Bidirectional DC / DC converter based on wide gain and method

Abstract

The invention discloses a wide-gain-based bidirectional DC / DC converter and a method. The wide-gain-based bidirectional DC / DC converter comprises a thin-film capacitor (FC), a power Bat and a novel wide-gain bidirectional DC / DC converter, a low-voltage side is a thin-film capacitor (FC), and a high-voltage side direct-current bus capacitor CH is connected with a motor inverter direct-current bus in parallel; when a vehicle works in a decelerating or braking state, the novel wide-gain bidirectional DC / DC converter stores braking energy on a high-voltage direct-current bus side in a thin-film capacitor (FC); when the vehicle works in an acceleration state, the novel wide-gain bidirectional DC / DC converter boosts the energy of the thin-film capacitor (FC) and then sends the boosted energy to the DC bus CH, and the boosted energy is connected with the power Bat in parallel to be used by a driving motor, so that the dynamic performance of the power Bat is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics and relates to a wide-gain bidirectional DC / DC converter topology structure and a control method for a hybrid power system of an electric vehicle. Background Art

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

[0003] The hybrid power system composed of supercapacitors and power batteries can effectively utilize the braking energy generated during the driving of electric vehicles, and can effectively increase the mileage of electric vehicles (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 system. However, the supercapacitor has poor voltage resistance, and a voltage balancing circuit must be configured to avoid capacitor voltage overshoot caused by consistency differences. This not only increases the control difficulty and cost of the system, but also limits the further increase in the working voltage of the supercapacitor group, and cannot give full play to the role of the supercapacitor. In addition, the problem of large internal resistance makes the supercapacitor's ability to resist voltage and current pulsation very limited. Under complex urban working conditions, large-scale fluctuations in voltage and current will cause serious heating of the supercapacitor, which will not only reduce the service life of the supercapacitor, but also reduce the system efficiency. At the same time, the maximum operating temperature of the supercapacitor is only 70°C, which reduces the reliability of the hybrid power system under complex working conditions. In contrast, the voltage of a film capacitor can reach up to 1200V, and it can match the high-voltage DC bus without series connection. The smaller equivalent internal resistance and the maximum operating temperature of 125℃ make it extremely able to withstand pulsating voltage and current. Compared with supercapacitors, the higher power density can more effectively absorb or release short-term high power, further improving the utilization rate of electric vehicle braking energy. Therefore, the hybrid power system based on film capacitors has a simpler system structure, higher efficiency and reliability.

[0004] Although film capacitors have the above advantages, their energy density is much lower than that of supercapacitors, and their unit capacitance cost is higher than that of supercapacitors. Therefore, hybrid power systems can only use small-capacity film capacitors as braking energy absorption units, which reduces the utilization rate of vehicle braking energy. To solve the above problems, we can make full use of the fact that film capacitors can withstand large pulsating currents, expand the operating voltage range of film capacitors to absorb and release more energy, and improve the utilization rate of braking energy. Therefore, the hybrid power energy storage system based on film capacitors requires a wide voltage gain bidirectional DC-DC converter to connect the film capacitors with the DC bus of the motor drive system.

[0005] Isolated DC / DC converters based on isolated converters such as forward converters, flyback converters, and half (full) bridge converters have high voltage gain. However, the use of transformers makes such converters have disadvantages such as high cost, large current ripple, and high voltage stress of power devices. Cascaded bidirectional DC / DC converters are constructed based on converters of the same structure in series, but the voltage gain is proportional to the number of devices. More devices make it impossible to further improve the power density and volume of the converter. Multi-level and coupled inductor types have a wider voltage gain range, but the former has a large number of power devices and the voltage stress is difficult to balance. The latter not only reduces the efficiency of the system due to the coupled inductor leakage inductance, but also causes a large power device shutdown voltage. 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 simplify the converter structure while improving the converter voltage gain. Therefore, such converters with high power density and high efficiency are very suitable for hybrid power systems of electric vehicles. However, the voltage gain of such bidirectional DC / DC converters is limited, and the advantages of film capacitors as energy storage devices cannot be fully utilized. However, inherent common problems such as large current ripple and non-common grounding of input and output will reduce the efficiency and reliability of the hybrid power system. The above analysis shows that the research on bidirectional converters with wide voltage gain, low voltage stress, low current ripple and absolute common grounding of input and output sides is of great significance and value for improving the performance of hybrid power systems based on film capacitors. Summary of the invention

[0006] In view of the problems existing in the existing bidirectional DC / DC converters, the present invention proposes a bidirectional DC / DC converter and method based on wide gain. The converter has a wide voltage gain range of 1 / 29-29 times, which significantly expands the working voltage range of the film capacitor and effectively improves the energy density of the film capacitor. The input and output of the converter are commonly grounded, which effectively suppresses electromagnetic interference and improves the reliability of the converter. Thanks to the unique structure of the converter of the present invention, 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 proposed in the present invention is used in a film capacitor hybrid power supply system to effectively improve the braking energy recovery effect of electric vehicles.

[0007] The present invention adopts the following technical scheme to achieve the above-mentioned purpose: a wide-gain bidirectional DC / DC converter, including a film capacitor (FC), a power battery (Power Bat), and a novel wide-gain bidirectional DC / DC converter; the low-voltage side is a film capacitor (FC), and the high-voltage side DC bus capacitor C HThe novel wide-gain bidirectional DC / DC converter is connected in parallel with the motor inverter DC bus; when the vehicle is working in the deceleration or braking state, the novel wide-gain bidirectional DC / DC converter stores the braking energy on the high-voltage DC bus side in the film capacitor (FC); when the vehicle is working in the acceleration state, the novel wide-gain bidirectional DC / DC converter boosts the energy of the film capacitor (FC) and sends it to the DC bus C H , connected in parallel with the power battery (Power Bat) to drive the motor to improve its dynamic performance.

[0008] Furthermore, the novel 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), and the first inductor (L1) and the first switch tube (S1) are connected in series and then connected in parallel with the first capacitor (C1); the active LC module 2 is composed of a second inductor (L2), a second capacitor (C2), and a second switch tube (S2) connected 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 to the positive electrode of the film capacitor (FC); the other end of the third inductor (L3) is connected to the second The drain of the switch tube (S2), the source of the third switch tube (S3), and the positive electrode of the second capacitor (C2) are connected; the negative electrode of the second capacitor (C2) is connected to 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 to the drain 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 to the source of the first switch tube (S1) and the drain of the fourth switch tube (S4); the positive electrode of the first capacitor (C1), the drain of the first switch tube (S1), and the high-voltage side DC bus capacitor C H The positive electrode of the second switch tube (S2), one end of the second inductor (L2), and the high-voltage side DC bus capacitor C H The negative electrode of is also connected to the negative electrode of the film capacitor (FC).

[0010] Furthermore, the novel wide-gain bidirectional DC / DC converter is based on the working state of the electric vehicle, the high-voltage DC bus capacitor voltage (U H ) works in buck mode:

[0011] The vehicle status control signal K is 0, and the film capacitor voltage (U L ) is lower than the set upper limit (U Set1 ), the power battery state of charge is lower than the set value (SOC *S ); When the electric vehicle brakes, the feedback energy causes the DC bus capacitor voltage (U H ) increases, the energy distribution controller controls the new bidirectional DC / DC converter to work in the buck mode, and the film capacitor (FC) absorbs the braking energy until it exceeds the set upper limit (U Set1 ); Then, the energy distribution controller controls the DC bus capacitor voltage (U H ) releases energy to the power battery until it reaches the power battery state of charge setting value (SOC * S ); When the power battery state of charge (SOC) and the film capacitor voltage (U L ) reach the set value, the braking energy is consumed by the energy consumption resistor to avoid the DC bus voltage being too high and causing the converter to be damaged. Further, the novel wide gain bidirectional DC / DC converter is based on the working state of the electric vehicle, the high-voltage DC bus capacitor voltage U H Working in boost mode:

[0012] The vehicle status control signal K corresponds to 1, and the film capacitor voltage (U L ) is higher than the set lower limit (U Set2 ), the instantaneous high power demand will cause the DC bus capacitor voltage (U H ) decreases, the energy distribution controller controls the new bidirectional DC / DC converter to work in boost mode, and the film capacitor (FC) is supplied to the DC bus capacitor (U H ) releases energy and works with the power battery to supply power to the motor until the film capacitor voltage (U L ) is lower than the set lower limit (U Set2 ); then, the energy distribution controller controls the power battery (Power Bat) to provide energy to the motor alone.

[0013] A method based on a wide-gain bidirectional DC / DC converter of the present invention comprises the following steps:

[0014] The controller working process in boost mode is as follows: First, the average reference current I on the low voltage side is obtained through the PI-A controller according to the bus voltage error. L3 * ; Further, the current is based on the instantaneous voltage u of the film capacitor L Adjust to i L3 * As the control target of the converter, the current error adjusts the duty cycle of the power device through the PI-B controller to achieve bus voltage stability and release of 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 of the present invention stops working; the above-mentioned PI-A controller and PI-B controller are both PI controllers;

[0015] The controller working process in buck mode is similar to that in boost mode. The difference is that when the emergency brake film capacitor cannot fully absorb the braking energy of the electric vehicle, the converter should set i according to the film capacitor voltage and the rated working current of the power device. L3 * At the same time, the power battery absorbs part of the braking energy to prevent damage caused by overvoltage of the film capacitor and overcurrent of the power device.

[0016] Furthermore, the new wide-gain bidirectional DC / DC converter buck mode gain expansion process:

[0017] In the buck mode, the bidirectional DC / DC converter alternately operates 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 remaining energy is transmitted to the first inductor (L1), the third inductor (L3), and the first capacitor (C1). Part of the energy of the second capacitor (C2) and the second inductor (L2) flows to the third inductor (L3), and the remaining 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 provided with energy 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, thereby further reducing the buck gain.

[0018] Furthermore, the new wide-gain bidirectional DC / DC converter boost mode gain expansion process is as follows:

[0019] In boost mode, the bidirectional DC / DC converter alternately operates 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 connected in series and the second capacitor (C2) and the second inductor (L2) jointly provide energy; in state two, the film capacitor (FC), the third inductor (L3), the first capacitor (C1), and the first inductor (L1) are connected in series to 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 novel bidirectional DC / DC converter of the present invention has the following characteristics: in the boost (step-down) mode, the active LC module works in the series (parallel) charging and parallel (series) discharge mode, significantly increasing (reducing) the voltage of the capacitor in the module; the module energy controlled unit controls the energy transfer between the thin film capacitor (high-voltage DC bus) and the active LC module, and finally obtains the wide voltage gain characteristics of the converter through the series connection of the inductor and capacitor of the LC module, greatly improving the braking energy recycling effect of the thin film capacitor on the low-voltage side; the active LC module is combined with the third inductor (L3) to further expand the gain range of the converter and maintain the continuity of the current on the low-voltage side; in the invention, except for the power switch tube S1, the voltage stress of all devices 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 novel bidirectional DC / DC converter of the present invention, the low voltage side is a film capacitor (FC), and the high voltage side DC bus capacitor C H Connect the motor inverter. When the electric vehicle brakes or decelerates, the converter reduces the voltage of the high-voltage energy obtained by the motor braking and stores it in the low-voltage side film capacitor (FC) until the FC reaches the maximum energy storage capacity, effectively avoiding high-current charging of the power battery and improving battery reliability and service life; under conditions such as acceleration and climbing, the power required by the electric vehicle increases, and the energy of the film capacitor is boosted by the new bidirectional DC / DC converter and transmitted to the high-voltage side capacitor C H , combined with the power battery to provide energy to the motor, improve the power performance of the electric vehicle, and avoid high current discharge of the power battery. This mode lasts 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 invention has the following beneficial effects:

[0023] 1. The bidirectional DC / DC converter proposed in the present invention has a maximum voltage gain of 29 and a minimum voltage gain of 1 / 29, which greatly broadens the operating voltage range of the film capacitor and significantly improves the braking energy utilization rate and power density of electric vehicles.

[0024] 2. The corresponding duty cycle of the bidirectional DC / DC converter proposed in the present invention is in the range of 0.2-0.8, which avoids the converter from operating in the critical area 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 by the present invention directly share a common ground, thereby avoiding the EMI electromagnetic interference problem caused by the separation of the high-voltage and low-voltage sides, and further improving the reliability of the converter operation.

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

[0027] Attached Figure 1 4 is a circuit diagram of a wide-gain bidirectional DC / DC converter of the present invention.

[0028] Attached Figure 2 It is a schematic diagram of the hybrid power system of an electric vehicle in the present invention.

[0029] Attached Figure 3 It is a schematic diagram of driving signals of each power device in the buck mode of the present invention.

[0030] Attached Figure 4 FIG. 1 is a schematic diagram of power flow in the buck mode of the present invention.

[0031] Attached Figure 5 It is a schematic diagram of power flow in state 2 of the buck mode in the present invention.

[0032] Attached Figure 6 It is a schematic diagram of the driving signals of each power device in the boost mode of the present invention.

[0033] Attached Figure 7 FIG. 1 is a schematic diagram of power flow in the boost mode of the present invention.

[0034] Attached Figure 8 It is a schematic diagram of power flow in state 2 of the boost mode in the present invention.

[0035] Attached Fig. 9 This is a control flow chart of the converter boost and buck modes in the present invention.

[0036] Attached Fig.10 Schematic diagram of the bidirectional control strategy of the converter in the present invention. DETAILED DESCRIPTION

[0037] The specific implementation of the wide-gain zero-current-ripple bidirectional DC / DC converter proposed by the present invention is further described in detail below with reference to the accompanying drawings and examples.

[0038] The present invention proposes a novel bidirectional wide gain DC / DC converter for a film capacitor hybrid power system, comprising: 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 HThe active LC module achieves high voltage gain and provides bidirectional power flow capability by changing the LC series-parallel structure; the module energy controlled unit controls the energy transfer between the film capacitor (high-voltage DC bus) and the active LC module by changing the connection form of the active LC module 1 and module 2, achieving flexible and controllable voltage gain; the third inductor (L3) is combined with the active LC module to further improve the voltage gain and maintain the continuity of the low-voltage side current.

[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 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 H The negative electrode of the third inductor (L3) is connected to the negative electrode of the film capacitor (FC); the other end of the third inductor (L3) is connected to the drain of the second switch tube (S2), the source 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 to 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 to the drain 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 to the source of the first switch tube (S1) and the drain of the fourth switch tube (S4); the positive electrode of the first capacitor (C1), the drain of the first switch tube (S1), and the high-voltage side DC bus capacitor C H The positive pole of the DC bus is also connected to the positive pole of the DC bus.

[0040] According to the FC energy storage situation, the power battery SOC and the electric vehicle operation state, the novel wide-gain bidirectional DC / DC converter of the present invention works in two modes: boost and buck. The buck mode corresponds to the electric vehicle braking and deceleration condition. The bidirectional DC / DC converter of the present invention stores the braking energy transmitted to the high-voltage DC bus in the low-voltage side FC after voltage reduction. The boost mode corresponds to the electric vehicle acceleration or starting condition. The bidirectional DC / DC converter of the present invention boosts the energy in the low-voltage side FC and sends it to the high-voltage side DC bus for use by the drive motor.

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

[0042] In buck mode, the power device control signal is as follows Figure 3As shown: the first switch tube (S1) and the third switch tube (S3) have the same control signal, the second switch tube (S2) and the fourth switch tube (S4) have the same control signal, and the above signals act in a complementary manner. The bidirectional DC / DC converter works in the buck state as follows Figure 4 and Figure 5 shown.

[0043] Figure 4 The first state of the buck mode is as follows: 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 braking energy of the electric vehicle 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 voltage of the film capacitor (FC) and the first capacitor (C1) increases, the current of the first inductor (L1) and the third inductor (L3) increases, 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 voltage of the film capacitor (FC) further increases. In this mode, since the voltages of the first inductor (L1), the third inductor (L3), the first capacitor (C1) and the film capacitor (FC) are in the same direction, the converter obtains a larger step-down voltage gain.

[0044] Figure 5 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 and are connected to the second capacitor (C2) and the DC bus capacitor (C H ) and the second inductor (L2) release energy, the voltage of the second capacitor (C2) increases, the current of the second inductor (L2) increases, and the above-mentioned device stores the braking energy of the electric vehicle; because the third inductor (L3) stores energy in the previous stage, in this state, the third inductor (L3) further releases the braking energy of the electric vehicle to the low-voltage side film capacitor (FC) through the second switch tube (S2).

[0045] In boost mode, the power device control signal is as follows Figure 6 As shown: the first switch tube (S1) and the third switch tube (S3) have the same control signal, the second switch tube (S2) and the fourth switch tube (S4) have the same control signal, and the above signals act in a complementary manner. The working principle of the bidirectional DC / DC converter in the boost state is as follows: Figure 7 and Figure 8 shown.

[0046] Figure 7 In boost mode state 1: 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 current of the third inductor (L3) increases and stores energy; the second capacitor (C2) is connected in parallel with the second inductor (L2) through the second switch tube (S2) and 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) increases, and the current of the first inductor (L1) increases. In this mode, the motor is powered by the high-voltage side DC bus capacitor C H Provide energy.

[0047] Figure 8 The boost mode state 2 is as follows: 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 paths: 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 film capacitor (FC) and the third inductor (L3) are connected in series to transfer 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 film capacitor (FC), the converter obtains a larger boost voltage gain.

[0048] Voltage stress analysis of the novel wide gain zero current ripple bidirectional DC / DC converter described in the invention

[0049] The novel wide gain zero current ripple bidirectional DC / DC converter described in the present invention significantly reduces the voltage stress of power devices and the voltage stress of capacitors. Figure 4 The power flow path of the bidirectional DC / DC converter in buck mode is shown, and the relationship equations between the inductor voltage and the capacitor voltage are listed as follows:

[0050]

[0051] according to Figure 5 The power flow path of the bidirectional DC / DC converter in buck mode is shown, and the relationship equations between the inductor voltage and the capacitor voltage are listed as follows:

[0052]

[0053] According to the inductor volt-second balance principle, the maximum voltage stress 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. The capacitor voltage stress calculation results in the boost mode are the same.

[0054] according to Figure 4 , Figure 5 The KVL equations are written in the buck mode of the bidirectional DC / DC converter, and the maximum voltage stress of the second switch tube (S2) and the third switch tube (S1) is solved to be 20 / 29 of the high-voltage side DC bus voltage, and the maximum voltage stress of the first switch tube (S1) and the fourth switch tube (S4) is 45 / 29 and 25 / 29 of the high-voltage side DC bus voltage, respectively. The voltage stress of the power device calculated in the boost mode is the same. The above analysis shows that the capacitance and power device voltage stress of the new bidirectional DC / DC converter proposed in the present invention are significantly reduced. Therefore, the new wide gain zero current ripple bidirectional DC / DC converter described in the present invention can achieve low voltage stress operation of the power device in both boost and buck modes, and now improve the reliability of the hybrid power system.

[0055] Novel wide gain zero current ripple bidirectional DC / DC converter energy control strategy described in the invention

[0056] The novel bidirectional DC / DC converter is based on the vehicle status signal K, the high-voltage side DC bus capacitor voltage (U H ), low voltage side film capacitor working voltage (U L ) and power battery state of charge (SOC) related parameters control. The above parameters of the energy distribution controller control the converter working mode. The specific control process is as follows Fig. 9 As shown:

[0057] Electric vehicle deceleration or braking status:

[0058] The vehicle status control signal K is 0, and the film capacitor voltage (U L ) is lower than the set upper limit (U Set1 ), the power battery state of charge is lower than the set value (SOC * S When the electric vehicle brakes, the feedback energy causes the DC bus capacitor voltage (U H ) increases, the energy distribution controller controls the new bidirectional DC / DC converter to work in the buck mode, and the film capacitor (FC) absorbs the braking energy until it exceeds the set upper limit (U Set1 Then, the energy distribution controller controls the DC bus capacitor voltage (U H ) releases energy to the power battery until it reaches the power battery state of charge setting value (SOC * S). When the power battery state of charge (SOC) and the film capacitor voltage (U L ) reach the set value, and the energy consumption resistor consumes the braking energy to avoid the DC bus voltage being too high and causing damage to the converter. The above working process shows that the hybrid power system based on film capacitors can effectively absorb the braking energy of electric vehicles and avoid the power battery (Power Bat) working in a high current charging mode. In the above process, the energy release should be controlled according to the set value of the high-voltage side DC bus voltage to avoid bus undervoltage operation.

[0059] Electric vehicle acceleration or climbing state:

[0060] The vehicle status control signal K corresponds to 1, and the film capacitor voltage (U L ) is higher than the set lower limit (U Set2 The instantaneous high power demand will cause the DC bus capacitor voltage (U H ) decreases, the energy distribution controller controls the new bidirectional DC / DC converter to work in boost mode, and the film capacitor (FC) is supplied to the DC bus capacitor (U H ) releases energy and works with the power battery to supply power to the motor until the film capacitor voltage (U L ) is lower than the set lower limit (U Set2 ). Then, the energy distribution controller controls the power battery (Power Bat) to provide energy to the motor alone. The above working process shows that the hybrid power system based on film capacitors can effectively meet the instantaneous high power demand and avoid the power battery (Power Bat) working in a high current discharge mode. In the above process, the film capacitor (FC) should be controlled to release energy according to the set value of the high-voltage side DC bus voltage to avoid bus overvoltage operation.

[0061] Fig.10 This is a novel bidirectional DC / DC converter control strategy proposed in the present invention, which aims to control the DC bus voltage stability and realize efficient utilization of braking energy. H * , U L * are bus voltage and film capacitor voltage reference values, U H and u L is the detection value of bus voltage and film capacitor voltage, i L3 * It is the reference value of the output current of the film capacitor.

[0062] The controller working process in boost mode is as follows: First, the average reference current I on the low voltage side is obtained through the PI-A controller according to the bus voltage error. L3 * ; Further, the current is based on the instantaneous voltage u of the film capacitor L Adjust to iL3 * As the control target of the converter, the current error adjusts the duty cycle of the power device through PI-B to achieve bus voltage stability and release of energy stored in the film capacitor. When the film capacitor voltage is lower than the set minimum voltage, the converter of the present invention stops working. The controller working process in the buck mode is similar to that in the boost mode, except that when the emergency braking film capacitor cannot fully absorb the braking energy of the electric vehicle, the converter should set i according to the film capacitor voltage and the rated working current of the power device. L3 * At the same time, the power battery absorbs part of the braking energy to prevent damage caused by overvoltage of the film capacitor and overcurrent of the power device.

[0063] The novel wide-gain bidirectional DC / DC converter proposed in the present invention has the following advantages: the high voltage gain characteristic expands the voltage variation range of the film capacitor, improves the power density of the film capacitor, and can effectively absorb and release energy according to the operating state of the electric vehicle, thereby improving the utilization rate of the braking energy; the low voltage stress of the device can effectively reduce the energy loss of the converter during operation, and further improve the reliability and service life of the converter on the basis of improving the efficiency of the hybrid energy system; the power converter also has the advantages of a small number of power devices and an 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 novel bidirectional DC / DC converter proposed in the present invention can be used in the hybrid power system of electric vehicles to effectively improve the reliability of the system and the utilization rate of the braking energy, and can significantly improve the mileage of electric vehicles under the existing power battery technology conditions.

Claims

1. A wide-gain bidirectional DC / DC converter, characterized in that: Including film capacitor (FC), power battery (Power Bat), new wide gain bidirectional DC / DC converter; the low voltage side is film capacitor (FC), the high voltage side DC bus capacitor C H The novel wide-gain bidirectional DC / DC converter is connected in parallel with the motor inverter DC bus; when the vehicle is working in the deceleration or braking state, the novel wide-gain bidirectional DC / DC converter stores the braking energy on the high-voltage DC bus side in the film capacitor (FC); when the vehicle is working in the acceleration state, the novel wide-gain bidirectional DC / DC converter boosts the energy of the film capacitor (FC) and sends it to the DC bus C H , connected in parallel with the power battery (Power Bat) to drive the motor to improve its dynamic performance.

2. According to claim 1, a wide-gain bidirectional DC / DC converter, characterized in that: The novel 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); The active LC module 1 is composed of a first inductor (L1), a first capacitor (C1), and a first switch tube (S1), and the first inductor (L1) and the first switch tube (S1) are connected in series and then connected in parallel with the first capacitor (C1); the active LC module 2 is composed of a second inductor (L2), a second capacitor (C2), and a second switch tube (S2) connected 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 to the positive electrode of the film capacitor (FC); the other end of the third inductor (L3) is connected to the second The drain of the switch tube (S2), the source of the third switch tube (S3), and the positive electrode of the second capacitor (C2) are connected; the negative electrode of the second capacitor (C2) is connected to 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 to the drain 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 to the source of the first switch tube (S1) and the drain of the fourth switch tube (S4); the positive electrode of the first capacitor (C1), the drain of the first switch tube (S1), and the high-voltage side DC bus capacitor C H The positive electrode of the second switch tube (S2), one end of the second inductor (L2), and the high-voltage side DC bus capacitor C H The negative electrode of is also connected to the negative electrode of the film capacitor (FC).

3. According to claim 2, a wide-gain bidirectional DC / DC converter, characterized in that: The novel wide-gain bidirectional DC / DC converter is designed to convert the electric vehicle into a DC converter according to the working state of the electric vehicle and the high-voltage DC bus capacitor voltage (U H ) works in buck mode: the vehicle status control signal K is 0, the film capacitor voltage (U L ) is lower than the set upper limit (U Set1 ), the power battery state of charge is lower than the set value (SOC * S ); When the electric vehicle brakes, the feedback energy causes the DC bus capacitor voltage (U H ) increases, the energy distribution controller controls the new bidirectional DC / DC converter to work in the buck mode, and the film capacitor (FC) absorbs the braking energy until it exceeds the set upper limit (U Set1 ); Then, the energy distribution controller controls the DC bus capacitor voltage (U H ) releases energy to the power battery until it reaches the power battery state of charge setting value (SOC * S ); When the power battery state of charge (SOC) and the film capacitor voltage (U L ) reach the set value, and the braking energy is consumed by the energy-consuming resistor to avoid damage to the converter caused by excessive DC bus voltage.

4. According to claim 2, a wide-gain bidirectional DC / DC converter, characterized in that: The novel wide-gain bidirectional DC / DC converter is designed to convert the electric vehicle into a DC converter according to the working state of the electric vehicle and the high-voltage DC bus capacitor voltage U H Working in boost mode: the vehicle status control signal K corresponds to 1, and the film capacitor voltage (U L ) is higher than the set lower limit (U Set2 ), the instantaneous high power demand will cause the DC bus capacitor voltage (U H ) decreases, the energy distribution controller controls the new bidirectional DC / DC converter to work in boost mode, and the film capacitor (FC) is supplied to the DC bus capacitor (U H ) releases energy and works with the power battery to supply power to the motor until the film capacitor voltage (U L ) is lower than the set lower limit (U Set2 ); then, the energy distribution controller controls the power battery (Power Bat) to provide energy to the motor alone.

5. The method based on a wide gain bidirectional DC / DC converter according to claim 1, characterized in that: The following steps are involved: The controller working process in boost mode is as follows: First, the average reference current I on the low voltage side is obtained through the PI-A controller according to the bus voltage error. L3 * ; Further, the current is based on the instantaneous voltage u of the film capacitor L Adjust to i L3 * As the control target of the converter, the current error adjusts the duty cycle of the power device through the PI-B controller to achieve bus voltage stability and release of 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 of the present invention stops working; the above-mentioned PI-A controller and PI-B controller are both PI controllers; The controller working process in buck mode is similar to that in boost mode. The difference is that when the emergency brake film capacitor cannot fully absorb the braking energy of the electric vehicle, the converter should set i according to the film capacitor voltage and the rated working current of the power device. L3 * At the same time, the power battery absorbs part of the braking energy to prevent damage caused by overvoltage of the film capacitor and overcurrent of the power device.

6. The method based on a wide gain bidirectional DC / DC converter according to claim 5, characterized in that: New wide-gain bidirectional DC / DC converter buck mode gain expansion process: In the buck mode, the bidirectional DC / DC converter alternately operates 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 remaining energy is transmitted to the first inductor (L1), the third inductor (L3), and the first capacitor (C1). Part of the energy of the second capacitor (C2) and the second inductor (L2) flows to the third inductor (L3), and the remaining 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 provided with energy 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, thereby further reducing the buck gain.

7. The method based on a wide gain bidirectional DC / DC converter according to claim 5, characterized in that: The process of gain expansion in boost mode of the new wide-gain bidirectional DC / DC converter: In boost mode, the bidirectional DC / DC converter alternately operates 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 connected in series and the second capacitor (C2) and the second inductor (L2) jointly provide energy; in state two, the film capacitor (FC), the third inductor (L3), the first capacitor (C1), and the first inductor (L1) are connected in series to 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.

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