Static synchronous compensator device based on quasi-harmonic theory and control method thereof

Abstract

The invention provides a static synchronous compensator device based on a quasi-harmonic theory and a control method thereof, mainly comprises a static synchronous compensator and a voltage stability control method based on the quasi-harmonic theory, and is used for solving the problem of system oscillation under the condition of a weak power grid at the receiving end of a photovoltaic power generation system. The static synchronous compensator comprises a bridge circuit based on a three-phase two-level voltage source type current converter, a direct current side energy storage capacitor and a passive inductance capacitance filter. The static synchronous compensator is connected in parallel with a receiving end power grid part, and a voltage stability control method based on the quasi-harmonic theory is adopted for compensating the oscillation component of the voltage of a grid-connected point. According to the voltage stability control method based on the quasi-harmonic theory, the quasi-harmonic current of the grid-connected point can be extracted without an additional harmonic extraction filter, and a control system can be simplified; in addition, the method can increase the response speed of the current loop to the harmonic current, and can more quickly and accurately compensate the oscillation voltage, thereby improving the suppression effect of system oscillation.

Description

Technical Field

[0001] The invention belongs to the field of power electronic static synchronous compensator control, and relates to a static synchronous compensator device and a control method based on the quasi-harmonic theory, which are applicable to the control of power electronic static synchronous compensators. Background Art

[0002] In recent years, driven by technological innovation, policy incentives and market demand, renewable energy power generation represented by photovoltaic and wind turbines has become an important part of modern power systems. Since new energy power generation bases are usually located in remote areas far from cities, the local receiving AC power grid is weak, and impedance interaction mismatches occur between new energy power generation stations and the receiving weak power grid. Therefore, the new energy power generation grid-connected system is prone to system oscillations in the case of a receiving weak power grid, resulting in serious power losses and equipment damage. When the new energy power generation system oscillates in the case of a receiving weak power grid, serious voltage sub-synchronous oscillations will occur at the grid connection point. Therefore, the stability of the new energy power generation system under a receiving weak power grid can be improved by suppressing the voltage sub-synchronous oscillations at the grid connection point. Existing voltage sub-synchronous oscillation suppression strategies mainly focus on improving the control method of photovoltaic inverters. For the existing voltage differential feed-forward control method of photovoltaic inverters, high-frequency harmonics will also be amplified while suppressing oscillations, reducing the grid-connected power quality of photovoltaic inverters.

[0003] In addition, due to the large number of photovoltaic inverter manufacturers and technical secrecy, it is sometimes difficult to optimize the control method of photovoltaic inverters. As a reactive power regulation device, static synchronous compensators are widely used in photovoltaic power generation systems. However, the static synchronous compensator based on classical direct reactive power control cannot suppress voltage sub-synchronous oscillations. Optimizing the control method of the static synchronous compensator to suppress the voltage sub-synchronous oscillations at the grid connection point of the photovoltaic power generation system is often a good choice. The existing virtual synchronous generator-based control method for static synchronous compensators will reduce the dynamic response speed of the static synchronous compensator due to the inertial characteristics of the virtual synchronous generator, and the dynamic compensation performance of the static synchronous compensator will be reduced.

[0004] Therefore, a control method for a static synchronous compensator device based on the quasi-harmonic theory is proposed. By sampling the voltage at the point of common coupling, the fundamental amplitude of the voltage at the point of common coupling and the equivalent impedance of the power grid are used to calculate the quasi-harmonic current, which is fed forward to the current loop to make the static synchronous compensator generate an oscillating compensation voltage. Moreover, a first-order inertial controller is embedded between the voltage loop and the current loop to enhance the influence of the quasi-harmonic current on the current loop control, enabling the static synchronous compensator to compensate for the oscillating voltage more quickly and accurately according to the quasi-harmonic current. The control method for the static synchronous compensator based on the quasi-harmonic theory does not require an additional harmonic extraction filter, reducing the complexity of the control system; the embedding of the first-order inertial controller increases the response speed of the current loop to the quasi-harmonic current and improves the oscillating voltage compensation efficiency of the static synchronous compensator. Summary of the Invention

[0005] The present invention proposes a control method for a static synchronous compensator based on the quasi-harmonic theory, without a harmonic extraction structure of an additional harmonic extraction filter, which can improve the voltage stability at the point of common coupling of a photovoltaic power generation system under a weak power grid. The steps during use are as follows:

[0006] 1) Connect the static synchronous compensator in parallel with the receiving-end power grid at the point of common coupling; the static synchronous compensator is composed of a bridge circuit based on a three-phase two-level voltage source converter, a DC-side energy storage capacitor, and an inductance-capacitance filter; connect the upper and lower tubes of each bridge arm of the bridge circuit to the positive and negative electrodes of the energy storage capacitor respectively, and connect the midpoint of the upper and lower tubes to the inductance-capacitance filter;

[0007] 2) Subtract the sampled value v sdc_ref from the reference value V sdc of the voltage of the DC-side energy storage capacitor, and perform proportional-integral controller calculation on the voltage difference (V sdc_ref -v sdc ) to obtain the d-axis control current i sdv . The current i sdv is:

[0008] i sdv =G sv (V dc_ref -v dc );

[0009] where G sv is the transfer function of the proportional-integral controller of the voltage loop;

[0010] Collect the voltages v a , v b and v c at the point of common coupling and perform abc / dq transformation to obtain the d-axis and q-axis voltage components v d and v q . The voltages v d and v q are:

[0011]

[0012] Among them, π is the coefficient of pi, f is the instantaneous frequency of the voltage, t is the time coefficient, cos(*) is the cosine function, and sin(*) is the sine function;

[0013] Subtract the grid-connected point voltage fundamental amplitude V1 from the voltage v d to obtain the quasi-harmonic voltage (v d -V1). Calculate the quasi-harmonic current i d through the quasi-harmonic voltage (v g -V1) and the equivalent impedance Z of the power grid sd_ff . The quasi-harmonic current i sd_ff is:

[0014]

[0015] Calculate the d-axis current loop command i sdv and i sd_ff as well as the first-order inertia controller and its controller parameters D g and D i . Calculate the q-axis current loop command I sd_ref through the rated reactive power Q0 of the static var compensator and the voltage V1. The current loop commands i q_ref and I sd_ref and I sq_ref are:

[0016]

[0017] Among them, s is the differential operator;

[0018] 3): Collect the inductor currents i sa , i sb and i sc of the inductor-capacitor filter and perform abc / dq transformation to obtain the d-axis and q-axis current components i sd and i sq . The currents i sd and i sq are:

[0019]

[0020] Subtract the currents i sd_ref and I sq_ref from the currents i sd and i sq respectively. By taking the difference between the current differences (i sd_ref -i sd ) and (I sq_ref -i sq)The proportional-integral controller is calculated to obtain the control voltage e sd and e sq , and the voltages e sd and e sq are:

[0021]

[0022] where G si is the transfer function of the current-loop proportional-integral controller, L sf is the filter inductance value of the inductor-capacitor filter of the static synchronous compensator, ω0 is the rated angular frequency of the power grid, v d and v q are v a , v b and v c voltages in the dq coordinate system;

[0023] The internal voltage signals e sd and e sq are used to calculate the internal voltage signals e sa , e sb and e sc , and the internal voltage signals e sa , e sb and e sc are:

[0024]

[0025] The modulation signals S sa , e sb and e sc are calculated as S sa = e sa / (v sdc / 2), S sb = e sb / (v sdc / 2) and S sc = e sc / (v sdc / 2). Based on the modulation signals S sa , S sb and S sc , pulse-width modulation is performed to control the conduction and turn-off of the switches of the static synchronous compensator;

[0026] 4): By using the dq impedance modeling method, the dq impedance matrix Z sdq of the static synchronous compensator under the said control method is obtained. The dq impedance matrix Z sdq is:

[0027]

[0028] where G1 is the loop matrix, G2 is the system matrix, G3 is the feedforward matrix, G4 is the decoupling matrix, G de is the delay matrix, is the current phase-locked matrix, is the voltage phase-locked matrix, G p is the inertia matrix, H1 is the inertia transfer function of the first-order inertia controller,

[0029] H1 = D i / (s + D i ); H2 is the gain transfer function of the first-order inertia controller, H2 = D g / (s + D i ); A is the d-axis reduction factor, A = V d + sL sf I sd +

[0030] K sd I sq ; B is the q-axis reduction factor, B = V q + sL sf I sq - K sd I sd ; G dc is the DC conversion matrix, G dc = 1.5 / (sC sdc V sdc ); T PLL is the phase-locked loop transfer function, T PLL = V1H PLL / [1 + V1H PLL , H PLL is the q-axis phase-locked transfer function, H PLL = G PLL / s; G PLL is the transfer function of the proportional-integral controller of the phase-locked loop, ω0 is the rated angular frequency of the power grid, L sf is the filter inductor of the static synchronous compensator, T s is the sampling time, I sd and I sq are the fundamental wave amplitudes of the currents i sd and i sq respectively, V d and V q are the fundamental wave amplitudes of the voltages v d and v q respectively, K sd is the current loop decoupling coefficient, Csdc and V sdc are respectively the DC-side energy storage capacitor of the static synchronous compensator and the steady-state value of the energy storage capacitor voltage, (*) -1 represents matrix inversion;

[0031] By means of the dq impedance to sequence impedance method, the sequence impedance Z of the static synchronous compensator under the said control method is obtained ss , the sequence impedance Z ss is:

[0032]

[0033] wherein, Z g is the grid equivalent impedance, Z 11 , Z 12 , Z 21 and Z 22 are respectively the first row and first column element, the first row and second column element, the second row and first column element, and the second row and second column element of the reduced-order impedance matrix Z red , and the reduced-order impedance matrix Z red is:

[0034]

[0035] wherein, j is the imaginary unit;

[0036] According to the sequence impedance Z ss and the system circuit relationship, the parallel equivalent impedance Z of the static synchronous compensator and the receiving-end grid under the said control method can be obtained par is:

[0037]

[0038] wherein, C sf and R sd are respectively the filtering capacitor and damping resistor of the inductance-capacitance filter of the static var compensator, C pf and R pd are respectively the filtering capacitor and damping resistor of the inductance-capacitance filter of the photovoltaic inverter, L g is the equivalent inductance of the grid, R g is the equivalent resistance of the grid.

[0039] Correspondingly, the present invention also provides a static synchronous compensator device based on the quasi-harmonic theory, including a static synchronous compensator based on the quasi-harmonic theory, a photovoltaic inverter, and a receiving-end grid; the static synchronous compensator is connected in parallel with the photovoltaic inverter and the receiving-end grid at the connection point; the control process of the static synchronous compensator based on the quasi-harmonic theory is mainly: taking the difference between the reference value V sdc_ref of the energy storage capacitor voltage and the sampled value v sdc , by taking the voltage difference (Vsdc_ref -v sdc ) Calculate the proportional-integral controller to obtain the d-axis control current i sdv ; Collect the grid-connected voltage v a , v b and v c and perform abc / dq transformation to obtain the d-axis and q-axis voltage components v d and v q , Subtract the grid-connected voltage fundamental amplitude V1 from the voltage v d to obtain the quasi-harmonic voltage (v d - V1), and calculate the quasi-harmonic current i d through the quasi-harmonic voltage (v g - V1) and the grid equivalent impedance Z sd_ff ; Calculate the d-axis current loop command i sdv through the current i sd_ff and the first-order inertia controller parameters D g and D i , and calculate the q-axis current loop command I sd_ref through the static var compensator rated reactive power Q0 and the voltage V1 q_ref ; Collect the inductor currents i sa , i sb and i sc of the inductor-capacitor filter and perform abc / dq transformation to obtain the d-axis and q-axis current components i sd and i sq ; Subtract the current i sd_ref and I sq_ref from the current i sd and i sq respectively, and calculate the control voltages e sd_ref - i sd ) and (I sq_ref - i sq ) through proportional-integral controller calculation sd and e sq ; Calculate the internal voltage signals e sd and e sq through the voltages e sa , e sb and e sc ; Calculate the modulation signals S sa , e sb and e sc through the internal voltage signals e sa , S sb and S sc , and according to the modulation signals S sa , S sb and S scPerform pulse width modulation to control the conduction and cutoff of the switching tubes of the static synchronous compensator.

[0040] The present invention has the following advantages and effects compared with the prior art:

[0041] 1) The present invention proposes a static synchronous compensator device based on the quasi-harmonic theory, and adopts a voltage stability control method based on the quasi-harmonic theory. The control method does not require the use of an additional harmonic extraction filter, reducing the complexity of the control system;

[0042] 2) The present invention embeds a first-order inertia controller between the voltage loop and the current loop, which can increase the response speed of the current loop to the quasi-harmonic current, enabling the static synchronous compensator to compensate for the oscillating voltage more quickly and accurately according to the quasi-harmonic current, thereby improving the suppression effect of system oscillation. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is the control method and system block diagram of the static synchronous compensator based on the quasi-harmonic theory.

[0044] Figure 2 is the comparison diagram of the impedance frequency characteristics of the static synchronous compensator under the control method and the direct reactive power control method.

[0045] Figure 3 is the comparison diagram of the impedance frequency characteristics of the parallel equivalent impedance of the static synchronous compensator and the receiving-end power grid and the impedance of the photovoltaic inverter under the control method and the direct reactive power control method.

[0046] Figure 4 is the experimental waveform diagram of the grid-connected point voltage of the static synchronous compensator under the direct reactive power control method.

[0047] Figure 5 is the experimental waveform diagram of the grid-connected point voltage of the static synchronous compensator under the control method. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] A control method for a static synchronous compensator based on the quasi-harmonic theory proposed by the present invention is described in detail as follows in conjunction with the accompanying drawings:

[0049] Figure 1 is the control method and system block diagram of the static synchronous compensator based on the quasi-harmonic theory. The photovoltaic inverter is connected to the grid after passing through an inductor-capacitor filter, and a shunt static synchronous compensator is used as a reactive power regulation device. Inductor L g and resistor R g constitute the equivalent impedance of the power grid.

[0050] The impedance Z ps of the photovoltaic inverter is:

[0051]

[0052] where j is the imaginary unit, s is the differential operator, K pwm is the modulation signal gain, K pd and K pf are the decoupling coefficient and the current feedforward coefficient respectively, L pf is the filtering inductance of the inductance-capacitance filter of the photovoltaic inverter, G pi is the current inner-loop transfer function of the photovoltaic inverter, ω0 is the rated angular frequency of the power grid, V pdc is the rated value of the DC-side voltage of the photovoltaic inverter, V1 is the amplitude of the grid-connected point voltage, T PLL is the phase-locked loop transfer function, T PLL = V1H PLL / [1 + V1H PLL , H PLL is the q-axis phase-locked transfer function, H PLL = G PLL / s, G PLL is the transfer function of the proportional-integral controller of the phase-locked loop, G d is the control delay transfer function, G d = 1 / (1 + 1.5T s s), T s is the sampling time, I1 is the vector current, I1 = 0.5(I pd1 + jI pq1 ), I pd1 and I pq1 are the fundamental current amplitudes of the current i pf of the inductance L pa , i pb and i pc in the dq coordinate system respectively, M1 is the modulation factor, M1 = 0.5[(jω0L pf I pd1 + V1) / (K pwm V pdc G d - V1K pf V pdc G d .

[0053] The static synchronous compensator is connected in parallel with the receiving-end power grid; the static synchronous compensator consists of a bridge circuit based on a three-phase two-level voltage source converter, a DC-side energy storage capacitor and an inductance-capacitance filter; the inductance current of the inductance-capacitance filter is i sa , i sb and i sc , and the output current of the static synchronous compensator is i soa , i sob and i soc .

[0054] Then, a static synchronous compensator is modeled under the said control method, and the reference value V of the DC-side energy storage capacitor voltage sdc_ref is subtracted from the sampled value v sdc . By calculating the voltage difference (V sdc_ref -v sdc ) through a proportional-integral controller, the d-axis control current i sdv is obtained. The current i sdv is as follows:

[0055] i sdv =G sv (V dc_ref -v dc ) (2)

[0056] where G sv is the transfer function of the voltage-loop proportional-integral controller.

[0057] The grid-connected point voltages v a , v b and v c are collected and subjected to abc / dq transformation to obtain the d-axis and q-axis voltage components v d and v q . The voltages v d and v q are as follows:

[0058]

[0059] where π is the coefficient of pi, f is the instantaneous frequency of the voltage, t is the time coefficient, cos(*) is the cosine function, and sin(*) is the sine function.

[0060] The difference between the voltage v d and the fundamental wave amplitude V1 of the grid-connected point voltage is used to obtain the quasi-harmonic voltage (v d -V1). The quasi-harmonic current i d -V1) and the grid equivalent impedance Z g are used to calculate the quasi-harmonic current i sd_ff . The quasi-harmonic current i sd_ff is as follows:

[0061]

[0062] The d-axis current-loop command i sdv is calculated through the currents i sd_ff and i g as well as the first-order inertia controller and its controller parameters D i . The q-axis current-loop command I sd_ref is calculated through the rated reactive power Q0 of the static var compensator and the voltage V1. The current-loop command i q_ref is sd_refand I sq_ref is:

[0063]

[0064] where s is the differential operator.

[0065] Collect the inductor current i of the inductive-capacitive filter sa , i sb and i sc and perform abc / dq transformation to obtain the d-axis and q-axis current components i sd and i sq , the current i sd and i sq is:

[0066]

[0067] Subtract the current i sd_ref and I sq_ref from the current i sd and i sq respectively. By performing proportional-integral controller calculations on the current differences (i sd_ref - i sd ) and (I sq_ref - i sq ), obtain the control voltages e sd and e sq , the voltages e sd and e sq are:

[0068]

[0069] where G si is the transfer function of the current-loop proportional-integral controller, L sf is the filter inductance value of the inductive-capacitive filter of the static synchronous compensator, ω0 is the rated angular frequency of the power grid, v d and v q are v a , v b and v c in the dq coordinate system.

[0070] Calculate the internal voltage signals e sd and e sq , the internal voltage signals e sa , e sb and e sc , the internal voltage signals e sa , e sb and e sc are:

[0071]

[0072] Calculate the modulation signal S through the internal voltage signals e sa , e sb and e sc as S sa = e sa / (v sdc / 2), S sb = e sb / (v sdc / 2) and S sc = e sc / (v sdc / 2). Perform pulse-width modulation based on the modulation signals S sa , S sb and S sc to control the conduction and cutoff of the switches of the static synchronous compensator.

[0073] Using the dq impedance modeling method, obtain the dq impedance matrix Z of the static synchronous compensator under the said control method sdq , where the dq impedance matrix Z sdq is:

[0074]

[0075] where G1 is the loop matrix, G2 is the system matrix, G3 is the feedforward matrix, G4 is the decoupling matrix, G de is the delay matrix, is the current phase-locked matrix, is the voltage phase-locked matrix, G p is the inertia matrix, H1 is the inertia transfer function of the first-order inertia controller,

[0076] H1 = D i / (s + D i ); H2 is the gain transfer function of the first-order inertia controller, H2 = D g / (s + D i ); A is the d-axis reduction factor, A = V d + sL sf I sd +

[0077] K sd I sq ; B is the q-axis reduction factor, B = V q + sL sf I sq - K sd I sd ; Gdc is the DC conversion matrix, G dc = 1.5 / (sC sdc V sdc )); T PLL is the PLL transfer function, T PLL = V1H PLL / [1 + V1H PLL , H PLL is the q-axis PLL transfer function, H PLL = G PLL / s; G PLL is the transfer function of the PI controller of the PLL, ω0 is the rated angular frequency of the power grid, L sf is the filter inductor of the static synchronous compensator, T s is the sampling time, I sd and I sq are the fundamental wave amplitudes of the currents i sd and i sq respectively, V d and V q are the fundamental wave amplitudes of the voltages v d and v q respectively, K sd is the decoupling coefficient of the current loop, C sdc and V sdc are the DC side energy storage capacitor of the static synchronous compensator and the steady-state value of the energy storage capacitor voltage respectively, (*) -1 represents matrix inversion.

[0078] By using the dq impedance to sequence impedance method, the sequence impedance Z ss of the static synchronous compensator under the said control method is obtained. The sequence impedance Z ss is:

[0079]

[0080] wherein, Z g is the equivalent impedance of the power grid, Z 11 , Z 12 , Z 21 and Z 22 are the first row and first column element, the first row and second column element, the second row and first column element, and the second row and second column element of the reduced-order impedance matrix Z red respectively. The reduced-order impedance matrix Z red is:

[0081]

[0082] wherein, j is the imaginary unit.

[0083] According to the sequence impedance Z ssThe parallel equivalent impedance Z of the static synchronous compensator and the receiving-end power grid under the described control method can be obtained from the relationship with the system circuit par is:

[0084]

[0085] where C sf and R sd are respectively the filter capacitor and damping resistor of the inductor-capacitor filter of the static var compensator, C pf and R pd are respectively the filter capacitor and damping resistor of the inductor-capacitor filter of the photovoltaic inverter, L g is the equivalent inductance of the power grid, and R g is the equivalent resistance of the power grid.

[0086] Figure 2 is the comparison diagram of the impedance frequency characteristics of the static synchronous compensator under the described control method and the direct reactive power control method. From Figure 2 it can be observed that in the entire medium and low frequency bands, the impedance amplitude of the static synchronous compensator under the described control method is smaller than that of the static synchronous compensator under the direct reactive power control method.

[0087] Figure 3 is the comparison diagram of the parallel equivalent impedance of the static synchronous compensator and the receiving-end power grid and the impedance frequency characteristics of the photovoltaic inverter under the described control method and the direct reactive power control method. The short-circuit ratio is the ratio of the system short-circuit capacity to the equipment capacity. When the short-circuit ratio is less than 3, it is called a weak power grid. From Figure 3 it can be observed that when the short-circuit ratio = 2, the amplitude-frequency characteristic curves of the parallel equivalent impedance of the static synchronous compensator and the receiving-end power grid and the amplitude-frequency characteristic curves of the impedance of the photovoltaic inverter under the direct reactive power control method intersect, and there are two intersection points at 73 Hz and 78 Hz respectively. At 73 Hz and 78 Hz, the phase differences between the phase-frequency characteristic curves of the parallel equivalent impedance of the static synchronous compensator and the receiving-end power grid and the impedance of the photovoltaic inverter under the direct reactive power control method are 232° and 141° respectively. According to the impedance interaction stability determination criterion, the phase difference at 73 Hz is greater than 180°, so the system is unstable, and the phase difference at 78 Hz is less than 180°, so the system is stable. The impedance interaction stability determination criterion is:

[0088]

[0089] where Z ps represents the impedance of the photovoltaic inverter, and Z parIt represents the parallel equivalent impedance of the static synchronous compensator and the receiving-end power grid. |*| represents taking the absolute value, arg{*} represents taking the phase degree, and ω represents the instantaneous angular frequency of the impedance. In addition, when the short-circuit ratio = 2, there is no intersection between the amplitude-frequency characteristic curve of the parallel equivalent impedance of the static synchronous compensator and the receiving-end power grid and the amplitude-frequency characteristic curve of the photovoltaic inverter under the control method, so the system is stable.

[0090] According to Figure 1 Build an experimental platform for the control method and system of the static synchronous compensator based on the quasi-harmonic theory based on dSPACE. The experimental results are as Figure 4 and Figure 5 shown.

[0091] Figure 4 It is the experimental waveform diagram of the grid connection point voltage of the static synchronous compensator under the direct reactive power control method. Through Figure 4 the experimental results, it can be seen that when the short-circuit ratio drops from 8 to 2, the grid connection point voltage of the photovoltaic power generation system with the static synchronous compensator under the direct reactive power control method undergoes sub-synchronous oscillation. The total voltage distortion rate is 23.34%, and the oscillation frequencies are 73 Hz and 27 Hz. Among them, the sub-synchronous oscillation component at 27 Hz is coupled from the oscillation component at 73 Hz.

[0092] Figure 5 It is the experimental waveform diagram of the grid connection point voltage of the static synchronous compensator under the control method. Through Figure 5 the experimental results, it can be seen that after the short-circuit ratio of the photovoltaic grid-connected system with the static synchronous compensator under the control method drops from 8 to 2, the grid connection point voltage of the photovoltaic grid-connected system does not generate sub-synchronous oscillation, and the total voltage distortion rate is 3.37%, meeting the national power quality requirements. Therefore, the control method and system of the static synchronous compensator based on the quasi-harmonic theory can well suppress the voltage sub-synchronous oscillation under a weak grid, improve the stability of the system and the grid-connected power quality.

[0093] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A control method for a static synchronous compensator device based on quasi-harmonic theory, characterized in that: The harmonic extraction structure without additional harmonic extraction filter can improve the voltage stability of the photovoltaic power generation system grid connection point under weak power grid. The steps in the use process are: 1) Connecting a static synchronous compensator in parallel with a receiving-end power grid at a grid connection point; the static synchronous compensator is composed of a bridge circuit based on a three-phase two-level voltage source converter, a DC side energy storage capacitor and an inductor capacitor filter; connecting the upper and lower tubes of each bridge arm of the bridge circuit to the positive and negative electrodes of the energy storage capacitor respectively, and connecting the midpoints of the upper and lower tubes to the inductor capacitor filter; 2) Set the reference value of the energy storage capacitor voltage V sdc_ref With the sample value v sdc By making a difference in voltage (V sdc_ref -v sdc ) to calculate the proportional-integral controller and obtain the d-axis control current i sdv ; Collect the grid voltage v a ,v b and v c And perform abc / dq transformation to obtain the d-axis and q-axis voltage components v d and v q , the voltage v d The quasi-harmonic voltage (v d -V1), through the quasi-harmonic voltage (v d -V1) and the equivalent impedance of the power grid Z g The quasi-harmonic current i is calculated sd_ff ; through the current i sdv and i sd_ff and the first-order inertial controller parameter D g and D i Calculate the d-axis current loop command i sd_ref , the q-axis current loop command I is calculated by the static VAR compensator rated reactive power Q0 and voltage V1 q_ref ; 3) Collect the inductor current i of the inductor-capacitor filter sa ,i sb and i sc And perform abc / dq transformation to obtain the d-axis and q-axis current components i sd and i sq ; The current i sd_ref and I sq_ref With current i sd and i sq By making a difference in the current difference (i sd_ref -i sd ) and (I sq_ref -i sq ) to calculate the proportional-integral controller and obtain the control voltage e sd and e sq ; through the voltage e sd and e sq Calculate the internal voltage signal e sa ,e sb and e sc ; Through the internal voltage signal e sa ,e sb and e sc The modulated signal S is calculated sa =e sa / (v sdc / 2), S sb =e sb / (v sdc / 2) and S sc =e sc / (v sdc / 2, according to the modulation signal S sa ,S sb and S sc Perform pulse width modulation to control the on and off of the static synchronous compensator switch tube; 4) Through the dq impedance modeling method, the dq impedance matrix Z of the static synchronous compensator under the control method is obtained sdq ; Through the dq impedance to sequence impedance method, the sequence impedance Z of the static synchronous compensator under the control method is obtained ss ; According to the sequence impedance Z ss The relationship between the static synchronous compensator and the receiving power grid in parallel under the control method is obtained by par .

2. The control method of a static synchronous compensator device based on quasi-harmonic theory according to claim 1, characterized in that: Step 2) The d-axis and q-axis voltage components v d and v q for: Among them, π is the coefficient of pi, f is the instantaneous frequency of voltage, t is the time coefficient, cos(*) is the cosine function, and sin(*) is the sine function.

3. The control method of a static synchronous compensator device based on quasi-harmonic theory according to claim 1, characterized in that: In step 2), the current loop command i sd_ref and I sq_ref for: Among them, s is the differential operator, i sd_ff is the quasi-harmonic current, i sd_ff =(v d -V1) / Z g , v d is the three-phase voltage v at the grid connection point acb The d-axis voltage component in the dq coordinate system, V1 is the fundamental amplitude of the grid-connected point voltage, Z g is the equivalent impedance of the power grid, i sdv is the d-axis control current, i sdv =G sv (V sdc_ref -v sdc ), G sv is the transfer function of the voltage loop proportional-integral controller, V sdc_ref and v sdc They are respectively the reference value and sampling value of the DC side energy storage capacitor voltage of the static synchronous compensator.

4. The control method of a static synchronous compensator device based on quasi-harmonic theory according to claim 1, characterized in that: Step 3) The d-axis and q-axis current components i sd and i sq for:

5. The control method of a static synchronous compensator device based on quasi-harmonic theory according to claim 1, characterized in that: Step 3) Medium voltage e sd and e sq for: Among them, G si is the transfer function of the current loop proportional-integral controller, L sf is the filter inductance of the static synchronous compensator’s inductor-capacitor filter, ω0 is the rated angular frequency of the power grid, v d and v q v a ,v b and v c Voltage in dq coordinate system.

6. The control method of a static synchronous compensator device based on quasi-harmonic theory according to claim 1, characterized in that: In step (3), the voltage e sd and e sq Calculate the internal voltage signal e sa ,e sb and e sc , internal voltage signal e sa ,e sb and e sc for: Through the internal voltage signal e sa ,e sb and e sc Calculate the modulation signal S sa =e sa / (v sdc / 2), S sb =e sb / (v sdc / 2) and S sc =e sc / (v sdc / 2), according to the modulation signal S sa ,S sb and S sc Pulse width modulation is performed to control the on and off of the static synchronous compensator switch tube.

7. The control method of a static synchronous compensator device based on quasi-harmonic theory according to claim 1, characterized in that: Step 4) dq impedance matrix Z sdq for: Among them, G1 is the loop matrix, G2 is the system matrix, G3 is the feedforward matrix, G4 is the decoupling matrix, G de is the delay matrix, is the current phase-locking matrix, is the voltage phase-locked matrix, G p is the inertia matrix, H1 is the inertia transfer function of the first-order inertial controller, H1=D i / (s+D i );H2 is the gain transfer function of the first-order inertial controller, H2=D g / (s+D i );A is the d-axis simplification factor, A=V d +sL sf I sd +K sd I sq ; B is the q-axis simplification factor, B = V q +sL sf I sq -K sd I sd ; G dc is the DC conversion matrix, G dc =1.5 / (sC sdc V sdc );T PLL is the phase-locked loop transfer function, T PLL =V1H PLL / [1+V1H PLL ], H PLL is the q-axis phase-locked transfer function, H PLL =G PLL / s; G PLL is the transfer function of the proportional-integral controller of the phase-locked loop, ω0 is the rated angular frequency of the power grid, L sf is the filter inductance of the static synchronous compensator, T s is the sampling time, I sd and I sq The current i sd and i sq Fundamental amplitude, V d and V q The voltage v d and v q The fundamental amplitude, K sd is the current loop decoupling coefficient, C sdc and V sdc are the DC side energy storage capacitor and the steady-state value of the energy storage capacitor voltage of the static synchronous compensator, respectively, (*) -1 Represents matrix inversion.

8. The control method of a static synchronous compensator device based on quasi-harmonic theory according to claim 1, characterized in that: The sequence impedance Z of the static synchronous compensator in step 4) ss for: Among them, Z g is the equivalent impedance of the power grid, Z 11 , Z 12 , Z 21 and Z 22 They are the reduced-order impedance matrices Z red The first row and first column elements, the first row and second column elements, the second row and first column elements, and the second row and second column elements, the reduced-order impedance matrix Z red for: Here, j is the imaginary unit.

9. The control method of a static synchronous compensator device based on quasi-harmonic theory according to claim 1, characterized in that: The equivalent impedance Z of the static synchronous compensator connected in parallel with the receiving power grid under the control method described in step 4) par for: Among them, C sf and R sd are the filter capacitor and damping resistor of the inductor and capacitor filter of the static VAR compensator, C pf and R pd are the filter capacitor and damping resistor of the photovoltaic inverter inductor and capacitor filter, L g is the equivalent inductance of the power grid, R g is the equivalent resistance of the power grid.

10. A static synchronous compensator device based on quasi-harmonic theory, characterized in that: The invention comprises a static synchronous compensator based on quasi-harmonic theory, a photovoltaic inverter and a receiving-end power grid; the static synchronous compensator is connected in parallel with the photovoltaic inverter and the receiving-end power grid at the grid connection point; the control process of the static synchronous compensator based on quasi-harmonic theory is mainly as follows: the reference value V of the energy storage capacitor voltage is set to sdc_ref With the sample value v sdc By making a difference in voltage (V sdc_ref -v sdc ) to calculate the proportional-integral controller and obtain the d-axis control current i sdv ; Collect the grid voltage v a ,v b and v c And perform abc / dq transformation to obtain the d-axis and q-axis voltage components v d and v q , the voltage v d The quasi-harmonic voltage (v d -V1), through the quasi-harmonic voltage (v d -V1) and the equivalent impedance of the power grid Z g The quasi-harmonic current i is calculated sd_ff ; through the current i sdv and i sd_ff and the first-order inertial controller parameter D g and D i Calculate the d-axis current loop command i sd_ref , the q-axis current loop command I is calculated by the static VAR compensator rated reactive power Q0 and voltage V1 q_ref ; Collect the inductor current i of the inductor capacitor filter sa ,i sb and i sc And perform abc / dq transformation to obtain the d-axis and q-axis current components i sd and i sq ; The current i sd_ref and I sq_ref With current i sd and i sq By making a difference in the current difference (i sd_ref -i sd ) and (I sq_ref -i sq ) to calculate the proportional-integral controller and obtain the control voltage e sd and e sq ; through the voltage e sd and e sq Calculate the internal voltage signal e sa ,e sb and e sc ; Through the internal voltage signal e sa ,e sb and e sc The modulated signal S is calculated sa , S sb and S sc , according to the modulation signal S sa ,S sb and S sc Pulse width modulation is performed to control the on and off of the static synchronous compensator switch tube; the static synchronous compensator is composed of a bridge circuit based on a three-phase two-level voltage source converter, a DC side energy storage capacitor and an inductor capacitor filter; the upper and lower tubes of each bridge arm of the bridge circuit are respectively connected to the positive and negative electrodes of the energy storage capacitor, and the midpoints of the upper and lower tubes are connected to the inductor capacitor filter.

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