Functional Descriptions
4.12 Current Measurements and Hardware Current limits
Inverter, Rectifier, and Battery Current Measurements are made on the IO board. The measurements are made by the LEM-LAS100 closed loop hall sensor. All measurements made are choke current measurements. There are two chokes in parallel in each phase of the Inverter and Rectifier, but only 1 choke is measured. The battery converter has 6 chokes in staggered parallel;
however, only 3 chokes are measured, one from each power module. See paragraph 4.5.3 for respective choke connections.
Table 18. Phase and Battery Chokes
Sensor Converter Choke Split
B1 Rectifier Line 1 L7A 2
B2 Rectifier Line 2 L4A 2
B3 Rectifier Line 3 L1A 2
B7 Inverter Line 1 L9A 2
B6 Inverter Line 2 L6A 2
B4 Inverter Line 3 L3A 2
B8 Battery L2A L5A L8A 2
LEM sensors are powered by +5V which is derived from the control board.
They output a nominal 2.5V with no current. The +5V is buffered and divided to 3.3V and used as the reference voltage for N3-A, N3-B, N3-C, D, C, N5-B and N5-A. Each Op amp will now put out a nominal +3.3V with no current running through its respective LEM sensor. Measurements are scaled so that control board hardware current limit is set at approximately 240Apk @ 20kHz.
This allows for overload conditions and system non-linear loads with high crest factors. Calibration takes care of any slop caused by current splitting scheme used to measure current. Software current limits are also in place.
4.12.1 Output Current Measurement
Line 1, 2, 3 phase currents are monitored by B5, B9, B10 CTs respectively.
These measurements (currents) are not split. R54 and R55 adjusts gain for Line 1 measurement, R146 and R147 adjusts Line 2 measurement gain, and R148 and R149 adjusts Line 3 measurement gain. This measurement is sized to handle 110% overload on the inverter with 1% low tolerance and a 3:1 crest factor. Measurement will also handle the 150% overload at low line at a 2.2:1 crest factor per the PDR (reference 1).
4.12.2 Input and Output Filtering Scheme
High Frequency Y-Caps are provided on Input, Output, Neutral, and Battery Connections to Chassis:
High Frequency X-Caps are provided on Input, Output Connections to Neutral and across the Battery:
• Ferrite cores are also placed strategically to form a common mode choke
• Input and output filter capacitors for the rectifier and inverter carrier rejection are provided on the I/O board:
- C115-117, C129-134, C210-212
These caps along with the system inductor provide a 2nd order filter with the following corner frequency:
fr = 1/ (2π√L⋅C) = 1960Hz where L = 50µH and C = 132µF
4.12.3 Inverter/Rectifier Fault Methodology
An input breaker feeds the rectifier path, which may trip if there is a bus fault with the rectifier or inverter. If the fault is due to a inverter IGBT module failure, fuses (F1, 2, 3) may clear also. The inverter and rectifier have hardware and software current limit protection.
The inverter output path is fused with 160A LET semiconductor fuses (F1, 2, 3).
The inverter path is connected through a contactor to the bypass SCR output.
These paths are OR’d, which leads to fast transfer times in the unit. This connection is then run through the load CTs.
In an output short circuit condition, the inverter will current limit, transfer to bypass, and then open the inverter contactor if the load short circuit does not clear. Software keeps the inverter from going back online after bypass until the load short circuit has cleared. The bypass feed is protected by fuses (not on this board), and an upstream (customer) circuit breaker.
4.12.4 Single Feed/Dual Feed Input Contactors
The Low Voltage UPS module uses either a single feed or dual feed by adding or removing a jumper. There are separate contactors for the Bypass and
Rectifier paths. The redundant drive for the rectifier contactor (circuit consisting of K12, K14, X27) is located on this board. The drive for the inverter contactor (circuit consisting of K11, X21) is located on this board. Both drives are
powered from the 24V reservoir capacitors. It takes approximately 4A for about 100ms (100W) to pull in the contactors.
4.12.5 Battery Relay, Battery Start and Current Measurement
The Low voltage UPS module contains a system battery breaker; Battery + and Battery – connections come to the IO board.Battery capacitors C15, 81, 14 are provided and work with the two parallel battery chokes to form a carrier ripple filter.
The Battery Relay (K5-10—six 40 Amp relays in parallel), is driven by way of V7D and V7C and clamped with V1. The battery relay connects the battery-to-battery chokes once the rails are charged, so there is no inrush. Battery
current is then measured by LEM sensor B8. Choke currents from each power module are each split by two (see paragraph 4.5.3) so that half of battery current is sensed by the LEM.
During a battery start SCR V6 provides battery start capability in absence of utility. This SCR is triggered by a battery start pushbutton connected to X79 once the battery breaker is closed. This circuit then provides power to the AAUX supply. Once the battery start circuit latches, control board power comes up and the control board comes alive.
A precharge circuit then pumps up the positive rail to hold up the AAUX power supply. The balancer relay (K19-21) closes and the L1 rectifier converter, acting as a balancer, transfers charge to the negative rail. Software waits for a
“UPS on” command from the front display. If the unit is not started, software properly shuts down the unit.
4.12.6 Balancer Relays and Drive
A Line 1 Rectifier converter is used to balance the rails to neutral when on battery and during startup. Balancer Relay (K1-4) is used to connect Line 1 after the contactor is opened to Neutral.
The coils are powered with +24V from AAUX and are driven by V8-C, V8-G and are clamped by V11.
Firmware is in place to keep the Balancer relay and the rectifier contactor from being closed at the same time avoiding a short on the utility and welded relays.
4.12.7 Battery CB Trip
This circuit shunt trips the battery CB. It gets its power from +24V reservoir capacitors through FET V105 out connector X50. It takes approx 4A for
~100ms (100W) to trip the breaker.
4.12.8 Input/Output CB Trip
The circuit (K4,14, X2, 78) shunt trips the input/output CB. It gets its power for the input trip coil from the L1 input and for the output trip coil from the L1
output.
4.12.9 Other Sensing
There are three buffers dedicated for sensing. The state of the Battery CB is reported back to the control board through buffer V91-G from connector X50.
The state of the SPARE_IN1 is reported back to the control board through buffer V91-D from connector X61. The state of the SPARE_IN2 is reported back to the control board through buffer V91-C from connector X60. Ambient temperature is sensed by U1.
4.12.10 X-Slots
Connectors X55 and X56 go out to the two X-Slots. The X-Slots each get +12V_2 through a 5 ohm 1A PTC thermistor R285, R286 plus signals to and from the control board.
4.12.11 AC Fans
There are three AC fans powered from this board. Fan 1 (X65) is connected phase L3- N across the inverter. Fan 2 (X66) is connected phase L2-N across the inverter. Fan 3 (X67) is connected phase L1-N across the inverter. All are located after the inverter fuse. They can also be powered by the output when the inverter is off by closing the inverter contactor.
4.12.12 Chassis GND
Chassis screws E14, E15, normally ground logic common. The emi Y-caps are connected via screws E13, E16.
4.12.13 Troubleshooting 4.12.13.1 Fuses
The IO Board contains the inverter (F1-3) fuses that disconnect any failed converters on the power modules.
4.12.13.2 Circuits
If the display is not working check the F4 fuse going to the AAUX supply. Look for the presence of +24V on X44.
4.12.13.3 Relays
Check for welded balancer relays (K1-3) if the rectifier CB is tripped open or a rectifier converter has failed. Check for welded battery relays (K5-10) after a battery converter failure.