Industrial UPS System Product

Overview

An industrial uninterruptible power supply keeps a critical load — data center rows, process control systems, hospital theatres, substation protection — energized through any disturbance on the utility feed. This is an online double-conversion unit: every watt delivered to the load passes through the IGBT Rectifier, onto the DC Link, and back out through the IGBT Inverter. The load never sees raw mains. Sags, swells, frequency drift, and harmonic pollution are all absorbed at the rectifier; the output is regenerated as a fresh 400 V sine wave regulated to ±1%.

The unit is classified VFI-SS-111 under IEC 62040-3, the strictest performance class: output voltage and frequency are independent of the input, and the transfer time on mains failure is zero, because the Battery System is permanently coupled to the DC bus.

How it works

The rectifier is a three-phase PWM boost converter built from six IGBT Power Modules switching at around 15 kHz. Three Input Boost Chokes shape the line current into a sinusoid, giving an input power factor above 0.99 and current distortion under 3% — the UPS itself looks like a clean resistive load to the upstream generator or transformer. An EMI Filter keeps switching residue off the mains, and the Precharge Circuit limits inrush while the bus capacitors charge at power-up.

The DC Link holds the energy reservoir: twelve 4700 µF DC Bus Capacitors arranged as a ±400 V split bus, tied together by a low-inductance Laminated Busbar. Each series pair carries an Balancing Resistor, and fast DC Fuses clear a shorted bridge before the capacitor bank can dump into it.

The IGBT Inverter rebuilds the AC output. A three-level bridge of six more IGBT Power Modules chops the DC bus under space-vector PWM; the Output Filter Chokes and AC Filter Capacitors strip the switching frequency, leaving total harmonic distortion under 1% into a linear load. Hall Sensors on each phase close the current loop at the full switching rate, which is what lets the inverter hold voltage within ±2% even on a 100% step load.

Battery and autonomy

Energy storage is a single series string of forty 12 V VRLA Battery Blocks — 480 V nominal — mounted in an Battery Rack and isolated by a DC-rated Battery Breaker. During normal operation the rectifier float-charges the string at 2.27 V per cell, compensated against the Battery Temperature Probe readings at −3 mV/°C/cell to prevent overcharge in warm rooms. A BMS Board watches block voltages and internal-resistance trends, flagging a weak block years before it would fail a discharge. At 100 kW the string supports the load for 10–15 minutes, long enough to ride through reclosures or start a standby generator.

Bypass and fault behavior

The Static Bypass Switch is the second path to the load. Three Thyristor Modules — one anti-parallel SCR pair per phase — sit between raw mains and the output bus. If the inverter overloads beyond its 150%/60 s rating, hits an internal fault, or needs to clear a downstream short with full mains fault current, the controller gates the thyristors and blocks the inverter within a quarter cycle. Because the inverter normally tracks bypass frequency and phase, the transfer is seamless. The Backfeed Contactor satisfies IEC 62040-1 by guaranteeing the bypass cannot energize a dead utility feed, and the manual Maintenance Bypass Switch wraps power around the whole UPS so it can be serviced dead while the load stays up.

Control, monitoring, and cooling

Two processors in the Control & Monitoring assembly split the work: a DSP runs the rectifier and inverter current loops at the switching frequency, while a supervisor Microcontroller handles state machines, the LCD Panel mimic display, event logging, and the Network Management Card, which exposes SNMP and Modbus for building management and triggers graceful server shutdown when autonomy runs low. Four Relay dry contacts report summary alarm, on-battery, low-battery, and on-bypass states to hardwired SCADA.

Conversion losses of roughly 3.5% — about 3.5 kW at full load — leave through two IGBT Heatsinks cooled by an N+1 pair of Blower Motor fans in a hot-swappable Fan Tray. NTC Temperature Sensors on each heatsink drive fan speed and force a derate or bypass transfer if a fan set fails. Everything mounts in the welded Cabinet Frame behind bolted Sheet Metal Panels, with the Input Breaker, Output Breaker, and Power Busbar Set occupying the lower switchgear bay and field cables entering through the Cable Gland Plate.