An output current control method for an isolated bidirectional DC / DC converter circuit

Abstract

This invention discloses an output current control method for an isolated bidirectional DC / DC converter circuit. Based on the target current value and the calculated ts and k values, the current of the low-voltage side output inductor is adjusted for error. After multiple adjustments, the error decreases until the error current output value is zero. At this point, the actual time signal value modulates the on / off state of each switch transistor via a PWM controller, making the current value of the low-voltage side output inductor equal to the required target current. Loop control of the current stabilizes and adjusts the actual current value of the output inductor. The PWM controller controls the on / off state of each switch transistor. Using the above circuit structure, combined with the body diode inside the switch transistor, bidirectional power transmission can be achieved. While ensuring high-efficiency operation, the modulation scheme is simplified. Furthermore, under full-load conditions, the reactive current of the transformer is relatively small, resulting in high operating efficiency. This method can be applied to energy storage, electric vehicles, new energy fields, and other areas.

Description

Technical Field

[0001] This invention relates to the field of DC-DC converter output current control technology, and specifically to an output current control method for an isolated bidirectional DC / DC converter circuit. Background Technology

[0002] Energy storage devices are connected to the DC bus via bidirectional DC / DC converters, enabling bidirectional flow between the energy storage device and the bus. Some energy storage devices have a wide voltage fluctuation range, but their voltage level is much lower than that of the DC bus. Therefore, a wide-range bidirectional DC / DC converter is needed to boost the output voltage of the energy storage device. High-power isolated DC / DC converters can be divided into resonant and non-resonant types. Non-resonant isolated DC / DC converters include phase-shifted full-bridge and DAB (Dual-active Bridge) circuits, but these circuit structures have certain limitations. For example, traditional phase-shifted full-bridge converters can only transmit power in one direction, and traditional DAB circuits have complex phase-shifting modulation methods and poor stability, thus affecting power conversion. Summary of the Invention

[0003] Based on the above analysis, this invention proposes an output current control method for an isolated bidirectional DC / DC converter circuit to address the shortcomings of existing technologies.

[0004] This invention is mainly achieved through the following technical solutions:

[0005] This invention also provides an output current control method for an isolated bidirectional DC / DC converter circuit, used to control the isolated bidirectional DC / DC converter circuit. The isolated bidirectional DC / DC converter circuit includes a high-voltage side full-bridge module, a transformer, a low-voltage side full-bridge module, and a controller. The high-voltage side full-bridge module has a first filter unit at both ends. A resonant inductor is provided between the high-voltage side of the transformer and the high-voltage side full-bridge module. The low-voltage side of the transformer is electrically connected to the low-voltage side full-bridge module. The low-voltage side full-bridge module is connected in series with an output inductor and then electrically connected to both ends of a second filter module. The high-voltage side full-bridge module includes a first switch, a second switch, a third switch, and a fourth switch. The low-voltage side full-bridge module includes a fifth switch, a sixth switch, a seventh switch, and an eighth switch. Each switch is connected in parallel with a body diode. The controller includes a PWM controller electrically connected to the control terminals of each switch.

[0006] Includes the following steps:

[0007] Collect the input voltage V across the first filter unit. H The output voltage V across the second filter module L ;

[0008] According to the input voltage V H Output voltage V L Given the current sampling period Ts and the winding turns ratio N1:N2 on the high-voltage and low-voltage sides of the transformer, calculate the time signal value ts of the low-voltage side switch tube being fully on under no-load conditions and the corresponding time signal value k of the low-voltage side switch tube under the target current.

[0009] Based on the target current values ​​Iref, ts, and k, the time signal value tb corresponding to the full conduction of the low-voltage side switch under the current target current is obtained;

[0010] Obtain the target current value Iref and the current I of the output inductor. Lo The error current value between the two values ​​is adjusted by PI error control to obtain the error current output value.

[0011] Based on the error current output value and tb, obtain the time signal value td after error adjustment;

[0012] When tb≠td, repeat the error adjustment until tb=td. At this point, td is the actual time signal value after error calibration.

[0013] The PWM wave emitted by the PWM controller, which is controlled by the actual time signal value td, controls the on / off state of each switching transistor, so that the actual current value of the low-voltage side output inductor is equal to the target current value Iref.

[0014] Furthermore, the formula for calculating ts is as follows:

[0015] Furthermore, the formula for calculating k is as follows:

[0016]

[0017] Furthermore, the formula for calculating the target time value tb is as follows:

[0018] tb=k·Iref+ts (3).

[0019] Furthermore, td is the sum of the error current output value after PI adjustment and the target time signal value tb.

[0020] Furthermore, the isolated bidirectional DC / DC converter circuit includes zero-current mode, boost mode, and buck mode;

[0021] When the isolated bidirectional DC / DC converter circuit is in zero-current mode, it includes four operating modes:

[0022] Switching Mode 1: Before time t0, the third and second switches on the high-voltage side are turned on, and the sixth and seventh switches on the low-voltage side are turned on simultaneously. The current I on the resonant inductor Lc With a slope of -V Lo / Lo increases in reverse, and the current I in the output inductor increases. Lo With slope V Lo / Lo increases in the positive direction, where Lo is the inductance value of the output inductor 9.

[0023] Among them, V Lo V is the voltage of the low-voltage side output inductor. AB V is the voltage across points A and B on the high-voltage side of the transformer. CD This represents the voltage across points C and D on the low-voltage side of the transformer.

[0024] Switching Mode 2: During the time interval [t0, t1], at time t0, the fifth and eighth switches on the low-voltage side are turned on. At this time, all four switches on the low-voltage side are turned on, and the transformer 3 on the low-voltage side is short-circuited. V CD =0, the polarity of the voltage across the output inductor changes, I Lo With slope V Lo / Lo begins to decrease; simultaneously, due to the short circuit in the low-voltage side transformer, the voltage in the high-voltage side transformer is clamped at 0V, therefore I Lc With a slope of -V H / Lc continues to increase in the opposite direction;

[0025] Where Lc is the inductance value of the resonant inductor;

[0026] Switching Mode 3: During the time interval [t1, t2], at time t1, the second and third switches on the high-voltage side are off, and after a short dead time, the first and fourth switches are on, while the sixth and seventh switches on the low-voltage side are off; at this time, the high-voltage side V AB =V H I Lc Similar to the high-voltage side current of the transformer, I Lo The current is the same as the low-voltage side current of the transformer; since the high-voltage side current and the low-voltage side current have not yet reached a balance, the body diodes of all the switching transistors on the low-voltage side are still in the conducting state during this period, therefore V CD If it still equals 0V, then I Lc A current loop is formed by the body diodes D1 and D4 of the first and fourth high-voltage side switching transistors. After the first and fourth switching transistors are turned on, the polarity of the voltage across the resonant inductor changes, therefore I... Lc During this period, the slope is V H / Lc begins to decrease, I Lo The direction increases in the opposite direction at time t1, and its slope is V. Lo / Lo;

[0027] Switching mode 4: During the time interval [t2, t3], at time t2, the high-voltage side current and the low-voltage side current are balanced, i.e., I Lc = (N2 / N1)*I Lo Since the body diode of the low-voltage side switch no longer freewheels, the transformer is no longer short-circuited. V CD = (N2N1)*V H Energy transfer begins between the high-voltage and low-voltage sides, and simultaneously, I Lo With slope V Lo / Lo decreases in the reverse direction and then increases in the positive direction, I Lc It also decreases in the opposite direction with the same slope and then increases in the positive direction.

[0028] Furthermore, when the isolated bidirectional DC / DC converter circuit is in boost mode or buck mode, the current change mode switches between switching mode 1 and switching mode 4.

[0029] Furthermore, the first, second, third, fourth, fifth, sixth, seventh, and eighth switching transistors are insulated-gate bipolar transistors or metal-oxide-semiconductor field-effect transistors.

[0030] Furthermore, the first filtering unit includes a first capacitor.

[0031] Furthermore, the second filter unit includes a second capacitor.

[0032] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0033] 1. This invention provides an output current control method for an isolated bidirectional DC / DC converter circuit. Based on the target current value and the calculated ts and k values, the current of the low-voltage side output inductor is adjusted for error. After multiple error adjustments, the error is reduced until the error current output value is zero. At this point, the actual time signal value is modulated by the PWM controller to switch the transistors on and off, making the current value of the low-voltage side output inductor equal to the target current. Loop control of the current is used to stabilize and adjust the actual current value of the output inductor. The PWM controller controls the on / off state of each transistor, and the PI controller is used to adjust the error. Using the above circuit structure, bidirectional power transmission can be achieved by controlling the conduction state of the transistors and the internal body diode. While ensuring high-efficiency operation, the modulation scheme is simplified. At the same time, the reactive current of the transformer is small under full load conditions, so the operating efficiency is high. It can be applied to energy storage, electric vehicles, new energy and other fields.

[0034] 2. On the high-voltage side, only the switching transistors need to be controlled to open and close simultaneously. On the low-voltage side, only the opening time of the four switching transistors needs to be controlled simultaneously. No phase shift control is required. The circuit's operating state does not change abruptly during the buck-boost mode transition.

[0035] 3. Isolation between the high-voltage and low-voltage sides is achieved through a transformer. Compared with the traditional dual-active bridge circuit, under the same low-voltage side current ripple rate, the effective value of the current flowing through the second filter unit is smaller because the second filter unit and the output inductor filter together. Therefore, the circuit requires relatively less capacitance. The full-bridge structure is adopted. Compared with the half-bridge structure, the electrical stress of the switching transistor can be reduced by half when high power is transmitted in boost mode. During energy transmission, the induced inductance of the resonant inductor and the output inductor resonates with the parasitic capacitance of the switching transistor to achieve zero-voltage switching. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the modulation principle of an isolated bidirectional DC / DC converter circuit provided by an embodiment of the present invention applied to the corresponding converter.

[0038] Figure 2 This is a control principle diagram of the PWM controller provided in an embodiment of the present invention;

[0039] Figure 3 This is a waveform diagram of each device in zero-current mode of an output current control method for an isolated bidirectional DC / DC converter circuit provided in an embodiment of the present invention.

[0040] Figure 4 This is a waveform diagram of each device in buck mode of an isolated bidirectional DC / DC converter circuit provided in an embodiment of the present invention.

[0041] Figure 5 This is a waveform diagram of each device in boost mode of an isolated bidirectional DC / DC converter circuit output current control method provided in an embodiment of the present invention.

[0042] Figure 6 This is the equivalent circuit of the isolated bidirectional DC / DC converter circuit in switching mode 1 under zero current mode provided in the embodiments of the present invention;

[0043] Figure 7 This is the equivalent circuit of the isolated bidirectional DC / DC converter circuit in switching mode 2 under zero current mode provided in the embodiments of the present invention;

[0044] Figure 8 This is the equivalent circuit of the isolated bidirectional DC / DC converter circuit in the zero-current mode switching mode 3 provided in the embodiments of the present invention;

[0045] Figure 9 This is the equivalent circuit of the isolated bidirectional DC / DC converter circuit provided in the embodiment of the present invention in switching mode 4 under zero current mode.

[0046] The attached figures are labeled as follows:

[0047] 1. High-voltage side full-bridge circuit; 2. Transformer; 3. Low-voltage side full-bridge circuit; 4. PWM controller. Detailed Implementation

[0048] To enable those skilled in the art to better understand the present invention and to more clearly define the scope of protection of the present invention, the present invention will be described in detail below with reference to certain specific embodiments. It should be noted that the following are only some specific embodiments of the present invention, and are merely a part of the embodiments of the present invention. The specific and direct descriptions of related structures are only for the convenience of understanding the present invention, and the specific features do not necessarily or directly limit the scope of the present invention. Conventional choices and substitutions made by those skilled in the art under the guidance of the present invention should be considered within the scope of protection of the present invention.

[0049] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0050] Example 1

[0051] like Figure 1 As shown, the present invention also provides an output current control method for an isolated bidirectional DC / DC converter circuit, used to control the isolated bidirectional DC / DC converter circuit.

[0052] The isolated bidirectional DC / DC converter circuit includes a high-voltage side full-bridge circuit 1, a transformer 2, a low-voltage side full-bridge circuit 3, and a controller. The high-voltage side full-bridge circuit 1 has a first filter unit at both ends. A resonant inductor is provided between the high-voltage side of the transformer 2 and the high-voltage side full-bridge circuit 1. The low-voltage side of the transformer 2 is electrically connected to the low-voltage side full-bridge circuit 3. The low-voltage side full-bridge circuit 3 is connected in series with an output inductor and then electrically connected to both ends of the second filter unit. The high-voltage side full-bridge circuit 1 includes a first switch S1, a second switch S2, a third switch S3, and a fourth switch S4. The low-voltage side full-bridge circuit 3 includes a fifth switch S5, a sixth switch S6, a seventh switch S7, and an eighth switch S8. Each switch is connected in parallel with a body diode. The controller includes a PWM controller 4 that is electrically connected to the control terminals of each switch.

[0053] Specifically, the first switch S1 and the second switch S2 are connected in series, and the third switch S3 and the fourth switch S4 are connected in series. The first end of the third switch S3 and the first end of the first switch S1 are electrically connected to the first end of the first filter unit, respectively. The second ends of the second switch S2 and the second end of the fourth switch S4 are electrically connected to the second end of the first filter unit, respectively. One end of the high-voltage winding of the transformer 2 is electrically connected to the series connection of the first switch S1 and the second switch S2 through a resonant inductor, i.e., point A. The other end of the high-voltage winding of the transformer 2 is electrically connected to the series connection of the third switch S3 and the fourth switch S4, i.e., point B.

[0054] The fifth switch S5 and the sixth switch S6 are connected in series, and the seventh switch S7 and the eighth switch S8 are connected in series. The first ends of the fifth switch S5 and the seventh switch S7 are connected together and electrically connected to the first end of the second filter unit through the output inductor. The second ends of the sixth switch S6 and the eighth switch S8 are respectively electrically connected to the second end of the second filter unit. One end of the low-voltage winding of transformer 2 is electrically connected to the connection point of the fifth switch S5 and the sixth switch S6, i.e., point C. The other end of the low-voltage winding of transformer 3 is electrically connected to the connection point of the seventh switch S7 and the eighth switch S8, i.e., point D.

[0055] An isolated bidirectional DC / DC converter circuit of the present invention is part of the DC / DC converter between photovoltaic module 1 and battery 5 in an energy storage inverter system. It can realize the function of isolated step-up and step-down, and can replace transformer 2 and resonant inductor with transformer with larger leakage inductance.

[0056] In this embodiment, the first switch S1, the second switch S2, the third switch S3, the fourth switch S4, the fifth switch S5, the sixth switch S6, the seventh switch S7, and the eighth switch S8 are insulated-gate bipolar transistors or metal-oxide-semiconductor field-effect transistors. NMOS transistors are preferred.

[0057] Preferably, the first filter unit includes a first capacitor C1, and the second filter unit includes a second capacitor C2.

[0058] In this embodiment, the resonant inductor is inductor Lc, the output inductor is inductor Lo, the number of turns of the high-voltage side winding is N1, and the number of turns of the low-voltage side winding is N2, wherein N1>N2. The specific number of turns needs to be designed according to the actual input and output voltage requirements. The selection of parameters for the first capacitor C1, the second capacitor C2, the inductor Lc, the inductor Lo, and each switching transistor needs to be determined according to the output current ripple requirements.

[0059] Specifically, the first filter unit is set at both ends of the high-voltage side power supply, and the second filter unit is set at both ends of the low-voltage side power supply.

[0060] In this embodiment, the high-voltage side power supply is a photovoltaic module, and the low-voltage side power supply is a battery. The voltage across the photovoltaic module is V. H The voltage across the battery is V. L .

[0061] The control method includes the following steps:

[0062] Collect the input voltage V across the first filter unit. H The output voltage V across the second filter unit L ;

[0063] According to the input voltage V H Output voltage V L Given the current sampling period Ts and the turns ratio N1:N2 on the high-voltage and low-voltage sides of transformer 2, calculate the time signal value ts of the low-voltage side switch tube being fully on under no-load conditions and the corresponding time signal value k of the low-voltage side switch tube under the target current.

[0064] Based on the target current values ​​Iref, ts, and k, the time signal value tb corresponding to the full conduction of the low-voltage side switch under the current target current is obtained;

[0065] Obtain the target current value Iref and the current I of the output inductor. Lo The error current value between the two values ​​is adjusted by PI error control to obtain the error current output value.

[0066] Based on the error current output value and tb, obtain the time signal value td after error adjustment;

[0067] When tb≠td, repeat the error adjustment until tb=td. At this point, td is the actual time signal value after error calibration.

[0068] The PWM controller 4, controlled by the actual time signal value td, generates a PWM wave that controls the on / off state of each switching transistor, so that the actual current value of the low-voltage side output inductor is equal to the target current value Iref.

[0069] In this embodiment, after multiple error control steps, the error continuously decreases until the error current output value is 0, at which point tb = td. The target current value Iref is determined based on the actual load requirements.

[0070] With the voltage requirements on the high-voltage side and the low-voltage side remaining unchanged, the duration of simultaneous conduction of the four transistors on the low-voltage side is controlled, namely t0 and t1, but t2-t0 remains unchanged. Figure 3 This refers to the circuit's operating mode in zero-current mode, i.e., under no-load conditions; such as Figure 4 As shown, in buck mode, if the high-voltage side bus needs to charge the low-voltage side battery, the conduction time of the four transistors on the low-voltage side is shorter than in zero-current mode; for example... Figure 5 As shown, in boost mode, if the high-voltage side bus needs to be powered by the low-voltage side battery, the conduction time of the four transistors on the low-voltage side is longer than that in zero-current mode.

[0071] Where t0 represents the moment when all the low-voltage side switches are turned on, t1 represents the moment when all the low-voltage side switches are turned off, and t2 represents the moment when the high-voltage side current multiplied by the transformer turns ratio equals the low-voltage side current.

[0072] like Figure 2 As shown, because the diagonal switches on the high-voltage side and the low-voltage side are simultaneously turned on and off—that is, the first switch S1 and the fourth switch S4 are simultaneously turned on and off, the second switch S2 and the third switch S3 are simultaneously turned on and off, the fifth switch S5 and the eighth switch S8 are simultaneously turned on and off, and the sixth switch S6 and the seventh switch S7 are simultaneously turned on and off—therefore… Figure 2-4 The diagram only indicates the switching state of one switch on each diagonal, while the shaded area on the low-voltage side indicates that all four switches on the low-voltage side are open simultaneously.

[0073] Specifically, such as Figure 3-5 As shown, the isolated bidirectional DC / DC converter circuit includes zero-current mode, boost mode, and buck mode;

[0074] When the isolated bidirectional DC / DC converter circuit is in zero-current mode, it includes four operating modes:

[0075] Switching mode 1: such as Figure 6As shown, before time t0, the third switch S3 and the second switch S2 on the high-voltage side are turned on, and the sixth switch S6 and the seventh switch S7 on the low-voltage side are turned on simultaneously. Therefore... The current I on the resonant inductor Lc With a slope of -V Lo / Lo increases in reverse, and the current I in the output inductor increases. Lo With slope V Lo / Lo increases in the positive direction, where Lo is the inductance value of the output inductor 9.

[0076] Among them, V Lo V is the voltage of the low-voltage side output inductor. AB V is the voltage across points A and B on the high-voltage side of transformer 2. CD Let be the voltage across points C and D on the low-voltage side of transformer 2.

[0077] Switching mode 2: such as Figure 7 As shown, during the time interval [t0, t1], at time t0, the fifth switch S5 and the eighth switch S8 on the low-voltage side are turned on. At this time, all four switches on the low-voltage side are turned on, and the transformer 2 on the low-voltage side is short-circuited. V CD =0, the polarity of the voltage across output inductor 7 changes, I Lo With slope V Lo / Lo begins to decrease; simultaneously, due to the short circuit of low-voltage transformer 2, the voltage of high-voltage transformer 2 is clamped at 0V, therefore I Lc With a slope of -V H / Lc continues to increase in the opposite direction;

[0078] Where Lc is the inductance value of resonant inductor 6;

[0079] Switching mode 3: such as Figure 8 As shown, during the time interval [t1, t2], at time t1, the second switch S2 and the third switch S3 on the high-voltage side are turned off, and after a short dead time, the first switch S1 and the fourth switch S4 are turned on, while the sixth switch S6 and the seventh switch S7 on the low-voltage side are turned off; at this time, the high-voltage side V AB =V H I Lc The current on the high-voltage side of transformer 2 is the same, I Lo The current is the same as the low-voltage side current of transformer 2; since the high-voltage side current and the low-voltage side current have not yet reached a balance, the body diodes of all the switching transistors on the low-voltage side are still in the conducting state during this period, therefore V CD If it still equals 0V, then I LcA current loop is formed by the body diodes D1 and D4 of the first and fourth high-voltage side switches S1 and S4. After the first and fourth switches S1 and S4 are turned on, the polarity of the voltage across the resonant inductor changes, therefore I... Lc During this period, the slope is V H / Lc begins to decrease, I Lo The direction increases in the opposite direction at time t1, and its slope is V. Lo / Lo;

[0080] Switching mode 4: such as Figure 9 As shown, during the time interval [t2, t3], the high-voltage side current and the low-voltage side current are balanced at time t2, i.e., I Lc = (N2 / N1)*I Lo Since the body diode of the low-voltage side switch no longer freewheels, transformer 2 is no longer short-circuited, V CD = (N2 / N1)*V H Energy transfer begins between the high-voltage and low-voltage sides, and simultaneously, I Lo With slope V Lo / Lo decreases in the reverse direction and then increases in the positive direction, I Lc It also decreases in the opposite direction with the same slope and then increases in the positive direction. Based on the theoretical basis of the slope of the current rise or fall, the values ​​of ts and k can be derived.

[0081] Preferably, when the isolated bidirectional DC / DC converter circuit is in boost mode or buck mode, the current change mode switches between switching mode 1 and switching mode 4. That is, the circuit operating state does not change abruptly during buck-boost mode switching.

[0082] Preferably, the formula for calculating ts is as follows:

[0083] In this embodiment, ts is half the difference between the time signal value at time t2 and the time signal value at time t0.

[0084] Preferably, the formula for calculating k is as follows:

[0085]

[0086] Specifically, the formula for calculating the target time value tb is as follows:

[0087] tb=k·Iref+ts (3).

[0088] Specifically, td is the sum of the error current output value after PI regulation and the target time signal value tb.

[0089] In this embodiment, td is the difference between the time signal value at time t1 and the time signal value at time t0.

[0090] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for controlling the output current of an isolated bidirectional DC / DC converter circuit, used to control the isolated bidirectional DC / DC converter circuit, characterized in that, The isolated bidirectional DC / DC converter circuit includes a high-voltage side full-bridge circuit (1), a transformer (2), a low-voltage side full-bridge circuit (3), and a controller. The high-voltage side full-bridge circuit (1) is provided with a first filter unit at both ends. A resonant inductor is provided between the high-voltage side of the transformer (2) and the high-voltage side full-bridge circuit (1). The low-voltage side of the transformer (2) is electrically connected to the low-voltage side full-bridge circuit (3). The low-voltage side full-bridge circuit (3) is connected in series with an output inductor and then electrically connected to both ends of the second filter unit. The high-voltage side full-bridge circuit (1) includes a first switch, a second switch, a third switch, and a fourth switch. The low-voltage side full-bridge circuit (3) includes a fifth switch, a sixth switch, a seventh switch, and an eighth switch. Each switch is connected in parallel with a body diode. The controller includes a PWM controller (4) that is electrically connected to the control terminals of each switch. Includes the following steps: Collect the input voltage across the first filter unit. The output voltage across the second filter unit ; According to the input voltage Output voltage 1. Current sampling period Ts and the winding turns ratio N1:N2 of the high voltage side and low voltage side of the transformer (2). Calculate the time signal value ts of the low voltage side switch tube fully on under no-load conditions and the time signal value k of the low voltage side switch tube under the target current. Based on the target current value , ts, k, to obtain the time signal value tb of the low-voltage side switch tube being fully on under the current target current; Obtain the target current value With the current of the output inductor The error current value between the two values ​​is adjusted by PI error control to obtain the error current output value. Based on the error current output value and tb, obtain the time signal value td after error adjustment; When tb≠td, repeat the error adjustment until tb=td. At this point, td is the actual time signal value after error calibration. The PWM wave emitted by the PWM controller (4), controlled by the actual time signal value td, controls the on / off state of each switching transistor and the duration of simultaneous conduction of the four transistors on the low-voltage side, so that the actual current value of the low-voltage side output inductor is close to the target current value. equal; The isolated bidirectional DC / DC converter circuit includes zero-current mode, boost mode, and buck mode; In buck mode, the conduction time of the four transistors on the low-voltage side is shorter than that in zero-current mode; in boost mode, the conduction time of the four transistors on the low-voltage side is longer than that in zero-current mode.

2. The output current control method for an isolated bidirectional DC / DC converter circuit as described in claim 1, characterized in that, The formula for calculating ts is as follows: (1) 3. The output current control method for an isolated bidirectional DC / DC converter circuit as described in claim 2, characterized in that, The formula for calculating k is as follows: （2）； The aforementioned This is the inductance value of the resonant inductor.

4. The output current control method for an isolated bidirectional DC / DC converter circuit as described in claim 3, characterized in that, The formula for calculating the time signal value tb of the low-voltage side switch being fully on under the current target current is as follows: （3） 。 5. The output current control method for an isolated bidirectional DC / DC converter circuit as described in claim 4, characterized in that, The td is the sum of the error current output value after PI regulation and the signal value tb of the time when the low-voltage side switch is fully on under the current target current.

6. The output current control method for an isolated bidirectional DC / DC converter circuit as described in claim 1, characterized in that, When the isolated bidirectional DC / DC converter circuit is in zero-current mode, it includes four operating modes: Switching mode 1: In Before that time, the third and second switches on the high-voltage side turned on, and the sixth and seventh switches on the low-voltage side turned on simultaneously. , The current in the resonant inductor With slope The current in the output inductor increases in the reverse direction. With slope Positive increase, The inductance value of the output inductor. ; in, The voltage of the low-voltage side output inductor. The voltage across points A and B on the high-voltage side of transformer (2) is... The voltage across points C and D on the low-voltage side of transformer (2); Switching mode 2: in [ , During the time period, At this moment, the fifth and eighth switching transistors on the low-voltage side are open, and all four switching transistors on the low-voltage side are open, short-circuiting the transformer (2) on the low-voltage side. The polarity of the voltage across the output inductor changes. With slope The voltage begins to drop; simultaneously, due to the short circuit of the low-voltage side transformer (2), the voltage of the high-voltage side transformer (2) is clamped at 0V, therefore... With slope Continue to increase in the opposite direction; in, This is the inductance value of the resonant inductor; Switching mode 3: in [ , During the time period, At any given moment, the second and third switches on the high-voltage side are closed, and after a short dead time, the first and fourth switches are open, while the sixth and seventh switches on the low-voltage side are turned off; at this time, the high-voltage side... , The current on the high-voltage side of transformer (2) is the same. The current on the low-voltage side is the same as that on transformer (2); since the current on the high-voltage side and the current on the low-voltage side have not yet reached a balance, the body diodes of all the switching transistors on the low-voltage side are still in the conducting state during this period. If it still equals 0V, then A current loop is formed by the body diodes D1 and D4 of the first and fourth high-voltage side switching transistors. After the first and fourth switching transistors are turned on, the polarity of the voltage across the resonant inductor changes. During this period, the slope is Start to decrease, The direction is The time increases in the opposite direction, and its slope is ; Switching mode 4: in [ , During the time period, At all times, the high-voltage side current and the low-voltage side current are in balance, that is... Since the body diode of the low-voltage side switch no longer freewheels, the transformer (2) is no longer short-circuited. Energy transfer begins between the high-voltage and low-voltage sides, simultaneously. With slope After decreasing in the reverse direction, it increases in the positive direction. It also decreases in the opposite direction with the same slope and then increases in the positive direction.

7. The output current control method for an isolated bidirectional DC / DC converter circuit as described in claim 6, characterized in that, When the isolated bidirectional DC / DC converter circuit is in boost mode or buck mode, the current change mode switches between switching mode 1 and switching mode 4.

8. The output current control method for an isolated bidirectional DC / DC converter circuit as described in claim 1, characterized in that, The first, second, third, fourth, fifth, sixth, seventh, and eighth switching transistors are insulated-gate bipolar transistors or metal-oxide-semiconductor field-effect transistors.

9. The output current control method for an isolated bidirectional DC / DC converter circuit as described in claim 1, characterized in that, The first filtering unit includes a first capacitor.

10. The output current control method for an isolated bidirectional DC / DC converter circuit as described in claim 1 or 9, characterized in that, The second filter unit includes a second capacitor.

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