A method for monitoring inverter system parameters based on second-order system step response

Abstract

The present invention discloses a method for monitoring inverter system parameters based on a second-order system step response. The present invention is applicable to the estimation of the capacitance value of the LC filter capacitor of a single-phase inverter and a three-phase three-bridge-arm inverter. By injecting a step response into the inverter system, sampling and obtaining the step response of the filter inductor current and the filter capacitor voltage, and comparing with the standard second-order system, the system's natural damping frequency, damping ratio, overshoot, peak time and other parameters are obtained, and the filter inductance value, filter capacitor value and circuit equivalent resistance of the inverter LC filter are calculated by reverse calculation; compared with the existing LC filter capacitor capacitance test method, the proposed method can realize online monitoring without disassembling the existing device, the calculation process is simple, the operation method is concise, the controller performance requirements are lower, and the measurement accuracy is higher.

Description

Technical Field

[0001] The invention belongs to the technical field of inverter detection, and in particular relates to an inverter system parameter monitoring method based on second-order system step response. Background Art

[0002] As the installed capacity of renewable energy power generation continues to increase, its impact on the power grid is also increasing. Every failure of renewable energy power generation equipment will cause huge losses to the power grid, which requires better reliability design for power electronic systems in renewable energy applications. In the study of power electronic reliability, power devices, inductors and capacitors are relatively weak, which is related to the overall reliability of the system. Generally speaking, the failure mode of inverter LC filter can be divided into sudden failure caused by overstress and aging failure caused by long-term service and continuous deterioration of equipment. Among them, aging failure is the main failure mode, and aging failure occurs when the capacitance value drops to 95% of the initial capacitance. Inverters often rely on excessive margin design and high operation and maintenance costs in exchange for safe and reliable operation, and scientific health status assessment is required to guide design, manufacturing and operation and maintenance. Accurately measuring filter parameters and quantifying the health status of key components are prerequisites for analyzing inverter reliability.

[0003] Through literature search, it is found that researchers have proposed a variety of solutions for monitoring methods of inductors and capacitors. For example, a low-power sinusoidal alternating current is injected into the circuit, and the capacitor current and voltage are obtained through discrete fast Fourier transform (DFFT) analysis, and the capacitance is calculated through its phase amplitude relationship. However, offline capacitor monitoring technology requires the capacitor to be removed from the system, which is inconvenient in practical applications; there is also the principle of time domain model parameter identification, using the Kalman filter to solve the time domain model of the capacitor; or based on hybrid system modeling, a parameter identification method for power electronic circuits is designed using the least squares method. There is also a voltage and current signal injection measurement method to obtain the characteristic quantity of the capacitor at the output. This method has high accuracy, but the design and calculation are relatively complicated.

[0004] In summary, the existing methods have the following limitations: (1) Offline capacitor monitoring technology requires the capacitor to be removed from the system, which is inconvenient in practical applications; (2) Online monitoring methods often have cumbersome modeling processes and complex calculations. (3) Traditional methods require high-frequency triggering of switching devices, which places high demands on controller performance. Summary of the invention

[0005] In view of the technical problems existing in the prior art, in order to estimate the capacitance of the inverter LC filter and improve the reliability of the inverter, it is necessary to adopt a suitable state monitoring capacitance test method.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides an inverter system parameter monitoring method based on a second-order system step response, comprising:

[0008] By injecting a step response into the inverter system and collecting capacitor voltage and inductor current information, the step response of the filter inductor current and filter capacitor voltage is obtained. By comparing with the standard second-order system, the system's natural damping frequency, damping ratio, overshoot, peak time and other parameters are obtained, and the filter inductance value, filter capacitor value and circuit equivalent resistance of the inverter LC filter are calculated in reverse.

[0009] The inverter system includes a single-phase inverter or a three-phase three-leg inverter.

[0010] As a further improvement of the present invention, the single-phase inverter comprises a single-phase inverter input DC power supply V dc , filter inductor L f And the equivalent resistance R f , filter capacitor C f And the equivalent resistance R c .

[0011] As a further improvement of the present invention, after the single-phase inverter injects a step response, the capacitor voltage and inductor current information are collected, the loop is subjected to KVL analysis and Laplace transformation, and the capacitor voltage U is obtained. c (s) for step input U ab The transfer function of (s) and the inductor current i L (s) for step input U ab (s) transfer function.

[0012] As a further improvement of the present invention, the capacitor voltage U c (s) for step input U ab The transfer function of (s) and the inductor current i L (s) for step input U ab The transfer function of (s) is:

[0013]

[0014] Where U c is the capacitor voltage, U ab is a step input, i L Inductor current, L f is the filter inductor, R f is the equivalent resistance of the filter inductor, C f is the filter capacitor, R c is the equivalent resistance of the filter capacitor; capacitor voltage U c (s) for step input U ab The transfer function of (s) is in the same form as the standard second-order system.

[0015] As a further improvement of the present invention, the natural damping frequency, damping ratio, overshoot, peak time and other parameters of the system are obtained by comparing with the standard second-order system, including:

[0016] Corresponding to the standard second-order system The corresponding natural damping frequency ω in the single-phase inverter system is obtained n And the expression of damping ratio ζ:

[0017]

[0018]

[0019] In the formula, ω n is the natural damping frequency, ζ is the damping ratio, L f is the filter inductor, R f is the equivalent resistance of the filter inductor, C f is the filter capacitor, R c is the equivalent resistance of the filter capacitor.

[0020] As a further improvement of the present invention, the capacitors in the three-phase three-bridge-arm inverter are connected in a triangle, including capacitor C ab , capacitor C bc , capacitor C ac , including filter inductor L a 、Filter inductor L b 、Filter inductor L c , equivalent resistance R a , equivalent resistance R b , equivalent resistance R c .

[0021] As a further improvement of the present invention, after the three-phase three-bridge-leg inverter injects a step response, it includes:

[0022] 1) Inject step response into phases a and c, perform KVL analysis on the loop, and obtain the currents of phases a and c and the three-phase capacitance C ab , C bc , C ac The voltage-current relationship of

[0023] 2) For phase a and phase c current i a 、i c , three-phase capacitance U ab , U bc , U ac The voltage-current relationship is Laplace transformed to obtain the current flowing through the capacitor C ab The current i ab (s) for step input V dc (s) and flows through capacitor Cbc The current i bc (s) for step input V dc (s) transfer function;

[0024] 3) will u ab (s),u bc (s) for step input V dc The transfer function of (s) is combined to obtain the capacitor voltage U ac (s) for step input V dc (s) transfer function;

[0025] The same method is used to conduct the three phases and obtain the parameter C AC , C AB , C BC , Lian Li C AC , C AB , C BC Establish a three-variable equation system about the filter capacitor and solve for C ab , C bc , C ac .

[0026] As a further improvement of the present invention, the three-phase capacitor C ab , C bc , C ac The voltage-current relationship is:

[0027]

[0028] Where V dc is the DC input voltage of the inverter, U ab , U bc , U ac They are capacitor C ab , C bc , C ac The voltage value on i a is the phase a current, i c is the c-phase current, L a , L b , L c is the three-phase filter inductance, C ab , C bc , C ac is the three-phase capacitance, i ab 、i bc 、i ac is the current flowing through capacitor C ab , C bc , C ac The current, R a , R b , R c is the equivalent resistance in the three-phase circuit;

[0029] u ab (s),u bc (s) for step input V dc The transfer function of (s) is:

[0030]

[0031]

[0032] Where V dc is the DC input voltage of the inverter, U ab , U bc , U ac They are capacitor C ab , C bc , C ac The voltage value on i a is the phase a current, i c is the c-phase current, L a , L b , L c is the three-phase filter inductance, C ab , C bc , C ac is the three-phase capacitance, i ab 、i bc 、i ac is the current flowing through capacitor C ab , C bc , C ac The current, R a , R b , R c is the equivalent resistance in the three-phase circuit;

[0033] Capacitor voltage U ac (s) for step input V dc The transfer function of (s) is:

[0034]

[0035] As a further improvement of the present invention, the three-phase three-bridge-arm inverter second-order system calculation method structure, the same method is used to conduct the three phases to obtain the parameter C AC , C AB , C BC , Lian Li C AC , C AB , C BC Establish a three-variable equation system about the filter capacitor and solve for C ab , C bc , C ac , the expression is as follows:

[0036]

[0037] In the formula, C ab , C bc , C ac is the capacitance of the three capacitors, C AC , C AB , C BC is a newly defined parameter, which is defined by C ab , C bc , C ac Composition; the specific expression is:

[0038]

[0039] As a further improvement of the present invention, the natural damping frequency, damping ratio, overshoot, peak time and other parameters of the system are obtained by comparing with the standard second-order system, including:

[0040] Corresponding to the standard second-order system The corresponding natural damping frequency ω in the three-phase inverter system is obtained n And the expression of damping ratio ζ:

[0041]

[0042]

[0043] In the formula, ω n is the natural damping frequency, ζ is the damping ratio, C ab , C bc , C ac is the three-phase capacitance, L a , L c They are the filter inductors of phases a and c, R a , R c is the equivalent resistance in the a and c phase circuits.

[0044] Compared with the prior art, the present invention has the following advantages:

[0045] In this method, it is only necessary to turn on the switch tube of the inverter a limited number of times, and obtain the second-order response signal of the system by collecting the capacitor voltage and inductor current information, and then obtain the system's natural damping frequency, damping ratio, overshoot, peak time and other parameters, and use the corresponding parameters to infer the system's equivalent resistance, filter inductance and filter capacitor parameters. Compared with the existing LC filter capacitance test method, the proposed method can realize online monitoring without disassembling the existing device, with a simple calculation process, concise operation method, lower requirements on controller performance, and higher measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0047] Figure 1 Schematic diagram of the proposed inverter equivalent circuit topology, (a) is the equivalent circuit diagram of a single-phase inverter; (b) is the equivalent circuit diagram of a three-phase three-bridge-leg inverter;

[0048] Figure 2 It is the schematic diagram of the inductor current and capacitor voltage of the LC filter;

[0049] Figure 3 It is the equivalent circuit diagram of the three-phase three-bridge-arm inverter with phases a and c turned on;

[0050] Figure 4 It is a schematic diagram of the simulation waveform of the single-phase LC filter inverter;

[0051] Figure 5 It is a schematic diagram of the simulation waveform of the a and b phases of the three-phase three-bridge-arm LC filter inverter. DETAILED DESCRIPTION

[0052] In order to make the purpose and technical solution of the present invention clearer and easier to understand, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0053] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more. In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0054] Based on the limitations of existing methods, the present invention proposes an inverter system parameter monitoring method based on second-order system step response. The inverter mentioned in the present invention includes a single-phase inverter and a three-phase three-leg inverter, including an LC filter and an LCL filter including a grid-connected relay.

[0055] The present invention provides an inverter system parameter monitoring method based on a second-order system step response, comprising:

[0056] By injecting a step response into the inverter system and collecting capacitor voltage and inductor current information, the step response of the filter inductor current and filter capacitor voltage is obtained. By comparing with the standard second-order system, the system's natural damping frequency, damping ratio, overshoot, peak time and other parameters are obtained, and the filter inductance value, filter capacitor value and circuit equivalent resistance of the inverter LC filter are calculated in reverse.

[0057] The inverter system includes a single-phase inverter or a three-phase three-leg inverter.

[0058] In this method, it is only necessary to turn on the switch tube of the inverter a limited number of times, and obtain the second-order response signal of the system by collecting the capacitor voltage and inductor current information, and then obtain the system's natural damping frequency, damping ratio, overshoot, peak time and other parameters, and use the corresponding parameters to reversely deduce the system's equivalent resistance, filter inductance and filter capacitor parameters. Compared with the existing method, the test method proposed by the present invention does not require the disassembly of the device, the calculation process is simple, the controller performance requirements are lower, and the measurement accuracy is higher.

[0059] The technical solution proposed in the present invention is mainly divided into the following parts:

[0060] 1. The inverter system parameter monitoring method proposed in the present invention is aimed at a single-phase inverter and a three-phase three-leg inverter, respectively. Figure 1 As shown in (a) and (b).

[0061] The DC side of the inverter is supplied by a constant DC voltage source V dc It means that the output is through the LC filter, where the filter inductor contains the inductance value L f And the equivalent resistance R f , the filter capacitor includes a capacitance of C f And the equivalent resistance R c ; The capacitors in the three-phase three-leg topology are connected in a triangle, that is, the capacitors include C ab , C bc , C ac , the filter inductor includes L a , L b , L c And the equivalent resistance R a , R b , R c .

[0062] The system conduction loop is analyzed by Kirchhoff's law to obtain the KVL expression of the inductor current and capacitor voltage. The capacitor voltage U is derived by Laplace transformation of the equation. C (s) for step input U dc The transfer function of (s) and the inductor current i L (s) for step input U dc The transfer function of (s) is compared with the standard second-order response to obtain the system's damping ratio, overshoot and peak time, and the inductance, capacitance and equivalent resistance of the inverter LC filter are calculated.

[0063] The standard second-order system can be represented by the natural damping frequency ω n And the damping ratio ζ is expressed as formula (1). Among them, there is the damped natural frequency ω d , peak time t p , overshoot σ% can be expressed as formula (2). Figure 2is the schematic diagram of the inverter inductor current and capacitor voltage, i peak is the peak value of the inductor current, u peak is the peak value of capacitor voltage, and σ% is the overshoot of capacitor voltage.

[0064]

[0065]

[0066] In the single-phase inverter circuit structure, KVL analysis of the loop can be performed to obtain equation (3), which is then transformed into equation (4). After simplification, the capacitor voltage U c (s) for step input U ab The transfer function of (s) and the inductor current i L (s) for step input U ab The transfer function of (s) is shown in formula (5).

[0067]

[0068]

[0069]

[0070] Where U c is the capacitor voltage, U ab is a step input, i L Inductor current, L f is the filter inductor, R f is the equivalent resistance of the filter inductor, C f is the filter capacitor, R c is the equivalent resistance of the filter capacitor; capacitor voltage U c (s) for step input U ab The transfer function of (s) is the same as that of the standard second-order system, so in the single-phase inverter system, the capacitor voltage U c Identify system parameters.

[0071] Therefore, in a single-phase inverter system, the standard second-order system The corresponding natural damping frequency ω n The expression of the damping ratio ζ is as shown in formula (6).

[0072]

[0073] In the formula, ω n is the natural damping frequency, ζ is the damping ratio, L f is the filter inductor, R f is the equivalent resistance of the filter inductor, C f is the filter capacitor, R cis the equivalent resistance of the filter capacitor. The natural damping frequency determines the response speed of the second-order system; the damping ratio determines the oscillation performance of the second-order system. ω represented by the inductance, capacitance and equivalent resistance of the single-phase inverter n ,ζThe system parameters can be inferred from the system response.

[0074] In the three-phase three-leg inverter circuit structure, when the filter capacitor is connected in triangle, the equivalent formula of the triangle connection and star connection capacitor is as follows: Figure 3 As shown, by performing KVL analysis on the loop, we can obtain formula (8).

[0075]

[0076]

[0077] Where V dc is the DC input voltage of the inverter, U ab , U bc , U ac They are capacitor C ab , C bc , C ac The voltage value on i a is the phase a current, i c is the c-phase current, L a , L b , L c is the three-phase filter inductance, C ab , C bc , C ac is the three-phase capacitance, i ab 、i bc 、i ac is the current flowing through capacitor C ab , C bc , C ac The current, R a , R b , R c is the equivalent resistance in the three-phase circuit.

[0078] By performing Laplace transformation on it, we get formula (9), and by combining it, we can get formula (10) ab (s) for step input V dc (s) and i bc (s) for step input V dc The transfer function of (s) is the same as that of (11)u ab (s),u bc (s) for step input V dc (s) transfer function.

[0079]

[0080]

[0081]

[0082] Where V dc is the DC input voltage of the inverter, U ab , U bc , U ac They are capacitor C ab , C bc , C ac The voltage value on i a is the phase a current, i c is the c-phase current, L a , L b , L c is the three-phase filter inductance, C ab , C bc , C ac is the three-phase capacitance, i ab 、i bc 、i ac is the current flowing through capacitor C ab , C bc , C ac The current, R a , R b , R c is the equivalent resistance in the three-phase circuit. It can be seen that the capacitor voltage U ab (s), U bc (s) for step input V dc The transfer function of (s) does not completely match the standard second-order system form, so it is necessary to change U ab (s) and U bc (s) Merger, i.e. U ac (s).

[0083] For u in formula (11) ab (s),u bc (s) for step input V dc By combining the transfer function of (s), we can get the transfer function (12) corresponding to the standard second-order system of (1), that is, the capacitor voltage U ac (s) for step input V dc (s) transfer function.

[0084]

[0085] Where V dc is the DC input voltage of the inverter, U ab , U bc , U ac They are capacitor Cab , C bc , C ac The voltage value on i a is the phase a current, i c is the c-phase current, L a , L b , L c is the three-phase filter inductance, C ab , C bc , C ac is the three-phase capacitance, i ab 、i bc 、i ac is the current flowing through capacitor C ab , C bc , C ac The current, R a , R b , R c is the equivalent resistance in the three-phase circuit. It can be seen that the capacitor voltage U ac (s) for step input V dc The transfer function of (s) is the same as that of the standard second-order system, so in the three-phase inverter system, the capacitor voltage U ac Identify system parameters.

[0086] Therefore, in the three-phase three-leg inverter system, the standard second-order system The corresponding natural damping frequency ω n The expression of the damping ratio ζ is as shown in formula (13).

[0087]

[0088] In the formula, ω n is the natural damping frequency, ζ is the damping ratio, C ab , C bc , C ac is the three-phase capacitance, L a , L c They are the filter inductors of phases a and c, R a , R c is the equivalent resistance in the a and c phase circuits.

[0089] It can be seen that the inverter mentioned in the present invention includes a single-phase inverter and a three-phase three-bridge arm inverter. By injecting a step response signal into the system corresponding to the switch tube of the turned-on inverter, the step response of the filter inductor current and the filter capacitor voltage is sampled, and the waveform is compared with the standard second-order system to obtain the system's natural damping frequency, damping ratio, overshoot, peak time and other parameters, and the filter inductance value, filter capacitor value and circuit equivalent resistance of the inverter LC filter are calculated in reverse. Compared with the existing LC capacitor capacitance test method, the proposed method can realize online monitoring without disassembling the existing device, the calculation process is simple, the operation method is concise, the controller performance requirements are lower, and the measurement accuracy is higher.

[0090] In order to enable those skilled in the art to better understand the present invention, the present invention is further described in detail below. The specific steps are as follows:

[0091] For a single-phase inverter, calculate L f , C f , R c +R f The parameters require the following steps:

[0092] Step 1: Turn on the upper tube of phase a and the lower tube of phase b, and measure the peak value of the inductor current i in the step response system when the DC input voltage U0 is applied. peak , and the capacitor voltage value u at this time c , since the inductor voltage is 0 at this time, the voltage drop of the input and capacitor is generated on the equivalent resistance, so R can be calculated c +R f , as shown in formula (14).

[0093]

[0094] Step 2, measure the maximum value of the capacitor voltage. Since the capacitor voltage amplitude is equal to the DC side input voltage amplitude in steady state, the overshoot σ% of the capacitor voltage can be obtained. At this time, the damping ratio ζ can be inferred, as shown in formula (15).

[0095]

[0096] The time from switch on to capacitor voltage reaching its peak value is called peak time t p , then the damped natural frequency ω can be calculated d , and then the natural damping frequency ω is calculated according to the damping ratio ζ in formula (15): n .

[0097] Step 3: From equations (6), (14), and (15), we can deduce the inductance value L f , and then according to ω n Introducing filter capacitor value C fFinally, the lower tube of phase a and phase b is turned on to discharge the charge on the filter capacitor and restore the initial state.

[0098] In order to verify the above theoretical analysis, the present invention provides a practical design example. The main circuit parameters are as follows: U0 = 100V; L f =150uH; C f =1200uF; R c +R f =0.2Ω.

[0099] Figure 4 The simulation waveform of the step response of the single-phase inverter LC filter is given. It can be seen that when the upper tube of phase a and the lower tube of phase b are turned on at 0.02s, a step input is generated, and the capacitor voltage waveform is in the form of a standard second-order system underdamped oscillation, and the final voltage is stabilized at 100V. The inductor current is also in the form of a standard second-order system underdamped oscillation, and the final current is stabilized at 0A. When the lower tube of phase a and the lower tube of phase b are turned on at 0.05s, the capacitor voltage discharges back to 0V. The simulation results of the step response of the single-phase inverter system are shown in Table 1.

[0100] Table 1: Single-phase inverter system step response simulation results

[0101] parameter Single Phase Inductor peak current 193.7A Capacitor voltage 61.02V Overshoot 0.396 Peak Time 1.391ms

[0102] According to the simulation results, L f , R c +R f , C f The parameters are shown in Table 2. It can be seen that they are basically consistent with the actual parameters of the circuit, with an error of about 1%.

[0103] Table 2: Single-phase inverter system parameter estimation results

[0104] parameter Monitoring value Actual value <![CDATA[Filter inductor L f > 150.98uH 150uH <![CDATA[Equivalent resistance R c +R f > 0.20124Ω 0.2Ω <![CDATA[Filter capacitor C f > 1192.87uF 1200uF

[0105] For a three-phase three-leg inverter, calculate R a , R b , R c , L a , L b , L c , C ab , C bc , C ac The parameters require the following steps:

[0106] Step 1, taking phases a and c as an example, turn on the upper tube of phase a and the lower tube of phase c, and measure the peak value i of the inductor current of phase a in the step response system when the DC side input voltage U0 is peaka (same as phase c), and the capacitor voltage value u at this time ac, since the inductor voltage is 0 at this time, the voltage drop of the input and capacitor is generated on the equivalent resistance, so R can be calculated a +R c , as shown in formula (16).

[0107]

[0108] Step 2, measure the capacitance C ac The maximum value of the voltage. Since the capacitor voltage amplitude is equal to the DC input voltage amplitude in steady state, the capacitor voltage overshoot σ% can be obtained. At this time, the damping ratio ζ can be inferred, as shown in formula (15). The time from the switch turning on to the capacitor voltage reaching the peak value is the peak time t p , at this time, the damped natural frequency ω of the a and c phase circuits can be calculated d , and then the natural damping frequency ω is calculated according to the damping ratio ζ in formula (18): n .

[0109] Step 3: From equations (13), (15), and (16), we can deduce the inductance L a +L c Sensitivity value, then according to ω n Derived capacitance value C AC , where C AC Can be C ab , C bc , C ac The three are expressed as formula (17).

[0110]

[0111] Finally, the lower tube of phase a and phase c is turned on to release the charge on the filter capacitor and restore the initial state.

[0112] Step 4: Same as the measurement method for phases a and c, turn on phases a and b to get R a +R b , L a +L b , C AB ; Turn on phases b and c to get R b +R c , L b +L c , C BC Combine the above parameters to establish two three-variable linear equations about equivalent resistance and filter inductance, and solve R a , R b , R c , L a , L b , L c . The final joint C AC , C AB , CBC Establish a three-variable equation system about the filter capacitor and solve C according to equation (18) ab , C bc , C ac .

[0113]

[0114] In the formula, C ab , C bc , C ac is the capacitance of the three capacitors, C AC , C AB , C BC is a newly defined parameter, which is defined by C ab , C bc , C ac The specific expression is:

[0115]

[0116] In order to verify the above theoretical analysis, the present invention provides a practical design example. The main circuit parameters are as follows: U0 = 80V; L a =L b =L c =2mH, C ab =C bc =C ac =30uF, R a =R b =R c =0.5Ω.

[0117] Figure 5 The simulation waveform of the LC filter step response of the three-phase three-bridge-leg inverter when phase a and phase b are turned on is given. It can be seen that when the upper tube of phase a and the lower tube of phase b are turned on at 0.1s, a step input is generated, and the capacitor C ab The voltage waveform is in the form of a standard second-order system underdamped oscillation, and the final voltage is stabilized at 80V. The inductor current i La 、i Lb It also presents the form of underdamped oscillation of the standard second-order system, and the final current stabilizes at 0A. When the lower tube of phase a and the lower tube of phase b are turned on at 0.2s, the capacitor voltage discharges back to 0V; when the upper tube of phase a and the lower tube of phase c are turned on at 0.3s, a step input is generated, and when the lower tube of phase a and the lower tube of phase c are turned on at 0.4s, the capacitor voltage discharges back to 0V; when the upper tube of phase b and the lower tube of phase c are turned on at 0.5s, a step input is generated, and when the lower tube of phase b and the lower tube of phase c are turned on at 0.6s, the capacitor voltage discharges back to 0V. The simulation results of the step response of the three-phase three-bridge-leg inverter system are shown in Table 3.

[0118] Table 3: Simulation results of step response of three-phase three-leg inverter system

[0119] parameter a, b phase b, c phase a, c phase Inductor peak current 7.8281A 7.8265A 7.8295A Capacitor voltage 72.11V 72.29V 72.29V Overshoot 0.8463 0.8462 0.8465 Peak Time 1.336ms 1.336ms 1.336ms

[0120] According to the simulation results, L a , L b , L c , C ab , C bc , C ac , R a , R b , R c The parameters are shown in Table 4. It can be seen that they are basically consistent with the actual parameters of the circuit, with an error of about 1%.

[0121] Table 4: Three-phase three-leg inverter system parameter estimation results

[0122] parameter Monitoring value Actual value <![CDATA[Phase A inductance L a > 2.02mH 2mH <![CDATA[Inductor L of Phase B b > 2.01mH 2mH <![CDATA[Inductor L of Phase C c > 1.93mH 2mH <![CDATA[A-phase ESRR a > 0.504Ω 0.5Ω <![CDATA[Phase B ESRR b > 0.504Ω 0.5Ω <![CDATA[Phase C ESRR c > 0.481Ω 0.5Ω <![CDATA[AB-phase capacitor C ab > 29.36uF 30uF <![CDATA[AB-phase capacitor C ab > 30.79uF 30uF <![CDATA[AB-phase capacitor C ab > 30.65uF 30uF

[0123] Through actual design examples, it is proved that the LC filter health monitoring method proposed in the present invention is applicable to single-phase inverters, three-phase three-leg inverters and three-phase four-leg inverters, and the calculation results of the system equivalent resistance, filter inductance and filter capacitance values ​​have small errors with the actual parameters.

[0124] The above are only preferred embodiments of the present invention and do not limit the present invention in any way. Any simple modifications, changes and equivalent structural changes made to the above embodiments based on the technical essence of the present invention are still within the protection scope of the technical solution of the present invention.

[0125] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art can still modify or make equivalent substitutions to the specific implementation schemes of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the scope of protection of the claims of the present invention.

[0126] The above content is a further detailed description of the present invention. It cannot be determined that the specific implementation methods of the present invention are limited to these. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, they can also make several simple deductions or substitutions, which should be regarded as belonging to the protection scope of the present invention determined by the submitted claims.

Claims

1. A method for monitoring inverter system parameters based on second-order system step response, characterized in that: include: By injecting a step response into the inverter system and collecting capacitor voltage and inductor current information, the step response of the filter inductor current and filter capacitor voltage is obtained. By comparing with the standard second-order system, the natural damping frequency, damping ratio, overshoot, and peak time parameters of the system are obtained, and the filter inductance value, filter capacitor value, and circuit equivalent resistance of the inverter LC filter are calculated in reverse. The inverter system includes a single-phase inverter or a three-phase three-leg inverter; The single-phase inverter includes a single-phase inverter input DC power supply V dc , filter inductor L f And the equivalent resistance R f , filter capacitor C f And the equivalent resistance R c ; After the single-phase inverter injects a step response, the capacitor voltage and inductor current information are collected, and the loop is subjected to KVL analysis and Laplace transformation to obtain the capacitor voltage U c (s) for step input U ab The transfer function of (s) and the inductor current i L (s) for step input U ab (s) transfer function; The capacitor voltage U c (s) for step input U ab The transfer function of (s) and the inductor current i L (s) for step input U ab The transfer function of (s) is: Where U c is the capacitor voltage, U ab is a step input, i L Inductor current, L f is the filter inductor, R f is the equivalent resistance of the filter inductor, C f is the filter capacitor, R c is the equivalent resistance of the filter capacitor; capacitor voltage U c (s) for step input U ab The transfer function of (s) is in the same form as the standard second-order system; By comparing with the standard second-order system, the natural damping frequency, damping ratio, overshoot, and peak time parameters of the system are obtained, including: Corresponding to the standard second-order system The corresponding natural damping frequency ω in the single-phase inverter system is obtained n And the expression of damping ratio ζ: In the formula, ω n is the natural damping frequency, ζ is the damping ratio, L f is the filter inductor, R f is the equivalent resistance of the filter inductor, C f is the filter capacitor, R c is the equivalent resistance of the filter capacitor.

2. The inverter system parameter monitoring method based on second-order system step response according to claim 1 is characterized in that: The capacitors in the three-phase three-bridge-arm inverter are connected in a triangle, including capacitor C ab , capacitor C bc , capacitor C ac , including filter inductor L a , filter inductor L b , filter inductor L c , equivalent resistance R a , equivalent resistance R b , equivalent resistance R c .

3. The inverter system parameter monitoring method based on second-order system step response according to claim 1, characterized in that: After the three-phase three-leg inverter is injected with a step response, it includes: 1) Inject step response into phases a and c, perform KVL analysis on the loop, and obtain the currents of phases a and c and the three-phase capacitance C ab , C bc , C ac The voltage-current relationship of 2) For phase a and phase c current i a 、i c , three-phase capacitance U ab , U bc , U ac The voltage-current relationship is Laplace transformed to obtain the current flowing through the capacitor C ab The current i ab (s) for step input V dc (s) and flows through capacitor C bc The current i bc (s) for step input V dc (s) transfer function; 3) will u ab (s),u bc (s) for step input V dc The transfer function of (s) is combined to obtain the capacitor voltage U ac (s) for step input V dc (s) transfer function; The same method is used to conduct the three phases and obtain the parameter C AC , C AB , C BC , Lian Li C AC , C AB , C BC Establish a three-variable equation system about the filter capacitor and solve for C ab , C bc , C ac .

4. The inverter system parameter monitoring method based on second-order system step response according to claim 3 is characterized in that: Three-phase capacitor C ab , C bc , C ac The voltage-current relationship is: Where V dc is the DC input voltage of the inverter, U ab , U bc , U ac They are capacitor C ab , C bc , C ac The voltage value on i a is the phase a current, i c is the c-phase current, L a , L b , L c is the three-phase filter inductance, C ab , C bc , C ac is the three-phase capacitance, i ab 、i bc 、i ac is the current flowing through capacitor C ab , C bc , C ac The current, R a , R b , R c is the equivalent resistance in the three-phase circuit; u ab (s),u bc (s) for step input V dc The transfer function of (s) is: Where V dc is the DC input voltage of the inverter, U ab , U bc , U ac They are capacitor C ab , C bc , C ac The voltage value on i a is the phase a current, i c is the c-phase current, L a , L b , L c is the three-phase filter inductance, C ab , C bc , C ac is the three-phase capacitance, i ab 、i bc 、i ac is the current flowing through capacitor C ab , C bc , C ac The current, R a , R b , R c is the equivalent resistance in the three-phase circuit; Capacitor voltage U ac (s) for step input V dc The transfer function of (s) is:

5. The inverter system parameter monitoring method based on second-order system step response according to claim 3 is characterized in that: The structure of the three-phase three-bridge-arm inverter second-order system calculation method is characterized in that the same method is used to conduct the three phases and obtain the parameter C AC , C AB , C BC , Lian Li C AC , C AB , C BC Establish a three-variable equation system about the filter capacitor and solve for C ab , C bc , C ac , the expression is as follows: In the formula, C ab , C bc , C ac is the capacitance of the three capacitors, C AC , C AB , C BC is a newly defined parameter, which is defined by C ab , C bc , C ac Composition; the specific expression is:

6. The inverter system parameter monitoring method based on second-order system step response according to claim 3, characterized in that: By comparing with the standard second-order system, the system's natural damping frequency, damping ratio, overshoot, peak time and other parameters are obtained, including: Corresponding to the standard second-order system The corresponding natural damping frequency ω in the three-phase inverter system is obtained n And the expression of damping ratio ζ: In the formula, ω n is the natural damping frequency, ζ is the damping ratio, C ab , C bc , C ac is the three-phase capacitance, L a , L c They are the filter inductors of phases a and c, R a , R c is the equivalent resistance in the a and c phase circuits.

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