Hybrid cascade energy storage converter control method and system

Abstract

The invention provides a hybrid cascaded energy storage converter control method and system. A nearest level approximation modulation strategy is adopted to enable a cascaded H-bridge converter to operate in a fundamental frequency switching mode, and PWM is adopted to enable a high-frequency two-level voltage source inverter to operate in a high-frequency switching mode to eliminate harmonic components brought by CHB. According to the hybrid modulation scheme, high-frequency and low-frequency switching frequencies are separated, and high-voltage large-scale energy storage and switching loss reduction are both considered. A hierarchical control strategy is adopted, and switching loss reduction, active power control, reactive power compensation and in-phase / inter-phase battery charge state equalization are realized at the same time, so that the hybrid cascade energy storage converter realizes SOC equalization of each battery in the hybrid cascade energy storage converter during high-voltage energy storage and reactive compensation, and safe and stable operation of the system is guaranteed.

Description

Technical Field

[0001] This invention belongs to the technical field of energy storage converter control, and particularly relates to a control method and system for a hybrid cascaded energy storage converter. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] In recent years, with the rapid development of wind and solar renewable energy and policy promotion, large-scale new energy power generation has been integrated into the power grid. The problem of "wind and solar curtailment" caused by insufficient new energy absorption capacity urgently needs to be addressed. High-voltage direct-connected energy storage, as a key measure to solve the "wind and solar curtailment" problem, has received widespread attention and research from the industry. Considering the fluctuating and intermittent characteristics of new energy sources such as wind and solar power, high-voltage high-power energy storage technology has become an important auxiliary means for grid connection of high-penetration new energy sources because it can quickly respond to changes in power demand, in order to improve the stability of AC / DC hybrid power grids and achieve efficient power transmission and distribution. Cascaded H-bridge converters consist of single-phase H-bridges connected in a chain, achieving high-voltage output from low-voltage devices. They have advantages such as high equivalent switching frequency, low output voltage harmonics, and easy modular expansion, and occupy an important position in high-voltage, high-capacity energy storage converters. However, cascaded H-bridge converters used in high-voltage energy storage applications have a large number of cascaded units and high DC-side voltage of the H-bridges, making the disadvantages of high switching losses and high voltage stress more prominent, which in turn reduces system efficiency and increases the failure rate of switching transistors.

[0004] Fortunately, the hybrid cascaded topology of CHB and 2LVSI in series offers flexible modulation schemes, providing an effective method to resolve the contradiction between high-voltage cascaded energy storage and high switching losses. However, as the number of cascaded units increases, the modulation schemes combining PDPWM and SVM, as well as improved PWM methods, proposed in existing technologies become very complex. To address this, existing technologies have proposed having the 2LVSI withstand a higher DC voltage to reduce the number of cascaded H-bridges in the STATCOM, thus mitigating the cost issues caused by the CHB containing numerous switches and capacitors. Because the 2LVSI withstands a higher DC voltage, reducing the switching frequency of the two-level units requires consideration of lowering the switching frequency to reduce switching losses and voltage stress. Therefore, existing technologies have proposed that the 2LVSI operate in a base-frequency switching mode, while the CHB operates in a higher-frequency PS-PWM mode. However, if the 2LVSI withstands a higher DC voltage to reduce the number of H-bridge units, it will lead to a reduction in the number of H-bridges and batteries, resulting in insufficient energy storage system capacity, which contradicts the concept of high-voltage direct-connected energy storage. In addition, existing technologies have proposed a hybrid modulation scheme in which CHB and 2LVSI output fundamental frequency stepped waves and high frequency shaped waves, respectively. However, in this method, the conduction times of different H-bridge modules within the same phase differ greatly, which will lead to uneven distribution of losses and device health status among H-bridge modules in the long run.

[0005] Meanwhile, when HCESC is applied to high-voltage direct-connected energy storage and static var compensator (SVC), the issue of inconsistent SOC among the batteries in the energy storage system must be carefully considered. Differences in battery production batches, wiring, and switching transistors can lead to inconsistent SOC among the batteries during system operation. When inconsistent SOC occurs in the energy storage system, it affects the performance of the entire system.

[0006] In summary, the hybrid cascaded topology consisting of CHB and 2LVSI in series needs improvement in terms of battery SOC balancing and reducing switching losses. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, this invention provides a hybrid cascaded energy storage converter control method and system. The hybrid modulation scheme separates the high and low frequency switching frequencies, taking into account both high-voltage large-scale energy storage and reduced switching losses. The hierarchical control strategy achieves SOC balance of each battery, ensuring the safe and stable operation of the system.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a control method for a hybrid cascaded energy storage converter, wherein the hybrid cascaded energy storage converter is composed of a cascaded H-bridge converter and a high-frequency two-level voltage source inverter connected in series, wherein the cascaded H-bridge converter operates in baseband switching mode using a nearest-level approximation modulation strategy, and the high-frequency two-level voltage source inverter operates in high-frequency switching mode using PWM modulation.

[0010] The control method includes:

[0011] Based on the average SOC of the battery in each phase of the cascaded H-bridge converter and the average SOC of the battery in the high-frequency two-level voltage source inverter, the threshold voltage conversion amount for phase-to-phase SOC equalization is determined.

[0012] Based on the average SOC of the battery in the high-frequency two-level voltage source inverter and the average SOC of the battery in the hybrid cascaded energy storage converter, the threshold voltage conversion amount for hybrid SOC equalization is determined.

[0013] Based on the threshold voltage transformation amount of inter-phase SOC equalization and the threshold voltage transformation amount of hybrid SOC equalization, the new DC bus threshold voltage is determined, and then the reference output voltage of each H-bridge unit in each phase is obtained.

[0014] Based on the reference output voltage of each H-bridge unit in each phase, and utilizing the characteristic of generating different active power using different switching functions, the actual switching function of each H-bridge unit in each phase is determined, thereby achieving the balance of battery SOC within the phase.

[0015] Secondly, the present invention provides a hybrid cascaded energy storage converter control system, wherein the hybrid cascaded energy storage converter is composed of a cascaded H-bridge converter and a high-frequency two-level voltage source inverter connected in series, wherein the cascaded H-bridge converter operates in baseband switching mode using a nearest-level approximation modulation strategy, and the high-frequency two-level voltage source inverter operates using PWM modulation.

[0016] The control system includes:

[0017] The first equalization module is configured to determine the threshold voltage conversion amount for phase-to-phase SOC equalization based on the average value of the battery SOC of each phase H-bridge unit of the cascaded H-bridge converter and the average value of the battery SOC of the high-frequency two-level voltage source inverter.

[0018] The second equalization module is configured to determine the threshold voltage conversion amount for hybrid SOC equalization based on the average value of the battery SOC of the high-frequency two-level voltage source inverter and the average value of the battery SOC of the hybrid cascaded energy storage converter.

[0019] The calculation module is configured to: determine the new DC bus threshold voltage based on the threshold voltage transformation amount of inter-phase SOC equalization and the threshold voltage transformation amount of hybrid SOC equalization, and then obtain the reference output voltage of each H-bridge unit in each phase.

[0020] The third equalization module is configured to: determine the actual switching function of each H-bridge unit in each phase based on the reference output voltage of each H-bridge unit in each phase, and utilize the characteristic of generating different active power by different switching functions, thereby achieving equalization of the battery SOC within the phase.

[0021] Thirdly, the present invention provides an electronic device including a memory and a processor, and computer instructions stored in the memory and running on the processor, wherein the computer instructions, when executed by the processor, perform the method described in the first aspect.

[0022] The above one or more technical solutions have the following beneficial effects:

[0023] In this invention, a nearest-level approximation modulation strategy is employed to operate the cascaded H-bridge converter in baseband switching mode, while PWM modulation is used to operate the high-frequency two-level voltage source inverter in high-frequency switching mode to eliminate harmonic components introduced by CHB. This hybrid modulation scheme separates the high and low frequency switching frequencies, balancing high-voltage large-scale energy storage with reduced switching losses.

[0024] In this invention, a hierarchical control strategy is adopted to simultaneously reduce switching losses, control active power, compensate reactive power, and balance the state of charge (SOC) of batteries within and between phases. This enables the hybrid cascaded energy storage converter to achieve SOC balance of its internal batteries while performing high-voltage energy storage and reactive power compensation, thus ensuring the safe and stable operation of the system.

[0025] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0027] Figure 1 This is a schematic diagram of the hybrid cascaded energy storage converter structure in Embodiment 1 of the present invention;

[0028] Figure 2(a) is a schematic diagram of the principle of the existing cascaded H-bridge converter using the nearest level approximation modulation;

[0029] Figure 2(b) is a schematic diagram of the output voltage waveform of the cascaded H-bridge converter after the improvement of the nearest level approximation modulation in Embodiment 1 of the present invention;

[0030] Figure 3 This is a schematic diagram of the PWM modulation principle of the high-frequency two-level voltage source inverter in Embodiment 1 of the present invention;

[0031] Figure 4 This is a control block diagram of the hierarchical control strategy in Embodiment 1 of the present invention;

[0032] Figure 5 This is a schematic diagram illustrating the principle of changing the on / off time of the H-bridge unit in Embodiment 1 of the present invention.

[0033] Figure 6(a) is a schematic diagram of the phase-to-phase SOC equalization control principle in Embodiment 1 of the present invention;

[0034] Figure 6(b) is a waveform diagram of phase-to-phase SOC equalization control in Embodiment 1 of the present invention;

[0035] Figure 7(a) is a schematic diagram of the hybrid SOC equalization control principle in Embodiment 1 of the present invention;

[0036] Figure 7(b) is a waveform diagram of the hybrid SOC equalization control in Embodiment 1 of the present invention;

[0037] Figure 8 This is a flowchart of the intra-phase SOC equalization control in Embodiment 1 of the present invention;

[0038] Figure 9(a) is a simulation diagram of the grid voltage and load current of HCESC and CESC in Embodiment 1 of the present invention;

[0039] Figure 9(b) is a simulation diagram of the grid current and output power of the HCESC scheme in Embodiment 1 of the present invention;

[0040] Figure 9(c) is a simulation diagram of the grid current and output power of the CESC scheme in Embodiment 1 of the present invention;

[0041] Figure 10 This is a schematic diagram comparing the output voltage and single-phase output voltage of each cascaded H-bridge unit of HCEC in Embodiment 1 of the present invention, using hybrid modulation and PS-PWM modulation respectively.

[0042] Figure 11(a) is a schematic diagram of the simulation results of intra-phase SOC equalization control in Embodiment 1 of the present invention;

[0043] Figure 11(b) is a schematic diagram of the simulation results of phase-to-phase SOC equalization control in Embodiment 1 of the present invention;

[0044] Figure 11(c) is a schematic diagram of the simulation results of the hybrid SOC equalization control in Embodiment 1 of the present invention. Detailed Implementation

[0045] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0046] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations of the present invention.

[0047] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0048] Example 1

[0049] Cascaded H-bridge converters, which do not require power frequency step-up transformers, offer advantages such as low cost, high efficiency, and small footprint, making them highly favored in the field of high-voltage, high-capacity electrochemical energy storage. However, with the increase in the number of cascaded units, the high switching losses and battery state of charge (SOC) imbalance issues of cascaded H-bridge converters become more prominent. Connecting a cascaded H-bridge (CHB) converter in series with a high-frequency two-level voltage source inverter (2LVSI) to form a hybrid cascade energy storage converter (HCESC) provides a feasible solution to reduce the high switching losses of transformerless high-voltage power conversion systems.

[0050] This embodiment discloses a control method for a hybrid cascaded energy storage converter. The hybrid cascaded energy storage converter is composed of a cascaded H-bridge converter and a high-frequency two-level voltage source inverter connected in series. The cascaded H-bridge converter operates in baseband switching mode using the nearest level approximation modulation strategy, and the high-frequency two-level voltage source inverter operates in high-frequency switching mode using PWM modulation.

[0051] The control method includes:

[0052] Based on the average SOC of the battery in each phase of the cascaded H-bridge converter and the average SOC of the battery in the high-frequency two-level voltage source inverter, the threshold voltage conversion amount for phase-to-phase SOC equalization is determined.

[0053] Based on the average SOC of the battery in the high-frequency two-level voltage source inverter and the average SOC of the battery in the hybrid cascaded energy storage converter, the threshold voltage conversion amount for hybrid SOC equalization is determined.

[0054] Based on the threshold voltage transformation amount of inter-phase SOC equalization and the threshold voltage transformation amount of hybrid SOC equalization, the new DC bus threshold voltage is determined, and then the reference output voltage of each H-bridge unit in each phase is obtained.

[0055] Based on the reference output voltage of each H-bridge unit in each phase, and utilizing the characteristic of generating different active power using different switching functions, the actual switching function of each H-bridge unit in each phase is determined, thereby achieving the balance of battery SOC within the phase.

[0056] HCESC circuit topology as follows Figure 1 As shown, the hybrid cascaded energy storage converter is composed of CHB and 2LVSI connected in series. Each phase includes N H-bridge units composed of IGBT switches and one two-level unit composed of MOSFET switches. The number N of cascaded H-bridges can be appropriately changed according to system requirements and application scenarios.

[0057] To avoid the "weakest link" effect in energy storage systems, it is necessary to control the state of charge (SOC) of the CHB's batteries. mn (m = a, b, c; n = 1, 2, ..., N) and the state of charge (SOC) of the battery in the two-level unit. T1 SOC T2 The same. The nominal voltage of the CHB DC-side battery is U. dcH The nominal voltage of the 2LVSI DC-side battery is U. dcT The nominal voltage of the DC-side battery for CHB and 2LVSI is set to 1:K, i.e., U dcT =KU dcH The voltage coefficient K can also be changed according to system requirements and usage scenarios. L is the grid-connected filter inductance; R is the equivalent resistance; C is the H-bridge DC bus filter capacitor. sm i sm ω and u represent the phase voltage, phase current, and grid frequency of the power grid, respectively; m and i m These represent the output voltage and current of the HCESC, respectively; i lm This indicates the output current of the load.

[0058] The voltage and current mentioned above have the following relationship:

[0059]

[0060] i sm =i m +i lm (2)

[0061] u is transformed by equal amplitude coordinate transformation sm i m i lmThe transformation from a three-phase stationary coordinate system to a two-phase rotating coordinate system can be expressed as:

[0062]

[0063] Where ω is the power grid frequency, U d and U q I represents the d-axis and q-axis components of the grid voltage. ld and I lq Represents the d-axis and q-axis components of the load current.

[0064] To reduce the switching losses of HCESC, this embodiment proposes a hybrid modulation method in which the cascaded H-bridge unit operates in nearest-level approximation modulation, and the two-level unit operates in pulse width modulation. A detailed discussion and analysis are provided below, along with modulation waveforms for CHB and 2LVSI in simulation experiments with N=5.

[0065] For CHB (Chip-Bridge Block): When HCESCs are used in high-voltage applications, the CHB section plays a major role, bearing most of the voltage, and the number of cascaded H-bridges is usually large. Therefore, using nearest-level approximation modulation on the CHB to make its internal switches operate in the baseband switching state can effectively reduce the switching frequency and reduce the switching losses of the HCESC. However, in existing modulation schemes, when the number of cascaded units N is large, the conduction time difference between different H-bridge modules within the phase is extremely large, which will cause a very uneven loss distribution and battery health state among the H-bridge modules, affecting the operational safety of the HCESC. To address this shortcoming, an improved method for generating the baseband stepped wave of the CHB unit in the hybrid modulation scheme is proposed.

[0066] The principle of the improved CHB unit's nearest-level approximation modulation is as follows:

[0067]

[0068] Among them, u m * Indicates the rated output voltage of the hybrid cascade device. This represents the derivative of the rated output voltage signal of the hybrid cascaded device, where Umn represents the output voltage of the nth H-bridge cell in the m-phase configuration, and V... cmpn_m This represents the threshold voltage of the nth DC bus in phase m. Hmn ref This is the reference output voltage of the nth H-bridge unit in the m-phase, used to generate the switching signals for each switch in the H-bridge. The reference output voltage of the m-phase CHB is v. Hm ref ,Right now

[0069] A schematic diagram of CHB nearest-level approximation modulation is shown below. Figure 2(a)-Figure 2(b)As shown in Figure 2(b), the on-time of the H-bridge cell before the improvement decreases as n increases, and the on-time of the first H-bridge cell is much longer than that of the fifth cell. After the improvement, the on-time of each H-bridge cell within the phase is basically the same.

[0070] For 2LVSI: The output voltage of CHB is a stepped-wave voltage resulting from the superposition of the square wave output voltages of each H-bridge unit. Therefore, 2LVSI needs to operate in PWM mode with a high switching frequency to eliminate unwanted harmonic components introduced by CHB, allowing HCES to effectively generate or absorb active power and compensate for reactive power of the load according to grid energy dispatch. The reference output voltage v of PWM modulation for 2LVSI is... Tm ref It is calculated by the following formula:

[0071] v Tm ref =v m -v Hm ref (6)

[0072] in, This represents the reference output voltage of the m-phase CHB, v m This represents the m-phase output voltage modulation signal for power control.

[0073] A schematic diagram of PWM for 2LVSI is shown below. Figure 3 As shown.

[0074] The output voltage of the HCESC consists of CHB and 2LVSI, with the DC bus threshold voltage V selected from the H-bridge. cmpn Certain rules need to be followed. Now, we will discuss the selection of the DC bus threshold voltage under the ideal state of SOC equalization of the batteries inside the energy storage system.

[0075] In an ideal state, u Hmn ref =u m *, u m * represents the ideal output voltage of the converter, because i m Relative to u sm and u m The amplitude is very small, so let's take u as a general value based on formula (1). m *=u sm .according to Figure 3 The constraints are summarized as follows:

[0076]

[0077] Among them, U m * indicates u mThe maximum value of *, n = 1, 2, ..., N, where n represents the nth H-bridge unit.

[0078] Will U dcT =KU dcH Substituting into formula (6), we get:

[0079]

[0080] Therefore, the number of CHBs N in HCESC and the DC bus threshold voltage V of the H-bridge. cmpn The nominal voltage coefficient K of the battery must meet the condition of formula (7), and other parameters such as u m * and U dcH It depends on the usage scenario of the converter and the battery configuration.

[0081] This embodiment designs a hierarchical control strategy for HCESC. While the control system generates or absorbs active power and compensates for reactive power from the load according to grid energy dispatch, it also needs to achieve battery SOC balancing within the system to avoid the "weakest link" effect of the energy storage system. The block diagram of the hierarchical control strategy is shown below. Figure 4 As shown, it includes power control, hybrid control, inter-phase SOC equalization control, and intra-phase SOC equalization control, which will be explained in detail below.

[0082] 1. Power control.

[0083] Overall control utilizes grid energy dispatch commands and reactive power from the load to generate the current reference value required for HCEC, thereby achieving system power control. Current reference value (I d * ,I q * This can be represented as:

[0084]

[0085] Analyzing the above formula, I d * Power grid energy dispatch command P * and the d-axis component U of the grid voltage d Calculations show that the energy storage system can charge and discharge according to grid demand. To fully compensate for the load's reactive power, the converter needs to generate reactive power opposite to that of the load. Therefore, the converter's I... q * It is equal to the negative of the q-axis component of the load current, i.e., -I. lq .

[0086] Based on the HCC-BESS circuit model, the current reference value (I) in the above equation is... d * ,Iq * Current decoupling control is performed to obtain the system's reference voltage signal (v). m ), subsequently combined with the reference output voltage (V) of CHB Hm ref Further, a 2LVSI reference voltage signal (v) is obtained. Tm ref ).

[0087] 2. Interphase SOC equalization control.

[0088] In the hybrid modulation scheme, the CHB unit uses NLM modulation to output a power frequency stepped voltage, while the 2LVSI unit uses PWM modulation to output a high-frequency pulse-shaped voltage. By appropriately delaying or advancing the turn-on and turn-off times of the CHB unit, the phase and pulse width of the CHB unit's output stepped voltage can be changed. Utilizing this characteristic, different proportions of active power can be allocated to the CHB and 2LVSI units in different power frequency cycles by changing the DC bus threshold voltage; that is, power transfer can be achieved between the CHB and 2LVSI units. The schematic diagram of the power transfer is shown below. Figure 5 As shown, taking CHB unit cascade number N=1 and phase a as an example, the power transfer principle of CHB and 2LVSI is explained in detail.

[0089] Let phase a reference output voltage u Hmn ref =V ref sinωt, phase current i a =Isin(ωt-θ), then the power borne by the CHB unit in phase a is:

[0090]

[0091] In the formula, P Ha u represents the active power generated by the CHB unit in phase a. aH Let i be the output voltage of phase a CHB unit. a Let be the phase current.

[0092] Depend on Figure 5 The pulse width W1 of the CHB unit's output voltage before and after the change in the DC bus threshold voltage can be obtained. 11 W 12 Combining equation (10), the active power of the CHB unit before and after the change can be calculated:

[0093]

[0094] In the formula, W1, W 11 W 12 These are the pulse widths of the CHB output voltage before and after the change, based on the modulation strategy in the previous section and Figure 5 We can conclude that:

[0095]

[0096] By combining equations (11), (12), and (14), the difference between the active power of the CHB unit before and after the transformation can be obtained as the change in active power before and after the transformation:

[0097]

[0098] Therefore, it can be seen that after selecting the hardware parameters and the DC bus threshold voltage, ΔP Ha It is related to ΔV cmp1 Functions related to θ. Since θ is related to power grid dispatch commands, ΔV can be designed appropriately. cmp1 By appropriately delaying or advancing the turn-on and turn-off times of the H-bridge unit, different proportions of active power can be allocated to the CHB unit and the 2LVSI unit in different power frequency cycles. This conclusion still holds even when the number of CHB units cascaded N is increased, which provides a theoretical basis for the hybrid SOC equalization control and interphase SOC equalization control discussed later.

[0099] Ideally, the switching states of the three-phase H-bridge units are identical, maintaining a balanced average SOC between the three phases. However, in actual system operation, some non-ideal factors always exist, causing deviations in the SOC between phases. Therefore, the H-bridge unit must have the ability to adjust the SOC. Because the 2LVSI three-phase units share a single DC bus, the active power of the 2LVSI three-phase units can be automatically exchanged and balanced. Therefore, by utilizing the characteristics of the common DC bus of the 2LVSI units, the unbalanced active power between the three phases of the CHB unit can be transferred from the H-bridge unit to the 2LVSI unit by appropriately delaying or advancing the on / off time of the H-bridge unit. Then, the unbalanced active power between the phases can be freely exchanged on the common DC bus of the 2LVSI units, ultimately achieving the effect of balancing the SOC between the phases of the CHB unit. The principle diagram of the inter-phase SOC balancing control is shown below. Figures 6(a)-6(b) As shown.

[0100] Based on the above principles, an interphase SOC equalization method was designed by changing the turn-on and turn-off times of the H-bridge units. The threshold voltage transformation ΔV for interphase SOC equalization is introduced. cmpn_m clu_prec and ΔV cmpn_m clu_foll The time difference required to delay or advance the H-bridge unit is determined. Considering the reference reactive power Q*, the threshold voltage transformation for phase-to-phase SOC equalization is derived using a PI controller.

[0101]

[0102] In the formula, m = a,b,c represents the three phases a, b, and c of the power grid. This represents the average SOC of the battery in the m-phase H-bridge cell. This represents the average SOC of all batteries in CHB. and Let represent the proportional and integral coefficients of the PI controller, respectively, and s represent the complex frequency variable in the Laplace domain (frequency domain).

[0103] 3. Hybrid control.

[0104] To balance the State of Charge (SOC) between the CHB and 2LVSI batteries, hybrid control is needed to regulate the active power distribution between them. This is essentially the same as the phase-to-phase SOC balancing control described above, which redistributes the unbalanced active power between the CHB and 2LVSI batteries by appropriately delaying or advancing the on / off times of the H-bridge cells. The threshold voltage transformation ΔV for introducing hybrid SOC balancing is... cmpn hyb_prec and ΔV cmpn hyb_foll To determine the time difference that the H-bridge unit needs to delay or advance. The threshold voltage transformation quantity for hybrid SOC equalization is derived using a PI controller. The hybrid SOC equalization control principle diagram is shown below. Figures 7(a)-7(b) As shown.

[0105]

[0106] In the formula, HCESC represents the average SOC of the battery. and These represent the proportional and integral coefficients of the PI controller, respectively.

[0107] In summary, the DC bus threshold voltage of the nth H-bridge in m phases can be obtained:

[0108]

[0109] Determine the new DC bus threshold voltage that incorporates phase-to-phase SOC equalization and hybrid SOC equalization. and Then, according to the modulation principle equation (5) above, the principle of the closest level approximation modulation of the CHB unit after adding interphase SOC equalization control and hybrid SOC equalization control is shown in equation (19), and the reference output voltage v of 2LVSI is... Tm ref It is calculated from the above formula (6).

[0110]

[0111] 4. Intra-phase SOC equalization control.

[0112] Based on the modulation principle described above, the DC bus threshold voltage can be determined. and With ideal output voltage u m *Compare to obtain the nth reference output voltage v of phase m. Hmn ref This is used to generate the reference switching functions s. mn ref Within the same phase, the current on the AC side of each stage of the H-bridge is the same, but the switching function s mn ref Since the corresponding H-bridge turn-on and turn-off times are different, it can be seen from the following formula that the active power generated by different switching functions acting on the H-bridge unit within one cycle is also different.

[0113] P mn ref =v Hmn ref ·i m =U dcH ·s mn ref ·i m (20)

[0114] In the formula, s mn ref P represents the nth reference switching function of the m-phase obtained by hybrid modulation. mn ref Represents the reference switch function s mn ref With m-phase current i m The reference output power obtained by the action.

[0115] By utilizing the characteristic that different switching functions generate different active power, a novel intra-phase SOC equalization control method is designed, as shown in the flowchart below. Figure 8 As shown, the reference switching function s is calculated first. mn ref The corresponding reference power P on the DC side of the H-bridge mn ref Next, the SOC of the DC-side battery of each H-bridge is detected, and the actual switching function s of the H-bridge unit with the largest battery SOC is determined. mn act Assigning a switching function s with a small reference power mn ref The actual switching function s of the H-bridge unit with small battery SOC mn act Assign a switching function s with a large reference power mn ref The allocation principle confirms the actual switching function s of the nth H-bridge unit in phase m. mn act This leads to the balance of the state of charge (SOC) of the cells within the phase.

[0116] Furthermore, to avoid frequent switching of the actual switching function when the SOCs of each H-bridge unit are close, increasing switching losses, the switching function allocation is performed every 0.02 seconds. Compared to the traditional method of superimposing a reference voltage modulation wave that is in phase with the current, the new method fully utilizes the characteristic that the currents of each stage of hybrid modulation are the same, simplifying the calculation and avoiding the complex parameter tuning process of the PI controller.

[0117] To verify the effectiveness of the proposed modulation scheme and control strategy, simulation results are presented in this embodiment. Simulation parameters are shown in Table 1. A simulation model of the HCESC was established using MATLAB / Simulation, with N=5 cascaded H-bridge units and K=1 parameter. The HCESC and a three-phase series RLC load were connected in the power grid, and the load was set to inject 500 kvar of inductive reactive power into the grid. The control experiment used a cascaded energy storage converter (CESC) with a traditional cascaded H-bridge topology. To ensure consistent output levels in the control experiment, the number of cascaded H-bridge units in the CESC was set to N=6, PS-PWM modulation was used, and the carrier frequency was set to 1 kHz.

[0118] Table 1:

[0119]

[0120] A. Simulation Experiment of Hybrid Modulation and Power Control

[0121] Select the DC bus threshold voltage V of the H-bridge cmpn The voltage levels are 530V, 1700V, 2900V, 4100V, and 4700V respectively, and the grid energy dispatch command P* = 1MW. Figure 5 and Figures 6(a)-6(b) The simulation results of HCESC and CESC are presented.

[0122] like Figures 9(a)-9(c) As shown, before reactive power compensation by the converter, the grid current i sabc Lagging grid voltage u sabc Phase π / 2, after compensation by the energy storage converter, the grid current i sabc and grid voltage u sabc In phase. The grid currents i of HCESC and CESC. sabcThe THD values ​​were 0.92% and 0.84%, respectively. The active and reactive power fluctuations of HCESC and CESC were 48kW (4.8%) and 40kvar (4%), and 41kW (4.1%) and 40kvar (4%), respectively. Therefore, HCESC has similar high-voltage energy storage and reactive power compensation performance to CESC. Meanwhile, by... Figure 10 It can be seen that the switching frequency of CESC is approximately 42 times that of HCESC in one power frequency cycle. HCESC operates at power frequency using a hybrid modulation scheme, while the switching frequency of HCESC is significantly lower than that of CESC operating at high frequency using carrier phase-shift modulation. Therefore, the hybrid modulation scheme proposed in this paper can significantly reduce the switching losses of HCESC, and further reduces the switching losses as the number of cascaded H-bridges increases and the nominal voltage U of the DC bus battery increases. dcH As the power loss is increased, the advantage of HCESC's hybrid modulation scheme in reducing power loss will become even more significant.

[0123] B. Simulation Experiment of Battery SOC Balancing Control.

[0124] To verify the proposed system battery SOC equalization control strategy, each battery was given a different initial state of charge, and simulation experiments were conducted on intra-phase SOC equalization control, inter-phase SOC equalization, and hybrid SOC equalization control. Figures 11(a)-11(c) It can be known that the state of charge (SOC) of the in-phase cell in CHB is... mn The variance of the phase-to-phase cell SOC Hm The variance and the average SOC of CHB batteries H And the average SOC of 2LVSI batteries T The variance of all parameters decreases over time. Simulation results demonstrate the effectiveness of the proposed control strategy, which can achieve active power control, reactive power compensation, and battery SOC balancing within the energy storage system.

[0125] This embodiment introduces a hybrid cascaded topology into the field of high-voltage energy storage, proposing a novel hybrid modulation scheme and a hierarchical control method suitable for HCESCs to simultaneously achieve low switching losses, active power control, reactive power compensation, and battery SOC equalization. First, the hybrid modulation scheme uses nearest-level approximation modulation to make the CHB operate in a power frequency switching state, and PWM modulation to make the 2LVSI operate in a high-frequency switching state. Simulation experiments show that the proposed modulation scheme can effectively reduce the system's switching frequency and switching losses without affecting active power control and reactive power compensation. Second, the proposed hierarchical control strategy effectively manages the power flow of the HCESC, enabling rapid SOC equalization of the batteries even with different initial SOCs, reducing the negative impact of the "weakest link" effect on the energy storage system. Therefore, the hybrid cascaded topology shows greater application potential than the traditional CHB topology in high-voltage energy storage, reactive power compensation, and high-order harmonic compensation.

[0126] Example 2

[0127] The purpose of this embodiment is to provide a hybrid cascaded energy storage converter control system. The hybrid cascaded energy storage converter is composed of a cascaded H-bridge converter and a high-frequency two-level voltage source inverter connected in series. The cascaded H-bridge converter operates in baseband switching mode using a nearest-level approximation modulation strategy, and the high-frequency two-level voltage source inverter operates using PWM modulation.

[0128] The control system includes:

[0129] The first equalization module is configured to determine the threshold voltage conversion amount for phase-to-phase SOC equalization based on the average value of the battery SOC of each phase H-bridge unit of the cascaded H-bridge converter and the average value of the battery SOC of the high-frequency two-level voltage source inverter.

[0130] The second equalization module is configured to determine the threshold voltage conversion amount for hybrid SOC equalization based on the average value of the battery SOC of the high-frequency two-level voltage source inverter and the average value of the battery SOC of the hybrid cascaded energy storage converter.

[0131] The calculation module is configured to: determine the new DC bus threshold voltage based on the threshold voltage transformation amount of inter-phase SOC equalization and the threshold voltage transformation amount of hybrid SOC equalization, and then obtain the reference output voltage of each H-bridge unit in each phase.

[0132] The third equalization module is configured to: determine the actual switching function of each H-bridge unit in each phase based on the reference output voltage of each H-bridge unit in each phase, and utilize the characteristic of generating different active power by different switching functions, thereby achieving equalization of the battery SOC within the phase.

[0133] In further embodiments, the following is also provided:

[0134] An electronic device includes a memory and a processor, as well as computer instructions stored in the memory and running on the processor. When executed by the processor, the computer instructions perform the method described in Embodiment 1. For brevity, further details are omitted here.

[0135] It should be understood that in this embodiment, the processor can be a central processing unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor, etc.

[0136] Memory may include read-only memory and random access memory, and provides instructions and data to the processor. A portion of memory may also include non-volatile random access memory. For example, memory may also store information about the device type.

[0137] A computer-readable storage medium for storing computer instructions, which, when executed by a processor, perform the method described in Embodiment 1.

[0138] The method in Embodiment 1 can be directly implemented by a hardware processor, or implemented by a combination of hardware and software modules within the processor. The software modules can reside in readily available storage media in the art, such as random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, or registers. This storage medium is located in memory; the processor reads information from the memory and, in conjunction with its hardware, completes the steps of the above method. To avoid repetition, a detailed description is not provided here.

[0139] A computer program product includes a computer program that, when executed by a processor, implements the method described in Embodiment 1.

[0140] The present invention also provides at least one computer program product tangibly stored on a non-transitory computer-readable storage medium. The computer program product includes computer-executable instructions, such as instructions included in program modules, which execute in a device on a target real or virtual processor to perform the processes / methods described above. Typically, program modules include routines, programs, libraries, objects, classes, components, data structures, etc., that perform specific tasks or implement specific abstract data types. In various embodiments, the functionality of program modules can be combined or divided among program modules as needed. The machine-executable instructions for the program modules can execute within a local or distributed device. In a distributed device, the program modules can reside in both local and remote storage media.

[0141] The computer program code used to implement the methods of the present invention may be written in one or more programming languages. This computer program code may be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device, such that when executed by the computer or other programmable data processing device, the program code causes the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code may be executed entirely on a computer, partially on a computer, as a stand-alone software package, partially on a computer and partially on a remote computer, or entirely on a remote computer or server.

[0142] In the context of this invention, computer program code or related data may be carried by any suitable carrier to enable a device, apparatus, or processor to perform the various processes and operations described above. Examples of carriers include signals, computer-readable media, and the like. Examples of signals may include electrical, optical, radio, sound, or other forms of propagation signals, such as carrier waves, infrared signals, etc.

[0143] Those skilled in the art will recognize that the units and algorithm steps described in conjunction with the embodiments herein can be implemented in electronic hardware or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0144] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A control method for a hybrid cascaded energy storage converter, characterized in that, The hybrid cascaded energy storage converter is composed of a cascaded H-bridge converter and a high-frequency two-level voltage source inverter connected in series. The cascaded H-bridge converter operates in baseband switching mode using the nearest level approximation modulation strategy, and the high-frequency two-level voltage source inverter operates in high-frequency switching mode using PWM modulation. The control method includes: Based on the average SOC of the battery in each phase of the cascaded H-bridge converter and the average SOC of the battery in the high-frequency two-level voltage source inverter, the threshold voltage conversion amount for phase-to-phase SOC equalization is determined. Based on the average SOC of the battery in the high-frequency two-level voltage source inverter and the average SOC of the battery in the hybrid cascaded energy storage converter, the threshold voltage conversion amount for hybrid SOC equalization is determined. Based on the threshold voltage transformation amount of inter-phase SOC equalization and the threshold voltage transformation amount of hybrid SOC equalization, the new DC bus threshold voltage is determined, and then the reference output voltage of each H-bridge unit in each phase is obtained. Based on the reference output voltage of each H-bridge unit in each phase, and utilizing the characteristic of generating different active power using different switching functions, the actual switching function of each H-bridge unit in each phase is determined, thereby achieving the balance of battery SOC within the phase.

2. The control method for a hybrid cascaded energy storage converter as described in claim 1, characterized in that, Based on the average SOC of the batteries in each phase of the cascaded H-bridge converter and the average SOC of the batteries in the high-frequency two-level voltage source inverter, the threshold voltage conversion amount for phase-to-phase SOC equalization is determined, specifically as follows: Where m = a,b,c represents the three phases a, b, and c of the power grid. This represents the average SOC of the battery in the m-phase H-bridge cell. This represents the average SOC of all batteries in CHB; and These represent the proportional and integral coefficients of the PI controller, respectively; Q* is the reference reactive power.

3. The control method for a hybrid cascaded energy storage converter as described in claim 1, characterized in that, Based on the average SOC of the battery in the high-frequency two-level voltage source inverter and the average SOC of the battery in the hybrid cascaded energy storage converter, the threshold voltage conversion amount for hybrid SOC equalization is determined, specifically as follows: in, HCESC represents the average SOC of the battery; and These represent the proportional and integral coefficients of the PI controller, respectively; Q* is the reference reactive power.

4. The control method for a hybrid cascaded energy storage converter as described in claim 1, characterized in that, Based on the DC bus threshold voltage, the threshold voltage transformation amount of phase-to-phase SOC equalization, and the threshold voltage transformation amount of hybrid SOC equalization, the new DC bus threshold voltage of each H-bridge unit in each phase is determined; based on the comparison results of the new DC bus threshold voltage and the ideal output voltage of the hybrid cascaded energy storage converter, the reference output voltage of each H-bridge unit in each phase is obtained.

5. The control method for a hybrid cascaded energy storage converter as described in claim 1, characterized in that, Based on the reference output voltage of each H-bridge unit in each phase, and utilizing the characteristic that different switching functions generate different active power, the actual switching function of each H-bridge unit in each phase is determined to achieve the balance of battery SOC within the phase, specifically: Calculate the reference power on the DC side of the H-bridge corresponding to the reference switching function, and detect the SOC of the DC side battery of each H-bridge; The actual switching function of each H-bridge unit in each phase is determined by allocating the actual switching function of the H-bridge unit with a large battery SOC to the switching function with a small reference power, and the actual switching function of the H-bridge unit with a small battery SOC to the switching function with a large reference power, thereby achieving the balance of battery SOC within the phase.

6. The control method for a hybrid cascaded energy storage converter as described in claim 1, characterized in that, The cascaded H-bridge converter operates in baseband switching mode using a nearest-level approximation modulation strategy, specifically: Among them, u m * Indicates the rated output voltage of the hybrid cascade device. This represents the derivative of the rated output voltage signal of the hybrid cascaded device, where Umn represents the output voltage of the nth H-bridge cell in the m-phase configuration, and V... cmpn_m This represents the threshold voltage of the nth DC bus in phase m. Hmn ref It is the reference output voltage of the nth H-bridge unit in phase m, used to generate the switching signals for each switch in the H-bridge. Hm ref It is the reference output voltage of the m-phase cascaded H-bridge converter.

7. The control method for a hybrid cascaded energy storage converter as described in claim 6, characterized in that, The new DC bus threshold voltage is determined based on the threshold voltage transformation amount of inter-phase SOC equalization and hybrid SOC equalization, as well as the DC bus threshold voltage.

8. A hybrid cascaded energy storage converter control system, characterized in that, The hybrid cascaded energy storage converter is composed of a cascaded H-bridge converter and a high-frequency two-level voltage source inverter connected in series. The cascaded H-bridge converter operates in baseband switching mode using the nearest level approximation modulation strategy, and the high-frequency two-level voltage source inverter operates using PWM modulation. The control system includes: The first equalization module is configured to determine the threshold voltage conversion amount for phase-to-phase SOC equalization based on the average value of the battery SOC of each phase H-bridge unit of the cascaded H-bridge converter and the average value of the battery SOC of the high-frequency two-level voltage source inverter. The second equalization module is configured to determine the threshold voltage conversion amount for hybrid SOC equalization based on the average value of the battery SOC of the high-frequency two-level voltage source inverter and the average value of the battery SOC of the hybrid cascaded energy storage converter. The calculation module is configured to: determine the new DC bus threshold voltage based on the threshold voltage transformation amount of inter-phase SOC equalization and the threshold voltage transformation amount of hybrid SOC equalization, and then obtain the reference output voltage of each H-bridge unit in each phase. The third equalization module is configured to: determine the actual switching function of each H-bridge unit in each phase based on the reference output voltage of each H-bridge unit in each phase and the characteristic of generating different active power using different switching functions, thereby achieving equalization of the battery SOC within the phase.

9. A computer-readable storage medium, characterized in that, Used to store computer instructions, which, when executed by a processor, perform the method described in any one of claims 1-7.

10. An electronic device, characterized in that, It includes a memory and a processor, as well as computer instructions stored in the memory and running on the processor, which, when executed by the processor, perform the method according to any one of claims 1-7.

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