Wireless charging transfer device supporting wide operation range using DC-DC converter and control method therefor

Abstract

Disclosed are an electric vehicle wireless charging system having a wide battery voltage range and coupling variability, and a control method therefor. A wireless charging transfer device includes an AC-DC converter, a DC-AC inverter, and a DC-DC converter that is connected between the AC-DC converter and the DC-AC inverter and varies a DC link voltage. A control unit controls the duty of the DC-AC inverter and the output voltage of the DC-DC converter in association with each other. The inverter duty is primarily adjusted to control output, and if the inverter duty reaches an upper limit or is insufficient to satisfy a target output, the output voltage of the DC-DC converter is secondarily actively adjusted to change the DC link voltage and thereby supplement the output. A separate DC-DC converter for voltage matching may be excluded in a receiving device of a wireless charging system using a transfer device, for example, on the vehicle side. Accordingly, stable charging is possible even over a wide battery voltage range and in conditions of coupling variation between coils, vehicle-side cost, weight, and volume can be reduced, and system compatibility and efficiency can be improved.

Description

Wireless charging transmitter supporting a wide operating range using a DC-DC converter and its control method

[0001] The present invention relates to the field of wireless power transfer (WPT) technology, and more particularly, to a wireless charging system and its operating method for charging the battery of an electric vehicle (EV) in a non-contact manner. In particular, the present invention relates to a power conversion circuit structure of a wireless charging transmitter (charging station or infrastructure side) constituting the wireless charging system and a control method of the transmitter, and relates to a technology that supports stable and efficient charging even under a wide range of battery voltages and various coil alignment conditions.

[0002] Recently, due to strengthened environmental regulations and growing interest in sustainable energy, the spread of electric vehicles (EVs) is rapidly expanding. Furthermore, wireless power transfer (WPT) technology for EV charging, designed to maximize charging convenience for EV users, is gaining attention as a next-generation charging method, and active research, development, and commercialization efforts are underway.

[0003] A typical electric vehicle wireless charging system uses the magnetic field formed between a ground-based charging pad (transmitter) and a receiving pad (receiver) under the vehicle to transfer power in a contactless manner. In a typical system configuration, the transmitter receives power from an external power grid (e.g., a three-phase AC power supply), converts it to direct current (DC) through an AC-DC converter, then converts it to high-frequency alternating current (e.g., 85 kHz AC) through a DC-AC inverter, and then transmits it wirelessly through an impedance matching circuit and a transmitting coil. The receiving device on the vehicle induces high-frequency AC power into the receiving coil, which then passes through an impedance matching circuit and is converted to DC by a rectifier, and then charges the battery.

[0004] However, several technical challenges exist for the effective application of this wireless charging technology across a wide range of vehicle models and real-world usage environments. One of the most significant challenges is the extremely wide range of battery charging voltages required for each electric vehicle model. For example, the charging voltage levels required for traditional 400V battery systems differ significantly from those required for modern 800V high-voltage battery systems. Even within the same battery, the terminal voltage can fluctuate significantly depending on the state of charge (SoC).

[0005] The most common conventional approach to meeting this wide battery charging voltage range is to add a separate DC-DC converter on the wireless charging receiver side (i.e., the vehicle side). This DC-DC converter on the receiver side boosts or bucks the DC voltage output from the rectifier to match the current battery voltage level and delivers it, implementing a constant current / constant voltage (CC / CV) charging profile.

[0006] However, equipping each vehicle with a DC-DC converter on the receiving end entails the following obvious drawbacks. First, the addition of an expensive power conversion device to every electric vehicle increases vehicle manufacturing costs. Second, the DC-DC converter takes up space and weight, which limits vehicle design and can negatively impact fuel economy. Third, the presence of an additional power conversion stage within the vehicle inevitably results in energy loss, reducing overall charging efficiency, and the converter itself must also manage heat generation. Fourth, the DC-DC converter must be permanently installed in the vehicle, despite its limited use primarily for wireless charging, making it inefficient in terms of resources and costs.

[0007] Furthermore, in actual parking environments, the alignment (horizontal position) between the transmitting and receiving pads can shift, or the distance (vertical gap) between the vehicle and the ground can fluctuate depending on driver inattention or the type of vehicle. These variations in magnetic coupling coefficients significantly impact wireless power transfer efficiency and the amount of power that can be transferred. Conventional methods, particularly those relying solely on the DC-DC converter on the receiving side, may have limitations in robustly addressing these coupling variability and ensuring stable charging performance.

[0008] Therefore, there is a need for the development of new technologies that can implement a more efficient, economical, and versatile electric vehicle wireless charging system that can effectively respond to a wide battery voltage range and various coupling fluctuation conditions while eliminating the burden of adding power conversion devices to individual vehicles.

[0009] The present invention primarily aims to address the problem of conventional electric vehicle wireless charging systems requiring individual DC-DC converters on each vehicle (receiving device) to support a wide battery charging voltage range. Specifically, the present invention seeks to overcome the limitations of conventional technologies, such as increased costs associated with adding DC-DC converters to each vehicle, increased vehicle weight and volume, decreased system efficiency, and inefficient resource utilization.

[0010] To this end, the present invention proposes a new approach that integrates the DC-DC converter function, which was previously located on the receiving device side, to the wireless charging transmitter (charging infrastructure) side and actively controls the output voltage of the DC-DC converter built into the transmitter, i.e., the DC link voltage supplied to the DC-AC inverter. Through this configuration, the purpose is to provide an improved wireless charging system and its control method that can comprehensively support a wide range of battery voltages at the charging infrastructure level without the burden of adding a separate power conversion device to each vehicle.

[0011] In addition, the present invention has an additional purpose of stably transmitting the target charging power by robustly coping with fluctuations in the magnetic coupling coefficient due to misalignment or air gap changes between the transmitting and receiving coils that frequently occur in an actual use environment by utilizing the voltage control function of the transmitting DC-DC converter.

[0012] In order to solve the above-described problem, according to one aspect of the present invention, a wireless charging transmitter using a DC-DC converter is provided, comprising: an AC-DC converter for converting AC power into DC; a DC-AC inverter for converting DC power into AC power; a DC-DC converter installed between the AC-DC converter and the DC-AC inverter; and a control unit for controlling the duty of the DC-AC inverter and the output voltage of the DC-DC converter.

[0013] The above DC-DC converter can have an output voltage that can be adjusted within a range of 200 V to 1000 V.

[0014] The above DC-DC converter is a non-isolated converter and may be any one selected from a buck converter, a boost converter, and a buck-boost converter.

[0015] The above DC-DC converter may be an isolated converter equipped with a transformer.

[0016] The wireless charging transmitter may further include a communication unit that communicates with the wireless charging receiver to receive data including battery status information.

[0017] In another aspect of the present invention, a wireless charging receiving device that wirelessly receives power from a wireless charging transmitting device is provided, the wireless charging receiving device including a rectifier that converts alternating current into direct current; and a battery that is directly connected to the rectifier without using a DC-DC converter.

[0018] In another aspect of the present invention, a method for controlling a wireless charging transmitter is provided, comprising: (a) a step of increasing the duty of the DC-AC inverter while determining whether a reference parameter reaches a target value; and (b) a step of adjusting an output voltage of the DC-DC converter when the reference parameter does not reach the target value even though the duty of the DC-AC inverter reaches an upper limit in the step (a).

[0019] In the above step (a), it is preferable that the duty control of the DC-AC inverter is performed using a phase shift technique.

[0020] The above reference parameter may be the output power of the wireless charging transmitter.

[0021] The target value of the above reference parameter can be provided from a wireless charging receiving device that receives power from the wireless charging transmitting device.

[0022] The above reference parameter may be a current of a wireless charging receiving device that receives power from the wireless charging transmitting device.

[0023] Preferably, the wireless charging transmitter can receive data including battery status information from the wireless charging receiver, and when the battery voltage of the wireless charging receiver is lower than or equal to a predetermined voltage, the reference parameter is determined as a current of the wireless charging receiver, and when the battery voltage of the wireless charging receiver is higher than or equal to a predetermined voltage, the reference parameter is determined as an output power of the wireless charging transmitter.

[0024] Before the above step (a), a step of setting the output voltage of the DC-DC converter to a predetermined minimum voltage may be further included.

[0025] In the above step (b), the regulation of the output voltage of the DC-DC converter may include both an increase and a decrease.

[0026] According to the wireless charging transmitter with built-in DC-DC converter and the control method thereof according to the present invention, the following effects can be obtained.

[0027] First, by providing a DC-DC converter capable of variable DC link voltage control inside the transmitter, stable maximum power charging is possible without loss or derating of power amount without a separate DC-DC converter on the receiving side even if the charging voltage range of the receiving side battery is very wide.

[0028] Second, the DC-DC converter on the transmission side actively compensates the DC link voltage to stably transmit the target power even over a wide range where the magnetic coupling coefficient between the transmitting and receiving coils fluctuates significantly due to errors in the vehicle's parking position or changes in ground clearance, thereby providing robust charging performance for various actual usage environments.

[0029] Third, by concentrating the ability to respond to a wide voltage range and coupling changes on the shared charging infrastructure (transmitter) rather than on expensive individual vehicles, each electric vehicle equipped with wireless charging eliminates the need for a DC-DC converter for voltage matching. This contributes to lower manufacturing costs, weight reduction, increased design space, and improved fuel efficiency.

[0030] Fourth, the overall energy efficiency of the system can be improved by omitting additional power conversion steps on the vehicle side, and economic efficiency can be improved by sharing charging infrastructure resources.

[0031] Fifth, it increases the versatility and interoperability of wireless charging infrastructure by enabling a single standard transmitter (charger) to be compatible with various types of electric vehicles with different battery voltage specifications.

[0032] FIG. 1 is a block diagram of the entire configuration of a wireless charging system according to one embodiment of the present invention.

[0033] Figure 2 is a flowchart schematically showing an example of a control method of a wireless charging transmitter according to the present invention.

[0034] Figure 3a is a simulation graph showing the output voltage and current waveforms of a DC-AC inverter when the DC link voltage is 280 V under minimum gap and constant position conditions.

[0035] Figure 3b is a simulation graph showing the high-frequency current waveforms flowing in each of the transmitting coil and the receiving coil under the above conditions.

[0036] Figure 3c is a simulation graph showing the output voltage and current waveforms of the receiving-side rectifier under the above conditions.

[0037] Figure 3d is a simulation graph showing the DC voltage and current waveforms finally applied to the battery terminals under the above conditions.

[0038] Figure 3e is a simulation graph showing the power transfer efficiency (ratio of battery charging power to input power) of the wireless charging system under the above conditions.

[0039] Figure 4a is a simulation graph showing the DC voltage and current waveforms finally applied to the battery terminals when the DC link voltage is 400 V under the conditions of minimum gap and standard maximum deviation.

[0040] Figure 4b is a simulation graph showing the power transfer efficiency (ratio of battery charging power to input power) of the wireless charging system under the above conditions.

[0041] Figure 5a is a simulation graph showing the DC voltage and current waveforms ultimately applied to the battery terminals when the DC link voltage is 700 V under the conditions of maximum gap and standard maximum deviation.

[0042] Figure 5b is a simulation graph showing the power transfer efficiency (ratio of battery charging power to input power) of the wireless charging system under the above conditions.

[0043] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. Identical or similar components are given identical or similar drawing reference numerals, and redundant descriptions thereof are omitted. In describing the embodiments disclosed in this specification, if a detailed description of a related known technology is judged to obscure the gist of the embodiments disclosed in this specification, the detailed description thereof will be omitted. The attached drawings are only intended to facilitate easy understanding of the embodiments disclosed in this specification, and the technical ideas disclosed in this specification are not limited by the attached drawings, and should be understood to include all modifications, equivalents, and replacements included in the spirit and technical scope of the present invention.

[0044] Terms containing ordinal numbers, such as "first," "second," etc., may be used to describe various components; however, these terms are used solely to distinguish one component from another and are not limited to the components in question. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0045] The terms “comprises,” “includes,” or “has” as used herein should be understood to limit the presence of a feature, step, component, or combination thereof described in the specification, but not to exclude the possibility that one or more other features, steps, components, or combinations thereof may be present or added.

[0046]

[0047] FIG. 1 is a block diagram of the entire configuration of a wireless charging system according to one embodiment of the present invention, in which a DC-DC converter (120) is placed between an AC-DC converter (110) and a DC-AC inverter (130) within a transmitter (100).

[0048] The wireless charging system illustrated in FIG. 1 is largely composed of a three-phase power supply (10) that supplies power, a wireless charging transmitter (100) that converts the power and wirelessly transmits it, and a wireless charging receiver that wirelessly receives power from the wireless charging transmitter (100) and charges a battery (20). The wireless charging transmitter (100) may include an AC-DC converter (110), a DC-DC converter (120), a DC-AC inverter (130), a transmitting-side impedance matching network (140), a resonant capacitor (150), and a transmitting coil (160), and the wireless charging receiver may include a receiving coil (260), a receiving-side impedance matching network (240), and a rectifier (210).

[0049] One of the important features of the system configuration according to the present invention is that, as clearly illustrated in FIG. 1, the output terminal of the rectifier (210) is directly connected to the input terminal of the battery (20). That is, unlike some conventional methods, there is no separate DC-DC converter on the receiving side to additionally convert the voltage between the rectifier and the battery according to the battery voltage level or to precisely control the charging current / voltage. This is possible because the DC-DC converter (120) inside the transmitting device (100), which is a main feature of the present invention, actively controls the DC link voltage, thereby remotely adjusting the output voltage / current of the rectifier (210) to satisfy the requirements of the battery (20) (e.g., charging voltage, constant current / constant voltage charging profile, etc.). This simplifies the structure of the receiving device and has the effect of reducing cost and weight.

[0050]

[0051] A three-phase power supply (10) is an external power supply source that supplies power required to drive a wireless charging system according to one embodiment of the present invention, specifically, a wireless charging transmitter (100). The three-phase power supply (10) may generally refer to a commercial power grid or electrical grid, and may be, for example, standard AC power generated at a power plant and supplied through a transmission and distribution network.

[0052] Since electric vehicle charging infrastructure to which the present invention can be applied often requires high power, it is common to use a three-phase AC power source as illustrated in Fig. 1. The three-phase power source (10) serves to provide AC power having a specific voltage level (e.g., 220 V, 380 V, 480 V, etc. according to national or regional standards) and a specific frequency (e.g., 50 Hz or 60 Hz) to the input terminal of the wireless charging transmitter (100), i.e., the AC-DC converter (110). Accordingly, the wireless charging transmitter (100) receives stable power from the three-phase power source (10) to operate.

[0053] The AC-DC converter (110) is located at the very front end of the wireless charging transmitter (100) and performs the function of converting three-phase alternating current (AC) power supplied from an external three-phase power source (10) into direct current (DC) power. This is an essential power conversion process because the main power conversion stages within the wireless charging transmitter (100), such as the DC-DC converter (120) and DC-AC inverter (130) described below, operate based on DC power.

[0054] In addition to the function of simply rectifying AC to DC, it is highly desirable for the AC-DC converter (110) to perform a power factor correction (PFC) function as shown in the drawing. The PFC function is intended to solve problems that occur when the AC-DC converter (110) is connected to an alternating current system such as a three-phase power supply (10). The PFC circuit improves the input power factor to nearly 1 by controlling the input current waveform to be close to a sine wave in phase with the input voltage waveform. This plays an important role in reducing unnecessary reactive power consumption from the power system, improving power quality by suppressing the occurrence of current harmonics, and satisfying related international standards (e.g., IEC 61000-3-2). As a result, it increases energy efficiency and contributes to system stability.

[0055] In order to implement these AC-DC conversion and PFC functions in an integrated manner, the AC-DC converter (110) can be configured with various circuit topologies. For example, it can be implemented with a combination of a three-phase diode rectifier and a boost DC-DC converter, and a three-phase PFC converter topology such as a PWM (Pulse Width Modulation) rectifier with improved performance through more active control, such as a Vienna rectifier, can also be applied.

[0056] The DC power converted in the AC-DC converter (110) is transmitted to the input terminal of the next stage, the DC-DC converter (120), through its output terminal. The DC voltage output at this time can be designed to maintain a relatively stable level.

[0057]

[0058] The DC-DC converter (120) is connected in series between the output terminal of the AC-DC converter (110) and the input terminal of the DC-AC inverter (130). The DC-DC converter (120) is one of the components that implements the core features of the technical idea of ​​the present invention, and plays a role in varying the voltage level of the DC power supplied from the AC-DC converter (110) and transmitting it to the DC-AC inverter (130). In other words, it actively controls the DC link voltage, which is the input voltage of the DC-AC inverter (130).

[0059] The voltage variable function of this DC-DC converter (120) is not shown and is performed under the precise control of a control unit described later. The control unit comprehensively considers information received from the wireless charging receiver (e.g., battery voltage, charging required current / power, etc.) and / or the magnetic coupling state between the transmitting and receiving coils (160, 260), and determines and controls the target DC link voltage value that the DC-DC converter (120) should output in order to secure optimal charging efficiency and stability.

[0060] In particular, in the present invention, the DC-DC converter (120) is arranged inside the transmitter (100) and its output voltage is adjustable over a wide range (e.g., 200 V to 1000 V), thereby achieving the following important effects. First, it is possible to flexibly respond to the nominal voltage of the battery (20), which may be different for each electric vehicle model, or the battery voltage that changes during charging. This eliminates the need to mount a separate DC-DC converter on every receiver (vehicle) side as in the prior art, thereby increasing the cost efficiency and space efficiency of the system. Second, even if the alignment state or distance between the transmitter coil (160) and the receiver coil (260) changes due to a change in the parking position error of the vehicle or a change in the ground clearance, thereby fluctuating the magnetic coupling coefficient, the DC-DC converter (120) appropriately compensates (increases or decreases) the DC link voltage, thereby enabling the target charging power to be stably transmitted.

[0061] The above DC-DC converter (120) may be configured to include switching elements, inductors, capacitors, and in some cases, transformers. Depending on the implementation method, it may be designed as a non-isolated converter in which the input and output terminals are not electrically isolated, or as an isolated converter in which the input and output terminals are electrically isolated using a transformer. Examples of non-isolated converters include a buck converter, a boost converter, a buck-boost converter, etc., and an appropriate topology may be selected in consideration of system requirements, input / output voltage ranges, etc.

[0062]

[0063] A DC-AC inverter (130, denoted as 'Inverter' in FIG. 1) is connected to the output terminal of a preceding DC-DC converter (120) and receives (variable) DC power provided from the DC-DC converter (120). The main function of the DC-AC inverter (130) is to convert the input DC power into high-frequency alternating current (AC) power for use in wireless power transmission. In the field of wireless power transmission, especially in the field of wireless charging of electric vehicles, it is common to use high-frequency AC of a specific frequency band (e.g., 85 kHz band recommended by the SAE J2954 standard) considering efficiency, coil size, etc., and 85 kHz is indicated as an example in FIG. 1. However, the present invention is not necessarily limited to this frequency, and other high frequencies may be used depending on the system design.

[0064] The above DC-AC inverter (130) is important in that, in addition to its simple DC-AC conversion function, it also plays a primary output control role in the two-stage control strategy of the present invention. That is, a control unit, which is not shown and will be described later, primarily controls the switching operation of the DC-AC inverter (130) in order to ultimately control the power transmitted through the transmission coil (160). The control unit can control the basic waveform, size, or phase of the high-frequency AC voltage output by adjusting the on / off timing of the switching elements (e.g., MOSFET, IGBT, etc.) constituting the DC-AC inverter (130).

[0065] In particular, when a full-bridge inverter topology is used, the control unit can vary the output power by controlling the phase shift between the voltages output from the two legs of the inverter (Phase Shift Control) or by directly controlling the duty cycle of each switch (PWM method) (see claim 9). In the control method according to the present invention (see FIG. 2 described below), in order to achieve a charging target value (e.g., target current or power), the duty (or phase difference) of the DC-AC inverter (130) is first controlled within an available range (e.g., from 0% to an upper limit). If the duty (or phase difference) reaches the upper limit but does not satisfy the target value, the output voltage (i.e., DC link voltage) of the preceding DC-DC converter (120) is controlled as a secondary control means.

[0066] To perform such high-frequency switching operations, the DC-AC inverter (130) is typically implemented as a voltage source inverter (VSI) and may have a topology such as a half-bridge or full-bridge. The high-frequency AC power generated in the DC-AC inverter (130) is transmitted to the transmission-side impedance matching network (140) at the rear end.

[0067]

[0068] Referring to FIG. 1, a wireless charging system according to an embodiment of the present invention may include a transmitting-side impedance matching network (IMN) 140 and a receiving-side impedance matching network (IMN) 240, respectively, for efficient power transmission. An impedance matching network (IMN) is a circuit that is generally inserted to minimize power reflection caused by a mismatch between the output impedance of the source side and the input impedance of the load side when the two impedances are different, and to maximize the transmitted effective power.

[0069] Specifically, the transmitter-side impedance matching network (140) is located between the output terminal of the preceding DC-AC inverter (130) and the transmitter-side resonant circuit (or the transmitter coil itself), which may be composed of the following resonant capacitor (150) and the transmitter coil (160). In order for the DC-AC inverter (130) to operate at optimal efficiency and transmit maximum power to the transmitter coil (160), the load impedance seen by the inverter needs to match a specific value (e.g., the optimal load impedance assumed during inverter design). The transmitter-side IMN (140) plays a role in converting between the inverter output impedance and the resonant circuit input impedance (which may also include an impedance component reflected by the receiver-side circuit and coupling state) so as to satisfy this impedance matching condition.

[0070] Likewise, the receiving-side impedance matching network (240) is located between the output terminal of the receiving coil (260) and the input terminal of the following rectifier (210). In order to transmit the energy induced in the receiving coil (260) to the following rectifier (210) and the final load, the battery (20), with minimal loss, it is necessary to match the load impedance seen by the receiving coil (260) (i.e., the input impedance seen from the rectifier (210) side) and the output impedance of the receiving coil (260) itself. The receiving-side IMN (240) performs this impedance matching to increase the receiving efficiency. In particular, in a wireless charging environment, the mutual inductance and reflected impedance between the coils may change depending on changes in the distance or alignment between the transmitting coil (160) and the receiving coil (260), and an appropriately designed IMN (240) can contribute to maintaining a certain level of performance even with such changes.

[0071] These transmitting-side and receiving-side impedance matching networks (140, 240) are generally composed of a combination of inductors (L) and capacitors (C), which are passive elements with low loss. Depending on the circuit configuration (topology), there are various types such as L-section, π-section, and T-section matching networks, and appropriate topologies and element values ​​are selected in consideration of the target impedance conversion ratio, operating frequency, bandwidth, filtering characteristics, etc. In Fig. 1, the IMN (140) and the resonant capacitor (150) are illustrated as separate blocks, but in some cases, the IMN circuit may be implemented in a form that includes the resonant capacitor.

[0072]

[0073] A resonant capacitor (150, indicated as 'Cap. Box' in the drawing) is a part of a wireless charging transmitter (100), and typically functions to form a resonant circuit (resonant tank) on the transmitter side by being combined with a transmission coil (160) at the rear end. It may be positioned between the output of a preceding transmission-side impedance matching network (IMN, 140) and the transmission coil (160), and may be connected in series or in parallel with the transmission coil (160) depending on the connection method.

[0074] In wireless power transmission, especially in systems that use magnetic induction or magnetic resonance, the resonance phenomenon is actively utilized to increase transmission efficiency and transmission range. The resonance capacitor (150) is selected so that its capacitance value and the inductance value of the transmitting coil (160) cause electrical resonance at the operating frequency of the system (e.g., 85 kHz). In the resonance state, the imaginary part of the impedance is canceled out, so that the circuit impedance exhibits a characteristic of decreasing (series resonance) or increasing (parallel resonance), and this allows a large resonance current to flow in the transmitting coil (160) even with a relatively small driving voltage. This amplified current generates a strong time-varying magnetic field in the transmitting coil (160), enabling efficient transfer of sufficient energy to the receiving coil (260) across the air gap.

[0075] The resonant capacitor (150) may not simply be a single capacitor element. Since the wireless charging system handles relatively high power and voltage / current, it may be provided in the form of a capacitor bank or capacitor module composed of multiple capacitor elements combined in series and / or parallel to meet the required capacitance capacity and voltage / current withstand specifications. Such a capacitor combination may be mounted within a separate housing or module.

[0076] The specific capacitance value of the resonant capacitor (150) and the connection method (series / parallel) with the transmitting coil (160) determine the topology of the transmitting-side resonant circuit (e.g., series resonant topology (S), parallel resonant topology (P), LCC topology, LCCL topology, etc.), which is an important consideration in system design because it affects the impedance characteristics, efficiency, voltage / current gain, etc. of the entire system. The impedance matching network (140) described above is designed in consideration of the characteristics of this resonant circuit.

[0077]

[0078] The transmitting coil (160) is responsible for wirelessly radiating high-frequency energy generated in the wireless charging transmitter (100). The transmitting coil (160) receives high-frequency alternating current (AC) from a preceding transmitting-side resonant circuit (e.g., including an impedance matching network (140) and a resonant capacitor (150)).

[0079] When a high-frequency AC current is applied to the transmitting coil (160), a time-varying magnetic field is generated around the coil according to the principle of electromagnetic induction. This time-varying magnetic field contains energy and is propagated through space (mainly an air gap) toward the receiving coil (260) located in the wireless charging receiving device. The receiving coil (260) detects this change in the magnetic field and induces AC power again, thereby receiving energy.

[0080] The above-mentioned transmitting coil (160) is typically manufactured by winding a conductor (e.g., copper wire) having high electrical conductivity multiple times in a specific shape. The shape of the transmitting coil (160) can be designed in various ways, such as circular, rectangular, solenoidal, DD (Double D), bipolar, etc., taking into consideration the desired magnetic field distribution, coupling characteristics, space constraints, etc. In particular, in electric vehicle wireless charging systems, it is often manufactured in the form of a flat pad for charging between the bottom of the vehicle and the ground.

[0081] Additionally, the transmitting coil (160) is often configured with a magnetic core or shielding material. Placing a high-permeability material, such as ferrite, on the rear or inside of the coil can guide and concentrate the path of magnetic flux lines in a desired direction, thereby strengthening the magnetic coupling with the receiving coil (260) and increasing transmission efficiency. At the same time, it also suppresses (shields) the magnetic field from leaking in an undesired direction, thereby minimizing the impact on other electronic devices or the human body in the vicinity.

[0082] The transmitting coil (160) has a unique inductance value due to its structure, and this inductance value, together with the capacitance value of the resonance capacitor (150) described above, becomes a key design parameter that determines the resonance frequency of the transmitting-side resonance circuit.

[0083]

[0084] The receiving coil (260) is mounted on a wireless charging receiving device, for example, the bottom of an electric vehicle, and is responsible for capturing and receiving the time-varying magnetic field energy radiated from the transmitting coil (160) of the wireless charging transmitting device (100).

[0085] When the time-varying magnetic field generated by the transmitting coil (160) passes through the receiving coil (260), an electromotive force is induced inside the coil according to the electromagnetic induction phenomenon, particularly Faraday's law of induction, thereby generating a high-frequency alternating current (AC) voltage and current. In this way, the magnetic field energy is converted back into electric energy and supplied to the receiving circuit. The amount of power received is determined by the transmission power, the magnetic coupling coefficient between the transmitting coil (160) and the receiving coil (260), and the receiving load conditions.

[0086] The physical structure of the receiving coil (260) is generally designed in a similar shape to that of the transmitting coil (160). That is, it can be manufactured by winding it in various shapes such as a circle, a square, and a DD (Double D) shape for efficient coupling with the transmitting coil (160). Since it is often attached to the bottom of an electric vehicle, it often takes the shape of a flat pad. The receiving coil (260) is also generally mounted together with a ferrite core and / or a metal shielding material to effectively focus the magnetic force lines to increase the coupling coefficient and to prevent the magnetic field from leaking to other parts of the vehicle or the passenger space. The design of the receiving coil (260) is optimized by comprehensively considering the specifications of the transmitting coil (160), the required charging distance (air gap), the mounting space on the bottom of the vehicle, etc.

[0087] The receiving coil (260) has a unique inductance value depending on its structure, and the high-frequency AC power induced here is transmitted to the next stage, the receiving-side impedance matching network (240), for subsequent processing.

[0088]

[0089] A rectifier (210) is connected to the output terminal of a preceding receiving-side impedance matching network (IMN, 240) within a wireless charging receiver to receive high-frequency alternating current (AC) power. The core function of the rectifier (210) is to convert the input high-frequency AC power into direct current (DC) power that can be used to charge the final load, i.e., the battery (20). This is the opposite process to the DC-AC inverter (130) converting DC into AC.

[0090] There are several ways to implement a rectifier (210). The most basic form is a passive rectifier using diode elements. For example, a full-wave bridge rectifier, which consists of four diodes connected in a bridge configuration, can generate a DC output using both the positive and negative half-cycles of the input AC waveform.

[0091] However, the diode exhibits a forward voltage drop of approximately 0.7 V to 1 V when current flows in the forward direction, which causes significant power loss (conduction loss), especially in high-power wireless charging systems where large currents flow. Therefore, in order to improve the overall efficiency of the system, a synchronous rectification (SR) method has been widely used recently, which uses power semiconductor switches (e.g., MOSFETs) with very low on-resistance instead of diodes and actively turns these switches on and off according to the polarity of the AC input voltage. Since a synchronous rectifier has a much lower conduction loss compared to the voltage drop of a diode, it can significantly improve the efficiency on the receiving side. The switches of the synchronous rectifier are typically precisely controlled by a receiving-side control unit (not shown).

[0092] The DC output converted through the rectifier (210) generally contains a ripple component corresponding to the switching frequency or its multiple frequency. Therefore, the output terminal of the rectifier (210) is typically equipped with an output filter circuit (e.g., a filter composed of one or more capacitors) to smooth out such voltage and current ripples and supply stable DC power to the battery (20).

[0093]

[0094] The battery (20) is the final load of the wireless charging system and is an energy storage device that stores DC power transmitted wirelessly and rectified in the receiving circuit. Typically, the battery (20) is installed inside a mobile vehicle equipped with a wireless charging receiver, for example, an electric vehicle (EV).

[0095] The above battery (20) is generally a secondary battery that can be charged and discharged, and may be a lithium-ion battery pack widely used in electric vehicles. Such a battery pack is composed of a plurality of unit cells connected in series and / or parallel, and provides high voltage and energy required for the vehicle's driving motor. In particular, with the development of electric vehicle technology, the nominal voltage of the battery (20) reaches several hundred volts (e.g., 400 V or 800 V), and its terminal voltage fluctuates within a certain range depending on the state of charge (SoC). The main purpose of the present invention is to effectively support such a wide and diverse battery voltage range from the transmitter (100) side.

[0096] The actual battery pack (20) includes a battery management system (BMS) (not shown) that performs safe and efficient charge and discharge management, cell balancing, and status monitoring (voltage, current, temperature, SoC, etc.). During wireless charging, the BMS can determine status information of the battery (20) and charging requirements (e.g., target charging current or voltage) and transmit them (ultimately to the control unit of the transmitter (100)) via a communication interface (not shown).

[0097] As mentioned above in the description of the rectifier (210), in the configuration of the present invention, the output of the rectifier (210) is directly connected to the battery (20) for charging without a separate DC-DC converter for voltage matching (although it may pass through a protection circuit of the BMS, etc.).

[0098] Meanwhile, although not explicitly illustrated in FIG. 1, in order for the wireless charging system according to the present invention to operate stably and efficiently, and in particular, to perform charging control optimized for the state of the battery (20), mutual information exchange between the wireless charging transmitter (100) and the wireless charging receiver (e.g., vehicle side) is essential. To this end, the wireless charging transmitter (100) and the wireless charging receiver each have a communication unit capable of transmitting and receiving data, or include a communication interface that enables data exchange between the two devices.

[0099] Various information can be exchanged bidirectionally through this communication interface. In particular, information that is significantly used in implementing the control method of the present invention is data transmitted from the receiver to the transmitter (100). This may include real-time status information of the battery (20) described above, such as battery terminal voltage (Vbat), charging current (Ibat), temperature, and state of charge (SoC). In addition, optimal charging requirements determined by a battery management system (BMS) (not shown) linked to the battery (20), such as target charging current (in constant current mode) or target charging power (in constant power mode), may be provided to the transmitter (100) through the communication interface. In addition, information such as the system readiness status of the receiver, auxiliary information related to alignment, and whether an error has occurred may be exchanged. In the opposite direction, the transmitter (100) may also transmit charging start / stop / pause commands, system status information, and authentication-related data to the receiver.

[0100] There are various ways to implement communication between the transmitter (100) and the receiver. For example, an in-band communication method that modulates a signal within a frequency band (e.g., 85 kHz) for transmitting power and communicates, or an out-of-band communication method that uses a channel independent of the power transmission path, such as Wi-Fi, Bluetooth Low Energy (BLE), near-field communication (NFC), or wireless communication using a separate designated frequency band, is possible. Certain wireless charging standards (e.g., SAE J2954) also define specifications for such communication methods and protocols.

[0101] In conclusion, the information related to the receiver and battery (20) obtained through this communication interface is used as essential input data for the control unit (not shown) to be described below to accurately recognize the current system status and perform the control method according to the present invention.

[0102]

[0103] Although not illustrated in FIG. 1, the wireless charging transmitter (100) according to the present invention includes a control unit that controls the overall operation of the system and coordinates the power conversion process. The control unit can typically be implemented with a microcontroller unit (MCU), a digital signal processor (DSP), a field-programmable gate array (FPGA), or a combination thereof, and performs a control algorithm preset by built-in firmware or software.

[0104] The above control unit is responsible for several tasks as follows: First, it monitors the operating status information of the system (e.g., input / output voltage, current, temperature of each stage, etc.) in real time from various sensors (not shown) installed inside the transmitter (100). Second, it receives the status information (voltage, current, temperature, SoC, etc.) and charging requirements (target current / power, etc.) of the battery (20) from the wireless charging receiver through the communication interface (not shown) described above. Third, it comprehensively judges such input information and executes the control method according to the present invention. Fourth, it generates and outputs a precise control signal (e.g., PWM (Pulse Width Modulation) signal, gate drive signal, etc.) for driving the switching elements of each power conversion unit, particularly the DC-DC converter (120) and the DC-AC inverter (130), according to the calculated control command. In some cases, it may also be involved in the operation of the AC-DC converter (110) (e.g., PFC control). An example of the core charging control logic performed by the above control unit can be more clearly understood with reference to the control flowchart of FIG. 2 described below.

[0105] In particular, the control unit can utilize status information, such as the current voltage (Vbat) value of the battery (20) received via the communication interface, to dynamically determine the optimal charging mode appropriate for the battery's charging stage and set a control target accordingly. For example, the control unit can compare the received battery voltage (Vbat) with a preset specific reference voltage (e.g., a threshold value Vlimit around the battery's nominal voltage).

[0106] As a result of the comparison, if the battery voltage is lower than the reference voltage (e.g. Vbat <Vlimit), 이는 통상적으로 배터리 충전 초기 단계에 해당하므로, 제어부는 정전류(Constant Current, CC) 충전 모드를 선택할 수 있다. 이 경우, 후술할 제어 루프(예: 도 2의 S300 판단)에서 사용되는 '기준 파라미터'는 배터리로 공급되는 '충전 전류'(또는 수신측 전류)가 되며, 제어부는 BMS 등으로부터 전달받은 '목표 전류값'을 '목표치'로 설정하여 제어를 수행한다.

[0107] Conversely, if the battery voltage is higher than the reference voltage (e.g., Vbat≥Vlimit), this means that the battery is significantly charged and may be in the late charging stage, so the control unit may select the constant power (CP) charging mode (or constant voltage (CV) mode, as the case may be). In this case, the 'reference parameter' used in the control loop becomes the 'output power' of the transmitter (100), and the control unit performs control by setting the received 'target power value' as the 'target value'.

[0108] In this way, the control unit intelligently determines the charging mode and control parameters (reference parameters and target values) according to the battery status, and then performs the two-step control (inverter duty control and DC-DC voltage control) logic schematically illustrated in Fig. 2 to achieve this.

[0109]

[0110] FIG. 2 is a flowchart schematically illustrating an example of a two-step control method in which a control unit (not shown) of a wireless charging transmitter (100) according to the present invention sequentially utilizes duty control of a DC-AC inverter (130) and output voltage control of a DC-DC converter (120). Hereinafter, the control method of a wireless charging transmitter (100) according to the present invention will be described in detail step by step with reference to FIG. 2.

[0111]

[0112] First, in the initial stage when the wireless charging process is initiated or the control loop is started, the control unit (not shown) controls the output voltage of the DC-DC converter (120) located inside the wireless charging transmitter (100) to set it to a predefined minimum voltage value (Vmin) within the voltage range that the DC-DC converter (120) can output (S100). The output voltage of the DC-DC converter (120) is applied as the input voltage of the DC-AC inverter (130) connected to the rear end, i.e., the DC link voltage. Therefore, step S100 corresponds to an initialization process that sets the initial value of the DC link voltage to the lowest level available in the system.

[0113]

[0114] After the DC link voltage is set to the minimum value at step S100, the control unit (not shown) gradually increases the duty of the DC-AC inverter (130) to perform the primary output control of the present invention (S200). Here, 'duty' means a control parameter that adjusts the size of the output power or voltage of the DC-AC inverter (130), and depending on the inverter topology and control method used, it may be the duty cycle of the switching element itself, or, for example, in the case of a full-bridge inverter, it may correspond to the phase shift angle between the outputs of two legs.

[0115] The purpose of step S200 is to achieve the target charging power or current (the 'reference parameter' and 'target value' of step S300 to be described later) within the output control range of the DC-AC inverter (130). The control unit monitors the system output (reference parameter) that changes as a result while gradually increasing the duty (or phase difference) of the DC-AC inverter (130) starting from 0 or a minimum value. This process is repeated or proceeds to the next step depending on the judgment results of steps S300 and S400 to be described later. In other words, this step S200 corresponds to an operation to control the output only by inverter control while the DC link voltage is fixed to a minimum.

[0116]

[0117] After the duty (or phase difference) of the DC-AC inverter (130) is adjusted in step S200, or the output voltage (DC link voltage) of the DC-DC converter (120) is adjusted in step S500, which will be described later, the control unit (not shown) determines whether the current value of the 'reference parameter' has reached the preset 'target value' in order to evaluate the control status of the current system (S300). This step corresponds to the core feedback judgment process of the control loop.

[0118] Here, the 'reference parameter' refers to a target variable to be controlled by the control unit, and this may vary depending on the currently performed charging mode (e.g., constant current (CC), constant power (CP), constant voltage (CV) mode). For example, in the constant current (CC) mode in the initial stage of battery charging, the reference parameter may be the size of the charging current actually flowing into the battery (20) (or the current value at a specific point on the receiving side representing the current). In the constant power (CP) mode after the battery voltage rises above a certain level, the size of the effective power output by the wireless charging transmitter (100) may be the reference parameter. The current value of this reference parameter may be directly measured through a sensor inside the transmitter (100), or may be estimated through information received through communication and a system model.

[0119] The "target value" is the desired setpoint that the above-mentioned reference parameter must reach. This target value is determined based on the battery's condition, such as the type of battery (20), state of charge (SoC), and temperature, as well as the manufacturer's recommended charging profile. Typically, a battery management system (BMS) (not shown) calculates the optimal target value, and this value can be transmitted from the receiving device to the control unit of the transmitting device (100) via the communication interface (not shown) described above.

[0120] In the judgment step (S300), the current reference parameter value is compared to see if it is greater than (>=) the set target value. If the comparison result is 'Yes' (i.e., the reference parameter >= the target value), this means that the desired charging target has been successfully achieved through the current control operation. Therefore, the control unit stops adjusting the control variable (duty or voltage) to increase the output, maintains the current control state, and continues the stable charging mode (step S600 described later).

[0121] On the other hand, if the comparison result is 'No' (i.e., the reference parameter < the target value), this means that the target state of charge has not yet been reached and the output must be increased further. In this case, the control flow proceeds to the next decision step, S400.

[0122]

[0123] If it is determined in the preceding step S300 that the reference parameter has not yet reached the target value ('No' path), i.e., in a situation where the current control state is insufficient for output, the control unit (not shown) determines whether the duty (or phase difference) of the DC-AC inverter (130), which is the primary control variable, has already reached the maximum available limit, i.e., the preset 'upper limit' (S400).

[0124] The above 'upper limit' refers to the maximum allowable range of the duty (or phase difference) value that the DC-AC inverter (130) can control. This upper limit may be predefined, for example, by physical constraints of the inverter switching elements, ensuring the stability of the control algorithm, considering system efficiency, or by conventions in a specific operating mode. For example, in the case of phase difference control, theoretically, up to 180 degrees is possible, but in practice, a smaller value may be set as the upper limit.

[0125] The result of the judgment step (S400) determines the control flow as follows:

[0126] If it is determined that the current duty (or phase difference) of the DC-AC inverter (130) is still below the upper limit ('No' path), this means that there is still room to further increase the system output through the inverter duty (or phase difference) adjustment, which is the primary control means. Therefore, the control unit returns the control flow to step S200 and performs an operation to further increase the duty (or phase difference) of the DC-AC inverter (130).

[0127] Conversely, if it is determined that the duty (or phase difference) of the current DC-AC inverter (130) has already reached or exceeded the upper limit ('Yes' path), this indicates that the output can no longer be increased by the primary control means, that is, the inverter duty (or phase difference) control, and nevertheless, the target value has not been reached. In this case, the control unit must recognize the limitation of the primary control means and activate the secondary control means to further increase the system output. Therefore, the control flow proceeds to the next step S500, and starts an operation to control (increase) the output voltage of the DC-DC converter (120), i.e., the DC link voltage.

[0128] Ultimately, the S400 stage acts as a branch point that checks the control capacity of the primary control means (inverter duty / phase) and switches to the secondary control means (DC-DC voltage) only when this means reaches its limit.

[0129]

[0130] If it is determined in the preceding step S400 that the duty (or phase difference) of the DC-AC inverter (130) has already reached the upper limit ('Yes' path), this means that the target output cannot be achieved using only the primary control means. Therefore, the control unit (not shown) actively controls (regulates) the output voltage of the DC-DC converter (120), i.e., the DC link voltage applied to the DC-AC inverter (130), as a secondary control means (S500).

[0131] When entering the S500 stage through the 'Yes' path of S400, the target output is insufficient, so the 'DC-DC converter output voltage control' performed at this time is typically performed in the direction of increasing the DC link voltage from the current value. When the DC link voltage increases, the output voltage and power of the DC-AC inverter (130) increase even at the same inverter duty (upper limit), thereby compensating for the insufficient output and approaching closer to the target value. The control unit adjusts the output voltage as necessary to achieve the target value within the voltage range in which the DC-DC converter (120) can operate (e.g., from Vmin to Vmax).

[0132] However, 'controlling the output voltage of the DC-DC converter' (S500) does not necessarily mean only increasing the voltage. For example, in cases where the target power must be exceeded during constant power (CP) control and the output must be lowered, or the optimal operating point must be found according to changes in system conditions, the control unit (not shown) may control the output voltage of the DC-DC converter (120) in the direction of decreasing it. This bidirectional voltage control capability contributes to increasing the control flexibility of the present invention.

[0133] After the output voltage of the DC-DC converter (120) is adjusted in step S500, the control flow returns to step S300 to recheck whether the current reference parameter satisfies the target value as an adjusted result.

[0134]

[0135] If the current reference parameter value is determined to be greater than the set target value in the preceding step S300 ('Yes' path), this indicates that the system has successfully achieved the desired charging target (e.g., a specific charging current or power) through the control operation of the control unit (not shown). At this time, the control unit enters the current control state, i.e., the 'maintain charging mode' step (S600).

[0136] The 'Maintain Charging Mode' (S600) step refers to a state in which the control unit does not intentionally change the control variables (i.e., the duty or phase difference of the DC-AC inverter (130) and the output voltage of the DC-DC converter (120)) to further increase the system output. In other words, by maintaining the control variable values ​​at the time when the target value satisfaction determination is made in S300, the reference parameter is stably maintained at the target value level. In this state, the wireless charging system continuously supplies energy to the battery (20) under the target conditions.

[0137] Although the flowchart of Fig. 2 does not explicitly indicate the next step after step S600, this step does not mean the complete end of control in the operation of the actual control system. Even when the control unit is in the 'maintain charging mode' state, it continuously monitors the state variables (reference parameters, etc.) of the system and maintains a feedback loop. If the reference parameters deviate from the target value again due to external factors (e.g., gradual increase in the voltage of the battery (20), change in coupling between coils due to slight movement of the vehicle, etc.), or if the state of charge (SoC) of the battery (20) reaches a certain value and it is time to move to the next step in the overall charging profile (e.g., transition from constant current (CC) mode to constant voltage (CV) mode), the control unit sets a new target value and actively adjusts the control variables through a control loop starting from step S200 again to track the new target state.

[0138] The control method of the present invention described above with reference to the flow chart of FIG. 2 has a key feature of providing a DC-DC converter (120) inside a wireless charging transmitter (100) and organically combining it with the duty (or phase difference) control of a DC-AC inverter (130) to sequentially apply it in two stages.

[0139] This control method provides the following important operational effects. First, by primarily utilizing the control range of the DC-AC inverter (130) and, if this reaches its limit or is insufficient to achieve the target value, secondarily actively controlling (increasing or decreasing) the DC link voltage through the DC-DC converter (120), it effectively responds to a very wide range of voltage fluctuations of the receiving battery (20) (e.g., including both 400 V and 800 V battery systems) to enable stable charging. Second, even when the magnetic coupling coefficient fluctuates significantly due to misalignment between the transmitting and receiving coils (160, 260) or changes in the air gap that may occur when the vehicle is parked, the system secures a wide operating range in which it can stably transmit the target charging power through the voltage compensation capability of the DC-DC converter (120).

[0140] Consequently, the control method of the present invention addresses the inefficiency of the conventional method, which required individual installation of expensive DC-DC converters for voltage matching on each receiving device (vehicle), and enables flexible response to various vehicle types and charging environment conditions through intelligent control on the transmitting device (charging infrastructure) side. This has the effect of improving the overall compatibility, stability, economy, and convenience of wireless charging systems.

[0141] Below, the specific operating characteristics and performance of the wireless charging system of the present invention to which this control method is applied will be described in more detail with reference to drawings illustrating simulation results for verifying the same.

[0142]

[0143] Figures 3a to 3e are drawings showing simulation results when the output voltage (DC link voltage) of the DC-DC converter (120) is controlled to 280 V in a minimum gap and fixed position alignment state (X=0 mm, Y=0 mm, Z=110 mm).

[0144] Hereinafter, FIGS. 3a to 3e are simulation results of a wireless charging system to which the control method of the present invention is applied, exemplifying a case in which charging is performed under the most favorable power transfer conditions of minimum air gap (e.g., Z = 110 mm) and fixed position alignment (X = 0 mm, Y = 0 mm). In this simulation condition, the output voltage (DC link voltage) of the DC-DC converter (120) is operated at 280 V. Considering that the lower limit of the voltage variable range of the DC-DC converter (120) in the present invention is 200 V, this suggests that, although it is the most favorable coupling condition, the DC-DC converter (120) had to increase the DC link voltage to 280 V, which is higher than the minimum voltage (200 V), in order to achieve the target charging power / current. Accordingly, this state may correspond to a scenario in which, in the control logic of FIG. 2, the DC link voltage is initially set to 200 V at step S100, the duty (phase difference) of the DC-AC inverter (130) is increased to the upper limit at step S200 (S400 = 'Yes'), and since it still falls short of the target value, the output voltage of the DC-DC converter (120) is further increased to 280 V at step S500, and as a result, the target value is finally reached (S300 = 'Yes') and the state is maintained (S600).

[0145] Figure 3a shows the output voltage (Via, Vib) and current (lia, lib) waveforms of a DC-AC inverter (130) operating under these conditions, i.e., a DC link voltage of 280 V and an inverter duty (phase difference) near the upper limit. The inverter output voltage waveform switches based on the DC link voltage (280 V) level, and the current appears as a sine wave close to a sine wave through the resonant circuit.

[0146] Figure 3b shows the high-frequency resonant current waveforms flowing in the transmitting coil (160, current supply coil currents Ipa, Ipb) and the receiving coil (260, current collection coil currents Isa, Isb) by the inverter output. Since the DC link voltage has increased compared to when it was 200 V, it shows that a larger resonant current flows and transmits the target power even under the same coupling conditions.

[0147] Figure 3c shows the voltage (Voa, Vob) and current (loa, lob) waveforms at the output terminal of a rectifier (210) that receives high-frequency AC power induced in a receiving coil (260) and converts it into DC. It shows the rectifier output that reflects the increased DC link voltage and the inverter control result.

[0148] Finally, FIG. 3e illustrates a graph showing the overall power transfer efficiency achieved by the wireless charging system of the present invention under the minimum air gap and position alignment conditions described above. According to the simulation analysis results under the same conditions (X=0 mm, Y=0 mm, Z=110 mm), the input power (Pi_kW, which may be, for example, the output of the AC-DC converter (110) or the input power of the DC-DC converter (120)) of the system is about 107 kW (1.077×102 kW), and the output power (Po_kW) finally transferred to the battery (20) stage was calculated to be about 100 kW (1.006×102 kW). Based on this, the power transfer efficiency (η=Po / Pi×100%) of the overall system calculated was found to be about 92.8%.

[0149] Therefore, Figure 3e provides specific numerical results supporting the claim that the system of the present invention can achieve extremely high power transfer efficiency under ideal conditions of optimal magnetic coupling between coils. This high efficiency is a critical factor in minimizing energy loss in the system and ensuring effective charging.

[0150]

[0151] Figures 4a and 4b are graphs showing the battery terminal waveform (Figure 4a) and the system power transfer efficiency (Figure 4b) when the DC link voltage is operated at 400 V under minimum gap and standard maximum deviation conditions (X=75 mm, Y=100 mm, Z=110 mm).

[0152] Figures 4a and 4b show the results when the DC link voltage is operated at 400 V under the same minimum gap (Z=110 mm) condition as in Figures 3a-3e, but with the alignment between the transmitting and receiving coils (160, 260) misaligned by the standard maximum deviation of X=75 mm, Y=100 mm. The biggest difference compared to the state of fixed alignment is that the magnetic coupling coefficient (K) is relatively lowered due to the misalignment between the coils.

[0153] This decrease in coupling coefficient becomes a factor that reduces the power transmitted to the receiver under the same inverter output conditions. Therefore, in order to maintain the target charging power or current, the control unit (not shown) performs a compensation operation according to the control logic of the present invention (step S500 of FIG. 2). That is, simply increasing the duty (phase difference) of the DC-AC inverter (130) to the upper limit is not enough, so the output voltage of the DC-DC converter (120) is increased to 400 V, which is significantly higher than the case (280 V) of FIG. 3, to compensate for the DC link voltage. This clearly shows that the secondary control means (DC link voltage variation), which is the core of the present invention, operates effectively when an actual alignment error occurs to maintain the power transmission capability. At this time, the DC-AC inverter (130) is likely to operate with a duty (phase difference) at the upper limit or very close thereto.

[0154] Fig. 4a shows the DC voltage (Vout) and current (Iout) waveforms applied to the final battery (20) as a result of this control. Noteworthy is that, compared to the results of Fig. 3d (fixed position, 280 V DC link), despite the occurrence of a significant alignment error, the battery terminal voltage (Vout) is stably maintained at a similar level through compensation control that increases the DC link voltage to 400 V, and the target charging current (Iout) is also supplied consistently at almost the same level. This demonstrates that the control system of the present invention can robustly cope with external conditions (coupled changes) to consistently maintain the desired charging performance.

[0155] Figure 4b shows the system power transfer efficiency under these conditions (minimum gap, standard maximum deviation). Referring to the simulation results, the efficiency is calculated as an input power (Pi_kW) of approximately 108 kW (1.083×102 kW) and an output power (Po_kW) of approximately 105 kW (1.053×102 kW), resulting in a power transfer efficiency of approximately 97.2%. This efficiency value (97.2%) is actually higher than the previously discussed on-position / minimum gap condition (92.8% for Figure 3e). This suggests that under certain alignment error conditions, even though the DC link voltage had to be increased, the operating points of the power converters or the impedance characteristics of the resonant circuit may have shifted to a more advantageous point in terms of overall system efficiency. For example, a combination of factors may have contributed, such as a change in reflected impedance due to a decrease in coupling coefficient, which in turn reduces switching losses in the inverter or rectifier.

[0156] In conclusion, FIGS. 4a and 4b are important simulation results that demonstrate that the system of the present invention can supply a stable charging current / voltage to the battery through active DC link voltage control via the DC-DC converter (120) even when a significant alignment error occurs, and that under certain conditions, it may even achieve higher system efficiency than when the alignment is perfect.

[0157] Figures 5a and 5b are graphs showing the battery terminal waveform (Figure 5a) and the system power transfer efficiency (Figure 5b) when the DC link voltage is operated at 700 V under maximum gap and standard maximum deviation conditions (X=75 mm, Y=100 mm, Z=160 mm).

[0158] Figures 5a and 5b show the system operation results under conditions that are much harsher than the previous simulation conditions, namely, when the maximum air gap (Z = 160 mm) and the standard maximum deviation (X = 75 mm, Y = 100 mm) of alignment errors occur simultaneously. This corresponds to the most unfavorable situation for wireless power transfer, as the magnetic coupling coefficient between the transmitting and receiving coils (160, 260) is the lowest among the simulated conditions. To overcome this worst-case coupling condition and maintain the target output, the DC link voltage was increased to 700 V, which is significantly higher than the previous cases (280 V, 400 V).

[0159] This shows that in addition to driving the DC-AC inverter (130) at maximum duty (phase difference) to compensate for the extremely low coupling coefficient (S400='Yes' in FIG. 2), the control unit (not shown) actively increased the output voltage of the DC-DC converter (120) to a very high value of 700 V within the voltage variable range (200 V-1000 V) (step S500 in FIG. 2). This strongly supports that the wide DC link voltage variable range provided by the transmitting-side DC-DC converter (120) in the present invention is a key factor in greatly expanding the operating area of ​​the system.

[0160] Figure 5a shows that even under such extreme compensation control, the DC voltage (Vout) and current (Iout) waveforms applied to the final battery (20) terminal remain stable, similar to the previous cases (Figures 3d and 4a). That is, even under the worst coupling conditions, the system of the present invention can successfully achieve and maintain the target state of charge (constant Vout and Iout) by supplying the required power while increasing the DC link voltage up to 700 V. This demonstrates the robustness of the system and control method of the present invention.

[0161] Figure 5b shows the system power transfer efficiency under these maximum gap and standard maximum deviation conditions. Referring to the simulation results for the presented conditions (X=75mm, Y=100mm, Z=160mm), the output power (Po_kW) was calculated to be approximately 106kW (1.062×102kW) compared to the input power (Pi_kW) of approximately 112kW (1.120×102kW), and the power transfer efficiency was analyzed to be approximately 94.6%.

[0162] This efficiency value (94.6%) is lower than that of Fig. 4b (minimum gap, standard maximum deviation, 97.2%), which can be interpreted as an increase in losses occurring in the DC-DC converter (120) and other circuit components (e.g., inverter switches, etc.) while increasing the DC link voltage to a high level of 700 V to overcome the very low coupling coefficient. Nevertheless, the fact that it maintains a high efficiency of over 94% even under the harshest conditions demonstrates the practicality and excellence of the system of the present invention.

[0163] In conclusion, FIGS. 5A and 5B comprehensively demonstrate that the wireless charging system and control method of the present invention can provide stable charging performance by maximizing the wide voltage variability of the DC-DC converter (120) even in highly challenging operating environments where maximum air gap and standard maximum deviation alignment errors occur simultaneously, while still maintaining high efficiency at a practical level. This strongly suggests that the present invention has secured a wide operating range and robustness capable of covering a wide range of actual usage conditions.

[0164]

[0165] The foregoing detailed description is not to be construed as limiting in any way and is to be considered illustrative. The scope of the present invention should be determined by a reasonable interpretation of the appended claims, and all changes within the equivalent scope of the present invention are intended to be included within the scope of the present invention.

Claims

1. A wireless charging transmitter using a DC-DC converter, AC-DC converter that converts AC power to DC; DC-AC inverter that converts DC power into AC power; A DC-DC converter installed between the AC-DC converter and the DC-AC inverter; and A control unit that controls the duty of the DC-AC inverter and the output voltage of the DC-DC converter. A wireless charging transmitter including:

2. In claim 1, The above DC-DC converter has an output voltage that can be adjusted within the range of 200 V to 1000 V. A wireless charging transmitter characterized by:

3. In claim 1, The above DC-DC converter is a non-isolated converter. A wireless charging transmitter characterized by:

4. In claim 3, The above DC-DC converter is one selected from among a buck converter, a boost converter, and a buck-boost converter. A wireless charging transmitter characterized by:

5. In claim 1, The above DC-DC converter is an isolated converter equipped with a transformer. A wireless charging transmitter characterized by:

6. In claim 1, A communication unit that communicates with a wireless charging receiver and receives data including battery status information. A wireless charging transmitter characterized by further including:

7. A wireless charging receiving device that wirelessly receives power from the wireless charging transmitting device described in claim 1, A rectifier that converts alternating current into direct current; and A battery directly connected to the rectifier without using a DC-DC converter A wireless charging receiver including:

8. A method for controlling a wireless charging transmitter described in claim 1, (a) a step of determining whether a reference parameter reaches a target value while increasing the duty of the DC-AC inverter; and, (b) a step of adjusting the output voltage of the DC-DC converter when the duty of the DC-AC inverter reaches the upper limit in the step (a) but the reference parameter does not reach the target value. A method for controlling a wireless charging transmitter including a .

9. In claim 8, In the above step (a), the duty control of the DC-AC inverter is performed using a phase shift technique. A control method for a wireless charging transmitter characterized by:

10. In claim 8, The above reference parameter is the output power of the wireless charging transmitter. A control method for a wireless charging transmitter characterized by:

11. In claim 10, The target value of the above reference parameter is provided from the wireless charging receiving device that receives power from the wireless charging transmitting device. A control method for a wireless charging transmitter characterized by:

12. In claim 8, The above reference parameter is the current of the wireless charging receiver that receives power from the wireless charging transmitter. The target value of the above reference parameter is provided from the wireless charging receiving device that receives power from the wireless charging transmitting device. A control method for a wireless charging transmitter characterized by:

13. In claim 8, A step of receiving data including battery status information from a wireless charging receiving device that receives power from the wireless charging transmitting device. Including more, When the battery voltage of the wireless charging receiver is below a predetermined voltage, the reference parameter is determined by the current of the wireless charging receiver. When the battery voltage of the wireless charging receiver is higher than a predetermined voltage, the reference parameter is determined by the output power of the wireless charging transmitter. A control method for a wireless charging transmitter characterized by:

14. In claim 8, Before the above step (a), a step of setting the output voltage of the DC-DC converter to a predetermined minimum voltage A control method for a wireless charging transmitter, characterized in that it further includes.

15. In claim 14, In the above step (b), the regulation of the output voltage of the DC-DC converter includes both an increase and a decrease. A control method for a wireless charging transmitter characterized by:

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