The proposed self-starting auxiliary circuit utilizes a battery and Schottky diodes for this purpose see Fig. For the successful operation of this self-starting circuit, the battery nominal volt- age Vb should be less than the target output voltage Vo minus the forward voltage drop of a diode Vf , and it should be above the minimum voltage requirements of the controller and driver Fig.
Design graphs. At the In Fig. Vo is not available, the controller and the driver circuit will be Using this chart, the MOSFET current rating and converter duty powered by the battery through the Schottky diode Db. This cycle can be selected. With these selected values of the duty will allow the converter to charge the output capacitor to the cycle and the MOSFET maximum current, the inductor value reference voltage. In steady state, when the output voltage has and the switching frequency can be obtained form The reached the value 3.
At this time, they will be powered from the converter Using these charts and the equations, the initial values of the output through the diode Da. During this condition, the battery key components of the converter can be decided. Further, opti- will remain under floating condition. It can be noted that only mum values of the components can be selected by carrying out a very small amount of energy is taken from the battery for detailed loss analysis of the converter and by minimizing the the startup of the energy harvesting system.
Furthermore, the losses. It can be noted that the value of the maximum current used energy of the battery can be replenished by recharging it Im ax changes proportionally with the input power Pin of the from the output of converter through the diode Dc.
Therefore, converter. Therefore, the size of the MOSFETs can be scaled the entire amount of energy used for the converter operation, as per the power requirement of the load.
This is applicable including the energy used during its starting, is harvested from for even low-power applications, demanding less than 1 mW of the ambience. Circuit diagram of the energy-harvesting converter. The reference output voltage Vref is the components, this auxiliary circuit can be used to operate the considered to be 3.
The energy-harvesting converter is de- energy harvesting system virtually for indefinite period of time. The sensed output voltage of the converter is processed design guidelines, discussed earlier in the Sections II and III. The error signal is used by the PI selected to realize the switches S1 and S2. The forward volt- controller to estimate the control voltage that is compared with age of the selected MOSFET body diode is about 0. The nominal duty cycle that can be enabled by external signals.
The comparators in the of the converter is chosen to be 0. The inductor is designed polarity detector unit enable the appropriate buffers to produce to have a standard value of 4. Based on these designed values, the switching frequency In this study, the resonance-based electromagnetic microgen- of the converter is selected to be 50 kHz [see Fig. The erator is modeled as an ac voltage source. A signal generator diodes, D1 and D2 are chosen to be schottky type with low followed by a high-current buffer is used to realize the micro- forward voltage 0.
The converter simulations ized by using a power operational amplifier in voltage follower are carried out in Saber. Circuit models of the selected devices mode. Further, it can be mentioned that the self-resistance and and components, available from the manufacturers, are used in self-inductance of the electromagnetic microgenerator are very the simulations. Various values for circuit components of the small, therefore, the self-impedance of the microgenerators are designed converter are presented in Table I.
To verify the pro- not included for the analysis of the proposed converter oper- posed control techniques, at first simulation is carried out for the ation. In the simulation, the duty cy- system. The buck—boost converter duty cycle Dc is calculated from the estimated duty cycle Db and The input current V. The quency is considered in this study for verification of the pro- total input current and the microgenerator output voltage vi posed converter topology see Fig.
The closed-loop simula- are shown in Fig. Furthermore, from Fig. These corroborate the earlier conclusion from the analysis in Section II see Fig. Hence, to achieve simple control structure, less component counts and for all other prac- tical advantages, both the boost converter and the buck—boost converter can be controlled with same duty cycle for such high step-up applications.
It can be seen from these figures that with the equal duty ratio control, the converter can successfully produce the desired out- put voltage with similar voltage ripple. This control scheme is further used for experimentation of the converter prototype. The Fig. The converter is operated during negative half cycle of the microgen- output voltage under this load condition is shown in Fig. The converter output voltage and the duty The simulations are carried out with the self-starting circuit cycles, estimated by the controller are shown in Fig.
The bat- b , respectively. The estimated source of 3. The battery voltage level 0. It can be noted from Fig. Power and voltages during self start-up. Curves i , ii , iii , and iv show the power supplied by the battery, power draw from the converter output, lier, the output voltage of the microgenerator is considered as battery voltage, and converter output voltage, respectively.
A power operational amplifier LT from Linear Technology is used as a high-current buffer. A figure. It can be seen from these plots that at the beginning, signal generator followed by the current buffer is used to emu- when the converter output voltage is building, the power con- late the output voltage of the microgenerator see Fig. The sumed by the control circuit is only supplied by the battery. At source amplitude and frequency are set to mV and Hz, point A, as shown in Fig. The reference output voltage Vref and the full- comes higher than the battery voltage.
From this point onwards, load resistance selected are 3. The the power consumed by the control circuit is supplied by the various components used in the prototype of the converter are converter, and the power draw from the battery becomes zero presented in the earlier section.
The proposed control scheme see Fig. This is less than the half cycle period implemented. Further, it can be obtained The measured duty cycle, generated by the PI controller, is that the average power consumed by the control circuit is about about 0. This matches with the duty cycle obtained from 2.
The measured input voltage and the input current are shown in Fig. The output voltage of the converter is shown VI. It can be seen that the low ac input voltage is success- A prototype of the converter is built using commercially avail- fully boosted to a well-regulated higher dc voltage 3.
The able components to verify the operation and performance of the duty ratio of the boost and the buck—boost converters are kept to proposed converter and the control scheme.
As explained ear- be the same. A selected part of the boost converter gate pulses and the input current waveforms are shown in Fig. It can be seen that the inductor current builds up in a slightly nonlinear fashion due to the parasitic resistances of the circuit see Table I. The gate pulses of the boost converter and buck—boost converter are shown in Fig. The input voltage and the input current under this load condition are shown in Fig.
The output voltage for this load is shown in Fig. It can be seen that converter success- fully maintains the output voltage to the reference voltage level. The gate pulses and the input current waveforms for a selected part during the boost converter operation are shown in Fig. This matches with the duty cycle cal- culated from the earlier analysis of Section II and the simulation results [see Fig. Hence, the proposed scheme can suc- cessfully control the converter under different load conditions.
The power consumed by the entire control circuit is estimated from the results of the earlier analysis presented in Section V, Fig.
From this loss analysis, the estimated converter efficiency is This estimation agrees with the measurements and earlier simulation results. Hence, with proper design of the conductor and the magnetic components, the converter efficiency can be improved.
Therefore, with the Fig. From this figure, it can be seen that VII. From this point onwards, The presented direct ac-to-dc low voltage energy-harvesting the converter voltage remains higher than the battery voltage. The proposed converter consists of is about 5 ms. These measurements match closely with the a boost converter in parallel with a buck—boost converter. The simulation results presented in the previous section. It can be negative gain of the buck—boost converter is utilized to boost the mentioned that due to the inaccessibility of the PCB traces in voltage of the negative half cycle of the microgenerator to posi- the prototype of the converter, the required currents could not tive dc voltage.
Detailed analysis of the converter for direct ac- be measured to estimate the start-up power draw by the control to-dc power conversion is carried out and the relations between circuit of the converter. Based on the analysis, a simplified control scheme is converter, the currents in the components of the converter cir- proposed for high-voltage step-up application.
Design guide- cuits were measured and the values of the parasitic components lines are presented for selecting values of the key components see Table I were estimated.
The measured currents, voltages, and control parameters of the converter. A self-startup circuit, and the estimated component values were used to calculate the using a battery only during the beginning of the converter opera- loss components analytically.
In Table II, various loss compo- tion, is proposed for the energy-harvesting converter. Cao, W. Chiang, Y. King, and Y. Power analysis and the design guidelines, a prototype of the converter Electron.
The proposed control scheme with the self-startup [17] G. Ottman, H. Hofmann, and G. Power Electron. The loss components of the converter are estimated. The mea- [18] G. Hofmann, A. Bhatt, and G. Ferrari, V. Ferrari, D. Marioli, and A. Paradiso and T. Mitcheson, T. Green, E. Yeatman, and A. Meninger, J. Mur-Miranda, R. Amirtharajah, A. Chandrakasan, May Dwari, R. Dayal, and L. IEEE Ind. El-Hami, P. Glynne-Jones, N. White, M. Hill, S.
Beeby, E. James, Annu. Brown, and J. Richelli, L. Colalongo, S. Tonoli, and Z. Actuators A: Phys. Thul, S. Lorenz, and L. CPES Semin. Sound Vibrations, vol. Amirtharajah and A. Solid-State Circuits, vol. Stark, P. Mitcheson, M. Peng, T. Yeatman, and electrical engineering from Indian Institute of Tech- A. Williams and R. Use of this web site signifies your agreement to the terms and conditions.
This paper presents an efficient ac-to-dc power converter that avoids the bridge rectification and directly converts the low AC input voltage to the required high dc output voltage at a higher efficiency. The proposed converter consists of a boost converter in parallel with a buck-boost converter, which are operated in the positive half cycle and negative half cycle, respectively. Detailed analysis of the converter is carried out to obtain relations between the power, circuit parameters, and duty cycle of the converter.
Based on the analysis, control schemes are proposed to operate the converter. Design guidelines are presented for selecting the converter component and control parameters. A self-starting circuit is proposed for independent operation of the converter.
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