Self-adaptive control strategy and oscillation suppression algorithm suitable for network construction type control system

Abstract

The invention discloses a self-adaptive control strategy and an oscillation suppression algorithm suitable for a network construction type control system, and belongs to the technical field of power electronic device control, the self-adaptive control strategy comprises a direct current side circuit control strategy and an alternating current side self-adaptive control strategy, and a direct current side circuit is a boost chopper circuit; the AC side adaptive control strategy is based on traditional VSG control, and after disturbance is detected by the oscillation suppression algorithm, a reactive power control loop of the VSG is adaptively switched to a DC current loop. The oscillation suppression algorithm mainly comprises the steps that the absolute value of frequency deviation in the alternating current system is compared with a preset allowable deviation value, and when the absolute value of the frequency deviation is large, it is judged that disturbance occurs in the alternating current system. According to the oscillation suppression algorithm, whether disturbance exists in the system can be detected, the self-adaptive control strategy is matched, the modulation coefficient (MI) is automatically controlled to be increased after the disturbance is generated by the system, the direction of the capacitance current is opposite to the direction of the current generated at the moment before the self-adaptive algorithm is adopted, and the oscillation of the system is suppressed in a mode of suppressing the resonance current.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of power electronic device control, and specifically to an adaptive control strategy and oscillation suppression algorithm applicable to a network-forming control system. Background Art

[0002] With the large-scale penetration of new energy distributed generation into the power system, the traditional power grid is no longer the previous rigid power system and has become flexibly controllable. As a result, the inertia and damping of the system have been greatly reduced, which easily leads to an increase in the amplitude of system frequency and voltage fluctuations. Moreover, the volatility and randomness of renewable energy further exacerbate this oscillation form. In order to improve the inertia and damping of the system, the virtual synchronous generator (VSG) control technology is introduced into the power electronic converters of distributed generation units to improve the inertia and damping of the grid-connected system. However, the stable operation of the grid-connected inverter under VSG control is a prerequisite for the VSG control to support the inertia and damping of the power system in a friendly manner. What is more worthy of attention from engineers and scientists is the stability of the grid-connected VSG itself.

[0003] As a non-linear control strategy, the adaptive control strategy, combined with a disturbance detection algorithm, can automatically switch control methods in different situations by reasonably designing control strategies in different situations, so as to improve the anti-disturbance performance of the system.

[0004] In the current research on the adaptive control strategy based on the VSG control strategy, all of them focus on designing better algorithms to adaptively adjust the virtual inertia and damping coefficients of the system to help the system smoothly pass through the transient process. Although the method of adaptively adjusting inertia and damping to suppress oscillation is effective, its action speed is slow and it cannot quickly suppress oscillation. As an important concept in the field of power electronics, the modulation wave still has no relevant research work focusing on suppressing system oscillation by changing the modulation wave of VSG control.

[0005] The principle that MI can suppress the resonance of the circuit system was expounded by Japanese scholar Yasuhiko Neba as early as 2005. However, he only expounded the relevant principle, did not explain how to increase MI when a disturbance occurs, and did not extend this method to more other systems. To make up for the deficiencies of the above work, the present invention designs an oscillation suppression adaptive control strategy and algorithm applicable to a dual-pole system of an energy storage system-network-forming inverter. Summary of the Invention

[0006] The technical solution of the present invention addresses the technical problem of the overly single solution of the prior art, providing a solution significantly different from the prior art. One of the technical problems to be solved by the present invention is to provide an adaptive control strategy applicable to a network-forming control system, concretize the method of suppressing oscillations by MI, and extend it to more system applications.

[0007] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0008] An adaptive control strategy applicable to a network-forming control system includes a DC-side circuit control strategy and an AC-side adaptive control strategy. The DC-side circuit is a DC-DC boost chopper circuit; the AC-side adaptive control strategy is based on traditional VSG control. After the oscillation suppression algorithm detects a disturbance, the reactive power control loop of VSG is adaptively switched from the AC-side reactive power inertia damping loop to the DC current loop. The modulation wave amplitude is generated by subtracting the actual value from the DC power supply side current reference value, then multiplying by a proportional amplification factor, and finally adding the voltage reference value.

[0009] Specifically, the control loop structure of the DC-side circuit is as follows: the outer voltage proportional-integral control loop, the middle current inertia damping control loop, and the inner voltage proportional-integral control loop are connected in sequence. After subtracting the DC power supply side current from the output of the inner loop and scaling it by a proportional coefficient, it is added to the duty cycle obtained through (1 - V s / V dc )to obtain the actual duty cycle, and finally compared with the carrier wave to generate a trigger signal; V dc represents the actual value of the voltage across the DC-side capacitor, and V s represents the voltage of the DC voltage source.

[0010] Specifically, the AC-side adaptive control strategy includes an active control loop and a reactive control loop. In the active control loop, after subtracting the actual value from the active power reference value, passing through an inertia damping link, adding the frequency reference value, and then passing through an integral link, the phase information at the outlet of the network-forming inverter is obtained.

[0011] Specifically, when the oscillation suppression algorithm does not detect a disturbance, the reactive control loop is a reactive power inertia damping loop, and the modulation wave amplitude is generated by subtracting the actual value from the reactive power reference value, passing through an inertia damping link, and then adding the voltage reference value.

[0012] Another technical problem to be solved by the present invention is to provide an oscillation suppression algorithm applicable to a network-forming control system, which is used as an oscillation detection work and adaptive control mode switching tool, and is used in conjunction with the adaptive control strategy to suppress system oscillations together.

[0013] The oscillation suppression algorithm mainly includes: comparing the absolute value of the frequency deviation in the AC system with a preset allowable deviation value, and determining that the AC system has a disturbance when the absolute value of the frequency deviation is greater than the preset allowable deviation value. The specific steps are as follows: S1. Sample the frequency of the AC system; S2. Calculate the absolute value of the frequency deviation; S3. Determine whether the absolute value of the frequency deviation is greater than the preset allowable deviation value. If so, go to step S4-1; if not, go to step S4-2; S4-1. K enable2 = 1, δE = (I vir - I s ) K stiff； S4-2. K enable1 = 1, δE = (Q ref - Q* ) / (J q s + D q ).

[0014] Among them, K enable1 and K enable2 respectively represent the adaptive algorithm trigger coefficients, which have no special physical meaning and are a pair of complementary coefficients used to switch the control algorithm; δE represents the voltage deviation; I vir represents the DC power supply side current reference value; I s represents the actual value of the DC power supply side current; K stiff represents the adaptive current loop amplification coefficient; Q ref represents the reactive power reference value; J q represents the inertia of the reactive power control channel in the VSG system; D q represents the damping of the reactive power control channel in the VSG system; s represents the Laplace operator.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] The adaptive control strategy proposed by the present invention is based on the traditional VSG control. After the oscillation suppression algorithm detects a disturbance, the reactive power control loop of the VSG adaptively switches from the AC-side reactive power inertia damping loop to the DC current loop to increase the MI when a disturbance occurs, so as to change the direction of the current in the DC-side capacitor of the inverter, making the direction of the capacitor current opposite to the direction of the current at the moment of disturbance generation when the adaptive algorithm is not adopted, and suppressing the resonant current to achieve the purpose of suppressing system oscillation. Compared with the prior art, the adaptive control strategy proposed by the present invention can suppress the resonance of the circuit system faster and provides a fast and effective resonance suppression method from a new perspective. In addition, the present invention also proposes an oscillation suppression algorithm, which can be used in conjunction with the proposed adaptive control strategy to efficiently and quickly suppress the resonance of the energy storage system-network-forming inverter bipolar system.

[0017] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. Brief Description of the Drawings

[0018] Figure 1 It is a schematic diagram of the topological structure and control algorithm of the energy storage system-network-forming inverter bipolar system hardware circuit of the present invention;

[0019] Figure 2 It is a flowchart of the oscillation suppression algorithm of the present invention;

[0020] Figure 3 It is a simulation result diagram in the embodiment of the present invention. Detailed Embodiments

[0021] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present invention are given in the drawings, but the present invention can be implemented in different forms and is not limited to the embodiments described in the text. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art belonging to the technical field of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0023] The adaptive control strategy applicable to the energy storage system-network-forming inverter bipolar system includes the DC-side DC-DC boost chopper circuit control strategy and the AC-side adaptive control strategy.

[0024] The DC-side DC-DC boost chopper circuit control strategy is based on the reference value V of the voltage across the DC-side capacitordcref Subtract the actual value V dc Then pass through a proportional-integral controller PI1, and then subtract the DC-side output current value I o , then pass through a virtual inertia damping link (1 / Js) and then subtract the actual value of the voltage across the DC-side capacitor V dc , then pass through a proportional-integral controller PI2 and then subtract the DC power supply-side current I s , then multiply by a proportional scaling factor K pwm , and then add it to the duty cycle obtained through (1 - V s / V dc ) to obtain the actual duty cycle. The actual duty cycle is compared with the carrier wave to generate the trigger signals for the two IGBTs (insulated gate bipolar transistors) of the chopper circuit. J represents the inertia in the VSG system; s represents the Laplace operator; V s represents the voltage of the DC-side voltage source.

[0025] The AC-side adaptive control strategy is based on the traditional VSG control strategy. The active power control loop consists of the active power reference value P ref Subtract the actual value P e Then pass through the inertia damping link (1 / J p ω g s) and then add the angular frequency reference value ω g , and then pass through an integral link (1 / s) to obtain the phase information θ at the output of the grid-forming inverter. J p represents the inertia of the active power control channel in the VSG system.

[0026] The reactive power control loop needs to select the modulation wave generation method through the oscillation suppression algorithm. The oscillation suppression algorithm is as Figure 2 shown, including the following process: S1. Sample the frequency f of the AC system; S2. Calculate the absolute value of the frequency deviation |FB|; S3. Judge whether |FB| is greater than the given allowable deviation value TVL. If so, go to step S4-1; if not, go to step S4-2; S4-1. K enable2 = 1, δE = (I vir - I s )K stiff ; S4-2. K enable1 = 1, δE = (Q ref - Q* ) / (J q s + D q ).

[0027] K enable1 and Kenable2 They respectively represent the trigger coefficients of the adaptive algorithm, which have no specific physical meaning and are a pair of complementary coefficients used to switch control algorithms; δE represents the voltage offset; is the expression of the low-pass filter (LPF); J q represents the inertia of the reactive power control channel in the VSG system; D q represents the damping of the reactive power control channel in the VSG system.

[0028] If the algorithm detects the existence of resonance (disturbance) in the system, that is Figure 2 in the algorithm shown, the absolute value of the frequency offset |FB| is greater than the given allowable offset value TLV. At this time, the reactive power control loop in the AC VSG control loop automatically switches from the original reactive power inertia damping loop to the DC current proportional amplification loop to increase the MI (modulation coefficient, the ratio of the amplitude of the modulation wave to the amplitude of the carrier wave) when the disturbance occurs, so as to change the direction of the current in the DC-side capacitor of the inverter, making the direction of the capacitor current opposite to the direction of the current at the moment of disturbance generation when the adaptive algorithm is not adopted, and suppressing the resonance current to achieve the purpose of suppressing system oscillation. Specifically: the algorithm switches the generation method of the modulation wave to the DC power supply side current reference value I vir subtracting the actual value I s and then passing through proportional amplification, and then adding the voltage reference value E ref to generate a new significantly larger modulation wave amplitude.

[0029] If no resonance is detected in the system, that is Figure 2 in the algorithm shown, the absolute value of the frequency offset |FB| is less than the given allowable offset value TLV. At this time, the AC-side control loop is a traditional VSG control loop, that is, the active power control loop is an active power inertia damping loop, and the reactive power control loop is a reactive power inertia damping loop. The modulation wave amplitude is generated by subtracting the actual value Q ref from the reactive power reference value Q e and then passing through an inertia damping link (1 / J q s) and then adding the voltage reference value E ref to generate.

[0030] It should be noted that the selection of the threshold value TLV and the adaptive current loop amplification coefficient K stiff in the algorithm has different effects on oscillation suppression under different values.

[0031] Next, verify the adaptive converter control strategy and oscillation suppression algorithm proposed in the present invention for the energy storage system - grid-forming inverter bipolar system.

[0032] Under the following three working conditions, simulations with and without adaptive control are carried out to obtain Figure 3 the simulation results shown.

[0033] Operating condition 1: R f : 0.4 Ω, L f : 4.4 mH, R tr : 0.4 Ω, L tr : 4.4 mH, R g : 0.4 Ω, L g : 4.4 mH, J p : 0.03125, D p : 109.96, J q : 1, D q : 1000, TLV: 1.001, K stiff : 20;

[0034] Operating condition 2: R f : 0.4 Ω, L f : 4.4 mH, R tr : 0.4 Ω, L tr : 4.4 mH, R g : 0.6 Ω, L g : 6.6 mH, J p : 0.03125, D p : 109.96, J q : 1, D q : 1000, TLV: 1.001, K stiff : 20;

[0035] Operating condition 3: R f : 0.4 Ω, L f : 4.4 mH, R tr : 0.4 Ω, L tr : 4.4 mH, R g : 1 Ω, L g : 11 mH, J p : 0.03125, D p : 201.06, J q : 1, D q : 1000, TLV: 1.001, K stiff : 20.

[0036] Figure 3Among them, (a) and (b) are the simulation results of the AC-side frequency and DC-side output voltage when the adaptive control is added and not added under operating condition 1. Among them, the black curve CVT is the simulation result without adding the adaptive control, and the red curve SAC is the simulation result with the adaptive control added; (c) and (d) are the simulation results of the AC-side frequency and DC-side output voltage when the adaptive control is added and not added under operating condition 2. Among them, the black curve is the simulation result without adding the adaptive control, and the red curve is the simulation result with the adaptive control added; (e) and (f) are the simulation results of the AC-side frequency and DC-side output voltage when the adaptive control is added and not added under operating condition 3. Among them, the black curve is the simulation result without adding the adaptive control, and the red curve is the simulation result with the adaptive control added.

[0037] It can be seen from Figure 3 that under the same conditions, the simulation results with the adaptive control added are better than those without the adaptive control added. This shows that when the system is disturbed, the proposed adaptive control strategy and algorithm can quickly and effectively suppress the resonance of the energy storage system - grid-forming inverter bipolar system, and can not only effectively suppress the frequency oscillation on the AC side, but also suppress the voltage oscillation on the DC side.

[0038] The present invention is also applicable to any other system adopting grid-forming control, that is, by increasing MI after detecting the occurrence of disturbance to suppress the resonance of the circuit system.

[0039] Compared with the prior art, the adaptive control strategy proposed in the present invention provides a new, faster and more efficient method for suppressing the resonance of the grid-forming system. In addition, an oscillation suppression algorithm is provided, which is used together with the adaptive control to realize the rapid detection and suppression of the resonance of the circuit system.

[0040] The above description of the present invention with reference to the accompanying drawings is exemplary. Obviously, the specific implementation of the present invention is not limited by the above methods. As long as such non-substantial improvements are made by adopting the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. An adaptive control strategy applicable to a network-constituting control system, characterized in that: It includes a DC-side circuit control strategy and an AC-side adaptive control strategy. The DC-side circuit is a DC-DC boost chopper circuit. The AC-side adaptive control strategy is based on the traditional VSG control. After the oscillation suppression algorithm detects a disturbance, the reactive power control loop of the VSG is adaptively switched from the AC-side reactive power inertia damping loop to the DC current loop. The amplitude of the modulation wave is generated by subtracting the actual value from the DC power supply side current reference value, then amplifying it proportionally, and then adding the voltage reference value.

2. The adaptive control strategy applicable to the network-constructing control system according to claim 1, characterized in that: The control loop structure of the DC side circuit is as follows: the outer voltage proportional-integral control loop, the middle current inertia damping control loop, and the inner voltage proportional-integral control loop are connected in sequence. After subtracting the DC power supply side current from the output of the inner loop and scaling it by a proportionality coefficient, it is added to the duty cycle obtained through (1 - V s / V dc ), and the actual duty cycle is obtained. Finally, it is compared with the carrier wave to generate a trigger signal; V dc represents the actual value of the voltage across the DC side capacitor, and V s represents the voltage of the DC side voltage source.

3. The adaptive control strategy applicable to the network-constructing control system according to claim 1, characterized in that: The AC-side adaptive control strategy includes an active power control loop and a reactive power control loop. The active power control loop obtains the phase information at the outlet of the grid-forming inverter by subtracting the actual value from the active power reference value, passing through an inertia damping link, adding the frequency reference value, and then passing through an integral link.

4. The adaptive control strategy applicable to the network-forming control system according to claim 1, characterized in that: When the oscillation suppression algorithm does not detect a disturbance, the reactive power control loop is a reactive power inertia damping loop, and the amplitude of the modulation wave is generated by subtracting the actual value from the reactive power reference value, passing through an inertia damping link, and then adding the voltage reference value.

5. An oscillation suppression algorithm applicable to a network-forming control system, which is applied to the adaptive control strategy described in any one of claims 1-4; characterized in that: Compare the absolute value of the frequency deviation in the AC system with the preset allowable deviation value. When the absolute value of the frequency deviation is greater than the preset allowable deviation value, it is determined that a disturbance has occurred in the AC system.

6. The oscillation suppression algorithm applicable to the network-forming control system according to claim 5, characterized in that: It includes the following steps: S1. Sample the frequency of the AC system; S2. Calculate the absolute value of the frequency deviation; S3. Judge whether the absolute value of the frequency deviation is greater than the preset allowable deviation value. If so, go to step S4-1; if not, go to step S4-2; S4-1, K enable2 = 1, δE = (I vir - I s )K stiff； S4-2, K enable1 = 1, δE = (Q ref - Q* ) / (J q s + D q ); Among them, K enable1 and K enable2 respectively represent the adaptive algorithm trigger coefficients, which have no specific physical meaning and are a pair of complementary coefficients used to switch the control algorithm; δE represents the voltage offset; I vir represents the DC power supply side current reference value; I s represents the actual value of the DC power supply side current; K stiff represents the adaptive current loop amplification coefficient; Q ref represents the reactive power reference value; J q represents the inertia of the reactive power control channel in the VSG system; D q represents the damping of the reactive power control channel in the VSG system; s represents the Laplace operator.

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