Main Control PCB

2. MAIN CONTROL PCB ASSEMBLIES (CNTL)
These assemblies are the control center of UPS. It is composed of three major circuits as following.
(1) Regulation & control
(2) Protection
(3) Signaling

2-(1) REGULATION & CONTROL SUB-SYSTEM :
This portion can be seen as brain of the UPS. It provides the control pulses to the switching elements which deliver power to the output. The sub-system also regulates the output to ensure that the UPS is delivering constant AC voltage to the loads.
The inverter signal is sensed directly by resistor division. It is compared with a reference signal from sine wave generator. The difference of these two signals (error signal) alter the pulse widths of PWM signals which control the duty cycles of switching elements to regulate the output voltage within specification

2-(2) PROTECTION SUB-SYSTEM :
The UPS provides the following protection circuits :
1. Overload protectionThe load detector senses the load current. i.e. the inverter current, and sends the signal by two paths. The UPS will go to failure mode if overload condition happened. The panel will indicate the fault condition. There are two kinds of protection in our UPS :

a. Overload Protection: 

The UPS collects the continuous overload signals through CPU switch the output relay.
In line mode, if the output load is higher than 103% and lower than 110% of rated load (VA,
or Wattage) the UPS will warning, after 5minutes go to fault mode. If the output load is
between 110% and 130% of rated load (VA, or Wattage) the UPS will warning, after
10seconds go to fault mode.. If the output load is higher than 130% of rated load, the UPS
will go to fault mode after 1second. In battery mode, if the output load is higher than 110% and lower than 120% of rated load (VA, or Wattage) the UPS will warning, after 0.5minutes go to fault mode. If the output load is between 120% and 130% of rated load (VA, or Wattage) the UPS will warning, after 10seconds go to fault mode.. If the output load is higher than 130% of rated load, the UPS will go to fault mode after 1second.

b. Cycle by Cycle Current Limit : 

When output loads sink a high surge current for a short time, a high inverter current is detected and the inverter switches, i.e. the MOSFET's, are turned off pulse by pulse to protect themselves from thermal runaway. The output relay stays at inverter output position unless a continuous overload is detected or an abnormal inverter operation occurs.

2. Battery over or under shut down
Upon the battery voltage declines to battery-under/over level, the UPS will warn and the LCD will display the fault code, and then shut down.
In case of the battery voltage is high voltage, the UPS will warn and the LCD will display the fault code.

3. Inverter output abnormal protection
The inverter failure signal shuts down the inverter immediately, makes the buzzer a continuous alarm, and the LCD displays the fault code.
“The failure signal latches itself unless SW off or battery is empty".

4. Over temperature protection
The thermal switch detects the temperature of PSDR heat sink. The thermal switch is electrically connected to the CPU. An opened thermal switch is thought as temperature failure by the UPS. The LCD will display the fault code.

5. Bus over/under protection
To protect any BUS over/under condition. The LCD will display the fault code.

2-3 Signaling Sub-System :
When the AC line is unable to supply, the batteries release energy inside to supply the inverter immediately. At the same time, the buzzer beeps every 4 seconds.
Upon the batteries are discharged to battery-low level, the battery-low signal is activated and the buzzer beeps every 1 second. Remote shutdown signal is enabled only when the line fails.