Harmonic voltage mitigation method, device, and dielectric based on hybrid power flow controller

Abstract

This application relates to a harmonic voltage mitigation method, device, and medium based on a hybrid power flow controller (UPFC), belonging to the field of flexible interconnection technology for distribution networks. Addressing the coupling problem between the output port of the phase-shifting transformer in the hybrid power flow controller and the harmonic voltage distribution of the lines, the application provides a technical solution including the following steps: Quantitatively analyzing the harmonic voltage distribution characteristics in the lines connected to the hybrid power flow controller; constructing a relationship between the phase-shifting transformer output winding switching position and the reference value of the HPFC output compensation harmonic voltage; calculating the compensation voltage reference value; establishing a harmonic voltage mitigation model for the hybrid power flow controller based on the parallel-side harmonic sampling voltage, used to control the UPFC to track the reference value and output compensation harmonic voltage. This application quantitatively analyzes the impact of different phase-shifting transformer winding switching positions on the UPFC output compensation harmonic voltage, proposes harmonic voltage mitigation, and achieves harmonic voltage compensation using only the parallel voltage sampling value, reducing the number of sensors and control costs.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power distribution network flexible interconnection, and relates to a harmonic voltage treatment method, device and medium based on a hybrid power flow controller. BACKGROUND

[0002] Under the trend of continuous expansion of the power distribution network and increasing diversification of the load, a hybrid power flow controller (HPFC) has an important role in ensuring safe, stable and economic operation of the power grid due to its advantages of efficient regulation and control of line power flow. The hybrid power flow controller can realize high-power flow regulation and power quality treatment functions such as harmonic compensation through the coordinated work of power electronics and electromagnetic components, and has advantages in performance and cost.

[0003] Existing researches on the hybrid power flow controller mostly focus on topology optimization and power flow regulation strategies, and researches on harmonic voltage treatment are widely focused on active power filters and unified power quality controllers, which are pure power electronic devices, and there is a lack of attention to the realization of harmonic treatment functions of HPFC. The different winding switching positions of the phase-shift transformer will affect the harmonic distribution characteristics of the line, and thus change the harmonic voltage compensation value due to the coupling of the phase-shift transformer and the converter on the series side of the HPFC.

[0004] The traditional harmonic voltage treatment method based on the unified power quality controller needs to additionally set a voltage sensor on the series side to calculate the harmonic voltage compensation instruction through the real-time collected voltage, thereby increasing the system control cost. SUMMARY

[0005] In view of the coupling problem of the output port of the phase-shift transformer in the hybrid power flow controller and the harmonic voltage distribution of the line, the application provides a harmonic voltage treatment method, device and medium based on a hybrid power flow controller, which is used to solve the influence of different winding switching positions of the phase-shift transformer in the hybrid power flow controller on the harmonic voltage treatment accuracy. The hybrid power flow controller only needs to compensate the harmonic voltage by collecting the parallel side voltage, without the need of additionally increasing the voltage sensor on the series side. The application widens the harmonic treatment function of the hybrid power flow controller, and effectively reduces the number of sensors and the system cost.

[0006] The application provides a harmonic voltage treatment method based on a hybrid power flow controller, which includes the following steps:

[0007] S1, quantitatively analyze the harmonic voltage distribution characteristics in the line connected with the hybrid power flow controller, construct a relationship between the output winding switching position of the phase-shift transformer and the harmonic voltage compensation reference value of the HPFC, and realize the calculation of the compensation voltage reference value by collecting the harmonic voltage at the parallel access point of the HPFC.

[0008] S2, based on the derived harmonic compensation voltage reference value, a hybrid power flow controller harmonic voltage control model based on the parallel side harmonic acquisition voltage is established, which is used to control the UPFC to track the reference value and output specific order compensation harmonic voltage, and realize harmonic voltage control based on parallel voltage sampling.

[0009] Installing sensors on high-voltage lines or near series transformers requires special insulation design, protective shell and installation structure, which increases engineering and installation costs. While the parallel side sensor is itself required for UPFC in common power control scenarios. In this way, the sensor is installed on the low-voltage side or on the ground, with higher reliability and lower cost.

[0010] Further, the step S1 comprises:

[0011] S1.1, initializing the field winding turns ratio, winding switching position parameters, and establishing the hybrid power flow controller output voltage expression under different winding switching positions;

[0012] S1.2, based on the structure of the hybrid power flow controller, the UPFC output compensation harmonic voltage reference value is obtained;

[0013] S1.3, combining the hybrid power flow controller output voltage expression under different winding switching positions and the compensation harmonic voltage reference value, the harmonic distribution relationship from the parallel access side to the series side of the hybrid power flow controller is constructed, so as to calculate the compensation voltage reference value by acquiring the harmonic voltage at the HPFC parallel access point.

[0014] Further, the hybrid power flow controller topology structure comprises an improved Sen transformer, a unified power flow controller (UPFC) and an isolation transformer. The improved Sen transformer is composed of a parallel field winding and a series output winding, the UPFC is composed of a back-to-back converter, the UPFC parallel side step-down transformer shares the core with the improved Sen transformer field winding, and the series converter output and the improved Sen transformer series winding are coupled to the line through the isolation transformer.

[0015] Hybrid power flow controller output voltage expression under different winding switching positions:

[0016]

[0017] In the formula, is the HPFC output voltage vector; is the IST output voltage vector; is the UPFC output voltage vector; is the HPFC parallel access point voltage vector; is the IST parallel field winding turns ratio; The IST adjustment order is different, and the winding switching position is different. When the adjustment order is m , .

[0018] The IST parallel side winding is generally Y-connected, and the parallel side harmonic voltage is coupled to the line through the series winding, which affects the harmonic distribution of the line.

[0019] The output compensation harmonic voltage reference value of the UPFC is:

[0020]

[0021] In combination with the above formula, the relationship between the phase-shifting transformer output winding switching position and the HPFC output compensation harmonic voltage reference value can be further obtained as:

[0022]

[0023] In the formula, is the three-phase harmonic compensation voltage command value; is the three-phase parallel side harmonic voltage.

[0024] Further, the step S2 includes the following specific process:

[0025] S2.1, the three-phase phase-locked loop based on the second-order generalized integrator is phase-locked to the parallel side sampling voltage, and the voltage fundamental positive sequence component is extracted;

[0026] S2.2, based on the extracted voltage fundamental positive sequence component and the obtained relationship between the phase-shifting transformer output winding switching position and the HPFC output compensation harmonic voltage reference value, the harmonic compensation voltage reference value is obtained, and the UPFC is controlled to perform PIR-based double closed-loop control, so as to make the UPFC quickly respond to the output stable harmonic compensation voltage, and realize the governance of harmonics.

[0027] Further, the step S2.1 includes the following specific process:

[0028] S2.1.1, through the PI controller, the , component after the coordinate transformation of the parallel side voltage sampling value is respectively passed through the SOGI to generate two-phase orthogonal voltage signals;

[0029] S2.1.2, through the integral element, the two-phase orthogonal voltage signals are combined into the voltage fundamental positive sequence component in the coordinate system.

[0030] Further, the step S2.2 includes the following specific process:

[0031] S2.2.1, the obtained voltage fundamental positive sequence component is subjected to coordinate transformation to obtain a parallel side voltage three-phase fundamental component;

[0032] S2.2.2, based on the relationship between the output winding switching position of the phase-shifting transformer and the HPFC output compensation harmonic voltage reference value, combined with the IST ratio and the winding switching position, the UPFC harmonic compensation voltage reference value is generated after coordinate transformation;

[0033] S2.2.3, the difference between the obtained UPFC harmonic compensation voltage reference value and the UPFC output voltage sampling value is subjected to PIR controller to generate a current inner loop reference value;

[0034] S2.2.4, the difference between the generated current inner loop reference value and the actual value of the UPFC inductance current is subjected to proportional controller and combined with the current feedforward decoupling amount to synthesize a modulation signal in the dq coordinate system;

[0035] S2.2.5, the modulation signal in the dq coordinate system is converted into a modulation signal in the three-phase coordinate system through coordinate transformation.

[0036] The application is a harmonic voltage treatment method, device and medium based on a hybrid power flow controller, aiming at harmonic voltage treatment of the hybrid power flow controller, quantitatively analyzing the influence of different winding switching positions of the phase-shifting transformer on the harmonic voltage distribution characteristics of the line, combining the relationship between the output winding switching position of the phase-shifting transformer and the HPFC output compensation harmonic voltage reference value, and proposing a model for harmonic voltage treatment using parallel side harmonic voltage sampling value. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a flow chart of the harmonic voltage treatment method of the hybrid power flow controller;

[0038] Figure 2 is a topology structure diagram of the hybrid power flow controller;

[0039] Figure 3 is a system equivalent circuit diagram of the hybrid power flow controller connected to the line;

[0040] Figure 4 is a three-phase phase-locked loop (DSOGI-PLL) control block diagram based on a second-order generalized integrator;

[0041] Figure 5 is a harmonic voltage treatment strategy block diagram based on HPFC parallel side voltage sampling;

[0042] Figure 6 is a voltage and current waveform diagram of the UPFC output;

[0043] Figure 7 is a line series side voltage and current waveform diagram;

[0044] Figure 8 is a THD comparison diagram of series side voltage and current before and after harmonic governance. DETAILED DESCRIPTION

[0045] The application will be described in detail below with reference to the drawings and specific embodiments.

[0046] Embodiment 1

[0047] This embodiment is a harmonic voltage governance method based on a hybrid power flow controller, and the implementation process is as shown in Figure 1 , and specifically includes the following steps:

[0048] S1, quantitatively analyze the harmonic voltage distribution characteristics in the line connected with the hybrid power flow controller, construct the relationship between the output winding switching position of the phase-shifting transformer and the harmonic voltage reference value compensated by the HPFC, and realize the calculation of the compensation voltage reference value by collecting the harmonic voltage at the parallel connection point of the HPFC;

[0049] S1.1, initialize the field winding ratio and winding switching position parameters, and establish the output voltage expression of the hybrid power flow controller under different winding switching positions;

[0050] The topology structure of the hybrid power flow controller (HPFC) is as shown in Figure 2 , which is composed of an improved Sen transformer (IST) and a unified power flow controller (UPFC), and the series output voltage expression of the HPFC is as follows:

[0051]

[0052] In the formula, is the HPFC output voltage vector; is the IST output voltage vector; is the UPFC output voltage vector; is the HPFC parallel connection point voltage vector; is the IST parallel field winding ratio; is the IST regulation level, and different regulation levels correspond to different winding switching positions. When the regulation level is m , .

[0053] S1.2, based on the structure of the hybrid power flow controller, the UPFC output compensation harmonic voltage reference value is obtained; to ensure that the IST can accurately obtain the harmonic voltage compensation instruction under different winding switching positions.

[0054] The IST parallel side winding is generally in Y connection mode, at which time the parallel side harmonic voltage will be coupled to the line through the series winding, affecting the harmonic distribution of the line. The harmonic voltage distribution equivalent model of the hybrid power flow controller connected to the interconnection system is shown in Figure 3 . are the harmonic voltage sources of the grid 1 and the grid 2 sides respectively; the line current passes through the grid 1 side line equivalent harmonic impedance to generate the harmonic voltage at the HPFC parallel connection point; at the series side through the grid 2 side line equivalent harmonic impedance.

[0055] According to Figure 3 , the harmonic distribution relationship from the HPFC parallel connection side to the series side is as follows:

[0056]

[0057] In the formula, is the UPFC series output harmonic voltage; is the parallel connection point harmonic voltage; is the IST series output harmonic voltage; is the load side harmonic voltage.

[0058] To make the harmonic voltage 0, let , so the output compensation harmonic voltage reference value of the UPFC is:

[0059]

[0060] S1.3, in combination with the hybrid power flow controller output voltage expression under different winding switching positions and the compensation harmonic voltage reference value, the harmonic distribution relationship from the hybrid power flow controller parallel connection side to the series side is constructed, so as to realize the calculation of the compensation voltage reference value through the collection of the HPFC parallel connection point harmonic voltage. That is, in combination with the above formula, the following can be further obtained:

[0061]

[0062] In the formula, is the three-phase harmonic compensation voltage command value; is the three-phase parallel side harmonic voltage.

[0063] According to the above formula, it can be seen that when the UPFC performs harmonic voltage management, the output compensation voltage reference value is related to the IST winding switching position, and the compensation voltage reference value can be calculated only through the collection of the HPFC parallel connection point harmonic voltage.

[0064] ​S2, based on the derived harmonic compensation voltage instruction value, a hybrid power flow controller harmonic voltage control model based on the parallel side harmonic voltage is established, which is used to control the UPFC to track the reference value and output specific order compensation harmonic voltage, and realize the harmonic voltage control based on the parallel voltage sampling.

[0065] S2.1, the three-phase phase-locked loop based on the second-order generalized integrator is used to phase-lock the sampling voltage on the parallel side, and the voltage fundamental positive sequence component is extracted; the DOSGI-PLL phase-locked loop control strategy is as shown in Figure 4 .

[0066] S2.1.1, through the PI controller, the α and β components of the parallel side voltage sampling value after coordinate transformation are respectively passed through the SOGI to generate two-phase orthogonal voltage signals, i.e. 、 and 、 ;

[0067] S2.1.2, through the integral element, the two-phase orthogonal voltage signals ( 、 and 、 ) are synthesized into the voltage fundamental positive sequence component in the , coordinate system. The transfer function of the SOGI element is:

[0068]

[0069]

[0070] In the formula, is the resonant angular frequency. The smaller the value is, the better the filtering effect is, but it will affect the real-time performance. Both are selected comprehensively .

[0071] S2.2, based on the extracted voltage fundamental positive sequence component 、 , the IST excitation winding transformation ratio and the relationship formula of the obtained phase-shifting transformer output winding switching position ( ) and the HPFC output compensation harmonic voltage reference value, the harmonic compensation voltage reference value is obtained, and the UPFC is controlled to carry out the double closed-loop control based on PIR. The harmonic voltage control strategy based on the parallel side voltage sampling value of the HPFC is as shown in Figure 5 .

[0072] S2.2.1, the obtained voltage fundamental positive sequence component 、 , the three-phase fundamental component of the voltage at the parallel side is obtained after coordinate transformation , , , and the harmonic component of the voltage at the parallel side is obtained by subtracting the sampling voltage from the above value , , ;

[0073] S2.2.2, based on the relationship between the output winding switching position of the phase-shifting transformer and the harmonic voltage reference value of the HPFC output compensation, combined with the IST ratio and the winding switching position, the UPFC harmonic compensation voltage reference value is generated after coordinate transformation , ;

[0074] S2.2.3, the difference between the obtained UPFC harmonic compensation voltage reference value , and the UPFC output voltage sampling value , is generated by the PIR controller to generate the current inner loop reference value , ;

[0075] S2.2.4, the difference between the generated current inner loop reference value , and the actual value of the UPFC inductance current , is combined with the current feedforward decoupling quantity after the proportional controller to synthesize the modulation signal in the dq coordinate system;

[0076] S2.2.5, by coordinate transformation, the modulation signal in the dq coordinate system is converted into the modulation signal in the three-phase coordinate system , , . The transfer function expression of the PIR controller is:

[0077]

[0078] In the formula, is the proportional coefficient; is the integral coefficient; is the resonance coefficient; is the cutoff frequency, generally 3-5 rad / s; is the fundamental frequency rad / s.

[0079] The application provides a harmonic voltage treatment method based on a hybrid power flow controller, aiming at the coupling problem of the output port of a phase-shifting transformer in the hybrid power flow controller and the harmonic voltage distribution of a line, quantitatively analyzes the influence of different winding switching positions of the phase-shifting transformer on the UPFC output compensation harmonic voltage, and further proposes a harmonic voltage treatment strategy. The method only uses parallel voltage sampling values to realize compensation of the harmonic voltage, and reduces the number of sensors and control cost.

[0080] Embodiment 2

[0081] A harmonic voltage treatment device based on a hybrid power flow controller, comprising:

[0082] A construction module quantitatively analyzes the harmonic voltage distribution characteristics of the hybrid power flow controller in the line, constructs a relationship between the switching position of the output winding of the phase-shifting transformer and the harmonic voltage reference value of the HPFC output compensation, and realizes the calculation of the compensation voltage reference value by collecting the harmonic voltage of the parallel access point of the HPFC;

[0083] A treatment module, based on the obtained harmonic compensation voltage reference value, establishes a harmonic voltage treatment model of the hybrid power flow controller based on the parallel side harmonic collection voltage, which is used to control the UPFC to track the reference value to output a specific order compensation harmonic voltage, and realizes the harmonic voltage treatment based on the parallel voltage sampling.

[0084] Embodiment 3

[0085] A harmonic voltage treatment device based on a hybrid power flow controller, characterized by comprising a memory and one or more processors, the memory stores executable code, and the one or more processors execute the executable code to implement the harmonic voltage treatment method based on the hybrid power flow controller in embodiment 1.

[0086] Embodiment 4

[0087] A computer readable medium having a program stored thereon, the program being executed by a processor to implement the harmonic voltage treatment method based on the hybrid power flow controller in embodiment 1.

[0088] Application example

[0089] The effectiveness of the scheme is further illustrated by specific examples. In Plecs, a HPFC simulation model based on the harmonic treatment scheme is built, and the simulation parameters are shown in Table 1.

[0090] Table 1

[0091]

[0092] The voltage and current waveforms of the UPFC output are as follows Figure 6It can be seen that the harmonic current is generated due to the line impedance after the harmonic voltage is injected at 1.0s, and the UPFC sends the harmonic compensation voltage at 1.2s. The line voltage and current waveforms at the series side are shown in Fig. 4. Figure 7 It can be seen that the line voltage and current are distorted after 1.0s, and the harmonic content of the voltage and current is reduced and the sinusoidal degree of the waveforms is improved when the UPFC sends the harmonic compensation voltage at 1.2s. The THD of the line voltage and current before and after the harmonic control is shown in Fig. 5. Figure 8 Figure 8 Fig. 5 is a THD comparison chart of the voltage and current at the series side before the harmonic control, wherein (a) and (b) are respectively the THD comparison chart of the voltage and current at the series side before the harmonic control, Figure 8 Fig. 5 is a THD comparison chart of the voltage and current at the series side before the harmonic control, wherein (a) and (b) are respectively the THD comparison chart of the voltage and current at the series side before the harmonic control,

[0093] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application rather than limit it, although the present application has been described in detail with reference to the above examples, the ordinary skilled in the art can still modify or equivalently replace the specific embodiments of the present application without departing from the spirit and scope of the present application, and any modification or equivalent replacement which does not depart from the spirit and scope of the present application should be covered in the protection scope of the claims of the present application.​

Claims

1. A method for harmonic voltage management based on a hybrid power flow controller, characterized in that, Comprise the following steps: S1, quantitative analysis of harmonic voltage distribution characteristics in the mixed type of flow controller access line, the relationship between the output winding of phase shifting transformer and the HPFC output compensation harmonic voltage reference value is constructed, the compensation voltage reference value is calculated by collecting the harmonic voltage of the parallel access point of HPFC; Including: S1.1, initialize the excitation winding ratio, winding switching position parameters, and establish the output voltage expression of the mixed type of flow controller under different winding switching positions; S1.2, based on the structure of the mixed type of flow controller, the UPFC output compensation harmonic voltage reference value is obtained; S1.3, combined with the output voltage expression of the mixed type of flow controller under different winding switching positions and the compensation harmonic voltage reference value, the harmonic distribution relationship from the parallel side to the series side of the mixed type of flow controller is constructed, so as to calculate the compensation voltage reference value by collecting the harmonic voltage of the parallel access point of HPFC; The relationship between the output winding of phase shifting transformer and the HPFC output compensation harmonic voltage reference value is: In the formula, is a harmonic compensation voltage instruction value of three phases; is a parallel side harmonic voltage of three phases, is a IST parallel excitation winding ratio, is an IST adjustment stage number, and different adjustment stage numbers correspond to different winding switching positions; S2, based on the obtained harmonic compensation voltage instruction value, the harmonic voltage control model of the mixed type of flow controller based on the harmonic voltage sampling of the parallel side is established, which is used to control UPFC to track the reference value and output specific compensation harmonic voltage, and realize the harmonic voltage control based on the sampling of parallel voltage.

2. The method of claim 1, wherein the hybrid power flow controller is configured to: The specific process of step S2 includes: S2.1, the three-phase phase-locked loop based on the second-order generalized integrator is used to phase-lock the sampling voltage on the parallel side, and the voltage fundamental positive sequence component is extracted; S2.2, based on the extracted voltage fundamental positive sequence component, the IST excitation winding ratio and the obtained relationship between the output winding switching position of phase shifting transformer and the HPFC output compensation harmonic voltage reference value, the harmonic compensation voltage reference value is obtained, and the UPFC is controlled to carry out PIR-based double closed loop control.

3. The method of claim 2, wherein the hybrid power flow controller is configured to inject a harmonic voltage into the power system. The specific process of step S2.1 includes: S2.1.1, the parallel side voltage sampling value after coordinate transformation is passed through a PI controller 、 component respectively through SOGI to generate two-phase orthogonal voltage signals; S2.1.2, by integrating link, two-phase quadrature voltage signal into the voltage fundamental positive sequence component under the coordinate system.

4. The method of claim 2, wherein the hybrid power flow controller is a superconducting magnetic energy storage (SMES) device. The specific process of step S2.2 includes: S2.2.1, the obtained voltage fundamental positive sequence component is transformed into the three-phase fundamental component of the parallel side voltage after coordinate transformation, and then the difference between the sampling voltage and the three-phase fundamental component of the parallel side voltage is obtained to obtain the harmonic component of the parallel side voltage; S2.2.2, based on the relationship between the output winding switching position of phase shifting transformer and the HPFC output compensation harmonic voltage reference value, combined with the IST ratio and the winding switching position, the UPFC harmonic compensation voltage reference value is generated after coordinate transformation; S2.2.3, the difference between the obtained UPFC harmonic compensation voltage reference value and the UPFC output voltage sampling value is transformed into the current inner loop reference value through the PIR controller; S2.2.4, the difference between the generated current inner loop reference value and the actual value of UPFC inductance current is combined with the current feedforward decoupling quantity after the proportional controller to synthesize the modulation signal in dq coordinate system; S2.2.5, the modulation signal in dq coordinate system is converted into the modulation signal in three-phase coordinate system through coordinate transformation.

5. A hybrid power flow controller based harmonic voltage management device, characterized by, Including: The constructing module quantitatively analyzes the harmonic voltage distribution characteristics in the line to which the hybrid power flow controller is connected, constructs a relationship between the output winding switching position of the phase-shifting transformer and the harmonic voltage reference value compensated by the HPFC, and realizes the calculation of the compensation voltage reference value by collecting the harmonic voltage at the parallel connection point of the HPFC; the method comprises the following steps: initializing the field winding ratio and winding switching position parameters, and establishing the output voltage expression of the hybrid power flow controller under different winding switching positions; based on the structure of the hybrid power flow controller, the UPFC output compensation harmonic voltage reference value is obtained; combining the output voltage expression of the hybrid power flow controller under different winding switching positions and the compensation harmonic voltage reference value, the harmonic distribution relationship from the parallel connection side to the series connection side of the hybrid power flow controller is constructed, so as to realize the calculation of the compensation voltage reference value by collecting the harmonic voltage at the parallel connection point of the HPFC; the relationship between the output winding switching position of the phase-shifting transformer and the harmonic voltage reference value compensated by the HPFC is as follows: In the formula, is a three-phase harmonic compensation voltage instruction value; is a three-phase parallel side harmonic voltage, is an IST parallel excitation winding ratio, is an IST regulation stage number, different regulation stage numbers correspond to different winding switching positions; The treatment module establishes a harmonic voltage treatment model of the hybrid power flow controller based on the harmonic voltage collected at the parallel connection side based on the obtained harmonic compensation voltage reference value, and is used for controlling the UPFC to track the reference value to output a specific order compensation harmonic voltage, so as to realize the harmonic voltage treatment based on the sampling of the parallel voltage.

6. A hybrid power flow controller based harmonic voltage management device characterized in that, The memory stores executable code, and the one or more processors execute the executable code to implement the hybrid power flow controller-based harmonic voltage treatment method in any one of claims 1-4.

7. A computer readable medium having a program stored thereon, the program being executed by a processor to implement the hybrid power flow controller-based harmonic voltage treatment method in any one of claims 1-4.

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