A soft start and light load control method and device for a dual active full-bridge DC-DC converter

Abstract

The present invention discloses a soft start and light load control method and device for a dual active full bridge DC-DC converter. The converter includes a plurality of switch tubes of a primary bridge and a plurality of switch tubes of a secondary bridge, including: step 1, in the first PWM cycle, setting the switch tube conduction duty cycle D to 0.5, the primary bridge inward shift phase D1 to 1, the primary bridge and the secondary bridge outward shift phase D2 to 0, and the secondary bridge inward shift phase D3 to 1; step 2, obtaining the difference between the output reference voltage and the output voltage, and obtaining the output duty cycle D through proportional integral regulation processing. P ; Step 3, according to the output duty cycle D P Determine different modes; Step 4, generate control pulses of the primary bridge and the secondary bridge switch tubes according to the output duty cycle; Step 5, if no shutdown command is received or a fault occurs, return to Step 2. The present invention flexibly selects the working mode according to the range of PI adjustment output, and realizes the soft start of the DAB circuit and voltage stability in the full load range.

Description

Technical Field

[0001] The invention relates to a high-frequency switching power supply in the field of power electronics, and in particular to a soft-start and light-load control method and device for a dual-active full-bridge DC-DC converter. Background Art

[0002] The use of an isolated DC-DC converter (Dual Active Bridge, DAB) topology can achieve energy transmission between different voltage levels. As a high-efficiency DC converter, the dual active full-bridge DC-DC converter has the advantages of high power density, wide input and output voltage range, symmetrical structure, and low voltage and current stress of switching devices. It is used in various medium and high power occasions in DC microgrid systems and energy storage systems. The dual active full-bridge DC-DC converter has three controllable variables. According to the combination of these three variables, there are generally three types of control methods: traditional single phase shift control, double phase shift control, and triple phase shift control.

[0003] Traditional single phase shift control or simply single phase shift control is the simplest control method. The H-bridge switching devices on the primary and secondary sides of the transformer are turned on at a 50% duty cycle, and the transmission power size and direction are adjusted by controlling the phase shift angle between the two H-bridges. This control strategy is simple and has a fast dynamic response, but there is a large reflux power and the converter efficiency is low.

[0004] At this time, the two bridge power conversion units on both sides of the transformer are turned on at a 50% duty cycle, and the size and direction of the transmission power are adjusted by controlling the phase shift angle between the two bridge power conversion units. This control method is simple to operate and is easy to achieve soft switching under heavy load operation, which is beneficial to reduce switching losses and improve the switching frequency and overall efficiency of the converter; but when the input and output voltages do not match, it is difficult for the converter to achieve soft switching under light load operation, the loop current in the converter is high, there is circulating energy, the circulating loss increases, and the converter efficiency decreases.

[0005] Based on the traditional single-phase shift control, the double-phase shift control adds the internal phase shift angle of the H-bridge on the high-voltage side or the low-voltage side on the basis of the single-phase shift control. Compared with the single-phase shift control, it adds a degree of freedom, which can effectively reduce the effective value of the inductor current and reduce the converter's reflux power.

[0006] Compared with the traditional single-phase shift control, this method adds a degree of freedom, and therefore adds an optimization target, which can effectively reduce the effective value of the inductor current and reduce the converter's reflux power. However, this control method cannot achieve soft switching within the full load range, resulting in increased circulating current losses, and the control system is difficult to implement, there is asymmetry, and the system dynamic performance is poor.

[0007] Triple phase-shift control is to control three controllable variables at the same time. In addition to controlling the phase-shift angle between the two bridge power conversion units to adjust the size and direction of the transmission power, there are two other controllable variables to achieve two optimization goals. This control method can better reduce the peak value, effective value and circulating power of the converter's inductor current, and has obvious advantages in improving system efficiency. However, this control method cannot achieve soft switching in the full load range, resulting in increased circulating loss, and the converter has more working modes under this control method, and the corresponding control system is more complex.

[0008] The triple phase-shift control increases the phase-shift angle in the H-bridges on both sides at the same time, achieving more precise control and better reducing the peak value, effective value and circulating power of the converter's inductor current, which has obvious advantages in improving system efficiency.

[0009] In order to improve the working efficiency of the converter under light load, there is also a method for improving the circuit topology of the dual active full-bridge DC-DC converter.

[0010] Currently, the focus of DAB converters is on optimizing the converter conversion efficiency and dynamic characteristics. Multiple phase-shift control and soft switching are means to improve conversion efficiency, while the dynamic characteristics focus particularly on the current shock problem during the startup process.

[0011] Among them, the internal phase shift ratio of double phase shift and triple phase shift control must be calculated in real time according to the load conditions to reduce the DAB circulating current power and improve the efficiency of the converter, which has also become the focus of DAB research.

[0012] At the same time, the soft switching implementation of DAB circuit is another research hotspot. Under ideal conditions, when the DAB circuit is in a matching state and single-phase shift control is adopted, all switches work in ZVS turn-on and hard turn-off states, and all diodes work in hard turn-on and ZCS turn-off states.

[0013] In fact, multiple phase shift control and the polarity reversal of the H-bridge output voltage caused by the dead zone effect may destroy the soft switching characteristics of the DAB circuit. Therefore, it is necessary to optimize the control strategy or improve the circuit.

[0014] Although the single-phase, double-phase and triple-phase control strategies can stabilize the DAB output voltage in most load ranges, there is still much room for improvement in the startup process and light-load conditions.

[0015] The output end of the DAB circuit is usually connected to a filter capacitor. During startup transient, the output capacitor will be considered as a short circuit, resulting in a large startup transient surge current. In high-voltage and high-power situations, this surge current will be more prominent.

[0016] In an invention application with publication number CN108880264A, the applicant is Hefei University of Technology, "Control method of dual active bridge DC converter with soft start function", a soft start control strategy is proposed, which realizes the slow rise of the equivalent input voltage of the DAB circuit and reduces the starting impact current by linearly increasing the on-duty ratio D of the primary and secondary H bridges at the same time. However, the disadvantages of this method are as follows: 1) The minimum on-duty ratio of the IGBT leads to the minimum output voltage of the primary H bridge, and this method cannot achieve true zero impact current starting; 2) The control strategy ignores the influence of the dead zone effect; 3) The control strategy is clearly divided into two stages, and the switching smoothness between the stages is not enough.

[0017] The mathematical model of phase-shift control usually does not take the dead zone of the switch tube into consideration. When the dead zone of the switch tube is large, the mathematical model will have deviations.

[0018] Assume that the DAB circuit dead time is: MT hs

[0019] Among them, T hs is half a switching period, and M is the equivalent duty cycle of the dead time in half a switching period.

[0020] Under ideal conditions:

[0021] M=0 (1)

[0022] The transmission power P of single phase shift control is the phase shift duty ratio D2 (or phase shift time D2T) between H bridges. hs ) is as shown in Eq.

[0023]

[0024] Please combine Figure 1 The transmission power curve is shown in FIG. 1 , where the ordinate p is the per-unit value of the transmission power P, and the abscissa D2 is the phase shift duty cycle.

[0025] Under ideal conditions, M=0, and the per-unit value p of the transmission power takes the maximum value 1 when the phase shift duty ratio D2=0.5; when the phase shift duty ratio D2=0, the transmission power is 0.

[0026] After considering the dead zone effect, the power transmission mathematical model has a large deviation and phase drift occurs. When the phase shift between the two H bridges is 0, there is still power transmission, and p changes with M, such as Figure 1 As shown by the dotted line in .

[0027] Figure 1 This is the relationship curve among transmission power, external phase shift ratio D2 and dead time proportion M when the DAB circuit adopts single phase shift control.

[0028] In the figure, p is the per-unit value of the transmission power P. Under ideal conditions, dead time does not exist, M = 0, and p takes the maximum value of 1 when D2 = 0.5; when D2 = 0, the transmission power is 0, and the entire power transmission curve is symmetrical about D2 = 0.5.

[0029] After considering the dead zone effect, the power transmission mathematical model has a large deviation, and phase drift occurs. When the two H bridges are shifted outward compared to D2 being 0, there is still power transmission (corresponding to Figure 1 When D2 = 0, p is not equal to 0), and p changes with M, such as Figure 1 As shown by the dotted line in . As a result, the output voltage of the DAB circuit is too high when it is lightly loaded, and voltage regulation control cannot be performed. Summary of the invention

[0030] It is to be understood that both the foregoing general description and the following detailed description of the present disclosure are exemplary and explanatory and are intended to provide further explanation of the disclosure as claimed.

[0031] In view of the above problems, the present invention provides a soft start and light load control method of a dual active full-bridge DC-DC converter, wherein the converter includes a plurality of switch tubes of a primary bridge and a plurality of switch tubes of a secondary bridge, and is characterized in that the method includes:

[0032] Step 1: In the first PWM cycle, the output voltage of the primary and secondary bridges of the converter in the startup state is set to zero;

[0033] Step 2: Obtain the output duty cycle D based on the difference between the output reference voltage and the output voltage P ;

[0034] Step 3: According to the output duty cycle D P Identify different patterns;

[0035] Step 4, generating control pulses of the primary bridge and the secondary bridge switch tubes according to the output duty cycle;

[0036] Step 5: If no shutdown command is received or a fault occurs, return to step 2.

[0037] Preferably, the present invention further discloses a soft start and light load control method for a dual active full bridge DC-DC converter, characterized in that:

[0038] In step 2, the output duty cycle D is obtained by using proportional integral regulation. P , if the output duty cycle D P satisfy:

[0039] 0 <D P <1

[0040] The working condition of the converter is light load mode, the switch tube conduction duty cycle D is set to 0.5, and the primary side bridge inward shift phase D1=1-D P , the outward displacement ratio between the primary side bridge and the secondary side bridge is D2=0, and the inward displacement ratio of the secondary side bridge is D3=1-D P .

[0041] Preferably, the present invention further discloses a soft start and light load control method for a dual active full bridge DC-DC converter, characterized in that in the step 2, a proportional integral regulation process is used to obtain an output duty cycle D P , if the output duty cycle D P satisfy:

[0042] 1 <D P <1.5

[0043] The working condition of the converter is normal mode, the switch tube conduction duty cycle D is set to 0.5, and the external shift ratio between the primary bridge and the secondary bridge is D2=D P -1, the output voltage is stabilized by adjusting the outward shift ratio D2 between the primary bridge and the secondary bridge.

[0044] Preferably, the present invention further discloses a soft start and light load control method for a dual active full bridge DC-DC converter, characterized in that the step 1 further comprises:

[0045] The switch tube conduction duty cycle D is 0.5, the inward shift phase ratio D1 of the primary bridge is 1, the outward shift phase ratio D2 between the primary bridge and the secondary bridge is 0, the inward shift phase ratio D3 of the secondary bridge is 1, and the output voltage of the primary bridge is fixed at 0; therefore, the output voltage of the secondary bridge is 0, achieving zero output voltage startup.

[0046] Preferably, the present invention further discloses a soft start and light load control method for a dual active full-bridge DC-DC converter, characterized in that the step before step 5 further includes waiting for the next PWM interrupt moment to be triggered.

[0047] Preferably, the present invention further discloses a soft start and light load control method for a dual active full bridge DC-DC converter, characterized in that the output duty cycle D P The output limit is 0~1.5.

[0048] Preferably, the present invention further discloses a soft start and light load control method of a dual active full bridge DC-DC converter, characterized in that, in the normal mode, the converter operates in any one of single phase shift control, extended phase shift control, double phase shift control and triple phase shift control.

[0049] Preferably, the present invention further discloses a soft start and light load control method for a dual active full bridge DC-DC converter, characterized in that the primary side bridge internal shift phase D1=D OPT1 , the secondary bridge moves inward compared to D3 = D OPT3 , where D OPT1 and D OPT3 Compared with the optimized inward shift of the primary and secondary side bridges.

[0050] The present invention also discloses a soft start and light load control device for a dual active full bridge DC-DC converter, wherein the converter comprises a plurality of switch tubes of a primary bridge and a plurality of switch tubes of a secondary bridge, and is characterized in that the device comprises:

[0051] A setting unit, in the first PWM cycle, sets the output voltage of the primary and secondary bridges of the converter to zero in the startup state;

[0052] The output voltage adjustment unit obtains the output duty cycle D according to the difference between the output reference voltage and the output voltage. P , according to the output duty cycle D P Identify different patterns;

[0053] A PWM generating unit, generating control pulses of the primary bridge and the secondary bridge switch tubes of the converter according to the output duty cycle;

[0054] The timing control and protection unit waits for the next PWM interrupt to be triggered, and switches to the output voltage regulation unit when no shutdown command is received or a fault occurs.

[0055] Preferably, the present invention further discloses a soft start and light load control device for a dual active full-bridge DC-DC converter, characterized in that:

[0056] The output voltage regulating unit includes a proportional integral regulating unit. P When satisfied:

[0057] 0 <D P <1

[0058] The converter light load mode is selected, the switch conduction duty cycle D is set to 0.5, and the primary bridge inward shift phase D1 = 1-D P , the outward displacement ratio between the primary side bridge and the secondary side bridge is D2=0, and the inward displacement ratio of the secondary side bridge is D3=1-D P .

[0059] Preferably, the present invention further discloses a soft start and light load control device for a dual active full-bridge DC-DC converter, characterized in that:

[0060] The output voltage regulating unit includes a proportional integral regulating unit. P When satisfied:

[0061] 1 <D P <1.5

[0062] The converter is selected as the normal mode, the switch tube conduction duty cycle D is set to 0.5, and the shift ratio between the primary bridge and the secondary bridge is D2=D P -1, the output voltage is stabilized by adjusting the outward shift ratio D2 between the primary bridge and the secondary bridge.

[0063] Preferably, the present invention further discloses a soft start and light load control device for a dual active full-bridge DC-DC converter, characterized in that:

[0064] The setting unit makes the switch tube conduction duty cycle D be 0.5, the primary bridge inward shift phase D1 be 1, the primary bridge and secondary bridge outward shift phase D2 be 0, the secondary bridge inward shift phase D3 be 1, and the primary bridge output voltage is fixed to 0; therefore, the secondary bridge output voltage is 0, achieving zero output voltage startup.

[0065] Preferably, the present invention further discloses a soft start and light load control device for a dual active full-bridge DC-DC converter, characterized in that:

[0066] The output duty cycle D of the proportional-integral regulation control unit P The output limit is 0~1.5.

[0067] Preferably, the present invention further discloses a soft start and light load control device for a dual active full-bridge DC-DC converter, characterized in that:

[0068] In the normal mode, the converter operates in any one of single phase shift control, extended phase shift control, double phase shift control and triple phase shift control.

[0069] Preferably, the present invention further discloses a soft start and light load control device for a dual active full-bridge DC-DC converter, characterized in that:

[0070] The original side bridge is moved inwards by D1=D OPT1 , the secondary bridge moves inward compared to D3 = D OPT3 , where D OPT1 and D OPT3 Compared with the optimized inward shift of the primary and secondary side bridges.

[0071] The present invention adopts a PI regulated output voltage stabilization, flexibly selects the working mode according to the range of the PI regulated output, and realizes the soft start of the DAB circuit and the voltage stability in the full load range. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. Reference will now be made in detail to preferred embodiments of the present disclosure, examples of which are shown in the accompanying drawings. Wherever possible, the same reference numerals will be used in all drawings to represent the same or similar parts. In addition, although the terms used in the present disclosure are selected from well-known and commonly used terms, some of the terms mentioned in the present disclosure may be selected by the applicant at his or her discretion, and their detailed meanings are explained in the relevant parts of the description herein. In addition, it is required to understand the present disclosure not only by the actual terms used, but also by the meaning implied by each term.

[0073] The above and other objects, features and advantages of the present invention will become apparent to those skilled in the art from the detailed description of the present invention with reference to the accompanying drawings below.

[0074] Figure 1 The relationship curve between the transmission power, the external phase shift ratio D2 and the dead time ratio M when the DAB circuit adopts single phase shift control;

[0075] FIG. 2( a ) is a schematic diagram of a topology of a dual active full-bridge DC-DC converter according to an embodiment of the present invention;

[0076] FIG2( b ) is an equivalent circuit diagram of FIG2( a );

[0077] FIG3( a ) shows a voltage stabilization control block diagram of the control method of the present invention;

[0078] FIG3( b ) shows the control flow chart of the application of FIG3( a );

[0079] Figure 4 A schematic diagram of the relationship between the light load mode drive and the output voltage waveform is given;

[0080] Figure 5 A schematic diagram of a soft-start waveform of a DAB converter using the method of the present invention;

[0081] Figure 6 It is a block diagram of the control device of the present invention.

[0082] Reference numerals

[0083] 61 - Setting unit

[0084] 62 - Output voltage adjustment unit 63 - PWM generation unit

[0085] 64 - Timing control and protection unit DETAILED DESCRIPTION

[0086] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are only some examples or embodiments of the present application. For ordinary technicians in this field, the present application can also be applied to other similar scenarios based on these drawings without creative work. Unless it is obvious from the language environment or otherwise explained, the same reference numerals in the figures represent the same structure or operation.

[0087] As shown in this application and claims, unless the context clearly indicates an exception, the words "a", "an", "an" and / or "the" do not refer to the singular and may also include the plural. Generally speaking, the terms "include" and "comprise" only indicate the inclusion of the steps and elements that have been clearly identified, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements.

[0088] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps set forth in these embodiments do not limit the scope of the present application. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to those of ordinary skill in the relevant field may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be considered as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so that once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0089] In the description of the present application, it should be understood that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction, and therefore cannot be understood as limiting the scope of protection of the present application; the directional words "inside and outside" refer to the inside and outside relative to the contours of each component itself.

[0090] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0091] In addition, it should be noted that the use of words such as "first" and "second" to define components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above words have no special meaning and cannot be understood as limiting the scope of protection of this application. In addition, although the terms used in this application are selected from well-known and commonly used terms, some terms mentioned in the specification of this application may be selected by the applicant at his or her discretion, and their detailed meanings are explained in the relevant parts of the description of this article. In addition, it is required to understand this application not only by the actual terms used, but also by the meaning implied by each term.

[0092] Flowcharts are used in the present application to illustrate the operations performed by the system according to the embodiments of the present application. It should be understood that the preceding or following operations are not necessarily performed accurately in order. On the contrary, various steps may be processed in reverse order or simultaneously. At the same time, other operations may be added to these processes, or one or more operations may be removed from these processes.

[0093] Please refer to FIG. 2( a ), which is a topological diagram of a dual active full-bridge DC-DC converter according to an embodiment of the present invention.

[0094] The dual active bridge DC converter involved in the control method of the present invention comprises an input voltage V1, an input capacitor C in , a primary side H1 bridge, a phase shift inductor L r , a high-frequency isolation transformer T, a secondary side H2 bridge, an output capacitor C o and an output voltage V2.

[0095] The primary side H1 bridge includes four switch tubes, which are denoted as switch tubes Si (i=1, 2, 3, 4), and the secondary side H2 bridge includes four switch tubes, which are denoted as switch tubes Si (i=5, 6, 7, 8).

[0096] Among the four switch tubes Si (i=1, 2, 3, 4) of the primary side H1 bridge, the switch tube S1 is connected in series with the switch tube S2, and the switch tube S3 is connected in series with the switch tube S4 to respectively constitute two bridge arms of the primary side H1 bridge, and the two bridge arms are connected in parallel as the DC end of the primary side H1 bridge; the series connection point of the switch tube S1 and the switch tube S2 is led out as the AC port A of the primary side H1 bridge, and the series connection point of the switch tube S3 and the switch tube S4 is led out as the AC output port B of the primary side H1 bridge.

[0097] Among the four switch tubes Si (i=5, 6, 7, 8) of the secondary side H2 bridge, the switch tube S5 is connected in series with the switch tube S6, and the switch tube S7 is connected in series with the switch tube S8 to respectively constitute two bridge arms of the secondary side H bridge, and the two bridge arms are connected in parallel as the DC end of the secondary side H2 bridge; the series connection point of the switch tube S5 and the switch tube S6 leads to the AC port C of the secondary side H2 bridge, and the series connection point of the switch tube S7 and the switch tube S8 leads to the AC port D of the secondary side H2 bridge.

[0098] The input voltage V1 is connected in parallel with the input capacitor Cin and then connected in parallel with the DC end of the primary H1 bridge. The AC port A of the primary H1 bridge is connected to one end of the phase-shifting inductor Lr, and the other end of the phase-shifting inductor Lr is connected to the same-name terminal E of the primary side of the high-frequency isolation transformer T, and the opposite-name terminal G of the primary side of the high-frequency isolation transformer T is connected to the AC port B of the primary H1 bridge (Note: Lr is often the leakage inductance of the transformer T); the same-name terminal e of the secondary side of the high-frequency isolation transformer T is connected to the AC port C of the secondary side H2 bridge, and the opposite-name terminal g of the secondary side of the high-frequency isolation transformer T is connected to the AC port D of the secondary side H2 bridge. The output voltage V2 is connected in parallel with the output capacitor Co and then connected to the DC end of the secondary side H2 bridge. The transformation ratio of the high-frequency isolation transformer T is n, n is a positive number, and the current of the inductor L is defined as the inductor current i Lr , the direction of current flowing from the AC port A of the primary H bridge to the inductor Lr is positive.

[0099] According to the working principle of the converter, k is defined as the voltage regulation ratio, where:

[0100] k=V1 / nV2 (1)

[0101] Define the converter switching frequency as f s , the switching period is T s , the half switching period is T hs .

[0102] The switch tube S1~S8 conduction duty cycle is D (or conduction time DT s), the internal phase shift of the primary side H1 bridge (i.e. the full bridge circuit on the input voltage V1 side) is D1 (or the phase shift time D1T hs ), the internal phase shift of the secondary side H2 bridge (i.e. the full bridge circuit on the output voltage V2 side) is D3 (or the phase shift time D3T hs ), the phase shift between the primary side H bridge 1 and the secondary side H2 bridge is D2 (or the phase shift time D2T hs ).

[0103] For the convenience of analysis, the magnetizing inductance of the transformer is ignored and the secondary side of the transformer is folded to the primary side. Then the bidirectional full-bridge DC-DC converter shown in Figure 2(a) can be simplified to the equivalent circuit model shown in Figure 2(b).

[0104] Among them, V H1 With V H2 is the equivalent output voltage of the primary and secondary bridges H1 and H2. The bidirectional transmission and storage of energy in the dual active full-bridge DC-DC converter, i.e., the DAB circuit, mainly depends on the equivalent inductance L r .

[0105] Applied to the inductor L r The voltage on is as follows:

[0106] v Lr =v H1 -v H2 (2)

[0107] From the above formula, we can see that the reasons for excessive starting impact current and the failure to stabilize voltage under light load are very similar, both are V H1 Output is too large.

[0108] When the DAB circuit is started, the output voltage V2 is 0, and the equivalent output voltage V H2 is also 0; if the primary equivalent output voltage V H1 The initial output value is large and is applied to the inductor L r The voltage on the output is high; the output terminal is connected to a capacitive load, and the output voltage V2 rises slowly, causing the inductor current i Lr Increase rapidly, causing current shock.

[0109] When the DAB circuit uses single phase shift control with light load, it is assumed that the switch tube conduction duty cycle D is 0.5 and the H-bridge phase shift ratio D2 is also 0.

[0110] Under ideal conditions:

[0111] V H1 =V H2 (3)

[0112] At this time, there is no power transmission on both sides; however, the existence of the dead zone causes the primary side equivalent output voltage V H1The adjustment range is limited, and the primary side H1 bridge has a minimum output voltage (V H1 )min, the output corresponding to the output voltage V2 also has a minimum voltage (V2) min .

[0113] FIG3( a ) illustrates a soft start and light load control method of a DAB provided in an embodiment of the present application.

[0114] The complete flow chart of the controller of the present application is shown in FIG3( b ), and the content shown in FIG3( a ) is simplified to the PI voltage regulator controller link of FIG3( b ).

[0115] FIG3( a ) is a schematic diagram showing a PI controller for regulating the output voltage V2 .

[0116] Among them, V2 * is the reference value of the output voltage V2, the output reference voltage V2 * Start from 0 and ramp up to the final target value V2 ** ,Right now:

[0117]

[0118] In the above formula, T R is the ramp-up time, and the PI controller transfer function is as follows:

[0119]

[0120] Among them, K P , K I are the proportional and integral coefficients respectively.

[0121] According to Figure 3(a), the output reference voltage V2 * The difference between the output voltage V2 and the output voltage V2 is the feedback error. Through the PI voltage regulation process, the output duty cycle D is obtained. P This application is based on the duty cycle D P Take control.

[0122] PI controller output duty cycle D P The output is limited to 0~1.5, and the initial value is 0.

[0123] Please refer to FIG. 3( b ) to describe the control process of the present invention in detail as follows:

[0124] Step S31, start-up phase

[0125] The startup phase includes: in the first PWM cycle, the switch tube conduction duty cycle D=0.5, the inward shift ratio of the primary H-bridge H1 is D1=1, the outward shift ratio between the primary and secondary H-bridges is D2=0, and the inward shift ratio of the secondary H-bridge H2 is D3=1; the input voltage is V1, the inward shift ratio D1=1 of the input side H-bridge H1, the switch tubes S1 and S3 are turned on at the same time, the switch tubes S2 and S4 are turned on at the same time, and the output voltage VH1 of the primary side H-bridge H1 is fixed to 0; the output voltage is V2, the inward shift ratio D3=1 of the output side H-bridge H2, the switch tubes S5 and S7 are turned on at the same time, the switch tubes S6 and S8 are turned on at the same time, so the output voltage VH2 of the secondary side H-bridge H2 is also 0; the circuit starts from zero output voltage.

[0126] This step corresponds to Figure 6 The setting unit 61 is implemented in the given control device.

[0127] Step S32, as the reference voltage V2 is output * Increase, through proportional integral regulation (PI regulation for short), PI regulation output duty cycle is D P , according to the output duty cycle D P The converter can choose to work in the following two working conditions. Step S331,

[0128] When 0 <D P <1, the DAB circuit operates in light load mode condition 1.

[0129] At this time, the switch tube conduction duty cycle is set to D = 0.5, and the primary side H bridge H1 is shifted inward compared to D1 = 1-D P , the outward shift ratio between the primary and secondary H bridges is D2 = 0, and the inward shift ratio between the secondary H bridge H2 is D3 = 1-D P ; When the dead zone is ignored, the switch tubes S1, S4, S2, and S3 are turned on at the same time for a time period of D P Ths, the output voltage VH1 of the primary H-bridge H1 changes into positive and negative pulse waves with a pulse width of D P Ths, with an amplitude of ±V1; the primary equivalent output voltage VH1 transmits energy through the inductor Lr, and the inductor current iLr gradually increases from 0. The waveform of the output voltage VH2 of the secondary H-bridge H2 is the same as that of VH1, and the output voltage V2 continues to increase until the circuit is balanced.

[0130] Figure 4 Schematic diagram of the relationship between light load mode drive and output voltage waveform.

[0131] Step S332,

[0132] When 1 <D P <1.5, the DAB circuit operates in the second working condition of the normal mode.

[0133] At this time, as the transmission power continues to increase, PI adjusts the output duty cycle D P It may be greater than 1, making the switch conduction duty cycle D = 0.5, and the primary and secondary side H bridges are moved outward compared to D2 = D P ―1, at this time, the output voltage V2 is stabilized by adjusting D2. At this time, the converter can choose to work in traditional single-phase shift control, extended phase shift control, double phase shift control and triple phase shift control. The internal phase shift ratio of the original secondary side H bridge is expressed as D1 = D OPT1 and D3=D OPT3 .

[0134] The above steps are performed by Figure 6 The output voltage regulating unit 62 in the given control device is implemented. Step S34, generating control pulses of the primary side H1 bridge switch tubes S1, S2, S3, S4 and the secondary side H2 bridge switch tubes S5, S6, S7, S8 according to the above generated D, D1, D2, D3;

[0135] The above steps are performed by Figure 6 The implementation of the PWM generation unit 63 in the control device is given.

[0136] Step S35, waiting for the next interruption time, (Note: usually the entire PWM pulse control program is placed in the microprocessor's timing interruption program or PWM interruption program, the control program runs periodically, and when the program runs, it will wait for the next interruption trigger and run again);

[0137] Step S36, determining whether an external shutdown command is received or a fault protection is triggered to shut down. If no shutdown request is received, proceed to step S32 to continue voltage stabilization control;

[0138] Step S37: If a shutdown request is received in step S36, the entire process ends.

[0139] The above steps are performed by Figure 6 The timing control and protection unit 64 is provided.

[0140] It should be noted that the normal mode DAB circuit can selectively operate in single phase shift, extended phase shift, double phase shift and triple phase shift control modes, which is consistent with the conventional control strategy.

[0141] If single phase shift control is adopted, the primary and secondary H1 and H2 bridges on both sides do not adopt internal phase shift, D1 = 0, D3 = 0;

[0142] If extended phase shift control is adopted, the high voltage side adopts internal phase shift, and the low voltage side has no internal phase shift, that is, D1 = D OPT1 , D3=0 (or D1=0, D3=D OPT3 , D OPT is the calculated optimized internal shift comparison);

[0143] If the dual phase shift control strategy is adopted, D1=D OPT1 , D3=D OPT3 (D OPT1 =D OPT3 ); if triple phase shift control is adopted, D1=D OPT1 , D3=D OPT3 ;

[0144] The above four control strategies can be summarized as D1=D OPT1 , D3=D OPT3 .

[0145] In summary, the present invention proposes a dual active full-bridge DC-DC converter (DAB) soft start and light load mode control method, adopts a PI to adjust the output voltage stabilization, flexibly selects the working mode according to the range of the PI adjustment output, and realizes the soft start of the DAB circuit and the voltage stability in the full load range.

[0146] By applying the soft start and light load control method and device of the present invention, the following technical effects can be obtained:

[0147] First, the startup current impact of the DAB circuit is eliminated, and the primary H1 bridge output voltage V H1 Starting from zero and gradually increasing, the output voltage V2 and the inductor current i Lr The synchronous increase enables zero-impact start-up of the inductor current. The simulation results are as follows: Figure 5 The dual active full-bridge DC-DC converter soft start waveform is shown.

[0148] Figure 5 During the startup process of the DAB circuit, V2 increases from 0V to 110V in ramp mode and finally remains stable.

[0149] Among them, the inductor current i Lr The current gradually increases from 0A to about ±45A. There is no large peak in the entire envelope of the inductor current, that is, there is no current shock during the startup process.

[0150] Secondly, the output voltage V2 is stabilized within the full load range, eliminating the problem of the output voltage being unable to stabilize to a reference value when the DAB circuit is unloaded or lightly loaded due to the dead zone.

[0151] Third, flexible switching between light-load mode and normal working mode is achieved. The working mode is selected only according to the PI adjustment output range. The judgment conditions are simple and easy to implement, and the switching is smooth.

[0152] Fourth, the present invention is compatible with DAB single phase shift, extended phase shift, double phase shift and triple phase shift control algorithms.

[0153] Fifth, the present invention is implemented through software, which does not increase hardware costs, and the method is universal and easy to promote.

[0154] The basic concepts have been described above. Obviously, for those skilled in the art, the above invention disclosure is only used as an example and does not constitute a limitation of the present application. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements and amendments to the present application. Such modifications, improvements and amendments are suggested in the present application, so such modifications, improvements and amendments still belong to the spirit and scope of the exemplary embodiments of the present application.

[0155] At the same time, the present application uses specific words to describe the embodiments of the present application. For example, "one embodiment", "an embodiment", and / or "some embodiments" refer to a certain feature, structure or characteristic related to at least one embodiment of the present application. Therefore, it should be emphasized and noted that "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or more in different positions in this specification does not necessarily refer to the same embodiment. In addition, some features, structures or characteristics in one or more embodiments of the present application can be appropriately combined.

[0156] Similarly, it should be noted that in order to simplify the description of the disclosure of this application and thus help understand one or more embodiments of the invention, in the above description of the embodiments of this application, multiple features are sometimes combined into one embodiment, figure or description thereof. However, this disclosure method does not mean that the features required by the object of this application are more than the features mentioned in the claims. In fact, the features of the embodiments are less than all the features of the single embodiment disclosed above.

[0157] In some embodiments, numbers describing the number of components and attributes are used. It should be understood that such numbers used in the description of the embodiments are modified by the modifiers "about", "approximately" or "substantially" in some examples. Unless otherwise specified, "about", "approximately" or "substantially" indicate that the numbers are allowed to vary by ± 20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximate values, which may change according to the required features of individual embodiments. In some embodiments, the numerical parameters should take into account the specified significant digits and adopt the general method of retaining the digits. Although the numerical domains and parameters used to confirm the breadth of the range in some embodiments of the present application are approximate values, in specific embodiments, the setting of such numerical values ​​is as accurate as possible within the feasible range.

[0158] Although the present application has been described with reference to the current specific embodiments, ordinary technicians in this technical field should recognize that the above embodiments are only used to illustrate the present application, and various equivalent changes or substitutions may be made without departing from the spirit of the present application. Therefore, as long as the changes and modifications to the above embodiments are within the essential spirit of the present application, they will fall within the scope of the claims of the present application.

Claims

1. A soft start and light load control method for a dual active full bridge DC-DC converter, wherein the converter comprises a plurality of switch tubes of a primary bridge and a plurality of switch tubes of a secondary bridge, characterized in that: The method comprises: Step 1: In the first PWM cycle, the output voltage of the primary and secondary bridges of the converter in the startup state is set to zero; Step 2: Obtain the output duty cycle D based on the difference between the output reference voltage and the output voltage P ; Step 3: According to the output duty cycle D P Identify different patterns; Step 4, generating control pulses of the primary bridge and the secondary bridge switch tubes according to the output duty cycle; Step 5: If no shutdown command is received or a fault occurs, return to step 2; In step 2, the output duty cycle D is obtained by using proportional integral regulation. P In step 3, if the output duty cycle D P Satisfied: 0 <D P <1, the operating condition of the converter is light load mode; In step 2, the output duty cycle D is obtained by using proportional integral regulation. P In step 3, if the output duty cycle D P Satisfaction: 1 <D P <1.5, the converter operates in normal mode.

2. The soft start and light load control method of the dual active full bridge DC-DC converter according to claim 1, characterized in that: The working condition of the converter is light load mode, the switch tube conduction duty cycle D is set to 0.5, and the primary side bridge inward shift phase D1=1-D P , the outward displacement ratio between the primary side bridge and the secondary side bridge is D2=0, and the inward displacement ratio of the secondary side bridge is D3=1-D P .

3. The soft start and light load control method of the dual active full bridge DC-DC converter according to claim 1, characterized in that: The working condition of the converter is normal mode, the switch tube conduction duty cycle D is set to 0.5, and the external shift ratio between the primary bridge and the secondary bridge is D2=D P -1, the output voltage is stabilized by adjusting the outward shift ratio D2 between the primary bridge and the secondary bridge.

4. The soft start and light load control method of the dual active full bridge DC-DC converter according to claim 2 or 3, characterized in that: The step 1 further comprises, The switch tube conduction duty cycle D is 0.5, the inward shift phase ratio D1 of the primary bridge is 1, the outward shift phase ratio D2 between the primary bridge and the secondary bridge is 0, the inward shift phase ratio D3 of the secondary bridge is 1, and the output voltage of the primary bridge is fixed at 0; therefore, the output voltage of the secondary bridge is 0, achieving zero output voltage startup.

5. The soft start and light load control method of the dual active full bridge DC-DC converter according to claim 4, characterized in that: The step 5 further includes waiting for the next PWM interrupt to be triggered.

6. The soft start and light load control method of the dual active full bridge DC-DC converter according to claim 5, The output duty cycle D of the proportional integral regulation P The output limit is 0~1.

5.

7. The soft start and light load control method of the dual active full bridge DC-DC converter according to claim 6, characterized in that: In the normal mode, the converter operates in any one of single phase shift control, extended phase shift control, double phase shift control and triple phase shift control.

8. The soft start and light load control method of the dual active full bridge DC-DC converter according to claim 7, characterized in that: The original side bridge is moved inwards by D1=D OPT1 , the secondary bridge moves inward compared to D3 = D OPT3 , where D OPT1 and D OPT3 Compared with the optimized inward shift of the primary and secondary side bridges.

9. A soft start and light load control device for a dual active full bridge DC-DC converter, the converter comprising a plurality of switch tubes of a primary bridge and a plurality of switch tubes of a secondary bridge, characterized in that: The device comprises: A setting unit, in the first PWM cycle, sets the output voltage of the primary and secondary bridges of the converter to zero in the startup state; The output voltage adjustment unit obtains the output duty cycle D according to the difference between the output reference voltage and the output voltage. P , according to the output duty cycle D P Identify different patterns; A PWM generating unit, generating control pulses of the primary bridge and the secondary bridge switch tubes of the converter according to the output duty cycle; The timing control and protection unit waits for the next PWM interrupt to be triggered, and switches to the output voltage regulation unit if no shutdown command is received or a fault occurs; The output voltage regulating unit includes a proportional integral regulating unit. P When satisfied: 0 <D P <1, select the light load mode of the converter; The output voltage regulating unit includes a proportional integral regulating unit. P When satisfied: 1 <D P <1.5, the converter is selected as normal mode.

10. The soft start and light load control device of the dual active full bridge DC-DC converter according to claim 9, characterized in that: Select the light load mode of the converter, set the switch tube conduction duty cycle D to 0.5, and the primary bridge inward shift phase D1 = 1-D P , the outward displacement ratio between the primary side bridge and the secondary side bridge is D2=0, and the inward displacement ratio of the secondary side bridge is D3=1-D P .

11. The soft start and light load control device of the dual active full bridge DC-DC converter according to claim 9, characterized in that: The converter is selected as the normal mode, the switch tube conduction duty cycle D is set to 0.5, and the external shift ratio D2 between the primary bridge and the secondary bridge is D P -1, the output voltage is stabilized by adjusting the outward shift ratio D2 between the primary bridge and the secondary bridge.

12. The soft start and light load control device of the dual active full bridge DC-DC converter according to claim 10 or 11, characterized in that: The setting unit makes the switch tube conduction duty cycle D be 0.5, the primary bridge inward shift phase D1 be 1, the primary bridge and secondary bridge outward shift phase D2 be 0, the secondary bridge inward shift phase D3 be 1, and the primary bridge output voltage is fixed to 0; therefore, the secondary bridge output voltage is 0, achieving zero output voltage startup.

13. The soft start and light load control device of the dual active full bridge DC-DC converter according to claim 12, characterized in that: The output duty cycle D of the proportional-integral regulation control unit P The output limit is 0~1.

5.

14. The soft start and light load control device of the dual active full bridge DC-DC converter according to claim 13, characterized in that: In the normal mode, the converter operates in any one of single phase shift control, extended phase shift control, double phase shift control and triple phase shift control.

15. The soft start and light load control device of the dual active full bridge DC-DC converter according to claim 14, characterized in that: The original side bridge is moved inwards by D1=D OPT1 , the secondary bridge moves inward compared to D3 = D OPT3 , where D OPT1 and D OPT3 Compared with the optimized inward shift of the primary and secondary side bridges.

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