Low-modulation-ratio topological high-reliability high-voltage direct-hanging energy storage system and method

Abstract

The invention provides a low-modulation-ratio topological high-reliability high-voltage direct-hanging energy storage system and method.The system comprises three phases of energy storage unit chains, each phase of energy storage unit chain is formed by cascading a plurality of energy storage units, and the connecting ends of the three phases of energy storage unit chains are sequentially connected with an alternating current side filter inductor in series and then connected with a power grid; the energy storage unit comprises an H-bridge power unit, a bus capacitor, a direct current side filter inductor, a battery side pre-charging device, a direct current side contactor and a battery cluster; the direct current side positive electrode of the H-bridge power unit is sequentially connected with the direct current side contactor, the battery side pre-charging device, the battery cluster and the direct current side filter inductor in series and then is connected with the direct current side negative electrode of the H-bridge power unit, and the alternating current side positive electrode of the H-bridge power unit is sequentially connected in series. According to the invention, the high-voltage direct-hanging energy storage system can fully utilize the DC voltage redundancy to realize the frequency doubling current suppression of the battery cluster by utilizing the low modulation ratio characteristic, and the ripple current pulsation amplitude of the battery meets the national standard requirement under the condition that the device cost is not increased.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical automation equipment, and in particular to a low modulation ratio topology high reliability high voltage direct-mounted energy storage system and method. Background Art

[0002] Existing battery energy storage systems can be roughly divided into two categories: low-voltage energy storage systems and high-voltage energy storage systems. Low-voltage battery energy storage systems are composed of battery stacks and battery management systems (BMS), low-voltage converters (PCS) and step-up transformers. The increase in its single-unit capacity can only rely on the increase in the scale of battery cells in the battery stack. However, the scale of battery cells in series and parallel is limited by technologies such as battery materials, battery grouping and BMS, and the economic and safe capacity of battery stacks is generally in the hundreds of kW level. To build a 100-MW energy storage power station, hundreds of devices are generally operated in parallel on the low-voltage AC side. Its power collection and information systems are complex, coordinated control is difficult, stability is poor, and command response time is long, which cannot meet future development needs.

[0003] The high-voltage large-capacity battery energy storage system divides the massive battery cells required by the system into many battery clusters (composed of battery cells connected in series) through high-voltage direct PCS, and distributes them to the DC side of the power module, and cascades the AC side to increase the PCS output voltage and single-unit capacity, and can be directly connected to a high-voltage grid of 35kV and above without a transformer. The high-voltage energy storage system has a highly modular structure, which can theoretically meet the needs of large-capacity single-unit energy storage systems. Taking a multi-star structure as an example, when directly connected to a 35kV grid, its theoretical maximum capacity can reach hundreds of MW, which is more suitable for the large-scale development of new energy in the future. However, in actual applications, the battery cluster of the high-voltage energy storage system is directly connected to the DC bus of the H-bridge power module. Due to the small internal resistance of the battery cluster, the DC side voltage is clamped by the battery, and the secondary pulsating power of the H-bridge single-phase converter will basically flow into the battery in the form of a double-frequency pulsating current. The double-frequency pulsating current will affect the BMS's estimation accuracy of the battery pack SOC, and it is necessary to suppress it. Adding a filter inductor between the battery pack and the H-bridge power module to form an LC passive filter together with the DC bus capacitor can also suppress the double frequency current. Under reasonable volume, efficiency and cost considerations, the LC passive filter can only suppress the double frequency current amplitude to between 10-20% of the rated current, which cannot meet the standard requirements. The double frequency current can be completely suppressed by harmonic voltage injection, but the modulation ratio is extremely high. At present, the rated modulation ratio of the high-voltage direct-mounted energy storage system (when the DC side battery cluster is at rated voltage) is generally around 0.8, which is generally difficult to meet the harmonic voltage injection conditions. In addition, under the existing system design, the larger filter inductor design on the DC side causes the DC bus capacitor voltage ripple voltage to increase, resulting in the inevitable circulation in the double star or three-star structure derived from it. In addition, the intra-phase SOC balancing control and the inter-phase SOC balancing control based on zero-sequence voltage injection will also cause overshoot in the system, resulting in limited rate and capacity of intra-phase and inter-phase SOC balancing. At present, the redundant design margin of the energy storage unit of the general system is insufficient, resulting in reduced system reliability when the module fails. Moreover, it is currently difficult to maintain and overhaul high-voltage energy storage systems without shutting down the system, and there is no effective way to achieve non-stop maintenance of the system. Summary of the invention

[0004] In view of the defects in the prior art, the object of the present invention is to provide a high-reliability high-voltage direct-mounted energy storage system and method with a low modulation ratio topology.

[0005] A low modulation ratio topology high reliability high voltage direct-mounted energy storage system provided by the present invention comprises:

[0006] High voltage energy storage unit;

[0007] The high-voltage energy storage unit comprises a three-phase energy storage unit chain; in the three-phase energy storage unit chain, each phase energy storage unit chain is composed of a plurality of energy storage units in cascade, and the connection ends of the three-phase energy storage unit chain are sequentially connected in series with the AC side filter inductor and then connected to the power grid;

[0008] The energy storage unit includes an H-bridge power unit, a bus capacitor, a DC side filter inductor, a battery side pre-charging device, a DC side contactor and a battery cluster;

[0009] The DC side positive pole of the H-bridge power unit is connected in series with the DC side contactor, the battery side pre-charging device, the battery cluster, and the DC side filter inductor in sequence, and then connected to the DC side negative pole of the H-bridge power unit, and the AC side positive pole of the H-bridge power unit is connected in series in sequence.

[0010] Preferably, in the three-phase energy storage unit chain, the number of cascaded energy storage units and the DC voltage in each phase make the system modulation ratio less than or equal to 0.67.

[0011] Preferably, the topological structure of the three-phase energy storage unit chain includes a single star chain, a double star parallel chain and a delta chain.

[0012] Preferably, each phase is composed of multiple energy storage containers connected in series, each energy storage container is composed of multiple internal energy storage units cascaded, and a fault bypass switch K1 and fault isolation switches S1 and S2 are added to the outlet of the container; when a power module fails, the fault partition is isolated by controlling the energy storage container where it is located.

[0013] Preferably, the fault partition isolation by controlling the energy storage container includes:

[0014] The container where the faulty energy storage unit is located is removed from the system and isolated; the output voltage of the energy storage container is controlled to become 0, the AC side fault bypass switch K1 of the container is closed, and the fault isolation switches S1 and S2 of the container are disconnected;

[0015] After maintaining the faulty energy storage unit, put the energy storage container into system operation; close the isolating switches S1 and S2 of the energy storage container, control the output voltage of the energy storage container to 0, and disconnect the AC bypass switch of the energy storage container.

[0016] Preferably, it also includes:

[0017] Power conversion unit; when the power conversion unit fails, the energy storage unit is bypassed as a whole through the AC side bypass switch, and when the battery cluster fails or warns, the battery cluster is cut off through the contactor of the DC side positive and negative busbars.

[0018] According to the present invention, a low modulation ratio topology high reliability high voltage direct hanging energy storage method is provided, comprising:

[0019] Step S1: Set the initial parameters of the system and calculate the critical modulation ratio m of the system when the double frequency current is fully suppressed. l ;

[0020] The system initial parameters include the number of redundant modules;

[0021] Step S2: The critical modulation ratio m is obtained l , calculate the critical value Q of the cell capacity that meets the system critical modulation ratio requirements cl ;

[0022] Step S3: Calculate the number of cascade units per phase according to the number of redundant modules set in the system and the efficiency of the power conversion system;

[0023] Step S4: According to the calculation results, the DC side LC filter parameters that meet the pulsating current, voltage standards and circulating current limiting requirements are obtained.

[0024] Preferably, the step S1 comprises:

[0025] The critical modulation ratio m is obtained according to the following formula l :

[0026]

[0027] Where N is the number of power modules cascaded per phase, V bnom is the rated voltage of the battery cluster, E m3 The third harmonic voltage amplitude required to be injected to completely suppress the double frequency current of the battery cluster;

[0028] Critical modulation ratio m l satisfy:

[0029]

[0030] Among them, V sm is the amplitude of the grid-connected phase voltage.

[0031] Preferably, step S2 comprises:

[0032] According to the following formula, the critical value Q of the cell capacity that meets the system critical modulation ratio requirement is obtained: cl :

[0033]

[0034] Preferably, step S4 comprises:

[0035] The four-fold frequency ripple rate γ of the battery current is calculated according to the following formula: i :

[0036]

[0037] Calculate the capacitor voltage quadruple frequency ripple rate γ u :

[0038]

[0039] Where M is the modulation ratio, I m is the AC grid-connected current amplitude, is the power factor angle, R b is the internal resistance of the battery, V b is the battery cluster voltage, V c is the average value of the pulsating voltage on the capacitor, ω4 is the quadrupled angular frequency;

[0040] Combining the above two equations, we can obtain the capacitance value C and the inductance value L.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. The present invention can utilize the low modulation ratio characteristics so that the high-voltage direct-mounted energy storage system can fully utilize the DC voltage redundancy to achieve battery cluster double frequency current suppression, and make the battery ripple current pulsation amplitude meet the national standard requirements without increasing the device cost.

[0043] 2. The present invention makes full use of the DC voltage redundancy to realize dynamic SOC balancing control, taking into account both the SOC balancing rate and effect.

[0044] 3. The present invention can utilize the low modulation ratio characteristics to increase the redundant number of energy storage units and the DC voltage redundancy, realize fault removal and redundant operation control of energy storage containers, and improve the reliability and maintainability of the system.

[0045] Other beneficial effects of the present invention will be explained in the specific implementation manner through the introduction of specific technical features and technical solutions. Through the introduction of these technical features and technical solutions, those skilled in the art should be able to understand the beneficial technical effects brought about by the technical features and technical solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0047] Figure 1 A structural diagram of a low modulation ratio topology high reliability high voltage direct-mounted energy storage equipment system and its power module basic unit provided by the present invention.

[0048] Figure 2 A design flow chart of a low modulation ratio topology high reliability high voltage direct-mounted energy storage equipment provided by the present invention.

[0049] Figure 3 A control strategy block diagram of a low modulation ratio topology high reliability high voltage direct-mounted energy storage device provided by the present invention. DETAILED DESCRIPTION

[0050] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0051] The present invention provides a high-reliability high-voltage direct-mounted energy storage equipment with a low modulation ratio topology. The internal structure of the high-voltage energy storage unit includes: a battery cluster, a power conversion unit, an AC fault bypass circuit, a bus capacitor, a DC side filter inductor, a power buffer link, a DC contactor, a pre-charging and protection circuit, etc. The DC side positive pole of the H-bridge power unit is connected in series with the DC side filter inductor, the DC side pre-charging device and protection device, and the battery cluster in sequence, and then connected to the DC side negative pole of the H-bridge power unit. The AC side positive pole of the H-bridge power unit is connected in series in sequence, and the bus capacitor is connected in parallel to the DC side poles of the H-bridge or half-bridge power unit. Based on the above standard energy storage unit, after being configured by the upper main control system, a high-voltage and large-capacity energy storage system with different requirements can be conveniently constructed. The system structure includes a single star, a double star or a delta structure. The triple star structure can be derived from a single star or double star structure. Each structure contains multiple energy storage unit chains, and the energy storage unit chain is composed of a plurality of energy storage units in cascade. The connection end of each phase energy storage unit chain is connected to the power grid after passing through the AC side filter inductor. In the low modulation ratio topology high reliability high voltage direct-mounted energy storage equipment system, the energy storage unit is under low modulation ratio working conditions, which brings new methods to the main circuit parameter design, double frequency current suppression, internal circulating current suppression, SOC balancing and system fault redundancy control of the high voltage direct-mounted energy storage system.

[0052] The battery cluster is formed by connecting a plurality of battery cells in series.

[0053] The H-bridge power unit adopts a full-bridge topology.

[0054] A low modulation ratio topology high reliability high voltage direct hanging energy storage device provided by the present invention includes the following contents:

[0055] Content 1: Establish the main circuit parameter design method of low modulation ratio topology high reliability high voltage direct-mounted energy storage equipment, including the battery selection design, power module number and module DC voltage selection, and main circuit filter parameter design considering the combination of software and hardware solutions to completely suppress the double frequency ripple current;

[0056] Content 2: AC / DC fault-tolerant control technology of fault submodules and the state of charge (SOC) balancing control strategy of the remaining energy storage units. When a power conversion unit fails, the energy storage unit can be bypassed as a whole through the AC side bypass switch. When a battery cluster fails or an early warning occurs, the battery cluster is removed through the contactor of the DC side positive and negative busbars. The remaining power conversion units can participate in the system operation normally and maintain the low modulation ratio characteristics of the system. The amplitude and phase of the zero-sequence voltage to be injected are calculated based on the number and location of the faulty energy storage units.

[0057] Content 3: A high-voltage online operation and maintenance control method for energy storage container partition isolation of low modulation ratio topology high-reliability high-voltage direct-mounted energy storage equipment, including energy storage container fault removal and re-commissioning method, and remaining system SOC balancing control after container removal;

[0058] Content 4: Establish a control method for low modulation ratio topology high reliability high voltage direct-mounted energy storage equipment, including upper control steps: system charging and discharging power control; lower control steps: inter-phase and intra-phase balancing control of low modulation ratio topology high reliability high voltage direct-mounted energy storage equipment, energy storage unit fault redundancy control, energy storage container fault isolation and redundant operation control.

[0059] According to a low modulation ratio topology high reliability high voltage direct-mounted energy storage equipment provided by the present invention, three expansion schemes including single star chain, double star chain and delta chain are provided. The selection of a specific expansion scheme shall comprehensively consider the application scenario, single machine capacity and selected battery type and other influencing factors.

[0060] The above are basic embodiments of the present invention. The technical solution of the present invention is further described below through four preferred embodiments.

[0061] Example 1

[0062] Reference Figure 1 (a) shows a power module structure diagram of a low modulation ratio topology high reliability high voltage direct-mounted energy storage equipment disclosed in this embodiment. The internal structure of the high voltage energy storage power module includes: a power conversion unit, an AC side fault bypass circuit, a bus capacitor, a DC side filter inductor, a power buffer link, a starting circuit, a DC contactor, a battery cluster, etc. The DC side positive pole of the H-bridge power unit is connected in series with the DC side pre-charging device, the DC protection device, the DC contactor, the battery cluster, and the DC side filter inductor, and then connected to the DC side negative pole of the H-bridge power unit. The AC side positive pole of the H-bridge power unit is connected in series in sequence, and the bus capacitor is connected in parallel to the two poles of the DC side of the H-bridge power unit. Based on the above standard submodules, the module displays an AC power port and an information communication port to the outside. After being configured by the upper main control system, high voltage and large capacity energy storage equipment with different needs can be easily constructed.

[0063] This embodiment provides three power module system construction solutions, such as Figure 1 (b) The single star type low modulation ratio topology high voltage direct hanging scheme, such as Figure 1 (c) The triangle type low modulation ratio topology high voltage direct hanging scheme and Figure 1 (d) is a double star parallel low modulation ratio topology high voltage direct hanging scheme. Under each system scheme, each phase or each energy storage unit chain is composed of energy storage containers in series. The energy storage container contains a certain number of energy storage units. The AC outlet of the energy storage container has added a fault bypass switch K1 and fault isolation switches S1 and S2. When a fault occurs in the energy storage unit inside the energy storage container, the isolation switches S1 and S2 are first disconnected, and the fault bypass switch K1 is closed at the same time. The faulty energy storage container is removed by switch bypass and isolated from the entire system to ensure that the remaining normal system can continue to operate. Under normal operating conditions, the fault bypass switch K1 is disconnected and the fault isolation switches S1 and S2 are closed.

[0064] Example 2

[0065] Reference Figure 2 The figure shows a design flow chart of a low modulation ratio topology high reliability high voltage direct hanging energy storage equipment provided by the present invention. The specific implementation is carried out in the following steps, namely:

[0066] Step S0: Determine the requirement for the critical modulation ratio of the system when the double frequency current is fully suppressed, that is, determine the critical modulation ratio m l

[0067]

[0068] Where N is the number of power modules cascaded per phase, V bnom is the rated voltage of the battery cluster, E m3 The third harmonic voltage amplitude required to be injected to completely suppress the double frequency current of the battery cluster.

[0069] The critical modulation ratio should satisfy the following relationship

[0070]

[0071] Where V sm is the amplitude of the grid-connected phase voltage (the maximum value within the grid voltage fluctuation range).

[0072] Step S1: Determine the critical value Q of the cell capacity that meets the system critical modulation ratio requirement when fully doubling the frequency current suppression cl , which satisfies the following conditions

[0073]

[0074] This critical capacity is a dividing line for system design. When the selected cell capacity is the critical capacity, the system just meets the modulation ratio requirement when the system double frequency current is completely suppressed. cnom cl Under this condition, when the system power and capacity requirements are met, the system frequency doubling current must be completely suppressed to meet the modulation ratio requirements. Under the appropriate power module quantity design, the fault redundancy requirements can also be met at the same time. cnom >Q cl At this time, although there is capacity redundancy, the system does not meet the modulation ratio requirement for complete suppression of the double frequency current.

[0075] Step S2: Determine the number of cascaded power modules of each energy storage unit chain according to the redundant module number requirement of the system setting and the efficiency of the power conversion system.

[0076] Step S3: Determine the design method of the DC side passive LC filter parameters so that the quadruple frequency pulsating current meets the national standard requirements and the circulating current size requirements. The quadruple frequency ripple rate γ of the battery current i It can be calculated as

[0077]

[0078] Capacitor voltage quadruple frequency ripple rate γ u It can be calculated as follows

[0079]

[0080] Where M is the modulation ratio, I m is the AC grid-connected current amplitude, is the power factor angle, R b is the internal resistance of the battery, V b is the battery cluster voltage, V c is the average value of the pulsating voltage on the capacitor, and ω4 is the quadruple angular frequency. After determining the ripple rate of the capacitor voltage and the inductor current, the above two equations can be combined to obtain the capacitance value C and the inductance value L. The selection of the bus capacitor voltage ripple rate should take into account the influence of the standard requirements and the factors that generate circulating current.

[0081] Example 3

[0082] ​The present invention proposes a high-voltage online operation and maintenance technology for energy storage containers with high reliability and low modulation ratio topology and high-voltage direct-mounted energy storage equipment. When it is implemented specifically, it is necessary to add a fault bypass switch K1 and fault isolation switches S1 and S2 to the AC output port of the container. When a fault occurs in the energy storage unit, the faulty energy storage unit can be removed through the AC side bypass switch or the DC side contactor according to the fault situation, and the energy storage unit fault redundant operation control can be performed. When the system needs to be repaired and maintained, the energy storage container is then isolated by the combination of the AC side fault bypass switch and the isolation switch for fault partitioning. The remaining system can work normally, and then the container where the faulty energy storage unit is located can be operated and maintained online.

[0083] The specific implementation includes the following steps:

[0084] Step S0: Remove and isolate the container where the faulty energy storage unit is located from the system

[0085] Step S0.1: controlling the output voltage of the energy storage container to 0;

[0086] Step S0.2: close the AC side fault bypass switch K1 of the container;

[0087] Step S0.3: Disconnect the container fault isolation switches S1 and S2;

[0088] Step S1: After the energy storage container where the faulty energy storage unit is located is removed, the SOC balancing control strategy of the remaining normal system is executed.

[0089] Step S2: After the online maintenance is completed, the energy storage container is put into system operation

[0090] Step S2.1: Close the isolating switches S1 and S2 of the energy storage container;

[0091] Step S2.2: Control the output voltage of the energy storage container to 0;

[0092] Step S2.3: disconnect the AC bypass switch of the energy storage container;

[0093] Example 4

[0094] Reference Figure 3 As shown, it is a control block diagram of a low modulation ratio topology high reliability high voltage direct hanging energy storage equipment provided by the present invention. The specific implementation is carried out in the following steps, namely:

[0095] Step S0: Grid-connected control of charging and discharging of low modulation ratio topology high reliability high voltage direct-mounted energy storage equipment;

[0096] Step S1: By injecting the third harmonic voltage, the double frequency current of the 100MW high-voltage direct-mounted energy storage with low modulation ratio control to a single cluster of batteries is completely suppressed, and the low modulation ratio characteristics of the system are used to inject a specific third harmonic voltage without overshoot to achieve complete suppression of the double frequency current. For a single star-connected high-voltage direct-mounted energy storage power conversion system, the double frequency harmonic can be completely eliminated by directly superimposing the set triple frequency common mode voltage on the modulation voltage of each phase bridge arm. The implementation method includes the following steps:

[0097] Step S1.1: First, extract the d-axis and q-axis components i of the AC output current of the power conversion system d and i q , and its modulation voltage d, q axis components u dref0 and u qref0 (Output of the inner current loop control). Calculate the amplitude of the AC output current I according to the following formula: vm1 and the amplitude of the bridge arm modulation voltage U vm1 ,for:

[0098]

[0099] Step S1.2: Next, calculate the phase angle δ1 and The values ​​are:

[0100]

[0101] Step S1.3: Finally, the modulation voltage of the three-phase bridge arm is obtained:

[0102]

[0103] Where: u xref represents the modulation voltage of the three-phase bridge arm after the triple frequency common mode voltage is injected, and the subscripts x = a, b, c represent the three phases A, B, and C respectively; θ p Indicates the angle of the phase-locked loop output.

[0104] Where:

[0105] 1) e3 represents the injected third harmonic voltage; E m3 and δ3 represent the magnitude and phase of e3;

[0106] 2) N represents the number of cascaded energy storage units; u ca 、u cb 、u cc Respectively represent the submodule capacitor voltages of phases a, b, and c (assuming that there is consistency between the submodules);

[0107] Step S2: SOC balancing control within and between phases

[0108] The SOC balancing control of the power module battery cluster is divided into inter-phase SOC control and intra-phase SOC control. Formula (1) gives the SOC of each phase and the definition of the SOC of the BESS, where SOC kj is the state of charge of the jth battery module in phase k, N k It is the number of modules in normal operation of phase k, which is less than or equal to the number of cascaded power modules N in the energy storage unit chain.

[0109]

[0110] The SOC balance within a phase is mainly based on the SOC of the phase as the reference value, which is achieved by superimposing a voltage component on the module reference voltage.

[0111]

[0112] Among them, u kref is the reference voltage of phase k, γ is the intra-phase balancing coefficient, E nom is the rated voltage of the battery module.

[0113] Phase-to-phase balancing uses the SOC of the BESS as a reference value and adjusts the power distribution of the three phases through zero-sequence voltage injection, thereby balancing the three-phase SOC. The phase-to-phase power ΔP required for phase-to-phase SOC balancing is k1 As shown in formula (3)

[0114]

[0115] Among them, λ is the phase SOC balance coefficient, P nom is the rated active power of the system.

[0116] Step S3: Fault redundancy control of energy storage container and energy storage unit. Usually, energy storage unit redundancy is used to improve the reliability of the converter. When the power conversion unit of the energy storage unit inside the energy storage container fails, the energy storage unit can be bypassed as a whole through the AC side bypass switch. When the battery cluster fails or an early warning occurs, the battery cluster is removed through the contactor of the DC side positive and negative busbars. The remaining power conversion units can participate in the system operation normally and maintain the low modulation ratio characteristics of the system. When it is necessary to perform fault inspection and online maintenance on the faulty energy storage unit, the faulty energy storage container can be removed through the combined control of the energy storage container's isolation switches S1 and S2 and the fault bypass switch K1, and it can be isolated from the entire system to ensure that the remaining normal system can continue to operate.

[0117] To offset the impact of the bypass of the energy storage container or energy storage unit, the power ΔP that needs to be adjusted for each phase k2 for:

[0118]

[0119] Where Nk is the number of power modules remaining in normal operation in each phase, P ref is the reference power given by the system.

[0120] Obviously, whether it is module fault control or inter-phase SOC balancing control, its essence is to change the charge and discharge power of each phase through the zero-sequence voltage, thereby changing the SOC of each phase battery module. For each phase, the power changed by the zero-sequence voltage is equal to the sum of equations (3) and (4), so we have

[0121]

[0122] Since the current on the grid side always maintains three-phase symmetry, we can solve

[0123]

[0124] The zero-sequence voltage calculated by equation (6) is superimposed on the reference voltage of each phase energy storage unit chain to achieve power balancing control

[0125] The present invention provides three expansion schemes including star, double star and triangle low modulation ratio topologies. The selection of a specific expansion scheme should comprehensively consider the application scenario, single machine capacity and selected battery type and other influencing factors. Under different combined expansion schemes, the submodules in the system are all cascaded on the AC side to form a single-phase bridge arm, and the difference lies in the connection relationship between the bridge arms.

[0126] Under the low modulation ratio design, the present invention enables the high-voltage direct-mounted energy storage system to fully utilize the DC voltage redundancy to achieve battery cluster frequency doubling current suppression, and the battery ripple current pulsation amplitude meets the national standard requirements without increasing the device cost. The DC voltage redundancy can be fully utilized to achieve dynamic SOC balancing control, taking into account the SOC balancing rate and effect; at the same time, the redundant number of energy storage units and the DC voltage redundancy are increased, which can realize energy storage container fault removal and redundant operation control, thereby improving the reliability and maintainability of the system.

[0127] Those skilled in the art know that, in addition to realizing the system and its various devices, modules, and units provided by the present invention in a purely computer-readable program code, it is entirely possible to realize the same functions in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered as a hardware component, and the devices, modules, and units included therein for realizing various functions can also be regarded as structures within the hardware component; the devices, modules, and units for realizing various functions can also be regarded as both software modules for realizing the method and structures within the hardware component.

[0128] The specific embodiments of the present invention are described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A low modulation ratio topology high reliability high voltage direct hanging energy storage system, characterized in that: include: High voltage energy storage unit; The high-voltage energy storage unit comprises a three-phase energy storage unit chain; in the three-phase energy storage unit chain, each phase energy storage unit chain is composed of a plurality of energy storage units in cascade, and the connection ends of the three-phase energy storage unit chain are sequentially connected in series with the AC side filter inductor and then connected to the power grid; The energy storage unit includes an H-bridge power unit, a bus capacitor, a DC side filter inductor, a battery side pre-charging device, a DC side contactor and a battery cluster; The DC side positive pole of the H-bridge power unit is connected in series with the DC side contactor, the battery side pre-charging device, the battery cluster, and the DC side filter inductor in sequence, and then connected to the DC side negative pole of the H-bridge power unit, and the AC side positive pole of the H-bridge power unit is connected in series in sequence.

2. The low modulation ratio topology high reliability high voltage direct hanging energy storage system according to claim 1 is characterized in that: In the three-phase energy storage unit chain, the number of cascaded energy storage units and the DC voltage in each phase make the system modulation ratio less than or equal to 0.

67.

3. The low modulation ratio topology high reliability high voltage direct hanging energy storage system according to claim 2 is characterized in that: The topological structure of the three-phase energy storage unit chain includes a single star chain, a double star parallel chain and a delta chain.

4. The low modulation ratio topology high reliability high voltage direct hanging energy storage system according to claim 3 is characterized in that: Each phase is composed of multiple energy storage containers in series, and each energy storage container is composed of multiple internal energy storage units in cascade. A fault bypass switch K1 and fault isolation switches S1 and S2 are added to the outlet of the container; when a power module fails, the fault partition is isolated through the control of the energy storage container.

5. The low modulation ratio topology high reliability high voltage direct hanging energy storage system according to claim 4 is characterized in that: The fault partition isolation by controlling the energy storage container includes: The container where the faulty energy storage unit is located is removed from the system and isolated; the output voltage of the energy storage container is controlled to become 0, the AC side fault bypass switch K1 of the container is closed, and the fault isolation switches S1 and S2 of the container are disconnected; After maintaining the faulty energy storage unit, put the energy storage container into system operation; close the isolating switches S1 and S2 of the energy storage container, control the output voltage of the energy storage container to 0, and disconnect the AC bypass switch of the energy storage container.

6. The low modulation ratio topology high reliability high voltage direct hanging energy storage system according to claim 1 is characterized in that: Also includes: Power conversion unit; when the power conversion unit fails, the energy storage unit is bypassed as a whole through the AC side bypass switch, and when the battery cluster fails or warns, the battery cluster is cut off through the contactor of the DC side positive and negative busbars.

7. A low modulation ratio topology high reliability high voltage direct hanging energy storage method, based on the low modulation ratio topology high reliability high voltage direct hanging energy storage system according to any one of claims 1 to 6, characterized in that: include: Step S1: Set the initial parameters of the system and calculate the critical modulation ratio m of the system when the double frequency current is fully suppressed. l ; The system initial parameters include the number of redundant modules; Step S2: The critical modulation ratio m is obtained l , calculate the critical value Q of the cell capacity that meets the system critical modulation ratio requirements cl ; Step S3: Calculate the number of cascade units per phase according to the number of redundant modules set in the system and the efficiency of the power conversion system; Step S4: According to the calculation results, the DC side LC filter parameters that meet the pulsating current, voltage standards and circulating current limiting requirements are obtained.

8. The low modulation ratio topology high reliability high voltage direct hanging energy storage method according to claim 7 is characterized in that: The step S1 comprises: The critical modulation ratio m is obtained according to the following formula l : Where N is the number of power modules cascaded per phase, V bnom is the rated voltage of the battery cluster, E m3 The third harmonic voltage amplitude required to be injected to completely suppress the double frequency current of the battery cluster; Critical modulation ratio m l satisfy: Among them, V sm is the amplitude of the grid-connected phase voltage.

9. The low modulation ratio topology high reliability high voltage direct hanging energy storage method according to claim 8 is characterized in that: The step S2 comprises: According to the following formula, the critical value Q of the cell capacity that meets the system critical modulation ratio requirement is obtained: cl :

10. The low modulation ratio topology high reliability high voltage direct hanging energy storage method according to claim 9 is characterized in that: The step S4 comprises: The four-fold frequency ripple rate γ of the battery current is calculated according to the following formula: i : Calculate the capacitor voltage quadruple frequency ripple rate γ u : Where M is the modulation ratio, I m is the AC grid-connected current amplitude, is the power factor angle, R b is the internal resistance of the battery, V b is the battery cluster voltage, V c is the average value of the pulsating voltage on the capacitor, ω4 is the quadrupled angular frequency; Combining the above two equations, we can obtain the capacitance value C and the inductance value L.

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