ELECTRIC CURRENT CONVERSION 1

(FROM AC TO DC AND DC TO AC)

The choice of electric current to use, whether  alternating current ( ac) or direct current( dc)  depends on the purpose or application in which it is to be put in service. Alternating current (ac) and direct current (dc)   possess some unique properties that are exclusive to themselves only. For instance, converting direct current to alternating current (ac) enables us to exploit the exceptional properties of alternating current (ac) low power losses over long distances at higher voltages. Similarly for storage in batteries, it is inevitable to use or convert alternating current (ac) to direct current( dc), since it is the only electric current form that can be used or acceptable to store electrical energy in batteries.

There are several methods employed to convert ac to dc and they are; the first method involves using rectification. The rectification method involves using diodes or thyristors. The second method is the switch mode conversion and this involves using power electronics switches (e.g. IGBTs, MOSFETs). The last method involves using linear regulators to convert alternating current (ac) to direct current (dc).

However rectification is the most common method of conversion from alternating current (ac) to direct current (dc). There are three types of rectification methods and they are; half wave rectification, which converts one half of the alternating current (ac) waveform to direct current (dc). The second method the full wave rectification converts both halves of the alternating current (ac) waveform to direct current( dc) and the third the bridge rectification method uses four diodes to convert alternating current( ac) to direct current( dc).

The alternating current (ac) to direct current( dc)   conversion process involves the following; filtering the ac input to remove noise and harmonics before rectification using diodes or thyristors to convert alternating current (ac) to direct current( dc). Thereafter the direct current (dc) output current is smoothed to reduce ripples, onward to regulating the resultant output to maintain a consistent or constant voltage. The constant direct current (dc)   output is then filtered to remove noise and ripples again before use.

Similarly for direct current (dc) to alternating current (ac) conversion, there are several methods of converting from direct current (dc)   to alternating current (ac), namely; the first method is the inversion method and it uses power electronic switches (e.g. IGBTs, MOSFETs) to convert direct current( dc)  to alternating current(ac). The second method involves the use of oscillators to convert direct current (dc)   to alternating current (ac). The third method involves using modulation techniques to convert direct current (dc)   to alternating current (ac).

The direct current (dc) to alternating current (ac) conversion process using the inversion method, involves; first filtering the direct current (dc) input to remove noise and ripples prior to inversion, which converts direct current (dc) to alternating current (ac) using power electronic switches. Thereafter the output ac is modulated to achieve the desired frequency and amplitude. Finally the alternating current (ac) output is filtered to remove noise and ripples before use.

Alternating current (ac) to direct current (dc) conversion is used in the following; power supplies to computers, television, electronic devices, renewable energy systems including solar and wind power systems, industrial control systems, motor drives and so on.

Direct current (dc) to alternating current (ac) conversion is used in power systems like grid tie inverters for solar and wind power, uninterruptible power supply, motor drives to control ac motor and so on.

Alternating current (ac) to direct current( dc) and direct current( dc)  to alternating current (ac)  conversion systems both offers the following advantages; efficient energy transfer, reduced energy loss, and compact designs. The challenges of both are in minimizing energy loss and reduction in the thermal stress generated due to its operation as well as the electromagnetic inferences issues during use.

The future of alternating (ac) to direct current( dc)  and direct current( dc) alternating current ( ac ) conversion technologies is based on the following; for alternating current (ac) to direct current( dc)   conversion the development of high efficiency rectifiers and wide band gap semiconductors will greatly improve their performance and reliability. Also the development of resonant conversion technologies will reduce switching losses thereby increasing efficiency. The use of advanced digital control algorithms will optimize performance, reduce harmonics and improve power factor.

However for direct current (dc)   to alternating current (ac) Conversion the following trend is expected also for the future; increased switching frequencies and the use of wide band gap semiconductors to improve the overall efficiency and power of a more compact converter. Also novel modulation methods will enhance or optimize efficiency, reduce harmonics and improve or increase grid stability.

 

 

SOURCES;

• Power electronics: converters, applications and design by Ned Mohan.
• Power electronics: Devices, Drivers and applications by B.W Williams.
• Electric power conversion by Yoshihiro Konishi.
• The power electronics handbook edited by Timothy L. Skvarenina.
• Power conversation and control for renewable energy systems edited by Frede Blaabjerg.