CZ2015621A3 - The method of determining the maximum output that can be drawn from a photovoltaic panel - Google Patents

Abstract

The method of determining the maximum power that can be taken from a photovoltaic panel allows the regulator to periodically find the optimum load on the solar panels to maximize the amount of energy that can be extracted from it and dispose of it, for example, in an electric heating coil designed to heat water. batteries. The method is that the controller repeatedly scans the entire power characteristics of the solar panels to find the largest of all current power peaks that may be due to external influences outside the manufacturer's predicted area. The regulator then sets its working point to this maximum and maintains it until the selected new maximum search time period expires. The method can be used wherever the load permits a change in the load of the solar panels over a wide range, such as a resistive heating coil or battery charger, or an inverter supplying power to the grid.

Description

Method of determining the maximum power that can be taken from a photovoltaic panel

Field of technology

The invention relates to the optimization of the amount of electrical energy obtained from photovoltaic (hereinafter referred to as solar) panels. This is a method of determining the optimal power consumption of an electrical appliance, in which the maximum amount of energy can be extracted from solar panels regardless of their type, size, number, connection, lighting or shading, temperature, covering or soiling the surface or change the electrical properties of the load. It can also be used for parallel connection of solar panel chains directed in different directions. The method can be used both in controllers for water heating in the boiler and in inverters supplying energy to the network or in rechargeable batteries.

Prior art

Current controllers use various Maximum Power Point Tracking MPPT methods, which are methods of keeping the operating point of the solar panel load in the optimal area so that the amount of energy gained is as large as possible. At present, almost two dozen of these methods are known for determining the optimal operating point of a solar panel. Most MPPT methods work correctly with the ideal VA characteristic of a single solar panel, but fail to serialize multiple panels if their overall VA characteristic deviates from the ideal VA characteristic. These are mainly cases where due to different properties of individual photovoltaic panels, eg due to changing lighting (sun movement) or shading (clouds, obstacles in the path of light, sliding snow, removal of dirt by rain), changes in panel temperature, or changes electrical load parameters, two or more power maxima will appear on the total VA characteristic. In such cases, conventional MPPT controllers remain at the beginning of the searched maximum and do not react to the newly created maxima.

The essence of the invention

These disadvantages are eliminated by the method of determining the maximum power point (MPPS), which can be taken from the solar panel, the essence of which is that the controller gradually loads the solar panel in the entire range of power characteristics from zero to maximum load, while continuously measuring the delivered power and we record the highest achieved maximum delivered power in the power characteristic and its corresponding operating point of the controller, then we set the operating point of the controller, ie solar panel load to such a level as recorded when reaching the maximum delivered power to the load and keep the operating point of the controller in this newly found optimal areas using one of the MPPT (Maximum Power Point Tracking) methods until the selected time elapses, after which the controller repeats the test of the entire power characteristic, finds and sets a new optimal operating point and maintains it again for the selected time, resulting in determining the value of the maximum output the one that can be taken from the connection of solar panels with different actual power.

The newly designed Maximum Power Point Searching - MPPS method eliminates all the mentioned effects of existing methods in determining the optimal operating point. This is an active, regularly recurring search for the optimal operating point over the entire range of possible loads. Controllers using this method will check the entire VA characteristic of the photovoltaic panels, find all the maxima and select the largest one.

Explanation of the drawing

AFeat the picture

Giant. 1. Ideal VA characteristics of solar panels

Giant. 2. Ideal performance characteristics of solar panels

Giant. 3. Practical VA characteristics of solar panels

Giant. 4. Practical performance characteristics of solar panels

Giant. 5. MPPS method of finding the optimal working point - flow chart.

Giant. 6. Record the step change of the operating point of the MPPS controller.

DETAILED DESCRIPTION OF THE INVENTION

When developing a controller that determines the maximum power that can be taken from solar panels, we first used the common MPPT method, in which the control is captured at the peak of the maximum power characteristic and by adjusting the control parameters tries to maintain it. This method works well if all solar panels are the same and the same lighting. Fig. 1 shows the VA characteristic of 8 panels in series with a total power of 2000 W, measured by the manufacturer. On the vertical axis is the current in amperes, on the horizontal axis is the voltage in volts. From this VA characteristic it is possible to derive the power characteristic of the panels (Fig. 2), on which the power in the vertical axis is in watts. At the top of the power characteristic is the optimal operating point (output voltage) of the panels, at which the panels deliver the maximum power to the load. Controllers using MPPT methods first determine this optimal operating point and then try to maintain it throughout the operation.

However, practical measurements have shown that the overall VA characteristic of several panels connected in series can differ significantly from the ideal VA characteristic. In general, the more panels with different actual power connected in a series, the more local maxima can be found on the power characteristics. The performance of the panel can be affected by many factors: lighting or shading, covering with snow or dirt, temperature, aging, etc., but it can also depend on the electrical properties of the load. With a small deviation from the ideal VA characteristic, the optimal operating point can only shift, to which most MPPT methods can respond. However, new, local maxima may also appear, to which no MPPT method can react unless it regularly repeats the search for the entire performance characteristics of solar panels.

During the development, we performed a practical experiment and covered one of the panels on about 40% of the area. This reduced its performance to 60% of the performance of other panels. The total VA characteristic is in Fig. 3, the corresponding power characteristic in Fig. 4. Since there are two groups of panels with different powers, there are two maxima on the power characteristic. The first corresponds to seven panels operating at 100% power, the second corresponds to 8 panels operating at power limited by the weakest panel. The standard MPPT controller keeps the operating point still at the original MAXIMUM2 peak and does not notice that due to the power drop of one of the panels, another maximum was created on the power curve at the MAXIMUM1 point. It can be seen from the example in Fig. 4 that in this case the difference in the delivered power is around 20%.

After verifying that the optimal point can be located outside the area assumed by the ideal VA characteristic of the manufacturer, we designed a method, which is described in the flowchart in Fig. 5. We programmed the algorithm into the memory of the microprocessor controlling the controller / Ten at regular intervals. units of minutes) gradually loads the solar panels from zero to the possible maximum that the load allows. The microprocessor records the operating points at which a maximum is reached. At the end of the test, the microprocessor selects the largest of the maxima found and switches the controller to the corresponding operating point. It then maintains the operating point for a set period of time using the conventional MPPT method. After the selected time has elapsed, the microprocessor retests the solar panels over the full range of possible loads and the cycle is repeated continuously.

The described algorithm was first used in MPPS controllers type MR4316DC and MR4316AC from the manufacturer BEL s.r.o., which are designed to adapt solar panels and heating coil of an electric boiler. Fig. 6 is a record of the voltage, current and power profile of an assembly of eight panels with a peak power of 2000 W and the MR4316DC controller in real operation. The graphs show that in the morning, at about 8:30, the two panels will be significantly better lit, while the remaining six panels remain shaded. During the regular overall test of all panels, the MR4316DC controller found a new maximum and switched the operating point to it. In the voltage graph, this change manifested itself as a step drop in voltage, in the current graph as a step increase in current. There is no step change in the performance graph, only the performance starts to grow significantly faster after the change of the working point. The absence of a power step change is logical, because the controller always selects the highest maximum reached and the operating point is switched when the power at the new operating point is the same (or slightly higher) than it was at the old operating point. The difference in the power obtained is the higher, the more different power is given by the individual panels arranged in series and the more there are. Practical measurements have shown that with the new method it is possible to obtain about 10% more energy during the day, even more in difficult lighting conditions.

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Industrial applicability:

In controllers, inverters and chargers that allow you to change the load of solar panels in a wide range, especially:

- in controllers, adaptation of boilers powered by solar panels

- in inverters supplied from DC panels by DC voltage (mains)

- in rechargeable batteries powered by solar panels

Claims (1)

Patent claims 1. Method of determining the maximum power Maximum Power Point Searching - MPPS, which can be taken from the solar panel, characterized by the controller gradually loading the solar panel in the entire range of power characteristics from zero to maximum load, while continuously measuring the delivered power and recording the highest achieved maximum delivered power in the power characteristic and the corresponding operating point of the controller, then set the operating point of the controller, ie the solar panel load to the level recorded when reaching the maximum delivered power to the load and maintain the operating point of the controller in this newly found optimal area using some of the MPPT (Maximum Power Point Tracking) methods until the selected time elapses, after which the controller repeats the test of the entire power characteristic, finds and sets a new optimal operating point and maintains it again for the selected time, resulting in the value of the maximum power that can be taken from connection of solar panels with different current output.