Inverters
AC Power Inverters
Power Conditioning Units Inverter Features and Specifications
If voltage and current signals are either always positive or always negative, they are DC waveforms. If the signals switch between positive and negative, they are AC waveforms.
AC waveforms can take a variety of shapes.
Certain parameters are integral to defining the characteristics of an AC waveform
Three-phase power is composed of three separate voltage wave-forms that are 120° out of phase.
Voltage variations outside allowable ranges include voltage drops, voltage swells, and transients.
Resistive loads keep the voltage and current waveforms in phase, while reactive loads cause the current waveform to lead or lag the voltage waveform.
Inverters are available in many different configurations and ratings.
Stand-alone inverters are connected to the battery bank.
Interactive inverters are connected to the PV array.
Solid-state switching devices used in PV inverters include transistors and thyristors.
Line-commutated inverters use an external AC signal to activate and deactivate the inverter switching devices.
Push-pull inverter circuits use one pair of switching devices and a transformer to alternate the direction of direct current.
Square waves can be modified by adjusting the duration and magnitude of the pulses.
Combining multiple modified square waves with different magnitudes and durations results in a multistepped modified square wave that more closely approximates a sine wave.
Pulse-width modulation at high frequencies generates the truest approximation of a sine wave.
Power conditioning units are inverters that also perform other power control and conversion functions.
Transformers use induced magnetic fields to transfer AC power from one circuit to another and transform the power to higher or lower voltages.
The primary and secondary windings in an autotransformer share some of the same windings.
At high temperatures, an inverter may limit current input by raising the input voltage, which also lowers power input and output.
Most inverters operate from a relatively wide range of input voltages, but the range for MPPT operation is smaller.
In order to output AC voltage within the spec-ified range, the DC input voltage must meet certain minimum values.
Inverters may limit maximum DC input current with increasing DC input voltage.
Most sine wave inverters maintain high efficiency over a wide operating-power range.
Inverter enclosures may include protective devices such as disconnects.
Inverter interfaces include on-board screens, remote data monitors, and computerized data acquisition and processing software.
