Rail transit emergency traction multipath interleaving parallel direct current converter

Abstract

The invention provides a design of a low-voltage large-current multi-path interleaved parallel direct-current converter. High-voltage output is achieved through a train storage battery, multi-path interleaving parallel connection is adopted, output current ripples and power loss are effectively reduced, large-current output and power density improvement are achieved, electrical stress borne by power devices is reduced, device loss is reduced, the service life of the devices is prolonged, branch inductive current ripples are mutually restrained at the input end, and the output voltage is improved. And the input current ripples are effectively reduced. And moreover, automatic switching of voltage control modes is realized through software control, the adaptability to voltage regulation under different working conditions such as light load and normal conditions is obviously improved, and the output voltage requirements under various conditions are met. Meanwhile, when a branch fault occurs, the fault branch is quitted from running, other branches are organized to continue running, and the running reliability of the equipment is improved.

Description

Technical Field

[0001] The invention relates to the field of operation and control of rail transit traction systems, and in particular to a rail transit emergency traction multi-path staggered parallel DC converter. Background Art

[0002] When the train is pulled by batteries, due to the characteristics of the batteries themselves and the high power, harsh working environment and complex working conditions of rail transit vehicles, the output voltage of the batteries fluctuates greatly, the output voltage and current ripple is large, and it is impossible to discharge for a long time and at high power, which causes the temperature of the traction motor and traction inverter to rise, causing a great impact on the train traction system, reducing the efficiency of the train traction motor, affecting the working stability and continuous working ability of the battery emergency traction system, reducing the emergency traction performance, and significantly affecting the battery life, seriously affecting the safe and stable operation of the subway train battery emergency traction.

[0003] At present, most domestic trains use 110V batteries for direct power supply or batteries combined with DC / AC and DC / DC of single-branch converters to provide power for emergency traction, so as to realize the traction function of the train in an emergency. However, the traction system usually has a large power. The existing solution has a large single-circuit current, large electrical stress, high requirements for power devices, and may damage the battery life, easily causing equipment damage and insufficient output power, while causing large current ripple. The existing technical solution has only one voltage control mode in the output mode, and is not well adapted to the voltage regulation requirements under different working conditions, especially the slow voltage recovery at the moment of battery traction, which can easily lead to the failure of pre-charging of the traction system, and the whole system will be out of operation when any branch fails, and the reliability is poor. In addition, the existing products generally do not have data communication capabilities, and can only be started by the driver manually operating the knife closure to connect the converter to the battery. The system circuit is complex and the reliability is low. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a rail transit emergency traction multi-path staggered parallel DC converter, which adopts a PWM controlled Boost circuit topology, including a control module, a sampling module, and a switch tube control circuit;

[0005] The switch tube control circuit includes 9 parallel Boost circuits, which are evenly divided into 3 groups. The switch tube PWM control pulses are rearranged and combined by combining intra-group phase shifting and inter-group phase shifting to perform phase shift control on each circuit.

[0006] Wherein, the control module adopts a model prediction algorithm;

[0007] The sampling module is used to sample the voltage and current of each circuit.

[0008] Furthermore, the inter-group control phase shift angle lags by 40°, and the intra-group control phase shift angle lags by 120°.

[0009] Furthermore, when one or more circuits are identified to have failed, an emergency operation mode is adopted: a control strategy of individually shifting the phase of each branch is adopted, and phase shift angles are sequentially allocated to normal branches.

[0010] Furthermore, the specific steps of the model prediction algorithm are:

[0011] Establish a discrete state model of the system represented by state-space equations;

[0012] According to the model design software control, after sampling the voltage and current at the current moment, the estimated value of the variable at the next moment is calculated;

[0013] Constrain the results according to the limit values ​​of the actual working conditions of the system;

[0014] Obtain the compensation control signal of the system according to minimization of the objective function;

[0015] The compensation control signal is combined with the control signal of the dual closed-loop output, and after feedforward compensation, the optimal duty cycle value is finally calculated as the actual control signal of the current phase circuit, which is used to control the switching of each main switch tube.

[0016] Furthermore, the control module also adopts a group operation control strategy, specifically:

[0017] If the current output power is small, one or two groups of branches are put into operation;

[0018] If the current output power is large, all branches are put into operation.

[0019] Furthermore, the DC converter also includes a judgment module;

[0020] The judgment module judges based on the current output voltage and current:

[0021] If the current is less than the set value, it is judged to enter the pre-charge / light load process and switched to the light load mode for control;

[0022] If the current is greater than the set value, it is judged to enter the normal operation process and switch to the operation mode for control.

[0023] Furthermore, the DC converter also includes a protection module, including hardware protection and software protection;

[0024] The hardware protection includes IGBT drive protection, overcurrent protection, overload protection, and overtemperature protection;

[0025] The software protection includes overvoltage and undervoltage protection and software overcurrent protection.

[0026] Furthermore, the DC converter also includes a communication module, which performs data transmission according to a prescribed communication protocol and displays the information on a control screen for the train driver.

[0027] Furthermore, the DC converter also includes a host computer for on-site debugging and parameter adjustment.

[0028] In a second aspect, the present invention provides a voltage and current dual closed-loop control combined with a feedforward control strategy based on model predictive control optimization, the specific steps are:

[0029] According to the circuit topology of the DC converter, a corresponding number of current inner loops and voltage outer loops are set;

[0030] Establish a discrete state model of the system represented by state-space equations;

[0031] According to the model design software control, after sampling the voltage and current at the current moment, the estimated value of the variable at the next moment is calculated;

[0032] Constrain the results according to the limit values ​​of the actual working conditions of the system;

[0033] Obtain the compensation control signal of the system according to minimization of the objective function;

[0034] The compensation control signal is combined with the control signal of the dual closed-loop output, and after feedforward compensation, the optimal duty cycle value is finally calculated as the actual control signal of the current phase circuit to control the switching of each main switch tube.

[0035] Beneficial effects of the present invention:

[0036] Compared with the power supply mode of directly powering by a battery or through a single branch converter, the DC / DC converter mode of the present invention has a simple device structure, easy control algorithm implementation, large output power, high efficiency, and can realize multi-circuit current sharing and stable control, high control accuracy, and can realize high-performance control at low switching frequency, and has low requirements on devices, high device reliability, strong stability, and low cost. The present invention adopts multi-path staggered parallel connection, effectively reduces output current ripple and power loss, realizes large current output and power density improvement, reduces the electrical stress of each power device, reduces device loss, and improves device life. The branch inductor current ripples are mutually suppressed at the input end, effectively reducing the input current ripple. And the voltage control mode is automatically switched through software control, and the voltage regulation adaptability to different working conditions such as light load and normal is significantly improved, meeting the output voltage requirements under various conditions. At the same time, the present invention can realize that when a branch fault occurs, the faulty branch is withdrawn from operation, and other branches are organized to continue to operate, thereby improving the reliability of equipment operation. The present invention also designs a data communication module for DCDC, which can transmit detailed data such as system status with external devices such as batteries and host computers, and use control signals to operate the equipment to start and stop. It has a simple and effective structure, and when a fault occurs, it can transmit fault information to the driver and other upper layers through the communication protocol. It has a high degree of visualization, which is convenient for technical personnel to analyze and deal with. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention has the following accompanying drawings:

[0038] Figure 1 A topological schematic diagram of the present invention;

[0039] Figure 2 Schematic diagram of staggered parallel connection;

[0040] Figure 3 Examples of emergency operation modes;

[0041] Figure 4 Control strategy block diagram;

[0042] Figure 5 Schematic diagram of group operation control;

[0043] Figure 6 Host computer interface example;

[0044] Figure 7 Virtual oscilloscope interface example;

[0045] Figure 8 Example of remote programming interface. DETAILED DESCRIPTION

[0046] In order to make the objects, advantages and features of the present invention more obvious, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] This embodiment uses the train's DC110V battery to achieve a 500V voltage output, and adopts a staggered parallel, dual closed-loop master-slave setting method to provide stable voltage, current and power output for the train and traction system, so that the train can obtain a single-battery traction mode and run a certain distance at a certain speed, generally to the next station or return to the previous station, so that operations such as passenger evacuation and train return can be carried out, reducing the impact on normal operation, or daily operations such as shunting and car washing within the section can be carried out.

[0048] like Figure 1 , which is a topological diagram of a rail transit emergency multi-path staggered parallel DC converter of the present invention. The basic principle of this DC / DC converter is the principle of a Boost circuit controlled by PWM. The control method includes controlling the converter by a model prediction algorithm based on voltage and current sampling. It also has current sharing control, automatic mode switching, fault and protection control, and the ability to communicate by means of CAN, Ethernet, etc. At the same time, detection software is designed to detect the status of the equipment and conduct on-site debugging.

[0049] like Figure 2 , Group interleaving control is to divide the nine parallel boost circuits into three groups, and use the combination of intra-group phase shifting and inter-group phase shifting to re-arrange and combine the switch tube PWM control pulses, and perform phase shift control on each circuit. For example: the fourth circuit of the inter-group control lags 40° behind the first circuit, that is, the phase shift angle, and the second circuit of the intra-group control lags 120° behind the first circuit, and so on. Through interleaving, the effect of eliminating harmonics in different circuits can be achieved, thereby optimizing the output control effect and achieving a better current sharing effect.

[0050] The present invention can perform emergency operation in the case of single-line or multi-line faults. If one or more lines stop running due to a fault, it can be forced to enter the emergency operation mode, detect the fault-free branches, and regroup them through software. At this time, the system no longer uses the above-mentioned group phase shifting and inter-group phase shifting strategies, but adopts a control strategy of phase shifting for each branch separately, and allocates phase shift angles to normal branches in turn, such as Figure 3 , if three branches are out of operation, the phase shift angle of each remaining branch is 60°, and so on. At the same time, the system limits the output command according to the remaining number of branches to avoid equipment damage. This enables the equipment to ensure power output under emergency conditions and improve equipment reliability.

[0051] like Figure 4In order to make each phase of the staggered parallel Boost circuit in the DC / DC converter realize current sharing, the present invention designs a voltage and current dual closed-loop control based on model predictive control optimization combined with a feedforward control strategy, and sets 9 current inner loops and 1 voltage outer loop. First, by sampling each current and output voltage, after dual closed-loop calculation, the output control signal is obtained after limiting and anti-interference. At the same time, the control accuracy is improved to obtain a better phase-to-phase current sharing effect. The present invention optimizes and adopts a model predictive control strategy, establishes a system discrete state model represented by a state space equation, and designs software control according to the established prediction model. After sampling the voltage and current at the current moment, the variable estimate value at the next moment is calculated based on this, and the result is constrained according to the limit value of the actual working condition of the system. At the same time, in order to ensure the dynamic performance of the system, the software also designs the minimization of the objective function to obtain the compensation control signal of the system. The signal is combined with the control signal output by the dual closed-loop, and after feedforward compensation, the optimal duty cycle value is finally calculated as the actual control signal of the current phase circuit to control the switching of each main switch tube. Through the model prediction algorithm and the superposition of dual closed-loop and feedforward compensation, the control accuracy of the converter is greatly improved, with better current sharing control performance, strong anti-interference ability, and better ability to achieve voltage stabilization output.

[0052] like Figure 5 The present invention has the ability to operate in a closed loop with a single branch group. It judges through voltage and current sampling. If the current output power is small, only one or two groups (each group has three branches) are put into operation. If the current output power is large, all branches are put into operation. This strategy can flexibly adjust the running branches to avoid the circuit entering the intermittent mode and causing the efficiency to decrease. It can effectively reduce the switching loss and reduce the current ripple. Such a modular design also enables the equipment to be optimized for different train traction powers.

[0053] In a preferred embodiment, the present invention also proposes a control method for automatic mode switching of the converter, and realizes the function of automatic mode switching, which is mainly used to switch control parameters under different load conditions to achieve better voltage dynamic effects and avoid the occurrence of faults such as failure of pre-charging of the traction system. By collecting the current output voltage and current and entering the judgment module for judgment, if the current is less than the set value, it is judged to enter the pre-charging / light-load process, and switch to the light-load mode for control to improve the voltage dynamic performance, meet the pre-charging voltage and current requirements or quickly follow the equipment operation mode; if the current is greater than the set value, it is judged to enter the normal operation process, and switch to the operation mode for control to improve the equipment operation stability and avoid short-term overvoltage, overcurrent and other faults caused by large-scale fluctuations in voltage and current.

[0054] In a preferred embodiment, the present invention designs a fault and protection control method, which has the functions of equipment hardware protection and software protection. In order to prevent the equipment from being damaged due to overcurrent and other reasons, the hardware includes IGBT drive protection, overcurrent protection, overload protection, overtemperature protection, etc. When a fault occurs, the device detects the fault data, quickly responds to the protection signal, and blocks the IGBT drive pulse in microseconds to shut down the equipment. And according to the communication protocol, the corresponding fault code is output to the DSP, and the DSP reports the fault. Software protection includes overvoltage and undervoltage protection, software overcurrent protection, etc. If a related fault occurs (such as voltage below a certain level) for a certain period of time, the software program blocks the IGBT drive pulse and reports the fault code.

[0055] In a preferred embodiment, the present invention has a CAN bus communication function, which can realize data transmission such as battery power and fault information between the battery and the DCDC module according to the prescribed communication protocol, and display the information on the train driver's control screen. When the train is running, the system is always electrically connected to the battery until the driver switches to the emergency traction mode, and the vehicle transmits a start signal through CAN communication to start the device.

[0056] In order to better explain the host computer, Figure 6 It is the host computer interface. In order to facilitate on-site debugging and parameter adjustment, and intuitively understand the operating status of the equipment, the present invention has developed a host computer software that can realize system status, version, and fault display, and can also display system voltage, current, and various parameters. The software is a WinForm form application developed in the Visual Studio environment based on the C# language. It uses a database, and the program is written using the ADO.NET component provided by VS to access the database. The Socket communication method is used to complete the communication between the host computer and the control board. A fixed IP address is assigned to the control board for communication. The host computer also uses a fixed IP address synchronously, and a communication protocol is designed to establish a communication connection to complete transparent data transmission.

[0057] In the stage from the host computer to the DSP (sending), the trigger of the host computer sending data downward is realized by clicking the interface button. After clicking the control, the program encapsulates the current instruction information to be sent according to the data packet format specified by the communication protocol and sends it to the control board. In the stage from the DSP to the host computer (receiving), according to the communication protocol, the bottom communication unit sends data of a specified length to the host computer every second. The host computer parses the received data and displays it on the interface.

[0058] Figure 7It is a virtual oscilloscope interface. To facilitate monitoring and debugging, the present invention develops a virtual oscilloscope software. The software is connected through Ethernet and uses Socket communication to realize the connection between the host computer and the underlying board, and a fixed IP address is assigned to the control board. The sampling frequency of the virtual oscilloscope can be changed according to actual conditions. It has 6 observation channels, each of which can adjust the horizontal and vertical axis display ratio, waveform position, etc., and has the functions of pausing observation and cursor measurement, and can automatically calculate the peak-to-peak value, average value, and effective value of each waveform.

[0059] Figure 8 For the remote burning interface and to facilitate on-site debugging, the present invention designs a remote burning function based on the host computer, which can realize the burning of the DSP program through the network cable in the form of serial port to Ethernet without connecting the emulator. The host computer communicates with the DSP through MAX232 and CPLD after data processing. After the remote burning function is started, the host computer sends handshake data according to the communication protocol. After the handshake is successful, the CPLD performs the remote burning action of the DSP: after resetting the DSP and setting the BOOT mode of the DSP, the CPLD replies one byte of data to the host computer through the data line, indicating that remote burning is allowed, and the CPLD will no longer forward the data sent by the DSP; after the host computer reads the data replied by the CPLD, the file compiled and generated by the DSP is converted and sent to the DSP through the CPLD for remote burning.

[0060] The above implementation modes are only used to illustrate the present invention, but not to limit the present invention. Ordinary technicians in the relevant technical field can make various changes and modifications without departing from the essence and scope of the present invention. Therefore, all equivalent technical solutions also belong to the scope of the present invention. The scope of patent protection of the present invention should be limited by the claims.

[0061] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A rail transit emergency traction multi-path staggered parallel DC converter, using a PWM controlled Boost circuit topology, characterized in that: It includes a control module, a sampling module, and a switch tube control circuit; The switch tube control circuit includes 9 parallel Boost circuits, which are evenly divided into 3 groups. The switch tube PWM control pulses are rearranged and combined by combining intra-group phase shifting and inter-group phase shifting to perform phase shift control on each circuit. Wherein, the control module adopts a model prediction algorithm; The sampling module is used to sample the voltage and current of each circuit.

2. The DC converter according to claim 1, characterized in that: The phase shift angle of inter-group control lags by 40°; the phase shift angle of intra-group control lags by 120°.

3. The DC converter according to claim 1, characterized in that: When one or more circuits are identified to have failed, the emergency operation mode is adopted: a control strategy of phase shifting is adopted for each branch individually, and phase shift angles are allocated to the normal branches in turn.

4. The DC converter according to claim 1, characterized in that: The specific steps of the model prediction algorithm are: Establish a discrete state model of the system represented by state-space equations; According to the model design software control, after sampling the voltage and current at the current moment, the estimated value of the variable at the next moment is calculated; Constrain the results according to the limit values ​​of the actual working conditions of the system; Obtain the compensation control signal of the system according to minimization of the objective function; The compensation control signal is combined with the control signal of the dual closed-loop output, and after feedforward compensation, the optimal duty cycle value is finally calculated as the actual control signal of the current phase circuit, which is used to control the switching of each main switch tube.

5. The DC converter according to claim 1, characterized in that: The control module also adopts a group operation control strategy, specifically: If the current output power is small, one or two groups of branches are put into operation; If the current output power is large, all branches are put into operation.

6. The DC converter according to claim 1, characterized in that: Also includes a judgment module; The judgment module judges based on the current output voltage and current: If the current is less than the set value, it is judged to enter the pre-charge / light load process and switched to the light load mode for control; If the current is greater than the set value, it is judged to enter the normal operation process and switch to the operation mode for control.

7. The DC converter according to claim 1, characterized in that: It also includes protection modules, including hardware protection and software protection; The hardware protection includes IGBT drive protection, overcurrent protection, overload protection, and overtemperature protection; The software protection includes overvoltage and undervoltage protection and software overcurrent protection.

8. The DC converter according to claim 1, characterized in that: It also includes a communication module that transmits data in accordance with the specified communication protocol and displays the information on the train driver's control screen.

9. The DC converter according to claim 1, characterized in that: It also includes a host computer for on-site debugging and parameter adjustment.

10. A voltage and current double closed-loop control combined with a feedforward control strategy based on model predictive control optimization, characterized in that: Based on the DC converter as described in any of claims 1 to 9, the specific steps are: According to the circuit topology of the DC converter, a corresponding number of current inner loops and voltage outer loops are set; Establish a discrete state model of the system represented by state-space equations; According to the model design software control, after sampling the voltage and current at the current moment, the estimated value of the variable at the next moment is calculated; Constrain the results according to the limit values ​​of the actual working conditions of the system; Obtain the compensation control signal of the system according to minimization of the objective function; The compensation control signal is combined with the control signal of the dual closed-loop output, and after feedforward compensation, the optimal duty cycle value is finally calculated as the actual control signal of the current phase circuit to control the switching of each main switch tube.

Images