Analysis of Symmetric Dual Switch Converter under High Switching Frequency Conditions

: Electric vehicle batteries have the problem of low output voltage, so the application of a high-gain converter is a research hotspot. The symmetrical dual-switch high gain converter has the merits of simple structure, low voltage and current stress, and low EMI. Due to the deterioration of circuit performance caused by circuit parasitic parameters under high frequency operating conditions, the former analysis under low frequency condition cannot satisfy the requirements for performance evaluation. To clarify whether the symmetrical dual-switch high-gain converter can maintain its operating characteristics under high-frequency operating conditions, this paper establishes the converter model considering parasitic parameters, and deduces the sneak circuit modes at high frequency. The effects of parasitic parameters at high frequency on voltage gain, switch stress, and symmetrical operating are analyzed, which is beneficial for the selection and optimization of power devices. This paper believes that considering parasitic parameters may reduce the output gain of the symmetrical double-switch high-gain converter considering parasitic parameters under high frequency conditions, increase the switching stress, and affect the symmetry of the circuit operation when the parasitic parameter values are different. Finally, an experimental platform rated on 200 W with 200 kHz switching frequency is established, and experimental verification is given to verify the analysis. D.K.;


Introduction
With the increasingly serious problems of environmental pollution and energy crisis, the new energy vehicle battery has gradually become a research hotspot in the field of new energy vehicles [1]. The new energy vehicle battery refers to a kind of power source that provides driving power source for electric vehicles, electric trains, electric bicycles, and other transportation tools. Compared with battery usage scenarios such as the energy supply of electronic and electrical equipment and the energy storage of energy storage power stations, the new energy vehicle battery has to adapt to the harsh usage scenarios of various vehicles. This requires that the battery should have the characteristics of high energy density, high charge and discharge power, high safety, long life, and low cost. Currently, there are many different types of battery technology systems that can provide power for vehicles, including lead-acid batteries, nickel-metal hydride batteries, lithium-ion batteries, supercapacitors, metal-air batteries, etc.
The new energy vehicle battery is the core component of the power system of electric vehicles, and its comprehensive performance directly affects the performance of electric vehicles. Electric vehicle high voltage gain. Since the voltage of the capacitor is constant in steady-state, the voltage of S2 is clamped by Co1 and Ci2, and the voltage of S1 is clamped by Co2 and Ci1. Due to the symmetry of the structure, the converter can achieve the voltage balance of both switches either in steady-state or dynamic-state.  Use the mesh combination analysis method to analyze the sneak circuit caused by the parasitic parameters at high frequency. First, establish its undirected graph model as shown in Figure 3 below. For devices in the converter circuit: the inductors L 1 , L 2 consider its parasitic resistances R L1 , R L2 ; diodes D 1 , D 2 consider their parasitic capacitors C D01 , C D02 ; for MOSFET: C ds1 , C ds2 are the parasitic capacitors between the drain-source, L d_in , L s_in are the parasitic inductor of the drain and the source. R s , R d are the external equivalent parasitic resistor of the switch. L d_ex , L s_ex are the external equivalent parasitic inductors of the switch. For the convenience of calculations, let L d = L d_in + L d_ex , L s = L s_in + L s_ex . The converter model after considering parasitic parameters is given in Figure 2.
Electronics 2020, 9, x FOR PEER REVIEW 3 of 17 high voltage gain. Since the voltage of the capacitor is constant in steady-state, the voltage of S2 is clamped by Co1 and Ci2, and the voltage of S1 is clamped by Co2 and Ci1. Due to the symmetry of the structure, the converter can achieve the voltage balance of both switches either in steady-state or dynamic-state.  Use the mesh combination analysis method to analyze the sneak circuit caused by the parasitic parameters at high frequency. First, establish its undirected graph model as shown in Figure 3 below. Use the mesh combination analysis method to analyze the sneak circuit caused by the parasitic parameters at high frequency. First, establish its undirected graph model as shown in Figure 3 below. According to the mesh combination analysis method, the maximum number of sub-circuits of the dual-switch converter can be obtained as 236. After removing duplicate sub-circuits, 106 actual sub-circuits are obtained. According to the working principle of the converter, the five effective working modes of the converter are obtained. Comparing these five working modes with the ideal working mode, the three normal modes and two sneak circuit modes caused by parasitic parameters under high-frequency conditions are obtained as follows: For the convenience of reference, the parameters used in this article are defined as follows: U Rs is the terminal voltage of R s ; U Rd is the terminal voltage of R d ; U Ls is the terminal voltage of L s ; U Ld is the terminal voltage of L d ; U C ds is the terminal voltage of C ds , U C ds max is the maximum value of U C ds , U C ds min is the minimum value of U Cds , U C dsp-p is the peak-to-peak voltage; I R is the current of R s ; I Rd is the current of R d ; I Ls is the current of L s ; I Ld is the current of L d ; I C ds is the current of C ds .

Analysis of Normal Modes
Mode 1, t ∈ [mT s , t on ]: When the gate drive voltage reaches U G , the switches are turned on. During this period, the switches S 1 , S 2 remain on, and the diodes D 1 , D 2 remain off. The power supply V in charges the inductors L 1 , L 2 , and the inductor current i L increases linearly. The load side is powered by C o1 , C o2 . Its equivalent circuit is shown in Figure 4.  According to the mesh combination analysis method, the maximum number of sub-circuits of the dual-switch converter can be obtained as 236. After removing duplicate sub-circuits, 106 actual sub-circuits are obtained. According to the working principle of the converter, the five effective working modes of the converter are obtained. Comparing these five working modes with the ideal working mode, the three normal modes and two sneak circuit modes caused by parasitic parameters under high-frequency conditions are obtained as follows: For the convenience of reference, the parameters used in this article are defined as follows: URs is the terminal voltage of Rs; URd is the terminal voltage of Rd; ULs is the terminal voltage of Ls; ULd is the terminal voltage of Ld; UCds is the terminal voltage of Cds, UCdsmax is the maximum value of UCds, UCdsmin is the minimum value of UCds, UCdsp-p is the peak-to-peak voltage; IR is the current of Rs; IRd is the current of Rd; ILs is the current of Ls; ILd is the current of Ld; ICds is the current of Cds.

Analysis of Normal Modes
: When the gate drive voltage reaches UG, the switches are turned on.
During this period, the switches S1, S2 remain on, and the diodes D1, D2 remain off. The power supply Vin charges the inductors L1, L2, and the inductor current iL increases linearly. The load side is powered by Co1, Co2. Its equivalent circuit is shown in Figure 4. : At the time tr, the diodes D1, D2 are still in the conducting state, the energy storage in the power supply and the inductors L1, L2 continues to be transferred to the load, and the inductor current iL decreases linearly. At the same time, all the energy stored in the parasitic inductors Ld, Ls of the MOSFET is released. The equivalent circuit is given in Figure 5. Mode 2, t ∈ [t r , t o f f ]: At the time t r , the diodes D 1 , D 2 are still in the conducting state, the energy storage in the power supply and the inductors L 1 , L 2 continues to be transferred to the load, and the inductor current i L decreases linearly. At the same time, all the energy stored in the parasitic inductors L d , L s of the MOSFET is released. The equivalent circuit is given in Figure 5. : Due to the energy consumption of the resistances in the circuit and the parasitic parameters, the inductor current iL will attenuate to zero at time tDCM. At this time, the inductor current can be regarded as zero, and the output capacitors Co1, Co2 continue to provide energy to the load, and their equivalent circuits are shown in Figure 6.

Sneak Mode 1, t [ , ]
on r tt  : The switches S1, S2 are turned off at the time ton, and the inductor current iL is transferred from the switches S1, S2 to the diodes D1, D2, and the energy is transferred to the load end. At the ton moment, the voltage across CD01 increases from UCDmin to UCdsmax, the voltages across Cds1, Cds2 increase from UCdsmin to UCdsmax. The inductors and the parasitic capacitors in the circuit resonate. The equivalent circuit is shown in Figure 7, and the equations of Sneak Mode 1 can be obtained as  Mode 3, t ∈ [t DCM , (m + 1)T s ]: Due to the energy consumption of the resistances in the circuit and the parasitic parameters, the inductor current i L will attenuate to zero at time t DCM . At this time, the inductor current can be regarded as zero, and the output capacitors C o1 , C o2 continue to provide energy to the load, and their equivalent circuits are shown in Figure 6. : Due to the energy consumption of the resistances in the circuit and the parasitic parameters, the inductor current iL will attenuate to zero at time tDCM. At this time, the inductor current can be regarded as zero, and the output capacitors Co1, Co2 continue to provide energy to the load, and their equivalent circuits are shown in Figure 6.

Sneak Mode 1, t [ , ]
on r tt  : The switches S1, S2 are turned off at the time ton, and the inductor current iL is transferred from the switches S1, S2 to the diodes D1, D2, and the energy is transferred to the load end. At the ton moment, the voltage across CD01 increases from UCDmin to UCdsmax, the voltages across Cds1, Cds2 increase from UCdsmin to UCdsmax. The inductors and the parasitic capacitors in the circuit resonate. The equivalent circuit is shown in Figure 7, and the equations of Sneak Mode 1 can be obtained as

Analysis of Sneak Modes
Sneak Mode 1, t ∈ [t on , t r ]: The switches S 1 , S 2 are turned off at the time t on , and the inductor current i L is transferred from the switches S 1 , S 2 to the diodes D 1 , D 2 , and the energy is transferred to the load end. At the t on moment, the voltage across C D01 increases from U C D min to U C ds max , the voltages across C ds1 , C ds2 increase from U C ds min to U C ds max . The inductors and the parasitic capacitors in the circuit resonate. The equivalent circuit is shown in Figure 7, and the equations of Sneak Mode 1 can be obtained as Electronics 2020, 9, 2183 6 of 17 Figure 6. Equivalent circuit of Mode 3.

Analysis of Sneak Modes
on r tt  : The switches S1, S2 are turned off at the time ton, and the inductor current iL is transferred from the switches S1, S2 to the diodes D1, D2, and the energy is transferred to the load end. At the ton moment, the voltage across CD01 increases from UCDmin to UCdsmax, the voltages across Cds1, Cds2 increase from UCdsmin to UCdsmax. The inductors and the parasitic capacitors in the circuit resonate. The equivalent circuit is shown in Figure 7, and the equations of Sneak Mode 1 can be obtained as  It can be seen from the formulas that U C ds p-p is very small compared with U C ds max . If U C ds p-p is small enough at time t > t on , it can be considered that the operation process of the converter circuit at high frequency will cross the Sneak Mode. Set the boundary value equation as : When the t off time is reached, the inductor current decreases and then increases in the reverse direction, the parasitic capacitor and the inductor resonate, the voltage across the diode's parasitic capacitor C D discharges from U C D max to U C D min , and the voltage of the switch parasitic capacitor C ds discharges from U C ds max to U C ds min . When the discharge voltage reaches the turn-on voltage of diodes, the diodes are turned on, and the converter then enters the reverse recovery process. The equivalent circuit is shown in Figure 8. Similarly, the equations of Sneak Mode 2 can be obtained as Electronics 2020, 9, 2183 7 of 17 then increases in the reverse direction, the parasitic capacitor and the inductor resonate, the voltage across the diode's parasitic capacitor CD discharges from UCDmax to UCDmin, and the voltage of the switch parasitic capacitor Cds discharges from UCdsmax to UCdsmin. When the discharge voltage reaches the turnon voltage of diodes, the diodes are turned on, and the converter then enters the reverse recovery process. The equivalent circuit is shown in Figure 8. Similarly, the equations of Sneak Mode 2 can be obtained as  The analysis shows that the inductor current i L in Sneak Mode 2 is a sinusoidal wave with resonant angular frequency ω. Substituting the voltage of C D into the previous equation, the voltage expression of U CD can be obtained as From the above analysis of the sneak circuit, considering the parasitic parameters of the devices under high-frequency conditions will cause the converter to resonate due to the parasitic junction capacitors and the inductors in the circuit, which will affect the output characteristic of the converter.
In the DCM mode, the circuit modes operation sequences are Mode 1, Sneak Mode 1, Mode 2, Sneak Mode 2, Mode 3. In the CCM (continuous conduction mode) mode, the circuit modes operation sequences are Mode 1, Sneak Mode 1, Mode 2, Sneak Mode 2. The operation process of the circuit in the CCM mode and the DCM mode is shown in the Figure 9 below. Electronics 2020, 9, The analysis shows that the inductor current iL in Sneak Mode 2 is a sinusoidal wave with resonant angular frequency ω. Substituting the voltage of CD into the previous equation, the voltage expression of UCD can be obtained as From the above analysis of the sneak circuit, considering the parasitic parameters of the devices under high-frequency conditions will cause the converter to resonate due to the parasitic junction capacitors and the inductors in the circuit, which will affect the output characteristic of the converter. In

Considering the Influences of Parasitic Parameters on Converter Characteristic
According to the law of conservation of energy, write the following equation for the column

Considering the Influences of Parasitic Parameters on Converter Characteristic
According to the law of conservation of energy, write the following equation for the column Electronics 2020, 9, 2183 8 of 17 During t ∈ [t on , t o f f ] the inductor current satisfies the equation as Among them, DT s = t o f f − t on .

In the Ideal Case
According to the volt-second equilibrium principle and the relationship between i L and i D in ideal mode, the voltage gain of an ideal dual-switch step-up converter can be obtained as

Considering Parasitic Parameters
According to the volt-second equilibrium principle and the law of energy conservation, the voltage gain of the dual-switch converter with parasitic parameters can be obtained as follows: Switch on period: Switch off period: Simultaneous equations are obtained: From the above equations, the relationship between input voltage and output voltage is a constant value when the circuit parameters and operating period of the converter are determined in the ideal working state. When the converter considering parasitic parameters, the relationship is an exponentially decreasing expression.
Set the rated parasitic parameters values as follows: C ds = 232 pF, C D = 60 pF, R s = 0.05 Ω, L e = 147 nH. In the case where the ideal circuit parameter values are unchanged, the influences of the changes in the values of each parasitic parameter on the output gain characteristics of the converter are shown in Figure 10. The above figures show the results that those four parasitic parameters share the common characteristic: the larger the values of the parasitic parameter, the more obvious the effects of reducing the output gain.

Effects of Parasitic Parameters on Switch Stress
List the voltage and current stress of the switching devices in the ideal model and the model considering parasitic parameters as follows: 1. Ideal conditions 12 12 = + 2. Conditions considering parasitic parameters The above figures show the results that those four parasitic parameters share the common characteristic: the larger the values of the parasitic parameter, the more obvious the effects of reducing the output gain.

Effects of Parasitic Parameters on Switch Stress
List the voltage and current stress of the switching devices in the ideal model and the model considering parasitic parameters as follows:

2.
Conditions considering parasitic parameters Electronics 2020, 9,2183 10 of 17 Set the rated parasitic parameter values as follows: C ds = 232 pF, C D = 60 pF, R s = 0.05 Ω, L e = 147 nH. The voltage stress of the ideal model and the model considering the parasitic parameter are shown in Figure 11 below.
Set the rated parasitic parameter values as follows: Cds = 232 pF, CD = 60 pF, Rs = 0.05 Ω, Le = 147 nH. The voltage stress of the ideal model and the model considering the parasitic parameter are shown in Figure 11 below. It can be seen from the above figures that, compared with the voltage stress under ideal conditions, the voltage stress when considering parasitic parameters of the converter is greater. The larger the values of the parasitic capacitors, the larger the amplitude of the resonance voltage of the switches. If the device selection does not consider the impacts of the inductor current fluctuations and the switching stress differences, it may cause new modes or circuit failures in the circuit, which means the selections of devices in circuits under high-frequency conditions must take the effects of parasitic parameters into account.

Influence of Parasitic Parameters Asymmetry on Circuit
In the ideal model, due to the symmetrical structure of the converter, the voltage balance of the switches S1, S2 can be achieved under both steady-state and dynamic conditions, and the centerline has no charge and discharge current. However, if the parasitic parameter values are different for the same type of devices, the symmetric circuit will present an asymmetric working state, which will bring adverse effects on the performance of the converter.
The analysis equations about the voltages of the MOSFET in the sneak modes is re-wrote in this paper to get the expressions of the voltage difference of the parasitic capacitors of the MOSFETs as follows: 01max 02max The analytical equations for the inductor current and diode voltage in Sneak Mode is re-wrote in this paper to get the difference expressions as follows: It can be seen from the above figures that, compared with the voltage stress under ideal conditions, the voltage stress when considering parasitic parameters of the converter is greater. The larger the values of the parasitic capacitors, the larger the amplitude of the resonance voltage of the switches. If the device selection does not consider the impacts of the inductor current fluctuations and the switching stress differences, it may cause new modes or circuit failures in the circuit, which means the selections of devices in circuits under high-frequency conditions must take the effects of parasitic parameters into account.

Influence of Parasitic Parameters Asymmetry on Circuit
In the ideal model, due to the symmetrical structure of the converter, the voltage balance of the switches S 1 , S 2 can be achieved under both steady-state and dynamic conditions, and the centerline has no charge and discharge current. However, if the parasitic parameter values are different for the same type of devices, the symmetric circuit will present an asymmetric working state, which will bring adverse effects on the performance of the converter.
The analysis equations about the voltages of the MOSFET in the sneak modes is re-wrote in this paper to get the expressions of the voltage difference of the parasitic capacitors of the MOSFETs as follows: Electronics 2020, 9, 2183 11 of 17 The analytical equations for the inductor current and diode voltage in Sneak Mode is re-wrote in this paper to get the difference expressions as follows: The influences of the parasitic parameters C ds , C D are reflected in the influences on the oscillation frequency ω r and equivalent inductor Lq. The influences of the parasitic parameter R L are reflected in the influences on oscillation frequency ω r , equivalent parameter ρ, and equivalent inductor Lq. The change of parasitic parameters will result in different inductor current values of i L1 , i L2 , and the occurrence times of the resonance currents, which makes the charge and discharge currents appear in the centerline of the circuit. The two MOSFETs and diodes have different resonance amplitudes and resonance appearance times. The operation symmetry of the circuit is destroyed, which may cause new modalities or circuit failures. Draw the waveform of the stress difference formulas considering the parasitic parameters as shown in Figure 12.
The influences of the parasitic parameters Cds, CD are reflected in the influences on the oscillation frequency ωr and equivalent inductor Lq. The influences of the parasitic parameter RL are reflected in the influences on oscillation frequency ωr, equivalent parameter ρ, and equivalent inductor Lq. The change of parasitic parameters will result in different inductor current values of iL1, iL2, and the occurrence times of the resonance currents, which makes the charge and discharge currents appear in the centerline of the circuit. The two MOSFETs and diodes have different resonance amplitudes and resonance appearance times. The operation symmetry of the circuit is destroyed, which may cause new modalities or circuit failures. Draw the waveform of the stress difference formulas considering the parasitic parameters as shown in Figure 12.

Simulations and Experiment Verification
An experimental platform for the symmetric dual switch high-gain converter is built in the laboratory. The devices selections and parameter values settings of the experimental platform are shown in Table 1. Table 1. Parameter values of devices.

Components
Parameter Values 60 pF

Simulations in Saber
The simulated waveforms of the inductor current, switch voltage and diode voltage are shown in Figure 13. The inductor current waveform shows a trend of first rising and then falling. The inductor current, MOSFET voltage, and diode voltage waveforms are all resonant. Compared with ideal conditions, the voltage amplitudes of MOSFETs and diodes are increased due to the influences of resonance when considering parasitic parameters under high-frequency conditions.

Simulations in Saber
The simulated waveforms of the inductor current, switch voltage and diode voltage are shown in Figure 13. The inductor current waveform shows a trend of first rising and then falling. The inductor current, MOSFET voltage, and diode voltage waveforms are all resonant. Compared with ideal conditions, the voltage amplitudes of MOSFETs and diodes are increased due to the influences of resonance when considering parasitic parameters under high-frequency conditions.
The simulation waveforms show that, due to the high-frequency resonance under highfrequency conditions, the amplitudes of inductor currents, MOSFET voltage and diode voltage all increases due to the parasitic capacitors resonate with the inductors in the sneak circuit, in line with the previous analysis. The simulation waveforms show that, due to the high-frequency resonance under high-frequency conditions, the amplitudes of inductor currents, MOSFET voltage and diode voltage all increases due to the parasitic capacitors resonate with the inductors in the sneak circuit, in line with the previous analysis.

Experimental Verification
The experimental platform of the dual-switch high-gain converter built in the laboratory is shown in the Figure 14 below.

Experimental Verification
The experimental platform of the dual-switch high-gain converter built in the laboratory is shown in the Figure 14 below.  The parasitic parameter values of the devices are sot as R S1 = R S2 = 0.05 Ω, C ds1 = C ds2 = 232 pF, in the case of symmetrical parasitic parameters, the experimental waveforms of P o = 200 W are shown in Figure 15.

Experimental Verification
The experimental platform of the dual-switch high-gain converter built in the laboratory is shown in the Figure 14 below.  After the output power in the original experiment is adjusted from 200 W to 80 W, the diagrams of the experimental waveforms of Po = 80 W are shown in Figure 16. From the diagrams of the experimental waveforms, the amplitude of the current resonance reduces 0.4 A, and the amplitude of the MOSFET voltage reduces 8.5 V, which confirms the theoretical analysis.  After the output power in the original experiment is adjusted from 200 W to 80 W, the diagrams of the experimental waveforms of Po = 80 W are shown in Figure 16. From the diagrams of the experimental waveforms, the amplitude of the current resonance reduces 0.4 A, and the amplitude of the MOSFET voltage reduces 8.5 V, which confirms the theoretical analysis.

Comparative Analysis of Simulation and Experimental Waveforms
The resonance current amplitudes values in experimental waveforms Figure 15a are i L1 = 8.8 A, i L2 = 8.7 A, and resonance current amplitudes values in simulation waveforms Figure 13a are i L1 = 8.9 A, i L2 = 8.7 A. The amplitudes are almost the same.
By comparing the experimental waveforms, the simulation waveforms, and theoretical analysis of the inductor currents, it can be known that the analysis of the influences of the parasitic parameters on the inductor currents is in line with the actual working situations.
The resonance voltage amplitudes values in experimental waveforms Figure 15b are U Cds1 = 188 V, U Cds2 = 183 V, and voltage amplitudes values in simulation waveforms Figure 13b are U Cds1 = 187 V, U Cds2 = 184 V. The experimental waveforms of MOSFETs resonant voltages are consistent with the simulated waveforms.
From above analysis, it can be known that the parasitic capacitors and the inductors in the circuit resonate under high-frequency conditions, and the amplitudes of the voltages are increased by the influences of resonance, which is consistent with the conclusions obtained from theoretical analysis.
From the above experimental waveform Figure 17a, it can be seen that the resonance current peak value of the inductor current i L2 is enhanced by 0.64 A compared to i L1 , and the appearance time is advanced by 8.3 us. Since the inductor currents i L1 and i L2 no longer maintain the same phase and amplitude, the centerline will have charge and discharge currents. Experimental waveform Figure 17b shows the current in the converter centerline to prove this conclusion. Through the above analysis of the experimental waveforms of the inductor currents i L1 and i L2 in the asymmetric condition, it can be known that the symmetry of the ideal symmetric dual switch high-gain converter will be destroyed and the dynamic balance characteristics of converters will be affected when considering parasitic parameters under high-frequency conditions.
From the experimental waveform Figure 17c, it can be seen that the peak value of the resonance voltage U Cds2 increases by 7 V than U Cds1 , and the phases of the two voltages U Cds1 , U Cds2 are no longer the same. From the waveform Figure 17d, it can be seen that the peak value of the resonance voltage U CD02 increases by 13 V than U CD01 , and the phases of the two voltages U CD01 , U CD02 are different. Through the above analysis, it can be known that the amplitudes of the resonance voltages of MOSFETs and diodes no longer maintains the same values after considering the parasitic parameters values asymmetry, which puts more precise requirements for the selection of devices and the selection of device-rated voltages in actual applications.
From the above experimental waveforms, it can be seen when the values of the parasitic parameters become larger, the voltage stress values of the corresponding switches will be greater. Through the comparisons of experimental waveforms with the same and different parasitic parameter values, it can be seen that when the parasitic parameter values of the devices are different, the symmetry of the ideal symmetric dual switch high-gain converter will be destroyed and the dynamic balance characteristics of converters will be affected and the resonance voltages amplitudes of the MOSFETs are no longer the same, which puts more precise requirements for the selections of devices and the selections of device rated voltages in actual high-frequency application conditions. A comparison of voltage gains obtained from the experiment and calculation is shown in Figure 18.  Figure 18 are acquired by adding external capacitors, inductors, and resistors across the device terminals. Figure 18 proves that by varying the values of parasitic parameters while other parameters remain unchanged, the greater the parasitic parameter values, the more obvious the impacts on the output gain, which consistent with theoretical results. The results of the theoretical analysis and experiments verify that the sneak circuit phenomena can be reduced by choosing the value of parameters appropriately, which means higher requirements for the selection and optimization of power devices.

Conclusions
This paper takes the symmetrical dual-tube high-gain converter as the research object, and analyzes the characteristics of the high-frequency down-converter considering the parasitic parameters. A model of the symmetrical dual-switch high-gain converter considering parasitic parameters is established, and two sneak operating modes-Sneak Mode 1 and Sneak Mode 2-are found through sneak circuit analysis. Through the analysis of operating characteristics, it is found that considering the parasitic parameters of devices such as Cds, CD, RL, LS, Ld, and RS under high frequency will reduce the voltage gain, increase the switching stress, and affect the symmetry of the circuit operation when the parasitic parameter values are different. Finally, the conclusions obtained through simulation and experiment are consistent with the theoretical analysis, which proves the correctness of the above analysis. The analysis of the working characteristics of the converter under high frequency in this paper has certain reference value for the selection of devices and the selection of margin under high frequency.  In Condition 1, the values of parasitic parameters are: C ds = 232 pF, C D = 60 pF, R s = 0.05 Ω, L e = 147 nH. In Condition 2, the values of parasitic parameters are: C ds = 232 pF, C D = 120 pF, R s = 0.1 Ω, L e = 147 nH. The different values in Figure 18 are acquired by adding external capacitors, inductors, and resistors across the device terminals. Figure 18 proves that by varying the values of parasitic parameters while other parameters remain unchanged, the greater the parasitic parameter values, the more obvious the impacts on the output gain, which consistent with theoretical results. The results of the theoretical analysis and experiments verify that the sneak circuit phenomena can be reduced by choosing the value of parameters appropriately, which means higher requirements for the selection and optimization of power devices.

Conclusions
This paper takes the symmetrical dual-tube high-gain converter as the research object, and analyzes the characteristics of the high-frequency down-converter considering the parasitic parameters. A model of the symmetrical dual-switch high-gain converter considering parasitic parameters is established, and two sneak operating modes-Sneak Mode 1 and Sneak Mode 2-are found through sneak circuit analysis. Through the analysis of operating characteristics, it is found that considering the parasitic parameters of devices such as C ds , C D , R L , L S , L d , and R S under high frequency will reduce the voltage gain, increase the switching stress, and affect the symmetry of the circuit operation when the parasitic parameter values are different. Finally, the conclusions obtained through simulation and experiment are consistent with the theoretical analysis, which proves the correctness of the above analysis. The analysis of the working characteristics of the converter under high frequency in this paper has certain reference value for the selection of devices and the selection of margin under high frequency.