Full Bridge Inverter
A full-bridge inverter is a type of H-bridge inverter employed for converting DC power into AC power . In contrast to single-phase half-bridge inverters, it utilizes twice the number of components . The circuit comprises four diodes and four controlled switches, often thyristors. These switches, which can be BJT , IGBT , MOSFET or thyristors , play a crucial role in the inversion process. The power circuit of a single phase full bridge inverter is constructed with precision, featuring four thyristors labeled T1 to T4 , four diodes D1 to D4 and a two wire DC input power source denoted as Vs . The four diodes , also known as freewheeling or feedback diodes, facilitate the redirection of stored energy in the load back to the DC source , particularly beneficial for non-pure resistive loads. This feedback mechanism enhances efficiency and stability . The full-bridge inverter configuration provides versatility in adapting to various applications and load types , making it a widely utilized topology in DC to AC power conversion systems . The diodes are strategically placed in antiparallel configuration with the thyristors ; for instance , D1 is connected in antiparallel with T1 and similarly for the rest . These diodes are known as freewheeling diodes or feedback diodes because these The circuit is designed to facilitate the conversion of direct current from the input source into alternating current for various applications .
Case1 (T1 and T2 are ON) : The depicted circuit operates with transistors T1 and T2 in the conducting state while T3 and T4 remain non-conductive . Assuming a current “i” flowing from point A to B , the current path traverses points A – B – C- D .Consequently , T1 and T2 act as a short circuit , facilitating the flow of current in this direction . The output voltage is positive at point A with respect to B . Upon examination of the circuit , it is evident that the supply voltage is directly connected to the load terminal , resulting in a short circuit . This implies that the supplied voltage , denoted as +Vs , will instantaneously appear across the load terminal . The current convention , assuming it flows from A to B , deems the output current positive . In essence , the output voltage +Vs , reflecting the direct supply connection to the load terminal . This design ensures that any input voltage is immediately across the load , simplifying analysis by employing an equivalent circuit that highlights the short circuit condition .In the time period (0<t<= T/2) , thyristors T1 and T2 conducts and load voltage V0 = Vs.
Case 2 ( T3 and T4 are ON ) : Assuming switches T3 and T4 are ON and T2 and T2 are turned off so the circuit is as shown below . Switches T3 and T4 are short circuited and current starts flowing through the supply from here (a – b- c- d-e -f) and returns to the source . In this configuration , the output current is considered negative as it flows from point B to A , aligning with our established convention. Consequently , the output voltage is also negative. The supplied voltage , +Vs is directly connected to point B , yielding a positive potential , while the negative terminal is directly linked to point A , resulting in a negative potential . Thus the output voltage is -Vs. To comprehend the DC to AC conversion process, a focus on waveform is essential triggering of transistors T1 and T2 initiates the pulse generation . T1 and T2 remain on for a specified duration, directing current from point A to B . Subsequently , T3 and T4 are triggered, allowing T1 and T2 to turn off . This sequential operation prevents simultaneous conduction , averting a short circuit . Analyzing the pulses and timings of T1/T2 and T3/T4 reveals the transformation of DC to AC , providing insight into the circuit’s functionality and ensuring optimal performance without compromising the supply integrity . In the time period (T/2)<t<= T , thyristors T3 and T4 conducts and the load voltage V0 = -Vs .
Here , it is seen that for 0 < t <= T/2 , SCR s T1 , T2 conduct and the load is subjected to a voltage Vs . At t= T/2 , SCRs T1 , T2 are commutated and T3 , T4 are gated on . During the period T/2 < t <= T , SCRs T3 , T4 conduct and the load is subjected to a voltage -Vs . It is seen that load voltage is an alternating voltage waveform of amplitude Vs and of frequency 1/T Hz . Frequency of the inverter output voltage can be changed by controlling T . From the above waveform , we can observe that the direction of current flowing through the load in mode 1 (0<= t <=T/2) is opposite to the current flowing through mode 2 (T/2 < =t <=T ). Thus an alternating output is obtained at the output side from a DC power . Whereas when an inductive load is connected to the inverter , the load current lags behind the load voltage .The function of the diodes is to feed the reactive power back to the source provided by the load is inductive . If the load is purely resistive reactive power will be zero and hence the need for diodes is eliminated .
Single Phase Inverter
The primary objective of a single phase inverter is to generate an AC output waveform that ideally replicates a sinusoidal pattern with minimal harmonic content. This sinusoidal waveform closely resembles the standard AC electricity supplied by utility grids. The importance of achieving a high-quality sinusoidal waveform cannot be overstated. It serves to mitigate harmonic distortion, ensuring the proper functioning of a wide array of loads, including sensitive electronic equipment and electric motors. By minimizing the harmonic content, single-phase inverters contribute to the overall stability and reliability of electrical systems. The ability to produce a clean sinusoidal waveform enables these inverters to meet the stringent requirements of modern electrical devices ultimately, facilitating the seamless integration of DC and AC power source. Some industrial applications of inverters are for adjustable-speed AC drives, induction heating, stand by air-craft power supplies, UPS for computers, HVDC transmission lines, etc.
Here in this article, we will discuss types of single phase inverters, and their essential parts, applications, advantages, and disadvantages. Single phase inverters are ideal for use in home appliances, power tools, office equipment, water pumping in agriculture, adjustable speed ac drives, induction heating, vehicles UPS, and grid connected applications.
Table of Content
- Single Phase Inverter
- Types
- Advantages
- Disadvantages
- Applications
- Solved Example
- FAQs