Energy storage converter power unit and energy storage converter

Abstract

The utility model discloses an energy storage converter power unit and an energy storage converter. The energy converter power unit comprises a full-bridge power unit, an LC low-pass filter and a frequency multiplication suppression branch, the full-bridge power unit is connected with the frequency multiplication suppression branch in parallel, a first capacitor in the LC low-pass filter is connected with the full-bridge power unit and the frequency multiplication suppression branch in parallel, and a second capacitor in the LC low-pass filter is connected with the full-bridge power unit and the frequency multiplication suppression branch in parallel. And a reactor in the LC low-pass filter is connected in series between the first capacitor and the frequency doubling suppression branch. Through the frequency multiplication suppression branch, the ripple current flowing through the battery can be effectively suppressed, the safety and reliability of the energy storage system are improved, the loss is reduced, and the service life of the energy storage battery is prolonged.

Description

Technical Field

[0001] This application relates to the field of energy storage system technology, and in particular to an energy storage converter power unit and an energy storage converter. Background Technology

[0002] With the large-scale application of high-voltage cascaded energy storage systems in the energy storage market, the suppression of DC link ripple current in H-bridge power units is receiving increasing attention. Currently, there are two main methods: control algorithms and adding additional hardware filter circuits.

[0003] The control algorithm utilizes the injection of third harmonic current into the modulated signal wave to cancel the second harmonic low-frequency current component. However, the third harmonic current will bring a fourth harmonic current of the same amplitude, which may cause an imbalance in the state of charge (SOC) of the battery energy storage unit. Methods for adding filtering circuits include common solutions such as capacitors and LC low-pass filters based on passive filtering circuits. Methods based on active filtering circuits include DC-APF (DC Active Power Filter) suppression strategies, buck active power decoupling (APD) circuits, and two-stage circuit topologies.

[0004] Obviously, active filtering reduces the overall efficiency of the system and greatly increases the cost and size. The effect of a single passive filter is not ideal. The commonly used LC low-pass filter can also achieve the suppression effect by increasing the capacitance and inductance values, but there will still be residual double frequency current flowing through the energy storage battery.

[0005] It should be noted that the statements herein provide only background information relevant to this application and do not necessarily constitute prior art. Utility Model Content

[0006] In view of the above problems, this application proposes an energy storage converter power unit and an energy storage converter that overcome or at least partially solve the above problems.

[0007] The embodiments of this application adopt the following technical solutions:

[0008] In a first aspect, embodiments of this application provide an energy storage converter power unit, the energy storage converter power unit comprising: a full-bridge power unit, an LC low-pass filter, and a frequency doubling suppression branch, the full-bridge power unit and the frequency doubling suppression branch being connected in parallel, a first capacitor in the LC low-pass filter being connected in parallel with both the full-bridge power unit and the frequency doubling suppression branch, and a reactor in the LC low-pass filter being connected in series between the first capacitor and the frequency doubling suppression branch.

[0009] Preferably, the frequency doubling suppression branch includes an LC resonant branch, and the resonant frequency of the LC resonant branch is selected as an integer multiple of the power grid frequency.

[0010] Preferably, the LC resonant branch includes an inductor and a second capacitor, the capacitance of the second capacitor being less than the capacitance of the first capacitor, and the inductance of the inductor being less than the inductance of the reactor.

[0011] Preferably, the full-bridge power unit includes at least four fully controlled IGBTs and anti-parallel diodes used in conjunction with the IGBTs.

[0012] Preferably, the energy storage converter power unit further includes a DC soft start circuit, which is connected in series between the LC resonant branch and the battery.

[0013] Preferably, the DC soft starter circuit includes a first DC contactor, a second DC contactor, and a pre-charging resistor, wherein the first DC contactor and the pre-charging resistor are connected in series and then connected in parallel with the second DC contactor.

[0014] Preferably, the energy storage converter power unit further includes a first disconnect switch and a second disconnect switch, which are respectively disposed at both ends of the battery.

[0015] Secondly, embodiments of this application also provide an energy storage converter, including an energy storage converter power unit as described in any of the first aspects.

[0016] The above-described technical solutions adopted in the embodiments of this application can achieve the following beneficial effects:

[0017] This application proposes an energy storage converter power unit with frequency doubling (second frequency doubling) ripple current suppression. Through the LC resonant branch, the ripple current flowing through the battery can be effectively suppressed, improving the safety and reliability of the energy storage system and helping to increase the life of the energy storage battery.

[0018] The above description of the technical solution of this application is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0019] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0020] Figure 1 This is a schematic diagram of the power unit of the energy storage converter in the embodiments of this application;

[0021] Figure 2 This is a Bode plot of the transfer function in the embodiments of this application;

[0022] Figure 3 This is a comparison diagram of the power unit performance of the energy storage converter in the embodiments of this application.

[0023] In the diagram, 1-full-bridge power unit, 2-LC low-pass filter, and 3-frequency harmonic suppression branch. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] The concept of this application is to address the current situation in the technology where the DC output side of the energy storage converter power unit mainly includes second-harmonic ripple current in addition to the DC component used for charging and discharging the energy storage battery. The application proposes a universal energy storage converter power unit that, by adding an LC resonant branch, completely suppresses the second-harmonic ripple current flowing through the energy storage battery. No additional control strategy is required, and the unit is effective in all four quadrants of the system, demonstrating universal adaptability.

[0026] The technical solutions provided by the various embodiments of this application are described in detail below with reference to the accompanying drawings.

[0027] This application provides an energy storage converter power unit device and an energy storage converter, such as... Figure 1 The diagram shows a schematic of a power unit for an energy storage converter in an embodiment of this application. The power unit includes a full-bridge power unit 1, an LC low-pass filter 2, and a frequency doubling suppression branch 3. The full-bridge power unit 1 and the frequency doubling suppression branch 3 are connected in parallel. The first capacitor (DC stabilizing capacitor C1) in the LC low-pass filter 2 is connected in parallel with both the full-bridge power unit 1 and the frequency doubling suppression branch 3. The reactor (smoothing reactor L1) in the LC low-pass filter is connected in series between the first capacitor C1 and the frequency doubling suppression branch 3. In this application, the frequency doubling suppression branch 3 includes an LC resonant branch, and the resonant frequency of the LC resonant branch is selected as an integer multiple of the grid frequency. The LC resonant branch 3 includes an inductor L2 and a second capacitor C2. The capacitance of the second capacitor C2 is less than the capacitance of the first capacitor C1, and the inductance of the inductor L2 is less than the inductance of the reactor L1.

[0028] In this application, such as Figure 1 As shown, each energy storage converter power unit chain includes a full-bridge power unit composed of four fully controlled IGBTs and their anti-parallel diodes, an LC low-pass filter composed of DC regulated capacitor C1 and smoothing reactor L1, an LC resonant branch composed of capacitor C2 and inductor L2, a DC soft starter circuit consisting of first DC contactor J1, second DC contactor J2, pre-charge resistor R1, and disconnect switch K. m The LC resonant branch is connected in parallel with the (energy storage) battery, and the DC soft starter circuit is connected in series between the LC resonant branch and the battery. The isolating switch K... m The circuit includes a first disconnect switch and a second disconnect switch, which are respectively located at both ends of the battery. A first DC contactor J1 is connected in series with a pre-charging resistor R1 and then connected in parallel with the second DC contactor J2. When the DC soft-start circuit in this application is working, the first DC contactor J1 is closed first, and after the circuit stabilizes, the second DC contactor J2 is closed while the first DC contactor J1 is opened simultaneously. This is because before the contactors are closed, the capacitor has no charge; if the second DC contactor J2 is closed directly, a large starting current will occur, damaging the circuit. By closing the first DC contactor J1 first, the starting current is relatively stable due to the presence of the pre-charging resistor R1.

[0029] like Figure 1 As shown, V O I O I represents the AC side voltage and current of the energy storage converter power unit, and I1 represents the DC output current. C1 I is the current of the DC regulated capacitor. L1 I is the smoothing reactor current. LC For the LC resonant branch current, I bat Let R be the battery current and R be the battery internal resistance. From the perspective of power conservation, it can be seen that the full-bridge power unit uses a single-pole frequency multiplication method for modulation. The AC side outputs a fundamental frequency voltage and current with a grid frequency of f0 = 50Hz. The DC output current I1 mainly contains a DC component, a second harmonic component, and a high-frequency component related to the switching frequency of the fully controlled power device.

[0030] In this application, L1 and C1 constitute a low-pass filter, which can filter out high-frequency components and attenuate second harmonic components to a certain extent. Therefore, I L1 The medium current is mainly composed of DC and second harmonic components. L2 and C2 form a circuit based on twice the grid frequency f. 02 In an LC resonant circuit with 2f0 = 100Hz, the L2C2 resonant branch will short-circuit the second harmonic current, thus achieving separation of the second harmonic component and the DC component of the current, i.e., I... LC The current component in I is basically the second harmonic current component. batThe current is primarily a DC current component, and the current ripple flowing through the battery is greatly improved. It's understandable that if L2 and C2 form an LC resonant circuit based on an N-fold power grid frequency, the L2C2 resonant branch will short-circuit the N-fold frequency current, thus achieving separation of the N-fold frequency component of the current from the DC component.

[0031] In this application, the admittance expression for the L2C2 resonant branch is:

[0032] Where s = jω, ω = 2πf 02 .

[0033] When L2C2 achieves series resonance

[0034] This is the condition for the L2C2 branch to generate series resonance with the second harmonic current.

[0035] In this application, to better verify the effect of the energy storage converter power unit on frequency harmonic suppression, a transfer function is constructed and simulation observations are conducted, taking the suppression of second harmonics as an example:

[0036] DC side output current I1(s) to battery current I bat The transfer function of (s) is

[0037]

[0038] To achieve the desired simulation effect, a set of parameters is set for the transfer function. Taking this application as an example, let C1 = 33000uF, L1 = 0.25mH, C2 = 10000uF, L2 = 0.253mH, and R = 0.15Ω. Based on this, the Bode plot of the force transfer function is obtained, as follows: Figure 2 As shown, the second harmonic component of the battery current is well suppressed at an angular frequency of 100*2π (rad / s).

[0039] In this application, a model was built using MATLAB / SIMULINK for verification, resulting in a comparison of the performance of the energy storage converter power unit based on the LC resonant branch, as shown in the figure. Figure 3 As shown in the figure, the dashed line represents the battery current after LC low-pass filtering + LC resonant branch filtering, and the solid line represents the battery current when only the LC low-pass filter is used. From the Bode plot of the transfer function ( Figure 2 Comparison chart of the effects of power units of energy storage converters and energy storage converters ( Figure 3 It can be seen that the added LC resonant branch can greatly suppress the second harmonic current component in the battery current, improve the battery working environment, and help improve the life of the energy storage battery and the safety and reliability of the battery system.

[0040] This application also provides an energy storage converter, including the energy storage converter power unit as described above. Other parts of the energy storage converter can be found in the prior art, and will not be described in detail here. The PCS system of the energy storage converter in this application has low harmonic content and can effectively reduce power loss.

[0041] The energy storage converter in this application is used in a high-voltage cascaded energy storage system. The main components of the high-voltage cascaded energy storage system are power unit links. The energy storage batteries are connected to the power units in a distributed manner and operate at a lower voltage. They are directly connected to the medium- and high-voltage power grid through multiple links in series. Since the power units in this application can effectively suppress frequency doubling, the cost is low and the effect is good, which improves the battery life and the stability of the high-voltage cascaded energy storage system.

[0042] It is understandable that the power unit design scheme of the energy storage converter in this application increases the cost of the power unit (hardware) to some extent, but it improves the safety and reliability of the system and reduces losses by effectively suppressing the ripple current flowing through the battery (second harmonic frequency of the grid). Moreover, from the perspective of long-term system operation, it is beneficial to increase the life of the energy storage battery, thereby reducing costs.

[0043] It should be noted that in the description of this application, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0044] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between components; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0045] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0046] Any process or method described in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of this application includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the function involved, as will be understood by those skilled in the art to which embodiments of this application pertain.

[0047] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0048] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A power unit for an energy storage converter, characterized in that, The power converter power unit includes: a full-bridge power unit, an LC low-pass filter, and a frequency doubling suppression branch. The full-bridge power unit and the frequency doubling suppression branch are connected in parallel. The first capacitor in the LC low-pass filter is connected in parallel with both the full-bridge power unit and the frequency doubling suppression branch. The reactor in the LC low-pass filter is connected in series between the first capacitor and the frequency doubling suppression branch.

2. The energy storage converter power unit as described in claim 1, characterized in that, The frequency doubling suppression branch includes an LC resonant branch, and the resonant frequency of the LC resonant branch is selected as an integer multiple of the power grid frequency.

3. The energy storage converter power unit as described in claim 2, characterized in that, The LC resonant branch includes an inductor and a second capacitor, the capacitance of the second capacitor being less than the capacitance of the first capacitor, and the inductance of the inductor being less than the inductance of the reactor.

4. The energy storage converter power unit as described in claim 1, characterized in that, The full-bridge power unit includes at least four fully controlled IGBTs and anti-parallel diodes used in conjunction with the IGBTs.

5. The energy storage converter power unit as described in claim 3, characterized in that, The energy storage converter power unit also includes a DC soft start circuit, which is connected in series between the LC resonant branch and the battery.

6. The energy storage converter power unit as described in claim 5, characterized in that, The DC soft start circuit includes a first DC contactor, a second DC contactor, and a pre-charging resistor. The first DC contactor and the pre-charging resistor are connected in series and then connected in parallel with the second DC contactor.

7. The energy storage converter power unit as described in claim 6, characterized in that, The energy storage converter power unit also includes a first disconnect switch and a second disconnect switch, which are respectively disposed at both ends of the battery.

8. An energy storage converter, characterized in that, Includes the energy storage converter power unit as described in any one of claims 1-7.

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