Vehicle auxiliary power supply DC-DC converter and control method thereof

Abstract

The present invention aims to provide a vehicle-mounted auxiliary power DC-DC converter, including an input capacitor C1, a Buck converter, a Boost converter, an output capacitor C2, and an LLC resonant converter; the Buck converter and the Boost converter are respectively composed of two branches, and the two branches of the Buck converter are connected in series with the two branches of the Boost converter in a one-to-one correspondence to form two groups of parallel Buck-Boost branch structures; the Buck-Boost branch structure is connected to the vehicle power battery in parallel with the input capacitor C1, and the Buck-Boost branch structure is connected to the input end of the LLC resonant converter in parallel with the output capacitor C2. The present invention also provides an integrated digital control method for a vehicle-mounted auxiliary power DC-DC converter. The converter overcomes the defects of the prior art and has the characteristics of a wide input voltage range, low conduction loss, and low cost.

Description

Technical Field

[0001] The present invention relates to the field of new energy vehicle power auxiliary equipment, and in particular to a vehicle-mounted auxiliary power DC-DC converter and a control method thereof. Background Art

[0002] Traditional fuel vehicles consume a lot of energy, and also bring a series of problems such as environmental pollution and greenhouse effect. Energy shortage and environmental pollution have become the most prominent problems in the world today, and the development of new energy vehicles has become inevitable. In the power system solution of new energy vehicles, the power battery (high-voltage battery) as the main energy source is generally used to power the motor to provide power for the vehicle's driving; the low-voltage auxiliary battery is used to power the vehicle's air conditioning, audio and entertainment system, front and rear wiper motors, front and rear washing motors, headlights, fog lights and other on-board auxiliary equipment. Regarding the low-voltage auxiliary battery used, traditional fuel vehicles mostly use lead-acid batteries, while the low-voltage auxiliary battery of new energy vehicles can use lithium-ion batteries with better performance. Generally speaking, the low-voltage auxiliary battery has limited storage energy and cannot provide power for a long time. For this reason, the solution currently used in new energy vehicles is: the power battery charges the low-voltage auxiliary battery through the auxiliary power DC-DC converter, and can temporarily power the on-board auxiliary equipment. Although lithium-ion batteries have excellent performance in all aspects, they have strict requirements on the charging method. They are generally charged in a constant current-constant voltage manner, and the battery life and capacity changes depend on various factors such as the number of cycles and the charging mode. To this end, the auxiliary power supply DC-DC converter needs to accurately control the voltage and current during the charging process to ensure the constant current-constant voltage charging process of the lithium-ion battery. On the other hand, the output voltage of the power battery is used as the input of the auxiliary power supply DC-DC converter, but the voltage fluctuation range is large, generally 200V-450V, so the auxiliary power supply DC-DC converter must meet the requirements of a wide input voltage range. In addition, the auxiliary power supply DC-DC converter is generally required to have a high conversion efficiency, low voltage and current ripple, and the power switch tube used has low voltage and current stress.

[0003] Most of the existing vehicle auxiliary power DC-DC converters still have many shortcomings: the input voltage range is not wide enough; it is not easy to achieve zero voltage conduction of the power switch tube; the conduction loss is large and the conversion efficiency is low; the power switch tube is subjected to high thermal stress and electrical stress; the required capacity is large; the overall cost is high, etc. Summary of the invention

[0004] The present invention aims to provide a vehicle-mounted auxiliary power supply DC-DC converter, which overcomes the defects of the prior art and has the characteristics of wide input voltage range, low conduction loss, low cost, etc.

[0005] The technical solution of the present invention is as follows:

[0006] A vehicle-mounted auxiliary power DC-DC converter, comprising an input capacitor C1, a Buck converter, a Boost converter, an output capacitor C2, and an LLC resonant converter;

[0007] The Buck converter and the Boost converter are respectively composed of two branches, and the two branches of the Buck converter are connected in series with the two branches of the Boost converter in a one-to-one correspondence to form two sets of parallel Buck-Boost branch structures;

[0008] The Buck-Boost branch structure is connected in parallel with the input capacitor C1 and then connected to the vehicle power battery. The Buck-Boost branch structure is connected in parallel with the output capacitor C2 and then connected to the input end of the LLC resonant converter.

[0009] Preferably, the Buck converter includes a power switch tube D1, a power switch tube D2, a diode d1, a diode d2, an inductor L1, and an inductor L2; the collectors of the power switch tube D1 and the power switch tube D2 are both connected to the positive electrode of the input capacitor C1, and are connected to the positive electrode of the vehicle power battery as terminal S1; the emitter of the power switch tube D1 and the negative electrode of the diode d1 are both connected to one end of the inductor L1; the emitter of the power switch tube D2 and the negative electrode of the diode d2 are both connected to one end of the inductor L2; the positive electrode of the diode d1 and the positive electrode of the diode d2 are both connected to the negative electrode of the input capacitor C1, and are connected to the negative electrode of the vehicle power battery as terminal S2.

[0010] Preferably, the Boost converter includes a power switch tube D3, a power switch tube D4, a diode d3, a diode d4, an inductor L1, and an inductor L2; the collector of the power switch tube D3 and the positive electrode of the diode d3 are both connected to the other end of the inductor L1; the collector of the power switch tube D4 and the positive electrode of the diode d4 are both connected to the other end of the inductor L2; the emitter of the power switch tube D3 and the emitter of the power switch tube D4 are both connected to the terminal S2, the cathodes of the diode d3 and the diode d4 are both connected to the positive electrode of the output capacitor C2, and the cathode of the output capacitor C2 is connected to the terminal S2, wherein the inductor L1 and the inductor L2 are shared with the Buck converter.

[0011] Preferably, the LLC resonant converter comprises a power switch tube D5, a power switch tube D6, a resonant inductor L3, a transformer T1, a resonant capacitor C3, a MOSFET tube M1, a MOSFET tube M2, and a filter capacitor C4; the collector of the power switch tube D5 is connected to the positive electrode of the capacitor C2, the emitter of the power switch tube D5 and the collector of the power switch tube D6 are both connected to one end of the resonant inductor L3; the emitter of the power switch tube D6 and one end of the resonant capacitor C3 are both connected to the terminal S2, and the primary side of the transformer T1 is connected to the positive electrode of the capacitor C2. The other end of the resonant inductor L3 is connected; the non-same-name end of the primary side of the transformer T1 is connected to the other end of the resonant capacitor C3; the same-name end of the secondary side of the transformer T1 is connected to the source of the MOSFET tube M1; the drain of the MOSFET tube M1 and the drain of the MOSFET tube M2 are both connected to the positive electrode of the filter capacitor C4, as the terminal O1; the secondary side middle tap f1 of the transformer T1 is connected to the negative electrode of the filter capacitor C4, as the terminal O2; the transformation ratio of the primary side of the transformer T1 and the two secondary sides separated by the secondary side middle tap f1 is n:1:1;

[0012] The terminal S1 is connected to the positive terminal of the power battery, and the terminal S2 is connected to the negative terminal of the power battery; the terminal O1 serves as the positive output terminal of the vehicle auxiliary power DC-DC converter; the terminal O2 is connected to the negative output terminal of the vehicle auxiliary power DC-DC converter.

[0013] Preferably, it also includes a controller, a PWM pulse generator I, a PWM pulse generator II, a PWM pulse generator III, a PWM pulse generator IV, a PWM pulse generator V and an inverter. The pulse output ends of the PWM pulse generator I, the PWM pulse generator II, the PWM pulse generator III, the PWM pulse generator IV, the PWM pulse generator V and the inverter are respectively connected to the gate g1 of the power switch tube D1, the gate g2 of the power switch tube D2, the gate g3 of the power switch tube D3, the gate g4 of the power switch tube, the gate g5 of the power switch tube, and the gate g6 of the power switch tube D6; the input ends of the PWM pulse generator I, the PWM pulse generator II, the PWM pulse generator III, the PWM pulse generator IV and the PWM pulse generator V are connected to the controller to receive the control signal sent by the controller; the input end of the inverter is connected to the pulse output end of the PWM pulse generator V.

[0014] The present invention also provides a control method for a vehicle-mounted auxiliary power DC-DC converter, which utilizes the above-mentioned vehicle-mounted auxiliary power DC-DC converter and includes the following steps:

[0015] A. Collect the following analog parameters of the vehicle auxiliary power DC-DC converter through sensors: power battery voltage V in , the current I flowing through the inductor L1 L1 , the current I flowing through the inductor L2 L2 , LLC resonant converter input voltage V 1 , the output current I of the vehicle auxiliary power DC-DC converter O , the output voltage V of the vehicle auxiliary power DC-DC converter O ; Convert the above analog parameters through an A / D converter to obtain corresponding digital parameters as the input of step B;

[0016] B. SOC estimation and charging judgment: V O ,I O The SOC is estimated to obtain the state of charge of the on-board auxiliary battery, and the auxiliary battery charging judgment is performed on the on-board auxiliary battery state of charge. When the judgment result is that the on-board auxiliary power DC-DC converter does not charge the auxiliary battery, or supplies power to the automobile auxiliary electrical equipment in a constant voltage form, "0" is output as the input of step C; when the judgment result is that the on-board auxiliary power DC-DC converter charges the auxiliary battery, "1" is output to the constant voltage and constant current charging judgment unit, and the constant voltage and constant current charging judgment unit performs a judgment on V O ,I O Make a judgment, and when the judgment result is the constant voltage charging stage, output "0" as the input of step C; when the judgment result is the constant current charging stage, output "1" as the input of step C;

[0017] C. Outer loop control: preset reference output voltage V Oref , reference output current I Oref ; V O With V Oref Subtract to get the voltage deviation value V Δ , will I O with I Oref Subtract to get the voltage deviation value I Δ , judge according to the input of step C: when the input of step C is "1", then I Δ Perform constant current correction to obtain V 1 The reference voltage V 1ref ; When the input of step C is "0", when V Δ Perform constant voltage correction to obtain V 1 The reference voltage V 1ref ; V 1ref Enter step D;

[0018] D. Middle loop control: There is a voltage controller preset to set V 1 With V 1refSubtract to get the voltage deviation value V' Δ , V′ Δ Input voltage controller, output reference current I Lref ; will I Lref Enter step E;

[0019] E. Inner loop control: There are current controllers I and II preset, and I L1 with I Lref Subtract to get the current deviation value L Δ1 , will I L2 with I Lref Subtract to get the current deviation value L Δ2 , L Δ1 Input current controller I outputs the controlled duty cycle Z c1 , L Δ2 The input current controller II outputs the controlled duty cycle Z c2 , Z c1 , Z c2 Enter step F;

[0020] F. Duty cycle calculation:

[0021] The pulse duty ratios of the PWM pulse generator I, PWM pulse generator II, PWM pulse generator III, PWM pulse generator IV, PWM pulse generator V and the inverter output are Z 1 , Z 2 , Z 3 , Z 4 , Z 5 , Z 6 ;

[0022] By V 1ref 、V in Calculate the initial duty cycle Z 0 :

[0023]

[0024] When Z 0 <1-Δ:

[0025] Z 1 =Z c1 ; Z 2 =Z c2 ; Z 3 =Z 4 =0; Z 5 =Z 6 =0.5;

[0026] When Z 0 >1+Δ:

[0027] Z 1 =Z2 =1; Z 3 =Z c1 -1; Z 4 =Z c2 -1; Z 5 =Z 6 =0.5;

[0028] When 1-Δ <Z 0 <1+Δ:

[0029]

[0030] Where Δ is a small positive number defined;

[0031] G. Output control: The pulse duty ratio of the pulses output by PWM pulse generator I, PWM pulse generator II, PWM pulse generator III, PWM pulse generator IV, PWM pulse generator V and inverter is Z. 1 , Z 2 , Z 3 , Z 4 , Z 5 , Z 6 The pulse signals are respectively output to the gate g1 of the power switch tube D1, the gate g2 of the power switch tube D2, the gate g3 of the power switch tube D3, the gate g4 of the power switch tube, the gate g5 of the power switch tube, and the gate g6 of the power switch tube D6, so as to control the power switch tubes D1 to D6; in the above pulse signals, the pulse signals of the PWM pulse generator II are all phase-shifted by 180° relative to the pulse signals of the PWM pulse generator I; the pulse signals of the PWM pulse generator IV are all phase-shifted by 180° relative to the pulse signals of the PWM pulse generator III;

[0032] H. Repeat steps AG to complete the closed-loop control of the vehicle auxiliary power DC-DC converter.

[0033] Preferably, the Z c1 , Z c2 The range is 0-2.

[0034] The present invention adopts a Buck-Boost-LLC converter system with a unique structural layout, which realizes high-precision and wide-range voltage regulation compared with similar systems with the same power capacity; the scheme of the present invention can adopt an inductor with a smaller inductance, and the Buck conversion and the Boost conversion share the inductors L1, L2 and the capacitors C1, C2; the Buck converter and the Boost converter adopt a two-phase staggered parallel topology structure to form two parallel branches, and the current balance between the parallel branches is easy to achieve, with lower inductor current ripple, thereby reducing switching losses, and the current and voltage stress of each device is small, the power consumption of the entire converter system is low, the converter efficiency is improved, and the weight is reduced. The new control method can be integrated for all different operation modes, such as Buck, Boost, Buck-Boost, continuous conduction mode (CCM) at high power load and discontinuous conduction mode (DCM) at low power load, without switching between independent control strategies as in the traditional way, and there is no situation that the dynamic response of the converter may be deteriorated or even worsened due to switching; in addition, constant current-constant voltage charging of the auxiliary battery is realized, which is beneficial to prolong the service life of the auxiliary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic diagram of the circuit structure of an integrated vehicle-mounted auxiliary power supply DC-DC converter provided in Example 1 of the present invention;

[0036] Figure 2 A schematic diagram of an integrated vehicle auxiliary power supply DC-DC converter circuit provided in Example 1 of the present invention;

[0037] Figure 3 A schematic flow chart of a control method for a vehicle auxiliary power DC-DC converter provided in Embodiment 1 of the present invention;

[0038] Figure 4 This is a schematic diagram of a conventional single-stage vehicle-mounted auxiliary power supply DC-DC converter circuit provided in Comparative Example 1;

[0039] Figure 5 This is a schematic diagram of a conventional cascaded vehicle-mounted auxiliary power supply DC-DC converter circuit provided in Comparative Example 2. DETAILED DESCRIPTION

[0040] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0041] Example 1

[0042] like Figure 1-2As shown, the vehicle-mounted auxiliary power DC-DC converter provided in this embodiment includes an input capacitor C1, a Buck converter, a Boost converter, an output capacitor C2, and an LLC resonant converter;

[0043] The Buck converter and the Boost converter are respectively composed of two branches, and the two branches of the Buck converter are connected in series with the two branches of the Boost converter in a one-to-one correspondence to form two sets of parallel Buck-Boost branch structures;

[0044] The Buck-Boost branch structure is connected in parallel with the input capacitor C1 and then connected to the vehicle power battery. The Buck-Boost branch structure is connected in parallel with the output capacitor C2 and then connected to the input end of the LLC resonant converter.

[0045] The Buck converter includes a power switch tube D1, a power switch tube D2, a diode d1, a diode d2, an inductor L1, and an inductor L2; the collectors of the power switch tube D1 and the power switch tube D2 are both connected to the positive electrode of the input capacitor C1, and are connected to the positive electrode of the vehicle power battery as a terminal S1; the emitter of the power switch tube D1 and the negative electrode of the diode d1 are both connected to one end of the inductor L1; the emitter of the power switch tube D2 and the negative electrode of the diode d2 are both connected to one end of the inductor L2; the positive electrode of the diode d1 and the positive electrode of the diode d2 are both connected to the negative electrode of the input capacitor C1, and are connected to the negative electrode of the vehicle power battery as a terminal S2;

[0046] The Boost converter includes a power switch tube D3, a power switch tube D4, a diode d3, a diode d4, an inductor L1, and an inductor L2; the collector of the power switch tube D3 and the positive electrode of the diode d3 are both connected to the other end of the inductor L1; the collector of the power switch tube D4 and the positive electrode of the diode d4 are both connected to the other end of the inductor L2; the emitter of the power switch tube D3 and the emitter of the power switch tube D4 are both connected to the terminal S2, the cathodes of the diode d3 and the diode d4 are both connected to the positive electrode of the output capacitor C2, and the cathode of the output capacitor C2 is connected to the terminal S2, wherein the inductor L1 and the inductor L2 are shared with the Buck converter;

[0047] The LLC resonant converter includes a power switch tube D5, a power switch tube D6, a resonant inductor L3, a transformer T1, a resonant capacitor C3, a MOSFET tube M1, a MOSFET tube M2, and a filter capacitor C4; the collector of the power switch tube D5 is connected to the positive electrode of the capacitor C2, the emitter of the power switch tube D5 and the collector of the power switch tube D6 are both connected to one end of the resonant inductor L3; the emitter of the power switch tube D6 and one end of the resonant capacitor C3 are both connected to the terminal S2, and the primary end of the transformer T1 is connected to the resonant The other end of the inductor L3 is connected; the non-same-name end of the primary side of the transformer T1 is connected to the other end of the resonant capacitor C3; the same-name end of the secondary side of the transformer T1 is connected to the source of the MOSFET tube M1; the drain of the MOSFET tube M1 and the drain of the MOSFET tube M2 are both connected to the positive electrode of the filter capacitor C4 as the terminal O1; the secondary side middle tap f1 of the transformer T1 is connected to the negative electrode of the filter capacitor C4 as the terminal O2; the transformation ratio of the primary side of the transformer T1 and the two secondary sides separated by the secondary side middle tap f1 is n:1:1;

[0048] The terminal S1 is connected to the positive terminal of the power battery, and the terminal S2 is connected to the negative terminal of the power battery; the terminal O1 is used as the positive output terminal of the vehicle auxiliary power DC-DC converter; the terminal O2 is used as the negative output terminal of the vehicle auxiliary power DC-DC converter;

[0049] It also includes a controller, a PWM pulse generator I, a PWM pulse generator II, a PWM pulse generator III, a PWM pulse generator IV, a PWM pulse generator V and an inverter. The pulse output ends of the PWM pulse generator I, the PWM pulse generator II, the PWM pulse generator III, the PWM pulse generator IV, the PWM pulse generator V and the inverter are respectively connected to the gate g1 of the power switch tube D1, the gate g2 of the power switch tube D2, the gate g3 of the power switch tube D3, the gate g4 of the power switch tube, the gate g5 of the power switch tube, and the gate g6 of the power switch tube D6; the input ends of the PWM pulse generator I, the PWM pulse generator II, the PWM pulse generator III, the PWM pulse generator IV and the PWM pulse generator V are connected to the controller to receive the control signal sent by the controller; the input end of the inverter is connected to the pulse output end of the PWM pulse generator V.

[0050] like Figure 3 As shown, the control method of the vehicle auxiliary power DC-DC converter in this embodiment includes the following steps:

[0051] A. Collect the following analog parameters of the vehicle auxiliary power DC-DC converter through sensors: power battery voltage V in, the current I flowing through the inductor L1 L1 , the current I flowing through the inductor L2 L2 , LLC resonant converter input voltage V 1 , the output current I of the vehicle auxiliary power DC-DC converter O , the output voltage V of the vehicle auxiliary power DC-DC converter O ; Convert the above analog parameters through an A / D converter to obtain corresponding digital parameters as the input of step B;

[0052] B. SOC estimation and charging judgment: V O ,I O The SOC is estimated to obtain the state of charge of the on-board auxiliary battery, and the auxiliary battery charging judgment is performed on the on-board auxiliary battery state of charge. When the judgment result is that the on-board auxiliary power DC-DC converter does not charge the auxiliary battery, or supplies power to the automobile auxiliary electrical equipment in a constant voltage form, "0" is output as the input of step C; when the judgment result is that the on-board auxiliary power DC-DC converter charges the auxiliary battery, "1" is output to the constant voltage and constant current charging judgment unit, and the constant voltage and constant current charging judgment unit performs a judgment on V O ,I O Make a judgment, and when the judgment result is the constant voltage charging stage, output "0" as the input of step C; when the judgment result is the constant current charging stage, output "1" as the input of step C;

[0053] C. Outer loop control: preset reference output voltage V Oref , reference output current I Oref ; V O With V Oref Subtract to get the voltage deviation value V Δ , will I O with I Oref Subtract to get the voltage deviation value I Δ , judge according to the input of step C: when the input of step C is "1", then I Δ Perform constant current correction to obtain V 1 The reference voltage V 1ref ; When the input of step C is "0", when V Δ Perform constant voltage correction to obtain V 1 The reference voltage V 1ref ; V 1ref Enter step D;

[0054] D. Middle loop control: There is a voltage controller preset to set V 1 With V 1ref Subtract to get the voltage deviation value V Δ ′, V Δ′ Input voltage controller, output reference current I Lref ; will I Lref Enter step E;

[0055] E. Inner loop control: There are current controllers I and II preset, and I L1 with I Lref Subtract to get the current deviation value L Δ1 , will I L2 with I Lref Subtract to get the current deviation value L Δ2 , L Δ1 Input current controller I outputs the controlled duty cycle Z c1 , L Δ2 The input current controller II outputs the controlled duty cycle Z c2 , Z c1 , Z c2 Enter step F;

[0056] F. Duty cycle calculation:

[0057] The pulse duty ratios of the PWM pulse generator I, PWM pulse generator II, PWM pulse generator III, PWM pulse generator IV, PWM pulse generator V and the inverter output are Z 1 , Z 2 , Z 3 , Z 4 , Z 5 , Z 6 ;

[0058] By V 1ref 、V in Calculate the initial duty cycle Z 0 :

[0059]

[0060] When Z 0 When <1-Δ, it is in step-down mode, i.e. Buck mode;

[0061] Z 1 =Z c1 ; Z 2 =Z c2 ; Z 3 =Z 4 =0; Z 5 =Z 6 =0.5;

[0062] When Z 0 When >1+Δ, it is in boost mode, i.e. Boost mode;

[0063] Z 1 =Z2 =1; Z 3 =Z c1 -1; Z 4 =Z c2 -1; Z 5 =Z 6 =0.5;

[0064] When 1-Δ <Z 0 <1+Δ; in voltage regulation mode, i.e. Buck-Boost mode;

[0065]

[0066] Where Δ is a small positive number defined;

[0067] G. Output control: The pulse duty ratio of the outputs of PWM pulse generator I, PWM pulse generator II, PWM pulse generator III, PWM pulse generator IV, PWM pulse generator V and inverter is Z. 1 , Z 2 , Z 3 , Z 4 , Z 5 , Z 6 The pulse signals are respectively output to the gate g1 of the power switch tube D1, the gate g2 of the power switch tube D2, the gate g3 of the power switch tube D3, the gate g4 of the power switch tube, the gate g5 of the power switch tube, and the gate g6 of the power switch tube D6, so as to control the power switch tubes D1 to D6; in the above pulse signals, the pulse signals of the PWM pulse generator II are all phase-shifted by 180° relative to the pulse signals of the PWM pulse generator I; the pulse signals of the PWM pulse generator IV are all phase-shifted by 180° relative to the pulse signals of the PWM pulse generator III;

[0068] H. Repeat steps AG to complete the closed-loop control of the vehicle auxiliary power DC-DC converter;

[0069] The Z c1 , Z c2 The range is 0-2;

[0070] The above control process is implemented through microprocessor system programming, in which the "constant current given correction", "constant voltage given correction", "voltage controller", "current controller I" and "current controller II" can all be implemented using conventional PI control algorithms or other appropriate control algorithms.

[0071] Comparative Example 1

[0072] In order to further illustrate the present invention, a conventional single-stage vehicle auxiliary power DC-DC converter described in the prior art is provided. Figure 4 The present invention discloses a full-bridge phase-shifted LLC converter, comprising power switch tubes D9, D10, D11, D12, resonant inductor L4, transformer T2, resonant capacitor C4, diodes D5, D6, and filter capacitor C5. The converter has a simple topology, uses fewer components, and can utilize the resonance between the transformer leakage inductance and the parasitic capacitance of the power switch tube. All power switch tubes can achieve ZVS without any auxiliary circuit, and their voltage stress is clamped to the input voltage, so they are widely used in small and medium power occasions. However, it also has the following two major shortcomings: (1) It cannot fully meet the requirements of a wide input voltage range. If its input voltage range is to be increased, the transformer excitation inductance of the converter needs to be designed to be small enough, but this will increase the resonant current, and the conduction loss and hysteresis loss will increase accordingly, which will reduce the efficiency of the converter. (2) As the load decreases, the ZVS range of the lagging bridge arm power switch tube of the converter becomes narrower, and the converter efficiency decreases. Although the ZVS range of the lagging bridge arm switch can be expanded by increasing the transformer leakage inductance of the converter, the trigger pulse duty cycle is easily lost and the primary side conduction loss increases; or the ZVS range can be expanded by reducing the transformer excitation inductance, but the primary side current effective value stress and conduction loss are increased, and the output inductance is also relatively large.

[0073] Comparative Example 2

[0074] In order to overcome the main problems described in Comparative Example 1, a cascade converter can be used, that is, a front-stage DC / DC converter plus an LLC resonant converter. The output voltage of the front-stage DC-DC converter is stable, so that the LLC resonant converter has a fixed input voltage, which is easy to select and design its component parameters, and improves the efficiency of the entire converter system. Figure 5 A conventional cascade vehicle auxiliary power DC-DC converter recorded in the prior art is provided, including a Buck-Boost converter and a half-bridge LLC resonant converter. The Buck-Boost converter is formed by connecting power switch tubes D13, D14, D15, D16, an inductor L5, and a capacitor C7; the half-bridge LLC resonant converter has the same topology as the LLC resonant converter in the embodiment of the present invention, and both adopt a half-bridge form (D17 and D18, D5 and D6). Compared with comparative example 1, since the front-stage DC-DC converter (Buck-Boost converter) has the functions of bucking and boosting, and outputs a relatively stable voltage, the voltage stress of the power switch tube of the LLC resonant converter is reduced, so a half-bridge form can be adopted to reduce the number of power switch tubes, and the embodiment 1 of the present invention uses power switch tubes M1 and M2 instead of rectifier diodes d7 and d8, which is more conducive to the low-voltage and high-current working state of the output side of the converter, and can work in a synchronous rectification state to reduce its conduction loss.

[0075] Embodiment 1 of the present invention and Figure 5 Compared with the comparative example 2 system shown, the main differences are: the front-stage Buck-Boost converter of embodiment 1 of the present invention adopts a two-phase staggered parallel topology structure, the voltage level and power capacity requirements of the power switch tube of each parallel branch are lowered, it is easy to achieve current balance, and has a lower inductor current ripple, thereby reducing switching losses; the power switch tube can have a higher switching frequency, so that the entire converter system has a higher power density; the input current is shared by two staggered parallel inductors, and the inductor storage energy is only half of that of comparative example 2, thereby effectively reducing the volume of the inductor; each power switch tube can easily achieve zero voltage switching (ZVS) within the full input voltage and full load range, further reducing the power switch tube loss and improving the converter efficiency and reliability.

[0076] Furthermore, compared with comparative example 2, embodiment 1 of the present invention adopts a unique integrated digital control method, which can be integrated for all different operating modes (such as Buck, Boost, Buck-Boost, continuous conduction mode (CCM) at high power loads and discontinuous conduction mode (DCM) at low power loads), without the need to switch between independent control strategies as in the traditional way, and there is no situation where the dynamic response of the converter may deteriorate or even worsen due to switching; in addition, constant current-constant voltage charging of the auxiliary battery is achieved, which is beneficial to extending the service life of the auxiliary battery; from the control strategy, the two parallel branches are further balanced in current, and the inductor current ripple is even smaller.

[0077] In summary, the solution of Example 1 of the present application is significantly more advanced than the existing technical solutions.

Claims

1. A control method for a vehicle-mounted auxiliary power DC-DC converter, using the vehicle-mounted auxiliary power DC-DC converter described below: The vehicle auxiliary power DC-DC converter includes input capacitor C1, Buck converter, Boost converter, output capacitor C2, and LLC resonant converter; The Buck converter and the Boost converter are respectively composed of two branches, and the two branches of the Buck converter are connected in series with the two branches of the Boost converter in a one-to-one correspondence to form two sets of parallel Buck-Boost branch structures; The Buck-Boost branch structure is connected in parallel with the input capacitor C1 and then connected to the vehicle power battery. The Buck-Boost branch structure is connected in parallel with the output capacitor C2 and then connected to the input end of the LLC resonant converter. The Buck converter includes a power switch tube D1, a power switch tube D2, a diode d1, a diode d2, an inductor L1, and an inductor L2; the collectors of the power switch tube D1 and the power switch tube D2 are both connected to the positive electrode of the input capacitor C1, and are connected to the positive electrode of the vehicle power battery as a terminal S1; the emitter of the power switch tube D1 and the negative electrode of the diode d1 are both connected to one end of the inductor L1; the emitter of the power switch tube D2 and the negative electrode of the diode d2 are both connected to one end of the inductor L2; the positive electrode of the diode d1 and the positive electrode of the diode d2 are both connected to the negative electrode of the input capacitor C1, and are connected to the negative electrode of the vehicle power battery as a terminal S2; The Boost converter includes a power switch tube D3, a power switch tube D4, a diode d3, a diode d4, an inductor L1, and an inductor L2; the collector of the power switch tube D3 and the positive electrode of the diode d3 are both connected to the other end of the inductor L1; the collector of the power switch tube D4 and the positive electrode of the diode d4 are both connected to the other end of the inductor L2; the emitter of the power switch tube D3 and the emitter of the power switch tube D4 are both connected to the terminal S2, the cathodes of the diode d3 and the diode d4 are both connected to the positive electrode of the output capacitor C2, and the cathode of the output capacitor C2 is connected to the terminal S2; wherein the inductor L1 and the inductor L2 are shared with the Buck converter; The LLC resonant converter includes a power switch tube D5, a power switch tube D6, a resonant inductor L3, a transformer T1, a resonant capacitor C3, a MOSFET tube M1, a MOSFET tube M2, and a filter capacitor C4; the collector of the power switch tube D5 is connected to the positive electrode of the capacitor C2, the emitter of the power switch tube D5 and the collector of the power switch tube D6 are both connected to one end of the resonant inductor L3; the emitter of the power switch tube D6 and one end of the resonant capacitor C3 are both connected to the terminal S2, and the primary end of the transformer T1 is connected to the resonant The other end of the inductor L3 is connected; the non-same-name end of the primary side of the transformer T1 is connected to the other end of the resonant capacitor C3; the same-name end of the secondary side of the transformer T1 is connected to the source of the MOSFET tube M1; the drain of the MOSFET tube M1 and the drain of the MOSFET tube M2 are both connected to the positive electrode of the filter capacitor C4 as the terminal O1; the secondary side middle tap f1 of the transformer T1 is connected to the negative electrode of the filter capacitor C4 as the terminal O2; the transformation ratio of the primary side of the transformer T1 and the two secondary sides separated by the secondary side middle tap f1 is n:1:1; The terminal S1 is connected to the positive terminal of the power battery, and the terminal S2 is connected to the negative terminal of the power battery; the terminal O1 is used as the positive output terminal of the vehicle auxiliary power DC-DC converter; the terminal O2 is used as the negative output terminal of the vehicle auxiliary power DC-DC converter; It also includes a controller, a PWM pulse generator I, a PWM pulse generator II, a PWM pulse generator III, a PWM pulse generator IV, a PWM pulse generator V and an inverter. The pulse output ends of the PWM pulse generator I, the PWM pulse generator II, the PWM pulse generator III, the PWM pulse generator IV, the PWM pulse generator V and the inverter are respectively connected to the gate g1 of the power switch tube D1, the gate g2 of the power switch tube D2, the gate g3 of the power switch tube D3, the gate g4 of the power switch tube, the gate g5 of the power switch tube, and the gate g6 of the power switch tube D6; the input ends of the PWM pulse generator I, the PWM pulse generator II, the PWM pulse generator III, the PWM pulse generator IV and the PWM pulse generator V are connected to the controller to receive the control signal sent by the controller; the input end of the inverter is connected to the pulse output end of the PWM pulse generator V; Features The following steps are involved: A. Collect the following analog parameters of the vehicle auxiliary power DC-DC converter through sensors: power battery voltage V in , the current I flowing through the inductor L1 L1 , the current I flowing through the inductor L2 L2 , LLC resonant converter input voltage V1, vehicle auxiliary power DC-DC converter output current I O , the output voltage V of the vehicle auxiliary power DC-DC converter O ; Convert the above analog parameters through an A / D converter to obtain corresponding digital parameters as the input of step B; B. SOC estimation and charging judgment: V O ,I O The SOC is estimated to obtain the state of charge of the vehicle auxiliary battery, and the auxiliary battery charging judgment is performed on the state of charge of the vehicle auxiliary battery. When the judgment result is that the vehicle auxiliary power DC-DC converter does not charge the auxiliary battery, or supplies power to the vehicle auxiliary electrical equipment in a constant voltage form, "0" is output as the input of step C; when the judgment result is that the vehicle auxiliary power DC-DC converter charges the auxiliary battery, "1" is output to the constant voltage and constant current charging judgment unit, and the constant voltage and constant current charging judgment unit performs a judgment on V O ,I O Make a judgment, and when the judgment result is the constant voltage charging stage, output "0" as the input of step C; when the judgment result is the constant current charging stage, output "1" as the input of step C; C. Outer loop control: preset reference output voltage V Oref , reference output current I Oref ; V O With V Oref Subtract to get the voltage deviation value V Δ , will I O with I Oref Subtract to get the voltage deviation value I Δ , judge according to the input of step C: when the input of step C is "1", then I Δ Perform constant current setting correction to obtain the reference voltage V of V1 1ref ; When the input of step C is "0", when V Δ Perform constant voltage correction to obtain the reference voltage V of V1 1ref ; V 1ref Enter step D; D. Middle loop control: There is a voltage controller preset to connect V1 and V 1ref Subtract to get the voltage deviation value V Δ ′, V Δ ′ Input voltage controller, output reference current I Lref ; will I Lref Enter step E; E. Inner loop control: There are current controllers I and II preset, and I L1 with I Lref Subtract to get the current deviation value L Δ1 , will I L2 with I Lref Subtract to get the current deviation value L Δ2 , L Δ1 Input current controller I outputs the controlled duty cycle Z c1 , L Δ2 The input current controller II outputs the controlled duty cycle Z c2 , Z c1 , Z c2 Enter step F; F. Duty cycle calculation: The pulse duty ratios of the outputs of PWM pulse generator I, PWM pulse generator II, PWM pulse generator III, PWM pulse generator IV, PWM pulse generator V and the inverter are Z1, Z2, Z3, Z4, Z5 and Z6 respectively; By V 1ref 、V in Calculate the initial duty cycle Z0: When Z0<1-Δ: Z1=Z c1 ;Z2=Z c2 ;Z3=Z4=0;Z5=Z6=0.5; When Z0>1+Δ: Z1=Z2=1;Z3=Z c1 -1;Z4=Z c2 -1;Z5=Z6=0.5; When 1-Δ<Z0<1+Δ: Where Δ is a small positive number defined; G. Output control: PWM pulse generator I, PWM pulse generator II, PWM pulse generator III, PWM pulse generator IV, PWM pulse generator V and inverter respectively output pulse signals with pulse duty ratios of Z1, Z2, Z3, Z4, Z5 and Z6, and output the above pulse signals to gate g1 of power switch tube D1, gate g2 of power switch tube D2, gate g3 of power switch tube D3, gate g4 of power switch tube, gate g5 of power switch tube and gate g6 of power switch tube D6, so as to control power switch tubes D1 to D6; among the above pulse signals, the pulse signals of PWM pulse generator II are all phase-shifted by 180° relative to the pulse signals of PWM pulse generator I; the pulse signals of PWM pulse generator IV are all phase-shifted by 180° relative to the pulse signals of PWM pulse generator III; H. Repeat steps AG to complete the closed-loop control of the vehicle auxiliary power DC-DC converter.

2. The control method of the vehicle auxiliary power DC-DC converter according to claim 1, characterized in that: The Z c1 , Z c2 The range is 0-2.

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