Low-voltage, low-frequency, multilevel power converter

Abstract

This invention discloses a low-voltage, low-frequency, multi-level power converter capable of power conversion. The power converter may include a low-voltage, low-frequency circuit comprising multiple phase-shift inverters connected in series; multiple low-voltage source inputs; and multiple phase-shift inverters connected in series. Each of the multiple phase-shift inverters can be configured to receive at least one of the multiple low-voltage source inputs and generate at least one square wave output. A half-sine wave output can be derived from the generated at least one square wave output.

Description

[0001] This application is a divisional application of Chinese invention patent application No. 201780011525.7, filed on January 17, 2017, entitled "Low-voltage low-frequency multi-level power converter".

[0002] Cross-reference to related applications

[0003] This application claims priority to U.S. Provisional Application No. 62 / 291,333 and U.S. Provisional Application No. 62 / 278,832, both entitled LOW VOLTAGE, LOW FREQUENCY, MULTI LEVEL POWER CONVERTER, the entire contents of which are incorporated herein by reference as if they were described in their entirety. Technical Field

[0004] This disclosure generally relates to power conversion, such as solar inverters and battery-coupled inverters / chargers, and more specifically to low-voltage, low-frequency, multi-level power converters. Summary of the Invention

[0005] According to certain embodiments of this disclosure, low-voltage, low-frequency, multilevel power converter (LV LF MLPC) apparatus and methods for power conversion (i.e., DC / AC or AC / DC) can be provided. This disclosure can use low-voltage, low-cost, high-performance components (e.g., MOSFETs, diodes, capacitors, inductors, resistors, etc.) and can drive power devices (e.g., MOSFETs and diodes) at low frequencies (e.g., common frequencies) to generate the required voltage and current waveforms (e.g., 220Vrms / 50Hz or 240Vrms / 60Hz half-sine waves) for AC loads. Therefore, this disclosure can provide several advantages, such as low cost, high efficiency, low environmental impact (e.g., low THD, low EMI, low leakage current, etc.), high reliability, and safety standard compliance.

[0006] LV LF MLPCs can be used in some embodiments to convert electricity from a power source (e.g., a photovoltaic (PV) panel, battery, fuel cell, etc.) to a load (e.g., a utility or any other AC load). Individual LV LF power converters (LV LFPCs) can be integrated with a power source (e.g., a PV panel or battery module), for example, to manufacture integrated AC modules. As an example, multiple AC modules can be connected in series to manufacture an LV LF MLPC system.

[0007] As a non-limiting example, the LV LF MLPC and power conversion systems described herein can be applied to a wide range of systems, from residential to commercial, industrial to utility, and, for example, as non-limiting examples, as grid-connected solar inverters, off-grid solar inverters, solar cell-coupled inverters, grid-connected battery chargers, etc. Furthermore, depending on the geographic region of the application (e.g., the United States, Europe, etc.), the input power source (solar, battery, etc.), the load (single-phase / three-phase utility, AC load, etc.), and the required power level, the LV LF MLPC system can be any type of three-phase / single-phase, PFC / non-PFC, etc.

[0008] As a non-limiting example, the disclosed LV LF MLPC can generate a 240Vrms, 60Hz voltage wave by adding a predetermined number (e.g., up to 14) of series-connected low-voltage (e.g., 24.2Vdc), low-frequency (e.g., 60Hz) phase-shifted power supplies. As an example, the power supply can come from a PV panel integrated with a DC / DC optimizer, or from a battery integrated with a bidirectional DC / DC charger.

[0009] As a non-limiting example, the disclosed LV LF MLPC is less expensive and uses lower-voltage, more efficient components compared to existing solutions in the solar inverter industry, such as AC microinverters, power optimizers, and string inverters. It also eliminates the need for isolation transformers and dissipates less power in the switching interval due to the very low switching frequency and low device blocking voltage during typical operation.

[0010] The disclosed embodiments can also use series cables, eliminating the need for expensive bus connector systems. Furthermore, compared to DC power optimizers, the disclosed LV LF MLPC can significantly reduce system costs by eliminating string inverters (which typically account for a large portion of the system cost). Moreover, the disclosed embodiments can achieve higher overall system efficiency than existing technologies, for example, by avoiding high-frequency switching of high-voltage devices and switches during the inversion phase.

[0011] Compared to previously known string inverters, the disclosed LV LF MLPC benefits from module-level control, which may ultimately be required by the National Electrical Code (NEC) and Underwriters Laboratories (UL), and also from module-level maximum power point tracking (MPPT), which utilizes the PV board at its most efficient operating point. By avoiding the need for various additional high-voltage components, the embodiment also saves on overall cost and improves efficiency.

[0012] Therefore, some embodiments may provide a low-voltage, low-frequency multilevel power converter, which may include a low-voltage, low-frequency circuit comprising: a plurality of low-voltage source inputs; and a plurality of phase-shift inverters connected in series. Each of the plurality of phase-shift inverters may be configured to receive at least one of the plurality of low-voltage source inputs and generate at least one square wave output. A half-sine wave output may be derived from the generated at least one square wave output. Attached Figure Description

[0013] Referring now to the accompanying drawings, which are incorporated herein by reference, non-limiting embodiments of the present disclosure are shown, wherein like numerals denote like elements, and wherein:

[0014] Figure 1A A block diagram of a square wave-based LV LF MLPC is shown;

[0015] Figure 1B This shows an enlarged view of a portion of the square wave output of each inverter in the LV LF MLPC;

[0016] Figure 2 Asymmetrical and symmetrical (centered) square wave patterns are shown;

[0017] Figure 3 A block diagram of a sine wave-based LV LF MLPC is shown;

[0018] Figure 4 A block diagram of a square-wave-based LV LF MLPC with an expanded H-bridge converter is shown.

[0019] Figure 5 A block diagram of a sinusoidal LV LF MLPC with an expanded H-bridge converter is shown;

[0020] Figure 6 An example of a power supply configuration as an input to an LV LF PC is shown;

[0021] Figure 7A A non-limiting example of an LV LF MLPC for regulating output voltage is shown;

[0022] Figure 7B An enlarged view of the LV SVR and the grid interconnection circuitry is shown;

[0023] Figure 8 The rise / fall time of the step voltage at the square wave output of the LV LF MLPC inverter is shown.

[0024] Figure 9 The advanced connection of the LV SVR900 between the LV LF MLPC connected to the PV panel and the load and power grid is shown;

[0025] Figure 10 A PV and battery storage system integrated with public utilities is shown;

[0026] Figure 11 A block diagram of the integrated AC PV module and AC battery module in an LV LF MLPC system is shown.

[0027] Figure 12 An exemplary database calculation of the phase shift angle is shown; and

[0028] Figure 13 Exemplary calculations of THD and optimal phase shift are shown for some embodiments. Detailed Implementation

[0029] The accompanying drawings and descriptions provided herein have been simplified to illustrate aspects relevant to a clear understanding of the apparatus, systems, and methods described herein, while other aspects that may be found in typical similar apparatuses, systems, and methods have been omitted for clarity. Those skilled in the art will therefore recognize that other elements and / or operations may be desirable and / or necessary for implementing the apparatuses, systems, and methods described herein. However, because such elements and operations are known in the art and because they are not conducive to a better understanding of this disclosure, a discussion of such elements and operations may not be provided herein for the sake of brevity. Nevertheless, this disclosure is still considered to include all such elements, variations, and modifications of the described aspects that are known to those skilled in the art.

[0030] Embodiments are provided throughout this disclosure to make the present disclosure thorough and to fully convey the scope of the disclosed embodiments to those skilled in the art. Numerous specific details, such as examples of specific components, apparatus, and methods, are set forth to provide a thorough understanding of embodiments of the present disclosure. However, it will be apparent to those skilled in the art that certain specific details of the disclosure are not necessary, and that embodiments may be implemented in different forms. Thus, the disclosed embodiments should not be construed as limiting the scope of the present disclosure. As noted above, in some embodiments, well-known processes, well-known device structures, and well-known techniques may not be described in detail.

[0031] The terminology used herein is for the purpose of describing particular implementations only and should not be construed as limiting. For example, unless otherwise stated, the singular forms “a,” “an,” and “described” as used herein should also include the plural forms. The terms “comprising,” “including,” and “having” are inclusive and thus specify the presence of the illustrated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or combinations thereof. The steps, processes, and operations described herein should not be construed as necessarily interpreting their respective performance in the specific order discussed or shown, unless explicitly identified as a preferred or desired performance order. It should also be understood that additional or alternative steps may be used in place of or in combination with the disclosed aspects.

[0032] When a component or layer is referred to as “on,” “above,” “connected to,” or “coupled to” another component or layer, unless otherwise explicitly stated, it may be directly on, directly connected to, or directly coupled to the other component or layer, or there may be intermediate components or layers. Conversely, if a component is stated as “directly on,” “directly above,” “directly connected to,” or “directly coupled to,” it indicates that there are no intermediate components or layers. Other terms used to describe relationships between components should be interpreted in a similar manner (e.g., “between” vs. “directly between,” “adjacent” vs. “directly adjacent,” etc.). Furthermore, the term “and / or” as used herein includes any and all combinations of one or more of the related listed items.

[0033] Furthermore, while the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers, and / or portions, these elements, components, regions, layers, and / or portions should not be limited by these terms. These terms may only be used to distinguish one element, component, region, layer, or portion from another. Therefore, unless explicitly stated in the context, terms such as “first,” “second,” and other numerical terms used herein do not imply order or sequence. Thus, the first element, component, region, layer, or portion discussed below may be referred to as the second element, component, region, layer, or portion without departing from the teachings of the embodiments.

[0034] As a non-limiting example, the foregoing figures may illustrate specific component types, such as MOSFETs, rather than the more general bidirectional devices; however, unless otherwise indicated, these component choices are not intended to limit the embodiments. That is, the figures have been described in sufficient detail to enable those skilled in the art to practice this disclosure, but it should be understood that at least other configurations can be utilized, and structural, facilitatory, and electrical characteristics can be changed without departing from the scope of this disclosure. Therefore, the following description of exemplary embodiments should not be considered limiting.

[0035] refer to Figure 1A and 1B The diagram shows an LV LF MLPC 100, which is adapted to pass a device with an appropriate phase angle of 104 ( The input voltages 102 (V1, ..., Vn) (e.g., 24.2V) are summed from n (e.g., 14) voltage sources 102 to generate a common rated voltage wave V_MLI 120 (e.g., 240Vrms, 60Hz). Those skilled in the art will understand that the input voltages 102 (V1, ..., Vn) do not need to be equal and can be different in many applications. Furthermore, the phase angle ( The phase angles can be equal (symmetrical or centered) or unequal (asymmetrical). Furthermore, the phase angle can be adjusted based on the number (n) and voltage values ​​(V1, ..., Vn) of the input power supplies. To reduce total harmonic distortion (THD) and increase the balanced power consumed by a single power source; however, the dependence of THD on the power supply voltage value is not significant, and in many cases, as non-limiting examples and as follows regarding Figure 12 and 13 Further discussion suggests that the phase angles can be calculated offline and are considered fixed. The phase angles can be equal (symmetrical) and the pulse duty cycles (Di+ and Di-) ​​can be adjusted to achieve a similar common rated voltage waveform with similar THD levels. However, this configuration may result in more unbalanced power being drawn from the individual power supplies.

[0036] Additionally, the input power source used in the disclosed embodiments can vary. As a non-limiting example, the input power source may include, but is not limited to, batteries, fuel cells, solar cells and / or particularly solar panels (and / or associated batteries).

[0037] Return now Figure 1AThe power inverter 110 can switch at very low frequencies, such as common frequencies (e.g., 50Hz or 60Hz); however, the switching frequency can be higher, such as 2, 3, or 4 times the mains frequency. Furthermore, since the power inverter 110 is connected in series, the circuit components can be low-voltage, providing the benefits of low cost, fast switching speed, and low conduction losses. Moreover, since the disclosed inverter 110 can be driven at low frequencies, switching losses, electromagnetic interference (EMI), and common-mode current (leakage current) can be very low. The low switching frequency also allows for regulation of voltage step rise / fall times to further reduce EMI and leakage current, with acceptable increments in switching losses. Furthermore, the output voltage (V_MLI) quality (THD) is less dependent on the load level and may not change across the entire load range. The output voltage V_MLI and output current I can be in phase (unity power factor), leading, or lagging (non-unity power factor), as... Figure 1A The bidirectional system shown is illustrated. Optionally, the series voltage regulator 112 may be coupled (e.g., in series) to one or more inverters 110 to smooth voltage steps at the output 120. The series voltage regulator 112 may take the form of a full-bridge converter or any other type of voltage regulator known in the art.

[0038] As a non-limiting example, for an asymmetric case study and considering that the supply voltage is equal to 24.2Vdc, i.e., V = [24.2V, 24.2V, ..., 24.2V], and the phase angle is equal to = [1.8°, 6.1°, 10.5°, 14.4°, 18.9°, 23.4°, 27.9°, 32.4°, 37.8°, 43.2°, 48.6°, 55.8°, 63°, 75.6°], the duty cycle of the high-side device is equal to D+ = D- = [28.5%, 30.8%, 31.6%, 32.5%, 32.75%, 33%, 33.25%, 33%, 32.75%, 32.5%, 31.6%, 30.8%, 28.5%], and the duty cycle of the low-side device is equal to 1-D+ (or 1-D-), the output voltage (V_MLI) THD will be 2.8%. Clearly, the output voltage THD is independent of the output load, which is important to those skilled in the art.

[0039] Assuming a 14.7A rms load half-sinusoidal current (V_MLI = 240Vrms, load resistance = 16.3ohms), and knowing that all converters are connected in series and handle the same load current, the output power of each converter will be different, such as P = [199W, 231W, 246W, 260W, 267W, 272W, 275W, 275W, 272W, 267W, 260W, 246W, 231W, 199W], the total power will be 3500W. Since the order in which converters are turned on in a series converter chain should not affect the output voltage waveform, as a non-limiting example, one way to balance the average power among similar power supplies is to “cyclically” rotate the on-time of the converters so that the output power of individual power supplies is balanced over n(14) or n / 2(7) common voltage cycles (e.g., at 60Hz, the cycle would be 16.66ms).

[0040] As a non-limiting example, another method for balancing power between similar power sources is described below. Assuming the input power supply voltage is controllable, adjusting the input voltage V = [30.9V, 26.6V, 25V, 23.8V, 23V, 22.5V, 22.3V, 22.3V, 22.5V, 23V, 23.8V, 25V, 26.6V, 30.9V] while maintaining the phase angle and duty cycle at their previous values ​​will result in an output voltage THD of 3.6% and an output power of 250W for each power source (balanced power).

[0041] As mentioned above, the output voltage THD is not significantly dependent on the input supply voltage and can be easily kept below the desired value, which is typical of global standards. For example, considering the same phase angle and duty cycle of the 14 supplies in an LV LF MLPC system 100, the THD values ​​for different case studies would be as follows:

[0042] V=[24.2V, 24.2V, 24.2V, 24.2V, 24.2V, 24.2V, 24.2V, 24.2V, 24.2V, 24.2V, 24.2V, 24.2V, 24.2V, 24.2V] THD=2.8%

[0043] V=[30.9V, 26.6V, 25V, 23.8V, 23V, 22.5V, 22.3V, 22.3V, 22.5V, 23V, 23.8V, 25V, 26.6V, 30.9V] THD=3.6%

[0044] V=[30V,16V,13V,32V,20V,15V,10V,33V,38V,24V,24V,12V,36V,24V] THD=4.35%

[0045] V=[33V,8V,45V,20V,33V,12V,8V,40V,22V,36V,11V,20V,45V,8V] THD=4.4%

[0046] V=[0V,31V,31V,0V,31V,31V,31V,31V,0V,31V,31V,31V,31V,31V] THD=4.7%

[0047] V=[15V,16V,13V,32V,28V,15V,32V,33V,38V,24V,24V,20V,20V,24V] THD=4.8%

[0048] It should be noted that in the absence of LV SVR (e.g., Figure 7A and Figure 7B In the case of the LV SVR shown, the low THD value discussed above can be achieved.

[0049] As a non-restrictive example, Figure 1A and 1B This illustrates one of many modes for generating a half-sinusoidal voltage wave from n series-connected LV LF inverters 110s. Relatedly, Figure 2 The power converter's on-state modes are shown, both asymmetrical and symmetrical. For example, compared to the third pattern 206 (far right), which shows a symmetrical or centered pattern, Figure 2 The first two signal patterns, 202 and 204 on the left, illustrate the asymmetric pattern as described earlier. However, all modes may result in the same output voltage waveform (V_MLI), and the main difference may lie in the amount of power drawn from each power source. In short, the asymmetric mode helps to distribute output power more evenly among all power sources (assuming similar power sources) in each half-cycle, while the symmetric mode allows for a more even distribution of output power among all power sources over one or more full cycles. Because the power converter in... Figure 2 In the example, the series connection is a chain (i.e., the inverters are connected in series as shown in the figure), so the switching sequence of the converters has significant flexibility, and therefore has a cyclical switching sequence, making it highly feasible to balance equal power among converters with similar input power supplies.

[0050] Figure 3A block diagram of a sinusoidal LV LF MLPC 302 is shown, adapted to generate a common voltage rated voltage wave V_MLI 120 (e.g., 240Vrms, 60Hz) by summing n (e.g., 14) in-phase power supplies 102, i.e., V1, ..., Vn (e.g., 24Vrms). As shown in the example, all power supplies are fully rectified sine waves, and all power supplies are at the same frequency (e.g., 120Hz) and in phase. Differences can be voltage amplitudes and the power levels of the sources. Input voltages (V1, ..., Vn) can be the same or different. Requirements may include the sum peak meeting the rated load voltage (e.g., 240Vrms). Since all the inverters shown can be connected in series (as shown) and drive the load current, the power output of individual power converters depends on the voltage amplitude (e.g., Vi-pk) and the phase angle of their current waves.

[0051] Assuming the power supply voltage is a pure rectified sine wave and no current distortion occurs at the zero-crossing point, the LV LF MLPC 302 based on a sine wave can outperform the LV LF MLPC 100 based on a square wave (without LV SVR, e.g., regarding...). Figure 1A The described LV SVR 112 better improves THD, EMI, and leakage current. It is worth noting that in the square-wave-based LV LF MLPC system 100, small voltage steps in the output voltage (V_MLI) can lead to some degree of THD, EMI, and leakage current. It should be noted that including an LV SVR (e.g., LV SVR 112) in series with the LV LF MLPC 100 can improve THD, EMI, and leakage current more significantly than the sinusoidal-wave-based LV LF MLPC 302, and also allows for a smaller common frequency filter size. Furthermore, THD can be load-independent.

[0052] Figure 4 A block diagram of the square wave-based LV LF MLPC 400 is shown, which can be used with... Figure 1A The exemplary embodiments are distinguished. As shown, the difference could be that the power converter 110 can use a half-bridge topology instead of an H-bridge topology. In this case, a high-voltage expanded H-bridge converter 402 can be connected between the MLPC stage and the output stage to generate a half-sine voltage from a fully rectified half-sine wave. More specifically, Figure 4 The power converter 400 shown can provide a multilevel inverter that uses, for example, DC bus capacitors to generate a half-sine wave. In view of the foregoing and the known applications of multilevel inverters, the embodiment can provide higher speeds and lower dissipation than existing known efforts, for example, for devices below 100V.

[0053] Therefore, embodiments can provide multilevel inverters to achieve distributed power conversion, for example, via cable connection. Furthermore, such as Figure 4 The embodiments illustrated in the examples can use several pulsed power supplies connected in series to generate a half-sine wave power supply. However, Figure 4 The multilevel converter 400 shown can still accept single-center control and can integrate components as compactly as possible to avoid voltage spikes and similar inefficiencies.

[0054] Furthermore, in the embodiments discussed throughout the text, particularly regarding... Figure 4 In the example embodiment, the wave frequency can alter motor speed control, and considering the need to fix capacitor voltages and control them, an active filter can be employed in the embodiment. It goes without saying that the active filter that can be used in the disclosed application is significantly smaller in size and therefore more suitable and efficient in the disclosed application compared to the passive filters of the prior art. Furthermore, in the prior art, where voltage source inverters are used, performing PWM for each pulse requires increasingly large and expensive passive filters. However, current source inverters can be driven by the current pulses shown, and active filtering can be used, thus avoiding the inherent difficulties of the prior art.

[0055] Figure 5 A block diagram of a sine wave-based LV LF MLPC 500 is shown, which has the same characteristics as... Figure 3 Examples of different aspects. As shown in the figure, the difference is that the series LV power converter can be replaced by a high-voltage expanded H-bridge converter 502 connected between the series power supply and the output stage, for example, to generate a sinusoidal voltage from a fully rectified sine wave.

[0056] Figure 6 Some of the many potential input power sources are shown. As a non-limiting example, the power source for each power converter could be a PV board 602 or a battery 604. To utilize the PV board at its maximum deliverable power operating point, a power optimizer or maximum power point tracker may be required. Many different power converter topologies can implement MPPT to a PV board. As a non-limiting example, a single-inductor buck-boost converter with a DC or sinusoidal rectified output voltage could be such a converter.

[0057] Furthermore, to effectively utilize the battery, battery manufacturers recommend different charging cycles depending on the battery chemistry. To achieve these recommendations, different types of power converters can be used. As a non-limiting example, a single-inductor buck-boost converter with a DC or rectified sinusoidal output voltage can be used. For battery charging, the input power supply and load can interchange their roles, so the power supply and current directions can be opposite. With bidirectional devices (such as MOSFETs), current can flow in both directions, and since a single-inductor buck-boost converter is a symmetrical circuit, there is no difference in the case of opposite power supply flows, as long as the voltage and current ratings of the devices are considered.

[0058] Figure 7A A non-limiting example of the LV LF MLPC 702 is shown for regulating the output voltage and smoothing voltage steps in the LV LF MLPC output voltage Vg. The LV LF MLPC 702 can be used with... Figure 7A and Figure 7B The low-voltage series voltage regulator (LV SVR) 704 shown is connected in series to smooth voltage steps in the LV LF MLPC output voltage waveform Vg. Together with the LV LF MLPC 702, the LV SVR 704 generates a half-sine wave that can significantly improve the load current THD. Furthermore, the LV SVR 704 can have a fast response time. Therefore, the LV SVR 704 can respond to transient grid demands and prevent them from affecting the performance of the LV LF MLPC. When connected to photovoltaic (PV) panels, in response to rapid changes in sunlight or shading, the LV SVR 704 can compensate for the difference between the desired output voltage and the voltage Vg that the LV LF MLPC 702 can temporarily deliver before the control system can respond accordingly. Subsequently, the LV LF MLPC 702 readjusts itself, takes over, and restores operation to normal mode. Since the LF inverter 706 (H-bridge (4 MOSFETs)) is driven at a low frequency (e.g., 60Hz), switching losses are not a problem, so it is feasible to slow down the switching time without a significant increase in switching losses. This slowed switching time can reduce the rise / fall time of step voltages, such as... Figure 8 As shown, this can help the LV SVR control system 704 to more effectively control and smooth out step voltages (half-sine waves) in the output voltage. Furthermore, the LV SVR 704 can include grid interconnect circuitry 708 to facilitate integration with the power grid. Figure 7B An enlarged view of the power grid interconnection circuit 708 is described, showing its components.

[0059] Figure 9An advanced connection of an LV SVR 900 between an LV LF MLPC 902 connected to a PV panel 904 and a load 906 and a power grid 908 is shown. In this configuration, the DC bus 910 can be a regulated DC bus capacitor bank or a voltage source. The LVSVR 900 also benefits from low-voltage and high-performance power supply components, but can switch at higher switching frequencies (e.g., 100 kHz). As a result, the LV SVR 900 can utilize small passive components, such as magnetic materials and capacitors. This allows the LVSVR 900 to help reduce leakage (common-mode) current between the PV panel 904 and the power grid 908. The structure of the PV panel 904 may result in stray capacitors between the PV cells and the panel frame. In addition to the PV panel structure, capacitance also depends on environmental conditions such as rain and dust. The maximum known capacitance can be as high as approximately 160 nF / kW. Therefore, high-frequency leakage current can be exhibited at least in part due to the suppression of voltage steps in the LV LF MLPC output voltage Vg, resulting in a common frequency (e.g., 60Hz) portion of the leakage current after the addition of the LV SVR 900, which may be relatively small and can be controlled by a common-mode choke.

[0060] Figure 10 A storage system 1000, consisting of a PV 1002 and a battery 1004, integrated with public utilities, is shown. Clearly, many alternatives exist for manufacturing such systems; therefore... Figure 10 The examples provided are non-limiting in nature. These examples emphasize that the disclosed LV LF MLPC system 1000 is a bidirectional system and can be used in any power flow direction. For example, in the case of a battery as a power source, during a charging cycle, the battery becomes a load and the output (e.g., the power grid or PV system) becomes a power source. As described above, the LV LF MLPC system 1000 can therefore be controlled to perform the same function in the opposite direction.

[0061] As a non-restrictive example, Figure 11 A block diagram of the integrated AC PV module 1102 and AC battery module 1104 in the LV LF MLPC system 1100 is shown. As an example, the LV SVR 1106 can be added as a module or integrated into another module.

[0062] Figure 12An exemplary database calculation of the phase shift angle using THD as an indicator, according to a disclosed embodiment, is shown to obtain a half-sine wave in the form of a phase-shifted square wave. At least due to the square wave, real-time but low-frequency (e.g., 60Hz) THD calculation is readily achievable and can be used to avoid offline phase shift angle calculations, updating the optimal angle in real-time mode when needed. To explore this workload, Fourier series and THD calculations can be developed for 14PV board systems. The Fourier series and THD calculation equations are as follows... Figure 13 As shown.

[0063] Those skilled in the art will understand that various methods for calculating THD are known, and Figure 12 and 13 The examples provided empirically insert different angles to calculate the optimal angle for a given parameter (e.g., Vrms) in a particular application. It is, of course, to understand, that the empirical angle used will change, for example, when the output voltage and / or the number of active solar modules change.

[0064] The description provided in this disclosure is intended to enable any person skilled in the art to implement or use the disclosed embodiments. Various modifications to this disclosure will be apparent to those skilled in the art, and other variations can be applied to the general principles defined herein without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not limited to the examples and designs described herein, but is consistent with the widest scope of the principles and novel features disclosed herein.

Claims

1. A photovoltaic power converter comprising: a plurality of low voltage source inputs derived from the photovoltaic power source; a plurality of phase-shifted inverters in series, each of the plurality of phase-shifted inverters configured to: receive at least one of the plurality of low voltage source inputs, and generate at least one square wave output therefrom; at least one low voltage series voltage regulator coupled in series with one or more of the plurality of phase-shifted inverters, adapted to twice smooth the at least one square wave output into a half-sine wave output and facilitate integration with a power grid through a grid interconnection circuit.

2. The power converter of claim 1, wherein at least one of the low voltage source inputs is a semi-direct current (DC) power source.

3. The power converter of claim 1, wherein a total harmonic distortion level is substantially independent of a driven load.

4. The power converter of claim 1, wherein the grid interconnection circuit comprises an output filter.

5. The power converter of claim 1, wherein the plurality of low voltage source inputs comprises a plurality of photovoltaic (PV) modules, each of the plurality of PV modules coupled to the photovoltaic power source.

6. The power converter of claim 5, wherein each of the plurality of PV modules comprises at least one of: a maximum power point tracking system, a rapid shutdown circuit, and an arc fault protection circuit.

7. The power converter of claim 6, wherein the PV module comprises an operating mode having a maximum power point voltage value substantially matching an inverter desired input voltage.

8. The power converter of claim 7, wherein the PV module stores energy at an inverter DC bus capacitor.

9. The power converter of claim 1, wherein at least one of the plurality of low voltage source inputs comprises one selected from at least one of: a battery, a fuel cell, and a solar cell.

10. The power converter of claim 1, further comprising an integrated circuit capable of electrically integrating at least one of the plurality of low voltage source inputs with the plurality of inverters.

11. The power converter of claim 8, wherein the PV module further comprises a dedicated module level controller.

12. The power converter of claim 5, further comprising an integrated circuit capable of integrating the plurality of the PV modules.

13. The power converter of claim 1, wherein at least one of the plurality of low voltage sources is a residential photovoltaic panel.

14. The power converter of claim 1, wherein at least one of the plurality of low voltage sources is a commercial photovoltaic panel.

15. The power converter of claim 1, wherein the half-sine wave output is coupled to a utility grid.

16. The power converter of claim 1, wherein some of the plurality of inverters comprise a single inductor buck-boost converter.

17. The power converter of claim 16, wherein the power converter is bidirectional.

18. The power converter of claim 1, wherein some of the plurality of inverters comprise a half-bridge topology.

19. The power converter of claim 1, wherein ones of the plurality of inverters comprise an H-bridge topology.

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