Cascade grid simulator fault diagnosis method based on frequency-modulated carrier and related equipment

Abstract

The embodiment of the application provides a kind of based on frequency conversion carrier modulation cascaded grid simulator fault diagnosis method and related equipment, belong to power electronics technical field.The method includes: when system normal operation, inverter side adopts carrier phase-shifted sinusoidal pulse width modulation strategy;When detecting system output voltage exception, switch to frequency conversion carrier modulation strategy, wherein the triangular carrier frequency of each H bridge module is different from each other;The total output voltage of the system after switching modulation mode is spectrum analyzed, and the harmonic content at the characteristic frequency corresponding to each module carrier frequency is extracted;The harmonic content at each characteristic frequency is compared with the corresponding fault diagnosis threshold value respectively, and the H bridge module that fails is determined according to the comparison result.The application can realize the rapid and accurate positioning of the module-level fault of the inverter side of the cascaded grid simulator without adding additional hardware sampling circuit, which significantly improves the operation and maintenance efficiency and operation reliability of the equipment.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a fault diagnosis method and related equipment for a cascaded power grid simulator based on frequency conversion carrier modulation. Background Technology

[0002] A power grid simulator is a device that simulates the characteristics of a power grid and is widely used in scenarios such as new energy grid connection testing and distributed generation system access verification. The inverter side of a cascaded power grid simulator adopts a cascaded H-bridge structure, consisting of multiple independent H-bridge modules connected in series, containing a large number of switching elements (IGBTs), and capable of outputting multi-level AC voltages. As the number of modules increases, output harmonics are greatly reduced and waveform quality is significantly improved, but the probability of failure also increases accordingly.

[0003] In practical engineering applications of power grid simulators, the inverter side only needs to rely on the overall output signal of the entire unit to complete closed-loop control. To simplify the structure and reduce costs, voltage and current sensors are typically configured only at the overall system output, without setting up independent sampling circuits for each individual H-bridge module. This configuration makes it easy for weak fault characteristics of a single module to be masked by the overall output waveform, making it difficult to locate and isolate faults on the inverter side of a cascaded power grid simulator in a timely manner. After a fault occurs, maintenance personnel need to check each module one by one, which not only significantly extends equipment downtime but also significantly increases maintenance costs. Furthermore, the inability to isolate faulty modules in a timely manner also affects the overall reliability and lifespan of the equipment. Therefore, achieving accurate fault location at the inverter side module level is of significant engineering importance for improving the maintenance efficiency and operational reliability of power grid simulators.

[0004] Currently, fault diagnosis on the inverter side of cascaded power grid simulators mainly falls into two technical categories: The first type of method achieves system-level fault diagnosis based on the system's total output voltage and current signals. This type of method uses existing sensors at the total output terminal to collect signals and determines whether a system fault has occurred by analyzing the waveform distortion, harmonic increments, or energy changes in specific frequency bands of the total output voltage. However, when open-circuit faults occur in the IGBTs of different H-bridge modules, the waveform distortions and harmonic increments caused by the faults in each module will couple and superimpose in the total output signal. The voltage and current characteristics of faults in similar devices in different modules are highly similar, which means that this method can only determine that a system fault has occurred, but it is difficult to distinguish which specific module has failed, resulting in a very limited localization effect.

[0005] The second type of method involves adding voltage sensors to each H-bridge module to measure the output voltage or DC-side capacitor voltage of each module and performing residual analysis to locate the fault. While this method can locate the faulty module relatively accurately, it requires additional voltage sensors and corresponding sampling circuits in each module. As the number of cascaded modules increases, hardware costs and system complexity rise sharply, making it unsuitable for high-power, multi-module power grid simulator scenarios. Furthermore, the additional sensors can introduce new potential fault points, reducing the overall reliability of the system. Summary of the Invention

[0006] The main objective of this application is to propose a fault diagnosis method, electronic device, storage medium, and program product for a cascaded power grid simulator based on frequency conversion carrier modulation, in order to at least solve one of the following problems: the problem that fault characteristics of different modules are coupled and it is difficult to distinguish fault modules in existing fault diagnosis methods based on the total output signal of the system; the problem that existing fault diagnosis methods based on module-level voltage sampling require a large number of additional sensors and have high hardware costs; and the problem that existing fault diagnosis methods based on harmonic analysis use fixed empirical thresholds and are difficult to adapt to different power levels and power grid environments.

[0007] To achieve the above objectives, one aspect of this application proposes a fault diagnosis method for a cascaded power grid simulator based on frequency conversion carrier modulation. The cascaded power grid simulator includes N cascaded H-bridge modules, where N ≥ 2. The method includes: During normal operation, the inverter side of the cascaded power grid simulator adopts a carrier phase-shift sinusoidal pulse width modulation strategy; The system monitors the total output voltage in real time. When the total output voltage exceeds the preset fault threshold, it is determined that an IGBT open circuit fault has occurred in the system, and the modulation strategy is switched to frequency conversion carrier modulation. The triangular carrier frequencies of each H-bridge module are different, so that the switching harmonics of each module are distributed in independent frequency bands. Spectral analysis was performed on the total output voltage of the system after switching modulation modes, and the harmonic content at the characteristic frequencies corresponding one-to-one with the carrier frequencies of each H-bridge module was extracted. Based on the comparison results of the harmonic content at each characteristic frequency and the corresponding fault diagnosis threshold, the H-bridge module where the IGBT open circuit fault occurred is located.

[0008] In some embodiments, the preset fault threshold is 1.3 times the output voltage reference value; when the total system output voltage satisfy When an IGBT open-circuit fault is detected, the system switches to frequency conversion carrier modulation. For the output capacity of a single H-bridge module, This is the output voltage reference value; when When a short circuit fault is detected, a power outage inspection is performed; when The system continues to run.

[0009] In some embodiments, the frequency conversion carrier modulation strategy in the first... The triangular carrier frequency of each H-bridge module is set as follows:

[0010] in, , For fixed frequency multiples, This is the reference carrier frequency for the first H-bridge module.

[0011] In some embodiments, in the frequency conversion carrier modulation strategy, the first The triangular wave carrier phase of each H-bridge module is set as follows:

[0012] in, This represents the total number of cascaded H-bridge modules. For fixed frequency multiples, .

[0013] In some embodiments, the step of performing spectrum analysis on the total output voltage of the system after switching modulation modes and extracting the harmonic content at characteristic frequencies corresponding one-to-one with the carrier frequencies of each H-bridge module includes: Fast Fourier Transform is used to perform spectral analysis on the total output voltage signal of the system, and the time-domain signal is decomposed into a superposition of sinusoidal components of different frequencies. Using the harmonic content relative to the fundamental frequency as a fault characteristic quantity, the relative amplitude of the nth harmonic... ,in Let n be the absolute amplitude of the nth harmonic. This represents the absolute amplitude of the fundamental component.

[0014] In some embodiments, the fault diagnosis threshold is set as follows: Before system commissioning or after maintenance, collect M normal operating condition samples within the rated load range, and analyze each characteristic frequency. relative amplitude of harmonics at the location Perform statistical analysis and calculate the average value under normal operating conditions. With statistical volatility :

[0015]

[0016] in, The characteristic frequency in the j-th sampling The relative amplitude of harmonics at the location; Fault diagnosis thresholds for each characteristic frequency ,in This is a safety multiple.

[0017] In some embodiments, the real-time harmonic amplitude The degree of deviation from the statistical benchmark is converted into a deviation multiple. ;when When determining the characteristic frequency The corresponding H-bridge module experienced an IGBT open-circuit fault.

[0018] In some embodiments, the carrier phase-shift sinusoidal pulse width modulation strategy is a frequency-doubled carrier phase-shift sinusoidal pulse width modulation strategy.

[0019] To achieve the above objectives, another aspect of this application provides an electronic device, which includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the method described above.

[0020] To achieve the above objectives, another aspect of the embodiments of this application proposes a computer-readable storage medium storing a computer program that, when executed by a processor, implements the method described above.

[0021] To achieve the above objectives, another aspect of the embodiments of this application proposes a computer program product, including a computer program that, when executed by a processor, implements the method described above.

[0022] The embodiments of this application include at least the following beneficial effects: This application provides a fault diagnosis method, electronic device, storage medium, and program product for a cascaded power grid simulator based on variable frequency carrier modulation. This solution constructs a dual-mode collaborative architecture that "uses CPS-SPWM during normal operation and switches to variable frequency carrier modulation during faults." Firstly, it ensures that the power grid simulator obtains excellent multi-level output waveforms and low harmonic characteristics under normal operating conditions through carrier phase-shifting technology, without affecting its normal operating quality. When the total system output voltage abnormally triggers modulation switching, the variable frequency carrier naturally reduces the switching harmonics of each H-bridge module in the frequency domain. By decoupling, and without adding any additional voltage sensors or sampling circuits, the system can extract the characteristic frequency harmonic content uniquely corresponding to each fault module by performing FFT spectrum analysis using only the existing total output voltage signal. Combined with threshold comparison, this enables precise module-level localization. Thus, this application fundamentally overcomes the drawbacks of traditional system-level diagnosis where multiple module fault characteristics are mutually coupled and it is difficult to distinguish the fault location. This significantly reduces hardware costs and system complexity, and enables rapid identification of fault modules to shorten downtime for troubleshooting. It also significantly improves the operation and maintenance efficiency and operational reliability of cascaded power grid simulators. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the equivalent topology of the inverter side of the cascaded power grid simulator in this application embodiment (taking two units cascaded as an example); Figure 2 This is a simulation block diagram of frequency converter carrier control using a three-tiered H-bridge inverter as an example in the embodiments of this application; Figure 3 This is a waveform diagram of the inverter phase voltage and three-phase line voltage output under normal operating conditions in the embodiments of this application; Figure 4 This is a comparison chart of the phase voltage FFT analysis spectrum under normal operating conditions and different bridge arm open circuit fault conditions in the embodiments of this application; Figure 5 This is a flowchart of a fault diagnosis method for a cascaded power grid simulator based on frequency conversion carrier modulation, provided in an embodiment of this application; Figure 6 This is a schematic diagram of the hardware structure of the electronic device provided in the embodiments of this application. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit it. In the following description, when referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with those of this application; they are merely examples of apparatuses and methods consistent with some aspects of the embodiments of this application as detailed in the appended claims.

[0025] 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 herein is for the purpose of describing embodiments of this application only and is not intended to limit this application.

[0026] Grid simulators are devices that simulate the characteristics of a power grid and are widely used in scenarios such as new energy grid connection testing. Cascaded grid simulators employ a cascaded H-bridge structure on the inverter side, consisting of multiple independent H-bridge modules connected in series. Containing numerous switching elements, they can output multi-level AC voltages. While the number of modules significantly reduces output harmonics, the probability of failure also increases. Furthermore, in grid simulator applications, the inverter side only needs to rely on the overall output signal to complete closed-loop control. To simplify the structure and reduce costs, sensors are typically configured only at the overall system output, without setting independent sampling circuits for each independent H-bridge module. This makes it easy for weak fault characteristics of a single module to be masked by the overall output waveform, making it difficult to locate and isolate faults on the inverter side of the cascaded grid simulator in a timely manner. After a fault occurs, maintenance personnel must check each module one by one, which not only prolongs equipment downtime but also increases maintenance costs. Simultaneously, the inability to isolate faulty modules in a timely manner also affects the overall reliability and lifespan of the equipment. Therefore, achieving accurate fault location at the inverter side module level is of significant engineering importance for improving the maintenance efficiency and operational reliability of grid simulators.

[0027] Currently, most inverter-side fault diagnosis methods rely on system-level fault diagnosis based on the total output voltage and current signals of the system. Fault location is achieved by measuring the output voltage of each H-bridge module or measuring the capacitor voltage and performing residual analysis. This type of method requires adding a voltage sensor to each module. As the number of modules increases, this method increases equipment costs and is not suitable for high-power grid simulator scenarios.

[0028] In addition, for the location method based on the total output voltage and current of the system, when the IGBTs of different H-bridge modules on the inverter side of the cascaded power grid simulator have open-circuit faults, the waveform distortion and harmonic increments caused by the fault will be coupled and superimposed, and the voltage and current characteristics of the same type of fault in different modules will be highly similar, resulting in limited location effect.

[0029] To address the shortcomings of existing technologies, this application proposes a fault diagnosis method, electronic equipment, storage medium, and program product for a cascaded power grid simulator based on variable frequency carrier modulation, taking advantage of the programmable operating conditions of the cascaded power grid simulator. This solution configures differentiated carrier frequencies for different H-bridge modules, distributing the switching harmonics of each module within independent frequency bands, thus enabling rapid and accurate location of module-level faults on the inverter side. Furthermore, this application eliminates the need for additional hardware sampling circuitry, enabling rapid identification of faulty modules and significantly improving equipment operation and maintenance efficiency and reliability.

[0030] like Figure 5 As shown, this embodiment provides a fault diagnosis method for a cascaded power grid simulator based on frequency conversion carrier modulation. The cascaded power grid simulator includes N cascaded H-bridge modules, where N≥2. The method includes the following steps: Step S1: During normal operation, the inverter side of the cascaded power grid simulator adopts a carrier phase-shift sinusoidal pulse width modulation strategy; Step S2: Real-time detection of the total output voltage of the system. When the total output voltage of the system exceeds the preset fault threshold, it is determined that an IGBT open circuit fault has occurred in the system, and the modulation strategy is switched to frequency conversion carrier modulation. Step S3: Perform spectrum analysis on the total output voltage of the system after switching modulation mode, and extract the harmonic content at the characteristic frequencies that correspond one-to-one with the carrier frequencies of each H-bridge module; Step S4: Based on the comparison results of the harmonic content at each characteristic frequency and the corresponding fault diagnosis threshold, locate the H-bridge module where the IGBT open circuit fault occurs.

[0031] The solutions of the embodiments of this application will be described in detail and explained below with reference to specific application examples.

[0032] In this embodiment, the inverter-side modulation strategy for the cascaded H-bridge inverter adopts CPS-SPWM modulation under normal operation and switches to inverter carrier modulation during faults. This achieves high-quality output under normal conditions and precise location of the faulty module during faults, thereby improving equipment reliability. The specific scheme is as follows.

[0033] Step 1: During normal operation, the inverter side of the cascaded power grid simulator adopts the CPS-SPWM modulation strategy.

[0034] Figure 1This is a cascaded H-bridge main circuit topology consisting of converter units A1 and A2. The overall system is composed of two identical H-bridge converter units connected in series, with each H-bridge unit consisting of four IGBT switching devices. The total output voltage of the inverter is synthesized by superimposing the output voltages of each series-connected H-bridge unit. Multi-level output characteristics are achieved through the superposition of multi-unit levels, effectively improving the output waveform quality.

[0035] The DC-side voltage of the single H-bridge unit is set to U d When the voltage drop of the switching devices is ignored, a single H-bridge can output Three voltage levels. Under normal operation, a frequency-doubled carrier phase-shift modulation strategy (CPS-SPWM) is adopted. Each unit uses the same sinusoidal modulation wave, and pulse interleaving control is achieved by configuring different carrier phases. A stepped multi-level voltage waveform is generated by relying on the superposition effect of multi-unit PWM waveforms.

[0036] Frequency doubled carrier phase shift modulation (CPS-SPWM) is currently the mainstream modulation strategy for cascaded grid simulators. This modulation method uses triangular carriers with the same frequency and phase shift for all modules, which can achieve a higher equivalent output frequency at a lower device switching frequency, effectively suppress low-order harmonics on the output side, and ensure excellent output waveform quality of the inverter.

[0037] Bipolar frequency doubling modulation exhibits frequency multiplication characteristics. Within a single carrier cycle, the H-bridge output voltage can complete two level-to-level transitions, making the equivalent output switching frequency of the unit twice the triangular wave carrier frequency. If the carrier frequency of a single H-bridge is... The harmonics of the three-level waveform output by this unit are mainly concentrated in... Frequency band.

[0038] For a cascaded system containing N H-bridge units, the traditional CPS-SPWM strategy uniformly distributes the phase shift angle among adjacent units, with the carrier phase difference between units being... The harmonics of each unit switch are symmetrically distributed within a fixed frequency band. Harmonic cancellation is achieved through phase vector superposition, causing the total output harmonics of the system to shift to higher frequencies. Ultimately, the output voltage harmonics are mainly distributed in... High-frequency bands can significantly eliminate low-order harmonic components, thus greatly optimizing output power quality. Taking a two-unit cascaded topology as an example, the carrier amplitude and frequency of the two units are consistent, but their phases differ. By combining it with a reverse sine wave modulation, a five-level output waveform can be generated, whose harmonics are mainly concentrated in... The surrounding area is consistent with the aforementioned theoretical principles.

[0039] Each H-bridge unit uses complementary switching logic control, and the IGBT drive signals of the upper and lower IGBTs in the same bridge arm are strictly complementary, i.e., g i1 =1-g i2 g i3=1-g i4 This can eliminate bridge arm shoot-through faults from the control mechanism. Defining a switch signal of 1 for device conduction and 0 for device deactivation, the output voltage of the i-th H-bridge unit can be expressed as:

[0040] In the formula, the switch signal g i1 g i3 The value can be either 0 or 1. When g i1 Conductivity, g i3 Off, i.e., g i1 =1, g i3 When =0, the unit outputs a positive DC voltage; when g is turned off... i1 g i3 Conduction, i.e., g i1 =0, g i3 When =1, the unit outputs a negative DC voltage; when the upper and lower bridge arm switches are in the same state, i.e. g i1 =g i3 When =0 or =1, the unit outputs zero voltage. The total output voltage of the inverter is the sum of the output voltages of all series-connected H-bridge units, and its expression is:

[0041] Step 2: The system output voltage overvoltage is diagnosed as a fault. The modulation method is switched to frequency conversion carrier modulation, and the output voltage after the modulation method is switched is recorded.

[0042] This embodiment proposes a method for diagnosing overvoltage in system output voltage, which utilizes the existing total output voltage measurement device of a cascaded power grid simulator without the need to add additional sensing equipment.

[0043] Let the total output voltage of the system be U. o Let the output capacity of a single H-bridge be U. h The number of modules is N. Since the output voltage reference value in the closed-loop control of the system output voltage in the power grid simulator application scenario is U... ref The equipment needs to have a certain degree of redundant output capability, therefore U ref <(N-1)U h Based on this, the fault criterion is proposed as follows: When NU h >u o >1.3U ref When the output voltage deviation exceeds 30% of the output voltage reference value, it is determined that an IGBT open circuit fault has occurred in the system, and the CPS-SPWM modulation is switched to frequency conversion carrier modulation.

[0044] If U o ≥NU h In case of a serious fault such as a short circuit, immediately shut off the power and inspect the affected area.

[0045] When U o ≤1.3U ref The system is within the normal voltage fluctuation range and can continue to operate.

[0046] The frequency conversion carrier modulation employs a frequency-incrementing, phase-adaptive correction strategy, as detailed below: This strategy sets the triangular wave carrier frequency of the first H-bridge module as the reference frequency. The initial phase is , No. i The triangular wave carrier frequency of each H-bridge module is set as follows:

[0047] in, x This is a fixed frequency multiplication factor. In this configuration, the carrier frequency of each module increases progressively with the module number, and the corresponding carrier period is compressed inversely with the frequency. i The carrier period of each module is:

[0048] In the formula, The reference carrier period.

[0049] In traditional same-frequency carrier phase-shift modulation logic, the carrier frequency and period of each module are the same, and the phase follows the complete carrier period. Uniform distribution, achieved by interleaving switching pulses through a fixed phase difference. In this embodiment, the carrier periods of each module are different. Traditional phase-sharing methods would cause multiple module switching pulses to jump simultaneously, resulting in large instantaneous current surges and voltage spike distortion. To suppress this problem, this embodiment, based on traditional phase-sharing logic, introduces a frequency multiple correction term, deriving the... i The triangular wave carrier phase of each H-bridge module is:

[0050] Through this carrier configuration method, each H-bridge unit achieves asynchronous pulse control: reasonable initial phase configuration can avoid synchronous transitions of multi-module switching pulses, effectively reducing instantaneous impact; the variable carrier frequency ensures that the harmonics of the main switches of each module are distributed in independent frequency bands, providing a natural frequency domain decoupling condition for fault location. During normal operation, constrained by the symmetry of bipolar frequency doubling modulation, the harmonics of each module are mainly concentrated near the even harmonics of its carrier frequency, and the fundamental frequency component is canceled out; when an open-circuit fault occurs in an IGBT inside a certain H-bridge, the modulation symmetry of that module is destroyed, and only the harmonic components of its corresponding carrier fundamental frequency band increase abnormally, while the harmonic distribution of other healthy modules remains undisturbed. Compared with the problem of severe fault feature coupling and difficulty in distinguishing faulty modules in traditional modulation methods, this solution makes the faults of similar devices in different modules exhibit differentiated frequency domain characteristics from the modulation mechanism level. Based on this characteristic, the faulty module can be quickly identified according to the frequency band of the abnormal harmonics, achieving precise fault location at the module level, while also taking into account the switching impact suppression requirements during normal operation.

[0051] Step 3: Perform harmonic analysis on the output voltage after switching the modulation mode.

[0052] The output voltage signal of the cascaded H-bridge converter is analyzed using Fast Fourier Transform (FFT). The time-domain signal of the output voltage can be decomposed into a superposition of sinusoidal components of different frequencies.

[0053] Where U0 is the DC component, U n Let n be the amplitude of the nth harmonic. The fundamental angular frequency, This is the fundamental frequency of the power grid.

[0054] To eliminate the influence of fundamental frequency amplitude fluctuations on fault diagnosis results, the harmonic content relative to the fundamental frequency is used as a fault characteristic quantity, and its calculation formula is as follows:

[0055] in, The relative amplitude of the nth harmonic (unit: % of Fundamental). This represents the absolute amplitude of the fundamental component.

[0056] Based on the differentiated carrier modulation characteristics proposed above ( =1,2,……,N), where N is the number of cascaded modules. The method in this embodiment extracts the carrier frequencies corresponding one-to-one with the carrier frequencies of the i-th H-bridge module. The harmonic content at the location is used as the basis for fault diagnosis. Under this configuration, the fault characteristics of different modules are completely decoupled in the frequency domain and will not interfere with each other, solving the problem of severe coupling of fault characteristics and difficulty in distinguishing faulty modules in traditional co-frequency carrier phase-shift modulation.

[0057] Based on the distribution characteristics of the aforementioned characteristic frequencies, this embodiment proposes a fast fault diagnosis method based on statistical thresholds. The fault diagnosis process is as follows: Before system commissioning or after maintenance, collect M normal operating condition samples within the rated load range, where M ≥ 100, covering conditions from light load to full load and typical power grid fluctuations. For each characteristic frequency... ( =1,2, The relative amplitudes Hi of the harmonics of N are statistically analyzed, and the average value under normal operating conditions is calculated. With statistical volatility :

[0058]

[0059] in, The characteristic frequency in the j-th sampling The relative amplitude of harmonics at the location; It reflects the inherent harmonic level of this frequency under normal operating conditions; It reflects the normal fluctuation amplitude under the combined effects of load fluctuation, grid voltage fluctuation, temperature drift and measurement noise.

[0060] Based on the aforementioned normal statistical benchmark, fault diagnosis thresholds are set for each characteristic frequency. :

[0061] In the formula: k is the safety factor, representing the maximum allowable normal fluctuation range; in engineering, k=3 is used. The threshold for the low harmonic content frequency band is determined by... The threshold for high-harmonic content frequencies is determined by the actual fluctuation range of on-site noise and power grid background harmonics; the threshold for high-harmonic content frequencies is located above the normal harmonic level. The level is matched with the inherent harmonic levels of different frequency bands.

[0062] The threshold H th,i normal statistical benchmark With safety margin The amplitude threshold is synthesized into a physical quantity threshold, facilitating engineering calibration and intuitive understanding. During online diagnostics, to eliminate the incomparability caused by differences in normal harmonic levels across different characteristic frequencies, the real-time harmonic amplitude H is... i The degree of deviation from the statistical benchmark is converted into a deviation factor Di:

[0063] For all satisfying D i For any characteristic frequency ≥ k, the corresponding H-bridge module is identified as a faulty module. Since a fault in a single H-bridge module only causes a significant change in the harmonic amplitude of its corresponding characteristic frequency point, while the characteristic frequency amplitudes of other modules remain within the normal fluctuation range, the above quantitative judgment rule can achieve accurate location of a single faulty module.

[0064] Example: Building a simulation model and conducting operational condition verification analysis Taking a three-tiered H-bridge inverter as an example, the total number of tiered modules is taken as follows. frequency coefficient Reference carrier frequency Taking a safety factor of k=3, the carrier parameters of the three H-bridge modules are as follows: First H-bridge: Initial Phase 500Hz; Second H-bridge: Initial phase 1000Hz; The third H-bridge: initial phase , frequency 1500Hz.

[0065] Each unit employs bipolar frequency-doubled carrier phase-shift modulation, and the control simulation model is as follows: Figure 2 As shown, pwm1 to pwm4 are the drive signals for the first H-bridge.

[0066] (1) Normal operating condition analysis Under normal operating conditions, the inverter phase voltage and three-phase line voltage waveforms have good quality and no obvious distortion; the inverter phase voltage and three-phase line voltage output waveforms under normal operating conditions are as follows: Figure 3 As shown.

[0067] (2) Fault condition analysis An IGBT open-circuit fault is simulated by stepping the IGBT switch gate signal to 0, with the step time set to a random number to simulate faults at different times. The parameters are set as follows: the total system output voltage is U. o The output capacity of a single H-bridge is U h =500V (RMS), number of modules N=3. Since in the power grid simulator application scenario, the output voltage reference value in the closed-loop control of the system output voltage is U... ref =1000V, and fault diagnosis simulation test was carried out under this parameter.

[0068] U after the fault o >1.3U refAt 1300V, the system switches modulation modes. The system output voltage is recorded under normal operating conditions and after switching to differentiated carrier modulation for harmonic analysis. The spectrum under normal and fault conditions is as follows: Figure 4 As shown, where: Figure 4 (a) shows the spectrum of the system during normal operation, where the harmonic amplitudes at each characteristic frequency are at normal levels; Figure 4 (b) shows the spectrum of the fault in the upper transistor of the first H-bridge module, with a significant harmonic peak at 500Hz. Figure 4 (c) shows the fault spectrum of the upper transistor in the second H-bridge module, with a significant harmonic peak at 1000Hz. Figure 4 The spectrum of the fault in the upper tube of the third H-bridge module is shown in (d), with a significant harmonic peak at 1500Hz.

[0069] An ideal model was built in the Simulink simulation platform. M=200 steady-state operating condition samples were obtained by scanning load parameters. The relative amplitudes of harmonics at each characteristic frequency were statistically analyzed to obtain the normal statistical benchmark as follows: 500Hz characteristic frequency: =0.12%; 1000Hz characteristic frequency: =9.52% 1500Hz characteristic frequency: =0.25% Because there are no power grid background harmonics and measurement noise in the ideal simulation environment, the statistical fluctuation is close to zero. In practical engineering applications, the statistical fluctuation... The calibration needs to be performed based on the sampling circuit accuracy of the specific device, the background harmonic level of the power grid, and the on-site electromagnetic environment. An example of statistical fluctuation is given. =0.60%, =1.16% Taking 0.58% as an example, the fault diagnosis threshold is as follows: 500Hz characteristic frequency: H th,1 =0.12% + 3 × 0.60% = 1.92%; 1000Hz characteristic frequency: H th,2 =9.52% + 3 × 1.16% = 13.00%; 1500Hz characteristic frequency: H th,3 =0.25% + 3 × 0.58% = 1.99%.

[0070] After the fault, the output voltage signal was acquired in real time and FFT analysis was performed. Table 1 shows the comparison data of characteristic harmonic amplitudes under different operating conditions. The relative harmonic amplitudes corresponding to the three core characteristic frequencies of 500Hz, 1000Hz, and 1500Hz were extracted and compared with the threshold H. th,iCompare and calculate the deviation multiple D i As shown in Table 2. If the amplitude of a certain characteristic frequency is greater than the threshold of the corresponding frequency or the D of the amplitude of a certain characteristic frequency. i If the value is greater than 3, the H-bridge module corresponding to that frequency carrier is determined to be faulty, thus enabling accurate differentiation of faults in different modules.

[0071] Table 1 Comparison of harmonic amplitudes at various characteristic frequencies under different operating conditions

[0072] Table 2. Deviation multiples of characteristic frequencies under different operating conditions

[0073] The differentiated carrier modulation strategy used in this embodiment allows the harmonic energy of each module to be naturally distributed in different frequency bands: The first H-bridge harmonic energy is mainly concentrated around 1000Hz and 2000Hz; The second H-bridge harmonic energy is mainly concentrated around 2000Hz and 4000Hz; The third H-bridge harmonic energy is mainly concentrated around 3000Hz.

[0074] As shown in Tables 1 and 2, when the first H-bridge fails, the amplitude of the 500Hz characteristic frequency H1 = 8.16% ≥ H th,1 =1.92%, and D_500Hz=13.40≥3, the first H-bridge is determined to be faulty; when the second H-bridge is faulty, the amplitude of the 1000Hz characteristic frequency H2=14.94%≥H th,2 =13.00%, and D_1000Hz=4.67≥3, the second H-bridge is determined to be faulty; when the third H-bridge is faulty, the amplitude of the 1500Hz characteristic frequency H3=7.71%≥H th,3 =1.99%, and D_1500Hz=12.86≥3, indicating a fault in the third H-bridge. The above determination result is consistent with the fault injection location, verifying the effectiveness of the method.

[0075] The aforementioned differential harmonic characteristics are directly related to the distortion mechanism of the output waveform after different module failures. Taking the open-circuit fault of the upper arm switch of the first H-bridge module as an example, the fault mechanism analysis shows that the H-bridge output waveform exhibits significant distortion after the fault: the constant turn-off of the upper switch leads to the complete loss of the positive half-cycle output capability; when the modulation wave is greater than the carrier wave, the positive voltage that should have been output fails, and only a small number of non-ideal spikes are generated due to the cascade coupling effect; the bipolar frequency doubling symmetrical operating condition is destroyed, and the negative half-cycle cannot form a regular output, and the waveform degenerates into an asymmetric distorted pulsating sequence.

[0076] Spectral characteristic analysis reveals that the key premise for suppressing the 500Hz carrier component under normal operating conditions is the symmetrical characteristic of the positive and negative waveforms in bipolar modulation. After the bridge arm is disconnected, the half-wave anti-symmetry characteristic is disrupted, and the originally mutually canceling 500Hz carrier fundamental frequency component is no longer suppressed, resulting in a significant 500Hz harmonic peak in the spectrum. Simultaneously, the amplitudes of the 1000Hz and 2000Hz even harmonics are attenuated, and the low-frequency harmonic content increases.

[0077] Similarly, a fault in the upper transistor of module 2 will produce a characteristic harmonic at 1000Hz, while a fault in the upper transistor of module 3 will produce a characteristic harmonic at 1500Hz. Faults in the same type of device in different modules exhibit different frequency domain characteristics, which can directly locate the faulty module.

[0078] In summary, compared with the prior art, the method of this embodiment has at least the following advantages and beneficial effects: 1) Achieve precise module-level location without increasing hardware costs. This application uses frequency conversion carrier modulation to distribute the switching harmonics of each H-bridge module within independent frequency bands. Utilizing only the existing total output voltage measurement device, the faulty module can be accurately located by performing FFT spectrum analysis on the total output voltage after switching modulation methods. Compared to existing methods based on the system's total output signal, this approach can distinguish faults in similar devices across different modules; compared to existing methods based on module-level residual analysis, it eliminates the need to add voltage sensors to each module, significantly reducing hardware costs and system complexity.

[0079] 2) Dual-mode modulation synergy balances normal operation performance and fault diagnosis requirements. This application employs CPS-SPWM modulation during normal operation to ensure excellent output waveform quality and low harmonic characteristics of the inverter; it only switches to inverter carrier modulation when the system detects an abnormal output voltage, ensuring that the harmonics of each module are distributed in independent frequency bands. The synergistic cooperation of the two modulation methods not only guarantees power quality during normal operation but also creates conditions for fault diagnosis.

[0080] 3) Frequency domain decoupling of fault characteristics is achieved at the modulation mechanism level. In the frequency conversion carrier strategy designed in this application, the carrier frequency of each module is determined according to... The harmonics increase progressively. During normal operation, constrained by the symmetry of bipolar frequency doubling modulation, the harmonics of each module are mainly concentrated near the even harmonics of its carrier frequency, and the fundamental frequency component is canceled out. When an open-circuit fault occurs in an IGBT within an H-bridge, the modulation symmetry of that module is disrupted, and only the harmonic components in its corresponding carrier fundamental frequency band increase abnormally, while the harmonic distribution of other healthy modules remains undisturbed. This characteristic ensures, mechanistically, that faults in the same type of device across different modules exhibit differentiated frequency domain characteristics, providing a natural decoupling condition for module-level localization.

[0081] 4) The adaptive threshold setting method has good portability. This application is based on the statistical benchmark of normal operating conditions (average μ).i Statistical fluctuation σ i Constructing the fault diagnosis threshold H th,i =μ i +kσ i The threshold for the low harmonic content frequency band is naturally determined by the fluctuations in on-site noise, while the threshold for the high harmonic content frequency band adapts to the inherent harmonic level. Compared to the traditional fixed empirical threshold method, this application does not require specifying empirical constants for different frequency bands, can adapt to different power levels and different power grid environments, and has good portability and engineering applicability.

[0082] 5) A unified standard for determining the deviation ratio enables fair comparison across frequency bands. This application introduces a deviation ratio... As a unified judgment index across frequency bands, it eliminates the incomparability caused by differences in normal harmonic levels among different characteristic frequencies, enabling the use of a unified judgment standard for high harmonic content frequency bands and low harmonic content frequency bands. Meanwhile, this judgment indicator is compatible with both upper and lower limit bidirectional detection, which can detect both harmonic surges caused by IGBT open circuits and harmonic suppression caused by drive loss, making the judgment logic more complete.

[0083] This application also provides an electronic device, which includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the above-described method. This electronic device can be any smart terminal, including tablet computers, in-vehicle computers, etc.

[0084] It is understood that the content of the above method embodiments is applicable to this device embodiment. The specific functions implemented by this device embodiment are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0085] Please see Figure 6 , Figure 6 The hardware structure of an electronic device according to another embodiment is illustrated. The electronic device includes: The processor 601 can be implemented using a general-purpose CPU (Central Processing Unit), microprocessor, application-specific integrated circuit (ASIC), or one or more integrated circuits, and is used to execute relevant programs to implement the technical solutions provided in the embodiments of this application. The memory 602 can be implemented as a read-only memory (ROM), a static storage device, a dynamic storage device, or a random access memory (RAM). The memory 602 can store the operating system and other applications. When the technical solutions provided in the embodiments of this specification are implemented through software or firmware, the relevant program code is stored in the memory 602 and is called and executed by the processor 601 using the methods described in the embodiments of this application. The input / output interface 603 is used to implement information input and output; The communication interface 604 is used to enable communication and interaction between this device and other devices. Communication can be achieved through wired means (such as USB, network cable, etc.) or wireless means (such as mobile network, WIFI, Bluetooth, etc.). Bus 605 transmits information between various components of the device (e.g., processor 601, memory 602, input / output interface 603, and communication interface 604); The processor 601, memory 602, input / output interface 603, and communication interface 604 are connected to each other within the device via bus 605.

[0086] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described method.

[0087] It is understood that the content of the above method embodiments is applicable to this storage medium embodiment. The specific functions implemented in this storage medium embodiment are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved in the above method embodiments.

[0088] Memory, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs and non-transitory computer-executable programs. Furthermore, memory may include high-speed random access memory, and may also include 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, memory may optionally include memory remotely located relative to the processor, and these remote memories can be connected to the processor via a network. Examples of such networks include, but are not limited to, the Internet, intranets, local area networks, mobile communication networks, and combinations thereof.

[0089] This application also provides a computer program product, including a computer program that, when executed by a processor, implements the above-described method.

[0090] It is understood that the content of the above method embodiments is applicable to the embodiments of this program product. The specific functions implemented in the embodiments of this program product are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved in the above method embodiments. The executable computer program code or "code" used to perform the various embodiments can be written in high-level programming languages ​​such as C, C++, Python, Smalltalk, Java, JavaScript, Visual Basic, Structured Query Language (e.g., Transact-SQL), Perl, or in various other programming languages.

[0091] The embodiments described in this application are for the purpose of more clearly illustrating the technical solutions of the embodiments of this application, and do not constitute a limitation on the technical solutions provided by the embodiments of this application. As those skilled in the art will know, with the evolution of technology and the emergence of new application scenarios, the technical solutions provided by the embodiments of this application are also applicable to similar technical problems.

[0092] Those skilled in the art will understand that the technical solutions shown in the figures do not constitute a limitation on the embodiments of this application, and may include more or fewer steps than shown, or combine certain steps, or different steps.

[0093] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0094] Those skilled in the art will understand that all or some of the steps in the methods disclosed above, as well as the functional modules / units in the systems and devices, can be implemented as software, firmware, hardware, or suitable combinations thereof.

[0095] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0096] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0097] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of the units described above is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0098] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0099] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0100] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it 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 all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes multiple 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 of the various embodiments of this application. The aforementioned storage medium includes various media capable of storing programs, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0101] The preferred embodiments of the present application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and substance of the embodiments of the present application shall be within the scope of the claims of the present application.

Claims

1. A fault diagnosis method for a cascaded power grid simulator based on variable frequency carrier modulation, characterized in that, The cascaded power grid simulator includes N cascaded H-bridge modules, where N ≥ 2, and the method includes the following steps: During normal operation, the inverter side of the cascaded power grid simulator adopts a carrier phase-shift sinusoidal pulse width modulation strategy; The system monitors the total output voltage in real time. When the total output voltage exceeds the preset fault threshold, it is determined that an IGBT open circuit fault has occurred in the system, and the modulation strategy is switched to frequency conversion carrier modulation. Spectral analysis was performed on the total output voltage of the system after switching modulation modes, and the harmonic content at the characteristic frequencies corresponding one-to-one with the carrier frequencies of each H-bridge module was extracted. Based on the comparison results of the harmonic content at each characteristic frequency and the corresponding fault diagnosis threshold, the H-bridge module where the IGBT open circuit fault occurred is located.

2. The method according to claim 1, characterized in that, The preset fault threshold is the output voltage reference value. Times; when the total output voltage of the system satisfy When an IGBT open-circuit fault is detected, the system switches to frequency conversion carrier modulation. For the output capacity of a single H-bridge module, This is the output voltage reference value; when When a short circuit fault is detected, a power outage inspection is performed; when The system continues to run.

3. The method according to claim 1, characterized in that, The frequency conversion carrier modulation strategy in the first The triangular carrier frequency of each H-bridge module is set as follows: in, , For fixed frequency multiples, This is the reference carrier frequency for the first H-bridge module.

4. The method according to claim 1, characterized in that, In the aforementioned frequency conversion carrier modulation strategy, the first... The triangular wave carrier phase of each H-bridge module is set as follows: in, This represents the total number of cascaded H-bridge modules. For fixed frequency multiples, .

5. The method according to claim 1, characterized in that, The process of performing spectrum analysis on the total output voltage of the system after switching modulation methods, and extracting the harmonic content at characteristic frequencies corresponding one-to-one with the carrier frequencies of each H-bridge module, includes: Fast Fourier Transform (FFT) is used to perform spectral analysis on the total output voltage signal of the system, decomposing the time-domain signal into a superposition of sinusoidal components of different frequencies; the harmonic content relative to the fundamental frequency is used as a fault characteristic quantity, and the relative amplitude of the nth harmonic is... ,in Let be the absolute amplitude of the nth harmonic. This represents the absolute amplitude of the fundamental component.

6. The method according to claim 1, characterized in that, The fault diagnosis threshold is set in the following manner: Before system commissioning or after maintenance, collect M normal operating condition samples within the rated load range, and analyze each characteristic frequency. relative amplitude of harmonics at the location Perform statistical analysis and calculate the average value under normal operating conditions. With statistical fluctuation : in, The characteristic frequency in the j-th sampling The relative amplitude of harmonics at the location; Fault diagnosis thresholds for each characteristic frequency ,in This is a safety multiple.

7. The method according to claim 6, characterized in that, Real-time harmonic amplitude The degree of deviation from the statistical benchmark is converted into a deviation multiple. ;when When determining the characteristic frequency The corresponding H-bridge module experienced an IGBT open-circuit fault.

8. The method according to claim 1, characterized in that, The carrier phase-shift sinusoidal pulse width modulation strategy is a frequency-doubled carrier phase-shift sinusoidal pulse width modulation strategy.

9. An electronic device, characterized in that, The electronic device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the method according to any one of claims 1 to 8.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the method of any one of claims 1 to 8.

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