2. System Modeling and Analysis of the Wireless Power Supply System
3. Modeling and Optimization Design of Energy Harvesting Device
3.1. Theoretical Analysis
3.2. Parameters Optimization Design with Threshold Constraints
3.2.1. Parameter Optimization Design of the Core
3.2.2. Design Optimization of the Secondary Coil
- The inner resistance of the coil should not be larger than the load resistance to ensure maximum output power:
- Since the core is composed of two semicircles, a maximum Ns is achieved when the secondary coil covers half of the core at most, which means Ns is determined by the inner radius of the core:
4.1. Simulation Analysis of the Energy Harvesting Device
- According to Figure 7, both the optimal secondary coil turn Ns1 to achieve maximum output power and secondary coil turn Ns2 to ensure the minimum demanded power can be determined, which should comply with Ns2 > Ns1.
- Use a Rogowski coil to sample the current of HVPL in the form of induced voltage. A digital integrator is applied to transform the transient voltage signal e(t) into a stable signal E. The sampled voltage when the current equal to 500 A (less than or equal to the saturation current of core) is set as the standard value.
- The digital comparator is in charge of comparing the sampled E with the standard value. It outputs high-level signals (“1”) when d1 < d2 and outputs low-level signals (“0”) when d1 > d2.
- The diode is shut off when the comparator outputs high-level signals and the secondary coil turn is set to be Ns1 so that maximum output power is achieved. On the contrary, the diode is turned on and the secondary coil turn is set to be Ns2 so that minimum demanded power is acquired. The control strategy greatly reduces the impact of power increase on the load and realizes the goal to obtain relatively stable output power, regardless of current fluctuation.
4.2. Experimental verification
- Output power increases with the increase of core inner radius when other parameters remain certain;
- The increase of core radial thickness (b-a) and core height h will contribute to the increase of output power but the former one has a more pronounced effect;
- The smaller core gap is, the more output power the device can obtain once it holds true for Equation (16) and other parameters remain unchanged;
- Maximum output power can be acquired with the optimized secondary coil turns when other parameters remain certain. In this experiment specifically, Po (Ns = 80) > Po (Ns = 100).
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|Device Number||a (cm)||(b-a) (cm)||h (cm)||δ (mm)||Ns||PL (W)|
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