Improved virtual synchronous machine control method for improving transient stability and application thereof

Abstract

The invention discloses an improved virtual synchronous machine control method for improving transient stability and application of the improved virtual synchronous machine control method. The method comprises the following steps: constructing a virtual synchronous machine, and acquiring characteristic parameters including active reference power and output power of the virtual synchronous machine; and then on the basis of the constructed virtual synchronous machine, respectively constructing phase power coupling feedback correlation models, and coupling the obtained correlation models with the virtual synchronous machine obtained in the step S1 through an integral-differential mode. According to the method, power coupling feedback control is introduced on the basis of an original virtual synchronous machine, and the transient stability of the converter under any impedance characteristic is effectively improved. Based on the excellent effect of the method, the method is applied to the control of the power electronic converter, and the control method is still stable when the power grid voltage drops from 1p.u. To 0.44 p.u. In a high-inductive line impedance power grid with Lg = 4mH and Rg = 0.08 omega through testing, so that an important guiding effect is provided for the industrial application of a virtual synchronous machine system.

Description

Technical Field

[0001] The present invention relates to a virtual synchronous machine control method, in particular to an improved virtual synchronous machine control method for improving transient stability and application thereof, belonging to the technical field of microgrid and power control. Background Art

[0002] Microgrids are widely used to facilitate the large-scale integration of renewable energy sources such as photovoltaics, wind power, fuel cells, and storage units. The operation of microgrids can be divided into grid-connected mode and island mode. In grid-connected mode, with the support of the grid, frequency / voltage stability and power balance can be guaranteed. In island mode, due to the widespread use of power electronic converters and the reduction of the rotational inertia of synchronous generators, microgrids lack sufficient inertia to support frequency stability. Insufficient inertia leads to too high a minimum frequency point and too high a frequency change rate, making the stability of the microgrid more fragile.

[0003] In order to overcome the problem of insufficient inertia in isolated microgrids, a virtual synchronous generator (VSG) was proposed. VSG introduces the swing equation of the synchronous generator into the control algorithm, so that the inverter can simulate both the steady-state characteristics of the synchronous generator and the transient characteristics of the synchronous generator, providing sufficient inertial support. While maintaining the existing power system architecture, VSG is becoming the most effective control solution to enhance system inertia and improve frequency stability.

[0004] However, as a representative of grid-type control, the control performance of the virtual synchronous machine is highly dependent on the line impedance characteristics. In different high-voltage and low-voltage application scenarios, the line impedance output characteristics are complex, and the power electronic equipment is fragile. It is urgent to improve its ability to maintain synchronization under large disturbances, that is, to improve the transient stability of the virtual synchronous machine control converter. Most of the existing improved control methods consider the transient stability of the virtual synchronous machine under high inductive line impedance, but do not consider the impact of different line impedance characteristics on transient stability. Summary of the invention

[0005] In view of the problems existing in the prior art, the first object of the present invention is to provide an improved virtual synchronous machine control method for improving transient stability. Based on the original virtual synchronous machine, the method introduces power coupling feedback control, especially strictly controls phase angle reactive feedback, voltage active feedback, reactive droop coefficient and phase angle active feedback, so as to achieve the universality of the converter in complex impedance characteristics such as high inductance, high resistance and equivalent resistance and inductance, and effectively improve the transient stability of the converter under any impedance characteristics, which has an important guiding role in the industrial application of the virtual synchronous machine system.

[0006] The second object of the present invention is to provide an application of an improved virtual synchronous machine control method for improving transient stability, which is used for power electronic converter control. Based on the excellent technical effects of the above-mentioned virtual synchronous machine, it is applied to the control of power electronic converters, which can effectively improve the transient stability of the converter under large disturbances. After testing, in a high-inductive line impedance power grid with Lg=4mH and Rg=0.08Ω, when the grid voltage drops from 1p.u to 0.44pu, the control method is still stable, and for both the inductive equivalent impedance and high resistive impedance power grids, this method can achieve transient stability improvement when the grid voltage drops.

[0007] In order to achieve the above technical objectives, the present invention provides an improved virtual synchronous machine control method for improving transient stability, comprising:

[0008] Step S1, constructing a virtual synchronous machine and obtaining its characteristic parameters including active reference power and output power;

[0009] Step S2, based on the virtual synchronous machine obtained in step S1, constructing a correlation model of phase angle reactive feedback and phase angle active feedback with respect to the phase angle of the virtual synchronous machine;

[0010] Step S3, based on the virtual synchronous machine obtained in step S1, constructing a correlation model between reactive power droop coefficient and voltage active power feedback with respect to the voltage amplitude of the virtual synchronous machine;

[0011] Step S4, coupling the correlation model obtained in step S2 and step S3 with the virtual synchronous machine obtained in step S1 through an integral-differential method, thereby obtaining:

[0012] As a preferred scheme, the characteristic parameters include: angular frequency, nominal angular frequency, phase angle, active reference power, output power, inertia coefficient, damping coefficient, reactive droop coefficient, voltage amplitude, amplitude reference, reactive reference power, output power, phase angle active feedback coefficient, phase angle reactive feedback coefficient and voltage active feedback coefficient.

[0013] As a preferred solution, the virtual synchronous machine is controlled by control parameters including angular frequency, nominal angular frequency, active reference power and output power, and the expression is:

[0014] Formula 1:

[0015] In formula 1: J i is the inertia coefficient, ω* represents the nominal angular frequency, ω i represents the angular frequency of the ith virtual synchronous machine, P * and P i Denote the active reference power and output power of the ith inverter respectively, D i is the damping coefficient.

[0016] As a preferred solution, the expression of the correlation model of the phase angle reactive feedback and the phase angle active feedback with respect to the phase angle of the virtual synchronous machine is:

[0017] Formula 2: δ i =∫ω i dt-m d P i +n x Q i ;

[0018] In formula 2: i represents the phase angle of the i-th virtual synchronous machine, ω i represents the angular frequency of the ith virtual synchronous machine, m d Represents the phase angle active feedback coefficient, P i represents the output power of the ith inverter, n x Represents the phase angle reactive feedback coefficient, Q i represents the output power of the i-th inverter.

[0019] As a preferred solution, the expression of the correlation model of the reactive power droop coefficient and the voltage active power feedback with respect to the voltage amplitude of the virtual synchronous machine is:

[0020] Formula 3: V i =V * -n d (Q i -Q * )-m x P i ;

[0021] In formula 3: V i represents the voltage amplitude of the ith virtual synchronous machine, V * Indicates the amplitude reference, n d Represents the reactive power droop coefficient, Q i represents the output power of the ith inverter, Q * represents the reactive reference power of the ith inverter, m x Represents the voltage active feedback coefficient, P i represents the output power of the i-th inverter.

[0022] As a preferred solution, the expression of the improved virtual synchronous machine obtained by the coupling is:

[0023] Formula 4:

[0024] In formula 4: J i is the inertia coefficient, ω* represents the nominal angular frequency, ω i represents the angular frequency of the ith virtual synchronous machine, P* and P i Denote the active reference power and output power of the ith inverter respectively, D i is the damping coefficient, δ i represents the phase angle of the i-th virtual synchronous machine, ω i represents the angular frequency of the ith virtual synchronous machine, m d Represents the phase angle active feedback coefficient, n x Represents the phase angle reactive feedback coefficient, Q i represents the output power of the ith inverter, V i represents the voltage amplitude of the ith virtual synchronous machine, V * Indicates the amplitude reference, n d Represents the reactive power droop coefficient, Q * represents the reactive reference power of the ith inverter, m x Indicates the voltage active feedback coefficient.

[0025] The present invention also provides an application of an improved virtual synchronous machine control method for improving transient stability, which is used for power electronic converter control.

[0026] As a preferred solution, the power electronic converter is controlled in the following manner: under high inductive line impedance, the phase angle reactive feedback coefficient and the voltage active feedback coefficient are increased, and the reactive droop coefficient and the phase angle active feedback coefficient are reduced; under high resistive line impedance, the small reactive droop coefficient and the phase angle active feedback coefficient are increased, and the phase angle reactive feedback coefficient and the voltage active feedback coefficient are reduced.

[0027] Compared with the prior art, the beneficial technical effects of the technical solution of the present invention are:

[0028] 1) The control method provided by the present invention is based on the original virtual synchronous machine. By introducing power coupling feedback control, especially strictly controlling the phase angle reactive feedback coefficient, the voltage active feedback coefficient, the reactive droop coefficient and the phase angle active feedback coefficient, the universality of the converter in complex impedance characteristics such as high inductance, high resistance and equivalent resistance and inductance is achieved, and the transient stability of the converter under any impedance characteristics is effectively improved, which has an important guiding role in the industrial application of the virtual synchronous machine system.

[0029] 2) In the technical solution provided by the present invention, based on the excellent technical effects of the above-mentioned virtual synchronous machine, it is applied to the control of power electronic converters, which can effectively solve the transient stability of the converter under large disturbances in the prior art. After testing, in a high-inductive line impedance power grid with Lg=4mH, Rg=0.08Ω, when the grid voltage drops from 1p.u. to 0.44pu, the control method is still stable, and for power grids with equivalent impedance and high resistive impedance, this method can achieve transient stability control when the grid voltage drops under equivalent impedance and high resistive impedance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The phase plane diagram under different grid voltage drops under high inductive impedance provided by Embodiment 1 of the present invention; wherein, Figure 1 (a) is the traditional virtual synchronous machine control method, Figure 1 (b) is the method of the present invention, n x =4e-6,m d =0,m x =4e-4;

[0031] Figure 2 It is a phase plane diagram under different grid voltage drops under the impedance equivalent to the impedance provided by the second embodiment of the present invention; wherein, Figure 2 (a) is the traditional virtual synchronous machine control method, Figure 2 (b) is the method of the present invention, n x =2e-6,m d =5e-6,m x =2e-4;

[0032] Figure 3 The phase plane diagram under different grid voltage drops under high resistive impedance provided by Example 3 of the present invention;

[0033] in, Figure 3 (a) is a traditional virtual synchronous machine control method. Figure 3 (b) is the method of the present invention, n x =1e-6,m d =5e-6,m x =1e-4;

[0034] Figure 4 A schematic diagram of grid voltage, active power, phase angle and current waveform when the grid voltage drops from 0.8pu to 0.44pu under high inductive impedance provided by Embodiment 1 of the present invention;

[0035] in, Figure 4 (a) is the traditional virtual synchronous machine control method, Figure 4 (b) is the method provided by the present invention;

[0036] Figure 5 A schematic diagram of grid voltage, active power, phase angle and current waveforms when the grid voltage drops from 0.8pu to 0.25pu under high inductive impedance provided by Embodiment 2 of the present invention;

[0037] in, Figure 5 (a) is the traditional virtual synchronous machine control method, Figure 5 (b) is the method provided by the present invention;

[0038] Figure 6 A schematic diagram of grid voltage, active power, phase angle and current waveforms when the grid voltage drops from 0.8pu to 0.3pu under high inductive impedance provided by Embodiment 3 of the present invention;

[0039] in, Figure 6 (a) is the traditional virtual synchronous machine control method, Figure 6 (b) is the method proposed by the present invention. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the present invention more obvious, the exemplary embodiments according to the present invention will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments of the present invention, and it should be understood that the present invention is not limited to the exemplary embodiments described herein. Based on the embodiments of the present invention described in the present invention, all other embodiments obtained by those skilled in the art without creative work should fall within the protection scope of the present invention.

[0041] In order to facilitate the description of the beneficial technical effects of the technical solution of the present invention, the improved virtual synchronous machine control methods used in Examples 1 to 3 are as follows:

[0042] An improved virtual synchronous machine control method for improving transient stability is shown in Equation 4:

[0043] Formula 4:

[0044] In formula 4: J i is the inertia coefficient, ω* represents the nominal angular frequency, ω i represents the angular frequency of the ith virtual synchronous machine, P * and P i Denote the active reference power and output power of the ith inverter respectively, D i is the damping coefficient, δ i represents the phase angle of the i-th virtual synchronous machine, ω i represents the angular frequency of the ith virtual synchronous machine, m d Represents the phase angle active feedback coefficient, n xRepresents the phase angle reactive feedback coefficient, Q i represents the output power of the ith inverter, V i represents the voltage amplitude of the ith virtual synchronous machine, V * Indicates the amplitude reference, n d Represents the reactive power droop coefficient, Q * represents the reactive reference power of the ith inverter, m x Indicates the voltage active feedback coefficient.

[0045] Example 1

[0046] The improved virtual synchronous machine control method provided by the present invention and the traditional virtual synchronous machine control method, namely the VSG control method, are used for phase plane analysis. The results are as follows: Figure 1 shown.

[0047] Under the high inductive line impedance of Lg=4mH, Rg=0.08Ω, when the grid voltage drops from 1p.u. to 0.44pu, the traditional virtual synchronous machine control scheme has become unstable, while the improved virtual synchronous machine control method proposed to improve transient stability is still stable, which shows that the proposed method is helpful to improve the large signal stability under grid voltage drop while following the parameter design principles.

[0048] In order to further verify the transient stability of the control method of the present invention, the present invention also conducts a control hardware in the loop experiment, the results of which are as follows: Figure 4 As shown, when the grid voltage drops from 1 p.u. to 0.44 pu, the stability of the control method provided by the present invention is significantly better than the traditional VSG control method, which effectively verifies the effectiveness of the proposed control method in improving transient stability.

[0049] Example 2

[0050] The improved virtual synchronous machine control method provided by the present invention and the traditional virtual synchronous machine control method, namely the VSG control method, are used for phase plane analysis. The results are as follows: Figure 2 shown.

[0051] Under the equivalent line impedance of Lg=2mH, Rg=0.5Ω, when the grid voltage drops from 1p.u. to 0.25pu, the traditional virtual synchronous machine control scheme has become unstable, while the improved virtual synchronous machine control method proposed to improve transient stability is still stable. This shows that the proposed method is helpful to improve the large signal stability under grid voltage drop while following the parameter design principles.

[0052] In order to further verify the transient stability of the control method of the present invention, the present invention also conducts a control hardware in the loop experiment, the results of which are as follows: Figure 5As shown, when the grid voltage drops from 1 p.u. to 0.25 pu, the stability of the control method provided by the present invention is significantly better than the traditional VSG control method, which effectively verifies the effectiveness of the proposed control method in improving transient stability.

[0053] Example 3

[0054] The improved virtual synchronous machine control method provided by the present invention and the traditional virtual synchronous machine control method, namely the VSG control method, are used for phase plane analysis. The results are as follows: Figure 3 shown.

[0055] Under the high-resistance line impedance of Lg=0.1mH, Rg=2Ω, when the grid voltage drops from 1p.u. to 0.3pu, the traditional virtual synchronous machine control scheme has become unstable, while the improved virtual synchronous machine control method proposed to improve transient stability is still stable, which shows that the proposed method is helpful to improve the large signal stability under grid voltage drop while following the parameter design principles.

[0056] In order to further verify the transient stability of the control method of the present invention, the present invention also conducts a control hardware in the loop experiment, the results of which are as follows Figure 6 As shown, when the grid voltage drops from 1 p.u. to 0.3 pu, the stability of the control method provided by the present invention is significantly better than the traditional VSG control method, which effectively verifies the effectiveness of the proposed control method in improving transient stability.

Claims

1. An improved virtual synchronous machine control method for improving transient stability, characterized in that: include: Step S1, constructing a virtual synchronous machine and obtaining its characteristic parameters including active reference power and output power; Step S2, based on the virtual synchronous machine obtained in step S1, constructing a correlation model of phase angle reactive feedback and phase angle active feedback with respect to the phase angle of the virtual synchronous machine; Step S3, based on the virtual synchronous machine obtained in step S1, constructing a correlation model between reactive power droop coefficient and voltage active power feedback with respect to the voltage amplitude of the virtual synchronous machine; Step S4, coupling the correlation model obtained in step S2 and step S3 with the virtual synchronous machine obtained in step S1 through an integral-differential method, thereby obtaining:

2. The improved virtual synchronous machine control method for improving transient stability according to claim 1, characterized in that: The characteristic parameters include: angular frequency, nominal angular frequency, phase angle, active reference power, output power, inertia coefficient, damping coefficient, reactive droop coefficient, voltage amplitude, amplitude reference, reactive reference power, output power, phase angle active feedback coefficient, phase angle reactive feedback coefficient and voltage active feedback coefficient.

3. The improved virtual synchronous machine control method for improving transient stability according to claim 2, characterized in that: The virtual synchronous machine is controlled by control parameters including angular frequency, nominal angular frequency, active reference power and output power, and the expression is: Formula 1: In formula 1: J i is the inertia coefficient, ω* represents the nominal angular frequency, ω i represents the angular frequency of the ith virtual synchronous machine, P * and P i Denote the active reference power and output power of the ith inverter respectively, D i is the damping coefficient.

4. The improved virtual synchronous machine control method for improving transient stability according to claim 2, characterized in that: The expression of the correlation model of the phase angle reactive feedback and the phase angle active feedback with respect to the phase angle of the virtual synchronous machine is: formula 2: d i =bo i dt-m d P i +n x Q i ; In formula 2: i represents the phase angle of the i-th virtual synchronous machine, ω i represents the angular frequency of the ith virtual synchronous machine, m d Represents the phase angle active feedback coefficient, P i represents the output power of the ith inverter, n x Represents the phase angle reactive feedback coefficient, Q i represents the output power of the i-th inverter.

5. The improved virtual synchronous machine control method for improving transient stability according to claim 2, characterized in that: The expression of the correlation model of the reactive power droop coefficient and the voltage active power feedback with respect to the voltage amplitude of the virtual synchronous machine is: Formula 3: V i =V * -n d (Q i -Q * )-m x P i ; In formula 3: V i represents the voltage amplitude of the ith virtual synchronous machine, V * Indicates the amplitude reference, n d Represents the reactive power droop coefficient, Q i represents the output power of the ith inverter, Q * represents the reactive reference power of the ith inverter, m x Represents the voltage active feedback coefficient, P i represents the output power of the i-th inverter.

6. The improved virtual synchronous machine control method for improving transient stability according to claim 2, characterized in that: The expression of the improved virtual synchronous machine obtained by the coupling is: Formula 4: In formula 4: J i is the inertia coefficient, ω* represents the nominal angular frequency, ω i represents the angular frequency of the ith virtual synchronous machine, P * and P i Denote the active reference power and output power of the ith inverter respectively, D i is the damping coefficient, δ i represents the phase angle of the i-th virtual synchronous machine, ω i represents the angular frequency of the ith virtual synchronous machine, m d Represents the phase angle active feedback coefficient, n x Represents the phase angle reactive feedback coefficient, Q i represents the output power of the ith inverter, V i represents the voltage amplitude of the ith virtual synchronous machine, V * Indicates the amplitude reference, n d Represents the reactive power droop coefficient, Q * represents the reactive reference power of the ith inverter, m x Indicates the voltage active feedback coefficient.

7. Application of an improved virtual synchronous machine control method for improving transient stability according to any one of claims 1 to 6, characterized in that: For power electronic converter control.

8. The application of the improved virtual synchronous machine control method for improving transient stability according to claim 7, characterized in that: The control method of the power electronic converter is: under high inductive line impedance, the phase angle reactive feedback coefficient and the voltage active feedback coefficient are increased, and the reactive droop coefficient and the phase angle active feedback coefficient are reduced; under high resistive line impedance, the small reactive droop coefficient and the phase angle active feedback coefficient are increased, and the phase angle reactive feedback coefficient and the voltage active feedback coefficient are reduced.

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