CN112736888A - Sliding mode control-based improved self-adaptive droop control strategy for direct-current micro-grid - Google Patents

Sliding mode control-based improved self-adaptive droop control strategy for direct-current micro-grid Download PDF

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CN112736888A
CN112736888A CN202011560609.6A CN202011560609A CN112736888A CN 112736888 A CN112736888 A CN 112736888A CN 202011560609 A CN202011560609 A CN 202011560609A CN 112736888 A CN112736888 A CN 112736888A
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adaptive
current
sliding mode
controller
droop
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吕艳玲
崔皓璞
滕翀
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Harbin University of Science and Technology
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Harbin University of Science and Technology
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
    • H02J1/10—Parallel operation of dc sources
    • H02J1/102—Parallel operation of dc sources being switching converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators

Abstract

An improved self-adaptive droop control strategy of a direct current micro-grid based on sliding mode control belongs to the field of control of DC-DC converters. Step 1, establishing a state space model and a sliding mode control equation of sliding mode control; step 2, establishing a self-adaptive PI controller model, wherein one PI controller continuously adjusts a droop coefficient according to an instantaneous error to overcome the change of system parameters and loading conditions by adjusting a proportional coefficient and an integral gain; the other self-adaptive PI controller is specially used for a secondary control loop and adjusts the direct-current bus voltage of the microgrid by changing the down vertical line; and 3, the sliding mode control and the PI controller jointly form a direct-current micro-grid self-adaptive droop control system. The invention solves the problems of poor control performance and slow output response of the traditional control method due to the nonlinearity and the fixed droop coefficient of the system when the system parameters or the load of the direct current micro-grid are greatly changed in the traditional droop control.

Description

Sliding mode control-based improved self-adaptive droop control strategy for direct-current micro-grid
Technical Field
An improved self-adaptive droop control strategy of a direct current micro-grid based on sliding mode control belongs to the field of control of DC-DC converters.
Background
When the traditional droop control is applied to the direct-current power distribution network, disturbance or fault occurs, the stability of the direct-current power distribution network under voltage is poor in transient state due to nonlinearity and fixed droop coefficients of the system. The traditional droop control has the following defects: the droop coefficient is a fixed value determined by the capacity of the converter station, and when the system is disturbed, each converter station of the direct-current power distribution network adjusts active power output according to the original droop coefficient, so that the converter station with smaller power margin is easy to run in full load or overload, and the stability of the system is reduced.
Improvements to conventional droop control may better improve system stability. Therefore, an adaptive improved droop control strategy is provided, the method comprises the steps of using sliding mode control to simultaneously control the output voltage and the input current of each converter, and adjusting a droop coefficient through one of adaptive PI controllers to eliminate the current sharing error of each unit in the microgrid; and the other adaptive PI controller is specially used for a secondary control loop and adjusts the control strategy of the direct-current bus voltage of the microgrid by changing the down vertical line. The invention solves the problem that the traditional droop control method has poor control performance and slow output response due to the nonlinearity and fixed droop coefficient of the system when the system parameters or load of the direct current micro-grid change greatly.
Disclosure of Invention
In order to solve the technical problems, the invention provides an improved adaptive droop control strategy of a sliding mode control-based direct current microgrid, which is characterized in that: the method comprises the following steps:
step 1, establishing a state space model and a sliding mode control equation of sliding mode control;
step 2, establishing a self-adaptive PI controller model, wherein one PI controller overcomes the change of system parameters and loading conditions by continuously adjusting a proportional and integral gain adjustment droop coefficient according to an instantaneous error; the other self-adaptive PI controller is specially used for a secondary control loop and adjusts the direct-current bus voltage of the microgrid by changing the down vertical line;
and 3, the sliding mode control and the PI controller jointly form a direct-current micro-grid self-adaptive droop control system.
Further, the mathematical model of the DC-DC boost converter is:
Figure BDA0002859287910000011
Figure BDA0002859287910000012
in the formula, viAnd iiThe output voltage and the output current of the ith boost converter are respectively; i.e. iLIs the inductor current; e is the input electromotive force; u is a switching function.
Further, step 1 specifically includes:
step 1.1 the state space model is:
X1＝vref,i-vi
X2＝iref,L-iL
Figure BDA0002859287910000027
in the formula, Vref,iAnd iref,LRespectively representing the output voltage reference and the inductor current, X, of the ith converter1And X2Is a system state variable, and the system state matrices A, B (X) and D are:
Figure BDA0002859287910000021
Figure BDA0002859287910000022
Figure BDA0002859287910000023
step 1.2, selecting a slip form surface as follows: s ═ C1X1+C2X2＝CTX12
In the formula CT＝[C1C2]Is a sliding mode surface coefficient vector, and the equation describes a pathThe straight line of the origin, the sliding mode surface divides the plane into two regions, and each region has a specific opening and closing state to enable the system to track the sliding mode surface.
The error signal is allowed to be known by using the hysteresis characteristic, so that the sliding mode control equation is as follows:
Figure BDA0002859287910000024
in the formula, k is an allowable error.
Further, the existence condition of the sliding mode controller is as follows:
Figure BDA0002859287910000025
for simplicity, the presence condition can be expressed as:
Figure BDA0002859287910000026
further, droop techniques are used to set the voltage reference of the DC-DC converters according to the following equation to ensure that each converter shares power according to its rating.
vref,i＝vref-rd,iii
In the formula vrefIs the reference voltage at idle; disturbance, rd,iIs the droop resistance of the ith converter.
Further, the adaptive PI controller model may be represented as:
Figure BDA0002859287910000031
in the formula, KcIs a constant number, KpIs the proportional gain, KiIs the integral gain, e (t) is the error signal. The proportional gain and the integral gain are continuously adjusted according to the following formula:
Figure BDA0002859287910000032
Figure BDA0002859287910000033
in the formula, alpha1And alpha2Is a constant value and accelerates the response of the system by increasing the gain K.
Further, the sliding mode control and the PI controller form a dc microgrid adaptive droop control system, which can be described as:
vref,i＝vref-rd,iii+δvMG
Figure BDA0002859287910000034
in the formula, ev(t)＝vMG,ref–vMG，Kpv(t) and Kiv(t) proportional and integral gains, K, of the secondary side loop adaptive PI controller, respectivelycvIs a constant.
Calculating the current expected value of the ith converter
Figure BDA0002859287910000035
The following settings are set:
Figure BDA0002859287910000036
in the formula iMGIs the load current, Irated,iThe rated current of the ith converter is adopted, the droop resistor is required to be continuously adjusted in order to eliminate the error between the real current and the expected value, and the current sharing error of each converter is processed by the adaptive PI controller to adjust the value of the droop resistor according to the following rule.
Figure BDA0002859287910000041
rd,i＝VRi+rd,i,ols
In the formula (I), the compound is shown in the specification,
Figure BDA0002859287910000042
is the current sharing error of the ith converter, Kpi(t) and Kii(t) proportional and integral gains, respectively, of the current loop of the adaptive PI controller, KciIs a constant.
Compared with the prior art, the invention has the advantages that under the condition of steady-state operation, the stability is good and the error is small; a PI controller overcomes the variation of system parameters and loading conditions by continuously adjusting the proportional and integral gain adjustment droop coefficients according to instantaneous error; and the other adaptive PI controller is specially used for a secondary control loop and adjusts the direct-current bus voltage of the microgrid by changing the down vertical line. The invention solves the problems of poor control performance and slow output response of the traditional control method due to the nonlinearity and the fixed droop coefficient of the system when the system parameters or the load of the direct current micro-grid are greatly changed in the traditional droop control.
Drawings
Fig. 1 is a control block diagram of a self-adaptive control system for a direct-current microgrid provided by the invention;
FIG. 2 is an equivalent circuit diagram of a DC-DC boost converter;
FIG. 3 is a block diagram of an adaptive PI controller according to the present invention;
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without any creative efforts shall fall within the protection scope of the present invention.
As shown in fig. 1, it is a topology structure of the DC-DC boost converter of the present embodiment;
the improved adaptive droop control strategy of the sliding mode control-based direct-current microgrid of the embodiment is shown in the attached figure 2 and is characterized in that: the method comprises the following steps:
step 1, establishing a state space model and a sliding mode control equation of sliding mode control;
step 1.1 the state space model is:
X1＝vref,i-vi
X2＝iref,L-iL
Figure BDA0002859287910000043
in the formula, Vref,iAnd iref,LRespectively representing the output voltage reference and the inductor current, X, of the ith converter1And X2Is a system state variable, and the system state matrices A, B (X) and D are:
Figure BDA0002859287910000051
Figure BDA0002859287910000052
Figure BDA0002859287910000053
step 1.2, selecting a slip form surface as follows: s ═ C1X1+C2X2＝CTX12
In the formula, CT＝[C1C2]The system is a sliding mode surface coefficient vector, the equation describes a straight line passing through an origin, the sliding mode surface divides a plane into two regions, and each region has a specific opening and closing state so that the system tracks the sliding mode surface.
The error signal is allowed to be known by using the hysteresis characteristic, so that the sliding mode control equation is as follows:
Figure BDA0002859287910000054
in the formula, k is an allowable error.
Step 1.3, the existence condition of the sliding mode controller is as follows:
Figure BDA0002859287910000055
for simplicity, the presence condition can be expressed as:
Figure BDA0002859287910000056
step 1.4, the droop technique is used to set the voltage reference of the DC-DC converters according to the following equation to ensure that each converter shares power according to its rated value.
vref,i＝vref-rd,iii
In the formula vrefIs the reference voltage at idle; disturbance, rd,iIs the droop resistance of the ith converter.
Step 2, establishing a self-adaptive PI controller model, as shown in figure 3, wherein one PI controller overcomes the change of system parameters and loading conditions by continuously adjusting a proportional and integral gain adjustment droop coefficient according to an instantaneous error; and the other adaptive PI controller is specially used for a secondary control loop and adjusts the direct-current bus voltage of the microgrid by changing the down vertical line.
The adaptive PI controller model may be represented as:
Figure BDA0002859287910000061
in the formula, KcIs a constant number, KpIs the proportional gain, KiIs the integral gain, e (t) is the error signal. Proportional gain and integral gain rootContinuously adjusting according to the following formula:
Figure BDA0002859287910000062
Figure BDA0002859287910000063
in the formula, alpha1And alpha2Is a constant value and accelerates the response of the system by increasing the gain K.
Step 3, forming a direct current microgrid self-adaptive droop control system by the sliding mode control and the PI controller, wherein the self-adaptive droop system can be described as follows:
vref,i＝vref-rd,iii+δvMG
Figure BDA0002859287910000064
in the formula, ev(t)＝vMG,ref–vMG，Kpv(t) and Kiv(t) proportional and integral gains, K, of the secondary side loop adaptive PI controller, respectivelycvIs a constant.
Calculating the current expected value of the ith converter
Figure BDA0002859287910000065
The following settings are set:
Figure BDA0002859287910000066
in the formula iMGIs the load current, IratedAnd i is the rated current of the ith converter, the droop resistor is required to be continuously adjusted in order to eliminate the error between the real current and the expected value, and the current sharing error is processed by the adaptive PI controller to adjust the value of the droop resistor according to the following rule for each converter.
vref,i＝vref-rd,iii+δvMG
Figure BDA0002859287910000067
In the formula (I), the compound is shown in the specification,
Figure BDA0002859287910000068
is the current sharing error of the ith converter, Kpi(t) and Kii(t) proportional and integral gains, respectively, of the current loop of the adaptive PI controller, KciIs a constant.
The foregoing descriptions of embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and their practical applications, to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is, therefore, to be understood that the invention is intended to cover all modifications and equivalents within the scope of the following claims.

Claims (7)

1. An improved self-adaptive droop control strategy of a sliding mode voltage-based direct current micro-grid is characterized in that: the method comprises the following steps:
step 1, establishing a state space model and a sliding mode control equation of sliding mode control;
step 2, establishing a self-adaptive PI controller model, wherein one PI controller continuously adjusts a droop coefficient according to an instantaneous error to overcome the change of system parameters and loading conditions by adjusting a proportional coefficient and an integral gain; the other self-adaptive PI controller is specially used for a secondary control loop and adjusts the direct-current bus voltage of the microgrid by changing the down vertical line;
and 3, the sliding mode control and the PI controller jointly form a direct-current micro-grid self-adaptive droop control system.
2. The improved adaptive droop control strategy for the sliding-mode voltage-based direct-current micro-grid according to claim 1, is characterized in that: the mathematical model of the DC-DC boost converter is as follows:
Figure FDA0002859287900000011
Figure FDA0002859287900000012
in the formula, viAnd iiThe output voltage and the output current of the ith boost converter are respectively; i.e. iLIs the inductor current; e is the input electromotive force; u is a switching function.
3. The improved adaptive droop control strategy for the sliding-mode voltage-based direct-current micro-grid according to claim 1, is characterized in that: the step 1 specifically comprises the following steps:
step 1.1 the state space model is:
X1＝vref,i-vi
X2＝iref,L-iL
Figure FDA0002859287900000013
in the formula, Vref,iAnd iref,LRespectively representing the output voltage reference and the inductor current, X, of the ith converter1And X2Is a system state variable, and the system state matrices A, B (X) and D are:
Figure FDA0002859287900000014
Figure FDA0002859287900000015
Figure FDA0002859287900000016
step 1.2, selecting a slip form surface as follows: s ═ C1X1+C2X2＝CTX
In the formula CT＝[C1C2]Is a coefficient vector of the sliding mode surface, the equation describes a straight line passing through an origin, the sliding mode surface is divided into two regions by a plane, and each region has a specific opening and closing state to enable the system to track the sliding mode surface.
The error signal is allowed to be known by using the hysteresis characteristic, so that the sliding mode control equation is as follows:
Figure FDA0002859287900000021
where k is the allowable error.
4. The improved adaptive droop control strategy for the sliding-mode voltage-based direct-current micro-grid according to claim 1, is characterized in that: the existence condition of the sliding mode controller is as follows:
Figure FDA0002859287900000022
for simplicity, the presence condition can be expressed as:
Figure FDA0002859287900000023
5. the improved adaptive droop control strategy for the sliding-mode voltage-based direct-current micro-grid according to claim 1, is characterized in that:
droop techniques are used to set the voltage reference of the DC-DC converters according to the following equation to ensure that each converter shares power according to its rating.
vref,i＝vref-rd,iii
In the formula vrefIs the reference voltage at idle; disturbance, rd,iIs the droop resistance of the ith converter.
6. The improved adaptive droop control strategy for the sliding-mode voltage-based direct-current micro-grid according to claim 1, is characterized in that:
the adaptive PI controller model may be represented as:
Figure FDA0002859287900000024
in the formula, KcIs a constant number, KpIs the proportional gain, KiIs the integral gain, e (t) is the error signal. The proportional gain and the integral gain are continuously adjusted according to the following formula:
Figure FDA0002859287900000031
Figure FDA0002859287900000032
in the formula, alpha1And alpha2Is a constant value and accelerates the response of the system by increasing the gain K.
7. The improved adaptive droop control strategy for the sliding-mode voltage-based direct-current micro-grid according to claim 1, is characterized in that:
the sliding mode control and the PI controller form a direct-current microgrid self-adaptive droop control system, and the self-adaptive droop system can be described as follows:
vref,i＝vref-rd,iii+δvMG
Figure FDA0002859287900000033
in the formula, ev(t)＝vMG,ref–vMG，Kpv(t) and Kiv(t) proportional and integral gains, K, of the secondary side loop adaptive PI controller, respectivelycvIs a constant.
Calculating the current expected value of the ith converter
Figure FDA0002859287900000034
The following settings are set:
Figure FDA0002859287900000035
in the formula iMGIs the load current, Irated,iThe rated current of the ith converter is adopted, the droop resistor is required to be continuously adjusted in order to eliminate the error between the real current and the expected value, and the current sharing error of each converter is processed by the adaptive PI controller to adjust the value of the droop resistor according to the following rule.
Figure FDA0002859287900000036
rd,i＝ΔRi+rd,i,ols
In the formula (I), the compound is shown in the specification,
Figure FDA0002859287900000037
is the current sharing error of the ith converter, Kpi(t) and Kii(t) proportional and integral gains, respectively, of the current loop of the adaptive PI controller, KciIs a constant.
CN202011560609.6A 2020-12-25 2020-12-25 Sliding mode control-based improved self-adaptive droop control strategy for direct-current micro-grid Pending CN112736888A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113221064A (en) * 2021-05-12 2021-08-06 南方电网数字电网研究院有限公司 Model processing method, model processing device, computer equipment and storage medium

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113221064A (en) * 2021-05-12 2021-08-06 南方电网数字电网研究院有限公司 Model processing method, model processing device, computer equipment and storage medium

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Application publication date: 20210430