CN112688589A

CN112688589A - Single-stage three-phase high-frequency link combined bidirectional AC/DC converter

Info

Publication number: CN112688589A
Application number: CN202011577309.9A
Authority: CN
Inventors: 江加辉; 张韬; 马大壮; 陈道炼
Original assignee: Qingdao University
Current assignee: Qingdao University
Priority date: 2020-12-28
Filing date: 2020-12-28
Publication date: 2021-04-20

Abstract

The single-stage three-phase high-frequency link combined bidirectional AC/DC converter is formed by sequentially cascading a three-phase alternating current filter, a three-phase cycle converter, n primary side series high-frequency transformers, n output parallel high-frequency bidirectional full-bridge rectifiers and a direct current filter, wherein each transformer secondary side is respectively connected with one high-frequency bidirectional full-bridge rectifier, and the output ends of the n full-bridge rectifiers are connected in parallel; the single-stage three-phase high-frequency link combined bidirectional AC/DC converter adopts a double-current-loop direct active power partition SVPWM control strategy to realize unit power factor control of direct current side current and alternating current side, and the converter can work in a rectification and inversion mode to realize bidirectional power flow. The converter belongs to single-stage power conversion, has no direct current link, solves the problems of short service life and the like of a direct current bus electrolytic capacitor, and improves the reliability of the converter; the combination of n transformers and full-bridge rectifiers with the primary side connected in series and the secondary side connected in parallel improves the capacity of the converter, and is suitable for high-power occasions.

Description

Single-stage three-phase high-frequency link combined bidirectional AC/DC converter

The technical field is as follows:

the invention relates to a single-stage three-phase high-frequency link combined bidirectional AC/DC converter, belonging to the field of electric energy conversion.

Background art:

with the rapid development of economy and the improvement of living standard, automobiles become indispensable transportation tools, new energy is used for gradually replacing traditional fossil fuels to drive the automobiles, and the automobile transportation tool is a necessary trend for the development of the automobile industry in the future. Under the support of a new infrastructure background, the construction of the charging equipment is rapidly developed along with the increase of the number of the electric automobiles, and the charging equipment has a wide development space.

A large number of electric automobiles are connected to a power grid, and the research hotspot of reasonably utilizing the interaction between the automobiles and the power grid and realizing optimal charging is realized. Charging the electric vehicles if the vehicles are caused to absorb energy from the grid during the electricity utilization trough period; in the peak period of power utilization, the energy of the storage battery of the electric automobile is fed back to the power grid, so that the daily power utilization load peak-valley difference of the power grid can be effectively reduced, the peak clipping and valley filling effects on the power grid are realized, a bidirectional inverter charging technology is realized, namely, the electric automobile and the power grid are in bidirectional interaction (V2G), the electric automobile has the functions of load management and system peak regulation, so that the reasonable distribution of energy is realized, the win-win situation between the power grid and users is achieved, and the V2G technology becomes an important ring for energy interconnection in the long term.

The bidirectional AC/DC converter is used as an important link for connecting an electric automobile and a power grid, the existing research is mainly focused on a two-stage structure, and the two-stage structure has the problems of two-stage power conversion, low power density, unsatisfactory conversion efficiency, short service life of a direct-current bus electrolytic capacitor and the like. Therefore, the bidirectional AC/DC converter with single-stage power conversion, simple circuit topology, electric isolation, high efficiency and high power density has important theoretical and practical value.

The invention content is as follows:

the invention aims to provide a single-stage three-phase high-frequency link combined bidirectional AC/DC converter which has the characteristics of single-stage power conversion, simple circuit topology, electric isolation, high efficiency, high power density and the like.

In order to achieve the technical purpose, the technical scheme of the invention is as follows:

a single-stage three-phase high-frequency link combined bidirectional AC/DC converter is formed by sequentially cascading a three-phase alternating current filter, a three-phase periodic wave converter, n primary side series high-frequency transformers, n output parallel high-frequency bidirectional full-bridge rectifiers and a direct current filter, wherein each secondary side of each high-frequency transformer is connected to one high-frequency bidirectional full-bridge rectifier, and the output ends of the n high-frequency bidirectional full-bridge rectifiers are connected in parallel. The combination of n transformers and full-bridge rectifiers with the primary side connected in series and the secondary side connected in parallel is adopted, so that the capacity of the converter is improved, and the converter is suitable for high-power occasions.

The converter can work in a rectification mode and an inversion mode to realize bidirectional power flow. Under a rectification mode, the converter is a Boost type rectifier, energy storage and energy release of a three-phase energy storage inductor are realized through switching operation of the three-phase cycle converter, and unit power factor control of an alternating current side is realized; in the inversion mode, the converter is a Buck type grid-connected inverter, and unit power factor grid connection or reactive power regulation can be realized according to requirements.

The converter adopts a double-current-loop direct active power partition SVPWM control strategy, an outer loop controls direct current side current, and an inner loop controls alternating current side current. The inner loop current control is carried out in a two-phase synchronous speed dq coordinate system, and the purpose of power factor correction is achieved by controlling instantaneous active power and instantaneous reactive power.

The invention can realize single-stage AC/DC conversion, realize the functions of charging the electric automobile by the power grid, generating electricity by the electric automobile to the power grid, participating in reactive power regulation of the power grid and the like, and has the characteristics of single-stage power conversion, simple circuit topology, electric isolation, high efficiency, high power density and wide range of adapting of a direct current port to working voltage.

Description of the drawings:

FIG. 1 is a block diagram of the converter;

FIG. 2 is a diagram of an example of a circuit topology of the converter;

FIG. 3 is a sector division diagram of a three-phase current reference wave;

FIG. 4 is a voltage vector space distribution diagram;

FIG. 5 is a waveform diagram of the switching drive of the converter;

FIG. 6 is an equivalent circuit of the high frequency switching process in the operation process of the converter, which includes (a), (b), (c), (d), (e), (f),

(g) (h)8 subgraphs;

fig. 7 is a SVPWM control block diagram of the dual current loop direct active power partition.

The specific implementation mode is as follows:

the technical scheme of the invention is further described in detail by the specific examples and the attached drawings of the specification.

A single-stage three-phase high-frequency link combined bidirectional AC/DC converter is formed by sequentially cascading a three-phase alternating current filter, a three-phase periodic wave converter, n primary side series high-frequency transformers, n output parallel high-frequency bidirectional full-bridge rectifiers and a direct current filter, wherein each transformer secondary side is respectively connected with one high-frequency bidirectional full-bridge rectifier, and the output ends of the n full-bridge rectifiers are connected in parallel. The single-stage three-phase high-frequency link combined bidirectional AC/DC converter adopts a double-current-loop direct active power partition SVPWM control strategy to realize unit power factor control of direct current side current and alternating current side, and the converter can work in a rectification and inversion mode to realize bidirectional power flow. An example of a circuit topology of the converter is shown in fig. 2, where v is 2_AN、v_BN、v_CNIs a three-phase voltage source, L_A、L_B、L_CIs a three-phase filter inductor, S₁-S₆、S₁'-S₆' is a power switch, Q, of a three-phase cycloconverter₁-Q₈Power switch being a high-frequency bidirectional full-bridge rectifier, T₁、T₂Is a high-frequency transformer, C_oIs a DC filter capacitor, V_DCIs a dc power supply.

Three-phase current reference wave i_A*、i_B*、i_CThe power frequency cycle is divided into 6 sectors of 60 degrees, which are sequentially marked as sectors I, II, III, IV, V, VI, as shown in fig. 3. The operation process of the converter operating in the rectification mode will be described below with reference to an equivalent circuit diagram of a single-stage three-phase high-frequency link combined bidirectional AC/DC converter, taking the synchronous operation mode of the sector I and 2 high-frequency bidirectional full-bridge rectifiers as an example.

And the three-phase alternating-current side current reference wave is modulated by SVPWM (space vector pulse width modulation), and the switching drive signals of the three-phase cycle converter and the high-frequency bidirectional full-bridge rectifier are output. What is needed isThe SVPWM modulation mode comprises six effective vectors V₁(000111)、V₂(011100)、V₃(001110)、V₄(110001)、V₅(100011)、V₆(111000) and two zero vectors V₀(010101)、V₇(101010) in which the vector (S)₁S₂S₃S₄S₅S₆) Middle S _j1 or 0 denotes a power switching tube S, respectively_jAnd S_j' on or off. The voltage vector spatial distribution is shown in fig. 4. The vector of sector I contribution has V₀、V₇、V₄、V₆The vector for sector II has a V₀、V₇、V₂、V₆The vector for sector III has V₀、V₇、V₂、V₃The vector for sector IV has V₀、V₇、V₁、V₃The vector for which the sector V acts has V₀、V₇、V₁、V₅The vector of the effect of sector VI has V₀、V₇、V₄、V₅。

Fig. 5 and fig. 6 show the switching driving waveform and the high-frequency switching process equivalent circuit of the single-stage three-phase high-frequency link combined bidirectional AC/DC converter during the SVPWM control of the dual-current loop direct active power partition, respectively.

Mode 1: vector V₀Action, primary side switch tube S₂、S₂'、S₄、S₄'、S₆、S₆' on, S₁、S₁'、S₃、S₃'、S₅、S₅' off, v_LA>0、v_LB>0、v_LC<0，L_AEnergy storage, L_BEnergy storage, L_CStoring energy; secondary side power switch Q₁、Q₄、Q₅、Q₈On, Q₂、Q₃、Q₆、Q₇Off, T₁And T₂The secondary voltage is clamped to the output voltage.

Mode 2: vector V₄Active, primary side power switch S₁、S₁'、S₂、S₂'、S₆、S₆' on, S₃、S₃'、S₄、S₄'、S₅、S₅' off, v_LA<0、v_LB>0、v_LC>0，L_AEnergy releasing, L_BEnergy storage, L_CEnergy is released; the secondary side power switch maintains the previous mode state unchanged.

Modality 3: vector V₆Active, primary side power switch S₁、S₁'、S₂、S₂'、S₃、S₃' on, S₄、S₄'、S₅、S₅'、S₆、S₆' off, v_LA<0、v_LB<0、v_LC>0，L_AEnergy releasing, L_BEnergy releasing, L_CEnergy is released; the secondary side power switch maintains the previous mode state unchanged.

Modality 4: vector V₇Active, primary side power switch S₁、S₁'、S₃、S₃'、S₅、S₅' on, S₂、S₂'、S₄、S₄'、S₆、S₆' off, v_LA>0、v_LB>0、v_LC<0，L_AEnergy storage, L_BEnergy storage, L_CStoring energy; the secondary side power switch maintains the previous mode state unchanged.

Mode 5: vector V₇Acting, the primary side power switch state remains unchanged from the previous mode state, v_LA>0、v_LB>0、v_LC<0，L_AEnergy storage, L_BEnergy storage, L_CStoring energy; secondary side power switch Q₂、Q₃、Q₆、Q₇On, Q₁、Q₄、Q₅、Q₈Off, T₁And T₂The secondary voltage is clamped to a negative output voltage.

Modality 6: vector V₁Active, primary side power switch S₄、S₄'、S₅、S₅'、S₆、S₆' on, S₁、S₁'、S₂、S₂'、S₃、S₃' off, v_LA>0、v_LB>0、v_LC<0，L_AEnergy storage, L_BEnergy storage, L_CStoring energy; the secondary side power switch maintains the previous mode state unchanged.

Modality 7: vector V₃Active, primary side power switch S₃、S₃'、S₄、S₄'、S₅、S₅' on, S₁、S₁'、S₂、S₂'、S₆、S₆' off, v_LA>0、v_LB<0、v_LC<0，L_AEnergy storage, L_BEnergy releasing, L_CStoring energy; the secondary side power switch maintains the previous mode state unchanged.

Modality 8: vector V₀Active, Primary side Power switch State is the same as Modal 1 State, S₂、S₂'、S₄、S₄'、S₆、S₆' on, S₁、S₁'、S₃、S₃'、S₅、S₅' off, v_LA>0、v_LB>0、v_LC<0，L_AEnergy storage, L_BEnergy storage, L_CStoring energy; the secondary side power switch maintains the previous mode state unchanged.

The time of the mode 1 is equal to that of the mode 8, the time of the mode 2 is equal to that of the mode 7, the time of the mode 3 is equal to that of the mode 6, and the time of the mode 4 is equal to that of the mode 5, so that the high-frequency magnetic reset of the transformer is realized.

The single-stage three-phase high-frequency link combined bidirectional AC/DC converter adopts a double-current-loop direct active power partition SVPWM control strategy, so that the current control at a direct current side and the unit power factor at an alternating current side are realized, and the converter can work in bidirectional power flow. The control strategy comprises a direct current side current outer ring and an alternating current side current inner ring, wherein the direct current side current outer ring is used for realizing output (or input) of stable and high-quality direct current, the alternating current side current inner ring realizes control of unit power factor of the alternating current side, and a control block diagram is shown in fig. 7.

Current outer ring sampling direct current i_dcGiven reference to DC currentConsideration I_dcComparing, and outputting the reference quantity i of the active current of the inner loop of the alternating current side current after PI calculation_p*. The equivalent circuit of the switch of the converter under the rectification mode and the inversion mode is consistent when a reference quantity I is given_dc*>At 0, the converter operates in a rectification mode; i is_dc*<At 0, the converter operates in inverter mode, changing I_dcThe value of x is then free to switch the direction of power flow of the converter.

The control of the inner loop of the alternating current side current is carried out in a two-phase synchronous speed dq coordinate system, the d axis of the dq coordinate system is superposed with the space vector of the alternating current side voltage, and the direct-axis current i is at the moment_dQuadrature current i equal to active current_qThe amplitude and the sign of the reactive current are equal and opposite, and the direct-axis voltage is V in a symmetrical three-phase alternating-current power grid_dThe quadrature axis voltage is 0 when the value of E is 1.732E, and the effective value of the phase voltage of the three-phase alternating current network is obtained, so that the instantaneous active power is p when the value of P is 1.732Ei_pThe instantaneous reactive power q is 1.732Ei_q。

The controller samples A, B the two-phase current I_A、I_BAnd calculating the C phase current I_CTransformation to dq coordinate system to obtain i_dAnd i_q。i_dAnd a reference quantity i_dComparison, i_qComparing with the reference quantity 0, respectively calculating by PI, and transforming to ABC three-phase coordinate system to obtain the three-phase AC side current reference wave i_A*、i_B*、i_C*. In steady state operation of the converter, i_dIs a constant value of i_qThe value is 0, constant instantaneous active power conversion can be realized, the reactive power is constant 0, and the unit power factor of an alternating current side can be realized.

Claims

1. A single-stage three-phase high-frequency link combined bidirectional AC/DC converter, characterized in that: the converter is composed of a three-phase AC filter, a three-phase cyclic converter, n primary series high-frequency transformers, n output A parallel high-frequency bidirectional full-bridge rectifier and a DC filter are cascaded in sequence; the three-phase AC filter is composed of a three-phase single-inductance L filter or a three-phase LCL filter; the three-phase cycle converter includes six The four-quadrant switch constitutes three bridge arms, and each four-quadrant switch is composed of two two-quadrant power switches in reverse series; the primary windings of the n high-frequency transformers are connected in series, and the secondary sides are respectively connected to a high-frequency bidirectional full-bridge rectifier ; The output terminals of the high-frequency bidirectional full-bridge rectifier are connected in parallel; the DC filter is composed of a single-capacitor C filter or a CL filter.

2. The single-stage three-phase high-frequency link combined bidirectional AC/DC converter according to claim 1, characterized in that: the positive ends of the three-phase AC filters of the converter are respectively connected to the AC three-phase power frequency power grid. Phase A, B and C, the negative terminals are respectively connected to the midpoints of the first, second, and third bridge arms of the three-phase cycloconverter; the first bridge arm of the three-phase cycloconverter consists of an upper bridge arm and a The upper bridge arm is composed of power switches S ₁ and S ₁ ′, and the lower bridge arm is composed of power switches S ₄ and S ₄ ′; the second bridge arm of the three-phase cycloconverter is composed of an upper bridge arm A bridge arm and a lower bridge arm are formed, wherein the upper bridge arm is formed by power switches S ₃ , S ₃ ′, and the lower bridge arm is formed by power switches S ₆ , S ₆ ′; the third bridge arm of the three-phase cycloconverter It consists of an upper bridge arm and a lower bridge arm, wherein the upper bridge arm is constituted by power switches S ₅ and S ₅ ', and the lower bridge arm is constituted by power switches S ₂ and S ₂ '; The terminal is connected to the node P, and the common terminal of the three lower bridge arms is connected to the node N; the n high-frequency transformer primary windings are connected in series between the P and N nodes in sequence; the n high-frequency bidirectional full-bridge rectifiers are respectively connected with the secondary windings of n high-frequency transformers; the output ends of the n high-frequency bidirectional full-bridge rectifiers are connected in parallel to both ends of the DC filter; the output of the DC filter is connected in parallel to both ends of the DC side power supply.

3. The single-stage three-phase high-frequency link combination bidirectional AC/DC converter according to claim 1, characterized in that: the primary side of the converter is connected in series with the secondary side in parallel with n transformer-full-bridge rectifier combinations can work In synchronous mode, it can also work in asynchronous mode; when working in synchronous mode, n transformer-full-bridge rectifier combinations output balanced power; when working in asynchronous mode, the converter can realize n transformer-full-bridge rectifiers Combined power distribution, one or more of the transformer-full-bridge rectifier combinations can also be turned off to adjust the output power level.

4. The single-stage three-phase high-frequency link combined bidirectional AC/DC converter according to claim 1, is characterized in that: the converter adopts the dual current loop direct active power partition SVPWM control strategy, and realizes the DC side current and AC side unit power factor control, the converter can work in rectification mode and inverter mode to realize bidirectional power flow; the control strategy adopts the double closed-loop control of the DC side current outer loop, the AC side current inner loop, and the DC side current outer loop It is used to realize the output (or input) of stable and high-quality DC current, and the inner loop of the AC side current realizes the control of the unity power factor of the AC side; the outer loop of the DC side current is to sample the DC current, and the reference value of the DC current is given. For comparison, after the PI calculation, the reference value of the AC side current inner loop is output. The AC side current inner loop control is carried out in the two-phase synchronous speed dq coordinate system. The A and B two-phase currents are sampled and the C-phase current is calculated, and transformed into the dq coordinate system. The d-axis current and q-axis current are obtained, the d-axis current is compared with the reference value of the current inner loop output by the outer current loop, the q-axis current is compared with the reference value 0, and after PI calculation, it is transformed into the ABC three-phase coordinate system, and the three Phase AC side current reference, the three-phase reference is divided into 6 60° sectors in one power frequency cycle, and the switching drive signal of the three-phase cycle converter and the high-frequency bidirectional full-bridge rectifier is output through SVPWM modulation.