CN113937800B - 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 PDFInfo
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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
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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
- H02J3/01—Arrangements for reducing harmonics or ripples
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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
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
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- 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
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- 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]
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- 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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Abstract
The application discloses a nonlinear load current compensation control method and device based on flywheel energy storage, wherein the control method realizes 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 PWM (pulse-width modulation) is utilized to drive and control a main circuit switching tube, the current of the device is controlled, the harmonic current is compensated, and the fundamental wave active current with a certain amplitude is injected or absorbed into a power grid; the compensated current is sinusoidal current in phase with the active current of the load fundamental wave, and the amplitude of the current is smaller than or larger than the active current of the load fundamental wave. Real-time and dynamic compensation of nonlinear load current is realized, each subharmonic can be dynamically eliminated, and current waveform is improved; the method has a wide voltage and power application range, avoids frequent switching of the main circuit between the inverter and the rectifier, and solves the problems of strong limitation of harmonic compensation capability, small voltage and power application range and low overall service life of the main circuit switching tube in the existing method.
Description
Technical Field
The application 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
There are a large number of nonlinear loads such as rolling mills, electric welding machines, elevators and electric locomotives in industrial and commercial users, 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 affected.
The existing harmonic suppression method is mostly implemented by adopting an LC filter or an Active Power Filter (APF). The LC filter can inhibit harmonic waves and compensate reactive power, but the compensation characteristic is easily influenced by the impedance and the running state of a power grid, and parallel resonance is easily generated with a system, so that harmonic amplification is caused, and overload and even burnout of the LC tuning filter are easily caused. Furthermore, LC filters can only compensate for harmonics of fixed frequencies and the compensation effect is not ideal. The LC tuning filter is still widely used due to its simple structure, low cost and easy arrangement.
An Active Power Filter (APF) is a novel power electronic device for dynamically suppressing harmonics, compensating for reactive power, compensating for harmonics varying in both size and frequency, dynamically eliminating the harmonics, and not generating resonance. However, the filter is not applicable to high-voltage, high-frequency and high-power occasions, the passband range is limited by the bandwidth of an active device, the direct-current side capacitor is limited by withstand voltage, and a higher capacitance value is difficult to achieve, so that the magnitude of direct-current side voltage amplitude Uc is limited, the magnitude of Uc variation and the magnitude of energy exchange are influenced, compensation of high-amplitude harmonic current is difficult to achieve, and the compensation capacity, voltage and power adaptation range of an active power filter are influenced. In addition, when compensating harmonic current, the 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 high speed, thereby reducing the service life of the switching tube and increasing the system loss.
Disclosure of Invention
The technical problem to be solved by the application is to provide a nonlinear load current compensation control method and device based on flywheel energy storage, which can realize real-time and dynamic compensation of nonlinear load current, dynamically eliminate various subharmonics and improve current waveforms; the method has a wide voltage and power application range, avoids frequent switching of the main circuit between the inverter and the rectifier, and solves the problems of strong limitation of harmonic compensation capability, small voltage and power application range and low overall service life of the main circuit switching tube in the existing method.
In order to solve the problems, the application adopts the following technical scheme:
a nonlinear load current compensation control method based on flywheel energy storage realizes conversion between electric energy and mechanical energy through the charging and discharging processes of a flywheel energy storage device; in the energy conversion process, the controller utilizes PWM to drive and control the switching tube of the main circuit, so as to control the current of the device, and the current with the same amplitude and opposite direction to the harmonic current is added into the charging or discharging current, so that the harmonic current is compensated, and meanwhile, the fundamental active current with a certain amplitude is injected or absorbed into the power grid; the compensated current is sinusoidal current in phase with the active current of the load fundamental wave, and the amplitude of the current is smaller than or larger than the active current of the load fundamental wave.
The control method is further improved, and the specific control method comprises the following steps:
step S1, initializing system parameters, presetting a working mode of a compensation device to be a charging mode, and sending a signal for synchronously entering the charging mode to a bidirectional DC/DC converter and a bidirectional inverter by a main controller;
s2, collecting a state of charge value SOC of the flywheel energy storage device now ；
Step S3, judging the state of charge SOC of the flywheel energy storage device now Whether or not it is greater than the minimum value SOCL limit If SOC is now Less than SOCL limit Returning to the step S2;
s4, collecting a load current value and a power grid voltage value, and calculating a harmonic current value; collecting load side power grid voltage U in real time L Load current I L Calculating load fundamental wave current I based on instantaneous reactive power theory Lf And load harmonic current I Lh And calculate the total harmonic current distortion THD i ；
Step S5, collecting the direct-current side voltage U of the energy conversion main circuit d ；
Step S6, judging the working mode of the current compensation device, and according to the state of charge value SOC of the current flywheel now Determining whether mode switching is needed or not according to the working mode of the scanning-up period compensation device, and updating to a new working mode if the mode switching is needed;
step S7, sending a synchronous working mode instruction, wherein the main controller sends a synchronous charging mode entering signal to the bidirectional DC/DC converter and the bidirectional inverter, and the main controller sends a synchronous charging mode entering signal to the bidirectional DC/DC converter and the bidirectional inverter;
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 compensation device * O ；
Step S10, according to the output current target value I * O And an actual value of the output current I O Performing current tracking control;
step S11, controlling and outputting the actual compensation current I O 。
In a further improvement of the control method, in step S4, the calculation formula for compensating all harmonic currents is as follows:
I Lh ＝I L -I Lf
THD i ＝I Lh /I L 。
in step S6, the working mode of the compensation device is determined as follows: based on the state of charge value SOC of the current flywheel now And combining the working modes of the scanning-up periodic compensation device to determine whether mode switching is needed, and updating the working modes into new working modes if the mode switching is needed.
Further improvement of the control method, the working state of the compensation device is divided into three working modes of a charging mode, a discharging mode and a standby mode;
in a charging mode, the flywheel extracts energy from a power grid through an energy conversion circuit, and the harmonic current part in the load current is compensated on the basis of increasing fundamental active current by controlling the charging current waveform, so that the current after the current of the compensation device is overlapped with the load current is in a sine waveform;
in a discharging mode, the flywheel itself discharges energy to the power grid through the energy conversion circuit, and the discharging current waveform is controlled to compensate harmonic current parts in the load current on the basis of outputting a certain amount of fundamental wave active current to the power grid, so that the current after the current of the compensating device is overlapped with the load current is in a sine waveform, and the energy of the current is derived from the energy stored by the flywheel; in standby mode, there is no energy exchange between flywheel and power grid, only maintaining own energy consumption.
Further improvement of control method, the compensating device adopts flywheel charge state and DC/DC converter output DC side voltage U d The working mode judgment is carried out in a control combined mode, and 2 charge state nodes are set according to the charge and discharge start-stop states: SOC (State of Charge) L 、SOC H Wherein SOC is Llimit <SOC L <SOC H 。
Further improvement of the control method, the working mode switching control logic of the compensation device is as follows:
1) When the calculated harmonic current is abnormalVariable rate THD i THD of less than or equal to permit At the moment, and the charge state of flywheel energy storage is not lower than SOC L Entering a standby mode, and returning to the step S2 of the control method;
2) When the charge state of flywheel energy storage is lower than SOC L When the compensating device enters the charging mode until the charge state of the flywheel rises to be higher than the SOC H When the charging mode is ended, a discharging mode is entered;
3) When THD is i Greater than THD permit When the charge state of the flywheel energy storage is higher than the SOC H When the compensating device enters a discharging mode until the charge state of the flywheel is reduced to be lower than the SOC L When the discharging mode is ended, the charging mode is entered.
4) When THD is i Greater than THD permit In the discharging mode, when the energy is converted to the DC side U of the main circuit d <U dL When the current flywheel charge state is insufficient to maintain the harmonic compensation energy output, if the compensation device does not enter the charging mode, the compensation device directly enters the charging mode to compensate the flywheel energy until U rises to U d >U dL +△U d When and flywheel charge state is higher than SOC H When the charging mode is ended, the discharging mode is entered. U (U) dL Representing the voltage lower limit value of the DC side of the energy conversion main circuit, deltaU d Indicating the dc side voltage control hysteresis offset.
Further improvement of the control method, in step S9, the compensation device outputs a current I * O Consists of two overlapped parts, namely harmonic compensation output current I c ，I c With load harmonic current I Lh The amplitude values are equal and the directions are opposite, and the fundamental wave active current I required by the charging or discharging of the flywheel energy storage device is output b . Calculating a target value I of the output current according to the current working mode of the compensation device * O ：
I * O ＝I c +I b；
In the charging mode, the compensation device extracts energy from the power grid, I * O The calculation formula is as follows:
I * O ＝I c +I b-charge
I b-charge rated charge current I by compensation means r-charge Harmonic compensated output current I c Decision, I b-charge The instantaneous value of (2) satisfies the following constraint:
I b-charge +I c <I r-charge
I b-charge +I c >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 overlapped with the compensation output current * O Instantaneous value is maximum rated charging current I r-charge Instantaneous maximum, I b-charge The calculation is performed according to the following formula:
I D-discharge ＝I B sin(ωt)
I b-charge +I c ＝I r-charge
according to the above formula, calculate I B Maximum value of (2) to obtain I b-charge Is used for discharging fundamental wave active current. Thereby calculating and obtaining the output current target value I of the compensation device in the charging mode * O
In the discharging mode, the compensating device releases energy to the power grid, I * O ＝I b-discharge -I c ，I b-discharge Rated discharge current I by compensation means r-discharge Harmonic compensated output current I c Decision, I b-discharge The instantaneous value of (2) satisfies the following constraint
I b-discharge -I c <I r-discharge
I b-discharge -I c >0
At this time, in order to operate the flywheel in this mode for a long time, the flywheel discharge speed is slowed down, and the instantaneous value of the discharge current of the compensation device is taken to be the minimum value, namely, the current target value I after the discharge current and the compensation output current are overlapped is obtained at the moment (n pi) except for the integral multiple of the half period * O The minimum instantaneous value is 0 and is the minimum value of zero point after the superposition of current values, I b-discharge The calculation is performed according to the following formula:
I b-discharge ＝-I A sin(ωt)
I b-discharge I c ＝0
according to the above formula, calculate I A To obtain the minimum value of I b-discharge Is used for discharging fundamental wave active current. Thereby calculating and obtaining the output current target value I of the compensating device in the discharging mode * O 。
Further improvement of the control method, step S10, the current tracking control adopts an instantaneous value comparator or a triangular wave comparator to perform output current tracking control by comparing the output current target value I * O And an actual value of the output current I O Obtaining PWM control signals of all switching devices in a main circuit;
step S11, controlling and outputting the actual compensation current I O The process is as follows: the PWM control signal controls the on-off of each switch tube of the main circuit through the driving circuit module, and the driving energy conversion main circuit outputs the actual compensation current I O . 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 and a double-inverterThe device comprises a 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 in bidirectional electrical connection 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 the power grid in a bidirectional parallel manner 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 conducted or cut 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 wave current, calculating a harmonic compensation target current value, controlling the flywheel to charge and discharge and converting a charge-discharge mode, calculating and outputting PWM control signals of each switching tube of the main circuit according to the compensation target current value and an actual value, and outputting working mode switching signals to the outside for synchronizing an energy conversion mode;
the acquisition device is used for acquiring load current, grid voltage, flywheel charge state, a DC/DC converter working mode and a bidirectional inverter working mode signal in real time.
The beneficial effects of adopting above-mentioned technical scheme to produce lie in:
(1) The compensation device can realize full compensation of nonlinear load harmonic current. The control method calculates a harmonic current value by collecting load current in real time and utilizing an instantaneous reactive power theory, and takes the harmonic current value as a control target to realize full compensation of the harmonic current in the process of flywheel charging and discharging.
(2) And frequent switching of the energy flow 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 flow direction is fixed. In the flywheel charging process, the main circuit only works in a rectifier mode, and energy flows to the flywheel from the power grid; during the flywheel discharging process, the main circuit only works in the inverter mode, and energy flows from the flywheel to the power grid. Only the working mode of the main circuit is required to be changed when the flywheel is subjected to charge-discharge switching, so that the mode switching of the main circuit between the rectifier and the inverter is avoided, the switching loss can be effectively reduced, and the overall service lives of the switching tube and the compensation device are prolonged.
(3) The harmonic current compensation effect is stable, and the application scene adaptability to different power and voltage is strong. The essence of the harmonic current compensation of the application is that the energy required by harmonic current compensation is superposed in the charging or discharging energy conversion process of the compensation device, so that sufficient electric energy can be ensured to compensate the harmonic current all the time, and the conditions of voltage fluctuation and instability of the direct current side of the main circuit faced by the APF do not exist, therefore, the harmonic current compensation effect of the method of the application is very stable, and the method has very strong adaptability to application scenes under different power and voltage.
(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 in time, avoids the problem of discontinuous compensation effect, can automatically adapt to the change of load harmonic current, and always maintains 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 quite large, and the energy storage volume is quite 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. The energy level required by nonlinear load current compensation is not very large, and the flywheel rotating speed can be very high, so that the flywheel body can be designed to be very small in size so as to store enough energy for harmonic current compensation. When the system is specially used for compensating low-power load, the whole size of the system can be small, and the system is convenient for field installation and use.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments or the description of the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of control of compensation device for nonlinear load current compensation;
FIG. 2 is a flow chart of the switching of the modes of operation of the compensation device;
FIG. 3 is a schematic diagram of a compensating device;
FIG. 4 is a schematic diagram of nonlinear load current and fundamental current;
FIG. 5 is a schematic diagram of the compensated current in the charging mode;
FIG. 6 is a schematic diagram of the compensated current in the charging mode;
fig. 7 is a schematic diagram of harmonic current compensation during normal operation of the compensation device.
Detailed Description
The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments. The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the application, its application, or uses. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the 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 exemplary embodiments according to the present application. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
The control target of the nonlinear load current compensation device based on flywheel energy storage is as follows: firstly, compensating nonlinear load harmonic current in real time; secondly, keeping the voltage of the direct current side of the energy conversion main circuit 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 a working mode of a compensation device to be a charging mode, and sending a signal for synchronously entering the charging mode to a bidirectional DC/DC converter and a bidirectional inverter by a main controller;
s2, collecting a state of charge value SOC of the flywheel energy storage device now ；
Step S3, judging the state of charge SOC of the flywheel energy storage device now Whether or not it is greater than the minimum limit value SOC Llimit If SOC is now Less than SOC Llimit Returning to the step 2;
and S4, collecting a load current value and a power grid voltage value, and calculating a harmonic current value. Collecting load side power grid voltage U in real time L Load current I L Calculating load fundamental wave current I based on instantaneous reactive power theory Lf And load harmonic current I Lh And calculate the total harmonic current distortion THD i Take the example of compensating all harmonic currents:
I Lh ＝I L -I Lf
THD i ＝I Lh /I L
step S5, collecting the direct-current side voltage U of the energy conversion main circuit d ；
And S6, judging the working mode of the current compensation device. Based on the state of charge value SOC of the current flywheel now And combining the working modes of the scanning-up periodic compensation device to determine whether mode switching is needed, and updating the working modes into new working modes if the mode switching is needed.
The normal operation of the compensation 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 compensation device can be divided into three working modes of a charging mode, a discharging mode and a standby mode. In a charging mode, the flywheel extracts energy from a power grid through an energy conversion circuit, and the harmonic current part in the load current is compensated on the basis of increasing fundamental active current by controlling the charging current waveform, so that the current after the current of the compensation device is overlapped with the load current is in a sine waveform; in a discharging mode, the flywheel itself discharges energy to the power grid through the energy conversion circuit, and the discharging current waveform is controlled to compensate harmonic current parts in the load current on the basis of outputting a certain amount of fundamental wave active current to the power grid, so that the current after the current of the compensating device is overlapped with the load current is in a sine waveform, and the energy of the current is derived from the energy stored by the flywheel; in standby mode, there is no energy exchange between flywheel and power grid, only maintaining own energy consumption.
The compensating device adopts flywheel charge state and DC/DC converter to output DC side voltage U d The working mode is judged by combining control, and 2 charge state nodes are set according to the charge and discharge start-stop states, [ SOC ] L ,SOC H ]Wherein SOC is Llimit <SOC L <SOC H The working mode switching control logic is as follows:
1) When the calculated total harmonic current distortion THD i THD of less than or equal to permit At the moment, and the charge state of flywheel energy storage is not lower than SOC L And (4) entering a standby mode and returning to the step (2).
2) When the charge state of flywheel energy storage is lower than SOC L When the compensating device enters the charging mode until the charge state of the flywheel rises to be higher than the SOC H When the charging mode is ended, the discharging mode is entered.
3) When THD is i Greater than THD permit When the charge state of the flywheel energy storage is higher than the SOC H When the compensating device enters a discharging mode until the charge state of the flywheel is reduced to be lower than the SOC L When the discharging mode is ended, the charging mode is entered.
4) When THD is i Greater than THD permit In the discharging mode, when the energy is converted to the DC side U of the main circuit d <U dL When the current flywheel charge state is insufficient to maintainHarmonic compensation energy output, if the compensation device does not enter the charging mode, the compensation device directly enters the charging mode to compensate flywheel energy until U rises to U d >U dL +△U d When and flywheel charge state is higher than SOC H When the charging mode is ended, the discharging mode is entered. U (U) dL Representing the voltage lower limit value of the DC side of the energy conversion main circuit, deltaU d Indicating the dc side voltage control hysteresis offset.
And step S7, sending a synchronous working mode instruction. The main controller sends a synchronous charging mode entering signal to the bidirectional DC/DC converter and the bidirectional inverter.
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 7 if the working modes are different;
step S9, calculating the output current target value I of the compensation device * O . Taking compensation of all harmonic currents as an example for explanation, the compensation device outputs a current I * O Consists of two overlapped parts, namely harmonic compensation output current I c ，I c With load harmonic current I Lh The amplitude values are equal and the directions are opposite, and fundamental wave active current I required by charging or discharging of the flywheel energy storage device is output b . Calculating a target value I of the output current according to the current working mode of the compensation device * O 。
I * O ＝I c +I b
1) In the charging mode, the compensation device extracts energy from the power grid, I * O The calculation formula is as follows:
I * O ＝I c +I b-charge
I b-charge rated charge current I by compensation means r-charge Harmonic compensated output current I c Decision, I b-charge The instantaneous value of (2) satisfies the following constraint:
I b-charge +I c <I r-charge
I b-charge +I c >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 overlapped with the compensation output current * O Instantaneous value is maximum rated charging current I r-charge Instantaneous maximum, I b-charge The calculation is performed according to the following formula:
I b-charge ＝I B sin(ωt)
I b-charge +I c ＝I r-oharge
according to the above formula, calculate I B Maximum value of (2) to obtain I b-charge Is used for discharging fundamental wave active current. Thereby calculating and obtaining the output current target value I of the compensation device in the charging mode * O
2) In the discharging mode, the compensating device releases energy to the power grid, I * O ＝I b-discharge -I c ，I b-discharge Rated discharge current I by compensation means r-discharge Harmonic compensated output current I c Decision, I b-discharge The instantaneous value of (2) satisfies the following constraint
I b-discharge -I c <I r-discharge
I b-discharge -I c >0
At this time, in order to operate the flywheel in this mode for a long time, the flywheel discharge speed is slowed down, and the instantaneous value of the discharge current of the compensation device is taken to be the minimum value, namely, the current target value I after the discharge current and the compensation output current are overlapped is obtained at the moment (n pi) except for the integral multiple of the half period * O The minimum instantaneous value is 0 and is the minimum value of zero point after the superposition of current values, I b-discharge The calculation is performed according to the following formula:
I b-disoharge ＝I A sin(ωt)
I b-discharge -I c ＝0
according to the above formula, calculate I A To obtain the minimum value of I b-discharge Is used for discharging fundamental wave active current. Thereby calculating and obtaining 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 * O And an actual value of the output current I O And (5) performing current tracking control. Tracking control of output current by using instantaneous value comparator or triangular wave comparator, and comparing the target value I of output current * O And an actual value of the output current I O Obtaining PWM control signals of all switching devices in a main circuit;
step S11, controlling and outputting the actual compensation current I O . PWM control signals control the on-off of all switching tubes of a main circuit through a driving circuit module, and drive the energy conversion main circuit to output actual compensation current I O . 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 utilizes PWM to drive and control the switching tube of the main circuit, thereby controlling the current of the device, adding the current with the same amplitude and opposite direction to the harmonic current into the charging or discharging current, and injecting (flywheel discharging) or absorbing (flywheel charging) the fundamental wave active current with a certain amplitude into the power grid while compensating the harmonic current. The compensated current is sinusoidal current in phase with the active current of the load fundamental wave, and the amplitude is smaller than (flywheel discharging) or larger than (flywheel charging) 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 rotation speed of the flywheel is increased, and the stored mechanical energy is increased; when the compensating device releases energy to the grid, the flywheel rotational speed decreases and the stored mechanical energy decreases. The flywheel body is coaxially coupled to the generator/motor.
The generator/motor is connected with the alternating current side of the bidirectional inverter in a bidirectional way, when the flywheel is charged, the flywheel operates in a motor mode, and the motor converts electric energy into mechanical energy to drive the flywheel to rotate in an accelerating way; when the flywheel discharges, the flywheel operates 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 in bidirectional connection with the bidirectional DC/DC converter, and when the flywheel is charged, the bidirectional inverter inverts the electric energy of the direct current side into 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 direct current electric energy is output through the bidirectional DC/DC converter.
The bidirectional DC/DC converter is in bidirectional connection with the direct current side of the energy conversion main circuit, and when the flywheel is charged, the bidirectional DC/DC converter converts the direct current side electric energy of the energy conversion main circuit into direct current side electric energy of the bidirectional inverter; 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 the power grid in a bidirectional parallel manner through an inductor, and when the compensating 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 alternating-current side electric energy into direct-current side electric energy. The main circuit forms a three-phase full-control bridge by 6 full-control switching tubes during three-phase compensation, and every 2 switching tubes are connected in series to form a bridge arm. The main circuit is a full-control bridge formed by 4 full-control switching tubes during single-phase compensation, 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 conducted or cut off.
The main controller is used for sending an acquisition instruction and receiving current, voltage and parameters acquired by the acquisition device, calculating load fundamental wave current and harmonic wave current, calculating harmonic wave compensation target current values, controlling the flywheel to charge and discharge and converting a charge-discharge mode, calculating and outputting PWM control signals of each switching tube of the main circuit according to the compensation target current values and actual values, and outputting working mode switching signals to the outside for synchronizing energy conversion modes.
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 is characterized in that:
(1) 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, so that the energy flow direction is fixed. In the flywheel charging process, the main circuit only works in a rectifier mode, and energy flows to the flywheel from the power grid; during the flywheel discharging process, the main circuit only works in the inverter mode, and energy flows from the flywheel to the power grid. Only the working mode of the main circuit is required to be changed when the flywheel is subjected to charge-discharge switching, so that the mode switching of the main circuit between the rectifier and the inverter is avoided, the switching loss can be effectively reduced, and the overall service lives of the switching tube and the compensation device are 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 under other application scenes, such as flywheel UPS, rail transit flywheel and the like, and the suppression capability for harmonic current is improved on the original basis when the method and device are applied.
(3) A nonlinear load current compensation control method and device based on flywheel energy storage belong to parallel compensation devices.
(4) The energy level required by nonlinear load current compensation is not very large, and the flywheel rotating speed can be very high, so that the flywheel body can be designed to be very small in size so as to store enough energy for harmonic current compensation. When the system is specially used for compensating low-power load, the whole size of the system can be small, and the system is convenient for field installation and use.
(5) The essence of the application is that the energy required by 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 faced by the APF do not exist, so the application has strong voltage and power adaptability and excellent harmonic current compensation performance.
(6) The charge and discharge current design of the flywheel energy storage device should satisfy: at any phase time within a cycle, the instantaneous amplitude of the rated charge current and the instantaneous amplitude of the rated discharge current should be at least greater than the in-phase amplitude of the harmonic current 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 switching tube of the main circuit so as to meet the changed harmonic current compensation requirement.
The embodiment relates to a nonlinear load current compensation control method and device, wherein an LC filter or an active power filter is generally adopted for nonlinear load harmonic current suppression in the prior art, the LC filter has a simple structure and low cost, but can only suppress harmonic waves with fixed frequency, and the suppression effect is poor. The active power filter can dynamically eliminate various subharmonics, but is not applicable to high-voltage, high-frequency and high-power occasions, and because the main circuit constantly carries out high-frequency conversion on the energy direction, higher switching loss is caused, and the stability and the service life of the device are affected.
According to the nonlinear load current compensation control method and device based on flywheel energy storage, the characteristics that the flywheel energy storage can absorb/release energy rapidly are utilized, and 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, direct-current side voltage of a main circuit and flywheel charge state in real time, calculating harmonic current values by utilizing an instantaneous reactive power theory, taking full compensation harmonic current, keeping flywheel SOC value and direct-current side voltage of the main circuit as targets according to the harmonic current values and flywheel charge-discharge current, designing a compensation device to output a current target value, outputting PWM control signals through current tracking control, driving and controlling a switching tube of the main circuit, controlling device current, overlapping currents with the same amplitude and opposite directions of the harmonic current into charge-discharge current, and injecting (flywheel discharge) or absorbing (flywheel charge) fundamental wave active current with a certain amplitude into a power grid while compensating the harmonic current. The compensated current is sinusoidal current in phase with the active current of the load fundamental wave, and the amplitude is smaller than (flywheel discharging) or larger than (flywheel charging) the active current of the load fundamental wave. The device has the advantages of solving the problem that the APF frequently switches the energy flow direction of the main circuit, solving the problems of dynamic compensation and eliminating nonlinear load harmonic current of each time, being capable of compensating large-amplitude harmonic current due to high flywheel response speed and large output power, being suitable for occasions with different voltages, frequencies and powers, along with the characteristic of long service life of flywheel energy storage, and being high in economical efficiency and popularization.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and are not limiting; although the application 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 scheme described in the foregoing embodiments can be modified or some of the technical features thereof can be replaced by equivalents; it is obvious to a person skilled in the art to combine several embodiments of the application. Such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present application.
Claims (8)
1. A nonlinear load current compensation control method based on flywheel energy storage is characterized in that: the conversion between the electric energy and the mechanical energy is realized through the charging and discharging processes of the flywheel energy storage device; in the energy conversion process, the controller utilizes PWM to drive and control the switching tube of the main circuit, so as to control the current of the device, and the current with the same amplitude and opposite direction to the harmonic current is added into the charging or discharging current, so that the harmonic current is compensated, and meanwhile, the fundamental active current with a certain amplitude is injected or absorbed into the power grid; the compensated current is sinusoidal current in phase with the active current of the load fundamental wave, and the amplitude of the current is smaller than or larger than the active current of the load fundamental wave;
the specific control method comprises the following steps:
step S1, initializing system parameters, presetting a working mode of a compensation device to be a charging mode, and enabling a main controller to perform bidirectional DC/DC
The converter and the bidirectional inverter send out a signal for synchronously entering a charging mode;
s2, collecting a state of charge value SOC of the flywheel energy storage device now ；
Step S3, judging the state of charge SOC of the flywheel energy storage device now Whether or not it is greater than the minimum value SOCL limit If SOC is now Less than SOCL limit Returning to the step S2;
s4, collecting a load current value and a power grid voltage value, and calculating a harmonic current value; collecting load side power grid voltage U in real time L Load current I L Calculating load fundamental wave current I based on instantaneous reactive power theory Lf And load harmonic current I Lh And calculate the total harmonic current distortion THD i ；
Step S5, collecting the direct-current side voltage U of the energy conversion main circuit d ；
Step S6, judging the working mode of the current compensation device, and according to the state of charge value SOC of the current flywheel now Combining the working modes of the scanning-up periodic compensation device to determine whether mode switching is needed, and updating the working modes into new working modes if the mode switching is needed
A formula (I);
step S7, sending a synchronous working mode instruction, wherein the main controller sends a synchronous charging mode entering signal to the bidirectional DC/DC converter and the bidirectional inverter, and the main controller sends a synchronous charging mode entering signal to the bidirectional DC/DC converter and the bidirectional inverter;
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 compensation device * O ；
Step S10, according to the output current target value I * O And an actual value of the output current I O Performing current tracking control;
step S11, controlling and outputting the actual compensation current I O ；
The working mode switching control logic of the compensation device is as follows:
1) When the calculated total harmonic current distortion THD i THD of less than or equal to permit At the moment, and the charge state of flywheel energy storage is not lower than SOC L Entering a standby mode, and returning to the step S2 of the control method;
2) When the charge state of flywheel energy storage is lower than SOC L When the compensating device enters the charging mode until the charge state of the flywheel rises to be higher than the SOC H When the charging mode is ended, a discharging mode is entered;
3) When THD is i Greater than THD permit When the charge state of the flywheel energy storage is higher than the SOC H When the compensating device enters a discharging mode until the charge state of the flywheel is reduced to be lower than the SOC L When the discharging mode is ended, entering a charging mode;
4) When THD is i Greater than THD permit In the discharging mode, when the energy is converted to the DC side U of the main circuit d <U dL When the current flywheel charge state is insufficient to maintain the harmonic compensation energy output, if the compensation device does not enter the charging mode, the compensation device directly enters the charging mode to compensate the flywheel energy until U rises to U d >U dL +△U d When and flywheel charge state is higher than SOC H When the charging mode is ended, a discharging mode is entered; u (U) dL Representing the voltage lower limit value of the DC side of the energy conversion main circuit, deltaU d Representing DC side voltageAnd controlling hysteresis offset.
2. The flywheel energy storage-based nonlinear load current compensation control method as claimed in claim 1, wherein,
in step S4, the calculation formula for compensating all harmonic currents is as follows:
I Lh ＝I L -I Lf
THD i ＝I Lh /I L 。
3. the flywheel energy storage-based nonlinear load current compensation control method as claimed in claim 1, wherein,
in step S6, the working mode of the compensation device is determined as follows: based on the state of charge value SOC of the current flywheel now And combining the working modes of the scanning-up periodic compensation device to determine whether mode switching is needed, and updating the working modes into new working modes if the mode switching is needed.
4. The flywheel energy storage-based nonlinear load current compensation control method as claimed in claim 3, 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 the charging mode, the flywheel itself draws energy from the grid through the energy conversion circuit, by controlling the charging current waveform,
on the basis of increasing fundamental active current, compensating a harmonic current part in load current, so that the current after the current of a compensation device is overlapped with the load current is in a sine waveform;
in the discharging mode, the flywheel itself discharges energy to the power grid through the energy conversion circuit, and by controlling the discharging current waveform,
on the basis of outputting a certain amount of fundamental wave active current to a power grid, compensating a harmonic current part in load current, 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 is derived from the energy stored by a flywheel;
in standby mode, there is no energy exchange between flywheel and power grid, only maintaining own energy consumption.
5. The flywheel energy storage-based nonlinear load current compensation control method as claimed in claim 4, wherein,
the compensating device adopts flywheel charge state and DC/DC converter to output DC side voltage U d The working mode judgment is carried out in a control combined mode, and 2 charge state nodes are set according to the charge and discharge start-stop states: SOC (State of Charge) L 、SOC H Wherein SOC is Llimit <SOC L <SOC H 。
6. The flywheel energy storage-based nonlinear load current compensation control method as claimed in claim 5, wherein,
in step S9, the compensation device outputs a current I * O Consists of two overlapped parts, namely harmonic compensation output current I c ，I c With load harmonic current I Lh The amplitude values are equal and the directions are opposite, and the fundamental wave active current I required by the charging or discharging of the flywheel energy storage device is output b The method comprises the steps of carrying out a first treatment on the surface of the Calculating a target value I of the output current according to the current working mode of the compensation device * O ：
I * O ＝I c +I b ；
In the charging mode, the compensation device extracts energy from the power grid, I * O The calculation formula is as follows:
I * O ＝I c +I b-charge
I b-charge rated charge current I by compensation means r-charge Harmonic compensated output current I c Decision, I b-charge The instantaneous value of (2) satisfies the following constraint:
I b-charge +I c <I r-charge
I b-charge +I c >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 charging current and the compensation output electricity
Current target value I after flow superposition * O Instantaneous value is maximum rated charging current I r-charge Instantaneous maximum, I b-charge The calculation is performed according to the following formula:
I b-charge ＝I B sin(ωt)
I b-charge +I c ＝I r-charge
according to the above formula, calculate I B Maximum value of (2) to obtain I b-charge Is used for discharging fundamental wave active current; thereby calculating and obtaining the output current target value I of the compensation device in the charging mode * O
In the discharging mode, the compensating device releases energy to the power grid, I * O ＝I b-discharge -I c ，I b-discharge Rated discharge current I by compensation means r-discharge Harmonic compensated output current I c Decision, I b-discharge The instantaneous value of (2) satisfies the following constraint
I b-discharge -I c <I r-discharge
I b-discharge -I c >0
At this time, in order to make the flywheel operate in this mode for a long time, the discharging speed of the flywheel needs to be slowed down, and the compensating device is taken out to discharge
The instantaneous value of the current being the minimum, i.e. the target value of the current I after superposition of the discharge current and the compensating output current at times other than an integer multiple of half-cycles (nn) * O The instantaneous value is at least 0 and is obtained by superposing the current valuesMinimum value of zero point occurrence, I b-discharge The calculation is performed according to the following formula:
I b-discharge ＝-I A sin(ωt)
I b-discharge -I c ＝0
according to the above formula, calculate I A To obtain the minimum value of I b-discharge Is used for discharging fundamental wave active current; thereby calculating and obtaining the output current target value I of the compensating device in the discharging mode * O 。
7. The flywheel energy storage-based nonlinear load current compensation control method as claimed in claim 5, wherein,
step S10, the current tracking control adopts an instantaneous value comparator or a triangular wave comparator to perform output current tracking control, and the output current target value I is compared * O And an actual value of the output current I O Obtaining PWM control signals of all switching devices in a main circuit;
step S11, controlling and outputting the actual compensation current I O The process is as follows: the PWM control signal controls the on-off of each switch tube of the main circuit through the driving circuit module, and the driving energy conversion main circuit outputs the actual compensation current I O And returning to the step 2.
8. A control device based on the flywheel energy storage nonlinear load current compensation control method of any one of claims 1 to 7, characterized by comprising a flywheel body,
The system comprises 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 in bidirectional electrical connection 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 the power grid in a bidirectional parallel manner 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 conducted or cut 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 wave current, calculating a harmonic compensation target current value, controlling the flywheel to charge and discharge and converting a charge-discharge mode, calculating and outputting PWM control signals of each switching tube of the main circuit according to the compensation target current value and an actual value, and outputting working mode switching signals to the outside for synchronizing an energy conversion mode;
the acquisition device is used for acquiring load current, grid voltage, flywheel charge state, a DC/DC converter working mode and a bidirectional inverter working mode signal in real time.
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