Estimation method for minimum turn-on current required by zero-voltage turn-on of inverter

Abstract

The invention discloses a method for estimating the minimum turn-on current required by zero-voltage turn-on of an inverter. The minimum turn-on current required by zero-voltage turn-on of the inverter is estimated by utilizing ISWmin = 2.5 Qos / (tdead-td (off)); in the formula, Qos is a process (the output voltage of the voltage type inverter is changed from-Uin to 0, Uin is the input direct-current voltage of the inverter) in a first commutation time period, the output current of the inverter is supplied to the charge quantity of a parasitic capacitor of the MOS tube, tdead is the dead time of a driving signal of the inverter, and td (off) is the turn-off delay of the MOS tube; the predicted value is highly matched with the experimental value of a prototype, and the prediction precision is high; an applicable system is a wireless charging system containing a voltage type full-bridge inverter.

Description

Technical Field

[0001] The invention relates to a method for estimating a minimum switching current required for zero-voltage switching of an inverter, is applicable to wireless charging systems such as automatic guided vehicles and electric vehicles, and belongs to the field of power conversion. Background Art

[0002] Wireless Power Transfer (WPT) technology is widely used in charging devices for systems such as automatic guided vehicles and electric vehicles. Inductive wireless charging technology is one of the main ways to achieve wireless charging, which mainly includes input DC source, inverter, contactless transformer, compensation network, rectifier, filter and load. In order to reduce the switching loss of the inverter and thus improve the system efficiency, it is usually necessary to implement soft switching of the inverter; for voltage-type inverters, the specific type of soft switching is zero voltage (Zero Voltage Switching, ZVS) switching. In order to achieve ZVS switching of voltage-type inverters, the switching current of the inverter, that is, the instantaneous value of the output current at the initial moment of inverter commutation, must meet certain requirements. Therefore, during the design process, it is necessary to accurately estimate the minimum switching current required for zero voltage switching of the inverter.

[0003] The minimum switching current required for zero voltage switching of the existing inverter |I SW | min There are two main estimation methods: one is to regard the inverter output current during commutation as being equal to the turn-on current I SW The estimated formula for the minimum turn-on current required for the inverter ZVS turn-on is |I SW | min =2C oss U in / t dead (e.g., Y. Zhang, X. Li, S. Chen, and Y. Tang, “Soft Switching for Strongly Coupled Wireless Power Transfer System with 90° Dual-Side Phase Shift,” IEEE Trans. Ind. Electron., vol. 69, no. 1, pp. 282–292, 2022, doi: 10.1109 / TIE.2021.3055158.); second, the inverter output current during the commutation period is regarded as the output current of the turn-on current I SW Linearly decreases to zero, the minimum turn-on current required for the inverter ZVS turn-on is estimated as |I SW | min =4C oss U in / tdead (For example: X. Wang, J. Xu, M. Leng, H. Ma, and S. He, "A Hybrid Control Strategy of LCC-S Compensated WPTSystem for Wide Output Voltage and ZVS Range with Minimized ReactiveCurrent," IEEE Trans.Ind.Electron.,vol.68,no.9,pp.7908–7920,2021,doi:10.1109 / TIE.2020.3013788.). In the above two formulas, U in Inverter input DC voltage, t dead is the dead time of the inverter drive signal, C oss The MOS tube drain-source voltage V given in the device manual DS =U in The existing method regards the inverter output current during the commutation period as being constant to the turn-on current or linearly decreasing from the turn-on current to zero, which is significantly different from the actual situation of the inverter output current during the commutation period, affecting the minimum turn-on current |I required for the inverter ZVS turn-on SW | min The estimation accuracy; In addition, the drain-source voltage V DS is dynamically changing, while in the existing method, C oss The MOS tube drain-source voltage V given in the device manual DS =U in The parasitic capacitance value under the condition affects the minimum turn-on current |I required for the inverter ZVS to turn on SW | min Therefore, an accurate minimum on-current |I required for inverter ZVS on-state is proposed. SW | min The estimation method is of great significance. Summary of the invention

[0004] The purpose of the present invention is to solve the problem of the minimum switching current required for zero voltage switching of the existing inverter. SW | min To solve the problem of large estimation error, the present invention provides an accurate method for estimating the minimum turn-on current required for zero-voltage turn-on of an inverter.

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

[0006] The method for estimating the minimum switching current required for zero voltage switching of the inverter is characterized by: using |ISW | min =2.5Q oss / (t dead -t d(off) ) estimates the minimum turn-on current required for zero voltage turn-on of the inverter; where Q oss Q is the charge provided by the inverter output current to the parasitic capacitance of the MOS tube during the first phase change period. The estimated formula is oss =Q oss,on +Q oss,off , where Q oss,on Q is the charge provided by the inverter output current to the turn-on MOS parasitic capacitor. oss,off Q is the charge provided by the inverter output current to the turn-off MOS parasitic capacitor. oss,on and Q oss,off All are estimated through the capacitance dynamic curve diagram given in the MOS tube device manual; t dead is the dead time of the inverter drive signal, t d(off) is the turn-off delay of the MOS tube; the first switching period is when the inverter output voltage changes from -U in The process of U in Input DC voltage to the inverter.

[0007] In order to make the technical solution of the present invention clearer, the technical solution of the present invention is further described in conjunction with the accompanying drawings.

[0008] The method for estimating the minimum switching current required for zero voltage switching of the inverter of the present invention is applicable to the wireless charging system as shown in the attached Figure 1 As shown, it includes an input 101 DC source, 102 inverter, 103 primary compensation network, 104 non-contact transformer, 105 secondary compensation network, 106 rectifier, 107 filter and 108 DC load; the DC source 101 is a DC voltage source; the inverter 102 is a voltage-type full-bridge inverter; the primary compensation network 103 is series compensation or LCC compensation, etc.; the non-contact transformer 104 is composed of a primary winding and a secondary winding, and there is no physical contact between the primary winding and the secondary winding; the secondary compensation network 105 is series compensation, parallel compensation, series-parallel compensation or LCC compensation, etc.; the rectifier 106 is a diode uncontrolled rectifier or a controlled rectifier; the filter 107 is a capacitor filter or an inductive-capacitive filter; the load 108 is a battery or other DC load.

[0009] Attached Figure 2 is the inverter output voltage u AB and the output current i AB Waveform. t0 is the initial moment of inverter commutation, t1 is the moment of commutation completion, and t2 is the current i ABIn order to achieve zero voltage switching of the inverter, the commutation must be completed within the period of t0 to t2, that is, t0 <t1<t2。I SW is the inverter opening current, that is, the output current i at the initial moment of commutation AB During the commutation process, the output voltage u AB By -U in Change to U in .

[0010] Attached Figure 3 is the current i AB The commutation process under four different waveform conditions. The commutation process includes two periods: The first period: the voltage u AB By -U in Becomes 0; Second period: voltage u AB From 0 to U in . Case A: During commutation, the current i AB Always equal to the inverter turn-on current I SW , the duration of both periods is t d , then the commutation time t Cmt Equal to 2t d ; The following situation B, situation C and the actual situation of the commutation time t Cmt The t of case A d Case B: During the commutation period (two periods), the current i AB The current i decreases linearly to 0 during the commutation period. AB The average value is half of that in case A, so the commutation time t Cmt Equal to 4t d . Case C: In the first period, the current i AB Always equal to the turn-on current I SW , in the second period, the current i AB Linearly decreases to 0, then the length of the first period is t d , the second period is 2t d , commutation time t Cmt Equal to 3t d The actual situation is between situation A and situation C, that is, in the first period, the current i AB Approximately equal to the turn-on current I SW , in the second period, the current i AB The commutation time t Cmt Between 2t d and 3t d The present invention takes the commutation time as:

[0011] t Cmt = 2.5t d (1)

[0012] t d The calculation formula is:

[0013] t d = -Q oss / I SW (2)

[0014] In the formula, Q oss is the current i in the first period of commutation AB The amount of charge supplied to the turn-off MOS parasitic capacitance and the turn-on MOS parasitic capacitance.

[0015] Taking into account the calculation accuracy of the inverter drive signal dead time and the safety margin of zero voltage switching, the dead time should meet the following requirements:

[0016] t dead ≥ t d(off) + t Cmt -t d(on) ≈ t d(off) + t Cmt (3)

[0017] In the formula, t d(off) is the turn-off delay of the MOS tube, t d(on) It is the turn-on delay of MOS tube.

[0018] From formula (1) to (3), we can get: I SW ≤-2.5Q oss / (t dead -t d(off) ), that is, the minimum switching current required for the inverter to switch on at zero voltage is:

[0019] |I SW | min = 2.5Q oss / (t dead -t d(off) ) (4)

[0020] In the formula, Q oss The calculation method of is introduced as follows.

[0021] Since the parasitic capacitance of the MOS tube increases with the drain-source voltage V DS Dynamically changing, the present invention uses the capacitance dynamic curve diagram given in the MOS tube device manual to estimate Q oss , the estimated formula is Q oss =Q oss,on +Q oss,off ; In the formula, Q oss,on Q is the charge provided by the inverter output current to the turn-on MOS parasitic capacitor. oss,offThe amount of charge provided by the inverter output current to the turn-off MOS parasitic capacitance.

[0022] In order to highlight the difference between the method of the present invention and the prior art method, further description is given as follows.

[0023] Prior art method 1: As shown in the attached Figure 3 In case A, the current i during the inverter commutation period is AB Considered constant, the current is always equal to the inverter turn-on current I SW , the duration of both periods is t d , then the commutation time is t Cmt =2t d ;t d =-Q oss / I SW , where Q oss Adopt Q oss =C oss U in Make an estimate; ignore the MOS tube turn-off delay t d(off) and opening delay t d(on) , then t dead ≥t Cmt ; From the above relationship, we can get I SW ≤-2C oss U in / t dead , that is, the minimum switching current required for the inverter to switch on at zero voltage is: |I SW | min =2C oss U in / t dead .

[0024] Prior art method 2: As shown in the attached Figure 3 In case B, the current i during the inverter commutation period is AB Considered as the turn-on current I SW The current i decreases linearly to 0 during the commutation period. AB The average value is half of that in case A, so the commutation time is t Cmt =4t d ;t d =-Q oss / I SW , where Q oss Adopt Q oss =C oss U in Make an estimate; ignore the MOS tube turn-off delay t d(off) and opening delay t d(on) , then t dead ≥t Cmt ; From the above relationship, we can get I SW ≤-4Coss U in / t dead , that is, the minimum switching current required for the inverter to switch on at zero voltage is: |I SW | min =4C oss U in / t dead .

[0025] Table 1 compares the prior art method and the method of the present invention. The assumptions of the commutation current waveform, the commutation duration and the estimation of the charge amount of the method of the present invention are more in line with the actual situation, and the estimation of the minimum turn-on current required for zero-voltage turn-on of the inverter is more accurate.

[0026] Table 1 Comparison between the prior art method and the method of the present invention

[0027]

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] Compared with the prior art, the technical solution of the present invention is more in line with the actual situation in terms of the preset commutation current waveform, commutation duration and charge estimation, and the estimation of the minimum switching current required for zero-voltage switching of the inverter is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Attached Figure 1 It is a basic block diagram of a wireless charging system to which the present invention is applicable.

[0031] Attached Figure 2 are the inverter output voltage and output current waveforms.

[0032] Attached Figure 3 is the current i AB Commutation process of four different waveforms.

[0033] Attached Figure 4 is a bilateral LCC compensated wireless charging system of an embodiment.

[0034] Attached Figure 5 It is the dynamic capacitance in the data sheet of the Infineon MOS tube BSC320N20NS3-G of the embodiment.

[0035] Attached Figure 6 is the dead time t of the inverter drive signal of the embodiment dead .

[0036] Attached Figure 7 is the inverter turn-on current I of the embodiment SW , commutation time t Cmt And the duration of the first phase of commutation t d . DETAILED DESCRIPTION

[0037] 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.

[0038] Example:

[0039] The embodiments of the present invention are shown in the attached drawings. Figure 4 As shown, it is a bilateral LCC compensation wireless charging system, including 401 DC voltage source, 402 voltage-type full-bridge inverter, 403 primary-side LCC compensation, 404 non-contact transformer, 405 secondary-side LCC compensation, 406 full-bridge uncontrolled rectifier, 407 capacitor filter, 408 DC load equivalent resistance. The DC voltage source 401 has a size of U in The voltage-type full-bridge inverter 402 is composed of four MOS tubes S1 to S4; the primary LCC compensation 403 is composed of an inductor L f,p , capacitor C f,p and capacitor C p The contactless transformer 404 is composed of a primary winding and a secondary winding, and the primary winding and the secondary winding have no physical contact; the secondary LCC compensation 405 is composed of an inductor L f,s , capacitor C f,s and capacitor C s The 406 full-bridge uncontrolled rectifier is composed of four diode tubes D R1 ~D R4 The capacitor filter 407 is composed of a capacitor C o The equivalent resistance of the 408 DC load is R o .

[0040] The steps for estimating the minimum turn-on current required for zero voltage turn-on of the inverter are as follows:

[0041] a) Estimate the current i during the first phase of commutation AB The amount of charge Q provided to the turn-off MOS parasitic capacitance and the turn-on MOS parasitic capacitance oss .

[0042] During the first phase change period, the output voltage u of the 402 voltage-type full-bridge inverter is AB From -Uin to 0, the output current i AB The amount of charge provided to the parasitic capacitance of the turned-on MOS tube S1 is Q oss,on , so that the voltage of the parasitic capacitance of the MOS tube S1 is changed from U in Change to U in / 2; 402 voltage-type full-bridge inverter output current i AB The amount of charge provided to the parasitic capacitance of the turn-off MOS tube S2 is Q oss,off , so that the voltage of the parasitic capacitor of the MOS tube S2 is changed from 0 to Uin / 2.

[0043] Check the parasitic capacitance with drain-source voltage V in the MOS device manual. DS Dynamic curve chart of changes, using this curve chart to estimate Q oss , the estimated formula is Q oss =Q oss,on +Q oss,off In the formula, Q oss,on Corresponding to the drain-source voltage V of the MOS tube DS Range is U in ~U in / 2, Q oss,off Corresponding to the drain-source voltage V of the MOS tube that is turned off DS Voltage range: 0~U in / 2.

[0044] b) Estimate the minimum switching current |I required for zero voltage switching of the inverter SW | min .

[0045] Utilize |I SW | min =2.5Q oss / (t dead -t d(off) ) Estimate the minimum turn-on current required for zero voltage turn-on of voltage source full-bridge inverter |I SW | min , where t dead is the dead time of the voltage-type full-bridge inverter drive signal, t d(off) It is the turn-off delay of the MOS tube.

[0046] Application examples:

[0047] In order to verify the accuracy of the method for estimating the minimum switching current required for zero-voltage switching of the inverter of the present invention, a prototype was manufactured to conduct experimental verification.

[0048] In the prototype system, the MOS tube of the inverter adopts BSC320N20NS3-G of Infineon; the diode of the rectifier adopts V30202C of Vishay; the system input voltage U in is 60V; the L of the primary LCC compensation network f,p 25.36μH, C f,p is 157.22nF, C p is 157.06nF; L of the secondary side LCC compensation network f,s 29.22μH, C f,s 136.22nF, C s is 184.31nF; the primary inductance of the non-contact transformer is Lp is 50.93μH, the secondary inductance L s It is 50.78μH, the coupling coefficient between the primary and secondary sides is 0.297; the inverter switching frequency is 80kHz.

[0049] a) Estimate the charge Q oss .

[0050] Attached Figure 4 This is the dynamic capacitance curve of the MOS tube BSC320N20NS3-G data sheet of Infineon. In the first period of commutation, the output current i AB The amount of charge provided to the parasitic capacitance of the turned-on MOS tube S1 is Q oss,on , so that the voltage of the parasitic capacitance of the MOS tube S1 is changed from U in Change to U in / 2, that is, from 60V to 30V; the output current i AB The amount of charge provided to the parasitic capacitance of the turn-off MOS tube S2 is Q oss,off , so that the voltage of the parasitic capacitor of the MOS tube S2 is changed from 0 to U in / 2, that is, from 0 to 30V. According to the estimation formula Q oss =Q oss,on +Q oss,off It can be seen that: Q oss Equal to Figure 4 The shaded area is Q oss =52.7nC.

[0051] b) Estimate the minimum on-state current |I SW | min .

[0052] Preset the dead time t of the inverter drive signal dead The turn-off delay t is 238ns. The data sheet of the MOS tube BSC320N20NS3-G of Infineon Technologies can be used to obtain its turn-off delay t d(off) The typical value is 22ns. Substituting |I SW | min =2.5Q oss / (t dead -t d(off) ) can be obtained: |I SW | min The estimated value is 0.61A.

[0053] c) Experimental verification.

[0054] By adjusting the 408 load resistor R o The size of the MOS tube driving signal u GS2 From the start of the decline to the completion of the commutation (output voltage u AB Change to Uin ) is 238ns, that is, the MOS tube turn-off delay t d(off) and commutation time t Cmt The sum is 238ns, as shown in the attached Figure 5 As shown in the above formula (3), it can be known that the minimum dead time of the inverter drive signal is 238ns. Figure 6 As shown, at the initial moment of commutation, the inverter output current i AB The instantaneous value of is the minimum turn-on current required for the inverter ZVS |I SW | min The absolute value was measured to be 0.604A, which is highly consistent with the estimated value of 0.61A in step b), verifying the accuracy of the method of the present invention.

[0055] In order to compare with the existing methods, U in =60V and C oss ≈180pF(V DS =U in =60V) into |I SW | min =2C oss U in / t dead , the estimated value of the existing method 1 is 0.09A; Substituting |I SW | min =4C oss U in / t dead The estimated value of the existing method 2 is 0.18 A. It can be seen that the estimated value of the existing method deviates greatly from the experimental value, has a large error, and has poor precision; the precision of the method of the present invention is much higher than that of the existing method.

[0056] 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 the minimum switching current required for zero voltage switching of an inverter, characterized in that: Utilize |I SW | min =2.5Q oss / (t dead -t d(off) ) estimates the minimum turn-on current required for zero voltage turn-on of the inverter; where Q oss The amount of charge provided by the inverter output current to the parasitic capacitor of the MOS tube during the first phase switching period; the first phase switching period is when the inverter output voltage changes from -U in The process of U in Input DC voltage to the inverter; t dead is the dead time of the inverter drive signal, t d(off) It is the turn-off delay of the MOS tube.

2. The method for estimating the minimum switching current required for zero voltage switching of the inverter according to claim 1, characterized in that: The charge Q in the formula oss Q oss,on With Q oss,off The sum of oss,on The amount of charge provided by the inverter output current to the turn-on MOS parasitic capacitor, Q oss,off Q is the charge provided by the inverter output current to the turn-off MOS parasitic capacitor. oss,on and Q oss,off All are estimated through the capacitance dynamic curve diagram given in the MOS tube device manual; Q oss,on Corresponding to the drain-source voltage V of the MOS tube DS Range is U in ~U in / 2, Q oss,off Corresponding to the drain-source voltage V of the MOS tube that is turned off DS Voltage range: 0~U in / 2.

3. The method for estimating the minimum switching current required for zero voltage switching of the inverter according to claim 1, characterized in that: The derivation of the estimation formula is based on the condition that, in the first period of commutation, the current i AB Approximately equal to the turn-on current I SW , the second phase of commutation, the current i AB The second phase change period is when the inverter output voltage changes from 0 to U in process.

4. The method for estimating the minimum switching current required for zero voltage switching of the inverter according to claim 1, characterized in that: An applicable wireless charging system includes an input DC source, an inverter, a primary compensation network, a contactless transformer, a secondary compensation network, a rectifier, a filter and a DC load; the DC source is a DC voltage source; the inverter is a voltage-type full-bridge inverter; the primary compensation network is series compensation or LCC compensation, etc.; the contactless transformer is composed of a primary winding and a secondary winding, and there is no physical contact between the primary winding and the secondary winding; the secondary compensation network is series compensation, parallel compensation, series-parallel compensation or LCC compensation, etc.; the rectifier is a diode uncontrolled rectifier or a controlled rectifier; the filter is a capacitor filter or an inductive-capacitive filter; the load is a battery or other DC load.

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