Accurate design method for LC resonant cavity parameters required by rectifier discontinuous mode correction of wireless charging system

Abstract

The invention provides an accurate design method for LC resonant cavity parameters required by correction of a discontinuous mode of a rectifier of a wireless charging system, an accurate analytical expression for LC resonant cavity parameter design is provided, and an accurate design value of the LC resonant cavity parameters can be quickly obtained only by substituting related parameters into the analytical expression; according to the LC resonant cavity designed by the method, a double-LCC compensation system of a light-load CCM and a heavy-load DCM can be corrected into a full-load-range CCM system, and the constant-current output characteristic and the low rectifier input current peak value of the system in the full-load range are ensured. The method is suitable for induction type wireless charging systems of automatic guided vehicles, electric vehicles and the like.

Description

Technical Field

[0001] The invention relates to a precise design method for LC resonant cavity parameters required for discontinuous mode correction of a wireless charging system rectifier, is applicable to inductive wireless charging systems such as automatic guided vehicles and electric vehicles, and belongs to the field of power conversion. Background Art

[0002] Inductive Power Transfer (IPT) technology is one of the main ways to achieve wireless charging and is widely used in wireless charging of systems such as automatic guided vehicles and electric vehicles. An inductive power transfer wireless charging system generally includes an input DC source, a high-frequency inverter, a contactless transformer, a compensation network, a rectifier, a DC filter, and a load. As the load size changes, the rectifier on the secondary side of the system may operate in continuous conduction mode (CCM) or discontinuous conduction mode (DCM). For example, in an inductive wireless charging system with bilateral LCC compensation, the rectifier operates in CCM when light loads and in DCM when heavy loads. However, the existence of DCM will cause several problems: First, it will cause the constant voltage or constant current output characteristics of the system to be destroyed. Before the prototype is manufactured, the system is generally analyzed and designed by the fundamental harmonic approximation (FHA) in the frequency domain, so that the system has a constant voltage or constant current output characteristic at the resonant frequency point, while DCM will cause the system output to deviate from the expected constant voltage value or constant current value. Second, it causes the rectifier input current (the DC filter is C filtering) or voltage (the DC filter is LC filtering) to become more distorted and the peak value to become larger, which leads to increased rectifier losses. Third, the DCM system requires complex rectifier working mode identification.

[0003] In order to avoid the above problems caused by rectifier DCM, Professor Xu Dianguo of Harbin Institute of Technology "Yousu Yao, Yijie Wang, Xiaosheng Liu, Fanfan Lin, and Dianguo Xu. A Novel Parameter Tuning Method for a Double-Sided LCL Compensated WPT System With Better Comprehensive Performance." IEEE Transactions on Power Electronics 33(10):8525–36." designed a wireless charging system with full load range CCM through a new tuning method, so that the rectifier always works in CCM. However, this method requires solving cubic equations and judging the validity of multiple solutions. The design process is complicated and difficult to implement. Therefore, Professor Qu Xiaohui of Southeast University "Xiaohui Qu, Yanyan Jing, Jing Lian, Siu Chung Wong, and Chi K. Tse. Design for continuous-current-mode operation of inductive-power-transfer converters with load-independent output," IET Power Electron., vol.12, no.10, pp.2458–2465, 2019” A rectifier DCM correction method is proposed, that is, an LC resonant cavity is connected in series in front of the rectifier of the wireless charging system to expand the system CCM load range (i.e., reduce the DCM load range); however, the author did not study the relationship between the LC resonant cavity parameters and the CCM load range, so the LC resonant cavity parameters cannot be accurately designed with a given CCM load range as the target, resulting in the LC resonant cavity parameters may be too large or too small. Therefore, it is of great significance to propose a method for accurately designing the LC resonant cavity parameters. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the above-mentioned existing DCM correction method and provide a precise design method for the LC resonant cavity parameters required for DCM correction of the rectifier of a wireless charging system.

[0005] The specific technical solutions of the present invention are as follows:

[0006] A precise design method for LC resonant cavity parameters required for discontinuous mode correction of a wireless charging system rectifier, characterized in that: the applicable wireless charging system comprises an input DC source, a high-frequency inverter, a contactless transformer, a bilateral LCC compensation network, an LC resonant cavity, a rectifier, a DC filter and a load; the input DC source is a DC voltage source U in The high-frequency inverter is a full-bridge inverter composed of four metal oxide field effect transistors (MOSFETs); the contactless transformer is composed of a primary winding and a secondary winding, there is no physical contact between the primary winding and the secondary winding, and the inductance of the primary winding and the secondary winding are L p and L s , the coupling coefficient between the primary winding and the secondary winding is k; the primary side of the bilateral LCC compensation network consists of an inductor L f,p and two capacitors C f,p and C p The secondary side consists of an inductor L f,s and two capacitors C f,s and C s The inductance and capacitance of the compensation network meet Where f0 is the resonant frequency; the rectifier is a full-bridge rectifier composed of four power diodes, and the conduction voltage drop of each diode is U D The DC filter consists of a capacitor C o The load resistance is R o , whose maximum value is R o,max The LC resonant cavity is an inductor L connected in series before the rectifier. F and a capacitor C F ;

[0007] The method for accurately designing the parameters of the LC resonant cavity is as follows: Substituting the relevant parameters into Calculate the inductance parameter L of the LC resonant cavity F , L F Substitute C F =1 / [(2πf0) 2 L F ] Calculate the capacitance parameter C of the LC resonant cavity F Through the precise design of the parameters of the LC resonant cavity, the rectifier of the bilateral LCC compensation wireless charging system is o =R o,max ), that is, it is at the critical point between CCM and DCM, thereby correcting the rectifier's operating mode from "light load CCM and heavy load DCM" to "full load CCM".

[0008] Furthermore, when the forward voltage drop of the diode is U DWhen U is small, D can be ignored, then the inductance parameter L of the LC resonant cavity is F The calculation formula is simplified to L F =R o,max / (π 2 f0)-L f,s , capacitor C F The parameter calculation formula remains unchanged.

[0009] Compared with the prior art, the present invention has the following beneficial effects:

[0010] 1. The present invention provides a precise design method for the LC resonant cavity parameters required for discontinuous mode correction of a wireless charging system rectifier. It does not require solving high-order equations or judging the validity of multiple solutions. It only requires substituting relevant parameters into formula calculations to quickly obtain precise design values ​​of the LC resonant cavity parameters. The design process is simple and easy to implement.

[0011] 2. The present invention provides a precise design method for the LC resonant cavity parameters required for discontinuous mode correction of the rectifier of a wireless charging system, provides a precise analytical expression for the LC resonant cavity parameters, does not cause the LC resonant cavity parameters to be too large or too small, and enables the rectifier to operate in CRM when fully loaded, thereby ensuring that the rectifier is in CCM within the full load range, thereby ensuring the constant current output characteristics of the bilateral LCC compensation system within the full load range and a lower rectifier input current peak. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Attached Figure 1 It is a schematic diagram of the bilateral LCC compensation inductive wireless charging system of the present invention.

[0013] Attached Figure 2 A secondary side equivalent circuit of a bilateral LCC compensated inductive wireless charging system of the present invention.

[0014] Attached Figure 3 (ac) are three working modes of the rectifier of the bilateral LCC compensation inductive wireless charging system of the present invention, Figure 3 a is the rectifier CCM, Figure 3 b is the rectifier CRM, attached Figure 3 c is the rectifier DCM.

[0015] Attached Figure 4 (ac) is the experimental waveform of the rectifier input terminal before DCM correction in the embodiment of the present invention. Figure 4 a is R before correction o =6Ω when the rectifier input terminal experimental waveform; Attachment Figure 4 b is R before correction o =12Ω when the rectifier input terminal experimental waveform; Attachment Figure 4 c is R before correction o=25Ω when the rectifier input terminal experimental waveform.

[0016] Attached Figure 5 (ac) is the experimental waveform of the rectifier input end after the DCM of the embodiment of the present invention is corrected by the LC resonant cavity. Figure 5 a is the corrected R o =6Ω when the rectifier input terminal experimental waveform; Attachment Figure 5 b is the corrected R o =12Ω when the rectifier input terminal experimental waveform; Attachment Figure 5 c is the corrected R o =25Ω when the rectifier input terminal experimental waveform.

[0017] Attached Figure 6 is the system output DC current before and after correction.

[0018] Attached Figure 7 is the peak value of the rectifier input current before and after correction. DETAILED DESCRIPTION

[0019] The accompanying drawings disclose a specific embodiment of the present invention in a non-limiting manner. Considering the forward voltage drop U of the diode D , the present invention is further described as follows in conjunction with the accompanying drawings.

[0020] Example:

[0021] The present invention provides a method for accurately designing LC resonant cavity parameters for discontinuous mode correction of a rectifier, which is applicable to an inductive wireless charging system. The system schematic diagram is shown in the attached figure. Figure 1 As shown, it includes 101 DC input voltage source U in , 102 high frequency full-bridge inverter, 103 primary side LCC compensation network, 104 contactless transformer, 105 secondary side LCC compensation network, 106 LC resonant cavity, 107 full-bridge rectifier, 108 DC filter, 109 load resistor.

[0022] The secondary side equivalent circuit of the system is shown in the attached figure. Figure 2 As shown, C F Moved to L f,s Previously, because the capacitor harmonic impedance was much smaller than the inductor harmonic impedance, the square wave voltage U ab The harmonic components are almost all distributed in the inductor L f,s and L F So the voltage U QS Approximately sinusoidal.

[0023] The waveforms of the rectifier in three working modes are shown in the attached figure. Figure 3 (ac) as shown, where the current i ab The time from negative to zero is θ a , square wave voltage u abThe magnitude of the output U o With rectifier conduction voltage drop 2U D The sum of U o +2U D . When u Qs (θ a )>U o +2U D , the rectifier works in CCM mode, at this time θ a >32.48°, as attached Figure 3 a; on the contrary, when u Qs (θ a ) o +2U D , the rectifier works in DCM mode, at this time θ a <32.48°, as attached Figure 3 c; when u Qs (θ a )=U o +2U D , the rectifier works in CRM, which is the critical point between CCM and DCM. At this time, θ a =32.48°, as shown in the attached Figure 3 As shown in b.

[0024] Since the bilateral LCC compensation system has the characteristics of light load CCM and heavy load DCM at the resonant frequency point, in order to make the system CCM in the full load range, the system must be at the heaviest load (full load R o =R o,max ) CRM. Substitute the relevant parameters into Calculate the inductance parameter L of the LC resonant cavity F ; L F Substitute C F =1 / [(2πf0) 2 L F ] Calculate the capacitance parameter C of the LC resonant cavity F Furthermore, when the forward voltage drop of the diode is U D When U is small, D can be ignored, then the inductance parameter L of the LC resonant cavity is F The calculation formula is simplified to L F =R o,max / (π 2 f0)-L f,s , C F The calculation formula remains unchanged.

[0025] Application examples:

[0026] In order to verify the accuracy of the precise design method of the LC resonant cavity parameters required for discontinuous mode correction of the rectifier of a wireless charging system of the present invention, a prototype was made for experimental verification.​

[0027] The parameters of the bilateral LCC compensation prototype system before DCM correction are: p =57.85μH, L s =57.77μH, L f,p =35.44μH, L s =15.64μH,C p =180.65nF, C s =94.20nF, C f,p =111.24nF, C f,s =254.25nF, k=0.3, f0=80kHz, U D =0.54V, U in =24V, I o =3A, R o,max =25Ω. Before DCM correction, the waveform at the rectifier input is as shown in the attached figure. Figure 4 (ac) as shown. Figure 4 a is the light load CCM waveform (R o =6Ω); Figure 4 b is the medium load CRM waveform (R o =12Ω), then θ a =35.71°, which is very close to the theoretical value of 32.48°. The small error comes from the voltage u QS The sine approximation and neglect of the commutation time of the rectifier are taken into consideration. Figure 4 c is the full-load DCM waveform (R o =25Ω).

[0028] Apply the technical solution of the present invention and substitute the relevant parameters into L F and C F After calculating the formula, we get L F =16.51μH, C F =239.76nF, the actual measured value of the prototype is L F =16.47μH,C F =240.31nF. The waveform at the input of the rectifier is shown in the attached figure. Figure 5 (ac) as shown. Figure 5 a is the light load CCM waveform (R o =6Ω); Figure 5 b is the medium load CCM waveform (R o =12Ω); Figure 5 c is the fully loaded CRM waveform (R o =25Ω), then θ a =36.86°, which is very close to the theoretical value of 32.48°. The small error comes from the voltage u QSFactors such as the sinusoidal approximation and the neglect of the rectifier commutation time.

[0029] It can be seen that the method of the present invention successfully realizes the correction of a bilateral LCC compensation system with light load CCM and heavy load DCM to a full load CRM system (ie, a full load range CCM system).

[0030] The system output DC current before and after correction is shown in the attached figure. Figure 6 As shown, it can be seen that: relative to the ideal constant DC 3A, the full-load current deviation (maximum deviation) is reduced from 0.36A before correction to 0.18A, that is, the corrected full-load CCM system has better constant current output characteristics.

[0031] The peak values ​​of the rectifier input current before and after correction are shown in the attached figure. Figure 7 As shown, the maximum peak current before the system correction is 5.70A, and the maximum peak current after the system correction is 4.99A. It can be seen that the rectifier input current peak of the full-load CCM system after correction is reduced by 12.46%.

[0032] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for accurately designing the LC resonant cavity parameters required for discontinuous mode correction of a wireless charging system rectifier, characterized in that: The applicable wireless charging system includes an input DC source, a high frequency inverter, a contactless transformer, a bilateral LCC compensation network, an LC resonant cavity, a rectifier, a DC filter and a load; the input DC source is a DC voltage source U in ; The high-frequency inverter is a full-bridge inverter composed of four metal oxide field effect transistors (MOSFET); The contactless transformer is composed of a primary winding and a secondary winding. There is no physical contact between the primary winding and the secondary winding. The inductances of the primary winding and the secondary winding are L p and L s , the coupling coefficient between the primary winding and the secondary winding is k; the primary side of the bilateral LCC compensation network consists of an inductor L f,p and two capacitors C f,p and C p The secondary side consists of an inductor L f,s and two capacitors C f,s and C s The inductance and capacitance of the compensation network meet Where f0 is the resonant frequency; the rectifier is a full-bridge rectifier composed of four power diodes, and the conduction voltage drop of each diode is U D The DC filter is composed of capacitor C o The load resistance is R o , whose maximum value is R o,max The LC resonant cavity is an inductor L connected in series before the rectifier. F and a capacitor C F ; The precise design method of the LC resonant cavity parameters is as follows: Substitute the relevant parameters into Calculate the inductance parameter L of the LC resonant cavity F , L F Substitute C F =1 / [(2πf0) 2 L F ] Calculate the capacitance parameter C of the LC resonant cavity F .

2. The method for accurately designing LC resonant cavity parameters according to claim 1, characterized in that: Through the precise design of the parameters of the LC resonant cavity, the rectifier of the bilateral LCC compensation wireless charging system is o =R o,max ), that is, it is at the critical point between CCM and DCM, thereby correcting the rectifier's operating mode from "light load CCM and heavy load DCM" to "full load CCM", thereby ensuring the constant current output characteristics of the dual LCC compensation system within the full load range and a lower rectifier input current peak.

3. The method for accurately designing LC resonant cavity parameters according to claim 1, characterized in that: There is no need to solve high-order equations or judge the validity of multiple solutions. The precise design values ​​of the LC resonant cavity parameters can be quickly obtained by simply substituting relevant parameters into the formula. The design process is simple and easy to implement.

4. The method for accurately designing LC resonant cavity parameters according to claim 1, characterized in that: An accurate analytical expression for the LC resonant cavity parameters is provided, which will not cause the LC resonant cavity parameters to be too large or too small.

5. The method for accurately designing LC resonant cavity parameters as claimed in claim 1, further comprising: when the on-state voltage drop U D When U is small, D can be ignored, then the inductance parameter L of the LC resonant cavity is F The calculation formula is simplified to L F =R o,max / (π 2 f0)-L f,s , capacitor C F The parameter calculation formula remains unchanged.

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