Presentation on theme: "High Frequency Saturable Reactor"— Presentation transcript:
1 High Frequency Saturable Reactor Inderpreet ObhiEE136
2 What is a HF Saturable Reactor The HF SR is a regulator that is used in high frequency switching regulatorsIt is also known as a saturable core magnetic regulator and a magnetic pulse width modulatorSR is used in high frequency switch mode supplies as a flux- saturation controlled power switch. It provides regulation by using secondary pulse width control techniques.
3 Basic principle of a SR * selection of correct core mat. it must act like a good magnetic on/ off switchit must have high effective inductive reactance in its off state and low effective inductive reactance when it is in the on stateHigher the inductance the more it will oppose the change in current
4 Basic Principle cont.The saturated state is the on state and the non-saturated state will be the off state of the switch.as the core does not saturate there would be a very small current flowas the current does not flow in the non-saturated state, our reactor will act like an off switch
5 Basic Principle Cont. points s2 and s3--no change in H no change in current wrt change in Bmore change in B than is seen for Hpermeability is very highinductor wound with this core characteristic we would see infinite inductance
6 Basic Switching Analysis On switch Analysisobserve the core at point s1No change in B significant change in HH translates to zero permeability and zero inductanceZ equiv to winding.(small)No resistance to current flowReactor is in its On stateOff switch Analysisas long as the core does not saturatevery small current flowsas long as the current does not flow in the non-saturated statereactor is an off switch
7 Things to Consider area of ideal B-H loop is very small translates to negligible energy lossnegligible loss is important when the ideal core is switching from on to off at high frequenciesmust exhibit low loss in order to have a very efficient reactor.
8 Example of a Saturable Reactor power regulator Single winding SR regulatorsimple voltage controlled reset transistor Q1assume the core of the SR is unsaturated at s3
9 SR example Assuming short on state change in the flux density B is negligiblecore does not saturate and B moves next to s2leads to a small magnetization and core loss currentsecondary winding on T1 goes positive due to a power pulse at the inputD1 will conductsvoltage drop across the winding SRFrom s3 accumulated v/swill increase the flux density B from s3 to positive saturationoffOn
10 Effect of Q1 on switching If Q1 is on or saturated during the off state lead to a reversed voltage on transformer T1core will be reset to point s3the same small loop will be followed by the next power pulsethe only current that is passed to the output is the magnetization and loss current of the reactoroff switching operation allowing negligible current to flow to the output
11 SR example. Q1 off Time duration from S2 to saturation td = (N * B * Ac)/ VsIf core was not reset after 1st Fwd V-pulseCore will reset to level with s22 nd Fwd V pulse takes core from s2 to saturationZ of reactor is lowLarge current flows via D1 and L1 to Output
12 Design of a Saturable Reactor: details to core materials, core size, which in turn depends on the application, frequency and performance that is desiredminimum secondary voltage required from the converter transformer must be calculatedVs = Vout ( ton+ toff)/ ( ton)select core size and number of turnslast step is to calculate temperature rise, which depends on the core and winding losses
13 ResultsReduction of effective pulse widthReduction of output voltage