Wide voltage automatic identification circuit and application thereof

Abstract

The application discloses a wide-voltage automatic identification circuit and application thereof, and relates to the technical field of circuits.The power supply comprises an AC input rectification module, a SiC hybrid totem pole Boost power factor correction module, a bus sampling module integrated with a wide-voltage system identification, a high-frequency isolation driving module, a silicon carbide inverter power module, a DSP full-digital control module and an output filtering module.Through high-speed optocoupler phase number detection and linear optocoupler voltage level detection circuit, the application realizes single-phase 110-240V and three-phase 208-575V input automatic identification, and manual gear switching or phase sequence distinguishing is not needed;the application adopts a silicon carbide MOSFET power device and a hybrid totem pole PFC topology, the overall efficiency is greater than or equal to 85%, the power factor is greater than or equal to 0.92, and energy saving is 15%-25%;multiple intelligent protections are integrated, the application is suitable for complex industrial power grids, and is suitable for manual electric arc welding, argon arc welding, carbon arc gas gouging, gas shielded welding and cutting machines.

Description

Technical Field

[0001] This invention relates to the field of circuit technology, and in particular to a wide voltage automatic identification circuit and its application. Background Technology

[0002] Inverter-type plasma systems are widely used in industrial applications such as steel structure processing, construction site work, equipment maintenance, and pipeline engineering. However, existing products have the following technical shortcomings:

[0003] 1. Poor voltage adaptability: Traditional cutting machines have a fixed input system. Single-phase and three-phase power supply require manual switching of gears or rewiring. They cannot automatically identify the power grid system. The voltage adaptability range is narrow. They cannot adapt to wide voltage inputs of 110-240V single-phase and 208-575V three-phase. They are prone to shutdown and failure when the power grid fluctuates.

[0004] 2. Insufficient performance of power devices: Silicon-based MOSFETs and IGBT power devices are commonly used, resulting in high switching losses, high temperature rise, low overall efficiency, poor energy-saving effect, and easy derating when operating at full load for a long time.

[0005] 3. Low power factor and high power grid pollution: The front-end lacks a complete power factor correction (PFC) circuit, resulting in large harmonic currents and a low power factor, which interferes with the industrial power grid.

[0006] 4. Low reliability and inadequate protection: Power devices have weak gate anti-interference and anti-spike capabilities, lack complete isolation drive and multiple protections, and are easily damaged in harsh power supply environments such as construction sites and the field.

[0007] 5. Poor performance: Traditional analog control methods have low current and voltage closed-loop accuracy, unstable arc initiation, rough cutting surface, and poor cutting quality.

[0008] Therefore, there is an urgent need to develop a circuit for inverter welding and cutting power supplies that can automatically identify single-phase / three-phase wide voltage, silicon carbide low loss, PFC power factor correction, fully digital control, and multiple intelligent protections, in order to overcome the shortcomings of existing technologies. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a wide voltage automatic identification circuit and its application, which realizes automatic identification of single-phase 110-240V and three-phase 208-575V input without debugging. It uses silicon carbide (SiC) power devices to reduce switching losses, front-stage PFC correction to improve power factor, full digital DSP precise control, multiple intelligent protections, adapts to complex industrial power grids, and realizes efficient, energy-saving, stable and reliable plasma cutting operations.

[0010] To achieve the above-mentioned objectives, the present invention adopts the following standardized technical solution:

[0011] In a first aspect, the present invention provides a wide voltage automatic identification circuit, including an AC input rectifier module, a power factor correction module, an inverter power module, a drive module, a control module, and an output filter module, and further including a wide voltage standard identification module, and:

[0012] The AC input rectifier module adopts a dual parallel rectifier bridge structure to receive single-phase 110-240V or three-phase 208-575V wide voltage AC input and rectify and output pulsating DC.

[0013] The power factor correction module adopts a SiC hybrid totem pole Boost topology and is connected to the AC input rectifier module. It is used to perform boost conversion and power factor correction on pulsating DC and output a stable high-voltage DC bus.

[0014] The wide voltage system identification module is integrated into the bus sampling module, including a phase number detection unit and a voltage level detection unit, which is used to collect the phase number and voltage amplitude signals of the power grid and feed them back to the control module;

[0015] The driving module adopts a high-frequency isolated driving architecture and is connected to the control module. It is used to isolate, amplify, and protect the gate of the PWM driving signal.

[0016] The inverter power module adopts a dual-path half-bridge parallel topology, is equipped with silicon carbide MOSFET power devices, and is connected to the drive module and the high-voltage DC bus to invert high-voltage DC into high-frequency AC.

[0017] The output filtering module is connected to the inverter power module and is used to smooth high-frequency ripple and output a stable welding and cutting current.

[0018] The control module is a DSP fully digital control module, which is used to automatically match operating parameters according to the wide voltage standard identification signal, realize voltage and current dual closed-loop control, and integrate multiple safety protection logics.

[0019] Preferably, the dual parallel rectifier bridge structure of the AC input rectifier module can adaptively adapt to single-phase 110-240V and three-phase 208-575V AC input conditions. When powered by single-phase power, it automatically matches the live and neutral wire circuits. When powered by three-phase power, it achieves full-bridge rectification and supports 50Hz / 60Hz input frequency adaptation without distinguishing the phase sequence.

[0020] Preferably, the SiC hybrid totem pole Boost topology includes a PFC boost inductor, upper and lower bridge silicon carbide power transistors, an ultrafast recovery freewheeling diode, a PFC main control chip, and a high-speed MOS driver chip; the PFC main control chip controls the high-frequency switching of the silicon carbide power transistors by adjusting the PWM duty cycle to achieve boost and power factor correction.

[0021] Preferably, the bus sampling module includes a high-voltage divider voltage sampling unit, a manganese copper resistor or Hall device current sampling unit, a high-speed optocoupler phase number detection unit, and a linear optocoupler voltage level detection unit, which simultaneously collects bus voltage, bus current, grid phase number, and voltage amplitude signals, completes system identification within 100ms after power-on, and continuously monitors the grid status during operation.

[0022] Preferably, the high-speed optocoupler phase number detection unit includes a high-voltage resistor divider network, a rectifier bridge, a high-speed optocoupler, a transistor amplifier circuit, and a voltage comparator, outputting a phase number / phase loss signal; the linear optocoupler voltage level detection unit includes a high-voltage resistor divider network, a voltage follower, a high-precision linear optocoupler, a differential amplifier, and a sampling ratio calibration potentiometer, outputting a voltage sampling signal proportional to the grid voltage.

[0023] Preferably, the high-frequency isolation drive module includes an isolation drive chip, a high-frequency pulse transformer, and a silicon carbide-specific gate shaping and protection circuit; the gate shaping and protection circuit is used to realize drive current amplification, rapid gate charge discharge, voltage clamping, and high-frequency spike absorption, adapting to the switching characteristics of silicon carbide MOSFETs.

[0024] Preferably, the dual half-bridge parallel topology of the silicon carbide inverter power module consists of two silicon carbide MOSFETs connected in parallel to form the upper bridge arm, and another two silicon carbide MOSFETs connected in parallel to form the lower bridge arm; a spike absorption capacitor is connected in parallel to the drain and source of each silicon carbide MOSFET.

[0025] Preferably, the rated efficiency of the whole machine is ≥85%, the power factor is ≥0.92, and it can stably output the rated power within the range of ±15% fluctuation of the grid voltage, and the load duty cycle can reach 60%-100%.

[0026] Preferably, the multiple safety protection logic includes overvoltage protection, undervoltage protection, overcurrent protection, overheat protection, phase loss protection, phase imbalance protection, and inverter fault self-test protection; under abnormal operating conditions, the system automatically blocks the drive signal, cuts off the power output, and displays the corresponding fault code; the output filtering module adopts an RC combined spike absorption and high-frequency filtering network to output multiple modes of operation.

[0027] In a second aspect, the present invention provides the circuitry of the first aspect for applications including, but not limited to, manual arc welding, argon arc welding, carbon arc gouging, gas shielded welding, and cutting machines.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. Wide voltage automatic identification, no manual adjustment required: Automatically identifies single-phase 110-240V and three-phase 208-575V power supply system upon power-on, without the need for DIP switches, rewiring, or phase sequence differentiation. It is plug-and-play and compatible with power supply standards in multiple regions around the world.

[0030] 2. High efficiency and energy saving of silicon carbide devices: SiC MOSFET power devices are used, which greatly reduces switching losses, saves energy by 15%-25%, has an overall efficiency of ≥85%, a power factor of ≥0.92, and a load duty cycle of 60% to 100%. It has a stronger load-carrying capacity in the same volume and does not reduce capacity when working at full load for a long time.

[0031] 3. Strong grid adaptability: Supports ±15% grid voltage fluctuation self-adaptation, resists grid distortion and harmonic interference, continuously monitors grid status during operation, and is suitable for complex power supply environments such as construction sites and the field.

[0032] 4. Multiple intelligent protections, industrial-grade durability: Integrated overvoltage, undervoltage, overcurrent, overheat, phase loss, phase imbalance, and fault self-check protection; complete clamping, current limiting, and absorption protection for the gate; adopts independent air duct high-flow forced air cooling and independent heat dissipation design of silicon carbide module; industrial-grade sheet metal chassis, dustproof, oil-proof, and shock-resistant, with a low failure rate, suitable for long-term continuous operation under harsh conditions.

[0033] 5. Fully digital precision control, superior cutting performance: DSP fully digital dual closed-loop control ensures stable arc initiation, fast cutting speed, and smooth and flat cut surface. It is compatible with multiple modes of operation, including plasma cutting and marking. Attached Figure Description

[0034] Figure 1 is a schematic diagram of the front-end SiC hybrid totem pole Boost power factor correction circuit of the present invention.

[0035] Figure 2 is a schematic diagram of the subsequent silicon carbide inverter drive and power main circuit of the present invention.

[0036] Figure 3 is a schematic diagram of the wide voltage system identification and protection detection circuit of the present invention. Detailed Implementation

[0037] To enable those skilled in the art to clearly and completely understand the technical solution and implementation of the present invention, the following detailed and systematic implementation description of the overall hardware structure, working principle of each module and complete operation process of the whole machine is provided in conjunction with the circuit schematic diagram of the present invention.

[0038] This invention discloses a wide-voltage automatic identification circuit. Based on a novel hardware architecture and control logic design, it addresses the technical pain points of existing technologies, such as poor voltage adaptation, high energy consumption, low control accuracy, and inadequate protection. The overall hardware architecture of this invention is uniformly divided into: an AC input rectifier module, a SiC hybrid totem-pole Boost power factor correction module, a bus sampling module integrating wide-voltage system identification, a high-frequency isolation drive module, a silicon carbide inverter power module, a DSP fully digital control module, and an output filter module. These modules work collaboratively to achieve wide-voltage automatic adaptation, efficient boost voltage regulation, high-precision inverter output, and comprehensive safety protection.

[0039] AC input rectifier module: Adopting a dual parallel rectifier bridge structure, it can adaptively accommodate single-phase 110-240V and three-phase 208-575V wide voltage AC input conditions, and supports 50Hz / 60Hz input frequency adaptation without distinguishing phase sequence; when powered by single phase, it automatically matches the live wire and neutral wire circuit; when powered by three phase, it achieves full-bridge rectification, and outputs pulsating DC after rectification, providing basic power input for subsequent power circuits without the need for manual switching of speed range or rewiring.

[0040] The SiC hybrid totem pole Boost power factor correction module is electrically connected to the AC input rectifier module. It serves as the core boost and harmonic correction unit in the front-end of the entire unit, integrating a PFC boost inductor, silicon carbide switching power transistors, ultra-fast recovery freewheeling diodes, a PFC main control unit, and a high-speed drive unit. It completes the energy storage and boost conversion of pulsating DC through high-frequency switching, while correcting the grid current waveform, effectively suppressing grid harmonics, improving the overall power factor, and outputting a stable high-voltage DC bus.

[0041] The bus sampling module for bandwidth voltage system identification integrates a high-voltage divider voltage sampling unit, a current sampling unit, a high-speed optocoupler phase number detection unit, and a linear optocoupler voltage level detection unit. It can simultaneously and in real time acquire four core signals: bus voltage, bus current, grid phase number, and grid voltage amplitude. It completes system identification in milliseconds upon power-on, continuously monitors the grid status during operation, and feeds back all sampled signals to the DSP fully digital control module in real time, providing data support for automatic grid system identification, voltage closed-loop regulation, and current closed-loop current limiting.

[0042] High-frequency isolated drive module: Electrically connects the DSP fully digital control module and the silicon carbide inverter power module. It adopts a completely isolated architecture for low-voltage and high-voltage circuits, including an isolation drive chip, a high-frequency pulse transformer, and a dedicated gate shaping and protection circuit for silicon carbide. It can isolate, amplify, regulate, and absorb spikes in the PWM high-frequency drive pulses output by the DSP, and output drive signals adapted to the switching characteristics of silicon carbide devices, avoiding high-voltage crosstalk and device breakdown risks.

[0043] Silicon carbide inverter power module: It adopts a dual-path half-bridge parallel power topology, which is composed of multiple silicon carbide MOSFET power devices to form the upper and lower bridge arm power circuits. Each silicon carbide power device is equipped with an independent spike absorption protection structure. It can receive the drive signal output from the isolation drive module, invert the high-voltage DC bus voltage into high-frequency AC power, and then step down the voltage through the intermediate frequency transformer and perform secondary rectification, or invert it again to adapt to the needs of all operating conditions.

[0044] 6. DSP All-Digital Control Module: This is the core control hub of the entire machine, with built-in dedicated recognition algorithms and dual closed-loop control programs. It can automatically determine the single-phase / three-phase power grid supply system based on the sampling signals fed back by the bus sampling module and adaptively match the PFC boost parameters, inverter PWM parameters, and current closed-loop control parameters. At the same time, it monitors the operating status of the entire machine in real time and integrates multiple protection logics for overvoltage, undervoltage, overcurrent, overheating, phase loss, phase imbalance, and inverter fault self-check.

[0045] 7. Output Filtering Module: It adopts an RC combined peak absorption and high-frequency filtering network, which is electrically connected to the output terminal of the silicon carbide inverter power module. It can effectively smooth the high-frequency current ripple of the inverter output, suppress voltage peak interference, and output a stable and pure DC plasma cutting current, ensuring stable operation and a smooth cutting surface.

[0046] Example 1: Overall Hardware Circuit Architecture of the Equipment

[0047] The hardware circuit of this application adopts a two-stage architecture design of "front-stage wide-voltage PFC boost regulation + rear-stage SiC high-frequency inverter". It is divided into three core parts: front-stage SiC hybrid totem pole Boost power factor correction circuit, wide-voltage system identification and protection detection circuit, and rear-stage silicon carbide inverter drive and power main circuit. The three-stage circuit works together to achieve wide-voltage automatic adaptation, high-efficiency boost regulation, high-frequency inverter output and multiple safety protection functions, adapting to complex single-phase / three-phase power supply conditions.

[0048] (1) Front-end SiC hybrid totem pole Boost power factor correction circuit (as shown in Figure 1)

[0049] The front-end circuit provides a stable high-voltage DC bus power supply for the entire unit, while also achieving power factor correction and grid fluctuation adaptation. Its core consists of an AC input rectifier unit, a PFC boost power circuit, a drive control unit, and a bus sampling and soft-start protection unit. The AC input rectifier unit has three compatible input terminals (AC1, AC2, and AC3) and a parallel structure of dual rectifier bridges (UD1 and UD2). It can adaptively adapt to single-phase 110-240V and three-phase 208-575V input conditions. In single-phase power supply, it automatically matches the live and neutral wire circuits; in three-phase power supply, it achieves full-bridge rectification, outputting a pulsating DC voltage. This voltage, along with the C9 primary filter capacitor, filters out low-frequency voltage ripple, providing the basic power supply for the subsequent boost circuit. The PFC boost power circuit adopts a SiC hybrid totem pole boost topology, consisting of an LT boost inductor, two SiC power transistors (VS-1 and V8), and ultra-fast recovery freewheeling diodes (D3 and D4). High-frequency switching of the power transistors enables inductor energy storage and release, completing the voltage boost conversion. Simultaneously, an RC spike absorption circuit composed of R187 and C10 effectively absorbs instantaneous voltage spikes during switching, reducing overall EMI and improving circuit stability. The drive control unit uses the Infineon ICE3PCS03G dedicated PFC main control chip as the core controller, combined with a TC4420 high-speed MOS driver chip for signal amplification and drive. The main control chip can adjust the switching frequency and PWM duty cycle in real time, achieving dual closed-loop control of voltage and current. Externally, gate current-limiting resistors (R55, R56, R57), a C27 ​​absorption capacitor, and a D9 voltage regulator are configured to effectively stabilize the gate operating state of the SiC power transistors and prevent device breakdown. The bus sampling and soft-start unit acquires the bus voltage signal through an R64-R80 high-voltage resistor divider network and acquires the bus current signal through an R50 (4mΩ) manganese copper sampling resistor. The sampled signals are synchronously transmitted to the DSP main controller and PFC chip to achieve closed-loop voltage regulation and overcurrent protection. Combined with the soft-start circuit composed of R30, R31, R32 and C16, it can effectively suppress the inrush current at the moment of power-on and achieve smooth start-up.

[0050] I. Overall Circuit Architecture

[0051] The circuit employs a fully electrical isolation design, with the high-voltage AC side and low-voltage control side physically isolated via linear optocouplers, switching optocouplers, and isolated power supply modules, significantly enhancing the equipment's safety and anti-interference capabilities. It is divided into five core functional modules:

[0052] AC input rectification and voltage divider sampling, isolated auxiliary power supply, linear isolation voltage sampling and processing, phase loss detection and signal output, detection signal output interface

[0053] PFC preamplifier circuit

[0054] like Figure 1 , Figure 2 As shown, AC mains power is input through terminals AC3 and AC1. To increase the rectified current capacity and reduce the temperature rise of individual components, this embodiment adopts a rectification scheme in which the first rectifier bridge UD1 and the second rectifier bridge UD2 are connected in parallel. The AC sides of the two rectifier bridges are connected in parallel to AC3 and AC1 respectively, the DC positive output terminal is connected in parallel to node D+, and the DC negative output terminal is connected in parallel to system ground. The rectified 100Hz pulsating DC is filtered by the high-frequency filter capacitor C0 to remove spikes before being sent to the Boost converter circuit.

[0055] The boost converter circuit consists of a boost energy storage inductor L1, a power switching unit, a boost rectifier unit, and a bus capacitor. Inductor L1 uses an iron-silicon-aluminum magnetic powder core, and its inductance is designed based on the switching frequency and input voltage range. In this embodiment, the switching frequency is set to 65kHz–100kHz, and the inductance is selected as 100μH–300μH to ensure continuous conduction mode (CCM) operation across the entire input voltage and load range. The power switching unit uses a first power MOSFET V8 and a second power MOSFET V6 of the same type connected in parallel. Their drains are connected in parallel at the power switching node (i.e., the right end of inductor L1), and their sources are connected in parallel with a current sampling resistor R50 (4mΩ) connected in series to ground. This parallel structure halves the equivalent on-resistance, significantly reducing conduction losses and single-tube heat load. The boost rectifier unit uses a first boost diode D3 and a second boost diode D4 connected in parallel. Their anodes are connected in parallel at the power switching node, and their cathodes are connected in parallel to the positive terminal DC+ of the DC bus.

[0056] D3 and D4 are preferably ultrafast recovery diodes (reverse recovery time trr < 50 ns) or silicon carbide Schottky diodes to minimize reverse recovery charge and loss.

[0057] To suppress the reverse recovery voltage spikes and EMI generated by D3 and D4 during the turn-off process, this embodiment incorporates an RC snubber circuit in parallel across the boost rectifier unit. This snubber circuit consists of a resistor R187 (power type, such as 2W) and a high-voltage capacitor C10 (1000pF / 1kV or 2kV) connected in series. This snubber network effectively absorbs leakage inductance energy, clamps turn-off spikes, and protects the diodes and power switching transistors.

[0058] The PFC control and drive circuit is based on the ICE3PCS01G (U1).

[0059] according to Figure 1The pin definitions are as follows: Pin 1 is ISEN (current sensing), Pin 2 is GND, Pin 3 is ICOMP (current loop compensation), Pin 4 is FREQ (frequency setting), Pin 5 is BOP (power-down protection), Pin 6 is VCC, Pin 7 is VFB (voltage feedback), and Pin 8 is GATE (gate drive output). U1 integrates a voltage error amplifier, a current error amplifier, a multiplier, and gate drive logic, and uses average current mode control.

[0060] Pin 1 (ISEN) is connected to the current sampling resistor R50 via a filter network consisting of resistors R30 and R31 and capacitors C23 and C110 to obtain a signal proportional to the inductor current. Pin 7 (VFB) of U1 is filtered by resistor R48 and capacitor C20 and then connected to the midpoint of a multi-stage series voltage divider network consisting of R69, R67, R68, R66, R81, R79, R80, and R78. This voltage divider network takes the signal from DC+, attenuates the several hundred volt bus voltage by approximately 1 / 120–1 / 150, and then sends it to U1. The signal is filtered at the end by capacitor C13 (0.15μF). Based on the voltage and current errors, U1 generates a sinusoidal current reference through an internal multiplier, causing the average inductor current to track the input voltage waveform, thereby achieving power factor correction.

[0061] Pin 8 (GATE) of U1 outputs a PWM signal, which is sent to pin 2 (IN) of the high-speed MOSFET driver TC4420 (U5). U5 has a peak drive capability of 6A. Its pin 6 (OUT) outputs the signal through resistor R38, and a clamping protection network is formed by fast recovery diode ES2D (anode grounded, cathode connected to the back end of R38) to prevent drive voltage overshoot. The U5 output is connected to the gate of V8 through gate resistor R56 and to the gate of V6 through gate resistor R55. R56 and R55 are 10Ω–22Ω to suppress gate ringing; R54 and R57 are gate-source pull-down resistors to ensure reliable gate discharge when the drive signal is lost or the device is powered off; Zener diode D9 is connected in parallel between the source of V8 / V6 and the node to ground to provide source node clamping protection to prevent abnormal overvoltage from breaking down the sampling resistor or interfering with the control signal.

[0062] Pin 5 (BOP) of U1 is connected to ground via resistor R32 and capacitor C16 (100nF), forming a brown-out protection mechanism. When the input AC voltage falls below a set threshold (e.g., 160V), U1 shuts off the PWM output to prevent damage to the device under low-voltage, high-current conditions; it automatically restarts after the voltage recovers. Pin 4 (FREQ) of U1 is connected to resistor R33 and capacitor C24 to set the minimum switching frequency and soft-start slope, avoiding inrush current during startup. Pin 3 (ICOMP) of U1 is connected to an external current loop compensation network consisting of resistor R46, capacitor C4 (100pF), capacitor C23, and capacitor C110, ensuring the stability of the inner current loop. The auxiliary power supply network +UB provides a stable 15V low-voltage power supply to pin 6 (VCC) of U1 and the power supply terminal of U5.

[0063] The DC bus output filter is completed by electrolytic capacitors or film capacitors C11 and C12 connected in parallel, stabilizing the PFC output voltage at 380V–400V, and providing a low-ripple bus for the subsequent LLC resonant converter.

[0064] II. Detailed Analysis by Module

[0065] 1. AC input rectification and voltage divider sampling

[0066] Core component: 3GBJ2516 (three-phase bridge rectifier, 25A / 1600V)

[0067] Working principle:

[0068] Three-phase AC power is input through the AC-IN interface (Header 3) and rectified into pulsating DC voltage by the 3GBJ2516.

[0069] The high-voltage DC voltage is stepped down by a precision resistor divider consisting of R62 (33K), R63 (2K), and R64 (3.9K) to obtain a low-voltage sampling signal suitable for subsequent circuit processing.

[0070] ZD2 is a varistor (surge protection) used to absorb transient overvoltages in the power grid and protect downstream circuits.

[0071] 2. Isolation auxiliary power supply (lower middle section)

[0072] Core component: F1518S-3W (isolated DC-DC power module, 3W power)

[0073] Working principle:

[0074] It receives an externally supplied +24V DC voltage and outputs isolated +15V and VSS2 (isolation ground).

[0075] C56 (0.1uF) is the input filter capacitor, and C54 (47uF / 25V) and C55 (0.1uF) are the output filter capacitors, which filter out power supply ripple and provide a stable operating power supply for operational amplifiers, optocouplers and other chips.

[0076] This power supply is completely isolated from the high-voltage AC side, which is the basis for the electrical isolation of the entire circuit.

[0077] 3. Linear isolation voltage sampling and processing (bottom left + bottom right)

[0078] This module enables high-precision isolated sampling of high-voltage AC voltage, transmitting analog voltage signals to the low-voltage control side without distortion.

[0079] (1) Voltage buffer stage (U6: LM321 single op amp)

[0080] It forms a voltage follower (buffer) with extremely high input impedance and extremely low output impedance, avoiding the load effect of voltage divider circuits and ensuring sampling accuracy.

[0081] R59 (1M) is a pull-down resistor, and C49 (1nF) is a high-frequency filter capacitor to filter out high-frequency interference in the power grid.

[0082] (2) Linear isolation transmission stage (U7: HCNR200 high-precision linear optocoupler)

[0083] Unlike ordinary switching optocouplers, the HCNR200 contains one light-emitting diode and two matching photodiodes, achieving linear isolation transmission of analog signals through closed-loop feedback with a linearity of up to 0.01%.

[0084] The light-emitting diode is driven by U6, and the feedback photodiode is connected back to the inverting input of U6 to form a closed loop to ensure transmission linearity; the output photodiode generates a current signal that is proportional to the input current.

[0085] (3) Signal conditioning stage (U8D, U4A: LM324 quad op amp)

[0086] U8D: Forms an IV conversion circuit, converting the current signal output by HCNR200 into a voltage signal. R67 (200K) is a feedback resistor, W1 (200K) is an adjustable calibration resistor used to precisely adjust the sampling gain; C58 (1uF) is a phase compensation capacitor to prevent circuit self-oscillation.

[0087] U4A: Forms an inverting proportional / level conversion circuit, which adjusts the voltage output by U8D to a level range that can be recognized by the ADC of the back-end main control board, and finally outputs the VPN signal to the detection interface.

[0088] 4. Phase loss detection and signal output

[0089] This module is used to detect whether there is a phase loss fault in the three-phase AC power supply and outputs high and low level signals for the main control board to judge.

[0090] (1) AC signal isolation (U2: TLP627 switch type optocoupler)

[0091] The other phase AC voltage is current-limited by R33 (100K) and R64 (100R), voltage-divided by R36 (390K) and R37 (5.1K), filtered by C3 (1nF), and clamped by D23 (5.2V) Zener diode before driving the internal LED of TLP627.

[0092] During the positive half-cycle of AC operation, the optocoupler conducts and cuts off during the negative half-cycle, outputting a square wave signal with the same frequency as the power grid, thus achieving strong and weak current isolation.

[0093] (2) Square wave to DC conversion (Q2: 2N5401 PNP transistor + RC integrating circuit)

[0094] Q2 forms an inverting switch circuit to invert the square wave output by the optocoupler.

[0095] An RC integrating circuit is composed of a C52 (22uF) and an R34 (15.1K).

[0096] During normal power supply, the square wave continuously charges and discharges C52, and the two ends of C52 maintain a high DC voltage;

[0097] When a phase is lost, there is no AC signal input, the optocoupler remains off, Q2 remains on, C52 discharges rapidly through R34, and the voltage drops to a low level.

[0098] (3) Voltage Comparison and Output (U4B: LM324 op-amp)

[0099] A voltage comparator is formed, with the inverting input terminal provided with a reference voltage of approximately 7.5V by a voltage divider consisting of R35 (5.1K) and R42 (5.1K).

[0100] Normal power supply: Integral voltage > Reference voltage → Output high level;

[0101] Phase loss fault: Integral voltage < reference voltage → Output low level.

[0102] The output signal is current limited by R38 (5.1K), filtered by C24 (1uF) and C41 (1nF), and clamped by D19 (5.1V) Zener diode before the phase loss signal is output to the detection interface.

[0103] (2) Post-stage silicon carbide inverter drive and power main circuit

[0104] The core power output unit of the subsequent circuit mainly performs high-frequency inversion, electrical isolation, gate protection, and current filtering output functions. It consists of a drive signal input unit, a high-frequency electrical isolation unit, a gate shaping and protection unit, a SiC inverter power unit, and an output filtering unit. The drive signal input unit receives the high-frequency PWM drive pulse from the IMOUT1 output of the DSP main control. Signal preprocessing is completed through external bias current-limiting resistors R17-R19 and R27-R28. Combined with filter capacitors C13, C25, and C35 and a Zener diode ZD14, the drive signal voltage is stabilized, ensuring a pure and stable input signal. The high-frequency electrical isolation unit is equipped with dual high-frequency pulse transformers TR1 and TR2 to achieve complete electrical isolation between the control low-voltage circuit and the power high-voltage circuit. This completely prevents high voltage from entering the main control circuit and damaging the DSP chip, significantly improving the equipment's anti-interference capability and operational safety. The gate shaping and protection unit is a key structure for adapting SiC power devices. It uses four NPN transistors (Q2, Q3, Q4, and Q5) to amplify the drive current and improve the gate drive capability. It also incorporates an SS14 Schottky diode and a 4148 high-speed diode to quickly discharge residual gate charge, enabling rapid turn-off of the power transistor. Furthermore, it uses dual-specification 5.1V and 20V Zener diodes to clamp the gate voltage, along with a 15Ω gate current-limiting resistor and a 2.2nF high-frequency absorption capacitor to effectively suppress high-frequency switching oscillations and absorb voltage spikes, providing comprehensive protection for SiC power devices and preventing damage from overvoltage breakdown and high-frequency interference. The SiC inverter power unit adopts an industrial-grade high-power dual-half-bridge parallel topology, equipped with four 12M2H017 third-generation SiC MOSFET power transistors. T3 and T5 form the upper bridge arm parallel structure, and T4 and T6 form the lower bridge arm parallel structure, significantly improving the overall load capacity and supporting long-term full-load operation without derating. Each SiC power transistor is independently equipped with a 1nF peak absorption capacitor to further optimize high-frequency switching characteristics and reduce switching losses. The output filtering unit consists of an RC filter network composed of CU1 and CU1-1 high-voltage filter capacitors and a matching resistor array, which can effectively smooth the high-frequency current ripple of the inverter output and suppress voltage spikes at the output terminal. Finally, the plasma cutting current is stably output through the BLACK M4 conductive frame power output terminal, ensuring stable current and a smooth cutting surface during operation.

[0105] (3) Wide voltage system identification and protection detection circuit

[0106] like Figure 3As shown, the stable DC+ output from the PFC preamplifier is fed into a dual-channel LLC resonant converter. This embodiment uses two LLC resonant channels with identical structures and parameters to improve the output power level and optimize heat distribution.

[0107] The first LLC resonant channel consists of a half-bridge driver N1, a first transformer TR2, a first resonant capacitor C4 (2.2nF), a first upper transistor T3, and a first lower transistor T4. N1 uses an IR2110 or similar high- and low-side half-bridge driver chip. Its high-side output is connected to the gate of T3 via a gate resistor, and its low-side output is connected to the gate of T4 via a gate resistor. The drain of T3 is connected to DC+, and its source is connected to the drain of T4, forming the midpoint of the first half-bridge. The source of T4 is grounded. The midpoint of the first half-bridge is connected in series with the primary winding of the first transformer TR2 via the first resonant capacitor C4 and then returns to ground. The leakage inductance of TR2 and C4 constitute the series resonant part of the LLC resonant cavity, and the magnetizing inductance participates in the parallel resonance. When the switching frequency is close to the resonant frequency, T3 and T4 achieve zero-voltage turn-on (ZVS), which significantly reduces switching losses and EMI. The secondary side of TR2 is equipped with a first-stage synchronous rectifier switch T1 and a second-stage synchronous rectifier switch T2 (model 12M28017), which rectifies the high-frequency AC of the transformer secondary side into DC.

[0108] The second LLC resonant channel consists of a half-bridge driver N2, a second transformer TR1, second resonant capacitors C5 and C6 (2.2nF), and a second upper transistor T5 and a second lower transistor T6. Its circuit topology is completely symmetrical to the first channel: N2 drives T5 and T6 to form the second half-bridge arm, and the midpoint of the second half-bridge resonates with the primary winding of TR1 via C5 and C6; the secondary winding of TR1 is equipped with a synchronous rectifier switch to rectify the high-frequency AC to DC.

[0109] The resonant parameters of the two channels are designed to be consistent: based on the measured leakage inductance Lr of the transformer (typically 50μH–150μH), a resonant capacitor of 2.2nF is selected so that the resonant frequency fr = 1 / (2π√(Lr·Cr)) falls around 100kHz. During operation, the two channels are driven in phase and at the same frequency, or a fixed frequency is used at the resonant point to achieve maximum efficiency; alternatively, the output voltage can be maintained stable by fine-tuning the frequency (±5%–10%) to compensate for load changes.

[0110] The bootstrap auxiliary power supply provides a floating power source for the high-side drive of N1 and N2. Taking the first channel as an example: the high-frequency voltage induced by the auxiliary winding (or primary center tap) of transformer TR2 is rectified by Schottky diode D30 (SS14), filtered by capacitor C55 (1500pF) and resistor R22 (330Ω), adjusted by transistors Q1 and Q2, and then regulated by Zener diode ZD3 (5.1V) to charge the high-side bootstrap capacitor of N1, forming a stable floating power source VB. Similarly, the second channel consists of diodes D34, D37, and D38, transistors Q3 and Q4, and Zener diodes ZD6, ZD7, ZD8, and ZD9 forming a symmetrical bootstrap power supply network. This scheme eliminates the need for an independent auxiliary power supply, simplifies the circuit structure, and improves reliability.

[0111] The output rectification and filtering consists of two secondary windings connected in series or parallel, followed by filtering by high-voltage filter capacitors CU1 and CU2 (2.2μF / 800V). Equalizing resistors R14 and R15 (10kΩ) are connected in parallel across the output capacitors to ensure voltage balance and provide a discharge path after power-off. The output negative terminal is connected to the BLACK terminal, and the high-voltage positive terminal is connected to the conductive frame Mn, directly driving the electrostatic load.

[0112] Current detection and protection are achieved by a current transformer MGU71 connected in series in the main output circuit. MGU71 detects the load current in real time, and its secondary side signal is rectified and filtered before being sent to the subsequent control circuit (not shown). When the electrostatic load experiences arcing or a short circuit, causing a sudden increase in current, the control circuit immediately reduces the LLC switching frequency or shuts off the PWM output of N1 and N2, entering hiccup protection mode or constant current limiting mode, effectively protecting the power devices and the load.

[0113] This circuit is the core hardware unit for achieving "wide voltage automatic identification without debugging." It integrates grid phase number detection, voltage level detection, and phase loss protection functions. All detection signals are synchronously output to the DSP all-digital control module and PFC main control chip through the Input detect1 interface, providing data support for automatic parameter matching. The circuit first uses the U5 (F1518S-3W) isolated DC-DC power supply module to convert the system's 24V auxiliary power supply to ±15V isolated power, powering all detection operational amplifiers and optocouplers. This achieves complete electrical isolation between the detected low-voltage signals and the grid's high-voltage signals, preventing high-voltage crosstalk from damaging the main control components. The power grid phase number and phase loss detection unit acquires the grid line voltage through a series voltage divider network of high-voltage resistors R82, R47, R71, and R72. This voltage is rectified into pulsating DC by a Bridge1 (3GBJ2516) rectifier and then input to a high-speed optocoupler U2 (TLP627) for isolation and conversion. The optocoupler output signal is amplified by a transistor Q2 (2N5401) and then sent to a voltage comparator U4B (LM324) for discrimination, ultimately outputting the phase loss / phase loss signal. During three-phase power supply, the line voltage is continuous, and the comparator outputs a low level. During single-phase power supply, the line voltage is half-wave, and the comparator outputs a pulse of a specific frequency. During phase loss, the line voltage disappears, and the comparator outputs a high-level fault signal. The DSP automatically determines whether the current input is single-phase or three-phase power supply by detecting the frequency and level of this signal, thus implementing phase loss protection. The grid voltage level detection unit acquires the grid voltage amplitude through a high-voltage resistor divider network of R62, R63, and R64. After the load-carrying capacity is improved by a voltage follower U6 (LM321), the signal is input to a high-precision linear optocoupler U7 (HCNR200) ​​for linear isolation transmission. The weak signal output from the optocoupler is amplified by a differential amplifier U8D (LM324), and after the sampling ratio is calibrated by a potentiometer W1 (200K), a stable VPN voltage sampling signal is output by a voltage follower U4A (LM324). The amplitude of this signal is proportional to the grid input voltage. By reading the VPN voltage value, the DSP can automatically determine whether the current voltage is 110-240V low voltage or 208-575V high voltage, and match the corresponding PFC boost parameters and inverter current limiting threshold.

[0114] Example 2: Complete Workflow of the Whole Machine

[0115] After the device in this embodiment is powered on, the entire unit operates in an orderly manner according to the closed-loop logic of grid identification, voltage regulation and boosting, inverter output, and real-time monitoring and protection, without any manual intervention. It can automatically adapt to complex power supply environments. After the device is connected to single-phase or three-phase wide-voltage AC power, it first completes AC rectification through the front-stage dual parallel rectifier bridge to output a pulsating DC voltage. At the same time, the wide-voltage system identification circuit shown in Figure 3 starts synchronously. The high-speed optocoupler phase number detection unit collects the grid phase number signal, and the linear optocoupler voltage level detection unit collects the grid voltage amplitude signal. The two signals are transmitted synchronously to the DSP all-digital main control chip. The DSP quickly analyzes the sampled signal through its built-in algorithm and automatically determines whether the current input is a single-phase 110-240V or three-phase 208-575V power supply system within 100ms. Based on the identification result, it automatically matches the corresponding PFC soft-start parameters, bus voltage regulation threshold, inverter drive parameters, and current closed-loop control parameters to complete the debugging-free adaptive adaptation. After parameter matching, the PFC main control chip outputs a precise PWM control signal, which is amplified by a high-speed driver chip and then drives the high-frequency switch of the totem-pole SiC power transistor. Energy is stored and released through a boost inductor to complete the boost conversion of pulsating DC, outputting a stable high-voltage DC bus voltage. Simultaneously, the grid current waveform is corrected, raising the overall power factor to above 0.92 and effectively reducing grid harmonic interference. Once the high-voltage bus voltage is stabilized, the DSP outputs a high-frequency PWM drive pulse with the corresponding duty cycle based on the user-preset plasma cutting parameters. After pre-amplification, electrical isolation by a high-frequency transformer, and gate shaping and voltage regulation protection, the drive signal precisely drives the high-frequency alternating switch of the subsequent dual-channel half-bridge SiC inverter power array, inverting the high-voltage DC into high-frequency AC. The inverted high-frequency AC is stepped down by an external intermediate frequency transformer, rectified twice, and then transmitted to the output filter network. After RC ripple suppression and voltage spike absorption, a stable and clean DC operating current is output, meeting the requirements of various plasma cutting conditions. Throughout the entire operation of the machine, the DSP main controller continuously monitors key parameters such as grid voltage fluctuations, bus current, power device temperature, and operating phase in real time, achieving adaptive adjustment for ±15% grid fluctuations. Once abnormal conditions such as overvoltage, undervoltage, overcurrent, overheating, phase loss, phase imbalance, or inverter faults are detected, the system will immediately block the drive signal, cut off the power output, trigger a fault code prompt, and lock the equipment status. Normal operation can only be resumed after manual troubleshooting and equipment restart, ensuring comprehensive equipment operation safety and operational stability.

[0116] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features of the invention herein.

Claims

1. A wide-voltage automatic identification circuit, comprising an AC input rectifier module, a power factor correction module, an inverter power module, a drive module, a control module, and an output filter module, characterized in that, It also includes a wide voltage standard recognition module, and: The AC input rectifier module adopts a single-bridge or dual-parallel rectifier bridge structure to receive single-phase 110-240V or three-phase 208-575V wide-voltage AC input and rectifies and outputs pulsating DC. The power factor correction module adopts a SiC hybrid totem-pole Boost topology and is connected to the AC input rectifier module to perform boost conversion and power factor correction on the pulsating DC, outputting a stable high-voltage DC bus. The wide-voltage system identification module is integrated into the bus sampling module, including a phase number detection unit and a voltage level detection unit, to collect the phase number and voltage amplitude signals of the power grid and feed them back to the control module. The drive module adopts a high-frequency isolated drive architecture and is connected to the control module to isolate, amplify, and protect the PWM drive signal. The inverter power module adopts a dual-path half-bridge parallel topology, equipped with silicon carbide MOSFET power devices, and is connected to the drive module and the high-voltage DC bus to invert high-voltage DC into high-frequency AC. The output filter module is connected to the inverter power module to smooth high-frequency ripple and output a stable operating current. The control module is a DSP fully digital control module, which is used to automatically match operating parameters according to the wide voltage standard identification signal, realize voltage and current dual closed-loop control, and integrate multiple safety protection logics.

2. The wide voltage automatic identification circuit according to claim 1, characterized in that, The dual parallel rectifier bridge structure of the AC input rectifier module can adaptively adapt to single-phase 110-240V and three-phase 208-575V AC input conditions. When powered by single-phase power, it automatically matches the live and neutral wire circuits. When powered by three-phase power, it achieves full-bridge rectification and supports 50Hz / 60Hz input frequency adaptation without distinguishing the phase sequence.

3. The wide voltage automatic identification circuit according to claim 1, characterized in that, The SiC hybrid totem pole Boost topology includes a PFC boost inductor, upper and lower bridge silicon carbide power transistors, an ultra-fast recovery freewheeling diode, a PFC main control chip, and a high-speed MOS driver chip. The PFC main control chip controls the high-frequency switching of the silicon carbide power transistors by adjusting the PWM duty cycle, thereby achieving boost and power factor correction.

4. The wide voltage automatic identification circuit according to claim 1, characterized in that, The bus sampling module includes a high-voltage divider voltage sampling unit, a manganese copper resistor or Hall device current sampling unit, a high-speed optocoupler phase number detection unit, and a linear optocoupler voltage level detection unit. It synchronously collects bus voltage, bus current, grid phase number, and voltage amplitude signals, completes system identification within 100ms after power-on, and continuously monitors the grid status during operation.

5. The wide voltage automatic identification circuit according to claim 4, characterized in that, The high-speed optocoupler phase number detection unit includes a high-voltage resistor divider network, a rectifier bridge, a high-speed optocoupler, a transistor amplifier circuit, and a voltage comparator, and outputs a phase number / phase loss signal; The linear optocoupler voltage level detection unit includes a high-voltage resistor divider network, a voltage follower, a high-precision linear optocoupler, a differential amplifier, and a sampling ratio calibration potentiometer, and outputs a voltage sampling signal that is proportional to the grid voltage.

6. The wide voltage automatic identification circuit according to claim 1, characterized in that, The high-frequency isolation drive module includes an isolation drive chip, a high-frequency pulse transformer, and a dedicated gate shaping and protection circuit for silicon carbide. The gate shaping and protection circuit is used to amplify the drive current, rapidly discharge the gate charge, clamp the voltage, and absorb high-frequency spikes, adapting to the switching characteristics of silicon carbide MOSFETs.

7. The wide voltage automatic identification circuit according to claim 1, characterized in that, The dual-half-bridge parallel topology of the silicon carbide inverter power module consists of two silicon carbide MOSFETs connected in parallel to form the upper bridge arm and two silicon carbide MOSFETs connected in parallel to form the lower bridge arm; each silicon carbide MOSFET has a spike absorption capacitor connected in parallel to its drain and source.

8. The wide voltage automatic identification circuit according to claim 1, characterized in that, The unit has a rated efficiency of ≥85%, a power factor of ≥0.92, and can stably output rated power within a range of ±15% fluctuation of grid voltage. The duty cycle can reach 60%-100%.

9. The wide voltage automatic identification circuit according to claim 1, characterized in that, The multiple safety protection logic includes overvoltage protection, undervoltage protection, overcurrent protection, overheat protection, phase loss protection, phase imbalance protection, and inverter fault self-check protection. Under abnormal operating conditions, the system automatically blocks the drive signal, cuts off the power output, and displays the corresponding fault code. The output filtering module adopts an RC combined peak absorption and high-frequency filtering network to output a customizable plasma cutting current of 20A-300A, compatible with multiple modes of plasma cutting and marking operations.

10. An application of the wide voltage automatic identification circuit of claim 1 in, including but not limited to, manual arc welding, argon arc welding, carbon arc gouging, gas shielded welding and cutting machines.

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