Improved d-statcom control method, apparatus, and medium

Abstract

The application relates to an improved D-STATCOM control method, device and medium for unbalanced sag, adopting a double closed-loop control strategy, an outer ring realizing voltage control, and an inner ring realizing fast current tracking, wherein an error correction link of a negative sequence component is introduced in the inner ring part, after the negative sequence component of the voltage and current is corrected, the correction result of a positive sequence component is combined to generate a control signal input into SPWM to obtain an IGBT trigger signal, and the D-STATCOM is controlled. Compared with the prior art, the application has the advantages of improving the reactive power compensation capability of the D-STATCOM during short-circuit fault and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system control, and particularly relates to an improved D-STATCOM control method for unbalanced sag, a device and a medium. BACKGROUND

[0002] A static synchronous compensator (STATCOM) is a static type of power electronic device, which is connected to a place needing compensation of reactive power in an inverter state through a variable flow circuit composed of a converter and an inductor. It is praised for its advantages such as smooth reactive power regulation and fast dynamic compensation characteristics. With the improvement of technology and the upgrading and optimization of the structure of the power system, it is found that there is great development space for on-site compensation and power quality control of the distribution network, and it is more in line with actual demand, so STATCOM is gradually applied to the distribution network as an end user, and this kind of device is collectively referred to as a distribution static synchronous compensator (D-STATCOM). The compensator connected to the distribution network can avoid long-distance flow of reactive power and timely suppress power quality problems caused by single-phase high-power equipment or nonlinear loads, so that the performance of the STATCOM can be maximized.

[0003] A relatively classic control strategy of the D-STATCOM is to adopt double closed-loop control, in which an outer loop realizes voltage control and an inner loop realizes fast tracking of current. When a short-circuit fault occurs in the system, the existing control link of the D-STATCOM mainly compensates for the positive sequence component in the system. However, when unbalanced sag (for example, asymmetric fault) occurs in the system, there is a negative sequence component in the system in addition to the positive sequence component, but the existing control method does not consider this point. SUMMARY

[0004] The purpose of the present application is to provide an improved D-STATCOM control method for unbalanced sag, a device and a medium. The error correction link of the negative sequence component is introduced in the inner loop part of the control system, the original control system is improved, and the reactive power compensation capability of the D-STATCOM in the short-circuit fault is improved.

[0005] The purpose of the present application can be achieved by the following technical solutions:

[0006] An improved D-STATCOM control method for unbalanced voltage sag, which adopts a double closed-loop control strategy, the outer loop realizes voltage control, and the inner loop realizes fast current tracking. The method introduces an error correction link of negative sequence component in the inner loop part. After correction of the negative sequence components of voltage and current, the correction results of the positive sequence components are combined to generate control signals input into SPWM to obtain the trigger signals of IGBT for controlling D-STATCOM.

[0007] The method comprises the following steps:

[0008] Obtaining the detected voltage and current;

[0009] Extracting the positive and negative sequence components of the voltage and current, and transforming the positive and negative sequence components from the stationary α-β coordinate system to the rotating d-q coordinate system;

[0010] Inputting the positive and negative sequence components of the current and voltage into corresponding links of the inner loop control of D-STATCOM respectively, and outputting the positive and negative sequence reference voltages;

[0011] Transforming the positive and negative sequence reference voltages from the d-q coordinate system to the α-β coordinate system to obtain the reference voltages in the stationary coordinate system and input them into the SPWM link, and outputting the trigger signals of IGBT after modulation to control D-STATCOM to output or absorb reactive power.

[0012] The extraction of the positive and negative sequence components of the voltage and current is specifically: using 1 / 4 delay calculation method to extract the positive and negative sequence components.

[0013] The calculation method for transforming the positive and negative sequence components of the voltage from the stationary α-β coordinate system to the rotating d-q coordinate system is:

[0014]

[0015] Wherein, u dp ,u qp is the positive sequence component of the voltage in the d-q coordinate system, u dn ,u qn is the negative sequence component of the voltage in the d-q coordinate system, u αp ,u βp is the positive sequence component of the voltage in the α-β coordinate system, is the phase angle estimation value, which is obtained by using SPLL estimation.

[0016] The calculation method for transforming the positive and negative sequence components of the current from the stationary α-β coordinate system to the rotating d-q coordinate system is:

[0017]

[0018]

[0019] Among them, i dp i qp Let i be the positive sequence component of the current in the dq coordinate system. dn i qn Let i be the negative sequence component of the current in the dq coordinate system. αp i βp Let be the positive sequence component of the current in the α-β coordinate system. The phase angle is estimated using SPLL estimation.

[0020] During the error correction process of the inner loop control, when the error... At that time, u dp (k)=i dp (k)=0, u qp (k)=i qp (k)=1, because It is very small, so it is approximated as:

[0021]

[0022] The angular velocity deviation is calculated using a PI converter.

[0023] Δω(k)=(K P +K I / (z-1))u dp (k) or Δω(k)=(K) P +K I / (z-1))i dp (k)

[0024] Where K P and K I These are the proportional and integral coefficients of the PI controller, respectively.

[0025] Calculate the angular velocity ω(k) = Δω(k) + ω * , where ω * =2πf * =100π;

[0026] Calculate the phase angle increment Δθ(k) = T s ·ω(k) yields the estimated phase angle.

[0027] use Perform a coordinate transformation from the α-β coordinate system to the dq coordinate system, and calculate the new u. dp (k),u qp (k), i dp (k),i qp (k), until u dp(k) = i dp (k) = 0, u qp (k) = i qp (k) = 1.

[0028] The positive sequence component u dqp of the voltage, the positive sequence component i dqp of the current are input into the inner loop control error correction link of the positive sequence component, the negative sequence component u dqn of the voltage, the negative sequence component i dqn of the current are input into the inner loop control error correction link of the negative sequence component, and the positive sequence reference voltage U dqrefp and the negative sequence reference voltage U dqrefn are output.

[0029] The positive sequence reference voltage U dqrefp and the negative sequence reference voltage U dqrefn are respectively transformed from the d-q coordinate system to the alpha-beta coordinate system, and U αβrefp and U αβrefn are obtained, and the two are added to obtain the reference voltage for inputting to the SPWM, that is, U αβref = U αβrefp + U αβrefn .

[0030] An improved D-STATCOM control device for unbalanced sag, comprising a memory, a processor, and a program stored in the memory, and the processor implements the method as described above when executing the program.

[0031] A storage medium having a program stored thereon, and the program implements the method as described above when executed.

[0032] Compared with the prior art, the present application has the following beneficial effects:

[0033] 1、After the compensation of the negative sequence current voltage is added, when facing asymmetric faults, the reference voltage formed by the reactive power compensation device STATCOM through the inner loop control is more accurate, the signal input to the IGBT is also more accurate, the target can be quickly compensated in voltage and reactive power, and the damage caused by voltage sag to the equipment is reduced.

[0034] 2、After the compensation of the negative sequence current voltage is added, for the unbalanced load at the user, when a fault occurs, the current and voltage can be detected more accurately, accurate information is fed back to the compensation device, the current and voltage are compensated quickly and accurately, and economic losses caused by the fault are reduced. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 A schematic diagram of a D-STATCOM access system is shown in the figure;

[0036] Figure 2 Fig. 1 is a schematic diagram of α-β coordinate system transformation to a rotating d-q coordinate system;

[0037] Figure 3 Fig. 2 is a schematic diagram of a voltage phasor aligned with the d-axis of the moving reference frame;

[0038] Figure 4 Fig. 3 is a flow chart of the method of the present application;

[0039] Figure 5 Fig. 4 is a schematic diagram of the operation of an SPLL;

[0040] Figure 6 Fig. 5 is a flow chart of an inner loop control based on positive sequence classification in the prior art;

[0041] Figure 7 Fig. 6 is a schematic diagram of the operation of an improved SPLL for a voltage signal according to the present application;

[0042] Figure 8 Fig. 7 is a flow chart of an improved inner loop control according to the present application;

[0043] Figure 9 Fig. 8 is a block diagram of an improved control loop according to the present application;

[0044] Figure 10 Fig. 9 is a comparison of STATCOM output reactive power in Example 2;

[0045] Figure 11 Fig. 10 is a comparison of compensation voltage in Example 2;

[0046] Figure 12 Fig. 11 is a comparison of STATCOM output reactive power in Example 3;

[0047] Figure 13 Fig. 12 is a comparison of compensation voltage in Example 3. DETAILED DESCRIPTION

[0048] The present application will be described in detail below with reference to the accompanying drawings and specific embodiments. The embodiments are implemented on the basis of the technical solution of the present application, and detailed implementation and specific operation processes are given, but the scope of protection of the present application is not limited to the following embodiments.

[0049] The present embodiment provides an improved D-STATCOM control method for unbalanced sag, which adopts a double closed loop control strategy, the outer loop realizes voltage control, and the inner loop realizes fast tracking of current. The method introduces an error correction link of negative sequence components in the inner loop part, and generates a control signal input into SPWM to obtain the trigger signal of IGBT after correcting the negative sequence components of voltage and current in combination with the correction results of positive sequence components, so as to control the D-STATCOM.

[0050] The working principle of D-STACOM is introduced first in this embodiment.

[0051] The working principle of D-STACOM is that when the access point voltage / reactive power deviates from the set value, the control system is started to adjust and pull the voltage / reactive power back to the set value. Figure 1 The schematic diagram of D-STATCOM accessing the system is shown in the figure, wherein the D-STATCOM is composed of an inverter, a direct-current storage capacitor, and a connecting reactor or transformer, the direct-current side capacitor provides direct-current voltage support for the D-STATCOM, the inverter converts the direct-current voltage into alternating-current voltage, and the STATCOM is connected to the power system through the reactor.

[0052] The basic working principle is as follows:

[0053]

[0054] System both sides are multiplied by C 32 , the abc coordinate system is converted into the α-β coordinate system, and

[0055]

[0056] wherein C 32 is the coefficient matrix for converting the abc coordinate system into the α-β coordinate system.

[0057]

[0058] Further, the static α-β coordinate system is converted into the rotating d-q coordinate system, as shown in Figure 2 , let θ=ωt, and the equation (2) is multiplied by e jθ on both sides, and the following equation is obtained:

[0059]

[0060] Definition f represents the voltage or current. The real part and the imaginary part are separated, and the following equation is obtained:

[0061]

[0062] The power provided by the SSTACOM to the system is shown in the following equation,

[0063]

[0064] The three-phase three-wire system does not contain the zero sequence component because it does not have a neutral line, and does not contain the negative sequence component if the system three-phase is symmetrical

[0065]

[0066] The d-q component is used to express:

[0067]

[0068] Adopting Figure 3 Reference: Let Then:

[0069]

[0070] At this time, a phase-locked loop (PLL) system is required to keep the voltage synchronized,

[0071]

[0072] Specifically, as shown in the figure, the method of the present application comprises the following steps: Figure 4

[0073] S1, obtaining the detected voltage and current.

[0074] S2, extracting the positive and negative sequence components of the voltage and current, and transforming the positive and negative sequence components from the stationary α-β coordinate system to the rotating d-q coordinate system.

[0075] This embodiment adopts double closed-loop control, the outer loop realizes voltage control, and the inner loop tracks the current quickly. When the detected current and voltage are transformed from the stationary α-β coordinate system to the rotating d-q coordinate system, a phase-locked loop (PLL) is generally used to correct θ, the function of the PLL is executed by software, and the positive and negative sequence components are extracted by using 1 / 4 delay calculation method (DSC), and the extraction process of the positive sequence component of the voltage is as shown in the figure. Figure 5

[0076] The three-phase voltage u a ,u b ,u c in the abc coordinate system is represented as shown in formula (11):

[0077]

[0078] The reference voltage V is obtained by normalization (ignore subscript *, and subsequent values are normalized values):

[0079]

[0080] Then, it is transformed into the α-β coordinate system, that is:

[0081]

[0082] After the DSC algorithm, the positive and negative sequence components are extracted by using the T / 4 delay calculation method, and the positive sequence component u αp ,u βp and the negative sequence component u αn ,u​​βn The positive sequence component is transformed from the α-β coordinate system to the d-q coordinate system to obtain u dp u qp :

[0083]

[0084] Wherein, Substitute formula (13) into formula (14) to obtain

[0085]

[0086] When the error u dp (k) = 0, u qp (k) = 1, because is very small, so it is approximately considered that

[0087]

[0088] The angular velocity deviation is calculated through the PI link:

[0089] Δω(k) = (K P + K I / (z-1))u dp (k) (17)

[0090] Wherein, K P and K I are the proportional and integral coefficients of the PI controller respectively. The angular velocity ω(k) = Δω(k) + ω * is calculated, wherein ω * = 2πf * = 100π. The phase angle increment Δθ(k) = T s · ω(k) is calculated, and the phase angle estimation value The α-β coordinate system to the d-q coordinate system transformation is performed by using to calculate the new u dp (k), u qp (k), until u dp (k) = 0, u qp (k) = 1.

[0091] Similarly, the negative sequence component is transformed from the α-β coordinate system to the d-q coordinate system to obtain u dn u qn :

[0092]

[0093] u dn u qnis the negative sequence component of the voltage in the d-q coordinate system. The error control process of the negative sequence component can refer to the above positive sequence component, which will not be described here in this embodiment.

[0094] Similarly, the calculation method of transforming the positive and negative sequence components of the current from the stationary α-β coordinate system to the rotating d-q coordinate system is:

[0095]

[0096] wherein i dp is the positive sequence component of the current in the d-q coordinate system, i qp is the negative sequence component of the current in the d-q coordinate system, i dn is the positive sequence component of the current in the α-β coordinate system, qn is the negative sequence component of the current in the α-β coordinate system, αp is the positive sequence component of the current in the α-β coordinate system, βp is the negative sequence component of the current in the α-β coordinate system. is the phase angle estimation value, which is estimated by SPLL.

[0097] The error correction process of the positive and negative sequence components of the current can refer to the above error correction process of the positive sequence component of the voltage, which will not be described here in this embodiment. After the above process, the positive sequence component i dp of the current and the negative sequence component i qp can be obtained. dn qn

[0098] In the prior art, as shown in Figure 6 , the positive sequence components of the current and the voltage are input into the inner loop control of the STATCOM, and the reference voltage U dqrefp is output, then the d-q coordinate system is transformed into the α-β coordinate system to obtain U αβrefp , which is input into the SPWM link, and the trigger signal of the IGBT is output after modulation, so as to control the STATCOM to output or absorb the reactive power. The control idea of the above control system is to compensate only the positive sequence components of the voltage and current after transformation, but the negative sequence components of the voltage and current are ignored. However, when an unbalanced sag occurs in the system (for example, a sag caused by an asymmetric fault), there are negative sequence components in the system in addition to the positive sequence components. Therefore, the error correction link of the above negative sequence component is introduced into the inner loop part of the control system, and the original control system is improved. The improved SPLL working principle diagram for the voltage signal is shown in Figure 7 , and the SPLL for the current signal can refer to the SPLL for the voltage signal, only the input needs to be changed.

[0099] S3, the positive and negative sequence components of the current and the voltage are respectively input into the corresponding links of the inner loop control of the D-STATCOM, and the positive sequence reference voltage and the negative sequence reference voltage are output.​​

[0100] The positive sequence component of the voltage u dqp , the positive sequence component of the current i dqp The inner loop control error correction link of the input positive sequence component, the negative sequence component of the voltage u dqn , the negative sequence component of the current i dqn The inner loop control error correction link of the input negative sequence component, output the positive sequence reference voltage U dqrefp and the negative sequence reference voltage U dqrefn .

[0101] S4, the positive sequence reference voltage and the negative sequence reference voltage are transformed from the d-q coordinate system to the α-β coordinate system, the reference voltage in the stationary coordinate system is obtained and input into the SPWM link, the trigger signal of the IGBT is output after modulation, the D-STATCOM is controlled, and the reactive power is output or absorbed.

[0102] The positive sequence reference voltage U dqrefp and the negative sequence reference voltage U dqrefn are respectively transformed from the d-q coordinate system to the α-β coordinate system, U αβrefp and U αβrefn are obtained, and the reference voltage for inputting into the SPWM is obtained by adding U αβref = U αβrefp + U αβrefn ; the result U αβref of the accumulation of the negative sequence reference voltage and the positive sequence reference voltage is sent into the SPWM link, the trigger signal of the IGBT is output, the STATCOM is controlled, and the reactive power is output or absorbed. The improved inner loop control flow chart is shown in Figure 8 .

[0103] Embodiment 2

[0104] Based on the method described in the above embodiment 1, the following example analysis is provided.

[0105] The model is completed in PSCAD, and the main parameters of the D-STATCOM are shown in Table 1. The main control and improved part links are shown in Figure 9 .

[0106] Table 1 STATCOM main parameters

[0107] Parameter Value Capacity 30 MVA Voltage 10.5 Kv DC side capacitance 128 uf Frequency 50 Hz

[0108] The simulation results of the specific simulation are shown in Figure 10 and Figure 11 As the single-phase grounding fault is an asymmetric fault, there is a negative sequence component at this time, and after considering the negative sequence component, the compensation voltage and the reactive power are significantly improved.

[0109] Embodiment 3

[0110] The system structure diagram and the main parameters of the STATCOM of this embodiment are the same as those of Embodiment 2. This embodiment occurs a fault at node 1 at 1.5 seconds, with a grounding resistance of 1 ohm; the fault disappears at 2 seconds. In the outer loop control, voltage and reactive power coordinated control is considered. Case 2-1 three-phase grounding fault, only considering positive sequence component correction (prior art), Case 2-2 three-phase grounding fault, considering positive and negative sequence component correction (the present application). The specific simulation results are shown in Figure 12 and 13 As the three-phase fault is a symmetric fault, there is no negative sequence component during the fault process, so the compensation voltage and the reactive power will have a slight improvement, but it can be ignored compared to the total compensation target, and can be considered as no improvement.

[0111] Embodiment 4

[0112] The embodiment provides an improved D-STATCOM control device for unbalanced sag, which comprises a memory, a processor, and a program stored in the memory, and the processor implements the method of Embodiment 1 when executing the program.

[0113] In a preferred embodiment, the device comprises:

[0114] A voltage and current acquisition module is configured to acquire detected voltage and current.

[0115] A positive and negative sequence component extraction and coordinate conversion module is configured to extract positive and negative sequence components of the voltage and current, and convert the positive and negative sequence components from a stationary α-β coordinate system to a rotating d-q coordinate system.

[0116] A reference voltage generation module is configured to input the positive and negative sequence components of the current and voltage into corresponding links of the inner loop control of the D-STATCOM respectively, and output positive and negative sequence reference voltages.

[0117] The control module is used for transforming the positive sequence reference voltage and the negative sequence reference voltage from the d-q coordinate system to the alpha-beta coordinate system, obtaining the reference voltage in the stationary coordinate system and inputting into the SPWM link, outputting the trigger signal of the IGBT after modulation, controlling the D-STATCOM, and making it output or absorb the reactive power.

[0118] Those skilled in the art can clearly understand that, for the convenience and brevity of the description, the specific working process of the described modules can refer to the corresponding process in the foregoing method embodiments, which will not be described here.

[0119] Embodiment 5

[0120] The embodiment provides a storage medium, which has a program stored thereon, the program being executed to implement the method in the foregoing embodiment 1.

[0121] The storage medium includes permanent and non-permanent, removable and non-removable media, which can be implemented by any method or technology to store information. The information can be computer readable instructions, data structures, program modules or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transmission medium that can be used to store information accessible by a computing device. According to the definition herein, the computer readable medium does not include transitory computer readable media such as modulated data signals and carriers.

[0122] The preferred embodiments of the present application are described in detail above. It should be understood that those skilled in the art can make many modifications and changes to the embodiments without creative work based on the concept of the present application. Therefore, any technical solution obtained by logical analysis, reasoning or limited experiments based on the prior art according to the concept of the present application should be within the protection scope determined by the claims.

Claims

1. An improved D-STATCOM control method for unbalanced voltage sag, adopting a double closed-loop control strategy, the outer loop realizes voltage control, and the inner loop realizes fast current tracking, characterized in that, The method introduces an error correction link of negative sequence components in the inner loop part, generates a control signal input into SPWM to obtain the trigger signal of IGBT after correcting the negative sequence components of voltage and current, and combines the correction result of positive sequence components to control D-STATCOM. The method comprises the following steps: Obtaining the detected voltage and current; The positive and negative sequence components of the voltage and current are extracted and transformed from the stationary coordinate system to the rotating coordinate system; The positive sequence components and the negative sequence components of the current and the voltage are respectively input into corresponding links of the inner loop control of D-STATCOM to output positive sequence reference voltage and negative sequence reference voltage. The positive sequence reference voltage and the negative sequence reference voltage are obtained from coordinate system to coordinate system, to obtain the reference voltage in the stationary coordinate system and input into the SPWM link, and output the trigger signal of the IGBT after modulation to control the D-STATCOM to output or absorb the reactive power; wherein the positive sequence component of the voltage , the positive sequence component of the current is input to the inner loop control error correction element of the positive sequence component, the negative sequence component of the voltage , the negative sequence component of the current is input to the inner loop control error correction element of the negative sequence component, and the positive sequence reference voltage and the negative sequence reference voltage are output; The positive sequence reference voltage and the negative sequence reference voltage are respectively made coordinate system to coordinate system, get and , the sum of the two is used for input to the SPWM reference voltage, that is .

2. The improved D-STATCOM control method for unbalanced sag according to claim 1, characterized in that, The positive sequence and the negative sequence components of the voltage and current are extracted by using 1 / 4 delay calculation method.

3. The improved D-STATCOM control method for unbalanced sag according to claim 1, characterized in that, The positive and negative sequence components of the voltage are transformed from the stationary coordinate system into the rotating coordinate system by means of the following calculation method: wherein is the positive sequence component of the voltage in the coordinate system, is the negative sequence component of the voltage in the coordinate system, k denotes the time instant, is the positive sequence component of the voltage in the coordinate system, is the phase angle estimate, which is estimated using a SPLL.

4. The improved D-STATCOM control method for unbalanced sag according to claim 3, characterized in that, The positive and negative sequence components of the current are transformed from the stationary coordinate system into the rotating coordinate system by means of the calculation method wherein is the positive sequence component of the current in the coordinate system, is the negative sequence component of the current in the coordinate system, is the positive sequence component of the current in the coordinate system, is the phase angle estimate, estimated using a SPLL.

5. The improved D-STATCOM control method for unbalanced sag according to claim 4, characterized in that, In the error correction process of inner loop control, when the error =0, , , since is very small, it is approximately considered that: The PI link is used to calculate the angular velocity deviation: or wherein and are the proportional and integral coefficients of the PI controller, respectively; Computing angular velocity wherein ; Computing phase angle increment , obtaining phase angle estimate ; Utilizing Performing Coordinate transformation of the coordinate system to d - q Calculate new , , until , .

6. An improved D-STATCOM control device against unbalanced sag comprising a memory, a processor, and a program stored in the memory, characterized by, The processor executes the program to realize the method in any one of claims 1-5.

7. A storage medium having stored thereon a program, characterized by The program is executed to realize the method in any one of claims 1-5.

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