Half Bridge Inverter
The half bridge inverter architecture serves as a fundamental building block in the realm of single phase inverters, offering a straight forward structure that efficiently converts direct current into alternating current . This configuration consists of two switch components often transistors, IGBT’s , MOSFET’s arranged in series across a DC voltage source . Additionally , two feedback diodes and two capacitors establish connections between the source and load . In this setup , the load is strategically positioned between the midpoint of the capacitors and the midpoint of the diodes and switches. Through complementary switching operations of the components , an alternating current output voltage is generated across the load. Feedback diodes come into play particularly with inductive loads, ensuring a smooth and controlled current flow.
Half Bridge Inverter with Resistive Load
The circuit given below is a single phase inverter with resistive load where RL is resistive load , Vs/2 is taken as the voltage source and self commutating switches S1 and S2 , each is connected in parallel with diodes D1 and D2. S1 conducts when the voltage is positive and current is negative , while S2 conducts when both voltage and current are negative . Diode D1 conducts during positive voltage and negative current , whereas diode D2 conducts during negative voltage and positive current . This configuration ensures a continuous current flow through the load. The self-commutating nature of the switches allows for precise control, enabling S1 and S2 to alternate conduction based on voltage and current polarities . Overall , this design facilitates efficient conversion of the DC input into AC output, making it suitable for various applications , especially where resistive-inductive load are involved.
Case 1 : When switch S1 is ON from 0 to T/2 time period, then diode D1 and D2 are reverse biased and switch S2 is OFF.
By applying Kirchhoff’s voltage law ,
Output voltage V0 = Vs/2 Output current i0 = V0/ R = Vs/2R
If switch current is1 = i0 = Vs/2R , is2 = 0 and also the diode current
id1 = id2 = 0
Case 2 : when switch S2 is ON from T/2 to T time period , then diode D1 and D2 are reverse biased and switch S1 is OFF .
By applying Kirchhoff’s voltage law ,
Output voltage V0 = -Vs /2
Output current i0 = V0/R = -Vs/2R
If switch current is1 = 0, is2 = -Vs/2R and also the diode current
iD1 = iD2 = 0
These voltage waveforms are drawn on the assumption that each thyristor conducts for the duration its gate pulse is present and is commutated as soon as this pulse is removed . It is seen that for 0< t <= T/2 , SCR T1 conducts and the load is subjected to a voltage Vs/2 due to upper voltage source . At t=T/2 , SCR T1 is commutated and T2 is gated on . During the period T/2 < t <T , SCR T2
conducts and the load is subjected to a voltage -Vs/2 due to the lower voltage source. It is seen that load voltage is an alternating voltage waveform of amplitude Vs/2 and of frequency 1/T Hz . Frequency of the inverter output voltage can be changed by controlling T .
Half Bridge Inverter with R-L Load
The single phase half-bridge inverter circuit comprises essential components, including two switches , two diodes and a voltage supply . The R-L load is positioned between two points A and O , with A denoting the positive terminal and O representing the negative terminal . Current direction is defined such that when flowing from A to O , it is considered positive, and conversely , when flowing from O to A , it is treated as negative. The switches control the flow of current through the load , enabling the inverter to alternate the polarity of the output . This alternating current facilitates the conversation of direct current from the supply into an alternating current across the load , essential for various applications such as motor drives and power electronics . The diodes play a crucial role in providing a return path for the inductive components , ensuring the smooth operation of the circuit .
Case 1 (0 < t < t1) : In this time period , both the switches S1 and S2 are OFF and diode D2 is in reverse bias condition . During this period , the inductor releases its energy through diode D1 then output current decreases exponentially from negative peak value to zero. V0 = Vs/2. By applying Kirchhoff’s voltage law
Output voltage V0 > 0Output current i0 < 0Switch current is1 = 0Diode current id2 = -i0
Case 2 (t1 < t < T/2) : In this time period , switch S1 is closed and S2 is OFF and both the diodes are in reverse biased condition . In this period inductor starts to store the energy , and output current increases from zero to its positive peak value . Vo = Vs/2 .By applying Kirchhoff’s voltage law.
Output voltage V0 > 0Output current i0 > 0Switch current is1 = i0Diode current id1 = 0
Case 3 (T/2 < t < t2) : In this time period , both the switches S1 and S2 are OFF , diode D1 is reverse biased and diode D2 id reverse biased. In this period inductor releases its energy through diode D2 and the output current decreases exponentially from its positive peak value to zero . V0 = -Vs/2 . By applying Kirchhoff’s voltage law.
Output voltage V0 < 0Output current i0 > 0Switch current is1 = 0Diode current id1 = 0
Case 4 (t2 < t < T) : In this time period , switch S1 is OFF and S2 is closed , diode D1 and D2 are reverse biased . In this period , the inductor charged to negative peak value to zero . V0 = Vs/2 . By applying Kirchhoff’s voltage law.
Output voltage V0 < 0Output current i0 < 0Switch current is1 = 0Diode current id1 = 0
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