CN114725960B

CN114725960B - Automatic frequency modulation energy storage system based on PCS power adjustment and control method

Info

Publication number: CN114725960B
Application number: CN202210640057.2A
Authority: CN
Inventors: 金成�; 张乐; 孙玉坤
Original assignee: Wuxi Taihu University
Current assignee: Wuxi Taihu University
Priority date: 2022-06-08
Filing date: 2022-06-08
Publication date: 2022-08-26
Anticipated expiration: 2042-06-08
Also published as: CN114725960A

Abstract

The invention discloses an automatic frequency modulation energy storage system based on PCS power regulation and a control method thereof, wherein the automatic frequency modulation energy storage system comprises a battery, a PCS unit,The system comprises a transformer and a system controller, wherein the system controller is respectively connected with a PCS unit, a power grid alternating current side and a battery, the PCS unit is provided with N groups, and N is

An integer of 2. The automatic frequency modulation energy storage system provided by the invention has the advantages that two or more PCS units are arranged, the operation time of the power grid requirement function is considered, the power of each PCS is reasonably distributed, the utilization rate of the PCS is improved, the energy storage and release requirements of the power grid when the working frequency fluctuates are met, and the frequency drift of a power system caused by load fluctuation is avoided.

Description

Automatic frequency modulation energy storage system based on PCS power adjustment and control method

Technical Field

The invention relates to an energy storage system with an AFC function for adjusting the frequency of a power grid, in particular to an automatic frequency modulation energy storage system based on PCS power adjustment and a control method, and belongs to the technical field of power system frequency adjustment.

Background

An important function and application direction of the energy storage system is the Automatic Frequency Control (AFC) auxiliary function service. The AFC function is to stabilize the frequency of the grid by drawing/sourcing active power to the grid. Because the energy storage system has the characteristic of rapid charging and discharging, the frequency of the power system can be adjusted by actively adjusting the charging and discharging actions, which can help to maintain the frequency drift of the power system caused by the load fluctuation.

AFC functionality is a 24-hour, all-weather, uninterrupted service, so power consumption (or efficiency) and reliability (requiring uninterrupted continuous operation in addition to scheduled maintenance) requirements for energy storage systems are particularly high. According to published data, the energy storage system with the AFC function works for more than 95% of the working time in a low-load section with less than 10% of power, and specific statistical data are shown in a reference. The references are: B. xu, A, Oudalov, J, Poland, A, Ulblig, and G, Andersson, "BESS control sequences for particulate in grid frequency alignment," IFAC Proceedings Volumes, vol 47, No. 3, pp. 4024-.

How to improve reliability at low power and reduce power consumption is a problem to be solved.

The reference also introduces four features of the AFC function, where fig. 1(a) is a statistical representation of the probability of occurrence of frequency modulated powerCurve, abscissa adjustment power (P) in FIG. 1(a) _n ) Expressing the frequency modulation power, and expressing the occurrence probability by an ordinate Occurance (%); FIG. 1(b) is a statistical graph of the frequency modulation power and the frequency modulation time, and the abscissa of FIG. 1(b) represents the development events energy through output (P) _n h) The product of the frequency modulation power and time (hours) is shown, and the ordinate Occurance (%) shows the occurrence probability. In the figure, an EU PFC (EU TSO-E primary frequency control) represents the requirement of the cooperation association of the European power transmission system operator on primary frequency modulation control; PJMRegD indicates dynamic frequency modulation control (Dynaic frequency modulation) requirements for the power market in compliance with the requirements of the PJM manual in the united states. Two time/power-related characteristics of the AFC frequency modulation function can be seen from fig. 1(a) and 1 (b):

characteristic 1) the power level is inversely proportional to the probability of occurrence, <10% of the power demand accounts for more than 95% of the runtime, and the other power demands are within 5% of the runtime;

and 2) the power and the occurrence probability are symmetrically distributed and are distributed in an approximate Gaussian curve.

Fig. 2 is a typical frequency adjustment curve, and from fig. 2, two frequency/power characteristics of the AFC frequency modulation function can be seen:

characteristic 3) power is proportional to the frequency increment (difference from the fundamental frequency f 0), with the greater the difference, the more power is required. f0 is different according to different regional power grids, namely 50Hz in China and 60Hz in the United states;

feature 4) P0 may be a positive or negative number, a positive number representing power being drawn from the battery to the grid and a negative number representing power being drawn from the grid to the battery.

The conventional MW-level energy storage system mainly comprises a battery, a pcs (power Conditioning system) power Conditioning system, and an isolation transformer, and has a structure shown in fig. 3. The electric power storage (charging the battery) and release (discharging the battery) of alternating current (grid) and direct current (battery) are realized by the PCS having the AFC function. The isolation transformer enables power conversion of low voltage alternating current (e.g. 380 Vac) to a medium voltage grid (e.g. 10 kV).

The PCS equipment mainly comprises electronic components, and the reliability and efficiency of the PCS greatly influence the reliability and efficiency of the whole energy storage system, so that the energy storage system with high efficiency and reliability and adaptive to the AFC function is especially important to design.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides an automatic frequency modulation energy storage system based on PCS power adjustment, and the automatic frequency modulation energy storage system is high in working efficiency and high in availability.

Another object of the present invention is to provide a control method for an automatic frequency modulation energy storage system based on PCS power regulation.

The invention is realized by the following technical scheme:

the automatic frequency modulation energy storage system based on PCS power adjustment comprises a battery, a PCS unit, a transformer and a system controller, wherein the system controller is respectively connected with the PCS unit, a power grid alternating current side and the battery, the PCS unit is provided with N groups, and N is

2 is an integer; the PCS units are connected in parallel, the alternating current side of each PCS unit is connected with the alternating current side of a power grid through a transformer, the direct current side of each PCS unit is connected with a battery, each group of PCS units is respectively provided with a group of PCS controllers, and each group of PCS controllers is respectively connected with the PCS unit, the alternating current side of the power grid and a system controller;

in the N groups of PCS units, the power of one group of PCS units meets the requirement of the maximum required frequency modulation power Pmax of the power grid, and the sum of the powers of the other groups of PCS units is 10% -30% of the maximum required frequency modulation power of the power grid;

the system controller is used for controlling the enabling states of the N groups of PCS units;

the PCS controllers are configured to control the output power of the respective PCS units.

Furthermore, the N groups of PCS units share one group of transformers, or are respectively provided with one group of transformers;

when a group of transformers are shared, the capacity of the transformers is matched with the maximum required frequency modulation power Pmax of the power grid;

when the transformers are configured respectively, the capacity of each group of transformers is matched with the capacity of the PCS unit.

Furthermore, N groups of PCS units share one group of batteries or are respectively configured with one group of batteries;

when N groups of PCS units share one group of batteries, the capacity of the group of batteries is matched with the maximum required frequency modulation power Pmax of the power grid;

when each set of PCS units is provided with one set of batteries, the capacity of each set of batteries is matched with the respective PCS capacity.

Furthermore, each group of PCS units with the sum of power accounting for 10% -30% of the maximum required frequency modulation power of the power grid equally divides or distributes the 10% -30% power according to a set proportion.

Furthermore, two or three groups of PCS units are arranged, wherein the power of one group of PCS units meets the requirement of the maximum required frequency modulation power Pmax of the power grid; the sum of the power of the other group of PCS units or the power of the other two groups of PCS units is 10% -30% of the maximum required frequency modulation power of the power grid.

Furthermore, the power of the other group of PCS units is 10% of the maximum required frequency modulation power of the power grid; or the sum of the power of the other two groups of PCS units is 10% of the maximum required frequency modulation power of the power grid, and the power is divided equally to occupy 5% of each.

The control method of the automatic frequency modulation energy storage system based on PCS power adjustment comprises the following control processes:

1) according to the relation between the total power demand of the power grid and the frequency change of the power grid, establishing a power and frequency change relation curve and arranging the power and frequency change relation curve in a system controller; respectively establishing PCS power and frequency relation curves according to the power relation between the power of each group of PCS units and the total power demand of the power grid, and respectively arranging the PCS power and frequency relation curves in respective PCS controllers;

2) the method comprises the steps that a system controller obtains power grid frequency and state information of an energy storage battery, and frequency difference value delta f between the power grid frequency f and power grid basic frequency f0 is calculated, wherein delta f = f-f 0; meanwhile, judging the state of the energy storage batteries, if the state of each energy storage battery is normal, searching the power and frequency change relation curve according to the frequency difference value to determine the enabling states of N groups of PCS units PCS _ 1-PCS _ N, and outputting a PCS enabling signal; if the status bits of one or more groups of energy storage batteries show faults, all PCS units are enabled to stand by and report errors;

3) the PCS controller of each group of enabled PCS units acquires the frequency of a power grid, searches a built-in PCS power and frequency relation curve look-up table to obtain the output power of the group of PCS units, and adjusts the output power of the PCS units to be matched with the output power of the group of PCS units; the disabled PCS unit is in standby state and the output power is 0.

Further, in step 1), in the power-to-frequency variation curve, the enabling states of the PCS units in each group are set to correspond to the frequency variation intervals, and the enabling states of the PCS units are determined according to positions of the frequency variation intervals in which the calculated frequency difference Δ f falls, specifically as follows:

if the < DELTA > f1, EN _1=1, EN _ X =0, X > 1;

if delta f1< | delta f | ≦ delta f2, then EN _1=1, EN _2=1, EN _ X =0, X > 2;

if delta f (N-2) < delta f | < delta f (N-1), EN _ X =1, X = 1-N-1, EN _ N = 0;

if the delta f (N-1) < delta f | is less than or equal to delta fN, EN _ X =0, X = 1-N-1, and EN _ N = 1;

according to the comparison relation between the | Δ f | and the | Δ f1 to Δ fN, the power grid frequency variation range is divided into N intervals, EN _ X represents the enabling state of the Xth group of PCS controllers, EN _ X =1 represents that PCS works, and EN _ X =0 represents that PCS is standby; the size of each frequency change interval delta fX is set according to the percentage of the power of the corresponding PCS unit in the maximum required frequency modulation power Pmax of the power grid, and X = 1-N.

Further, regarding the divided frequency change intervals, taking the deviation delta fz ranges on two sides of the end point of each frequency change interval as hysteresis dead zones; for a certain frequency change interval, the frequency change in the hysteresis dead zone range is consistent with the enable state of the PCS unit in the frequency change interval, which is as follows:

for the PCS unit enable state corresponding to the interval [0, + Deltaf 1], after the hysteresis dead zone is increased, when the frequency rises, the PCS unit enable state in the interval [0, + Deltaf 1+ Deltafz ] is kept unchanged;

for the intervals [ + Deltaf 1, + Deltaf 2], the PCS unit enable state at the interval [ + Deltaf 1, + Deltaf 2+ Deltafz ] remains unchanged as the frequency increases after increasing the hysteresis dead zone; the PCS unit enable state at interval [. DELTA.f 1- Δ fz, +. DELTA.f 2] remains unchanged as the frequency decreases;

and so on for other interval cases.

Further, the deviation Δ fz < Δf1, preferably the deviation Δ f1= 10%. Δ f 1.

Compared with the prior art, the invention has the following beneficial effects:

1. the automatic frequency modulation energy storage system based on PCS power adjustment reasonably distributes the power of each group of PCS units by setting two or more groups of PCS units and considering the running time of the power grid demand function so as to improve the availability (availability) of the PCS units, meet the energy storage and release requirements when the working frequency of a power grid fluctuates and avoid frequency drift of a power system caused by load fluctuation.

2. When the PCS units are configured, the power of one group of PCS units is set to be the power meeting the maximum required frequency modulation power Pmax of the power grid, and the sum of the power of the other groups of PCS units is 10% -30% of the maximum required frequency modulation power of the power grid. The requirement that the power required by a power grid is less than 10% in the operation time of more than 95% can be met, the power of the PCS unit is reasonably configured, the reliability of the energy storage system is guaranteed, and the availability of the PCS unit is improved.

3. According to the control method of the automatic frequency modulation energy storage system based on PCS power adjustment, frequency changes delta f 1-delta fN are divided into a plurality of intervals according to a relation curve between power and frequency, and conversion among PCS units is controlled according to the intervals.

4. The control method of the invention also sets hysteresis dead zones delta fz at two sides of the frequency end point, and the design can avoid frequent switching among different PCS units caused by the fluctuation of the power grid frequency near the switching frequency of the PCS units, prolong the service life of the energy storage system and reduce the damage rate of the system.

5. The control method of the invention stabilizes the frequency of the power grid by the active power generation/absorption of the power grid through the energy storage system, and can avoid the frequency drift of the power system caused by load fluctuation.

Drawings

FIG. 1(a) is a distribution curve of frequency modulated power and frequency modulated operating time;

FIG. 1(b) is a distribution curve of frequency modulated power versus time duration (hours) product and frequency modulated operating time;

FIG. 2 is a typical frequency adjustment curve;

FIG. 3 is a block diagram of a conventional energy storage system;

FIG. 4 is a schematic block diagram of an energy storage system with N sets of PCS, N sets of transformers, and 1 set of batteries;

FIG. 5 is a control flow diagram of the system controller;

FIG. 6 is a control flow diagram of a PCS controller;

FIG. 7 is a frequency modulation power versus frequency variation curve for setting a hysteresis dead zone;

FIG. 8 is a schematic block diagram of an energy storage system with N sets of PCS, 1 set of transformers, and 1 set of batteries;

FIG. 9 is a schematic block diagram of an energy storage system with N sets of PCS, 1 set of transformers, and N sets of batteries;

FIG. 10 is a schematic block diagram of an energy storage system with 3 PCS sets, 3 transformers sets and 1 battery set;

FIG. 11 is a schematic block diagram of an energy storage system with 2 PCS sets, 2 transformers sets and 1 battery set;

fig. 12 is a typical PCS efficiency vs. power curve.

Detailed Description

The first embodiment is as follows:

the automatic frequency modulation energy storage system based on PCS power adjustment comprises a battery, N groups of PCS units, N groups of transformers and a system controller, wherein the N groups of PCS units are PCS _1, PCS _2 and PCS _2 in sequence,

PCS _ N, N groups of transformers are sequentially a transformer _1, a transformer _2,

BecomeDepressor _ N, N is

An integer of 2. The system controller is respectively connected with each group of PCS units, the alternating current side of the power grid and the battery, and can independently sample the frequency of the power grid; each group of PCS units are connected in parallel, the alternating current side of each PCS unit is connected with the alternating current side of a power grid through a transformer, the direct current side of each PCS unit is connected with a battery, each group of PCS units is provided with a group of PCS controllers, each PCS controller is respectively connected with the PCS unit, the alternating current side of the power grid and a system controller which are controlled by each PCS controller, and each PCS controller can independently sample the frequency of the power grid;

in N groups of PCS units, the power of PCS _ N meets the requirement of the maximum required frequency modulation power Pmax of the power grid, and the sum of the powers of the other PCS units is 10% -30% of the maximum required frequency modulation power of the power grid;

the system controller is used for controlling the enabling state of the N groups of PCS units;

the PCS controllers are used to control the output power of the respective PCS units.

Example two:

a further alternative design of this embodiment is: in this example, the N groups of PCS units share one group of transformers, or are respectively provided with one group of transformers;

when a set of transformers is shared, as shown in fig. 8, N sets of PCS units and a set of transformers are arranged in the energy storage system, the N sets of PCS units share the transformers, and the capacity of the transformers matches with the maximum required frequency modulation power Pmax of the power grid.

When the transformers are respectively configured, as shown in fig. 4, the energy storage system is provided with N sets of PCS units and N sets of transformers, where the N sets of transformers are, in order, transformer _1, transformer _2, and transformer _2,

And a transformer _ N, wherein the alternating current side of each group of PCS units is correspondingly connected with a power grid through a group of transformers respectively, the capacity of each group of transformers is matched with the capacity of the corresponding PCS unit, and the energy storage system is provided with the transformers due to the arrangement of the PCS units of the N groups respectivelyThe system has higher safety and reliability, and can prevent the condition that the whole energy storage system is paralyzed due to the fault of a single transformer.

Example three:

a further alternative design of this embodiment is: in this example, the N groups of PCS units share one group of batteries, or are respectively configured with one group of batteries;

when N groups of PCS units share one group of batteries, as shown in fig. 4 and 8, the capacity of the group of batteries is matched with the maximum required frequency modulation power Pmax of the power grid;

when each set of PCS units is provided with one set of batteries, as shown in FIG. 9, N sets of batteries are arranged in the energy storage system, namely a battery 1, a battery 2 and,

And the direct current side of each group of PCS units is correspondingly connected with one group of batteries respectively, the capacity of each group of batteries is matched with the respective PCS capacity, and the safety and the reliability of the energy storage system are higher because each group of PCS units is provided with one group of batteries respectively.

Example four:

a further alternative design of this embodiment is: in this example, N sets of PCS units are provided, in order PCS _1, PCS _2,

And PCS _ N, wherein the power of PCS _ N meets the requirement of the maximum required frequency modulation power Pmax of the power grid, the sum of the powers of the other PCS units is 10% of the maximum required frequency modulation power of the power grid, and the power is divided equally.

Example five:

this embodiment provides a control method for an automatic frequency modulation energy storage system based on PCS power adjustment, in which the control system is provided with N groups of PCS units, PCS _1, PCS _2, and,

And PCS _ N, wherein the power of PCS _ N meets the requirement of the maximum required frequency modulation power Pmax of the power grid, and the other PCS units PCS _ 1-PCS _ N-1 equally divide or distribute 1 of the maximum required frequency modulation power of the power grid according to a set proportion0 percent. The control method, as shown in fig. 5, includes the following control processes:

1) according to the relation between the total power demand of the power grid and the frequency change of the power grid, establishing a power and frequency change relation curve and arranging the power and frequency change relation curve in a system controller; respectively establishing PCS power and frequency relation curves according to the relation between the power of each group of PCS units and the total power required by the power grid, and respectively arranging the PCS power and frequency relation curves in respective PCS controllers;

3) as shown in fig. 6, the PCS controller of each enabled PCS unit obtains the grid frequency, retrieves the built-in PCS power and frequency relation curve lookup table to obtain the output power of the set of PCS units, and adjusts the output power of the PCS unit to match the output power; the PCS unit that is not enabled is in a standby state and the output power is 0.

Example six:

the present embodiment is further designed on the basis of the fifth embodiment, in step 1), in the power-frequency variation relationship curve, the enabling states of the PCS units in each group are set to correspond to the frequency variation intervals, and the enabling states of the PCS units are determined according to the positions of the frequency variation intervals where the calculated frequency difference Δ f falls, which is specifically as follows:

if the < DELTA > f1, EN _1=1, EN _ X =0, X > 1;

if delta f1< | delta f | ≦ delta f2, then EN _1=1, EN _2=1, EN _ X =0, X > 2;

if delta f (N-2) < delta f | < delta f (N-1), EN _ X =1, X = 1-N-1, EN _ N = 0;

according to the comparison relationship between the | Δ f | and the | Δ f1 to Δ fN, the power grid frequency variation range is divided into N intervals, EN _ X represents the enabling state of the Xth group of PCS controllers, EN _ X =1 represents that PCS works, and EN _ X =0 represents that PCS is standby; the size of each frequency change interval delta fX is set according to the percentage of the power of the corresponding PCS unit in the maximum required frequency modulation power Pmax of the power grid, and X = 1-N.

The frequency variation interval corresponds to the enabled state of the PCS unit as follows

The interval between [ -. DELTA.f 1, +. DELTA.f 1] corresponds to PCS _1 working, and the other is standby;

the intervals of [ -. DELTA.f 2, -. DELTA.f 1). sup.U (. DELTA.f 1,. DELTA.f 2] correspond to the operation of PCS _1 and PCS _2, and the rest are in standby;

and [ - [ delta ] fN, - [ delta ] f (N-1)) [ U ] ([ delta ] f (N-1), [ delta ] fN ] corresponds to the PCS _ N which meets the maximum required frequency modulation power Pmax of the power grid to work, and the other devices are in standby.

For example, for an energy storage system with 3 groups of PCS units, the power of two groups of PCS units is divided into 10% of the maximum required frequency modulation power of the power grid, and is 5% of the maximum required frequency modulation power of the power grid, and the power of the other PCS unit is 100% of the maximum required frequency modulation power of the power grid. Then Δ f1 represents 5% of Δ f3, and since PCS _1+ PCS _2 represents 10% of Pmax power, Δ f2 represents 10% of Δ f 3.

Example seven:

the embodiment is further designed on the basis of the sixth embodiment, as shown in fig. 7, for frequency change intervals divided by | Δ f1| - | Δ fN |, the deviation Δ fz ranges on both sides of the end point of each frequency change interval are used as hysteresis dead zones; for a certain frequency change interval, the frequency change in the hysteresis dead zone range is consistent with the enabling state of the PCS unit in the frequency change interval, and the specific steps are as follows:

for the PCS unit enable state corresponding to the interval [0, + [ delta ] f1], after the hysteresis dead zone Δ fz is increased, the PCS unit enable state in the interval [0, + [ delta ] f1+ Δ fz ] is kept unchanged when the frequency rises;

for the intervals [ + Deltaf 1, + Deltaf 2], after increasing the hysteresis dead zone Δ fz, the PCS unit enable state at the interval (Deltaf 1, + Deltaf 2+ Deltafz ] remains unchanged as the frequency increases, and the PCS unit enable state at the interval [ + Deltaf 1-Deltafz, + Deltaf 2] remains unchanged as the frequency decreases;

and so on for other interval cases.

The deviation Δ fz < Δf1 in this example, and the deviation Δ f1=10% Δ f1 in this example.

As shown in FIG. 7, the switching control of the enabled states of PCS _1 to PCS _ N is to prevent the frequency fluctuation around the PCS switching frequency (e.g. at Δ f1, Δ f 2) from causing frequent switching among different PCS because the grid operating frequency f is changed at any time. By adding an appropriate hysteresis dead zone 2 Δ fz at the switching frequency, frequent switching of the PCS can be effectively prevented.

For example: as can be seen from the partial enlarged portion in fig. 7, PCS enables the state transition condition after the hysteresis dead zone is added:

the first change state is as follows:

for the interval [0, + [ delta ] f1], the interval [0, + [ delta ] f1+ [ delta ] fz ] after the hysteresis dead zone [ delta ] fz is increased.

As the frequency changes around Δ f1, increasing at Δ f1, the PCS unit enable state of [0, + Δ f1+ Δ fz ] remains unchanged; EN _1=1 and the other enabled devices are 0.

And a second change state:

for the intervals [ + Deltaf 1, + Deltaf 2], the post-hysteresis dead zone Δ fz interval (. DELTA.f 1- Δ fz, +. DELTA.f 2+ Δ fz) is increased.

When the frequency varies around Δ f2, the PCS unit enable state at the interval (Δ f1, + Δ f2+ Δ fz) remains unchanged when the frequency rises, EN _1=1, EN _2=1, and the other enable states are 0.

When the frequency varies around Δ f2, the PCS unit enable state at the interval [. DELTA.f 1- Δ fz, +. DELTA.f 2] remains unchanged as the frequency decreases; EN _1=1, EN _2=1, and the other enable state is 0.

Application example one:

as shown in fig. 10, this example simulates the automatic fm energy storage system based on PCS power regulation, which requires 1MW/1MWh of power and capacity, respectively, and includes 1 battery set, 3 PCS units, 3 transformers and a system controller, wherein the 3 PCS units are PCS _1, PCS _2 and PCS _3, and the PCS _1, PCS _2 and PCS _3 have 50kW, 50kW and 1000kW of power, respectively. The 3 groups of transformers are sequentially a transformer _1, a transformer _2 and a transformer _3, and the power of the transformer _1, the power of the transformer _2 and the power of the transformer _3 are respectively 50kVA, 50kVA and 1000 kVA. And the alternating current side of each group of PCS units is correspondingly connected with a power grid through a group of transformers. The 3 groups of PCS units share one battery.

For example: when a relation curve of power and frequency is established, the power is 50kW corresponding to the delta f1, 100kW corresponding to the delta f2, 1000kW corresponding to the delta f3, and 5kW corresponding to the delta fz.

Only PCS _1 is required to work 60% of the time in the energy storage system, PCS _1 and PCS _2 are required to work together 35% of the time to meet the power requirement of the AFC function, and PCS _3 is required to work 5% of the time to meet the power requirement of the AFC function.

Application example two:

in the embodiment, the automatic frequency modulation energy storage system based on PCS power adjustment is subjected to simulation calculation to obtain a calculation result of the energy storage system related to high efficiency and high availability, the required power and capacity of the energy storage system are respectively 1MW/1MWh, the energy storage system comprises 1 group of batteries, 2 groups of PCS units, 2 groups of transformers and a system controller, the 2 groups of PCS units are sequentially PCS _1 and PCS _2, and the power of the PCS _1 and PCS _2 is respectively 100kW and 1000 kW. The 2 groups of transformers are sequentially a transformer _1 and a transformer _2, and the power of the transformer _1 and the power of the transformer _2 are respectively 100kVA and 1000 kVA. And the alternating current side of each group of PCS units is correspondingly connected with a power grid through a group of transformers. 2 groups of PCS units share one battery.

In the energy storage system, 95% of the time can meet the power requirement of the AFC function only by the operation of PCS _1, and 5% of the time can meet the power requirement of the AFC function only by the operation of PCS _ 2.

The operating mode of the energy storage system in fig. 11 is PCS _1 operation and PCS _2 backup, or PCS _2 operation and PCS _1 backup; whereas the conventional operating mode is PCS _2 alone.

Assuming that the annual availability of each PCS is 99%, the annual availability of the PCS corresponding to the working mode of the energy storage system is 1- (1-0.99%) (1-0.99%) = 99.99%; the traditional mode of operation corresponds to 99% annual availability of PCS.

Further, considering that 95% of the time is operated on PCS _1 and 5% of the time is operated on PCS _2, the annual availability of the integrated PCS of the energy storage system of the present invention is: 0.95 × 99.99% +0.05 × 99% = 99.9405%. Therefore, the energy storage system has high reliability, the annual utilization rate of the PCS unit is high, and the high requirement of the AFC function on the reliability can be met.

FIG. 12 shows a PCS operating efficiency vs. power curve for the energy storage system of this example, with power on the abscissa; the ordinate represents the operating efficiency. Generally, the higher the operating power of the PCS unit, the higher the efficiency, and at 100% power (rated power), the highest efficiency. The average annual efficiency of the prior art energy storage system shown in fig. 3 is 82.1% by 0.95+97.5% by 0.05= 82.87%.

The average efficiency of the energy storage system of this example is (97.5% + 82.1%)/2 =89.8% in operating mode 1 and 97.5% in operating mode 2, so the average annual efficiency of the energy storage system of this example: 89.8% by 0.95+97.5% by 0.1= 95.06%.

As can be seen from the above, the annual average operating system efficiency of the integrated PCS unit of the energy storage system of the present invention is greatly improved compared to the conventional energy storage system.

The comparison shows that the system reliability (annual utilization rate) of the energy storage system is greatly improved from 99% to 99.9405%, and the annual average operation system efficiency is also greatly improved from 82.87% to 95.06%.

Claims

1. The utility model provides an automatic frequency modulation energy storage system based on PCS power regulation, includes battery, PCS unit, transformer and system controller, system controller is connected with PCS unit, electric wire netting alternating current side and battery respectively, its characterized in that: the PCS unit is provided with N groups, N is

the system controller is used for controlling the enabling state of the N groups of PCS units; the PCS controller is used for controlling the output power of each PCS unit; the automatic frequency modulation process of the system is as follows:

2) the method comprises the steps that a system controller obtains power grid frequency and state information of an energy storage battery, and frequency difference delta f between the power grid frequency f and power grid basic frequency f0 is calculated, wherein the delta f = f-f 0; meanwhile, judging the state of the energy storage batteries, if the state of each energy storage battery is normal, searching the power and frequency change relation curve according to the frequency difference value to determine the enabling states of N groups of PCS units PCS _ 1-PCS _ N, and outputting a PCS enabling signal; if the status bits of one or more groups of energy storage batteries show faults, all PCS units are enabled to stand by and report errors;

3) the PCS controller of each enabled PCS unit acquires the power grid frequency, searches a built-in PCS power and frequency relation curve lookup table to obtain the output power of the PCS unit, and adjusts the output power of the PCS unit to be matched with the output power; the PCS unit which is not enabled is in a standby state, and the output power is 0;

in 1) above, in the power-frequency variation curve, setting the enabling state of each group of PCS units corresponding to each frequency variation interval, and determining the enabling state of each PCS unit according to the position of the frequency variation interval in which the calculated frequency difference Δ f falls, specifically as follows:

if | < less than or equal to f1, EN _1=1, EN _ X =0, X > 1;

if Δ f1| < Δ f | ≦ f2, then EN _1=1, EN _2=1, EN _ X =0, X > 2;

if Δ f (N-2) less than or equal to Δ f (N-1), EN _ X =1, X = 1-N-1, EN _ N = 0;

if Δ f (N-1) less than or equal to Δ fN, EN _ X =0, X = 1-N-1, EN _ N = 1;

the power grid frequency variation range is divided into N intervals according to the comparison relation between Δ f | and Δ f 1. fN, EN _ X represents the enabling state of the X group of PCS controllers, EN _ X =1 represents that PCS works, and EN _ X =0 represents that PCS is in standby; the size of each frequency change interval Δ fX is set according to the percentage of the power of the corresponding PCS unit in the maximum required frequency modulation power Pmax of the power grid, and X = 1-N.

2. The PCS power regulation based auto-frequency modulation energy storage system of claim 1 wherein: the N groups of PCS units share one group of transformers, or are respectively provided with one group of transformers;

3. The PCS power regulation based automatic frequency modulation energy storage system of claim 2 wherein: the N groups of PCS units share one group of batteries or are respectively configured with one group of batteries;

when each set of PCS units is configured with one set of batteries, the capacity of each set of batteries is matched with the respective PCS capacity.

4. The PCS power regulation based auto-frequency modulated energy storage system of claim 3 wherein: and each group of PCS units with the power sum accounting for 10% -30% of the maximum required frequency modulation power of the power grid equally divides or distributes the 10% -30% power according to a set proportion.

5. The PCS power regulation based auto-frequency modulation energy storage system of claim 4 wherein: the PCS units are provided with two groups or three groups, wherein the power of one group of PCS units meets the requirement of the maximum required frequency modulation power Pmax of the power grid; the sum of the power of the other group of PCS units or the power of the other two groups of PCS units is 10% -30% of the maximum required frequency modulation power of the power grid.

6. The PCS power regulation based automatic frequency modulation energy storage system of claim 5 wherein: the power of the other group of PCS units is 10% of the maximum required frequency modulation power of the power grid; or the sum of the power of the other two groups of PCS units is 10% of the maximum required frequency modulation power of the power grid, and the power is divided equally to occupy 5% of each.

7. An automatic frequency modulation energy storage system based on PCS power regulation according to any of claims 1-6, characterized in that: in the automatic frequency modulation process of the system, when frequency change intervals are divided, the range of the deviation delta fz at two sides of the end point of each frequency change interval is used as a hysteresis dead zone; for a certain frequency change interval, the frequency change in the hysteresis dead zone range is consistent with the enabling state of a PCS unit in the frequency change interval, and the details are as follows;

for the PCS unit enable state corresponding to the interval [0, Δ f1], increasing the hysteresis dead zone, and keeping the PCS unit enable state unchanged at the interval [0, Δ f1+ Δ fz ] when the frequency rises;

for the interval [ + [ Δ f1, + [ Δ f2], after increasing the dead zone of hysteresis, when the frequency rises, the enabled state of the PCS unit in the interval [ [ f1, + [ Δ f2+ Δ fz ] remains unchanged; when the frequency decreases, the enabled state of the PCS unit at the interval [. Δ f1- Δ fz, +. Δ f2] remains unchanged;

and so on for other interval cases.

8. The PCS power regulation based auto-frequency modulated energy storage system of claim 7 wherein: in the automatic frequency modulation process of the system, the value range of the deviation delta fz at two sides of the end point of each frequency change interval is as follows: Δ fz equal to 1.