Plasma ignition circuit capable of adaptively adjusting voltage frequency

Abstract

The invention discloses a plasma ignition circuit capable of adaptively adjusting voltage frequency. A power supply VCC is connected to a high-voltage arc striking circuit and a high-frequency pilot arc circuit, and the high-voltage arc striking circuit and the high-frequency pilot arc circuit are both connected to the ground; the arc striking positive end and the arc striking negative end of the high-voltage arc striking circuit are connected to the output protection circuit, the pilot arc positive end and the pilot arc negative end of the high-frequency pilot arc circuit are connected to the output protection circuit, and the output positive end and the output negative end of the output protection circuit are connected with an ignition electric nozzle of the aero-engine. The high-voltage arc striking circuit is used for generating high-voltage and low-current voltage pulses and puncturing a discharge gap of the ignition electric nozzle after being output by the output protection circuit; the high-frequency pilot arc circuit is used for generating a high-frequency voltage source through a high-frequency sine wave signal, and the high-frequency voltage source generated by the high-frequency pilot arc circuit is used for generating an electric arc after a discharge gap of the ignition electric nozzle is broken down, so that an ignition function is realized; wherein the high-frequency pilot arc circuit is internally provided with two MOS (Metal Oxide Semiconductor) tubes, the two MOS tubes are alternately conducted in a positive half cycle or a negative half cycle of a high-frequency sine wave signal, and a resonant loop is formed in the high-frequency pilot arc circuit, so that current in the circuit is output to the ignition electric nozzle according to sine waves of resonant frequency. According to the technical scheme, the problems that an existing capacitive energy storage ignition circuit is usually applied to a low-power ignition system with the power smaller than 100 w, and the high-altitude ignition effect is poor are solved.

Description

Technical Field

[0001] The present invention relates to, but is not limited to, the field of aviation and aerospace engine ignition technology, and in particular to a plasma ignition circuit capable of adaptively adjusting voltage frequency. Background Art

[0002] At present, the main ignition circuit of aircraft engines is capacitor energy storage ignition, the principle of which is to store a certain amount of energy in a capacitor and discharge it at a certain frequency according to a discharge control circuit.

[0003] like Figure 1 As shown, it is a schematic diagram of the topological structure of the existing capacitor energy storage ignition circuit; the energy storage size and discharge frequency of the existing capacitor energy storage ignition circuit are related to the ignition effect, and the capacitor energy storage ignition circuit is usually used in a low-power ignition system with a power of less than 100w, and its high-altitude ignition effect is not good. Summary of the invention

[0004] Purpose of the present invention: In order to solve the above technical problems, the embodiment of the present invention provides a plasma ignition circuit with adaptive voltage and frequency adjustment to solve the problem that the existing capacitor energy storage ignition circuit is usually used in a low-power ignition system with a power of less than 100w, and its high-altitude ignition effect is not good.

[0005] Technical solution of the present invention: The embodiment of the present invention provides a plasma ignition circuit capable of adaptively adjusting voltage and frequency, comprising: a high-voltage arc starting circuit, a high-frequency arc maintaining circuit and an output protection circuit;

[0006] The power supply VCC is connected to the high-voltage arc starting circuit and the high-frequency arc piloting circuit respectively, and both the high-voltage arc starting circuit and the high-frequency arc piloting circuit are connected to the ground; the arc starting positive terminal and the arc starting negative terminal of the high-voltage arc starting circuit are connected to the output protection circuit, the arc piloting positive terminal and the arc piloting negative terminal of the high-frequency arc piloting circuit are connected to the output protection circuit, and the output positive terminal and the output negative terminal 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 arc, thereby realizing the ignition function;

[0009] Among them, the high-frequency arc-maintaining circuit has two MOS tubes, which are alternately turned on in the positive half-cycle or the negative half-cycle of the high-frequency sine wave signal, and form a resonant loop in the high-frequency arc-maintaining 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 maintenance circuit includes: a driving circuit and a transformer assembly; a high-frequency sine wave signal is generated by the driving circuit, and a high-frequency voltage source output by the high-frequency arc maintenance circuit is obtained after the high-frequency voltage is boosted by the transformer;

[0011] Among them, the high-frequency sinusoidal wave signal is used to maintain arc burning after boosting through the transformer, and is also used to make the two MOS tubes in the high-frequency maintenance circuit alternately turned on when switching between positive and negative; and the switching frequency of the MOS tube is the same as the oscillation frequency of the high-frequency sinusoidal wave signal.

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

[0013] The current limiting resistor R3 and the current limiting resistor 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 the MOS tube Q1, the other end of the choke inductor L2 is connected to the drain of the MOS tube Q2, the sources of the MOS tube Q1 and the MOS tube Q2 are connected and grounded, and the other end of the choke inductor L1 and the other end 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 end of the choke inductor L1 and the other end of the choke inductor L2;

[0014] The other end of the current limiting resistor R3 is connected to the gate of the MOS transistor Q1, one end of the pull-down resistor R1 and the cathode of the clamping diode D3 connected in parallel with R1 are connected to the gate of the MOS transistor Q1, the other end of the pull-down resistor R1 and the anode of the clamping diode D3 are connected to the source of the MOS transistor Q1 and are grounded, the cathode of the diode D1 is connected to the drain of the MOS transistor Q1, and the anode is connected to the gate of the MOS transistor Q2;

[0015] The other end of the current limiting resistor R4 is connected to the gate of the MOS tube Q2, one end of the pull-down resistor R2 and the cathode of the clamping diode D4 connected in parallel with R2 are connected to the gate of the MOS tube Q2, the other end of the pull-down resistor R2 and the anode of the clamping diode D4 are connected to the source of the MOS tube Q2 and are grounded, the cathode of the diode D2 is connected to the drain of the MOS tube Q2, and the anode is connected to the gate of the MOS tube Q1.

[0016] Optionally, in the plasma ignition circuit for adaptively adjusting voltage frequency as described above, the working mode of the high frequency maintenance circuit includes:

[0017] The working mode of the first half cycle of the high-frequency sinusoidal wave signal is as follows: at the moment of power-on, the power supply VCC is directly added to the gates of the MOS tubes Q1 and Q2 through the current limiting resistors R3 and R4. Based on the slight difference between the current limiting resistors R3 and R4 and the slight difference between the junction capacitances of the two MOS tubes, one of the MOS tubes is turned on first; the MOS tube Q1 is set to turn on the power first, and VCC charges the resonant capacitor C1 and the resonant capacitor C2 through the choke inductor L2; after the resonant capacitor C1 and the resonant capacitor 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 of 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 sinusoidal wave signal, and the current of the parallel resonant circuit flows to the ground through the drain and source of the MOS tube Q1; in the above process, the MOS tube Q2 is in the off state;

[0018] The working mode of the second half cycle of the high-frequency sinusoidal signal is as follows: when the current of the parallel resonant circuit formed by the primary inductor JP2 of the step-up transformer and the resonant capacitor C1 and the resonant capacitor C2 oscillates according to the waveform of the positive half cycle of the sinusoidal signal, as time goes by, when the sinusoidal signal oscillates to 0 potential, the drain of the MOS tube Q1 becomes high level, and the diode D1 is turned off. At this time, the gate of the MOS tube Q2 is high level, and the MOS tube Q2 is turned on, so that the diode D2 is turned on and the MOS tube Q1 is turned off; the power supply VCC charges the resonant capacitor C1 and the resonant capacitor C2 through the choke inductor L1; after the resonant capacitor C1 and the resonant capacitor 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 of 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 sinusoidal signal, and the current of the parallel resonant circuit flows to the ground through the drain and source of the MOS tube Q2; in the above process, the MOS tube Q1 is in the off state.

[0019] Optionally, in the plasma ignition circuit for adaptively adjusting voltage frequency as described above, the working mode of the high frequency maintenance circuit further includes:

[0020] As time goes on, the current in the parallel resonant circuit formed by the primary inductance JP2 of the step-up transformer and the resonant capacitors C1 and C2 alternately completes the positive half-cycle waveform oscillation and the negative half-cycle waveform oscillation according to the sine wave signal waveform, thereby forming a continuous sinusoidal current oscillation state; a high-voltage and high-frequency sinusoidal voltage will be induced on the secondary inductance of the step-up transformer.

[0021] Optionally, in the plasma ignition circuit for adaptively adjusting voltage frequency as described above, the circuit parameter acquisition of the high-frequency maintenance circuit includes: component selection and calculation of parameters of the step-up transformer;

[0022] The component selection includes: MOS tube selection, capacitor selection, diode selection, and resistor selection.

[0023] Optionally, in the plasma ignition circuit for adaptively adjusting voltage frequency as described above, in the selection of components of the high-frequency maintenance circuit,

[0024] a) MOS tube selection methods include:

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

[0026] Based on the fact that each MOS tube bears a half-cycle of sinusoidal voltage, the average value of the drain voltage is equal to the power supply voltage; that is, the peak value of the drain voltage of the MOS tube is 3.14 times the power supply voltage; then for a 28VDC plasma ignition circuit, the maximum voltage that the MOS tube bears is 87.92V;

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

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

[0029] b) Capacitor selection methods include:

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

[0031] c) Diode selection methods include:

[0032] The diode D1 and the diode D2 switch between on and off states during the oscillation process. Based on the higher oscillation frequency, the diode D1 and the diode D2 are fast recovery diodes.

[0033] Diode D3 and diode D4 are used to protect the gate of the MOS tube from being broken down by high voltage. Diode D3 and diode D4 are 12V voltage regulator tubes.

[0034] d) Resistor selection methods include:

[0035] For the current limiting resistors R3 and R4, the selection is based on the rising speed of the MOS tube gate voltage and the loss of the MOS tube during the switching process;

[0036] The pull-down resistors R1 and R2 realize the function of ensuring the gate voltage, and the resistance value of the pull-down resistors is much greater than the resistance value of the current limiting resistor.

[0037] Optionally, in the plasma ignition circuit for adaptively adjusting voltage frequency as described above, in the selection of components of the high-frequency maintenance circuit, calculating the parameters of the step-up transformer includes:

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

[0039] According to the operating frequency of the step-up transformer, the number of turns of the primary coil and the secondary coil is determined; the number of turns per volt of the primary coil n1 is:

[0040] n1=0.225÷(fB m S);

[0041] Where, f is the operating frequency / Hz; B m is the maximum magnetic induction intensity; S is the cross-sectional area of ​​the magnetic core;

[0042] Determine the number of turns of the secondary coil according to the transformer ratio and the required output voltage 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, the cross-sectional area of ​​the primary conductor determines the primary coil diameter;

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

[0045] Beneficial effects of the present invention: The plasma ignition circuit with adaptive voltage frequency adjustment provided by the embodiment of the present invention generates a high voltage and low current voltage pulse through a high voltage arc starting circuit, and breaks down the discharge gap of the ignition nozzle after being output through an output protection circuit; generates a high frequency sinusoidal voltage signal through a high frequency arc maintenance circuit, and when the discharge gap of the ignition nozzle is broken down, the high frequency sinusoidal voltage signal generated by the high frequency arc maintenance circuit is used to generate an arc, thereby realizing the ignition function. Among them, based on the device characteristics in the high frequency arc maintenance circuit, one of the MOS tubes is turned on first, and the two MOS tubes are alternately turned on in the positive half cycle or negative half cycle of the high frequency sinusoidal voltage signal, and a resonant circuit is formed in the high frequency arc maintenance circuit, and the resonant frequency is the same as the switching frequency of the MOS tube, so that the current in the circuit is output to the ignition nozzle according to the sine wave of the resonant frequency. Compared with the existing ignition circuit, the plasma ignition circuit provided by the embodiment of the present invention has greater power and can generate a longer arc for ignition.

[0046] The plasma ignition circuit with adaptive voltage and frequency adjustment provided by the present invention has been used in a plasma ignition device and has been tested in a simulated combustion chamber, and the use effect is good. A high-altitude ignition test was carried out in the engine combustion chamber, and the results showed that the circuit significantly improved the ignition height of the engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The accompanying drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present invention and do not constitute a limitation on the technical solution of the present invention.

[0048] Figure 1 It is a schematic diagram of the topological structure of the existing capacitor energy storage ignition circuit;

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

[0050] Figure 3 for Figure 1 A schematic diagram of the circuit structure of a high-frequency arc maintenance circuit in a plasma ignition circuit provided in the illustrated embodiment;

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

[0052] Figure 5 Schematic diagram of arc plasma under different airflow conditions in an ignition test of an embodiment of the present invention. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solution and advantages of the present invention more clear, the embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other arbitrarily without conflict.

[0054] As described in the above background technology, the existing capacitor energy storage ignition circuit is usually used in a low-power ignition system with a power of less than 100w, and its high-altitude ignition effect is not good.

[0055] There is another ignition method in the prior art, which is plasma ignition. The principle is to convert the 220V / 50Hz power supply into high voltage electricity through a transformer, or to first rectify the 220V / 50Hz alternating current 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 aircraft engines. In addition, the plasma ignition scheme also does not meet the use requirements of high-altitude ignition.

[0056] In order to solve the above problems, an embodiment of the present invention provides a plasma ignition circuit that can adaptively adjust voltage frequency, provides a structural form of a plasma ignition circuit that can achieve spark energy control, and realizes the output of different voltage frequencies, thereby improving the output power quality and efficiency.

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

[0058] Figure 2 The circuit block diagram of a plasma ignition circuit with adaptive voltage and frequency adjustment provided by an embodiment of the present invention is shown in FIG. Figure 1 As shown, the main structure of the plasma ignition circuit with adaptive voltage and frequency adjustment provided by the embodiment of the present invention includes: a high-voltage arc starting 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 by an embodiment of the present invention, JP1 is a terminal connected to a power supply, the power supply Vcc is respectively connected to a high-voltage arc starting circuit and a high-frequency arc pilot circuit, and both the high-voltage arc starting circuit and the high-frequency arc pilot circuit are connected to ground; the arc starting positive terminal and the arc starting negative terminal of the high-voltage arc starting circuit are connected to an output protection circuit, the arc pilot positive terminal and the arc pilot negative terminal of the high-frequency arc pilot circuit are connected to the output protection circuit, and the output positive terminal and the output negative terminal of the output protection circuit are connected to an ignition nozzle of an aircraft engine.

[0060] like Figure 2 As shown, the high-voltage arc-starting circuit is used to generate a high-voltage, low-current voltage pulse to break through the discharge gap of the ignition nozzle. 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-voltage arc-maintaining circuit is used to generate an arc, thereby realizing the ignition function.

[0061] The high-frequency arc-maintaining circuit has two MOS tubes, which are alternately turned on in the positive half cycle or the negative half cycle of the high-frequency sine wave signal, and form a resonant loop in the high-frequency arc-maintaining circuit, so that the current in the circuit is output to the ignition nozzle according to the sine wave of the resonant frequency.

[0062] The high-frequency maintenance circuit can be divided into a drive circuit and a transformer assembly. The drive circuit is used to generate a high-frequency sinusoidal wave signal, which is boosted by the transformer to obtain a high-frequency voltage source output by the high-frequency arc maintenance circuit.

[0063] The oscillation of high-frequency sinusoidal wave signal has two main effects: 1) The high-frequency sinusoidal wave signal maintains the arc burning after being stepped up by the transformer; 2) When the high-frequency sinusoidal wave signal switches between positive and negative, the two MOS tubes in the circuit are alternately turned on, and the switching frequency of the switch tube is the same as the oscillation frequency.

[0064] The specific implementation of the high-frequency arc maintenance circuit in the embodiment of the present invention is described in detail below from the two aspects of the circuit structure and circuit parameters of the high-frequency maintenance circuit.

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

[0066] In one implementation of the present invention, an implementation scheme of a high-frequency arc maintenance circuit is provided, such as Figure 3 As shown, Figure 1 The circuit structure diagram of the high-frequency arc-maintaining circuit in the plasma ignition circuit provided in the illustrated embodiment. The high-frequency arc-maintaining circuit in this implementation includes: pull-down resistors R1 and R2, current-limiting resistors R3 and R4, MOS transistors Q1 and Q2, diodes D1 and D2, clamping diodes D3 and D4, choke inductors L1 and L2, resonant capacitors C1 and C2, and primary inductor JP2 of a step-up transformer. Among them, the current limiting resistor R3 and the current limiting resistor 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 the MOS tube Q1, the other end of the choke inductor L2 is connected to the drain of the MOS tube Q2, the sources of the MOS tube Q1 and the MOS tube Q2 are connected and grounded, and the other end of the choke inductor L1 and the other end of the choke inductor L2 are respectively connected to the primary inductor JP2, and the parallel resonant capacitors C1 and C2 are connected between the other end of the choke inductor L1 and the other end of the choke inductor L2.

[0067] The other end of the current limiting resistor R3 is connected to the gate of the MOS transistor Q1, one end of the pull-down resistor R1 and the cathode of the clamping diode D3 connected in parallel with R1 are connected to the gate of the MOS transistor Q1, the other end of the pull-down resistor R1 and the anode of the clamping diode D3 are connected to the source of the MOS transistor Q1 and are grounded, the cathode of the diode D1 is connected to the drain of the MOS transistor Q1, and the anode is connected to the gate of the MOS transistor Q2;

[0068] The other end of the current limiting resistor R4 is connected to the gate of the MOS tube Q2, one end of the pull-down resistor R2 and the cathode of the clamping diode D4 connected in parallel with R2 are connected to the gate of the MOS tube Q2, the other end of the pull-down resistor R2 and the anode of the clamping diode D4 are connected to the source of the MOS tube Q2 and are grounded, the cathode of the diode D2 is connected to the drain of the MOS tube Q2, and the anode is connected to the gate of the MOS tube Q1.

[0069] Based on the circuit structure of the high-frequency maintenance circuit provided by the implementation, the working principle of the high-frequency maintenance circuit is:

[0070] The working principle of the upper half cycle of the sine wave signal is as follows: at the moment of power-on, the power supply VCC is directly added to the gates of the MOS tubes Q1 and Q2 through the current limiting resistors R3 and R4. Due to the slight difference between the two resistors R3 and R4) and the slight difference between the junction capacitances of the two MOS tubes (Q1 and Q2), one of the MOS tubes is turned on first; assuming that Q1 is turned 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 of 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, and the current of the parallel resonant circuit flows to the ground through the drain and source of the MOS tube Q1. In the above process, the diode D1 is turned on to pull down the gate voltage of the MOS tube Q2, so that the MOS tube Q2 is in the off state.

[0071] The working principle of the lower half cycle of the sine wave signal is as follows: when the current of the parallel resonant circuit formed by the primary inductor JP2 of the boost transformer and the resonant capacitor C1 and the resonant capacitor C2 oscillates according to the waveform of the positive half cycle of the sine wave signal, as time goes by, when the sine wave signal oscillates to 0 potential, the drain of the MOS tube Q1 becomes high level, and the diode D1 is turned off. At this time, the gate of the MOS tube Q2 is high level, and the MOS tube Q2 is turned on, that is, the diode D2 is turned on and the MOS tube Q1 is turned off; the power supply VCC charges the resonant capacitor C1 and the resonant capacitor C2 through the choke inductor L1; after C1 and C2 are charged, they form a parallel resonant circuit with the primary inductor JP2 of the boost transformer, thereby generating a pulse current. The current of 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 waveform of the negative half cycle of the sine wave signal, and the current of the parallel resonant circuit flows to the ground through the drain and source of the MOS tube Q2. In the above process, the diode D2 is turned on to lower the gate voltage of the MOS transistor Q1 , so that the MOS transistor Q1 is in the off state.

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

[0073] (II) Calculation of key circuit parameters of high-frequency arc-maintaining circuit

[0074] 2.1, Component Selection

[0075] a) MOS tube selection:

[0076] On the one hand, after the circuit oscillates stably, the two MOS tubes (Q1 and Q2) each withstand half a cycle of sinusoidal voltage, and the drain voltage is a half-wave rectified waveform, and its average value should be equal to the power supply voltage, so the drain voltage peak of the MOS tube is approximately 3.14 times the power supply voltage; therefore, for a 28VDC plasma ignition circuit, the maximum voltage that the MOS tube withstands is 87.92V.

[0077] On the other hand, the voltage expression of the yoke inductance L1 is Considering the operating frequency of 25kHz and the duty cycle of 0.5, the maximum current flowing through the yoke inductor L1 is 8.7A. Considering the current margin, the drain current of the MOS tube should be at least 15A.

[0078] Combining the above two reasons, the IRFP250 MOS tube is selected, which has a drain current of 33A and a drain voltage of 200V, which can meet the usage requirements.

[0079] b) Capacitor selection:

[0080] When the circuit oscillates stably, the capacitor energy is equal to the inductor energy of the step-up transformer, and the calculation formula for 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 the oscillation process. Since the oscillation frequency is relatively high, approximately 25kHz, a fast recovery diode should be selected, and FR107 fast recovery diode can be selected.

[0083] Diodes D3 and D4 are used to protect the gate of the MOS tube from being broken down by high voltage. Therefore, 12V voltage regulator tubes can be selected for D3 and D4. 1N4742 is selected in this solution.

[0084] d)Resistor selection:

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

[0086] 2.2, Step-up transformer calculation

[0087] The functions of the step-up transformer mainly include two aspects: providing high-voltage arc-starting pulses and high-power arc-maintaining current. Therefore, the step-up transformer should be able to meet the requirements of high-voltage and high-power output at the same time. The design requirements of the step-up transformer are as follows:

[0088] Input voltage: 60V;

[0089] Output voltage: ≥10kV;

[0090] Working frequency: ≥5kHz;

[0091] Rated power: 300W.

[0092] Considering the cost and processing time, the iron core is selected from the existing UY20 ferrite core in the factory. The maximum power of this size of core can reach 500W, and it has the advantages of wide application and simple structure. When determining the number of turns of the primary coil and the secondary coil, considering that the operating frequency of the step-up transformer is 25kHz, the number of turns per volt of the primary coil n1 is:

[0093] n1=0.225÷(fB m S);

[0094] Where: f is the operating frequency / Hz; B m is the maximum magnetic induction intensity; S is the cross-sectional area of ​​the magnetic core.

[0095] After calculation, the number of turns per volt of the primary coil is about 0.045, and the primary voltage is 60V, so the number of turns of the primary coil is 3 turns (rounded), and combined with engineering experience, the number of turns of the primary coil can be selected as 5. According to the transformer ratio, the secondary coil needs to output a voltage of 10kV. At this time, the ratio of the step-up transformer is 167. During use, a certain margin (usually 50%) needs to be reserved to improve the breakdown performance. Therefore, the ratio can be selected as 240, and the number of turns of the secondary coil is 1200.

[0096] The primary current is equal to the maximum current flowing through the capacitor in the resonant circuit, the effective value is 15A, and the current density j = 4A / mm 2 , the cross-sectional area of ​​the primary conductor is 4mm 2 Since the ignition coil works for a short time, the overload capacity of the transformer can be used. The diameter of the primary coil can be selected as 2mm, and the cross-sectional area is 3.14mm. 2 , meeting the use requirements. The selection of the secondary coil wire should take into account the current passing through the arc. Usually the plasma voltage does not exceed 1000V, the current is considered to be 0.3A, and the secondary coil wire diameter can be selected as 0.3mm. Since the ignition coil is used for no more than 30s, the selection of the secondary coil wire diameter can meet the use requirements.

[0097] In order to improve the energy storage capacity of the transformer and also to meet the volt-ampere characteristics of arc operation, a certain air gap should be added to the iron core of the transformer to increase the leakage reactance of the transformer so that after the electrode gap is broken down, the output voltage of the transformer can be rapidly reduced to meet the arc burning.

[0098] After the transformer was wound and insulated with varnish, the primary inductance was measured to be 31μH and the leakage inductance was 120μH.

[0099] The plasma ignition circuit with adaptive voltage frequency adjustment provided by the embodiment of the present invention generates a high-voltage, low-current voltage pulse through a high-voltage arc-starting circuit, and breaks down the discharge gap of the ignition nozzle after being output through an output protection circuit; generates a high-frequency sinusoidal voltage signal 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 realizing the ignition function. Among them, based on the device characteristics in the high-frequency arc-maintaining circuit, one of the MOS tubes is turned on first, and the two MOS tubes are alternately turned on in the positive half cycle or negative half cycle of the high-frequency sinusoidal voltage signal, and a resonant circuit is formed in the high-frequency arc-maintaining circuit. The resonant frequency is the same as the switching frequency of the MOS tube, so that the current in the circuit is output to the ignition nozzle according to the sinusoidal wave of the resonant frequency. Compared with the existing ignition circuit, the plasma ignition circuit provided by the embodiment of the present invention has greater power and can generate a longer arc for ignition.

[0100] The ignition effect of the plasma ignition circuit with adaptive voltage and frequency adjustment provided by the embodiment of the present invention is verified through an ignition test as follows.

[0101] The test uses an igniter connected to the rear end of the ignition circuit to ignite the oil-gas mixture. The airflow in the simulated combustion chamber is 100L / min, and the ignition system power supply voltage is 28VDC. Figure 4 The figure shows the schematic diagram of the plasma ejected from the igniter. It can be seen that the plasma is in the shape of a torch outside the igniter, and its flame length is about 2 cm. At the center of the igniter outlet, the plasma burns most violently and brightest, and the brightness begins to dim as it moves away from the outlet. At 2 cm from the outlet, the plasma changes from white to yellow, and the density becomes thin, indicating that the arc can no longer be maintained at this point.

[0102] The gas flow rate in the engine combustion chamber was changed to 50L / min, 100L / min, 150L / min and 200L / min, and ignition tests were carried out respectively. The arc plasma was photographed as follows: Figure 5 As shown, Figure 5The figure is a schematic diagram of arc plasma under different airflow conditions in the ignition test of an embodiment of the present invention. The airflow size has little effect on the length of the plasma jet, and the ignition jet length fluctuates within the range of (2 to 2.5) cm. When the airflow becomes larger, the plasma begins to burn slightly off-center, that is, the "tip" of the flame is not on the central axis of the igniter. It is speculated that the reason may be that after the airflow increases, the local airflow is unbalanced, blowing the plasma in a direction that deviates from the central axis. There is no plasma deviation in the simulation, because the simulation assumes that the model is a two-dimensional rotation axis symmetric model, and no airflow is applied to offset the arc. Therefore, the arc will 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 oil-gas mixture in the combustion chamber, whether it is lean oil or heavy oil conditions, and the ignition is successful, indicating that the ignition system works reliably and has good ignition performance.

[0104] The plasma ignition circuit with adaptive voltage and frequency adjustment provided by the present invention has been used in a plasma ignition device and has been tested in a simulated combustion chamber, and the use effect is good. A high-altitude ignition test was carried out in the engine combustion chamber, and the results showed that the circuit significantly improved the ignition height of the engine.

[0105] Although the embodiments disclosed in the present invention are as above, the contents are only embodiments adopted to facilitate understanding of the present invention and are not intended to limit the present invention. Any technician in the field to which the present invention belongs can make any modifications and changes in the form and details of implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A plasma ignition circuit with adaptive voltage and frequency adjustment, characterized in that: include: High voltage arc starting circuit, high frequency arc maintaining circuit and output protection circuit; The power supply VCC is connected to the high-voltage arc starting circuit and the high-frequency arc piloting circuit respectively, and both the high-voltage arc starting circuit and the high-frequency arc piloting circuit are connected to the ground; the arc starting positive terminal and the arc starting negative terminal of the high-voltage arc starting circuit are connected to the output protection circuit, the arc piloting positive terminal and the arc piloting negative terminal of the high-frequency arc piloting circuit are connected to the output protection circuit, and the output positive terminal and the output negative terminal 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 arc, thereby realizing the ignition function; Among them, the high-frequency arc-maintaining circuit has two MOS tubes, which are alternately turned on in the positive half-cycle or the negative half-cycle of the high-frequency sine wave signal, and form a resonant loop in the high-frequency arc-maintaining circuit, so that the current in the circuit is output to the ignition nozzle according to the sine wave of the resonant frequency.

2. The plasma ignition circuit with adaptive voltage and frequency adjustment according to claim 1, characterized in that: The high-frequency maintenance circuit includes: a driving circuit and a transformer assembly; a high-frequency sine wave signal is generated by the driving circuit, and a high-frequency voltage source output by the high-frequency arc maintenance circuit is obtained after the transformer boosts the voltage; Among them, the high-frequency sinusoidal wave signal is used to maintain arc burning after boosting through the transformer, and is also used to make the two MOS tubes in the high-frequency maintenance circuit alternately turned on when switching between positive and negative; and the switching frequency of the MOS tube is the same as the oscillation frequency of the high-frequency sinusoidal wave signal.

3. The plasma ignition circuit with adaptive voltage and frequency adjustment according to claim 2, characterized in that: The high-frequency maintenance circuit includes: pull-down resistors R1 and R2, current limiting resistors R3 and R4, MOS transistors Q1 and Q2, diodes D1 and D2, clamping diodes D3 and D4, choke inductors L1 and L2, resonant capacitors C1 and C2, and a primary inductor JP2 of a step-up transformer; The current limiting resistor R3 and the current limiting resistor 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 the MOS tube Q1, the other end of the choke inductor L2 is connected to the drain of the MOS tube Q2, the sources of the MOS tube Q1 and the MOS tube Q2 are connected and grounded, and the other end of the choke inductor L1 and the other end 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 end of the choke inductor L1 and the other end of the choke inductor L2; The other end of the current limiting resistor R3 is connected to the gate of the MOS transistor Q1, one end of the pull-down resistor R1 and the cathode of the clamping diode D3 connected in parallel with R1 are connected to the gate of the MOS transistor Q1, the other end of the pull-down resistor R1 and the anode of the clamping diode D3 are connected to the source of the MOS transistor Q1 and are grounded, the cathode of the diode D1 is connected to the drain of the MOS transistor Q1, and the anode is connected to the gate of the MOS transistor Q2; The other end of the current limiting resistor R4 is connected to the gate of the MOS tube Q2, one end of the pull-down resistor R2 and the cathode of the clamping diode D4 connected in parallel with R2 are connected to the gate of the MOS tube Q2, the other end of the pull-down resistor R2 and the anode of the clamping diode D4 are connected to the source of the MOS tube Q2 and are grounded, the cathode of the diode D2 is connected to the drain of the MOS tube Q2, and the anode is connected to the gate of the MOS tube Q1.

4. The plasma ignition circuit with adaptive voltage and frequency adjustment according to claim 3, characterized in that: The working mode of the high frequency protection circuit includes: The working mode of the first half cycle of the high-frequency sinusoidal wave signal is as follows: at the moment of power-on, the power supply VCC is directly added to the gates of the MOS tubes Q1 and Q2 through the current limiting resistors R3 and R4. Based on the slight difference between the current limiting resistors R3 and R4 and the slight difference between the junction capacitances of the two MOS tubes, one of the MOS tubes is turned on first; the MOS tube Q1 is set to turn on the power first, and VCC charges the resonant capacitor C1 and the resonant capacitor C2 through the choke inductor L2; after the resonant capacitor C1 and the resonant capacitor 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 of 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 sinusoidal wave signal, and the current of the parallel resonant circuit flows to the ground through the drain and source of the MOS tube Q1; in the above process, the MOS tube Q2 is in the off state; The working mode of the second half cycle of the high-frequency sinusoidal signal is as follows: when the current of the parallel resonant circuit formed by the primary inductor JP2 of the step-up transformer and the resonant capacitor C1 and the resonant capacitor C2 oscillates according to the waveform of the positive half cycle of the sinusoidal signal, as time goes by, when the sinusoidal signal oscillates to 0 potential, the drain of the MOS tube Q1 becomes high level, and the diode D1 is turned off. At this time, the gate of the MOS tube Q2 is high level, and the MOS tube Q2 is turned on, so that the diode D2 is turned on and the MOS tube Q1 is turned off; the power supply VCC charges the resonant capacitor C1 and the resonant capacitor C2 through the choke inductor L1; after the resonant capacitor C1 and the resonant capacitor 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 of 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 sinusoidal signal, and the current of the parallel resonant circuit flows to the ground through the drain and source of the MOS tube Q2; in the above process, the MOS tube Q1 is in the off state.

5. The plasma ignition circuit with adaptive voltage and frequency adjustment according to claim 4, characterized in that: The working mode of the high frequency protection circuit also includes: As time goes on, the current in the parallel resonant circuit formed by the primary inductance JP2 of the step-up transformer and the resonant capacitors C1 and C2 alternately completes the positive half-cycle waveform oscillation and the negative half-cycle waveform oscillation according to the sine wave signal waveform, thereby forming a continuous sinusoidal current oscillation state; a high-voltage and high-frequency sinusoidal voltage will be induced on the secondary inductance of the step-up transformer.

6. The plasma ignition circuit with adaptive voltage and frequency adjustment according to any one of claims 3 to 5, characterized in that: The circuit parameter acquisition of the high-frequency maintenance circuit includes: component selection and calculation of parameters of the step-up transformer; The component selection includes: MOS tube selection, capacitor selection, diode selection, and resistor selection.

7. The plasma ignition circuit with adaptive voltage and frequency adjustment according to claim 6, characterized in that: In the selection of components for the high-frequency protection circuit, a) MOS tube selection methods include: S11, calculate the maximum voltage that the MOS tube can withstand, including: Based on the fact that each MOS tube bears a half-cycle of sinusoidal voltage, the average value of the drain voltage is equal to the power supply voltage; that is, the peak value of the drain voltage of the MOS tube is 3.14 times the power supply voltage; then for a 28VDC plasma ignition circuit, the maximum voltage that the MOS tube bears is 87.92V; S12, calculate the drain current of the MOS tube, including: The voltage expression based on the yoke inductance is: At an operating frequency of 25kHz and a duty cycle of 0.5, the maximum current flowing through the yoke inductor is 8.7A; based on the current margin design principle, the drain current of the MOS tube is at least 15A; b) Capacitor selection methods include: When the circuit oscillates stably, the capacitor energy is equal to the inductor energy of the step-up transformer, and the calculation formula for the capacitor current is: The maximum current of the capacitor is 21A. c) Diode selection methods include: The diode D1 and the diode D2 switch between on and off states during the oscillation process. Based on the higher oscillation frequency, the diode D1 and the diode D2 are fast recovery diodes. Diode D3 and diode D4 are used to protect the gate of the MOS tube from being broken down by high voltage. Diode D3 and diode D4 are 12V voltage regulator tubes. d) Resistor selection methods include: For the current limiting resistors R3 and R4, the selection is based on the rising speed of the MOS tube gate voltage and the loss of the MOS tube during the switching process; The pull-down resistors R1 and R2 realize the function of ensuring the gate voltage, and the resistance value of the pull-down resistors is much greater than the resistance value of the current limiting resistor.

8. The plasma ignition circuit with adaptive voltage and frequency adjustment according to claim 6, characterized in that: In the selection of components for the high-frequency protection circuit, the parameters of the step-up transformer are calculated including: Based on the design requirements of the step-up transformer, select a magnetic core that meets the power requirements; According to the operating frequency of the step-up transformer, the number of turns of the primary coil and the secondary coil is determined; the number of turns per volt of the primary coil n1 is: n1=0.225÷(fB m S); Where, f is the operating frequency / Hz; B m is the maximum magnetic induction intensity; S is the cross-sectional area of ​​the magnetic core; Determine the number of turns of the secondary coil according to the transformer ratio and the required output voltage of the secondary coil; Based on the fact that the primary current is equal to the maximum current flowing through the capacitor in the resonant circuit, the cross-sectional area of ​​the primary conductor determines the primary coil diameter; The selection of the wire for the secondary coil should take into account the current passing through the arc and the maximum value of the plasma voltage to determine the diameter of the secondary coil wire.

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