Single-stage bidirectional DC converter and single-phase household storage inverter based on single-stage bidirectional DC converter

Abstract

The invention discloses a single-stage bidirectional DC converter and a single-phase household storage inverter based on the single-stage bidirectional DC converter, the single-stage bidirectional DC converter is used for bidirectional charging and discharging of a battery and energy storage of household users, a DC bus side of the single-stage bidirectional DC converter is connected between a photovoltaic MPPT and the inverter or connected with other loads, a low-voltage side of the single-stage bidirectional DC converter is connected with the battery, and the single-phase household storage inverter is connected with the single-stage bidirectional DC converter. The topological structure of the single-stage bidirectional DC converter is simple, the number of components is small, and the equipment cost is reduced. The high-voltage side of the single-stage bidirectional DC converter can be connected in series with a single-phase inverter circuit, a half-bridge inverter circuit, a three-phase inverter circuit, a three-phase three-level inverter circuit or a split-phase inverter circuit, the neutral-point voltage can be balanced, the output bus voltage is stable, and the application scene of the household storage inverter is expanded.

Description

Technical Field

[0001] The present invention relates to the technical field of bidirectional DC conversion, and in particular to a single-phase household storage inverter based on a single-stage bidirectional DC converter. Background Art

[0002] Household storage inverter refers to the energy storage inverter on the household user side. Generally speaking, the power is below 30kW and the energy ranges from a few degrees to dozens of degrees. Its main functions are backup power supply, energy cost management, and maximizing the use of photovoltaic self-generated electricity.

[0003] In applications such as energy storage inverters, off-grid inverters, and grid-connected and off-grid inverters, inverter bridges (H4) or Heric (H6) are generally used, plus the maximum power point tracking (MPPT) part from Boost to the bus. It can be used to realize functions such as solar energy charging the battery, mains charging the battery, solar energy inverter grid-connected or off-grid output, battery inverter grid-connected or off-grid output, etc.

[0004] There are many topologies for bidirectional DC conversion circuits. Currently, the industry usually adopts LLC+buck / boost topology, or in some low-cost applications, only LLC bidirectional conversion is adopted. When LLC+buck / boost topology is adopted, the performance of this topology is better, but the cost is relatively high; when a single LLC solution is adopted, relevant conversion can be achieved, but there is a situation of voltage instability.

[0005] In energy storage inverters, off-grid inverters, grid-connected and off-grid inverters and other applications, when there is AC power, power is taken from the grid and converted into bus voltage, and then the battery is charged through bidirectional DC conversion; in LLC+buck / boost applications, due to the two-stage conversion, control and regulation can be easily achieved, and stable bus voltage output can be achieved, which is beneficial for inverter output parallel connection and MPPT application; in applications using LLC single-stage bidirectional conversion, in order to achieve soft switching control, due to the unstable bus voltage, when charging the battery, output parallel connection, grid-connected application, etc., the performance of the inverter is limited, which can easily cause the circuit to enter the protection state or even be damaged. Summary of the invention

[0006] In view of this, it is necessary to provide a single-stage bidirectional DC converter that can support bidirectional operation of battery charging and discharging and a single-phase household storage inverter based on the single-stage bidirectional DC converter.

[0007] A single-stage bidirectional DC converter for bidirectional battery charging and discharging, comprising a transformer T1, a bus-side circuit, a battery-side circuit and a controller, wherein the bus-side circuit is electrically connected to the primary side of the transformer T1, and the battery-side circuit is electrically connected to the secondary side of the transformer T1; The bus side circuit includes at least one energy storage branch, each of the energy storage branches includes a bus side switch tube, the battery side circuit includes a battery side switch tube, the controller is used to control the conduction and shutdown of the bus side switch tube and the battery side switch tube, and the battery side switch tube and the bus side switch tube are complementary switches.

[0008] Preferably, the energy storage branch includes a first inductor L1, a third capacitor C3 and a first switch tube Q1, the first inductor L1 and the third capacitor C3 are connected in series and connected to the same-name end of the primary winding of the transformer T1, and the free end of the first inductor L1 is connected to the DC bus VBUS; the drain of the first switch tube Q1 is connected to the midpoint of the first inductor L1 and the third capacitor C3, the source of the first switch tube Q1 is connected to the opposite-name end of the primary winding of the transformer T1 and is grounded, and the first capacitor C1 is connected between the free end of the first inductor L1 and the ground wire; The battery side circuit includes a second switch tube Q2, the drain of the second switch tube Q2 is connected to the opposite end of the secondary winding of the transformer T1, the source of the second switch tube Q2 is grounded, the same end of the secondary winding of the transformer T1 is connected to the positive electrode VBAT of the battery, and a fifth capacitor C5 is connected between the same end of the secondary winding of the transformer T1 and the ground line.

[0009] And, a single-phase household storage inverter based on a single-stage bidirectional DC converter, comprising the single-stage bidirectional DC converter as described above and an inverter circuit connected to the single-stage bidirectional DC converter, wherein the bus side circuit in the single-stage bidirectional DC converter comprises two energy storage branches, and the two energy storage branches are respectively connected to the DC bus positive electrode VBUS+ and the DC bus negative electrode VBUS-; Each of the energy storage branches includes a bus side switch tube, and the battery side circuit includes a battery side switch tube. The controller is used to control the conduction and shutdown of the bus side switch tube and the battery side switch tube, the bus side switch tubes are synchronously switched, and the battery side switch tube and the bus side switch tube are complementary switches.

[0010] Preferably, the two energy storage branches include a first energy storage branch and a second energy storage branch, the first energy storage branch and the second energy storage branch are respectively connected to the same-name end and the opposite-name end of the primary winding of the transformer T1, and the middle tap of the primary winding of the transformer T1 is grounded; the first energy storage branch includes an inductor L1-A, a third capacitor C3 and a first switch tube Q1, and the second energy storage branch includes an inductor L1-B, a fourth capacitor C4 and a second switch tube Q2; The inductor L1-A and the third capacitor C3 are connected in series and connected between the same-name end of the primary winding of the transformer T1 and the DC bus positive electrode VBUS+, the drain of the first switch tube Q1 is connected to the midpoint of the inductor L1-A and the third capacitor C3, and the source of the first switch tube Q1 is connected to the middle tap of the primary winding of the transformer T1 and grounded; The inductor L1-B and the fourth capacitor C4 are connected in series and connected between the opposite-name end of the secondary winding of the transformer T1 and the negative electrode VBUS- of the DC bus; the source of the second switch tube Q2 is connected to the midpoint of the inductor L1-B and the fourth capacitor C4; the drain of the second switch tube Q2 is connected to the middle tap of the primary winding of the transformer T1 and is grounded; A first capacitor C1 and a second capacitor C2 are respectively connected between the DC bus positive electrode VBUS+ and the DC bus negative electrode VBUS- and the middle tap of the primary winding of the transformer T1.

[0011] Preferably, the battery side circuit includes a third switch tube Q3, the drain of the third switch tube Q3 is connected to the opposite end of the secondary winding of the transformer T1, the source of the third switch tube Q3 is grounded, the same end of the secondary winding of the transformer T1 is connected to the positive electrode VBAT of the battery, and a fifth capacitor C5 is connected between the same end of the secondary winding of the transformer T1 and the ground wire.

[0012] Preferably, the inverter circuit adopts a single-phase inverter circuit, and the single-phase inverter circuit includes a switch tube Q4, a switch tube Q5, a switch tube Q7, a switch tube Q8, an inductor L3 and an inductor L4; After the switch tubes Q4, Q5, Q7 and Q8 form two inverter bridges, they are connected between the DC bus positive electrode VBUS+ and the DC bus negative electrode VBUS-. The inductor L3 and the inductor L4 are respectively connected between the two inverter bridge arms and the input power lines VL and VN.

[0013] Preferably, the inverter circuit adopts a half-bridge inverter circuit, and the half-bridge inverter circuit includes a capacitor C6, a capacitor C7, a switch tube Q4, a switch tube Q7, an inductor L3 and an inductor L4; Capacitor C6 and capacitor C7 are connected in series and connected between the positive pole VBUS+ of the DC bus and the negative pole VBUS- of the DC bus. Switch tube Q4 and switch tube Q7 are connected in series and connected between the positive pole VBUS+ of the DC bus and the negative pole VBUS- of the DC bus. The two ends of inductor L4 are respectively connected to the midpoint of capacitor C6 and capacitor C7 and the input power line VN. The two ends of inductor L3 are respectively connected to the midpoint of switch tube Q4 and switch tube Q7 and the input power line VL.

[0014] Preferably, the inverter circuit adopts a three-phase inverter circuit, and the three-phase inverter circuit includes a fourth switch tube Q4, a fifth switch tube Q5, a sixth switch tube Q6, a seventh switch tube Q7, an eighth switch tube Q8, a ninth switch tube Q9, a third inductor L3, a fourth inductor L4 and a fifth inductor L5; The fourth switch tube Q4, the fifth switch tube Q5, the sixth switch tube Q6, the seventh switch tube Q7, the eighth switch tube Q8, and the ninth switch tube Q9 form three inverter bridges and are connected in parallel between the DC bus positive electrode VBUS+ and the DC bus negative electrode VBUS-, and the third inductor L3, the fourth inductor L4, and the fifth inductor L5 are respectively connected between the three inverter bridge arms and the input power lines VA, VB, and VC.

[0015] Preferably, the inverter circuit adopts a three-phase three-level inverter circuit, which includes three parallel three-level inverter branches, and the three three-level inverter branches are staggered by 120°; each of the three-level inverter branches includes a T-type three-level inverter, a first inverter inductor and a first output capacitor, and the T-type three-level inverter includes a first switch unit, a second switch unit and a third switch unit connected in T shape, the first switch unit and the second switch unit are connected in series and connected between the DC bus positive electrode VBUS+ and the DC bus negative electrode VBUS-, the third switch unit is connected between the middle tap of the transformer T1 and the midpoint of the first switch unit and the second switch unit, the midpoint of the first switch unit and the second switch unit is connected to the first output end through the first inverter inductor, and the second output end is connected to the DC bus negative electrode VBUS-; Wherein, the third switch unit comprises a pair of switch tubes connected back to back; The first output capacitor is connected between the first output terminal and the second output terminal.

[0016] Preferably, the inverter circuit adopts a split-phase inverter circuit, which includes two split-phase inverter branches connected back to back in parallel, and there is a predetermined angle of phase misalignment between the two split-phase inverter branches; each of the split-phase inverter branches includes a split-phase inverter, a second inverter inductor and a second output capacitor, and the split-phase inverter includes a fourth switch unit, a fifth switch unit and a sixth switch unit connected in T-type, and the fourth switch unit and the fifth switch unit are connected in series and connected between the positive pole VBUS+ of the DC bus and the negative pole VBUS- of the DC bus, and the sixth switch unit is connected between the middle tap of the transformer T1 and the midpoint of the fourth switch unit and the fifth switch unit, and the midpoint of the fourth switch unit and the fifth switch unit is connected to the first output terminal through the second inverter inductor, and the second output terminal is connected to the negative pole VBUS- of the DC bus; Wherein, the sixth switch unit comprises a pair of switch tubes connected back to back; The second output capacitor is connected between the first output terminal and the second output terminal.

[0017] In the above-mentioned single-stage bidirectional DC converter and the single-phase household storage inverter based on the single-stage bidirectional DC converter, first, the DC bus side of the single-stage bidirectional DC converter is connected between the photovoltaic MPPT and the inverter, or connected to other loads, and the low-voltage side is connected to the battery. The topological structure of the single-stage bidirectional DC converter is simple, the number of components is small, and the equipment cost is reduced. The high-voltage side of the single-stage bidirectional DC converter can be connected in series with a single-phase inverter circuit, a half-bridge inverter circuit, a three-phase inverter circuit, a three-phase three-level inverter circuit or a split-phase inverter circuit, which can balance the midpoint voltage, stabilize the output bus voltage, and expand the applicable scenarios of the household storage inverter. The circuit structure of the present invention is easy to implement, low-cost, and easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The structure of the single-stage bidirectional DC converter of the first embodiment of the present invention is shown in FIG. Figure 1 .

[0019] Figure 2 The structure of the single-stage bidirectional DC converter of the first embodiment of the present invention is shown in FIG. Figure 2 .

[0020] Figure 3 The structure of the single-stage bidirectional DC converter of the first embodiment of the present invention is shown in FIG. Figure 3 .

[0021] Figure 4 1 is a circuit structure diagram of a single-phase household storage inverter based on a single-stage bidirectional DC converter according to a second embodiment of the present invention (single-phase inverter circuit).

[0022] Figure 51 is a circuit diagram of a single-phase household storage inverter (half-bridge inverter circuit) based on a single-stage bidirectional DC converter according to a third embodiment of the present invention.

[0023] Figure 6 1 is a circuit structure diagram of a single-phase household storage inverter based on a single-stage bidirectional DC converter according to a fourth embodiment of the present invention (three-phase inverter circuit).

[0024] Figure 7 1 is a schematic diagram of the circuit structure of a single-phase household storage inverter based on a single-stage bidirectional DC converter according to the fifth embodiment of the present invention (three-phase three-level inverter circuit).

[0025] Figure 8 1 is a circuit diagram of a single-phase household storage inverter based on a single-stage bidirectional DC converter according to a sixth embodiment of the present invention (a split-phase inverter circuit). DETAILED DESCRIPTION

[0026] This embodiment takes a single-stage bidirectional DC converter and a single-phase household storage inverter based on the single-stage bidirectional DC converter as an example, and the present invention will be described in detail below in conjunction with specific embodiments and drawings.

[0027] Embodiment 1 See also Figure 1 , showing a single-stage bidirectional DC converter of the first embodiment of the present invention, used for bidirectional charging and discharging of a battery, comprising a transformer T1, a bus-side circuit, a battery-side circuit and a controller, wherein the bus-side circuit is electrically connected to the primary side of the transformer T1, and the battery-side circuit is electrically connected to the secondary side of the transformer T1; The bus side circuit includes at least one energy storage branch, each of the energy storage branches includes a bus side switch tube, the battery side circuit includes a battery side switch tube, the controller is used to control the conduction and shutdown of the bus side switch tube and the battery side switch tube, and the battery side switch tube and the bus side switch tube are complementary switches.

[0028] Specifically, the single-stage bidirectional DC converter is connected to the power transmission and transformation grid, wherein the bus side circuit is connected between the MPPT and the inverter, the battery side circuit is connected to the energy storage battery, and the single-stage bidirectional DC converter is used to control the bidirectional transmission of energy between the power grid and the energy storage battery.

[0029] Preferably, the energy storage branch includes a first inductor L1, a third capacitor C3 and a first switch tube Q1. The first inductor L1 and the third capacitor C3 are connected in series and connected to the same-name end of the primary winding of the transformer T1, and the free end of the first inductor L1 is connected to the DC bus VBUS; the drain of the first switch tube Q1 is connected to the midpoint of the first inductor L1 and the third capacitor C3, the source of the first switch tube Q1 is connected to the opposite-name end of the primary winding of the transformer T1 and is grounded, and the first capacitor C1 is connected between the free end of the first inductor L1 and the ground wire.

[0030] The battery side circuit includes a second switch tube Q2, the drain of the second switch tube Q2 is connected to the opposite end of the secondary winding of the transformer T1, the source of the second switch tube Q2 is grounded, the same end of the secondary winding of the transformer T1 is connected to the positive electrode VBAT of the battery, and a fifth capacitor C5 is connected between the same end of the secondary winding of the transformer T1 and the ground line.

[0031] Preferably, the bus-side switch tube and the battery-side switch tube are MOSFET, IGBT, bipolar transistor or diode.

[0032] Specifically, when the battery VBAT is charged, the single-stage bidirectional DC converter works in the forward direction. When the first switch tube Q1 is turned on, the second switch tube Q2 is turned off, the first inductor L1 stores energy through the first switch tube Q1, and the first transformer T1 and the third capacitor C3 are reset. When the first switch tube Q1 is turned off, the second switch tube Q2 is turned on, and the energy of the first inductor L1 is transferred to the battery side through the third capacitor C3 and the first transformer T1, so as to realize the battery VBAT charging.

[0033] When the battery VBAT is discharged, the single-stage bidirectional DCDC conversion circuit works in reverse. When the second switch tube Q2 is turned on, the first switch tube Q1 is turned off, and the energy of the battery is transferred to the power bus side through the first transformer T1 and the third capacitor C3, and the first inductor L1 stores energy. When the second switch tube Q2 is turned off, the first switch tube Q1 is turned on, the first inductor L1 continues to flow, and releases energy to the DC bus VBUS, and the third capacitor C3 and the first transformer T1 are reset.

[0034] In this embodiment, the first switch tube Q1 and the second switch tube Q2 are components with switching performance such as MOSFET, IGBT, bipolar transistor or diode. Figure 2 A diode is used for the first switch tube Q1. Figure 3 A diode is used for the second switch tube Q2.

[0035] Embodiment 2 See also Figure 4 , showing a single-phase household storage inverter based on a single-stage bidirectional DC converter according to a second embodiment of the present invention, which is used for energy storage of household users, including a single-stage bidirectional DC converter and an inverter circuit connected to the single-stage bidirectional DC converter, wherein the inverter circuit is connected in series to the bus side of the single-stage bidirectional DC converter to realize indoor power supply for household users.

[0036] The single-stage bidirectional DC converter includes a transformer T1, a bus-side circuit, a battery-side circuit and a controller. The bus-side circuit is electrically connected to the primary side of the transformer T1, and the battery-side circuit is electrically connected to the secondary side of the transformer T1.

[0037] The bus side circuit includes two energy storage branches, and the two energy storage branches are respectively connected to the DC bus positive pole VBUS+ and the DC bus negative pole VBUS-; each of the energy storage branches includes a bus side switch tube, and the battery side circuit includes a battery side switch tube. The controller is used to control the conduction and shutdown of the bus side switch tube and the battery side switch tube, the bus side switch tubes are synchronously switched, and the battery side switch tube and the bus side switch tube are complementary switches.

[0038] Preferably, the two energy storage branches include a first energy storage branch and a second energy storage branch, the first energy storage branch and the second energy storage branch are respectively connected to the same-name end and the opposite-name end of the primary winding of the transformer T1, and the middle tap of the primary winding of the transformer T1 is grounded; the first energy storage branch includes an inductor L1-A, a third capacitor C3 and a first switch tube Q1, and the second energy storage branch includes an inductor L1-B, a fourth capacitor C4 and a second switch tube Q2; The inductor L1-A and the third capacitor C3 are connected in series and connected between the same-name end of the primary winding of the transformer T1 and the DC bus positive electrode VBUS+, the drain of the first switch tube Q1 is connected to the midpoint of the inductor L1-A and the third capacitor C3, and the source of the first switch tube Q1 is connected to the middle tap of the primary winding of the transformer T1 and grounded; The inductor L1-B and the fourth capacitor C4 are connected in series and connected between the opposite-name end of the secondary winding of the transformer T1 and the negative electrode VBUS- of the DC bus; the source of the second switch tube Q2 is connected to the midpoint of the inductor L1-B and the fourth capacitor C4; the drain of the second switch tube Q2 is connected to the middle tap of the primary winding of the transformer T1 and is grounded; A first capacitor C1 and a second capacitor C2 are respectively connected between the DC bus positive electrode VBUS+ and the DC bus negative electrode VBUS- and the middle tap of the primary winding of the transformer T1.

[0039] Specifically, the inductor L1 -A and the inductor L1 -B are coupled inductors or uncoupled inductors.

[0040] Preferably, the battery side circuit includes a third switch tube Q3, the drain of the third switch tube Q3 is connected to the opposite end of the secondary winding of the transformer T1, the source of the third switch tube Q3 is grounded, the same end of the secondary winding of the transformer T1 is connected to the positive electrode VBAT of the battery, and a fifth capacitor C5 is connected between the same end of the secondary winding of the transformer T1 and the ground wire.

[0041] In this embodiment, the inverter circuit adopts a single-phase inverter circuit, and the single-phase inverter circuit includes a switch tube Q4, a switch tube Q5, a switch tube Q7, a switch tube Q8, an inductor L3 and an inductor L4; After the switch tubes Q4, Q5, Q7 and Q8 form two inverter bridges, they are connected between the DC bus positive electrode VBUS+ and the DC bus negative electrode VBUS-. The inductor L3 and the inductor L4 are respectively connected between the two inverter bridge arms and the input power lines VL and VN.

[0042] Specifically, the single-phase inverter circuit can be connected to a single-bus bidirectional DC converter or a dual-bus bidirectional DC converter. When connected to a single-bus bidirectional DC converter, the negative electrode VBUS- of the DC bus is equivalent to the ground wire.

[0043] Embodiment 3 See also Figure 5 , a single-phase household storage inverter based on a single-stage bidirectional DC converter according to a third embodiment of the present invention is shown, comprising a single-stage bidirectional DC converter and an inverter circuit connected to the single-stage bidirectional DC converter, wherein the inverter circuit is connected in series to the bus side of the single-stage bidirectional DC converter. The circuit structure of the single-stage bidirectional DC inverter part in this embodiment is the same as the circuit structure of the single-stage bidirectional DC inverter part in the second embodiment, and will not be described in detail.

[0044] The inverter circuit in this embodiment adopts a half-bridge inverter circuit, and the half-bridge inverter circuit includes a capacitor C6, a capacitor C7, a switch tube Q4, a switch tube Q7, an inductor L3 and an inductor L4; Capacitor C6 and capacitor C7 are connected in series and connected between the positive pole VBUS+ of the DC bus and the negative pole VBUS- of the DC bus. Switch tube Q4 and switch tube Q7 are connected in series and connected between the positive pole VBUS+ of the DC bus and the negative pole VBUS- of the DC bus. The two ends of inductor L4 are respectively connected to the midpoint of capacitor C6 and capacitor C7 and the input power line VN. The two ends of inductor L3 are respectively connected to the midpoint of switch tube Q4 and switch tube Q7 and the input power line VL.

[0045] Embodiment 4 See also Figure 6, a single-phase household storage inverter based on a single-stage bidirectional DC converter according to a fourth embodiment of the present invention is shown, comprising a single-stage bidirectional DC converter and an inverter circuit connected to the single-stage bidirectional DC converter, wherein the inverter circuit is connected in series to the bus side of the single-stage bidirectional DC converter. The circuit structure of the single-stage bidirectional DC inverter part in this embodiment is the same as the circuit structure of the single-stage bidirectional DC inverter part in the second embodiment, and will not be described in detail.

[0046] The inverter circuit in this embodiment adopts a three-phase inverter circuit, and the three-phase inverter circuit includes a fourth switch tube Q4, a fifth switch tube Q5, a sixth switch tube Q6, a seventh switch tube Q7, an eighth switch tube Q8, a ninth switch tube Q9, a third inductor L3, a fourth inductor L4 and a fifth inductor L5; The fourth switch tube Q4, the fifth switch tube Q5, the sixth switch tube Q6, the seventh switch tube Q7, the eighth switch tube Q8, and the ninth switch tube Q9 form three inverter bridges and are connected in parallel between the DC bus positive electrode VBUS+ and the DC bus negative electrode VBUS-, and the third inductor L3, the fourth inductor L4, and the fifth inductor L5 are respectively connected between the three inverter bridge arms and the input power lines VA, VB, and VC.

[0047] Embodiment 5 See also Figure 7 , a single-phase household storage inverter based on a single-stage bidirectional DC converter according to a fifth embodiment of the present invention is shown, comprising a single-stage bidirectional DC converter and an inverter circuit connected to the single-stage bidirectional DC converter, wherein the inverter circuit is connected in series to the bus side of the single-stage bidirectional DC converter. The circuit structure of the single-stage bidirectional DC inverter part in this embodiment is the same as the circuit structure of the single-stage bidirectional DC inverter part in the second embodiment, and will not be described in detail.

[0048] The inverter circuit in this embodiment adopts a three-phase three-level inverter circuit, which includes three parallel three-level inverter branches, and the three three-level inverter branches are staggered by 120°; each of the three-level inverter branches includes a T-type three-level inverter, a first inverter inductor and a first output capacitor, and the T-type three-level inverter includes a first switch unit, a second switch unit and a third switch unit connected in a T-type, the first switch unit and the second switch unit are connected in series and connected between the DC bus positive electrode VBUS+ and the DC bus negative electrode VBUS-, the third switch unit is connected between the middle tap of the transformer T1 and the midpoint of the first switch unit and the second switch unit, the midpoint of the first switch unit and the second switch unit is connected to the first output end through the first inverter inductor, and the second output end is connected to the DC bus negative electrode VBUS-; Wherein, the third switch unit comprises a pair of switch tubes connected back to back; The first output capacitor is connected between the first output terminal and the second output terminal.

[0049] Specifically, the first AC output terminals of the three three-level inverter branches are respectively the out-of-phase output terminals Va, Vb, and Vc, and the second AC output terminal is the common terminal N of the three three-level inverter branches.

[0050] Specifically, in the present embodiment, in the first three-level inverter branch, the first switch unit is the switch tube Q6, the second switch unit is the switch tube Q7, the third switch unit is the switch tube Q4 and the switch tube Q5 connected back to back, the first inverter inductor is the inductor LA, and the first output capacitor is the capacitor C6; the switch tubes Q4, Q5, Q6 and Q7 form a T-type three-level inverter, which is connected to the output terminal Va through the inductor LA, and the capacitor C6 is connected between the output terminal Va and the common terminal N.

[0051] In the second three-level inverter branch, the first switch unit is the switch tube Q12, the second switch unit is the switch tube Q11, the third switch unit is the switch tube Q9 and the switch tube Q10 connected back to back, the first inverter inductor is the inductor LB, and the first output capacitor is the capacitor C7; the switch tubes Q9, Q10, Q11 and Q12 form a T-type three-level inverter, which is connected to the output terminal Vb through the inductor LB, and the capacitor C7 is connected between the output terminal Vb and the common terminal N.

[0052] In the third three-level inverter branch, the first switch unit is the switch tube Q15, the second switch unit is the switch tube Q16, the third switch unit is the switch tube Q13 and the switch tube Q14 connected back to back, the first inverter inductor is the inductor LC, and the first output capacitor is the capacitor C8; the switch tubes Q13, Q14, Q15 and Q16 form a T-type three-level inverter, which is connected to the output terminal Vc through the inductor LC, and the capacitor C8 is connected between the output terminal Vc and the common terminal N.

[0053] Specifically, in this embodiment, capacitor C4 and capacitor C5 are respectively connected between the DC bus positive electrode VBUS+ and the DC bus negative electrode VBUS- and the middle tap of transformer T1. When the upper and lower half cycles of the inverter are unbalanced, the voltages on capacitor C4 and capacitor C5 will be unequal. For example, the voltage of capacitor C4 is higher than that of capacitor C5. Since the two windings of the secondary side connected to capacitor C4 and capacitor C5 in transformer T1 are on the same magnetic core and the number of winding turns is equal, the voltages of the two windings are equal. Switch tube Q2 and switch tube Q3 are switched synchronously, and switch tube Q1 is switched complementary to switch tube Q2 and switch tube Q3, so that the energy on capacitor C4 flows back to capacitor C5 through inductor L1_A, capacitor C2, the secondary winding of transformer T1, capacitor C3 and inductor L1_B, thereby dynamically maintaining the voltages on capacitor C4 and capacitor C5 equal, thereby achieving voltage balance at the output end of the inverter.

[0054] Embodiment 6 See also Figure 8 , a single-phase household storage inverter based on a single-stage bidirectional DC converter according to the sixth embodiment of the present invention is shown, comprising a single-stage bidirectional DC converter and an inverter circuit connected to the single-stage bidirectional DC converter, wherein the inverter circuit is connected in series to the bus side of the single-stage bidirectional DC converter. The circuit structure of the single-stage bidirectional DC inverter part in this embodiment is the same as the circuit structure of the single-stage bidirectional DC inverter part in the second embodiment, and will not be repeated.

[0055] The inverter circuit in this embodiment adopts a split-phase inverter circuit, which includes two split-phase inverter branches connected back to back in parallel, and there is a predetermined angle of phase misalignment between the two split-phase inverter branches; each of the split-phase inverter branches includes a split-phase inverter, a second inverter inductor and a second output capacitor, and the split-phase inverter includes a fourth switch unit, a fifth switch unit and a sixth switch unit connected in T-type, and the fourth switch unit and the fifth switch unit are connected in series and connected between the positive pole VBUS+ of the DC bus and the negative pole VBUS- of the DC bus, and the sixth switch unit is connected between the middle tap of the transformer T1 and the midpoint of the fourth switch unit and the fifth switch unit, and the midpoint of the fourth switch unit and the fifth switch unit is connected to the first output terminal through the second inverter inductor, and the second output terminal is connected to the negative pole VBUS- of the DC bus; Wherein, the sixth switch unit comprises a pair of switch tubes connected back to back; The second output capacitor is connected between the first output terminal and the second output terminal.

[0056] Specifically, the first AC output ends of the two split-phase inverter branches are staggered output ends Va and Vb respectively, and the second AC output end is the common end N of the two split-phase inverter branches.

[0057] Specifically, in the present embodiment, in the first split-phase inverter branch, the fourth switch unit is the switch tube Q6, the fifth switch unit is the switch tube Q7, the sixth switch unit is the switch tube Q4 and the switch tube Q5 connected back to back, the second inverter inductor is the inductor LA, and the second output capacitor is the capacitor C6; the switch tubes Q4, Q5, Q6 and Q7 form a split-phase inverter, which is connected to the output terminal Va through the inductor LA, and the capacitor C6 is connected between the output terminal Va and the common terminal N.

[0058] In the second split-phase inverter branch, the fourth switch unit is the switch tube Q12, the fifth switch unit is the switch tube Q11, the sixth switch unit is the switch tube Q9 and the switch tube Q10 connected back to back, the second inverter inductor is the inductor LB, and the second output capacitor is the capacitor C7; the switch tubes Q9, Q10, Q11 and Q12 form a split-phase inverter, which is connected to the output terminal Vb through the inductor LB, and the capacitor C7 is connected between the output terminal Vb and the common terminal N.

[0059] Specifically, the output terminal Va and the output terminal Vb can effectively maintain the voltage balance of the positive and negative half cycles. The circuit principle is the same as that of the fifth embodiment and will not be described in detail.

[0060] In the above-mentioned single-stage bidirectional DC converter and the single-phase household storage inverter based on the single-stage bidirectional DC converter, first, the DC bus side of the single-stage bidirectional DC converter is connected between the photovoltaic MPPT and the inverter, or connected to other loads, and the low-voltage side is connected to the battery. The topological structure of the single-stage bidirectional DC converter is simple, the number of components is small, and the equipment cost is reduced. The high-voltage side of the single-stage bidirectional DC converter can be connected in series with a single-phase inverter circuit, a half-bridge inverter circuit, a three-phase inverter circuit, a three-phase three-level inverter circuit or a split-phase inverter circuit, which can balance the midpoint voltage, stabilize the output bus voltage, and expand the applicable scenarios of the household storage inverter. The circuit structure of the present invention is easy to implement, low-cost, and easy to promote.

[0061] It should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A single-stage bidirectional DC converter for bidirectional charging and discharging of batteries, characterized in that: It includes a transformer T1, a bus side circuit, a battery side circuit and a controller, wherein the bus side circuit is electrically connected to the primary side of the transformer T1, and the battery side circuit is electrically connected to the secondary side of the transformer T1; The bus side circuit includes at least one energy storage branch, each of the energy storage branches includes a bus side switch tube, the battery side circuit includes a battery side switch tube, the controller is used to control the conduction and shutdown of the bus side switch tube and the battery side switch tube, and the battery side switch tube and the bus side switch tube are complementary switches.

2. The single-stage bidirectional DC converter according to claim 1, characterized in that: The energy storage branch includes a first inductor L1, a third capacitor C3 and a first switch tube Q1. The first inductor L1 and the third capacitor C3 are connected in series and connected to the same-name end of the primary winding of the transformer T1. The free end of the first inductor L1 is connected to the DC bus VBUS. The drain of the first switch tube Q1 is connected to the midpoint of the first inductor L1 and the third capacitor C3. The source of the first switch tube Q1 is connected to the opposite-name end of the primary winding of the transformer T1 and is grounded. The first capacitor C1 is connected between the free end of the first inductor L1 and the ground line. The battery side circuit includes a second switch tube Q2, the drain of the second switch tube Q2 is connected to the opposite end of the secondary winding of the transformer T1, the source of the second switch tube Q2 is grounded, the same end of the secondary winding of the transformer T1 is connected to the positive electrode VBAT of the battery, and a fifth capacitor C5 is connected between the same end of the secondary winding of the transformer T1 and the ground line.

3. A single-phase household storage inverter based on a single-stage bidirectional DC converter, characterized in that: The invention comprises a single-stage bidirectional DC converter according to any one of claims 1 to 2 and an inverter circuit connected to the single-stage bidirectional DC converter, wherein the bus-side circuit in the single-stage bidirectional DC converter comprises two energy storage branches, and the two energy storage branches are respectively connected to the DC bus positive electrode VBUS+ and the DC bus negative electrode VBUS-; Each of the energy storage branches includes a bus side switch tube, and the battery side circuit includes a battery side switch tube. The controller is used to control the conduction and shutdown of the bus side switch tube and the battery side switch tube, the bus side switch tubes are synchronously switched, and the battery side switch tube and the bus side switch tube are complementary switches.

4. The single-phase household storage inverter based on a single-stage bidirectional DC converter as claimed in claim 3, characterized in that: The two energy storage branches include a first energy storage branch and a second energy storage branch, the first energy storage branch and the second energy storage branch are respectively connected to the same-name end and the opposite-name end of the primary winding of the transformer T1, and the middle tap of the primary winding of the transformer T1 is grounded; the first energy storage branch includes an inductor L1-A, a third capacitor C3 and a first switch tube Q1, and the second energy storage branch includes an inductor L1-B, a fourth capacitor C4 and a second switch tube Q2; The inductor L1-A and the third capacitor C3 are connected in series and connected between the same-name end of the primary winding of the transformer T1 and the DC bus positive electrode VBUS+, the drain of the first switch tube Q1 is connected to the midpoint of the inductor L1-A and the third capacitor C3, and the source of the first switch tube Q1 is connected to the middle tap of the primary winding of the transformer T1 and grounded; The inductor L1-B and the fourth capacitor C4 are connected in series and connected between the opposite-name end of the secondary winding of the transformer T1 and the negative electrode VBUS- of the DC bus; the source of the second switch tube Q2 is connected to the midpoint of the inductor L1-B and the fourth capacitor C4; the drain of the second switch tube Q2 is connected to the middle tap of the primary winding of the transformer T1 and is grounded; A first capacitor C1 and a second capacitor C2 are respectively connected between the DC bus positive electrode VBUS+ and the DC bus negative electrode VBUS- and the middle tap of the primary winding of the transformer T1.

5. The single-phase household storage inverter based on a single-stage bidirectional DC converter as claimed in claim 3, characterized in that: The battery side circuit includes a third switch tube Q3, the drain of the third switch tube Q3 is connected to the opposite end of the secondary winding of the transformer T1, the source of the third switch tube Q3 is grounded, the same end of the secondary winding of the transformer T1 is connected to the positive electrode VBAT of the battery, and a fifth capacitor C5 is connected between the same end of the secondary winding of the transformer T1 and the ground wire.

6. The single-phase household storage inverter based on a single-stage bidirectional DC converter as claimed in claim 3, characterized in that: The inverter circuit adopts a single-phase inverter circuit, and the single-phase inverter circuit includes a switch tube Q4, a switch tube Q5, a switch tube Q7, a switch tube Q8, an inductor L3 and an inductor L4; After the switch tubes Q4, Q5, Q7 and Q8 form two inverter bridges, they are connected between the DC bus positive electrode VBUS+ and the DC bus negative electrode VBUS-. The inductor L3 and the inductor L4 are respectively connected between the two inverter bridge arms and the input power lines VL and VN.

7. The single-phase household storage inverter based on a single-stage bidirectional DC converter as claimed in claim 3, characterized in that: The inverter circuit adopts a half-bridge inverter circuit, and the half-bridge inverter circuit includes a capacitor C6, a capacitor C7, a switch tube Q4, a switch tube Q7, an inductor L3 and an inductor L4; Capacitor C6 and capacitor C7 are connected in series and connected between the positive pole VBUS+ of the DC bus and the negative pole VBUS- of the DC bus. Switch tube Q4 and switch tube Q7 are connected in series and connected between the positive pole VBUS+ of the DC bus and the negative pole VBUS- of the DC bus. The two ends of inductor L4 are respectively connected to the midpoint of capacitor C6 and capacitor C7 and the input power line VN. The two ends of inductor L3 are respectively connected to the midpoint of switch tube Q4 and switch tube Q7 and the input power line VL.

8. The single-phase household storage inverter based on a single-stage bidirectional DC converter as claimed in claim 3, characterized in that: The inverter circuit adopts a three-phase inverter circuit, and the three-phase inverter circuit includes a fourth switch tube Q4, a fifth switch tube Q5, a sixth switch tube Q6, a seventh switch tube Q7, an eighth switch tube Q8, a ninth switch tube Q9, a third inductor L3, a fourth inductor L4 and a fifth inductor L5; The fourth switch tube Q4, the fifth switch tube Q5, the sixth switch tube Q6, the seventh switch tube Q7, the eighth switch tube Q8, and the ninth switch tube Q9 form three inverter bridges and are connected in parallel between the DC bus positive electrode VBUS+ and the DC bus negative electrode VBUS-, and the third inductor L3, the fourth inductor L4, and the fifth inductor L5 are respectively connected between the three inverter bridge arms and the input power lines VA, VB, and VC.

9. The single-phase household storage inverter based on a single-stage bidirectional DC converter as claimed in claim 3, characterized in that: The inverter circuit adopts a three-phase three-level inverter circuit, which includes three parallel three-level inverter branches, and the three three-level inverter branches are staggered by 120°; each of the three-level inverter branches includes a T-type three-level inverter, a first inverter inductor and a first output capacitor, and the T-type three-level inverter includes a first switch unit, a second switch unit and a third switch unit connected in T-type, the first switch unit and the second switch unit are connected in series and connected between the positive electrode VBUS+ of the DC bus and the negative electrode VBUS- of the DC bus, the third switch unit is connected between the middle tap of the transformer T1 and the midpoint of the first switch unit and the second switch unit, the midpoint of the first switch unit and the second switch unit is connected to the first output end through the first inverter inductor, and the second output end is connected to the negative electrode VBUS- of the DC bus; Wherein, the third switch unit comprises a pair of switch tubes connected back to back; The first output capacitor is connected between the first output terminal and the second output terminal.

10. The single-phase household storage inverter based on a single-stage bidirectional DC converter according to claim 3, characterized in that: The inverter circuit adopts a split-phase inverter circuit, which includes two split-phase inverter branches connected back to back in parallel, and there is a predetermined angle of phase misalignment between the two split-phase inverter branches; each of the split-phase inverter branches includes a split-phase inverter, a second inverter inductor and a second output capacitor, and the split-phase inverter includes a fourth switch unit, a fifth switch unit and a sixth switch unit connected in T-type, and the fourth switch unit and the fifth switch unit are connected in series and connected between the positive pole VBUS+ of the DC bus and the negative pole VBUS- of the DC bus, and the sixth switch unit is connected between the middle tap of the transformer T1 and the midpoint of the fourth switch unit and the fifth switch unit, and the midpoint of the fourth switch unit and the fifth switch unit is connected to the first output terminal through the second inverter inductor, and the second output terminal is connected to the negative pole VBUS- of the DC bus; Wherein, the sixth switch unit comprises a pair of switch tubes connected back to back; The second output capacitor is connected between the first output terminal and the second output terminal.

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