9. Inverter AC from DC

Type of Inverter

A. Utility-Interactive Inverter
   1. Direct Grid
   2. Battery Based
B. Stand-alone Inverter

(A.1)  Grid Direct Inverter

• No storage
• High over all Efficiency
• Works in parallel with the system

Point-1 -->  All grid tied inverters works between 150- 600Volt

Point-2 -->  600Volt is the maximum voltage as per code

Point-3 -->  Will monitor the voltage and frequency of the utility power for Anti-Islanding safety features

Point-4 -->  If low frequency or low voltage will be detected in the grid, the inverter will be automatically                            disconnected from grid power with Anti-Islanding features

Point-5 -->  If the voltage and frequency retains in the grid, the inverter will restart again after monitoring five minutes

• If any brownout will come, the invertor may shut down.
• If the voltage drop happens, the inverter may shut down.

GFP - Ground Fault protection in the system.
Will protect from fire 
GFCI - Ground fault circuit interrupter - used for human protections.

Multiplicity - inverter with more than one MPPT.


Technologies in Inverter - Transformer

1. Large transformer and Low frequency Technology.
2. Small transformer and High frequency Technology.
3. Transformer less Technology.

Large transformer and Low frequency Technology.

• Take High DC voltage from PV array
• covert DC to AC voltage.

The frequency of the switches operates will be relatively low comparing to other systems.

* Robust System.
* Less number of components.
! Large transformer, too heavy
! Less Efficiency, due to transformer loss.

Small transformer and High frequency Technology.

• Technology similar to hgh voltage Technology
• Swiching more faster, smaller light wt. transformer will be used.
• Few manufacturers with multiple invertor.

Eg. Three invertors in a single system, will operate only one, if the power load is less. the power increases the second invertor will be switched on.

Transformer Less Technology.

AC converts to DC with electronic components 
Referred as ungrounded Invertor.
Only equipment grounding requires, only for shock hazards.

Pros
High Efficieny
Less Wt.
Cons
Additional regulation as per NEC.

Battery Based Inverter

When Utility is working.

1. PV Array starts producing power and sends it to battery banks.
2. When Battery bank is full, power will send to inverter. (from PV)
3. Inverter Pass the power to Load Center
4. If PV Solar produces more power, then it passes to the utility grid, and the meter runs.
5. If the PV array slows down, the load center will consume power from the utility grid.

If Utility is down.

1. Automatically, the isolator will disconnects from grid power (Anti-Islanding feature) and monitor the voltage and frequency of the grid power.
2. Draw power from battery bank to backup the load center, until battery bank become empty. 
3. Battery bank may charge directly from Utility also.

Stand Alone Inverter

1. Take DC Power from Battery bank, turns to AC power.
2. If Battery power is empty or less than 80%, the alert can turn on the generator/ change over switch.
3. Feature - Low battery alert 
4. No ground fault protection needed.

Sizes of Battery based inverter

1. Starts from 100W to 6kW.
2. Can connects in field.
3. Low frequency transformer technology.
4. Max input voltage is 48VDC.

Selecting an Inverter

DC Voltage window --> Input voltage range DC voltage from PV array - typical is 250VDC - 600VDC

AC Power Output Value --> Related to PV array input value 15% to 25% extra.

PV  ---->  Inverter (3000W)

3000 x 115% = 3450W
3000 x 125% = 3750W

Right specification for the project -->
Disconnect input with inverter -->

As per NEC code, disconnect/ Isolator should be near to inverter.
Monitoring facility - Based on customer needs.

Battery Based Inverter
Select the AC power source.
Surge rating of the inverter for motor loads.