Input-series output-series back-to-back bidirectional DC-DC converter

Abstract

The invention provides a back-to-back bidirectional DC-DC converter with series input and series output. Comprising a DC input source, a first converter module and a second converter module. The control module outputs a voltage target value according to an output voltage sampling value, an output voltage target value, a half of an input voltage sampling value, a first input voltage sampling value of the first converter module or a second input voltage sampling value of the second converter module. Calculating a first output current target value of the first converter module and a second output current target value of the second converter module, and generating a first duty ratio for controlling the first converter module according to the first output current target value and a first output current sampling value of the first converter module, and generating a second duty ratio for controlling the second converter module according to the second output current target value and a second output current sampling value of the second converter module. Therefore, the balance of the output voltage can be ensured to a certain extent even if no extra hardware voltage balance circuit is arranged on the output side.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power electronic control, and more particularly, to an input series output series back-to-back bidirectional DC-DC converter. BACKGROUND

[0002] The four-switch Buck-Boost (FSBB) converter has the advantages of few passive devices, small voltage stress of the switch, same voltage polarity, wide voltage gain range, etc. Two FSBBs are back-to-back connected, and the input and output are series connected (ISOS), so that a multi-module series combination system can be obtained. Each module provides half of the power of the entire system, which is suitable for high voltage level occasions. In addition, this scheme can simplify the thermal design of the system, reduce the voltage stress of the power device, and improve the reliability of the system. However, the control of the series combination system of the FSBB is more complex, and when the output impedances of the upper and lower sub-modules are different, the power will be concentrated on one of the sub-modules, which may even burn the power device.

[0003] Therefore, there is a need for a new solution. SUMMARY

[0004] In order to solve the control and voltage sharing problems of the existing FSBB back-to-back input series output series conversion topology, the present application provides an input series output series back-to-back bidirectional DC-DC converter.

[0005] According to an aspect of the present application, an input series output series back-to-back bidirectional DC-DC converter is provided, comprising: a direct current input source; a first converter module and a second converter module, the circuit structures of the first converter module and the second converter module are the same, the positive input end of the first converter module is connected to the positive pole of the direct current input source, the negative input end of the first converter module is connected to the positive input end of the second converter module, the negative input end of the second converter module is connected to the negative pole of the direct current input source, the positive output end of the first converter module is connected to the positive pole of the direct current bus, the negative output end of the first converter module is connected to the positive output end of the second converter module, and the negative output end of the second converter module is connected to the negative pole of the direct current bus; The control module is configured to calculate a first output current target value of the first converter module and a second output current target value of the second converter module based on the output voltage sample value of the DC-DC converter, the target output voltage value of the DC-DC converter, half of the input voltage sample value, the first input voltage sample value of the first converter module, or the second input voltage sample value of the second converter module; and generate a first duty cycle for controlling the first converter module based on the first output current target value and the first output current sample value of the first converter module, and generate a second duty cycle for controlling the second converter module based on the second output current target value and the second output current sample value of the second converter module. The driving module is used to generate a driving signal for driving the first converter module according to the first duty cycle, and to generate a driving signal for driving the second converter module according to the second duty cycle.

[0006] The back-to-back bidirectional DC-DC converter with series input and series output of the present invention has the following advantages: In the present invention, the external voltage loop of the FSBB-ISOS conversion topology is used as the overall output voltage control loop, and half of the input voltage is used as the desired value, with the output voltage of one of the FSBBs used as feedback to construct the internal voltage equalization loop; the outputs of the external voltage loop and the voltage equalization loop are superimposed as the reference for the internal current loop, so as to achieve input voltage and output voltage balance when the output impedances of the two sub-modules are different; it ensures that even if there is no additional hardware voltage equalization circuit on the output side, the output voltage balance can be guaranteed to a certain extent. Attached Figure Description

[0007] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort: Figure 1 The diagram shown is a circuit topology of a back-to-back bidirectional DC-DC converter with serial input and serial output provided in Embodiment 1 of the present invention. Figure 2 The diagram shown is a control block diagram of the control module of a back-to-back bidirectional DC-DC converter with serial input and serial output provided in Embodiment 1 of the present invention. Figure 3 The diagram shown is a circuit topology of a back-to-back bidirectional DC-DC converter with serial input and serial output provided in Embodiment 2 of the present invention. Figure 4The diagram shown is a control block diagram of the control module of the back-to-back bidirectional DC-DC converter with serial input and serial output provided in Embodiment 2 of the present invention. Figure 5 The following is a simulation result of the scheme in Boost mode in Example 1; Figure 6 The following is a simulation result of the scheme in Example 1 in Buck-Boost mode; Figure 7 The simulation results of the scheme in Example 1 are shown in Buck mode.

[0008] Figure 8 The following is a simulation result of the scheme in Example 2 in Boost mode; Figure 9 The simulation results of the scheme in Example 2 are shown in Buck-Boost mode; Figure 10 The simulation results of the scheme in Example 2 are shown in Buck mode. Detailed Implementation

[0009] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Typical embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0010] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0011] Example 1 Figure 1 The diagram shown is a circuit topology of a back-to-back bidirectional DC-DC converter with series input and series output provided in Embodiment 1 of the present invention. Figure 1As shown, this invention provides a back-to-back bidirectional DC-DC converter with series input and series output, comprising a DC input source Vbattery, a first converter module 10, a second converter module 20, a control module (not shown), and a drive module (not shown). The positive input terminal of the first converter module is connected to the positive terminal of the DC input source; the negative input terminal of the first converter module is connected to the positive input terminal of the second converter module; the negative input terminal of the second converter module is connected to the negative terminal of the DC input source; the positive output terminal of the first converter module is connected to the positive terminal of the DC bus; the negative output terminal of the first converter module is connected to the positive output terminal of the second converter module; and the negative output terminal of the second converter module is connected to the negative terminal of the DC bus.

[0012] Specifically, in this embodiment, the first converter module 10 includes a full-bridge power unit composed of a first switch Q1, a second switch Q2, a third switch Q3, and a fourth switch Q4, a filter inductor L1, a first filter capacitor C1, and a second filter capacitor C3. The series connection point of the first and second switches forms the midpoint of the first bridge arm, and the series connection point of the third and fourth switches forms the midpoint of the second bridge arm. The first and second switches are complementary in conduction, and the third and fourth switches are complementary in conduction. The filter inductor is connected between the midpoint of the first and second bridge arms. The first filter capacitor is connected in parallel between the positive input terminal and the negative input terminal of the converter module. The second filter capacitor is connected in parallel between the positive output terminal and the negative output terminal of the converter module.

[0013] Specifically, in this embodiment, the second converter module 20 includes a full-bridge power unit composed of a first switch Q11, a second switch Q22, a third switch Q33, and a fourth switch Q44, a filter inductor L2, a first filter capacitor C2, and a second filter capacitor C4. The series connection point of the first and second switches forms the midpoint of the first bridge arm, and the series connection point of the third and fourth switches forms the midpoint of the second bridge arm. The first and second switches are complementary in conduction, and the third and fourth switches are complementary in conduction. The filter inductor is connected between the midpoint of the first and second bridge arms. The first filter capacitor is connected in parallel between the positive input terminal and the negative input terminal of the converter module. The second filter capacitor is connected in parallel between the positive output terminal and the negative output terminal of the converter module.

[0014] Specifically, in this embodiment, such as Figure 1As shown, the conversion topology consists of two FSBB converter modules arranged back-to-back with their inputs and outputs in series. Due to the series input and output configuration, the input and output currents of each FSBB are naturally equal and do not require control. Therefore, to ensure equal input and output voltages for the two FSBBs, this invention uses the external voltage loop of the FSBB-ISOS conversion topology as the overall output voltage control loop, taking half of the input voltage as the desired value, and using the output voltage of one FSBB as feedback to construct an internal voltage equalization loop. The outputs of the external voltage loop and the voltage equalization loop are superimposed as the reference for the internal current loop, thereby achieving input voltage balance between the two FSBBs. Therefore, in this embodiment, the control module calculates the first output current target value of the first converter module and the second output current target value of the second converter module based on the output voltage sample value of the DC-DC converter, the target output voltage value of the DC-DC converter, half of the input voltage sample value, the first input voltage sample value of the first converter module, or the second input voltage sample value of the second converter module. It then generates a first duty cycle for controlling the first converter module based on the first output current target value and the first output current sample value of the first converter module, and generates a second duty cycle for controlling the second converter module based on the second output current target value and the second output current sample value of the second converter module. The drive module generates a drive signal for driving the first converter module based on the first duty cycle, and generates a drive signal for driving the second converter module based on the second duty cycle.

[0015] Furthermore, such as Figure 2As shown, in this embodiment, the voltage loop is given by the desired output voltage of the converter, and the feedback value of the voltage loop is the actual output voltage of the converter. The difference between the two is used as the input of the voltage loop PI controller. The desired value of the voltage equalization loop is half of the input voltage, and the feedback value of the voltage equalization loop is the output voltage of one of the FSBBs. The difference between the two is used as the input of the voltage equalization loop PI controller. Therefore, the control module includes an external voltage loop control unit, used to use the difference between the sampled output voltage value of the DC-DC converter and the target output voltage value of the DC-DC converter as the input of the external voltage loop PI controller to generate the target output current value of the DC-DC converter; a voltage equalization loop control unit, used to use half of the sampled input voltage value and the difference between the first sampled input voltage value and the second sampled input voltage value as the input of the voltage equalization loop PI controller to generate the output current adjustment value of the DC-DC converter; and an output current target value calculation unit, used to calculate the target output current value of the DC-DC converter based on the target output current value of the DC-DC converter and the output voltage of the DC-DC converter. The system includes a current adjustment value, which calculates the first target output current value and the second target output current value; a first duty cycle calculation unit, which uses the difference between the first target output current value and the first output current sample value as the input of the first current loop PI controller to generate the first duty cycle, wherein the first output current sample value is the average inductor current of the filter inductor of the first converter module; and a second duty cycle calculation unit, which uses the difference between the second target output current value and the second output current sample value as the input of the second current loop PI controller to generate the second duty cycle, wherein the second output current sample value is the average inductor current of the filter inductor of the second converter module.

[0016] Further, in this embodiment, when the voltage equalization ring control unit uses the difference between half of the input voltage sample value and the first input voltage sample value as the input of the voltage equalization ring PI controller, the first output current target value is the difference between the output current target value of the DC-DC converter and the output current adjustment value of the DC-DC converter, and the second output current target value is the sum of the output current target value of the DC-DC converter and the output current adjustment value of the DC-DC converter; when the voltage equalization ring control unit uses the difference between half of the input voltage sample value and the second input voltage sample value as the input of the voltage equalization ring PI controller, the first output current target value is the sum of the output current target value of the DC-DC converter and the output current adjustment value of the DC-DC converter, and the second output current target value is the difference between the output current target value of the DC-DC converter and the output current adjustment value of the DC-DC converter.

[0017] For example, in Figure 2In the illustrated embodiment, the output of the voltage loop minus the output of the voltage equalization loop serves as the current loop reference for submodule FSBB1, and the output of the voltage loop plus the output of the voltage equalization loop serves as the current loop reference for submodule FSBB2. When the input voltage of FSBB1 is too high, the output of the voltage equalization loop is negative, which is equivalent to increasing the current loop reference, increasing the duty cycle of the power device, i.e., increasing the discharge time of the input capacitor of FSBB1, and reducing the voltage of the input capacitor to achieve the purpose of balancing the input voltage. The feedback value of the inner current loop is the average value of the inductor currents of the two FSBBs. The difference between the expected value and the feedback value of the current loop is used as the input of the current loop PI controller. Since the two FSBBs are back-to-back, the feedback value of the inductor current of the lower FSBB2 needs to be inverted. The output of the current loop PI controller is the duty cycle of the power device.

[0018] In this embodiment, the control method can achieve input and output voltage balance even when the output impedances of the two converter modules are different. Furthermore, due to the presence of the voltage equalization ring control unit, output voltage balance can be guaranteed to a certain extent even without additional hardware voltage equalization circuitry on the output side.

[0019] Furthermore, in this embodiment, the control module adopts a three-mode control method. First, it determines the operating mode of the converter based on the input voltage and the desired output voltage. Therefore, the control module also includes an operating mode determination unit, which determines the operating mode of the DC-DC converter based on the sampled input voltage value and the target output voltage value. Specifically, when the input voltage is less than the output voltage minus the hysteresis loop width, it is Boost mode; when the input voltage is greater than the output voltage plus the hysteresis loop width, it is Buck mode; and when the input voltage is greater than the output voltage minus the hysteresis loop width but less than the output voltage plus the hysteresis loop width, it is Buck-Boost mode. Under three-mode control, FSBB power devices Q1 and Q2 are complementaryly turned on, and Q3 and Q4 are complementaryly turned on. Let the duty cycle of Q1 be D1, the duty cycle of Q4 be D4, and the gain be: M = D1 / (1 D4). The output voltage can be controlled by adjusting the duty cycle of Q1 and Q4.

[0020] Further, in this embodiment, when the operating mode is Boost mode, the duty cycles of the power devices in the FSBB are as follows: Q1 duty cycle is 1, and Q4 duty cycle is the output of the current loop PI controller of the control module. That is, the duty cycles of the first switches (Q1 and Q11) of the first converter module 10 and the second converter module 20 are set to 1, the first duty cycle D1 is used to control the fourth switch Q4 of the first converter module, and the second duty cycle D2 is used to control the fourth switch Q44 of the second converter module 20. Therefore, when the operating mode is Boost mode, the drive module is configured to output a constant high-level drive signal to the first switch Q1 of the first converter module 10, output a constant low-level drive signal to the second switch Q2 of the first converter module 10, output a drive signal with the first duty cycle D1 to the fourth switch Q4 of the first converter module 10, and output a drive signal complementary to the drive signal of the fourth switch Q4 of the first converter module 10 to the third switch Q3 of the first converter module 10; output a constant high-level drive signal to the first switch Q11 of the second converter module 20, output a constant low-level drive signal to the second switch Q22 of the second converter module 20, output a drive signal with the second duty cycle D2 to the fourth switch Q44 of the second converter module 20, and output a drive signal complementary to the drive signal of the fourth switch Q44 of the second converter module 20 to the third switch Q33 of the second converter module 20.

[0021] Further, in this embodiment, in Buck mode, the duty cycles of the power devices in the FSBB are as follows: the duty cycle of Q1 is the output of the current loop PI controller, and the duty cycle of Q4 is 0. That is, the duty cycles of the fourth switches (Q4 and Q44) of the first converter module 10 and the second converter module 20 are set to 0. The first switch Q1 of the first converter module is controlled by the first duty cycle D1, and the first switch Q11 of the second converter module 20 is controlled by the second duty cycle D2. Therefore, when the operating mode is Buck mode, the drive module is configured to output a drive signal with the first duty cycle D1 to the first switch Q1 of the first converter module 10, output a drive signal complementary to the drive signal of the first switch Q1 of the first converter module 10 to the second switch Q2 of the first converter module 10, output a constant high-level drive signal to the third switch Q3 of the first converter module 10, and output a constant low-level drive signal to the fourth switch Q4 of the first converter module 10; output a drive signal with the second duty cycle D2 to the first switch Q11 of the second converter module 20, output a drive signal complementary to the drive signal of the first switch Q11 of the second converter module 20 to the second switch Q22 of the second converter module 20, output a constant high-level drive signal to the third switch Q33 of the second converter module 20, and output a constant low-level drive signal to the fourth switch Q44 of the second converter module 20.

[0022] Furthermore, in this embodiment, when the operating mode is Buck-Boost mode, the input voltage is approximately equal to the output voltage. To reduce the inductor current, the waveform of the inductor current is changed to a quadrilateral shape. The conduction sequence is then: Q1Q4 → Q1Q3 → Q2Q3, and the gain M = U2 / U_1 = (D_4 + ... D) / (1 D4). Among them D = D1 - D4, Q1 duty cycle is the output of the current loop PI controller, and Q4 duty cycle is D1 - D4. D. Therefore, the drive module is configured to output a drive signal with the first duty cycle D1 to the first switch Q1 of the first converter module 10, output a drive signal complementary to the drive signal of the first switch Q1 of the first converter module 10 to the second switch Q2 of the first converter module 10, output a drive signal with a third duty cycle to the fourth switch Q4 of the first converter module 10, and output a drive signal complementary to the drive signal of the fourth switch Q4 of the first converter module 10 to the third switch Q3 of the first converter module 10, wherein the third duty cycle is the first duty cycle D1 and a preset duty cycle variation value. The difference of D; outputting a drive signal with the second duty cycle D2 to the first switch Q11 of the second converter module 20, outputting a drive signal complementary to the drive signal of the first switch Q11 of the second converter module 20 to the second switch Q22 of the second converter module 20, outputting a drive signal with a fourth duty cycle to the fourth switch Q44 of the second converter module 20, and outputting a drive signal complementary to the drive signal of the fourth switch Q44 of the second converter module 20 to the third switch Q33 of the second converter module 20, wherein the fourth duty cycle is the second duty cycle D2 and a preset duty cycle variation value. The difference in D.

[0023] In normal Buck-Boost mode, Q1 and Q4, and Q2 and Q3 are simultaneously turned on or off. At this time, D1 = D4, and the gain M = U2 / U1 = D_1 / (1 D_1), D_1=U2 / (U1+U2), but the inductor current is triangular, and the average value of the inductor current is almost twice the average value of the output current. This invention optimizes the conduction sequence of power devices in Buck-Boost mode of the three modes by controlling the duty cycle, so that the inductor current is trapezoidal, reducing the average value of the inductor current, reducing losses and improving conversion efficiency.

[0024] Figure 5 The results show the simulation results in Boost mode. The battery voltage is 400V, and the bus voltage is 1000V. Figure 5 In (a), the green line represents the input voltage, the blue line represents the output voltage, and the red line represents the voltage setpoint. Figure 5 In (b), the red waveform represents the inductor current waveform of FSBB1, and the blue waveform represents the inductor current waveform of FSBB2. In Boost mode, the inductor current is a triangular wave. Figure 5 In (c), red represents the input-side capacitor voltage waveform of FSBB1, and blue represents the input-side capacitor voltage waveform of FSBB2. Figure 5In (d), red represents the output capacitor voltage waveform of FSBB1, and blue represents the output capacitor voltage waveform of FSBB2. As can be seen from the figure, the input voltages of the first converter module 10 and the second converter module 20 exhibit excellent voltage balancing under the action of the voltage equalization ring. Because a resistor is connected in parallel to the output capacitor of the second converter module 20, this resistor consumes the capacitor's energy, causing a voltage drop at the output. Therefore, there is a voltage difference at the output. However, the voltage equalization at the output ensures power balance between the two converter modules, preventing power from concentrating on one sub-module and causing device burnout.

[0025] Figure 6 The image shows the simulation results for Buck-Boost mode. The battery voltage is 900V, and the bus voltage is 900V. Figure 6 In (a), the green line represents the input voltage, the blue line represents the output voltage, and the red line represents the voltage setpoint. Figure 6 In (b), the red waveform represents the inductor current waveform of FSBB1, and the blue waveform represents the inductor current waveform of FSBB2. In Buck-Boost mode, the inductor current is trapezoidal. Figure 6 In (c), red represents the input-side capacitor voltage waveform of FSBB1, and blue represents the input-side capacitor voltage waveform of FSBB2. Figure 6 In (d), red represents the output capacitor voltage waveform of FSBB1, and blue represents the output capacitor voltage waveform of FSBB2. As can be seen from the figure, the input voltages of the first converter module 10 and the second converter module 20 exhibit excellent voltage balancing under the action of the voltage equalization ring. Similarly, the equalization of the output voltages determines the power balance of the two converter modules, preventing power from concentrating on one sub-module and causing device burnout.

[0026] Figure 7 The results show the Buck mode simulation. The battery voltage is 1500V, and the bus voltage is 780V. Figure 7 In (a), the green line represents the input voltage, the blue line represents the output voltage, and the red line represents the voltage setpoint. Figure 7 In (b), the red waveform represents the inductor current waveform of FSBB1, and the blue waveform represents the inductor current waveform of FSBB2. In Buck mode, the inductor current is a triangular wave. Figure 7 In (c), red represents the input-side capacitor voltage waveform of FSBB1, and blue represents the input-side capacitor voltage waveform of FSBB2. Figure 7In (d), red represents the output capacitor voltage waveform of FSBB1, and blue represents the output capacitor voltage waveform of FSBB2. As can be seen from the figure, the input voltages of the first converter module 10 and the second converter module 20 exhibit excellent voltage balancing under the action of the voltage equalization ring. Similarly, the equalization of the output voltages determines the power balance of the two converter modules, preventing power from concentrating on one sub-module and causing device burnout.

[0027] The back-to-back bidirectional DC-DC converter with series input and series output of this invention is based on a three-mode control method. First, by controlling the duty cycle, the conduction sequence of power devices in Buck-Boost mode is optimized, resulting in a trapezoidal inductor current, reducing the average inductor current and improving conversion efficiency. Second, by designing an internal voltage equalization loop, the input and output voltages of the two FSBBs are balanced even with different output impedances. Even without an external bus equalization circuit, the balance of positive and negative DC bus voltages can be maintained to a certain extent, preventing the input and output voltages from shifting to one of the FSBBs. Simulation results show that the FSBB-ISOS back-to-back converter topology using this method exhibits fast dynamic response, small steady-state error, and good voltage equalization effect in all three modes.

[0028] Example 2 Figure 3 The diagram shown is a circuit topology of a back-to-back bidirectional DC-DC converter with series input and series output provided in Embodiment 2 of the present invention. Figure 3 As shown, compared to Figure 1 The illustrated embodiment further includes an external voltage balancing module composed of a balancing inductor L3, a first balancing switch Q5, and a second balancing switch Q6. The first and second balancing switches are connected in series between the positive and negative terminals of the DC bus. The balancing inductor is connected between the series connection point of the first and second balancing switches and the negative output terminal of the first converter module.

[0029] like Figure 4As shown, Vo1 is the voltage of the second filter capacitor C3 of the first converter module 10, and Vo2 is the voltage of the second filter capacitor C4 of the second converter module 20. The front stages of C3 and C4 are regarded as DC power supplies. If Vo1 > Vo2, the first balancing switch tube Q5 conducts, and the second balancing switch tube Q6 turns off. The DC power supply, Q5, L3, and C4 form a loop to charge C4; when both Q5 and Q6 are off, L3, C4, and the freewheeling diode of Q6 form a loop, and the balancing inductor L3 releases the stored energy to charge C4, and the voltage of C4 rises to balance with the voltage of C3. If Vo1 < Vo2, Q6 conducts, and Q5 turns off. The DC power supply, C3, L3, and Q6 form a loop to charge C3; when both Q5 and Q6 are off, L3, the freewheeling diode of Q5, and C3 form a loop, and the inductor L3 releases the stored energy to charge C3, and the voltage of C3 rises to balance with the voltage of C4. Q5 and Q6 conduct complementarily (the existence of dead time can ensure that both Q5 and Q6 are off), so the conduction duty cycle of Q5 can be controlled to achieve voltage balancing control of C3 and C4.

[0030] Specifically, in this embodiment, the difference between Vo1 and Vo2 is input to the voltage outer-loop PI controller, and the output value Iref3 is used as the reference of the current inner loop. The current IL3 of the inductor L3 is used as feedback, and the difference is input to the current inner-loop PI controller. The controller outputs D5 as the conduction duty cycle of Q5, which is used as the drive signal of Q5 after carrier modulation. The drive signal of Q5 is inverted to be used as the drive signal of Q6. If Vo1 > Vo2, the conduction time of Q5 is increased. If Vo1 < Vo2, the conduction time of Q5 is decreased. Therefore, in this embodiment, the control module is further configured to use the difference between the voltage sampling value of the second filter capacitor C3 of the first converter module 10 and the voltage sampling value of the second filter capacitor C4 of the second converter module 20 as the input of the voltage balancing outer-loop PI controller to generate the balanced current target value Iref3; and use the difference between the balanced current target value Iref3 and the current sampling value IL3 of the balancing inductor as the input of the current balancing inner-loop PI controller to generate the fifth duty cycle D5; the drive module is further configured to output a drive signal with the fifth duty cycle to the first balancing switch tube Q5, and output a drive signal complementary to the drive signal of the first balancing switch tube to the second balancing switch tube Q6.

[0031] The external voltage balancing module can enhance the balancing ability under half-wave load conditions and under extremely light load conditions, thereby better ensuring the balance of the positive and negative bus voltages.

[0032] Figure 8 The following shows the simulation results in Boost mode. Among them, the battery voltage is 400V, and the bus voltage is 1000V. At Figure 8In (a), the green line represents the input voltage, the blue line represents the output voltage, and the red line represents the voltage setpoint. Figure 8 In (b), the red waveform represents the inductor current waveform of FSBB1, and the blue waveform represents the inductor current waveform of FSBB2. In Boost mode, the inductor current is a triangular wave. Figure 8 In (c), red represents the input-side capacitor voltage waveform of FSBB1, and blue represents the input-side capacitor voltage waveform of FSBB2. Figure 8 In (d), the red waveform represents the output capacitor voltage of FSBB1, and the blue waveform represents the output capacitor voltage of FSBB2. As can be seen from the figure, this control strategy can achieve voltage balancing between the input and output capacitors even with different output impedances, and exhibits good dynamic and steady-state control performance overall.

[0033] Figure 9 The image shows the simulation results for Buck-Boost mode. The battery voltage is 900V, and the bus voltage is 900V. Figure 9 In (a), the green line represents the input voltage, the blue line represents the output voltage, and the red line represents the voltage setpoint. Figure 9 In (b), the red waveform represents the inductor current waveform of FSBB1, and the blue waveform represents the inductor current waveform of FSBB2. In Buck-Boost mode, the inductor current is trapezoidal. Figure 9 In (c), red represents the input-side capacitor voltage waveform of FSBB1, and blue represents the input-side capacitor voltage waveform of FSBB2. Figure 9 In (d), the red waveform represents the output capacitor voltage of FSBB1, and the blue waveform represents the output capacitor voltage of FSBB2. As can be seen from the figure, this control strategy can achieve voltage balancing between the input and output capacitors even with different output impedances, and exhibits good dynamic and steady-state control performance overall.

[0034] Figure 10 The results show the Buck mode simulation. The battery voltage is 1500V, and the bus voltage is 780V. Figure 10 In (a), the green line represents the input voltage, the blue line represents the output voltage, and the red line represents the voltage setpoint. Figure 10 In (b), the red waveform represents the inductor current waveform of FSBB1, and the blue waveform represents the inductor current waveform of FSBB2. In Buck mode, the inductor current is a triangular wave. Figure 10 In (c), red represents the input-side capacitor voltage waveform of FSBB1, and blue represents the input-side capacitor voltage waveform of FSBB2. Figure 10In (d), the red waveform represents the output capacitor voltage of FSBB1, and the blue waveform represents the output capacitor voltage of FSBB2. As can be seen from the figure, this control strategy can achieve voltage balancing between the input and output capacitors even with different output impedances, and exhibits good dynamic and steady-state control performance overall.

[0035] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0036] Similarly, it should be understood that, in order to simplify this disclosure and aid in understanding one or more of the various aspects of the invention, in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof. However, this method of disclosure should not be construed as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as reflected in the following claims, inventive aspects lie in fewer than all features of a single foregoing disclosed embodiment. Therefore, the claims following the detailed description are hereby expressly incorporated into this detailed description, wherein each claim itself is a separate embodiment of the invention.

[0037] Those skilled in the art will understand that modules in the device of the embodiments can be adaptively changed and placed in one or more devices different from that embodiment. Modules, units, or components in the embodiments can be combined into a single module, unit, or component, and further, they can be divided into multiple sub-modules, sub-units, or sub-components. Except where at least some of such features and / or processes or units are mutually exclusive, any combination can be used to combine all features disclosed in this specification (including the accompanying claims, abstract, and drawings) and all processes or units of any method or device so disclosed. Unless expressly stated otherwise, each feature disclosed in this specification (including the accompanying claims, abstract, and drawings) may be replaced by an alternative feature that serves the same, equivalent, or similar purpose.

[0038] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of the invention and form different embodiments. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0039] It should be noted that the above embodiments are illustrative of the invention and not restrictive, and that those skilled in the art can devise alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses should not be construed as limiting the claims. The word "comprising" does not exclude the presence of elements or steps not listed in the claims. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by means of hardware comprising several different elements and by means of a suitably programmed computer. In the unit claims enumerating several means, several of these means may be embodied by the same item of hardware. The use of the words first, second, and third, etc., does not indicate any order. These words can be interpreted as names.

Claims

1. A back-to-back bidirectional DC-DC converter with series input and series output, characterized in that, include: DC input source; A first converter module and a second converter module have the same circuit structure. The positive input terminal of the first converter module is connected to the positive terminal of the DC input source, and the negative input terminal of the first converter module is connected to the positive input terminal of the second converter module. The negative input terminal of the second converter module is connected to the negative terminal of the DC input source. The positive output terminal of the first converter module is connected to the positive terminal of the DC bus, and the negative output terminal of the first converter module is connected to the positive output terminal of the second converter module. The negative output terminal of the second converter module is connected to the negative terminal of the DC bus. The control module is configured to calculate a first output current target value of the first converter module and a second output current target value of the second converter module based on the output voltage sample value of the DC-DC converter, the target output voltage value of the DC-DC converter, half of the input voltage sample value, the first input voltage sample value of the first converter module, or the second input voltage sample value of the second converter module; and generate a first duty cycle for controlling the first converter module based on the first output current target value and the first output current sample value of the first converter module, and generate a second duty cycle for controlling the second converter module based on the second output current target value and the second output current sample value of the second converter module. The driving module is used to generate a driving signal for driving the first converter module according to the first duty cycle, and to generate a driving signal for driving the second converter module according to the second duty cycle.

2. The back-to-back bidirectional DC-DC converter with series input and series output according to claim 1, characterized in that, Each of the converter modules includes: The full-bridge power unit consists of a first switch, a second switch, a third switch, and a fourth switch. The series connection point of the first switch and the second switch forms the midpoint of the first bridge arm, and the series connection point of the third switch and the fourth switch forms the midpoint of the second bridge arm. The first switch and the second switch are complementary in conduction, and the third switch and the fourth switch are complementary in conduction. A filter inductor is connected between the midpoint of the first bridge arm and the midpoint of the second bridge arm; The first filter capacitor is connected in parallel between the positive input terminal and the negative input terminal of the converter module; The second filter capacitor is connected in parallel between the positive output terminal and the negative output terminal of the converter module.

3. The back-to-back bidirectional DC-DC converter with series input and series output according to claim 2, characterized in that, The control module includes: An external voltage loop control unit is used to take the difference between the sampled output voltage value of the DC-DC converter and the target output voltage value of the DC-DC converter as the input of the external voltage loop PI controller to generate the target output current value of the DC-DC converter; The voltage equalization loop control unit is used to take half of the input voltage sample value and the difference between the first input voltage sample value or the second input voltage sample value as the input of the voltage equalization loop PI controller to generate the output current adjustment value of the DC-DC converter; The output current target value calculation unit is used to calculate the first output current target value and the second output current target value based on the output current target value of the DC-DC converter and the output current adjustment value of the DC-DC converter; The first duty cycle calculation unit is used to generate the first duty cycle based on the difference between the first output current target value and the first output current sample value as the input of the first current loop PI controller, wherein the first output current sample value is the average inductor current of the filter inductor of the first converter module. The second duty cycle calculation unit is used to generate the second duty cycle based on the difference between the second output current target value and the second output current sample value as the input of the second current loop PI controller, wherein the second output current sample value is the average inductor current of the filter inductor of the second converter module.

4. The back-to-back bidirectional DC-DC converter with series input and series output according to claim 3, characterized in that, When the voltage equalization ring control unit takes half of the input voltage sample value and the difference between the first input voltage sample value as the input of the voltage equalization ring PI controller, the first output current target value is the difference between the output current target value of the DC-DC converter and the output current adjustment value of the DC-DC converter, and the second output current target value is the sum of the output current target value of the DC-DC converter and the output current adjustment value of the DC-DC converter; When the equalizing ring control unit uses half of the input voltage sample value and the difference between the second input voltage sample value as the input of the equalizing voltage ring PI controller, the first output current target value is the sum of the output current target value of the DC-DC converter and the output current adjustment value of the DC-DC converter, and the second output current target value is the difference between the output current target value of the DC-DC converter and the output current adjustment value of the DC-DC converter.

5. The back-to-back bidirectional DC-DC converter with series input and series output according to claim 3, characterized in that, The control module also includes: The operating mode determination unit is used to determine the operating mode of the DC-DC converter based on the input voltage sampling value and the output voltage target value of the DC-DC converter.

6. The back-to-back bidirectional DC-DC converter with series input and series output according to claim 5, characterized in that, When the operating mode is Boost mode, the driver module is configured as follows: A constant high-level drive signal is output to the first switch of the first converter module, a constant low-level drive signal is output to the second switch of the first converter module, a drive signal with the first duty cycle is output to the fourth switch of the first converter module, and a drive signal complementary to the drive signal of the fourth switch of the first converter module is output to the third switch of the first converter module. A constant high-level drive signal is output to the first switch of the second converter module, a constant low-level drive signal is output to the second switch of the second converter module, a drive signal with the second duty cycle is output to the fourth switch of the second converter module, and a drive signal complementary to the drive signal of the fourth switch of the second converter module is output to the third switch of the second converter module.

7. The back-to-back bidirectional DC-DC converter with series input and series output according to claim 5, characterized in that, When the operating mode is Buck mode, the driver module is configured as follows: The first switch of the first converter module outputs a drive signal with the first duty cycle, the second switch of the first converter module outputs a drive signal complementary to the drive signal of the first switch of the first converter module, the third switch of the first converter module outputs a drive signal with a constant high level, and the fourth switch of the first converter module outputs a drive signal with a constant low level. The second converter module outputs a drive signal with the second duty cycle to the first switch, outputs a drive signal complementary to the drive signal of the first switch to the second switch, outputs a constant high-level drive signal to the third switch, and outputs a constant low-level drive signal to the fourth switch.

8. The back-to-back bidirectional DC-DC converter with series input and series output according to claim 5, characterized in that, When the operating mode is Buck-Boost mode, the driver module is configured as follows: A drive signal with the first duty cycle is output to the first switch of the first converter module; a drive signal complementary to the drive signal of the first switch of the first converter module is output to the second switch of the first converter module; a drive signal with the third duty cycle is output to the fourth switch of the first converter module; and a drive signal complementary to the drive signal of the fourth switch of the first converter module is output to the third switch of the first converter module, wherein the third duty cycle is the difference between the first duty cycle and a preset change value of the duty cycle. The second converter module outputs a drive signal with the second duty cycle to the first switch, outputs a drive signal complementary to the drive signal of the first switch to the second switch, outputs a drive signal with the fourth duty cycle to the fourth switch, and outputs a drive signal complementary to the drive signal of the fourth switch to the third switch, wherein the fourth duty cycle is the difference between the second duty cycle and a preset duty cycle change value.

9. The back-to-back bidirectional DC-DC converter with series input and series output according to claim 2, characterized in that, It also includes an external voltage equalization module, which includes an equalization inductor, a first equalization switch and a second equalization switch. The first equalization switch and the second equalization switch are connected in series between the positive and negative terminals of the DC bus. The equalization inductor is connected between the series connection point of the first equalization switch and the second equalization switch and the output negative terminal of the first converter module.

10. The back-to-back bidirectional DC-DC converter with series input and series output according to claim 9, characterized in that, The control module is also used to take the voltage sample value of the second filter capacitor of the first converter module and the voltage sample value of the second filter capacitor of the second converter module as the input of the voltage equalization outer loop PI controller to generate the equalization current target value. The difference between the target value of the equalization current and the current sampling value of the equalization inductor is used as the input of the current equalization inner loop PI controller to generate a fifth duty cycle; the driving module is also used to output a driving signal with the fifth duty cycle to the first equalization switch and to output a driving signal that is complementary to the driving signal of the first equalization switch to the second equalization switch.

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