Improved electromagnetic hybrid power flow controller control strategy

Abstract

The invention provides a control strategy of an improved electromagnetic hybrid power flow controller, which comprises the following steps of: forming continuous decoupling control of the improved electromagnetic hybrid power flow controller on system power flow on the basis of topology and a model of the improved electromagnetic hybrid power flow controller; according to the amplitude and the phase angle of the voltage of the electromagnetic hybrid power flow controller, the Sen transformer adjusts the position of a tap to enable the Sen transformer to reach a switching position closest to a target point, and discrete adjustment of the injection voltage is completed; the rotary power flow controller completes the continuous adjustment of the voltage injected into the line by changing the alpha 1 and the alpha 2, and guarantees the indifference control of the electromagnetic hybrid power flow controller on the system. Therefore, under the cooperation of the Sen transformer and the rotary power flow controller, through the cooperative control of the gear of the Sen transformer and the rotor angle of the rotary power flow controller, an arbitrary continuous regulation voltage vector in a large range can be formed. Finally, accurate control of the line power flow can be realized.

Description

Technical Field

[0001] The invention belongs to the field of power transmission and distribution network flow control, and in particular relates to an improved electromagnetic hybrid power flow controller control strategy. Background Art

[0002] While interconnected power grids improve the reliability of power systems, they also bring about the problem of uneven distribution of system power flows, which affects the transmission capacity of the power grid and reduces the safety and economy of the power system. Therefore, it is necessary to carry out necessary power flow control on the power system to make the system flexible and controllable.

[0003] The "Sen" transformer was proposed by KKSen. Its main body is a three-phase four-winding transformer structure, including one primary winding and three secondary windings. It can realize independent control of active and reactive functions and provide discrete compensation voltage. It has higher reliability and low cost.

[0004] The primary winding of the "Sen" transformer is connected to the line bus in parallel, and the three secondary windings of each phase are connected in series to the three-phase circuit through the voltage regulating switch. The discrete regulation of the system voltage can be achieved by adjusting the tap position. The accuracy of the voltage regulation depends on the number of tap switches, and the response time is limited by the tap switch. Therefore, it has the disadvantages of poor control accuracy and slow response speed in the power flow control process.

[0005] Existing research has mostly focused on circuit topology and steady-state modeling, but there are few studies on the switching control strategies of “Sen” transformers;

[0006] The rotating power flow controller is a flexible AC power transmission device based on traditional transformers and rotating phase-shifting transformers. It has the advantages of strong applicability, low cost and high reliability. It integrates the topological structure and steady-state voltage source model of the rotating power flow controller to realize the flexible closed-loop model and control strategy of the phase difference line of the rotating power flow controller based on the principle of phase synthesis.

[0007] The study shows that the rotating power flow controller can flexibly control the line compensation voltage without being affected by the line current, thus providing a new method for economical, flexible and frequent control of power systems;

[0008] Based on the above background, a power flow control strategy for flexible closing of active distribution network is needed; combining the advantages of "Sen" transformer and rotating power flow controller, a power flow control strategy of hybrid power flow controller based on large-capacity "Sen" transformer and small-capacity rotating power flow controller is proposed. With the cooperation of "Sen" transformer and rotating power flow controller, an arbitrary continuously adjustable voltage vector within a large range can be formed, thereby realizing efficient control of line power by electromagnetic hybrid power flow controller. Summary of the invention

[0009] The purpose of the present invention is to address the deficiencies of the above-mentioned prior art and to propose an improved electromagnetic hybrid power flow controller control strategy based on an improved electromagnetic hybrid power flow controller topology structure and a steady-state voltage source model structure.

[0010] The "Sen" transformer has the characteristics of low cost and can provide discrete voltage, and the rotary power flow controller has the characteristic of continuous voltage regulation. This control strategy comprehensively considers the advantages of both, and at the same time, under the background of determining the capacity of the "Sen" transformer and the rotary power flow controller, a power flow control strategy based on the electromagnetic hybrid power flow controller is proposed.

[0011] The technical solution of the present invention is a power flow control strategy of an electromagnetic hybrid power flow controller based on a large-capacity "Sen" transformer and a small-capacity rotary power flow controller. The control strategy uses the discontinuous regulation characteristics of the "Sen" transformer according to the voltage amplitude and phase angle of the electromagnetic hybrid power flow controller to select the nearest point as the switching position of the target point, so that the "Sen" transformer provides the largest possible voltage, and finally completes the control strategy of the "Sen" transformer in the improved electromagnetic hybrid power flow controller;

[0012] After the first step of discrete adjustment of the "Sen" transformer, the rotary power flow controller can provide a 360° continuously adjustable voltage vector, realizing the characteristics of continuous decoupling control of line power, thus making up for the high cost of the rotary power flow controller and the lack of discrete adjustment of the "Sen" transformer, and achieving the goal of supplementing the remaining small part of the voltage;

[0013] In the process of controlling the system power flow, the rotating power flow controller adopts a double closed-loop PI control strategy. As the outer loop control target value, the angles α of the two sets of rotating phase-shifting transformers obtained are 1ref , α 2ref As the target of the outer loop control, the actual values ​​of α1 and α2 are finally output through a speed limit module, and the corresponding values ​​are output in the system. Ultimately, error-free control of the electromagnetic hybrid power flow controller system is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Simplified circuit diagram for electromagnetic hybrid power flow controller

[0015] Figure 2 Diagram of the tap switching position of the "Sen" transformer

[0016] Figure 3 Rotor angle control for rotary power flow controller

[0017] Figure 4 This is the control block diagram of the electromagnetic hybrid power flow controller

[0018] Figure 4 Formula (19) is:

[0019] Figure 4 Formula (21) is:

[0020] Figure 4 Formula (22) is:

[0021] Figure 4 Formula (23) is:

[0022] Figure 4 Formula (24) is: DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] See also Figure 1 The simplified circuit diagram of the electromagnetic hybrid power flow controller in the dq coordinate system, based on the instantaneous reactive power theory, can be obtained that the power calculation formula below the access point of the electromagnetic hybrid power flow controller (rotating power flow controller) is as follows:

[0025]

[0026] Where P s.RPFC , Q s.RPFC They are the instantaneous active power and reactive power below the access point of the electromagnetic hybrid power flow controller; It is the voltage below the access point of the electromagnetic hybrid power flow controller.

[0027] See also Figure 1 It can be obtained that the voltage below the access point of the electromagnetic hybrid power flow controller and the voltage at the head end of the system have the following relationship:

[0028]

[0029] In the formula, R and L are the sum of the equivalent resistance and equivalent inductance of ST and RPFC respectively. As the reference voltage is fixed on the d-axis, we have make Then the relationship between the electromagnetic hybrid power flow controller and the set line transmission power can be expressed as:

[0030]

[0031] Where P s.RPFC * and Q s.RPFC * They are respectively the active and reactive power after being adjusted by PI closed-loop control by making the difference between the actual power value and the set value.

[0032] For the switching strategy of the "Sen" transformer, the line power flow can be effectively controlled by adjusting the voltage phasor of the electromagnetic hybrid power flow controller in series with the line. As a part of the synthesized voltage phasor of the electromagnetic hybrid power flow controller, the specific switching strategy of the "Sen" transformer can be expressed as:

[0033] (1) Based on The phase angle β determines the direction of the voltage phasor of the electromagnetic hybrid power flow controller, and at the same time determines its specific position according to its amplitude.

[0034] according to Specific location, calculate the amplitude and phase angle of the surrounding intersection points, that is The value of .

[0035] Calculate the four groups separately and Vector distance, select the point with the closest distance as the target point's cutting position, and you can get Figure 2 middle As the final cutting point [**].

[0036] For the switching strategy of the rotating power flow controller, the above formula can be used to calculate the The value of The angles of the two sets of rotating phase-shifting transformers of the rotating power flow controller can be calculated at this time. The specific control process is as follows: Figure 3 shown.

[0037] Among them, the voltage relationship between the rotary power flow controller, the "Sen" transformer and the electromagnetic hybrid power flow controller is:

[0038]

[0039] In order to ensure the error-free control of the overall control system of the electromagnetic hybrid power flow controller, a double closed-loop PI control strategy is selected in the control of the rotating power flow controller. As the outer loop control target value, the two sets of rotating phase-shifting transformer angles α are solved at the same time. 1ref , α 2ref , and use it as the target of the outer loop control, and finally output the actual values ​​of α1 and α2 through a speed limit module, and output the corresponding

[0040] like Figure 4 As shown, by integrating the control strategies of the "Sen" transformer and the rotating power flow controller, the coordinated control strategy block diagram of the electromagnetic hybrid power flow controller can be obtained.

[0041] in are the instantaneous voltage and current of the three-phase transmission system respectively, let P s.RPFCref , Q s.RPFCref As the control target of the system's active and reactive power, precise control of the line flow is achieved by collaboratively controlling the "Sen" transformer gear position and the rotor angle of the rotary power flow controller.

Claims

1. An improved electromagnetic hybrid power flow controller control strategy, characterized in that: include: Based on the construction of the topology of the improved electromagnetic hybrid power flow controller and the steady-state voltage source model, the control strategy of the improved electromagnetic hybrid power flow controller is formed by analyzing the switching control strategy of the "Sen" transformer control model and the switching control strategy of the steady-state voltage source model of the rotating power flow controller: The "Sen" transformer forms a topological model including an iron core magnetic circuit, primary and secondary series windings and an on-load tap changer; an equivalent circuit of the primary and secondary sides is established based on the topological structure principle diagram of the "Sen" transformer, and after the topology and equivalent model of the "Sen" transformer are constructed, the switching strategy of the "Sen" transformer in the improved electromagnetic hybrid power flow controller is analyzed to achieve discrete regulation of the injected voltage by adjusting the tap position; The switching strategy of the "Sen" transformer is to determine the position of its voltage phasor according to the phase angle β of the electromagnetic hybrid power flow controller, and to determine its specific position according to its amplitude, and finally complete the control strategy of the "Sen" transformer in the improved electromagnetic hybrid power flow controller; The rotating power flow controller can derive the mathematical relationship between various electrical quantities on the rotating power flow controller side through the analysis of the topological structure principle and the construction of the equivalent circuit diagram; The simplified circuit model of the rotary power flow controller and the mathematical relationship between its various electrical quantities are used to analyze the switching strategy of the rotary power flow controller in the improved electromagnetic hybrid power flow controller; The rotating power flow controller realizes continuous regulation of the injected voltage by adjusting the positions of the stator and rotor voltage phase shift angle taps α1 and α2 of the two rotating power flow controllers; and finally completes the control strategy of the rotating power flow control in the improved electromagnetic hybrid power flow controller; In order to achieve zero-difference control of the electromagnetic hybrid power flow controller system, it is necessary to select a double closed-loop PI control strategy in the rotating power flow controller control, set the rotating power flow controller voltage as the outer loop control target value, and solve the two sets of rotating phase-shifting transformer angles α at the same time. 1ref , α 2ref , and use it as the target of the outer loop control, and finally output the actual values ​​of α1 and α2 through a speed limit module, and output the corresponding rotating power flow controller voltage in the system; The control strategy for the electromagnetic hybrid power flow controller achieves precise control of the line power flow by collaboratively controlling the "Sen" transformer gear and rotating the power flow controller rotor angle.

2. The control strategy of the electromagnetic hybrid power flow controller according to claim 1 is characterized in that: Mathematical analysis of the equivalent circuit diagram of the electromagnetic hybrid power flow controller: In the dq coordinate system, based on the instantaneous reactive power theory, the power calculation formula below the access point of the electromagnetic hybrid power flow controller (rotating power flow controller) can be obtained as follows: Where P s.RPFC , Q s.RPFC They are the instantaneous active power and reactive power below the access point of the electromagnetic hybrid power flow controller; The voltage below the access point of the electromagnetic hybrid power flow controller; According to the "Sen" transformer tap switching strategy, the voltage below the electromagnetic hybrid power flow controller access point and the system head end voltage have the following relationship: In the formula, R and L are the sum of the equivalent resistance and equivalent inductance of ST and RPFC respectively. As the reference voltage is fixed on the d-axis, we have make Then the relationship between the electromagnetic hybrid power flow controller and the set line transmission power can be expressed as:

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