Introduction To Dc Dc Converter Engineering Essay

Introduction To Dc Dc Converter Engineering Essay buncoA biface dc-dc convertor is used for dc-dc indicator re soreal applications. The major power convertor includes two dependable tie convertors This Bi concernal dc-dc converter is beaver for galvanical vehicle applications. A bifacial, isolated topology is proposed in comity of the differing provoke cell characteristics from traditional chemical-power bombing and safety requirements. The topology proposed in the paper has advantages of simple lap covering with soft selling implementation without excess twistings, spicy susceptibility and simple control.INTRODUCTION TO DC-DC convertorDC-DC converters ar devices which variety show one level of direct oc watercourse/ electromotive force to another (either high or turn down) level. They atomic number 18 primarily of use in battery-powered appliances and machines which hold numerous sub tours, each requiring different levels of electric potentials. A DC-D C converter enables such(prenominal) equipment to be powered by batteries of a single level of potency, preventing the hold to use numerous batteries with varying electric potentials to power each individual component.1.1. BUCK-BOOST CONVERTER chassis. 1 schematic for frivol away- advertise converterWith continuous conduction for the Buck-Boost converter Vx =Vin when the electronic transistor is ON. When the transistor is OFF the inductance in trying to maintain the current in the same direction reverses its polarity as a outlet of which the diode is forward biased and Vx =Vo. For zero net current form over a period the average voltage across the inductor is zero. common fig. 9 Waveforms for kill-boost converterVin ton + Vo toff = 0which gives the voltage proportionalityand the corresponding currentSince the job ratio D is amidst 0 and 1 the issue voltage arsehole vary in the midst of pocket-sizeder or higher(prenominal) than the input voltage in magnitude. The negat ive planetary house indicates a reversal of sense of the output voltage.CONVERTER COMPARISONThe voltage ratios achievable by the DC-DC converters is summarised in design. 10.We f low gearerpot notice that provided the buck converter shows a linear relationship between the control (duty ratio) and output voltage. The buck-boost gutter subordinate or increase the voltage ratio with unit gain for a duty ratio of 50%. public figure. 10 similarity of Voltage ratio1.3 BI-DIRECTIONAL DC-TO-DC CONVERTERA DC-DC converter which can be operated alternately as a step-up converter in a first direction of energy be given and as a release converter in a second direction of energy f natural depression is disclosed. Potential isolation between the low-voltage align and the high-energy typeface of the converter is achieved by a magnetic compound unit, which has not completely a transformer function but withal an energy remembering function. The converter operates as a push-pull conve rter in both directions of energy flow.The DC-DC converter can be used for example in motor vehicles with an electric drive fed by fuel cells.A bi-directional converter for converting voltage bi-directionally between a high voltage bus and a low voltage bus, comprising a switching converter machine-accessible across the high voltage bus, the switching converter comprising first and second switching modules committed in series across the high voltage bus, a switched customer disposed between the switching modules being joined to an inductor, the inductor connected to a first electrical capacity, the connection between the inductor and the first capacitor comprising a mid-voltage bus, the first and second switching modules being controllable so that the switching converter can be operated as a buck converter or a boost converter depending upon the direction of passage from the high voltage bus to the low voltage bus or vice versa the mid-voltage bus being coupled to a first resp ectable bridge switching circuit comprising two pairs of series connected switches with switched nodes between each of the pairs of switches being connected across a first tangled of a transformer having a preset turns ratio and a second just bridge switching circuit comprising two pairs of series connected switches with switched nodes between each of the pairs of switches being connected across a second cockeyeddering(a) of the transformer, the second full bridge switching circuit being coupled to a second capacitor comprising a low voltage node.1.3.3 work OF DC-DC ConvertersIn its simplest form, a DC-DC converter simply uses resistors as needed to abeyance up the flow of incoming energy this is called linear conversion. However, linear conversion is a wasteful process which unnecessarily dissipates energy and can contract to overheating. A more complex, but more efficient, manner of DC-DC conversion is switched-mode conversion, which operates by storing power, switching of f the flow of current, and restoring it as needed to provide a steadily modulated flow of electricity corresponding to the circuits requirements. This is far little wasteful than linear conversion, saving up to 95% of otherwise purposeless energy.1.3.2 biface DC-DC CONVERTERS TOPOLOGIES there are many circuit topologies for bidirectional dc-dc converter. or so of them areNon isolated (Without transformer)Full bridge bidirectional dc-dc converter (shown in fig)Half bridge bidirectional dc-dc converterII. Isolated (with transformer)Full bridge bidirectional dc-dc converter ( shown in fig)Half bridge bidirectional dc-dc converter1.3 NON-ISOLATED bifacial DC-DC CONVERTERFig2 Full bridge bidirectional dc-dc converterFig 17 shows a basic circuit diagram of a full bridge bidirectional DC-DC converter.It has interleaved cognitive process for both boost and buck modesIt has smaller passive componentsIt has less battery pucker current1.3.2.2 ISOLATED BIDIRECTIONAL DC-DC CONVERTER (PRO POSED CONVERTER)Fig18 lv-side current source and hv-side voltage sourceFig 18 shows the circuit diagram of an Isolated DC-DC converter. This converter has the following featuresSimple voltage clamp circuit implementationSimple transformer winding structure and low turns ratioHigh choke ripple frequency (2fs)Start up problem will be present in this circuit1.4 semiconductor unit SWITCHINGSemi conductor switching are of two types. They are1. Hard Switching2. Soft Switching1.4.2 SOFT SWITCHING more(prenominal) recently, new power conversion topologies have been developed which dramatically reduce the power dissipated by With soft switching techniques, reduction in wasted power will often improve the efficiency of a unit by more than 2%. While this does not grievous significant, it can account for a saving of more than 20 W in a 1000 W power put up. This 20 W is power that would have been dissipated by the main power transistors, the to the highest degree critical and most heavily str essed semi-conductors in any switch mode power supply. Reducing the power here lowers their junction temperature, full-grown increased thermal ope rating(a) margins and, hence, a longer life for the power supply. Not only does a soft switching power supply generate significantly less electrical noise, it achieves greater efficiency, longer mean time between failures (MTBF), and higher immunity to the effects of other equipment direct nearby.It is desirable for power converters to have high efficiencies and high power densities. promotional material and cost limitations require that the converter have a small personal size and weight. Power density and electrical operation are mutually beneficial on the switching frequency as it determines the values of the reactive components in the converter. Thus, high frequency operation of the converter is highly craved. However, operation at high frequency results in higher switching losses and higher switching stresses caused by the circ uit parasitics (stray inductance, junction capacitance).The circuit topology of the proposed bidirectional isolated converter is shown in Fig. According to the power ow directions, there are two operation modes for the proposed converter. When power ows from the low-voltage side (LVS) to the high-voltage side (HVS), the circuit operates in boost mode to draw energy from the battery. In the other power ow direction, the circuit operates in buck mode to charge the battery from the high-voltage dc bus. Based on the symbols and signal polarities introduced in Fig. 2, the theoretical wave forms of the two operation modes are shown in Fig. (a) and (b), respectively.Fig42 Theoretical waveform under (a) boost and (b) buck operationBoost system (Discharging Mode) featWhen the dc bus voltage in the HVS is not at the desired high level, such as during a cold start, the power gaunt from the low-voltage battery flows into the high-voltage dc bus. During this mode, the proposed converter is operated as a current-fed circuit to boost the HVS bus voltage. The LVS switches Q1, Q4 and Q2, Q3 operate at asymmetrical duty ratios and 1- which require a trivial overlapping conduction interval. Referring to the equivalent circuits for the boost mode operation in Fig. 43, the detailed operating principle can be explained as follows.Although the LVS switches subject to higher voltage stress, this is an advantage because the battery voltage is low. Because the overlapping interval for the LVS switches Q1, Q4 and Q2, Q3 is very short, the LVS transformer current flows through only one LVS switch at most time. Thus, the conduction losses for Q1, Q4 and Q2, Q4 can be greatly reduced to improve the conversion efficiency. Moreover, the LVS circuit produces a relatively ripple free battery current that is desirable for the low voltage battery. The voltage transfer ratio Mboost for the boost mode operation for the proposed dc-dc converter can be derived from the volt-second balance cond ition across the inductor L1 represented by (7). The current stresses of the inductor windings can be also unyielding as (6).The inductances of the power inductor L1 can be determined for their given peak-to-peak current ripples, I1Where (%) is the ripple percentage of the inductor currents IL1B. Buck Mode (Charging Mode) OperationDifferent from the traditional electric vehicle driving system, the fuel cell powered system needs an additional energy storage device to absorb the feedback power from the electric machine. This energy storage device may be a lead-acid battery as shown in Fig44 . The proposed circuit works in buck mode to recharge the battery from high-voltage dc bus. During this mode, the proposed converter is operated as an asymmetrical half bridge circuit with synchronous rectification current doubler to recharge the battery from high-voltage dc bus.The HVS switches Q5, Q8 and Q6, Q7 operate at asymmetrical duty ratios and 1- which require short and fountainhead-defi ned dead time between the conduction intervals. Referring to the equivalent circuits in Fig. , the detailed operating principle of this mode can be explained as follows.Fig44 modes of operation in buck modeWhile the LVS switches, Q1, Q4 and Q2, Q3, share odds-on voltage and current stresses, the HVS switches, Q5, Q8 and Q6, Q7, share equal voltage stresses as (8). thus the current stresses of the HVS switches can be found asDESIGN CONSIDERATIONS FOR report COMPONENTSTo verify the feasibility of the proposed scheme, a 2-kW laboratory prototype operated at 20 kHz was built. The simulation and data-based results will be shown and discussed in the future(a) section. The LVS of the design example was connected to a 12-V lead-acid battery whose terminal voltage could swing from 10-15 V. The nominal voltage on the HVS dc bus was knowing to 300 V, with an operating range from 150-400 V. The design considerationsBased on (5), the turn-ratio plectrum of transformer can be calculated as (15). The HVS device ratings can consequently be calculated use (8)-(10) as followsB. Power InductorsLet the peak-to-peak current ripples be 20% of the inductor currents under full power. The current rating and the inductance of the power inductor L1 can be determined using (6)- (7) as followsBecause of the ripple cancellation on the battery current, a larger ripple current in inductor L1 and can be allowed in serviceable applications. Thus, the inductance and the size of the inductors L1 might be smaller.To verify the theoretical operating principles, a 2-kW design example was simulated by using MATLAB. There is a good agreement between the simulation results and theoretical analysis. In this research, a 2-kW laboratory prototype was implemented and tested to evaluate the performance of the proposed bidirectional isolated dc-dc converter.. The ripple cancellation between two inductor currents can be observed. This is desirable for a low-voltage battery.7.1 BOOST OPERATION FOR BI DIRECTIONAL DC-DC CONVERTERCONVENTIONAL CIRCUIT FOR BOOST MODE7.3 RESULTANT range FORM7.3.1 BOOST OPERATIONInput and Output waveformFig 48CONVENTIONAL CIRCUIT FOR BUCK MODEFig477.4 RESULTANT waveform FOR BUCK OPERATION Input and Output voltage waveformFig 49Proposed Bidirectional DC-DC converterInput and Output Voltage WaveformsFig50Fig 51Inductor Current WaveformsFig52CONCLUSIONA soft-switched isolated bidirectional dc-dc converter has been implemented in this paper. The operation, analysis, features and design consideration were illustrated. Simulation and experimental results for the 45W, 20 kHz prototype was shown as per principle. It is shown that ZVS in either direction of power flow is achieved with no lossy components involved As results, advantages of the new circuit including ZVS with full load range, decreased device count, high efficiency (measured more than 94% at rated power), and low cost as well as less control and accessory power needs, make the proposed converter very promising for medium power applications with high power density.