FIELD OF THE DISCLOSURE

The present disclosure is directed generally to power conversion, such as solar inverters and battery coupled inverters/chargers, and more particularly is directed to a low voltage, low frequency, multi-level power converter.

SUMMARY

According to certain embodiments of the present disclosure, a low voltage, low frequency multi level power converter (LV LF MLPC) apparatus and method for power conversion (i.e., DC/AC or AC/DC) may be provided. The present disclosure may use low voltage, low cost, high performance components (e.g. MOSFETs, diodes, capacitors, inductors, resistors, etc.) and may drive the power devices (e.g. MOSFETs and diodes) at low frequency (e.g., utility frequency) to generate a desired voltage and current wave (e.g., a semi-sine wave at 220Vrms/50 Hz or 240Vrms/60 Hz) for an AC load. As a result, the present disclosure may 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.

LV LF MLPC may be used in certain embodiments to convert electricity from a power source (e.g., a photovoltaic (PV) panel, battery, fuel cell, etc.) to a load (e.g., public utility or any other AC loads). The individual LV LF power converters (LV LF PC) may be integrated with power sources, such as in PV panels or battery modules, such as to make integrated AC modules. A number of AC modules may be connected in series to make a LV LF MLPC system, by way of example.

By way of non-limiting example, a LV LF MLPC and power conversion system as described herein may be applied to a wide variety of systems, from residential to commercial, industrial to utility scale, and such as, by way of non-limiting example, as grid-tied solar inverters, off-grid solar inverters, solar battery coupled inverters, grid-tied battery chargers, etc. Further, depending on the geographic region of application (e.g., US, Europe, etc.), the input power source (solar, battery, etc.), the load (single/three phase public utility, AC loads, etc.), and the desired power level, the LV LF MLPC system may be any type of a 3-phase/1-phase, PFC/non-PFC, or the like.

By way of non-limiting example, the disclosed LV LF MLPC may create a 240 Vrms, 60 Hz voltage wave by adding a predetermined number, such as up to 14, series low voltage (e.g. 24.2Vdc), low frequency (e.g. 60 Hz), and phase shifted power sources. The power sources may be from a PV panel in conjunction with a DC/DC optimizer, or from a battery in conjunction with a bidirectional DC/DC charger, by way of example.

By way of non-limiting example, in the solar inverter industry and in comparison with existing solutions (e.g. AC micro-inverters, power optimizers and string inverters), the disclosed LV LF MLPC is lower cost and uses lower voltage with more efficient components. It may also eliminate the need for an isolation transformer, and may dissipate less power in switching intervals due to very lower switching frequency and lower device blocking voltages during typical operation.

Disclosed embodiments may also use series cabling, which eliminates the need for an expensive bus connector system. Further, in comparison with DC power optimizers, the disclosed LV LF MLPC may result in large system cost savings due to elimination of a string inverter (to which is often allocated a large portion of the system cost). Also, disclosed embodiments may result in higher overall system efficiency than in the known art, such as due to avoiding high voltage devices and switching at high frequency at the inverting stage.

In comparison with previously known string inverters, the disclosed LV LF MLPC may benefit from module level control, which may ultimately be required by National Electric Code (NEC) and Underwriters Laboratories (UL), and may also benefit from module level Maximum Power Point Tracking (MPPT), which utilizes the PV panels at their most efficient operating point. Embodiments also may result in overall cost saving and efficiency improvements by avoiding the need for various additional high voltage components.

Accordingly, certain of the embodiments may provide a low voltage, low frequency multi-level power converter that may include a low voltage, low frequency circuit that includes a plurality of low voltage source inputs; and a plurality of phase-shifting inverters in series. Each of the plurality of phase-shifting 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 semi-sine wave output may be derived from the generated at least one square wave output.

