Model Predictive Voltage Control Method for the Power Inverter Circuit of an Electric Energy Router

Abstract

The present disclosure belongs to the field of power electronics technology, and particularly relates to a model predictive voltage control method for the power inverter circuit of an energy router, including: obtaining the time-domain state equation of the power inverter circuit of the energy router; performing discretization processing on the obtained time-domain state equation to obtain a discrete model of the power inverter circuit; canceling the predicted value of the inductor current in the obtained discrete model to obtain the desired output voltage equation of the discrete model; performing an approximate equivalence of the predicted value of the current on the obtained desired output voltage equation to obtain a simplified discrete model based on the desired output voltage, and calculating the desired value of the output voltage of the power inverter circuit; constructing a candidate vector cost function according to the obtained desired value of the output voltage; evaluating the constructed candidate vector cost function to obtain the minimum value of the candidate vector; and tracking the desired value of the output voltage according to the obtained minimum value of the candidate vector to achieve voltage control of the energy router.

Description

Technical Field

[0001] The present disclosure belongs to the field of power electronics technology, and particularly relates to a model predictive voltage control method for a power inverter circuit of an energy router. Background Art

[0002] The statements in this part only provide background technical information related to the present disclosure and do not necessarily constitute prior art.

[0003] The energy router is interconnected with the power grid, regional microgrids, and distributed generation systems to achieve a high degree of integration of information flow and power flow, and is the core hub in the energy Internet. Among them, the AC port of the energy router is a key device for constructing a connection channel with an AC source (or AC load), and mostly uses an LC-type power inverter topology with high output power quality and simple structure as the hardware circuit. Therefore, the effective control of the LC-type power inverter topology is of great significance for realizing the interconnection of alternating current.

[0004] As understood by the inventor, in the existing model predictive voltage control methods for LC-type power inverter circuits, the coefficients of the discrete models are mostly in the form of exponential or trigonometric functions, which occupy a large amount of computing resources and affect the dynamic performance of the AC port. In addition, the existing model predictive voltage control methods require a large number of sensors of various types such as capacitor voltage, inductor current, load / voltage current, etc., reducing the power density and system reliability. Moreover, in the existing model predictive evaluation framework, in each control period, each candidate vector needs to be evaluated by performing a model predictive calculation once to obtain the proposed output capacitor voltage, and then compared with the reference voltage to find the optimal solution. As a result, the candidate vector evaluation process in each control period requires multiple model predictive calculations, which is not conducive to rapid evaluation, further increasing the dependence on high-performance digital processing chips and being not conducive to engineering applications. Therefore, the control of the power inverter circuit of the energy router has problems of poor reliability, cumbersome control, and large computing resources that need to be solved urgently. Summary of the Invention

[0005] In order to solve the above problems, the present disclosure proposes a model predictive voltage control method for a power inverter circuit of an energy router, which improves the control performance of the LC-type power inverter circuit at the AC port of the energy router. A simplified discrete model is constructed according to the state equation of the LC-type power inverter circuit, reducing the number of variables, thereby avoiding complicated model calculations and greatly reducing the number of sensors; the model predictive evaluation framework of the AC port of the energy router is reconstructed, and a prediction preposition method is proposed, so that only one model predictive calculation is required in each control period, greatly reducing the computational amount of model prediction in each evaluation.

[0006] According to some embodiments, the solution of the present disclosure provides a model predictive voltage control method for a power inverter circuit of an energy router, adopting the following technical solutions:

[0007] A model predictive voltage control method for the power inverter circuit of an electric energy router, comprising:

[0008] Obtaining the time-domain state equation of the power inverter circuit of the electric energy router;

[0009] Performing discretization processing on the obtained time-domain state equation to obtain a discrete model of the power inverter circuit;

[0010] Canceling the predicted value of the inductor current in the obtained discrete model to obtain the desired output voltage equation of the discrete model;

[0011] Approximating and equating the predicted value of the current in the obtained desired output voltage equation to obtain a simplified discrete model based on the desired output voltage, and calculating the expected value of the output voltage of the power inverter circuit;

[0012] Constructing a candidate vector cost function according to the obtained expected value of the output voltage;

[0013] Evaluating the constructed candidate vector cost function to obtain the minimum value of the candidate vector;

[0014] Tracking the expected value of the output voltage according to the obtained minimum value of the candidate vector to achieve voltage control of the electric energy router.

[0015] As a further technical limitation, the time-domain state equation of the power inverter circuit of the electric energy router is obtained through Kirchhoff's law, and its expression in the α-β reference coordinate system is:

[0016]

[0017] Among them, i is the inductor current, v is the capacitor voltage, v i is the output voltage, i o is the load current, L is the inductor, and C is the capacitor.

[0018] Furthermore, the obtained time-domain state equation is discretized by using the backward Euler discretization method to obtain a discrete model of the power inverter circuit, and its expression in the α-β reference coordinate system is:

[0019]

[0020] Among them, T s is the control period; x(k) represents the value of the x variable at the k-th moment, and x(k + 1) represents the value of the x variable at the (k + 1)-th moment, where x represents v αβ 、i αβ 、i oαβ or v iαβ ; i αβ 、v αβ 、viαβ and \(i\) oαβ are respectively the inductor current, capacitor voltage, output voltage and load current in the α-β reference coordinate system.

[0021] Furthermore, the predicted value \(i\) αβ (k + 1) of the inductor current in the discrete model of the power inverter circuit is cancelled out by using the elimination method, and a discrete equation of the power inverter circuit with 5 variables is obtained. Its expression in the α-β reference coordinate system is as follows:

[0022]

[0023] wherein, is the desired output voltage, is the reference capacitor voltage, \(i\) αβ , \(v\) αβ , \(v\) iαβ and \(i\) oαβ are respectively the inductor current, capacitor voltage, output voltage and load current in the α-β reference coordinate system.

[0024] Furthermore, the difference between the inductor current and the load current is replaced by the capacitor current, and the predicted value of the current in the obtained desired output voltage equation is approximately equivalent, and a simplified discrete model based on the desired output voltage is obtained. Its expression in the α-β reference coordinate system is as follows:

[0025]

[0026] Furthermore, the reference coordinate system is not limited to the α-β reference coordinate system, d-q reference coordinate system and a-b-c reference coordinate system.

[0027] As a further technical limitation, the expected value of the output voltage and the candidate vectors are both evaluated cyclically.

[0028] As a further technical limitation, the expected value is linearly related to the reference value, and tracking the reference value can be equivalent to tracking the expected value; therefore, in order to realize the tracking of the expected value by the inverter circuit, the constructed candidate vector cost function is:

[0029]

[0030] wherein, \(v\) can (k + 1) is the candidate vector.

[0031] As a further technical limitation, the output expected value is linearly related to the reference value, and the tracking of the reference value by the inverter circuit can be equivalent to the tracking of the output expected value; when the optimal vector corresponding to the cost function acts on the inverter circuit, the output value of the inverter circuit is closest to the output expected value, that is, the effect of tracking the reference value is the best.

[0032] As a further technical limitation, the effects of the candidate vectors are evaluated, that is, the sizes of the cost functions corresponding to the candidate vectors are compared; the vector with the smallest corresponding cost function and the best effect is selected as the optimal vector; the obtained optimal vector is applied to the inverter circuit so that its output voltage tracks the expected value of the output voltage, thereby realizing voltage control of the power router; wherein the expected value of the output voltage is calculated from the reference value.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. The present disclosure adopts the backward Euler discretization method to simplify the discrete equation of the LC power inverter circuit of the AC port of the power router. The coefficients of the expression do not contain exponential and trigonometric function forms, which can reduce the amount of calculation and improve the model prediction calculation speed applied to the AC port of the power router.

[0035] 2. The present disclosure does not adopt a matrix calculation method, but instead uses the elimination method to combine two discrete equations to obtain a discrete equation with fewer variables, which simplifies the complexity of the calculation and is simple and reliable.

[0036] 3. In the present disclosure, the current load current value (or the current microgrid current value) approximately replaces the load current prediction value (or the microgrid current prediction value), which can omit the calculation process of the prediction value and further improve the calculation speed of the model prediction of the AC port of the power router.

[0037] 4. The present invention is based on a simplified model prediction method. The difference between the previous inductor current and the previous load current value (or the current microgrid current value) is replaced by the current inductor current value, reducing the variables of the discrete model to 4. The obtained discrete model based on the expected output voltage greatly simplifies the discrete form.

[0038] 5. In the present disclosure, within one control cycle, the candidate vector evaluation process based on the AC port of the power router only calculates the expected value of the output voltage of the LC-type power inverter circuit once, that is, before the output voltage value generated by the candidate vector is compared with the expected value, rather than directly participating in the calculation when the capacitor voltage value generated by the candidate vector is compared with the expected capacitor voltage value. Therefore, the expected value calculation process of the output voltage does not participate in the evaluation cycle, which greatly reduces the amount of calculation in the evaluation process.

[0039] 6. The present invention realizes optimal control of the optimal inverter output capacitor voltage based on a simplified prediction model and an optimized model prediction evaluation framework of an LC-type power inverter circuit in a discrete domain, and is suitable for a digital controller, which is of great significance for the application of the AC port of an electric energy router. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings forming a part of this disclosure are used to provide a further understanding of the disclosure. The schematic embodiments and descriptions thereof of the disclosure are used to explain the disclosure and do not constitute an improper limitation of the disclosure.

[0041] Figure 1 is a flowchart of a model predictive voltage control method for an LC-type power inverter circuit of an AC port of an electric energy router in an embodiment of the disclosure;

[0042] Figure 2 is a schematic control block diagram of an AC port of an electric energy router in an embodiment of the disclosure;

[0043] Figure 3 is a waveform diagram of the estimated value of the capacitor current under different load switching states in an embodiment of the disclosure;

[0044] Figure 4 is a schematic block diagram of an evaluation process in an embodiment of the disclosure;

[0045] Figure 5 is a waveform diagram of the capacitor voltage and a waveform diagram of the load current in an embodiment of the disclosure. Detailed implementation manners

[0046] The disclosure will be further described below in conjunction with the accompanying drawings and embodiments.

[0047] It should be noted that the following detailed descriptions are all exemplary and are intended to provide a further description of the disclosure. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the disclosure belongs.

[0048] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary implementation manners according to the disclosure. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0049] In the case of no conflict, the embodiments in the disclosure and the features in the embodiments can be combined with each other.

[0050] Embodiment

[0051] An embodiment of the disclosure introduces a model predictive voltage control method for a power inverter circuit of an electric energy router.

[0052] As Figure 1 shown, a model predictive voltage control method for a power inverter circuit of an electric energy router includes:

[0053] Step S01: Based on the state equation of the LC-type power inverter circuit at the AC port of the power electronic router, a discrete model of the LC-type power inverter circuit is obtained through discretization.

[0054] Step S02: Use the elimination method to cancel out the predicted value of the inductor current in the discrete model of the LC-type power inverter circuit.

[0055] Step S03: Approximately equate the current load current value (or the current microgrid current value) to the predicted load current value (or the predicted microgrid current value), and organize to obtain a discrete model based on the desired output voltage.

[0056] Step S04: The measurement of the capacitor current value is detected by a digital observer, reducing the number of sensors, optimizing the cost, and improving the performance of the power electronic router. After arrangement, a simplified discrete model based on the desired output voltage is obtained.

[0057] Step S05: During the evaluation process, first calculate the expected value of the output voltage of the LC-type power inverter circuit. Then evaluate the minimum value of the expected output voltage and the candidate vectors to achieve the control of the capacitor voltage for optimal inverter output.

[0058] As one or more embodiments, as Figure 2 shown, in Step S01, according to Kirchhoff's law, the state equation of the LC-type power inverter circuit is obtained, and its expression form is as follows

[0059]

[0060] where, i is the inductor current, v is the capacitor voltage, v i is the output voltage, i o is the load current (or microgrid current), L is the inductor, and C is the capacitor.

[0061] The state equation of the LC-type power inverter circuit is discretized using the backward Euler discretization method to obtain a discrete model, and its expression form in the α-β reference coordinate system is as follows

[0062]

[0063] where, T s is the control period, x(k) represents the value of the x variable (x = v αβ , i αβ , i oαβ , v iαβ ) at the k-th moment, and x(k + 1) represents the value of the x variable at the (k + 1)-th moment.

[0064] As one or more embodiments, in Step S02, use the elimination method to cancel out the predicted value of the inductor current i in the discrete model of the LC-type power inverter circuitαβ (k + 1) is cancelled out. After arrangement, the discrete equation of the LC-type power inverter circuit with five variables is obtained, and its expression in the α-β reference coordinate system is as follows

[0065]

[0066] Among them, is the expected output voltage, is the reference capacitor voltage.

[0067] As one or more embodiments, in step S03, the load current value (or microgrid current value) changes relatively slowly within a control period. To simplify the prediction calculation of the current i oαβ (k + 1), the predicted value of the load current (or predicted value of the microgrid current) i oαβ (k + 1) is approximately equivalent to the current load current value (or current microgrid current value) i oαβ (k). After arrangement, the simplified discrete equation of the LC-type power inverter circuit is obtained.

[0068] As one or more embodiments, in step S04, the difference between the inductor current i αβ and the predicted value of the load current (or predicted value of the microgrid current) i αβ can be equivalent to the capacitor current i Cαβ , and its expression in the α-β reference coordinate system is as follows

[0069] i Cαβ (k) = i αβ (k) - i oαβ (k)

[0070] Among them, i Cαβ (k) is the capacitor current at the k-th moment.

[0071] Therefore, within a control period, substituting the capacitor current into the discrete model based on the expected output voltage, the simplified discrete equation is obtained, and its expression in the α-β reference coordinate system is as follows

[0072]

[0073] To optimize the cost and improve the system performance, the measurement of the capacitor current value is changed from being detected by a current sensor to being detected by a digital observer. Taking the Kalman digital observer as an example, its expression is as follows

[0074] X - (k) = FX - (k - 1) + Bu(k - 1)

[0075] P - (k) = F(k)P(k - 1)F(k)T +Q(k - 1)

[0076] K(k) = P - (k)H T [HP - (k)H T +R(k)] -1

[0077] X(k) = X - (k)+K(k)[Z(k)-HX - (k)]

[0078] P(k)=[I - K(k)H]P - (k)

[0079] Wherein, X - is the state vector, F is the transition matrix, B is the noise input matrix, u is the process noise, P - is the estimation error variance matrix, Q is the symmetric non - negative definite variance matrix of the system process noise, K is the filter gain matrix, H is the observation matrix, R is the symmetric positive definite variance matrix of the observation noise, X is the state estimation, Z is the observation sequence of the system, P is the estimation error variance matrix, and I is the identity matrix.

[0080] As Figure 3 shown in the capacitive current waveform diagram of the digital observer, it can be obtained from the simulation results that the capacitive current waveform obtained by the digital observer is basically the same as the waveform measured by the sensor.

[0081] As one or more embodiments, in step S05, to achieve the optimal control of the port voltage of the power router, the model - predictive capacitive current detection process of this embodiment is as Figure 4 shown. In one control period, the capacitive voltage reference value participates in the simplified model of the LC - type power inverter circuit based on the desired voltage, and then the expected value of the output voltage is calculated, that is, the expected value is linearly related to the reference value. Tracking the port voltage reference value of the power router can be equivalent to tracking the expected value of the inverter circuit. Therefore, a cost function CF of the candidate vector and the expected value is constructed, and its expression is as follows:

[0082]

[0083] Wherein, v can (k + 1) is the candidate vector.

[0084] Evaluate the difference between the voltage value generated when the candidate vector acts on the inverter circuit and the expected value, that is, the cost function CF. Finally, select the vector corresponding to the minimum cost function min(CF) as the optimal candidate vector, so that the inverter circuit can achieve the tracking of the expected value of the output voltage, and then achieve the tracking of the port voltage reference value of the power router.

[0085] As one or more embodiments, within one control period, the expected value of the output voltage is calculated only once; the expected value of the output voltage and the candidate vectors participate in the evaluation loop.

[0086] Such as Figure 5 As shown in the output voltage waveform and current of the power router port, it can be seen from the simulation results that the output capacitor waveform of the LC-type power inverter circuit using the method of this embodiment can be well adjusted, and the power router port works normally.

[0087] From the above simulation results, it can be known that a model predictive voltage control method for the power inverter circuit of the power router proposed in this embodiment can effectively improve the performance of the power router.

[0088] This embodiment simplifies the model predictive control process of the LC-type power inverter circuit by using methods such as the backward Euler discretization simplification method, approximation of the predicted value of the load current (microgrid current), digital observer estimation, and simplified evaluation framework, and realizes the effective control of the capacitor voltage of the LC-type power inverter circuit under the requirement of lower computing resources. This embodiment can greatly simplify the model predictive voltage control method of the LC-type power inverter circuit, and the implementation method is simple and reliable, and has high research and application significance.

[0089] It can be understood that this embodiment is a real-time optimization process. Based on the simplified model predictive method of the LC-type power inverter circuit, it realizes the optimal regulation of the power router port voltage under different states and improves the performance of the power router.

[0090] It can be understood that all the calculations in this embodiment are not limited to the α-β reference coordinate system, d-q reference coordinate system, a-b-c reference coordinate system. This disclosure is not limited to the actual requirements of a specific microgrid, nor is it limited to the LC-type power inverter topology, and is applicable to the forms of single-phase and three-phase busbars of the microgrid. At the same time, this embodiment is not limited to the DC-side power supply form of the power inverter topology, and is applicable to different occasions such as low voltage, medium voltage, and high voltage, and has strong scalability and practicability. In addition, this embodiment is not limited to the inverter state of the power inverter topology, and is also applicable to the rectifier state.

[0091] Although the specific implementation manners of the present disclosure have been described above in conjunction with the accompanying drawings, it is not a limitation to the protection scope of the present disclosure. Those skilled in the art should understand that, based on the technical solutions of the present disclosure, various modifications or deformations that can be made by those skilled in the art without creative efforts are still within the protection scope of the present disclosure.

Claims

1. A model predictive voltage control method for the power inverter circuit of an electric energy router, characterized in that, it includes: Obtain the time-domain state equation of the power inverter circuit of the electric energy router; Perform discretization processing on the obtained time-domain state equation to obtain the discrete model of the power inverter circuit; Cancel the predicted value of the inductor current in the obtained discrete model to obtain the expected output voltage equation of the discrete model; Perform approximate equivalence of the predicted value of the current on the obtained expected output voltage equation to obtain a simplified discrete model based on the expected output voltage, and calculate the expected value of the output voltage of the power inverter circuit; Construct a candidate vector cost function according to the obtained expected value of the output voltage; Evaluate the constructed candidate vector cost function to obtain the minimum value of the candidate vector; According to the obtained minimum value of the candidate vector, track the expected value of the output voltage to achieve voltage control of the electric energy router; Obtain the time-domain state equation of the power inverter circuit of the electric energy router through Kirchhoff's law, and its expression in the α-β reference coordinate system is: where i is the inductor current, v is the capacitor voltage, v i is the output voltage, i o is the load current, L is the inductor, and C is the capacitor; Use the backward Euler discretization method to perform discretization processing on the obtained time-domain state equation to obtain the discrete model of the power inverter circuit, and its expression in the α-β reference coordinate system is: where T s is the control period; x(k) represents the value of the x variable at time k, and x(k + 1) represents the value of the x variable at time k + 1, where x represents v αβ , i αβ , i oαβ or v iαβ ; i αβ , v αβ , v iαβ and i oαβ are the inductor current, capacitor voltage, output voltage, and load current in the α-β reference coordinate system, respectively; Using the elimination method to cancel out the predicted value \(i_{L}(k + 1)\) of the inductor current in the discrete model of the power inverter circuit, a discrete equation of the power inverter circuit with 5 variables is obtained, and its expression in the α-β reference coordinate system is as follows: αβ (k + 1), and a discrete equation of the power inverter circuit with five variables is obtained. Its expression in the α-β reference coordinate system is: Among them, is the expected output voltage, is the reference capacitor voltage, i αβ 、v αβ 、v iαβ and i oαβ are the inductor current, capacitor voltage, output voltage and load current in the α-β reference coordinate system, respectively; Replace the difference between the inductor current and the load current with the capacitor current, and approximately equivalent the predicted current value of the obtained desired output voltage equation to obtain a simplified discrete model based on the desired output voltage. Its expression in the α-β reference coordinate system is: where, i Cαβ (k) is the capacitor current at the k-th moment; The expected value is linearly correlated with the reference value, and tracking the reference value can be equivalently regarded as tracking the expected value; the constructed candidate vector cost function is as follows: where, v can (k + 1) is the candidate vector.

2. A model predictive voltage control method for the power inverter circuit of an electric energy router as described in claim 1, characterized in that, The reference coordinate system is not limited to the α-β reference coordinate system, the d-q reference coordinate system, and the a-b-c reference coordinate system.

3. A model predictive voltage control method for the power inverter circuit of an electric energy router as described in claim 1, characterized in that, Both the expected value of the output voltage and the candidate vector are evaluated in a loop.

4. A model predictive voltage control method for the power inverter circuit of an electric energy router as described in claim 1, characterized in that, The expected output value is linearly related to the reference value, and the tracking of the reference value by the inverter circuit can be equivalent to the tracking of the expected output value; when the optimal vector corresponding to the cost function acts on the inverter circuit, the output value of the inverter circuit is closest to the expected output value, that is, the effect of tracking the reference value is the best.

5. A model predictive voltage control method for the power inverter circuit of an electric energy router as described in claim 1, characterized in that, Evaluate the effect of the candidate vector, that is, compare the magnitudes of the cost functions corresponding to the candidate vectors; select the vector with the smallest corresponding cost function and the best effect as the optimal vector; apply the obtained optimal vector to the inverter circuit to make its output voltage track the expected value of the output voltage, and achieve voltage control of the electric energy router; wherein, the expected value of the output voltage is calculated from the reference value.

Images