WO2010061392A1

WO2010061392A1 - Apparatus and method for processing power signals

Info

Publication number: WO2010061392A1
Application number: PCT/IL2009/001123
Authority: WO
Inventors: Shaul Ozeri
Original assignee: Shaul Ozeri
Priority date: 2008-11-30
Filing date: 2009-11-30
Publication date: 2010-06-03

Abstract

The subject matter discloses a method and apparatus for producing applicable electrical power from a photovoltaic source. The method comprises receiving a DC voltage signal from the photovoltaic source and converting the DC voltage signal into a first AC voltage signal having a first frequency. The first frequency is not applicable to provide voltage signal for a standard electrical appliance. The method also comprises inputting the first AC voltage signal having the first frequency into a switching circuit operating in a second frequency, the difference between the first frequency and the second frequency is a function of a desired frequency. The apparatus comprises two conversion modules, one from a DC power into an AC signal in a non-applicable frequency and the second to convert the AC signal in a non-applicable frequency to a signal in an applicable frequency.

Description

APPARATUS AND METHOD FOR PROCESSING POWER SIGNALS

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION The present invention relates to producing power using photovoltaic panels in general and to methods of generating efficient power signals in particular.

DISCUSSION OF THE RELATED ART

Photovoltaic (PV) technology converts solar radiation into direct current electricity. Each module that uses such technology is named a PV source, such as PV panel, PV module, cell or array. The power generated by the PV source is provided in the form of direct current (DC), while the power mostly used in a network grid and in common electrical appliances is AC. Hence, there is a need to convert the voltage signal generated by the PV source from DC to AC. Common conversions are performed by DC to AC transformation, maximum power point tracking (MPPT), inversion from DC to AC and the like.

Typical PV power systems comprise a PV source, a DC load and a control unit performing MPPT to maximize the outputted power. The output of the PV is transformed into AC using an inverter that converts the DC voltage signal into an AC voltage signal. The inverter is costly and requires maintenance. Further, inverters reduce the amount of power in the AC compared to the power of the DC. The inverters employ large electrolytic capacitors and heavy inductors that cause short life span of the inverters. Relying on one inversion module is especially precarious since failure of such module results in suspending the entire system and hindering power to the electric grid. SUMMARY OF THE PRESENT INVENTION

It is a first object of the subject matter to disclose a method of producing applicable voltage signal from a photovoltaic source, the method comprises receiving a DC voltage signal from the photovoltaic source and converting the DC voltage signal into a first AC voltage signal having a first frequency, said first frequency is not applicable to provide voltage signal for a standard electrical appliance. Then, the method comprises inputting the first AC voltage signal having the first frequency into a switching circuit operating in a second frequency, the difference between the first frequency and the second frequency is a function of a desired frequency that is applicable to provide voltage signal for a standard electrical appliance and generating an output voltage signal from the multiplication of the first AC voltage signal and the second AC voltage signal

In some embodiments, the method further comprises a step of filtering the output voltage signal. In some embodiments, the method further comprises a step of summing two or more output voltage signals generated from DC voltage signals of two or more photovoltaic sources. In some embodiments, the method further comprises a step of determining an optimal duty cycle in which the power provided in the output voltage signal is maximal. In some embodiments, converting the DC voltage signal into the first AC voltage signal is performed using an AC bridge that comprises a plurality of switches switched in the first frequency.

It is another object of the subject matter to disclose a method for handling AC voltage signals, the method comprising receiving a first AC voltage signal having a first frequency, the first AC voltage signal is converted from signal generated by a photovoltaic source, said first frequency is not applicable to provide voltage signal for a standard electrical appliance. The method further comprises obtaining a second AC voltage signal having a second frequency, the difference between the first frequency and the second frequency is a function of a desired frequency that is applicable to provide voltage signal for a standard electrical appliance. The method further comprises periodically sampling the second AC voltage signal to determine a current value of the second AC signal and summing the first AC value a predefined number of times, said predefined number of times is a function of the sampled current value of the second AC signal. In some cases, the method further comprises a step of disabling at least some of a plurality of input voltage signals as a function of the sampled AC voltage signal.

It is another object of the subject matter to disclose a system for handling voltage signals, the system comprises a first conversion module for receiving a

DC voltage signal and producing a first AC voltage signal in a frequency not applicable in a standard electrical appliance. The system further comprises a second conversion module for receiving the first AC voltage signal and generating a second first AC voltage signal having a frequency applicable in a standard electrical appliance.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary non-limited embodiments of the disclosed subject matter will be described, with reference to the following description of the embodiments, in conjunction with the figures. The figures are generally not shown to scale and any sizes are only meant to be exemplary and not necessarily limiting. Corresponding or like elements are optionally designated by the same numerals or letters.

Figure 1 shows a photovoltaic power generation environment for converting power signals from a photovoltaic panel to an electronic appliance, according to exemplary embodiments of the subject matter; Figure 2 shows a voltage signal-adapting unit used in a PV generator for converting voltage signal to be used by an electronic appliance, according to exemplary embodiments of the subject matter;

Figure 3 shows a flow of voltage signal process used in a PV generator, according to exemplary embodiments of the subject matter Figure 4 shows a DC bridge and an AC bridge, according to exemplary embodiments of the subject matter;

Figure 5 shows a general PV architecture of a PV power generating environment providing voltage signal to a grid, according to exemplary embodiments of the subject matter; Figure 6 shows a flow of a method used to convert a DC voltage signal into a voltage signal applicable in a standard electrical appliance, according to some exemplary embodiments of the disclosed subject matter;

Figure 7 discloses a method for converting a first AC signal into an AC signal having an applicable frequency, according to some exemplary embodiments of the disclosed subject matter;

Figure 8 shows a conversion system for converting an AC voltage signal having a non-applicable frequency into an AC voltage signal that can be used in a standard electrical appliance, according to exemplary embodiments of the disclosed subject matter; Figures 9A and 9B show an environment for manipulating voltage signals, according to exemplary embodiments of the disclosed subject matter;

Figures 1OA and 1OB shows an apparatus for creating a vector of voltage signals, according to exemplary embodiments of the disclosed subject matter; Figure 11 shows a current fed converter generating multiple Isolated DC outputs from a single PV source, according to exemplary embodiments of the disclosed subject matter;

Figures 12A and 12B show a system for manipulating voltage signals, according to exemplary embodiments of the disclosed subject matter; Figure 13 shows a system for manipulating voltage signals without an AC bridge, according to exemplary embodiments of the disclosed subject matter;

Figure 14 illustrates a series connection of a PV sources fed by a common DC source, according to exemplary embodiments of the disclosed subject matter.

DETAILED DESCRIPTION

One technical challenge disclosed in the subject matter is converting a DC signal into an AC signal in a desired frequency that us applicable to a standard electrical appliance. Another technical challenge is performing said conversion without the need for a centralized inverter.

One technical solution of the disclosed subject matter is performing a multiplication of two or more voltage signals derived from a PV source in order to generate an AC voltage signal in a desired frequency. The PV source is connected to a voltage signal-adapting unit that performs the multiplication other operations such as filtering the residues of a sinusoidal voltage signal that results from the multiplication in order to provide the desired voltage signal. Another technical solution is inputting an AC voltage signal having a first frequency into a switching circuitry operating in a second frequency, wherein the difference between the first and second frequencies is the desired frequency of the electrical appliance or electronic grid.

Figure 1 shows a photovoltaic power generation environment for converting power signals from a PV source to an electronic appliance, according to exemplary embodiments of the subject matter. Photovoltaic (PV) power generation environment 100 comprises a plurality of PV generators such as 102, 104. Each PV generator comprises one or more PV source such as 110, 112 and 114. The plurality of PV sources may be arranged as an array, as a cell, group of arrays and the like. Each panel or array of panels outputs a power signal.

Each PV generator comprises a signal-adapting unit such as 120 of PV generator 102 that verifies that the output voltage signal of the PV generator 102 is an utilizable AC voltage signal having a desired frequency. The signal-adapting unit such as 120 may be implemented on a chip or ASIC. The signal-adapting unit 120 may comprise modules that provide at least some of the PV functionality, such as Maximal Power Point Tracking (MPPT), DC to AC conversion, line synchronization and the like. In some exemplary embodiments, one signal- adapting unit such as 120 may be connected to a variety of PV sources. The Photovoltaic power generation environment 100 further comprises or is connected to an electronic load 105 that receives an output power signal of the PV generators. Such electronic load 105 may be any electronic appliance that consumes electric power, and may further be an electric grid. The signal generated by the PV sources, or by an array of such PV sources, is typically a DC voltage signal having properties different from the properties required in order to supply power the electronic load 105. The signal-adapting unit 120 is used to adapt the power signal generated by the PV source such as 110, 112 and 114 to the properties of the electronic load 105. Figure 2 shows a signal-adapting unit used in a PV generator for converting voltage signal to be used by an electronic appliance, according to exemplary embodiments of the subject matter. The signal-adapting unit 120 receives as input one or more input voltage signals from one or more PV sources. Each voltage signal is characterized by at least voltage signal amplitude and a frequency. A commonly used input voltage signal frequency is 2000Hz, while the common frequency of an electronic grid is 50Hz. The signal-adapting unit 120 outputs a voltage signal having a different frequency while maintaining the power properties.

In some exemplary embodiment of the disclosed subject matter, the signal-adapting unit 120 comprises a full bridge 140 and an AC bridge 142. The full bridge is also known as H-bridge. The full bridge 140 comprises a V_DC input and two pairs of switches as disclosed in figure 4. Each pair comprises two switches connected in series. The pairs are connected in parallel. In some cases, each switch comprises a diode and a transistor, such as Ql and Gl. The V_DC is the output of the PV source. According to figure 4, the full bridge 140 comprises a first branch and a second branch connected in parallel. The first branch comprises switch Ql and switch Q3. The second branch comprises switch Q2 and switch Q4. At a given time, one switch of each branch is open, which enables the DC voltage signal on a load to change its sign frequently, upon changing the open and closed switches. For example, from To to T₅ switches Ql and Q4 are open, and the DC voltage signal on the load 440 is positive. Then, from T₅ to T₁₀, switches Q2 and Q3 are open, and the DC voltage signal on the load is negative. A square wave AC voltage signal named V_brj_dge having positive and negative values is the output of full bridge 140 and the input of the AC bridge 142. The frequency of the V_bri_dge is a function of the frequency of the full bridge 140 that can be determined by a user or by a computer, and can also be varied.

AC bridge 142 comprises switches that can manipulate AC voltage signals. The switching frequency of the AC bridge 142 is higher or lower than the switching frequency of the full bridge 140 by a predetermined frequency value that refers to the desired frequency. For example, in case the desired frequency is 100Hz and the full bridge 140 switching frequency is 1000Hz, the AC bridge switching frequency may be 900Hz or 1100 Hz. Other manipulations between frequency values may also be applicable. The switching frequencies of both the full bridge 140 and the AC bridge 142 is determined by an external module, such as control unit 170. The control unit 170 may be part of the PV generator, or may be connected thereto, either wired or wirelessly. The control unit 170 may implement a set of rules using software, hardware and the like, and may operate automatically or according to user's commands. The output voltage signal of AC bridge 142 is a complex signal, having harmonics in multiple frequencies. For example, in case the input frequency of the voltage signal inputted into the full bridge 140 was 50KHz, and the desired frequency is 50Hz, the output of the AC bridge will have phases in 50Hz and other phases.

The signal-adapting unit 120 may further comprise a filtering unit 160 for filtering the phases in the non-desired frequencies, thereby isolating only a sinusoid voltage signal in the desired frequency of an electrical grid or an electrical appliance or load that receive power from the PV generator. The filtering unit 160 may comprise one or more filters. Such filters may be low pass filters, Band pass filters, or any other filter desired by a person skilled in the art such that the output from the AC bridge is filtered besides the phase in the desired frequency. The signal-adapting unit 120 may further comprise a MPPT unit 150 for providing a maximal output power of the voltage signal provided to the electrical load such as 105 of figure 1. The maximal power may be a multiplication of the voltage signal and the current. In some exemplary embodiments, the maximal power is achieved without the MPPT unit 150. In such case, a detector detects the power of the voltage signal in various duty cycles and determines the optimal duty cycle.

The voltage signal-adapting unit 120 may further comprise a spread spectrum unit 130 for varying the energy on various frequency bands while keeping the output voltage signal in the desired frequency. The spread spectrum unit 130 modulates the frequency of the switches in both the full bridge 140 and the AC bridge 142 while keeping the difference between the two frequencies as a function of the desired frequency of the electrical grid. As such, the spread spectrum unit 130 may modulate the frequency in a predetermined amount of Hertz every predefined period of time. Such modulation may alternatively be performed according to an alert notification, or by a person managing the PV field.

Figure 3 shows a flow of a voltage signal process used in a PV generator, according to exemplary embodiments of the subject matter. The flow begins with a Vi_n value 205 inputted into a full bridge 210. The Vj_n value 205 is a DC voltage signal having a Fo frequency that cannot be used by a conventional electrical appliance, for example 5000Hz. The output of the full bridge 210 is V_brid_ge 215, which is an AC voltage signal having the same F₀ frequency as Vj_n 205. The V_bri_dge 215 entered into AC bridge 220 is converted into Vac 225 which is an AC voltage signal having multiple phases, one of the multiple phases is of a desired frequency that can be used in a standard electrical appliance. Filtering the V_ac 225 results in V_outpul 230 that contains phases in the desired frequency only.

Figure 4 shows the DC bridge and the AC bridge, according to exemplary embodiments of the subject matter. The DC bridge is disclosed in details in figure 2. The AC bridge is a switching circuitry operating in a frequency determined by an operator or by a control unit (not shown). The frequency of the switching circuitry may vary during operation. The desired frequency of the output voltage signal is a function of the difference between the frequency of the AC voltage signal inputted into the switching circuitry and the frequency of the switching circuitry, for example the frequency in which the switches are opened and closed. In some cases, the control unit varies the switching frequency of the first DC bridge while varying also the switching frequency of the second bridge to keep the difference frequency is sometimes used as a control method such as commonly used at resonance or quasi resonance conversion topologies. In some exemplary embodiments, the switching circuitry 450 comprises more than one switch positioned in parallel. The switches in switching circuitry 450 are opened and closed in a frequency different from the frequency of the input voltage signal by the desired frequency. The output of the switching circuitry is equivalent to multiplying the inputted AC voltage signal with another signal having the frequency of the switching circuitry 450.

In some exemplary embodiments, the switching circuitry 450 comprises pairs of switches to handle AC voltage signal having both positive and negative values. Such pair of switches comprises, for example, switches Ql Ia, Ql Ib. The switches Ql Ia, Ql Ib operate in different directions, and as such, can allow voltage to flow in the circuitry when the voltage signal value is either positive or negative. In some cases, the switching circuitiy comprises more than one pair of switches and each pair of switches operate similarly to one switch in the H bridge 140 described above. The switching frequency is determined to have a specific difference from the difference of the AC voltage signal inputted into the switching circuitry 450. One exemplary embodiment for such switch may consist of a transistor and a diode. Other implementations may also be applicable. One example of a transistor may be a MOFSET transistor, a bi-polar transistor and the like.

Figure 5 shows a PV power-generating environment providing voltage signal to a grid, according to exemplary embodiments of the subject matter. The PV power-generating environment 500 comprises a plurality of PV generators 502, 504, 506 connected to each other in series. At least some of the PV generators 502, 504, 506 receive DC input from a PV source (not shown). The output of the PV generators 502, 504, 506 is an AC voltage signal in a desired frequency used by a standard electrical appliance or a standard electrical grid. In some cases, the amplitude of the AC voltage signal outputted from some of the PV generators is lower than the voltage signal required in a standard electrical appliance, for example 220 volts. As such, the voltage signals from multiple outputs of PV generators are summed and the output voltage signal 520 from the PV power-generating environment 500 is sufficient for immediate use by an electrical grid or appliance.

Figure 6 shows a flow of a method used to convert a DC voltage signal into a voltage signal applicable in a standard electrical appliance, according to some exemplary embodiments of the disclosed subject matter. In step 610, the voltage signal-adapting unit configured to manipulate voltage signals receives a DC signal from a PV source, such as a PV panel, PV array and the like. In step 620, the DC signal is modified into a first AC signal. The first AC signal may consist of a square wave or a sinusoid wave having a first frequency not applicable in a standard electrical appliance. A control unit, a set of rules, or a user may determine the first frequency. According to some exemplary embodiments, modification of the DC signal into the first AC voltage signal may be performed using an electrical component that comprise a plurality of switches that switch in a first switching frequency. The frequency of the first AC voltage signal may be a function of the first switching frequency. The sign of the first AC signal, the output of the conversion electrical component, consists of positive and negative values as the sign changes according to the frequency of the switching. A control unit may determine parameters related to the first AC voltage signal, for example the duty cycle, frequency and the like. The frequency may be determined by changing the switching frequency of a switching circuitry used for generating the first AC voltage signal. In some exemplary embodiments, the duty cycle is about 66 percents or two thirds of a period.

In step 630, the first AC voltage signal is converted into a second AC voltage signal having a second frequency applicable in a standard electrical appliance. The second frequency may be for example 100Hz, 50Hz or any value desired by a person skilled in the art. In some exemplary embodiments of the disclosed subject matter, the conversion is performed by multiplying the first AC voltage signal having the first frequency with a second AC signal having a second frequency. In such case, the difference between the first frequency and the second frequency is a function of the desired frequency. The second AC signal is produced by the system of the subject matter, for example using a switching mechanism assembled in an electrical component. The result of the multiplication is an output AC voltage signal having multiple frequency components. The main component of the output AC voltage signal is in the desired frequency, and other phases are in frequencies different from the desired frequency in other harmonics. In a numeric example, the first frequency is 5000Hz and the desired frequency is 50Hz. The second AC voltage signal is 5050Hz. Multiplying the first AC signal and the second AC signal results in a output AC signal having a main phase in 50Hz and other phases in frequencies such as 5050Hz, 10050Hz and the like. In step 640, the output AC voltage signal is filtered, hence only the phase in the desired frequency remains. Such filtering may be performed on one output AC voltage signal, or on several AC signals having the same frequencies and the same desired frequency. Filtering the plurality of output voltage signals is performed in parallel or in series, after the plurality of output voltage signals are summed to each other. Such summation is disclosed in step 650, and provides for a stronger voltage signal that can suffice with system requirements. For example, voltage signal of 220 volts is required in some electrical grids, and may be achieved by an output voltage signal of a single PV source. Hence, two or more output voltage signals are summed and result in a voltage signal having an applicable frequency and a sufficient voltage amplitude. Filtering the output voltage signal may be performed using a low pass filter, a band pass filter or another filter desired by a person skilled in the art.

Figure 7 discloses a method for converting a first AC voltage signal into an output AC voltage signal having an applicable frequency, according to some exemplary embodiments of the disclosed subject matter. In step 710, two AC voltage signals are received at an electrical module performing the conversion. The two AC voltage signals are a first and second AC voltage signals having a first and second frequency, respectively. One of the AC voltage signals is provided from a PV source. In some cases, more than one AC voltage signal are inputted, having the same frequency and phase. Both AC voltage signals are of a sinusoidal form or a square wave form. The difference between the first and second frequencies is predefined and can be determined by a module handling production of power from a PV source. In step 720, the current value of the second AC signal is sampled. In some cases, the step of sampling further comprises a step of quantizing the sampled value.

In step 730, the first AC voltage signal is multiplied by the sampled current value of the second AC signal. In some exemplary embodiments of the disclosed subject matter, multiplication is performed by summing the first AC voltage signal a number of times. Such number of times is a function of the sampled value of the second AC voltage signal. The electronic summation module performing the summation receives multiple voltage signals representing the first AC voltage signal, connected in series. The number of the voltage signals inputted into the electronic summation module is a function of the maximal value of the second AC voltage signal. The electronic summation module comprises a disabling mechanism for at least a portion of the input points of the multiple first AC voltage signal inputted into the summation module. The value of the AC voltage signal provided from the PV sources may be multiplied by 1, 0 or -1 in case of negative voltage values. Another example of disabling an input signal is closing two switches in the same branch of an H bridge, such as Lower switches or two higher switches of the H bridge. In step 740, the number of enabled voltage signals is determined as a function of the sampled value of the second DC signal. In step 750, at least a portion of the inputted first voltage signals are disabled. Disabling may be performed by any method desired by a person skilled in the art, for example by multiplying the value by zero. In step 760, the electronic summation module sums the enabled input voltage signals. In some exemplary embodiments, the summed voltage signals vary in time. This may be performed by changing the indices of the summed voltage signals when there are 20 input voltage signals to be summed, and only 4-7 are required. For example, in a first second signals 1-4 are summed and in the next second signals 5-8 are summed, to maintain an output signal that reflects the values of all input signals. The summation of a predefined number of first DC voltage signals is equivalent to multiplying the first DC voltage signal and the second DC voltage signal. The result of such multiplication is equivalent to the output signal resulting in step 630 of figure 6 and has a main phase in a desired frequency.

Figure 8 shows a conversion system for converting an AC voltage signal having a non-applicable frequency into an AC voltage signal that can be used in a standard electrical appliance, according to exemplary embodiments of the disclosed subject matter. The conversion system 800 comprises multiple input units such as input units 802, 804, 806. Each of the input units enables a voltage signal to be inputted into the conversion system. At least a portion of the input units comprises or are connected to disable mechanisms, such as 812, 814 and 816. Each of the disable mechanisms is capable of disabling the voltage signal provided by the input unit associated with the disable mechanism. For example, disable mechanism can disable the voltage signal provided by the input unit 802. Each disable mechanism may receive a command from a control unit 840. Alternatively, a set of rules may be embedded in each disable mechanism, according to said set of rules the disable mechanism determines when to disable the input unit associated thereto. The conversion unit fϊirther comprises a sampling module 830 for sampling the second AC voltage signal. The sampled value of the voltage signal is a parameter used when determining the number of enabled input units. The number of enabled input units provide for summing the first AC voltage signals. The multiple summed first AC voltage signals are equivalent to multiplying the AC first voltage signal and the second AC voltage signals. The outcome of such multiplication is an output voltage signal. Said output voltage signal may then be filtered or summed using conventional modules.

Figures 9A and 9B show an environment for manipulating voltage signals, according to exemplary embodiments of the disclosed subject matter. PV sources 902, 904 and 916 generate a DC voltage signals manipulated by signal-adapting units 912, 914, 916 respectively. In case the amplitude of the voltage signals outputted from the signal-adapting units 912, 914, 916 is lower than required, the voltage signals are added to each other. The voltage signals are arranged serially to enable the summation. For example, in case the output voltage signal from the signal-adapting unit 912 is 20 volts and the electrical appliance requires at least 100 volts to operate, at least five identical PV sources will sum the output voltage signals and produce the summation to the electrical appliance.

Figure 9B shows a general description of a system that generates AC output at a desired line voltage and frequency. The system is based on a momentary sum of active power cells connected in series. The control unit 930 determines the momentary operating mode of each PV source, which can obtain 3 modes of operation: Positive active, Negative active, zero output voltage. The control unit 930 interchanges the active and non-cells so that each PV source outputs its power (on average) so that each PV source is not discharged nor overcharged over time. It is desired that each PV source will output an equal power on average over a given time period.

Figures 1OA and 1OB shows an apparatus for creating a vector of voltage signals, according to exemplary embodiments of the disclosed subject matter. PV source 1010 outputs a voltage signal into a Multiple Output Current Fed Converter (MOCFC) 1015 creating a vector of n floating DC voltage sources. The MOCFC 1015 processes power of a single PV source. The MOCFC 1015 is controlled to operate at the maximum output power point of the PV source. Each DC source Vl- Vn, feeds a single power cell of the series chain. Figure 1OB show a system comprising a plurality of PV sources 1010,

1020, 1030. A current fed converter such as 1015, 1025, 1035 is connected to a PV source and receive a Dc voltage signal from the PV source. In some exemplary embodiments, at least a portion of the current fed converters 1015, 1025, 1035 generate a plurality of similar voltage sources Vl- Vn is processing the signal received from each PV source. All output DC voltages generated by the current fed converters 1015, 1025, 1035 that have the same indices are connected in parallel. For example Vl output from current fed converter 1015 is connected in parallel to Vl output from current fed converter 1025. Such a configuration minimizes the influence of possibly different output voltage of each PV source on the AC output voltage.

Figure 11 shows a current fed converter generating multiple Isolated DC outputs from a single PV source, according to exemplary embodiments of the disclosed subject matter.

Figures 12A and 12B show a system for manipulating voltage signals, according to exemplary embodiments of the disclosed subject matter. The system of figure 12A comprises a plurality of PV sources or outputs of PV generators connected in series to achieve a desired line voltage. According to the exemplary embodiment, each PV source provides a DC voltage signal to an input filter. The output of the input filter is a DC voltage signal inputted into a DC H bridge. All the DC H bridges operate at the same switching frequency fθ, and all AC H bridge operate at the same frequency fl. Switching frequencies are determined by the control unit to provide an output voltage signal in a desired and applicable frequency. Figure 12B shows a similar system, in which the input signals provided from the plurality of PV sources are similar, as the plurality of PV sources are being fed by a vector of multiple DC floating sources such as generated by the current fed converter of figure 1OB. voltage fed converters can also provide for the same functionality as the current fed converter. The topology disclosed above is suitable in case of a single PV source. It should be noted that each power cell could work at a different pair of frequencies fO and fl, as long as the difference between frequencies is the desired frequency used by all power cells. The frequency fO and fl of a power cell can be swept in order to achieve better performance of the power cell such as increased efficiency.

Figure 13 shows a system for manipulating voltage signals without an AC bridge, according to exemplary embodiments of the disclosed subject matter. The system comprises a comprising a 1st stage of a current fed converter generating a plurality of AC voltage signals at a common frequency fO. The current fed converter may receive a DC voltage signal as input and outputs the plurality of AC signals. The array of the AC voltage signals Vl - Vn is processed by an array of AC H bridges operating at the same frequency fl. The 1st current fed converter can be realized by various topologies of current fed converters as desired by a person skilled in the art.

Figure 14 illustrates a series connection of a PV sources fed by a common

DC source, according to exemplary embodiments of the disclosed subject matter. Such topology requires isolation of the channels by transformers. This configuration enables voltage boosting with a reduced primary — secondary turn ratio of the transformer.

While the disclosure has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings without departing from the essential scope thereof. Therefore, it is intended that the disclosed subject matter not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but only by the claims that follow.

Claims

CLAIMS 1. A method of producing applicable electrical power from a photovoltaic source, the method comprising: receiving a DC voltage signal from the photovoltaic source; converting the DC voltage signal into a first AC voltage signal having a first frequency, said first frequency is not applicable to provide voltage signal for a standard electrical appliance; inputting the first AC voltage signal having the first frequency into a switching circuit operating in a second frequency, the difference between the first frequency and the second frequency is a function of a desired frequency that is applicable to provide voltage signal for a standard electrical appliance; generating an output voltage signal from the multiplication of the first Ac voltage signal and the second AC voltage signal 2. The method according to claim I₅ further comprises a step of filtering the output voltage signal.

3. The method according to claim I₅ further comprises a step of summing two or more output voltage signals generated from DC voltage signals of two or more photovoltaic sources.

4. The method according to claim I₅ further comprises a step of determining an optimal duty cycle in which the power provided in the output voltage signal is maximal.

5. The method according to claim I₅ wherein converting the DC voltage signal into the first AC voltage signal is performed using a bridge that comprises a plurality of switches switched in the first frequency.

6. A method for handling AC voltage signals, the method comprising: receiving a first AC voltage signal having a first frequency, the first AC voltage signal is converted from signal generated by a photovoltaic source, said first frequency is not applicable to provide voltage signal for a Standard electrical appliance; obtaining a second AC voltage signal having a second frequency, the difference between the first frequency and the second frequency is a function of a desired frequency that is applicable to provide voltage signal for a standard electrical appliance; sampling the second AC voltage signal to determine a current value of the second AC signal; summing the first AC value a predefined number of times, said predefined number of times is a function of the sampled current value of the second AC signal.

7. The method according to claim 6, further comprises a step of disabling at least some of a plurality of input voltage signals as a function of the sample4

AC voltage signal.

8. A system for handling voltage signals, the system comprising: a first conversion module for receiving a DC voltage signal and producing a first AC voltage signal in a frequency not applicable in a standard electrical appliance; a second conversion module for receiving the first AC voltage signal and generating a second first AC voltage signal having a frequency applicable in a standard electrical appliance.

9. The system according to claim 8, wherein the first conversion module is a voltage fed converter.

10. The system according to claim 8, wherein the first conversion module is a DC H bridge.

11. The system according to claim 8, wherein the first conversion module is a current fed converter.