Solar micro inverters, the critical balance-of-system (BOS) components in photovoltaic systems, allow the use of common AC powered equipment. Solar micro inverters have special features for photovoltaic arrays, including maximum power point tracking and anti-islanding protection.
1. Classification of solar micro inverters
Solar inverters can be divided into three main categories:
Standalone inverters for use in isolated systems where the inverter extracts DC energy from batteries charged by a photovoltaic array. Many stand-alone inverters also have integrated battery chargers to replenish the batteries when AC power is available. Typically, they are not connected to the utility grid in any way and therefore do not need to have anti-islanding protection.
A grid-tie inverter with phase matching to the sine wave supplied by the utility. For safety reasons, grid-connected inverters are designed to shut down automatically when the utility power is interrupted. They do not provide backup power during utility outages.
Battery backup inverters are purpose-built inverters designed to draw energy from the battery, manage the battery charge through the on-board charger, and export excess energy to the utility grid. These inverters are capable of supplying AC energy to selected loads during utility outages and are required to have anti-islanding protection.
A smart hybrid inverter manages the photovoltaic array, battery storage and utility grid, all directly coupled to the unit. These modern all-in-one systems are often highly versatile and can be used for grid-tie, stand-alone or backup applications, but their primary function is to consume themselves through the use of storage.
2. xxx Power Point Tracking for Solar Micro inverters
Solar inverters use maximum power point tracking (MPPT) to obtain maximum possible power from the PV array. Solar cells have a complex relationship between solar radiation, temperature, and total resistance, which creates a non-linear output efficiency known as an IV curve. The purpose of the MPPT system is to sample the output of the battery and determine the resistance (load) to obtain the fill factor of xxx power under any given environmental conditions, by its abbreviation usually referred to as FF, is a parameter that is related to The open circuit voltage (V OC) and short circuit current (I SC of the panel) determine the maximum power from a solar cell. The fill factor is defined as the ratio of the maximum power of a solar cell to the product of V oc and I sc.
There are three main types of MPPT algorithms: perturbation and observation, incremental conductance, and constant voltage. The first two methods are often referred to as hill-climbing methods; they rely on a power curve plotted against voltage rising to the left of the xxx power point and falling to the right of the voltage.
3. Solar micro inverter
A solar micro inverter is an inverter designed to work with a single PV module. Microinverters convert the DC output from each panel to AC. Its design allows parallel connection of several independent units in a modular fashion.
Advantages of microinverters include: single-panel power optimization, independent operation of each panel, plug-and-play installation, improved installation and fire safety, minimized system design costs and minimized inventory.
A 2011 Appalachian State University study reported that a separate integrated inverter setup increased power in unshaded conditions compared to a series setup using one inverter. About 20%, and 27% more power in shaded conditions. Both setups use the same solar panels.
3.1 Grid-connected solar micro inverter
Solar grid-tie inverters are designed to quickly disconnect from the grid in the event of a utility grid failure. This is an NEC requirement that ensures that in the event of a blackout, grid-tie inverters will shut down to prevent the energy they produce from harming any line workers sent to repair the grid.
Grid-connected inverters on the market today use a variety of different technologies. The inverter can use a newer high frequency transformer, a conventional low frequency transformer, or no transformer. Instead of converting DC directly to 120 or 240 volts AC, a high frequency transformer uses a computerized, multi-step process that involves converting the power supply to high frequency AC, then to DC, to the final AC output voltage .
Historically, there have been concerns about feeding transformerless electrical systems into the utility grid. The cause for concern is the lack of electrical isolation between the DC and AC circuits, which could allow dangerous DC faults to pass through the AC side. The NFPA's NEC has allowed the use of transformerless (or non-electrical) inverters since 2005. VDE 0126-1-1 and IEC 6210 have also been amended to allow and define the security mechanisms required for such systems. First, residual current or ground current detection is used to detect possible fault conditions. Isolation testing is also performed to ensure DC to AC separation.
Many solar inverters are designed to be connected to the utility grid and will not operate without detecting the presence of the grid. They contain specialized circuitry to precisely match the voltage, frequency and phase of the grid.
3.2 Pumped solar micro inverter
Advanced solar pumping inverters convert the DC voltage from the solar array to AC voltage to directly drive submersible pumps without the need for batteries or other energy storage devices. By utilizing MPPT (xxx Power Point Tracking), the solar water pump inverter can adjust the output frequency to control the speed of the water pump so as not to damage the water pump motor.
Solar pumped hydro inverters typically have multiple ports to allow input of DC current generated by the PV array; one port to allow output of AC voltage; and another port for input from a water level sensor.