A method for decoupling DC virtual inertia and voltage loop stability margin

Abstract

The present invention discloses a decoupling design method for DC virtual inertia and voltage loop stability margin, belonging to the field of power electronic control technology. Aiming at the challenge that the gain coefficient of differential control in the traditional DC microgrid virtual inertia control is limited by the voltage loop stability margin of the converter, by introducing a low-pass filter time constant as a new degree of freedom, a virtual resistor and a virtual capacitor series structure are constructed, and the parameter design of the DC virtual inertia and the loop stability margin is decoupled, so that a larger virtual DC inertia is achieved under the premise of satisfying the voltage loop control stability margin, thereby suppressing the bus voltage fluctuation of the DC microgrid.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronic control, and in particular relates to a method for decoupling direct current virtual inertia and voltage loop stability margin. Background Art

[0002] A DC microgrid is a low-inertia system with power electronic converters as its main body. Its bus voltage is quite sensitive to source-load power imbalance. Large disturbances such as frequent load switching and random power fluctuations of renewable energy can easily lead to drastic changes in DC bus voltage, thereby reducing the efficiency of the converter, endangering sensitive loads and even affecting the stability of the DC microgrid.

[0003] Voltage source converters can use DC virtual inertia control to respond to system disturbances in a timely manner and suppress voltage fluctuations by quickly releasing or absorbing power. Traditional virtual inertia methods can achieve good dynamic performance by directly applying voltage differential or high-pass filters to the voltage control loop to simulate the characteristics of DC capacitors. However, the gain coefficient of differential control is limited by the loop stability margin of the converter's voltage loop, resulting in a small virtual DC inertia even when the power supply side has sufficient capacity. Summary of the invention

[0004] In order to realize large virtual inertia control of voltage source converter, the present invention proposes a method for decoupling DC virtual inertia and voltage loop stability margin. By introducing new adjustment degrees of freedom and reconstructing the voltage loop control structure, the parameter design of DC virtual inertia and loop stability margin is decoupled. A larger virtual DC inertia is achieved while satisfying the voltage loop control stability margin, thereby suppressing the bus voltage fluctuation of the DC microgrid.

[0005] The method for decoupling direct current virtual inertia and voltage loop stability margin proposed in the present invention comprises the following steps:

[0006] 1) In the converter voltage control, the converter sampling port output voltage value u dc , the voltage reference value u ref Subtract the sampled output voltage value u dc , and the voltage error u is obtained err ;

[0007] 2) Voltage error u err The current component i of the droop control link is calculated through the voltage droop control link. p :

[0008] i p =u err ·K pv

[0009] Among them, K pvIt is the proportional control coefficient of the voltage droop control link, realizing voltage-current droop control;

[0010] 3) Voltage error u err The current component i of the virtual inertia control link is calculated by the virtual inertia control link. vir , used for inner loop current control tracking, the voltage control link expression is:

[0011]

[0012] Among them, R v is a virtual resistor that provides loop damping to ensure the stability margin of voltage control. v is a virtual capacitor, s is a Laplace operator; virtual inertia control of the DC bus voltage is realized, and the decoupling design of the loop stability margin and the DC virtual inertia is realized through the structure of the virtual resistor and the virtual capacitor in series;

[0013] 4)i p with i vir Add together to get the reference current i output by the voltage control link ref :

[0014] i ref =i p +i vir

[0015] 5) The reference current i output by the voltage control link ref The output power of the converter is controlled through proportional-integral tracking, modulation and driving of the inner current loop.

[0016] Based on the above technical solution, the present invention has the following beneficial technical effects:

[0017] In a DC microgrid, the traditional solution for the virtual inertia control of the voltage loop of the power converter is a differential controller:

[0018] i vir =u err ·C v s

[0019] This solution only has C v The virtual inertia is designed with one degree of freedom, and the value of inertia affects the stability margin of the voltage control loop. The present invention introduces the low-pass filter time constant as a new control degree of freedom, and then proposes a virtual resistor R v With virtual capacitance C v The series control structure realizes the decoupling of the converter voltage loop stability margin design and the system DC virtual inertia design, achieving beneficial technical effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the Buck converter circuit and control structure;

[0021] Figure 2 It is the specific implementation block diagram of the voltage controller;

[0022] Figure 3 This is a stability comparison diagram between the traditional solution and the solution of the present invention;

[0023] Figure 4 This is a voltage waveform diagram of the solution of the present invention as the virtual inertia increases. DETAILED DESCRIPTION

[0024] To explain the present invention in more detail, the present invention is further described in detail below by taking Buck converter as an example in combination with the accompanying drawings and embodiments. It should be noted that the method of the present invention is applicable to any converter with a direct current output port, including various topologies of AC-DC and DC-DC converters.

[0025] Figure 1 The schematic diagram of the Buck converter circuit and control structure is shown in Figure 2. The converter samples the DC bus capacitor C dc The bus voltage u dc , as the input of the voltage control link, and the voltage control output is used as the reference value i of the current inner loop control ref , the inductor current i is realized through the current inner loop L The error-free tracking of the converter port can be controlled. ref is the DC bus voltage reference value, G c (s) and G v (s) are the inductor current controller and the DC bus voltage controller respectively.

[0026] Figure 2 is a specific implementation block diagram of the voltage controller, which includes the voltage droop control link and the virtual inertia control link. pv is the proportional control coefficient, R v is the virtual resistance, C v is a virtual capacitor.

[0027] 1) In the converter voltage control, the voltage reference value u ref Subtract the voltage sampling value u dc , and the voltage error u is obtained err ;

[0028] 2) Voltage error u err After the voltage droop control link G pv (s) corresponds to the calculated current component i of the droop control link p :

[0029] ip =u err ·G pv (s) = u err ·K pv

[0030] 3) Voltage error u err Through the virtual inertial control link G cvir (s) corresponds to the calculated current component i of the virtual inertia control link vir , used for inner loop current control tracking, the voltage control link expression is:

[0031]

[0032] Among them, the virtual resistance R v Provide loop damping to ensure the stability margin of voltage control, virtual capacitor C v The virtual inertia required for suppressing the DC bus voltage is provided, and the decoupling design of the loop stability margin and the DC virtual inertia is realized through the structure of the virtual resistor and the virtual capacitor connected in series.

[0033] 4)i p with i vir Add together to get the reference current i output by the voltage control link ref :

[0034] i pfr =e i +i vir

[0035] 5)i ref The output power of the converter is controlled through proportional-integral tracking control, carrier modulation, and drive of the inner current loop, thereby suppressing the bus voltage fluctuation of the DC system.

[0036] exist Figure 1 The inverter circuit and control structure shown in the figure are verified, and the parameters are set as follows: DC bus capacitor C dc The upper part is 5mF, the bus voltage reference value is u ref is 200V, the voltage controller droop coefficient K pv The time domain waveforms of the conventional solution and the solution of the present invention have the same trend when facing load jump, but the virtual capacitor C v When the voltage reaches 25mF, the traditional solution will become unstable. Figure 3 As shown, the solution of the present invention introduces a 0.2Ω virtual resistor, thereby achieving a decoupling design of the loop stability margin and the DC virtual inertia, and the bus voltage remains stable.

[0037] Furthermore, in view of the fluctuation of renewable energy power generation, the scheme of the present invention can achieve a larger virtual inertia C under the premise of satisfying the voltage loop control stability margin. v , suppress bus voltage fluctuations. Figure 4 As shown in the figure, the virtual resistance is kept constant at 0.2Ω, and the loop stability margin remains unchanged. When the virtual capacitance increases from 5mF to 500mF, the voltage control of the converter remains stable, and the bus voltage fluctuation is greatly reduced, achieving the requirement of large virtual inertia.

[0038] The above description of the embodiments is to facilitate the understanding and application of the present invention by those skilled in the art. It is obvious that those familiar with the art can easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made to the present invention by those skilled in the art based on the disclosure of the present invention should be within the scope of protection of the present invention, such as adopting different converter structures, different current inner loop control, etc. Therefore, the claims are intended to cover all variations within the true concept and scope of the present invention.

Claims

1. A method for decoupling DC virtual inertia and voltage loop stability margin, characterized in that: The following steps are involved: 1) In the converter voltage control, the converter is a Buck converter, and the bus voltage output voltage value u is obtained by sampling the bus voltage on the DC bus capacitor in the Buck converter. dc , the voltage reference value u ref Subtract the sampled output voltage value u dc , and get the voltage error u err ; 2) Voltage error u err The current component i of the droop control link is calculated through the voltage droop control link. p : and p =in err ·K pv Among them, K pv It is the proportional control coefficient of the voltage droop control link, realizing voltage-current droop control; 3) Voltage error u err The current component i of the virtual inertia control link is calculated by the virtual inertia control link. vir , used for inner loop current control tracking, the voltage control link expression is: Among them, R v is a virtual resistor that provides loop damping to ensure the stability margin of voltage control. v is a virtual capacitor, s is a Laplace operator; virtual inertia control of the DC bus voltage is realized, and the decoupling design of the loop stability margin and the DC virtual inertia is realized through the structure of the virtual resistor and the virtual capacitor in series; 4)i p with i vir Add together to get the reference current i output by the voltage control link ref : i ref =i p +i vir 5) The reference current i output by the voltage control link ref The output power of the converter is controlled through proportional-integral tracking, modulation and driving of the inner current loop.

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