Low-cost converter regulation and control method and system for standby power supply system

Abstract

The invention belongs to the field of regulation and control of standby power supply loop devices, and provides a low-cost converter regulation and control method and system for a standby power supply system, and the method comprises the steps: sampling load voltage and current, inductive current, and DC side upper and lower capacitor voltage; selecting inductive current to perform decoupling operation, calculating expected output voltage of the converter based on a dead-beat control principle, and performing normalization processing; determining a sector with an optimal size according to an amplitude condition and a boundary condition of the expected output voltage; based on discrete space vector modulation, selecting a low common-mode voltage vector to synthesize a virtual small vector and a virtual medium vector, and expanding a candidate vector set; determining a switching sequence at the next moment according to the large and small sectors where the expected output voltage is located and the voltage difference value of the upper and lower capacitors on the direct current side to balance the neutral point voltage and the fixed switching frequency; and calculating the action time of the voltage vector according to the value function, outputting the duty ratio of the voltage vector, and applying the duty ratio to a switching device of the converter.

Description

Technical Field

[0001] The invention belongs to the technical field of regulating and controlling of standby power supply loop devices, and particularly relates to a low-cost converter regulating method and system for a standby power supply system. Background Art

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

[0003] Three-level inverters have obvious advantages such as low voltage stress of power switching tubes, high output waveform quality, and small filter volume, and are widely used in power supply and distribution systems. In addition, compared with three-level converters with only L filters, three-level converters with LC filters have advantages such as higher converter efficiency, lower harmonic content in the output waveform, and less electromagnetic interference. Therefore, three-level converters with LC filters are widely used in Uninterruptible Power Supplies (UPS) and Emergency Power Supplies (EPS).

[0004] The low-cost three-level converter topology reduces the number of power switching tubes by using a coupled switch unit, thereby reducing the system cost and having a wide application prospect in the standby power field. The common-mode voltage is generated by the high-frequency switching action of power switching tubes. In a system with distributed photovoltaic power generation units, due to the existence of parasitic capacitors, leakage current is likely to be induced, resulting in output current distortion of the converter, increased system power loss, and even a threat to personal safety. When the standby power supply system is applied to motor variable-frequency drive, the motor will inductively generate shaft voltage under the influence of the common-mode voltage, which is likely to break down the insulating oil film between the motor bearings, damage the motor bearings, and increase the system electromagnetic interference.

[0005] As the inventor understands, the existing traditional linear regulation methods for low-cost three-level converters with LC filters include Proportional Integral (PI) control and Proportional Resonance (PR) control. However, the performance of this method depends on the value of the gain module, and there are also problems such as slow dynamic response and difficulty in achieving neutral point potential balance. Model predictive control has obvious advantages in the following aspects, such as fast dynamic response ability, superior anti-interference ability, and flexible multi-objective control ability. Therefore, model predictive control is more suitable for application in standby power supply systems to meet the performance indicators of high reliability and fast switching of the system.

[0006] However, due to the limitations of its own topology, the existing common-mode voltage suppression method for the original three-level converter cannot be applied to this topology. At the same time, for the existing model predictive control methods for low-cost three-level converters, they are only applicable to the topology with an L filter and cannot be directly applied to the topology with an LC filter. If the traditional model predictive control method is improved and applied to the topology with an LC filter, it has the following disadvantages, such as high common-mode voltage, high harmonic content in the load voltage, non-fixed switching frequency, and complex control algorithm operation. Summary of the Invention

[0007] To solve the above problems, the present invention proposes a control method and system for a low-cost converter in a standby power supply system. The present invention can effectively suppress the common-mode voltage of the system, fix the switching frequency, reduce the harmonic of the load voltage, reduce the operation amount of the control algorithm, and significantly improve the system performance.

[0008] According to some embodiments, the first solution of the present invention provides a control method for a low-cost converter in a standby power supply system, adopting the following technical solutions:

[0009] The control method for a low-cost converter in a standby power supply system includes:

[0010] Obtain the load voltage and current, inductor current, and the voltages of the upper and lower capacitors on the DC side of the low-cost three-level converter at the current moment, and calculate the expected output voltage;

[0011] Optimize the vector candidate set by discarding high common-mode voltage vectors, and synthesize virtual small vectors and virtual medium vectors based on discrete space vector modulation to expand the vector candidate set to obtain the latest vector candidate set;

[0012] Based on the amplitude relationship and boundary conditions of the expected output voltage in the 60-degree coordinate system, determine the optimal large sector and the optimal small sector where the expected output voltage is located;

[0013] Based on the latest vector candidate set, determine the initial switching sequence in the optimal small sector according to the DC side capacitor voltage difference;

[0014] Taking the minimum load voltage tracking error as the goal, calculate the optimal action time of the selected basic voltage vector, and optimize the initial switching sequence according to the minimum number of switching actions and the balance of the DC side neutral point voltage to obtain the optimal switching sequence;

[0015] Generate corresponding drive signals based on the optimal switching sequence to control the conduction and cutoff of the switching devices of the low-cost three-level converter.

[0016] According to some embodiments, the second solution of the present invention provides a control system for a low-cost converter in a standby power supply system, adopting the following technical solutions:

[0017] A low-cost converter control system for an emergency power supply system, comprising:

[0018] An expected output voltage calculation module, configured to obtain the load voltage and current, inductor current, and upper and lower capacitor voltages on the DC side of a low-cost three-level converter at the current moment, and calculate the expected output voltage;

[0019] A vector candidate set determination module, configured to optimize the vector candidate set by deprecating high common-mode voltage vectors, and expand the vector candidate set based on discrete space vector modulation to synthesize virtual small vectors and virtual medium vectors, to obtain the latest vector candidate set;

[0020] An optimal sector determination module, configured to determine the optimal large sector and the optimal small sector where the expected output voltage is located respectively based on the amplitude relationship and boundary conditions of the expected output voltage in a 60-degree coordinate system;

[0021] An initial switching sequence design module, configured to determine the initial switching sequence in the optimal small sector based on the latest vector candidate set and according to the DC side capacitor voltage difference;

[0022] A neutral point voltage balance and switching sequence optimization module, configured to take minimizing the load voltage tracking error as the goal, calculate the optimal action time of the selected basic voltage vector, and optimize the initial switching sequence according to minimizing the number of switching actions and balancing the neutral point voltage on the DC side, to obtain the optimal switching sequence;

[0023] A drive signal conversion module, configured to generate corresponding drive signals based on the optimal switching sequence to control the conduction and cutoff of the switching devices of the low-cost three-level converter.

[0024] According to some embodiments, the third aspect of the present invention provides a computer-readable storage medium.

[0025] A computer-readable storage medium, on which a computer program is stored, and when the program is executed by a processor, it implements the steps in the low-cost converter control method for an emergency power supply system described in the first aspect above.

[0026] According to some embodiments, the fourth aspect of the present invention provides a computer device.

[0027] A computer device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, and when the processor executes the program, it implements the steps in the low-cost converter control method for an emergency power supply system described in the first aspect above.

[0028] According to some embodiments, the fifth aspect of the present invention provides a computer program product or a computer program.

[0029] The present invention provides a computer program product or a computer program. The computer program product or the computer program includes computer instructions stored in a computer-readable storage medium. A processor of a computer device reads the computer instructions from the computer-readable storage medium, and the processor executes the computer instructions, so that the computer device executes the steps in the low-cost type converter regulation method for a backup power supply system as described in the first aspect above.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] The present invention can reduce the common-mode voltage and improve the system reliability; introduce the concept of virtual vectors, synthesize the load voltage with multiple vectors, reduce the voltage ripple, and improve the power quality of the output voltage; use a value function to determine the optimal action time of the voltage vector required for synthesizing the load voltage, further reducing the voltage ripple; cleverly design the switching sequence to achieve a fixed switching frequency, which is beneficial to the efficient filtering of voltage harmonics; flexibly select the switching sequence, and cleverly control the neutral point voltage of the DC side to achieve the balance of the neutral point voltage of the DC side; the optimal sector judgment method in the 60-degree coordinate system avoids complex trigonometric function calculations through simple numerical comparisons, simplifies the algorithm operation process, and greatly reduces the complexity of the control algorithm. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0033] Figure 1 It is a structural diagram of a low-cost type three-level converter system applicable to a backup power supply system;

[0034] Figure 2 It is a control block diagram of a low-cost type three-level converter system applicable to a backup power supply system of the present invention;

[0035] Figure 3 It is a low common-mode basic space vector diagram of a low-cost type three-level converter system applicable to a backup power supply system of the present invention;

[0036] Figure 4 It is an extended space vector diagram of a low-cost type three-level converter system applicable to a backup power supply system of the present invention;

[0037] FIG. 5(a) shows the DC side capacitor voltage, line voltage, load current, load voltage, and common-mode voltage of a low-cost type three-level converter system applicable to a backup power supply system of the present invention using a single-vector model predictive control;

[0038] Figure 5(b) shows the DC-side capacitor voltage, line voltage, load current, load voltage, and common-mode voltage of the low-cost three-level converter system applicable to the backup power supply system of the present invention using the optimal switching sequence model predictive control;

[0039] Figure 5(c) shows the DC-side capacitor voltage, line voltage, load current, load voltage, and common-mode voltage of the low-cost three-level converter system applicable to the backup power supply system of the present invention using the low common-mode model predictive control proposed by the present invention;

[0040] Figure 6(a) shows the Fast Fourier Transform (FFT) of the low-cost three-level converter system applicable to the backup power supply system of the present invention using the single-vector model predictive control;

[0041] Figure 6(b) shows the Fast Fourier Transform of the low-cost three-level converter system applicable to the backup power supply system of the present invention using the optimal switching sequence model predictive control;

[0042] Figure 6(c) shows the Fast Fourier Transform of the low-cost three-level converter system applicable to the backup power supply system of the present invention using the low common-mode model predictive control proposed by the present invention;

[0043] Figure 7(a) shows the dynamic response waveform of the low-cost three-level converter system applicable to the backup power supply system of the present invention using the single-vector model predictive control;

[0044] Figure 7(b) shows the dynamic response waveform of the low-cost three-level converter system applicable to the backup power supply system of the present invention using the optimal switching sequence model predictive control;

[0045] Figure 7(c) shows the dynamic response waveform of the low-cost three-level converter system applicable to the backup power supply system of the present invention using the low common-mode model predictive control proposed by the present invention. Detailed implementation manners

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

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

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

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

[0050] Embodiment 1

[0051] This embodiment provides a low-cost converter control method for a backup power supply system. This embodiment takes the application of this method to a server as an example. It can be understood that this method can also be applied to a terminal, and can also be applied to a system including a terminal and a server, and is realized through the interaction between the terminal and the server. The server can be an independent physical server, or a server cluster or distributed system composed of multiple physical servers, or a cloud server providing basic cloud computing services such as cloud services, cloud databases, cloud computing, cloud functions, cloud storage, web servers, cloud communications, middleware services, domain name services, security services CDN, and big data and artificial intelligence platforms. The terminal can be a smart phone, a tablet computer, a notebook computer, a desktop computer, a smart speaker, a smart watch, etc., but is not limited thereto. The terminal and the server can be directly or indirectly connected through wired or wireless communication methods, and this application does not make any restrictions here. In this embodiment, the method includes the following steps:

[0052] Obtain the load voltage, current, inductor current, and the voltages of the upper and lower capacitors on the DC side of the low-cost three-level converter at the current moment, and calculate the expected output voltage;

[0053] Optimize the vector candidate set by deprecating high common-mode voltage vectors, and synthesize virtual small vectors and virtual medium vectors based on discrete space vector modulation to expand the vector candidate set, and obtain the latest vector candidate set;

[0054] Based on the amplitude relationship and boundary conditions of the expected output voltage in the 60-degree coordinate system, determine the optimal large sector and the optimal small sector where the expected output voltage is located;

[0055] Based on the latest vector candidate set, determine the initial switching sequence in the optimal small sector according to the DC side capacitor voltage difference;

[0056] With the goal of minimizing the load voltage tracking error, calculate the optimal action time of the selected basic voltage vector, and optimize the initial switching sequence according to minimizing the number of switching actions and balancing the neutral point voltage on the DC side to obtain the optimal switching sequence;

[0057] Generate corresponding drive signals based on the optimal switching sequence to control the conduction and turn-off of the switching devices of the low-cost three-level converter.

[0058] The present invention proposes a high-performance regulation method for a low-cost converter applicable to a backup power supply system to achieve suppression of the common-mode voltage and output voltage harmonics of the low-cost three-level converter. The method of the present invention is applicable to both the discharge state and the charging state of the backup power supply. The following takes the discharge state of the backup power supply as an example for specific elaboration, and further explanation is made in combination with the drawings and embodiments.

[0059] In one or more embodiments, the control object of the high-performance regulation method for the low-cost converter applicable to the backup power supply system is the low-cost three-level converter system. Refer to Figure 1 . Figure 1 It is a structural diagram of a low-cost three-level converter system applicable to a backup power supply system.

[0060] Under ideal conditions, the DC-side voltage V dc is evenly distributed by C1 and C2. The neutral point of the DC side (i.e., Figure 1 midpoint O) is selected as the reference point. As Figure 1 shown, for the convenience of expression, the common module is further divided into an upper bridge arm module and a lower bridge arm module; their output voltages are represented by V H and V L respectively. The working principle of the common module can be expressed as:

[0061]

[0062] The common module is connected to the three-phase independent modules through V H and V L . The common module is connected to the filter and the load through the midpoint of the three-phase independent modules. The three-phase output voltages of the low-cost three-level converter applicable to the backup power supply system are expressed as:

[0063]

[0064] Among them, S x (x = 1, 2, ···, 10) satisfies the following relationship:

[0065]

[0066] Therefore, through the permutation and combination of different switching states, the system has a total of 21 voltage vectors. The common-mode voltage of the system can be expressed as:

[0067]

[0068] The power switch tube can be implemented by any controllable power electronic switch tube. Specifically, an Insulate-Gate Bipolar Transistor (IGBT) can be used; it can also be implemented by other forms of transistors, and specific selection can be made according to the actual needs of those skilled in the art.

[0069] In the present invention, by abandoning the basic voltage vectors whose common-mode voltage amplitude exceeds V dc / 6, the common-mode voltage of the system is suppressed, and the system stability is enhanced. In addition, due to the existence of the common module, the converter mentioned above can output at most two level signals at the same time, so that the medium vector cannot be generated. Therefore, the low-cost three-level converter has only thirteen available low common-mode basic voltage vectors, referring to Figure 3 .

[0070] To solve the above problems, the present invention proposes a model predictive voltage control method for a low-cost converter applicable to a standby power system. In this embodiment, the method includes the following steps:

[0071] Based on the state equation of the LC-type power conversion circuit at the AC port of the low-cost converter, after discretization and coordinate transformation, a discrete mathematical model of the LC-type power conversion circuit in the 60-degree coordinate system is obtained;

[0072] Using the "one-step estimation method", the estimated result of the inductor current is approximated as the actual value of the inductor current, and the gradient equation of the load voltage is sorted out;

[0073] To simultaneously achieve flexible control of the neutral point voltage on the DC side, reduce the output voltage ripple, and reduce the calculation difficulty of the optimal action time, virtual vectors are synthesized based on the basic principle of discrete space vector modulation;

[0074] Sample the load voltage, load current, inductor current, and the voltages of the upper and lower capacitors on the DC side of the low-cost three-level converter and perform coordinate transformation processing;

[0075] Calculate the expected output voltage of the low-cost three-level converter, and determine the optimal large and small sectors according to the amplitude relationship and boundary conditions of the expected output voltage in the 60-degree coordinate system;

[0076] Based on minimizing the output voltage tracking error, calculate the optimal action time of each vector at the k+1 moment;

[0077] Determine the switching mode at the next moment according to the voltage difference between the upper and lower capacitors on the DC side to balance the neutral point voltage on the DC side, and obtain the optimal switching sequence by optimizing the switching sequence, so as to achieve a fixed switching frequency;

[0078] Generate corresponding drive signals based on the optimal switching sequence to control the conduction and cutoff of the switching devices of the low-cost three-level converter.

[0079] Figure 2 This is the control block diagram of the low-cost three-level converter system applicable to the standby power supply system of the present invention, which specifically includes the following links:

[0080] A. Construct a system dynamic model

[0081] Based on Figure 1 And obtain the continuous dynamic equation of the system according to Kirchhoff's law, and its expression is as follows:

[0082]

[0083] To reduce the complexity of the control algorithm, the present invention performs the following coordinate transformation, and the transformation formula is as follows:

[0084]

[0085] Where, [x a x b x c T is the coordinate of the AC voltage or AC current in the abc three-phase coordinate system; [x g x h T is the coordinate of the AC voltage or AC current in the 60-degree coordinate system.

[0086] After the above coordinate transformation, the continuous dynamic equation of the system in the 60-degree coordinate system can be obtained, and its expression is as follows:

[0087]

[0088] Where, v og and v oh are the coordinates of the load voltage in the 60-degree coordinate system, i g and i h are the coordinates of the inductor current in the 60-degree coordinate system, i og and i oh are the coordinates of the load current in the 60-degree coordinate system, v g and v h are the coordinates of the output voltage in the 60-degree coordinate system, L f and C f are the filter inductor and filter capacitor respectively.

[0089] As a further technical solution, according to the forward Euler method, discretize the system dynamic equation, and the expression of the discrete dynamic model in the 60-degree coordinate system is as follows:

[0090] ​​

[0091] Among them, v og (k + 1), v oh (k + 1), i og (k + 1), i oh (k + 1), v og (k), v oh (k), i og (k) and i oh (k) respectively represent the expressions of the load voltage and load current at the (k + 1)-th and k-th moments in the 60-degree coordinate system; i g (k), i h (k), v g (k) and v h (k) respectively represent the expressions of the inductor current and output voltage at the k-th moment in the 60-degree coordinate system; T s represents the sampling period.

[0092] Obviously, based on Equations (9) and (10), the system state variables: the inductor current and the load voltage are cross-coupled with each other. At the same time, the output voltage cannot directly control the load voltage. The system control performance is restricted by the above coupling relationship.

[0093] As a further technical solution, to maintain the balance of the DC-side voltage, from Figure 1 the following relationship between the DC-side capacitor current and the capacitor voltage can be obtained:

[0094]

[0095] Among them, C1 and C2 are the upper and lower capacitors of the distributed DC power supply unit respectively, V C1 and V C2 are the upper and lower capacitor voltages respectively, i p and i n are the currents flowing through the upper and lower capacitors respectively.

[0096] Similarly, according to the forward Euler method, discretizing Equation (11), the discrete dynamic model of the distributed DC power supply unit is obtained as:

[0097]

[0098] Therefore, according to Equation (12), the expressions of the upper and lower capacitor voltages of the distributed DC power supply unit at the (k + 1)-th moment can be obtained, which can be expressed as:

[0099]

[0100] In addition, i p and i n satisfy the following relationship:

[0101] i np = i p -i n (14)

[0102] where i np is the current flowing through the neutral point O.

[0103] In addition, according to Equation (13) and Equation (14), the voltage difference V diff (k + 1) of the upper and lower capacitors of the distributed DC power supply unit at the (k + 1)-th moment can be obtained, which is expressed as:

[0104]

[0105] Therefore, to predict the voltage difference of the upper and lower capacitors of the distributed DC power supply unit at the (k + 1)-th moment, an additional current sensor is required, which increases the cost and complexity of the system design.

[0106] B. System Decoupling Control and Load Voltage Gradient Calculation

[0107] The optimal switching sequence is a control algorithm based on the change gradient of the controlled object by the selected voltage vector. Therefore, to accurately predict the load voltage, it is first necessary to obtain the gradient of the basic voltage vector with respect to the load voltage. However, for a low-cost type converter with an LC filter, the output voltage v gh of the converter directly affects the inductor current i gh , and the load voltage v ogh cannot be directly controlled. Therefore, to obtain the load voltage gradient corresponding to each basic voltage vector and predict the load voltage, decoupling operation must be performed.

[0108] The present invention adopts a "one-step estimation" strategy to achieve the decoupling operation between state variables. Specifically, this strategy assumes that after applying a voltage vector throughout the control period, the estimated value of the inductor current is used as the inductor current at the k-th moment. The mathematical model of the "one-step estimation" strategy can be expressed as:

[0109]

[0110] where and are the estimated values of the inductor current in the 60-degree coordinate system at the k-th moment.

[0111] According to Equation (7), the calculation formula for the load voltage gradient before decoupling is as follows:

[0112]

[0113] where f vog and f vohis the load voltage gradient in the 60-degree coordinate system. Substitute Equation (16) into Equation (17) for decoupling operation, and at the same time discretize the load voltage gradient according to the forward Euler method. The discretized expression of the load voltage gradient is expressed as:

[0114]

[0115] C. Establish a prediction model

[0116] To simultaneously achieve the control objectives of low output voltage ripple and reduced algorithm complexity, the present invention selects three voltage vectors V v1 , V v2 and V v3 in each control cycle to synthesize the reference voltage, and their action times are t1, t2 and t3 respectively. The above action times satisfy the following relational expressions:

[0117] t1 + t2 + t3 = T s (19)

[0118] According to Equation (18), the predicted values v og (k + 1) and v oh (k + 1) of the load voltage at the (k + 1)-th moment in the 60-degree coordinate system can be expressed as:

[0119]

[0120] Among them, f Vvg,1 , f Vvg,2 , f Vvg,3 , f Vvh,1 , f Vvh,2 and f Vvh,3 are the load voltage gradients of the voltage vectors V v1 , V v2 and V v3 on the g-axis and h-axis respectively.

[0121] The predicted values and of the reference voltage at the (k + 1)-th moment are obtained by the second-order Lagrange extrapolation theorem:

[0122]

[0123] For the multi-objective control to simultaneously achieve low output voltage ripple and maintain the neutral point voltage balance of the DC side, the initial value function J0 can be expressed as:

[0124]

[0125] Among them, λ is the weight factor for maintaining the neutral point voltage balance of the DC side.

[0126] D. Synthetic Virtual Vector and Neutral Point Voltage Balance Control

[0127] 1) Synthetic virtual small vector

[0128] According to Figure 3 it can be seen that after the high common-mode voltage vector is deprecated, the existing small vectors no longer have redundant states, which brings great difficulties to the neutral point voltage balance control of the DC side. To address the above problems, six newly synthesized virtual small vectors and the existing small vectors form a new redundant relationship, thereby flexibly controlling the DC neutral point voltage.

[0129] According to Figure 3 it can be seen that among the existing basic voltage vectors, the neutral point voltage of the DC side is only affected by the small vectors. Each virtual small vector is synthesized by three basic voltage vectors V1, V2, and V3. To ensure that the newly synthesized virtual small vector and the corresponding small vector have equal amplitudes and opposite polarities within one control period, the above three basic voltage vectors need to satisfy the following constraint conditions: np is equal in amplitude and opposite in polarity, the above three basic voltage vectors need to satisfy the following constraint conditions:

[0130] i npv1 +i npv2 +i npv3 =-i npv (23)

[0131] where, i npv1 、i npv2 and i npv3 are the i np generated by the basic voltage vectors V1, V2, and V3 respectively, and i npv is the i np generated by the real small vector corresponding to the virtual small vector, that is, the current flowing through the neutral point O.

[0132] The virtual small vectors synthesized by the present invention and their combinations of basic voltage vectors are shown in Table 1.

[0133] Table 1 Virtual Small Vectors and Their Basic Voltage Vectors

[0134]

[0135]

[0136] The virtual small vector V vx (x = 1,…,6) and its basic voltage vectors need to satisfy the constraint conditions:

[0137]

[0138] where, T vx is the action time of the virtual small vector V vx , and t1, t2, and t3 are the action times of the basic voltage vectors V1, V2, and V3 respectively.

[0139] 2) Synthesize the virtual middle vector

[0140] According to Figure 3 it can be seen that when the reference voltage is in region B, to ensure the optimal action time of each vector, it is necessary to perform three partial derivative calculations on the four selected voltage vectors according to the value function, which will undoubtedly increase the algorithm complexity. Region B can be further divided into two sub-sectors according to the virtual middle vector. In the newly divided sub-sectors, only two partial derivative calculations are required to determine the optimal action time of each vector, thus reducing the algorithm complexity. To avoid the influence of the virtual middle vector on the neutral point voltage of the DC side, only two large vectors are selected as the basic voltage vectors for the newly synthesized virtual middle vector.

[0141] The above virtual middle vector and its basic voltage vectors are shown in Table 2.

[0142] Table 2 Virtual middle vector and its basic voltage vectors

[0143] Virtual middle vector Basic voltage vector <![CDATA[i np > <![CDATA[V v7 > [PNN], [PPN] 0 <![CDATA[V v8 > [PPN], [NPN] 0 <![CDATA[V v9 > [NPN], [NPP] 0 <![CDATA[V v10 > [NPP], [NNP] 0 <![CDATA[V v11 > [NNP], [PNP] 0 <![CDATA[V v12 > [PNP], [PNN] 0

[0144] Virtual middle vector V vx (x = 7,…, 12) and its basic voltage vectors need to satisfy the constraint conditions:

[0145]

[0146] Among them, T vx is the action time of the virtual middle vector V vx , and t1 and t2 are the action times of the basic voltage vectors V1 and V2 respectively.

[0147] 3) Neutral point voltage balance control of the DC side

[0148] Figure 4 is the extended space vector diagram of the low-cost three-level converter system applicable to the standby power supply system in this embodiment. According to Figure 4 it can be seen that there are a total of twenty-five voltage vectors after optimization for the low-cost three-level converter applicable to the standby power supply system.

[0149] It should be noted that two different switching sequences can be generated in each small sector. They have the same influence on the load voltage but have opposite influences on the neutral point voltage of the DC side. When the neutral point voltage of the DC side is too high, the switching sequence containing the N-type small vector is selected; when the neutral point voltage of the DC side is too low, the switching sequence containing the P-type small vector is selected. Through the two switching sequences mentioned above, the weighting factor λ in Equation (22) can be eliminated. Therefore, the new value function can be expressed as:

[0150]

[0151] According to Equation (26), there is no weight factor in the new value function, so there is no need for an additional DC-side current sampling circuit.

[0152] E. Calculation of the Optimal Action Time of Voltage Vectors

[0153] The basic requirement of model prediction is to minimize the value function. Combining Equation (20), Equation (21) and Equation (26), the value function J can be expressed as an equation about t1 and t2. By taking the partial derivatives of the value function J, the optimal solutions of t1 and t2 are obtained. The calculation formula for the optimal action time of voltage vectors is as follows:

[0154]

[0155] Solving Equation (27), the explicit solutions of the optimal action times t1, t2 and t3 can be expressed as:

[0156]

[0157] where

[0158] F. Judgment of the Optimal Subsector

[0159] If the traditional method is still used to calculate the action times of all switching sequences in each control period, the complexity of the control algorithm will increase significantly, thus restricting its application in the standby power supply field. Therefore, the present invention first uses deadbeat control to obtain the expected output voltage of the low-cost type converter in the 60-degree coordinate system and Combining Equation (16) - Equation (18), the expected output voltage can be expressed as:

[0160]

[0161] Taking V dc / 3 as the reference, and are normalized. The normalized expected output voltages and are:

[0162]

[0163] Furthermore, for simplicity of calculation, the reference voltages are rotated into Sector 1 during sector conversion. The relationship between the expected output voltages and after sector conversion and the normalized expected output voltages and is as follows:

[0164]

[0165] where N is the number of large sectors.

[0166] 1) Large sector division

[0167] First, based on and the amplitude conditions in the 60-degree coordinate system, the optimal large sector N can be determined simply and quickly. Table 3 shows different large sectors and their corresponding amplitude conditions.

[0168] Table 3 Corresponding relationship between amplitude conditions of expected output voltage and different large sectors

[0169]

[0170]

[0171] 2) Small sector division

[0172] Secondly, combining and the boundary conditions in the 60-degree coordinate system can further determine the optimal small sector S. Table 4 shows different small sectors and their corresponding boundary conditions.

[0173] Table 4 Corresponding relationship between boundary conditions of expected output voltage and different small sectors

[0174]

[0175] G. Switching sequence design

[0176] Through sector division, the above method only needs to calculate the action time of the voltage vector once and does not need to perform multiple rolling comparison calculations, greatly simplifying the control algorithm.

[0177] Considering factors such as reducing the harmonic content of the output voltage, maintaining the balance of the neutral point voltage on the DC side, and fixing the switching frequency, the switching sequence is designed.

[0178] When the expected output voltage is in the first small sector of sector 1 and V C1 < V C2 , the designed switching sequence is: [OOO]-[OON]-[PNN]-[ONO]-[PNN]-[OON]-[OOO].

[0179] When the expected output voltage is in the first small sector of sector 1 and V C1 > V C2 , the designed switching sequence is: [OOO]-[POO]-[PPN]-[OPO]-[PPN]-[POO]-[OOO].

[0180] When the expected output voltage is in the second small sector of sector 1 and VC1 <V C2 When, the designed switching sequence is: [OON]-[PPN]-[PNN]-[ONO]-[PNN]-[PPN]-[OON].

[0181] When the desired output voltage is in the second smallest sector of sector 1 and V C1 >V C2 When, the designed switching sequence is: [POO]-[PNN]-[PPN]-[OPO]-[PPN]-[PNN]-[POO].

[0182] When the desired output voltage is in the third smallest sector of sector 1 and V C1 <V C2 When, the designed switching sequence is: [OON]-[PPN]-[PNN]-[ONO]-[PNN]-[PPN]-[OON].

[0183] When the desired output voltage is in the third smallest sector of sector 1 and V C1 >V C2 When, the designed switching sequence is: [PPN]-[PNN]-[POO]-[PNN]-[PPN].

[0184] When the desired output voltage is in the fourth smallest sector of sector 1 and V C1 <V C2 When, the designed switching sequence is: [PNN]-[PPN]-[OON]-[PPN]-[PNN].

[0185] When the desired output voltage is in the fourth smallest sector of sector 1 and V C1 >V C2 When, the designed switching sequence is: [POO]-[PNN]-[PPN]-[OPO]-[PPN]-[PNN]-[POO].

[0186] When the desired output voltage is in the first smallest sector of sector 2 and V C1 <V C2 When, the designed switching sequence is: [OOO]-[OON]-[NPN]-[NOO]-[NPN]-[OON]-[OOO].

[0187] When the desired output voltage is in the first smallest sector of sector 2 and V C1 >V C2 When, the designed switching sequence is: [OOO]-[OPO]-[PPN]-[POO]-[PPN]-[OPO]-[OOO].

[0188] When the desired output voltage is in the second smallest sector of sector 2 and V C1<V C2 When C2 , the designed switching sequence is: [OON]-[PPN]-[NPN]-[NOO]-[NPN]-[PPN]-[OON].

[0189] When the desired output voltage is in the second smallest sector of sector 2 and V C1 >V C2 When C1 > C2 , the designed switching sequence is: [OPO]-[NPN]-[PPN]-[POO]-[PPN]-[NPN]-[OPO].

[0190] When the desired output voltage is in the third smallest sector of sector 2 and V C1 <V C2 When C1 < C2 , the designed switching sequence is: [NPN]-[PPN]-[OON]-[PPN]-[NPN].

[0191] When the desired output voltage is in the third smallest sector of sector 2 and V C1 >V C2 When C1 > C2 , the designed switching sequence is: [OPO]-[NPN]-[PPN]-[POO]-[PPN]-[NPN]-[OPO].

[0192] When the desired output voltage is in the fourth smallest sector of sector 2 and V C1 <V C2 When C1 < C2 , the designed switching sequence is: [OON]-[PPN]-[NPN]-[NOO]-[NPN]-[PPN]-[OON].

[0193] When the desired output voltage is in the fourth smallest sector of sector 2 and V C1 >V C2 When C1 > C2 , the designed switching sequence is: [PPN]-[NPN]-[OPO]-[NPN]-[PPN].

[0194] When the desired output voltage is in the first smallest sector of sector 3 and V C1 <V C2 When C1 < C2 , the designed switching sequence is: [OOO]-[NOO]-[NPN]-[OON]-[NPN]-[NOO]-[OOO].

[0195] When the desired output voltage is in the first smallest sector of sector 3 and V C1 >V C2 When C1 > C2 , the designed switching sequence is: [OOO]-[OPO]-[NPP]-[OOP]-[NPP]-[OPO]-[OOO].

[0196] When the desired output voltage is in the second smallest sector of sector 3 and V C1 <VC2 When it is, the designed switching sequence is: [NOO]-[NPP]-[NPN]-[OON]-[NPN]-[NPP]-[NOO].

[0197] When the desired output voltage is in the second smallest sector of sector 3 and V C1 >V C2 When it is, the designed switching sequence is: [OPO]-[NPN]-[NPP]-[OOP]-[NPP]-[NPN]-[OPO].

[0198] When the desired output voltage is in the third smallest sector of sector 3 and V C1 <V C2 When it is, the designed switching sequence is: [NOO]-[NPP]-[NPN]-[OON]-[NPN]-[NPP]-[NOO].

[0199] When the desired output voltage is in the third smallest sector of sector 3 and V C1 >V C2 When it is, the designed switching sequence is: [NPP]-[NPN]-[OPO]-[NPN]-[NPP].

[0200] When the desired output voltage is in the fourth smallest sector of sector 3 and V C1 <V C2 When it is, the designed switching sequence is: [NPN]-[NPP]-[NOO]-[NPP]-[NPN].

[0201] When the desired output voltage is in the fourth smallest sector of sector 3 and V C1 >V C2 When it is, the designed switching sequence is: [OPO]-[NPN]-[NPP]-[OOP]-[NPP]-[NPN]-[OPO].

[0202] When the desired output voltage is in the first smallest sector of sector 4 and V C1 <V C2 When it is, the designed switching sequence is: [OOO]-[NOO]-[NNP]-[ONO]-[NNP]-[NOO]-[OOO].

[0203] When the desired output voltage is in the first smallest sector of sector 4 and V C1 >V C2 When it is, the designed switching sequence is: [OOO]-[OOP]-[NPP]-[OPO]-[NPP]-[OOP]-[OOO].

[0204] When the desired output voltage is in the second smallest sector of sector 4 and V C1 <V C2When, the designed switching sequence is: [NOO]-[NPP]-[NNP]-[ONO]-[NNP]-[NPP]-[NOO].

[0205] When the desired output voltage is in the second smallest sector of sector 4 and V C1 >V C2 When, the designed switching sequence is: [OOP]-[NNP]-[NPP]-[OPO]-[NPP]-[NNP]-[OOP].

[0206] When the desired output voltage is in the third smallest sector of sector 4 and V C1 <V C2 When, the designed switching sequence is: [NNP]-[NPP]-[NOO]-[NPP]-[NNP].

[0207] When the desired output voltage is in the third smallest sector of sector 4 and V C1 >V C2 When, the designed switching sequence is: [OOP]-[NNP]-[NPP]-[OPO]-[NPP]-[NNP]-[OOP].

[0208] When the desired output voltage is in the fourth smallest sector of sector 4 and V C1 <V C2 When, the designed switching sequence is: [NOO]-[NPP]-[NNP]-[ONO]-[NNP]-[NPP]-[NOO].

[0209] When the desired output voltage is in the fourth smallest sector of sector 4 and V C1 >V C2 When, the designed switching sequence is: [NPP]-[NNP]-[OOP]-[NNP]-[NPP].

[0210] When the desired output voltage is in the first smallest sector of sector 5 and V C1 <V C2 When, the designed switching sequence is: [OOO]-[ONO]-[NNP]-[NOO]-[NNP]-[ONO]-[OOO].

[0211] When the desired output voltage is in the first smallest sector of sector 5 and V C1 >V C2 When, the designed switching sequence is: [OOO]-[OOP]-[PNP]-[POO]-[PNP]-[OOP]-[OOO].

[0212] When the desired output voltage is in the second smallest sector of sector 5 and V C1 <V C2When, the designed switching sequence is: [ONO]-[PNP]-[NNP]-[NOO]-[NNP]-[PNP]-[ONO].

[0213] When the desired output voltage is in the second smallest sector of sector 5 and V C1 >V C2 When, the designed switching sequence is: [OOP]-[NNP]-[PNP]-[POO]-[PNP]-[NNP]-[OOP].

[0214] When the desired output voltage is in the third smallest sector of sector 5 and V C1 <V C2 When, the designed switching sequence is: [ONO]-[PNP]-[NNP]-[NOO]-[NNP]-[PNP]-[ONO].

[0215] When the desired output voltage is in the third smallest sector of sector 5 and V C1 >V C2 When, the designed switching sequence is: [PNP]-[NNP]-[OOP]-[NNP]-[PNP].

[0216] When the desired output voltage is in the fourth smallest sector of sector 5 and V C1 <V C2 When, the designed switching sequence is: [NNP]-[PNP]-[ONO]-[PNP]-[NNP].

[0217] When the desired output voltage is in the fourth smallest sector of sector 5 and V C1 >V C2 When, the designed switching sequence is: [OOP]-[NNP]-[PNP]-[POO]-[PNP]-[NNP]-[OOP].

[0218] When the desired output voltage is in the first smallest sector of sector 6 and V C1 <V C2 When, the designed switching sequence is: [OOO]-[ONO]-[PNN]-[OON]-[PNN]-[ONO]-[OOO].

[0219] When the desired output voltage is in the first smallest sector of sector 6 and V C1 >V C2 When, the designed switching sequence is: [OOO]-[POO]-[PNP]-[OOP]-[PNP]-[POO]-[OOO].

[0220] When the desired output voltage is in the second smallest sector of sector 6 and V C1 <V C2When it is, the designed switching sequence is: [ONO]-[PNP]-[PNN]-[OON]-[PNN]-[PNP]-[ONO].

[0221] When the desired output voltage is in the second smallest sector of sector 6 and V C1 >V C2 When it is, the designed switching sequence is: [POO]-[PNN]-[PNP]-[OOP]-[PNP]-[PNN]-[POO].

[0222] When the desired output voltage is in the third smallest sector of sector 6 and V C1 <V C2 When it is, the designed switching sequence is: [PNN]-[PNP]-[ONO]-[PNP]-[PNN].

[0223] When the desired output voltage is in the third smallest sector of sector 6 and V C1 >V C2 When it is, the designed switching sequence is: [POO]-[PNN]-[PNP]-[OOP]-[PNP]-[PNN]-[POO].

[0224] When the desired output voltage is in the fourth smallest sector of sector 6 and V C1 <V C2 When it is, the designed switching sequence is: [ONO]-[PNP]-[PNN]-[OON]-[PNN]-[PNP]-[ONO].

[0225] When the desired output voltage is in the fourth smallest sector of sector 6 and V C1 >V C2 When it is, the designed switching sequence is: [PNP]-[PNN]-[POO]-[PNN]-[PNP].

[0226] Convert the switching sequence into the drive signals of the power switching tubes, and then control the operation of the low-cost three-level converter system.

[0227] As shown in Figs. 5(a), 5(b) and 5(c), the DC-side capacitor voltage, line voltage, load voltage, load current and common-mode voltage of the low-cost three-level converter system applicable to the backup power supply system of the present invention adopting single-vector model predictive control, optimal switching sequence model predictive control and the low common-mode model predictive control proposed by the present invention are presented. And the total harmonic distortion rates of the load voltage of the three methods are 4.47%, 0.39% and 0.42% respectively. Obviously, compared with the existing single-vector model predictive control method, the proposed method and the optimal switching sequence model predictive control method greatly reduce the output voltage ripple and improve the output power quality; at the same time, the proposed method reduces the common-mode voltage amplitude to half of the traditional model predictive control method, improving the stability of the system; the proposed method realizes the balance of the DC-side midpoint voltage by flexibly selecting the action of small vectors and virtual small vectors.

[0228] As shown in Figs. 6(a), 6(b) and 6(c), the fast Fourier analysis of the low-cost three-level converter system applicable to the backup power supply system of the present invention adopting single-vector model predictive control, optimal switching sequence model predictive control and the low common-mode model predictive control proposed by the present invention is presented. Compared with the single-vector model predictive control method, the proposed method and the optimal switching sequence model predictive control method have smaller voltage harmonics, and are more concentratedly distributed at the switching frequency and its multiples, which is beneficial to the filter parameter design for more efficient filtering.

[0229] As shown in Figs. 7(a), 7(b) and 7(c), the dynamic response waveforms of the load voltage and load current of the low-cost three-level converter system applicable to the backup power supply system of the present invention adopting single-vector model predictive control, optimal switching sequence model predictive control and the low common-mode model predictive control proposed by the present invention are presented. It can be seen from the waveforms that the proposed method can maintain a constant AC output voltage during load switching, and at the same time, it also realizes low voltage ripple and fast and stable dynamic response.

[0230] Therefore, by adopting the high-performance regulation method of low-common-mode model predictive control applicable to the low-cost three-level converter system for the standby power supply system in this embodiment, the common-mode voltage can be reduced, and the system reliability can be improved; the concept of virtual vectors is introduced, and the expected output voltage is fitted with multiple vectors to reduce the voltage ripple and improve the power quality of the output voltage; the value function is used to select the action time of the voltage vector required for predicting the synthesized load voltage at the moment k+1, further reducing the voltage ripple; the switching sequence is cleverly designed to achieve a fixed switching frequency, which is beneficial to the efficient filtering of voltage harmonics; the switching sequence is flexibly selected to achieve the balance of the midpoint potential of the DC side; the optimal sector judgment method in the 60-degree coordinate system avoids complex trigonometric calculations through simple numerical comparisons, greatly reducing the complexity of the control algorithm; high-reliability and high-performance control are achieved, the implementation is simple, and the practicability is strong, with broad application prospects in industrial fields such as standby power supply systems.

[0231] Embodiment 2

[0232] This embodiment provides a low-cost converter regulation system for a standby power supply system, including:

[0233] An expected output voltage calculation module, configured to obtain the load voltage and current, inductor current, and upper and lower capacitor voltages on the DC side of the low-cost three-level converter at the current moment, and calculate the expected output voltage;

[0234] A vector candidate set determination module, configured to optimize the vector candidate set by deprecating high-common-mode voltage vectors, and expand the vector candidate set based on discrete space vector modulation to synthesize virtual small vectors and virtual medium vectors to obtain the latest vector candidate set;

[0235] An optimal sector determination module, configured to determine the optimal large sector and the optimal small sector where the expected output voltage is located respectively based on the amplitude relationship and boundary conditions of the expected output voltage in the 60-degree coordinate system;

[0236] An initial switching sequence design module, configured to determine the initial switching sequence in the optimal small sector based on the latest vector candidate set according to the difference in DC side capacitor voltages;

[0237] A neutral point voltage balance and switching sequence optimization module, configured to calculate the optimal action time of the selected basic voltage vector with the goal of minimizing the load voltage tracking error, and optimize the initial switching sequence according to minimizing the number of switching actions and balancing the neutral point voltage on the DC side to obtain the optimal switching sequence; a drive signal conversion module, configured to generate corresponding drive signals based on the optimal switching sequence to control the conduction and cutoff of the switching devices of the low-cost three-level converter.

[0238] The regulation system further includes a drive circuit, a protection circuit, and a signal sampling and conditioning circuit.

[0239] A high-performance controller for a low-cost three-level converter applicable to a backup power supply system is connected to a drive circuit. The drive signal output by the high-performance controller is sent to the gate of the power switch device through the drive circuit to control its conduction and cutoff. The output signal of the low-cost three-level converter applicable to the backup power supply system is connected to the high-performance controller through a signal sampling circuit and a conditioning circuit; the protection circuit realizes the functions of overcurrent and overvoltage protection.

[0240] Among them, the signal sampling and conditioning circuit is responsible for sampling the upper and lower capacitor voltages (V C1 and V C2 ), inductor currents (i a , i b and i c ), output reference voltages ( and ), load currents (i oa , i ob and i oc ) and load voltages (v oa , v ob and v oc ) of the distributed DC power supply unit.

[0241] The examples and application scenarios implemented by the above modules and corresponding steps are the same, but are not limited to the content disclosed in the above Embodiment 1. It should be noted that the above modules, as part of the system, can be executed in a computer system such as a set of computer-executable instructions.

[0242] In the above embodiments, the descriptions of each embodiment have their own emphases. For parts not detailed in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0243] The proposed system can be implemented in other ways. For example, the system embodiments described above are merely illustrative. For example, the above division of modules is only a logical function division. In actual implementation, there can be other division methods. For example, multiple modules can be combined or integrated into another system, or some features can be ignored or not executed.

[0244] Embodiment 3

[0245] This embodiment provides a computer-readable storage medium, on which a computer program is stored. When the program is executed by a processor, it implements the steps in the method for controlling a low-cost converter applicable to a backup power supply system as described in the above Embodiment 1.

[0246] Embodiment 4

[0247] This embodiment provides a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, it implements the steps in the low-cost type converter regulation method for the backup power supply system as described in the above-mentioned Embodiment 1.

[0248] Embodiment 5

[0249] This embodiment provides a computer program product or a computer program. The computer program product or the computer program includes computer instructions, and these computer instructions are stored in a computer-readable storage medium. The processor of the computer device reads these computer instructions from the computer-readable storage medium, and the processor executes these computer instructions, so that the computer device executes the steps in the low-cost type converter regulation method for the backup power supply system as described in the above-mentioned Embodiment 1.

[0250] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a hardware embodiment, a software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories and optical memories, etc.) that contain computer-usable program code.

[0251] The present invention is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, as well as the combination of flows and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for implementing the functions specified in Figure 1 one or more flows and / or blocks Figure 1 one or more blocks.

[0252] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including an instruction device, and the instruction device implements the functions specified in Figure 1 one or more flows and / or blocks Figure 1 one or more blocks.

[0253] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus, so that a series of operation steps are performed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing instructions for implementing the functions specified in one process or multiple processes and / or blocks Figure 1 one process or multiple processes and / or blocks Figure 1 steps for implementing the functions specified in one block or multiple blocks.

[0254] Those of ordinary skill in the art can understand that all or part of the processes of the methods in the above embodiments can be completed by instructing relevant hardware through a computer program. The program can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above methods. Among them, the storage medium can be a magnetic disk, an optical disk, a read-only memory (ROM), or a random access memory (RAM), etc.

[0255] Although the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, they are not limitations on the protection scope of the present invention. Those skilled in the art should understand that, based on the technical solutions of the present invention, various modifications or deformations that can be made without creative efforts by those skilled in the art are still within the protection scope of the present invention.

Claims

1. A low-cost converter control method for an emergency power supply system, characterized in that, Including: Obtain the load voltage, current, inductor current, and the voltages of the upper and lower capacitors on the DC side of the low-cost three-level converter at the current moment, and calculate the expected output voltage; Optimize the vector candidate set by deprecating high common-mode voltage vectors, and expand the vector candidate set by synthesizing virtual small vectors and virtual medium vectors based on discrete space vector modulation to obtain the latest vector candidate set; Determine the optimal large sector and the optimal small sector where the expected output voltage is located respectively based on the amplitude relationship and boundary conditions of the expected output voltage in the 60-degree coordinate system; Based on the latest vector candidate set, determine the initial switching sequence in the optimal small sector according to the DC-side capacitor voltage difference; Aim at minimizing the load voltage tracking error, calculate the optimal action time of the selected basic voltage vector, and optimize the initial switching sequence according to minimizing the number of switching actions and balancing the neutral point voltage on the DC side to obtain the optimal switching sequence; Generate corresponding drive signals based on the optimal switching sequence to control the conduction and turn-off of the switching devices of the low-cost three-level converter.

2. The low-cost type converter control method for the backup power supply system according to claim 1, wherein Obtain the load voltage and current, inductor current, and the voltages of the upper and lower DC-side capacitors of the low-cost three-level converter at the current moment, and calculate the expected output voltage and where, i og and i oh respectively represent the values of the load current in the 60-degree coordinate system, i g and i h respectively represent the values of the inductor current in the 60-degree coordinate system, v og and v oh are the coordinates of the load voltage in the 60-degree coordinate system, T s represents the sampling period, the predicted value of the reference voltage at the (k + 1)th moment and the predicted value of the load voltage at the kth moment and 3. The low-cost type converter regulation method for a backup power supply system according to claim 1, characterized in that, The method of optimizing the vector candidate set by deprecating high common-mode voltage vectors, expanding the vector candidate set by synthesizing virtual small vectors and virtual medium vectors based on discrete space vector modulation to obtain the latest vector candidate set is specifically as follows: Deprecate high common-mode voltage vectors, synthesize virtual small vectors using three basic voltage vectors, and the sum of the currents flowing through the neutral point generated by the three basic voltage vectors is opposite in polarity and equal in amplitude to the current flowing through the neutral point generated by the real small vector corresponding to the virtual small vector; Synthesize virtual medium vectors using two large vectors as basic voltage vectors; Based on the virtual small vectors and virtual medium vectors, obtain the latest vector candidate set.

4. The low-cost type converter control method for a backup power supply system according to claim 1, characterized in that The method of determining the optimal large sector and the optimal small sector where the expected output voltage is located respectively based on the amplitude relationship and boundary conditions of the expected output voltage in the 60-degree coordinate system is specifically as follows: Based on V dc / 3 as a reference, for and perform normalization to obtain the expected output voltage and which is: Among them, the expected output voltage of the low-cost three-level converter in the 60-degree coordinate system and the DC-side voltage V dc , k is the current moment, and the expected output voltage and Expected output voltage after sector conversion and the expected output voltage after normalization and The relationship is as follows: Determine the optimal large sector where the expected output voltage is located according to the amplitude relationship of the normalized expected output voltage in the 60-degree coordinate system; Determine the optimal small sector where the expected output voltage is located according to the boundary conditions of the expected output voltage after sector conversion in the 60-degree coordinate system.

5. The low-cost type converter control method for a backup power supply system according to claim 1, characterized in that, The method of aiming at minimizing the load voltage tracking error and calculating the optimal action time of the selected basic voltage vector is specifically as follows: where J is the objective function of the output voltage tracking error, and t1 and t2 are the acting times of voltage vectors V v1 and V v2 respectively; Among them, the predicted values \(v_{(k + 1)}\) and \(v_{(k + 1)}\) of the load voltage at the \((k + 1)\)-th moment in the 60-degree coordinate system, the reference values of the reference voltage at the \((k + 1)\)-th moment og (k + 1) and \(v\) oh (k + 1), the reference value of the reference voltage at the \((k + 1)\)-th moment and 6. The low-cost type converter control method for the standby power supply system according to claim 1, characterized in that The method of optimizing the initial switching sequence according to minimizing the number of switching actions and balancing the neutral point voltage on the DC side to obtain the optimal switching sequence is specifically as follows: When the neutral point voltage on the DC side is too high, select a switching sequence containing N-type small vectors; When the neutral point voltage on the DC side is too low, select a switching sequence containing P-type small vectors; On the premise of minimizing the number of switching actions, design a seven-segment or five-segment symmetric switching sequence to ensure that the number of actions of the same type of switching sequence is the same; Based on the above rules, obtain the optimal switching sequence.

7. A low-cost type converter control system for an emergency power supply system, characterized in that, Including: An expected output voltage calculation module configured to obtain the load voltage, current, inductor current, and the voltages of the upper and lower capacitors on the DC side of the low-cost three-level converter at the current moment, and calculate the expected output voltage; A vector candidate set determination module, configured to optimize the vector candidate set by deprecating high common-mode voltage vectors, expand the vector candidate set based on discrete space vector modulation to synthesize virtual small vectors and virtual medium vectors, and obtain the latest vector candidate set; An optimal sector determination module, configured to determine the optimal large sector and the optimal small sector where the desired output voltage is located respectively based on the amplitude relationship and boundary conditions of the desired output voltage in the 60-degree coordinate system; An initial switching sequence design module, configured to determine the initial switching sequence in the optimal small sector based on the latest vector candidate set and according to the DC-link capacitor voltage difference; A neutral point voltage balance and switching sequence optimization module, configured to calculate the optimal action time of the selected basic voltage vector with the goal of minimizing the load voltage tracking error, and optimize the initial switching sequence according to minimizing the number of switching actions and balancing the DC-side neutral point voltage to obtain the optimal switching sequence; A drive signal conversion module, configured to generate corresponding drive signals based on the optimal switching sequence to control the conduction and turn-off of the switching devices of the low-cost three-level converter.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by a processor, it implements the steps in the low-cost converter control method for a backup power supply system described in any one of claims 1-6.

9. A computer device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in the low-cost converter control method for a backup power supply system described in any one of claims 1-6.

10. A computer program product, characterized in that, The computer program product includes a computer program, which when executed by a processor, implements the steps in the low-cost converter control method for a backup power supply system described in any one of claims 1-6.

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