Calculation method for controllable rectification equivalent impedance of wireless charging system

Abstract

The invention provides a controllable rectification equivalent impedance calculation method for a wireless charging system, which can realize high-precision controllable rectification equivalent modeling. Comprising the following steps: constructing a controllable rectification input voltage uab equation based on a controllable rectification system, and obtaining a fundamental wave expression of the controllable rectification input voltage uab through Fourier transform; constructing a controllable rectification input current equation, and obtaining a fundamental wave expression of the controllable rectification input current through Fourier transform; and obtaining the equivalent load impedance of the controllable rectification according to the fundamental wave expression of the controllable rectification input voltage uab and the fundamental wave expression of the controllable rectification input current.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless charging, and in particular to a method for calculating a controllable rectifier equivalent impedance of a wireless charging system. Background Art

[0002] Wireless power transmission technology has achieved electrical isolation between the power supply end and the load end, and does not require the use of wires for connection, which effectively improves the safety and flexibility of power supply and has received more and more attention. In the wireless charging system of electric vehicles, in order to achieve a wide range of voltage regulation and respond to the load voltage requirements faster, the system generally uses controlled rectification on the secondary side to convert the system from AC to controllable DC to respond to the system load voltage requirements. Therefore, the construction of accurate controlled rectification equivalent modeling has become an urgent problem to be solved in the field of wireless charging of electric vehicles. Patent CN107979298A discloses an uncontrolled rectification equivalent load method, but does not involve an equivalent resistance calculation method for controlled rectification. Patent CN113472089A discloses a controlled rectification method, but the equivalent method adopted is based on the premise that the rectifier input current is completely regarded as a pure sine wave. In controlled rectification, as the duty cycle of the secondary side changes, the rectifier input current will be greatly distorted, and the equivalent resistance modeling will become inaccurate, which will also affect the characteristics and design of the wireless charging system.

[0003] Based on this, a method is needed to perform high-precision equivalent calculation on the controllable rectifier equivalent load of the wireless charging system. Summary of the invention

[0004] In view of the above problems, the present invention provides a method for calculating the controlled rectifier equivalent impedance of a wireless charging system, which can achieve high-precision controlled rectifier equivalent modeling.

[0005] The present invention adopts the following technical solution: a method for calculating the equivalent impedance of a controlled rectifier of a wireless charging system, characterized in that it comprises the following steps:

[0006] Based on the controlled rectifier system, construct a controlled rectifier input voltage u ab Equation, and through Fourier transform, obtain the controlled rectifier input voltage u ab The fundamental wave expression of

[0007] Construct a controlled rectifier input current equation, and obtain the fundamental wave expression of the controlled rectifier input current through Fourier transform;

[0008] According to the controlled rectifier input voltage u ab The fundamental wave expression of and the fundamental wave expression of the controlled rectifier input current are used to obtain the equivalent load impedance of the controlled rectifier.

[0009] Further, the controllable rectification system comprises a controllable rectification module for rectifying output;

[0010] A controllable rectifier control module, connected to the controllable rectifier module, and used to detect the zero-crossing information of the controllable rectifier input current flowing into the controllable rectifier module, so as to provide a rectifier control signal to the controllable rectifier module;

[0011] Further, the controllable rectifier module includes at least two controllable switch tubes. When the controllable rectifier control module detects that the controllable rectifier input current crosses a zero point in a positive direction, one of the controllable switch tubes among the at least two switch tubes is controlled to be turned on; when the controllable rectifier control module detects that the controllable rectifier input current crosses a zero point in a negative direction, another of the at least two switch tubes is controlled to be turned on;

[0012] Furthermore, the controllable rectifier input voltage u ab The equation is:

[0013]

[0014] The controllable rectifier input voltage u ab The fundamental wave expression is:

[0015]

[0016] Among them, U bat is the load voltage, a is the controlled rectifier conduction angle, and ω is the angular frequency;

[0017] Furthermore, the controllable rectifier input current equation is:

[0018]

[0019] Among them, U C is the voltage amplitude before the input inductor of the rectifier bridge, θ is the angle variable, L f2 Input inductance for the rectifier bridge;

[0020] Furthermore, the fundamental wave expression of the controllable rectifier input current is:

[0021]

[0022] in,

[0023]

[0024] M=aπ-2π 2 +4-4 cos a

[0025] N=πtanθ(2π-a)-4 sin a

[0026] a 1 and b 1 are Fourier coefficients; R L For load;

[0027] Furthermore, the load current I is obtained by the formula 0 , the expression is:

[0028]

[0029] Combination formula: 2U C cosθ=(2π-a)U bat

[0030] Get the controllable rectifier conduction angle a and load R L The relationship between them is:

[0031]

[0032] Furthermore, by combining the controllable rectifier input voltage u ab The fundamental wave expression of and the fundamental wave expression of the controlled rectifier input current, the equivalent load impedance of the controlled rectifier is obtained as follows:

[0033]

[0034] in,

[0035]

[0036] R represents the real part of the equivalent load impedance, and X represents the imaginary part of the equivalent load impedance.

[0037] The beneficial effect of the present invention is that the established equivalent load impedance model of the controllable rectification is not affected by the current distortion on the input side, and can accurately reflect the actual load characteristics in the controlled rectification, thereby ensuring the characteristics and design of the wireless charging system, and having good use value. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The circuit principle of the controllable rectifier system in the embodiment of the present invention;

[0039] Figure 2 A schematic diagram of a controllable rectifier waveform in an embodiment of the present invention;

[0040] Figure 3 Schematic diagram of the secondary-side controlled rectification equivalent in an embodiment of the present invention;

[0041] Figure 4 is a flow chart of the present invention;

[0042] Figure 5This is a comparison diagram of equivalent loads between the present invention and the prior art patent. DETAILED DESCRIPTION

[0043] The present invention is further described below in conjunction with the accompanying drawings and embodiments. It should be noted that the following description is only for explaining the present invention and does not limit its content.

[0044] like Figure 1 to Figure 5 As shown, a method for calculating the controllable rectifier equivalent impedance of a wireless charging system of the present invention comprises the following steps:

[0045] Based on the time domain relationship of the secondary controlled rectifier in the controlled rectifier system, the controlled rectifier input voltage u is constructed. ab Equation, and through Fourier transform, obtain the controlled rectifier input voltage u ab The fundamental wave expression of

[0046] Specifically, the controllable rectifier input voltage u ab The equation is:

[0047]

[0048] Controllable rectifier input voltage u ab The fundamental wave expression is:

[0049]

[0050] Among them, U bat is the load voltage, a is the controllable rectifier conduction angle of the controllable switch tubes M1 and M2, and ω is the angular frequency;

[0051] Based on the voltage relationship of the controlled rectifier system, the controlled rectifier input current equation is constructed, and the fundamental wave expression of the controlled rectifier input current is obtained through Fourier transform;

[0052] Specifically, according to Figure 3 The voltage relationship of the controlled rectifier system is obtained Figure 2 The controlled rectifier input current under the control waveform, that is, the controlled rectifier input current equation is:

[0053]

[0054] Among them, U C The voltage before the input inductance of the rectifier bridge, that is, the capacitance C f2 Voltage amplitude;

[0055] θ is the angle variable, L f2 Input inductance for the rectifier bridge;

[0056] The fundamental wave expression of the controlled rectifier input current is:

[0057]

[0058] in,

[0059]

[0060] M=aπ-2π 2 +4-4 cos a

[0061] N=πtanθ(2π-a)-4 sin a

[0062] a 1 and b 1 are Fourier coefficients; R L For load;

[0063] According to the rectification characteristic relationship, Fourier transform is obtained Figure 3 Medium load current I 0 , the expression is:

[0064]

[0065] Combination formula: 2U C cosθ=(2π-a)U bat

[0066] Get the controllable rectifier conduction angle a and load R L The relationship between them is:

[0067]

[0068] According to the controlled rectifier input voltage u ab The fundamental wave expression of and the fundamental wave expression of the controlled rectifier input current are used to obtain the equivalent load impedance of the controlled rectifier;

[0069] Specifically, the equivalent load impedance of the controlled rectifier is expressed as:

[0070]

[0071] in,

[0072]

[0073] R represents the real part of the equivalent load impedance, and X represents the imaginary part of the equivalent load impedance.

[0074] like Figure 1 As shown, the controlled rectifier system in the embodiment of the present invention includes a DC power supply 1, a high-frequency inverter 2, a primary LCC compensation module 3, a primary-secondary coil 4, a secondary LCC compensation module 5, a controlled rectifier module 6, a controlled rectifier control module 7, and a load module 8.

[0075] The high frequency inverter 2 is composed of switch tubes S1, S2, S3, and S4, and forms two bridge arms;

[0076] The primary LCC compensation module 3 includes an inductor L f1 , capacitor C f1 , capacitor C 1 ;

[0077] The primary and secondary coils 4 include a primary coil L 1 , secondary coil L 2 ;

[0078] The secondary side LCC compensation module 5 includes an inductor L f2 , capacitor C f2 , capacitor C 2 ;

[0079] The controllable rectifier module 6 is used for rectifying the output, and is composed of two bridge arms formed by connecting diodes Q1, Q2 and controllable switch tubes M1, M2 in series respectively;

[0080] The controllable rectifier control module 7 is connected to the controllable rectifier module 6 and is used to detect the controllable rectifier input current. Zero-crossing point information is used to provide a rectification control signal to the controllable rectification module 6; the controllable rectification control module adopts an existing functional module with current sampling and drive control functions.

[0081] When the controlled rectifier control module detects that the controlled rectifier input current crosses zero in the positive direction, one of the two switch tubes is controlled to be turned on; when the controlled rectifier control module detects that the controlled rectifier input current crosses zero in the negative direction, the other of the two switch tubes is controlled to be turned on; specifically, Figure 2 As shown, when the controlled rectifier input current At the positive zero crossing point, the controllable rectifier control module outputs a control signal PMM_M1 to control the controllable switch tube M1 to conduct, and the conduction angle is a; when the controllable rectifier input current When the negative direction crosses the zero point, the controllable rectifier control module outputs the control signal PMM_M2 to control the controllable switch tube M 2 conduction, the conduction angle is a.

[0082] Figure 3 The equivalent schematic diagram of the secondary side controlled rectifier is shown in Figure 1. It converts the primary side into an equivalent AC source on the secondary side. Figure 3 Take the controlled rectifier as an example to perform load equivalence.

[0083] In order to verify the accuracy of the equivalent load impedance model constructed by the present invention, the embodiment of the present invention is compared with the method proposed in the existing patent CN113472089A:

[0084] Figure 5 This is a comparison diagram of equivalent impedance between the present invention and the method proposed in patent CN113472089A, in which the duty cycle D=a / 2π;

[0085] Figure 5 (I) is a comparison diagram of the real part of equivalent impedance, and (II) is a comparison diagram of the imaginary part of equivalent impedance; the proposed method refers to the technical solution of the present invention;

[0086] In the present invention, as the duty cycle increases, the real part of the equivalent impedance increases first and then decreases; as for the imaginary part, as the duty cycle D increases, the imaginary part first increases to zero and then decreases to less than zero, that is, as the duty cycle D increases, the equivalent impedance increases. L First, it is equivalent to a resistor plus an inductor. As the duty cycle D increases, the load R L It is equivalent to a resistor plus a capacitor;

[0087] In patent CN113472089A, as the duty cycle increases, the equivalent impedance is always equivalent to a resistor plus a capacitor.

[0088] The following table 1 is Figure 3 Comparison of the theoretical value of the present invention with the result of the method proposed in patent CN113472089A under equivalent circuit

[0089] Table 1

[0090] Duty cycle D <![CDATA[Simulated θ 1 > <![CDATA[Theoretical θ 1 > <![CDATA[CN:θ 1 ]]> Theory R CN:R Theory X CN:X 0.5 10.124 9.999 0 15.723 16.211 2.772 0 0.55 -3.232 -3.245 -9 15.764 15.428 -0.894 -2.443 0.6 -15.082 -14.712 -18 13.717 13.263 -3.604 -4.309 0.75 -42.569 -42.36 -45 4.426 4.053 -4.036 -4.053

[0091] In Table 1, θ 1 for u 1 and i 2 The phase angle of , a negative number means the voltage leads the current;

[0092] CN represents the results under the equivalent method of patent CN113472089A;

[0093] From θ 1 By comparison, it can be seen that the equivalent value obtained in the present invention is basically consistent with the value obtained by the existing time domain simulation calculation method. It can be seen that the method proposed in the present invention can accurately reflect the actual load characteristics, and with the increase of the controllable duty cycle, the system equivalent impedance changes from inductive to capacitive. The present invention takes into account the influence of current distortion on the rectifier input side, and the equivalent resistance is equivalent to an inductive load or a capacitive load with the controllable rectifier duty cycle, which better reflects the actual situation and has higher accuracy.

[0094] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0095] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for calculating the equivalent impedance of a controlled rectifier of a wireless charging system, characterized in that: The following steps are involved: Based on the controlled rectifier system, construct a controlled rectifier input voltage u ab Equation, and through Fourier transform, obtain the controlled rectifier input voltage u ab The fundamental wave expression of Construct a controlled rectifier input current equation, and obtain the fundamental wave expression of the controlled rectifier input current through Fourier transform; According to the controlled rectifier input voltage u ab The fundamental wave expression of and the fundamental wave expression of the controlled rectifier input current are used to obtain the equivalent load impedance of the controlled rectifier.

2. The method for calculating the controlled rectifier equivalent impedance of a wireless charging system according to claim 1, characterized in that: The controllable rectification system comprises a controllable rectification module for rectifying output; The controllable rectifier control module is connected to the controllable rectifier module and is used to detect the zero-crossing point information of the controllable rectifier input current flowing into the controllable rectifier module so as to provide a rectifier control signal to the controllable rectifier module.

3. The method for calculating the controlled rectifier equivalent impedance of a wireless charging system according to claim 2, characterized in that: The controllable rectifier module includes at least two controllable switch tubes. When the controllable rectifier control module detects that the controllable rectifier input current crosses the zero point in the positive direction, one of the controllable switch tubes among the at least two switch tubes is controlled to be turned on; when the controllable rectifier control module detects that the controllable rectifier input current crosses the zero point in the negative direction, the other of the at least two switch tubes is controlled to be switched on.

4. The method for calculating the controlled rectifier equivalent impedance of a wireless charging system according to claim 1, characterized in that: The controllable rectifier input voltage u ab The equation is: The controllable rectifier input voltage u ab The fundamental wave expression is: Among them, U bat is the load voltage, a is the controlled rectifier conduction angle, and ω is the angular frequency.

5. The method for calculating the controlled rectifier equivalent impedance of a wireless charging system according to claim 4, characterized in that: The controllable rectifier input current equation is: Among them, U C is the voltage amplitude before the input inductor of the rectifier bridge, θ is the angle variable, L f2 Input inductance for the rectifier bridge.

6. A method for calculating the controlled rectifier equivalent impedance of a wireless charging system according to claim 5, characterized in that: The fundamental wave expression of the controllable rectifier input current is: in, M=aπ-2π 2 +4-4thing N=πtanθ(2π-a)-4sina a1 and b1 are Fourier coefficients respectively; R L For load.

7. A method for calculating the controlled rectifier equivalent impedance of a wireless charging system according to claim 6, characterized in that: The load current is obtained by the formula: Combination formula: 2U C cosθ=(2π-a)U bat Get the controllable rectifier conduction angle a and load R L The relationship between them is: Among them, I0 is the load current.

8. The method for calculating the controlled rectifier equivalent impedance of a wireless charging system according to claim 7, characterized in that: By combining the controlled rectifier input voltage u ab The fundamental wave expression of and the fundamental wave expression of the controlled rectifier input current, the equivalent load impedance of the controlled rectifier is obtained as follows: in, R represents the real part of the equivalent load impedance, and X represents the imaginary part of the equivalent load impedance.

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