An IGBT-based high-frequency resonant closed-loop control system and a closed-loop control method thereof

Abstract

The application discloses a high-frequency resonant closed-loop control system based on IGBT and a closed-loop control method thereof, and the system comprises the following steps: an inverter unit is composed of N IGBT inverter modules in parallel; a signal acquisition module acquires load electrical parameter signals; a frequency control module generates a frequency instruction according to the phase of the electrical parameter signals; a power control module generates an adjusting instruction according to the comparison between the amplitude of the electrical parameter signals and an external given value; a driving module comprises N inverter module driving channels and one BUCK chopper driving channel, the frequency instruction is used for controlling the inverter module driving channels to output out-of-phase switching sequences so that the equivalent frequency of the load is N times of the actual frequency of each module, and the adjusting instruction is used for controlling the BUCK chopper driving channel to output a variable duty cycle switching sequence to realize power control through voltage regulation; the signal acquisition module is connected with the frequency control module and the driving module to form a frequency tracking closed loop, and is connected with the power control module and the driving module to form a power tracking closed loop.

Description

Technical Field

[0001] This invention belongs to the field of power electronics and high-frequency inverter control technology, specifically relating to a high-frequency resonant closed-loop control system based on IGBT and its closed-loop control method, to achieve high-frequency, efficient and stable resonant inverter control, which is particularly suitable for high-frequency inverter application scenarios such as induction heating. Background Technology

[0002] Currently, induction heating technology is widely used in metal heat treatment, smelting, welding and other fields. With the development of IGBT (Insulated Gate Bipolar Transistor) technology, high-frequency (100-300kHz) high-power (500kW and above) induction heating power supplies have become the mainstream solution.

[0003] In the prior art, a typical series resonant induction heating power supply scheme is as follows: The main circuit adopts a structure of "three-phase uncontrolled rectifier + filter capacitor + single IGBT full-bridge inverter + series resonant load"; The control adopts open-loop fixed-frequency PWM drive, and the switching frequency is preset to the nominal resonant frequency; Power regulation is achieved through phase-controlled voltage regulation on the rectifier side or DC chopper; Some solutions use phase-locked loops (PLLs) to achieve frequency tracking, but the PLL and power control are independent of each other and lack coordination.

[0004] However, the aforementioned existing technical solutions have at least the following technical defects: Frequency bottleneck: The switching frequency of a single IGBT inverter bridge is limited by the characteristics of the devices, making it difficult to achieve high-frequency output. The switching speed of power devices becomes the bottleneck restricting the improvement of system output frequency.

[0005] Resonance mismatch: Fixed-frequency control cannot follow the load resonant frequency drift (e.g., drift with changes in temperature, workpiece material, etc.), causing the inverter to operate in a non-resonant state, resulting in increased switching losses, reduced efficiency, and deteriorated power factor.

[0006] Control coupling: Frequency tracking and power regulation are controlled independently, lacking a unified closed-loop architecture, resulting in slow dynamic response and susceptibility to oscillation. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a high-frequency resonant closed-loop control system based on IGBTs and its closed-loop control method, thereby overcoming the technical defects in the prior art, such as the limited switching frequency of a single IGBT inverter bridge, the inability to automatically track resonant frequency drift, and the mutual coupling between frequency tracking and power regulation.

[0008] This invention achieves high-frequency, high-efficiency, and stable resonant inverter control by employing a dual closed-loop control architecture that combines "multiple IGBT parallel inverter bridges operating alternately in a time-sharing manner" with "phase-locked loop frequency automatic tracking" and "power closed-loop regulation".

[0009] Specifically, this invention uses N sets of IGBT full-bridge inverter modules connected in parallel between the DC bus and the series resonant load. Each of the N inverter modules is driven by N PWM signals with a phase difference of 360° / N. The switching frequency of each inverter module is equal to the frequency output by the PLL. However, because the N inverter modules operate alternately in a time-sharing manner, the equivalent output frequency is N times higher. The actual switching frequency of each IGBT is only 1 / N of the output frequency, effectively reducing the requirements for the switching speed of the power devices. Simultaneously, the PLL frequency tracking subsystem detects the load resonance state in real time and automatically adjusts the inverter operating frequency, ensuring the system always operates near the resonance point. The power outer-loop PI regulator outputs adjustment commands to the BUCK chopper IGBT drive channel in the drive module, controlling this channel to output a variable duty cycle switching sequence to adjust the DC bus voltage, achieving a power closed loop. The frequency inner loop and power outer loop act on the system through different control channels, naturally decoupled by the load resonance characteristics, and do not interfere with each other. Ultimately, the system operates in a weakly capacitive quasi-resonant state, achieving ZVS (zero-voltage switching) soft switching and reducing switching losses.

[0010] Thus, this invention realizes a complete control closed loop from parallel frequency multiplication output of multiple inverter modules to automatic frequency tracking and power closed-loop regulation, significantly improving the output frequency capability, efficiency and power factor of the high-frequency inverter system.

[0011] According to one aspect of the present invention, a high-frequency resonant closed-loop control system based on IGBT is provided, comprising: The inverter unit is composed of N IGBT inverter modules connected in parallel, where N is an integer greater than or equal to 2. The inverter unit is provided with a DC input terminal for connecting to the power supply terminal, and the AC output terminal of each IGBT inverter module is used to connect in parallel to the resonant load. The signal acquisition module has an input terminal for connecting to the resonant load, and an output terminal for connecting to the input terminal of the frequency control module and the input terminal of the power control module, respectively. The signal acquisition module is used to acquire and output the electrical parameter signals of the resonant load. The frequency control module receives the electrical parameter signal output by the signal acquisition module at its input terminal, and its output terminal is connected to the frequency command input terminal of the drive module. The frequency control module is used to generate a frequency command based on the phase characteristics of the electrical parameter signal and output it to the drive module. The power control module receives the electrical parameter signal output by the signal acquisition module and the external given signal at its input terminal. The output terminal of the power control module is connected to the adjustment command input terminal of the drive module. The power control module is used to generate an adjustment command based on the comparison result between the amplitude characteristics of the electrical parameter signal and the external given signal and output it to the drive module. The drive module includes N parallel inverter module IGBT drive channels and one BUCK chopper IGBT drive channel. The output terminal of each inverter module IGBT drive channel is connected to the control electrode of the IGBT in the respective IGBT inverter module. The output terminal of the BUCK chopper IGBT drive channel is connected to the control electrode of the BUCK chopper IGBT. The frequency command input terminal of the drive module receives the frequency command, and the adjustment command input terminal receives the adjustment command. The drive module controls the output of each inverter module IGBT drive channel to output a switching sequence with mutually staggered phases according to the frequency command, so that each IGBT inverter module works alternately in a time-sharing manner and the equivalent frequency of the resonant load is N times the actual operating frequency of each IGBT inverter module. The drive module controls the BUCK chopper IGBT drive channel to output a switching sequence with a variable duty cycle according to the adjustment command, so as to drive the IGBT in the BUCK chopper circuit to work, adjust the DC bus voltage, and realize power closed-loop control. The signal acquisition module, the frequency control module, and the drive module form a frequency tracking closed loop, and the signal acquisition module, the power control module, and the drive module form a power tracking closed loop.

[0012] Compared with the prior art, the present invention has the following beneficial effects: High-frequency output capability: Through N-fold frequency multiplication technology, each IGBT group only needs to handle a switching frequency of 1 / N of the output frequency, which can achieve N-fold frequency output without increasing the requirements of the device, breaking through the switching frequency limit of a single IGBT group.

[0013] Automatic resonance tracking: The PLL automatically detects and tracks changes in the load's resonant frequency, always maintaining a quasi-resonant operating state, resulting in high efficiency and a good power factor.

[0014] Control decoupling: The frequency inner loop and power outer loop are decoupled, resulting in fast dynamic response and high steady-state accuracy, avoiding oscillations caused by mutual interference between the two.

[0015] Simple structure: No additional frequency sweeping start circuit or complex frequency search algorithm is required, and the start-up process is simple and reliable. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a block diagram of the overall structure of the IGBT-based high-frequency resonant closed-loop control system provided in an embodiment of the present invention. Figure 2 This is a diagram of the DC chopper power regulation topology circuit provided in the embodiments of the present invention; Figure 3 This is a diagram of the inverter topology provided in an embodiment of the present invention; Figure 4 This is a timing diagram of the IGBT gate control signal of the inverter circuit provided in this embodiment of the invention, where the vertical axis represents the drive signal level (V) and the horizontal axis represents time (V). s), refer to Figure 3 AH is the drive signal for Q11 and Q14, AL is the drive signal for Q13 and Q12; BH is the drive signal for Q21 and Q24, BL is the drive signal for Q23 and Q22; CH is the drive signal for Q31 and Q34, and CL is the drive signal for Q33 and Q32. The three sets of drive signals are sequentially 120° out of phase. Figure 5 This is a schematic diagram of the IGBT gate dead time of the inverter circuit provided in this embodiment of the invention, where the horizontal axis represents time (…). T_dead represents the dead time, which is the conduction delay interval between the drive signals of two IGBTs (e.g., Q13 and Q14) on the same bridge arm. Figure 6 The above is a waveform diagram of the ZVS zero-voltage switch conduction provided in an embodiment of the present invention, wherein, Figure 6 The horizontal axis represents time ( The left vertical axis represents voltage (V) corresponding to Vce (IGBT collector-emitter voltage), and the right vertical axis represents current (A) corresponding to Ir (resonant current). Figure 7 This is a PLL phase-locked loop topology diagram provided in an embodiment of the present invention; Figure 8 This is a power control topology diagram provided in an embodiment of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] The embodiments of this invention are written in a progressive manner.

[0020] To facilitate understanding of the technical solution of this invention, some technical terms appearing in the specification are explained as follows: IGBT (Insulated Gate Bipolar Transistor): It is a composite fully controllable voltage-driven power semiconductor device composed of BJT (Bipolar Junction Transistor) and MOSFET (Insulated Gate Field Effect Transistor). It combines the advantages of high input impedance of MOSFET and low on-state voltage drop of BJT, and is widely used in high-frequency high-power inverter circuits.

[0021] PLL (Phase-Locked Loop): A frequency and phase synchronization technology that uses feedback control principle. It compares the phase difference between the input signal and the feedback signal through a phase detector, and adjusts the output frequency through low-pass filtering and frequency synthesis to keep the output signal in a fixed phase relationship with the input signal.

[0022] ZVS (Zero Voltage Switching) is a soft-switching technology that refers to the power switching device turning on or off when the voltage across its terminals is zero, thereby significantly reducing switching losses and electromagnetic interference.

[0023] PWM (Pulse Width Modulation): is a technique that controls output voltage or power by modulating the on-time of switching devices.

[0024] EMI (Electromagnetic Interference) refers to the interference of electromagnetic waves generated by electronic devices during operation on external devices or systems.

[0025] BUCK chopper circuit: a DC-DC step-down converter that controls the output voltage to be lower than the input voltage by turning the IGBT on and off.

[0026] LC low-pass filter network: A filter circuit consisting of an inductor (L) and a capacitor (C) is used to smooth the DC bus voltage and filter out high-frequency ripple.

[0027] XOR phase detector: A phase detection circuit based on XOR logic, used to compare the phase difference of two square wave signals and output a pulse signal with a pulse width proportional to the phase difference.

[0028] SiC MOSFET: Silicon carbide metal oxide semiconductor field-effect transistor, is a wide bandgap power device with advantages such as fast switching speed, high voltage withstand, and low conduction loss.

[0029] GaN HEMT: Gallium nitride high electron mobility transistor, is a wide bandgap power device with advantages such as good high-frequency characteristics and fast switching speed.

[0030] The terms used above are only for explaining specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art will understand that other existing technologies with the same or similar functions can be employed without departing from the concept of the present invention.

[0031] Example 1: System Architecture This invention provides a high-frequency resonant closed-loop control system based on IGBTs. Its core lies in connecting N sets of IGBT full-bridge inverter modules in parallel between the DC bus and the series resonant load. It adopts a dual closed-loop control architecture that combines "multiple sets of IGBT parallel inverter modules working alternately in a time-sharing manner" with "phase-locked loop frequency automatic tracking" and "power closed-loop regulation" to achieve high-frequency, efficient and stable resonant inverter control.

[0032] The system adopts a modular architecture, consisting of an inverter unit, a signal acquisition module, a frequency control module, a power control module, and a drive module. The modules work together to form a complete control closed loop, from the parallel frequency multiplication output of multiple inverter modules to automatic frequency tracking and power closed-loop regulation.

[0033] Specifically, such as Figure 1 As shown, the system includes the following functional modules: Power supply end: such as Figure 2As shown, the power supply terminal includes a rectifier unit and a DC conditioning unit. The input terminal of the rectifier unit is connected to an AC power source, and the output terminal of the rectifier unit is connected to the input terminal of the DC conditioning unit. The output terminal of the DC conditioning unit serves as the power supply terminal and is connected to the DC input terminal of the inverter unit. The DC conditioning unit includes a BUCK chopper circuit and an LC low-pass filter network. The input terminal of the BUCK chopper circuit serves as the input terminal of the DC conditioning unit and is connected to the output terminal of the rectifier unit. The output terminal of the BUCK chopper circuit is connected to the input terminal of the LC low-pass filter network. The output terminal of the LC low-pass filter network serves as the output terminal of the DC conditioning unit and is connected to the DC input terminal of the inverter unit. Three-phase AC power is converted into DC power through a three-phase uncontrolled rectifier bridge. The DC voltage is regulated by the BUCK chopper circuit according to the power requirement, and then smoothed by the LC low-pass filter network composed of filter inductor Lf and filter capacitor Cf, providing a smooth DC bus voltage for the subsequent inverter unit.

[0034] Inverter Unit: Composed of N IGBT inverter modules connected in parallel, where N is an integer greater than or equal to 2. The inverter unit has a DC input terminal for connecting to the power supply, and the AC output terminals of each IGBT inverter module are connected in parallel to a resonant load. For example... Figure 3 As shown, each IGBT inverter module is an IGBT full-bridge inverter module, consisting of a first upper bridge arm IGBT, a first lower bridge arm IGBT, a second upper bridge arm IGBT, and a second lower bridge arm IGBT. Each IGBT is connected in anti-parallel to a diode. The first upper bridge arm IGBT and the first lower bridge arm IGBT are connected in series to form the first bridge arm, and the second upper bridge arm IGBT and the second lower bridge arm IGBT are connected in series to form the second bridge arm. The first bridge arm and the second bridge arm are connected in parallel between the DC input terminals of the inverter unit. The series connection nodes of the first upper bridge arm IGBT and the first lower bridge arm IGBT, and the series connection nodes of the second upper bridge arm IGBT and the second lower bridge arm IGBT serve as the AC output terminals of the IGBT full-bridge inverter module. The control terminals of each IGBT are connected to the output terminals of the corresponding drive channels in the drive module to receive the corresponding upper bridge arm drive signals or lower bridge arm drive signals.

[0035] Resonant load: The load consists of an equivalent resistance R, a resonant inductance L, and a resonant capacitance C connected in series. Resonant frequency. When the inverter's operating frequency equals the resonant frequency, the load is purely resistive, and the power factor is at its maximum.

[0036] Signal acquisition module: Its input terminal is used to connect to the resonant load, and its output terminal is connected to the input terminal of the frequency control module and the input terminal of the power control module, respectively. The signal acquisition module is used to acquire and output the electrical parameter signals of the resonant load. The electrical parameter signals include voltage signals and current signals.

[0037] Frequency control module: Its input terminal receives the electrical parameter signal output by the signal acquisition module, and its output terminal is connected to the frequency command input terminal of the drive module. The frequency control module is used to generate a frequency command based on the phase characteristics of the electrical parameter signal and output it to the drive module. The frequency control module includes a voltage zero-crossing comparator, a current zero-crossing comparator, a phase detection unit, a filtering unit, and a frequency synthesis unit. The voltage zero-crossing comparator receives the voltage signal from the signal acquisition module at its input and connects to the first input of the phase detector unit to detect zero crossings and output a voltage square wave signal. The current zero-crossing comparator receives the current signal from the signal acquisition module at its input and connects to the second input of the phase detector unit to detect zero crossings and output a current square wave signal. The phase detector unit connects to the input of the filter unit to output a pulse width signal based on the phase difference between the voltage and current square wave signals. The filter unit connects to the first input of the frequency synthesis unit to filter the pulse width signal and output a phase error signal. The frequency synthesis unit receives the nominal frequency signal at its second input and the jitter signal at its third input. Its output serves as the output of the frequency control module, combining the nominal frequency signal, phase error signal, and jitter signal to synthesize a frequency command. At system startup, the frequency synthesis unit uses the superimposed nominal frequency signal and jitter signal as the initial value for the frequency command. During the initialization phase, the phase-locked loop is not yet locked, the phase error signal is invalid, and the frequency synthesis unit synthesizes the initial frequency command based only on the nominal frequency signal and the jitter signal. After the system establishes a resonant response, the phase error signal is connected to the frequency synthesis unit to participate in closed-loop regulation.

[0038] Power control module: such as Figure 8As shown, its input terminal receives the electrical parameter signal output by the signal acquisition module and an external given signal. The output terminal of the power control module is connected to the adjustment command input terminal of the drive module. The power control module is used to generate an adjustment command based on the comparison result between the amplitude characteristics of the electrical parameter signal and the external given signal, and output it to the drive module. The power control module includes a power calculation unit, a low-pass filter unit, a comparison unit, and an adjustment unit. The input terminal of the power calculation unit serves as the input terminal of the power control module, used to receive voltage and current signals from the electrical parameter signals, and calculate instantaneous power based on the voltage and current signals; the input terminal of the low-pass filter unit is connected to the output terminal of the power calculation unit, used to perform low-pass filtering on the instantaneous power and output the average power; the first input terminal of the comparison unit is connected to the output terminal of the low-pass filter unit, and the second input terminal is used to receive the power setpoint signal, used to compare the average power with the power setpoint signal and output the power error signal; the adjustment unit is a PI regulator, the input terminal of the adjustment unit is connected to the output terminal of the comparison unit, and the output terminal of the adjustment unit serves as the output terminal of the power control module, connected to the adjustment command input terminal of the drive module, used to output adjustment commands to the drive module based on the power error signal.

[0039] The drive module comprises N parallel inverter module IGBT drive channels and one BUCK chopper IGBT drive channel. The output of each inverter module IGBT drive channel is connected to the control electrode of the IGBT in the respective inverter module; the output of the BUCK chopper IGBT drive channel is connected to the control electrode of the BUCK chopper IGBT. The drive module receives the frequency command input and the adjustment command input. According to the frequency command, the drive module controls the IGBT drive channels of each inverter module to output a phase-shifting switching sequence, causing each IGBT inverter module to operate alternately in a time-sharing manner, and the equivalent frequency of the resonant load is N times the actual operating frequency of each IGBT inverter module. According to the adjustment command, the drive module controls the BUCK chopper IGBT drive channel to output a switching sequence with a variable duty cycle, providing an adjustable input voltage to the subsequent inverter unit, thereby achieving power control. In the drive module, the switching sequences output by each inverter module drive channel are PWM signal groups, with each PWM signal group having a phase difference of 360° / N. The duty cycle of the PWM signal output from the BUCK chopper IGBT drive channel is controlled by adjustment commands and is continuously adjustable.

[0040] The six functional modules described above work together to form a complete closed-loop system. The three-phase AC power supply, after passing through the rectifier and DC conditioning units, provides a smooth DC bus voltage to the inverter unit. The signal acquisition module acquires the electrical parameter signals of the resonant load and sends them to the frequency control module and power control module, respectively. The frequency control module generates a frequency command based on the phase characteristics of the electrical parameter signals, and the power control module generates an adjustment command based on the amplitude characteristics of the electrical parameter signals compared with an external given signal. The drive module generates N mutually staggered switching sequences based on the frequency and adjustment commands, driving N IGBT inverter modules to operate alternately in a time-sharing manner, ensuring that the equivalent frequency of the resonant load is N times the actual operating frequency of each IGBT inverter module. The signal acquisition module, frequency control module, and drive module form a frequency tracking closed loop; the signal acquisition module, power control module, and drive module form a power tracking closed loop. All modules communicate through well-defined electrical connections and signal interfaces, ensuring the system's scalability and stability.

[0041] Example 2: General Process Combination Figures 1 to 8 As shown, this invention provides a high-frequency resonant closed-loop control method based on IGBTs. Its core lies in achieving frequency multiplication output through the time-sharing alternating operation of N sets of IGBT full-bridge inverter modules, achieving automatic frequency tracking through a phase-locked loop, and achieving power closed-loop control through PI regulation in the power outer loop. Specifically, it includes the following steps: Step S1: Power Supply and Filtering The three-phase AC power supply provides a smooth DC bus voltage to the inverter unit through a rectifier unit and a DC conditioning unit. Specifically, the three-phase AC power supply obtains DC power through a three-phase uncontrolled rectifier bridge, performs DC chopping and voltage regulation according to power requirements through a BUCK chopper circuit, and then performs smooth filtering through an LC low-pass filter network composed of filter inductor Lf and filter capacitor Cf to provide a smooth DC bus voltage to the subsequent inverter unit.

[0042] Step S2: Inverter and frequency multiplier output The inverter unit consists of N IGBT inverter modules connected in parallel, where N is an integer greater than or equal to 2. The AC output terminals of each IGBT inverter module are connected in parallel to the resonant load. The drive module contains N parallel drive channels, each outputting a staggered switching sequence according to a frequency command, causing the IGBT inverter modules to operate alternately in a time-sharing manner. The equivalent frequency of the resonant load is N times the actual operating frequency of each IGBT inverter module.

[0043] In the drive module, the switching sequence output by each drive channel is a PWM signal group. Each PWM signal group includes an upper bridge arm drive signal and a lower bridge arm drive signal. The upper bridge arm drive signal and the lower bridge arm drive signal in the same group are complementary signals and there is a dead time between them to prevent the upper and lower bridge arms from being turned on at the same time and causing a short circuit. The phase difference between each PWM signal group is 360° / N.

[0044] Step S3: Frequency Tracking The frequency control module generates a frequency command based on the phase characteristics of the electrical parameter signals acquired by the signal acquisition module and outputs it to the drive module. The frequency control module includes a voltage zero-crossing comparator, a current zero-crossing comparator, a phase detector unit, a filtering unit, and a frequency synthesis unit. The voltage zero-crossing comparator detects the zero-crossing of the voltage signal and outputs a voltage square wave signal; the current zero-crossing comparator detects the zero-crossing of the current signal and outputs a current square wave signal; the phase detector unit outputs a pulse width signal based on the phase difference between the voltage and current square wave signals; the filtering unit filters the pulse width signal and outputs a phase error signal; and the frequency synthesis unit superimposes the nominal frequency signal, the phase error signal, and the jitter signal to synthesize the frequency command.

[0045] During system startup, the frequency synthesis unit superimposes the nominal frequency signal and the jitter signal as the initial value for the frequency command. The jitter signal causes a slight disturbance in the inverter output frequency near the nominal frequency, stimulating the load resonant response. The resulting voltage-current phase difference is detected by the phase detector and automatically pulled into a locked state through closed-loop regulation. During the frequency locking process, the PLL output frequency is gradually adjusted from the nominal frequency and eventually locked to the load resonant frequency.

[0046] Step S4: Power Control The power control module generates adjustment commands and outputs them to the drive module based on the comparison results between the amplitude characteristics of the electrical parameter signals acquired by the signal acquisition module and an external given signal. The power control module includes a power calculation unit, a low-pass filtering unit, a comparison unit, and an adjustment unit. The power calculation unit receives the voltage and current signals from the electrical parameter signals and calculates the instantaneous power based on them; the low-pass filtering unit performs low-pass filtering on the instantaneous power and outputs the average power; the comparison unit compares the average power with the power given signal and outputs a power error signal; the adjustment unit is a PI controller that outputs adjustment commands to the drive module based on the power error signal. The drive module adjusts the duty cycle of each switching sequence according to the adjustment commands.

[0047] Step S5: Dual Closed-Loop Coordination The frequency control inner loop uses the phase difference between the load voltage and current as the control target. It automatically adjusts the inverter's operating frequency via a PLL to maintain a quasi-resonant state, offering a fast response and directly acting on the PWM carrier frequency. The power control outer loop uses output power as the control target, achieving power closed-loop control by adjusting the PWM duty cycle. Its response speed is slower than the inner loop, achieving decoupled control of frequency and power. The frequency inner loop and power outer loop act on the system through different control channels, naturally decoupled by the load resonant characteristics, and do not interfere with each other.

[0048] During steady-state operation, the load voltage and current are approximately sinusoidal, and the system operates in a weakly capacitive quasi-resonant state (the current phase slightly leads the voltage phase), achieving ZVS (zero-voltage switching) soft switching and reducing switching losses.

[0049] Example 3: Application of a 3x Frequency High-Frequency Induction Heating Power Supply like Figures 4 to 7 As shown, taking a high-frequency induction heating power supply with N=3 and a frequency of 3 times as an example, the system uses three sets of IGBT full-bridge inverter modules connected in parallel. The switching frequency of each inverter module is equal to the frequency output by the PLL. Because the three inverter modules work alternately in a time-sharing manner, the equivalent output frequency is 3× This achieves a 3x frequency multiplication effect, with the actual switching frequency of each IGBT being only 1 / 3 of the output frequency, effectively reducing the requirements for the switching speed of power devices.

[0050] The drive module contains three parallel drive channels, each outputting a switching sequence of PWM signal groups, with each PWM signal group having a phase difference of 120°. The PWM signals of the A, B, and C inverter modules have phase differences of 120°, ensuring that only one inverter module is in commutation mode at any given time, while the other two are in off mode, thus reducing system switching losses and EMI interference.

[0051] System startup consists of the following stages: Initialization phase: The PLL output is initialized to the nominal resonant frequency. The duty cycle is set to the initial value; Frequency pull-in stage: The jitter signal perturbs and excites the resonant response. The PLL detects the phase difference and automatically adjusts the frequency to pull the operating point into the quasi-resonant region. Power build-up phase: After resonance is established, the power PI controller gradually adjusts the duty cycle according to the power error, so that the output power approaches the given value; Steady-state operation phase: Dual closed-loop coordinated operation, with the inner frequency loop maintaining resonance tracking and the outer power loop maintaining constant power.

[0052] This invention is not only applicable to the 3x frequency multiplication scheme with N=3, but can also be extended to any N≥2 Nx frequency multiplication scheme. It achieves N times frequency output by connecting N sets of inverter modules in parallel, and is suitable for various high-frequency inverter application scenarios such as induction heating power supplies, with broad application prospects.

[0053] One or more embodiments in this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments in this application should be included within the protection scope of this application.

[0054] The above provides a detailed description of a high-frequency resonant closed-loop control system and its closed-loop control method based on IGBTs, as provided in this application. The above description of the disclosed embodiments enables those skilled in the art to implement or use this application. 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 this application. Therefore, this application 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 disclosed herein.

Claims

1. A high-frequency resonant closed-loop control system based on IGBT, characterized in that, include: A DC conditioning unit, the input of which is used to connect to the power supply terminal, the DC conditioning unit includes a BUCK chopper circuit, and the output of the DC conditioning unit is connected to the DC input terminal of the inverter unit; The inverter unit is composed of N IGBT inverter modules connected in parallel, where N is an integer greater than or equal to 2. The AC output terminal of each IGBT inverter module is used to connect in parallel to the resonant load. The signal acquisition module has an input terminal for connecting to the resonant load, and an output terminal for connecting to the input terminal of the frequency control module and the input terminal of the power control module, respectively. The signal acquisition module is used to acquire and output the electrical parameter signals of the resonant load. The frequency control module receives the electrical parameter signal output by the signal acquisition module at its input terminal, and its output terminal is connected to the frequency command input terminal of the drive module. The frequency control module is used to generate a frequency command based on the phase characteristics of the electrical parameter signal and output it to the drive module. The power control module receives the electrical parameter signal output by the signal acquisition module and the external given signal at its input terminal. The output terminal of the power control module is connected to the adjustment command input terminal of the drive module. The power control module is used to generate an adjustment command based on the comparison result between the amplitude characteristics of the electrical parameter signal and the external given signal and output it to the drive module. The drive module includes N parallel inverter module IGBT drive channels and 1 BUCK chopper IGBT drive channel. The output terminal of each inverter module IGBT drive channel is connected to the control electrode of the IGBT in each IGBT inverter module. The output terminal of the BUCK chopper IGBT drive channel is connected to the control electrode of the BUCK chopper IGBT. The frequency command input terminal of the drive module receives the frequency command, and the adjustment command input terminal receives the adjustment command. The drive module controls the IGBT drive channels of each inverter module to output a switching sequence with mutual phase shifts according to the frequency command, so that each IGBT inverter module works alternately in a time-sharing manner and the equivalent frequency of the resonant load is N times the actual operating frequency of each IGBT inverter module; the drive module controls the BUCK chopper IGBT drive channel to output a switching sequence with a variable duty cycle according to the adjustment command, so as to drive the IGBT in the BUCK chopper circuit to work, adjust the DC bus voltage output by the DC conditioning unit, and realize power closed-loop control; The signal acquisition module, the frequency control module, and the drive module form a frequency tracking closed loop, and the signal acquisition module, the power control module, and the drive module form a power tracking closed loop.

2. The high-frequency resonant closed-loop control system based on IGBT according to claim 1, characterized in that, The frequency control module includes a voltage zero-crossing comparator, a current zero-crossing comparator, a phase detection unit, a filtering unit, and a frequency synthesis unit; The input terminal of the voltage zero-crossing comparator is used to receive the voltage signal output by the signal acquisition module, and the output terminal is connected to the first input terminal of the phase detection unit, which is used to perform zero-crossing detection on the voltage signal and output a voltage square wave signal. The input terminal of the current zero-crossing comparator is used to receive the current signal output by the signal acquisition module, and the output terminal is connected to the second input terminal of the phase detection unit to perform zero-crossing detection on the current signal and output a current square wave signal. The output terminal of the phase detection unit is connected to the input terminal of the filter unit, and is used to output a pulse width signal based on the phase difference between the voltage square wave signal and the current square wave signal. The output of the filtering unit is connected to the first input of the frequency synthesis unit, and is used to filter the pulse width signal and output a phase error signal. The second input terminal of the frequency synthesis unit is used to receive the nominal frequency signal, and the third input terminal is used to receive the jitter signal. The output terminal of the frequency synthesis unit serves as the output terminal of the frequency control module, and is used to superimpose the nominal frequency signal, the phase error signal, and the jitter signal to synthesize the frequency command.

3. The high-frequency resonant closed-loop control system based on IGBT according to claim 2, characterized in that, When the system starts up, the frequency synthesis unit superimposes the nominal frequency signal and the jitter signal as the initial value of the frequency command.

4. The high-frequency resonant closed-loop control system based on IGBT according to claim 1, characterized in that, The power control module includes a power calculation unit, a low-pass filter unit, a comparison unit, and an adjustment unit; The input terminal of the power calculation unit serves as the input terminal of the power control module, used to receive the voltage and current signals in the electrical parameter signals, and to calculate the instantaneous power based on the voltage and current signals. The input terminal of the low-pass filter unit is connected to the output terminal of the power calculation unit, and is used to perform low-pass filtering on the instantaneous power and output the average power; The first input terminal of the comparison unit is connected to the output terminal of the low-pass filter unit, and the second input terminal is used to receive the power command signal, compare the average power with the power command signal, and output a power error signal. The adjustment unit is a PI regulator. The input terminal of the adjustment unit is connected to the output terminal of the comparison unit. The output terminal of the adjustment unit serves as the output terminal of the power control module and is connected to the adjustment command input terminal of the drive module. It is used to output the adjustment command to the drive module according to the power error signal.

5. The high-frequency resonant closed-loop control system based on IGBT according to claim 1, characterized in that, In the drive module, the switching sequence output by the IGBT drive channel of each inverter module is a PWM signal group. Each PWM signal group includes an upper bridge arm drive signal and a lower bridge arm drive signal. The upper bridge arm drive signal and the lower bridge arm drive signal in the same group are complementary signals and there is a dead time between them. The phase difference between the PWM signal groups output by the IGBT drive channels of each inverter module is 360° / N. The switching sequence output by the BUCK chopper IGBT drive channel is a single-channel PWM signal, and its duty cycle is controlled by the adjustment command.

6. The high-frequency resonant closed-loop control system based on IGBT according to claim 5, characterized in that, The IGBT inverter module is an IGBT full-bridge inverter module. Each IGBT full-bridge inverter module consists of a first upper bridge arm IGBT, a first lower bridge arm IGBT, a second upper bridge arm IGBT, and a second lower bridge arm IGBT. Each IGBT is connected in anti-parallel with a diode. The first upper bridge arm IGBT and the first lower bridge arm IGBT are connected in series to form the first bridge arm, and the second upper bridge arm IGBT and the second lower bridge arm IGBT are connected in series to form the second bridge arm. The first bridge arm and the second bridge arm are connected in parallel between the DC input terminals of the inverter unit. The series connection node of the first upper bridge arm IGBT and the first lower bridge arm IGBT, and the series connection node of the second upper bridge arm IGBT and the second lower bridge arm IGBT serve as the AC output terminal of the IGBT full-bridge inverter module. The control electrode of each IGBT is connected to the output terminal of the corresponding drive channel in the drive module, and is used to receive the corresponding upper arm drive signal or the lower arm drive signal.

7. The high-frequency resonant closed-loop control system based on IGBT according to claim 1, characterized in that, The resonant load is a series resonant load, consisting of an equivalent resistance, a resonant inductance, and a resonant capacitor connected in series.

8. The high-frequency resonant closed-loop control system based on IGBT according to claim 1, characterized in that, The power supply terminal includes a rectifier unit, the input terminal of which is connected to an AC power source, and the output terminal of which is connected to the input terminal of the DC conditioning unit.

9. The high-frequency resonant closed-loop control system based on IGBT according to claim 1, characterized in that, The DC conditioning unit includes a BUCK chopper circuit and an LC low-pass filter network. The output terminal of the BUCK chopper circuit is connected to the input terminal of the LC low-pass filter network, and the output terminal of the LC low-pass filter network serves as the output terminal of the DC conditioning unit and is connected to the DC input terminal of the inverter unit. The BUCK chopper circuit is driven by a variable duty cycle switching sequence output from the BUCK chopper IGBT drive channel in the drive module.

10. A closed-loop control method implemented using the IGBT-based high-frequency resonant closed-loop control system as described in any one of claims 1-9, characterized in that, Includes the following steps: Acquire and output the electrical parameter signals of the resonant load; A frequency command is generated based on the phase characteristics of the electrical parameter signal; An adjustment command is generated based on the comparison between the amplitude characteristics of the electrical parameter signal and the external given signal; N mutually phase-shifted switching sequences are generated according to the frequency command, which drive N IGBT inverter modules to work alternately in a time-division manner, so that the equivalent frequency of the resonant load is N times the actual operating frequency of each IGBT inverter module. The adjustment command generates a switching sequence for controlling the duty cycle of the IGBTs in the BUCK chopper circuit, thereby adjusting the DC bus voltage. A frequency tracking closed loop is formed by using the phase characteristics of the electrical parameter signal as the feedback quantity, and a power tracking closed loop is formed by using the comparison result between the amplitude characteristics of the electrical parameter signal and the external given signal as the feedback quantity.

Images