A bidirectional three-phase LLC DC resonant converter

Abstract

This invention discloses a bidirectional three-phase LLC DC-DC resonant converter, comprising a primary-side circuit, a resonant network, a transformer, a secondary-side circuit, and a voltage divider circuit connected in series, as well as a control device for controlling the secondary-side circuit. The secondary-side circuit includes three three-level bridge arms and three clamping circuits. The first to fourth switches in each three-level bridge arm are connected in series between the positive and negative external terminals of the secondary side of the bidirectional three-phase LLC DC-DC resonant converter. A clamping circuit is connected in parallel between the connection points of the first and second switches and the connection points of the third and fourth switches in each three-level bridge arm. Each clamping circuit is used to clamp the voltage stress borne by each switch in the corresponding three-level bridge arm to half of the secondary-side input voltage. The control device is configured to provide drive for each switch in each three-level bridge arm using a two-level control method. This invention can fully utilize the characteristics of the switching devices.

Description

Technical Field

[0001] This utility model relates to the field of power supply technology, and in particular to a bidirectional three-phase LLC DC resonant converter. Background Technology

[0002] Traditional bidirectional three-phase LLC DC-DC resonant converters employ a three-phase six-switch structure on both the primary and secondary sides, resulting in a simple circuit. While one side operates in three-phase inverter mode, the other operates in three-phase rectification mode, enabling a wide soft-switching range and high efficiency. The interleaved parallel connection of the three phases minimizes capacitor ripple. Furthermore, the star or Y-connection on both the primary and secondary sides achieves self-current sharing, simplifying the control strategy. Therefore, they have significant application value in various energy transfer applications.

[0003] However, traditional bidirectional three-phase LLC DC resonant converters also have certain drawbacks. The voltage stress on their switching transistors is equal to the maximum value of the input voltage on both sides, making them unsuitable for high-voltage applications.

[0004] For example, in a DC / DC converter after a three-phase power factor correction circuit, the input voltage is usually above 700V. Considering that the voltage capacity of the switching transistors needs to be left with a margin, the primary side of the bidirectional three-phase LLC DC resonant converter must use switching transistors with a withstand voltage of 1000V or higher.

[0005] For example, in bidirectional power supply applications with a 230Vdc output voltage level, the secondary side of the bidirectional three-phase LLC DC resonant converter must use switching devices with a withstand voltage of 300V or higher. However, in practice, only 650V-level switching devices can be selected. This will result in insufficient utilization of device characteristics, leading to a decrease in power supply performance and an increase in cost. Utility Model Content

[0006] In view of this, the technical problem to be solved by this utility model is to provide a bidirectional three-phase LLC DC resonant converter that overcomes at least one of the defects in the prior art.

[0007] To solve the above-mentioned technical problems, the technical solution of the bidirectional three-phase LLC DC resonant converter of this utility model is as follows:

[0008] A bidirectional three-phase LLC DC-DC resonant converter includes a primary-side circuit, a resonant network, a transformer, a secondary-side circuit, and a voltage divider circuit connected in series, and a control device for controlling the secondary-side circuit, wherein:

[0009] The secondary-side circuit includes three three-level bridge arms and three clamping circuits. The first, second, third, and fourth switches in each three-level bridge arm are connected in series and then connected between the positive and negative external terminals of the secondary side of the bidirectional three-phase LLC DC resonant converter. A clamping circuit is connected in parallel between the connection point of the first and second switches and the connection point of the third and fourth switches in each three-level bridge arm. Each clamping circuit is used to clamp the voltage stress borne by each switch in the corresponding three-level bridge arm to half of the secondary-side input voltage of the bidirectional three-phase LLC DC resonant converter.

[0010] The control device is configured to provide drive for each switching transistor in each three-level bridge arm using a two-level control method, specifically:

[0011] The first and second switches in each three-level bridge arm are driven in the same way, and the third and fourth switches are driven in the same way.

[0012] The driving of the first and second switches in each three-level bridge arm is complementary to the driving of the third and fourth switches.

[0013] The driving of the first and second switches in the first three-level bridge arm, the driving of the first and second switches in the second three-level bridge arm, and the driving of the first and second switches in the third three-level bridge arm are phase-shifted by 120°.

[0014] Preferably, the transformer comprises three independent transformers or one magnetically integrated transformer.

[0015] Preferably, the connection method of the three independent transformers or one magnetic integrated transformer includes: both the primary and secondary sides are delta-connected; or the primary side is delta-connected and the secondary side is Y-connected; or both the primary and secondary sides are Y-connected; or the primary side is Y-connected and the secondary side is delta-connected.

[0016] Preferably, the clamping circuit includes a first clamping diode, a second clamping diode, and a clamping capacitor. The cathode of the first clamping diode is connected to the connection point of the first and second switching transistors in the three-level bridge arm. The anode of the first clamping diode and the cathode of the second clamping diode are simultaneously connected to the voltage divider point of the voltage divider circuit. The anode of the second clamping diode is connected to the connection point of the third and fourth switching transistors in the three-level bridge arm. The clamping capacitor is connected between the cathode of the first clamping diode and the anode of the second clamping diode.

[0017] Furthermore, the clamping circuit also includes an energy dissipation unit connected between the cathode of the first clamping diode and the anode of the second clamping diode.

[0018] Preferably, the energy-consuming unit is a resistor.

[0019] Preferably, the control device is a digital IC.

[0020] Preferably, the digital IC is HXX320F280025CPNS or 3065PNPIRH.

[0021] Preferably, the voltage divider circuit includes two capacitors connected in series.

[0022] Furthermore, the capacitance values ​​of the two capacitors are equal.

[0023] The bidirectional three-phase LLC DC-DC resonant converter of this embodiment enables the voltage stress on the secondary-side switching devices to be half that of the secondary-side input voltage. This allows for full utilization of the switching device characteristics, improving power efficiency, reducing size, and lowering cost. Furthermore, the use of a two-level control method on the three-level bridge arm simplifies control complexity and reduces the cost of the control IC. Detailed analysis of the beneficial effects is as follows:

[0024] (1) The secondary side circuit of the bidirectional three-phase LLC DC resonant converter in this embodiment adopts a three-level three-bridge arm structure. Through the clamping circuit and voltage divider circuit, the voltage stress of each switch in the secondary side three-level bridge arm is clamped to half of the secondary side input voltage, which reduces the stress of the switching device. Especially when the secondary side input is around 230V, 150V or 200V low voltage MOS transistors can be selected. Compared with the previously selected 650V high voltage MOS or IGBT, the switching loss of the power supply can be reduced and the efficiency can be improved. Furthermore, by increasing the switching frequency, the size of the magnetic device can be reduced, thereby reducing the cost of the power supply.

[0025] (2) The bidirectional three-phase LLC DC resonant converter of this utility model adopts a two-level control method on the three-level bridge arm, which simplifies the 18 drive signals (6 primary side + 12 secondary side) into 12 drive signals (6 primary side + 6 secondary side), which simplifies the control complexity. Thus, the requirements can be met by using only conventional digital ICs, reducing the cost of control ICs. Attached Figure Description

[0026] Figure 1 The circuit diagram of the bidirectional three-phase LLC DC resonant converter of this utility model shows the YY connection.

[0027] Figure 2 The circuit diagram of the bidirectional three-phase LLC DC resonant converter of this utility model shows a Y-Δ connection.

[0028] Figure 3The circuit diagram of the bidirectional three-phase LLC DC resonant converter of this utility model shows the Δ-Y connection.

[0029] Figure 4 The circuit diagram of the bidirectional three-phase LLC DC resonant converter of this utility model shows a Δ-Δ connection.

[0030] Figure 5 This is a diagram showing the clamping state of the secondary side three-level bridge arm of this utility model;

[0031] Figure 6 This is the timing diagram for driving the switching transistor when the switching frequency is equal to the resonant frequency. Detailed Implementation

[0032] To make the above-mentioned objectives, features, and advantages of this utility model more apparent and understandable, the specific embodiments of this utility model will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0033] It should be noted that the terms "comprising" and "having" and any variations thereof described in the specification and claims of this application are intended to cover non-exclusive inclusion. For example, including a series of components, unit circuits or control timings is not necessarily limited to those components, unit circuits or control timings that are explicitly listed, but may include components, unit circuits or control timings that are not explicitly listed or that are inherent to these circuits.

[0034] Furthermore, unless otherwise specified, the embodiments and features described in this application may be combined with each other.

[0035] It should be understood that, in the specification and claims, when an element is described as being "connected" to another element, that element may be "directly connected" to that other element or "connected" to that other element through a third element; when a step is described as being connected to another step, that step may be connected directly to that other step or connected to that other step through a third step.

[0036] This utility model provides a bidirectional three-phase LLC DC-DC resonant converter, comprising a primary-side circuit, a resonant network, a transformer, a secondary-side circuit, and a voltage divider circuit connected in series, and a control device for controlling the secondary-side circuit, wherein:

[0037] The secondary-side circuit includes three three-level bridge arms and three clamping circuits. The first, second, third, and fourth switches in each three-level bridge arm are connected in series and then connected between the positive and negative external terminals of the secondary side of the bidirectional three-phase LLC DC resonant converter. A clamping circuit is connected in parallel between the connection point of the first and second switches and the connection point of the third and fourth switches in each three-level bridge arm. Each clamping circuit is used to clamp the voltage stress borne by each switch in the corresponding three-level bridge arm to half of the secondary-side input voltage of the bidirectional three-phase LLC DC resonant converter.

[0038] The control device is configured to provide drive for each switch in each three-level bridge arm using a two-level control method, specifically:

[0039] The first and second switches in each three-level bridge arm are driven in the same way, and the third and fourth switches are driven in the same way.

[0040] The driving of the first and second switches in each three-level bridge arm is complementary to the driving of the third and fourth switches.

[0041] The driving of the first and second switches in the first three-level bridge arm, the driving of the first and second switches in the second three-level bridge arm, and the driving of the first and second switches in the third three-level bridge arm are phase-shifted by 120°.

[0042] Figure 1-4 The topology diagram of the bidirectional three-phase LLC DC resonant converter of this invention is given, including the primary side circuit, resonant network, transformer, secondary side circuit and voltage divider capacitor connected in series.

[0043] The primary side circuit is a three-phase two-level bridge arm, consisting of switches Q1 to Q6. Each switch is connected in parallel with a parasitic diode and a capacitor. The drive signals of the upper and lower switches of each bridge arm are complementary, and the phase difference of the drive signals between each bridge arm is 120°.

[0044] Connect the series resonant network composed of Cr1, Lr1, Cr2, Lr2, Cr3, and Lr3 through the midpoints A, B, and C of the bridge arms, respectively.

[0045] Resonant network series transformer, the connection method between the windings of three independent or one magnetically integrated transformer includes... Figure 4 The primary and secondary sides of T1, T2, and T3 shown are all connected by triangles. Figure 3 The primary triangles T1, T2, and T3 shown are connected to the secondary triangles in a Y-shape. Figure 1 The primary and secondary sides of T1, T2, and T3 shown are all Y-shaped connections, and Figure 2 The primary side Y-shaped connection of T1, T2, and T3 to the secondary side triangle is shown.

[0046] In addition to being connected between the bridge arm and the transformer, the resonant network can also be connected individually between the three-phase transformer windings for each phase.

[0047] The transformer is connected in series with the secondary side circuit via terminals a, b, and c. The secondary side circuit consists of a three-phase three-level bridge arm and clamping circuits. The three-phase three-level bridge arm is composed of switches S1 to S12, each with a parasitic diode and a capacitor connected in parallel. The three clamping circuits consist of terminals D1 to D6, capacitors C1 to C3, and resistors R1 to R3. The two ends of the clamping circuits are connected to the midpoint of the three-level bridge arm, and the midpoint of the clamping circuits is connected to the midpoint O of the voltage divider capacitors.

[0048] Figure 5 The diagram shows the clamping state of the three-level bridge arm on the secondary side of this invention, indicating the clamping state of the MOSFET when the three-level bridge arm adopts a two-level control method. The clamping capacitor voltage is equal to the voltage of a single voltage divider capacitor, which is equal to half of the secondary side input voltage.

[0049] The working principle of the clamping circuit will be explained in detail below using a bridge arm as an example. Figure 5 As shown in the left figure, when switches S1 and S2 are on, switches S3 and S4 are complementary off. At this time, the current flow path is: positive terminal of voltage divider capacitor CF1 → switch S1 → clamping capacitor C1 → clamping diode D2 → negative terminal of voltage divider capacitor CF1. Voltage divider capacitor CF1 clamps clamping capacitor C1 through switch S1 and clamping diode D2. Since switch S2 is on, the voltage of lower transistor S3 is clamped by clamping capacitor C1. The voltage stress of switch S3 is equal to the voltage of clamping capacitor C1 and equal to the voltage of voltage divider capacitor CF1 (ignoring the forward voltage drop of switch S1 and clamping diode D2). If the capacitance values ​​of voltage divider capacitor CF1 and voltage divider capacitor CF2 are set to be equal, then the voltage across switches S3 and S4 is equal to half of the secondary side input voltage.

[0050] It should be noted that if the clamping capacitor voltage C1 is higher than the voltage of the voltage divider capacitor CF1 during voltage sudden changes or peak energy accumulation, then... Figure 5 In the left diagram, clamping diode D2 will be reverse biased and cut off, preventing the voltage of the lower switch S3 from being clamped. The voltage stress on switch S3 is equal to the voltage of the clamping capacitor, but higher than the voltage of CF1, resulting in uneven voltage distribution between the two lower transistors (switches S3 and S4). Figure 5 In the left diagram, the energy consumption unit (i.e., resistor R1) connected in parallel with the clamping capacitor can dissipate the peak energy in the circuit in a timely manner, so that the excess energy of the clamping capacitor is consumed by the energy consumption unit, thus effectively maintaining the voltage equalization of switches S3 and S4.

[0051] like Figure 5 As shown in the right figure, when switches S3 and S4 are on, switches S1 and S2 are complementaryly off. Those skilled in the art can refer to the above... Figure 5The working principle under the condition shown in the left figure can be derived by yourself; it will not be elaborated here.

[0052] The beneficial effects of the above circuit are, for example, when the secondary side input voltage is around 230V, the voltage of a single voltage divider capacitor is 115V. At this time, the plateau voltage of a single MOSFET in a three-level bridge arm is 115V, so a 150V low-voltage transistor can be selected. If a three-phase two-level bridge arm is used, considering the transient voltage spike margin, a switching transistor of 300V or higher should be selected. Market research shows that in the actual market, only 650V voltage level devices are available for 300V devices. However, the switching speed, switching loss, and on-resistance of 650V voltage level switching devices are poor, and the cost is also higher than that of low-voltage devices.

[0053] Therefore, this utility model can improve power supply efficiency, reduce size, and lower cost by reducing the voltage stress of the three-phase three-level bridge arm switching devices on the secondary side and optimizing device selection.

[0054] Figure 6 The following is a timing diagram of the switching transistors driven by the bidirectional three-phase LLC DC resonant converter of this invention when the switching frequency is equal to the resonant frequency. The driving of S1 and S2 is the same, the driving of S3 and S4 is the same, the driving of S5 and S6 is the same, the driving of S7 and S8 is the same, the driving of S9 and S10 is the same, and the driving of S11 and S12 is the same.

[0055] S1 and S2 drivers complement S3 and S4 drivers; S5 and S6 drivers complement S7 and S8 drivers; S9 and S10 drivers complement S11 and S12 drivers.

[0056] The drive signals S1, S2, S5, S6, S9, and S10 are phase-shifted by 120°.

[0057] Therefore, this utility model simplifies the drive signals of the three-phase three-level bridge arm switching devices on the secondary side and adopts a two-level control method, thereby reducing the total number of drive signals in the bidirectional three-phase LLC DC resonant converter. The 18 drive signals (6 on the primary side + 12 on the secondary side) are simplified to 12 drive signals (6 on the primary side + 6 on the secondary side), which simplifies the control complexity. The requirements can be met by using only conventional digital ICs (such as HXX320F280025CPNS from Zhongke Haoxin or 3065PNPIRH from HiSilicon), thus reducing the cost of the control IC.

[0058] The above are merely embodiments of this utility model. It should be particularly noted that the above embodiments should not be regarded as limitations on this utility model. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of this utility model, and these improvements and modifications should also be regarded as protection scope of this utility model.

Claims

1. A bidirectional three-phase LLC DC-DC resonant converter, comprising a primary-side circuit, a resonant network, a transformer, a secondary-side circuit, and a voltage divider circuit connected in series, and a control device for controlling the secondary-side circuit, characterized in that: The secondary-side circuit includes three three-level bridge arms and three clamping circuits. The first, second, third, and fourth switches in each three-level bridge arm are connected in series and then connected between the positive and negative external terminals of the secondary side of the bidirectional three-phase LLC DC resonant converter. A clamping circuit is connected in parallel between the connection point of the first and second switches and the connection point of the third and fourth switches in each three-level bridge arm. Each clamping circuit is used to clamp the voltage stress borne by each switch in the corresponding three-level bridge arm to half of the secondary-side input voltage of the bidirectional three-phase LLC DC resonant converter. The control device is configured to provide drive for each switching transistor in each three-level bridge arm using a two-level control method, specifically: The first and second switches in each three-level bridge arm are driven in the same way, and the third and fourth switches are driven in the same way. The driving of the first and second switches in each three-level bridge arm is complementary to the driving of the third and fourth switches. The driving of the first and second switches in the first three-level bridge arm, the driving of the first and second switches in the second three-level bridge arm, and the driving of the first and second switches in the third three-level bridge arm are phase-shifted by 120°.

2. The bidirectional three-phase LLC DC-DC resonant converter according to claim 1, characterized in that: The transformer may consist of three independent transformers or one magnetically integrated transformer.

3. The bidirectional three-phase LLC DC-DC resonant converter according to claim 1, characterized in that, The connection methods of the three independent transformers or one magnetic integrated transformer include: both the primary and secondary sides are delta-connected; or the primary side is delta-connected and the secondary side is Y-connected; or both the primary and secondary sides are Y-connected; or the primary side is Y-connected and the secondary side is delta-connected.

4. The bidirectional three-phase LLC DC-DC resonant converter according to claim 1, characterized in that: The clamping circuit includes a first clamping diode, a second clamping diode, and a clamping capacitor. The cathode of the first clamping diode is connected to the connection point of the first and second switching transistors in the three-level bridge arm. The anode of the first clamping diode and the cathode of the second clamping diode are simultaneously connected to the voltage divider point of the voltage divider circuit. The anode of the second clamping diode is connected to the connection point of the third and fourth switching transistors in the three-level bridge arm. The clamping capacitor is connected between the cathode of the first clamping diode and the anode of the second clamping diode.

5. The bidirectional three-phase LLC DC-DC resonant converter according to claim 4, characterized in that: The clamping circuit further includes an energy dissipation unit connected between the cathode of the first clamping diode and the anode of the second clamping diode.

6. The bidirectional three-phase LLC DC-DC resonant converter according to claim 1, characterized in that: The energy-consuming unit is a resistor.

7. The bidirectional three-phase LLC DC-DC resonant converter according to claim 1, characterized in that: The control device is a digital IC.

8. The bidirectional three-phase LLC DC-DC resonant converter according to claim 7, characterized in that: The digital IC is either HXX320F280025CPNS or 3065PNPIRH.

9. The bidirectional three-phase LLC DC-DC resonant converter according to claim 1, characterized in that: The voltage divider circuit includes two capacitors connected in series.

10. The bidirectional three-phase LLC DC-DC resonant converter according to claim 9, characterized in that: The two capacitors have the same capacitance value.

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