A low-power bidirectional dc conversion circuit for energy storage inverters

Abstract

The utility model relates to a kind of low-power bidirectional direct current conversion circuit for energy storage inverter, one end of flyback transformer primary side is connected with high-voltage side direct current bus positive pole through primary inductance, the other end is connected with high-voltage side direct current bus negative pole through primary main power switch tube, it is also connected to high-voltage side direct current bus positive pole through the primary clamping switch tube, primary clamping capacitor in series, one end of flyback transformer secondary side is connected with low-voltage side energy storage battery positive pole through secondary inductance, the other end is connected with low-voltage side energy storage battery negative pole through secondary main power switch tube, it is also connected to low-voltage side energy storage battery positive pole through the secondary clamping switch tube, secondary clamping capacitor in series, diode and capacitor are simultaneously parallel in the two ends of primary main power switch tube, primary clamping switch tube, secondary main power switch tube, secondary clamping switch tube, primary capacitor is also parallel in the two ends of high-voltage side direct current bus, secondary capacitor is also parallel in the two ends of low-voltage side energy storage battery.

Description

Technical Field

[0001] This utility model belongs to the technical field of photovoltaic power supply, specifically relating to a low-power bidirectional DC-DC converter circuit for energy storage inverters. Background Technology

[0002] Residential energy storage systems convert direct current (DC) electricity generated by photovoltaic (PV) panels into AC electricity usable by the home. They also intelligently manage energy dispatching between PV systems, storage batteries, loads, and the grid, making them a key component for home energy self-sufficiency and experiencing rapid growth overseas in recent years. Based on the voltage level of the storage batteries, these systems can be categorized into high-voltage energy storage systems and 48V low-voltage energy storage systems, with the latter being more widely used in cost-sensitive countries and regions.

[0003] In a typical low-voltage residential photovoltaic-storage system, the low-voltage bidirectional DC-DC converter is responsible for the bidirectional flow of energy between the low-voltage energy storage battery and the high-voltage DC bus. Its function is to convert the electrical energy transmitted from the PV or the grid to the DC bus and store it in the low-voltage energy storage battery according to energy management instructions. Alternatively, it can convert the battery electrical energy in the reverse direction and put it into the DC bus, and then provide it to the load or feed it to the grid for sale through the inverter circuit. Therefore, its performance directly affects the working efficiency, reliability, power density and cost of the entire system.

[0004] Currently, low-voltage bidirectional DC-DC converters mostly use a non-isolated bidirectional BUCK-BOOST half-bridge + single-phase bidirectional LLC resonant circuit. The BUCK-BOOST half-bridge is used for closed-loop regulation of the magnitude and direction of the bidirectional current between the DC bus and the low-voltage energy storage battery. The single-phase bidirectional LLC resonant circuit provides appropriate voltage boost to the low-voltage battery to improve the efficiency of the entire system. Energy is transferred in a resonant manner through the leakage inductance and magnetizing inductance of the transformer. However, the disadvantages of resonance are also very obvious. It will bring a large ripple current to the DC filter capacitors on the high-voltage side / low-voltage side. Furthermore, since two stages of conversion are required, namely the BUCK-BOOST bidirectional converter and the single-phase full-bridge bidirectional LLC resonant converter, to regulate the voltage difference between the BUS DC bus and the low-voltage battery pack BAT and to control the bidirectional current, the overall conversion efficiency is relatively low, the number of components is relatively large, and the cost is high. Utility Model Content

[0005] To address the aforementioned technical problems, this utility model provides a low-power bidirectional DC-DC converter circuit for energy storage inverters. This circuit solves both the problem of large ripple current in existing single-phase LLC converters and the technical issues of existing converters requiring two stages of BUCK-BOOST + LLC resonant converters to adjust the voltage difference between the DC bus and the low-voltage battery pack, resulting in a large number of components and high costs.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A low-power bidirectional DC-DC converter circuit for an energy storage inverter includes a flyback transformer. One end of the primary winding of the flyback transformer is connected to the positive terminal of the high-voltage side DC bus via a primary inductor, and the other end is connected to the negative terminal of the high-voltage side DC bus via a primary main power switch. The primary winding is also connected to the positive terminal of the high-voltage side DC bus via a primary clamping switch and a primary clamping capacitor connected in series. One end of the secondary winding of the flyback transformer is connected to the positive terminal of the low-voltage side energy storage battery via a secondary inductor, and the other end is connected to the negative terminal of the low-voltage side energy storage battery via a secondary main power switch. It is also connected to the positive terminal of the low-voltage side energy storage battery via a series-connected secondary clamping switch and a secondary clamping capacitor. A diode and a capacitor are connected in parallel across the primary main power switch, the primary clamping switch, the secondary main power switch, and the secondary clamping switch. A primary capacitor is connected in parallel across both ends of the high-voltage side DC bus, and a secondary capacitor is connected in parallel across both ends of the low-voltage side energy storage battery.

[0007] Furthermore, when charging the low-voltage side energy storage battery through the high-voltage side DC bus, the primary main power switch is used as the switch of the forward active clamp flyback circuit, and the secondary main power switch and its parallel diode are used as the rectifier of the forward active clamp flyback circuit, and both are turned on at the same time. When discharging from the low-voltage side energy storage battery to the high-voltage side DC bus, the secondary main power switch is used as the switch for the reverse active clamp flyback circuit, and the primary main power switch and its parallel diode are used as the rectifier for the reverse active clamp flyback circuit, and both are turned on simultaneously.

[0008] Furthermore, the primary main power switch, the primary clamping switch, the secondary main power switch, and the secondary clamping switch are all configured as field-effect transistors (FETs), and the diodes and capacitors connected in parallel are either the body diode and parasitic capacitance of the FET itself or external diodes and external capacitors.

[0009] Furthermore, both the primary inductor and the secondary inductor are configured as the leakage inductance of the flyback transformer or as an external inductor.

[0010] Furthermore, the flyback transformer is configured as a flyback transformer with an open air gap in the magnetic core and energy storage capacity in the windings.

[0011] Compared with the prior art, the beneficial effects of this utility model are: The bidirectional DC-DC converter circuit of this utility model is also a bidirectional active clamp flyback converter scheme. The bidirectional active clamp flyback converter utilizes the energy storage characteristics of the flyback transformer and PWM modulation to transfer energy. The voltage and current regulation is linearly related to the PWM duty cycle. The PWM duty cycle has a wide adjustable range and can adapt to bidirectional input and output wide voltage range applications. There is no need to add an additional power conversion circuit to achieve voltage regulation. Therefore, only one power conversion stage is needed, the number of components is small, the cost is low, and it is more suitable for low-power residential energy storage inverters.

[0012] Existing LLC converters require sinusoidal resonance to transfer energy to achieve soft switching of the switching transistors. The resonant current, in addition to the active current, is superimposed with a significant reactive current. Flyback converters, however, utilize leakage inductance and clamping circuits to achieve soft switching. The continuous current mode transfers energy in an approximate square wave manner, outputting the same power while exhibiting a smaller peak ripple current than existing technologies. Furthermore, all switching transistors can achieve soft switching, and the rectifier diodes can achieve synchronous rectification, resulting in high efficiency at low power outputs. In addition, due to the symmetrical primary and secondary circuits of the bidirectional flyback converter, bidirectional energy flow is possible, requiring fewer components than the two unidirectional active clamp flyback circuits in existing technologies. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the circuit structure of this utility model. Detailed Implementation

[0014] To make the technical means, creative features, objectives and effects of this utility model easier to understand, the following embodiments, in conjunction with the accompanying drawings, specifically illustrate the low-power bidirectional DC-DC converter circuit for energy storage inverters of this utility model. It should be noted that the description of these embodiments is for the purpose of helping to understand this utility model, but does not constitute a limitation on this utility model.

[0015] like Figure 1 As shown, this utility model provides a low-power bidirectional DC-DC converter circuit for an energy storage inverter, including a flyback transformer Tr. One end of the primary winding of the flyback transformer Tr is connected to the positive terminal of the high-voltage side DC bus through a primary inductor Lp, and the other end is connected to the negative terminal of the high-voltage side DC bus through a primary main power switch Qp1. It is also connected to the positive terminal of the high-voltage side DC bus through a primary clamping switch Qp2 and a primary clamping capacitor Cp3 connected in series. One end of the secondary winding of the flyback transformer is connected to the positive terminal of the low-voltage side energy storage battery through the secondary inductor Ls, and the other end is connected to the negative terminal of the low-voltage side energy storage battery through the secondary main power switch Qs1. It is also connected to the positive terminal of the low-voltage side energy storage battery through a secondary clamping switch Qs2 and a secondary clamping capacitor Cs3 connected in series. Diodes Dp1, Dp2, Ds1, and Ds2, and capacitors Cp1, Cp2, Cs, and Cs2 are connected in parallel across the primary main power switch Qp1, the primary clamping switch Qp2, the secondary main power switch Qs1, and the secondary clamping switch Qs2. A primary capacitor Cbus is connected in parallel across both ends of the high-voltage side DC bus, and a secondary capacitor Cbat is connected in parallel across both ends of the low-voltage side energy storage battery.

[0016] When the high-voltage side DC bus needs to charge the low-voltage side energy storage battery pack (i.e., when the bidirectional DC-DC converter circuit of this invention operates in the forward direction), the secondary main power switch Qs1 is also synchronously turned on during the conduction period of diode Ds1, which can realize synchronous rectification on the low-voltage side and reduce the same-mode loss, especially when charging the battery in the forward direction. Similarly, when the low-voltage side energy storage battery pack needs to discharge to the high-voltage side DC bus (i.e., when the bidirectional DC-DC converter circuit of this invention operates in the reverse direction), the primary main power switch Qp1 is also synchronously turned on during the conduction period of diode Dp1, which can realize synchronous rectification on the high-voltage side.

[0017] Thus, the bidirectional DC-DC converter circuit of this invention can achieve zero-voltage soft-start for the switching transistor and zero-current soft-start for the rectifier diode, regardless of whether it is operating in the forward or reverse direction, resulting in high operating efficiency.

[0018] The primary main power switch Qp1, the primary clamping switch Qp2, the secondary main power switch Qs1, and the secondary clamping switch Qs2 are all field-effect transistors (FETs). The diodes and capacitors connected in parallel are either the body diodes and parasitic capacitances of the FETs themselves or external diodes and external capacitors.

[0019] Both the primary inductor Lp and the secondary inductor Ls can be set as the leakage inductance of the flyback transformer Tr or as an external inductor.

[0020] The flyback transformer Tr needs to be configured as a flyback transformer with an open air gap in the magnetic core and the windings capable of storing energy.

[0021] The specific process of energy conversion using the bidirectional DC-DC converter circuit of this invention is as follows: When the high-voltage side DC bus needs to charge the low-voltage side energy storage battery pack, Cbus, Qp1, Cp1, Qp2, Cp2, Lp and the primary winding Np of the flyback transformer Tr constitute the switching circuit of the forward active clamp flyback converter circuit. Qp1 is used as the switching transistor of the forward active clamp flyback converter circuit, and Qp2 is used as the clamping transistor. The secondary winding Ns, Ls, Cbat, Qs1, and Ds1 of the flyback transformer Tr constitute the rectifier circuit of the forward active clamp flyback converter circuit. Qs1 and Ds1 are used as rectifier transistors of the forward active clamp flyback converter circuit. The timing sequence of the forward flyback converter circuit during a complete switching cycle is described as follows: During the time period [t0-t1], Qp1 is turned on, Qp2, Qs1, and Qs2 are turned off, and the loop current Ip formed by Cbus, Lp, Np, and Qp1 increases linearly, with energy stored in Np; During the time interval [t1-t2], Qp1 starts to turn off at time t1. Due to the presence of Lp and Np, the current cannot immediately become zero or transfer to the secondary side. Therefore, the loop current Ip charges Cp1 in a resonant manner and discharges Cp2 in a resonant manner. During the time period [t2-t3], starting at time t2, the voltage drop of Qp1 is clamped to Vbus+Vcp3, the voltage drop of Qp2 is clamped to near zero, and the Np voltage is clamped to Vcp3; During the time interval [t3-t4], starting at time t3, Qp2 is turned on with zero voltage. Since Cp3 has a relatively large capacitance and a relatively stable voltage, the loop current Ip decreases linearly and reverses (flows out from the same-name terminal). At the same time, the loop current Is increases linearly, Ds1 is turned on with zero current, and the loop current Is flows out from the non-same-name terminal of Ns, through the Ls, Cbat, and Ds1 loops, and flows into its same-name terminal. That is, the energy stored in Np begins to be transferred to the secondary side. During the time period [t4-t5], at time t4, Qp2 is turned off. Due to the presence of Lp, the loop current Ip cannot change abruptly. It discharges Cp1 and charges Cp2 in a resonant manner. During the time period [t5-t6], at time t5, Cp1 is completely discharged, Dp1 starts to conduct, and the voltage of Cp2 is clamped to Vbus+Vcp3. During the time interval [t6-t0], at time t6, Qp1 is turned on with zero voltage. During this period, the loop current Ip decreases in the reverse direction and changes back to the positive direction (flowing out from the non-same-name terminal). The loop current Is begins to decrease linearly to zero. At time t0, the next switching cycle begins again.

[0022] When the low-voltage side energy storage battery pack needs to discharge to the high-voltage side DC bus, Cbat, Qs1, Cs1, Qs2, Cs2, Ls and the secondary winding Ns of the flyback transformer Tr constitute the switching circuit of the reverse active clamp flyback converter circuit. Qs1 is used as the switching transistor of the reverse active clamp flyback converter circuit, and Qs2 is used as the clamping transistor. The primary winding Np, Lp, Cbus, Qp1, and Dp1 of the flyback transformer Tr constitute the rectifier circuit of the reverse active clamp flyback converter circuit. Qp1 and Dp1 are used as rectifier transistors of the reverse active clamp flyback converter circuit. The circuit structures of the reverse flyback converter circuit and the forward flyback converter circuit are symmetrical. The working timing principle of the reverse flyback converter circuit in a complete switching cycle is the same as that of the forward flyback converter circuit.

[0023] It is important to note that the schemes and arrangements of this application shown in the exemplary embodiments are merely exemplary. Although only a few embodiments are described in detail in this disclosure, those who consult this disclosure will readily understand that many modifications are possible (e.g., variations in various parameter values ​​(temperature, power, humidity, etc.), installation arrangements, names, colors, logical orders, etc.) without substantially departing from the novel teachings and advantages of the subject matter described in this application. Therefore, all such modifications are also included within the scope of the invention, and the order or sequence of any process or method steps may be changed or rearranged according to alternative embodiments. In the claims, any "apparatus plus function" clause is intended to cover the structure described herein for performing the function, and not only structurally equivalent but also equivalent in structure. Other substitutions, modifications, alterations, and omissions may be made in the design, operation, and arrangement of the exemplary embodiments without departing from the scope of the invention. Therefore, the invention is not limited to the particular embodiments but extends to a variety of modifications that still fall within the scope of the appended claims.

[0024] Furthermore, in order to provide a concise description of exemplary embodiments, not all features of actual embodiments (i.e., those features that are not relevant to the best mode of carrying out the invention as currently considered, or those features that are not relevant to implementing the invention) may be omitted.

[0025] It should be understood that numerous specific implementation decisions can be made during the development of any practical implementation, such as in any engineering or design project. Such development efforts may be complex and time-consuming, but for those skilled in the art who benefit from this disclosure, the development effort will be a routine work of design, manufacturing, and production without requiring much experimentation.

[0026] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A low-power bidirectional DC-DC converter circuit for an energy storage inverter, characterized in that: This includes a flyback transformer. One end of the primary winding of the flyback transformer is connected to the positive terminal of the high-voltage side DC bus via a primary inductor, and the other end is connected to the negative terminal of the high-voltage side DC bus via a primary main power switch. It is also connected to the positive terminal of the high-voltage side DC bus via a primary clamping switch and a primary clamping capacitor connected in series. One end of the secondary winding of the flyback transformer is connected to the positive terminal of the low-voltage side energy storage battery via a secondary inductor, and the other end is connected to the negative terminal of the low-voltage side energy storage battery via a secondary main power switch. It is also connected to the positive terminal of the low-voltage side energy storage battery via a series-connected secondary clamping switch and a secondary clamping capacitor. A diode and a capacitor are connected in parallel across the primary main power switch, the primary clamping switch, the secondary main power switch, and the secondary clamping switch. A primary capacitor is connected in parallel across both ends of the high-voltage side DC bus, and a secondary capacitor is connected in parallel across both ends of the low-voltage side energy storage battery.

2. The low-power bidirectional DC-DC converter circuit for an energy storage inverter according to claim 1, characterized in that: When charging the low-voltage side energy storage battery through the high-voltage side DC bus, the primary main power switch is used as the switch of the forward active clamp flyback circuit, and the secondary main power switch and its parallel diode are used as the rectifier of the forward active clamp flyback circuit, and both are turned on at the same time. When discharging from the low-voltage side energy storage battery to the high-voltage side DC bus, the secondary main power switch is used as the switch for the reverse active clamp flyback circuit, and the primary main power switch and its parallel diode are used as the rectifier for the reverse active clamp flyback circuit, and both are turned on simultaneously.

3. The low-power bidirectional DC-DC converter circuit for an energy storage inverter according to claim 2, characterized in that: The primary main power switch, the primary clamping switch, the secondary main power switch, and the secondary clamping switch are all field-effect transistors (FETs). The diodes and capacitors connected in parallel are either the body diode and parasitic capacitance of the FET itself or external diodes and external capacitors.

4. The low-power bidirectional DC-DC converter circuit for an energy storage inverter according to claim 1, characterized in that: Both the primary inductor and the secondary inductor are configured as the leakage inductance of the flyback transformer or as an external inductor.

5. The low-power bidirectional DC-DC converter circuit for an energy storage inverter according to claim 1, characterized in that: The flyback transformer is configured as a flyback transformer with an open air gap in the magnetic core and energy storage capacity in the windings.

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