Solid-state on-load automatic voltage regulation circuit of mining medium-voltage power supply system and control method

Abstract

The invention discloses a solid-state on-load automatic voltage regulation circuit of a mining medium-voltage power supply system and a control method, and relates to the technical field of power supply systems. The circuit comprises a control module, a rectification module, a DC module, an inversion module, a filtering module, a compensation transformer, a rectification switch and a bypass switch. According to the application condition of the circuit, when power is supplied through the solid-state on-load automatic voltage regulation circuit, the bypass switch is switched off, and the rectification switch is switched on; when power is directly supplied through the mobile substation, the bypass switch is closed, and the rectification switch is opened. Under the condition of uninterruptible power supply, continuous and automatic adjustment can be carried out according to the requirement of the motor at the tail end of the line on voltage, and the voltage is kept basically stable.

Description

Technical Field

[0001] This invention relates to the field of power supply system technology, and in particular to a solid-state on-load automatic voltage regulation circuit and control method for a medium-voltage power supply system for mining. Background Technology

[0002] In recent years, with the increase in coal mine production capacity, mining depth and breadth, and the continuous expansion of roadway networks, the power supply distance to underground mining faces has been continuously extended. The distance between electrical equipment and the power distribution point at the working face is getting farther and farther. The increase in power supply distance and installed capacity has led to a significant increase in voltage loss caused by load current on the lines. Coupled with the harsh working face environment, large load variations of mining equipment, significant voltage fluctuations in power supply lines, and high harmonic content, power quality has deteriorated, seriously affecting the normal start-up and operation of electric machinery at the end of the line. On the one hand, this causes difficulties in starting motors, reduced output torque, and under low voltage conditions, motors may overheat or even burn out, seriously affecting production and even threatening personal safety. On the other hand, during light loads, no-load periods, and maintenance of power distribution points and roadways, voltage increases due to reduced load and cable capacitance effects can endanger system insulation and create new safety hazards. Summary of the Invention

[0003] The purpose of this invention is to provide a solid-state on-load automatic voltage regulation circuit and control method for a medium-voltage power supply system in mining, aiming to solve or improve at least one of the above-mentioned technical problems. The solution of this invention is as follows:

[0004] A solid-state on-load automatic voltage regulation circuit for a medium-voltage power supply system in a mine includes: a control module, a rectifier module, a DC module, an inverter module, a filter module, a compensation transformer, a rectifier switch, and a bypass switch;

[0005] One end of the rectifier switch is connected to the secondary output terminal of the mobile substation, and the other end is connected to the rectifier module; the rectifier module, the DC module, the inverter module, the filter module, and the compensation transformer are connected in sequence; the bypass switch is installed on the cable line; the control module is connected to the rectifier module, the DC module, and the inverter module respectively;

[0006] The rectifier switch is used to draw three-phase power from the secondary side of the mobile substation to obtain a 3.3kV line voltage; the rectifier module is used to perform three-phase rectification according to the PWM rectification control signal; the DC module is used to supply power to the inverter module according to the charge and discharge control signal; the inverter module is used to perform three-phase inversion according to the PWM inverter control signal; the filter module is used to output a sinusoidal AC voltage and connect it in series to the cable line through the secondary winding of the compensation transformer; the control module is used to generate PWM rectification control signal, charge and discharge control signal, and PWM inverter control signal according to the voltage regulation strategy; the voltage regulation strategy includes a segmented automatic voltage regulation control strategy, a phase tracking control strategy, a dual closed-loop rectification control strategy, and an inverter control strategy based on a voltage drop model;

[0007] Depending on the circuit application, when powered by a solid-state on-load automatic voltage regulating circuit, the bypass switch is disconnected and the rectifier switch is closed; when powered directly by a mobile substation, the bypass switch is closed and the rectifier switch is disconnected.

[0008] This invention also provides a control method for a solid-state on-load automatic voltage regulation circuit in a mining medium-voltage power supply system, applied to the circuit described above, comprising:

[0009] Collect the voltage at the beginning of the cable line and the line current, and evaluate and calculate the voltage at the end;

[0010] Based on the evaluation calculation results, the load operation stage is determined according to the segmented automatic voltage regulation control strategy, thereby adjusting the terminal voltage reference value to the set value of the corresponding stage and generating a charging and discharging control signal.

[0011] A phase tracking control strategy is used to lock the grid voltage and current, and the phase arc is transmitted to the rectifier module and the inverter module. During the execution of the dual closed-loop rectifier control strategy and the inverter control strategy based on the voltage drop model, the amplitude and phase of the compensation voltage are controlled, thereby stabilizing the amplitude and phase of the voltage at the end of the line to the set value. The dual closed-loop rectifier control strategy is used to output the PWM rectifier control signal; the inverter control strategy based on the voltage drop model is used to output the PWM inverter control signal.

[0012] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0013] This invention discloses a solid-state on-load automatic voltage regulation circuit and control method for a medium-voltage power supply system in mining. The circuit includes a control module, a rectifier module, a DC module, an inverter module, a filter module, a compensation transformer, a rectifier switch, and a bypass switch. Depending on the application, when power is supplied through the solid-state on-load automatic voltage regulation circuit, the bypass switch is disconnected and the rectifier switch is closed; when power is supplied directly through a mobile substation, the bypass switch is closed and the rectifier switch is disconnected. This invention can continuously and automatically adjust the voltage according to the voltage requirements of the motor at the end of the line, maintaining a basically stable voltage under uninterrupted power supply conditions. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the topology of the 3.3kV solid-state voltage regulator (SSVR) for mining in this embodiment;

[0016] Figure 2 This is a schematic diagram of the SSVR rectifier module in this embodiment;

[0017] Figure 3 This is a schematic diagram of the SSVR inverter module in this embodiment;

[0018] Figure 4 This is a schematic diagram of the LCL filter circuit in this embodiment;

[0019] Figure 5 This is a schematic diagram of the compensation transformer in this embodiment;

[0020] Figure 6 This is a schematic diagram of the equivalent circuit of the 3.3kV long-distance power supply system in the coal mine in this embodiment;

[0021] Figure 7 This is a schematic diagram of the PLL control model in this embodiment;

[0022] Figure 8 This is the PLL phase tracking diagram in this embodiment;

[0023] Figure 9 This is a diagram showing the input and output structure of the rectifier module in this embodiment;

[0024] Figure 10 This is a schematic diagram of the rectifier module current control loop (inner loop) in this embodiment;

[0025] Figure 11This is a schematic diagram of the voltage control loop (outer loop) of the rectifier module in this embodiment;

[0026] Figure 12 This is a schematic diagram of the dual closed-loop rectification control strategy in this embodiment;

[0027] Figure 13 This is a diagram showing the actual structure of the rectifier module's inner current loop in this embodiment;

[0028] Figure 14 This is a diagram showing the actual structure of the outer voltage loop of the rectifier module in this embodiment;

[0029] Figure 15 This is the decoupling control diagram of the inverter module current loop in this embodiment;

[0030] Figure 16 This is the phasor diagram of SSVR voltage in-phase compensation in this embodiment; where (a) is the normal in-phase compensation case; and (b) is the case of insufficient in-phase compensation capacity.

[0031] Figure 17 This is the phasor diagram of the SSVR voltage fully compensated in this embodiment; where (a) represents the normal fully compensated condition; and (b) represents the condition of insufficient fully compensated capacity.

[0032] Figure 18 This is a phasor diagram of the SSVR critical state and voltage anti-phase compensation in this embodiment; where (a) is the buck-boost critical state; and (b) is the anti-phase voltage compensation state.

[0033] Figure 19 This is a schematic diagram of the voltage control loop (outer loop) based on the voltage drop model in this embodiment;

[0034] Figure 20 This is a schematic diagram of the inverter control strategy based on the voltage loss model in this embodiment. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] The purpose of this invention is to provide a solid-state on-load automatic voltage regulation circuit and control method for a medium-voltage power supply system for mining, aiming to solve or improve at least one of the above-mentioned technical problems.

[0037] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] like Figure 1 As shown, the present invention provides a solid-state on-load automatic voltage regulation circuit for a medium-voltage power supply system in a mine, including: a control module, a rectifier module, a DC module, an inverter module, a filter module, a compensation transformer, a rectifier switch, and a bypass switch.

[0039] One end of the rectifier switch is connected to the secondary output terminal of the mobile substation, and the other end is connected to the rectifier module; the rectifier module, the DC module, the inverter module, the filter module, and the compensation transformer are connected in sequence; the bypass switch is installed on the cable line; the control module is connected to the rectifier module, the DC module, and the inverter module respectively.

[0040] The rectifier switch is used to draw three-phase power from the secondary side of the mobile substation to obtain a 3.3kV line voltage; the rectifier module is used to perform three-phase rectification according to the PWM rectification control signal; the DC module is used to supply power to the inverter module according to the charge and discharge control signal; the inverter module is used to perform three-phase inversion according to the PWM inverter control signal; the filter module is used to output a sinusoidal AC voltage and connect it in series to the cable line through the secondary winding of the compensation transformer; the control module is used to generate PWM rectification control signal, charge and discharge control signal and PWM inverter control signal according to the voltage regulation strategy; the voltage regulation strategy includes a segmented automatic voltage regulation control strategy, a phase tracking control strategy, a dual closed-loop rectification control strategy and an inverter control strategy based on a voltage drop model.

[0041] Depending on the circuit application, when powered by a solid-state on-load automatic voltage regulating circuit, the bypass switch is disconnected and the rectifier switch is closed; when powered directly by a mobile substation, the bypass switch is closed and the rectifier switch is disconnected.

[0042] As a specific implementation, this circuit is a solid-state voltage regulator (SSVR). The topology is based on the principle of "parallel voltage regulation and series compensation." It is installed at the secondary side outlet of the mobile substation, i.e., the beginning of the power supply line. The input side of the SSVR draws three-phase power from the secondary side of the mobile substation via a rectifier switch. This side is connected in parallel with the line, with a line voltage of 3.3kV. After passing through a three-phase rectifier module, a stable DC voltage is obtained across the DC capacitor. The DC module includes a DC capacitor, a buffer resistor branch, and a bleeder resistor branch. The buffer resistor branch is used to slow down the pre-charging process of the DC capacitor during SSVR startup, preventing excessive inrush current in a short time. The bleeder resistor branch is used for... When the SSVR is shut down, it releases the residual charge on the DC capacitor, which provides a stable DC voltage to the three-phase inverter module. The control module generates a PWM wave according to a control strategy to control the switching of the rectifier and inverter module IGBTs. The inverter module outputs a sinusoidal AC voltage through a filter module, which is then connected in series to the power supply line via the secondary winding of a compensation transformer. This allows the adjustable voltage (both amplitude and phase adjustable) obtained from the inverter filter to be supplied to the power supply line in series. The compensated voltage is then superimposed with a positive or negative adjustment voltage to increase or decrease the supply voltage. This ensures that the voltage at the end of the line remains stable around the rated value while preventing excessive voltage from threatening the system insulation. When it is necessary to disconnect the SSVR or perform maintenance on it, the series bypass switch can be closed and the parallel rectifier switch opened, allowing the line to continue to be directly powered by the mobile substation.

[0043] As a further technical solution, the hardware circuit is broken down in detail as follows:

[0044] Explosion-proof enclosure:

[0045] An explosion-proof enclosure houses all electrical components so that even if a gas explosion occurs inside the enclosure, the flame will be ejected through the mating surfaces without causing an explosion of the explosive mixture outside the enclosure. An explosion-proof enclosure is an electrical equipment enclosure capable of withstanding the explosion pressure of the internal explosive gas mixture and preventing the internal explosion from propagating to the explosive mixture surrounding the enclosure.

[0046] Rectifier module:

[0047] Unlike dynamic voltage restorers, SSVRs address voltage deviation issues in end-motor systems caused by long-distance power supply. They require wide-range, sustained voltage regulation and have a large conversion capacity, making them unsuitable for using energy storage power supplies to power the rectifier module. Therefore, the SSVR's rectifier module draws power directly from the 3.3kV grid side (secondary side of the mobile substation). Figure 2 As shown.

[0048] The left side of the diagram is connected to the power grid as the input side. The resistor RS is the equivalent resistance contained in the switching transistor and the filter inductor LS. The three phases are connected to the rectifier bridge arm at points A, B, and C, respectively. After rectification, the power is supplied to the load on the back side through the DC filter capacitor Cdc. The DC low-voltage common terminal is denoted as point N, and the neutral point on the power grid side is denoted as point O. Subsequent chapters will analyze the circuit and design the control strategy based on this schematic diagram.

[0049] Considering the large load power, a higher DC-side voltage level can reduce the internal current of the SSVR. Since the grid side uses a filter inductor to store energy, this embodiment adopts PWM fully controlled rectification with the DC-side voltage set to 7000V. This rectification method is a boost rectification. The switching device uses IGBTs, which have fast switching speed, relatively low switching losses, and can complete switching within microseconds. It requires a small drive current, can withstand high voltage levels, has a small on-state voltage drop, and has high efficiency under high current conditions, which is beneficial for energy saving. It also has good thermal stability and is easy to modularly integrate and install.

[0050] When all IGBTs are not conducting, only the freewheeling diode remains in the circuit. This is equivalent to uncontrolled rectification. Therefore, the DC-side voltage of PWM rectification is adjusted upward based on the maximum DC-side voltage of the uncontrolled rectifier circuit, while the DC-side voltage of phase-controlled rectification is adjusted downward based on the maximum DC-side voltage of the uncontrolled rectifier circuit.

[0051] Compared to uncontrolled rectification and phase-controlled rectification, SSVR adopts three-phase bridge PWM fully controlled rectification, and the reference waveform uses SPWM modulation technology. It can not only continuously adjust the output DC voltage to achieve DC constant voltage control, but also improve the input current waveform, increase the power factor, and reduce harmonic pollution to the grid side through control strategies.

[0052] SSVR voltage source inverter module:

[0053] Unlike inverters that directly control the motor, SSVR inverter modules need to convert the DC capacitor voltage into a constant frequency voltage of 50Hz, meaning they do not change the frequency but only adjust the amplitude and phase of the compensation voltage to keep the terminal voltage stable under different operating conditions and line losses. This inverter mode is also called Variable Voltage Constant Frequency (VVCF). SSVR inverter modules require a stable DC power supply from the front-end DC capacitor, therefore they belong to the Voltage Source Inverter (VSI) type. They have good voltage following characteristics and relatively simple control methods. Commonly used technologies include SPWM (Sinusoidal Pulse Width Modulation) control, which can generate high-quality sine waveforms and achieve voltage compensation that can be adjusted in both magnitude and phase.

[0054] The principle of SSVR inverter module is as follows Figure 3 As shown, a three-phase bridge two-level inverter is used, and the main switch is a fully controlled IGBT. The inverter-side filter inductance and equivalent resistance are L... g and R g When using different filter circuits, they can be replaced with the corresponding equivalent filter circuits. The primary winding of the compensation transformer connected to the inverter output side can be equivalent to an AC voltage source. The control strategy of the inverter is to control the output current and voltage so that the compensation voltage obtained on the secondary winding of the compensation transformer is superimposed with the grid voltage. The superimposed voltage at the beginning of the line can still meet the starting and running requirements of the motor load at the end of the line after long-distance line loss.

[0055] Filtering module:

[0056] The main function of the filtering module is to filter the rectifier input current and the PWM square wave output by the inverter module, filtering out most of the high-order harmonics, so that the waveform output by the inverter module is as close as possible to the ideal sine wave, thereby reducing harmonic pollution to the power grid, meeting the grid-connected power quality standards, and improving the power factor.

[0057] Commonly used inverter filter circuits are divided into passive and active filters (PPF and APF). Passive filters mainly include inductive filters, LC filters, LCL filters, and multi-stage filters. Pure inductive filters have a simple structure and low cost, and can effectively suppress high-order harmonics, but their ability to suppress low-order harmonics is poor. LC filters consist of inductors and capacitors and can be designed as bandpass or bandstop filters to eliminate harmonics of specific frequencies or bands. However, improper parameter design can cause grid parameter resonance, resulting in resonant overvoltage. LCL filters suppress harmonics more effectively by adding a series inductor, providing better current waveform quality. Under certain designs, the size and weight of the filter can be reduced. However, improper parameter design can also cause high-frequency resonance. Multi-stage filters further optimize voltage and current waveforms and provide better power quality through the cascading of the above individual filters. However, they have a complex structure, increased control difficulty, high cost, and may have multiple resonance points. In power generation and transmission systems, they may also cause subsynchronous oscillations, threatening system stability. Therefore, they require precise design and control. Active power filters can actively generate a reverse-phase compensation current that can cancel out the harmonic current of the power grid, and have excellent harmonic suppression effect. They can also adapt to changes in power grid and load conditions, achieve dynamic compensation, and have high compensation accuracy. They are currently widely used. However, because the control and hardware are more complex than passive filters, the cost is also higher.

[0058] In summary, to achieve relatively good filtering results at a lower cost, this embodiment uses a three-phase LCL filter circuit to filter the input side of the SSVR rectifier module and the output side of the inverter module. The circuit diagram for one phase is shown below. Figure 4As shown, the filtered material is connected to the primary winding of the compensation transformer.

[0059] When designing the parameters of inductor L1, its minimum value needs to be calculated based on the maximum ripple coefficient, the fundamental RMS value of the inductor current, the DC-side voltage, and the carrier period. Then, its maximum value is calculated based on the minimum ripple coefficient, the output-side voltage, and the current. Values ​​between the minimum and maximum values ​​are acceptable. The filter capacitor can be calculated based on the ripple coefficient, output power, and operating voltage. The output-side inductor L2 needs to satisfy the condition that the resonant frequency of LCL is greater than 10 times the power frequency and less than half the carrier frequency. Then, based on the main harmonic frequencies and peak values ​​to be filtered, and the previously determined L1 and C, the minimum value of inductor L2 is calculated. Using the resonant frequency as a reference, appropriate L2 parameters can be selected. Typically, connecting a passive damping resistor in series with the filter capacitor can improve the filtering effect.

[0060] Compensating transformer:

[0061] As the final link in the SSVR, the compensation transformer has a primary winding that receives the output voltage of the inverter module and a secondary winding that is connected in series to the beginning of the power supply line. It couples the inverter voltage in series to the beginning of the line and superimposes it with the grid voltage to form a regulated total voltage. Because this link plays a role in compensating for the voltage deviation at the end of the line caused by line voltage loss, the transformer used is called a compensation transformer.

[0062] The compensation transformer adopts a three-phase isolation transformer design, such as Figure 5 As shown, there is no direct electrical connection between the primary and secondary windings except for magnetic coupling. This can cut off common-mode interference, prevent internal faults of the inverter module from directly interfering with the power grid, and also isolate power grid faults to prevent damage to the solid-state voltage regulator.

[0063] Compared to voltage compensation methods that use parallel coupling capacitors to the grid, the series coupling compensation method employed by the compensation transformer can, on the one hand, proportionally increase or decrease the inverter voltage through turns ratio design, reducing the voltage and current withstand load on the rectifier and inverter modules. On the other hand, it provides good electrical isolation, reducing the mutual impact of faults between the SSVR output side and the grid, and also suppressing high-order harmonics to some extent. The maximum voltage regulation range required in this implementation is ±30% of the rated voltage of 3.3kV, i.e., the compensated phase voltage range is:

[0064]

[0065] If the rectifier module uses an uncontrolled or phase-controlled method, the maximum DC-side voltage is:

[0066]

[0067] In the formula: U PN This represents the phase voltage of the power grid.

[0068] The phase-controlled rectification is adjusted downwards based on this value. If PWM fully controlled rectification is used, the lowest DC-side voltage is given by equation (2). If the rectification side uses uncontrolled or phase-controlled methods, the effective value of the maximum inverter voltage is:

[0069]

[0070] Will U N Substituting 3300V into the above formula, we get the effective value of the inverter voltage as U. out =1575V, therefore the transformer turns ratio is k com =1575V / 571V. In this embodiment, the SSVR rectifier side adopts PWM full control mode, that is, this ratio is the minimum ratio designed for the compensation transformer. The specific ratio value needs to be adjusted according to the DC voltage obtained by rectification and the inverter method.

[0071] The compensation transformer connects the adjustable AC voltage generated by the rectifier and inverter in series to the beginning of the line. Therefore, the compensation capacity of the SSVR is the same as the capacity of the compensation transformer, denoted as S. com Let the maximum compensation voltage of SSVR, i.e., the effective value of the maximum phase voltage of the secondary winding of the compensation transformer, be U. cmax If the rated load current of the line is I, then the compensation capacity of the SSVR is:

[0072] S com =3U cmax I (4)

[0073] Because the secondary winding of the compensation transformer is connected in series with the main power supply line, the total output voltage of the SSVR is equal to the input grid voltage U. G The total capacity of the SSVR, including the compensation voltage, is:

[0074] S ssvr =3(U G +U cmax )I (5)

[0075] Taking the long-distance power supply system of the 3.3kV mining face of Coal Mine A as an example, the load at the end of the line is motor M1 with an installed capacity of 1000kW and motor M2 with an installed capacity of 2000kW. That is, the total installed capacity of the system load is 3000kW, the rated current of the line is 621.4A, and the maximum compensation voltage of SSVR is designed to be 30% of the rated voltage. Then, from equation (4), the compensation capacity of SSVR is 1065.53kVA, and from equation (5), the total capacity of SSVR is 3551.78kVA.

[0076] If the power supply system has only one 1000kW motor M1 as its load, and other conditions remain unchanged, then the corresponding SSVR compensation capacity should be 363.35kVA, and the total SSVR capacity should be 1211.17kVA. If the power supply system has only one 2000kW motor M2 as its load, and other conditions remain unchanged, then the corresponding SSVR compensation capacity should be 702.18kVA, and the total SSVR capacity should be 2340.61kVA.

[0077] This invention also provides a control method for a solid-state on-load automatic voltage regulation circuit in a mining medium-voltage power supply system, applied to the circuit described above, comprising:

[0078] Step 100: Collect the voltage at the beginning of the cable line and the line current, and evaluate and calculate the voltage at the end.

[0079] Step 200: Based on the evaluation calculation results, determine the load operation stage according to the segmented automatic voltage regulation control strategy, thereby adjusting the terminal voltage reference value to the set value of the corresponding stage and generating a charging and discharging control signal.

[0080] Step 300: The phase tracking control strategy is used to lock the grid voltage and current, and the phase arc is transmitted to the rectifier module and the inverter module. During the execution of the dual closed-loop rectifier control strategy and the inverter control strategy based on the voltage drop model, the amplitude and phase of the compensation voltage are controlled to stabilize the amplitude and phase of the voltage at the end of the line to the set value. The dual closed-loop rectifier control strategy is used to output the PWM rectifier control signal. The inverter control strategy based on the voltage drop model is used to output the PWM inverter control signal.

[0081] As a specific implementation method, the specific processing procedures for each step as described above are provided.

[0082] For step 100, the SSVR control strategy, as an important component of the controller software, is crucial for achieving automatic control of the line end voltage. First, the line end voltage is evaluated and calculated based on the voltage and current collected at the line head end through phase analysis and the line end voltage algorithm. Then, the load operation stage is determined according to the segmented automatic voltage regulation strategy, thereby adjusting the line end voltage reference value to the set value of the corresponding stage. The corresponding head end reference voltage is calculated through the voltage loss model. By comparing the reference value with the measured value, the inverter closed-loop control strategy generates a modulation wave and a corresponding SPWM square wave signal, which drives the IGBT to switch on and off, thereby achieving dynamic regulation of the inverter compensation voltage. During this process, the rectifier control strategy is responsible for keeping the branch capacitor voltage stable at the set value.

[0083] The method for evaluating and calculating the voltage at the end of a line is briefly described as follows: For Figure 6 The equivalent circuit of a 3.3kV power supply system for a coal mine is shown.

[0084] The equivalent internal impedance in the figure is Z. T =R T +jX T The output voltage of the transformer secondary side, i.e., the voltage at the beginning of the line, is The provided complex power is The voltage at the end of the cable line with impedance Z = R + jX is... Given the equivalent impedance Z L =R L +jX L The complex power provided by the load motor is Based on the voltage at the beginning of the line The reference voltage, i.e. The line current is:

[0085]

[0086] In the formula: "*" represents the conjugate operation of phasors.

[0087] The voltage drop of the cable line is:

[0088]

[0089] In the formula: ΔU v It is the longitudinal component of the line voltage loss, expressed in terms of line current and impedance as:

[0090]

[0091] ΔU h It is the transverse component of the line voltage loss, expressed in terms of line current and impedance as:

[0092]

[0093] In the formula: Voltage at the beginning of the line Leading the line current The phase angle.

[0094] Therefore, the voltage phasor at the end of the cable line is:

[0095]

[0096] The terminal voltage amplitude is:

[0097]

[0098] The control strategies in steps 200 and 300 will be explained separately.

[0099] Control strategy for solid-state voltage regulators (SSVRs):

[0100] As a crucial component of the controller software, the SSVR control strategy is critical for achieving automatic control of the line-end voltage. First, based on the voltage and current collected at the line head, the line-end voltage is evaluated and calculated using phase analysis and a line-end voltage algorithm. Then, according to the segmented automatic voltage regulation strategy described below, the load operating stage is determined, thereby adjusting the line-end voltage reference value to the corresponding stage's setpoint. The corresponding head-end reference voltage is calculated using a voltage drop model. By comparing the reference value with the measured value, a modulation wave is generated through the inverter closed-loop control strategy, producing a corresponding SPWM square wave signal to drive the IGBT switching, achieving dynamic regulation of the inverter compensation voltage. During this process, the rectifier control strategy is responsible for maintaining the branch capacitor voltage stable at the setpoint. The control strategies involved in the SSVR operation are described below.

[0101] Segmented automatic voltage regulation control strategy:

[0102] To prevent excessive current during motor startup, reduced-voltage starting is preferable. However, excessively low terminal voltage can lead to insufficient starting torque and difficulty in starting. Therefore, the starting voltage should not be lower than 75% of the rated voltage. According to the national standard GB / T13957-2022, motors should operate within ±10% of their rated voltage. This means that under normal operating conditions, the motor's supply voltage should be maintained between 90% and 110% of its rated voltage to ensure normal operation and service life. It is evident that the optimal voltage required for motor startup and stable operation differs. Therefore, this embodiment proposes a segmented automatic voltage regulation strategy, setting different target voltages for startup and operation to meet the motor's needs at different stages of operation.

[0103] The rated currents of motors M1 and M2 are denoted as I. N1 and I N2 The minimum no-load operating current of the line is I s0 The lower limit of the motor starting judgment threshold should avoid overload current. According to the requirements of the national standard GB / T 1408.4-2020 Low-voltage switchgear and controlgear, when 1.2I N <I<1.5I N When the motor's inverse-time overload protection trips, twice the rated current is used as the lower limit of the starting judgment setting for a single motor. When the current exceeds the short-circuit protection current, the motor's short-circuit protection will trip. According to the national standard GB / T 5590-2008 "Explosion-proof Low-voltage Electromagnetic Starters for Mining," the motor's short-circuit protection setting is to avoid the maximum current during motor startup, which is usually less than 8 times the rated current. Therefore, 2I can be used. N1 <I<8I N2 This is set as the criterion for motor starting. When motor M2 is started while M1 is already running, the maximum current I in the circuit is...sm As the upper limit of the motor starting judgment setting value, that is, 2I N1 <I<I sm As a criterion for initiation.

[0104] In underground coal mines, two motors connected to the same power supply line in the fully mechanized mining face and roadways are typically started sequentially, not simultaneously, due to their large power and specific operating sequence requirements. If the line initially has no current, it is assumed that neither motor is running. Therefore, when a motor starting is detected, the target value of the terminal voltage is set to 0.75U. N When the circuit originally had current and satisfied I... s0 <I indicates that one motor is already running. Therefore, when the effective value increment ΔI of the line current is detected, it satisfies 2I. N1 <ΔI<I sm When the activation criterion is applied, the target value of the terminal voltage is set to 0.9U. N To avoid excessive impact on already running motors; since motor M2 has a large rated current, the current is reduced to meet the condition I < 1.2I. N2 Based on this, it is determined that the motor startup is nearing completion, and at this point, the target voltage is automatically set to U. N The above process is called segmented automatic voltage regulation, which can automatically select different terminal voltage reference values ​​according to different operating conditions.

[0105] After setting the line impedance parameters R, X, and the terminal voltage setting value U, set (The default value is the phase voltage U corresponding to the line rated voltage of 3.3kV) PN The controller reads the three-phase voltage, current, and phase difference angle measurements. If the system is fault-free, it sets the SSVR to voltage regulation mode. At this time, the rectifier switch closes, the bypass switch opens, the charging resistor engages, and the rectifier module starts working to pre-charge the DC capacitor. The program calculates the line-end voltage U2 based on the collected and preset parameters. The segmented automatic voltage regulation strategy determines the current motor startup and operation status, selects a suitable end-voltage reference value based on the operating status, and assigns it to U2. set Therefore, the inverter control strategy performs closed-loop control on the SSVR output voltage based on the reference value given by the segmented automatic voltage regulation, so that the terminal voltage is stabilized to the reference value and meets the voltage requirements of the terminal motor under different operating conditions.

[0106] Phase tracking control strategy:

[0107] SSVR (Series-Side Voltage Regulator) regulates grid voltage through compensated transformer series coupling. To ensure the accuracy and stability of SSVR voltage regulation, the inverter output voltage magnitude and phase must match the reference voltage. To track the grid voltage phase in real time and eliminate harmonic interference in the actual grid, a phase-locked loop (PLL) with strong tracking characteristics is required. Software PLLs are widely used due to their high control accuracy, strong stability, and adaptability. Software PLLs based on dq-conversion PI control, such as... Figure 7 As shown, the phase-locked loop (PLL) precisely locks the phase of the grid voltage and current, and transmits the phase radian to the rectifier and inverter modules. Through rectifier and inverter control strategies, it controls the amplitude and phase of the SSVR compensation voltage, thereby stabilizing the amplitude and phase of the voltage at the line end to the reference value. The simulation results of the above PLL model are shown in the diagram below. Figure 8 As shown, it can accurately track the phase of the fundamental power frequency.

[0108] Dual closed-loop rectifier control strategy:

[0109] The rectifier module employs a three-phase bridge fully controlled rectifier, with the bridge consisting of three common-cathode IGBTs on the upper side and three common-anode IGBTs on the lower side connected in parallel. Common rectifier control methods include phase control and PWM control. Phase control commonly uses thyristors as switching devices, resulting in a simple structure, low cost, and ease of control. However, it suffers from a lagging power factor, significant reactive power, inability to control current magnitude in real time, and output current containing numerous harmonics, impacting power quality. Using a sine wave as the modulation signal is the classic PWM modulation method, also known as SPWM technology. SPWM control uses fully controlled switching devices such as IGBTs, and through control strategies, it can control the magnitude and phase of the input current in real time, reducing input current harmonics, meeting power grid harmonic standards, and offering high power conversion efficiency and good DC voltage regulation dynamic performance. Therefore, the SSVR rectifier module adopts SPWM fully controlled rectification.

[0110] To achieve the above control effect, a control model for the rectifier module needs to be established. Firstly, [the model needs to be developed]. Figure 8 Write the KVL equations for each of the three phases of the rectifier circuit shown:

[0111]

[0112] The IGBT switching state is denoted as a switching function:

[0113]

[0114] In the formula: K represents phases a, b, and c.

[0115] The three-phase switching functions are denoted as S. A S B S CThe voltage relationship at the connection points of each phase bridge arm when the switch is turned on and off is as follows:

[0116]

[0117] Since both the grid voltage and the input current are three-phase symmetrical, we can conclude that:

[0118]

[0119] Analysis of the DC-side current yields the following results:

[0120] i dc =S A i sa +S B i sb +S C i sc (15)

[0121] Due to u AO =u AN +u NO The other two are similar, and with the addition of DC, equation (11) can be expressed as:

[0122]

[0123] The coordinate transformation of the above three-phase equations yields the following equations in the dq coordinate system:

[0124]

[0125] It is evident that in the dq rotating coordinate system, the d-axis equation contains a coupling term with the q-axis, and the q-axis equation contains a coupling term with the d-axis, with the coupling coefficients being equal in magnitude and opposite in sign. To control the phase of the input current and synchronize it with the grid voltage phase, thereby improving the power factor, the bridge arm voltage u... d and u q As input, the input-side current i d and i q As the output, and by performing a Laplace transform on equation (17), we obtain the complex frequency domain form of the rectifier equation:

[0126]

[0127] The input / output structure diagram of the rectifier module can be drawn according to equation (18) as follows: Figure 9 As shown.

[0128] Due to the presence of current coupling terms, the control of the dq axis components affects each other. Therefore, it is necessary to add a current cross-decoupling stage to the current control stage to eliminate the q-axis coupling in the d-axis equation and the d-axis coupling in the q-axis equation. Observing equation (18), it can be seen that there is still a disturbance e in the current equation. dand e q This refers to the grid-side voltage. Therefore, the current control loop also needs to incorporate feedforward control. This involves introducing a quantity with the opposite sign to these two disturbances into the controller. This effectively compensates for the impact of these disturbances on the system, improves anti-interference capability, and reduces steady-state error. The current control loop is as follows: Figure 10 As shown.

[0129] By introducing a cross-decoupling stage into the current control circuit, i can be... q Reference value i qref Setting it to 0 for independent control eliminates the q-axis component of the input current, achieving the current control goal of a power factor of 1 on the input side. Simultaneously, feedforward control is introduced during decoupling, resulting in a superimposed signal u. dref and u qref That is Figure 9 DC voltage signal u of the rectifier module d and u q This enables control of the rectifier module.

[0130] Since another objective of rectification control is to stabilize the DC-side voltage to a given value, a voltage control loop needs to be added outside the current control loop to form a control closed loop, i.e., the actual DC voltage signal U... dc As feedback quantity and given DC voltage target value U dc_ref For comparison, the error signal is input into the voltage control circuit, such as... Figure 11 As shown, the output of the voltage loop serves as the reference value i for the current loop. dref .

[0131] Thus, the rectifier module has achieved dual closed-loop control with an inner current control loop dominated by the input current and an outer voltage control loop dominated by the DC output voltage. The entire control diagram is as follows: Figure 12 As shown.

[0132] All transformations between the dq reference frame and the abc reference frame in the control process require a phase-locked loop to provide the grid voltage phase angle ωt. The output signal of the dual closed-loop control is transformed by dq-abc to generate a three-phase voltage reference waveform. After normalization, it is used as a unit modulation signal and its amplitude is compared with the carrier wave to generate an SPWM pulse signal, which controls the turn-on and turn-off of the six IGBTs, ultimately making the DC capacitor reach the target voltage.

[0133] The following section describes the tuning of the PI parameters for the current loop controller. Since the rectifier module requires signal sampling during actual operation, exhibiting unit pulse function characteristics, there is a calculation delay of approximately one carrier cycle during PWM modulation. According to automatic control principles, handling the difference problem often involves using a zero-order hold, which further introduces a delay. PWM control has a small inertia characteristic. Let the inverter gain of the inverter module be K. pwmThe actual control structure of the inner current loop is obtained by multiplying the transfer functions of the above delay elements and performing a first-order Taylor expansion. Figure 13 As shown.

[0134] Ignoring feedforward disturbances, the open-loop transfer function of the current loop is:

[0135]

[0136] In the formula: τ i The proportional coefficient K of the controller p With integral coefficient K i The ratio of .

[0137] This ensures that the controller's PI parameters can cancel out the structural zeros and poles of the rectifier module, i.e.:

[0138]

[0139] Therefore, the current loop transfer function is:

[0140]

[0141] The current loop PI parameters are obtained from the optimal damping ratio of 0.707 for a Type I second-order system:

[0142]

[0143] The closed-loop transfer function of the current loop can be obtained from equation (19). Since the sampling period T is very small when the sampling frequency is high, the coefficients contain s of T. 2 The term can be ignored, thus the simplified closed-loop transfer function is obtained as follows:

[0144]

[0145] It can be seen that the current control element can be approximated as an inertial element.

[0146] Then, the PI parameters of the voltage loop controller are tuned. Since the ultimate goal of the SSVR's rectifier module is to output a stable DC voltage, it needs strong anti-interference capability and small steady-state error. Therefore, the voltage loop is tuned according to a Type II system. Similar to the current loop delay characteristic, it can be approximated as an inertial loop. Let the voltage outer loop sampling model be:

[0147]

[0148] The SPWM modulation function is:

[0149]

[0150] The current is:

[0151]

[0152] Substituting into equation (15) and simplifying, we get:

[0153]

[0154] The controller should be written in the following form:

[0155]

[0156] Therefore, the actual structure of the entire voltage outer loop is as follows: Figure 14 As shown.

[0157] Substituting the simplified closed-loop transfer function (23) of the inner current loop into the equation, and taking the modulation index m to its maximum value of 1, the value of equation (27) is 0.75. The time constants of each stage are combined to obtain the open-loop transfer function of the rectifier module as follows:

[0158]

[0159] Compare with the typical form of Type II system:

[0160]

[0161] Its optimal mid-frequency bandwidth is:

[0162]

[0163] The coefficient K is:

[0164]

[0165] By matching the parameters of the transfer function in equation (29) with the corresponding values, we can obtain:

[0166]

[0167] Substituting into equation (27), the voltage control parameters can be obtained as follows:

[0168]

[0169] In actual operating conditions, adjustments should be made based on this setpoint, and parameters should be corrected according to simulation or actual conditions. When correcting parameters using simulation, disconnect the DC-side load and connect a DC voltage source with a DC regulated target value of 7000V. Disconnect the outer voltage loop to disable the voltage control circuit, and apply a unit step signal to the current loop input side as the current loop d-axis setpoint i. dref The PI parameters for the dq-axis current loop are the same; first, adjust the proportional coefficient K. p At this point, the integral coefficient K should be... i Take the smallest possible value to reduce the impact on K p Disturbance in the adjustment process will cause K to be affected. pAdjust the value around the calculated value of equation (22) and observe i. dref and i d The trend of change, until i d It can effectively follow i dref The change, although there will be a certain steady-state error, at this time K p Stop increasing and take the oscillation time K. p Approximately 0.75 times as K p Correct the value, then K i Adjust the value around the calculated value in equation (22) until i d Able to communicate with i dref Tracking without steady-state error.

[0170] Then, the voltage outer loop control parameters are corrected. The DC voltage source is removed, and a load is added to both ends of the DC capacitor. The load is divided into multiple stages and switched on and off at different times to observe the effect of different loads on the DC voltage. The voltage outer loop parameter correction method is similar to the current inner loop method. It is adjusted based on the calculated value of equation (34). First, the proportional coefficient is corrected, and then the integral coefficient is corrected, until the output DC voltage can follow the given voltage U without steady-state error. dc_ref When adjusting parameters, other indicators such as small overshoot, fast response, and high stability margin should also be considered.

[0171] Inverter control strategy based on voltage drop model:

[0172] The SSVR inverter module operates in VVCF mode, employing bipolar synchronous modulation, meaning both the triangular carrier frequency and the modulation wave frequency remain constant. All three phases use the same triangular carrier. To reduce harmonics, SPWM modulation is still used. The modulation wave phase and amplitude are given by the control strategy, and the frequency is consistent with the grid frequency. The control objective of the SSVR inverter module is to ensure that the output voltage magnitude and phase follow the given values. Analysis of the inverter module reveals... a v b v c The filtered output voltage, i, is the primary voltage of the compensation transformer. ga i gb i gc For the output current, the KVL equation is as follows:

[0173] Still using the switching function of equation (7), then:

[0174]

[0175] Due to the symmetry of the three-phase voltage and current:

[0176]

[0177] then:

[0178] DC side has:

[0179]

[0180] i l =S A i ga +S B i gb +S C i gc (40)

[0181] The system state equations can be written as follows:

[0182] The state equations in the dq rotating reference frame obtained by performing the dq transformation are as follows:

[0183]

[0184] In the formula: v d v q i is the filter output voltage in the rotating reference frame. d i q The output current is given in the rotating reference frame.

[0185] The Laplace transform yields the complex frequency domain equation as follows:

[0186]

[0187] It can be observed that the inverter state equation is similar to that of the rectifier, and there is also coupling. Therefore, a feedforward decoupling circuit is added to the controller to reduce the DC side voltage u. d and u q Treat it as a disturbance, and use the output voltage v d and v q As the control variable, the current loop control is obtained as follows: Figure 15 As shown.

[0188] The following phasor analysis is performed on the compensation voltage output of the SSVR based on the voltage loss model of long-distance cable lines. Two suitable voltage compensation methods for the head-end of long-distance power supply systems are in-phase compensation and full compensation. Figure 16 The diagram shows the in-phase compensation method.

[0189] In the picture The voltage at the beginning of the line before voltage regulation, which is the grid voltage. This is the voltage at the end of the line before voltage regulation. For line voltage loss, This refers to the line current before voltage regulation. This is the phase angle at which the voltage at the beginning of the line leads the line current. The load impedance angle, also known as the load power factor angle, is δ, where δ is the phase angle difference between the voltage at the beginning and end of the line. This is the compensation value of SSVR for the voltage at the beginning of the line. This is the compensation voltage obtained at the end of the line. This refers to the voltage at the beginning of the line after SSVR compensation. To obtain the maximum range of the SSVR-compensated voltage phasor, draw a circle with the endpoint of the first-end voltage phasor as the center and the maximum voltage regulation amplitude of the SSVR as the radius. After voltage regulation, the line current becomes

[0190] Figure 16 Image (a) shows the normal operation of the SSVR in-phase voltage compensation. That is, the voltage across the winding connected in series with the transformer at the beginning of the line (i.e., the secondary winding). With the voltage phase being the same as the grid voltage, the primary and secondary windings of the compensation transformer can be designed with zero phase difference. Therefore, the output voltage obtained by the inverter module after filtering is in phase with the grid voltage, hence the term "in-phase voltage compensation." In this case, the voltage phase at the beginning of the line remains unchanged after voltage regulation. Therefore, when the load impedance angle remains unchanged, the voltage phase at the end of the line also remains unchanged. The voltage amplitude at the end increases along the original phase to the set value. The compensation path is simple, and the compensation voltage utilization efficiency is high.

[0191] Figure 16 (b) shows the in-phase compensation situation when the voltage deficit at the line end exceeds the maximum adjustable range of the SSVR. Clearly, the SSVR compensation voltage... Maximum voltage regulation range has been reached. The edge, and the end voltage Due to excessive amplitude deficiency, the voltage at the beginning of the line before voltage regulation failed to reach the reference value. The amplitude.

[0192] Figure 17 The diagram shown is a phasor diagram of the SSVR voltage full compensation mode. In the voltage full compensation mode, after SSVR voltage regulation, the voltage at the end of the line not only has the same amplitude as the grid voltage, but also maintains the same phase as the grid voltage.

[0193] Figure 17 (a) shows the case when the SSVR voltage is fully compensated and operating normally. It can be seen that the SSVR-compensated voltage phase leads the grid voltage, causing the originally lagging voltage phase at the line end to advance, resulting in a change in the line end voltage after voltage regulation. Compared with the grid voltage, i.e., the voltage at the beginning of the line before voltage regulation The phase and amplitude are the same. This voltage regulation method requires a higher SSVR capacity than in-phase compensation, as it compensates not only for the amplitude of the lost voltage but also for the phase, thus making it prone to problems. Figure 17 The insufficient capacity shown in Figure (b) and The amplitude and phase are exactly the same, but the required compensation voltage is different. This exceeds the maximum voltage regulation range of the SSVR. Outside the dashed circle.

[0194] Figure 18 (a) shows the critical state of SSVR boost and buck, i.e., the compensation voltage. The finish line is located at When the amplitude is on a circle with a radius of 1, the voltage amplitude at the end of the line does not change compared to before voltage regulation; only the phase changes. If the endpoint falls inside the circle, then and When the phase difference is greater than 90 degrees, SSVR is in buck mode. If the endpoint falls outside the circle, then and When the phase difference is less than 90 degrees, SSVR is in boost mode. Figure 18 (b) shows the case of SSVR reverse phase voltage compensation, where the voltage amplitude at the line end is higher than the reference value, i.e. When the endpoint falls outside the blue dashed line, the SSVR outputs a voltage that is out of phase with the grid voltage, thus achieving voltage reduction.

[0195] In summary, the in-phase compensation method only requires amplitude adjustment, with the highest efficiency achieved by increasing the amplitude and requiring less SSVR capacity. Similarly, the anti-phase compensation method achieves the highest efficiency by decreasing the voltage amplitude. This compensation voltage regulation method fully meets the starting and operation requirements of the motor on the load side. However, since the phase difference between the line current and the grid voltage does not change when the load impedance is constant, the improvement in the system power factor is mainly reflected in the improvement of the motor's own power factor due to the improved starting and operation conditions. Therefore, the power factor on the grid side is not significantly improved. The full compensation method requires the compensated voltage phase to lead the grid voltage, that is, it requires additional compensation for the voltage phase difference caused by line losses. This can advance the load current phase, thereby reducing the phase difference angle between the grid voltage and the line current, which can significantly improve the grid power factor. However, the disadvantage of the full compensation method is that the equivalent impedance changes continuously during motor load startup and operation at different load rates, and the voltage loss also changes continuously. The phase that needs to be compensated also changes continuously, increasing the control complexity and cost, and requiring a larger SSVR capacity. This embodiment of SSVR is designed for voltage regulation in low-voltage long-distance power supply systems in underground coal mines. The ultimate control objective is to stabilize the voltage amplitude at the motor terminal at the end of the line within the reference value. Since voltage phase has no impact on motor operation, considering control and capacity costs, SSVR preferentially employs a control strategy of in-phase compensation boost and anti-phase compensation buck. If a high power factor requirement is placed on the grid side, a full compensation voltage regulation strategy can also be used. With the reference direction set to zero (i.e., the phase angle is zero), the maximum voltage regulation amplitude U of SSVR can be determined from the geometric relationship of the phasor diagram. cmax With the maximum voltage drop amplitude ΔU max The relationship should satisfy equation (44):

[0196]

[0197] Will U 1com and ΔU max The percentage converted to grid voltage U1, i.e., each variable in equation (3.39) divided by the amplitude U1, simplifies to:

[0198]

[0199] In the formula: k ssvr The maximum voltage U that the secondary winding of the SSVR compensation transformer can provide cmax The ratio of k to the grid voltage amplitude U1 lost The maximum line voltage drop amplitude ΔU max The ratio of the voltage amplitude U1 to the grid voltage is equivalent to the two expressions.

[0200] Based on the above compensation voltage regulation analysis and the line voltage loss analysis in Chapter 2, the voltage loss model equation for long-distance cable lines can be written as follows:

[0201]

[0202] In the formula: u 1a u 1b u 1c The voltage is the three-phase voltage before voltage regulation at the beginning of the line, i.e., the grid voltage, u 1coma u 1comb u 1comc The voltage of the secondary winding of the SSVR compensation transformer connected in series at the beginning of the line is the compensation voltage output by the compensation transformer. la i lb i lc For the three-phase current of the line, u 2a u 2b u 2c The voltage at the end of the line is the three-phase voltage, i.e., the motor terminal voltage. The voltage transformation ratio of the primary and secondary windings of the compensation transformer is n, i.e.:

[0203]

[0204] Substituting equation (47) into equation (46) and performing the abc-dq transformation, we obtain the voltage loss equation for the dq coordinates as follows:

[0205]

[0206] Transforming to the complex frequency domain, the voltage equation at the line end in the voltage drop model is as follows:

[0207]

[0208] Since the SSVR voltage regulation process is based on the known target voltage at the end of the line, i.e., the reference voltage at the end, u... 2dref and u 2qref Therefore, it is necessary to calculate the reference value of the compensation voltage v based on the above calculations. d and v q Therefore, by transforming equation (49), we can obtain the compensation voltage equation based on the voltage loss model:

[0209]

[0210] The reference value for the compensation voltage can be obtained according to equation (50). Figure 15 Add the aforementioned voltage control loop based on the voltage drop model to the outside of the current loop, such as... Figure 19 As shown, the inverter-side compensation voltage reference value v can be generated based on the voltage reference value at the end of the line. d and v q This, in turn, causes the voltage at the end of the line to follow the reference value by acting on the outer voltage loop through the inner current loop. When performing the abc-dq transformation, all the above variables use the synchronous phase obtained from the grid voltage through software phase-locking.

[0211] Thus, the inverter module has achieved dual closed-loop control with a current inner loop dominated by the output current and a voltage outer loop dominated by the compensation voltage generated based on the voltage drop model reference value. The entire inverter control process is as follows: Figure 20 As shown.

[0212] The inverter module adopts a dual closed-loop control strategy based on a voltage loss model, which can achieve the control objective of adjustable inverter voltage magnitude and phase, thereby stabilizing the voltage at the end of the line to the reference value.

[0213] The following is the tuning calculation of the inverter current loop PI parameters. Taking into account the sampling delay, calculation delay, and zero-order hold delay, the results are obtained as follows: Figure 13 Given the same actual structure of the inverter module's inner current loop, by analogy with equation (19), the open-loop transfer function of the inverter module's current loop is obtained as follows:

[0214]

[0215] To reduce overshoot and make the current loop a Type I second-order system, the zeros and poles of the controller function and the inverter function are canceled out, the process being the same as in equations (20) and (21). Then, based on the optimal damping ratio of 0.707 for the Type I second-order system, the PI parameters of the inverter module current loop are obtained as follows:

[0216]

[0217] Its closed-loop transfer function can still be simplified to equation (23), which is equivalent to a first-order inertial element. If the current loop parameters of the Type II system can be adjusted to reduce steady-state error and improve anti-interference capability, the PI parameters of the inverter module current loop for the Type II system can be obtained by analogy with the adjustment method of the outer loop of the rectifier module voltage:

[0218]

[0219] In actual operating conditions and simulations, the parameter correction method described for the rectifier module should be used to adjust and correct the PI control parameters of the current loop and voltage loop.

[0220] Therefore, to address the voltage deviation problem in the 3.3kV long-distance power supply system for mines, an on-load solid-state automatic voltage regulator (SSVR) based on a series compensation topology is proposed. This structure draws power from the grid in parallel on the input side, generates a compensation voltage through rectification and inversion, and finally adjusts the voltage at the end of the line from the beginning to the end through series coupling between the output side of the compensation regulator and the grid. This achieves on-load automatic smooth stepless voltage regulation and also has segmented automatic voltage regulation function. The rectifier module adopts dual closed-loop fully controlled rectification to improve the power factor on the input side and increase the SSVR capacity. An inverter control strategy based on the line voltage loss model is proposed, which can compensate for the voltage loss at the beginning of the line to achieve the purpose of adjusting the voltage at the end of the line according to demand.

[0221] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A solid-state on-load automatic voltage regulation circuit for a medium-voltage power supply system in mining, characterized in that, include: Control module, rectifier module, DC module, inverter module, filter module, compensation transformer, rectifier switch and bypass switch; One end of the rectifier switch is connected to the secondary output terminal of the mobile substation, and the other end is connected to the rectifier module; the rectifier module, the DC module, the inverter module, the filter module, and the compensation transformer are connected in sequence; the bypass switch is installed on the cable line; the control module is connected to the rectifier module, the DC module, and the inverter module respectively; The rectifier switch is used to draw three-phase power from the secondary side of the mobile substation to obtain a 3.3kV line voltage; the rectifier module is used to perform three-phase rectification according to the PWM rectification control signal; the DC module is used to supply power to the inverter module according to the charge and discharge control signal; the inverter module is used to perform three-phase inversion according to the PWM inverter control signal; the filter module is used to output a sinusoidal AC voltage and connect it in series to the cable line through the secondary winding of the compensation transformer; the control module is used to generate PWM rectification control signal, charge and discharge control signal, and PWM inverter control signal according to the voltage regulation strategy; the voltage regulation strategy includes a segmented automatic voltage regulation control strategy, a phase tracking control strategy, a dual closed-loop rectification control strategy, and an inverter control strategy based on a voltage drop model; Depending on the circuit application, when powered by a solid-state on-load automatic voltage regulating circuit, the bypass switch is disconnected and the rectifier switch is closed; when powered directly by a mobile substation, the bypass switch is closed and the rectifier switch is disconnected.

2. The solid-state on-load automatic voltage regulation circuit for a mining medium-voltage power supply system according to claim 1, characterized in that, The DC module includes a DC capacitor, a buffer resistor branch, and a bleed resistor branch; the DC capacitor is used to provide a stable DC voltage; the buffer resistor branch is used to slow down the pre-charging process of the DC capacitor when the circuit starts up, preventing excessive inrush current in a short period of time; the bleed resistor branch is used to release the residual charge on the DC capacitor when the circuit stops.

3. The solid-state on-load automatic voltage regulation circuit for a mining medium-voltage power supply system according to claim 1, characterized in that, The rectifier module adopts a three-phase bridge fully controlled rectifier, and the rectifier bridge is composed of three common cathode IGBTs on the upper side and three common anode IGBTs on the lower side connected in parallel.

4. A control method for a solid-state on-load automatic voltage regulation circuit in a mining medium-voltage power supply system, applied to the circuit as described in any one of claims 1-3, characterized in that, include: Collect the voltage at the beginning of the cable line and the line current, and evaluate and calculate the voltage at the end; Based on the evaluation calculation results, the load operation stage is determined according to the segmented automatic voltage regulation control strategy, thereby adjusting the terminal voltage reference value to the set value of the corresponding stage and generating a charging and discharging control signal. A phase tracking control strategy is used to lock the grid voltage and current, and the phase arc is transmitted to the rectifier module and the inverter module. During the execution of the dual closed-loop rectifier control strategy and the inverter control strategy based on the voltage drop model, the amplitude and phase of the compensation voltage are controlled, thereby stabilizing the amplitude and phase of the voltage at the end of the line to the set value. The dual closed-loop rectifier control strategy is used to output the PWM rectifier control signal; the inverter control strategy based on the voltage drop model is used to output the PWM inverter control signal.

5. The control method for the solid-state on-load automatic voltage regulation circuit of the mining medium-voltage power supply system according to claim 4, characterized in that, The process of evaluating and calculating the terminal voltage is as follows: Construct the equivalent circuit of a 3.3kV power supply system; Based on the equivalent circuit of the 3.3kV power supply system, the equivalent internal impedance, complex power and equivalent impedance are set, and the line current and cable line voltage loss are calculated in sequence with the voltage at the beginning of the line as the reference voltage. The terminal voltage is evaluated and calculated based on the starting voltage and the voltage loss of the cable line to obtain the terminal voltage phasor and the terminal voltage amplitude.

6. The control method for the solid-state on-load automatic voltage regulation circuit of the mining medium-voltage power supply system according to claim 4, characterized in that, The specific processing procedure of the segmented automatic voltage regulation control strategy is as follows: Read the three-phase voltage and current and the corresponding phase difference angle measurement values. If the system is determined to be fault-free, set the circuit to voltage regulation mode. At this time, the rectifier switch is closed, the bypass switch is open, the charging resistor is engaged, and the rectifier module starts to work to precharge the DC capacitor. The line end voltage is calculated based on the collected data and preset parameters. The segmented automatic voltage regulation strategy is used to determine the current running status of the motor. A suitable end voltage reference value is selected according to the running status and assigned to the end voltage setpoint. During the execution of the corresponding control strategy, the circuit output voltage is controlled in a closed loop according to the reference value given by the segmented automatic voltage regulation to stabilize the end voltage to the reference value and meet the voltage requirements of the end motor under different running states.

7. The control method for the solid-state on-load automatic voltage regulation circuit of the mining medium-voltage power supply system according to claim 4, characterized in that, The dual closed-loop rectification control strategy adopts SPWM full-control rectification.

8. The control method for the solid-state on-load automatic voltage regulation circuit of the mining medium-voltage power supply system according to claim 4, characterized in that, The specific processing procedure of the inverter control strategy based on the voltage drop model is as follows: Based on the set values ​​for the corresponding stage, the corresponding first-end reference voltage is calculated through the voltage loss model. The reference value is compared with the measured value, and a modulation wave is formed through the inverter closed-loop control strategy to generate the corresponding PWM square wave signal, which drives the IGBT to switch on and off, thereby realizing the dynamic control of the inverter compensation voltage.

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