Wide gain-based bidirectional DC / DC converter and method

Abstract

Disclosed in the present invention are a wide gain-based bidirectional direct-current (DC) / DC converter and a method. The converter comprises a thin-film capacitor (FC), a power battery, and a novel w

Description

Wide gain based bidirectional DC / DC converter and method TECHNICAL FIELD

[0001] The present application belongs to the technical field of power electronics, and relates to a wide gain bidirectional DC / DC converter topology and control method for a hybrid power supply system of an electric vehicle. BACKGROUND

[0002] With the gradual shift of the global energy structure to renewable energy, the transportation industry has ushered in large-scale electrification, and electric vehicles, as an important part of renewable energy integration, have developed rapidly. However, the low power density, poor low-temperature performance, and slow charging speed of power batteries have seriously restricted the further promotion of electric vehicles.

[0003] A hybrid power supply system composed of supercapacitors and power batteries can effectively utilize the braking energy generated during the driving of an electric vehicle, effectively increasing the driving range of the electric vehicle (up to 40%) without increasing the capacity of the power battery. However, the single voltage of the supercapacitor is low (only 2.7V), and it needs to be connected in series to form a high-voltage supercapacitor group to be used in the hybrid power supply system. However, the supercapacitor has poor voltage resistance, and a voltage equalization circuit must be configured to avoid voltage overshoot caused by poor consistency. This not only increases the control difficulty and cost of the system, but also limits the further increase of the working voltage of the supercapacitor group, which cannot fully play the role of the supercapacitor. In addition, the problem of large internal resistance makes the supercapacitor have very limited ability to resist voltage and current pulsation. Under complex urban conditions, large fluctuations in voltage and current will cause the supercapacitor to heat up severely, which not only reduces the service life of the supercapacitor, but also reduces the system efficiency. At the same time, the maximum working temperature of the supercapacitor is only 70℃, which reduces the reliability of the hybrid power supply system under complex conditions. In contrast, the single voltage of the thin film capacitor can be up to 1200V, which can be matched with the high-voltage DC bus without being connected in series. The small equivalent internal resistance and the maximum working temperature of 125℃ make it have very high ability to withstand pulsating voltage and current. Compared with the supercapacitor, the higher power density of the thin film capacitor can more effectively absorb or release short-time high power, further improving the utilization rate of braking energy of electric vehicles. Therefore, the hybrid power supply system based on the thin film capacitor has a simpler system structure, higher efficiency and reliability.

[0004] Although the thin film capacitor has the above advantages, its energy density is much smaller than that of the super capacitor, and the unit capacitance cost is higher than that of the super capacitor. Therefore, the hybrid power system can only use a small capacity thin film capacitor as a braking energy absorption unit, which reduces the utilization rate of vehicle braking energy. To solve the above problems, the thin film capacitor can be fully utilized to withstand large pulsating current. By expanding the operating voltage range of the thin film capacitor to absorb and release more energy, the utilization rate of braking energy is improved. Therefore, the hybrid power storage system based on the thin film capacitor needs a wide voltage gain bidirectional DC-DC converter to connect the thin film capacitor and the DC bus of the motor drive system.

[0005] The isolation type DC / DC converter based on isolation type converters such as forward converter, flyback converter, half / full bridge converter has high voltage gain. However, the use of transformers makes such converters have the disadvantages of high cost, large current ripple, high voltage stress of power devices, etc. Cascaded bidirectional DC / DC converters are constructed by connecting converters with the same structure in series, but the voltage gain and the number of devices are proportional. More devices make it difficult to further improve the power density and volume of the converter. The multi-level type and coupled inductor type have a wide voltage gain range, but the former has many power devices and the voltage stress is difficult to balance. The latter not only reduces the efficiency of the system due to the leakage inductance of the coupled inductor, but also causes a large turn-off voltage of the power device. Although active (passive) clamping circuits can alleviate the above problems, they increase the complexity of the circuit. Bidirectional converters based on switched capacitor and switched inductor technology can improve the voltage gain of the converter while simplifying the structure of the converter, so such converters with high power density and high efficiency are very suitable for electric vehicle hybrid power systems. However, the voltage gain of such bidirectional DC / DC converters is limited, which cannot fully utilize the advantages of thin film capacitors as energy storage devices. The inherent common problems such as large current ripple and input and output not common ground will reduce the efficiency and reliability of the hybrid power system. The above analysis shows that it is of great significance and value to study bidirectional converters with wide voltage gain, low voltage stress, low current ripple, and absolute common ground on the input and output sides, which can improve the performance of the thin film capacitor-based hybrid power system. SUMMARY

[0006] In view of the problems existing in the prior art bidirectional DC / DC converter, the application provides a wide-gain bidirectional DC / DC converter and a method. The converter has a wide voltage gain range of 1 / 29-29, significantly expands the working voltage range of the film capacitor, and effectively improves the energy density of the film capacitor. The converter has a common ground at the input and output, effectively suppresses electromagnetic interference, and improves the reliability of the converter. Thanks to the unique structure of the converter, the voltage stress of the switch tube and the capacitor is significantly reduced, further reducing the cost of the converter and improving the efficiency of the converter. In summary, the new wide-gain bidirectional DC / DC converter can effectively improve the braking energy recovery effect of the electric vehicle when used in the film capacitor hybrid power system.

[0007] The application is realized by adopting the following technical scheme: a wide-gain bidirectional DC / DC converter, comprising a film capacitor (FC), a power battery (Power Bat), and a new wide-gain bidirectional DC / DC converter; the low-voltage side is the film capacitor (FC), and the high-voltage side is a DC bus capacitor C H Parallelly connected with a motor inverter DC bus; when the vehicle works in a deceleration or braking state, the new wide-gain bidirectional DC / DC converter stores the braking energy of the high-voltage DC bus side in the film capacitor (FC); when the vehicle works in an acceleration state, the new wide-gain bidirectional DC / DC converter sends the energy of the film capacitor (FC) to the DC bus capacitor C H Parallelly connected with a power battery (Power Bat) for driving the motor to improve the dynamic performance.

[0008] Further, the new wide-gain bidirectional DC / DC converter is composed of an active LC module 1, an active LC module 2, a module energy controlled unit, an energy storage inductor, and a high-voltage side DC bus capacitor C H The energy storage inductor is a third inductor (L3);

[0009] The active LC module 1 is composed of a first inductor (L1), a first capacitor (C1), and a first switch tube (S1). The branch of the first inductor (L1) and the first switch tube (S1) in series is connected with the first capacitor (C1) in parallel. The active LC module 2 is composed of a second inductor (L2), a second capacitor (C2), and a second switch tube (S2) in series. The module energy controlled unit is composed of a third switch tube (S3) and a fourth switch tube (S4). One end of the third inductor (L3) is connected with the positive pole of the film capacitor (FC). The other end of the third inductor (L3) is connected with the drain of the second switch tube (S2), the source of the third switch tube (S3), and the positive pole of the second capacitor (C2). The negative pole of the second capacitor (C2) is connected with the source of the fourth switch tube (S4) and the other end of the second inductor (L2). One end of the first inductor (L1) is connected with the drain of the third switch tube (S3) and the negative pole of the first capacitor (C1). The other end of the first inductor (L1) is connected with the source of the first switch tube (S1) and the drain of the fourth switch tube (S4). The positive pole of the first capacitor (C1), the drain of the first switch tube (S1), and the positive pole of the high-voltage side DC bus capacitor C H are simultaneously connected with the positive pole of the DC bus. The source of the second switch tube (S2), one end of the second inductor (L2), and the negative pole of the high-voltage side DC bus capacitor C H are simultaneously connected with the negative pole of the film capacitor (FC).

[0010] Further, the new wide-gain bidirectional DC / DC converter works in the step-down mode according to the working state of the electric vehicle, the high-voltage DC bus capacitor voltage (U H ):

[0011] The vehicle state control signal K is 0, the film capacitor voltage (U L ) is lower than the set upper limit value (U Set1 ), and the state of charge of the power battery is lower than the set value (SOC * S When the electric vehicle brakes, the feedback energy causes the DC bus capacitor voltage (U H ) to rise, the energy distribution controller controls the new bidirectional DC / DC converter to work in the step-down mode, the film capacitor (FC) absorbs the braking energy until it is higher than the set upper limit value (U Set1 ). Then, the energy distribution controller controls the DC bus capacitor voltage (U H ) to release energy to the power battery until it reaches the set value of the state of charge of the power battery (SOC * S );When the state of charge of the power battery (SOC) and the film capacitor voltage (U L) reach the set value, the braking energy is consumed by the energy consumption resistor, and damage of the converter caused by excessively high DC bus voltage is avoided. Further, the novel wide-gain bidirectional DC / DC converter works in the boost mode according to the working state of the electric vehicle, the high-voltage DC bus capacitor voltage U H works in the boost mode:

[0012] The vehicle state control signal K is 1, and the film capacitor voltage (U L ) is higher than the set lower limit value (U Set2 ), the instantaneous high-power demand causes the DC bus capacitor voltage (U H ) to drop, the energy distribution controller controls the novel bidirectional DC / DC converter to work in the boost mode, the film capacitor (FC) releases energy to the DC bus capacitor (U H ), and the power battery jointly supplies power to the motor until the film capacitor voltage (U L ) is lower than the set lower limit value (U Set2 ), and then the energy distribution controller controls the power battery (Power Bat) to supply energy to the motor alone.

[0013] The method based on the wide-gain bidirectional DC / DC converter comprises the following steps:

[0014] The working process of the controller in the boost mode is as follows: first, the bus voltage error is obtained through the PI-A controller to obtain the low-voltage side average reference current I L3 * ; further, the current is adjusted to i L according to the instantaneous voltage u L3 * As the control target of the converter, the current error is adjusted through the PI-B controller to adjust the duty cycle of the power device, so that the bus voltage is stabilized and the energy stored in the film capacitor is released; when the film capacitor voltage is lower than the set minimum voltage, the novel wide-gain bidirectional DC / DC converter stops working; the PI-A controller and the PI-B controller are both PI controllers;

[0015] The working process of the controller in the boost mode is similar to that in the boost mode, and the difference is that when the film capacitor cannot completely absorb the braking energy of the electric vehicle in emergency braking, the converter should set i L3 * at this time, the power battery absorbs part of the braking energy to avoid overvoltage of the film capacitor and overcurrent of the power device, which causes damage.

[0016] Further, the gain expansion process of the novel wide-gain bidirectional DC / DC converter in the boost mode is as follows:

[0017] In the step-down mode, the bidirectional DC / DC converter alternately works in state one and state two, in the state one, the high-voltage side part of the energy is transmitted to the film capacitor (FC), the rest of the energy is transmitted to the first inductor (L1), the third inductor (L3), the first capacitor (C1), the second capacitor (C2) and the second inductor (L2), part of the energy flows to the third inductor (L3), and the rest of the energy is transmitted to the film capacitor (FC); in the state two, the first capacitor (C1) and the first inductor (L1) transmit energy to the second capacitor (C2) and the second inductor (L2), and the film capacitor (FC) is only provided with energy by the third inductor (L3), and at this time, the energy of the third inductor (L3) is far less than the energy provided by the high-voltage side, so the step-down gain is further reduced.

[0018] Further, the new wide gain bidirectional DC / DC converter has the following characteristics in the step-up mode:

[0019] In the step-up mode, the bidirectional DC / DC converter alternately works in state one and state two, in the state one, the energy of the third inductor (L3) is only provided by the film capacitor (FC), and the first capacitor (C1) and the first inductor (L1) are in series and are jointly provided with energy by the second capacitor (C2) and the second inductor (L2); in the state two, the film capacitor (FC), the third inductor (L3), the first capacitor (C1) and the first inductor (L1) are in series and transmit energy to the high-voltage side DC bus; the high-voltage side voltage is the sum of the voltages of the film capacitor (FC), the third inductor (L3) and the first capacitor (C1), which significantly improves the gain.

[0020] The new bidirectional DC / DC converter has the following characteristics: in the step-up (step-down) mode, the active LC module works in the series (parallel) charging and parallel (series) discharging mode, which significantly improves (reduces) the voltage of the capacitor in the module; the module energy control unit controls the energy transmission between the film capacitor (high-voltage DC bus) and the active LC module, and finally obtains the wide voltage gain characteristic of the converter through the series connection of the inductor and the capacitor of the LC module, which greatly improves the braking energy reuse effect of the low-voltage side film capacitor; the active LC module and the third inductor (L3) further expand the gain range of the converter and maintain the continuous current on the low-voltage side; in the invention, the voltage stress of all devices except the power switch tube S1 is less than the DC bus voltage, which reduces the cost of the power converter and improves the efficiency and safety of the hybrid power system.

[0021] In the new bidirectional DC / DC converter, the low-voltage side is a film capacitor (FC), and the high-voltage side DC bus capacitor C HConnect the motor inverter. When the electric vehicle brakes or decelerates, the converter reduces the high-voltage energy obtained by the motor brake to the voltage and stores it in the low-voltage side film capacitor (FC) until the FC reaches the maximum energy storage capacity, effectively avoiding the large current charging of the power battery, improving the reliability and service life of the battery; Under the conditions of acceleration, climbing and the like, the film capacitor energy is boosted by the new bidirectional DC / DC converter and delivered to the high-voltage side capacitor C H , the power battery provides energy to the motor, provides the power performance of the electric vehicle, and avoids large current discharge of the power battery. This mode until the motor reaches the predetermined working state or the FC reaches the minimum energy storage requirement.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] 1. The maximum voltage gain of the bidirectional DC / DC converter proposed in the present application is 29, and the minimum voltage gain is 1 / 29, which greatly widens the working voltage range of the film capacitor and significantly improves the brake energy utilization rate and power density of the electric vehicle.

[0024] 2. The bidirectional DC / DC converter proposed in the present application corresponds to a duty cycle in the range of 0.2-0.8, avoids working in the critical region of the converter, and effectively improves the reliability of the bidirectional DC / DC converter.

[0025] 3. The high-voltage side and the low-voltage side of the bidirectional DC / DC converter proposed in the present application are directly grounded, which avoids the EMI electromagnetic interference problem caused by the separation of the high-voltage side and the low-voltage side, and further improves the reliability of the converter working.

[0026] 4. The maximum capacitor stress of the bidirectional DC / DC converter proposed in the present application is 16U H / 29, and the maximum voltage stress of most power devices is lower than U H , which not only reduces the cost of the converter, but also improves the working efficiency of the converter. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a circuit diagram of the wide-gain bidirectional DC / DC converter of the present application.

[0028] Figure 2 is a schematic diagram of the hybrid power supply system of the electric vehicle in the present application.

[0029] Figure 3 is a schematic diagram of the driving signal of each power device in the step-down mode of the present application.

[0030] Figure 4 is a schematic diagram of the power flow in state one in the step-down mode of the present application.

[0031] Figure 5 is a schematic diagram of the power flow in state two in the step-down mode of the present application.

[0032] Fig. 6 is a schematic diagram of driving signals of power devices in a boost mode of the application.

[0033] Fig. 7 is a schematic diagram of power flow in state one in a boost mode of the application.

[0034] Fig. 8 is a schematic diagram of power flow in state two in a boost mode of the application.

[0035] Fig. 9 is a flow chart of control of the converter in a boost mode and a buck mode of the application.

[0036] Fig. 10 is a schematic diagram of a bidirectional control strategy of the converter of the application. DETAILED DESCRIPTION

[0037] The wide-gain zero-current ripple bidirectional DC / DC converter of the application is described in detail below in combination with the accompanying drawings and examples.

[0038] The application provides a novel bidirectional wide-gain DC / DC converter for a thin-film capacitor hybrid power system, which comprises an active LC module 1, an active LC module 2, a module energy controlled unit, a third inductor (L3) and a high-voltage side DC bus capacitor C H The active LC module achieves high voltage gain and provides bidirectional power flow capability by changing the series-parallel connection of LC. The module energy controlled unit controls the energy transfer between the thin-film capacitor (high-voltage DC bus), the active LC module 1 and the active LC module 2 by changing the connection form of the active LC module 1 and the active LC module 2, thereby achieving flexible and controllable voltage gain. The third inductor (L3) further improves the voltage gain in combination with the active LC module and maintains low-voltage side current continuity.

[0039] The active LC module 1 is composed of a first inductor (L1), a first capacitor (C1) and a first switch tube (S1). The active LC module 2 is composed of a second inductor (L2), a second capacitor (C2) and a second switch tube (S2). The module energy controlled unit is composed of a third switch tube (S3) and a fourth switch tube (S4). One end of the third inductor (L3) is connected to the positive electrode of the thin-film capacitor (FC). The source electrode of the second switch tube (S2), one end of the second inductor (L2) and the high-voltage side DC bus capacitor C HThe negative electrode of the third inductor (L3) is connected with the drain electrode of the second switch tube (S2), the source electrode of the third switch tube (S3) and the positive electrode of the second capacitor (C2); the negative electrode of the second capacitor (C2) is connected with the source electrode of the fourth switch tube (S4) and the other end of the second inductor (L2); one end of the first inductor (L1) is connected with the drain electrode of the third switch tube (S3) and the negative electrode of the first capacitor (C1); the other end of the first inductor (L1) is connected with the source electrode of the first switch tube (S1) and the drain electrode of the fourth switch tube (S4); the positive electrode of the first capacitor (C1) and the drain electrode of the first switch tube (S1) are connected with the high-voltage side DC bus capacitor C H The positive electrode of the third inductor (L3) is connected with the drain electrode of the second switch tube (S2), the source electrode of the third switch tube (S3) and the positive electrode of the second capacitor (C2); the negative electrode of the second capacitor (C2) is connected with the source electrode of the fourth switch tube (S4) and the other end of the second inductor (L2); one end of the first inductor (L1) is connected with the drain electrode of the third switch tube (S3) and the negative electrode of the first capacitor (C1); the other end of the first inductor (L1) is connected with the source electrode of the first switch tube (S1) and the drain electrode of the fourth switch tube (S4); the positive electrode of the first capacitor (C1) and the drain electrode of the first switch tube (S1) are connected with the high-voltage side DC bus capacitor C

[0040] According to the FC energy storage, the power battery SOC and the electric vehicle operating state, the novel wide gain bidirectional DC / DC converter works in boost and buck modes. The buck mode corresponds to the electric vehicle braking deceleration condition, and the bidirectional DC / DC converter of the application stores the braking energy transmitted to the high-voltage DC bus in the low-voltage side FC after being stepped down; the boost mode corresponds to the electric vehicle acceleration or starting condition, and the bidirectional DC / DC converter of the application sends the energy in the low-voltage side FC to the high-voltage side DC bus for driving motor after being boosted.

[0041] Analysis of the working principle of the novel wide gain zero-current ripple bidirectional DC / DC converter

[0042] In the buck mode, the power device control signals are as shown in Figure 3: the control signals of the first switch tube (S1) and the third switch tube (S3) are the same, the control signals of the second switch tube (S2) and the fourth switch tube (S4) are the same, and the above-mentioned signals are complementary to each other. The working state of the bidirectional DC / DC converter in the buck mode is shown in Figures 4 and 5.

[0043] Fig. 4 is the voltage reduction mode state one: the first switch tube (S1) and the third switch tube (S3) are turned on, and the second switch tube (S2) and the fourth switch tube (S4) are turned off. The electric vehicle braking energy is fed back to the high-voltage DC bus side, and the braking energy further flows through two paths: one is stored in the film capacitor (FC) through the first capacitor (C1), the third switch tube (S3), and the third inductor (L3); the other is stored in the film capacitor (FC) through the first switch tube (S1), the first inductor (L1), the third switch tube (S3), and the third inductor (L3). In the above process, the film capacitor (FC) and the first capacitor (C1) voltage rises, the first inductor (L1) and the third inductor (L3) current rises, and the stored energy increases. At the same time, the second capacitor (C2) and the second inductor (L2) transfer energy to the third inductor (L3) and the low-voltage side film capacitor (FC), and the film capacitor (FC) voltage further increases. In this mode, because the first inductor (L1), the third inductor (L3) voltage, and the first capacitor (C1) voltage are in the same direction as the film capacitor (FC), the converter obtains a larger voltage reduction voltage gain.

[0044] Fig. 5 is the voltage reduction mode state two: the first switch tube (S1) and the third switch tube (S3) are turned off, and the second switch tube (S2) and the fourth switch tube (S4) are turned on. The first capacitor (C1) and the first inductor (L1) are connected in series through the fourth switch tube (S4) to release energy to the second capacitor (C2), the DC bus capacitor (C H ), and the second inductor (L2), the second capacitor (C2) voltage rises, the second inductor (L2) current rises, and the above devices store electric vehicle braking energy; because the third inductor (L3) stores energy in the previous stage, in this state, the third inductor (L3) further releases electric vehicle braking energy to the low-voltage side film capacitor (FC) through the second switch tube (S2).

[0045] In the boost mode, the power device control signal is as shown in Fig. 6: the first switch tube (S1) and the third switch tube (S3) control signals are the same, the second switch tube (S2) and the fourth switch tube (S4) control signals are the same, and the above signals complement each other. The working principle of the bidirectional DC / DC converter in the boost state is shown in Fig. 7 and Fig. 8.

[0046] Fig. 7 is the boost mode state one: the first switch tube (S1) and the third switch tube (S3) are turned off, and the second switch tube (S2) and the fourth switch tube (S4) are turned on. The low-voltage side film capacitor (FC) releases energy to the third inductor (L3) through the second switch tube (S2), and the third inductor (L3) current increases and stores energy; the second capacitor (C2) is connected in parallel with the second inductor (L2) through the second switch tube (S2) and releases energy to the high-voltage side DC bus capacitor C H, the fourth switch tube (S4) releases energy to the first capacitor (C1) and the first inductor (L1), the voltage across the first capacitor (C1) rises, and the current of the first inductor (L1) rises, in this mode, the motor is powered by the high-voltage side DC bus capacitor C H Energy is provided.

[0047] Fig. 8 is the boost mode state two: the first switch tube (S1) and the third switch tube (S3) are both turned on, and the second switch tube (S2) and the fourth switch tube (S4) are both turned off. Energy flows through two channels: one is transmitted to the high-voltage DC bus through the third inductor (L3), the third switch tube (S3), and the first capacitor (C1); the other is transmitted to the high-voltage DC bus through the third inductor (L3), the third switch tube (S3), the first inductor (L1), and the first switch tube (S1). At the same time, the low-voltage side thin film capacitor (FC) and the third inductor (L3) are connected in series to deliver energy to the second capacitor (C2) and the second inductor (L2). In this mode, because the voltages of the first inductor (L1), the third inductor (L3), and the first capacitor (C1) are in the same direction as the thin film capacitor (FC), the converter obtains a larger boost voltage gain.

[0048] Voltage stress analysis of the new wide-gain zero-current ripple bidirectional DC / DC converter

[0049] The new wide-gain zero-current ripple bidirectional DC / DC converter significantly reduces the voltage stress of power devices and the voltage stress of capacitors. According to the power flow path of the bidirectional DC / DC converter in the boost mode shown in Fig. 4, the relationship equations between the inductor voltage and the capacitor voltage are written as follows:

[0050] According to the power flow path of the bidirectional DC / DC converter in the boost mode shown in Fig. 5, the relationship equations between the inductor voltage and the capacitor voltage are written as follows:

[0051] According to the inductor volt-second balance principle, the maximum voltage stresses of the first capacitor (C1) and the second capacitor (C2) are 24 / 29 and 16 / 29 of the high-voltage side DC bus voltage, respectively, and the calculation results of the capacitor voltage stress in the boost mode are the same.

[0052] According to the KVL equation group of the bidirectional DC / DC converter in the step-down mode in FIGS. 4 and 5, the maximum voltage stresses of the second switch (S2) and the third switch (S1) are 20 / 29 of the DC bus voltage of the high-voltage side, and the maximum voltage stresses of the first switch (S1) and the fourth switch (S4) are 45 / 29 and 25 / 29 of the DC bus voltage of the high-voltage side, respectively. The voltage stress results of the power devices in the step-up mode are the same. The above analysis shows that the voltage stresses of the capacitors and the power devices of the new bidirectional DC / DC converter are significantly reduced. Therefore, the new wide-gain zero-current ripple bidirectional DC / DC converter realizes low voltage stress operation of the power devices in the step-up and step-down modes, and improves the reliability of the hybrid power system.

[0053] Energy control strategy of the new wide-gain zero-current ripple bidirectional DC / DC converter

[0054] The new bidirectional DC / DC converter is controlled according to the vehicle state signal K, the DC bus capacitor voltage (U H ) of the high-voltage side, the working voltage (U L ) of the low-voltage side thin film capacitor, and the state of charge (SOC) related parameters of the power battery.

[0055] When the electric vehicle is decelerating or braking:

[0056] The vehicle state control signal K is 0, the thin film capacitor voltage (U L ) is lower than the set upper limit value (U Set1 ), and the state of charge of the power battery is lower than the set value (SOC * S When the electric vehicle is braking, the feedback energy causes the DC bus capacitor voltage (U H ) to rise, the energy distribution controller controls the new bidirectional DC / DC converter to work in the step-down mode, and the thin film capacitor (FC) absorbs the braking energy until it is higher than the set upper limit value (U Set1 ). Then, the energy distribution controller controls the DC bus capacitor voltage (U H ) to release energy to the power battery until it reaches the set value of the state of charge (SOC * S ) of the power battery. When the state of charge (SOC) of the power battery and the thin film capacitor voltage (U LAll values ​​reach the set value, and the braking energy is consumed by the energy-dissipating resistor, preventing damage to the converter due to excessive DC bus voltage. The above process demonstrates that the hybrid power system based on thin-film capacitors can effectively absorb the braking energy of electric vehicles and prevent the power battery from operating in a high-current charging mode. During this process, energy release should be controlled according to the set value of the high-voltage side DC bus voltage to avoid undervoltage operation of the bus.

[0057] Electric vehicle acceleration or hill climbing status:

[0058] The vehicle status control signal K corresponds to 1, and the film capacitor voltage (U) L ) higher than the set lower limit (U) Set2 A sudden surge in power demand can cause a drop in DC bus capacitor voltage (U). H The voltage drops, and the energy distribution controller controls the new bidirectional DC / DC converter to operate in boost mode, with the film capacitor (FC) supplying power to the DC bus capacitor (U). H The energy is released and, together with the power battery, supplies power to the motor until the thin-film capacitor voltage (U) is reached. L ) lower than the set lower limit (U) Set2 Then, the energy distribution controller controls the power battery to supply energy to the motor independently. The above process demonstrates that a hybrid power system based on thin-film capacitors can effectively meet instantaneous high-power demands and prevent the power battery from operating in a high-current discharge mode. During this process, the release of energy by the thin-film capacitor (FC) should be controlled according to the high-voltage side DC bus voltage setting to avoid overvoltage operation of the bus.

[0059] Figure 10 illustrates the novel bidirectional DC / DC converter control strategy proposed in this invention. Its goal is to stabilize the DC bus voltage while simultaneously achieving efficient utilization of braking energy. In the figure, U... H * U L * These are the reference values ​​for bus voltage and film capacitor voltage, respectively, U H and u L These are the detected values ​​of bus voltage and film capacitor voltage, i L3 * This is the reference value for the output current of the thin-film capacitor.

[0060] In boost mode, the controller's workflow is as follows: First, based on the bus voltage error, the average reference current I on the low-voltage side is obtained via the PI-A controller. L3 * Furthermore, this current is based on the instantaneous voltage u of the thin-film capacitor. L Adjust to i L3 *As the converter control target, the current error is adjusted by PI-B to the duty cycle of the power device, to realize bus voltage stability and thin film capacitor energy release. When the thin film capacitor voltage is lower than the set minimum voltage, the converter stops working. The controller working process in the step-down mode is similar to that in the step-up mode, with the difference that when the emergency braking thin film capacitor cannot completely absorb the braking energy of the electric vehicle, the converter should set i L3 * At the same time, the power battery absorbs part of the braking energy to avoid overvoltage of the thin film capacitor and overcurrent of the power device, which can cause damage.

[0061] The new wide-gain bidirectional DC / DC converter has the following advantages: the high-voltage gain characteristic expands the voltage variation range of the thin film capacitor, improves the power density of the thin film capacitor, and can effectively absorb and release energy according to the running state of the electric vehicle, thereby improving the utilization rate of braking energy; the low-voltage stress of the device can effectively reduce the energy loss during the working of the converter, and on the basis of improving the efficiency of the hybrid energy system, further improve the reliability and service life of the converter; the power converter also has the advantages of fewer power devices and absolute common ground on the input and output sides, which further improves the reliability of the system while improving the power density of the system. Therefore, the new bidirectional DC / DC converter for the electric vehicle hybrid power supply system can effectively improve the reliability of the system and the utilization rate of braking energy, and can significantly improve the driving range of the electric vehicle under the existing power battery technology conditions.

Claims

1. A wide gain bidirectional DC / DC converter based on, characterized by, Including thin film capacitor (FC), power battery (Power Bat), new wide gain bidirectional DC / DC converter; low voltage side is thin film capacitor (FC), high voltage side DC bus capacitor C H Parallel with motor inverter DC bus; the vehicle works in deceleration or braking state, the new wide gain bidirectional DC / DC converter stores the braking energy of high voltage DC bus side in thin film capacitor (FC); when the vehicle works in acceleration state, the new wide gain bidirectional DC / DC converter sends the energy of thin film capacitor (FC) to DC bus C after voltage boosting H Parallel with power battery (Power Bat) for driving motor to use, to improve its dynamic performance.

2. The wide gain bidirectional DC / DC converter of claim 1, wherein, The novel wide-gain bidirectional DC / DC converter comprises an active LC module 1, an active LC module 2, a module energy controlled unit, an energy storage inductor and a high-voltage side DC bus capacitor C H The novel wide-gain bidirectional DC / DC converter comprises an active LC module 1, an active LC module 2, a module energy controlled unit, an energy storage inductor and a high-voltage side DC bus capacitor C The active LC module 1 is composed of a first inductor (L1), a first capacitor (C1) and a first switch tube (S1), and the branch of the first inductor (L1) and the first switch tube (S1) in series is connected with the first capacitor (C1) in parallel; the active LC module 2 is composed of a second inductor (L2), a second capacitor (C2) and a second switch tube (S2) in series; the module energy controlled unit is composed of a third switch tube (S3) and a fourth switch tube (S4); one end of the third inductor (L3) is connected with the positive pole of the film capacitor (FC); the other end of the third inductor (L3) is connected with the drain of the second switch tube (S2), the source of the third switch tube (S3) and the positive pole of the second capacitor (C2); the negative pole of the second capacitor (C2) is connected with the source of the fourth switch tube (S4) and the other end of the second inductor (L2); one end of the first inductor (L1) is connected with the drain of the third switch tube (S3) and the negative pole of the first capacitor (C1); the other end of the first inductor (L1) is connected with the source of the first switch tube (S1) and the drain of the fourth switch tube (S4); the positive pole of the first capacitor (C1), the drain of the first switch tube (S1) and the positive pole of the high-voltage side DC bus capacitor C H are simultaneously connected with the positive pole of the DC bus; the source of the second switch tube (S2), one end of the second inductor (L2) and the negative pole of the high-voltage side DC bus capacitor C H are simultaneously connected with the negative pole of the film capacitor (FC).

3. The wide gain bidirectional DC / DC converter of claim 2, wherein, The novel wide-gain bidirectional DC / DC converter is based on the operating status of the electric vehicle and the high-voltage DC bus capacitor voltage (U). H Operating in buck mode: Vehicle status control signal K is 0, film capacitor voltage (U) L ) lower than the set upper limit (U) Set1 The state of charge (SOC) of the power battery is lower than the set value. * S When an electric vehicle brakes, the feedback energy causes the DC bus capacitor voltage (U) to increase. H As the voltage rises, the energy distribution controller controls the new bidirectional DC / DC converter to operate in buck mode, and the thin-film capacitor (FC) absorbs braking energy until it exceeds the set upper limit (U). Set1 Then, the energy distribution controller controls the DC bus capacitor voltage (U). H Energy is released to the power battery until it reaches the power battery's state of charge (SOC) setpoint. * S When the state of charge (SOC) of the power battery and the voltage of the thin-film capacitor (U) L All values ​​reach the set value, and the braking energy is consumed by the energy-consuming resistor to avoid damage to the converter due to excessive DC bus voltage.

4. The wide gain bidirectional DC / DC converter of claim 2, wherein, The novel wide-gain bidirectional DC / DC converter works in the boost mode according to the working state of the electric vehicle, the high-voltage DC bus capacitor voltage U H The working state control signal K corresponds to 1, and the film capacitor voltage (U L ) is higher than the set lower limit value (U Set2 ), the instantaneous high-power demand causes the DC bus capacitor voltage (U H ) to drop, the energy distribution controller controls the novel bidirectional DC / DC converter to work in the boost mode, the film capacitor (FC) releases energy to the DC bus capacitor (U H ), and the power battery jointly supplies power to the motor until the film capacitor voltage (U L ) is lower than the set lower limit value (U Set2 ); then, the energy distribution controller controls the power battery (Power Bat) to supply energy to the motor alone.

5. The method of claim 1, wherein the wide gain bidirectional DC / DC converter is based on a topology of: Comprising the following steps: The controller working flow in the boost mode is as follows: firstly, the low-voltage side average reference current I L3 * is obtained according to the bus voltage error through a PI-A controller L ; further, the current is adjusted to i L3 * As the converter control target, the current error is adjusted through a PI-B controller to adjust the duty ratio of the power device, so as to realize the bus voltage stabilization and the release of the energy stored in the film capacitor; when the film capacitor voltage is lower than the set minimum voltage, the novel wide-gain bidirectional DC / DC converter stops working; the PI-A controller and the PI-B controller are both PI controllers. The controller working flow in the voltage reduction mode is similar to that in the voltage increase mode, except that when the emergency braking film capacitor cannot completely absorb the braking energy of the electric vehicle, the converter should set i L3 * At the same time, the power battery absorbs part of the braking energy to avoid overvoltage of the film capacitor and overcurrent of the power device, which may cause damage.

6. The method of claim 5, wherein the wide gain bidirectional DC / DC converter is based on a topology of: The gain expansion process of the new wide-gain bidirectional DC / DC converter in buck mode: In buck mode, the bidirectional DC / DC converter alternately works in state one and state two. In state one, part of the energy on the high-voltage side is transmitted to the film capacitor (FC), and the rest of the energy is transmitted to the first inductor (L1), the third inductor (L3), the first capacitor (C1), the second capacitor (C2), and the second inductor (L2). Part of the energy flows to the third inductor (L3), and the rest of the energy is transmitted to the film capacitor (FC). In state two, the first capacitor (C1) and the first inductor (L1) transmit energy to the second capacitor (C2) and the second inductor (L2), and the film capacitor (FC) is only powered by the third inductor (L3). At this time, the energy of the third inductor (L3) is much smaller than the energy provided by the high-voltage side, so the buck gain is further reduced.

7. The method of claim 5, wherein the wide gain bidirectional DC / DC converter is based on a half-bridge topology. The gain expansion process of the new wide-gain bidirectional DC / DC converter in boost mode: In boost mode, the bidirectional DC / DC converter alternately works in state one and state two. In state one, the energy of the third inductor (L3) is only provided by the film capacitor (FC), and the first capacitor (C1) and the first inductor (L1) are in series and are powered by the second capacitor (C2) and the second inductor (L2). In state two, the film capacitor (FC), the third inductor (L3), the first capacitor (C1), and the first inductor (L1) in series transmit energy to the high-voltage DC bus. The voltage on the high-voltage side is the sum of the voltages on the film capacitor (FC), the third inductor (L3), and the first capacitor (C1), which significantly improves the gain.

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