A three-phase microinverter is a type of solar microinverter specifically design to supply three-phase electric power. In conventional microinverter designs that work with one-phase power, the energy from the panel must be stored during the period where the voltage is passing through zero, which it does twice per cycle (at 50 or 60 Hz). In a three phase system, throughout the cycle, one of the three wires has a positive (or negative) voltage, so the need for storage can be greatly reduced by transferring the output of the panel to different wires during each cycle. The reduction in energy storage significantly lowers the price and complexity of the converter hardware, as well as potentially increasing its expected lifetime.
Conventional alternating current power is a sinusoidal voltage pattern that repeats over a defined period. That means that during a single cycle, the voltage passes through zero two times. In European systems the voltage at the plug has a maximum of 230 V and cycles 50 times a second, meaning that there are 100 times a second where the voltage is zero, while North American derived systems are 120 V 60 Hz, or 120 zero voltages a second.
Inexpensive inverters can convert DC power to AC by simply turning the DC side of the power on and off 120 times a second, inverting the voltage every other cycle. The result is a square-wave that is close enough to AC power for many devices. However, this sort of solution is not useful in the solar power case, where the goal is to convert as much of the power from the solar power into AC as possible. If one uses these inexpensive types of inverters, all of the power generated during the time that the DC side is turned off is simply lost, and this represents a significant amount of each cycle.
To address this, solar inverters use some form of energy storage to buffer the panel's power during those zero-crossing periods. When the voltage of the AC goes above the voltage in the storage, it is dumped into the output along with any energy being developed by the panel at that instant. In this way, the energy produced by the panel through the entire cycle is eventually sent into the output.
The problem with this approach is that the amount of energy storage needed when connected to a typical modern solar panel can only economically be provided through the use of electrolytic capacitors. These are relatively inexpensive but have well-known degradation modes that mean they have lifetime expectancy on the order of a decade. This has led to a great debate in the industry over whether or not microinverters are a good idea, because when these capacitors start to fail at the end of their expected life, replacing them will require the panels to be removed, often on the roof.
In comparison to normal household current on two wires, current on the delivery side of the power grid uses three wires and phases. At any given instant, the sum of those three is always positive (or negative). So while any given wire in a three-phase system undergoes zero-crossing events in exactly the same fashion as household current, the system as a whole does not, it simply fluctuates between the maximum and a slightly lower value.
A microinverter designed specifically for three-phase supply can eliminate much of the required storage by simply selecting which wire is closest to its own operating voltage at any given instant. A simple system could simply select the wire that is closest to the maximum voltage, switching to the next line when that begins to approach the maximum. In this case, the system only has to store the amount of energy from the peak to the minimum of the cycle as a whole, which is much smaller both in voltage difference and time.
This can be further improved further by selecting the wire that is closest to its own DC voltage at any given instant, instead of switching from one to the other purely on a timer. At any given instant two of the three wires will have a positive (or negative) voltage and using the one closer to the DC side will take advantage of slight efficiency improvements in the conversion hardware.
The reduction, or outright elimination, of energy storage requirements, simplifies the device and eliminates the one component that is expected to define its lifetime. Instead of a decade, a three-phase microinverter could be built to last for the lifetime of the panel. Such a device would also be less expensive and less complex, although at the cost of requiring each inverter to connect to all three lines, which possibly leads to more wiring.
The primary disadvantage of the three-phase inverter concept is that the only sites with three-phase power than can take advantage of these systems. Three-phase is easily available at utility-scale and commercial sites, and it was to these markets that the systems were aimed. However, the main advantages of the microinverter concept involve issues of shading and panel orientation, and in the case of large systems, these are easily addressed by simply moving the panels around, the benefits of the three-phase micro are very limited compared to the residential case with limited space to work in.
As of 2014, observers believed that three-phase micros had not yet managed to reach the price point where their advantages appeared worthwhile.
It is important to contrast a native three-phase inverter with three single-phase micro-inverters wired to output in three-phase. The latter is a relatively common feature of most inverter designs, allowing you to connect three identical inverters together, each across a pair of wires in a three-phase circuit. The result is three-phase power, but each inverter in the system is outputting a single phase. These sorts of solutions do not take advantage of the reduced energy storage needs outlined above.
A power supply is an electrical device that supplies electric power to an electrical load. The primary function of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a result, power supplies are sometimes referred to as electric power converters. Some power supplies are separate standalone pieces of equipment, while others are built into the load appliances that they power. Examples of the latter include power supplies found in desktop computers and consumer electronics devices. Other functions that power supplies may perform include limiting the current drawn by the load to safe levels, shutting off the current in the event of an electrical fault, power conditioning to prevent electronic noise or voltage surges on the input from reaching the load, power-factor correction, and storing energy so it can continue to power the load in the event of a temporary interruption in the source power.
A power inverter, or inverter, is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC).
A switched-mode power supply is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently. Like other power supplies, an SMPS transfers power from a DC or AC source to DC loads, such as a personal computer, while converting voltage and current characteristics. Unlike a linear power supply, the pass transistor of a switching-mode supply continually switches between low-dissipation, full-on and full-off states, and spends very little time in the high dissipation transitions, which minimizes wasted energy. A hypothetical ideal switched-mode power supply dissipates no power. Voltage regulation is achieved by varying the ratio of on-to-off time. In contrast, a linear power supply regulates the output voltage by continually dissipating power in the pass transistor. This higher power conversion efficiency is an important advantage of a switched-mode power supply. Switched-mode power supplies may also be substantially smaller and lighter than a linear supply due to the smaller transformer size and weight.
A DC-to-DC converter is an electronic circuit or electromechanical device that converts a source of direct current (DC) from one voltage level to another. It is a type of electric power converter. Power levels range from very low to very high.
A solar inverter or PV inverter, is a type of electrical converter which converts the variable direct current (DC) output of a photovoltaic (PV) solar panel into a utility frequency alternating current (AC) that can be fed into a commercial electrical grid or used by a local, off-grid electrical network. It is a critical balance of system (BOS)–component in a photovoltaic system, allowing the use of ordinary AC-powered equipment. Solar power inverters have special functions adapted for use with photovoltaic arrays, including maximum power point tracking and anti-islanding protection.
Power electronics is the application of solid-state electronics to the control and conversion of electric power.
A variable-frequency drive (VFD) or adjustable-frequency drive (AFD), variable-voltage/variable-frequency (VVVF) drive, variable speed drive (VSD), AC drive, micro drive or inverter drive is a type of adjustable-speed drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage.
Maximum power point tracking (MPPT) or sometimes just power point tracking (PPT)) is a technique used commonly with wind turbines and photovoltaic (PV) solar systems to maximize power extraction under all conditions.
The term solar panel is used colloquially for a photo-voltaic (PV) module.
Islanding is the condition in which a distributed generator (DG) continues to power a location even though electrical grid power is no longer present. Islanding can be dangerous to utility workers, who may not realize that a circuit is still powered, and it may prevent automatic re-connection of devices. Additionally, without strict frequency control the balance between load and generation in the islanded circuit is going to be violated, leading to abnormal frequencies and voltages. For those reasons, distributed generators must detect islanding and immediately disconnect from the circuit; this is referred to as anti-islanding.
A grid-tie inverter converts direct current (DC) into an alternating current (AC) suitable for injecting into an electrical power grid, normally 120 V RMS at 60 Hz or 240 V RMS at 50 Hz. Grid-tie inverters are used between local electrical power generators: solar panel, wind turbine, hydro-electric, and the grid.
A photovoltaic system, also PV system or solar power system, is a power system designed to supply usable solar power by means of photovoltaics. It consists of an arrangement of several components, including solar panels to absorb and convert sunlight into electricity, a solar inverter to convert the output from direct to alternating current, as well as mounting, cabling, and other electrical accessories to set up a working system. It may also use a solar tracking system to improve the system's overall performance and include an integrated battery solution, as prices for storage devices are expected to decline. Strictly speaking, a solar array only encompasses the ensemble of solar panels, the visible part of the PV system, and does not include all the other hardware, often summarized as balance of system (BOS). As PV systems convert light directly into electricity, they are not to be confused with other solar technologies, such as concentrated solar power or solar thermal, used for heating and cooling.
A power optimizer is a DC to DC converter technology developed to maximize the energy harvest from solar photovoltaic or wind turbine systems. They do this by individually tuning the performance of the panel or wind turbine through maximum power point tracking, and optionally tuning the output to match the performance of the string inverter. Power optimizers are especially useful when the performance of the power generating components in a distributed system will vary widely, such as due to differences in equipment, shading of light or wind, or being installed facing different directions or widely separated locations.
A solar micro-inverter, or simply microinverter, is a plug-and-play device used in photovoltaics, that converts direct current (DC) generated by a single solar module to alternating current (AC). Microinverters contrast with conventional string and central solar inverters, in which a single inverter is connected to multiple solar panels. The output from several microinverters can be combined and often fed to the electrical grid.
A solid-state AC-to-AC converter converts an AC waveform to another AC waveform, where the output voltage and frequency can be set arbitrarily.
A solar cable is the interconnection cable used in photovoltaic power generation. Solar cables interconnect solar panels and other electrical components of a photovoltaic system. Solar cables are designed to be UV resistant and weather resistant. They can be used within a large temperature range and are generally laid outside.
A nanoinverter, also referred as nano inverter or solar nano inverter, converts direct current (DC) from a single solar cell or small solar panel to alternating current (AC). Nanoinverters contrast with microinverter devices, which are connected to larger than 100 Watt solar panels.
Enphase Energy is a NASDAQ-listed energy technology company headquartered in Fremont, California. Enphase designs and manufactures software-driven home energy solutions that span solar generation, home energy storage and web-based monitoring and control. Enphase has shipped about twenty million solar microinverters, primarily into the residential and commercial markets in North America, Europe and Australia. Microinverters convert the direct current power from the solar panel (DC) directly into grid-compatible alternating current (AC) for use or export. Enphase was the first company to successfully commercialise the microinverter on a wide scale, and remains the market leader in their production.
Synchronverters or virtual synchronous generators are inverters which mimic synchronous generators to provide "synthetic inertia" for ancillary services in electric power systems. Inertia is a property of standard synchronous generators associated with the rotating physical mass of the system spinning at a frequency proportional to the electricity being generated. Inertia has implications towards grid stability as work is required to alter the kinetic energy the spinning physical mass and therefore opposes changes in grid frequency. Inverter based generation inherently lacks this property as the waveform is being created artificially via power electronics.
A multi-level converter (MLC) is a method of generating high-voltage wave-forms from lower-voltage components. MLC origins go back over a hundred years, when in the 1880s, the advantages of DC long-distance transmission became evident.