Three-level converter and model predictive control method and device thereof and power supply equipment

Abstract

The application discloses a three-level converter and a model predictive control method and device thereof and a power supply equipment, and the method comprises the following steps: determining a next switching vector and a second next switching vector according to a current switching vector of an NPC converter in the three-level converter; calculating a target capacitor voltage corresponding to each second next switching vector and a predicted current in a preset rotating coordinate system according to input and output collection information, the next switching vector and the second next switching vector; determining a target switching vector according to the target capacitor voltage, the predicted current and a second next reference current corresponding to a current reference current of a voltage outer loop control, so as to output a corresponding driving pulse by using the target switching vector; wherein the target switching vector is any second next switching vector; the application only performs traversal optimization on switching vectors with small switching times, reduces the traversal number of switching vectors in the MPC control process, reduces the action times of switching tubes, and improves the converter efficiency.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a model predictive control method, device, three-level converter, and power supply equipment for a three-level converter. Background Technology

[0002] Currently, phase-locked control (PLC) of three-level converters (such as three-level rectifiers or three-level inverters) requires model predictive control (MPC) of the NPC (Neutral Point Clamped) converter. During MPC, all switching vectors of the NPC converter are traversed to select the appropriate vectors for control, resulting in a large computational load and low converter efficiency. Therefore, reducing the number of switching vector traversals, lowering the computational load, and improving converter efficiency are urgent problems to be solved. Summary of the Invention

[0003] The purpose of this invention is to provide a model predictive control method, apparatus, device, and computer-readable storage medium for a three-level converter, so as to reduce the number of switching vector traversals and the number of switching transistor actions during the MPC control process, thereby improving converter efficiency.

[0004] To solve the above-mentioned technical problems, the present invention provides a model predictive control method for a three-level converter, comprising:

[0005] Based on the current switch vector of the NPC converter in the three-level converter, determine the next switch vector and the next two switch vectors; wherein, the first switch vector is the switch vector after the current switch vector is activated once and the state of one phase is adjusted, and the second switch vector is the switch vector after the NPC converter is activated once and the state of one phase is adjusted, corresponding to each of the first switch vectors;

[0006] Based on the input / output acquisition information, the next-step switch vector, and the next two-step switch vector, calculate the target capacitor voltage and the predicted current in a preset rotating coordinate system corresponding to each of the next two-step switch vectors; wherein, the target capacitor voltage includes the voltage of the upper bus capacitor and / or the lower bus capacitor on the DC bus of the NPC converter, the input / output acquisition information includes AC acquisition information and DC acquisition information, the AC acquisition information includes AC voltage and AC current, and the DC acquisition information includes the current step voltage of the upper bus capacitor and / or the lower bus capacitor;

[0007] Based on the target capacitor voltage, the predicted current, and the next two-phase reference current corresponding to the current-phase reference current of the voltage outer loop control, a target switching vector is determined so as to output a corresponding drive pulse using the target switching vector; wherein, the target switching vector is any of the next two-phase switching vectors.

[0008] On the other hand, determining the next-step switching vector and the next two-step switching vector based on the current-step switching vector of the NPC converter in the three-level converter includes:

[0009] Based on the current switch vector and the preset traversal vector table, the next switch vector and the next two-phase switch vector are determined; wherein, the preset traversal vector table includes the correspondence between each switch vector and the next switch vector after the switching transistor in the respective NPC converter adjusts the state of one phase once, the switch vectors in the preset traversal vector table include zero vectors, large vectors, medium vectors and small vectors, the small vectors include type 1 small vectors with a corresponding number of 3 next-phase switch vectors and type 2 small vectors with a corresponding number of 5 next-phase switch vectors; the number of switch vectors in the preset traversal vector table is 25, and the zero vectors include 000.

[0010] On the other hand, the number of switch vectors in the preset traversal vector table is 25. The zero vector includes OOO, the large vectors include PNN, PPN, NPN, NPP, NNP and PNP, the medium vectors include PON, OPN, NPO, NOP, ONP and PNO, the first type of small vectors includes ONN, PPO, NON, OPP, NNO, POP and ONN, and the second type of small vectors includes POO, OON, OPO, NOO, OOP and ONO.

[0011] On the other hand, the step of calculating the target capacitor voltage and the predicted current in the preset rotating coordinate system corresponding to each of the next two-step switching vectors based on the input / output acquisition information, the next-step switching vector, and the next-second-step switching vector includes:

[0012] Based on the AC voltage and AC current in the AC acquisition information, determine the current AC current and current AC voltage in the preset rotating coordinate system.

[0013] Based on the next-step switch vector, the next two-step switch vector, the current-step AC current, and the current-step AC voltage, calculate the predicted current in the preset rotating coordinate system corresponding to each of the next two-step switch vectors;

[0014] Based on the DC acquisition information, the AC current in the AC acquisition information, the current AC current of the current step, and the next two step switching vector, calculate the target capacitor voltage corresponding to each of the next two step switching vectors.

[0015] On the other hand, when the preset rotating coordinate system is an αβ rotating coordinate system and the three-level converter is a three-level rectifier, the step of calculating the predicted current in the preset rotating coordinate system corresponding to each of the next two-step switching vectors based on the next-step switching vector, the next two-step switching vector, the current-step AC current, and the current-step AC voltage includes:

[0016] pass Calculate the predicted current in the preset rotating coordinate system corresponding to a certain next two-step switching vector; where k is the current step, i αβ (k+2) is the predicted current in the preset rotating coordinate system corresponding to a certain next two-step switching vector, T is the sampling frequency, L is the inductance value of a single inductor on the AC side of the NPC converter, and e αβ (k) represents the current AC voltage, u αβ (k) represents the equivalent output voltage corresponding to the current switch vector in the αβ rotating coordinate system, u αβ (k+1) is the equivalent output voltage corresponding to the next-step switching vector of a certain second-step switching vector in the αβ rotating coordinate system, i αβ (k) represents the current AC current, e αβ (k+1)=e αβ (k)e jwT e jwT It is a complex function.

[0017] On the other hand, when the preset rotating coordinate system is an αβ rotating coordinate system, and the target capacitor voltage includes the voltage of the upper bus capacitor on the DC bus of the NPC converter, the step of calculating the target capacitor voltage corresponding to each of the next two-step switching vectors based on the DC acquisition information, the AC current in the AC acquisition information, the current AC current, and the next two-step switching vector includes:

[0018] pass Calculate the target capacitor voltage corresponding to a certain next two-step switching vector; where, u C1 (k+2) is the target capacitor voltage corresponding to a certain next two-step switching vector, C is the capacitance value of a single capacitor on the DC side of the NPC converter, C1 is the upper bus capacitor, Q is the three-dimensional clamping vector corresponding to a certain next two-step switching vector, i abc (k) represents the alternating current in the acquired AC information, u C1 (k) represents the current beat voltage of the upper bus capacitor in the DC acquisition information, i abc (k+1) represents the AC current i in the next cycle. αβ The three-phase current corresponding to (k+1), iαβ (k+1)=i αβ (k)e jwT .

[0019] On the other hand, when the preset rotating coordinate system is an αβ rotating coordinate system, the three-level converter is a three-level rectifier, and the target capacitor voltage includes the voltages of the upper and lower bus capacitors on the DC bus of the NPC converter, the target switching vector is determined based on the target capacitor voltage, the predicted current, and the next two-step reference current corresponding to the current step reference current controlled by the voltage outer loop. This includes:

[0020] via i′ αβ (l+1)=i′ αβ (l)e jwT Calculate the reference current for the next two beats; where l is the current beat k or the next beat k+1, i′ αβ (k) represents the current reference current in the αβ rotating coordinate system, i′ αβ (k+2) is the reference current for the next two cycles, e jwT It is a complex function;

[0021] via G=(i′) oα (k+2)-i rα (k+2)) 2 +(i o ′ β (k+2)-i rβ (k+2)) 2 +λ(u C1 (k+2)-u C2 (k+2)) 2 Calculate the index function corresponding to each of the next two-step switching vectors; where G is the index function, i′ oα (k+2) and i′ oβ (k+2) represents the current value in the αβ rotating coordinate system corresponding to the next two-phase reference current, i rα (k+2) and i rβ (k+2) represents the current value in the αβ rotating coordinate system corresponding to the predicted current, C1 is the upper bus capacitor, C2 is the lower bus capacitor, and u C1 (k+2) is the voltage of the upper bus capacitor in the target capacitor voltage, and u C2 (k+2) is the voltage of the lower bus capacitor in the target capacitor voltage;

[0022] The next two-step switch vector corresponding to the smallest index function is determined as the target switch vector.

[0023] The present invention also provides a model predictive control device for a three-level converter, comprising:

[0024] The switch determination module is used to determine the next switch vector and the next two switch vectors based on the current switch vector of the NPC converter in the three-level converter; wherein, the first switch vector is the switch vector after the switch transistor in the NPC converter corresponding to the current switch vector operates once to adjust the state of one phase, and the second switch vector is the switch vector after the switch transistor in the NPC converter corresponding to each of the first switch vectors operates once to adjust the state of one phase;

[0025] The traversal prediction module is used to calculate the target capacitor voltage and the predicted current in a preset rotating coordinate system corresponding to each of the next two-step switch vectors based on the input / output acquisition information, the next-step switch vector, and the next two-step switch vector; wherein, the target capacitor voltage includes the voltage of the upper bus capacitor and / or the lower bus capacitor on the DC bus of the NPC converter, the input / output acquisition information includes AC acquisition information and DC acquisition information, the AC acquisition information includes AC voltage and AC current, and the DC acquisition information includes the current step voltage of the upper bus capacitor and / or the lower bus capacitor;

[0026] The traversal selection module is used to determine the target switching vector based on the target capacitor voltage, the predicted current, and the next two-phase reference current corresponding to the current-phase reference current of the voltage outer loop control, so as to output a corresponding drive pulse using the target switching vector; wherein, the target switching vector is any of the next two-phase switching vectors.

[0027] The present invention also provides a three-level converter, comprising:

[0028] Memory, used to store computer programs;

[0029] A processor is used to implement the steps of the model predictive control method for a three-level converter as described above when executing the computer program.

[0030] In addition, the present invention also provides a power supply device, including: a three-level converter as described above.

[0031] The present invention provides a model predictive control method for a three-level converter, comprising: determining the next-phase switching vector and the next two-phase switching vector based on the current-phase switching vector of the NPC converter in the three-level converter; wherein, the first switching vector is the switching vector after one phase state adjustment by the switching transistor in the NPC converter corresponding to the current-phase switching vector, and the second switching vector is the switching vector after one phase state adjustment by the switching transistor in the NPC converter corresponding to each of the first switching vectors; and calculating the target capacitor voltage and the target capacitor voltage corresponding to each of the next two-phase switching vectors based on the input / output acquisition information, the next-phase switching vector, and the next two-phase switching vector. The system includes a preset predicted current in a rotating coordinate system; the target capacitor voltage includes the voltage of the upper bus capacitor and / or lower bus capacitor on the DC bus of the NPC converter; the input / output acquisition information includes AC acquisition information and DC acquisition information; the AC acquisition information includes AC voltage and AC current; and the DC acquisition information includes the current step voltage of the upper bus capacitor and / or lower bus capacitor. Based on the target capacitor voltage, the predicted current, and the next two-step reference current corresponding to the current step reference current of the voltage outer loop control, the target switching vector is determined to output the corresponding drive pulse using the target switching vector; the target switching vector is any next two-step switching vector.

[0032] As can be seen, by determining the next and second-to-last switching vectors based on the current switching vector of the NPC converter in a three-level converter, this invention can identify switching vectors with fewer switching cycles. Therefore, optimization is only performed on these switching vectors, reducing the number of switching vector traversals during MPC control and the number of switching transistor actions, thus improving converter efficiency. Furthermore, this invention also provides a model predictive control device for a three-level converter, a three-level converter, and a power supply device, which also possess the aforementioned beneficial effects. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0034] Figure 1 A flowchart of a model predictive control method for a three-level converter provided in an embodiment of the present invention;

[0035] Figure 2a This is a simplified schematic diagram of a conventional three-level NPC converter.

[0036] Figure 2b This is a schematic diagram of a conventional three-level NPC rectifier.

[0037] Figure 3 This is a diagram illustrating a typical three-level space vector.

[0038] Figure 4 This is a diagram illustrating a small vector next-step switching vector provided in an embodiment of the present invention.

[0039] Figure 5 This is a diagram illustrating another small vector next-step switching vector provided in an embodiment of the present invention;

[0040] Figure 6 A diagram illustrating the switching vector table for another model predictive control method for a three-level converter provided in an embodiment of the present invention;

[0041] Figure 7 A model predictive control block diagram of an NPC rectifier provided in an embodiment of the present invention;

[0042] Figure 8 This is a diagram illustrating the effect of model predictive control of an NPC rectifier provided in an embodiment of the present invention.

[0043] Figure 9 This is a structural block diagram of a model prediction control device for a three-level converter provided in an embodiment of the present invention;

[0044] Figure 10 This is a schematic diagram of a three-level converter provided in an embodiment of the present invention. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] Please refer to Figure 1 , Figure 1 A flowchart illustrating a model predictive control method for a three-level converter provided in an embodiment of the present invention. The method may include:

[0047] Step 101: Determine the next switch vector and the next two switch vectors based on the current switch vector of the NPC converter in the three-level converter.

[0048] Wherein, the first switch vector is the switch vector of the NPC converter corresponding to the current switch vector after the switch tube in the NPC converter adjusts the state of one phase after one operation, and the second switch vector is the switch vector of the NPC converter corresponding to each first switch vector after the switch tube in the NPC converter adjusts the state of one phase after one operation.

[0049] It is understood that the three-level converter provided in this embodiment can be configured with an NPC converter, such as a three-level rectifier or a three-level inverter. Taking a type I NPC converter as an example, such as... Figure 2a As shown, the operating principle of the Type I NPC converter in the three-level converter can be expressed as shown in equation (1).

[0050] e abc =u abc +Ldi abc (1)

[0051] In equation (1), e abc This refers to the three-phase power grid voltage value; u abc The three-phase voltage values ​​output from the AC side of the NPC converter, such as... Figure 2b The voltage between the source of switch S2 and the drain of switch S3 in stages A, B, and C (i.e., the midpoint voltage of the bridge arm); L is the inductance value of a single inductor on the AC side of the NPC converter, i abc This refers to the current values ​​on the three inductors on the AC side of the NPC converter, i.e., the three-phase AC current; in this embodiment, the subscripts abc can represent three-phase electricity, such as e abc and i abc These can be the three-phase voltage values ​​and the three-phase current values, respectively. The spatial vector diagram of different switching states of the NPC converter in a three-level converter is shown below. Figure 3 As shown, this includes 27 space vectors (i.e., switching vectors, such as OOO and ONP); the NPC converter modulates the AC side voltage u by switching different switching states. abc This is to control the sinusoidal nature of the input current and the unity power factor.

[0052] Correspondingly, during the operation of the NPC converter, the switch clamping to the midpoint of the DC side will cause the input current to be injected, resulting in fluctuations in the DC side capacitor voltage, as shown in equation (2).

[0053]

[0054] In equation (2), C is the capacitance of a single capacitor on the DC side of the NPC converter, C1 is the upper bus capacitor on the DC bus of the NPC converter (as shown in Figure 2), u C1 Let Q be the voltage of the upper bus capacitor C1, and let Q be the three-dimensional clamping vector. Q is a 3-dimensional vector, Q = [K(1)K(2)K(3)], and each term in Q can represent the clamping state of the switch, as shown in equation (3).

[0055]

[0056] In equation (3), i = 1, 2, 3, and X can represent the three phases A, B and C, i.e. X = A, B, C; for example, the three-dimensional clamping vector Q corresponding to the switch vector POO is [0 1 1].

[0057] Therefore, according to equations (2) and (3), the influence of the switching vector corresponding to each switching state on the midpoint voltage can be obtained. Correspondingly, the influence of each switching vector on the midpoint current can be shown in Table 1.

[0058] Table 1 shows the midpoint current of each switch vector.

[0059]

[0060] Correspondingly, conventional model predictive control requires traversing all switching vectors, resulting in a large computational load. However, this embodiment, by determining the switching vector for the next cycle and the next two cycles, only performs traversal optimization on switching vectors with fewer switching cycles. That is, the switching vector after each cycle ensures that the switching transistor operates only one phase and only once between the switching vector of that cycle and the switching vector of the current cycle. Taking a small vector as an example, such as switching vector ONN, when ensuring that the switching transistor operates only one phase and only once in the next cycle, there are three possible switching vectors for the next cycle to choose from, as follows: Figure 4 As shown, OON, PNN, and ONO are respectively. Therefore, during the traversal optimization, ONN only needs to traverse these three switch vectors in the next cycle. However, the redundant vector POO of ONN has a total of 5 switch vectors in the next cycle, as follows: Figure 5 As shown. In this embodiment, small vectors with three types of next-step switching vectors can be divided into 1 type of small vectors, and small vectors with five types of next-step switching vectors can be divided into 2 types of small vectors.

[0061] Similarly, such as Figure 6 As shown, a medium vector can have 4 types of next-step switching vectors, a large vector can have 3 types of next-step switching vectors, and a zero vector OOO can have 6 types of next-step switching vectors.

[0062] Correspondingly, in this embodiment, the next-phase switch vector can be the switch vector of the next phase corresponding to the current-phase switch vector, and the next two-phase switch vector can be the switch vector of the next phase corresponding to each of the next-phase switch vectors corresponding to the current-phase switch vector. Regarding the specific method by which the processor determines the next-phase switch vector and the next two-phase switch vector based on the current-phase switch vector of the NPC converter in the three-level converter in this step, the processor can determine the next-phase switch vector and the next two-phase switch vector based on the current-phase switch vector and a preset traversal vector table. The preset traversal vector table includes the correspondence between each switch vector and the next-phase switch vector after each switch action in the respective NPC converter adjusts the state of one phase. The switch vectors in the preset traversal vector table include zero vectors, large vectors, medium vectors, and small vectors. Small vectors include type 1 small vectors with a corresponding next-phase switch vector quantity of 3 and type 2 small vectors with a corresponding next-phase switch vector quantity of 5. The number of switch vectors in the preset traversal vector table is 25, and zero vectors include 000. For example... Figure 6 As shown, for the large vector 2(j), that is, the switch vector in row 2 and column j, the corresponding next switch vector can be 1(j), 3(j) and 3(j-1).

[0063] Step 102: Based on the input and output acquisition information, the next-step switch vector, and the next two-step switch vector, calculate the target capacitor voltage and the predicted current in the preset rotating coordinate system corresponding to each next two-step switch vector.

[0064] The target capacitor voltage includes the voltage of the upper bus capacitor (C1 in Figure 2) and / or the lower bus capacitor (C2 in Figure 2) on the DC bus of the NPC converter, i.e., the upper bus capacitor voltage and / or the lower bus capacitor voltage in the next two steps; the input and output acquisition information includes AC acquisition information and DC acquisition information, and the AC acquisition information includes AC voltage (such as the three-phase grid voltage value e mentioned above). abc ) and alternating current (as mentioned above i) abc The DC acquisition information includes the current beat voltage of the upper bus capacitor and / or lower bus capacitor, that is, the voltage u of the upper bus capacitor in the current beat k. C1 (k) and / or the voltage u of the upper bus capacitor C2 (k).

[0065] It is understood that the preset rotation coordinates in this embodiment can be either the αβ rotation coordinate system or the dq rotation coordinate system. Taking the three-level converter as a three-level rectifier and the preset rotation coordinates as the αβ rotation coordinate system as an example, by performing a rotation coordinate transformation on the above equation (1), the model of the grid-connected NPC converter (i.e., the three-phase NPC rectifier) ​​can be obtained as shown in equation (4).

[0066]

[0067] In equation (4), e αβ For the three-phase power grid voltage e abc The value of u in the αβ rotating coordinate system αβ The AC side output voltage (u) of the NPC converter abc The voltage value in the αβ rotating coordinate system; in this embodiment, the subscript αβ can represent the αβ rotating coordinate system, such as e αβ It can be the three-phase power grid voltage e abc Values ​​in the αβ rotating coordinate system.

[0068] By linear discretizing and rearranging equation (4), we can obtain equation (5) as follows.

[0069]

[0070] In equation (5), T is the sampling frequency, u αβ (k) represents the equivalent output voltage of the switching state at the k-th time step, i.e., the midpoint voltage u of the bridge arm corresponding to the switching state at the k-th time step. abc The value in the αβ rotating coordinate system. According to equation (5), when the sampling frequency is high, the input current of the next step can be predicted using the current value and voltage value of the current step (the kth step). Since there is a delay of one step in digital control, a two-step prediction method is adopted, that is, using the value of the current step (i.e., the kth step), the current value of the k+1th step (i.e., the next step) is calculated according to equation (5), and then the current of the k+2th step (i.e., the next two steps) is predicted, as shown in equation (6).

[0071]

[0072] In equation (6), the grid voltage of the (k+1)th cycle can be calculated according to equation (7).

[0073] e αβ (k+1)=e αβ (k)e jwT (7)

[0074] In equation (7), e jwT It is a complex function. Similarly, by discretizing the above equation (2), we can obtain the discrete equation for the two-part prediction, as shown in equation (8).

[0075]

[0076] Accordingly, the specific method by which the processor calculates the target capacitor voltage and predicted current in the preset rotating coordinate system corresponding to each of the next two-phase switch vectors based on the input / output acquisition information, the next-phase switch vector, and the next-second-phase switch vector can be set by the designer. For example, it can be set according to the type of the three-phase converter and the type of the preset rotating coordinate system. For instance, in this step, the processor can determine the current AC current and current AC voltage in the preset rotating coordinate system based on the AC voltage and current in the AC acquisition information; calculate the predicted current in the preset rotating coordinate system corresponding to each of the next two-phase switch vectors based on the next-phase switch vector, the next-second-phase switch vector, the current AC current, and the current AC voltage; and calculate the target capacitor voltage corresponding to each of the next two-phase switch vectors based on the DC acquisition information, the AC current in the AC acquisition information, the current AC current, and the next-second-phase switch vector.

[0077] Accordingly, when the preset rotating coordinate system is the αβ rotating coordinate system and the three-level converter is a three-level rectifier, the above calculation of the predicted current in the preset rotating coordinate system corresponding to each of the next two-step switching vectors based on the next-step switching vector, the next two-step switching vector, the current-step AC current, and the current-step AC voltage can include: through Calculate the predicted current in a preset rotating coordinate system corresponding to a given two-step switching vector; where k is the current step, i αβ (k+2) represents the predicted current in a preset rotating coordinate system corresponding to a certain second-phase switching vector, T is the sampling frequency, L is the inductance value of a single inductor on the AC side of the NPC converter, and e αβ (k) represents the AC voltage of the current frame, such as the AC voltage in the AC acquisition information (i.e., the AC voltage e of the current frame). abc (k) Voltage after αβ transformation; u αβ (k) represents the equivalent output voltage corresponding to the current switch vector in the αβ rotating coordinate system (i.e., the bridge arm midpoint voltage in the αβ rotating coordinate system), u αβ (k+1) represents the equivalent output voltage corresponding to the next switching vector in a given second-phase switching vector within the αβ rotating coordinate system, i αβ (k) represents the AC current of the current frame, such as the AC current in the AC data acquisition information (i.e., the AC current i of the current frame). abc (k) The current after αβ transformation; e αβ (k+1)=e αβ (k)e jwT e jwT It is a complex function.

[0078] Where the target capacitor voltage includes the voltage of the upper bus capacitor on the DC bus of the NPC converter, the above-mentioned calculation of the target capacitor voltage corresponding to each of the next two-phase switch vectors based on the DC acquisition information, the AC current in the AC acquisition information, the current AC current of the current phase, and the next two-phase switch vector can include: through Calculate the target capacitor voltage corresponding to a given two-step switching vector; where u C1 (k+2) represents the target capacitor voltage corresponding to a certain second-phase switching vector, C is the capacitance value of a single capacitor on the DC side of the NPC converter, C1 is the upper bus capacitor, Q is the three-dimensional clamping vector corresponding to a certain second-phase switching vector, and i abc (k) represents the AC current in the AC data acquisition, i.e., the three-phase AC current of the current frame (k) acquired; u C1 (k) represents the current beat voltage of the upper bus capacitor in the DC acquisition information, i abc (k+1) represents the AC current i in the next cycle. αβ The three-phase current corresponding to (k+1), i αβ (k+1)=i αβ (k)e jwT Correspondingly, if the target capacitor voltage includes the voltage of the lower bus capacitor, a similar approach can be used, utilizing the current beat voltage u of the lower bus capacitor from the DC acquisition information. C2 (k) Calculate the voltage u of the lower bus capacitor in the target capacitor voltage corresponding to a certain next two-step switch vector, based on the AC current, current of the current step, and the next two-step switch vector from the AC acquisition information. C2 (k+2).

[0079] Step 103: Determine the target switching vector based on the target capacitor voltage, the predicted current, and the reference current of the next two steps corresponding to the current step reference current of the voltage outer loop control, so as to output the corresponding drive pulse using the target switching vector; wherein, the target switching vector is any next two step switching vector.

[0080] Correspondingly, in this step, the processor can use the reference current of the next two steps corresponding to the current step reference current controlled by the voltage outer loop, as well as the target capacitor voltage and the predicted current in the preset rotating coordinate system corresponding to each next two step switch vector, to determine the target switch vector from each next two step switch vector, as the prediction result of the model predictive control, and thus output the corresponding drive pulse to control the switching transistor of the NPC converter.

[0081] It should be noted that the method provided in this embodiment may also include the process of obtaining the reference current for the next two cycles corresponding to the current cycle reference current of the current cycle controlled by the voltage outer loop; for example, when the preset rotating coordinate system adopts the αβ rotating coordinate system, the processor can obtain the reference current for the next two cycles corresponding to the current cycle reference current of the current cycle control by i′. αβ (l+1)=i′αβ (l)e jwT Calculate the reference current for the next two steps; where l is the current step k or the next step k+1, i′ αβ (k) represents the current reference current in the αβ rotating coordinate system, i′ αβ (k+2) is the reference current for the next two cycles, e jwT It is a complex function. That is, the processor can convert the reference current of the voltage outer loop control input into the current-phase reference current i′ in the αβ rotating coordinate system. αβ (k); via i′ αβ (k+1)=i′ αβ (k)e jwT and i′ αβ (k+2)=i′ αβ (k+1)e jwT Calculate the current reference current i′ in the current pulse. αβ (k) corresponds to the next two-phase reference current i′ αβ (k+2).

[0082] Correspondingly, the specific method by which the processor determines the target switching vector based on the target capacitor voltage, predicted current, and the reference current of the next two steps corresponding to the current step reference current controlled by the voltage outer loop in this step can be set by the designer. For example, the processor can determine the target switching vector based on the difference between the predicted current and the reference current of the next two steps corresponding to each next two-step switching vector, as well as the difference between the upper bus capacitor voltage and the lower bus capacitor voltage of the next two steps. In some embodiments, the objective function for the model predictive control of the three-level converter can be the tracking effect on the output current reference value, with the balance of the midpoint voltage as the cost function, to construct an index function. For example, when the preset rotating coordinate system is the αβ rotating coordinate system, the index function G = (i′ oα (k+2)-i rα (k+2)) 2 +(i o ′ β (k+2)-i rβ (k+2)) 2 +λ(u C1 (k+2)-u C2 (k+2)) 2 , i′ oα (k+2) and i′ oβ (k+2) represents the current value in the αβ rotating coordinate system corresponding to the reference current in the next two clock cycles, λ is the penalty coefficient, and i rα (k+2) and i rβ (k+2) represents the current value in the αβ rotating coordinate system corresponding to the predicted current; u C1 (k+2) is the voltage of the upper bus capacitor in the next two cycles, u C2(k+2) represents the lower bus capacitor voltage in the next two cycles. For example, the target capacitor voltage may include the voltage of the upper bus capacitor on the DC bus of the NPC converter (i.e., u). C1 (k+2)) and the voltage of the lower bus capacitor (i.e., u) C2 (k+2)), or the target capacitor voltage includes u C1 When (k+2), the DC output voltage of the next two steps and u can be calculated. C1 The difference of (k+2) yields u. C2 (k+2). That is to say, in this step, the processor can use G = (i′) oα (k+2)-i rα (k+2)) 2 +(i o ′ β (k+2)-i rβ (k+2)) 2 +λ(u C1 (k+2)-u C2 (k+2)) 2 Calculate the index function corresponding to each of the next two-step switching vectors; determine the next two-step switching vector corresponding to the smallest index function as the target switching vector.

[0083] For example, if a three-level converter is a three-level rectifier, and the target capacitor voltage includes the voltage of the upper bus capacitor on the DC bus of the NPC converter (i.e., the NPC rectifier), then the model predictive control of the NPC converter (i.e., the NPC rectifier) ​​in the three-level rectifier can be as follows: Figure 7 As shown, the control system can adopt dual-loop control, with the voltage value on the grid side (e) abc ) and input current value (i abc After sampling and phase-locked loop (PLL) startup, the outer loop can use PI (Proportional-Integral-Derivative) control to control the DC-side output voltage and output current reference value. This value, after αβ transformation, is sent to the inner current loop as the current reference value (i′) for MPC control. αβ ); the sampled grid-side voltage value (e abc ) and input current value (i abc The predicted current value (i) for the next two cycles is calculated using the above formula (6). αβ (k+2)), similarly, the voltage (u) of the DC-side bus capacitor after sampling. C1 The predicted value (u) of the upper bus capacitor voltage is calculated using the above formula (8). C1 (k+2)); The predicted and reference values ​​can be optimized by iterating through the switching vectors of each of the next two steps according to the index function G. The switching vectors (Sa, Sb, and Sc) that minimize the index function G are the predicted switching states of the (k+2)th step (i.e., the target switching vector). Figure 8 As shown, when using the above model predictive control method, even if the three-phase grid current input to the NPC rectifier (such as the A-phase grid current i) is... a Even if a sudden change occurs, the target switching vector used by the model predictive control can still ensure the tracking effect of the output current reference value.

[0084] In this embodiment, the present invention determines the next-phase switch vector and the next two-phase switch vector based on the current-phase switch vector of the NPC converter in the three-level converter. This allows the determination of switch vectors with fewer switching cycles, thereby optimizing only the switch vectors with fewer switching cycles. This reduces the number of switch vector traversals during MPC control and also reduces the minimum number of actions of the switching transistors, thus improving converter efficiency.

[0085] Corresponding to the above method embodiments, this invention also provides a model predictive control device for a three-level converter. The model predictive control device for a three-level converter described below and the model predictive control method for a three-level converter described above can be referred to in correspondence.

[0086] Please refer to Figure 9 , Figure 9 This is a structural block diagram of a model prediction control device for a three-level converter provided in an embodiment of the present invention. The device may include:

[0087] The switch determination module 10 is used to determine the next switch vector and the next two switch vectors based on the current switch vector of the NPC converter in the three-level converter; wherein, the first switch vector is the switch vector after the switch transistor in the NPC converter corresponding to the current switch vector operates once to adjust the state of one phase, and the second switch vector is the switch vector after the switch transistor in the NPC converter corresponding to each first switch vector operates once to adjust the state of one phase.

[0088] The traversal prediction module 20 is used to calculate the target capacitor voltage and the predicted current in the preset rotating coordinate system corresponding to each of the next two-step switch vectors based on the input and output acquisition information, the next-step switch vector, and the next two-step switch vector. The target capacitor voltage includes the voltage of the upper bus capacitor and / or the lower bus capacitor on the DC bus of the NPC converter. The input and output acquisition information includes AC acquisition information and DC acquisition information. The AC acquisition information includes AC voltage and AC current. The DC acquisition information includes the current step voltage of the upper bus capacitor and / or the lower bus capacitor.

[0089] The traversal selection module 30 is used to determine the target switching vector based on the target capacitor voltage, the predicted current, and the next two-step reference current corresponding to the current step reference current of the voltage outer loop control, so as to output the corresponding drive pulse using the target switching vector; wherein, the target switching vector is any next two-step switching vector.

[0090] In some embodiments, the traversal prediction module 20 can be specifically used to determine the next-phase switch vector and the next two-phase switch vector based on the current-phase switch vector and a preset traversal vector table; wherein, the preset traversal vector table includes the correspondence between each switch vector and the next-phase switch vector after the switching transistor in the respective NPC converter adjusts the state of one phase once, the switch vectors in the preset traversal vector table include zero vectors, large vectors, medium vectors and small vectors, the small vectors include type 1 small vectors with a corresponding number of 3 next-phase switch vectors and type 2 small vectors with a corresponding number of 5 next-phase switch vectors; the number of switch vectors in the preset traversal vector table is 25, and the zero vectors include 000.

[0091] In some embodiments, the number of switch vectors in the preset traversal vector table is 25. Zero vectors include OOO, large vectors include PNN, PPN, NPN, NPP, NNP and PNP, medium vectors include PON, OPN, NPO, NOP, ONP and PNO, class 1 small vectors include ONN, PPO, NON, OPP, NNO, POP and ONN, and class 2 small vectors include POO, OON, OPO, NOO, OOP and ONO.

[0092] In some embodiments, the traversal selection module 30 may include:

[0093] The rotation transformation submodule is used to determine the current AC current and current AC voltage in the preset rotating coordinate system based on the AC voltage and AC current in the AC acquisition information.

[0094] The current prediction submodule is used to calculate the predicted current in the preset rotating coordinate system corresponding to each of the next two-step switching vectors based on the next-step switching vector, the next two-step switching vector, the current AC current, and the current AC voltage.

[0095] The voltage prediction submodule is used to calculate the target capacitor voltage corresponding to each of the next two-step switching vectors based on the DC acquisition information, the AC current in the AC acquisition information, the current AC current of the current step, and the next two-step switching vector.

[0096] In some embodiments, when the preset rotating coordinate system is an αβ rotating coordinate system and the three-level converter is a three-level rectifier, the current prediction submodule can be specifically used to... Calculate the predicted current in a preset rotating coordinate system corresponding to a given two-step switching vector; where k is the current step, i αβ (k+2) represents the predicted current in a preset rotating coordinate system corresponding to a certain second-phase switching vector, T is the sampling frequency, L is the inductance value of a single inductor on the AC side of the NPC converter, and e αβ (k) represents the current AC voltage, uαβ (k) represents the equivalent output voltage corresponding to the current switch vector in the αβ rotating coordinate system, u αβ (k+1) represents the equivalent output voltage corresponding to the next switching vector in a given second-phase switching vector within the αβ rotating coordinate system, i αβ (k) represents the current AC current, e αβ (k+1)=e αβ (k)e jwT e jwT It is a complex function.

[0097] In some embodiments, the voltage prediction submodule may be specifically used to... Calculate the target capacitor voltage corresponding to a given two-step switching vector; where u C1 (k+2) represents the target capacitor voltage corresponding to a certain second-phase switching vector, C is the capacitance value of a single capacitor on the DC side of the NPC converter, C1 is the upper bus capacitor, Q is the three-dimensional clamping vector corresponding to a certain second-phase switching vector, and i abc (k) represents the alternating current in the AC data acquisition process, u C1 (k) represents the current beat voltage of the upper bus capacitor in the DC acquisition information, i abc (k+1) represents the AC current i in the next cycle. αβ The three-phase current corresponding to (k+1), i αβ (k+1)=i αβ (k)e jwT .

[0098] In some embodiments, when the preset rotating coordinate system is an αβ rotating coordinate system, the three-level converter is a three-level rectifier, and the target capacitor voltage includes the voltages of the upper bus capacitor and the lower bus capacitor on the DC bus of the NPC converter, the traversal selection module 30 may include:

[0099] Refer to the adjustment submodule for use via i′ αβ (l+1)=i′ αβ (l)e jwT Calculate the reference current for the next two steps; where l is the current step k or the next step k+1, i′ αβ (k) represents the current reference current in the αβ rotating coordinate system, i′ αβ (k+2) is the reference current for the next two cycles, e jwT It is a complex function;

[0100] The indicator calculation submodule is used to calculate the index using G = (i′ oα (k+2)-i rα (k+2)) 2 +(i o ′ β(k+2)-i rβ (k+2)) 2 +λ(u C1 (k+2)-u C2 (k+2)) 2 Calculate the index function corresponding to each of the next two-step switching vectors; where G is the index function, i′ oα (k+2) and i′ oβ (k+2) represents the current value in the αβ rotating coordinate system corresponding to the reference current in the next two cycles, i rα (k+2) and i rβ (k+2) represents the predicted current value in the αβ rotating coordinate system, C1 is the upper bus capacitance, C2 is the lower bus capacitance, and u C1 (k+2) represents the voltage of the upper bus capacitor in the target capacitor voltage, u C2 (k+2) is the voltage of the lower bus capacitor in the target capacitor voltage;

[0101] The target determination submodule uses the next two-step switch vector corresponding to the smallest index function as the target switch vector.

[0102] In this embodiment, the present invention uses the switch determination module 10 to determine the next switch vector and the next two switch vectors based on the current switch vector of the NPC converter in the three-level converter. This allows the switch vectors with fewer switching cycles to be determined, thus only performing traversal optimization on the switch vectors with fewer switching cycles. This reduces the number of traversals of the switch vectors during the MPC control process and also reduces the number of switching transistor actions, thereby improving the converter efficiency.

[0103] Corresponding to the above method embodiments, this invention also provides a three-level converter. The three-level converter described below and the model predictive control method of the three-level converter described above can be referred to each other.

[0104] Please refer to Figure 10 , Figure 10 This is a schematic diagram of a three-level converter provided in an embodiment of the present invention. The three-level converter may include:

[0105] Memory D1 is used to store computer programs;

[0106] Processor D2 is used to implement the steps of the model predictive control method for the three-level converter provided in the above method embodiments when executing a computer program.

[0107] The steps in the model predictive control method for the three-level converter described above can be implemented using the structure of the three-level converter.

[0108] Corresponding to the three-level converter embodiment above, this invention also provides a power supply device. The power supply device described below can be referred to in correspondence with the three-level converter described above.

[0109] A power supply device includes a three-level converter as provided in the above embodiments.

[0110] Corresponding to the above method embodiments, this invention also provides a computer-readable storage medium. The computer-readable storage medium described below and the model predictive control method for a three-level converter described above can be referred to and correspond to each other.

[0111] A computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the model predictive control method for a three-level converter as described in the above method embodiments.

[0112] The computer-readable storage medium can specifically be a USB flash drive, a portable hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk, or any other readable storage medium capable of storing program code.

[0113] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus, three-level converter, power supply device, and computer-readable storage medium disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0114] The above provides a detailed description of the model predictive control method, apparatus, three-level converter, and power supply device for a three-level converter provided by the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the protection scope of the present invention.

Claims

1. A model predictive control method for a three-level converter, characterized in that, The method comprises the steps of: determining a next switching vector and a second next switching vector according to a current switching vector of an NPC converter in a three-level converter; wherein the next switching vector is a switching vector after a switching tube in the NPC converter corresponding to the current switching vector is adjusted once in a phase state, and the second next switching vector is a switching vector after a switching tube in the NPC converter corresponding to each of the next switching vectors is adjusted once in a phase state; calculating a target capacitor voltage corresponding to each of the second next switching vectors and a predicted current in a preset rotating coordinate system according to input and output collection information, the next switching vector and the second next switching vector; wherein the target capacitor voltage comprises a voltage of an upper bus capacitor and / or a lower bus capacitor on a DC bus of the NPC converter, the input and output collection information comprises AC collection information and DC collection information, the AC collection information comprises AC voltage and AC current, and the DC collection information comprises a current switching vector voltage of the upper bus capacitor and / or the lower bus capacitor; determining a target switching vector according to the target capacitor voltage, the predicted current and a second next switching vector corresponding to a current switching vector of a voltage outer loop control, so as to output a corresponding driving pulse by using the target switching vector; wherein the target switching vector is any of the second next switching vectors; the method further comprises the steps of: determining the next switching vector and the second next switching vector according to the current switching vector of the NPC converter in the three-level converter; wherein the next switching vector is a switching vector after a switching tube in the NPC converter corresponding to the current switching vector is adjusted once in a phase state, and the second next switching vector is a switching vector after a switching tube in the NPC converter corresponding to each of the next switching vectors is adjusted once in a phase state; determining the next switching vector and the second next switching vector according to the current switching vector and a preset traversal vector table; wherein the preset traversal vector table comprises a corresponding relationship between each switching vector and a next switching vector after a switching tube in the NPC converter corresponding to each switching vector is adjusted once in a phase state, the switching vectors in the preset traversal vector table comprise zero vectors, large vectors, middle vectors and small vectors, the small vectors comprise a first type of small vector with a corresponding number of next switching vectors being 3 and a second type of small vector with a corresponding number of next switching vectors being 5; the number of switching vectors in the preset traversal vector table is 25, and the zero vectors comprise OOO; the method further comprises the steps of: determining a current AC current and a current AC voltage in the preset rotating coordinate system according to the AC voltage and the AC current in the AC collection information; calculating the predicted current in the preset rotating coordinate system corresponding to each of the second next switching vectors according to the next switching vector, the second next switching vector, the current AC current, and the current AC voltage; calculating the target capacitor voltage corresponding to each of the second next switching vectors according to the DC collection information, the AC current in the AC collection information, the current AC current and the second next switching vector.

2. The model predictive control method of a three-level converter according to claim 1, characterized in that, The number of switching vectors in the preset traversal vector table is 25, the zero vector includes OOO, the large vector includes PNN, PPN, NPN, NPP, NNP and PNP, the medium vector includes PON, OPN, NPO, NOP, ONP and PNO, the 1st small vector includes ONN, PPO, NON, OPP, NNO, POP and ONN, and the 2nd small vector includes POO, OON, OPO, NOO, OOP and ONO.

3. The model predictive control method of a three-level converter according to claim 1, characterized in that, The preset rotating coordinate system is The rotating coordinate system, when the three-level converter is a three-level rectifier, and the calculation of the predicted current corresponding to each of the next two switching vectors in the preset rotating coordinate system according to the next switching vector, the next two switching vectors, the current AC current and the current AC voltage comprises: pass Calculate the predicted current in the preset rotating coordinate system corresponding to a certain next two-step switching vector; wherein, For the current shot, The predicted current in the preset rotating coordinate system corresponding to a certain next two-step switching vector. Sampling frequency, The inductance value of a single inductor on the AC side of the NPC converter. The current AC voltage is... For the The equivalent output voltage corresponding to the current switch vector in the rotating coordinate system. For the The equivalent output voltage corresponding to the next switching vector of a certain second-phase switching vector in a rotating coordinate system. The current AC current is described. , It is a complex function.

4. The model predictive control method of a three-level converter according to claim 3, characterized in that, The preset rotating coordinate system is The rotating coordinate system, when the target capacitor voltage includes a voltage of an upper bus capacitor on a DC bus of the NPC converter, the calculation of the target capacitor voltage corresponding to each of the lower two-shot switching vectors according to the DC acquisition information, the AC current in the AC acquisition information, the current shot AC current, and the lower two-shot switching vector includes: By , calculating a target capacitor voltage corresponding to a certain said lower two-beat switching vector; wherein, is a target capacitor voltage corresponding to a certain said lower two-beat switching vector, is a capacitance value of a single capacitor on the DC side of the NPC converter, is the upper bus capacitor, is a three-dimensional clamping vector corresponding to a certain said lower two-beat switching vector, is an AC current in the AC collection information, is a current beat voltage of the upper bus capacitor in the DC collection information, is a next-beat AC current corresponding three-phase current, .

5. The model predictive control method of a three-level converter according to any one of claims 1 to 4, characterized in that, The preset rotating coordinate system is The rotating coordinate system, the three-level converter is a three-level rectifier, when the target capacitor voltage includes the voltage of the upper bus capacitor and the lower bus capacitor on the DC bus of the NPC converter, determining a target switching vector according to the target capacitor voltage, the predicted current, and the lower two-beat reference current corresponding to the current of the voltage outer loop control. By , calculating the next two-beat reference current; wherein, is the current beat or the next beat , is the current beat reference current in the rotating coordinate system, is the next two-beat reference current, is the next two-beat reference current, is a complex function; By , calculate the index function corresponding to each of the lower two-beat switch vectors; wherein, is the index function, and is the current value in the rotating coordinate system corresponding to the lower two-beat reference current, and is the current value in the rotating coordinate system corresponding to the predicted current, is the upper bus capacitance, is the lower bus capacitance, is the voltage of the upper bus capacitance in the target capacitance voltage, and the is the voltage of the lower bus capacitance in the target capacitance voltage; The switching vector corresponding to the minimum index function is determined as the target switching vector.

6. A model predictive control apparatus for a three-level converter, characterized by The method comprises the steps of: The switching determination module is configured to determine a next switching vector and a second next switching vector according to a current switching vector of an NPC converter in a three-level converter; wherein the next switching vector is a switching vector after a switching tube in the NPC converter corresponding to the current switching vector is adjusted once in a phase state, and the second next switching vector is a switching vector after a switching tube in the NPC converter corresponding to each of the next switching vectors is adjusted once in a phase state; The traversal prediction module is configured to calculate a target capacitor voltage corresponding to each of the second next switching vectors and a predicted current in a preset rotating coordinate system according to input and output collection information, the next switching vector and the second next switching vector; wherein the target capacitor voltage includes a voltage of an upper bus capacitor and / or a lower bus capacitor on a direct current bus of the NPC converter, the input and output collection information includes alternating current collection information and direct current collection information, the alternating current collection information includes alternating current voltage and alternating current, and the direct current collection information includes a current switching vector of the upper bus capacitor and / or the lower bus capacitor; The traversal selection module is configured to determine a target switching vector according to the target capacitor voltage, the predicted current and a second next reference current corresponding to a current switching vector of a voltage outer loop control, so as to output a corresponding driving pulse by using the target switching vector; wherein the target switching vector is any of the second next switching vectors. The switching determination module is specifically configured to determine the next switching vector and the second next switching vector according to the current switching vector and a preset traversal vector table; wherein the preset traversal vector table includes a corresponding relationship between each switching vector and a next switching vector after a switching tube in the NPC converter corresponding to each of the next switching vectors is adjusted once in a phase state, the switching vector in the preset traversal vector table includes a zero vector, a large vector, a medium vector and a small vector, the small vector includes a 1st small vector corresponding to the next switching vector with a number of 3 and a 2nd small vector corresponding to the next switching vector with a number of 5; the number of switching vectors in the preset traversal vector table is 25, and the zero vector includes OOO. The traversal prediction module comprises: The rotating transformation submodule is configured to determine a current alternating current and a current alternating voltage in the preset rotating coordinate system according to alternating current voltage and alternating current in the alternating current collection information. a current prediction submodule, configured to calculate a predicted current corresponding to each of the second next switching vectors in a preset rotating coordinate system according to the next switching vector, the second next switching vectors, the current AC current, and the current AC voltage; a voltage prediction submodule, configured to calculate a target capacitor voltage corresponding to each of the second next switching vectors according to the DC collection information, an AC current in the AC collection information, the current AC current, and the second next switching vectors.

7. A three-level converter, characterized by comprising: a memory, configured to store a computer program; a processor, configured to execute the computer program to implement the steps of the model predictive control method of the three-level converter according to any one of claims 1 to 5.

8. A power supply device characterized by comprising: comprising: the three-level converter according to claim 7.

Images