What is a Full Bridge Inverter : Working & Its ApplicationThe inverter is an electrical device that converts DC input supply to symmetric AC voltage of standard magnitude and frequency at the output side. It is also named as DC to AC converter. An ideal inverter input and output can be represented either in a sinusoidal and non-sinusoidal waveforms. If the input source to the inverter is a voltage source, then the inverter is said to be called a voltage source inverter (VSI) and if the input source to the inverter is a current source then it is called as current source inverter (CSI). Inverters are classified into 2 types according to the type of load being used i.e, single-phase inverters, and three-phase inverters. Single-phase inverters are further classified into 2 types of half-bridge inverter and full-bridge inverter. This article explains the detailed construction and working of a full-bridge inverter.What is a Single Phase Full Bridge Inverter?Definition: A full bridge single phase inverter is a switching device that generates a square wave AC output voltage on the application of DC input by adjusting the switch turning ON and OFF based on the appropriate switching sequence, where the output voltage generated is of the form +Vdc, -Vdc, Or 0. Classification of InvertersInverters are classified into 5 types they areAccording to the output characteristicsSquare wave inverterSine wave inverterModified sine wave inverter.According to the source of the inverterCurrent source inverterVoltage source inverterAccording to the type of load Single-phase inverterHalf-bridge inverterFull bridge inverterThree-phase inverters 180-degree mode120-degree modeAccording to different PWM techniqueSimple pulse width modulation (SPWM)Multiple pulse width modulation (MPWM)Sinusoidal pulse width modulation (SPWM)Modified sinusoidal pulse width modulation (MSPWM)According to the number of output levels.Regular 2 level invertersMulti-level inverter.ConstructionThe construction of full-bridge inverter is, it consists of 4 choppers where each chopper consists of a pair of a transistor or a thyristor and a diode, pair connected together that isT1 and D1 are connected in parallel,T4 and D2 are connected in parallel,T3 and D3 are connected in parallel, andT2 and D4 are connected in parallel.A load V0 is connected between the pair of choppers at “AB” and the end terminals of T1 and T4 are connected to voltage source VDC as shown below.Circuit Diagram Of Full Bridge Single Phase InverterAn equivalent circuit can be represented in the form of the switch as shown belowDiode Current EquationWorking of Single Phase Full Bridge InverterThe working of single-phase full-bridge using RLC load inverter can be explained using the following scenariosOverdamping and UnderdampingFrom graph at 0 to T/2 if we apply DC excitation to RLC load. The output load current obtained is in the sinusoidal waveform. Since the RLC load is being used the reactance of the RLC load is represented in 2 conditions as XL and XCCodition1: If XL> XC, it acts like lagging load and is said to be called as an overdamped system andCondition2: If XL< XC, it acts like leading load and is said to be called an underdamped system.Full Bridge Inverter Wave FormConduction AngleConduction angle of each switch and each diode can be determined using the waveform of V0 and I0.At Lagging Load ConditionCase1: From φ to π, V0 > 0 and I0 > 0 then switches S1, S2 conducts Case2: From 0 to φ, V0 > 0 and I0 < 0 then diodes D1, D2 conducts Case3: From π + φ to 2 π, V0 < 0 and I0 < 0 then switches S3, S4 conducts Case4: Form π to π + φ, V0 < 0 and I0 > 0 then diodes D3, D4 conducts.At Leading Load ConditionCase1: From 0 to π – φ, V0 > 0 and I0 > 0 then switches S1, S2 conductsCase2: From π – φ to π, V0 > 0 and I0 < 0 then diodes D1, D2 conductsCase3: From π to 2 π – φ, V0 < 0 and I0 < 0 then switches S3, S4 conductsCase4: Form 2 π – φ to 2 π, V0 < 0 and I0 > 0 then diodes D3, D4 conductsCase 5: Prior to φ to 0, D3, and D4 conduct.Therefore conduction angle of each diode is “φ” and the conduction angle of each Thyristor or Transistor is “π – φ”.Forced Commutation and Self CommutationSelf Commutation Situation can be Observed in Leading Load ConditionFrom the graph, we can observe that “φ to π – φ”, S1and S2 is conducting and after “π – φ”, D1, D2 are conducting, at this point, the forward voltage drop across D1 and D2 is 1 Volt. Where S1 and S2 are facing negative voltage after “π – φ” and so S1 and S2 turn off. Hence self commutation is possible in this case.Full Bridge Inverter Wave FormForced Commutation Situation can be Observed in Lagging Load ConditionFrom the graph, we can observe that “o to φ”, D1 and D2 are conducting, and from π to φ, S1, and S2 are conducting and are short-circuited. After “φ” D3 and D4 conduct only if S1 and S2 are turned off, but this condition can be satisfied only by forcing S1 and S2 to turn off. Hence, we use the concept of forced commutation.Formulas1). The conduction angle of each diode is φ2). The conduction angle of each Thyristor is π – φ.3). Self-commutation is possible only in leading power factor load or underdamped system at of circuit turn off time tc = φ / w0. Where w0 is the fundamental frequency.4). Fourier series V0 (t) = ∑n=1,3,5α [ 4 VDC / nπ ] Sin n w0 t5). I0 (t) = ∑n=1,3,5α [ 4 VDC / nπ l zn l ] Sin n w0 t + φn 6). V01max = 4 Vdc / π7). I01max = 4 Vdc / π Z18). Mod Zn = R2 + ( n w0 L – 1/ n w0 C) ; where n = 1,2,3,4…..9). φn = tan -1 [ ( / R ]10). Fundamental Displacement factor FDF = cos φ11). Diode current equation ID and waveform is given as follows ID01 (avg) = 1/2π [ ∫0φ I01 max Sin ( w0 t – φ1 ) ]dwtID01 (rms) = [ 1/2π [ ∫0φ I012 max Sin2 ( w0 t – φ1 ) dwt ] ]1/2Diode Current Equation12). Switch or thyristor current equation IT and waveform is given as followsIT01 (avg) = 1/2π [ ∫φπ I01 max Sin ( w0 t – φ1 ) ]dwtIT01 (rms) = [ 1/2π [ ∫φπ I012 max Sin2 ( w0 t – φ1 ) dwt ] ]1/2Thyristor Wave FormAdvantages of Single Phase Full Bridge InverterThe following are the advantagesAbsence of voltage fluctuation in the circuitSuitable for high input voltageEnergy efficientThe current rating of the power devices is equal to the load current.Disadvantages of Single Phase Full Bridge InverterThe following are the disadvantagesThe efficiency of the full-bridge inverter ( 95% ) is less than half the bridge inverter (99%).Losses are highHigh noise.Applications of Single Phase Full Bridge InverterThe following are the applicationsApplicable in applications like low and medium power example square wave / quasi square wave voltageA sinusoidal wave which is distorted is used as input in high power applicationsUsing high-speed power semiconductor devices, the harmonic contents at the output can be reduced by PWM techniquesother applications like AC variable motor, heating induction device, standby power supplySolar Inverterscompressors, etcThus, an inverter is an electrical device that converts DC input supply to asymmetric AC voltage of standard magnitude and frequency at the output side. According to the type of load a single-phase inverter is classified into 2 types, like half-bridge inverter and full-bridge inverter. This article explains about full bridge single phase inverter. It consists of 4 thyristors and 4 diodes which together act like switches. Depending upon the switch positions the full-bridge inverter operates. The main advantage of the full-bridge over half-bridge is that the output voltage is 2 times input voltage and output power is 4 times compared to a half-bridge inverter. 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