Prediction method for turn-on current of voltage type inverter

Abstract

The invention discloses a method for predicting the turn-on current of a voltage type inverter, comprehensively considers the inverter harmonic wave, the rectifier harmonic wave, the inverter commutation duration and the influence of the rectifier commutation duration on the turn-on current, and provides an accurate prediction method for the turn-on current of the voltage type inverter. Mathcad software is used for solving an implicit function equation with the direct-current loads and the turn-on currents as variables, the turn-on currents under different direct-current loads can be conveniently predicted, and therefore accurate design of the turn-on currents is facilitated. The induction type wireless charging system is suitable for automatic guided vehicles, electric vehicles, artificial hearts and other devices.

Description

Technical Field

[0001] The invention relates to a prediction method for a voltage-type inverter start-up current, is applicable to an inductive wireless charging system for devices such as an automatic guided vehicle, an electric vehicle and an artificial heart, and belongs to the field of power conversion. Background Art

[0002] Wireless charging systems for devices such as automatic guided vehicles, electric vehicles, and artificial hearts are mainly implemented through inductive wireless charging technology. The inverter is an important unit of the inductive wireless charging system, including two types: voltage-type inverter and current-type inverter. Among them, the voltage-type inverter is more widely used. The voltage-type inverter converts the input DC voltage into an alternating positive and negative square-wave AC output voltage. The frequency of the AC output voltage is determined by the switching frequency of the MOS tube in the inverter.

[0003] The switching process of the MOS tube includes the turn-on process and the turn-off process, and the turn-on process of the MOS tube has received more attention. During the turn-on process of the MOS tube, its drain-source voltage drops and the current flowing through it rises. The turn-on process of the MOS tube includes two forms: hard turn-on and soft turn-on. (1) Hard turn-on: During the turn-on process of the MOS tube, the falling drain-source voltage overlaps with the rising current, that is, there is a situation where the voltage and current are not zero at the same time, resulting in a large turn-on loss of the MOS tube, especially when the switching frequency is high, resulting in a large turn-on loss of the inverter, which reduces the overall efficiency of the system. (2) Soft turn-on: Before the MOS tube is turned on, its drain-source voltage is not zero. The parasitic capacitance of the MOS tube to be turned on is reversely charged by the inverter output current until its voltage drops to zero. The anti-parallel diode of the MOS tube is turned on. Before the inverter output current commutates, the voltage across the MOS tube remains zero. At this time, a high level is applied to the MOS tube to drive it to turn on, which can achieve zero voltage switching (ZVS). Unlike hard turn-on, during the ZVS turn-on process, the falling drain-source voltage of the MOS tube does not overlap with the rising current, and the turn-on loss is theoretically zero, which greatly improves the system efficiency and has been widely used. In order to achieve ZVS turn-on of the voltage-source inverter, the key is to ensure that the voltage of the parasitic capacitance of the MOS tube is reversely charged to zero by the inverter output current before the turn-on, and this process corresponds to the inverter's commutation process. The smaller the inverter output current (usually referred to as the "turn-on current") at the initial moment of commutation, the longer the commutation time; and the inverter dead time must be higher than the commutation time. If the commutation time is too long, the dead time will be too long, resulting in too low utilization of the inverter input DC voltage. Therefore, it is necessary to ensure that the turn-on current is large enough to limit the commutation time, so as to limit the dead time to a target value. However, excessive turn-on current will also cause additional reactive power loss. Therefore, the design value of the turn-on current is generally slightly larger than the minimum turn-on current required for ZVS turn-on, and the turn-on current needs to be accurately designed. In order to achieve accurate design of turn-on current, it is necessary to accurately predict the turn-on current before prototyping. It can be seen that it is of great significance to propose an accurate prediction method for turn-on current.

[0004] Existing method 1 (M. Li, J. Deng, D. Chen, W. Wang, Y. Li, and Z. Wang, "A Minimum ZVS Current Control Strategy of Semi Bridgeless Active Rectifier for Wide Operation Range Based on LCC-S Compensated WPT System," IEEE Trans. Ind. Appl., vol. 59, no. 3, pp. 3481–3492, 2023, doi: 10.1109 / TIA.2023.3238705.) only considers the impact of inverter harmonics on the turn-on current, ignoring the impact of rectifier harmonics, inverter commutation time, and rectifier commutation time on the turn-on current, and has low prediction accuracy; Existing method 2 (S. Li, W. Li, J. Deng, TDNuyen, and CCMi, "A Double-Sided LCC Compensation Network and Its Tuning Method for Wireless Power Transfer," IEEE Trans. Veh. Technol., vol. 64, no. 6, pp. 2261–2273, 2015, doi: 10.1109 / TVT.2014.2347006.) The influence of inverter harmonics and rectifier harmonics on the turn-on current is considered at the same time, but the influence of inverter commutation time and rectifier commutation time on the turn-on current is ignored. In addition, there are multiple phase angle approximations in the prediction method, which leads to low prediction accuracy of the turn-on current under heavy load. The existing method has low prediction accuracy for the turn-on current, which affects the accurate design of the turn-on current. Summary of the invention

[0005] The purpose of the present invention is to solve the problem of low accuracy of the existing voltage-type inverter turn-on current prediction method. The present invention comprehensively considers the influence of inverter harmonics, rectifier harmonics, inverter commutation time, and rectifier commutation time, and provides an accurate prediction method for the turn-on current of the voltage-type inverter.

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

[0007] A prediction method for the turn-on current of a voltage source inverter is characterized in that: the applicable system is a fixed-frequency wireless power supply system with bilateral LCC compensation and approximate constant current output characteristics, including a DC voltage source U in , voltage type full-bridge inverter, primary side LCC compensation network, contactless transformer, secondary side LCC compensation network, full-bridge uncontrolled rectifier, capacitor filter Co , DC load resistance R o 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 of the primary winding and the secondary winding are L p and L s The primary LCC compensation network includes a primary series compensation inductor L f,p , primary parallel compensation capacitor C f,p And the primary side series compensation capacitor C p The secondary side LCC compensation network includes a secondary side series compensation inductor L f,s , secondary side parallel compensation capacitor C f,s And the secondary side series compensation capacitor C s ; The parameters of the bilateral LCC compensation network satisfy Wherein, f0 is the resonant frequency, ω0 is the resonant angular frequency; the fixed frequency means that the operating frequency of the voltage-type full-bridge inverter is fixed to the resonant frequency f0; the approximate constant current output characteristic means that when the DC load changes, the DC output current I o The size remains basically unchanged;

[0008] The voltage source inverter turns on the current I SW One prediction method is:

[0009] Utilization Turn on the current I SW Prediction; where the DC input voltage U in , primary series compensation inductor L f,p , resonant angular frequency ω0, DC output current I o All are known quantities; The inverter output voltage is given by -U in The phase angle corresponding to the commutation period that becomes zero is calculated by Calculate, where Q C The inverter output current is The period is the charge provided by the parasitic capacitance of the MOS tube, which can be obtained by referring to the device data sheet; Arg(Z ab,1 ) is the rectifier input impedance Z ab,1 The impedance angle is Calculate, where L f,s is a known quantity, The rectifier input voltage is composed of the negative DC load voltage -U o The phase angle corresponding to the commutation period in which π becomes zero is 1% of 2π. and Arg(Z ab,1 ) Get an R o and I SWThe implicit function equation is a variable. Mathcad software can be used to easily predict the R o The turn-on current I SW .

[0010] The voltage source inverter of the present invention is turned on with a current I SW A prediction method that comprehensively considers the effects of inverter harmonics, rectifier harmonics, inverter commutation time, and rectifier commutation time on the turn-on current I SW The impact of It reflects the effect of inverter commutation time on the turn-on current I SW The impact of It reflects the effect of inverter harmonics on the turn-on current I SW The impact of It reflects the effect of rectifier commutation time on turn-on current I SW The impact of It reflects the effect of rectifier harmonics on the turn-on current I SW impact.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] The invention discloses a method for predicting the start-up current of a voltage-type inverter, which comprehensively considers the influence of inverter harmonics, rectifier harmonics, inverter commutation time, and rectifier commutation time, and has high prediction accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Attached Figure 1 The invention is a fixed-frequency wireless power supply system with bilateral LCC compensation and approximate constant-current output characteristics.

[0014] Attached Figure 2 (ab) are the inverter output waveform and rectifier input waveform of the embodiment. Figure 2 (a) is the complete waveform, attached Figure 2 (b) is an enlarged view of the waveforms of the inverter and rectifier commutation process.

[0015] Attached Figure 3 is different load R o The turn-on current I SW The predicted and experimental values.

[0016] Attached Figure 4 is different load R o The turn-on current I SW The error of the predicted value relative to the experimental value. DETAILED DESCRIPTION

[0017] 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.

[0018] Example:

[0019] A prediction method for the turn-on current of a voltage source inverter is applicable to the following systems: Figure 1 The fixed-frequency wireless power supply system with bilateral LCC compensation and approximate constant current output characteristics shown in the figure includes 101 a DC voltage source, 102 a voltage-type full-bridge inverter, 103 a primary-side LCC compensation, 104 a contactless transformer, 105 a secondary-side LCC compensation, 106 a full-bridge uncontrolled rectifier, 107 a capacitor filter, and 108 a DC load equivalent resistor. The DC voltage source 101 has a size of U in The voltage-type full-bridge inverter 102 is composed of four MOS tubes S1 to S4, u AB and i AB are the output voltage and current of the inverter respectively; the primary LCC compensation 103 is composed of the inductor L f,p , capacitor C f,p and capacitor C p The contactless transformer 104 is composed of a primary winding and a secondary winding; the secondary LCC compensation 105 is composed of an inductor L f,s , capacitor C f,s and capacitor C s The 106 full-bridge uncontrolled rectifier is composed of four diode tubes D R1 ~D R4 Composition, u ab and i ab are the input voltage and current of the rectifier respectively; the 107 capacitor filter is composed of capacitor C o The equivalent resistance of the 108 DC load is R o .

[0020] Attached Figure 2 , which are the inverter output waveform and rectifier input waveform of the embodiment. Figure 2 (a) is the complete waveform, attached Figure 2 (b) is an enlarged view of the inverter and rectifier commutation process waveform. in and U o are the DC input voltage and load DC voltage respectively, u AB and u ab are the inverter output voltage and the rectifier input voltage respectively, i AB 、i AB,1 and Σi AB,m are the sum of the inverter output current, output fundamental current and output harmonic current, i ab 、i ab,1 and Σi ab,m are the sum of the rectifier input current, input fundamental current and input harmonic current, I SW ,ISW,1 and I SW,m They are the inverter output current i AB , output fundamental current i AB,1 And the sum of output harmonic current Σi AB,m The instantaneous values ​​of the three quantities at the initial moment of commutation; among them, I SW It is called the turn-on current and its value is and The sum of the turn-on current prediction value is: In the formula, the DC input voltage U in , primary series compensation inductor L f,p , resonant angular frequency ω0, DC output current I o are all known quantities; Figure 2 As shown in (b), The inverter output voltage is given by -U in The phase angle corresponding to the commutation period that becomes zero is calculated by Calculate, where Q C The inverter output current is The amount of charge provided by the parasitic capacitance of the MOS tube during this period can be obtained by referring to the device data sheet; Figure 2 As shown in (b), Arg(Z ab,1 ) is the rectifier fundamental input impedance Z ab,1 The phase angle, i.e. the fundamental current i ab,1 Lagging fundamental voltage u ab,1 (with voltage u ab In phase), through Calculate, where L f,s is a known quantity, The input voltage of the rectifier is given by -U o The phase angle corresponding to the commutation period that becomes zero is 1% of 2π, that is, 0.02π.

[0021] Application examples:

[0022] In order to verify the accuracy of a method for predicting the turn-on current of a voltage source inverter of the present invention, a prototype was manufactured to conduct experimental verification.

[0023] The prototype system parameters of the present invention are as follows: The prototype system uses Infineon's BSC320N20NS3-G MOS tube to form a voltage-type full-bridge inverter, the inverter switching frequency is 80kHz, and the V30202C diode of Vishay is used to form an uncontrolled full-bridge rectifier. The input voltage U in The primary side LCC compensation network parameters are L f,p =25.36μH, C f,p =157.22nF, C p=157.06nF, the parameters of the secondary side LCC compensation network are L f,s =29.22μH, C f,s =136.22nF, C s =184.31nF, primary inductance L of contactless transformer p =50.93μH, secondary inductance L s =50.78μH, the coupling coefficient between the primary and secondary is 0.297. Different loads R o The turn-on current I SW The experimental values ​​are shown in the attached Figure 3 shown.

[0024] Substitute the relevant parameters into In the formula, Q C About 52.7nC (obtained from Infineon's BSC320N20NS3-G device data sheet), Take the value 0.02π (1% of 2π) and use Mathcad software to solve the above R o and I SW The implicit function equation of the variable is obtained for different loads R o The turn-on current I SW The predicted values ​​are as follows Figure 3 shown.

[0025] By the attached Figure 3 It can be seen that the turn-on current I SW The predicted values ​​are highly consistent with the experimental values; Figure 4 As shown, the maximum error of the predicted value relative to the experimental value is 8.1%, and the prediction accuracy is high.

[0026] 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 predicting the turn-on current of a voltage source inverter, characterized in that: The applicable system is a fixed-frequency wireless power supply system with bilateral LCC compensation and approximate constant current output characteristics, including a DC voltage source U in , voltage type full-bridge inverter, primary side LCC compensation network, contactless transformer, secondary side LCC compensation network, full-bridge uncontrolled rectifier, capacitor filter C o , DC load resistance R o 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 of the primary winding and the secondary winding are L p and L s The primary LCC compensation network includes a primary series compensation inductor L f,p , primary parallel compensation capacitor C f,p And the primary side series compensation capacitor C p The secondary side LCC compensation network includes a secondary side series compensation inductor L f,s , secondary side parallel compensation capacitor C f,s And the secondary side series compensation capacitor C s ; The parameters of the bilateral LCC compensation network satisfy Wherein, f0 is the resonant frequency, ω0 is the resonant angular frequency; the fixed frequency means that the operating frequency of the voltage-type full-bridge inverter is fixed to the resonant frequency f0; the approximate constant current output characteristic means that when the DC load changes, the DC output current I o The size remains basically unchanged; The voltage source inverter turns on the current I SW One prediction method is: Utilization Turn on the current I SW Prediction; where the DC input voltage U in , primary series compensation inductor L f,p , resonant angular frequency ω0, DC output current I o All are known quantities; The inverter output voltage is given by -U in The phase angle corresponding to the commutation period that becomes zero is calculated by Calculate, where Q C The inverter output current is The period is the charge provided by the parasitic capacitance of the MOS tube, which can be obtained by referring to the device data sheet; Arg(Z ab,1 ) is the rectifier input impedance Z ab,1 The impedance angle is Calculate, where L f,s is a known quantity, The rectifier input voltage is composed of the negative DC load voltage -U o The phase angle corresponding to the commutation period in which π becomes zero is 1% of 2π. and Arg(Z ab,1 ) Get an R o and I SW The implicit function equation is a variable. Mathcad software can be used to easily predict the R o The turn-on current I SW .

2. A method for predicting the start-up current of a voltage source inverter as claimed in claim 1, characterized in that: The effects of inverter harmonics, rectifier harmonics, inverter commutation time, and rectifier commutation time on the turn-on current I are fully considered. SW The impact of It reflects the effect of inverter commutation time on the turn-on current I SW The impact of It reflects the effect of inverter harmonics on the turn-on current I SW The impact of It reflects the effect of rectifier commutation time on turn-on current I SW The impact of It reflects the effect of rectifier harmonics on the turn-on current I SW impact.

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