A method for analyzing PCS topology of distributed energy storage converter

Abstract

The present invention relates to a method for analyzing the PCS topology structure of a distributed energy storage converter, comprising the following steps: step 1, calculating the consistency of the PCS topology structure of the distributed energy storage converter; step 2, calculating the efficiency of the PCS topology structure of the distributed energy storage converter; step 3, calculating the reliability of the PCS topology structure of the distributed energy storage converter. The analysis method of the present invention can systematically interpret the characteristics of the distributed PCS topology structure from the three aspects of consistency, efficiency and reliability, which is conducive to analyzing the advantages and disadvantages of the PCS topology structure of the distributed energy storage converter and promoting the large-scale application of the distributed PCS topology structure.

Description

Technical Field

[0001] The present invention relates to the field of electric power, and in particular to a method for analyzing the topological structure of a distributed energy storage converter PCS. Background Art

[0002] In order to better achieve the goals of carbon peak and carbon neutrality, renewable energy such as wind and solar have been vigorously developed, but the randomness and volatility of their output require a certain energy storage system to increase their flexible control. The development of energy storage technology directly affects the development and comprehensive utilization of renewable energy, and the energy storage converter PCS plays the role of connecting the power grid and the energy storage system. It is the most critical link in the entire energy storage control technology and the key equipment for connecting energy storage batteries to the power system. It is related to whether the energy storage system can operate safely, efficiently and orderly. In order to adapt to the growing application needs, energy storage converters have also developed from traditional centralized structures to distributed modular structures. Therefore, it is necessary to carry out research on analytical methods for designing PCS topological structures. Summary of the invention

[0003] In order to solve the above technical problems, the present invention proposes an analysis method for designing a PCS topology structure. Through the method of the present invention, the advantages of a distributed PCS topology structure over a centralized PCS topology structure can be analyzed and judged from the perspectives of consistency, efficiency and reliability.

[0004] The technical solution of the present invention is: a method for analyzing the PCS topology structure of a distributed energy storage converter, comprising the following steps:

[0005] Step 1, calculating the consistency of the PCS topology structure of the distributed energy storage converter;

[0006] Step 2, calculating the efficiency of the PCS topology of the distributed energy storage converter;

[0007] Step 3: Calculate the reliability of the PCS topology of the distributed energy storage converter.

[0008] Furthermore, the step 2, calculating the efficiency of the PCS topology structure of the distributed energy storage converter, is as follows:

[0009] The efficiency of PCS is calculated as follows:

[0010]

[0011] Among them, P p is the input power of PCS, ΔP p Power loss, including conduction loss of power switching devices, switching loss and output unit filter inductance loss;

[0012] String PCS has been rapidly developed due to its advantages of networking and flexible control. It is composed of multiple modules, so the efficiency curves of PCSs of different power levels composed of the same modules are the same;

[0013] Select the rated power as P pmr Modules, forming PCSs with multiple power levels, namely P pr,z =z×P pmr , that is, Z P pmr Module; Assume that the rated power is P pcsr The PCS system is a power level P pcsr PCS with power P pcsr PCS group; In order to achieve the highest efficiency of the system, the following objective function is constructed:

[0014] min-η=-∑ω z η z (2)

[0015] where η z is the efficiency of a single PCS, ω z is the corresponding weight;

[0016] The constraints are as follows:

[0017] Balance of power rating:

[0018] P pcsr =∑P pr,z (3)

[0019] Where P pr,z is the rated power of a single PCS, P pcsr is the total rated power of the PCS;

[0020] Actual power balance:

[0021] P pcs =∑P p,z (4)

[0022] Where P p,z is the actual power of a single PCS, P pcs is the actual total power of the PCS.

[0023] Maximum power constraint:

[0024] 0≤P p,z ≤P pr,z (5)

[0025] Single PCS efficiency function:

[0026]

[0027] Furthermore, the step 3, calculating the reliability of the PCS topology structure of the distributed energy storage converter is as follows:

[0028] Assume that the PCS maintenance and replacement cycle is t p =M days, service life is c p =N years

[0029] The failure rate

[0030] Repair replacement rate

[0031] Its reliability is

[0032] Right now

[0033] When there are b PCSs, the probability of their normal operation is:

[0034] 1-(1-p p ) b (7)

[0035] As the value of b increases, that is, the number of PCSs increases, the probability that the PCS system works normally increases.

[0036] Beneficial effects:

[0037] The existing technology has little analysis on the distributed PCS topology structure, and most of them focus on the description of one aspect of the characteristics, and the breadth and depth need to be further improved. The analysis method of the present invention systematically interprets the advantages of the distributed PCS topology structure from the three aspects of consistency, efficiency and reliability, which is conducive to promoting the large-scale application of the distributed PCS topology structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Centralized PCS topology;

[0039] Figure 2 Distributed PCS topology;

[0040] Figure 350kW module efficiency diagram. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0042] With the rapid development of string-type modular PCS, the cost difference of PCSs of different power levels is getting smaller and smaller. That is, at the same power level, the cost of a high-power PCS is not much different from the cost of a PCS group composed of multiple low-power PCSs in parallel. Figure 1 , is the topology of a PCS, Figure 2 It is a topological structure of multiple parallel PCSs.

[0043] A distributed energy storage converter PCS topology analysis method of the present invention specifically comprises the following steps:

[0044] Step 1, calculating the consistency of the PCS topology structure of the distributed energy storage converter;

[0045] Step 2, calculating the efficiency of the PCS topology of the distributed energy storage converter;

[0046] Step 3, calculating the reliability of the PCS topology structure of the distributed energy storage converter;

[0047] According to one embodiment of the present invention, the step 1 of calculating the consistency of the PCS topology structure of the distributed energy storage converter is specifically as follows:

[0048] Battery energy storage systems are generally composed of a large number of battery cells. It is crucial to ensure the consistency of each battery cell. However, due to differences in the materials used and the manufacturing process, there are inevitably inconsistencies in the single battery. Coupled with different operating conditions, even batteries with good consistency still have differences after long-term operation. The battery cell with the worst capacity performance often determines the charging and discharging efficiency of the entire battery pack. When the battery cell with poor performance reaches the charge and discharge cut-off condition first during charging and discharging, the entire battery pack will not be able to continue charging and discharging, and the remaining battery capacity will be idle; in addition, the inconsistency of battery cells will also cause circulation between battery clusters, affecting the reliable operation of the battery energy storage system, thereby affecting the overall efficiency of the system. Therefore, inconsistency will reduce battery capacity and shorten battery life. In severe cases, it may also cause battery combustion or explosion, directly leading to safety accidents.

[0049] Due to the inconsistency of single cell capacity, internal resistance, self-discharge rate, etc., the capacity utilization rate and cycle life of grouped batteries are far inferior to those of single cells. Therefore, minimizing the number of series and parallel connections of battery cells can improve the consistency of the battery system. The distributed PCS topology can divide the battery system into multiple independently powered units, which can reduce the circulation between different battery groups. Therefore, the use of a distributed PCS topology can improve the consistency of the battery system compared to the centralized PCS topology.

[0050] According to one embodiment of the present invention, the step 2 calculates the efficiency of the PCS topology structure of the distributed energy storage converter; specifically, as follows:

[0051] Traditional efficiency analysis is mainly aimed at integrated cabinet PCS, that is, non-modular PCS. Generally, the higher the power level, the higher the efficiency. The centralized PCS topology is more advantageous when operating at high power. However, the maximum efficiency of string PCS, that is, modular PCS, is the same for PCS composed of the same module. When operating at high power, the efficiency of the two is the same, but when operating at low power, the decentralized PCS topology is more advantageous.

[0052] The efficiency of PCS can be calculated as follows:

[0053]

[0054] Among them, P p is the input power of PCS, ΔP p It is power loss, which generally includes conduction loss of power switching devices, switching loss and output unit filter inductance loss.

[0055] A string PCS is composed of multiple modules, so the efficiency curves of PCSs of different power levels composed of the same modules are the same.

[0056] Select the rated power as P pmr Modules can form PCSs with multiple power levels, namely P pr,z =z×P pmr , z∈N * , N* represents a natural number set excluding 0. Assume that the rated power is P pcsr The PCS system can be a power level P pcsr PCS with power P pcsr PCS group. In order to achieve the highest efficiency of the system, the following objective function is constructed:

[0057] min-η=-∑ω z η z (2)

[0058] where η z is the efficiency of a single PCS, ω z is the corresponding weight.

[0059] constraint:

[0060] Rated power balance

[0061] P pcsr =∑P pr,z (3)

[0062] Where P pr,z is the rated power of a single PCS, P pcsris the total rated power of the PCS.

[0063] Actual power balance

[0064] P pcs =∑P p,z (4)

[0065] Where P p,z is the actual power of a single PCS, P pcs is the actual total power of the PCS.

[0066] Maximum power constraint

[0067] 0≤P p,z ≤P pr,z (5)

[0068] Single PCS efficiency function

[0069]

[0070] Assuming a PCS system with a rated power of 100kW and using modules with a rated power of 50kW, there are multiple PCS combinations, such as [50,50],

[100] .

[0071] Figure 3 The measured efficiency of the module with a rated power of 50kW. The efficiency increases first and then decreases as the power increases. The efficiency calculated for different actual powers is shown in Table 1, Table 2, and Table 3. It can be seen that when the actual power is large, the efficiency of the distributed PCS topology and the centralized PCS topology is the same. As the actual power decreases, the efficiency of the distributed PCS topology gradually exceeds the efficiency of the centralized PCS topology.

[0072] Table 1 Efficiency of 100kW actual power

[0073]

[0074] Table 2 Efficiency of 10kW actual power

[0075]

[0076] Table 3 Efficiency of 5kW actual power

[0077]

[0078] Therefore, the smaller the actual power, the more obvious the efficiency advantage of the decentralized PCS topology.

[0079] According to one embodiment of the present invention, the step 3 calculates the reliability of the PCS topology structure of the distributed energy storage converter; specifically as follows:

[0080] 3.1 Battery System Reliability

[0081] assumed Figure 2 If a serious fault occurs in the battery unit in the PCS1 area, the distributed topology can remove the area without affecting the normal operation of other areas, thereby preventing the spread of the fault and preventing the occurrence of system cascading failures. The centralized topology does not have this advantage, so the distributed PCS topology has higher operational reliability than the centralized PCS topology.

[0082] 3.2 PCS Reliability

[0083] Assume that the PCS maintenance and replacement cycle is t p = 10 days, service life is c p =20 years

[0084] The failure rate

[0085] Repair replacement rate

[0086] Its reliability is

[0087] Right now

[0088] When there are b (b ≥ 1) PCSs, the probability of their normal operation is:

[0089] 1-(1-p p ) b =1-0.0014 b (7)

[0090] It can be seen that as the value of b increases, that is, the number of PCS increases, the probability of normal operation of the PCS system increases. The operation reliability of the distributed PCS topology is higher than that of the centralized PCS topology.

[0091] Although the above describes the illustrative specific embodiments of the present invention to facilitate those skilled in the art to understand the present invention, and it should be clear that the present invention is not limited to the scope of the specific embodiments, for those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A method for analyzing the PCS topology structure of a distributed energy storage converter, characterized in that: The steps include: Step 1: Calculate the consistency of the PCS topology of the distributed energy storage converter, and use a distributed PCS topology to improve the consistency of the battery system compared to a centralized PCS topology; Step 2, calculating the efficiency of the PCS topology of the distributed energy storage converter; Step 3, calculating the reliability of the PCS topology structure of the distributed energy storage converter; The step 2, calculating the efficiency of the distributed energy storage converter PCS topology structure, is as follows: The efficiency of PCS is calculated as follows: (1) in, is the input power of PCS, Power loss, including conduction loss of power switching devices, switching loss and output unit filter inductance loss; String PCS is composed of multiple modules, so the efficiency curves of PCSs of different power levels composed of the same modules are the same; Select the rated power Modules, forming PCSs of multiple power levels, namely , that is, Z Module; Assume that the rated power is The PCS system is a power level PCS with power of PCS group; In order to achieve the highest efficiency of the system, the following objective function is constructed: (2) in is the efficiency of a single PCS, is the corresponding weight; The constraints are as follows: Balance of power rating: (3) in is the rated power of a single PCS, is the total rated power of the PCS; Actual power balance: (4) in is the actual power of a single PCS, is the actual total power of PCS; Maximum power constraint: (5) Single PCS efficiency function: (6) The step 3 calculates the reliability of the PCS topology structure of the distributed energy storage converter; specifically, as follows: Assuming PCS maintenance and replacement cycle = M days, the service life is =N years The failure rate , Repair replacement rate , Its reliability is , Right now , When there are b PCSs, the probability of their normal operation is: (7) As the value of b increases, that is, the number of PCSs increases, the probability that the PCS system works normally increases.

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