Bus voltage control method and system of pfc side conversion circuit, vehicle and medium

Abstract

The application discloses a bus voltage control method and system of a PFC side conversion circuit, a vehicle and a medium. The bus voltage control method is applied to a three-port vehicle-mounted charger and comprises the following steps: judging a working mode of the three-port vehicle-mounted charger; if the working mode is an OBC+DCDC mode, controlling a switch tube in the PFC side conversion circuit to work at a preset first duty cycle D1; if the working mode is a DCAC+DCDC mode, controlling the switch tube in the PFC side conversion circuit to work at a preset second duty cycle D2; and if the working mode is a DCDC mode, determining a safe duty cycle according to an input voltage U of a high-voltage side conversion circuit and an output power P of a low-voltage side conversion circuit, and controlling the switch tube in the PFC side conversion circuit to work at the safe duty cycle. The application can avoid damage of devices caused by excessively high bus voltage of the PFC side conversion circuit and reduce the cost.

Description

Technical Field

[0001] This invention belongs to the field of electric vehicle charging technology, specifically relating to a bus voltage control method, system, vehicle, and medium for a PFC-side conversion circuit. Background Technology

[0002] With the rapid development of the new energy industry, on-board chargers with high power density, small product size, and high integration are increasingly favored by the industry. The three-port magnetic integration solution deeply integrates the OBC and DC-DC main power transformer to form a three-port on-board charger. This type of three-port on-board charger has advantages in terms of cost, size, and weight, but it also has certain drawbacks. These mainly include lower charging efficiency under light loads, complex software algorithms and logic control, and in certain independent operating conditions (such as DC-DC mode), only two ends of the three-terminal transformer need to work and transfer energy. The idle end (i.e., the port connected to the PFC side conversion circuit) generates alternating energy due to leakage magnetic coupling to charge its bus capacitor, which can lead to excessively high bus voltage in the PFC side conversion circuit, or even overvoltage, damaging the components.

[0003] CN113972729A discloses an on-board charger for electric vehicles, including an AC input circuit, a primary-side circuit, a transformer, a secondary-side circuit, a high-voltage battery pack, and a motor. The AC input circuit is connected to the primary-side circuit, which is connected to the primary coil of the transformer. The secondary coil of the transformer is connected to the high-voltage battery pack through the secondary-side circuit. A first mode switch K1 is provided between the AC input circuit and the primary-side circuit. The motor is connected between the first mode switch K1 and the primary-side circuit through a second mode switch K2. This device belongs to the field of electric vehicle chargers and solves the problem that existing on-board chargers have a single operating mode, failing to meet the charging, motor driving, and diversified charging needs of electric vehicles. It can achieve both charging and driving operating modes, satisfying the diverse charging needs of electric vehicles. However, in the low-voltage charging mode (i.e., the high-voltage battery pack charges the low-voltage battery through the low-voltage charging circuit, corresponding to the DC-DC mode), to avoid damage to components due to excessively high voltage in the primary-side circuit, the method used is to disconnect the changeover switch in the primary-side circuit, thus disabling the primary-side changeover circuit. This type of on-board charger must have a changeover switch, resulting in higher product costs.

[0004] CN208452807U discloses a charging and discharging circuit integrating a bidirectional OBC and a bidirectional DC / DC converter, used to realize energy flow between an external power source, an electric vehicle's energy storage component, an electric vehicle load, and an electric vehicle energy feedback input terminal. The charging and discharging circuit includes a bidirectional OBC circuit unit and a bidirectional DC / DC converter circuit unit. The bidirectional OBC circuit unit is electrically connected to the bidirectional DC / DC converter circuit unit. The OBC circuit unit is used to connect the external power source and the electric vehicle's energy storage component. The bidirectional DC / DC converter circuit unit is also electrically connected to the electric vehicle load and the electric vehicle energy feedback input terminal. The bidirectional OBC circuit unit is used to implement the bidirectional OBC function, and the bidirectional DC / DC converter circuit unit is used to implement the bidirectional DC / DC converter function. When the power battery pack supplies power to a low-voltage load, to prevent damage to components due to excessively high voltage in the primary-side conversion circuit, the following method is used: relay RLY1 is disconnected, shutting down the corresponding switching transistor. The primary winding is in an open-circuit state, the high-voltage secondary winding is the energy input side, and the low-voltage secondary winding is the output side. The power battery pack is in a discharging state, supplying power to the vehicle's low-voltage load, thus realizing the function of an on-board DC / DC converter. This charging and discharging circuit requires relay RLY1, resulting in higher product costs.

[0005] Alternatively, adding a discharge circuit or other voltage regulation circuit can prevent the primary-side conversion circuit from over-voltage from damaging the device, but these methods all require additional hardware and will increase product costs. Summary of the Invention

[0006] The purpose of this invention is to provide a method, system, vehicle, and medium for controlling the bus voltage of a PFC-side conversion circuit, so as to avoid damage to the device due to excessively high bus voltage in the PFC-side conversion circuit, while reducing costs.

[0007] The three-port on-board charger includes a three-terminal transformer, a resonant inductor, a resonant capacitor, a DC blocking capacitor, and a PFC-side switching circuit connected to the primary winding of the three-terminal transformer, a high-voltage side (HV side) switching circuit connected to the first secondary winding of the three-terminal transformer, and a low-voltage side (LV side) switching circuit connected to the second secondary winding of the three-terminal transformer; it also includes a controller for controlling the switching transistors in the PFC-side switching circuit, the high-voltage side switching circuit, and the low-voltage side switching circuit to turn on / off.

[0008] Three-port on-board chargers have three main operating modes in the vehicle:

[0009] The first type is the OBC+DCDC mode (i.e., a dual charging mode of charging the high-voltage power battery and charging the low-voltage 12V storage battery). In the OBC+DCDC mode, all the switching transistors (i.e., power switching devices) in the three-port on-board charger work effectively, and the two energy transmission paths are: from the PFC side conversion circuit to the high-voltage side conversion circuit and from the PFC side conversion circuit to the low-voltage side conversion circuit; that is, the PFC side conversion circuit is the input side, and the high-voltage side conversion circuit and the low-voltage side conversion circuit are the output sides.

[0010] The second type is the DCAC+DCDC mode (i.e., AC inverter discharge + low-voltage 12V battery charging mode). In the DCAC+DCDC mode, all the switching transistors (i.e., power switching devices) in the three-port on-board charger work effectively, and the two energy transmission paths are: high-voltage side conversion circuit to PFC side conversion circuit and high-voltage side conversion circuit to low-voltage side conversion circuit; that is, the high-voltage side conversion circuit is the input side, and the PFC side conversion circuit and the low-voltage side conversion circuit are the output sides.

[0011] The third type is the DC-DC mode (i.e., low-voltage 12V battery charging or load power consumption mode). In DC-DC mode, the three-port on-board charging system only requires the switching transistors in the high-voltage and low-voltage conversion circuits to operate. The effective energy transfer path is from the high-voltage to the low-voltage conversion circuit. The duty cycles of the switching transistors in the high-voltage and low-voltage conversion circuits are adjusted according to the input voltage, output voltage, and power transmission. In DC-DC mode, energy transfer from the high-voltage to the PFC conversion circuit is not intended. However, due to the magnetic coupling of the three-terminal transformer, the primary winding of the three-terminal transformer connected to the PFC conversion circuit will generate an alternating voltage, storing energy in the resonant inductor and resonant capacitor. Furthermore, the three-terminal transformer will store a certain amount of leakage magnetic energy in each conversion cycle. This energy coupled from the high-voltage side to the PFC side forms an energy transfer path through the rectifier circuit (formed by the parasitic diodes of the switching transistors in the PFC conversion circuit), continuously charging the bus capacitor in the PFC conversion circuit. This causes the bus voltage of the PFC conversion circuit to continuously rise, potentially leading to overvoltage and damage to components. Therefore, relevant controls are needed to prevent the PFC-side conversion circuit from being damaged by excessively high bus voltage.

[0012] The bus voltage control method for the PFC-side conversion circuit described in this invention is applied to a three-port on-board charger. The method includes: determining the operating mode of the three-port on-board charger; if the operating mode is OBC+DCDC mode, controlling the switching transistor in the PFC-side conversion circuit to operate with a preset first duty cycle D1; if the operating mode is DCAC+DCDC mode, controlling the switching transistor in the PFC-side conversion circuit to operate with a preset second duty cycle D2; if the operating mode is DCDC mode, determining a safe duty cycle based on the input voltage U of the high-voltage side conversion circuit and the output power P of the low-voltage side conversion circuit, and controlling the switching transistor in the PFC-side conversion circuit to operate with the safe duty cycle.

[0013] Preferably, the method for determining the safe duty cycle based on the input voltage U of the high-voltage side conversion circuit and the output power P of the low-voltage side conversion circuit is as follows:

[0014] When U < U1 and P < P1, the safe duty cycle is set to 0. Here, U1 represents the first voltage threshold, and P1 represents the power threshold. Because the input voltage of the high-voltage side conversion circuit is low, and the output power of the low-voltage side conversion circuit is small, the energy coupled to the PFC side conversion circuit is very limited in this state. At this time, the bus voltage of the PFC side conversion circuit is much lower than the rated withstand voltage of its bus capacitor, and the bus voltage of the PFC side conversion circuit is in a very safe low-voltage stable state. The switching transistors in the PFC side conversion circuit do not need to be turned on (therefore, the safe duty cycle is 0).

[0015] When U1≤U<U2 and P<P1, the safe duty cycle is set to the preset third duty cycle D3. Here, U2 represents the second voltage threshold, U2>U1, D3<D1, and D3<D2. When U1≤U<U2 and P<P1, the input voltage of the high-voltage side conversion circuit is relatively high. The switching transistor in the PFC side conversion circuit must operate with a relatively small duty cycle to maintain the bus voltage of the PFC side conversion circuit within a relatively safe voltage range. After the switching transistor in the PFC side conversion circuit operates, similar to energy transfer in normal charging mode, each high-frequency switching cycle stores part of the energy on the bus capacitor in the PFC side conversion circuit in the energy storage resonant cavity composed of the resonant inductor and resonant capacitor. This energy is then transferred to the low-voltage side conversion circuit through a three-terminal transformer, thereby releasing the leakage magnetic energy coupled to the PFC side conversion circuit due to the relatively high input voltage. This reduces the bus voltage of the PFC side conversion circuit while achieving energy recovery.

[0016] When U < U2 and P ≥ P1, the safe duty cycle is determined according to P, thereby controlling the bus voltage in the PFC side conversion circuit within the safe operating voltage range.

[0017] When U≥U2, the safe duty cycle is made equal to the duty cycle of the switching transistor in the high-voltage side switching circuit (that is, the safe duty cycle completely follows the duty cycle of the switching transistor in the high-voltage side switching circuit). When U≥U2, regardless of the output power, the duty cycle of the switching transistor in the PFC side switching circuit follows the duty cycle of the switching transistor in the high-voltage side switching circuit. Because the input voltage of the high-voltage side conversion circuit is too high, without considering leakage magnetic energy, the plateau voltage directly coupled to the PFC side conversion circuit through the turns ratio of the three-terminal transformer is very close to the rated withstand voltage of the bus capacitor in the PFC side conversion circuit. Even if the low-voltage side conversion circuit output is unloaded, the switching transistor in the PFC side conversion circuit must operate at a certain duty cycle (equal to the duty cycle of the switching transistor in the high-voltage side conversion circuit) to maintain the bus voltage of the PFC side conversion circuit within a relatively safe range. After the switching transistor in the PFC side conversion circuit is working, the energy transfer is the same as in the normal charging mode. Each high-frequency switching cycle stores part of the energy on the bus capacitor in the PFC side conversion circuit in the energy storage resonant cavity composed of the resonant inductor and resonant capacitor, and then transfers it to the low-voltage side conversion circuit through the three-terminal transformer. Energy recovery can be achieved while reducing the bus voltage of the PFC side conversion circuit.

[0018] Preferably, when U < U2 and P ≥ P1, the method for determining the safe duty cycle based on P is as follows:

[0019] When U < U1 and P ≥ P1, the safe duty cycle is: Among them, P max D1 represents the preset maximum output load power, D4 represents the preset fourth duty cycle, D5 represents the preset fifth duty cycle, and P1 < P2. max D4 < D3 ≤ D5, D5 < D1, D5 < D2. When U < U1 and P ≥ P1, the output power increases relatively. The switching transistor in the PFC-side conversion circuit must operate with a relatively small duty cycle to maintain the bus voltage of the PFC-side conversion circuit within a relatively safe voltage range. The duty cycle of the switching transistor in the PFC-side conversion circuit is linearly adjusted between D4 and D5 according to the output power P. The smaller P is, the smaller the duty cycle; the larger P is, the larger the duty cycle. After the switching transistor in the PFC-side conversion circuit operates, the energy transfer is the same as in the normal charging mode. In each high-frequency switching cycle, part of the energy on the bus capacitor in the PFC-side conversion circuit is stored in the energy storage resonant cavity composed of the resonant inductor and resonant capacitor. Then, it is transferred to the low-voltage side conversion circuit through the three-terminal transformer, thereby releasing the leakage magnetic energy coupled to the PFC-side conversion circuit due to the increase in output power. Energy recovery can be achieved while reducing the bus voltage of the PFC-side conversion circuit.

[0020] When U1≤U<U2 and P≥P1, the safe duty cycle is: Where D6 is the preset sixth duty cycle, D7 is the preset seventh duty cycle, and D5 < D6 < D7, D7 < D1, D7 < D2. When U1 ≤ U < U2 and P ≥ P1, the increased output power and higher input voltage result in greater leakage magnetic energy. The switching transistor in the PFC-side switching circuit must operate with a larger duty cycle to maintain the bus voltage of the PFC-side switching circuit within a relatively safe voltage range. The duty cycle of the switching transistor in the PFC-side switching circuit is linearly adjusted between D6 and D7 according to the output power P. The smaller P is, the smaller the duty cycle; the larger P is, the larger the duty cycle. After the switching transistor in the PFC-side conversion circuit is working, the energy transfer is the same as in the normal charging mode. In each high-frequency switching cycle, part of the energy on the bus capacitor in the PFC-side conversion circuit is stored in the energy storage resonant cavity composed of resonant inductor and resonant capacitor. Then, it is transferred to the low-voltage side conversion circuit through the three-terminal transformer. This releases the leakage magnetic energy coupled to the PFC-side conversion circuit due to the increase in output power or input voltage. Energy recovery can be achieved while reducing the bus voltage of the PFC-side conversion circuit.

[0021] Preferably, U1 = A*U max U2 = B*U max P1 = C * P max A is the preset first coefficient, B is the preset second coefficient, C is the preset third coefficient, A < B < 1, C < 1, U max The preset voltage is the voltage of the power battery when fully charged. The first voltage threshold U1 is designed to be A times the voltage of the power battery when fully charged, and the second voltage threshold U2 is designed to be B times the voltage of the power battery when fully charged, with A < B. This ensures sufficient voltage margin for the bus capacitor in the PFC-side conversion circuit. The power threshold P1 is designed to be C times the maximum output load power, which also ensures sufficient voltage margin for the bus capacitor in the PFC-side conversion circuit.

[0022] Preferably, the input voltage U of the high-voltage side conversion circuit is the real-time acquired voltage of the high-voltage side power battery terminal. The high-voltage side power battery terminal voltage is obtained by real-time voltage sampling through an isolated sampling chip inside the controller.

[0023] Preferably, the output voltage and output current of the low-voltage-side conversion circuit are multiplied in real time to obtain the output power P of the low-voltage-side conversion circuit. The output voltage of the low-voltage-side conversion circuit is obtained by real-time voltage sampling by the controller, and the output current of the low-voltage-side conversion circuit is obtained by real-time sampling through a high-precision sampling resistor and a differential amplifier.

[0024] Preferably, the preset first coefficient A has a value range of 0.6 to 0.8, the preset second coefficient B has a value range of 0.85 to 0.95, and the preset third coefficient C has a value range of 0.25 to 0.35.

[0025] Preferably, the preset first coefficient A = 0.7, the preset second coefficient B = 0.9, and the preset third coefficient C = 0.3.

[0026] Preferably, the preset third duty cycle D3 = 5%, the preset fourth duty cycle D4 = 1%, the preset fifth duty cycle D5 = 5%, the preset sixth duty cycle D6 = 20%, and the preset seventh duty cycle D7 = 30%.

[0027] Preferably, the preset first duty cycle D1 = 50% and the preset second duty cycle D2 = 50%.

[0028] The bus voltage control system for the PFC-side conversion circuit of the present invention includes a controller, which is programmed to perform the steps of the bus voltage control method for the PFC-side conversion circuit described above.

[0029] The present invention also provides a vehicle that includes the bus voltage control system of the above-described PFC-side conversion circuit.

[0030] The present invention also provides a medium storing a computer-readable program, which, when invoked, can execute the steps of the bus voltage control method of the PFC-side conversion circuit described above.

[0031] The present invention has the following effects:

[0032] (1) No additional circuits or devices are required. By simply improving the software, the excessively high bus voltage of the PFC side conversion circuit can be avoided, thus preventing damage to the devices. This ensures the safety and stability of the bus voltage of the PFC side conversion circuit. It also has advantages in terms of overall material cost, product size, and PCB layout design, thereby reducing costs.

[0033] (2) The bus voltage of the PFC side conversion circuit is stabilized in real time within a certain range, reducing the repeated impact and lifespan effects caused by voltage instability.

[0034] (3) When the switching transistor in the PFC side conversion circuit is working, it transfers the energy of the bus capacitor in the PFC side conversion circuit back to the output terminal (i.e., the low-voltage side conversion circuit), which improves the transmission efficiency of the charging system and realizes energy recovery. Attached Figure Description

[0035] Figure 1 This is the circuit topology diagram of a three-port on-board charger.

[0036] Figure 2 This is a power transmission diagram for a three-port on-board charger.

[0037] Figure 3 This is a flowchart of the bus voltage control for the PFC-side conversion circuit in this embodiment.

[0038] Figure 4 This is a timing diagram of the switching transistors Q1 to Q4 with a duty cycle of 50% in the non-DC-CDC mode in this embodiment.

[0039] Figure 5 This is a timing diagram showing the duty cycle of switching transistors Q1 to Q4 being 0 in the DC-DC mode of this embodiment.

[0040] Figure 6 This is a timing diagram showing the duty cycle of switching transistors Q1 to Q4 in the DC-DC mode of this embodiment, with a duty cycle of 5%.

[0041] Figure 7 This is a timing diagram showing the duty cycle of switching transistors Q1 to Q4 in the DC-DC mode of this embodiment, with a duty cycle of 20%.

[0042] Figure 8 This is a timing diagram showing the duty cycle of switching transistors Q1 to Q4 following the duty cycle of switching transistors Q5 to Q8 in the DC-DC mode of this embodiment. Detailed Implementation

[0043] like Figure 1As shown, the three-port on-board charger includes a controller, a three-terminal transformer T, a resonant inductor Lr, a resonant capacitor Cr, a DC blocking capacitor Cd, a PFC-side conversion circuit 1, a high-voltage side (HV side) conversion circuit 2, and a low-voltage side (HV side) conversion circuit 3. The PFC-side conversion circuit 1 includes a bus capacitor Cbus1 and a full-bridge circuit composed of transistors Q1, Q2, Q3, and Q4. The high-voltage side (HV side) conversion circuit 2 includes a bus capacitor Cbus2 and a full-bridge circuit composed of transistors Q5, Q6, Q7, and Q8. The low-voltage side (HV side) conversion circuit 3 includes a bus capacitor Cbus3, a half-bridge circuit composed of transistors Q9 and Q10, and a two-stage switching regulator circuit 31 composed of transistor Q11, capacitor C1, diode D1, and inductor Lf. A resonant inductor Lr and a resonant capacitor Cr are connected in series as a resonant element. One end of the resonant element is connected to one end of the primary winding of the three-terminal transformer T, and the other end is connected to one end of the PFC-side conversion circuit 1. The other end of the PFC-side conversion circuit 1 is connected to the other end of the primary winding of the three-terminal transformer T. One end of the DC blocking capacitor Cd is connected to one end of the first secondary winding of the three-terminal transformer T, and the other end of the DC blocking capacitor Cd is connected to one end of the high-voltage side conversion circuit 2. The other end of the high-voltage side conversion circuit 2 is connected to the other end of the first secondary winding of the three-terminal transformer T. The low-voltage side conversion circuit 3 is connected to the second secondary winding of the three-terminal transformer T. The bus voltage of the PFC-side conversion circuit 1 is a stable high-voltage DC obtained from the 220V single-phase AC power of the mains network after passing through the PFC (Power Factor Correction) power conversion circuit. The high-voltage side conversion circuit 2 is connected to the power battery bus, providing a port connection and path for the power battery to perform slow charging or inverter discharge. The low-voltage side conversion circuit 3 is connected to the vehicle's low-voltage 12V battery bus to provide power to the vehicle's low-voltage power supply system.

[0044] The controller is connected to switching transistors Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, Q10, and Q11, and controls the on / off state (i.e., adjusts the duty cycle) of these transistors to achieve high-frequency switching. It chops the DC current at the port bus into a high-frequency AC voltage, which is then coupled and transmitted through an energy storage and conversion device composed of a three-terminal transformer T, a resonant inductor Lr, and a resonant capacitor Cr, thus realizing energy transfer between the three ports.

[0045] like Figure 2 As shown, the three-port on-board charger has three main operating modes in the vehicle:

[0046] The first type is the OBC+DCDC mode (i.e., a dual charging mode that combines high-voltage power battery charging with low-voltage 12V battery charging).

[0047] In OBC+DCDC mode, all switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, Q10, and Q11 in the three-port on-board charger are effectively operational. The controller controls switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, and Q10 to operate at a preset first duty cycle of 50% (i.e., D1 = 50%). The controller then adjusts the operating parameters accordingly. The value controls the duty cycle of the switching transistor Q11 (this is prior art; Vin represents the input voltage of the secondary switching regulator circuit 31, and Vo represents the output voltage of the secondary switching regulator circuit 31). Two energy transfer paths (see...). Figure 2 The solid lines and hollow arrows in the diagram represent: PFC side conversion circuit 1 to high voltage side conversion circuit 2 and PFC side conversion circuit 1 to low voltage side conversion circuit 3; that is, PFC side conversion circuit 1 is the input side, and high voltage side conversion circuit 2 and low voltage side conversion circuit 3 are the output sides.

[0048] The second type is DCAC+DCDC mode (i.e., AC inverter discharge + low-voltage 12V battery charging mode).

[0049] In DCAC+DCDC mode, switching transistors Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, Q10, and Q11 all operate effectively. The controller controls switching transistors Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, and Q10 to operate at a preset second duty cycle of 50% (i.e., D2 = 50%). The controller then... The value controls the duty cycle of the switching transistor Q11 (this is prior art; Vin represents the input voltage of the secondary switching regulator circuit 31, and Vo represents the output voltage of the secondary switching regulator circuit 31). Two energy transfer paths (see...). Figure 2 The dashed hollow arrows in the diagram represent the high-voltage side conversion circuit 2 to the PFC side conversion circuit 1 and the high-voltage side conversion circuit 2 to the low-voltage side conversion circuit 3, respectively; that is, the high-voltage side conversion circuit 2 serves as the input side, and the PFC side conversion circuit 1 and the low-voltage side conversion circuit 3 serve as the output side.

[0050] The third type is the DC-DC mode (i.e., low-voltage 12V battery charging or load power consumption mode).

[0051] In DC-DC mode, the three-port on-board charging system only requires switches Q5, Q6, Q7, Q8, Q9, Q10, and Q11 to operate. The effective energy transfer path is from high-voltage side conversion circuit 2 to low-voltage side conversion circuit 3 (see...). Figure 2 (Solid line filled arrow in the image) The controller controls the duty cycle of switches Q5, Q6, Q7, Q8, Q9, and Q10 based on the input voltage, output voltage, and transmitted power. The controller also controls switch Q11 to remain normally closed (i.e., controls switch Q11 to operate at 100% duty cycle). In DC-DC mode, energy transfer from the high-voltage side conversion circuit 2 to the PFC side conversion circuit 1 is not intended. However, due to the magnetic coupling of the three-terminal transformer T, the primary winding of the three-terminal transformer T will generate an alternating voltage, storing energy in the resonant inductor Lr and the resonant capacitor Cr. Furthermore, the three-terminal transformer T will store a certain amount of leakage magnetic energy in each conversion cycle. This energy coupled from the high-voltage side to the PFC side forms an energy transfer path through the rectifier circuit (formed by the parasitic diodes of switches Q1, Q2, Q3, and Q4), continuously charging the bus capacitor Cbus1. This causes the voltage of the bus capacitor Cbus1 to continuously rise, potentially leading to overvoltage and damage to the components. Therefore, relevant controls are needed to prevent the PFC-side conversion circuit from being damaged by excessively high bus voltage.

[0052] To ensure sufficient energy transfer under various charging conditions, the magnetic coupling between the windings of the three-terminal transformer T is designed to be very tight. The greater the output power, the more energy is coupled between the primary and secondary sides. The higher the input voltage of the high-voltage side conversion circuit, the higher the bus voltage of the PFC side conversion circuit. Furthermore, the bus voltage of the PFC side conversion circuit continuously increases as the output power of the low-voltage side conversion circuit increases. When the low-voltage side conversion circuit is unloaded, its duty cycle is at its minimum, the leakage magnetic energy of the three-terminal transformer T is at its minimum, and the energy coupled to the bus of the PFC side conversion circuit is at its minimum, resulting in the lowest bus voltage. When the low-voltage side conversion circuit is fully loaded, its duty cycle is at its maximum, the leakage magnetic energy of the three-terminal transformer T is relatively maximum, and the energy coupled to the bus of the PFC side conversion circuit is relatively greater, resulting in the highest bus voltage. This embodiment uses software control to prevent the bus voltage of the PFC side conversion circuit from becoming excessively high, thus maintaining a relatively stable bus voltage.

[0053] like Figure 3 As shown, the bus voltage control method of the PFC-side conversion circuit in this embodiment is applied to a three-port on-board charger. The method includes the following steps:

[0054] Step 1: Determine if the three-port on-board charger is operating in OBC+DCDC mode. If so, proceed to Step 3; otherwise, proceed to Step 2.

[0055] Step 2: Determine whether the three-port on-board charger is operating in DCAC+DCDC mode. If so, proceed to Step 3; otherwise (i.e., if the operating mode is DCDC mode), proceed to Step 4.

[0056] Step 3: Control switches Q1, Q2, Q3, and Q4 to operate at a 50% duty cycle (see...). Figure 4 Then it ends. In OBC+DCDC mode and DCAC+DCDC mode, the controller will control switches Q5, Q6, Q7, Q8, Q9, and Q10 to operate at a 50% duty cycle (this is existing technology). The controller will then... The value controls the duty cycle of the switching transistor Q11 (this is prior art; Vin represents the input voltage of the secondary switching regulator circuit 31, and Vo represents the output voltage of the secondary switching regulator circuit 31). In this operating state, the maximum operating voltage of the bus capacitor Cbus1 is below 440V, providing a working margin of over 35V compared to its rated withstand voltage (475V). Therefore, there is no risk of overvoltage damage to the bus capacitor Cbus1.

[0057] Step 4: Determine if U < U1. If yes, proceed to Step 5; otherwise, proceed to Step 8. Here, U represents the input voltage of the high-voltage side conversion circuit, and U is equal to the real-time acquired voltage at the high-voltage side power battery terminal (i.e., from...). Figure 1 The voltage input at HV). The voltage at the high-voltage side power battery terminal is obtained by real-time voltage sampling from the isolated sampling chip inside the controller. U1 represents the first voltage threshold, U1 = A * U max A is the preset first coefficient, U max This is the preset voltage of the power battery when fully charged. In this embodiment, A = 0.7. Currently, the voltage of mainstream power batteries when fully charged is generally around 450V to 500V. The power battery used in this embodiment has a fully charged voltage of 480V, i.e., U... max =480V, then U1 = 0.7 * 480 = 336V. Through the turns ratio calculation of the three-terminal transformer T, when the input voltage U of the high-voltage side conversion circuit 2 is less than 336V, because the turns ratio of the primary side and the first secondary side of the three-terminal transformer is less than 1, the bus voltage fed back to the PFC side conversion circuit 1 is less than 336V. In this embodiment, the rated withstand voltage of the bus capacitor Cbus1 is a polarized capacitor with a rated withstand voltage of 475V. The bus voltage margin of the PFC side conversion circuit is about 139V, and the first voltage threshold design is reasonable.

[0058] Step 5: Determine if P < P1. If yes, proceed to Step 6; otherwise, proceed to Step 7. Here, P represents the output power of the low-voltage side conversion circuit (i.e., from...). Figure 1 The output power P of the low-voltage side conversion circuit is obtained by multiplying the output voltage and output current of the low-voltage side conversion circuit, which are acquired in real time. The output voltage of the low-voltage side conversion circuit is obtained by real-time voltage sampling by the controller, and the output current of the low-voltage side conversion circuit is obtained by real-time sampling through a high-precision sampling resistor and a differential amplifier. P1 represents the power threshold, P1 = C * P max C is the preset third coefficient, P max The maximum output load power is preset. In this embodiment, C = 0.3. The maximum output load power of a DCDC charger is generally 2kW to 2.5kW. In this embodiment, the maximum output load power P of the three-port on-board charger in DCDC mode is... max =2kW, therefore P1 = 0.3 * 2kW = 600W.

[0059] Step 6: Set the safe duty cycle to 0 (see...) Figure 5 Then proceed to step thirteen. Because the input voltage of the high-voltage side conversion circuit 2 is low and the output power of the low-voltage side conversion circuit 3 is small, the energy coupled to the PFC side conversion circuit is very limited in this state. At this time, the bus voltage of the PFC side conversion circuit 1 is much smaller than the rated withstand voltage of its bus capacitor Cbus1. The bus voltage of the PFC side conversion circuit 1 is in a very safe low-voltage stable state, and the switching transistors Q1, Q2, Q3, and Q4 do not need to be turned on (therefore, the safe duty cycle is 0).

[0060] Step 7: Set the safe duty cycle to: Then proceed to step thirteen. Here, D4 ​​is the preset fourth duty cycle, and D5 is the preset fifth duty cycle. In this embodiment, D4 = 1%, D5 = 5%. When U < U1 and P ≥ P1, the output power increases relatively. Switches Q1, Q2, Q3, and Q4 must operate with relatively small duty cycles to maintain the bus voltage of the PFC-side conversion circuit 1 within a relatively safe voltage range. This ensures that the duty cycles of switches Q1, Q2, Q3, and Q4 are linearly adjusted between 1% and 5% according to the output power P. The smaller P is, the smaller the duty cycle; the larger P is, the larger the duty cycle. This guarantees that the bus capacitor Cbus1 has a voltage margin of at least approximately 50V. Figure 6 It shows that P = P maxThe timing diagram shows that the duty cycle of switches Q1, Q2, Q3, and Q4 is 5%. After switches Q1, Q2, Q3, and Q4 operate, the energy transfer is the same as in normal charging mode. In each high-frequency switching cycle, a portion of the energy on the bus capacitor Cbus1 is stored in the energy storage resonant cavity composed of the resonant inductor Lr and the resonant capacitor Cr. This energy is then transferred to the low-voltage side conversion circuit 3 through the three-terminal transformer T. This releases the leakage magnetic energy coupled to the PFC side conversion circuit 1 due to the increased output power, achieving energy recovery while reducing the bus voltage of the PFC side conversion circuit 1.

[0061] Step 8: Determine if U1 ≤ U < U2. If yes, proceed to Step 9; otherwise, proceed to Step 12. Here, U2 represents the second voltage threshold, U2 = B * U. max B is a preset second coefficient. In this embodiment, B = 0.9, so U2 = 0.9 * 480 = 432V. Through the turns ratio calculation of the three-terminal transformer T, when the input voltage U of the high-voltage side conversion circuit 2 is less than 432V, because the turns ratio of the primary side and the first secondary side of the three-terminal transformer is less than 1, the bus voltage fed back to the PFC side conversion circuit 1 is less than 432V. In this embodiment, the rated withstand voltage of the bus capacitor Cbus1 is a polarized capacitor with a voltage rating of 475V. The bus voltage margin of the PFC side conversion circuit is about 43V, and the second voltage threshold design is reasonable.

[0062] Step 9: Determine if P < P1. If yes, proceed to step 10; otherwise, proceed to step 11.

[0063] Step 10: Set the safe duty cycle to the preset third duty cycle D3, and then execute Step 13. In this embodiment, the preset third duty cycle D3 = 5% (see...). Figure 6 When U1≤U<U2 and P<P1, the input voltage U of the high-voltage side conversion circuit 2 is relatively high. Switches Q1, Q2, Q3, and Q4 must operate with relatively small duty cycles to maintain the bus voltage of the PFC side conversion circuit 1 within a relatively safe voltage range. After switching Q1, Q2, Q3, and Q4 operate, the energy transfer is the same as in the normal charging mode. In each high-frequency switching cycle, part of the energy on the bus capacitor Cbus1 is stored in the energy storage resonant cavity composed of the resonant inductor Lr and the resonant capacitor Cr. Then, it is transferred to the low-voltage side conversion circuit 3 through the three-terminal transformer T, thereby releasing the leakage magnetic energy coupled to the PFC side conversion circuit 1 due to the relatively high input voltage. Energy recovery is achieved while reducing the bus voltage of the PFC side conversion circuit 1.

[0064] Step 11: Set the safe duty cycle to: Then proceed to step thirteen. Here, D6 is the preset sixth duty cycle, and D7 is the preset seventh duty cycle. In this embodiment, D6 = 20%, and D7 = 30%. When U1 ≤ U < U2, and P ≥ P1, the increased output power and higher input voltage result in greater leakage magnetic energy. Switches Q1, Q2, Q3, and Q4 must operate with a larger duty cycle to maintain the bus voltage of the PFC-side conversion circuit within a relatively safe voltage range. This ensures that the duty cycles of switches Q1, Q2, Q3, and Q4 are linearly adjusted between 20% and 30% according to the output power P. The smaller P is, the smaller the duty cycle; the larger P is, the larger the duty cycle. This guarantees that the bus capacitor Cbus1 has a voltage margin of at least approximately 50V. Figure 7 The timing diagram shows the duty cycle of switches Q1, Q2, Q3, and Q4 at 20% when P = P1. After switching Q1, Q2, Q3, and Q4 operate in the same energy transfer manner as in normal charging mode. In each high-frequency switching cycle, a portion of the energy on the bus capacitor Cbus1 is stored in the energy storage resonant cavity composed of the resonant inductor Lr and the resonant capacitor Cr. This energy is then transferred to the low-voltage side conversion circuit 3 through the three-terminal transformer T. This releases the leakage magnetic energy coupled to the PFC-side conversion circuit 1 due to increased output power or increased input voltage, thus achieving energy recovery while reducing the bus voltage of the PFC-side conversion circuit 1.

[0065] Step 12: Make the safe duty cycle equal to the duty cycles of switching transistors Q5, Q6, Q7, and Q8 (i.e., the safe duty cycle completely follows the duty cycles of switching transistors Q5, Q6, Q7, and Q8, see [link]). Figure 8When U ≥ U2, regardless of the output power, the duty cycles of switches Q1, Q2, Q3, and Q4 follow those of switches Q5, Q6, Q7, and Q8, effectively controlling the bus voltage of the PFC-side conversion circuit below 430V. When U ≥ U2, the minimum operating duty cycle of switches Q5, Q6, Q7, and Q8 is greater than 5% (the minimum duty cycle is determined by parameters such as the converter's hardware architecture, input and output voltage information, and output voltage stability), and the larger the output power P, the larger the duty cycle. Because the input voltage of the high-voltage side conversion circuit is too high, without considering leakage magnetic energy, the platform voltage directly coupled to the PFC side conversion circuit through the turns ratio of the three-terminal transformer is very close to the rated withstand voltage of the bus capacitor in the PFC side conversion circuit. Even if the low-voltage side conversion circuit output is unloaded, the switching transistors Q1, Q2, Q3, and Q4 must operate at a certain duty cycle to maintain the bus voltage of the PFC side conversion circuit within a relatively safe range. After the switching transistors Q1, Q2, Q3, and Q4 are working, the energy transmission is the same as in the normal charging mode. In each high-frequency switching cycle, part of the energy on the bus capacitor Cbus1 is stored in the energy storage resonant cavity composed of the resonant inductor Lr and the resonant capacitor Cr, and then transmitted to the low-voltage side conversion circuit 3 through the three-terminal transformer. Energy recovery is achieved while reducing the bus voltage of the PFC side conversion circuit 1.

[0066] Step 13: Control switches Q1, Q2, Q3, and Q4 to operate at a safe duty cycle, then terminate. In DCDC mode, the controller controls the duty cycles of switches Q5, Q6, Q7, Q8, Q9, and Q10 based on the input voltage, output voltage, and transmitted power (this is prior art). The controller keeps switch Q11 normally closed (i.e., controls switch Q11 to operate at 100% duty cycle, which is prior art).

[0067] In DC-DC mode, during each switching cycle of switching transistors Q1, Q2, Q3, and Q4, the energy of the high-voltage side conversion circuit 2 is coupled and transmitted through the primary winding of the PFC side and the second secondary winding of the low-voltage side, transferring the energy of the PFC side to the low-voltage output terminal, effectively reducing the loss of system leakage magnetic energy.

[0068] The control method in this embodiment only reuses the switching transistor of the idle end (i.e., the PFC side conversion circuit) of the three-port on-board charger and controls it with software algorithm. Under different input voltage and output power conditions, it controls its different duty cycle output, which can realize the safety and stability of the idle end bus capacitor voltage. At the same time, it realizes the repeated utilization of leakage magnetic energy. There is no need to add an additional discharge circuit or connect a power switching switch in series. It has the advantages of superior performance and low cost.

[0069] This embodiment also provides a bus voltage control system for a PFC-side conversion circuit, including a controller programmed to execute the steps of the bus voltage control method for the PFC-side conversion circuit described above.

[0070] This embodiment also provides a vehicle that includes the bus voltage control system of the PFC-side conversion circuit described above.

[0071] This embodiment also provides a medium storing a computer-readable program, which, when invoked, can execute the steps of the bus voltage control method of the PFC-side conversion circuit described above.

Claims

1. A method for controlling the bus voltage of a PFC-side conversion circuit, applied to a three-port on-board charger, characterized in that, The method includes: Determine the operating mode of the three-port on-board charger; If the working mode is OBC+DCDC mode, the switching transistor in the PFC side conversion circuit (1) is controlled to work with the preset first duty cycle D1. If the working mode is DCAC+DCDC mode, the switching transistor in the PFC side conversion circuit (1) is controlled to work with the preset second duty cycle D2. If the working mode is DC-DC mode, the safe duty cycle is determined according to the input voltage U of the high-voltage side conversion circuit (2) and the output power P of the low-voltage side conversion circuit (3), and the switching transistor in the PFC side conversion circuit (1) is controlled to work at the safe duty cycle. The method for determining the safe duty cycle based on the input voltage U of the high-voltage side conversion circuit (2) and the output power P of the low-voltage side conversion circuit (3) is as follows: When U < U1 and P < P1, make the safe duty cycle 0; When U1≤U<U2 and P<P1, the safe duty cycle is set to the preset third duty cycle D3; When U < U2 and P ≥ P1, the safe duty cycle is determined based on P; When U≥U2, make the safe duty cycle equal to the duty cycle of the switching transistor in the high-voltage side switching circuit (2); When U < U2 and P ≥ P1, the method for determining the safe duty cycle based on P is as follows: When U < U1 and P ≥ P1, the safe duty cycle is: ; When U1≤U<U2 and P≥P1, the safe duty cycle is: ; U1 represents the first voltage threshold, U2 represents the second voltage threshold, P1 represents the power threshold, U1 < U2, D3 < D1, D3 < D2, P max D1 is the preset maximum output load power, D4 is the preset fourth duty cycle, D5 is the preset fifth duty cycle, D6 is the preset sixth duty cycle, D7 is the preset seventh duty cycle, and P1 < P2. max , D4<D3≤D5<D6<D7, D7<D1, D7<D2.

2. The bus voltage control method for the PFC-side conversion circuit according to claim 1, characterized in that: The U1=A*U max U2=B*U max P1 = C * P max A is the preset first coefficient, B is the preset second coefficient, C is the preset third coefficient, A < B < 1, C < 1, U max This is the preset voltage of the power battery when fully charged.

3. The bus voltage control method for the PFC-side conversion circuit according to claim 1 or 2, characterized in that: The input voltage U of the high-voltage side conversion circuit is the voltage of the high-voltage side power battery that is collected in real time. The output voltage and output current of the low-voltage side conversion circuit (3) are multiplied by the real-time collected data to obtain the output power P of the low-voltage side conversion circuit (3).

4. The bus voltage control method for the PFC-side conversion circuit according to claim 2, characterized in that: The preset first coefficient A has a value range of 0.6 to 0.8, the preset second coefficient B has a value range of 0.85 to 0.95, and the preset third coefficient C has a value range of 0.25 to 0.

35.

5. The bus voltage control method for the PFC-side conversion circuit according to claim 2, characterized in that: The preset first coefficient A = 0.7, the preset second coefficient B = 0.9, and the preset third coefficient C = 0.

3.

6. The bus voltage control method for the PFC-side conversion circuit according to claim 1, characterized in that: The preset third duty cycle D3=5%, the preset fourth duty cycle D4=1%, the preset fifth duty cycle D5=5%, the preset sixth duty cycle D6=20%, and the preset seventh duty cycle D7=30%.

7. The bus voltage control method for the PFC-side conversion circuit according to claim 1, characterized in that: The preset first duty cycle D1 = 50%, and the preset second duty cycle D2 = 50%.

8. A bus voltage control system for a PFC-side conversion circuit, comprising a controller, characterized in that: The controller is programmed to perform the steps of the bus voltage control method for the PFC-side conversion circuit as described in any one of claims 1 to 7.

9. A vehicle, characterized in that: A bus voltage control system including the PFC-side conversion circuit as described in claim 8.

10. A medium, characterized in that: It contains a computer-readable program that, when invoked, performs the steps of the bus voltage control method for the PFC-side conversion circuit as described in any one of claims 1 to 7.

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