Wide output voltage LLC resonant converter topological structure and control method thereof

Abstract

The invention belongs to the technical field of electric vehicle charging, and particularly relates to a wide-output-voltage LLC resonant converter topological structure for vehicle-mounted charging of an electric vehicle and a control method of the wide-output-voltage LLC resonant converter topological structure. Aiming at the problems of low efficiency and the like caused by difficulty in designing a magnetic element and wider switching frequency of a high-power LLC resonant converter, the invention adopts a topological structure that primary sides of transformers are connected in parallel, secondary sides of the transformers are connected in series and then are connected to a load through a rectifying circuit, and automatic current sharing of an input side is realized by multiplexing a resonant inductor; and the current stress and cost of the device are reduced. Meanwhile, switching of the LLC resonant converter in three working modes of low gain, medium gain and high gain is realized by controlling six paths of PWM modulation signals, the working range of switching frequency is effectively reduced, the design difficulty of a magnetic element is reduced, the efficiency of the converter is improved, and relatively wide voltage gain is realized at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric vehicle charging, and particularly relates to a wide output voltage LLC resonant converter topology for on-vehicle charging of electric vehicles and a control method thereof. Background Art

[0002] With the continuous advancement of the economic construction process and the implementation of the concept of Green China, the new energy vehicle industry in China has developed rapidly. In order to improve the charging efficiency of electric vehicles, its charging technology has been widely studied by many scholars at home and abroad. Among them, the LLC resonant converter has a relatively wide application background in the field of electric vehicle charging due to its advantages such as high power density, low electromagnetic interference, soft-switching implementation, easy magnetic integration, and high conversion efficiency. However, at the same time, the traditional LLC resonant converter also faces problems such as low light-load efficiency, difficult magnetic component design, and large magnetic losses. Therefore, the improvement and optimization of the traditional LLC resonant converter have received more and more attention.

[0003] In view of the problems existing in the traditional LLC resonant converter, the published document "An LLC Converter With Multiple Operation Modes for Wide Voltage Gain Range Application" proposes an improved LLC resonant converter, which adopts the transformer primary side in parallel, the secondary side in series and then connected to the load through the rectifier circuit. The converter has three operating modes: dual full-bridge, full-bridge and dual half-bridge. Its voltage gain range is large and suitable for wide voltage applications. At the same time, the converter reduces the range of switching frequency, simplifies the design of magnetic components, effectively reduces the circulating current in the circuit, and improves the conversion efficiency. However, the converter has more components, large switching loss and high cost. At the same time, there is no obvious improvement on the problems of low light load efficiency existing in the traditional LLC resonant converter. The document "An Improved LLC Resonant Converter With Reconfigurable Hybrid Voltage Multiplier and PWM-Plus-PFM Hybrid Control for Wide Output Range Applications" proposes an improved LLC resonant converter suitable for electric vehicle charging applications. The converter can be regarded as a matrix converter by adding magnetic components and switch tubes. Its structure adopts a primary transformer in series, and the secondary side is connected to the load through a rectifier circuit. The converter increases the conduction and shutdown of the switch tube on the secondary side, so that the converter can work in three working modes: full-bridge rectification, hybrid voltage doubler rectification, and voltage doubler rectification. The converter has a wide voltage gain range through a high-efficiency circuit structure, and the voltage gain is always maintained at a high level. At the same time, the converter realizes zero voltage turn-on of the primary switch tube and zero current turn-off of the secondary diode in the full range, reducing switching losses and improving conversion efficiency. However, the basic structure of the converter adds two switch tubes to the secondary side of the transformer, which increases the turn-on loss and is not conducive to improving efficiency. At the same time, since the primary side of the transformer adopts a series structure, the current stress of the primary side device is large, which is not conducive to the long-term operation of the converter.

[0004] In view of this, the inventors hope to design a wide output voltage LLC resonant converter topology structure and a control method thereof for on-board charging of electric vehicles. Summary of the invention

[0005] The object of the present invention is to overcome the problems of difficult design of the transformer and magnetic components in the traditional LLC resonant converter and a relatively large switching frequency range, and to provide a wide output voltage LLC resonant converter topology and its control method for on-vehicle charging of electric vehicles. It can meet the requirements of wide output voltage through the switching of working modes, and at the same time, the voltage gain of the converter can always be maintained at a relatively high level, increasing the conversion efficiency. At the same time, the converter adopts a structure in which the primary side of the transformer is connected in parallel, and the secondary side is connected in series and then connected to the load through a rectifier circuit, reducing the design difficulty of the transformer and magnetic components, reducing the current stress of the primary side devices, and improving the conversion efficiency.

[0006] To achieve the above technical objectives and reach the above technical effects, the present invention is realized through the following technical solutions:

[0007] The present invention provides a wide output voltage LLC resonant converter topology for on-vehicle charging of electric vehicles. The structure includes a main circuit and a control circuit. The main circuit includes an input-side inverter circuit, an LLC resonant network, a high-frequency transformer T 1 and T 2 , an anti-series switching tube Q 5 , a bidirectional auxiliary switch Q composed of back-to-back MOS switching tubes 6 , a secondary-side rectifier and filter circuit, and a voltage-dividing resistor. The two bridge arms of the input-side inverter circuit are connected to the LLC resonant network composed of a resonant inductor L r , a resonant capacitor C r1 , C r2 , an exciting inductor L m1 , L m2 . The high-frequency transformers T 1 and T 2 connected in parallel on the primary side transmit electrical energy to the rectifier circuit composed of the anti-series switching tube Q 5 , the bidirectional auxiliary switch Q composed of back-to-back MOS switching tubes 6 , and the secondary-side rectifier and filter circuit, and finally connected to the load;

[0008] The control circuit includes an output voltage and output current sampling circuit, a DSP digital controller, and a driving circuit. The output voltage and output current sampling circuit obtains a part of the voltage and current signals through the voltage-dividing resistor and current sampling resistor set at the output end, and after amplification processing, inputs them into the A / D conversion circuit to convert the analog signals into digital signals, and finally inputs them into the DSP digital controller; the PWM module inside the DSP digital controller can generate PWM drive pulse signals with specific frequencies, duty cycles, and phases according to the control algorithm and the received feedback signals. The PWM signals are output from the PWM output pins of the DSP digital controller and connected to the driving circuit.

[0009] Further, when the primary side switching transistors Q 1 and Q 4 and Q 2 and Q 3 are always in the alternating conduction and turn-off states, and the anti-series switching transistor Q 5 and the bidirectional auxiliary switch Q 6 are always in the turn-off state, the LLC resonant converter operates in the low-gain operation mode.

[0010] Further, when the primary side switching transistors Q 1 and Q 4 and Q 2 and Q 3 are always in the alternating conduction and turn-off states, the anti-series switching transistor Q 5 is always in the conduction state, and the bidirectional auxiliary switch Q 6 is always in the turn-off state, the LLC resonant converter operates in the medium-gain operation mode.

[0011] Further, when the primary side switching transistors Q 1 and Q 4 and Q 2 and Q 3 are always in the alternating conduction and turn-off states, the anti-series switching transistor Q 5 and the bidirectional auxiliary switch Q 6 are always in the conduction state, the LLC resonant converter operates in the high-gain operation mode.

[0012] Further, the LLC resonant converter can switch among the low-gain, medium-gain, and high-gain operation modes;

[0013] To enable the resonant converter to operate stably and keep its voltage gain at a relatively high level, during the constant-current charging stage, the output power and are selected as the working mode switching points, and the corresponding output voltages are and Meanwhile, through the hysteresis comparison circuit, frequent switching of the switching points is effectively prevented;

[0014] To keep the voltage gain of the LLC converter at a relatively high level, during the constant-current charging stage, the switching point (point a) for switching from the low-gain mode to the medium-gain mode is set. At this time, the output voltage V o , the output current I o and the output power P o are respectively:

[0015]

[0016] The gain mode in the converter setting is switched to the high-gain mode switching point (point b), and the output voltage V at this time o , the output current I o , and the output power P o are respectively

[0017]

[0018] In the constant-current charging stage, the output current of the LLC resonant converter always remains at the rated current I N , and its output voltage rises continuously

[0019] Furthermore, when the output voltage is greater than the threshold voltage , the anti-series switching transistor Q 5 conducts continuously, and the LLC resonant conversion circuit switches from the low-gain operating mode to the medium-gain operating mode; when the output voltage continues to increase to the threshold voltage , the auxiliary switch Q 6 conducts continuously, and the LLC resonant conversion circuit switches from the medium-gain operating mode to the high-gain operating mode; the constant-current stage continues until the output voltage V o increases to the rated voltage V N and then ends

[0020] Furthermore, the LLC resonant converter adopts the form of parallel connection on the primary side of the transformer, and realizes automatic current sharing on the input side by multiplexing the resonant inductor, reducing the current stress of the primary-side devices

[0021] The present invention also provides a control method for a wide-output-voltage LLC resonant converter topology for on-vehicle charging of electric vehicles, including the following steps

[0022] S1. The current-voltage sampling circuit samples the output voltage V of the main circuit o , the output current I o , and performs analog-to-digital conversion to the DSP digital controller

[0023] S2. The DSP digital controller uses the feedback voltage v f , the current i f as the input signals of the internal digital closed-loop control program, compares them with the threshold voltage and the set value current, and determines whether it is in the constant-current charging mode or the constant-voltage charging mode; if it is in the constant-current charging mode, then uses the output current I o and the rated reference current I N to form a closed-loop negative feedback system, and at the same time samples the output voltage V o ; when the output voltage V o has not reached the threshold voltage then the controller outputs a PWM modulation signal to control Q 1 、Q 4and Q 2 and Q 3 conduct alternately, and the anti-series switch Q 5 and the auxiliary switch Q 6 are turned off, and the resonant converter operates in the low-gain operation mode; when the output voltage V o reaches the threshold voltage (point a), the controller outputs a PWM modulation signal to control Q 1 and Q 4 and Q 2 and Q 3 to conduct alternately, the anti-series switch Q 5 conducts, and the auxiliary switch Q 6 is turned off, and the resonant converter switches from the low-gain operation mode to the medium-gain operation mode; when the output voltage V o reaches the threshold voltage (point b), the controller outputs a PWM modulation signal to control Q 1 and Q 4 and Q 2 and Q 3 to conduct alternately, the anti-series switch Q 5 and the auxiliary switch Q 6 continuously conduct, and the resonant converter switches from the medium-gain operation mode to the high-gain operation mode until the output voltage V o increases to the rated voltage V N (point c), and the constant-current stage ends;

[0024] If it is in the constant-voltage charging mode, the next step is executed;

[0025] S3. When the LLC resonant converter is in the constant-voltage charging stage, the output voltage V o is equal to the rated voltage V N , and the converter has been in the high-gain operation mode; when the output current I o gradually decreases from the rated current to 30% I N (point d), the requirements of automotive charging applications are met, and the constant-voltage charging stage ends.

[0026] The beneficial effects of the present invention are:

[0027] 1. The LLC resonant converter proposed by the present invention adopts a structure in which the primary side of the transformer is connected in parallel, and the secondary side is connected in series to the load through a rectifier circuit. The resonant cavity reduces the magnetic components to reduce costs by multiplexing the resonant inductor, and at the same time realizes automatic current sharing on the input side of the transformer, reduces the current stress of the primary-side devices, reduces the switching loss of the devices, and is beneficial to the long-term stable operation of the converter.

[0028] 2. The present invention proposes to control the switch Q 1 and Q4 and Q 2 、Q 3 、anti - series switching transistor Q 5 、bidirectional auxiliary switch Q 6 By controlling the conduction and turn - off of Q, the LLC resonant converter operates in three operating modes: low - gain, medium - gain, and high - gain, reducing the operating range of the switching frequency and simplifying the design of magnetic components. At the same time, the LLC resonant converter operates in a weakly inductive region throughout the process, achieving zero - voltage turn - on of the primary - side switching transistor and zero - current turn - off of the secondary - side diode, reducing the switching losses of the devices and improving the conversion efficiency.

[0029] 3. The LLC resonant converter proposed in the present invention adopts a structure with parallel connection on the primary side of the transformer, which not only reduces the current stress of the primary - side devices, but also reduces the magnetizing current, the root - mean - square current of the circuit, and the design difficulty of the exciting inductance, reduces the magnetic loss of the transformer, and ensures the high - efficiency operation of the circuit.

[0030] 4. The LLC resonant converter proposed in the present invention controls the conduction and turn - off of the switching transistor and the auxiliary switch through the PWM modulation signal, enabling the converter to operate in three operating modes: low - gain, medium - gain, and high - gain. While achieving a wide voltage gain, it also ensures that the voltage gain of the converter remains at a high level throughout the range, meeting the requirements of electric vehicle charging applications.

[0031] Of course, it is not necessary for any product implementing the present invention to achieve all of the above advantages simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0033] Figure 1 is a schematic diagram of the topology structure of the wide - output - voltage LLC resonant converter for on - vehicle charging of electric vehicles according to the present invention;

[0034] Figure 2 is the AC equivalent circuit diagram obtained by the fundamental - wave analysis method for the LLC resonant converter;

[0035] Figure 3 is the PWM waveform diagram of the LLC resonant converter;

[0036] wherein, a - switching from the low - gain operating mode to the medium - gain operating mode, b - switching from the medium - gain operating mode to the high - gain operating mode;

[0037] Figure 4 It is a logic flowchart for the working mode switching of an LLC resonant converter;

[0038] Figure 5 It is a curve graph of the charging characteristics of a charging power supply;

[0039] Figure 6 It is a closed-loop control block diagram of an LLC resonant converter for low-gain, medium-gain, and high-gain working mode switching;

[0040] Figure 7 It is a DC gain curve graph of an LLC resonant converter under the same load conditions. Specific implementation manners

[0041] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0042] This embodiment provides a wide output voltage LLC resonant converter topology structure for on-vehicle charging of electric vehicles. This structure includes a main circuit 1 and a control circuit 9. The main circuit 1 includes an input-side inverter circuit 2, an LLC resonant network 3, high-frequency transformers T 1 and T 2 4, anti-series switching tubes Q 5 5, a bidirectional auxiliary switch Q composed of back-to-back MOS switching tubes 6 6, a secondary-side rectification and filtering circuit 7, and a voltage-dividing resistor 8. The two bridge arms of the input-side inverter circuit 2 are connected to the LLC resonant network 3 composed of a resonant inductor L r , resonant capacitors C r1 , C r2 , and exciting inductors L m1 , L m2 . The high-frequency transformers T 1 and T 2 4 in parallel on the primary side transmit electrical energy to the rectification circuit composed of the anti-series switching tubes Q 5 5, the bidirectional auxiliary switch Q composed of back-to-back MOS switching tubes 6 6, and the secondary-side rectification and filtering circuit 7, and finally connect to the load;

[0043] The control circuit 9 includes an output voltage 10, an output current sampling circuit, a DSP digital controller 11, and a drive circuit 12. The output voltage 10 and the output current sampling circuit obtain a partial proportion of voltage and current signals through a voltage-dividing resistor 8 and a current sampling resistor provided at the output end. After amplification processing, they are input into an A / D conversion circuit to convert the analog signals into digital signals, and finally input into the DSP digital controller 11. The PWM module inside the DSP digital controller 11 can generate a PWM drive pulse signal with a specific frequency, duty cycle, and phase according to the control algorithm and the received feedback signal. The PWM signal is output from the PWM output pin of the DSP digital controller 11 and connected to the drive circuit 12.

[0044] When the primary side switching transistors Q 1 、Q 4 and Q 2 、Q 3 are always in an alternating on and off state, and the anti-series switching transistor Q 5 and the bidirectional auxiliary switch Q 6 are always in an off state, the LLC resonant converter operates in a low-gain operating mode. When the primary side switching transistors Q 1 、Q 4 and Q 2 、Q 3 are always in an alternating on and off state, the anti-series switching transistor Q 5 is always in an on state, and the bidirectional auxiliary switch Q 6 is always in an off state, the LLC resonant converter operates in a medium-gain operating mode. When the primary side switching transistors Q 1 、Q 4 and Q 2 、Q 3 are always in an alternating on and off state, the anti-series switching transistor Q 5 and the bidirectional auxiliary switch Q 6 are always in an on state, the LLC resonant converter operates in a high-gain operating mode.

[0045] The LLC resonant converter can switch among three operating modes: low gain, medium gain, and high gain.

[0046] To enable the resonant converter to operate stably and keep its voltage gain at a relatively high level, during the constant current charging stage, the output power and are selected as the operating mode switching points, and the corresponding output voltages are and Meanwhile, through the hysteresis comparison circuit, the frequent switching of the switching points is effectively prevented.

[0047] To keep the voltage gain of the LLC converter at a relatively high level, during the constant-current charging stage, the switching point from the low-gain mode to the medium-gain mode (point a) is set. At this time, the output voltage V o , output current I o , and output power P o are respectively:

[0048]

[0049] The converter sets the switching point from the medium-gain mode to the high-gain mode (point b). At this time, the output voltage V o , output current I o , and output power P o are respectively:

[0050]

[0051] During the constant-current charging stage, the output current of the LLC resonant converter always remains at the rated current I N , and its output voltage keeps rising.

[0052] When the output voltage is greater than the threshold voltage , the anti-series switching transistor Q 5 conducts continuously, and the LLC resonant conversion circuit switches from the low-gain operating mode to the medium-gain operating mode; when the output voltage continues to increase to the threshold voltage , the auxiliary switch Q 6 conducts continuously, and the LLC resonant conversion circuit switches from the medium-gain operating mode to the high-gain operating mode; the constant-current stage continues until the output voltage V o increases to the rated voltage V N and then ends.

[0053] The LLC resonant converter adopts the form of parallel connection on the primary side of the transformer, and realizes automatic current sharing on the input side by multiplexing the resonant inductor, reducing the current stress of the primary-side devices.

[0054] This embodiment also provides a control method for a wide-output-voltage LLC resonant converter topology, including the following steps:

[0055] S1. The current-voltage sampling circuit samples the output voltage V o and output current I o of the main circuit, and performs analog-to-digital conversion to the DSP digital controller;

[0056] S2. The DSP digital controller uses the feedback voltage v f , current i fAs an input signal of the internal digital closed-loop control program, it is compared with the threshold voltage and the set value current to determine whether it is in the constant current charging mode or the constant voltage charging mode; if it is in the constant current charging mode, the output current I is used o forms a closed-loop negative feedback system with the rated reference current I N while sampling the output voltage V o ; when the output voltage V o does not reach the threshold voltage the controller outputs a PWM modulation signal to control Q 1 、Q 4 and Q 2 、Q 3 to conduct alternately, the anti-series switch tube Q 5 and the auxiliary switch Q 6 are turned off, and the resonant converter operates in the low-gain operating mode; when the output voltage V o reaches the threshold voltage (point a), the controller outputs a PWM modulation signal to control Q 1 、Q 4 and Q 2 、Q 3 to conduct alternately, the anti-series switch tube Q 5 conducts, the auxiliary switch Q 6 is turned off, and the resonant converter switches from the low-gain operating mode to the medium-gain operating mode; when the output voltage V o reaches the threshold voltage (point b), the controller outputs a PWM modulation signal to control Q 1 、Q 4 and Q 2 、Q 3 to conduct alternately, the anti-series switch tube Q 5 and the auxiliary switch Q 6 continue to conduct, and the resonant converter switches from the medium-gain operating mode to the high-gain operating mode until the output voltage V o increases to the rated voltage V N (point c), and the constant current stage ends;

[0057] If it is in the constant voltage charging mode, the next step is executed;

[0058] S3. When the LLC resonant converter is in the constant voltage charging stage, the output voltage V o is equal to the rated voltage V N , and the converter has been operating in the high-gain operating mode; when the output current I o gradually decreases from the rated current to 30% I N (point d), it meets the requirements of automotive charging applications, and the constant voltage charging stage ends.

[0059] Such asFigure 1 As shown, the input - side DC power supply passes through the input - side inverter circuit, then through the LLC resonant network 3, and then through the high - frequency transformer T 1 and T 2 4 to the secondary side. After passing through the secondary - side rectifier and filter circuit 7, it is connected to the load. The control circuit mainly samples the output voltage V o and the output current I o through the voltage - dividing sampling circuit, and inputs the sampling results into the output - voltage 10 and input - current sampling circuits. Then, the results are input into the DSP digital controller 11. Through the drive circuit 12, corresponding PWM modulation signals are output to make the LLC resonant converter operate in low - gain, medium - gain, and high - gain working modes. During this process, the DSP digital controller 11 determines whether the converter is in the constant - current charging stage or the constant - voltage charging stage based on the output voltage V o and the output current I o .

[0060] When the converter is in the constant - current charging stage, its characteristics are: the output current I o = I N , and the output voltage V o rises continuously. The DSP digital controller 11 needs to determine whether the converter operates in low - gain, medium - gain, or high - gain working mode by judging the magnitude of the output voltage. When the output voltage V o is less than the threshold voltage , the DSP digital controller 11 outputs six - channel variable - frequency PWM signals to the drive circuit 12. The drive circuit 12 controls the switching tubes Q 1 , Q 4 and Q 2 , Q 3 in the input - side inverter circuit to conduct alternately, and the anti - series switching tube Q 5 and the bidirectional auxiliary switch Q 6 are turned off. When the output voltage V o rises to the threshold voltage V 1 , the DSP digital controller 11 outputs six - channel variable - frequency PWM signals to the drive circuit 12. The drive circuit 12 controls the switching tubes Q 1 , Q 4 and Q 2 , Q 3 in the input - side inverter circuit to conduct alternately, the anti - series switching tube Q 5 is turned on, and the bidirectional auxiliary switch Q 6 is turned off. At this time, the converter operates in the medium - gain mode, and its characteristics are: the output current I o = I N , and the output voltage V o continues to rise continuously. When the output voltage V o rises to the threshold voltage When, the DSP digital controller 11 outputs six-way variable-frequency PWM signals to the drive circuit 12, and the drive circuit 12 controls the switching transistors Q 1 , Q 4 and Q 2 , Q 3 to conduct alternately, the anti-series switching transistor Q 5 and the bidirectional auxiliary switch Q 6 are turned on. At this time, the converter operates in the high-gain mode, characterized by: the output current I o =I N , and the output voltage V o continues to rise continuously. When the output voltage V o rises to the rated voltage V N , the constant-current charging stage of the converter ends, and it enters the constant-voltage charging stage.

[0061] When the converter is in the constant-voltage charging stage, its characteristics are: the output voltage V o =V N , and the output current I o gradually decreases from the rated current I N to 30%I N . The converter always operates in the high-gain mode during the constant-voltage charging stage, that is, the DSP digital controller 11 outputs six-way variable-frequency PWM signals to the drive circuit 12, and the drive circuit 12 controls the switching transistors Q 1 , Q 4 and Q 2 , Q 3 to conduct alternately, the anti-series switching transistor Q 5 and the auxiliary switch Q 6 are turned on. When the output current I o decreases to 30%I N , the constant-voltage charging stage of the converter ends.

[0062] As Figure 2 shown, the resonant inductor L r , the resonant capacitors C r1 , C r2 and the exciting inductors L m1 , L m2 form a resonant network, V in,FHA is the input voltage; I r,FHA is the total current of the resonant tank; V o1,FHA , V o2,FHA are the secondary-side voltages of the transformer; I rec is the rectified current; R o,ac is the equivalent load resistance. The normalized DC voltage gain formula of this LLC resonant converter is obtained from the AC equivalent circuit as follows:

[0063]

[0064] Among them, L n is the ratio of the excitation inductance to the resonant inductance, Q is the quality factor, and f n is the normalized frequency. When the converter is in the low-gain operation mode, α = 0.5; when the converter is in the medium-gain operation mode, α = 1; when the converter is in the high-gain operation mode, α = 2.

[0065] As Figure 3 shown, the drive circuit 12 outputs the drive waveforms of PWM1, PWM2, PWM3, PWM4, PWM5, and the switching signal PWM6 according to the output result of the DSP digital controller 11. When the converter operates in the low-gain operation mode, the switching transistors Q 1 , Q 4 and Q 2 , Q 3 conduct alternately, the anti-series switching transistor Q 5 and the bidirectional auxiliary switch Q 6 are continuously turned off; when the converter operates in the medium-gain operation mode, the switching transistors Q 1 , Q 4 and Q 2 , Q 3 conduct alternately, the anti-series switching transistor Q 5 is continuously turned on, and the bidirectional auxiliary switch Q 6 is continuously turned off; when the converter operates in the high-gain operation mode, the switching transistors Q 1 , Q 4 and Q 2 , Q 3 conduct alternately, the anti-series switching transistor Q 5 and the bidirectional auxiliary switch Q 6 are continuously turned on.

[0066] As Figure 4 shown, during the constant-current charging stage, its output current remains I o = I N unchanged, and the output voltage V o increases continuously. When the output voltage V o increases to the threshold voltage (point a), the output voltage 10 and the output current sampling circuit input the sampling result into the DSP digital controller 11, and the DSP digital controller 11 controls the drive circuit 12 to realize the conduction and turn-off of the switching transistors and the auxiliary switch, that is, the switching transistors Q 1 , Q 4 and Q 2 , Q 3 conduct alternately, the anti-series switching transistor Q 5 is continuously turned on, and the bidirectional auxiliary switch Q6 Continuously turn off to complete the switching of the converter from the low-gain operating mode to the medium-gain operating mode. When the output voltage V o continues to increase to the threshold voltage (point b), the output voltage 10 and the output current sampling circuit input the sampling result into the DSP digital controller 11. The DSP digital controller 11 controls the drive circuit 12 to realize the conduction and turn-off of the switching tube and the auxiliary switch, that is, the switching tubes Q 1 , Q 4 and Q 2 , Q 3 conduct alternately, the anti-series switching tube Q 5 and the bidirectional auxiliary switch Q 6 conduct continuously to complete the switching of the converter from the medium-gain operating mode to the high-gain operating mode.

[0067] As Figure 5 shown, when the LLC resonant converter is in the constant-current charging stage, the output current remains I o = I N unchanged, and the output voltage V o continues to increase. When t = t 1 , the output voltage V o increases to the threshold voltage (point a), the converter switches from the low-gain operating mode to the medium-gain operating mode, and the output current remains I o = I N unchanged, and the output voltage V o continues to increase. When t = t 2 , the output voltage V o increases to the threshold voltage (point b), the converter switches from the medium-gain operating mode to the high-gain operating mode, and the output current remains I o = I N unchanged, and the output voltage V o continues to increase. When t = t 3 , the output voltage V o increases to the rated voltage V N (point c), the constant-current charging stage ends, and the converter enters the constant-voltage charging stage. Entering the constant-voltage charging stage, its characteristic is: maintaining the output voltage V o = V N , and the output current I o gradually decreases. When t = t 4 , the output current I o decreases to 30%I N , and the constant-voltage charging stage ends.

[0068] As Figure 6 shown, by measuring the output voltage V oWith the output current I o is sampled, and its sampling result is compared with the reference voltage and the reference current to determine whether the converter operates in the constant current charging mode or the constant voltage charging mode. At the same time, by comparing the output voltage V o with the threshold voltage and The duty cycles of the anti-series switching transistor Q 5 and the bidirectional auxiliary switch Q 6 are output through the PWM generator. Finally, according to different working modes, the corresponding PWM waveforms are closed-loop output to control the conduction and turn-off of the corresponding switching transistors.

[0069] As Figure 7 shown, f n is the normalized voltage gain, and f min is the minimum value of the normalized voltage gain. It can be seen from the figure that this curve can meet the maximum gain requirement of this LLC resonant converter, enabling it to operate in the weak inductive region throughout the process, achieving zero-voltage turn-on of the primary switching transistor and zero-current turn-off of the secondary diode. To meet the requirements of electric vehicle charging applications, when the voltage gain of the previous working mode of the converter is small, the switching of the working mode can be achieved through the conduction and turn-off of the anti-series switching transistor and the auxiliary switch, so that its voltage gain continues to work at a higher level.

[0070] To meet the requirements of electric vehicle charging applications, and at the same time aiming at the problems of difficult design of the transformer and magnetic components of the traditional LLC resonant converter and a relatively large switching frequency range, a wide output voltage LLC resonant converter topology structure and its control method for on-board charging of electric vehicles are proposed. This resonant converter adopts a structure in which the primary side of the transformer is connected in series, the secondary side is connected in parallel, and then connected to the load through a rectifier circuit. By controlling the PWM modulation signal to control the conduction and turn-off of the primary switching transistors Q 1 , Q 4 and Q 2 , Q 3 , the anti-series switching transistor Q 5 and the bidirectional auxiliary switch Q composed of back-to-back MOS switches 6 , the converter is enabled to operate in three working modes: low gain, medium gain, and high gain.

[0071] The primary side of the converter can achieve automatic current sharing of the input current on the primary side of the transformer through the structure of multiplexing the resonant inductor and connecting the primary side of the transformer in parallel, reducing the current stress of the devices and the device cost. Secondly, by switching among three operating modes, the converter not only broadens the output voltage but also reduces the operating range of the switching frequency, enabling zero-voltage turn-on of the primary-side switching transistor and zero-current turn-off of the secondary-side diode throughout the whole process of the converter, reducing the switching losses and magnetic losses. While meeting the requirements of electric vehicle charging applications, the conversion efficiency of the converter is also greatly improved.

[0072] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and utilize the present invention well. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A wide output voltage LLC resonant converter topology for on-board charging of electric vehicles, characterized in that: The structure comprises a main circuit (1) and a control circuit (9). The main circuit (1) comprises an input side inverter circuit (2), an LLC resonant network (3), high frequency transformers T1 and T2 (4), an anti-series switch tube Q5 (5), a bidirectional auxiliary switch Q6 (6) composed of back-to-back MOS switch tubes, a secondary side rectifier filter circuit (7) and a voltage divider resistor (8). The two groups of bridge arms of the input side inverter circuit (2) are connected to a resonant inductor L r , resonant capacitor C r1 , C r2 And the excitation inductance L m1 , L m2 The LLC resonant network (3) formed is connected, and the high-frequency transformers T1 and T2 (4) connected in parallel on the primary side transmit the electric energy to the rectifier circuit composed of the anti-series switch tube Q5 (5), the bidirectional auxiliary switch Q6 (6) composed of the back-to-back MOS switch tubes, and the secondary side rectifier filter circuit (7), and finally connected to the load; The control circuit (9) comprises an output voltage (10), an output current sampling circuit, a DSP digital controller (11) and a drive circuit (12); the output voltage (10) and output current sampling circuits obtain a portion of the voltage and current signals through a voltage divider resistor (8) and a current sampling resistor arranged at the output end, and input the signals into an A / D conversion circuit after amplification processing, convert the analog signals into digital signals, and finally input the signals into the DSP digital controller (11); the PWM module inside the DSP digital controller (11) can generate a PWM drive pulse signal with a specific frequency, duty cycle and phase according to a control algorithm and a received feedback signal; the PWM signal is output from a PWM output pin of the DSP digital controller (11) and connected to the drive circuit (12).

2. The wide output voltage LLC resonant converter topology structure according to claim 1, characterized in that: When the primary switch tubes Q1, Q4 and Q2, Q3 are always in an alternate on and off state, and the anti-series switch tube Q5 and the bidirectional auxiliary switch Q6 are always in the off state, the LLC resonant converter operates in a low gain operation mode.

3. The wide output voltage LLC resonant converter topology structure according to claim 2, characterized in that: When the primary switch tubes Q1, Q4 and Q2, Q3 are always in an alternating on and off state, the anti-series switch tube Q5 is always in an on state, and the bidirectional auxiliary switch Q6 is always in an off state, the LLC resonant converter operates in a medium gain operating mode.

4. The wide output voltage LLC resonant converter topology structure according to claim 3, characterized in that: When the primary switch tubes Q1, Q4 and Q2, Q3 are always in an alternating on and off state, and the anti-series switch tube Q5 and the bidirectional auxiliary switch Q6 are always in an on state, the LLC resonant converter operates in a high gain operation mode.

5. The wide output voltage LLC resonant converter topology structure according to claim 4, characterized in that: The LLC resonant converter can switch between three operating modes: low gain, medium gain, and high gain; In the constant current charging stage, select the output power as well as As the working mode switching point, the corresponding output voltage is as well as In the constant current charging stage, the low gain mode is set to switch to the medium gain mode switching point. At this time, the output voltage V o , output current I o And the output power P o They are: The converter is set to switch from the gain mode to the high gain mode switching point. At this time, the output voltage V o , output current I o And the output power P o They are: During the constant current charging stage, the output current of the LLC resonant converter is always maintained at the rated current I N , its output voltage continues to rise.

6. The wide output voltage LLC resonant converter topology structure according to claim 5, characterized in that: When the output voltage is greater than the threshold voltage When the output voltage continues to increase to the threshold voltage, the anti-series switch tube Q5 is continuously turned on, and the LLC resonant conversion circuit switches from the low-gain working mode to the medium-gain working mode. When the auxiliary switch Q6 is continuously turned on, the LLC resonant converter circuit switches from the medium gain working mode to the high gain working mode; the constant current stage lasts until the output voltage V o Increase to the rated voltage V N Then it ends.

7. The wide output voltage LLC resonant converter topology structure according to claim 6, characterized in that: The LLC resonant converter adopts the form of parallel connection of the primary side of the transformer, and realizes automatic current sharing on the input side by reusing the resonant inductor, thereby reducing the current stress of the primary side devices.

8. The control method of the wide output voltage LLC resonant converter topology structure according to claim 7, characterized in that: The steps include: S1, current and voltage sampling circuit outputs voltage V to the main circuit o , output current I o Sampling, performing digital-to-analog conversion to the DSP digital controller; S2, DSP digital controller will feedback voltage v f 、Current i f As the input signal of the internal digital closed-loop control program, it is compared with the threshold voltage and the set value current to determine whether it is in constant current charging mode or constant voltage charging mode; if it is in constant current charging mode, the output current I o With the rated reference current I N A closed-loop negative feedback system is formed, and the output voltage V is sampled at the same time. o ; When the output voltage V o Threshold voltage not reached The controller outputs a PWM modulation signal to control Q1, Q4 and Q2, Q3 to turn on alternately, the anti-series switch Q5 and the auxiliary switch Q6 to turn off, and the resonant converter works in a low-gain working mode; when the output voltage V o Reaching the threshold voltage The controller outputs a PWM modulation signal to control Q1, Q4 and Q2, Q3 to turn on alternately, the anti-series switch Q5 to turn on, the auxiliary switch Q6 to turn off, and the resonant converter switches from the low-gain working mode to the medium-gain working mode; when the output voltage V o Reaching the threshold voltage The controller outputs a PWM modulation signal to control Q1, Q4 and Q2, Q3 to turn on alternately, the anti-series switch Q5 and the auxiliary switch Q6 to continue to turn on, and the resonant converter switches from the medium gain working mode to the high gain working mode until the output voltage V o Increase to the rated voltage V N , the constant current stage ends; If it is in constant voltage charging mode, proceed to the next step; S3, when the LLC resonant converter is in the constant voltage charging stage, the output voltage V o With rated voltage V N equal, the converter is always in high gain mode; when the output current I o Gradually reduce the rated current to 30% I N When the vehicle charging application requirements are met, the constant voltage charging stage ends.

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