CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of China application no. 202110702252.9, filed on Jun. 24, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND
Field of the Disclosure

The disclosure relates to the technical field of power electronics, in particular to a single-stage isolated bidirectional converter and a control method of the single-stage isolated bidirectional converter.

Description of Related Art

Isolated bidirectional converters (AC/DC bidirectional converters) are power electronic devices used for power conversion. The isolated bidirectional converters can work in rectification mode and inverter mode, providing energy transmission between alternating current and direct current, and providing electrical isolation through transformers. The isolated AC/DC bidirectional converters may be used in various fields such as driving motors, charging and discharging for electric vehicle power battery, and lithium battery energy storage.

In the related art, most of the isolated AC/DC bidirectional converters adopt a two-stage structure, which consists of a one-stage bidirectional non-isolated AC/DC converter and a one-stage bidirectional isolated DC/DC converter, and a DC bus capacitor is connected in parallel between the two stages as an energy buffer unit. However, the two-stage isolated AC/DC bidirectional converter has the following disadvantages: (1) When the two-stage isolated AC/DC bidirectional converter is adopted, the power transmission between the AC port and the DC port can only be completed through two conversions, resulting in low conversion efficiency; (2) In the two-stage isolated AC/DC bidirectional converter, the bus capacitor is required as the energy buffer unit of the two-stage converter, and the required capacitance value is high, and thus aluminum electrolytic capacitors are used normally. However, aluminum electrolytic capacitors are large in size and short in service life, which causes the two-stage isolated AC/DC bidirectional converters to have a large size and short service life; (3) The bidirectional non-isolated AC/DC bidirectional converters need to adopt a boost inductor with a large inductance to reduce the current ripple, thereby reducing the electromagnetic interference conducted to the AC terminal, and reducing the power loss on the semiconductor switch tube and the inductor.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a single-stage isolated bidirectional converter and a control method thereof, which only include one-stage power conversion.

The technical solution adopted in the present disclosure is as follows:

A single-stage isolated bidirectional converter includes a DC voltage port, an AC voltage port, a first full-bridge circuit unit, a half-bridge circuit unit, a second full-bridge circuit unit, a phase-shift unit, a transformer and a filter capacitor. The AC voltage port includes a first port and a second port; and the DC voltage port includes a third port and a fourth port. The transformer includes a first winding and a second winding, and the first winding is provided with a center tap. The center tap is connected with the first port, the two ends of the first winding are connected with the midpoints of two bridge arms of the first full-bridge circuit unit through the phase-shift unit respectively, and the two ends of the second winding are connected with the midpoints of the two bridge arms of the second full-bridge circuit unit respectively. The two ends of the first full-bridge circuit unit are respectively connected with the two ends of the half-bridge circuit unit; the two ends of the half-bridge circuit unit are further connected with the two ends of the filter capacitor, and the midpoint of the bridge arm of the half-bridge circuit unit is connected with the second port. The two ends of the second full-bridge circuit unit are respectively connected with the third port and the fourth port.

The first full-bridge circuit unit includes: a first switch tube and a second switch tube connected in series, the first end of the first switch tube is connected to the first end of the second switch tube, and the connection point between the first switch tube and the second switch tube is the midpoint of a bridge arm of the first full-bridge circuit unit; a third switch tube and a fourth switch tube connected in series, a first end of the third switch tube is connected with a first end of the fourth switch tube, and the connection point between the third switch tube and the fourth switch tube is the midpoint of the other bridge arm of the first full-bridge circuit unit; a second end of the third switch tube is connected to a second end of the first switch tube, and a second end of the fourth switch tube is connected to a second end of the second switch tube.

The half-bridge circuit unit includes: a fifth switch tube and a sixth switch tube connected in series, a first end of the fifth switch tube is connected to a first end of the sixth switch tube, and the connection point between the fifth switch tube and the sixth switch tube is the midpoint of the bridge arm of the half-bridge circuit unit; a second end of the fifth switch tube is connected with a second end of the third switch tube, and a second end of the six switch tube is connected to a second end of the fourth switch tube.

The phase-shift unit includes: a first phase-shift inductor, one end of the first phase-shift inductor is connected to the midpoint of one bridge arm of the first full-bridge circuit unit, and the other end of the first phase-shift inductor is connected to one end of the first winding; a second phase-shift inductor, one end of the second phase-shift inductor is connected to the midpoint of the other bridge arm of the first full-bridge circuit unit, and the other end of the second phase-shift inductor is connected to the other end of the first winding.

The second full-bridge circuit unit includes: a seventh switch tube and an eighth switch tube connected in series, a first end of the seventh switch tube is connected to a first end of the eighth switch tube, and a connection point between the seventh switch tube and the eighth switch tube is the midpoint of a bridge arm of the second full-bridge circuit unit; a ninth switch tube and a tenth switch tube connected in series, a first end of the ninth switch tube is connected to a first end of the tenth switch tube, and a connection point between the ninth switch tube and the tenth switch tube is the midpoint of the other bridge arm of the second full-bridge circuit unit; a second end of the ninth switch tube is connected to a second end of the seventh switch tube, and a second end of the tenth switch tube is connected to a second end of the eighth switch tube.

A control method of a single-stage isolated bidirectional converter includes the following steps: after a rectification or inverter control command is received, a corresponding driving signal with duty ratio of 50% is sent to the driving terminals of the first to the tenth switch tubes to control only one of the two switch tubes in the same bridge arm in the first full-bridge circuit unit to be in a conducting state, to control only one of the two switch tubes in the half-bridge circuit unit to be in a conducting state, and to control only one of the two switch tubes in the same bridge arm in the second full-bridge circuit unit to be in a conducting state, so that the single-stage isolated bidirectional converter operates in the rectification mode or the inverter mode. When the single-stage isolated bidirectional converter operates in the rectification mode, the driving signal corresponding to the first full-bridge circuit unit is precedent to the driving signal corresponding to the second full-bridge circuit unit. When the single-stage isolated bidirectional converter operates in the inverter mode, the driving signal corresponding to the first full-bridge circuit unit lags behind the driving signal corresponding to the second full-bridge circuit unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural view of a single-stage isolated bidirectional converter according to an embodiment of the present disclosure.

FIG. 2a is a waveform diagram of various switch driving signals, voltages and currents when the single-stage isolated bidirectional converter operates in a rectification mode according to a specific embodiment of the present disclosure.

FIG. 2b is a waveform diagram of various switch driving signals, voltages and currents when the single-stage isolated bidirectional converter operates in a rectification mode according to another specific embodiment of the present disclosure.

FIG. 3 is a schematic view of a single-stage isolated bidirectional converter when operating in the first stage of a rectification mode according to a specific embodiment of the present disclosure.

FIG. 4 is a schematic view of a single-stage isolated bidirectional converter when operating in the second stage of a rectification mode according to a specific embodiment of the present disclosure.

FIG. 5 is a schematic view of a single-stage isolated bidirectional converter when operating in the third stage of a rectification mode according to a specific embodiment of the present disclosure.

FIG. 6 is a schematic view of a single-stage isolated bidirectional converter when operating in the fourth stage of a rectification mode according to a specific embodiment of the present disclosure.

FIG. 7 is a schematic view of a single-stage isolated bidirectional converter when operating in the fifth stage of a rectification mode according to a specific embodiment of the present disclosure.

FIG. 8 is a schematic view of a single-stage isolated bidirectional converter when operating in the sixth stage of a rectification mode according to a specific embodiment of the present disclosure.

DESCRIPTION OF EMBODIMENTS

The technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present disclosure. Clearly, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope to be protected by the present disclosure.

FIG. 1 is a schematic structural view of a single-stage isolated bidirectional converter according to an embodiment of the present disclosure.

At present, isolated AC/DC bidirectional converters are mostly composed of a one-stage bidirectional non-isolated AC/DC converter and a one-stage bidirectional isolated DC/DC converter, and a DC bus capacitor connected in parallel between the two stages is used as an energy buffer unit. The common topologies of bidirectional non-isolated AC/DC converters are totem-pole power factor correctors, etc.; and the common topologies of bidirectional isolated DC/DC converters are CLLC resonant converters, dual active bridge converters, etc.

However, (1) When the two-stage isolated AC/DC bidirectional converter is adopted, the power transmission between the AC port and the DC port can only be completed through two conversions, resulting in low conversion efficiency; (2) In the two-stage isolated AC/DC bidirectional converter, the bus capacitor is required as the energy buffer unit of the two-stage converter, and the required capacitance value is high, and thus aluminum electrolytic capacitors are used normally. However, aluminum electrolytic capacitors are large in size and short in service life, which causes the two-stage isolated AC/DC bidirectional converters to have a large size and short service life; (3) The bidirectional non-isolated AC/DC bidirectional converters need to adopt a boost inductor with a large inductance to reduce the current ripple, thereby reducing the electromagnetic interference conducted to the AC terminal, and reducing the power loss on the semiconductor switch tube and the inductor.

Therefore, the present disclosure provides a single-stage isolated bidirectional converter, which significantly improves the conversion efficiency of the bidirectional converter, and does not need to use a bus capacitor, thus reducing the size of the bidirectional converter. Meanwhile, the single-stage isolated bidirectional converter does not need to use a boost inductor, and therefore the size of the bidirectional converter is further reduced, and the cost is lower.

Specifically, as shown in FIG. 1, the single-stage isolated bidirectional converter according to the embodiment of the present disclosure may include: a DC voltage port 100, an AC voltage port 200, a first full-bridge circuit unit 300, a half-bridge circuit unit 400, a second full-bridge circuit unit 500, a phase-shift unit 600, a transformer 700 and a filter capacitor 800.

The AC voltage port 200 includes a first port and a second port. The DC voltage port 100 includes a third port and a fourth port. The transformer 700 includes a first winding 710 and a second winding 720, and the first winding 710 is provided with a center tap. The center tap is connected to the first port. The two ends of the first winding 710 are respectively connected to the midpoints of the two bridge arms of the first full-bridge circuit unit 300 through the phase-shift unit 600. The two ends of the second winding 720 are respectively connected to the midpoints of the two bridge arms of the second full-bridge circuit unit 500. The two ends of the first full-bridge circuit unit 300 are respectively connected to the two ends of the half-bridge circuit unit 400. The two ends of the half-bridge circuit unit 400 are also connected to the two ends of the filter capacitor 800, and the filter capacitor is a high-frequency filter capacitor, configured for filtering the current ripple of the switching frequency. The midpoint of the bridge arm of the half-bridge circuit unit 400 is connected to the second port. The two ends of the second full-bridge circuit unit 500 are respectively connected to the third port and the fourth port.

According to an embodiment of the present disclosure, as shown in FIG. 1, the first full-bridge circuit unit 300 includes: a first switch tube S₁and a second switch tube S₂connected in series, the first end of the first switch tube S₁is connected to the first end of the second switch tube S₂, and the connection point a between the first switch tube S₁and the second switch tube S₂is the midpoint of a bridge arm of the first full-bridge circuit unit 300; a third switch tube S₃and a fourth switch tube S₄connected in series, a first end of the third switch tube S₃is connected with a first end of the fourth switch tube S₄, and the connection point b between the third switch tube S₃and the fourth switch tube S₄is the midpoint of the other bridge arm of the first full-bridge circuit unit 300; a second end of the third switch tube S₃is connected to a second end of the first switch tube S₁, and a second end of the fourth switch tube S₄is connected to a second end of the second switch tube S₂.

According to an embodiment of the present disclosure, as shown in FIG. 1, the half-bridge circuit unit 400 includes: a fifth switch tube S₅and a sixth switch tube S₆connected in series, a first end of the fifth switch tube S₅is connected to a first end of the sixth switch tube S₆, and the connection point between the fifth switch tube S₅and the sixth switch tube S₆is the midpoint of the bridge arm of the half-bridge circuit unit 400; a second end of the fifth switch tube S₅is connected with a second end of the third switch tube S₃, and a second end of the six switch tube S₆is connected to a second end of the fourth switch tube S₄.

According to an embodiment of the present disclosure, as shown in FIG. 1, the phase-shift unit 600 includes: a first phase-shift inductor L1, one end of the first phase-shift inductor L1 is connected to the midpoint (i.e., the connection point a) of one bridge arm of the first full-bridge circuit unit 300, and the other end of the first phase-shift inductor L1 is connected to one end of the first winding 710; a second phase-shift inductor L2, one end of the second phase-shift inductor L2 is connected to the midpoint (i.e., the connection point b) of the other bridge arm of the first full-bridge circuit unit 300, and the other end of the second phase-shift inductor L2 is connected to the other end of the first winding 710.

The inductances of the first phase-shift inductor L1 and the second phase-shift inductor L2 are the same, and there may be no coupling relationship or there may be a coupling relationship between them. If there is no coupling relationship between the first phase-shift inductor L1 and the second phase-shift inductor L2, the inductance of the first phase-shift inductor L1 and the second phase-shift inductor L2 may be denoted as L_p; if there is a coupling relationship between the first phase-shift inductor L1 and the second phase-shift inductor L2, the differential mode inductance may be denoted as L_p,dm, and the common mode inductance may be denoted as L_p,cm. The coils of the first phase-shift inductor L1 and the second phase-shift inductor L2 may be respectively wound on two magnetic posts of a magnetic core, or may be wound on two magnetic cores respectively, and may further be used as a leakage inductance winding on the magnetic core of the transformer 700.

According to an embodiment of the disclosure, as shown in FIG. 1, the second full-bridge circuit unit 500 includes: a seventh switch tube S₇and an eighth switch tube S₈connected in series, a first end of the seventh switch tube S₇is connected to a first end of the eighth switch tube S₈, and a connection point c between the seventh switch tube S₇and the eighth switch tube S₈is the midpoint of a bridge arm of the second full-bridge circuit unit 500; a ninth switch tube S₉and a tenth switch tube S₁₀connected in series, a first end of the ninth switch tube S₉is connected to a first end of the tenth switch tube S₁₀, and a connection point d between the ninth switch tube S₉and the tenth switch tube S₁₀is the midpoint of the other bridge arm of the second full-bridge circuit unit 500; a second end of the ninth switch tube S₉is connected to a second end of the seventh switch tube S₇, and a second end of the tenth switch tube Sip is connected to a second end of the eighth switch tube S₈.

In order to make the single-stage isolated bidirectional converter in the embodiments of the present disclosure more comprehensible to those skilled in the art, the operation mode of the single-stage isolated bidirectional converter will be described in detail below with reference to specific embodiments.

Specifically, by inputting driving signals to the driving terminals of the first to fourth switch tubes S₁to S₄, the first to fourth switch tubes S₁to S₄are controlled to be turned on or off, thereby controlling the first full-bridge circuit unit 300 to operate in the following two modes:

Mode 1: When the first switch tube S₁and the fourth switch tube S₄are in a conducting state, the second switch tube S₂and the third switch tube S₃are in an off state. Mode 2: When the second switch tube S₂and the third switch tube S₃are in a conducting state, the first switch tube S₁and the fourth switch tube S₄are in an off state.

The duty ratios of the driving signals of the first to fourth switch tubes S₁to S₄are 50%, and only one of the two switch tubes of the same bridge arm is in a conducting state. In each switch cycle T_smode 1 and mode 2 are respectively executed once, and the durations of mode 1 and mode 2 each account for 50%.

By inputting driving signals to the driving terminals of the fifth switch tube S₅and the sixth switch tube S₆to control the fifth switch tube S₅and the sixth switch tube S₆to be turned on or off, the half-bridge circuit unit 400 is controlled to operate in the following manner:

If the single-stage isolated bidirectional converter operates in the rectification mode, when the AC terminal voltage V_gis positive, the sixth switch tube S₆is in the on state or the off state, and the fifth switch tube S₅is in the off state. When the AC terminal voltage V_gis negative, the fifth switch tube S₅is in the on state or the off state, and the sixth switch tube S₆is in the off state. If the single-stage isolated bidirectional converter operates in the inverter mode, when the AC terminal voltage V_gis positive, the fifth switch tube S₅is in the on state, and the sixth switch tube S₆is in the off state. When the AC terminal voltage V_gis negative, the sixth switch tube S₆is in the on state, and the fifth switch tube S₅is in the off state.

By inputting driving signals to the driving terminals of the seventh to tenth switch tubes S₇to S₁₀, the seventh to tenth switch tubes S₇to S₁₀are controlled to be turned on or off, so as to control the second full-bridge circuit unit 500 to operate according to the following four modes:

Mode 1: When the seventh switch tube S₇and the tenth switch tube S₁₀are in the conducting state, the eighth switch tube S₈and the ninth switch tube S₉are in the off state. Mode 2: When the eighth switch tube S₈and the ninth switch tube S₉are in the conducting state, the seventh switch tube S₇and the tenth switch tube S₁₀are in the off state. Mode 3: When the seventh switch tube S₇and the ninth switch tube S₉are in the conducting state, the eighth switch tube S₈and the tenth switch tube S₁₀are in the off state. Mode 4: When the eighth switch tube S₈and the tenth switch tube S₁₀are in the conducting state, the seventh switch tube S₇and the ninth switch tube S₉are in the off state.

The duty ratios of the driving signals of the seventh switch tube S₇and the tenth switch tube S₁₀are 50%, and only one of the two switch tubes of the same bridge arm is in a conducting state. In each switch cycle T_smode 1, mode 2, mode 3 and mode 4 are executed once respectively, and the execution sequence and time of each mode depend on the internal phase relationship of the driving signals of each switch tube.

It should be noted that the internal phase relationship between the driving signal of each switch tube in the second full-bridge circuit unit 500 and the external phase relationship between the driving signal of the second full-bridge circuit unit 500 and the driving signal of the first full-bridge circuit unit 300 may control the power factor of the AC terminal current i_gand the input/output power of the DC terminal. In the rectification mode, the driving signal of the first full-bridge circuit unit 300 is precedent to the driving signal of the second full-bridge circuit unit 500, and the energy is transmitted from the AC terminal to the DC terminal. In the inverter mode, the driving signal of the first full-bridge circuit unit 300 lags behind the driving signal of the second full-bridge circuit unit 500, and energy is transmitted from the DC terminal to the AC terminal.

According to a specific embodiment of the present disclosure, taking the rectification mode as an example, FIG. 2a shows the operation waveform of a single-stage isolated bidirectional converter in a power frequency cycle of 20 ms, and the waveform of one switch cycle in FIG. 2a is amplified, thus obtaining the waveform of FIG. 2b. As shown in FIG. 2a, in one power frequency cycle, the half-bridge circuit unit 400 operates twice, that is, when the AC terminal voltage V_gis positive, the sixth switch tube S₆is in the conducting state, and the fifth switch tube S₅is in the off state. When the AC terminal voltage V_gis negative, the fifth switch tube S₅is in the conducting state, and the sixth switch tube S₆is in the off state.

As shown in FIG. 2a and FIG. 2b, the duty ratios of the driving signals of the first to fourth switch tubes S₁to S₄in the first full-bridge circuit unit 300 are all 50%. The voltage

u
cc

=

❘
"[LeftBracketingBar]"

V
g

❘
"[RightBracketingBar]"

1
-
0.5

across the filter capacitor 800 may be calculated through the transformation ratio formula of the boost converter. Therefore, the voltage u_ccacross the filter capacitor 800 is twice the absolute value of the grid voltage, i.e., |2 V_g|. Since the single-stage isolated bidirectional converter operates in the rectification mode, the AC terminal voltage V_gis in the same phase with the current i_g.

As shown in FIG. 2a, the driving signals of the first switch tube S₁, the fourth switch tube S₄, the second switch tube S₂, and the third switch tube S₃in the first full-bridge circuit unit 300 have a phase difference of 180°. The voltage u_ccacross the filter capacitor 800 is inverted to the voltage u_abbetween the midpoints of the bridge arms of the first full-bridge circuit unit 300. The cycle of u_abis the switch cycle T_s, the positive and negative cycles each account for 50%, and the amplitude of the outer envelope is u_cc.

As shown in FIG. 2a, the duty ratios of the driving signals of the seventh to tenth switch tubes S₇to S₁₀in the second full-bridge circuit unit 500 are all 50%, and the driving signals of the seventh switch tube S₇and the eighth switch tube S₈are precedent to the phase φ_i; of the driving signals of the ninth switch tube S₉and the tenth switch tube S₁₀. The DC terminal voltage V_bis inverted to the voltage u_cdbetween the midpoints the bridge arms of the second full-bridge circuit unit 500, the cycle of u_cdis the switch cycle T_s, the positive and negative cycles are symmetrical, the amplitude is V_b, and the duty ratio of voltage is less than or equal to 50%.

As shown in FIG. 2a, the secondary current i_kof the transformer 700 is a high-frequency alternating current, and does not include a power-frequency alternating current component. The current i₁of the first phase-shift inductor L1 and the current i₂of the second phase-shift inductor L2 include power frequency components and high-frequency components. The power frequency components of the currents i₁and i₂are both equal to half of the AC side current, namely

❘
"[LeftBracketingBar]"

i
g

❘
"[RightBracketingBar]"

2

,

the high-frequency component of the current i₁is equal to −i_k, and the high-frequency component of the current i₂is equal to i_k.

For ease of description, it may be assumed that the transformation ratio of the first winding 710 and the second winding 720 of the transformer 700 is equal to 1, the first phase-shift inductor L1 and the second phase-shift inductor L2 have no coupling relationship, and the inductance is L_p.

Correspondingly, in the first stage of the operation stage of the rectification mode, namely stage 1, as shown in FIG. 3, the first switch tube S₁, the fourth switch tube S₄, the sixth switch tube S₆, the eighth switch tube S₈and the ninth switch tube S₉are in the conducting state; the second switch tube S₂, the third switch tube S₃, the fifth switch tube S₅, the seventh switch tube S₇and the tenth switch tube S₁₀are in the off state, which corresponds to the stage I of FIG. 2b. The potential difference u_abat the midpoint of the bridge arm of the first full-bridge circuit unit 300 is equal to u_cc, and the potential difference u_cdat the midpoint of the bridge arm of the second full-bridge circuit unit 500 is equal to −V_b. The current i₁of the first phase-shift inductor L1 decreases linearly with a rate of

-

u
cc

-

V
b

2
⁢

L
p

;

the current i₂of the second phase-shift inductor L2 increases linearly with a rate of

u
cc

+

V
b

2
⁢

L
p

.

The AC terminal current i_gis equal to the sum of the currents i₁and i₂, and the current i₁falls at approximately the same rate as the current i₂rises, so the AC terminal current i_gapproximately maintains unchanged with the amplitude I_g. The secondary currents i_kand i₂of the transformer rise at approximately the same rate.

In the second stage of the rectification mode, that is, stage 2, as shown in FIG. 4, the first switch tube S₁, the fourth switch tube S₄, the sixth switch tube S₆, the eighth switch tube S₈and the tenth switch tube S₁₀are in a conducting state, and the second switch tube S₂, the third switch tube S₃, the fifth switch tube S₅, the seventh switch tube S₇, and the ninth switch tube S₉are in the off state, which corresponds to stage II of FIG. 2b. The potential difference u_abat the midpoint of the bridge arm of the first full-bridge circuit unit 300 is equal to u_cc, and the potential difference u_cdat the midpoint of the bridge arm of the second full-bridge circuit unit 500 is equal to zero. The current i₁of the first phase-shift inductor L1 decreases linearly with a rate of

-

u
cc

2
⁢

L
p

;

the current i₂of the second phase-shift inductor L2 increases linearly with a rate of

u
cc

2
⁢

L
p

.

The AC terminal current i_gis equal to the sum of the currents i₁and i₂, and the current i₁falls at approximately the same rate as the current i₂rises, so the AC terminal current i_gapproximately keeps unchanged with the amplitude I_g. The secondary currents i_kand i₂of the transformer rise at approximately the same rate.

In the third stage of the rectification mode, namely stage 3, as shown in FIG. 5, the first switch tube S₁, the fourth switch tube S₄, the sixth switch tube S₆, the seventh switch tube S₇and the tenth switch tube S₁₀are in the conducting state, and the second switch tube S₂, the third switch tube S₃, the fifth switch tube S₅, the eighth switch tube S₈, and the ninth switch tube S₉are in the off state, which corresponds to stage III of FIG. 2b. The potential difference u_abat the midpoint of the bridge arm of the first full-bridge circuit unit 300 is equal to u_cc, and the potential difference u_cdat the midpoint of the bridge arm of the second full-bridge circuit unit 500 is equal to V_b. The current i₁of the first phase-shift inductor L1 rises linearly at a rate of

-

u
cc

+

V
b

2
⁢

L
p

;

the current i₂of the second phase-shift inductor L2 decreases linearly at a rate of

u
cc

-

V
b

2
⁢

L
p

.

The AC terminal current i_gis equal to the sum of the currents i₁and i₂, and the current i₁rises at approximately the same rate as the current i₂falls, so the AC terminal current i_gapproximately keeps unchanged with the amplitude I_g. The secondary currents i_kand i₂of the transformer fall at approximately the same rate.

In the fourth stage of the rectification mode, namely stage 4, as shown in FIG. 6, the second switch tube S₂, the third switch tube S₃, the sixth switch tube S₆, the seventh switch tube S₇and the tenth switch tube S₁₀are in the conducting state, and the first switch tube S₁, the fourth switch tube S₄, the fifth switch tube S₅, the eighth switch tube S₈, and the ninth switch tube S₉are in the off state, which corresponds to stage IV of FIG. 2b. The potential difference u_abat the midpoint of the bridge arm of the first full-bridge circuit unit 300 is equal to −u_cc, and the potential difference u_cdat the midpoint of the bridge arm of the second full-bridge circuit unit 500 is equal to V_b. The current i₁of the first phase-shift inductor L1 rises linearly with a rate of

u
cc

+

V
b

2
⁢

L
p

;

the current i₂of the second phase-shift inductor L2 decreases linearly with a rate of

u
cc

+

V
b

2
⁢

L
p

.

The AC terminal current i_gis equal to the sum of the currents i₁and i₂, and the current i₁rises at approximately the same rate as the current i₂falls, so the AC terminal current i_gapproximately keeps unchanged with the amplitude I_g. The secondary currents i_kand i₂of the transformer fall at approximately the same rate.

In the fifth stage of the rectification mode, namely stage 5, as shown in FIG. 7, the second switch tube S₂, the third switch tube S₃, the sixth switch tube S₆, the seventh switch tube S₇and the ninth switch tube S₉are in a conducting state, and the first switch tube S₁, the fourth switch tube S₄, the fifth switch tube S₅, the eighth switch tube S₈, and the tenth switch tube S₁₀are in the off state, which corresponds to the stage V of FIG. 2b. The potential difference u_abat the midpoint of the bridge arm of the first full-bridge circuit unit 300 is equal to −u_aband the potential difference u_cdat the midpoint of the bridge arm of the second full-bridge circuit unit 500 is equal to zero. The current i₁of the first phase-shift inductor L1 increases linearly with the rate of

u
cc

L
p

;

the current i₂of the second phase-shift inductor L2 decreases linearly with the rate of

-

u
cc

L
p

.

The AC terminal current i_gis equal to the sum of the currents i₁and i₂, and the current i₁rises at approximately the same rate as the current i₂falls, so the AC terminal current i_gapproximately keeps unchanged with the amplitude I_g. The secondary currents i_kand i₂of the transformer fall at approximately the same rate.

In the sixth stage of the rectification mode, namely stage 6, as shown in FIG. 8, the second switch tube S₂, the third switch tube S₃, the sixth switch tube S₆, the eighth switch tube S₈and the ninth switch tube S₉are in the conducting state, and the first switch tube S₁, the fourth switch tube S₄, the fifth switch tube S₅, the seventh switch tube S₇, and the tenth switch tube S₁₀are in an off state, which corresponds to the stage VI of FIG. 2b. The potential difference u_abat the midpoint of the bridge arm of the first full-bridge circuit unit 300 is equal to −u_cc, and the potential difference u_cdat the midpoint of the bridge arm of the second full-bridge circuit unit 500 is equal to zero. The current i₁of the first phase-shift inductor L1 decreases linearly with a rate of

u
cc

-

V
b

2
⁢

L
p

;

the current i₂of the second phase-shift inductor L2 increases linearly with a rate of

-

u
cc

+

V
b

2
⁢

L
p

.

The AC terminal current i_gis equal to the sum of currents i₁and i₂, and the current i₁rises at approximately the same rate as the current i₂falls, so the AC terminal current i_gapproximately keeps unchanged with the amplitude I_g. The secondary currents i_kand i₂of the transformer fall at approximately the same rate.

To sum up, the single-stage isolated bidirectional converter of the present disclosure includes only one stage of power conversion, so the loss of the converter is small and the conversion efficiency is high. Moreover, the single-stage isolated bidirectional converter of the present disclosure includes only high-frequency filter capacitor with small capacitance to filter the current ripple at the switching frequency, and does not include the bus capacitor with large capacitance as an energy buffer unit, so there is no need to use aluminum electrolytic capacitors. Accordingly, the converter is small in size and has a long service life. Furthermore, the single-stage isolated bidirectional converter of the present disclosure does not need a boost inductor, has little electromagnetic interference to the power grid, and does not cause additional loss for semiconductor switch tube and loss for phase-shift inductor core. Besides, the topology does not have the characteristics of a boost inductor. Therefore, the size and magnetic loss of the converter are reduced, and the cost of the converter is reduced.

According to the single-stage isolated bidirectional converter in the embodiment of the present disclosure, the converter includes: a DC voltage port, an AC voltage port, a first full-bridge circuit unit, a half-bridge circuit unit, a second full-bridge circuit unit, a phase-shift unit, a transformer and a filter capacitor. The AC voltage port includes a first port and a second port; the DC voltage port includes a third port and a fourth port; and the transformer includes a first winding and a second winding. The first winding is provided with a center tap, and the center tap is connected to the first port. The two ends of the first winding are respectively connected to the midpoints of the two bridge arms of the first full-bridge circuit unit through the phase-shift unit, and the two ends of the second winding are respectively connected to the midpoints of the two bridge arms of the second full-bridge circuit unit. The two ends of the first full-bridge circuit unit are respectively connected to the two ends of the half-bridge circuit unit; the two ends of the half-bridge circuit unit are also connected to the two ends of the filter capacitor. The midpoint of the bridge arm of the half-bridge circuit unit is connected to the second port; the two ends of the second full-bridge circuit unit are respectively connected to the third port and the fourth port. Therefore, the single-stage isolated bidirectional converter of the present disclosure only includes one-stage power conversion, so the loss is small and the conversion efficiency is high. Moreover, the single-stage isolated bidirectional converter only includes a filter capacitor with a small capacitance value, and there is no need to use a bus capacitor with a large capacitance value as an energy buffer unit. Therefore, the converter is small in size and has a long service life. In the meantime, the single-stage isolated bidirectional converter of the present disclosure does not need a boost inductor, that is, the topology does not have the characteristics of a boost inductor, so the size and magnetic loss of the converter is reduced, thereby reducing the cost of the converter.

Corresponding to the above embodiments, the present disclosure further provides a control method for a single-stage isolated bidirectional converter.

The control method for a single-stage isolated bidirectional converter described in an embodiment of the present disclosure includes the following steps: after a rectification or inverter control command is received, a corresponding driving signal with duty ratio of 50% is sent to the driving terminals of the first to the tenth switch tubes to control only one of the two switch tubes in the same bridge arm in the first full-bridge circuit unit to be in a conducting state, to control only one of the two switch tubes in the half-bridge circuit unit to be in a conducting state, and to control only one of the two switch tubes in the same bridge arm in the second full-bridge circuit unit to be in a conducting state, so that the single-stage isolated bidirectional converter operates in the rectification mode or the inverter mode. When the single-stage isolated bidirectional converter operates in the rectification mode, the driving signal corresponding to the first full-bridge circuit unit is precedent to the driving signal corresponding to the second full-bridge circuit unit. When the single-stage isolated bidirectional converter operates in the inverter mode, the driving signal corresponding to the first full-bridge circuit unit lags behind the driving signal corresponding to the second full-bridge circuit unit.

Specifically, based on the single-stage isolated bidirectional converter in the above embodiment, by inputting driving signals to the driving terminals of the first to fourth switch tubes S₁to S₄, the first to fourth switch tubes S₁to S₄are controlled to be turned on or off, thereby controlling the first full-bridge circuit unit 300 to operate in the following two modes: