A control method for a braking resistor system

Abstract

This invention discloses a control method for a braking resistor system, relating to the field of electric vehicle technology. This control method outputs a PWM signal through the control strategy of the control module and uses the braking resistor to achieve DC-side voltage reduction and energy balance regulation, thereby ensuring battery SOC safety and voltage safety, improving driving experience, and protecting the battery and vehicle safety. Furthermore, this control method also outputs a PWM signal through the control strategy of the control module and uses the braking resistor to dissipate energy stored in the capacitor, thus achieving a safer active discharge method. Simultaneously, based on a voltage detection feedback closed loop, it achieves timely and safe control of active discharge, saving the passive discharge resistor in the high-voltage circuit of the motor controller and effectively optimizing control costs.

Description

Technical Field

[0001] This invention relates to the field of electric vehicle technology, and in particular to a control method for a braking resistor system. Background Technology

[0002] Compared to conventional gasoline vehicles, new energy vehicles can convert the vehicle's kinetic energy into electrical energy and store it in the battery through the drive system. However, in some special situations, such as when the vehicle is at a high SOC, recharging on a long downhill slope, or abnormally overcharged and the battery is saturated, continuing to convert the vehicle's kinetic energy into electrical energy will lead to battery overcharging, which can cause vehicle malfunctions and render the vehicle unable to drive, or even compromise vehicle safety. On the other hand, if the vehicle's kinetic energy is not converted into electrical energy in a timely manner, the vehicle's braking effect will become weak, which will also affect driving safety.

[0003] To address the aforementioned issues, Chinese Patent Application No. 201611090436.X discloses a braking resistor system and its control method for electric vehicles. This braking method determines whether to activate the braking resistor to dissipate excess regenerative braking energy based on the SOC value of the power battery. However, this method cannot simultaneously achieve DC voltage reduction under overvoltage conditions in the vehicle, thus having certain limitations.

[0004] Furthermore, a key safety concern with new energy vehicles is the high-voltage safety risk posed by the high-voltage electricity stored in the capacitors supporting the new energy components after the vehicle is powered off. A commonly used active discharge method in the industry involves the drive system discharging through the motor windings. By providing a D-axis current Id, the energy stored in the capacitors is released through the losses in the motor stator windings and power devices. However, this method may result in torque output during active discharge if there is a deviation in the initial position angle of the resolver, posing a safety risk to the vehicle's torque. Active discharge is also not feasible in situations such as low-voltage power loss or motor failure, similarly presenting safety risks. Summary of the Invention

[0005] This invention provides a control method for a braking resistor system, the main purpose of which is to solve the problems existing in the prior art.

[0006] The present invention adopts the following technical solution:

[0007] A control method for a braking resistor system, the braking resistor system comprising a control module, a drive module, and a power module interconnected; the power module is disposed between a power battery and a drive system, and the power module includes IGBT transistors and a braking resistor connected in series; the control method includes the following steps:

[0008] S11. Set the switching frequency f and period T of the IGBT tube according to the principle of minimum energy consumption;

[0009] S12. Real-time acquisition of DC terminal voltage U in this cycle, comparison of DC terminal voltage U with the set trigger threshold voltage U1 and hysteresis threshold U2, thereby determining whether there is overvoltage, and calculation of the conduction time t1 required to realize DC terminal step-down IGBT according to formula (1);

[0010]

[0011] In the formula: C is the capacitance value of the busbar support capacitor, R is the resistance value of the braking resistor, and t0 is the discharge time of the support capacitor required for overvoltage protection response.

[0012] S13. Real-time acquisition of torque T, speed n, and battery allowable charging power P within this cycle. B And static power P0, by checking whether the direction of rotational speed T and torque n is consistent, it is determined whether the vehicle has entered the energy recovery state, and the minimum conduction time t2 required for the IGBT tube to achieve energy balance is calculated according to formula (2);

[0013]

[0014] In the formula: P c For the feedback power of the drive system;

[0015] S14. Configure the on-time T of the IGBT tube within this cycle by combining the set period T and the on-times t1 and t2. on and disconnection time T off This controls the effective switching of the IGBT transistor, thereby controlling the braking resistor to achieve energy consumption;

[0016] S15. Repeat steps S12 to S14 to perform data acquisition, conduction time calculation and energy consumption for the next cycle until the vehicle stops and the machine is shut down, at which point the operation stops.

[0017] Furthermore, in step S14, a minimum disconnection time is set based on the actual engineering application. and maximum conduction time The conduction time T of the IGBT transistor on and disconnection time T off The rule for the value of is:

[0018] (a) If but

[0019] (b) If Then T on =t1+t2,T off =TT on ;

[0020] (c) If t1 + t2 = 0, then T on=0,T off =T.

[0021] Furthermore, it also includes the following steps:

[0022] S21. When the high voltage of the vehicle is detected to be down, the DC terminal voltage U in this cycle is obtained in real time, and the conduction time t3 required for the IGBT tube to achieve active discharge is calculated according to formula (3):

[0023]

[0024] Where: t is the discharge time of the supporting capacitor as required by national standards;

[0025] S22. Configure the on-time T of the IGBT tube within this cycle by combining the set period T and the on-time t3. on and disconnection time T off This controls the effective switching of the IGBT transistor, thereby controlling the braking resistor to achieve active discharge;

[0026] S23. Repeat steps S21 and S22 to perform data acquisition, conduction time calculation and active discharge for the next cycle until the vehicle stops and the machine is powered off, at which point the operation stops.

[0027] Furthermore, in step S22, a minimum disconnection time is set based on the actual engineering application. and maximum conduction time The conduction time T of the IGBT transistor on and disconnection time T off The rule for the value of is:

[0028] (a) If but

[0029] (b) If Then T on =t3,T off =TT on ;

[0030] (c) If t3 = 0, then T on =0,T off =T.

[0031] Furthermore, a pre-charge circuit is provided between the power battery and the drive system, and the power module is located at the rear end of the pre-charge circuit; in step S21, the control module determines whether the vehicle has completed the high-voltage power-off action by the status of the main relay and the pre-charge relay in the pre-charge circuit.

[0032] Furthermore, in step S13, the feedback power P c The calculation formula is:

[0033]

[0034] In the formula: η is the conversion efficiency of the driving system.

[0035] Furthermore, the driving module includes a driving chip circuit, a push-pull circuit, a gate resistor, and a clamping diode connected in sequence.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] 1. This invention outputs a PWM signal through the control strategy of the control module, and realizes DC voltage reduction and energy balance regulation through the braking resistor, thereby ensuring battery SOC safety and voltage safety, improving driving experience, and protecting battery and vehicle safety.

[0038] 2. This invention outputs a PWM signal through the control strategy of the control module and consumes energy stored in the capacitor through the braking resistor, thereby realizing a safer active discharge method. At the same time, based on the voltage detection feedback closed loop, it realizes timely and safe control of active discharge, saves the passive discharge resistor in the high voltage circuit of the motor controller, and effectively optimizes the control cost. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the principle of the present invention.

[0040] Figure 2 This is a circuit diagram of the present invention.

[0041] Figure 3 This is a high-voltage topology diagram of the present invention.

[0042] Figure 4 This is a schematic diagram of the IGBT tube cycle in this invention.

[0043] Figure 5 This is a schematic diagram of the trigger threshold voltage U1 and hysteresis threshold U2 in this invention.

[0044] Figure 6 This is a control principle diagram for achieving DC-side voltage reduction and energy recovery balance in this invention.

[0045] Figure 7 This is a schematic diagram illustrating the control principle for active discharge in this invention. Detailed Implementation

[0046] Specific embodiments of the present invention will now be described with reference to the accompanying drawings. Many details are described below to provide a comprehensive understanding of the invention; however, those skilled in the art will be able to implement the invention without these details.

[0047] like Figure 1 , Figure 2 and Figure 3 As shown, a braking resistor system includes a control module, a drive module, and a power module interconnected. The power module is located between the power battery and the drive system, and includes IGBT transistors and a braking resistor connected in series. The drive module amplifies the control signal from the control module and controls the IGBT transistors to open or close, thereby controlling the braking resistor to achieve energy consumption between the power battery and the drive system. Since the output current and output voltage of the control module generally do not meet the driving requirements of the power module, the drive module is needed to amplify the drive signal to meet the driving requirements of the power module. The braking resistor control system of this invention integrates the control module, drive module, and power module. Through the cooperation of the control module and drive module, efficient PWM control of the IGBT transistors can be performed, enabling the braking resistor to intelligently balance the energy between the power battery and the drive system in real time, thereby ensuring battery SOC safety and voltage safety.

[0048] like Figure 1 , Figure 2 and Figure 3 As shown, the drive module includes a drive chip circuit, a push-pull circuit, a gate resistor, and a clamping diode connected in sequence. Therefore, the drive module also features protection functions, fault feedback, drive signal interlocking, Miller clamping, and drive isolation. The control process of the drive module is as follows: the control module sends a control pulse, which amplifies the drive current through the drive chip; the drive chip output signal increases the circuit's load capacity through the push-pull circuit; the gate resistor selection and configuration optimize the voltage spikes and switching losses caused by high-current fast switching; the diode clamping protects the gate from voltage cutoff from the Miller capacitor; and the control signal controls the power module to achieve switching of the high-power side.

[0049] like Figure 1 , Figure 2 and Figure 3 As shown, the push-pull circuit includes a first push-pull circuit, a second push-pull circuit, and a third push-pull circuit that are interconnected. The three push-pull circuits can increase the drive current, ensure heat dissipation when under load, and increase the load-carrying capacity.

[0050] like Figure 1 , Figure 2 and Figure 3 As shown, a pre-charge circuit is provided between the power battery and the drive system, with the power module located at the rear end of the pre-charge circuit. Compared to a topology where the power module is located at the front end of the pre-charge circuit, this invention reduces the number of high-voltage devices recovering energy to the braking resistor, thus resulting in fewer failure points and a shorter high-voltage circuit. Furthermore, by utilizing the topology where the power module is located at the rear end of the pre-charge circuit, the active discharge function of the braking resistor can be achieved.

[0051] like Figure 1 , Figure 2 and Figure 3 As shown, the control module is connected to the CAN bus, so it can obtain the vehicle's operating status in real time through the CAN bus, such as the real-time status of the battery, the operating status of the drive system, and the safety status of the high-voltage circuit.

[0052] like Figure 1 , Figure 2 and Figure 3 As shown, as a preferred option, the chip model used in the driver chip circuit is IED020I12FA2.

[0053] like Figure 1 , Figure 2 and Figure 3 As shown, the preferred solution is a DSP control board.

[0054] The braking resistor system provided by this invention can not only achieve DC-end voltage reduction and energy balance regulation, but also achieve active discharge of the DC-end supporting capacitor. For example... Figure 6 As shown, the specific control method of the braking resistor system when performing DC-side voltage reduction and energy balance regulation includes the following steps:

[0055] S11. Set the switching frequency f and period T of the IGBT transistor according to the principle of minimum energy consumption. Specifically, the switching frequency is calculated based on key parameters such as the power battery, drive system, and braking resistor, and is set under the premise of meeting the low power consumption requirements of the power module and the power consumption of the braking resistor within the minimum cycle. More specifically, in application, parameters such as the capacitance value of the DC-side support capacitor C1, the power specification of the braking resistor, and the switching losses of the power module can be comprehensively considered, and the switching frequency f can be determined in combination with the actual application, thereby determining the period T.

[0056] Existing technologies typically employ hysteresis control to dissipate excess reclaimed energy in the drive system. Specifically, if the DC terminal voltage exceeds the hysteresis voltage, a braking resistor is activated to dissipate the excess energy in one go. This method results in the IGBT switching frequency varying with the excess energy difference, making it difficult to maintain a fixed frequency. This can easily lead to the DC terminal voltage being mixed with harmonics over a wide frequency range, causing abnormalities in the overall high-voltage environment. Therefore, this embodiment sets a fixed switching frequency and adjusts the IGBT's on-time T based on the duty cycle within a single cycle. on and disconnection time T off This effectively ensures stable and reliable DC terminal voltage.

[0057] like Figure 4 It can be seen that the conduction time T of the IGBT transistor within a single cycle on and disconnection time T off The relationship between the values ​​is: T = T on +Toff Therefore, in the following steps, it is necessary to control the conduction time T of the IGBT. on and disconnection time T off A detailed solution is then performed.

[0058] S12. Real-time acquisition of the DC terminal voltage U (i.e., the voltage at the supporting capacitor terminal) within this cycle, comparison of the DC terminal voltage U with the set trigger threshold voltage U1 and hysteresis threshold U2, thereby determining whether there is overvoltage, and calculation of the conduction time t1 required for the DC terminal step-down IGBT tube to achieve the following according to formula (1):

[0059]

[0060] In the formula: C is the capacitance value of the busbar support capacitor, R is the resistance value of the braking resistor, and t0 is the discharge time of the support capacitor required for overvoltage protection response.

[0061] During vehicle operation, high-voltage components may experience short-term overvoltage due to unforeseen factors. To ensure voltage safety, this invention introduces a control method that uses a braking resistor to reduce DC voltage, protecting the system's electrical components from damage. Specifically, the voltage safety involved is the minimum value among the maximum allowable operating voltages of all high-voltage components in the vehicle. Combined with system robustness settings, specific values ​​for the trigger threshold U1 and hysteresis threshold U2 can be set. Schematic diagrams of the threshold voltage U1 and hysteresis threshold U2 are shown below. Figure 5 As shown. Therefore, by comparing the real-time collected DC terminal voltage U with the set trigger threshold U1 and hysteresis threshold U2, and configuring the conduction time t1 based on the abnormal voltage deviation state, DC terminal voltage reduction can be achieved.

[0062] S13. Real-time acquisition of torque T, speed n, and battery allowable charging power P within this cycle. B And static power P0, by checking whether the directions of rotational speed T and torque n are consistent, it is determined whether the vehicle has entered the energy recovery state, and the minimum conduction time t2 required for the IGBT tube to achieve energy balance is calculated according to formula (2):

[0063]

[0064] In the formula: P c This is the feedback power for the drive system.

[0065] Specifically, when the drive system performs energy recovery, in order to ensure the vehicle's energy balance, the minimum allowable charging power P of the battery should be met. B Static power P0, energy consumed by braking resistor P r The sum of these three equals the feedback power P of the drive system. c ,Right now:

[0066] PB +P0+P e =P c (2.1)

[0067] In formula (2.1), the battery's allowable charging power P B This can be obtained in real time via the CAN bus; the static power P0 is the power of the high and low voltage components of the vehicle when the vehicle is stationary, and this power consumption can be identified by the static power consumption of the DC terminal when the vehicle is stationary and stable; and combined with the fixed frequency set in step S11, it can be known that the energy consumed by the braking resistor P in a single cycle is... r The calculation formula is:

[0068]

[0069] Therefore, by combining formulas (2.1) and (2.2), we can obtain the above formula (2).

[0070] Based on the vehicle's energy flow state determined by the rotational speed n and torque T, and considering the drive system's conversion efficiency η, the drive system's feedback power P is then determined. c The calculation formula is:

[0071]

[0072] Therefore, by combining equations (2) and (2.3), we can further obtain the formula for calculating the conduction time t2 when the braking resistor consumes the reclaimed energy of the drive system:

[0073]

[0074] S14. Configure the on-time T of the IGBT tube within this cycle by combining the set period T and the on-times t1 and t2. on and disconnection time T off This controls the effective switching of the IGBT transistor, thereby controlling the braking resistor to achieve energy consumption.

[0075] Under normal circumstances, the on-time T of the IGBT in the current cycle can be obtained by effectively summing the on-times t1 and t2. on That is, T on =t1+t2; Simultaneously, by combining this with the set period T, the IGBT tube's off-time T within this period can be calculated. off That is, T off =TT on .

[0076] However, considering that in actual calculations, if the conduction time t1 required to achieve DC-side step-down IGBT and / or the conduction time t2 required to achieve energy balance IGBT are large, it will lead to a large IGBT off-time T within a single cycle.off The value ≤0 affects the set switching frequency f. Therefore, this invention sets a minimum disconnection time based on practical engineering applications. and maximum conduction time The actual conduction time T of the IGBT in a single cycle on and disconnection time T off The value should be determined based on the magnitude of t1+t2. If t1+t2 = 0, it indicates that there is no overvoltage at the DC end and the vehicle's energy remains balanced; therefore, the power module does not need to operate during this cycle. From this, we can determine the conduction time T of the IGBT transistor. on and disconnection time T off The value of should follow the following rules:

[0077] (a) If but

[0078] (b) If Then T on =t1+t2,T off =TT on ;

[0079] (c) If t1 + t2 = 0, then T on =0,T off =T.

[0080] S15. Repeat steps S12 to S14 to perform data acquisition, conduction time calculation and energy consumption for the next cycle until the vehicle stops and the machine is shut down, at which point the operation stops.

[0081] As can be seen from steps S11 to S15, the design concept of this invention is to output a PWM signal through the control strategy of the control module, and to realize DC voltage reduction and energy balance regulation through the braking resistor, thereby ensuring battery SOC safety and voltage safety, improving driving experience, and protecting battery and vehicle safety.

[0082] like Figure 7 As shown, the control method of the braking resistor system during active discharge of the DC-terminal supporting capacitor includes the following steps:

[0083] S21. When the high voltage of the vehicle is detected to be down, the DC terminal voltage U in this cycle is obtained in real time, and the conduction time t3 required for the IGBT tube to achieve active discharge is calculated according to formula (3):

[0084]

[0085] In the formula, t represents the discharge time of the supporting capacitor as required by national standards. According to GB / T 18488.1-2015, when the power supply to the drive motor controller is cut off, the capacitor of the drive motor controller should discharge to below 60V. Specifically, when there is an active discharge requirement for the drive motor controller, the discharge time of the supporting capacitor should not exceed 3 seconds. Based on market application needs, the active discharge time is generally controlled to be around 1 second.

[0086] Specifically, the control module determines whether the vehicle has completed the high-voltage power-off action by checking the status of the main relay SW1 and the pre-charge relay SW2 in the pre-charge circuit. When both the main relay SW1 and the pre-charge relay SW2 are detected to be in the open state, it indicates that the vehicle has been powered off, thus meeting the conditions for initiating active discharge.

[0087] Under the condition of satisfying the active discharge start-up, the control module first obtains the DC terminal voltage U, thereby calculating the energy stored in the DC terminal capacitor, and further calculates the conduction time t3 required by the IGBT to realize active discharge. In order to improve the calculation efficiency, this invention has summarized and refined this step, so the conduction time t3 can be quickly calculated by simply using formula (3).

[0088] S22. Configure the on-time T of the IGBT tube within this cycle by combining the set period T and the on-time t3. on and disconnection time T off Similarly, in order to maintain a fixed switching frequency f, the conduction time T of the IGBT during active discharge is... on and disconnection time T off The value of should follow the following rules:

[0089] (a) If but

[0090] (b) If Then T on =t3,T off =TT on ;

[0091] (c) If t3 = 0, then T on =0,T off =T.

[0092] S23. Repeat steps S21 and S22 to perform data acquisition, conduction time calculation and active discharge for the next cycle until the vehicle stops and the machine is powered off, at which point the operation stops.

[0093] As can be seen from steps S21 to S23, the design concept of this invention is to output a PWM signal through the control strategy of the control module and consume the energy stored in the capacitor through the braking resistor, thereby realizing a safer active discharge method. At the same time, based on the voltage detection feedback closed loop, timely and safe control of active discharge is realized, saving the passive discharge resistor of the high voltage circuit of the motor controller and effectively optimizing the control cost.

[0094] The above are merely specific embodiments of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention using this concept shall be considered as infringing upon the protection scope of the present invention.

Claims

1. A control method of a braking resistor system, characterized by: The braking resistance system comprises a control module, a driving module and a power module connected with each other; the power module is arranged between a power battery and a driving system, and comprises IGBT tubes and braking resistors connected with each other in series; the control method comprises the following steps: S11, setting the switching frequency f and the period T of the IGBT tube according to the principle of minimum energy consumption; S12, real-time acquisition of the DC terminal voltage U between the bus support capacitor in this period, the DC terminal voltage U and the set trigger threshold voltage and hysteresis threshold Comparison, thus determine whether overvoltage, and according to formula (1) to calculate the required conduction time of DC terminal voltage reduction IGBT tube ; In the formula, C is the capacitance value of the bus support capacitor, and R is the resistance value of the braking resistor. Discharge time of the support capacitor required for the overvoltage protection response S13, real-time acquisition of torque T, speed n, and battery allowable charging power in the current period and static power , whether the vehicle enters the energy recovery state is judged by whether the directions of speed T and torque n are consistent, and the conduction time required for the IGBT tube to achieve energy balance is calculated according to formula (2) ; In the formula: is the feedback power of the drive system; S14, combine the set period T and the on time and Configure the on time of the IGBT tube in this period and off time , thus controlling the effective switching of the IGBT tube, thereby controlling the energy consumption of the braking resistor; based on the actual engineering application, set the minimum off time and the maximum on time , the value law of the on time and off time of the IGBT tube is: (a) if then , ; (b) if then , ; (c) if then , ; S15, repeating steps S12 to S14 to perform data acquisition, conduction time calculation and energy consumption in the next period until the vehicle is parked and shut down, and then stopping working.

2. A control method of a braking resistor system according to claim 1, characterized by: Further comprising the following steps: S21, when detecting the whole vehicle high voltage power down, real-time acquisition of the direct current terminal voltage in this period And according to formula (3) to calculate the required conduction time of IGBT tube when active discharge is realized : In the formula, t is the discharge time of the support capacitor required by the national standard; S22, combine the set period T and the on time Configure the on time of the IGBT tube in this period And the off time , thereby controlling the effective switching of the IGBT tube, thereby controlling the braking resistance to achieve active discharge; S23, repeating steps S21 and S22 to perform data acquisition, conduction time calculation and active discharge in the next period until the vehicle is parked and shut down, and then stopping working.

3. A control method of a braking resistor system according to claim 2, characterized in that: In step S22, the minimum off time is set based on actual engineering application and the maximum on time , the value rule of the on time and off time of the IGBT tube is: (a) if then , ; (b) if then , ; (c) if then , .

4. A control method of a braking resistor system according to claim 2, characterized by: A pre-charging circuit is arranged between the power battery and the driving system, and the power module is arranged at the rear end of the pre-charging circuit; in step S21, the control module judges whether the vehicle completes the high-voltage power-off action through the states of the main relay and the pre-charging relay in the pre-charging circuit.

5. The control method of a braking resistor system according to claim 1, characterized by: In step S13, the feedback power is calculated as follows: In the formula: The drive system conversion efficiency.

6. A control method of a braking resistor system according to claim 1, characterized by: The driving module comprises a driving chip circuit, a push-pull circuit, a gate-level resistor and a clamping diode connected in sequence.

Images