A three-phase three-level ANPC series resonant dual active bridge DC / DC converter

Abstract

The invention discloses a three-phase three-level ANPC series resonant dual active bridge DC / DC converter, belonging to the field of DC / DC converters, comprising: a control unit, a three-phase transformer, and two three-phase hybrid power device ANPC three-level circuits respectively connected to two sides of the three-phase transformer, a three-phase resonant network is connected between the primary side of the three-phase transformer and the three-phase hybrid power device ANPC three-level circuit connected thereto; the control unit is used to control the on and off of each switch tube in the three-phase hybrid power device ANPC three-level circuit, so that the neutral point level of the three-phase transformer is V dc / 6, 0 or V dc / 6, the voltage at the output of each half-bridge ANPC three-level bridge arm relative to the connection point of the two DC voltage-dividing capacitors is ‑2V dc / 3, ‑V dc / 2, ‑V dc / 3, 0, V dc / 3, V dc / 2 or 2V dc / 3, the resonant tank voltage of each phase is an eleven-level voltage. A three-phase three-level ANPC active bridge is designed in the DC / DC converter, so that the resonant tank voltage waveform is a multi-level voltage step wave that is closer to a sine wave, thereby reducing the reactive loss of the converter and the current stress borne by the switch tube.

Description

Technical Field

[0001] The invention belongs to the field of DC / DC converters, and more specifically, relates to a three-phase three-level ANPC series resonant dual active bridge DC / DC converter. Background Art

[0002] Dual Active Bridge (DAB) DC / DC converters have been widely studied and applied in the fields of renewable energy and DC power distribution. The common DAB converter topology consists of a two-level dual H-bridge, and the voltage stress borne by each switch in the converter is the DC bus voltage. In high-voltage applications, the voltage level requirements for switching devices are high. The use of multi-level circuit topology can reduce the voltage stress of the switch, thereby significantly improving the performance of the converter. How to increase the number of levels of the DAB converter is of great significance for reducing the voltage stress of the switch in the converter. In high-power applications, single-phase DC / DC converters have the problem of high stress on the switching elements. How to solve this problem is also crucial to improving the performance of the converter.

[0003] The three-phase DC-DC converter has the advantages of small input and output current ripple, high efficiency, and high power density, and has a good application prospect in high-power DC-DC converters. The three-phase DC-DC converter is not a simple combination of three single-phase DABs. In terms of circuit topology, it has fewer busbars than the parallel structure of three single-phase DABs, and the three-phase transformer is smaller in size. Combined with the unique three-phase modulation algorithm, it has the advantages of small input and output current ripple, high efficiency, and high power density. In high-power applications, the DC-DC converter adopts a three-phase structure to obtain higher efficiency and performance. The three-phase three-level DAB topology uses more switching devices and has high requirements for the thermal distribution of the devices. It is necessary to adopt a three-level topology that can adjust the loss distribution.

[0004] The three-level circuit can be realized by a diode-clamped three-level circuit (Diode Neutral Point Clamped, DNPC). This topology has low voltage stress and small switching loss, but has high conduction loss, and the clamping diode clamping effect is not complete, the reverse recovery loss is also large, and the midpoint voltage also needs to be controlled separately. At the same time, the loss distribution of each switch tube in the DNPC bridge arm is uneven, the heat sink design is difficult, the device life is affected, and the reliability is reduced. The active clamped three-level (active neutral point clamped, ANPC) circuit introduces two active switching devices to replace the clamping diode in the DNPC circuit. This topology uses a switch tube for clamping, so the clamping effect is more effective. In addition, the main advantage of this topology is that it has sufficient redundant switching states, can adjust the loss distribution of power devices, and use hybrid power devices to improve efficiency.

[0005] The current of the DAB converter switch tube when it is turned off is the peak value of the inductor current in one cycle. Therefore, the converter has a large turn-off loss. At the same time, it is difficult for the DAB converter to achieve soft switching operation within the full power range. How to achieve soft switching operation of the DAB converter within the full power range is of great significance to reducing device switching losses and increasing the converter operating frequency, thereby reducing the volume of magnetic components and increasing power density. Summary of the invention

[0006] In view of the defects of the prior art and the need for improvement, the present invention provides a three-phase three-level ANPC series resonant dual active bridge DC / DC converter, the purpose of which is to design a three-phase three-level ANPC active bridge in the DC / DC converter so that the resonant tank voltage waveform is a multi-level voltage step wave that is closer to a sine wave, thereby reducing the reactive loss of the converter and the current stress borne by the switch tube.

[0007] To achieve the above-mentioned object, the present invention provides a three-phase three-level ANPC series resonant dual active bridge DC / DC converter, comprising: a control unit, a three-phase transformer, and two three-phase ANPC three-level circuits respectively connected to both sides of the three-phase transformer, wherein a three-phase resonant network is connected between the primary side of the three-phase transformer and the three-phase ANPC three-level circuit connected to the primary side; the three-phase ANPC three-level circuit comprises three half-bridge ANPC three-level bridge arms connected between the positive and negative poles of a DC bus, and two DC voltage-dividing capacitors connected between the positive and negative poles of the DC bus; the control unit is used to control the on and off of each switch tube in the three-phase ANPC three-level circuit, so that the neutral point level of the three-phase transformer is -V dc / 6, 0 or V dc / 6, the voltage at the output end of each half-bridge ANPC three-level bridge arm relative to the connection point of the two DC voltage-dividing capacitors is -2V dc / 3, -V dc / 2, -V dc / 3, 0, V dc / 3, V dc / 2 or 2V dc / 3, where V dc is the voltage between the positive and negative poles of the DC bus, and the resonant tank voltage of each phase is an eleven-level voltage, which is the difference between the output voltage of the primary side half-bridge ANPC three-level bridge arm and the output voltage of the secondary side half-bridge ANPC three-level bridge arm.

[0008] Furthermore, the half-bridge ANPC three-level bridge arm includes a first switch tube, a second switch tube, a third switch tube and a fourth switch tube connected in sequence between the positive and negative poles of the DC bus, and a fifth switch tube and a sixth switch tube, each of which has one end connected to the two DC voltage-dividing capacitor connection points, the other end of the fifth switch tube is connected to the connection point of the first switch tube and the second switch tube, the other end of the sixth switch tube is connected to the connection point of the third switch tube and the fourth switch tube, the second switch tube and the third switch tube are SiC tubes, and the remaining switch tubes are Si tubes.

[0009] Furthermore, the control unit includes a redundant zero-state pulse width modulation subunit; the redundant zero-state pulse width modulation subunit is used to control the on and off of each switch tube in the three-phase ANPC three-level circuit, so that the switching process of the switch state of the three-phase ANPC three-level circuit in one cycle is: P→OO1→OO2→OO3→N→OO3→OO2→OO1→P, so as to concentrate all hard switches on the second switch tube and the third switch tube; the switch states of the first switch tube to the sixth switch tube in the P state are: 1, 1, 0, 0, 0, 1; in the N state, the switching states of the first to sixth switch tubes are: 0, 0, 1, 1, 1, 0; in the OO1 state, the switching states of the first to sixth switch tubes are: 0, 1, 0, 1, 1, 0; in the OO2 state, the switching states of the first to sixth switch tubes are: 1, 0, 1, 0, 0, 1; in the OO3 state, the switching states of the first to sixth switch tubes are: 0, 1, 1, 0, 1, 1; among them, 0 corresponds to the switch tube being turned off, and 1 corresponds to the switch tube being turned on.

[0010] Furthermore, the control unit includes a resonant tank voltage and current control subunit; if P>P Max0 The resonant tank voltage and current control subunit is used to control the on and off of each switch tube in the three-phase ANPC three-level circuit so that D1=D2=1 and adjust the phase shift angle To adjust the transmission power of the three-phase transformer; if P≤P Max0 And v p ≥v s The resonant tank voltage and current control subunit is used to control the on and off of each switch tube in the three-phase ANPC three-level circuit to make D2 = 1, and adjust D1 and the phase shift angle Until the secondary side reactive current is minimum; if P≤P Max0 And v p <v s The resonant tank voltage and current control subunit is used to control the on and off of each switch tube in the three-phase ANPC three-level circuit, so that D1=1, and adjust D2 and the phase shift angle Until the reactive current on the primary side is minimum; where D1 is the duty cycle of the three-level voltage output by the primary side half-bridge ANPC three-level bridge arm, D2 is the duty cycle of the three-level voltage output by the secondary side half-bridge ANPC three-level bridge arm, P is the actual active transmission power of the converter, P Max0 is the maximum active transmission power of the converter, v p is the voltage at the input end of the primary side three-phase ANPC three-level circuit, v s It is the voltage at the input end of the secondary side three-phase ANPC three-level circuit.

[0011] Furthermore, the three-phase resonant network includes three resonant tanks, each of which includes a resonant inductor and a resonant capacitor connected in series, and the resonant tank is connected between the transformer of the corresponding phase and the half-bridge ANPC three-level bridge arm.

[0012] Furthermore, it also includes a calculation unit for performing Fourier decomposition on the output voltage of each half-bridge ANPC three-level bridge arm using the fundamental wave analysis principle to calculate the active power, reactive power and maximum transmission power of the converter under each winding connection mode.

[0013] Furthermore, the winding connection mode of the three-phase transformer is YY connection, and the active power, reactive power, and maximum active transmission power calculated by the calculation unit are respectively:

[0014]

[0015]

[0016]

[0017] Among them, P Y-Y is the active power of the converter in YY connection mode, Q Y-Y is the reactive power of the converter in YY connection mode, P Y-Ymax is the maximum active transmission power of the converter under the YY connection mode, k is the voltage conversion ratio of the three-phase transformer, v p is the voltage at the input end of the primary side three-phase ANPC three-level circuit, n is the turns ratio of the three-phase transformer, F n is the ratio of the switching frequency to the resonant frequency, Z0 is the resonant tank impedance, is the phase shift angle, D1 is the duty cycle of the three-level voltage output by the primary side half-bridge ANPC three-level bridge arm, and D2 is the duty cycle of the three-level voltage output by the secondary side half-bridge ANPC three-level bridge arm.

[0018] Furthermore, the winding connection mode of the three-phase transformer is a Δ-Δ connection, and the active power, reactive power, and maximum active transmission power calculated by the calculation unit are respectively:

[0019]

[0020]

[0021]

[0022] Among them, P Δ-Δ is the active power of the converter in the Δ-Δ connection mode, Q Δ-Δ is the reactive power of the converter in the Δ-Δ connection mode, P Δ-Δmax It is the maximum active transmission power of the converter under the Δ-Δ connection mode.

[0023] Furthermore, the winding connection mode of the three-phase transformer is Y-Δ connection, and the active power, reactive power and maximum active transmission power calculated by the calculation unit are respectively:

[0024]

[0025]

[0026]

[0027] Among them, P Y-Δ is the active power of the converter in Y-Δ connection mode, Q Y-Δ is the reactive power of the converter in Y-Δ connection mode, P Y-Δmax It is the maximum active transmission power of the converter under the Y-Δ connection mode.

[0028] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0029] (1) The structure of a three-phase three-level ANPC series resonant dual active bridge DC / DC converter is designed, and the three-phase ANPC three-level circuit is applied to the DC / DC converter. Through the coupling effect of the neutral point voltage of the three-phase transformer, the resonant tank voltage of each phase is increased to eleven levels. The multi-level voltage step wave makes the voltage waveform closer to the sine wave, reduces reactive power loss, reduces the current peak, and reduces the current stress borne by the switching device. Compared with the single-phase structure, the power of the converter is increased and the triple frequency ripple in the resonant tank voltage is eliminated, which is beneficial to improve efficiency. The three-phase three-level topology also reduces the size of the DC side capacitor and improves the power density. Since the three-phase magnetic structure introduces a new coupling relationship, the three-phase structure is more complex than the single-phase structure, the number of resonant tank voltage waveform levels is large, and the control is complex. The present invention proposes an eleven-level control system to achieve reliable control of the converter.

[0030] (2) The half-bridge three-level circuit structure can be used to apply low-voltage devices to high-voltage fields, effectively improving the performance of the converter. In a three-phase three-level circuit, there are many switch tubes, and there are challenges in the heat dissipation performance and cost of the devices. The present invention adopts an ANPC three-level half-bridge, and through hybrid power devices and loss concentration modulation, the switching losses are concentrated on the SiC MOSFET with better performance. Only two SiC MOSFETs can bear all hard switches, reducing the switching losses while controlling the cost. In particular, the ANPC three-level half-bridge can better adjust the thermal distribution of the switch tube and improve the reliability of the device compared to the DNPC three-level half-bridge.

[0031] (3) The present invention adopts a resonant converter topology, in which the inductor and capacitor of the resonant tank oscillate, thereby improving the soft switching capability, reducing the harmonics of the inductor current, further reducing the loss of transmission power, and improving efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A structural block diagram of a three-phase three-level ANPC series resonant dual active bridge DC / DC converter provided by an embodiment of the present invention;

[0033] Figure 2 A circuit diagram of a three-phase three-level ANPC active bridge provided by an embodiment of the present invention;

[0034] Figure 3 A topological diagram of a three-phase three-level ANPC series resonant dual active bridge DC / DC converter provided in an embodiment of the present invention;

[0035] Figure 4 A schematic diagram of a resonant tank voltage waveform of a three-phase three-level ANPC series resonant dual active bridge DC / DC converter provided by an embodiment of the present invention;

[0036] Figure 5 A schematic diagram of the resonant voltage and current waveforms of a three-phase three-level ANPC series resonant dual active bridge DC / DC converter provided in an embodiment of the present invention;

[0037] Figure 6 A circuit diagram of a fundamental wave equivalent circuit provided by an embodiment of the present invention;

[0038] Figure 7 A comparison of the fundamental voltage vector schematic diagram provided by the embodiment of the present invention;

[0039] Figure 8 P≤P provided in the embodiment of the present invention Max0 And v p ≥v s Schematic diagram of voltage waveform under time optimization;

[0040] Fig. 9A schematic diagram of a loss-concentrated modulation driving waveform provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention 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 invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0042] In the present invention, the terms "first", "second", etc. (if any) in the present invention and the accompanying drawings are used to distinguish similar objects but not necessarily to describe a specific order or sequence.

[0043] Figure 1 This is a structural block diagram of a three-phase three-level ANPC series resonant dual active bridge DC / DC converter provided by an embodiment of the present invention. Figure 1 , combined with Figure 2-Figure 9 , the three-phase three-level ANPC series resonant dual active bridge DC / DC converter in this embodiment is described in detail.

[0044] See also Figure 1 The three-phase three-level ANPC series resonant dual active bridge DC / DC converter includes: a control unit, a three-phase transformer, and two three-phase ANPC three-level circuits respectively connected to both sides of the three-phase transformer, and a three-phase resonant network is connected between the primary side of the three-phase transformer and the three-phase ANPC three-level circuit connected to the primary side. The three-phase ANPC three-level circuit includes three half-bridge ANPC three-level bridge arms connected between the positive and negative poles of the DC bus, and two DC voltage dividing capacitors connected between the positive and negative poles of the DC bus.

[0045] The control unit is used to control the on and off of each switch in the three-phase ANPC three-level circuit, so that the neutral point level of the three-phase transformer is -V dc / 6, 0 or V dc / 6, the voltage at the output end of each half-bridge ANPC three-level bridge arm relative to the connection point of the two DC voltage-dividing capacitors is -2V dc / 3, -V dc / 2, -V dc / 3, 0, V dc / 3, V dc / 2 or 2V dc / 3,V dc is the voltage between the positive and negative poles of the DC bus, and the voltage of each phase resonant slot is an eleven-level voltage, such as Figure 4 and Figure 5As shown. Among them, the resonant tank voltage is the difference between the output voltage of the primary half-bridge ANPC three-level bridge arm and the output voltage of the secondary half-bridge ANPC three-level bridge arm. The multi-level voltage step wave makes the voltage waveform closer to the sine wave, reduces reactive power loss, reduces current peak value, and reduces the current stress on the switching device.

[0046] The three-phase DC-DC converter in this embodiment is not a simple combination of three single-phase DABs. In terms of circuit topology, it has fewer busbars than the parallel structure of three single-phase DABs, and the three-phase transformer is smaller in size. Combined with a unique three-phase modulation algorithm, it has the advantages of small input and output current ripple, high efficiency, high power density, etc. In high-power applications, the DC-DC converter adopts a three-phase structure to obtain higher efficiency and performance.

[0047] See also Figure 2 Taking phase A as an example, its half-bridge ANPC three-level bridge arm includes a first switch tube S connected in sequence between the positive and negative electrodes of the DC bus. A1 , the second switch tube S A2 , the third switch tube S A3 and the fourth switch tube S A4 , and a fifth switch tube S having one end connected to the connection point of the two DC voltage dividing capacitors (C1, C2) A5 and the sixth switch tube S A6 , the fifth switch tube S A5 The other end is connected to the first switch tube S A1 And the second switch tube S A2 The connection point of the sixth switch tube S A6 The other end is connected to the third switch tube S A3 and the fourth switch tube S A4 The second switch tube S A2 and the third switch tube S A3 The connection point is the output end of the A-phase half-bridge ANPC three-level bridge arm, the connection point O of the DC voltage divider capacitor C1 and the DC voltage divider capacitor C2 is the neutral point, and the voltage on each DC voltage divider capacitor is V dc / 2, the voltage stress on each switch tube is also V dc / 2. The structure of the B-phase and C-phase half-bridge ANPC three-level bridge arms is the same as that of the A-phase half-bridge ANPC three-level bridge arms, and will not be described in detail here.

[0048] The three-phase transformer is, for example, a high-frequency transformer, which is composed of three-phase transformers A, B, and C. The three-phase transformer has three connection modes: star-star connection (YY), star-delta connection (Y-Δ), and delta-delta connection. The internal voltage waveform and transmission power expression of the converter are different under different connection modes. The magnetic coupling of the three-phase transformer makes its voltage and current characteristics more complex than those of the single-phase converter. It is not a simple superposition of three single-phase transformers. The overall performance of the three-phase converter, such as efficiency, power density, and cost, is also better than that of three single-phase converters.

[0049] Preferably, in the embodiment of the present invention, the second switch tube and the third switch tube in each half-bridge ANPC three-level bridge arm are set to SiC tubes (i.e. SiC MOSFET), and the remaining switch tubes are set to Si tubes (i.e. Si IGBT). For the three-phase three-level ANPC series resonant dual active bridge DC / DC converter based on hybrid power devices, a redundant zero-state pulse width modulation subunit is set in its control unit.

[0050] SiC MOSFET has better switching performance than Si IGBT, but its cost is higher. In this embodiment, the second and third switch tubes in the half-bridge ANPC three-level bridge arm are designed as SiC MOSFET, and the other switch tubes are designed as Si IGBT. Through a suitable modulation strategy, all hard switches are concentrated on SiC MOSFET, which can take into account both cost and efficiency.

[0051] The redundant zero-state pulse width modulation subunit is used to control the on and off of each switch tube in the three-phase ANPC three-level circuit, so that the switching process of the switch state of the three-phase ANPC three-level circuit within one cycle is: P→OO1→OO2→OO3→N→OO3→OO2→OO1→P, so as to concentrate all hard switches on the second switch tube and the third switch tube, that is, all hard switches are concentrated on the SiC tube.

[0052] In the P state, the switch states of the first to sixth switch tubes are: 1, 1, 0, 0, 0, 1, and the corresponding half-bridge ANPC three-level bridge arm output voltage is V dc / 2. The switch states of the first to sixth switch tubes in the N state are: 0, 0, 1, 1, 1, 0, and the corresponding half-bridge ANPC three-level bridge arm output voltage is -V dc / 2. In the OO1 state, the switching states of the first to sixth switch tubes are: 0, 1, 0, 1, 1, 0, and the corresponding half-bridge ANPC three-level bridge arm output voltage is 0. In the OO2 state, the switching states of the first to sixth switch tubes are: 1, 0, 1, 0, 0, 1, and the corresponding half-bridge ANPC three-level bridge arm output voltage is 0. In the OO3 state, the switching states of the first to sixth switch tubes are: 0, 1, 1, 0, 1, 1, and the corresponding half-bridge ANPC three-level bridge arm output voltage is 0. The driving state of each switch tube in one cycle is as follows: Fig. 9 shown.

[0053] During the above two state switching process of P→OO1→OO2→OO3→N→OO3→OO2→OO1→P, the state of each switch tube in the half-bridge ANPC three-level bridge arm is shown in Table 1, where ZVS represents zero voltage switching and Hard represents hard switching.

[0054] Table 1

[0055]

[0056] Based on the above control strategy of the redundant zero-state pulse width modulation subunit, no matter how the current direction changes, when switching from the zero state to the non-zero state, one of the second switch tube and the third switch tube will always be a hard switch and one switch tube will be a soft switch. When switching within the three different non-zero states, all switch tubes are soft switches. Therefore, no matter what the current direction is, the switching loss is concentrated on the second switch tube and the third switch tube. Therefore, the switching loss in this embodiment is mainly borne by SiC MOSFET, the efficiency is higher than that of the full Si IGBT converter, and the cost is lower than that of the full SiC MOSFET converter, taking into account both efficiency and cost.

[0057] See also Figure 3 The three-phase resonant network includes three resonant tanks, each of which includes a resonant inductor L connected in series. ri and resonant capacitor C ri , i = A, B, C, the resonant tank is connected between the primary side terminal of the transformer of the corresponding phase and the output terminal of the half-bridge ANPC three-level bridge arm. During the operation of the converter, the resonant inductor and the resonant capacitor jointly generate oscillations. In order to better realize power transmission and reduce losses, it is necessary to fully consider the voltage and current oscillations of the resonant capacitor and accurately control the voltage and current of the resonant tank. Furthermore, a resonant tank voltage and current control subunit is set in the control unit.

[0058] See also Figure 8In order to reduce the resonant inductor current stress and improve the converter efficiency, this embodiment uses the resonant tank voltage and current control subunit to optimize the resonant tank current effective value. The primary or secondary voltage of the converter will be a three-level and two-level waveform. At this time, under the same transmission power, the duty cycle D1, D2 and phase shift angle There are still many combinations, and this feature provides the possibility for optimization of control.

[0059] The transmission power P0 of the converter is:

[0060]

[0061] The maximum transmission power P that can be used for optimization Max0 for:

[0062]

[0063] In this embodiment, the resonant tank voltage and current control subunit adopts fixed frequency phase shift control, which has three control degrees of freedom, namely, the duty cycle D1 of the three-level voltage output by the primary side half-bridge ANPC three-level bridge arm, the duty cycle D2 of the three-level voltage output by the secondary side half-bridge ANPC three-level bridge arm, and the phase shift angle The size of D1 and D2 determines the effective value of the three-level voltage output by the bridge arm, thus affecting the size of the transmission power. The overall phase difference between the secondary side switch tube drive pulse and the primary side switch tube drive pulse is the phase shift angle The positive or negative value determines the direction of power transmission, and the size affects the amount of transmission power. When , power flows from the primary side to the secondary side; When the power flows from the secondary side to the primary side, the power flows from the secondary side to the primary side. For the three-phase three-level active bridges on the primary side and the secondary side, the voltage duty cycle output by the three-phase ANPC bridge arm inside each three-phase three-level active bridge is consistent. The control strategy of the resonant tank voltage and current control subunit is as follows.

[0064] When P>P Max0 When the resonant tank voltage and current control subunit is used to control the on and off of each switch tube in the three-phase ANPC three-level circuit, so that D1 = D2 = 1, and adjust the phase shift angle To adjust the transmission power of the three-phase transformer.

[0065] When P≤P Max0 And v p ≥v s When the resonant tank voltage and current control subunit is used to control the on and off of each switch tube in the three-phase ANPC three-level circuit, so that D2 = 1, and adjust D1 and the phase shift angle Until the secondary side reactive current is minimum.

[0066] When P≤PMax0 And v p <v s When the resonant tank voltage and current control subunit is used to control the on and off of each switch tube in the three-phase ANPC three-level circuit, so that D1 = 1, and adjust D2 and the phase shift angle Until the primary side reactive current is minimum.

[0067] Where P is the actual active transmission power of the converter, P Max0 is the maximum active transmission power of the converter, v p is the voltage at the input end of the primary side three-phase ANPC three-level circuit, v s It is the voltage at the input end of the secondary side three-phase ANPC three-level circuit.

[0068] P≤P Max0 、v p ≥v s When the voltage and current control subunit controls the primary and secondary voltage waveforms of phase A, Figure 4 As shown, at this time, the output voltage of the primary bridge arm is three-level, and the output voltage of the secondary bridge arm is two-level. By properly designing D1 and The value of can minimize the secondary side reactive current. Max0 、v p <v s When the output voltage of the primary bridge arm becomes two-level, the output voltage of the secondary bridge arm becomes three-level.

[0069] With v p ≥v s Take 2 as an example to analyze the optimization of the minimum resonant tank current effective value under fundamental wave. The phase difference between the primary and secondary voltage vectors is The magnitude of the voltage vector is related to D1 and D2 respectively. When the transmission power is not particularly large, the resonant tank voltage can be perpendicular to the secondary side voltage vector, the secondary side has only active power, the reactive power is 0, and the effective value of the resonant tank current is the minimum. When the transmission power is large, the primary side voltage vector cannot make the resonant tank voltage perpendicular to the secondary side voltage vector even if it is maximized. At this time, D1=D2=1 is taken, and only the phase shift angle is used. Controls the transmission power.

[0070] According to an embodiment of the present invention, the three-phase three-level ANPC series resonant dual active bridge DC / DC converter further includes a calculation unit, which is not shown in the figure. The calculation unit is used to perform Fourier decomposition on the output voltage of each half-bridge ANPC three-level bridge arm using the fundamental wave analysis principle to calculate the active power, reactive power and maximum transmission power of the converter under each winding connection mode. The fundamental wave equivalent circuit is as follows Figure 6 As shown, the corresponding fundamental voltage vector analysis is as follows Figure 7 shown.

[0071] In this embodiment, the switching frequency of the converter is f s , the resonant frequency is f r , switching period T s =1 / f s , half switching period T hs =T s / 2, the switching angular frequency is ω s , the equivalent impedance of the resonant tank is X LC =jω s L r +1 / (jω s C r ). The resonant inductance value L of the three phases A, B, and C rA =L rB =L rC =L r , resonant capacitance value C rA =C rB =C rC =C r ; For the primary side, the DC bus voltage V dc =V p ; For the secondary side, the DC bus voltage V dc =V s . Switching frequency f s With the resonant frequency f r The ratio is F n =f s / f r .

[0072] Taking the winding connection mode of the three-phase transformer as an example, the voltage and current of the converter are analyzed. When the three-phase three-level ANPC series resonant dual active bridge DC / DC converter is YY connected, the output points of the primary bridge arm are A1, B1, and C1, the midpoint of the primary three-level is O1, and one end of the primary A, B, and C phases are connected together, which is called the primary center point m1 of the transformer. The end of the other phases that are not connected to the transformer is connected to the A, B, and C phases of the resonant network; the output points of the secondary bridge arm are A2, B2, and C2, and the midpoint of the secondary three-level is O2. The three phases of A, B, and C on the secondary side are connected together at one end, which is called the secondary center point m2 of the transformer. The end that is not connected to the other phases of the transformer is connected to the series midpoint of the second and third switch tubes in the A, B, and C three-phase half-bridge ANPC three-level bridge arm on the secondary side. Taking O1 as the reference potential, the voltage v of each phase on the primary side of the converter A1O1 、v B1O1 、v C1O1 The waveform is three-level, the voltage duty cycle is D1, and the transformer center point voltage v m1O1 A rectangular wave three times the switching frequency:

[0073]

[0074] v i1m1 =v i1O1 -v m1O1

[0075] Using the fundamental wave analysis method, the output voltage of the three-phase bridge arm of the converter is decomposed by Fourier to obtain:

[0076]

[0077] Taking phase A as an example, its fundamental component v i1m1，1 for:

[0078]

[0079] Similarly, the secondary side A phase v A2m2 Fundamental component v i2m2，1 for:

[0080]

[0081] Resonant tank voltage v LrCr，1 for:

[0082]

[0083] Inductor current i LrCr,1_Y-Y (t) and capacitor voltage v Cr,1_Y-Y (t) can be expressed as:

[0084]

[0085]

[0086] In the YY connection mode, when the switching frequency is constant, the active power, reactive power, and maximum active transmission power calculated by the calculation unit are:

[0087]

[0088]

[0089]

[0090] Among them, P Y-Y is the active power of the converter in YY connection mode, Q Y-Y is the reactive power of the converter in YY connection mode, P Y-Ymax is the maximum active transmission power of the converter under the YY connection mode, k is the voltage conversion ratio of the three-phase transformer, v pis the voltage at the input end of the primary side three-phase ANPC three-level circuit, n is the turns ratio of the three-phase transformer, F n is the ratio of the switching frequency to the resonant frequency, Z0 is the resonant tank impedance, L r is the inductance of the resonant inductor, C r is the capacitance value of the resonant capacitor, is the phase shift angle, D1 is the duty cycle of the three-level voltage output by the primary side half-bridge ANPC three-level bridge arm, and D2 is the duty cycle of the three-level voltage output by the secondary side half-bridge ANPC three-level bridge arm.

[0091] According to another embodiment of the present invention, the winding connection mode of the three-phase transformer is a Δ-Δ connection. When the switching frequency is constant, the active power, reactive power, and maximum active transmission power calculated by the calculation unit are respectively:

[0092]

[0093]

[0094]

[0095] Among them, P Δ-Δ is the active power of the converter in the Δ-Δ connection mode, Q Δ-Δ is the reactive power of the converter in the Δ-Δ connection mode, P Δ-Δmax It is the maximum active transmission power of the converter under the Δ-Δ connection mode.

[0096] Inductor current i Lr,1_Δ-Δ (t) and capacitor voltage v Cr,1_Δ-Δ (t) can be expressed as:

[0097]

[0098]

[0099] According to another embodiment of the present invention, the winding connection mode of the three-phase transformer is Y-Δ connection, and the active power, reactive power, and maximum active transmission power calculated by the calculation unit are respectively:

[0100]

[0101]

[0102]

[0103] Among them, P Y-Δ is the active power of the converter in Y-Δ connection mode, Q Y-Δis the reactive power of the converter in Y-Δ connection mode, P Y-Δmax It is the maximum active transmission power of the converter under the Y-Δ connection mode.

[0104] Inductor current i Lr,1_Y-Δ (t) and capacitor voltage v Cr,1_Y-Δ (t) can be expressed as:

[0105]

[0106]

[0107] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A three-phase three-level ANPC series resonant dual active bridge DC / DC converter, characterized in that: include: A control unit, a three-phase transformer, and two three-phase ANPC three-level circuits respectively connected to both sides of the three-phase transformer, wherein a three-phase resonant network is connected between the primary side of the three-phase transformer and the three-phase ANPC three-level circuit connected to the primary side; The three-phase ANPC three-level circuit comprises three half-bridge ANPC three-level bridge arms connected between the positive and negative poles of the DC bus, and two DC voltage-dividing capacitors connected between the positive and negative poles of the DC bus; The control unit is used to control the on and off of each switch tube in the three-phase ANPC three-level circuit so that the neutral point level of the three-phase transformer is -V dc / 6, 0 or V dc / 6, the voltage at the output end of each half-bridge ANPC three-level bridge arm relative to the connection point of the two DC voltage-dividing capacitors is -2V dc / 3, -V dc / 2, -V dc / 3, 0, V dc / 3, V dc / 2 or 2V dc / 3, where V dc is the voltage between the positive and negative poles of the DC bus, the resonant tank voltage of each phase is an eleven-level voltage, and the resonant tank voltage is the difference between the output voltage of the primary side half-bridge ANPC three-level bridge arm and the output voltage of the secondary side half-bridge ANPC three-level bridge arm; The half-bridge ANPC three-level bridge arm includes a first switch tube, a second switch tube, a third switch tube and a fourth switch tube connected in sequence between the positive and negative electrodes of the DC bus, and includes a fifth switch tube and a sixth switch tube, each of which has one end connected to the two DC voltage-dividing capacitor connection points, the other end of the fifth switch tube is connected to the connection point of the first switch tube and the second switch tube, the other end of the sixth switch tube is connected to the connection point of the third switch tube and the fourth switch tube, the second switch tube and the third switch tube are SiC tubes, and the remaining switch tubes are Si tubes; The control unit includes a redundant zero-state pulse width modulation subunit; The redundant zero-state pulse width modulation subunit is used to control the on and off of each switch tube in the three-phase ANPC three-level circuit, so as to concentrate all hard switches on the second switch tube and the third switch tube; The control unit includes a resonant tank voltage and current control subunit.

2. The three-phase three-level ANPC series resonant dual active bridge DC / DC converter according to claim 1, characterized in that: The switching process of the switch state of the three-phase ANPC three-level circuit in one cycle is: P→OO1→OO2→OO3→N→OO3→OO2→OO1→P; In the P state, the switching states of the first to sixth switching tubes are: 1, 1, 0, 0, 0, 1; The switch states of the first to sixth switch tubes in the N state are: 0, 0, 1, 1, 1, 0; In the OO1 state, the switching states of the first to sixth switching tubes are: 0, 1, 0, 1, 1, 0; In the OO2 state, the switching states of the first to sixth switching tubes are: 1, 0, 1, 0, 0, 1; In the OO3 state, the switching states of the first to sixth switching tubes are: 0, 1, 1, 0, 1, 1; Among them, 0 corresponds to the switch tube being turned off, and 1 corresponds to the switch tube being turned on.

3. The three-phase three-level ANPC series resonant dual active bridge DC / DC converter according to claim 1, characterized in that: If P>P Max0 The resonant tank voltage and current control subunit is used to control the on and off of each switch tube in the three-phase ANPC three-level circuit so that D1=D2=1, and adjust the phase shift angle φ to adjust the transmission power of the three-phase transformer; If P≤P Max0 And v p ≥v s The resonant tank voltage and current control subunit is used to control the on and off of each switch tube in the three-phase ANPC three-level circuit so that D2=1, and adjust D1 and the phase shift angle φ until the secondary side reactive current is minimum; If P≤P Max0 And v p <v s The resonant tank voltage and current control subunit is used to control the on and off of each switch tube in the three-phase ANPC three-level circuit so that D1=1, and adjust D2 and the phase shift angle φ until the primary side reactive current is minimum; Where D1 is the duty cycle of the three-level voltage output by the primary side half-bridge ANPC three-level bridge arm, D2 is the duty cycle of the three-level voltage output by the secondary side half-bridge ANPC three-level bridge arm, P is the actual active transmission power of the converter, P Max0 is the maximum active transmission power of the converter, v p is the voltage at the input end of the primary side three-phase ANPC three-level circuit, v s It is the voltage at the input end of the secondary side three-phase ANPC three-level circuit.

4. The three-phase three-level ANPC series resonant dual active bridge DC / DC converter according to claim 1, characterized in that: The three-phase resonant network includes three resonant tanks, each of which includes a resonant inductor and a resonant capacitor connected in series, and the resonant tank is connected between the transformer of the corresponding phase and the half-bridge ANPC three-level bridge arm.

5. The three-phase three-level ANPC series resonant dual active bridge DC / DC converter according to any one of claims 1 to 4, characterized in that: It also includes a calculation unit for performing Fourier decomposition on the output voltage of each half-bridge ANPC three-level bridge arm using the fundamental wave analysis principle to calculate the active power, reactive power and maximum transmission power of the converter under each winding connection mode.

6. The three-phase three-level ANPC series resonant dual active bridge DC / DC converter according to claim 5, characterized in that: The winding connection mode of the three-phase transformer is YY connection, and the active power, reactive power and maximum active transmission power calculated by the calculation unit are respectively: Among them, P Y-Y is the active power of the converter in YY connection mode, Q Y-Y is the reactive power of the converter in YY connection mode, P Y-Ymax is the maximum active transmission power of the converter under the YY connection mode, k is the voltage conversion ratio of the three-phase transformer, v p is the voltage at the input end of the primary side three-phase ANPC three-level circuit, n is the turns ratio of the three-phase transformer, F n is the ratio of the switching frequency to the resonant frequency, Z0 is the resonant tank impedance, is the phase shift angle, D1 is the duty cycle of the three-level voltage output by the primary side half-bridge ANPC three-level bridge arm, and D2 is the duty cycle of the three-level voltage output by the secondary side half-bridge ANPC three-level bridge arm.

7. The three-phase three-level ANPC series resonant dual active bridge DC / DC converter according to claim 6, characterized in that: The winding connection mode of the three-phase transformer is Δ-Δ connection, and the active power, reactive power and maximum active transmission power calculated by the calculation unit are respectively: Among them, P Δ-Δ is the active power of the converter in the Δ-Δ connection mode, Q Δ-Δ is the reactive power of the converter in the Δ-Δ connection mode, P Δ-Δmax It is the maximum active transmission power of the converter under the Δ-Δ connection mode.

8. The three-phase three-level ANPC series resonant dual active bridge DC / DC converter according to claim 6, characterized in that: The winding connection mode of the three-phase transformer is Y-Δ connection, and the active power, reactive power and maximum active transmission power calculated by the calculation unit are respectively: Among them, P Y-Δ is the active power of the converter in Y-Δ connection mode, Q Y-Δ is the reactive power of the converter in Y-Δ connection mode, P Y-Δmax It is the maximum active transmission power of the converter under the Y-Δ connection mode.

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