Inverse time limit overload protection method and device for doubly-fed motor rotor winding

Abstract

The invention discloses an inverse time limit overload protection method and device for a doubly-fed motor rotor winding. The method comprises the following steps: acquiring three-phase current of the doubly-fed motor rotor winding; rectifying the three-phase current signal of the rotor winding, and converting the three-phase current signal into a rectified current signal with six pulsating waveforms; converting an overload reference current; calculating a heat accumulation value in real time by adopting an inverse time limit heat accumulation equation based on the overload reference current and the rectified current; whether the heat accumulation value is larger than or equal to a heat accumulation threshold value or not is judged, and if yes, the protection system sends out a tripping signal. According to the technical scheme of the invention, the three-phase AC signal is rectified, and the overload heat accumulation value of the rectified output signal is calculated and discriminated by converting the overload reference current, so that the problem that the conventional inverse time limit protection method cannot meet the requirements of accuracy and timeliness when processing the extremely-low-frequency rotor current is solved. And accurate and timely inverse time limit overload protection is provided for the doubly-fed motor.

Description

Technical Field

[0001] This invention belongs to the field of power systems, and specifically relates to a method and device for inverse-time overload protection of the rotor winding of a doubly fed motor. Background Technology

[0002] With the rapid development of my country's economy, electricity demand has continued to rise, the peak-valley load difference has widened, and the proportion of large-scale grid connection of new energy sources such as wind and solar power has increased significantly, leading to power fluctuations that pose a challenge to the safe and stable operation of the power grid. Against this backdrop, the role of pumped storage power stations is becoming increasingly prominent. Compared to fixed-speed units, variable-speed pumped storage units improve the flexibility and reliability of the power system by flexibly adjusting the amplitude, phase, and frequency of the AC excitation current. Inverse-time overload protection is particularly important in pumped storage unit motors. It can use a set thermal accumulation model to calculate the thermal accumulation state of the motor windings in real time based on the degree of current overload and disconnect the motor before overheating, thus effectively preventing motor damage. Therefore, accurate inverse-time overload protection for the motor is crucial.

[0003] Currently, traditional inverse-time overload protection methods mainly rely on monitoring and protecting the motor current. When the current exceeds the lower limit setting, the inverse-time protection is activated and begins accumulating heat. Once the accumulated heat value exceeds the set value, the protection device sends a trip signal, thereby cutting off the motor power supply to prevent damage. However, this method is not suitable for doubly-fed motors. A doubly-fed motor is a type of motor that can maintain a constant grid frequency even when the speed changes. Its rotor windings are powered by a frequency converter, and the frequency of the excitation current output by the frequency converter is related to the rotor speed, characterized by an extremely low-frequency three-phase current varying in the range of 0–5 Hz. Conventional inverse-time overload protection methods cannot accurately calculate the winding heat accumulation state, thus failing to meet the accuracy and timeliness requirements of doubly-fed motor overload protection. Therefore, a new inverse-time overload protection method needs to be introduced for doubly-fed motors. Summary of the Invention

[0004] The purpose of this application is to provide a method for inverse-time overload protection of the rotor winding of a doubly fed motor, so as to solve the problem that conventional inverse-time protection methods cannot be used for extremely low frequency rotor current in a doubly fed motor.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows:

[0006] According to the first aspect of this application, a method for inverse-time overload protection of the rotor winding of a doubly-fed induction generator is proposed, comprising:

[0007] Collect the three-phase current of the rotor winding of the doubly-fed motor;

[0008] The three-phase current signal of the rotor winding is rectified and converted into a six-pulse waveform rectified current signal.

[0009] Calculate the overload reference current; based on the overload reference current and the rectified current, calculate the heat accumulation value in real time using the inverse time-limited heat accumulation equation;

[0010] If the heat accumulation value is greater than or equal to the heat accumulation threshold, the protection system will issue a trip signal.

[0011] According to some embodiments, the rectification of the three-phase current signal of the rotor winding into a six-pulse waveform rectified current signal is implemented using hardware or software methods.

[0012] According to some embodiments, the hardware method is as follows: the three-phase current signal of the rotor winding is converted into a voltage signal through a conversion circuit, and the voltage signal is input into a three-phase bridge rectifier circuit for rectification to obtain the rectified current output by the three-phase bridge rectifier circuit.

[0013] According to some embodiments, the calculation formula for rectification using the software method is as follows:

[0014] i t =max[abs(i ab ),abs(i bc ),abs(i ca )]

[0015] Where t represents time, i t Let i be the rectified current at time t; ab i bc and i ac These represent the line currents between phases AB, BC, and AC of the doubly fed motor, respectively; abs is the absolute value function, and max is the maximum value function.

[0016] According to some embodiments, the specific method for calculating the overload reference current is as follows:

[0017] I base =λI ezd

[0018] Among them, I base I is the rotor overload reference current, and λ is the equivalent coefficient; ezd This is the secondary value of the rated rotor current of the doubly fed motor.

[0019] According to some embodiments, the value range of the equivalence coefficient is 1.5 to 3.

[0020] According to some embodiments, the inverse time-limited heat accumulation equation is specifically as follows:

[0021]

[0022] Where A represents the heat accumulation value during the time interval from the initial moment to time T; i t I represents the rectified current at time t; base Indicates the rotor overload reference current; k srzd The value represents the heat dissipation effect coefficient; t represents time; T0 represents the start time of the inverse time protection; and T represents the current time.

[0023] According to some embodiments, the inverse-time start-up time refers to the moment when any one of the three-phase currents in the rotor winding of the doubly fed motor is greater than the overload protection current setting value.

[0024] According to some embodiments, the heat dissipation effect coefficient ranges from 1.02 to 1.05.

[0025] According to a second aspect of this application, a doubly-fed motor rotor winding inverse-time overload protection device is proposed, comprising an electrical quantity acquisition unit, a rectification unit, an overload protection calculation unit, and an overload protection control unit, wherein:

[0026] The electrical quantity acquisition unit is used to acquire the three-phase current of the rotor winding of the doubly fed motor;

[0027] The rectifier unit rectifies the three-phase current signal of the rotor winding and converts it into a six-pulse waveform rectified current signal.

[0028] The overload protection calculation unit is used to convert the overload reference current and calculate the heat accumulation value in real time based on the overload reference current and the rectified current using the inverse time-limited heat accumulation equation.

[0029] The overload protection control unit is used to determine whether the heat accumulation value is greater than or equal to the heat accumulation threshold, and if so, to issue a trip signal.

[0030] According to a third aspect of this application, an electronic device is proposed, including a processor and a memory, wherein the memory stores a program that can be loaded by the processor to execute the aforementioned doubly fed motor rotor winding inverse-time overload protection method.

[0031] According to a fourth aspect of this application, a computer-readable storage medium is proposed, which stores a computer program that, when executed by a processor, implements the aforementioned doubly-fed motor rotor winding inverse-time overload protection method.

[0032] Compared with existing technologies, the beneficial effects of this application are as follows: This invention addresses the problem that conventional inverse-time protection methods cannot meet the accuracy and timeliness requirements when handling extremely low-frequency rotor currents. On one hand, by rectifying the three-phase AC signal, the AC current signal is converted into a six-pulse waveform current signal, ensuring signal stability and consistency and reducing errors caused by current fluctuations. On the other hand, by using a converted overload reference current to calculate and determine the overload heat accumulation value of the rectified output signal, the accuracy and response speed of the inverse-time overload protection are improved, ensuring timely triggering of protection actions under overload conditions. This solves the problem that conventional inverse-time protection methods cannot meet the accuracy and timeliness requirements when handling extremely low-frequency rotor currents, ensuring accurate and timely inverse-time overload protection for doubly-fed motors, and effectively preventing damage to the rotor windings of doubly-fed motors due to overload. Attached Figure Description

[0033] Figure 1 This is a schematic flowchart of a method for inverse-time overload protection of a doubly fed motor rotor winding according to the present invention.

[0034] Figure 2 This is a schematic diagram of the application system of the inverse-time overload protection method for the rotor winding of a doubly fed motor according to the present invention.

[0035] Figure 3 This is a schematic diagram of the current signal conversion circuit of the present invention. Figure 3 middle,

[0036] i O For input current;

[0037] u O This refers to the output voltage.

[0038] A is an operational amplifier;

[0039] R is the input resistance;

[0040] R L This is the load resistance.

[0041] Figure 4 This is a schematic diagram of the three-phase bridge rectifier circuit of the present invention. Figure 4 middle,

[0042] VT1, VT3, and VT5 represent three diodes with their cathodes connected together, known as a common cathode group;

[0043] VT2, VT4, and VT6 represent three diodes with their anodes connected together, forming a common anode group;

[0044] u a u b u cThe voltage signal is obtained by converting the three-phase alternating current signal through a conversion circuit.

[0045] Figure 5 This is a schematic diagram of the voltage waveform after rectification by the three-phase bridge rectifier circuit of the present invention. Figure 5 middle,

[0046] u d1 This represents the envelope of the phase voltage during the positive half-cycle.

[0047] u d2 This represents the envelope of the phase voltage during the negative half-cycle.

[0048] u d This represents the total rectified output voltage, which is the difference between the two envelopes.

[0049] u ab u ac u bc u ba u ca u cb This indicates that a period of the waveform is divided into six segments, with each segment outputting a rectified voltage.

[0050] Figure 6 This invention relates to an inverse-time overload protection device for the rotor winding of a doubly fed motor.

[0051] Figure 7 This application provides a structural diagram of an electronic device. Detailed Implementation

[0052] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0053] Doubly fed motors (DFFMs) maintain a constant grid frequency despite speed variations. Their rotor windings are powered by a frequency converter, whose output excitation current frequency is related to the rotor speed, characterized as an extremely low-frequency three-phase current varying within the 0–5 Hz range. Conventional inverse-time overload protection methods struggle to accurately calculate the winding thermal accumulation state, thus failing to meet the accuracy and timeliness requirements of DFFM overload protection. Therefore, this application proposes a novel technical approach to address the issue of the inability to employ conventional inverse-time protection methods for extremely low-frequency rotor currents in DFFMs.

[0054] like Figure 1 The image shows an embodiment of a doubly-fed motor rotor winding inverse-time overload protection method provided in this application, comprising:

[0055] S100: Collects the three-phase current of the rotor winding of a doubly fed motor.

[0056] like Figure 2 In the schematic diagram of the application system for the inverse-time overload protection method of the doubly-fed motor rotor winding shown, the three-phase current i of the doubly-fed motor rotor winding is collected by NCCT. a i b i c .

[0057] S200: Rectifies the acquired three-phase current signal of the rotor winding and converts it into a six-pulse waveform current signal.

[0058] The three-phase current signal of the rotor winding is rectified and converted into a six-pulse waveform rectified current signal. This can be achieved using either hardware or software methods.

[0059] In some embodiments, the hardware method involves using a three-phase bridge rectifier circuit for rectification. This involves converting the acquired three-phase AC current signal into a voltage signal via a conversion circuit, then inputting the resulting voltage signal into the three-phase bridge rectifier circuit for rectification, thereby obtaining the rectified current i output by the three-phase bridge rectifier circuit. t .

[0060] like Figure 3 The diagram shows a current signal conversion circuit provided in an embodiment of this application, wherein i O For input current; u O R is the output voltage; A is the operational amplifier; R is the input resistance; R L The load resistor is used. The AC current signal is connected to i. O port, in u O The port receives a voltage signal.

[0061] like Figure 4 The diagram shown is a schematic of a three-phase bridge rectifier circuit provided in an embodiment of this application, which converts the voltage signal u obtained through the conversion circuit. a u b u c Inputting a three-phase bridge rectifier circuit yields the rectified current i output by the three-phase bridge rectifier circuit. t The voltage waveform after rectification by the three-phase bridge rectifier circuit is as follows: Figure 5 As shown, where u d1 This represents the envelope of the phase voltage during the positive half-cycle; u d2 This represents the envelope of the phase voltage during the negative half-cycle; u d This represents the total rectified output voltage, which is the difference between the two envelopes; u ab u ac u bc u ba u ca u cbThis indicates that a period of the waveform is divided into six segments, with each segment outputting a rectified voltage.

[0062] In some embodiments, the calculation formula for rectification using a software method is as follows:

[0063] i t =max[abs(i ab ),abs(i bc ),abs(i ca )]

[0064] Where t represents time, i t Let i be the rectified current at time t; ab i bc and i ac These represent the line currents between phases AB, BC, and AC of the doubly fed motor, respectively; abs is the absolute value function, and max is the maximum value function.

[0065] S300: Calculate the overload reference current; calculate the heat accumulation value in real time using the inverse time-limited heat accumulation equation based on the overload reference current and the rectified current.

[0066] The specific method for calculating the overload reference current is as follows:

[0067] I base =λI ezd

[0068] Among them, I base I is the rotor overload reference current, and λ is the equivalent coefficient; ezd This represents the secondary value of the rated rotor current of the doubly-fed induction generator. The equivalent coefficient λ ranges from 1.5 to 3.

[0069] The method for calculating λ, the equivalent coefficient, is to solve it by comparing the calculated value of heat accumulation over a fixed time period with that of the traditional heat accumulation method.

[0070] In the application system of the doubly-fed generator rotor winding overload protection method shown in the figure, the doubly-fed generator specification of the pumped storage unit is 330MW, and λ can be taken as 2.3; I ezd The secondary rated current of the doubly-fed induction generator rotor is 0.853A, using a 7500:1 current transformer. base I represents the rotor overload reference current, which is obtained through calculation. base The value is 1.962A.

[0071] The rotor overload reference current is substituted into the inverse-time thermal accumulation equation to calculate the thermal accumulation value A in real time for the rectified output signal. In some embodiments, the calculation formula is as follows:

[0072]

[0073] Where A represents the heat accumulation value during the time interval from the initial moment to time T; i t I represents the rectified current at time t; base Indicates the rotor overload reference current; k srzd The value represents the heat dissipation effect coefficient; t represents time; T0 represents the start time of the inverse time protection; and T represents the current time.

[0074] In some embodiments, the inverse-time start-up time refers to the moment when any one of the three-phase currents in the rotor winding of the doubly fed motor is greater than the overload protection current setting value.

[0075] In some embodiments, the heat dissipation effect coefficient ranges from 1.02 to 1.05.

[0076] S400: Determine whether the heat accumulation value is greater than or equal to the heat accumulation threshold. If so, the protection system issues a trip signal.

[0077] The discriminant formula is:

[0078] A≥KS zd

[0079] Among them, KS zd This represents the heat accumulation setpoint. Based on the actual situation of the doubly-fed generator in this 300MW pumped storage unit, 40.0 is taken.

[0080] Substituting the above parameters into the inverse time overload protection thermal accumulation value judgment formula to calculate that when the thermal accumulation value exceeds the thermal accumulation set value at time t = 12.83s, the protection system immediately issues a trip signal.

[0081] Figure 6 The image shows an embodiment of a doubly-fed motor rotor winding inverse-time overload protection device 500, comprising an electrical quantity acquisition unit 501, a rectifier unit 502, an overload protection calculation unit 503, and an overload protection control unit 504. Wherein:

[0082] The electrical quantity acquisition unit 501 is used to acquire the three-phase current of the rotor winding of a doubly fed motor.

[0083] The rectifier unit 502 rectifies the three-phase current signal of the rotor winding and converts it into a six-pulse waveform rectified current signal.

[0084] The overload protection calculation unit 503 is used to convert the overload reference current and calculate the heat accumulation value in real time based on the overload reference current and the rectified current using the inverse time-limited heat accumulation equation.

[0085] The overload protection control unit 504 is used to determine whether the heat accumulation value is greater than or equal to the heat accumulation threshold, and if so, to issue a trip signal.

[0086] The device performs functions similar to those described above; other functions are described in the preceding descriptions and will not be repeated here.

[0087] Figure 7 The diagram shown is a structural diagram of an electronic device provided in this application. It includes a processor and a memory. The memory stores computer instructions; when the processor executes the computer instructions, it causes the processor to perform the computer instructions to achieve the following: Figure 1 The method and its detailed scheme are shown.

[0088] It should be understood that the above-described device embodiments are merely illustrative, and the device disclosed in this invention can be implemented in other ways. For example, the division of units / modules described in the above embodiments is only a logical functional division, and there may be other division methods in actual implementation. For example, multiple units, modules, or components may be combined, integrated into another system, or some features may be ignored or not executed.

[0089] Furthermore, unless otherwise specified, the functional units / modules in the various embodiments of the present invention can be integrated into one unit / module, or each unit / module can exist physically separately, or two or more units / modules can be integrated together. The integrated units / modules described above can be implemented in hardware or as software program modules.

[0090] If the integrated unit / module is implemented in hardware, the hardware can be digital circuits, analog circuits, etc. The physical implementation of the hardware structure includes, but is not limited to, transistors, memristors, etc. Unless otherwise specified, the processor or chip can be any suitable hardware processor, such as a CPU, GPU, FPGA, DSP, and ASIC, etc. Unless otherwise specified, the on-chip cache, off-chip memory, and storage can be any suitable magnetic or magneto-optical storage medium, such as resistive random access memory (RRAM), dynamic random access memory (DRAM), static random access memory (SRAM), enhanced dynamic random access memory (EDRAM), high-bandwidth memory (HBM), hybrid memory cube (HMC), etc.

[0091] If the integrated unit / module is implemented as a software program module and sold or used as an independent product, it can be stored in a computer-readable storage device (CMD). Based on this understanding, the technical solution of this invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a memory and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this disclosure. The aforementioned memory includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0092] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, causes the processor to perform the following actions: Figure 1 The method and its detailed scheme are shown.

[0093] It should be clearly understood that this application describes how specific examples are formed and used, but this application is not limited to any details of these examples. Rather, based on the teachings of the disclosure of this application, these principles can be applied to many other embodiments.

[0094] Furthermore, it should be noted that the above figures are merely illustrative representations of the processes included in the method according to exemplary embodiments of this application, and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Additionally, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0095] The above embodiments are merely illustrative of the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solutions based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A method for inverse-time overload protection of the rotor winding of a doubly-fed induction generator, characterized in that, include: Collect the three-phase current of the rotor winding of the doubly-fed motor; The three-phase current signal of the rotor winding is rectified and converted into a six-pulse waveform rectified current signal. Calculate the overload reference current; The heat accumulation value is calculated in real time using the inverse time-limited heat accumulation equation based on the overload reference current and the rectified current. If the heat accumulation value is greater than or equal to the heat accumulation threshold, the protection system will issue a trip signal.

2. The method for inverse-time overload protection of the rotor winding of a doubly-fed motor as described in claim 1, characterized in that: The rectification of the three-phase current signal of the rotor winding into a six-pulse waveform rectified current signal is achieved by hardware or software methods.

3. The method for inverse-time overload protection of the rotor winding of a doubly-fed motor as described in claim 2, characterized in that, The hardware method is as follows: the three-phase current signal of the rotor winding is converted into a voltage signal through a conversion circuit, and the voltage signal is input into a three-phase bridge rectifier circuit for rectification to obtain the rectified current output by the three-phase bridge rectifier circuit.

4. The method for inverse-time overload protection of the rotor winding of a doubly-fed motor as described in claim 2, characterized in that, The software method uses the following formula for calculating rectification: i t =max[abs(i ab ),abs(i bc ),abs(i ca )] Where t represents time, i t Let i be the rectified current at time t; ab i bc and i ac These represent the line currents between phases AB, BC, and AC of the doubly fed motor, respectively; abs is the absolute value function, and max is the maximum value function.

5. The method for inverse-time overload protection of the rotor winding of a doubly-fed motor as described in claim 1, characterized in that: The specific method for calculating the overload reference current is as follows: I base =λI ezd Among them, I base I is the rotor overload reference current, and λ is the equivalent coefficient; ezd This is the secondary value of the rated rotor current of the doubly fed motor.

6. The method for inverse-time overload protection of the rotor winding of a doubly-fed motor as described in claim 5, characterized in that: The value range of the equivalent coefficient is 1.5 to 3.

7. The method for inverse-time overload protection of the rotor winding of a doubly-fed motor as described in claim 1, characterized in that: The inverse time-limited heat accumulation equation is as follows: Where A represents the heat accumulation value during the time interval from the initial moment to time T; i t I represents the rectified current at time t; base Indicates the rotor overload reference current; k srzd The value represents the heat dissipation effect coefficient; t represents time; T0 represents the start time of the inverse time protection; and T represents the current time.

8. The method for inverse-time overload protection of the rotor winding of a doubly-fed motor as described in claim 7, characterized in that: The inverse-time start-up moment refers to the moment when the current in any one of the three phases of the rotor winding of the doubly fed motor is greater than the overload protection current setting value.

9. The method for inverse-time overload protection of the rotor winding of a doubly-fed motor as described in claim 7, characterized in that: The value range of the heat dissipation effect coefficient is 1.02 to 1.

05.

10. A doubly-fed motor rotor winding inverse-time overload protection device, characterized in that, It includes an electrical quantity acquisition unit, a rectification unit, an overload protection calculation unit, and an overload protection control unit, wherein: The electrical quantity acquisition unit is used to acquire the three-phase current of the rotor winding of the doubly fed motor; The rectifier unit rectifies the three-phase current signal of the rotor winding and converts it into a six-pulse waveform rectified current signal. The overload protection calculation unit is used to convert the overload reference current and calculate the heat accumulation value in real time based on the overload reference current and the rectified current using the inverse time-limited heat accumulation equation. The overload protection control unit is used to determine whether the heat accumulation value is greater than or equal to the heat accumulation threshold, and if so, to issue a trip signal.

11. An electronic device, characterized in that: It includes a processor and a memory, wherein the memory stores a program that can be loaded by the processor to execute the method as described in any one of claims 1-9.

12. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the method according to any one of claims 1-9.

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