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based H-bridge conguration and high frequency (30 KHz) PWM (Pulse Width Modulation) technique. The low
frequency, low voltage synthesized sine wave is then stepped up to 120 VAC pure sine wave voltage using a low
frequency Isolation Transformer and ltration circuit to remove 30 KHz PWM frequency component. This type of
DC to AC inversion is called Hybrid Type – a combination of low and high frequency implementation. Distinctive
features of the Inverter Section are given below:
Soft Start: The inverter design incorporates “Soft Start” feature with the following advantages and protections:
- When the unit powers up, it starts in Inverting Mode rst. The output voltage ramps up gradually from
around 48 VAC to 120 VAC in around 200 ms. This reduces otherwise very high starting inrush current
drawn by AC loads like Switched Mode Power Supplies (SMPS) and motor driven loads like fans, pumps,
compressors etc. This will result in lower motor inrush current (which typically can be up to 650% of the full
load current of the motor), which means lesser mechanical stresses, wear and tear and increased lifetime
of the motor, coupling and fan. Additionally, the impact on the load side components is greatly reduced,
meaning less likelihood of causing problematic voltage drops during starting.
Power Surge – Up to 300%:
- The inverter is able to deliver very high surge power / current of up to 300% for 1 ms followed by 200%
for 100 ms. This range of high instantaneous power is delivered at the rated voltage and hence, it is able to
provide very high starting torque for difcult motor driven loads like compressors and pumps that require
higher Locked Rotor Current during startup.
- If the power drawn by the load exceeds the above surge ratings, the inverter protects itself by limiting the
load current to 300% / 200% which results in reduction of output voltage and consequent reduction in load
current. The output voltage recovers automatically when power drawn by the load drops below the above
surge limits
Power Boost up to 150%: Higher percentage of rated power can be provided for limited time periods as follows:
• 150% for 30 sec
• 140% for 1 min
• 120% for 10 min
• 110% for 30 min
4.4 TRANSFER RELAY SECTION
Transfer Relay Section is used to either feed AC input power from external AC input source (e.g. Grid/Generator)
to the Battery Charger Section and at the same time, pass through the AC power from the external AC input
power source to the load (As long as the external AC input power is available and is within the programmed limits
of voltage and frequency) or to transfer the load to the Inverter Section (In case of loss of the external AC input
power source or if this source is not within the programmed limits of voltage and frequency). Typical transfer time
is 16 milliseconds from the AC input source to Inverter and <1ms from Inverter to the AC input source. Heavy duty
40A, Transfer Relay [RY1, Fig 4.1] is used for reliable transfer of power.
4.4.1 AC Transfer and Output Neutral To Chassis Ground Bond Switching
As required by NEC and UL Standard 458, automatic switching of bonding between the Ouput Neutral and Chassis
Ground has been provided in EVO through “Output Neutral to Chassis Ground Bond Switching Relay” [RY.2 in Fig
4.1]. Switching of bonding is carried out as follows:
SECTION 4 | General Description & Principles of Operation
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