchart illustrating a method of tracking a maximum power point by the shadow track of FIG. 3. Referring to FIG.

As shown in the figure, when the tracking of the maximum power point by the shadow track is started, the control unit 70 sets the reference voltage according to the following equation (S51).

At this time, the flag determines the direction of the reference voltage. That is, the control unit 70 can set the reference voltage through the very large value disturbance (? Vbig) corresponding to the optimal voltage (Vmpp) stored in S36 and the flag set to 1 in S35 and 50 to 70% of the open- . It is to be understood, however, that the present invention is not limited to these numerical values.

 At this time, the control unit 70 checks the power fluctuation amount again and returns to the maximum power point tracking based on the variation observation of FIG. 3 when the power fluctuation amount is less than the set value (S52).

The control unit 70 calculates the slope of the power variation amount with respect to the voltage variation amount (S56). If the slope is the positive direction (S58), it continuously tracks in the same direction. If the slope is the negative direction It means that there is a power point, and the maximum power point is tracked by the variation observation (S59).

Thereafter, the power and voltage (Pmpp, Vmpp) are stored at the present time (S61) and compared (S62).

Through this process, the controller 70 can track the maximum power point of the solar array 10 both when the solar radiation amount is uniform, when there is no environmental change, and when there is an environmental change.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. Accordingly, the true scope of the present invention should be determined by the following claims.

10: solar array 20: boost converter
30: inverter 40: load
50: current measuring unit 60: voltage measuring unit

Claims (14)

Setting an initial reference voltage corresponding to a predetermined ratio of the open-circuit voltage of the solar array and a predetermined power variation;
Receiving an output voltage and an output current of the solar array;
Tracking the maximum power point by a variation observation; And
And tracking the maximum power point by setting a disturbance with respect to the open-circuit voltage at a predetermined ratio when the variation amount of the power output to the load is larger than the set power variation amount.
The method according to claim 1,
And storing the power and voltage at the maximum power point when the maximum power point is determined by the variation observation.
2. The method of claim 1, wherein tracking by the variation observation comprises:
Determining an output power using an output voltage and an output current of the solar array;
Setting a reference voltage by moving a predetermined voltage in the same direction as the current tracking direction when the current output power is higher than the previous output power; And
And setting the reference voltage by shifting by a predetermined voltage in a direction opposite to the current tracking direction when the current output power is lower than the previous output power.
2. The method of claim 1,
Wherein the open circuit voltage is determined to be 85% of the open voltage of the solar array.
The method according to claim 1,
And setting a flag that determines the direction of the reference voltage.
6. The method of claim 5, wherein tracking the maximum power point comprises:
Resetting the reference voltage through a disturbance corresponding to a predetermined ratio of the voltage at the optimum power point determined by the variation observation and the flag and the open-circuit voltage;
Calculating a slope of a power variation amount with respect to a voltage variation amount; And
And setting a reference voltage by moving a predetermined voltage in the same direction as the current tracking direction when the slope is positive.
7. The method according to claim 6, wherein the reset reference voltage is determined by the following equation.

(Where Vmpp is a voltage at a maximum power point, Flag is a flag, and? Vbig is a disturbance corresponding to a predetermined ratio of an open-circuit voltage)
8. The method according to claim 6 or 7,
50 to 70% of the open-circuit voltage.
7. The method of claim 6, wherein tracking the maximum power point comprises:
And returning to the step of tracking the maximum power point by the variation observation when the variation amount of the power output to the load is smaller than the set power variation amount.
Solar array;
A voltage measuring unit for measuring an output voltage of the solar array;
A current measuring unit for measuring an output current of the solar array;
A boost converter for converting a DC power generated by the solar array and outputting the DC power to an inverter for driving a load; And
When the variation amount of the power output to the load is larger than the set power variation amount, the disturbance with respect to the open voltage is set at a predetermined ratio to track the maximum power point, and when the variation amount of the power output to the load is smaller than the set power variation amount, And a control section for tracking the maximum power point by the variation observation.
11. The apparatus according to claim 10,
And sets an initial reference voltage corresponding to a predetermined ratio of the open-circuit voltage of the solar array and a predetermined amount of power variation.
12. The apparatus according to claim 11,
The solar power generation system sets the initial reference voltage to 85% of the open circuit voltage of the solar array.
9. The apparatus according to claim 8,
The output voltage is determined by using the output voltage and the output current of the solar array, and when the present output power is higher than the previous output power, the reference voltage is set by moving a predetermined voltage in the same direction as the current tracking direction, Wherein when the power is lower than the previous output power, the maximum power point is traced by the variation observation by moving the predetermined voltage in the direction opposite to the current tracking direction to set the reference voltage.
9. The apparatus according to claim 8,
A reference voltage is set through a disturbance corresponding to a predetermined ratio of the voltage at the optimum power point determined by the variation observation and a predetermined ratio of the flag and the open voltage and the slope of the power variation amount with respect to the voltage variation amount is calculated, And sets a reference voltage by moving a predetermined voltage in the same direction as the current tracking direction to set a disturbance with respect to the open voltage at a predetermined ratio to track the maximum power point.

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