FIELD OF INVENTION :
The present invention relates to a high frequency full bridge series resonant inverter with AC input source.
BACKGROUND OF THE INVENTION :
An inverter, is a circuitry or electronic device which changes direct current (DC) to alternating current (AC) from sources such as batteries or, rechargeable batteries, DC power supplies, solar cells or fuel cells to AC electricity at any desired voltage and frequency. The inverter does not produce any power, the power is provided by the DC source. The inverter translates the form of the power from direct current to an alternating current waveform. An inverter can produce square wave, modified sine wave, pulsed sine wave, or sine wave depending on circuit design. An inverter can be classified on the basis of operating frequency which is an essential requirement for different field of application. Basically there are two types of inverters such as Low frequency or power frequency inverters and high frequency inverters. Low frequency or power frequency inverters are suitable for an uninterruptible power supply (UPS) or variable-frequency speed control of motor (like: industrial motor driven equipment, electric vehicles and rail transport systems etc.). Whereas, high frequency inverters are suitable for a switch mode power supply (SMPS),

electroshock weapons, application of solar power in aircraft, application of induction heating, contactless power transfer or microwave heating. In low-frequency or power frequency inverters, the switching frequency is same as that of the AC sine wave i.e. 50 Hz (50 times per second). This requires the inverter's transformer to work a bit harder, plus demands it to be larger and heavier, thus results in a heavier, bigger package. High-frequency models typically drive the switches at a frequency closer to 50KHz (50,000 times per second) or in the rage from 20 KHz to 1 MHz, thus allowing the user to use a smaller, more efficient transformer and overall smaller package. The developed scheme converts the power frequency AC to high frequency AC. But the rectifier and DC link stage of the prior art is absent in the new art.
Low frequency and high frequency inverters perform the same function: they transform the Direct Current (DC) into Alternating Current (AC) that is used by most types of motors and appliances. However, they traditionally differ because the low frequency converters use an iron core transformer to step up the voltage, whereas high frequency models are "transformer-less" i.e. air core or ferrite core transformer. The core-loss is almost absent in the high frequency inverters. Implementation of high frequency inverters is a smarter way to reduce the total losses in the application of induction heating. The cost of high frequency inverters is more than others but overall gain is more in long life span.

Choosing the exact inverter is an important task for switch mode power supply (SMPS), electroshock weapons, application of solar power in aircraft, application of induction heating, contactless power transfer or microwave heating. The three dominant commercialized waveform types are square wave, modified sine wave and sine wave. Out of three wave-shapes, the sine wave composition is more suitable for high frequency inverters.
Considering the above points, within the present work, a replacement of circuit topology of high frequency full bridge resonant inverter with a novel high frequency full bridge resonant inverter with AC input source, is developed that generates more RMS output voltage across the load.
PRIOR ART OF CIRCUIT TOPOLOGY FOR HIGH FREQUENCY INVERTERS:
Prior art circuit diagram of high frequency full bridge resonant inverter is shown in Figure 1. In the prior art, high frequency conversion scheme from 50 Hz AC input source using DC-link inverter, is shown in Figure 2. in this scheme, at first the 50 Hz single phase AC supply is rectified to DC through an uncontrolled rectifier. Then this DC voltage is converted to high frequency AC through a high frequency full bridge resonant inverter. The inverter is equipped with MOSFET (Metal Oxide Semiconductor Field Effect Transistor) switches

(MOSFET 1, MOSFET 2 and MOSFET 3 AND MOSFET 4). Here the anti-parallel diodes (D1, 02, 03, D4) connected with the MOSFETs are acting as the freewheeling diode in case of inductive load. At first, the MOSFET 1 and MOSDET 4 are made on and a resonant current flows through the load. In the next half cycle, these two switches are made off and MOSFET 2 and MOSFET 3 are made on. So the load current flows in the reverse direction. So. a high frequency alternating voltage is produced across the load. Due to high frequency switching, high frequency harmonics are generated in the load side which backflow to the supply side and can distort the supply waveform. This can cause deterioration of performance of other loads, which are connected to the supply. So to prevent the injection of these harmonics AC filter is incorporated at the supply side. Figure 3 depicts the real time output voltage of the prior art of high frequency full bridge resonant inverter.
OBJECTS OF THE INVENTION :
Therefore, it is an object of the invention to make a high frequency full bridge series resonant inverter with AC input source which is capable of having the RMS value of output voltage and output current significantly more and hence more heat generation compared to that of the prior art.

Another object of the invention is to propose a high frequency full bridge series resonant inverter with AC input source which is capable of working effectively with half the number of diodes compared to the prior Art making the arrangement cost effective and highly reliable.
A further object of the invention is to propose a high frequency full bridge series resonant inverter with AC input source which is able to make the efficiency higher compared to the prior art because of single block being involved for conversion from low frequency AC input source to high frequency AC.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS:
Fig.l : Shows the Prior Art of high frequency Full Bridge series Resonant inverter with DC source.
Fig.2 : Shows the Prior Art circuit diagram of high frequency conversion scheme using DC-link inverter and AC filter with single face AC supply.
Fig.3 : Shows a prior Art real time output voltage of high frequency full bridge series resonant inverter.
Fig.4 : Shows new art circuit diagram of high frequency full bridge series resonant inverter with single phase AC supply.

Fig.S : Depicts the real time output voltage of the new art of high frequency full bridge series resonant inverter.
Fig.6 : Shows a block diagram of Prior Art.
Fig.7 : Shows a block diagram of the present invention. Here LR refers to inductor in resonant condition, Rt refers to internal resistance of the inductor and CR refers capacitor in resonant condition.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION:
NEW ART OF CIRCUIT TOPOLOGY FOR HIGH FREQUENCY INVERTERS:
Compared to the circuit of the previous art, a new art of high frequency conversion scheme using single block full bridge resonant inverter is developed in figure 4. Here there is no separate block of uncontrolled rectifier for the rectification of single phase AC to DC. The DC link is also absent in this scheme. Here the single phase AC supply (S) is applied directly to the inverter consisting of MOSFET switches (MOSFET 1, 2, 3 and 4) along with anti-parallel diodes and an AC filter (F). Here the anti-parallel diodes (D1, D2, D3, D4) connected with the MOSFETs are acting as the freewheeling diode in case of inductive load. The anti-parallel diodes also serve the additional purpose of rectification in the new art. The rectifier DC voltage is produced across the capacitor. This DC voltage is

converted to AC by the inverter operating at high switching frequency. So this circuit is acting like an AC to AC converter. The inverter is operating at high switching frequency and due to this a high frequency alternating voltage is produced across the load. Figure 5 depicts the real time output voltage of the new art of high frequency full bridge resonant inverter. It can be seen from the figure that the RM5 voltage of the output is more than the prior art. RM5 voltage of prior art is 153.7 volt when that of invented arrangement is 324.48 volt. So this topology is highly efficient and acceptable for the users.
ADVANTAGES:
The developed scheme has several advantages over the conventional systems
which are as follows:
(i) The RM5 value of output voltage is significantly more compared to that of
the conventional systems (prior art).
(ii) Moreover, the RM5 value of output current is appreciably large compared
to that of the conventional systems (prior art).
(iii) Total number of diodes is reduced to half as compared to the previous
circuit topology. So this arrangement is cost effective and has less circuit
complexity as compared to the previous one (prior art).

(iv) As number of components in this circuit is less, so it is cost effective and highly reliable in comparison with the prior art.
(v) Efficiency becomes higher because single block is involved for conversion from low frequency AC input source to high frequency AC.
Considering these above mentioned advantages, the novel high frequency full bridge resonant inverter with AC input source is more suitable for high frequency applications like switch mode power supply (SMPS), electroshock weapons, application of solar power in aircraft, application of induction heating, contactless power transfer or microwave heating.
Considering the block diagram (fig.6) of prior art we have an AC filter (i), DC rectifier (2), DC filter (3) and High frequency inverter (4). Let us consider the efficiency of DC rectifier (2) as 95%, the efficiency of DC filter as 98%, the efficiency of High frequency inverter as 95%, when overall efficiency ηoverall of
the system is
ηoverall = 0.95 x 0.98x0.95 = 88.44%
But in new art as shown in Fig.7, the overall efficiency of the invented inverter is

ηoverall = the efficiency of the High Frequency inverter as there is no DC rectifier
(2) or DC filter (3)
= 0.95 = 95%
Hence there is a significant improvement of the efficiency from 88.44% to
95%.
In case of prior art, the DC Filter is connected to the. points A and B as shown in Fig.G. But in case of invented arrangement, 50 Hz single phase AC supply with AC Filter is directly connected to X and Y of the output which generates more RMS output voltage across the load.
Since, RMS value of the load voltage of the new art is more than the RMS value of the load voltage of prior art, the heat generation in the new art is also more.

WE CLAIM
1. A high frequency full bridge series Resonant inverter with AC input source
comprising;
an AC input source;
an AC filter;
a plurality of anti-parallel diodes (D!, D2, D3, D4);
a capacitor (C);
a plurality of metal oxide semiconductor field effect transistor (MOSFET 1,
2, 3, 4) and characterized in that,
the said AC supply is applied directly to the inverter, the said inverter having a plurality of metal oxide semiconductor field effect transistor (MOSFET) switches (MOSFET 1, 2, 3, 4) for resulting the current flowing through the load in direction (X to Y) for half cycles and making the current flowing in the reverse direction (Y to X) for next half cycle producing a high frequency alternating voltage across the load wherein the anti-parallel diodes (Dl, D2, D3, D4) are disposed in the arrangement and connected to the MOSFETs for serving the purpose of rectification when the rectified DC voltage produced across the capacitor (C) is converted to AC by the inverter operating at high switching frequency making the arrangement acting like an AC to AC converter wherein the inverter operating at high switching frequency produces a high frequency alternating voltage across the load.

2. A high frequency full bridge series Resonant inverter as claimed in claim 1, wherein four numbers of MOSFET switches are disposed in the arrangement when MOSFET 1 and 4 being made ON, results current to flow from X to Y and when MOSFET 2 and 3 being made ON, results current to flow from Y to X.
3. A high frequency full bridge series Resonant inverter as, claimed in claim 1, wherein four numbers of diodes (D1, D2, D3, D4) are disposed in the arrangement.