PRINCIPLE OF OPERATION
This PRO801(S/L)_1KVA & PRO8015(S/L)_1.5KVA high input power factor UPS system contains two major PCB assemblies. They are including:
This PRO801(S/L)_1KVA & PRO8015(S/L)_1.5KVA high input power factor UPS system contains two major PCB assemblies. They are including:
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| The simplified schematic in figure 1 shows how the major circuits are connected and illustrates the overall system functions. |
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| Figure 1 : Circuit Connection for 1KVA-1.5KVA |
The locations of these assemblies in Tower structure are shown in figure 2.1.
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| Figure 2.1 : Sub-assembly location in Tower |
The block diagram in figure 3, shows the UPS at normal operation from left to right. When a protection circuit is triggered or a fault condition occurs, the output supply is transferred immediately from inverter to AC mains by a bypass relay. The operation principle will be explained in later section. Basically, this ON-LINE UPS system utilizes high frequency PWM techniques to achieve high efficient performance. This UPS can deliver a clean, regulated sine-wave output at any load under full load. The sub-systems are described as below :
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| Figure 3: Block Diagram for UPS |
1.POWER STAGE (PSDR)
As shown in figure1, the power stage consists of charger, unit power factor correction, DC
power supply, DC-DC converter, inverter and output circuits.
1-1 Charger Sub-System : The purpose of charger is to charge and to maintain the batteries at full charged condition.
Refer to figure 4, the voltage flyback switching power supply provides a constant DC voltage (42.4Vdc ) for batteries. Besides providing constant voltage, the power supply also limits the current flowing into batteries and therefore protects and prolongs the life time of charged batteries.
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| Figure 4: Charger Circuit Diagram |
The input of the DC power supply is connected to the battery bus, i.e., the output of the
charger. The output of DC power supplies provides +12 Vdc for the bias supply of IC’s working voltage and the fan(s) voltage. The DC power supply works only when the 12 Vdc regulator supplies Vcc to its control IC. To have proper operation of 12 Vdc regulators, its input power is controlled by the switch as indicated in figure 5.
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| Figure 5: Schematic for DC power supply |
The UPS transfers (＋), (－) DC bus voltages to the AC output voltage through an inverter of half bridge configuration at normal operation. The schematic diagram of inverter is shown in figure 6. To construct a high frequency (19.2 kHz) PWM inverter, the drivers receive switching signals from PWM generation circuit through a pair of photo-couplers to trigger the upper IGBT and the lower IGBT alternately. The output of IGBT’s is filtered by an LC circuit to reduce the o/p voltage harmonics distortion.
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| Figure 6: Schematics for inverter |
The bypass relay receives signal from control circuit to switch the output of the UPS from bypass to inverter, and vice versa. The output noise filter circuit blocks EMI noise to the loads.
1-5 Input Power Factor Correction Sub-System :
The purpose of power factor correction (P.F.C.) circuit is to make the input current and voltage in phase and therefore achieve a high input power factor. The schematic is indicated in figure 7. When the input AC power cord is plugged in, the AC relay is activated and the AC power goes through noise filter to the charger and to the line detector. Both DC buses present voltages at about 1.4 times of input RMS voltage. When the “on” switch is pressed, the P.F.C. circuit is enabled and the DC buses are regulated at ±360 Vdc.
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| Figure 7 : I/P PFC Corection |
The major function of the UPS is to deliver accurate AC power to the loads connected to it whenever the AC line is correct or fails. In this system, the batteries release the stored energy to supply inverter immediately upon AC line fails.
Refer to figure 8, the battery voltage is transformed through a push-pull DC-DC converter to ±360Vd as DC buses for inverter. When the line fails, the ±360Vdc DC sources are caught up to supply the power needed by the inverter immediately.
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| DC-DC Circuit for 1K series |
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.
In order to avoid un-wanted surge current at the transfer of bypass relay, the bypass signal activates the tracking circuit. It matches the inverter voltage with the line voltage by having the amplitude of the reference signal following the variation of line voltage.
When the main is applied and the switch is turned on, a 10-second timer is triggered. The bypass relay stays at bypass position in this time period. At the end of this period, the bypass signal is removed and the relay transfers to inverter output.
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. In battery mode, 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 bypass relay. If the output load is lower than 110% of rated load (VA ,or Wattage) the UPS keeps running on inverter running and warning. If the output load is between 110% and 130% of rated load (VA ,or Wattage) the UPS transfers to bypass after 12s. If the output load is higher than 130% of rated load, the UPS transfers to bypass after 1.5s immediately.
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 IGBT’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/unbalance-voltage protection
To protect any BUS over/under/unbalance –voltage condition especially for the half-bridge load.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.
3. Front Panel :
The front panel consists 2 parts: push button and display LCD set. The push button is used to turn on and off the UPS. LCD display indicates the load level, the battery voltage level and operation status of the UPS. Besides, when the system works abnormally, The LCD will display the fault code.
List below are some test points and procedures when a qualified service person wants to check whether EUT (Equipment Under Test) will works properly. Before beginning following procedures, please make sure that EUT is OFF and disconnected from Utility.
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| Figure 9 : Circuit for test output balance |
Due to careful design and strict tests of our products, fail of UPS seldom occurs. However,
once they do fail in some situations, please check them according to Trouble Shooting Chart, which will help you solve the most problems on UPS.
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| Trouble Shooting Chart |
LCD display wordings index
There are three parameters to set up the UPS.
Parameter 1: It’s for program alternatives.
There are 8 programs to set up:
1. output voltage setting
2. frequency converter (enable/disable )
3. output frequency setting
4. ECO (enable/disable)
5. ECO voltage range setting
6. Bypass (enable/disable)
7. Bypass voltage range setting
8. Programmable outlets (enable/disable)/Programmable setting and exit.
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