If electric vehicles have to be truly sustainable, it is essential to charge them from sustainable sources of electricity, such as solar or wind energy. In this paper, the design of solar powered e-bike charging station that provides AC, DC and wireless charging of e-bikes is investigated. The charging station has integrated battery storage that enables for both grid-connected and off-grid operation. The DC charging uses the DC power from the photovoltaic panels directly for charging the e-bike battery without the use of an AC charging adapter. For the wireless charging, the e-bike can be charged through inductive power transfer via the bike kickstand (receiver) and a specially designed tile (transmitter) at the charging station, which provides maximum convenience to the user.

In inductive power transfer applications that use resonant compensation networks, the commonly employed H-bridge inverter should be kept operating in soft-switching to ensure high power efficiency and low irradiated electromagnetic noise. To achieve so, the zero-crossing detection circuit for the resonant current or voltage must be fast and accurate in any operating condition. This paper researches the concept of an auto-resonant control for the typical H-bridge resonant converter used in wireless charging systems. In the method proposed here, the reference levels for the zero-crossing detection of the inverter's current are automatically adapted depending on the slope of the current itself at the zero-crossing. In this way, it is possible to compensate for the circuit delay even in the presence of parameters' variation and to ensure that the soft-switching is always maintained. The functionality of this control method is proven first mathematically, and then with circuit simulations. The core steps for the implementation are described with the support of functional blocks. Finally, the system start-up strategy is explained, which uses an auxiliary timed oscillator to modulate the inverter with a fixed 50% duty cycle at a higher frequency than the nominal. This guarantees that the start-up is in the inductive region and, thus, the zero-voltage switching turn-on. Once the detection circuits sense the current flow, the oscillator is automatically disabled, and the nominal power transfer starts.

In high-power wireless battery charging that uses inductive power transfer, a considerable amount of power losses are located in the transmitter and receiver coils because they carry high resonant currents and typically have a loose coupling between them which increases eddy current losses. Therefore, the nominal operation needs to be chosen such that the coils' losses are minimized. Additionally, the inverter's semiconductors soft-switching improves both the power conversion efficiency and the electromagnetic compatibility of the system, thus it needs to be safeguarded for a wide operating range. However, depending on the chosen quality factor of the coils, it might happen that the minimum coils' losses and soft-switching are not satisfied at the same time. This paper defines a guideline on the parametric selection of the coils' quality factor such that the optimum operation of both the coils and the resonant converter can be achieved simultaneously. This parametric guideline is proposed for resonant converters implementing the four basic compensation networks: series-series, series-parallel, parallel-series, and parallel-parallel. Finally, circuit examples are provided for an 11 kW wireless battery charging system.

In charging applications, wireless power transfer (WPT) is mostly used in the form of inductive power transfer with magnetic resonant coupling. Therefore, both the transmitter and the receiver coils are combined with capacitors, such that only active power is transferred. To evaluate the operation of the WPT charging system, its equivalent circuit can be analyzed in the frequency domain. However, this is limiting since the H-bridge inverter operation is not intrinsically considered. As an example, the operating points of both zero current switching (ZCS) and zero voltage switching (ZVS) operations might be still analyzed, but it is not possible to assess their performance in terms of efficiency. In this paper, the advantage of ZVS over the ZCS is evaluated in terms of the efficiency and the delivered output power. To enable the full potential of ZVS, this is tuned considering the switch capacitance and the dead time.

This paper proposes a way to supply a vacuum cleaner from a DC grid instead from an AC grid. Problems caused by the transition from an AC supply to a DC supply will be discussed, like the high inrush current during turn-on and the arc that occurs when a mechanical switch is used to turn-off. These problems will be solved in a low-cost manner. Therefore, a power MOSFET is used to control the motor of the vacuum cleaner. A simple PWM controller is used to control the MOSFET, thus the motor. This PWM controller limits the inrush current with a current sensing feature which turns the PWM controllers output OFF when the peak-current exceeds the threshold value. Furthermore, the ON/OFF button of the vacuum cleaner is also connected to the PWM controller. Turning off the vacuum cleaner will also turn off the output of the PWM controller. Because of this the motor will gradually slow down, the current is regulated towards zero and this prevents a current arc. A prototype was build inside the housing of the vacuum cleaner to validate the design. The experimental tests prove the functionality of the circuit by testing the control of the motor and current sensing feature. Finally, de result of the tests will be discussed and recommendation for possible improvements or alternative designs will be given.