CN106208113B - A kind of hybrid energy-storing hierarchical coordinative control method based on state-of-charge - Google Patents

Abstract

The invention relates to a hybrid energy storage layered coordinated control method based on the state of charge, which is used for the control of a microgrid containing a hybrid energy storage unit. The DC converter is connected to the DC bus, and the DC bus is connected to the AC bus of the microgrid through the DC/AC converter. The method includes the following steps: obtaining the AC bus voltage of the microgrid, the frequency of the AC bus and the comprehensive state of charge of the hybrid energy storage unit for upper layer Power optimization control obtains the output power command of the DC/AC converter, and then controls the operation of the DC/AC converter; obtains the DC bus voltage, and performs lower-level power distribution with the goal of stabilizing the DC bus voltage, and obtains the charging and discharging power of the battery and super capacitor respectively Instructions, and then control the corresponding DC/DC converter work. Compared with the prior art, the invention can effectively prevent overcharge or overdischarge of the hybrid energy storage battery.

Description

A hierarchical coordinated control method for hybrid energy storage based on state of charge

technical field

The invention relates to a hybrid energy storage control method, in particular to a state-of-charge-based hierarchical coordination control method for hybrid energy storage.

Background technique

In recent years, with the rapid development of renewable energy, people have put forward higher requirements for the reliability and stability of microgrids. In order to improve the power balance, stability, and power quality in the microgrid system, it is one of the effective means to suppress power pulsation to equip an energy storage device with a more stable output power. The energy storage system has the ability to quickly absorb and release power in a short time Therefore, it can effectively overcome the shortcomings of intermittent and fluctuating output power of renewable energy. In order to make up for the shortcomings of traditional single energy storage equipment, hybrid energy storage units using power-type supercapacitors and energy-type batteries are one of the current development directions of energy storage technology. Supercapacitors have fast response speed, high power output capability, and energy conversion. It is a typical power-type energy storage device with the characteristics of high efficiency and long cycle life. The coordinated operation of supercapacitors and batteries can greatly improve the peak power input and output capabilities of energy storage devices, reduce internal losses, and reduce the number of charge and discharge times of batteries, thereby increasing the service life of equipment. Therefore, applying hybrid energy storage to renewable power systems has great technical and economic advantages.

At present, many researchers have made important achievements in hybrid energy storage control technology. ASAO T proposes to use a low-pass filter method to compensate specific frequency band components in wind power, but because the state of charge (SOC) of the energy storage device is not considered, it is easy to cause overcharging and overdischarging of the equipment.

Contents of the invention

The purpose of the present invention is to provide a state-of-charge-based coordinated control method for hybrid energy storage layers in order to overcome the above-mentioned defects in the prior art.

The purpose of the present invention can be achieved through the following technical solutions:

A state-of-charge-based hierarchical coordinated control method for hybrid energy storage, which is used for the control of a microgrid containing a hybrid energy storage unit. The hybrid energy storage unit includes a storage battery and a supercapacitor, and the storage battery and the supercapacitor are respectively The DC bus is connected to the DC bus through the DC/DC converter, and the DC bus is connected to the AC bus of the microgrid through the DC/AC converter. The method includes the following steps:

(1) Obtain the microgrid AC bus voltage U, AC bus frequency f and hybrid energy storage unit comprehensive state of charge SOC _HESS , perform upper-level power optimization control according to U, f and SOC _HESS to obtain the output power command of the DC/AC converter, Then control the work of the DC/AC converter;

(2) Obtain the DC bus voltage V _dc , aim at stabilizing the DC bus voltage to carry out lower-layer power distribution, and obtain the charge and discharge power commands of the battery and supercapacitor respectively, and then control the corresponding DC/DC converter.

In step (1), the upper-layer power optimization control is specifically obtained through a fuzzy logic algorithm, specifically including:

(101) The deviation between the AC bus frequency f and the AC bus rated frequency f _ref is adjusted by PI to obtain the active power deficit value P _ref , and at the same time, the deviation between the AC bus voltage U and the rated voltage U _ref of the AC bus is adjusted by PI to obtain the reactive power Power shortfall value Q _ref ;

(102) The hybrid energy storage unit comprehensive state of charge SOC _HESS and active power deficit value P _ref are used as inputs to obtain the active power correction value ΔP through the fuzzy logic algorithm, and the hybrid energy storage unit comprehensive state of charge SOC _HESS and reactive power The shortfall value Q _ref is used as input to obtain the reactive power correction value ΔQ through the fuzzy logic algorithm;

(103) Summing the active power deficit value P _ref and the active power correction value ΔP to obtain the output active power command P′ _ref of the DC/AC converter, and summing the reactive power deficit value Q _ref and the reactive power correction value ΔQ The output reactive power command Q′ _ref of the DC/AC converter is obtained.

The comprehensive state of charge SOC _HESS of the hybrid energy storage unit is obtained by the following formula:

Among them, Q _VRLAB , Q _SC are the rated capacities of the storage battery and the supercapacitor, respectively, and SOC _VRLAB , SOC _SC are the states of charge of the storage battery and the supercapacitor, respectively.

Described step (2) specifically comprises:

(201) adjusting the deviation between the DC bus rated voltage V _ref and the DC bus voltage V _dc through PI adjustment to obtain the charging and discharging power P _HESS of the hybrid energy storage unit;

(202) Filter the charging and discharging power P _HESS of the hybrid energy storage unit through a low-pass filter to obtain a low-frequency component as the battery charging and discharging power command P _bat , and simultaneously use the high-frequency component as the supercapacitor charging and discharging power command P _sc .

After the battery charge and discharge power command P _bat and the super capacitor charge and discharge power command P _sc are obtained, it needs to be corrected, specifically:

(a) Calculate the charging and discharging correction power ΔP′ according to the following formula:

ΔP'=(SOC _SC -SOC _VRLAB )×|P _HESS |×β,

Among them, SOC _VRLAB and SOC _SC are the state of charge of the battery and supercapacitor respectively, P _HESS is the charging and discharging power of the hybrid energy storage unit, β is the correction coefficient, and the range of β is 1.1 to 1.3;

(b) Calculating the battery charging and discharging power command correction value P′ _bat : P′ _bat =P _bat +ΔP′, and calculating the supercapacitor charging and discharging power command correction value P′ _sc : P′ _sc =P _sc -ΔP′;

Furthermore, the battery charging and discharging power command correction value _P'bat is used as the battery charging and discharging power command, and the super capacitor charging and discharging power command correction value _P'sc is used as the super capacitor charging and discharging power command to control the corresponding DC/DC converter.

Compared with prior art, the present invention has following advantage:

(1) The present invention takes into account the comprehensive state of charge SOC _HESS of the hybrid energy storage unit when performing the upper-level power optimization control, thereby ensuring the overcharge or overdischarge of the hybrid energy storage unit while stabilizing the AC bus voltage and frequency, and ensuring the storage system security;

(2) The power distribution of the lower layer of the present invention distributes the high-frequency power to the supercapacitor through a low-pass filter filtering mode, and distributes the low-frequency power to the storage battery, which greatly brings into play the advantages of the two energy storage elements of the storage battery and the supercapacitor;

(3) The present invention also performs power correction through the state of charge of the storage battery and the supercapacitor when performing power distribution on the lower layer. The power correction of the two energy storage elements is relatively small. When the difference between the states of charge of the two energy storage elements is relatively large, the value of the correction power ΔP' is relatively large, that is, the power correction is relatively large, so that the charge of the two energy storage elements The state is relatively maintained in a balanced state, preventing a certain energy storage element from overcharging or overdischarging, and prolonging the life of the energy storage element.

Description of drawings

Figure 1 is a structural block diagram of a microgrid with hybrid energy storage units;

Fig. 2 is a control block diagram of upper layer power optimization control;

Fig. 3 is a control block diagram of lower layer power distribution;

Figure 4 is a comparison diagram of the curves of the hybrid energy storage unit's comprehensive state of charge SOC _HESS ;

Figure 5 is a graph comparing the curves of the SOC _SC of the supercapacitor state of charge;

Fig. 6 is a curve comparison diagram of battery state of charge SOC _VRLAB ;

1 is a storage battery, 2 is a supercapacitor, 3 is a first DC/DC converter, 4 is a second DC/DC converter, and 5 is a DC/AC converter.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example

A state-of-charge-based hierarchical coordinated control method for hybrid energy storage, which is used for the control of microgrids with hybrid energy storage units. Figure 1 shows the structural block diagram of a microgrid with hybrid energy storage units. The unit includes a battery 1 and a supercapacitor 2, and the battery 1 and the supercapacitor 2 are respectively connected to the DC bus through a DC/DC converter, that is, the first DC/DC converter 3 and the second DC/DC converter 4 in the figure, and the DC bus It is connected to the microgrid AC busbar through a DC/AC converter 5, and the storage battery 1 is a lithium iron phosphate battery.

The hybrid energy storage hierarchical coordination control method based on the state of charge of the present invention includes the following steps:

(1) Obtain the microgrid AC bus voltage U, AC bus frequency f and hybrid energy storage unit comprehensive state of charge SOC _HESS , perform upper-level power optimization control according to U, f and SOC _HESS to obtain the output power command of the DC/AC converter, Then control the work of the DC/AC converter;

(2) Obtain the DC bus voltage V _dc , aim at stabilizing the DC bus voltage to carry out lower-layer power distribution, and obtain the charge and discharge power commands of the battery and supercapacitor respectively, and then control the corresponding DC/DC converter.

In step (1), the upper-layer power optimization control is specifically obtained through a fuzzy logic algorithm, and the specific flow chart is shown in Figure 2:

First, the deviation between the AC bus frequency f and the AC bus rated frequency f _ref is adjusted by PI to obtain the active power deficit value P _ref , and at the same time, the deviation between the AC bus voltage U and the rated voltage U _ref of the AC bus is adjusted by PI to obtain the reactive power Shortage value Q _ref ;

Secondly, the hybrid energy storage unit’s comprehensive state of charge SOC _HESS and active power deficit value P _ref are used as inputs to obtain the active power correction value ΔP through the fuzzy logic algorithm, and at the same time, the hybrid energy storage unit’s comprehensive state of charge SOC _HESS and reactive power deficit value The value Q _ref is used as an input to obtain the reactive power correction value ΔQ through the fuzzy logic algorithm, and the comprehensive state of charge SOC _HESS of the hybrid energy storage unit is obtained by the following formula:

Among them, Q _VRLAB , Q _SC are the rated capacities of the storage battery and the supercapacitor, respectively, and SOC _VRLAB , SOC _SC are the states of charge of the storage battery and the supercapacitor, respectively.

In order to distinguish the operating state of the hybrid energy storage unit, according to the size of the hybrid energy storage unit SOC _HESS , the hybrid energy storage unit is divided into 7 working states, because the capacity of the lithium iron phosphate battery in the hybrid energy storage unit is larger than that of the supercapacitor. And the working range of the state of charge of the supercapacitor is 0.1-1, and the working range of the state of charge of the lithium iron phosphate battery is 0.2-0.9. Here, the working range of the state of charge of the lithium iron phosphate battery is selected as the approximate charge of the hybrid energy storage unit. The working range of the state of charge, that is, the working range of the state of charge of the hybrid energy storage unit is 0.2-0.9. The working status of the division is as follows:

A. When the SOC _HESS is running between 0.4 and 0.7, it is called the optimal state area. In this interval, the hybrid energy storage unit has enough power for discharging operation and sufficient remaining capacity for charging operation. Under the circumstances, it is not necessary to correct the active power deficit value Pre and reactive power deficit value _{Q ref output} by the PI controller, and directly use them as the power command of the energy storage system.

B. When the SOC _HESS is running between 0.7-0.8 or 0.3-0.4, it is called the sub-optimal state area. At this time, the hybrid energy storage unit may be overcharged or overdischarged. Taking SOC _HESS between 0.7 and 0.8 as an example, the hybrid energy storage unit may be overcharged at this time. If the hybrid energy storage unit is absorbing power from the AC side of the microgrid, the energy absorbed by the hybrid energy storage unit should be reduced at this time, that is, the energy storage unit should be abandoned. Compensation of partial unbalanced power in microgrids.

C. When the SOC _HESS is between 0.8-0.9 or 0.2-0.3, it is called the alert state area, and at this time the hybrid energy storage unit has approached the boundary line of overcharge or overdischarge. Take the SOC _HESS of 0.8 to 0.9 as an example. At this time, the hybrid energy storage unit is approaching the boundary of overcharging. If it continues to absorb power from the microgrid, it will cause overcharging of the hybrid energy storage unit. At this time, it is necessary to give up unbalanced microgrid. Power compensation, and choose the right time to make the hybrid energy storage unit enter the discharge state.

D. When the SOC _HESS is lower than 0.2 or higher than 0.9, the hybrid energy storage unit has completely entered the alarm state area. Taking the SOC _HESS higher than 0.9 as an example, if the hybrid energy storage unit is absorbing energy from the microgrid at this time, it should Immediately switch the hybrid energy storage unit from the charge state to the discharge state until the SOC _HESS is lower than 0.9, and switch to the alert state area.

To formulate fuzzy rules according to the working state of the hybrid energy storage and the corresponding operation given, it is necessary to design the first fuzzy controller and the second fuzzy controller, taking the correction of active power as an example, that is, to design the first fuzzy controller, the fuzzy controller The controller adopts two-input-single-output two-dimensional fuzzy control structure. The following describes the process of fuzzy operation on input and output variables.

Input E1: hybrid energy storage unit SOC _HESS , its variation range (basic domain) is [0, 100%], fuzzy domain is {-3,-2,-1,0,1,2,3}, corresponding to The fuzzy subsets of {"Negative Big (NB)", "Negative Medium (NM)", "Negative Small (NS)", "Zero (ZO)", "Positive Small (PS)", "Positive Medium (PM) ", "Zhengda (PB)"}, which respectively indicate the current working state of the hybrid energy storage unit: over-discharge state, low power state, low power state, normal power state, high power state, high power state , Overcharged state.

Input E2: The active power command P _ref output by the PI controller, its value range is limited by the rated charging and discharging power of the hybrid energy storage unit. In this paper, the rated active power of the hybrid energy storage unit is selected as 10kW, so its value range is -10kW～10kW, that is, the basic domain of discourse is [-10, 10], the fuzzy domain of discourse is {-3,-2,-1,0,1,2,3}, and the corresponding fuzzy subset is {"negative Large (NB)", "Negative Medium (NM)", "Negative Small (NS)", "Zero (ZO)", "Positive Small (PS)", "Positive Medium (PM)", "Positive Big (PB)" }, indicating the positive, negative and magnitude of the command power value of the hybrid energy storage unit respectively: the charging power value is large, the charging power value is medium, the charging power value is small, no charging and no discharge, the discharging power value is small, the discharging power value is medium, the discharging power value is The power value is great.

Output U: active power correction value ΔP, its value range is subject to the value range of the active power command of the PI controller, in order to be able to switch the charge and discharge state of the battery when the battery SOC is too low, the range of ΔP should be larger than the active power command Slightly larger, considering the value range of Pre _ref , ΔP takes -12kW ~ 12kW, that is, the basic domain of discourse is [-12, 12]. The domain of fuzzy discourse is {-3,-2,-1,0,1,2,3}, and the corresponding fuzzy subsets are {"Negative Big (NB)", "Negative Medium (NM)", "Negative Small ( NS)", "Zero (ZO)", "Positive Small (PS)", "Positive Medium (PM)", "Positive Big (PB)"}, corresponding to the correction power ΔP negative large, negative medium, negative small, zero, Right small, right middle, right big.

According to the relationship between SOC _HESS and _Pref introduced earlier and the correction value ΔP, its control rules are shown in Table 1.

Table 1 Fuzzy control rules

Based on the same correction rule, the fuzzy control rule of reactive power is the same as Table 1, and the range of reactive power deficit value _Qref output by PI controller is -5kvar～5kvar, and the range of reactive power correction value ΔQ is -6kvar ~6kvar.

Finally, sum the active power deficit value P _ref and the active power correction value ΔP to obtain the output active power command P′ _ref of the DC/AC converter, and sum the reactive power deficit value Q _ref and the reactive power correction value ΔQ to obtain The output reactive power command Q′ _ref of the DC/AC converter.

As shown in Figure 3, it is a control block diagram of lower-layer power distribution, and step (2) includes the following steps:

(201) adjusting the deviation between the DC bus rated voltage V _ref and the DC bus voltage V _dc through PI adjustment to obtain the charging and discharging power P _HESS of the hybrid energy storage unit;

(202) Filter the charging and discharging power P _HESS of the hybrid energy storage unit through a low-pass filter to obtain a low-frequency component as the battery charging and discharging power command P _bat , and simultaneously use the high-frequency component as the supercapacitor charging and discharging power command P _sc .

After the battery charge and discharge power command P _bat and the super capacitor charge and discharge power command P _sc are obtained, it needs to be corrected, specifically:

(a) Calculate the charging and discharging correction power ΔP′ according to the following formula:

ΔP'=(SOC _SC -SOC _VRLAB )×|P _HESS |×β,

Among them, SOC _VRLAB and SOC _SC are the state of charge of the battery and supercapacitor respectively, P _HESS is the charging and discharging power of the hybrid energy storage unit, β is the correction coefficient, and the range of β is 1.1 to 1.3;

(b) Calculate battery charge and discharge power command correction value P′ _bat : P′ _bat =P _bat +ΔP′, calculate supercapacitor charge and discharge power command correction value P′ _sc : P′ _sc =P _sc -ΔP′;

Furthermore, the battery charging and discharging power command correction value _P'bat is used as the battery charging and discharging power command, and the super capacitor charging and discharging power command correction value _P'sc is used as the super capacitor charging and discharging power command to control the corresponding DC/DC converter.

In this embodiment, a hybrid energy storage layered coordination control method based on the state of charge is used to carry out a comparison experiment with a hybrid energy storage unit charging and discharging allocation strategy using a common low-pass filter algorithm. Fig. 4 is a curve comparison diagram of the comprehensive state of charge SOC _HESS of the hybrid energy storage unit, and the curve a1 in the figure is the comprehensive state of charge of the hybrid energy storage unit according to the hybrid energy storage hierarchical coordination control method based on the state of charge of the present invention SOC _HESS curve, curve a2 is the hybrid energy storage unit comprehensive state of charge SOC _HESS curve of the common low-pass filter algorithm, as can be seen from the figure, the hybrid energy storage unit of the hybrid energy storage hierarchical coordination control method based on the state of charge of the present invention The variation range of the comprehensive state of charge SOC _HESS is controlled between 0.2 and 0.8, which is maintained within a reasonable range and effectively prevents overcharging or overdischarging of the hybrid energy storage unit. Fig. 5 is the curve comparison chart of SOC _SC of supercapacitor state of charge, and curve b1 among the figure is the SOC _SC curve of supercapacitor state of charge under the control method of the present invention, and curve b2 is the _QSC curve of state of charge of supercapacitor under common control method. Fig. 6 is a graph comparing curves of battery state of charge SOC _VRLAB , in which curve c1 is the SOC _VRLAB curve of the battery state of charge under the control method of the present invention, and curve c2 is the SOC _VRLAB curve of the battery state of charge under the common control method. It can be seen from Fig. 5 and Fig. 6 that under the control method of the present invention, the variation range of the state of charge of the supercapacitor and the storage _battery is much smaller in the whole process. The power state SOC _VRLAB ranges from 0.25 to 0.78, and there is no overcharge or overdischarge.

Claims (4)

1. a kind of hybrid energy-storing hierarchical coordinative control method based on state-of-charge, for containing the micro-capacitance sensor for mixing energy-storage units Control, the hybrid energy-storing unit includes accumulator and super capacitor, and the accumulator and super capacitor pass through DC/ respectively DC converters are connected to DC bus, and DC bus is connected to micro-capacitance alternating current bus by DC/AC converters, and feature exists In this method comprises the following steps：

(1) micro-capacitance alternating current bus voltage U, ac bus frequency f and hybrid energy-storing unit comprehensive state-of-charge SOC are obtained_HESS, According to U, f and SOC_HESSIt carries out upper layer power optimization to control to obtain the output power instruction of DC/AC converters, and then controls DC/ AC converters work；

(2) DC bus-bar voltage V is obtained_dc, lower layer's power distribution is carried out by target of stable DC busbar voltage, respectively obtains storage The charge-discharge electric power of battery and super capacitor instructs, and then controls corresponding DC/DC converters work；

Power optimization control obtains step (1) especially by fuzzy logic algorithm at the middle and upper levels, specifically includes：

(101) by ac bus frequency f and ac bus rated frequency f_refDeviation adjust to obtain active power shortage value through PI P_ref, while by the rated voltage U of ac bus voltage U and ac bus_refDeviation adjust to obtain reactive power vacancy through PI Value Q_ref；

(102) by hybrid energy-storing unit comprehensive state-of-charge SOC_HESSWith active power shortage value P_refIt is patrolled by fuzzy as input Volume algorithm obtains active power correction value Δ P, while by hybrid energy-storing unit comprehensive state-of-charge SOC_HESSIt is lacked with reactive power Volume value Q_refAs input reactive power correction value Δ Q is obtained by fuzzy logic algorithm；

(103) to active power shortage value P_refThe output for summing to obtain DC/AC converters with active power correction value Δ P is active Power instruction P '_ref, to reactive power vacancy value Q_refIt sums to obtain the output of DC/AC converters with reactive power correction value Δ Q Reactive power instructs Q '_ref。

2. a kind of hybrid energy-storing hierarchical coordinative control method based on state-of-charge according to claim 1, feature exist In the hybrid energy-storing unit comprehensive state-of-charge SOC_HESSIt is obtained by following formula：

Wherein, Q_VRLAB、Q_SCThe respectively rated capacity of accumulator and super capacitor, SOC_VRLAB、SOC_SCRespectively accumulator and super The state-of-charge of grade capacitance.

3. a kind of hybrid energy-storing hierarchical coordinative control method based on state-of-charge according to claim 1, feature exist In the step (2) specifically includes：

(201) by DC bus rated voltage V_refWith DC bus-bar voltage V_dcDeviation adjust to obtain hybrid energy-storing unit through PI Charge-discharge electric power P_HESS；

(202) by the charge-discharge electric power P of hybrid energy-storing unit_HESSIt filters to obtain low frequency component by low-pass filter and is used as storage Battery charging and discharging power instruction P_bat, while instructing P using high fdrequency component as super capacitor charge-discharge electric power_sc。

4. a kind of hybrid energy-storing hierarchical coordinative control method based on state-of-charge according to claim 3, feature exist In obtaining accumulator cell charging and discharging power instruction P_batP is instructed with super capacitor charge-discharge electric power_scAfter also need to be modified it, Specially：

(a) charge and discharge corrected output Δ P ' is sought according to the following formula：

Δ P '=(SOC_SC-SOC_VRLAB)×|P_HESS| × β,

Wherein, SOC_VRLAB、SOC_SCThe respectively state-of-charge of accumulator and super capacitor, P_HESSFor the charge and discharge of hybrid energy-storing unit Electrical power, β are correction factor, and β value ranges are 1.1~1.3；

(b) calculating accumulator charge-discharge electric power instruction correction value P '_bat：P′_bat=P_bat+ Δ P ' calculates super capacitor charge and discharge electric work Rate instructs correction value P '_sc：P′_sc=P_sc-ΔP′；

In turn by accumulator cell charging and discharging power instruction correction value P '_batAs accumulator cell charging and discharging power instruction, super capacitor is filled Discharge power instructs correction value P '_scIt is instructed as super capacitor charge-discharge electric power, to control corresponding DC/DC converters work Make.