CN112421605A - Direct current micro-grid improved droop control method based on passive integration - Google Patents

Direct current micro-grid improved droop control method based on passive integration Download PDF

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CN112421605A
CN112421605A CN202011455920.4A CN202011455920A CN112421605A CN 112421605 A CN112421605 A CN 112421605A CN 202011455920 A CN202011455920 A CN 202011455920A CN 112421605 A CN112421605 A CN 112421605A
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converter
voltage
control
error
output
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CN112421605B (en
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韩杨
曾浩
赵恩盛
王丛岭
杨平
熊静琪
孙燕
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University of Electronic Science and Technology of China
Guangdong Electronic Information Engineering Research Institute of UESTC
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Guangdong Electronic Information Engineering Research Institute of UESTC
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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
    • 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
    • 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
    • H02J1/106—Parallel operation of dc sources for load balancing, symmetrisation, or sharing
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static 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
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0025—Arrangements for modifying reference values, feedback values or error values in the control loop of a converter

Abstract

The invention discloses a direct-current micro-grid variable droop coefficient control method based on passive integral control. Compared with the traditional droop control method, the improved droop control method has the advantages that the passive integral controller is selected for adjusting the capacitor voltage, the direct current bus voltage control and the output current sharing control are added, and the Constant Power Load (CPL) working condition can be well adapted. The method ensures that the voltage of the direct current bus is equal to the set original reference voltage through the reference voltage compensation quantity of the converter. According to the invention, the droop coefficient correction is obtained by outputting the current sharing error, the current non-sharing caused by different impedances of each line is eliminated, and a good current sharing effect can be achieved. Compared with other improved droop control methods, the droop control method has the advantages that system oscillation cannot occur under the condition of constant-power load, the adjusting speed is high, and the stable state can be quickly achieved.

Description

Direct current micro-grid improved droop control method based on passive integration
Technical Field
The invention belongs to the field of direct current micro-grid control of an electric power system, relates to an improved droop control method based on passive integral control, and particularly relates to a reference voltage compensation control and droop coefficient correction control method under a passive integral controller and a direct current micro-grid system with a Constant Power Load (CPL) and a resistive load controlled by applying the method.
Background
Along with the wider application of the microgrid in a new energy system, the research on the control method of the microgrid is also gradually deepened. The microgrid can be divided into an alternating current microgrid and a direct current microgrid. Compared with an alternating-current microgrid, the direct-current microgrid has the advantages of no reactive power balance problem, easiness in realizing access control of distributed renewable energy sources, low loss, high stability and the like, and is concerned. The load conditions of the direct current microgrid are various, wherein due to the fact that the incremental impedance of the CPL presents a negative impedance characteristic, the stability and the dynamic characteristic of the system are affected. How to control and realize current equalization and bus voltage control under constant power load is a key research point.
In the direct-current microgrid control, the droop control is widely used. Droop control is simple and easy to realize, and can be realized only by capacitance voltage feedback and output current feedback of each topology. The control reduces communication, improves stability, reduces cost and is very suitable for a direct current micro-grid. However, conventional droop control uses a fixed droop coefficient and a reference voltage, and there is typically variability in line impedance. This results in no way for conventional droop control to ensure current proportioning while ensuring bus voltage control. Bus voltage control and output current equal-division control become a pair of inherent contradictions. To resolve this conflict, some improved droop control has been proposed. The application publication No. CN110323735A patent describes a method of improved droop control with bus voltage recovery. The resistance information of the active measurement line is utilized, and the voltage recovery unit is introduced, so that the defect of the traditional droop control is overcome. The method has simple control idea and is easy to realize, but when the scale of the direct current microgrid reaches a certain degree, impedance measurement has certain difficulty. Also, the complex communication required to measure the impedance can affect the stability of the system.
The general improved droop control is not ideal for controlling the CPL operating condition, and the system may be unstable when the constant power load varies. Therefore, there is a need to develop an adaptive control method that can better adapt to a constant power load and can simultaneously achieve better bus voltage control accuracy and output current sharing effect.
Disclosure of Invention
The invention aims to achieve the following aims: firstly, two direct current boost converters are connected in parallel to a direct current bus, and the voltage of the direct current bus is ensured to be equal to a reference voltage value; correcting the droop coefficient to realize current sharing under different line impedances; and thirdly, when the load is a Constant Power Load (CPL), the bus voltage can still be stabilized and an ideal current sharing effect can be achieved after the load is adjusted for a period of time after jumping.
The purpose of the invention is realized by the following technical scheme: the direct-current microgrid consists of 2 boost converters. The 2 BOOST converters are named as a #1 converter and a #2 converter respectively, the circuit parameters of the two converters are the same, but the line impedance of the output end is different. The load is connected into a resistive load or a constant power load in parallel with the direct current bus, and can be switched into the resistive load or the constant power load through two switches.
Further, the control of the converter #1 and the converter #2 is mainly divided into three parts. The first part is the compensation of reference voltage, the second part is the correction of droop coefficient, and the third part is the passive integral control of capacitor voltage.
Further, the control strategy of the present invention can be divided into the following steps:
s1, completing the collection of the electric quantity and obtaining the bus voltage ubusThen the set reference voltage value urefComparing, and obtaining the voltage control error u by differenceerror；
S2, obtaining the voltage control deviation u from the step S1errorAnd sending the signals to a PI controller. The #1 converter and the #2 converter respectively adopt two different PI controllers, and the two controllers input the same control error voltage and output different control quantities. #1 converter obtains the reference voltage offset Δ u1Compensating the reference voltage by an amount Δ u1And the original reference voltage value urefSumming to obtain a new reference voltage value uref1. Similarly, the #2 converter obtains the reference voltage compensation amount delta u through the PI controller2Compensating the reference voltage by an amount Δ u2And the original reference voltage value urefSumming to obtain a new reference voltage value uref2；
S3, for the converter #1, the droop coefficient is kept constant K, and the output current i of the converter #1 is adjusted1Multiplying by the droop coefficient K to obtain drop1Then drop1New voltage reference vector u obtained in step S2ref1Obtaining a new capacitance voltage reference value u of the #1 converter by difference1 *. Then u will be obtained1 *Minus the feedback value u of the capacitor voltage1Obtaining a capacitor voltage control error uc_error_1. The expression of the capacitance voltage control error of the #1 converter and the #2 converter is shown as the formula (1);
Figure BDA0002828322550000021
s4, calculating the capacitance voltage control error u of the #2 converter according to the formula (1)c_error_2. The droop coefficient K of the #2 converter needs a correction quantity delta K, and the output current i of the #2 converter is adjusted2Multiplying the sum K of the droop coefficient K and the correction quantity delta K2To obtain a drop2Then drop2New voltage reference value u obtained in step S2ref2Obtaining a new #2 converter capacitor voltage reference value u by difference2 *. Wherein correction quantity delta K is output current i according to #1 converter and #2 converter1、i2Difference i oferrorAnd (4) obtaining an output result through a PI controller. Using the obtained u2 *Subtracting the feedback value u of the capacitor voltage2Obtaining a capacitor voltage control error uc_error_2；
S5, converting u obtained in the step S3 into uc_error_1And #1 converter capacitor voltage u1Inductor current iL1Input DC voltage value Vdc1As the input quantity of the passive integral controller, the output quantity d of the controller is obtained after passing through the passive integral controller1Then d is1Sending the signal into a triangular wave comparator for PWM modulation to obtain a control signal PWM of a switching tube of the #1 converter1. Similarly, u obtained in step S4c_error_2And #2 converter capacitor voltage u2Inductor current iL2Input DC voltage value Vdc2As the input quantity of the passive integral controller, the output quantity d of the controller is obtained after passing through the passive integral controller2Then d is2Sending the signal into a triangular wave comparator for PWM modulation to obtain a control signal PWM of a switching tube of a #2 converter2。
Further, the passive integral controller in step S5 includes the following steps:
s51, for a non-linear single-signal input single-signal output system (SISO) Boost circuit, the system can be expressed as:
Figure BDA0002828322550000031
wherein the content of the first and second substances,
Figure BDA0002828322550000032
is the differential of a 2-dimensional column state vector, the state variables of which comprise the inductive current and the capacitive voltage; y and h (x) represent the output function, with y1、y2Represents the output function of the #1 and #2 converters; the function u is a switching function, and when the switching frequency is sufficiently high, the function u can be used in step S5Continuous quantity d1、d2Represents; f (x) is called vector field, g (x) is an n × p matrix vector field.
S52, selecting a suitable storage function v (x) for the BOOST system determined in step S51, so that the system satisfies the following condition, that is, the system is a passive system;
Figure BDA0002828322550000033
s53, selecting storage function V of #1 converter and #2 converter1(x)、V2(x) So that the following relation is satisfied, namely a passive condition is achieved:
Figure BDA0002828322550000034
wherein v ise、ieThe balance point capacitor output voltage and the inductive current of the converter are respectively, and the v of the #1 converter and the v of the #2 converter are the same due to the same circuit parameterseAnd ieAs such. k represents a constant, deAnd deThe' expression is the equilibrium point duty cycle, the sum of which is 1. z is a radical of1And z2Respectively representing the control error uc_error_1And control error uc_error_2Is calculated. L is1、L2Representing the inductance of the dc converter and R the equivalent resistance of the load.
S54 selecting output function y of converter #1 and converter #21、y2：
Figure BDA0002828322550000041
S55, multiplying the output function in the step S54 by d1、d2The obtained result is compared with the formula (4) in step S53. It can be said that the system satisfies the passive condition (3) in step S52. Then, the control law of the #1 converter and the #2 converter is obtained:
Figure BDA0002828322550000042
wherein phimaxIs a constant.
The invention has the beneficial effects that:
according to the improved droop control of the direct current micro-grid based on the passive integral control, a control error is obtained by comparing the output voltage of each topology with the voltage of the direct current bus, PI control is carried out to obtain a reference voltage compensation quantity, the voltage values of output capacitors of all converters are guaranteed to be larger than or equal to the original reference voltage, and the voltage of the direct current bus is guaranteed to be equal to the set original reference voltage.
According to the invention, the droop coefficient correction quantity delta K is obtained by utilizing the control error obtained by the output current of each direct current converter through the PI controller. Therefore, the droop coefficients of the direct current converters are different, the current unequal caused by different line impedances is eliminated, and a good current equal-dividing effect can be achieved.
Compared with other improved droop control methods, the method has the advantages that the load jump working condition under the constant-power load condition is high in adjusting speed, short in required adjusting time and capable of quickly achieving a stable state, and system oscillation cannot occur.
Drawings
FIG. 1 is a schematic diagram of a main circuit topology and a control flow thereof according to an embodiment of the present invention;
FIG. 2 is a block diagram of the passive modeling and control method according to an embodiment of the present invention;
fig. 3 is a voltage waveform diagram of a dc bus before and after resistive load jumps in the PLECS simulation according to the embodiment of the present invention;
FIG. 4 is a waveform diagram of output current of a DC converter before and after resistive load jump in PLECS simulation according to an embodiment of the present invention;
fig. 5 is a voltage waveform diagram of the dc bus before and after CPL jumps in the PLECS simulation according to the embodiment of the present invention;
FIG. 6 is a waveform diagram of output current of the DC converter before and after CPL jump in PLECS simulation according to the embodiment of the present invention;
Detailed Description
The technical scheme of the invention is further explained by combining the attached drawings.
As shown in fig. 1, the dc microgrid system is composed of 2 boost converters. The 2 BOOST converters are named as a #1 converter and a #2 converter respectively, the circuit parameters of the two converters are the same, but the line impedance of the output end is different. The load is connected into a resistive load or a constant power load in parallel with the direct current bus, and can be switched into the resistive load or the constant power load through two switches.
Further, the control of the converter #1 and the converter #2 is mainly divided into three parts. The first part is the compensation of reference voltage, the second part is the correction of droop coefficient, and the third part is the passive integral control of capacitor voltage.
As shown in fig. 2, a modeling and control process for droop control based on passive integral control is shown. The transfer relationships of the variables are illustrated.
Further, the control strategy of the present invention can be divided into the following steps:
s1, completing the collection of the electric quantity and obtaining the bus voltage ubusThen the set reference voltage value urefComparing, and obtaining the voltage control error u by differenceerror；
S2, obtaining the voltage control deviation u from the step S1errorAnd sending the signals to a PI controller. The #1 converter and the #2 converter respectively adopt two different PI controllers, and the two controllers input the same control error voltage and output different control quantities. #1 converter obtains the reference voltage offset Δ u1Compensating the reference voltage by an amount Δ u1And the original reference voltage value urefSumming to obtain a new reference voltage value uref1. Similarly, the #2 converter obtains the reference voltage compensation amount delta u through the PI controller2Compensating the reference voltage by an amount Δ u2And the original reference voltage value urefSumming to obtain a new reference voltage value uref2；
S3, for the #1 converter, the droop coefficient is kept constant with KThe output current i of the #1 converter1Multiplying by the droop coefficient K to obtain drop1Then drop1New voltage reference vector u obtained in step S2ref1Obtaining a new capacitance voltage reference value u of the #1 converter by difference1 *. Then u will be obtained1 *Minus the feedback value u of the capacitor voltage1Obtaining a capacitor voltage control error uc_error_1. The expression of the capacitance voltage control error of the #1 converter and the #2 converter is shown as the formula (1);
Figure BDA0002828322550000061
s4, calculating the capacitance voltage control error u of the #2 converter according to the formula (1)c_error_2. The droop coefficient K of the #2 converter needs a correction quantity delta K, and the output current i of the #2 converter is adjusted2Multiplying the sum K of the droop coefficient K and the correction quantity delta K2To obtain a drop2Then drop2New voltage reference value u obtained in step S2ref2Obtaining a new #2 converter capacitor voltage reference value u by difference2 *. Wherein correction quantity delta K is output current i according to #1 converter and #2 converter1、i2Difference i oferrorAnd (4) obtaining an output result through a PI controller. Using the obtained u2 *Subtracting the feedback value u of the capacitor voltage2Obtaining a capacitor voltage control error uc_error_2；
S5, converting u obtained in the step S3 into uc_error_1And #1 converter capacitor voltage u1Inductor current iL1Input DC voltage value Vdc1As the input quantity of the passive integral controller, the output quantity d of the controller is obtained after passing through the passive integral controller1Then d is1Sending the signal into a triangular wave comparator for PWM modulation to obtain a control signal PWM of a switching tube of the #1 converter1. Similarly, u obtained in step S4c_error_2And #2 converter capacitor voltage u2Inductor current iL2Input DC voltage value Vdc2As input for a passive integral controller viaObtaining controller output d after passing through passive integral controller2Then d is2Sending the signal into a triangular wave comparator for PWM modulation to obtain a control signal PWM of a switching tube of a #2 converter2。
Further, the passive integral controller in step S5 includes the following steps:
s51, for a non-linear single-signal input single-signal output system (SISO) Boost circuit, the system can be expressed as:
Figure BDA0002828322550000062
wherein the content of the first and second substances,
Figure BDA0002828322550000063
is the differential of a 2-dimensional column state vector, the state variables of which comprise the inductive current and the capacitive voltage; y and h (x) represent the output function, with y1、y2Represents the output function of the #1 and #2 converters; the function u is a switching function, and when the switching frequency is sufficiently high, the continuous quantity d in step S5 can be used1、d2Represents; f (x) is called vector field, g (x) is an n × p matrix vector field.
S52, selecting a suitable storage function v (x) for the BOOST system determined in step S51, so that the system satisfies the following condition, that is, the system is a passive system;
Figure BDA0002828322550000064
s53, selecting storage function V of #1 converter and #2 converter1(x)、V2(x) So that the following relation is satisfied, namely a passive condition is achieved:
Figure BDA0002828322550000071
wherein v ise、ieBalance point capacitance output power of converterVoltage and inductor current, v for the #1 converter and the #2 converter, due to the same circuit parameterseAnd ieAs such. k represents a constant, deAnd deThe' expression is the equilibrium point duty cycle, the sum of which is 1. z is a radical of1And z2Respectively representing the control error uc_error_1And control error uc_error_2Is calculated. L is1、L2Representing the inductance of the dc converter and R the equivalent resistance of the load.
S54 selecting output function y of converter #1 and converter #21、y2：
Figure BDA0002828322550000072
S55, multiplying the output function in the step S54 by d1、d2The obtained result is compared with the formula (4) in step S53. It can be said that the system satisfies the passive condition (3) in step S52. Then, the control law of the #1 converter and the #2 converter is obtained:
Figure BDA0002828322550000073
wherein phimaxIs a constant.
The invention has the beneficial effects that:
according to the improved droop control of the direct current micro-grid based on the passive integral control, a control error is obtained by comparing the output voltage of each topology with the voltage of the direct current bus, PI control is carried out to obtain a reference voltage compensation quantity, the voltage values of output capacitors of all converters are guaranteed to be larger than or equal to the original reference voltage, and the voltage of the direct current bus is guaranteed to be equal to the set original reference voltage.
According to the invention, the droop coefficient correction quantity delta K is obtained by utilizing the control error obtained by the output current of each direct current converter through the PI controller. Therefore, the droop coefficients of the direct current converters are different, the current unequal caused by different line impedances is eliminated, and a good current equal-dividing effect can be achieved.
Compared with other improved droop control methods, the method has the advantages that the load jump working condition under the constant-power load condition is high in adjusting speed, short in required adjusting time and capable of quickly achieving a stable state, and system oscillation cannot occur.
In order to verify the feasibility of the proposed passive integral control-based direct current microgrid for improving droop control, a direct current microgrid simulation model containing two BOOST converters is built in a PLECS simulation environment. And a comparison test is carried out to compare the difference of the control effect of improving the droop control under the passive integral control and the PI control. The first BOOST converter input voltage is 12V and the second BOOST converter input voltage is 12V. The inductances of the first BOOST converter and the second BOOST converter are both 200 muH, L1＝L2The output capacitance of the first BOOST converter and the second BOOST converter is 200 muF, i.e. C, 200 muH1＝C2200 μ F. The line resistance of the first BOOST converter is 2.5 Ω and the line resistance of the second BOOST converter is 1 Ω. The load selection resistive load jumps from 10 Ω to 5 Ω and then back to 10 Ω. If the load selects a constant power load, the power will jump from 57.6W to 115.2W and then back to 57.6W. The voltage reference is set to 24V.
Fig. 3 shows a dc bus voltage waveform of the dc microgrid system before and after a resistive load jump. The input dc voltage is kept constant at 12V and the load changes from 10 Ω to 5 Ω and back to 10 Ω. Under two load conditions, the bus voltage can reach the target set value of 24V after a certain adjusting time, and the steady-state error is zero. However, compared with waveforms under PI control and passive integral control, the improved droop control under the passive integral control has more outstanding dynamic performance, does not have large voltage drop and voltage rise, and can recover to reset the set direct-current bus voltage after a certain adjusting time.
Fig. 4 shows the output current waveform of the converter before and after the resistive load jump of the direct-current micro-grid system. FIG. 4(a) shows DC converter output current for improved droop control based on PI control; fig. 4(b) shows the dc converter output current based on the improved droop control of passive integration. The input dc voltage is held constant at 12V, and the load changes from 10 Ω to 5 Ω at 0.4s, and then back to 10 Ω at 0.8 s. Under both load conditions, it can be seen that the improved droop control can achieve a good current sharing effect. The output current of the #1 converter and the output current of the #2 converter can reach the current sharing effect of 1:1 faster than the output current of the converter after the load jumps.
Fig. 5 shows the voltage waveform of the direct-current bus of the direct-current microgrid system before and after the CPL jump condition. The input dc voltage is held constant at 12V, the load is changed from 57.6W to 115.2W at 0.4s and then back to 57.6W at 1.4 s. Compared with the bus voltage waveform of the improved droop control under the PI control and the passive integral control, the improved droop control under the PI control cannot maintain the constant voltage of the direct current bus after the CPL jumps, and the voltage of the direct current bus is in constant amplitude oscillation. The improved droop control based on the passive integral control can recover the direct current bus voltage to 24V after a certain adjusting time, so that the steady-state error is zero.
Fig. 6 shows output current waveforms of the dc converters before and after CPL jump of the dc microgrid system. FIG. 6(a) shows DC converter output current for improved droop control based on PI control; fig. 6(b) shows the dc converter output current for improved droop control based on passive integration. The input dc voltage is held constant at 12V, the load is changed from 57.6W to 115.2W at 0.4s and then back to 57.6W at 1.4 s. Compared with the output current waveform of the direct current converter with improved droop control under PI control and passive integral control, the improved droop control under PI control cannot maintain the output current after CPL jumps, and the output currents of the #1 converter and the #2 converter show constant amplitude oscillation. The improved droop control based on the passive integral control can achieve a good current sharing effect after a certain adjusting time, and the output current ratio is 1: 1.
The simulation and comparison results fully show that the improved droop control based on the passive integral control provided by the method has feasibility, and has good direct-current bus voltage control precision and current sharing effect of the output current of the converter under the CPL jump. The method for obtaining the reference voltage compensation value by utilizing the reference voltage and the direct current bus voltage control error in a self-adaptive mode can control the direct current bus voltage, and the direct current bus voltage is equal to the set reference voltage. The problem of voltage drop caused by the traditional droop control is solved; the method for obtaining the control error and further obtaining the droop coefficient correction by utilizing the output current of the converter can achieve a good current equalizing effect, realize 1:1 distribution of current and eliminate the adverse effect of line impedance on current distribution.
It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention, and it is to be understood that the scope of the invention is not to be limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the teachings of the present invention without departing from the spirit and scope of the invention.

Claims (2)

1. A DC microgrid is composed of 2 boost converters. The 2 BOOST converters are named as a #1 converter and a #2 converter respectively, the circuit parameters of the two converters are the same, but the line impedance of the output end is different. The load is connected into a resistive load or a constant power load in parallel with the direct current bus, and can be switched into the resistive load or the constant power load through two switches.
2. The control of the converter #1 and the converter #2 is mainly divided into three parts. The first part is the compensation of reference voltage, the second part is the correction of droop coefficient, and the third part is the passive integral control of capacitor voltage. When the load selects the constant power load, the control strategy needs to achieve a better control effect, and output oscillation cannot occur, and the control strategy of the invention can be divided into the following steps:
s1, completing the collection of the electric quantity and obtaining the bus voltage ubusThen the set reference voltage value urefComparing, and obtaining the voltage control error u by differenceerror；
S2, obtaining the voltage control deviation u from the step S1errorAnd sending the signals to a PI controller. The #1 converter and the #2 converter respectively adopt two different PI controllers, and the two controllers input the same control error voltage and output different control quantities. #1 converter obtains the reference voltage offset Δ u1Compensating the reference voltage by an amount Δ u1And the original reference voltage value urefSumming to obtain a new reference voltage value uref1. Similarly, the #2 converter obtains the reference voltage compensation amount delta u through the PI controller2Compensating the reference voltage by an amount Δ u2And the original reference voltage value urefSumming to obtain a new reference voltage value uref2；
S3, for the converter #1, the droop coefficient is kept constant K, and the output current i of the converter #1 is adjusted1Multiplying by the droop coefficient K to obtain drop1Then drop1New voltage reference vector u obtained in step S2ref1Obtaining a new capacitance voltage reference value u of the #1 converter by difference1 *. Then u will be obtained1 *Minus the feedback value u of the capacitor voltage1Obtaining a capacitor voltage control error uc_error_1. The expression of the capacitance voltage control error of the #1 converter and the #2 converter is shown as the formula (1);
Figure FDA0002828322540000011
s4, calculating the capacitance voltage control error u of the #2 converter according to the formula (1)c_error_2. The droop coefficient K of the #2 converter needs a correction quantity delta K, and the output current i of the #2 converter is adjusted2Multiplying the sum K of the droop coefficient K and the correction quantity delta K2To obtain a drop2Then drop2New voltage reference value u obtained in step S2ref2Obtaining a new #2 converter capacitor voltage reference value u by difference2 *. Wherein correction quantity delta K is output current i according to #1 converter and #2 converter1、i2Difference i oferrorAnd (4) obtaining an output result through a PI controller. Using the obtained u2 *Subtracting the feedback value u of the capacitor voltage2Obtain a capacitorPressure control error uc_error_2；
S5, converting u obtained in the step S3 into uc_error_1And #1 converter capacitor voltage u1Inductor current iL1Input DC voltage value Vdc1As the input quantity of the passive integral controller, the output quantity d of the controller is obtained after passing through the passive integral controller1Then d is1Sending the signal into a triangular wave comparator for PWM modulation to obtain a control signal PWM of a switching tube of the #1 converter1. Similarly, u obtained in step S4c_error_2And #2 converter capacitor voltage u2Inductor current iL2Input DC voltage value Vdc2As the input quantity of the passive integral controller, the output quantity d of the controller is obtained after passing through the passive integral controller2Then d is2Sending the signal into a triangular wave comparator for PWM modulation to obtain a control signal PWM of a switching tube of a #2 converter2。
Further, the passive integral controller in step S5 includes the following steps:
s51, for a non-linear single-signal input single-signal output system (SISO) Boost circuit, the system can be expressed as:
Figure FDA0002828322540000021
wherein the content of the first and second substances,
Figure FDA0002828322540000024
is the differential of a 2-dimensional column state vector, the state variables of which comprise the inductive current and the capacitive voltage; y and h (x) represent the output function, with y1、y2Represents the output function of the #1 and #2 converters; the function u is a switching function, and when the switching frequency is sufficiently high, the continuous quantity d in step S5 can be used1、d2Represents; f (x) is called vector field, g (x) is an n × p matrix vector field.
S52, selecting a suitable storage function v (x) for the BOOST system determined in step S51, so that the system satisfies the following condition, that is, the system is a passive system;
Figure FDA0002828322540000022
s53, selecting storage function V of #1 converter and #2 converter1(x)、V2(x) So that the following relation is satisfied, namely a passive condition is achieved:
Figure FDA0002828322540000023
wherein v ise、ieThe balance point capacitor output voltage and the inductive current of the converter are respectively, and the v of the #1 converter and the v of the #2 converter are the same due to the same circuit parameterseAnd ieAs such. k represents a constant, deAnd deThe' expression is the equilibrium point duty cycle, the sum of which is 1. z is a radical of1And z2Respectively representing the control error uc_error_1And control error uc_error_2Is calculated. L is1、L2Representing the inductance of the dc converter and R the equivalent resistance of the load.
S54 selecting output function y of converter #1 and converter #21、y2：
Figure FDA0002828322540000031
S55, multiplying the output function in the step S54 by d1、d2The obtained result is compared with the formula (4) in step S53. It can be said that the system satisfies the passive condition (3) in step S52. Then, the control law of the #1 converter and the #2 converter is obtained:
Figure FDA0002828322540000032
wherein phimaxIs oneA constant.
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