TECHNICAL FIELD

The present disclosure relates to the combination of multiple DC power sources, and more particularly to the combination of multiple DC power sources that have different voltage, current, or maximum power points, into at least a single output.

BACKGROUND ART

Combining multiple power sources of different voltages or currents efficiently can be a challenge in the field of electronics. When power sources are combined in series, they may not have the same current at the maximum power point, and since the current must be equal across all sources, one or all will not be operating at their respective maximum power point. Alternatively, if power sources are combined in parallel, they may not have the same voltage at the maximum power point. Since the voltage across all power sources must be the same in a parallel configuration, some or all of the power sources may not be operating at their respective maximum power point.

Various topologies have been developed to connect multiple power sources to a load, and fall under several categories. One category is the individual control and regulation of each power source, of which one example is in the Patent Literature 1. Each power source has a maximum power point tracking (MPPT) module connected to it, with the outputs of the MPPT modules connected together. The output voltage of the each MPPT module is regulated to the output of the string. Various topologies for the MPPT modules, various control methods, and various connections between MPPT modules exist.

Another method to combine power sources is to connect them together through a transformer, with each power source having windings around a common core. This method is fundamentally a buck- boost type dc-dc converter system with the inductor being substituted with a transformer, which has multiple input windings. An example of one such system is described in the Non Patent Literature 1. There are various implementations of this system, which have different configuration of the windings, DC-DC regulation, and control systems. Citation List Patent Literature

[PTL 1] PCT patent application No. PCT/US2013/064477 Non Patent Literature

[NPL 1] H. Matsuo et al., "Characteristics of the Multiple-Input DC-DC Converter," IEEE Trans. Ind. Electron., vol. IE-51, pp. 625-631, Jun. 2004.

DISCLOSURE OF INVENTION

A system for the combination of multiple input power sources into at least a single output is provided. The electronics system maximizes the power of the output or outputs, from a plurality of input power sources. In certain embodiments, the electronics system may be used with any suitable power source at the inputs, including photovoltaics, wind turbines, and batteries. The electronics system is able to detect the power produced by each power source, intelligently monitor the input, and switch the configuration of energy storage elements. The switches change the electrical connections of the energy storage elements between the input and the output or outputs. The system operates in order to obtain the maximum power from each of the sources, for any environmental conditions.

The advantages of using this system may be to provide an alternative to connecting power sources in series or parallel, that vary in voltage or current output, in order to avoid power losses. This advantage may be observed when the system is used with photovoltaics, where sources of inefficiency, including uneven cloud cover, can cause the power outputs of a plurality of cells to be mismatched. The advantages of this system over the current art include the decreased number of components, design simplicity, and the absence of expensive components such as transformers or inductors.

The WRPC system comprises a plurality of power sources, the electronics switching system, the energy storage elements, measurement device(s), and the controller. The controller is used to control switches and take measurements from the energy storage elements. In some embodiments, the controller is an intelligent controller that utilizes control algorithms. The controller monitors input from the energy stored in the energy storage elements, and the controller intelligently switches the configuration of the connections of the energy storage elements, between the input power sources and the output or outputs, in such a way as to ensure the maximum power output from each source.

In some embodiments, the method of operation of the device is that each power source has two energy storage elements which are charged by the power source. Each energy storage element has an input switch connecting it to its power source, and an output switch connecting it to the output or outputs. The system can disconnect any one of the energy storage elements from the power source to connect it to the output. While one of the energy storage elements is connected to the output, the power source continues to charge the other energy storage element(s). The other power sources whose energy storage elements are not connected to the output, continue to charge both energy storage elements. In some embodiments, more than two energy storage elements per power source may be used. In some embodiments, an energy storage element can be used at the output to smooth variances in the voltage.

In some embodiments, the controller will use information about the amount of energy stored in the energy storage elements to determine the charge rate of the elements. The maximum power point of the source is found by searching for the voltage that produces the highest charge rate of the energy storage elements. This is carried out such that the search space is within the tolerances of the energy storage elements and the switching system, and the maximum and minimum desired output power or voltage.

In some embodiments the switches are controlled in such a way that the inputs are isolated from one another through time division multiplexing.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 illustrates a block diagram of an embodiment of the wide range power combiner (WRPC) switching system.

Figure 2 Illustrates one period of an unoptimized switch timing diagram, where each energy storage element is individually connected to the output, in sequence. Figure 3 Illustrates an example of the maximum power point of an input power source to the wide range power combiner (WRPC)

Figure 4 Illustrates a block diagram of an intelligent control algorithm that can be utilized by the controller, to control the wide range power combiner (WRPC) switching system.

BEST MODE OF CARRYING OUT INVENTION

Embodiments of the invention are described more fully hereinafter with reference to the drawings.

In some embodiments the switches may be transistors, and the energy storage elements may be capacitors.

In the case of two energy storage elements per power source, as shown in Fig. 1 , each storage element is connected to the power source through an input switch. Each switch is controlled independently by the controller. When the switch between the power source and the capacitor is closed the energy storage element will be charged by the power source.

Every storage element is also connected to the output through a switch. When the energy storage element is being charged from the power source, the output switch will be open, and the energy storage element will be disconnected from the output. When an energy storage element is connected to the output, the input switch will be open, and the energy storage element will be disconnected from the power source. While the energy storage element is providing power to the output, the power source continues to charge the second energy storage element. Only one energy storage element is connected to the output at a time.

Due to limitations of MOSFETs, proper considerations need to be taken to ensure that no current is conducted between energy storage elements across different input power sources.

The timing of the switches is controlled by a controller. In some embodiments the controller can be a micro controller. The controller can control the switches using a timing diagram as in Fig. 2, where one period of switching is shown, or the controller can utilize an intelligent control algorithm to ensure efficient operation and ensuring that each input power source is operating at its maximum power point. A control algorithm is described below. The energy in the capacitors is measured by measuring the voltage, and using the known capacitance according to the formula:

E=l/2* C*V2

Where E is the total energy stored in Joules, C is the capacitance of the capacitor in Farads, and V is the measured voltage in Volts. The change in energy in the energy storage element(s) would be equal to the output power of the power source. This can be used to determine the maximum power point of the power source, because as the voltage of the capacitor increases, the rate of charge will also change as shown in Fig. 3.

Once the maximum power point of the source is found, the controller will intelligently select the energy storage element which must be connected to the output. This selection is made to ensure that the voltage of each energy storage element remains at the voltage of the maximum power point of its input power source. An example of such a control algorithm is shown in Fig. 4.

In the control algorithm of Fig. 4, an energy storage element is selected, and if it has not yet been measured, the voltage of the selected energy storage element is measured. This is repeated until the voltage of all energy storage elements have been measured. Next, the difference between the voltage of each storage element and the voltage at the maximum power point of its source is determined. The energy storage element that is currently connected to the output is disconnected, and then connected to its power source. The energy storage element with the largest difference, that also has a greater voltage than that of the maximum power point of its input power source, is then disconnected from its power source and connected to the output. All stored measurement values are cleared and the controller begins the process of selecting the next energy storage element, to connect to the output, from the beginning.

A dynamically changing load can be used at the output of the wide range power combiner (WRPC) to ensure that all input power sources are operating at their maximum power point. A DC-DC converter can be used to dynamically change the apparent output load of the wide range power combiner. A DC- DC converter can be a boost converter. If the boost converter is intelligently controlled, at a frequency that is relatively high in comparison to that of the switching frequency of the WRPC switching system, it can adapt to the changes in the WRPC output. The use of the DC-DC converter at the output of the WRPC can provide a fixed DC output voltage.