Application Cases

Experiment Title: Quasi-Constant Mutual Inductance Calculation and Optimization of Novel Coil Structures in Wireless Power Transfer Systems

Research Direction: Wireless Power Transfer

Test Objective:
Starting from the optimal design of the coil structure itself, based on the quasi-constant mutual inductance calculation and optimization method, a novel coil structure with high misalignment tolerance in the horizontal direction is designed. Without the need for any additional resonant compensation networks or auxiliary control devices, the system's anti-misalignment capability in the horizontal direction can be significantly improved.

Testing Equipment: ATA-3090 Power Amplifier, Arbitrary Waveform Function Generator, Digital Power Analyzer, Oscilloscope, 3D Translation Stage, Transmitting Coil, Transmitting-side Compensation Capacitor, Receiving Coil, Receiving-side Compensation Capacitor, Non-Inductive Load Resistor.

Experimental Procedure:

Figure 1: Wireless Power Transfer Experimental Platform

First, an MCR-WPT system prototype and wireless power transfer experimental platform were constructed, as shown in Figure 1 above. The experimental instruments in the figure are the power amplifier, arbitrary waveform function generator, and digital power analyzer. The system power supply consists of the arbitrary waveform function generator and the Aigtek ATA-3090 power amplifier. The load resistor is a high-precision, non-inductive, adjustable rheostat. The high-precision 3D translation platform enables horizontal misalignment between coils with a movement accuracy of 0.1 mm. An oscilloscope is used to observe the input and output waveforms of the system, ensuring it maintains a resonant state. A digital power analyzer is used to analyze the system's output power and efficiency. By continuously varying the misalignment distance along the Y-axis of the receiving coil (which has a reverse-series structure of two receiving coils), the variations of system input voltage, input current, output voltage, output current, and transmission efficiency with misalignment distance were obtained, as shown in Figures 2 and 3.

Figure 2: Relationship Between Output Power, Transmission Efficiency, and Misalignment Distance

Figure 2 shows the relationship between the system's output power and transmission efficiency as a function of misalignment distance. System transmission efficiency is defined as the ratio of load power to the input power from the source. When the coils are aligned, the system output power is 54.63 W, and the transmission efficiency is 91.37%. When the transmitting coil is misaligned to the limit distance of +240 mm along the Y-axis, the system output power is 55.33 W, and the transmission efficiency is 91.18%. When the transmitting coil is misaligned to the limit distance of -240 mm along the Y-axis, the system output power is 57.22 W, and the transmission efficiency is 90.03%. Beyond the misalignment limit distance in either the +Y or -Y direction, as the misalignment distance further increases, the system transmission efficiency decreases more rapidly, which is attributed to the reduction in mutual inductance. Simultaneously, the system output power also increases rapidly. This is because the decrease in mutual inductance within a certain range causes the current in the transmitting coil (Tx) to increase, thereby leading to an increase in output power.

Figure 3: Relationship Between Output Voltage, Output Current, and Misalignment Distance

The relationship between the system's output voltage (Uout) and output current (Iout) as a function of misalignment distance is shown in Figure 3. From the system output voltage curve, the limit misalignment distance in the +Y direction is 240 mm, where Uout is 24.18 V. The limit misalignment distance in the -Y direction is also 240 mm, where Uout is 24.52 V. Beyond the limit misalignment distances in the +Y and -Y directions, Uout cannot stabilize at 24 V and increases as the misalignment distance increases.

Experimental Results:

The reverse-series structure of two circular receiving coils exhibits strong anti-misalignment performance. For the magnetic coupling mechanism with a transmitting coil outer diameter of 465 mm and a receiving coil outer diameter of 610 mm, within the limit misalignment range of 240 mm in both the +Y and -Y directions, the system's transmission efficiency remains almost unchanged with misalignment distance, consistently staying above 90%. The output power variation does not exceed 5%. Without any auxiliary control devices, the system's output voltage and output current can also remain substantially constant.

Through optimized design, the reverse-series structure of two receiving coils achieves over 90% high-efficiency energy transfer within a 240 mm misalignment range (equivalent to 51.6% of the transmitting coil's outer diameter) in any horizontal direction (including both X and Y axes) without adding any impedance matching networks or auxiliary control devices. The output power and transmission efficiency remain nearly constant, and both constant voltage and constant current output can be achieved. This significantly simplifies the constant voltage or constant current control strategy for MCR-WPT systems and reduces system cost and control complexity. This structure is suitable not only for static wireless power transfer systems for portable and household mobile electronic devices but also for dynamic wireless power transfer systems such as those for electric vehicles and industrial robots.

Figure: ATA-3090C Power Amplifier Specifications and Parameters