CN108847669B - Multi-synchronous rotation coordinate system-based multifunctional grid-connected inverter harmonic treatment method - Google Patents
Multi-synchronous rotation coordinate system-based multifunctional grid-connected inverter harmonic treatment method Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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Abstract
The invention discloses a multi-synchronous rotating coordinate system-based harmonic treatment method for a multifunctional grid-connected inverter. The inverter synthesizes the dc quantities into a corresponding alternating current as a harmonic compensation component. After obtaining the fundamental wave reference component and the harmonic compensation component, the multifunctional grid-connected inverter tracks the alternating current component by using the proportional resonant controller under an abc coordinate system, thereby realizing the harmonic treatment function of the multifunctional grid-connected inverter. The method can transmit data to the multifunctional grid-connected inverter terminal with lower bandwidth, and in addition, the method simply solves the problem of harmonic pollution caused by nonlinear load, improves the reliability of electric energy quality, and is beneficial to improving the utilization efficiency of energy.
Description
Technical Field
The invention relates to a harmonic wave treatment method, in particular to a multifunctional grid-connected inverter harmonic wave treatment method based on a multi-synchronous rotating coordinate system, and belongs to the field of electric energy quality improvement.
Background
The grid-connected inverter is used for connecting a distributed power supply system and a power grid and realizing electric energy transmission and exchange. Of course, the grid-connected inverter can also work in a grid-disconnected state, namely independently supplying power to users independently of the power grid. In fact, due to the fact that a large number of nonlinear loads are connected in the power grid at present, and the power electronization degree of the power system is continuously deepened, the power quality problems of harmonic waves, three-phase imbalance, voltage sag and the like caused by the power quality problems are greatly reduced, so that power grid pollution and power quality decline are caused, power supply and power utilization equipment faults are caused, even serious fire accidents and the like are caused, and the safe, economical and stable operation of the power system is continuously threatened.
There are two main directions to improve the quality of electric energy at present:
firstly, add extra electric energy quality and improve the device, mainly divide into: the passive filter device, the active filter device and the reactive power compensation device; although the passive filter has extremely low cost, economy and simplicity, the passive filter has weak capability of suppressing harmonic waves and poor effect, such as an LC series filter; for an active filter, the active filter can compensate timely, capacitive elements of a power grid are not added, and the filtering effect is good, but the active filter is limited by the voltage resistance of power electronic elements and the development of rated current, so that the cost is extremely high, the manufacturing of the active filter is more complex than that of a passive filter, and the cost is much higher, for example, the active filter (APF); the reasonable selection of the reactive power compensation device can reduce the loss of the network to the maximum extent and improve the quality of the power grid, but if the device is selected or used improperly, various factors such as a power supply system, voltage fluctuation, even harmonic wave increase and the like can be caused, for example, a Static Var Compensator (SVC) and the like.
And secondly, modifying an algorithm on the basis of active output of the inverter, so that the inverter can compensate harmonic waves, unbalance, reactive power and the like of a system on the basis of active output, namely a multifunctional grid-connected inverter (MGFTI). The method does not need to increase initial investment cost, fully utilizes the residual capacity of the inverter, and is an economical and effective way for solving the problem of power quality. In the multifunctional grid-connected inverter, common methods for analyzing the harmonic component of the load current are instantaneous reactive power theory (pq theory) and Fast Fourier Transform (FFT).
In summary, how to provide a method for managing harmonics based on a multifunctional grid-connected inverter becomes a problem to be solved urgently by those skilled in the art.
Disclosure of Invention
The invention aims to solve the defects of the prior art, and provides a multi-functional grid-connected inverter harmonic treatment method based on a multi-synchronous rotating coordinate system. Therefore, on the basis of active power output, the treatment of load harmonic waves is realized, and the limitation that the existing multifunctional inverter needs to locally acquire load information is solved.
The technical solution of the invention is as follows:
the multi-synchronous rotation coordinate system-based multifunctional grid-connected inverter harmonic treatment method comprises the following steps:
s1: obtaining fundamental wave angular frequency; by designing a phase-locked loop, carrying out phase locking on system voltage at the same time with the multifunctional grid-connected inverter on a load side to obtain a value of angular frequency;
s2: the calculation of the fundamental wave reference current comprises the following steps:
s21: on the inverter side, converting the system voltage from an abc static coordinate system to a dq coordinate system through Park conversion, and calculating corresponding dq-axis reference current by using dq-axis voltage in the dq coordinate system and given active power P and reactive power Q;
the formula of Park transformation is:
the dq-axis reference current
The calculation method comprises the following steps:
s211: the system voltage v is converted by using Park conversion formulaabcConverted into a voltage component on the dq axis,
then the calculation formula of the instantaneous power in dq coordinate system is:
s212: for a given active power P and reactive power Q, the formula for the dq-axis current component is:
s213 according to the upper energy management system or the maximum outputtable power instruction P*，Q*Thereby calculating the dq-axis reference current
S22: adding the d-axis reference current and the d-axis current consumed by the compensation system, and performing Park inverse transformation on the d-axis reference current and the q-axis reference current to obtain fundamental wave reference current under an abc static coordinate system;
fundamental wave reference current in the abc static coordinate system
Comprises the following steps:
wherein the content of the first and second substances,
the fundamental component of the d-axis reference current for compensating the inverter loss;
the method for acquiring the d-axis current consumed by the compensation system is to acquire the difference between the actual value of the capacitor voltage and the given direct-current side voltage and then perform PI closed-loop control;
s3: the calculation of the harmonic reference current comprises the following steps:
s31: analyzing harmonic components in the load current on the load side;
s32: for different harmonic components, respectively carrying out Park conversion on the load current at proper times of fundamental wave angular frequency, carrying out low-pass filtering on components under the dq axis to obtain corresponding direct current components, and obtaining direct current components of harmonic components in the load current;
s33: packaging the direct current component of the harmonic component and sending the direct current component to the side of the multifunctional grid-connected inverter;
s34: the multifunctional grid-connected inverter performs Park inverse transformation on the direct-current component of the harmonic component at proper times of fundamental angular frequency, so that harmonic reference current under an abc coordinate system is locally synthesized;
s4: synthesizing reference current of the multifunctional grid-connected inverter; synthesizing the fundamental wave reference current in the step S2 and the harmonic wave reference current in the step S3 into a multifunctional grid-connected inverter reference current;
s5: tracking the reference current of the multifunctional grid-connected inverter; in an abc static coordinate system, unsteady error tracking of an alternating current component is realized by designing a proper proportional coefficient and a proper resonance coefficient of a proportional resonance controller and providing infinite gain at a resonance point;
the reference current of the multifunctional grid-connected inverter comprises fundamental wave reference current and harmonic wave reference current, and the fundamental wave reference current is determined by an upper energy management system or the maximum output power.
Preferably, the multifunctional grid-connected inverter is a three-phase three-wire system, and a capacitor on the direct current side of the multifunctional grid-connected inverter is connected with the distributed power supply or the energy storage direct current output end in parallel; the output end of the multifunctional grid-connected inverter is connected with a power distribution network.
Preferably, the distributed power supply or energy storage dc output terminal is: one or more of a rectification output end of the wind driven generator, an output end of the photovoltaic equipment, an output end of the fuel cell, an output end of the gas turbine, an output end of the storage battery pack, an output end of the flywheel energy storage and an output end of the super capacitor.
Preferably, the connection mode of the output end of the multifunctional grid-connected inverter and the power distribution network is as follows: the output end of the multifunctional grid-connected inverter is directly connected with the power distribution network through a filter, or the output end of the multifunctional grid-connected inverter is respectively connected with the power distribution network through the filter and a transformer.
Preferably, the filter is a RL filter, an LC filter or an LCL filter.
Preferably, the basic task of the phase-locked loop in step S1 is to quickly and accurately track the frequency and phase of the grid signal;
the phase-locked loop comprises a phase discriminator, a loop filter and a voltageA controlled oscillator; the basic principle of the phase-locked loop is as follows: will the network voltage vabcConverting the grid voltage into an alpha beta reference frame through Clark conversion, converting the grid voltage into a dq reference frame, and converting a q-axis component v of the grid voltage under the dq reference frameqComparing with a given 0 signal, and obtaining a reference angular frequency omega by a PI controllertWill be ωtAnd obtaining the phase angle theta of the power grid voltage after integration.
Preferably, the calculation formula of the reference current of the multifunctional grid-connected inverter in the step S4 is as follows:
preferably, the transfer function of the proportional resonant controller in step S5 is:
omega in the formulacTo cut-off frequency, ωhNatural angular frequency, K, of fundamental and harmonicPIs the proportional gain, K, of the PR controllerrIs the resonant integral coefficient of the PR controller.
The invention provides a multi-synchronous rotation coordinate system-based multifunctional grid-connected inverter harmonic wave treatment method, which converts harmonic wave alternating flow into direct current quantity through multi-synchronous rotation coordinate conversion, so that the direct current quantity can be packaged and then sent to an inverter side from a load side through a low-bandwidth channel, and after Park inverse conversion is carried out on the inverter side, harmonic wave components required to be treated can be reproduced. The method enables the inverter to be free from directly collecting harmonic information of the load side and ensuring that the load is in the electric downstream of the inverter, so that the inverter is more flexible. In addition, by adopting the proportional resonant controller under the three-phase static coordinate system, a reference current tracking control algorithm is simplified, and the calculation efficiency is improved.
The following detailed description of the embodiments of the present invention is provided in connection with the accompanying drawings for the purpose of facilitating understanding and understanding of the technical solutions of the present invention.
Drawings
FIG. 1 is a schematic view of the present invention;
FIG. 2 is a power supply side current harmonic analysis of the multifunctional grid-connected inverter of the present invention when not switched in;
FIG. 3 is a power supply side current harmonic analysis of the multifunctional grid-connected inverter only compensating for harmonics below 25;
FIG. 4 Power supply side Current IsAnd output current I of multifunctional inverterg。
Detailed Description
The harmonic suppression method of the multifunctional grid-connected inverter based on the multi-synchronous rotating coordinate system is characterized in that the multifunctional grid-connected inverter is a three-phase three-wire system, and a capacitor on the direct current side of the multifunctional grid-connected inverter is connected with a distributed power supply or an energy storage direct current output end in parallel; the output end of the multifunctional grid-connected inverter is connected with a power distribution network.
Further, the distributed power supply (DG) or the energy storage dc output terminal is: one or more of a rectification output end of the wind driven generator, an output end of the photovoltaic equipment, an output end of the fuel cell, an output end of the gas turbine, an output end of the storage battery pack, an output end of the flywheel energy storage and an output end of the super capacitor. In this embodiment, the distributed power supply or the energy storage dc output terminal is: the system comprises a rectification output end of the wind driven generator, a photovoltaic equipment output end, a fuel cell output end, a gas turbine output end, a storage battery pack output end, a flywheel energy storage output end and a super capacitor output end.
Furthermore, the connection mode of the output end of the multifunctional grid-connected inverter and the power distribution network is as follows: the output end of the multifunctional grid-connected inverter is directly connected with the power distribution network through a filter, or the output end of the multifunctional grid-connected inverter is respectively connected with the power distribution network through the filter and a transformer; the filter is an RL filter, an LC filter or an LCL filter. In the technical scheme of the invention, the output end of the multifunctional grid-connected inverter is connected with a power distribution network through a filter and a transformer respectively, and the filter is an LC filter.
The multi-functional grid-connected inverter harmonic treatment method based on the multi-synchronous rotating coordinate system, as shown in fig. 1, comprises the following steps:
s1: obtaining fundamental wave angular frequency; by designing a phase-locked loop (PLL), carrying out phase locking on system voltage at the same time with the multifunctional grid-connected inverter on a load side to obtain a value of angular frequency;
the basic task of the phase-locked loop is to quickly and accurately track the frequency and the phase of a power grid signal;
the phase-locked loop comprises a phase discriminator, a loop filter and a voltage-controlled oscillator; the basic principle of the phase-locked loop is as follows: will the network voltage vabcConverting the grid voltage into an alpha beta reference frame through Clark conversion, converting the grid voltage into a dq reference frame, and converting a q-axis component v of the grid voltage under the dq reference frameqComparing with a given 0 signal, and obtaining a reference angular frequency omega by a proportional-derivative (PI) controllertWill be ωtAnd obtaining the phase angle theta of the power grid voltage after integration.
S2: calculation of the fundamental reference current, wherein the involved Park transformation is formulated as
The method for calculating the fundamental wave reference current comprises the following steps:
s21: on the inverter side, converting the system voltage from an abc static coordinate system to a dq coordinate system through Park conversion, and calculating corresponding dq-axis reference current by using dq-axis voltage in the dq coordinate system and given active power P and reactive power Q; the dq-axis reference current
The calculation method comprises the following steps:
s211: the system voltage v is converted by using Park conversion formulaabcConverted into a voltage component on the dq axis,
then the calculation of instantaneous power in dq coordinate systemThe formula is as follows:
s212: for a given active power P and reactive power Q, the formula for the dq-axis current component is:
s213 according to the upper energy management system or the maximum outputtable power instruction P*，Q*Thereby calculating the dq-axis reference current
S22: adding the d-axis reference current and the d-axis current consumed by the compensation system, and performing Park inverse transformation on the d-axis reference current and the q-axis reference current to obtain fundamental wave reference current under an abc static coordinate system; fundamental wave reference current in the abc static coordinate system
Comprises the following steps:
wherein the content of the first and second substances,
the fundamental component of the d-axis reference current for compensating the inverter loss;
the method for acquiring the d-axis current for compensating the system loss is obtained by acquiring the difference between the actual value of the capacitor voltage and the given direct-current side voltage and then performing PI closed-loop control.
S3: the calculation of the harmonic reference current comprises the following steps:
s31: analyzing harmonic components in the load current on the load side;
s32: for different harmonic components, respectively carrying out Park conversion on the load current at proper times of fundamental wave angular frequency, carrying out low-pass filtering on components under the dq axis to obtain corresponding direct current components, and obtaining direct current components of harmonic components in the load current;
s33: packaging the direct current component of the harmonic component and sending the direct current component to the side of the multifunctional grid-connected inverter;
s34: the multifunctional grid-connected inverter performs Park inverse transformation on the direct-current component of the harmonic component at proper times of fundamental angular frequency, so that harmonic reference current under an abc coordinate system is locally synthesized;
s4: synthesizing reference current of the multifunctional grid-connected inverter; synthesizing the fundamental wave reference current in the step S2 and the harmonic wave reference current in the step S3 into the multifunctional grid-connected inverter reference current, namely, the calculation formula of the multifunctional grid-connected inverter reference current is as follows:
s5: tracking the reference current of the multifunctional grid-connected inverter; under an abc static coordinate system, by designing a proper proportional coefficient and a resonance coefficient of a proportional resonance controller and providing an infinite gain mode at a resonance point, unsteady error tracking of an alternating current component is realized. The reference current of the multifunctional grid-connected inverter comprises fundamental wave reference current and harmonic wave reference current, and the fundamental wave reference current is determined by an upper energy management system or the maximum output power. Wherein, the transfer function of the proportional resonance controller is as follows:
omega in the formulacTo cut-off frequency, ωhNatural angular frequency, K, of fundamental and harmonicPIs the proportional gain, K, of the PR controllerrIs the resonant integral coefficient of the PR controller.
The following detailed description will be made with reference to the accompanying drawings, which are provided for the purpose of illustrating the present invention and are intended to provide a detailed description and a specific operation process, but the scope of the present invention is not limited to the following embodiments.
The embodiment provides a multi-functional grid-connected inverter harmonic treatment method based on a multi-synchronous rotating coordinate system.
As shown in fig. 1, in the present embodiment, the topology of the multifunctional inverter is a three-phase and three-wire system, so there is no zero sequence component and no 3 n-th harmonic component in the circuit. The DC side of the inverter is provided with a capacitor which is connected with a DC power supply in parallel. The direct current power supply is used for simulating a distributed power supply or an energy storage direct current output end, and specifically comprises the following components: the system comprises a rectification output end of the wind driven generator, an output end of the photovoltaic equipment, an output end of the fuel cell, an output end of the gas turbine and an output end of the storage battery pack/flywheel energy storage/super capacitor. The resistor connected with the direct current power supply in series is used for simulating the internal resistance of the power supply. The nonlinear load consists of a resistive uncontrolled rectifying circuit, and the load current of the circuit only contains 6n +/-1 subharmonic components.
The working process is as follows: extracting a load current iLOmega obtained by means of a phase-locked looptPerforming park transformation. And packaging the obtained data and sending the data to a multifunctional grid-connected inverter end (MGFTI), performing inverse park transformation on harmonic components in the data, summing the harmonic components with filter inductance current and fundamental wave reference current, performing tracking control by a Proportional Resonance (PR) controller, and sending the harmonic components into a Pulse Width Modulation (PWM) generator to generate a control signal to be transmitted to an inverter port to adjust the on-off of a switching tube. The specific operation process is as follows:
s1: calculation of fundamental angular frequency
In the Park conversion process, the fundamental angular frequency of the system voltage is needed, and the phase-locking technique is used to obtain the value of the angular frequency. The phase-locked loop has the basic task of quickly and accurately tracking the frequency and the phase of a power grid signal and mainly comprises a phase discriminator, a loop filter and a voltage-controlled oscillator. The present embodiment uses a single synchronous coordinate system software phase-locked loop (SSRF-SPLL) to achieve phase-locking of the voltage vector. The basic principle of SSRF-SPLL is: will the network voltage vabcAnd converting the reference frame into an alpha beta reference frame through a Clark transformation, and then converting the reference frame into a dq reference frame. Calculating the q-axis component v of the grid voltage in dq reference systemqComparing with a given 0 signalThen obtaining the reference angular frequency omega through a PI controllertWill be ωtAnd obtaining the phase angle theta of the power grid voltage after integration.
S2: calculation of fundamental reference current
On the inverter side, the system voltage is converted from an abc static coordinate system to a dq coordinate system through Park conversion, and a corresponding dq-axis reference current is calculated by using the dq-axis voltage in the dq coordinate system and given active power P and reactive power Q. In order to maintain the stability of the voltage on the dc side, the d-axis needs to provide an additional active current in addition to the grid-connected current to compensate the system loss. And after the difference between the actual value of the capacitor voltage and the given direct current side voltage is acquired, PI control is performed to obtain d-axis current for compensating the system loss. And adding the two d-axis currents, and performing Park inverse transformation on the d-axis currents and the q-axis currents to obtain fundamental wave reference currents in an abc static coordinate system.
The Park transformation formula adopted by the method is as follows:
phase voltage v of acquisition systemabcIt can be converted into a direct current component on the dq axis by using Park transformation.
The instantaneous power in dq coordinate system is calculated as follows:
p＝vdid+vqiq
q＝vqid-vdiq
then, with the active power P and the reactive power Q being followed, the calculation formula of the dq-axis current component is as follows:
thereby, according to the upper energy management system or the maximum output power instruction P*，Q*The corresponding dq-axis reference current can be calculated
As shown in FIG. 1, to maintain the DC side voltage UdcStable by collecting the DC side capacitance voltage and comparing it with a reference value
And performing PI closed-loop control after the difference is made. The output end of the PI controller is a fundamental component in d-axis reference current for compensating the loss of the inverter
The resulting d-axis component of the fundamental reference current is thus determined by
And
two parts are formed. Carrying out Park inverse transformation on the dq axis fundamental wave component to obtain the fundamental wave reference current under the abc static coordinate system
S3: calculation of harmonic reference currents
As shown in fig. 1, the grid-connected inverter does not directly collect the harmonic current at the load, but receives the harmonic component transmitted from the load side, and thereby locally reproduces the harmonic component. The scheme has certain flexibility for the fact that the load is independent of the installation position of the inverter.
On the load side, harmonic components in the load current can be analyzed first. For example, in a three-phase three-wire system, 3 nth harmonic components (n is an integer) are not included, so that the required Park transformation and inverse transformation times can be greatly reduced. As the nonlinear load in the example is a resistive uncontrolled rectifying circuit, the load current of the circuit only contains 6n +/-1 subharmonic components, wherein the 6n +1 subharmonic is a positive sequence component, and the 6n-1 subharmonic is a negative sequence component.
For the 6n +1 subharmonic component, the load current is subjected to Park transformation by (6n +1) times of the fundamental angular frequency, and the component under the dq axis is subjected to low-pass filtering to obtain a corresponding direct-current component.
For the 6n-1 harmonic component, performing Park transformation on the load current by (1-6n) times of the fundamental angular frequency, and performing low-pass filtering on the component under the dq axis to obtain a corresponding direct-current component.
Load current ILabcRespectively with (6n +1) omegatt、(1-6n)ωtAnd carrying out Park transformation on the phase angle of t to obtain an alternating variable on the dq axis. The direct current component in the dq axis can be extracted by using a second-order low-pass filter, so that the dq axis amplitude of the 6n +/-1 harmonic component in the load current is obtained. According to the practical application scene and the inverter capacity, a designer can select a single harmonic component or a harmonic component below 25 or 50, and the harmonic component is packaged and sent to the inverter side for harmonic compensation.
S4: synthesis of reference current of multifunctional grid-connected inverter
After receiving the harmonic component information of the load current side, the inverter side carries out Park inverse transformation on the direct current component corresponding to the higher harmonic by (6n +1) or (1-6n) times of fundamental angular frequency, thereby locally synthesizing the harmonic reference current in the abc coordinate system
And synthesizing the harmonic reference current and the fundamental wave reference current to obtain the final reference current of the multifunctional grid-connected inverter. The final fundamental reference current is calculated by the formula:
s5: tracking of reference current of multifunctional grid-connected inverter
In the abc stationary coordinate system, the conventional PI controller cannot perform unsteady-state error tracking on the alternating current component. By designing the proportional coefficient and the resonance coefficient of the proper proportional resonant controller and providing an infinite gain mode at a resonance point, the unsteady state error tracking of the alternating current component can be realized, and thus the active output and harmonic wave treatment functions are realized.
The transfer function of the PR controller is as follows:
omega in the formulacRepresenting the cut-off frequency, ωhNatural angular frequency, K, representing fundamental and harmonicPIs the proportional gain, K, of the PR controllerrIs the resonance integral coefficient of PR controller, in this example, take KPIs 10, KrIs 4400.
According to the designed PR controller, the steady-state error tracking of the reference current of the inverter can be realized.
FIG. 2 shows a simulation result diagram of the multi-functional grid-connected inverter harmonic treatment method based on a multi-synchronous rotating coordinate system
As shown in fig. 2, before 0.2s, the grid-connected inverter is not put into operation, and the harmonic component in the load current is completely injected into the Point of Common Coupling (PCC). From the results of fourier analysis of 10 periodic current waveforms at the PCC point, it can be known that harmonic components in the load current are mainly 5, 7, 11, and 13 harmonics, and the total harmonic distortion rate is 24.5%, which is far greater than the national standard of 5%.
And at 0.2s, the multifunctional grid-connected inverter is put into operation. In order to clearly display the harmonic wave treatment and active grid-connected functions of the inverter, only the harmonic wave treatment function of the multifunctional grid-connected inverter is switched on at 0.2 s. As can be seen from fig. 3, after the multifunctional grid-connected inverter compensates the harmonic component of 25 th or less in the load current, the total harmonic distortion at the PCC point is reduced to 1.58%, which meets the requirement of 5% in the national standard.
As can be seen from fig. 3, at 0.4s, the multifunctional grid-connected inverter receives an upper energy management system or a maximum power output command, so that an active current is output while a harmonic suppression function is realized, and a fundamental current drawn by a load from a power supply side is reduced.
Fig. 4 shows a power source side current and an output current of the multifunctional grid-connected inverter. Fig. 4 shows the output current and the corresponding power source side current of the multifunctional grid-connected inverter in different working modes.
The invention utilizes a multi-rotation synchronous coordinate system method to convert each high-order harmonic alternating component in the load current into direct current quantity under a corresponding coordinate system, thereby being capable of sending data to an MFGTI end with lower bandwidth. This method is particularly applicable to situations where the load is installed electrically upstream of the MGFTI. The method simply solves the problem of harmonic pollution caused by nonlinear load, improves the reliability of electric energy quality, and is beneficial to improving the utilization efficiency of energy.
It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims.
Claims (8)
1. The multi-synchronous rotation coordinate system-based multi-functional grid-connected inverter harmonic wave treatment method is characterized by comprising the following steps:
s1: obtaining fundamental wave angular frequency; by designing a phase-locked loop, carrying out phase locking on system voltage at the same time with the multifunctional grid-connected inverter on a load side to obtain a value of angular frequency;
s2: the calculation of the fundamental wave reference current comprises the following steps:
s21: on the inverter side, converting the system voltage from an abc static coordinate system to a dq coordinate system through Park conversion, and calculating corresponding dq-axis reference current by using dq-axis voltage in the dq coordinate system and given active power P and reactive power Q;
the formula of Park transformation is:
the dq-axis reference current
The calculation method comprises the following steps:
s211: the system voltage v is converted by using Park conversion formulaabcConverted into a voltage component on the dq axis,
then the calculation formula of the instantaneous power in dq coordinate system is:
s212: for a given active power P and reactive power Q, the formula for the dq-axis current component is:
s213 according to the upper energy management system or the maximum output power instruction P*，Q*Thereby calculating the dq-axis reference current
S22: adding the d-axis reference current and the d-axis current consumed by the compensation system, and performing Park inverse transformation on the d-axis reference current and the q-axis reference current to obtain fundamental wave reference current under an abc static coordinate system;
fundamental wave reference current in the abc static coordinate system
Comprises the following steps:
wherein the content of the first and second substances,
the fundamental component of the d-axis reference current for compensating the inverter loss;
the method for acquiring the d-axis current consumed by the compensation system is to acquire the difference between the actual value of the capacitor voltage and the given direct-current side voltage and then perform PI closed-loop control;
s3: the calculation of the harmonic reference current comprises the following steps:
s31: analyzing harmonic components in the load current on the load side;
s32: for different harmonic components, respectively carrying out Park conversion on the load current at proper times of fundamental wave angular frequency, carrying out low-pass filtering on components under the dq axis to obtain corresponding direct current components, and obtaining direct current components of harmonic components in the load current;
s33: packaging the direct current component of the harmonic component and sending the direct current component to the side of the multifunctional grid-connected inverter;
s34: the multifunctional grid-connected inverter performs Park inverse transformation on the direct-current component of the harmonic component at proper times of fundamental angular frequency, so that harmonic reference current under an abc coordinate system is locally synthesized;
s4: synthesizing reference current of the multifunctional grid-connected inverter; synthesizing the fundamental wave reference current in the step S2 and the harmonic wave reference current in the step S3 into a multifunctional grid-connected inverter reference current;
s5: tracking the reference current of the multifunctional grid-connected inverter; in an abc static coordinate system, unsteady error tracking of an alternating current component is realized by designing a proper proportional coefficient and a proper resonance coefficient of a proportional resonance controller and providing infinite gain at a resonance point;
the reference current of the multifunctional grid-connected inverter comprises fundamental wave reference current and harmonic wave reference current, and the fundamental wave reference current is determined by an upper energy management system or the maximum output power.
2. The multi-functional grid-connected inverter harmonic treatment method based on the multi-synchronous rotating coordinate system according to claim 1, characterized in that: the multifunctional grid-connected inverter is a three-phase three-wire system, and a capacitor on the direct current side of the multifunctional grid-connected inverter is connected with the distributed power supply or the energy storage direct current output end in parallel; the output end of the multifunctional grid-connected inverter is connected with a power distribution network.
3. The multi-functional grid-connected inverter harmonic treatment method based on the multi-synchronous rotating coordinate system according to claim 2, characterized in that: the distributed power supply or the energy storage direct current output end is as follows: one or more of a rectification output end of the wind driven generator, an output end of the photovoltaic equipment, an output end of the fuel cell, an output end of the gas turbine, an output end of the storage battery pack, an output end of the flywheel energy storage and an output end of the super capacitor.
4. The multi-functional grid-connected inverter harmonic treatment method based on the multi-synchronous rotating coordinate system according to claim 2, characterized in that: the connection mode of the output end of the multifunctional grid-connected inverter and the power distribution network is as follows: the output end of the multifunctional grid-connected inverter is directly connected with the power distribution network through a filter, or the output end of the multifunctional grid-connected inverter is respectively connected with the power distribution network through the filter and a transformer.
5. The multi-functional grid-connected inverter harmonic treatment method based on the multi-synchronous rotating coordinate system according to claim 4, wherein: the filter is an RL filter, an LC filter or an LCL filter.
6. The multi-functional grid-connected inverter harmonic treatment method based on the multi-synchronous rotating coordinate system according to claim 1, characterized in that: the basic task of the phase-locked loop in the step S1 is to quickly and accurately track the frequency and phase of the grid signal;
the phase-locked loop comprises a phase discriminator, a loop filter and a voltage-controlled oscillator; the basic principle of the phase-locked loop is as follows: will the network voltage vabcConverting the reference frame into alpha beta reference frame and then into dq reference frame through Clark transformationThe q-axis component v of the grid voltage in the dq reference frameqComparing with a given 0 signal, and obtaining a reference angular frequency omega by a PI controllertWill be ωtAnd obtaining the phase angle theta of the power grid voltage after integration.
7. The multi-functional grid-connected inverter harmonic treatment method based on the multi-synchronous rotating coordinate system according to claim 1, characterized in that: the calculation formula of the reference current of the multifunctional grid-connected inverter in the step S4 is as follows:
8. the multi-functional grid-connected inverter harmonic treatment method based on the multi-synchronous rotating coordinate system according to claim 1, characterized in that: the transfer function of the proportional resonant controller in step S5 is:
omega in the formulacTo cut-off frequency, ωhNatural angular frequency, K, of fundamental and harmonicpIs the proportional gain, K, of the PR controllerrIs the resonant integral coefficient of the PR controller.
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| CN110994649A (en) * | 2019-12-10 | 2020-04-10 | 东北电力大学 | Three-phase unbalanced load current active compensation control method |
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