Control method for fast switching from heavy load to light load of LCC resonant converter

Abstract

The invention discloses a control method for fast switching from heavy load to light load of an LCC resonant converter, and relates to the technical field of power electronic converter control. The method comprises the following steps: S1, building an LCC resonant converter; s2, monitoring load current in real time, and identifying a load abrupt change signal; s3, calculating coordinates of an intersection point of the current working point and the target light load trajectory according to the state trajectory model; and S4, triggering a switch tube advanced turn-off instruction at the switching point, and switching the driving system to a light load mode along the transition track. According to the invention, a specific switching period is introduced during frequency switching, so that the resonant converter can be rapidly and stably switched from a heavy-load working mode to a light-load working mode. According to the switching mode, the voltage overshoot phenomenon during load sudden change can be effectively suppressed, the response time can be shortened, and the dynamic response performance of the resonant converter can be greatly improved. Compared with a traditional scheme, the system stability is improved, and the power loss is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic converter control, and in particular relates to a control method for fast switching of an LCC resonant converter from heavy load to light load. Background Art

[0002] High-performance high-voltage DC power supplies (HVPS) play a vital role in the national economy and are widely used in a variety of fields, including military, scientific research, medical, and industrial applications. These high-voltage power supplies provide stable and reliable power for a wide range of devices and systems, driving the advancement of many technologies and applications. In these applications, the performance, stability, and response speed of the power supply directly impact the overall efficiency and reliability of the system, making the design and optimization of HVPS particularly important.

[0003] In recent years, the series-parallel (LCC) resonant converter has become a mainstream design in the high-voltage DC power supply field due to its unique advantages. LCC resonant converters fully utilize the leakage inductance and parasitic capacitance of the high-voltage transformer as resonant elements. This design not only simplifies the circuit structure but also improves overall system efficiency. Its soft switching characteristics across the full power range effectively reduce switching losses under varying load conditions, extending the life of the equipment. Furthermore, LCC resonant converters offer a wide range of input and output characteristics, adapting to various operating environments and load variations, thereby meeting users' diverse power supply needs.

[0004] Recent research has seen significant progress in the application of LCC resonant converters in high-voltage DC power supplies. However, with the continuous advancement of technology and increasing application demands, the current dynamic response speed still cannot meet the rapid development of high-voltage DC power supply technical indicators.

[0005] Therefore, a control method for fast switching from heavy load to light load of an LCC resonant converter is proposed. Summary of the Invention

[0006] The object of the present invention is to provide a control method for fast switching of an LCC resonant converter from heavy load to light load, so as to solve the problem of insufficient dynamic response performance of the LCC resonant converter under sudden load changes.

[0007] To solve the above technical problems, the present invention is achieved through the following technical solutions:

[0008] The present invention provides a control method for fast switching of an LCC resonant converter from heavy load to light load, comprising the following steps:

[0009] S1. Build an LCC resonant converter;

[0010] S2, real-time monitoring of load current and identification of load mutation signals;

[0011] S3. Calculate the intersection coordinates of the current working point and the target light-load trajectory according to the state trajectory model;

[0012] S4. Trigger the early shutdown command of the switch tube at the switching point, and drive the system to switch to the light load mode along the transition trajectory.

[0013] In one embodiment, the state trajectory model is modeled by a circuit differential equation and plotted in a current-voltage coordinate system. The heavy-load trajectory is a closed curve of a multi-modal combination, and the light-load trajectory is a combination of a circle and an ellipse.

[0014] In one embodiment, the LCC resonant converter includes an inverter circuit A, a resonant circuit B, a transformer C, and a rectifier filter circuit D. The inverter circuit A inverter circuit module is composed of four power switch tubes Q1-Q4; by controlling the on and off of the four switch tubes, the input DC voltage V in Inverted into a high frequency AC voltage; the resonant circuit B consists of a resonant capacitor C r , resonant inductor L r And the primary parasitic capacitance C of the transformer p ; Transformer module primary voltage V p The transformer transforms the voltage according to the turns ratio n and transfers the energy to the secondary side. The rectifier filter circuit module consists of four diodes D1-D4 forming a rectifier bridge, which rectifies the high-frequency AC voltage output by the secondary side of the transformer into a DC voltage. Then, the output capacitor C o Filter and smooth the output voltage to provide a smooth load L Provides a stable DC voltage V o .

[0015] In one embodiment, according to the switching states of the switching tubes Q1-Q4 and the conduction status of the rectifier bridge, the four switching tubes Q1-Q4 of the H-bridge have two switching states, and the four diodes D1-D4 of the rectifier bridge have three conduction states. Therefore, the LCC resonant converter can be divided into 6 operating modes, which are Mode I, Mode II, Mode III, Mode IV, Mode V and Mode VI.

[0016] In one embodiment, the mode I is that the switches Q1 and Q4 are turned on, Q2 and Q3 are turned off, and the output voltage of the H bridge is V in ; Diodes D2 and D3 are turned on, D1 and D4 are turned off, and the voltage of the secondary winding of the transformer is -V o ; Parallel capacitor C p It does not participate in resonance and its voltage always remains at -V o / n.

[0017] In one embodiment, the mode II is that the switches Q1 and Q4 are turned on, Q2 and Q3 are turned off, and the output voltage of the H bridge is V in ; All four diodes are in the cut-off state, and there is no energy transfer between the primary and secondary sides of the transformer; the parallel capacitor C p Participate in resonance and charge it through resonance.

[0018] In one embodiment, the mode III is that the switches Q1 and Q4 are turned on, Q2 and Q3 are turned off, and the output voltage of the H-bridge is V in ; Diodes D1 and D4 are turned on, D2 and D3 are turned off, and the voltage of the secondary winding of the transformer is V o ; Parallel capacitor C p It does not participate in resonance and its voltage always remains at V o / n.

[0019] In one embodiment, the mode IV is that the switches Q2 and Q3 are turned on, Q1 and Q4 are turned off, and the output voltage of the H-bridge is -V in ; Diodes D1 and D4 are turned on, D2 and D3 are turned off, and the voltage of the secondary winding of the transformer is V o ; Parallel capacitor C p It does not participate in resonance and its voltage always remains at V o / n.

[0020] In one embodiment, the mode V is that the switches Q2 and Q3 are turned on, Q1 and Q4 are turned off, and the output voltage of the H-bridge is -V in ; All four diodes are in the cut-off state, there is no energy transfer between the primary and secondary sides of the transformer, and the output current is supplied by capacitor C o Provide; parallel capacitor C p Participate in resonance, and it is in the three-element resonance stage.

[0021] In one embodiment, the mode VI is that the switches Q2 and Q3 are turned on, Q1 and Q4 are turned off, and the output voltage of the H-bridge is -V in ; Diodes D2 and D3 are turned on, D1 and D4 are turned off, and the voltage of the secondary winding of the transformer is -V o ; Parallel capacitor C p It does not participate in resonance and its voltage always remains at -V o / n.

[0022] The present invention has the following beneficial effects:

[0023] This state-trajectory-based load switching strategy introduces a specific switching cycle during frequency switching, enabling the resonant converter to quickly and smoothly switch from a heavy-load to a light-load mode. This efficient switching method effectively suppresses voltage overshoot during sudden load changes and shortens response time, significantly enhancing the resonant converter's dynamic response performance. Compared to traditional solutions, this approach not only improves system stability but also reduces power loss, providing a new solution for optimizing the control of LCC resonant converters over a wide load range.

[0024] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 This is the circuit topology diagram of the LCC resonant converter;

[0027] Figure 2 This is the steady-state waveform diagram of heavy load mode;

[0028] Figure 3 It is the trajectory diagram of the heavy load mode;

[0029] Figure 4 This is the steady-state waveform diagram of light load mode;

[0030] Figure 5 This is the state trajectory diagram of light load mode;

[0031] Figure 6 This is a schematic diagram of the trajectory switching from heavy load to light load. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0033] In the description of the present invention, it should be understood that the terms "upper", "middle", "outer", "inner" and the like indicating directions or positional relationships are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the components or elements referred to must have a specific direction, be constructed and operate in a specific direction, and therefore should not be understood as limiting the present invention.

[0034] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "provided with," "connected," etc., should be understood in a broad sense. For example, "connected" may refer to a fixed connection, a detachable connection, or an integral connection; it may refer to a mechanical connection or an electrical connection; it may refer to a direct connection or an indirect connection through an intermediate medium; it may refer to internal communication between two components. Those skilled in the art will be able to understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0035] Example 1

[0036] See also Figures 1-6 As shown, the present invention is a control method for fast switching of an LCC resonant converter from heavy load to light load, comprising the following steps:

[0037] S1. Build an LCC resonant converter;

[0038] S2, real-time monitoring of load current and identification of load mutation signals;

[0039] S3. Calculate the intersection coordinates of the current working point and the target light-load trajectory according to the state trajectory model;

[0040] S4. Trigger the early shutdown command of the switch tube at the switching point, and drive the system to switch to the light load mode along the transition trajectory.

[0041] Preferably, the state trajectory model is modeled by a circuit differential equation and plotted in a current-voltage coordinate system. The heavy-load trajectory is a closed curve of a multi-modal combination, and the light-load trajectory is a combination of a circle and an ellipse.

[0042] Preferably, according to the switching states of the switching tubes Q1-Q4 and the conduction state of the rectifier bridge, the four switching tubes Q1-Q4 of the H bridge have two switching states, and the four diodes D1-D4 of the rectifier bridge have three conduction states, so the LCC resonant converter can be divided into 6 working modes;

[0043] Preferably, the six working modes are mode I, mode II, mode III, mode IV, mode V and mode VI;

[0044] Mode I is when switches Q1 and Q4 are on, Q2 and Q3 are off, and the output voltage of the H-bridge is V in ; Diodes D2 and D3 are turned on, D1 and D4 are turned off, and the voltage of the secondary winding of the transformer is -Vo ; Parallel capacitor C p It does not participate in resonance and its voltage always remains at -V o / n;

[0045] Mode II is when switches Q1 and Q4 are on, Q2 and Q3 are off, and the output voltage of the H-bridge is V in ; All four diodes are in the cut-off state, and there is no energy transfer between the primary and secondary sides of the transformer; the parallel capacitor C p Participate in resonance and charge it through resonance;

[0046] Mode III is when switches Q1 and Q4 are on, Q2 and Q3 are off, and the output voltage of the H-bridge is V in ; Diodes D1 and D4 are turned on, D2 and D3 are turned off, and the voltage of the secondary winding of the transformer is V o ; Parallel capacitor C p It does not participate in resonance and its voltage always remains at V o / n;

[0047] Mode IV is when switches Q2 and Q3 are on, Q1 and Q4 are off, and the output voltage of the H-bridge is -V in ; Diodes D1 and D4 are turned on, D2 and D3 are turned off, and the voltage of the secondary winding of the transformer is V o ; Parallel capacitor C p It does not participate in resonance and its voltage always remains at V o / n;

[0048] Mode V is when switches Q2 and Q3 are on, Q1 and Q4 are off, and the output voltage of the H-bridge is -V in ; All four diodes are in the cut-off state, there is no energy transfer between the primary and secondary sides of the transformer, and the output current is supplied by capacitor C o Provide; parallel capacitor C p Participate in resonance, at this time it is in the three-element resonance stage;

[0049] Mode VI is when switches Q2 and Q3 are on, Q1 and Q4 are off, and the output voltage of the H-bridge is -V in ; Diodes D2 and D3 are turned on, D1 and D4 are turned off, and the voltage of the secondary winding of the transformer is -V o ; Parallel capacitor C p It does not participate in resonance and its voltage always remains at -V o / n;

[0050] Example 2

[0051] See also Figures 1-6 As shown, this embodiment is a specific implementation of a control method for fast switching from heavy load to light load of an LCC resonant converter:

[0052] Defining Impedance Angular frequency Angular frequency f sw is the switching frequency. Based on modal modeling analysis, simplified trajectory equations for heavy and light loads are obtained. Based on the circuit differential equation, the coordinate values of the state trajectory plotted in the coordinate system of current I(t) and voltage V(t) are obtained.

[0053] like Figure 2 As shown in FIG, the operating mode switching order of the LCC resonant converter working in heavy load mode within one switching cycle is: Ⅰ-Ⅱ-Ⅲ-Ⅳ-Ⅴ-Ⅵ-Ⅰ;

[0054] In heavy load mode, the normalized value of the capacitor voltage at t1 and t2 is v z (t1), v z (t2) is as follows:

[0055]

[0056] Where: I o is the resonant current.

[0057] The state trajectory in mode I between t0-t1 is a circle with a radius R1:

[0058] R1=|v z (t1)-1|

[0059] The state trajectory in mode II between t1 and t2 is an ellipse, half of its major axis is R1, and at time t2 the inductor L r The normalized value of the current is i(t2):

[0060]

[0061] The state trajectory in mode III between t2 and t3 is a circle, and its radius R2 is:

[0062]

[0063] At time t3, according to the circular trajectory equation, the coordinates are solved as follows:

[0064]

[0065] Therefore, the mode between t3-t6 is similar to the mode between t0-t3, and its coordinates and state trajectory are symmetrical about the origin with respect to t0-t3, as shown in Figure 3 As shown in Figure 2, the state trajectory can be drawn based on the solved state trajectory coordinates and its parameter equations.

[0066] like Figure 4As shown, the operating mode switching order of the LCC resonant converter working in light load mode within one switching cycle is: II-I-II-V-IV-V-II.

[0067] In light load mode, the normalized values of the capacitor voltage at t1 and t2 are:

[0068]

[0069] Where: I o is the resonant current.

[0070] Depend on Figure 4 It can be seen that the state trajectory in mode I between t1 and t2 is a circle, and its radius is r2:

[0071] r2=|v q (t2)-1|

[0072] At time t1, the inductor L r The normalized current value i(t1) is:

[0073]

[0074] The state trajectory in mode II between t0-t1 is an ellipse, and half of its major axis r1 is:

[0075]

[0076] At time t3, the coordinates of the state trajectory [v q (t3),i q (t3)] is:

[0077]

[0078] Therefore, the mode between t3-t6 is similar to the mode between t0-t3, and its coordinates and state trajectory are symmetrical about the origin with respect to t0-t3; Figure 5 As shown in Figure 2, the state trajectory can be drawn based on the solved state trajectory coordinates and its parameter equations.

[0079] like Figure 6 As shown, purple is the steady-state trajectory of heavy load, red is the steady-state trajectory of light load, and green is the trajectory of switching from heavy load to light load; when the switching state of the switch tube changes, the three conduction states of the four diodes of the rectifier bridge do not change, so when the switch tubes Q1 and Q4 are turned off in advance, the operating state of the LCC converter does not change, which means that the new operating trajectory formed after the switch tube is turned off in advance is the same as the operating trajectory after the switch tube is turned off normally.

[0080] like Figure 6 As shown in the figure, the switch tube isz3 The trajectory of operation after normal shutdown z3 -t z4 is circular; therefore, the switch tube is Q The trajectory of operation after premature shutdown Q -t q4 Also circular; in heavy load mode t z3 -t z4 Circular trajectory and t in light load mode q4 -t q5 The circular trajectory of the switch is centered at (-1, 0), which means that a new operating trajectory t is formed after the switch is turned off in advance. Q -t q4 Compared with the circular trajectory in light load mode t q4 -t q5 They are all on a circle with (-1,0) as the center and r2 as the radius; before the state trajectory switches, the state of the LCC converter runs clockwise on the purple trajectory. Q The switch tube is turned off in advance, and the state of the LCC converter moves from the green switching trajectory to the red light-load trajectory, thereby achieving a rapid switch from heavy-load mode to light-load mode within one cycle.

[0081] Light load mode t q4 -t q5 The trajectory equation is:

[0082] i 2 (t)+[v(t)+1] 2 =r2 2

[0083] Reload mode z2 -t z3 The radius R2 of the trajectory is:

[0084]

[0085] Reload mode z2 -t z3 The trajectory equation is:

[0086] i 2 (t)+[v(t)-1] 2 =R2 2

[0087] By combining the trajectory equations under the above two modes, the intersection point t can be obtained Q The coordinate v tQ And the switching trajectory equation is as follows:

[0088]

[0089] i 2(t)+[v(t)+1] 2 =r2 2

[0090] Define T1 as t z0 -t z1 time, T2 is t z1 -t z2 time, T3 is t z2 -t Q time, T4 is t Q -t q5 time, T5 is t q5 -t q6 Time:

[0091]

[0092]

[0093] The sum of the above times is the time it takes for the LCC resonant converter to switch from heavy-load mode to light-load mode within one cycle, where T1-T3 is the movement time of the LCC resonant converter trajectory before the switch tube is switched; T4-T5 is the movement time of the trajectory after the switch tube is switched.

[0094] Throughout this specification, references to terms such as "one embodiment," "example," and "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0095] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A control method for fast switching of an LCC resonant converter from heavy load to light load, characterized by: The following steps are involved: S1. Build an LCC resonant converter; S2, real-time monitoring of load current and identification of load mutation signals; S3. Calculate the intersection coordinates of the current working point and the target light-load trajectory according to the state trajectory model; S4. Trigger the early shutdown command of the switch tube at the switching point, and drive the system to switch to the light load mode along the transition trajectory.

2. The control method for fast switching of an LCC resonant converter from heavy load to light load according to claim 1, characterized in that: The LCC resonant converter includes an inverter circuit A, a resonant circuit B, a transformer C and a rectifier filter circuit D. The inverter circuit A inverter circuit module consists of four power switch tubes Q1-Q4; by controlling the on and off of the four switch tubes, the input DC voltage V in Inverted into a high frequency AC voltage; the resonant circuit B consists of a resonant capacitor C r , resonant inductor L r And the primary parasitic capacitance C of the transformer p ; Transformer module primary voltage V p The energy is transferred to the secondary side through the transformer by transforming the voltage according to the turns ratio n; The rectifier filter circuit module consists of four diodes D1-D4 to form a rectifier bridge, which rectifies the high-frequency AC voltage output from the secondary side of the transformer into a DC voltage; then the output capacitor C o Filter and smooth the output voltage to provide a smooth load L Provides a stable DC voltage V o .

3. The control method for fast switching of an LCC resonant converter from heavy load to light load according to claim 2, characterized in that: According to the switching state of the switching tubes Q1-Q4 and the conduction condition of the rectifier bridge, the four switching tubes Q1-Q4 of the H-bridge have two switching states, and the four diodes D1-D4 of the rectifier bridge have three conduction states. Therefore, the LCC resonant converter can be divided into 6 working modes, which are Mode I, Mode II, Mode III, Mode IV, Mode V and Mode VI.

4. The control method for fast switching of an LCC resonant converter from heavy load to light load according to claim 3, characterized in that: In mode I, the switches Q1 and Q4 are turned on, Q2 and Q3 are turned off, and the output voltage of the H-bridge is V in ; Diodes D2 and D3 are turned on, D1 and D4 are turned off, and the voltage of the secondary winding of the transformer is -V o ; Parallel capacitor C p It does not participate in resonance and its voltage always remains at -V o / n.

5. The control method for fast switching of an LCC resonant converter from heavy load to light load according to claim 3, characterized in that: In mode II, the switches Q1 and Q4 are turned on, Q2 and Q3 are turned off, and the output voltage of the H-bridge is V in ; All four diodes are in the cut-off state, and there is no energy transfer between the primary and secondary sides of the transformer; the parallel capacitor C p Participate in resonance and charge it through resonance.

6. The control method for fast switching of an LCC resonant converter from heavy load to light load according to claim 3, characterized in that: In mode III, the switches Q1 and Q4 are turned on, Q2 and Q3 are turned off, and the output voltage of the H-bridge is V in ; Diodes D1 and D4 are turned on, D2 and D3 are turned off, and the voltage of the secondary winding of the transformer is V o ; Parallel capacitor C p It does not participate in resonance and its voltage always remains at V o / n.

7. The control method for fast switching of an LCC resonant converter from heavy load to light load according to claim 3, characterized in that: In mode IV, the switches Q2 and Q3 are turned on, Q1 and Q4 are turned off, and the output voltage of the H-bridge is -V in ; Diodes D1 and D4 are turned on, D2 and D3 are turned off, and the voltage of the secondary winding of the transformer is V o ; Parallel capacitor C p It does not participate in resonance and its voltage always remains at V o / n.

8. The control method for fast switching of an LCC resonant converter from heavy load to light load according to claim 3, characterized in that: In mode V, the switches Q2 and Q3 are turned on, Q1 and Q4 are turned off, and the output voltage of the H-bridge is -V in ; All four diodes are in the cut-off state, there is no energy transfer between the primary and secondary sides of the transformer, and the output current is supplied by capacitor C o Provide; parallel capacitor C p Participate in resonance, and it is in the three-element resonance stage.

9. The control method for fast switching of an LCC resonant converter from heavy load to light load according to claim 3, characterized in that: In mode VI, the switches Q2 and Q3 are turned on, Q1 and Q4 are turned off, and the output voltage of the H-bridge is -V in ; Diodes D2 and D3 are turned on, D1 and D4 are turned off, and the voltage of the secondary winding of the transformer is -V o ; Parallel capacitor C p It does not participate in resonance and its voltage always remains at -V o / n.

10. The method for controlling fast switching of an LCC resonant converter from heavy load to light load according to claim 1, characterized in that: The state trajectory model is modeled by circuit differential equations and plotted in a current-voltage coordinate system. The heavy-load trajectory is a closed curve of a multi-modal combination, and the light-load trajectory is a combination of a circle and an ellipse.

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