Wide range power regulation method for wireless power receiving unit by using hybrid multi-level topology

Abstract

A power receiving unit (PRU) for power regulation of an RWPT system includes: an ML post-regulation stage via which a load is connected to the PRU; a controller circuit adapted to: determine target / predicted values of voltage and current of a power transmitting unit (PTU) of the RWPT system; determining wireless medium characteristics and resonance frequency of the RWPT system; generating an overall system model by using first harmonic approximation (FHA); determining an expected output power; calculating the voltage VS1 of the first harmonic; calculating the equivalent reflection impedance ZO of the load by using the VS1; and calculating the duty ratio d using the predicted value of the efficiency [eta], the conversion ratio M (D), and the calculated equivalent reflection impedance ZO.

Description

Technical Field

[0001] The present invention relates to the field of wireless power transmission (WPT) systems. More specifically, the present invention relates to a high performance power regulation and impedance matching method for a power receiving unit (PRU) in a wireless power transmission system. Background Art

[0002] Advanced wireless power technology applications, such as portable electronics, virtual and augmented reality, autonomous robots, drones, etc., require both extended power periods and spatial freedom. While wireless power transmission (WPT) technology enables extended power periods and reduces (or even eliminates) the use of bulky batteries, the spatial freedom that allows 3-D movement depends largely on the coupling method and the power regulation capabilities of the system.

[0003] In dynamic WPT applications consuming low to high power (a few watts to a few kilowatts), resonance-based WPT methods are preferred because they enable better power transmission characteristics such as spatial freedom, distance, and power level. However, resonance-based WPT is not enough because for most applications, the output power (voltage, current, or both) should be well regulated regardless of changes in the power transmission medium.

[0004] There are three types of state-of-the-art power regulation methods for wireless power receiving units (PRUs): passive regulation, active rectification and using a post-regulation stage.

[0005] Passive regulation (based on resonant network configuration) is a simple approach where a constant voltage or current can be obtained at the output by appropriate resonant network design. However, this approach is very limited for industrial and commercial applications that require spatial freedom, because in practice, wireless power transmission systems are affected by variations in the wireless medium, circuits, and resonators. In addition, passive power regulation is not suitable for applications with load transitions, such as smartphones, laptops, tablets, etc.

[0006] Active rectification is based on controlling the on-time of the power switch of the AC-DC rectifier. Therefore, the amount of current delivered to the load is controlled to obtain regulation at the output. Active rectification enables single-stage regulation without compromising overall efficiency too much. However, since resonance-based WPT systems typically operate in a multi-MHz range within the industrial-scientific-medical (ISM) band (6.78MHz, 13.56MHz, 27.12MHz), the sensing circuit system and controller can be very complex and cumbersome. Moreover, this solution requires that the power switch of the rectifier will be a high-performance wide bandgap (WBG) device, such as silicon carbide (SiC) and gallium nitride (GaN). This leads to higher costs and labor-intensive design work for some cases, especially when the end-use application consumes medium to high power levels.

[0007] The third approach for regulating power in wireless applications is to use a post-regulation stage, where the rectifier stage is cascaded by a low dropout (LDO) regulator or a DC-DC converter. LDO regulators are an effective solution (both cost and area) that can provide accurate voltage regulation while maintaining relatively small voltage ripple at the output. Another advantage of the LDO approach is that it can be integrated with the controller of the PRU into a single power system on chip (PSoC). However, for significant voltage (and power) levels, LDO regulators are limited by their voltage-current rating, power conversion efficiency, and overall dynamics. This limitation can be improved by using a DC-DC post-regulation stage (e.g., buck, boost, buck-boost). The post-regulator is closest to the point of load (PoL) and its dynamics are significantly better than other approaches. For commercial applications based on batteries and current control, DC-DC post-regulators are the only candidate that can meet the stringent requirements for accurate load current regulation. In addition to impedance matching for regulating the target power to the load, the post-regulator can also be used for maximum efficiency tracking in the PRU, where a specific equivalent impedance is required. While DC-DC post-regulators allow for improved spatial freedom in WPT applications, at extreme misalignments and moderate variations (coupling coefficient variations, where a wider compensation range and higher conversion ratio are required), conventional post-regulators introduce significant losses, thereby reducing the overall end-to-end efficiency of the WPT system.

[0008] The hybrid multi-level (HML) topology provides a large buck / boost conversion ratio while maintaining high efficiency and power density compared to conventional DC-DC converters. Although this requires additional switches and passive components, in the context of very high conversion ratios, the overall volume is not greatly affected compared to conventional converters (assuming the same operating conditions).

[0009] Also, in the context of wireless power systems, a framework for the analysis and design of post-regulation stages has not yet been addressed.

[0010] It would be very beneficial if this design framework for WPT is utilized, since both the steady-state and dynamic characteristics of the post-regulation stage are tightly coupled with the WPT stage.

[0011] Therefore, an object of the present invention is to provide a wide range power regulation method for wireless PRU with a post regulation stage and a wide impedance matching range.

[0012] Another object of the present invention is to provide a wide range power regulation method for wireless PRUs, making a performance trade-off between a conventional regulator and a HML regulator in a resonance-based WPT system.

[0013] Another object of the present invention is to provide a wide range power regulation method for wireless PRUs while improving the performance and characteristics of HML post-regulator based WPT systems operating under various misalignments and variations.

[0014] Other objects and advantages of the invention will become apparent as the description proceeds. Summary of the invention

[0015] A power regulation method for a power receiving unit (PRU) of a RWPT system, comprising:

[0016] a) Connect the load to the PRU via the ML post-regulation stage;

[0017] b) determining target / predicted values ​​of voltage and current of a power transmitting unit (PTU) of the RWPT system;

[0018] c) Determine the dielectric characteristics and resonant frequency of the RWPT system;

[0019] d) Generate an overall system model by using the first harmonic approximation (FHA);

[0020] e) determine the expected output power;

[0021] f) Calculate the voltage V of the first harmonic S1 ;

[0022] g) Use V S1 Calculate the equivalent reflected impedance Z of the load O ;

[0023] h) Using the predicted value of efficiency η, the conversion ratio M(D) and the calculated Z O Calculate the duty cycle d.

[0024] The method may further include the step of checking the duty cycle range and post regulator performance for the corner operating point of the RWPT system.

[0025] The ML post-regulation stage can be integrated into the PRU.

[0026] The ML post-regulation stage may be adapted to perform a step-up conversion ratio, a step-down conversion ratio, or both a step-up conversion ratio and a step-down conversion ratio.

[0027] The ML post-regulation stage can be implemented in a hybrid multi-level (HML) topology with a high conversion ratio.

[0028] The method may further include the step of performing wide impedance matching for the WPT system using HML post-regulation.

[0029] The HML post regulator can be cascaded with the AC-DC rectifier stage.

[0030] A power transmission unit (PTU) can be modeled as a current controlled module.

[0031] The method may also include the step of working under optimal operating conditions.

[0032] The ML post-regulation stage can be designed according to the specific target wireless operating conditions.

[0033] PTUs can include:

[0034] a) DC-DC pre-regulation stage;

[0035] b) DC-AC power inverter;

[0036] c) a transmitter resonator, resonating at the same frequency as the resonator of the PRU;

[0037] d) a power transmission element; and

[0038] e) Controller, used to compensate for the misalignment between PTU and PRU.

[0039] PRUs may include:

[0040] a) Pick up components;

[0041] b) a receiver resonator, resonating at the same frequency as the resonator of the PTU;

[0042] c) AC-DC rectifier;

[0043] d) DC-DC hybrid post-regulation stage; and

[0044] e) Controller, used to compensate for the misalignment between PTU and PRU.

[0045] Power regulation can be directed to several PRUs simultaneously, where each PRU includes a corresponding HML post-regulator.

[0046] The PRU may include a high conversion HML buck type post regulation stage.

[0047] The buck post-regulator stage may include:

[0048] a) Four power switches;

[0049] b) Flying capacitor;

[0050] c) Output inductor;

[0051] d) Output capacitor;

[0052] e) Sensing circuitry for the controller.

[0053] A power receiving unit (PRU) for power regulation of a RWPT system, comprising:

[0054] a) ML post-regulator stage, through which the load is connected to the PRU;

[0055] b) A controller circuit suitable for:

[0056] c) Determine target / predicted values ​​of voltage and current of the power transmitting unit (PTU) of the RWPT system;

[0057] d) Determine the wireless medium characteristics and resonant frequency of the RWPT system;

[0058] e) Generate an overall system model by using the first harmonic approximation (FHA);

[0059] f) determine the expected output power;

[0060] g) Calculate the voltage V of the first harmonic S1 ;

[0061] h) Use V S1 Calculate the equivalent reflected impedance Z of the load O ;

[0062] i) Using the predicted value of efficiency η, the conversion ratio M(D) and the calculated equivalent reflected impedance Z O Calculate the duty cycle d. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The above and other features and advantages of the present invention will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention with reference to the accompanying drawings, in which:

[0064] Figure 1A block diagram of a controlled RWPT system with a hybrid multi-stage post-regulator at a PRU according to an embodiment of the present invention is shown;

[0065] Figure 2a (Prior Art) illustrates a typical capacitively coupled RWPT system;

[0066] Figure 3a (Prior Art) illustrates an inductor-based RWPT system with a double-sided LC network;

[0067] Figure 3b (Prior Art) shows an inductive wireless medium model;

[0068] Figure 3c (Prior Art) shows typical current and voltage waveforms of an inductive RWPT system at a PRU;

[0069] Figure 3d (Prior Art) shows the overall system model by adopting the first harmonic approximation;

[0070] Figure 4 shows a simplified schematic diagram of a PRU output stage according to an embodiment of the present invention;

[0071] Figure 5 The diagram shows a capacitively coupled double-sided LC RWPT system with a wide input step-down HML buck post-regulation stage;

[0072] Figure 6 a-6c shows the typical waveform of a multi-level buck converter in steady state;

[0073] Figure 7 The diagram shows the behavior model of the PRU when the transmitter is controlled by current;

[0074] Figure 8 1. illustrates a simulation test bench that has been constructed in the PSIM platform for the analyzed capacitive RWPT system of the present invention;

[0075] Figure 9a and Figure 9b The simulation results of the current and voltage of the transmitter and receiver are shown respectively;

[0076] Fig.10a The simulation test bench for the behavioral model on the PRU side in the PSIM platform is shown;

[0077] Fig.10b shows the simulated waveforms of voltage and current;

[0078] Figures 11a-11c Modifications in the behavioral model test bench are shown;

[0079] Figure 12a-12b Results are shown for a compensated system and an uncompensated system;

[0080] Waveforms of the PRU behavior model for moderate changes in boost voltage: (a) with compensation, (b) without compensation.

[0081] Figure 13a-13b Waveforms of the PRU behavior model for medium changes in boost voltage with and without compensation are shown respectively;

[0082] Fig.14 shows the conversion ratio range of different post regulators for RWPT systems;

[0083] Fig.15a shows the efficiency measurement of the HML buck as a function of load current at an input voltage of 88V;

[0084] Fig.15b shows the loss decomposition of the HML buck as a function of input voltage;

[0085] Figure 16a-16b The experimental results of the system when it is misaligned by 75 mm (CM≈14 pF) are shown;

[0086] Figures 17a-17d shows experimental measurements of a capacitive RWPT system for a moderate change in boost voltage (14pF to 20pF); and

[0087] Figures 18a-18d Experimental measurements of a capacitive RWPT system for a moderate change in voltage drop (14 pF to 8 pF) are shown. DETAILED DESCRIPTION

[0088] The present invention provides a method for power regulation of a power receiving unit (PRU) in a resonant wireless power transmission (RWPT) system by using a hybrid multi-level (HML) post-regulator. A behavioral model for a PRU including an additional regulation stage has been developed. By using an HML stage for power regulation, a significantly wider impedance matching range has been achieved, which leads to better spatial freedom for the wireless power system. The method of the present invention also provides design trade-offs between several post-regulators in terms of efficiency, coupling range, and conversion range.

[0089] Figure 1 A block diagram of a controlled RWPT system with a hybrid multi-stage post-regulator at a PRU according to an embodiment of the present invention is shown.

[0090] The basic topology is a RWPT system with a double-sided LC resonant converter configuration. The goal is to ensure that the voltage across the load (V load) will also remain constant. The ML post-regulator stage or the HML post-regulator module consisting of a multi-stage DC-DC converter is used to regulate the voltage V load Wide impedance matching capability is provided to maintain high efficiency and low losses for any desired power level under all conditions. The ML post-regulator stage can be integrated into the PRU. The HML post-regulator can be cascaded with the AC-DC rectifier stage.

[0091] Figure 2a (Prior Art) shows a typical capacitively coupled RWPT system. The wireless medium consists of two pairs of conductive coupling plates (such as copper foil or aluminum). The capacitive medium can be modeled as a π-type network, such as Figure 2b Assume loosely coupled operation, i.e., the coupling capacitor C M , C M1 , C M2 With C P and C S Compared to the relatively low, driving frequency f INV Close to the resonator natural frequency (i.e., ), then the current and voltage of the passive components are almost sinusoidal. This is because the effective output impedance of the resonator in the transmitter is relatively high, which naturally promotes high-Q operation.

[0092] Figure 2c (Prior Art) shows the typical waveform of the system. Although the transmitter and receiver voltages V P and V S is a square wave, but due to the high Q operation of the circuit, the current is a sine wave. Since a full-bridge inverter is used at the front end, the transmitter voltage V P At ±V in switches between, while the receiver voltage V S At ±V out It can also be seen that for both the transmitter and receiver sides, the current is in phase with the voltage, while the receiver current I S Lagging behind the transmitter current I P 90°(for voltage V S and V P By adopting the first harmonic approximation (FHA) and by using the capacitive dielectric model (such as Figure 2b ), the entire system can be modeled as Figure 2d VP1 and VS1 represent square waves V P and V S The first harmonic of the wave, the value of which is 4V in / π and 4V out / π;Z O is the reflected impedance relative to the load, so that The above results are obtained under the assumption that the transmitter and receiver resonate at the same frequency.

[0093] Figure 3a (Prior Art) shows an inductor-based RWPT system with a double-sided LC network. The wireless inductive medium can be modeled as a T-type network, such as Figure 3b Assume that the inductive system is also loosely coupled and both the transmitting and receiving sides resonate at the same frequency, and by employing FHA on the inductive RWPT system, the behavior of the main currents and voltages of the inductive system can be extracted (in a similar manner to the capacitance-based system analysis).

[0094] Figure 3c (Prior Art) shows the receiver current and voltage before and after the rectification stage, V S1 is the voltage of the first harmonic, and where I S1 is the first harmonic current. Assume I out filtered by the output capacitor, then the average output current and voltage are

[0095]

[0096] Similar to the capacitive system, the overall inductive RWPT system can be modeled by adopting FHA, as Figure 3d (Prior Art) shown.

[0097] Figure 2c and Figure 3c The above analytical relationships and waveform behaviors shown in are valid for both overlaid RWPT systems.

[0098] Equivalent impedance reflection

[0099] Figure 4 A simplified schematic diagram of a PRU output stage according to an embodiment of the present invention is shown. Assuming steady-state conditions, the post-regulation can be considered as a three-port stage including input power, output power and control signals, so that the output voltage can be expressed in a general form as follows:

[0100] V Load =M(D)·V out , (2)

[0101] Where V out is the voltage after the rectification stage, and M(D) is the conversion ratio of the post regulator in steady state. M(D) is a function of the duty cycle d(t). By taking into account the efficiency factors in this type of regulator, it can be assumed that the general form of the output current is

[0102]

[0103] Among them I out is the current after the rectification stage, and η is the efficiency of the regulator. By substituting (2) into (3), the equivalent input resistance of the post-regulator can be expressed as

[0104]

[0105] By using the FHA relationship discussed above, the reflected impedance Z seen by the input of the rectifier stage is O Can be relative to the load (R Load ) and the conversion ratio M(D) are expressed as

[0106]

[0107] Z O It can also be directly expressed as

[0108]

[0109] Where P O =P Load / η is Z O of equivalent power.

[0110] From (5) and (6), it can be seen that for a given target output power and the limited efficiency of the post-regulation, the wider the range of M(d), the greater the value of Z. O The wider the range. O The wider the range, the better the V S The better the compensation of changes, the better the V S The variations are mainly due to medium-range variations and the cross-coupling relationship between the transmitter and receiver, which will be discussed later.

[0111] Example: Capacitor-based RWPT with hybrid multi-stage buck post-regulator

[0112] Figure 5 The diagram shows a capacitively coupled double-sided LC RWPT system with a wide input step-down HML buck post-regulator stage (a buck converter is a DC-DC power converter that steps down the voltage from its input to its output). The HML buck converter has several significant advantages over conventional buck converters. First, assuming that the flying capacitor C f If the charge is balanced, then the voltage swing at the switch node is half the input voltage, which in the context of a WTP system is the rectified voltage V S The effective switching frequency at the switch node (1 / T SW,eff )V SW is the switching frequency f SW =1 / T SWThese features mean better power density and less work on the overall heat dissipation of the converter. In addition, in a conventional buck converter, due to the blocking voltage V ds requirements, both switches need to be rated for a maximum input voltage V S In a multi-stage buck converter, there are S / 2. Since the silicon area used to implement the switches is approximately the same as V ds The overall semiconductor area of ​​a multi-stage and conventional buck converter can be equivalent because the output filter is proportional. Typically, the volume of the output filter is significantly larger than the volume of the semiconductor components. In the case of the HML buck converter, the output filter is further reduced due to the combined reduction in the voltage swing at the switch node and the two-fold increase in the effective switching frequency. Therefore, the additional switches introduce virtually no volume penalty. The multi-stage buck converter does not require any additional peripherals, and the core control is the same as for a conventional buck converter, but the dynamics are likely to be improved.

[0113] Figure 6 a-6c shows the typical waveform of a multi-stage buck converter in steady state. The operation of the buck converter is divided into four switching phases, where Q1 is complementary to Q4, Q2 is complementary to Q3, and Q2 is delayed T from Q1. SW / 2. It can be seen that for V Load <V S / 2 case( Figure 6 a), the switch node is between 0 and V S / 2 switch between; for V Load =V S / 2( Figure 6 b), and ignoring the flying capacitor charge balance mismatch, the switch node is almost constant and equal to V S / 2=V Load , and the inductor current is also almost constant I L =I Load ; For V S / 2<V Load <V S ( Figure 6 c), the switch node is at V S / 2 and V S It can be observed that for the entire operating region, the maximum voltage drop across the inductor (and switch) is V S / 2.

[0114] The conversion ratio function M(D) of the HML buck converter is exactly the same as that of the conventional buck converter and is equal to d(t). Therefore, by using (5), the equivalent reflected impedance Z of the multi-stage buck converter is O,ML-Buck for

[0115]

[0116] According to (7), the duty cycle d can be calculated as

[0117]

[0118] One of the methods to control the transmitter in a RWPT system (and especially in a multi-receiver RWPT system) is through constant current regulation. By adopting this control method on the capacitive system under analysis, the voltage V CP can be considered as a constant. Therefore, Figure 5 The circuit in can be simplified to Figure 7 The circuit shown in Figure 7 Applying Kirchhoff's voltage law to the circuit, the voltage V CS can be expressed as

[0119]

[0120] Voltage V S1 can be expressed as

[0121]

[0122] By substituting (9) into (10) and rearranging the expressions, V S1 can be expressed as

[0123]

[0124] And if it is assumed to operate under resonant conditions, V S1 can be simplified to

[0125]

[0126] By substituting the expression in (6) into (12), and after some processing, V S1 It can also be expressed as

[0127]

[0128] RWPT systems operate in the MHz range. Therefore, typical capacitance values ​​for the resonator are in the hundreds of pF range, the inductance is tens to hundreds of μH, and the mutual coupling capacitance C M is of the order of several pF. Therefore, the expression in (13) can be simplified to the following general expression:

[0129]

[0130] By having the relationships given in (6), (8) and (14), it is possible to vary the transmitter operating conditions, the medium change (converted to C M The system can be adapted to operate under optimal operating conditions, under which maximum efficiency is obtained.

[0131] Using the above analysis, a generalized design guideline to examine and design an end-to-end RWPT system with a post-regulation stage is performed as follows:

[0132] Given a target / predicted value for a power sending unit (PTU), this can be modeled as a current controlled module.

[0133] 1) Transmitter voltage and current, wireless medium characteristics, resonator value and resonant frequency.

[0134] 2) Assume operation in the resonant regime and extract the overall system model by employing FHA.

[0135] 3) Given the target output power, substitute (6) into (12) and calculate V S1 .

[0136] 4) Use V S1 Calculate Z according to (6) O .

[0137] 5) Given a nominal operating point, based on the selected post-regulator, the predicted efficiency η, M(d) and Z O Insert (5) and calculate the duty cycle d.

[0138] 6) Check the duty cycle range and post regulator performance for the corner operating point of the RWPT system (this determines the desired voltage-current point at which the RWPT system should operate).

[0139] In one embodiment, a PTU includes a DC-DC pre-regulation stage, a DC-AC power inverter, a transmitter resonator for resonating at the same frequency as a resonator of a PRU, a power transmission element, and a controller for compensating for misalignment between the PTU and the PRU.

[0140] In one embodiment, the PRU includes a pick-off element; a receiver resonator resonating at the same frequency as a resonator of the PTU; an AC-DC rectifier; a DC-DC hybrid post-regulation stage; and a controller for compensating for misalignment between the PTU and the PRU.

[0141] In one embodiment, several PRUs are power regulated simultaneously, wherein each PRU includes a corresponding HML post-regulator.

[0142] The PRU includes a high conversion HML step-down post-regulation stage.

[0143] In one embodiment, a buck post-regulation stage includes four power switches; a flying capacitor; an output inductor; an output capacitor; and sensing circuitry for a controller.

[0144] Figure 8 The diagram shows a simulation test bench for the capacitive RWPT system analyzed in the present invention that has been constructed in the PSIM platform (PowerSim Corporation - PSIM is an electronic circuit simulation software package designed specifically for power electronics and motor drive simulation). The input voltage is 25V, the dielectric mutual capacitance C M = 14pF, the resonant frequency is f0 = 3MHz. The resonators used for the transmitter and receiver have been chosen to be L P =20.8μH、C P =120pF and L S =21.65μH、C S =130pF. The output stage includes the load resistor R Load =10Ω, output capacitor C Load =90μF, output inductor L = 10μH and flying capacitor C fly =10μF. The switching frequency of the post regulator is f SW is 250kHz, and the target output power is 40W, with a constant load voltage of V Load = 20 V. The overall parameters and values ​​of the test bench are summarized in Table I.

[0145] Table I - Simulation test bench values ​​and parameters under nominal operation

[0146]

[0147] Figure 9a and 9b The simulation results of the current and voltage of the transmitter and receiver are shown respectively. Figure 9a It can be seen that the voltage V P Switches between -25 and 25 V. A sinusoidal voltage V CP The peak value is 1.2kV, where V P With V CP The phase difference is about 90° as expected.

[0148] Figure 9b shows the relative V CP Receiver waveform. It can be seen that the sinusoidal voltage V CS Hysteresis V CP About 90°. In addition, the voltage V SSwitching between -88 and 88 V, this means that the rectified voltage (i.e., the input voltage of the multi-stage buck) is 88 V. Moreover, given the target load condition, the duty cycle of the post regulator is d = 0.225, i.e., V Load = 20 V, which is in good agreement with the theoretical predictions in (6), (8), and (14). Assuming the efficiency of the simulation test bench is 100%, and by using expressions (1) and (3), the load current is found to be I Load =2A, which is also in good agreement with the target load specification.

[0149] Fig.10a shows a simulation test bench, where it is assumed that V CP is a constant (1.2kV peak), C M , L S and C S has been set according to Table I, and based on the expression in (7), the equivalent reflected impedance is Z O =160.3Ω.

[0150] Fig.10b The simulation results of the PRU first harmonic of voltage and current are shown. It can be seen that the current I S1 The switching range is between -0.75 and 0.75 A, which is consistent with theoretical predictions and end-to-end simulation results ( Fig.10b ) is very consistent. The primary harmonic voltage V S1 The peak value is 112V, which is consistent with Fig.10b Considering the rms values ​​obtained by the behavioral model, it can be observed that the equivalent output power is 40W as the target.

[0151] Figures 11a-11c The modification in the behavioral model test bench is shown. The coupling capacitor C M The continuously variable capacitor model ( Fig.11b ) is replaced, and the reflected impedance Z O The continuously variable resistor model ( Fig.11c ) has been replaced. An approach to modeling continuous time elements has been adopted based on 0. By doing so, the behavioral model of the PRU is optimized for C M The dynamic changes of Z are further analyzed and adjusted accordingly. O .

[0152] A first moderate change has been performed by changing the initial coupling capacitance from 14pF to 20pF (i.e., better coupling), which means that Z O It has been adjusted from 160.3Ω to 308Ω, or in terms of the duty cycle of the post regulator, from d=0.225 to d=0.16.

[0153] Figure 12a-12bThe results for the compensated system and the uncompensated system are shown. It can be seen that after the change, for the compensated system ( Fig.12a ), the current drops from 0.75A to 0.5A, and the voltage increases to 157V, while the overall output power remains at 40W. On the other hand, for the uncompensated system ( Figure 12b ), it can be seen that the current and voltage increase to 0.93A and 150V respectively. More importantly, the output power increases to 70W, which means that the overall system specifications are not obtained.

[0154] C M Changing from 14pF to 8pF (i.e., worse coupling) translates into moving Z O Adjusted to 49Ω and d = 0.4. a shows that after the transition due to the medium change, the tuned system maintains 40W operation, with the current and voltage stabilized at 1.2A and 61V, respectively. b shows that for the given medium change, the output power of the untuned system drops significantly to 15W.

[0155] To further highlight the advantages of the HML buck converter as a post-regulation stage, a more thorough comparison of the buck converter with the multi-level buck converter over a wide range of coupling capacitances is performed given the above operating conditions, e.g. Fig.14 As shown in . The losses of the two topologies are estimated at different duty cycles. It can be seen that for a given RWPT system, under very weak coupling (C M <6pF), conventional buck converters have reasonable efficiencies of over 91%. However, as the operating point moves toward the strongly coupled region (C M >14pF), the efficiency of the buck converter drops below 80%, while the efficiency of the HML buck converter drops to less than C M ≈40pF maintains efficiency above 80%.

[0156] It should be noted that the blocking voltage of the selected switches for both converters is V ds =100V. Therefore, in practice, for a given RWPT system, regardless of the efficiency criteria, the conversion range of the buck converter is limited to d = 0.2, while the duty cycle of the HML buck may be pushed to 0.1. It should be further emphasized that by compromising the operating range so that 0.35≤d≤0.9, the switch of the buck converter can be operated with a lower blocking voltage V ds = 60V optimization, resulting in better efficiency (similar to HML buck type), such as Fig.14 As shown by the dotted line in .

[0157] Fig.14The conversion range of the series capacitor (SC) buck converter is also depicted to illustrate more design considerations for the post regulator in WPT. For simplicity, the parameters of the SC buck are the same as the previous converter, and by using the expression in (5), the duty cycle of the SC buck can be expressed as follows

[0158]

[0159] Although the maximum duty cycle of the SC buck converter is limited to 50%, it can be seen that if the system is in C M >15pF while maintaining a significantly wider operating range, then the SC buck converter would be a better choice for this post-regulation task.

[0160] A first set of experimental validation has been performed by characterizing the operating range and power conversion efficiency of the post-regulation stage. Fig.15a Efficiency measurements as a function of load current are shown for the HML buck under nominal conditions, ie input voltage of 88 V and load voltage of 20 V. It can be seen that the efficiency is above 96% over a wide range of operating points. Fig.15b The loss breakdown of the post regulator at various input voltages is shown. It can be seen that as the input voltage increases, the switching losses become dominant, which means that for the case of a conventional buck converter, the switching losses will be higher, further limiting the mid-range misalignment.

[0161] Fig.16a The waveforms of the resonant WPT system are shown. A 40W load output power has been examined, with a misalignment of 75mm, which translates to ~14pF, making the transmitter's resonant current I P is regulated to 2.5A peak, and the voltage V P Switches between -35 and 35 V. The rectifier voltage V on the receiver side S Switches between -90 and 90 V, while the current I S The peak value of 1 A is obtained. Although the rectifier behavior is slightly imperfect due to parasitic capacitances, the experimental results agree well with the theoretical predictions in section V.

[0162] Fig.16b The main waveforms of the HML buck in steady state operation are shown. It can be observed that the load voltage is 20V, the effective switching frequency is ~500kHz, and the effective duty cycle is 22.4% (half the switch node duty cycle).

[0163] Figures 17a-17dExperimental measurements are shown for a moderate boost, ie, from 75 mm misalignment to fully aligned coupling, which translates into a coupling change of 14 pF to 20 pF (a boost converter is a DC-DC power converter that steps up the voltage from its input to its output). Fig.17a The main PRU waveform without the post regulator is depicted. It can be seen that after the coupler change, V S and I S The load power is increased to a peak of 115V and 1.5A respectively. This results in a load output power of ~85W, approximately twice the target load power. Fig.17b The main waveform of the PRU with a post-regulation stage is shown. S There is not much change, but it can be seen that I S The drop was 20% and the load power was well regulated to 40W. Fig.17c shows a zoomed-in view of the transmitter and receiver main waveforms in steady state with a post regulator, and Fig.17d The HML post regulator main waveform is shown, where the effective duty cycle is 16.66%.

[0164] Figures 18a-18d Experimental measurements of a capacitive RWPT system for a moderate change in voltage drop (14pF to 8pF) are shown. The system was also examined for a voltage drop change from 75mm to 150mm (14pF to 8pF). Fig.18a shows that without post regulation, the load power drops by a factor of two to the 20W range, whereas for the regulated system ( Fig.18b ), the target load power is maintained. Fig.18c Figure 1 depicts a zoomed-in view of the main waveforms of the transmitter and receiver using the post regulator. It can be seen that due to the low coupling at this misalignment (which adds more losses to the end-to-end system), the transmitter voltage V P increases slightly to 40V peak, while the receiver voltage V S Down to 55 V, ie, a duty cycle of 37%, which is in good agreement with theoretical predictions. Fig.18d The post regulator main waveform is shown.

[0165] Although some embodiments of the invention have been described by way of illustration, it is obvious that the invention is susceptible to numerous modifications, variations and adaptations, and to the use of numerous equivalents or alternative solutions within the purview of those skilled in the art, without departing from the scope of the claims.

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Claims

1. A power regulation method for a power receiving unit (PRU) of a RWPT system, comprising: a) connecting a load to the PRU via an ML post-regulation stage; b) determining target / predicted values ​​of voltage and current of a power transmitting unit (PTU) of the RWPT system; c) determining the wireless medium characteristics and resonant frequency of the RWPT system; d) Generate an overall system model by using the first harmonic approximation (FHA); e) determine the expected output power; f) Calculate the voltage V of the first harmonic S1 ; g) Use V S1 Calculate the equivalent reflected impedance Z of the load O ; as well as h) Using the predicted value of the efficiency η, the conversion ratio M(D) and the calculated equivalent reflected impedance Z O Calculate the duty cycle d.

2. The method of claim 1 , further comprising checking the duty cycle range and post regulator performance for the corner operating point of the RWPT system.

3. The method of claim 1, wherein the ML post-regulation stage is integrated into the PRU. 4 . The method of claim 1 , wherein the ML post-regulation stage performs a step-up conversion ratio, a step-down conversion ratio, or both a step-up conversion ratio and a step-down conversion ratio.

5. The method of claim 1, wherein the ML post-regulation stage is implemented in a hybrid multi-level (HML) topology with a high conversion ratio.

6. The method of claim 1, further comprising performing wide impedance matching for the WPT system using HML post-regulation.

7. The method of claim 5, wherein the HML post regulator is cascaded with the AC-DC rectifier stage.

8. The method of claim 1, wherein a power transmission unit (PTU) is modeled as a current controlled module.

9. The method of claim 1, further comprising operating under optimal operating conditions.

10. The method of claim 1, wherein the ML post-conditioning stage is designed according to specific target wireless operating conditions.

11. The method of claim 1 , wherein the PTU comprises: a) DC-DC pre-regulation stage; b) DC-AC power inverter; c) a transmitter resonator, resonating at the same frequency as the resonator of the PRU; d) power transmission elements; as well as e) A controller, configured to compensate for the misalignment between the PTU and the PRU.

12. The method of claim 1, wherein the PRU comprises: a) Pick up components; b) a receiver resonator, resonating at the same frequency as the resonator of the PTU; c) AC-DC rectifier; d) DC-DC hybrid post-regulation stage; as well as e) A controller, configured to compensate for the misalignment between the PTU and the PRU.

13. The method of claim 1, wherein power regulation is performed for several PRUs simultaneously, wherein each PRU comprises a corresponding HML post-regulator.

14. The method of claim 3, wherein the PRU comprises a high conversion HML buck type post regulation stage.

15. The method of claim 14, wherein the buck post-regulation stage comprises: a) Four power switches; b) Flying capacitor; c) Output inductor; d) Output capacitor; e) Sensing circuitry for the controller.

16. A power receiving unit (PRU) for power regulation of a RWPT system, comprising: a) an ML post-regulator stage, via which the load is connected to the PRU; b) A controller circuit suitable for: c) Determine target / predicted values ​​of voltage and current of the power transmission unit (PTU) of the RWPT system; d) Determine the wireless medium characteristics and resonant frequency of the RWPT system; e) Generate an overall system model by using the first harmonic approximation (FHA); f) determine the expected output power; g) Calculate the voltage V of the first harmonic S1 ; h) Use V S1 Calculate the equivalent reflected impedance Z of the load O ; i) Using the predicted value of efficiency η, the conversion ratio M(D) and the calculated equivalent reflected impedance Z O Calculate the duty cycle d.

17. The power regulated PRU of claim 16, wherein the controller is adapted to check the duty cycle range and post regulator performance for the corner operating point of the RWPT system.

18. The power regulated PRU of claim 16, wherein the ML post-regulation stage is integrated into the PRU.

19. The power regulated PRU of claim 16, wherein the ML post-regulation stage performs a step-up conversion ratio, a step-down conversion ratio, or both a step-up conversion ratio and a step-down conversion ratio.

20. The power regulated PRU of claim 16, wherein the ML post-regulation stage is implemented in a hybrid multi-level (HML) topology with a high conversion ratio.

21. The power regulated PRU of claim 16, wherein HML post regulation is used to perform wide impedance matching for the WPT system.

22. The power regulated PRU of claim 16, wherein the HML post regulator is cascaded with the AC-DC rectifier stage.

23. The power regulated PRU of claim 16, wherein a power transmission unit (PTU) is modeled as a current controlled module.

24. The power regulated PRU of claim 16, wherein the controller circuit is tuned to operate under optimal operating conditions.

25. The power regulated PRU of claim 16, wherein the ML post regulation stage is designed according to specific target radio operating conditions.

26. The power regulated PRU of claim 16, wherein the PTU comprises: a) DC-DC pre-regulation stage; b) DC-AC power inverter; c) a transmitter resonator, resonating at the same frequency as the resonator of the PRU; d) power transmission elements; as well as e) Controller, used to compensate for the misalignment between PTU and PRU.

27. The power regulated PRU of claim 16, wherein the PRU comprises: a) Pick up components; b) a receiver resonator, resonating at the same frequency as the resonator of the PTU; c) AC-DC rectifier; d) DC-DC hybrid post-regulation stage; as well as e) Controller, used to compensate for the misalignment between PTU and PRU.

28. The power regulated PRU of claim 16, wherein power regulation is performed for several PRUs simultaneously, wherein each PRU comprises a corresponding HML post-regulator.

29. The power regulated PRU of claim 16, wherein the PRU comprises a high conversion HML buck type post regulation stage.

30. The power regulated PRU of claim 16, wherein the buck-type post-regulation stage comprises: a) Four power switches; b) Flying capacitor; c) Output inductor; d) Output capacitor; e) Sensing circuitry for the controller.

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