A plasma ignition circuit with adaptive voltage and frequency adjustment

Abstract

This invention discloses a plasma ignition circuit with adaptive voltage and frequency adjustment. The power supply VCC is connected to a high-voltage arc-starting circuit and a high-frequency arc-maintaining circuit, both of which are connected to ground. The positive and negative terminals of the high-voltage arc-starting circuit are connected to an output protection circuit, and the positive and negative terminals of the high-frequency arc-maintaining circuit are also connected to the output protection circuit. The positive and negative output terminals of the output protection circuit are connected to the ignition nozzle of an aero-engine. The high-voltage arc-starting circuit generates a high-voltage, low-current voltage pulse, which, after being output through the output protection circuit, breaks down the discharge gap of the ignition nozzle. The high-frequency arc-maintaining circuit generates a high-frequency voltage source using a high-frequency sine wave signal. When the discharge gap of the ignition nozzle is broken down, the high-frequency voltage source generated by the high-frequency arc-maintaining circuit generates an arc, thereby achieving the ignition function.

Description

Technical Field

[0001] This invention relates to, but is not limited to, the field of ignition technology for aerospace engines, and particularly to a plasma ignition circuit that adaptively adjusts voltage frequency. Background Technology

[0002] Currently, the main ignition circuit for aero engines is capacitor-based ignition, which works by storing a certain amount of energy in a capacitor and discharging it at a certain frequency according to the discharge control circuit.

[0003] like Figure 1 The diagram shows a schematic of the topology of an existing capacitor energy storage ignition circuit. The energy storage capacity and discharge frequency of this existing capacitor energy storage ignition circuit are related to the ignition effect. This capacitor energy storage ignition circuit is usually used in low-power ignition systems with a power of less than 100W, and its high-altitude ignition effect is poor. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned technical problems. This invention provides a plasma ignition circuit with adaptive voltage frequency adjustment to solve the problem that existing capacitor energy storage ignition circuits are usually used in low-power ignition systems with power less than 100W and have poor high-altitude ignition performance.

[0005] The technical solution of the present invention: The embodiments of the present invention provide a plasma ignition circuit with adaptive voltage frequency adjustment, including: a high-voltage arc ignition circuit, a high-frequency arc maintenance circuit and an output protection circuit;

[0006] Among them, the power supply VCC is connected to the high-voltage arc ignition circuit and the high-frequency arc maintenance circuit respectively, and both the high-voltage arc ignition circuit and the high-frequency arc maintenance circuit are connected to ground; the positive and negative terminals of the high-voltage arc ignition circuit are connected to the output protection circuit, the positive and negative terminals of the high-frequency arc maintenance circuit are connected to the output protection circuit, and the positive and negative terminals of the output protection circuit are connected to the ignition nozzle of the aircraft engine.

[0007] The high-voltage arc-starting circuit is used to generate a high-voltage, low-current voltage pulse, which is used to break down the discharge gap of the ignition nozzle after being output through the output protection circuit.

[0008] The high-frequency arc-maintaining circuit is used to generate a high-frequency voltage source through a high-frequency sine wave signal. When the discharge gap of the ignition nozzle is broken down, the high-frequency voltage source generated by the high-frequency arc-maintaining circuit is used to generate an electric arc, thereby realizing the ignition function.

[0009] The high-frequency arc circuit has two MOS transistors, which are alternately turned on during the positive or negative half-cycle of the high-frequency sine wave signal and form a resonant circuit in the high-frequency arc circuit, so that the current in the circuit is output to the ignition nozzle according to the sine wave of the resonant frequency.

[0010] Optionally, in the plasma ignition circuit with adaptive voltage frequency adjustment as described above, the high-frequency arc-maintaining circuit includes: a drive circuit and a transformer assembly; a high-frequency sine wave signal is generated by the drive circuit, and after being stepped up by the transformer, a high-frequency voltage source output by the high-frequency arc-maintaining circuit is obtained.

[0011] The high-frequency sine wave signal is used to maintain the arc burning after being stepped up by the transformer, and also to make the two MOS transistors in the high-frequency arc-maintaining circuit conduct alternately when switching between positive and negative; and the switching frequency of the MOS transistors is the same as the oscillation frequency of the high-frequency sine wave signal.

[0012] Optionally, in the plasma ignition circuit with adaptive voltage frequency adjustment as described above, the high-frequency arc circuit includes: pull-down resistors R1 and R2, current-limiting resistors R3 and R4, MOSFETs Q1 and Q2, diodes D1 and D2, clamping diodes D3 and D4, choke inductors L1 and L2, resonant capacitors C1 and C2, and the primary inductor JP2 of the step-up transformer;

[0013] Wherein, one end of the current-limiting resistors R3 and R4, and one end of the choke inductor L1 and the current-limiting resistor L2 are respectively connected to the power supply VCC, the other end of the choke inductor L1 is connected to the drain of MOSFET Q1, the other end of the choke inductor L2 is connected to the drain of MOSFET Q2, the sources of MOSFET Q1 and MOSFET Q2 are connected and grounded, and the other ends of the choke inductor L1 and the other ends of the choke inductor L2 are respectively connected to the primary inductor JP2 of the step-up transformer, and the parallel resonant capacitors C1 and C2 are connected between the other ends of the choke inductor L1 and the other ends of the choke inductor L2;

[0014] The other end of the current-limiting resistor R3 is connected to the gate of MOSFET Q1. One end of the pull-down resistor R1 and the negative terminal of the clamping diode D3 connected in parallel with R1 are connected to the gate of MOSFET Q1. The other end of the pull-down resistor R1 and the positive terminal of the clamping diode D3 are connected to the source of MOSFET Q1 and grounded. The negative terminal of diode D1 is connected to the drain of MOSFET Q1, and the positive terminal is connected to the gate of MOSFET Q2.

[0015] The other end of the current-limiting resistor R4 is connected to the gate of MOSFET Q2. One end of the pull-down resistor R2 and the negative terminal of the clamping diode D4 connected in parallel with R2 are connected to the gate of MOSFET Q2. The other end of the pull-down resistor R2 and the positive terminal of the clamping diode D4 are connected to the source of MOSFET Q2 and grounded. The negative terminal of diode D2 is connected to the drain of MOSFET Q2, and the positive terminal is connected to the gate of MOSFET Q1.

[0016] Optionally, in the plasma ignition circuit with adaptive voltage frequency adjustment as described above, the high-frequency arc-maintaining circuit operates in the following ways:

[0017] The high-frequency sine wave signal operates as follows during the first half-cycle: Upon power-up, the power supply VCC is directly applied to the gates of MOSFETs Q1 and Q2 through current-limiting resistors R3 and R4. Due to the slight difference between current-limiting resistors R3 and R4 and the slight difference in the junction capacitance of the two MOSFETs, one of the MOSFETs turns on first. MOSFET Q1 is set to turn on first, and VCC charges resonant capacitors C1 and C2 through choke inductor L2. After charging, resonant capacitors C1 and C2 form a parallel resonant circuit with the primary inductor JP2 of the boost transformer, thereby generating a pulse current. The current in the parallel resonant circuit formed by the primary inductor JP2 of the boost transformer and the charging of C1 and C2 oscillates according to the positive half-cycle waveform of the sine wave signal. The current in the parallel resonant circuit flows to ground through the drain and source of MOSFET Q1. During the above process, MOSFET Q2 is in the off state.

[0018] The operation mode of the high-frequency sine wave signal in the second half-cycle is as follows: When the primary inductor JP2 of the step-up transformer and the resonant capacitors C1 and C2 form a parallel resonant circuit, the current oscillates according to the waveform of the positive half-cycle of the sine wave signal. As time progresses, when the sine wave signal oscillates to 0 potential, the drain of MOSFET Q1 becomes high, turning off diode D1. At this time, the gate of MOSFET Q2 is high, and MOSFET Q2 is turned on, causing diode D2 to turn on and MOSFET Q1 to turn off. The power supply VCC charges the resonant capacitors C1 and C2 through the choke inductor L1. After the resonant capacitors C1 and C2 are charged, they form a parallel resonant circuit with the primary inductor JP2 of the step-up transformer, thereby generating a pulse current. The current in the parallel resonant circuit formed by the primary inductor JP2 of the step-up transformer and C1 and C2 oscillates according to the waveform of the negative half-cycle of the sine wave signal. The current in the parallel resonant circuit flows to ground through the drain and source of MOSFET Q2. During the above process, MOSFET Q1 is in the off state.

[0019] Optionally, in the plasma ignition circuit with adaptive voltage frequency adjustment as described above, the operation mode of the high-frequency arc-maintaining circuit further includes:

[0020] As time continues, the current in the parallel resonant circuit formed by the primary inductor JP2 of the step-up transformer and the resonant capacitors C1 and C2 alternates between positive and negative half-cycle waveform oscillations according to the sinusoidal signal waveform, thus forming a continuous sinusoidal current oscillation state; a high-voltage, high-frequency sinusoidal voltage will be induced in the secondary inductor of the step-up transformer.

[0021] Optionally, in the plasma ignition circuit with adaptive voltage frequency adjustment as described above, the acquisition of circuit parameters for the high-frequency arc circuit includes: component selection and calculation of the parameters of the step-up transformer;

[0022] The selection of components includes: selection of MOSFETs, capacitors, diodes, and resistors.

[0023] Optionally, in the plasma ignition circuit with adaptive voltage frequency adjustment as described above, the selection of components for the high-frequency arc-maintaining circuit includes...

[0024] a) MOSFET selection methods include:

[0025] S11, calculate the maximum voltage that the MOSFET can withstand, including:

[0026] Based on the fact that each MOSFET withstands a sinusoidal voltage for half a cycle, the average drain voltage is equal to the power supply voltage; that is, the peak drain voltage of the MOSFET is 3.14 times the power supply voltage; therefore, for a 28VDC plasma ignition circuit, the maximum voltage that the MOSFET can withstand is 87.92V.

[0027] S12, calculate the drain current of the MOSFET, including:

[0028] The voltage expression based on the choke inductor is: With an operating frequency of 25kHz and a duty cycle of 0.5, the maximum current flowing through the choke inductor is 8.7A; based on the current margin design principle, the drain current of the MOSFET is at least 15A.

[0029] b) Capacitor selection methods include:

[0030] When the circuit oscillates stably, the energy of the capacitor is equal to the energy of the step-up transformer inductance. The formula for calculating the capacitor current is: The maximum current of the capacitor is 21A.

[0031] c) Diode selection methods include:

[0032] Diodes D1 and D2 switch between on and off states during oscillation. Based on the high oscillation frequency, fast recovery diodes are selected for diodes D1 and D2.

[0033] Diodes D3 and D4 are used to protect the gate of the MOSFET from being damaged by high voltage. Diodes D3 and D4 are selected as 12V Zener diodes.

[0034] d) Resistor selection methods include:

[0035] The current-limiting resistors R3 and R4 are selected based on the rise rate of the MOSFET gate voltage and the losses of the MOSFET during the switching process.

[0036] Pull-down resistors R1 and R2 are used to ensure the gate voltage, and the resistance value of the pull-down resistors is much larger than that of the current-limiting resistors.

[0037] Optionally, in the plasma ignition circuit with adaptive voltage frequency adjustment as described above, the calculation of the parameters of the step-up transformer in the component selection of the high-frequency arc circuit includes:

[0038] Based on the design requirements of the step-up transformer, a magnetic core that meets the power requirements is selected;

[0039] Determine the number of turns in the primary and secondary coils based on the operating frequency of the step-up transformer; the number of turns per volt in the primary coil. n 1 is:

[0040] ;

[0041] in, f Operating frequency (Hz); B m The maximum magnetic flux density; S This represents the cross-sectional area of ​​the magnetic core.

[0042] Based on the transformer turns ratio and the required output voltage of the secondary coil, determine the number of turns of the secondary coil;

[0043] Based on the fact that the primary current is equal to the maximum current flowing through the capacitor in the resonant circuit, and the cross-sectional area of ​​the primary conductor, the diameter of the primary coil is determined.

[0044] The selection of the secondary coil wire should take into account the current passing through during arcing and the maximum value of the plasma voltage to determine the secondary coil wire diameter.

[0045] The beneficial effects of this invention are as follows: This invention provides an adaptive voltage-frequency adjustable plasma ignition circuit. A high-voltage, low-current voltage pulse is generated by a high-voltage arc-starting circuit and output through an output protection circuit to break down the discharge gap of the ignition nozzle. A high-frequency arc-maintaining circuit generates a high-frequency sinusoidal voltage signal. When the discharge gap of the ignition nozzle is broken down, the high-frequency sinusoidal voltage signal generated by the high-frequency arc-maintaining circuit is used to generate an arc, thereby achieving the ignition function. Based on the characteristics of the devices in the high-frequency arc-maintaining circuit, one MOSFET is turned on first, and the two MOSFETs alternately conduct during the positive or negative half-cycle of the high-frequency sinusoidal voltage signal, forming a resonant circuit in the high-frequency arc-maintaining circuit. The resonant frequency is the same as the switching frequency of the MOSFETs, causing the current in the circuit to be output to the ignition nozzle according to a sinusoidal wave at the resonant frequency. Compared with existing ignition circuits, the plasma ignition circuit provided by this invention has higher power and can generate a longer arc for ignition.

[0046] The adaptive voltage-frequency adjustable plasma ignition circuit provided by this invention has been used in a plasma ignition device and has undergone simulated combustion chamber tests, showing good results. High-altitude ignition tests were also conducted in an engine combustion chamber, demonstrating that the circuit significantly improves the engine's ignition altitude. Attached Figure Description

[0047] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of the present invention and do not constitute a limitation on the technical solutions of the present invention.

[0048] Figure 1 This is a schematic diagram of the topology of an existing capacitor energy storage ignition circuit.

[0049] Figure 2 A circuit block diagram of an adaptive voltage frequency adjustment plasma ignition circuit provided in an embodiment of the present invention;

[0050] Figure 3 for Figure 2 A schematic diagram of the high-frequency arc circuit in the plasma ignition circuit provided in the embodiment shown.

[0051] Figure 4 A schematic diagram of the plasma ejected by the igniter;

[0052] Figure 5 This is a schematic diagram of the arc plasma under different airflow conditions during the ignition test of an embodiment of the present invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

[0054] As explained in the background section above, existing capacitor energy storage ignition circuits are typically used in low-power ignition systems with a power of less than 100W, and their high-altitude ignition performance is poor.

[0055] Another ignition method in the existing technology is plasma ignition. Its principle is to convert 220V / 50Hz power to high voltage through a transformer, or to first rectify 220V / 50Hz AC power and then invert and boost it, and output it to the ignition nozzle to form a plasma flame. The existing plasma ignition method is currently only used in gas turbines and has not been used in aero engines. Moreover, this plasma ignition scheme does not meet the requirements for high-altitude ignition.

[0056] To address the aforementioned issues, this invention provides an adaptively adjustable voltage frequency plasma ignition circuit, offering a structural form capable of controlling spark energy and enabling output at different voltage frequencies, thereby improving the quality and efficiency of the output power.

[0057] The present invention provides the following specific embodiments, which can be combined with each other. For the same or similar concepts or processes, they may not be described again in some embodiments.

[0058] Figure 2 This is a circuit block diagram of a plasma ignition circuit with adaptive voltage frequency adjustment provided in an embodiment of the present invention. Figure 2 As shown, the main structure of the plasma ignition circuit with adaptive voltage frequency adjustment provided in this embodiment of the invention includes: a high-voltage arc ignition circuit, a high-frequency arc maintenance circuit, and an output protection circuit.

[0059] like Figure 2 As shown, in the plasma ignition circuit with adaptive voltage and frequency adjustment provided in this embodiment of the invention, JP1 is a terminal for connecting the power supply. The power supply Vcc is connected to the high-voltage arc ignition circuit and the high-frequency arc maintenance circuit, and both the high-voltage arc ignition circuit and the high-frequency arc maintenance circuit are connected to ground. The positive and negative terminals of the high-voltage arc ignition circuit are connected to the output protection circuit, and the positive and negative terminals of the high-frequency arc maintenance circuit are connected to the output protection circuit. The positive and negative terminals of the output protection circuit are connected to the ignition nozzle of the aero-engine.

[0060] like Figure 2As shown, the high-voltage arc-starting circuit generates a high-voltage, low-current voltage pulse to break down the discharge gap of the ignition nozzle. The high-frequency arc-maintaining circuit generates a high-frequency voltage source using a high-frequency sine wave signal. When the discharge gap of the ignition nozzle is broken down, the high-frequency voltage source generated by the high-voltage arc-maintaining circuit generates an electric arc, thereby achieving the ignition function.

[0061] The high-frequency arc circuit has two MOSFETs, which alternately conduct during the positive or negative half-cycle of the high-frequency sine wave signal and form a resonant circuit in the high-frequency arc circuit, so that the current in the circuit is output to the ignition nozzle according to the sine wave of the resonant frequency.

[0062] High-frequency arc circuits can be divided into drive circuits and transformer components. The drive circuit is used to generate high-frequency sine wave signals, which are then stepped up by the transformer to obtain the high-frequency voltage source output by the high-frequency arc circuit.

[0063] The oscillation of high-frequency sine wave signals has two main functions: 1) the high-frequency sine wave signal is boosted by a transformer to maintain the arc burning; 2) when the high-frequency sine wave signal switches between positive and negative, it causes the two MOS transistors in the circuit to conduct alternately, and the switching frequency of the switching transistors is the same as the oscillation frequency.

[0064] The following details the specific implementation of the high-frequency arc circuit in this embodiment of the invention, focusing on both its circuit structure and circuit parameters.

[0065] (I) Circuit structure of high-frequency arc circuit

[0066] In one implementation of this invention, an embodiment of a high-frequency arc-maintaining circuit is provided, such as... Figure 3 As shown, Figure 2 The illustrated embodiment provides a schematic diagram of the high-frequency arc-maintaining circuit in the plasma ignition circuit. This high-frequency arc-maintaining circuit includes: pull-down resistors R1 and R2, current-limiting resistors R3 and R4, MOSFETs Q1 and Q2, diodes D1 and D2, clamping diodes D3 and D4, choke inductors L1 and L2, resonant capacitors C1 and C2, and the primary inductor JP2 of the step-up transformer. Among them, one end of the current-limiting resistors R3 and R4, and one end of the choke inductor L1 and the current-limiting resistor L2 are respectively connected to the power supply VCC. The other end of the choke inductor L1 is connected to the drain of MOSFET Q1, and the other end of the choke inductor L2 is connected to the drain of MOSFET Q2. The sources of MOSFETs Q1 and Q2 are connected and grounded. The other ends of choke inductors L1 and L2 are respectively connected to the primary inductor JP2. The parallel resonant capacitors C1 and C2 are connected between the other ends of choke inductors L1 and L2.

[0067] The other end of the current-limiting resistor R3 is connected to the gate of MOSFET Q1. One end of the pull-down resistor R1 and the negative terminal of the clamping diode D3 connected in parallel with R1 are connected to the gate of MOSFET Q1. The other end of the pull-down resistor R1 and the positive terminal of the clamping diode D3 are connected to the source of MOSFET Q1 and grounded. The negative terminal of diode D1 is connected to the drain of MOSFET Q1, and the positive terminal is connected to the gate of MOSFET Q2.

[0068] The other end of the current-limiting resistor R4 is connected to the gate of MOSFET Q2. One end of the pull-down resistor R2 and the negative terminal of the clamping diode D4 connected in parallel with R2 are connected to the gate of MOSFET Q2. The other end of the pull-down resistor R2 and the positive terminal of the clamping diode D4 are connected to the source of MOSFET Q2 and grounded. The negative terminal of diode D2 is connected to the drain of MOSFET Q2, and the positive terminal is connected to the gate of MOSFET Q1.

[0069] Based on the circuit structure of the high-frequency arc circuit provided by this implementation method, the working principle of the high-frequency arc circuit is as follows:

[0070] The working principle of the first half-cycle of a sine wave signal is as follows: At the instant of power-on, the power supply VCC is directly applied to the gates of MOSFETs Q1 and Q2 through current-limiting resistors R3 and R4. Due to the slight difference between the two resistors R3 and R4 and the slight difference in the junction capacitance of the two MOSFETs (Q1 and Q2), one of the MOSFETs turns on first. Assuming Q1 turns on first, VCC charges the resonant capacitors C1 and C2 through the choke inductor L2. After C1 and C2 are charged, they form a parallel resonant circuit with the primary inductor JP2 of the step-up transformer, thereby generating a pulse current. The current in the parallel resonant circuit formed by the primary inductor JP2 of the step-up transformer and the charging of C1 and C2 oscillates according to the positive half-cycle waveform of the sine wave signal. The current in the parallel resonant circuit flows to ground through the drain and source of MOSFET Q1. During the above process, diode D1 is in the conducting state to pull down the gate voltage of MOSFET Q2, so that MOSFET Q2 is in the off state.

[0071] The working principle of the second half-cycle of a sine wave signal is as follows: When the primary inductor JP2 of the step-up transformer forms a parallel resonant circuit with resonant capacitors C1 and C2, the current oscillates according to the waveform of the positive half-cycle of the sine wave signal. As time progresses, when the sine wave signal oscillates to 0 potential, the drain of MOSFET Q1 becomes high, turning off diode D1. At this time, the gate of MOSFET Q2 is high, and MOSFET Q2 is turned on, i.e., diode D2 is turned on and MOSFET Q1 is turned off. The power supply VCC charges resonant capacitors C1 and C2 through choke inductor L1. After C1 and C2 are charged, they form a parallel resonant circuit with the primary inductor JP2 of the step-up transformer, thereby generating a pulse current. The current in the parallel resonant circuit formed by the primary inductor JP2 of the step-up transformer and the charging of C1 and C2 oscillates according to the waveform of the negative half-cycle of the sine wave signal. The current in the parallel resonant circuit flows to ground through the drain and source of MOSFET Q2. During the above process, diode D2 is turned on to pull down the gate voltage of MOSFET Q1, so that MOSFET Q1 is turned off.

[0072] As time continues, the current in the parallel resonant circuit formed by the primary inductor JP2 and C1 and C2 of the step-up transformer alternates between positive and negative half-cycle oscillations according to a sinusoidal signal waveform, thus forming a continuous sinusoidal current oscillation state. A high-voltage, high-frequency sinusoidal voltage will be induced in the secondary inductor of the step-up transformer.

[0073] (II) Calculation of key circuit parameters for high-frequency arc-controlled circuits

[0074] 2.1 Component Selection

[0075] a) MOSFET selection:

[0076] On the one hand, after the circuit stabilizes and oscillates, each of the two MOSFETs (Q1 and Q2) bears a sinusoidal voltage for half a cycle. The drain voltage is a half-wave rectified waveform, and its average value should be equal to the power supply voltage. Therefore, the peak value of the drain voltage of the MOSFET is about 3.14 times the power supply voltage. Thus, for a 28VDC plasma ignition circuit, the maximum voltage that the MOSFET bears is 87.92V.

[0077] On the other hand, the voltage expression for the choke inductor L1 is: Assuming an operating frequency of 25kHz and a duty cycle of 0.5, the maximum current flowing through the choke inductor L1 is 8.7A. Considering the current margin, the drain current of the MOSFET should be at least 15A.

[0078] Considering both of the above, the IRFP250 MOSFET is selected, with a drain current of 33A and a drain voltage of 200V, which can meet the application requirements.

[0079] b) Capacitor selection:

[0080] When the circuit oscillates stably, the energy of the capacitor is equal to the energy of the step-up transformer inductance. The formula for calculating the capacitor current is: The maximum current of the capacitor is 21A.

[0081] c) Diode selection:

[0082] Diodes D1 and D2 switch between on and off states during oscillation. Since the oscillation frequency is relatively high, about 25kHz, fast recovery diodes should be selected, such as the FR107 fast recovery diode.

[0083] Diodes D3 and D4 are used to protect the gate of the MOSFET from being broken down by high voltage. Therefore, 12V Zener diodes can be selected for D3 and D4. In this solution, 1N4742 is selected.

[0084] d) Resistor selection:

[0085] R3 and R4 are current-limiting resistors, and a 470Ω resistor can be selected. If the current-limiting resistor is too large, the gate voltage rises more slowly, increasing the losses of the MOSFET during the switching process. R1 and R2 are pull-down resistors used to ensure the gate voltage. The pull-down resistor value should be much larger than the current-limiting resistor value, and a 10kΩ resistor can be selected.

[0086] 2.2 Calculation of Step-Up Transformer

[0087] The main functions of a step-up transformer are twofold: to provide high-voltage arc-initiating pulses and high-power arc-maintaining current. Therefore, a step-up transformer should be able to simultaneously meet the requirements of high voltage and high power output. The design requirements for a step-up transformer are as follows:

[0088] Input voltage: 60V;

[0089] Output voltage: ≥10kV;

[0090] Operating frequency: ≥5kHz;

[0091] Rated power: 300W.

[0092] Considering cost and processing time, the existing UY20 ferrite core was selected for the iron core. This size of core can achieve a maximum power of 500W and has the advantages of wide applicability and simple structure. When determining the number of turns in the primary and secondary coils, considering the operating frequency of the step-up transformer is 25kHz, the number of turns per volt in the primary coil is... n 1 is:

[0093] ;

[0094] In the formula: f Operating frequency (Hz);B m The maximum magnetic flux density; S Let be the cross-sectional area of ​​the magnetic core.

[0095] Calculations show that the primary coil has approximately 0.045 turns per volt. With a primary voltage of 60V, the primary coil should have 3 turns (rounded to the nearest integer). Based on engineering experience, 5 turns can be chosen for the primary coil. According to the transformer turns ratio, the secondary coil needs to output 10kV. In this case, the step-up transformer turns ratio is 167. During use, a certain margin (usually 50%) needs to be reserved to improve breakdown performance; therefore, a turns ratio of 240 can be selected, resulting in 1200 turns for the secondary coil.

[0096] The primary current is equal to the maximum current flowing through the capacitor in the resonant circuit, with an effective value of 15A. The current density is also taken as... j =4A / mm 2 The primary conductor has a cross-sectional area of ​​4 mm². 2 Since the ignition coil operates for a short time, the transformer's overload capacity can be utilized. The primary coil diameter can be selected as 2mm, resulting in a cross-sectional area of ​​3.14mm². 2 The selection of the secondary coil wire should take into account the current passing through during arcing. Typically, the plasma voltage does not exceed 1000V, and the current is considered to be 0.3A. The secondary coil wire diameter can be selected as 0.3mm. Since the ignition coil is used for no more than 30 seconds, the selection of the secondary coil wire diameter can meet the usage requirements.

[0097] To improve the energy storage capacity of the transformer and to meet the volt-ampere characteristics of arc operation, a certain air gap should be added to the transformer core to increase the leakage reactance of the transformer. This allows the output voltage of the transformer to drop rapidly after the electrode gap breaks down, thus meeting the requirements for arc combustion.

[0098] After the transformer was wound, it underwent impregnation insulation. The primary inductance was measured to be 31μH and the leakage inductance to be 120μH.

[0099] The plasma ignition circuit with adaptive voltage and frequency adjustment provided in this invention generates a high-voltage, low-current voltage pulse through a high-voltage arc-starting circuit, which is then output through an output protection circuit to break down the discharge gap of the ignition nozzle. A high-frequency sinusoidal voltage signal is generated through a high-frequency arc-maintaining circuit. When the discharge gap of the ignition nozzle is broken down, the high-frequency sinusoidal voltage signal generated by the high-frequency arc-maintaining circuit is used to generate an arc, thereby achieving the ignition function. Based on the characteristics of the components in the high-frequency arc-maintaining circuit, one MOSFET is turned on first, and the two MOSFETs alternately conduct during the positive or negative half-cycle of the high-frequency sinusoidal voltage signal, forming a resonant circuit in the high-frequency arc-maintaining circuit. The resonant frequency is the same as the switching frequency of the MOSFETs, causing the current in the circuit to be output to the ignition nozzle according to a sinusoidal wave at the resonant frequency. Compared with existing ignition circuits, the plasma ignition circuit provided in this invention has higher power and can generate a longer arc for ignition.

[0100] The following ignition test verifies the ignition effect of the plasma ignition circuit with adaptive voltage and frequency adjustment provided in the embodiment of the present invention.

[0101] The experiment used an igniter connected to the rear end of the ignition circuit to ignite the air-fuel mixture. The simulated combustion chamber airflow was 100 L / min, and the ignition system power supply voltage was 28VDC. Figure 4 The diagram shows the plasma ejected from the igniter. It can be seen that the plasma forms a torch shape outside the igniter, with a flame length of approximately 2 cm. The plasma burns most intensely and is brightest at the center of the igniter's outlet, gradually dimming as it moves away from the outlet. At a distance of 2 cm from the outlet, the plasma changes from white to yellow, and its density decreases, indicating that arc combustion can no longer be sustained at this point.

[0102] The gas flow rate inside the engine combustion chamber was varied, with ignition tests conducted at flow rates of 50 L / min, 100 L / min, 150 L / min, and 200 L / min. The resulting images of the electric arc plasma were captured. Figure 5 As shown, Figure 5 This is a schematic diagram of the arc plasma under different airflow conditions during the ignition test of this invention. The airflow magnitude has little effect on the plasma jet length, which fluctuates within the range of (2~2.5) cm. When the airflow increases, the plasma begins to show slight off-center burning, meaning the "tip" of the flame is not on the central axis of the igniter. The presumed reason is that the increased airflow causes local airflow imbalance, pushing the plasma away from the central axis. No plasma offset was observed in the simulation because the simulation model is assumed to be a two-dimensional rotationally axisymmetric model, and no airflow was applied to cause the arc to deviate. Therefore, the arc does not deviate in the simulation, and its central axis is the same as the igniter axis.

[0103] Under different airflow conditions, the plasma ignition circuit can ignite the fuel-air mixture in the combustion chamber. Whether under lean or heavy fuel conditions, ignition is successful, indicating that the ignition system is reliable and has good ignition performance.

[0104] The adaptive voltage-frequency adjustable plasma ignition circuit provided by this invention has been used in a plasma ignition device and has undergone simulated combustion chamber tests, showing good results. High-altitude ignition tests were also conducted in an engine combustion chamber, demonstrating that the circuit significantly improves the engine's ignition altitude.

[0105] While the embodiments disclosed in this invention are as described above, they are merely illustrative of the embodiments to facilitate understanding of the invention and are not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and variations in the form and details of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection for this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A plasma ignition circuit with adaptive voltage and frequency adjustment, characterized in that, include: High-voltage arc ignition circuit, high-frequency arc sustaining circuit, and output protection circuit; Among them, the power supply VCC is connected to the high-voltage arc ignition circuit and the high-frequency arc maintenance circuit respectively, and both the high-voltage arc ignition circuit and the high-frequency arc maintenance circuit are connected to ground; the positive and negative terminals of the high-voltage arc ignition circuit are connected to the output protection circuit, the positive and negative terminals of the high-frequency arc maintenance circuit are connected to the output protection circuit, and the positive and negative terminals of the output protection circuit are connected to the ignition nozzle of the aircraft engine. The high-voltage arc-starting circuit is used to generate a high-voltage, low-current voltage pulse, which is used to break down the discharge gap of the ignition nozzle after being output through the output protection circuit. The high-frequency arc-maintaining circuit is used to generate a high-frequency voltage source through a high-frequency sine wave signal. When the discharge gap of the ignition nozzle is broken down, the high-frequency voltage source generated by the high-frequency arc-maintaining circuit is used to generate an electric arc, thereby realizing the ignition function. The high-frequency arc circuit includes: pull-down resistors R1 and R2, current-limiting resistors R3 and R4, MOSFETs Q1 and Q2, diodes D1 and D2, clamping diodes D3 and D4, choke inductors L1 and L2, resonant capacitors C1 and C2, and the primary inductor JP2 of the step-up transformer. Wherein, one end of the current-limiting resistors R3 and R4, and one end of the choke inductors L1 and L2 are respectively connected to the power supply VCC, the other end of the choke inductor L1 is connected to the drain of MOSFET Q1, the other end of the choke inductor L2 is connected to the drain of MOSFET Q2, the sources of MOSFET Q1 and MOSFET Q2 are connected and grounded, and the other ends of the choke inductors L1 and L2 are respectively connected to the primary inductor JP2 of the step-up transformer, and the parallel resonant capacitors C1 and C2 are connected between the other ends of the choke inductors L1 and L2. The other end of the current-limiting resistor R3 is connected to the gate of MOSFET Q1. One end of the pull-down resistor R1 and the cathode of the clamping diode D3 connected in parallel with the pull-down resistor R1 are connected to the gate of MOSFET Q1. The other end of the pull-down resistor R1 and the anode of the clamping diode D3 are connected to the source of MOSFET Q1 and grounded. The cathode of the diode D1 is connected to the drain of MOSFET Q1, and the anode is connected to the gate of MOSFET Q2. The other end of the current-limiting resistor R4 is connected to the gate of MOSFET Q2. One end of the pull-down resistor R2 and the cathode of the clamping diode D4 connected in parallel with the pull-down resistor R2 are connected to the gate of MOSFET Q2. The other end of the pull-down resistor R2 and the anode of the clamping diode D4 are connected to the source of MOSFET Q2 and grounded. The cathode of the diode D2 is connected to the drain of MOSFET Q2, and the anode is connected to the gate of MOSFET Q1.

2. The plasma ignition circuit with adaptive voltage and frequency adjustment according to claim 1, characterized in that, The operation modes of the high-frequency arc circuit include: The high-frequency sine wave signal operates as follows during the first half-cycle: Upon power-up, the power supply VCC is directly applied to the gates of MOSFETs Q1 and Q2 through current-limiting resistors R3 and R4. Due to the slight difference between current-limiting resistors R3 and R4 and the slight difference in the junction capacitance of the two MOSFETs, one MOSFET turns on first. With MOSFET Q1 turned on first, VCC charges resonant capacitors C1 and C2 through choke inductor L2. After charging, resonant capacitors C1 and C2 form a parallel resonant circuit with the primary inductance JP2 of the step-up transformer, thereby generating a pulse current. The current in the parallel resonant circuit oscillates according to the positive half-cycle waveform of the sine wave signal, and the current in the parallel resonant circuit flows to ground through the drain and source of MOSFET Q1. During the above process, MOSFET Q2 is in the off state. The high-frequency sine wave signal operates in the second half-cycle as follows: When the primary inductor JP2 of the step-up transformer, along with resonant capacitors C1 and C2, forms a parallel resonant circuit, the current oscillates according to the waveform of the positive half-cycle of the sine wave signal. As time progresses, when the sine wave signal oscillates to 0 potential, the drain of MOSFET Q1 becomes high, turning off diode D1. At this time, the gate of MOSFET Q2 is high, and MOSFET Q2 is turned on, causing diode D2 to turn on and MOSFET Q1 to turn off. The power supply VCC charges resonant capacitors C1 and C2 through choke inductor L1. After charging, resonant capacitors C1 and C2 form a parallel resonant circuit with the primary inductor JP2 of the step-up transformer, thereby generating a pulse current. The current in the parallel resonant circuit oscillates according to the waveform of the negative half-cycle of the sine wave signal, and the current in the parallel resonant circuit flows to ground through the drain and source of MOSFET Q2. During the above process, MOSFET Q1 is in the off state.

3. The plasma ignition circuit with adaptive voltage and frequency adjustment according to claim 2, characterized in that, The operation mode of the high-frequency arc circuit also includes: As time continues, the current in the parallel resonant circuit formed by the primary inductor JP2 of the step-up transformer and the resonant capacitors C1 and C2 alternates between positive and negative half-cycle waveform oscillations according to the sinusoidal signal waveform, thus forming a continuous sinusoidal current oscillation state; a high-voltage, high-frequency sinusoidal voltage will be induced in the secondary inductor of the step-up transformer.

4. The plasma ignition circuit with adaptive voltage frequency adjustment according to any one of claims 1 to 3, characterized in that, The acquisition of circuit parameters for the high-frequency arc circuit includes: component selection and calculation of the parameters of the step-up transformer; The selection of components includes: selection of MOSFETs, capacitors, diodes, and resistors.

5. The plasma ignition circuit with adaptive voltage and frequency adjustment according to claim 4, characterized in that, In the selection of components for the high-frequency arc circuit, a) MOSFET selection methods include: S11, calculate the maximum voltage that the MOSFET can withstand, including: Based on the fact that each MOSFET withstands a sinusoidal voltage for half a cycle, the average drain voltage is equal to the power supply voltage; that is, the peak drain voltage of the MOSFET is 3.14 times the power supply voltage; therefore, for a 28VDC plasma ignition circuit, the maximum voltage that the MOSFET can withstand is 87.92V. S12, calculate the drain current of the MOSFET, including: The voltage expression based on the choke inductor is: With an operating frequency of 25kHz and a duty cycle of 0.5, the maximum current flowing through the choke inductor is 8.7A; based on the current margin design principle, the drain current of the MOSFET is at least 15A. b) Capacitor selection methods include: When the circuit oscillates stably, the energy of the capacitor is equal to the energy of the step-up transformer inductance. The formula for calculating the capacitor current is: The maximum current of the capacitor is 21A. c) Diode selection methods include: Diodes D1 and D2 switch between on and off states during oscillation. Based on the high oscillation frequency, fast recovery diodes are selected for diodes D1 and D2. Clamping diodes D3 and D4 are used to protect the gate of the MOSFET from being broken down by high voltage. Clamping diodes D3 and D4 are selected as 12V Zener diodes. d) Resistor selection methods include: For the current-limiting resistors R3 and R4, the selection is based on the rise rate of the MOSFET gate voltage and the losses of the MOSFET during the switching process. The pull-down resistors R1 and R2 are used to ensure the gate voltage, and their resistance values ​​are much larger than those of the current-limiting resistors R3 and R4.

6. The plasma ignition circuit with adaptive voltage and frequency adjustment according to claim 4, characterized in that, The parameters for calculating the step-up transformer include: Based on the design requirements of the step-up transformer, a magnetic core that meets the power requirements is selected; Determine the number of turns in the primary and secondary coils based on the operating frequency of the step-up transformer; the number of turns per volt in the primary coil. n 1 is: ； in, f Operating frequency (Hz); B m The maximum magnetic flux density; S This represents the cross-sectional area of ​​the magnetic core. Based on the transformer turns ratio and the required output voltage of the secondary coil, determine the number of turns of the secondary coil; The diameter of the primary coil is determined based on the fact that the primary current is equal to the maximum current flowing through the capacitor in the resonant circuit and the cross-sectional area of ​​the primary conductor. The selection of the secondary coil wire is based on the maximum value of the current passing through the plasma during arcing, determining the secondary coil wire diameter.

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