A DAB soft start and fault ride-through control method for bidirectional OBC

Abstract

The application provides a DAB soft start and fault ride-through control method for bidirectional OBC, which comprises the following steps: initializing the controller after the system is powered on; starting PWM and collecting the primary side current i-p(t) and output voltage V-out(t) during the PWM starting process; in two adjacent control periods, the intelligent core predicts the current value of the next period or the current value of several periods in the previous period; the executor adjusts the working state of the PWM according to the predicted current value; a fault ride-through state machine and a fault ride-through management method are created in the intelligent core; the fault flag of the PWM is monitored in the closed-loop control mode, and preset actions are performed according to the fault ride-through management method. The application realizes soft start based on predictive state observation, and realizes multi-mode modulation and smooth switching mechanism through the creation of the fault ride-through state machine, so that stronger dynamic performance and real-time response performance are obtained.

Description

Technical Field

[0001] This invention belongs to the field of bidirectional on-board charger start-up control technology, and particularly relates to a DAB soft start and fault ride-through control method for bidirectional OBC. Background Technology

[0002] Bidirectional on-board chargers (DBAs) are key components for vehicle-to-grid (V2G) interaction in new energy vehicles, and their core power conversion stage often employs a dual active bridge topology. DBAs achieve electrical isolation and bidirectional energy transfer through high-frequency transformers, offering advantages such as a wide soft-switching range, high power density, and ease of bidirectional flow implementation. However, a DBA is a high-order nonlinear system with complex dynamic processes, including startup and operation. During startup, in the initial stage, the transformer flux needs to be established, and a large amount of capacitance on the secondary side needs to be charged. If a large displacement ratio is applied directly at this time, it is equivalent to applying voltage to a near-short-circuit circuit, which will inevitably lead to current spikes.

[0003] During operation: The OBC (On-Board Charger), as the interface between the power grid and the battery, needs to cope with various non-ideal operating conditions such as grid fluctuations, sudden power requests from the battery management system (BMS), and even communication loss. These transient events can instantly disrupt the power balance of the DAB, leading to current or voltage runaway.

[0004] The closest existing technical solution: Currently, the most common solution is "fixed slope open-loop soft start + overcurrent / overvoltage closed-loop protection".

[0005] 1. Soft start phase: The control system starts with a safe, small shift ratio (or duty cycle) and gradually increases the shift ratio at a preset, fixed slope until the output voltage or current reaches the target value, then switches to closed-loop control mode. This process is usually open-loop.

[0006] 2. Fault Protection Phase: During operation, key parameters (such as transformer primary and secondary currents and DC bus voltage) are monitored in real time by sensors. Once overcurrent or overvoltage is detected, the protection circuit will act immediately, usually by "hard-shutting down" all switching transistors or "locking up" the drive signal to shut down the system. Restarting will be attempted after the fault disappears.

[0007] As can be seen from the above, the existing system has the disadvantages of poor adaptability, slow response, and blindness, and is not suitable for the current development needs of new energy electric vehicles. Summary of the Invention

[0008] To address the shortcomings of existing systems described in the background art, such as poor adaptability, slow response, and blind operation, which make them unsuitable for the current development needs of new energy electric vehicles, this invention proposes the following technical solution: A method for DAB soft start and fault ride-through control for bidirectional OBC includes: initializing the controller after the system is powered on; PWM is started and the primary current ip(t) and output voltage V-out(t) are acquired during the PWM startup process; In two adjacent control cycles, the intelligent central control system predicts the current value for the next cycle or the current value for several cycles in the previous cycle. The actuator adjusts the operating state of the PWM according to the predicted current value; A fault-travel state machine and a fault-travel management method are created within the intelligent hub. In closed-loop control mode, the fault flag of the PWM is monitored, and preset actions are executed according to the fault ride-through management method.

[0009] The operating states of the fault-finding drone include: normal state, detection state, crossing state, and recovery state. When the system is in closed-loop control mode, the fault-finding drone is in normal state. When the fault marker is within the safe zone, the fault-finding drone is in detection state. When the fault marker leaves the safe zone, the fault-finding drone is in crossing state, and the controller executes a preset action, causing the fault-finding drone to enter recovery state after the fault marker returns to the safe zone. After the fault-finding drone enters recovery state, the system gradually returns to closed-loop control mode.

[0010] Furthermore, within each control cycle, the control center predicts the next cycle based on a prediction function formed by the rate of change of current and the rate of change of voltage; wherein, the prediction function is: i-predict=ip(t)+(di / dt)*ΔT.

[0011] Furthermore, after system initialization, the controller first starts the PWM with an initial phase shift ratio D-start; when the system enters closed-loop control mode, the intelligent hub adjusts the phase shift ratio of the controller through predicted values, thereby controlling the operating state of the PWM.

[0012] Furthermore, within the closed-loop control mode, the current output by the PWM needs to be output through a dynamic limiter after passing through the current loop. When the PWM is first started and when the fault-riding machine is in the riding state, the output of the dynamic limiter is limited to the initial value.

[0013] Further, after the intelligent central unit completes the prediction, it needs to make a judgment based on the predicted value; if i-predict < K*I-safe-softstart, the actuator increases the phase shift ratio at a set slope; if i-predict ≥ K*I-safe-softstart, the actuator immediately maintains or reduces the current phase shift ratio until the predicted current value returns to the normal range.

[0014] Further, after the PWM is started, the intelligent central unit continuously makes predictions in each control cycle until the output voltage of the PWM enters the regulation range of the closed-loop control.

[0015] Beneficial effects: The present invention performs soft start based on state-observation prediction, and realizes multi-mode modulation and smooth switching mechanism by creating a fault ride-through state machine, thereby obtaining stronger dynamic performance and real-time response performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 FIG. is a schematic structural diagram of a DAB soft start and fault ride-through control method for a bidirectional OBC according to an embodiment of the present invention. DETAILED DESCRIPTION

[0017] In order to make the objectives, technical solutions, and advantages of the present application clearer, the present invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] It should be understood that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing this patent and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this patent.

[0019] Figure 1 FIG. is a schematic structural diagram of a DAB soft start and fault ride-through control method for a bidirectional OBC according to an embodiment of the present invention.

[0020] Refer to Figure 1 , according to an embodiment of the present invention Figure 1 A DAB soft start and fault ride-through control method for a bidirectional OBC according to an embodiment of the present invention includes: S000. Initialize the controller after the system is powered on.

[0021] S010. Start the PWM and collect the primary - side current \(i_p(t)\) and the output voltage \(V_{out}(t)\) during the PWM startup process.

[0022] Specifically, in this step, it is necessary to collect the primary - side current \(i_p(t)\) and the output voltage \(V_{out}(t)\) during the PWM startup process to provide a basis for subsequent prediction by the intelligent central unit. During this process, the controller needs to sample at a set frequency. And during the PWM startup process, the controller needs to set a relatively conservative initial moving ratio, and the specific value is adjusted according to different product performances.

[0023] S020. In two adjacent control cycles, the intelligent central unit predicts the current value in the next cycle or the current values in the next few cycles in the previous cycle.

[0024] Specifically, in this step, within two adjacent control cycles, the intelligent central unit predicts the current value in the next cycle or the current values in the subsequent few cycles one cycle in advance according to the prediction function formed by the control central unit based on the current change rate and the voltage change rate. The prediction function is:

[0025] \(i_{predict}=i_p(t)+(di / dt)*\Delta T\).

[0026] S030. The actuator adjusts the working state of the PWM according to the predicted current value.

[0027] Specifically, in this step, after the intelligent central unit obtains the current prediction value, it needs to adjust the operation of the PWM according to the predicted current value. Among them, the current prediction value generated by the intelligent central unit needs to be compared with the safety threshold \(I_{safe - softstart}\) set by the system. If \(i_{predict}<K*I_{safe - softstart}\), the actuator increases the moving ratio at a set slope; if \(i_{predict}\geq K*I_{safe - softstart}\), the actuator immediately maintains or reduces the current moving ratio until the predicted current value returns to the normal range. Here, \(K\) is a margin coefficient, which is specifically set according to different systems.

[0028] Furthermore, the prediction process of the intelligent central unit needs to continue until the PWM output voltage enters the regulation range of the closed - loop control before it can end, and after the prediction ends, the intelligent central unit seamlessly switches to the closed - loop control mode through the controller.

[0029] S040. Create a fault - ride - through state machine and a fault - ride - through management method in the intelligent central unit.

[0030] Specifically, during the initial system run, a fault-crossing state machine and corresponding fault-crossing management methods need to be created within the intelligent hub. Upon entering closed-loop control mode, the intelligent hub executes pre-set operations based on the state of the fault-crossing state machine. The operating states of the fault-crossing machine include: detection state, crossing state, and recovery state.

[0031] When the fault marker is within the safe zone, the fault-faulting ride-on vehicle is in detection mode. When the fault marker leaves the safe zone, the ride-on vehicle is in traversal mode, and the controller executes a preset action, causing the ride-on vehicle to enter recovery mode after the fault marker returns to the safe zone. After the ride-on vehicle enters recovery mode, the system gradually returns to closed-loop control mode and then resumes the inspection state.

[0032] S050. In closed-loop control mode, the fault flag of the PWM is monitored, and preset actions are performed according to the fault ride-through management method.

[0033] Specifically, in this step, it is necessary to monitor the fault flags of the PWM (Pulse Width Modulator) in real time, such as: (input voltage greater than the normal threshold or output current greater than the normal threshold, i.e., Vin - Vin_nom| > ΔV_in_threshold, or |I_p| > I_max_normal). When the PWM output is within the above range, it can be determined that the PWM has failed. At this time, the RCD drone executes the preset actions mentioned above. If there is a grid fluctuation, it switches to the "voltage regulation and current limiting" mode to prioritize the stability of the battery side and strictly limit the power drawn from the grid within a safe range. If there is a sudden load drop (such as the BMS suddenly reducing the charging current): the phase shift is quickly reduced, and it may switch to a modulation mode that can better handle the return power (such as extended phase shift).

[0034] Furthermore, in the closed-loop control, the current loop output passes through a dynamic limiter. During startup and ride-through, this limiter is set to a lower value; under normal conditions, it is set to the rated value. This limiter can be dated based on the heatsink temperature measured by a thermistor.

[0035] In summary, this invention achieves stronger dynamic performance and real-time response performance by performing soft start based on the predictive nature of state observation and realizing multi-mode modulation and smooth switching mechanism by creating a fault-crossing state machine.

[0036] The foregoing has described specific embodiments of the invention. Other embodiments are within the scope of the appended claims.

[0037] The terms “exemplary,” “example,” etc., used throughout this specification mean “serving as an example, instance, or illustration” and do not imply “preferred” or “advantageous” than other embodiments. Detailed descriptions are included for the purpose of providing an understanding of the described techniques. However, these techniques can be practiced without these detailed descriptions. In some instances, well-known structures and apparatuses are shown in block diagram form to avoid obscuring the concepts of the described embodiments.

[0038] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above embodiments. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention.

[0039] The foregoing description of this specification is provided to enable any person skilled in the art to implement or use the content of this specification. Various modifications to the content of this specification will be apparent to those skilled in the art, and the general principles defined herein can be applied to other variations without departing from the scope of protection of this specification. Therefore, this specification is not limited to the examples and designs described herein, but is consistent with the widest scope of the principles and novel features disclosed herein.

Claims

1. A method for DAB soft start and fault ride-through control for bidirectional OBC, characterized in that, Comprising: Initialize the controller after the system powers on. Start the PWM and collect the primary side current \(i_p(t)\) and the output voltage \(V_{out}(t)\) during the PWM startup process. In two adjacent control cycles, the intelligent center predicts the current value for the next cycle or the current values for the next few cycles in the previous cycle. The actuator adjusts the working state of the PWM according to the predicted current value. Create a fault ride-through state machine and a fault ride-through management method within the intelligent center. Monitor the fault flag of the PWM in the closed-loop control mode and execute preset actions according to the fault ride-through management method.

2. The DAB soft-start and fault-ride control method for bidirectional OBC as described in claim 1, characterized in that, The operating states of the fault ride-through machine include: detection state, ride-through state, and recovery state; where, when the fault flag is within the safe range, the fault ride-through machine is in the detection state; when the fault flag exits the safe range, the fault ride-through machine is in the ride-through state, and the controller executes preset actions to make the fault ride-through machine enter the recovery state after the fault flag returns to the safe range; when the fault ride-through machine enters the recovery state, the system gradually returns to the closed-loop control mode and re-enters the inspection state.

3. The DAB soft-start and fault-ride control method for bidirectional OBC as described in claim 2, characterized in that, In each control cycle, the control center predicts the next cycle according to the prediction function formed by the current change rate and the voltage change rate; where, the prediction function is: \(i_{predict}=i_p(t)+(\frac{di}{dt})*\Delta T\).

4. The DAB soft-start and fault-ride control method for bidirectional OBC as described in claim 3, characterized in that, After the system initialization, the controller first starts the PWM with the initial phase shift ratio \(D_{start}\). When the system enters the closed-loop control mode, the intelligent center adjusts the phase shift ratio of the controller through the predicted value, thereby controlling the operating state of the PWM.

5. The DAB soft-start and fault-ride control method for bidirectional OBC as described in claim 3, characterized in that, Within the closed-loop control mode, the current output by the PWM needs to pass through a dynamic limiter after passing through the current loop, and when the PWM starts for the first time and when the fault ride-through machine is in the ride-through state, the output of the dynamic limiter is limited to the initial value.

6. The DAB soft-start and fault-ride control method for bidirectional OBC according to claim 4, characterized in that, When the intelligent center completes the prediction, the intelligent center needs to judge according to the predicted value; if \(i_{predict}<K*I_{safe - softstart}\), the actuator increases the phase shift ratio at a set slope; if \(i_{predict}\geq K*I_{safe - softstart}\), the actuator immediately maintains or reduces the current phase shift ratio until the predicted current value returns to the normal range.

7. The DAB soft-start and fault-ride control method for bidirectional OBC according to claim 4, characterized in that, After the PWM starts, the intelligent center continuously makes predictions in each control cycle until the output voltage of the PWM enters the regulation range of the closed-loop control.

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