Double-layer inertia control method and device for interconnection converter of alternating current-direct current power grid

Abstract

The invention discloses a double-layer inertia control method and device for an AC / DC power grid interconnected converter, and the method comprises the steps: controlling an AC / DC converter through a virtual synchronous machine, and controlling a DC-side capacitor of the interconnected converter to release inertia during frequency disturbance; additional frequency differential control is adopted for the DC / DC converter, a frequency differential item is added to a voltage outer ring, and the frequency change of the alternating current micro-grid is responded. According to the method, the alternating-current frequency is supported by the direct-current inertia, the direct-current side capacitor of the interconnected converter and the double inertia of the direct-current micro-grid are fully utilized, switching of control modes is not needed, the requirement for the capacity of system energy storage equipment is effectively reduced, meanwhile, the frequency stability of the alternating-current micro-grid under disturbance is improved, and the system reliability is improved. Therefore, impact in the control process is reduced, and higher stability is achieved.

Description

Technical Field

[0001] The present invention relates to a technology in the field of power grid control, specifically a dual-inertia control method and device for an AC / DC power grid interconnected converter. Background Art

[0002] Most of the control strategies for interconnected converters maintain the stability of frequency or DC voltage, and it is difficult to utilize the inertia of the DC capacitor of the interconnected converter and the inertia of the DC microgrid simultaneously. Summary of the Invention

[0003] Aiming at the above deficiencies of the existing technology, the present invention proposes a dual-inertia control method and device for an AC / DC power grid interconnected converter, which uses DC inertia to support the AC frequency, makes full use of the dual inertia of the DC side capacitor of the interconnected converter and the DC microgrid, does not require switching of control modes, effectively reduces the demand for the capacity of the system energy storage device, and is beneficial to improving the frequency stability of the AC microgrid under disturbances, thereby reducing the impact during the control process and having higher stability.

[0004] The present invention is realized through the following technical solutions:

[0005] The present invention relates to a dual-inertia control method for an AC / DC power grid interconnected converter. By establishing a dual-inertia control model for the interconnected converter and adopting virtual synchronous machine control for the AC / DC converter therein, the DC side capacitor of the interconnected converter is controlled to release inertia during frequency disturbances; for the DC / DC converter therein, additional frequency differential control is adopted, and a frequency differential term is added to the voltage outer loop to respond to the change of the AC microgrid frequency. Brief Description of the Drawings

[0006] Figure 1 It is the system structure and control block diagram of the interconnected converter system;

[0007] Figure 2 The comparison diagram of the strategy and the strategy effect of the present invention;

[0008] In the figure: (a) frequency, (b) DC voltage, (c) power of the interconnected converter. Detailed Embodiment

[0009] As Figure 1 shown, this embodiment relates to a dual-inertia control method for an AC / DC power grid interconnected converter, including:

[0010] Step 1: Establish a dual-inertia control model for the interconnected converter, specifically including: a VSM virtual inertia module and a frequency differential module, wherein: the VSM virtual inertia module controls the DC capacitor to release virtual inertia according to the rotor motion equation of the synchronous machine, and the frequency differential module performs differential processing based on the AC frequency information to obtain the change amount of the DC microgrid current reference value.

[0011] Step 2: Based on the double-layer inertia control model established in Step 1, the virtual synchronous machine control is adopted for the AC / DC converter, specifically as follows: Where: H is the virtual inertia constant, P M is the mechanical power of the virtual synchronous machine, P e is the electromagnetic power of the virtual synchronous machine, D is the damping coefficient, P D = D(ω VSM - ω grid ) is the damping power, ω grid is the AC bus angular frequency, ω VSM is the virtual angular frequency, and δ is the rotor angular displacement of the virtual synchronous machine.

[0012] The virtual synchronous machine on the AC / DC side of the interconnected converter simulates the dynamic characteristics and synchronization mechanism of a synchronous motor, adjusts the active and reactive power according to the AC grid frequency and voltage characteristics, and analogizes the mechanical equation of the synchronous motor to provide virtual inertia and damping to the microgrid using the DC side capacitor power.

[0013] Step 3: Based on the double-layer inertia control model established in Step 1, the additional frequency differential control is adopted for the DC / DC converter, and a frequency differential term is added to the voltage outer loop to respond to the AC microgrid frequency change, specifically as follows: Where: U dc is the DC microgrid bus voltage, U dcref is the DC bus voltage reference value, k is the coefficient of the frequency differential term, and adjusting k can adjust the magnitude of the inertia power provided by the DC microgrid. k p is the proportional coefficient, and k i is the integral coefficient.

[0014] The frequency differential control enables the DC microgrid to respond to the disturbance and instantaneously provide inertia power at the moment of the AC microgrid frequency disturbance. The power transmitted through the interconnected converter provides frequency support for the AC side, improves the response speed, and effectively optimizes the dynamic characteristics of the AC microgrid frequency.

[0015] In the specific experimental stage, a PSCAD simulation software is used to build a hybrid microgrid simulation model as Figure 1 shown. The simulation verification is carried out for the AC side load fluctuation condition and the effect of the control strategy of the interconnected converter. The simulation parameters are shown in Table 1.

[0016] Table 1 Simulation Parameters <![CDATA[AC microgrid voltage U ac0 > 380V <![CDATA[AC microgrid frequency f0]]> 50Hz Virtual inertia constant H 0.0005 Damping coefficient D 0.5 AC load 0.6MW <![CDATA[DC voltage U dc0 > 700V Frequency derivative coefficient k 0.1 DC load 0.6MW <![CDATA[Initial active power value P0 transmitted by the interconnected converter]]> 0

[0017] Operating Condition: AC Load Fluctuation

[0018] When the load on the AC grid side suddenly increases, causing the frequency to drop, and the DC microgrid has sufficient power, the control system detects the change in frequency and adjusts the DC microgrid bus voltage to provide inertia to the AC microgrid. At the same time, the AC / DC converter releases the inertia of the DC capacitor of the interconnection converter through virtual synchronous machine control to suppress the frequency fluctuation of the AC microgrid.

[0019] At the beginning of the simulation, the AC load is 0.6 MW. At 16 s, the AC load suddenly increases by 0.3 MW. The simulation results are as Figure 2 shown.

[0020] Compared with the prior art, when the sudden increase in the AC load causes the frequency to drop, while optimizing the dynamic response of the system frequency, the present invention ensures that the DC voltage is within a reasonable operating range, makes full use of the double inertia of the DC capacitor and the DC microgrid, can quickly support the AC frequency, speeds up the frequency recovery speed, and reduces the frequency deviation; In summary, the present invention can simultaneously utilize the double inertia of the interconnection converter and the DC microgrid to quickly support the AC frequency, effectively ensuring the stability of the hybrid microgrid system.

[0021] The above specific implementation can be locally adjusted by those skilled in the art in different ways without departing from the principle and purpose of the present invention. The protection scope of the present invention is subject to the claims and is not limited by the above specific implementation. All implementation solutions within its scope are subject to the present invention.

Claims

1. A double-inertia control method for an AC-DC grid-connected converter, characterized in that, By establishing a double-layer inertia control model for interconnected converters and adopting virtual synchronous machine control for the AC / DC converter therein, the DC-side capacitor of the interconnected converter is controlled to release inertia during frequency disturbances; for the DC / DC converter therein, additional frequency differential control is adopted, and a frequency differential term is added to the voltage outer loop to respond to the frequency change of the AC microgrid.

2. The double-inertia control method for an AC-DC grid-connected converter according to claim 1, characterized in that, The double-layer inertia control model of the interconnected converter specifically includes: a VSM virtual inertia module and a frequency differential module. Among them, the VSM virtual inertia module controls the DC capacitor to release virtual inertia according to the synchronous machine rotor motion equation, and the frequency differential module performs differential processing based on the AC frequency information to obtain the change amount of the DC microgrid current reference value.

3. The double-inertia control method for an AC-DC grid-connected converter according to claim 1, characterized in that, The so-called virtual synchronous machine control, that is, the virtual synchronous machine control is adopted for the AC / DC converter in the double-layer inertia control model, specifically as follows: Where: H is the virtual inertia constant, P M is the mechanical power of the virtual synchronous machine, P e is the electromagnetic power of the virtual synchronous machine, D is the damping coefficient, P D =D(ω VSM -ω grid ) is the damping power, ω grid is the AC bus angular frequency, ω VSM is the virtual angular frequency, and δ is the rotor angular displacement of the virtual synchronous machine.

4. The double-inertia control method for an AC-DC grid-connected converter according to claim 3, characterized in that, The virtual synchronous machine on the AC / DC side of the interconnected converter simulates the dynamic characteristics and synchronization mechanism of a synchronous motor, adjusts the active and reactive power according to the AC grid frequency and voltage characteristics, and analogizes the synchronous machine mechanical equation to provide virtual inertia and damping to the microgrid using the DC-side capacitor power.

5. The double-inertia control method for an AC-DC grid-connected converter according to claim 1, characterized in that, The adoption of additional frequency differential control means that additional frequency differential control is adopted for the DC / DC converter in the double-layer inertia control model, and a frequency differential term is added to the voltage outer loop to respond to the frequency change of the AC microgrid. Specifically: Where: U dc is the DC microgrid bus voltage, U dcref is the reference value of the DC bus voltage, k is the frequency derivative coefficient, adjusting k can adjust the magnitude of the inertial power provided by the DC microgrid, k p is the proportionality coefficient, k i is the integral coefficient.

6. The double-inertia control method for an AC-DC grid-connected converter according to claim 5, characterized in that, The frequency differential control enables the DC microgrid to respond to disturbances instantaneously and provide inertial power instantaneously at the moment of frequency disturbance in the AC microgrid. The power transmitted through the interconnected converter provides frequency support for the AC side, improves the response speed, and effectively optimizes the frequency dynamic characteristics of the AC microgrid.

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