Switching Frequency Technology and Power Quality

SWITCHING
FREQUENCY
TECHNOLOGY AND
POWER QUALITY

INTRODUCTION
• Basically, the technology of the switching frequency in a converter or an inverter is the rate at
which the used switching device is turned off and on during the DC voltage pulse width
modulation process of switching power supply. This technology of the switching frequency has
significant impacts on power quality. For instance, higher switching frequency helps in reducing
the sizes which are linked to the devices like transformers, resistors, capacitors, inductors among
others. It also helps in reducing the required space on the board as well as the cables employed
in the installation of these different components. The switching frequency has a great effect on
the quality of power; some of these include the following;
• Higher switching frequency increases the power factor which is very significant in improving the
power quality utilized.
• The technology of frequency switching is also employed in motor control where Variable
frequency drives are employed. This variable frequency drives which use the principles of
frequency switching help in the reduction of energy consumed as the AC motor operates.
• At higher switching frequency the sizes of electrical devices reduce in size hence less costly.
Such devices include capacitor, resistors, and inductors.
• The square waves or the sine waves which are basically employed to convert the rectified or Dc
voltage to a higher frequency (Deng, 2015). The PFM which is known as the pulse Frequency
Modulation increases the variable switching frequency thus governing the number of times the
device is switching ON and OFF for every second. For this switching technology, the PFM should
have constant OFF time and constant ON time. For most cases the square wave is employed in
frequency switching since it is very easy to filter and to control the square waves as compared to
the sine waves (Xu, 2016). The diagram below illustrates the prototype of a typical switched mode
power supply which can be employed in switching frequency.

Objectives and Aims
This project is aimed at analyzing the impact of the switching frequency on quality of power.
The following diagram represents a prototype of a typical switched mode power supply is as shown
below;

LITERATURE REVIEW
Increase the power factor
• Currently, the switching frequency is very common for electrical power usage in most electrical components. A
conventional AC connected power basically has a full wave diode rectifier having a big capacitive output filter (Chen,
2018). This then leads to important AC line current distorted, therefore, degrading the input power quality. This is true
since the poor power quality can result in ineffective usage on the electrical grid and also can result in damage to the
electrical devices (Al-Haddad, 2015). Thus the higher switching frequency is preferred as the major components
characterizing the quality of power are power factor of the input current. Through definition active power ratio to
apparent power is given as below;
• PF= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
• Where PF is the power factor, Peal is the real or active power, Vin rams is the input rms value and I in rms is the input
rms current value.
• And it is also known that the power factor is a function of phase which is between the input current and voltage
fundament a harmonic can also be given by the following equation 2;
• PF= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
•
• Where THD is the total harmonic distortion,
• From equation 2 above when the THD input current is increased, the value of power factor will be reduced this will
result in degradation of power quality of the input power. Power Factor correction converter can work either in
discontinuous mode, continuous mode or conduction mode. These converters are made work in the discontinuous
mode for applications which require very low power consumptions (Li, 2015). For an adjusted control method to lower
the THD, the current at the input and improvement of the power factor of the discontinuous conduction mode of the
power factor correction.
• For boosting power factor using the switching frequency there are some three main control methods, these include the
average current control methods, hysteresis control as well as the peak current control (Wang, 2017). But of the three
the average current control method is mostly preferred over the other two since it has relatively higher immunity to
noise, therefore, it is not easily affected by the noise. The schematic diagram for the average current control is
illustrated using the following diagram;