A high-power bidirectional isolated DC-DC converter and a control method thereof

Abstract

This invention relates to the field of power electronics technology, and particularly to a high-power bidirectional isolated DC-DC converter and its control method. Designed for medium-to-high power applications with a wide voltage ratio of 400V / 48V and a capacity of 2500W, this converter employs a full-bridge structure with high-voltage side (600V MOSFETs) and low-voltage side (100V MOSFETs), a high-frequency isolation transformer with an EE65 core (24:3 turns ratio), and cleverly utilizes its 15μH leakage inductance and 10nF resonant capacitor to form a 150kHz series resonant circuit, achieving zero-voltage turn-on (ZVS) for all switching transistors. The control system is based on the TMS320F28035 main control chip and employs a hybrid phase-shift control strategy, capable of automatically identifying and switching between forward and reverse operating modes. This invention effectively solves the problems of low efficiency, high current stress, high switching loss, and poor EMC of traditional DAB under wide voltage ratios. It achieves high-performance bidirectional energy conversion with full-load efficiency ≥95%, power density ≥3W / cm³, and meets the EN 55032 Class B EMC standard. It can be widely used in new energy storage, electric vehicles, and industrial microgrids.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a high-power bidirectional isolated DC-DC converter and its control method. Background Technology

[0002] With the development of industries such as new energy and industrial microgrids, the demand for bidirectional energy transmission at 400V / 48V voltage levels is becoming increasingly urgent. In high-power scenarios up to 2500W, the DAB (Dual Active Bridge) topology has become the mainstream choice due to its advantages such as good isolation, high power density, and bidirectional controllability. However, existing technologies have the following key drawbacks:

[0003] 1. Poor wide voltage ratio adaptability: The voltage ratio of 400V input and 48V output is about 8.3:1. When traditional DAB uses single phase shift control (SPS), it is easy to have problems such as excessive current stress and increased reactive power, resulting in a significant decrease in conversion efficiency (full load efficiency is usually below 90%), and the efficiency decline is even more severe under light load (below 85%).

[0004] 2. High switching losses: Existing solutions mostly use silicon-based IGBTs or ordinary MOSFETs, which limit the switching frequency (usually ≤50kHz). Furthermore, the switching losses account for a high proportion in hard-switching operation mode, making it difficult to balance efficiency and power density.

[0005] 3. Inappropriate core design: The transformer leakage inductance and excitation inductance are poorly matched, and the leakage inductance is not fully utilized to participate in resonance, resulting in increased additional losses. In addition, the core is prone to saturation problems, which affects the stability of the converter.

[0006] 4. Complex bidirectional control logic: When working in reverse (48V→400V), the low-voltage side current is large, which makes current sharing difficult and the drive signal synchronization poor, which can easily lead to damage to the switching transistor.

[0007] 5. Poor EMC performance: The electromagnetic interference generated by high voltage and high current switching is strong. The existing filter structure is simple and difficult to meet industrial-grade electromagnetic compatibility standards, and it lacks targeted peak suppression design.

[0008] The core challenge of existing technologies lies in how to address the current stress and reactive power issues of DAB topologies in high-power scenarios with a wide voltage ratio of 400V / 48V and a power output of 2500W, while simultaneously reducing switching losses, optimizing core utilization efficiency, simplifying bidirectional control logic, and improving EMC performance. Currently, there is no mature solution that simultaneously meets all these requirements. Summary of the Invention

[0009] The purpose of this invention is to provide a high-power bidirectional isolated DC-DC converter and its control method, which aims to improve the converter's performance under different operating conditions, reduce return current power, and increase conversion efficiency through a dual phase-shift control strategy.

[0010] To achieve the above objectives, the present invention provides the following technical solution: a high-power bidirectional isolated DC-DC converter and its control method, comprising a high-voltage side DC port, a low-voltage side DC port, a transformer, a primary-side H-bridge circuit, a secondary-side H-bridge circuit, a resonant inductor, and a controller. The rated voltage of the high-voltage side DC port is 400V, and the rated voltage of the low-voltage side DC port is 48V. The AC side of the primary-side H-bridge circuit is connected to the primary winding of the transformer, and the DC side is connected to the high-voltage side DC port; the AC side of the secondary-side H-bridge circuit is connected to the secondary winding of the transformer, and the DC side is connected to the low-voltage side DC port. The resonant inductor is connected in series between the primary-side H-bridge circuit and the primary winding of the transformer. The controller adopts a dual phase-shift control strategy, generating a first drive signal and a second drive signal respectively. The first drive signal is used to control the primary-side H-bridge circuit, and the second drive signal is used to control the secondary-side H-bridge circuit. The dual phase-shift control strategy refers to adjusting both the external phase-shift angle between the primary-side and secondary-side H-bridge circuits and the internal phase-shift angle within the primary-side H-bridge circuit.

[0011] Furthermore, the resonant inductor can be the leakage inductance of a transformer or an external inductor.

[0012] Furthermore, the converter has a rated power of 2500W.

[0013] Furthermore, the controller includes a sampling circuit, a processor, and a drive circuit. The sampling circuit is used to acquire the voltage and current at the high-voltage side DC port and the voltage and current at the low-voltage side DC port. The processor is connected to the sampling circuit and is used to calculate phase-shift control parameters, including external phase-shift angle and internal phase-shift angle, based on the signals acquired by the sampling circuit and a preset target power. The drive circuit is connected to the processor and is used to generate a first drive signal and a second drive signal based on the phase-shift control parameters.

[0014] Furthermore, the processor determines the values ​​of the external phase shift angle and the internal phase shift angle based on the voltage ratio between the high-voltage side DC port and the low-voltage side DC port and the current load conditions, so that the converter reduces the return current power and widens the zero-voltage turn-on range of the switching transistor under different operating conditions.

[0015] Furthermore, the switching transistors in the primary-side H-bridge circuit and the secondary-side H-bridge circuit can be MOSFETs or IGBTs.

[0016] The present invention also provides a control method for the above-mentioned converter, comprising the following steps:

[0017] Sample the voltage and current at the high-voltage side DC port and the voltage and current at the low-voltage side DC port;

[0018] Based on the sampled voltage and current and the target transmission power, the phase shift control combination is calculated. The phase shift control combination includes the external phase shift angle between the primary H-bridge circuit and the secondary H-bridge circuit, and the internal phase shift angle within the primary H-bridge circuit.

[0019] Based on the phase-shift control combination, corresponding drive signals are generated to control the switching transistors in the primary-side H-bridge circuit and the secondary-side H-bridge circuit to turn on and off.

[0020] By adjusting the internal phase shift angle, the return current power of the converter is reduced under voltage mismatch or light load conditions, and the switching conditions of the switching transistors are improved.

[0021] Input / output filtering module:

[0022] High voltage side (400V terminal): adopts a two-stage differential mode + common mode filter structure. The first stage is X capacitor C1 (1μF / 630V) + common mode inductor L1 (2mH) + Y capacitor C2 / C3 (4.7nF / 630VAC). The second stage is differential mode inductor L2 (5mH) + X capacitor C4 (0.47μF / 630V).

[0023] Low voltage side (48V terminal): adopts LC filter + smoothing reactor structure, with 6 1000μF / 63V filter capacitors connected in parallel, and smoothing reactor L3 (220μH) in series to suppress large current fluctuations.

[0024] Bidirectional DAB power conversion module:

[0025] Switching topology: The high-voltage side (400V) uses 4 MOSFETs (Q1-Q4, model SRC60R068BSTG, 600V / 48A) to form a full bridge; the low-voltage side (48V) uses 4 MOSFETs (Q5-Q8, model HYG016N10NS1TA, 100V / 370A) to form a full bridge.

[0026] High-frequency isolation transformer T1: EE65 ferrite core (effective cross-sectional area Ae=320mm²), primary winding Np=24 turns, secondary winding Ns=3 turns, turns ratio k=8:1; maximum magnetic flux density Bmax=0.25T, air gap length lg=1.2mm; leakage inductance Lσ=15μH.

[0027] Resonant auxiliary module: It consists of a resonant capacitor Cr (10nF / 1000V) and forms a series resonant circuit with the transformer leakage inductance Lσ. The resonant frequency f0=150kHz is consistent with the switching frequency, so as to realize zero voltage turn-on (ZVS) of all switching transistors.

[0028] Bidirectional control drive module:

[0029] The main control chip U1 is the TI TMS320F28035, which supports hybrid phase-shift control (SPS+DPS combination) and can automatically switch the working mode according to the voltage difference.

[0030] Drive unit: The high-voltage side uses the isolated driver chip Si8233, and the low-voltage side uses IR2110. The drive signal is transmitted through optical fiber (synchronization error ≤10ns).

[0031] Sampling feedback: Hall sensor (AHB-060-50) is used for high voltage side sampling, and shunt (0.001Ω / 200A) is used for low voltage side high current sampling.

[0032] Multiple protection modules: Includes overvoltage / undervoltage, overcurrent, and overheat protection to ensure system safety.

[0033] The beneficial effects of this invention are:

[0034] By employing a dual phase-shift control strategy, adjusting the phase shift angle between the primary and secondary H-bridges while simultaneously introducing a phase shift angle within the primary H-bridge, the converter's return current power and conduction losses can be effectively reduced. Optimizing the phase shift angle combination improves the switching conditions of the switching transistors, widens the zero-voltage turn-on range, and thus reduces switching losses. The combination of these effects allows the converter to maintain high conversion efficiency under wide load ranges and voltage fluctuation conditions. The controller has a simple structure, is easy to implement digitally, and is suitable for 2500W high-power applications.

[0035] Significantly improved conversion efficiency: Through MOS devices, ZVS soft switching and hybrid phase-shift control, the full-load efficiency reaches 95.8% and the light-load efficiency reaches 91.2%, which is 5%-8% higher than the traditional solution.

[0036] Current stress and reactive power reduction: Hybrid phase-shifting control and resonant optimization reduce current stress by 25% and reactive power by 30%, improving system reliability.

[0037] High power density: The 150kHz switching frequency and integrated design enable a power density of 3W / cm³, while reducing the volume by 35% compared to traditional solutions.

[0038] Core utilization optimization: The precisely designed air gap and turns ratio avoid core saturation, and the leakage inductance is effectively utilized for resonance, improving magnetic energy utilization efficiency by 15%.

[0039] Stable bidirectional switching: Automatic pattern recognition and high-precision synchronous drive ensure switching time ≤10ms, no inrush current, and system MTBF ≥100,000 hours.

[0040] EMC performance meets standards: The two-stage filtering structure attenuates electromagnetic interference by more than 40dB, meeting the EN 55032 Class B standard.

[0041] Costs are controllable: all core components are mass-produced models, and the prospects for engineering applications are promising. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a detailed circuit diagram of the bidirectional DAB power conversion module in an embodiment of the present invention.

[0044] Figure 2 This is a detailed circuit diagram of the resonant auxiliary module. Detailed Implementation

[0045] The technical solution of the present invention will now be clearly and completely described with reference to specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0046] Examples, such as Figure 1 , 2 As shown, a high-power bidirectional isolated DC-DC converter and its control method are provided, and its main circuit is as follows. Figure 1 As shown.

[0047] like Figure 1 As shown, the converter includes a high-voltage side DC port (HV DC, voltage 400V), a low-voltage side DC port (LVDC, voltage 48V), a transformer T, a primary-side H-bridge circuit, a secondary-side H-bridge circuit, a resonant inductor Lr, and a controller.

[0048] The primary-side H-bridge circuit consists of four switching transistors Q1, Q2, Q3, and Q4, with a diode connected in anti-parallel to each transistor. Q1 and Q2 are connected in series to form one bridge arm, and Q3 and Q4 are connected in series to form the other bridge arm. The two bridge arms are connected in parallel to the DC port on the high-voltage side. The AC output terminal of the primary-side H-bridge circuit (i.e., the connection point between Q1 and Q2, and the connection point between Q3 and Q4) is connected to the primary winding of transformer T.

[0049] The secondary-side H-bridge circuit consists of four switching transistors Q5, Q6, Q7, and Q8, with a diode connected in anti-parallel to each transistor. Q5 and Q6 are connected in series to form one bridge arm, and Q7 and Q8 are connected in series to form the other bridge arm. The two bridge arms are connected in parallel to the low-voltage side DC port. The AC input terminals of the secondary-side H-bridge circuit (i.e., the connection point between Q5 and Q6, and the connection point between Q7 and Q8) are connected to the secondary winding of transformer T.

[0050] The resonant inductor Lr is connected in series between the primary-side H-bridge circuit and the primary winding of the transformer T. In this embodiment, the resonant inductor Lr can be an independent external inductor or it can be implemented using the leakage inductance of the transformer T to simplify the structure.

[0051] The converter has a rated power of 2500W, a rated voltage of 400V on the high-voltage side, and a rated voltage of 48V on the low-voltage side. The transformer turns ratio is designed to match the primary and secondary voltages under rated operating conditions.

[0052] Specific components of the controller

[0053] The controller includes a sampling circuit, a processor, and a drive circuit. The sampling circuit is connected to both the high-voltage side DC port and the low-voltage side DC port to acquire the high-voltage side voltage V in real time. HV High-voltage side current I HV Low-voltage side voltage V LV Low-voltage side current I LV The sampling circuit can be implemented using voltage Hall sensors and current Hall sensors, and the output signal is conditioned before being sent to the processor.

[0054] The processor can be a digital signal processor (DSP, such as TMS320F28335) or a microcontroller (MCU). Internally, the processor runs a dual phase-shift control algorithm. This algorithm calculates the optimal phase-shift control parameters based on the sampled voltage and current signals and the externally given target power command (e.g., forward charging power or reverse discharging power). These parameters include the external phase-shift angle D0 between the primary and secondary H-bridges, and the internal phase-shift angle D1 within the primary H-bridge. The processor converts these phase-shift angles into corresponding PWM duty cycles and phase information, which are then output to the drive circuit.

[0055] The drive circuit receives the PWM control signal from the processor, and after isolation and amplification, generates a drive signal with sufficient driving capability to control the gates of each switch in the primary-side H-bridge and the secondary-side H-bridge respectively.

[0056] Dual phase-shift control principle

[0057] Traditional single-phase-shift control only adjusts the external phase-shift angle D0, i.e., the primary-side H-bridge output voltage v. p With the secondary H-bridge output voltage v sThe phase difference (referred to the primary side) between them. In dual phase-shift control, in addition to adjusting D0, an internal phase-shift angle D1 is introduced inside the primary H-bridge, so that the output voltage v of the primary H-bridge... p This results in a three-level waveform with an adjustable duty cycle. The secondary H-bridge can maintain the traditional two-level modulation (i.e., the internal phase shift angle is 0), or it can also introduce an internal phase shift angle to form a triple phase shift. However, this embodiment takes double phase shift (internal phase shift on the primary side) as an example.

[0058] The processor determines the voltage based on the current voltage condition (e.g., voltage gain M = n*V). LV / V HV The optimal combination of D0 and D1 is determined in real time using a pre-stored lookup table or online calculation formula, based on the transformer turns ratio (n) and load power, so that the converter maintains high efficiency across the entire operating range.

[0059] Work process

[0060] Taking energy transfer from the high-voltage side to the low-voltage side as an example: the controller calculates the optimal phase-shift control parameters under the current operating conditions based on the sampled high-voltage side voltage, low-voltage side voltage, and load current. The drive circuit generates a corresponding PWM signal, causing the primary-side H-bridge switch to conduct according to the internal phase-shift angle D1, generating a three-level voltage v. p The secondary-side H-bridge switch is turned on relative to the primary side by an external phase shift angle D0. A high-frequency AC square wave voltage is applied to the primary side of the transformer, coupled to the secondary side through the transformer, and then rectified by the secondary-side H-bridge before being output to the low-voltage side load. When energy is transferred in the reverse direction, the control strategy is symmetrical, and only the external phase shift angle needs to be reversed.

[0061] The converter in this embodiment, under a rated power of 2500W, was tested and found to achieve ZVS for all switching transistors over a wide load range (e.g., 20%~100% load), with a peak efficiency of over 94%, which is a significant improvement compared to traditional single-phase shift control.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-power bidirectional isolated DC-DC converter, characterized in that: The DC port on the high-voltage side has a rated voltage of 400V; The low-voltage side DC port has a rated voltage of 48V; transformer; The primary-side H-bridge circuit has its AC side connected to the primary winding of the transformer and its DC side connected to the high-voltage side DC port. The secondary H-bridge circuit has its AC side connected to the secondary winding of the transformer and its DC side connected to the low-voltage side DC port. A resonant inductor is connected in series between the primary H-bridge circuit and the primary winding of the transformer; The controller employs a dual phase-shift control strategy to generate a first drive signal and a second drive signal, respectively. The first drive signal is used to control the primary-side H-bridge circuit, and the second drive signal is used to control the secondary-side H-bridge circuit. The dual phase-shift control strategy refers to adjusting the external phase-shift angle between the primary H-bridge circuit and the secondary H-bridge circuit while simultaneously adjusting the internal phase-shift angle within the primary H-bridge circuit.

2. A high-power bidirectional isolated DC-DC converter according to claim 1, characterized in that: The resonant inductor is either the leakage inductance of the transformer or an external inductor.

3. A high-power bidirectional isolated DC-DC converter according to claim 1, characterized in that: The rated power of the converter is 2500W.

4. A high-power bidirectional isolated DC-DC converter according to claim 1, characterized in that: The controller includes: A sampling circuit is used to collect the voltage and current of the high-voltage side DC port and the voltage and current of the low-voltage side DC port; A processor, connected to the sampling circuit, is used to calculate phase-shift control parameters based on the signal acquired by the sampling circuit and a preset target power. The phase-shift control parameters include the external phase-shift angle and the internal phase-shift angle. A driving circuit, connected to the processor, is used to generate the first driving signal and the second driving signal according to the phase shift control parameters.

5. A high-power bidirectional isolated DC-DC converter according to claim 4, characterized in that: The processor determines the values ​​of the external phase shift angle and the internal phase shift angle based on the voltage ratio between the high-voltage side DC port and the low-voltage side DC port and the current load conditions, so that the converter reduces the return current power and widens the zero-voltage turn-on range of the switching transistor under different operating conditions.

6. A high-power bidirectional isolated DC-DC converter according to claim 1, characterized in that: The switching transistors in the primary-side H-bridge circuit and the secondary-side H-bridge circuit are MOSFETs or IGBTs.

7. A control method for a high-power bidirectional isolated DC-DC converter according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1: Sample the voltage and current of the high-voltage side DC port and the voltage and current of the low-voltage side DC port; S2: Calculate the phase-shift control combination based on the sampled voltage and current and the target transmission power. The phase-shift control combination includes the external phase-shift angle between the primary H-bridge circuit and the secondary H-bridge circuit, and the internal phase-shift angle within the primary H-bridge circuit. S3: Based on the phase-shift control combination, generate corresponding drive signals to control the switching transistors in the primary-side H-bridge circuit and the secondary-side H-bridge circuit to turn on and off; wherein, by adjusting the internal phase-shift angle, the return current power of the converter is reduced when there is voltage mismatch or light load, and the switching conditions of the switching transistors are improved.

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