Low cost converter regulation method and system for backup power systems

Abstract

The application belongs to the field of backup power supply loop device regulation and control, and provides a low-cost converter regulation method and system for a backup power supply system, samples load voltage and current, inductance current, and DC side upper and lower capacitor voltages; selects the inductance current for decoupling operation, simultaneously calculates the expected output voltage of the converter based on the zero-error control principle, and performs normalization processing; determines the optimal size sector through the amplitude condition and boundary condition of the expected output voltage; selects low common-mode voltage vectors to synthesize virtual small vectors and virtual medium vectors based on discrete space vector modulation, and expands the candidate vector set; determines the switching sequence at the next moment according to the size sector where the expected output voltage is located and the DC side upper and lower capacitor voltage difference, so as to balance the neutral point voltage and fix the switching frequency; calculates the action time of the voltage vector according to the value function and outputs the duty cycle thereof, which is applied to the switching device of the converter.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of regulating and controlling of backup power supply circuit device, and particularly relates to a low-cost converter regulating and controlling method and system for a backup power supply system. BACKGROUND

[0002] The statements in this section merely provide background information related to the present application and do not necessarily constitute the prior art.

[0003] Three-level inverters have obvious advantages such as low voltage stress of power switch tubes, high quality of output waveform, and small size of filter, and are widely used in power supply systems. In addition, compared with three-level converters with only L filters, three-level converters with LC filters have higher converter efficiency, lower harmonic content of 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] Low-cost three-level converter topologies reduce the number of power switch tubes and system cost by utilizing coupled switch cells, and have wide application prospects in the field of backup power supplies. Common-mode voltage is generated by the high-frequency switching action of power switch tubes. In systems containing distributed photovoltaic power generation units, due to the existence of parasitic capacitance, leakage current is easily induced, leading to distortion of converter output current and increase of system power loss, and even threatening personal safety. When the backup power supply system is applied to motor variable frequency drives, the motor will be affected by the common-mode voltage to induce shaft voltage, which is easy to break through the insulation oil film between the motor bearings, damage the motor bearings, and increase the system electromagnetic interference.

[0005] According to the inventors' understanding, the existing traditional linear regulating and controlling method for low-cost three-level converters with LC filters includes proportional integral (PI) control and proportional resonance (PR) control. However, the performance of this method depends on the value of the gain module, and at the same time, there are 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 capability, superior anti-interference capability, and flexible multi-objective control capability. Therefore, model predictive control is more suitable for application in backup power supply systems to meet the performance indicators of high reliability and fast switching of the system.

[0006] However, due to the limitation of the topology itself, the original three-level converter common-mode voltage suppression method cannot be applied to this topology. At the same time, the existing model predictive control method for low-cost three-level converters is only applicable to the topology with L filter and cannot be directly applied to the topology with LC filter. If the traditional model predictive control method is improved and applied to the topology with LC filter, it has the following shortcomings, such as high common-mode voltage, high load voltage harmonic content, fixed switching frequency, and complex control algorithm operation. SUMMARY

[0007] In order to solve the above problems, the present application provides a low-cost converter regulation method and system for backup power supply system, which can effectively suppress the common-mode voltage of the system, fix the switching frequency, reduce the load voltage harmonic, reduce the control algorithm operation amount, and significantly improve the system performance.

[0008] According to some embodiments, the first aspect of the present application provides a low-cost converter regulation method for a backup power supply system, which adopts the following technical solution:

[0009] The low-cost converter regulation method for a backup power supply system comprises:

[0010] Obtaining the load voltage and current, inductor current, and DC side upper and lower capacitor voltages of the low-cost three-level converter at the current time, and calculating the expected output voltage;

[0011] Optimizing the vector candidate set by discarding the high common-mode voltage vector, expanding the vector candidate set based on the discrete space vector modulation to synthesize virtual small vectors and virtual middle vectors, and obtaining 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, the optimal large sector and the optimal small sector where the expected output voltage is located are determined;

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

[0014] Taking the minimization of load voltage tracking error as the target, the optimal action time of the selected basic voltage vector is calculated, the initial switching sequence is optimized according to the minimization of switching action times and the balance of DC side neutral point voltage, and the optimal switching sequence is obtained;

[0015] Based on the optimal switching sequence, the corresponding driving signal is generated to control the conduction and turn-off of the switching devices of the low-cost three-level converter.

[0016] According to some embodiments, the second aspect of the present application provides a low-cost converter regulation system for a backup power supply system, which adopts the following technical solution:

[0017] A low-cost converter control system for backup power systems, including:

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

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

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

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

[0022] The neutral point voltage balancing and switching sequence optimization module is configured to minimize the load voltage tracking error. It calculates the optimal action time of the selected basic voltage vector and optimizes the initial switching sequence to obtain the optimal switching sequence by minimizing the number of switching operations and balancing the DC side neutral point voltage.

[0023] The driving signal conversion module is configured to generate a corresponding driving signal based on the optimal switching sequence to control the switching device of the low-cost three-level converter to be turned on and off.

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

[0025] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the low-cost converter control method for a backup power system as described in the first aspect above.

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

[0027] A computer device comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the steps of the low-cost converter control method for a backup power system as described in the first aspect above are implemented.

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

[0029] The application provides a computer program product or computer program, which comprises 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 converter regulation method for a backup power supply system according to the first aspect.

[0030] Compared with the prior art, the application has the following beneficial effects:

[0031] The application can reduce common-mode voltage and improve system reliability, introduces the concept of virtual vector, synthesizes load voltage by multiple vectors, reduces voltage ripple, and improves the power quality of output voltage, determines the optimal action time of voltage vector required for synthesizing load voltage by using a value function, further reduces voltage ripple, ingeniously designs a switching sequence, realizes fixed switching frequency, is conducive to efficient filtering of voltage harmonics, flexibly selects a switching sequence, ingeniously controls the neutral point voltage on the DC side, realizes neutral point voltage balance on the DC side, and the optimal sector judgment method in the 60-degree coordinate system avoids complex trigonometric function calculation through simple numerical comparison, simplifies the algorithm operation process, and greatly reduces the control algorithm complexity. BRIEF DESCRIPTION OF DRAWINGS

[0032] The drawings accompanying the specification of the application form a part of the application and serve to further understand the application. The illustrative embodiments of the application and their description serve to explain the application without forming an improper limitation of the application.

[0033] Figure 1 A low-cost three-level converter system structure diagram suitable for a backup power supply system;

[0034] Figure 2 A low-cost three-level converter system control block diagram suitable for a backup power supply system of the application;

[0035] Figure 3 A low-common-mode basic space vector diagram of a low-cost three-level converter system suitable for a backup power supply system of the application;

[0036] Figure 4 An extended space vector diagram of a low-cost three-level converter system suitable for a backup power supply system of the application;

[0037] FIG. 5(a) is a DC side capacitor voltage, line voltage, load current, load voltage and common-mode voltage of a low-cost three-level converter system suitable for a backup power supply system of the application using a single vector model predictive control;

[0038] Fig. 5(b) is the DC side capacitor voltage, line voltage, load current, load voltage and common mode voltage of the low cost three-level converter system for the backup power system of the present application using the optimal switching sequence model predictive control;

[0039] Fig. 5(c) is the DC side capacitor voltage, line voltage, load current, load voltage and common mode voltage of the low cost three-level converter system for the backup power system of the present application using the low common mode model predictive control proposed by the present application;

[0040] Fig. 6(a) is the Fast Fourier Transform (FFT) of the low cost three-level converter system for the backup power system of the present application using the single vector model predictive control;

[0041] Fig. 6(b) is the Fast Fourier Transform of the low cost three-level converter system for the backup power system of the present application using the optimal switching sequence model predictive control;

[0042] Fig. 6(c) is the Fast Fourier Transform of the low cost three-level converter system for the backup power system of the present application using the low common mode model predictive control proposed by the present application;

[0043] Fig. 7(a) is the dynamic response waveform of the low cost three-level converter system for the backup power system of the present application using the single vector model predictive control;

[0044] Fig. 7(b) is the dynamic response waveform of the low cost three-level converter system for the backup power system of the present application using the optimal switching sequence model predictive control;

[0045] Fig. 7(c) is the dynamic response waveform of the low cost three-level converter system for the backup power system of the present application using the low common mode model predictive control proposed by the present application. DETAILED DESCRIPTION

[0046] The present application is further described in conjunction with the accompanying drawings and examples.

[0047] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0048] It is to be noted that the terms used herein are merely for the purpose of describing specific embodiments and are not intended to limit exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise, and it is further understood that the terms "comprising" and / or "including" when used in this specification, 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 application and the features in the embodiments can be combined with each other.

[0050] Embodiment one

[0051] The embodiment provides a low-cost converter regulation method for a backup power supply system. The embodiment takes the method applied to a server as an example. It can be understood that the 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 interaction of the terminal and the server. The server can be a physical server, a server cluster composed of multiple physical servers or a distributed system, and can also be a cloud server providing basic cloud computing services such as cloud services, cloud databases, cloud computing, cloud functions, cloud storage, network 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 and the like, but is not limited thereto. The terminal and the server can be directly or indirectly connected through wired or wireless communication, which is not limited in the present application. In the embodiment, the method comprises the following steps:

[0052] Obtaining load voltage and current, inductor current and DC side upper and lower capacitor voltages of the low-cost three-level converter at the current moment, and calculating an expected output voltage;

[0053] Optimizing the vector candidate set by discarding high common-mode voltage vectors, expanding the vector candidate set based on discrete space vector modulation to synthesize virtual small vectors and virtual middle vectors, and obtaining 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, respectively, determining the optimal large sector and the optimal small sector where the expected output voltage is located;

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

[0056] Taking minimization of load voltage tracking error as the target, calculating the optimal action time of the selected basic voltage vector, optimizing the initial switching sequence according to minimization of switching action times and balancing of the DC side neutral point voltage, and obtaining the optimal switching sequence.

[0057] Based on the optimal switching sequence, a corresponding driving signal is generated to control the switching devices of the low-cost three-level converter to be turned on and off.

[0058] This invention proposes a low-cost, high-performance converter control method for backup power systems, achieving common-mode voltage and output voltage harmonic suppression for low-cost three-level converters. This method is applicable to both the backup power supply's discharging and charging states. The following detailed description uses the backup power supply's discharging state as an example, further illustrated with reference to the accompanying figures and examples.

[0059] In one or more embodiments, the control object of the low-cost converter high-performance control method applicable to the backup power system is a low-cost three-level converter system. Figure 1 . Figure 1 The diagram shows the structure of a low-cost three-level converter system suitable for backup power systems.

[0060] Under ideal conditions, the DC side voltage V dc It is evenly distributed by C1 and C2. Select the DC side neutral point (i.e. Figure 1 The midpoint O) is used as the reference point. Figure 1 As shown, for ease of description, the common module is further subdivided into upper bridge arm module and lower bridge arm module; their output voltages are denoted by V H and V L The working principle of the common module can be expressed as:

[0061]

[0062] Public modules pass V H and V L The common module is connected to the filter and load via the midpoint of the three-phase independent module. The three-phase output voltage of the low-cost three-level converter suitable for backup power supply system is expressed as:

[0063]

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

[0065]

[0066] Therefore, through the arrangement and combination of different switch 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 adopted; or other forms of transistors can be adopted, specifically, the actual needs of those skilled in the art can be selected.

[0069] The application suppresses the common-mode voltage of the system and enhances the stability of the system by discarding the basic voltage vector whose common-mode voltage amplitude exceeds V dc / 6, and the above-mentioned converter can output at most two kinds of signals at the same time, so that the middle vector cannot be generated. Therefore, the low-cost three-level converter has only thirteen available low common-mode basic voltage vectors, and the reference Figure 3 .

[0070] To solve the above problems, the application provides a model predictive voltage control method suitable for a low-cost converter of a backup power supply system. In the embodiment, the method comprises the following steps:

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

[0072] The estimation result of the inductor current is approximated to the actual value of the inductor current by using the "one-step estimation method", and the gradient equation of the load voltage is obtained;

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

[0074] The load voltage, load current, inductor current and DC side upper and lower capacitor voltages of the low-cost three-level converter are sampled and processed through coordinate transformation;

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

[0076] Based on the minimization of the output voltage tracking error, the optimal action time of each vector at k+1 time is calculated;

[0077] The switching mode at the next time is determined according to the voltage difference of the DC side upper and lower capacitors, so as to balance the neutral point voltage of the DC side, and the optimal switching sequence is obtained through optimization of the switching sequence, so as to realize fixed switching frequency;

[0078] The corresponding driving signal is generated based on the optimal switch sequence to control the switch device conduction and turn-off of the low-cost three-level converter.

[0079] Figure 2 The low-cost three-level converter system control block diagram suitable for the standby power supply system of the application specifically comprises the following links:

[0080] A. Constructing system dynamic model

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

[0082]

[0083] In order to reduce the complexity of the control algorithm, the following coordinate transformation is performed, and the transformation formula is as follows:

[0084]

[0085] Wherein, [x a x b x c ] T is the coordinate of alternating voltage or alternating current in abc three-phase coordinate system; [x g x h ] T is the coordinate of alternating voltage or alternating current in 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 the expression is as follows:

[0087]

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

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

[0090]

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

[0092] Obviously, based on equation (9) and equation (10), the system state variables: inductor current and 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 limited by the above coupling relationship.

[0093] As a further technical solution, in order to maintain the balance of the DC side voltage, by Figure 1 The DC side capacitor current and capacitor voltage satisfy the following relationship:

[0094]

[0095] where 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, discretize equation (11), and 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 k+1 can be obtained, which can be represented 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 the formula (13) and the formula (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 moment can be obtained, and is expressed as:

[0104]

[0105] Therefore, in order to predict the voltage difference of the upper and lower capacitors of the distributed DC power supply unit at the k+1 moment, an additional current sensor is needed, which increases the cost and complexity of 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 selected voltage vector to the controlled object, and therefore, in order to accurately predict the load voltage, the gradient of the basic voltage vector to the load voltage needs to be obtained first. However, for a low-cost 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, in order 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 application adopts a "one-step estimation" strategy to realize the decoupling operation between state variables. Specifically, the strategy assumes that after applying a voltage vector in the entire control period, the estimated value of the inductor current is taken as the inductor current at the k 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 at the k moment in the 60-degree coordinate system.

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

[0112]

[0113] where f vog and f vohis the load voltage gradient in 60-degree coordinate system. Substitute equation (16) into equation (17) to decouple the operation, and discretize the load voltage gradient according to the forward Euler method, the discretized expression of the load voltage gradient is represented as:

[0114]

[0115] C. Establishing a prediction model

[0116] To achieve the control objectives of low output voltage ripple and low algorithm complexity, the present application selects three voltage vectors V v1 , V v2 and V v3 to synthesize the reference voltage in each control period, and the action time of the three voltage vectors is t1, t2 and t3 respectively. The above action time satisfies the following relationship:

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

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

[0119]

[0120] Wherein, 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.

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

[0122]

[0123] To achieve the multi-objective control of low output voltage ripple and balanced neutral point voltage on the DC side, the initial value function J0 can be represented as:

[0124]

[0125] Wherein, λ is the weight factor of the balanced neutral point voltage on the DC side.

[0126] D. Synthesis of virtual vector and neutral point voltage balance control

[0127] 1) Synthesis of virtual small vector

[0128] According to Figure 3 , after the high common-mode voltage vector is abandoned, the existing small vector is no longer in a redundant state, which brings great difficulty to the neutral point voltage balance control of the DC side. In view of the above problem, the newly synthesized six virtual small vectors and the existing small vectors constitute a new redundancy relationship, and then the DC neutral point voltage is flexibly controlled.

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

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

[0131] Among them, 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 corresponding real small vector of the virtual small vector, that is, the current flowing through the neutral point O.

[0132] The virtual small vector synthesized by the present application and its basic voltage vector combination is shown in Table 1.

[0133] Table 1 Virtual small vector and its basic voltage vector

[0134]

[0135]

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

[0137]

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

[0139] 2) Synthesis of virtual middle vector

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

[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 Fundamental voltage vector i np ]]> V v7 ]]> [PNN], [PPN] 0 V v8 ]]> [PPN], [NPN] 0 V v9 ]]> [NPN], [NPP] 0 V v10 ]]> [NPP], [NNP] 0 V v11 ]]> [NNP], [PNP] 0 V v12 ]]> [PNP], [PNN] 0

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

[0145]

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

[0147] 3) DC side neutral point voltage balance control

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

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

[0150]

[0151] According to formula (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 vector

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

[0154]

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

[0156]

[0157] in,

[0158] F. Optimal sub-sector determination

[0159] If the traditional method is still used to calculate the action time of all switching sequences in each control cycle, the complexity of the control algorithm will be greatly increased, thereby limiting its application in the field of backup power supply. Therefore, the present invention first uses deadbeat control to obtain the expected output voltage of the low-cost converter in the 60-degree coordinate system. and Combining equations (16) to (18), the expected output voltage can be expressed as:

[0160]

[0161] V dc / 3 is the benchmark, and Normalization is performed. The expected output voltage after normalization is and for:

[0162]

[0163] Furthermore, to simplify the calculation, the sector conversion rotates the reference voltage to sector 1. The expected output voltage after sector conversion is and Normalized to the desired output voltage and The relationship is as follows:

[0164]

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

[0166] 1) Large sector division

[0167] Firstly, according to and The amplitude condition in 60-degree coordinate system can determine the optimal large sector N concisely and quickly. Table 3 is the correspondence between the amplitude condition of the expected output voltage and different large sectors.

[0168] Table 3 Correspondence between the amplitude condition of the expected output voltage and different large sectors

[0169]

[0170]

[0171] 2) Small sector division

[0172] Secondly, combined with and The boundary condition in 60-degree coordinate system can further determine the optimal small sector S. Table 4 is the correspondence between the boundary condition of the expected output voltage and different small sectors.

[0173] Table 4 Correspondence between the boundary condition of the 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 voltage vector action time once, without the need for 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 located in the first small sector in sector 1 and V C1 <V C2 , the switching sequence is designed as: [OOO]-[OON]-[PNN]-[ONO]-[PNN]-[OON]-[OOO].

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

[0180] When the expected output voltage is located in the second small sector in 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 located in the second small sector in 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 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 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 4th sector in 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 4th sector in 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 small 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 small 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 located in the second small sector in sector 2 and V C1<V C2 When the desired output voltage is in the 1st sub-sector in sector 2 and V

[0189] When the desired output voltage is in the 1st sub-sector in sector 2 and V C1 <V C2 When the desired output voltage is in the 1st sub-sector in sector 2 and V

[0190] When the desired output voltage is in the 1st sub-sector in sector 2 and V C1 <V C2 When the desired output voltage is in the 1st sub-sector in sector 2 and V

[0191] When the desired output voltage is in the 1st sub-sector in sector 2 and V C1 <V C2 When the desired output voltage is in the 1st sub-sector in sector 2 and V

[0192] When the desired output voltage is in the 1st sub-sector in sector 2 and V C1 <V C2 When the desired output voltage is in the 1st sub-sector in sector 2 and V

[0193] When the desired output voltage is in the 1st sub-sector in sector 2 and V C1 <V C2 When the desired output voltage is in the 1st sub-sector in sector 2 and V

[0194] When the desired output voltage is in the 1st sub-sector in sector 3 and V C1 <V C2 When the desired output voltage is in the 1st sub-sector in sector 3 and V

[0195] When the desired output voltage is in the 1st sub-sector in sector 3 and V C1 <V C2 When the desired output voltage is in the 1st sub-sector in sector 3 and V

[0196] When the desired output voltage is in the 1st sub-sector in sector 3 and V C1 <VC2 When the desired output voltage is in the 1st sector in sector 3 and V

[0197] When the desired output voltage is in the 1st sector in sector 3 and V C1 > C2 When the desired output voltage is in the 1st sector in sector 3 and V

[0198] When the desired output voltage is in the 1st sector in sector 3 and V C1 < C2 When the desired output voltage is in the 1st sector in sector 3 and V

[0199] When the desired output voltage is in the 1st sector in sector 3 and V C1 > C2 When the desired output voltage is in the 1st sector in sector 3 and V

[0200] When the desired output voltage is in the 1st sector in sector 3 and V C1 < C2 When the desired output voltage is in the 1st sector in sector 3 and V

[0201] When the desired output voltage is in the 1st sector in sector 3 and V C1 > C2 When the desired output voltage is in the 1st sector in sector 3 and V

[0202] When the desired output voltage is in the 1st sector in sector 4 and V C1 < C2 When the desired output voltage is in the 1st sector in sector 4 and V

[0203] When the desired output voltage is in the 1st sector in sector 4 and V C1 > C2 When the desired output voltage is in the 1st sector in sector 4 and V

[0204] When the desired output voltage is in the 1st sector in sector 4 and V C1 < C2When , the designed switching sequence is: [NOO]-[NPP]-[NNP]-[ONO]-[NNP]-[NPP]-[NOO].

[0205] When the desired output voltage is located in the second small sector in 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 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 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 4th small sector in 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 4th small sector in 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 small sector in 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 small sector in 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 small sector in 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 small sector in 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 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 sector of sector 5 and V C1 >V C2 When , the design switching sequence is: [PNP]-[NNP]-[OOP]-[NNP]-[PNP].

[0216] When the desired output voltage is in the 4th sector in 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 4th sector in 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 small 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 small 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 located in the second small sector in sector 6 and V C1 <V C2When , the designed switching sequence is: [ONO]-[PNP]-[PNN]-[OON]-[PNN]-[PNP]-[ONO].

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

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

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

[0224] When the desired output voltage is in the 4th sector in sector 6 and V C1 <V C2 When , the designed switching sequence is: [ONO]-[PNP]-[PNN]-[OON]-[PNN]-[PNP]-[ONO].

[0225] When the desired output voltage is in the 4th sector in sector 6 and V C1 >V C2 When , the designed switching sequence is: [PNP]-[PNN]-[POO]-[PNN]-[PNP].

[0226] The switching sequence is converted into a driving signal for the power switch tube, thereby controlling the operation of the low-cost three-level converter system.

[0227] As shown in FIG. 5(a), FIG. 5(b) and FIG. 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 suitable for the backup power supply system of the application are predicted by using single-vector model predictive control, optimal switching sequence model predictive control, low common-mode model predictive control proposed by the application. The total harmonic distortion of the load voltage of the three methods is 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 vector and virtual small vector.

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

[0229] As shown in FIG. 7(a), FIG. 7(b) and FIG. 7(c), the dynamic response waveforms of the load voltage and load current of the low-cost three-level converter system suitable for the backup power supply system of the application are shown, which uses single-vector model predictive control, optimal switching sequence model predictive control, low common-mode model predictive control proposed by the application. As can be seen from the waveforms, the proposed method can maintain a constant AC output voltage when the load switching occurs, while also achieving low voltage ripple and fast and stable dynamic response.

[0230] Therefore, the low-cost three-level converter system suitable for the backup power supply system adopts the high-performance regulation method suitable for the low common-mode model predictive control, can reduce the common-mode voltage and improve the system reliability, introduces the concept of virtual vector, fits the expected output voltage with multiple vectors, reduces the voltage ripple and improves the power quality of the output voltage, selects the action time of the voltage vector required for predicting the load voltage at k+1 time point by using the value function, further reduces the voltage ripple, ingeniously designs the switching sequence, realizes the fixed switching frequency, is conducive to efficient filtering of voltage harmonics, flexibly selects the switching sequence, realizes the balance of the midpoint potential of the DC side, realizes the optimal sector judgment method in the 60-degree coordinate system, avoids complex trigonometric function calculation through simple numerical comparison, greatly reduces the control algorithm complexity, realizes high-reliability high-performance control, is simple to realize, has strong practicality, and has wide application prospect in the industrial field such as the backup power supply system.

[0231] Embodiment two

[0232] The embodiment provides a low-cost converter regulation system for a backup power supply system, comprising:

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

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

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

[0236] An initial switching sequence design module is configured to determine the initial switching sequence in the optimal small sector based on the latest vector candidate set and the DC side capacitor voltage difference.

[0237] A neutral point voltage balance and switching sequence optimization module is configured to minimize the load voltage tracking error, calculate the optimal action time of the selected basic voltage vector, optimize the initial switching sequence based on the minimization of the switching action times and the balance of the DC side neutral point voltage, and obtain the optimal switching sequence. A drive signal conversion module is 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.

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

[0239] The low-cost three-level converter for backup power supply system is connected with a high-performance regulator and a driving circuit, the driving signal output by the high-performance regulator is sent to the gate of the power switch device through the driving circuit to control the turn-on and turn-off of the power switch device. The output signal of the low-cost three-level converter for backup power supply system is connected to the high-performance regulator 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 (V and V ), 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 above modules and the corresponding steps realize the same examples and application scenarios as the above embodiment one, but are not limited to the disclosure of the above embodiment one. 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] The description of each embodiment in the above embodiments has its own emphasis, and the parts not described in detail in a certain embodiment can refer to the related description of other embodiments.

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

[0244] Embodiment three

[0245] The embodiment provides a computer readable storage medium, which stores a computer program, and the program is executed by a processor to realize the steps in the low-cost converter regulation method for a backup power supply system as described in the above embodiment one.

[0246] Embodiment four

[0247] The embodiment provides a computer device, comprising a memory, a processor and a computer program stored in the memory and executable on the processor, and the processor implements the steps in the low-cost converter regulation method for a backup power supply system according to the embodiment one.

[0248] Embodiment five

[0249] The embodiment provides a computer program product or computer program, which comprises 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 converter regulation method for a backup power supply system according to the embodiment one.

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

[0251] The present application is described with reference to flowcharts and / or block diagrams of the method, device (system) and computer program product according to the embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of the 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 a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to produce a machine, so that the instructions executed by the computer or other programmable data processing device produce a device that implements the functions specified in the flowcharts and / or block diagrams. Figure 1 one or more flows and / or blocks Figure 1 means for performing the functions specified in the flow or flows and / or block or blocks.

[0252] These computer program instructions can also be stored in a computer readable storage medium that can direct the computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable storage medium produce a manufactured product comprising instruction means, which implements the functions specified in the flowcharts and / or block diagrams. Figure 1 one or more flows and / or blocks Figure 1 means for performing the functions specified in the flow or flows and / or block or blocks.

[0253] These computer program instructions can also be loaded into a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 Figure 1

[0254] Those of ordinary skill in the art can understand that all or part of the flow of the above-mentioned embodiment method can be completed by instructing the relevant hardware through a computer program, and the program can be stored in a computer readable storage medium. When the program is executed, it can include the flow of the above-mentioned embodiment of each method. The storage medium can be a magnetic disc, an optical disc, a read-only memory (ROM), a random access memory (RAM), or the like.

[0255] Although the specific embodiments of the present application are described above with reference to the drawings, the description is not a limitation on the scope of protection of the present application. Those skilled in the art should understand that various modifications or changes made on the basis of the technical solutions of the present application without creative labor are still within the scope of protection of the present application.​​

Claims

1. A low-cost converter control method for a backup power system, characterized in that: include: Obtain the current load voltage and current, inductor current, and DC side upper and lower capacitor voltages of the low-cost three-level converter to calculate the expected output voltage. The vector candidate set is optimized by discarding high common mode voltage vectors, and the vector candidate set is expanded 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 desired output voltage is located based on the amplitude relationship and boundary conditions of the desired output voltage in the 60-degree coordinate system; Based on the latest vector candidate set and the DC side capacitor voltage difference, the initial switching sequence in the optimal small sector is determined; With the goal of minimizing the load voltage tracking error, the optimal action time of the selected basic voltage vector is calculated. The initial switching sequence is optimized to obtain the optimal switching sequence by minimizing the number of switching operations and balancing the DC side neutral point voltage. Based on the optimal switching sequence, a corresponding driving signal is generated to control the switching devices of the low-cost three-level converter to be turned on and off.

2. The low-cost converter control method for a backup power system according to claim 1, wherein: Obtain the current load voltage and current, inductor current, and DC side upper and lower capacitor voltages of the low-cost three-level converter and calculate the expected output voltage and : ； in, i og and i oh They represent the values ​​of the load current in the 60-degree coordinate system, i g and i h They represent the values ​​of the inductor current in the 60-degree coordinate system, v og and v oh is the coordinate of the load voltage in the 60-degree coordinate system, T s represents the sampling period, , , the reference voltage is k Predicted value at time +1 and , load voltage k+1 Predicted value at time v og (k+1) and v oh (k+1) , L f and C f They are filter inductor and filter capacitor respectively. k For the current moment, i og (k) and i oh (k) Indicates that the load current is in the 60-degree coordinate system k The expression of time, i g (k) and i h (k) Indicates the inductor current in the 60-degree coordinate system k The expression of time, v og (k) and v oh (k) Indicates that the load voltage is in the 60 degree coordinate system k Expression of moment.

3. The low-cost converter control method for a backup power system according to claim 1, wherein: The vector candidate set is optimized by discarding high common mode voltage vectors, and the vector candidate set is expanded based on discrete space vector modulation to synthesize virtual small vectors and virtual medium vectors to obtain the latest vector candidate set, specifically: Abandoning the high common-mode voltage vector, the three basic voltage vectors are used to synthesize a virtual small vector. The sum of the currents flowing through the neutral point generated by the three basic voltage vectors and the current flowing through the neutral point generated by the real small vector corresponding to the virtual small vector have opposite polarities and equal amplitudes. Use two large vectors as basic voltage vectors to synthesize a virtual neutral vector; Based on the virtual small vector and the virtual medium vector, the latest vector candidate set is obtained.

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

5. The low-cost converter control method for a backup power system according to claim 1, wherein: The optimal action time of the selected basic voltage vector is calculated with the goal of minimizing the load voltage tracking error, specifically: ； in, J is the output voltage tracking error objective function, t 1 and t 2 are voltage vectors V v1 and V v2 duration of action; ； Among them, k Predicted value of load voltage at time +1 in 60-degree coordinate system and , the reference voltage is k +1 reference value at time and .

6. The low-cost converter control method for a backup power system according to claim 1, wherein: According to minimizing the number of switching operations and balancing the DC side neutral point voltage, the initial switching sequence is optimized to obtain the optimal switching sequence, which is specifically: When the DC side neutral point voltage is high, a switching sequence containing an N-type small vector is selected; When the DC side neutral point voltage is low, a switching sequence containing a small P-type vector is selected; Under the premise of minimizing the number of switching operations, design a seven-stage or five-stage symmetrical switching sequence to ensure the same number of switching operations for the same type of switching sequence; Based on the above rules, the optimal switching sequence is obtained.

7. A low-cost converter control system for a backup power system, characterized in that: include: The expected output voltage calculation module is configured to obtain the load voltage and current, the inductor current, and the upper and lower capacitor voltages of the low-cost three-level converter at the current moment and calculate the expected output voltage; A vector candidate set determination module is configured to optimize the vector candidate set by discarding high common mode voltage vectors, and to expand the vector candidate set based on discrete space vector modulation to synthesize virtual small vectors and virtual medium vectors to obtain a latest vector candidate set; an optimal sector determination module configured to determine an optimal large sector and an optimal small sector where the desired output voltage is located based on the amplitude relationship and boundary conditions of the desired output voltage in a 60-degree coordinate system; An initial switching sequence design module is configured to determine an initial switching sequence in an optimal small sector based on a latest vector candidate set and a DC side capacitor voltage difference; The neutral point voltage balancing and switching sequence optimization module is configured to minimize the load voltage tracking error. It calculates the optimal action time of the selected basic voltage vector and optimizes the initial switching sequence to obtain the optimal switching sequence by minimizing the number of switching operations and balancing the DC side neutral point voltage. The driving signal conversion module is configured to generate a corresponding driving signal based on the optimal switching sequence to control the switching device of the low-cost three-level converter to be turned on and off.

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

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the steps of the low-cost converter control method for a backup power system according to any one of claims 1 to 6 are implemented.

10. A computer program product, characterized in that The computer program product comprises a computer program, and when the computer program is executed by a processor, the computer program implements the steps of the low-cost converter control method for a backup power system according to any one of claims 1 to 6.

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