Frequency conversion control battery wireless charging system characteristic parameter estimation method

Abstract

The invention provides a method for estimating characteristic parameters of a wireless battery charging system with variable frequency control, which is simple in process, small in calculation amount and easy to implement, provides an analytic expression of the relationship between the characteristic parameters of the system and the working frequency, and can be used for quickly estimating the characteristic parameters by using the analytic expression; frequency range limitation is avoided, and frequency range solving is not needed; the pre-estimation result is highly matched with the result of a circuit simulation method, and the precision is high. The method is suitable for S / S compensation battery wireless charging systems of automatic guided vehicles, electric vehicles and the like.

Description

Technical Field

[0001] The invention relates to a method for estimating characteristic parameters of a variable frequency controlled battery wireless charging system, which is applicable to battery wireless charging systems such as automatic guided vehicles and electric vehicles, and belongs to the field of electric energy conversion. Background Art

[0002] Compared with the traditional contact power transmission method, the wireless power transmission system is safer and more convenient because there is no physical contact between the transmitter and the receiver, especially in harsh environments and weather conditions, its advantages are more obvious. Inductive power transmission technology is a power transmission technology based on the principle of electromagnetic induction and is one of the main ways to achieve wireless power transmission. In order to improve the power transmission capacity and efficiency of the inductive wireless charging system, the reactive power in the system can be compensated through a compensation network.

[0003] Usually, before making a prototype, the designer needs to estimate the system characteristic parameters to ensure that the prototype can meet the system design index requirements. The main methods for estimating the characteristic parameters of the battery wireless charging system are circuit simulation method and system modeling analysis method. With the help of mature circuit simulation software such as Saber and LTspice, the circuit simulation method can obtain more accurate simulation results, but the simulation process is time-consuming and cannot reveal the relationship between the system component parameters and the system characteristics. Compared with the circuit simulation method, the system modeling analysis method can use mathematical calculation software such as Mathcad to quickly estimate the system characteristic parameters and obtain the direct relationship between the system component parameters and the system characteristics.

[0004] System modeling and analysis methods mainly include time domain analysis and frequency domain analysis. Among them, the time domain analysis method has higher accuracy. For example, "Alireza Safaee, and Konrad Woronowicz. Time-Domain Analysis of Voltage-Driven Series-Series Compensated Inductive Power Transfer Topology. IEEE Transactions on Power Electronics 32(7):4981–5003, 2017." accurately estimated the S / compensation system, but its analysis process is complex and the amount of calculation is large. The frequency domain analysis method mainly uses the fundamental wave approximation method, which ignores the system harmonics introduced by the inverter and rectifier and only considers the fundamental wave. The modeling process is simple and is widely used in the estimation of characteristic parameters of wireless power transmission systems; however, the fundamental wave approximation method ignores the influence of harmonics and has low estimation accuracy. To this end, "Alireza Namadmalan, Jose Marcos Alonso, and Atif Iqbal. Accurate Fundamental Harmonic Modeling of Inductive Power Transfer Battery Chargers. IEEE Transactions on Transportation Electrification 8(1): 627–35, 2022." proposed an improved fundamental wave approximation method, which has higher accuracy than the fundamental wave approximation method and is close to the accuracy of the circuit simulation method, while the amount of calculation is greatly reduced. However, the improved fundamental wave approximation method still has two shortcomings: first, the analysis process is still complicated and requires solving the quartic equation. The analytical expression of the relationship between the system characteristic parameters and the operating frequency is not given, which is not easy to implement; second, the applicable frequency range is limited and the frequency range needs to be solved. Therefore, under the premise of ensuring high accuracy, it is of great significance to propose a system characteristic parameter estimation method that is simple, easy to implement, and has no frequency range restrictions. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned existing system characteristic parameter estimation methods (circuit simulation method, time domain method, fundamental wave approximation method and improved fundamental wave approximation method), and to provide a battery wireless charging system characteristic parameter estimation method with high accuracy, simple process, easy implementation and no frequency range limitation.

[0006] The specific technical solutions of the present invention are as follows:

[0007] The method for estimating characteristic parameters of a variable frequency controlled battery wireless charging system is characterized in that: the applicable battery wireless charging system includes an input source, a high frequency inverter, a contactless transformer, a compensation network, a rectifier, a DC filter and a battery load. The input 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), and the on-resistance of each MOSFET is r DS 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 inductance and internal resistance of the primary winding are L p and r Lp , the inductance and internal resistance of the secondary winding are L s and r Ls , the coupling coefficient between the primary winding and the secondary winding is k; the compensation network is series / series (S / S) compensation, that is, a capacitor C is connected in series with the primary side of the transformer. p , a capacitor C is connected in series on the secondary side of the transformer s , and satisfies Wherein, ω0=2πf0 is the resonant angular frequency, 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 and inductor L o The voltage of the battery load is U B .

[0008] The basic steps of the characteristic parameter estimation method are:

[0009] Step 1: Derivation of basic relationship of S / S compensation system parameters.

[0010] Based on the fundamental wave approximation method and considering the influence of the secondary harmonics of the system, the analytical expression of the relationship between the system characteristic parameters and the system working angular frequency ω is deduced.

[0011] The tangent of the input impedance angle of the rectifier bridge is:

[0012]

[0013] Where P B It is the power output by the system to the battery load, that is, the power absorbed by the battery.

[0014] Rectifier bridge fundamental input impedance Z ab,1 for:

[0015]

[0016] Primary fundamental impedance Z p,1and the secondary fundamental impedance Z s,1 They are:

[0017]

[0018] In the formula, Z ab,1 As shown in formula (2).

[0019] Primary current I p,1 and the secondary current I s,1 They are:

[0020]

[0021] In the formula, Z p,1 and Z s,1 As shown in formula (3) and formula (4) respectively.

[0022] Step 2: S / S compensation system output power P B Estimate.

[0023] The power output of the system to the battery load is:

[0024]

[0025] In the formula, and I s,1 As shown in formula (1) and formula (6) respectively.

[0026] From formula (1), we can see that For ω and P B function; From formulas (1) to (6), it can be seen that I s,1 Also ω and P B function; then formula (6) is based on ω and P B is an implicit function of the variable. Formula (7) can be used to estimate the power P output by the system to the battery load at different angular frequencies ω. B .

[0027] Step 3: Estimate the fundamental impedance and impedance angle of the S / S compensation system.

[0028] a. Resistance R of the battery load B Estimate. Based on P obtained in step 2 B The estimated value, the resistance of the battery load is estimated to be: R B =U B 2 / P B .

[0029] b. Rectifier bridge fundamental input impedance Z ab,1 Estimate. B Substituting the estimated value into formula (1) we can get estimated value; The estimated value and P obtained in step 2 B Substituting the estimated value into formula (2) we can get Z ab,1 Estimated value.

[0030] c. Primary fundamental input impedance Z AB,1 Estimation. From formula (3), we can get Z p,1 , the estimated Z in step 3b ab,1 Substituting into equation (4) we can get Z s,1 , then Z AB,1 The estimated value is:

[0031]

[0032] The primary fundamental input impedance angle is estimated as: Step 4: Estimate the fundamental current and phase angle, fundamental voltage and phase angle of the S / S compensation system.

[0033] a. Primary current I p,1 and the secondary current I s,1 Estimate. Substitute the Z obtained in step 3c into p,1 and Z s,1 Substituting the estimated value into equation (5) and equation (6) yields I p,1 and I s,1 Estimated value. p,1 and I s,1 The phase estimates are: and

[0034]

[0035] b. Obtained from step 3b Estimated value and step 4a Estimated value, we can get U ab,1 The phase estimate is U ab,1 The estimated value is:

[0036]

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The method for estimating characteristic parameters of the variable frequency controlled battery wireless charging system of the present invention is simple in process and provides an analytical expression for the relationship between the system characteristic parameters and the system operating angular frequency ω. It has a small amount of calculation and is easy to implement. It does not require solving a quartic equation. That is, by using an angular frequency ω and an output power P B The implicit function equation with variables can be used to calculate the output power P at different angular frequencies ω. B Make fast and accurate estimates; BBased on the estimated value, other system characteristic parameters can be quickly estimated through simple algebraic operations and phasor operations.

[0039] 2. The method for estimating characteristic parameters of the variable frequency controlled battery wireless charging system of the present invention has no frequency range limitation and does not require frequency range solution.

[0040] 3. The estimation result of the method for estimating characteristic parameters of the variable frequency controlled battery wireless charging system of the present invention is highly consistent with the result of the circuit simulation method, which shows that the accuracy of the method of the present invention is relatively high. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Attached Figure 1 It is the principle diagram of the S / S compensation system of the present invention.

[0042] Attached Figure 2 It is the fundamental wave equivalent circuit diagram of the S / S compensation system of the present invention.

[0043] Attached Figure 3 It is a secondary voltage and current waveform diagram of the S / S compensation system of the present invention.

[0044] Attached Figure 4 It is a comparison chart of the output power estimation result of the S / S compensation system of the present invention and the output power estimation result of the circuit simulation method.

[0045] Attached Figure 5 It is a comparison diagram of the input phase angle prediction result of the S / S compensation system of the present invention and the input phase angle prediction result of the circuit simulation method.

[0046] Attached Figure 6 It is the phase angle estimation result of the voltage, current and other characteristic parameters of the S / S compensation system of the present invention. DETAILED DESCRIPTION

[0047] The accompanying drawings disclose a specific embodiment of the present invention in a non-limiting manner. The present invention is further described as follows in conjunction with the accompanying drawings.

[0048] Example:

[0049] Considering the MOSFET on-resistance r DS , the internal resistance of the primary winding r Lp , the secondary winding internal resistance r Ls and the diode’s forward voltage drop U D The system characteristic parameter estimation method of the present invention is applicable to a battery wireless charging system with variable frequency control. 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 series compensation capacitor C p , 104 non-contact transformer, 105 secondary side series compensation capacitor Cs , 106 full bridge rectifier, 107 DC filter, 108 battery load. Figure 2 is the system fundamental wave equivalent circuit, where U AB,1 is the fundamental effective value of the inverter output voltage (primary input voltage), U ab,1 is the rectifier input voltage fundamental effective value, I p,1 is the primary fundamental current, I s,1 is the secondary side fundamental current; L p and L s are the inductances of the primary and secondary windings, respectively; k is the coupling coefficient between the primary and secondary windings; r DS is the on-resistance of each MOSFET in the inverter, r Lp is the internal resistance of the primary winding, r Ls is the internal resistance of the secondary winding, and the total internal resistance of the primary winding is 2r DS +r Lp ; Z AB,1 , Z p,1 , Z s,1 and Z ab,1 They are primary fundamental input impedance, primary fundamental impedance, secondary fundamental impedance and rectifier bridge fundamental input impedance. The secondary waveform of the system is shown in the attached figure. Figure 3 As shown, U AB,1 is the reference phase, U ab,1 ,I p,1 and I s,1 The phases are and The amplitude of the square wave voltage input to the rectifier bridge is the battery voltage U B With rectifier bridge conduction voltage drop 2U D The sum of U B +2U D ; Attachment Figure 3 The waveform is only and The situation is used as an example, but the technical solution is general and applicable to other situations.

[0050] Application examples:

[0051] Considering the MOSFET on-resistance r DS 、Primary winding internal resistance r Lp , the secondary winding internal resistance r Ls and the diode’s forward voltage drop U D The system parameters are: L p =L s =100μH,C p =C s =100nF,k=0.25,f0=50.3kHz,r DS=25mΩ,r Lp =r Ls =0.2Ω,U D =0.5V,U in =24V,U B =17V.

[0052] Applying the technical solution of the present invention, the system output power P is obtained. B Estimated value as attached Figure 4 As shown, the primary input impedance angle Estimated value as attached Figure 5 As shown. It can be seen that the method for estimating the characteristic parameters of the variable frequency controlled battery wireless charging system of the present invention has no frequency range limitation and does not require frequency range solution. In order to verify the accuracy of the present invention, this example uses the circuit simulation software LTspice for simulation research. Figure 4 and attached Figure 5 The system output power P is given respectively. B , primary input impedance angle By comparing the simulation results with the estimated values ​​of the present invention, it can be seen that the estimation method of the characteristic parameters of the variable frequency controlled battery wireless charging system of the present invention has a high degree of consistency with the results of the circuit simulation method, indicating that the accuracy of the method of the present invention is high. The phase angle estimation values ​​of characteristic parameters such as voltage and current are shown in the attached figure. Figure 6 shown.

[0053] 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 estimating characteristic parameters of a variable frequency controlled battery wireless charging system, characterized in that: An applicable battery wireless charging system comprises an input source, a high frequency inverter, a contactless transformer, a compensation network, a rectifier, a DC filter and a battery load; the input 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), and the on-resistance of each MOSFET is r DS 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 inductance and internal resistance of the primary winding are L p and r Lp , the inductance and internal resistance of the secondary winding are L s and r Ls , the coupling coefficient between the primary winding and the secondary winding is k; the compensation network is series / series (S / S) compensation, that is, a capacitor C is connected in series with the primary side of the transformer. p , a capacitor C is connected in series on the secondary side of the transformer s , and satisfies Where ω0 is the resonant angular 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 and inductor L o The voltage of the battery load is U B The frequency conversion control is to adjust the system output power P by adjusting the system operating angular frequency ω B ; The system characteristic parameter estimation method is: 1) System output power P B Estimate; use in Estimate the system output power P under different operating angular frequencies ω B ; 2) Estimation of system fundamental impedance and impedance angle; a.P B Substitute the estimated value into R B =U B 2 / P B , estimate the resistance value of the battery load; b.P B Substitute estimated value Estimating the fundamental input impedance angle of the rectifier bridge P B Estimated value and Substitute estimated value Estimate the fundamental input impedance Z of the rectifier bridge ab,1 ; c. Z ab,1 Substitute estimated value The secondary impedance Z s,1 ; Set the secondary impedance Z s,1 and primary impedance Substitution Estimated primary fundamental input impedance Z AB,1 , and estimate the primary fundamental input impedance angle as: 3) System fundamental current and phase angle, fundamental voltage and phase angle estimation; a. Change Z p,1 and Z s,1 Substitute estimated value and Estimated primary fundamental current I p,1 and the secondary fundamental current I s,1 , and estimate I p,1 and I s,1 The phases are: and b. Utilization Estimated value and Estimated value, estimated rectifier bridge fundamental input voltage U ab,1 The phase value is: Estimated U ab,1 for:

2. The method for estimating system characteristic parameters according to claim 1, characterized in that: The process is simple and provides an analytical expression for the relationship between the system characteristic parameters and the operating frequency. The calculation amount is small and the implementation is easy. That is, the characteristic parameters can be quickly estimated using the analytical expression.

3. The method for estimating system characteristic parameters according to claim 1, characterized in that: There is no frequency range restriction and no frequency range solution is required.

4. The method for estimating system characteristic parameters according to claim 1, characterized in that: The estimated results are highly consistent with those of the circuit simulation method and have high accuracy.

5. The method for estimating system characteristic parameters as claimed in claim 1, further comprising: when the on-resistance r of the MOSFET constituting the inverter is DS When the inverter is small, the on-resistance 2r DS Can be ignored.

6. The system characteristic parameter estimation method according to claim 1 is further designed as follows: when the internal resistance of the primary winding r Lp and the secondary winding internal resistance r Ls When r is small, Lp and r Ls Can be ignored.

7. The method for estimating system characteristic parameters as claimed in claim 1, further comprising: when the conduction voltage drop U of the diode constituting the rectifier is D When the rectifier is small, the on-state voltage drop resistance 2U D Can be ignored.

Images