Grid-connected energy storage VSG inertia adaptive control method considering power coupling

Abstract

The invention relates to a power electronic technology, and aims to provide a grid-connected energy storage VSG inertia self-adaptive control method considering power coupling. Comprising the steps of obtaining an active power variable quantity and a reactive power variable quantity according to a power value output by a grid-connected energy storage VSG, and then introducing a control ring of the grid-connected energy storage VSG to realize inertia self-adaptive adjustment in virtual synchronous machine control; and the generated angular frequency reference value is used for voltage and current loop control, and finally, the grid-connected energy storage VSG is controlled through an SPWM (Sinusoidal Pulse Width Modulation) link. According to the invention, the inertia coefficient of the VSG can be automatically adjusted along with the change of active power and reactive power, and the frequency change rate output by the grid-connected energy storage VSG is limited; compared with an existing self-adaptive inertia technology, a better frequency change rate suppression effect can be provided in an active and reactive coupling environment; the system can be widely applied to various environments such as grid connection, islands and micro-grids, and stable operation of the system is kept.

Description

Technical Field

[0001] The present invention relates to the technical fields of power electronics and VSG grid-connected control technology, and particularly relates to a grid-connected energy storage VSG control method with adaptive inertia considering power coupling. Background Art

[0002] Under the trend of rapid development of renewable energy, more and more distributed generation devices are connected to the grid. Most of the existing grid-connected converters adopt grid-following control, that is, direct current control based on the phase-locked loop synchronization principle. However, with the further increase in the scale of new energy grid connection and the increase in transmission distance, the grid connection point gradually shows a weak grid trend, and the stability of the grid decreases accordingly.

[0003] To solve the above problems, the virtual synchronous generator control technology (VSG) is proposed. By simulating the mechanical equation of the synchronous machine, the output external characteristics of the grid-connected converter are made close to those of the synchronous machine, thereby alleviating the reduction of grid stability caused by the grid connection of large-scale new energy generation devices. However, different from traditional synchronous generators, due to the power electronics characteristics of the converter, VSG has a wider frequency response range; when the parameter design is unreasonable, it may trigger a dynamic process different from that of the synchronous generator. For example, if the inertia link is set too small, there is no obvious influence on the frequency change; if the inertia link is set too large, it will cause system oscillation; and there is no clear influence of inertia on the rate of change of frequency, and the rate of change of frequency of the system cannot be directly designed.

[0004] Considering the above reasons, most of the current adaptive inertia control technologies only use active power for feedback, and this method has a good inhibitory effect on the frequency change caused by the sudden change of active power output. However, due to the power coupling phenomenon in the grid-connected system, the change of reactive power output will also cause the change of active power and then affect the rate of change of frequency. At this time, if only the adaptive inertia control method considering active power feedback is used, the actual inhibitory effect on frequency change is not ideal.

[0005] Therefore, it is necessary to propose a new solution to solve the above problems. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a grid-connected energy storage VSG inertia adaptive control method considering power coupling.

[0007] To solve the technical problem, the solution of the present invention is:

[0008] Provide a grid-connected energy storage VSG inertia adaptive control method considering power coupling, including the following steps:

[0009] (1)Collect the three-phase voltages \(v\) a , \(v\) b , \(v\) c and the three-phase currents \(i\) a , \(i\) b , \(i\) c output by the grid-connected energy storage VSG, and calculate the instantaneous active power \(P\) and instantaneous reactive power \(Q\) output by the grid-connected energy storage VSG;

[0010] (2)Use the instantaneous active power \(P\) and the given active power reference value \(P\) ref , the instantaneous reactive power \(Q\) and the given reactive power reference value \(Q\) ref to obtain the power change Δ\(P\) and the power change Δ\(Q\) respectively; introduce the two into the control loop of the grid-connected energy storage VSG to achieve the inertia adaptive adjustment in the virtual synchronous generator control and generate the angular frequency reference value \(\omega\) ref of the grid-connected energy storage VSG;

[0011] (3)Use the angular frequency reference value \(\omega\) ref generated by the virtual synchronous generator in step (2) for voltage and current loop control, and finally achieve the control of the grid-connected energy storage VSG through the SPWM link.

[0012] As a preferred solution of the present invention, in the step (1), the instantaneous active power \(P\) and the instantaneous reactive power \(Q\) are calculated by the following formula:

[0013]

[0014] where \(P\) is the instantaneous active power output by the grid-connected energy storage VSG, \(Q\) is the instantaneous reactive power output by the grid-connected energy storage VSG; \(v\) a , \(v\) b , \(v\) c are the three-phase voltages output by the grid-connected energy storage VSG respectively, and \(i\) a , \(i\) b , \(i\) c are the three-phase currents output by the grid-connected energy storage VSG.

[0015] As a preferred solution of the present invention, in the step (2), the instantaneous active power \(P\) is subtracted from the given active power reference value \(P\) ref to obtain the active power change Δ\(P = P\) ref - \(P\); after taking the absolute value of the active power change Δ\(P\), it is used for subsequent operations.

[0016] As a preferred solution of the present invention, in the step (2), the instantaneous reactive power \(Q\) is subtracted from the given reactive power reference value \(Q\) ref to obtain the reactive power change Δ\(Q = Q\) ref-Q; After taking the absolute value of the reactive power variation ΔQ, it is used for subsequent operations.

[0017] As a preferred solution of the present invention, in the step (2), the inertia self - adaptation adjustment in the virtual synchronous generator control is specifically realized in the following way to generate the angular frequency reference value ω of the grid - connected energy storage VSG ref :

[0018]

[0019] In the formula, ω ref is the angular frequency reference value for the voltage and current loop control in the grid - connected energy storage VSG; P ref is the active power reference value; P is the instantaneous active power; D is the damping coefficient of virtual synchronization; ω0 is the initial setting value of the output angular frequency of the grid - connected energy storage VSG; J is the inertia constant of the virtual synchronous generator; J0 is the initial value of the inertia in the virtual synchronous generator; k ωP is the active power adjustment coefficient; k ωQ is the reactive power adjustment coefficient; Q is the instantaneous reactive power output by the grid - connected energy storage VSG.

[0020] As a preferred solution of the present invention, in the step (3), the relationship between the output power variation of the grid - connected energy storage VSG and the frequency variation rate is as follows:

[0021]

[0022] In each formula: k ωP is the active power adjustment coefficient; k ωQ is the reactive power adjustment coefficient; ΔP is the active power variation; ΔQ is the reactive power variation; J0 is the initial value of the inertia in the virtual synchronous generator; ω is the actual output angular frequency of the grid - connected energy storage VSG.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. The present invention introduces the active power variation and reactive power variation into the inertia control of the virtual synchronous generator, enabling the inertia coefficient of the VSG to be adjusted autonomously with the changes in active power and reactive power, thereby limiting the frequency variation rate of the output of the grid - connected energy storage VSG.

[0025] 2. Compared with the existing adaptive inertia technology, due to the introduction of the reactive power variation, it can provide a better frequency variation rate suppression effect in the environment of active - reactive power coupling.

[0026] 3. The method of the present invention can be widely applied in various environments such as grid - connected, islanded, and micro - grid, maintaining the stable operation of the system. Brief Description of the Drawings

[0027] Figure 1 It is a control block diagram of a traditional virtual synchronous generator.

[0028] Figure 2 It is a control block diagram of an adaptive inertia energy storage virtual synchronous generator (VSG) in the present invention.

[0029] Figure 3 It is a waveform of the active power change caused by the reactive power change in the grid-connected system.

[0030] Figure 4 It is a simulation comparison diagram of the frequency change suppression effects between the adaptive inertia control method of the present invention and two control methods in the prior art. Specific implementation manners

[0031] The technical solutions of the invention will be described in detail below with reference to the drawings. The control strategy described in the following examples is applied to the virtual synchronous generator of the energy storage system. It can be understood that when it needs to be applied to other types of new energy power generation systems, it can also be used with reference in the same way.

[0032] Figure 1 It is a control block diagram of a traditional virtual synchronous generator. The control equations of this virtual synchronous generator are shown in Equations (1)-(3):

[0033]

[0034] In the formula, J is the inertia constant of the virtual synchronous generator; T m is the mechanical torque of the virtual synchronous generator; T e is the electromagnetic torque of the virtual synchronous generator; D is the damping coefficient of the virtual synchronization; ω is the actual output angular frequency of the energy storage VSG; ω0 is the initial set value of the output angular frequency of the energy storage VSG; k ω is the power feedback coefficient; v a , v b , v c are the three-phase voltage signals output by the energy storage VSG in the distribution network respectively, and i a , i b , i c are the three-phase current signals respectively; P is the instantaneous active power; P ref is the given power reference value.

[0035] In the control strategy of this virtual synchronous generator, if the inertia link is set too small, there is no obvious influence on the frequency change; if the inertia link is set too large, it will cause system oscillation; and there is no clear influence of inertia on the frequency change rate, and the frequency change rate of the system cannot be directly designed.

[0036] In the existing grid-connected VSG adaptive inertia control technology, since the focus is on the response speed of active power, the inertia coefficient is mostly adjusted by the "change in active power". However, the applicant has found through long-term in-depth research that due to the problem of active and reactive power coupling in grid-connected VSG control, that is, when the reactive power output changes, the active power will also be affected accordingly. At this time, if only active power is used for compensation, the rate of change of frequency cannot be well restricted, and the change in reactive power needs to be added to the feedback control. Aiming at the situation in traditional energy storage grid-connected VSG control where the fixed inertia link cannot meet the requirements of the inverter for stable operation under different working conditions, and the existing adaptive inertia control technology only uses active power for feedback.

[0037] The present invention proposes a new virtual synchronous generator control method with adaptive inertia, aiming to limit the rate of change of the inverter frequency within a certain range and improve the stability of the grid-connected system. The innovative idea of the present invention is to adaptively adjust the output inertia of the grid-connected energy storage VSG according to the magnitudes of the change in active power and the change in reactive power, so as to suppress the rate of change of the frequency of the grid-connected energy storage VSG and enhance the stability of the operation of the grid-connected system when the power output of the grid-connected energy storage VSG suddenly changes or other fault conditions occur.

[0038] The following describes the specific implementation process of the present invention in conjunction with the accompanying drawings:

[0039] (1) Collect the signals of the three-phase voltages v a 、v b ,v c and the three-phase currents i a 、i b 、i c output by the energy storage VSG in the distributed distribution network, and calculate the instantaneous active power P and reactive power Q output by the grid-connected energy storage VSG;

[0040] Specifically, as shown in Equation (1):

[0041]

[0042] (2) Subtract the instantaneous active power P from the given active power reference value P ref to obtain the change in active power ΔP = P ref - P; subtract the instantaneous reactive power Q from the given reactive power reference value Q ref to obtain the change in reactive power ΔQ = Q ref - Q. After taking the absolute values of the change in active power ΔP and the change in reactive power ΔQ respectively, they are used for subsequent operations.

[0043] Such as Figure 2As shown, the active power variation ΔP and the reactive power variation ΔQ are introduced into the control loop of the virtual synchronous generator, and while generating the angular frequency reference value ω of the grid-connected energy storage VSG ref the self-adaptive adjustment of the inertia in the virtual synchronous generator control is realized along with the active power variation and the reactive power variation.

[0044] This process is specifically expressed as Formulas (5) and (6):

[0045]

[0046] Figure 2 The upper half block diagram in it is the frequency-domain expression form of Formula 5, and s in the figure represents the differential operator.

[0047] (3) Use the angular frequency reference value ω ref generated in the power control link in step (2) for voltage and current loop control, and after dq inverse transformation, use the SPWM modulation method to control the photovoltaic energy storage VSG.

[0048] This part of the content belongs to conventional technical content and will not be elaborated in this invention.

[0049] Next, the impact of introducing the reactive power variation ΔQ on the inertia self-adaptive control of the VSG is calculated, analyzed and the effect is verified.

[0050] Due to the good tracking performance of the voltage loop and the current loop, it can be approximately considered that

[0051] ω = ω ref (7)

[0052] Then Formula (5) can be expressed as

[0053]

[0054] Ignoring the damping coefficient and simplifying Formula (8), we can get:

[0055]

[0056] Because the absolute value of ΔP = |P ref - P|, the absolute value of ΔQ = |Q ref - Q|, thus obtaining the relationship between the output power variation of the grid-connected energy storage VSG and the frequency change rate:

[0057]

[0058] In the above formulas: J0 is the initial value of the inertia in the virtual synchronous generator; ω ref is the reference value of the output angular frequency of the photovoltaic energy storage VSG; k ωP is the active power adjustment coefficient; k ωQis the reactive power adjustment coefficient; the definitions of the remaining parameters are the same as those described previously.

[0059] Since is a quantity greater than 0, compared with only using the feedback of the active power change, after adding the reactive power change, can be limited to a smaller range, further reducing the frequency change rate of the grid-connected energy storage VSG.

[0060] From Figure 3 it can also be seen that when the reactive power output of the system increases by 5000 Var at 1 s, due to power coupling at this time, the active power will have a large impact. Since this impact is not caused by the change of P ref the ΔP is small at the initial stage of the impact and cannot be used as an ideal feedback quantity to provide the required inertia for the system; on the contrary, ΔQ is at its maximum value at this time and is more suitable as a feedback quantity. The applicant's research team experimentally verified the frequency change suppression effects of the adaptive inertia control method, non-adaptive inertia control method, and adaptive inertia control method with only active power participation proposed in the present invention. The control parameters used in different control methods are kept consistent during the simulation process. Figure 4 The curves in

[0061] show the corresponding simulation comparison results. It can be seen that after the reactive power changes, the method of the present invention obviously has a better frequency change suppression effect compared with other existing technologies. In summary, the present invention adopts a virtual synchronous machine control method with adaptive inertia. By sampling the three-phase voltage and current values output by the grid-connected energy storage VSG, the instantaneous active and reactive powers output by the grid-connected VSG are calculated. The active power change and the reactive power change are calculated and introduced into the inertia control of the virtual synchronous machine, so that the dynamic adjustment of the inertia coefficient of the virtual synchronous machine can be realized. Compared with the existing adaptive inertia technology, due to the introduction of the reactive power change, considering power coupling, the system can better limit the frequency change rate and further enhance the stability of the grid-connected system.

Claims

1. A grid-connected energy storage VSG inertia adaptive control method considering power coupling, characterized in that Including the following steps: (1)Collect the three-phase voltages v a and v b of the grid-connected energy storage VSG output, as well as v c and the three-phase currents i a 、i b 、i c signals, and calculate the instantaneous active power P and instantaneous reactive power Q output by the grid-connected energy storage VSG; (2) By using the instantaneous active power P and the given active power reference value P ref and the instantaneous reactive power Q and the given reactive power reference value Q ref , the power change ΔP and the power change ΔQ are obtained respectively; the two are introduced into the control loop of the grid-connected energy storage VSG to achieve the inertia self-adaptive adjustment in the virtual synchronous generator control and generate the angular frequency reference value ω ref ; (3) Use the angular frequency reference value ω generated by the virtual synchronous machine in step (2) ref for voltage and current loop control, and finally achieve the control of the grid-connected energy storage VSG through the SPWM link.

2. The method according to claim 1, characterized in that, In the step (1), the sum of the instantaneous active power P and the instantaneous reactive power Q is obtained by the following formula: Where P is the instantaneous active power output by the grid-connected energy storage VSG, and Q is the instantaneous reactive power output by the grid-connected energy storage VSG; v a , v b , v c are the three-phase voltages output by the grid-connected energy storage VSG, and i a , i b , i c are the three-phase currents output by the grid-connected energy storage VSG.

3. The method according to claim 1, characterized in that In the said step (2), the instantaneous active power P is subtracted from the given active power reference value P ref to obtain the active power variation ΔP = P ref - P; after taking the absolute value of the active power variation ΔP, it is then used for subsequent operations.

4. The method according to claim 1, characterized in that, In the step (2), the instantaneous reactive power Q is subtracted from the given reactive power reference value Q ref to obtain a reactive power change ΔQ = Q ref - Q. After taking the absolute value of the reactive power change ΔQ, it is then used for subsequent operations.

5. The method according to claim 1, characterized in that In the step (2), the inertia self - adaptation adjustment in the virtual synchronous generator control is specifically implemented in the following manner to generate the angular frequency reference value ω of the grid - connected energy storage VSG ref : Where ω ref is the angular frequency reference value for voltage and current loop control in the grid-connected energy storage VSG; P ref is the active power reference value; P is the instantaneous active power; D is the damping coefficient of virtual synchronization; ω0 is the initial set value of the output angular frequency of the grid-connected energy storage VSG; J is the inertia constant of the virtual synchronous machine; J0 is the initial value of the inertia in the virtual synchronous machine; k ωP is the active power adjustment coefficient; k ωQ is the reactive power adjustment coefficient; Q is the instantaneous reactive power output by the grid-connected energy storage VSG.

6. The method according to claim 1, characterized in that, In the step (3), the relationship between the output power change of the grid-connected energy storage VSG and the frequency change rate is as follows: In each formula: k ωP is the active power adjustment coefficient; k ωQ is the reactive power adjustment coefficient; ΔP is the change in active power; ΔQ is the change in reactive power; J0 is the initial value of the inertia in the virtual synchronous generator; ω is the actual output angular frequency of the grid-connected energy storage VSG.

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