What Is an Auxiliary Power Supply?
An auxiliary power supply is connected to the power supply unit of a main unit and is a power supply device that is used to supplement the power supply that tends to be in short supply, separately from the main power supply.
For example, if the main power supply of a railroad car is mainly used to drive the car, an auxiliary power supply is used to provide a stable power supply for the air conditioning and lighting in the car. Similarly, power supplies for graphic displays in personal computers are also typical auxiliary power supplies.
Note that an auxiliary power supply is also a power supply that receives power from the same power supply unit as the main unit.
Uses of Auxiliary Power Supplies
The main application of auxiliary power supplies is to provide a stable supply of power for air conditioning and lighting in railcars, as mentioned above.
High-voltage power (1500V to 2500V) supplied from overhead wires is converted to low-voltage power (440V to 100V) via an auxiliary power supplies unit. This is because most train cars are designed to use 100 VAC for various lighting and indicator lights, 3-phase 440V for air conditioning equipment, and 100 VDC for door opening/closing devices, etc.
Apart from this example, a storage battery-type power supply called a UPS is also an auxiliary power supply in the broad sense of the term, as it is used to protect personal computers and network computers from data loss due to instantaneous power failure in the event of a power company blackout.
Principle of Auxiliary Power Supplies
There are two main types of auxiliary power supplies for vehicles: MGs (Motor Generators) and SIVs (Stationary Inverters).
The MG, also called an electric generator, has long been used as an auxiliary power supply.
On the other hand, the SIV (Static Inverter) uses IGBTs, which are typical high-power semiconductor devices, in the inverter circuit. There are different types of SIVs, including 3-level, 2-level, and 2-level inverters, as withstand voltage improvements were made according to the IGBTs’ development period at the time. SIVs are also known as pulse-width modulation (PWM) control inverters, which can now be supported by small AC filters, contributing greatly to the miniaturization and high efficiency of auxiliary power supplies.
The low-voltage power supply generated by the SIV is an AC power supply. Therefore, the 100 VDC required for control equipment is converted by a rectifier.