CN105656067B - Multistage online mobile energy storage power supply system and control method thereof - Google Patents

Abstract

The invention provides a control method of a multistage online mobile energy storage power supply system, which comprises the following steps: (1) collecting power grid and system operation data; (2) judging the power grid running state according to the collected data, and calculating the charging power P of the PCS at the power grid side if the power grid runs normally_1#PCSAnd discharge power P of load side PCS_2#PCSAnd entering the step (3); otherwise, the power grid side PCS is stopped, the load side PCS is operated in a V/F mode, the direct current bus side DC/DC is operated in a constant voltage control mode, and the step (1) is skipped; (3) and judging whether the power grid fails, if so, stopping the power grid side PCS, operating the load side PCS in a V/F mode, operating the direct current bus side DC/DC in a constant voltage control mode, and otherwise, controlling according to the SOC state. The invention can realize seamless switching between the on-line mode and the off-line mode, realize on-line power supply for users, prolong the service life of the energy storage system and reduce the operation cost of the system.

Description

Multistage online mobile energy storage power supply system and control method thereof

Technical Field

The invention relates to a mobile energy storage system and a control method, in particular to a multistage online mobile energy storage power supply system and a control method thereof.

Background

With the increasing dependence on electric energy and the rapid increase of electricity demand in modern society, the requirement on power supply quality is higher and higher, and sudden power failure inevitably damages the normal life order of people and the normal operation of society, especially to the load which is particularly important in the first-class load, and once the power supply is interrupted, the power supply can cause great political influence or economic loss. As the main power of the power grid emergency power supply equipment, the mobile power supply vehicle has the advantages of flexibility in movement, mature technology, rapid starting and the like, and plays an increasingly remarkable role in small and medium-sized power utilization places such as political power conservation, urban power grid emergency, major natural disaster resistance, temporary power utilization in power shortage areas and the like. In addition, in some regions with low annual power utilization load rate and periodic or seasonal peak power utilization, the mobile power supply vehicle is also needed, and the mobile emergency power supply vehicle is used as power supply supplement in the regions, so that the power utilization peak value can be effectively reduced, the pressure of a power grid can be relieved, the design capacity of distribution transformer can be reduced, and the utilization rate of rural power grid equipment and the power supply efficiency can be improved.

At present, a diesel generator is mostly adopted by a mobile power supply system as a standby power supply, but the diesel generator needs 5-30 s for long starting time, the power supply voltage and frequency fluctuation are large, the efficiency is low, and the environmental and noise pollution is inevitably brought by the use of diesel generator.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides the multistage online mobile energy storage power supply system and the control method thereof.

In order to achieve the purpose of the invention, the invention adopts the following technical scheme:

a control method of a multistage online mobile energy storage power supply system comprises the following steps:

(1) collecting power grid and system operation data;

(2) judging the power grid running state according to the collected data, and calculating the charging power P of the PCS at the power grid side if the power grid runs normally_1#PCSAnd discharge power P of load side PCS_2#PCSAnd entering the step (3); otherwise, the power grid side PCS is stopped, the load side PCS is operated in a V/F mode, the direct current bus side DC/DC is operated in a constant voltage control mode, and the step (1) is skipped;

(3) and judging whether the power grid fails, if so, stopping the power grid side PCS, operating the load side PCS in a V/F mode, operating the direct current bus side DC/DC in a constant voltage control mode, and otherwise, controlling according to the SOC state.

Preferably, in the step (1), the collected power grid and system operation data includes a power grid side voltage U_GRIDCurrent I_GRIDAC side voltage U of power grid side PCS_1#PCSCurrent I_1#PCSDirect side current I_{DC_1#PCS}Load side PCS AC side voltage U_2#PCSCurrent I_2#PCSDirect side current I_{DC_2#PCS}DC/DC voltage U on the side of the DC bus_DCCurrent I_DCOutput voltage U of energy storage system_BatCurrent I_BatAnd a state of charge, SOC, of the energy storage system.

Preferably, in the step (2), the collected data includes grid-side voltage and current data.

Preferably, in the step (2), the charging power P of the power grid side PCS is calculated_1#PCSAnd discharge power P of load side PCS_2#PCSThe formula of (1) is as follows:

preferably, in the step (3), the electric quantity of the energy storage system is divided into 5 regions according to the SOC state, where the 5 regions include:

when SOC is less than or equal to SOC_minThe energy storage system is a region with low electric quantity;

when SOC > SOC_minAnd SOC < SOC_s2Then, the energy storage system is in a hysteresis zone with low electric quantity;

when SOC is more than or equal to SOC_s2And SOC < SOC_s1Then, the energy storage system is in a proper electric quantity area;

when SOC is more than or equal to SOC_s1And SOC < SOC_maxThe energy storage system is a hysteresis zone with higher electric quantity;

when SOC is more than or equal to SOC_maxThe energy storage system is a region with higher electric quantity;

therein, SOC_max、SOC_minRespectively the maximum value and the minimum value of the state of charge of the energy storage unit, SOC_s1、SOC_s2Respectively upper and lower limits of rated state, and SOC_min＜SOC_s2＜SOC_s1＜SOC_max。

Preferably, in the step (3), the controlling according to the SOC state includes:

when SOC is less than or equal to SOC_minIncrease P at regular time_1#PCSLet P stand_1#PCS＞P_2#PCSIn the state, the energy storage system is charged through the 1# PCS to ensure the energy storage electric quantity until the SOC is more than the SOC_s1；

When SOC > SOC_minFurther judgment is made if SOC > SOC_maxThen P is decreased_1#PCSLet P stand_1#PCS＜P_2#PCSIn the state, the electricity consumption of the load is larger than the output electricity of the power grid, the insufficient part is supplemented by energy storage and discharge, and the electricity of the energy storage system is reduced until the SOC is smaller than the SOC_s2；

If SOC is less than or equal to 95%, adjusting P_1#PCSSize, P_1#PCS＝P_2#PCSAnd in the state, the load electricity consumption is the same as the output electricity of the power grid, and the energy storage system keeps the current electricity.

Preferably, the multi-stage online mobile energy storage power supply system comprises an alternating current-direct current conversion unit, an energy storage system and a monitoring platform;

the alternating current-direct current conversion unit comprises a power grid side PCS and a load side PCS, wherein the power grid side PCS is used for AC/DC conversion and is connected with a power grid, the power grid normally operates at a constant voltage to ensure that the energy storage system has sufficient electric quantity, and the power grid stops when in fault; the load side PCS is used for DC/AC conversion and is connected with a load to ensure power supply to the load;

the energy storage system is connected with the direct current sides of the power grid side PCS and the load side PCS, and is used for providing stable direct current voltage for the load side PCS by a direct current source when the power grid fails;

the monitoring platform realizes bidirectional communication with the power grid side PCS, the load side PCS and the energy storage system, and is used for monitoring the running state of each device and performing coordination control.

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

the energy storage system has short starting time, is mostly millisecond-level, and can realize seamless switching of two operation modes of grid connection and grid disconnection. The energy storage system is optimally charged and discharged, the service life of the energy storage system is prolonged, and the operation cost of the system is reduced. Meanwhile, the movable energy storage system can be used as a power supply and can interact with a power distribution network, the charging is carried out in the power utilization valley, the discharging is carried out in the power utilization peak, the purposes of peak clipping and valley filling, the electric energy quality is improved, the electric energy is integrated and fully utilized, and the power supply pressure in the power utilization peak period is relieved are achieved, and the movable energy storage system has important economic and social benefits.

Drawings

FIG. 1 is a structural diagram of a multi-stage online mobile energy storage power supply system according to the present invention

FIG. 2 is a flowchart of a control method of a multi-stage online mobile energy storage power supply system according to the present invention

FIG. 3 is a schematic diagram of the power partitioning of the energy storage system according to the present invention

FIG. 4 is a structural diagram of an experiment of a multi-stage online mobile energy storage power supply system provided by the present invention

FIG. 5 is a waveform diagram of no-load operation of the system under the grid-connected condition provided by the invention

FIG. 6 is a waveform diagram of 20kW load operation of the system provided by the invention

FIG. 7 is a waveform diagram of a system in case of power grid failure according to the present invention

FIG. 8 is a waveform diagram of a system for recovering from a grid fault according to the present invention

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings.

The invention aims to realize online power supply of a mobile power supply system, and the system coordinates a power grid side PCS under the condition of grid connection, ensures DC/DC output of a direct current bus side, ensures the electric quantity of an energy storage system, and ensures constant-voltage constant-frequency output of the load side PCS; under the off-grid condition, the power supply of a load side PCS to a load is ensured by coordinating the energy storage output of a direct current side; and coordinating the operation of a network side PCS and a bus side DC/DC during switching of the grid-connected mode and the off-grid mode, ensuring the voltage stability of a direct current bus, realizing the stable output of the load side PCS and realizing the seamless switching of the grid-connected mode and the off-grid mode of the system.

As shown in fig. 1, the multi-stage online mobile energy storage power supply system topology is mainly composed of an ac/dc conversion unit, an energy storage unit, and a monitoring system. The system can ensure reliable power supply to the accessed load, and the functions of each part are as follows:

AC-DC conversion unit: the part consists of two PCS, wherein a network side PCS performs AC/DC conversion and is connected with a power grid, the power grid normally performs constant voltage operation to ensure that the energy storage unit has sufficient electric quantity, and the power grid is stopped when in failure. The load side PCS performs DC/AC conversion and is connected with a load to ensure reliable power supply to the load;

an energy storage unit: and the DC side of the AC/DC conversion unit and the DC/AC conversion unit are connected, and the DC/AC conversion unit is used as a DC source to provide stable DC voltage for the DC/AC when the power grid fails, so that the normal V/F operation of the DC/AC conversion unit is ensured. Meanwhile, for the convenience of control, the electric quantity of the energy storage unit is divided into 5 regions as shown in figure 2, wherein the SOC is_max、SOC_minRespectively the maximum value and the minimum value of the state of charge of the energy storage unit, SOC_s1、SOC_s2Respectively, the upper and lower limits of the rated state. SOC_max、SOC_min、SOC_s1、SOC_s2The specific value needs to be set according to the energy storage type and the actual requirement;

the monitoring system comprises: the monitoring system can realize the two-way communication with the AC/DC conversion unit, the DC/AC conversion unit and the energy storage unit, monitor the running state of each device and carry out coordination control, thereby ensuring the safe and reliable running of the whole system.

Fig. 3 shows a control flow of a multi-stage online mobile energy storage power supply system, which includes the following steps:

step 1: collecting power grid and system operation data including grid side voltage U_GRIDCurrent I_GRID1# PCS AC side voltage U_1#PCSCurrent I_1#PCSDirect side current I _{DC_1#PCS}2# PCS AC side voltage U_2#PCSCurrent I_2#PCSDirect side current I_{DC_2#PCS}DC/DC voltage U on the side of the DC bus_DCCurrent I_DCOutput voltage U of energy storage unit_BatCurrent I_BatAnd an SOC;

step 2: judging the power grid running state according to the collected grid side voltage and current data, and calculating 1# PCS power P _1#PCS2# PCS output Power P_2#PCSThe method comprises the following steps:

and step 3: if the power grid fails, stopping the 1# PCS, performing V/F operation on the 2# PCS, performing constant-voltage control operation on the DC/DC, and otherwise, performing further control according to the SOC state;

and 4, step 4: when SOC is less than or equal to SOC_minIncrease P at regular time_1#PCSLet P stand_1#PCS＞P_2#PCSIn the state, the energy storage system is charged through the 1# PCS to ensure the energy storage electric quantity until the SOC is more than the SOC_s1；

And 5: when SOC > SOC_minFurther judgment is made if SOC > SOC_maxThen P is decreased_1#PCSLet P stand_1#PCS＜P_2#PCSIn the state, the electricity consumption of the load is larger than the output electricity of the power grid, the insufficient part is supplemented by energy storage and discharge, and the electricity of the energy storage system is reduced until the SOC is smaller than the SOC_s2；

Step 6: if SOC is less than or equal to 95%, adjusting P_1#PCSSize, P_1#PCS＝P_2#PCSAnd in the state, the load electricity consumption is the same as the output electricity of the power grid, and the energy storage system keeps the current electricity.

As shown in fig. 4, two 50kWPCS dc sides are connected to each other, wherein the 1# PCS ac side is connected to the grid through a circuit breaker, and the 2# PCS ac side is connected to the 30kVA RLC adjustable load through a circuit breaker. The direct current sides of the two PCS are connected with a 50kW/50kWh lithium iron battery through a 50kW bidirectional DC/DC, and the voltage of a direct current bus is stabilized at 600V.

The circuit breaker QS1 is closed to simulate the normal working condition of a power grid, QS3 is closed, QS2 is opened, 1# PCS performs constant-voltage current-limiting operation, 2# PCS performs V/F operation, the no-load operation waveform of the system is shown in figure 5, the measured voltage is A-phase voltage, and the measured current is A-phase current. The QS1, QS3 switching state, and PCS operating state remain unchanged, putting a QS2 closed system into a 20kW three-phase resistive load waveform as shown in fig. 6. As can be seen from the figure, the output voltage of the 2# PCS is not distorted in the load putting process, and stable 220V/50Hz power supply can be provided. And (3) disconnecting the QS1 in the grid-connected operation process of the system, and simulating the grid fault condition. After QS1 is switched off, 1# PCS stops running, 2# PCS still does V/F running, and system waveforms before and after QS1 is switched are shown in figure 7. As can be seen from the waveform diagram, no change occurs in the output voltage of # 2 PCS and the load current at the grid fault point, i.e. it is demonstrated that the sudden grid fault has no influence on the system output. And after the system runs off the grid for a period of time, QS1 is closed, and the simulation grid is recovered. At this time, the 1# PCS resumes constant power operation, and the 2# PCS is still V/F operated. The system waveforms before and after the power grid recovery are shown in fig. 8, and it can be seen from the waveform diagrams that both the output voltage of # 2 PCS and the load current are distorted at the power grid recovery point, that is, the power grid recovery has no influence on the system output. Experiments show that the system can ensure stable output voltage frequency under the steady-state conditions of grid connection and grid disconnection and in the grid connection/disconnection switching process, and reliable power supply to loads is realized.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.

Claims (3)

1. A control method for a multistage online mobile energy storage power supply system is characterized by comprising the following steps:

(1) collecting power grid and system operation data;

(2) judging the running state of the power grid according to the collected data;

(3) judging whether the power grid fails or not; if the operation is normal, calculating the charging power P of the PCS at the power grid side_1#PCSAnd discharge power P of load side PCS_2#PCSAnd control is carried out according to the SOC state; otherwise the grid side PCS is shut down,the PCS at the load side operates in a V/F mode, the DC/DC at the direct current bus side operates in a constant voltage control mode, and the step (1) is skipped;

in the step (1), the collected power grid and system operation data comprises power grid side voltage U_GRIDCurrent I_GRIDAC side voltage U of power grid side PCS_1#PCSCurrent I_1#PCSDirect side current I_{DC_1#PCS}Load side PCS AC side voltage U_2#PCSCurrent I_2#PCSDirect side current I_{DC_2#PCS}DC/DC voltage U on the side of the DC bus_DCCurrent I_DCOutput voltage U of energy storage system_BatCurrent I_BatAnd a state of charge, SOC, of the energy storage system;

in the step (2), the charging power P of the power grid side PCS is calculated_1#PCSAnd discharge power P of load side PCS_2#PCSThe formula of (1) is as follows:

in the step (3), dividing the electric quantity of the energy storage system into 5 regions according to the SOC state, where the 5 regions include:

when SOC is less than or equal to SOC_minThe energy storage system is a region with low electric quantity;

when SOC > SOC_minAnd SOC < SOC_s2Then, the energy storage system is in a hysteresis zone with low electric quantity;

when SOC is more than or equal to SOC_s2And SOC < SOC_s1Then, the energy storage system is in a proper electric quantity area;

when SOC is more than or equal to SOC_s1And SOC < SOC_maxThe energy storage system is a hysteresis zone with higher electric quantity;

when SOC is more than or equal to SOC_maxThe energy storage system is a region with higher electric quantity;

therein, SOC_max、SOC_minRespectively the maximum value and the minimum value of the state of charge of the energy storage unit, SOC_s1、SOC_s2Respectively upper and lower limits of rated state, and SOC_min＜SOC_s2＜SOC_s1＜SOC_max；

In the step (3), the controlling according to the SOC state includes:

when SOC is less than or equal to SOC_minIncrease P at regular time_1#PCSLet P stand_1#PCS＞P_2#PCSIn the state, the energy storage system is charged through the 1# PCS to ensure the energy storage electric quantity until the SOC is more than the SOC_s1；

When SOC > SOC_minFurther judgment is made if SOC > SOC_maxThen P is decreased_1#PCSLet P stand_1#PCS＜P_2#PCSIn the state, the electricity consumption of the load is larger than the output electricity of the power grid, the insufficient part is supplemented by energy storage and discharge, and the electricity of the energy storage system is reduced until the SOC is smaller than the SOC_s2；

If SOC is less than or equal to 95%, adjusting P_1#PCSSize, P_1#PCS＝P_2#PCSAnd in the state, the load electricity consumption is the same as the output electricity of the power grid, and the energy storage system keeps the current electricity.

2. The control method of claim 1, wherein in step (2), the collected data comprises grid-side voltage and current data.

3. The multistage online mobile energy storage power supply system applying the control method of the multistage online mobile energy storage power supply system according to claim 1 is characterized by comprising an alternating current-direct current conversion unit, an energy storage system and a monitoring platform;

the alternating current-direct current conversion unit comprises a power grid side PCS and a load side PCS, wherein the power grid side PCS is used for AC/DC conversion and is connected with a power grid, the power grid normally operates at a constant voltage to ensure that the energy storage system has sufficient electric quantity, and the power grid stops when in fault; the load side PCS is used for DC/AC conversion and is connected with a load to ensure power supply to the load;

the energy storage system is connected with the direct current sides of the power grid side PCS and the load side PCS, and is used for providing stable direct current voltage for the load side PCS by a direct current source when the power grid fails;

the monitoring platform realizes bidirectional communication with the power grid side PCS, the load side PCS and the energy storage system, and is used for monitoring the running state of each device and performing coordination control.

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