Morgan Chopper : Working with Output Waveforms

Morgan Chopper : Working and Output Waveforms Important Features It uses current commutation and it is a Class B type commutation. It uses saturable reactor (SR) Commutation circuit consists of capacitor C, Diode D and saturable reactor SR Assume the exciting current of SR negligibly small What is Saturable Reactor ? It is a special type of inductor in which magnetic core is deliberately saturated by direct electric current in a control winding . With the change in direction of current the saturation polarity is also changed i.e. if one direction of current SR will be in positive saturation and for another direction of current SR will be in negative saturation It has very low inductance during saturated condition and very high inductance during un saturated condition Difference between air core inductor and Saturable reactor? Air core inductor As air can take any amount of flux, it never saturates. Saturable reactor It can be saturated at low exciting current. Therefore the inductance offered by SR is very low. Assumptions: Load current is constant Exciting current of SR is negligibly small. Modes of Operation Morgan chopper has three modes of operation: Mode-0, Mode-1 & Mode-2 MODE-0 : At t = 0⇒ TM is OFF Initially TM is OFF and the capacitor is charged with VC = +VS Voltage across capacitor appears across SR. Free wheeling diode and diode D is ON SR is in positive saturation condition MODE-1 : At t = t1⇒ TM is turned ON Voltage across capacitor appears across SR. Core flux flows from positive saturation to negative saturation. Voltage across capacitor remains constant until core flux reaches negative saturation. After core flux reaches negative saturation , capacitor discharges Inductance of SR falls. Discharge of capacitor occurs in very short time. V0 = +VS C & SR forms resonant circuit and its discharge time is equal to 𝛑√(𝐋_𝐬 𝐂) . 𝐋_𝐬 𝐢s the inductance after saturation Therefore discharging time of capacitor is less than the charging time of capacitor Mode-2 At t = t2 Capacitor is negatively charged VC = -VS for short time. Voltage across capacitor appears across SR. Core flux is driven into positive saturation from negative saturation. Inductance of SR falls Discharge of capacitor occurs in very short time. A negative current flows through TM and it goes into OFF condition After TM goes OFF, discharge current flows through diode D. V0 = +VS Features of Morgan Chopper : The time required to saturate the core is constant. The conduction period of TM is fixed & depends on C & 𝐋_𝐬 The total ON time of TM is determined by time required by SR to +ve saturation to –ve saturation and vice versa. Turn ON time of TM is always constant due to constant time of core saturation and it depends on 𝛑√(𝐋_𝐬 𝐂) . The average output voltage can be changed by changing output frequency. #MorganChopper #MorganChopperWorking #MorganChopperOutputWaveforms #SaturableReactor #DifferenceBetweenAircoreInductorAndSaturableReactor