CN109510248B - Virtual synchronous inverter control method and storage medium capable of suppressing active oscillation - Google Patents
Virtual synchronous inverter control method and storage medium capable of suppressing active oscillation Download PDFInfo
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- H—ELECTRICITY
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Abstract
本发明提供一种可抑制有功振荡的虚拟同步逆变器控制方法及存储介质，可解决现有相关技术使系统不稳定的技术问题。包括：在有功功率控制环上，加入虚拟阻尼控制算法，提取频率低频振荡分量，调整有功功率控制环电磁转矩，减弱虚拟同步逆变器的有功振荡；在无功功率控制环上，加入虚拟阻抗控制算法，调整无功功率控制环输出电压调制信号，减少有功功率与无功功率的耦合，实现瞬时功率增量均分条件，从而抑制有功振荡的激励；本发明能够从抑制振荡激励和增强虚拟同步逆变器自身阻尼两个方面解决负荷波动时虚拟同步逆变器有功功率振荡的问题，并保证在抑制振荡的同时提高有功功率的精确均分和无功功率均分性能，保证PCC点的电压稳定。
The present invention provides a virtual synchronous inverter control method and a storage medium capable of suppressing active oscillation, which can solve the technical problem of system instability in the prior art. Including: adding a virtual damping control algorithm to the active power control loop, extracting the frequency low-frequency oscillation component, adjusting the electromagnetic torque of the active power control loop, and weakening the active oscillation of the virtual synchronous inverter; adding a virtual synchronous inverter to the reactive power control loop. The impedance control algorithm adjusts the output voltage modulation signal of the reactive power control loop, reduces the coupling between the active power and the reactive power, and realizes the instantaneous power increment equalization condition, thereby suppressing the excitation of the active oscillation; the present invention can suppress the oscillation excitation and enhance the The virtual synchronous inverter's own damping solves the problem of the virtual synchronous inverter's active power oscillation when the load fluctuates, and ensures that the oscillation is suppressed while improving the accurate and reactive power sharing performance, ensuring the PCC point. voltage is stable.
Description
Technical Field
The invention relates to the technical field of inverter control, in particular to a virtual synchronous inverter control method and a storage medium capable of inhibiting active oscillation.
Background
A virtual synchronous inverter that simulates the use of a conventional synchronous machine is a grid friendly inverter. The virtual synchronous inverter has inertia characteristics, so that the virtual synchronous inverter has great advantages in the aspects of restraining high-frequency fluctuation of system frequency and maintaining the stability of the system frequency. The introduction of inertia is the root cause of the virtual synchronous inverter to realize the rapid response of output power and the suppression of high-frequency jitter. However, due to the introduction of inertia, the virtual synchronous inverter has the characteristic of small damping similar to a synchronous generator system, so that active power oscillation is easy to occur. For a synchronous generator, because of strong overcurrent capacity, short-term power oscillation cannot cause excessive damage, and different inverters, because of the limitation of the capacity of a switching device, the damage of the power oscillation to a virtual synchronous inverter is far greater than that of the synchronous generator. The power oscillation caused by the fluctuation of the load threatens the safe operation of the inverter and also has serious influence on the power grid. Therefore, it is necessary to provide an effective method for suppressing active oscillation of a multi-virtual synchronous inverter system.
The related art for suppressing power oscillation when the load of the parallel system of the virtual synchronous inverter fluctuates is as follows: the oscillation suppression is realized by adjusting the control parameters of the virtual synchronous inverter such as inertia characteristics, droop coefficients and the like, and the fundamental mechanism of the control can be attributed to the improvement of the self damping of the virtual synchronous inverter. The virtual impedance is introduced to realize the suppression of the power oscillation, and the fundamental mechanism of the method can be attributed to the suppression of the oscillation excitation.
However, the above related art has the following drawbacks:
1) the method for realizing oscillation suppression by dynamically adjusting the inertia coefficient J usually needs to introduce a differentiation link or a proportional-integral link, and the differentiation link is easy to amplify high-frequency signals and difficult to be practically applied. The proportional-integral link causes more nonlinear break points to appear in the system frequency, which affects the stability of the system.
2) The detection link of oscillation-dependent power oscillation is suppressed through the self-adaptive damping coefficient Dp, and uneven distribution of the steady-state power of the system is easily caused.
3) The virtual impedance is introduced to suppress oscillation only for a specific situation, and the condition that the obtained system power oscillation is completely suppressed is that parameters including a droop coefficient, an inertia time constant, the virtual impedance and the like are all required to be completely correspondingly proportional, and the actual situation is difficult to strictly realize.
Disclosure of Invention
Technical problem to be solved
The invention provides a virtual synchronous inverter control method and a storage medium capable of inhibiting active oscillation, which can solve the technical problem that the system is unstable in the prior art.
(II) technical scheme
In order to achieve the purpose, the invention is realized by the following technical scheme:
a virtual synchronous inverter control method capable of suppressing active oscillation comprises the following steps:
a. adding a virtual damping control algorithm to an active power control loop of a virtual synchronous inverter control algorithm, and adjusting electromagnetic torque of the active power control loop by extracting frequency low-frequency oscillation components to reduce the difference between mechanical torque and electromagnetic torque and reduce the variation of angular frequency, thereby weakening the active oscillation of the virtual synchronous inverter;
b. adding a virtual impedance control algorithm to a reactive power control loop of a virtual synchronous inverter control algorithm, adjusting a voltage modulation signal output by the reactive power control loop, and changing an equivalent inductive impedance from the virtual synchronous inverter to a PCC point, so that the equivalent inductive impedance from the virtual synchronous inverter to the PCC point is greater than line impedance, the coupling of active power and reactive power is reduced, an instantaneous power increment and sharing condition is realized, and the excitation of active oscillation of the virtual synchronous inverter is restrained;
c. the active oscillation suppression of the virtual synchronous inverter is realized through the steps a and b.
Further, after the virtual impedance control algorithm is added in the step b, a PCC point bus voltage estimation algorithm is added, so that the voltage amplitude detected by the virtual synchronous inverter is close to the voltage value of the PCC point.
Further, the extracting the low-frequency oscillation component of the frequency in the step a includes: the cut-off frequency is set so that the fluctuation component in the frequency passes through the DC blocking filter, and the DC component cannot pass through the filter, thereby obtaining the frequency fluctuation amount without the DC component.
Further, the virtual damping control algorithm comprises multiplying the frequency fluctuation amount without the direct current component by a damping coefficient, and adding the frequency fluctuation amount to the electromagnetic torque to form additional damping to the electromagnetic torque and damp power oscillation.
Further, the virtual impedance control algorithm comprises:
firstly, converting a PWM (pulse-width modulation) signal of output voltage of a virtual synchronous inverter from three phases to two phases under alpha beta coordinates;
then introducing virtual impedance, and adding a voltage modulation signal output by a virtual synchronous inverter to the voltage drop on the virtual impedance to obtain PWM modulation signal voltage under an alpha beta coordinate system after virtual impedance adjustment;
and finally, performing inverse transformation from the two-phase alpha beta to the three-phase abc coordinate system, converting the inverse transformation into voltage under the abc three-phase coordinate system, and changing the equivalent output impedance of the virtual synchronous inverter by adjusting the value of the virtual impedance so as to change the equivalent line impedance from the virtual synchronous inverter to the PCC point.
Further, the PCC point bus voltage estimation algorithm includes:
firstly, the three-phase voltage detected by the virtual synchronous inverter is converted into two-phase alpha beta coordinate, and then the equivalent impedance X is addedtObtaining the correction voltage under the alpha beta coordinate system through the voltage drop, and obtaining the voltage amplitude V of the PCC point through an amplitude detection linkbus；
Meanwhile, the calculation formula of Q in the virtual synchronous inverter control algorithm is replaced by an expression (11),
where Q denotes the inverter potential output reactive power, ia，ib，icIs the output current of the inverter, eoa，eob，eocThe voltages are in a three-phase coordinate system.
Further, the amplitude detection link specifically includes:
firstly, the corrected voltage under alpha beta coordinate is inversely transformed and converted into PCC point approximate estimation voltage v under abc three-phase coordinate systema，vb，vcThen obtaining the voltage amplitude V of the PCC point by the formula (10)bus；
In another aspect, the present invention provides a computer storage medium having a virtual inverter control algorithm stored thereon, wherein the method is implemented when the virtual inverter control algorithm is executed by a processor.
(III) advantageous effects
The invention discloses a virtual synchronous inverter control method system capable of inhibiting active oscillation, which can solve the problem of active power oscillation of a traditional virtual synchronous inverter during load fluctuation from two aspects of inhibiting oscillation excitation and enhancing self damping of the synchronous inverter and improve the stability of the system. Load fluctuation is instantly different by utilizing virtual impedance, power between virtual synchronous inverters (synchroverters) is equally divided according to the inertia, and oscillation excitation caused by inconsistent initial angular velocity change of each virtual synchronous inverter is inhibited; the virtual damping control technology is utilized to enable the interior of the virtual synchronous inverter to generate damping for inhibiting power oscillation, so that oscillation energy is consumed rapidly, and the angular speeds of the virtual synchronous inverters are consistent. And finally, when the load fluctuation is realized, the active oscillation of the multi-virtual synchronous inverter system is inhibited. The method can quickly and effectively inhibit the active power oscillation among the synchronous inverters with different rated powers and different inertia time constants from the angle of the control algorithm, and can improve the accurate equipartition and reactive power equipartition performance of the active power while inhibiting the oscillation, thereby ensuring the voltage stability of the PCC points.
Meanwhile, the invention is provided with a bus voltage prediction link for improving the reactive power equipartition performance of the system. The virtual synchronous inverter has the advantages of simplicity, reliability and extremely low requirement on hardware, and can realize the functions without detecting the outlet voltage.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a topology diagram of a virtual synchronous inverter grid-connected system;
FIG. 2 is a virtual synchronous inverter control algorithm;
FIG. 3 is a schematic diagram of a control method according to an embodiment of the present invention;
FIG. 4 is a block diagram of a virtual synchronous control with active oscillation suppression capability according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a virtual impedance control algorithm according to an embodiment of the present invention;
FIG. 6 is a schematic diagram illustrating the operation principle of the PCC point voltage estimation method according to the embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The virtual synchronous control strategy is a novel grid-connected control strategy based on a non-salient pole type synchronous generator second-order model. Compared with the traditional inverter, the virtual synchronous inverter simulates a rotor equation of a synchronous motor and combines the energy storage function of the direct-current bus, so that the body of the virtual synchronous inverter has certain inertia, the disturbance resistance of the micro-source inverter is enhanced, and the overall stability of the micro-grid system is guaranteed.
The virtual synchronous inverter grid-connected topology is shown in fig. 1. Wherein L iss、RsRespectively equivalent inductance and resistance L from the output end of the virtual synchronous inverter to the PCC pointg、RgEquivalent inductance and resistance from the PCC point to the public power grid, E is a voltage drive signal with amplitude represented by E, θ*Is given a reference angular frequency, P*、Q*Reference values are respectively given for the active and the reactive of the virtual synchronous control unit.
According to fig. 1, the virtual synchronous inverter is composed of a power module and an electric control part. The power module is composed of a direct current bus capacitor, a converter and an LC filter and is mainly used for converting direct current into power frequency alternating current; the electric control part completes the regulation and control of the system, and the core algorithm of the electric control part is shown in figure 2. Wherein J represents the introduced virtual moment of inertia, Dp is the virtual mechanical friction coefficient, K is the reactive power inertia element coefficient, DqIs the voltage droop coefficient.
The upper part of the algorithm block diagram shown in fig. 2 is an active control loop, which realizes the control of frequency and active power; the lower half part is a reactive control loop to realize the control of voltage and reactive power. The basic control principle of the algorithm is shown in formulas (1) and (2). The formula (1) is a basic equation formed by power calculation and reference voltage, and the formula (2) and the formula (3) are a frequency inertia link equation and a voltage inertia link equation in virtual synchronous control respectively.
In the formula, TeRepresents an electromagnetic torque; t ismRepresenting a mechanical torque; θ represents the phase of the virtual rotor, and its differential value is both the angular velocity of the virtual synchronous generator and the angular frequency of the drive voltage signal e; i isfIs an exciting current; mfSimulating the maximum mutual inductance between the stator winding and the excitation winding; q is actual output reactive power; i is three-phase stator current; symbol<，>Represents a conventional dot product operation, in which:
the virtual synchronous control strategy simulates a traditional synchronous generator model to introduce virtual inertia, is very beneficial to the fluctuation of a power grid, can compensate for response lag caused by system adjustment, and can inhibit active and reactive high-frequency jitter on the grid side.
The embodiment of the invention deeply analyzes the generation mechanism and the influence factors of power oscillation caused by load fluctuation when the virtual synchronous inverters are powered in parallel, and obtains the conclusion that: the uneven distribution of the instantaneous active power is a direct reason for the oscillation generation, and the small damping and the large inertia of the vibration generator are intrinsic factors for the oscillation generation. The virtual synchronous inverter control method capable of inhibiting active oscillation comprises an oscillation excitation inhibiting technology based on virtual impedance, wherein effective inhibition of power oscillation excitation is realized by taking an inertia parameter instead of a capacity parameter as a design standard of a virtual impedance ratio; the method comprises a virtual damping technology independent of a phase-locked loop, and the damping of the system is improved on the premise of not changing the stability performance of the system; therefore, the oscillation energy is quickly consumed, and the angular speed of each virtual synchronous inverter is consistent. And a bus voltage prediction link is added for improving the reactive power sharing performance of the system.
As shown in fig. 3, the virtual synchronous inverter control method capable of suppressing active oscillation according to the embodiment of the present invention includes:
the active oscillation of the virtual synchronous inverter is inhibited by adding a control link on a power control loop of a traditional virtual synchronous control algorithm;
the method comprises the following specific steps:
step 1: on an active power control loop of a traditional virtual synchronous control algorithm, a damping part is added
By varying electromagnetic torque TeIncreasing the electromagnetic torque of the active ring to
Original mechanical torque TmWith new electromagnetic torque
The difference is reduced to reduce the variation of angular frequency
Reducing, accelerating the attenuation of power oscillations;
step 2: adding a virtual impedance part on a reactive power control loop of a traditional virtual synchronous control algorithm, and enabling the traditional virtual synchronous reactive loop to output a voltage modulation signal e through the virtual impedance control algorithmrefSubtracting the virtual impedance wnLvsMultiplied by the inverter output current igTo obtain a new voltage modulation signal eo＝eref-wnLvs*igIn turn, the equivalent inductive reactance X of the inverter to the PCC point is changedtThe equivalent inductive reactance from the inverter to the PCC point is far larger than the line impedance, the coupling of active power and reactive power can be reduced, the condition of equal division of instantaneous power increment is realized, and the power oscillation excitation is inhibited;
and step 3: on the reactive power control loop of the traditional virtual synchronous control algorithm, the method is addedA PCC point bus voltage estimation link leads the feedback voltage e obtained by the original measurementa，eb，ec(amplitude E) plus equivalent impedance XtMultiplying by the sense current i, i.e. by the original feedback voltage plus the equivalent impedance XtTo obtain a new feedback voltage vbusa，vbusb，vbusc(amplitude of V)bus) And the influence of the virtual impedance on voltage feedback and reactive power calculation is reduced.
FIG. 4 is a block diagram of a virtual synchronous control with active oscillation suppression capability according to an embodiment of the present invention; equation (5) is specifically expressed as follows:
wherein T iseRepresents an electromagnetic torque; t ismRepresenting a mechanical torque; θ represents a phase of the virtual rotor, and a differential value thereof is an angular velocity of the virtual synchronous generator; i isfIs an exciting current; mfSimulating the maximum mutual inductance between the stator winding and the excitation winding; q is actual output reactive power; i is three-phase stator current; symbol<，>Representing a conventional dot product operation.
The following describes an embodiment of the present invention in detail with reference to fig. 4:
virtual damping based oscillation rapid attenuation principle
The virtual damping link is added to the active power control loop of the traditional virtual synchronous control algorithm to extract frequency low-frequency oscillation components and inhibit the oscillation of electromagnetic torque; the device comprises two parts, namely a frequency low-frequency oscillation component extraction unit and a virtual damping unit for suppressing the oscillation of the electromagnetic torque. Frequency oscillation component extraction unitMeta-pass setting reasonable cut-off frequency fw(having a period of TW) The fluctuation component in the frequency passes through the DC blocking filter, and the DC part cannot pass through the DC blocking filter, so that the frequency fluctuation amount without the DC component can be obtained; and finally multiplying the low-frequency oscillation component by a damping coefficient D, and adding the damping coefficient D to the electromagnetic torque to form additional damping to the electromagnetic torque so as to quickly attenuate oscillation power.
Equation (6) is the transfer function of the angular frequency after virtual damping, where ω istFor angular frequency after virtual damping, fwTo cut-off frequency, TwFor its period, Tw＝1/fwAnd s is a complex frequency domain representation parameter.
TwThe value of (A) is the key point for effectively realizing the method, and the value of (B) should follow the following principle:
1. ensuring that the oscillation component is as possible;
2. the amplification of high frequencies and the influence on the phase advance of the oscillation component are as small as possible.
Therefore, TwThe value of (A) is not too small, so that the required oscillation component is prevented from being filtered, and the value of (B) is not too large, so that the phase advance is prevented from being too much.
From the trajectory of the system, with TwThe pole of the system is far from the imaginary axis first and then close to the imaginary axis, and the point corresponding to the point farthest from the imaginary axis corresponds to TwThe value of (d) is the optimal solution. Then follows TwFurther increase in the number of the feature roots gradually crosses the imaginary axis to the positive half axis, the system is unstable. Is obviously TwThe non-instability value range needs to be reasonably selected according to the solution of the characteristic equation of the system, so that T can be realizedwThe oscillation can be suppressed in a wide range, and the method has obvious value in practical application.
The virtual damping link in the embodiment of the invention only acts when the internal frequencies of each unit have differences and does not act in a stable state, so that the power sharing effect in the dynamic process of the system is effectively enhanced, and the influence of the virtual damping link on the steady-state performance of the system is reduced.
Virtual impedance based oscillation excitation suppression principle
It is known from theoretical analysis that the excitation of the power oscillation is caused by the non-uniform division of the instantaneous power increase, i.e. the instantaneous power increase is only averaged when the following formula (7) is satisfied, where XtIs the equivalent line impedance from the inverter to the PCC point (including the inverter equivalent output impedance, the inverter output filter impedance, and the line impedance), and J is the virtual inertia of the virtual synchronous inverter.
The disproportion of the inertia magnitude and the line impedance causes the excitation of power oscillation, and if the line impedance is changed to satisfy the relation of the formula (7) with the inertia, the excitation can be greatly weakened. However, changing the line impedance is obviously impractical and uneconomical, and therefore embodiments of the present invention propose a virtual impedance approach as shown in fig. 4 to suppress the excitation of power oscillations.
Such that, after adding the virtual impedance, the equivalent line impedance of the inverter to the PCC point satisfies equation (7), such that:
ΔP1∶ΔP2＝PJ1∶PJ2 (8)
wherein Δ P1，ΔP2For the change of the output power of the inverter, P, caused by load fluctuationsJ1，PJ2Power is adjusted for virtual synchronous inertia.
The virtual impedance is embodied in fig. 4, and the principle is shown in fig. 5:
firstly, the traditional virtual synchronous inverter output voltage PWM modulation signal is converted under the alpha beta coordinate from three phases to two phases, and then virtual impedance is introduced. Such that the conventional virtual synchronous inverter outputs a voltage modulated signal plus the voltage drop across the virtual impedance (i.e., the sensed current multiplied by the virtual impedance). Thereby obtaining the alpha and beta coordinate system after the virtual impedance adjustmentPWM modulates signal voltage, then carries out inverse transformation from two-phase alpha beta to three-phase ABC, and converts the signal voltage into voltage e under ABC three-phase coordinate systemoa，eob，eoc。
Obviously, by adjusting the virtual impedance Lvs1And Lvs2Can change the equivalent output impedance of the inverter, thereby changing the equivalent line impedance X from the inverter to the PCC pointtAnd further, the condition of uniform increment of instantaneous power is realized, and the effective suppression of oscillation excitation is realized.
PCC point voltage estimation method principle
After the virtual impedance is added, the system has the following advantages: the inductive reactance is far larger than the impedance, and the active and reactive power realize decoupling; the transient power imbalance due to the difference in J is attenuated, thereby attenuating the excitation of power oscillations. However, a principle error exists in reactive power calculation, that is, the reactive power calculated according to the control algorithm of the conventional virtual synchronous inverter includes reactive loss on the virtual impedance, which further causes that reactive power sharing is difficult to realize; in addition, the increased virtual impedance enables the port voltage to drop more, and the voltage fluctuation range of the PCC points is increased.
As shown in formula (9).
Qout1 *-Qout2 *＝-Dq *(E1 *-E2 *) (9)
Wherein Qoutl *，Qout2 *Respectively representing per unit values of the reactive power output by the two inverters; dq *A per unit value representing the reactive droop coefficient of the inverter; e1 *，E2 *Respectively representing the per unit values of the voltage amplitudes of respective reactive feedback inputs of the two inverters; when E is1 *，E2 *When the deviation is large, Qoutl *，Qout2 *There is also a large deviation, i.e. the reactive power cannot be equally divided.
To alleviate this problem, embodiments of the present invention have been developed accordingly. The deviation of the feedback voltage of the virtual synchronous inverter is an important factor causing the reactive power to be unevenly distributed. Therefore, a bus voltage prediction link shown in fig. 4 is added, and the voltage amplitude detected by the inverter is made to approach the voltage value of the PCC point as much as possible, so that the problems of reactive power non-uniform distribution and overlarge voltage fluctuation range of the PCC point caused by different voltages are solved, and the internal working principle of the module is shown in fig. 6:
firstly, the detected three-phase voltage is converted into two-phase alpha beta coordinate, then the equivalent impedance X is addedtThe voltage drop (i.e. the detection current is multiplied by the equivalent impedance from the inverter to the pc point) on the upper surface of the substrate is obtained, so as to obtain the correction voltage under the alpha beta coordinate system, and then the correction voltage is obtained through an amplitude detection loop (amplitude detection) to obtain VbusThe amplitude detection step comprises the steps of performing inverse transformation on the corrected voltage under the alpha-beta coordinate, converting the corrected voltage into PCC point approximate estimated voltage v under an abc three-phase coordinate systema，vb，vcThen obtaining the voltage amplitude V of the PCC point by the formula (10)buso
Further, the calculation of Q in the conventional virtual synchronous inverter control algorithm needs to be synchronized instead of equation (10)
Wherein Q represents inverter potential output reactive power; i.e. ia，ib，icIs the output current of the inverter.
Obviously, the method has the advantages that the traditional virtual synchronous inverter only needs to measure the output current of the inverter without measuring the voltage of the outlet of the inverter, and the voltage stability and the reactive power of the PCC point are improved to a certain extent.
Obviously, the problem of voltage deviation caused by virtual impedance and the like can be reduced by estimating the voltage of the PCC point, and the influence on the accuracy of the reactive power uniform distribution can be further weakened.
Embodiments of the present invention further provide a computer storage medium having a virtual inverter control algorithm stored thereon, where the control method can be implemented when a processor executes the virtual inverter control algorithm.
In summary, embodiments of the present invention provide a virtual synchronous inverter control method and a storage medium capable of suppressing active oscillation, which are mainly configured by adding a virtual impedance module, a virtual damping module, and a bus voltage prediction link on the basis of an original virtual synchronous inverter control algorithm module, a three-phase inverter bridge module, and a PWM driving module. The structure can effectively overcome the problem of active power oscillation of the traditional virtual synchronous inverter during load fluctuation from two aspects of the inhibition of oscillation excitation and the enhancement of the self damping of the synchronous inverter. And the bus voltage prediction link is used for improving the reactive power uniform performance of the system.
When the system load fluctuates, the original virtual synchronous inverter control algorithm module outputs the internal angular frequency of the algorithm as an input signal of the virtual damping module, and the virtual damping output signal is sent to an active control loop in the original virtual synchronous inverter control algorithm module, so that the damping of the system is improved on the premise of not changing the steady-state performance of the system, the oscillation energy is quickly consumed, and the angular speeds of the virtual synchronous inverters are consistent;
meanwhile, a voltage modulation signal output by the original virtual synchronous inverter control algorithm module and the detected inverter output current are used as input signals of the virtual impedance module, and a new voltage modulation signal is output to the PWM driving module, so that the effective suppression of power oscillation excitation is realized;
and thirdly, the detected output voltage amplitude of the inverter is used as an input signal of a bus voltage prediction link. And an output signal of the inverter is sent to an original virtual synchronous inverter control algorithm module, so that the detection amplitude of the inverter is close to the actual voltage value of the PCC point, and the problems of reactive power unevenness and overlarge voltage fluctuation range of the PCC point caused by different voltages are solved.
Claims (8)
1. A virtual synchronous inverter control method capable of inhibiting active oscillation is characterized by comprising the following steps:
a. adding a virtual damping control algorithm to an active power control loop of a virtual synchronous inverter control algorithm, and adjusting electromagnetic torque of the active power control loop by extracting frequency low-frequency oscillation components to reduce the difference between mechanical torque and electromagnetic torque and reduce the variation of angular frequency, thereby weakening the active oscillation of the virtual synchronous inverter;
b. adding a virtual impedance control algorithm to a reactive power control loop of a virtual synchronous inverter control algorithm, adjusting a voltage modulation signal output by the reactive power control loop, and changing an equivalent inductive reactance from the virtual synchronous inverter to a PCC point, so that the equivalent inductive reactance from the virtual synchronous inverter to the PCC point is greater than line impedance, the coupling of active power and reactive power is reduced, an instantaneous power increment sharing condition is realized, and the excitation of active oscillation of the virtual synchronous inverter is restrained;
c. the active oscillation suppression of the virtual synchronous inverter is realized through the steps a and b.
2. The virtual synchronous inverter control method capable of suppressing the active oscillation according to claim 1, wherein after the virtual impedance control algorithm is added in the step b, a PCC point bus voltage estimation algorithm is added to make the voltage amplitude detected by the virtual synchronous inverter approach to the PCC point voltage value.
3. The virtual synchronous inverter control method capable of suppressing active oscillation according to claim 1 or 2, wherein the step a of extracting the low-frequency oscillation component comprises: the cutoff frequency is set so that the fluctuation component in the frequency passes through the dc blocking filter, and the dc component is not passed through, thereby obtaining a frequency fluctuation amount without the dc component.
4. The virtual synchronous inverter control method capable of suppressing active oscillation according to claim 3, wherein the virtual damping control algorithm comprises multiplying the frequency fluctuation amount without direct current component by a damping coefficient and adding to the electromagnetic torque to form additional damping to the electromagnetic torque and damp the power oscillation.
5. The virtual synchronous inverter control method capable of suppressing active oscillation according to claim 1, wherein the virtual impedance control algorithm comprises:
firstly, converting a PWM (pulse-width modulation) signal of output voltage of a virtual synchronous inverter from three phases to two phases under alpha beta coordinates;
then introducing virtual impedance, and adding a voltage modulation signal output by a virtual synchronous inverter to the voltage drop on the virtual impedance to obtain the PWM modulation signal voltage under the alpha beta coordinate system after the virtual impedance is adjusted; the output voltage modulation signal of the virtual synchronous inverter is a two-phase alpha beta virtual synchronous inverter output voltage PWM modulation signal;
and finally, performing inverse transformation from the two-phase alpha beta to the three-phase abc coordinate system, converting the transformed voltage into voltage under the abc three-phase coordinate system, and changing the equivalent output impedance of the virtual synchronous inverter by adjusting the value of the virtual impedance so as to change the equivalent line impedance from the virtual synchronous inverter to a PCC point.
6. The virtual synchronous inverter control method capable of suppressing active oscillation according to claim 2, wherein the PCC point bus voltage estimation algorithm comprises:
firstly, the three-phase voltage detected by the virtual synchronous inverter is converted into two-phase alpha beta coordinate, and then the equivalent impedance X is addedtThe correction voltage under the alpha beta coordinate system is obtained through the voltage drop, and the voltage amplitude V of the PCC point is obtained through an amplitude detection linkbus(ii) a The equivalent impedance Xt is equivalent impedance from the inverter to a PCC point;
meanwhile, the calculation formula of Q in the virtual synchronous inverter control algorithm is replaced by an expression (11),
in the formula, Q meterIndicating the potential of the inverter to output reactive power, ia，ib，icIs the output current of the inverter, eoa，eob，eocThe PWM modulation signal voltage under the alpha beta coordinate system after the virtual impedance adjustment is subjected to inverse transformation from two-phase alpha beta to three-phase ABC and is converted into the voltage under the ABC three-phase coordinate system.
7. The virtual synchronous inverter control method capable of suppressing active oscillation according to claim 6, wherein the amplitude detection unit specifically includes:
firstly, the corrected voltage under alpha beta coordinate is inversely transformed and converted into PCC point approximate estimation voltage v under abc three-phase coordinate systema，vb，vcThen obtaining the voltage amplitude V of the PCC point by the formula (10)bus；
8. A computer storage medium having a virtual synchronous inverter control algorithm stored thereon, wherein the method of any of claims 1-7 is implemented when the virtual synchronous inverter control algorithm is executed by a processor.
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