CN114509945B - Dynamic reference prediction control method and system for two-stage solid-state transformer - Google Patents
Dynamic reference prediction control method and system for two-stage solid-state transformer Download PDFInfo
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Abstract
The present disclosure provides a dynamic reference prediction control method and system for a two-stage solid-state transformer, the method comprising the steps of: acquiring control target parameter data of a transformer at the current moment; setting a calculation formula of a real-time dynamic reference value of each control target according to the control step length of the current control target reaching the fixed reference value, and calculating to obtain the real-time dynamic reference value of each control target parameter; and constructing a cost function by taking the minimum difference value between the transformer control target parameter data and the corresponding real-time dynamic reference value as a target, and solving the constructed two-stage solid-state transformer system model according to the real-time dynamic reference value to minimize the value of the cost function to obtain the control parameter of the transformer at the next moment and control the converter of the transformer. The use of an outer ring of a controller is eliminated in the predictive control of the transformer, the overall dynamic characteristics of the solid-state transformer are effectively improved, and the regulating capability is improved.
Description
Technical Field
The disclosure relates to the technical field of transformer control, in particular to a dynamic reference prediction control method and a dynamic reference prediction control system for a two-stage solid-state transformer.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
In a two-stage solid-state transformer control strategy, a more mature scheme is a cascade control structure based on a multi-linear controller (such as a proportional integral PI controller). Namely, two stages of the solid-state transformer are respectively controlled by a set of cascade control system: in each stage of conversion system, the inner loop reference value is output in real time through the outer loop PI controller, and then the modulation command of the stage is output by the inner loop PI controller; such control strategies suffer from the following principle drawbacks: (1) Belongs to 'correction after error' type control, and cannot guarantee the dynamic performance of a control target; (2) The optimization method with limited control targets is difficult to consider for a plurality of control targets of the solid-state transformer; (3) Not flexibly containing various nonlinear constraints (such as switching frequency, heat dissipation requirement, etc.); (4) In the aspects of dynamic characteristics, regulation range and regulation capability, the DC/DC stage of the solid-state transformer is usually far higher than the rectification stage of the solid-state transformer, and direct current bus fluctuation and even instability are easily caused by no linkage between the two poles.
The model predictive control is used as an emerging third generation control strategy, and becomes a more promising control method for the solid-state transformer, and the use of the model predictive control effectively improves the response speed of the inner ring of the solid-state transformer, so that the problem of the control of the multi-linear controller is solved to a certain extent. However, the rectifier stage outer loop of the model predictive control still uses PI as its controller. The dynamic characteristic of the control system depends on the outer ring, so that the overall dynamic characteristic cannot be greatly improved. This problem will be more pronounced especially in view of the frequent bi-directional power flows in the new distribution network. The same problem is faced by the DC/DC stage of a solid state transformer. On the other hand, the DC/DC stage requires n-1 (n is the number of modules) input voltage balancing control loops. The essence of the method is that an inner loop model predictive control correction term is generated according to the difference value between the real-time input voltage and the average voltage of the module. For the cost function of model predictive control, the reference command at this time is not a global optimal command, and thus the solution obtained is not a global optimal solution. The regulation capability of the control system on the low-voltage direct-current bus and the balancing capability of the input voltage are limited to a certain extent.
In summary, the dynamic characteristics of the conventional model predictive control applied to the two-stage solid-state transformer mainly depend on the outer ring, resulting in lower dynamic characteristics. Meanwhile, the cost function of the controller of the traditional model predictive control cannot solve the optimal solution in real time, and the adjusting capacity of the controller is limited.
Disclosure of Invention
In order to solve the problems, the present disclosure provides a dynamic reference prediction control method and system for a two-stage solid-state transformer, which eliminates the use of an outer ring of a controller in the prediction control of the transformer, effectively improves the overall dynamic characteristics of the solid-state transformer, and improves the adjustment capability.
In order to achieve the above purpose, the present disclosure adopts the following technical scheme:
one or more embodiments provide a dynamic reference prediction control method for a two-stage solid-state transformer, including the steps of:
acquiring control target parameter data of a transformer at the current moment;
setting a calculation formula of a real-time dynamic reference value of each control target according to the control step length of the current control target reaching the fixed reference value, and calculating to obtain the real-time dynamic reference value of each control target parameter;
and constructing a cost function by taking the minimum difference value between the transformer control target parameter data and the corresponding real-time dynamic reference value as a target, and solving the constructed two-stage solid-state transformer system model according to the real-time dynamic reference value and the acquired control target parameter data to ensure that the value of the cost function is minimum, so as to acquire the control parameter of the transformer at the next moment and control the converter of the transformer.
One or more embodiments provide a dynamic reference predictive control system for a dual-stage solid state transformer, comprising:
the acquisition module is used for: is configured to acquire control target parameter data of the transformer at the current moment;
and a reference value updating module: the control method comprises the steps of setting a calculation formula of a real-time dynamic reference value of each control target according to a control step length of a current control target reaching a fixed reference value, and calculating to obtain the real-time dynamic reference value of each control target parameter;
and a solving control module: the method comprises the steps of setting up a cost function by taking the minimum difference value of transformer control target parameter data and a corresponding real-time dynamic reference value as a target, and obtaining control parameters of a transformer at the next moment and controlling a converter of the transformer according to the real-time dynamic reference value and the acquired control target parameter data so as to enable the value of the cost function to be minimum, solving the built two-stage solid-state transformer system model.
An electronic device comprising a memory and a processor and computer instructions stored on the memory and running on the processor, which when executed by the processor, perform the steps of the method described above.
A computer readable storage medium storing computer instructions which, when executed by a processor, perform the steps of the method described above.
Compared with the prior art, the beneficial effects of the present disclosure are:
the outer ring based on the PI controller, which is used by each stage of the solid-state transformer, is removed, all control targets can be controlled by each stage through only one cost function, the system bandwidth is greatly improved, and the overall response speed of the system is greatly improved. Meanwhile, the DC/DC stage can directly solve the optimal solution under the input balance and output voltage reference command through the cost function, and the adjusting capability of the DC/DC stage is improved.
The advantages of the present disclosure, as well as those of additional aspects, will be described in detail in the following detailed description of embodiments.
Drawings
The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate and explain the exemplary embodiments of the disclosure and together with the description serve to explain and do not limit the disclosure.
FIG. 1 is a single-phase circuit topology of a dual-stage solid-state transformer diagram of embodiment 1 of the present disclosure;
fig. 2 (a) is a two-level converter topology employed by a rectifying stage module of the transformer of embodiment 1 of the present disclosure;
fig. 2 (b) is a three-level converter topology employed by the rectifier stage module of the transformer of embodiment 1 of the present disclosure;
FIG. 2 (c) is a topology of a dual active bridge converter employed by a DC/DC stage module of the transformer of embodiment 1 of the present disclosure;
FIG. 3 is a dynamic reference predictive control block diagram of a two-stage solid state transformer of embodiment 1 of the present disclosure;
fig. 4 is a flowchart of a dynamic reference prediction control method of a two-stage solid-state transformer according to embodiment 1 of the present disclosure.
The specific embodiment is as follows:
the disclosure is further described below with reference to the drawings and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments in accordance with the present disclosure. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof. It should be noted that, without conflict, the various embodiments and features of the embodiments in the present disclosure may be combined with each other. The embodiments will be described in detail below with reference to the accompanying drawings.
Example 1
As shown in fig. 1, a two-stage solid state transformer single phase topology may be as shown in fig. 1. The transformer AC side is connected with a medium-voltage AC distribution network, a medium-voltage DC bus is formed through a rectification-level converter, and a low-voltage DC bus is formed through a DC/DC-level converter. The low-voltage direct current bus can be connected into energy storage and new energy sources or used as a low-voltage direct current power grid interface.
In one or more embodiments, as shown in fig. 1 to 4, a dynamic reference prediction control method for a two-stage solid-state transformer includes the following steps:
step 1: acquiring control target parameter data of a transformer at the current moment;
step 2: according to the transformation relation of all levels of converters in the transformer, constructing a system model of the two-stage solid-state transformer for predicting the parameter data of the next moment through the parameter data of the current moment;
step 3: setting a calculation formula of a real-time dynamic reference value of each control target according to the control step length of the current control target reaching the fixed reference value, and calculating to obtain the real-time dynamic reference value of each control target parameter;
step 4: and constructing a cost function by taking the minimum difference value between the control target parameter data of the transformer and the corresponding real-time dynamic reference value as a target, solving a system model to enable the value of the cost function to be minimum according to the real-time dynamic reference value and the acquired control target parameter data, acquiring the optimal modulation ratio of the rectifier stage converter of the transformer and the optimal moving angle of the DC/DC stage converter at the next moment, and controlling the on-off of the converter switching tube of the transformer.
In the embodiment, the outer ring based on the PI controller used by each stage of the solid-state transformer is removed, and each stage can control all control targets only through one cost function, so that the system bandwidth is greatly improved, and the overall response speed of the system is greatly improved. Meanwhile, the DC/DC stage can directly solve the optimal solution under the input balance and output voltage reference command through the cost function, and the adjusting capability of the DC/DC stage is improved.
Step 1: the transformer control target parameters include control target parameters of the transformer rectifier stage module and control target parameters of the transformer DC/DC stage module.
The control target parameters of the transformer rectifying stage module include: net side active power P g Reactive power Q at network side g Medium voltage DC bus voltage Sigma U dc ；
The control target parameters of the transformer DC/DC stage module include: the low-voltage direct-current voltage and the DC/DC stage module balance voltage;
a dynamic reference predictive control block diagram of a two-stage solid state transformer is shown in fig. 3.
In step 1, obtaining the transformer control target parameter data at the current moment, which specifically comprises the following steps:
step 11: acquiring network-side voltages, currents, and converting the sensor samples to an alpha-beta coordinate system, e.g. U in the figure g α[k+1]And U g β[k+1]The active power P of the current network side is calculated by a power calculation formula g Reactive power Q g ；
Step 12: obtaining capacitance voltage U of rectifier module sampled by sensor dci The voltage of each module is added to obtain the current medium voltage DC bus voltage value Sigma U dc 。
Step 13: the current medium-voltage direct-current bus voltage value Sigma U dc Dividing the average voltage by the number n of the rectifying stage modules to obtain the average voltage U of the rectifying stage modules dc_av The average voltage is the reference value for the balance control of the DC/DC stage.
In step 2, the system model of the two-stage solid-state transformer comprises a prediction model of a rectifying stage and a prediction model of a DC/DC stage, and the construction process is as follows:
in order to simplify the analysis, in this embodiment, a two-level converter is taken as an example to perform the analysis by using a rectifying stage module, and only the system model of the a phase of the solid-state transformer is analyzed, and the other two phases can be analogized according to the a phase model.
The single-phase topology of the two-stage solid-state transformer in fig. 1 is an input series and input parallel structure as a whole, and can realize bidirectional flow of power, namely four-quadrant operation.
Alternatively, the rectifying stage of the two-stage solid-state transformer may be a two-level converter, as shown in fig. 2 (a); or a three-level converter as shown in fig. 2 (b); the DC/DC stage may be a dual active bridge converter as shown in fig. 2 (c).
As shown in fig. 1, the a-phase of the two-stage solid-state transformer includes an inductor L g Parasitic resistance R g The method comprises the steps of carrying out a first treatment on the surface of the Module medium-voltage direct-current bus capacitor C 1 Low-voltage direct-current bus capacitor C 2 The method comprises the steps of carrying out a first treatment on the surface of the The direction of current flowing from the power grid into the solid state transformer is defined as the positive direction and is denoted as i g The grid voltage is u g The voltage of the ith module of the medium-voltage direct-current bus is U dci The converter port to ground voltage is u conv 。
The network side power dynamic model is as follows:
wherein P is g 、Q g Active power and reactive power of the network side are respectively; u (u) gα 、u gβ 、u convα 、u convβ Real axis and imaginary axis components of the grid voltage and the converter port voltage respectively; u (u) gm Is the magnitude of the grid voltage.
The control target of the rectifying stage module is the medium-voltage direct-current bus voltage, so that the dynamic model of the medium-voltage direct-current bus voltage is as follows:
wherein I is ini And I outi The current input to the capacitor and the current output from the capacitor by the ith module respectively.
The converter port voltage and each sub-module DC voltage relationship is as follows:
where d is the modulation ratio of the rectifying stage.
The relationship between the direct current output current of the rectifying stage module and the network side current is as follows:
I in ＝i gα d α +i gβ d β (5)
wherein I is in Is the sum of all module direct current output currents (I in ＝∑I ini )；d α And d β The real axis component and the imaginary axis component of the modulation ratio of the rectification stage are respectively.
Since model predictive control needs to be completed in a discrete space, the formulas (1) - (3) are discretized by a forward euler formula, so that a discrete model of the ac side system, namely a predictive model of a rectifying stage, such as formulas (6) - (8), can be obtained:
Q g [k+1]＝t 1 Q g [k]+t 2 P g [k]+t 3 (u gα [k]u convβ [k]-u gβ [k]u convα [k]) (7)
wherein t is 1 ＝1-R g T sc /L g ，t 2 ＝w g T sc ，t 3 ＝Tsc/Lg，t 4 ＝nT sc /C 1 N is the number of rectifying stage modules, T sc Is the sampling frequency of the rectifying stage.
The control objective of the DC/DC stage is to keep the low voltage DC bus voltage track of its reference value and to balance the DC/DC stage module input voltage,
the control objective of the DC/DC stage is to make the voltage of the low-voltage direct current bus track the reference value, namely: uo=uo; another objective of the DC/DC stage is to control the balancing of the DC/DC stage module input voltages, even if the input voltage of each DC/DC stage module is the average of all input voltages, i.e.: u (U) dc1 ＝U dc2 ＝…＝U dci＝ ∑U dc /n。
The dynamic equation of the low-voltage direct current bus is:
wherein I is 1i Outputting a current for the ith DC/DC stage module; i oi Is the load current of the ith DC/DC stage module. The DC/DC stage module is a DC/DC converter.
The dynamic equation of the input voltage of the DC/DC stage module is as follows:
input current I of DC/DC stage module outi Output current I 1i Angle of movement D with the stage module i The relationship of (2) is as follows:
wherein k is the transformation ratio of the high-frequency transformer of the DC/DC level module; l (L) k Leakage inductance which is folded to the primary side of the high-frequency transformer; f (f) sd Is the switching frequency of the DC/DC stage module.
Because model predictive control needs to be completed in a discrete space, the formulas (9) and (10) are discretized through a forward Euler formula, and a discrete model of the low-voltage direct-current side system can be obtained, namely a DC/DC-level predictive model is as follows:
U oi [k+1]＝U oi [k]+k 2 [I 1i [k]-I oi [k]) (13)
U dci [k+1]＝U dci [k]+k 1 (I ini [k]-I outi [k]) (14)
wherein k2=t sd /C 2 ，T sd Sampling frequency of the DC/DC stage module; k1 =t sd /C 1 。
Obtaining a prediction model of the rectification stage through formulas (6) - (8); and obtaining a DC/DC level prediction model through formulas (13) and (14).
In the solving process in step 4, the system model is solved, wherein Σi required in the equation (8) out [k]An optimal shift angle D that can be solved for by equation (11) and the current DC/DC stage cost function i [k]Obtained. I required in equation (14) ini [k]Can be calculated from equation (5) and the current rectifier stage cost functionThe optimal modulation ratio d [ k ] is solved]Obtained.
In step 4, a cost function is built by taking the minimum difference value between the transformer control target parameter data and the corresponding real-time dynamic reference value as a target, wherein the cost function comprises a cost function of the rectifying stage module and a cost function of the DC/DC stage module.
The model predictive control essence is the problem of solving the optimal solution that minimizes the cost function. The control of the rectifying stage and the DC/DC stage on the respective control targets is only completed by the own cost function, and the use of an external ring based on PI is avoided.
In this embodiment, the control target parameters of the rectifying stage of the transformer include: network side active power, network side reactive power and medium voltage direct current bus voltage.
The cost function of the rectifier stage module of the transformer is: and the transformer rectifying stage module is used for weighting and summing the differences between each control target parameter and the corresponding control target parameter reference value.
The optimal solution to solve the cost function is the solution to minimize the cost function. The cost function of the rectifier stage module is as follows:
in this embodiment, the transformer DC/DC stage control target includes a low voltage direct current voltage and a DC/DC stage module balance voltage.
The cost function of the DC/DC stage module of the transformer is: the transformer DC/DC stage module is used for weighting and summing the differences between each control target parameter and the corresponding control target parameter reference value. The optimal solution to solve the cost function is the solution to minimize the cost function.
The cost function of the DC/DC stage module is as follows:
in step 3, according to the control step length that the current control target reaches the fixed reference value, a calculation formula of a real-time dynamic reference value of each control target of the rectifying stage is set, wherein the calculation formula comprises a voltage reference value of a medium-voltage direct-current bus, a dynamic reference value of active power of a transformer network side and a reference value of reactive power of the network side.
The voltage reference value calculation formula of the medium-voltage direct current bus is as follows:
wherein U is dc_ref U is a fixed reference value of a medium-voltage direct-current bus * dc [k+1]The real-time reference value of the medium-voltage direct-current bus at the next moment; u (U) dc [k]For the voltage of the medium-voltage direct-current bus at the current moment, ns is the step length, i.e. how many control periods are needed to reach the real-time dynamic reference value U * dc [k+1]。
Voltage reference value of medium voltage dc bus, specifically: and controlling the sum of the single-step adjustment value of the medium-voltage direct-current bus voltage close to the fixed target reference value and the medium-voltage direct-current bus voltage value at the last moment.
It can be seen that the medium voltage dc bus voltage is updated in real time every control period, and is updated step by step according to the adjusted voltage adjustment value. Compared with the regulation and control of a fixed reference value, the accuracy of voltage regulation can be improved by dynamically updating the reference value in real time.
The dynamic reference values of the active power of the transformer network side comprise: correction term P for real-time error between current value and fixed reference value gcom [k]The dynamic reference value of the active power of the transformer network side is specifically as follows:
wherein I is ^ o DC/DC stage module load current I observed by observer oi And (3) summing; i * dc [k+1]To meet Sigma U * dc [k+1]Capacitor charge (discharge) current under reference, U * dc [k+1]The real-time reference value of the medium-voltage direct-current bus at the next moment; p (P) gcom [k]Is an error correction term.
Capacitor charging (discharging) current I in the above * dc [k+1]The following formula should be satisfied:
to eliminate the parameter error of the system or the error caused by low switching frequency, a correction term P is added to the network side active power reference of the system gcom [k]The term is shown as follows:
the correction term P gcom [k]The real-time error between the current value and the fixed reference value is included, so that the error caused by parameter error or low switching frequency is eliminated.
The reference values for the network side reactive power are as follows:
solving the real-time reference value in the step 3, wherein the reference value U is fixed by the medium-voltage direct-current voltage dc_ref Network side reactive fixed reference value Q g_ref Medium voltage d.c. voltage sigma U at present moment dc [k]And the sum of the module load currents I observed by the observer ^ o [k]The rectification stage real-time dynamic reference value P can be generated by formulas (17), (18) and (21) * g [k+1]、Q * g [k+1]、∑U * dc [k+1]。
The dynamic reference prediction control method provided by the embodiment improves the overall dynamic characteristics of the system and increases the adjusting capability of the system. According to the method, the PI-based outer ring controller used by each stage is removed, all control targets can be controlled by each stage through only one cost function, the system bandwidth is greatly improved, and the overall response speed of the system is greatly improved. The DC/DC stage can directly solve the optimal solution under the input balance and output voltage reference command simultaneously through the cost function, and the adjusting capability of the stage is improved.
Example 2
Based on embodiment 1, this embodiment provides a dynamic reference prediction control system of a two-stage solid-state transformer, including:
the acquisition module is used for: is configured to acquire control target parameter data of the transformer at the current moment;
and a reference value updating module: the control method comprises the steps of setting a calculation formula of a real-time dynamic reference value of each control target according to a control step length of a current control target reaching a fixed reference value, and calculating to obtain the real-time dynamic reference value of each control target parameter;
and a solving control module: the method comprises the steps of setting up a cost function by taking the minimum difference value of transformer control target parameter data and a corresponding real-time dynamic reference value as a target, solving the built two-stage solid-state transformer system model according to the real-time dynamic reference value to enable the value of the cost function to be minimum, obtaining control parameters of a transformer at the next moment, and controlling a converter of the transformer.
Example 3
The present embodiment provides an electronic device comprising a memory and a processor, and computer instructions stored on the memory and running on the processor, which when executed by the processor, perform the steps recited in the method of embodiment 1.
Example 4
The present embodiment provides a computer readable storage medium storing computer instructions that, when executed by a processor, perform the steps of the method of embodiment 1.
The foregoing description of the preferred embodiments of the present disclosure is provided only and not intended to limit the disclosure so that various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.
While the specific embodiments of the present disclosure have been described above with reference to the drawings, it should be understood that the present disclosure is not limited to the embodiments, and that various modifications and changes can be made by one skilled in the art without inventive effort on the basis of the technical solutions of the present disclosure while remaining within the scope of the present disclosure.
Claims (8)
1. The dynamic reference prediction control method for the double-stage solid-state transformer is characterized by comprising the following steps of:
acquiring transformer control target parameter data at the current moment;
the control parameters of the transformer comprise the optimal modulation ratio of the rectifier stage converter and the optimal direction-shifting angle of the DC/DC stage converter;
the control target parameters of the transformer rectifying stage module include: network side active power, network side reactive power and medium voltage direct current bus voltage;
the control target parameters of the transformer DC/DC stage module include: the low-voltage direct-current voltage and the DC/DC stage module balance voltage;
setting a calculation formula of a real-time dynamic reference value of each control target according to the control step length of the current control target reaching the fixed reference value, and calculating to obtain the real-time dynamic reference value of each control target parameter;
the calculation formula of the real-time dynamic reference value of each control target of the rectifying stage comprises the calculation formulas of the voltage reference value of the medium-voltage direct-current bus, the dynamic reference value of the active power of the transformer network side and the reference value of the reactive power of the network side;
the calculation of the dynamic reference value of the active power at the transformer network side comprises a correction term of real-time error between the current value and the fixed reference value;
constructing a cost function by taking the minimum difference value between the transformer control target parameter data and the corresponding real-time dynamic reference value as a target, and according to the real-time dynamic reference value and the acquired control target parameter data, solving the constructed two-stage solid-state transformer system model with the minimum value of the cost function to acquire the control parameter of the transformer at the next moment and control the converter of the transformer;
the voltage reference value calculation formula of the medium-voltage direct-current bus is as follows:
wherein U is dc_ref U is a fixed reference value of a medium-voltage direct-current bus * dc [k+1]The real-time reference value of the medium-voltage direct-current bus at the next moment; u (U) dc [k]For the medium voltage dc bus voltage at the current time, ns is the step size, i.e. how many control cycles are needed to reach the real-time dynamic reference value U * dc [k+1]；
The dynamic reference value calculation formula of the active power at the transformer network side is as follows:
wherein I≡ o DC/DC stage module load current I observed by observer oi And (3) summing; i * dc [k+1]To meet Sigma U * dc [k+1]Capacitor charge (discharge) current under reference, U * dc [k+1]The real-time reference value of the medium-voltage direct-current bus at the next moment; p (P) gcom [k]Is an error correction term;
the calculation formula of the reference value of the network side reactive power is as follows:
the prediction model of the rectification stage is as follows:
Q g [k+1]＝t 1 Q g [k]+t 2 P g [k]+t 3 (u gα [k]u convβ [k]-u gβ [k]u convα [k])
wherein t is 1 ＝1-R g T sc /L g ，t 2 ＝w g T sc ，t 3 ＝Tsc/Lg，t 4 ＝nT sc /C 1 N is the number of rectifying stage modules, T sc Is the sampling frequency of the rectifying stage;
the predictive model of the DC/DC stage is as follows:
U oi [k+1]＝U oi [k]+k 2 (I 1i [k]-I oi [k])
U dci [k+1]＝U dci [k]+k 1 (I ini [k]-I outi [k])
wherein k2=t sd /C 2 ，T sd Sampling frequency of the DC/DC stage module; k1 =t sd /C 1 ；
The cost function of the rectifier stage module is as follows:
the cost function of the DC/DC stage module is as follows:
2. the dynamic reference prediction control method for a two-stage solid-state transformer according to claim 1, wherein: and constructing a system model of the two-stage solid-state transformer for predicting the parameter data at the next moment according to the transformation relation of all stages of converters in the transformer, wherein the system model comprises a prediction model of a rectifying stage and a prediction model of a DC/DC stage.
3. The dynamic reference prediction control method for a two-stage solid-state transformer according to claim 1, wherein: a cost function comprising a cost function of the rectifier stage module and a cost function of the DC/DC stage module; the cost function of the rectifier stage module of the transformer is: and the transformer rectifying stage module is used for weighting and summing the differences between each control target parameter and the corresponding control target parameter reference value.
4. The dynamic reference prediction control method for a two-stage solid-state transformer according to claim 3, wherein: the cost function of the DC/DC stage module of the transformer is: the transformer DC/DC stage module is used for weighting and summing the differences between each control target parameter and the corresponding control target parameter reference value.
5. The dynamic reference prediction control method for a two-stage solid-state transformer according to claim 1, wherein: the voltage reference value of the medium-voltage direct current bus is as follows: and controlling the sum of the single-step adjustment value of the medium-voltage direct-current bus voltage close to the fixed target reference value and the medium-voltage direct-current bus voltage value at the last moment.
6. A dynamic reference predictive control system for a two-stage solid state transformer, comprising:
the acquisition module is used for: is configured to acquire control target parameter data of the transformer at the current moment;
the control parameters of the transformer comprise the optimal modulation ratio of the rectifier stage converter and the optimal direction-shifting angle of the DC/DC stage converter;
the control target parameters of the transformer rectifying stage module include: network side active power, network side reactive power and medium voltage direct current bus voltage;
the control target parameters of the transformer DC/DC stage module include: the low-voltage direct-current voltage and the DC/DC stage module balance voltage;
and a reference value updating module: the control method comprises the steps of setting a calculation formula of a real-time dynamic reference value of each control target according to a control step length of a current control target reaching a fixed reference value, and calculating to obtain the real-time dynamic reference value of each control target parameter;
the calculation formula of the real-time dynamic reference value of each control target of the rectifying stage comprises the calculation formulas of the voltage reference value of the medium-voltage direct-current bus, the dynamic reference value of the active power of the transformer network side and the reference value of the reactive power of the network side;
the calculation of the dynamic reference value of the active power at the transformer network side comprises a correction term of real-time error between the current value and the fixed reference value;
and a solving control module: the system is configured to be used for constructing a cost function by taking the minimum difference value between the transformer control target parameter data and the corresponding real-time dynamic reference value as a target, and according to the real-time dynamic reference value, the constructed two-stage solid-state transformer system model is solved according to the minimum value of the cost function, so that the control parameter of the transformer at the next moment is obtained, and the converter of the transformer is controlled;
the voltage reference value calculation formula of the medium-voltage direct-current bus is as follows:
wherein U is dc_ref U is a fixed reference value of a medium-voltage direct-current bus * dc [k+1]The real-time reference value of the medium-voltage direct-current bus at the next moment; u (U) dc [k]For the medium voltage dc bus voltage at the current time, ns is the step size, i.e. how many control cycles are needed to reach the real-time dynamic reference value U * dc [k+1]；
The dynamic reference value calculation formula of the active power at the transformer network side is as follows:
wherein I is ^ o DC/DC stage module load current I observed by observer oi And (3) summing; i * dc [k+1]To meet Sigma U * dc [k+1]Capacitor charge (discharge) current under reference, U * dc [k+1]The real-time reference value of the medium-voltage direct-current bus at the next moment; p (P) gcom [k]Is an error correction term;
the calculation formula of the reference value of the network side reactive power is as follows:
the prediction model of the rectification stage is as follows:
Q g [k+1]＝t l Q g [k]+t 2 P g [k]+t 3 (u gα [k]u convβ [k]-u gβ [k]u convα [k])
wherein t is 1 ＝1-R g T sc /L g ，t 2 ＝w g T sc ，t 3 ＝Tsc/Lg，t 4 ＝nT sc /C 1 N is the number of rectifying stage modules, T sc Is the sampling frequency of the rectifying stage;
the predictive model of the DC/DC stage is as follows:
U oi [k+1]＝U oi [k]+k 2 (I 1i [k]-I oi [k])
U dci [k+1]＝U dci [k]+k 1 (I ini [k]-I outi [k])
wherein k2=t sd /C 2 ，T sd Sampling frequency of the DC/DC stage module; k1 =t sd /C 1 ；
The cost function of the rectifier stage module is as follows:
the cost function of the DC/DC stage module is as follows:
7. an electronic device comprising a memory and a processor and computer instructions stored on the memory and running on the processor, which when executed by the processor, perform the steps of the method of any one of claims 1-5.
8. A computer readable storage medium storing computer instructions which, when executed by a processor, perform the steps of the method of any of claims 1-5.
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