Bipolar auxiliary adjustment quasi-single-stage DC / DC converter based on four-quadrant DAB converter

Abstract

The invention relates to the technical field of power electronics, in particular to a bipolar auxiliary adjustment quasi-single-stage DC / DC converter based on a four-quadrant DAB converter, which comprises an LLC-DCX main converter and a BHT-DAB auxiliary converter, the LLC-DCX main converter comprises a primary side H full bridge arranged at the input end of the LLC-DCX main converter, a secondary side H full bridge arranged at the output end of the LLC-DCX main converter and a main transformer arranged between the primary side H full bridge and the secondary side H full bridge; the BHT-DAB auxiliary converter comprises a secondary side half bridge arranged at the input end of the BHT-DAB auxiliary converter, a capacitor series circuit arranged at the input end of the BHT-DAB auxiliary converter and connected with the secondary side half bridge in parallel, and an auxiliary transformer arranged between the primary side H full bridge and the secondary side half bridge; the input end of the LLC-DCX main converter and the input end of the BHT-DAB auxiliary converter are connected in series to form the input end of the quasi-single-stage DC / DC converter. And the output end of the LLC-DCX main converter is the output end of the quasi-single-stage DC / DC converter. According to the invention, the overall efficiency of the converter under the rated input voltage can be improved, and meanwhile, the voltage regulation capability under the non-rated input voltage is considered.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and particularly to a bipolar auxiliary regulation quasi-single-stage DC / DC converter based on a four-quadrant DAB converter. Background Art

[0002] In application scenarios such as data centers, on-vehicle chargers, and battery charging and discharging of energy storage systems, a single-stage DC / DC converter is required. The working principle of the single-stage DC / DC converter is that most of the power is directly transmitted through the main power converter, while a small part of the power is transmitted through the auxiliary converter. The input and output voltages of the main converter are completely matched to transmit power efficiently, and the auxiliary converter is used to regulate the voltage.

[0003] Since the main converter is always in a state where the input and output voltages are completely matched, it can operate in a high-efficiency but voltage-regulation-capability-lacking DC transformer (DCX) mode. Compared with the CLLC-DCX converter, the LLC-DCX converter has fewer resonant elements, which is more conducive to achieving high power density. Therefore, the main power converter generally can select the LLC-DCX converter. The design of the auxiliary converter is more diverse.

[0004] In the prior art, Solution 1 introduces a sigma converter. It consists of an LLC-DCX converter and a buck converter, which are connected in series at the input end and in parallel at the output end. Most of the power is effectively transmitted through the LLC-DCX converter, and the remaining small part of the power is used to regulate the output voltage through the buck converter. However, this converter does not provide electrical isolation. Solution 2 adopts the same sigma architecture, in which the DAB converter replaces the buck converter to provide electrical isolation. However, this converter uses a large number of power switching tubes, which affects the improvement of power density. Solution 3 is based on Solution 2, where the secondary side of the DAB converter is connected in parallel with the secondary side of the LLC-DC converter, and the power switching tubes at the output port are reused, thereby reducing the number of power switching tubes. Solution 4 introduces a quasi-single-stage DC / DC converter, which adopts a three-port LLC-DCX with two transformers. At the lowest input voltage, most of the power is transmitted through the main transformer, and the rest is transmitted through the auxiliary transformer. At the maximum input voltage, the voltage of the excitation inductor of the auxiliary transformer increases significantly, and most of the power is transmitted to the load. Therefore, both transformers need relatively large rated powers, which limits the improvement of efficiency. Solution 5 introduces a quasi-single-stage DC / DC converter, which has an auxiliary PWM converter cascaded to the primary side of the DCX converter. The PWM converter operates in triangular current mode to achieve ZVS of all power switches. The switching frequency of the three-port LLC-DCX converter matches the resonant frequency, and the working principle and synchronous rectification logic are simple and clear.

[0005] The applicant has found that the above-mentioned existing quasi-single-stage DC / DC converters all have a common drawback: the LLC-DCX main converter is designed for the lowest input voltage. Therefore, the auxiliary port must withstand a certain voltage at the rated input voltage, resulting in a considerable part of the power continuing to flow through the auxiliary converter, thus limiting the improvement of efficiency. Summary of the Invention

[0006] Aiming at the deficiencies of the above-mentioned existing technologies, the technical problem to be solved by the present invention is: how to provide a bipolar auxiliary regulation quasi-single-stage DC / DC converter based on a four-quadrant DAB converter, which can improve the overall efficiency of the converter under the rated input voltage while taking into account the voltage regulation ability under non-rated input voltages.

[0007] To solve the above technical problem, the present invention adopts the following technical solutions:

[0008] A bipolar auxiliary regulation quasi-single-stage DC / DC converter based on a four-quadrant DAB converter includes an LLC-DCX main converter and a BHB-DAB auxiliary converter;

[0009] The LLC-DCX main converter includes a primary H full bridge provided at its input end, a secondary H full bridge provided at its output end, and a main transformer provided between the primary H full bridge and the secondary H full bridge; wherein, the primary port of the main transformer is connected between the upper bridge arm and the lower bridge arm of the primary H full bridge, and the secondary port of the main transformer is connected between the upper bridge arm and the lower bridge arm of the secondary H full bridge;

[0010] The BHB-DAB auxiliary converter includes a secondary half bridge provided at its input end, a capacitor series circuit connected in parallel with the secondary half bridge at its input end, and an auxiliary transformer provided between the primary H full bridge and the secondary half bridge; wherein, the primary port of the auxiliary transformer is connected between the upper bridge arm and the lower bridge arm of the primary H full bridge, and the secondary port of the auxiliary transformer is connected between the upper bridge arm, the lower bridge arm and the capacitor series circuit;

[0011] The input ends of the LLC-DCX main converter and the BHB-DAB auxiliary converter are connected in series to form the input end of the quasi-single-stage DC / DC converter; the output end of the LLC-DCX main converter is the output end of the quasi-single-stage DC / DC converter.

[0012] Preferably, when the quasi-single-stage DC / DC converter operates in a steady state, the relationship between the input voltage V1 at the input end of the LLC-DCX main converter and the output voltage V0 at the output end of the quasi-single-stage DC / DC converter is expressed as:

[0013] V1 = N1V o ;

[0014] The input voltage V2 at the input terminal of the BHB-DAB auxiliary converter is expressed as:

[0015] V2 = V in -V1 = V in -N1V o ;

[0016] Where: V in represents the input voltage at the input terminal of the quasi-single-stage DC / DC converter; N1 represents the turns ratio of the main transformer;

[0017] When the input voltage V in increases, the input voltage V2 of the BHB-DAB auxiliary converter can be adjusted accordingly to offset the increase in V in to ensure that the input voltage V1 of the LLC-DCX main converter remains constant and maintain a stable output voltage V0.

[0018] Preferably, when the input voltage V2 of the BHB-DAB auxiliary converter < 0, all the power emitted from the input terminal (port 11') of the quasi-single-stage DC / DC converter and the input terminal (port 33') of the BHB-DAB auxiliary converter flows into the input terminal (port 22') of the LLC-DCX main converter. A part of the power is transmitted to the output terminal (port 44') of the quasi-single-stage DC / DC converter through the LLC-DCX main converter, and another part of the power is transmitted to the input terminal (port 33') of the BHB-DAB auxiliary converter through the BHB-DAB auxiliary converter;

[0019] When the input voltage V2 of the BHB-DAB auxiliary converter > 0, the power emitted from the input terminal (port 11') of the quasi-single-stage DC / DC converter is divided into two parts. One part flows into the input terminal (port 22') of the LLC-DCX main converter and is directly transmitted to the output terminal (port 44') of the quasi-single-stage DC / DC converter through the LLC-DCX main converter, and the other part flows into the input terminal (port 33') of the BHB-DAB auxiliary converter and is transmitted to the output terminal (port 44') of the quasi-single-stage DC / DC converter after passing through the BHB-DAB auxiliary converter and the LLC-DCX main converter;

[0020] The power at the output terminal of the quasi-single-stage DC / DC converter is expressed as:

[0021]

[0022] Where: P 44' represents the power flowing through the output terminal (port 44') of the quasi-single-stage DC / DC converter; P 11' represents the power flowing through the input terminal (port 11') of the quasi-single-stage DC / DC converter; P 33’Indicates the power flowing through the input terminal (port 33') of the BHB-DAB auxiliary converter; η1 represents the efficiency of the LLC-DCX main converter, and η2 represents the efficiency of the BHB-DAB auxiliary converter.

[0023] Preferably, the overall efficiency η of the quasi-single-stage DC / DC converter is calculated by the following formula:

[0024]

[0025] In the formula: k = P 33' / P 11' = |V2| / V in , which represents the power ratio of the power flowing through the input terminal (port 33') of the BHB-DAB auxiliary converter and the input terminal (port 11') of the quasi-single-stage DC / DC converter.

[0026] Preferably, a resonant capacitor C r and a resonant inductor L r are connected in series between the primary H-bridge and the primary port of the main transformer;

[0027] An auxiliary inductor L k is connected in series between the primary H-bridge and the primary port of the secondary transformer;

[0028] An exciting inductor L m is connected in parallel to the primary port of the main transformer.

[0029] Preferably, the LLC-DCX main converter further includes an input capacitor C1 connected in parallel with the primary H-bridge at its input end, an output capacitor C0 connected in parallel with the secondary H-bridge at its output end, and a resistor R connected in parallel with the secondary H-bridge and the capacitor C0 at its output end L .

[0030] Preferably, the primary H-bridge is composed of an upper switch tube Q1 and a lower switch tube Q2 connected in series, which are connected in parallel with an upper switch tube Q3 and a lower switch tube Q4 connected in series; Q1 and Q3 connected in parallel form a pair of upper bridge arms, and Q2 and Q4 connected in parallel form a pair of lower bridge arms;

[0031] Two terminals of the primary port of the main transformer are respectively connected between Q1 and Q2, and between Q3 and Q4;

[0032] Two terminals of the primary port of the auxiliary transformer are respectively connected between Q1 and Q2, and between Q3 and Q4.

[0033] Preferably, the secondary H-bridge is composed of an upper switch tube Q5 and a lower switch tube Q6 connected in series, which are connected in parallel with an upper switch tube Q7 and a lower switch tube Q8 connected in series; Q5 and Q7 connected in parallel form a pair of upper bridge arms, and Q6 and Q8 connected in parallel form a pair of lower bridge arms;

[0034] The two terminals of the secondary side port of the main transformer are respectively connected between Q5 and Q6, and between Q7 and Q8.

[0035] Preferably, the secondary side half-bridge is composed of an upper power switch tube S 1a and a lower power switch tube S 1b , which is connected in series with an upper power switch tube S 2a and a lower power switch tube S 2b ; The anti-series S 1a and S 1b constitute an upper bridge arm, and the anti-series S 2a and S 2b constitute a lower bridge arm;

[0036] The capacitor series circuit includes a series-connected capacitor C 21 and a capacitor C 22 ;

[0037] The two terminals of the secondary side port of the auxiliary transformer are respectively connected between S 1b and S 2a , and between C 21 and C 22 .

[0038] Preferably, the closed-loop control strategy of the quasi-single-stage DC / DC converter includes:

[0039] S1: Determine that the input variables required for control include the output voltage V0 and the input voltage V in ;

[0040] S2: Calculate the difference x between the output voltage V0 and the set reference value V ref ;

[0041] S3: Feed the difference x into the PI controller and calculate the phase displacement angle D0 between the primary side port of the main transformer and the secondary side port of the auxiliary transformer;

[0042] S4: If the difference x < 0, then control S 1a and S 2a to be always on, and control S 1b and S 2b to operate at a high-frequency switching frequency;

[0043] S5: If the difference x ≥ 0, then control S 1b and S 2b to be always on, and control S 1a and S 2a to operate at a high-frequency switching frequency;

[0044] S6: Generate the drive signals for Q1 to Q8 by loading the phase shift angle D0 through a PWM generator.

[0045] Compared with the prior art, the bipolar auxiliary regulated quasi-single-stage DC / DC converter based on the four-quadrant DAB converter in the present invention has the following beneficial effects:

[0046] In the present invention, the circuit structure of the quasi-single-stage DC / DC converter enables the regulation of the output voltage of the quasi-single-stage DC / DC converter by changing the voltage at the output port of the BHB-DAB auxiliary converter, making the DC / DC converter applicable to a wide range of scenarios, and can be used in scenarios where the input voltage of the DC / DC converter varies within a wide range, thereby improving the flexibility of the quasi-single-stage DC / DC converter. At the same time, the voltage regulation range of the quasi-single-stage DC / DC converter can be adjusted arbitrarily, which can improve the efficiency under the rated input voltage, so as to achieve the improvement of the overall efficiency of the converter under the rated input voltage while taking into account the voltage regulation ability under non-rated input voltages. In addition, the quasi-single-stage DC / DC converter can transmit all power through the LLC-DCX main converter under the rated input voltage, thereby improving the operating efficiency of the quasi-single-stage DC / DC converter. And the topology structure of the quasi-single-stage DC / DC converter is simple. Brief Description of the Drawings

[0047] In order to make the objectives, technical solutions, and advantages of the invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings, where:

[0048] Figure 1 is a schematic structural diagram of the quasi-single-stage DC / DC converter.

[0049] Figure 2 is the variation curves of V1 and V2 when the input voltage varies.

[0050] Figure 3 is a schematic diagram of the power flow inside the auxiliary converter: (a) is for V2 < 0; (b) is for V2 > 0.

[0051] Figure 4 is the control block diagram of the topology proposed in the present invention.

[0052] Figure 5 is the relationship between the power ratio k and the input voltage V under different N1 values in between.

[0053] Figure 6 is the design process of the resonant parameters of the main converter.

[0054] Figure 7 is for L k The design constraint of: (a) is the L required to achieve ZVS kValue; (b) is the relationship between the maximum output power at voltage V2 and L k Relationship.

[0055] Figure 8 Is S 1a / S 2a ZVS region.

[0056] Figure 9 Are the key voltage and current experimental waveforms of the quasi-single-stage DC / DC converter when the output power is 1000W: (a) is V in = 320V; (b) is V in = 360V; (c) is V in = 450V.

[0057] Figure 10 Are the ZVS waveforms of the primary and secondary power switch tubes of the LLC-DCX main converter under different input voltages: (a) is V in = 320V; (b) is V in = 360V; (c) is V in = 450V.

[0058] Figure 11 Are the ZVS waveforms of the secondary power switch tubes of the BHB-DAB converter under different input voltages: (a) is V in = 320V; (b) is V in = 360V; (c) is V in = 450V.

[0059] Figure 12 Are the transient waveforms of the input voltage and load current: (a) is the input voltage jump; (b) is V in = 360V, load jump; (c) is V in = 450V, load jump.

[0060] Figure 13 Is the efficiency curve of the topology of the present invention under different input voltages and load conditions. Detailed implementation mode

[0061] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Components of the embodiments of the present invention generally described and illustrated in the drawings herein can be arranged and designed in a variety of different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0062] It should be noted that like reference numerals and letters denote like items in the following drawings. Therefore, once an item is defined in one drawing, it does not require further definition and explanation in subsequent drawings. In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the inventive product is usually placed during use. This is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used for descriptive distinction and should not be construed as indicating or implying relative importance. In addition, terms such as "horizontal" and "vertical" do not mean that the components are required to be absolutely horizontal or hanging, but can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined. In the description of the present invention, it should also be noted that unless otherwise clearly specified and defined, the terms "set", "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0063] The following is a more detailed description through specific embodiments:

[0064] Embodiment:

[0065] In this embodiment, a bipolar auxiliary regulation quasi-single-stage DC / DC converter based on a four-quadrant DAB converter is disclosed.

[0066] AsFigure 1 As shown, a bipolar auxiliary regulated quasi-single-stage DC / DC converter based on a four-quadrant DAB converter includes an LLC-DCX (resonant DC transformer) main converter (main LCC converter) and a BHB-DAB (bipolar half-bridge - dual active bridge) auxiliary converter (auxiliary bipolar half-bridge DAB converter);

[0067] The LLC-DCX main converter includes a primary H full-bridge arranged at its input end, a secondary H full-bridge arranged at its output end, and a main transformer arranged between the primary H full-bridge and the secondary H full-bridge; wherein, the primary port of the main transformer is connected between the upper arm and the lower arm of the primary H full-bridge, and the secondary port of the main transformer is connected between the upper arm and the lower arm of the secondary H full-bridge; the turns ratio of the main transformer is N1.

[0068] The BHB-DAB auxiliary converter includes a secondary half-bridge arranged at its input end, a capacitor series circuit arranged in parallel with the secondary half-bridge at its input end, and an auxiliary transformer arranged between the primary H full-bridge and the secondary half-bridge; wherein, the primary port of the auxiliary transformer is connected between the upper arm and the lower arm of the primary H full-bridge, and the secondary port of the auxiliary transformer is connected between the upper arm and the lower arm and the capacitor series circuit; the turns ratio of the auxiliary transformer is N2.

[0069] The input ends of the LLC-DCX main converter and the BHB-DAB auxiliary converter are connected in series to form the input end of the quasi-single-stage DC / DC converter; the output end of the LLC-DCX main converter is the output end of the quasi-single-stage DC / DC converter.

[0070] Specifically:

[0071] A resonant capacitor C is connected in series between the primary H full-bridge and the primary port of the main transformer r and a resonant inductor L r ;

[0072] An auxiliary inductor L is connected in series between the primary H full-bridge and the primary port of the secondary transformer k ;

[0073] An exciting inductor L is connected in parallel to the primary port of the main transformer m .

[0074] The LLC-DCX main converter further includes an input capacitor C1 arranged at its input end and connected in parallel with the primary H full-bridge, an output capacitor C0 arranged at its output end and connected in parallel with the secondary H full-bridge, and a resistor R arranged at its output end and connected in parallel with the secondary H full-bridge and the capacitor C0 L .

[0075] The primary H - bridge is composed of the upper switch Q1 and the lower switch Q2 connected in series, which are in parallel with the upper switch Q3 and the lower switch Q4 connected in series; Q1 and Q3 in parallel form a pair of upper bridge arms, and Q2 and Q4 in parallel form a pair of lower bridge arms;

[0076] The two terminals of the primary port of the main transformer are respectively connected between Q1 and Q2, and between Q3 and Q4;

[0077] The two terminals of the primary port of the auxiliary transformer are respectively connected between Q1 and Q2, and between Q3 and Q4.

[0078] The secondary H - bridge is composed of the upper switch Q5 and the lower switch Q6 connected in series, which are in parallel with the upper switch Q7 and the lower switch Q8 connected in series; Q5 and Q7 in parallel form a pair of upper bridge arms, and Q6 and Q8 in parallel form a pair of lower bridge arms;

[0079] The two terminals of the secondary port of the main transformer are respectively connected between Q5 and Q6, and between Q7 and Q8.

[0080] The secondary half - bridge is composed of the upper power switch S 1a and the lower power switch S 1b , which are in series with the upper power switch S 2a and the lower power switch S 2b ; S 1a and S 1b form an upper bridge arm, and S 2a and S 2b form a lower bridge arm;

[0081] The capacitor series circuit includes the capacitor C 21 and the capacitor C 22 ;

[0082] The two terminals of the secondary port of the auxiliary transformer are respectively connected between S 1b and S 2a , and between C 21 and C 22 .

[0083] In Figure 1 , the part between port 22′ and port 44′ is called the main converter, and the part between port 22′ and port 33′ is called the auxiliary converter. v ab and v cd respectively represent the primary port and the secondary port of the main transformer, while v ef represents the secondary port of the auxiliary transformer.

[0084] To improve efficiency and simplify the synchronous rectification method, the resonant frequency of the LLC-DCX main converter is the same as the switching frequency of the BHB-DAB auxiliary converter. The output port voltage V2 of the BHB-DAB auxiliary converter can vary bipolarity and can be zero under the rated input voltage; thus, the power flowing through the BHB-DAB auxiliary converter is zero, and all power is transmitted through the main converter, improving the efficiency under the rated input voltage. As the input voltage changes, V2 will be adjusted accordingly to keep the input voltage V1 at a constant level, thereby ensuring the stability of the output voltage V0.

[0085] In the present invention, the circuit structure of the quasi-single-stage DC / DC converter enables the adjustment of the output voltage of the quasi-single-stage DC / DC converter by changing the voltage of the output port of the BHB-DAB auxiliary converter, making the DC / DC converter have a wide range of applications and can be used in scenarios where the input voltage of the DC / DC converter varies within a wide range, thereby improving the flexibility of the quasi-single-stage DC / DC converter. At the same time, the voltage regulation range of the quasi-single-stage DC / DC converter can be adjusted arbitrarily, which can improve the efficiency under the rated input voltage, thereby achieving the improvement of the overall efficiency of the converter under the rated input voltage while taking into account the voltage regulation ability under non-rated input voltages. In addition, the quasi-single-stage DC / DC converter can transmit all power through the LLC-DCX main converter under the rated input voltage, thereby improving the operating efficiency of the quasi-single-stage DC / DC converter. And the topology structure of the quasi-single-stage DC / DC converter is simple.

[0086] To better introduce the technical solution of the present invention, this embodiment is described through the following several parts.

[0087] I. Voltage gain regulation characteristics

[0088] To simplify the analysis in this section, transformer losses and the on-resistance of power switching tubes are ignored, all inductors and capacitors are regarded as ideal components, and dead-time effects are not considered. When the quasi-single-stage DC / DC converter operates in a steady state, the voltages across the input capacitor C1 and the output capacitor C0 remain constant and can be regarded as voltage sources. Since the LLC-DCX main converter operates at the resonant frequency f r and its voltage gain is independent of the load, the relationship between the input voltage V1 at the input end of the LLC-DCX main converter and the output voltage V0 at the output end of the quasi-single-stage DC / DC converter is expressed as:

[0089] V1 = N1V o (1)

[0090] Since the proposed converter adopts an input series structure, according to the KVL law, the input voltage V2 at the input end of the BHB-DAB auxiliary converter is expressed as:

[0091] V2 = V in -V1 = V in -N1V o (2)

[0092] Where: V in represents the input voltage at the input end of the quasi-single-stage DC / DC converter; N1 represents the turns ratio of the main transformer.

[0093] Based on the above calculation formula, the voltage regulation principle of the converter proposed by the present invention is as Figure 2 shown. When the input voltage V in increases, the input voltage V2 of the BHB-DAB auxiliary converter can be adjusted accordingly to offset the increase in V in , ensuring that the input voltage V1 of the LLC-DCX main converter remains constant, thereby maintaining a stable output voltage V0.

[0094] II. Power Distribution Characteristics and Theoretical Efficiency Analysis

[0095] For the quasi-single-stage DC / DC converter proposed by the present invention, since the average value of the input current is positive, the polarity of the output voltage V2 of the H-bridge PWM converter determines the power flow direction of the converter. For the sake of convenient expression, the part between port 22' and port 44' is called the main converter, and the part between port 22' and port 33' is called the auxiliary converter.

[0096] As Figure 3 (a) shows, when the input voltage V2 of the BHB-DAB auxiliary converter < 0, all the power emitted from the input end (port 11') of the quasi-single-stage DC / DC converter and the input end (port 33') of the BHB-DAB auxiliary converter flows into the input end (port 22') of the LLC-DCX main converter. Part of the power is transmitted to the output end (port 44') of the quasi-single-stage DC / DC converter through the LLC-DCX main converter, and the other part of the power is transmitted to the input end (port 33') of the BHB-DAB auxiliary converter through the BHB-DAB auxiliary converter;

[0097] As Figure 4 shown, when the input voltage V2 of the BHB-DAB auxiliary converter > 0, the power emitted from the input end (port 11') of the quasi-single-stage DC / DC converter is divided into two parts. One part flows into the input end (port 22') of the LLC-DCX main converter and is directly transmitted to the output end (port 44') of the quasi-single-stage DC / DC converter through the LLC-DCX main converter, and the other part flows into the input end (port 33') of the BHB-DAB auxiliary converter and is transmitted to the output end (port 44') of the quasi-single-stage DC / DC converter after passing through the BHB-DAB auxiliary converter and the LLC-DCX main converter;

[0098] The power at the output terminal of the quasi-single-stage DC / DC converter is expressed as:

[0099]

[0100] Where: P ii' represents the power flowing through port ii′ (taking positive value regardless of the direction); P 44' represents the power flowing through the output terminal of the quasi-single-stage DC / DC converter (port 44′); P 11' represents the power flowing through the input terminal of the quasi-single-stage DC / DC converter (port 11′); P 33’ represents the power flowing through the input terminal of the BHB-DAB auxiliary converter (port 33′); η1 represents the efficiency of the LLC-DCX main converter, and η2 represents the efficiency of the BHB-DAB auxiliary converter.

[0101] Specifically, the overall efficiency η of the quasi-single-stage DC / DC converter is calculated by the following formula:

[0102]

[0103] Where: k = P 33' / P 11' = |V2| / V in , representing the power ratio of the input terminal of the BHB-DAB auxiliary converter (port 33′) to the input terminal of the quasi-single-stage DC / DC converter (port 11′).

[0104] III. Closed-loop control strategy

[0105] One of the main advantages of the topology proposed in the present invention is the simplicity of the control method. To achieve closed-loop control of the output voltage, the control strategy shown in Figure 4 is adopted.

[0106] Specifically, the closed-loop control strategy of the quasi-single-stage DC / DC converter includes:

[0107] S1: Determine that the input variables required for control include the output voltage V0 and the input voltage V in ;

[0108] S2: Calculate the difference x between the output voltage V0 and the set reference value V ref ;

[0109] S3: Feed the difference x into the PI controller and calculate the phase displacement angle D0 between the primary side port of the main transformer and the secondary side port of the auxiliary transformer;

[0110] S4: If the difference x < 0, then (through the controller) control S 1a and S2a Always on, and control S 1b and S 2b to operate at a high-frequency switching frequency;

[0111] S5: If the difference x≥0, then (through the controller) control S 1b and S 2b Always on, and control S 1a and S 2a to operate at a high-frequency switching frequency;

[0112] S6: Generate the drive signals of Q1 to Q8 by loading the phase shift angle D0 through the PWM generator, and control S 1a / S 2a and S 1b / S 2b status.

[0113] In this embodiment, the drive signals are directly generated by the EPWM module in the controller.

[0114] IV. Parameter Optimization Design of the Converter

[0115] The present invention focuses on the performance of the DC / DC converter under a wide input voltage range. The relevant specification parameters investigated are shown in Table 1. In this embodiment, the parameters of the proposed quasi-single-stage DC / DC converter will be optimized according to the specifications in Table 1.

[0116] Table 1 DC / DC Converter Design Requirements

[0117]

[0118] 1. Main Transformer Turns Ratio Design

[0119] Combining Equation (2) with the expression of the power ratio k, the relationship between the power ratio k and the input voltage V in is:

[0120]

[0121] When the output voltage V0 = 360V, the curves of the power ratio k and the input voltage V in under different N1 values are as Figure 5 shown. As the value of N1 increases, the corresponding k-V in curve moves downward. When N1 = 1, at the rated input voltage of 360V, the absolute value of k is the smallest, thus reducing the power flowing through the auxiliary converter. Under the condition of ensuring the same output power, the overall efficiency of the converter is improved. Therefore, when N1 is designed to be 1, almost no power flows through the auxiliary converter at the rated input voltage.

[0122] 2. Auxiliary Transformer Turns Ratio Design

[0123] When N1 is fixed at 1, V1 is constant at 360V to achieve a 360V voltage output, which makes V2 vary between -40V and 90V. The range of the voltage conversion ratio M of the auxiliary converter can be solved as follows:

[0124]

[0125] Among them, M < 0 means that the power in the BHB-DAB auxiliary converter flows from v ab to v ef , while M > 0 means that the power flows from v ef to v ab . In order to make full use of the SPS modulation scheme, it is always desired that the input voltage and the output voltage match as much as possible, that is, |M| = 1. When the absolute value of M is the largest, the power in the BHB-DAB auxiliary converter also reaches the maximum value. Since the maximum absolute value of V2 appears at V 2-max , the turns ratio N2 is set to 8 to ensure that the voltage conversion ratio is as close to 1 as possible at the maximum power, thereby reducing the power loss when the BHB-DAB auxiliary converter transmits the maximum power.

[0126] 3. Design of the resonance parameters of the main converter

[0127] Ignoring the dead time, within half a cycle, the voltage across the magnetizing inductor L m1 is clamped at mV0 or -mV0, so the waveform of the magnetizing current is a triangular wave, and the expression is:

[0128]

[0129] Since the resonance current at the resonance frequency is a sine wave, it can be expressed as

[0130]

[0131] Here I rms1 is the effective value of the resonance current, and φ is the initial phase of the resonance current. At the beginning of each half-switching cycle, the magnetizing current is equal to the resonance current, which means:

[0132]

[0133] On the other hand, the difference between the resonance current and the magnetizing current is the current transferred to the secondary side, so:

[0134]

[0135] Combining equations (18) - (21), the effective value of the resonance current can be obtained as:

[0136]

[0137] It should be noted that the above analysis process of the main LLC resonant converter is derived on the premise of assuming forward power flow. Due to the symmetry of the LLC resonant converter, when the power flows reversely, the relevant current expressions remain unchanged.

[0138] As mentioned before, during the dead time of stage 4, since the amplitude of the exciting current is large and the duration is short, the exciting current can be assumed to be constant. During the dead time td, if the exciting current and the auxiliary inductor current charge and discharge the junction capacitance of the switching tubes, ZVS turn-on of Q1-Q4 and Q5-Q8 can be achieved. Therefore, the conditions for Q1-Q8 to achieve ZVS are as follows:

[0139]

[0140] where C oss_L represents the junction capacitance of the power switches Q1-Q8. The current expressions of i Lk at different moments can be found in the literature (A. Rodriguez, A. Vazquez, D. G. Lamar, M. M. Hernando, and J. Sebastian, “Different Purpose Design Strategies and Techniques to Improve the Performance of a Dual Active Bridge With Phase-Shift Control,” IEEE Trans. Power Electron., vol. 30, no. 2, pp. 790–804, Feb. 2015.). After substituting V1 = N1V0, the following expressions can be derived:

[0141]

[0142] When V2 ≤ 0 and |M| ≤ 1, the second term in the denominator is greater than 0, indicating that the current i Lk always helps to charge and discharge these junction capacitances. When V2 > 0, the conditions for Q1-Q8 to achieve ZVS can be derived as follows:

[0143]

[0144] When M ≤ 1, the second term in the denominator is also greater than 0, and the current i LkIt always helps to charge and discharge these junction capacitances. Therefore, regardless of the polarity of V2, the operation of the BHB-DAB auxiliary converter always helps to achieve ZVS for the power switch tubes of the LLC-DCX main converter. The worst case for achieving ZVS for the power switch tubes of the LLC-DCX main converter occurs when the BHB-DAB auxiliary converter is not working and the voltage conversion ratio is equal to 1. In this case, the auxiliary converter does not provide current to charge and discharge the junction capacitances of the switch tubes of the main converter. The junction capacitances of all switch tubes are only charged and discharged by the magnetizing current. As can be seen from (11), the smaller the magnetizing inductance, the larger the RMS value of the resonant current. In order to reduce the conduction loss, the magnetizing inductance should be selected as the maximum value in its worst case.

[0145] For the LLC-DCX converter that does not regulate the output voltage by changing the frequency, selecting a very high inductance ratio (exceeding 20) can compensate for the variation of the resonant element values. The design process of the resonant parameters of the main converter is as Figure 6 shown. First, the worst case for achieving ZVS for the power switch tubes of the LLC-DCX main converter is used to determine the magnetizing inductance L m . Then, the transformer is manufactured according to the known turns ratio and magnetizing inductance value. After the transformer is designed, the actual leakage inductance is measured and used as the resonant inductance. During the actual manufacturing process of the transformer, the measured magnetizing inductance is 710 μH, which is very close to the designed value. The leakage inductance is measured to be 1.56 μH, and the corresponding inductance ratio far exceeds 20, thus meeting the conditions analyzed previously. Therefore, in this embodiment, the leakage inductance of the transformer is used instead of the resonant inductance to meet the design requirements and at the same time improve the power density. Finally, after determining the switching frequency and the resonant inductance value, the resonant capacitance value can be calculated according to the following formula:

[0146]

[0147] 4. Design of the Inductance Parameters of the Auxiliary Converter

[0148] When the BHB-DAB auxiliary converter adopts the SPS modulation scheme, in order to ensure that the proposed quasi-single-stage DC / DC converter has the best performance, ZVS should be achieved for all switch tubes as much as possible. In the BHB-DAB auxiliary converter, if the energy stored in the auxiliary inductor can fully charge and discharge the junction capacitance C oss_D of the secondary-side switch tube, then ZVS turn-on of S 1a -S 2a and S 1b -S 2b can be achieved. Therefore, the ZVS conditions for achieving S 1a -S 2a and S 1b -S 2b are as follows:

[0149]

[0150] Therefore, L k has the following constraint conditions:

[0151]

[0152] In addition, L k must also meet the requirements of the output power. The output power of the auxiliary converter can be expressed as:

[0153]

[0154] Assume that the maximum steady-state phase-shift angle is defined as D 0_max , and combined with the power ratio based on (18), the maximum value of L k can be derived:

[0155]

[0156] By substituting the parameters of the system into (17), the value of L k required to achieve the ZVS condition can be obtained, as shown in Figure 7 (a). Obviously, a lower D0 value requires a lower L k value to achieve ZVS. To ensure a good linear relationship between the control parameter D0 and the output voltage, D 0-max is selected as 0.15. According to (19), the maximum output power that needs to be transmitted for each output voltage V2 is shown in Figure 7 (b). As the voltage V2 increases, the maximum output power that needs to be transmitted also increases, and the maximum L k value increases with the increase of the output power.

[0157] Figure 8 Plots the ZVS boundary of S 1a / S 2a . It can be seen that a larger inductance value is beneficial to achieving ZVS for the secondary side switching tubes of the BHB-DAB auxiliary converter. Considering a 1 / 3 power transmission margin, the inductance value is the maximum allowed value.

[0158] V. Experimental Description

[0159] To better introduce the advantages of the technical solution of the present invention, the following experiments are disclosed in this embodiment.

[0160] Figure 9 Shows the experimental waveforms when the input voltage is 320V, 360V, 450V and the output power is 1000W. These waveforms include v ab and v ef voltages, the resonant current of the LLC-DCX main converter Waveforms and the auxiliary inductor current of the BHB-DAB auxiliary converter Waveforms. With the output power kept constant, the resonant current remains consistent under different input voltages. However, the auxiliary inductor current varies because the magnitude of the input voltage determines the direction and magnitude of the power flow through the BHB-DAB auxiliary converter. When the input voltage is lower than 360V, the v ab voltage phase leads the v ef voltage phase, indicating that the power through the BHB-DAB auxiliary converter flows from the v ab port to the v ef port. When the input voltage is higher than 360V, the v ab voltage phase lags behind the v ef voltage phase, meaning that the power through the BHB-DAB auxiliary converter flows from the v ef port to the v ab port. When the input voltage is 360V, the v ab voltage phase is the same as the v ef voltage phase, indicating that no power flows through the BHB-DAB auxiliary converter. The LLC-DCX main converter always operates at the resonant frequency, while the phase-shift angle of the BHB-DAB auxiliary converter varies with the input voltage, indicating that the output voltage is regulated through the BHB-DAB auxiliary converter.

[0161] Figure 10 Shows the drain-source voltage and gate-source voltage waveforms of the power switches Q1 and Q5 at an output power of 1000W. The primary-side and secondary-side power switches of the LLC-DCX main converter achieve ZVS turn-on at all input voltages. Figure 11 Shows the drain-source voltage and gate-source voltage waveforms of the power switches S 1a and S 1b . When the input voltage is lower than 360V, S 1a is always on, while S 1b switches at a high switching frequency. At this time, since the energy stored in the auxiliary inductor is not sufficient to fully charge and discharge the output capacitance of the MOSFET, S 1b cannot achieve ZVS turn-on. When the input voltage is higher than 360V, S 1b is always on, while S 1a switches at a high switching frequency and achieves ZVS turn-on. Since the output power of the BHB-DAB auxiliary converter is low, the impact of not achieving ZVS on power loss is very small. Therefore, the experimental results are consistent with the previous theoretical analysis, proving the voltage regulation ability of the converter proposed in the present invention within a wide input voltage range and the correctness of the parameter optimization design.

[0162] Figure 12 The experimental waveforms showing the input voltage variation under full-load conditions and the load variation under different input voltages are presented. These results indicate that when the input voltage or the load fluctuates, the output voltage remains stable at 360 V and the voltage overshoot is small. Therefore, the effectiveness of the proposed control strategy can be demonstrated.

[0163] Figure 13 The efficiency curves under different input voltages and loads are shown. The topology reaches the highest efficiency at the rated input voltage of 360 V and the lowest efficiency at an input voltage of 320 V. Because when the input voltage is 360 V, V2 is equal to zero and all the power is directly transferred to the load through the LLC-DCX main converter without passing through the auxiliary converter, resulting in the lowest loss at this time. On the contrary, when the input voltage is 320 V, V2 is less than zero and there is some backflow power in the auxiliary converter, leading to an increase in loss. While at 450 V, V2 is greater than zero and part of the power is transferred to the load through the auxiliary converter. The highest efficiency of the topology proposed in the present invention exceeds 98%, and the efficiency at the rated input voltage and power reaches 97.9%.

[0164] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Those of ordinary skill in the art should understand that any modifications or equivalent replacements made to the technical solutions of the present invention without departing from the spirit and scope of the present technical solution shall be covered by the scope of the claims of the present invention.

Claims

1. A bipolar auxiliary regulation quasi-single-stage DC / DC converter based on a four-quadrant DAB converter, characterized in that, It includes an LLC-DCX main converter and a BHB-DAB auxiliary converter; The LLC-DCX main converter includes a primary H full-bridge arranged at its input end, a secondary H full-bridge arranged at its output end, and a main transformer arranged between the primary H full-bridge and the secondary H full-bridge; wherein, the primary port of the main transformer is connected between the upper bridge arm and the lower bridge arm of the primary H full-bridge, and the secondary port of the main transformer is connected between the upper bridge arm and the lower bridge arm of the secondary H full-bridge; The BHB-DAB auxiliary converter includes a secondary half-bridge arranged at its input end, a capacitor series circuit arranged in parallel with the secondary half-bridge at its input end, and an auxiliary transformer arranged between the primary H full-bridge and the secondary half-bridge; wherein, the primary port of the auxiliary transformer is connected between the upper bridge arm and the lower bridge arm of the primary H full-bridge, and the secondary port of the auxiliary transformer is connected between the upper bridge arm, the lower bridge arm and the capacitor series circuit; The input ends of the LLC-DCX main converter and the BHB-DAB auxiliary converter are connected in series to form the input end of the quasi-single-stage DC / DC converter; the output end of the LLC-DCX main converter is the output end of the quasi-single-stage DC / DC converter.

2. The bipolar auxiliary regulation quasi-single-stage DC / DC converter based on a four-quadrant DAB converter as claimed in claim 1, wherein: When the quasi-single-stage DC / DC converter operates in a steady state, the relationship between the input voltage V1 at the input end of the LLC-DCX main converter and the output voltage V0 at the output end of the quasi-single-stage DC / DC converter is expressed as: V1 = N1V o ; The input voltage V2 at the input end of the BHB-DAB auxiliary converter is expressed as: V2 = V in -V1 = V in -N1V o ; Where: V in represents the input voltage at the input terminal of the quasi-single-stage DC / DC converter; N1 represents the turns ratio of the main transformer; When the input voltage V in increases, the input voltage V2 of the BHB-DAB auxiliary converter can be adjusted accordingly to offset the increase in V in , ensuring that the input voltage V1 of the LLC-DCX main converter remains constant and maintaining a stable output voltage V0.

3. The bipolar auxiliary regulation quasi-single-stage DC / DC converter based on a four-quadrant DAB converter according to claim 2, wherein: When the input voltage V2 of the BHB-DAB auxiliary converter < 0, all the power emitted from the input end (port 11') of the quasi-single-stage DC / DC converter and the input end (port 33') of the BHB-DAB auxiliary converter flows into the input end (port 22') of the LLC-DCX main converter. A part of the power is transmitted to the output end (port 44') of the quasi-single-stage DC / DC converter through the LLC-DCX main converter, and another part of the power is transmitted to the input end (port 33') of the BHB-DAB auxiliary converter through the BHB-DAB auxiliary converter; When the input voltage V2 of the BHB-DAB auxiliary converter > 0, the power emitted from the input end (port 11') of the quasi-single-stage DC / DC converter is divided into two parts. One part flows into the input end (port 22') of the LLC-DCX main converter and is directly transmitted to the output end (port 44') of the quasi-single-stage DC / DC converter through the LLC-DCX main converter, and the other part flows into the input end (port 33') of the BHB-DAB auxiliary converter and is transmitted to the output end (port 44') of the quasi-single-stage DC / DC converter after passing through the BHB-DAB auxiliary converter and the LLC-DCX main converter; The power at the output end of the quasi-single-stage DC / DC converter is expressed as: Where: P 44′ represents the power flowing through the output terminal of the quasi-single-stage DC / DC converter (port 44'); P 11′ represents the power flowing through the input terminal (port 11') of the quasi-single-stage DC / DC converter; P 33’ represents the power flowing through the input terminal (port 33') of the BHB-DAB auxiliary converter; η1 represents the efficiency of the LLC-DCX main converter, and η2 represents the efficiency of the BHB-DAB auxiliary converter.

4. The bipolar auxiliary regulation quasi-single-stage DC / DC converter based on the four-quadrant DAB converter according to claim 3, wherein: The overall efficiency η of the quasi-single-stage DC / DC converter is calculated by the following formula: where: k = P 33′ / P 11′ = |V2| / V in , representing the power ratio flowing through the input terminal (port 33') of the BHB-DAB auxiliary converter and the input terminal (port 11') of the quasi-single-stage DC / DC converter.

5. The bipolar auxiliary regulation quasi-single-stage DC / DC converter based on a four-quadrant DAB converter according to claim 2, characterized in that: A resonant capacitor C is connected in series between the primary side H full-bridge and the primary side port of the main transformer r and a resonant inductor L r ; An auxiliary inductor L is connected in series between the primary side H of the full-bridge and the primary side port of the secondary transformer k ; An exciting inductor L is connected in parallel to the primary side port of the main transformer m .

6. The bipolar auxiliary regulation quasi-single-stage DC / DC converter based on the four-quadrant DAB converter according to claim 2, characterized in that: The LLC-DCX main converter further includes an input capacitor C1 disposed at its input end and in parallel with the primary H full bridge, an output capacitor C0 disposed at its output end and in parallel with the secondary H full bridge, and a resistor R disposed at its output end and in parallel with the secondary H full bridge and the capacitor C0 L .

7. The bipolar auxiliary regulation quasi-single-stage DC / DC converter based on a four-quadrant DAB converter according to claim 2, wherein: The primary H full-bridge is composed of an upper switch tube Q1 and a lower switch tube Q2 connected in series, which are connected in parallel with an upper switch tube Q3 and a lower switch tube Q4 connected in series; Q1 and Q3 connected in parallel form a pair of upper bridge arms, and Q2 and Q4 connected in parallel form a pair of lower bridge arms; The two terminals of the primary side port of the main transformer are respectively connected between Q1 and Q2, and between Q3 and Q4; The two terminals of the primary side port of the auxiliary transformer are respectively connected between Q1 and Q2, and between Q3 and Q4.

8. The bipolar auxiliary regulation quasi-single-stage DC / DC converter based on the four-quadrant DAB converter according to claim 7, characterized in that: The secondary side H-bridge is composed of the upper switch tube Q5 and the lower switch tube Q6 connected in series, which are connected in parallel with the upper switch tube Q7 and the lower switch tube Q8 connected in series; Q5 and Q7 connected in parallel form a pair of upper bridge arms, and Q6 and Q8 connected in parallel form a pair of lower bridge arms; The two terminals of the secondary side port of the main transformer are respectively connected between Q5 and Q6, and between Q7 and Q8.

9. The bipolar auxiliary regulation quasi-single-stage DC / DC converter based on the four-quadrant DAB converter according to claim 8, wherein: The secondary side half-bridge consists of the upper power switch S connected in anti-series 1a and the lower power switch S 1b , which is connected in series with the upper power switch S connected in anti-series 2a and the lower power switch S 2b ; The S connected in anti-series 1a and S 1b form an upper bridge arm, and the S connected in anti-series 2a and S 2b form a lower bridge arm; The capacitive series circuit includes capacitors C connected in series 21 and capacitor C 22 ; The two terminals of the secondary side port of the auxiliary transformer are respectively connected between S 1b and S 2a , and between C 21 and C 22 .

10. The bipolar auxiliary regulation quasi-single-stage DC / DC converter based on a four-quadrant DAB converter according to claim 9, characterized in that: The closed-loop control strategy of the quasi-single-stage DC / DC converter includes: S1: Determine the input variables required for control, including the output voltage V0 and the input voltage V in ; S2: Calculate the difference x between the output voltage V0 and the set reference value V ref ; S3: Send the difference x into the PI controller to calculate the phase displacement angle D0 between the primary side port of the main transformer and the secondary side port of the auxiliary transformer; S4: If the difference value x < 0, then control S 1a and S 2a to always conduct, and control S 1b and S 2b to operate at a high switching frequency; S5: If the difference value x≥0, then control S 1b and S 2b to be always on, and control S 1a and S 2a to operate at a high switching frequency; S6: Load the phase displacement angle D0 through the PWM generator to generate the drive signals of Q1 to Q8.

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