Inverter output filter parameter design methods, systems, equipment and media

Abstract

This application provides a method, system, device, and medium for designing output filter parameters for a frequency converter, relating to the field of frequency converter filtering technology. The method includes: obtaining target parameters of the frequency converter; determining a first resonant frequency constraint condition for the output filter in the frequency converter based on the rated fundamental frequency and pulse width modulation switching frequency; determining the total control delay based on the pulse width modulation switching frequency, and determining a second resonant frequency constraint condition for the output filter based on the total control delay and the controller parameters of the frequency converter, thereby determining the resonant frequency range of the output filter; determining the range of filter capacitor parameters for the output filter based on the rated voltage, rated current, and rated fundamental frequency; and determining the target resonant frequency, target filter capacitor parameters, and target filter inductance parameters for the output filter based on the resonant frequency range, the filter capacitor parameter range, and the motor stator inductance. This application can effectively suppress the resonance of the frequency converter output filter and effectively avoid the risk of instability.

Description

Technical Field

[0001] This application relates to the field of frequency converter filtering technology, specifically to a method, system, device, and medium for designing output filter parameters for a frequency converter. Background Technology

[0002] With the rapid development of high-speed and ultra-high-speed motors, the output frequency of frequency converters is also constantly increasing. However, due to the significant increase in output frequency, the pulse width modulation switching frequency cannot be increased synchronously due to switching losses, resulting in a significant decrease in the carrier ratio. An excessively low carrier ratio not only exacerbates output harmonic components but also brings the harmonic frequency band closer to the fundamental frequency, making it difficult for the motor inductor to effectively filter out harmonics, thus significantly increasing the harmonic content in the motor stator current. This phenomenon not only increases motor losses but also affects the stability of torque control.

[0003] By adding a filter composed of inductors and capacitors on the output side, harmonic components in the output voltage can be effectively suppressed. However, resonance may occur between the inductor and capacitor components of this filter and the stator inductance of the motor, causing AC voltage and current oscillations, which in turn affect the normal operation of the frequency converter. Existing solutions to the resonance problem are mainly divided into hardware and software methods: the hardware method involves connecting a damping resistor in series in the capacitor branch. While this method is simple to implement and has a significant damping effect, it reduces filtering performance and introduces additional losses, thus affecting system efficiency. The software method implements the damping function through algorithms, but this increases system cost and complexity, and its practical application is limited because the resonant frequency may change during operation. Therefore, there is an urgent need to effectively solve the problem of resonance suppression in filters of high-speed and ultra-high-speed motor frequency converters, which leads to instability in the motor control system. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the prior art, this application provides a method, system, device and medium for designing output filter parameters of frequency converters, which effectively solves the resonance suppression problem of filters in high-speed and ultra-high-speed motor frequency converters.

[0005] In a first aspect, this application provides a method for designing output filter parameters for a frequency converter, the method comprising:

[0006] Obtain the target parameters of the frequency converter, which include at least the rated fundamental frequency, pulse width modulation switching frequency, rated voltage, rated current, and motor stator inductance;

[0007] Based on the rated fundamental frequency and the pulse width modulation switching frequency, determine the first resonant frequency constraint condition of the output filter in the inverter;

[0008] The total control delay is determined based on the pulse width modulation switching frequency, and the second resonant frequency constraint condition of the output filter is determined based on the total control delay and the controller parameters of the frequency converter.

[0009] The resonant frequency range of the output filter is determined based on the first resonant frequency constraint and the second resonant frequency constraint.

[0010] The range of filter capacitor parameters for the output filter is determined based on the rated voltage, the rated current, and the rated fundamental frequency.

[0011] Based on the resonant frequency range, the filter capacitor parameter range, and the motor stator inductance, determine the target resonant frequency, target filter capacitor parameters, and target filter inductance parameters of the output filter.

[0012] In an optional implementation, the first resonant frequency constraint condition of the output filter in the frequency converter is determined based on the rated fundamental frequency and the pulse width modulation switching frequency, including:

[0013] The resonant frequency of the output filter is greater than or equal to 5 times the rated fundamental frequency, and the resonant frequency is less than or equal to 2 / 3 of the pulse width modulation switching frequency.

[0014] In an optional implementation, determining the total control delay based on the pulse width modulation switching frequency includes:

[0015] The control cycle of the frequency converter is determined based on the pulse width modulation switching frequency.

[0016] The total control delay is determined based on the control cycle and the control delay type of the controller.

[0017] In an optional implementation, determining the second resonant frequency constraint condition based on the total control delay and the controller parameters of the frequency converter includes:

[0018] Determine the phase range of the open-loop transfer function of the controlled object, and the hysteresis phase range of the controller at the resonant frequency;

[0019] Determine the total hysteresis phase introduced by the total control delay at the resonant frequency;

[0020] Determine the stable phase range of the controller at the resonant frequency;

[0021] The range of the total lag phase of the total control delay is determined based on the stable phase range of the controller, the phase range of the open-loop transfer function of the controlled object, and the lag phase range of the controller.

[0022] The second resonant frequency constraint condition is determined based on the range of the total lag phase of the total control delay.

[0023] In an optional implementation, determining the resonant frequency range of the output filter based on the first resonant frequency constraint and the second resonant frequency constraint includes:

[0024] Compare the minimum boundary values ​​of the first resonant frequency constraint and the second resonant frequency constraint, and take the maximum value of the two as the minimum resonant frequency.

[0025] Compare the maximum boundary values ​​of the first resonant frequency constraint and the second resonant frequency constraint, and take the minimum value of the two as the maximum resonant frequency.

[0026] The resonant frequency of the output filter is greater than or equal to the minimum resonant frequency and less than or equal to the maximum resonant frequency.

[0027] In an optional implementation, determining the range of filter capacitor parameters for the output filter based on the rated voltage, the rated current, and the rated fundamental frequency includes:

[0028] Determine the target ratio range of the reactive current generated by the filter capacitor of the output filter relative to the rated current at the rated voltage;

[0029] The range of filter capacitor parameters is determined based on the rated voltage, the rated current, the rated fundamental frequency, and the target proportional range.

[0030] In an optional implementation, the target resonant frequency, target filter capacitor parameters, and target filter inductance parameters of the output filter are determined based on the resonant frequency range, the filter capacitor parameter range, and the motor stator inductance, including:

[0031] The target resonant frequency is selected according to the resonant frequency range;

[0032] Select the target filter capacitor parameters according to the range of filter capacitor parameters;

[0033] The target filter inductance parameters are obtained by calculating based on the target resonant frequency, the target filter capacitor parameters, and the motor stator inductance.

[0034] Secondly, this application provides a system for designing output filter parameters for a frequency converter, the system comprising:

[0035] The parameter acquisition module is used to acquire the target parameters of the frequency converter, which include at least the rated fundamental frequency, pulse width modulation switching frequency, rated voltage, rated current and motor stator inductance.

[0036] The first constraint module is used to determine the first resonant frequency constraint condition of the output filter in the inverter based on the rated fundamental frequency and the pulse width modulation switching frequency.

[0037] The second constraint module is used to determine the total control delay based on the pulse width modulation switching frequency, and to determine the second resonant frequency constraint condition of the output filter based on the total control delay and the controller parameters of the frequency converter.

[0038] The frequency determination module is used to determine the resonant frequency range of the output filter based on the first resonant frequency constraint condition and the second resonant frequency constraint condition.

[0039] The capacitor determination module is used to determine the range of filter capacitor parameters of the output filter based on the rated voltage, the rated current and the rated fundamental frequency;

[0040] The parameter determination module is used to determine the target resonant frequency, target filter capacitor parameters, and target filter inductance parameters of the output filter based on the resonant frequency range, the filter capacitor parameter range, and the motor stator inductance.

[0041] Thirdly, this application provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the inverter output filter parameter design method as described in the first aspect of this application.

[0042] Fourthly, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the inverter output filter parameter design method as described in the first aspect of this application.

[0043] The inverter output filter parameter design method, system, equipment, and medium provided in this application actively constrain the resonant frequency of the output filter within a specific resonant frequency range determined by the pulse width modulation switching frequency and the total control delay. Based on this resonant frequency range, reasonable capacitance and inductance parameters of the output filter are further determined, thereby achieving the purpose of filter resonance suppression. While achieving harmonic filtering, the phase lag generated at the resonant frequency by the control delay fundamentally avoids the risk of instability caused by the output filter. At the same time, the resonant frequency takes into account both fundamental frequency attenuation and minimum harmonic suppression, achieving synergistic optimization of filtering performance and system stability under low carrier ratio conditions, significantly improving the robustness, efficiency, and engineering applicability of high-frequency inverters. Attached Figure Description

[0044] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a schematic diagram of a motor control system using an LC filter on the output side of a frequency converter.

[0046] Figure 2 It is the Bode plot of the open-loop transfer function of the controlled object in the motor control system;

[0047] Figure 3 It is the Bode plot of the open-loop transfer function of the controlled object in the motor control system after the addition of a digital controller;

[0048] Figure 4 This is a schematic flowchart of the inverter output filter parameter design method provided in the embodiments of this application;

[0049] Figure 5 This is the open-loop transfer function Bode plot of the motor control system after adding the designed output filter and controller in the embodiments of this application;

[0050] Figure 6 This is a schematic diagram of the system structure for designing the output filter parameters of a frequency converter according to an embodiment of this application;

[0051] Figure 7 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application.

[0052] Explanation of key component symbols:

[0053] 200. Output filter parameter design system for frequency converter; 210. Parameter acquisition module; 220. First constraint module; 230. Second constraint module; 240. Frequency determination module; 250. Capacitor determination module; 260. Parameter determination module; 300. Electronic equipment; 310. Processor; 320. Communication interface; 330. Memory; 340. Communication bus. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be further described clearly and completely below with reference to the accompanying drawings of the embodiments. It should be noted that the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0055] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0056] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0057] Currently, by adding an LC filter composed of inductors and capacitors to the output side of the frequency converter, harmonic components in the output voltage can be significantly filtered out. The inductance and capacitance of the filter are combined with the stator inductance of the motor to form a second-order LCL filter. Figure 1 This is a schematic diagram of a motor control system with an LC filter on the output side of the frequency converter, as shown below. Figure 1 As shown, the LC filter consists of a three-phase inductor L1, a set of three-phase capacitors C1, and a motor stator inductor L2. After the LC filter is connected, a portion of the high-frequency current is discharged through the three-phase capacitor C1, thereby reducing the harmonic current injected into the motor stator inductor L2.

[0058] However, adding an LC filter to the inverter output side causes resonance in the inductors, capacitors, and motor stator inductors within the LC filter, leading to AC voltage and current oscillations and preventing the inverter from functioning properly. To investigate the impact of the LC filter on inverter resonance, the transfer function from inverter voltage to inverter current can be obtained through modeling and derivation as follows:

[0059]

[0060] In the above formula, G ( s () indicates the transfer of function values. s Represents the Laplace operator. L m This represents the inductance value of the motor stator inductance L2. C fThis indicates the capacitance value of the three-phase capacitor C1. L f This represents the inductance value of the three-phase inductor L1. R m This represents the resistance value of the motor stator inductance L2. R f This indicates the resistance value of the three-phase inductor L1.

[0061] The corresponding Bode plot can be drawn based on the transfer function. Figure 2 It is the Bode plot of the open-loop transfer function of the controlled object in the motor control system, such as... Figure 2 As shown, the solid line represents the Bode curve of the open-loop transfer function of the controlled object without an LC filter, while the dashed line represents the Bode curve of the open-loop transfer function of the controlled object with an LC filter. Before adding the LC filter, the open-loop transfer function of the controlled object is a first-order inertial element with a maximum phase lag of -90°. After adding the LC filter, the characteristics of the controlled object change drastically, and the open-loop transfer function becomes a second-order element with two resonant points. At the first resonant point, the amplitude-frequency characteristic shows a dip, which is caused by the parallel resonance of the filter capacitor and the motor inductor. Since the amplitude-frequency characteristic is negative, this resonant point does not affect stability and will not be discussed further. At the second resonant point, the amplitude-frequency characteristic shows a spike, and the phase changes abruptly from 90° to -90°. This is because the filter inductor, filter capacitor, and motor stator inductor resonate in series, resulting in a series impedance of 0. Therefore, a small voltage will cause a large current, leading to the spike in the amplitude-frequency characteristic.

[0062] When a digital controller is added, it will inevitably produce a control delay. This delay will cause phase lag at the resonant point. When this lag is superimposed on the original phase of the controlled object, it will cause the open-loop transfer function Bode plot of the controlled object to change. Figure 3 This is the Bode plot of the open-loop transfer function of the controlled object in the motor control system after the addition of a digital controller, such as... Figure 3 As shown, the solid line is the open-loop transfer function (Baud rate) curve of the controlled object without an LC filter after adding a digital controller. It can be seen that, considering the controller delay, although the phase frequency response undergoes a negative crossing of the -180° phase line, the amplitude frequency response at the crossing point is negative, and the entire motor control system is stable. The dashed line is the open-loop transfer function (Baud rate) curve of the controlled object with an LC filter after adding a controller. After superimposing the controller phase shift, the phase frequency response undergoes a negative crossing of the -180° line at the resonance point. Since the amplitude frequency response at this point is positive, according to the Nyquist criterion, this means that the motor control system is unstable. Therefore, the resonance suppression introduced by the LC filter may cause the originally stable motor control system to become unstable.

[0063] Example 1

[0064] This application provides a method for designing the output filter parameters of a frequency converter, which effectively solves the problem of resonance suppression in the filter of high-speed and ultra-high-speed motor frequency converters, leading to instability in the motor control system. Figure 4 This is a schematic flowchart of the inverter output filter parameter design method provided in this application embodiment, as shown below. Figure 4 As shown, the method includes the following steps:

[0065] S100. Obtain the target parameters of the frequency converter. The target parameters include at least the rated fundamental frequency, pulse width modulation switching frequency, rated voltage, rated current, and motor stator inductance.

[0066] In this embodiment, the rated fundamental frequency that the inverter needs to output is determined by the motor speed and load requirements. This is a system-level input parameter, which is usually fixed and can be directly obtained from the inverter parameters. The rated fundamental frequency is denoted as... f n The pulse width modulation (PWM) switching frequency is constrained by the type of power device and hardware conditions such as circuitry and heat dissipation. It is also determined in a specific inverter design and can be directly obtained. The PWM switching frequency is denoted as... f s The rated voltage and rated current of the frequency converter, as well as the stator inductance of the motor, can all be obtained from the parameters of the frequency converter and the corresponding motor parameters.

[0067] Furthermore, the series of harmonic frequencies generated by pulse width modulation are collectively denoted as... f h Based on the classical theory and simulation studies of pulse width modulation (PWM) principle and double Fourier analysis, it is shown that harmonic energy is highly concentrated at odd multiples of the PWM switching frequency, and sideband harmonics are formed on both sides of these center frequencies with the rated fundamental frequency as the interval. Therefore, the following relationship can be derived:

[0068]

[0069] In the above formula, f h This indicates the harmonic frequency of the frequency converter. f s This indicates the pulse width modulation switching frequency of the frequency converter. k 1 indicates an odd number of terms.

[0070] S200. Based on the rated fundamental frequency and the pulse width modulation switching frequency, determine the first resonant frequency constraint condition of the output filter in the frequency converter.

[0071] In this embodiment, the output filter in the frequency converter is a second-order LCL filter. In a second-order filter, the cutoff frequency and resonant frequency are very close. Therefore, second-order filters typically require a resonant frequency much higher than the rated fundamental frequency. For example, when the resonant frequency is greater than 10 times the rated fundamental frequency, the fundamental frequency is in the flat passband region of the second-order filter, and its voltage amplitude attenuation is extremely small, calculated to be less than 0.5%. The phase shift is also almost negligible, thus avoiding impact on the normal output and control accuracy of the motor. Therefore, to reduce the influence of the second-order filter on the useful signal, the resonant frequency of the second-order filter is generally required to be greater than 10 times the rated fundamental frequency, so that the filter's attenuation of the fundamental amplitude does not exceed 0.5%. Conversely, to effectively suppress harmonics, the resonant frequency of the second-order filter is required to be significantly lower than the lowest critical harmonic frequency. That is, if the resonant frequency is not greater than half of the harmonic frequency, the gain of the lowest frequency harmonic at the second-order filter will drop to below approximately 44.7%, and the attenuation of higher-order harmonics will be even greater. When the resonant frequency is no greater than half the pulse width modulation switching frequency, the resonant frequency is definitely no greater than half the harmonic frequency. Therefore, according to the above principle, the following relationship can be derived:

[0072]

[0073] In the above formula, f res The resonant frequency of the output filter in the frequency converter can be derived from the above formula:

[0074]

[0075] This means the carrier ratio needs to be greater than 20, which is difficult to meet for high-frequency and ultra-high-frequency inverters. When the output frequency is high, the carrier ratio can drop as low as 8, making the above-mentioned second-order filter design principle unsuitable. Conversely, low carrier ratios are precisely the scenario where output harmonics are high, requiring the LC filter to function effectively.

[0076] Based on this, the embodiments of this application impose the following requirements on the resonant frequency of the second-order LCL filter: the resonant frequency is greater than 5 times the fundamental frequency, so that the amplitude attenuation of the second-order LCL filter at the rated fundamental frequency does not exceed 2%. In a closed-loop system, this is acceptable because the fundamental output voltage can be automatically compensated by the closed-loop system. Simultaneously, the resonant frequency is required to be less than 2 / 3 of the minimum harmonic frequency, i.e., the pulse width modulation switching frequency. f s This reduces the amplitude of the lowest frequency harmonic to 55.4%, and other higher frequency harmonics will be attenuated even more. Therefore, the relationship for the constraint condition of the first resonant frequency can be obtained as follows:

[0077]

[0078] Furthermore, the following relationship can be derived:

[0079]

[0080] That is, under this condition, the carrier ratio is constrained to be no less than 7.5, which is satisfied in actual motor control systems, because if the carrier ratio is lower, the motor control system will lose control due to too few sampling points and too much delay.

[0081] It is understandable that, within the resonant frequency range specified above, the resonant frequency... f res The larger the frequency, the closer it is to the lowest harmonic frequency, and the worse the filtering effect. Conversely, the resonant frequency... f res The smaller the value, the better the filtering effect. However, the closer it is to the rated fundamental frequency, the greater the impact on the fundamental amplitude and phase, and the more it will increase the inverter output current, thus increasing cost and losses.

[0082] S300. Determine the total control delay based on the pulse width modulation switching frequency, and determine the second resonant frequency constraint condition of the output filter based on the total control delay and the controller parameters of the frequency converter.

[0083] In this embodiment, the impact of resonant frequency selection on the stability of the motor control system also needs to be considered to obtain the second resonant frequency constraint. When a controller is used in the motor control system, a corresponding control delay will occur, and the total control delay will bring a phase lag proportional to the resonant frequency. When this phase lag is superimposed with the inherent sharp phase jump of the second-order LCL filter at the resonant point and the additional phase lag of the controller, it may cause [problems related to] the stability of the motor control system. The negative crossing of the 180° line causes instability in the motor control system. Therefore, the total control delay can be determined based on the pulse width modulation switching frequency, and then the second resonant frequency constraint condition of the output filter can be determined based on the total control delay and the controller parameters of the frequency converter.

[0084] Determining the total control delay based on the pulse width modulation switching frequency includes the following steps: First, determine the inverter's control cycle based on the pulse width modulation switching frequency. T s That is, the pulse width modulation switching frequency. f s The reciprocal of the first, and secondly, when using a digital controller, digital signal sampling, signal filtering, and pulse width modulation output holding all introduce delays. If the total control delay is... T d The total control delay is T d With control cycle T s Related.

[0085] For example, if digital signal sampling introduces a control cycle delay, and the pulse width modulation output zero-order hold introduces a half-control cycle signal delay, then the total control delay... T d =1.5 T s Another example is that if digital signal sampling introduces a control cycle delay, pulse width modulation loading introduces half a control cycle delay, and the pulse width modulation output zero-order hold introduces half a control cycle signal delay, then the total control delay... T d =2 T s As another example, if digital signal sampling introduces a control cycle delay, signal filtering introduces a control cycle delay, and the pulse width modulation output zero-order hold introduces a half-cycle sampling delay, then the total control delay... T d =2.5 T s .

[0086] Understandably, based on the examples above, the total control delay can be calculated as follows: T d With control cycle T s The following relationship exists:

[0087]

[0088] In the above formula, k 2 represents a constant term, which can take values ​​such as 1.5, 2, and 2.5.

[0089] Furthermore, obtaining the constraint condition for the second resonant frequency specifically includes the following steps:

[0090] S310. Determine the phase range of the open-loop transfer function of the controlled object, and the hysteresis phase range of the controller at the resonant frequency.

[0091] Understandably, according to Figure 1 As can be seen, at the resonant point, the phase frequency response curve of the controlled object undergoes a negative crossover from 90° to -90°, and the entire phase frequency response lies within the range of -90° to 90°. Therefore, the phase of the open-loop transfer function of the controlled object satisfies the following relationship:

[0092]

[0093] In the above formula, This represents the phase of the open-loop transfer function of the controlled object.

[0094] For example, the current regulation controller in a motor control system can be a PI regulator, with the PI regulator having a lag phase at the resonant frequency.α PI The lag is related to the relative magnitudes of the PI controller's cutoff frequency and resonant frequency: when the resonant frequency is much lower than the cutoff frequency, the integral action dominates, and the PI controller exhibits a phase lag at the resonant frequency. α PI Approaching -90°; when the resonant frequency is much higher than the cutoff frequency, the proportional action dominates, and the PI controller lags behind at the resonant frequency. α PI Approaching 0°; when the resonant frequency and the cutoff frequency are close, the hysteresis phase of the PI controller at the resonant frequency... α PI The hysteresis is 45°. Therefore, regardless of the PI controller parameters being set, the hysteresis phase of the PI controller at the resonant frequency is always 45°. α PI The hysteresis phase of the PI regulator at the resonant frequency is always within the range of (-90°, 0°).

[0095] S320. Determine the total lag phase introduced by the total control delay at the resonant frequency.

[0096] Understandably, the total control delay T d At the resonant frequency f res The total lag phase introduced at point is:

[0097]

[0098] In the above formula, This represents the total lag phase of the total control delay.

[0099] S330. Determine the stable phase range of the controller at the resonant frequency.

[0100] It is understandable that, based on the transfer function from inverter voltage to inverter current, the open-loop transfer function of the inverter does not have poles in the right half-plane. According to the Nyquist stability criterion, when the amplitude of the amplitude-frequency characteristic is greater than 1, if the phase-frequency characteristic is incorrect... k If a negative crossover occurs at the ×180° line, the motor control system is stable. k It is an odd number. Therefore, the phase frequency characteristic of the open-loop transfer function of the controlled object is not... k When the ×180° line undergoes a negative crossover, the corresponding phase range is used as the stable phase range of the controller at the resonant frequency.

[0101] For example, if, after considering the controller and control delay, the total phase of the open-loop transfer function of the controlled object corresponding to the controller is located between the -180° line and the -540° line at the resonant frequency, there will be no interference with the controller.k If the negative crossover of the ×180° line occurs, then the stable phase range of the controller at the resonant frequency is (-540°, -180°).

[0102] S340. Determine the range of the total lag phase of the total control delay based on the stable phase range of the controller, the phase range of the open-loop transfer function of the controlled object, and the lag phase range of the controller.

[0103] In this embodiment, after considering the controller and control delay, the stable phase of the controller at the resonant frequency is: α sys2 At this point, the following expression exists:

[0104]

[0105] In the above formula, This represents the stable phase of the controller at the resonant frequency, taking into account the controller and control delay. This represents the phase of the open-loop transfer function of the controlled object. α PI This indicates the hysteresis phase of the controller at the resonant frequency. This represents the total lag phase of the total control delay.

[0106] By combining the controller's stable phase range, the open-loop transfer function phase range of the controlled object, and the controller's hysteresis phase range, the total hysteresis phase range of the total control delay can be obtained as follows:

[0107]

[0108] S350. Determine the second resonant frequency constraint condition based on the range of the total lag phase of the total control delay.

[0109] It is understandable that this is related to the total control delay in step S320. T d At the resonant frequency f res By defining the expression for the total lag phase and its range, the expression for the second resonant frequency constraint can be determined as follows:

[0110]

[0111] At this point, as long as the resonant frequency of the filter satisfies the above formula, the resonance can be guaranteed not to affect the stability of the motor control system.

[0112] It is understandable that, since the controller in this embodiment uses a PI regulator, once the PI regulator parameters are determined, the hysteresis phase introduced by the PI regulator at the resonant point is a fixed value within the range of -90° to 0°. The resonant frequency range calculated above is estimated based on the maximum range of -90° to 0°. Therefore, in practical applications, the specific resonant frequency range can be adjusted in conjunction with the PI regulator parameters. Similarly, using other controllers, the hysteresis phase introduced at the resonant point can also be calculated based on the controller parameters, thereby calculating the resonant frequency range and obtaining the second resonant frequency constraint condition.

[0113] S400. Determine the resonant frequency range of the output filter based on the first resonant frequency constraint and the second resonant frequency constraint.

[0114] In this embodiment, the minimum boundary values ​​of the first and second resonant frequency constraints are compared, and the maximum value is taken as the minimum resonant frequency. Simultaneously, the maximum boundary values ​​of the first and second resonant frequency constraints are compared, and the minimum value is taken as the maximum resonant frequency. The resonant frequency of the output filter is greater than or equal to the minimum resonant frequency and less than or equal to the maximum resonant frequency. That is, combining the first and second resonant frequency constraints, the resonant frequency range of the output filter can be obtained as follows:

[0115]

[0116] In the above formula, max ( • )and min (•) represent the maximum value function and the minimum value function, respectively.

[0117] Based on this, the determination of the resonant frequency range breaks through the limitation of traditional filter design relying on a high carrier ratio. First, the resonant frequency is set in the range of more than 5 times the rated fundamental frequency and less than 2 / 3 of the pulse width modulation switching frequency, ensuring that the fundamental voltage attenuation is controlled within 2% and that the main harmonics are effectively attenuated. Second, the inherent sampling, filtering, and pulse width modulation output delay of the digital control system are actively utilized to introduce a defined phase lag at the resonant frequency, so that the total phase frequency characteristic of the motor control system avoids k times the rated fundamental frequency. The 180° negative crossover fundamentally avoids the resonance instability problem caused by second-order LCL filters.

[0118] S500. Determine the range of filter capacitor parameters for the output filter based on the rated voltage, rated current, and rated fundamental frequency.

[0119] In this embodiment, the target ratio range of reactive current generated by the filter capacitor of the output filter relative to the rated current at rated voltage is first determined. When the filter capacitor value is too small, the filtering effect of the filter is limited; when the filter capacitor value is too large, the rated voltage will also generate reactive current on the filter capacitor, increasing the inverter's output current and capacity requirements. Based on industry experience, the capacitor value range is determined to be 5% to 10% of the inverter's rated current, i.e.:

[0120]

[0121] In the above formula, U n Indicates the rated voltage. f n Indicates the rated fundamental frequency. C f This represents the filter capacitor parameters of the output filter. I n Indicates the rated current. k 3 represents a constant term, with a value ranging from 0.05 to 1.

[0122] Then, the range of filter capacitor parameters is determined based on the rated voltage, rated current, rated fundamental frequency, and target proportional range. This can be derived from the above formula:

[0123]

[0124] In the above formula, k 3 takes a value from 0.05 to 1, as... k 3. Changes in the value of the filter capacitor parameter C f And it changes accordingly, based on this k 3. Value range: The range of filter capacitor parameters can be determined by combining the corresponding rated voltage, rated current, and rated fundamental frequency.

[0125] S600. Based on the resonant frequency range, the filter capacitor parameter range, and the motor stator inductance, determine the target resonant frequency, target filter capacitor parameters, and target filter inductance parameters of the output filter.

[0126] In this embodiment, the resonant frequency can be obtained by performing circuit analysis on the second-order LCL filter. f res The relationship between the filter parameters and motor parameters is as follows:

[0127]

[0128] In the above formula, f res Indicates the resonant frequency. Lf Indicates the filter inductance parameters. L m This indicates the stator inductance parameters of the motor. C f This indicates the parameters of the filter capacitor.

[0129] Understandably, the target resonant frequency is selected based on the resonant frequency range, and the target filter capacitor parameters are selected based on the filter capacitor parameter range. Since the motor stator inductance parameters are known, the corresponding target filter inductance parameters can be derived, thus completing the parameter design of the output filter.

[0130] Furthermore, it's understandable that in practical applications, determining the specific parameter values ​​of the output filter requires considering the desired filtering effect, as well as factors such as the size and cost of capacitors and inductors. For example, increasing the resonant frequency within its allowable range means a worse filtering effect, but reduces the demand for filter capacitors and inductors, thus reducing size and cost. Conversely, choosing a smaller resonant frequency within its allowable range improves the filtering effect, but requires increasing the capacitance or inductance, inevitably increasing size and cost. At the same resonant frequency, choosing a smaller capacitor parameter reduces capacitor size and cost, but increases inductor size and cost; choosing a larger capacitor parameter increases capacitor size and cost, but reduces the demand for inductors.

[0131] To verify the effectiveness of the inverter output filter parameter design method provided in this application embodiment, a second-order LCL filter is designed as the output filter for an inverter of a motor control system. The inverter parameters of the motor control system are shown in Table 1.

[0132] Table 1. Schematic diagram of inverter parameters for a certain motor control system

[0133]

[0134] The actual total control delay of the motor control system is 2. T s ,Right now k Since 2=2, the resonant frequency range determined by the expression for the resonant frequency range of the output filter is: 3000Hz≤ f res ≤4000Hz. Considering both the filtering effect and cost of the output filter, the resonant frequency is chosen. f res =3500Hz, so the amplitude of the lowest harmonic frequency 8000Hz can be attenuated to:

[0135]

[0136] likek If we take 0.05, then the filter capacitor parameters can be calculated based on the rated voltage, rated current, and rated fundamental frequency. C f as follows:

[0137]

[0138] Based on the resonant frequency f res and filter capacitor parameters C f We can conclude that:

[0139]

[0140] That is, the filter inductor parameters L f With motor stator capacitor L m The parallel value needs to reach 258. μH The stator capacitor of the motor L m Only 250 μH This is clearly impossible. This explains the resonant frequency of the aforementioned filter. f res Selecting too low and filter capacitor parameters C f Choosing an inductor that is too small results in an excessively high demand for inductance. In this case, a different inductance should be chosen. k 3=0.1, then the filter capacitor parameters C f 16 μH The filter inductor parameters were recalculated. L f =266 μH This value is comparable to the stator inductance of the motor, so the output filter is obviously feasible.

[0141] Furthermore, if you want to reduce costs, you can adjust the resonant frequency. f res Choose a larger value within the resonant frequency range, for example, select the resonant frequency. f res =3750Hz, while maintaining filter capacitor parameters C f While keeping the parameters constant, the filter inductance parameters can be obtained. L f =204 μH The inductance value is lower than the previous design, effectively reducing costs. However, a downside is a weakening of the filtering effect, with a reduced attenuation of the lowest frequency 8000Hz harmonic amplitude.

[0142]

[0143] Therefore, the embodiments of this application can select specific parameter values ​​based on the resonant frequency range and the filter capacitor parameter range, and design the output filter parameters according to the application requirements.

[0144] For example, the parameters of the output filter designed based on the above method are as follows: resonant frequency. f res =3750Hz, filter capacitor parameters C f =16 μH Filter inductor parameters L f =204 μH The controller uses a PI regulator, and the total control delay is 2 control cycles. Figure 5 This is the open-loop transfer function Bode plot of the motor control system after incorporating the designed output filter and controller in the embodiments of this application, such as... Figure 5 As shown, within the resonance range indicated by the dashed box, although the amplitude-frequency characteristic is greater than 0, the phase-frequency characteristic does not exhibit negative crossover. Therefore, the motor control system is stable, thus effectively verifying the effectiveness of the inverter output filter parameter design method provided in this application embodiment.

[0145] The inverter output filter parameter design method provided in this application actively constrains the resonant frequency of the output filter within a specific resonant frequency range determined by the pulse width modulation switching frequency and the total control delay. Based on this resonant frequency range, reasonable capacitance and inductance parameters of the output filter are further determined, thereby achieving the purpose of suppressing resonance. While achieving the harmonic filtering effect, the phase lag generated at the resonant frequency by the control delay fundamentally avoids the risk of instability caused by the output filter.

[0146] Example 2

[0147] Based on the same technical concept as Embodiment 1 above, this application provides a system for designing output filter parameters for a frequency converter. Figure 6 This is a schematic diagram of the system structure for designing the output filter parameters of a frequency converter according to an embodiment of this application, as shown below. Figure 6 As shown, the inverter output filter parameter design system 200 includes:

[0148] The parameter acquisition module 210 is used to acquire the target parameters of the frequency converter. The target parameters include at least the rated fundamental frequency, pulse width modulation switching frequency, rated voltage, rated current and motor stator inductance.

[0149] The first constraint module 220 is used to determine the first resonant frequency constraint condition of the output filter in the frequency converter based on the rated fundamental frequency and the pulse width modulation switching frequency.

[0150] The second constraint module 230 is used to determine the total control delay based on the pulse width modulation switching frequency, and to determine the second resonant frequency constraint condition of the output filter based on the total control delay and the controller parameters of the frequency converter.

[0151] The frequency determination module 240 is used to determine the resonant frequency range of the output filter based on the first resonant frequency constraint and the second resonant frequency constraint.

[0152] The capacitor determination module 250 is used to determine the range of filter capacitor parameters for the output filter based on the rated voltage, rated current, and rated fundamental frequency.

[0153] The parameter determination module 260 is used to determine the target resonant frequency, target filter capacitor parameters, and target filter inductance parameters of the output filter based on the resonant frequency range, the filter capacitor parameter range, and the motor stator inductance.

[0154] The inverter output filter parameter design system provided in this application embodiment does not require additional hardware or software measures such as damping resistors, virtual resistors or adaptive notch filters, thereby reducing inverter losses, costs and complexity, and significantly improving the robustness, efficiency and engineering applicability of high-frequency inverters.

[0155] It is understood that the implementation method of the inverter output filter parameter design method in the above embodiment 1 is also applicable to this embodiment and can achieve the same technical effect, so it will not be described again here.

[0156] Example 3

[0157] Based on the same concept, this application also provides an electronic device. Figure 7 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application, such as... Figure 7 As shown, the electronic device 300 may include a processor 310, a communication interface 320, a memory 330, and a communication bus 340, wherein the processor 310, the communication interface 320, and the memory 330 communicate with each other via the communication bus 340. The processor 310 can call logic instructions in the memory 330 to execute the steps of the inverter output filter parameter design method as described in the above embodiments. For example, this includes:

[0158] S100. Obtain the target parameters of the frequency converter. The target parameters include at least the rated fundamental frequency, pulse width modulation switching frequency, rated voltage, rated current, and motor stator inductance.

[0159] S200. Determine the first resonant frequency constraint condition of the output filter in the frequency converter based on the rated fundamental frequency and the pulse width modulation switching frequency.

[0160] S300. Determine the total control delay based on the pulse width modulation switching frequency, and determine the second resonant frequency constraint condition of the output filter based on the total control delay and the controller parameters of the frequency converter.

[0161] S400. Determine the resonant frequency range of the output filter based on the first resonant frequency constraint and the second resonant frequency constraint.

[0162] S500. Determine the range of filter capacitor parameters for the output filter based on the rated voltage, rated current, and rated fundamental frequency.

[0163] S600. Based on the resonant frequency range, the filter capacitor parameter range, and the motor stator inductance, determine the target resonant frequency, target filter capacitor parameters, and target filter inductance parameters of the output filter.

[0164] The processor 310 can be a central processing unit (CPU). The processor can also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or combinations of the above types of chips.

[0165] Furthermore, the logical instructions in the aforementioned memory 330 can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium 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 application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0166] The memory 330 may include a program storage area and a data storage area. The program storage area may store the operating system and applications required for at least one function; the data storage area may store data created by the processor, etc. Furthermore, the memory may include high-speed random access memory and non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some embodiments, the memory may optionally include memory remotely located relative to the processor, which can be connected to the processor via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.

[0167] Example 4

[0168] Based on the same concept, embodiments of this application also provide a computer-readable storage medium storing a computer program containing at least one piece of code executable by a master control device to control the master control device to implement the steps of the inverter output filter parameter design method as described in the above embodiments. For example, it includes:

[0169] S100. Obtain the target parameters of the frequency converter. The target parameters include at least the rated fundamental frequency, pulse width modulation switching frequency, rated voltage, rated current, and motor stator inductance.

[0170] S200. Determine the first resonant frequency constraint condition of the output filter in the frequency converter based on the rated fundamental frequency and the pulse width modulation switching frequency.

[0171] S300. Determine the total control delay based on the pulse width modulation switching frequency, and determine the second resonant frequency constraint condition of the output filter based on the total control delay and the controller parameters of the frequency converter.

[0172] S400. Determine the resonant frequency range of the output filter based on the first resonant frequency constraint and the second resonant frequency constraint.

[0173] S500. Determine the range of filter capacitor parameters for the output filter based on the rated voltage, rated current, and rated fundamental frequency.

[0174] S600. Based on the resonant frequency range, the filter capacitor parameter range, and the motor stator inductance, determine the target resonant frequency, target filter capacitor parameters, and target filter inductance parameters of the output filter.

[0175] Based on the same technical concept, this application also provides a computer program, which, when executed by a main control device, is used to implement the above-described method embodiments.

[0176] The computer program may be stored, in whole or in part, on a computer-readable storage medium packaged with the processor, or in part or in whole on a memory not packaged with the processor.

[0177] Based on the same technical concept, embodiments of this application also provide a processor for implementing the above-described method embodiments. The processor may be a chip.

[0178] In summary, the inverter output filter parameter design method, system, equipment, and medium provided in this application actively constrain the resonant frequency of the output filter within a specific resonant frequency range determined by the pulse width modulation switching frequency and the total control delay. Based on this resonant frequency range, reasonable capacitance and inductance parameters of the output filter are further determined, thereby achieving the purpose of filter resonance suppression. While achieving harmonic filtering, the phase lag generated at the resonant frequency by the control delay fundamentally avoids the risk of instability caused by the output filter. Simultaneously, the resonant frequency balances fundamental frequency attenuation and minimum harmonic suppression, achieving synergistic optimization of filtering performance and system stability under low carrier ratio conditions, significantly improving the robustness, efficiency, and engineering applicability of high-frequency inverters.

[0179] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0180] The embodiments described above are merely examples of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the protection scope of this application.

[0181] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for designing output filter parameters for a frequency converter, characterized in that, The method includes: Obtain the target parameters of the frequency converter, which include at least the rated fundamental frequency, pulse width modulation switching frequency, rated voltage, rated current, and motor stator inductance; Based on the rated fundamental frequency and the pulse width modulation switching frequency, the first resonant frequency constraint condition of the output filter in the frequency converter is determined. The first resonant frequency constraint condition includes: the resonant frequency of the output filter is greater than or equal to 5 times the rated fundamental frequency, and the resonant frequency is less than or equal to 2 / 3 of the pulse width modulation switching frequency. The total control delay is determined based on the pulse width modulation switching frequency, and the second resonant frequency constraint condition of the output filter is determined based on the total control delay and the controller parameters of the frequency converter. The resonant frequency range of the output filter is determined based on the first resonant frequency constraint and the second resonant frequency constraint. The range of filter capacitor parameters for the output filter is determined based on the rated voltage, the rated current, and the rated fundamental frequency. Based on the resonant frequency range, the filter capacitor parameter range, and the motor stator inductance, determine the target resonant frequency, target filter capacitor parameters, and target filter inductance parameters of the output filter.

2. The method for designing output filter parameters of a frequency converter according to claim 1, characterized in that, The step of determining the total control delay based on the pulse width modulation switching frequency includes: The control cycle of the frequency converter is determined based on the pulse width modulation switching frequency. The total control delay is determined based on the control cycle and the control delay type of the controller.

3. The method for designing output filter parameters of a frequency converter according to claim 2, characterized in that, The determination of the second resonant frequency constraint condition based on the total control delay and the controller parameters of the frequency converter includes: Determine the phase range of the open-loop transfer function of the controlled object, and the hysteresis phase range of the controller at the resonant frequency; Determine the total hysteresis phase introduced by the total control delay at the resonant frequency; Determine the stable phase range of the controller at the resonant frequency; The range of the total lag phase of the total control delay is determined based on the stable phase range of the controller, the phase range of the open-loop transfer function of the controlled object, and the lag phase range of the controller. The second resonant frequency constraint condition is determined based on the range of the total lag phase of the total control delay.

4. The method for designing output filter parameters of a frequency converter according to claim 1, characterized in that, Determining the resonant frequency range of the output filter based on the first resonant frequency constraint and the second resonant frequency constraint includes: Compare the minimum boundary values ​​of the first resonant frequency constraint and the second resonant frequency constraint, and take the maximum value of the two as the minimum resonant frequency. Compare the maximum boundary values ​​of the first resonant frequency constraint and the second resonant frequency constraint, and take the minimum value of the two as the maximum resonant frequency. The resonant frequency of the output filter is greater than or equal to the minimum resonant frequency and less than or equal to the maximum resonant frequency.

5. The method for designing output filter parameters of a frequency converter according to claim 1, characterized in that, The step of determining the range of filter capacitor parameters for the output filter based on the rated voltage, the rated current, and the rated fundamental frequency includes: Determine the target ratio range of the reactive current generated by the filter capacitor of the output filter relative to the rated current at the rated voltage; The range of filter capacitor parameters is determined based on the rated voltage, the rated current, the rated fundamental frequency, and the target proportional range.

6. The method for designing output filter parameters of a frequency converter according to claim 1, characterized in that, Based on the resonant frequency range, the filter capacitor parameter range, and the motor stator inductance, the target resonant frequency, target filter capacitor parameters, and target filter inductance parameters of the output filter are determined, including: The target resonant frequency is selected according to the resonant frequency range; Select the target filter capacitor parameters according to the range of filter capacitor parameters; The target filter inductance parameters are obtained by calculating based on the target resonant frequency, the target filter capacitor parameters, and the motor stator inductance.

7. A system for designing output filter parameters for a frequency converter, characterized in that, The system includes: The parameter acquisition module is used to acquire the target parameters of the frequency converter, which include at least the rated fundamental frequency, pulse width modulation switching frequency, rated voltage, rated current and motor stator inductance. The first constraint module is used to determine the first resonant frequency constraint condition of the output filter in the inverter based on the rated fundamental frequency and the pulse width modulation switching frequency. The first resonant frequency constraint condition includes: the resonant frequency of the output filter is greater than or equal to 5 times the rated fundamental frequency, and the resonant frequency is less than or equal to 2 / 3 of the pulse width modulation switching frequency. The second constraint module is used to determine the total control delay based on the pulse width modulation switching frequency, and to determine the second resonant frequency constraint condition of the output filter based on the total control delay and the controller parameters of the frequency converter. The frequency determination module is used to determine the resonant frequency range of the output filter based on the first resonant frequency constraint condition and the second resonant frequency constraint condition. The capacitor determination module is used to determine the range of filter capacitor parameters of the output filter based on the rated voltage, the rated current and the rated fundamental frequency; The parameter determination module is used to determine the target resonant frequency, target filter capacitor parameters, and target filter inductance parameters of the output filter based on the resonant frequency range, the filter capacitor parameter range, and the motor stator inductance.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, The processor executes the computer program to implement the inverter output filter parameter design method as described in any one of claims 1-6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the inverter output filter parameter design method as described in any one of claims 1-6.

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