Super-capacitor-based flicker suppression method for network construction type STATCOM (Static Synchronous Compensator)

Abstract

The invention relates to a super-capacitor-based flicker suppression method for a network construction type STATCOM (Static Synchronous Compensator). The method comprises the steps of network construction outer ring control, fundamental current control and harmonic current control, a virtual synchronous machine VSG control algorithm is adopted for network construction outer ring control, the frequency modulation characteristic and the inertia damping characteristic are decoupled, and the suppression of the active power high-frequency fluctuation quantity through a super capacitor serves as an effective means for flicker suppression; load harmonic current control open-loop control and closed-loop control are combined to achieve an optimal control effect, a first-order differential link and a second-order low-pass filter are cascaded to serve as a correction link, open-loop control gain is improved, resonance between a passive filter and a power grid is suppressed, a second-order low-pass filter link is added to reactive power of a PCC (point of common coupling), and the optimal control effect is achieved. The problem of harmonic amplification caused by the fact that the fundamental reactive power compensation speed is too high and conflicts with a harmonic rapid compensation link is avoided; the flicker suppression effect and the harmonic compensation rate are improved, and pollution of an arc load to a power grid is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply quality control of power supply networks, and in particular to a supercapacitor-based STATCOM flicker suppression method. Background Art

[0002] The steel industry is an important foundation of the national economy and a strategic industry. It directly affects the level and competitiveness of national industrial production, is an important support for building a modern power, and is also an important indicator of a country's comprehensive national strength and national defense strength. It has a significant impact on my country's strategic development plan. With the development of my country's socialist market economy, industrialization and internationalization are advancing rapidly, and the steel industry has developed rapidly. After a long period of rapid growth, its equipment and technology have leapt to the forefront of the world.

[0003] Electric arc furnace plays an important role in the metallurgical industry and is a commonly used smelting equipment in the metallurgical industry. Electric arc furnace has many advantages in smelting in the steel industry, such as the main source of materials is obsolete waste, which greatly reduces the initial cost, saves space and occupies a small area, and has high product manufacturing efficiency. New equipment is constantly updated and iterated, and the types of electric arc furnaces, generation efficiency, and product quality have all been significantly improved.

[0004] However, the commissioning of a large number of arc furnace equipment has led to flicker and harmonic pollution in the power grid, reduced the power quality of the public power grid, affected the safe operation of the power system, and caused a series of varying degrees of impact on the normal operation of electrical equipment in the power grid, causing disorder in the power system, affecting the normal production of enterprises, and causing unnecessary economic losses. Summary of the invention

[0005] The present invention provides a supercapacitor-based STATCOM flicker suppression method, which improves the flicker suppression effect and harmonic compensation rate and reduces the pollution of arc loads to the power grid.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A supercapacitor-based STATCOM flicker suppression method includes the following contents:

[0008] 1) Grid outer loop control: The virtual synchronous machine (VSG) control algorithm is adopted, including reactive power and voltage control, active power and frequency control, to decouple the frequency modulation characteristics and inertia damping characteristics, simulate the swing equation of the synchronous generator, fully simulate the power frequency regulation characteristics of the synchronous generator, and synchronize the internal three-phase stator electromotive force with the grid voltage;

[0009] The virtual synchronous machine VSG control algorithm adopts the virtual rotation inertia of the integral link, and the corresponding time constant is recorded as T J; Added the proportional Kp feedback link of the electromagnetic power VSG_P_PU output by VSG;

[0010] Using supercapacitors as energy storage elements, the high-frequency fluctuation of active power caused by arc furnace operation can be suppressed through the rapid charge and discharge control of supercapacitors;

[0011] 2) Fundamental current control and harmonic current control: The fundamental current is controlled by the reference voltage e abc * Harmonic current control reference voltage Vref Har Superimposed on the feedforward voltage V g On the top, the modulation wave S is generated Mode , the modulation wave S Mode Generate gate control signals for fully controlled devices and send them to cascaded power unit control modules;

[0012] The harmonic current control adopts a control strategy combining open loop and closed loop. The open loop control uses a second-order bandpass filter to extract the fundamental frequency signal, and the closed loop control uses a first-order differential link and a second-order low-pass filter cascade as a correction link.

[0013] Furthermore, the reactive power and voltage control is performed by calculating the reactive power given value Q ref Reactive power Q at the point of common connection e Passed through a second-order low-pass filter Output Q eLPF The deviation value is obtained through the PI regulator, and the voltage deviation value is compared with the VSG rated output voltage VSG e0 The final output voltage VSG is adjusted by superposition e , i.e. the internal electromotive force amplitude, is combined with the internal electromotive force phase VSG_θ to generate the internal electromotive force VSG_E;

[0014] Among them, the reactive power given value Q ref The command value is 0MVar, A n is the filter passband gain, ω n is the transfer function cutoff frequency, s is the transfer function complex frequency operator, and ξ is the filter damping coefficient.

[0015] Furthermore, the active power and frequency control is the internal stator electromotive force VSG e With the grid voltage V g The difference is applied to the virtual stator impedance On, where R V is the virtual stator resistance, L V is the virtual stator inductance; generates the current command VSG_I, multiplies it with the internal electromotive force VSG_E to get the output electromagnetic power VSG_P, and divides it by the rated capacity base value S BaseGenerate per-unit value VSG_P_PU. Use second-order low-pass filter to extract the stable component in VSG_P_PU. After removing the stable component from the original signal VSG_P_PU, the high-frequency component ΔP_PU of the arc furnace active power to be suppressed by the grid-type STATCOM is obtained;

[0016] The high-frequency component of the active power of the arc furnace ΔP_PU is controlled by the outer loop of the network, and the frequency deviation Δf is calculated. pu , added to the per-unit rated value 1.0 and passed through the limiter to obtain the per-unit value f of the frequency signal pu , rated angular frequency ω0 and frequency per unit value f pu After multiplication, the angular frequency VSG_ω of VSG is obtained, and after the integration link, it becomes its phase angle VSG_θ.

[0017] Furthermore, the current command signal of the open-loop control link comes from the EAF load current i load , a second-order bandpass filter is used to extract the fundamental frequency signal, and the load current i load Subtract the fundamental frequency signal to obtain the load current harmonic component i load_Har ;

[0018] The current command signal of the closed-loop control link comes from the transformer secondary total current i g , using the first-order differential link K d s and a second-order low-pass filter Cascading as a correction link.

[0019] Furthermore, the output signal i of the correction link g_comp , a second-order bandpass filter is used to extract the fundamental frequency signal, the original signal i g_comp Subtract the fundamental frequency signal to obtain the power supply current harmonic component i g_Har , and the load current harmonic component i load_Har After adding, the total harmonic component iref is obtained Har , the harmonic current is generated by the proportional-resonant regulator to control the reference voltage Vref Har .

[0020] Furthermore, the fundamental current control is the current command VSG_I and the current feedback VSG_I fbk The difference is the current inner loop control error, and the fundamental current control reference voltage e is generated through the quasi-proportional resonant regulator. abc *.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1) The traditional virtual synchronous machine VSG control algorithm is improved, the frequency modulation characteristics and inertia damping characteristics are decoupled, the power frequency regulation characteristics of the synchronous generator can be fully simulated, and the decoupling control of the primary frequency modulation and damping oscillation functions is realized. The method is simple and has strong feasibility, which effectively improves the controllability and operation performance of the grid-type STATCOM. Supercapacitors are used as energy storage elements. Through the rapid charge and discharge control of supercapacitors, the high-frequency fluctuation of active power caused by the operation of the arc furnace is suppressed, which is an effective means of flicker suppression;

[0023] 2) The load current of the arc furnace has random changes and nonlinear characteristics, especially in the melting period, which produces randomly changing harmonic currents. To address this problem, the grid-type STATCOM load harmonic current adopts a control strategy that combines open-loop and closed-loop control. The open-loop control ensures the response speed, and the closed-loop control improves the control accuracy. The combination of the two achieves the optimal control effect and significantly improves the harmonic compensation rate. The first-order differential link and the second-order low-pass filter cascade are used as the correction link to improve the open-loop control gain and suppress the resonance between the passive filter and the power grid. It has good compensation characteristics. The second-order low-pass filter link is added to the reactive power of the common connection point (PCC point), thereby dividing the dynamic response into two processes: "fast" and "slow". The purpose is to avoid the fundamental reactive power compensation speed being too fast, which conflicts with the harmonic fast compensation link and causes harmonic amplification problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a block diagram of the network outer loop control algorithm of the present invention.

[0025] Figure 2 It is a topological diagram of the network-type STATCOM cascade H-bridge converter of the present invention.

[0026] Figure 3 It is a control block diagram of fundamental current and harmonic current control of the present invention. DETAILED DESCRIPTION

[0027] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings:

[0028] The present invention provides a supercapacitor-based STATCOM flicker suppression method, comprising the following contents:

[0029] 1) Network outer loop control: see Figure 1-2 , Figure 1 is a block diagram of the network outer loop control algorithm of the present invention, Figure 2 It is a topological diagram of the network-type STATCOM cascade H-bridge converter of the present invention.

[0030] The virtual synchronous machine VSG control algorithm is adopted, including reactive power and voltage control, active power and frequency control, to decouple the frequency modulation characteristics and inertia damping characteristics, simulate the swing equation of the synchronous generator, fully simulate the power frequency regulation characteristics of the synchronous generator, and realize the synchronization of the internal three-phase stator electromotive force and the grid voltage. The specific implementation process is as follows:

[0031] Reactive power and voltage control (excitation control) are mainly achieved by calculating the reactive power given value Q ref Reactive power Q at the point of common connection e Passed through a second-order low-pass filter Output Q eLPF The deviation value is obtained through the PI regulator, and the voltage deviation value is compared with the VSG rated output voltage VSG e0 The final output voltage VSG is adjusted by superposition e , that is, the internal electromotive force amplitude, combined with the internal electromotive force phase VSG_θ to generate the internal electromotive force VSG_E; among them, the reactive power given value Q ref The command value is usually 0MVar because the power factor compensation target is 1.0 (inductive).

[0032] Internal stator electromotive force VSG e With the grid voltage V g The difference is applied to the virtual stator impedance The current command VSG_I is generated, and the output electromagnetic power VSG_P is obtained by multiplying it with the internal electromotive force VSG_E, and then divided by the rated capacity base value S Base Generate the per-unit value VSG_P_PU; use a second-order low-pass filter to extract the stable component in VSG_P_PU, and after removing the stable component from the original signal VSG_P_PU, obtain the high-frequency component ΔP_PU of the arc furnace active power to be suppressed by the grid-forming STATCOM, thereby reducing the rate of change of the active power absorbed by the arc furnace from the power grid, as one of the means to suppress flicker.

[0033] The traditional virtual synchronous machine VSG control outer loop adopts Due to the damping coefficient D, the primary frequency modulation and inertia damping are coupled. The VSG control algorithm is improved and the virtual rotation inertia of the integral link is adopted. The corresponding time constant is recorded as T J ; Added the proportional Kp feedback link of the electromagnetic power VSG_P_PU output by VSG to avoid the interference between the frequency modulation characteristics and the inertia damping characteristics, realize the separate control of the two, and be compatible The link has the advantages of fast dynamic response, simple and effective implementation method, etc. The high-frequency component ΔP_PU of the active power of the arc furnace is calculated through the improved network control loop to obtain the frequency deviation Δf pu, added to the per-unit rated value 1.0 and passed through the limiter to obtain the per-unit value f of the frequency signal pu .

[0034] Rated angular frequency ω0 and frequency per unit value f pu After multiplication, the angular frequency VSG_ω of VSG is obtained, and after the integration link, it becomes its phase angle VSG_θ.

[0035] Among them, the meanings of some variables in the network outer loop control method are as follows:

[0036] R V : virtual stator resistance;

[0037] L V : virtual stator inductance;

[0038] T J : virtual moment of inertia time constant;

[0039] D: Damping coefficient.

[0040] Among them, the PR controller transfer function used is:

[0041]

[0042] The meanings of the variables in this section are as follows:

[0043] K p : Regulator proportional coefficient;

[0044] K r : Regulator resonance coefficient;

[0045] ω n : Regulator resonant frequency;

[0046] s: transfer function complex frequency operator.

[0047] The first-order differential transfer function is:

[0048] G(s)=K d s (2)

[0049] The meanings of the variables in this section are as follows:

[0050] K d : differential gain constant;

[0051] s: transfer function complex frequency operator.

[0052] Among them, the low-pass filter (LPF) transfer function used is:

[0053]

[0054] The meanings of the variables in this section are as follows:

[0055] s: transfer function complex frequency operator;

[0056] A n : filter passband gain;

[0057] ω n : transfer function shear frequency;

[0058] ξ: filter damping coefficient.

[0059] The PI regulator transfer function used in this part is:

[0060]

[0061] The meanings of the variables in this section are as follows:

[0062] K p : Regulator proportional coefficient;

[0063] K i : Regulator proportional coefficient;

[0064] s: transfer function complex frequency operator.

[0065] Transfer function of a SOGI (Second-Order Generalized Integrator).

[0066] Supercapacitors are used as energy storage elements. Through the rapid charge and discharge control of supercapacitors, the high-frequency fluctuation of active power caused by the operation of arc furnaces can be suppressed, which is an effective means of flicker suppression.

[0067] 2) Fundamental current control and harmonic current control: see Figure 3 , fundamental current and harmonic current control block diagram, the specific process is as follows:

[0068] Harmonic current control adopts a control strategy that combines open-loop and closed-loop control. Open-loop control ensures response speed, while closed-loop control improves control accuracy. The combination of the two achieves the optimal control effect.

[0069] The current command signal of the open-loop control link comes from the EAF load current i load , a second-order bandpass filter is used to extract the fundamental frequency signal, and the load current i load Subtract the fundamental frequency signal to obtain the load current harmonic component i load_Har .

[0070] The current command signal of the closed-loop control link comes from the transformer secondary total current i g , using the first-order differential link K d s and a second-order low-pass filter The cascade is used as a correction link. The function of this correction link is to use the prediction function of the differential link to produce control action in advance, connect a second-order low-pass filter in series, filter out high-frequency noise, and avoid system instability caused by noise; at the same time, the gain K of the differential link should be appropriately increased. d , improve the gain of the open-loop control link, strengthen the resonance suppression effect between the passive filter and the power grid, and obtain good compensation characteristics.

[0071] Correction link output signal i g_comp , a second-order bandpass filter is used to extract the fundamental frequency signal, the original signal i g_comp Subtract the fundamental frequency signal to obtain the power supply current harmonic component i g_Har . And the load current harmonic component i load_Har After adding, the total harmonic component iref is obtained Har , the harmonic current is generated by the proportional-resonant regulator to control the reference voltage Vref Har .

[0072] Current command VSG_I and current feedback VSG_I fbk The difference is the current inner loop control error, and the fundamental current control reference voltage e is generated through the quasi-proportional resonant regulator. abc *.

[0073] The fundamental current is controlled by the reference voltage e abc * Harmonic current control reference voltage Vref Har Superimposed on the feedforward voltage V g On the top, the modulation wave S is generated Mode , using PWM modulation technology to modulate the wave S Mode Generate gate control signals for fully controlled devices and send them to the cascaded power unit control modules.

[0074] Among them, the PR controller transfer function used is:

[0075]

[0076] The meanings of the variables in this section are as follows:

[0077] K p : Regulator proportional coefficient

[0078] K r : Regulator resonance coefficient

[0079] ω n : Regulator resonant frequency;

[0080] S: Transfer function complex frequency operator.

[0081] The above embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the above embodiments. The methods used in the above embodiments are conventional methods unless otherwise specified.

Claims

1. A supercapacitor-based STATCOM flicker suppression method, characterized in that: Includes the following: 1) Grid outer loop control: The virtual synchronous machine (VSG) control algorithm is adopted, including reactive power and voltage control, active power and frequency control, to decouple the frequency modulation characteristics and inertia damping characteristics, simulate the swing equation of the synchronous generator, fully simulate the power frequency regulation characteristics of the synchronous generator, and synchronize the internal three-phase stator electromotive force with the grid voltage; The virtual synchronous machine VSG control algorithm adopts the virtual rotation inertia of the integral link, and the corresponding time constant is recorded as T J ; Added the proportional Kp feedback link of the electromagnetic power VSG_P_PU output by VSG; Using supercapacitors as energy storage elements, the high-frequency fluctuation of active power caused by arc furnace operation can be suppressed through the rapid charge and discharge control of supercapacitors; 2) Fundamental current control and harmonic current control: The fundamental current is controlled by the reference voltage e abc * Harmonic current control reference voltage Vref Har Superimposed on the feedforward voltage V g On the top, the modulation wave S is generated Mode , the modulation wave S Mode Generate gate control signals for fully controlled devices and send them to cascaded power unit control modules; The harmonic current control adopts a control strategy combining open loop and closed loop. The open loop control uses a second-order bandpass filter to extract the fundamental frequency signal, and the closed loop control uses a first-order differential link and a second-order low-pass filter cascade as a correction link.

2. A method for suppressing flicker in a supercapacitor-based grid-type STATCOM according to claim 1, characterized in that: The reactive power and voltage control is achieved by calculating the reactive power setpoint Q ref Reactive power Q at the point of common connection e Passed through a second-order low-pass filter Output Q eLPF The deviation value is obtained through the PI regulator, and the voltage deviation value is compared with the VSG rated output voltage VSG e0 The final output voltage VSG is adjusted by superposition e , i.e. the internal electromotive force amplitude, is combined with the internal electromotive force phase VSG_θ to generate the internal electromotive force VSG_E; Among them, the reactive power given value Q ref The command value is 0MVar, A n is the filter passband gain, ω n is the transfer function cutoff frequency, s is the transfer function complex frequency operator, and ξ is the filter damping coefficient.

3. A method for suppressing flicker in a supercapacitor-based grid-type STATCOM according to claim 1, characterized in that: The active power and frequency control is the internal stator electromotive force VSG e With the grid voltage V g The difference is applied to the virtual stator impedance On, where R V is the virtual stator resistance, L V is the virtual stator inductance; generates the current command VSG_I, multiplies it with the internal electromotive force VSG_E to get the output electromagnetic power VSG_P, and divides it by the rated capacity base value S Base Generate per-unit value VSG_P_PU. Use second-order low-pass filter to extract the stable component in VSG_P_PU. After removing the stable component from the original signal VSG_P_PU, the high-frequency component ΔP_PU of the arc furnace active power to be suppressed by the grid-type STATCOM is obtained; The high-frequency component of the active power of the arc furnace ΔP_PU is controlled by the outer loop of the network, and the frequency deviation Δf is calculated. pu , added to the per-unit rated value 1.0 and passed through the limiter to obtain the per-unit value f of the frequency signal pu , rated angular frequency ω0 and frequency per unit value f pu After multiplication, the angular frequency VSG_ω of VSG is obtained, and after the integration link, it becomes its phase angle VSG_θ.

4. The method for suppressing flicker of a supercapacitor-based grid-type STATCOM according to claim 1, characterized in that: The current command signal of the open-loop control link comes from the EAF load current i load , a second-order bandpass filter is used to extract the fundamental frequency signal, and the load current i load Subtract the fundamental frequency signal to obtain the load current harmonic component i load_Har ; The current command signal of the closed-loop control link comes from the transformer secondary total current i g , using the first-order differential link K d s and a second-order low-pass filter Cascade as a correction link, where K d is the differential gain constant.

5. A method for suppressing flicker in a supercapacitor-based grid-type STATCOM according to claim 4, characterized in that: The output signal i of the correction link g_comp , a second-order bandpass filter is used to extract the fundamental frequency signal, the original signal i g_comp Subtract the fundamental frequency signal to obtain the power supply current harmonic component i g_Har , and the load current harmonic component i load_Har After adding, the total harmonic component iref is obtained Har , the harmonic current is generated by the proportional-resonant regulator to control the reference voltage Vref Har .

6. A method for suppressing flicker in a supercapacitor-based grid-type STATCOM according to claim 1, characterized in that: The fundamental current control is the current command VSG_I and the current feedback VSG_I fbk The difference is the current inner loop control error, and the fundamental current control reference voltage e is generated through the quasi-proportional resonant regulator. abc *.

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