Modeling of self-oscillation in the freewheeling process of gan hemt devices

Abstract

This invention discloses a self-excited oscillation modeling method for the freewheeling process of GaN HEMT devices, applied to a dual-pulse test circuit using GaN HEMT devices as the upper and lower transistors. The method includes the following steps: making modeling assumptions; simplifying the dual-pulse test circuit based on these assumptions to obtain an equivalent circuit for the freewheeling process of the GaN HEMT device; further establishing a self-excited oscillation circuit model for the GaN HEMT device based on the equivalent circuit; since the oscillation is caused by the resonance of the parasitic inductance of the loop and the parasitic capacitance of the device, the oscillation occurrence condition of the system is derived according to the Barkhausen criterion. Self-excited oscillation occurs when Re{H(ω1)}>1 or Re{H(ω2)}>1. The necessary condition for self-excited oscillation, derived and simplified, is: L p (C ds +C oss )>L g C gs +g m C gd R g L g Similarly, the condition for no self-excited oscillation is: L p (C ds +C oss )￡L g C gs +g m C gd R g L g .

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, and in particular, it is a self-excited oscillation modeling method for the freewheeling process of GaN HEMT devices. Background Technology

[0002] like Figure 1 The diagram shows a half-bridge circuit in the prior art, including the upper transistor (freewheeling diode) Q. _H Both the lower MOSFET (under test) Q and the upper MOSFET are composed of GaN HEMT devices. To simulate different operating conditions, a double-pulse test is used in the half-bridge circuit. The first pulse stores energy in the load inductor L, and the second pulse is used to test the switching characteristics of the lower MOSFET under the test conditions in the circuit.

[0003] During the double-pulse test, a continuous self-oscillation phenomenon was observed even after the lower transistor Q was turned off, a phenomenon not seen in Si (or SiC) MOSFET devices. This is mainly because GaN HEMT devices have different reverse conduction characteristics. Since GaN HEMT devices do not have an internal body diode, when Q is turned off, the load inductor current I... L From the upper tube Q _H The current flows from the source to the drain and back to Q. _H The output capacitor is charged, thereby increasing the gate-drain voltage v. gd Increase until v gd Exceeding the gate-drain threshold voltage V gd_th This exceeds the limit, thus allowing the two-dimensional electron gas to be reconstructed, at which point Q... _H Reverse conduction. During this process, due to the small parasitic capacitance and unique reverse conduction characteristics of GaN HEMT devices, the lower transistor Q may also experience continuous self-oscillation, which may even damage the power device in severe cases. However, this type of self-oscillation problem has been rarely studied, and there is a lack of specific models and parameter quantification design indicators to suppress the oscillation. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a self-excited oscillation modeling method for GaN HEMT devices in the freewheeling process, which provides design guidance for parameter setting and optimization of GaN HEMT devices in half-bridge circuits when facing the self-excited oscillation problem.

[0005] To solve the above-mentioned technical problems, the solution provided by the present invention is as follows:

[0006] A self-oscillation modeling method for GaN HEMT devices during freewheeling, applied to a dual-pulse test circuit where GaN HEMT devices are used as the upper and lower transistors, includes the following steps:

[0007] Modeling assumptions: Since the continuous oscillation occurs after the lower transistor is turned off, the gate-source voltage V after the lower transistor is turned off... gs Approximately clamped to 0, the gate and source of the lower transistor are equivalent to the output capacitor C. oss Since the high-frequency impedance of the bus capacitance and load inductance is much smaller than the parasitic parameters of the device, its impact on high-frequency oscillation can be ignored.

[0008] Based on the modeling assumptions, the dual-pulse test circuit is simplified to obtain the equivalent circuit of the GaN HEMT device freewheeling process.

[0009] Based on the equivalent circuit of the freewheeling process, a self-excited oscillation circuit model for the GaN HEMT device is further established, in which the bus capacitance C DC Short circuit, inductor L is open circuit, driving resistor is R g The loop stray resistance is R loop The driving stray inductance is L g The parasitic inductance of the circuit is L p =L s +L d That is, the sum of the source parasitic inductance and the drain parasitic inductance; since the lower transistor Q is already turned off at this time, its output capacitor C is used. oss Replacement, upper tube Q _H Equivalent to a voltage-controlled current source and its parasitic capacitance, transconductance g m This represents the gate-source voltage V. gs For drain-source current I ds Due to the influence of the gate-source parasitic capacitance, it is C gs The gate-drain parasitic capacitance is C. gd The drain-source parasitic capacitance is C. ds ;

[0010] Since the oscillation is caused by the resonance of the parasitic inductance of the circuit and the parasitic capacitance of the device, the oscillation condition of the system is derived according to the Barkhausen criterion. Self-excited oscillation occurs when Re{H(ω1)}>1 or Re{H(ω2)}>1. Through derivation and simplification, the boundary condition, i.e. the necessary condition for self-excited oscillation, is obtained as: L p (C ds +C oss )>L g C gs +g m C gd R g L g Similarly, the condition for no self-excited oscillation is: L p (C ds +C oss )￡L g C gs +g m Cgd R g L g .

[0011] The beneficial effects of this invention are at least as follows: Addressing the persistent self-oscillation phenomenon of the drain-source voltage of GaN HEMT devices under specific conditions during freewheeling, this invention analyzes the operating modes of the circuit when self-oscillation occurs, derives an analytical model for the system's self-oscillation, solves for the open-loop gain of the circuit using this model, and determines the boundary conditions for oscillation occurrence based on the Barkhausen criterion, thereby proposing a parameter optimization method to suppress oscillation. This invention provides a theoretical basis and design reference for the testing of the switching characteristics of GaN HEMT devices and their industrial applications. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of a dual-pulse test circuit in the prior art.

[0013] Figure 2 This is the equivalent circuit of the GaN HEMT device freewheeling process in the self-excited oscillation modeling method of the GaN HEMT device freewheeling process in the embodiment of the present invention.

[0014] Figure 3 This is the self-excited oscillation circuit model in the self-excited oscillation modeling method for the freewheeling process of GaN HEMT devices in this embodiment of the invention;

[0015] Figure 4 This is a waveform diagram illustrating the conditions for oscillation in the self-excited oscillation modeling method during the freewheeling process of a GaN HEMT device according to an embodiment of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] This invention provides a cost-effective method for modeling self-oscillation during the freewheeling process of GaN HEMT devices. Applied to a dual-pulse test circuit using GaN HEMT devices as the upper and lower transistors, the method includes the following steps:

[0018] by Figure 1 Taking a dual-pulse test circuit as an example for analysis, in order to obtain the equivalent circuit of the freewheeling process of the GaN HEMT device, the modeling assumptions are made as follows: Since the continuous oscillation occurs after the lower transistor is turned off, the gate-source voltage V after the lower transistor is turned off is... gsApproximately clamped to 0, the gate and source of the lower transistor are equivalent to the output capacitor C. oss Since the high-frequency impedance of the bus capacitance and load inductance is much smaller than the parasitic parameters of the device, its impact on high-frequency oscillation can be ignored.

[0019] Based on these modeling assumptions, Figure 1 Equivalent simplification is performed on the double-pulse test circuit to obtain... Figure 2 Equivalent circuit of freewheeling process in GaN HEMT device;

[0020] Based on the equivalent circuit of the freewheeling process, a self-excited oscillation circuit model for the GaN HEMT device is further established, in which the bus capacitance C DC Short circuit, inductor L is open circuit, driving resistor is R g The loop stray resistance is R loop The driving stray inductance is L g The parasitic inductance of the circuit is L p =L s +L d That is, the sum of the source parasitic inductance and the drain parasitic inductance; since the lower transistor Q is already turned off at this time, its output capacitor C is used. oss Replacement, upper tube Q _H Equivalent to a voltage-controlled current source and its parasitic capacitance, transconductance g m This represents the gate-source voltage V. gs For drain-source current I ds Due to the influence of the gate-source parasitic capacitance, it is C gs The gate-drain parasitic capacitance is C. gd The drain-source parasitic capacitance is C. ds , specifically Figure 3 As shown;

[0021] Since the oscillation is caused by the resonance of the circuit's parasitic inductance and the device's parasitic capacitance, the oscillation condition of the system is derived according to the Barkhausen criterion. Self-excited oscillation occurs when Re{H(ω1)}>1 or Re{H(ω2)}>1. Through derivation and simplification, the necessary boundary condition for self-excited oscillation is obtained as: L p (C ds +C oss )>L g C gs +g m C gd R g L g Similarly, the condition for no self-excited oscillation is: L p (C ds +C oss )￡L g C gs +g mC gd R g L g .

[0022] Half-bridge circuits composed of GaN HEMT devices, or half-bridge circuits containing GaN HEMT devices, including various full-bridge circuits and three-phase bridge circuits containing half-bridge units, may exhibit continuous self-oscillation during the freewheeling process of GaN HEMT devices.

[0023] A half-bridge circuit consists of an upper arm and a lower arm. When both the upper and lower arms are composed of GaN HEMT devices, continuous self-oscillation may occur during the freewheeling process of either the upper or lower GaN HEMT device. When the half-bridge circuit includes only one GaN HEMT device, continuous self-oscillation may occur during the freewheeling process of the non-GaN HEMT device (GaN HEMT device turned off). In all circuits containing half-bridge units and GaN HEMT devices, continuous self-oscillation may occur during the freewheeling process of the non-GaN HEMT device (GaN HEMT device turned off). During the freewheeling process of the GaN HEMT device, due to its small parasitic capacitance and unique reverse conduction characteristics, self-oscillation can occur at the drain-source of the complementary bridge arm. When the bridge arm device is turned off, the load inductor current freewheels through the complementary bridge arm device, flowing from the source to the drain, charging the output capacitor of the complementary bridge arm device. This increases the gate-drain voltage of the complementary bridge arm device, reconstructing the two-dimensional electron gas, and causing the complementary bridge arm device to conduct in reverse. Based on the equivalent circuit of the freewheeling process, a self-excited oscillation circuit model of the GaN HEMT device is further established, where the bus capacitor is short-circuited, the load inductor is open-circuited, and it includes the drive resistor, loop stray resistance, and loop parasitic inductance. Since the bridge arm device is turned off at this time, it can be replaced by its output capacitor. The complementary bridge arm is equivalent to a voltage-controlled current source and its parasitic capacitance.

[0024] Specifically, the process of deriving the conditions for preventing self-excited oscillations includes: Figure 3 The open-loop gain is:

[0025]

[0026] Impedance Z p With Z g Defined as:

[0027]

[0028]

[0029] Substituting (2) and (3) into (1) yields:

[0030]

[0031] Where f(ω) is a complex function, it can be defined as:

[0032]

[0033] The numerator of equation (4) has a purely imaginary value, so the angular frequency when Im{H}=0 is the solution of Re{f(ω)}=0.

[0034]

[0035] Equation (6) is ω 2 The quadratic equation in the equation has two positive solutions. Let ω1 and ω2 represent these solutions, assuming ω1 < ω2. Since the oscillation is caused by the resonance of the circuit's parasitic inductance and the device's parasitic capacitance, the oscillation condition of the system can be derived according to the Barkhausen criterion: self-excited oscillation occurs when Re{H(ω1)} > 1 or Re{H(ω2)} > 1. Therefore, the oscillation condition of the system is:

[0036]

[0037] The numerator in equation (7) is a positive value; therefore, equation (7) can be expressed as:

[0038]

[0039] in:

[0040]

[0041] Substituting equation (9) into equation (8), we get:

[0042]

[0043] Finally, we can obtain:

[0044]

[0045] Where a and b are the stability boundaries of ω1. Similarly, Re{H(ω2)}>1 can also be expressed as:

[0046] a <w2<b (12)

[0047] However, due to the excessive complexity of the stability boundary conditions, it is not convenient to directly perform stability analysis on the system. Further simplification is needed to obtain the design parameters of the system. Let x = ω2, equation (6) can be expressed as a quadratic equation in one variable:

[0048]

[0049] Substituting the upper boundary b of the angular frequency into the equation g(x) and simplifying, we get:

[0050]

[0051] g(b) 2 Both sides simultaneously riding L p L g (R g C gs +R loop (C ds +C oss )) 2 We can obtain:

[0052]

[0053] From equation (15), we can see that g(b) 2 The value is negative. Since g(x) is a quadratic function, ω1 2 ω2 2 a 2 b 2 The relationship between them can be used Figure 4 Indicates. When a 2 <ω1 2 2 <ω2 2 When ω1... 2 2 2 <ω2 2 At that time, the system will not oscillate.

[0054] Depend on Figure 4 It can be seen that equation (12) cannot be satisfied. Therefore, the oscillation condition of the system can be further equivalent to:

[0055] g(a 2 )>0 (16)

[0056] Similarly, substituting the lower boundary 'a' of the angular frequency into the equation g(x) and simplifying, we get:

[0057]

[0058] g(a) 2 Both sides simultaneously riding L p L g (R g C gs +R loop (C ds +C oss )+g m ​​​C gd R loop R g ) 2 We can obtain:

[0059]

[0060] The second term on the right side of equation (18) is negative, so g(a) 2 At least the first term must be positive. Furthermore, in typical PCB design, L... g C gs <L p C ds Therefore, the necessary condition for self-excited oscillation is:

[0061] L p (C ds +C oss )>L g C gs +g m C gd R g L g (19)

[0062] Similarly, from equation (19), we can also deduce that the condition for the circuit not to oscillate is:

[0063] L p (C ds +C oss )￡L g C gs +g m C gd R g L g (20)

[0064] It can be deduced that when the circuit parameters satisfy equation (20), the GaN HEMT device will not experience self-oscillation during freewheeling. Based on the above stability boundary conditions, the following conclusion can be drawn:

[0065] 1. GaN HEMT devices are typically able to operate at high frequencies primarily due to their lower Cg. gd Value, but too low C gd This value makes GaN HEMT devices more prone to self-oscillation problems.

[0066] 2. Parasitic inductance of the circuit L p It should be designed to be as small as possible to avoid the occurrence of self-excited oscillations.

[0067] 3. Increase the driving resistor R g and drive inductor L g It can also suppress self-oscillation, but increasing Rg It will increase losses and increase L. g This may lead to resonance in the drive circuit. The boundary conditions for oscillation are given above, so a reasonable R can be selected within a minimum range. g The value of is chosen to avoid the problem of self-excited oscillation.

[0068] The above conclusions provide design guidance for parameter settings and optimization of GaN HEMT devices in half-bridge circuits when facing self-oscillation problems.

[0069] It should be understood that the exemplary embodiments described herein are illustrative and not restrictive. Although one or more embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art will understand that various changes in form and detail may be made without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A self-oscillation modeling method for the freewheeling process of GaN HEMT devices, applied to a dual-pulse test circuit where GaN HEMT devices are used as the upper and lower transistors, characterized in that, Includes the following steps: Modeling assumptions: Since the continuous oscillation occurs after the lower transistor is turned off, the gate-source voltage V after the lower transistor is turned off... gs Approximately clamped to 0, the gate and source of the lower transistor are equivalent to the output capacitor C. oss Since the high-frequency impedance of the bus capacitance and load inductance is much smaller than the parasitic parameters of the device, the effect on high-frequency oscillation is ignored. Based on the modeling assumptions, the dual-pulse test circuit is simplified to obtain the equivalent circuit of the GaN HEMT device freewheeling process. Based on the equivalent circuit of the freewheeling process, a self-excited oscillation circuit model for the GaN HEMT device is further established, in which the bus capacitance C DC Short circuit, inductor L is open circuit, driving resistor is R g The loop stray resistance is R loop The driving stray inductance is L g The parasitic inductance of the circuit is L p =L s +L d That is, the sum of the source parasitic inductance and the drain parasitic inductance; since the lower transistor Q is already turned off at this time, its output capacitor C is used. oss Replacement, upper tube Q _H Equivalent to a voltage-controlled current source and its parasitic capacitance, transconductance g m This represents the gate-source voltage V. gs For drain-source current I ds Due to the influence of the gate-source parasitic capacitance, it is C gs The gate-drain parasitic capacitance is C. gd The drain-source parasitic capacitance is C. ds ; Since the oscillation is caused by the resonance of the circuit's parasitic inductance and the device's parasitic capacitance, the condition for the system to oscillate is derived according to the Barkhausen criterion. or When self-excited oscillation occurs, the necessary boundary conditions for self-excited oscillation, obtained through derivation and simplification, are: Similarly, the condition for preventing self-excited oscillation is: .

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