Virtual Synchronous Generator Control Method Based on Angular Acceleration in Islanding Mode

Abstract

The present invention discloses a virtual synchronous generator control method based on angular acceleration in island mode, which is applicable to an inverter supplying power to an AC system. A DC power supply supplies power to the inverter controlled by VSG through a voltage stabilizing capacitor, and the alternating current output by the inverter supplies power to the AC system after passing through an LCL filter. The VSG control method is set to include transient damping control and angular acceleration feedback control, which are used to suppress the active power oscillation between multiple parallel VSGs, effectively reduce the rate of change of the system frequency, and thus avoid the problem that a large rate of change of frequency causes electrical equipment damage and leads to system collapse. In particular, it also has an inhibitory effect on the phenomenon of increased oscillation caused by constant power loads in the power system.

Description

Technical Field

[0001] The present invention relates to a control method for a virtual synchronous generator, and more specifically to a control method for a virtual synchronous generator based on angular acceleration in an island mode. Background Art

[0002] The virtual synchronous machine technology uses a power electronic converter to provide virtual inertia for an electrified power system by making full use of the surplus energy of renewable energy power generation devices and energy storage, which can effectively stabilize the system state and increase its anti-interference ability. Renewable energy power generation equipment is generally connected in multiple points in a distributed manner. In order to make full use of its surplus energy, virtual synchronous machine control is often used for these devices respectively, resulting in a large number of working conditions of two machines or even multiple machines in parallel. When traditional virtual synchronous machine control is in parallel operation of two machines, significant active power oscillations will occur due to power shocks, seriously endangering the safety of equipment; on the other hand, improved control attempts to solve the oscillations often cause a high rate of frequency change, leading to a series of serious problems such as misoperation of protection devices. Therefore, it is necessary to effectively improve the control method of the virtual synchronous machine so that it can suppress both power oscillations and the rate of frequency change. Summary of the Invention

[0003] The present invention aims to avoid the deficiencies of the above-mentioned prior art, and provides a control method for a virtual synchronous generator based on angular acceleration in an island mode, so as to further reduce the rate of frequency change of the system while maintaining the advantage of suppressing the active power oscillation of the original system, and prevent the collapse of the entire microgrid system caused by an excessive rate of frequency change of the system.

[0004] The present invention adopts the following technical solutions to solve the technical problems:

[0005] The control method for a virtual synchronous generator based on angular acceleration in an island mode of the present invention is applicable to an inverter for supplying power to an AC system. A DC power supply supplies power to the inverter controlled by VSG through a voltage stabilizing capacitor, and the alternating current output by the inverter is supplied to the AC system after passing through an LCL filter. Its characteristic is that the VSG control method is set to include transient damping control and angular acceleration feedback control, which are used to suppress the active power oscillation between multiple parallel VSGs, reduce the rate of frequency change of the system, and avoid the problem of system collapse caused by damage to electrical equipment due to a large rate of frequency change.

[0006] The virtual synchronous generator control method based on angular acceleration in the island mode of the present invention is applicable to an inverter supplying power to an AC system. A DC power supply supplies power to the inverter controlled by VSG through a voltage-stabilizing capacitor, and the alternating current output by the inverter supplies power to the AC system after passing through an LCL filter. Its feature is that, for a power system with a constant-power load, since the system generates a negative impedance, which causes the exacerbation of the active power frequency oscillation of the system, a VSG control method is set up, including transient damping control and angular acceleration feedback control, to alleviate the exacerbated active power oscillation.

[0007] The feature of the virtual synchronous generator control method based on angular acceleration in the island mode of the present invention also lies in that the VSG control method includes the following steps:

[0008] Step 1: Establish a mathematical model simulating the dynamic characteristics of a synchronous generator. The mathematical model is a VSG active power controller mathematical model characterized by Equation (1.1) and a VSG reactive power controller mathematical model characterized by Equation (1.2):

[0009]

[0010] Where: i represents the i-th VSG, that is, VSGi;

[0011] J i is the virtual inertia of VSGi;

[0012] ω i is the output voltage angular frequency of VSGi;

[0013] ω n is the rated angular frequency of all VSGs. The rated angular frequency ω n is the reference angular frequency of the simulated synchronous generator;

[0014] D pi is the damping coefficient of VSGi; D qi is the voltage droop coefficient of VSGi;

[0015] P ni is the active power reference value of VSGi; Q ni is the reactive power reference value of VSGi;

[0016] K qi is the reactive power regulation inertia coefficient of VSGi;

[0017] U nom is the rated voltage of all VSGs, and the values of the rated voltages of all VSGs are equal;

[0018] U oi is the amplitude of the output voltage of VSGi;

[0019] E mi is the root mean square value of the internal electromotive force of VSGi;

[0020] P i is the active power output of VSGi, Q i is the reactive power output of VSGi, and there is:

[0021]

[0022] u oabci is the output voltage of VSGi;

[0023] i Labci is the output current of VSGi.

[0024] is the power factor angle of the system;

[0025] Step 2. Add feedback control P pfb and P dfb to the active power controller of the VSG characterized by Equation (1.1), and establish a mathematical model of the VSG with decentralized transient damping feedback control as Equation (2). Use the feedback control P pfb and P dfb to provide decentralized transient damping when the system is subjected to a large power disturbance, and is used to suppress the active power oscillation generated when switching under a large power disturbance;

[0026]

[0027] In Equation (2), P pfbi and P dfbi are respectively expressed as Equations (3.1) and (3.2):

[0028]

[0029] P dfbi = D mi (ω i - ω bus )(3.2)

[0030] Where:

[0031] T ei is the time constant of the electromagnetic power compensation of VSGi; K ei is the corresponding compensation coefficient of VSGi;

[0032] D mi is the transient damping control coefficient of VSGi; ω bus is the angular frequency of the point of common coupling;

[0033] Step 3: Add feedback control based on angular acceleration to the VSG mathematical model of the distributed transient damping feedback control represented by Equation (2) to obtain the VSG control method based on angular acceleration feedback control represented by Equation (4):

[0034]

[0035] This provides virtual inertia for the VSG and increases the rotational inertia of the system.

[0036] Compared with the existing technologies, the beneficial effects of the present invention are as follows:

[0037] 1. In the case of multiple virtual synchronous generators operating in parallel, when there are significant load changes in the system or after a system fault is removed, a large power shock will occur. By adding angular acceleration feedback control, the present invention provides additional virtual rotational inertia for the system. When a system with two or more parallel virtual synchronous machines is subjected to a power shock, the control method of the present invention can effectively suppress the active power oscillation and significantly reduce the system frequency change rate, preventing system collapse.

[0038] 2. By adding rotational inertia and electromagnetic power feedback control, the present invention can better resist the significant amplification effect of constant power load connection on active power oscillation and maintain the stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a schematic diagram of the topological structure of the usage scenario of the VSG control method of the present invention;

[0040] Figure 2 is the complex frequency domain control block diagram of the VSG mathematical model represented by Equations (1.1) and (1.2);

[0041] Figure 3 is the complex frequency domain control block diagram of the VSG distributed transient damping feedback control mathematical model represented by Equation (3);

[0042] Figure 4 is the complex frequency domain control block diagram of the VSG angular acceleration feedback control mathematical model represented by Equation (4). DETAILED DESCRIPTION OF THE INVENTION

[0043] See Figure 1, in this embodiment, the virtual synchronous generator control method based on angular acceleration in the island mode is applicable to the inverter supplying power to the AC system. The VSG control technology can output PWM waves to control the on and off of the two-level inverter. The DC power supply supplies power to the inverter controlled by VSG through a voltage stabilizing capacitor, and the alternating current output by the inverter supplies power to the AC system after passing through the LCL filter; it is set that the VSG control method includes transient damping control and angular acceleration feedback control, which are used to suppress the active power oscillation between multiple parallel VSGs, reduce the rate of change of the system frequency, and avoid the problem of system collapse caused by damage to electrical equipment due to a large rate of change of frequency.

[0044] In the virtual synchronous generator control method based on angular acceleration in the island mode in this embodiment, the VSG control method includes the following steps:

[0045] Step 1, refer to Figure 2 , establish a mathematical model simulating the dynamic characteristics of a synchronous generator. The mathematical model is the VSG active power controller mathematical model characterized by Equation (1.1) and the VSG reactive power controller mathematical model characterized by Equation (1.2):

[0046]

[0047] Among them: Let i represent the i-th VSG, that is, VSGi;

[0048] J i is the virtual moment of inertia of VSGi;

[0049] ω i is the output voltage angular frequency of VSGi;

[0050] ω n is the rated angular frequency of all VSGs. The rated angular frequency ω n is the reference angular frequency of the simulated synchronous generator;

[0051] D pi is the damping coefficient of VSGi; D qi is the voltage droop coefficient of VSGi;

[0052] P ni is the active power reference value of VSGi; Q ni is the reactive power reference value of VSGi;

[0053] K qi is the reactive power regulation inertia coefficient of VSGi;

[0054] U nom is the rated voltage of all VSGs, and the values of the rated voltages of all VSGs are equal;

[0055] Uoi is the amplitude of the output voltage of VSGi;

[0056] E mi is the root mean square value of the internal electromotive force of VSGi;

[0057] P i is the active power output of VSGi, Q i is the reactive power output of VSGi, and there is:

[0058]

[0059] u oabci is the output voltage of VSGi;

[0060] i Labci is the output current of VSGi.

[0061] is the power factor angle of the system;

[0062] Step 2, refer to Figure 3 , add feedback control P pfb and P dfb to the active power controller of VSG characterized by Equation (1.1). The feedback control is added because it can provide decentralized transient damping, and the transient damping can suppress the active power oscillation of the system when a large power shock occurs in the system. The mathematical model of VSG with decentralized transient damping feedback control is shown in Equation (2). Use the feedback control P pfb and P dfb to provide decentralized transient damping when the system is subjected to a large power disturbance, and to suppress the active power oscillation generated when switching under a large power disturbance;

[0063]

[0064] In Equation (2), P pfbi and P dfbi are respectively expressed as Equations (3.1) and (3.2):

[0065]

[0066] P dfbi = D mi (ω i - ω bus ) (3.2)

[0067] Where:

[0068] T ei is the time constant of the electromagnetic power compensation of VSGi; K ei is the corresponding compensation coefficient of VSGi;

[0069] D mi is the transient damping control coefficient of VSGi; ω bus is the angular frequency of the point of common coupling;

[0070] Step 3, refer to Figure 4 , add further angular acceleration feedback control. The significance of this is that the decentralized transient damping control in Step 2 will reduce the inertia of the system and increase the rate of change of the system frequency. To address this problem, angular acceleration feedback control is added to increase the moment of inertia of the system when the system is subjected to a high-power impact, so as to further improve the inertia of the system and prevent the rate of change of the system frequency from being too high, resulting in system collapse. Based on the VSG mathematical model of the decentralized transient damping feedback control characterized by Equation (2), angular acceleration-based feedback control is added to obtain the VSG control method characterized by Equation (4):

[0071]

[0072] This provides virtual inertia for the VSG and increases the moment of inertia of the system.

[0073] In this embodiment, the virtual synchronous generator control method based on angular acceleration in the island mode, in a power system with a constant power load, due to the system generating negative impedance, which causes the exacerbation of the active power frequency oscillation, the VSG control method is set to include transient damping control and angular acceleration feedback control, which is used to alleviate the exacerbated active power oscillation.

Claims

1. A virtual synchronous generator control method based on angular acceleration in an island mode, which is applicable to an inverter that supplies power to an AC system, wherein a DC power supply supplies power to an inverter controlled by a VSG via a voltage stabilizing capacitor, and the AC power output by the inverter supplies power to the AC system after passing through an LCL filter; wherein the method is characterized in that: The VSG control method includes transient damping control and angular acceleration feedback control, which is used to suppress the active power oscillation between multiple parallel VSGs, reduce the frequency change rate of the system, and avoid the problem of large frequency change rate causing damage to electrical equipment and causing system collapse; or, for a power system with a constant power load, the system generates negative impedance, which causes the system active frequency oscillation to intensify, and the VSG control method includes transient damping control and angular acceleration feedback control to alleviate the intensified active power oscillation; the VSG control method includes the following steps: Step 1: Establish a mathematical model that simulates the dynamic characteristics of a synchronous generator. The mathematical model is a VSG active power controller mathematical model represented by formula (1.1) and a VSG reactive power controller mathematical model represented by formula (1.2): Where: i represents the i-th VSG, namely VSGi; Ji is the virtual moment of inertia of VSGi; ω i is the output voltage angular frequency of VSGi; ω n is the rated angular frequency of all VSGs, the rated angular frequency ω n is the reference angular frequency of the simulated synchronous generator; D pi is the damping coefficient of VSGi; D qi is the voltage droop coefficient of VSGi; P ni is the active power reference value of VSGi; Q ni is the reactive power reference value of VSGi; K qi is the reactive power regulation inertia coefficient of VSGi; U nom is the rated voltage of all VSGs, and the values ​​of the rated voltage of all VSGs are equal; U oi is the amplitude of the output voltage of VSGi; E mi is the RMS value of the internal electromotive force of VSGi; P i is the output active power of VSGi, Q i is the output reactive power of VSGi, and: u oabci is the output voltage of VSGi; i Labci is the output current of VSGi; is the power factor angle of the system; Step 2: Add feedback control P to the active power controller of the VSG represented by equation (1.1) pfb and P dfb , establish the VSG mathematical model of decentralized transient damping feedback control as shown in formula (2), and use the feedback control P pfb and P dfb Provides distributed transient damping when the system is subject to high-power disturbances, used to suppress active power oscillations generated when the system is switched on and off due to high-power disturbances; In formula (2), P pfbi and P dfbi They are respectively expressed as formula (3.1) and formula (3.2): P dfbi =D mi (oh i -oh bus ) (3.2) in: T ei is the time constant of electromagnetic power compensation of VSGi; K ei is the corresponding compensation coefficient of VSGi; D mi is the transient damping control coefficient of VSGi; ω bus is the angular frequency of the common coupling point; Step 3: Add angular acceleration-based feedback control to the VSG mathematical model of decentralized transient damping feedback control represented by equation (2) to obtain the VSG control method based on angular acceleration feedback control represented by equation (4): This provides virtual inertia for the VSG and increases the system's moment of inertia.

Images