In this paper, a single-stage ac–dc power electronic converter is proposed to efficiently manage the energy harvested from electromagnetic microscale and mesoscale generators with low output voltage. The proposed topology combines a boost converter and a buck-boost converter to condition the positive and negative half cycles of the input ac voltage. Only one inductor and capacitor are used in both circuitries to reduce the size of the converter. A prototype has been designed and tested at 10-kHz switching frequency. The input ac voltage with 9-V amplitude is rectified and stepped up to 40-V dc. Here PWM is generated with the help of TMS320F2812. Detailed design guidelines are provided with the purpose is to reduce the size, weight, and power loss. The theoretical analyses are validated by the experiment results.
Mode I: This mode begins when S2 is turned ON at t0. The inductor current is zero at t0. The turn on of S2 is achieved through zero current switching (ZCS) to reduce switching loss. Inductor L is energized by the input voltage as both S1 and S2 are conducting. Both diodes are reverse biased. The load is powered by the energy stored in the output filter capacitor C.
Mode II: S2 is turned OFF at t1, where t1 - t0 = d1Ts, d1 is the duty cycle of the boost operation, and Ts is the switching period. The energy stored in the inductor during Mode I is transferred to the load. The inductor current decreases linearly. During this mode, switching loss occurs during the turn on of diode D2.
Mode III: D2 is automatically turned OFF as soon as the inductor current becomes zero at t2 (t2 - t1 = d2Ts). This avoids the reverse recovery loss of diode. The load is again powered by the stored energy in the capacitor. The converter would return to Mode I as soon as S2 is turned ON, if the input voltage is still in positive cycle.
Mode IV: During the negative input cycle, Mode IV starts as soon as S1 is turned ON at t’0. ZCS condition can also be achieved by ensuring the converter operation in DCM. The energy is transferred to the inductor L again, while the output filter capacitor C feeds the load.
Mode V: At t’1, S1 is turned OFF, where t’1 – t’0 = d’1 Ts, d’1is the duty cycle of the buck-boost operation. The energy stored in the inductor during Mode IV is transferred to the load. The inductor current decreases linearly. During this mode, switching loss occurs during the turn on of the diode D1.
Mode VI: When the inductor current decreases to zero at t’2 (t’2 – t’1 = d’2Ts), D1 is turned OFF at zero current. The load is continuously powered by the charge stored in the output capacitor. The converter would return to Mode IV as soon as S1 is turned ON, if the input voltage is still negative.
Information about TMS320F2812
ZCD (Zero Crossing Detector) is generated with reference to the input sine wave of the bridgeless boost rectifier. Below image explains how ZCD is generated.
PWM (Pulse Width Modulation) is generated with reference to ZCD. This PWM is given to bridgeless boost converter for switching MOSFET. It is explained below with an image.
Shows the PWM for M1 (MOSFET) with reference to ZCD
Shows the PWM for M2 (MOSFET) with reference to ZCD
The pulse which is given to the bridgeless boost converter MOSFET (switching devices) are of exact opposite these switching pulses are compared and explained below.
Comparison between PWM of M1 and M2 (MOSFET)
Input as 9VAC
Output as 40VDC
A single stage ac–dc topology for low-voltage low-power energy harvesting applications is proposed in this paper. The topology uniquely combines a boost converter and a buck-boost converter to condition the positive input cycles and negative input cycles, respectively. Only one inductor and one filter capacitor are required in this topology. This prototype successfully boosts the 9V/50Hz AC to 40V DC at 60% of duty cycle in PWM. In comparison to state-of-the-art low-voltage bridgeless rectifiers, this study employs the minimum number of passive energy storage components, and achieves the maximum conversion efficiency.
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