Safety mechanisms, wake up and shutdown methods in distributed power installations

FIELD AND BACKGROUND

0001The present invention relates to distributed power systems and, more particularly, wake-up and shutdown algorithms for the photovoltaic distributed power systems.

0002Utility networks provide an electrical power system to utility customers. The distribution of electric power from utility companies to customers utilizes a network of utility lines connected in a grid-like fashion, referred to as an electrical grid. The electrical grid may consist of many independent energy sources energizing the grid in addition to utility companies energizing the grid, with each independent energy source being referred to as a distributed power (DP) generation system. The modern utility network includes the utility power source, consumer loads, and the distributed power generation systems which also supply electrical power to the network. The number and types of distributed power generation systems is growing rapidly and can include photovoltaics, wind, hydro, fuel cells, storage systems such as battery, super-conducting flywheel, and capacitor types, and mechanical devices including conventional and variable speed diesel engines, Stirling engines, gas turbines, and micro-turbines. These distributed power generation systems are connected to the utility network such that they operate in parallel with the utility power sources.

0003A conventional installation of a solar distributed power system <b>10</b>, including multiple solar panels <b>101</b>, is illustrated in <figref idref="f0001">Figure 1</figref>. Since the voltage provided by each individual solar panel <b>101</b> is low, several panels <b>101</b> are connected in series to form a string <b>103</b> of panels <b>101.</b> For a large installation, when higher current is required, several strings <b>103</b> may be connected in parallel to form overall system <b>10.</b> The interconnected solar panels <b>101</b> are mounted outdoors, and connected to a maximum power point tracking (MPPT) module <b>107</b> and then to an inverter <b>104.</b> MPPT <b>107</b> is typically implemented as part of inverter <b>104</b> as shown in <figref idref="f0001">Figure 1</figref>. The harvested power from DC sources <b>101</b> is delivered to inverter <b>104</b>, which converts the direct-current (DC) into alternating-current (AC) having a desired voltage and frequency, which is usually 110V or 220V at 60Hz, or 220V at 50Hz. The AC current from inverter <b>104</b> may then be used for operating electric appliances or fed to the power grid.

0004As noted above, each solar panel <b>101</b> supplies relatively very low voltage and current. A problem facing the solar array designer is to produce a standard AC current at 120V or 220V root-mean-square (RMS) from a combination of the low voltages of the solar panels. The delivery of high power from a low voltage requires very high currents, which cause large conduction losses on the order of the second power of the current <i>i²</i>. Furthermore, a power inverter, such as inverter <b>104</b>, which is used to convert DC current to AC current, is most efficient when its input voltage is slightly higher than its output RMS voltage multiplied by the square root of 2 (which is the peak voltage). Hence, in many applications, the power sources, such as solar panels <b>101</b>, are combined in order to reach the correct voltage or current. A large number of panels <b>101</b> are connected into a string <b>103</b> and strings <b>103</b> are connected in parallel to power inverter <b>104.</b> Panels <b>101</b> are connected in series in order to reach the minimal voltage required for inverter <b>104.</b> Multiple strings <b>103</b> are connected in parallel into an array to supply higher current, so as to enable higher power output.

0005<figref idref="f0001">Figure 1B</figref> illustrates one serial string <b>103</b> of DC sources, <i>e.g.</i>, solar panels <b>101a</b> - <b>101d</b>, connected to MPPT circuit <b>107</b> and inverter <b>104</b>. The current versus voltage (IV) characteristics is plotted (<b>110a - 110d</b>) to the left of each DC source <b>101.</b> For each DC power source <b>101</b>, the current decreases as the output voltage increases. At some voltage value, the current goes to zero, and in some applications the voltage value may assume a negative value, meaning that the source becomes a sink. Bypass diodes (not shown) are used to prevent the source from becoming a sink. The power output of each source <b>101</b>, which is equal to the product of current and voltage (<i>P</i>=<i>i</i>*<i>V</i>), varies depending on the voltage drawn from the source. At a certain current and voltage, close to the falling off point of the current, the power reaches its maximum. It is desirable to operate a power generating cell at this maximum power point (MPP). The purpose of the MPPT is to find this point and operate the system at this point so as to draw the maximum power from the sources.

0006In a typical, conventional solar panel array, different algorithms and techniques are used to optimize the integrated power output of system <b>10</b> using MPPT module <b>107.</b> MPPT module <b>107</b> receives the current extracted from all of solar panels <b>101</b> together and tracks the maximum power point for this current to provide the maximum average power such that if more current is extracted, the average voltage from the panels starts to drop, thus lowering the harvested power. MPPT module <b>107</b> maintains a current that yields the maximum average power from system <b>10.</b>

0007However, since power sources <b>101a - 101d</b> are connected in series to single MPPT <b>107</b>, MPPT <b>107</b> selects a maximum power point which is some average of the maximum power points of the individual serially connected sources <b>101</b>. In practice, it is very likely that MPPT <b>107</b> would operate at an I-V point that is optimum for only a few or none of sources <b>101.</b> In the example of <figref idref="f0001">Figure 1B</figref>, the selected point is the maximum power point for source <b>101b</b>, but is off the maximum power point for sources <b>101a</b>, <b>101c</b> and <b>101d.</b> Consequently, the arrangement is not operated at best achievable efficiency.

0008The present applicant has disclosed in co-pending <patcit id="pcit0001" dnum="US11950271B"><text>US application 11/950,271</text></patcit> entitled "Distributed Power Harvesting Systems Using DC Power Sources", the use of an electrical power converter, <i>e.g.</i> DC-to-DC converter, attached to the output of <i>each</i> power source, <i>e.g.</i> photovoltaic panel. The electrical power converter converts input power to output power by monitoring and controlling the <i>input</i> power at a maximum power level.

0009The term "signaling" or "signaling mechanism" as used herein refers to either a signal modulated on an electromagnetic carrier signal or a simple unmodulated signal such as an on/off signal "keep alive" signal or "dry contact" signal. For a modulated signal, the modulation method may be by any such method known in the art by way of example, frequency modulation (FM) transmission, amplitude modulation (AM), FSK (frequency shift keying) modulation, PSK (phase shift keying) modulation, various QAM (Quadrature amplitude modulation) constellations, or any other method of modulation.

0010The term "power module" as used herein includes power converters such as a DC-DC power converter but also includes modules adapted to control the power passing through the module or a portion of the power, whether by switching or other means.

0011<patcit id="pcit0002" dnum="US2008236648A1"><text>US 2008/236648 A1</text></patcit> discloses a solar cell installation comprising a DC power source in the form of solar cell modules, and a regulator module which may be connected to an inverter.

0012<patcit id="pcit0003" dnum="WO2004107543A2"><text>WO 2004/107543 A2</text></patcit> discloses a solar panel array generation system in which DC/DC converters are configured to require a signal from a control system to output power.

0013<patcit id="pcit0004" dnum="US2005275979A"><text>US 2005/275979</text></patcit> discloses a signalling system for a power distribution system with a signal generator which provides a local generator control signal with a preset protocol, the local generator being shut down when the control signal is not detected.

SUMMARY

0014The following summary of the invention is included in order to provide a basic understanding of some aspects and features of the invention. This summary is not an extensive overview of the invention and as such it is not intended to particularly identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented below.

0015According to an aspect of the present invention, there is provided a distributed power system according to claim 1, including a DC power source and a power module. The power module includes an input coupled respectively to the DC power source and an output. An inverter is coupled to the output. The inverter converts power input from the output of the power module to output power. A signaling mechanism comprised by the inverter is adapted for controlling operation of the power module. During operation of the distributed power the signaling mechanism superimposes a signal on the output of the power module. The signaling mechanism may include a switch integrated with the inverter, the switch modulating the signal onto the output of the power module. A receiver integrated with the power modules receives the signal from the inverter. Optionally a detection mechanism in the power module detects a signal at the frequency of the electrical grid. Optionally, a signal from the electrical grid is detected in the output of the power module at a higher frequency up-converted from the frequency of the electrical grid. Optionally, a detection mechanism in the power module detects a switching frequency of the inverter. The power modules are configured for operation in a safety mode, and during the safety mode, the power at the output of the power module, the voltage across the output of the power module, and/or the current flowing through it, are limited so as not to endanger personnel. The power module may include a detection mechanism wherein during operation of the distributed power system, the detection mechanism detects a signal from the inverter. Based on the signal, the operation of the power module is varied from the safety mode of operation to a normal mode of operation for converting power of the DC power source from the input to the output of the power module.

0016According to another aspect of the present invention there is provided a method according to claim 8 for operating a distributed power system. The system includes a DC power source and a power module. The power module includes an input coupled to the DC power source. The power module includes an output. An inverter is coupled to the output of the power module. The inverter converts a power output from the power module to an output power. The method includes operating the power modules in a safety mode by limiting the power output from the power module. The safety mode is characterized by having less than a predetermined amount (e.g. ten milliamperes) of current flow and/or less than a predetermined amount (e.g. 2 Volts) through the output of the power module. A signal from the inverter is preferably monitored and upon detecting the signal from the inverter, the power input to the inverter is increased by operating the power module in a normal mode of operation for converting power of the DC power source from the input to the output of the power module. Upon detecting the signal and prior to the operation of the power module in the normal mode of operation, the voltage of the output of the power module is preferably ramped up slowly. The normal mode of operation of the power module may include controlling a maximum peak power at the input coupled to the DC power sources.

0017The foregoing and/or other aspects will become apparent from the following detailed description when considered in conjunction with the accompanying drawing figures.

0018In the following description the term "embodiment" may have been used for subject-matter that is not part of the invention as defined by the appended claims. Only those examples that comprise all the features of the independent claims are part of the invention and thus embodiments of the invention. Parts of the subject-matter of the description not covered by the claims constitutes background art or examples useful for understanding the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

0019The accompanying drawings, which are incorporated in and constitute a part of this specification, exemplify embodiments of the present invention and, together with the description, serve to explain and illustrate principles of the invention. The drawings are intended to illustrate various features of the illustrated embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are not necessarily drawn to scale.

0020The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: <ul id="ul0001" list-style="none"><li><figref idref="f0001">Figure 1</figref> is a block diagram of a conventional power harvesting system using photovoltaic panels as DC power sources;</li><li><figref idref="f0001">Figure 1B</figref> illustrates current versus voltage characteristic curves for one serial string the DC power sources of <figref idref="f0001">Figure 1</figref>;</li><li><figref idref="f0002">Figure 2</figref> is a simplified block diagram illustrating a distributed power harvesting circuit, based on the disclosure in <patcit id="pcit0005" dnum="US950271" dnum-type="L"><text>U.S. application 11/950,271</text></patcit>, according to an aspect of the present invention;</li><li><figref idref="f0002">Figure 2A</figref> is a simplified block diagram of a DC-to-DC converter, including a feature of the present invention;</li><li><figref idref="f0003">Figure 3</figref> illustrates an exemplary DC-to-DC converter, is a simplified block diagram illustrating in more detail;</li><li><figref idref="f0004">Figure 4</figref> is a simplified block diagram of another exemplary system, according to an embodiment of the present invention;</li><li><figref idref="f0004">Figure 4A</figref> is a simplified block diagram illustrating in more detail, a power module according to the embodiment of <figref idref="f0004">Figure 4</figref>;</li><li><figref idref="f0005">Figure 4B</figref> is a simplified block diagram illustrating in more detail, a signaling mechanism attached to a conventional inverter, according to embodiments of the present invention;</li><li><figref idref="f0006">Figure 5</figref> is a simplified flow diagram illustrating a method for wake-up and shutdown of a power harvesting system with a safety mode, according to a feature of the present invention;</li><li><figref idref="f0007">Figure 5A</figref> is a flow diagram illustrating methods for wake-up and shutdown of a power harvesting system, according to embodiments of the present invention, the flow diagram including method steps performed by the power converters/modules; and</li><li><figref idref="f0008">Figure 6</figref> is another flow diagram illustrating methods for wake-up and shutdown of a power harvesting system, according to embodiments of the present invention, the flow diagram including method steps performed by the inverter of <figref idref="f0002">Figure 2</figref> or signaling block of <figref idref="f0005">Figure 4B</figref>.</li></ul>

DETAILED DESCRIPTION

0021Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.

0022It should be noted, that although the discussion herein relates primarily to wake-up and shutdown methods in photovoltaic systems and more particularly to those systems previously disclosed in U.S. Application Serial No. <patcit id="pcit0006" dnum="US11950271B"><text>11/950,271</text></patcit>, the present invention may, by non-limiting example, alternatively be configured as well using conventional photovoltaic distributed power systems and other distributed power systems including (but not limited to) wind turbines, hydroturbines, fuel cells, storage systems such as battery, super-conducting flywheel, and capacitors, and mechanical devices including conventional and variable speed diesel engines, Stirling engines, gas turbines, and micro-turbines.

0023By way of introduction, it is important to note that aspects of the present invention have important safety benefits. While installing or performing maintenance on photovoltaic systems according to certain aspects of the present invention, installers are protected from danger of shock or electrocution since systems according to embodiments of the present invention do not output potentially dangerous high voltage and/or currents when an operational inverter is not connected during installation and maintenance procedures.

0024Before explaining embodiments of the invention in detail, it is to be understood that the invention is not limited in its application to the details of design and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

0025Reference is now made to <figref idref="f0002">Figure 2</figref> which illustrates a distributed power harvesting circuit <b>20</b>, based on the disclosure in <patcit id="pcit0007" dnum="US950271" dnum-type="L"><text>U.S. application 11/950,271</text></patcit>. Circuit <b>20</b> enables connection of multiple distributed power sources, for example solar panels <b>101a - 101d</b>, to a single power supply. Series string <b>203</b> of solar panels <b>101</b> may be coupled to an inverter <b>204</b> or multiple connected strings <b>203</b> of solar panels <b>101</b> may be connected to a single inverter <b>204.</b> In configuration <b>20</b>, each solar panel <b>101a - 101d</b> is connected individually to a separate power converter circuit or a module <b>205a - 205d</b>. Each solar panel <b>101</b> together with its associated power converter circuit <b>205</b> forms a power generating element <b>222.</b> (Only one such power generating element <b>222</b> is marked in <figref idref="f0002">Figure 2</figref>.) Each converter <b>205a - 205d</b> adapts optimally to the power characteristics of the connected solar panel <b>101a - 101d</b> and transfers the power efficiently from input to output of converter <b>205.</b> Converters <b>205a - 205d</b> are typically microprocessor controlled switching converters, <i>e.g.</i> buck converters, boost converters, buck/boost converters, flyback or forward converters, etc. The converters <b>205a - 205d</b> may also contain a number of component converters, for example a serial connection of a buck and a boost converter. Each converter <b>205a - 205d</b> includes a control loop <b>221</b>, <i>e.g.</i> MPPT loop that receives a feedback signal, not from the converter's output current or voltage, but rather from the converter's input coming from solar panel <b>101.</b> The MPPT loop of converter <b>205</b> locks the input voltage and current from each solar panel <b>101a - 101d</b> at its optimal power point, by varying one or more duty cycles of the switching conversion typically by pulse width modulation (PWM) in such a way that maximum power is extracted from each attached panel <b>101a - 101d.</b> The controller of converter <b>205</b> dynamically tracks the maximum power point at the converter input. Feedback loop <b>221</b> is closed on the input power in order to track maximum input power rather than closing a feedback loop on the output voltage as performed by conventional DC-to-DC voltage converters.

0026As a result of having a separate MPPT circuit in each converter <b>205a - 205d</b>, and consequently for each solar panel <b>101a - 101d</b>, each string <b>203</b> may have a different number or different specification, size and/or model of panels <b>101a - 101d</b> connected in series. System <b>20</b> of <figref idref="f0002">Figure 2</figref> continuously performs MPPT on the output of each solar panel <b>101a - 101d</b> to react to changes in temperature, solar radiance, shading or other performance factors that effect one or more of solar panels <b>101a</b> - <b>101d</b>. As a result, the MPPT circuit within the converters <b>205a - 205d</b> harvests the maximum possible power from each panel <b>101a - 101d</b> and transfers this power as output regardless of the parameters effecting other solar panels <b>101a - 101d.</b>

0027The outputs of converters <b>205a - 205d</b> are series connected into a single DC output that forms the input to inverter <b>204.</b> Inverter <b>204</b> converts the series connected DC output of converters <b>205a</b> - <b>205d</b> into an AC power supply, Inverter <b>204</b>, regulates the voltage at the input of inverter <b>204.</b> In this example, an independent control loop <b>220</b> holds the voltage input to inverter <b>204</b> at a set value, say 400 volts. The current at the input of inverter <b>204</b> is typically fixed by the power available and generated by photovoltaic panels <b>101</b>.

0028According to a feature of the present invention, information regarding wakeup or shut-down may be conveyed from inverter <b>204</b> to converters <b>205</b>. The information may be transmitted using any of the methods well known to those experienced in the art. According to certain embodiments, a modulation method may be used, by way of example, frequency modulation (FM) transmission, amplitude modulation (AM), FSK (frequency shift keying) modulation, PSK (phase shift keying) modulation, various QAM (Quadrature amplitude modulation) constellations, or any other method of modulation. Alternatively, inverter <b>204</b>, while converting power from its input to its output, actively creates a frequency ripple in serial string <b>203.</b> During normal operation, the 100Hz (or 120Hz in USA) ripple is detectable in serial string <b>203</b> since the capacitors of inverter <b>204</b> do not entirely block the alternating current (AC), and an additional signaling mechanism is not required to produce the 100/120 Hz signal in serial string <b>203.</b> Alternatively or in addition, one or more switching frequencies of inverter <b>204</b>, typically 16Khz or 32 KHz may be detectable as leakage or provided intentionally to serial string <b>203.</b>

0029Reference is now made to <figref idref="f0002">Figure 2A</figref> which illustrates a feature of the present invention. In <figref idref="f0002">Figure 2A</figref>, converter <b>205</b> is shown in more detail. Integrated with power converter <b>205</b> is a detector/receiver <b>207</b>, according to a feature of the present invention which is configured to receive, optionally amplify and detect the signal, <i>e.g</i> at 100/120 Hz originating in inverter <b>204</b>.

0030Controller <b>306</b> preferably either polls a signal input <b>209</b> from receiver/detector <b>207</b> or uses signal input <b>209</b> as an interrupt so that only when detector/receiver <b>207</b> detects the 100/120Hz signal, is module <b>205</b> in a normal operating mode converting power from its input to its output. Receiver <b>207</b> is alternatively configured to detect the 16/32 KHz inverter switching frequency and provides an enabling signal to controller on signal input <b>209</b> while inverter <b>204</b> is operating.

0031Reference is now made to <figref idref="f0003">Figure 3</figref> which illustrates an exemplary DC-to-DC converter <b>205</b>, according to a feature of the present invention. DC-to-DC converters are used to either step down or step up a DC voltage input to a higher or a lower DC voltage output, depending on the requirements of the output circuit. However, in the embodiment of <figref idref="f0003">Figure 3</figref> the DC-DC converter <b>205</b> is used as a power converter, i.e., transferring the input power to output power, the input voltage varying according to the MPPT at the input, while the output current is dictated by the constant input voltage to inverter <b>104</b>, <b>204</b>. That is, the input voltage and current may vary at any time and the output voltage and current may vary at any time, depending on the operating condition of DC power sources <b>101.</b>

0032Converter <b>205</b> is connected to a corresponding DC power source <b>101</b> at input terminals <b>314</b> and <b>316</b>. The converted power of the DC power source <b>101</b> is output to the circuit through output terminals <b>310</b>, <b>312</b>. Between the input terminals <b>314</b>, <b>316</b> and the output terminals <b>310</b>, <b>312</b>, the converter circuit includes input and output capacitors <b>320</b>, <b>340</b>, backflow prevention diodes <b>322</b>, <b>342</b> and a power conversion circuit including a controller <b>306</b> and an inductor <b>308.</b>

0033Diode <b>342</b> is in series with output <b>312</b> with a polarity such that current does not backflow into the converter <b>205</b>. Diode <b>322</b> is coupled between the positive output lead <b>312</b> through inductor <b>308</b> which acts a short for DC current and the negative input lead <b>314</b> with such polarity to prevent a current from the output <b>312</b> to backflow into solar panel <b>101</b>.

0034A potential difference exists between wires <b>314</b> and <b>316</b> due to the electron-hole pairs produced in the solar cells of panel <b>101</b>. Converter <b>205</b> maintains maximum power output by extracting current from the solar panel <b>101</b> at its peak power point by continuously monitoring the current and voltage provided by panel <b>101</b> and using a maximum power point tracking algorithm. Controller <b>306</b> includes an MPPT circuit or algorithm for performing the peak power tracking. Peak power tracking and pulse width modulation (PWM) are performed together to achieve the desired input voltage and current. The MPPT in controller <b>306</b> may be any conventional MPPT, such as, <i>e.g.</i>, perturb and observe (P&amp;O), incremental conductance, etc. However, notably the MPPT is performed on panel <b>101</b> directly, i.e., at the input to converter <b>205</b>, rather than at the output of converter <b>205</b>. The generated power is then transferred to the output terminals <b>310</b> and <b>312</b>. The outputs of multiple converters <b>205</b> may be connected in series, such that the positive lead <b>312</b> of one converter <b>205</b> is connected to the negative lead <b>310</b> of the next converter <b>205</b>.

0035In <figref idref="f0003">Figure 3</figref>, converter <b>205</b> is shown as a buck plus boost converter. The term "buck plus boost" as used herein is a buck converter directly followed by a boost converter as shown in <figref idref="f0003">Figure 3</figref>, which may also appear in the literature as "cascaded buck-boost converter". If the voltage is to be lowered, the boost portion is substantially shorted. If the voltage is to be raised, the buck portion is substantially shorted. The term "buck plus boost" differs from buck/boost topology which is a classic topology that may be used when voltage is to be raised or lowered, and sometimes appears in the literature as "cascaded buck-boost". The efficiency of "buck/boost" topology is inherently lower then a buck or a boost. Additionally, for given requirements, a buck-boost converter will need bigger passive components then a buck plus boost converter in order to function. Therefore, the buck plus boost topology of <figref idref="f0003">Figure 3</figref> has a higher efficiency than the buck/boost topology. However, the circuit of <figref idref="f0003">Figure 3</figref> continuously decides whether it is bucking or boosting. In some situations when the desired output voltage is similar to the input voltage, then both the buck and boost portions may be operational.

0036The controller <b>306</b> may include a pulse width modulator, PWM, or a digital pulse width modulator, DPWM, to be used with the buck and boost converter circuits. Controller <b>306</b> controls both the buck converter and the boost converter and determines whether a buck or a boost operation is to be performed. In some circumstances both the buck and boost portions may operate together. That is, the input voltage and current are selected independently of the selection of output current and voltage. Moreover, the selection of either input or output values may change at any given moment depending on the operation of the DC power sources. Therefore, in the embodiment of <figref idref="f0003">Figure 3</figref>, converter <b>205</b> is constructed so that at any given time a selected value of input voltage and current may be up converted or down converted depending on the output requirement.

0037In one implementation, an integrated circuit (IC) <b>304</b> may be used that incorporates some of the functionality of converter <b>205</b>. IC <b>304</b> is optionally a single ASIC able to withstand harsh temperature extremes present in outdoor solar installations. ASIC <b>304</b> may be designed for a high mean time between failures (MTBF) of more than 25 years. However, a discrete solution using multiple integrated circuits may also be used in a similar manner. In the exemplary embodiment shown in <figref idref="f0003">Figure 3</figref>, the buck plus boost portion of the converter <b>305</b> is implemented as the IC <b>304</b>. Practical considerations may lead to other segmentations of the system. For example, in one aspect of the invention, the IC <b>304</b> may include two ICs, one analog IC which handles the high currents and voltages in the system, and one simple low-voltage digital IC which includes the control logic. The analog IC may be implemented using power FETs which may alternatively be implemented in discrete components, FET drivers, A/Ds, and the like. The digital IC may form controller <b>306</b>.

0038In the exemplary circuit <b>205</b> shown, the buck converter includes input capacitor <b>320</b>, transistors <b>328</b> and <b>330</b>, diode <b>322</b> positioned in parallel to transistor <b>328</b>, and inductor <b>308</b>. Transistors <b>328</b>, <b>330</b> each have a parasitic body diode <b>324</b>, <b>326</b>. The boost converter includes inductor <b>308</b>, which is shared with the buck converter, transistors 348 and <b>350</b> a diode <b>342</b> positioned in parallel to transistor <b>350</b>, and output capacitor <b>340</b>. Transistors <b>348</b>, <b>350</b> each have a parasitic body diode <b>344</b>, <b>346</b>.

0039System <b>20</b> includes converters <b>205</b> which are connected in series and carry the current from string <b>203</b>. If a failure in one of the serially connected converters <b>205</b> causes an open circuit in failed converter <b>205</b>, current ceases to flow through the entire string <b>203</b> of converters <b>205</b>, thereby causing system <b>20</b> to stop functioning. Aspects of the present invention provide a converter circuit <b>205</b> in which electrical components have one or more bypass routes associated with them that carry the current in case of an electrical component failing within one of converters <b>205</b>. For example, each switching transistor of either the buck or the boost portion of the converter has its own diode bypass. Also, upon failure of inductor <b>308</b>, the current bypasses the failed inductor <b>308</b> through parasitic diodes <b>344</b>,<b>346.</b>

0040In <figref idref="f0003">Figure 3</figref>, detector/receiver block <b>207</b> is shown which is configured to provide an enable signal <b>209</b> to microcontroller <b>306</b> when the communications signal originating in inverter <b>104</b>,<b>204</b> is detected.

0041Reference in now made to <figref idref="f0004">Figures 4</figref>, which illustrate system <b>40</b>, according to an embodiment of the present invention. For simplicity, a single string <b>423</b> is shown of distributed power sources, <i>e.g.</i> solar panels <b>101a-101d</b> connected to respective power modules <b>405a-d.</b> Serial string <b>423</b> is input to conventional inverter <b>104</b> through wires <b>412</b> and <b>410.</b> The output of inverter <b>104</b> is connected to and supplies electrical power to the electrical grid. At the input of inverter <b>104</b>, is connected a signaling mechanism <b>420</b> which superimposes a signal on serial string <b>423</b> through wires <b>412</b> and <b>410</b> when inverter <b>104</b> is converting power to the grid.

0042Reference is now also made to <figref idref="f0005">Figure 4B</figref> which illustrates in more detail signaling mechanism <b>420.</b> Signaling mechanism <b>420</b> includes a relay <b>428</b> which is normally open and controlled by a microcontroller <b>422.</b> Relay <b>428</b> is switched at a given rate, <i>e.g.</i> 100 Hz, and the signal is superimposed by action of relay <b>428</b> onto serial string <b>423</b> over wires <b>410</b> and <b>412.</b> Microcontroller <b>422</b> typically provides the control of the signal, <i>e.g.</i> 100Hz, during normal operation of distributed power system <b>40.</b> Microcontroller <b>422</b> is typically connected to one or more sensors in order to monitor the operation of inverter <b>104.</b> In the example of <figref idref="f0005">Figure 4B</figref>, microcontroller 422 monitors over-voltage of the input DC voltage to inverter <b>104.</b> The example shown in <figref idref="f0005">Figure 4B</figref> includes an input DC voltage tap <b>432</b> connected to an analog to digital converter (A/D) <b>430</b>, the output of which is provided to microcontroller <b>422.</b> The tap 432 may be, e.g., a Hall-effect sensors, series connected resistor across which the voltage drop is measured, etc. In one embodiment, an over-voltage condition as measured by microcontroller <b>422</b>, results in microcontroller <b>422</b> stopping the signaling through relay <b>428</b> and/or opening one or more protective relays <b>424</b>, <b>426</b> in series with the input DC voltage to inverter <b>104.</b> Note that one switch <b>424 or 426</b> may be enough for performing the required action, and two switches in series are shown solely for the purpose of illustration that double protection might be required by some regulatory bodies. A power management block <b>434</b> taps voltage for powering microcontroller <b>422</b> and any other active electronics components (not shown) in block <b>420.</b>

0043Reference is now made to <figref idref="f0004">Figure 4A</figref> which illustrates in more detail certain aspects of power module <b>405.</b> Integrated with power module <b>405</b> is detector/receiver <b>207</b> which is configured to receive, optionally amplify and detect the signal, <i>e.g.</i> at 100 Hz, produced by signal mechanism <b>420.</b> Controller <b>306</b> preferably either polls signal input <b>209</b> or uses signal input <b>209</b> as an interrupt so that only when detector/receiver <b>207</b> detects the 100Hz signal, is module <b>405</b> operating in a normal operating mode. Power module <b>405</b> is shown to include a bypass diode <b>414.</b> Optionally, power module <b>405</b> may include a conventional DC/DC switching converter with a control loop based on output power, Power module <b>405</b> includes at least one switch <b>416</b> controlled by controller <b>306</b> which functions to stop normal operation of power from the input of module <b>405</b> to the output of <b>405</b> when signal input <b>209</b> is absent indicating that inverter <b>104</b> is not transferring power to the electrical grid.

0044Reference is now made to <figref idref="f0006">Figure 5</figref> which illustrates a simplified method for safe operation of system <b>40</b>, according to an aspect of the present invention. In step <b>501</b>, active control circuits, <i>e.g.</i> microcontroller <b>306</b>, are turned on. Module <b>205</b>, <b>405</b> begins operation (step <b>53</b>) in a safety mode. In safety mode, output current and/or voltage from module <b>405</b> is limited, for instance output voltage is limited to 2 volts and output current is limited to 10mA so that a person can touch the wires of serial string <b>203, 423</b> without any danger of electrocution.

0045Controller <b>306</b> maintains safety mode operation (step <b>53</b>) until a communications signal, <i>e.g.</i> 100 Hz, is received (decision box <b>505</b>) by receiver/detector <b>207</b> from inverter <b>204</b> or signaling block <b>420.</b> When the communications signal is received (decision block <b>505</b>) indicating inverter <b>104</b> or <b>204</b> is connected and converting power, safety mode (step <b>53</b>) of operation ends. When the communications signal is received (decision block <b>505</b>), module <b>405</b> preferably enters a normal operation mode (step <b>57</b>), typically with maximum power point tracking. The normal operation of transferring power is maintained as long as the communications signal, <i>e.g.</i> 100Hz is received from inverter <b>204</b> or signal mechanism <b>420</b>, and no other warning condition is present. If the communications signal is not detected, or another warning condition is present, the normal mode (step <b>57</b>) is typically ended and power conversion of modules <b>405</b> is typically turned off. If in decision box <b>509</b>, the communications signal is not detected, or another warning condition is present, the normal mode (step <b>57</b>) is typically ended and power conversion of modules <b>405</b> is typically turned off.

0046Reference is now made to <figref idref="f0007">Figure 5A</figref>, which illustrates a method <b>50</b> for wake-up and shutdown of module <b>405</b>, according to embodiments of the present invention. Method <b>50</b> is applicable to both systems <b>20</b> and <b>40</b>. In step <b>501</b>, active control circuits, <i>e.g.</i> microcontroller <b>306</b>, are turned on. Active control circuits are typically turned on (step <b>501</b>) in the early morning when there is sufficient light to power the active control circuits typically with voltage of DC voltage source <b>101</b> reaching three volts, In decision block <b>503</b>, when voltage output - or power output - from DC voltage source <b>101</b> is sufficiently high and stable (<i>e.g</i>. voltage input to module <b>405</b> is ten volts for a period of 30 seconds), then module <b>205</b>,<b>405</b> begins operation (step <b>53</b>) in a safety mode. In safety mode, output current and/or voltage from module <b>405</b> is limited, for instance output voltage is limited to 2 volts and output current is limited to 10mA so that a person can touch the wires of serial string <b>203</b>,<b>423</b> without any danger of electrocution. Note also, that in this case even if 25 modules are connected in series, the maximum output voltage of the string doesn't exceed 50V - which means the string voltage is still safe. Referring back to <figref idref="f0003">Figure 3</figref>, safety mode may be achieved by controller <b>306</b> in module <b>405</b> by turning on FET <b>330</b> and turning off FETS <b>328</b>, <b>348</b>, and <b>350</b>. Output wire <b>412</b> is held close to zero volts. Alternatively, the controller 306 may alternate the switches (e.g. switches 324 &amp; 326 of buck converter) at a low duty-cycle in order to maintain a low output voltage.

0047Referring back to <figref idref="f0007">Figure 5A</figref>, controller <b>306</b> maintains safety mode operation (step <b>53</b>) until a communications signal, <i>e.g.</i> 100 Hz, is received by receiver/detector <b>207</b> from inverter <b>204</b> or signaling block <b>420.</b> When the communications signal is received (decision block <b>505</b>) indicating inverter <b>104</b> or <b>204</b> is connected and converting power, safety mode (step <b>53</b>) of operation ends. When the communications signal is received (decision block <b>505</b>), module <b>405</b> preferably enters a voltage control mode (step <b>55</b>) and voltage output between wires <b>412</b>,<b>410</b> is slowly ramped up. Voltage continues to ramp up, typically as high as +60V until module <b>205</b>,<b>405</b> detects that current is being drawn (step <b>507</b>). When sufficient current is drawn (step <b>507</b>), module <b>205</b>, <b>405</b> begins normal operation, (step <b>57</b>) <i>e.g.</i> for module <b>205</b>, the normal mode is the maximum power point (MPP) tracking mode of converting DC power from its input to its output by maintain maximum power at its input. The normal operation of transferring power is maintained as long as the communications signal, <i>e.g.</i> 100Hz is received from inverter <b>204</b> or signal mechanism <b>420</b>, and no other warning condition is present. If the communications signal is not detected, or another warning condition is present, the normal mode (step <b>57</b>) is typically ended and power conversion of modules <b>405</b> is typically turned off. Exemplary warning conditions in decision box <b>509</b>, which cause module <b>205</b>,<b>405</b> to end normal mode (step <b>57</b>) and to stop transferring power to its output include: (i) input voltage less than predetermined value, e.g. about 10 volts for 5 seconds, (ii) rapid change in output voltage, for instance greater than 20% in 100 milliseconds, (iii) reception of signal requesting to stop producing power, (iv) not receiving a signal to produce power (in the case where recurring "allow production" signals are required for the converter to function), or (v) output exceeds over voltage threshold caused for instance when multiple modules <b>205</b> in string <b>203</b> are converting power (step 57) and one of modules <b>205</b> of string <b>203</b> shuts down, then the other modules <b>205</b> of string <b>203</b> have a raise of output voltage.

0048Reference is now made to <figref idref="f0008">Figure 6</figref>, which illustrates a method <b>60</b> performed by inverter <b>204</b> or signaling block <b>420</b> attached at the input of inverter <b>104</b>. In step <b>601</b>, inverter <b>104</b> is off or inverter <b>204</b> is on standby, and not converting power to its output. In decision box <b>603</b>, start conditions for turning on inverter <b>104</b>,<b>204</b> are determined. Typically, as a safety requirement, inverter <b>104</b> delays operation (converting power to its output) until after at least 5 minutes of connection to a functioning AC-grid at its output. This safety requirement may be achieved using microcontroller <b>422</b> and at least one of relays <b>424</b> and <b>426</b> in signaling block <b>420</b>. In inverter <b>204</b>, a minimum voltage is required at the input to inverter 204 (<i>e.g</i>. if the safety output voltage of each module is 2V, and the minimal-length string allowed contains 5 modules, the inverter will wait until at least 10V are present at its DC input) and only thereafter does inverter <b>204</b> begin to charge its input, typically to a specified standard input of 400V.

0049In step <b>605</b>, communications signal, <i>e.g</i> 100Hz, is superimposed on serial string <b>203</b>,<b>423</b> either from signaling mechanism <b>420</b> or from inverter <b>204</b> for instance when at least a 50 Watt load is attached to the output of inverter <b>204</b>. In decision box <b>607</b>, when the specified input voltage is reached, <i>e.g</i> 400V for inverter <b>204</b>, inverter <b>204</b> is turned on or inverter <b>104</b> is attached to serial string <b>423</b> by mechanism <b>420.</b> In decision box <b>609</b>, if a time out occurs before the minimum specified input voltage is reached of inverter <b>204</b>,<b>404</b> then inverter is returned to the off or standby state (step <b>601</b>). Otherwise inverter <b>204</b>,<b>404</b> is connected or turned on in step <b>611</b>. Inverter <b>204</b>, <b>404</b> remains on and connected unless a warning condition (decision box <b>613</b>) occurs. Possible warning conditions include, (i) disconnection from the electrical grid, (ii) electrical grid stops producing power (islanding), (iii) less than 50 Watts transferred in the last minute, (iv) input voltage to inverter <b>204</b>,<b>404</b> is over the maximum limit, and (v) input power is over the maximum limit. If a warning condition occurs (decision box <b>613</b>) communications signal is turned off (step <b>615</b>) for inverter <b>404</b> or inverter <b>204</b> is turned off or put into standby.

0050The present invention has been described in relation to particular examples, which are intended in all respects to be illustrative rather than restrictive. Those skilled in the art will appreciate that many different combinations of hardware, software, and firmware will be suitable for practicing the present invention. Moreover, other implementations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. Various aspects and/or components of the described embodiments may be used singly or in any combination in the server arts. It is intended that the specification and examples be considered as exemplary only.

0051While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made.