Virtual synchronous generator control method based on angular acceleration in island mode

Abstract

The invention discloses a virtual synchronous generator control method based on angular acceleration in an island mode, which is suitable for an inverter for supplying power to an alternating current system, a direct current power supply supplies power to the inverter controlled by a VSG through a voltage stabilizing capacitor, and alternating current output by the inverter supplies power to the alternating current system after passing through an LCL filter; the VSG control method comprises transient damping control and angular acceleration feedback control and is used for restraining active power oscillation among the multiple VSGs connected in parallel, the frequency change rate of the system is effectively reduced, and therefore the problem that the system collapses due to the fact that electrical equipment is damaged due to the large frequency change rate is avoided. And particularly, an effect of suppressing an oscillation aggravation phenomenon caused by a constant-power load in an electric power system is achieved.

Description

Technical Field

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

[0002] Virtual synchronous machine technology uses power electronic converters to fully utilize the surplus energy of renewable energy generation devices and energy storage to provide virtual inertia for power electronic power systems. This can effectively stabilize the system state and increase its anti-interference ability. Renewable energy generation equipment is generally connected in a distributed manner at multiple points. In order to fully utilize its surplus energy, virtual synchronous machine control is often used for these devices, which leads to a large number of conditions where two or even multiple machines are connected in parallel. When two machines are connected in parallel, traditional virtual synchronous machine control will produce significant active power oscillations due to power shocks, which seriously endangers the safety of the equipment; on the other hand, attempts to improve control to solve oscillations often cause a high frequency change rate, leading to a series of serious problems such as false operation of protection devices. Therefore, it is necessary to effectively improve the control method of virtual synchronous machines so that they can suppress power oscillations and frequency change rates at the same time. Summary of the invention

[0003] In order to avoid the deficiencies of the above-mentioned prior art, the present invention provides a virtual synchronous generator control method based on angular acceleration in island mode, so as to further reduce the frequency change rate of the system under the advantage of the original suppression of system active power oscillation, and prevent the collapse of the entire microgrid system due to the excessive frequency change rate of the system.

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

[0005] The present invention discloses a virtual synchronous generator control method based on angular acceleration in an island mode, which is suitable for an inverter that supplies power to an AC system. 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. The method is characterized in that a VSG control method is provided including transient damping control and angular acceleration feedback control, which are used to suppress active power oscillations between multiple parallel VSGs, reduce the frequency change rate of the system, and avoid the problem of a large frequency change rate causing damage to electrical equipment and causing system collapse.

[0006] The present invention discloses a virtual synchronous generator control method based on angular acceleration in an island mode, which is suitable for an inverter that supplies power to an AC system. 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. The method is characterized in that, for a power system with a constant power load, the system generates negative impedance, which causes the aggravation of the system's active frequency oscillation, and a VSG control method is set to include transient damping control and angular acceleration feedback control, so as to alleviate the aggravated active power oscillation.

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

[0008] 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):

[0009]

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

[0011] J i is the virtual moment of 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 voltage of all VSGs are equal;

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

[0019] E mi is the RMS value of the internal electromotive force of VSGi;

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

[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 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;

[0026]

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

[0028]

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

[0030] in:

[0031] T ei is the time constant of 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 common coupling point;

[0033] 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):

[0034]

[0035] This provides virtual inertia for the VSG and increases the system's moment of inertia.

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

[0037] 1. When multiple virtual synchronous generators are connected in parallel, a large power shock will occur when the system has a significant load change or the system fault is removed. The present invention provides an additional virtual moment of inertia for the system by adding angular acceleration feedback control. When a system with two or more virtual synchronous machines connected in parallel is subjected to a power shock, the control method of the present invention can effectively suppress active power oscillation and significantly reduce the frequency change rate of the system, thereby preventing the system from crashing.

[0038] 2. The present invention increases the moment of inertia and electromagnetic power feedback control, which can better resist the significant amplification effect of constant power load access on active power oscillation and maintain the stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of the topological structure of the use scenario of the VSG control method of the present invention;

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

[0041] Figure 3 The control block diagram of the VSG decentralized transient damping feedback control mathematical model represented by equation (3) in the complex frequency domain;

[0042] Figure 4 The control block diagram of the mathematical model of VSG angular acceleration feedback control represented by equation (4) in the complex frequency domain. DETAILED DESCRIPTION

[0043] See also Figure 1In this embodiment, the virtual synchronous generator control method based on angular acceleration in the island mode is suitable for the inverter that supplies power to the AC system. The VSG control technology can output PWM waves to control the opening and closing of the two-level inverter. The DC power supply supplies power to the inverter controlled by the VSG through the voltage stabilizing capacitor, and the AC power output by the inverter is used to power the AC system after passing through the 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, 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.

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

[0045] Step 1: See Figure 2 , a mathematical model simulating the dynamic characteristics of a synchronous generator is established, wherein 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):

[0046]

[0047] Where: i represents the i-th VSG, namely 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 voltage of all VSGs are equal;

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

[0056] E mi is the RMS value of the internal electromotive force of VSGi;

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

[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: See Figure 3 , add feedback control P to the active power controller of VSG represented by equation (1.1) pfb and P dfb The feedback control is added because it can provide decentralized transient damping. Transient damping can suppress the active power oscillation of the system when a large power shock occurs in the system. The VSG mathematical model of decentralized transient damping feedback control is established as shown in formula (2). Using 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;

[0063]

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

[0065]

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

[0067] in:

[0068] T ei is the time constant of 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 common coupling point;

[0070] Step 3, see Figure 4 , adding further angular acceleration feedback control, the significance of doing so is that the distributed transient damping control in step 2 will reduce the inertia of the system and increase the frequency change rate of the system. To address this problem, angular acceleration feedback control is added to increase the system's moment of inertia when the system is subjected to a high-power shock, so as to further increase the system's inertia and prevent the system's frequency change rate from being too high, causing the system to crash. For the VSG mathematical model of distributed transient damping feedback control represented by equation (2), feedback control based on angular acceleration is added to obtain the VSG control method based on angular acceleration feedback control represented by equation (4):

[0071]

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

[0073] In the present embodiment, the virtual synchronous generator control method based on angular acceleration in the island mode is used. In the power system with constant power load, the system active frequency oscillation is aggravated due to the negative impedance generated by the system. The VSG control method includes transient damping control and angular acceleration feedback control to alleviate the aggravated 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 are used to suppress active power oscillations 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.

2. A virtual synchronous generator control method based on angular acceleration in 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: For a power system with a constant power load, the system active frequency oscillation is aggravated due to the negative impedance generated by the system. A VSG control method including transient damping control and angular acceleration feedback control is set to alleviate the aggravated active power oscillation.

3. The virtual synchronous generator control method based on angular acceleration in island mode according to claim 1 or 2, characterized in that The VSG control method comprises 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; J i 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.

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