Coal mine power grid electric energy quality treatment method and coal mine power grid electric energy treatment system

Abstract

The invention provides an electric energy quality treatment method of a coal mine power grid and an electric energy treatment system of the coal mine power grid. The method comprises the steps that current information of a coal mine power grid is acquired, the current information is information of current generated by load operation in the coal mine power grid, and the current corresponding to the current information at least comprises harmonic current; switching pulse frequencies are obtained, the switching pulse frequencies are switching frequencies of a switch of the STATCOM between on and off, and the current information and the switching pulse frequencies are in one-to-one correspondence; and controlling the STATCOM to emit compensation current according to the switching pulse frequency so as to counteract harmonic current in current corresponding to the current information. According to the scheme, the problem of potential safety hazards of other equipment in a power grid caused by a large amount of current harmonics in the coal mine power grid in the prior art is solved.

Description

Technical Field

[0001] The present application relates to the technical field of power quality management, and specifically, to a method, device, computer program product and coal mine power grid power quality management system. Background Art

[0002] With the increasing application of electrical automation equipment in coal mines, power electronic equipment and various nonlinear loads are increasingly used in coal mines, such as high-power thyristor converters, variable frequency speed control devices, etc., resulting in a large number of current harmonics in coal mine power grids, among which the 5th current harmonic content is more serious than other harmonics. At the same time, due to the various high-power nonlinear loads causing a large amount of reactive impact when starting, a large amount of reactive power is injected into the power grid side, causing safety hazards to other equipment in the power grid. Summary of the invention

[0003] The main purpose of the present application is to provide a method, device, computer program product and coal mine power grid power quality management system for coal mine power grid, so as to at least solve the problem in the prior art that a large number of current harmonics exist in the coal mine power grid, causing safety hazards to other equipment in the power grid.

[0004] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a method for managing the power quality of a coal mine power grid is provided, comprising: obtaining current information of the coal mine power grid, wherein the current information is information about the current generated by the operation of a load in the coal mine power grid, and the current corresponding to the current information includes at least harmonic current; obtaining a switching pulse frequency, wherein the switching pulse frequency is the frequency at which a switch of a STATCOM switches between on and off, and the current information and the switching pulse frequency correspond one-to-one; and controlling the STATCOM to emit a compensation current according to the switching pulse frequency to offset the harmonic current in the current corresponding to the current information.

[0005] Optionally, the current information also includes the three-phase current value of the load. After obtaining the current information of the coal mine power grid, the method also includes: performing a CLARK transformation on the three-phase current value of the load to obtain a first load current value in an αβ coordinate system; performing a PARK transformation on the first load current value to obtain a second load current value in a dq coordinate system; performing a low-pass filtering on the second load current value to obtain a fundamental current value; and calculating the difference between the second load current value and the fundamental current value to obtain a harmonic current value.

[0006] Optionally, after calculating the difference between the second load current value and the fundamental current value to obtain the harmonic current value, the method further includes: using a PI regulator to calculate the difference between a reference voltage value and an actual voltage value to obtain a control deviation; calculating the sum of the control deviation and the harmonic current value to obtain an active current value; performing an inverse PARK transformation on the active current value and the reactive current value to obtain a reference current value of the αβ coordinate system, wherein the reference current value is used to allocate an initial given value of the switching pulse frequency.

[0007] Optionally, obtaining the switching pulse frequency includes: obtaining a vector, wherein the vector is a vector of the switch of the STATCOM; determining a duty cycle according to a size of a cost function of the vector, wherein the cost function and the duty cycle are negatively correlated, and the duty cycle is a ratio of the switch-on time of the STATCOM to the total time or a ratio of the switch-off time of the STATCOM to the total time; determining the switching pulse frequency according to the duty cycle, wherein the duty cycle and the switching pulse frequency correspond one-to-one.

[0008] Optionally, after acquiring the vector, the method further includes: calculating a current prediction value at time k+1 according to a power prediction formula, wherein the power prediction formula is:

[0009]

[0010] represents the predicted current value at time k+1, R represents the resistance value, T s represents the sampling period, L represents the inductance value, i c (k) represents the current value at time k, v x represents the switching vector, u s (k) The voltage value of the coal mine power grid.

[0011] Optionally, before determining the duty cycle according to the size of the cost function of the vector, the method further includes: acquiring the cost function of the vector, wherein the cost function is:

[0012]

[0013] g0 represents the first cost function corresponding to the zero vector, g1 represents the second cost function corresponding to the first effective vector, and g2 represents the third cost function corresponding to the second effective vector. represents the first reference current value of the αβ coordinate system, represents the second reference current value of the αβ coordinate system, and They respectively represent the current values ​​at time k+1 of the αβ coordinate system under the action of the zero vector, and respectively represent the current values ​​at time k+1 of the αβ coordinate system under the action of the first effective vector, and They respectively represent the current value at time k+1 of the αβ coordinate system under the action of the second effective vector.

[0014] Optionally, determining the duty cycle according to the size of the cost function of the vector includes: calculating the duty cycle according to a duty cycle formula, wherein the duty cycle formula is:

[0015]

[0016] d0 represents a first duty cycle corresponding to the zero vector, d1 represents a second duty cycle corresponding to the first effective vector, and d2 represents a third duty cycle corresponding to the second effective vector.

[0017] According to another aspect of the present application, a device for managing the power quality of a coal mine power grid is provided, comprising: a first acquisition unit, used to acquire current information of the coal mine power grid, wherein the current information is information about the current generated by the operation of a load in the coal mine power grid, and the current corresponding to the current information includes at least harmonic current; a second acquisition unit, used to acquire a switching pulse frequency, wherein the switching pulse frequency is the frequency at which a switch of a STATCOM switches between on and off, and the current information and the switching pulse frequency correspond one-to-one; and a management unit, used to control the STATCOM to emit a compensation current according to the switching pulse frequency to offset the harmonic current in the current corresponding to the current information.

[0018] According to another aspect of the present application, a computer program product is provided, comprising a computer program, wherein when the computer program is executed by a processor, the steps of any one of the methods for managing the power quality of a coal mine power grid are implemented.

[0019] According to another aspect of the present application, a coal mine power grid power management system is provided, comprising: one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and are configured to be executed by the one or more processors, and the one or more programs include a method for executing any one of the coal mine power grid power quality management methods.

[0020] By applying the technical solution of the present application, a STATCOM is added to eliminate harmonics in the coal mine power grid during operation. In addition, the switching frequency of the on-time and off-time of the IGBT switch of the STATCOM is predefined in the present solution, so that a fixed switching frequency can be achieved, thereby significantly reducing the total harmonic distortion rate of the current on the grid side of the coal mine underground and effectively compensating for the reactive power on the grid side, thereby improving the power quality of the coal mine underground power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings constituting part of the present application are used to provide a further understanding of the present application. The exemplary embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0022] Figure 1 A hardware structure block diagram of a mobile terminal for executing a method for managing the power quality of a coal mine power grid provided in an embodiment of the present application is shown;

[0023] Figure 2 A schematic diagram of a process for improving the power quality of a coal mine power grid according to an embodiment of the present application is shown;

[0024] Figure 3 A schematic diagram of the topological structure of STATCOM is shown;

[0025] Figure 4 A vector schematic diagram of a STATCOM is shown;

[0026] Figure 5 A schematic diagram of the control principle of M2PC is shown;

[0027] Figure 6 A schematic diagram of the control principle of a STATCOM based on M2PC is shown;

[0028] Figure 7 A control flow diagram of a STATCOM based on M2PC is shown;

[0029] Figure 8 A schematic diagram showing pulse distribution of M2PC is shown;

[0030] Fig. 9 A schematic diagram of the grid-side voltage is shown;

[0031] Fig.10 A schematic diagram of the grid-side current is shown;

[0032] Fig.11 A schematic diagram showing load current;

[0033] Fig.12 A schematic diagram showing the current flow of a STATCOM;

[0034] Fig.13 A schematic diagram showing the grid-side current harmonics before the scheme is put into use;

[0035] Fig.14 A schematic diagram showing the grid-side current harmonics after the scheme is put into use;

[0036] Fig.15 The waveform diagram of the active power P and reactive power Q on the grid side before and after the STATCOM is put into operation is shown;

[0037] Fig.16 The DC side voltage waveform after STATCOM is put into operation is shown;

[0038] Fig.17 A structural block diagram of a device for managing the power quality of a coal mine power grid provided according to an embodiment of the present application is shown.

[0039] The above drawings include the following reference numerals:

[0040] 102, processor; 104, memory; 106, transmission device; 108, input and output devices. DETAILED DESCRIPTION

[0041] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0042] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0043] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0044] As introduced in the background technology, in the prior art, there are a large number of current harmonics in the coal mine power grid, which causes safety hazards to other equipment in the power grid. To solve the above problems, the embodiments of the present application provide a method, device, computer program product and coal mine power grid power quality management system for a coal mine power grid.

[0045] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0046] The method embodiments provided in the embodiments of the present application can be executed in a mobile terminal, a computer terminal or a similar computing device. Taking running on a mobile terminal as an example, Figure 1 1 is a hardware structure block diagram of a mobile terminal of a method for managing the power quality of a coal mine power grid according to an embodiment of the present invention. Figure 1 As shown, the mobile terminal may include one or more ( Figure 1 Only one is shown in the figure) a processor 102 (the processor 102 may include but is not limited to a processing device such as a microprocessor MCU or a programmable logic device FPGA) and a memory 104 for storing data, wherein the mobile terminal may also include a transmission device 106 and an input / output device 108 for communication functions. It can be understood by those skilled in the art that Figure 1 The structure shown is only for illustration and does not limit the structure of the mobile terminal. Figure 1 More or fewer components as shown, or with Figure 1 Different configurations are shown.

[0047] The memory 104 can be used to store computer programs, for example, software programs and modules of application software, such as the computer program corresponding to the display method of device information in the embodiment of the present invention. The processor 102 executes various functional applications and data processing by running the computer program stored in the memory 104, that is, the above method is implemented. The memory 104 may include a high-speed random access memory, and may also include a non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memory. In some examples, the memory 104 may further include a memory remotely arranged relative to the processor 102, and these remote memories can be connected to the mobile terminal via a network. Examples of the above-mentioned network include but are not limited to the Internet, an intranet, a local area network, a mobile communication network, and a combination thereof. The transmission device 106 is used to receive or send data via a network. The above-mentioned specific examples of the network may include a wireless network provided by a communication provider of the mobile terminal. In one example, the transmission device 106 includes a network adapter (Network Interface Controller, referred to as NIC), which can be connected to other network devices through a base station so as to communicate with the Internet. In one example, the transmission device 106 may be a radio frequency (RF) module, which is used to communicate with the Internet wirelessly.

[0048] In this embodiment, a method for managing the power quality of a coal mine power grid running on a mobile terminal, a computer terminal or a similar computing device is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described may be executed in an order different from that shown here.

[0049] Figure 2 FIG. 1 is a flow chart of a method for improving the power quality of a coal mine power grid according to an embodiment of the present application. Figure 2 As shown, the method comprises the following steps:

[0050] Step S201, obtaining current information of a coal mine power grid, wherein the current information is information of current generated by the operation of loads in the coal mine power grid, and the current corresponding to the current information at least includes harmonic current;

[0051] Specifically, in the coal mine power grid system, the coal mine power grid is the infrastructure used for power supply in coal mine production, providing power support for the load. Current, as one of the key parameters in the operation of the power grid, has a great impact on the quality of the power grid. The general current includes harmonic current.

[0052] Step S202, obtaining a switch pulse frequency, wherein the switch pulse frequency is a frequency at which a switch of the STATCOM switches between on and off, and the current information corresponds to the switch pulse frequency one by one;

[0053] Specifically, the time when the switch of the STATCOM is turned on and the time when the switch of the STATCOM is turned off can be determined, and the on time and the off time are alternately performed, that is, the switching pulse frequency.

[0054] Step S203, controlling the STATCOM to emit a compensation current according to the switching pulse frequency to offset the harmonic current in the current corresponding to the current information.

[0055] Specifically, by controlling the on or off of the STATCOM switch through a predefined switching pulse frequency, a fixed switching frequency can be achieved. When there are harmonics in the power grid, a compensation current can be generated to remove the harmonic current.

[0056] Through this embodiment, during the operation of the coal mine power grid, STATCOM is added to eliminate the harmonics in the coal mine power grid, and the switching frequency of the on-time and off-time of the IGBT switch of the STATCOM is predefined in this solution, so that a fixed switching frequency can be achieved, thereby greatly reducing the total harmonic distortion rate of the coal mine underground grid side current and effectively compensating for the grid side reactive power, thereby improving the power quality of the coal mine underground grid.

[0057] Specifically, this solution uses a static synchronous compensator based on modulation model predictive control to achieve power quality management. At present, most coal mine power grids use direct parallel capacitors or static var generators (SVC) to compensate for system reactive power, but parallel capacitors cannot effectively adjust the reactive power required by the system, and SVC cannot effectively provide reactive power when the voltage is reduced. Static synchronous compensator (STATCOM) has the advantages of fast dynamic response, real-time compensation for the reactive power required by the system, and can eliminate harmonics, and is used in coal mine power grids.

[0058] Model Predictive Control (MPC) has the advantages of flexibility, simplicity, fast dynamic response, and the ability to control multiple targets simultaneously, and has been widely used in the field of power electronics. Among them, the finite control set MPC (FCS-MPC) traverses all switching states in a switching cycle to minimize the cost function and finally finds the optimal switching state. This control method has been applied in various power electronic topologies. However, due to the lack of a modulator, FCS-MPC has problems such as large ripple in the output current and the inability to fix the switching frequency. Modulated Model Predictive Control (M2PC) adds a modulation method based on MPC, which inherits the advantages of MPC, reduces the current ripple, and has a fixed switching frequency.

[0059] In order to achieve the smooth and efficient operation of the coal mine underground power grid, this solution adopts STATCOM power quality management based on M2PC. By controlling the harmonic current emitted by STATCOM and absorbing the excessive reactive power in the system, the power quality of the coal mine underground power grid system is improved.

[0060] Specifically, this scheme adopts a static synchronous compensator power quality management scheme based on modulation model predictive control. This scheme is aimed at the field of power quality management technology in coal mines. p -i q The harmonic current and reactive current in the power grid are detected as the reference current of M2PC, and two adjacent vectors in each sector are selected as effective vectors. The duty ratio of the two effective vectors and the zero vector of each sector of STATCOM is calculated. The cost function is defined in each sector, and the cost function is minimized to obtain the optimal sector and the duty ratio of the two optimal effective vectors and the zero vector corresponding to the sector. According to the method of space vector modulation (SVM), the switching pulses are distributed, and the switching device is turned on or off once in a switching cycle to achieve a fixed switching frequency, thereby controlling STATCOM to emit compensation current to offset the harmonic current and reactive current in the power grid. This scheme can greatly reduce the total harmonic distortion rate of the current on the grid side of the coal mine and effectively compensate for the reactive power on the grid side, thereby improving the power quality of the coal mine grid.

[0061] Specifically, this scheme adopts i p -i qThe harmonic current and reactive current on the grid side are extracted by the method and used as the reference given current of M2PC. M2PC controls STATCOM by selecting two adjacent effective vectors and zero vector synthesis in each sector. The duty cycle of the three vectors is calculated in each sector, and the cost function is defined. The optimal sector and the corresponding duty cycle of the two optimal effective vectors and the zero vector are obtained by minimizing the cost function. According to the duty cycle of the optimal effective vector and the zero vector, the switching pulse is allocated by the SVM method, and the IGBT only needs to be turned on or off once in a switching cycle to achieve a fixed switching frequency. The inventors of the present application found that before the M2PC-based STATCOM was put into use, the grid-side current was severely distorted, the reactive power on the grid side fluctuated greatly, and the power factor on the grid side fluctuated and was less than 1. After the M2PC-based STATCOM was put into use, the grid-side current THD was greatly reduced, the reactive power on the grid side was basically kept at 0, and the power factor on the grid side was stabilized at 1, which effectively improved the power quality.

[0062] Specifically, the above solution of the present application adopts i p -i q The method can detect harmonic current and reactive power in the system at the same time. According to the system harmonic current and reactive power, while stabilizing the DC side voltage, the M2PC algorithm is used to control STATCOM, which not only suppresses harmonic current but also compensates for reactive power. It can greatly reduce the total harmonic distortion rate of the grid-side current and effectively compensate for the reactive power on the grid side, thus improving the power quality of the coal mine power grid.

[0063] In order to reduce the difficulty of subsequent calculations, remove the noise part in the current value, and extract the harmonic current in the current, the above-mentioned current information also includes the three-phase current value of the above-mentioned load. After obtaining the current information of the coal mine power grid, the above-mentioned method also includes the following steps: performing a CLARK transformation on the above-mentioned three-phase current value of the above-mentioned load to obtain the first load current value of the αβ coordinate system; performing a PARK transformation on the above-mentioned first load current value to obtain the second load current value of the dq coordinate system; performing a low-pass filtering on the above-mentioned second load current value to obtain the fundamental part current value; calculating the difference between the above-mentioned second load current value and the above-mentioned fundamental part current value to obtain the harmonic current value.

[0064] In this scheme, through CLARK transformation, three-phase current can be converted into two-phase current, reducing the complexity of calculation. In the αβ coordinate system, the change of current can be clearer. Through PARK transformation, the control of current is directly related to the rotor position and speed of the motor, thereby realizing direct control of the motor torque and speed, further reducing the complexity of calculation. Through low-pass filtering, the noise and interference in the current can be removed to obtain the normal current, that is, the current value of the fundamental part, and then the total current value, that is, the second load current value, is subtracted from the current value of the fundamental part to extract a more accurate harmonic current value.

[0065] In order to further ensure the high control accuracy of the present scheme and further improve the power quality of the coal mine power grid, after calculating the difference between the second load current value and the fundamental current value to obtain the harmonic current value, the method further includes the following steps: using a PI regulator to calculate the difference between the reference voltage value and the actual voltage value to obtain a control deviation; calculating the sum of the control deviation and the harmonic current value to obtain an active current value; performing an inverse PARK transformation on the active current value and the reactive current value to obtain a reference current value of the αβ coordinate system, wherein the reference current value is used to allocate an initial given value of the switching pulse frequency.

[0066] In this scheme, the PI regulator can calculate the difference between the reference voltage value and the actual voltage value. This difference can reflect the gap between the current state and the expected state. The control deviation is added to the harmonic current value so that these harmonic components can be taken into account when calculating the active current, thereby more accurately reflecting the current demand. The reference current value of the αβ coordinate system can be obtained through the inverse PARK transformation, which can be directly used for the subsequent control of the switching operation of the STATCOM to generate the required current waveform. The use of the inverse PARK transformation to convert the control quantity back to the actual available coordinate system can improve the control accuracy, so as to achieve subsequent precise control of the current and further improve the power quality of the coal mine power grid.

[0067] Specifically, in the above scheme, the three-phase current i on the load side is detected. la ,i lb ,i lc , after CLARK transformation, the load current i in the αβ coordinate system is obtained lα ,i lβ . Detect the grid voltage u sa ,u sb ,u sc , the grid angle θ is obtained through the phase-locked loop. The load current i lα ,i lβ Perform PARK transformation to obtain the load current i in the d,q coordinate system ld ,i lq . to ild Perform low-pass filtering, that is, filter out the harmonic part and leave the fundamental part.

[0068] The unfiltered i ld Subtract i ld The fundamental part to the harmonic part This is the harmonic current on the load side.

[0069] In order to stabilize the DC side current of STATCOM, the voltage reference value V * dc With the DC side voltage value V dc Compare and get P through PI regulator loss Added to the harmonic current.

[0070] The active current i in the dq coordinate system ld and reactive current i lq After the inverse PARK transformation, the reference current given value of M2PC in the αβ coordinate system is obtained: and

[0071] M2PC uses the cost function minimization to select the optimal vector and adds a modulation strategy. The cost function of each sector is calculated, and then the minimum cost function among all sectors is found, that is, the optimal sector and duty cycle are found, and the switching pulses are distributed through space vector modulation to achieve the effect of fixed switching frequency.

[0072] The main purpose of coordinate transformation is to convert the three-phase current (or voltage) signal in the rectangular coordinate system into two orthogonal coordinates, which simplifies the parameters and facilitates the subsequent design of the control model. The low-pass filter is mainly used for processing to obtain the fundamental component. Angle θ is a key parameter accompanying the PARK coordinate transformation, which is obtained by detecting the grid voltage through the phase-locked loop.

[0073] V * dc is the theoretical value of the capacitor voltage, V dc is the actual value of the capacitor voltage. V * dc There is no specific range. It is mainly calculated based on Kirchhoff's voltage law, combined with the grid-side voltage, inductance, resistance and capacitance in the line.

[0074] PI regulator is a linear controller that forms a control deviation based on the given value and the actual output value, and uses the proportion and integral of the deviation to form a control quantity through linear combination to control the controlled object. The theory of PI regulator is relatively complicated, so it is only used as an application module here without theoretical analysis.

[0075] The active compensation value Ploss is obtained by the PI regulator. When it is added to the harmonic current, the active current ild can be obtained. The active current ild and the reactive current ilq are transformed by inverse PARK to obtain the reference current given value of M2PC in the αβ coordinate system. and

[0076] In the specific implementation process, obtaining the switching pulse frequency can be achieved through the following steps: obtaining a vector, wherein the above-mentioned vector is the vector of the switch of the above-mentioned STATCOM; determining the duty cycle according to the size of the cost function of the above-mentioned vector, wherein the above-mentioned cost function and the above-mentioned duty cycle are negatively correlated, and the above-mentioned duty cycle is the ratio of the switch conduction time of the above-mentioned STATCOM to the total time or the ratio of the switch off time of the above-mentioned STATCOM to the total time; determining the above-mentioned switching pulse frequency according to the above-mentioned duty cycle, wherein the above-mentioned duty cycle and the above-mentioned switching pulse frequency correspond one to one.

[0077] In this scheme, the vector of the STATCOM switch represents the different states of the switch. By calculating the cost function value of each vector and selecting the smallest vector, the time ratio that the switch should remain on or off, that is, the duty cycle, can be determined. When the duty cycle has been determined, the corresponding switching pulse frequency can be generated according to the duty cycle. By precisely controlling the switch state, accurate compensation for the reactive power of the power grid can be achieved, thereby further improving the voltage quality of the power grid.

[0078] Specifically, the solution of this application adopts i p -i q The basic principle is to first detect the three-phase load side current, then use a low-pass filter to filter out its harmonic part in the dq coordinate system, and then obtain its harmonic part and reactive part as the reference current of M2PC.

[0079] STATCOM compensates for reactive power in the grid by absorbing or emitting reactive power, and can also inject harmonic compensation current of equal magnitude but opposite direction to compensate for current harmonics. Therefore, the grid current becomes close to a sine wave and consistent with the voltage phase. The STATCOM topology is as follows: Figure 3 shown.

[0080] Depend on Figure 3 It can be seen that the grid-side current is composed of the load current and the STATCOM current, so it can be obtained:

[0081]

[0082] i sa 、i sb and i sc is the three-phase grid-side current, ila 、i lb and i lc is the three-phase load side current, i ca 、i cb and i cc is the three-phase STATCOM current.

[0083] according to Figure 3 And Kirchhoff's voltage law, the continuous domain mathematical model of STATCOM in the abc coordinate system can be obtained:

[0084]

[0085] L and R are the inductance and resistance of STATCOM filter inductor respectively, u ca 、u cb and u cc is the three-phase STATCOM output voltage, u sa 、u sb and u sc is the three-phase grid side voltage, C dc is the DC side capacitance, i dc is the DC side current.

[0086]

[0087] V dc is the DC side voltage; S a , S b , S c It is the three-phase switch state. When the upper bridge arm is turned on and the lower bridge arm is turned off, it is 1; when the lower bridge arm is turned on and the upper bridge arm is turned off, it is 0.

[0088] Specifically, all switching states are recorded, so for the two-level STATCOM, in the αβ coordinate system, there are a total of 8 switching vectors v x =v α,x +jv β,x (x∈{0, 1, ..., 7}), see Table 1, and is divided into 6 sectors, such as Figure 4 shown.

[0089] Table 1

[0090]

[0091] In the specific implementation process, after obtaining the vector, the method further includes the following steps: calculating the current prediction value at time k+1 according to the power prediction formula, wherein the power prediction formula is:

[0092]

[0093] represents the predicted current value at time k+1, R represents the resistance value, T s represents the sampling period, L represents the inductance value, i c (k) represents the current value at time k, v x represents the switching vector, u s (k) Voltage value of the coal mine power grid. The above formula is only exemplary, and any variation of the formula falls within the protection scope of this application.

[0094] In this solution, it can be determined through the above power prediction formula that the current values ​​at the previous moment and the next moment are related, so a more accurate prediction value of the current at the next moment can be obtained through the above formula of this solution.

[0095] Specifically, the Euler formula can be used to discretize equation (2), and the discretized equation (2) can be converted from the abc coordinate system to the αβ coordinate system using Clark transformation, and the vector expression of the STATCOM current prediction value at the next sampling moment (k+1 moment) can be obtained, that is, the current prediction formula (i.e., equation 4). c (k) is the STATCOM current vector at time k in the αβ coordinate system; u s (k) is the grid voltage vector at time k in the αβ coordinate system.

[0096] In some embodiments, before determining the duty cycle according to the size of the cost function of the vector, the method further includes the following steps: obtaining the cost function of the vector, wherein the cost function is:

[0097]

[0098] g0 represents the first cost function corresponding to the zero vector, g1 represents the second cost function corresponding to the first effective vector, and g2 represents the third cost function corresponding to the second effective vector. represents the first reference current value of the αβ coordinate system, represents the second reference current value of the above αβ coordinate system, and They respectively represent the current values ​​at time k+1 of the αβ coordinate system under the action of the zero vector, and represent the current values ​​at time k+1 of the αβ coordinate system under the action of the first effective vector, respectively, and They respectively represent the current value at time k+1 of the αβ coordinate system under the action of the second effective vector.

[0099] In this scheme, the cost value corresponding to each vector can be calculated by the above expression. The cost function can be used to evaluate the impact of the switching state of different switching vectors on the power grid, and then the subsequent duty cycle can be further accurately determined based on this impact.

[0100] Specifically, the M2PC algorithm controls STATCOM, selects the optimal vector by minimizing the cost function, and adds a modulation strategy. In one sampling period, two adjacent effective vectors and a zero vector in each sector are selected to reduce the output ripple. According to formula (4), the output current at time k+1 under the action of the effective vector and the zero vector can be obtained, so the cost function of these three vectors in the αβ coordinate system can be obtained:

[0101]

[0102] Where: g0, g1, g2 are the cost functions corresponding to the zero vector, the first valid vector, and the second valid vector respectively; are the STATCOM current reference values ​​at time k+1 in the αβ coordinate system. For simplicity, it is assumed that the current reference value will not change much within a sampling period, so it can be considered that i p α0 ,i p β0 are the STATCOM currents at time k+1 in the αβ coordinate system when the zero vector acts; i p α1 ,i p β1 are the STATCOM currents at time k+1 in the αβ coordinate system when the first effective vector acts; i p α2 ,i p β2 They are respectively the STATCOM currents at time k+1 in the αβ coordinate system when the second effective vector acts.

[0103] In some embodiments, the duty cycle is determined according to the size of the cost function of the vector, which can be specifically implemented by the following steps: calculating the duty cycle according to the duty cycle formula, wherein the duty cycle formula is:

[0104]

[0105] d0 represents the first duty cycle corresponding to the zero vector, d1 represents the second duty cycle corresponding to the first effective vector, and d2 represents the third duty cycle corresponding to the second effective vector.

[0106] In this scheme, the smaller the cost function of the vector is, the more precise the control using the vector is. Therefore, in order to maximize the control accuracy, the smaller the cost function is, the larger the duty cycle corresponding to the vector is. Therefore, the duty cycle formula of this scheme can further accurately determine the duty cycle corresponding to each vector.

[0107] Specifically, a cost function is defined in each sector:

[0108] g sx =d0g0+d1g1+d2g2,x∈{1,2,…,6} (Formula 6);

[0109] Where d0, d1, and d2 are the duty cycles of the zero vector, the first effective vector, and the second effective vector, respectively.

[0110] The smaller the cost function of a vector, the more accurate the control using that vector. Therefore, in order to maximize the control accuracy, the smaller the cost function, the larger the duty cycle corresponding to the vector. Therefore, it is stipulated here that the duty cycles corresponding to the three vectors are inversely proportional to their cost functions, and the sum of the three vectors is 1, from which we can get:

[0111]

[0112] It can be seen from equation (7) that the smaller the cost function vector is, the larger the duty cycle is, and vice versa, thereby maximizing the control accuracy. Solving equation 7, we can get the duty cycle formula, that is, equation 8, where the value range of d0, d1, d2 is [0, 1]. If d0, d1, d2 is greater than 1, then d0, d1, d2 is 1; if d0, d1, d2 is less than 0, then d0, d1, d2 is 0.

[0113] Taking sector 1 as an example, the first valid vector is v1, the second valid vector is v2, the zero vectors are v0 and v7, and the reference current given value at time k+1 is The cost function g of the two valid vectors and the zero vector in sector 1 is calculated by equations (4) and (5): 11 , g 21 , g 01 , and then calculate the duty cycle d corresponding to the three effective vectors through formula (8) 11 , d 21 , d 01 Finally, the cost function g of sector 1 is calculated according to formula (6): s1 Similarly, traverse all sectors and calculate the cost function g of the two valid vectors and the zero vector of each sector. 1x , g 2x , g 0x , duty cycle d 1x , d 2x , d 0xAnd the cost function g sx , find the minimum cost function among all sectors, that is, minimize the cost function g sx , get the best sector x _opt The corresponding duty ratio d of the two effective vectors and the zero vector 1_opt , d 2_opt , d 0_opt , and then distribute the switching pulses through the SVM method to achieve the effect of fixed switching frequency. Figure 5 shown.

[0114] The control principle of STATCOM based on M2PC is as follows: Figure 6 shown. Figure 6 in i s is the grid side current vector in the αβ coordinate system, i l is the load current vector in the αβ coordinate system, i c is the STATCOM current vector in the αβ coordinate system, u s is the grid voltage vector in the αβ coordinate system. p -i q The harmonic current on the grid side is detected in the dq coordinate system. and reactive current i lq Specifically, the power grid u at time k is firstly calibrated by a phase-locked loop (PLL). s (k) phase lock, get the grid angle θ. For the load current i at time k l (k) After sampling, perform CLARK transformation to obtain the value i of the load current in the αβ coordinate system lα and i lβ , and then perform PARK transformation to obtain the value of the load current in the dq coordinate system and i lq , load current of d axis The value after subtracting its low-pass filter is the harmonic current In order to stabilize the DC side voltage of STATCOM, the voltage is set to V * dc The actual voltage value V on the DC side at time k dc (k) Make a comparison and obtain the active compensation value P through the PI regulator loss Add to harmonic current On, we get the active current i ld . The active current i ld and reactive current i lq After the inverse PARK transformation, the reference current given value of M2PC in the αβ coordinate system is obtained: and

[0115] The STATCOM control process based on M2PC is as follows: Figure 7 First, measure the three-phase grid voltage u at time k s (k), STATCOM current i c (k) and DC side voltage V dc (k), and input a given reference current and Then, according to the basic principle of M2PC described above, traverse the six sectors and calculate the cost function g of each sector sx , and the duty cycle d of two adjacent effective vectors and zero vector 1x , d 2x , d 0x , the optimal sector x is obtained by minimizing the cost function _opt The duty cycle d of the three best vectors corresponding to the sector 1_opt , d 2_opt , d 0_opt Finally, the switching pulses are allocated according to the SVM method. Figure 7 g_opt is the cost function g after traversing 6 sectors. sx The minimum value of .

[0116] When the optimal sector is sector 1 (i _opt =1), the relationship between duty cycle and switch state is as follows Figure 8 As shown. Defined in one switching cycle T, t1 is the first effective vector action time, t2 is the second effective vector action time, and t0 is the zero vector action time:

[0117]

[0118] The same is true for other sectors. According to the SVM seven-segment pulse allocation method, the switching state of each sector can be obtained. Each switching state will only be turned on or off once in a switching cycle T, so a fixed switching frequency can be achieved.

[0119] Specifically, in order to demonstrate the effectiveness of this scheme, a two-level STATCOM simulation model was built in Matlab / Simulink. Uncontrolled rectifier diodes were used as nonlinear loads to simulate the nonlinear loads in the coal mine power grid. At the same time, reactive power was injected into the load side. The simulation parameters are shown in Table 2.

[0120] Table 2

[0121] Parameter name Numeric <![CDATA[Grid voltage u s (line)]]> 380V Filter inductor L 2mH Filter resistor R 0.1Ω <![CDATA[DC side voltage V dc > 600V <![CDATA[DC-side capacitor C dc > 2200μF <![CDATA[Sampling frequency f s > 20kHz <![CDATA[Switching frequency f w > 10kHz <![CDATA[Load-side resistor R l > 20Ω

[0122] Specifically, Fig. 9 , Fig.10 , Fig.11 and Fig.12They are the grid voltage u before and after STATCOM is put into operation at 0.5 seconds. a ,u b ,u c , grid side current i a ,i b ,i c , load current i la ,i lb ,i lc and STATCOM current i ca ,i cb ,i cc Waveform diagram. Fig.10 It can be seen that before STATCOM is put into use, the grid-side current is seriously distorted by the load current. After STATCOM is put into use, the grid-side current presents a sinusoidal waveform due to the injection of a current opposite to the harmonic current. At the same time, before and after STATCOM is put into use, the grid-side voltage and load current remain unchanged.

[0123] Specifically, Fig.13 and Fig.14 This is the harmonic analysis diagram of the grid-side current before and after the STATCOM is put into use. It can be seen that before the STATCOM is put into use, the grid-side current THD is 17.75%, and after the STATCOM is put into use, the grid-side current drops to 4.77%, which greatly reduces the grid-side current harmonics and THD and improves the power quality.

[0124] Specifically, Fig.15 The waveform diagram of the active power P and reactive power Q on the grid side before and after the STATCOM is put into operation is shown in Figure 2. Fig.15 It can be seen that before STATCOM was put into use, there was a large amount of reactive power in the system, and the reactive power fluctuated between 0 and 10 kvar. After STATCOM was put into use, the reactive power on the grid side was compensated by STATCOM and instantly maintained at around 0 kvar. At the same time, after STATCOM was put into use, the active power remained basically unchanged and became more stable from constant fluctuations.

[0125] Specifically, Fig.16 The DC voltage waveform after STATCOM is put into operation is shown in Figure 1. Fig.16 It can be seen that the DC side voltage V dc It fluctuates slightly above and below the given value and basically stabilizes near the given value.

[0126] In addition, in addition to the above solutions, the present application also provides the following implementation plans.

[0127] To locate the harmonic source, you first need to use a harmonic detection instrument to detect the current in the coal mine power grid to obtain the waveform and spectrum information of the harmonic current. Use a harmonic analysis instrument to analyze the obtained harmonic current waveform and spectrum information to determine the frequency, amplitude, phase and other parameters of the harmonics. According to the results of the harmonic analysis, the harmonic source can be located by calculating the path and mode of propagation of the harmonic current in the power grid and using a positioning algorithm. Commonly used positioning algorithms include time-frequency analysis, adaptive filtering, beam imaging, etc. These algorithms can determine the location of the harmonic source based on the propagation characteristics of the harmonic current in the power grid.

[0128] For example, the frequency of harmonic current detected in the coal mine power grid is 50Hz, the amplitude is 2A, and the phase is 0°. After harmonic analysis and positioning algorithm processing, it is determined that the harmonic source is located at transformer T1 near the main substation of the coal mine. By inspecting and optimizing transformer T1, the generation and propagation of harmonic current can be effectively reduced, and the stability and reliability of the power grid can be improved.

[0129] Harmonic current refers to the harmonic current in the power system whose frequency is an integer multiple of the fundamental frequency. Its waveform is usually not a sine waveform, but a complex waveform containing multiple frequency components.

[0130] The waveform information of the harmonic current includes one or more of: amplitude and phase information of different harmonic frequencies, periodic characteristics of the harmonic waveform, and a relative phase relationship between the harmonic waveform and the fundamental waveform.

[0131] The spectrum information of the harmonic current includes: one or more of the amplitude of the harmonic components of different harmonic frequencies, the ratio of the harmonic frequency to the fundamental frequency, the distribution of the harmonic frequency, and the relative strength of the harmonic frequency.

[0132] Specifically, the waveform of the harmonic current can be drawn to determine the periodicity and variation of the waveform. By determining the peak and valley values ​​of the waveform, the amplitude of the harmonic can be preliminarily estimated. Using the spectrum analysis method, the spectrum of the harmonic current is drawn. The position of the harmonic frequency in the spectrum is determined, and the value of each harmonic frequency is calculated. According to the spectrum of the harmonic current, the amplitude value corresponding to each harmonic frequency can be directly read. It can also be calculated by mathematical methods such as Fourier transform. By comparing the waveforms of different harmonic frequencies, the phase difference between the harmonics can be determined. According to the phase information of the waveform, the phase of each harmonic can be calculated.

[0133] Specifically, the topological structure of the power grid is obtained, including the connection relationship between each power supply, load and transmission line, as well as the harmonic sources and harmonic loads that may exist in the power grid. For the transmission lines in the power grid, it is necessary to calculate its impedance, inductance and capacitance and other parameters in order to analyze the propagation mode of harmonic currents in the transmission lines. Determine the frequency of the harmonics according to the actual situation. Generally, the harmonic frequency is an integer multiple of 50Hz, such as the second harmonic is 100Hz. Determine the amplitude and phase of the harmonic current according to the actual measurement data or simulation calculation results. According to the amplitude and phase of the harmonic current, the topological structure of the power grid and the parameters of the transmission line, the propagation path and mode of the harmonic current in the power grid are determined through simulation calculation or measured data analysis, including the reflection, transmission and coupling of the transmission line.

[0134] For example, in a simple power grid, there is a harmonic current with a second harmonic frequency of 100Hz, an amplitude of 10A, and a phase of 30 degrees. The power grid includes a generator, a transmission line, and a load. The parameters of the transmission line are impedance of 0.1Ω, inductance of 0.01H, and capacitance of 0.001F. According to the above steps, the propagation mode of the harmonic current in the transmission line can be calculated, including reflection, transmission, and coupling.

[0135] For harmonic control, we can analyze the harmonic situation in the coal mine power grid and understand the distribution of harmonic frequency and amplitude; design the control strategy of STATCOM, including harmonic detection, current injection, etc.; connect STATCOM to the coal mine power grid and eliminate harmonics through current injection, voltage regulation and other functions; debug the parameters of STATCOM so that it can effectively eliminate harmonics in the coal mine power grid.

[0136] For example, there is a 50Hz fundamental voltage and 5th and 7th harmonic voltages in the coal mine power grid, and the 5th harmonic amplitude is 10% of the fundamental voltage, and the 7th harmonic amplitude is 5% of the fundamental voltage. A STATCOM is designed to eliminate these harmonics, and the control strategy is current injection.

[0137] First, through harmonic detection, STATCOM detects the harmonics of 50Hz, 250Hz and 350Hz, and performs phase adjustment and current injection respectively. It is assumed that the current injection of STATCOM can eliminate 1% of the 50Hz fundamental voltage, 8% of the 5th harmonic voltage, and 4% of the 7th harmonic voltage.

[0138] Next, the STATCOM was connected to the coal mine power grid and its parameters were debugged to effectively eliminate harmonics. After debugging, the STATCOM successfully eliminated the 50Hz fundamental voltage, the 5th and 7th harmonic voltages, making the voltage in the coal mine power grid more stable and clear.

[0139] Specifically, a power quality analyzer or a digital oscilloscope can be used to measure the voltage and current waveforms in the power grid. The measured voltage and current waveforms are Fourier transformed to obtain harmonic components in the frequency domain. Based on the obtained harmonic components, the frequency and amplitude distribution of the harmonics are determined.

[0140] Perform Fourier transform on the original signal to get the spectrum of the signal. The spectrum can show all the frequency components contained in the signal. Find the frequency corresponding to the harmonic component in the spectrum, which can be obtained through the spectrum diagram or calculation. Based on the spectrum of the original signal and the frequency of the harmonic component, the frequency and amplitude of each harmonic component can be determined. It can be calculated through the coefficients of Fourier transform.

[0141] For example, the original signal is a sine wave signal with a fundamental frequency of 50 Hz, and its spectrum is as follows:

[0142] The fundamental frequency is 50Hz and the amplitude is 1;

[0143] The first harmonic frequency is 100 Hz and the amplitude is 0.5;

[0144] The second harmonic frequency is 150 Hz and the amplitude is 0.3;

[0145] According to the above steps, the frequency and amplitude distribution of harmonics can be determined. In this example, the frequency of the first harmonic is 100 Hz and the amplitude is 0.5; the frequency of the second harmonic is 150 Hz and the amplitude is 0.3.

[0146] Specifically, the control parameters of STATCOM can be set according to the harmonic characteristics and system requirements, including the voltage control link, the current control link and the harmonic filter parameters.

[0147] First, obtain the system requirements, including reactive power compensation capacity, harmonic filtering requirements, etc. According to the system voltage waveform requirements, determine the parameters of the voltage control link, including proportional gain, integral time constant, etc. According to the system current waveform requirements, determine the parameters of the current control link, including proportional gain, integral time constant, etc. According to the system harmonic filtering requirements, determine the parameters of the harmonic filter, including the filter order, cutoff frequency, etc. The current control link and harmonic filter parameters are jointly debugged to ensure that STATCOM can meet the system requirements.

[0148] For example, a system requires STATCOM for reactive power compensation, and requires that the voltage waveform does not change by more than 5%, the current waveform does not change by more than 10%, and the harmonic content does not exceed 5%. According to the system requirements, the proportional gain of the voltage control link can be set to 0.1, the integral time constant to 0.01, the proportional gain of the current control link to 0.05, the integral time constant to 0.03, the order of the harmonic filter to 2, and the cutoff frequency to 50Hz. Through joint debugging, it can be verified whether STATCOM can meet the system requirements. If not, the control parameters can be adjusted until the requirements are met.

[0149] This solution can also adjust the on-time of STATCOM, and calculate the current value that STATCOM needs to compensate according to the frequency and amplitude of the harmonics. Adjust the controller of STATCOM to make it output the corresponding current to offset the harmonic current in the power grid. Monitor the output current of STATCOM, and adjust the on-time of STATCOM switch according to the actual situation to achieve the best harmonic suppression effect.

[0150] For example, there are harmonics with a frequency of 50Hz and an amplitude of 10A in the coal mine power grid. After analysis and calculation, it is determined that STATCOM needs to output a current of 10A to offset the harmonic current. In actual operation, it is found that the output current of STATCOM can effectively suppress harmonics when the opening time is 1 second. Therefore, the controller of STATCOM is adjusted to open for 1 second in each cycle to achieve harmonic suppression.

[0151] The embodiment of the present application also provides a device for managing the power quality of a coal mine power grid. It should be noted that the device for managing the power quality of a coal mine power grid in the embodiment of the present application can be used to execute the method for managing the power quality of a coal mine power grid provided in the embodiment of the present application. The device is used to implement the above-mentioned embodiments and preferred implementation modes, and those that have been described will not be repeated. As used below, the term "module" can implement a combination of software and / or hardware for a predetermined function. Although the device described in the following embodiments is preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceivable.

[0152] The following introduces the power quality management device of the coal mine power grid provided in the embodiment of the present application.

[0153] Fig.17 1 is a structural block diagram of a device for managing the power quality of a coal mine power grid according to an embodiment of the present application. Fig.17 As shown, the device comprises:

[0154] A first acquisition unit 10 is used to acquire current information of a coal mine power grid, wherein the current information is information of current generated by the operation of a load in the coal mine power grid, and the current corresponding to the current information at least includes harmonic current;

[0155] A second acquisition unit 20 is used to acquire a switching pulse frequency, wherein the switching pulse frequency is a frequency at which a switch of the STATCOM switches between on and off, and the current information corresponds to the switching pulse frequency in a one-to-one manner;

[0156] The governance unit 30 is used to control the STATCOM to emit a compensation current according to the switching pulse frequency to offset the harmonic current in the current corresponding to the current information.

[0157] Through this embodiment, during the operation of the coal mine power grid, STATCOM is added to eliminate the harmonics in the coal mine power grid, and the switching frequency of the on-time and off-time of the IGBT switch of the STATCOM is predefined in this solution, so that a fixed switching frequency can be achieved, thereby greatly reducing the total harmonic distortion rate of the coal mine underground grid side current and effectively compensating for the grid side reactive power, thereby improving the power quality of the coal mine underground grid.

[0158] In order to reduce the difficulty of subsequent calculations, remove the noise part in the current value, and extract the harmonic current in the current, the above-mentioned current information also includes the three-phase current value of the above-mentioned load, and the above-mentioned device also includes a first conversion unit, a second conversion unit, a filtering unit and a first calculation unit. The first conversion unit is used to perform a CLARK transformation on the above-mentioned three-phase current value of the above-mentioned load after obtaining the current information of the coal mine power grid, so as to obtain the first load current value of the αβ coordinate system; the second conversion unit is used to perform a PARK transformation on the above-mentioned first load current value, so as to obtain the second load current value of the dq coordinate system; the filtering unit is used to perform a low-pass filtering on the above-mentioned second load current value, so as to obtain the fundamental part current value; the first calculation unit is used to calculate the difference between the above-mentioned second load current value and the above-mentioned fundamental part current value, so as to obtain the harmonic current value.

[0159] In this scheme, through CLARK transformation, three-phase current can be converted into two-phase current, reducing the complexity of calculation. In the αβ coordinate system, the change of current can be clearer. Through PARK transformation, the control of current is directly related to the rotor position and speed of the motor, thereby realizing direct control of the motor torque and speed, further reducing the complexity of calculation. Through low-pass filtering, the noise and interference in the current can be removed to obtain the normal current, that is, the current value of the fundamental part, and then the total current value, that is, the second load current value, is subtracted from the current value of the fundamental part to extract a more accurate harmonic current value.

[0160] In order to further ensure the high control accuracy of the present scheme and further improve the power quality of the coal mine power grid, the above-mentioned device also includes a second calculation unit, a third calculation unit and a third conversion unit. The second calculation unit is used to calculate the difference between the second load current value and the fundamental current value to obtain the harmonic current value, and then use the PI regulator to calculate the difference between the reference voltage value and the actual voltage value to obtain the control deviation; the third calculation unit is used to calculate the sum of the control deviation and the harmonic current value to obtain the active current value; the third conversion unit is used to perform an inverse PARK transformation on the active current value and the reactive current value to obtain the reference current value of the αβ coordinate system, wherein the reference current value is used to allocate the initial given value of the switching pulse frequency.

[0161] In this scheme, the PI regulator can calculate the difference between the reference voltage value and the actual voltage value. This difference can reflect the gap between the current state and the expected state. The control deviation is added to the harmonic current value so that these harmonic components can be taken into account when calculating the active current, thereby more accurately reflecting the current demand. The reference current value of the αβ coordinate system can be obtained through the inverse PARK transformation, which can be directly used for the subsequent control of the switching operation of the STATCOM to generate the required current waveform. The use of the inverse PARK transformation to convert the control quantity back to the actual available coordinate system can improve the control accuracy, so as to achieve subsequent precise control of the current and further improve the power quality of the coal mine power grid.

[0162] In the specific implementation process, the second acquisition unit includes an acquisition module, a first determination module and a second determination module, the acquisition module is used to acquire a vector, wherein the above-mentioned vector is the vector of the switch of the above-mentioned STATCOM; the first determination module is used to determine the duty cycle according to the size of the cost function of the above-mentioned vector, wherein the above-mentioned cost function and the above-mentioned duty cycle are negatively correlated, and the above-mentioned duty cycle is the ratio of the switch conduction time of the above-mentioned STATCOM to the total time or the ratio of the switch off time of the above-mentioned STATCOM to the total time; the second determination module is used to determine the above-mentioned switch pulse frequency according to the above-mentioned duty cycle, wherein the above-mentioned duty cycle and the above-mentioned switch pulse frequency correspond one to one.

[0163] In this scheme, the vector of the STATCOM switch represents the different states of the switch. By calculating the cost function value of each vector and selecting the smallest vector, the time ratio that the switch should remain on or off, that is, the duty cycle, can be determined. When the duty cycle has been determined, the corresponding switching pulse frequency can be generated according to the duty cycle. By precisely controlling the switch state, accurate compensation for the reactive power of the power grid can be achieved, thereby further improving the voltage quality of the power grid.

[0164] In a specific implementation process, the device further includes a fourth calculation unit, which is used to calculate the current prediction value at time k+1 according to the power prediction formula after obtaining the vector, wherein the power prediction formula is:

[0165]

[0166] represents the predicted current value at time k+1, R represents the resistance value, T s represents the sampling period, L represents the inductance value, i c (k) represents the current value at time k, v x represents the switching vector, u s (k) The voltage value of the coal mine power grid. The above formula is only exemplary, and any variation of the formula falls within the protection scope of this application.

[0167] In this solution, it can be determined through the above power prediction formula that the current values ​​at the previous moment and the next moment are related, so a more accurate prediction value of the current at the next moment can be obtained through the above formula of this solution.

[0168] In some embodiments, the apparatus further includes a third acquisition unit, which is used to acquire the cost function of the vector before determining the duty cycle according to the size of the cost function of the vector, wherein the cost function is:

[0169]

[0170] g0 represents the first cost function corresponding to the zero vector, g1 represents the second cost function corresponding to the first effective vector, and g2 represents the third cost function corresponding to the second effective vector. represents the first reference current value of the αβ coordinate system, represents the second reference current value of the above αβ coordinate system, and They represent the current values ​​at time k+1 of the αβ coordinate system under the action of the zero vector, and respectively represent the current values ​​at time k+1 of the αβ coordinate system under the action of the first effective vector, and They respectively represent the current value at time k+1 of the αβ coordinate system under the action of the second effective vector.

[0171] In this scheme, the cost value corresponding to each vector can be calculated by the above expression. The cost function can be used to evaluate the impact of the switching state of different switching vectors on the power grid, and then the subsequent duty cycle can be further accurately determined based on this impact.

[0172] In some embodiments, the first determination module includes a calculation module, and the calculation module is used to calculate the duty cycle according to a duty cycle formula, wherein the duty cycle formula is:

[0173]

[0174] d0 represents the first duty cycle corresponding to the zero vector, d1 represents the second duty cycle corresponding to the first effective vector, and d2 represents the third duty cycle corresponding to the second effective vector.

[0175] In this scheme, the smaller the cost function of the vector is, the more precise the control using the vector is. Therefore, in order to maximize the control accuracy, the smaller the cost function is, the larger the duty cycle corresponding to the vector is. Therefore, the duty cycle formula of this scheme can further accurately determine the duty cycle corresponding to each vector.

[0176] The above-mentioned coal mine power grid power quality management device includes a processor and a memory, and the above-mentioned first acquisition unit, the second acquisition unit and the management unit are all stored in the memory as program units, and the processor executes the above-mentioned program units stored in the memory to realize the corresponding functions. The above-mentioned modules are all located in the same processor; or, the above-mentioned modules are located in different processors in the form of any combination.

[0177] The processor includes a kernel, which retrieves the corresponding program unit from the memory. One or more kernels can be set to adjust kernel parameters to solve the problem of a large number of current harmonics in the coal mine power grid in the prior art, which causes safety hazards to other equipment in the power grid.

[0178] The memory may include non-permanent memory in a computer-readable medium, random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM, and the memory includes at least one memory chip.

[0179] An embodiment of the present invention provides a computer-readable storage medium, which includes a stored program, wherein when the program is running, the device where the computer-readable storage medium is located is controlled to execute the method for managing the power quality of the coal mine power grid.

[0180] An embodiment of the present invention provides a processor, which is used to run a program, wherein the method for managing the power quality of the coal mine power grid is executed when the program is run.

[0181] The embodiment of the present invention provides a device, which includes a processor, a memory, and a program stored in the memory and can be run on the processor, and when the processor executes the program, at least one step of the method for managing the power quality of the coal mine power grid is implemented. The device in this article can be a server, a PC, a PAD, a mobile phone, etc.

[0182] A computer program product includes a non-volatile computer-readable storage medium, wherein the non-volatile computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the method for controlling the power quality of the coal mine power grid in each embodiment of the present application are implemented.

[0183] The present application also provides a coal mine power grid power management system, comprising one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the above-mentioned memory and are configured to be executed by the above-mentioned one or more processors, and the above-mentioned one or more programs include methods for executing any one of the above-mentioned coal mine power grid power quality management methods.

[0184] Obviously, those skilled in the art should understand that the above modules or steps of the present invention can be implemented by a general computing device, they can be concentrated on a single computing device, or distributed on a network composed of multiple computing devices, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, and in some cases, the steps shown or described can be executed in a different order than here, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. Thus, the present invention is not limited to any specific combination of hardware and software.

[0185] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0186] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0187] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0188] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0189] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0190] The memory may include non-permanent memory in a computer-readable medium, random access memory (RAM) and / or non-volatile memory in the form of read-only memory (ROM) or flash RAM. The memory is an example of a computer-readable medium.

[0191] Computer readable media include permanent and non-permanent, removable and non-removable media that can be implemented by any method or technology to store information. 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 technology, compact disk read-only memory (CD-ROM), digital versatile disk (DVD) or other optical storage, magnetic cassettes, magnetic disk storage or other magnetic storage devices or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined herein, computer readable media does not include temporary computer readable media (transitory media), such as modulated data signals and carrier waves.

[0192] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0193] From the above description, it can be seen that the above embodiments of the present application achieve the following technical effects:

[0194] 1) The method for controlling the power quality of the coal mine power grid of the present application adds STATCOM to eliminate harmonics in the coal mine power grid during its operation. In addition, the switching frequency of the on-time and off-time of the IGBT switch of the STATCOM is predefined in this scheme, so that a fixed switching frequency can be achieved, thereby significantly reducing the total harmonic distortion rate of the current on the grid side of the coal mine underground and effectively compensating for the reactive power on the grid side, thereby improving the power quality of the coal mine underground power grid.

[0195] 2) The power quality management device of the coal mine power grid of the present application adds STATCOM to eliminate harmonics in the coal mine power grid during its operation. In addition, the switching frequency of the on-time and off-time of the IGBT switch of the STATCOM is predefined in this solution, so as to achieve a fixed switching frequency, thereby significantly reducing the total harmonic distortion rate of the current on the grid side of the coal mine and effectively compensating for the reactive power on the grid side, thereby improving the power quality of the coal mine grid.

[0196] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for improving the power quality of a coal mine power grid, characterized in that: include: Acquire current information of a coal mine power grid, wherein the current information is information of current generated by the operation of a load in the coal mine power grid, and the current corresponding to the current information at least includes harmonic current; Acquire a switching pulse frequency, wherein the switching pulse frequency is a frequency at which a switch of the STATCOM switches between on and off, and the current information corresponds to the switching pulse frequency one by one; The STATCOM is controlled to emit a compensation current according to the switching pulse frequency to offset the harmonic current in the current corresponding to the current information.

2. The method according to claim 1, characterized in that The current information also includes the three-phase current value of the load. After acquiring the current information of the coal mine power grid, the method further includes: Performing a CLARK transformation on the three-phase current value of the load to obtain a first load current value of an αβ coordinate system; Performing a PARK transformation on the first load current value to obtain a second load current value in a dq coordinate system; Performing low-pass filtering on the second load current value to obtain a fundamental wave current value; The difference between the second load current value and the fundamental wave current value is calculated to obtain a harmonic current value.

3. The method according to claim 2, characterized in that After calculating the difference between the second load current value and the fundamental wave current value to obtain the harmonic current value, the method further includes: The PI regulator is used to calculate the difference between the reference voltage value and the actual voltage value to obtain the control deviation; Calculating the sum of the control deviation and the harmonic current value to obtain an active current value; The active current value and the reactive current value are subjected to an inverse PARK transformation to obtain a reference current value of the αβ coordinate system, wherein the reference current value is used to allocate an initial given value of the switching pulse frequency.

4. The method according to claim 1, characterized in that: Get the switching pulse frequency, including: Acquire a vector, wherein the vector is a vector of a switch of the STATCOM; Determine a duty cycle according to the size of the cost function of the vector, wherein the cost function and the duty cycle are negatively correlated, and the duty cycle is the ratio of the switch-on time of the STATCOM to the total time or the ratio of the switch-off time of the STATCOM to the total time; The switching pulse frequency is determined according to the duty cycle, wherein the duty cycle and the switching pulse frequency correspond one to one.

5. The method according to claim 4, characterized in that After obtaining the vector, the method further includes: According to the power prediction formula, the current prediction value at time k+1 is calculated, where the power prediction formula is: represents the predicted current value at time k+1, R represents the resistance value, T s represents the sampling period, L represents the inductance value, i c (k) represents the current value at time k, v x represents the switching vector, u s (k) The voltage value of the coal mine power grid.

6. The method according to claim 4, characterized in that Before determining the duty cycle according to the size of the cost function of the vector, the method further includes: Obtain the cost function of the vector, wherein the cost function is: g0 represents the first cost function corresponding to the zero vector, g1 represents the second cost function corresponding to the first effective vector, and g2 represents the third cost function corresponding to the second effective vector. represents the first reference current value of the αβ coordinate system, represents the second reference current value of the αβ coordinate system, and They respectively represent the current values ​​at time k+1 of the αβ coordinate system under the action of the zero vector, and respectively represent the current values ​​at time k+1 of the αβ coordinate system under the action of the first effective vector, and They respectively represent the current value at time k+1 of the αβ coordinate system under the action of the second effective vector.

7. The method according to claim 6, characterized in that Determining a duty cycle according to the size of the cost function of the vector includes: The duty cycle is calculated according to a duty cycle formula, wherein the duty cycle formula is: d0 represents a first duty cycle corresponding to the zero vector, d1 represents a second duty cycle corresponding to the first effective vector, and d2 represents a third duty cycle corresponding to the second effective vector.

8. A device for controlling the power quality of a coal mine power grid, characterized in that: include: A first acquisition unit is used to acquire current information of a coal mine power grid, wherein the current information is information of current generated by the operation of a load in the coal mine power grid, and the current corresponding to the current information at least includes harmonic current; A second acquisition unit is used to acquire a switching pulse frequency, wherein the switching pulse frequency is a frequency at which a switch of the STATCOM switches between on and off, and the current information corresponds to the switching pulse frequency in a one-to-one manner; The governance unit is used to control the STATCOM to emit a compensation current according to the switching pulse frequency to offset the harmonic current in the current corresponding to the current information.

9. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method for controlling the power quality of a coal mine power grid as described in any one of claims 1 to 7 are implemented.

10. A coal mine power grid power management system, characterized in that: include: One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and are configured to be executed by the one or more processors, and the one or more programs include a method for controlling the power quality of a coal mine power grid as described in any one of claims 1 to 7.

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