Introduction To Dc Dc Converter Engineering Essay

Introduction To Dc Dc Converter Engineering EssayABSTRACTA bi counselor-at-lawal dc-dc convertor is utilize for dc-dc power conversion applications. The power convertor includes two full bridge convertors This Bidirectional dc-dc converter is best for galvanic vehicle applications. A bidirectional, obscure analysis situs is proposed in con caseration of the differing fuel cell characteristics from tralatitious chemical-power bombing and safety requirements. The topographic anatomy proposed in the paper has advantages of simple circumference with soft switching slaying without additional devices, higher(prenominal) efficiency and simple control.INTRODUCTION TO DC-DC CONVERTERDC-DC converters are devices which change one level of direct current/ electric potential to another (either higher(prenominal) or lower) level. They are primarily of use in bombardment-powered appliances and machines which possess numerous sub circuits, each requiring different levels of voltages. A DC-DC converter enables such equipment to be powered by batteries of a single level of voltage, preventing the need to use numerous batteries with varying voltages to power each individual component.1.1. scoot-BOOST CONVERTERFig. 1 schematic for flick- wage hike converterWith continuous conduction for the Buck-Boost converter Vx =Vin when the transistor is ON. When the transistor is OFF the inductor in trying to maintain the current in the same direction reverses its polarity as a result of which the diode is forward biased and Vx =Vo. For zero net current change over a period the reasonable voltage across the inductor is zero.Fig. 9 Waveforms for buck-boost converterVin ton + Vo toff = 0which gives the voltage ratioand the corresponding currentSince the duty ratio D is between 0 and 1 the output voltage can vary between lower or higher than the input voltage in magnitude. The banish sign indicates a reversal of sense of the output voltage.CONVERTER COMPARISONThe voltage ratios achievable by the DC-DC converters is summarised in Fig. 10.We can notice that only the buck converter shows a linear relationship between the control (duty ratio) and output voltage. The buck-boost can reduce or increase the voltage ratio with unit increment for a duty ratio of 50%.Fig. 10 Comparison of Voltage ratio1.3 BI-DIRECTIONAL DC-TO-DC CONVERTERA DC-DC converter which can be plightd alternately as a step-up converter in a startle direction of energy guide and as a step-down converter in a second direction of energy flow is disclosed. Potential isolation between the low-voltage side and the high-voltage side of the converter is achieved by a magnetized compound unit, which has not only a transformer function but also an energy storage function. The converter operates as a push-pull converter in some(prenominal) directions of energy flow.The DC-DC converter can be used for example in motor vehicles with an voltaic 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 affiliated across the high voltage bus, the switching converter comprising first and second switching modules affiliated in series across the high voltage bus, a switched node accustomed between the switching modules being join to an inductor, the inductor connected to a first capacitor, 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 conversion from the high voltage bus to the low voltage bus or vice versa the mid-voltage bus being joined to a first full 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 winding of a transformer ha ving a preset turns ratio and a second full 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 winding of the transformer, the second full bridge switching circuit being coupled to a second capacitor comprising a low voltage node.1.3.3 WORKING OF DC-DC ConvertersIn its simplest form, a DC-DC converter simply uses resistors as needed to break up the flow of incoming energy this is called linear conversion. However, linear conversion is a wasteful process which unnecessarily dissipates energy and can lead to overheating. A more than complex, but more efficient, manner of DC-DC conversion is switched-mode conversion, which operates by storing power, switching off 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 less wasteful than linear conversion, saving up to 95% o f otherwise wasted energy.1.3.2 BIDIRECTIONAL DC-DC CONVERTERS TOPOLOGIESThere are more circuit topologies for bidirectional dc-dc converter. Some of them areNon isolated (Without transformer)Full bridge bidirectional dc-dc converter (shown in fig)Half bridge bidirectional dc-dc converterII. obscure (with transformer)Full bridge bidirectional dc-dc converter ( shown in fig)Half bridge bidirectional dc-dc converter1.3 NON-ISOLATED BIDIRECTIONAL 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 operation for both boost and buck modesIt has small passive componentsIt has less battery ripple current1.3.2.2 ISOLATED BIDIRECTIONAL DC-DC CONVERTER (PROPOSED 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 ratio blue choke ripple frequency (2fs)Start up problem will be present in this circuit1.4 SEMICONDUCTOR SWITCHINGSemi managing director switching are of two types. They are1. Hard Switching2. Soft Switching1.4.2 SOFT SWITCHINGMore recently, untried power conversion topologies necessitate been developed which dramatically reduce the power dissipated by With soft switching techniques, reduction in wasted power will often mitigate the efficiency of a unit by more than 2%. While this does not sound significant, it can account for a saving of more than 20 W in a 1000 W power supply. This 20 W is power that would bring been dissipated by the main power transistors, the close critical and most heavily stressed semi-conductors in any switch mode power supply. Reducing the power here lowers their junction temperature, giving change magnitude thermal in operation(p) margins and, hence, a longer life for the power supply. Not only does a sof t 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 operating nearby.It is desirable for power converters to have high efficiencies and high power densities. Packaging and cost limitations require that the converter have a small physical size and weight. agent density and electrical performance are dependent on the switching frequency as it determines the values of the reactive components in the converter. Thus, high frequency operation of the converter is super desired. However, operation at high frequency results in higher switching losses and higher switching stresses caused by the circuit 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 o ws 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 load the battery from the high-voltage dc bus. Based on the symbols and signal polarities introduced in Fig. 2, the theoretical waveforms of the two operation modes are shown in Fig. (a) and (b), respectively.Fig42 Theoretical waveform under (a) boost and (b) buck operationBoost Mode (Discharging Mode) OperationWhen the dc bus voltage in the HVS is not at the desired high level, such as during a cold start, the power drawn 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 short overlapping conduction interval. Referring to the equivalent circuits for the boost mode op eration 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 by dint of 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 condition across the inductor L1 represented by (7). The current stresses of the inductor windings can be also determined as (6).The inductances of the power inductor L1 can be determined for their given peak-to-peak current ripples, I1Where (%) is the rip ple 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 well-defined 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 unequal voltage and current stresses, the HVS switches, Q5, Q8 and Q6, Q7, share equal voltage stresses as (8). Then the current stresses of the HVS switches can be found asDESIGN CONSIDERATIONS FOR KEY COMPONENTSTo verify the feasibleness of the proposed scheme, a 2-kW laboratory prototype operated at 20 kHz was built. The simulation and experimental results will be shown and discussed in the next section. The LVS of the number 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 designed to 300 V, with an operating range from 150-400 V. The design considerationsBased on (5), the turn-ratio selection of transformer can be calculated as (15). The HVS device ratings can then be calculated using (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 practicable 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 BIDIRECTIONAL DC-DC CONVERTERCONVENTIONAL lap FOR BOOST MODE7.3 RESULTANT WAVE FORM7.3.1 BOOST OPERATIONInput and payoff 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. fashion model 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.