Operation of modified SEPIC converter.

As stated above a modified SEPIC is built by adding only two components diode D_M and capacitor C_M to the classical SEPIC circuit. The circuit diagram for modified SEPIC without magnetic coupling is in fig 1.3. Modified SEPIC operates in continuous conduction mode and discontinuous conduction mode. For continuous conduction mode modified SEPIC operates in two stages depending upon the on and off condition of switch.

Stage 1. When the switch is in off state.

At time t₀ the switch is turned off; the input energy stored in inductor L₁ is passed on to the output through C_M and output diode D₀, and also to C_M through diode D_M. Here the switch voltage is same as the voltage across C_M, the energy stored in inductor L₂ is passed on to output through diode D₀.

During this time period, the current in L₁ is equal to input current i.e. i_L1 = i_In. As the diode is in conducting state voltage across it is zero, while current through it is in decaying state. The waveforms to understand these operations are shown in fig.

Stage 2 – When switch is in on state.

At t₁, the switch is turned on and the circuit is as shown in fig. In this mode the inductors instead of transferring energy, they store it. The input energy is applied to L₁, i.e.   Voltage is applied to inductor L₂.The diodes D_M and D₀ are reverse biased

The current through inductor L₂ is equal to output current. Switch is in conducting state so voltage across it is zero, while current flowing through switch is equal to addition of current flowing through both the inductors. i.e.  .Voltage across diode D_O = V_CM, and . The waveforms to understand these operations are shown in fig.

Modified SEPIC converter.

           In modified SEPIC converter, a voltage multiplier circuit is applied to the classical boost converter, for higher output voltage, improved efficiency and low switch voltage. This is done by adding diode D_M and Capacitor C_M to the classical SEPIC as shown in fig..

            Capacitor C_M of the modified SEPIC is charged with the output voltage, hence when the switch is conducting the voltage applied to inductor  is higher than that in traditional SEPIC. In case of modified SEPIC converter, the losses due to diode reverse recovery current are reduced and soft commutation is obtained with regenerative snubber circuit. The static gain of modified SEPIC is higher than classical boost converter for high values of duty cycle, and low input voltage.A gain up to 5 is considered as standard static gain, gain larger than 10 is high static gain and that larger than gain equal to 20 is considered as very high static gain. If compared with other converters for high gain, modified SEPIC utilizes lesser number of switches and less passive components than those converters.

           The main purpose of magnetic coupling in modified SEPIC is to increase the voltage gain leading to boost in the output voltage. In past various other techniques like voltage multiplier, interleaved boost converter, zero voltage switching boost integration technique, etc each of them have certain advantages and disadvantages and can be implemented as per application. If compared with these techniques for high gain, proposed modified SEPIC with magnetic coupling utilizes lesser number of switches and less passive components.

The theoretical explanation, working and simulation results of modified SEPIC without magnetic coupling and modified SEPIC with magnetic coupling are explained in following sections. For magnetic coupling an inductor operating as a flyback transformer is used.

SEPIC(Single Ended Primary Inductor Converter)

A SEPIC is a short form for Single Ended Primary Inductor Converter. SEPIC is a DC-DC buck- boost converter, whose output is controlled by controlling the duty cycle of the control transistor present in the circuit. SEPIC is different from the conventional buck-boost converter in terms of polarity of the output. The conventional buck boost converter has inverted output, while the SEPIC has advantage of non-inverted output. The circuit diagram for classical SEPIC converter is as shown in fig.

Fig.– Circuit diagram of classical SEPIC.

The classical SEPIC consists of two identical inductors, a control transistor (switch) two capacitors and a diode. The inductors L₁ and L₂ are coupled inductors. Coupled inductors are inductors that share the flux lines, i.e. voltage in second inductor is induced because of the voltage in first inductor. A coupled inductor is at a low cost than two separate inductors and also it takes less space on PCB. The inductors are selected on the basis of peak to peak ripple current, it should be approximately equal to 38%-40% of the maximum input current at maximum input voltage. C_S is the coupled capacitor, and isolates the input from output protecting against shorted load. C_S is such selected that RMS current though it must be very small. The control transistor can be FET or MOSFET. In case of power MOSFET selection, minimum threshold voltage, the ON resistance, gate-drain charge, and the maximum drain to source voltage are considered. The output diode should be able to handle peak current and reverse voltage, hence it should be selected accordingly. The output capacitor C_O, is charged with inductor current L₂, hence must sustain maximum RMS current.

Basics needed for studying wireless power transmission

Conceptual basics necessary  to study wireless power transmission(WPT)

Its been a long time since I posted the previous blog where  the necessity of wireless power transmission  was discussed as in the aspect of smart India . In this blog the conceptual basics needed to  study the WPT are explained at an very easy level so that people other than technical backgrounds can also understand.

1. Electricity

2. Magnetism

3. Mutual  Induction

4. Resonance

5. Microwave radiation

6. Laser beam technology

1. Electricity - In simple language electricity is a “ flow of charge”. To understand this the basic physics is required. The discussion has to be then transferred to the structure of atom. Atom is invisible to us with the naked eyes, many atoms combine to make a molecule, which builds the matter which one can physically see and touch. Atom is made up of 3 different particles the protons , neutrons and electrons. Atom has a central nucleus where it consists of protons and neutrons. Protons have positive charge and neutrons have neutral charge. The orbiting particles in an atom are known as electrons .They carry negative charge.  For the flow of charge we need the charge carriers. These electrons and protons help us in that matter. The electrons in the outer orbit of an atom are known as the valence electrons. When the outside force is strong enough , a valence electron can escape orbit of the atom and become free. Free electrons allow us to move charge, which is known as electricity.

2. Magnetism- Magnetism is a property of a material to attract or repel other material. For e.g. magnets attract material having iron in it and does not attracts material having  aluminum,steel,plastic etc in it. Magnets can be of two types - permanent magnet or electro magnet.  Permanent magnet is a material having magnetic  property by nature, while electromagnet is prepared by winding a electric wire on a normal iron piece and when the  electricity passes through  it , it acts as an electromagnet.  Every magnet has its own area only in which it can attract the objects. This is known as a magnetic  field. The force of attraction or repulsion in between the two magnets depends upon their poles. Every magnet has 2 poles i.e. north  pole and the south pole. The two opposite poles attract  each other and the same poles repel each other.  Magnetism is caused due to the alignment of electrons in a specific manner.

3. Mutual Induction – The power from one circuit can be transferred to another circuit without any physical connection between them , but the circuits must be magnetically coupled. This concept is known as mutual induction. This is used only for power transfer and not for power generation. To study mutual induction , consider two circuits  , a primary circuit and a secondary circuit. The primary circuit is connected to mains and produces its own flux. This flux circulates in magnetic core and gets linked with the secondary circuit. According to the Faraday’s law of electromagnetism an electromotive force gets induced in the circuit due to the linked flux . This is a technique used for short range power transfer between two circuits. Not all the flux gets linked from one circuit to another , some of it does not link and it is known as the leakage flux.

4. Resonance – Resonance means a vibration caused in an object  due to vibration effect  in another object. Firstly one  should know  that every object has its own frequency  , and when due to any vibration / movement if the frequency of two objects matches with each other , then they start to vibrate at abnormal frequency. This frequency is known as resonant frequency. Resonance is of two types – 1) Series resonance and 2) Parallel resonance .When the inductive reactance and the capacitive reactance becomes equal Resonance is said to happen. For wireless power transmission resonant inductive coupling and resonant magnetic coupling techniques are utilized.

5. Microwave radiation - Micro means extremely small and wave means movement  and radiation means energy emission, so in simple words microwave radiation means movement of extremely small energy emissions. In a microwave radiation the transmitter transmits the signal which is then received by the receiver at other end. The transmitter and receiver needs to stay in line of sight for the transfer. The detailed study of microwave radiation will be posted in the upcoming posts.

6. Laser beam technology - A laser is an abbreviation for ‘Light Amplification by Stimulated Emission of Radiation’. It is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. Laser are distinguished from other light sources by their  spatial coherence. Spatial coherence allows a laser to stay narrow over great distances enabling applications such as laser pointers.The output of the laser is hence diffraction limited. Laser beams can be focused to very tiny spots, achieving a very high radiance so that they can have very low divergence in order to concentrate their power at a single point.

Wireless transmission-A step towards smart India.

We so frequently use the word “SMART” to refer any person, gadget, Idea, etc , but what it actually means? Smart is an acronym which stands for S-specific,M-measurable,A-achievable,R-realistic,T-time-specific.It means abridge your efforts and hard work to bring out the best results in an easy but logical and efficient manner.

We live in a world where smartness is overloaded,all we need is from smart people to smart phones and smart city to smart homes.In such a phase why not take a small step to reform our country from “INDIA” to “SMART INDIA”.

If you make a survey and ask people out there whether they prefer a landline or a mobile phone,then 8/10 people would probably go with the mobile phone option because of the obvious reasons. One of the important and basic reason behind this is that the cords have been cut. In the same manner imagine your surrounding,your city,your country free from the overhead hanging ,the danger alarming heavily voltage stuffed transmission lines. We always warn our kids to stay away from the electric poles as we fear the electric shock, also many a times we observe birds die due to severe shocks of transmission lines.

Besides these general problems some technical problems like heating of transmission lines,power loss, power theft,etcalso exist. Even the weather conditions hamper the transmission system.

Well to avoid or reduce these problems a wonderful concept of Wireless Power Transmission (WPT)  or wireless transmission of electricity(witricity) can be implemented .WPT concept  was first invented and conceived by the commonly known as Father of wireless- Nikola Tesla in 1892. Further research and study is still being continued.

Witricity can be implemented at domestic level i.e. restricted to our homes may be for charging devices,running equipments with less power requirement ,  etc by using the technique of 1)mutual induction or 2) Magnetic resonant coupling .Other domestic applications are in artificial cardiac pacemakers, charging of electric vehicles, RFID tags. On large scale also it can be applied by using the laser beam technology or the concept of microwave power transmission. The solar power satellites,wireless powered drone aircraft are an important applications of WPT on large scale.

The problems discussed above  are cured in WPT. The other advantages are power can be delivered in any direction i.e. omnidirectional, the cost of conductors is reduced to zero, any human interference b/w the transmitter and receiver neither harms the person nor hampers the transmission process if the WPT is applied under the safety level strengths of radiations.

But as a coin has two sides there are also some drawbacks of this techniques which we can overcome by the study , research and experiments in this aspect. Once this is achieved it will be a boon for the society to free ourselves from the tangles wires thus improving the view of our country. This can prove a smart step ,taken in  a smart way for a smart INDIA.