Dual converters are mainly found in variable speed drives (VFDs). In a dual converter, two converters are linked together back to back. The operation of a dual converter is explained using the diagram below. It is assumed that −

• A dual converter is an ideal one (gives pure DC output) at its terminals.

• Each two-quadrant converter is a controlled DC source in series with a diode.

• Diodes D1 and D2 show the unidirectional flow of current.

Considering a dual converter operating without circulating current, the AC current is barred from flowing by controlled firing pulses. This ensures that the converter carrying the load current conducts while the other converter is blocked. This means that a reactor between the converters is not needed.

Battery Charger

A battery charger also known as a recharger utilizes electric current to store energy in a secondary cell. The charging process is determined by the type and size of the battery. Different types of batteries have different tolerance levels to overcharging. The recharging process may be achieved by connecting it to a constant voltage or constant current source.

Charging Rate (C)

The charging rate is defined as the rate of charging or discharging a battery and is equal to the battery capacity in one hour.

A battery charger is specified in terms of its charging rate C. For example, a battery charger with a rating of C/10 would give a charging capacity in 10 hours while one rated 3C would charge a battery in 20 minutes.

Types of Battery Chargers

There are many types of battery chargers. In this tutorial, we will consider the five main types.

• Simple chargers − Operates by supplying a constant DC power source into the battery being charged.

• Fast chargers − Uses control circuitry to charger the battery rapidly and in the process prevent the battery cells from damage.

• Inductive chargers − Uses electromagnetic induction to charge the battery.

• Intelligent chargers − Used to charge a battery that contains a chip that communicates with the smart charger.

• Motion powered charger − Makes use of human motion to charge a battery. A magnet placed between two springs is moved up and down by human motion thus charging the battery.