Glossary

Defence Power Electronics Glossary

Short definitions of the terms used on our product pages and technical guides. Each entry gives one definition, a value taken from a product datasheet and a link to the page that covers the topic in depth.

Frequency conversion and 400 Hz power

400 Hz power

400 Hz power is AC supply at 400 hertz, typically 115 VAC, instead of the 50 or 60 Hz of a public grid. Naval, radar and land-system electronics use it because transformers, filters and power supplies built for 400 Hz are smaller and lighter. Sites and shore connections provide 50/60 Hz, so 400 Hz is produced near the load by a frequency converter.

Datasheet example: PowerGuard Static 400 converts a 3-phase 360–440 VAC, 50–60 Hz input to 115–220 VAC at 60–400 Hz; PowerGuard Outdoor has two 3-phase 115 VAC 400 Hz outputs of 4 kVA each.

Read more: military frequency converters

Static frequency converter

Changes the frequency of an AC supply electronically: a rectifier, a DC link and an inverter rebuild the output at the required frequency and voltage, with no rotating machine.

Datasheet example: PowerGuard Static 400: 3-phase 360–440 VAC, 50–60 Hz in; 115–220 VAC, 60–400 Hz out.

Rotary (motor-generator) frequency converter

A rotary frequency converter is a motor-generator set: a mains-fed electric motor turns a generator on a shared shaft, and the generator design fixes the output frequency, for example 400 Hz. It is the older alternative to the static converter, which does the same job with semiconductors and has no rotating parts.

Datasheet example: PowerGuard Outdoor is a static counterpart: static double conversion, microprocessor controlled, with IGBT-based high-frequency PWM.

THD (total harmonic distortion)

THD expresses how much of an AC waveform is made up of harmonics, multiples of the fundamental frequency, relative to the fundamental itself. It is given as a percentage: the lower the figure, the closer the waveform is to a pure sine wave.

Datasheet example: MIL-UPS-2K3: output THD below 3% (linear load); PowerGuard Outdoor and PowerGuard Static 400: output THD below 5%.

Frequency modulation (power output)

In a power supply specification, frequency modulation is the limit on how far the output frequency may rise and fall around its nominal value while load and input are constant. It has nothing to do with FM radio. It is given in hertz; a smaller figure means a steadier frequency.

Datasheet example: PowerGuard Outdoor: max. 1 Hz; PowerGuard Static 400 and PowerGuard AC-AC 12 kVA: max. 4 Hz.

Voltage modulation

Voltage modulation is the limit on how much the amplitude of the output voltage may rise and fall repeatedly while load and input are constant. It is stated in volts rms (Vrms); a smaller figure means a steadier supply for sensitive electronics.

Datasheet example: PowerGuard Static 400 and PowerGuard Outdoor: max. 2.5 Vrms; PowerGuard Static 400 reaches steady-state values in 200 ms.

AFE (active front end)

An active front end is an input rectifier built from controlled power switches instead of a passive diode bridge. Its control loop shapes the input current to follow the supply voltage, which reduces the harmonics fed back to the mains or generator and raises the power factor.

Datasheet example: PowerGuard TPS-115 uses an AFE power topology; MIL-UPS-2K3 reaches an input power factor above 0.95 with its AFE architecture.

MIL-STD-1399-300B

MIL-STD-1399 is the US military standard series for the interface between shipboard electric power systems and the equipment they supply. Section 300B covers alternating-current power at 60 Hz and 400 Hz: the voltage and frequency characteristics equipment must accept and the quality limits the supply must meet.

Datasheet example: PowerGuard Static 400 defines its output voltage and frequency requirements to MIL-STD-1399-300B.

Wye (star) and delta connection

Two 3-phase connections: wye references each phase to a neutral (115 VAC line to neutral); delta has no neutral (115 VAC line to line).

Datasheet example: PowerGuard Static 400: wye 115 VAC L-N, power factor min. 0.85; delta 115 VAC L-L, min. 0.80; both at 400 Hz.

Power distribution and protection

PDU (power distribution unit)

Takes one or more power inputs and splits them into protected, switchable outputs for equipment on a platform or in a rack.

Datasheet example: PDU-RT5002: 3 × 220 VAC 50 Hz inputs, 10 × 25 A protected AC/DC outputs, 4U 19"; TDG-EDP-D0X: (+) and (−) 400 A bus bars.

Read more: military power distribution units

DC busbar

A rigid conductor, usually copper, that collects DC sources at one point and feeds the outputs from there; it carries more current than cable.

Datasheet example: TDG-EDP-D0X: (+) and (−) 400 A power bus bars collect the Battery 1, Battery 2, alternator and battery charger inputs.

Read more: what is a DC busbar

MIDI fuse

A MIDI fuse is a bolt-down fuse: its fuse strip is screwed onto busbar or terminal studs instead of being pushed into a holder. The bolted joint suits vibration and the high currents of vehicle DC circuits, which is why MIDI fuses are common on vehicle distribution outputs.

Datasheet example: TDG-EDP-D0X: MIDI output fuses rated 100 A, 60 A and 30 A @ 28 VDC, with spare MIDI fuses from 30 A up to 200 A.

Bypass switch (PDU)

A bypass switch keeps power flowing when the protection logic of a distribution unit would otherwise cut an output after a fault or an exceeded limit. It is meant for critical moments when losing the load is worse than the fault itself, so it should be used deliberately and switched back afterwards.

Datasheet example: PDU-RT5002: with the BYPASS switch on, all faults and warnings are ignored and the system keeps supplying power; PDU-R2D4 has emergency stop and bypass buttons on its front panel.

Surge protection device (SPD)

A surge protection device diverts short overvoltage transients on a mains or generator line, such as switching surges and lightning-induced spikes, to earth before they reach the equipment. It is fitted at the input of a panel or distribution unit.

Datasheet example: PowerGuard PDU-R2D4 has an integrated SPD on the input line with LED status; the ED0 and EDX schematics of the AC power distribution panel include a surge arrester.

EMI gasket

An EMI gasket is a conductive seal fitted between a door or cover and the enclosure body. It closes the gap electrically, so the metal enclosure stays a continuous shield against electromagnetic interference, and it also seals the enclosure.

Datasheet example: TDG-EDP-D0X has an EMI gasket on the door; the AC power distribution panel has an EMI gasket on the enclosure door, together with door and body grounding.

Battery disconnect

A battery disconnect is a switch or contactor that separates the vehicle batteries from the distribution bus. It leaves the downstream wiring de-energised for maintenance and lets the crew isolate the batteries quickly in an emergency.

Datasheet example: TDG-EDP-D0X has a battery disconnect and an emergency stop button; its input contactor opens below 21 VDC and disconnects the batteries from the system.

Input and load contactor

A contactor is a power switch operated by a coil, so a low-current control signal can open or close a high-current circuit. In a distribution unit the input contactor connects the source to the bus, while a load contactor switches a group of outputs on or off.

Datasheet example: TDG-EDP-D0X: the input contactor closes above 21.5 VDC and opens below 21 VDC, also opening the load contactor; the emergency stop opens both. MAR-2 manages its outputs centrally through contactors K1 and K2.

ATS (automatic transfer switch)

Switches the load to the next source in a set priority order when the active source fails, without operator action.

Datasheet example: PDU-RT5002: UPS, mains and generator inputs (3 × 220 VAC); mains is the primary source, with transfer to generator when necessary.

Read more: PDU-RT5002 mil-spec rack PDU

Mains–generator selection panel

A panel on which the operator selects one of two AC sources, mains or generator, by hand and distributes it to output groups. Unlike an ATS, the changeover is manual.

Datasheet example: MAR-2: 220 VAC 50 Hz mains/generator input, manual AC source selector, 9 × 220 VAC outputs.

Read more: mains generator selection panel

19-inch rack and rack unit (U)

The standard cabinet width for mounting equipment; height is counted in rack units (U), so a 4U unit is four times as tall as a 1U unit.

Datasheet example: PDU-RT5002: 4U, 19" rack; PDU-R2D4: 2U, 19″, 482.6 mm front panel.

AC-DC and DC-DC power conversion

AC-DC converter

Converts an AC supply (mains, generator or 400 Hz) to a regulated DC output for electronics, batteries and vehicle loads.

Datasheet example: PowerGuard-A1000: 90–265 VAC, 45–420 Hz input; 24 VDC / 1 kW output.

DC-DC converter

Converts one DC voltage to another, for example a 12 VDC vehicle bus to 24 VDC for equipment, usually with regulation and often with isolation.

Datasheet example: PowerGuard-D1000: 10–18 VDC input (12 VDC nominal), 24 VDC / 1 kW output.

Active PFC (power factor correction)

Active power factor correction is an input stage that makes a power supply draw current in phase with the supply voltage and close to a sine wave. It brings the power factor close to 1, so the same useful power needs less current from the mains or generator and less harmonic distortion is fed back.

Datasheet example: PowerGuard-A1000: PF ≥ 0.99 at 50/60 Hz full load (≈ 0.75–0.8 at 400 Hz); PowerGuard-A 380: PF ≥ 0.95 (typ.); PowerGuard-A 380/30: ≥ 0.95 at full load (preliminary value).

Galvanic isolation

Galvanic isolation means there is no direct conductive path between two circuits, typically the input and output of a converter; energy crosses through the magnetic field of a transformer. It breaks ground loops, keeps faults and noise on one side from reaching the other, and is stated as the test voltage the barrier withstands.

Datasheet example: PowerGuard-D1000: 1500 VDC input–output; PowerGuard-A1000: 2000 VAC (1 min factory test); TPS-24DCAC: all outputs isolated from the input and from each other.

Conduction cooling

In conduction cooling, heat leaves the electronics through a metal baseplate bolted to the mounting surface instead of being blown away by a fan. With no air path, the enclosure can be fully sealed and silent, and there is no fan to wear out or clog with dust.

Datasheet example: PowerGuard-A1000 and PowerGuard-D1000 use a conduction-cooled baseplate and deliver 1 kW continuous up to +55 °C without derating.

Read more: 1 kW mil-spec AC-DC converter

Derating

Derating is the planned reduction of the continuous power a unit may deliver as ambient temperature (or altitude) rises. The datasheet gives it as a table or curve; reading the rating at the real installation temperature, not at room temperature, avoids overheating and shutdowns.

Datasheet example: TPS-24DCAC: 100% from −20 °C to +40 °C; power reduction begins at +50 °C; at +60 °C, DC-DC modules 70% and DC-AC modules 60% continuous. PowerGuard-A1000 and D1000: no derating up to +55 °C.

Read more: military power conversion unit

Hold-up time

Hold-up time is how long a power supply keeps its output within regulation after the input disappears, using energy stored in its capacitors. It carries the load through short interruptions, source changeovers and voltage dips during engine cranking.

Datasheet example: PowerGuard-A1000: 20 ms at full load with 230 VAC input; PowerGuard-D1000: 5 ms typical from internal capacitance, with external bulk capacitance optional.

UVLO (undervoltage lockout)

Undervoltage lockout switches a converter off when its input voltage falls below a set threshold and switches it back on only after the input has risen above a higher threshold. The gap between the two (hysteresis) prevents on-off chattering, for example while a vehicle battery recovers after engine start.

Datasheet example: PowerGuard-D1000: UVLO 8.5 V min. – 9.5 V max., hysteresis controlled; PowerGuard-A 380 lists UVLO among its input protections.

Motor drives, UPS and power protection

Frequency inverter (VFD)

Sets motor speed by changing the frequency and voltage supplied to the motor. Unlike a frequency converter, its output feeds a motor winding, not general equipment.

Datasheet example: Mil-Drive-55: 5.5 kW nominal (optional up to 18 kW), 3 × 400 VAC, 0–500 Hz.

FOC (field-oriented control)

A vector control method that splits motor current into a torque-producing and a flux-producing component and controls each separately, giving precise torque and speed down to low speeds.

Datasheet example: Mil-Drive-55: sensored and sensorless FOC, selectable 4–32 kHz PWM, ramp-up/ramp-down 0.1–600 s.

STO (Safe Torque Off)

A drive safety function that cuts the energy producing torque at the motor; while it is active the motor cannot generate torque, without the main supply of the drive having to be disconnected.

Datasheet example: Mil-Drive-55: dual-channel STO input plus a separate emergency stop.

Regenerative braking resistor

When a motor slows down or is driven by its load, it acts as a generator and returns energy to the DC bus of the drive. A regenerative braking resistor, connected outside the drive, turns that energy into heat so the DC bus voltage does not rise to a level that trips the drive.

Datasheet example: Mil-Drive-55 has a dedicated connector for an external regenerative resistor (KN6, 24WE6SA) and an overload capacity of 150% for 60 s and 175% for 2.5 s.

Read more: military induction motor drive

Online double conversion

In online double conversion, incoming AC is first rectified to DC and then rebuilt as AC by an inverter, so the load is always fed by the inverter. When the input fails, the battery takes over on the DC side and there is no transfer moment at the output. Static frequency converters use the same AC-DC-AC principle.

Datasheet example: MIL-UPS-2K3: online (double conversion), 2.3 kVA, 30 min backup; PowerGuard Outdoor: static double conversion, microprocessor controlled.

Read more: military UPS system

UPS (uninterruptible power supply)

Keeps critical loads powered from a battery when the input supply fails, and conditions the output while the input is present.

Datasheet example: MIL-UPS-2K3: 115 VAC 60 Hz pure sine output, 2.3 kVA online, 30 min backup from sealed VRLA gel batteries.

Read more: military UPS system

Pure sine wave output

AC output that closely follows an ideal sine wave with low harmonic content, unlike the modified-sine or square-wave output of simpler inverters.

Datasheet example: MIL-UPS-2K3: PWM-controlled inverter with < 3% THD and ±2% voltage regulation; TPS-24DCAC: 120 VAC and 220 VAC pure sine outputs.

Supercapacitor (ultracapacitor)

A supercapacitor stores energy electrostatically, in an electric double layer, rather than through a chemical reaction as a battery does. It charges and discharges much faster and accepts high peak currents, which suits short, high-power backup on a vehicle bus.

Datasheet example: PowerGuard EBB: 3600 F supercapacitor for 16–32 VDC vehicle systems; it keeps supplying power for 3 hours after ignition off.

Read more: supercapacitor backup power unit

Reverse polarity protection

Protects equipment and wiring when a battery or jump-start cable is connected with plus and minus swapped.

Datasheet example: PowerGuard TPB-01: 12 / 24 VDC, up to 500 A, IP67; shuts the alternator down 8 s after excite is removed.

Vehicle electronics and military standards

Vetronics

Short for vehicle electronics: the power, data, display, camera and control electronics integrated into a military vehicle.

Datasheet example: SENTRA KBM: 28 VDC (MIL-STD-1275E) input, 11 isolated camera outputs.

Read more: military vetronics

MIL-STD-1275

The US military standard that defines the characteristics of 28 VDC electrical systems in military ground vehicles: the steady-state voltage range and the ripple, surges and spikes that connected equipment must withstand.

Datasheet example: SENTRA KBM: 28 VDC input (MIL-STD-1275E); TDG-VMS-111: 28 VDC, MIL-STD-1275E (Rev. 01 preliminary design values).

CAN-Bus

A two-wire, multi-node serial data bus (ISO 11898) on which vehicle control units, sensors and displays exchange messages.

Datasheet example: SENTRA-16: 32 channels (16 seat + 16 belt) on CAN-Bus, ISO 11898.

Read more: seat belt monitoring system

SAE J1939

A higher-layer protocol for heavy vehicles that runs on CAN 2.0B and defines standard messages for engine, transmission and other vehicle data.

Datasheet example: TDG-VMS-111: 2 × CAN 2.0B (J1939 / custom); camera views switch automatically from CAN J1939 vehicle signals (Rev. 01 preliminary design values).

NVIS compatibility

NVIS (night vision imaging system) compatibility means a display or light emits so little energy in the wavelengths that night-vision goggles amplify that it does not wash out the goggle image. MIL-STD-3009 defines the compatibility types and classes.

Datasheet example: TDG-DSP-101, supplied and integrated by TEDEG, offers an optional MIL-STD-3009 NVIS Type I Class B compatible dual-mode backlight.

Read more: rugged vehicle display

BLACKOUT mode

A light-discipline mode that switches off the visible indicators and audible alerts of a unit for covert operation.

Datasheet example: T-Light warning unit: blackout mode disables visual and audible alerts; TPS-24DCAC: the BLACKOUT switch turns off the panel LEDs through a relay group.

Read more: programmable warning unit

IP69K

An ingress protection rating for dust-tight enclosures that withstand close-range, high-pressure, high-temperature water jets such as pressure washing.

Datasheet example: The vehicle-mounted T-Light Searchlight and the searchlight head of T-Light Turret are rated IP69K.

MIL-STD-461 and MIL-STD-810

MIL-STD-461 sets electromagnetic interference and compatibility (EMI/EMC) limits for emissions and susceptibility; MIL-STD-810 sets environmental test methods such as temperature, vibration, shock and humidity.

Datasheet example: Mil-Drive-55: construction designed to MIL-STD-810G and electromagnetic design to MIL-STD-461F.

Searchlights and lighting

Searchlight vs spotlight

A searchlight concentrates its light into a narrow, high-intensity beam that reaches far and sweeps an area to find targets. A spotlight lights a fixed point or a small area at short range, where an even spot matters more than reach. For long-range use, compare peak intensity in candela, not lumens alone.

Datasheet example: T-Light Turret: 191,900 cd peak intensity (10° lens), 4,590 lm. Vehicle-mounted T-Light Searchlight: white 30 W / 4,500 lm and IR 30 W / 940 nm.

Pan-tilt

A pan-tilt mount moves a searchlight or camera on two axes: pan is rotation in the horizontal plane, tilt is movement up and down. A motorised pan-tilt unit is steered from a control box inside the vehicle, so the crew can aim the beam without leaving cover.

Datasheet example: Vehicle-mounted T-Light Searchlight: unlimited 360° horizontal and 135° vertical movement (optional 360°), controlled from an IP65 control box.

940 nm infrared illumination

Infrared illumination at a wavelength of 940 nanometres lies outside the range the human eye can see, so the light gives no visible glow. A night-vision camera sees the illuminated scene, which allows covert observation and driving.

Datasheet example: Vehicle-mounted T-Light Searchlight: IR 30 W at 940 nm, effective illumination range ≈ 100 m with a night-vision camera.

Lumen, candela and lux

Lumen (lm) is the total light a source emits; candela (cd) is luminous intensity in one direction; lux (lx) is the light falling on a surface. Searchlight range is read from candela and a target illuminance: 1 lux for search, 5 lux to recognise a person or vehicle.

Datasheet example: T-Light Turret: 191,900 cd (10°) gives ~440 m search range at 1 lux and ~195 m recognition range at 5 lux; the 15° version, 85,350 cd, gives ~290 m and ~130 m; both emit 4,590 lm. T-Light Tower: 112,000 lm.

Read more: military searchlight · mobile lighting tower