Inverters, Converters and Power Conditioning
Functions
Inverters, Converters and Power Conditioning covers conversion between DC and AC and the quality of that output. An inverter changes DC from the array or battery into AC. Off-grid inverters usually supply standalone loads; grid-tied inverters synchronise with the utility and must stop exporting during a grid failure (anti-islanding). Hybrid inverters combine battery charging, PV input and AC output. DC–DC converters change one DC voltage to another, for example 24 V array to 12 V battery.
Selection rules
Check continuous and surge ratings, input voltage window, output waveform, idle consumption and derating at high ambient temperature. Pure sine wave is needed for motors, pumps, fans and many electronics; modified sine wave can cause overheating and hum. Grid-tied inverters must match local grid voltage and frequency and be installed with the required protection.
Worked example
A 12 V inverter is rated 1500 W continuous and 3000 W surge for 5 s. At 1500 W and 90 % efficiency, DC current = 1500 / (12 × 0.90) = 139 A. The DC cable, fuse and terminals must be rated above this continuous current, and the surge must not blow a slow fuse. A 12 V system at this power is impractical; a 24 V or 48 V battery bank is better.
Traps
Do not connect an inverter to a battery without a fuse at the battery terminal. Do not assume a 1500 W inverter can run a 1500 W motor, because motor starting surge can be several times the running current. Do not bond neutral and earth incorrectly on a grid-tied system.