In recent years, DC-DC converters have been widely used and promoted in renewable energy power generation systems, electric vehicles, and aviation power supplies. However, the output DC voltage of renewable energy sources is low. Increasing the duty cycle can improve the high gain but brings problems such as high voltage spikes across semiconductors, high losses, and low efficiency. A high step-up and high-efficiency DC-DC converter is necessary, which can be achieved by busing switched-inductor, switched-capacitor, coupled inductor, and other techniques. Simultaneously, the practical application has imposed stringent requirements on DC-DC converters, including miniaturization and lightweight design. Using magnetic integration technology can partially fulfill the developmental needs of the converter.

Based on the quadratic Boost converter, the switched capacitor and clamping branch combination is simplified using device multiplexing. Subsequently, the coupled inductor is integrated with decoupled magnetic technology, effectively reducing the volume and number of magnetic components. Therefore, a high step-up quadratic converter is achieved with a dual-coupled inductor’s magnetic and switched capacitor. The working principle of the proposed converter is analyzed, the parameters are derived, the calculation methods for loss and efficiency are provided, and the related diagrams depicting loss proportion and efficiency analysis are generated. The structure and parameters of the integrated magnetic component are designed and simulated. The volume of the integrated magnetic component is reduced by about 13.4% compared with the discrete magnetic component. Finally, an experimental prototype is built, and the feasibility of the topology is validated.

The proposed converter’s input voltage is 12 V, switching frequency is 50 kHz, turn ratio is 1, output voltage is 185 V, output power is 200 W, and load is 170 Ω. Different output power can be obtained by adjusting the load size. When the output power is 140, 160, 180, 200, 220 and 240 W, the corresponding efficiency is 91.6%, 91.9%, 92.4%, 93%, 93.3%, and 92.7%, respectively. Under the load of 200 W, the experimental efficiency reaches 93%.

The proposed converter has the following characteristics: (1) the dual-coupled inductors improve the voltage gain. The duty cycle and turn ratio can be adjusted to obtain high voltage gain, and the switch has low voltage stress. When the duty cycle is 0.5 and the turn ratio is 1, the voltage stress is about 25% of the output voltage, and the voltage gain is 16 times. (2) The clamping structure can absorb the leakage inductor of the coupled inductor, which effectively alleviates the voltage spike on the switch. (3) The diodes experience low voltage stress, ranging from 16% to 66% of the output voltage, allowing for the selection of diodes with a low withstand voltage. (4) The decoupled magnetic integration technology is adopted, which reduces the number and volume of magnetic components.

AC-DC converters are key equipment to interface the AC grid, DC loads, and renewable generation sources. Efficiency and power density are the main factors in the design and implementation of AC-DC converters. The two-stage power conversion has low system efficiency and high cost. A single-stage AC-DC converter achieves AC-side current regulation, DC-side voltage regulation, and high-frequency galvanic isolation simultaneously through only one stage of high-frequency power conversion, which has the potential advantages of high efficiency and power density. However, the design and implementation of single-stage AC-DC converters are difficult.

This paper presents a resonant single-stage isolated AC-DC converter based on a fixed frequency pulse width modulation strategy. When the switching frequency of the converter is set to the resonant frequency of the series-resonant tank, the impedance of the resonant tank always features zero impedance. Therefore, in steady-state, the total voltage applied on the resonant tank must also be zero, which means the fundamental voltage generated by the primary-side and secondary-side switching bridges must be equal. Following this idea, the converter can operate in both voltage step-down and step-up modes, and the equivalent voltage gain of the converter is continuously adjustable in a wide range by adjusting the pulse width of the high-frequency excitation voltages applied on the resonant tank. Hence, the voltage and current regulation requirements of the single-stage AC-DC converter can be satisfied. Voltage step-down regulation can be achieved by adjusting the primary-side duty ratio D_p, while the voltage step-up regulation can be achieved by adjusting the secondary-side duty ratio D_s.

In order to realize the soft-switching of all switches within a wide voltage range, the soft-switching characteristics of the converter are analyzed in detail. It is found that the magnetizing inductance L_m and quality factor Z_r of the resonant tank must be small enough within the entire AC voltage range, leading to much higher conduction losses. When the instantaneous AC voltage is low, the switching losses of switches are also low. Therefore, it is unnecessary to achieve soft-switching within the entire AC voltage range, and trade-offs between switching loss and conduction loss must be made to design the converter’s parameters. Therefore, an optimized parameters design method is proposed for the resonant single-stage AC-DC converter.

An experimental prototype is built and tested. The experimental results indicate that through the fixed-frequency pulse-width modulation strategy, step-up and step-down power conversions, the AC and DC side voltage and current regulation, and high power factor can be realized. With the proposed parameter optimization design method, soft switching of switches can be achieved in a wide input voltage range. The efficiency of the converter is up to 94.2%. In addition, experimental results indicate that the converter has excellent dynamic and steady-state performance.

In the application of new energy, energy storage, and emerging power loads, the power supply architecture using the DC bus has more advantages than the AC bus, which is the development direction of the future power supply system. Bipolar DC microgrid systems are often used to connect various renewable energy sources and emerging loads due to their higher reliability, flexibility, and efficiency. This paper proposes a synthesis method for non-isolated bipolar output DC-DC converters. A series of bipolar output DC-DC converter topologies are deduced. In order to further improve the performance of bipolar output converter, a novel high-voltage-gain DC-DC converter with a three-winding coupled-inductor is proposed by introducing coupled- inductor and switched-capacitor step-up technology to Boost bipolar output DC-DC converter.

Based on the characteristics of the bipolar output converter, the topology synthesis principle of the proposed bipolar output DC-DC converter is given. The input ends of a positive output DC-DC converter and a negative output DC-DC converter are connected in parallel, and the output ends are in series. This paper gives a series of bipolar output DC-DC converters by classifying and combining traditional DC-DC converters. However, the boost capacity of these converters is limited, and the positive and negative output voltages are only regulated by the duty cycle of the switch. Thus, a bipolar high-voltage-gain DC-DC converter with a three-winding coupled-inductor is proposed. The bipolar output voltages can be adjusted flexibly by the turns ratio of the coupled inductor and the duty ratio. This paper gives the construction principle, operating mode, voltage gain, and stress derivation of the high-voltage-gain bipolar output converter. Compared with the converters in the literature, the proposed converter has apparent advantages in voltage gain and device voltage stress. An experimental prototype with a rated power of 200 W is designed. Experimental results show that the input current ripple is small, and the actual voltage gain of the converter is 380/32=11.875, slightly lower than the calculated (3+n₁+n₂)/(1-D)=12, which is caused by parasitic resistance and control signal delay. The efficiency of the proposed converter is 95.5% at full load and 96.7% at half load.

The following conclusions can be drawn. (1) High voltage gain can be achieved with low input current ripple and small switching device voltage spikes. (2) Symmetrical bipolar output voltage can be achieved, reducing the need for high voltage gain of power supply and load. (3) The converter power is distributed on two DC bus bars, which makes the system more efficient. (4) Part of the diode realizes zero voltage switching turn-off, reduces the diode reverse recovery loss, and improves the efficiency of the proposed bipolar output converter.

Wireless charging technology is safer and more convenient than traditional wired charging, and has been widely used in the field of electric vehicles. However, wireless charging systems have the characteristic of separating the ground end and the vehicle end, and there are issues with the selection and measurement of power metering points. The mainstream approach is to set the measurement position of the wireless charging system on the transmitting coil. However, the current and voltage of the transmitting coil are relatively high, so that directly using sensors for measurement can lead to high sensor costs. To address the aforementioned issues, this paper proposed a non-contact measurement method for output power of transmitting coil of wireless charging systems using multi coil collaboration. This method did not require specialized high-power high-frequency current and voltage sensors, and adapted well to practical scenarios such as different power levels, horizontal and vertical ground displacement of cars, and shielding materials, and had high measurement accuracy.

The paper utilized the law of electromagnetic induction to measure the output power of transmitting coil by setting sensing coils. Firstly, it was inferred that there was a relationship between the output power of transmitting coil and the voltage product of the sensing coil. Secondly, the fitting coefficient was used to fit this relationship, and it was derived that when the positions of detection coils and transmission coil were fixed, the fitting coefficient did not shift with the receiving coil. After obtaining the fitting coefficient, only the terminal voltage of the sensing coil needed to be measured. Finally, by constructing the voltage matrix of sensing coils and the standard output power of transmitting coil matrix, the fitting coefficients were obtained, and a coupling matrix model was established between the voltage phasor of each sensing coil and the output power of transmitting coil considering horizontal offset, vertical offset, and power variation.

The experimental results show that under different power levels, the maximum measurement error of the proposed method is within 1.5% when the wireless charging system undergoes offset in both horizontal and vertical ground directions. Under the condition of 2 square sensing coils, the maximum error in power measurement was 47%. When the number of sensing coils increased to 6, the maximum error decreased to within 1.5%. This result indicates that as the number of sensing coils increases, the accuracy will further improve. Meanwhile, research has found that when the transmitting and receiving coil are square, using a square sensing coil results in more ideal accuracy. In addition, with the use of 6 detection coils, 3, 5, and 9 power sampling points were used within the measured power range. The maximum errors in power measurement were 7.8%, 3.6%, and 1.5%, respectively, indicating that the more sampling points are, the more accurate the model is. Finally, further exploration is conducted on the practical scenario of placing multiple sensing coils horizontally, which can avoid the problem of vertical stacking height affecting the short distance power measurement.

This method has been proven to be effective through simulation and experimental analysis. Through comparative analysis of the results, the following conclusions can be drawn: (1) The size and quantity of detection coils are key to ensuring the accuracy of the model. A sufficient number of sensing coils will bring higher model accuracy, but at the same time, it will also increase the number of samples in the model solving process. Therefore, in practice, a reasonable selection can be made based on the measured power error requirements. (2) For coupling devices where both the transmitting and receiving coils are square coils, the measurement accuracy using square sensing coils is more ideal compared to circular sensing coils. (3) A sufficient number of sampling points in model solving can also affect the accuracy of the entire system model. In practice, a reasonable selection can be made based on the measured power error requirements. (4) Horizontal placement of multiple sensing coils can achieve high-precision power measurement, just like vertical stacking. In practical scenarios, placing multiple sensing coils horizontally can avoid the problem of vertical stacking height affecting the short distance measurement of the transmitting and receiving coils.

Wireless power transfer (WPT) technology provides an effective way to solve the problem of stable power supply for rotating equipment. However, in practical applications, the relative misalignment between the rotating side and the stationary side is inevitable. In the practical application of WPT system, due to the presence of ferrite cores, the misalignment of the coupling mechanism will significantly affect the self-inductance and mutual inductance parameters of the coils, resulting in output power fluctuations and efficiency reduction. In order to enhance the anti-misalignment capability of WPT systems under changes in coil parameters, this paper proposes a detuned WPT system anti-misalignment method that considers changes in coil parameters. The detuned WPT system is constructed using changes in coil self-inductance to counteract the output power fluctuations caused by changes in mutual inductance.

Firstly, using the finite element simulation software, the parameter variation laws of the rotary coupling mechanism under axial and radial offsets were summarized. The study found that the self-inductance and mutual inductance of the coupling mechanism have the same trend of change, and the degree of change is similar within a certain offset range. And based on this, the idea of using self-inductance changes to dynamically adjust the degree of system detuning to offset output fluctuations caused by mutual inductance changes was proposed.

Secondly, the influence of parameter changes on system operation was obtained through circuit analysis, and the constant voltage output conditions for the degree of receiver detuning and mutual inductance changes were derived, providing a theoretical basis for the coupling mechanism design and compensation parameters optimization. The coupling mechanism design revolves around the number of turns on the secondary side, and the compensation parameters optimization is based on the particle swarm optimization (PSO) algorithm. With the goal of constant output and efficiency improvement, the compensation topology parameters of the inductor-capacitor-capacitor-series (LCC-S) are comprehensively optimized to achieve good axial and radial anti-misalignment capabilities of the rotary WPT system.

Finally, a 170 W experimental setup was constructed to validate the effectiveness of the proposed method. The experimental results show that within the range of axial offset ±30 mm and radial offset ±5 mm, the maximum mutual inductance change of the rotary coupling mechanism is 74%, the self-inductance change is 48%, and the coupling coefficient is 0.39 to 0.89. The maximum output voltage fluctuation is only 9.5% (axial) and 2.8% (radial), and the maximum efficiency of the system is 93%. This method utilizes the equilibrium characteristic of the parameter changes for the coupling mechanism itself. Its significant advantages lie in simple and effective structure, no DC-DC converter, no communication and closed-loop control, and a more stable and reliable system. It is particularly suitable for WPT system in harsh environments such as high temperature, high voltage, and high-frequency vibration underground, reducing the failure rate of the system and improving power supply reliability.

In recent years, non-isolated inverters have gained widespread attention in commercial and residential PV grid-connected systems due to their cost, efficiency, and flexibility advantages. However, in practical applications, the output voltage of the PV panel is generally low. Due to the loss of the electrical isolation of the transformer, the high-frequency switching action of the conventional inverter may produce a common mode voltage applied to the parasitic capacitance between the PV array and the ground, resulting in a common mode leakage current, which affects the safe operation of the system. This paper proposes a non-isolated five-level Boost inverter with no leakage current and its dual-mode modulation strategy to enhance the applicability and practicability of the inverter.

Firstly, the circuit structure combines the dual-output Boost converter with the five-level inverter to create a five-level Boost inverter topology. The Boost capability is expanded, suitable for PV power generation applications with low DC voltage on the input side. Secondly, the dual-mode modulation strategy of unipolar carrier level shifted is studied, providing five-level output capability and increasing the equivalent switching frequency under the same carrier frequency. By comparing the PV panel’s DC output voltage and the grid voltage’s absolute value, two working modes of Boost voltage and buck voltage are realized, and the energy transmission efficiency of the converter is improved. In addition, a five-level voltage is output on the side of the bridge arm, and more levels make the output voltage closer to the sine wave, which is conducive to improving the quality of incoming current. Furthermore, the negative polarity of the DC side of the topology is directly connected to the voltage neutral of the AC side to eliminate the common mode leakage current of the stray capacitor to the ground. Finally, the working principle of the inverter circuit and the realization method of the specific modulation strategy are provided, and the key parameters are designed.

An experimental prototype was built. The experimental results show that: (1) The inverter’s two working modes overcome the limitation that the traditional multilevel inverter can only step down, making it suitable for a wide range of input voltage changes. (2) The common ground structure can effectively inhibit leakage current. (3) The output voltage V_AB of the bridge arm presents five voltage levels, and the energy storage capacitor can be charged and discharged at a high switching frequency, ensuring the stationarity of the output voltage of each level. Hence, the output voltage waveform is symmetrical in the positive and negative half cycles. At the same time, the incoming current i_g can accurately track the phase of the grid voltage V_g, producing a smooth output waveform with little distortion, which meets the requirements for grid-connected current quality. (4) The proposed inverter can output reactive power output, which meets the requirements of non-unit power factor operation in IEEE grid-connected standards.

Permanent magnet synchronous motor (PMSM) has become a core component of complex electromechanical systems such as electric vehicles, new energy urban rail vehicles, and wind power generation due to its advantages of high efficiency, high power density, and high torque density. The model predictive control strategy based on the mathematical model of the controlled object has been widely applied in PMSMs. However, there is inevitably a mismatch between the actual parameters of the motor system and the application parameters of the model predictive controller, which seriously affects the performance of the predictive control system. This paper proposes a novel model-free stator flux sliding mode control (MF-FSMC) method to achieve high-performance control under parameter mismatch.

The model-free flux sliding mode controller is adopted to replace the model predictive control algorithm that relies on the controlled object. First, a mathematical model of PMSM is established under parameter mismatch, and an ultralocal stator flux linkage model considering parameter mismatch is constructed under a rotating coordinate system. The novel MF-FSMC method is proposed, a model-free flux sliding mode controller based on a novel reaching law is designed, and a one-beat speed predictive controller is constructed. Finally, the composite integral sliding mode disturbance observer online estimation strategy is proposed, which can effectively observe the unknown disturbance part in the ultralocal model of PMSM under parameter mismatch.

Simulation and experimental results show that the proposed method can effectively improve the steady-state performance, significantly reduce the stator flux and torque ripple, and enhance the robustness and anti- interference performance of the PMSM system under parameter mismatch. The designed composite integral sliding mode disturbance observer can accurately observe the stator flux values and unknown disturbances on the dq axis. Compared with conventional model predictive control methods, the proposed MF-FSMC method can reduce torque ripple from 75 N·m to 45 N·m in the case of flux linkage parameter mismatch. In addition, with the proposed MF-FSMC method, the distortion of stator current has also been significantly improved, and the static error of stator flux linkage has been reduced from 0.35 Wb to ±0.01 Wb. In the case of inductance parameter mismatch, the proposed MF-FSMC method can reduce torque ripple from 110 N·m to 80 N·m and the fluctuation value of stator flux linkage error from ±0.235 Wb to ±0.02 Wb.

The MF-FSMC method proposed can obtain the following conclusions: (1) The composite integral sliding mode disturbance observer can accurately observe unknown disturbances and stator flux linkage, effectively enhancing the robustness of predictive control systems under parameter mismatch. (2) The proposed model-free stator flux sliding mode control method designs a model-free flux sliding mode controller in the inner loop of the controller and constructs a one-beat speed predictive controller in the outer loop of the controller. The proposed MF-FSMC method can effectively improve the control accuracy of stator flux, significantly reduce the stator flux/torque ripple of the motor, and ensure the strong robustness of the predictive control system under parameter mismatch.

Traditional I-f control for sensorless control of the permanent magnet synchronous motor (PMSM) suffers from poor damping and disturbance rejection, which lead to large speed oscillations at motor startup and long transition time when switching to close-loop control. It is unfavorable for multi-rotor unmanned aerial vehicles and electric vertical take-off vehicles. According to the differentiation of d-axis voltage and transition strategy, this paper proposes an improved I-f control strategy with frequency compensation to increase damping and improve disturbance rejection of the I-f control based on decoupling current dynamics and angle dynamics. Speed oscillations at motor startup are suppressed significantly, and a fast transition from I-f control to closed-loop control is achieved smoothly with less mechanical dynamics.

Firstly, a small-signal perturbation model of the I-f control is deduced with detailed analyses of its damping characteristics. To increase damping and suppress speed oscillations, differentiation of the open-loop d-axis voltage is used to compensate for the open-loop frequency. Secondly, to improve the load disturbance rejection when switching to closed-loop control, the angle of the reference current vector is rotated via Park transformation. In contrast, the open loop angle is increased to gradually approach the real rotor angle obtained by the angle observer. Since the reference current vector is stationary relative to the real rotor angle during this transition process, no mechanical dynamics are generated. This transition can even be done at zero angle error between the real rotor coordinate and the open-loop coordinate, which indicates no current and angle dynamics at the switching instant. The amplitude of the reference current vector is kept unchanged throughout the whole I-f control. Therefore, the load disturbance is effectively rejected, even during the transition process. Finally, after switching to closed-loop control successfully, the d-axis current is decreased to 0 according to a certain trajectory, and normal closed-loop control takes over.

Two experiments demonstrate the improvement of system damping and load disturbance rejection. In the first experiment, the proposed strategy is compared with the traditional I-f control and the perturbation of active power in literature. The experimental results show that under traditional I-f control, significant speed oscillations occur during the starting phase, and the peak-to-peak value of speed oscillations is about 80 r/min. With perturbation of active power, speed oscillations rapidly decay in 0.1 seconds, and the peak-to-peak value of speed drops to about 10 r/min in the steady state. The motor attenuates speed oscillations fast, and the peak-to-peak value of speed drops to about 5 r/min in the steady state.

The second experiment compares the proposed transition strategy and the strategy by reducing the q-axis current in the literature. The experimental results show that reducing the q-axis current generates large mechanical dynamics at the transition stage under sudden load disturbances. The speed decreases by about 260 r/min at the load disturbance of 0.064 N·m, and the motor is out of control at the load disturbance of 0.16 N·m. Mechanical dynamics are much smaller using the proposed method. The speed decreases by about 40 r/min at the load disturbance of 0.064 N·m, and the motor can still maintain normal operation at the load disturbance of 0.512 N·m.

The proposed improved I-f control strategy has better damping effect on speed oscillations and can transition to closed-loop control with strong rejection of load disturbances.

Rotor-unmanned aerial vehicles (R-UAV) have structural irregularities and problems with docking offset. The traditional unipolar CP magnetic structure increases the wind resistance of the R-UAV due to its mechanical structure characteristics, which, in turn, affects the flight stability of the R-UAV. At the same time, the asymmetric characteristics of the original secondary side can generate high stray magnetic fields, affecting the stable operation of the R-UAV. Therefore, applying the wireless charging system to R-UAVs is challenging. In order to build a stable wireless charging system for R-UAVs, it is necessary to conduct a targeted optimization design based on the mechanical structure of the R-UAV. This paper proposes an “I工I” magnetic structure with high anti-offset and low stray magnetic field constraints for the wireless charging system of R-UAVs and designs a multi-stage constant current-constant voltage (MCC-CV) control strategy with soft switching capability based on the characteristics of series-series (S-S) networks.

Firstly, this paper comprehensively analyzes the characteristics of series-series (S-S) networks, develops an MCC-CV control strategy for wireless charging of lithium batteries, and designs a full-bridge phase-shift soft-switching half-bridge workflow to solve the output current oscillation problem caused by the energy storage characteristics of the resonant network during the multi-stage constant current switching process. By incorporating soft switching capabilities, the system can transition smoothly between different stages of the charging process, minimizing current oscillations and ensuring a stable charging experience. Then, a three-dimensional model of the “I工I” magnetic structure is proposed and established. The transmission structure of this coupling structure is a “I工I” core, while the receiving side structure is an “I” core integrated within the landing gear of the R-UAV. Integrating the magnetic structure within the landing gear allows for zero wind resistance characteristics in wireless charging of R-UAV. Based on the low magnetic resistance characteristics of ferrite cores, the design of the “I” core is completed. Through magnetic circuit analysis and finite element simulations, the magnetic circuit shaping and low stray magnetic field characteristics of the “I” core are determined, and a passive constraint magnetic circuit shaping method for stray magnetic fields is derived. The “I” core distribution is adjusted to increase the anti-offset capability of the “I工I” magnetic structure, thereby achieving a high anti-offset wireless charging system design.

Finally, a prototype of the “I工I” magnetic structure is built. It is shown that the system can maintain a constant output current under radial offset of 100 mm and rotational offset of 360°, with only a 2% fluctuation in transmission efficiency. At the same time, the distribution characteristics of the stray magnetic field outside the launch platform are measured, and a distribution diagram of the stray magnetic field is drawn. The proposed “I工I” is lightweight and efficient.

Wireless power transfer (WPT) technology has garnered widespread attention in recent years due to its advantages in safety, reliability, and flexibility. However, these benefits are often dependent on the precise alignment of the coupling mechanism. In practical applications, as perfect alignment cannot always be ensured, misalignment leads to a reduction in the coupling coefficient, significantly degrading transmission efficiency and system performance. Traditional flat solenoid coils perform well in resisting longitudinal misalignment, but when lateral misalignment occurs, especially near the coil's edge, the coupling coefficient and efficiency drop rapidly. To address this issue, this paper proposes an improved flat solenoid coil WPT system.

First, an equivalent model of the LCC/S compensation circuit is established to analyze the effects of circuit parameters on output characteristics, and a method for configuring the parameters of resonant elements is derived, revealing key circuit parameters affecting voltage gain. Then, an equivalent magnetic circuit model is built to analyze the magnetic field distribution characteristics of the coil, demonstrating that core shape and winding configuration significantly influence the coupling coefficient. Consequently, an optimized winding distribution is proposed using an arithmetic progression for the inter-turn spacing, and the specific optimization process is provided. Additionally, the core shape of the transmitter coil in the traditional flat solenoid design is improved to better concentrate the magnetic field lines, enhancing magnetic field uniformity and increasing the misalignment tolerance of the coupling mechanism.

To verify the optimization effects, multiple simulation models were created with core shape and winding configuration as variables for comparison. Finite element simulation results show that the improved transmitter core achieves more uniform magnetic flux density distribution, significantly reducing the rate of change in the coupling coefficient. Magnetic field uniformity and misalignment tolerance are markedly improved. Finally, a 100 W WPT system prototype was built, and thermal imaging was used to analyze the system’s loss distribution.

Experimental results show that when the receiver is laterally misaligned within ±50% in both the X and Y directions, the output voltage fluctuation is controlled within 5%, and transmission efficiency reaches 89%. These results validate the effectiveness and feasibility of the proposed system.