Constant-current voltage-limiting pulse power supply for linear cutting machine tool

Abstract

The utility model discloses a constant-current voltage-limiting pulse power supply for a linear cutting machine tool, which adopts a strategy of constant-current energy storage and energy release of a transformer, and specifically comprises an adjustable direct-current power supply VS1, a filter capacitor C1, a main control circuit, an H bridge consisting of three field-effect transistors Q1, Q2 and Q3 and a diode D1, a transformer T1 and a rectifier diode D2, wherein the main control circuit comprises gate driving chips U1 and U4, a main control chip U3, a gate driving optocoupler U2, resistors R1-R13, an adjustable direct-current power supply interface CN1 and an output interface CN2. During a pulse intermittent period, constant-current control is carried out on the primary side current of the transformer, and during pulse discharging, the effect of constant-current pulse discharging with a steep leading edge is obtained; a current-limiting resistor is not needed; therefore, the breakdown voltage is adjustable and controllable, and the output pulse current can be subdivided in a stepless manner. According to the utility model, requirements for sampling and operation speed are low, and control is not needed during the discharge period of a single pulse.

Description

TECHNICAL FIELD

[0001] The utility model relates to wire cutting machine tool technical field, especially, relate to a constant current voltage limiting pulse power supply for wire cutting machine tool. BACKGROUND

[0002] When wire cutting machine tool processes, require pulse power supply, output rectangular current pulse:

[0003] 1. in the breakdown stage of the discharge pulse front, first with higher, adjustable voltage, break down the processing gap as soon as possible, enter the discharge stage. Breakdown voltage must be adjustable and controllable to adapt to different materials, different thickness of workpiece, avoid the formation of arc by high voltage and damage the workpiece.

[0004] 2. in the discharge stage after breakdown, require discharge current to rise to target value quickly, thereafter keep stable to realize smooth discharge. Discharge current should be able to be infinitely subdivided.

[0005] 3. finally, when entering the pulse intermittent stage after discharge ends, current should be cut off as soon as possible, reduce tailing, oscillation, to facilitate rapid chip removal, cooling, eliminate ionization. Pulse intermittent time is usually more than 2 times of discharge time.

[0006] 4. electric isolation between commercial power and workpiece to ensure safe production.

[0007] 5. should improve the utilization rate of electric energy as much as possible and reduce energy consumption.

[0008] Traditional pulse power supply scheme relies on resistance current limiting, needs multiple field effect tubes and high-power resistors to obtain multiple discharge current. But it can not subdivide current infinitely, and the heat dissipation of resistor is large, and the utilization rate of electric energy is low.

[0009] The current more advanced scheme is to use multi-phase interleaved parallel Buck, Boost topology, and FPGA or DSP to perform fast sampling and operation. During a single discharge pulse, multiple inductance discharges are superimposed into the required current and voltage waveform. The basic idea is multi-channel time-sharing superposition. It can better realize the required current and voltage waveform, but the circuit is complex and difficult to implement. SUMMARY

[0010] The utility model aims at providing a kind of constant current pulse power supply for wire cutting machine tool, output before and after edge steep, approximate rectangular constant current pulse, the peak value of breakdown voltage is adjustable.

[0011] The utility model specifically includes adjustable direct current power VS1, filter capacitor C1, main control circuit, 3 field effect tubes Q1, Q2, Q3 and the H bridge of diode D1, transformer primary side T1A, transformer secondary side T1B, rectifier diode D2.

[0012] The positive and negative poles of the adjustable direct current power VS1 and the parallel filter capacitor C1 form a direct current bus.

[0013] The left bridge arm of the H-bridge is composed of a diode D1 and a field effect transistor Q1 in series, the anode of the diode D1 is connected with the drain of the field effect transistor Q1, the cathode of the diode D1 is connected with the positive pole of the direct current bus, and the source of the field effect transistor Q1 is connected with the negative pole of the direct current bus.

[0014] The right bridge arm of the H-bridge is composed of a field effect transistor Q2 and a field effect transistor Q3 in series, the source of the field effect transistor Q2 is connected with the drain of the field effect transistor Q3, the drain of the field effect transistor Q2 is connected with the positive pole of the direct current bus, and the source of the field effect transistor Q3 is connected with the negative pole of the direct current bus.

[0015] The same end of the primary side T1A of the transformer is connected with the midpoint of the left bridge arm, and the different end is connected with the midpoint of the right bridge arm.

[0016] The same end of the secondary side T1B of the transformer is connected with the anode of the rectifier diode D2, and the cathode of the rectifier diode D2 and the different end of the secondary side T1B of the transformer are connected with the discharge gap through a molybdenum wire, a wire and a processed workpiece.

[0017] Further, the utility model discloses a current sensor for detecting the current of the primary side T1A of the transformer.

[0018] The utility model discloses the specific working process, and is divided into 3 working states:

[0019] I: discharge intermittent state.

[0020] During the discharge intermittent period, constant current control is performed on the primary side current to prepare for discharge, and the state is divided into two control stages:

[0021] I-I: current maintaining stage.

[0022] The main control circuit outputs a signal to turn off the field effect transistor Q2, turn on the field effect transistor Q1 and the field effect transistor Q3, and the primary side T1A of the transformer, the field effect transistor Q1 and the field effect transistor Q3 form a primary side current maintaining path, at this time, the primary side T1A of the transformer is short-circuited, the voltage thereof is approximately zero, the voltage of the secondary side T1B of the transformer is also approximately zero, and the transformer current and magnetic field energy can be maintained. Due to circuit loss, the primary side current will slowly decay.

[0023] The main control circuit samples the current of the primary side T1A of the transformer, calculates the charging duration according to the real-time value and the set value, and outputs a control signal to charge the primary side to realize the effect of constant primary side current.

[0024] I-II: charging stage.

[0025] According to the required charging time, the main control circuit outputs a signal, turns off the field effect transistor Q3, turns on the field effect transistor Q1 and the field effect transistor Q2, and the adjustable direct current power VS1 charges the primary side T1A of the transformer, the primary side current increases, and the transformer magnetic field energy increases. According to the same name end, at this time, the diode D2 is turned off due to reverse bias, and the secondary side T1B of the transformer has no current.

[0026] In the discharge interval state, the above two control stages are repeated to realize constant current control of the primary side current.

[0027] II: Discharge state.

[0028] When pulse discharge is required, the main control circuit outputs a control signal, turns off the field effect transistor Q1 and the field effect transistor Q2, and turns on the field effect transistor Q3. The time width of the pulse discharge is preset by the user. Two cases are described as follows:

[0029] II-I: Before the discharge gap is broken down, the secondary side T1B of the transformer is in an open circuit state, and the current is zero. The primary side current charges the direct current bus filter capacitor C1 through the field effect transistor Q3, the primary side T1A of the transformer and the diode D1; the primary side voltage is clamped to the direct current bus voltage by the diode D1 and the field effect transistor Q3, and the voltage polarity of the same name end of the transformer primary side T1A is positive.

[0030] At the same time, according to the same name end, a positive polarity voltage is induced at the same name end of the secondary side T1B of the transformer, and the diode D2 is forward biased and turned on. The induced voltage of the secondary side T1B of the transformer is applied to the discharge gap through the wire, the molybdenum wire and the workpiece to form a breakdown voltage Vob. The breakdown voltage Vob is proportional to the primary side voltage Vp of the transformer, and is specifically as follows:

[0031] Vob = Ns / Np * Vp;

[0032] = Ns / Np * Vdc;

[0033] In the above formula, Vob is the breakdown voltage, Np is the number of turns of the primary side, Ns is the number of turns of the secondary side, Vp is the primary side voltage, and Vdc is the bus voltage.

[0034] Ignoring the on-voltage drop of the switching device, the primary side voltage Vp is clamped to the bus voltage Vdc, and therefore the secondary side output voltage is clamped, ensuring that the workpiece is not damaged due to excessive voltage at any time.

[0035] II-II: After the discharge gap is broken down, the discharge between the molybdenum wire and the workpiece forms, and the secondary side output discharge current Is is proportional to the primary side current Ip, and is specifically as follows:

[0036] Is = Np / Ns * Ip;

[0037] Where Ip is the primary current, Is is the secondary discharge current, Np is the primary turns, and Ns is the secondary turns.

[0038] At the same time, the secondary voltage drops below the breakdown voltage during discharge. The primary voltage drops synchronously, and the diode D1 is reverse-biased and cut off when the primary voltage is lower than the bus voltage, and the primary current is zero.

[0039] As can be seen, the discharge current Is is clamped, and even if short-circuited, it will not run out of control.

[0040] During discharge, the transformer magnetic field energy is transferred to the discharge gap.

[0041] III: Reverse pulse fast cut-off state.

[0042] At the end of discharge, due to the existence of the dispersion inductance of the molybdenum wire and the wire, the discharge current cannot be immediately cut off, and a current tail phenomenon is formed. As shown in Figure 4 .

[0043] To improve the current tail phenomenon, at the end of discharge, the main control circuit outputs a control signal to turn off the field effect transistor Q3 and turn on the field effect transistor Q1 and the field effect transistor Q2. The primary side T1A of the transformer is connected to the two ends of the DC bus, with the same name being negative and the non-same name being positive. At this time, the same name end voltage of the secondary side T1B of the transformer is negative, and the output is a reverse pulse opposite to the direction of the tail current.

[0044] The reverse pulse application time can be derived as follows:

[0045] According to Vs = ( Ls+Ld ) * d i / d t

[0046] ⇒ d t = (Ls+Ld) * d i / Vs

[0047] In the above formula, Vs is the secondary reverse pulse voltage, and

[0048] Vs = Vp * Ns / Np

[0049] Vp ≈ Vdc;

[0050] ⇒ d t ≈ (Ls+Ld) * d i / ( Vdc * Ns / Np )

[0051] In the above formula, Ls is the secondary inductance, Ld is the line dispersion inductance, Np is the primary turns, Ns is the secondary turns, Vp is the primary voltage, Vdc is the bus voltage, and d iIs is the instantaneous value of the secondary current, namely Is.

[0052] According to the above formula, the reverse pulse action time d is calculated t Under the action of the reverse pulse, the tail current drops rapidly.

[0053] When the tail current drops to zero, under the action of the reverse pulse voltage, the diode D2 is reverse-biased off, so that no reverse current is formed on the discharge gap.

[0054] The reverse pulse action time d t After the end, return to the pulse intermittent state, prepare for the next discharge.

[0055] Further, a sampling resistor can be connected in series at the source of the field effect transistor Q1 or Q3 to sample the primary current of the transformer T1A at low cost; the field effect transistor can also be used to replace the diode D2 to adopt synchronous rectification technology to further reduce power consumption.

[0056] The utility model adopts the strategy of transformer constant current energy storage and release. Beneficial effects are obtained:

[0057] 1) During the pulse intermittent period, constant current control is implemented on the primary current of the transformer, and during the pulse discharge, the effect of constant current pulse discharge with steep front edge is obtained; the current tail phenomenon is improved by outputting the reverse pulse voltage;

[0058] 2) No current limiting resistor is needed, and the power utilization rate is improved;

[0059] 3) Compared with the multi-phase interleaved parallel scheme, the circuit is simplified;

[0060] 4) The breakdown voltage is adjustable and controllable, and the output pulse current can be infinitely subdivided;

[0061] 5) The sampling and operation speed requirement is low. During the discharge period of a single pulse, sampling and operation do not need to be performed. BRIEF DESCRIPTION OF DRAWINGS

[0062] Figure 1 It is a circuit topology diagram;

[0063] Figure 2 It is a transformer current path schematic diagram;

[0064] Figure 3 It is a circuit block diagram.

[0065] Figure 4 It is a waveform schematic diagram.

[0066] Figure 5 The implementation circuit schematic diagram is shown in the figure. DETAILED DESCRIPTION

[0067] The utility model is further described below in combination with the drawings and examples.

[0068] As shown in Figure 1 and 5 The constant current and voltage limiting pulse power supply for the wire cutting machine tool adopts the strategy of transformer constant current energy storage and release, and specifically comprises an adjustable DC power supply VS1, a filter capacitor C1, a main control circuit, an H-bridge composed of three field effect tubes Q1, Q2 and Q3 and a diode D1, a transformer T1 and a rectifier diode D2.

[0069] The positive and negative poles of the adjustable DC power supply VS1 are connected in parallel with the filter capacitor C1 to form a DC bus; the first and second pins of the adjustable DC power supply interface CN1 are respectively connected with the positive and negative poles of an adjustable DC power supply and the positive and negative poles of the filter capacitor C1 to form the positive pole Vdc and the negative pole GND of the DC bus.

[0070] The diode D1 and the first field effect tube Q1 are connected in series to form the left bridge arm of the H-bridge; the positive pole of the diode D1 and the drain of the first field effect tube Q1 are connected with the same-named end of the primary side T1A of the transformer; the source of the first field effect tube Q1 is grounded, and the negative pole of the diode D1 is connected with the positive pole Vdc of the DC bus.

[0071] The second field effect tube Q2 and the third field effect tube Q3 are connected in series to form the right bridge arm of the H-bridge; the drain of the third field effect tube Q3 and the source of the second field effect tube Q2 are connected with the non-same-named end of the primary side T1A of the transformer; the source of the third field effect tube Q3 is grounded, and the drain of the second field effect tube Q2 is connected with the positive pole Vdc of the DC bus.

[0072] The same-named end of the secondary side T1B of the transformer is connected with the positive pole of the rectifier diode D2; the negative pole of the third diode D2 and the non-same-named end of the secondary side T1B of the transformer are connected through the output interface CN1, a molybdenum wire, a lead wire and a workpiece to be processed, and are externally connected with a discharge gap.

[0073] The first pin of the gate drive chip U1 is externally connected with a 12V voltage; the fourth and fifth pins of the gate drive chip U1 are grounded; the second and third pins of the gate drive chip U1 are respectively connected with one end of the resistor R1 and one end of the resistor R2; the other end of the resistor R1 and the other end of the resistor R2 are connected with one end of the resistor R3 and the gate of the first field effect tube Q1; the other end of the resistor R3 is connected with the source of the first field effect tube Q1 and is grounded; the sixth pin of the gate drive chip U1 is connected with one end of the resistor R4 and the forty-third pin of the main control chip U3; the other end of the resistor R4 is externally connected with a 3.3V voltage.

[0074] The 1st pin of the gate drive optocoupler U2 is connected with the 8th pin of the main control chip U3; the 3rd pin of the gate drive optocoupler U2 is grounded through the resistor R5; the 4th pin of the gate drive optocoupler U2 is connected with the non-same end of the primary side T1A of the transformer; the 5th pin of the gate drive optocoupler U2 is connected with one end of the resistor R7; the other end of the resistor R7, one end of the resistor R9 and the gate of the second field effect tube Q2 are connected; the other end of the resistor R9 is connected with the source of the second field effect tube Q2 and the non-same end of the primary side T1A of the transformer; the 6th pin of the gate drive optocoupler U2 is externally connected with a 15V voltage, so that there is a 15V power supply between the 6th pin and the 4th pin of the gate drive optocoupler U2.

[0075] The 6th pin of the gate drive chip U4 is connected with one end of the resistor R6 and the 2nd pin of the main control chip U4, and the other end of the resistor R6 is grounded; the 1st pin of the gate drive chip U4 is externally connected with a 12V voltage; the 4th and 5th pins of the gate drive chip U4 are grounded; the 2nd pin of the gate drive chip U4 is connected with one end of the resistor R8, and the other end of the resistor R8 is connected with one end of the resistor R9, one end of the resistor R11 and the gate of the third field effect tube Q3; the other end of the resistor R9 is connected to the 3rd pin of the gate drive chip U4; the other end of the resistor R11, the source of the third field effect tube Q3 and one end of the milliohm resistor CS1 are connected with one end of the resistor R14;

[0076] The other end of the milliohm resistor CS1 is connected with one end of the resistor R13 and grounded;

[0077] The other end of the resistor R13 is connected with the 13th pin of the main control chip U3;

[0078] The other end of the resistor R14 and one end of the resistor R12 are simultaneously connected to the 17th pin of the main control chip U3;

[0079] The other end of the resistor R12 is simultaneously connected to the 14th and 23rd pins of the main control chip.

[0080] The 27th, 15th, 31st, 47th and 63rd pins of the main control chip U3 are grounded.

[0081] The 16th, 28th, 29th, 32nd, 48th and 64th pins of the main control chip U3 are externally connected with a 3.3V power supply.

[0082] Further, the circuit of the utility model specifically realizes the process as follows:

[0083] During the discharge interval, the primary side is charged with constant current to realize energy storage of the transformer, and the specific process is as follows:

[0084] During the discharge interval, the control chip U3 outputs TIM_CH2 as high level, and the first field effect tube Q1 is turned on through the gate drive chip U1 and the resistors R1 and R2;

[0085] The control chip U3 outputs complementary output signals TIM_CH1H and TIM_CH1N. The output signal TIM_CH1H drives the second field effect transistor Q2 through the gate drive optical coupler U2 and the resistor R7. The output signal TIM_CH1N drives the third field effect transistor Q3 through the gate drive chip U4 and the resistors R8 and R9.

[0086] Further, during the period when the output signal TIM_CH1 is low and TIM_CH2N is high, the second field effect transistor Q2 is off, and the third field effect transistor Q3 is on. At this time, because the second field effect transistor Q2 is off and the first field effect transistor Q1 and the third field effect transistor Q3 are on, the primary side T1A of the transformer is short-circuited by the first field effect transistor Q1, the third field effect transistor Q3 and the milliohm resistor CS1, forming a primary side current maintenance path. As shown in FIG. 4, the primary side voltage of the transformer is zero, and the secondary side T1B voltage of the transformer is also zero, so the output voltage and current of the discharge gap are both zero. Figure 2

[0087] The primary side current forms a voltage signal on the milliohm resistor CS1. The voltage signal is amplified by the OPAMP1 built-in the control chip U3, and is transferred from the pin 14 to the pin 23 of the control chip U3, reaching the ADC circuit built-in the control chip U3. The control chip U3 performs the following operations:

[0088] a) The real-time value of the primary side current is obtained by performing analog-to-digital conversion through the ADC circuit;

[0089] b) According to the set value of the primary side current and the real-time value of the primary side current, the existing PID algorithm built-in the control chip U3 is executed to obtain the primary side charging time, i.e. the PWM duty cycle;

[0090] c) The output signal TIM_CH2N is output as low to turn off the third field effect transistor Q3 through the gate drive chip U4 and the resistors R8 and R8, and the output signal TIM_CH1 is output as high to turn on the second field effect transistor Q2 through the gate drive optical coupler U2 and the resistor R7.

[0091] Further, during the period when the output signal TIM_CH1 is high and TIM_CH2N is low, the second field effect transistor Q2 is on, and the third field effect transistor Q3 is off. At this time, because the third field effect transistor Q3 is off and the first field effect transistor Q1 and the second field effect transistor Q2 are on, the primary side T1A of the transformer is connected to the DC bus through the first field effect transistor Q1 and the second field effect transistor Q2. The current of the primary side T1A of the transformer rises. This is the process of charging and storing energy for the transformer.

[0092] ​At this time, the voltage polarity of the same name end of the primary side of the transformer T1A is negative, the induced voltage polarity of the same name end of the secondary side of the transformer T1B is also negative, and the rectifier diode D2 is turned off due to reverse bias. Therefore, the output voltage and current of the discharge gap are both zero; the transformer can be simplified as an inductor with only the primary side.

[0093] In summary, during the discharge interval, the control chip U3 detects the current signal, executes the PID algorithm, and outputs the output signal to achieve constant current control of the primary side, so as to approach the set current value.

[0094] Further, during the pulse discharge, the transformer discharges energy, specifically as follows:

[0095] During the pulse discharge, the control chip U3 outputs TIM_CH2 as a low level, which is turned off through the gate drive chip U1 and resistors R1 and R2.

[0096] TIM_CH1 is output as a low level, which is turned off through the gate drive optocoupler U2 and resistor R7.

[0097] TIM_CH1H is output as a high level, which is turned on through the gate drive chip U4 and resistors R8 and R9.

[0098] Further, before the discharge gap is broken down, the transformer secondary side T1B current is zero. The primary side current is discharged to the DC bus filter capacitor C1 through the third field effect transistor Q3, the transformer primary side T1A and the diode D1; the primary side voltage Vp is clamped to the DC bus voltage Vdc through the diode D1, the third field effect transistor Q3 and the milliohm resistor CS1. At this time, the voltage polarity of the same name end of the transformer primary side T1A is positive.

[0099] At the same time, at the same name end of the transformer secondary side T1B, a positive polarity voltage is induced, and the rectifier diode D2 is turned on by forward bias. The induced voltage of the transformer secondary side T1B is applied to the discharge gap through the output interface CN2, the wire, the molybdenum wire and the workpiece to form the breakdown voltage Vob. The breakdown voltage Vob is proportional to the transformer primary side T1A voltage Vp.

[0100] Vp ≈ Vdc;

[0101] Vob = Ns / Np * Vp

[0102] = Ns / Np * Vdc;

[0103] In the above formula, Vob is the breakdown voltage, Np is the number of turns of the primary side, Ns is the number of turns of the secondary side, Vp is the primary side voltage, and Vdc is the bus voltage.

[0104] Further, the utility model discloses the conduction voltage drop of switch device is ignored, and the primary voltage Vp is clamped in the bus voltage Vdc.

[0105] Further, under the action of breakdown voltage Vob, the discharge gap is broken down, and the discharge between the molybdenum wire and the workpiece forms the secondary side output discharge current.

[0106] In the above process, the current, voltage waveform is described as Figure 4 .

[0107] During the discharge process, the transformer magnetic field energy is transferred to the discharge gap.

[0108] Further, the utility model realizes the working principle as follows:

[0109] Transformer primary energy storage Wp = 1 / 2 * Lp * Ip 2

[0110] Transformer secondary energy storage Ws = 1 / 2 * Ls * Is 2

[0111] In the above formula, Lp is the primary inductance, Ls is the secondary inductance, Ip is the primary current, and Is is the secondary current.

[0112] Wp = Ws;

[0113] ⇒Lp * Ip 2 = Ls * Is 2

[0114] ⇒Lp / Ls = ( Is / Ip ) 2 …(Formula 1)

[0115] According to the relationship between the primary and secondary inductance of transformer: the ratio of the inductance of the primary and secondary, equal to the square of the turns ratio:

[0116] Lp / Ls = ( Np / Ns ) 2 …(Formula 2)

[0117] By (Formula 1), (Formula 2) can be obtained:

[0118] ⇒Lp / Ls = ( Is / Ip ) 2= Lp / Ls = ( Np / Ns ) 2

[0119] = ( Np / Ns ) 2 = ( Np / Ns ) 2

[0120] = ( Np / Ns )

[0121] = ( Np / Ns )

[0122] In (Formula 3), Ip is the primary current, Is is the secondary current, Np is the primary number of turns, Ns is the secondary number of turns, and Np, Ns are constants.

[0123] As can be seen from (Formula 3), the discharge current Is is proportional to the primary current Ip, that is, it is clamped by Ip. Even if the molybdenum wire is short-circuited with the workpiece, the secondary discharge current Is will not increase dramatically.

[0124] In fact, during the pulse discharge, the situation of open circuit, breakdown and discharge of the discharge gap occurs continuously and repeatedly.

[0125] Further optimization can also use field effect tubes to replace diodes D2, and use synchronous rectification technology to further reduce power consumption.

[0126] Embodiment:

[0127] The adjustable DC power supply used in the utility model is 350V; KS250-090A double magnetic ring of Zhejiang Dongmu Koda Magnetic and Electric Co., Ltd. is used, the primary side has 77 turns, the secondary side has 22 turns, and a transformer is wound; The primary side is set to constant current 8.0A, and the output breakdown voltage is clamped at:

[0128] Vob = 350 * 22 / 77 = 100V ;

[0129] Pulse discharge current:

[0130] Is = 8.0 * 77 / 22 = 28A ;

[0131] To simplify the circuit, a diode can be used instead of a field effect tube Q3, but the power consumption increases. Field effect tubes can also be used instead of diodes D2, and step rectification technology can be used to further reduce power consumption.

[0132] Finally, it should be noted that the purpose of the disclosed embodiments is to help further understand the present application, but those skilled in the art can understand that various replacements and modifications are possible without departing from the spirit and scope of the present application and the appended claims. Therefore, the present application should not be limited to the disclosed content, and the scope of protection of the present application is defined by the scope of the claims.

Claims

1. A constant current, limited voltage pulsed power supply for a wire cutting machine tool, characterised in that The adjustable DC power supply VS1, the filter capacitor C1, the main control circuit, the H-bridge composed of three field effect tubes Q1, Q2, Q3 and diode D1, the transformer T1 composed of the primary side T1A and the secondary side T1B, and the rectifier diode D2; The positive and negative poles of the adjustable DC power supply VS1 are connected in parallel with the filter capacitor C1 to form a DC bus. The left bridge arm of the H-bridge is composed of the diode D1 and the field effect tube Q1 connected in series, the anode of the diode D1 is connected with the drain of the field effect tube Q1, the cathode of the diode D1 is connected with the positive pole of the DC bus, and the source of the field effect tube Q1 is connected with the negative pole of the DC bus. The right bridge arm of the H-bridge is composed of the field effect tube Q2 and the field effect tube Q3 connected in series, the source of the field effect tube Q2 is connected with the drain of the field effect tube Q3, the drain of the field effect tube Q2 is connected with the positive pole of the DC bus, and the source of the field effect tube Q3 is connected with the negative pole of the DC bus. The same poles of the transformer primary side T1A are connected with the midpoint of the left bridge arm, and the different poles are connected with the midpoint of the right bridge arm. The same poles of the transformer secondary side T1B are connected with the anode of the rectifier diode D2, and the cathode of the rectifier diode D2 and the different poles of the transformer secondary side T1B are connected with the discharge gap through the molybdenum wire, the wire and the workpiece.

2. The constant current, limited voltage pulsed power supply for a wire electrical discharge machine as defined in claim 1, wherein, The current sensor for detecting the current of the transformer primary side T1A is arranged.

3. The constant current, limited voltage pulsed power supply for a wire electrical discharge machine as defined in claim 1, wherein The sampling resistor is connected in series with the source of the field effect tube Q1 or Q3, and the current of the transformer primary side T1A is sampled during the discharge interval.

4. The constant current, limited voltage pulsed power supply for a wire electrical discharge machine as defined in claim 1, wherein, During the discharge interval, the main control circuit continuously samples the current of the transformer primary side T1A, calculates the charging duration according to the real-time value and the set value, and outputs the control signal to charge the primary side, thereby realizing the effect of constant primary side current.

5. The constant current, limited voltage pulsed power supply for a wire electrical discharge machine as defined in claim 4, wherein, When the control signal turns off the field effect tube Q3 and turns on the field effect tube Q1 and the field effect tube Q2, the adjustable DC power supply VS1 charges the transformer primary side T1A, the primary side current increases, and the transformer magnetic field energy increases; according to the same poles, at this time, the diode D2 is turned off due to reverse bias, and the transformer secondary side T1B has no current.

6. The constant current, limited voltage pulsed power supply for a wire electrical discharge machine as defined in claim 4, wherein, When the control signal turns off the field effect tube Q2 and turns on the field effect tube Q1 and the field effect tube Q3, the transformer primary side T1A, the field effect tube Q1 and the field effect tube Q3 form a primary side current maintaining path, and at this time, the transformer primary side T1A is short-circuited.

7. The constant current, limited voltage pulsed power supply for a wire electrical discharge machine as defined in claim 4, wherein, During pulse discharge, the main control circuit outputs the control signal to turn off the field effect tube Q1 and the field effect tube Q2 and turn on the field effect tube Q3; before the discharge gap is broken down, the secondary side is in an open circuit state and the current is zero; the primary side current discharges to the DC bus filter capacitor C1 through the field effect tube Q3, the transformer primary side T1A and the diode D1; the primary side voltage is clamped to the DC bus voltage by the diode D1 and the field effect tube Q3, and the voltage polarity of the same poles of the transformer primary side T1A is positive.

8. The constant current, limited voltage pulsed power supply for a wire electrical discharge machine as defined in claim 4, wherein, According to the same poles, a positive polarity voltage is induced at the same poles of the transformer secondary side T1B, and the diode D2 is turned on by forward bias; the induced voltage of the transformer secondary side T1B is applied to the discharge gap through the diode D2, the wire, the molybdenum wire and the workpiece to form the breakdown voltage Vob; the breakdown voltage Vob is proportional to the transformer primary side T1A voltage Vp, and the specific expression is as follows: Vob = Ns / Np * Vp; = Ns / Np * Vdc; In the above formula, Vob is the breakdown voltage, Np is the primary winding number, Ns is the secondary winding number, Vp is the primary voltage, Vdc is the bus voltage; the primary voltage Vp is clamped to the bus voltage Vdc, therefore, the secondary side output voltage is clamped.

9. The constant current, current limited, pulsed power supply for a wire electrical discharge machine as defined in claim 4 wherein, After the discharge gap is broken down, the discharge between the molybdenum wire and the workpiece forms, the secondary voltage drops, and is lower than the breakdown voltage; the primary voltage drops synchronously, and is lower than the bus voltage, then the diode D1 is reverse biased and cut off, and the primary current is zero; the secondary discharge current Is is proportional to the primary current Ip, and is as follows: Is = Np / Ns * Ip; Wherein, Ip is the primary current, Is is the secondary discharge current, Np is the primary winding number, Ns is the secondary winding number; It can be seen that the discharge current Is is clamped during discharge, and even if the discharge gap is short-circuited, it will not be out of control.

10. The constant current and limited voltage pulse power supply for a wire cutting machine tool according to claim 1, characterized in that, At the end of discharge, the main control circuit outputs a control signal to turn off the field effect transistor Q3 and turn on the field effect transistor Q1 and the field effect transistor Q2; the primary side T1A of the transformer is connected to the two ends of the DC bus, and the same end is negative and the non-same end is positive; at this time, the voltage polarity of the same end of the secondary side T1B of the transformer is negative, and the output is an anti-pulse opposite to the trailing current direction; the anti-pulse application time is derived as follows: According to Vs = ( Ls+Ld) * d i / d t ⇒ d t = (Ls+Ld) * d i / Vs Vs = Vp * Ns / Np Vp ≈ Vdc; ⇒ d t ≈ (Ls+Ld) * d i / ( Vdc * Ns / Np ) Wherein, Vs is the secondary side reverse pulse voltage, Ls is the secondary side inductance, Ld is the wire, molybdenum wire, workpiece loop line dispersion inductance, Np is the primary side number of turns, Ns is the secondary side number of turns, Vp is the primary side voltage, Vdc is the bus voltage; d i Is the secondary side current instantaneous value, that is, Is; According to the above formula, the calculation of the anti-pulse effect time d t ; under the action of the anti-pulse, the tail current drops rapidly, and when the tail current drops to zero, the diode D2 is reverse-biased off under the action of the anti-pulse voltage, so that no reverse current is formed on the discharge gap.

11. The constant current, limited voltage pulsed power supply for a wire electrical discharge machine as defined in claim 1, wherein, The main control circuit comprises gate drive chips U1 and U4, a main control chip U3, a gate drive optocoupler U2, resistors R1-R13, an adjustable DC power supply interface CN1, and an output interface CN2; The first and second pins of the adjustable DC power supply interface CN1 are respectively externally connected to the positive and negative poles of an adjustable DC power supply and the positive and negative poles of a filter capacitor C1, to form the positive pole Vdc and the negative pole GND of the DC bus; The first pin of the gate drive chip U1 is externally connected to a 12V voltage; the fourth and fifth pins of the gate drive chip U1 are grounded; the second and third pins of the gate drive chip U1 are respectively connected to one end of a resistor R1 and one end of a resistor R2, and the other end of the resistor R1 and the other end of the resistor R2 are connected to one end of a resistor R3 and the gate of a first field effect transistor Q1; the other end of the resistor R3 is connected to the source of the first field effect transistor Q1 and grounded; the sixth pin of the gate drive chip U1 is connected to one end of a resistor R4 and the forty-third pin of the main control chip U3; the other end of the resistor R4 is externally connected to a 3.3V voltage; The first pin of the gate drive optocoupler U2 is connected with the eighth pin of the main control chip U3; the third pin of the gate drive optocoupler U2 is grounded through the resistor R5; the fourth pin of the gate drive optocoupler U2 is connected with the non-same end of the transformer primary side T1A; the fifth pin of the gate drive optocoupler U2 is connected with one end of the resistor R7; the other end of the resistor R7, one end of the resistor R9 and the gate of the second field effect tube Q2 are connected; the other end of the resistor R9 is connected with the source of the second field effect tube Q2 and the non-same end of the transformer primary side T1A; the sixth pin of the gate drive optocoupler U2 is externally connected with a 15V voltage, so that there is a 15V power supply between the sixth pin and the fourth pin of the gate drive optocoupler U2; The sixth pin of the gate drive chip U4 is connected with one end of the resistor R6 and the second pin of the main control chip U4, and the other end of the resistor R6 is grounded; the first pin of the gate drive chip U4 is externally connected with a 12V voltage; the fourth and fifth pins of the gate drive chip U4 are grounded; the second pin of the gate drive chip U4 is connected with one end of the resistor R8, and the other end of the resistor R8 is connected with one end of the resistor R9, one end of the resistor R11 and the gate of the third field effect tube Q3; the other end of the resistor R9 is connected to the third pin of the gate drive chip U4; the other end of the resistor R11, the source of the third field effect tube Q3 and one end of the milliohm resistor CS1 are connected with one end of the resistor R14; The other end of the milliohm resistor CS1 is connected with one end of the resistor R13 and grounded; The other end of the resistor R13 is connected with the thirteenth pin of the main control chip U3; The other end of the resistor R14 and one end of the resistor R12 are simultaneously connected to the seventeenth pin of the main control chip U3; The other end of the resistor R12 is simultaneously connected to the fourteenth and twenty-third pins of the main control chip; The twenty-seventh, fifteenth, thirty-first, forty-seventh and sixty-third pins of the main control chip U3 are grounded; The sixteenth, twenty-eighth, twenty-ninth, thirty-second, forty-eighth and sixty-fourth pins of the main control chip U3 are externally connected with a 3.3V power supply.

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