Control method and system for suppressing series resonance of input end of variable frequency speed regulation system

Abstract

The invention discloses a control method and system for suppressing series resonance of an input end of a variable frequency speed regulation system, and relates to the technical field of electrical transmission, and the method comprises the steps: monitoring the voltage of a DC bus when an inversion module is in a standby state; after the control signal is triggered, resonance suppression control is started; and when the stop signal is triggered, the resonance suppression control is stopped. The control method for restraining series resonance of the input end of the variable frequency speed regulation system is suitable for general frequency converters and variable frequency air conditioner products, hardware design does not need to be changed, a step-down control program strategy is added, only the inverter module operates in a standby state, the burden of a control chip is not increased, execution of a main program is not affected, and the control cost is reduced. The problem of overvoltage caused by series resonance is solved.

Description

Technical Field

[0001] The present invention relates to the field of electric transmission technology, and in particular to a control method and system for suppressing series resonance at the input end of a variable frequency speed regulation system. Background Art

[0002] In the variable frequency speed control of electric motors, variable frequency speed controllers are widely used in various industries due to their advantages of high efficiency, energy saving and precise control. Low voltage variable frequency speed control systems (taking three-phase 380V AC power supply as an example) are usually composed of four modules: filtering, rectification, braking and inversion, of which the filtering and rectification modules constitute the input end.

[0003] The filter module generally includes a protection circuit (such as a varistor RV) and common-mode and differential-mode filter circuits (such as safety capacitors CX / CY and common-mode inductors LC) to ensure electromagnetic compatibility (EMC) to suppress high-frequency noise and electromagnetic interference; the rectifier module uses a full-bridge diode rectifier circuit and a smoothing capacitor to convert AC voltage into DC voltage. The rectifier module has the advantages of simple structure, low cost and strong overload capacity, but there is a problem of large input current harmonics. When such equipment is used in large quantities in low-voltage distribution networks, the grid voltage waveform is prone to distortion, affecting the quality of the grid.

[0004] In addition, the brake module is composed of a switching device IGBT and a brake resistor Rb in series. When the motor is in the power generation state, the energy will be fed back to the DC bus, causing the bus voltage to increase. The function of the brake module is to start the brake circuit, consume the feedback energy through the brake resistor, and stabilize the DC bus voltage. The inverter module converts the DC voltage into an AC voltage with adjustable frequency and amplitude through a full-bridge inverter circuit and a pulse width modulation (PWM) control circuit to achieve variable frequency speed control of the motor.

[0005] In order to reduce the harmonic distortion rate of input current, some variable frequency speed regulation systems have added AC inductors at the front end of the filter module. Although this measure is effective, there are still some problems in practical applications.

[0006] In large-scale industrial and commercial application scenarios, such as variable frequency central air conditioning systems, abnormal overvoltage protection and system lockout caused by input inductance often occur, and even line varistor overheating, smoothing capacitor overvoltage bursting, and power module breakdown. After analysis, it was found that the above abnormalities occurred under the following two conditions: (1) the power supply voltage is severely distorted; (2) the variable frequency speed regulation system is powered on without turning on the inverter output. In this case, the AC inductance at the input end will cause series resonance, resulting in high-frequency oscillations in the AC inductor and rectifier module, which increases the DC bus voltage.

[0007] The generation of series resonance is related to the parameters of the AC inductor and capacitor at the input end. When the power supply voltage contains harmonic components close to the resonant frequency, it will cause the input voltage of the rectifier circuit to contain high-amplitude resonant frequency components, causing the DC bus voltage to rise. Although resonance can be avoided by adjusting the parameters of the inductor and capacitor, adjustment is not a long-term solution because the inductor and capacitor values ​​are affected by the process and current and have large deviations. In addition, adjusting the circuit topology, such as moving the AC inductor to the output end, can also effectively prevent resonance, but this method requires product redesign, engineering implementation is difficult, and cannot be quickly applied to existing equipment. Therefore, the prior art urgently needs a control method that can effectively suppress the series resonance at the input end of the variable frequency speed regulation system to solve the above problems. Summary of the invention

[0008] In view of the above-mentioned problems, the present invention is proposed.

[0009] Therefore, the technical problem solved by the present invention is: the existing method of suppressing series resonance at the input end of the variable frequency speed regulation system has the disadvantages of relying on circuit parameter adjustment, unstable parameters of components such as inductance and capacitance, and high cost of topology adjustment, as well as how to optimize the suppression of series resonance without changing the existing circuit structure.

[0010] In order to solve the above technical problems, the present invention provides the following technical solutions: a control method for suppressing series resonance at the input end of a variable frequency speed regulation system, comprising:

[0011] When the inverter module is in standby mode, monitor the DC bus voltage;

[0012] When the control signal is triggered, the resonance suppression control is started;

[0013] When the stop signal is triggered, the resonance suppression control stops.

[0014] As a preferred scheme of the control method for suppressing the series resonance at the input end of the variable frequency speed regulation system described in the present invention, the control method is implemented while keeping the circuit topology structure of the filter module, the rectifier module and the inverter module at the input end of the variable frequency speed regulation system unchanged, and the AC inductance and capacitance value parameters in the filter module unchanged.

[0015] As a preferred solution of the control method for suppressing the series resonance at the input end of the variable frequency speed regulation system described in the present invention, the trigger control signal refers to the trigger signal when the DC bus voltage is monitored to be greater than the resonance suppression control starting threshold value U s1 And the voltage rise is caused by series resonance, the control signal generated.

[0016] As a preferred solution of the control method for suppressing the series resonance at the input end of the variable frequency speed regulation system described in the present invention, the resonance suppression control includes providing an energy release channel on the DC bus side to consume the resonance energy.

[0017] As a preferred scheme of the control method for suppressing the series resonance at the input end of the variable frequency speed regulation system described in the present invention, wherein: the providing of the energy release channel includes determining whether the variable frequency speed regulation system is configured with a braking module, and if the braking module is configured, control is performed according to the first resonance suppression scheme; if the braking module is not configured, control is performed according to the second resonance suppression scheme.

[0018] As a preferred solution of the control method for suppressing the series resonance at the input end of the variable frequency speed regulation system described in the present invention, the first resonance suppression scheme includes implementing PWM control on the brake switch, consuming the resonance electric energy by the brake resistor, and stabilizing the DC bus voltage U dc ; U dc The control cycle is 1 second, and the initial value of the on-duty ratio D is set to D0; if U dc Start to decrease, keep D unchanged; if U dc There is no decrease, D increases in steps of ΔD, increasing the consumption of resonant electric energy; when the DC bus voltage drops to U s2 After that, a stop signal is generated.

[0019] As a preferred solution of the control method for suppressing the series resonance at the input end of the variable frequency speed regulation system described in the present invention, the second resonance suppression scheme includes implementing ultra-low frequency and low current PWM output control on the inverter module, consuming the resonant electric energy by the stator winding of the motor, stabilizing U dc , and keep the motor rotor stationary; U dc The control cycle is 1 second, and the target output current I ref The initial value is set to I ref0 ;if U dc Start descending, keep I ref unchanged; if U dc No decline, I ref With ΔI ref The step size increases, increasing the consumption of resonant electric energy; when the DC bus voltage drops to U s2 After that, a stop signal is generated.

[0020] Another object of the present invention is to provide a control system for suppressing the series resonance at the input end of a variable frequency speed regulation system. By constructing a control system for suppressing the series resonance at the input end of a variable frequency speed regulation system, the present invention solves the problem of series resonance at the input end in the existing variable frequency speed regulation system, in which the resonant frequency is affected by current and voltage distortion, resulting in high-frequency voltage oscillation and abnormal increase in bus voltage.

[0021] In order to solve the above technical problems, the present invention provides the following technical solutions: a control system for suppressing series resonance at the input end of a variable frequency speed regulation system, comprising: a detection unit and a control unit; the detection unit is used to monitor the DC bus voltage when the inverter module is in standby mode; the control unit is used to start resonance suppression control when a control signal is triggered; and stop resonance suppression control when a stop signal is triggered.

[0022] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the control method for suppressing the series resonance at the input end of a variable frequency speed regulation system as described above are implemented.

[0023] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the control method for suppressing the series resonance at the input end of a variable frequency speed regulation system as described above.

[0024] Beneficial effects of the present invention: The control method for suppressing the series resonance at the input end of the variable frequency speed regulation system provided by the present invention is applicable to general frequency converters and variable frequency air-conditioning products. There is no need to change the hardware design. By adding a step-down control program strategy, it only runs when the inverter module is in standby mode, does not increase the burden on the control chip, does not affect the execution of the main program, and solves the problem of overvoltage caused by series resonance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0026] Figure 1 An overall flow chart of a control method for suppressing series resonance at the input end of a variable frequency speed regulation system provided by one embodiment of the present invention.

[0027] Figure 2 A resonance suppression control flow chart of a control method for suppressing series resonance at the input end of a variable frequency speed regulation system provided by an embodiment of the present invention.

[0028] Figure 3 A structural diagram of a variable frequency speed regulation system providing a control method for suppressing series resonance at the input end of a variable frequency speed regulation system according to an embodiment of the present invention.

[0029] Figure 4 A circuit diagram of a filter module for a control method for suppressing series resonance at the input end of a variable frequency speed regulation system provided by an embodiment of the present invention.

[0030] Figure 5 A waveform diagram of actually measured line voltage of a control method for suppressing series resonance at the input end of a variable frequency speed regulation system provided by an embodiment of the present invention.

[0031] Figure 6 A three-phase equivalent circuit diagram of a control method for suppressing series resonance at the input end of a variable frequency speed regulation system provided by an embodiment of the present invention.

[0032] Figure 7 A single-phase equivalent resonant circuit diagram of a control method for suppressing series resonance at the input end of a variable frequency speed regulation system provided by an embodiment of the present invention.

[0033] Figure 8 A diagram of simulation results when there is no inverter output for a control method for suppressing series resonance at the input end of a variable frequency speed regulation system provided by an embodiment of the present invention.

[0034] Fig. 9 A simulation result diagram of a control method for suppressing series resonance at the input end of a variable frequency speed regulation system provided by an embodiment of the present invention when there is no inverter output.

[0035] Fig.10 A graph showing a variation trend of a DC bus voltage when there is no inverter output in a control method for suppressing series resonance at the input end of a variable frequency speed regulation system provided by an embodiment of the present invention.

[0036] Fig.11 This is a diagram of experimental results of a control method for suppressing series resonance at the input end of a variable frequency speed regulation system provided by an embodiment of the present invention.

[0037] Fig.12 An overall structural diagram of a control method for suppressing series resonance at the input end of a variable frequency speed regulation system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0038] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0039] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0040] Example 1

[0041] Reference Figure 1-Figure 2 , is an embodiment of the present invention, and provides a control method for suppressing series resonance at the input end of a variable frequency speed regulation system, comprising:

[0042] When the inverter module is in standby mode, monitor the DC bus voltage;

[0043] When the control signal is triggered, the resonance suppression control is started;

[0044] When the stop signal is triggered, the resonance suppression control stops.

[0045] The control method is implemented while keeping the circuit topology of the filter module, the rectifier module and the inverter module at the input end of the variable frequency speed regulation system unchanged, and the parameters of the AC inductance and capacitance value in the filter module unchanged.

[0046] The trigger control signal refers to the situation when the DC bus voltage is greater than the resonance suppression control starting threshold U s1 And the voltage rise is caused by series resonance, the control signal generated.

[0047] Resonance suppression control involves providing an energy release channel on the DC bus side to consume the resonant energy.

[0048] Providing an energy release channel includes determining whether the variable frequency speed regulation system is equipped with a braking module, and if so, executing control according to a first resonance suppression scheme; if not, executing control according to a second resonance suppression scheme.

[0049] The first resonance suppression scheme includes implementing PWM control on the brake switch, using the brake resistor to consume the resonance energy and stabilize the DC bus voltage U dc ; U dc The control cycle is 1 second, and the initial value of the on-duty ratio D is set to D0; if U dc Start to decrease, keep D unchanged; if U dc There is no decrease, D increases in steps of ΔD, increasing the consumption of resonant electric energy; when the DC bus voltage drops to U s2 After that, a stop signal is generated.

[0050] The second resonance suppression scheme includes implementing ultra-low frequency and low current PWM output control on the inverter module, consuming the resonant electric energy through the stator winding of the motor to stabilize U dc , and keep the motor rotor stationary; U dc The control cycle is 1 second, and the target output current I ref The initial value is set to I ref0 ;if U dc Start descending, keep I ref unchanged; if U dcNo decline, I ref With ΔI ref The step size increases, increasing the consumption of resonant electric energy; when the DC bus voltage drops to U s2 After that, a stop signal is generated.

[0051] Example 2

[0052] Reference Figure 3-Figure 11 , which is an embodiment of the present invention, provides a control method for suppressing series resonance at the input end of a variable frequency speed regulation system. In order to verify the beneficial effects of the present invention, a scientific demonstration is carried out through simulation experiments.

[0053] The variable frequency speed control of the motor has the characteristics of high efficiency, energy saving and precise control, and has been widely used in various industries. The basic structure and power conversion links of the low voltage (three-phase 380V AC power supply) variable frequency speed control controller are as follows: Figure 3 As shown, it usually includes four modules: filtering, rectification, braking and inversion. The filtering module and the rectification module constitute the input end of the variable frequency speed regulation controller.

[0054] The filter module includes a protection circuit (varistor RV) to ensure EMC characteristics and a common mode / differential mode filter circuit (safety capacitor CX / CY and common mode inductor LC). Figure 4 shown.

[0055] The rectifier module consists of a full-bridge diode rectifier circuit and a smoothing capacitor C, which converts AC voltage into a relatively stable DC voltage. It has the advantages of simple structure, strong overload capacity and low cost, and is currently the preferred solution for variable frequency speed regulation products. However, its biggest disadvantage is that the harmonics of the input current are large. When there are a large number of such electrical devices in the low-voltage distribution network, the voltage waveform will be seriously distorted.

[0056] The braking module is composed of a switching device IGBT and a braking resistor Rb in series. When the motor is in the power generation state and the energy is fed into the DC bus through the inverter circuit, causing the DC bus voltage to rise sharply, the braking circuit starts, consumes the corresponding energy, and maintains the stability and safety of the DC bus voltage.

[0057] The inverter module consists of a full-bridge inverter circuit composed of fully controlled switching devices such as IGBT and a corresponding PWM control circuit, which converts the DC bus voltage into an AC voltage with variable frequency and amplitude, and implements variable frequency speed control on the motor.

[0058] In order to ensure the power quality of the low-voltage distribution network, the existing regulations stipulate the limits of harmonic current emission in the low-voltage power supply system for equipment with rated current ≤16A and >16A. In order to suppress the input current harmonics of the variable frequency speed regulation system, an AC inductor L is installed at the front end of the filter module. It is simple, reliable and cost-effective, and is a commonly used measure. Selecting an AC inductor with appropriate inductance within a reasonable voltage drop range can reduce the total harmonic distortion rate of the input current from 180% to 40%. In order to further suppress current harmonics, some products will use an AC inductor with a larger inductance.

[0059] However, new problems have recently been encountered in market applications. The variable frequency central air conditioning system running in a large industrial and commercial environment has abnormal overvoltage protection and lockout, and even has faults such as overheating and burning of the line varistor RV2, overvoltage burst of the smoothing capacitor, and overvoltage breakdown of the power module. Through on-site detection and analysis, it was found that the above abnormalities all occurred under the following two conditions: first, the power supply voltage was severely distorted; second, the variable frequency speed regulation system was powered on but the inverter output was not turned on. Figure 5 The waveforms are measured on site. The yellow curve is the power line voltage, and the green curve is the rectifier bridge input line voltage. It shows that there is a strong high-frequency oscillation on the AC inductor and the DC bus voltage rises abnormally.

[0060] Since the inverter module is in standby mode, the driver software is not running and outputting, so it is possible that resonance has occurred at the input end. Figure 4 The circuit shown in the figure is equipped with an AC inductor at the front end of the filter module for resonance analysis. In the absence of common-mode current interference and abnormal overvoltage, the common-mode inductor L C and the varistor R V Can be ignored; and the capacitance of C is μF level X In comparison, C Y The capacitance is only nF level and can be ignored. X The parallel resistor R X are all hundreds of kΩ, which can also be ignored; in addition, since the inverter module has no output in standby mode, the output of the DC bus can be equivalent to an open circuit state. This can be simplified as follows Figure 6 The equivalent circuit shown is a typical three-phase series resonant circuit and can be transformed into Figure 7 The single-phase equivalent resonant circuit shown in the figure, where R is the coil resistance of the AC inductor, L r =L1,C r =6C X .

[0061] According to Ohm's law of alternating current:

[0062]

[0063] Resonance frequency fr for

[0064]

[0065] The quality factor Q is the inductor voltage amplitude U at resonance L Or capacitor voltage amplitude U C Ratio to power supply voltage amplitude U

[0066]

[0067] Whether resonance occurs depends on whether the power supply voltage contains harmonic components that are consistent with or close to the resonant frequency. Assuming R = 0.2Ω, L r =30mH, C r =2μF, then from equations (2) and (3) we can get f r ≈650Hz, Q≈612, that is, if the power supply contains a 650Hz harmonic component with an amplitude of 1V, it will be amplified to 612V on the inductor and capacitor, resulting in the input voltage u of the rectifier module ac2 High frequency oscillation, DC bus voltage u dc Follow u ac2 The peak-to-peak variation of

[0068] based on Figure 3 The system structure is used to build a simulation calculation model, confirm the resonance development process, and verify the theoretical analysis results. Figure 5 Similar power supply voltage, as the input power supply of the variable frequency speed regulation system, Figure 8 and Fig. 9 This is the simulation waveform without inverter output (R = 0Ω, L = 30mH, C X =0.33μF), Figure 8 The power line voltage is the yellow line and the input line voltage of the rectifier bridge is the green line. The input voltage of the rectifier bridge oscillates violently at a frequency of 650Hz, which is consistent with the theoretical analysis results. The DC bus voltage gradually increases and can reach 1400V within 50 seconds. When there is an inverter output, the inductance of the AC inductor drops to 20mH due to the saturation characteristics, the resonant frequency of the circuit increases to 796Hz, there is no resonance phenomenon, the input voltage of the rectifier bridge is in the shape of a square wave, and the DC bus voltage is always lower than the peak-to-peak value of the power supply voltage.

[0069] The three-phase power supply has a symmetrical structure and theoretically contains only odd harmonics. However, the variable frequency speed regulation system usually adopts three-phase three-wire input and utilizes line voltage, so it is mainly affected by (6n±1) harmonics. Fig.10 The simulation results of the DC bus voltage changing with L when there is no inverter output are shown in Figure 2. The DC bus voltage changing with L when there is no inverter output (C X=0.33μF), indicating that resonance occurs only at the frequency point (6n±1)×50Hz and its vicinity, and the DC bus voltage increases significantly.

[0070] In summary, in an environment where the power supply voltage is severely distorted, a variable frequency speed control system with an AC inductor connected in series at the input may generate series resonance in standby mode, causing an abnormal increase in the DC bus voltage, which may trigger overvoltage protection and lock the system, or even damage circuit components. In principle, there are two ways to suppress series resonance.

[0071] The first method: keep the original circuit topology, change the parameters of the AC inductor and X capacitor, make the series resonance frequency close to (6n+3)×50Hz, and avoid the harmonic components of the three-phase power supply. However, the inductance deviation of the AC inductor is large and changes with the current, and the parameters of the X capacitor are not accurate, so this method of suppressing series resonance by adjusting component parameters still has considerable risks.

[0072] The second method is to change the circuit topology and move the AC inductor from the input end of the filter module to the output end, so that there is no series resonant circuit when the inverter module is in standby mode. However, this method requires redesigning and developing the product, which is a large workload and cannot quickly respond to the rectification of existing products and equipment that has been put into operation.

[0073] The simulation experiment uses a variable frequency air conditioner with the experimental equipment model KFRd-120QW / 7YAD82A.

[0074] The compressor drive motor is a brushless DC motor, with a rated cooling capacity of 7.1kW, a rated input power of 2.3kW, and a rated input current of 10.6A. The single-board integrated variable frequency speed regulation circuit includes filtering, rectification and inverter modules, but no brake module.

[0075] Filter module and Figure 4 The circuits shown are exactly the same, where the inductance of the AC inductor when a current of 1A flows through it is L = 29mH, and the equivalent nominal capacitance of the X capacitor is C X =0.33μF, so the corresponding series resonant frequency is about 650Hz.

[0076] The experimental power supply uses a programmable AC power supply, synthesized as Figure 5 The distorted power supply voltage waveform shown, assuming U s1 =730V, U s2 =700V, I ref0 =1A, ΔI ref =0.5A, when resonance occurs, resonance suppression control based on the inverter module is implemented.

[0077] Fig.11The yellow line is the inverter output current, and the red line is the DC bus voltage. When the series resonance causes U dc When the voltage exceeds 730V, the series resonance control is started, the output current frequency f = 0.05Hz, and the switching frequency f s =6kHz, continuous operation for 3 seconds, during which I ref Keep at 1A, U dc Reduced to 684V; after the suppression of series resonance control stops, U dc After 13.7 seconds, the voltage rises and exceeds 730V. The resonance suppression control restarts and repeats in this way. The operation effect is good and the abnormal rise of DC bus voltage is effectively suppressed.

[0078] Therefore, the method of the present invention is applicable to general frequency converters, variable frequency air conditioners and other products. There is no need to change the hardware design. A simple step-down control program module is added and only runs when the inverter module is in standby state. The burden of the control chip is not increased and the execution of the main program is not affected. The problem of overvoltage caused by series resonance is solved.

[0079] Example 3

[0080] An embodiment of the present invention is different from the first two embodiments in that:

[0081] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program codes.

[0082] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0083] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or, if necessary, processing in another suitable manner, and then stored in a computer memory.

[0084] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0085] Example 4

[0086] Reference Fig.12 , is an embodiment of the present invention, providing a control system for suppressing series resonance at the input end of a variable frequency speed regulation system, comprising:

[0087] Detection unit 100 and control unit 200;

[0088] The detection unit 100 is used to monitor the DC bus voltage when the inverter module is in the standby state;

[0089] The control unit 200 is used to start the resonance suppression control when a control signal is triggered, and to stop the resonance suppression control when a stop signal is triggered.

[0090] Example 5

[0091] Reference Figure 2 , is an embodiment of the present invention, which provides a control method for suppressing the series resonance at the input end of a variable frequency speed regulation system, a method for suppressing the series resonance by embedding a simple control program while keeping the circuit topology and parameters unchanged during the control process. The basic principle is to monitor the DC bus voltage when the inverter module is in standby mode, and when it is found that the DC bus voltage rises to the resonance suppression control start threshold Us1 due to series resonance, an energy release channel is provided on the DC bus side to break the series resonance circuit structure and suppress the DC bus voltage; when the DC bus voltage drops to the resonance suppression control stop threshold Us2, the energy release channel on the DC bus side is closed. Assume that the maximum line voltage peak value of the input power supply is U max , then U max s2 s1 Different energy release channels are used depending on whether the system is equipped with a brake module. The resonance suppression control process is as follows: Figure 2 shown.

[0092] 1. Resonance suppression control based on brake module:

[0093] The system with a brake module monitors the DC bus voltage U when the inverter module is in standby mode. dc , when it is found that U dc Reach U s1 After that, PWM control is implemented on the brake switch, and the brake resistor consumes the resonant energy to stabilize U dc ; U dc The control cycle is 1 second, and the initial value of the on-duty ratio D is set to D0. dc Start to decrease, keep D unchanged; if U dc There is no decrease, D increases in steps of ΔD, increasing the consumption of resonant electric energy; when the DC bus voltage drops to U s2 Then, turn off the brake switch.

[0094] 2. Resonance suppression control based on inverter module:

[0095] The system without brake module monitors U when the inverter module is in standby state. dc , when it is found that U dc Reach U s1 After that, the inverter module is controlled by ultra-low frequency and small current PWM output, and the stator winding of the motor consumes the resonant electric energy to stabilize U dc ​​, and keep the motor rotor basically stationary; U dc The control cycle is 1 second, and the target output current I ref The initial value is set to I ref0 , if U dc Start descending, keep I ref unchanged; if U dc No decline, I ref With ΔI ref The step size increases, increasing the consumption of resonant electric energy; when the DC bus voltage drops to U s2 Then turn off the inverter module.

[0096] The simulation and measured results show that during the series resonance process, it takes more than 10 seconds for the DC bus voltage to rise to 750V, indicating that the power injected into the DC bus is very small, so the above-mentioned resonance suppression control will not cause overheating of the braking resistor or the motor.

[0097] It should be noted that the spectrum resonance detection algorithm can be used to determine whether the U dc Reach U s1 .

[0098] The spectrum resonance detection algorithm includes collecting the DC bus voltage signal U dc (t), and calculate the mean value U of the instantaneous voltage during the sampling period avg It is expressed as,

[0099]

[0100] Among them, U dc (t) represents the real-time collected DC bus voltage signal, U avg represents the instantaneous voltage mean value within the sampling period, N represents the number of sampling times, U dc (i) represents the DC bus voltage sampled at the i-th time.

[0101] If U avg >U s1 , it enters the spectrum analysis step; otherwise, the system remains in standby mode and continues to monitor the voltage signal.

[0102] The collected voltage signal U dc (t) Perform fast Fourier transform (FFT) to obtain the target frequency band F res The amplitude of each frequency component in i ) is expressed as,

[0103] A(f i )=|FFT(U dc (t))| (5)

[0104] Among them, A(f i) represents the frequency f i The amplitude, F res Indicates the frequency range within the resonant target frequency band;

[0105] The sum of harmonic energy E calculated within the target frequency band is expressed as:

[0106]

[0107] Where E represents the sum of harmonic energy.

[0108] Introducing comprehensive parameter Q enh To enhance the accuracy of judgment, it is expressed as,

[0109]

[0110] Among them, Q enh represents the enhanced resonant detection parameter, E ref Indicates the harmonic energy reference value under normal system conditions, f adj Represents the sensitivity adjustment function, which is used to adjust the sensitivity. The specific definition is as follows:

[0111] Sensitivity adjustment function f adj (V fluc ,E trend ) Combined with the voltage fluctuation and harmonic energy trend value, the sensitivity is adaptively adjusted through the calculated results, which is expressed as:

[0112]

[0113] Among them, V fluc Indicates the fluctuation value of DC bus voltage, V ref represents the voltage fluctuation reference value, γ represents the sensitivity adjustment coefficient, and ΔE represents the difference between the current value of harmonic energy and the previous cycle.

[0114] If Q enh >Q th , it is determined to be in resonance state and continues to perform trend analysis; otherwise, it returns to standby state, where Q th Represents the resonance detection parameter threshold.

[0115] Using the amplitude change trend and time weighting term w t Calculate the trend parameter T enh , expressed as,

[0116]

[0117] Among them, T enh represents the trend analysis parameter, ΔA(f i ) represents the frequency f i The amplitude change, wt represents the time weighting factor, which increases with time to amplify the impact of the current trend, and M represents the number of frequency components.

[0118] The trend parameter T enh Associated with the voltage change trend, a comprehensive state parameter S is generated for further judgment enh , expressed as,

[0119] S enh =T enh ×(1+β·ΔU dc )·(1+δ·ΔE rate ) (10)

[0120] Among them, S enh represents the comprehensive state parameter, ΔU dc represents the current voltage change, β represents the voltage change influence coefficient, δ represents the energy change rate influence coefficient, ΔE rate Indicates the relative rate of change of harmonic energy in the previous cycle.

[0121] If S enh >S th , it is determined to be in a continuous resonance state and enters the next step of dynamic threshold adjustment; otherwise, it returns to the standby state, where S th Indicates the continuous resonance state judgment threshold.

[0122] If the system is judged to be in a continuous resonance state, U is dynamically adjusted according to the voltage fluctuation characteristics and trend analysis parameters. s1 The new threshold value, after each update U s1,new Value and current U avg For comparison, it is expressed as,

[0123]

[0124] Among them, U s1,new represents the updated threshold, U s1,old Represents the previous start threshold, k represents the adjustment coefficient, controls the step size of threshold update, and η represents the trend parameter adjustment coefficient.

[0125] Updated U s1,new with U dc Continuously monitor the value for comparison. dc >U s1,new , a control signal is generated to start the resonance suppression control.

[0126] It should be noted that in the traditional method, directly judging whether there is resonance based on the magnitude of the sum of harmonic energy E has the following defects:

[0127] The absolute value of harmonic energy E may be affected by grid voltage fluctuations, background noise, and other non-resonant interference factors. Relying solely on the value of E to determine the resonance state is prone to false alarms or missed alarms. When the background noise increases, although resonance does not actually occur, the value of E may increase, resulting in a misjudgment of the resonance state.

[0128] In the actual power grid environment, the changes in voltage and harmonic components are dynamic, and the E judgment method that simply uses a fixed threshold lacks adaptability. The grid conditions may change with time and load, resulting in fluctuations in harmonic energy. Even in normal conditions, E may fluctuate to an area close to the threshold.

[0129] Directly using E to judge cannot take into account the changing trend of harmonic energy. If the system has energy fluctuations in a short period of time instead of continuous resonance, this method may misjudge it as resonance.

[0130] In order to overcome the above problems, the improved algorithm not only relies on E for judgment, but also introduces an enhanced comprehensive parameter Q enh , the design ideas are as follows:

[0131] Combine the change of harmonic energy E with voltage fluctuation and historical trend parameters to generate a comprehensive parameter Q enh , in order to improve the sensitivity and accuracy of judgment. By adjusting the function f adj (V fluc ,E trend ), the system can dynamically adjust the judgment threshold to adapt to different grid conditions and reduce misjudgment.

[0132] Comprehensive parameter Q enh Considering the harmonic energy E and voltage fluctuation V fluc The proposed method can be used to accurately distinguish between resonant and non-resonant states even in the presence of grid fluctuations.

[0133] The system not only determines the instantaneous harmonic energy E, but also analyzes the trend parameter T enh and comprehensive state parameter S enh Consider the changing trend of the resonance energy. If a continuous resonance state is detected, the threshold U is dynamically adjusted. s1 , to avoid frequent false triggering of control signals.

[0134] The improved algorithm can still accurately determine the resonant state under different load and voltage fluctuation conditions, thereby reducing false positives and false negatives. Compared with the traditional single threshold judgment method, this multi-dimensional fusion parameter calculation method is more flexible and suitable for applications in complex power supply environments. enhDynamic adjustment based on the performance and trend analysis can achieve more efficient resonance suppression control and reduce the risk of overheating and damage to the system.

[0135] Furthermore, the sensitivity adjustment coefficient γ is used to adjust the sensitivity of resonance judgment to cope with the influence of voltage fluctuations in different power supply environments. Since different power grid environments (such as industrial power grids and commercial power grids) may have different harmonic interference intensities, the sensitivity needs to be adjusted to prevent misjudgment.

[0136] The initial value of γ is usually in the range of [0.5, 2.0] and is adjusted according to the actual situation of the power grid environment.

[0137] Through preliminary experiments, sampling was carried out in different environments (such as industrial power grid, commercial power grid and household power grid), and the changing trends of voltage fluctuations and harmonic energy were analyzed to adjust the value of γ.

[0138] This coefficient can be preset by analyzing historical data offline, or adjusted online through an adaptive algorithm. During online adjustment, the system automatically adjusts γ based on the detected voltage fluctuation and harmonic energy trend to balance the sensitivity and robustness of the system.

[0139] The voltage change influence coefficient β is used to evaluate the impact of voltage fluctuations on system stability. In actual power systems, voltage fluctuations are often a precursor to resonance, so the impact of voltage changes needs to be considered in the judgment process.

[0140] The initial value range of β is [0.1, 1.0], which is usually set based on historical data of voltage fluctuations. Higher β values ​​are suitable for industrial power grids with large fluctuations, while lower values ​​are suitable for more stable commercial power grids.

[0141] The method of adjusting β includes real-time monitoring of the voltage fluctuation amplitude in the system, and dynamic adjustment through statistical analysis of the voltage fluctuation amount in the previous cycle. A warning threshold can be set, and when the voltage fluctuation is detected to exceed the set threshold, the system will increase the value of β to improve the sensitivity of detection.

[0142] In addition, the adjustment of β can also be optimized by controlling the response speed of the control system, for example, increasing β when the power grid fluctuates frequently to ensure a fast response of the system.

[0143] δ is used to evaluate the impact of the harmonic energy change rate on the system. During spectrum analysis, if the relative change rate of harmonic energy is large, it may indicate that the system is experiencing resonance, so it is necessary to improve the accuracy of the judgment by adjusting δ.

[0144] The initial range of δ is usually set to [0.05, 0.5]. Higher δ values ​​are suitable for environments with frequent resonances, while lower values ​​are suitable for more stable power supply environments.

[0145] The system automatically adjusts δ based on historical harmonic energy data. For example, if frequent energy jumps are detected over the past few cycles, the system will increase δ to respond more quickly to potential resonances.

[0146] Adjustment methods include ΔE rate A regression analysis is performed on the changes in to determine the optimal δ value, which enables the system to respond quickly when resonance is detected while avoiding false positives.

[0147] The adjustment coefficient k is used to dynamically adjust the resonance start threshold U s1 , ensuring that the system can adapt to different voltage fluctuation environments. During long-term operation, the voltage threshold may need to be adjusted to adapt to changes in grid conditions.

[0148] The initial k value is usually between [0.01, 0.1] and is set based on historical voltage fluctuation data. Larger k values ​​are used for power grids with large voltage fluctuations, and smaller k values ​​are used for stable power grid environments.

[0149] The method of adjusting k includes regression analysis based on real-time voltage fluctuation characteristics, and the system adjusts the value of k according to the actual voltage fluctuation amplitude. For example, when the power grid fluctuates violently, the value of k is increased to make the threshold adjustment more flexible.

[0150] The adjustment of k can also be achieved through a closed-loop control strategy. When the system frequently misjudges resonance, the system will automatically reduce the value of k to reduce the possibility of misjudgment.

[0151] The trend parameter adjustment coefficient η is used to adjust the trend analysis parameter T enh Impact on resonance judgment. By considering the trend of voltage fluctuations and harmonic energy, the occurrence of resonance can be predicted more accurately.

[0152] The initial value of η is between [0.1, 1.0]. A higher η value is used to deal with situations with obvious resonance trends, while a lower η value is used for a relatively stable grid environment.

[0153] The system adjusts η through real-time trend analysis. For example, when a trend parameter T enh When the rate of change of accelerates, the system will increase the value of η to improve the sensitivity of trend detection.

[0154] Using an adaptive algorithm, the system will dynamically adjust η according to the voltage fluctuation characteristics and the trend change of harmonic energy to ensure the stability of resonance detection in complex power grid environments.

[0155] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A control method for suppressing series resonance at the input end of a variable frequency speed regulation system, characterized in that: include: When the inverter module is in standby mode, monitor the DC bus voltage; When the control signal is triggered, the resonance suppression control is started; When the stop signal is triggered, the resonance suppression control stops.

2. The control method for suppressing series resonance at the input end of a variable frequency speed regulation system according to claim 1, characterized in that: The control method is implemented while keeping the circuit topology of the filter module, the rectifier module and the inverter module at the input end of the variable frequency speed regulation system unchanged, and the parameters of the AC inductance and capacitance value in the filter module unchanged.

3. The control method for suppressing series resonance at the input end of a variable frequency speed regulation system as claimed in claim 2, characterized in that: The trigger control signal refers to the detection of a DC bus voltage greater than the resonance suppression control start threshold U s1 And the voltage rise is caused by series resonance, the control signal generated.

4. The control method for suppressing series resonance at the input end of a variable frequency speed regulation system as claimed in claim 3, characterized in that: The resonance suppression control includes providing an energy release channel on the DC bus side to consume the resonance energy.

5. The control method for suppressing series resonance at the input end of a variable frequency speed regulation system as claimed in claim 4, characterized in that: Providing the energy release channel includes determining whether the variable frequency speed regulation system is equipped with a braking module, and if so, executing control according to a first resonance suppression scheme; if not, executing control according to a second resonance suppression scheme.

6. The control method for suppressing series resonance at the input end of a variable frequency speed regulation system as claimed in claim 5, characterized in that: The first resonance suppression scheme includes implementing PWM control on the brake switch, consuming the resonance energy by the brake resistor, and stabilizing the DC bus voltage U dc ; U dc The control cycle is 1 second, and the initial value of the on-duty ratio D is set to D0; if U dc Start to decrease, keep D unchanged; if U dc There is no decrease, D increases in steps of ΔD, increasing the consumption of resonant electric energy; when the DC bus voltage drops to U s2 After that, a stop signal is generated.

7. The control method for suppressing series resonance at the input end of a variable frequency speed regulation system as claimed in claim 6, characterized in that: The second resonance suppression scheme includes implementing ultra-low frequency and low current PWM output control on the inverter module, consuming the resonant electric energy by the stator winding of the motor, and stabilizing U dc , and keep the motor rotor stationary; U dc The control cycle is 1 second, and the target output current I ref The initial value is set to I ref0 ;if U dc Start descending, keep I ref constant; If U dc No decline, I ref With ΔI ref The step size increases, increasing the consumption of resonant electric energy; when the DC bus voltage drops to U s2 After that, a stop signal is generated.

8. A system using the control method for suppressing the series resonance at the input end of a variable frequency speed regulation system according to any one of claims 1 to 7, characterized in that: include: A detection unit (100) and a control unit (200); The detection unit (100) is used to monitor the DC bus voltage when the inverter module is in a standby state; The control unit (200) is used to start the resonance suppression control when a control signal is triggered, and to stop the resonance suppression control when a stop signal is triggered.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the control method for suppressing the series resonance at the input end of the variable frequency speed regulation system according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by the processor, the steps of the control method for suppressing the series resonance at the input end of the variable frequency speed regulation system according to any one of claims 1 to 7 are implemented.

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