Fundamental Harmonic Approximation Method Research Articles

Analysis of two-section phase-controlled resonant voltage converter

Analysis of two-section resonant DC-to-DC converter with phase power control is carried out in this paper. Two-section converter is considered as a boundary case of the multi-section converter with only one controlled section and other uncontrolled sections. The converter sections are parallel resonant half-bridge voltage inverters with a common resonant capacitor connected to the load through a matching transformer, center-tapped rectifier and smoothing filter. One of the sections is the reference, relative to which the phase shift of the output pulses of the other section is adjusted. The switching frequency of the converter is constant, which improves its electromagnetic compatibility. Analysis is carried out by the fundamental harmonic approximation method. Analytical expressions for voltage and current phasors in both sections of the converters have been established. The dependence of the converter power on the phase shift between the pulses of the half-bridge inverter sections was obtained. The dependence of the efficiency of the converter on the power was analyzed. It is shown that the efficiency slightly decreases when the power is reduced in a wide range of powers and only at powers less than 10% of full load power it drops sharply. The problems of operation of section transistor switches in their zero-voltage switching mode is considered. Verification of the conducted analysis was carried out by simulation of the converter circuit using the PSIM program for modeling power electronics devices. The simulation results are in a good agreement with the analysis results.

Analytical modeling of resonant converters in frequency domain for wireless power transfer: Continuous current mode (CCM) operation

The major topology for wireless power transfer is resonant converters, which use fundamental harmonic approximation as a general analysis method. The accuracy of fundamental harmonic approximation (FHA) is unsatisfactory in some wireless power transfer applications, as the current has distortions due to the non-linear diode-bridge rectifier. Some frequency-domain models also consider harmonics beside fundamental component and indeed have a higher resolution. However, due to the difficulty of modeling the non-linear rectifier, most models are oversimplified by assuming a voltage source on the output to eliminate the rectifier. Moreover, the value of the voltage source is often treated as a fixed given number, which is not true for a resistive load. To cover a general case, this paper proposes a frequency-domain analytical model for resonant converters in continuous current mode (CCM) with the capability of considering any load and source situations in kHz frequency range. In terms of computation complexity, the proposed model only involves matrix operation (first-order). A simple algorithm has been chosen to demonstrate the fast convergency and high accuracy of the proposed model. The main findings are verified by the comparison between the theoretical calculation, time-domain simulation and experimental results, where the estimation of output power has 10% improvement than the FHA method.

High‐efficiency design method of LLC resonant converter for PHEV battery chargers (based on time‐domain model)

High efficiency, high power density and wide output voltage are required for on-board charger (OBC) applications. LLC resonant converter has the advantage of achieving zero-voltage switching for variable frequency and different load conditions. Compared with conventional fundamental harmonic approximation method, operation-mode analysis based on the time domain model provides an accurate description of resonant current, voltage and DC gain. In this study, the efficiency-oriented modified method is proposed based on the operation-mode analysis. The converter inductance ratio, characteristic impedance and transformer turns ratio are optimised and both-side soft switching can be achieved in the high output voltage region. Conduction loss can be minimised by optimising resonant parameters. Finally, a high-efficiency design method is proposed and validated through experiments on a 3.3 kW prototype applied in OBC. The prototype of the LLC resonant converter has been tested for dynamic charging voltage (230–430 V) with a peak efficiency value of 98.5%.

Family of DTMRC‐based DC–DC converters with an RZP

This study presents a novel family of dual-transformer multi-resonant DC–DC converters (DTMRCs) with a resonant zero point (RZP). The limitations of the conventional LLC resonant converter and its fundamental harmonic approximation (FHA) method are firstly discussed. On this basis, a unique RZP is combined with the dual-transformer architecture. As a result, both of the output voltage regulation capability and the over-current protection feature are promoted. Then, an extended describing modelling method is presented to improve the calculative accuracy of the FHA method. Moreover, by means of the appropriate placement of all three resonant frequencies, the fundamental and the third-order harmonic components are employed to transmit active power to the load simultaneously. The zero-voltage soft-switching characteristic is acquired for all the primary-side switches. Meanwhile, the preferable zero-current soft-switching feature is obtained for diodes both at the turn-on and turn-off moments. Therefore, the switching losses are significantly reduced for the proposed converters. Finally, with the employed SiC metal–oxide–semiconductor field-effect transistors, a 500-W half-bridge DTMRC prototype is built as an example, based on the P-type multi-resonant network. The experimental results demonstrate the validity and correctness of the theoretical analyses.

LC–CLC compensation topology for capacitive power transfer system to improve misalignment performance

To improve the coupler misalignment performance, this study proposes an LC–CLC compensation topology for high-power and long-distance capacitive power transfer system. The LC circuit in the transmitter and the CLC circuit in the receiver are adopted as the resonant tank for the capacitive coupler. The fundamental harmonics approximation method is employed to analyse the system working principle. Considering the misalignment of coupler, the characteristic of output power is provided against the variation of coupler capacitance. A 1 kW CPT system with 150 mm transfer distance is set up to validate the proposed compensation circuit under various misalignment conditions. The experiment results show that the system can transfer 1009 W output power with 90.56% DC–DC efficiency at 150 mm transfer distance when the coupler is well aligned. When the misalignment is 325 mm, the variation of the output power is only 10.6% in X -direction and 15.2% in Y -direction. The proposed system can achieve high anti-misalignment performance.

A Dual-Coupled LCC-Compensated IPT System With a Compact Magnetic Coupler

This paper proposes a dual-coupled LCC -compen-sated inductive power transfer system with a compact magnetic coupler to improve misalignment performance. In the magnetic coupler, the main coils form the first coupling, and compensation inductors are integrated with the main coils to form a second coupling. In the design presented in this paper, the main coils are unipolar and the compensation inductors are in a Double D structure. The fundamental harmonics approximation method is used to analyze the circuit, and the couplings between the main coils and compensation inductors are considered to determine the net power flow. In misalignment cases, it is shown that the coupling between the compensation inductors, and the cross couplings between the compensation inductors and main coils, contribute to increasing the system power. A 3.5 kW prototype is designed and implemented to validate the proposed dual-coupled system. The primary coil size is ${\text{450 mm}\times \text{450 mm}}$ , and the secondary coil size is ${\text{300 mm}\times \text{300 mm}}$ . Experimental results show that the proposed dual-coupled system can significantly improve the misalignment performance, and retains at least 56.8% and 82.6% of the well-aligned power at 150 mm misalignment in the x - and y -directions, respectively.

A Modified Gain Model and the Corresponding Design Method for an LLC Resonant Converter

In this paper, a modified gain model and the corresponding design method for an LLC resonant converter are proposed. To derive the gain model, two important factors-resonant factor and load factor are considered and discussed in detail by combining time domain and frequency domain. Compared with fundamental harmonic approximation (FHA) method, the accuracy of the gain model is highly improved. Referring to the modified gain model, the corresponding design method is also obtained that can inherit conciseness and practicability of the FHA method. Thus, the design method can be used to replace the FHA method in practical design procedures. Finally, the simulation results are given and a prototype of the LLC resonant converter used for power electronic traction transformer is built to verify the accuracy and validity of the proposed gain model and the corresponding design method.

An LC-Compensated Electric Field Repeater for Long-Distance Capacitive Power Transfer

This paper proposes an LC-compensated electric field repeater to extend the transfer distance of a capacitive power transfer (CPT) system. The repeater contains two metal plates connected with an external capacitor and an external inductor. The plates are used to generate electric fields to transfer power. The external inductor and capacitor are used to resonate with the plates in order to increase the voltage levels. The repeater is placed between a transmitter and a receiver, which also contains metal plates compensated by an LC network. The repeater can increase the transfer distance of the CPT system without significantly influencing the system power and efficiency. In this paper, the capacitive coupler structure and dimensions are designed and simulated using Maxwell software. Considering all the capacitive coupling between plates, an equivalent circuit model is derived. The fundamental harmonics approximation method is used to analyze the working principle of the circuit. A 150 W input power CPT system is designed as an example to validate the proposed repeater structure and compensation circuit topology. The system can achieve an efficiency of 66.9% from dc source to dc load, when the transfer distance is 360 mm and the repeater is placed between the transmitter and the receiver.

The FHA Analysis of Dual-Bridge LLC Type Resonant Converter

The dual bridge resonant converter is designed in this paper. In this converter the LLC type resonance configuration is proposed .This types is compared with the other configurations and its benefits are narrated in this paper. The steady-state analysis of the LLC configuration is done using fundamental harmonics approximation method and the values for the components of resonance configuration is found and used for simulation. The simulation results shows that the converter is able to achieve the zero voltage switching for the wide load range and attains a good efficiency. DOI: http://dx.doi.org/10.11591/ijpeds.v4i4.6513