Switching-free bidirectional direct-current converter and control process thereof

Abstract

The invention discloses a non-switching bidirectional direct current converter and a control process thereof, the converter comprises four transistors, four fly-wheel diodes, a power inductor L, two filter capacitors, a power battery B, a super capacitor C, a switch S and a direct current bus DC + / DC-, the four freewheel diodes are respectively and reversely connected in parallel with two ends of the four transistors, the power inductor L is bridged with a midpoint of a bridge arm formed by the transistors Q1Q2 and a midpoint of a bridge arm formed by the transistors Q3Q4, the power battery B and the filter capacitor C1 are connected in parallel with two ends of the transistors Q1Q2, and the super capacitor C, the filter capacitor C2 and the DC bus DC + / DC-are connected in parallel between the transistors Q3Q4. And a switch S is connected in series between the positive electrode of the super capacitor C and the direct-current bus DC +. According to the non-switching bidirectional direct-current converter provided by the invention, the reliability of the circuit is improved, the cost of the circuit is reduced, the installation and debugging difficulty of the circuit is reduced, and meanwhile, the energy feedback of the super capacitor is also realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic direct current converters, and more specifically, relates to a non-switching bidirectional direct current converter and a control process thereof. Background Art

[0002] Due to the characteristics of heavy-load electric drive vehicles such as high drive motor power and diverse load forms, the load power changes sharply when starting and stopping frequently and the road conditions are complex, which has a great impact on the on-board DC bus. The power battery B has a lag in controlling the stable bus voltage. Supercapacitor C has the advantages of high power density, short energy storage cycle, long cycle life, and wide operating temperature range. The composite energy storage device composed of power battery B and supercapacitor C is suitable for applications that require high power density and fast energy storage / release, such as stabilizing the DC bus voltage of heavy-load electric drive vehicles.

[0003] However, during the operation of heavy-load electric drive vehicles, the DC bus generally operates near the rated voltage, and at this time the voltage of the supercapacitor C is zero. If the supercapacitor C is directly connected to the DC bus, the charging current will be too large. Therefore, it is necessary to pre-charge the supercapacitor C. In order to protect the power battery B and prevent the frequent charging and discharging of the power battery B from affecting its life, the power battery B is generally connected to the bidirectional DC converter first, and then to the DC bus. During the maintenance of heavy-load electric drive vehicles, it is necessary to first discharge the wires of the supercapacitor C or feed them all back to the power battery B before maintenance can be carried out.

[0004] The design of the DC converter for heavy-duty electric drive vehicles requires that it be capable of precharging the supercapacitor C, controlling the charge and discharge of the power battery B, and discharging the supercapacitor C. However, the conventional precharging of the supercapacitor C mostly uses a relay-controlled bidirectional DC / DC converter, which reduces the reliability of the circuit, increases the cost of the circuit, and increases the difficulty of installing and debugging the circuit. At the same time, the conventional precharging scheme of the supercapacitor C does not consider the energy feedback of the supercapacitor C. When the supercapacitor C needs to be repaired and maintained, the power in the supercapacitor C needs to be completely discharged. The usual practice is to directly connect the supercapacitor C to the energy-consuming resistor and convert the electric energy of the supercapacitor C into heat energy through relay control. This scheme will cause a waste of electric energy in the supercapacitor C. There is no scheme that can simultaneously realize the precharging and energy feedback of the supercapacitor C.

[0005] In view of this, overcoming the technical defects of the above-mentioned prior art is an urgent problem to be solved in this technical field. Summary of the invention

[0006] In view of the above defects or improvement needs of the prior art, the present invention provides a non-switching bidirectional DC converter and its control process, which aims to solve the technical problem that the DC converter is currently unable to simultaneously realize the pre-charging of the supercapacitor C, the charging and discharging of the power battery B, and the energy feedback of the supercapacitor C.

[0007] To achieve the above object, according to one aspect of the present invention, a non-switching bidirectional DC converter is provided, the converter comprising:

[0008] Four transistors, four freewheeling diodes, power inductor L, two filter capacitors, power battery B, super capacitor C, switch S, DC bus DC+ / DC-, where:

[0009] The four transistors Q1 to Q4 form an H-bridge-like structure. The four freewheeling diodes are respectively connected in reverse parallel at both ends of the four transistors. The power inductor L is connected across the midpoint of the bridge arm composed of transistors Q1Q2 and the midpoint of the bridge arm composed of transistors Q3Q4. The power battery B and the filter capacitor C1 are connected in parallel at both ends of the transistors Q1Q2. The supercapacitor C, the filter capacitor C2 and the DC bus DC+ / DC- are connected in parallel between the transistors Q3Q4. A switch S is connected in series between the positive electrode of the supercapacitor C and the DC bus DC+.

[0010] As a further improvement and supplement to the above solution, the present invention also includes the following additional technical features.

[0011] Preferably, the non-switching bidirectional DC converter has four operating modes: forward Buck mode, forward Boost mode, reverse Buck mode and reverse Boost mode. The operating voltage of the supercapacitor C in the non-switching bidirectional DC converter is from a discharge threshold to an operating threshold.

[0012] Preferably, when the non-switching bidirectional DC converter operates in the forward Buck mode, the non-switching bidirectional DC converter is connected to the power battery B to pre-charge the voltage of the supercapacitor C from the discharge threshold to the first threshold; when the non-switching bidirectional DC converter operates in the forward Boost mode, the non-switching bidirectional DC converter is connected to the power battery B to pre-charge the voltage of the supercapacitor C from the first threshold to the operating threshold.

[0013] Preferably, when the non-switching bidirectional DC converter operates in the forward Buck mode, the non-switching bidirectional DC converter is connected to the power battery B to pre-charge the voltage of the supercapacitor C from the discharge threshold to the first threshold; when the non-switching bidirectional DC converter operates in the forward Boost mode, the non-switching bidirectional DC converter is connected to the power battery B to pre-charge the voltage of the supercapacitor C from the first threshold to the operating threshold.

[0014] Preferably, when the non-switching bidirectional DC converter operates in the reverse Buck step-down mode, the non-switching bidirectional DC converter is connected to the power battery B to discharge the voltage of the supercapacitor C from the operating threshold to the first threshold; when the non-switching bidirectional DC converter operates in the reverse Boost step-up mode, the non-switching bidirectional DC converter is connected to the power battery B to discharge the voltage of the supercapacitor C from the first threshold to the discharge threshold.

[0015] Preferably, when the switch S is closed and connected to the DC bus DC+, the non-switching bidirectional DC converter operates in the forward Boost mode to enable the power battery B to discharge to the bus; the non-switching bidirectional DC converter operates in the reverse Buck mode to enable the DC bus DC+ to charge the power battery B.

[0016] According to another aspect of the present invention, a control process of a non-switching bidirectional DC converter is provided, the process comprising:

[0017] Using the non-switching bidirectional DC converter described in the first aspect; the working process is divided into three stages: power-on pre-charging, connecting bus power supply, and power-off energy feeding;

[0018] In the power-on pre-charging stage, the non-switching bidirectional DC converter performs pre-charging and voltage detection of the supercapacitor C to determine whether the voltage of the supercapacitor C reaches a first threshold and an operating threshold. After reaching the operating threshold, the busbar connection power supply stage is entered;

[0019] During the bus power supply phase, the power battery B is controlled to discharge to the DC bus or the DC bus is controlled to charge to the power battery B according to requirements;

[0020] In the power-off energy feeding stage, the supercapacitor C is discharged and the voltage is detected to determine whether the voltage of the supercapacitor C reaches the discharge threshold. If so, the non-switching bidirectional DC converter ends its operation.

[0021] Preferably, the power-on pre-charging stage includes:

[0022] Connect power battery B, the non-switching bidirectional DC converter operates in the forward Buck step-down mode, and the voltage of the supercapacitor C is pre-charged from the discharge threshold to the first threshold by adjusting the duty cycle of Q1 within one cycle. The non-switching bidirectional DC converter switches to the forward Boost mode, Q1 is always on, and the voltage of the supercapacitor C is pre-charged from the first threshold to the working threshold by adjusting the duty cycle of Q4 within one cycle.

[0023] Preferably, the process of charging the power battery B from the DC bus includes:

[0024] The DC bus is equivalent to a voltage source, and the non-switching bidirectional DC converter operates in the reverse Buck step-down mode, adjusting the duty cycle of Q3 within a cycle to charge the power battery B.

[0025] Preferably, the process of discharging the power battery B to the DC bus includes:

[0026] The power battery B is equivalent to a voltage source, and the non-switching bidirectional DC converter works in the forward Boost mode. Q1 is always on, and the duty cycle of Q4 is adjusted within a cycle to control the power battery B to discharge to the DC bus.

[0027] Preferably, the power-off energy feeding stage includes:

[0028] The non-switching bidirectional DC converter operates in the reverse Buck step-down mode. By adjusting the duty cycle of Q3 within a cycle, the supercapacitor C charges the power battery B, and the voltage of the supercapacitor C drops from the working threshold to the first threshold; the non-switching bidirectional DC converter switches to the reverse Boost step-up mode, Q3 is always on, and by adjusting the duty cycle of Q2 within a cycle, the supercapacitor C charges the power battery B, and the voltage of the supercapacitor C drops from the first threshold to the discharge threshold.

[0029] In general, the above technical solution conceived by the present invention has the following beneficial effects compared with the prior art:

[0030] (1) High reliability: By reducing the use of relays, circuit reliability issues caused by relay failures are reduced. The design of the non-switching bidirectional DC converter (NSBC) reduces the use of switching devices, thereby improving the stability and reliability of the system.

[0031] (2) Cost-effectiveness: Due to the reduction in the use of relays, material costs and maintenance costs are reduced. At the same time, the circuit design is simplified, the difficulty of installation and debugging is reduced, and the overall cost is further reduced.

[0032] (3) High-efficiency energy conversion: The NSBC converter achieves efficient power conversion by precisely controlling the pre-charging and energy feedback processes. In the pre-charging stage, the efficient pre-charging of the supercapacitor C is achieved by rationally switching between the forward Buck step-down and forward Boost step-up operating modes. In the supercapacitor discharge stage, the reverse Buck step-down and reverse Boost step-up operating modes are also used to complete the charging of the supercapacitor to the power battery B, achieving energy feedback and reducing energy loss.

[0033] (4) Flexibility and adaptability: The design of the NSBC converter allows for flexible switching under different operating conditions to adapt to different application requirements. Whether it is the pre-charging of the supercapacitor C, the charging and discharging of the power battery B, or the energy feedback of the supercapacitor C, the NSBC converter can provide an effective solution.

[0034] (5) Easy maintenance: Due to the simplification of circuit design and the reduction of the number of relays, the system maintenance becomes easier. This not only reduces the maintenance cost, but also reduces the risk of system failure caused by improper maintenance.

[0035] (6) Environmentally friendly: By realizing energy feedback from the supercapacitor C, energy waste is reduced and energy utilization efficiency is improved. This design helps reduce energy consumption and environmental impact, and is in line with the concept of sustainable development.

[0036] (7) Innovation: The non-switching bidirectional DC converter topology and control method proposed in the present invention are innovations made to address the defects in the prior art. This innovation not only solves technical problems, but also provides new ideas for technological progress in related fields.

[0037] (8) Wide application: In addition to its application in the field of heavy-duty electric drive vehicles, the design of NSBC converter can also be extended to other occasions requiring efficient energy conversion and management, such as renewable energy systems, energy storage systems, etc., and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0039] Figure 1 This is a topological structure diagram of a non-switching bidirectional DC converter provided in the first embodiment;

[0040] Figure 2 is a control flow chart of a non-switching bidirectional DC converter provided in the first embodiment;

[0041] Figure 3 This is a schematic diagram of the operation of stage SPP-I-1 during the supercapacitor precharging process in this embodiment;

[0042] Figure 4 This is a schematic diagram of the operation of stage SPP-I-2 during the supercapacitor precharging process in this embodiment;

[0043] Figure 5This is a schematic diagram of the operation of stage SPP-II-1 during the supercapacitor precharging process in this embodiment;

[0044] Figure 6 This is a schematic diagram of the operation of stage SPP-II-2 during the supercapacitor precharging process in this embodiment;

[0045] Figure 7 1 is a schematic diagram of the operation of stage PBC-1 during the charging process of the power battery in this embodiment;

[0046] Figure 8 Schematic diagram of the operation of stage PBC-2 during the charging process of the power battery in this embodiment;

[0047] Fig. 9 Schematic diagram of the operation of stage PBD-1 in the discharge process of the power battery in this embodiment;

[0048] Fig.10 Schematic diagram of the operation of stage PBD-2 during the discharge process of the power battery in this embodiment;

[0049] Fig.11 This is a schematic diagram of the operation of stage SPF-I-1 in the process of electric energy feedback of the supercapacitor in this embodiment;

[0050] Fig.12 This is a schematic diagram of the operation of stage SPF-I-2 in the process of electric energy feedback of the supercapacitor in this embodiment;

[0051] Fig.13 This is a schematic diagram of the operation of stage SPF-II-1 in the process of electric energy feedback of the supercapacitor in this embodiment;

[0052] Fig.14 It is a schematic diagram of the operation of stage SPF-II-2 in the electric energy feedback process of the supercapacitor in this embodiment. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0054] The current supercapacitor precharging solution has the following problems:

[0055] 1. Too many relays, low circuit reliability, high cost, and difficulty in installation and debugging;

[0056] 2. The energy feedback of the supercapacitor is not realized, resulting in large energy loss.

[0057] Embodiment 1

[0058] This embodiment 1 provides a non-switching bidirectional DC converter, the topological structure of the converter is shown in FIG. Figure 1 As shown, the non-switching bidirectional DC converter comprises:

[0059] Four transistors, four freewheeling diodes, power inductor L, two filter capacitors, power battery B, super capacitor C, switch S, DC bus DC+ / DC-, where:

[0060] The four transistors Q1 to Q4 form a quasi-H bridge structure, the four freewheeling diodes are respectively connected in reverse parallel at both ends of the four transistors, the power inductor L is connected across the midpoint of the bridge arm composed of transistors Q1Q2 and the midpoint of the bridge arm composed of transistors Q3Q4, the power battery B and the filter capacitor C1 are connected in parallel at both ends of the transistors Q1Q2, the super capacitor C, the filter capacitor C2 and the DC bus DC+ / DC- are connected in parallel between the transistors Q3Q4, and a switch S is connected in series between the positive electrode of the super capacitor C and the DC bus DC+. The function of the parallel filter capacitors C1 and C2 in the circuit is to suppress the high-frequency AC component generated when the switch tube is working and improve the power quality in the circuit.

[0061] Common types of power electronic devices include MOS tubes, power transistors, and IGBTs. Their current carrying capacity and withstand voltage values ​​vary, and can be selected according to different application conditions. In this embodiment 1, IGBT is selected as the power electronic device. The freewheeling diode refers to a diode connected in reverse parallel at both ends of the IGBT module.

[0062] The non-switching bidirectional DC converter provided in the first embodiment can realize the following three functions:

[0063] (1) Precharging of supercapacitor C (supercapacitor precharging, referred to as SPP);

[0064] (2) The busbar charges the power battery B (powerbattery charging, referred to as PBC) and the power battery B discharges the power battery B to the busbar (powerbattery discharging, referred to as PBD);

[0065] (3) Discharge of supercapacitor C (supercapacitor feedback, SPF for short).

[0066] In the first embodiment, the operating voltage of the power battery B is 780-820V. It is connected to the bus through NSBC to supply power to or charge the bus. The voltage variation range of the supercapacitor C is 0-900V. It is directly connected in parallel with the bus. The DC bus is mainly powered by the engine-generator set to stabilize its voltage at 900V. The first threshold is set to 800V and the discharge threshold is set to 0V.

[0067] When the non-switching bidirectional DC converter is working, it mainly switches between three working conditions: supercapacitor C pre-charging, power battery B connected to bus power supply, and supercapacitor C discharging. The above three working conditions are introduced below:

[0068] (1) Pre-charging of supercapacitor C

[0069] The pre-charging of supercapacitor C includes two stages, SPP-I and SPP-II. When the system starts working, the DC bus voltage is the working threshold, and the voltage of supercapacitor C is 0V. If supercapacitor C is directly connected to the bus at this time, the working threshold voltage directly charges supercapacitor C, which will cause excessive charging current. Therefore, it is necessary to connect power battery B and make the NSBC converter work in the forward Buck step-down mode to pre-charge the voltage of supercapacitor C from 0V to the first threshold. This process is the SPP-I stage. Then the NSBC converter needs to be switched to the Boost step-up mode to pre-charge the voltage of supercapacitor C from the first threshold to the working threshold, so that it can be directly connected to the working threshold DC bus. This process is the SPP-II stage.

[0070] (2) Power battery B is connected to the busbar for power supply

[0071] When the system is working normally, the battery needs to be charged and discharged according to actual needs. The specific steps are as follows:

[0072] When the battery needs to be charged, the NSBC converter operates in the reverse Buck buck mode, and the working threshold DC bus charges the power battery B through Buck conversion (the converter operates in Buck buck mode);

[0073] When the battery needs to be discharged, the NSBC converter operates in the forward Boost mode, and the battery voltage is used to power the DC bus through Boost conversion (the converter operates in the Boost mode).

[0074] (3) Discharging of supercapacitor C

[0075] The discharge of supercapacitor C includes two stages, SPF-I and SPF-II. When the supercapacitor C needs to be inspected or maintained, the switch S between the supercapacitor C and the DC bus needs to be disconnected and all the electrical energy in the supercapacitor C needs to be discharged. Since the supercapacitor C is directly connected to the DC bus, the voltage is the working threshold, and the voltage of the power battery B is the first threshold. If the supercapacitor C directly charges the power battery B at this time, it will cause the charging current to be too large. Therefore, the supercapacitor C needs to be connected to the NSBC converter and made to work in the reverse Buck step-down mode to charge the power battery B. This process is the SPF-I stage. Then, since the supercapacitor C is continuously discharged, the voltage is lower than the first threshold and the power battery B cannot be charged. Therefore, the NSBC converter needs to be switched to the reverse Boost step-up mode, so that the supercapacitor C can continue to charge the power battery B, exhaust the electrical energy of the supercapacitor C, and complete the energy feedback of the supercapacitor C. This process is the SPF-II stage.

[0076] In combination with the embodiment of the present invention, there is also a preferred implementation scheme. Specifically, the non-switching bidirectional DC converter has four working modes: forward Buck buck mode, forward Boost boost mode, reverse Buck buck mode, and reverse Boost boost mode. The working voltage of the supercapacitor C in the non-switching bidirectional DC converter is from the discharge threshold to the working threshold.

[0077] In combination with the embodiment of the present invention, there is also a preferred implementation scheme. Specifically, when the non-switching bidirectional DC converter operates in the forward Buck step-down mode, the non-switching bidirectional DC converter is connected to the power battery B to pre-charge the voltage of the supercapacitor C from the discharge threshold to the first threshold; when the non-switching bidirectional DC converter operates in the forward Boost step-up mode, the non-switching bidirectional DC converter is connected to the power battery B to pre-charge the voltage of the supercapacitor C from the first threshold to the operating threshold.

[0078] When the NSBC converter operates in the forward Buck mode and is connected to the power battery B, the voltage of the supercapacitor C is pre-charged from the discharge threshold to the first threshold; when the NSBC converter switches to the forward Boost mode, the voltage of the supercapacitor C is pre-charged from the first threshold to the operating threshold.

[0079] In combination with the embodiment of the present invention, there is also a preferred implementation scheme. Specifically, when the non-switching bidirectional DC converter operates in the reverse Buck step-down mode, the non-switching bidirectional DC converter is connected to the power battery B to discharge the voltage of the supercapacitor C from the operating threshold to the first threshold; when the non-switching bidirectional DC converter operates in the reverse Boost step-up mode, the non-switching bidirectional DC converter is connected to the power battery B to discharge the voltage of the supercapacitor C from the first threshold to the discharge threshold.

[0080] When the NSBC converter operates in the reverse Buck mode, the supercapacitor C charges the power battery B, and the voltage of the supercapacitor C drops from the operating threshold to the first threshold; when the NSBC converter operates in the reverse Boost mode, the supercapacitor C charges the power battery B, and the voltage of the supercapacitor C drops from the first threshold to the discharge threshold.

[0081] In combination with the embodiment of the present invention, there is also a preferred implementation scheme. Specifically, when the switch S is closed and connected to the DC bus DC+, the non-switching bidirectional DC converter operates in the forward Boost mode to enable the power battery B to discharge to the bus; the non-switching bidirectional DC converter operates in the reverse Buck mode to enable the DC bus DC+ to charge the power battery B.

[0082] The use of the non-switching bidirectional DC converter provided in the first embodiment not only improves the reliability of the circuit, reduces the cost of the circuit, and reduces the difficulty of installing and debugging the circuit, but also realizes the energy feedback of the supercapacitor.

[0083] Embodiment 2:

[0084] This embodiment 2 provides a control process of a non-switching bidirectional DC converter. The process is as follows: Figure 2 As shown, the following steps are included:

[0085] Using the non-switching bidirectional DC converter in the first embodiment;

[0086] The non-switching bidirectional DC converter first performs pre-charging and voltage detection of the supercapacitor C to determine whether the voltage of the supercapacitor C reaches the first threshold and the working threshold; after reaching the working threshold, it enters the bus connection power supply stage, and controls the power battery B to discharge to the bus or charge from the bus according to requirements. When maintenance or shutdown is required, it enters the power-off energy feeding stage, discharges the supercapacitor C and detects the voltage to determine whether the voltage of the supercapacitor C reaches the discharge threshold. If so, the non-switching bidirectional DC converter ends its operation.

[0087] When judging whether the voltage of the supercapacitor C reaches the first threshold, if the voltage of the supercapacitor C reaches the first threshold, the SPP-II stage is entered to continue judging whether the voltage of the supercapacitor C reaches the working threshold. If the voltage of the supercapacitor C does not reach the first threshold, the SPP-I stage is entered, and then the voltage detection of the supercapacitor C is continued. When judging whether the voltage of the supercapacitor C reaches the working threshold, if so, the charge and discharge control of the power battery B is performed. If not, the SPP-II stage is re-entered, and then it is judged again whether the voltage of the supercapacitor C reaches the working threshold.

[0088] After the charge and discharge control of power battery B, determine whether power battery B needs to be charged. If so, enter the PBC stage, and then go through the charge and discharge control of power battery B again. If not, determine whether power battery B needs to be discharged. If power battery B needs to be discharged, enter the PBD stage, and then go through the charge and discharge control of power battery B again. If power battery B does not need to be discharged, determine whether supercapacitor C can feed back electric energy. If supercapacitor C can feed back electric energy, perform supercapacitor C voltage detection. If supercapacitor C cannot feed back electric energy, return to the charge and discharge control of power battery B again.

[0089] Both the power battery and the supercapacitor play a role in stabilizing the bus voltage. When the bus voltage increases, the supercapacitor reacts quickly and absorbs electric energy from the bus first. If the bus voltage continues to increase, the power battery is charged. When the bus voltage decreases, the supercapacitor reacts quickly and discharges to the bus first. If the bus voltage continues to decrease, the power battery is discharged. The specific process control is performed by the control module.

[0090] During the voltage detection of the supercapacitor C, if the voltage of the supercapacitor C is less than the first threshold, the SPF-II stage is entered; if the voltage of the supercapacitor C is greater than the first threshold, the SPF-I stage is entered, and the process returns to the voltage detection of the supercapacitor C. After entering the SPF-II stage, it is continued to determine whether the voltage of the supercapacitor C is less than or equal to the discharge threshold. If so, the non-switching bidirectional DC converter ends its operation; if not, it returns to the SPF-II stage, and then it is continued to determine whether the voltage of the supercapacitor C is greater than the discharge threshold.

[0091] In combination with the embodiment of the present invention, there is also a preferred implementation scheme, specifically, as follows Figures 3 to 6 As shown, the power-on pre-charging stage includes:

[0092] Connect power battery B, the non-switching bidirectional DC converter operates in the forward Buck step-down mode, and the voltage of the supercapacitor C is pre-charged from the discharge threshold to the first threshold by adjusting the duty cycle of Q1 within one cycle. The non-switching bidirectional DC converter switches to the forward Boost mode, Q1 is always on, and the voltage of the supercapacitor C is pre-charged from the first threshold to the working threshold by adjusting the duty cycle of Q4 within one cycle.

[0093] When power battery B is used and the NSBC converter operates in the forward Buck mode, the voltage of the supercapacitor C is pre-charged from 0V to the first threshold by adjusting the duty cycle of Q1 within one cycle. When power battery B is used and the NSBC converter operates in the forward Boost mode, Q1 is always on, and the voltage of the supercapacitor C is pre-charged from the first threshold to the operating threshold by adjusting the duty cycle of Q4 within one cycle.

[0094] When using power battery B and the NSBC converter works in the forward Buck mode, Q1 is turned on, Q2, Q3, and Q4 are turned off, and the current flows out of power battery B, passes through the turned-on Q1, inductor L, diode D3, and supercapacitor C, and then returns to power battery B to charge inductor L. Then Q1 is turned off, inductor L is used as an energy source, and the current flows through D3, supercapacitor C, diode D2, and finally returns to inductor L;

[0095] When power battery B is used and the NSBC converter works in the forward Boost mode, Q1 and Q4 are turned on, Q2 and Q3 are turned off, and the current flows out of power battery B, passes through the turned-on Q1, inductor L and turned-on Q4, and then returns to power battery B to charge inductor L. Then Q4 is disconnected, and power battery B and inductor L are used as energy sources together. The current flows through Q1, inductor L, diode D3, supercapacitor C, and finally returns to power battery B.

[0096] The pre-charging of the supercapacitor C includes the SPP-I stage and SPP-II. In the SPP-I stage, the power battery B is used and the NSBC converter works in the forward Buck mode to pre-charge the voltage of the supercapacitor C from 0V to the first threshold. The process can be divided into two stages SPP-I-1 and SPP-I-2. Figure 3 and Figure 4 In the SPP-II stage, the power battery B is used, and the NSBC converter works in the forward Boost mode to precharge the voltage of the supercapacitor C from the first threshold to the working threshold. The process can be divided into two stages, SPP-II-1 and SPP-II-2, as shown in Figure 5 and Figure 6 shown.

[0097] like Figure 3As shown, in stage SPP-I-1, Q1 is turned on, Q2, Q3, and Q4 are turned off, and the current flows out of power battery B, passes through the turned-on Q1, inductor L, diode D3, and supercapacitor C, and then returns to power battery B. This process charges the inductor. Figure 4 As shown, on the basis of stage SPP-I-1, stage SPP-I-2 disconnects Q1, and the inductor L is used as an energy source, and the current flows through D3, supercapacitor C, diode D2, and finally returns to the inductor L. By adjusting the duty cycle of Q1 within a cycle, the switching between stage SPP-I-1 and stage SPP-I-2 is controlled to realize the function of the Buck step-down circuit, and pre-charge the voltage of the supercapacitor C from 0V to the first threshold.

[0098] like Figure 5 As shown, in stage SPP-II-1, Q1 and Q4 are turned on, Q2 and Q3 are turned off, and the current flows out of power battery B, passes through the turned-on Q1, inductor L and the turned-on Q4, and then returns to power battery B. This process charges the inductor. Figure 6 As shown, on the basis of stage SPP-II-1, stage SPP-II-2 disconnects Q4, and the power battery B and the inductor L are used together as energy sources, and the current flows through Q1, the inductor L, the diode D3, the super capacitor C, and finally returns to the power battery B. By adjusting the duty cycle of Q4 within a cycle, the switching between stage SPP-II-1 and stage SPP-II-2 is controlled to realize the function of the Boost circuit, and the voltage of the super capacitor C is pre-charged from the first threshold to the working threshold, and then the super capacitor C is directly connected to the DC bus by closing the switch S.

[0099] In combination with the embodiment of the present invention, there is also a preferred implementation scheme, specifically, as follows Figures 7 to 10 As shown, the process of charging the power battery B from the DC bus includes:

[0100] The DC bus is equivalent to a voltage source, and the non-switching bidirectional DC converter operates in the reverse Buck step-down mode, adjusting the duty cycle of Q3 within a cycle to charge the power battery B.

[0101] The DC bus is equivalent to a voltage source, and the NSBC converter works in the reverse Buck step-down mode to charge the power battery B, adjusts the duty cycle of Q4 within a cycle, and charges the power battery B through Buck conversion of the DC bus voltage.

[0102] The cycle is the time for each circuit control, and the duty cycle is the ratio of the time the switch is turned on in one control cycle to the time of the entire cycle.

[0103] The DC bus is equivalent to a voltage source, which charges the power battery B through Buck conversion. Q1, Q2, and Q4 are turned off, and Q3 is turned on. The current flows out of the DC bus, passes through the turned-on Q3, inductor L, diode D1, and power battery B, and then returns to the DC bus to charge the inductor L. Then Q3 is disconnected. The inductor L acts as an energy source, and the current flows through the diode D1, power battery B, diode D4, and finally returns to the inductor L.

[0104] The charging process of power battery B can be divided into two stages: PBC-1 and PBC-2. The DC bus is equivalent to a voltage source, and the power battery B is charged through Buck conversion. Figure 7 and Figure 8 shown.

[0105] like Figure 7 As shown, in stage PBC-1, Q1, Q2, and Q4 are turned off, Q3 is turned on, and the current flows out of the DC bus, passes through the turned-on Q3, inductor L, diode D1, and power battery B, and then returns to the DC bus. This process charges the inductor L. Figure 8 As shown, on the basis of stage PBC-1, stage PBC-2 disconnects Q3, and inductor L is used as an energy source. The current flows through diode D1, power battery B, diode D4, and finally returns to inductor L. By adjusting the duty cycle of Q4 within a cycle, the switching between stage PBC-1 and stage PBC-2 is controlled to realize the function of the Buck step-down circuit, and the voltage of the DC bus is charged to power battery B through Buck conversion.

[0106] In combination with the embodiment of the present invention, there is also a preferred implementation scheme, specifically, as follows Figures 9 and 10 As shown, the process of discharging the power battery B to the DC bus includes:

[0107] The power battery B is equivalent to a voltage source, and the non-switching bidirectional DC converter works in the forward Boost mode. Q1 is always on, and the duty cycle of Q4 is adjusted within a cycle to control the power battery B to discharge to the DC bus.

[0108] The power battery B is equivalent to a voltage source, and the NSBC converter works in the forward Boost mode to discharge to the DC bus. Q1 is always on, and the duty cycle of Q4 is adjusted within a cycle to discharge the voltage of the power battery B to the DC bus through Boost conversion.

[0109] When discharging, the power battery is equivalent to a voltage source, and when charging, the DC bus is equivalent to a voltage source, and the current flows in the circuit in the opposite direction.

[0110] The power battery B is equivalent to a voltage source, which discharges the DC bus through Boost conversion. Q2 and Q3 are turned off, Q1 and Q4 are turned on, and the current flows out of the power battery B, passes through the turned-on Q1, inductor L, and turned-on Q4, and then returns to the power battery B to charge the inductor L. Then Q4 is disconnected, and the power battery B and the inductor L are used as energy sources together. The current flows through Q1, inductor L, diode D3, DC bus, and finally returns to the power battery B.

[0111] The discharge process of power battery B can be divided into two stages: PBD-1 and PBD-2. Power battery B is equivalent to a voltage source and discharges to the DC bus through Boost conversion.

[0112] like Fig. 9 As shown, in stage PBD-1, Q2 and Q3 are turned off, Q1 and Q4 are turned on, and the current flows out of the power battery B, passes through the turned-on Q1, the inductor L, the turned-on Q4, and then returns to the power battery B. This process charges the inductor L. Fig.10 As shown, on the basis of stage PBD-1, stage PBD-2 disconnects Q4, and the power battery B and inductor L are used as energy sources. The current flows through Q1, inductor L, diode D3, DC bus, and finally returns to the power battery B. By adjusting the duty cycle of Q4 within a cycle, the switching of stage PBD-1 and stage PBD-2 is controlled to realize the function of the Boost boost circuit, and the voltage of the power battery B is discharged to the DC bus through Boost conversion.

[0113] In combination with the embodiment of the present invention, there is also a preferred implementation scheme, specifically, as follows Figures 11 to 14 As shown, the power-off energy feeding stage includes:

[0114] The non-switching bidirectional DC converter operates in the reverse Buck step-down mode. By adjusting the duty cycle of Q3 within a cycle, the supercapacitor C charges the power battery B, and the voltage of the supercapacitor C drops from the working threshold to the first threshold; the non-switching bidirectional DC converter switches to the reverse Boost step-up mode, Q3 is always on, and by adjusting the duty cycle of Q2 within a cycle, the supercapacitor C charges the power battery B, and the voltage of the supercapacitor C drops from the first threshold to the discharge threshold.

[0115] By adjusting the duty cycle of Q3 within a cycle, the supercapacitor C charges the power battery B, and the voltage of the supercapacitor C drops from the working threshold to the first threshold; by adjusting the duty cycle of Q2 within a cycle, the supercapacitor C charges the power battery B, and the voltage of the supercapacitor C drops from the first threshold to the discharge threshold.

[0116] like Fig.11As shown, the supercapacitor C is used to charge the power battery B through Buck conversion. Q3 is turned on, Q1, Q2, and Q4 are turned off, and the current flows out of the supercapacitor C, passes through the turned-on Q3, inductor L and diode D1, and power battery B, and then returns to the supercapacitor C to charge the inductor. Q3 is then disconnected, and the inductor L is used as an energy source. The current flows through D1, power battery B, diode D4, and finally returns to the inductor L.

[0117] like Fig.12 As shown, the supercapacitor C is used to charge the power battery B through the Boost conversion, Q2 and Q3 are turned on, Q1 and Q4 are turned off, and the current flows out of the supercapacitor C, passes through the turned-on Q3, the inductor L and the turned-on Q2, and then returns to the supercapacitor C to charge the inductor. Then Q2 is disconnected, and the supercapacitor C and the inductor L are used as energy sources together. The current flows through Q3, the inductor L, and the power battery B of D1, and finally returns to the supercapacitor C.

[0118] The power feedback of supercapacitor C includes SPF-I stage and SPF-II stage. In SPF-I stage, supercapacitor C is used to charge power battery B through Buck conversion, and the process can be divided into two stages SPF-I-1 and SPF-I-2. In SPF-II stage, supercapacitor C is used to charge power battery B through Boost conversion, and the process can be divided into two stages SPF-I-1 and SPF-I-2.

[0119] like Fig.11 As shown, in stage SPF-I-1, Q3 is turned on, Q1, Q2, and Q4 are turned off, and the current flows out of the supercapacitor C, passes through the turned-on Q3, the inductor L, the diode D1, the power battery B, and then returns to the supercapacitor C. This process charges the inductor. Fig.12 As shown, in stage SPF-I-2, based on stage SPF-I-1, Q3 is disconnected, inductor L is used as an energy source, and current flows through D1, power battery B, diode D4, and finally returns to inductor L. By adjusting the duty cycle of Q3 within a cycle, the switching between stage SPF-I-1 and stage SPF-I-2 is controlled to realize the Buck step-down conversion function, and supercapacitor C charges power battery B, and the voltage drops from the working threshold to the first threshold.

[0120] like Fig.13 As shown, in stage SPF-II-1, Q2 and Q3 are turned on, Q1 and Q4 are turned off, and the current flows out of the supercapacitor C, passes through the turned-on Q3, the inductor L and the turned-on Q2, and then returns to the supercapacitor C. This process charges the inductor. Fig.14As shown, on the basis of stage SPF-II-1, stage SPF-II-2 disconnects Q2, and supercapacitor C and inductor L are used as energy sources together. The current flows through Q3, inductor L, D1 power battery B, and finally returns to supercapacitor C. By adjusting the duty cycle of Q2 within a cycle, the switching between stage SPF-II-1 and stage SPF-II-2 is controlled to realize the Boost conversion function, supercapacitor C charges power battery B, and the voltage drops from the first threshold to the discharge threshold, completing the energy feedback of supercapacitor C.

[0121] This embodiment aims at the pre-charging problem of the supercapacitor C mounted on the DC bus of a heavy-loaded electric-drive vehicle, provides a non-switching bidirectional DC-DC converter (NSBC) topology structure applied to the pre-charging and energy feedback of the supercapacitor C, designs a supercapacitor C pre-charging and energy feedback control method based on the NSPC converter, and the designed NSBC converter can realize the pre-charging of the supercapacitor C, the charging and discharging of the power battery B, and the electric energy feedback of the supercapacitor C by adjusting the working conditions. Compared with the existing pre-charging scheme of the supercapacitor C mounted on the DC bus of a heavy-loaded electric-drive vehicle, this embodiment reduces the number of relays, the size of the device, and the manufacturing and maintenance costs, while realizing the electric energy feedback of the supercapacitor C and improving the utilization rate of electric energy.

[0122] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A non-switching bidirectional DC converter, characterized in that: The converter comprises: Four transistors, four freewheeling diodes, power inductor L, two filter capacitors, power battery B, super capacitor C, switch S, DC bus DC+ / DC-, where: The four transistors Q1 to Q4 form an H-bridge-like structure. The four freewheeling diodes are respectively connected in reverse parallel at both ends of the four transistors. The power inductor L is connected across the midpoint of the bridge arm composed of transistors Q1Q2 and the midpoint of the bridge arm composed of transistors Q3Q4. The power battery B and the filter capacitor C1 are connected in parallel at both ends of the transistors Q1Q2. The supercapacitor C, the filter capacitor C2 and the DC bus DC+ / DC- are connected in parallel between the transistors Q3Q4. A switch S is connected in series between the positive electrode of the supercapacitor C and the DC bus DC+.

2. The non-switching bidirectional DC converter according to claim 1, characterized in that: The non-switching bidirectional DC converter has four working modes: forward Buck mode, forward Boost mode, reverse Buck mode and reverse Boost mode. The working voltage of the super capacitor C in the non-switching bidirectional DC converter is from a discharge threshold to a working threshold.

3. The non-switching bidirectional DC converter according to claim 1, characterized in that: When the non-switching bidirectional DC converter operates in the forward Buck mode, the non-switching bidirectional DC converter is connected to the power battery B to pre-charge the voltage of the supercapacitor C from the discharge threshold to the first threshold; when the non-switching bidirectional DC converter operates in the forward Boost mode, the non-switching bidirectional DC converter is connected to the power battery B to pre-charge the voltage of the supercapacitor C from the first threshold to the operating threshold.

4. The non-switching bidirectional DC converter according to claim 1, characterized in that: When the non-switching bidirectional DC converter operates in the reverse Buck mode, the non-switching bidirectional DC converter is connected to the power battery B to discharge the voltage of the supercapacitor C from the operating threshold to the first threshold; when the non-switching bidirectional DC converter operates in the reverse Boost mode, the non-switching bidirectional DC converter is connected to the power battery B to discharge the voltage of the supercapacitor C from the first threshold to the discharge threshold.

5. The non-switching bidirectional DC converter according to claim 1, characterized in that: When the switch S is closed and connected to the DC bus DC+, the non-switching bidirectional DC converter operates in the forward Boost mode to enable the power battery B to discharge to the bus; the non-switching bidirectional DC converter operates in the reverse Buck mode to enable the DC bus DC+ to charge the power battery B.

6. A control process of a non-switching bidirectional DC converter, characterized in that: The process includes: A non-switching bidirectional DC converter according to any one of claims 1 to 5 is used; the working process is divided into three stages: power-on pre-charging, bus connection power supply, and power-off energy feeding; In the power-on pre-charging stage, the non-switching bidirectional DC converter performs pre-charging and voltage detection of the supercapacitor C to determine whether the voltage of the supercapacitor C reaches a first threshold and an operating threshold. After reaching the operating threshold, the busbar connection power supply stage is entered; During the bus power supply phase, the power battery B is controlled to discharge to the DC bus or the DC bus is controlled to charge to the power battery B according to requirements; In the power-off energy feeding stage, the supercapacitor C is discharged and the voltage is detected to determine whether the voltage of the supercapacitor C reaches the discharge threshold. If so, the non-switching bidirectional DC converter ends its operation.

7. The control process of the non-switching bidirectional DC converter according to claim 6, characterized in that: The power-on pre-charging stage includes: Connect power battery B, the non-switching bidirectional DC converter operates in the forward Buck step-down mode, and the voltage of the supercapacitor C is pre-charged from the discharge threshold to the first threshold by adjusting the duty cycle of Q1 within one cycle. The non-switching bidirectional DC converter switches to the forward Boost mode, Q1 is always on, and the voltage of the supercapacitor C is pre-charged from the first threshold to the working threshold by adjusting the duty cycle of Q4 within one cycle.

8. The control process of the non-switching bidirectional DC converter according to claim 6, characterized in that: The process of charging the power battery B from the DC bus includes: The DC bus is equivalent to a voltage source, and the non-switching bidirectional DC converter operates in the reverse Buck step-down mode, adjusting the duty cycle of Q3 within a cycle to charge the power battery B.

9. The control process of the non-switching bidirectional DC converter according to claim 6, characterized in that: The process of discharging the power battery B to the DC bus includes: The power battery B is equivalent to a voltage source, and the non-switching bidirectional DC converter works in the forward Boost mode. Q1 is always on, and the duty cycle of Q4 is adjusted within a cycle to control the power battery B to discharge to the DC bus.

10. The control process of the non-switching bidirectional DC converter according to claim 6, characterized in that: The power-off energy feeding stage includes: The non-switching bidirectional DC converter operates in the reverse Buck step-down mode. By adjusting the duty cycle of Q3 within a cycle, the supercapacitor C charges the power battery B, and the voltage of the supercapacitor C drops from the working threshold to the first threshold; the non-switching bidirectional DC converter switches to the reverse Boost step-up mode, Q3 is always on, and by adjusting the duty cycle of Q2 within a cycle, the supercapacitor C charges the power battery B, and the voltage of the supercapacitor C drops from the first threshold to the discharge threshold.

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