A control method for an RLC electronic load applicable to sine current simulation

Abstract

A control method for an RLC electronic load applicable to sine current simulation, which relates to the field of electronic devices for measurement and testing, solves the problem of insufficient steady-state performance in the existing testing of RLC electronic loads for sine current simulation; in this application, by sampling the external voltage instantaneous command, the current command is calculated in real time through model iteration by Ohm's law and four arithmetic operations to realize the dynamic update of the current command and ensure the dynamic indexes of the system; at the same time, the second-order generalized integral algorithm is used to realize the sampling filtering of voltage and current and the prediction of voltage lead amount, so as to filter out the sampling noise and improve the system stability, and the algorithm adopted in this application is simple, and a DSP or FPGA with conventional performance can realize a higher-rate iterative calculation, improve the calculation accuracy and reduce the system cost.

Description

Technical Field

[0001] The present invention relates to the field of electronic devices for measurement and testing, and relates to an RLC electronic load control method applicable to sine current simulation. Background Art

[0002] An RLC AC electronic load is a power electronic device that can simulate energy-consuming impedance loads. It can simulate different values of resistors, inductors, capacitors, and their combinations. Usually, the AC electronic load controls the output of a current that conforms to the characteristics of a resistor, capacitor, or inductor by tracking the phase and amplitude of an external voltage. Currently, it is mostly applied to the aging test scenarios of electronic devices such as energy storage converters, grid-connected inverters, motor controllers, and in-vehicle OBCs. Due to the adoption of an energy feedback topology structure, the RLC electronic load simulation device is more energy-efficient, easier to adjust, more flexible in setting, smaller in volume, and lower in noise than a real energy-consuming RLC device.

[0003] For an RLC electronic load to accurately simulate the characteristics of real resistor, capacitor, and inductor currents, it needs to maintain high dynamic performance and good steady-state performance. A common method for a traditional RLC load simulation device to obtain a current command is not to perform voltage phase locking on an external voltage source, and to calculate through two basic differential equations, namely the capacitor current ic = C * du / dt and the inductor voltage UL = Ldi / dt. The current command calculation is achieved through the discretization of the differential equations. This method simply utilizes the differential relationship between the voltage and current of resistors, inductors, and capacitors, samples the instantaneous voltage of the external voltage source, and calculates the current command according to the differential equations of the voltage and current of the RLC model. The advantage of this algorithm is that the system response is fast, and the dynamic performance of the source response and the load response is high. However, the disadvantage is that the algorithm has a large amount of calculation, the differential link is prone to introducing interference, which easily causes system oscillation and current out-of-control, thereby reducing the steady-state index. Another method is to perform phase locking on the external voltage, calculate the effective value Irms command of the current according to the RLC model, and then use the product of Irms and the sine value of the phase-locked angle as the current command. The advantage of this method is high current stability and not easily affected by interference. The disadvantage is poor dynamic performance. When the voltage or current changes, it takes one cycle or half a cycle for the current effective value to be updated in a timely manner.

[0004] In addition, the patent application with the publication number CN112838774A proposes a control method for a high-power RLC AC electronic load, which simulates the characteristics of the RLC AC electronic load by controlling the controlled voltage source U2 in real time, and obtains the command voltage U2n+1 of the controlled voltage source U2 in three modes of R, RC, and RL; taking the calculated voltage command U2n+1 as the command voltage of the H-bridge, and controlling the output voltage by the way of single voltage loop open-loop wave generation, the output current characteristics of the RLC load to be simulated can be obtained. Since the current is realized through the voltage difference, the direct voltage control has a higher dynamic response than the direct current control. The comparative document indirectly controls the current by directly controlling the voltage, which is suitable for arbitrary waveform voltages (such as triangular wave square wave circuits, etc.), but there is still a problem of insufficient steady-state performance for the pure sine circuit in the comparative document. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that there is a problem of insufficient steady-state performance in the existing RLC electronic load test for simulating sinusoidal current.

[0006] The present invention solves the above technical problems through the following technical solutions:

[0007] An RLC electronic load control method applicable to sinusoidal current simulation includes the following steps:

[0008] Step S1: Obtain the current formula that satisfies Ohm's law in the complex frequency domain by simulating a constant RC load or a constant RL load.

[0009] Step S2: Eliminate the imaginary part of the current formula obtained in Step S1 and perform transformation to obtain the calculation formula of the real-time current command.

[0010] Step S3: Generate a 90° phase lag offset for the input AC sine signal through the second-order generalized integral SOGI algorithm to obtain two orthogonal signals, one of which has the same amplitude and phase as the input signal; the other signal lags the input signal by 90°, and taking the inverse is to lead the input signal by 90°.

[0011] Step S4: Substitute the obtained value through the inverse value obtained by the second-order generalized integral in Step S3 into the current command calculation formula obtained in Step S2 to obtain the current command i under the simulated constant RC load model C or the current command i under the simulated constant RL load model L .

[0012] In the present invention, the solution of the current command is simplified to a simple four arithmetic operations of Ohm's law in the complex frequency domain, avoiding complex differential equation calculations; a predicted signal with a 90° phase difference from the external voltage is obtained through the second-order generalized integral algorithm to achieve load current calculation, and the predictive control has good dynamics; at the same time, the signal is filtered through the second-order generalized integral (SOGI) algorithm, which can filter out high-frequency and low-frequency noises in the sampling signal, further improving the system stability performance, and the dynamic tracking performance can also be guaranteed; and the algorithm is relatively simple, and a DSP or FPGA with conventional performance can achieve a higher rate of iterative calculation, improving the calculation accuracy and reducing the system cost.

[0013] Preferably, in the step S1, the simulated constant RC load circuit includes an AC power supply e1, a simulated constant value resistor R, and a simulated constant value capacitor C. The AC power supply e1 forms a closed simulation circuit by connecting in series the simulated constant value resistor R and then connecting in series the simulated constant value capacitor C; assuming that the voltage frequency of e1 is w and the circuit current is i c , then there is a current formula satisfying Ohm's law in the complex frequency domain:

[0014]

[0015] In formula (1), s is the complex variable introduced in the Laplace transform. According to the correspondence between the Laplace transform and the Fourier transform, s = jw, and substituting s = jw into formula (1) gives:

[0016]

[0017] In formula (2), i c (jw) is the instantaneous value of the current, which is i c , and U(jw) is the instantaneous value of the external voltage e1, which is U.

[0018] Preferably, in the step S2, the numerator and denominator in formula (2) are multiplied by the conjugate complex number of the denominator to eliminate the imaginary part j in the denominator, and then through a little transformation, the calculation formula of the real-time current command is obtained:

[0019]

[0020] The jU in the imaginary part of formula (3) is a voltage leading the external voltage U by 90°, denoted as U q , and the whole imaginary part is U q multiplied by a fixed multiple wC / (R 2 w 2 C 2 +1).

[0021] Preferably, the implementation formulas of the two variables of SOGI in the step S3 are as follows:

[0022]

[0023] In Equation (4), D(s) is the transfer function of the band-pass filter, Q(s) is the transfer function of the low-pass filter, and k is the filter gain coefficient.

[0024] Preferably, in step S4, the known R and C values, the sampled U value, the locked w, and the leading 90° voltage signal obtained by taking the inverse of the second-order generalized integral in Equation (4) are substituted into Equation (3) to obtain the current command i under the RC load model c , as shown in Equation (5) below:

[0025]

[0026] Preferably, in step S1, the simulated constant RL load circuit includes an AC power supply e1, a simulated constant-value resistor R, and a simulated constant inductor L. The AC power supply e1 forms a closed simulation circuit by connecting in series the simulated constant-value resistor R and then the simulated constant inductor L; assuming that the voltage frequency of e1 is w and the circuit current is i L , then there is a current formula that satisfies Ohm's law in the complex frequency domain:

[0027]

[0028] In the formula, s is the complex variable in the Laplace transform, and s = jw. Substituting s = jw into Equation (7) gives:

[0029]

[0030] In Equation (7), i L (jw) is the instantaneous value of the current, which is i L , and U(jw) is the instantaneous value of the external voltage e1, which is U.

[0031] Preferably, in step S2, both the numerator and denominator in Equation (2) are multiplied by the conjugate complex number of the denominator to eliminate the imaginary part j in the denominator, and then with a little transformation, the calculation formula for the real-time current command is obtained:

[0032]

[0033] By substituting the voltage U of the external e1 into Equation (4), Uq is obtained, that is, -jU in Equation (8), and -jU represents a signal that lags U by 90°.

[0034] Preferably, the known R and L values, the sampled U value, the locked w, and the leading 90° voltage signal obtained by taking the inverse of the second-order generalized integral in Equation (4) are substituted into Equation (8) to obtain the current command i under the RL load model L , as shown in Equation (9) below:

[0035]

[0036] An electronic device includes a memory and a processor. The memory is used to store a program that supports the processor to execute the above-mentioned RLC electronic load control method applicable to sinusoidal current simulation, and the processor is configured to execute the program stored in the memory.

[0037] A storage medium stores a computer program. When the computer program is run by a processor, it executes the steps of the above-mentioned RLC electronic load control method applicable to sinusoidal current simulation.

[0038] The advantages of the present invention are as follows:

[0039] In the present invention, the solution of the current command is simplified to a simple four arithmetic operations of Ohm's law in the complex frequency domain, avoiding complex differential equation calculations; a prediction signal with a 90° phase difference from the external voltage is obtained through the second-order generalized integral algorithm to realize the calculation of the load current, and the prediction control has good dynamics; at the same time, the signal is filtered by the second-order generalized integral (SOGI) algorithm, which can filter out high-frequency and low-frequency noises in the sampling signal, further improving the stability performance of the system, and the dynamic tracking performance can also be guaranteed; and the algorithm is relatively simple, and a DSP or FPGA with conventional performance can achieve a higher rate of iterative calculation, improving the calculation accuracy and reducing the system cost. Description of the Drawings

[0040] Figure 1 It is a schematic diagram of an AC electronic analog constant RC load circuit of an RLC electronic load control method applicable to sinusoidal current simulation in the first embodiment of the present invention;

[0041] Figure 2 It is a schematic diagram of an AC electronic analog constant RL load circuit of an RLC electronic load control method applicable to sinusoidal current simulation in the first embodiment of the present invention. Detailed Embodiments

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0043] The technical solutions of the present invention will be further described below in conjunction with the drawings of the specification and specific embodiments:

[0044] Embodiment 1

[0045] A control method for an RLC electronic load applicable to sine current simulation, see Figure 1 The schematic diagram of an AC electronic analog constant RC load circuit of a control method for an RLC electronic load applicable to sine current simulation shown in the figure is for RC load simulation. The measured AC source is e1, simulating the current characteristics of a constant resistance R and a constant capacitance C. The AC source e1 is connected in series with a simulated constant resistance R and then in series with a simulated constant capacitance C to form a closed simulation circuit.

[0046] First, by assuming that the voltage frequency of e1 is w and the circuit current is i c , there is a current formula that satisfies Ohm's law in the complex frequency domain:

[0047]

[0048] In formula (1), s is the complex variable introduced in the Laplace transform (the s operator is understood as follows in a sine circuit. A sine wave Asin(theta) with a period of 360° multiplied by s = jw is equivalent to shifting the sine wave forward by 90°, that is, getting Asin(theta + 90°), which is equivalent to getting the differential signal of Asin(theta) (i.e., Acos(theta)). At the same time, introducing the s operator can transform the input sine signal into a cosine signal without using differentiation, simplifying the calculation process), s = jw. Substituting s = jw into formula (1) gives:

[0049]

[0050] In formula (2), i c (jw) is the instantaneous value of the current, abbreviated as i c , U(jw) is the instantaneous value of the external voltage e1, abbreviated as U; multiplying the numerator and denominator of the above formula by the conjugate complex number of the denominator to eliminate the imaginary part j in the denominator, and then making a slight transformation to obtain the calculation formula for the real-time current command:

[0051]

[0052] In formula (3), the real part is the external voltage U multiplied by a fixed multiple Rw 2 C 2 / (R 2 w 2 C 2 +1); the jU in the imaginary part can be understood as a voltage leading the external voltage U by 90°, denoted as U q (i.e., jU = Uq, and Uq leads U by 90°), that is, the whole imaginary part can be understood as Uq multiplied by a fixed multiple wC / (R 2 w 2 C 2 +1).

[0053] In summary, when R and C are known, the angular frequency ω is obtained by phase-locking the external e1 voltage. Obtaining the angular frequency ω through phase-locking is a prior art, and this application will not elaborate on it here. By sampling U (the instantaneous voltage value of the e1 voltage) and obtaining Uq, the current i in Equation (3) can be calculated. c The current command, and how to obtain Uq that is 90° ahead of U in real time is one of the cores of this method.

[0054] Through the second-order generalized integrator (SOGI), a 90° phase lag shift can be generated for the input AC sine signal to obtain two orthogonal signals (one D signal has the same amplitude and phase as the input signal U; the other Q signal lags the input signal U by 90°, and taking the inverse is 90° ahead). The implementation formulas for the two variables of SOGI are as follows:

[0055]

[0056] By performing the Q(s) transformation in Equation (4) on the input signal and then taking the inverse, the signal Uq that is ahead of the input signal U, that is, jU, is obtained. At the same time, by discretizing Equation (4) and the input U, it is convenient for the DSP controller to implement.

[0057] For further explanation, Equation 4 is the two formulas of the second-order generalized integrator SOGI. That is, the sine variable sampled externally will obtain two signals with a 90° difference through this formula, and it has the characteristics of no delay and filtering. While the conventional low-pass filter can filter, the signal is delayed, and the delay is unacceptable in the electronic load.

[0058] In Equation (4), D(s) has a band-pass filtering characteristic, Q(s) has a low-pass filtering characteristic, k is the filtering coefficient, and by adjusting the k value, the Uq variable with reduced noise can be obtained.

[0059] Therefore, the real-time voltage U and the feedback current i c can be subjected to the D(s) transformation in Equation 4, and the voltage and current with reduced noise are used for model calculation and closed-loop feedback to improve stability.

[0060] So far, for this RC load simulation circuit, substituting the known R and C values, the sampled U, the frequency-locked ω, and the inverse of Uq obtained through the second-order generalized integration in Equation (4) (that is, jU in Equation (3)) into Equation (3) to obtain the current command i for the RC load model c , as shown in the following Equation (5):

[0061]

[0062] Similarly, referring to Figure 2Schematic diagram of an AC electronic analog constant RL load circuit for a method of controlling an RLC electronic load applicable to sine current simulation, which is an RL load model. The AC source under test is e1, the simulated constant resistance is R, and the simulated constant inductance is L. The AC power supply e1 forms a closed simulation circuit by connecting the simulated constant resistance R in series and then connecting the simulated constant inductance L in series. Assuming the voltage frequency of e1 is w and the circuit current is i L , then the current formula of the RL load model satisfying Ohm's law in the complex frequency domain is:

[0063]

[0064] In the formula, s is the complex variable in the Laplace transform, and s = jw. Substituting s = jw into equation (7) gives:

[0065]

[0066] In equation (7), i L (jw) is the instantaneous value of the current, abbreviated as i L , U(jw) is the instantaneous value of the external voltage e1, abbreviated as U; at the same time, multiply the numerator and denominator of the above formula by the conjugate complex number of the denominator to eliminate the imaginary part j in the denominator, and then make a slight transformation to obtain the calculation formula of the real-time current command:

[0067]

[0068] By substituting the voltage U of the external e1 into the second formula in equation (4), Uq is obtained, that is, -jU (-jU represents a signal lagging U by 90°) in equation (8).

[0069] So far, for this RL load simulation circuit, the known values of R and L, the sampled U, the locked w, and Uq (that is, -jU in equation (8)) obtained by the second-order generalized integral in equation (4) are substituted into equation (8) to obtain the current command i of the RC load model L , as shown in the following equation (9):

[0070]

[0071] The key point of the present invention is to obtain the current commands of RC and RL load models through Ohm's law and four arithmetic operations in the complex frequency domain, predict the required voltage leading quantity in the current command formula through the second-order generalized integral algorithm, and filter the external voltage and feedback current, so as to improve the voltage and current accuracy and ensure the dynamic index and steady-state performance of the system. There are various improved types of the second-order generalized integral algorithm, which can filter the DC component of the AC signal and improve the phase-locked accuracy. At the same time, the present invention proposes to obtain the angular frequency of the voltage source by phase-locking the voltage source, obtain the complex impedance of the RLC load through the angular frequency, and use the quotient of the instantaneous voltage and the complex impedance as the current command of the electronic load. This method maintains the dynamic performance of the electronic load while taking into account the steady-state performance, and can greatly improve the performance index of the RLC electronic load.

[0072] Embodiment 2

[0073] An electronic device includes a memory and a processor. The memory is used to store a program that supports the processor to execute the above-mentioned RLC electronic load control method applicable to sinusoidal current simulation, and the processor is configured to execute the program stored in the memory.

[0074] Embodiment 3

[0075] A storage medium stores a computer program, and when the computer program is run by a processor, it executes the steps of the above-mentioned RLC electronic load control method applicable to sinusoidal current simulation.

[0076] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. And these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A RLC electronic load control method suitable for sinusoidal current simulation, characterized in that: The following steps are involved: Step S1, obtaining a current formula satisfying Ohm's law in a complex frequency domain by simulating a constant RC load and a constant RL load; Step S2, eliminating the imaginary part of the current formula obtained in step S1 and transforming it to obtain a calculation formula for the real-time current command; Step S3, using the second-order generalized integral SOGI algorithm to generate a 90° phase lag offset on the input AC sinusoidal signal, to obtain two orthogonal signals, one of which has the same amplitude and phase as the input signal; the other lags the input signal by 90°, and the inverse of the other lags the input signal by 90°; Step S4: Substitute the inverse value obtained by the second-order generalized integral in step S3 into the current command calculation formula obtained in step S2 to obtain the current command under the simulated constant RC load model. Or simulate the current command under the constant RL load model ; The simulated constant RC load circuit in step S1 includes an AC power supply e1, a simulated constant resistance resistor R, and a simulated constant capacitance capacitor C. The AC power supply e1 is connected in series with the simulated constant resistance resistor R and the simulated constant capacitance capacitor C to form a closed simulation circuit. Assume that the voltage frequency of e1 is , the circuit current is , then there is a current formula that satisfies Ohm's law in the complex frequency domain: （1） In formula (1), is the complex variable in the introduced Laplace transform. According to the corresponding relationship between Laplace transform and Fourier transform , and Substituting into formula (1), we get: （2） In formula (2), is the instantaneous value of current , The instantaneous value of the external voltage e1 is ; In step S2, the numerator and denominator of formula (2) are multiplied by the conjugate complex number of the denominator, and the imaginary part of the denominator is eliminated. , and then slightly transform to get the calculation formula of real-time current command: （3） The imaginary part of formula (3) is a voltage that leads the external voltage U by 90°, set q, the imaginary part is q multiplied by a fixed multiple ; The implementation formulas of the two variables of SOGI in step S3 are as follows: （4）； In formula (4) is the bandpass filter transfer function, is the low-pass filter transfer function, is the filter coefficient.

2. The RLC electronic load control method applicable to sinusoidal current simulation according to claim 1, characterized in that: In step S4, the known R and C values, the sampled U value, and the frequency-locked , the 90° leading voltage signal obtained by inverting the second-order generalized integral in equation (4) is substituted into equation (3) to obtain the current command under the RC load model , as shown in the following formula (5): （5）。 3. The RLC electronic load control method applicable to sinusoidal current simulation according to claim 1, characterized in that: The simulated constant RL load circuit in step S1 includes an AC power supply e1, a simulated constant resistance resistor R, and a simulated constant inductor L. The AC power supply e1 is connected in series with the simulated constant resistance resistor R and the simulated constant inductor L to form a closed simulation circuit. Assume that the voltage frequency of e1 is , the circuit current is , then there is a current formula that satisfies Ohm's law in the complex frequency domain: （6） In the formula The complex variable in the Laplace transform, and ,Will Substituting into formula (7), we get: （7） In formula (7) is the instantaneous value of current , The instantaneous value of the external voltage e1 is .

4. The RLC electronic load control method applicable to sinusoidal current simulation according to claim 3 is characterized in that: In step S2, the numerator and denominator of formula (2) are multiplied by the conjugate complex number of the denominator, and the imaginary part j in the denominator is eliminated, and then a calculation formula for the real-time current command is obtained by a slight transformation: （8） By substituting the voltage U of the external e1 into equation (4), we can obtain , that is, in formula (8) , Indicates hysteresis A signal at 90°.

5. The RLC electronic load control method applicable to sinusoidal current simulation according to claim 4, characterized in that: Substitute the known R and L values, the sampled U value, and the frequency-locked w into the 90° leading voltage signal obtained by inverting the second-order generalized integral in equation (4) and into equation (8) to obtain the current command under the RL load model: , as shown in the following formula (9): （9）。 6. An electronic device, comprising a memory and a processor, characterized in that: The memory is used to store a program that supports the processor to execute the RLC electronic load control method suitable for sinusoidal current simulation as described in any one of claims 1 to 5, and the processor is configured to execute the program stored in the memory.

7. A storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the RLC electronic load control method suitable for sinusoidal current simulation as claimed in any one of claims 1 to 5 are executed.

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