Right Selection of Inverter Systems and Harmonics Reduction: A Means of Enhancing Power Infrastructure in Nigeria

How to cite this paper: Akinwole O. O | Adewale A. S | Femi-Jemilohun, O. J "Right Selection of Inverter Systems and Harmonics Reduction: A Means of Enhancing Power Infrastructure in Nigeria" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 24566470, Volume-3 | Issue-3, April 2019, pp.1704-1707, URL: https://www.ijtsrd.c om/papers/ijtsrd23 550.pdf


INTRODUCTION
Harmonics are multiples of fundamental frequency of a waveform. There are even and odd harmonics. In other words, if the frequency of the fundamental is f, then even harmonics will be 2f, 4f, 6f and so on. In the same vein odd harmonics are 3f, 5f and 7f. In electric power system, the menace of harmonics cannot be overemphasized, they cause system malfunctions and increase the temperature of conductors, imagine a waveform with fundamental frequency, f producing its own I 2 R losses in form of heat, so also all the harmonics frequencies will produce theirs thus resulting to excessive heat and fire outbreaks. Maule Derek in its treatise in IEE review magazine of March, 2001 opined that the long term effects of harmonic distortions on a network's conductors and components are self evident. He explained that heating and resonant conductors will cause early components failure and the premature breakdown of insulation. He stressed that costs will rise and level of downtime will increase. Going by this, one should be conscious of which type of inverter unit to acquire; however, there have been debates and questions on the best choice for inverters installations. The buyers always ask a questionwhich types should we purchase; is it Sine wave, Modified Sine wave or Square wave inverters? Anyway, the choice depends on the loads to be powered by them. Majority of the buyers are either indifferent to this or they are not well informed about harmonics content of each type and how the phenomenon will affect their equipment and installation. In spite of this ignorance, there is an upsurge in the procurement of inverters. Especially in third world countries where there are crisis of low energy per capital, a smart business owner or successful house owner would want to generate his or her own power. Attachment to the technology is also borne out of the benefits accruable from it. An inverter power system does not pollute the environment with carbon monoxide poisoning -a factor that has contributed to avoidable death cases in the third world countries, which Nigeria is among. Also, the system does not generate noise. Inverters are DC powered devices that convert DC (Direct Current) to AC (Alternating Current) power by switching the DC input voltage in a predetermined sequence so as to generate AC voltage output, [9]. In a nutshell, they convert battery voltage which is DC to an alternating quantity which is usually 220V, 50Hz as we have in Nigeria. Figure 1 shows a simple block diagram of a power inverter system. As a result of crave to have alternative power sources, that is, renewable energy from the sun and

IJTSRD23550
International Journal of Trend in Scientific Research and Development (IJTSRD) @ www.ijtsrd.com eISSN: 2456-6470 Page: 1705 wind, the desire to have static inverters to convert generated Direct Current DC from these sources to Alternating Current AC quantity has increased tremendously, [2]. In olden days, there were rotary inverters that comprise DC motors that have AC generators connected to their shafts. Due to the presence of moving parts, they deliver lower efficiencies of about 60% and they have high idle power consumption, [7]. They are also classified to electric quantity at their sources, that is, Voltage Source Inverters (VSI) and Current Source Inverters (CSI). Current source types are less popular compared to Voltage Source types, [9].

Square Wave Inverters
They have square wave as their output waveforms. The output waveforms rise straight up, level off for a time at peak voltage and then drop straight down. It levels off for a time in the negative direction as shown in figure 2. They were the pioneer static inverters.
The Total Harmonic Distortion THD is about 45%, [2]. They are not efficient, parade poor regulation and are not conducive for some electronic devices, [3]. Electric motors could be powered by them but with excessive heat dissipation. [7].Other devices that may not work properly are laser printers, photocopiers, digital clocks, sewing machines with speed/microprocessor controls and other systems incorporating microprocessors.

Modified Sine Wave Inverters
A modified Sine wave inverter, also being referred to as quasi-Sine wave resembles square wave type except that it rests at zero for a short time, thus, has one additional step. [7]. This is the most common inverter output in the market, it has Total Harmonic Distortion THD of 23.8% which is lesser than that of a square wave type of about half of that of square wave, hence more electronics devices will work well with these types. This type has an improved efficiency and better regulation but its high number of harmonics still affects sensitive equipment such as medical monitors. It can also cause hum in a radio or sound system or snowy video picture. [8].

Sine Wave Inverters
They are also referred to as True Sine Wave or Pure Sine Wave Inverters. A Sine wave inverter waveform smoothly increases to its peak and smoothly decreases. They are very costly and are not common in the markets. A sine wave inverter has about 3% Total Harmonic Distortion (THD). [2].These types are reliable, harmless, devoid of interference and similar to the power obtainable from the power outlet. [3]. They allow motors to run faster, quieter and cooler. [8].
Pure Sine Wave inverters can safely run more sensitive devices like laser printers, laptop computers, power tools, digital clocks and medical equipment [1].

Inverters Output Waveforms and Timing Circuits of Devices
Timing circuits often work in accordance with zero crossing point. They tend to work for a period where voltages cross zero volts, at this point, they start their clocks. For example, a drill works by pressing its trigger. The trigger allows the electricity to pass depending on the time. A true Sine wave product has a zero crossing slope thus enabling the timing system to commence work. When a load is a simple type, maybe a bulb or resistive element or an induction load, Modified Sine wave performs optimally. But this is not the case with sensitive electronics products -here, a Sine wave inverter will perform better. Some digital clocks are synchronised with ac source voltages, the squaring circuits use the zero crossing points to generate square waves which are afterwards divided by counters for timing purposes.

Waveforms Generation
In electrical engineering, waveforms generations by an engineer can never be waved aside. Everything has to do with either manipulation or synthesizing signals or waveforms. The ideas of waveforms shaping for gating circuitries always highlight the ingenuity of engineers. A function is said to be periodic of its function value repeat it regular intervals of the independent variable. The regular interval between repetitions is the period of the oscillations, [6]. Fourier series indicates that a function is made up of sine components. The fundamental frequency consists the largest period and is also called first harmonics. To generate waveforms similar to that of the electricity supply authority, it has to be done in such a way that harmonics distortions are reduced. In some applications, harmonics cause degradation of equipment; hence it has to be de-rated. THD is measured [2] thus (1) In order to study harmonics, wave shapes understanding is priceless. And this can be done by employing Fourier series which is the tool for analysing wave shapes.

Fourier Series of A Square wave Inverter
If f(x) is defined on the interval -π x π and f(x) = f(x + π), that is, the waveform is periodic, [6].
The square waveform is an odd function since f (t) = -f (-t) or f ( Also, f (t) (9) It repeats itself in magnitude but reverses in phase after every half period. The same thing is applicable over a quarter wave. In this case, an = bn =0 for even n, that is, all even harmonics are absent.

Reduction of Harmonics
It has been established that harmonic distortion is the deviation of the generated waveform of the inverter voltage from the ideal sinusoidal waveform. Harmonics presence does affect the load powered by the device hence they have to be mitigated. This can be achieved by connecting harmonics trap filters across the output terminals of the inverter thereby filtering out the harmonics. An LC low pass filter is normally connected to the output terminals of the inverter to roll-off high frequency harmonics. The knowledge of the harmonics frequencies enables tuning of the cut-off frequency of the filter, [9]. The 3 rd harmonic is the hardest to filter out and is equal to of the magnitude of the fundamental, [2].