Control method and device for current source type static frequency converter applicable to synchronous condenser startup

Abstract

A control method and device for current-source static frequency converters (SSCs) applicable to synchronous condenser startup includes grid-side bridge control and machine-side bridge control. Grid-side bridge control employs a dual closed-loop control method (outer speed loop plus inner current loop) during SSC startup, controlling commutation based on grid-side voltage, machine-side bridge commutation status, and dual closed-loop output trigger angle. Machine-side bridge control, when the SSC is stationary, determines the thyristor sequence number triggered for the first time after the SSC is unlocked based on the SSC rotor position angle, providing the desired electromagnetic torque to the SSC. After the SSC drives the SSC to rotate, the machine-side bridge uses the machine terminal line voltage phase angle to determine the subsequent thyristor sequence numbers, providing the desired electromagnetic torque to the SSC and enabling smooth acceleration. This effectively improves speed control accuracy, reduces control complexity, and lowers motor startup failure rate.

Description

Technical Field

[0001] This invention belongs to the field of static inverter control technology, and relates to a current source type static inverter control method and device suitable for synchronous condenser startup. Background Technology

[0002] As a synchronous rotating device, the new type of synchronous condenser possesses unparalleled inertia advantages compared to power electronic devices. During transient grid faults, it exhibits strong voltage support, rapid transient response, and high overload capacity, along with a significant phase-leading capability. It can transmit the electromagnetic energy stored in the stator and rotor to the grid within tens of milliseconds, providing inertia and reactive power support for weak-sending systems that centrally transmit renewable energy, effectively suppressing transient overvoltages and undervoltages, and preventing large-scale grid disconnection of renewable energy sources due to grid faults. Furthermore, the new synchronous condenser is also a practical and effective solution to address the reactive power shortage problem in UHVDC transmission.

[0003] According to the plan, the State Grid will install new distributed synchronous condensers at new energy collection stations and the sending-end systems of multiple UHVDC projects. Therefore, these new distributed synchronous condensers will soon be widely used. However, synchronous condensers are essentially synchronous motors. To prevent the generation of huge inrush currents during grid connection, which could damage the condensers and cause severe interference to the power system, additional frequency converters are required during the startup and grid connection process.

[0004] The current source static frequency converter (SFC) uses a thyristor-based frequency converter to generate a variable frequency alternating current, which is fed into the stator winding of the synchronous condenser. Combined with the excitation control of the rotor winding, it accelerates the synchronous condenser to its rated speed. It is currently the preferred starting method for large pumped storage power stations, gas turbines, pumping stations, and synchronous condensers.

[0005] The commutation reliability of a current-source static inverter directly determines the starting performance of the motor. Currently, the control method commonly used in the industry for current-source static inverters is:

[0006] In the low-speed stage where the motor speed is below 10% of the rated speed: the grid-side bridge acts as the rectifier side, using constant firing angle or constant DC current control, and utilizes the grid voltage zero crossing point for natural commutation, resulting in an extremely low probability of commutation failure; the machine-side bridge uses a forced commutation method, providing commutation pulses based on the motor rotor position angle, and notifying the grid-side bridge to lock out before commutation, assisting it in commutation, resulting in a low probability of commutation failure.

[0007] When the motor speed reaches 10% or more of the rated speed at high speed: the grid-side bridge adopts a dual closed-loop control with an outer speed loop and an inner current loop to make the speed follow the set value. It utilizes the grid voltage zero crossing point for natural commutation, and the probability of commutation failure is extremely low. The machine-side bridge uses the motor back EMF to adopt a natural commutation method. It provides a trigger pulse based on the motor rotor position angle leading the commutation. Large rotor position angle error or improper selection of the leading commutation angle setting will lead to commutation failure.

[0008] Based on the above control method, in order to improve the success rate of startup, the motor speed and rotor position angle need to be accurately measured throughout the startup process; during the high-speed stage, it is necessary to ensure that the commutation angle of the machine-side bridge is greater than the sum of the commutation arc angle μ and the motor power angle φ, and leave a certain margin to prevent commutation failure.

[0009] However, the traditional method of measuring rotor position angle using mechanical encoders is inaccurate and faces problems such as high maintenance difficulty, and has been phased out. Current technology uses electrical quantities to estimate rotor position angle, but the calculation is extremely complex, and parameters such as motor electromagnetic torque and resistance torque are required at certain stages, making accurate measurement difficult during startup. The rotor position angle obtained through estimation has a large error, easily leading to commutation failure on the machine-side bridge. The accuracy of calculating the speed based on the rotor position angle is low, increasing the difficulty of smooth motor startup. Furthermore, during motor startup, the commutation arc angle μ varies with stator current, commutation circuit inductance, and motor speed, and increases with thyristor aging; the motor power angle φ varies with motor terminal line voltage, stator winding impedance, stator current, and motor speed, making it difficult to estimate. Currently, to avoid commutation failure on the machine-side bridge during the natural commutation stage, the leading commutation angle γ is selected as a constant value of 60°. In the early stage of the natural commutation stage, the margin is large, resulting in a low SFC power factor. When approaching the rated speed, the margin may be insufficient, leading to commutation failure, which in turn causes overcurrent in the circuit, triggers protection action, and motor start failure. Summary of the Invention

[0010] To address the shortcomings of existing technologies, this invention provides a current-source static inverter control method and device suitable for synchronous condenser startup, which can effectively improve speed control accuracy, reduce control complexity, and lower motor startup failure rate.

[0011] The present invention adopts the following technical solution:

[0012] A control method for a current-source static frequency converter applicable to the startup of a synchronous condenser, including grid-side bridge control and machine-side bridge control of the current-source static frequency converter, characterized in that:

[0013] The grid-side bridge control is as follows: During the startup process of the synchronous condenser, the grid-side bridge adopts a dual closed-loop control method with an outer speed loop and an inner current loop, and controls the commutation based on the grid-side voltage, the commutation status of the machine-side bridge, and the dual closed-loop output trigger angle.

[0014] The machine-side bridge control is as follows:

[0015] (1) When the synchronous condenser is stationary, the machine-side bridge determines the thyristor sequence number that is first triggered after the static inverter is unlocked based on the rotor position angle of the synchronous condenser, and provides the desired electromagnetic torque to the synchronous condenser.

[0016] (2) After the static inverter drives the synchronous condenser to rotate, the phase angle of the terminal line voltage is used to determine the sequence number of the thyristor to be triggered each time, so as to provide the desired electromagnetic torque for the synchronous condenser and make the synchronous condenser accelerate smoothly.

[0017] The present invention further includes the following preferred embodiments:

[0018] Preferably, during the startup process of the synchronous condenser, the grid-side bridge adopts a dual closed-loop control method consisting of an outer speed loop and an inner current loop. Commutation is controlled based on the grid-side voltage, the commutation status of the machine-side bridge, and the dual closed-loop output trigger angle. Specifically:

[0019] The actual value of the synchronous condenser speed and the set value of the synchronous condenser speed are used to obtain the synchronous condenser speed deviation. The synchronous condenser speed deviation is passed through the PI loop to give the DC current reference value. Combined with the actual value of the DC current, the DC current deviation is obtained. The DC current deviation is passed through the PI loop to give the trigger angle. The trigger angle is combined with the grid-side bridge commutation voltage to obtain the specific trigger pulse.

[0020] When the machine-side bridge is in forced commutation mode and during the commutation process, the trigger angle of the network bridge side is given a specified value or locked.

[0021] Preferably, in (1), the machine-side bridge adopts a forced commutation method for commutation, and the method of determining the first trigger thyristor sequence number by using the rotor position angle of the condenser is: no advance commutation control.

[0022] Preferably, in step (2), the phase angle of the terminal line voltage is obtained by frequency conversion locking the phase angle of the terminal line voltage after filtering the terminal line voltage, specifically:

[0023] After the static inverter drives the synchronous condenser to rotate, the synchronous condenser generates a terminal line voltage. The sampled value of the terminal line voltage is filtered by a second-order generalized integrator. After filtering, the phase-locked loop of frequency converter dq conversion is used to lock the accurate phase angle of the terminal line voltage.

[0024] In the variable frequency dq conversion phase-locked loop, the motor frequency setting value is used as the input frequency reference value, and the actual output frequency value of the phase-locked loop is the input frequency reference value superimposed with the output value of the phase-locked loop PI ring; the second-order generalized integrator filter uses the actual output frequency value of the phase-locked loop as the center frequency value of the filter to filter out all harmonics other than the center frequency.

[0025] Preferably, in step (2), after the synchronous condenser rotates, the commutation control of the machine-side bridge is divided into two stages:

[0026] In Phase 1, before the synchronous condenser reaches the mode switching speed setpoint, the machine-side bridge uses the phase angle of the machine terminal line voltage to determine the sequence number of the thyristor to be triggered each time, and adopts a forced commutation method for commutation.

[0027] In Phase 2, after the synchronous condenser reaches the mode switching speed setpoint, the machine-side bridge determines the subsequent thyristor sequence number based on the phase angle of the machine terminal line voltage and the arc angle μ, and adopts a natural commutation method for commutation.

[0028] Preferably, the mode switching speed setting is 10% of the rated speed.

[0029] Preferably, in stage 1, the method by which the machine-side bridge determines the sequence number of each subsequent thyristor trigger using the phase angle of the machine terminal line voltage is: no advance commutation control.

[0030] Preferably, in stage 2, the method by which the machine-side bridge determines the sequence number of each subsequent thyristor based on the phase angle of the machine terminal line voltage and the arc angle μ is: advance commutation control, and the advance commutation angle is γ, which is determined based on the arc angle μ.

[0031] Preferably, the method for determining the leading commutation angle γ is as follows: first, based on the triggering status of the previous cycle valve, the actual arc angle μ is measured; then, the leading commutation angle γ is determined, and the value is the arc angle μ plus a margin setpoint.

[0032] The margin is set to 10°.

[0033] A current-source type static frequency converter control device suitable for starting a synchronous condenser includes:

[0034] The grid-side bridge control module includes a speed closed-loop control module, a DC current closed-loop control module, and an α-angle control module, which are used to complete the dual closed-loop control of the speed outer loop and the current inner loop, and provide the grid-side bridge trigger angle α pulse;

[0035] The μ-angle calculation module is used to calculate the arc angle μ triggered by the previous valve on the computer-side bridge.

[0036] The rotor position angle measurement module is used to calculate the rotor position angle when the synchronous condenser is stationary.

[0037] The coefficient conversion module is used to calculate the frequency setting value based on the speed setting value;

[0038] The second-order generalized integrator filter module is used to filter out harmonics in the machine terminal line voltage and instantaneous drops caused by machine-side bridge commutation.

[0039] The DQ conversion frequency-locked loop module is used to lock the phase angle of the machine terminal line voltage and provide the actual value of the synchronous condenser speed and the actual frequency value.

[0040] The machine-side bridge trigger signal generation module is used for machine-side bridge commutation control and provides machine-side bridge trigger signals.

[0041] The machine-side bridge commutation timing determination module is used to determine the timing of machine-side bridge commutation triggering. During the forced commutation phase, the grid-side bridge assists the machine-side bridge in commutation.

[0042] The beneficial effect of this invention is that, compared with the prior art, the grid-side bridge adopts a dual closed-loop control method of speed outer loop and current inner loop throughout the entire process, so that the synchronous condenser speed value follows the motor speed set value in real time, and the speed control is more accurate and stable.

[0043] The machine-side bridge only measures the rotor position angle when the synchronous condenser is stationary. Using this rotor position angle, the thyristor valve sequence number for the first trigger of the machine-side bridge is given. After the motor rotates, the actual motor speed is no longer calculated using the rotor position angle. Instead, the actual motor speed and the phase angle of the machine terminal line voltage are obtained through filtering and frequency conversion phase-locked loop, and a trigger pulse for the machine-side bridge is given, realizing commutation based on the phase angle of the machine terminal line voltage. This method only measures the rotor position angle when stationary, eliminating the need for continuous measurement of the motor rotor position angle, thus avoiding complex rotor position angle measurement algorithms. Furthermore, the selection of the leading commutation angle at this time can neglect the influence of the power angle, avoiding commutation failure. More preferably, during the natural commutation stage, the machine-side bridge uses the phase angle of the machine terminal line voltage to provide the trigger pulse for leading commutation control, without needing to measure the rotor position angle. The selection of the leading commutation angle only considers the overlap angle μ, neglecting the influence of the motor power angle, reducing the difficulty of selecting control parameters. Real-time calculation of the overlap angle μ, with a certain commutation margin reserved, further reduces the difficulty of selecting control parameters, ensuring no risk of commutation failure while improving the power factor of the SFC. Attached Figure Description

[0044] Figure 1 This is the overall control logic block diagram of a current-source static frequency converter applicable to the startup of a synchronous condenser according to the present invention;

[0045] Figure 2 This is a structural diagram of the current source type static frequency converter of the present invention;

[0046] Figure 3 This is a block diagram of the dual closed-loop control of the network-side bridge in this invention;

[0047] Figure 4 This invention relates to a method for measuring the stationary rotor position angle of a camera converter.

[0048] Figure 5 The waveform diagram shows the test results of the terminal line voltage filtering and frequency conversion phase-locked control of this invention.

[0049] Figure 6 This is a test waveform diagram of the current source type static frequency converter of the present invention starting the synchronous condenser. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, other embodiments obtained by those skilled in the art without creative effort are all within the protection scope of this invention.

[0051] like Figure 1 As shown, Embodiment 1 of the present invention provides a current-source type static inverter control method suitable for synchronous condenser startup. In a preferred but non-limiting embodiment of the present invention, such as... Figure 2 As shown, the grid-side bridge of the current source static inverter is a 12-pulse commutator bridge, and the machine-side bridge is a 6-pulse commutator bridge. The output of the machine-side bridge is directly connected to the three-phase stator winding of the synchronous condenser. Figure 2 The 12-6 pulse inverter has a 12-pulse structure, meaning the grid-side bridge has 12 pulses and the machine-side bridge has 6 pulses. It currently has a large market share in the synchronous condenser starting field. In addition, there are 6-6 pulse inverters, where both the grid-side and machine-side bridges have 6 pulses; and 12-12 pulse inverters have a 12-pulse grid-side bridge and... Figure 2 The same applies; the machine-side bridge is also a 12-pulse bridge, and the output is connected to the motor stator winding after passing through a three-phase three-winding transformer. If the main circuit structure is changed to a 6-6 pulse inverter or a 12-12 pulse inverter, the content of this application still applies. It should also be noted that the motor in the accompanying drawings represents a synchronous condenser.

[0052] like Figure 1 As shown, the current-source static inverter control method applicable to synchronous condenser startup includes grid-side bridge control and machine-side bridge control.

[0053] I. Control of the network-side bridge

[0054] During the startup process of the synchronous condenser, the grid-side bridge adopts a dual closed-loop control method with an outer speed loop and an inner current loop, and controls the commutation based on the grid-side voltage (grid-side commutation voltage), the commutation status of the machine-side bridge, and the dual closed-loop output trigger angle.

[0055] More preferably, the commutation status of the generator-side bridge and the dual-closed-loop output firing angle determine the final firing angle. Using the firing angle and the grid-side bridge commutation voltage, a specific firing pulse is generated. The commutation voltage differs for each thyristor and can be collectively referred to as the secondary voltage of the grid-side bridge transformer. The transformer secondary voltage has a fixed relationship with the grid-side voltage; therefore, the above description can be interpreted as controlling commutation based on either the grid-side voltage, the generator-side bridge commutation status, and the dual-closed-loop output firing angle, or vice versa.

[0056] like Figure 3As shown, the synchronous condenser speed deviation is obtained based on the actual value of the synchronous condenser speed and the set value of the synchronous condenser speed. The synchronous condenser speed deviation is given a DC current reference value after passing through the PI loop. The DC current deviation is obtained by combining the actual value of the DC current. The DC current deviation is given a trigger angle after passing through the PI loop. The trigger angle is combined with the grid-side bridge commutation voltage to obtain the specific trigger pulse.

[0057] When the machine-side bridge is in forced commutation mode and during the commutation process, the trigger angle command value of the network bridge side is given as a specified value or locked. In this embodiment, the specified value method is selected, and the specified value is selected as 120°.

[0058] II. Machine Side Bridge Control

[0059] Based on the status of the synchronous condenser, and taking into account the stationary rotor position angle of the synchronous condenser, the phase angle of the machine terminal line voltage, and the arc angle μ of the previous valve triggering on the machine-side bridge, the commutation control method of the machine-side bridge is determined, specifically including:

[0060] (1) When the synchronous condenser is stationary, the rotor position angle is calculated using the rotor position measurement module. Based on the rotor position angle and the machine-side bridge control mode, the sequence number of the thyristor valve triggered for the first time after the stationary inverter is unlocked is determined. The rotor position angle measurement method is as follows: Figure 4 As shown, when the synchronous condenser is stationary, a sudden step current is applied. The rotor position angle is estimated based on the line voltage value at the motor terminals. Specifically, this includes: performing Park transformation on the line voltages at the three synchronous condensers to obtain the voltage components Eα and Eβ in the αβ coordinate system; integrating Eα and Eβ over time to obtain the flux linkage components ψα and ψβ in the αβ coordinate system; and determining the rotor position angle θ = arctan(ψα, ψβ) when the motor is stationary.

[0061] (2) After the static inverter drives the synchronous condenser to rotate, the second-order generalized integrator filter and the DQ conversion frequency lock loop module computer terminal line voltage phase angle are used. The μ angle calculation module is used to calculate the previous valve trigger arc angle μ. Based on the machine terminal line voltage phase angle, arc angle μ, and machine side bridge control mode, the subsequent thyristor valve sequence number is determined until the synchronous condenser reaches the set speed.

[0062] The machine-side bridge control mode is determined based on the actual value of the synchronous condenser speed and the synchronous condenser mode switching speed setpoint, including forced commutation mode and natural commutation mode.

[0063] In (1), when the synchronous condenser is stationary, the machine-side bridge adopts a forced commutation method based on the stationary rotor position angle;

[0064] In (2), after the synchronous condenser rotates, the commutation control of the machine-side bridge is divided into two stages:

[0065] Phase 1: Before the synchronous condenser reaches the mode switching speed setpoint, the machine-side bridge adopts a forced commutation method to commutate phases based on the phase angle of the machine terminal line voltage.

[0066] Phase 2: After the synchronous condenser reaches the mode switching speed setpoint, the machine-side bridge adopts a natural commutation method to commutate based on the phase angle of the machine terminal line voltage and the arc angle μ.

[0067] The switching speed setpoint for the synchronous condenser mode is set to 10% of the rated speed, which is 0.1 pu.

[0068] In (2), the phase angle of the terminal line voltage is obtained by frequency conversion locking the phase angle of the terminal line voltage after filtering the terminal line voltage. The specific method is as follows: Figure 1 As shown, this includes: using a second-order generalized integrator to filter the sampled value of the terminal line voltage, and then using a frequency-converting dq-transformer phase-locked loop to lock the accurate phase angle of the terminal line voltage.

[0069] The actual rotational speed of the synchronous condenser is obtained by a frequency conversion dq phase-locked loop;

[0070] The center frequency value of the input signal of the second-order generalized integrator is obtained by the frequency conversion dq transformation phase-locked loop;

[0071] The input frequency reference value of the frequency conversion dq conversion phase-locked loop adopts the starting frequency setting value of the synchronous condenser.

[0072] In (1), when the phase shifter is stationary, the method for determining the first trigger thyristor sequence number using the phase shifter rotor position angle is: no advance commutation control. The specific correspondence is as follows:

[0073] When the rotor position angle is within the 30-90° sector, the trigger-side bridge thyristor VT1 is turned on;

[0074] When the rotor position angle is within the 90-150° sector, the trigger-side bridge thyristor VT2 is turned on;

[0075] When the rotor position angle is within the sector of 150 to 210°, the trigger-side bridge thyristor VT3 is turned on.

[0076] When the rotor position angle is within the 210-270° sector, the trigger-side bridge thyristor VT4 is turned on;

[0077] When the rotor position angle is within the 270-330° sector, the trigger-side bridge thyristor VT5 is turned on;

[0078] When the rotor position angle is within the 330° to 30° sector, the trigger-side bridge thyristor VT6 is turned on;

[0079] In stage (2) 1, during the forced commutation stage of the machine-side bridge, the method for determining the subsequent thyristor trigger sequence number using the phase angle of the machine terminal line voltage is: no advance commutation control. The specific correspondence is as follows:

[0080] When the terminal line voltage UCA crosses zero in the positive direction, the thyristor VT1 on the machine side bridge is triggered to turn on.

[0081] When the reverse zero crossing of the terminal line voltage UBC occurs, the thyristor VT2 on the machine side bridge is triggered to conduct.

[0082] When the terminal line voltage UAB crosses zero in the positive direction, the thyristor VT3 on the machine side bridge is triggered to turn on.

[0083] When the reverse zero crossing of the terminal line voltage UCA occurs, the thyristor VT4 on the machine side bridge is triggered to conduct.

[0084] When the terminal line voltage UBC crosses zero in the positive direction, the thyristor VT5 on the machine side bridge is triggered to turn on.

[0085] When the reverse zero-crossing point of the terminal line voltage UAB is reached, the thyristor VT6 on the machine side bridge is triggered to conduct.

[0086] In stage 2 of (2), during the natural commutation stage of the machine-side bridge, the method for determining the subsequent thyristor trigger sequence number using the phase angle of the machine terminal line voltage is: advanced commutation control. The specific correspondence is as follows:

[0087] The positive zero-crossing point of the terminal line voltage UCA is advanced by γ angle, triggering the thyristor VT1 of the machine-side bridge to conduct;

[0088] At the reverse zero-crossing point of the terminal line voltage UBC, the thyristor VT2 on the machine side bridge is triggered to conduct by an angle γ.

[0089] The positive zero-crossing point of the terminal line voltage UAB is advanced by γ angle, triggering the thyristor VT3 of the machine-side bridge to conduct;

[0090] The reverse zero-crossing point of the terminal line voltage UCA is advanced by γ angle, triggering the thyristor VT4 of the machine-side bridge to conduct;

[0091] The positive zero-crossing point of the terminal line voltage UBC is advanced by γ angle, triggering the thyristor VT5 of the machine-side bridge to conduct;

[0092] The reverse zero-crossing point of the terminal line voltage UAB is advanced by γ angle, triggering the thyristor VT6 of the machine-side bridge to conduct;

[0093] The method for determining the leading commutation angle γ is as follows:

[0094] First, measure the actual arc angle μ based on the previous triggering of the machine-side bridge valve. Specifically, detect the zero-crossing point of the stator current at the machine terminal for each phase. The arc time of the previous valve triggering is the time when the current of the phase corresponding to the valve to be turned off crosses zero, minus the triggering pulse time of the valve to be turned on. The arc time T is converted into the arc angle μ according to the current synchronous condenser frequency value F. In practice, the arc angle μ = 0.36 * T * F, where μ is in degrees, T is in milliseconds, and the frequency is in Hertz.

[0095] Then, the leading phase angle γ is obtained by adding the margin determination to the arc angle μ;

[0096] The margin is set to 10°.

[0097] Embodiment 2 of the present invention provides a current-source type static frequency converter control device suitable for starting a synchronous condenser, comprising:

[0098] The grid-side bridge control module includes a speed closed-loop control module, a DC current closed-loop control module, and an α-angle control module, which are used to complete the dual closed-loop control of the speed outer loop and the current inner loop, and provide the grid-side bridge trigger angle α pulse;

[0099] The μ-angle calculation module is used to calculate the arc angle μ triggered by the previous valve on the computer-side bridge.

[0100] The rotor position angle measurement module is used to calculate the rotor position angle when the synchronous condenser is stationary.

[0101] The coefficient conversion module is used to calculate the frequency setting value based on the speed setting value;

[0102] The second-order generalized integrator filter module is used to filter out harmonics in the machine terminal line voltage and instantaneous drops caused by machine-side bridge commutation.

[0103] The DQ-conversion phase-locked loop (PLL) module is used to lock the phase angle of the generator terminal line voltage and provide the actual speed and frequency values ​​of the synchronous condenser. In specific implementation, the second-order generalized integrator filter module has two inputs: 1. The input signal source, i.e., the generator terminal line voltage; 2. The center frequency of the input signal source, i.e., the frequency value of the generator terminal line voltage. In this paper, the following logic is set in the second-order generalized integrator and DQ-conversion PLL stages: The set motor speed is used to calculate the set motor frequency (set frequency f(Hz) = set speed n(pu) * 50.0). This set motor frequency is used as the input frequency reference value of the DQ PLL, enabling the PLL to lock the phase more quickly and output the actual frequency value. The actual frequency value output by the PLL is sent to the second-order generalized integrator filter module as the frequency value of the generator terminal line voltage, filtering out harmonics other than this frequency value to achieve frequency conversion filtering.

[0104] The machine-side bridge trigger signal generation module is used for machine-side bridge commutation control and provides machine-side bridge trigger signals.

[0105] The machine-side bridge commutation timing determination module is used to determine the timing of machine-side bridge commutation triggering. During the forced commutation phase, the grid-side bridge assists the machine-side bridge in commutation.

[0106] Embodiment 3 of the present invention provides a controller, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program in accordance with the steps in the above method embodiments.

[0107] Figure 5 Based on Figure 1 In the synchronous condenser startup test conducted by the control logic, the waveform diagrams of the terminal line voltage filtering and frequency conversion phase-locked control effect test show that the filtering effect is good, and the speed measurement and phase-locked results are accurate.

[0108] Figure 6 Based on Figure 1 The control logic was used to test the waveforms of the entire startup process of the synchronous condenser. The results showed that the actual speed of the synchronous condenser could smoothly and accurately track the set value of the motor speed; the machine-side bridge control was good, there was no commutation failure, the electromagnetic torque had no negative value, and the power factor was high.

[0109] The beneficial effect of the present invention is that, compared with the prior art, the grid-side bridge adopts a dual closed-loop control method of speed outer loop and current inner loop throughout the entire process, so that the synchronous condenser speed value follows the command value in real time, and the speed control is more accurate and stable.

[0110] The machine-side bridge only measures the rotor position angle when the synchronous condenser is stationary. Using this rotor position angle, the thyristor valve sequence number for the first trigger of the machine-side bridge is given. After the motor rotates, the actual motor speed is no longer calculated using the rotor position angle. Instead, the actual motor speed and the phase angle of the machine terminal line voltage are obtained through filtering and frequency conversion phase-locked loop, and a trigger pulse for the machine-side bridge is given, realizing commutation based on the phase angle of the machine terminal line voltage. This method only measures the rotor position angle when stationary, eliminating the need for continuous measurement of the motor rotor position angle, thus avoiding complex rotor position angle measurement algorithms. Furthermore, the selection of the leading commutation angle at this time can neglect the influence of the power angle, avoiding commutation failure. More preferably, during the natural commutation stage, the machine-side bridge uses the phase angle of the machine terminal line voltage to provide the trigger pulse for leading commutation control, without needing to measure the rotor position angle. The selection of the leading commutation angle only considers the overlap angle μ, neglecting the influence of the motor power angle, reducing the difficulty of selecting control parameters. Real-time calculation of the overlap angle μ, with a certain commutation margin reserved, further reduces the difficulty of selecting control parameters, ensuring no risk of commutation failure while improving the power factor of the SFC.

[0111] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0112] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0113] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0114] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0115] Various aspects of this disclosure are described herein with reference to flowchart illustrations and / or block diagrams of methods and apparatus (systems) and computer program products according to embodiments of this disclosure. It should be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer-readable program instructions.

[0116] These computer-readable program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus to produce a machine such that, when executed by the processor of the computer or other programmable data processing apparatus, they create means for implementing the functions / actions specified in one or more blocks of the flowchart and / or block diagram. These computer-readable program instructions can also be stored in a computer-readable storage medium that causes a computer, programmable data processing apparatus, and / or other device to operate in a particular manner; thus, the computer-readable medium storing the instructions comprises an article of manufacture that includes instructions for implementing aspects of the functions / actions specified in one or more blocks of the flowchart and / or block diagram.

[0117] Computer-readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable data processing apparatus, or other device to produce a computer-implemented process, thereby causing the instructions executed on the computer, other programmable data processing apparatus, or other device to perform the functions / actions specified in one or more boxes of a flowchart and / or block diagram.

[0118] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of an instruction containing one or more executable instructions for implementing a specified logical function. In some alternative implementations, the functions marked in the blocks may occur in a different order than those shown in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0119] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A control method for a current-source static frequency converter (SSC) suitable for starting a synchronous condenser, comprising grid-side bridge control and machine-side bridge control of the current-source SSC, characterized in that: The grid-side bridge control is as follows: During the startup process of the synchronous condenser, the grid-side bridge adopts a dual closed-loop control method with an outer speed loop and an inner current loop, and controls the commutation based on the grid-side voltage, the commutation status of the machine-side bridge, and the dual closed-loop output trigger angle. The machine-side bridge control is as follows: (1) When the synchronous condenser is stationary, the machine-side bridge determines the thyristor sequence number that is first triggered after the static inverter is unlocked based on the rotor position angle of the synchronous condenser, and provides the desired electromagnetic torque to the synchronous condenser. (2) After the static inverter drives the synchronous condenser to rotate, the phase angle of the terminal line voltage is used to determine the sequence number of the thyristor for each subsequent triggering, providing the desired electromagnetic torque to the synchronous condenser and enabling it to accelerate smoothly, including: After the synchronous condenser reaches the mode switching speed setpoint, the machine-side bridge determines the thyristor sequence number for each subsequent triggering based on the phase angle of the machine terminal line voltage and the arc angle μ, and adopts a natural commutation method for commutation; The machine-side bridge determines the thyristor sequence number for each subsequent triggering based on the phase angle of the machine terminal line voltage and the arc angle μ by using advance commutation control, with an advance commutation angle of γ. The method for determining the leading commutation angle γ is as follows: first, based on the triggering status of the previous cycle valve, measure the actual arc angle μ; then determine the leading commutation angle γ, which is the arc angle μ plus a margin setpoint, where μ = 0.36 * T * F; In the formula, T is the arc stacking time of the last valve trigger, and F is the current synchronous condenser frequency value.

2. The current-source type static frequency converter control method for starting a synchronous condenser according to claim 1, characterized in that: During the startup process of the synchronous condenser, the grid-side bridge adopts a dual closed-loop control method with an outer speed loop and an inner current loop. Commutation is controlled based on the grid-side voltage, the commutation status of the machine-side bridge, and the dual closed-loop output trigger angle. Specifically: The actual value of the synchronous condenser speed and the set value of the synchronous condenser speed are used to obtain the synchronous condenser speed deviation. The synchronous condenser speed deviation is passed through the PI loop to give the DC current reference value. Combined with the actual value of the DC current, the DC current deviation is obtained. The DC current deviation is passed through the PI loop to give the trigger angle. The trigger angle is combined with the grid-side bridge commutation voltage to obtain the specific trigger pulse. When the machine-side bridge is in forced commutation mode and during the commutation process, the trigger angle of the network bridge side is given a specified value or locked.

3. The current-source type static frequency converter control method for starting a synchronous condenser according to claim 1, characterized in that: In (1), the machine-side bridge adopts a forced commutation method for commutation, and the method of determining the first trigger thyristor sequence number by using the rotor position angle of the condenser is: no advance commutation control.

4. The current-source type static frequency converter control method for starting a synchronous condenser according to claim 1, characterized in that: In (2), the phase angle of the terminal line voltage is obtained by frequency conversion locking the phase angle of the terminal line voltage after filtering the terminal line voltage. Specifically: After the static inverter drives the synchronous condenser to rotate, the synchronous condenser generates a terminal line voltage. The sampled value of the terminal line voltage is filtered by a second-order generalized integrator. After filtering, the phase-locked loop of frequency converter dq conversion is used to lock the accurate phase angle of the terminal line voltage. In the variable frequency dq conversion phase-locked loop, the motor frequency setting value is used as the input frequency reference value, and the actual output frequency value of the phase-locked loop is the input frequency reference value superimposed with the output value of the phase-locked loop PI ring; the second-order generalized integrator filter uses the actual output frequency value of the phase-locked loop as the center frequency value of the filter to filter out all harmonics other than the center frequency.

5. The current-source type static frequency converter control method for starting a synchronous condenser according to claim 1, characterized in that: In (2), after the synchronous condenser rotates, the commutation control of the machine-side bridge is divided into two stages: In Phase 1, before the synchronous condenser reaches the mode switching speed setpoint, the machine-side bridge uses the phase angle of the machine terminal line voltage to determine the sequence number of the thyristor to be triggered each time, and adopts a forced commutation method for commutation. In Phase 2, after the synchronous condenser reaches the mode switching speed setpoint, the machine-side bridge determines the subsequent thyristor sequence number based on the phase angle of the machine terminal line voltage and the arc angle μ, and adopts a natural commutation method for commutation.

6. The current-source type static frequency converter control method for starting a synchronous condenser according to claim 5, characterized in that: The mode switching speed setting is set to 10% of the rated speed.

7. The current-source type static frequency converter control method for starting a synchronous condenser according to claim 5, characterized in that: In stage 1, the method by which the machine-side bridge determines the thyristor sequence number for each subsequent triggering step using the phase angle of the machine terminal line voltage is: no advance commutation control.

8. The current-source type static frequency converter control method for starting a synchronous condenser according to claim 1, characterized in that: The margin setting is set to 10°.

9. A current-source static frequency converter control device suitable for starting a synchronous condenser, used to implement the current-source static frequency converter control method for starting a synchronous condenser as described in any one of claims 1-8, characterized in that: The current-source type static frequency converter control device suitable for starting a synchronous condenser includes: The grid-side bridge control module includes a speed closed-loop control module, a DC current closed-loop control module, and an α-angle control module, which are used to complete the dual closed-loop control of the speed outer loop and the current inner loop, and provide the grid-side bridge trigger angle α pulse; The μ-angle calculation module is used to calculate the arc angle μ triggered by the previous valve on the computer-side bridge. The rotor position angle measurement module is used to calculate the rotor position angle when the synchronous condenser is stationary. The coefficient conversion module is used to calculate the frequency setting value based on the speed setting value; The second-order generalized integrator filter module is used to filter out harmonics in the machine terminal line voltage and instantaneous drops caused by machine-side bridge commutation. The DQ conversion frequency-locked loop module is used to lock the phase angle of the machine terminal line voltage and provide the actual value of the synchronous condenser speed and the actual frequency value. The machine-side bridge trigger signal generation module is used for machine-side bridge commutation control and provides machine-side bridge trigger signals. The machine-side bridge commutation timing determination module is used to determine the timing of machine-side bridge commutation triggering. During the forced commutation phase, the grid-side bridge assists the machine-side bridge in commutation.

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