Linear control method and system for energy storage system

Abstract

The invention provides a linearization control method and system for an energy storage system, and mainly provides a single-phase-shift frequency conversion modulation method applied to the linearization control method and system, the single-phase-shift frequency conversion modulation method is applied to a single-stage DAB type AC-DC converter, and the alternating current input voltage vac, the alternating current input current iac and the direct current output voltage Vdc of the single-stage DAB type AC-DC converter are sampled; based on the sampled alternating current input voltage vac, the alternating current input current iac and the direct current output voltage Vdc, a control variable theta is obtained through calculation; on the basis of the obtained control variable theta, at the moment when the leakage inductance peak current iLk has the maximum value, a mapping coefficient c of the leakage inductance peak current at the moment is obtained through a differential extreme value method; based on the obtained control variable theta and the mapping coefficient c, calculating to obtain a phase shift ratio D and a switching frequency fs; d = 1-c theta; fs = fa (c-c2theta); and based on the obtained phase shift ratio D and the switching frequency fs, a driving signal for single phase shift frequency conversion modulation is given.

Description

Technical Field

[0001] This invention belongs to the field of AC-DC technology for energy storage systems, and particularly relates to a linearization control method and system for energy storage systems. Background Technology

[0002] The core of energy storage systems lies in their efficient, reliable, and bidirectional power interaction with the power grid. As the interface component, the AC-DC converter requires bidirectional power transmission and electrical isolation. Traditional AC-DC converters often employ a two-stage structure, which, while simple and technologically mature, suffers from large size, high cost, and limited efficiency. Single-stage AC-DC converters, by integrating rectification and isolation, offer a compact structure, high efficiency, and better meet current power transmission requirements. Among these, single-stage AC-DC converters based on dual active bridges (DABs) have attracted widespread attention due to their high-frequency isolation, soft-switching capability, and bidirectional power flow characteristics.

[0003] The research focus of single-stage DAB-type AC-DC converters is on the control and optimization of the DAB. DAB converters typically employ phase-shift modulation strategies including single-phase-shift modulation, extended-phase-shift modulation, and triple-phase-shift modulation. For single-phase-shift modulation, due to the limitation of only one phase-shift degree of freedom, the peak leakage inductance current increases significantly under input-output voltage mismatch, accompanied by substantial return power. While extended-phase-shift modulation and triple-phase-shift modulation can optimize the DAB converter to varying degrees by adding phase-shift degrees of freedom to the single-phase-shift modulation, achieving soft-switching across the entire load range remains challenging.

[0004] Current research mainly focuses on optimizing converter performance through combinations of multiple modes or complex modulation strategies, such as optimizing soft-switching range, current stress, or return power. Summary of the Invention

[0005] The purpose of this invention is to address the problems of limited soft-switching range, large peak leakage inductance current, and control nonlinearity in traditional single-phase-shift modulation by proposing a linearized control method and system for energy storage systems. This invention linearizes the relationship between the transmission current and modulation variable of the AC-DC converter by proposing a linearized modulation strategy for single-phase-shift frequency conversion, simplifying the computational complexity of power factor correction. Simultaneously, it enables all switches of the DAB converter to achieve zero-voltage turn-on and minimize peak leakage inductance current within a certain voltage transfer ratio range or a wide output voltage range.

[0006] In view of the above problems, in a first aspect, this application provides a single-phase-shift frequency conversion modulation method for a single-stage DAB type AC-DC converter, which includes a DAB converter with a half-bridge primary side. The implementation steps are as follows: AC input voltage of a single-stage DAB type AC-DC converter v ac AC input current i ac DC output voltage V dc ; Based on sampled AC input voltage v ac AC input current i ac DC output voltage V dc Calculate and obtain control variables i : , In the formula, L k This is the total leakage inductance referred to the primary side of the transformer in the DAB converter; f a This is a virtual frequency, and the value is a preset value. I ref =2P / V ac The reference current amplitude for the AC input current; V ac This refers to the peak value of the AC input voltage. P This refers to the rated transmission power of the DAB converter; n This refers to the turns ratio of the transformer in the DAB converter; oh The angular frequency of the power grid; t For time; Based on the obtained control variables i At the peak leakage inductance current i Lk At the moment when the maximum value occurs, the mapping coefficient is obtained by using the differential extremum method for the peak leakage inductance at that moment. c : , In the formula, K The voltage transfer ratio of the DAB converter, 0 ≤ K ≤2; Based on the obtained control variables i and mapping coefficients c The shift ratio D and switching frequency are calculated. f s; D =1- cth f s = f a ( c - c 2 i ) Based on the obtained shift ratio D and switching frequency f s The driving signal for single-phase-shift frequency conversion modulation is given.

[0007] Specifically, by setting an appropriate transformer turns ratio n and DC output voltage V dc This makes the voltage transfer ratio K When the value is less than 1.677, a single-stage DAB-type AC-DC converter can simultaneously achieve ZVS turn-on of all switches and minimize the peak leakage inductance current.

[0008] Secondly, this application provides a single-stage DAB type AC-DC converter, which includes a DAB converter with a half-bridge primary side, and uses the aforementioned single-phase-shift frequency conversion modulation method when performing single-phase-shift frequency conversion.

[0009] Thirdly, this application provides an energy storage system, including an AC power grid, an AC-DC converter, and a DC voltage system. The DC voltage system is connected to the AC power grid through the AC-DC converter, and the AC-DC converter is the single-stage DAB type AC-DC converter described above.

[0010] Based on the above, the DC voltage system can be an electric vehicle charging system, a battery energy storage system, a photovoltaic system, a wind power system, or a household appliance energy storage system.

[0011] Fourthly, this application provides a linearization control method for an energy storage system. The energy storage system includes an AC power grid, an AC-DC converter, and a DC voltage system. The DC voltage system is connected to the AC power grid through the AC-DC converter. When performing single-phase-shift frequency conversion modulation on the AC-DC converter, the single-phase-shift frequency conversion modulation method is used.

[0012] This invention has outstanding substantive features and significant progress compared to the prior art, specifically: The single-phase-shift frequency conversion modulation strategy of this invention introduces a virtual frequency. f a Control variables iand mapping coefficients c It simplifies the calculation of input current control and power factor correction for single-stage DAB type AC-DC converters. With a voltage transfer ratio of less than 1.677, it can achieve zero-voltage turn-on of high-frequency switches across the entire range and optimize the peak leakage inductance current, resulting in a lower total harmonic distortion rate and a higher power factor. Attached Figure Description

[0013] Figure 1 It is a single-stage dual active bridge AC-DC converter topology; Figure 2 This is a waveform diagram of the steady-state operation of single-phase-shift modulation. Figure 3 Switching frequency f s With mapping coefficients c and virtual frequency f a Relationship; Figure 4 For ZVS constraint, the shift ratio D With mapping coefficients c A schematic diagram; Figure 5 Peak current I max Maximum value and c Relationship diagram; Figure 6 Input voltage v ac =50V / 50Hz, Output Voltage V dc =50V, steady-state experimental waveforms of voltage across transformer terminals and leakage current; Figure 7 Input voltage v ac =50V / 50Hz, Output Voltage V dc =50V, experimental diagram of ZVS implementation of switch S1; Figure 8 Input voltage v ac =50V / 50Hz, Output Voltage V dc =50V, experimental diagram of ZVS implementation of switch S3; Figure 9 Input voltage v ac =50V / 50Hz, Output Voltage V dc =50V, experimental diagram of ZVS implementation of switch S5; Figure 10This is a flowchart of the single-phase-shift frequency conversion modulation method of the present invention; Figure 11 This is a diagram of an energy storage system. Detailed Implementation

[0014] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of this application.

[0015] The terms “comprising” and “having”, and any variations thereof, in the specification, claims, and accompanying drawings of this application are intended to cover non-exclusive inclusion.

[0016] To facilitate understanding of the technical solutions provided in this application, the technical terms involved in the embodiments of this application are explained below.

[0017] Soft switching: Switching is achieved by controlling the device under specific conditions to avoid turning on or off under non-zero voltage or current conditions, thereby significantly reducing losses.

[0018] ZVS (Zero Voltage Switching) is a soft-switching technology commonly used in power electronic circuits, especially in applications such as DC-DC converters and inverters. Its main purpose is to reduce switching losses, improve circuit efficiency, and reduce electromagnetic interference (EMI) by switching the switching devices (such as MOSFETs or IGBTs) in a zero-voltage state.

[0019] Single-stage dual active bridge (DAB) AC-DC converter Figure 1 A single-stage DAB-type AC-DC converter topology is demonstrated, which consists of a front-end full-bridge rectifier circuit and a back-end DAB converter. Q1-Q4 form the front-end full-bridge rectifier, S1-S2 form the primary-side half-bridge of the back-end DAB converter, and S3-S6 form the secondary-side full-bridge of the back-end DAB converter. L 1 is the AC side input filter inductor. C 1 and C 2 is the filter capacitor. C dc This is the DC-side capacitor. L k The total leakage inductance on the primary side of the transformer is given by a turns ratio of... nThe transformer T connects the primary and secondary sides of the DAB converter. By controlling the turn-on sequence of the switching transistors in the back-end DAB converter, the performance of the single-stage DAB AC-DC converter can be optimized and controlled.

[0020] The present application will now be described in detail with reference to the accompanying drawings, through some embodiments and application scenarios.

[0021] Example 1 This embodiment proposes a single-phase-shift frequency conversion modulation method for a single-stage DAB type AC-DC converter, which includes a DAB converter with a half-bridge primary side. The specific implementation steps are as follows: AC input voltage of a single-stage DAB type AC-DC converter v ac AC input current i ac DC output voltage V dc ; Based on sampled AC input voltage v ac AC input current i ac DC output voltage V dc Calculate and obtain control variables i : , In the formula, L k This is the total leakage inductance referred to the primary side of the transformer in the DAB converter; f a This is a virtual frequency, and the value is a preset value. I ref =2P / V ac The reference current amplitude for the AC input current; V ac This refers to the peak value of the AC input voltage. P This refers to the rated transmission power of the DAB converter; n This refers to the turns ratio of the transformer in the DAB converter; oh The angular frequency of the power grid; t For time; Based on the obtained control variables i At the peak leakage inductance current i Lk At the moment when the maximum value occurs, the mapping coefficient is obtained by using the differential extremum method for the peak leakage inductance at that moment. c : , In the formula, K The voltage transfer ratio of the DAB converter, 0 ≤ K ≤2; Based on the obtained control variables i and mapping coefficients c The shift ratio D and switching frequency are calculated. f s ; D =1- cth f s = f a ( c - c 2 i ) Based on the obtained shift ratio D and switching frequency f s The driving signal for single-phase-shift frequency conversion modulation is given.

[0022] Preferably, when the voltage transfer ratio is satisfied... K <1.677, by setting an appropriate transformer turns ratio n and DC output voltage V dc This allows the DAB converter to simultaneously achieve ZVS turn-on of all switches and minimize the peak leakage inductance current.

[0023] It should be noted that: virtual frequency f a This is a preset value; in actual settings, when the AC input voltage... v ac and the rated transmission power of the DAB converter P Total leakage inductance L k Given, as long as the following conditions are met K <1.667, under each modulation method there is a mapping coefficient. c Minimize peak current and f a Corresponding. Because of the total leakage inductance. L k Once determined, the upper limit of the maximum switching frequency f smax It is certain that as long as K <1.667, regardless f a Which value to take? c and f aThe minimum peak current corresponding to the product of is fixed, and c and f a The product of all of them is less than or equal to f smax It can also achieve ZVS.

[0024] Effect verification The following section combines specific parameters. v ac =50V / 50Hz, V dc =50V, f a =35kHz, L k =25μH, P =100W, n =1 Verify the effectiveness of the method in this embodiment.

[0025] Figure 2 The steady-state operating waveform of single-phase-shift modulation is shown. By analyzing the voltage and current characteristics across the leakage inductor, the expression for the leakage inductor current at various times can be obtained: , The average transfer current of the single-stage DAB AC-DC converter is obtained by integrating the inductor current over half a switching cycle: , From the above formula, it can be seen that the shift ratio at this time is only D With one control variable, the DAB converter needs to ensure that the AC input voltage and input current are in phase, which means that PFC needs to be implemented. At this time, there are no other variables to optimize performance such as current stress, current root mean square, or soft-switching range. As a result, SPS modulation has problems such as limited soft-switching range, large current stress, and control nonlinearity under wide voltage transfer ratio.

[0026] To address the above issues, mapping coefficients are introduced. c And D According to the relation D =1- cth Mapped to i Simultaneously, a virtual frequency is introduced. f a The switching frequency is expressed by the formula f s = f a ( c - c 2 i When frequency conversion control is executed, the average transmission current of the single-stage DAB type AC-DC converter is... id With new control variables i The relationship becomes a linear relationship: .

[0027] Figure 3 Showing the switching frequency f s The relationship between mapping coefficients and virtual frequency. f s The maximum value with c Increase with the increase, f a The larger the value, the better. f s Throughout the entire transmission range ( ωt The greater the range of variation within the range of 0 to 180 degrees, the larger the variation. f a The value and c Too big f s Will ωt Negative values ​​appear around 90°.

[0028] To achieve PFC, it is necessary to satisfy... i d = I ref |sin( ωt )|, can be obtained i The expression is , Combination Figure 2 From the expressions for the leakage inductance current at various times, we can obtain the current when... ωt At 90°, the peak value of the leakage inductance current I max The maximum value has been reached. ωt At 90°, the peak leakage inductance current is obtained using the differential extremum method. I max for c partial derivatives A ; , when ωt =90° i and K Each of these is a constant greater than 0. i max and K max partial derivatives A The sign depends on the molecular part -2 Kth 2 c 2 +2 θc ( K +2)- K -2. This part is in 0 < c < There exists a zero point, and it is I max The local minimum point. This zero point (local minimum point) is , The above zero-point expression holds true only if 0 ≤ K ≤2.

[0029] Consider the ZVS turn-on implementation of a single-stage DAB-type AC-DC converter switch. (Shift ratio) D The following formula needs to be satisfied , It can be seen that when K When the value is greater than 1 / 2, the above condition must be met. Further analysis shows that... K When ≤2, D ≥1 / 2- K When / 4 is satisfied, D ≥1 / 2-1 / K It will definitely be satisfied; at this point, we only need to consider... D ≥1 / 2- K / 4 is sufficient. When K >2 hours, D ≥1 / 2-1 / K When satisfied, D ≥1 / 2- K / 4 is definitely satisfied; at this point, we only need to consider... D ≥1 / 2-1 / K That's it. Based on the above analysis, under the single-phase-shift frequency conversion modulation strategy proposed in this invention, only the following needs to be considered: D ≥1 / 2- K / 4 is sufficient.

[0030] Will D =1- cth , D ≥1 / 2- K / 4 and D <1 / 2 Simultaneously considering the mapping coefficients, we can obtain the mapping coefficients. c To achieve the minimum peak leakage inductance current, the constraint condition for ZVS is c1≥c2; where, , , c1≥c2 is equivalent to: (1) in, x =|sin( ωt )|; Solving equation (1) yields... , because x 2≥1 for K ≤2 always holds true, therefore we only need to ensure x ≥ x 1. D The range ≤1 / 2 can be equivalent to 1 / (2 c 1)≤ i ≤1 / c 1 can be converted into , Therefore, it is only necessary to satisfy x min ≥ x 1 can ensure that D The implementation of ZVS when <1 / 2, and the solution is obtained at this time. K max <1.677. By setting an appropriate transformer turns ratio n and DC output voltage V dc This allows the single-stage DAB-type AC-DC converter to simultaneously achieve ZVS turn-on of all switches and minimize the peak leakage inductance current.

[0031] Figure 4 It demonstrates the ZVS constraint shifting compared to D and mapping coefficients c The diagram shows that when D >1 / 2, at this point the ZVS turn-on condition for all high-frequency switching transistors must be met, when D When <1 / 2, c The value of satisfies the constraints derived above and can also ensure the implementation of ZVS.

[0032] Figure 5 Peak current was displayed I max Maximum value and c The diagram shows the relationship between peak current and peak current. Under the modulation strategy proposed in this invention, the peak current can reach a minimum value.

[0033] To verify the above theoretical analysis, a model was constructed. v ac =50V / 50Hz, V dc =50V, P =100W experimental prototype.

[0034] Figure 6 The waveforms are the voltage and leakage current waveforms across the transformer in steady state.

[0035] Figure 7~9 The diagram shows the ZVS implementation of switches S1, S3, and S5 in the DAB-level converter under light and heavy load conditions. Since the switches in the same bridge arm are complementary, it can be shown that S1-S6 achieve ZVS turn-on under both light and heavy load conditions.

[0036] Example 2 This embodiment provides a single-stage DAB type AC-DC converter, which includes a DAB converter with a half-bridge primary side. When performing single-phase-shift frequency conversion, the single-phase-shift frequency conversion modulation method described in Embodiment 1 is used.

[0037] It should be noted that the device embodiments are similar to the method embodiments, so the description is relatively simple. For relevant details, please refer to the method embodiments.

[0038] Example 3 This embodiment provides an energy storage system, such as Figure 11 As shown, it includes an AC power grid, an AC-DC converter, and a DC voltage system. The DC voltage system is connected to the AC power grid through the AC-DC converter. The AC-DC converter is a single-stage DAB type AC-DC converter as described in Example 2.

[0039] Preferably, the DC voltage system is an electric vehicle charging system, a battery energy storage system, a photovoltaic system, a wind power system, or a household appliance energy storage system.

[0040] Example 4 This embodiment provides a linearization control method for an energy storage system. The energy storage system includes an AC power grid, an AC-DC converter, and a DC voltage system. The DC voltage system is connected to the AC power grid through the AC-DC converter. When performing single-phase-shift frequency conversion modulation on the AC-DC converter, the single-phase-shift frequency conversion modulation method described in Embodiment 1 is used.

[0041] Preferably, the DC voltage system is an electric vehicle charging system, a battery energy storage system, a photovoltaic system, a wind power system, or a household appliance energy storage system.

[0042] The methods and systems provided in this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A single-phase-shift frequency conversion modulation method, characterized in that: Used in a single-stage DAB type AC-DC converter, which includes a DAB converter with a half-bridge primary side. The implementation steps are as follows: AC input voltage of a single-stage DAB type AC-DC converter v ac AC input current i ac DC output voltage V dc ; Based on sampled AC input voltage v ac AC input current i ac DC output voltage V dc Calculate and obtain control variables θ : ， In the formula, L k This is the total leakage inductance referred to the primary side of the transformer in the DAB converter; f a This is a virtual frequency, and the value is a preset value. I ref =2P / V ac The reference current amplitude for the AC input current; V ac This refers to the peak value of the AC input voltage. P This refers to the rated transmission power of the DAB converter; n This refers to the turns ratio of the transformer in the DAB converter; ω The angular frequency of the power grid; t For time; Based on the obtained control variables θ At the peak leakage inductance current i Lk At the moment when the maximum value occurs, the mapping coefficient is obtained by using the differential extremum method for the peak leakage inductance at that moment. c : ， In the formula, K The voltage transfer ratio of the DAB converter, 0 ≤ K ≤2; Based on the obtained control variables θ and mapping coefficients c The shift ratio D and switching frequency are calculated. f s ; D =1－ cθ f s = f a ( c － c 2 θ ) Based on the obtained shift ratio D and switching frequency f s The driving signal for single-phase-shift frequency conversion modulation is given.

2. The single-phase-shift frequency conversion modulation method according to claim 1, characterized in that: By setting an appropriate transformer ratio n and DC output voltage V dc This makes the voltage transfer ratio K When the value is less than 1.677, the single-stage DAB type AC-DC converter can simultaneously achieve ZVS turn-on of all switches and minimize the peak leakage inductance current.

3. A single-stage DAB-type AC-DC converter, characterized in that: The single-stage DAB type AC-DC converter includes a DAB converter with a half-bridge primary side. When performing single-phase-shift frequency conversion, it adopts the single-phase-shift frequency conversion modulation method described in claim 1 or 2.

4. An energy storage system, comprising an AC power grid, an AC-DC converter, and a DC voltage system, wherein the DC voltage system is connected to the AC power grid via the AC-DC converter, characterized in that: The AC-DC converter described in claim 3 is a single-stage DAB-type AC-DC converter.

5. The energy storage system according to claim 4, characterized in that: The DC voltage system can be an electric vehicle charging system, a battery energy storage system, a photovoltaic system, a wind power system, or a household appliance energy storage system.

6. A linearization control method for an energy storage system, the energy storage system comprising an AC grid, an AC-DC converter, and a DC voltage system, wherein the DC voltage system is connected to the AC grid via the AC-DC converter, characterized in that: When performing single-phase-shift frequency conversion modulation on the AC-DC converter, the single-phase-shift frequency conversion modulation method described in claim 1 is used.

7. The linearization control method for energy storage systems according to claim 6, characterized in that: The DC voltage system can be an electric vehicle charging system, a battery energy storage system, a photovoltaic system, a wind power system, or a household appliance energy storage system.

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