A boost type three-port energy storage inverter and control method thereof

Abstract

The present invention discloses a boost type three-port energy storage inverter and a control method thereof. The boost type three-port energy storage inverter includes a DC power supply, a battery, a bidirectional DC-DC converter, a boost inverter and an AC load; the inverter has three ports of input, output and energy storage, and has two working modes, and can convert the input DC source voltage or the single-stage high-gain boost of the battery into a stable, high-quality three-phase sinusoidal AC power; the control method is to centrally control the inverter and the battery charging and discharging control of the topology. The present invention improves the power density and efficiency of the energy storage system while improving the gain of the DC power supply; and adopts a control strategy to realize the bidirectional power flow between the ports, which can ensure the efficient operation of the energy storage system.

Description

Technical Field

[0001] The invention relates to power electronics technology and a battery energy storage system, and in particular to a boost-type three-port energy storage inverter and a control method thereof. Background Art

[0002] Energy storage is an important component and key technology of smart grid, renewable energy system and energy internet. During energy conversion, power electronic equipment can improve the utilization rate of electric energy and the stability of power flow through energy storage devices. The inverter topology can feed power to the grid from the energy storage device when the grid load is too high; and when the grid load is low, it is used to store the excess power generation of the grid to achieve the stability of grid energy transmission.

[0003] In the prior art, energy storage batteries need to be connected to the power grid through different power converters (DC-DC converters or AC-DC converters). For example, the paper "Application of Buck / Boost Bidirectional Converter Based on Complementary PWM Control in Supercapacitor Energy Storage" proposes to apply boost / buck bidirectional converters in energy storage. However, this multi-level structure requires a large number of components, and there is functional redundancy during power transmission, which is not conducive to the efficient operation of the system. Recently, multi-port converters have attracted widespread attention from relevant scholars, such as three-port converter networks using Z-source and quasi-Z-source topologies. In hybrid energy storage systems, the use of a three-port converter structure to connect batteries, supercapacitors, and local loads can reduce the number of power devices used, streamline the system, save costs, and make the system have higher power density and efficiency. At the same time, centralized control can be used to achieve bidirectional power flow between ports, which is convenient for designing optimized control strategies to ensure the efficient operation of energy storage systems in microgrids. However, in the three-port converter network of Z-source and quasi-Z-source topology, since the battery is connected in parallel at both ends of the energy storage capacitor, the battery is charged and discharged at a constant voltage by adjusting the direct duty cycle, and there is no research on the two-stage / three-stage charge and discharge control when the battery SOC is too small or too large, resulting in unstable charge and discharge of the energy storage battery, reduced life, and low safety. In addition, the traditional three-phase voltage source inverter (VSI) is a step-down structure, and the DC power loss is large. If a boost inverter is used, the DC power gain can be improved. Summary of the invention

[0004] The present invention aims to propose a boost type three-port energy storage inverter, which aims to improve the DC power gain while improving the power density and efficiency of the energy storage system. At the same time, a control strategy is adopted to achieve bidirectional power flow between each port to ensure the efficient operation of the energy storage system.

[0005] The technical solution to achieve the purpose of the present invention is: a boost type three-port energy storage inverter, including a battery, a DC power supply U IN , a storage capacitor C f, the first energy storage inductor L 1 , the second energy storage inductor L 2 , three anti-backflow diodes D 1 ~D 3 , eight power switch tubes S 1 ~S 8 , eight diodes connected in anti-parallel with the eight power switch tubes, AC side resistive inductive loads R, L and three single-pole double-throw switches, among which:

[0006] DC power supply U IN , six power switch tubes S 1 ~S 6 , a storage capacitor C f , the first energy storage inductor L 1 , three anti-backflow diodes D 1 ~D 3 Together they form a boost inverter circuit, the DC power supply U IN The positive electrode is connected to the first energy storage inductor L through two branches. 1 One end and the energy storage capacitor C f The negative pole of the first energy storage inductor L 1 The other end is connected through three anti-backflow diodes D 1 ~D 3 They are connected to the midpoints of the three-phase bridge arms of the boost inverter a, b, and c respectively, and the energy storage capacitor C f The positive pole is connected to the upper end of the three-phase bridge arm of the boost inverter a, b, c; the DC power supply U IN The negative electrode is connected to the lower end of the three-phase bridge arm a, b, c of the boost inverter;

[0007] The right AC side of the boost inverter is a resistive-inductive load R, L and three single-pole double-throw switches. The three single-pole double-throw switches have two terminals 1 and 2. Terminal 1 of each phase is connected to the midpoint of the corresponding bridge arm of the boost inverter, and terminal 2 of each phase is connected to the DC power supply U IN The positive pole is connected. When the boost inverter circuit works normally, the three single-pole double-throw switches are all thrown to terminal 1; when the six power switch tubes S of the boost inverter circuit are 1 ~S 6 When any one of them has an open circuit fault, the single-pole double-throw switch of the bridge arm corresponding to the power switch tube having the open circuit fault changes the connected terminal 1 to terminal 2, and the single-pole double-throw switches of other non-faulty bridge arms are still thrown to terminal 1; the fixed ends of the three single-pole double-throw switches are respectively connected to a resistive-inductive load R, L, and the other ends of the three resistive-inductive loads R, L are connected;

[0008] Two power switch tubes S 7 , S 8 , battery, second energy storage inductor L 2Together form a bidirectional DC-DC converter loop; the positive electrode of the battery and the second energy storage inductor L 2 connected, and the battery and the second energy storage inductor L 2 The series circuit is connected in parallel with the power switch tube S 8 Both ends; power switch tube S 7 , S 8 The connection mode is half-bridge connection, the power switch tube S 7 The anode is connected to the energy storage capacitor C f Positive electrode, S 8 The cathode is connected to the energy storage capacitor C f negative electrode.

[0009] Furthermore, the boost three-port energy storage inverter has two power supply modes, namely, DC power supply U IN Power supply for load and battery, as well as DC power supply U IN And the battery supplies power to the load.

[0010] A control method for a boost type three-port energy storage inverter comprises the following steps:

[0011] Step 1: Determine the basic voltage vector according to the switching state of the power switch tube in the boost inverter circuit, divide it into six sectors, and determine the vector action time of each sector;

[0012] Step 2: Based on the boost control strategy, reallocate the vector action time and determine the conduction time of the six power switches in the boost inverter loop;

[0013] Step 3, modulate the conduction time of the six power switch tubes in the boost inverter circuit with the triangular carrier, and output the switch tube PWM pulse signal;

[0014] Step 4: According to different states of charge (SOC) of the battery, the bidirectional DC-DC converter circuit is divided into two stages of control. When 30% ≤ SOC ≤ 90%, constant voltage charge and discharge control is adopted for the bidirectional DC-DC converter circuit; when SOC < 30% or SOC > 90%, constant power charge and discharge control is adopted for the bidirectional DC-DC converter circuit.

[0015] Step 5: When an open-circuit fault of a power switch occurs in the boost inverter circuit, the topology structure is switched according to the position of the faulty power switch. The boost control strategy of the boost inverter circuit adopts constant voltage setting control, and the bidirectional DC-DC converter circuit adopts constant voltage charge and discharge control.

[0016] Step 6: Reconstruct the basic voltage vector of the power switch tube in the boost inverter circuit according to the fault-tolerant topological structure, divide it into four sectors, and determine the vector action time of each sector;

[0017] Step 7: re-modulate the conduction time of the six power switch tubes in the boost inverter circuit with the triangular carrier, output the switch tube PWM pulse signal, and complete the fault-tolerant control.

[0018] Further, in step 1, the basic voltage vector is determined according to the switching state of the power switch tube in the boost inverter circuit, six sectors are divided, and the vector action time of each sector is determined. The specific method is:

[0019] Step 1.1, determining a basic voltage vector according to the switching state of the power switch tube in the boost inverter circuit;

[0020] Each phase of the boost inverter circuit has two power switch tubes, each of which has two switching states. The switching function (S a , S b , S c )Total 2 3 = 8 switch state combinations. When the upper tube of each phase is turned on and the lower tube is turned off, it is recorded as 1, otherwise it is recorded as 0. Therefore, the eight switch states are S 0 (000), S 1 (100), S 2 (110), S 3 (010), S 4 (011), S 5 (001), S 6 (101), S 7 (111); When the boost inverter is in S 0 (000), S 1 (100), S 2 (110), S 3 (010), S 4 (011), S 5 (001), S 6 (101) In these seven states, at least one phase of the switch tube of the lower bridge arm is turned on. At this time, the DC power supply supplies the first energy storage inductor L through the switch tube of the lower bridge arm. 1 Charging; when the switching state of the inverter is S 7 (111), the upper bridge arm of the three phases is turned on, and the lower bridge arm is turned off. At this time, the first energy storage inductor L 1 Through the upper bridge arm path to the energy storage capacitor C f Charge;

[0021] According to the switching function, the three-phase voltage on the load side is determined, and the calculation formula is:

[0022]

[0023] Where U a , U b , Uc is the three-phase voltage on the AC side of the boost inverter circuit, S a , S b , S c Respectively represent the switching states of the power switch tubes of the a, b, and c bridge arms of the boost inverter circuit; according to the different switching states of the power switch tubes, the switching functions (Sa, Sb, Sc) are formed, and combined with Table 1, the basic voltage vector is determined, including U 0 (000), U 1 (100), U 2 (110) U 3 (010), U 4 (011), U 5 (001), U 6 (101), U 7 (111);

[0024] Table 1 Basic voltage vector table

[0025]

[0026] Table U k is the basic voltage vector obtained after Clark transformation of the three-phase voltages a, b, and c, k ranges from 0 to 7, U dc is the DC input voltage.

[0027] Step 1.2, divide into six sectors;

[0028] The six basic voltage vectors U 1 ~U 6 Taking the α axis as the reference, 1 (100), U 2 (110) U 3 (010), U 4 (011), U 5 (001), U 6 (101) Rotate 60° counterclockwise successively, and divide the space vector hexagon into 6 large sectors I, II, III, IV, V, and VI, with two zero vectors of zero amplitude located at the origin;

[0029] Step 1.3, determine the synthetic rotating voltage vector V * The vector action time of each sector;

[0030] Select the action vector (V n1 ,V n2 ), sector I corresponds to a non-zero vector (U 1 ,U 2 ), sector II corresponds to the non-zero vector (U 2 ,U 3), sector III corresponds to the non-zero vector (U 3 ,U 4 ),IV sector corresponds to the non-zero vector (U 4 ,U 5 ), V sector corresponds to non-zero vector (U 5 ,U 6 ),VI sector corresponds to the basic vector (U 1 ,U 6 );

[0031] Determine the action time of each sector basic vector according to Table 2, T x is a non-zero vector V n1 Action time, T y is a non-zero vector V n2 Duration of action;

[0032] Table 2 Six-sector basic vector action time

[0033]

[0034]

[0035] Table U α * , U β * is the rotating voltage vector V * The component in the α-β two-phase stationary coordinate system, T s is the sampling period, U dc is the DC input voltage of the boost inverter.

[0036] Further, in step 2, based on the boost control strategy, the vector action time is reallocated to determine the conduction time of the six power switches of the boost inverter loop. The specific method is as follows:

[0037] Step 2.1, reallocate the vector action time based on the boost control strategy;

[0038] The boost control strategy first determines the relationship between the DC boost ratio and the zero vector action time:

[0039]

[0040] In the formula, the DC boost ratio of the boost inverter is defined as B, t x is the basic voltage vector U 7 The vector action time of (111);

[0041] t x That is, the inductor discharge time is set to zero vector U 7 The action time T of (111) z The minimum value (Tzmin ), the relationship is:

[0042]

[0043] Where M is the modulation index and is defined as:

[0044]

[0045] Zero vector U 7 (111) U 0 (000) The interaction time is T z , so the zero vector U 0 The action time of (000) is changed to T z -T zmin , the action time of the other six non-zero vectors remains unchanged. According to the six-sector division method, the allocation time of each vector corresponding to different sectors is shown in Table 3;

[0046] Table 3 Boost control strategy vector action time

[0047]

[0048] Table T 1 -T 6 Corresponding to the voltage vector U 1 (100), U 2 (110) U 3 (010), U 4 (011), U 5 (001), U 6 (101) duration of action;

[0049] The time calculation formula for the upper bridge arm power switch tube of phase a bridge arm is turned on and the lower bridge arm power switch tube is turned off:

[0050]

[0051] The time calculation formula for the upper bridge arm power switch tube of phase b bridge arm is turned on and the lower bridge arm power switch tube is turned off is:

[0052]

[0053] The calculation formula for the time when the upper bridge arm power switch tube of the c phase bridge arm is turned on and the lower bridge arm power switch tube is turned off is:

[0054]

[0055] The time during which the upper bridge arm power switch tube of the same bridge arm is turned on and the lower bridge arm power switch tube is turned off is referred to as the switch tube turn-on time. The switch tube turn-on time of different sectors is determined according to Table 4:

[0056] Table 4 Switching tube conduction time of different sectors

[0057]

[0058]

[0059] In a switching cycle, the time when the upper power switch tube of the same bridge arm is turned off and the lower power switch tube of the same bridge arm is turned on is complementary to the time when the upper power switch tube of the same bridge arm is turned on and the lower power switch tube of the same bridge arm is turned off.

[0060] Further, in step 3, the conduction time of the six power switch tubes in the boost inverter circuit is modulated with the triangular carrier to output the switch tube PWM pulse signal. The specific method is:

[0061] Using CPWM technology, the on-time of the switch tube is modulated with an isosceles triangle wave whose period is the sampling period and whose amplitude is half of the sampling period. The action sequence of the basic vectors is determined based on the symmetry principle and the minimum THD principle, and 6 PWM pulses can be obtained. The pulse signals act on 6 power switch tubes respectively to output three-phase voltage and current.

[0062] Further, in step 4, according to the different states of charge SOC of the battery, the bidirectional DC-DC converter circuit is divided into two stages of control. When 30%≤SOC≤90%, constant voltage charge and discharge control is adopted for the bidirectional DC-DC converter circuit; when SOC<30% or SOC>90%, constant power charge and discharge control is adopted for the bidirectional DC-DC converter circuit. The specific method is as follows:

[0063] State 1: When 30%≤SOC≤90%, constant voltage charge and discharge control is adopted for the bidirectional DC-DC converter circuit. By controlling the duty cycle of power switch tubes S7 and S8, the energy storage capacitor C connected in parallel with the bidirectional DC-DC converter circuit is f The voltage is the set value;

[0064] With energy storage capacitor C f Actual value of voltage across the two ends U Cf As the feedback quantity, the energy storage capacitor C f Voltage setting value U Cf * As the reference quantity, the difference ΔU Cf =U Cf -U Cf * Determine the battery charge and discharge status, and set ΔU Cf After inputting into the PI regulator, the power switch tube S is obtained. 7 The initial duty cycle D * , after limiting control, the power switch tube S is obtained7 The actual duty cycle D; the power switch tube S 7 , S 8 The duty cycle of the power switch tube S 8 The duty cycle is set to 1-D, at this time the energy storage capacitor C f Voltage U Cf Realize following control according to set value;

[0065] State 2: When SOC is less than 30% or SOC is greater than 90%, constant power charge and discharge control is adopted for the bidirectional DC-DC converter circuit, and the duty cycle of the power switches S7 and S8 is controlled to make the battery power the set value;

[0066] The real-time battery power P b is the feedback quantity, with the battery reference power P b * The set value is the reference value, and the difference between the two is ΔP b =P b -P b * Determine the battery charge and discharge status, and set ΔP b After inputting into the PI regulator, the power switch tube S is obtained. 7 The initial duty cycle D * , after limiting control, the power switch tube S is obtained 7 The actual duty cycle D; the power switch tube S 7 , S 8 The duty cycle of the power switch tube S 8 The duty cycle is set to 1-D, at this time the battery power P b Realize following control according to the set value.

[0067] Further, in step 5, when an open-circuit fault of the power switch tube occurs in the boost inverter circuit, the topology structure is switched according to the position of the faulty power switch tube, the boost control strategy of the boost inverter circuit adopts constant voltage setting control, and the bidirectional DC-DC converter circuit adopts constant voltage charge and discharge control. The specific method is:

[0068] Step 5.1, switching the topology structure according to the position of the faulty power switch tube;

[0069] When an open-circuit fault occurs in the power switch tube in the boost inverter circuit, the single-pole double-throw switch connected to the corresponding fault phase switches the switch position from terminal 1 to terminal 2; at this time, four of the six power switch tubes are actually working, and the corresponding positions are that when phase a fails, the boost inverter is controlled by the four switch tubes of phases b and c, when phase b fails, the boost inverter is controlled by the four switch tubes of phases c and a, and when phase c fails, the boost inverter is controlled by the four switch tubes of phases a and b;

[0070] Step 5.2, the boost control strategy of the boost inverter circuit adopts constant voltage setting control;

[0071] In order to meet the theoretical requirements of the four-switch control method, the energy storage capacitor C is set f Voltage across the terminals U Cf * The value is equal to the DC power supply U IN , at this time the DC voltage U in the boost inverter circuit dc The value is set to:

[0072] U dc =U Cf +U IN =2U IN

[0073] At this time, the load corresponding to the fault is connected to the positive pole of the DC power supply through a single-pole double-throw switch. The load corresponding to the fault is equivalent to the DC voltage U connected to the boost inverter circuit. dc at the midpoint;

[0074] Step 5.3, the bidirectional DC-DC converter circuit adopts constant voltage charge and discharge control;

[0075] With energy storage capacitor C f Actual value of voltage across the two ends U Cf As the feedback quantity, the energy storage capacitor C f Voltage setting value U Cf * =U IN As the reference quantity, the difference ΔU Cf =U Cf -U IN Determine the battery charge and discharge status, and set ΔU Cf After inputting into the PI regulator, the power switch tube S is obtained. 7 The initial duty cycle D * , after limiting control, the power switch tube S is obtained 7 The actual duty cycle D; the power switch tube S 7 , S 8 The duty cycle of the power switch tube S 8 The duty cycle is set to 1-D, at this time the energy storage capacitor C f Voltage U Cf =U IN .

[0076] Further, in step 6, the basic voltage vector of the power switch tube in the boost inverter circuit is reconstructed according to the fault-tolerant topology structure, divided into four sectors, and the vector action time of each sector is determined. The specific method is:

[0077] Step 6.1, reconstructing the basic voltage vector of the power switch tube in the boost inverter circuit according to the fault-tolerant topology structure, and dividing it into four sectors;

[0078] When the a-phase bridge arm switch fails, the a-phase of the boost inverter load side is connected to the energy storage capacitor C f The negative pole is the midpoint voltage of the inverter DC side, S a is always 1 / 2; at this time, the four switch tubes of the b and c phases of the boost inverter have four switching states: (Sb Sc) = (00), (Sb Sc) = (01), (Sb Sc) = (10), (Sb Sc) = (11); when the b phase bridge arm switch tube has an open circuit fault, the b phase of the boost inverter load side is connected to the energy storage capacitor C f The negative pole is the midpoint voltage of the inverter DC side, S b The four switch tubes of phase c and phase a of the boost inverter have four switching states: (Sc Sa) = (00), (Sc Sa) = (01), (Sc Sa) = (10), and (Sc Sa) = (11). When the switch tube of the phase c bridge arm fails to open, the phase c of the boost inverter load side is connected to the energy storage capacitor C f The negative pole is the midpoint voltage of the inverter DC side, S c The four switch tubes of the a and b phases of the boost inverter have four switching states: (Sa Sb) = (00), (Sa Sb) = (01), (Sa Sb) = (10), and (Sa Sb) = (11);

[0079] At this time, the rotating voltage vector V * :

[0080]

[0081] In the formula is the spatial rotation factor;

[0082] Determine the basic voltage vector under the condition of reconstructing a single-tube or single-phase fault, as shown in Table 5;

[0083] Table 5 Reconstructed basic voltage vector table

[0084]

[0085] After a phase among the three phases a, b, and c fails, U 0 '、U 1 '、U 2 '、U 3 'The four basic voltage vectors are in the plane according to U 0 '、U 1 '、U 3 '、U 2'Arranged clockwise, each adjacent vector is 90° apart, and the plane space is divided into four sectors according to the arrangement of the four basic voltage vectors.

[0086] Step 6.2, determine the vector action time of each sector;

[0087] The action vector includes the effective vector and the zero vector. 0 '~U 3 'As an effective vector alone, take two basic voltage vectors in opposite directions to synthesize an equivalent zero vector, that is, use U 0 '(00),U 3 '(11) Synthesize an equivalent zero vector, using U 1 '(01),U 2 '(10) synthesizing another equivalent zero vector; synthesizing the effective vector and the equivalent zero vector together into a reference vector;

[0088] Define intermediate variables:

[0089]

[0090] Assume that the effective vector of the first sector is U 0 '、U 2 '; The effective vector of the second sector is U 2 '、U 3 '; The effective vector of the third sector is U 3 '、U 1 '; The effective vector of the fourth sector is U 1 '、U 0 '; The action time of the effective vector of each sector is recorded as Tx and Ty respectively, and the action time of the effective vector of each sector is determined by Table 6;

[0091] Table 6 Action time of effective vectors in each sector

[0092]

[0093] Further, in step 7, the conduction time of the six power switch tubes in the boost inverter circuit is re-modulated with the triangular carrier, and the switch tube PWM pulse signal is output to complete the fault-tolerant control. The specific method is as follows:

[0094] Adopt CPWM technology, modulate the switch on and off time with a triangular carrier whose period is the switch period, add dead time according to the power switch on and off time, and get PWM pulse;

[0095] The 4-channel PWM pulses are applied to the power switch tube driving circuit of the boost inverter circuit, and the driving circuit controls the corresponding power switch tube to turn on and off.

[0096] The boost three-port energy storage inverter designed in the present invention can realize the energy flow of the three ports with fewer components and control algorithms, and combines the control method to ensure the efficient operation of the energy storage system in the microgrid.

[0097] Compared with the prior art, the present invention has the following significant advantages: 1) A boost-type three-port energy storage inverter topology is proposed, which integrates the topological structure of the traditional inverter and energy storage DC-DC converter, reduces the size, cost, weight and complexity of the system, and enables the three-port system to operate efficiently. 2) A control strategy that matches the topology is proposed, which can control the charging and discharging of the battery. When the DC power supply power of the inverter is large, part of the electric energy is transmitted to the battery for energy storage through the bidirectional DC-DC converter. When the peak power consumption comes, the battery energy storage can be used to supply power to its own load, or when it does not need too much power consumption and the battery capacity is large, the battery can be used to transmit electric energy to the power grid to alleviate the social power supply pressure. 3) The topology can be connected to the grid and can be used for energy storage and grid connection control in new energy power generation scenarios such as photovoltaic power generation and wind power generation. The boost inverter topology itself can increase the DC gain and realize the bidirectional flow of energy with the grid side, and the output three-phase current has less harmonic content. BRIEF DESCRIPTION OF THE DRAWINGS

[0098] Figure 1 It is a boost type three-port energy storage inverter of the present invention.

[0099] Figure 2(a) is the overall energy flow diagram of the system; Figure 2(b) is Mode 1: DC power supply U IN Power supply to load and battery; Figure 2(c) is mode 2: DC power supply U IN And the battery supplies power to the load.

[0100] Figure 3 This is the flow chart of the battery charging and discharging system.

[0101] Figure 4 This is the control block diagram of a boost three-port energy storage inverter.

[0102] Figure 5 is a simulation waveform diagram of a boost three-port energy storage inverter; Figure 5(a) is a three-phase current waveform diagram on the load side; Figure 5(b) is a harmonic analysis diagram of the three-phase current waveform diagram; Figure 5(c) is a three-phase voltage waveform diagram on the load side.

[0103] Figure 6(a) is the voltage waveform of the battery parallel capacitor; Figure 6(b) is the DC side inverter voltage U DC Waveform diagram of .

[0104] Figure 7(a) is the battery active power diagram; Figure 7(b) is the DC power supply active power diagram; Figure 7(c) is the load side three-phase active power diagram; Figure 7(d) is the battery SOC diagram.

[0105] Figure 8(a) is the three-phase current waveform of the energy storage inverter load side; Figure 8(b) is the energy storage capacitor C f Voltage across both ends. DETAILED DESCRIPTION

[0106] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0107] Figure 1 This is the topology diagram of the boost three-port energy storage inverter. 1 , D 2 , D 3 is a diode; L 1 is the energy storage inductor of the boost inverter circuit; L 2 is the energy storage inductor of the bidirectional DC-DC converter loop; C f is the energy storage capacitor; S 1 ~S 8 is the power switch tube; U In is the DC power supply; U dc is the DC input voltage; R is the AC load resistance; L is the AC load inductance.

[0108] Among them, the DC power supply U IN , six power switch tubes S 1 ~S 6 , a storage capacitor C f , the first energy storage inductor L 1 , three anti-backflow diodes D 1 ~D 3 Together they form a boost inverter circuit, the DC power supply U IN The positive electrode is connected to the first energy storage inductor L through two branches. 1 One end and the energy storage capacitor C f The negative pole of the first energy storage inductor L 1 The other end is connected through three anti-backflow diodes D 1 ~D 3 They are connected to the midpoints of the three-phase bridge arms of the boost inverter a, b, and c respectively, and the energy storage capacitor C f The positive pole is connected to the upper end of the three-phase bridge arm of the boost inverter a, b, c; the DC power supply U IN The negative electrode is connected to the lower end of the three-phase bridge arm a, b, c of the boost inverter;

[0109] The right AC side of the boost inverter is a resistive-inductive load R, L and three single-pole double-throw switches. The three single-pole double-throw switches have two terminals 1 and 2. Terminal 1 of each phase is connected to the midpoint of the corresponding bridge arm of the boost inverter, and terminal 2 of each phase is connected to the DC power supply U IN The positive pole is connected. When the boost inverter circuit works normally, the three single-pole double-throw switches are all thrown to terminal 1; when the six power switch tubes S of the boost inverter circuit are 1 ~S 6 When an open circuit fault occurs in any one of the power switch tubes, the single-pole double-throw switch of the bridge arm corresponding to the open circuit fault will change the connected terminal 1 to terminal 2, and the single-pole double-throw switches of other non-faulty bridge arms will still be thrown to terminal 1;

[0110] Two power switch tubes S 7 , S 8 , battery, second energy storage inductor L 2 Together form a bidirectional DC-DC converter loop; the positive electrode of the battery and the second energy storage inductor L 2 connected, and the battery and the second energy storage inductor L 2 The series circuit is connected in parallel with the power switch tube S 8 Both ends; power switch tube S 7 , S 8 The connection mode is half-bridge connection, the power switch tube S 7 The anode is connected to the energy storage capacitor C f Positive electrode, S 8 The cathode is connected to the energy storage capacitor C f negative electrode.

[0111] Figure 2(a) is the overall energy flow diagram of the system. The boost three-port energy storage inverter has two power supply modes: mode 1, in which the input DC source UIN supplies power to the output load and the battery, as shown in Figure 2(b); and mode 2, in which the input DC source UIN and the battery supply power to the output load, as shown in Figure 2(c).

[0112] Figure 3 The figure is a flow chart of the battery charging and discharging system. According to the content of the battery SOC, the battery charging and discharging control is divided into two stages of control.

[0113] Figure 4 The control block diagram of the boost three-port energy storage inverter is shown in Figure 2. The inverter part of the boost three-port energy storage inverter adopts a current inner loop closed loop design. The three-phase current on the load side is collected and transformed by Park to obtain the d and q axis currents, which are input into the PI regulator as the difference between the d and q axis current reference values, and the d and q axis voltage reference values ​​are output. After the Park inverse transformation, the α and β axis voltage reference values ​​are obtained. The SVPWM control module based on the zero vector control algorithm generates 6 signals to control the on and off of the IGBT gate. The bidirectional DC-DC converter loop control adopts a two-stage control strategy.

[0114] A control method for a boost three-port energy storage inverter comprises the following steps:

[0115] Step 1: determine the basic voltage vector according to the switching state of the power switch tube in the boost inverter circuit, divide it into six sectors, and determine the vector action time of each sector. The specific method is:

[0116] Step 1.1, determining a basic voltage vector according to the switching state of the power switch tube in the boost inverter circuit;

[0117] Each phase of the boost inverter circuit has two power switch tubes, each of which has two switching states. The switching function (S a , S b , S c )Total 2 3 = 8 switch state combinations. When the upper tube of each phase is turned on and the lower tube is turned off, it is recorded as 1, otherwise it is recorded as 0. Therefore, the eight switch states are S 0 (000), S 1 (100), S 2 (110), S 3 (010), S 4 (011), S 5 (001), S 6 (101), S 7 (111); When the boost inverter is in S 0 (000), S 1 (100), S 2 (110), S 3 (010), S 4 (011), S 5 (001), S 6 (101) In these seven states, at least one phase of the switch tube of the lower bridge arm is turned on. At this time, the DC power supply supplies the first energy storage inductor L through the switch tube of the lower bridge arm. 1 Charging; when the switching state of the inverter is S 7 (111), the upper bridge arm of the three phases is turned on, and the lower bridge arm is turned off. At this time, the first energy storage inductor L 1 Through the upper bridge arm path to the energy storage capacitor C f Charge;

[0118] According to the switching function, the three-phase voltage on the load side is determined, and the calculation formula is:

[0119]

[0120] Where U a , U b , U c is the three-phase voltage on the AC side of the boost inverter circuit, S a , S b , S c Respectively represent the switching states of the power switch tubes of the a, b, and c bridge arms of the boost inverter circuit; according to the different switching states of the power switch tubes, the switching functions (Sa, Sb, Sc) are formed, and combined with Table 1, the basic voltage vector is determined, including U 0 (000), U 1 (100), U 2 (110) U 3 (010), U 4 (011), U 5 (001), U 6 (101), U 7 (111);

[0121] Table 1 Basic voltage vector table

[0122]

[0123] Step 1.2, divide into six sectors;

[0124] The six basic voltage vectors U 1 ~U 6 Taking the α axis as the reference, 1 (100), U 2 (110) U 3 (010), U 4 (011), U 5 (001), U 6 (101) Rotate 60° counterclockwise successively, and divide the space vector hexagon into 6 large sectors I, II, III, IV, V, and VI, with two zero vectors of zero amplitude located at the origin;

[0125] Step 1.3, determine the synthetic rotating voltage vector V * The vector action time of each sector;

[0126] Select the action vector (V n1 ,V n2 ), sector I corresponds to a non-zero vector (U 1 ,U 2 ), sector II corresponds to the non-zero vector (U 2 ,U 3 ), sector III corresponds to the non-zero vector (U 3 ,U 4 ),IV sector corresponds to the non-zero vector (U4 ,U 5 ), V sector corresponds to non-zero vector (U 5 ,U 6 ),VI sector corresponds to the basic vector (U 1 ,U 6 );

[0127] Determine the action time of each sector basic vector according to Table 2, T x is a non-zero vector V n1 Action time, T y is a non-zero vector V n2 Duration of action;

[0128] Table 2 Six-sector basic vector action time

[0129]

[0130] Table U α * , U β * is the rotating voltage vector V * The component in the α-β two-phase stationary coordinate system, T s is the sampling period, U dc is the DC input voltage of the boost inverter.

[0131] Step 2: Based on the boost control strategy, redistribute the vector action time and determine the conduction time of the six power switches in the boost inverter loop. The specific method is as follows:

[0132] Step 2.1, reallocate the vector action time based on the boost control strategy;

[0133] The boost control strategy first determines the relationship between the DC boost ratio and the zero vector action time:

[0134]

[0135] In the formula, the DC boost ratio of the boost inverter is defined as B, t x is the basic voltage vector U 7 The vector action time of (111);

[0136] t x That is, the inductor discharge time is set to zero vector U 7 The action time T of (111) z The minimum value (T zmin ), the relationship is:

[0137]

[0138] Where M is the modulation index and is defined as:

[0139]

[0140] Zero vector U 7 (111) U 0 (000) The interaction time is T z , so the zero vector U 0 The action time of (000) is changed to T z -T zmin , the action time of the other six non-zero vectors remains unchanged. According to the six-sector division method, the allocation time of each vector corresponding to different sectors is shown in Table 3;

[0141] Table 3 Boost control strategy vector action time

[0142]

[0143] Table T 1 -T 6 Corresponding to the voltage vector U 1 (100), U 2 (110) U 3 (010), U 4 (011), U 5 (001), U 6 (101) duration of action;

[0144] The time calculation formula for the upper bridge arm power switch tube of phase a bridge arm is turned on and the lower bridge arm power switch tube is turned off:

[0145]

[0146] The time calculation formula for the upper bridge arm power switch tube of phase b bridge arm is turned on and the lower bridge arm power switch tube is turned off is:

[0147]

[0148] The calculation formula for the time when the upper bridge arm power switch tube of the c phase bridge arm is turned on and the lower bridge arm power switch tube is turned off is:

[0149]

[0150] The time during which the upper bridge arm power switch tube of the same bridge arm is turned on and the lower bridge arm power switch tube is turned off is referred to as the switch tube turn-on time. The switch tube turn-on time of different sectors is determined according to Table 4:

[0151] Table 4 Switching tube conduction time of different sectors

[0152]

[0153] In a switching cycle, the time when the upper power switch tube of the same bridge arm is turned off and the lower power switch tube of the same bridge arm is turned on is complementary to the time when the upper power switch tube of the same bridge arm is turned on and the lower power switch tube of the same bridge arm is turned off.

[0154] Step 3: modulate the conduction time of the six power switch tubes in the boost inverter circuit with the triangular carrier to output the switch tube PWM pulse signal. The specific method is:

[0155] Using CPWM technology, the on-time of the switch tube is modulated with an isosceles triangle wave whose period is the sampling period and whose amplitude is half of the sampling period. The action sequence of the basic vectors is determined based on the symmetry principle and the minimum THD principle, and 6 PWM pulses can be obtained. The pulse signals act on 6 IGBT power switch tubes respectively to output three-phase voltage and current.

[0156] Step 4: According to the different states of charge SOC of the battery, the bidirectional DC-DC converter circuit is divided into two stages of control. When 30%≤SOC≤90%, constant voltage charge and discharge control is adopted for the bidirectional DC-DC converter circuit; when SOC<30% or SOC>90%, constant power charge and discharge control is adopted for the bidirectional DC-DC converter circuit. The specific method is as follows:

[0157] The bidirectional DC-DC converter circuit division method is as follows Figure 3 As shown, state 1: when 30% ≤ SOC ≤ 90%, constant voltage charge and discharge control is adopted for the bidirectional DC-DC converter circuit, and the energy storage capacitor C connected in parallel with the bidirectional DC-DC converter circuit is controlled by controlling the duty cycle of the power switch tubes S7 and S8. f The voltage is the set value;

[0158] With energy storage capacitor C f Actual value of voltage across the two ends U Cf As the feedback quantity, the energy storage capacitor C f Voltage setting value U Cf * As the reference quantity, the difference ΔU Cf =U Cf -U Cf * Determine the battery charge and discharge status, and set ΔU Cf After inputting into the PI regulator, the power switch tube S is obtained. 7 The initial duty cycle D * , after limiting control, the power switch tube S is obtained 7 The actual duty cycle D; the power switch tube S 7 , S 8 The duty cycle of the power switch tube S 8 The duty cycle is set to 1-D, at this time the energy storage capacitor Cf Voltage U Cf Realize following control according to set value;

[0159] State 2: When SOC is less than 30% or SOC is greater than 90%, constant power charge and discharge control is adopted for the bidirectional DC-DC converter circuit, and the duty cycle of the power switches S7 and S8 is controlled to make the battery power the set value;

[0160] The real-time battery power P b is the feedback quantity, with the battery reference power P b * The set value is the reference value, and the difference between the two is ΔP b =P b -P b * Determine the battery charge and discharge status, and set ΔP b After inputting into the PI regulator, the power switch tube S is obtained. 7 The initial duty cycle D * , after limiting control, the power switch tube S is obtained 7 The actual duty cycle D; the power switch tube S 7 , S 8 The duty cycle of the power switch tube S 8 The duty cycle is set to 1-D, at this time the battery power P b Realize following control according to set value;

[0161] Step 5: When an open-circuit fault of the power switch tube occurs in the boost inverter circuit, the topology structure is switched according to the position of the faulty power switch tube. The boost control strategy of the boost inverter circuit adopts constant voltage setting control, and the bidirectional DC-DC converter circuit adopts constant voltage charge and discharge control. The specific method is as follows:

[0162] Step 5.1, switching the topology structure according to the position of the faulty power switch tube;

[0163] When an open-circuit fault occurs in the power switch tube in the boost inverter circuit, the single-pole double-throw switch connected to the corresponding fault phase switches the switch position from terminal 1 to terminal 2; at this time, four of the six power switch tubes are actually working, and the corresponding positions are that when phase a fails, the boost inverter is controlled by the four switch tubes of phases b and c, when phase b fails, the boost inverter is controlled by the four switch tubes of phases c and a, and when phase c fails, the boost inverter is controlled by the four switch tubes of phases a and b;

[0164] Step 5.2, the boost control strategy of the boost inverter circuit adopts constant voltage setting control;

[0165] In order to meet the theoretical requirements of the four-switch control method, the energy storage capacitor C is set f Voltage across the terminals UCf * The value is equal to the DC power supply U IN , at this time the DC voltage U in the boost inverter circuit dc The value is set to:

[0166] U dc =U Cf +U IN =2U IN

[0167] At this time, the load corresponding to the fault is connected to the positive pole of the DC power supply through a single-pole double-throw switch. The load corresponding to the fault is equivalent to the DC voltage U connected to the boost inverter circuit. dc At the midpoint.

[0168] Step 5.3, the bidirectional DC-DC converter circuit adopts constant voltage charge and discharge control;

[0169] With energy storage capacitor C f Actual value of voltage across the two ends U Cf As the feedback quantity, the energy storage capacitor C f Voltage setting value U Cf * =U IN As the reference quantity, the difference ΔU Cf =U Cf -U IN Determine the battery charge and discharge status, and set ΔU Cf After inputting into the PI regulator, the power switch tube S is obtained. 7 The initial duty cycle D * , after limiting control, the power switch tube S is obtained 7 The actual duty cycle D; the power switch tube S 7 , S 8 The duty cycle of the power switch tube S 8 The duty cycle is set to 1-D, at this time the energy storage capacitor C f Voltage U Cf =U IN ;

[0170] Further, in step 6, the basic voltage vector of the power switch tube in the boost inverter circuit is reconstructed according to the fault-tolerant topology structure, divided into four sectors, and the vector action time of each sector is determined. The specific method is:

[0171] Step 6.1, reconstructing the basic voltage vector of the power switch tube in the boost inverter circuit according to the fault-tolerant topology structure, and performing 4-sector division;

[0172] When the a-phase bridge arm switch fails, the a-phase of the boost inverter load side is connected to the energy storage capacitor C fThe negative pole is the midpoint voltage of the inverter DC side, S a is always 1 / 2; at this time, the four switch tubes of the b and c phases of the boost inverter have four switching states: (Sb Sc) = (00), (Sb Sc) = (01), (Sb Sc) = (10), (Sb Sc) = (11); when the b phase bridge arm switch tube has an open circuit fault, the b phase of the boost inverter load side is connected to the energy storage capacitor C f The negative pole is the midpoint voltage of the inverter DC side, S b The four switch tubes of phase c and phase a of the boost inverter have four switching states: (Sc Sa) = (00), (Sc Sa) = (01), (Sc Sa) = (10), and (Sc Sa) = (11). When the switch tube of the phase c bridge arm fails to open, the phase c of the boost inverter load side is connected to the energy storage capacitor C f The negative pole is the midpoint voltage of the inverter DC side, S c The four switch tubes of the a and b phases of the boost inverter have four switching states: (Sa Sb) = (00), (Sa Sb) = (01), (Sa Sb) = (10), and (Sa Sb) = (11);

[0173] At this time, the rotating voltage vector V * :

[0174]

[0175] In the formula is the spatial rotation factor;

[0176] Determine the basic voltage vector under the condition of reconstructing a single-tube or single-phase fault, as shown in Table 5;

[0177] Table 5 Reconstructed basic voltage vector table

[0178]

[0179] After a phase among the three phases a, b, and c fails, U 0 '、U 1 '、U 2 '、U 3 'The four basic voltage vectors are in the plane according to U 0 '、U 1 '、U 3 '、U 2 'Arranged clockwise, each adjacent vector is 90° apart, and the plane space is divided into four sectors according to the arrangement of the four basic voltage vectors.

[0180] Step 6.2, determine the vector action time of each sector;

[0181] The action vector includes the effective vector and the zero vector. 0 '~U 3 'As an effective vector alone, take two basic voltage vectors in opposite directions to synthesize an equivalent zero vector, that is, use U 0 '(00),U 3 '(11) Synthesize an equivalent zero vector, using U 1 '(01),U 2 '(10) synthesizing another equivalent zero vector; synthesizing the effective vector and the equivalent zero vector together into a reference vector;

[0182] Define intermediate variables:

[0183]

[0184] Assume that the effective vector of the first sector is U 0 '、U 2 '; The effective vector of the second sector is U 2 '、U 3 '; The effective vector of the third sector is U 3 '、U 1 '; The effective vector of the fourth sector is U 1 '、U 0 '; The action time of the effective vector of each sector is recorded as Tx and Ty respectively, and the action time of the effective vector of each sector is determined by Table 6;

[0185] Table 6 Action time of effective vectors in each sector

[0186]

[0187] Step 7: re-modulate the conduction time of the six power switch tubes in the boost inverter circuit with the triangular carrier, output the switch tube PWM pulse signal, and complete the fault-tolerant control. The specific method is as follows:

[0188] Adopt CPWM technology, modulate the switch on and off time with a triangular carrier whose period is the switch period, add dead time according to the power switch on and off time, and get PWM pulse;

[0189] The 4-channel PWM pulses are applied to the power switch tube driving circuit of the boost inverter circuit, and the driving circuit controls the corresponding power switch tube to turn on and off.

[0190] The hardware topology and control algorithm of the boost three-port energy storage inverter designed in the present invention can realize the three-port energy flow with fewer components and designed control algorithms, and the method can achieve high power quality and low harmonic current operation, and the battery can realize the function of energy storage and release according to control requirements.

[0191] Example

[0192] The present invention proposes a boost type three-port energy storage inverter topology structure, which integrates the topology of traditional inverter and energy storage DC-DC converter, reduces the size, cost, weight and complexity of the system, and enables the energy storage system to operate efficiently; and proposes a centralized control strategy for the topology, in which the battery and bidirectional DC-DC converter control parts have two working modes, and the inverter part is an SVPWM modulation method based on the zero vector control strategy. In order to verify the effectiveness of the scheme of the present invention, simulation verification of the topology and its control method is carried out.

[0193] Figure 5(a) shows the three-phase AC current on the load side of the boost three-port energy storage inverter. At this time, the reference setting value of the current inner loop is 2A. It can be seen that the amplitude of the output three-phase AC current is 2A. Referring to the harmonic (THD) value of the A-phase current, the harmonic content of the A-phase current is 1.10%, which is stable below 5%. This verifies that the waveform of the three-phase AC current output by the energy storage boost inverter is relatively stable and the harmonic content is low, and the control module can meet the control requirements.

[0194] Under higher voltage conditions, the three-phase line voltage on the load side of the energy storage boost inverter can still maintain a relatively stable output; Figure 6(b) shows that the DC energy storage is the energy storage capacitor C f Voltage U Cf The waveform diagram shows that the DC input voltage setting value U dc * The DC power supply voltage U is 250V. IN is 125V. It can be seen from the figure that U Cf The value is stable at around 125V, which verifies that the boost inverter can still meet the boost control requirements in energy storage application scenarios, and the system is relatively stable at this time.

[0195] Figure 7(a) is the battery active power diagram, which is about -70W; Figure 7(b) is the DC power supply active power diagram, which is about 160W; Figure 7(c) is the load side three-phase active power diagram, which is about 90W; at this time, the battery adopts a constant power control strategy, and the active power generated by the DC power supply is greater than the active power consumed by the load side. At this time, the battery is charged, and the charging power and the active power consumed by the load side are added to the active power generated by the DC power supply.

[0196] Figure 8(a) is a three-phase current waveform of the load side of the boost three-port energy storage inverter when the power switch tube is open-circuited. At this time, the current peak is about 2A. It can be seen from the figure that the three-phase current output is stable, indicating that the four-switch control method is well controlled; Figure 8(b) is the energy storage capacitor C f The voltage is set to U Cf*Value is equal to DC power supply value U IN It is 125V. It can be seen from the figure that the energy storage capacitor voltage U Cf It is stable at around 125V, which means the control effect is good and the fault-tolerant control strategy can run stably.

[0197] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0198] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A boost three-port energy storage inverter, characterized in that: Including battery, DC power supply U IN , a storage capacitor C f , a first energy storage inductor L1, a second energy storage inductor L2, three backflow prevention diodes D1-D3, eight power switch tubes S1-S8, eight diodes anti-parallel to the eight power switch tubes, AC side resistance-inductive loads R, L and three single-pole double-throw switches, wherein: DC power supply U IN , six power switch tubes S1~S6, one energy storage capacitor C f , the first energy storage inductor L1, and the three anti-backflow diodes D1 to D3 together form a boost inverter circuit, and the DC power supply U IN The positive electrode is connected to one end of the first energy storage inductor L1 and the energy storage capacitor C through two branches. f The other end of the first energy storage inductor L1 is connected to the midpoint of the three-phase bridge arm a, b, c of the boost inverter through three anti-backflow diodes D1~D3, and the energy storage capacitor C f The positive pole is connected to the upper end of the three-phase bridge arm of the boost inverter a, b, c; the DC power supply U IN The negative electrode is connected to the lower end of the three-phase bridge arm a, b, c of the boost inverter; The right AC side of the boost inverter is a resistive-inductive load R, L and three single-pole double-throw switches. The three single-pole double-throw switches have two terminals 1 and 2. Terminal 1 of each phase is connected to the midpoint of the corresponding bridge arm of the boost inverter, and terminal 2 of each phase is connected to the DC power supply U IN The positive poles are connected, and when the boost inverter circuit works normally, the three single-pole double-throw switches are all thrown to terminal 1; when any of the six power switch tubes S1 to S6 of the boost inverter circuit has an open circuit fault, the single-pole double-throw switch of the bridge arm corresponding to the power switch tube having the open circuit fault changes the connected terminal 1 to terminal 2, and the single-pole double-throw switches of other non-fault bridge arms are still thrown to terminal 1; the fixed ends of the three single-pole double-throw switches are respectively connected to a resistive-inductive load R, L, and the other ends of the three resistive-inductive loads R, L are connected; The two power switch tubes S7 and S8, the battery, and the second energy storage inductor L2 together form a bidirectional DC-DC converter loop; the positive electrode of the battery is connected to the second energy storage inductor L2, and the series circuit of the battery and the second energy storage inductor L2 is connected in parallel to the two ends of the power switch tube S8; the power switch tubes S7 and S8 are connected in a half-bridge connection, and the anode of the power switch tube S7 is connected to the energy storage capacitor C f The positive pole, cathode of S8 is connected to the energy storage capacitor C f negative electrode.

2. The boost three-port energy storage inverter according to claim 1, characterized in that: The boost three-port energy storage inverter has two power supply modes: DC power supply U IN Power supply for load and battery, as well as DC power supply U IN And the battery supplies power to the load.

3. A control method for the boost three-port energy storage inverter according to claim 1 or 2, characterized in that: The steps include: Step 1: Determine the basic voltage vector according to the switching state of the power switch tube in the boost inverter circuit, divide it into six sectors, and determine the vector action time of each sector; Step 2: Based on the boost control strategy, reallocate the vector action time and determine the conduction time of the six power switches in the boost inverter loop; Step 3, modulate the conduction time of the six power switch tubes in the boost inverter circuit with the triangular carrier, and output the switch tube PWM pulse signal; Step 4: According to different states of charge (SOC) of the battery, the bidirectional DC-DC converter circuit is divided into two stages of control. When 30% ≤ SOC ≤ 90%, constant voltage charge and discharge control is adopted for the bidirectional DC-DC converter circuit; when SOC < 30% or SOC > 90%, constant power charge and discharge control is adopted for the bidirectional DC-DC converter circuit. Step 5: When an open-circuit fault of a power switch occurs in the boost inverter circuit, the topology structure is switched according to the position of the faulty power switch. The boost control strategy of the boost inverter circuit adopts constant voltage setting control, and the bidirectional DC-DC converter circuit adopts constant voltage charge and discharge control. Step 6: Reconstruct the basic voltage vector of the power switch tube in the boost inverter circuit according to the fault-tolerant topological structure, divide it into four sectors, and determine the vector action time of each sector; Step 7: re-modulate the on-time of the four power switch tubes in normal operation in the boost inverter circuit with the triangular carrier, output the switch tube PWM pulse signal, and complete the fault-tolerant control.

4. The control method according to claim 3, characterized in that: Step 1: Determine the basic voltage vector according to the switching state of the power switch tube in the boost inverter circuit, divide it into six sectors, and determine the vector action time of each sector. The specific method is as follows: Step 1.1, determining a basic voltage vector according to the switching state of the power switch tube in the boost inverter circuit; Each phase of the boost inverter circuit has two power switch tubes, each of which has two switching states. The switching function (S a , S b , S c )Total 2 3 =8 switch state combinations, when the upper tube of each phase is turned on and the lower tube is turned off, it is recorded as 1, otherwise it is recorded as 0, so the eight switch states are S0 (000), S1 (100), S2 (110), S3 (010), S4 (011), S5 (001), S6 (101), S7 (111); when the boost inverter is in the seven states of S0 (000), S1 (100), S2 (110), S3 (010), S4 (011), S5 (001), S6 (101), the switch tube of at least one phase of the lower bridge arm is turned on, and at this time the DC power supply charges the first energy storage inductor L1 through the switch tube of the lower bridge arm; when the switch state of the inverter is in S7 (111), the upper bridge arms of the three phases are all turned on, and the lower bridge arms are turned off. At this time, the first energy storage inductor L1 charges the energy storage capacitor C through the path of the upper bridge arm. f Charge; According to the switching function, the three-phase voltage on the load side is determined, and the calculation formula is: Where U a , U b , U c is the three-phase voltage on the AC side of the boost inverter circuit, S a , S b , S c Respectively represent the switching states of the power switch tubes of the three-phase bridge arms a, b, and c of the boost inverter circuit; according to the different switching states of the power switch tubes, the switching functions (Sa, Sb, Sc) are formed, and combined with Table 1, the basic voltage vectors are determined, including U0, U1, U2, U3, U4, U5, U6, and U7, corresponding to U0 (000), U1 (100), U2 (110), U3 (010), U4 (011), U5 (001), U6 (101), and U7 (111), respectively; Table 1 Basic voltage vector table Table U k is the basic voltage vector obtained after Clark transformation of the three-phase voltages a, b, and c, k ranges from 0 to 7, U dc is the DC input voltage at the positive and negative ends of the three-phase bridge arms a, b, and c of the boost inverter circuit; Step 1.2, divide into six sectors; The six basic voltage vectors U1 to U6 are taken as reference by the α axis, and U1 (100), U2 (110), U3 (010), U4 (011), U5 (001), and U6 (101) are rotated 60° counterclockwise in sequence, and the space vector hexagon is divided into six large sectors I, II, III, IV, V, and VI, and the two zero vectors have zero amplitudes and are located at the origin; Step 1.3, determine the resultant rotating voltage vector V * The vector action time of each sector; Select the action vector (V n1 ,V n2 ), sector I corresponds to non-zero vector (U1, U2), sector II corresponds to non-zero vector (U2, U3), sector III corresponds to non-zero vector (U3, U4), sector IV corresponds to non-zero vector (U4, U5), sector V corresponds to non-zero vector (U5, U6), sector VI corresponds to basic vector (U1, U6); Determine the action time of each sector basic vector according to Table 2, T x is a non-zero vector V n1 Action time, T y is a non-zero vector V n2 Duration of action; Table 2 Six-sector basic vector action time Table U α * , U β * is the rotating voltage vector V * The component in the α-β two-phase stationary coordinate system, T s is the sampling period.

5. The control method according to claim 4, characterized in that: Step 2: Based on the boost control strategy, redistribute the vector action time and determine the conduction time of the six power switches in the boost inverter loop. The specific method is as follows: Step 2.1, reallocate the vector action time based on the boost control strategy; The boost control strategy first determines the relationship between the DC boost ratio and the zero vector action time: In the formula, the DC boost ratio of the boost inverter is defined as B, t x is the vector action time of the basic voltage vector U7 (111); t x That is, the inductor discharge time is set to the action time T of the zero vector U7 (111) z The minimum value (T zmin ), the relationship is: Where M is the modulation index and is defined as: The time for the zero vectors U7(111) and U0(000) to work together is T z , so the action time of zero vector U0(000) is modified to T z -T zmin , the action time of the other six non-zero vectors remains unchanged, and the allocation time of each vector corresponding to different sectors is shown in Table 3; Table 3 Boost control strategy vector action time In the table, T1-T6 correspond to the action time of voltage vectors U1(100), U2(110), U3(010), U4(011), U5(001), and U6(101) respectively; The time calculation formula for the upper bridge arm power switch tube of a phase bridge arm to be turned on and the lower bridge arm power switch tube to be turned off is: The time calculation formula for the upper bridge arm power switch tube of the other phase bridge arm to be turned on and the lower bridge arm power switch tube to be turned off is: The time calculation formula for the upper bridge arm power switch tube of another phase bridge arm to be turned on and the lower bridge arm power switch tube to be turned off is: The time during which the upper bridge arm power switch tube of the same bridge arm is turned on and the lower bridge arm power switch tube is turned off is referred to as the switch tube turn-on time. The switch tube turn-on time of different sectors is determined according to Table 4: Table 4 Switching tube conduction time of different sectors In a switching cycle, the time when the upper power switch tube of the same bridge arm is turned off and the lower power switch tube of the same bridge arm is turned on is complementary to the time when the upper power switch tube of the same bridge arm is turned on and the lower power switch tube of the same bridge arm is turned off.

6. The control method according to claim 5, characterized in that: Step 3: modulate the conduction time of the six power switch tubes in the boost inverter circuit with the triangular carrier to output the switch tube PWM pulse signal. The specific method is: Using CPWM technology, the on-time of the switch tube is modulated with an isosceles triangle wave whose period is the sampling period and whose amplitude is half of the sampling period. The action sequence of the basic vectors is determined based on the symmetry principle and the minimum THD principle, and 6 PWM pulses can be obtained. The pulse signals act on 6 IGBT power switch tubes respectively to output three-phase voltage and current.

7. The control method according to claim 6, characterized in that: Step 4: According to the different states of charge SOC of the battery, the bidirectional DC-DC converter circuit is divided into two stages of control. When 30%≤SOC≤90%, constant voltage charge and discharge control is adopted for the bidirectional DC-DC converter circuit; when SOC<30% or SOC>90%, constant power charge and discharge control is adopted for the bidirectional DC-DC converter circuit. The specific method is as follows: State 1: When 30%≤SOC≤90%, constant voltage charge and discharge control is adopted for the bidirectional DC-DC converter circuit. By controlling the duty cycle of power switch tubes S7 and S8, the energy storage capacitor C connected in parallel with the bidirectional DC-DC converter circuit is f The voltage is the set value; With energy storage capacitor C f Actual value of voltage across both ends U Cf As the feedback quantity, the energy storage capacitor C f Voltage setting value U Cf * As the reference quantity, the difference ΔU Cf =U Cf -U Cf * Determine the battery charge and discharge status, and set ΔU Cf After inputting into the PI regulator, the initial duty cycle D of the power switch tube S7 is obtained. * , the actual duty cycle D of the power switch tube S7 is obtained through limiting control; the duty cycles of the power switch tubes S7 and S8 are complementary, so the duty cycle of the power switch tube S8 is set to 1-D. At this time, the energy storage capacitor C f Voltage U Cf Realize following control according to set value; State 2: When SOC is less than 30% or SOC is greater than 90%, constant power charge and discharge control is adopted for the bidirectional DC-DC converter circuit, and the battery power is set to the set value by controlling the duty cycle of the power switches S7 and S8; The real-time battery power P b is the feedback quantity, with the battery reference power P b * The set value is the reference value, and the difference between the two is ΔP b =P b -P b * Determine the battery charge and discharge status, and set ΔP b After inputting into the PI regulator, the initial duty cycle D of the power switch tube S7 is obtained. * , the actual duty cycle D of the power switch tube S7 is obtained through limiting control; the duty cycles of the power switches S7 and S8 are complementary, so the duty cycle of the power switch tube S8 is set to 1-D. At this time, the battery power P b Realize following control according to the set value.

8. The control method according to claim 7, characterized in that: Step 5: When an open-circuit fault of the power switch tube occurs in the boost inverter circuit, the topology structure is switched according to the position of the faulty power switch tube. The boost control strategy of the boost inverter circuit adopts constant voltage setting control, and the bidirectional DC-DC converter circuit adopts constant voltage charge and discharge control. The specific method is as follows: Step 5.1, switching the topology structure according to the position of the faulty power switch tube; When an open-circuit fault occurs in the power switch tube in the boost inverter circuit, the single-pole double-throw switch connected to the corresponding fault phase switches the switch position from terminal 1 to terminal 2; at this time, four of the six power switch tubes are actually working, and the corresponding positions are that when phase a fails, the boost inverter is controlled by the four switch tubes of phases b and c, when phase b fails, the boost inverter is controlled by the four switch tubes of phases c and a, and when phase c fails, the boost inverter is controlled by the four switch tubes of phases a and b; Step 5.2, the boost control strategy of the boost inverter circuit adopts constant voltage setting control; In order to meet the theoretical requirements of the four-switch control method, the energy storage capacitor C is set f Voltage across the terminals U Cf * The value is equal to the DC power supply U IN , at this time the DC voltage U in the boost inverter circuit dc The value is set to: IN dc =U Cf +U IN =2U IN At this time, the load corresponding to the fault is connected to the positive pole of the DC power supply through a single-pole double-throw switch. The load corresponding to the fault is equivalent to the DC voltage U connected to the boost inverter circuit. dc at the midpoint; Step 5.3, the bidirectional DC-DC converter circuit adopts constant voltage charge and discharge control; With energy storage capacitor C f Actual value of voltage across both ends U Cf As the feedback quantity, the energy storage capacitor C f Voltage setting value U Cf * =U IN As the reference quantity, the difference ΔU Cf =U Cf -U IN Determine the battery charge and discharge status, and set ΔU Cf After inputting into the PI regulator, the initial duty cycle D of the power switch tube S7 is obtained. * , the actual duty cycle D of the power switch tube S7 is obtained through limiting control; the duty cycles of the power switch tubes S7 and S8 are complementary, so the duty cycle of the power switch tube S8 is set to 1-D. At this time, the energy storage capacitor C f Voltage U Cf =U IN .

9. The control method according to claim 8, characterized in that: Step 6, reconstruct the basic voltage vector of the power switch tube in the boost inverter loop according to the fault-tolerant topology structure, divide it into 4 sectors, and determine the vector action time of each sector. The specific method is: Step 6.1, reconstructing the basic voltage vector of the power switch tube in the boost inverter circuit according to the fault-tolerant topology structure, and performing 4-sector division; When the a-phase bridge arm switch fails, the a-phase of the boost inverter load side is connected to the energy storage capacitor C f The negative pole is the midpoint voltage of the inverter DC side, S a is always 1 / 2; at this time, the four switch tubes of the b and c phases of the boost inverter have four switching states: (Sb Sc) = (00), (Sb Sc) = (01), (Sb Sc) = (10), (Sb Sc) = (11); when the b phase bridge arm switch tube has an open circuit fault, the b phase of the boost inverter load side is connected to the energy storage capacitor C f The negative pole is the midpoint voltage of the inverter DC side, S b The four switch tubes of phase c and phase a of the boost inverter have four switching states: (Sc Sa) = (00), (Sc Sa) = (01), (Sc Sa) = (10), and (Sc Sa) = (11). When the switch tube of the phase c bridge arm fails to open, the phase c of the boost inverter load side is connected to the energy storage capacitor C f The negative pole is the midpoint voltage of the inverter DC side, S c The four switch tubes of the a and b phases of the boost inverter have four switching states: (Sa Sb) = (00), (Sa Sb) = (01), (Sa Sb) = (10), and (Sa Sb) = (11); At this time, the rotating voltage vector V * : In the formula is the spatial rotation factor; Determine the basic voltage vectors U0', U1', U2', and U3' under the condition of reconstructing a single-tube or single-phase fault, which correspond to U0'(00), U1'(01), U2'(10), and U3'(11), respectively, as shown in Table 5; Table 5 Reconstructed basic voltage vector table After a fault occurs in one of the three phases a, b, and c, the four basic voltage vectors U0', U1', U2', and U3' are arranged clockwise in the plane as U0', U1', U3', and U2', and each adjacent vector is 90° apart. The plane space is divided into four sectors according to the arrangement of the four basic voltage vectors. Step 6.2, determine the vector action time of each sector; The action vector includes an effective vector and a zero vector. The basic voltage vectors U0'~U3' are used as effective vectors alone. Two basic voltage vectors in opposite directions are used to synthesize an equivalent zero vector, that is, U0'(00) and U3'(11) are used to synthesize an equivalent zero vector, and U1'(01) and U2'(10) are used to synthesize another equivalent zero vector. The effective vector and the equivalent zero vector are synthesized together into a reference vector. Define intermediate variables: Assume that the effective vectors of the first sector are U0' and U2'; the effective vectors of the second sector are U2' and U3'; the effective vectors of the third sector are U3' and U1'; the effective vectors of the fourth sector are U1' and U0'; the action time of the effective vectors of each sector is T'x and T'y respectively, and the action time of the effective vectors of each sector is determined by Table 6; Table 6 Action time of effective vectors in each sector 10. The control method according to claim 9, characterized in that: Step 7: re-modulate the conduction time of the four power switch tubes in normal operation in the boost inverter circuit with the triangular carrier, output the switch tube PWM pulse signal, and complete the fault-tolerant control. The specific method is as follows: Adopt CPWM technology, modulate the switch on and off time with a triangular carrier whose period is the switch period, add dead time according to the power switch on and off time, and get PWM pulse; The 4-channel PWM pulses are applied to the power switch tube driving circuit of the boost inverter circuit, and the driving circuit controls the corresponding power switch tube to turn on and off.

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