CN102447285A - High-capacity battery converter and control method thereof - Google Patents

Abstract

The present invention is a large-capacity battery converter and a control method thereof. The converter of the present invention comprises a plurality of branch single-stage DC/AC converter modules connected in parallel with each other, and each battery cluster (BC) collects energy to the AC bus through each branch single-stage DC/AC converter module, and is connected to the AC power grid or independently operated with load after voltage transformation. The present invention solves the circulation and current sharing problems caused by the series and parallel connection of battery groups, and adopts the "module combination, rotation balance" technology to effectively improve the system efficiency and AC and DC side power quality under low power, and realize the balanced use of battery groups. Each battery branch can be intelligently charged and discharged, and the control function and protection function are completely independently configured to ensure the maximum availability of the system. The present invention has a simple structure, a small volume, low energy loss, easy modularization, high reliability, small output harmonics, good system scalability, and can be operated at a reduced capacity when a unit fails, and has low requirements on the insulation level of the converter. The control method of the large-capacity battery converter of the present invention is simple and convenient to operate and easy to implement.

Description

A large-capacity battery converter and its control method

technical field

The invention is a large-capacity battery converter and its control method, which belongs to the new technology of the large-capacity battery converter and its control method.

Background technique

With the wide application of various advanced technologies in power grids, intelligence has become an inevitable trend in the development of power grids, and the development of smart grids has reached a worldwide consensus. As a key link in the smart grid, energy storage technology can play a role in peak shaving and valley filling, peak shaving and frequency modulation, improving power quality, increasing system reserve capacity, delaying or even reducing grid expansion investment, smoothing intermittent problems of new energy, and improving distribution. power generation system or micro-grid stability. The battery energy storage system has the characteristics of being not affected by regional environmental factors and being flexible in layout. With the development of smart grid and new energy being paid more and more attention, the battery energy storage system has a broad application prospect in the power grid. The battery energy storage system is mainly composed of four parts: battery, energy conversion system, battery management system and monitoring system. Among them, the power conversion system (Power Conversion System, PCS) is the core equipment of the energy storage power station. At present, large-capacity battery energy storage power stations are still in the demonstration operation test stage worldwide. Domestic power electronic converter companies are mainly concentrated in new energy fields such as wind power generation and photovoltaic power generation. There are few manufacturers specializing in battery converters. Not very mature.

If the number of batteries required is large, in order to achieve a certain voltage, power and energy level, the batteries need to be used in series and in parallel. The use of batteries in series can achieve the required DC input voltage, but the problem of unbalanced batteries is very easy to occur. At the same time, the design of the balance circuit and daily maintenance are also difficult; the use of batteries in parallel can double the capacity of the single battery, and at the same time bring more Circulation and current sharing problems.

Contents of the invention

The object of the present invention is to consider the above problems and provide a large-capacity battery converter with reasonable design, simple structure, small volume, low energy loss and easy modularization. The invention has high reliability, small output harmonics, good system expansibility, strong derating operation capability when a unit fails, and low requirements on the insulation level of the converter.

Another object of the present invention is to provide a control method for a large-capacity battery converter that is simple and convenient to operate.

The technical solution of the present invention is: the large-capacity battery converter of the present invention includes several branch single-stage DC/AC converter modules connected in parallel, and each battery cluster BC is converted through each branch single-stage DC/AC converter module. The inverter module gathers energy to the AC bus, and after transformation, it can be connected to the AC grid or run independently with load.

The control method of the large-capacity battery inverter of the present invention, the above-mentioned inverter adopts the DC side to be connected in multiple groups, and the DC side control method is as follows:

The battery converter determines the number of DC/AC converter modules participating in power output according to power commands of different magnitudes, and weights the multi-objectives of each battery cluster BC including state of charge, charge and discharge times, and maintenance cycle After processing, charge and discharge management is performed on each battery cluster BC with high priority, so that the utilization of each battery cluster BC tends to be balanced; The single-stage DC/AC converter modules are in the dormant state in turn to improve the charging and discharging efficiency of the system.

Each of the DC/AC converter module branches participating in the output above will automatically perform intelligent charge and discharge management for each battery cluster BC according to the power allocated to it.

The AC side operation mode of the above converter is as follows:

a) Parallel operation with the AC power grid

When the converter is connected to the AC power grid, each DC/AC converter module adopts grid voltage-oriented vector control, a double closed-loop structure, the outer loop is a voltage loop, and the inner loop is a current loop, and the P , Q decoupling control and DC bus voltage control; the voltage space vector pulse width modulation (SVPWM) method is used to control the on-off of the switching device of the DC/AC converter module;

b) Independent load operation

When the converter is separated from the AC grid and operates independently with a load, each DC/AC converter module provides a constant voltage and frequency reference for the AC busbar, adopts V/f control, and uses closed-loop control of the effective value of the voltage to realize each The amplitude and frequency of the terminal voltage at the outlet of the DC/AC converter module after the filter are kept constant;

The above-mentioned multi-objective weighting process for each battery cluster BC, including the state of charge, charge and discharge times, and maintenance cycle, is to use the rechargeable/discharge power proportional distribution method and the average distribution method for power distribution, so that the usage of each battery cluster BC Tend to be the same, prolonging the service life of the battery, the said rechargeable/dischargeable power proportional distribution method and the average distribution method refer to each DC/AC converter module branch according to its rechargeable/dischargeable power ratio Active power is distributed in proportion to the total electricity for output. When the output of each branch exceeds its rated power, the active power is evenly distributed for output according to all dischargeable branches, and the output power is controlled by constant power charging/discharging.

The charging methods of the above-mentioned battery clusters BC adopt the four-stage charging method of pre-charging, fast charging, equalizing charging and floating charging. Among them, pre-charging, fast charging and floating charging are controlled by constant current and voltage limitation, and equalization is controlled by constant voltage and current limiting. control.

The charge and discharge modes of the above battery clusters BC adopt two modes of constant current charge and discharge or constant power charge and discharge.

The main circuit structure of the large-capacity battery converter of the present invention adopts a DC/AC single-stage structure. The single-stage topology has the advantages of simple structure, small volume, small energy loss, easy modularization, high reliability, small output harmonics, good system scalability, and strong derating operation capability when a unit fails. The insulation level of the converter is low. In addition, when the structure operates in an isolated grid state, the V/f control on the AC side is only realized by the DC/AC unit, and the control strategy is relatively simple and reliable. In addition, since each DC/AC converter module bears a relatively small current and capacity, the solution is relatively simple to implement. At the same time, the DC side is connected in multiple groups, which can reduce the number of series and parallel connections in each group of batteries when the batteries are grouped, and even realize the connection of a single battery string, which is conducive to battery maintenance and balanced management, and improves the reliability of the battery system. If the high-power centralized access method is adopted, a large number of battery packs are required to be connected in parallel on the DC side of the single-stage structure. This large-capacity direct parallel connection method not only produces a circulation problem, but also a single cell damage will cause the entire system to exit. The system reliability is greatly reduced. The converter adopts a multi-branch and modular connection mode, and each battery branch can be completely independently controlled, which not only solves the problem of circulating current and current sharing in series-parallel connection of battery packs, but also has a simple structure and is convenient for capacity expansion. In the present invention, each storage battery branch collects energy to the AC bus through the converter, and after being transformed, it is connected to the AC grid or independently operated with a load. The transformer can not only change the voltage to meet the output requirements, but also play an isolation role to improve the noise in the power supply. Since the battery system can achieve decoupling and rapid adjustment of active and reactive power, the optimal power distribution of each module can be realized through grouping and time-sharing rotation of DC/AC modules. Combined with the grouping modular design scheme, the power is distributed to each battery branch. When the power command obtained by the PCS deviates from its rated value, the unique "module combination, rotation balance" technology can effectively improve the low power System efficiency and output AC side power quality. The invention is a convenient and practical large-capacity battery converter with ingenious design, excellent performance and a control method thereof.

Description of drawings

Fig. 1 is a schematic diagram of the main circuit of the large-capacity battery converter of the present invention.

Detailed ways

Example:

The schematic diagram of the main circuit of the large-capacity battery converter of the present invention is shown in Figure 1. The large-capacity battery converter of the present invention includes several branched single-stage DC/AC converter modules connected in parallel, and each battery cluster BC The energy is collected to the AC bus through each branch single-stage DC/AC converter module, and after transformation, it can be connected to the AC grid or run independently with load. Through the parallel connection of multiple DC/AC converter modules, the converter can support group access of multiple battery clusters, realize electrical isolation and independent voltage control between battery clusters, and effectively prolong battery life and improve charging efficiency. The number of discharge cycles.

In the control method of the large-capacity battery converter of the present invention, the above-mentioned converter adopts the DC side to be connected in multiple groups, and the DC side control method is as follows:

The battery converter determines the number of DC/AC converter modules participating in power output according to power commands of different magnitudes, and weights the multi-objectives of each battery cluster BC including state of charge, charge and discharge times, and maintenance cycle After processing, charge and discharge management is performed on each battery cluster BC with high priority, so that the utilization of each battery cluster BC tends to be balanced; The single-stage DC/AC converter modules are in a dormant state in turn, so as to improve the utilization efficiency of the system.

Each of the DC/AC converter module branches participating in the output above will automatically perform intelligent charge and discharge management for each battery cluster BC according to the power allocated to it.

In the control method of the large-capacity battery converter of the present invention, the operation mode of the AC side of the above-mentioned converter is as follows:

a) Parallel operation with the AC power grid

When the converter is connected to the AC power grid, each DC/AC converter module adopts grid voltage-oriented vector control, a double closed-loop structure, the outer loop is a voltage loop, and the inner loop is a current loop, and the P , Q decoupling control and DC bus voltage control; the voltage space vector pulse width modulation (SVPWM) method is used to control the on-off of the switching device of the DC/AC converter module;

b) Independent load operation

When the converter is separated from the AC grid and operates independently with a load, each DC/AC converter module provides a constant voltage and frequency reference for the AC busbar, adopts V/f control, and uses closed-loop control of the effective value of the voltage to realize each The amplitude and frequency of the terminal voltage at the outlet of the DC/AC converter module after passing through the filter are kept constant.

The above-mentioned multi-objective weighting process for each battery cluster BC, including the state of charge, charge and discharge times, and maintenance cycle, is to use the rechargeable/discharge power proportional distribution method and the average distribution method for power distribution, so that the usage of each battery cluster BC Tend to be the same, prolonging the service life of the battery, the said rechargeable/dischargeable power proportional distribution method and the average distribution method refer to each DC/AC converter module branch according to its rechargeable/dischargeable power ratio The proportion of the total electricity is allocated to the active power for output.

In this embodiment, the above-mentioned charging methods of each battery cluster BC adopt four-stage charging methods of pre-charging, fast charging, equalizing charging and floating charging, wherein the pre-charging, fast charging and floating charging are controlled by constant current and voltage limit, For constant pressure and current limiting control.

The large-capacity battery converter of the present invention supports the access of multi-branch single-stage DC/AC module units, and each battery branch collects energy to the AC bus through the converter, and after transformation, it is connected to the AC grid or is independent Running with load; "module combination, rotation balance" technology can improve system efficiency and take into account the consistency of the battery. It has the following characteristics:

(1) The inverter adopts the design concept of grouping and modularization to optimize the connection, which reduces the circulation and current sharing problems caused by the series and parallel connection of large-capacity recombined batteries.

(2) The converter is connected in multiple groups on the DC side, and the number of DC/AC units and different connection modes can be set according to the actual capacity. The system flexibility of the scheme is significantly improved, and capacity expansion is convenient, which is beneficial to battery maintenance, Balance management to improve the reliability of the battery system.

(3) The converter adopts the distribution scheme of "module combination, rotation balance". For the DC/AC converter modules in the converter, the time-sharing rotation output and smooth switching are used to reduce the switching loss and the high cost of the reactor. frequency loss, while improving the quality of output power, to achieve comprehensive coordination of economic benefits and control performance.

(4) The converter adopts a multi-objective nonlinear optimization scheme for power distribution, and the DC/AC converter module will integrate multiple objectives such as the state of charge of the battery pack, the number of charge and discharge times, and the maintenance cycle to perform various different Weighting treatment, adopting chargeable/discharging electricity proportional distribution method and average distribution method for power distribution, so that the use of each branch battery tends to be consistent and prolongs the service life of the battery.

(5) The battery branch realizes automatic intelligent charging and discharging management, and adopts the four-stage control strategy of pre-charging, fast charging, equalizing charging and floating charging with maximum configuration. The strategy can be adjusted in real time according to user needs and is universal. The DC/AC branches operate independently of each other to meet the inconsistency of the input battery pack and realize the independent charging and discharging optimization control of each battery pack.

(6) The converter has complete protection functions to meet the safety of the equipment itself under various fault conditions. When receiving alarm information such as battery overcharge, overdischarge and overtemperature, it will reduce the battery charging and discharging current or stop charging and discharging to protect the safety of the battery pack. The control function and protection function of each battery branch are completely independently configured to ensure the maximum availability of the system.

The applicant of the present invention has explained and described the embodiment of the present invention in detail in conjunction with the accompanying drawings, but those skilled in the art should understand that the above embodiment is only a preferred embodiment of the present invention, and the detailed description is only to help readers better To understand the spirit of the present invention rather than limit the protection scope of the present invention, on the contrary, any improvement or modification made based on the spirit of the present invention shall fall within the protection scope of the present invention.

Claims (7)

1. high capacity cell converter; It is characterized in that including the some single stage type DC/AC of branch converter modules parallel with one another; Each storage battery bunch BC is pooled to ac bus through each the single stage type DC/AC of branch converter module with energy respectively, after transformation, is incorporated into the power networks or the free band load running with AC network.

2. the control method of a high capacity cell converter according to claim 1 is characterized in that above-mentioned converter adopts DC side to divide many groups to insert, and the DC side control method is following:

Said Battery Inverter is according to the power instruction of different magnitudes; The quantity of the DC/AC converter module that definite participation is exerted oneself; To each storage battery bunch BC include state-of-charge, discharge and recharge number of times, after the multiple target of time between overhauls(TBO) carries out weighted; Each storage battery bunch BC high to priority carries out management of charging and discharging, and the situation of utilizing of each storage battery bunch BC is tended to balance; When each storage battery bunch BC priority was identical, the mode of then rotating through timesharing let all the other the single stage type DC/AC of branch converter modules be in resting state in turn, to improve the efficiency for charge-discharge of system.

3. the control method of high capacity cell converter according to claim 2 is characterized in that each DC/AC converter module branch road that above-mentioned participation exerts oneself power according to its distribution, and each storage battery bunch BC will carry out the intelligent recharge and discharge management automatically.

4. the control method of high capacity cell converter according to claim 2 is characterized in that the AC side operational mode of above-mentioned converter is following:

A) be incorporated into the power networks with AC network

When said converter and AC network were incorporated into the power networks, each DC/AC converter module adopted the control of line voltage directional vector, and double circle structure, outer shroud are Voltage loop, and interior ring is an electric current loop, realized P, Q decoupling zero control and DC bus-bar voltage control down based on the dq coordinate; Adopt the break-make of space vector of voltage pulse-width modulation (SVPWM) method control DC/AC converter module switch device;

B) independent run with load

Said converter breaks away from AC network; During the free band load running; Each DC/AC converter module is that ac bus provides constant voltage and frequency reference; Adopt V/f control, adopt the effective value closed-loop control of voltage to realize that terminal voltage amplitude and the frequency of each DC/AC converter module outlet behind filter keeps constant.

5. the control method of high capacity cell converter according to claim 2; It is characterized in that above-mentioned to each storage battery bunch BC include state-of-charge, discharge and recharge number of times, to carry out weighted be to adopt chargeable/discharge electricity amount direct ratio apportion design and average distribution system to carry out power division to the multiple target of time between overhauls(TBO); The operating position of each storage battery bunch BC is reached unanimity; Prolonged the useful life of battery; Said chargeable/discharge electricity amount direct ratio apportion design and average distribution system, to be meant that each DC/AC converter module branch road accounts for by its chargeable/discharge electricity amount chargeable/the pro rate active power of the total electric weight of discharge exerts oneself, when each branch road is exerted oneself when exceeding its rated power; But exert oneself according to all discharge paths mean allocation active power, adopt permanent power charge/discharge mode to control its power output.

6. the control method of high capacity cell converter according to claim 5; The charging modes that it is characterized in that above-mentioned each storage battery bunch BC adopts preliminary filling, fills soon, all fills and floating charge four-part form charging modes; Wherein, Preliminary filling, fill with floating charge and be constant current pressure limiting control soon, all filling is constant voltage and current limiting control.

7. the control method of high capacity cell converter according to claim 5 is characterized in that the charge and discharge system of above-mentioned each storage battery bunch BC adopts constant current charge-discharge or permanent power to discharge and recharge dual mode.

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