KR20200079135A - Apparatus and method for driving control of power conversion system based on model predictive control - Google Patents

Abstract

The present invention relates to a driving control method of a power conversion system through model prediction control. The driving control method of a power conversion system through model prediction control can comprise the steps of: (a) selecting a part of subdivided voltage vectors as a candidate voltage vector; and (b) controlling the selected candidate voltage vector to be applied to a power conversion device by using the selected candidate voltage vector as input of a cost function.

Description

Driving control device and method of power conversion system through model prediction control {APPARATUS AND METHOD FOR DRIVING CONTROL OF POWER CONVERSION SYSTEM BASED ON MODEL PREDICTIVE CONTROL}

The present invention relates to a drive control device and method of a power conversion system through model prediction control. In particular, the present disclosure relates to an apparatus and method for controlling the operation of a grid-connected power conversion system without a DC link capacitor based on model prediction control.

Recently, research on renewable energy and a grid-connected power conversion system have been actively conducted due to strengthening environmental regulations and increasing industrial interest. Among these systems, a system that adopts a matrix converter, which is a power converter without a DC terminal capacitor (i.e., a grid-connected power conversion system without a DC terminal capacitor), has a DC terminal capacitor and has a small volume and high reliability. Control of the input power factor and bi-directional power flow without additional elements are possible, making it a popular next-generation system.

A grid-connected power conversion system without a DC link capacitor is generally controlled through a proportional-integral controller, and generally controls the magnitude, frequency, and power factor of the input-output current. For example, Korean Patent Registration No. 10-1178393 exists as a control technology of a grid-connected inverter using a proportional-integral controller.

However, such a proportional-integral controller has a problem in that its design and tuning are sensitive to environmental influences such as driving time, driving temperature and driving current of the system, and control dynamic characteristics are limited by the bandwidth of the controller. Therefore, as an alternative to this, various control methods have been developed that can perform control that is robust to changes in the external environment and has excellent dynamic characteristics.

There are hysteresis, sliding mode, artificial intelligence, prediction method, etc. as a control method of a grid-connected power conversion system without a DC link capacitor.

Hysteresis control is a method that uses the nonlinearity of the power converter, and switching of the power semiconductor is performed by comparing the measured value and command of the control target in consideration of the hysteresis width. Sliding mode control is a type of variable structure control, which is a non-linear control method, and has robust characteristics for discontinuous switching inputs that change the structure of the control system on a sliding plane. The artificial intelligence control method is divided into techniques such as fuzzy, neural network, neuro-fuzzy, etc., and means a control method based on artificial intelligence theory.

Since the above-described control methods (ie, hysteresis, sliding mode, and artificial intelligence-based control methods) are analog-based control methods, when implemented in a digital system, a very high switching frequency is required (eg, hysteresis) ), there is a problem with the output signal trembling (for example, in the case of a sliding mode), or it is difficult to implement in real time (for example, in the case of artificial intelligence) because an excessive amount of computation is required.

As the predictive control method, the computational performance of the digital signal processor used in the power conversion system has been dramatically improved, many studies have been conducted.

Among the predictive control methods, there is a Finite Control Set-Model Predictive Control (FCS-MPC) technique, which is one of the advanced control techniques suitable for use in a power conversion device. The finite control element model predictive control technique is robust to changes in the external environment, has excellent dynamic characteristics, and has the advantage of being easy to apply to non-linear loads, so its application to power conversion systems employing matrix converters for driving avionics and electric motors is expanded. Is becoming.

However, in the power conversion system to which the conventional model prediction control is applied, since the switching frequency is variable, the system may resonate, the frequency band is low, the audible noise is severe, and the input-output current ripple is considerable, so that the system connection is applied with technical regulation. There is a problem that is difficult to apply to the power converter. In other words, the power conversion system to which the conventional model prediction control is applied has a constant switching frequency, a low frequency band, and a large total harmonic distortion (THD) of the input-output current, so that technical regulations are strictly applied. There is a problem that is difficult to apply to a grid-connected power conversion system.

The present application is to solve the problems of the prior art described above, and provides a drive control apparatus and method of a power conversion system through model prediction control capable of driving a grid-connected power conversion system without a DC terminal capacitor with model prediction control The purpose is to do.

The present application is to solve the problems of the prior art described above, there is no risk of resonance of the system, the audible noise is not severe, the THD of the input-output current is within a specified value, and has a function capable of varying the power factor, so that the technical regulation is strictly It is an object of the present invention to provide a drive control device and method for a power conversion system through model prediction control that can be effectively applied (utilized) to a system-linked power conversion system.

However, the technical problems to be achieved by the embodiments of the present application are not limited to the technical problems as described above, and other technical problems may exist.

As a technical means for achieving the above technical problem, a driving control method of a power conversion system through model predictive control according to an embodiment of the present application includes: (a) selecting a partial voltage vector as a candidate voltage vector; ; And (b) using the selected candidate voltage vector as an input of a cost function to control it to be applied to the power converter.

In addition, in the step (a), the candidate voltage vector may be selected by estimating the command voltage at the inverter end using the back electromotive force and the command current of the system.

In addition, in the step (a), the subdivided voltage vector divided into 12 or more numbers may be used as the subdivided voltage vector.

In addition, in step (a), as the degree of subdivision of the subdivided voltage vector increases, the total harmonic distortion of the input-output current to the power converter may decrease.

In addition, in step (b), the voltage vector applied to the power converter may be the selected candidate voltage vector to which a spatial vector modulation technique is applied so that the switching frequency of the power converter is set constant.

Further, the power conversion device may be a power conversion device without a DC terminal capacitor.

On the other hand, the driving control apparatus of the power conversion system through the model prediction control according to an embodiment of the present application, the selection unit for selecting a portion of the subdivided voltage vector as a candidate voltage vector; And a control unit controlling the selected candidate voltage vector to be applied to the power converter by using it as an input of a cost function.

In addition, the selection unit may select the candidate voltage vector by estimating the command voltage on the inverter end side using the back electromotive force and the command current of the system.

In addition, the selection unit may use a subdivided voltage vector divided into 12 or more numbers as the subdivided voltage vector.

Further, the power conversion device may be a power conversion device without a DC terminal capacitor.

On the other hand, the power conversion system through the model prediction control according to an embodiment of the present application, a power conversion device for supplying the current generated from the three-phase voltage source to the system; And power to control the driving of the power conversion system through model prediction control that selects some of the subdivided voltage vectors as candidate voltage vectors and controls the selected candidate voltage vectors to be applied to the power converter by using the input of the cost function. And a drive control device for the conversion system.

The above-described problem solving means are merely exemplary and should not be construed as limiting the present application. In addition to the exemplary embodiments described above, additional embodiments may exist in the drawings and detailed description of the invention.

According to the above-described problem solving means of the present application, it is possible to control driving of a grid-connected power conversion system without a DC terminal capacitor based on model prediction control.

According to the above-described problem solving means of the present application, a drive control device and method of a power conversion system through model prediction control (in particular, a device for controlling the drive of a grid-connected power conversion system without a DC terminal capacitor based on model prediction control and By providing the method), there is no risk of resonance of the system, the audible noise is not severe, the THD of the input-output current is within a specified value, and has the function of varying the power factor. Can be effectively applied (utilized).

According to the above-mentioned problem solving means of the present application, by driving the grid-connected power conversion system without a DC terminal capacitor by a model predictive control method, it is robust to external environment changes, has excellent dynamic characteristics, and is easy to apply to nonlinear loads.

However, the effects obtainable herein are not limited to the effects described above, and other effects may exist.

1 is a diagram showing a schematic configuration of a power conversion system through model prediction control according to an embodiment of the present application.
2 is a diagram schematically showing the configuration of a power generation unit included in a power conversion system through model prediction control according to an embodiment of the present application.
3 is a diagram illustrating a spatial vector diagram of a rectifying stage included in a power conversion system through model prediction control according to an embodiment of the present application.
4 shows an example of a switching state and a DC terminal voltage according to a current vector of a rectifying stage.
5 is a diagram illustrating a spatial vector diagram of an inverter stage included in a power conversion system through model prediction control according to an embodiment of the present application.
6 is a diagram schematically showing a control configuration of a power conversion system through model prediction control according to an embodiment of the present application.
7 is a diagram illustrating a detailed spatial vector diagram of an inverter stage considered in a driving control apparatus of a power conversion system through model prediction control according to an embodiment of the present application.
FIG. 8 is a segmented spatial vector diagram of an inverter stage considered in a drive control apparatus of a power conversion system through model prediction control according to an embodiment of the present disclosure, in which coordinate values of a segmented voltage vector of first to third sectors are illustrated. It is a drawing showing.
9 is a coordinate vector of a subdivided voltage vector of a first sector in a subdivided spatial vector diagram of an inverter stage considered in a drive control apparatus of a power conversion system through model prediction control according to an embodiment of the present application, It is a figure showing coordinate values (b) of the subdivided voltage vector of the second sector and coordinate values (c) of the subdivided voltage vector of the third sector.
10 is a candidate voltage vector reduced around a reference voltage vector when N is 3, for example, by model prediction control proposed by the present invention in a driving control apparatus of a power conversion system through model prediction control according to an embodiment of the present application It is a diagram showing an example of.
11 is a view showing an example of simulation parameters considered in an experiment performed to verify the efficiency of a drive control device of a power conversion system through model prediction control according to an embodiment of the present application.
12 is a view showing a result of simulating the steady state performance of the proposed technique (Proposed MPC) compared to the conventional FCS-MPC (Conventional FCS-MPC).
13 is a diagram showing the simulation results of the dynamic performance of the technology proposed herein.
14 is an operation flowchart of a driving control method of a power conversion system through model prediction control according to an embodiment of the present application.

Hereinafter, embodiments of the present application will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present application pertains may easily practice. However, the present application may be implemented in various different forms and is not limited to the embodiments described herein. In addition, in order to clearly describe the present application in the drawings, parts irrelevant to the description are omitted, and like reference numerals are assigned to similar parts throughout the specification.

Throughout this specification, when a part is "connected" to another part, it is not only "directly connected", but also "electrically connected" or "indirectly connected" with another element in between. "It includes the case where it is.

Throughout this specification, when a member is positioned on another member “on”, “on the top”, “top”, “bottom”, “bottom”, “bottom”, it means that a member is on another member. This includes cases where there is another member between the two members as well as when in contact.

Throughout the present specification, when a part “includes” a certain component, it means that the component may further include other components, not to exclude other components, unless otherwise stated.

In the following description of the present application, the term'command' may be differently expressed by the term'reference'.

1 is a diagram illustrating a schematic configuration of a power conversion system 100 through model prediction control according to an embodiment of the present application. Hereinafter, the power conversion system 100 through model prediction control according to an embodiment of the present application will be referred to as the present system 100 for convenience of description.

Referring to FIG. 1, the system 100 is a power conversion system through model prediction control, and may be differently expressed as a system-linked power conversion system without a DC link capacitor through model prediction control.

The system 100 may include a drive control device 10 and a power generation unit 20 of a power conversion system.

The drive control device 10 of the power conversion system is a drive control device 10 of the power conversion system through model prediction control according to an embodiment of the present application, and in particular, a grid-connected type without a DC link capacitor through model prediction control It may mean the drive control device 10 of the power conversion system. Hereinafter, the driving control device 10 of the power conversion system, that is, the driving control device 10 of the power conversion system through model prediction control according to an embodiment of the present application will be referred to as the present device 10 for convenience of description.

The apparatus 10 may include a selection unit 11 and a control unit 12.

The apparatus 10 drives a power conversion system through model prediction control that selects a portion of the subdivided voltage vector as a candidate voltage vector and controls the selected candidate voltage vector to be applied to the power converter by inputting a cost function. Can be controlled. A more detailed description of the device 10 will be described later.

The description of the power generation unit 20 may be more easily understood with reference to FIG. 2.

2 is a diagram schematically showing the configuration of the power generation unit 20 included in the power conversion system 100 through model prediction control according to an embodiment of the present application.

Referring to FIG. 2, the power generation unit 20 may include a three-phase voltage source (3-Phase Voltage Source, 21), a power converter 22, and a grid (Grid, 26).

The power conversion device 22 may include a rectifying terminal 23, a DC terminal (DC-link, 24) and an inverter terminal 25. Here, the rectifying stage 23 may be represented differently as a current source rectifier (CSR, 23), and the inverter stage 25 may be represented differently as a voltage source inverter stage (Voltage Source Inverter, VSI, 25). In addition, the DC terminal 24 is a DC terminal 24 without a capacitor, and may mean a portion between the rectifying terminal 23 and the inverter terminal 25. The power converter 22 may be represented as a power converter 22 without a DC terminal capacitor.

In addition, in the present application, the power conversion device 22 may be represented differently as an indirect-matrix-converter (IMC). Here, the indirect matrix converter (IMC) may refer to the topology of the power converter 22 proposed herein, in which the rectifying stage 23 is directly connected to the inverter 25 without an energy storage element.

The power converter 22 may supply (transfer) the current generated from the three-phase voltage source 21 to the system 26.

The rectifying end 23 of the power conversion device 22 is disposed on the input side of the system 100 (especially, the power generation unit), and may be arranged to be connected to the three-phase voltage source 21. The rectifying stage 23 may be composed of six bidirectional switches, and one bidirectional switch may be formed by two sets of a combination of a unidirectional switch (IGBT) and a reverse diode in parallel connected in series.

The inverter stage 25 of the power conversion device 22 is disposed on the output side of the system 100 (especially the power generation unit), and may be arranged to be connected to the system 26. The voltage source inverter stage 25 may be formed of a combination of six unidirectional switches (IGBT) and reverse diodes.

On the input side of the system 100, a three-phase voltage source 21 output from a renewable energy system such as wind power generation, biomass, and small hydro power may be arranged to be connected to the rectifying stage 23. In addition, a system 26 such as a micro grid or a smart grid may be disposed on the output side of the system 100 to be connected to the inverter terminal 25.

Since the power conversion device 22 applied to the system 100 is a power conversion device 22 in a form of removing a DC terminal capacitor that deteriorates reliability due to its large volume and short life, the system 100 is conventionally connected to a general system. Compared to the type power conversion system, the volume and cost of the entire system can be reduced, and reliability can be improved. In other words, according to the IMC 22 proposed in the present application, since the DC terminal 24 does not require a capacitor, the volume of the system can be effectively reduced unlike the general system of AC-DC-AC power conversion. The IMC 22 can increase the reliability and power density of the system.

The input-side current ( i _a , i _b , i _c ) generated from the three-phase voltage source 21 for the power converter 22 and the output-side current ( i _r , i _s , i _t ) supplied to the system 26 All of them can be rapidly controlled in size and frequency by a model prediction control technique (method) that uses the subdivided voltage vector by the present apparatus 10 as a candidate, and can be robust against changes in the external environment. In addition, since the power conversion device 22 can control power factor of the three phases on the input-output side of the power conversion device 22, the device 10 and the system including the device 10 (ie, model prediction control) The grid-based power conversion system without a DC link capacitor, 100) can be effectively applied to the grid connection.

In other words, the power converter 22 may receive input current generated from the three-phase voltage source 21 as an input signal. The power converter 22 is an output signal and can supply the output current to the system 26. The magnitude and frequency of the input-output current to the power converter 22 can be controlled through a model prediction control technique by the apparatus 10 that is robust to changes in the external environment and has excellent dynamic characteristics. In addition, it is possible to control the input-output power factor of the three-phase voltage source 21 and the system 26 through the control of the system 100 by the apparatus 10.

The present system 100 is robust to external environment changes, has superior control dynamic characteristics, and is easy to drive a nonlinear load, as compared to a grid-connected power conversion system without a conventional DC terminal capacitor based on a proportional-integration controller, Control without mutual interference is possible. Therefore, the present apparatus 10 and the present system 100 to which the apparatus 10 is applied are a system including a non-linear load and require robustness and excellent control dynamic characteristics, and mutually independent control between each axis current is required. It can be effectively applied (used, used) in grid-connected power conversion applications.

That is, in the present application, model predictive control (MPC) using subdivided voltage vectors (subdivided voltage vectors) to reduce current ripple in the indirect matrix converters (IMC, 22) Suggestions for technology. In other words, the apparatus 10 may control driving of the grid-connected power conversion system 100 without a DC terminal capacitor through model prediction control using a subdivided voltage vector.

In the following description, the model prediction control technique proposed in this application (Proposed MPC) will be referred to as a technique proposed in the application (Proposed MPC) for convenience of description. The technology proposed in the present application may mean a driving control technology of a grid-connected power conversion system without a DC link capacitor through model predictive control by the device 10.

In the proposed MPC, the number of candidate voltage vectors can be increased by a subdivided voltage vector, which can reduce the input-output current ripple of the IMC 22. In addition, the apparatus 10 can reduce the computational load caused by subdivided voltage vectors by estimating the position of the reference voltage vector through the proposed MPC. Can. Therefore, according to the model prediction control (MPC) proposed by the apparatus 10, the input-output current ripple of the IMC 22 can be reduced without calculation burden. The effect of the proposed technique (Proposed MPC) can be verified by the simulation results described later.

Finite Control Set-Model Predictive Control (FCS-MPC) technology, which is one of various MPC technologies, uses a cost function that uses a load model to predict the output of the system. FCS-MPC uses candidate voltage vectors to determine the control input that minimizes the cost function. However, FCS-MPC has a disadvantage of having a low switching frequency because one basic voltage vector is applied during the control cycle.

When the FCS-MPC with a limited number of candidate voltage vectors is used for IMC drives, the output current ripple increases, which may mean that the output quality of the IMC is poor. To overcome the shortcomings of this FCS-MPC, the candidate voltage vector can be subdivided again. However, the subdivided voltage vector can increase the computational burden due to the multiple candidate voltage vectors.

Therefore, the present application proposes a model predictive control (MPC) technique using a subdivided voltage vector to reduce input/output current ripple in the IMC 22. In addition, the present application proposes a method for reducing the computational burden by estimating the reference voltage vector. Model prediction control (MPC) using such a subdivided voltage vector and position estimation of a reference voltage vector may be performed by the apparatus 10.

As described above, the power converters 22 and IMC may perform power conversion from the three-phase voltage source 21 to the grid 26. The rectifying stage 23 is connected to a three-phase voltage source 21 such as a power generation system, and the inverter stage 25 can be connected to a grid 26 with a filter.

Here, in the modulation process of the rectifying stage 23 and the modulation process of the inverter stage 25, a space-vector modulation (SVM) technique may be applied as an example, but is not limited thereto. Various modulation techniques that are known or developed in the future can be applied.

A more detailed description of the modulation process of the rectifying stage 23 is as follows.

3 is a diagram showing a spatial vector diagram (ie, a space vector current diagram of a rectifying stage) of the rectifying stages 23 and CSR included in the power conversion system 100 through model prediction control according to an embodiment of the present application. .

Referring to FIG. 3, in each sector, a reference current vector may be generated by a combination of two adjacent current vectors. Here, the reference current vector may be differently expressed as a command current vector. For example, the reference current vector in the sixth sector Sector VI may be synthesized using vectors such as I ₁ and I ₆ (active current vector). In addition, the instantaneous (instantaneous) DC terminal 24 voltage (DC-link voltage) of the IMC 22 according to the switching states of the rectifying stage 23 and the current vector (Current vector) It can be equal to 4.

4 shows an example of the switching state and the DC terminal 24 voltage according to the current vector of the rectifying stage 23.

In the present system 100, the reference current vector of the rectifying stage 23 may be expressed as Equation 1 below.

[Equation 1]

Here, i _i represents the magnitude (magnitude) of the reference current vector. Also, θ _ia , θ _ib , and θ _ic Denotes the phase angle of each of the reference current vector components ( i ^* _a , i ^* _b , i ^* _c ).

In order to perform rectification at a unity power factor, I ^* _i of the rectifying stage 23 must match the input voltage vector. In a balanced condition, the input voltage vector can be expressed as Equation 2 below.

[Equation 2]

Here, v _i is the magnitude of the input voltage vector, ω _i is the angular frequency of the three-phase voltage source 21, θ _va , θ _vb , and θ _vc Denotes the phase angle of each of the input voltage vector components ( v _a , v _b , v _c ).

In addition, since the sum of each component is 0 under the assumption that the three-phase voltage source 21 is balanced, the phase angle of the input voltage vector element may satisfy Equation 3 below.

[Equation 3]

When I ^* _i is located in the sixth sector (Sector VI ) as shown in FIG. 3, the upper switch of the A-leg may be clamped. Accordingly, the duty ratio ( d _x , d _y ) may be expressed as in Equation 4 below.

[Equation 4]

Where d _x And d _y denote the duty ratios of the lower switches of the B-leg and the C-leg, respectively.

In addition, the average of the voltage applied to the DC terminal 24, that is, the average DC terminal voltage, v _{DC ( avg ),} is a line-to-line voltage of the three-phase voltage source 21 ( v _ab and v _ca ) and It can be calculated (calculated) to satisfy the following equation 5 using the duty ratio ( d _x , d _y ).

[Equation 5]

Here, v _{DC ( avg )} means the average voltage that appears at the DC terminal 24 of the power converters IMC and 22 during the switching period. v _{DC ( avg )} may be used to calculate a reference voltage in the process of modulating the inverter stage 25, which will be described later.

For the remaining sectors (that is, the first sector to the fifth sector) other than the sixth sector among the first sector to the sixth sector, modulation may be performed in the same or similar manner to the modulation scheme described with respect to the sixth sector. That is, the contents described with respect to the sixth sector can be equally applied to the description of each of the remaining sectors (ie, the first sector to the fifth sector).

The modulation process of the rectifying stage 23 will be described again as follows.

The control unit 12 of the apparatus 10 may control the rectification stage 23 to be modulated. That is, under the control of the control unit 12, the rectifying stage 23 may perform a modulation process.

The controller 12 can sinely control the fundamental wave size and frequency of the input-side current through the modulation process of the rectifying stage 23. In addition, the control unit 12 may control the reactive power and the active power of the input side by adjusting the power factor (that is, the input power factor) of the rectifying stage 23, and at the same time, the voltage of the DC terminal 23 of the input side AC voltage It can be controlled to be applied at the maximum value.

Therefore, the voltage of the DC terminal 24 determines the magnitude of the switching state according to the modulation of the rectifying terminal 23, and the upper and lower bidirectional switches of the rectifying terminal 23 that are electrically connected (ON, short circuited) at every moment. Through the DC terminal 24 voltage can be maintained. In other words, the control unit 12 may control the magnitude of the voltage of the DC terminal 24 through control of a switching state according to modulation of the rectifying terminal 23. In addition, in order to maintain the voltage of the DC terminal 24, the controller 12 may control the upper bidirectional switch and the lower bidirectional switch of the rectifying terminal 23 to be turned on (ON, short circuited) every moment.

Referring to the spatial vector diagram of the rectifying stage 23 shown in FIG. 3, the control unit 12 includes six active current vectors and three reactive current vectors according to the switching state of the rectifying stage 23. It can be controlled to be applied to.

When the bidirectional switch of the upper part and the bidirectional switch of the lower part are conducting in different phases (legs, arms) under the control of the control unit 12, the system 26 and the DC terminal 24 may be connected. Can be applied. On the other hand, when the upper/lower switch of the same phase is conducted by the control of the control unit 12, the voltage of the system 24 is not applied to the DC terminal 24, and an invalid current vector may be applied.

The rectifying stage 23 may be modulated through the following process. When the phase of the command current vector (in other words, the reference current vector) is located in the sixth sector (sixth area), the control unit 12 generates two active current vectors I ₁ and I ₆ adjacent to the command current vector. By applying to the rectifying stage 23, a command current vector can be synthesized, and at this time, a command phase current ( i ^* _a , i ^* _b , i ^* _c ) may be generated as shown in Equation 1.

The control unit 12 controls to maintain (continue) the a-phase upper switch of the rectifying stage 23 during the switching cycle while applying two effective current vectors I ₁ and I ₆ in the sixth sector. can do. On the other hand, when the three-phase voltage source 21 maintains a balance (balance), the control unit 12 has a duty ratio ( d _x of Equation 4) during a period in which the lower and upper b-phase switches of the rectifying terminal 23 are switched. , d _y ) and one cycle times.

The average value of the voltage applied to the DC terminal 24 of the system 100 (ie, the average DC terminal voltage) v _{DC ( avg )} is the input line voltage ( v _ab and v _ca ) and the duty ratio ( d _x , d It can be calculated by Equation 5 through the product of _y ). For each of the other sectors (first sector to fifth sector), the rectifying stage 23 may be modulated according to the phase of the command current vector (reference current vector) in the same manner as the modulation scheme in the sixth sector.

A more detailed description of the modulation process of the inverter stage 25 is as follows.

In the modulation process of the inverter stages 25 and VSI, the modulated reference voltage may be determined based on the commutation of the average DC terminal voltage v _{DC ( avg )} and the rectifying stage 23. .

5 is a diagram illustrating a spatial vector diagram (ie, a spatial vector voltage diagram of an inverter stage) of the inverter stage 25 included in the power conversion system 100 through model prediction control according to an embodiment of the present application.

The modulation process of the inverter stage 25 may be similar to that of a general inverter. However, in the modulation process of the inverter stage 25 of the power converters 22 and IMC proposed in the present application, the rectifying stage 23, in order to satisfy the zero DC-link current commutation of the DC stage 24, The switching state of CSR) can be considered.

Therefore, two modulation reference voltages may be used in the modulation process of the inverter stage 25 of the power converters 22 and IMC herein.

The upper and lower limits of the modulation reference voltage in the R-phase may be expressed as Equation 6 below.

[Equation 6]

Where v _sn Means an offset voltage, which can be calculated to satisfy Equation 7 below. It can be added (provided, reflected) to the three-phase reference voltages ( v ^* _r , v ^* _s , v ^* _t ) to use the spatial vector modulation (SVM) technique.

The modulation process of the inverter stage 25 will be described again as follows.

The control unit 12 of the apparatus 10 may control the inverter stage 25 to be modulated. That is, under the control of the control unit 12, the inverter terminal 25 may perform a modulation process.

In the system 100, the modulation process of the inverter stage 25 may be similar to, for example, a general modulation technique of a two-level voltage source inverter.

Referring to the spatial vector diagram of the inverter stage 25 shown in FIG. 5, the control unit 12 uses six effective voltage vectors and two reactive voltage vectors according to the switching state of the inverter stage 25. Can be applied to.

For the modulation of the inverter stage 25, for example, a carrier-based spatial vector modulation technique may be used. In addition, when performing modulation control of the inverter stage 25, the controller 12 can reduce switching loss by performing zero current commutation using two command signals compared to the carrier. Here, the two command signals compared to the carrier may mean the _upper limit v ^* _upper and the lower limit v ^* _lower of the modulation reference voltage in R-phase expressed as Equation 6 above.

Hereinafter, the model prediction control (MPC) technology of the power converters 22 and IMC will be described in more detail.

First, the conventional Finite Control Element Model Predictive Control (FCS-MPC) (ie, Conventional FCS-MPC) will be described as follows.

Predicted current is required for FCS-MPC of the output current in the IMC, which can be calculated by each candidate voltage vectors and load model. In the continuous time domain, the output voltage vector V in the load model of the inverter stages 25 and VSI as shown in FIG. 2 may be expressed as Equation 8 below.

[Equation 8]

Here, L _of and R _of denote an inductive filter and a resistive filter, respectively. Variables such as the output current vector ( I ) and the grid voltage vector (E) of the power converter 22 can be expressed in the α-β stationary reference frame. have.

In order to implement FCS-MPC in a digital signal processor (DSP), a discretized model is required. The load model shown in Equation 8 may be discretized using the forward Euler method. In relation to the predicted current vector (predicted current vector) it can be expressed as Equation 9 below.

[Equation 9]

Here, I ( k ) and E ( k ) denote instantaneous output current and grid voltage vector obtained from the sensor, respectively. V ( k ) represents a candidate voltage vector, and T _s represents a sampling period.

In FCS-MPC, the cost function uses a reference current and a predicted current based on Equation 10 below in an α-β stationary reference frame. It can be defined as 10.

[Equation 10]

Consequently, the reference voltage vector for the FCS-MPC of the output current in the IMC can be selected such that the cost function is minimized. However, in the conventional FCS-MPC scheme, the number of candidate voltage vectors is limited to eight basic voltage vectors including zero voltage vectors. Therefore, the power conversion system to which the conventional FCS-MPC method is applied has a problem that the output current ripple of the IMC is significant, and only one vector is applied to the control cycle, so that the switching frequency is low. . Therefore, the conventional FCS-MPC has an inappropriate aspect for use in an electric power converter (IMC) connected to a system.

In other words, the conventional model predictive control technique predicts future grid current based on the grid model including candidate voltage vectors and filters of the power conversion system, and controls the grid current using the optimal input selected through the cost function.

However, a power conversion system to which a conventional model prediction control method (for example, FCS-MPC, etc.) is applied has a low switching frequency bandwidth and has a variable property, and thus can resonate according to input-output filters and load conditions. There is a risk, and there is a problem with severe audible noise. In addition, in the conventional model predictive control method, since only a limited number of candidate voltage vectors can be used, there is a problem in that the ripple of input-output current is significant and thus does not satisfy the grid linkage regulations set by the grid operator.

Accordingly, there is a need to develop a system capable of model predictive control of a grid-connected system without a DC link capacitor. In addition, the system link system without DC terminal capacitors based on model prediction control must have the ability to vary the power factor and the THD of the input-output current is within a specified value without risk of system resonance. The present application proposes a technique capable of satisfying these conditions. That is, the present application proposes an apparatus (this apparatus, 10) for model predictive control of a grid-connected system without a DC terminal capacitor. The present system 100 to which the present apparatus 10 is applied has a function capable of varying the power factor while the THD of the input-output current is within a prescribed value without the risk of system resonance.

Hereinafter, the proposed technology (Proposed MPC) will be described in more detail.

6 is a diagram schematically showing a control configuration of the power conversion system 100 through model prediction control according to an embodiment of the present application.

1 and 6, the control unit 12 of the apparatus 10 may control the driving of the power generation unit 20.

The control unit 12 may control the rectifying stage 23 disposed on the input side of the power conversion device 22. The control unit 12 determines the phase of the measured voltage with respect to the rectifying stage 23 (that is, the phase angle of the input voltage vector element, θ _v ), and obtains a desired power factor based on the voltage of the DC stage 24 voltage Duty ratio calculation (S1) can be calculated to maximize the (Duty Ratio Calculation, S1). At this time, the controller 12 may calculate the duty ratio based on Equation 4 above.

In addition, the control unit 12 may acquire a modulation signal (S2) of the rectifying terminal 23. At this time, the modulated signal of the rectifying stage 23 can be obtained using the calculated duty ratio.

In addition, the control unit 12 calculates the average DC link voltage v _{DC ( avg )} as the _{DC link} voltage using the magnitude ( V _i ) of the input line voltage on the system 26 side and the calculated duty ratio ( v _{DC(avg )} Calculation, S3).

In addition, the controller 12 may control the modulation of the rectifying stage 23 by performing a comparison of the modulated signal and the triangular carrier in the digital signal processing device (DSP). Through the modulation process of the rectifying stage 23, the controller 12 may control the input AC current to the rectifying stage 23, and may control the DC terminal 23 voltage to the maximum.

In other words, the controller 12 performs modulation of the rectifying stage 23 using the PWM (Pulse Width Modulation, S4) signal obtained through the comparison of the previously generated modulation signal (S2) and the triangular carrier (that is, rectification However, it can be controlled such that a modulation technique is applied). As a result, the controller 12 may provide (transfer) the reference current vector obtained through modulation of the rectifying stage 23 to the rectifying stage 23 as a gate signal (S5) signal.

In other words, the control unit 12 may control the input current (input alternating current) input to the power conversion device 22 through application of the modulation technique of the rectifying stage 23. At this time, the modulation technique of the rectifying stage 23 may be achieved through comparison of a modulated signal and a triangular carrier in a digital signal processing device (DSP). In addition, the input current input to the power converter 22 is a modulated signal of the rectifying stage to which the modulation technique of the rectifying stage 23 is applied, and the modulating signal of the rectifying stage 23 is such that the DC terminal 24 voltage is maximized. It may be obtained by using the calculated DC ratio and the DC voltage (especially, the average DC voltage) calculated using the calculated duty ratio and the magnitude and duty ratio of the input line voltage to the grid.

In addition, the control unit 12 may control the inverter stage 25 disposed on the output side of the power conversion device 22. The more detailed explanation is as follows.

The controller 12 for the proposed MPC (i.e., for model prediction control proposed herein), 8 basic voltages including an invalid voltage vector as a candidate voltage vector in the conventional FCS-MPC scheme Subdivided voltage vectors (segmentation) divided into 12 regions, unlike using vectors (existing voltage vectors) (in other words, the number of candidate voltage vectors was previously limited to 8 voltage vectors containing reactive voltage vectors) Voltage vector).

7 is a diagram illustrating a detailed spatial vector diagram of the inverter stage 25 considered in the drive control device 10 of the power conversion system through model prediction control according to an embodiment of the present application. 8 is a subdivided spatial vector diagram of the inverter stage 25 considered in the drive control device 10 of the power conversion system through model prediction control according to an embodiment of the present application, the first sector S ₁ It is a view showing coordinate values of subdivided voltage vectors of the third sector S ₃ . In particular, FIG. 9 is a subdivided spatial vector diagram of the inverter stage 25 considered in the drive control device 10 of the power conversion system through model prediction control according to an embodiment of the present application, in which the first sector S ₁ is The coordinate value of the subdivided voltage vector of (a), the coordinate value of the subdivided voltage vector of the second sector ( S ₂ ) (b), and the coordinate value of the subdivided voltage vector of the third sector ( S ₃ ) (c) It is a figure showing each.

7 to 9, in the subdivided voltage space vector diagram of the inverter stage 25 considered in the apparatus 10, a sector may be divided into ₁₂ sectors ( S ₁ to S ₁₂ ).

The controller 12 controls the output current of the power converter 22 to subdivided voltage vectors for 12 sectors when performing the proposed MPC. Can be used. That is, the controller 12 may control the output current of the power converter 22 by using a voltage vector subdivided for 12 sectors.

8 and 9 show coordinate values of subdivided voltage vectors of each of the first sector to the third sector, and the coordinate values in the sectors can be expressed by Equations 11 to 13, respectively.

[Equation 11]

[Equation 12]

[Equation 13]

Where x _i and y _i Denotes an index that describes coordinate values. N represents the number of subdivisions (ie, subdivided number). That is, N is an index indicating the degree of subdivision, and may be determined (set) by user input, for example. Other fourth sectors to twelfth sectors may be defined in the same or similar manner in this way.

As the value of N increases, the total harmonic distortion (THD) of the current may decrease, which can be said to be in a trade-off relationship with the control robustness and computation time. The apparatus 10 may control to satisfy the system linkage regulation by reducing all ripples of input-output current by using a subdivided voltage vector (segmented voltage vector) instead of using the conventional 8 voltage vectors, Power factor can also be controlled.

In addition, the control unit 12 may use a spatial vector modulation technique to apply the subdivided voltage vector to the system 26 through the power converter 22. Through this, the control unit 12 may make the switching frequency of the system 100 coincide with the carrier frequency to make it constant. In other words, the control unit 12 may apply a voltage vector to the power conversion device 22, wherein the voltage vector applied to the power conversion device 22 has a constant switching frequency of the power conversion device 22. It may be a candidate voltage vector to which the spatial vector modulation technique is applied.

On the other hand, since a computational burden is caused by many candidate voltage vectors, it can be said that it is impossible to predict every instant I ( k + 1) according to the subdivided voltage vector (subdivided voltage vector). have. Therefore, the position of the reference voltage vector needs to be determined through an estimation process.

In the apparatus 10, a technique for alleviating (reducing) the calculation load based on the estimation of the reference voltage vector may be considered for the proposed MPC.

In other words, all subdivided voltage vectors can be used as inputs to the cost function as in Equation 10 above and applied to the power conversion system. However, if all of them are considered (i.e., all subdivided voltage vectors are substituted into the cost function, and all other subdivided voltage vectors are applied as inputs to the cost function), an easy implementation of a grid linkage system requiring real-time control is required. It is difficult, and it requires an expensive digital signal processing device (DSP).

Therefore, referring to FIG. 6, the device 10 uses the back electromotive force ( e _d , e _q ) and the command current (reference current, I ^* ) of the system 26 to command voltage (reference to the inverter terminal 25) We propose a technique for reducing the amount of computation by reducing the number of candidate voltage vectors by estimating the size and position of the voltage, V ) (Position Estimation, S6). Such a calculation amount reduction technique may mean an estimation process of a reference voltage vector, which will be described later, and may be implemented through Equations 14 and 16 described later.

The selection unit 11 of the apparatus 10 candidates for some of all subdivided voltage vectors (all subdivided voltage vectors) based on the estimated size and position of the reference voltage (command voltage, V ) (S6). It can be selected as a voltage vector. That is, the selector 11 may select (calculate, calculate) a candidate voltage vector (Candidate Vector Selection, S7).

Thereafter, the control unit 12 may control the candidate voltage vector selected (calculated and calculated) in step S7 to be applied to the power conversion device 22 as an input of the cost function.

Specifically, the controller 12 may calculate a cost function for the selected candidate voltage vector by using the candidate voltage vector selected in step S7 as an input of the cost function (Cost function Calculation, S8). Subsequently, the controller 12 applies a spatial vector modulation technique so that the switching frequency of the power converter is set constant with respect to the result value V ^* of the cost function calculation for the selected candidate voltage vector (S2, S4). Can. That is, the controller 12 may control the selected candidate voltage vector to which the spatial vector modulation technique is applied to be applied to the inverter terminal 25. Through this, the control unit 12 controls the driving of the system 100 based on this, thereby reducing the ripple of the input-output current to the power converter 22 and real-time in a low-cost digital signal processing device. It can enable implementation.

The estimation process of the reference voltage vector can be derived through the following process. Specifically, in the process of estimating the reference voltage vector, the size ( v _mag ) and the position ( θ _ref ) of the reference voltage vector (V) may be estimated.

The output current vector of the power converter 22 may be expressed as Equation 14 below.

[Equation 14]

Here, Z represents the impedance of the filter, and f represents the fundamental frequency of the voltage of the grid 26. Further, θ is an angle between a reference voltage vector and a grid voltage vector, and may be expressed as Equation 15 below.

[Equation 15]

Accordingly, the phase angle θ _ref of the reference voltage vector may be determined to satisfy Equation 16 below.

[Equation 16]

Where θ _grid Denotes the angle of the system 26 voltage.

The magnitude of the reference voltage vector for the inverter stages 25 and VSI of the power converter 22 may have a predetermined variation due to the small resistance and inductance of the filter. Accordingly, the magnitude of the reference voltage vector for the inverter stages 25 and VSI may be similar to the reference voltage vector V ( k −1) of the last sampling period, and may be expressed as in Equation 17 below. Can.

[Equation 17]

Accordingly, the magnitude of the reference voltage vector for the inverter stages 25 and VSI may be as shown in Equation 18 below. Consequently, the index for determining the reference voltage vector can be expressed as Equation 19 and Equation 20 below.

[Equation 18]

[Equation 19]

[Equation 20]

Here, S and L mean small indices and large indices for determining the candidate voltage vectors closest to the reference voltage vector.

In the process of estimating the reference voltage vector, the number of candidate voltage vectors for the proposed MPC can be reduced (decreased) as shown in FIG. 10.

10 is a driving control apparatus 10 of a power conversion system through model prediction control according to an embodiment of the present application, by a technique proposed herein (Proposed MPC), for example, when N is 3 around a reference voltage vector A diagram showing an example of reduced candidate voltage vectors.

Referring to FIG. 10, by the process of estimating a reference voltage vector by the controller 12, the apparatus 10 determines the number of candidate voltage vectors used (considered) during model prediction control (Proposed MPC) proposed herein. It can be reduced as shown in FIG. That is, according to the proposed technology (Proposed MPC), the apparatus 10 can reduce (reduce) the output current ripple of the power converter 22 by using a subdivided voltage vector without calculation burden.

The apparatus 10 may control driving of the grid-connected power conversion system 100 without a DC terminal capacitor through model prediction control.

The selection unit 11 of the apparatus 10 may select a part of all (all) subdivided voltage vectors as candidate voltage vectors. Thereafter, the control unit 12 may control the candidate voltage vector selected by the selection unit 11 to be applied to the power conversion device 22 as an input of the cost function.

At this time, the selector 11 uses the back electromotive force ( e _d , e _q ) of the system 26 and the command current (reference current, I ^* ) to determine the reference voltage (reference voltage, V ) of the inverter terminal 25 side. A candidate voltage vector can be selected by estimating the magnitude ( v _mag ) and the location ( θ _ref ). In this case, the selection unit 11 may estimate the magnitude of the reference voltage ( v _mag ) to satisfy Equation 18, and the position of the reference voltage ( θ _ref ) may be estimated to satisfy Equation 16.

The selector 11 may select some of the subdivided voltage vectors as candidate voltage vectors, and specifically, the selector 11, as illustrated in FIG. 10, coordinate values of some of the coordinate values of the subdivided voltage vector. Can be selected as the coordinate value of the candidate voltage vector.

In addition, when selecting the candidate voltage vector, the selection unit 11 may use a subdivided voltage vector divided into 12 sectors (regions) S1 to S12, for example. In other words, the selection unit 1 may use a subdivided voltage vector divided into 12 or more numbers as subdivided voltage vectors (that is, all subdivided voltage vectors) considered when selecting a candidate voltage vector.

At this time, in the selection unit 11, as the degree of granularity N of the subdivided voltage vector increases, the total harmonic distortion THD of the input-output to the power converter 22 may decrease. In other words, in order to reduce the THD of the input-output of the power converter 22, the selector 11 may set the subdivision degree ( N ) of the subdivided voltage vector to a larger value, for example subdivision The degree of precision N can be set to any one of three or more values. However, it is not limited to this, and may be set to various values.

In addition, the voltage vector (final voltage vector) applied to the power converter 22 by the controller 12 is a selected candidate voltage to which the spatial vector modulation technique is applied so that the switching frequency of the power converter 22 is set constant. It can be a vector. In other words, the controller 12 may apply the selected candidate voltage vector to the power conversion device 22 as an input of the cost function, and at this time, as a voltage vector applied to the power conversion device 22, a space vector A selected candidate voltage vector to which a modulation technique is applied can be applied. Through this, the controller 12 can make the switching frequency of the system 100 (especially the power converter) consistent with the carrier frequency so that it is constant.

In addition, the power converter 22, which is a target to which a candidate voltage vector selected by the control of the control unit 12 (especially, a candidate voltage vector to which a spatial vector modulation technique is applied) is applied, has no DC terminal capacitor in the power generation unit 20. As a power conversion device 22, it can be otherwise represented by a matrix converter 22.

According to this, the present application proposes a model prediction control (MPC) technique that uses a subdivided voltage vector for reducing current ripple in the power converters 22 and IMC. That is, the apparatus 10 may control driving of the grid-connected power conversion system 100 without a DC terminal capacitor through model prediction control using a subdivided voltage vector.

In the apparatus 10, for the proposed MPC, the number of candidate voltage vectors can be increased by the subdivided voltage vectors. Therefore, the apparatus 10 can reduce the input-output current ripple of the power converters 22 and IMC, compared to the FCS-MPC, which is a conventional model prediction control technique. In addition, the apparatus 10 can effectively reduce the computational load generated by the subdivided voltage vector by estimating the angle and size of the reference voltage vector through the above-described estimation process of the reference voltage vector.

Hereinafter, simulation results for verifying the efficiency of the proposed technique (Proposed MPC) will be described.

In one experiment of the present application, as an example, PSIM software was used to perform efficiency verification of the proposed technology (Proposed MPC) for the power converters 22 and IMC connected to the system.

11 is a diagram illustrating an example of simulation parameters considered in an experiment performed to verify the efficiency of a drive control device 10 of a power conversion system through model prediction control according to an embodiment of the present application.

Referring to FIG. 11, in one experiment of the present application, as a simulation parameter, a three-phase voltage source (21) is 220 V _rms / 60 Hz, and the system 26 is 110 V _rms / 60 Hz, filter resistance ( Filter resistance) may be set to 0.1 Ω, filter inductance 3 mH, switching frequency 10 kHz, and subdivisions (Number of subdivisions) may be set to 3.

FIG. 12 shows the performance of the steady state of the proposed MPC (that is, the model prediction control technology by the apparatus 10) compared to the conventional FCS-MPC (Conventional FCS-MPC). It is a diagram showing the simulation result.

Specifically, in Figure 12 (a) is the input phase current (input phase currents), (b) is the DC terminal 24 voltage, (c) is the output phase current (output phase currents) and dq reference frame (reference frame) The transformed value at, (d) shows a graph for the α-β reference voltage vector.

Referring to FIG. 12, in one experiment of the present application, the three-phase output current of the power converter 22 may be controlled to 15A. In addition, the control scheme (control scheme) can be changed in 0.4 seconds from the conventional FCS-MPC to the technique proposed herein (Proposed MPC).

From the simulation results of FIG. 12, three important results for the proposed technology (Proposed MPC) can be confirmed.

First, according to the proposed technology (Proposed MPC), it can be seen that the input current ripple of the power converters 22 and IMC is significantly reduced compared to the conventional FCS-MPC. Second, according to the proposed technology (Proposed MPC), it can be seen that the output current ripple of the power converters 22 and IMC is significantly reduced. Third, it can be seen that the switching frequency of the power converters 22 and IMC appears constant at 10 kHz when the proposed MPC is applied. This can be said to be the result of subdivided voltage vectors considered in the calculation of the cost function (S8). The reference voltage vector ( V ^* ) generated by the subdivided voltage vector can be confirmed through FIG. 12D after 0.4 seconds.

13 is a diagram showing the simulation results of the dynamic performance (dynamic performance) of the proposed technique (Proposed MPC) herein.

In FIG. 13, (a) shows a graph for input phase currents, and (b) shows a graph for output phase currents and conversion values in a dq reference frame. Shows.

Referring to FIG. 13, according to the proposed MPC, the output current of the power converter 22 may be changed from 0.4 seconds to 15A to 7.5A. According to this, according to the proposed technology (Proposed MPC), it can be confirmed that the output current of the power converter 22 has a fast dynamic response.

According to this, the present application relates to a technology capable of controlling the grid-linked power conversion system 100 without a DC link capacitor by model predictive control, of a grid-linked power conversion system without a DC link capacitor through model prediction control. A driving control device (this device, 10) is proposed.

The apparatus 10 may determine the phase of the measured voltage, calculate the duty ratio of the DC terminal 24 voltage, and perform comparison of the modulated signal and the triangular carrier to control the input AC current. In addition, the apparatus 10 estimates (calculates) the magnitude and position of the command voltage at the inverter terminal 25 using the back electromotive force and the command current (reference current) of the system 26, and based on this, the candidate voltage vector Can reduce the number of According to the operation of the system 100 based on the reduced number of candidate voltage vectors, the apparatus 10 can effectively reduce the computation amount.

The apparatus 10 may improve control efficiency, such as reducing the amount of calculation and reducing ripple of input-output current by using a candidate voltage vector as a function of cost and reducing the amount of computation through the proposed MPC. .

In other words, the device 10 uses a subdivided spatial voltage vector to reduce the THD of the input-output current and to maintain a constant switching frequency. As it is possible to control, it can be effectively used in a grid-connected environment. In addition, since the device 10 is capable of responding to various loads that require fast dynamic characteristics or includes non-linear characteristics, it is effective in the field of system interconnection of distributed power sources utilizing renewable energy such as wind power generation, biomass, and small hydro power. Can be applied. In addition, the apparatus 10 may be implemented in a low-cost digital signal processing apparatus (DSP) through a computational amount reduction (decrease) technology.

As the apparatus 10 drives a grid-connected power conversion system without a DC terminal capacitor by a model predictive control method, it is possible to provide a system that is robust to external environment changes, has excellent dynamic characteristics, and can be applied to nonlinear loads. Do.

The present application proposes a grid-connected power conversion system 100 based on model prediction control, unlike a grid-connected inverter using a conventional proportional-integration controller. The present application proposes a configuration and modulation technique of a grid-connected power conversion system 100 without a DC terminal capacitor, as well as a control technique of a system based on model prediction control and a three-phase voltage source, and a calculation amount reduction technique.

The present application proposes a model prediction control technique including a subdivided voltage vector and a computation amount reduction technique. The present application proposes a system and current control technology for system interconnection using an indirect-matrix-converter (IMC). In addition, the present application can control driving of a three-phase resistance-inductance load using model predictive control in an indirect matrix converter.

In addition, the present application proposes a model prediction control technology that can be implemented as a low-cost digital signal processing device while satisfying the system connection regulation as a system link system without a DC link capacitor based on model prediction control. In addition, the present application proposes a model prediction control technique that can reduce the ripple of input-output current while avoiding an increase in switching frequency that causes loss, and is easy to implement in practice through a computation amount reduction technique.

The present invention relates to a device 10 for controlling the operation of a grid-connected power conversion system without a DC terminal capacitor based on model prediction control. This device 10 is robust to changes in the external environment, has excellent control dynamics, and has no mutual interference, so that its size, frequency, and power factor can be adjusted for the current of the three-phase voltage source on the input side and the current of the output side grid. Can be controlled.

In the system 100, a power converter 22 for adjusting the AC voltage and AC current on the grid side using an AC voltage and an AC current supplied from a three-phase voltage source, and a controller 12 for controlling the power converter 22 ). In addition, in the system 100, in order to reduce the content of the voltage/current harmonics, an LC filter is provided on the input side (especially between the three-phase voltage source and the rectifying stage), and on the output side (especially between the inverter stage and the grid). An L filter may be provided. In addition, the system 100 may include a grid 26 (grid power).

As described above, the input-side rectifying stage 23 of the system 100 may control the fundamental wave of the input-side current and maintain the DC-side voltage by using a bidirectional semiconductor element composed of an IGBT and a diode. In addition, the output-side inverter stage 25 of the system 100 may perform model prediction control using a subdivided voltage vector as a candidate along with a computational amount reduction technique proposed herein. At this time, the subdivided degree of the subdivided voltage vector (degree of subdivision, N ) may be set (adjusted) in consideration of the relationship between current quality, robustness, and computation time. The subdivided degree may be set (adjusted) by user input, for example.

The present application can be effectively applied in the field of distributed power system interconnection such as wind power generation, turbine power generation using biomass, and small hydro power generation because it is capable of responding to various applications including fast dynamic characteristics or nonlinear loads. In addition, the system 100 can control the sine wave input/output current through a model predictive control technique that is robust to changes in the external environment and has excellent control dynamics, and is also easy to use as a low-cost digital signal processing device by applying a computational reduction technique. Can be implemented.

The power conversion system to which the model predictive control developed so far has a low switching frequency and has variable resonance and audible noise, and the THD of the input-output current could not satisfy the system linkage regulation. On the other hand, the technology proposed herein (driving control technology of a system linkage system without a DC terminal capacitor based on model prediction control) can be effectively used in the field of grid linkage to which technical regulations are applied.

The present application satisfies regulations and is easy to implement with a low-cost digital signal processing device. In particular, the present application can be effectively applied (utilized) to a micro grid and a weak system field, which requires a control system that is robust to external environment changes and has excellent control dynamic characteristics due to poor system environment.

Hereinafter, based on the details described above, the operation flow of the present application will be briefly described.

14 is an operation flowchart of a driving control method of a power conversion system through model prediction control according to an embodiment of the present application. In particular, FIG. 14 is an operation flowchart of a drive control method of a grid-connected power conversion system without a DC link capacitor through model prediction control according to an embodiment of the present application.

The driving control method of the power conversion system through the model prediction control illustrated in FIG. 14 may be performed by the apparatus 10 described above. Therefore, even if omitted, the description of the apparatus 10 may be equally applied to the description of the driving control method of the power conversion system through model prediction control.

Referring to FIG. 14, in step S110, some of the subdivided voltage vectors may be selected as candidate voltage vectors.

At this time, in step S110, the candidate voltage vector can be selected by estimating the command voltage at the inverter end using the back electromotive force and the command current of the system.

In addition, in step S110, the subdivided voltage vector divided into 12 or more numbers may be used as the subdivided voltage vector.

Further, in step S110, as the degree of subdivision of the subdivided voltage vector increases, the total harmonic distortion (THD) of the input-output current to the power converter may decrease.

Next, in step S120, the candidate voltage vector selected in step S110 can be controlled to be applied to the power converter using the cost function as an input.

In addition, in step S120, the voltage vector applied to the power converter may be a selected candidate voltage vector to which the spatial vector modulation technique is applied so that the switching frequency of the power converter is set constant.

In other words, in step S120, the controller 120 may apply a voltage vector to the power conversion device. At this time, as a voltage vector (that is, a final voltage vector, V*) applied to the power conversion device, the power conversion device The selected candidate voltage vector to which the spatial vector modulation technique is applied may be applied so that the switching frequency of is constant.

In the above description, steps S110 and S120 may be further divided into additional steps or combined into fewer steps, depending on the implementation herein. In addition, some steps may be omitted if necessary, and the order between the steps may be changed.

The driving control method of the power conversion system through model prediction control according to an embodiment of the present application may be implemented in a form of program instructions that can be performed through various computer means and may be recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, or the like alone or in combination. The program instructions recorded on the medium may be specially designed and configured for the present invention, or may be known and usable by those skilled in computer software. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical media such as CD-ROMs, DVDs, and magnetic media such as floptical disks. Includes hardware devices specifically configured to store and execute program instructions such as magneto-optical media, and ROM, RAM, flash memory, and the like. Examples of program instructions include high-level language code that can be executed by a computer using an interpreter, etc., as well as machine language codes produced by a compiler. The hardware device described above may be configured to operate as one or more software modules to perform the operation of the present invention, and vice versa.

In addition, the driving control method of the power conversion system through the above-described model prediction control may also be implemented in the form of a computer program or application executed by a computer stored in a recording medium.

The above description of the present application is for illustrative purposes, and those skilled in the art to which the present application pertains will understand that it is possible to easily modify to other specific forms without changing the technical spirit or essential features of the present application. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the present application is indicated by the claims below, rather than the detailed description, and it should be interpreted that all changes or modifications derived from the meaning and scope of the claims and equivalent concepts thereof are included in the scope of the present application.

100: power conversion system through model prediction control
10: Drive control device of the power conversion system through model prediction control
11: Selection section
12: Control
20: power generation department

Claims (11)

As a driving control method of the power conversion system through model prediction control,
(a) selecting some of the subdivided voltage vectors as candidate voltage vectors; And
(b) controlling the selected candidate voltage vector to be applied to the power converter by using the cost function as an input,
A drive control method of a power conversion system through model prediction control including a. According to claim 1,
Step (a) is,
A drive control method of a power conversion system through model predictive control, wherein the candidate voltage vector is selected by estimating a command voltage at the inverter end using a back electromotive force and a command current of the system. According to claim 1,
In the step (a), the subdivided voltage vector divided into 12 or more numbers is used as the subdivided voltage vector, and the driving control method of the power conversion system through model prediction control. According to claim 3,
In step (a), as the degree of subdivision of the subdivided voltage vector increases, the total harmonic distortion of the input-output current to the power converter decreases, and the driving control method of the power conversion system through model prediction control. According to claim 1,
In step (b), the voltage vector applied to the power converter is the selected candidate voltage vector to which the spatial vector modulation technique is applied so that the switching frequency of the power converter is set constant. Driving control method of power conversion system through. According to claim 1,
The power conversion device is a DC-capacitor-free power conversion device, the drive control method of the power conversion system through model prediction control. As a drive control device of the power conversion system through model prediction control,
A selection unit for selecting some of the subdivided voltage vectors as candidate voltage vectors; And
Control unit for controlling the selected candidate voltage vector to be applied to the power conversion device as an input of the cost function,
A drive control device for a power conversion system through model prediction control including a. The method of claim 7,
The selection unit,
A drive control device for a power conversion system through model predictive control, wherein the candidate voltage vector is selected by estimating a command voltage at the inverter end using the back electromotive force and command current of the system. The method of claim 7,
The selection unit,
A drive control device for a power conversion system through model prediction control, wherein the subdivided voltage vector divided by 12 or more numbers is used as the subdivided voltage vector. The method of claim 7,
The power conversion device is a DC-capacitor-free power conversion device, a drive control device for a power conversion system through model prediction control. As a power conversion system through model prediction control,
A power conversion device that supplies current generated from a three-phase voltage source to the system; And
Power conversion that controls the driving of the power conversion system through model prediction control that selects some of the subdivided voltage vectors as candidate voltage vectors and controls the selected candidate voltage vectors to be applied to the power converter by using the input of the cost function. The drive control of the system,
Power conversion system through model prediction control including a.

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