CN114123203B - DC bus voltage ripple suppression strategy during unbalanced AC grid voltage - Google Patents
DC bus voltage ripple suppression strategy during unbalanced AC grid voltage Download PDFInfo
- Publication number
- CN114123203B CN114123203B CN202111259670.1A CN202111259670A CN114123203B CN 114123203 B CN114123203 B CN 114123203B CN 202111259670 A CN202111259670 A CN 202111259670A CN 114123203 B CN114123203 B CN 114123203B
- Authority
- CN
- China
- Prior art keywords
- voltage
- bus
- current
- axis
- direct current
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
Classifications
-
- 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
- H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
-
- 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
- Y02E40/40—Arrangements for reducing harmonics
-
- 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
- Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks
Abstract
The present invention relates to the field of power electronic control. A strategy for suppressing voltage ripple of a direct current bus when the voltage of an alternating current power grid is unbalanced, and step 1: the three-phase PWM converter is controlled to inhibit negative sequence current components on the side of the alternating current bus, so that sinusoidal and symmetrical currents on the side of the alternating current bus are ensured, namely, three-phase electricity on the side of the alternating current bus meets the angles of identical frequency, equal potential amplitude and 120-degree mutual difference of phase difference; step 2: and the fluctuation power on the direct current bus is transferred to the film capacitor by controlling the bidirectional Buck/Boost circuit, so that the direct current bus voltage ripple is restrained. When the power grid voltage is unbalanced, the problem that 2 times of harmonic waves of the direct current side voltage are restrained, a certain amount of negative sequence current exists in the alternating current side current, the alternating current side current is restrained, and the active power can fluctuate secondarily is solved.
Description
Technical field:
the present invention relates to the field of power electronic control.
The background technology is as follows:
grid voltage imbalance phenomena often occur, such as weak current grids in remote areas, uneven distribution of three-phase loads of micro-grids, high-power load access, and limitation of distributed power generation, which can cause voltage imbalance. The unbalanced voltage causes a large number of harmonic waves on both the AC side and the DC side, and the current mainly shows that the current on the AC side contains a negative sequence component, the voltage on the DC side generates ripple waves due to secondary pulsation, and the power transmission of the whole system generates a double frequency component. Voltage ripple and current ripple are major problems for dc micro-grids or dc buses in renewable energy systems and smart grids, which have attracted considerable attention in recent years, and a number of strategies have been developed to reduce ripple in order to obtain smooth dc buses.
The voltage fluctuation amplitude of the direct current side greatly influences the output current quality, in order to restrain the voltage fluctuation of a direct current bus, the traditional method is to connect an electrolytic capacitor with a large capacity in parallel on the direct current side to slow down the fluctuation, but the electrolytic capacitor has the defects of easy volatilization of electrolyte, large volume, low power density, short service life and the like, particularly when the fluctuation voltage is large, the fluctuation current repeatedly charges and discharges the electrolytic capacitor to accelerate the aging of the capacitor, the electrolytic capacitor needs to be replaced frequently, and the reliability of the device is influenced, so that the research on a control strategy for compensating the voltage ripple of the direct current bus without the electrolytic capacitor when the voltage of an alternating current power grid is unbalanced is very necessary.
At present, a great deal of literature research is carried out on the premise of not increasing a bus filter capacitance value (even reducing the bus filter capacitance value), the suppression of direct-current bus voltage fluctuation is realized, the active power filter has the functions of fast harmonic compensation and reactive compensation, and is an important device in power quality treatment, and the parallel active power filter (shunt active power filter, SAPF) is easily disconnected from a power grid when faults occur, and does not influence the operation of other equipment, so that the parallel active power filter is widely applied to power systems. In short, the energy fluctuation on the DC bus is transferred to the additional capacitor, three different circuit topology solutions (bidirectional Buck/Boost, flyback/Boost and multimode Buck/Boost) are proposed and compared in the document "High-Voltage Energy Storage: the Key to Efficient Holdup" for the High-voltage energy storage system to minimize the size of the DC bus capacitor, and the bidirectional Buck/Boost converter is adopted in the document "A High Power Density Single-Phase PWM Rectifier With Active Ripple Energy Storage" to reduce the DC bus capacitor, but the topology adopted in the document absorbs the energy of the DC bus during the step-down and releases the energy to the DC bus during the step-up, so that the voltage requirement of the additional capacitor can only be smaller than the voltage of the DC bus and the voltage regulation range of the capacitor is narrower.
The invention comprises the following steps:
the invention aims to solve the technical problems that: when the power grid is unbalanced, the voltage 2 times harmonic wave of the direct current side is restrained, the current of the alternating current side needs to have a certain amount of negative sequence current, the active power is restrained to have secondary fluctuation, if the two are in coordinated control, the system has the problem of secondary fluctuation of the negative sequence current and the power, the direct current bus voltage fluctuation can be restrained theoretically by increasing the capacitance value of the direct current bus capacitor, and the electrolytic capacitor is generally adopted as the direct current bus capacitor, but has the defects of easy volatilization of electrolyte, large volume, low power density, short service life and the like, and is unfavorable for large-scale expansion and application.
The technical scheme adopted by the invention is as follows: DC bus voltage ripple suppression strategy when AC power grid voltage is unbalanced, AC bus of three-phase AC is connected with DC bus through three-phase PWM converter, first full-control switch tube Q is installed on DC bus 1 Second full-control type switch tube Q 2 Decoupling inductance L a Thin film capacitor C a First full-control switch tube Q 1 And a second fully-controlled switching tube Q 2 One end of the series connection is connected with the positive electrode of the direct current bus, and the other end is connected with the thin film capacitor C a Film capacitor C a The other end of the decoupling inductance La is connected with the negative electrode of the direct current bus, and one end of the decoupling inductance La is connected with the first full-control switch tube Q 1 And a second fully-controlled switching tube Q 2 The other end is connected with the negative pole of the DC bus to form a bidirectional Buck/Boost circuit, and the DC bus voltage ripple suppression strategy when the AC power grid voltage is unbalanced is implemented according to the following steps
Step 1: the three-phase PWM converter is controlled to inhibit negative sequence current components on the side of the alternating current bus, so that sinusoidal and symmetrical currents on the side of the alternating current bus are ensured, namely, three-phase electricity on the side of the alternating current bus meets the angles of identical frequency, equal potential amplitude and 120-degree mutual difference of phase difference;
step 2: the fluctuation power on the direct current bus is transferred to the film capacitor C by controlling the bidirectional Buck/Boost circuit a And thereby suppressing dc bus voltage ripple.
The specific process of step 1 is to refer to the voltage reference value of the DC busSubtracting the DC bus voltage v dc The difference value is sent into a PI regulator, and the output is the reference value of the DC bus current>DC bus current reference value->Reference value of DC bus voltage>Multiplying to obtain reference value of average active power +.>Since unit power factor control is to be achieved, the average reactive power reference value is made +>0, and obtaining an alternating current command for inhibiting alternating negative sequence current control when the alternating current network voltage is unbalanced according to the formula 1And->Wherein->Positive sequence current reference value representing d-axis in dq coordinate system, < >>Positive sequence current reference value representing q-axis in dq coordinate system, < >>And->For three-phase ac bus voltage e a 、e b 、e c Q-axis voltage component e obtained through abc/dq0 coordinate transformation q Positive sequence component and d-axis voltage component e of (c) d Positive sequence component of (2)
AC current commandAnd->With three-phase ac bus current i a 、i b 、i c D-axis current component i obtained through abc/dq0 coordinate transformation d And q-axis current component i q Respectively making difference, then inputting the difference into PI regulator, and subtracting decoupling quantity i from d-axis control q * ωl and adding the decoupling amount i in q-axis control d * ωl, wherein ω=2pi f, f=50hz, L is the ac filter inductance of the three-phase PWM converter, and is then connected to the three-phase ac bus voltage e a 、e b 、e c D-axis voltage component e obtained through abc/dq0 coordinate transformation d And q-axis voltage component e q Adding to obtain d-axis modulation signal +.>And q-axis modulation signal->D-axis modulating signal of the modulating signal in the dq0 coordinate system>And q-axis modulation signal->Through coordinate transformation (T) abc /dq0) -1 Under abc coordinate system, the obtained product is input into SPWM to obtain a switching function S a 、S b 、S c Switching function S k To describe the operating state of the switching tubes of a three-phase PWM rectifier, k=a or b or c, corresponding to three-phase power, S k Expressed as:
the specific process in the step 2 is as follows
The direct current bus current i can obtain a second harmonic component through a resonant filter, and the expression is as follows:
where h=2, ζ is 0.01 or 0.02, the ripple current i to be obtained r And DC bias currentAdding to obtain the reference current of the active power filter>Then the duty ratio D of the charging mode is calculated according to the formulas 4 and 5 c And duty ratio D in discharge mode d Thereby generating gate signals g Q1 And g Q2 To power switch tube Q 1 And Q 2 The driving is carried out so that the driving is carried out,
for ripple current reference value, f r For switching frequency, L a Is the inductance value of the active power filter, V dc Is the voltage value of the direct current bus, V a For additional capacitor voltages.
DC bias currentThe generation method of (1) comprises the following steps:
will add the capacitanceVoltage V a Obtaining ripple voltage of the additional capacitor through the resonant filter, thereby obtaining peak-to-peak value DeltaV of the ripple voltage of the additional capacitor a At the additional capacitance voltage V a Is a direct current component V of (2) a0 The division gives the instantaneous ripple ratio R v The calculation formula is as follows:
wherein the capacitor voltage V is additionally applied a Is a direct current component V of (2) a0 Is composed of V a The transfer function obtained by holding the filter is:
the fundamental frequency of the ripple is twice the ac power supply frequency; additional capacitive voltage DC component V a0 Divided by the additional capacitance voltage V a Reference value of minimum voltage of +.>Substitution of the reference value +.8 for the ripple ratio> And R is R v The difference value of (2) is sent into a PI controller to obtain direct current bias current +.>
In general, an unbalanced three-phase vector can be decomposed into a form of a sum of a positive sequence component and a negative sequence component, and a negative sequence ac power supply voltage is often accompanied by an ac current generating a negative sequence and a converter terminal voltage of the negative sequence, so that an ac power supply voltage, a space vector of the ac current, can be expressed as:
wherein omega is the angular frequency of the electromotive force of the power grid,and->Is the complex vector of positive and negative sequence electromotive force of dq0 coordinate system,>andis the complex vector of positive and negative sequence currents of the dq0 coordinate system.
The transmission power under the unbalanced condition of the power grid is as follows:
wherein superscript ". Times.indicates the complex conjugate. According to the above equation, the active power that can be transmitted is:
P＝P 0 +P c2 cos(2ωt)+P s2 sin (2ωt) (11)
It can be seen that the negative sequence component of the grid will introduce 2 times the frequency of the power ripple on the dc bus, where P c2 And P s2 The method comprises the following steps:
analysis shows that the elimination of the negative sequence current component and the elimination of the fluctuating power are contradictory, that is, the two control targets of sinusoidal symmetrical alternating current and no direct current bus voltage fluctuation cannot be simultaneously achieved without an additional circuit.
In order to achieve two control targets of sinusoidal symmetric alternating current and ripple-free direct current, a direct current bus voltage ripple suppression strategy when alternating current grid voltage is unbalanced is provided, and the method is characterized by comprising the following steps:
step 1: the three-phase PWM converter is controlled to inhibit negative sequence current components on the side of the alternating current bus, so that sinusoidal and symmetrical currents on the side of the alternating current bus are ensured, namely, three-phase electricity on the side of the alternating current bus meets the angles of identical frequency, equal potential amplitude and 120-degree mutual difference of phase difference;
step 2: the fluctuation power on the direct current bus is transferred to the film capacitor C by controlling the bidirectional Buck/Boost circuit a And thereby suppressing dc bus voltage ripple.
Further, in the step 1, the three-phase AC/DC converter is controlled to suppress the negative sequence current component on the AC side, so as to ensure that the current on the AC side is sinusoidal and symmetrical, and the specific control method is as follows:
reference value of DC bus voltageSubtracting the DC bus voltage v dc The difference value is sent into a PI regulator, and the output is the reference value of the DC bus current>DC bus current reference value->Reference value of DC bus voltage>Multiplying to obtain reference value of average active power +.>Since unit power factor control is to be achieved, the average reactive power reference value is made +>An ac current command +.0 for suppressing ac negative sequence current control when the ac grid voltage is unbalanced is obtained according to equation 1>And->Wherein->Positive sequence current reference value representing d-axis in dq coordinate system, < >>Positive sequence current reference value representing q-axis in dq coordinate system, < >>And->For three-phase ac bus voltage e a 、e b 、e c Q-axis voltage component e obtained through abc/dq0 coordinate transformation q Positive sequence component and d-axis voltage component e of (c) d Positive sequence component of (2)
AC current commandAnd->Is intersected with three phasesCurrent bus current i a 、i b 、i c D-axis current component i obtained through abc/dq0 coordinate transformation d And q-axis current component i q Respectively making difference, then inputting the difference into PI regulator, and subtracting decoupling quantity i from d-axis control q * ωl and adding the decoupling amount i in q-axis control d * ωl, wherein ω=2pi f, f=50hz, L is the ac filter inductance of the three-phase PWM converter, and is then connected to the three-phase ac bus voltage e a 、e b 、e c D-axis voltage component e obtained through abc/dq0 coordinate transformation d And q-axis voltage component e q Adding to obtain d-axis modulation signal +.>And q-axis modulation signal->D-axis modulating signal of the modulating signal in the dq0 coordinate system>And q-axis modulation signal->Through coordinate transformation (T) abc /dq0) -1 Under abc coordinate system, the obtained product is input into SPWM to obtain a switching function S a 、S b 、S c Switching function S k To describe the operating state of the switching tubes of a three-phase PWM rectifier, k=a or b or c, corresponding to three-phase power, S k Expressed as:
further, the specific method for connecting the bidirectional Buck/Boost active power compensation circuit in parallel in the step 2 is as follows:
an alternating current bus of the three-phase alternating current is connected with a direct current bus through a three-phase PWM converter, and a first full-control switch tube Q is arranged on the direct current bus 1 Second full controlSwitch tube Q 2 Decoupling inductance L a Thin film capacitor C a First full-control switch tube Q 1 And a second fully-controlled switching tube Q 2 One end of the series connection is connected with the positive electrode of the direct current bus, and the other end is connected with the thin film capacitor C a Film capacitor C a The other end of the decoupling inductance La is connected with the negative electrode of the direct current bus, and one end of the decoupling inductance La is connected with the first full-control switch tube Q 1 And a second fully-controlled switching tube Q 2 The other end of the filter is connected with the negative electrode of the direct current bus to form a bidirectional Buck/Boost active power filter circuit.
In order to eliminate the voltage ripple on the dc bus, all ripple power should be transferred to the additional capacitor C a This involves two modes of operation: auxiliary capacitor C a Charging and discharging are performed. The active power filter operates in Discontinuous Conduction Mode (DCM) because in this case the PWM duty cycle of the power switch can be directly calculated and controlled without measuring the inductor current, which saves a current sensor and simplifies the design of the controller because the active power filter is a Buck/Boost circuit in charge-discharge mode, thus adding capacitor C a The voltage on can be lower or higher than the DC bus voltage, which provides for further reduction of the additional capacitance C a Possibility of capacitance.
When ripple current i r For positive, add-on capacitance C a In charging mode, ripple energy passes from the dc bus through the inductor L a Transfer to additional capacitance C a And (3) upper part. In this mode, the second fully controlled switching tube Q 2 Always closed, first full-control switch tube Q 1 Driven by PWM signals, diode D 2 Will induce a current i L To an additional capacitor C a And (3) upper part.
When the first fully-controlled switch tube Q 1 On, and duty cycle isThe inductor absorbs energy from the direct current bus and the inductor current i L Increasing, its rate of rise is:
when the first fully-controlled switch tube Q 1 Turn off, inductor current i L The reduction rate is as follows:
whenever V is a ＜V DC Or V (V) a ＞V DC They have the same current waveform shape but different falling rates, thereby calculating the duty ratio D in the charging mode c The method comprises the following steps:
when ripple current i r When negative, add-on capacitor C a In the discharging mode, an additional capacitor C a Through inductance L a Transmitting power to a DC bus, in which mode a first fully controlled switching tube Q 1 Always off, second full control switch tube Q 2 Driven by PWM signals, when the second fully-controlled switch tube Q 2 When the inductor is disconnected, the follow current of the inductor flows through the diode D 1 。
When the second fully-controlled switch tube Q 2 On, and duty cycle isInductor current i L Increasing, its rate of rise is:
when the second fully-controlled switch tube Q 2 Turn off, inductor current i L The reduction rate is as follows:
whenever V is a ＜V DC Or V (V) a ＞V DC The current waveforms are identical in shape but different in rising rate, thereby calculating the duty ratio D in the discharge mode d The method comprises the following steps:
further, the control method of the double Buck/Boost active power compensation circuit in the step 2 is as follows:
the second harmonic component can be obtained by passing the direct current bus current i through a resonant filter, and the transfer function is as follows:
where h=2, ω=2pi f, the ripple current i to be obtained r And DC bias currentAdding to obtain the reference current of the active power filter>Then the duty ratio D of the charging mode is calculated according to the formulas 4 and 5 c And duty ratio D in discharge mode d To PWM to generate gate signals g Q1 And g Q2 To power switch tube Q 1 And Q 2 And driving.
Further, the DC bias currentThe generation method of (1) comprises the following steps:
will add the capacitance voltage V a Obtaining ripple voltage of additional capacitance by resonant filter, thereby obtaining additional electricityPeak-to-peak value DeltaV of Rong Wenbo voltage a At the additional capacitance voltage V a Is a direct current component V of (2) a0 The division gives the instantaneous ripple ratio R v The calculation formula is as follows:
wherein the capacitor voltage V is additionally applied a Is a direct current component V of (2) a0 Is composed of V a The transfer function obtained by holding the filter is:
the fundamental frequency of the ripple is twice the ac power supply frequency; additional capacitive voltage DC component V a0 Divided by the additional capacitance voltage V a Reference value of minimum voltage of (2)Substitution of the reference value +.8 for the ripple ratio> And R is R v The difference value of (2) is sent into a PI controller to obtain direct current bias current +.>
The invention adopts the active power filter which is a Buck/Boost converter in both a charging mode and a discharging mode, thus adding a capacitor C a The voltage may be lower or higher than the DC bus voltage, which provides a voltage when it is controlled to be higher than the DC bus voltageThe possibility of further reducing the capacitance of the capacitor is further reduced because the additional capacitor stores energy asPeak-to-peak value Δv of the ripple voltage of the additional capacitor a The method comprises the following steps:
for a given ripple energy, an additional capacitance voltage V a The larger the additional capacitance C a The smaller the capacitance value; peak-to-peak value DeltaV of additional capacitance ripple voltage a The larger the additional capacitance C a The smaller the capacitance.
The peak-to-peak value of the fluctuation energy transmitted from the ac side to the dc bus is:
assuming that the rated DC voltage is + -k% in the allowable fluctuation range of the DC voltage, the maximum peak-to-peak value of the fluctuation energy flowing through the DC bus is:
when the traditional electrolytic capacitor is used as a fluctuation power compensation mode to compensate the secondary fluctuation power, the minimum capacitance capacity required is as follows:
in the method, in the process of the invention,representing the degree of voltage imbalance.
When the active compensation circuit provided by the invention is adopted to absorb direct current secondary fluctuation power, the capacity of the required minimum additional capacitor is as follows:
it can be seen that with the additional capacitance voltage V a The minimum capacitance required by the active compensation circuit will be substantially reduced; in addition, the minimum capacitance required is inversely proportional to the ac voltage imbalance, that is, the greater the ac voltage imbalance, the greater the capacitance required by the active power compensation circuit.
Compared with the traditional electrolytic capacitor compensation circuit and the compensation circuit provided by the invention, when the same-size double frequency fluctuation power is compensated, the capacitance-capacity ratio required by two compensation modes is theoretically:
wherein m=v a /V dc Representing the modulation factor of the compensation circuit, if each parameter takes the value as follows: m=1, k% =0.5%, compared to passive compensation, the capacitance capacity required by the active power compensator proposed by the present invention can be reduced by at least 50 times. Therefore, a thin film capacitor with a small volume can be used as an additional capacitor, thereby prolonging the service life of the system. The invention firstly adopts an AC/DC unbalanced control strategy, eliminates alternating negative sequence current through calculation of a current instruction, improves network side current waveform, ensures that three-phase current is basically symmetrical (does not contain negative sequence current), secondly adopts an active power filter with Buck/Boost during charge and discharge, the additional capacitance voltage of the active power filter can be controlled to be lower than or higher than the DC bus voltage, the adjustment range of the capacitance voltage is wider, the absorption or release of ripple energy under different bus voltage conditions can be satisfied, and the active power filter controls the additional capacitance C a Charging and discharging of the DC busTransfer to additional capacitance C a And (3) upper part. The problem that when a power grid is unbalanced, 2 times of harmonic waves of direct-current side voltage are restrained, a certain amount of negative sequence current exists in alternating-current side current, secondary fluctuation exists in active power is restrained, if the two are in coordinated control, the system can have the problem of secondary fluctuation of the negative sequence current and the power, and meanwhile, the control strategy can effectively reduce the direct-current side capacitor C dc The thin film capacitor can be used for replacing the traditional electrolytic capacitor with large capacitance, so that the reliability of the equipment is improved.
Compared with the prior art, the invention has the following advantages:
1) When the power grid voltage is unbalanced, the problem that 2 times of harmonic waves of the direct current side voltage are restrained, a certain amount of negative sequence current exists in the alternating current side current, the active power is restrained, and the secondary fluctuation exists is solved, so that the sine and symmetry of the alternating current side current are ensured, and the voltage ripple of a direct current bus is restrained well;
2) The voltage on the additional capacitor can be regulated to be lower than or higher than the voltage of the direct current bus, which relaxes the limit on the design of the system, so that the capacitance of the additional capacitor can be further reduced by increasing the voltage of the additional capacitor, namely, the traditional electrolytic capacitor can be replaced by a thin film capacitor;
3) In addition, the invention adopts an independent active electric power compensation device, which is simple to control and easy to realize.
Description of the drawings:
FIG. 1 is a schematic diagram of an AC/DC hybrid microgrid DC side parallel-type SAPF system topology;
FIG. 2 is a control block diagram for controlling a three-phase AC/DC converter to suppress negative sequence current components on the AC side;
FIG. 3 is a specific control block diagram of a parallel bi-directional Buck/Boost active power compensation circuit;
FIG. 4 is a graph of the required capacitance versus imbalance and additional capacitance voltage magnitude.
The specific embodiment is as follows:
the invention will be further described with reference to the drawings and the specific embodiments. It is to be understood, however, that the invention may be embodied in various forms and that the exemplary and non-limiting embodiments shown in the drawings and described below are not intended to limit the invention to the specific embodiments described.
FIG. 1 shows the topology of an AC/DC hybrid micro-grid parallel type SAPF system of the invention, the system comprises: three-phase power grid, alternating current filter inductance L s And resistance R s Three-phase PWM converter, DC capacitor C dc The direct-current side resistor R and the additional energy storage capacitor can work as an active power compensation device of Buck/Boost when absorbing and releasing energy. The specific method for the parallel bidirectional Buck/Boost active power compensation circuit comprises the following steps: an alternating current bus of the three-phase alternating current is connected with a direct current bus through a three-phase PWM converter, and a first full-control switch tube Q is arranged on the direct current bus 1 Second full-control type switch tube Q 2 Decoupling inductance L a Thin film capacitor C a First full-control switch tube Q 1 And a second fully-controlled switching tube Q 2 One end of the series connection is connected with the positive electrode of the direct current bus, and the other end is connected with the thin film capacitor C a Film capacitor C a The other end of the decoupling inductance La is connected with the negative electrode of the direct current bus, and one end of the decoupling inductance La is connected with the first full-control switch tube Q 1 And a second fully-controlled switching tube Q 2 The other end of the circuit is connected with the negative electrode of the direct current bus to form a bidirectional Buck/Boost circuit.
The DC bus voltage ripple suppression strategy when the AC network voltage is unbalanced is implemented according to the following steps
Step 1: the three-phase PWM converter is controlled to inhibit negative sequence current components on the side of the alternating current bus, so that sinusoidal and symmetrical currents on the side of the alternating current bus are ensured, namely, three-phase electricity on the side of the alternating current bus meets the angles of identical frequency, equal potential amplitude and 120-degree mutual difference of phase difference;
step 2: the fluctuation power on the direct current bus is transferred to the film capacitor C by controlling the bidirectional Buck/Boost circuit a And thereby suppressing dc bus voltage ripple.
The specific control method for suppressing the negative sequence current component on the alternating current bus side by controlling the three-phase PWM converter in the step 1 is shown in fig. 2, and the specific process is that,reference value of DC bus voltageSubtracting the DC bus voltage v dc The difference value is sent into a PI regulator, and the output is the reference value of the DC bus current>DC bus current reference value->Reference value for DC bus voltageMultiplying to obtain reference value of average active power +.>Since unit power factor control is to be achieved, the average reactive power reference value is made +>An ac current command +.0 for suppressing ac negative sequence current control when the ac grid voltage is unbalanced is obtained according to equation 1>And->Wherein->Positive sequence current reference value representing d-axis in dq coordinate system, < >>Positive sequence current reference value representing q-axis in dq coordinate system, < >>And->For three-phase ac bus voltage e a 、e b 、e c Q-axis voltage component e obtained through abc/dq0 coordinate transformation q Positive sequence component and d-axis voltage component e of (c) d Is a positive sequence component of (a).
AC current commandAnd->With three-phase ac bus current i a 、i b 、i c D-axis current component i obtained through abc/dq0 coordinate transformation d And q-axis current component i q Respectively making difference, then inputting the difference into PI regulator, and subtracting decoupling quantity i from d-axis control q * ωl and adding the decoupling amount i in q-axis control d * ωl, wherein ω=2pi f, f=50hz, L is the ac filter inductance of the three-phase PWM converter, and is then connected to the three-phase ac bus voltage e a 、e b 、e c D-axis voltage component e obtained through abc/dq0 coordinate transformation d And q-axis voltage component e q Adding to obtain d-axis modulation signal +.>And q-axis modulation signal->D-axis modulating signal of the modulating signal in the dq0 coordinate system>And q-axis modulation signal->Through coordinate transformation (T) abc /dq0) -1 Under abc coordinate system, the obtained product is input into SPWM to obtain a switching function S a 、S b 、S c Switching function S k To describe the operating state of the switching tubes of a three-phase PWM rectifier, k=a or b or c, corresponding to three-phase power, S k Expressed as:
in the step 2, a strategy for suppressing voltage ripple of the dc bus when the ac grid voltage is unbalanced is shown in fig. 3, and the specific process is as follows:
the direct current bus current i can obtain a second harmonic component through a resonant filter, and the expression is as follows:
where h=2, ζ is 0.01 or 0.02, the ripple current i to be obtained r And DC bias currentAdding to obtain the reference current of the active power filter>Then the duty ratio D of the charging mode is calculated according to the formulas 4 and 5 c And duty ratio D in discharge mode d Thereby generating gate signals g Q1 And g Q2 To power switch tube Q 1 And Q 2 The driving is carried out so that the driving is carried out,
for ripple current reference value, f r For switching frequency, L a Is the inductance value of the active power filter, V dc Is the voltage value of the direct current bus, V a For additional capacitor voltages.
DC bias currentThe generation method of (1) comprises the following steps:
will add the capacitance voltage V a Obtaining ripple voltage of the additional capacitor through the resonant filter, thereby obtaining peak-to-peak value DeltaV of the ripple voltage of the additional capacitor a At the additional capacitance voltage V a Is a direct current component V of (2) a0 The division gives the instantaneous ripple ratio R v The calculation formula is as follows:
wherein the capacitor voltage V is additionally applied a Is a direct current component V of (2) a0 Is composed of V a The transfer function obtained by holding the filter is:
wherein the method comprises the steps ofThe fundamental frequency of the ripple is twice the ac power supply frequency; additional capacitive voltage DC component V a0 Divided by the additional capacitance voltage V a Reference value of minimum voltage of +.>Substitution of the reference value +.8 for the ripple ratio> And R is R v The difference value of (2) is sent into a PI controller to obtain direct current bias current +.>
If the AC rated voltage of the converter is 380V, the DC voltage variation range is selected to be 500V-850V, the rated power of the system is 30KW, the relationship between the minimum additional capacitance capacity required on the DC side, the unbalance degree and the additional capacitance amplitude can be expressed as shown in figure 4, and the relationship with the additional capacitance voltage V can be known from the figure a The minimum capacitance required by the active compensation circuit will be substantially reduced; in addition, the minimum capacitance required is inversely proportional to the ac voltage imbalance, that is, the greater the ac voltage imbalance, the greater the capacitance required by the active power compensation circuit.
Compared with the traditional electrolytic capacitor compensation circuit and the compensation circuit provided by the invention, when the same-size double frequency fluctuation power is compensated, the capacitance-capacity ratio required by two compensation modes is theoretically:
wherein m=v a /V dc Representing the modulation factor of the compensation circuit, if each parameter takes the value as follows: m=1, k% =0.5%, compared to passive compensation, the capacitance capacity required by the active power compensator proposed by the present invention can be reduced by at least 50 times. Therefore, a thin film capacitor with a small volume can be used as an additional capacitor, thereby prolonging the service life of the system.
Claims (2)
1. The DC bus voltage ripple suppression strategy when the AC power grid voltage is unbalanced is characterized in that: an alternating current bus of the three-phase alternating current is connected with a direct current bus through a three-phase PWM converter, and a first full-control switch tube Q is arranged on the direct current bus 1 Second full-control type switch tube Q 2 Decoupling inductance L a Thin film capacitor C a First full-control switch tube Q 1 And a second fully-controlled switching tube Q 2 One end of the series connection is connected with the positive electrode of the direct current bus, and the other end is connected with the thin film capacitor C a Film capacitor C a The other end of the decoupling inductance La is connected with the negative electrode of the direct current bus, and one end of the decoupling inductance La is connected with the first full-control switch tube Q 1 And a second fully-controlled switching tube Q 2 The other end of the voltage transformer is connected with the negative electrode of the direct current bus to form a bidirectional Buck/Boost circuit, and the voltage ripple suppression strategy of the direct current bus when the voltage of the alternating current power grid is unbalanced is implemented according to the following steps:
step 1: the three-phase PWM converter is controlled to inhibit negative sequence current components on the side of the alternating current bus, so that sinusoidal and symmetrical currents on the side of the alternating current bus are ensured, namely, three-phase electricity on the side of the alternating current bus meets the angles of identical frequency, equal potential amplitude and 120-degree mutual difference of phase difference;
the specific process of step 1 is to refer to the voltage reference value of the DC busSubtracting the DC bus voltage v dc The difference value is sent into a PI regulator, and the output is the reference value of the DC bus current>DC bus current reference value->Reference value of DC bus voltage>Multiplying to obtain reference value of average active power +.>Since unit power factor control is to be achieved, the average reactive power reference valueAn ac current command +.0 for suppressing ac negative sequence current control when the ac grid voltage is unbalanced is obtained according to equation 1>Andwherein->Positive sequence current reference value representing d-axis in dq coordinate system, < >>Positive sequence current reference value representing q-axis in dq coordinate system, < >>And->For three-phase ac bus voltage e a 、e b 、e c Q-axis voltage component e obtained through abc/dq0 coordinate transformation q Positive sequence component and d-axis voltage component e of (c) d Positive sequence component of (2)
AC current commandAnd->With three-phase ac bus current i a 、i b 、i c D-axis current component i obtained through abc/dq0 coordinate transformation d And q-axis current component i q Respectively making difference, then inputting the difference into PI regulator, and subtracting decoupling quantity i from d-axis control q * ωl and adding the decoupling amount i in q-axis control d * ωl, wherein ω=2pi f, f=50hz, L is the ac filter inductance of the three-phase PWM converter, and is then connected to the three-phase ac bus voltage e a 、e b 、e c D-axis voltage component e obtained through abc/dq0 coordinate transformation d And q-axis voltage component e q Adding to obtain d-axis modulation signal +.>And q-axis modulation signal->D-axis modulating signal of the modulating signal in the dq0 coordinate system>And q-axis modulation signal->Through coordinate transformation (T) abc /dq0) -1 Under abc coordinate system, the obtained product is input into SPWM to obtain a switching function S a 、S b 、S c Switching function S k To describe the operating state of the switching tubes of a three-phase PWM rectifier, k=a or b or c, corresponding to three-phase power, S k Expressed as:
step 2: by controlling the bidirectional Buck/Boost circuit, the fluctuation on the direct current bus is controlledTransfer of power to film capacitor C a Suppressing dc bus voltage ripple;
the specific process in the step 2 is as follows:
the direct current bus current i can obtain a second harmonic component through a resonant filter, and the expression is as follows:
where h=2, ζ is 0.01 or 0.02, the ripple current i to be obtained r And DC bias currentAdding to obtain the reference current of the active power filter>Then the duty ratio D of the charging mode is calculated according to the formulas 4 and 5 c And duty ratio D in discharge mode d Thereby generating gate signals g Q1 And g Q2 To power switch tube Q 1 And Q 2 The driving is carried out so that the driving is carried out,
for ripple current reference value, f r For switching frequency, L a Is the inductance value of the active power filter, V dc Is the voltage value of the direct current bus, V a For additional capacitor voltages.
2. The dc bus voltage ripple suppression strategy for an ac grid voltage imbalance of claim 1, wherein the dc bias currentThe generation method of (1) comprises the following steps:
will add the capacitance voltage V a Obtaining ripple voltage of the additional capacitor through the resonant filter, thereby obtaining peak-to-peak value DeltaV of the ripple voltage of the additional capacitor a At the additional capacitance voltage V a Is a direct current component V of (2) a0 The division gives the instantaneous ripple ratio R v The calculation formula is as follows:
wherein the capacitor voltage V is additionally applied a Is a direct current component V of (2) a0 Is composed of V a The transfer function obtained by holding the filter is:
the fundamental frequency of the ripple is twice the ac power supply frequency; additional capacitive voltage DC component V a0 Divided by the additional capacitance voltage V a Reference value of minimum voltage of +.>Substitution of the reference value +.8 for the ripple ratio>And R is R v The difference value of (2) is sent into a PI controller to obtain direct current bias current +.>
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202111259670.1A CN114123203B (en) | 2021-10-28 | 2021-10-28 | DC bus voltage ripple suppression strategy during unbalanced AC grid voltage |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202111259670.1A CN114123203B (en) | 2021-10-28 | 2021-10-28 | DC bus voltage ripple suppression strategy during unbalanced AC grid voltage |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN114123203A CN114123203A (en) | 2022-03-01 |
| CN114123203B true CN114123203B (en) | 2023-08-29 |
Family
ID=80377282
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202111259670.1A Active CN114123203B (en) | 2021-10-28 | 2021-10-28 | DC bus voltage ripple suppression strategy during unbalanced AC grid voltage |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN114123203B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115693632B (en) * | 2022-09-07 | 2023-06-16 | 广东工业大学 | Control method for DC micro-grid power oscillation suppression device |
| CN115333133B (en) * | 2022-10-14 | 2023-02-28 | 锦浪科技股份有限公司 | Energy storage system control method and device and energy storage system |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN202406336U (en) * | 2011-11-16 | 2012-08-29 | 王金浩 | Novel LED isolation type drive power supply |
| WO2015140867A1 (en) * | 2014-03-15 | 2015-09-24 | 三菱電機株式会社 | Motor drive control device, compressor, fan, and air-conditioning machine |
| CN111740455A (en) * | 2020-07-22 | 2020-10-02 | 太原理工大学 | Bus interface converter control method for uniformly compensating alternating-current unbalanced voltage and direct-current pulsating voltage |
| CN111740454A (en) * | 2020-07-22 | 2020-10-02 | 太原理工大学 | Hybrid microgrid alternating current-direct current voltage unified control method based on bus interface converter |
| CN113098013A (en) * | 2021-04-09 | 2021-07-09 | 中国矿业大学 | Electrolytic capacitor-free parallel active power filter system and control method |
| CN113517724A (en) * | 2021-04-09 | 2021-10-19 | 国网山西省电力公司电力科学研究院 | Method for suppressing voltage ripple on direct current side of alternating current-direct current hybrid micro-grid |
-
2021
- 2021-10-28 CN CN202111259670.1A patent/CN114123203B/en active Active
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN202406336U (en) * | 2011-11-16 | 2012-08-29 | 王金浩 | Novel LED isolation type drive power supply |
| WO2015140867A1 (en) * | 2014-03-15 | 2015-09-24 | 三菱電機株式会社 | Motor drive control device, compressor, fan, and air-conditioning machine |
| CN111740455A (en) * | 2020-07-22 | 2020-10-02 | 太原理工大学 | Bus interface converter control method for uniformly compensating alternating-current unbalanced voltage and direct-current pulsating voltage |
| CN111740454A (en) * | 2020-07-22 | 2020-10-02 | 太原理工大学 | Hybrid microgrid alternating current-direct current voltage unified control method based on bus interface converter |
| CN113098013A (en) * | 2021-04-09 | 2021-07-09 | 中国矿业大学 | Electrolytic capacitor-free parallel active power filter system and control method |
| CN113517724A (en) * | 2021-04-09 | 2021-10-19 | 国网山西省电力公司电力科学研究院 | Method for suppressing voltage ripple on direct current side of alternating current-direct current hybrid micro-grid |
Non-Patent Citations (1)
| Title |
|---|
| 一种不平衡负载下直流微电网电压脉动抑制方法;朱晓荣;张雨;电工技术学报(第15期);全文 * |
Also Published As
| Publication number | Publication date |
|---|---|
| CN114123203A (en) | 2022-03-01 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN108667036A (en) | A kind of electric vehicle V2G inverter control methods | |
| CN114123203B (en) | DC bus voltage ripple suppression strategy during unbalanced AC grid voltage | |
| CN104052079A (en) | Electric energy feedback type electronic load | |
| CN108512452A (en) | A kind of control system and control method of direct-current grid grid-connection converter electric current | |
| CN104868762B (en) | A kind of electric power electric transformer and its control method of scattered energy storage | |
| CN110212535B (en) | Higher harmonic active stabilization device and method for AC/DC hybrid microgrid | |
| CN103490448A (en) | Power generation energy storage device based on cascade H bridge and multiport DC converter | |
| Liu et al. | Electronic power transformer with supercapacitors storage energy system | |
| CN100407540C (en) | Compound control method of injection mixed active power filter | |
| CN106849103A (en) | Transformerless type single-phase dynamic voltage compensator based on HVDC Modulation | |
| CN102570466A (en) | Current detecting and controlling method of hybrid parallel-connected electric energy quality regulator | |
| Song et al. | Power model free voltage ripple suppression method of three-phase PWM rectifier under unbalanced grid | |
| Singh et al. | Battery Energy Storage System for PV Output Power Leveling. | |
| CN106877333B (en) | PWM rectifier with active compensation capability and control method thereof | |
| Tanaka et al. | Novel simple harmonics compensation method for smart charger with constant DC-capacitor voltage control for electric vehicles on single-phase three-wire distribution feeders | |
| Madichetty et al. | Modeling and design of solid state smart transformer for microgrid | |
| Zharkin et al. | Development of Powerful Unified Inverter Modules for Energy Storage Systems | |
| Tareen et al. | A transformerless reduced switch counts three-phase APF-assisted smart EV charger | |
| CN113013919B (en) | Symmetrical dual-mode photovoltaic inverter device | |
| Mohamed et al. | FACTS Family for Voltage Sag Alleviation: Performance Study and Analysis | |
| Zhu et al. | A voltage ripple suppression method of DC microgrid under unbalanced load | |
| Rastogi et al. | Simultaneous active and reactive power compensation using STATCOM with supercapacitor energy storage system | |
| Huang et al. | An automatic power decoupling control method on three level DC-AC converter to suppress the double-line-frequency ripple | |
| Huang et al. | A Novel Double-Line-Frequency Ripple Suppression Method for Single Phase DC-AC Converter Based on Three-Level Topology | |
| Balam et al. | Dynamic Performance of 48-pulse STATCOM, SSSC and UPFC controller |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |