Power Allocation Method for Traction Power Supply Hybrid Energy Storage System Considering Flywheel Standby Losses

Abstract

This invention provides a power allocation method for a traction power supply hybrid energy storage system considering flywheel standby losses, comprising the following steps: S1. Determining the initial control variables and initial state variables of the traction power supply system, and constructing a power prediction model based on the initial control variables and initial state variables to predict the power sequence of the hybrid energy storage system at future times; S2. Determining the charging and discharging type of the hybrid energy storage system based on the power sequence of the hybrid energy storage system, wherein the charging and discharging type includes long-term charging and discharging and short-term charging and discharging; S3. Allocating the power of the energy storage battery and flywheel energy storage unit in the hybrid energy storage system based on the charging and discharging type.

Description

Technical Field

[0001] This invention relates to a power distribution method for an energy storage system, and more particularly to a power distribution method for a traction power supply hybrid energy storage system that takes into account flywheel standby losses. Background Technology

[0002] In traction power supply systems, hybrid energy storage systems are generally used to achieve both energy storage and power supply. The rationality of the power allocation of hybrid energy storage is an important guarantee for meeting the system load demand and a key to realizing the advantages and disadvantages of energy storage devices.

[0003] Existing hybrid energy storage power allocation strategies primarily focus on battery life degradation, and those that consider battery state of charge (SOC) generally exhibit excellent SOC control performance. For flywheel energy storage in hybrid systems, current research mainly addresses flywheel speed exceeding limits by incorporating flywheel speed into the power allocation process. However, in practice, flywheel energy storage units experience significant standby losses. Ignoring these losses during power allocation results in the flywheel frequently operating at high speeds for extended periods, leading to substantial standby energy waste.

[0004] Therefore, in order to solve the above-mentioned technical problems, it is urgent to propose a new technical approach. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a power allocation method for a traction power supply hybrid energy storage system that considers flywheel standby losses. Based on the power prediction model of the traction power supply system, the target power sequence of the traction power supply system is predicted. Then, the hybrid energy storage system is divided into three operating states: standby, long-term, and short-term. Power allocation is then performed for each of the three operating states. This can effectively reduce the impact of flywheel energy storage unit standby losses on power allocation, and reduce flywheel standby energy consumption while ensuring the stable operation of the traction power supply system, thus saving energy.

[0006] This invention provides a power allocation method for a traction power supply hybrid energy storage system that considers flywheel standby losses, comprising the following steps:

[0007] S1. Determine the initial control variables and initial state variables of the traction power supply system, and construct a power prediction model based on the initial control variables and initial state variables to predict the power sequence of the hybrid energy storage system at each future time.

[0008] S2. Determine the charging and discharging type of the hybrid energy storage system based on the power sequence of the hybrid energy storage system. The charging and discharging type includes long-term charging and discharging and short-term charging and discharging.

[0009] S3. Allocate power between the energy storage battery and flywheel energy storage unit in the hybrid energy storage system based on the charging and discharging type.

[0010] Furthermore, in step S1, the power prediction model is:

[0011]

[0012] Where: P T (k+1) represents the output power of the traction substation at time k+1, P R (k+1) represents the total power dissipated by the braking resistor at time k+1, P es (k+1) represents the output power of the energy storage system at time k+1, and the SOC. es (k+1) represents the state of charge of the energy storage system at time k+1, Q es.n T represents the rated capacity of the energy storage system. s To set the control cycle, P T (k) represents the output power of the traction substation at time k, P R (k) represents the total power dissipated by the braking resistor at time k, P es (k) represents the output power of the energy storage system at time k, SOC es (k) represents the state of charge of the energy storage system at time k, P cα (k) represents the power of the converter on the power supply side at time k, P cβ (k) represents the power of the β-side converter at time k, P Rα (k) represents the power dissipation of the train braking resistor on the α power supply side.

[0013] Furthermore, the constraints of the power prediction model are as follows:

[0014] When the total train load P at time k αβ When (k)≥0, the traction power supply system as a whole exhibits a traction energy consumption state, and the constraint condition at this time is:

[0015]

[0016] When the total train load P at time k αβ When (k) < 0, the traction power supply system is in a regenerative braking state, and the constraint condition at this time is:

[0017]

[0018] Where: P es.n This refers to the rated power of the energy storage system in the traction power supply system.

[0019] Furthermore, determining the charge / discharge type of a hybrid energy storage system based on its power sequence specifically includes:

[0020] The power sequence is determined to be: ..., P es (k-1), P es(k-2), P es (k-1), P es (k), P es (k+1), P es (k+2), ..., P es (k+N);

[0021] In the power sequence, P es (k+1) to P es In (k+N), if there exists a power sequence of 0 for more than one minute, the hybrid energy storage system will soon enter standby mode.

[0022] Find the point in the power sequence around time k where the power level crosses zero most closely with respect to time k. Then, calculate the duration T between these two points. D ;

[0023] Such as duration T D If the time threshold is less than or equal to the set time threshold, the hybrid energy storage and system are in a short-term charge-discharge state at time k; otherwise, the hybrid energy storage and system are in a long-term charge-discharge state at time k.

[0024] Furthermore, when time k is in a short-term charge / discharge state, the power distribution of the hybrid energy storage system is as follows:

[0025] Discharge state:

[0026] P f (k)=min{P es (k),P f.n}

[0027] P ba (k)=P es (k)-P f (k);

[0028] Charging status:

[0029] P f (k)=max{P es (k),-P f.n}

[0030] P ba (k)=P es (k)-P f (k);

[0031] Where: P f (k) represents the reference power for flywheel energy storage charging and discharging, P ba (k) represents the reference power for battery energy storage charging and discharging, P f.n The rated charge and discharge power of the flywheel energy storage unit.

[0032] Furthermore, when time k is in a long-term charge-discharge state, the power distribution of the hybrid energy storage system is as follows:

[0033] Discharge state:

[0034] P f (k)=min{P fw (k),P es (k),P f.n}

[0035] P ba (k)=P es (k)-P f (k)

[0036] Charging status:

[0037] P f (k)=max{-P fw (k),P es (k),-P f.n}

[0038] P ba (k)=P es (k)-P f (k);

[0039] Where: P fw (k) represents the flywheel regulation power;

[0040]

[0041] Where: n f.max n f.min These represent the maximum and minimum speeds of the flywheel, P. es (k) less than 0 indicates that the hybrid energy storage system is in a charging state, P es (k) greater than 0 indicates the hybrid energy storage system is in discharge state, σ is the adjustment coefficient and σ≥0, E N (k) is an intermediate variable and T s This refers to the control cycle of the traction power supply system.

[0042] The beneficial effects of this invention are as follows: Based on the power prediction model of the traction power supply system, the target power sequence of the traction power supply system is predicted. Then, the standby, long-term and short-term operating states of the hybrid energy storage system are divided. Power is then allocated according to the three operating states respectively, thereby effectively reducing the impact of the standby loss of the flywheel energy storage unit on the power allocation. While ensuring the stable operation of the traction power supply system, the standby energy consumption of the flywheel can be reduced, thus saving energy. Attached Figure Description

[0043] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0044] Figure 1 This is a flowchart of the present invention.

[0045] Figure 2 The topology of a high-speed rail regenerative braking energy utilization system that incorporates batteries and flywheel energy storage.

[0046] Figure 3 This is a schematic diagram of the energy storage system in its future standby state.

[0047] Figure 4 This is a schematic diagram of a complete discharge process of an energy storage system.

[0048] Figure 5 This represents the power distribution result between the battery and the flywheel.

[0049] Figure 6 This refers to the changes in battery SOC and flywheel speed.

[0050] Figure 7 This represents the power allocation result for charging conditions in standby mode in the future.

[0051] Figure 8 This represents the power allocation result for the discharge condition in the future standby state.

[0052] Figure 9 This represents the power distribution result under short-term charge and discharge conditions.

[0053] Figure 10 Whether the power distribution result of flywheel regulation power is taken into account during long-term charging.

[0054] Figure 11 The power distribution result under long-term discharge conditions is whether the flywheel regulation power is taken into account. Detailed Implementation

[0055] The present invention will be further described in detail below:

[0056] This invention provides a power allocation method for a traction power supply hybrid energy storage system that considers flywheel standby losses, comprising the following steps:

[0057] S1. Determine the initial control variables and initial state variables of the traction power supply system, and construct a power prediction model based on the initial control variables and initial state variables to predict the power sequence of the hybrid energy storage system at each future time.

[0058] S2. Determine the charging and discharging type of the hybrid energy storage system based on the power sequence of the hybrid energy storage system. The charging and discharging type includes long-term charging and discharging and short-term charging and discharging.

[0059] S3. Power allocation between the energy storage battery and flywheel energy storage unit in the hybrid energy storage system is performed based on the charging and discharging type. Using the above method, the target power sequence of the traction power supply system is predicted based on the power prediction model of the traction power supply system. Then, the hybrid energy storage system is divided into three operating states: standby, long-term, and short-term. Power allocation is then performed separately for each of these three operating states. This effectively reduces the impact of standby losses of the flywheel energy storage unit on power allocation, ensuring the stable operation of the traction power supply system while reducing flywheel standby energy consumption and saving energy. The traction power supply system adopts the following... Figure 2 The diagram shows the topology of a high-speed rail regenerative braking energy utilization system.

[0060] In this embodiment, the power prediction model in step S1 is:

[0061]

[0062] Where: P T (k+1) represents the output power of the traction substation at time k+1, P R (k+1) represents the total power dissipated by the braking resistor at time k+1, P es (k+1) represents the output power of the energy storage system at time k+1, and the SOC. es (k+1) represents the state of charge of the energy storage system at time k+1, Q es.n T represents the rated capacity of the energy storage system. s To set the control cycle, P T (k) represents the output power of the traction substation at time k, P R (k) represents the total power dissipated by the braking resistor at time k, P es (k) represents the output power of the energy storage system at time k, SOC. es (k) represents the state of charge of the energy storage system at time k, P cα (k) represents the power of the converter on the power supply side at time k, P cβ (k) represents the power of the β-supply-side converter at time k, P Rα (k) represents the power dissipation of the train braking resistor on the α power supply side.

[0063] Wherein: the constraints of the power prediction model are:

[0064] When the total train load P at time k αβ When (k)≥0, the traction power supply system as a whole exhibits a traction energy consumption state, and the constraint condition at this time is:

[0065]

[0066] When the total train load P at time k αβ When (k) < 0, the traction power supply system is in a regenerative braking state, and the constraint condition at this time is:

[0067]

[0068] Where: P es.n This refers to the rated power of the energy storage system in the traction power supply system. For example... Figure 3 As shown, let the current time be k;

[0069] Determining the charge / discharge type of a hybrid energy storage system based on its power sequence includes:

[0070] The power sequence is determined to be: ..., P es (k-1), P es (k-2), P es (k-1), P es (k), P es (k+1), P es (k+2), ..., P es (k+N);

[0071] In the power sequence, P es (k+1) to P es In (k+N), if there exists a power sequence of 0 for more than one minute, the hybrid energy storage system will soon enter standby mode.

[0072] Find the point in the power sequence around time k where the power level crosses zero most closely with respect to time k. Then, calculate the duration T between these two points. D ;like Figure 4 As shown;

[0073] Such as duration T D If the time threshold is less than or equal to the set time threshold, the hybrid energy storage and system are in a short-term charge-discharge state at time k; otherwise, the hybrid energy storage and system are in a long-term charge-discharge state at time k. The set time threshold is typically 2 minutes, but other time thresholds can be set according to actual operating conditions.

[0074] In this embodiment, when time k is in a short-term charge-discharge state, the power allocation of the hybrid energy storage system is as follows:

[0075] Discharge state:

[0076] P f (k)=min{P es (k),P f.n}

[0077] P ba (k)=P es (k)-P f (k);

[0078] Charging status:

[0079] P f (k)=max{P es (k),-P f.n}

[0080] P ba (k)=P es (k)-P f (k);

[0081] Where: P f (k) represents the reference power for flywheel energy storage charging and discharging, P ba (k) represents the reference power for battery energy storage charging and discharging, P f.n The rated charge and discharge power of the flywheel energy storage unit.

[0082] When time k is in a long-term charge-discharge state, the power distribution of the hybrid energy storage system is as follows:

[0083] Discharge state:

[0084] P f (k)=min{P fw (k),P es (k),P f.n}

[0085] P ba (k)=P es (k)-P f (k)

[0086] Charging status:

[0087] P f (k)=max{-P fw (k),P es (k),-P f.n}

[0088] P ba (k)=P es (k)-P f (k);

[0089] Where: P fw (k) represents the flywheel regulation power;

[0090]

[0091] Where: n f.max n f.min These represent the maximum and minimum speeds of the flywheel, P. es (k) less than 0 indicates that the hybrid energy storage system is in a charging state, P es (k) greater than 0 indicates the hybrid energy storage system is in discharge state, σ is the adjustment coefficient and σ≥0, EN (k) is an intermediate variable and T s This refers to the control cycle of the traction power supply system. In other words, as described above, both the flywheel energy storage unit and the energy storage battery operate according to the aforementioned power allocation results, i.e., according to the allocated charging and discharging reference power.

[0092] The following is a further explanation:

[0093] In this embodiment Figure 5 The power output of the battery and flywheel using the power distribution strategy proposed in this invention is... Figure 6 This refers to the changes in battery SOC and flywheel speed. Figures 7-11 The results show the hybrid energy storage power allocation for typical time periods corresponding to each operating condition.

[0094] In this embodiment Figure 7 and Figure 8 It shows the power distribution results in the future standby state. Figure 7 The allocation results for charging conditions show that... Figure 7 (a) During the period from 13:50 to 13:51, the flywheel prioritizes the allocation of the target charging power P for hybrid energy storage. es Flywheel energy storage and charging, rotational speed n f Rise, when P es When the flywheel's rated charge / discharge power exceeds the rated power of the energy storage system (7.5MW), the battery is recharged. However, between 13:51 and 13:53, the flywheel's allocated power decreases to 0MW, the battery assumes all target power, and the flywheel enters standby mode at its current speed of 19789 r / min. This is because the model predictive control of this invention has a future prediction time domain of 2 minutes. Therefore, during the period of 13:50-13:51, the future standby condition was not predicted, and a power allocation strategy prioritizing flywheel charge / discharge was adopted. During the period of 13:51-13:53, it was predicted that the energy storage system would enter standby mode, so the power allocation strategy of discharging the flywheel first and then charging was switched. Figure 7 (b) The power allocation results, without considering future entry into standby mode, show that the flywheel continuously charges before entering standby mode and enters standby mode at a speed of 27745 r / min. This indicates that the power allocation strategy proposed in this invention, which considers future standby mode, reduces the standby speed of the flywheel by 28.67% during this period. Figure 8 As can be seen from the distribution results of the discharge conditions, Figure 8 (a) From 14:11 to 14:13, the flywheel prioritizes the allocation of the total target power of the hybrid energy storage system, while the battery provides supplementary discharge. The flywheel continues to discharge at its maximum discharge power, and its rotational speed decreases from 31826 r / min to 19445 r / min. At 14:13:20, the hybrid energy storage system enters standby mode, and the flywheel enters standby mode at a rotational speed of 19445 r / min. Figure 8(b) The power allocation result without considering future entry into standby mode shows that the battery prioritizes the allocation of target power, and the flywheel enters standby mode at 14:13:20 with a rotational speed of 31009 r / min. This indicates that the power allocation strategy proposed in this invention, which considers future standby mode, reduces the flywheel's standby rotational speed by 37.29% during this period. Table 1 compares the average rotational speed of the flywheel in standby mode, showing that the flywheel's discharge-then-charge power allocation strategy, which considers future standby mode of energy storage, reduces the average rotational speed of the flywheel in standby mode by 29.35%.

[0095] In this embodiment Figure 9 The power distribution results under short-term charge and discharge conditions are shown. It can be seen that when the target power of the hybrid energy storage system does not exceed the rated power of the flywheel, the flywheel output power P f Equal to the target power P of the energy storage system es The flywheel is given priority in charging and discharging; when |P es With a power output greater than 7.5MW, the flywheel output power remains at 7.5MW, while the battery continues to charge and discharge. During charging, the flywheel speed continuously increases to 35341 r / min; during discharging, the flywheel speed continuously decreases to 15013 r / min. This indicates that during short-term charge and discharge, the flywheel is preferentially utilized, improving its utilization rate and conforming to the performance characteristics of a flywheel as a power storage device.

[0096] In this embodiment Figure 10 and Figure 11 The power distribution results under long-term charge and discharge conditions are shown, taking into account the flywheel regulation power. Figure 10 Based on the power allocation results for charging conditions, it can be seen that by adopting a power allocation strategy that takes into account the flywheel's regulation power, the flywheel energy storage charging power |P f |P with target power of hybrid energy storage| es | increases with the increase of |, until |P f | Reaching rated charging power. As the flywheel charging speed continuously increases, the flywheel charging power slowly decreases at 16:30:50, and the speed increase rate slows down. The flywheel speed reaches its upper limit at 16:33:10, then remains idle for 40 seconds before entering the next discharge cycle. Under the power distribution strategy without flywheel power regulation, the flywheel continuously charges at its rated charging power, and the flywheel speed increases rapidly, reaching its upper limit at 16:32:00 and entering standby mode for 110 seconds. Therefore, during the energy storage charging period from 16:29 to 16:34, the flywheel charging amount differs by only 1.8% between the two strategies, but the flywheel energy storage standby time with flywheel power regulation is shortened by 63.6%. Figure 11The power distribution results under the discharge conditions show that, under the power distribution strategy with flywheel power regulation, the flywheel discharge power decreases as the speed decreases, and the rate of decrease in flywheel speed slows down. At 10:25:30, the flywheel discharge power increases, and the flywheel accelerates its discharge. This is due to the future energy storage demand E. N Due to the impact of this, energy storage will enter a charging state in the future. N <0, flywheel regulating power P fw Increased acceleration during discharge resulted in the flywheel speed dropping to 4119 r / min at 10:27:00, with a standby time of 0 seconds. Under the power distribution strategy without flywheel power regulation, the flywheel continuously discharged at its rated charging power, causing a rapid decrease in speed. At 10:25:50, the speed dropped to 3697 r / min, entering standby mode for 70 seconds. Therefore, during the energy storage discharge period from 10:23 to 10:27, the flywheel discharge amount differed by 2.5% between the two strategies, but the standby time of the flywheel with power regulation was shortened by 100%. Table 2 compares the flywheel standby time and cumulative charge / discharge amount. It can be seen that under the flywheel power regulation, although the cumulative charge / discharge amount decreased by 3.57%, the standby time of flywheel energy storage within a day was shortened by 33.43%. This indicates that while the introduction of flywheel power regulation slightly reduces the flywheel utilization rate, it extends the flywheel charging / discharging time and significantly shortens the flywheel standby time.

[0097] Table 3 in this embodiment shows a comparison of flywheel standby losses. It can be seen that compared with the flywheel-priority power allocation strategy, the power allocation strategy proposed in this invention reduces the flywheel standby losses by 53.29%, indicating that this invention reduces the energy lost by the flywheel during standby by reducing the rotational speed and standby time of the flywheel when it enters standby mode.

[0098] Table 1

[0099]

[0100] Table 2

[0101]

[0102] Table 3

[0103]

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A power distribution method for a traction power supply hybrid energy storage system considering flywheel standby losses, characterized in that: Includes the following steps: S1. Determine the initial control variables and initial state variables of the traction power supply system, and construct a power prediction model based on the initial control variables and initial state variables to predict the power sequence of the hybrid energy storage system at each future time. S2. Determine the charging and discharging type of the hybrid energy storage system based on the power sequence of the hybrid energy storage system. The charging and discharging type includes long-term charging and discharging and short-term charging and discharging. S3. Allocate power between the energy storage battery and the flywheel energy storage unit in the hybrid energy storage system based on the charging and discharging type; In step S1, the power prediction model is: Where: P T (k+1) represents the output power of the traction substation at time k+1, P R (k+1) represents the total power dissipated by the braking resistor at time k+1, P es (k+1) represents the output power of the energy storage system at time k+1, and the SOC. es (k+1) represents the state of charge of the energy storage system at time k+1, Q es.n T represents the rated capacity of the energy storage system. s To set the control cycle, P T (k) represents the output power of the traction substation at time k, P R (k) represents the total power dissipated by the braking resistor at time k, P es (k) represents the output power of the energy storage system at time k, SOC es (k) represents the state of charge of the energy storage system at time k, P cα (k) represents the power of the converter on the power supply side at time k, P cβ (k) represents the power of the β-supply-side converter at time k, P Rα (k) represents the power dissipation of the train braking resistor on the α power supply side; Determining the charge / discharge type of a hybrid energy storage system based on its power sequence includes: The power sequence is determined to be: ..., P es (k-1), P es (k-2), P es (k-1), P es (k), P es (k+1), P es (k+2), ..., P es (k+N); In the power sequence, P es (k+1) to P es In (k+N), if there exists a power sequence of 0 for more than one minute, the hybrid energy storage system will soon enter standby mode. Find the point in the power sequence around time k where the power level crosses zero most closely with respect to time k. Then, calculate the duration T between these two points. D ; Such as duration T D If the time threshold is less than or equal to the set time threshold, the hybrid energy storage system is in a short-term charge-discharge state at time k; otherwise, the hybrid energy storage system is in a long-term charge-discharge state at time k.

2. The power allocation method for a traction power supply hybrid energy storage system considering flywheel standby losses according to claim 1, characterized in that: The constraints of the power prediction model are: When the total train load P at time k αβ When (k)≥0, the traction power supply system as a whole exhibits a traction energy consumption state, and the constraint condition at this time is: When the total train load P at time k αβ When (k) < 0, the traction power supply system is in a regenerative braking state, and the constraint condition at this time is: Where: P es.n This refers to the rated power of the energy storage system in the traction power supply system.

3. The power allocation method for a traction power supply hybrid energy storage system considering flywheel standby losses according to claim 1, characterized in that: When time k is in a short-term charge / discharge state, the power distribution of the hybrid energy storage system is as follows: Discharge state: P f (k)=min{P es (k),P f.n } P ba (k)=P es (k)-P f (k); Charging status: P f (k)=max{P es (k),-P f.n } P ba (k)=P es (k)-P f (k); Where: P f (k) represents the reference power for flywheel energy storage charging and discharging, P ba (k) represents the reference power for battery energy storage charging and discharging, P f.n The rated charge and discharge power of the flywheel energy storage unit.

4. The power allocation method for a traction power supply hybrid energy storage system considering flywheel standby losses according to claim 1, characterized in that: When time k is in a long-term charge-discharge state, the power distribution of the hybrid energy storage system is as follows: Discharge state: P f (k)=min{P fw (k),P es (k),P f.n } P ba (k)=P es (k)-P f (k) Charging status: P f (k)=max{-P fw (k),P es (k),-P f.n } P ba (k)=P es (k)-P f (k); Where: P fw (k) represents the flywheel regulation power; Where: n f.max n f.min These represent the maximum and minimum speeds of the flywheel, respectively, P es (k) less than 0 indicates that the hybrid energy storage system is in a charging state, P es (k) When the hybrid energy storage system is greater than or equal to 0, it is in a discharge state. σ is the adjustment coefficient and σ≥0. N (k) is an intermediate variable and T s The control cycle of the traction power supply system; P f (k) represents the reference power for flywheel energy storage charging and discharging, P ba (k) represents the reference power for battery energy storage charging and discharging, P f.n The rated charge and discharge power of the flywheel energy storage unit.

Images