Parameter identification method, device and system for high-frequency cascade transformer

Abstract

The application discloses a kind of high-frequency cascade transformer parameter identification method, device and system, belong to transformer parameter identification technical field;Using CTMI no-load test transient waveform of transformer identification obtains the excitation resistance and excitation inductance of transformer;At the same time, based on the amplitude-frequency characteristic of CTMI load test, the effective value of the fundamental component of the CTMI output voltage at the to-be-identified operating frequency is calculated, and then the difference loss between the effective value of the fundamental component of the CTMI output voltage at the to-be-identified operating frequency obtained by the CTMI load test is minimized, to identify the primary winding resistance, primary winding leakage inductance, secondary winding resistance and secondary winding leakage inductance of the transformer at the to-be-identified operating frequency.The application is suitable for square wave condition, does not depend on the type of transformer, and can accurately and effectively realize the parameter identification of high-frequency cascade transformer.

Description

Technical Field

[0001] This invention belongs to the field of transformer parameter identification technology, and more specifically, relates to a method, device and system for parameter identification of high-frequency cascaded transformers. Background Technology

[0002] As an improved version of the cascaded multilevel inverter, the Cascaded Transformer Multilevel Inverter (CTMI) uses cascaded transformers connected in series with H-bridge modules to achieve multilevel output. While retaining advantages such as low distortion, low voltage stress, and high scalability, it requires only a single DC source to expand voltage levels, simplifying the system and reducing the risk of failure. The cascaded transformer is a key component of the CTMI. Traditional power frequency CTMIs treat the transformer as an ideal component, considering only the transformer turns ratio during operation. However, in applications such as photovoltaic inverters, motor drives, and long-wave radio transmitters, CTMIs employ high-frequency cascaded transformers wound with Litz wire and nanocrystalline magnetic cores, capable of operating at a 30kHz fundamental frequency. Due to the higher frequency, the non-ideal parameters of the cascaded transformer generate significant impedance, affecting the CTMI's output voltage under different frequencies and loads. An accurate transformer model is crucial for predicting the behavior of the CTMI and improving the integration between the transformer and other components. Furthermore, the transformer's equivalent parameters can be used for protection circuit design, winding temperature monitoring, and transformer fault diagnosis. Therefore, the identification of equivalent parameters of high-frequency cascaded transformers in CTMI is crucial.

[0003] Existing transformer parameter identification methods primarily target single transformers under sinusoidal excitation. When the primary voltage is known, active power, primary current, secondary voltage, and RMS secondary current can be calculated using the transformer equivalent circuit and Kirchhoff's laws. Then, optimization algorithms are used to find the transformer equivalent parameters that minimize the error between the calculated results and measurement data under different loads, thus achieving online identification. However, cascaded transformers in CTMI are excited by high-frequency square wave voltage generated by the H-bridge submodule, which typically contains DC bias and higher harmonics. These voltage distortions alter the shape of the core hysteresis loop and the spatial magnetic field distribution, thereby changing the transformer equivalent parameters. This makes the parameter identification results under sinusoidal excitation unsuitable for square wave conditions. Furthermore, since inductors exhibit different reactances at different frequencies, magnetization reactance must consider both the fundamental frequency and harmonic components. Using only the RMS values ​​of power, voltage, and current cannot accurately calculate the inductor parameters under square wave excitation. Although existing optimization algorithms can extract transformer parameters from time-domain waveforms with high accuracy, these methods are only applicable to specific types of transformers and lack versatility. Overall, there is a lack of accurate and effective parameter identification methods for high-frequency cascaded transformers in CTMI. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a parameter identification method and system for high-frequency cascaded transformers, which solves the technical problem that the prior art cannot accurately and effectively identify the parameters of high-frequency cascaded transformers in CTMI.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a parameter identification method for a high-frequency cascaded transformer; the high-frequency cascaded transformer is a high-frequency cascaded transformer in a cascaded transformer multilevel inverter (CTMI); wherein, the parameters of each transformer in the high-frequency cascaded transformer are the same;

[0006] The above parameter identification methods include:

[0007] Obtain the input voltage signal u of any transformer A in the high-frequency cascaded transformers at the i-th operating frequency to be identified when CTMI is in an unloaded state. s0 and input current signal i s0 This allows us to identify the excitation resistance R of transformer A at the i-th operating frequency to be identified. m (i) and excitation inductance L m (i); where the input voltage signal u s0 and input current signal i s0 By disconnecting the CTMI from the load and applying the rated operating voltage V to the DC bus of the CTMI DC The results were obtained after measurement; where i = 1, 2, ..., M; M is the number of frequency points of the operating frequency to be identified;

[0008] Connect the CTMI to any resistive-inductive load and apply the rated operating voltage V to the DC bus of the CTMI. DC The effective value U of the fundamental frequency component of the CTMI output voltage is measured at the i-th operating frequency to be identified. g_meas (i) and the load resistance R of CTMI g (i) and load inductance L g (i);

[0009] Calculate the effective value of the fundamental frequency component of the CTMI output voltage at the i-th operating frequency to be identified.

[0010] By minimizing Identify the primary winding resistance R1(i), primary winding leakage inductance L1(i), secondary winding resistance R2(i), and secondary winding leakage inductance L2(i) of any transformer in the cascaded transformer at the i-th operating frequency to be identified.

[0011] Wherein, loss(U g_est (i),U g_meas (i)) represents U g_est (i) and corresponding Ug_meas The difference loss between (i); G(ω(i)) is the amplitude-frequency response value of CTMI at the i-th operating frequency ω(i) to be identified, and its expression is the same as R m (i), L m (i), R1(i), L1(i), R2(i) and L2(i) are related; U mul (i) is the effective value of the fundamental component of the equivalent cascade voltage of the H-bridge submodule in CTMI at the i-th operating frequency to be identified; the equivalent cascade voltage of the H-bridge submodule is the sum of the output voltages of all H-bridge submodules in CTMI.

[0012] More preferably, the amplitude-frequency response value G(ω(i)) of the CTMI at the i-th operating frequency to be identified is:

[0013]

[0014] in,

[0015]

[0016] Among them, X g (i)=ω(i)L g (i); ω(i) is the i-th operating frequency to be identified; N is the number of transformers in the high-frequency cascaded transformer; R′ 2_eq (i)=k 2 R 2_eq (i); R′ g (i)=k 2 R g (i); X′ 2_eq (i)=k 2 ω(i)L 2_eq (i); X′ g (i)=k 2 ω(i)L g (i); k is the turns ratio of the high-frequency cascaded transformer; X m (i)=ω(i)L m (i); X1(i) = ω(i)L1(i).

[0017] More preferably, the fundamental component RMS value U of the equivalent cascade voltage of the H-bridge submodule in the CTMI at the i-th operating frequency to be identified is... mul (i) is:

[0018]

[0019] Where N is the number of transformers in the high-frequency cascaded transformers; and Let be the Fourier expansion coefficient of the fundamental frequency component of the output voltage of the j-th H-bridge submodule in CTMI at the i-th operating frequency to be identified.

[0020] More preferably, the fundamental component RMS value U of the equivalent cascade voltage of the H-bridge submodule in the CTMI at the i-th operating frequency to be identified is... mul (i) is:

[0021] U mul (i)=U mul_s (i)

[0022]

[0023] Where N is the number of transformers in the high-frequency cascaded transformers; and The Fourier expansion coefficients of the fundamental frequency component of the output voltage of the j-th H-bridge submodule in the CTMI at the i-th operating frequency to be identified, after dead-zone compensation, are as follows:

[0024]

[0025] and The Fourier expansion coefficients of the fundamental frequency component of the output voltage of the j-th H-bridge submodule in CTMI; and The Fourier expansion coefficients of the fundamental frequency component of the dead zone error voltage of the j-th H-bridge submodule in CTMI at the i-th operating frequency to be identified;

[0026] when hour,

[0027] when hour,

[0028]

[0029] when hour,

[0030]

[0031] To connect the CTMI to any resistive-inductive load and apply the rated operating voltage V to the DC bus of the CTMI. DC Then, the phase angle of the primary current of any transformer in the high-frequency cascaded transformers is measured at the i-th operating frequency to be identified; θ s_j (i) represents the turn-on angle of the j-th H-bridge submodule in the CTMI at the i-th operating frequency to be identified; δ d (i) represents the angle corresponding to the dead time at the i-th operating frequency to be identified; δon_j (i) represents the angle corresponding to the switching delay time of the j-th H-bridge submodule at the i-th operating frequency to be identified; δ off_j (i) represents the angle corresponding to the turn-off delay time of the j-th H-bridge submodule in CTMI at the i-th operating frequency to be identified.

[0032] More preferably, the fundamental component RMS value U of the equivalent cascade voltage of the H-bridge submodule in the CTMI at the i-th operating frequency to be identified is... mul (i) is:

[0033]

[0034] ΔV=N·2R on_j (i)·I s (i)

[0035]

[0036] Where N is the number of transformers in the high-frequency cascaded transformers; R on_j (i) represents the on-state voltage drop of the j-th H-bridge submodule in the CTMI at the i-th operating frequency to be identified; and I s (i) Connect the CTMI to any resistive-inductive load and apply the rated operating voltage V to the DC bus of the CTMI. DC Then, the effective values ​​of the primary current phase angle and the fundamental frequency component of the primary current of any transformer in the high-frequency cascaded transformers are measured at the i-th operating frequency to be identified. and The Fourier expansion coefficients of the fundamental frequency component of the output voltage of the j-th H-bridge submodule in the CTMI at the i-th operating frequency to be identified, after dead-zone compensation, are as follows:

[0037]

[0038] and The Fourier expansion coefficients of the fundamental frequency component of the output voltage of the j-th H-bridge submodule in CTMI; and The Fourier expansion coefficients of the fundamental frequency component of the dead zone error voltage of the j-th H-bridge submodule in CTMI at the i-th operating frequency to be identified;

[0039] when hour,

[0040] when hour,

[0041]

[0042] when hour,

[0043]

[0044] θ s_j (i) represents the turn-on angle of the j-th H-bridge submodule in the CTMI at the i-th operating frequency to be identified; δ d (i) represents the angle corresponding to the dead time at the i-th operating frequency to be identified; δ on_j (i) represents the angle corresponding to the switching delay time of the j-th H-bridge submodule at the i-th operating frequency to be identified; δ off_j (i) represents the angle corresponding to the turn-off delay time of the j-th H-bridge submodule in CTMI at the i-th operating frequency to be identified.

[0045] More preferably, and They are respectively:

[0046]

[0047] θ e_j (i) and θ s_j (i) represent the turn-off angle and turn-on angle of the j-th H-bridge submodule in the CTMI at the i-th operating frequency to be identified, respectively; δ off_j (i) represents the angle corresponding to the turn-off delay time of the j-th H-bridge submodule in CTMI at the i-th operating frequency to be identified.

[0048] More preferably, the above is achieved by minimizing Identify the primary winding resistance R1(i), primary winding leakage inductance L1(i), secondary winding resistance R2(i), and secondary winding leakage inductance L2(i) of any transformer in the cascaded transformer at the i-th operating frequency to be identified, including:

[0049] Build to minimize Let R1(i) and R2(i) be the objective function for the objective. and This simplifies the objective function, and then the primary winding resistance R1(i), primary winding leakage inductance L1(i), secondary winding resistance R2(i), and secondary winding leakage inductance L2(i) of any transformer in the cascaded transformer at the i-th identified operating frequency are obtained.

[0050] in, ω(i) is the i-th operating frequency to be identified.

[0051] More preferably,

[0052] More preferably, the excitation resistance R of transformer A at the i-th operating frequency to be identified is... m (i) is:

[0053]

[0054] Where T is the voltage signal u s0 The period; u s0 (t) represents the voltage signal u s0 The voltage value at time t; i s0 (t) represents the current signal i s0 The current value at time t.

[0055] More preferably, the magnetizing inductance L of transformer A at the i-th operating frequency to be identified m (i) is:

[0056]

[0057] Where Δt(i) is the voltage signal u s0 The amplitude is equal to V DC Duration of time; Δi s (i) represents the current signal i s0 The change during the period Δt.

[0058] Secondly, the present invention provides a parameter identification device for a high-frequency cascaded transformer; the high-frequency cascaded transformer is a high-frequency cascaded transformer in a cascaded transformer multilevel inverter (CTMI); wherein, the parameters of each transformer in the high-frequency cascaded transformer are the same.

[0059] The above parameter identification device includes:

[0060] The first identification module is used to acquire the input voltage signal u of any transformer A in the high-frequency cascaded transformers at the i-th operating frequency to be identified when the CTMI is in an unloaded state. s0 and input current signal i s0 This allows us to identify the excitation resistance R of transformer A at the i-th operating frequency to be identified. m (i) and excitation inductance L m (i); where the input voltage signal u s0 and input current signal i s0 By disconnecting the CTMI from the load and applying the rated operating voltage V to the DC bus of the CTMI DC The results were obtained after measurement; where i = 1, 2, ..., M; M is the number of frequency points of the operating frequency to be identified;

[0061] The first parameter measurement module is used to connect the CTMI to any resistive-inductive load and apply the rated operating voltage V to the DC bus of the CTMI. DC The effective value U of the fundamental frequency component of the CTMI output voltage is measured at the i-th operating frequency to be identified. g_meas (i) and the load resistance R of CTMI g (i) and load inductance L g (i);

[0062] The RMS value calculation module is used to calculate the RMS value of the fundamental frequency component of the CTMI output voltage at the i-th operating frequency to be identified.

[0063] The second identification module is used to minimize... Identify the primary winding resistance R1(i), primary winding leakage inductance L1(i), secondary winding resistance R2(i), and secondary winding leakage inductance L2(i) of any transformer in the cascaded transformer at the i-th operating frequency to be identified.

[0064] Among them, loss(U g_est (i),U g_meas (i)) represents U g_est (i) and corresponding U g_meas The difference loss between (i); G(ω(i)) is the amplitude-frequency response value of CTMI at the i-th operating frequency ω(i) to be identified, and its expression is the same as R m (i), L m (i), R1(i), L1(i), R2(i) and L2(i) are related; U mul (i) is the effective value of the fundamental component of the equivalent cascade voltage of the H-bridge submodule in CTMI at the i-th operating frequency to be identified; the equivalent cascade voltage of the H-bridge submodule is the sum of the output voltages of all H-bridge submodules in CTMI.

[0065] More preferably, the parameter identification device further includes: a second parameter measurement module, used to disconnect the CTMI from the load and apply a rated operating voltage V to the DC bus of the CTMI. DC And measure the input voltage signal u of any transformer A in the high-frequency cascaded transformer at the i-th operating frequency to be identified. s and input current signal i s .

[0066] Thirdly, the present invention provides a cascaded transformer multilevel inverter system, comprising: a cascaded transformer multilevel inverter (CTMI) and a parameter identification module;

[0067] The parameter identification module is used to execute the parameter identification method provided in the first aspect of the present invention to identify the parameters of the high-frequency cascaded transformer in CTMI.

[0068] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0069] 1. This invention provides a parameter identification method for high-frequency cascaded transformers. It utilizes the transient waveform of the transformer during CTMI no-load testing to identify the transformer's magnetizing resistance and magnetizing inductance. Simultaneously, considering that the output voltage of the high-frequency CTMI varies with frequency due to the cascaded transformer parameters, this invention, based on the amplitude-frequency characteristics of the CTMI under load testing, calculates the effective value of the fundamental frequency component of the CTMI output voltage at the operating frequency to be identified. By minimizing the difference loss between this value and the effective value of the fundamental frequency component of the CTMI output voltage at the operating frequency to be identified obtained from the CTMI under load testing, the primary winding resistance, primary winding leakage inductance, secondary winding resistance, and secondary winding leakage inductance of the transformer at the operating frequency to be identified are identified. This invention utilizes the square wave excitation response of the CTMI no-load test and the amplitude-frequency characteristics of the load test, is applicable to square wave conditions, is independent of the transformer type, and can accurately and effectively identify the parameters of high-frequency cascaded transformers. It overcomes the performance limitations of traditional methods in a wide frequency range and solves the inductance identification distortion problem of traditional methods under non-sinusoidal excitation.

[0070] 2. Furthermore, the parameter identification method for high-frequency cascaded transformers provided by this invention, when obtaining the amplitude-frequency characteristics of CTMI, considers that if the transformers in CTMI are directly equivalently constructed using a T-type equivalent circuit, the constructed CTMI equivalent circuit would be a complex model containing 2N input ports and two output ports due to the coupling effect of multiple transformers, making subsequent calculations quite complex. To improve computational efficiency, this invention uses cascaded transformers of a T-type equivalent circuit for decoupling equivalence to construct the CTMI equivalent circuit, thereby deriving the amplitude-frequency characteristic model of CTMI, which has high computational accuracy and low complexity.

[0071] 3. Furthermore, the parameter identification method for high-frequency cascaded transformers provided by this invention takes into account the influence of the dead zone effect. For any transformer's input voltage, its actual input voltage is the superposition of the ideal voltage and the dead zone error voltage. Based on this, the effective value of the fundamental component of the equivalent cascaded voltage of the H-bridge submodule in CTMI at the operating frequency to be identified is calculated, which further improves the accuracy of identification.

[0072] 4. Furthermore, the parameter identification method for high-frequency cascaded transformers provided by this invention takes into account the on-resistance R of the switching transistors in the H-bridge submodule. onWhen current flows through the switching transistor, the resulting on-state voltage drop ΔV changes the effective value of the fundamental component of the equivalent cascade voltage of the H-bridge submodule in the CTMI at the operating frequency to be identified. Therefore, this invention further performs correction calculations. Based on the phasor diagram between relevant quantities and according to trigonometric function relationships, the effective value U of the fundamental component of the equivalent cascade voltage of the H-bridge submodule in the CTMI at the i-th operating frequency to be identified is... mul (i) Corrected to This further improves the accuracy of identification.

[0073] 5. Furthermore, the parameter identification method for high-frequency cascaded transformers provided by this invention establishes a skin effect correction model under high-frequency operating conditions, and expresses R1(i) and R2(i) in the objective function as: and This simplifies the objective function and further improves the solution efficiency. Attached Figure Description

[0074] Figure 1 This is a schematic diagram of the topology of a cascaded transformer multilevel inverter (CTMI) provided in an embodiment of the present invention.

[0075] Figure 2 A schematic diagram illustrating the acquisition of multilevel inverter switching angles using SHEPWM technology, provided in an embodiment of the present invention;

[0076] Figure 3 A T-type equivalent circuit diagram of a single transformer provided in an embodiment of the present invention;

[0077] Figure 4 This is a schematic diagram of the equivalent CTMI circuit after decoupling of the cascaded transformer provided in an embodiment of the present invention;

[0078] Figure 5 The following is a summary of the dead-zone effect of the sub-modules in the actual operation of the high-frequency cascaded multilevel inverter provided in the embodiments of the present invention; wherein, (a) is the case where the current crosses zero after the dead time ends, (b) is the case where the current crosses zero during the dead time, and (c) is the case where the current crosses zero before the dead time begins.

[0079] Figure 6 A phasor relationship diagram of the actual cascaded voltage on the primary side of the transformer, the on-state voltage drop of the switching devices, the ideal cascaded voltage on the primary side of the transformer, and the primary side current of the transformer provided for embodiments of the present invention;

[0080] Figure 7 The square wave excitation response waveform of a single transformer during no-load testing is provided in an embodiment of the present invention.

[0081] Figure 8The comparison results of transformer excitation parameters obtained by different identification methods are provided in the embodiments of the present invention; wherein, (a) is the identification result of excitation resistance, and (b) is the identification result of excitation inductance;

[0082] Figure 9 A frequency response curve of a high-frequency cascaded multilevel inverter provided in an embodiment of the present invention;

[0083] Figure 10 This is a schematic diagram of the convergence curve of the objective function when using the particle swarm optimization algorithm, provided in an embodiment of the present invention.

[0084] Figure 11 The present invention provides a comparison of transformer winding parameters obtained by different identification methods in an embodiment of the invention; wherein, (a) is the winding resistance identification result and (b) is the winding leakage inductance identification result. Detailed Implementation

[0085] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0086] To achieve the above objectives, in a first aspect, the present invention provides a parameter identification method for a high-frequency cascaded transformer; the high-frequency cascaded transformer is a high-frequency cascaded transformer in a cascaded transformer multilevel inverter (CTMI); wherein, the parameters of each transformer in the high-frequency cascaded transformer are the same, including: the excitation resistance, excitation inductance, primary winding resistance, primary winding leakage inductance, secondary winding resistance, and secondary winding leakage inductance of each transformer.

[0087] The above parameter identification methods include:

[0088] Obtain the input voltage signal u of any transformer A in the high-frequency cascaded transformers at the i-th operating frequency to be identified when CTMI is in an unloaded state. s0 and input current signal i s0 Based on the input voltage signal u s0 and input current signal i s0 The excitation resistance R of transformer A at the i-th operating frequency to be identified is obtained. m (i) and excitation inductance L m (i); where the input voltage signal u s0 and input current signal i s0 By disconnecting the CTMI from the load and applying the rated operating voltage V to the DC bus of the CTMI DCThe results were obtained after measurement; where i = 1, 2, ..., M; M is the number of frequency points of the operating frequency to be identified;

[0089] Connect the CTMI to any resistive-inductive load and apply the rated operating voltage V to the DC bus of the CTMI. DC The effective value U of the fundamental frequency component of the CTMI output voltage is measured at the i-th operating frequency to be identified. g_meas (i) and the load resistance R of CTMI g (i) and load inductance L g (i);

[0090] Calculate the effective value of the fundamental frequency component of the CTMI output voltage at the i-th operating frequency to be identified.

[0091] By minimizing Identify the primary winding resistance R1(i), primary winding leakage inductance L1(i), secondary winding resistance R2(i), and secondary winding leakage inductance L2(i) of any transformer in the cascaded transformer at the i-th operating frequency to be identified.

[0092] Wherein, loss(U g_est (i),U g_meas (i)) represents U g_est (i) and corresponding U g_meas The difference loss between (i); G(ω(i)) is the amplitude-frequency response value of CTMI at the i-th operating frequency ω(i) to be identified, and its expression is the same as R m (i), L m (i), R1(i), L1(i), R2(i) and L2(i) are related; U mul (i) is the effective value of the fundamental component of the equivalent cascade voltage of the H-bridge submodule in CTMI at the i-th operating frequency to be identified; the equivalent cascade voltage of the H-bridge submodule is the sum of the output voltages of all H-bridge submodules in CTMI.

[0093] It should be noted that the amplitude-frequency characteristic model of CTMI is derived from the equivalent circuit of CTMI; there are various ways to obtain the equivalent circuit of CTMI, which are not limited here. Preferably, in one optional implementation, a cascaded transformer of a T-type equivalent circuit is used for decoupling equivalence to construct the equivalent circuit of CTMI, thereby deriving the amplitude-frequency characteristic model of CTMI. In this case, the amplitude-frequency characteristic value G(ω(i)) of CTMI at the i-th operating frequency to be identified is:

[0094]

[0095] in,

[0096]

[0097]

[0098] Among them, X g (i)=ω(i)L g (i); ω(i) is the i-th operating frequency to be identified; N is the number of transformers in the high-frequency cascaded transformer; R′ 2_eq (i)=k 2 R 2_eq (i); R′ g (i)=k 2 R g (i); X′ 2_eq (i)=k 2 ω(i)L 2_eq (i); X′ g (i)=k 2 ω(i)L g (i); k is the turns ratio of the high-frequency cascaded transformer; X m (i)=ω(i)L m (i); X1(i) = ω(i)L1(i).

[0099] It should be noted that the fundamental component RMS value U of the equivalent cascade voltage of the H-bridge submodule in CTMI at the i-th operating frequency to be identified mul There are several ways to calculate (i):

[0100] In one alternative implementation, the fundamental component RMS value U of the equivalent cascade voltage of the H-bridge submodule in the CTMI at the i-th operating frequency to be identified is... mul (i) is:

[0101]

[0102] Where N is the number of transformers in the high-frequency cascaded transformers; and Let be the Fourier expansion coefficient of the fundamental frequency component of the output voltage of the j-th H-bridge submodule in CTMI at the i-th operating frequency to be identified.

[0103] In an optional second implementation, the effective value U of the fundamental component of the equivalent cascade voltage of the H-bridge submodule in the CTMI at the i-th operating frequency to be identified is... mul (i) is:

[0104] U mul (i)=U mul_s (i)

[0105]

[0106] Where N is the number of transformers in the high-frequency cascaded transformers; and The Fourier expansion coefficients of the fundamental frequency component of the output voltage of the j-th H-bridge submodule in the CTMI at the i-th operating frequency to be identified, after dead-zone compensation, are as follows:

[0107]

[0108] and The Fourier expansion coefficients of the fundamental frequency component of the output voltage of the j-th H-bridge submodule in CTMI; and The Fourier expansion coefficients of the fundamental frequency component of the dead zone error voltage of the j-th H-bridge submodule in CTMI at the i-th operating frequency to be identified;

[0109] when hour,

[0110] when hour,

[0111]

[0112] when hour,

[0113]

[0114] To connect the CTMI to any resistive-inductive load and apply the rated operating voltage V to the DC bus of the CTMI. DC Then, the phase angle of the primary current of any transformer in the high-frequency cascaded transformers is measured at the i-th operating frequency to be identified; θ s_j (i) represents the turn-on angle of the j-th H-bridge submodule in the CTMI at the i-th operating frequency to be identified; δ d (i) represents the angle corresponding to the dead time at the i-th operating frequency to be identified; δ on_j (i) represents the angle corresponding to the switching delay time of the j-th H-bridge submodule at the i-th operating frequency to be identified; δ off_j (i) represents the angle corresponding to the turn-off delay time of the j-th H-bridge submodule in CTMI at the i-th operating frequency to be identified.

[0115] In one optional implementation method three, the effective value of the fundamental component U of the equivalent cascade voltage of the H-bridge submodule in the CTMI at the i-th operating frequency to be identified is... mul (i) is:

[0116]

[0117] ΔV=N·2R on_j (i)·I s (i)

[0118]

[0119] Where N is the number of transformers in the high-frequency cascaded transformers; R on_j (i) represents the on-state voltage drop of the j-th H-bridge submodule in the CTMI at the i-th operating frequency to be identified; and I s (i) Connect the CTMI to any resistive-inductive load and apply the rated operating voltage V to the DC bus of the CTMI. DC Then, the effective values ​​of the primary current phase angle and the fundamental frequency component of the primary current of any transformer in the high-frequency cascaded transformers are measured at the i-th operating frequency to be identified. and The Fourier expansion coefficients of the fundamental frequency component of the output voltage of the j-th H-bridge submodule in CTMI at the i-th operating frequency to be identified are the coefficients after dead-zone compensation, as detailed in the optional implementation method two above.

[0120] In one alternative implementation, and They are respectively:

[0121]

[0122] θ e_j (i) and θ s_j (i) represent the turn-off angle and turn-on angle of the j-th H-bridge submodule in the CTMI at the i-th operating frequency to be identified, respectively; δ off_j (i) represents the angle corresponding to the turn-off delay time of the j-th H-bridge submodule in CTMI at the i-th operating frequency to be identified.

[0123] In one alternative implementation, the above is achieved by minimizing... Identify the primary winding resistance R1(i), primary winding leakage inductance L1(i), secondary winding resistance R2(i), and secondary winding leakage inductance L2(i) of any transformer in the cascaded transformer at the i-th operating frequency to be identified, including:

[0124] Build to minimize Let R1(i) and R2(i) be the objective function for the objective. and This simplifies the objective function, and then the primary winding resistance R1(i), primary winding leakage inductance L1(i), secondary winding resistance R2(i), and secondary winding leakage inductance L2(i) of any transformer in the cascaded transformer at the i-th identified operating frequency are obtained.

[0125] in, ω(i) is the i-th operating frequency to be identified.

[0126] It should be noted that minimizing There are various optimization algorithms available, including existing technologies such as genetic algorithms, particle swarm optimization, ant colony optimization, and immune algorithms; no specific limitation is made here. Preferably, in one optional implementation, the particle swarm optimization algorithm, which is simple, easy to implement, highly accurate, and has a fast convergence speed, is selected for the identification calculation.

[0127] It should be noted that U g_est (i) and corresponding U g_meas (i) difference loss (U g_est (i),U g_meas There are various ways to calculate (i), such as using squared error, absolute error, relative error, etc., which are not limited here; preferably, in an optional embodiment,

[0128] It should be noted that the excitation resistance R of transformer A at the i-th operating frequency to be identified m There are various identification methods for (i), such as three-dimensional finite element analysis, frequency response method, and recursive least squares method, which are not limited here. Preferably, in one optional implementation, the excitation resistance R of transformer A at the i-th operating frequency to be identified is... m (i) is:

[0129]

[0130] Where T is the voltage signal u s0 The period; u s0 (t) represents the voltage signal u s0 The voltage value at time t; i s0 (t) represents the current signal i s0 The current value at time t.

[0131] It should be noted that the magnetizing inductance L of transformer A at the i-th operating frequency to be identified m (i) There are various identification methods, such as resonance waveform analysis, which are not limited here. Preferably, in one optional implementation, the magnetizing inductance L of transformer A at the i-th operating frequency to be identified is... m(i) is:

[0132]

[0133] Where Δt(i) is the voltage signal u s0 The amplitude is equal to V DC Duration of time; Δi s (i) represents the current signal i s0 The change during the period Δt. This method is simple and accurate to calculate.

[0134] The above-mentioned preferred excitation resistor R m (i) and excitation inductance L m (i) The identification method of the present invention enables accurate identification of the equivalent parameters of high-frequency cascaded transformers in CTMI without the need for additional excitation equipment and without separating the transformer from the system.

[0135] To further illustrate the parameter identification method for high-frequency cascaded transformers provided by this invention, the following detailed description is provided in conjunction with specific embodiments:

[0136] Figure 1 This is a schematic diagram of the topology of a Cascaded Transformer Multilevel Inverter (CTMI), which adopts the topology of a single-phase cascaded H-bridge multilevel inverter with high-frequency transformers. Unlike traditional cascaded H-bridge converters, the H-bridge inverter submodule in CTMI consists of N cascaded high-frequency transformers with independent magnetic cores. Figure 1 In the middle, T1~T N These represent N transformers. The inputs of all submodules are connected in parallel to the same DC source, and the outputs are connected to the primary side of the transformers. The secondary sides of the transformers are connected in series. This topology using cascaded transformers avoids the requirement of multiple independent DC sources and is suitable for multilevel converters with a large number of submodules. Each inverter submodule is an H-bridge structure, with each bridge arm consisting of upper and lower switches, both of which are SiC MOSFETs. Based on the current direction, the bridge arm from which current flows is defined as the left bridge arm, and the bridge arm from which current flows is defined as the right bridge arm. The upper and lower switches of the left bridge arm, and the upper and lower switches of the right bridge arm, are respectively denoted as S1, S2, S3, and S4. Each submodule can generate -V DC 0 and +V DC Three levels, of which V DC This is the DC bus voltage. Since the fundamental frequency is as high as 30kHz, to suppress voltage harmonics and reduce switching losses, this multilevel converter employs... Figure 2 The fundamental frequency shown is equal to 1 / 4 of the switching frequency in a periodic symmetrical selective harmonic elimination pulse width modulation (SHEPWM). Where θ j(j=1,2,…,N) is the switching angle, satisfying 0<θ1<…<θ N <π / 2. A cascaded multilevel converter with N sub-modules can generate 2N+1 levels, theoretically eliminating all harmonics below the 2N-1th order.

[0137] Due to the high fundamental frequency of up to 30kHz, non-ideal parameters in cascaded transformers can severely affect the output characteristics of CMTI. To achieve high-precision control of CMTI, accurate transformer parameters are required. The transformer model is fundamental to parameter identification, and the most widely used transformer model is... Figure 3 The T-type equivalent circuit is shown. In this circuit, all transformers in the high-frequency cascaded transformer have the same parameters; R m L is the excitation resistance of the transformer. m R1 and R2 are the magnetizing inductance of the transformer, respectively; R1 and R2 are the resistances of the primary and secondary windings of the transformer, respectively; and L1 and L2 are the leakage inductances of the primary and secondary windings of the transformer, respectively. Due to the coupling effect of multiple transformers, directly applying this equivalent circuit would result in a complex model with 2N input ports and two output ports, which is difficult to apply in practice. Therefore, the cascaded transformers using the T-type equivalent circuit can be decoupled and equivalently represented, resulting in... Figure 4 The CTMI equivalent circuit is shown. Specifically, for any single transformer in a cascaded transformer system, its secondary side is connected to N-1 other transformers in addition to the transmission cables and load. To avoid affecting the harmonic characteristics of the transformers, the relationship between the parasitic parameters in the transformers and the load must remain unchanged before and after the equivalence. When the output level of the H-bridge submodule connected to the front stage of the transformer is 0, the primary side of the transformer forms a closed loop through the submodule power devices; when the output level of the H-bridge submodule connected to the front stage of the transformer is ±V... DC At this time, the primary side of the transformer forms a closed loop through the DC bus capacitor of the submodule. Since the magnetizing inductance of a single transformer is typically several kΩ, while the equivalent resistance of the power devices and bus capacitors is several mΩ, the voltage drop of the power devices and bus capacitors can be ignored. In the CTMI equivalent circuit, u mul R is the direct summation of the output voltages of all H-bridge submodules on the primary side of the transformer. g and L g These are the load resistance and inductance, R respectively. 2_eq and L 2_eq The equivalent winding resistance and leakage inductance on the secondary side of the transformer are defined as:

[0138]

[0139] Using the decoupling method described above, the multi-input cascaded transformer is equivalent to a two-port network. Because its circuit characteristics are similar to the T-type equivalent circuit of a traditional transformer, the cascaded transformer can be considered equivalent to a new two-port transformer. Since the parasitic parameters of the transformer and the circuit relationship of the subsequent load remain unchanged before and after the equivalence, this method does not affect the spectral characteristics of the cascaded transformer.

[0140] Since the input voltage of the cascaded transformer is the square wave voltage output by the H-bridge inverter submodule, the traditional method of directly identifying transformer parameters using the RMS values ​​of voltage and current will result in an inductance value that is higher than the actual value. Therefore, this invention provides a method for identifying cascaded transformer parameters based on the amplitude-frequency characteristics of a multilevel inverter. This method is inspired by the fact that the output voltage of a high-frequency CTMI (Continuous Transformer Interface) varies with frequency due to the parameters of the cascaded transformer. Therefore, if the relationship between the transformer parameters and the amplitude-frequency characteristics is obtained, an optimization algorithm can be used to inversely derive the equivalent model parameters by fitting the measured amplitude-frequency characteristics of the CTMI.

[0141] To achieve the above objectives, Figure 4 Circuit analysis yields the following amplitude-frequency response model for CTMI:

[0142]

[0143] Among them, U g U is the effective value of the fundamental frequency component of the output voltage when the operating angular frequency of the CTMI is ω. mul For u mul The effective value of the fundamental frequency component, R p and X p As a transition variable, it is calculated as follows:

[0144]

[0145] in,

[0146]

[0147] Among them, X m =ωL m ω is the angular frequency of the operating frequency to be identified; the apostrophe (') indicates the value of the secondary winding parameters referred to the primary side, i.e., R′. 2_eq =k 2 R 2_eq , R′ g =k 2 R g , X′ 2_eq =k 2 ωL 2_eq and X′ g =k 2 ωL g It can be seen that when Umul At a certain time, U g Will due to R m L m R1, R2, L1, and L2 vary with ω. Using mathematical algorithms, U can be fitted to different ω values. g To obtain transformer parameters. However, it's important to note that U... mul It is an equivalent cascaded voltage, which cannot be directly measured. Therefore, this invention provides a U mul The calculation method.

[0148] U mul For u mul The effective value of the fundamental frequency component, while u mul The calculation is as follows:

[0149]

[0150] Among them, u s_j This is the real-time input voltage of the j-th transformer. In this embodiment, the dead-time effect is considered first. For any transformer's input voltage, due to the dead-time effect, its actual input voltage u... s For ideal voltage u idl and dead zone error voltage u d The superposition of.

[0151] Figure 5 The dead-zone error voltage u of the submodule in the actual operation of the high-frequency cascaded multilevel inverter provided in this embodiment of the invention is... d In summary, "S1" to "S4" represent the switching transistors of the H-bridge submodule, and S1 to S4 are drive signals using a dead-time insertion method with delayed turn-on. Figure 5 In the diagram, (a) represents the output current i of the H-bridge submodule. s It crosses zero after the dead time ends. Figure 5 (b) in the text represents i s Crossing zero within the dead zone time, Figure 5 (c) in the text represents i s "u" crosses zero before the start of dead time. s "This refers to the output voltage of the H-bridge submodule (i.e., the input voltage of the connected transformer), "u d "This is the dead zone error voltage. When a resistive-inductive load is connected to the downstream stage, the cascaded multilevel inverter will exhibit the following in steady state": Figure 5 The three dead-zone voltage errors are shown. Among them, δ d δ on and δ off These represent the dead time t, respectively. d The turn-on delay t of the switching device on and shutdown delay time t offThe corresponding angle, δ d =ωt d δ on =ωt on and δ off =ωt off ω is the fundamental angular frequency, ω = 2πf0, where f0 is the fundamental frequency; θ s and θ e These are the turn-on angle and turn-off angle of the H-bridge inverter submodule, respectively. For the transformer input current i s The phase of the ideal output voltage of a multilevel inverter is defined as 0. For an inductive load, since the current lags behind the voltage, The range is 0 to π / 2. For u s Perform Fourier decomposition:

[0152]

[0153] in, and For u s The Fourier coefficients, where n is the harmonic order. s u idl and u d The Fourier coefficients of the fundamental frequency component satisfy the following relationship:

[0154]

[0155] in, and is u idl The fundamental frequency Fourier coefficients are calculated as follows:

[0156]

[0157] and is u d The fundamental frequency Fourier coefficients. Based on θ s and The relationship between them and The calculation is as follows:

[0158] when hour,

[0159] when hour,

[0160] when hour,

[0161] When only considering the dead zone effect, U mul=U mul_s ,in:

[0162]

[0163] In fact, due to the on-resistance R of the switching transistor in the H-bridge submodule... on When current flows through the switching transistor, the resulting on-state voltage drop ΔV will change U. mul Therefore, it is still necessary to use U mul_s Based on this, correction calculations are performed.

[0164] Figure 6 For U mul , ΔV, U mul_idl and i s The phasor diagram, according to trigonometric function relationships, U mul The calculation is as follows:

[0165]

[0166] Wherein, ΔV is calculated as:

[0167] ΔV=N·2R on ·I s

[0168] N represents the number of H-bridge submodules in CTMI (i.e., the number of transformers in the high-frequency cascaded transformers), R on For the on-state voltage drop of the H-bridge submodule, I s This is the effective value of the primary current of the transformer.

[0169] When identifying transformer parameters, R m and L m The frequency varies with the operating frequency. Furthermore, due to frequencies up to 30kHz, R1 and R2 will exhibit a skin effect. As the frequency increases, R1 and R2 will increase significantly. This is because R at each frequency... m L m Since R1 and R2 are different, it is difficult to directly identify the correct transformer parameters using optimization algorithms. To obtain accurate transformer parameters at different frequencies, this invention provides a method for identifying the parameters of a high-frequency cascaded transformer. First, the transient voltage and current waveforms from an open-circuit test are used to identify R1 and R2. m and L m Then, using the relationship between R1, R2, and the skin effect coefficient, and utilizing the measured CTMI amplitude-frequency characteristics, an optimization algorithm is used to identify R1, R2, L1, and L2. Specific steps include:

[0170] (S1) Determine the operating frequency at which transformer parameters need to be identified based on the CTMI's operating requirements;

[0171] (S2) Disconnect CTMI from the load and apply the rated operating voltage V to the DC bus. DC A no-load test was conducted at the operating frequency to be identified. Then, one of the cascaded transformers was randomly selected, and its input voltage signal u was recorded. s0 and input current signal i s0 And identify the excitation resistance R of the cascaded transformer. m And excitation inductance L m ;

[0172] In this embodiment, the excitation resistance R of transformer A at the i-th operating frequency to be identified m (i) is:

[0173]

[0174] Where P0 is the no-load loss, U s_rms It is a voltage signal u s0 The effective value; I s_rms It is a current signal i s0 The effective value; T is the voltage signal u s0 The period; u s0 (t) represents the voltage signal u s0 The voltage value at time t; i s0 (t) represents the current signal i s0 The current value at time t.

[0175] The magnetizing inductance L of transformer A at the i-th operating frequency to be identified m (i) is:

[0176]

[0177] Among them, such as Figure 7 As shown, Δt(i) is the voltage signal u s0 The amplitude is equal to V DC Duration of time; Δi s (i) represents the current signal i s0 The change during the period Δt.

[0178] (S3) Connect the CTMI to any resistive-inductive load and apply the rated operating voltage V to the DC bus. DC Record the effective value U of the fundamental frequency component of the CTMI output voltage at each operating frequency to be identified. g_meas CTMI's load resistance R g and load inductance L g Phase angle of the primary current of any transformer in a high-frequency cascaded transformer system and the effective value of the primary side current I s ;

[0179] (S4) Calculate the effective value of the fundamental frequency component of the CTMI output voltage at each operating frequency to be identified; where, the effective value of the fundamental frequency component of the CTMI output voltage at the i-th operating frequency to be identified is... G(ω(i)) and U mul (i) By substitution I s R g and L g get.

[0180] (S5) Construct the objective function J, as shown in the following formula, and use the optimization algorithm to solve for the primary winding resistance R1, primary winding leakage inductance L1, secondary winding resistance R2 and secondary winding leakage inductance L2 of the cascaded transformer.

[0181]

[0182] M represents the number of frequency points to be identified for the operating frequency; U g_meas (i) represents the effective value of the fundamental frequency component of the CTMI output voltage measured at the i-th operating frequency to be identified; U g_est (i) represents the effective value of the fundamental frequency component of the CTMI output voltage at the i-th operating frequency to be identified.

[0183] The actual objective of the optimization algorithm is to find the skin effect coefficient p of the primary winding resistance. 11 p 21 p 31 The skin effect coefficient p of the secondary winding resistance 12 p 22 p 32 The leakage inductance L1 of the primary winding and the leakage inductance L2 of the secondary winding are calculated, and finally the winding resistances of the primary and secondary sides of the transformer are calculated using the following formula.

[0184]

[0185] in, ω(i) is the i-th operating frequency to be identified.

[0186] This simplifies the objective function, and then solves for the primary winding resistance R1(i), primary winding leakage inductance L1(i), secondary winding resistance R2(i), and secondary winding leakage inductance L2(i) of any transformer in the cascaded transformer at the i-th identified operating frequency.

[0187] It should be noted that the optimization algorithm can be selected from existing technologies such as genetic algorithms, particle swarm optimization, ant colony optimization, and immune algorithms. In this embodiment, the particle swarm optimization algorithm, which is simple, easy to implement, highly accurate, and has a fast convergence speed, is selected for identification calculation. Specifically, it includes: 1. Setting the inertia weight, learning factor, and transformer parameter values ​​of the particle swarm optimization algorithm; 2. Initializing the particle swarm according to the constraints and determining the initial value of the optimal position of each particle and the initial value of the optimal position of the population; 3. Dynamically adjusting the particle state through the velocity-position update formula and simultaneously verifying the effectiveness of the constraints; calculating the particle performance based on the fitness function and tracking the individual extreme values ​​and the global optimal solution; iterating repeatedly until the convergence judgment condition is met, and finally outputting the optimal transformer parameter set.

[0188] In summary, 1) the high-frequency cascaded transformer parameter identification method provided in this embodiment uses the transformer transient waveform obtained from the no-load test of a multi-level inverter to identify the transformer's magnetizing resistance and magnetizing inductance. Then, considering the dead time effect and the on-state voltage drop of the switching transistor, the relationship between the transformer's equivalent parameters and the output voltage is derived. Based on the amplitude-frequency characteristic model of the cascaded transformer, and according to the effective value of the fundamental frequency component of the CTMI output voltage at different operating frequencies during the load test of the multi-level inverter, the winding resistance and leakage inductance of the primary and secondary sides of the transformer are identified. 2) This embodiment establishes a skin effect correction model under high-frequency operating conditions, and significantly improves the identification accuracy of the primary and secondary winding resistances through a frequency-varying resistance compensation mechanism, breaking through the performance limitations of traditional methods in a wide frequency range. At the same time, it innovatively utilizes the square wave excitation response of the CTMI no-load test and the amplitude-frequency characteristics of the load test to accurately extract the magnetizing inductance and winding leakage inductance, solving the inductance identification distortion problem of traditional methods under non-sinusoidal excitation. 3) The parameter identification method provided in this embodiment directly utilizes the sampling data during normal operation of the CTMI system, eliminating the need to separate the transformer from the CTMI system and removing the dependence on dedicated excitation equipment. This achieves integrated "operation-testing," significantly reducing testing complexity and cost. This embodiment can achieve accurate identification of equivalent parameters of high-frequency cascaded transformers in CTMI without the need for additional excitation equipment or separation of the transformer from the system.

[0189] The following specific simulation examples will further explain the beneficial effects that the present invention can achieve.

[0190] To verify the effectiveness of the high-frequency cascaded transformer parameter identification method based on the amplitude-frequency characteristics of multi-level inverters provided in this invention, a 17-level CTMI MATLAB / Simulink model was established, and the simulation parameters are shown in Table 1. The transformer parameters identified by the method of this invention were compared with the actual preset parameters, and also with the results obtained from standard tests based on open-circuit / short-circuit tests.

[0191] Table 1

[0192] Parameter name symbol numerical values DC bus voltage <![CDATA[V DC ]]> 200V Number of H-bridge inverter submodules N 8 Submodule supporting capacitor <![CDATA[C DC ]]> 135μF Fundamental frequency <![CDATA[f0]]> 5-30kHz Dead Time <![CDATA[t d ]]> 500ns Switching device turn-on delay time <![CDATA[t on ]]> 33.6ns Switching device turn-off delay time <![CDATA[t off ]]> 60.5ns Transformer winding coefficient k 21:9 Load parameters <![CDATA[R g ,L g ]]> 102.9Ω, 5.9μH

[0193] No-load experiments were conducted at different test frequencies f0, and R m and L m The identification results are as follows Figure 8 As shown in the figure; (a) represents the identification result of the excitation resistance, and (b) represents the identification result of the excitation inductance. It can be seen from the figure that, under different f0 values, the R identified by the proposed method... m and L m The results show a very good match with the actual values. This is because the standard tests and the proposed method calculate R... m The method is the same. Figure 8 (a) will not be repeated. However, because the reactive power under square wave excitation includes contributions from higher harmonics, the L identified by standard tests... m Greater than the actual value. The parameter identification accuracy is evaluated using the mean absolute error (MAPE). For standard testing, L m The identified MAPE was 9.67%. In comparison, the proposed method's R... m The MAPE identification rate was 0.51%, L m The MAPE identification rate was only 0.56%.

[0194] Connect the CTMI to a 102.9Ω, 5.9μH load. Keeping the DC voltage constant, increase f0 from 5kHz to 30kHz in 500Hz increments, and record the fundamental frequency RMS value U of the CTMI output voltage at different f0 values. g The measured U g See the -f0 feature. Figure 9 Using the particle swarm optimization algorithm, we can utilize U under different f0 values. g Calculate the transformer winding parameters. Select a particle count of 100 and a maximum iteration count of 50. Since standard tests can only calculate short-circuit impedance (R0),... k =R1+k 2 R2, L k =L1+k 2 L2), therefore, the winding parameters identified by the method proposed in this invention are converted into the same form for comparison. Figure 10 The convergence of the objective function J using the particle swarm optimization algorithm is shown. It can be seen that J begins to converge rapidly at iteration number 10, with a minimum value of 6.45 × 10⁻⁶. -10 . Figure 11 The transformer winding parameters identified using the proposed method are shown, along with the results of standard tests; (a) shows the identified winding resistance, and (b) shows the identified winding leakage inductance. Due to the very small winding losses, the R value identified by the standard tests is... k It is easily affected by measurement errors. When f0 is low, the R obtained from the standard test is...k It is close to the actual value, but as f0 increases, R... k The identification error has increased. (Compared to L) m Similarly, due to the influence of higher harmonics in the square wave voltage, the L obtained from standard tests... k It is also larger than the actual value. In comparison, the R identified by the method proposed in this invention... k and L k The proposed method shows excellent agreement with actual values ​​under different f0 values. The R-value of the proposed method is... k The MAPE identification rate was 3.29%, L k The MAPE identification rate was 1.95%. In comparison, the R of the standard test... k The MAPE identification rate was 4.52%, L k The MAPE identification rate is 8.71%. Compared with traditional methods, the proposed method has higher accuracy in identifying cascaded transformer parameters.

[0195] Secondly, the present invention provides a parameter identification device for a high-frequency cascaded transformer; the high-frequency cascaded transformer is a high-frequency cascaded transformer in a cascaded transformer multilevel inverter (CTMI); wherein, the parameters of each transformer in the high-frequency cascaded transformer are the same.

[0196] The above parameter identification device includes:

[0197] The first identification module is used to acquire the input voltage signal u of any transformer A in the high-frequency cascaded transformers at the i-th operating frequency to be identified when the CTMI is in an unloaded state. s0 and input current signal i s0 This allows us to identify the excitation resistance R of transformer A at the i-th operating frequency to be identified. m (i) and excitation inductance L m (i); where the input voltage signal u s0 and input current signal i s0 By disconnecting the CTMI from the load and applying the rated operating voltage V to the DC bus of the CTMI DC The results were obtained after measurement; where i = 1, 2, ..., M; M is the number of frequency points of the operating frequency to be identified;

[0198] The first parameter measurement module is used to connect the CTMI to any resistive-inductive load and apply the rated operating voltage V to the DC bus of the CTMI. DC The effective value U of the fundamental frequency component of the CTMI output voltage is measured at the i-th operating frequency to be identified. g_meas (i) and the load resistance R of CTMI g (i) and load inductance L g (i);

[0199] The RMS value calculation module is used to calculate the RMS value of the fundamental frequency component of the CTMI output voltage at the i-th operating frequency to be identified.

[0200] The second identification module is used to minimize... Identify the primary winding resistance R1(i), primary winding leakage inductance L1(i), secondary winding resistance R2(i), and secondary winding leakage inductance L2(i) of any transformer in the cascaded transformer at the i-th operating frequency to be identified.

[0201] Wherein, loss(U g_est (i),U g_meas (i)) represents U g_est (i) and corresponding U g_meas The difference loss between (i); G(ω(i)) is the amplitude-frequency response value of CTMI at the i-th operating frequency ω(i) to be identified, and its expression is the same as R m (i), L m (i), R1(i), L1(i), R2(i) and L2(i) are related; U mul (i) is the effective value of the fundamental component of the equivalent cascade voltage of the H-bridge submodule in CTMI at the i-th operating frequency to be identified; the equivalent cascade voltage of the H-bridge submodule is the sum of the output voltages of all H-bridge submodules in CTMI.

[0202] In one optional embodiment, the parameter identification device further includes: a second parameter measurement module, used to disconnect the CTMI from the load and apply a rated operating voltage V to the DC bus of the CTMI. DC And measure the input voltage signal u of any transformer A in the high-frequency cascaded transformer at the i-th operating frequency to be identified. s and input current signal i s .

[0203] The related technical solutions are the same as the parameter identification method for high-frequency cascaded transformers provided in the first aspect of this invention, and will not be repeated here.

[0204] Thirdly, the present invention provides a cascaded transformer multilevel inverter system, comprising: a cascaded transformer multilevel inverter (CTMI) and a parameter identification module;

[0205] The parameter identification module is used to execute the parameter identification method provided in the first aspect of the present invention to identify the parameters of the high-frequency cascaded transformer in CTMI.

[0206] The related technical solutions are the same as the parameter identification method for high-frequency cascaded transformers provided in the first aspect of this invention, and will not be repeated here.

[0207] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for parameter identification of a high-frequency cascaded transformer, characterized in that, The high-frequency cascaded transformer is the high-frequency cascaded transformer in the Cascaded Transformer Multilevel Inverter (CTMI); the parameters of each transformer in the high-frequency cascaded transformer are the same. The parameter identification method includes: When CTMI is in an unloaded state, obtain the value of any transformer A in the high-frequency cascaded transformers at the [missing information - likely a specific timeframe or condition]. i The input voltage signal at the operating frequency to be identified u s0 and input current signal i s0 Thus, it can be identified that transformer A was in the first stage. i Excitation resistor at the operating frequency to be identified R m ( i ) and magnetizing inductance L m ( i ); where, input voltage signal u s0 and input current signal i s0 By disconnecting the CTMI from the load and applying the rated operating voltage to the DC bus of the CTMI. V DC The measurements were obtained later; among them, M represents the number of frequency points whose operating frequency needs to be identified. Connect the CTMI to any resistive-inductive load and apply the rated operating voltage to the DC bus of the CTMI. V DC In the i The effective value of the fundamental frequency component of the CTMI output voltage is measured at the operating frequency to be identified. U g_meas ( i ) and CTMI's load resistance R g ( i and load inductance L g ( i ); Calculate the first i The effective value of the fundamental frequency component of the CTMI output voltage at the operating frequency to be identified. ; By minimizing For any transformer in a cascaded transformer, in the first... i The primary winding resistance at the operating frequency to be identified R 1( i ), primary winding leakage inductance L 1( i Secondary winding resistance R 2( i ) and secondary winding leakage inductance L 2( i To identify; in, k This refers to the turns ratio of a high-frequency cascaded transformer. express U g_est ( i ) and corresponding U g_meas ( i The difference between ) and loss; For the first i individual working frequencies to be identified The amplitude-frequency response value of CTMI is expressed as follows: R m ( i ), L m ( i ), R 1( i ), L 1( i ), R 2( i )and L 2( i Related; For the first i The effective value of the fundamental component of the equivalent cascade voltage of the H-bridge submodule in the CTMI at the operating frequency to be identified; the equivalent cascade voltage of the H-bridge submodule is the sum of the output voltages of all H-bridge submodules in the CTMI; The first i The amplitude-frequency response value of CTMI at the operating frequency to be identified for: in, in, ; N This refers to the number of transformers in a high-frequency cascaded transformer system. ; It is the first i The equivalent winding resistance of the secondary side of the transformer at the operating frequency to be identified; ; ; It is the first i The equivalent winding leakage inductance of the transformer secondary side at the operating frequency to be identified; ; ; .

2. The parameter identification method according to claim 1, characterized in that, The first i The fundamental component RMS value of the equivalent cascade voltage of the H-bridge module in the CTMI at the identified operating frequency. for: in, N This refers to the number of transformers in a high-frequency cascaded transformer system. and For the first i The first CTMI at the unknown operating frequency j Fourier expansion coefficients of the fundamental frequency component of the output voltage of each H-bridge submodule.

3. The parameter identification method according to claim 1, characterized in that, The first i The fundamental component RMS value of the equivalent cascade voltage of the H-bridge module in the CTMI at the identified operating frequency. for: in, N This refers to the number of transformers in a high-frequency cascaded transformer system. and For the first i The first CTMI at the unknown operating frequency j The Fourier expansion coefficients of the fundamental frequency component of the output voltage of each H-bridge submodule, after dead-zone compensation, are as follows: and For the first in CTMI j Fourier expansion coefficients of the fundamental frequency component of the output voltage of each H-bridge submodule; and For the first i The first CTMI at the unknown operating frequency j Fourier expansion coefficients of the fundamental frequency component of the dead-zone error voltage of each H-bridge submodule; when hour, ; ; when hour, when hour, To connect the CTMI to any resistive-inductive load and apply the rated operating voltage to the DC bus of the CTMI. V DC Afterwards, in the i The phase angle of the primary current of any transformer in a high-frequency cascaded transformer measured at the operating frequency to be identified; For the first i The first CTMI at the unknown operating frequency j The activation angle of each H-bridge module; In the first i The angle corresponding to the dead time at the operating frequency to be identified; In the first i The first working frequency to be identified j The angle corresponding to the switching delay time of each H-bridge submodule; For the first i The first CTMI at the unknown operating frequency j The angle corresponding to the shutdown delay time of each H-bridge submodule.

4. The parameter identification method according to claim 1, characterized in that, The first i The fundamental component RMS value of the equivalent cascade voltage of the H-bridge module in the CTMI at the identified operating frequency. for: in, N This refers to the number of transformers in a high-frequency cascaded transformer system. For the first i The first CTMI at the unknown operating frequency j The on-state voltage drop of each H-bridge submodule; and Connect the CTMI to any resistive-inductive load and apply the rated operating voltage to the DC bus of the CTMI. V DC Afterwards, in the i The effective values ​​of the primary current phase angle and the fundamental frequency component of the primary current of any transformer in a high-frequency cascaded transformer measured at the identified operating frequency. and For the first i The first CTMI at the unknown operating frequency j The Fourier expansion coefficients of the fundamental frequency component of the output voltage of each H-bridge submodule, after dead-zone compensation, are as follows: and For the first in CTMI j Fourier expansion coefficients of the fundamental frequency component of the output voltage of each H-bridge submodule; and For the first i The first CTMI at the unknown operating frequency j Fourier expansion coefficients of the fundamental frequency component of the dead-zone error voltage of each H-bridge submodule; when hour, ; ; when hour, when hour, For the first i The first CTMI at the unknown operating frequency j The activation angle of each H-bridge module; In the first i The angle corresponding to the dead time at the operating frequency to be identified; In the first i The first working frequency to be identified j The angle corresponding to the switching delay time of each H-bridge submodule; For the first i The first CTMI at the unknown operating frequency j The angle corresponding to the shutdown delay time of each H-bridge submodule.

5. The parameter identification method according to any one of claims 2-4, characterized in that, and They are respectively: and They represent the first i The first CTMI at the unknown operating frequency j The off-angle and on-angle of each H-bridge submodule; For the first i The first CTMI at the unknown operating frequency j The angle corresponding to the shutdown delay time of each H-bridge submodule.

6. The parameter identification method according to any one of claims 1-4, characterized in that, The minimize For any transformer in a cascaded transformer, in the first... i The primary winding resistance at the operating frequency to be identified R 1( i ), primary winding leakage inductance L 1( i Secondary winding resistance R 2( i ) and secondary winding leakage inductance L 2( i Identification is performed, including: Build to minimize The objective function is the target function, and the objective function contains... R 1( i )and R 2( i ) is represented as: and This simplifies the objective function, allowing us to solve for the value of any transformer in the cascaded transformer system at the 1st cascade. i The primary winding resistance at the operating frequency to be identified R 1( i ), primary winding leakage inductance L 1( i Secondary winding resistance R 2( i ) and secondary winding leakage inductance L 2( i ); in, ; For the first i One working frequency to be identified; p 11 , p 21 , p 31 The skin effect coefficient is the resistance of the primary winding. p 12 , p 22 , p 32 The skin effect coefficient is the resistance of the secondary winding.

7. The parameter identification method according to any one of claims 1-4, characterized in that, Transformer A in the first i Excitation resistor at the operating frequency to be identified R m ( i ) and magnetizing inductance L m ( i They are respectively: in, T voltage signal u s0 The cycle; voltage signal u s0 In time t The voltage value under these conditions; Current signal i s0 In time t The current value below; voltage signal u s0 The amplitude is equal to V DC The duration of time; Current signal i s0 In Δ t The amount of change during the period.

8. A parameter identification device for a high-frequency cascaded transformer, characterized in that, The high-frequency cascaded transformer is the high-frequency cascaded transformer in the Cascaded Transformer Multilevel Inverter (CTMI); the parameters of each transformer in the high-frequency cascaded transformer are the same. The parameter identification device includes: The first identification module is used to obtain the information of any transformer A in the high-frequency cascaded transformers when CTMI is in an unloaded state. i The input voltage signal at the operating frequency to be identified u s0 and input current signal i s0 Thus, it can be identified that transformer A was in the first stage. i Excitation resistor at the operating frequency to be identified R m ( i ) and magnetizing inductance L m ( i ); where, input voltage signal u s0 and input current signal i s0 By disconnecting the CTMI from the load and applying the rated operating voltage to the DC bus of the CTMI. V DC The measurements were obtained later; among them, M represents the number of frequency points whose operating frequency needs to be identified. The first parameter measurement module is used to connect the CTMI to any resistive-inductive load and apply the rated operating voltage to the DC bus of the CTMI. V DC In the i The effective value of the fundamental frequency component of the CTMI output voltage is measured at the operating frequency to be identified. U g_meas ( i ) and CTMI's load resistance R g ( i and load inductance L g ( i ); The effective value calculation module is used to calculate the first effective value. i The effective value of the fundamental frequency component of the CTMI output voltage at the operating frequency to be identified. ; The second identification module is used to minimize... For any transformer in a cascaded transformer, in the first... i The primary winding resistance at the operating frequency to be identified R 1( i ), primary winding leakage inductance L 1( i Secondary winding resistance R 2( i ) and secondary winding leakage inductance L 2( i To identify; in, k This refers to the turns ratio of a high-frequency cascaded transformer. express U g_est ( i ) and corresponding U g_meas ( i The difference between ) and loss; For the first i individual working frequencies to be identified The amplitude-frequency response value of CTMI is expressed as follows: R m ( i ), L m ( i ), R 1( i ), L 1( i ), R 2( i )and L 2( i Related; For the first i The effective value of the fundamental component of the equivalent cascade voltage of the H-bridge submodule in the CTMI at the operating frequency to be identified; the equivalent cascade voltage of the H-bridge submodule is the sum of the output voltages of all H-bridge submodules in the CTMI; The first i The amplitude-frequency response value of CTMI at the operating frequency to be identified for: in, in, ; N This refers to the number of transformers in a high-frequency cascaded transformer system. ; It is the first i The equivalent winding resistance of the secondary side of the transformer at the operating frequency to be identified; ; ; It is the first i The equivalent winding leakage inductance of the transformer secondary side at the operating frequency to be identified; ; ; .

9. A cascaded transformer multilevel inverter system, characterized in that, include: Cascaded transformer multilevel inverter CTMI and parameter identification module; The parameter identification module is used to execute the parameter identification method according to any one of claims 1-7 to identify the parameters of the high-frequency cascaded transformer in CTMI.

Images