Zero Phase Angle Research Articles

Unified Load-Independent ZPA Analysis and Design in CC and CV Modes of Higher Order Resonant Circuits for WPT Systems

This article proposes a general unified methodology for arbitrary higher order resonant circuits. With the proposed methodology, the equivalent circuits and the general resonant methods of the higher order resonant circuit are presented to realize the load-independent constant current (CC) and constant voltage (CV) outputs at two different load-independent zero phase angle (ZPA) frequencies. In addition, the corresponding regularized mathematical models of the constant output current and voltage and the purely resistive input impedances in CC and CV output modes are derived. All compensation topologies in both inductive and capacitive power transfer (CPT) systems have the essence of higher order resonant circuits. It means that the proposed methodology can be applied to investigate the load-independent output and input characteristics of any inductive power transfer (IPT) and CPT topologies. A 3.3-kW LCC -series-compensated IPT system for electric vehicles (EVs) was designed and manufactured to verify the theoretical analysis. The system operating frequencies in both the CC output with ZPA and the CV output with ZPA are in compliance with the SAE J2954 standard.

Comments on “Analysis, Design, and Optimization of $LC$ /S Compensation Topology With Excellent Load-Independent Voltage Output for Inductive Power Transfer”

In the article “Analysis, design, and optimization of LC /S compensation topology with excellent load-independent voltage output for inductive power transfer,” by Yao et al. , a novel LC /S (primary series-inductor parallel-capacitor/secondary series-capacitor) compensation topology was proposed. A single set of three-compensating-elements was derived, allowing to simultaneously attain LIVO and zero-voltage switching (ZVS). However, the inverter was not able to operate at a zero-phase angle (ZPA), minimizing its volt-ampere rating, with the proposed compensating element set. Since the proposed topology is extremely promising, the purpose of this note is to complement the presented analysis by pointing out the following: 1) A group of infinite three-compensating-elements sets exists (to which the set derived in the article belongs to), allowing to simultaneously achieve LIVO and ZVS; and 2) A unique three-compensating-elements set exists, allowing to simultaneously achieve LIVO and ZPA.

Decomposition and Synthesis of High-Order Compensated Inductive Power Transfer Systems for Improved Output Controllability

High-order compensation provides more design freedom for inductive power transfer systems and can help improve output voltage/current controllability. This paper develops a simplified decomposition and synthesis method for high-order-compensated inductive power transfer systems. It can achieve load-independent (LI) output under coupling variation, and easily fulfill the various charging requirements, such as constant voltage or constant current. The coupling independent resonance is ensured by using the induced source model, and the whole resonant tank is effectively decomposed as three parts. The power transfer characteristics are discussed for each part, and the requirements for LI output and zero phase angle (ZPA) operation are combined to generate the compensation candidates for both sides. Two families of topologies are synthesized for four kinds of conversions, i.e., voltage to voltage, voltage to current, current to voltage, and current to current. Meanwhile, the proposed method dramatically simplifies the evaluation for the influence of the coil equivalent series resistors on the transfer function and efficiency. These resistor-caused effects are quite different for two families of topologies. Finally, a 6.78-MHz system with 10-W output is designed to verify the difference between two-family topologies.

Frequency and Phase-Shift Control of Inductive Power Transfer for EV Charger with LCCL-S Resonant Network Considering Misalignment

In inductive power transfer (IPT) systems for electric vehicle applications, the coupling coefficient k and self-inductances of the pads can vary depending on the misalignment and vertical distance due to the presence of loosely coupled pads. Furthermore, the operating frequencies of IPT systems are restricted by a Society of Automotive Engineers standard. These frequencies lead to increases in volt-ampere rating and switching losses. Therefore, this paper proposes a control method for operation in a zero voltage switching region close to the zero phase angle frequency for a low volt-ampere rating considering k and the self-inductance variation in a limited operating frequency range. A mathematical analysis is performed, and the critical coupling coefficients of the proposed control are derived. Simulation and experimental results using a 3.3 kW IPT prototype are presented so as to verify the numerical analysis.

Zero-Phase-Angle Controlled Bidirectional Wireless EV Charging Systems for Large Coil Misalignments

Misalignment between charging coils is an unavoidable problem in all electric vehicle (EV) charging systems that are based on wireless power transfer (WPT) technology. This is because variations in both self- and mutual inductances of charging coils due to coil misalignments significantly affect the charging rate and efficiency of the EV charger. As a solution, this article proposes a new control technique that maintains the rated charging power level at optimum efficiency in spite of large coil misalignments. To compensate for the variations in inductances, the technique uses the information extracted from input impedance to operate the system essentially at unique converter voltages with zero phase angle, ensuring that charging will take place at rated power with optimal efficiency despite any pad misalignments. The article presents a comprehensive mathematical model, describing the theoretical basis of the proposed control philosophy. To demonstrate the validity of the proposed control concept, a 1-kW bidirectional WPT EV charging system is built and results are presented under misaligned coil conditions. Results convincingly indicate that the proposed controller is efficient and capable of maintaining the rated charging rate despite large coil misalignments and without any dedicated wireless communication.

Multiple Output Inductive Charger for Electric Vehicles

Multiple output chargers have widely been adopted in various electronic devices due to their benefit concerning cost, power density, and space for installation. On the contrary, inductive power transfer (IPT) has been applied increasingly in electric vehicles (EVs) since it is safer and more convenient as compared to conductive chargers. However, research works on multiple output chargers using an IPT system for EV charging applications are rarely presented. This paper proposes a new concept of a multiple output IPT charger, which can charge several output batteries independently and simultaneously by adopting only one full bridge inverter at the primary side combining with multiple transmitters. A total of two possible IPT-coil structures are analyzed, and the minimum distance between each channel's coils is determined to neglect the cross-coupling between them. A total of two options are proposed to attain a zero phase angle (ZPA) condition for the primary inverter of the proposed system. First option is to operate the compensation tanks of every output channel at exact ZPA frequencies. The other option is to let one channel work in the inductive region of its input impedance and other channel work in the capacitive region. By adopting an appropriate design, the reactive powers of these tanks can be nearly canceled by each other and the phase of inverter current can be nearly in-phase with the input voltage as a result. A total of two proposed options are compared to give recommendation whether option 1 or 2 should be selected according to various applications’ requirements. To simplify control complexity, IPT output current sources topologies are selected, compared, and analyzed to construct the proposed multiple output system in both above-mentioned options. Double-sided LCC and series–parallel topologies are adopted to demonstrate the proposed idea for options 1 and 2, respectively. In order to verify feasibility and validity of the proposed method, experimental results of two output channels with the total output power of 1.5 kW are provided. Experimental results indicate that the ZPA is achieved for the primary inverter with both of the above-mentioned options even under different load conditions. Some comparisons between the conventional and the proposed IPT charging structure in terms of cost, reliability, and complexity are included in the discussion section.

An IPT Battery Charger With Near Unity Power Factor and Load-Independent Constant Output Combating Design Constraints of Input Voltage and Transformer Parameters

Inductive power transfer (IPT) techniques are becoming popular in battery charging applications due to some unique advantages compared to the conventional plug-in systems. A high-performance IPT charger should provide the battery with an efficient charging profile consisting of constant charging current and constant charging voltage. However, with a wide load range, it is hard to realize the initial load-independent constant current (CC) and the subsequent load-independent constant voltage (CV) using a single IPT converter while maintaining nearly unity power factor and soft switching of power switches simultaneously. This paper systematically analyzed the characteristics of an LCC – LCC compensated IPT converter and proposed a design method to realize the required load-independent CC and CV outputs at two zero-phase angle frequencies. The design also combats the constraints of an IPT transformer and input voltage, thus facilitating the use of a simple duty cycle control operating at two fixed frequencies for both CC and CV operations. The design criteria, control logic, and sensitivities of compensation parameters to the input impedance and load-independent output are discussed. Finally, an IPT battery charger prototype with 1 A charging current and 24 V battery voltage is built to verify the analysis.

A Flexible Load-Independent Multi-Output Wireless Power Transfer System Based on Cascaded Double T-Resonant Circuits: Analysis, Design and Experimental Verification

There are practical applications requiring the wireless power transfer (WPT) system to supply multiple output voltages to a variety of loads. In this paper, in order to achieve this goal, multiple double T resonant circuits are connected to the common port of the receiver side. Based on the modeling and analysis of the double T resonant circuit, it is found that the load-independent output and input zero phase angle (ZPA) can be derived. The proposed WPT system presents the following merits: 1) output voltages are load independent and can be controlled synchronously against the disturbance from input DC source and mutual coupling by using only one closed loop; 2) the output voltages can be adjusted individually to different levels by configuring circuit parameters; 3) only passive components are used to achieve multiple outputs. The power loss can be reduced due to the parasitic resistance of the passive component is very small and can be negligible; and 4) the reactive power losses are minimized due to the input ZPA of the system. An experimental prototype with two output channels is built, based on which the load independent and the controllable characteristics of the output voltages are verified.

Three‐coil structure‐based WPT system design for electric bike CC and CV charging without communication

In comparison with the traditional plug-in charging systems for the electric bike (EB), wireless power transfer (WPT) systems have superior advantages of convenience and safety. Combining the application requirement range of the EB, this study proposes a three-coil structure-based WPT system in order to achieve ideal and reliable constant current (CC) output and constant voltage (CV) output without the need for a sophisticated control strategy and the real-time communication links between the transmitter and receiver sides. Two ac switches are utilised at the transmitter side to implement the change of charging mode from CC to CV. By correctly selecting the parameters of compensation components, the required load-independent CC and CV characteristics with zero phase angle in the CC and CV modes can be achieved. Besides this, a load identification method based on the active power calculation used to estimate the equivalent resistance of the battery in the whole charging process, is utilised to judge the switching point from CC to CV mode. Finally, the feasibility of the method is verified through the construction of a laboratory platform with a 3.3 A charging current and a 57 V charging voltage.

New parameter tuning method for LCC/LCC compensated IPT system with constant voltage output based on LC resonance principles

Compensation topologies with constant current (CC) or constant voltage (CV) play essential roles in inductive power transfer (IPT) systems. This article describes basic LC resonance principles, which can analyse the output characteristics of all the compensation topologies with CC or CV outputs. By combining LC principles, a new parameter tuning method for LCC/LCC topology with CV output is proposed, followed by efficiency analysis and sensitivity analysis as per various configurations. Moreover, comparing with conventional topologies, it indicates that the LCC/LCC topology has three advantages: (i) The output voltage is load-independent, and it can easily achieve zero phase angle (ZPA) or zero voltage switching (ZVS); (ii) This topology can free the design from the restrictions enforced by the loosely coupled transformer parameters; (iii) The topology is equipped with high-order harmonic suppression capability. Finally, a 1300-W laboratory-scale prototype with a 15 cm air gap was built to verify the theoretical analysis. The experimental results demonstrate the feasibility and superiority of the proposed LCC/LCC IPT system with new parameter tuning method.

Design of a Double-Sided LC Compensated Capacitive Power Transfer System With Capacitor Voltage Stress Optimization

Capacitive power transfer (CPT) systems usually have high voltage stresses among coupler plates and compensation capacitors due to small coupling capacitances. High voltages across the coupler plates will incur the strong electric field emission, and it is thus difficult to select compensation capacitors with high voltage stresses. To solve this problem, this brief analyzes a double-sided LC compensated CPT system systematically and finds an operating frequency to realize the load-independent constant current (CC) output and input zero-phase angle (ZPA) simultaneously. Without reactive power in the circuit, a design method is proposed to determine the compensation parameters and operating frequency using the given voltage ratings of coupler plates and compensation capacitors. Thus, voltage stresses among these capacitors could be optimized under their predesigned voltage ratings. The sensitivities of input impedance, output current to variations of compensation parameters are also discussed to realize soft switching. Finally, a prototype of the CPT converter with two types of proposed parameters and symmetric parameters is built to verify the analysis.

Sensitivity Analysis of Inductive Power Transfer Systems With Voltage-Fed Compensation Topologies

The output characteristics and the transfer efficiencies of inductive power transfer (IPT) systems are affected by (but not limited to) the variation of parameters such as, variable load, misalignment between the primary and secondary coils, and resonance frequency detuning. This paper first analyzes the resonant conditions of all voltage-fed compensation topologies in IPT systems to achieve the load-independent voltage transfer characteristic at load-independent zero phase angle frequency. With these conditions, the parameters sensitivity to the key performance factors of the S-SP, LCC-S, LCC-P, and double-sided LCC compensated IPT systems are systematically investigated when considering the losses in coils and compensation networks. Comparisons of the quantitative sensitivity analysis and experimental results for all IPT systems are made in terms of the voltage transfer ratio and efficiency. These analyses can provide guidance for the selection of superior compensation networks to minimize the additional converter effort and simplify the control algorithm of closed-loop IPT systems.

Reconfigurable Intermediate Resonant Circuit Based WPT System With Load-Independent Constant Output Current and Voltage for Charging Battery

In this letter, a compact battery charger based on wireless power transfer (WPT) technology without any communication requirement is proposed. Here, a new intermediate coil is developed to achieve load-independent constant current (CC) and constant voltage (CV) outputs. The intermediate coil is split into two coils and is overlapped with the receiver coil to form a compact structure. Two switches on the receiver side are used to reconfigure the intermediate resonant circuit in order to select different charging modes, i.e., CC mode or CV mode. The communication between the transmitter side and the receiver side as well as complex control strategies is not needed in the proposed structure. Besides, the proposed system can achieve zero phase angle operation, fixed operating frequency, and zero-voltage switching, which not only can lower the power rating of power devices but also improve the efficiency. A laboratory prototype with a 3.6 A charging current and a 48 V charging voltage is built to verify the feasibility of the proposed method.

Analysis, Design, and Experimental Verification of a Mixed High-Order Compensations-Based WPT System with Constant Current Outputs for Driving Multistring LEDs

Current imbalance in multistring light-emitting diodes (LEDs) is a critical issue. It may cause overcurrent in one or more LED strings, leading to rapid degradation. In this paper, a mixed high-order compensation networks-based wireless power transfer system is proposed to generate multiple constant current outputs. It is composed of an LCC resonant network in the transmitting side, a series resonant network, and multiple CLC resonant rectifiers in the receiving side. The CLC resonant rectifiers are connected in parallel to form multiple independent output channels, and each channel is then connected to an LED string. Based on the analysis of the T resonant circuit and the modeling of coupling coils, multiple constant output currents can be derived. As a result, current balance can be achieved, which is very suitable for driving multistring LEDs. The proposed system also offers a modular, scalable, and maintenance-free design, which can significantly reduce the construction cost and the control complexity. In addition, the inverter in the transmitting side can achieve zero phase angle. A laboratory prototype with dual independent output currents is built to verify the proposed method. The experimental results agree well with the theoretical analysis.

Design and Control of Inductive Power Transfer System for Electric Vehicles Considering Wide Variation of Output Voltage and Coupling Coefficient

In this paper, a design and control scheme of the inductive power transfer (IPT) system for electric vehicles are proposed, considering a wide variation in output voltage and coupling coefficient. The characteristics of the proposed IPT system and a design method for the resonant network are suggested. By utilizing the battery management converter at the secondary side, the design and control can be simplified while managing the output voltage and power of the battery. In order to achieve high efficiency by reducing the voltage–ampere rating, zero phase angle tracking control is proposed. In addition, a phase-shift control is applied to the primary side to ensure the stable system operation by limiting output voltage. A 3.3-kW laboratory prototype with magnetic power pads is manufactured, and the validity of the proposed design and control is verified through experimental results using the laboratory prototype.

A Switching Hybrid LCC-S Compensation Topology for Constant Current/Voltage EV Wireless Charging

Wireless power transfer (WPT) technology has been widely applied to automobile industries, household electronics and medical devices because of its many advantages. The hybrid battery charging scheme, which combines constant voltage (CV) and constant current (CC), is considered to be quite reasonable in view of the limitations of the conventional CC/CV implementation scheme. In this study, based on the inductance and double capacitances-series (LCC-S) compensation topology, a switching hybrid topology is proposed for CC/CV electric vehicle (EV) battery charging. The topology parameters are designed according to the specified CV and zero phase angle (ZPA). In the CC charging mode, two additional capacitances are added to the topology for CC and ZPA implementation. Based on the proposed weak communication, the CC and CV charging mode can be converted via two AC switches (ACSs). The proposed hybrid system provides a simple structure, easy controllability, and stable output. A 2.5-kW experimental prototype is configured to verify the proposed hybrid charger. The maximum DC efficiencies (at 2.5-kW) of the CC and CV charging modes are 89.28% and 88.33%, respectively.

Analysis and Design of Three-Coil Structure WPT System With Constant Output Current and Voltage for Battery Charging Applications

Compared with the traditional plug-in charging system, the wireless charging system for battery charging has broad application prospects due to its significant advantages, such as security, convenience, and aesthetics. In practical applications, in order to prolong the battery lifecycles, it is preferred to charge the battery with constant current (CC) and constant voltage (CV) modes. However, since the battery equivalent resistance varies greatly during charging, it is not easy to design a complete charging system owning CC and CV output characteristics. Besides, the equivalent input impedance of the system is preferably resistive to improve efficiency and enhance power transfer capability; therefore, achieving the zero phase angle (ZPA) operation is extremely important. Hence, a novel three-coil structure WPT system is proposed in this paper to solve the above issues. A comprehensive theoretical analysis for the three-coil system to realize the CC and CV charging modes with perfect ZPA operation at two fixed operating frequencies is presented. Furthermore, due to the parasitic losses of passive components and the instability of the dc input voltage, it is unrealistic to achieve accurate and stable CC and CV outputs through the inherent properties of the circuit itself. Consequently, a simple closed-loop controller is introduced into the system to enable the desired CC and CV charging characteristics with zero voltage switching (ZVS) operation by slightly adjusting the operating frequency. Finally, a confirmatory experimental prototype with 4.6-A charging current and 56-V charging voltage is fabricated to confirm the feasibility and validity of the proposed method. The experimental results agree well with the theoretical analysis.

What causes the abrupt changes in the light curve of a GEO satellite?

In the light curve of the geostationary earth orbit satellite (GEOS), there are 3 abrupt changes (AC) that are commonly to be seen. One of the AC that appears a peak near zero phase angle has been proved the specular reflection of solar panels leading to the phenomenon. However, the reasons of another two AC produced in the light curve are still unknown. In this paper, we proposed an advanced light curve model of GEOS and theoretically explained these unknown abrupt changes. Through calculating the satellite TDRS-8's light curve and comparing its actual observation, the proposed model is verified and the causes of the unknown abrupt changes are illustrated. The importance and purpose of this discovery are also emphasized at the end of the paper.

An Improved Autonomous Current-Fed Push-Pull Parallel-Resonant Inverter for Inductive Power Transfer System

In the inductive power transfer (IPT) system, it is recommended to drive the resonant inverter in zero-voltage switching (ZVS) or zero-current switching (ZCS) operation to reduce switching losses, especially in dynamic applications with variable couplings. This paper proposes an improved autonomous current-fed push-pull parallel-resonant inverter, which not only realizes the ZVS operation by tracking the zero phase angle (ZPA) frequency, but also improves the output power and overall efficiency in a wide range by reducing gate losses and switching losses. The ZPA frequencies characteristic of the parallel-parallel resonant circuit in both bifurcation and bifurcation-free regions is derived and verified by theory and experiments, and the comparative experimental results demonstrate that the improved inverter can significantly increase the output power from 7.68 W to 8.74 W and has an overall efficiency ranging from 63.5% to 72.5% compared with the traditional inverter at a 2 cm coil distance. Furthermore, with a 2-fold input voltage (24 V), the improved inverter can achieve an approximate 4-fold output power of 38.9 W and overall efficiency of 83.6% at a 2 cm coil distance.

A New-Variable-Coil-Structure-Based IPT System With Load-Independent Constant Output Current or Voltage for Charging Electric Bicycles

This letter presents an inductive power transfer system based on a new variable coil structure to achieve load-independent constant current (CC) and constant voltage (CV) outputs for charging electric bicycles (EBs), without involving complex control strategies. The new variable coil structure consists of three-layer coils, i.e., two bipolar coils and one unipolar coil, on the transmitter side and one unipolar coil on the receiver side. The compact and portable receiver with series compensation is installed in the EB, while two switches on the transmitter side at the power charging station are utilized to reconfigure the transmitter coil structure to select the charging mode, i.e., CC mode or CV mode. The proposed system can achieve zero phase angle operation, fixed operating frequency, and zero-voltage switching, which will lower the power rating of power switches and improve the efficiency. A laboratory prototype is built to verify the feasibility of the proposed method.