A three-phase inverter circuit and a charging module

Abstract

The utility model provides a kind of three-phase inverter circuit and charging module, wherein, three-phase inverter circuit includes: three half-bridge units, inverter capacitor and inverter inductance;The first end and the second end of three half-bridge units are electrically connected with direct current bus, the third end of three half-bridge units is electrically connected with corresponding inverter inductance respectively, one end of multiple inverter capacitors is electrically connected with corresponding inverter inductance respectively, the other end of multiple inverter capacitors is electrically connected with suspension midpoint.This application can flexibly adjust charging module input current waveform using three-phase half-bridge topology, to control the output or absorption of reactive power, realize high-performance reactive power compensation function, and there is no direct electrical connection between direct current bus midpoint and inverter capacitor midpoint, three-phase mutually coupled work, inverter inductance current ripple frequency is twice the switching frequency in half-bridge unit, can make inductance loss reduce, conducive to the improvement of electric energy conversion efficiency and power density.

Description

Technical Field

[0001] This utility model relates to the field of circuit technology, and in particular to a three-phase inverter circuit and a charging module. Background Technology

[0002] In the field of electric vehicle charging, the large filtering inductance and capacitance of the charging module can cause the voltage and current phases to be inconsistent on the transmission line, resulting in reactive power loss and causing significant reactive power loss on the line, which in turn causes additional losses to the power grid.

[0003] Traditional charging modules, due to topological limitations, cannot compensate for this reactive power, or their compensation performance is poor, leading to problems such as high harmonic distortion. For example, the three-phase Vienna topology, which is widely used in traditional electric vehicle charging, cannot achieve high-performance reactive power compensation. It can only adjust the power factor (PF) during charging to meet the needs of simple reactive power regulation, and adjusting the PF can also lead to problems such as deterioration of iTHD. Utility Model Content

[0004] This invention provides a three-phase inverter circuit and a charging module, aiming to solve the problem of poor reactive power compensation effect of charging modules in related technologies.

[0005] To address the aforementioned technical problems, the first aspect of this utility model provides three half-bridge units, inverter capacitors, and inverter inductors; the first and second ends of the three half-bridge units are electrically connected to a DC bus, the third ends of the three half-bridge units are respectively electrically connected to the first ends of the corresponding inverter inductors, the second ends of the three inverter inductors are all used for electrical connection to an external power grid, the first ends of multiple inverter capacitors are respectively electrically connected to the second ends of the corresponding inverter inductors, and the second ends of multiple inverter capacitors are all electrically connected to a floating midpoint; the frequency of the inverter inductor current is twice the frequency of the switching transistors in the half-bridge units.

[0006] Furthermore, the three-phase inverter circuit also includes three filter inductors, the first ends of the three filter inductors are respectively electrically connected to the second ends of the corresponding inverter inductors, and the second ends of the three filter inductors are all used for electrical connection to the external power grid.

[0007] Furthermore, it also includes two current sampling units, one of which is electrically connected to the second terminal of any one of the three inverter inductors, and the other of which is electrically connected to the second terminal of any one of the remaining two inverter inductors.

[0008] Furthermore, it also includes a voltage sampling unit, which is electrically connected to the second terminals of the three filter inductors respectively.

[0009] The second aspect of this utility model provides a charging module, including the three-phase inverter circuit as described in the first aspect of this utility model.

[0010] As can be seen from the above description, the three-phase half-bridge circuit used in this application can flexibly adjust the input current waveform to control the output or absorption of reactive power, realize high-performance reactive power compensation function and active power transmission, and there is no direct electrical connection between the DC bus midpoint and the inverter capacitor. The three phases work together with each other, and the inverter inductor current is affected by the two-phase half-bridge unit, so that the inductor current ripple frequency is twice the switching frequency in the half-bridge unit, which can reduce inductor loss and is beneficial to the improvement of power conversion efficiency and power density. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of a three-phase Vienna topology in related technologies;

[0012] Figure 2 This is a circuit diagram of a three-phase inverter circuit according to an embodiment of the present invention;

[0013] Figure 3 This is a circuit diagram of another three-phase inverter circuit according to an embodiment of the present invention;

[0014] Figure 4 This is a schematic diagram of a three-phase half-bridge topology with a neutral line in related technologies;

[0015] Figure 5 This is a diagram showing the phase correspondence between the inductor current waveform and the drive in a three-phase half-bridge topology with a neutral line in related technologies.

[0016] Figure 6 This is a diagram showing the phase correspondence between the inductor current waveform and the drive in a three-phase half-bridge circuit according to an embodiment of this utility model. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. Throughout the description, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the present utility model. Furthermore, the technical features involved in the various embodiments of the present utility model described below can be combined with each other as long as they do not conflict with each other.

[0018] In related technologies, electric vehicle charging modules mostly adopt the traditional three-phase Vienna topology, and its structure is as follows: Figure 1As shown, this topology, due to the presence of unidirectional diodes D1 to D6, cannot control bidirectional current flow, thus failing to achieve high-performance reactive power compensation regulation. To regulate reactive power, this topology can only adjust part of the current phase by controlling the conduction time of MOSFETs Q1 to Q6 during charging. However, to maintain sufficient charging power, this control method requires changing the MOSFET conduction time under different AC voltage phases, followed by filtering with a large filter to achieve the effect of changing the current phase. This inevitably leads to a deterioration in iTHD and makes reactive power compensation impossible when no DC power is output (such as in standby mode or when not charging to compensate for the reactive power of other devices). Therefore, this application provides a three-phase inverter circuit.

[0019] like Figure 2 The diagram shown is a circuit schematic of a three-phase inverter circuit according to an embodiment of the present invention. The three-phase inverter circuit includes: three half-bridge units 100, inverter capacitors (C1, C2, C3) and inverter inductors (L1, L2, L3); wherein, the first and second ends of the three half-bridge units 100 are electrically connected to the DC bus, the third ends of the three half-bridge units 100 are electrically connected to the first ends of the corresponding inverter inductors (L1, L2, L3), the second ends of the three inverter inductors (L1, L2, L3) are all used to connect to the external power grid, the first ends of the multiple inverter capacitors (C1, C2, C3) are electrically connected to the second ends of the corresponding inverter inductors (L1, L2, L3), and the second ends of the multiple inverter capacitors (C1, C2, C3) are all electrically connected to the floating midpoint.

[0020] Compared to the three-phase Vienna topology in related technologies, the three-phase half-bridge circuit used in this embodiment can flexibly adjust the input current waveform to control the output or absorption of reactive power, achieving high-performance reactive power compensation. Furthermore, there is no direct electrical connection between the DC bus neutral point and the inverter capacitors (C1, C2, C3) (i.e., no neutral line N connection). The three phases are mutually coupled, and the inverter inductor current is affected by the two-phase half-bridge unit 100, resulting in an inductor current ripple frequency twice the switching frequency in the half-bridge unit 100. This reduces inductor losses and improves energy conversion efficiency and power density. Further details can be found in the following sections. Figure 2 The three-phase inverter circuit also includes three filter inductors (L4, L5, L6). The first terminals of the three filter inductors (L4, L5, L6) are electrically connected to the second terminals of the corresponding inverter inductors (L1, L2, L3), and the second terminals of the three filter inductors (L4, L5, L6) are all used to connect to the external power grid.

[0021] Specifically, in this embodiment, the filter inductors (L4, L5, L6) can be combined with the inverter capacitors (C1, C2, C3) and inverter inductors (L1, L2, L3) to form an LCL filter, which is used to suppress high-frequency harmonics generated by the inverter circuit and improve the stability of the system.

[0022] like Figure 3 The diagram shown is a circuit schematic of another three-phase inverter circuit provided in this embodiment of the present invention. Please refer to [link / reference]. Figure 2 and Figure 3 The three-phase inverter circuit also includes two current sampling units 200. One current sampling unit 200 is electrically connected to the second terminal of any one of the three inverter inductors (L1, L2, L3), and the other current sampling unit 200 is electrically connected to the second terminal of any one of the remaining two inverter inductors.

[0023] Further, please see Figure 2 and Figure 3 The three-phase inverter circuit also includes a voltage sampling unit 300, which is electrically connected to the second terminals of three filter inductors (L4, L5, L6).

[0024] Specifically, in this embodiment, the three-phase inverter circuit further includes two current sampling units 200 and one voltage sampling unit 300. Current and voltage signals can be acquired through the current sampling units 200 and 300, respectively. These current and voltage signals can be used to adjust the drive control signals of the switching transistors in the half-bridge unit 100 for reactive power compensation control of the charging module. Furthermore, the three-phase half-bridge circuit structure of this embodiment allows for the acquisition of three-phase current using only two current sampling units 200, simplifying the circuit design. It should be understood that adjusting the drive control signals of the switching transistors in the half-bridge unit 100 using the sampled current and voltage signals can be achieved using mature related solutions, which will not be elaborated upon here.

[0025] Furthermore, please see Figure 2 and Figure 3 The current sampling unit 200 includes a first shunt (RS1 / RS3) and a second shunt (RS2 / RS4). The first terminal of the first shunt (RS1 / RS3) is electrically connected to the second terminal of the corresponding inverter inductor (L1 / L2 / L3). The second terminal of the first shunt (RS1 / RS3) is electrically connected to the first terminal of the corresponding inverter capacitor (C1 / C2 / C3) and the first terminal of the second shunt (RS2 / RS4). The second terminal of the second shunt (RS2 / RS4) is electrically connected to the first terminal of the corresponding filter inductor (L4 / L5 / L6). The shunts can also be replaced by current measuring devices such as Hall effect devices.

[0026] Furthermore, the voltage sampling unit 300 includes three voltage divider resistor units, each including a first resistor (R1 / R3 / R5) and a second resistor (R2 / R4 / R6). The first terminal of the first resistor (R1 / R3 / R5) is electrically connected to the second terminal of the corresponding filter inductor (L4 / L5 / L6), and the second resistor (R2 / R4 / R6) is electrically connected to the second terminal of the first resistor (R1 / R3 / R5) and the virtual midpoint, respectively.

[0027] Furthermore, please see Figure 2 and Figure 3 The three-phase inverter circuit also includes a first bus capacitor C4 and a second bus capacitor C5. The first bus capacitor C4 is electrically connected to the positive terminal of the DC bus and the first terminal of the second bus capacitor C5, respectively. The second terminal of the second bus capacitor C5 is electrically connected to the negative terminal of the DC bus. The bus capacitors can be used to smooth the DC voltage and store energy.

[0028] Furthermore, please see Figure 2 and Figure 3 The half-bridge unit 100 includes a first power switch (Q1 / Q3 / Q5) and a second power switch (Q2 / Q4 / Q6). The first terminal of the first power switch (Q1 / Q3 / Q5) is electrically connected to the positive terminal of the DC bus. The second terminal of the first power switch (Q1 / Q3 / Q5) is electrically connected to the corresponding inverter inductor (L1 / L2 / L3) and the first terminal of the second power switch (Q2 / Q4 / Q6), respectively. The second terminal of the second power switch (Q2 / Q4 / Q6) is electrically connected to the negative terminal of the DC bus. The third terminals of the first power switch (Q1 / Q3 / Q5) and the second power switch (Q2 / Q4 / Q6) are both used for external control circuit electrical connections.

[0029] Specifically, in this embodiment, each phase half-bridge unit 100 includes two power switching transistors connected in series. These power switching transistors can be MOSFETs, IGBTs, BJTs, or other power switching devices. Taking MOSFETs as an example, in each phase half-bridge, the drain of the upper transistor is connected to the positive DC bus, and its source is connected to the drain of the lower transistor. The source of the lower transistor is connected to the negative DC bus. The midpoint of each phase bridge arm is connected to one end of an inverter inductor (i.e., L1, L2, L3). The other ends of two inverter inductors (L1, L3) are connected to one end of a shunt (RS1, RS3). The other end of the shunt is connected to one end of an inverter capacitor (C1, C3). The other end of the other inverter inductor (L2) is directly connected to one end of an inverter capacitor (C2). The other ends of the three inverter capacitors (C1, C2, C3) are connected to the same floating midpoint, without being connected to the bus midpoint or the neutral line N. One end of the shunt RS1 and one end of the inverter capacitor C1 are simultaneously connected to one end of the shunt RS2. The other end of S2 is connected to one end of the filter inductor L4, and the other end of the filter inductor L4 is connected to the port. One end of the current sampling shunt RS3 and one end of the inverter capacitor C3 are simultaneously connected to one end of the shunt RS4, and the other end of the shunt RS4 is connected to one end of the filter inductor L6, and the other end of the filter inductor L6 is connected to the port. The other ends of the inverter inductor L2 and the inverter capacitor C2 are simultaneously and directly connected to the filter inductor L5, and the other end of the filter inductor L5 is connected to the port. The voltage sampling unit 300 has one voltage divider resistor unit in each phase output, and the ends of the three voltage divider resistor units are connected to the same floating virtual midpoint.

[0030] It should be noted that the three-phase half-bridge topology can provide high-performance reactive power compensation, but for a three-phase half-bridge topology with a neutral line, its structure is as follows: Figure 4 As shown, due to the presence of the neutral line N, the three phases are completely decoupled into three independent single-phase circuits. That is, each of the three phase circuits operates independently, and the frequency of its inductor current is equal to the switching frequency of the MOSFET. The phase correspondence between its inductor current waveform and the drive is as follows: Figure 5 As shown, this results in a large inductor current ripple, high losses, and low power conversion efficiency, leading to low power density in the product.

[0031] In this embodiment, the three-phase half-bridge circuit lacks a neutral line, and the three phases are coupled together. During reactive power compensation, the current flows from the positive bus, through the upper half-bridge arm of one phase (e.g., MOSFET Q1), through the inverter inductor L1 and inverter capacitor C1 of that phase, then through the inverter capacitor (e.g., capacitor C2) of another phase, to the inverter inductor L2, and finally through the lower half-bridge arm MOSFET Q4 of that phase before returning to the negative bus. Thus, the inductor current ripple is affected by the MOSFETs of two phases, and the inductor current ripple frequency is twice the MOSFET switching frequency. The corresponding phase relationship between the inductor current waveform and the drive is shown in the diagram below. Figure 6As shown, the peak-to-peak value of the inductor ripple is reduced under this topology, and the inductor loss is decreased, effectively improving the product's power conversion efficiency and power density. Furthermore, two current sampling units 200 and a voltage sampling unit 300 respectively acquire current and voltage signals. Since there is no direct electrical connection between the bus midpoint (i.e., point O) of the three-phase half-bridge circuit and the midpoint of the inverter capacitors (C1 to C3), the LCL filter unit can use an asymmetrical current sampling method, that is, only sampling the current before and after two phase inverter capacitors (i.e., the current through the four shunts), and then calculating the inverter capacitor current of that phase through the current difference before and after the same phase. This inverter capacitor current can be used for virtual impedance compensation and control; and by the three-phase vector sum being 0, the inverter inductor current and inverter capacitor current of the third phase (excluding the two phases mentioned above) can be calculated. In addition, since the three-phase half-bridge topology has no neutral line, voltages U1, U2, and U3 are sampled by voltage division relative to the virtual midpoint, and the line voltage can be obtained by subtracting each pair of voltages. By acquiring these current and voltage signals, the operating mode of the three-phase half-bridge circuit can be controlled. The operating modes of the three-phase half-bridge circuit include charging mode (PF is constant at 1) and pure reactive power compensation mode (no active power is output, and it is used as a reactive power compensator).

[0032] The three-phase inverter circuit provided in this application embodiment can flexibly adjust the input current waveform to control the output or absorption of reactive power, thereby achieving high-performance reactive power compensation. Furthermore, there is no direct electrical connection between the bus midpoint and the LCL filter unit; the three phases are coupled together. During reactive power compensation, the inductor current in the LCL filter unit is affected by the two-phase half-bridge unit, causing the inductor current ripple frequency to be twice the switching frequency in the half-bridge unit. This reduces inductor losses and improves energy conversion efficiency and power density. Current and voltage signals are acquired through current and voltage sampling units, and the drive control signals of the switching transistors in the half-bridge unit are adjusted based on these signals, thereby achieving reactive power compensation control. Moreover, based on this three-phase half-bridge circuit structure, the three-phase current can be acquired through only two current sampling units, simplifying the circuit design.

[0033] This embodiment of the invention also provides a charging module, which includes the aforementioned three-phase inverter circuit. This charging module can be used in the field of electric vehicles.

[0034] It should be noted that the various embodiments in this utility model are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0035] It should also be noted that, in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Additionally, the character " / " in this document generally indicates an "or" relationship between the preceding and following objects.

[0036] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined in the present invention may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A three-phase inverter circuit, characterized in that, include: Three half-bridge units, inverter capacitors, and inverter inductors; among which, The first and second ends of the three half-bridge units are electrically connected to the DC bus, the third ends of the three half-bridge units are electrically connected to the first ends of the corresponding inverter inductors, the second ends of the three inverter inductors are all used to connect to the external power grid, the first ends of the plurality of inverter capacitors are electrically connected to the second ends of the corresponding inverter inductors, and the second ends of the plurality of inverter capacitors are all electrically connected to the floating midpoint; the frequency of the inverter inductor current is twice the frequency of the switching transistor in the half-bridge unit.

2. The three-phase inverter circuit according to claim 1, characterized in that, It also includes three filter inductors, the first end of each of the three filter inductors being electrically connected to the second end of the corresponding inverter inductor, and the second end of each of the three filter inductors being used to be electrically connected to the external power grid.

3. The three-phase inverter circuit according to claim 2, characterized in that, It also includes two current sampling units, one of which is electrically connected to the second terminal of any one of the three inverter inductors, and the other of which is electrically connected to the second terminal of any one of the remaining two inverter inductors.

4. The three-phase inverter circuit according to claim 3, characterized in that, The current sampling unit includes a first shunt and a second shunt. The first end of the first shunt is electrically connected to the second end of the corresponding inverter inductor. The second end of the first shunt is electrically connected to the first end of the corresponding inverter capacitor and the first end of the second shunt. The second end of the second shunt is electrically connected to the first end of the corresponding filter inductor.

5. The three-phase inverter circuit according to claim 2, characterized in that, It also includes a voltage sampling unit, which is electrically connected to the second terminal of each of the three filter inductors.

6. The three-phase inverter circuit according to claim 5, characterized in that, The voltage sampling unit includes three voltage divider resistor units, each including a first resistor and a second resistor. The first end of the first resistor is electrically connected to the second end of the corresponding filter inductor, and the second resistor is electrically connected to the second end of the first resistor and the virtual midpoint, respectively.

7. The three-phase inverter circuit according to claim 1, characterized in that, It also includes a first bus capacitor and a second bus capacitor. The first bus capacitor is electrically connected to the positive terminal of the DC bus and the first terminal of the second bus capacitor, respectively, and the second terminal of the second bus capacitor is electrically connected to the negative terminal of the DC bus.

8. The three-phase inverter circuit according to claim 1, characterized in that, The half-bridge unit includes a first power switch and a second power switch. The first end of the first power switch is electrically connected to the positive terminal of the DC bus. The second end of the first power switch is electrically connected to the corresponding inverter inductor and the first end of the second power switch. The second end of the second power switch is electrically connected to the negative terminal of the DC bus. The third ends of both the first power switch and the second power switch are used for external control circuit electrical connections.

9. A charging module, characterized in that, Includes the three-phase inverter circuit as described in any one of claims 1 to 8.

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