DC-DC conversion circuit for balancing DC bus

Abstract

The DC-DC conversion circuit for balancing the DC buses comprises a first switch tube, a second switch tube, a third switch tube and a fourth switch tube which are connected in series between the DC buses and are respectively connected with a first diode, a second diode, a third diode and a fourth diode in anti-parallel connection; one end of the first inductor is connected to the positive electrode of the battery, and the other end of the first inductor is connected to a first node between the first switching tube and the second switching tube; one end of the second inductor is connected to the negative electrode of the battery, and the other end of the second inductor is connected to a third node between the third switching tube and the fourth switching tube; a first switch connected between the first inductor and the positive electrode of the battery or between the second inductor and the negative electrode of the battery; the third switch and the third inductor are connected in parallel and are connected between a second node between the second switch tube and the third switch tube and the ground; wherein the first switch and the third switch are controlled to realize the balance between the positive and negative DC buses.

Description

Technical Field

[0001] The invention relates to the field of power electronics, and in particular to a DC-DC conversion circuit for balancing a DC bus. Background Art

[0002] In some uninterruptible power supplies (UPS), the rectifier bridge arm is used when the battery is discharged. The DC-DC converter of the battery is only used for charging and cannot balance the DC bus voltage. Therefore, an additional balancing bridge arm is required to balance the DC bus voltage. The additional balancing bridge arm will increase the number of semiconductor devices in the UPS, increase the system cost, and reduce the integrated power density of the module. Therefore, a simple circuit and method are needed to balance the DC bus voltage. Summary of the invention

[0003] Based on the above problems in the prior art, the present invention provides a DC-DC conversion circuit for balancing a DC bus, comprising:

[0004] A first switch tube, a second switch tube, a third switch tube and a fourth switch tube connected in series between the DC bus bars, wherein the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are respectively connected in reverse parallel with a first diode, a second diode, a third diode and a fourth diode;

[0005] A first inductor, one end of which is connected to the positive electrode of the battery, and the other end of which is connected to a first node between the first switch tube and the second switch tube;

[0006] A second inductor, one end of which is connected to the negative electrode of the battery, and the other end of which is connected to a third node between the third switch tube and the fourth switch tube;

[0007] a first switch connected between the first inductor and the positive electrode of the battery or between the second inductor and the negative electrode of the battery;

[0008] A third switch and a third inductor connected in parallel, connected between a second node between the second switch tube and the third switch tube and ground;

[0009] The balance between the positive DC bus and the negative DC bus is achieved by controlling the first switch and the third switch.

[0010] In one embodiment, the invention further comprises a second switch connected between the negative electrode of the battery and the second inductor, the first switch is connected between the positive electrode of the battery and the first inductor, wherein the switching mode of the second switch is the same as that of the first switch.

[0011] In one embodiment, it further includes:

[0012] A fifth diode has an anode connected to the ground and a cathode connected to the first node.

[0013] In one embodiment, it further includes:

[0014] A sixth diode has a cathode connected to the ground and an anode connected to the third node.

[0015] In one embodiment, the anode of the first diode is connected to the first node, and the cathode is connected to the positive DC bus, the anode of the second diode is connected to the second node, and the cathode is connected to the first node, the anode of the third diode is connected to the third node, and the cathode is connected to the second node, and the anode of the fourth diode is connected to the negative DC bus, and the cathode is connected to the third node.

[0016] In one embodiment, when the first switch and the third switch are turned on, the DC-D conversion circuit operates in a charge-discharge mode, and when the first switch and the third switch are turned off, the DC-DC conversion circuit operates in a balance mode.

[0017] In one embodiment, in the balanced mode and when the current of the third inductor is greater than 0 (i.e., the current direction of the inductor current flows from the second node to the ground), the first switch tube and the second switch tube receive the same PWM signal, and the third switch tube and the fourth switch tube are disconnected;

[0018] When the first switch tube and the second switch tube are turned on, the current path is the positive DC bus-the first switch tube-the second switch tube-the third inductor-the ground;

[0019] When the first switch tube and the second switch tube are disconnected, the current path is the negative DC bus-the fourth diode-the third diode-the third inductor-the ground.

[0020] In one embodiment, in the balanced mode and when the current of the third inductor is less than 0 (i.e., the current direction of the inductor current flows from the ground to the second node), the third switch tube and the fourth switch tube receive the same PWM signal, and the first switch tube and the second switch tube are disconnected;

[0021] When the third switch tube and the fourth switch tube are turned on, the current path is ground-third inductor-third switch tube-fourth switch tube-negative DC bus;

[0022] When the third switch tube and the fourth switch tube are disconnected, the current path is ground-third inductor-second diode-first diode-positive DC bus.

[0023] In one embodiment, the first inductor and the second inductor are mutually coupled inductors.

[0024] In one embodiment, the first switch, the second switch and the third switch are relays, circuit breakers, IGBTs or MOSFETs.

[0025] The DC-DC conversion circuit for balancing a DC bus of the present invention can operate in a charging mode, a discharging mode and a balancing mode, and can effectively save system cost, reduce the number of semiconductor devices, and improve the integrated power density of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A circuit diagram of a DC-DC conversion circuit for balancing a DC bus according to an embodiment of the present invention is shown.

[0027] Figure 2 The current path of the DC-DC converter circuit in charging mode for balancing the DC bus is shown.

[0028] Figure 3 The current path of the DC-DC converter circuit in the discharge mode for balancing the DC bus is shown.

[0029] Figure 4 The current path of the DC-DC converter circuit for balancing the DC bus is shown in the balanced mode when the inductor current is greater than 0.

[0030] Figure 5 The current path of the DC-DC converter circuit for balancing the DC bus is shown in the balanced mode when the inductor current is less than 0. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be noted that the embodiments given in the present invention are only for illustration and do not limit the protection scope of the present invention.

[0032] Figure 1 FIG. 2 shows a circuit diagram of a DC-DC converter circuit for balancing a DC bus according to an embodiment of the present invention. Figure 1As shown, the DC-DC conversion circuit includes a switch tube T1, a switch tube T2, a switch tube T3 and a switch tube T4 connected in series between DC buses, wherein the switch tube T1, the switch tube T2, the switch tube T3 and the switch tube T4 respectively have a diode D1, a diode D2, a diode D3 and a diode D4 connected in reverse parallel therewith, wherein a node N1 is provided between the switch tube T1 and the switch tube T2, a node N2 is provided between the switch tube T2 and the switch tube T3, and a node N3 is provided between the switch tube T3 and the switch tube T4; an inductor L1, one end of which is connected to the switch K1, and the other end is connected to the node N1; the switch K1, one end of which is connected to the inductor L1, and the other end is connected to the positive electrode of the battery S1; the inductor L2, one end of which is connected to the switch K2, and the other end is connected to the node N3; the switch K2, one end of which is connected to the inductor L2, and the other end is connected to the negative electrode of the battery S1; the inductor L3, one end of which is connected to the node N2, and the other end is connected to the ground GND. A switch K3 is connected in parallel to both ends of the inductor L3; a diode D5 has a cathode connected to the node N1 and an anode connected to the ground GND; and a diode D6 has an anode connected to the node N3 and a cathode connected to the ground GND.

[0033] The switch tube T1 has a first end connected to the positive DC bus DC+, a second end connected to the switch tube T2, and a control end for receiving a control signal. The anode of the diode D1 is connected to the second end of the switch tube T1, and the cathode is connected to the first end of the switch tube T1. The switch tube T2 has a first end connected to the switch tube T1, a second end connected to the switch tube T3, and a control end for receiving a control signal. The anode of the diode D2 is connected to the second end of the switch tube T2, and the cathode is connected to the first end of the switch tube T2. The switch tube T3 has a first end connected to the switch tube T2, a second end connected to the switch tube T4, and a control end for receiving a control signal. The anode of the diode D3 is connected to the second end of the switch tube T3, and the cathode is connected to the first end of the switch tube T3. The switch tube T4 has a first end connected to the switch tube T3, a second end connected to the negative DC bus DC-, and a control end for receiving a control signal. The anode of the diode D4 is connected to the second end of the switch tube T4, and the cathode is connected to the first end of the switch tube T4.

[0034] In one embodiment, the control terminals of the switches T1-T4 are used to receive PWM signals. Figure 1The switch tubes T1-T4 are shown as NPN structures, but the present invention is not limited thereto, and the switch tubes T1-T4 can also be implemented as PNP structures. In one embodiment, the switch tubes T1-T4 include but are not limited to insulated gate bipolar transistors (IGBTs) and metal-oxide semiconductor field effect transistors (MOSFETs). In one embodiment, the switch tubes T1 and T4 are 950V IGBTs, and T2 and T3 are 650V IGBTs. The specifications of the switch tubes T1-T4 can be adjusted according to the power requirements.

[0035] In one embodiment, the switches K1 - K3 may be implemented as relays, circuit breakers, IGBTs, MOSFETs, etc.

[0036] exist Figure 1 The voltage between the DC buses is shown by power supplies S2 and S3. In the present invention, the voltage of the positive DC bus DC+ is V+, and the voltage of the negative DC bus DC- is V-.

[0037] The following combination Figure 2-Figure 5 The charging mode, discharging mode and balancing mode of the DC-DC conversion circuit for balancing the DC bus of the present invention are described.

[0038] Figure 2 The figure shows the current path of the DC-DC converter circuit for balancing the DC bus in the charging mode. In the charging mode, switches K1, K2 and K3 are turned on, the control terminals of the switch tubes T1 and T4 receive the same PWM signal, and are periodically turned on or off, while the switch tubes T2 and T3 remain off.

[0039] When the switches T1 and T4 are turned on, the current path is as follows: Figure 2 As shown by the solid arrow in the figure, the positive DC bus DC+-switch tube T1-inductor L1-switch K1-battery positive pole-battery negative pole-switch K2-inductor L2-switch tube T4-negative DC bus DC-. At this time, the DC bus charges the battery S1, and energy is stored in the inductors L1 and L2. Inductors L1 and L2 allow the current from the DC bus to rise slowly to prevent the current from being too large to damage the battery S1.

[0040] When the switches T1 and T4 are disconnected, the current path is as follows: Figure 2 As shown by the dotted arrow in FIG, that is, the negative electrode of the battery - switch K2 - inductor L2 - diode D3 - diode D2 - inductor L1 - switch K1 - positive electrode of the battery. At this time, the energy stored in the inductors L1 and L2 is discharged, and the battery S1 is charged at the same time.

[0041] Figure 3The figure shows the current path of the DC-DC converter circuit for balancing the DC bus in the discharge mode. In the discharge mode, switches K1, K2 and K3 are turned on, the control terminals of the switch tubes T2 and T3 receive the same PWM signal, and are periodically turned on or off, while the switch tubes T1 and T4 remain off.

[0042] When the switches T2 and T3 are turned on, the current path is as follows: Figure 3 As shown by the solid arrow in , that is, the positive electrode of the battery - switch K1 - inductor L1 - switch tube T2 - switch tube T3 - inductor L2 - switch K2 - negative electrode of the battery. At this time, the battery S1 is discharged into the inductors L1 and L2, and the electric energy is stored in the inductors L1 and L2.

[0043] When the switches T2 and T3 are disconnected, the current path is as follows: Figure 3 As shown by the dotted arrow in the figure, inductor L1-diode D1-positive DC bus DC+-negative DC bus DC--diode D4-inductor L2. At this time, inductors L1 and L2 discharge the stored energy to the DC bus.

[0044] Figure 4 The current path of the DC-DC converter circuit for balancing the DC bus is shown in the balanced mode and the inductor current is greater than 0 (i.e., the current direction of the inductor current flowing from the node N2 to the ground GND). That is, the voltage amplitude V+ of the positive DC bus DC+ is greater than the voltage amplitude |V-| of the negative DC bus DC-. In this mode, switches K1, K2 and K3 are disconnected, the control terminals of the switch tubes T1 and T2 receive the same PWM signal, and are periodically turned on or off, and the switch tubes T3 and T4 remain disconnected.

[0045] When the switches T1 and T2 are turned on, the current path is as follows: Figure 4 As shown by the solid arrow in the figure, that is, the positive DC bus DC+-switch tube T1-switch tube T2-inductor L3-ground GND. At this time, the electric energy of the positive DC bus DC+ is discharged, so that the voltage amplitude V+ of the positive DC bus DC+ becomes smaller, and finally the voltage amplitude V+ of the positive DC bus DC+ is equal to the voltage amplitude |V-| of the negative DC bus DC-. Inductor L3 is used for energy storage.

[0046] When the switches T1 and T2 are disconnected, the current path is as follows: Figure 4 As shown by the dotted arrow in the figure, the negative DC bus DC--diode D4-diode D3-inductor L3-ground GND. At this time, the electric energy of the negative DC bus DC- is discharged, so that the voltage amplitude |V-| of the negative DC bus DC- increases, and finally the voltage amplitude V+ of the positive DC bus DC+ is equal to the voltage amplitude |V-| of the negative DC bus DC-. Inductor L3 is used for energy storage.

[0047] Figure 5The current path of the DC-DC converter circuit for balancing the DC bus is shown in the balanced mode and the inductor current is less than 0 (i.e., the current direction of the inductor current flowing from the ground GND to the node N2). That is, the voltage amplitude V+ of the positive DC bus DC+ is less than the voltage amplitude |V-| of the negative DC bus DC-. In this mode, switches K1, K2 and K3 are disconnected, the control terminals of the switch tubes T3 and T4 receive the same PWM signal, and are periodically turned on or off, and the switch tubes T1 and T2 remain disconnected.

[0048] When the switches T3 and T4 are turned on, the current path is as follows: Figure 4 As shown by the solid arrow in , that is, ground GND-inductor L3-switch tube T3-switch tube T4-negative DC bus DC-. At this time, the electric energy stored in the inductor L3 is discharged to the negative DC bus DC-, so that the voltage amplitude |V-| of the negative DC bus DC- becomes smaller, and finally the voltage amplitude V+ of the positive DC bus DC+ is equal to the voltage amplitude |V-| of the negative DC bus DC-. The inductor L3 is used to provide electric energy.

[0049] When the switches T3 and T4 are disconnected, the current path is as follows: Figure 4 As shown by the dotted arrow in , that is, ground GND-inductor L3-diode D2-diode D1-positive DC bus DC+. At this time, the electric energy stored in the inductor L3 is discharged to the positive DC bus DC+, so that the voltage amplitude V+ of the positive DC bus DC+ increases, and finally the voltage amplitude V+ of the positive DC bus DC+ is equal to the voltage amplitude |V-| of the negative DC bus DC-. The inductor L3 is used to provide electric energy.

[0050] Diode D5 is used to provide voltage balancing for switch tubes T1 and T2 in balanced mode, and diode D6 is used to provide voltage balancing for switch tubes T3 and T4 in balanced mode to prevent the switch tubes from being damaged by excessive voltage and improve the reliability of the system. Figure 5 , in the balanced mode and the inductor current is less than 0, when the switches T3 and T4 are turned on, the voltage at the node N2 is V-, so the voltage that the switches T1 and T2 bear together is V+-V-. If there is no diode D5, there may be a situation where the voltage of the switches T1 and T2 is uneven. If the voltage division on the switch T1 or T2 is too large, the switch will be damaged. When the diode D5 is present, the voltage at the node N1 is about -0.7V, the voltage that the switch T2 bears is -0.7-V-, and the voltage that the switch T1 bears is (V+)-(-0.7V). Therefore, when the DC bus voltage is balanced, the voltages on the switches T1 and T2 are basically the same. In one embodiment, diodes D5 and D6 are small current Schottky diodes. In one embodiment, if the switches T1-T4 can withstand a sufficiently high voltage, diodes D5 and D6 can also be omitted.

[0051] Although two switches K1 and K2 are shown in the above embodiment, those skilled in the art should understand that the switches K1 and K2 are used to disconnect the current path between the battery S1 and the inductors L1 and L2, so the technical solution of the present invention can also be implemented using only one switch.

[0052] In one embodiment, the inductors L1 and L2 are two independent inductors. In another embodiment, the inductors L1 and L2 are mutually coupled inductors.

[0053] The DC-DC conversion circuit for balancing a DC bus of the present invention can operate in a charging mode, a discharging mode and a balancing mode, and can effectively save system cost, reduce the number of semiconductor devices, and improve the integrated power density of the system.

[0054] Although the present invention has been described through preferred embodiments, the present invention is not limited to the embodiments described herein but includes various changes and modifications that may be made without departing from the scope of the present invention.

Claims

1. A DC-DC conversion circuit for balancing a DC bus, comprising: A first switch tube, a second switch tube, a third switch tube and a fourth switch tube connected in series between the DC bus bars, wherein the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are respectively connected in reverse parallel with a first diode, a second diode, a third diode and a fourth diode; A first inductor, one end of which is connected to the positive electrode of the battery, and the other end of which is connected to a first node between the first switch tube and the second switch tube; A second inductor, one end of which is connected to the negative electrode of the battery, and the other end of which is connected to a third node between the third switch tube and the fourth switch tube; a first switch connected between the first inductor and the positive electrode of the battery or between the second inductor and the negative electrode of the battery; A third switch and a third inductor connected in parallel, connected between a second node between the second switch tube and the third switch tube and ground; The balance between the positive DC bus and the negative DC bus is achieved by controlling the first switch and the third switch.

2. The DC-DC conversion circuit for balancing a DC bus according to claim 1 further includes a second switch connected between the negative electrode of the battery and the second inductor, and the first switch is connected between the positive electrode of the battery and the first inductor, wherein the switching mode of the second switch is the same as that of the first switch.

3. The DC-DC conversion circuit for balancing a DC bus according to claim 1, further comprising: A fifth diode has an anode connected to the ground and a cathode connected to the first node.

4. The DC-DC conversion circuit for balancing a DC bus according to claim 1, further comprising: A sixth diode has a cathode connected to the ground and an anode connected to the third node.

5. The DC-DC conversion circuit for balancing a DC bus according to claim 1, wherein: The anode of the first diode is connected to the first node, and the cathode is connected to the positive DC bus. The anode of the second diode is connected to the second node, and the cathode is connected to the first node. The anode of the third diode is connected to the third node, and the cathode is connected to the second node. The anode of the fourth diode is connected to the negative DC bus, and the cathode is connected to the third node.

6. The DC-DC conversion circuit for balancing a DC bus according to claim 1, wherein: When the first switch and the third switch are turned on, the DC-DC conversion circuit operates in a charge-discharge mode, and when the first switch and the third switch are turned off, the DC-DC conversion circuit operates in a balance mode.

7. The DC-DC conversion circuit for balancing a DC bus according to claim 6, wherein: In the balance mode and when the current of the third inductor is greater than 0, the first switch tube and the second switch tube receive the same PWM signal, and the third switch tube and the fourth switch tube are disconnected; When the first switch tube and the second switch tube are turned on, the current path is the positive DC bus-the first switch tube-the second switch tube-the third inductor-the ground; When the first switch tube and the second switch tube are disconnected, the current path is the negative DC bus-the fourth diode-the third diode-the third inductor-the ground.

8. The DC-DC conversion circuit for balancing a DC bus according to claim 6, wherein: In the balance mode and when the current of the third inductor is less than 0, the third switch tube and the fourth switch tube receive the same PWM signal, and the first switch tube and the second switch tube are disconnected; When the third switch tube and the fourth switch tube are turned on, the current path is ground-third inductor-third switch tube-fourth switch tube-negative DC bus; When the third switch tube and the fourth switch tube are disconnected, the current path is ground-third inductor-second diode-first diode-positive DC bus.

9. The DC-DC conversion circuit for balancing a DC bus according to any one of claims 1 to 8, wherein: The first inductor and the second inductor are mutually coupled inductors.

10. The DC-DC conversion circuit for balancing a DC bus according to claim 2, wherein: The first switch, the second switch and the third switch are relays, circuit breakers, IGBTs or MOSFETs.

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