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CN-121124509-B - Switching control method based on SPWM soft start and pulse type load LLC resonant converter

CN121124509BCN 121124509 BCN121124509 BCN 121124509BCN-121124509-B

Abstract

The invention discloses a switching control method based on SPWM soft start and pulse load LLC resonant converter, which mainly comprises an LLC resonant converter, an H-bridge inverter circuit and a load thereof, wherein the control method comprises the steps of setting k-level SPWM modulation in a starting stage to realize smooth soft start of output voltage (k is any positive integer), accurately judging the load state through an H-bridge switching logic unit, and respectively adopting Burst intermittent control and linear frequency control for no-load and full-load in a steady state; when the load is switched, a nonlinear SOTC optimal track controller is adopted to perform two-pulse optimal control, so that the state is transited to a new mode along the shortest track, a dynamic response optimizer is introduced to compensate the switched frequency according to the state radius error so as to inhibit the voltage secondary fluctuation, the problems of slow dynamic response, large output voltage fluctuation and the like when the traditional linear control is applied to a pulse load LLC resonant converter are solved, and the stability and the anti-interference capability of the output voltage of the system are improved.

Inventors

  • LIANG BINGRAN
  • WANG JIAWEI
  • ZHANG GUIDONG

Assignees

  • 广东工业大学

Dates

Publication Date
20260508
Application Date
20250904

Claims (8)

  1. 1. A soft start and pulse type load LLC resonant converter based on SPWM is characterized by comprising a main circuit unit and a main control unit; the main circuit unit comprises a direct current power supply V in , a resonance capacitor C r , a resonance inductor L r , a transformer T, an input capacitor C in , an output capacitor C o , a first switching tube S 1 , a second switching tube S 2 , a third switching tube S 3 , a fourth switching tube S 4 , a fifth switching tube S 5 , a sixth switching tube S 6 , a seventh switching tube S 7 , an eighth switching tube S 8 , a first diode D 1 , a second diode D 2 , a third diode D 3 , a fourth diode D 4 and a load R L ; The positive electrode of the direct current power supply V in is connected with the first end of the input capacitor C in , the drain electrode of the first switching tube S 1 and the drain electrode of the third switching tube S 3 , and the negative electrode of the direct current power supply V in is connected with the second end of the input capacitor C in , the source electrode of the second switching tube S 2 and the source electrode of the fourth switching tube S 4 ; The first end of the resonance capacitor C r is connected with the source electrode of the first switch tube S 1 and the drain electrode of the second switch tube S 2 , and the second end of the resonance capacitor C r is connected with the first end of the resonance inductor L r ; The first end of the primary winding of the transformer T is connected with the second end of the resonant inductor L r , and the second end of the primary winding of the transformer T is connected with the source electrode of the third switching tube S 3 and the drain electrode of the fourth switching tube S 4 ; the excitation inductor L m is connected in parallel with the primary winding of the transformer T; the first end of the secondary winding of the transformer T is connected with the anode of the first diode D 1 and the cathode of the second diode D 2 , and the second end of the secondary winding of the transformer T is connected with the anode of the third diode D 3 and the cathode of the fourth diode D 4 ; the cathode of the first diode D 1 is connected to the cathode of the third diode D 3 , the first end of the output capacitor C o , the collector of the fifth switching tube S 5 , and the collector of the seventh switching tube S 7 ; the anode of the second diode D 2 is connected with the anode of the fourth diode D 4 , the second end of the output capacitor C o , the emitter of the sixth switching tube S 6 , and the emitter of the eighth switching tube S 8 ; The first end of the load R L is connected with the emitter of the fifth switching tube S 5 and the collector of the sixth switching tube S 6 , and the second end of the load R L is connected with the emitter of the seventh switching tube S 7 and the collector of the eighth switching tube S 8 ; the main control unit comprises an SPWM soft start controller, a driving circuit, an H-bridge modal identifier, a Burst controller, a PI controller, an SOTC controller, an adder SUM, a state observer, a dynamic response optimizer and a voltage-controlled oscillator; The first input end of the driving circuit is connected with the output end of the SPWM soft start controller, the second input end of the driving circuit is connected with the output end of the Burst controller, the third input end of the driving circuit is connected with the output end of the voltage-controlled oscillator, the fourth input end of the driving circuit is connected with the first output end of the SOTC controller, the first output end of the driving circuit is connected with the grid electrode of the first switching tube S 1 , the second output end of the driving circuit is connected with the grid electrode of the second switching tube S 2 , the third output end of the driving circuit is connected with the grid electrode of the third switching tube S 3 , the fourth output end of the driving circuit is connected with the grid electrode of the fourth switching tube S 4 , the first input end of the H-bridge mode identifier is connected with the grid electrode of the fifth switching tube S 5 , the second input end of the H-bridge mode identifier is connected with the grid electrode of the sixth switching tube S 6 , the second output end of the H-bridge identifier is connected with the grid electrode of the eighth switching tube S5629, the third output end of the H-bridge identifier is connected with the fourth switching tube S 4 , the second input end of the H-bridge identifier is connected with the eighth input end of the adder is connected with the eighth switching tube S input end of the H-bridge identifier, the third output end of the H-bridge modal identifier is connected with the input end of the SOTC controller, the input end of the PI controller is connected with the output end of the adder SUM, the output end of the PI controller is connected with the first input end of the voltage-controlled oscillator, the first input end of the dynamic response optimizer is connected with the output end of the state observer, the second input end of the dynamic response optimizer is connected with the second output end of the SOTC controller, and the output end of the dynamic response optimizer is connected with the second input end of the voltage-controlled oscillator; The H-bridge mode identifier outputs a mode indication signal model to accurately judge the load state of the LLC resonant converter, wherein the mode indication signal mode is used for indicating three working modes, wherein mode=0 is represented as no-load, mode=1 is represented as full-load, and mode=2 is represented as empty-full switching.
  2. 2. The SPWM soft start and pulse-based load LLC resonant converter of claim 1, wherein the first switching tube S 1 and the third switching tube S 3 are used as one group, the second switching tube S 2 and the fourth switching tube S 4 are used as another group, the two groups of switching tubes are alternately turned on, and the fifth switching tube S 5 , the sixth switching tube S 6 , the seventh switching tube S 7 and the eighth switching tube S 8 form an H-bridge inverter circuit, and the H-bridge provides pulse-based load for the LLC resonant converter by using low-frequency square wave modulation.
  3. 3. The switching control method based on the SPWM soft start and the pulse type load LLC resonant converter is characterized by being used for the LLC resonant converter as claimed in claim 1, and comprises the following specific control methods: The SPWM soft start controller generates k-level SPWM modulation signals according to a preset switching point, drives the grid electrodes of the first switching tube S 1 , the second switching tube S 2 , the third switching tube S 3 and the fourth switching tube S 4 through a driving circuit, precharges the output capacitor C o , achieves smooth rising of the output voltage V o , and completes a soft start process; S2, starting inversion conduction of the fifth switch tube S 5 , the sixth switch tube S 6 , the seventh switch tube S 7 and the eighth switch tube S 8 , performing mode identification on gate driving signals of the fifth switch tube S 5 , the sixth switch tube S 6 , the seventh switch tube S 7 and the eighth switch tube S 8 by the H-bridge mode identifier, judging that the load R L is equivalent to an empty load, a full load or an empty-full switching state at the LLC resonant converter side, and outputting a mode indication signal model, wherein the mode indication signal model is used for indicating three working modes, mode=0 is represented as empty load, mode=1 is represented as full load, and mode=2 is represented as empty-full switching; s3, the H-bridge modal identifier sends an enabling instruction to the Burst controller, the PI controller or the SOTC controller according to the mode indication signal model; If the model=0, enabling the Burst controller to switch between Burst-on and Burst-off states according to a voltage hysteresis control principle, driving the first switching tube S 1 , the second switching tube S 2 , the third switching tube S 3 and the fourth switching tube S 4 to maintain output of voltage in the Burst-on state, and rising the output voltage V o ; If model=1, enabling the PI controller, comparing the output voltage V o with the reference voltage V ref through the adder SUM to output an error voltage V e as an input signal of the PI controller, outputting an adjustment signal through the PI controller by the error voltage V e , outputting driving signals of the first switching tube S 1 , the second switching tube S 2 , the third switching tube S 3 and the fourth switching tube S 4 through the voltage-controlled oscillator by the adjustment signal, and performing variable frequency adjustment of pulse frequency modulation by the LLC resonant converter; If model=2, enabling the SOTC controller to calculate two optimal switching pulse widths according to a simplified optimal track control theory, and driving the first switching tube S 1 , the third switching tube S 3 , the second switching tube S 2 and the fourth switching tube S 4 respectively to realize the fast switching of the empty-full mode; And S4, enabling the dynamic response optimizer, wherein the state observer outputs normalized resonant capacitor voltage v CrN and resonant inductor current i LrN to form a state radius rho s according to input resonant inductor current i Lr after two switching pulses of the SOTC controller are executed, the dynamic response optimizer generates a frequency compensation command u T according to the deviation delta e of the state radius rho s and a target radius rho ref to inhibit secondary voltage oscillation possibly generated after SOTC switching, and further, exiting the dynamic response optimizer to directly enter the PI controller if the radius deviation delta e is within a preset value.
  4. 4. The soft start method based on the SPWM soft start and pulse type load LLC resonant converter as claimed in claim 3, wherein the SPWM soft start process is open loop control, its start logic is independent of load state, and is not dependent on feedback of load current or output voltage, and only k-stage SPWM driving signal output is performed at a preset switching point after the system is powered on, further, modulation degree and switching time point k are reasonably set to enable output voltage V o to rise smoothly in theory, and k is any positive integer greater than 1.
  5. 5. The soft start method based on an SPWM soft start and pulse-type load LLC resonant converter of claim 4, wherein the voltage of the kth switching point cavity V AB (t) of S1 satisfies the following equation: Wherein m k is the modulation degree of the SPWM in the kth section, and w m is the carrier angular frequency equal to the steady-state operation switching angular frequency of the converter, wherein the carrier frequency of the SPWM is equal to the steady-state operation switching frequency of the LLC resonant converter.
  6. 6. The switching control method based on the SPWM soft start and pulse type load LLC resonant converter according to claim 3, wherein the H-bridge mode identifier outputs a mode indication signal model to accurately determine the load state of the LLC resonant converter, the fifth switching tube S 5 , the seventh switching tube S 7 , or the sixth switching tube S 6 , and the eighth switching tube S 8 are turned on to be no-load model=0, the fifth switching tube S 5 , the eighth switching tube S 8 , or the sixth switching tube S 6 , and the seventh switching tube S 7 are turned on to be full-load model=1, and when the mode indication signal model changes from 0 to 1, the mode is switched from empty-full to be model=2.
  7. 7. A switching control method based on SPWM soft start and pulsed load LLC resonant converter in accordance with claim 3, wherein the two optimal switching pulse widths t 1 -t 0 and t 2 -t 1 of S3 are: Wherein v CrNC is the per unit value of the point C resonant capacitor voltage v Cr , i LrNB is the per unit value of the point B resonant inductor current i Lr , w r is the full load angular frequency, ρ is the per unit value of the peak value of the resonant inductor current i Lr , i.e Z r is a binary characteristic impedance, i.e I rms is the effective value of the resonant inductor current I Lr at full load, namely: Where T is the period of resonance, n is the number of transformer turns, and i o is the load R L current.
  8. 8. The switching control method based on the SPWM soft start and pulse type load LLC resonant converter according to claim 3, wherein the deviation Δe of the state radius ρ s of S4 from the target radius ρ ref is: Where ρ ref is the target steady state radius, state radius ρ s consists of v CrN and i LrN , i.e V CrN is the per unit value of the resonant capacitor voltage v Cr , i LrN is the per unit value of the resonant inductor current i Lr , and the dynamic response optimizer generates a frequency compensation command u T according to the deviation Δe as follows: Wherein f ref is the target steady-state operating resonant frequency, s G epsilon { +1, 1 Is a monotonic direction symbol of the working area, k p >0 is a proportional gain, and if Δe meets a preset radius deviation tolerance ɛ, the dynamic response optimizer exits, namely: Wherein ɛ is a predetermined radius deviation tolerance.

Description

Switching control method based on SPWM soft start and pulse type load LLC resonant converter Technical Field The invention relates to the technical field of power electronic converters, in particular to a switching control method based on an SPWM soft start and pulse type load LLC resonant converter. Background With the continuous development of power electronic technology, the LLC resonant converter can realize zero-voltage switching on of a primary side switching tube and zero-current switching off of a secondary side rectifying tube, is widely applied to occasions requiring high efficiency and high power density, such as data centers, new energy power generation, industrial power supply and the like, and solves the problems of high switching loss, serious electromagnetic interference and the like of the traditional hard switching converter. Under the extreme working conditions that the starting process and the load are suddenly changed from empty to full, the traditional LLC resonant converter still has obvious defects, is limited by the limited bandwidth of a linear control method, has slow dynamic response of the system, has larger overshoot or drop of the output voltage when coping with a pulse load such as a front-end DC-DC isolation unit in a cascade H-bridge photovoltaic inverter, and seriously affects the stable operation of the later-stage equipment and the overall reliability of the system. The invention discloses a switching control method based on an SPWM soft start and a pulse type load LLC resonant converter, which aims at the problems of slow response and large fluctuation of the traditional control method under a dynamic working condition, applies SPWM modulation to the LLC resonant converter in the soft start stage, judges the converter load state according to an H-bridge switching mode, dynamically switches Burst control, linear control and nonlinear SOTC optimal track control, and introduces a dynamic response optimizer to carry out frequency compensation so as to inhibit voltage secondary fluctuation. The invention realizes the smooth start of the output voltage of the LLC resonant converter and the rapid stabilization of the output voltage under the working condition of no-load and full-load switching, and remarkably improves the steady-state precision and the operation reliability of the system. Disclosure of Invention The invention discloses a switching control method based on an SPWM soft start and a pulse type load LLC resonant converter, and provides a corresponding multimode switching control mechanism, wherein the SPWM modulation strategy is adopted to realize voltage soft start, and the H bridge is used for identifying load state Burst control, linear control and nonlinear SOTC optimal track control. The converter mainly comprises an LLC resonant converter, a post-stage H-bridge inverter circuit and a load. The invention combines SPWM modulation and H-bridge load state identification methods to realize the stable control of soft start and pulse load switching of LLC resonant converter, and is different from traditional linear control, the invention has the advantages of quick dynamic response, small output voltage fluctuation, low switching stress and high reliability by SPWM soft start and multi-mode switching, and aims to solve the problems of slow dynamic response, large voltage overshoot, poor system stability and the like of the traditional LLC resonant converter control method under the starting and pulse load, and expand the application of LLC resonant converter in the fields of high-end industrial power supply and new energy power generation. A soft start and pulse type load LLC resonant converter based on SPWM comprises a main circuit unit and a main control unit; the main circuit unit comprises a direct current power supply V in, a resonance capacitor C r, a resonance inductor L r, a transformer T, an input capacitor C in, an output capacitor C o, a first switching tube S 1, a second switching tube S 2, a third switching tube S 3, a fourth switching tube S 4, a fifth switching tube S 5, a sixth switching tube S 6, a seventh switching tube S 7, an eighth switching tube S 8, a first diode D 1, a second diode D 2, a third diode D 3, a fourth diode D 4 and a load R L; the main control unit comprises an SPWM soft start controller, a driving circuit, an H-bridge modal identifier, a Burst controller, a PI controller, an SOTC controller, an adder SUM, a state observer, a dynamic response optimizer and a voltage-controlled oscillator; preferably, the first switching tube S 1, the second switching tube S 2, the third switching tube S 3 and the fourth switching tube S 4 are high-frequency MOSFETs, and preferably, the fifth switching tube S 5, the sixth switching tube S 6, the seventh switching tube S 7 and the eighth switching tube S 8 are low-frequency IGBTs; Preferably, the first switching tube S 1 and the third switching tube S 3 form one group, the second switching tube S 2