Please select the most similar patent number from A, B, C and D. Which number is?
A voltage control method. A train traveling speed can be acquired; a target transformation ratio corresponding to the train traveling speed is determined according to correspondences between train traveling speeds and transformation ratios, the transformation ratio being a ratio of an input voltage to an output voltage; an input voltage is then transformed according to the target transformation ratio to obtain an output voltage, the output voltage being used for driving a train to travel. The correspondences between train traveling speeds and transformation ratios are obtained according to correspondences between train traveling speeds and train traction forces at different transformation ratios. By means of the method, the most suitable transformation ratio can be provided according to a traveling speed of a maglev train, thereby increasing the traction force of the maglev train and improving running efficiency.
A: A vehicle braking method and device (200), and a train. The braking method comprises: obtaining the distance between a vehicle and a front vehicle (101); providing an alarm if the distance is smaller than or equal to a first threshold (102); receiving a first braking instruction triggered by a user, and braking the vehicle at a first preset deceleration according to the first braking instruction, wherein the first threshold is obtained according to the sum of a target idling stopping distance and an emergency braking distance, the target idling stopping distance is obtained according to at least one of a first idling stopping distance and a second idling stopping distance, the first idling stopping distance is the traveling distance of the vehicle in the process of obtaining the distance between the vehicle and the front vehicle, the second idling stopping distance is the traveling distance of the vehicle in the process of the user triggering the first braking instruction, and the emergency braking distance is the traveling distance for braking the vehicle at the first preset deceleration (103). The beneficial effects are that: a braking threshold is determined by considering the distance measuring capacity and the braking performance of a train, the rear-end collision risk with a front vehicle can be effectively reduced, and the running safety of the train is improved.
B: A train speed limit control method and device. The train speed limit control method comprises: detecting whether instability occurs during travelling of a train (S201, S301, S401, S501); if it is detected that instability occurs during travelling of the train, braking the train to limit the train speed to a first speed for traveling (S202, S302, S402, S502). The train speed limit control method implements automatic speed limit control during travelling of a train. The application of the train speed limit control method to train travel control can reduce the labor intensity of the driver, and automatically and timely limit the train speed when instability occurs during traveling of the train, thereby effectively preventing train travel safety from being affected by the driver&#39;s negligence.
C: A maglev train linear motor power supply circuit. Two sides of each levitation chassis are provided with linear motors. The linear motors on the same sides of levitation chassises on the same train section are connected to each other in series. The linear motors connected in series are divided into series units equal in amount. Series-parallel switch devices are disposed between the series units to achieve series-parallel switching of the series units. Also disclosed a power supply method for the maglev train linear motor power supply circuit. When a train starts to accelerate, the series-parallel switch devices are in a series position, and the series units operate in a series manner; when the train accelerates to a set speed, the series-parallel switch devices are in a parallel position, and the series units operate in parallel manner. The power supply circuit and the power supply method ensure both high-current tractive capacity for a train starting to accelerate and the requirement on high voltage of the linear motors when the train is in high-speed operation, and reduces the temperature rise of the linear motors.
D: A train overspeed protection method and device, the method comprising: when emergency braking is triggered for a train, obtaining an initial speed limit location point for each speed limit region from among a preset number of speed limit regions, and obtaining a first speed limit value corresponding to each initial speed limit location point so as to obtain a plurality of first speed limit values (S11); obtaining a current traveling location point of the train and a corresponding second speed limit value, and obtaining a current traveling speed of the train (S12); determining a plurality of deceleration speeds of the current traveling speed relative to each first speed limit value, selecting a deceleration speed from among the plurality of deceleration speeds which satisfies preset conditions, and setting the initial speed limit location point corresponding to the deceleration speed which satisfies the preset conditions as a target speed limit location point (S13); determining an emergency braking speed on the basis of a relative deceleration speed of the second speed limit value relative to the first speed limit value corresponding to the target speed limit location point (S14); performing overspeed protection on the train according to the emergency braking speed (S15). The method may effectively improve the accuracy of emergency braking speed calculation, reduce the calculation cycle, improve the traveling safety and efficiency of trains, and improve travel experience for users.
Answer: C