CN113937800A - Nonlinear load current compensation control method and device based on flywheel energy storage - Google Patents

Nonlinear load current compensation control method and device based on flywheel energy storage Download PDF

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Publication number
CN113937800A
CN113937800A CN202111070683.4A CN202111070683A CN113937800A CN 113937800 A CN113937800 A CN 113937800A CN 202111070683 A CN202111070683 A CN 202111070683A CN 113937800 A CN113937800 A CN 113937800A
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current
flywheel
mode
compensation
charge
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CN113937800B (en
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杨春来
杨鹏
袁晓磊
殷喆
李剑锋
王艳
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State Grid Corp of China SGCC
Electric Power Research Institute of State Grid Hebei Electric Power Co Ltd
State Grid Hebei Energy Technology Service Co Ltd
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State Grid Corp of China SGCC
Electric Power Research Institute of State Grid Hebei Electric Power Co Ltd
State Grid Hebei Energy Technology Service Co Ltd
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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
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/28—Arrangements for balancing of the load in a network by storage of energy
    • H02J3/30—Arrangements for balancing of the load in a network by storage of energy using dynamo-electric machines coupled to flywheels
    • 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
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • 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
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • 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
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
    • H02M7/68—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters
    • H02M7/72—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/79—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal 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
    • H02M7/797—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/20—Active power filtering [APF]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/16—Mechanical energy storage, e.g. flywheels or pressurised fluids

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  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)
  • Inverter Devices (AREA)

Abstract

The invention discloses a nonlinear load current compensation control method and a nonlinear load current compensation control device based on flywheel energy storage, wherein the control method realizes the conversion between electric energy and mechanical energy through the charging and discharging processes of a flywheel energy storage device; in the energy conversion process, a main circuit switching tube is driven and controlled by PWM (pulse width modulation), the current of the device is controlled, harmonic current is compensated, and fundamental active current with certain amplitude is injected or absorbed into a power grid; the compensated current is a sinusoidal current which is in phase with the load fundamental wave active current, and the amplitude is smaller than or larger than the load fundamental wave active current. Real-time and dynamic compensation of the nonlinear load current is realized, each harmonic can be eliminated dynamically, and the current waveform is improved; the method has wider voltage and power adaptation range, avoids frequent switching of the main circuit between the inverter and the rectifier, and solves the problems of strong harmonic compensation capability limitation, small voltage and power adaptation range and low overall service life of a main circuit switching tube in the existing method.

Description

Nonlinear load current compensation control method and device based on flywheel energy storage
Technical Field
The invention relates to a nonlinear load current compensation control method and device based on flywheel energy storage, and belongs to the technical field of energy storage technology application.
Background
A large number of nonlinear loads exist in industrial and commercial users, such as a rolling mill, an electric welding machine, an elevator and an electric locomotive, and the loads generate a large number of harmonic waves during operation, so that the pollution to a power grid is caused, the electric energy loss is increased, the power supply reliability is reduced, and the normal and safe operation of the power grid and equipment is seriously influenced.
The conventional harmonic suppression method is often implemented by using an LC filter or an Active Power Filter (APF). The LC filter can inhibit harmonic waves and compensate reactive power, but the compensation characteristic of the LC filter is easily influenced by the impedance and the running state of a power grid, parallel resonance is easily generated between the LC filter and a system, harmonic amplification is further caused, and the LC tuned filter is easily overloaded and even burnt out. In addition, the LC filter can compensate only the fixed frequency harmonics and the compensation effect is not ideal. The LC tuned filter is still widely used due to its simple structure, low cost and easy setup.
An Active Power Filter (APF) is a new type of power electronic device for dynamically suppressing harmonics and compensating reactive power, which can compensate for harmonics that vary in magnitude and frequency, dynamically eliminate harmonics, and do not generate resonance. However, the filter is not suitable for occasions with high voltage, high frequency and high power, the pass band range is limited by the bandwidth of an active device, the direct current side capacitor is limited by withstand voltage, and a high capacitance value is difficult to achieve, so that the magnitude of the direct current side voltage amplitude Uc is limited, the change amplitude and the energy exchange magnitude of the Uc are influenced, the compensation of large-amplitude harmonic current is difficult to achieve, and the compensation capability of an active power filter and the adaptive range of voltage and power are influenced. In addition, when the harmonic current is compensated, energy exchange exists between the APF direct current side and the power grid, so that the main circuit needs to continuously switch between two working modes of the inverter and the rectifier at a high speed, the service life of a switching tube is shortened, and the system loss is increased.
Disclosure of Invention
The invention aims to solve the technical problem of providing a nonlinear load current compensation control method and a device based on flywheel energy storage, realizing real-time and dynamic compensation of nonlinear load current, dynamically eliminating each subharmonic and improving current waveform; the method has wider voltage and power adaptation range, avoids frequent switching of the main circuit between the inverter and the rectifier, and solves the problems of strong harmonic compensation capability limitation, small voltage and power adaptation range and low overall service life of a main circuit switching tube in the existing method.
In order to solve the problems, the technical scheme adopted by the invention is as follows:
a nonlinear load current compensation control method based on flywheel energy storage realizes the conversion between electric energy and mechanical energy through the charging and discharging process of a flywheel energy storage device; in the energy conversion process, the controller drives and controls a main circuit switching tube by utilizing PWM (pulse-width modulation), so that the current of the device is controlled, the current which has the same amplitude and the opposite direction with the harmonic current is superposed into the charging or discharging current, and the fundamental wave active current with certain amplitude is injected or absorbed into a power grid while the harmonic current is compensated; the compensated current is a sinusoidal current which is in phase with the load fundamental wave active current, and the amplitude is smaller than or larger than the load fundamental wave active current.
The control method is further improved, and specifically comprises the following steps:
step S1, initializing system parameters, presetting the working mode of the compensation device as a charging mode, and sending a signal for synchronously entering the charging mode to the bidirectional DC/DC converter and the bidirectional inverter by the main controller;
step S2, acquiring the SOC value of the flywheel energy storage devicenow；
Step S3, judging the state of charge SOC of the flywheel energy storage devicenowWhether greater than the minimum SOCLlimitIf SOC isnowLess than SOCLlimitThen return to step S2;
step S4, collecting a load current value and a power grid voltage value, and calculating a harmonic current value; real-time collection of load side grid voltage ULLoad current ILCalculating the load fundamental current I based on the instantaneous reactive power theoryLfAnd load harmonic current ILhAnd calculating the total distortion rate THD of the harmonic currenti；
Step S5, collecting the DC side voltage U of the energy conversion main circuitd；
Step S6, judging the current compensation device working mode, and according to the current state of charge SOC of the flywheelnowDetermining whether mode switching is needed or not by combining with the working mode of the compensation device in the previous scanning period, and updating the working mode to a new working mode if the mode switching is needed;
step S7, sending a synchronous working mode instruction, sending a synchronous charging mode entering signal to the bidirectional DC/DC converter and the bidirectional inverter by the main controller, and sending a synchronous charging mode entering signal to the bidirectional DC/DC converter and the bidirectional inverter by the main controller;
step S8, judging whether the working modes are synchronous, collecting the working mode states of the bidirectional DC/DC converter and the bidirectional inverter, and returning to the step S7 if the working modes are different;
step S9, calculating the output current target value I of the compensating device* O；
Step S10, according to the output current target value I* OAnd output current actualValue IOCarrying out current tracking control;
step S11, controlling and outputting the actual compensation current IO。
In a further improvement of the control method, in step S4, the calculation formula for compensating all harmonic currents is as follows:
ILh＝IL-ILf
THDi＝ILh/IL。
in step S6, the operation mode determination process of the compensation device is as follows: according to the current state of charge (SOC) of the flywheelnowAnd determining whether mode switching is needed or not by combining the working mode of the compensation device in the last scanning period, and updating the working mode to a new working mode if the mode switching is needed.
The control method is further improved, and the working state of the compensation device is divided into three working modes, namely a charging mode, a discharging mode and a standby mode;
in a charging mode, the flywheel absorbs energy from a power grid through an energy conversion circuit, and compensates a harmonic current part in load current by controlling charging current waveform on the basis of increasing fundamental active current, so that the current of a compensation device and the current of the load after superposition are in a sine waveform;
in a discharging mode, the flywheel releases energy to a power grid through an energy conversion circuit, and a harmonic current part in a load current is compensated by controlling a discharging current waveform on the basis of outputting a certain amount of fundamental wave active current to the power grid, so that the current obtained by superposing the current of a compensation device and the load current is in a sine waveform, and the energy of the current comes from the energy stored in the flywheel; in the standby mode, no energy is exchanged between the flywheel and the power grid, and only self energy consumption is maintained.
The control method is further improved, and the compensating device adopts the charge state of a flywheel and the DC/DC converter to output the voltage U on the DC sidedThe mode that control combined together carries out the mode judgement, sets up 2 SOC nodes according to the start and stop state of charging and discharging: SOCL、SOCHWherein SOC isLlimit<SOCL<SOCH。
The control method is further improved, and the working mode switching control logic of the compensation device is as follows:
1) when the calculated total distortion rate THD of the harmonic currentiLess than or equal to THDpermitAt the moment, the state of charge of the energy stored by the flywheel is not lower than SOCLEntering the standby mode, and returning to step S2 of the control method;
2) when the state of charge of flywheel energy storage is lower than SOCLWhen the flywheel is charged, the compensation device enters a charging mode until the state of charge of the flywheel rises to be higher than the SOCHWhen the charging mode is finished, entering a discharging mode;
3) when THD is presentiGreater than THDpermitWhen the state of charge of flywheel energy storage is higher than SOCHWhen the flywheel is in the SOC state, the compensation device enters a discharging mode until the state of charge of the flywheel is reduced to be lower than the SOCLAnd then, ending the discharging mode and entering the charging mode.
4) When THD is presentiGreater than THDpermitWhen the energy is converted to the DC side U of the main circuit in the discharging moded<UdLIf the compensating device does not enter the charging mode, the charging mode is directly entered to compensate the energy of the flywheel until the U rises to the Ud>UdL+△UdTime and flywheel state of charge above SOCHAnd then, ending the charging mode and entering the discharging mode. U shapedLIndicates the voltage lower limit value,. DELTA.U, of the DC side of the main circuit for energy conversiondIndicating the dc side voltage control hysteresis offset.
Further development of the control method, in step S9, the compensating device outputs a current I* OIs formed by superposing two parts, namely harmonic compensation output current Ic，IcAnd load harmonic current ILhThe amplitudes are equal in size and opposite in direction, and the fundamental wave active current I required by the charging or discharging of the flywheel energy storage device is outputb. Calculating a target value I of the output current according to the current working mode of the compensating device* O：
I* O＝Ic+Ib；
In the charging mode, the compensating device draws energy from the grid, I* OThe calculation formula is as follows:
I* O＝Ic+Ib-charge
Ib-chargethe charging current I being rated by the compensating devicer-chargeAnd harmonic compensation output current IcDetermination of Ib-chargeSatisfies the following constraints:
Ib-charge+Ic<Ir-charge
Ib-charge+Ic>0
in order to accelerate the charging speed, the instantaneous value of the charging current of the compensation device is taken as the maximum value, namely the current target value I after the charging current is superposed with the compensation output current* OInstantaneous value maximum rated charging current Ir-chargeInstantaneous maximum value, Ib-chargeThe following formula is used for calculation:
ID-discharge＝IBsin(ωt)
Figure BDA0003260123360000041
Ib-charge+Ic＝Ir-charge
Figure BDA0003260123360000042
according to the above formula, calculate IBSo that I can be obtainedb-chargeThe discharge fundamental active current of (2). Thereby calculating the output current target value I of the compensating device in the charging mode* O
In the discharge mode, the compensating device releases energy to the grid, I* O＝Ib-discharge-Ic，Ib-dischargeRated discharge current I by compensation meansr-dischargeAnd harmonic compensation output current IcDetermination of Ib-dischargeSatisfies the following constraint conditions
Ib-discharge-Ic<Ir-discharge
Ib-discharge-Ic>0
At this time, in order to make the flywheel operate in the mode for a long time, the discharge speed of the flywheel needs to be slowed down, and the instantaneous value of the discharge current of the compensating device is taken as the minimum value at the moment (n pi) of integral multiple except for a half period, namely, the target value I of the current after the discharge current is superposed with the compensating output current* OThe instantaneous value is at least 0 and is the minimum value of zero point after the current values are superposed, Ib-dischargeThe following formula is used for calculation:
Ib-discharge＝-IAsin(ωt)
Figure BDA0003260123360000043
Ib-dischargeIc＝0
Figure BDA0003260123360000051
according to the above formula, calculate IASo that I can be obtainedb-dischargeThe discharge fundamental active current of (2). Thereby calculating the output current target value I of the compensating device in the discharging mode* O。
In a further improvement of the control method, step S10, the current tracking control uses an instantaneous value comparator or a triangular wave comparator for output current tracking control, and the target value I of the output current is compared* OAnd the actual value of the output current IOObtaining PWM control signals of each switching device in the main circuit;
step S11, controlling and outputting the actual compensation current IOThe process is as follows: the PWM control signal controls the on-off of each switching tube of the main circuit through the driving circuit module,driving energy conversion main circuit to output actual compensation current IO. And returning to the step 2. A nonlinear load current compensation control device based on flywheel energy storage comprises a flywheel body, a generator/motor, a bidirectional inverter, a bidirectional DC/DC converter, an energy conversion main circuit, a driving module, a main controller and an acquisition module; the flywheel body is coaxially and fixedly connected with the generator/motor;
the generator/motor is in bidirectional electrical connection with the alternating current side of the bidirectional inverter;
the direct current side of the bidirectional inverter is bidirectionally and electrically connected with the bidirectional DC/DC converter;
the bidirectional DC/DC converter is in bidirectional electrical connection with the direct current side of the energy conversion main circuit;
the energy conversion main circuit is a main circuit for compensating current output, and the alternating current side of the energy conversion main circuit is connected with a power grid in parallel in a bidirectional mode through an inductor;
the driving module is an energy conversion main circuit driving circuit and is used for driving a switching tube in the main circuit to be switched on or switched off;
the main controller is used for sending an acquisition instruction, receiving current, voltage and parameters acquired by the acquisition device, calculating load fundamental wave current and harmonic current, calculating a harmonic compensation target current value, controlling the flywheel to carry out charging and discharging and charging and discharging mode conversion, carrying out operation according to the compensation target current value and an actual value to output PWM control signals of each switching tube of the main circuit, and outputting working mode switching signals to the outside for synchronizing an energy conversion mode;
the acquisition device is used for acquiring load current, power grid voltage, flywheel charge state, DC/DC converter working mode and bidirectional inverter working mode signals in real time.
Adopt the produced beneficial effect of above-mentioned technical scheme to lie in:
(1) the compensation device can realize full compensation of the nonlinear load harmonic current. The control method comprises the steps of collecting load current in real time, calculating a harmonic current value by utilizing an instantaneous reactive power theory, and compensating the harmonic current value in full as a control target to realize the full compensation of the harmonic current in the process of charging and discharging the flywheel.
(2) The frequent switching of the energy flowing direction of the main circuit in the harmonic current compensation process is avoided. The main circuit keeps the same working mode in the charging or discharging process, and the energy flowing direction is fixed. In the process of charging the flywheel, the main circuit only works in a rectifier mode, and energy flows to the flywheel from a power grid; during the discharging process of the flywheel, the main circuit only works in an inverter mode, and energy flows to a power grid from the flywheel. The working mode of the main circuit is changed only when the flywheel is charged and discharged, so that the main circuit is prevented from frequently switching modes between the rectifier and the inverter, the switching loss can be effectively reduced, and the overall service life of the switching tube and the compensation device is prolonged.
(3) The harmonic current compensation effect is stable, and the adaptability to application scenes under different powers and voltages is high. The essence of the harmonic current compensation method is that the energy required by the harmonic current compensation is superposed in the charging or discharging energy conversion process of the compensation device, sufficient electric energy can be always ensured to compensate the harmonic current, and the conditions of fluctuation and instability of the voltage on the direct current side of the main circuit, which are faced by the APF, do not exist, so that the harmonic current compensation method has a stable effect on compensating the harmonic current and has strong adaptability to application scenes under different powers and voltages.
(4) The control method simultaneously considers the charge state of the flywheel and the direct-current side voltage of the main circuit, ensures the energy switching of the device to be timely, avoids the problem of discontinuous compensation effect, can automatically adapt to the change of the load harmonic current, and always keeps the full compensation of the harmonic current.
(5) The harmonic current compensation with larger amplitude can be realized. Because the output power of the flywheel energy storage device can be made to be very large, and the energy storage quantity is much larger than that of the traditional APF, the harmonic current compensation with larger amplitude can be realized.
(6) The compensating device has small size and is convenient to install and use. Because the energy magnitude required by the nonlinear load current compensation is not very large, and because the rotating speed of the flywheel can be very high, the flywheel body can be designed to have a very small size so as to store enough energy for harmonic current compensation. When the device is specially used for compensating low-power load, the whole size of the system can be small, and the device is convenient to install and use on site.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed for the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a flow chart of a control process for compensating a nonlinear load current by a compensation device;
FIG. 2 is a flow chart of the compensation device operating mode switching;
FIG. 3 is a schematic view of a compensating device;
FIG. 4 is a schematic of a nonlinear load current and a fundamental current;
FIG. 5 is a schematic diagram of compensated current in a charging mode;
FIG. 6 is a schematic diagram of compensated current in a charging mode;
fig. 7 is a schematic diagram of harmonic current compensation during normal operation of the compensation apparatus.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the application, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
The control targets of the nonlinear load current compensation device based on flywheel energy storage are as follows: compensating nonlinear load harmonic current in real time; secondly, the voltage on the direct current side of the energy conversion main circuit is kept stable; and thirdly, keeping the charge state of the flywheel in a normal working range.
The specific control method comprises the following steps:
step S1, initializing system parameters, presetting the working mode of the compensation device as a charging mode, and sending a signal for synchronously entering the charging mode to the bidirectional DC/DC converter and the bidirectional inverter by the main controller;
step S2, acquiring the SOC value of the flywheel energy storage devicenow；
Step S3, judging the state of charge SOC of the flywheel energy storage devicenowWhether it is greater than the lowest limit value SOCLlimitIf SOC isnowLess than SOCLlimitReturning to the step 2;
and step S4, collecting the load current value and the power grid voltage value, and calculating the harmonic current value. Real-time collection of load side grid voltage ULLoad current ILCalculating the load fundamental current I based on the instantaneous reactive power theoryLfAnd load harmonic current ILhAnd calculating the total distortion rate THD of the harmonic currentiTaking the compensation of all harmonic currents as an example:
ILh＝IL-ILf
THDi＝ILh/IL
step S5, collecting the DC side voltage U of the energy conversion main circuitd；
And step S6, judging the current working mode of the compensating device. According to the current state of charge (SOC) of the flywheelnowAnd determining whether mode switching is needed or not by combining the working mode of the compensation device in the last scanning period, and updating the working mode to a new working mode if the mode switching is needed.
The normal operation of the compensating device needs to ensure that the charge state of the flywheel is within a certain range, so that the flywheel needs to be charged or discharged according to the charge state of the flywheel. The working state of the compensating device can be divided into three working modes, namely a charging mode, a discharging mode and a standby mode. In a charging mode, the flywheel absorbs energy from a power grid through an energy conversion circuit, and compensates a harmonic current part in load current by controlling charging current waveform on the basis of increasing fundamental active current, so that the current of a compensation device and the current of the load after superposition are in a sine waveform; in a discharging mode, the flywheel releases energy to a power grid through an energy conversion circuit, and a harmonic current part in a load current is compensated by controlling a discharging current waveform on the basis of outputting a certain amount of fundamental wave active current to the power grid, so that the current obtained by superposing the current of a compensation device and the load current is in a sine waveform, and the energy of the current comes from the energy stored in the flywheel; in the standby mode, no energy is exchanged between the flywheel and the power grid, and only self energy consumption is maintained.
The compensating device adopts the charge state of a flywheel and a DC/DC converter to output a DC side voltage UdThe control is combined to judge the working mode, 2 charge state nodes are set according to the charge and discharge starting and stopping states, [ SOC ]L,SOCH]Wherein SOC isLlimit<SOCL<SOCHThe working mode switching control logic is as follows:
1) when the calculated total distortion rate THD of the harmonic currentiLess than or equal to THDpermitAt the moment, the state of charge of the energy stored by the flywheel is not lower than SOCLEntering a standby mode and returning to the step 2.
2) When the state of charge of flywheel energy storage is lower than SOCLWhen the flywheel is charged, the compensation device enters a charging mode until the state of charge of the flywheel rises to be higher than the SOCHAnd then, ending the charging mode and entering the discharging mode.
3) When THD is presentiGreater than THDpermitWhen the state of charge of flywheel energy storage is higher than SOCHWhen the flywheel is in the SOC state, the compensation device enters a discharging mode until the state of charge of the flywheel is reduced to be lower than the SOCLAnd then, ending the discharging mode and entering the charging mode.
4) When THD is presentiGreater than THDpermitWhen the energy is converted to the DC side U of the main circuit in the discharging moded<UdLIf the compensating device does not enter the charging mode, the charging mode is directly entered to compensate the energy of the flywheel until the U rises to the Ud>UdL+△UdTime and flywheel state of charge above SOCHAnd then, ending the charging mode and entering the discharging mode. U shapedLIndicates the voltage lower limit value,. DELTA.U, of the DC side of the main circuit for energy conversiondIndicating the dc side voltage control hysteresis offset.
In step S7, a synchronous operation mode command is sent. The main controller sends a signal for synchronously entering a charging mode to the bidirectional DC/DC converter and the bidirectional inverter.
In step S8, it is determined whether the operation mode is synchronized. Collecting the working mode states of the bidirectional DC/DC converter and the bidirectional inverter, and returning to the step 7 if the working modes are different;
step S9, calculating the output current target value I of the compensating device* O. Taking the example of compensating all harmonic currents as an example, the output current I of the compensation device* OIs formed by superposing two parts, namely harmonic compensation output current Ic，IcAnd load harmonic current ILhThe amplitudes are equal in size and opposite in direction, and the fundamental wave active current I required by the charging or discharging of the flywheel energy storage device is outputb. Calculating a target value I of the output current according to the current working mode of the compensating device* O。
I* O＝Ic+Ib
1) In the charging mode, the compensating device draws energy from the grid, I* OThe calculation formula is as follows:
I* O＝Ic+Ib-charge
Ib-chargethe charging current I being rated by the compensating devicer-chargeAnd harmonic compensation output current IcDetermination of Ib-chargeSatisfies the following constraints:
Ib-charge+Ic<Ir-charge
Ib-charge+Ic>0
in order to accelerate the charging speed, the instantaneous value of the charging current of the compensation device is taken as the maximum value, namely the current target value I after the charging current is superposed with the compensation output current* OInstantaneous value maximum rated charging current Ir-chargeInstantaneous maximum value, Ib-chargeThe following formula is used for calculation:
Ib-charge＝IBsin(ωt)
Figure BDA0003260123360000091
Ib-charge+Ic＝Ir-oharge
Figure BDA0003260123360000092
according to the above formula, calculate IBSo that I can be obtainedb-chargeThe discharge fundamental active current of (2). Thereby calculating the output current target value I of the compensating device in the charging mode* O
2) In the discharge mode, the compensating device releases energy to the grid, I* O＝Ib-discharge-Ic，Ib-dischargeRated discharge current I by compensation meansr-dischargeAnd harmonic compensation output current IcDetermination of Ib-dischargeSatisfies the following constraint conditions
Ib-discharge-Ic<Ir-discharge
Ib-discharge-Ic>0
At this time, in order to make the flywheel operate in the mode for a long time, the flywheel discharging speed needs to be slowed down, and the instantaneous value of the discharging current of the compensating device is taken as the minimum value at the moment, namely, the instantaneous value of the discharging current of the compensating device is taken asThe target value of current I after the discharge current is overlapped with the compensation output current except the integral multiple time (n pi) of the half period* OThe instantaneous value is at least 0 and is the minimum value of zero point after the current values are superposed, Ib-dischargeThe following formula is used for calculation:
Ib-disoharge＝IAsin(ωt)
Figure BDA0003260123360000101
Ib-discharge-Ic＝0
Figure BDA0003260123360000102
according to the above formula, calculate IASo that I can be obtainedb-dischargeThe discharge fundamental active current of (2). Thereby calculating the output current target value I of the compensating device in the discharging mode* O
Step S10, according to the output current target value I* OAnd the actual value of the output current IOAnd carrying out current tracking control. Tracking and controlling output current by using instantaneous value comparator or triangular wave comparator, and comparing target value I of output current* OAnd the actual value of the output current IOObtaining PWM control signals of each switching device in the main circuit;
step S11, controlling and outputting the actual compensation current IO. The PWM control signal controls the on-off of each switching tube of the main circuit through the driving circuit module to drive the energy conversion main circuit to output actual compensation current IO. And returning to the step 2.
The nonlinear load current compensation control method and device based on flywheel energy storage realize the conversion between electric energy and mechanical energy through the charging and discharging process of the flywheel energy storage device. In the energy conversion process, the controller drives and controls a main circuit switching tube by utilizing PWM (pulse width modulation), so that the current of the device is controlled, the current which is equal to the harmonic current in amplitude and opposite in direction is superposed into the charging or discharging current, and the fundamental wave active current with certain amplitude is injected (flywheel discharging) or absorbed (flywheel charging) into the power grid while the harmonic current is compensated. The compensated current is a sinusoidal current which is in phase with the active current of the load fundamental wave, and the amplitude is smaller (flywheel discharge) or larger (flywheel charge) than the active current of the load fundamental wave.
The nonlinear load current compensation device based on flywheel energy storage comprises a flywheel body, a generator/motor, a bidirectional inverter, a bidirectional DC/DC converter, an energy conversion main circuit, a driving module, a main controller and an acquisition module.
The flywheel body is an energy storage medium, when the compensating device absorbs energy from the power grid, the rotating speed of the flywheel rises, and the stored mechanical energy is increased; when the compensating device releases energy to the grid, the rotational speed of the flywheel drops and the stored mechanical energy drops. The flywheel body is coaxially connected with the generator/motor.
The generator/motor is bidirectionally connected with the alternating current side of the bidirectional inverter, when the flywheel is charged, the generator/motor runs in a motor mode, and the motor converts electric energy into mechanical energy to drive the flywheel to rotate in an accelerated mode; when the flywheel discharges, the flywheel runs in a generator mode, and mechanical energy stored by the flywheel is converted into electric energy through the generator to be output.
The direct current side of the bidirectional inverter is bidirectionally connected with the bidirectional DC/DC converter, and when the flywheel is charged, the bidirectional inverter inverts the electric energy on the direct current side into the alternating current electric energy to provide energy for the motor; when the flywheel discharges, the bidirectional inverter converts alternating current electric energy output by the generator into direct current electric energy, and the energy is output through the bidirectional DC/DC converter.
The bidirectional DC/DC converter is bidirectionally connected with the direct current side of the energy conversion main circuit, and converts the direct current side electric energy of the energy conversion main circuit into the direct current side electric energy of the bidirectional inverter when the flywheel is charged; when the flywheel discharges, the bidirectional DC/DC converter converts the direct-current side electric energy of the bidirectional inverter into the direct-current side electric energy of the energy conversion main circuit.
The energy conversion main circuit is a main circuit for compensating current output, the alternating current side of the energy conversion main circuit is connected with a power grid in parallel in a bidirectional mode through an inductor, and when the compensation device outputs current to the power grid, the energy conversion main circuit converts direct-current side electric energy into alternating-current side electric energy; when the compensation device absorbs current from the power grid, the energy conversion main circuit converts the alternating-current side electric energy into direct-current side electric energy. When three-phase compensation is carried out, a main circuit forms a three-phase fully-controlled bridge by 6 fully-controlled switching tubes, and every 2 switching tubes are connected in series to form a bridge arm. During single-phase compensation, the main circuit is composed of 4 full-control switching tubes to form a full-control bridge, and every 2 switching tubes are connected in series to form a bridge arm.
The driving module is an energy conversion main circuit driving circuit and is used for driving a switching tube in the main circuit to be switched on or switched off.
The main controller is used for sending an acquisition instruction, receiving current, voltage and parameters acquired by the acquisition device, calculating load fundamental wave current and harmonic current, calculating a harmonic compensation target current value, controlling the flywheel to perform charging and discharging and charging and discharging mode conversion, performing operation according to the compensation target current value and an actual value to output PWM control signals of all switching tubes of the main circuit, and outputting working mode switching signals for a synchronous energy conversion mode.
The acquisition device is used for acquiring signals such as load current, power grid voltage, flywheel charge state, DC/DC converter working mode, bidirectional inverter working mode and the like in real time.
The embodiment has the remarkable characteristics that:
(1) the full compensation of harmonic current can be realized in the process of charging and discharging the flywheel, and the main circuit keeps the same working mode in the process of charging or discharging, and the energy flowing direction is fixed. In the process of charging the flywheel, the main circuit only works in a rectifier mode, and energy flows to the flywheel from a power grid; during the discharging process of the flywheel, the main circuit only works in an inverter mode, and energy flows to a power grid from the flywheel. The working mode of the main circuit is changed only when the flywheel is charged and discharged, so that the main circuit is prevented from frequently switching modes between the rectifier and the inverter, the switching loss can be effectively reduced, and the overall service life of the switching tube and the compensation device is prolonged.
(2) The nonlinear load current compensation control method and device based on flywheel energy storage can be specially used for harmonic current compensation, and can also be applied to flywheel energy storage devices in other application scenes, such as flywheel UPS, rail transit flywheels and the like.
(3) A nonlinear load current compensation control method and device based on flywheel energy storage belong to a parallel compensation device.
(4) Because the energy magnitude required by the nonlinear load current compensation is not very large, and because the rotating speed of the flywheel can be very high, the flywheel body can be designed to have a very small size so as to store enough energy for harmonic current compensation. When the device is specially used for compensating low-power load, the whole size of the system can be small, and the device is convenient to install and use on site.
(5) The essential of the harmonic current compensation of the invention is that the energy required by the harmonic current compensation is superposed in the charging or discharging energy conversion process of the compensation device, and the conditions of voltage fluctuation and instability of the direct current side of the main circuit, which are faced by the APF, do not exist, so that the invention has strong voltage and power adaptability and excellent harmonic current compensation performance.
(6) The charging and discharging current design of the flywheel energy storage device should meet the following requirements: at any phase instant in a cycle, the nominal charging current instantaneous amplitude and the nominal discharging current instantaneous amplitude should be at least greater than the harmonic current in-phase amplitude to be compensated.
(7) When the load harmonic current changes, the compensation device automatically detects the changed load harmonic current instantaneous value and controls and changes the output of the main circuit switching tube, so that the changed harmonic current compensation requirement is met.
The present embodiment relates to a nonlinear load current compensation control method and apparatus, in the prior art, an LC filter or an active power filter is generally used to suppress a nonlinear load harmonic current, the LC filter has a simple structure and low cost, but can only suppress a harmonic with a fixed frequency, and the suppression effect is not good. The active power filter can dynamically eliminate each harmonic wave, but is not suitable for occasions of high voltage, high frequency and high power, and high switching loss is caused by high frequency conversion of the main circuit in the energy direction without stopping, so that the stability and the service life of the device are influenced.
According to the nonlinear load current compensation control method and device based on flywheel energy storage, the characteristic that the flywheel energy storage can absorb/release energy rapidly is utilized, and the current is controlled through the charging and discharging processes of the flywheel energy storage device, so that harmonic current compensation is achieved. The method comprises the steps of collecting load current, load voltage, main circuit direct-current side voltage and a flywheel charge state in real time, calculating a harmonic current value by using an instantaneous reactive power theory, fully compensating the harmonic current, keeping a flywheel SOC value and keeping the main circuit direct-current side voltage as targets according to the harmonic current value and flywheel charge-discharge current, designing a compensation device to output a current target value, outputting a PWM control signal through current tracking control, driving and controlling a main circuit switching tube, controlling the device current, superposing current with the same amplitude and the opposite direction as the harmonic current to the charge or discharge current, and injecting (flywheel discharge) or absorbing (flywheel charge) fundamental wave active current with certain amplitude to a power grid while compensating the harmonic current. The compensated current is a sinusoidal current which is in phase with the active current of the load fundamental wave, and the amplitude is smaller (flywheel discharge) or larger (flywheel charge) than the active current of the load fundamental wave. The device has the advantages that dynamic compensation is realized to eliminate nonlinear load harmonic current, the problem that APF frequently switches the energy flow direction of a main circuit is solved, and due to the fact that the flywheel is high in response speed and large in output power, large-amplitude harmonic current can be compensated, the device can adapt to different voltage, frequency and power occasions, and the flywheel is long in energy storage life.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; it is obvious as a person skilled in the art to combine several aspects of the invention. And such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (10)

1. A nonlinear load current compensation control method based on flywheel energy storage is characterized in that: the conversion between electric energy and mechanical energy is realized through the charging and discharging processes of the flywheel energy storage device; in the energy conversion process, the controller drives and controls a main circuit switching tube by utilizing PWM (pulse-width modulation), so that the current of the device is controlled, the current which has the same amplitude and the opposite direction with the harmonic current is superposed into the charging or discharging current, and the fundamental wave active current with certain amplitude is injected or absorbed into a power grid while the harmonic current is compensated; the compensated current is a sinusoidal current which is in phase with the load fundamental wave active current, and the amplitude is smaller than or larger than the load fundamental wave active current.
2. The flywheel energy storage based nonlinear load current compensation control method according to claim 1, characterized in that the specific control method comprises the following steps:
step S1, initializing system parameters, presetting the working mode of the compensation device as a charging mode, and sending a signal for synchronously entering the charging mode to the bidirectional DC/DC converter and the bidirectional inverter by the main controller;
step S2, acquiring the SOC value of the flywheel energy storage devicenow；
Step S3, judging the state of charge SOC of the flywheel energy storage devicenowWhether greater than the minimum SOCLlimitIf SOC isnowLess than SOCLlimitThen return to step S2;
step S4, collecting a load current value and a power grid voltage value, and calculating a harmonic current value; real-time collection of load side grid voltage ULLoad current ILCalculating the load fundamental current I based on the instantaneous reactive power theoryLfAnd load harmonic current ILhAnd calculating the total distortion rate THD of the harmonic currenti；
Step S5, collecting the DC side voltage U of the energy conversion main circuitd；
Step S6, judging the current compensation device working mode, and according to the current state of charge SOC of the flywheelnowIn combination with a scanning period compensation deviceMaking a mode, determining whether mode switching is needed, and if the mode switching is needed, updating the mode to a new working mode;
step S7, sending a synchronous working mode instruction, sending a synchronous charging mode entering signal to the bidirectional DC/DC converter and the bidirectional inverter by the main controller, and sending a synchronous charging mode entering signal to the bidirectional DC/DC converter and the bidirectional inverter by the main controller;
step S8, judging whether the working modes are synchronous, collecting the working mode states of the bidirectional DC/DC converter and the bidirectional inverter, and returning to the step S7 if the working modes are different;
step S9, calculating the output current target value I of the compensating device* O；
Step S10, according to the output current target value I* OAnd the actual value of the output current IOCarrying out current tracking control;
step S11, controlling and outputting the actual compensation current IO。
3. The flywheel energy storage based nonlinear load current compensation control method according to claim 2, wherein in step S4, the calculation formula for compensating all harmonic currents is as follows:
ILh＝IL-ILf
THDi＝ILh/IL。
4. the flywheel energy storage based nonlinear load current compensation control method according to claim 2, wherein in step S6, the working mode of the compensation device is determined as follows: according to the current state of charge (SOC) of the flywheelnowAnd determining whether mode switching is needed or not by combining the working mode of the compensation device in the last scanning period, and updating the working mode to a new working mode if the mode switching is needed.
5. The nonlinear load current compensation control method based on flywheel energy storage according to claim 4, wherein the working state of the compensation device is divided into three working modes, namely a charging mode, a discharging mode and a standby mode;
in a charging mode, the flywheel absorbs energy from a power grid through an energy conversion circuit, and compensates a harmonic current part in load current by controlling charging current waveform on the basis of increasing fundamental active current, so that the current of a compensation device and the current of the load after superposition are in a sine waveform;
in a discharging mode, the flywheel releases energy to a power grid through an energy conversion circuit, and a harmonic current part in a load current is compensated by controlling a discharging current waveform on the basis of outputting a certain amount of fundamental wave active current to the power grid, so that the current obtained by superposing the current of a compensation device and the load current is in a sine waveform, and the energy of the current comes from the energy stored in the flywheel;
in the standby mode, no energy is exchanged between the flywheel and the power grid, and only self energy consumption is maintained.
6. The nonlinear load current compensation control method based on flywheel energy storage as claimed in claim 5, characterized in that the compensation device adopts the state of charge of the flywheel and the DC/DC converter to output the DC side voltage UdThe mode that control combined together carries out the mode judgement, sets up 2 SOC nodes according to the start and stop state of charging and discharging: SOCL、SOCHWherein SOC isLlimit<SOCL<SOCH。
7. The flywheel energy storage based nonlinear load current compensation control method as claimed in claim 6, wherein the compensation device operation mode switching control logic is:
1) when the calculated total distortion rate THD of the harmonic currentiLess than or equal to THDpermitAt the moment, the state of charge of the energy stored by the flywheel is not lower than SOCLEntering the standby mode, and returning to step S2 of the control method;
2) when the state of charge of flywheel energy storage is lower than SOCLWhen the flywheel is charged, the compensation device enters a charging mode until the state of charge of the flywheel rises to be higher than the SOCHWhen the charging mode is finished, enter intoA discharge mode;
3) when THD is presentiGreater than THDpermitWhen the state of charge of flywheel energy storage is higher than SOCHWhen the flywheel is in the SOC state, the compensation device enters a discharging mode until the state of charge of the flywheel is reduced to be lower than the SOCLWhen the charging mode is finished, the charging mode is started;
4) when THD is presentiGreater than THDpermitWhen the energy is converted to the DC side U of the main circuit in the discharging moded<UdLIf the compensating device does not enter the charging mode, the charging mode is directly entered to compensate the energy of the flywheel until the U rises to the Ud>UdL+△UdTime and flywheel state of charge above SOCHWhen the charging mode is finished, entering a discharging mode; u shapedLIndicates the voltage lower limit value,. DELTA.U, of the DC side of the main circuit for energy conversiondIndicating the dc side voltage control hysteresis offset.
8. The flywheel energy storage based nonlinear load current compensation control method as claimed in claim 6, wherein in step S9, the compensating device outputs current I* OIs formed by superposing two parts, namely harmonic compensation output current Ic，IcAnd load harmonic current ILhThe amplitudes are equal in size and opposite in direction, and the fundamental wave active current I required by the charging or discharging of the flywheel energy storage device is outputb. Calculating a target value I of the output current according to the current working mode of the compensating device* O：
I* O＝Ic+Ib；
In the charging mode, the compensating device draws energy from the grid, I* OThe calculation formula is as follows:
I* O＝Ic+Ib-charge
Ib-chargethe charging current I being rated by the compensating devicer-chargeAnd harmonic compensation output current IcDetermination of Ib-chargeIs sufficient for the instantaneous value ofThe following constraints:
Ib-charge+Ic<Ir-charge
Ib-charge+Ic>0
in order to accelerate the charging speed, the instantaneous value of the charging current of the compensation device is taken as the maximum value, namely the current target value I after the charging current is superposed with the compensation output current* OInstantaneous value maximum rated charging current Ir-chargeInstantaneous maximum value, Ib-chargeThe following formula is used for calculation:
Ib-charge＝IBsin(ωt)
Figure FDA0003260123350000031
Ib-charge+Ic＝Ir-charge
Figure FDA0003260123350000032
according to the above formula, calculate IBSo that I can be obtainedb-chargeThe discharge fundamental active current of (2). Thereby calculating the output current target value I of the compensating device in the charging mode* O
In the discharge mode, the compensating device releases energy to the grid, I* O＝Ib-discharge-Ic，Ib-dischargeRated discharge current I by compensation meansr-dischargeAnd harmonic compensation output current IcDetermination of Ib-dischargeSatisfies the following constraint conditions
Ib-discharge-Ic<Ir-discharge
Ib-discharge-Ic>0
In order to operate the flywheel for a long time in this mode, the discharge speed of the flywheel needs to be slowed down, and the instantaneous value of the discharge current of the compensating device is taken as the minimum value except halfThe target current value I after the discharge current and the compensation output current are superposed at the integral multiple time (n pi) of the period* OThe instantaneous value is at least 0 and is the minimum value of zero point after the current values are superposed, Ib-dischargeThe following formula is used for calculation:
Ib-discharge＝-IAsin(ωt)
Figure FDA0003260123350000033
Ib-discharge-Ic＝0
Figure FDA0003260123350000034
according to the above formula, calculate IASo that I can be obtainedb-dischargeThe discharge fundamental active current of (2). Thereby calculating the output current target value I of the compensating device in the discharging mode* O。
9. The flywheel energy storage based nonlinear load current compensation control method according to claim 6, wherein in step S10, the current tracking control adopts instantaneous value comparator or triangular wave comparator to perform output current tracking control, and the target value I of the output current is compared by comparing* OAnd the actual value of the output current IOObtaining PWM control signals of each switching device in the main circuit;
step S11, controlling and outputting the actual compensation current IOThe process is as follows: the PWM control signal controls the on-off of each switching tube of the main circuit through the driving circuit module to drive the energy conversion main circuit to output actual compensation current IOAnd returning to the step 2.
10. A nonlinear load current compensation control device based on flywheel energy storage is characterized by comprising a flywheel body, a generator/motor, a bidirectional inverter, a bidirectional DC/DC converter, an energy conversion main circuit, a driving module, a main controller and an acquisition module;
the flywheel body is coaxially and fixedly connected with the generator/motor;
the generator/motor is in bidirectional electrical connection with the alternating current side of the bidirectional inverter;
the direct current side of the bidirectional inverter is bidirectionally and electrically connected with the bidirectional DC/DC converter;
the bidirectional DC/DC converter is in bidirectional electrical connection with the direct current side of the energy conversion main circuit;
the energy conversion main circuit is a main circuit for compensating current output, and the alternating current side of the energy conversion main circuit is connected with a power grid in parallel in a bidirectional mode through an inductor;
the driving module is an energy conversion main circuit driving circuit and is used for driving a switching tube in the main circuit to be switched on or switched off;
the main controller is used for sending an acquisition instruction, receiving current, voltage and parameters acquired by the acquisition device, calculating load fundamental wave current and harmonic current, calculating a harmonic compensation target current value, controlling the flywheel to carry out charging and discharging and charging and discharging mode conversion, carrying out operation according to the compensation target current value and an actual value to output PWM control signals of each switching tube of the main circuit, and outputting working mode switching signals to the outside for synchronizing an energy conversion mode;
the acquisition device is used for acquiring load current, power grid voltage, flywheel charge state, DC/DC converter working mode and bidirectional inverter working mode signals in real time.
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