A phase-shift full-bridge plasma power supply based on all-sic devices

Abstract

This invention discloses a phase-shifted full-bridge plasma power supply based on all SiC devices, belonging to the field of special power supply technology. It includes: a rectifier unit with a power factor correction circuit; an inverter unit containing a phase-shifted full-bridge topology composed of SiC power devices and an energy storage inductor, achieving zero-voltage switching through phase-shift control; a transformer unit; an output unit including an output filter capacitor; and a control unit that uses an incremental PID algorithm to generate phase-shift control signals. This invention analyzes the differences in zero-voltage switching between the leading and lagging bridge arms, utilizes the low output capacitance characteristics and dynamic dead-time adjustment of SiC devices, broadens the soft-switching range under light loads, effectively reduces output current ripple, and improves dynamic response speed and overall efficiency.

Description

Technical Field

[0001] This invention belongs to the field of special power supply technology, and particularly relates to a phase-shifted full-bridge plasma power supply based on all SiC devices. Background Technology

[0002] Plasma, as a high-energy-density, highly non-equilibrium state of matter, has wide applications in thermal spraying, materials surface engineering, plasma cleaning, plasma chemical reactions, and advanced manufacturing. Among these, plasma spraying technology has become a core process for preparing thermal barrier coatings in aerospace, gas turbines, and energy equipment. Its process stability and energy consistency directly determine the microstructure characteristics and service reliability of the coating. Numerous studies have shown that arc energy fluctuations, current ripple, and unstable heat input during plasma spraying are important causes of abnormal coating pore structure, decreased interfacial bonding strength, and early failure.

[0003] In practical industrial applications, plasma power supplies typically need to operate stably for extended periods under conditions of high power, high current, high frequency, and a wide load range. However, traditional plasma power supplies based on power frequency or intermediate frequency conversion are no longer sufficient to meet the demands of modern plasma spraying and high-end manufacturing in terms of power density, efficiency, and dynamic response performance. Therefore, high-frequency switching power supply technology has gradually become an important direction for the development of plasma power supplies, by increasing the switching frequency to reduce the size of magnetic components, increase system power density, and improve dynamic regulation performance.

[0004] Regarding the topology and control issues of high-frequency plasma power supplies, various solutions have been proposed in existing research. For example, some studies have designed high power factor plasma power supplies for atmospheric pressure plasma jet devices to improve input current quality and output stability; other studies have proposed high-frequency high-voltage power supply schemes for plasma cleaning and dielectric barrier discharge applications from the perspective of resonant topology and adaptive adjustment, verifying the feasibility of soft switching and self-tuning control under plasma loads.

[0005] With the development of third-generation wide-bandgap semiconductor devices, the device level of plasma power supplies is undergoing significant changes. SiC devices, with their high breakdown voltage, low conduction loss, and excellent high-frequency characteristics, provide a new path for realizing high-frequency, high-power plasma power supplies. Related research shows that LLC resonant converters and high-frequency inverters based on SiC devices have significant advantages in efficiency and power density.

[0006] Despite the positive progress made in the aforementioned research, high-frequency, high-power plasma power supplies still face several key challenges in engineering applications. On the one hand, switching losses and voltage stress increase significantly under high-frequency conditions, placing higher demands on soft-switching implementation. On the other hand, plasma loads exhibit strong nonlinearity and dynamic variation characteristics, making it particularly difficult for the power supply to maintain stable soft-switching and rapid dynamic response over a wide load range. Especially in commonly used topologies such as phase-shifted full-bridge and LLC, soft-switching conditions are often highly dependent on load current and parasitic parameters, and soft-switching failures are prone to occur under light load or rapid adjustment conditions, thereby reducing system efficiency and exacerbating device stress. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a phase-shifting full-bridge plasma power supply based on all-SiC devices, comprising: The rectifier unit includes a power factor correction circuit, which is used to correct the AC input voltage by power factor and output a stable DC bus voltage. The inverter unit, connected to the rectifier unit, includes a phase-shifted full-bridge topology composed of SiC power devices, used to invert the DC bus voltage into a high-frequency AC voltage and achieve zero-voltage switching through phase-shift control. A transformer unit, connected to the inverter unit, is used to boost the high-frequency AC voltage; An output unit, connected to the transformer unit, is used to convert the boosted high-frequency AC voltage into a DC output voltage to drive the plasma load. The control unit, connected to the output unit and the inverter unit, is used to generate a phase-shift control signal based on the error between the output current of the output unit and the preset target current, using an incremental PID control algorithm to control the operation of the inverter unit.

[0008] Optionally, the inverter unit includes: The first switch, the second switch, the third switch, and the fourth switch are connected in series to form a leading bridge arm, and the third switch and the fourth switch are connected in series to form a lagging bridge arm. All four switches are SiC power devices. An energy storage inductor is connected in series between the primary side of the transformer unit and the output terminal of the inverter unit.

[0009] Optionally, in the inverter unit: The first switching transistor is further connected in parallel with a first diode and a first capacitor; the second switching transistor is further connected in parallel with a second diode and a second capacitor; the third switching transistor is further connected in parallel with a third diode and a third capacitor; the fourth switching transistor is further connected in parallel with a fourth diode and a fourth capacitor. The first capacitor, the second capacitor, the third capacitor, and the fourth capacitor are the output capacitors of the first switch transistor, the second switch transistor, the third switch transistor, and the fourth switch transistor, respectively.

[0010] Optionally, the hysteresis arm is configured to charge and discharge the output capacitors of the third and fourth switches using the energy stored in the energy storage inductor and the primary current flowing through the hysteresis arm to achieve zero-voltage switching. The advanced bridge arm is configured to charge and discharge the output capacitors of the first and second switching transistors using the energy stored in the leakage inductance of the transformer unit to achieve zero-voltage switching.

[0011] Optionally, the first, second, third, and fourth switching transistors are all SiC power devices with low output capacitance characteristics. The low output capacitance characteristics enable the first and second switching transistors to charge and discharge the output capacitor through the energy stored in the leakage inductance of the transformer unit under light load conditions, thereby achieving zero-voltage switching.

[0012] Optionally, the control unit is further configured to dynamically adjust the dead time of the leading arm and the lagging arm according to the operating state of the inverter unit; The dead time of the leading arm is configured to be greater than the dead time of the lagging arm, and the dead time increases as the load current decreases.

[0013] Optionally, the control unit is further configured to set the dead time to match the resonant period of the resonant circuit formed by the energy storage inductor and the first, second, third, and fourth capacitors, so that the first, second, third, and fourth switches turn on when the drain-source voltage drops to zero in a resonant manner.

[0014] Optionally, the transformer unit includes a high-frequency transformer, the primary side of which is connected to the output terminal of the inverter unit; the output unit includes an output filter capacitor, which is connected to the secondary output terminal of the high-frequency transformer and is used to connect in parallel with the plasma load.

[0015] Optionally, the control unit includes: A sampling module, connected to the output unit, is used to acquire the output current signal; The controller, connected to the sampling module, is used to generate a phase-shift control signal based on the output current signal; The drive module is connected to the controller and the inverter unit respectively, and is used to drive the SiC power devices in the inverter unit according to the phase shift control signal.

[0016] Optionally, the sampling module includes a current sensor; the controller includes a microcontroller; and the driving module includes a driving chip. The current sensor is connected to the output terminal of the output unit and is used to collect the actual current value output by the output unit and feed the actual current value back to the microcontroller. The microcontroller is used to generate the phase-shift control signal based on the error between the actual current value and the preset target current value using an incremental PID control algorithm. The input terminal of the driver chip is connected to the microcontroller and is used to receive the phase shift control signal. The driver chip is used to isolate and amplify the phase shift control signal to drive the SiC power device in the inverter unit, and to perform protection actions when the SiC power device experiences a short circuit or overcurrent.

[0017] Compared with the prior art, the present invention has the following advantages and technical effects: This invention employs an all-SiC power device to construct a phase-shifted full-bridge topology, fully utilizing the high-frequency, low-loss, and low-output-capacitance characteristics of SiC devices. Combined with a differentiated design of the zero-voltage switching mechanism for the leading and lagging bridge arms, a resonant circuit formed by the energy storage inductor and the output capacitor of the switching transistor achieves stable zero-voltage switching over a wide load range, effectively reducing switching losses and voltage stress, and significantly improving overall system efficiency. By dynamically adjusting the dead time of the leading and lagging bridge arms and matching it with the resonant period, the problem of zero-voltage switching failure of the leading bridge arm under light load conditions is solved, expanding the operating range of soft switching and improving the system's operational reliability across the entire load range. The output unit incorporates an output filter capacitor directly connected to the secondary side of the high-frequency transformer, effectively reducing output current ripple, improving the stability of the plasma arc, and contributing to improved coating quality. The control unit uses an incremental PID control algorithm, generating a phase-shifted control signal in real time based on the output current error. This avoids the overshoot and lag problems caused by integral saturation in traditional PID control, significantly improving the system's dynamic response speed and control accuracy under conditions of sudden load changes and setpoint variations. The rectifier unit integrates a power factor correction circuit, improving the input-side power factor and reducing harmonic pollution to the power grid. The driver chip incorporates optocoupler isolation and desaturation protection circuits, achieving reliable isolation between the high-voltage and low-voltage sides and rapidly executing protective actions in the event of short circuits or overcurrents in power devices, enhancing system safety and reliability. This invention exhibits excellent performance in dynamic response, current ripple suppression, soft-switching range, and overall efficiency, providing an efficient and reliable solution for the engineering application of high-frequency, high-power plasma power supplies. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a circuit diagram of a phase-shifted full-bridge topology according to an embodiment of the present invention; Figure 2 The switching timing and primary-side voltage and current waveforms are shown in the embodiments of the present invention.

[0019] Figure 3 This is a waveform diagram of the collector voltage decrease in the resonant mode according to an embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the effect of different output capacitors on achieving ZVS in an embodiment of the present invention; Figure 5 This is a schematic diagram of PID control of the plasma power supply according to an embodiment of the present invention.

[0020] Figure 6 This is a simulation circuit diagram of an embodiment of the present invention; Figure 7 Duty cycle diagram generated for PID control in this embodiment of the invention; Figure 8 This is a PWM waveform diagram generated by the PID control in an embodiment of the present invention. Figure 9 The above diagram shows the GS and DS waveform simulation of the forearm in an embodiment of the present invention. Figure 10 The following is a simulation diagram of the GS and DS waveforms of the hysteresis arm in an embodiment of the present invention; Figure 11 This is a simulation diagram of the output voltage and transformer primary current in an embodiment of the present invention. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0023] Example 1 This embodiment provides a phase-shifting full-bridge plasma power supply based on all-SiC devices, including: The rectifier unit includes a power factor correction circuit, which is used to correct the AC input voltage by power factor and output a stable DC bus voltage. The inverter unit, connected to the rectifier unit, includes a phase-shifted full-bridge topology composed of SiC power devices, used to invert the DC bus voltage into a high-frequency AC voltage and achieve zero-voltage switching through phase-shift control. A transformer unit, connected to the inverter unit, is used to boost the high-frequency AC voltage; An output unit, connected to the transformer unit, is used to convert the boosted high-frequency AC voltage into a DC output voltage to drive the plasma load. The control unit, connected to the output unit and the inverter unit, is used to generate a phase-shift control signal based on the error between the output current of the output unit and the preset target current, using an incremental PID control algorithm to control the operation of the inverter unit.

[0024] This embodiment employs a phase-shifted full-bridge (PSFB) converter to achieve zero-voltage switching of the plasma power supply, thereby achieving higher conversion efficiency. Its core advantage lies in its ability to utilize the inherent resonant elements (energy storage inductor Lr) and parasitic capacitances (output capacitance C of the switching device) in the circuit to achieve zero-voltage switching of the switching device.

[0025] like Figure 1 As shown, the PSFB circuit topology of this embodiment consists of the following parts: (1) Input rectifier terminal: The AC input VA is rectified. in Rectified to DC input VD in (2) Full-bridge inverter: It consists of leading bridge arms Q1 and Q2 and lagging bridge arms Q3 and Q4. The leading bridge arms maintain a fixed duty cycle and drive ahead of the lagging bridge arms. The lagging bridge arms adjust the output power by controlling the lagging main bridge arm through phase shift. Lr is an energy storage inductor. (3) Transformer: It is used to realize high-voltage isolation and step-up. (4) Output rectifier and filter circuit: It rectifies and filters the high-frequency AC power from the secondary side of the transformer and uses it to drive the plasma load.

[0026] (1) (2) Regarding the above Figure 1 The key to achieving zero-voltage switching using the PSFB shown lies in satisfying sufficient inductive energy and dead time. To meet the inductive energy requirement, the PSFB must contain sufficient inductive energy EL to fully charge and discharge the output capacitor of the switching device according to formula (1). eq This represents the board-level equivalent capacitance, specifically including the output capacitance C of the switching devices. tr Parasitic capacitance C of transformers and printed circuit boards XFMR The overall description is shown in formula (2).

[0027] Furthermore, the inverter unit includes: a first switch Q1, a second switch Q2, a third switch Q3 and a fourth switch Q4. The first switch Q1 and the second switch Q2 are connected in series to form a leading bridge arm, and the third switch Q3 and the fourth switch Q4 are connected in series to form a lagging bridge arm. The first switch Q1, the second switch Q2, the third switch Q3 and the fourth switch Q4 are all SiC power devices. The energy storage inductor is connected in series between the primary side of the transformer unit and the output terminal of the inverter unit.

[0028] Furthermore, in the inverter unit: the first switch Q1 is also connected in parallel with the first diode D1 and the first capacitor C1; the second switch Q2 is also connected in parallel with the second diode D2 and the second capacitor C2; the third switch Q3 is also connected in parallel with the third diode D3 and the third capacitor C3; the fourth switch Q4 is also connected in parallel with the fourth diode D4 and the fourth capacitor C4, and the first capacitor C1, the second capacitor C2, the third capacitor C3 and the fourth capacitor C4 are respectively connected in series with the first resistor R1, the first resistor R2, the first resistor R3 and the first resistor R4; The first capacitor C1, the second capacitor C2, the third capacitor C3, and the fourth capacitor C4 are the output capacitors of the first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4, respectively.

[0029] Furthermore, the lagging bridge arm is configured to charge and discharge the output capacitors of the third switch Q3 and the fourth switch Q4 using the energy stored in the energy storage inductor and the primary current flowing through the lagging bridge arm to achieve zero-voltage switching. The lead bridge arm is configured to charge and discharge the output capacitors of the first switch Q1 and the second switch Q2 using the energy stored in the leakage inductance of the transformer unit to achieve zero-voltage switching.

[0030] Furthermore, the first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4 are all SiC power devices with low output capacitance characteristics. The low output capacitance characteristic allows the first and second switches to complete the charging and discharging of the output capacitor through the energy stored in the leakage inductance of the transformer unit under light load conditions, thereby achieving zero-voltage switching.

[0031] In this embodiment, the inductive energy available during commutation is different for the leading arm and the lagging arm because their capacitor charging and discharging occur at different times, such as... Figure 2As shown. When the output capacitor of the leading arm transistor is discharged, the primary current reverses its polarity. This causes the current in the secondary rectifier transistor to commutate, making the secondary voltage of the transformer zero. This indicates that the inductive energy available for achieving ZVS in the leading arm is mainly composed of the leakage inductance of the transformer, as defined by formula (3). The situation is more favorable for the lagging arm. This is because the primary current is at its maximum value when the capacitor discharges, and it is mainly formed by the current flowing through the secondary filter inductor Lf of the transformer and referred to the primary side. The current on this filter inductor also participates in the charging and discharging process of the capacitor, and its energy is defined by formula (4).

[0032] (3) (4) Where L eq_lead The effective inductance used for resonance during ZVS commutation of the leading bridge arm is typically close to the transformer leakage inductance L. lk I eq_lead For the moment of phase commutation of the advanced bridge arm, the L-shaped flow is instantaneous. eq_lead The primary current is small, and because its polarity is reversed at this time, its value is usually small and less affected by the output current. 2C tr This is the sum of the dynamic output capacitances of the two switching transistors on the lead-edge bridge arm. L eq_leg The effective inductance used for resonance during ZVS commutation of the lagging bridge arm is typically a series inductor, I. eq_leg For the momentary flow of L during commutation of the lagging bridge arm eq_leg The primary current, 2C tr This is the sum of the dynamic output capacitances of the two switching transistors on the lagging bridge arm.

[0033] As mentioned above, the leading arm relies on leakage inductance and a small current, while the lagging arm relies on series inductance L. r and larger current (I) _plag The difference between the lagging arm and the leading arm (which is determined by the load) in achieving ZVS makes it easier to achieve ZVS over a wide load range, while ZVS in the leading arm often fails under light loads. To address this issue, the first consideration is to add an auxiliary inductor. This inductor can provide sufficient inductive energy to charge and discharge the capacitor when the leading arm is under no-load conditions. This means that the transformer's magnetizing current alone is sufficient to achieve ZVS. This solution will improve efficiency under no-load conditions. However, the introduction of the auxiliary inductor also brings problems such as increased losses, phase shift limitations, and parasitic oscillations.

[0034] Furthermore, the control unit is also configured to dynamically adjust the dead time of the leading arm and the lagging arm according to the operating state of the inverter unit. The dead time of the leading arm is configured to be greater than that of the lagging arm, and the dead time increases as the load current decreases.

[0035] Furthermore, the control unit is also configured to set the dead time to match the resonant period of the resonant circuit composed of the energy storage inductor and the first, second, third, and fourth capacitors, so that the first, second, third, and fourth switches turn on when the drain-source voltage drops to zero in a resonant manner.

[0036] The second method is to ensure a sufficiently long dead time. The capacitive energy and inductive energy form a resonant circuit, therefore the voltage across the transistor decreases in a resonant manner, such as... Figure 3 As shown. When the dead time is less than a quarter of the resonant period Tr, zero-voltage switching (ZVS) cannot be achieved. Extending the dead time can achieve ZVS, but it unnecessarily prolongs the conduction time of the transistor's reverse diode, further increasing losses. An excessively long dead time can also cause ZVS failure. Therefore, the ideal dead time should be precisely set at the moment the voltage drops to zero. The problem is that the inductive energies of the two bridge arms are different, therefore the required dead times are also different, and this time is still related to the current magnitude. The ideal approach is to set different dead times for each bridge arm and dynamically adjust them according to the load.

[0037] The results show that reducing capacitor energy (i.e., reducing the output capacitance of the transistor) still has significant advantages. Figure 4 The waveforms in the figure show a comparison of the voltage drop across transistors with different output capacitances (C1>C2) when the inductive energy and load remain constant. This figure illustrates that when the output capacitance is large and the inductive energy is constant, even with a sufficiently long dead time, zero-voltage switching (ZVS) may not be achievable.

[0038] Based on all the foregoing analyses, and considering the goals of soft switching and control of high-frequency, high-voltage plasma power supplies as considered in this embodiment, it is necessary to properly tune important circuit components such as switching devices and other parameters to solve complex problems in specific applications.

[0039] Furthermore, based on the analysis of the soft-switching implementation mechanism of the phase-shifted full-bridge topology of the plasma power supply, and combined with the design goals of the high-frequency, high-voltage plasma power supply in this embodiment, the overall performance indicators of the power supply as shown in Table 1 were determined. This indicator system provides clear constraints and theoretical basis for the subsequent selection of key components and modular system design.

[0040] Table 1 The power supply design for the PFC module is as follows: In this embodiment, the plasma power supply input is the mains voltage with a rated line voltage of 220V and a frequency of 50Hz. The voltage enters the PFC module, and after power factor correction, it outputs a DC 380V bus voltage to power the power control board.

[0041] The PFC built-in control chip converts 220V AC power into 310V peak pulsating DC power, performs Boost voltage boosting, adjusts the PF value to approximately 1, and stably outputs 380V DC power, which then enters the power control board.

[0042] Specific parameter requirements for the PFC module: Input voltage AC100-240V, output voltage DC380V. With a power factor of 0.92-0.99 at full load, an efficiency of 0.95 or higher, and a rated power of 1000W, the XN-M0325M from Suzhou Xiniu Electronics Technology Co., Ltd. is selected.

[0043] Furthermore, the transformer unit includes a high-frequency transformer, the primary side of which is connected to the output terminal of the inverter unit; the output unit includes an output filter capacitor, which is connected to the secondary output terminal of the high-frequency transformer and is used to connect in parallel with the plasma load.

[0044] The transformer and filter capacitor design are as follows: To ensure the designed voltage is available at all times, the turns ratio of the high-frequency converter should be designed based on the minimum input voltage. Assuming the maximum duty cycle on the secondary side is Ds(max), the minimum voltage on the secondary side is: (5) In Formula 5, V O This is the output DC voltage value; V D V is the forward voltage drop of the rectifier diode; Lf Let V be the voltage drop across the output filter inductor. The output DC voltage is 310V, the on-state voltage drop is 1.35V, the voltage drop across the output filter inductor is 0.6V, and the minimum input voltage is 380V. Then the transformer turns ratio is: (6) The transformer is designed with 34 turns on the primary side and 800 turns on the secondary side, with a ratio N of [missing value]. The transformer's maximum external dimensions are 81.8mm × 94.1mm. The primary side assembly width is 53.0mm and the diameter is 33.9mm. The secondary side assembly width is 59.8mm and the height is 53.9mm. The output wire material is 3.14 cross-sectional area. The multi-strand yarn has a high-temperature coating that can withstand temperatures up to 180°C.

[0045] To facilitate the winding and design of high-frequency transformers, the transformer turns ratio is set to an integer. Simultaneously, to ensure efficient magnetic coupling and reduce power losses in the magnetic circuit, amorphous alloy materials are selected as the transformer material.

[0046] The output filter capacitors are 150mm×120mm×10mm on both the upper and lower plates, with a gap of 20mm; the copper sheet is 50mm×50mm×4mm, and the ceramic sheet is 60mm×60mm×2mm.

[0047] The core function of the secondary output capacitor differs fundamentally from the energy buffering function in traditional voltage source systems. For the specific requirements of the plasma power supply, the output does not need to rely on a large-capacity capacitor to maintain voltage stability; therefore, a 1µF capacitor is sufficient to meet the design requirements. Excessively large capacitance not only fails to improve system performance but may also introduce unnecessary energy storage, increase the uncertainty of the control loop, and consequently affect the accuracy and dynamic response characteristics of the constant current output.

[0048] The switching device is designed as follows: SiC switching devices achieve a comprehensive improvement in efficiency, power density, and reliability of power electronic systems through higher operating frequencies, lower losses, and higher temperature resistance. The SiC switching device selected in this embodiment withstands a maximum voltage equal to the peak voltage of the diodes in the three-phase rectifier bridge.

[0049] (7) To ensure safe operation of the devices when encountering voltage spikes caused by stray parameters, a voltage margin of approximately 20% is typically reserved. Therefore, the collector-emitter voltage withstand of the SiC switching device should meet 1.2 times the withstand voltage value. The full-bridge converter module has an output current of 250A and a transformer turns ratio of 24. To prevent excessive current stress, a margin of 1.5 to 2 times is generally reserved in engineering practice. The C3M0021120K SiC switching device was ultimately selected.

[0050] The plasma power supply system designed in this embodiment integrates several key modules. The drive circuit uses the Mitsubishi M57962AL chip, which has built-in high-speed optocoupler isolation and desaturation protection, with a transmission delay of only 1µs. Current and voltage sampling use CHB-1000S and CHV-25P Hall sensors, respectively, to achieve high-precision non-contact measurement. The main control unit is based on the STM32F334C8T6 microcontroller, which uses its high-resolution timer to realize digital closed-loop control and is equipped with hardware and software coordinated overcurrent and overvoltage protection mechanisms to ensure the system's dynamic response and operational safety.

[0051] Furthermore, the control unit includes: The sampling module, connected to the output unit, is used to acquire the output current signal; The controller, connected to the sampling module, is used to generate a phase-shift control signal based on the output current signal; The drive module is connected to both the controller and the inverter unit, and is used to drive the SiC power devices in the inverter unit according to the phase shift control signal.

[0052] Furthermore, the sampling module includes a current sensor; the controller includes a microcontroller; and the drive module includes a drive chip. The current sensor is connected to the output terminal of the output unit to collect the actual current value output by the output unit and feed the actual current value back to the microcontroller. The microcontroller is used to generate a phase-shifting control signal based on the error between the actual current value and the preset target current value using an incremental PID control algorithm; The input terminal of the driver chip is connected to the microcontroller to receive the phase-shift control signal. The driver chip is used to isolate and amplify the phase-shift control signal to drive the SiC power devices in the inverter unit, and to perform protection actions when the SiC power devices experience short circuits or overcurrents.

[0053] The specific control strategy is as follows: As discussed earlier regarding the selection of components for plasma power supplies, when the input power supply or load undergoes a sudden change, it will cause significant fluctuations in the overall output. In this case, it is necessary to apply control measures to ensure the quality and overall efficiency of the power supply, optimize the dynamic characteristics of the system, and reduce energy loss.

[0054] like Figure 5 As shown, this embodiment selects incremental PID control to control the plasma power supply. In the small-signal model of the full-bridge converter, the input error of the PID controller is usually determined by the difference between the system setpoint and the actual output value. Its error input is shown in Equation 8: (8) The control of the PID controller is shown in Formula 9 below: (9) Where u(t) represents the output of the PID controller, K p K I K D These represent the proportional, integral, and derivative coefficients, respectively. When used in digital controllers, the continuous PID algorithm needs to be discretized. To achieve discretization, the differential equations in the continuous system are usually replaced with difference equations, thus obtaining the discretized PID control law. After discretization, the expression of the control law is shown in Equation 10: (10) The incremental PID control algorithm is a significant optimization of the traditional PID control architecture. The algorithm's control output is based solely on the error change during the current sampling period, without accumulating historical errors, thus effectively avoiding integral saturation and the resulting overshoot and lag problems.

[0055] The expression for the incremental PID algorithm is shown in Equation 11: (11) To verify the present invention, the following simulation analysis was also performed: like Figure 6 The simulation circuit for a plasma power supply based on a phase-shifted full-bridge (PSFB) topology is shown. The simulation model mainly consists of two parts, as detailed below: The upper part includes: the system input is a three-phase 380V, 50Hz AC mains voltage, which, after rectification and filtering, outputs a stable 380V DC bus voltage as the energy source for the entire main power circuit. A current-limiting resistor R21 is connected in series between this DC bus and the subsequent phase-shifting full-bridge circuit. Its function is to limit the peak inrush current at power-on, preventing damage to the subsequent power devices due to surge current, thus providing protection.

[0056] Four MOSFETs form a full-bridge converter, which, driven by the generated four PWM signals, inverts the 380V DC bus voltage into a high-frequency AC square wave voltage. The leakage inductance, equivalent inductance, and junction capacitance of the switching transistors resonate, forming a key component for achieving ZVS (Zero-Voltage Switching). The primary side of the transformer receives the high-frequency voltage and current limited by the leakage inductance, while the secondary side outputs high-voltage AC after turns ratio transformation. This AC voltage is then rectified and filtered to drive the plasma load. This load exhibits strong nonlinear characteristics, with its impedance dynamically changing with the discharge state.

[0057] The AM5 current detection module samples the high-frequency current on the primary side of the transformer and outputs a proportional small-signal voltage; the Vm9 voltage detection module samples the voltage at key nodes of the power stage and outputs a small signal reflecting the actual operating voltage. After scaling and filtering by the feedback processing unit, the two signals form a standardized feedback signal, which is sent to the error signal generation node in the lower half of the circuit for comparison with a given reference value.

[0058] The oscilloscopes located in the upper part include: Scope12, which monitors the primary current waveform of the transformer to analyze the current commutation characteristics and ZVS implementation; Scope10, which monitors the drain-source voltage waveform of the switching transistor to directly determine whether zero-voltage turn-on has been achieved and to detect whether the voltage spike exceeds the device's withstand voltage limit; and Scope21, which monitors the output voltage waveform of the secondary side of the transformer or the load side to observe the amplitude, ripple, and dynamic response.

[0059] The lower part includes: an error signal generation node that calculates the difference between the externally given current reference value (Constant13) and the actual value fed back from the current detection module in the upper part, obtaining a deviation signal, which is then sent to the PID controller. The PID controller performs proportional, integral, and derivative operations on the error signal and outputs a control quantity, which essentially corresponds to the duty cycle adjustment signal required for phase-shift control. This control quantity enters the Symmetrical PWM Generation Module (Symmetrical PWM 3-Level), converting the continuous control quantity into a standard PWM signal, which is then processed by the Saturation Limiting Module to prevent the duty cycle from exceeding the safe range and ensure system stability.

[0060] The original PWM signal, as the main output (PWM1), directly drives the gate of the upper MOSFET in one arm of the full-bridge circuit. Simultaneously, a complementary signal is generated by the NOT logic inversion module for the basic drive of the lower MOSFET in the same arm, ensuring alternating conduction of the upper and lower MOSFETs. The complementary signal is then fed a fixed dead time by the Pulse Delay dead-time control module to prevent simultaneous conduction of the upper and lower MOSFETs in the same arm, thus preventing shoot-through faults and providing the necessary conditions for ZVS soft switching. A fixed delay is then applied by the Turn On Delay module to adjust the timing of the drive pulses. Furthermore, a time delay is introduced into a set of PWM signals by the delay module, creating a phase difference between the two arms to achieve phase-shift control. This phase shift directly determines the effective value of the full-bridge output voltage, thereby regulating the output power. Finally, the four generated PWM signals (PWM1~PWM4) are sent to the gates of the four MOSFETs in the upper half of the circuit.

[0061] The error signal generation node in the lower half receives the standardized feedback signal from the upper half and compares it with the given reference value, forming a complete closed-loop control system to achieve precise regulation of the output current. The system as a whole follows a closed-loop structure of "sampling-regulation-modulation-drive," with a PID controller at its core. Through the coordinated action of PWM generation, logic operations, phase-shift control, and dead-time protection, the phase-shift full-bridge converter achieves efficient and stable operation.

[0062] The oscilloscopes located in the lower half include: Scope20 for monitoring PWM waveforms and verifying whether the duty cycle, phase shift angle, and dead time meet the design requirements.

[0063] The voltage and current probes in the simulation software acquire real-time voltage and current signals across the output load and feed them back to the control loop. Based on the received feedback signals, the control circuit calculates and generates corresponding PWM drive waveforms in real time using an incremental PID control algorithm, thereby precisely adjusting the operating state of the switching elements and ultimately achieving high dynamic closed-loop control of the system.

[0064] To verify the dynamic response performance of the incremental PID control algorithm in the simulation model, such as Figure 7 , 8 The embodiment shown simulates the changes in system parameters in the simulation. Figure 9 The above diagram shows the GS and DS waveform simulation of the forearm in an embodiment of the present invention. Figure 10 The following is a simulation diagram of the GS and DS waveforms of the hysteresis arm in an embodiment of the present invention; Figure 10 The GS waveform in the image is a continuously high-level drive signal; Figure 10 The DS waveform clearly shows a switching process: from approximately 1.19188s to 1.19191s, the voltage stabilizes at around 380V, indicating that the MOSFET is in the off state and withstands the bus voltage; subsequently, from 1.19191s to 1.19192s, the voltage drops rapidly to near 0V, reflecting that the MOSFET begins to conduct under gate drive; after 1.19192s, the voltage remains near 0V, indicating that the transistor is fully turned on and the drain-source impedance is low. The overall waveform clearly shows the correspondence between gate drive and drain-source voltage, verifying that the switching characteristics of this lagging arm MOSFET meet the design expectations of power electronic circuits.

[0065] To verify the load dynamic performance of the incremental PID control algorithm in the simulation model, such as Figure 11 The embodiment shown simulates the waveform of load change in the simulation. Figure 11 The output voltage waveform is a bipolar symmetrical square wave, with the voltage periodically jumping between approximately +380V and -380V. This waveform is generated by the alternating conduction of the leading and lagging arm switches in the full-bridge topology. Its flat-top characteristic indicates that the switching action of the switches is clear, the drive timing is well coordinated, and there is no obvious voltage ringing or overshoot. Figure 11 The primary current waveform of the transformer exhibits quasi-sinusoidal bidirectional triangular wave characteristics, with the current periodically varying between approximately +8A and -8A, and strictly synchronized with the output voltage square wave. This waveform is typical of LLC resonant converters. The smooth change in current reflects the energy resonance characteristics of the resonant cavity and also indicates that the converter operates in a soft-switching state, effectively reducing switching losses. Overall, the coordination between the voltage square wave and the quasi-sinusoidal current verifies the energy transfer mechanism of this topology, while the symmetry and continuous change of the current waveform indicate stable converter operation without abnormalities such as magnetic bias or current distortion.

[0066] The following experimental tests were also conducted in this embodiment: This embodiment addresses the high-current output characteristics and heat accumulation issues of the power supply system by optimizing the power supply's heat dissipation structure design. In terms of circuit layout, the placement of components is optimized, and a staggered modular arrangement is used to form efficient heat dissipation channels. Combined with the heat diffusion design of the copper-aluminum composite heat dissipation substrate, localized heat accumulation is effectively reduced.

[0067] For the developed high-frequency, high-voltage plasma power supply, basic electrical characteristic tests were conducted on the prototype, including soft-switching tests, output current, response characteristics, external characteristics, and output efficiency. Furthermore, considering the requirements of plasma spraying, the power supply's output performance was comprehensively evaluated by adjusting key variables such as main electrical parameters, gas flow rate, and powder delivery rate.

[0068] Soft-switching test: The soft-switching waveform of the full-bridge circuit is displayed using an oscilloscope. When the GS drive signal completes the level transition, the DS voltage does not change abruptly synchronously, but rather slowly drops from the bus voltage to a low level after the drive signal is triggered. Through circuit resonance and other methods, the drain-source voltage is reduced to approximately zero before the device is turned on, avoiding the overlap of voltage and current in hard switching, significantly reducing switching losses, and fully realizing soft switching.

[0069] Output waveform test: To verify the output characteristics of the power supply prototype under high current conditions, the ripple suppression effect can characterize the ultimate performance of the topology when 11A is the maximum output current of the system design. Considering that the current adjustment range in actual plasma work is mostly concentrated in the ±10% range of the set value, the waveform of the output current is tested at 11.4A.

[0070] Plasma Ignition Experiment: In plasma spraying, the morphology, brightness, and stability of the plasma arc are key indicators for evaluating process performance. Observing the arc performance can verify the power supply performance, process control accuracy, and coating quality. High arc brightness indicates sufficient energy to fully melt the powder; uniform brightness distribution without fluctuations indicates good arc stability. Experiments show that, with an output current of 4.8A, an argon flow rate of 40 SLPM, and a hydrogen flow rate varying within the range of 0-10 SLPM, the purplish-pink plasma generated at the metal spray gun nozzle verifies the effectiveness of the plasma power supply designed in this embodiment.

[0071] This embodiment addresses the key technical challenges faced by high-frequency, high-power plasma power supplies in terms of efficiency, dynamic response, and soft-switching stability. It systematically conducts research on topology design, soft-switching mechanism analysis, device selection, control strategy design, and experimental verification. To address the shortcomings of traditional plasma power supplies under high-frequency, high-current conditions, such as hysteresis in dynamic response, high switching losses, and limited soft-switching range under light loads, a three-stage phase-shifted full-bridge (PSFB) high-frequency, high-voltage plasma power supply scheme based on all-SiC devices is proposed, and a corresponding digital closed-loop control system is constructed.

[0072] First, starting from the implementation mechanism of phase-shifted full-bridge soft switching, this paper analyzes in depth the essential differences between the leading and lagging bridge arms in terms of ZVS implementation conditions, focusing on the influence mechanism of inductive energy, dead time, and device output capacitance on the soft switching range. Addressing the issue of ZVS failure of the leading bridge arm under light load conditions, this paper comprehensively compares various improvement approaches, including the introduction of auxiliary inductors, dynamic adjustment of dead time, and selection of low-output-capacitance SiC devices, providing a clear design basis for soft switching optimization of high-frequency, high-power PSFB converters.

[0073] Secondly, for a plasma power supply with design specifications of 40kW, 4.7A, and 25kHz, the systematic design and parameter calculation of the rectifier stage, high-frequency transformer, SiC power devices, and secondary-side rectification and filtering modules were completed. At the control level, an incremental PID control strategy was introduced, effectively avoiding the integral saturation problem of traditional PID control during rapid high-current regulation, and significantly improving the dynamic stability of the system under conditions of sudden load changes and setpoint variations. A simulation model based on PLECS verified the effectiveness of the proposed control method in dynamic current regulation and load disturbance suppression.

[0074] Finally, a high-frequency, high-voltage plasma power supply prototype was developed and comprehensive experimental tests were conducted. Experimental results show that the power supply achieves a current ripple rate as low as 0.41% at 4.7 A output, a dynamic response time of approximately 2 ms during current step changes, and a maximum overall efficiency of 93.67%. Furthermore, it maintains excellent constant current characteristics and stable soft-switching operation across a wide load range. Plasma ignition and stable combustion experiments further validated the feasibility and reliability of the designed power supply in practical plasma power supply applications.

[0075] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A phase-shifted full-bridge plasma power supply based on all-SiC devices, characterized in that, include: The rectifier unit includes a power factor correction circuit, which is used to correct the AC input voltage by power factor and output a stable DC bus voltage. The inverter unit, connected to the rectifier unit, includes a phase-shifted full-bridge topology composed of SiC power devices, used to invert the DC bus voltage into a high-frequency AC voltage and achieve zero-voltage switching through phase-shift control. A transformer unit, connected to the inverter unit, is used to boost the high-frequency AC voltage; An output unit, connected to the transformer unit, is used to convert the boosted high-frequency AC voltage into a DC output voltage to drive the plasma load. The control unit, connected to the output unit and the inverter unit, is used to generate a phase-shift control signal based on the error between the output current of the output unit and the preset target current, using an incremental PID control algorithm to control the operation of the inverter unit.

2. The plasma power source according to claim 1, characterized in that, The inverter unit includes: The first switch, the second switch, the third switch, and the fourth switch are connected in series to form a leading bridge arm, and the third switch and the fourth switch are connected in series to form a lagging bridge arm. All four switches are SiC power devices. An energy storage inductor is connected in series between the primary side of the transformer unit and the output terminal of the inverter unit.

3. The plasma power source according to claim 2, characterized in that, In the inverter unit: The first switching transistor is further connected in parallel with a first diode and a first capacitor; the second switching transistor is further connected in parallel with a second diode and a second capacitor; the third switching transistor is further connected in parallel with a third diode and a third capacitor; the fourth switching transistor is further connected in parallel with a fourth diode and a fourth capacitor. The first capacitor, the second capacitor, the third capacitor, and the fourth capacitor are the output capacitors of the first switch transistor, the second switch transistor, the third switch transistor, and the fourth switch transistor, respectively.

4. The plasma power source according to claim 3, characterized in that, The hysteresis arm is configured to charge and discharge the output capacitors of the third and fourth switches using the energy stored in the energy storage inductor and the primary current flowing through the hysteresis arm to achieve zero-voltage switching. The advanced bridge arm is configured to charge and discharge the output capacitors of the first and second switching transistors using the energy stored in the leakage inductance of the transformer unit to achieve zero-voltage switching.

5. The plasma power source according to claim 4, characterized in that, The first, second, third, and fourth switching transistors are all SiC power devices with low output capacitance characteristics. The low output capacitance characteristic allows the first and second switching transistors to charge and discharge the output capacitor through the energy stored in the leakage inductance of the transformer unit under light load conditions, thereby achieving zero-voltage switching.

6. The plasma power source according to claim 4, characterized in that, The control unit is also configured to dynamically adjust the dead time of the leading arm and the lagging arm according to the operating state of the inverter unit. The dead time of the leading arm is configured to be greater than the dead time of the lagging arm, and the dead time increases as the load current decreases.

7. The plasma power source according to claim 6, characterized in that, The control unit is further configured to set the dead time to match the resonant period of the resonant circuit formed by the energy storage inductor and the first, second, third, and fourth capacitors, so that the first, second, third, and fourth switches turn on when the drain-source voltage drops to zero in a resonant manner.

8. The plasma power source according to claim 1, characterized in that, The transformer unit includes a high-frequency transformer, the primary side of which is connected to the output terminal of the inverter unit; the output unit includes an output filter capacitor, which is connected to the secondary output terminal of the high-frequency transformer and is used to connect in parallel with the plasma load.

9. The plasma power source according to claim 1, characterized in that, The control unit includes: A sampling module, connected to the output unit, is used to acquire the output current signal; The controller, connected to the sampling module, is used to generate a phase-shift control signal based on the output current signal; The drive module is connected to the controller and the inverter unit respectively, and is used to drive the SiC power devices in the inverter unit according to the phase shift control signal.

10. The plasma power source according to claim 9, characterized in that, The sampling module includes a current sensor; the controller includes a microcontroller; the driving module includes a driving chip. The current sensor is connected to the output terminal of the output unit and is used to collect the actual current value output by the output unit and feed the actual current value back to the microcontroller. The microcontroller is used to generate the phase-shift control signal based on the error between the actual current value and the preset target current value using an incremental PID control algorithm. The input terminal of the driver chip is connected to the microcontroller and is used to receive the phase shift control signal. The driver chip is used to isolate and amplify the phase shift control signal to drive the SiC power device in the inverter unit, and to perform protection actions when the SiC power device experiences a short circuit or overcurrent.

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