A novel three-phase interphase hybrid topology and its control method

Abstract

The present invention provides a novel three-phase interphase hybrid topology and a control method thereof. The topology comprises: an A-phase topology circuit, a B-phase topology circuit and a C-phase topology circuit. The A-phase topology circuit is a 5L-ANPC bridge arm circuit, and the 5L-ANPC bridge arm circuit comprises: eight power switches and a suspended capacitor. The B-phase topology circuit and the C-phase topology circuit are both three-level T-type bridge arm circuits, and the three-level T-type bridge arm circuit comprises: four power switches and does not contain a suspended capacitor.

Description

Technical Field

[0001] The present invention belongs to the field of multi-level inverters, and in particular relates to a novel three-phase interphase hybrid topology and a control method thereof. Background Art

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

[0003] Compared with the traditional two-level converter, the multi-level converter has significant advantages such as high output current quality, high system efficiency, and low electromagnetic interference. At present, three-phase multi-level converters have been applied in photovoltaic power generation and other fields.

[0004] Three-level converters, such as three-phase T-type three-level converters, have been widely used in new energy generation, car charging and other fields due to their five-level output voltage, small number of switches, and no floating capacitors. Five-level converters, such as five-level active neutral point clamping (5L-ANPC) converters, have a total of 24 power devices, which is twice the number of power devices of three-phase T-type three-level converters, which greatly increases their cost. In addition, the three phases contain a total of three floating capacitors. In order for the converter to work properly, in addition to controlling the midpoint voltage, the additional floating capacitor voltage also needs to be controlled compared to the three-level converter, making the modulation strategy of the 5L-ANPC converter more complicated. Therefore, this has become part of the reason for limiting the widespread application of 5L-ANPC converters. In applications applicable to multi-level converters, system cost and voltage quality need to be balanced. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a novel three-phase interphase hybrid topology and a control method thereof. The present invention can not only obtain high-quality multi-level output voltage, but also reduce the number of power devices of the multi-level converter, reduce costs, and simplify the multi-level control strategy.

[0006] According to some embodiments, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a novel three-phase interphase hybrid topology.

[0008] A novel three-phase interphase hybrid topology includes: an A-phase topology circuit, a B-phase topology circuit and a C-phase topology circuit, wherein the A-phase topology circuit is a 5L-ANPC bridge arm circuit, and the 5L-ANPC bridge arm circuit includes: eight power switches and a suspended capacitor, and the B-phase topology circuit and the C-phase topology circuit are both three-level T-type bridge arm circuits, and the three-level T-type bridge arm circuit includes: four power switches and does not contain a suspended capacitor.

[0009] The three-phase bridge arm of the new three-phase interphase hybrid multi-level topology consists of a 5L-ANPC converter bridge arm and two T-type three-level converter bridge arms, so it is named 3P-533L-IPHC (3-Phase 5-3-3Level Inter-phase Hybrid Converter). Therefore, the number of 3P-533L-IPHC power devices is 16, which is 8 fewer than the three-phase 5L-ANPC converter, which greatly reduces the cost. Compared with the three-phase T-type three-level converter, the number of power devices has increased by 4, but the output voltage has changed from 3 five-levels to 2 nine-levels and 1 five-level, and the number of output voltage layers has been significantly improved.

[0010] In addition, compared with the three-phase 5L-ANPC, the proposed 3P-533L-IPHC only contains one suspension capacitor in the bridge arm of the 5L-ANPC converter, reducing two suspension capacitors, which not only reduces the cost, but also simplifies the control strategy. At the same time, the present invention proposes a 3P-533L-IPHC MPC control strategy, which can very conveniently balance the suspension capacitor voltage and the midpoint voltage of the 3P-533L-IPHC converter, and can output multi-level voltage.

[0011] In a second aspect, the present invention provides a novel control method for a three-phase interphase hybrid topology.

[0012] A novel control method for three-phase interphase hybrid topology, comprising:

[0013] Based on the novel three-phase interphase hybrid topology, a space vector diagram is drawn;

[0014] A discrete mathematical model of the system is established, and the ideal output current at time k+1 is obtained by sampling the actual output current value and the ideal output current value at time k, and then the actual output voltage at time k+1 is obtained;

[0015] Based on the switching sequence of the space vector diagram and in combination with the actual output voltage at time k+1, determine the three-phase voltage in the αβ coordinate system, as well as the voltages in the αβ coordinate system of the switching state defined by the A phase, the switching state defined by the B phase, and the switching state defined by the C phase;

[0016] Establish a value function, solve the value function according to the three-phase voltage in the αβ coordinate system, and the voltages of the switch state defined by the A phase, the switch state defined by the B phase, and the switch state defined by the C phase in the αβ coordinate system, and determine the vector of the optimal tracking current;

[0017] According to the vector of the best tracking current, the best switching state is selected from the redundant vectors, and thereby the action of the novel three-phase interphase hybrid topology as described in the first aspect above is controlled.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. Compared with the three-phase 5L-ANPC converter, the proposed new topology 3P-533L-IPHC reduces the number of power devices from 24 to 16, greatly reducing the cost.

[0020] 2. Compared with the three-phase 5L-ANPC converter, the proposed new topology 3P-533L-IPHC reduces the number of floating capacitors from 3 to 1, which reduces the cost and the difficulty of regulation.

[0021] 3. Compared with the three-phase 5L-ANPC converter, the proposed new topology 3P-533L-IPHC three-phase output line voltage has two phases with nine levels, which is consistent with the 5L-ANPC converter, and the other line voltage is five levels. When weighing the system cost and voltage quality, the proposed new topology 3P-533L-IPHC can completely replace the three-phase 5L-ANPC converter in some occasions.

[0022] 4. Compared with the three-phase T-type three-level converter, the proposed new topology 3P-533L-IPHC converter increases the three-phase output line voltage from 3 five-levels to 2 nine-levels and 1 fifteen-level, improving the output current and voltage quality and reducing harmonics.

[0023] 5. The proposed MPC control strategy can eliminate the PI controller compared with the traditional double closed-loop control, which can reduce the complex work of setting PI parameters and also improve the response speed.

[0024] 6. Compared with the traditional double closed-loop control, the PI controller is omitted, which can reduce the complicated work of setting PI parameters and also improve the response speed.

[0025] 7. The proposed MPC control strategy can simultaneously control the midpoint voltage and the suspended capacitor voltage by setting up weight factors, and can track the reference current. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0027] Figure 1 This is the topology diagram of the 3P-533L-IPHC converter;

[0028] Figure 2 The vector diagram for the 3P-533L-IPHC converter;

[0029] FIG3( a ) is a simulation diagram of the output current of the 3P-533L-IPHC converter;

[0030] Figure 3(b) is the output current FFT simulation diagram of the 3P-533L-IPHC converter;

[0031] FIG3(c) is a simulation diagram of the output AB phase line voltage of the 3P-533L-IPHC converter;

[0032] Figure 3(d) is a simulation diagram of the output BC phase line voltage of the 3P-533L-IPHC converter;

[0033] Figure 3(e) is a simulation diagram of the output AC phase line voltage of the 3P-533L-IPHC converter;

[0034] FIG3( f ) is a simulation diagram of the A-phase output voltage of the 3P-533L-IPHC converter;

[0035] FIG3( g ) is a simulation diagram of the B-phase output voltage of the 3P-533L-IPHC converter;

[0036] Figure 3(h) is a simulation diagram of the C-phase output voltage of the 3P-533L-IPHC converter;

[0037] Figure 3(i) is a simulation diagram of the A-phase floating capacitor voltage of the 3P-533L-IPHC converter;

[0038] Figure 3(j) is a simulation diagram of the midpoint voltage of the 3P-533L-IPHC converter;

[0039] Figure 4 This is a control flow chart proposed by the present invention. DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0041] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0042] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the term "comprising" is used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0043] In the present invention, terms such as "connected" and "connection" should be understood in a broad sense, indicating that the connection can be fixed, integral or detachable; it can be directly connected or indirectly connected through an intermediate medium. Relevant scientific research or technical personnel in this field can determine the specific meaning of the above terms in the present invention according to specific circumstances, and they should not be understood as limiting the present invention.

[0044] Embodiment 1

[0045] This embodiment provides a novel three-phase interphase hybrid topology.

[0046] A novel three-phase interphase hybrid topology includes: an A-phase topology circuit, a B-phase topology circuit and a C-phase topology circuit, wherein the A-phase topology circuit is a 5L-ANPC bridge arm circuit, and the 5L-ANPC bridge arm circuit includes: eight power switches and a suspended capacitor, and the B-phase topology circuit and the C-phase topology circuit are both three-level T-type bridge arm circuits, and the three-level T-type bridge arm circuit includes: four power switches and does not contain a suspended capacitor.

[0047] This embodiment proposes a novel three-phase interphase hybrid multi-level topology, 3P-533L-IPHC and its MPC control strategy, which specifically include the following steps:

[0048] S1: According to the characteristics of the 3P-533L-IPHC topology, all the vectors of 3P-533L-IPHC are analyzed, drawn into a space vector diagram, and the sectors are divided into six large sectors;

[0049] S2: Establish a discrete mathematical model of the system, sample the actual output current value and the ideal output current value at time k, and thus obtain the actual output voltage and ideal output current at time k+1;

[0050] S3: The influence of all vectors in S1 on the midpoint voltage and the suspended capacitor voltage is analyzed, and the vectors are further divided into different categories according to the redundant switch states and the influence on the capacitor charging and discharging;

[0051] S4: Establish the value function of the MPC control strategy, first obtain the vector of the best tracking current; then bring the selected vector into the value function of controlling the floating capacitor voltage and the midpoint voltage, and finally select the appropriate switching state to generate a PWM signal to drive the 3P-533L-IPHC to work normally.

[0052] 3P-533L-IPHC converter topology diagram Figure 1As shown in the figure, the A phase of the topology is a 5L-ANPC bridge arm, which consists of 8 power switches and a suspended capacitor. The B and C phases are three-level T-type bridge arms, which consist of 4 power switches and do not contain suspended capacitors. The positive and negative DC terminals and the midpoint of the three phases are connected together and share a DC source. Figure 1 The current directions are all the positive directions specified in the topology of this embodiment.

[0053] S1:

[0054] exist Figure 1 In the topology shown, since phase A is a 5L-ANPC bridge arm, the phase voltage of phase A is five-level and can be expressed as:

[0055]

[0056] Among them, V dc is the DC voltage, V ao is the output phase voltage of phase A of the 3P-533L-IPHC converter, S a It is the switching state defined by phase A.

[0057] Similarly, in Figure 1 In the topology shown, since the B and C phases are three-level T-type bridge arms, the output phase voltages of the B and C phases can be expressed as:

[0058]

[0059] V bo 、V co They are the phase voltages of phases B and C of the 3P-533L-IPHC converter, S b and S c is the switch state defined by phases B and C. Then [S a S b S c ] is the vector of 3P-533L-IPHC converter. According to the number of three-phase levels, it can be obtained that the space vector diagram of 3P-533L-IPHC contains 45 vectors (5*3*3).

[0060] According to the Clarke transformation, all vectors of 3P-533L-IPHC can be plotted on Figure 2 The space vector diagram is shown in Figure 1. The space vector diagram is divided into 6 large sectors with 60° as one sector, as shown in Figure 1. Figure 2 shown.

[0061] S2:

[0062] Depend on Figure 1 The circuit shows:

[0063]

[0064] Where x = a, b, c; then i x is the three-phase output current of 3P-533L-IPHC, L is the output side filter inductance of the three phases, R L is the load. V xn It is the voltage between the output side of the converter and the common point of the three-phase load.

[0065] Discretizing (3), we can obtain:

[0066]

[0067] Among them, T s is the control period; x=a,b,c, then i x (k) is the actual three-phase output current of 3P-533L-IPHC at time k, i * x (k+1) is the ideal value of the three-phase output current at time k+1, V xn (k) is the predicted voltage between the output point and the common point on the load side at time k.

[0068] According to the Lagrange back-calculation method, the ideal current of the three-phase output current at time k+1 can be calculated by the following formula:

[0069] i * x (k+1)=3i * x (k)-3i * x (k-1)+i * x (k-2)(x=a,b,c) (5)

[0070] Where x = a, b, c, then i * x (k) is the ideal value of the three-phase output current at time k, i * x (k-1) is the ideal value of the three-phase output current at time k-1, i * x (k-2) is the ideal value of the three-phase output current at time k-2.

[0071] S3:

[0072] like Figure 1 As shown, since the A phase of the 3P-533L-IPHC converter is the 5L-ANPC bridge arm, its switching state should follow the 5L-ANPC converter. The eight switching states of the A phase of the 3P-533L-IPHC converter are summarized in the following table:

[0073] Table 1 3P-533L-IPHC converter A phase eight switching sequence

[0074]

[0075] Similarly, since the B and C phases are the bridge arms of the three-level T-type converter, the three switching states of the B and C phases of the 3P-533L-IPHC converter are summarized in the following table:

[0076] Table 2 3P-533L-IPHC converter B, C phase three switching sequences (y = b, c)

[0077]

[0078]

[0079] It can be found from Table 1 that when the switching sequence is A2, A3, A6, and A7, the impact on the suspended capacitor current is opposite, and the corresponding switch state of A2 and A3 is -2. In order to distinguish this switching state, the switch state of A2 is represented as -1.5, and the switch state of A3 is represented as -1; similarly, the switch sequences corresponding to A6 and A7 are also represented as 1 and 1.5 respectively. The other switching sequences of phase A have the same impact on the midpoint current and the suspended capacitor current, so the corresponding switching states do not need to be further distinguished. Similarly, since there is no redundant switching sequence for phases B and C, their corresponding switching states do not need to be further distinguished.

[0080] S4-1:

[0081] In this embodiment, due to the introduction of the space vector diagram, the MPC control strategy is carried out in the αβ coordinate system. This requires that the three-phase voltage in equation (4) be converted into the voltage in the αβ coordinate system, expressed as V * αβ (k), and the vector [S a S b S c ] is also expressed as V in the αβ coordinate system αβ (k).

[0082] Then the cost function for tracking current in this embodiment can be expressed as:

[0083] g(k)=|V * αβ (k)-V αβ (k)| (6)

[0084] Since the space vector diagram is divided into sectors in advance in S1. Figure 2 It can be seen that in each sector, the number of vectors is 9. Therefore, in each sector, the cost function (6) iss Then, the value of the value function with the smallest absolute value is selected, that is, the vector at this time has the best tracking effect on the current.

[0085] S4-2:

[0086] After S4-1 selects the vector with the best tracking effect, it can be found from Table 1 that phase A has a redundant switching sequence, so it is very likely that phase A of the selected vector contains a redundant switching sequence at this time, which needs to be further determined. The method for further determination is to select the best sequence from the redundant vectors to control the balance of the midpoint voltage and the floating capacitor voltage.

[0087] In the 3P-533L-IPHC converter, the midpoint voltage is controlled by the three phases. Combining Table 1 and Table 2, it can be found that the midpoint current corresponding to the A phase switch state -1, 0, 1 is i a , the midpoint current of phase B and phase C in switch state 0 is i y , so the midpoint parameter definition is as follows:

[0088]

[0089]

[0090] Among them, npa indicates whether the switch state corresponding to A will affect the midpoint current, 1 means yes, 0 means no. Similarly, npy indicates whether the switch state corresponding to B and C will affect the midpoint current, 1 means yes, 0 means no. For example, the vector (-1,2,0) indicates that current flows through the midpoint of phases A and C, but no current flows through the midpoint of phase B.

[0091] From the upper and lower capacitors on the DC side, we can get:

[0092]

[0093] i P 、i N is the current flowing through the upper and lower capacitors respectively, i o is the current flowing into or out of the midpoint o, C P , C N They are the capacitance of the upper and lower capacitors respectively. Under normal circumstances, they are equal and can be recorded as C.

[0094] Discretizing (10) and shifting the phase yields:

[0095]

[0096] Among them, the voltage difference of the capacitor on the DC side is ΔV PN (k) is denoted as:

[0097] ΔVPN (k) = V P (k)-V N (k) (12)

[0098] From Table 1 and Table 2, we can find that o It is related to the selected switching sequence, and the switching sequence is determined by the switching state, that is, the midpoint parameters of equations (7) and (8) can be determined, and the midpoint current is controlled by the three phases together, so we have:

[0099]

[0100] That is, through formula (13), the smaller the calculated absolute value is, the stronger the balancing ability of the switching sequence to the midpoint voltage is.

[0101] Unlike the midpoint voltage, in the 3P-533L-IPHC converter, only phase A contains a floating capacitor and the control of the floating capacitor voltage can only be controlled by phase A alone. The control of the floating capacitor voltage is related to the current flowing into or out of the floating capacitor. After the analysis of step S3, the corresponding floating capacitor parameters are established and defined as:

[0102]

[0103] Among them, fca represents the influence of the switch state corresponding to A on the floating capacitance of phase A, 1 represents the positive direction, that is, the capacitor is charged, 0 represents no influence on the capacitor, and -1 represents the negative direction, that is, the capacitor is discharged.

[0104] For the floating capacitance of phase A, there is:

[0105]

[0106] Among them, C af is the capacitance value of the A-phase floating capacitor, i af is flowing through C af of current.

[0107] Discretizing (15) yields:

[0108]

[0109] Among them, V af (k+1) is the capacitance voltage value of the A phase suspension capacitor at time k+1, V af (k) is the capacitance voltage value of the A-phase suspension capacitor at time k, i af (k) is the flow through C at time k af The current value.

[0110] Because V af Need to be controlled at V dc / 4, so subtracting the two gives:

[0111]

[0112] Where, ΔV af (k+1) is the capacitance voltage value of the A phase suspension capacitor at time k+1 and V dc / 4 difference, ΔV af (k) is the capacitance voltage value of the A phase suspension capacitor at time k and V dc / 4. The smaller the value of (17), the greater the difference in V af The more stable at V dc Around the value of / 4.

[0113] And i af (k) can be expressed as:

[0114] i af (k) = i a (k)·fca (18)

[0115] Substituting (18) into (17), we can obtain:

[0116]

[0117] By calculating formula (19), we can find that different fca corresponds to different ΔV af (k+1), so we can select the ΔV with the smallest absolute value af The fca corresponding to (k+1) means that the balancing effect of the A-phase floating capacitor voltage is the best at this time.

[0118] In order to balance the midpoint voltage and the floating capacitor voltage at the same time, it is necessary to weigh equations (13) and (19) at the same time. Therefore, the two can be balanced by setting a weight factor:

[0119] J(k+1)=λ1|ΔV PN (k+1)|+λ2|ΔV af (k+1)| (20)

[0120] Among them, λ1 and λ2 are the weight factors of the balanced midpoint voltage and the suspended capacitor voltage, respectively.

[0121] In this way, the minimum value of J(k+1) is obtained by calculation, and the corresponding switching sequence is found, which is the switching sequence that can achieve the best effect on capacitor voltage balance under this weight factor.

[0122] In summary, the current tracking can be achieved through step S4-1, and the switching sequence that can balance the capacitor voltage can be further determined by the vector selected by S4-1 through step S4-2, and finally a PWM signal can be formed to drive the 3P-533L-IPHC converter to work normally.

[0123] In this embodiment, the DC side voltage is 100V, the given current amplitude is 6A, the inductance is 3mL, the load resistance is 8Ω, and the weight factors are λ1=0.1 and λ2=0.12. As shown in Figure 3(a), the three-phase current is symmetrical and sinusoidal, smooth and without distortion, and the THD of the current is 2.53% as shown in Figure 3(b). The output line voltage is shown in Figures 3(c) to (e), two of which are nine-level and the other one is five-level. From the corresponding phase voltages, it can be seen that the proposed 3P-533L-IPHC topology phase A is five-level as shown in Figure 3(f), and the other two phases are three-level as shown in Figures 3(g) and (h), and all show step waves. The suspended capacitor voltage of phase A is controlled at 1 / 4V dc As shown in Figure 3(i), the midpoint voltage is 25V. dc As shown in FIG3(j), it is 50 V. This shows that the capacitor voltage control part in this embodiment has a good effect. The simulation diagram proves that the actual working state of the proposed 3P-533L-IPHC converter is consistent with the theory, and the proposed MPC control strategy can drive the 3P-533L-IPHC converter to work normally.

[0124] This embodiment designs a new three-phase interphase hybrid multilevel topology, 3P-533L-IPHC. The three-phase bridge arm of the new three-phase interphase hybrid multilevel topology is composed of a bridge arm of a 5L-ANPC converter and two bridge arms of a T-type three-level converter. Therefore, the number of 3P-533L-IPHC power devices is 16, which is 8 less than the three-phase 5L-ANPC converter, which greatly reduces the cost. Compared with the three-phase T-type three-level converter, the number of power devices has increased by 4, but the output voltage has changed from 3 five-levels to 2 nine-levels and 1 five-level, and the number of output voltage layers has been significantly improved. In addition, compared with the three-phase 5L-ANPC, the proposed 3P-533L-IPHC only contains one suspended capacitor in the bridge arm of the 5L-ANPC converter, reducing two suspended capacitors, which not only reduces the cost, but more importantly simplifies the regulation strategy.

[0125] Embodiment 2

[0126] This embodiment provides a novel control method for a three-phase interphase hybrid topology.

[0127] A novel control method for three-phase interphase hybrid topology, comprising:

[0128] Based on the novel three-phase interphase hybrid topology, a space vector diagram is drawn;

[0129] A discrete mathematical model of the system is established, and the ideal output current at time k+1 is obtained by sampling the actual output current value and the ideal output current value at time k, and then the actual output voltage at time k+1 is obtained;

[0130] Based on the switching sequence of the space vector diagram and in combination with the actual output voltage at time k+1, determine the three-phase voltage in the αβ coordinate system, as well as the voltages in the αβ coordinate system of the switching state defined by the A phase, the switching state defined by the B phase, and the switching state defined by the C phase;

[0131] Establish a value function, solve the value function according to the three-phase voltage in the αβ coordinate system, and the voltages of the switch state defined by the A phase, the switch state defined by the B phase, and the switch state defined by the C phase in the αβ coordinate system, and determine the vector of the optimal tracking current;

[0132] According to the vector of the best tracking current, the best switch state is selected from the redundant vectors, and the action of the novel three-phase interphase hybrid topology as described in the first embodiment is controlled thereby.

[0133] As one or more implementation modes, the discrete mathematical model is:

[0134]

[0135] Where Ts is the control period; x = a, b, c, then ix(k) is the actual three-phase output current of 3P-533L-IPHC at time k, i * x (k+1) is the ideal value of the three-phase output current at time k+1, and Vxn(k) is the predicted voltage between the output point and the common point on the load side at time k.

[0136] In one or more implementation modes, the value function is:

[0137] g(k)=|V * αβ (k)-V αβ (k)|

[0138] Among them, V * αβ (k) is the three-phase voltage in the αβ coordinate system, V αβ (k) is the voltage in the αβ coordinate system for the switching state defined by phase A, the switching state defined by phase B, and the switching state defined by phase C.

[0139] As one or more implementation modes, the process of determining the optimal switch state includes: determining a redundant vector according to the vector of the optimal tracking current, and selecting the optimal switch state that balances the midpoint voltage and the floating capacitor voltage from the redundant vector.

[0140] As one or more implementation modes, the balancing of the midpoint voltage specifically includes:

[0141] Determine whether the three corresponding switch states will affect the midpoint current;

[0142] Determine the current flowing into or out of the midpoint based on the current value flowing through the upper capacitor on the DC side and the current value flowing through the lower capacitor on the DC side;

[0143] Determine the voltage difference of the capacitor on the DC side based on the current flowing into or out of the midpoint;

[0144] The balance function of the midpoint voltage is determined based on whether the three corresponding switch states will affect the midpoint current, the current flowing into or out of the midpoint, and the voltage difference of the capacitor on the DC side.

[0145] As one or more implementation modes, the balance function of the midpoint voltage is:

[0146]

[0147] Among them, T s is the control period; C is the capacitance of the upper and lower capacitors on the DC side; x=a,b,c, then i x (k) is the actual three-phase output current of the new three-phase interphase hybrid topology at time k; npa indicates whether the switch state corresponding to A will affect the midpoint current; npb indicates whether the switch state corresponding to B will affect the midpoint current; npc indicates whether the switch state corresponding to C will affect the midpoint current; ΔV PN (k) is the voltage difference of the capacitor on the DC side.

[0148] As one or more implementation modes, the floating capacitor voltage balancing specifically includes:

[0149] By setting up a weight factor to simultaneously balance the voltage difference of the capacitor on the DC side at time k+1 and the voltage of the floating capacitor at time k+1, when the sum of the voltage difference of the capacitor on the DC side at time k+1 and the voltage of the floating capacitor at time k+1 is minimal, the corresponding switching sequence is the switching sequence that can achieve the best effect on balancing the floating capacitor voltage under this weight factor.

[0150] This embodiment proposes an MPC control method for 3P-533L-IPHC. Compared with the traditional dual closed-loop control, the proposed MPC control strategy does not need to set up PI parameters, which saves the time of selecting parameters and improves the response speed of the system. The MPC control method is carried out in two steps. The first step is responsible for selecting the vector with the best current tracking effect in the divided sectors; the second step is to further select the appropriate switching sequence based on the selected vector according to the capacitor voltage balance effect on the basis of the first step. The final PWM signal can correctly drive the work of 3P-533L-IPHC. This step-by-step control achieves the best current tracking and capacitor voltage trade-off balance, which is concise and clear, and is very suitable for the proposed 3P-533L-IPHC topology.

[0151] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A new three-phase interphase hybrid topology, characterized in that: include: A phase topology circuit, a B phase topology circuit and a C phase topology circuit, wherein the A phase topology circuit is a 5L-ANPC bridge arm circuit, and the 5L-ANPC bridge arm circuit includes: eight power switches and a suspended capacitor, and the B phase topology circuit and the C phase topology circuit are both three-level T-type bridge arm circuits, and the three-level T-type bridge arm circuit includes: four power switches and does not contain a suspended capacitor; The input end of the A-phase topology circuit, the input end of the B-phase topology circuit and the input end of the C-phase topology circuit are all connected in parallel with the DC side capacitor; The positive DC end of the A-phase topology circuit, the positive DC end of the B-phase topology circuit and the positive DC end of the C-phase topology circuit are all connected together, the negative DC end of the A-phase topology circuit, the negative DC end of the B-phase topology circuit and the negative DC end of the C-phase topology circuit are all connected together, and the midpoint of the A-phase topology circuit, the midpoint of the B-phase topology circuit and the midpoint of the C-phase topology circuit are all connected together; The phase voltage of phase A is five-level, expressed as: in, V dc For DC voltage measurement, V ao is the output phase voltage of phase A of the 3P-533L-IPHC converter, S a It is the switch state defined by phase A; Phases B and C are three-level T-type bridge arms, and the output phase voltages of phases B and C are expressed as: in, V bo , V co They are the phase voltages of phases B and C of the 3P-533L-IPHC converter, S b and S c It is the switching state defined by phases B and C.

2. A novel control method for three-phase interphase hybrid topology, characterized in that: include: Based on the novel three-phase interphase hybrid topology, a space vector diagram is drawn; Establish a discrete mathematical model of the system, according to k The actual output current value and the ideal output current value are sampled at all times to obtain k The ideal output current at time +1 is obtained k The actual output voltage at time +1; Based on the switching sequence of the space vector diagram, combined with k The actual output voltage at +1 moment determines αβ The three-phase voltage in the coordinate system, as well as the switch state defined by phase A, the switch state defined by phase B, and the switch state defined by phase C are in αβ Voltage in the coordinate system; Establish a value function based on αβ The three-phase voltage in the coordinate system, as well as the switch state defined by phase A, the switch state defined by phase B, and the switch state defined by phase C are in αβ Voltage in the coordinate system, solve the value function, and determine the vector of the best tracking current; According to the vector of the best tracking current, the best switching state is selected from the redundant vectors, and the action of the novel three-phase interphase hybrid topology described in claim 1 is controlled thereby.

3. The control method of the novel three-phase interphase hybrid topology according to claim 2 is characterized in that: The discrete mathematical model is: Where, Ts is the control period; x=a, b, c, then ix(k) is the actual three-phase output current of 3P-533L-IPHC at time k, i*x(k+1) is the ideal value of the three-phase output current at time k+1, and Vxn(k) is the predicted voltage between the output point and the common point on the load side at time k.

4. The control method of the novel three-phase interphase hybrid topology according to claim 2 is characterized in that: The value function is: Among them, V*αβ(k) is the three-phase voltage in the αβ coordinate system, and Vαβ(k) is the voltage of the switching state defined by phase A, the switching state defined by phase B, and the switching state defined by phase C in the αβ coordinate system.

5. The control method of the novel three-phase interphase hybrid topology according to claim 2 is characterized in that: The process of determining the optimal switch state includes: determining a redundant vector according to the vector of the optimal tracking current, and selecting the optimal switch state that balances the midpoint voltage and the suspension capacitor voltage from the redundant vector.

6. The control method of the novel three-phase interphase hybrid topology according to claim 5 is characterized in that: The balancing of the midpoint voltage specifically includes: Determine whether the three corresponding switch states will affect the midpoint current; Determine the current flowing into or out of the midpoint based on the current value flowing through the upper capacitor on the DC side and the current value flowing through the lower capacitor on the DC side; Determine the voltage difference of the capacitor on the DC side based on the current flowing into or out of the midpoint; The balance function of the midpoint voltage is determined based on whether the three corresponding switch states will affect the midpoint current, the current flowing into or out of the midpoint, and the voltage difference of the capacitor on the DC side.

7. The control method of the novel three-phase interphase hybrid topology according to claim 6 is characterized in that: The balance function of the midpoint voltage is: in, T s To control the cycle; C is the capacitance of the upper and lower capacitors on the DC side; x = a , b , c， but i x ( k )for k The actual three-phase output current of the new three-phase interphase hybrid topology at all times; npa Indicates whether the switch state corresponding to A will affect the midpoint current; npb Indicates whether the switch state corresponding to B will affect the midpoint current; NPCs Indicates whether the switch state corresponding to C will affect the midpoint current; Δ V PN ( k ) is the voltage difference of the capacitor on the DC side.

8. The control method of the novel three-phase interphase hybrid topology according to claim 5 is characterized in that: The floating capacitor voltage balancing specifically includes: By setting up a weight factor to simultaneously balance the voltage difference of the capacitor on the DC side at time k+1 and the voltage of the floating capacitor at time k+1, when the sum of the voltage difference of the capacitor on the DC side at time k+1 and the voltage of the floating capacitor at time k+1 is minimal, the corresponding switching sequence is the switching sequence that can achieve the best effect on balancing the floating capacitor voltage under this weight factor.

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