High-speed flywheel multi-level wide modulation ratio energy equalization cycle control method and device

Abstract

This invention relates to a method and apparatus for high-speed flywheel multi-level wide-modulation specific energy balance cyclic control. The method is applied to the recycling of regenerative braking energy in subway traction power supply systems. By selectively employing a bubble sorting-carrier phase-shift modulation method to maintain the voltage balance of sub-module capacitors, it can maintain voltage balance even when the voltage difference between sub-module capacitors is large, and generate PWM signals to control the switching on and off of sub-module switching devices, thus solving the problem of voltage balance control for modular multi-level converter sub-modules under high-frequency fundamental frequencies. This apparatus can be installed on the DC traction network side of the subway traction power supply system to recycle the subway's regenerative braking energy, perfectly matching the instantaneous energy demands of frequent subway starts and stops. Compared with existing technologies, this invention, utilizing a wide-modulation specific energy balance cyclic control method, achieves an energy-to-kinetic energy conversion efficiency of 90%-95%, far exceeding traditional energy storage systems.

Description

Technical Field

[0001] This invention relates to the field of urban rail transit, and in particular to a method and apparatus for high-speed flywheel multi-level wide modulation ratio energy equalization cycle control. Background Technology

[0002] During the operation of rail transit systems, frequent starts and stops not only waste energy but also impact the traction power supply system, leading to a series of problems such as voltage instability. These problems not only affect the normal traction output of trains but may even prevent trains from starting normally, causing widespread power supply system failures.

[0003] Therefore, in-depth research on high-speed flywheel energy storage multi-level wide modulation ratio energy balance cycle high-efficiency control methods and devices is of great significance. High-speed flywheel energy storage technology has advantages such as high efficiency, long lifespan, and no pollution, and is particularly suitable for short-duration, high-frequency rail transit scenarios. It can not only realize the recycling of regenerative braking energy in subways, but also effectively maintain the stability of DC traction network voltage.

[0004] However, in practical applications, the main challenge faced when using modular multilevel converters to control high-speed flywheel energy storage systems is the voltage balancing control of submodules under high-frequency fundamental frequencies. For example, Chinese patent application CN104393779A discloses a modular multilevel converter control method based on carrier stacked modulation. By adjusting the N layers of original modulation signals, N final modulation signals are obtained, and the N final modulation signals are used as switching signals to distribute to the switching devices of the N submodules in each arm of the three-phase modular multilevel converter, thereby achieving voltage balancing of the capacitors of each submodule in the three-phase modular multilevel converter. Although this does not cause additional switching actions, it cannot achieve voltage balancing.

[0005] The bubble sort algorithm can monitor and adjust the voltage of sub-modules in real time to ensure voltage balance among sub-modules, thereby improving the overall performance and reliability of the system. Nevertheless, there are still some challenges to be addressed in actual operation: (1) Traditional bubble sort will result in long sorting time and insufficient voltage control accuracy due to invalid comparisons. (2) Repeated discharge of a single sub-module will greatly reduce its service life. The charging and discharging sequence of the sub-modules needs to be adjusted. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the prior art by providing a high-speed flywheel multilevel wide modulation ratio energy balancing cyclic control method and device. A novel bubble sorting carrier phase shift modulation method is proposed to balance the voltage of the sub-module, ensuring high-precision modular multilevel converter voltage balance control under both low and high modulation ratio conditions.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A high-speed flywheel multi-level wide-modulation specific energy equalization cyclic control method is disclosed. The method is applied to the regenerative braking energy recycling of a subway traction power supply system. The system includes a DC traction network, a high-speed energy storage flywheel, and a modular multi-level converter. The modular multi-level converter includes multiple bridge arms, and each bridge arm includes multiple sub-modules. The method includes:

[0009] The DC traction network voltage, actual flywheel speed, submodule capacitor voltage, and bridge arm current direction are collected in real time and preprocessed to obtain the modulation signal;

[0010] Calculate the difference between the maximum and minimum submodule capacitor voltage in each bridge arm;

[0011] If the difference is less than the preset voltage difference, then based on the modulation signal and the pre-generated carrier signal, a preset carrier phase-shift modulation method is used to generate a PWM signal to control the switching devices of the submodule to turn on and off. Otherwise, based on the modulation signal and the pre-generated carrier signal, a bubble sorting-carrier phase-shift modulation method is used to maintain the voltage balance of the submodule capacitor, and a PWM signal is generated to control the switching devices of the submodule to turn on and off.

[0012] Furthermore, before the high-speed energy storage flywheel is used, the sub-module capacitors of the modular multilevel converter and the preset voltage difference need to be preset.

[0013] Furthermore, the process for presetting the submodule capacitor values ​​of the modular multilevel converter includes:

[0014] Based on the high-speed flywheel energy storage topology of the metro traction power supply system, a modular multilevel converter is mathematically modeled, and the submodule capacitance is calculated based on the actual collected bridge arm current and bridge arm voltage.

[0015] Furthermore, the preprocessing procedure includes:

[0016] Based on the preset DC traction network voltage SOC curve relationship, the DC traction network voltage is converted into a flywheel output speed setpoint.

[0017] The speed setpoint is subtracted from the actual speed of the flywheel to obtain the speed error value, which is then processed by a PI regulator to generate the q-axis current setpoint.

[0018] Subtract the preset d-axis current setpoint from the acquired d-axis feedback current to obtain the d-axis current error value; subtract the q-axis current setpoint from the q-axis feedback current to obtain the q-axis current error value.

[0019] The d-axis current error value and the q-axis current error value are converted to dq / abc by a PI controller to obtain the modulation signal.

[0020] Furthermore, the process of using the preset carrier phase-shift modulation method to generate PWM signals to control the switching devices of the submodule to turn on and off includes:

[0021] The carrier signal is paired with each submodule;

[0022] Based on the direction of the bridge arm current, determine the charging and discharging modes of the capacitors in the corresponding bridge arm submodules;

[0023] The modulation signal and the carrier signal are compared instantaneously. If the instantaneous value of the carrier signal is greater than the instantaneous value of the modulation signal, a low-level PWM signal is generated for the sub-module paired with the carrier signal based on the current sub-module capacitor mode. Otherwise, a high-level PWM signal is generated for the sub-module paired with the carrier signal based on the current sub-module capacitor mode.

[0024] Furthermore, the process of maintaining the submodule capacitor voltage balance using the bubble sorting-carrier phase-shift modulation method and generating PWM signals to control the switching devices of the submodule includes:

[0025] Based on the bubble sort algorithm, following the sorting strategy, the submodule capacitors in each bridge arm are sorted according to the voltage of the submodule capacitors.

[0026] Based on the direction of the bridge arm current, determine the charging and discharging modes of the corresponding bridge arm submodule capacitors, and determine the turn-on priority of the submodule capacitors according to the switching strategy, and balance the voltage of the submodule capacitors.

[0027] The modulation signal and the carrier signal are compared instantaneously, and the number of carrier signals whose amplitude is greater than that of the modulation signal is calculated as the number of sub-modules that need to be activated.

[0028] Based on the activation priority of each submodule capacitor and the number of submodules that need to be activated, a PWM signal is generated to control each submodule.

[0029] Furthermore, the specific sorting process of the bubble sort algorithm includes:

[0030] Starting with the voltage of the first submodule capacitor, the voltages of adjacent submodule capacitors are compared sequentially. If the voltages of adjacent submodules do not conform to the order from largest to smallest, their positions are swapped. If they conform to the order or their voltage values ​​are the same, the comparison is skipped and the process proceeds directly to the next round.

[0031] Furthermore, the process of determining the charging and discharging modes of the corresponding bridge arm submodule capacitors and determining the activation priority of the submodule capacitors according to the switching strategy includes:

[0032] When the direction of the bridge arm current is positive, that is, the current flows from the DC side to the AC side, it is determined that the current submodule capacitor is in a discharging state. The switching strategy is to prioritize the submodule with higher voltage and assign the submodules a lower priority in descending order of capacitor voltage.

[0033] When the current direction of the bridge arm is negative, that is, the current flows from the AC side to the DC side, it is determined that the current submodule capacitor is in a charging state. The switching strategy is to prioritize the submodule with the lower voltage and assign the submodule the turn-on priority from small to large according to the capacitor voltage.

[0034] Furthermore, when the train brakes and its regenerative braking energy is not absorbed by other subway trains, the modular multilevel converter, controlled by a PWM signal, enables the high-speed energy storage flywheel to operate as a motor, converting electrical energy into kinetic energy for storage. When the train starts, the modular multilevel converter, controlled by a PWM signal, enables the high-speed energy storage flywheel to operate as a generator, converting kinetic energy into electrical energy and transmitting it to the DC traction network.

[0035] A high-speed flywheel multi-level wide-modulation specific energy equalization cycle control device is applied to the regenerative braking energy recycling of a subway traction power supply system. The system includes a high-speed energy storage flywheel and a modular multi-level converter. The modular multi-level converter includes multiple bridge arms, and each bridge arm includes multiple sub-modules. The device includes:

[0036] Sampling module: Real-time acquisition of DC traction network voltage, actual flywheel speed and arm current direction, and transmission of data to the main controller module;

[0037] Main controller module: preprocesses the data collected by the sampling module and the sub-module control module to obtain the modulation signal; generates a carrier signal according to a preset strategy; calculates the difference between the maximum and minimum sub-module capacitor voltages in each bridge arm; if the difference is less than the preset voltage difference, then based on the modulation signal and the pre-generated carrier signal, a preset carrier phase-shift modulation method is used to generate PWM signals to control the switching devices of the sub-module to turn on and off; otherwise, based on the modulation signal and the pre-generated carrier signal, a bubble sorting-carrier phase-shift modulation method is used to maintain the sub-module capacitor voltage balance and generate PWM signals to control the switching devices of the sub-module to turn on and off.

[0038] Submodule control module: Collects the capacitor voltage of the submodule and sends it to the main controller module through an asynchronous transceiver communication protocol, and receives PWM signals sent by the main controller module to control the switching devices of the submodule to turn on and off.

[0039] Compared with the prior art, the beneficial effects of the present invention include:

[0040] 1. This invention effectively solves the shortcomings of traditional modulation methods that only control the output without considering voltage balance. By dynamically adjusting the switching priority of submodules, it avoids capacitor overvoltage / undervoltage, extends the service life of submodules, and improves the overall reliability of modular multilevel converters. This invention proposes a bubble sorting-carrier phase-shift modulation method. When the difference between the voltage of the largest and smallest submodule capacitors exceeds a preset threshold, the bubble sorting-carrier phase-shift modulation method is used to maintain the voltage balance of the submodule capacitors. This ensures high-precision voltage balance control of modular multilevel converters under both low and high modulation ratio conditions, solving the problem of voltage balance control of modular multilevel converter submodules under high-frequency fundamental frequency.

[0041] 2. Based on traditional carrier phase-shift modulation, this invention introduces voltage sorting decision logic. By improving bubble sorting to obtain the voltage priority of sub-modules in real time, and combining it with the bridge arm current direction to dynamically adjust the switching order, this invention solves the core defect of traditional carrier phase-shift modulation that lacks voltage equalization capability. It eliminates the need for an additional voltage equalization loop, achieves coordinated control of modulation and equalization, simplifies the structure, and provides a faster equalization response.

[0042] 3. In this invention, the bubble sort algorithm improves operating efficiency by optimizing the sorting process, reducing unnecessary steps, and sorting the charging and discharging modules separately.

[0043] 4. The control of the sub-module capacitor voltage of the modular multilevel converter in this invention can achieve stable control of the high-speed flywheel, thereby maintaining the voltage stability of the DC traction network and limiting voltage fluctuations within a certain range. Attached Figure Description

[0044] Figure 1 This is a topology diagram of the high-speed flywheel energy storage system of the subway traction power supply system of the present invention;

[0045] Figure 2 This is a detailed structural diagram of the three-phase modular multilevel converter topology of the present invention;

[0046] Figure 3 This is a topology diagram of the submodule of the present invention;

[0047] Figure 4 This is the equivalent topology diagram of the modular multilevel converter of the present invention;

[0048] Figure 5 This is a control block diagram of the flywheel energy storage of the present invention;

[0049] Figure 6This is a flowchart of the high-speed flywheel multi-level wide modulation ratio energy equalization cycle control method of the present invention;

[0050] Figure 7 This is a schematic diagram of the bubble sorting-carrier phase shift modulation algorithm of the present invention;

[0051] Figure 8 The voltage diagram of line AB when the modulation index M=0.25 is shown in the modulation simulation of the modular multilevel converter of this invention.

[0052] Figure 9 This is the voltage diagram of line AB when the modulation index M=1 in the modulation simulation of the modular multilevel converter of this invention;

[0053] Figure 10 This is a diagram showing the flywheel speed in the flywheel speed simulation of the present invention when the modular multilevel converter adopts low-profile control.

[0054] Figure 11 This is a diagram showing the flywheel speed in the flywheel speed simulation of the present invention when the modular multilevel converter is controlled by a high-regulation system.

[0055] Figure 12 Simulation waveform of capacitor voltage in phase A submodule when the given speed of the flywheel in this invention is dynamically changed using a low-profile regime;

[0056] Figure 13 The simulation waveform of the capacitor voltage of phase A submodule when the given speed of the flywheel of this invention is dynamically changed using a high-regulation system is shown. Detailed Implementation

[0057] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0058] Example 1

[0059] This embodiment discloses a high-speed flywheel multilevel wide modulation ratio energy equalization cycle control method. The method is based on a subway traction power supply system. The system includes a DC traction network, a high-speed energy storage flywheel, and a modular multilevel converter. The modular multilevel converter includes multiple bridge arms, and each bridge arm includes multiple sub-modules.

[0060] In this embodiment, the modular multilevel converter is presented as a three-phase bridge arm structure. Each phase includes an upper bridge arm and a lower bridge arm. Each bridge arm is composed of four sub-modules (SM, usually simplified by the half-bridge unit symbol, which implicitly includes capacitors and switching devices) connected in series, forming a three-phase modular multilevel converter topology.

[0061] Before using the subway traction power supply system, it is necessary to pre-set the sub-module capacitors and preset voltage difference values ​​of the modular multilevel converter.

[0062] The process of presetting the values ​​of the submodule capacitors in a modular multilevel converter includes:

[0063] Based on the high-speed flywheel energy storage topology of the metro traction power supply system, a modular multilevel converter is mathematically modeled, and the submodule capacitance is calculated based on the actual collected bridge arm current and bridge arm voltage.

[0064] The topology of the high-speed flywheel energy storage system for subway traction power supply is as follows: Figure 1 As shown, the modular multilevel converter is a modular multilevel converter; the subway train in the figure has a traction subway under traction conditions and a braking subway under braking conditions, which are connected to the DC traction network through a current collector (such as a pantograph, simplified as a parallel node in the topology) to realize the absorption of traction power or the feedback of braking energy; the DC traction network is presented in the form of a DC bus, that is, a straight line connecting the subway up and down to the 12-pulse rectifier, which is the core carrier of energy interaction between the subway train and the flywheel energy storage system, and directly connects the subway train to the DC side of the modular multilevel converter; the high-speed energy storage flywheel is a high-speed flywheel energy storage device based on a high-speed flywheel, which is shown in the figure as a combination of a motor and a flywheel mechanical structure, and is directly connected to the AC side of the modular multilevel converter.

[0065] The specific structure of the three-phase modular multilevel converter topology is as follows: Figure 2 As shown, the DC side (upper and lower DC buses) is directly connected in parallel to the DC traction network to form a DC energy channel, supporting bidirectional transmission of electrical energy. The AC side (three-phase output terminals a, b, and c) is directly connected to the three-phase input terminals of the flywheel energy storage to form an AC energy channel, realizing the conversion of electrical energy into kinetic energy.

[0066] Figure 2 In the middle, DC support capacitor Connected to DC side voltage respectively , Between the bridge arm and the ground reference point O, it is used to stabilize the DC bus voltage and filter out DC side ripple; there is one bridge arm resistor R for each phase upper and lower bridge arm, and it is connected to the bridge arm inductor. Series connection represents the equivalent resistance of the bridge arm (including line resistance, switching device losses, etc.); each phase of submodule SM contains 4 in both the upper and lower arms, such as... - For the A-phase upper bridge arm submodule, - This is the lower arm submodule of phase A; the same logic applies to phases B and C. The submodule internally has a half-bridge structure, such as... Figure 3 As shown, it contains two switching devices. and 2 anti-parallel diodes and and submodule capacitors Submodule capacitor The voltage is denoted as AC side inductance Connected to the AC output terminal of the modular multilevel converter , , Between the external AC system, i.e., the motor windings of the flywheel energy storage system, and the DC side voltage, it is used to filter AC side harmonics and limit AC current; , Provides DC power input for modular multilevel converters.

[0067] This topology achieves multi-level voltage output through the cascading of submodules. Combined with the coordination of bridge arm inductors and capacitors, it can efficiently complete DC-AC power conversion. At the same time, it facilitates capacitor voltage balance and energy management through submodule switching control.

[0068] The specific process of mathematical modeling the modular multilevel converter is as follows:

[0069] The modular multilevel converter topology is equivalent to, for example: Figure 4 The equivalent circuit of the j-phase (j=a,b,c) circulating current of the modular multilevel converter shown is a DC voltage source. and Using neutral point O as a common reference point, a dual-terminal DC power supply structure is formed; the bridge arm equivalent resistance The active power loss of the equivalent bridge arm (including submodule switching devices and circuits) connected in series in the circulating current path, such as the combined on-resistance and line resistance; circulating current equivalent inductance. equivalent resistance of bridge arm In series connection, the equivalent bridge arm inductance's suppression of the circulating current rate of change is a combined equivalent of the upper and lower bridge arm inductances, reflecting the characteristic of inductance limiting sudden changes in circulating current; bridge arm inductance Equivalent AC voltage source of the upper bridge arm respectively and the equivalent AC voltage source of the lower bridge arm Series connection is used to limit dynamic changes in the current of the bridge arms, such as the rate of current rise. AC output voltage; upper bridge arm equivalent AC voltage source The sum of the capacitor voltages of all engaged submodules in the upper bridge arm reflects the voltage contribution of the upper bridge arm to the AC side; the lower bridge arm is an equivalent AC voltage source. The capacitor voltage of all engaged submodules in the lower bridge arm is superimposed, and... Together they determine the output and circulating current characteristics of the AC side.

[0070] The expressions for the upper arm current and lower arm current of phase j are as follows:

[0071] ;

[0072] in, For the upper bridge arm current, For phase j circulation, For AC side output current, This represents the current in the lower bridge arm.

[0073] The expression for the j-phase circulation is as follows:

[0074] ;

[0075] According to Kirchhoff's voltage law, we can... and It is expressed as follows:

[0076] ;

[0077] The expression for the output voltage of phase j is as follows:

[0078] ;

[0079] AC output current of modular multilevel converter and AC output voltage The expression is as follows:

[0080]

[0081] ;

[0082] Among them, the peak value of the output current is used The peak value of the AC output voltage is indicated by... The frequency of the output voltage is indicated by... The power angle is represented by Ω.

[0083] The process of calculating the submodule capacitance based on the actual collected bridge arm current and bridge arm voltage is as follows:

[0084] Define the modulation ratio of the current as x, and express it as:

[0085] ;

[0086] Define the voltage modulation ratio as y, and its expression is:

[0087] ;

[0088] From the mathematical model of the modular multilevel converter established above, it can be seen that the energy change of the capacitor in one full charge-discharge cycle of a single-phase upper bridge arm of the modular multilevel converter is:

[0089] ;

[0090] in, For the instantaneous power of a single-phase upper arm, t, The start and end times of a complete charge and discharge cycle are defined as follows, and the charging energy and discharging energy are equal within the SM during a cycle.

[0091] Similarly, the energy change of the upper bridge arm capacitor within one cycle can also be expressed using the capacitor energy calculation formula:

[0092] ;

[0093] From the formula above, we can see that the capacitor voltage ripple factor is... The minimum capacitance value at that time is:

[0094] ;

[0095] Therefore, the minimum capacitance value was determined before the module was put into use to ensure that the capacitance of the submodule meets the charging and discharging requirements and to avoid voltage fluctuations exceeding the limit.

[0096] When the subway train is in traction mode, it acts as a load, absorbing electrical energy from the DC traction network to drive the train. When it is in braking mode, it acts as a temporary power source, generating regenerative braking energy and feeding it back to the DC traction network. If the energy is not absorbed by other trains, it needs to be stored through flywheel energy storage.

[0097] In the energy storage state (when the train brakes), the motor operates as an electric motor, driving the flywheel to rotate at high speed, converting the electrical energy transmitted by the modular multilevel converter into the kinetic energy of the flywheel for storage; in the energy release state (when the train starts), the motor operates as a generator, the flywheel decelerates, converting the kinetic energy into electrical energy, which is then rectified by the modular multilevel converter and sent to the DC traction network.

[0098] The control block diagram of flywheel energy storage is as follows: Figure 5 As shown, it includes three PI controllers (PI1-PI3), a dq-abc converter, an abc-dq converter, a modulation algorithm and sub-module voltage equalization module, an MCC converter, and a high-speed flywheel. Its purpose is to precisely control the flywheel speed and regulate the storage / release of traction network energy. The functions and logic of each part are as follows:

[0099] The speed loop, or outermost closed loop, takes the speed setpoint as its input. The actual rotational speed feedback n is used, and the rotational speed deviation is adjusted by the PI controller PI1 and output as a reference basis for the q-axis current.

[0100] The current loop, or inner double closed loop, consists of d-axis current control and q-axis current control, based on decoupled control using a synchronous rotating coordinate system (dq coordinate system).

[0101] To achieve unity power factor or simplify control, d-axis current control allows the d-axis to handle only the magnetic field, while the q-axis handles torque. Therefore, the d-axis current... When the input is 0, the PI3 controller participates in the control loop, obtaining feedback from the three-phase current after the abc-dq transformation. It is used to adjust the d-axis current deviation and stabilize the magnetic field.

[0102] The input data for q-axis current control is the output of PI1 controller. PI2 controller participates in the control loop, obtaining feedback from the three-phase current after abc-dq transformation. It is used to adjust the q-axis current deviation and precisely control the flywheel torque / speed.

[0103] The modulation algorithm and the sub-module voltage equalization module take the three-phase voltage command after dq-abc transformation as input. The three-phase voltage command is converted into the timing logic of PWM pulses through the modulation algorithm. The switching priority of the PWM pulses is adjusted according to the real-time sorting of the sub-module capacitor voltages to maintain the voltage balance of each sub-module capacitor in the modular multilevel converter. Finally, the output is the PWM signal that controls the switching devices of the sub-module to turn on and off.

[0104] The modular multilevel converter receives PWM signals and controls the switching of sub-modules to achieve bidirectional energy conversion between the DC side (DC1500V traction network) and the AC side (flywheel motor).

[0105] The specific method of this high-speed flywheel multi-level wide modulation ratio energy equalization cycle control is as follows: Figure 6 As shown, it includes:

[0106] Step S1: Real-time acquisition of DC traction network voltage, actual flywheel speed, submodule capacitor voltage, and bridge arm current direction;

[0107] Step S2: Preprocess the collected data to obtain the modulated signal;

[0108] Step S3: Calculate the difference between the maximum and minimum submodule capacitor voltages in each bridge arm. Compare the differences voltage difference with preset If the difference is less than the preset voltage difference, proceed to step S4; otherwise, proceed to step S5.

[0109] Step S4: Based on the modulation signal and the pre-generated carrier signal, a PWM signal is generated using a preset carrier phase-shift modulation method to control the switching devices of the submodule to turn on and off.

[0110] Step S5: Based on the modulation signal and the pre-generated carrier signal, the bubble sorting-carrier phase-shift modulation method is used to maintain the voltage balance of the submodule capacitor, and a PWM signal is generated to control the switching devices of the submodule to turn on and off.

[0111] When a train brakes and its regenerative braking energy is not absorbed by other subway trains, the modular multilevel converter, controlled by a PWM signal, enables the high-speed energy storage flywheel to operate as a motor, converting electrical energy into kinetic energy for storage. When the train starts, the modular multilevel converter, controlled by a PWM signal, enables the high-speed energy storage flywheel to operate as a generator, converting kinetic energy into electrical energy and transmitting it to the DC traction network.

[0112] In step S1, the preprocessing process includes:

[0113] Based on the preset DC traction network voltage SOC curve relationship, the DC traction network voltage is converted into a flywheel output speed setpoint.

[0114] The speed setpoint is subtracted from the actual speed of the flywheel to obtain the speed error value, which is then processed by a PI regulator to generate the q-axis current setpoint.

[0115] Subtract the preset d-axis current setpoint from the acquired d-axis feedback current to obtain the d-axis current error value; subtract the q-axis current setpoint from the q-axis feedback current to obtain the q-axis current error value.

[0116] The d-axis current error value and the q-axis current error value are converted to dq / abc by a PI controller to obtain the modulation signal.

[0117] The flywheel stores energy in the form of kinetic energy, and its State of Charge (SOC) can be indirectly characterized by its rotational speed (n). The higher the rotational speed, the higher the SOC. Starting from the energy balance and control logic of the modular multilevel converter, the theoretical relationship between the DC traction grid voltage and the flywheel speed is derived, thus obtaining a theoretical mathematical model of voltage and speed. By simulating urban rail traction conditions through an experimental platform, the DC traction grid voltage at different rotational speeds is collected, the theoretical mathematical model is corrected, and finally, the preset DC traction grid voltage SOC curve relationship is obtained.

[0118] After a period of time, the curve will need to be updated due to factors such as flywheel aging and temperature changes. In some implementations, the experiment is repeated periodically to collect new data to correct the model. In other implementations, algorithms such as Kalman filtering are combined to adjust the curve parameters in real time during operation to ensure accuracy.

[0119] The carrier signals used in steps S4 and S5 are directly generated by a field-programmable gate array (FPGA). This FPGA is the core hardware for implementing signal control and modulation logic in the system. The number of FPGAs generated corresponds to the number of modular multilevel converter sub-modules. Its core parameters, frequency, amplitude, and waveform type, need to be set according to the system control objectives. The waveform type adopts a regular waveform suitable for carrier phase-shift modulation to ensure that a stable pulse width modulation (PWM) signal can be output when compared with the modulation signal. The frequency and amplitude need to match the operating characteristics of the modular multilevel converter, such as the voltage balancing requirements under high-frequency fundamental wave and the voltage range of the sub-module capacitors, to avoid frequent switching of sub-modules or voltage fluctuations exceeding limits due to improper carrier parameters. The ultimate goal is to enable the generated PWM signal to accurately control the charging and discharging of the sub-modules and maintain voltage balance.

[0120] In step S4, the process of generating a PWM signal using a preset carrier phase-shift modulation method to control the switching devices of the submodule to turn on and off includes:

[0121] The carrier signal is paired with each submodule;

[0122] Based on the direction of the bridge arm current, determine the charging and discharging modes of the capacitors in the corresponding bridge arm submodules;

[0123] The modulation signal and the carrier signal are compared instantaneously. If the instantaneous value of the carrier signal is greater than the instantaneous value of the modulation signal, a low-level PWM signal is generated for the sub-module paired with the carrier signal based on the current sub-module capacitor mode. Otherwise, a high-level PWM signal is generated for the sub-module paired with the carrier signal based on the current sub-module capacitor mode.

[0124] The principle of bubble sort-carrier phase shift modulation algorithm is as follows: Figure 7 As shown, in step S5, the process of using the bubble sorting-carrier phase-shift modulation method to maintain the voltage balance of the submodule capacitor and generating a PWM signal to control the switching devices of the submodule includes:

[0125] Based on the bubble sort algorithm, following the sorting strategy, the submodule capacitors in each bridge arm are sorted according to the voltage of the submodule capacitors.

[0126] Based on the direction of the bridge arm current, the charging and discharging modes of the corresponding bridge arm submodule capacitors are determined, and the switching priority of the submodule capacitors is determined according to the switching strategy to balance the submodule capacitor voltages. When the bridge arm current direction is positive, i.e., the current flows from the DC side to the AC side, it is determined that the current submodule capacitor is in a discharging state, and the switching strategy is to prioritize the switching of submodules with higher voltages, assigning the submodules a lower switching priority in descending order of capacitor voltage. When the bridge arm current direction is negative, i.e., the current flows from the AC side to the DC side, it is determined that the current submodule capacitor is in a charging state, and the switching strategy is to prioritize the switching of submodules with lower voltages, assigning the submodules a higher switching priority in ascending order of capacitor voltage.

[0127] The modulating signal and the carrier signal are compared instantaneously, and the number of carrier signals whose amplitude is greater than that of the modulating signal is used as the number of sub-modules that need to be activated. ;

[0128] Based on the activation priority of each submodule capacitor and the number of submodules that need to be activated, a PWM signal is generated to control each submodule.

[0129] Figure 7 middle - It is the capacitor voltage of the submodule after being sorted by the bubble sort algorithm. - , - These are the PWM signals for each submodule.

[0130] The specific sorting process of the bubble sort algorithm includes:

[0131] Starting with the voltage of the capacitor in the first submodule, the voltages of adjacent submodule capacitors are compared sequentially. If the voltages of adjacent submodules do not conform to the descending order, their positions are swapped. In this case, each sorting requires traversing and swapping elements. For n elements, the first submodule is compared with other modules n-1 times, the second comparison is n-2 times, and so on, for a total of:

[0132]

[0133] If the order is correct or the voltage values ​​are the same, skip the comparison and proceed directly to the next round. This method effectively reduces the number of invalid comparisons and improves sorting efficiency in special cases. In the optimal case, the voltages of the submodules are already in descending order, and the number of comparisons is n.

[0134] The modular multilevel energy storage converter adopts a carrier phase-shifting-improved bubble sorting control method to support voltage stability in power conversion, making the output waveform of the modular multilevel converter smoother, maintaining the stability of DC power supply network voltage, and reducing the impact of rail transit start-up and shutdown.

[0135] Example 2

[0136] This embodiment, based on the method disclosed in Embodiment 1, discloses a high-speed flywheel multi-level wide modulation specific energy equalization cycle control device, the device comprising:

[0137] Sampling module: Real-time acquisition of DC traction network voltage, actual flywheel speed and arm current direction, and transmission of data to the main controller module;

[0138] Main controller module: preprocesses the data collected by the sampling module and the sub-module control module to obtain the modulation signal; generates a carrier signal according to a preset strategy; calculates the difference between the maximum and minimum sub-module capacitor voltages in each bridge arm; if the difference is less than the preset voltage difference, then based on the modulation signal and the pre-generated carrier signal, a preset carrier phase-shift modulation method is used to generate PWM signals to control the switching devices of the sub-module to turn on and off; otherwise, based on the modulation signal and the pre-generated carrier signal, a bubble sorting-carrier phase-shift modulation method is used to maintain the sub-module capacitor voltage balance and generate PWM signals to control the switching devices of the sub-module to turn on and off.

[0139] Submodule control module: Collects the capacitor voltage of the submodule and sends it to the main controller module through an asynchronous transceiver communication protocol, and receives PWM signals sent by the main controller module to control the switching devices of the submodule to turn on and off.

[0140] In this embodiment, the sampling module is AD7656, and the digital signal processing module is mainly responsible for sampling commands for analog and digital signals and transmitting the signals to the main controller.

[0141] The main controller module uses the TMS320F28335 as the core processor of the main controller, which is responsible for the overall logic control and data processing, and exchanges data with the digital signal processing module through the bus of the digital processing module.

[0142] The main controller module uses an Artix-7 series FPGA for its field-programmable gate array (FPGA), which is responsible for sending control commands for digital and analog signals, generating carrier signals, and exchanging data with the digital signal processing module via a bus.

[0143] When calculating the duty cycle of the modular multilevel controller, it sends control commands in digital and analog signals, exchanges data with the digital signal processing module via bus, controls the input and output signals, communicates with the sub-module controllers of the modular multilevel converter via the asynchronous transceiver communication protocol (UART), performs operations such as sorting sub-module capacitor voltages, and communicates with the touch screen via the RS-485 communication protocol.

[0144] The submodule controller of the modular multilevel converter is controlled by AFS250 PGQ208. It is mainly responsible for sending the acquired capacitor voltage of the submodule to the main controller through the asynchronous transceiver communication protocol, and processing the PWM and fault signals sent by the main controller.

[0145] Example 3

[0146] This embodiment is based on Embodiment 1 above, and its effectiveness is demonstrated by performing simulation verification on the method described above in Simulink.

[0147] The modulation of a modular multilevel converter was simulated under the given conditions of a carrier frequency of 1 kHz, a modulation frequency of 50 Hz, a DC-side voltage of 1600 V, and four sub-modules in each of the upper and lower bridge arms. The effectiveness of bubble sorting-carrier phase-shift modulation was verified by observing the number of conducting sub-modules in the upper and lower bridge arms of phase A and the line voltages of phases A and B. Simulation results under low-modulation and high-modulation regimes were also compared. Figure 8 It can be seen that when the modulation index M is 0.25, the line voltage is a five-level voltage; from Figure 9 It can be seen that when the modulation index M is 1, the line voltage is nine levels. When M=1, the line voltage is closer to a sine wave, resulting in a better effect.

[0148] Simulation verification of the control of the high-speed flywheel modular multilevel converter was carried out. The initial speed was given as 20000 r / min from 0 to 0.2 s; the maximum speed was given as 36000 r / min from 0.2 to 0.4 s; and the initial speed was given as 20000 r / min from 0.4 to 0.6 s.

[0149] A bubble sorting-carrier phase-shift modulation algorithm was adopted, and the flywheel speed was dynamically given to observe the flywheel speed tracking. The simulation results of the flywheel speed when the modular multilevel converter is controlled by a low-profile regime are as follows: Figure 10 As shown, Figure 10In the simulation, the lighter gray waveform represents the actual speed curve of the flywheel, while the darker black line represents the given speed. Initially, the speed fluctuates by 300 r / min before reaching a stable state of 20,000 r / min. During acceleration, the flywheel fluctuates by 200 r / min before reaching a stable state of 36,000 r / min. During deceleration (0.4–0.6 s), the flywheel continues to fluctuate. The simulated flywheel speed results for the modular multilevel converter using high-regulation control are as follows: Figure 11 As shown, Figure 11 Zhongyu Figure 10 Similarly, the lighter gray waveform represents the actual speed curve of the flywheel, while the darker black line represents the given speed. Initially, the speed fluctuates by 200 rpm before reaching a stable state of 20,000 rpm. During acceleration, the flywheel fluctuates by 100 rpm before reaching a stable state of 36,000 rpm. During deceleration from 0.4 to 0.6 seconds, the flywheel shows almost no fluctuation, resulting in better speed control.

[0150] When the given speed of the flywheel changes dynamically, and a low-frequency regime is adopted, the simulated waveform of the capacitor voltage of the A-phase submodule is as follows: Figure 12 As shown, the voltages of the eight sub-modules in phase A tend to be in a balanced state, with a maximum voltage fluctuation range of 0.4V. The simulated waveform of the capacitor voltage of the phase A sub-modules when using the high-modulation regime is shown below. Figure 13 As shown, the voltages of the eight sub-modules in phase A remain in a balanced state, and the capacitor voltage fluctuation range is 0.2V, which is relatively small.

[0151] Example 4

[0152] Based on Embodiment 1, this embodiment provides an electronic device, including: one or more processors and a memory, wherein the memory stores one or more programs, and the one or more programs include instructions for executing the aforementioned high-speed flywheel multi-level wide modulation ratio energy equalization cycle control method.

[0153] At the hardware level, the electronic device includes a processor, internal bus, network interface, memory, and non-volatile memory, and may also include other hardware required for business operations. The processor reads the corresponding computer program from the non-volatile memory into memory and then runs it to implement the aforementioned high-speed flywheel multi-level wide modulation ratio energy equalization cyclic control method. Of course, in addition to software implementation, this invention does not exclude other implementation methods, such as logic devices or a combination of hardware and software, etc. That is to say, the execution subject of the following processing flow is not limited to individual logic units, but can also be hardware or logic devices.

[0154] Memory may include non-persistent storage in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0155] Computer-readable media include both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0156] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A high-speed flywheel multi-level wide modulation ratio energy balance circulating control method, the method is applied to the recycling of regenerative braking energy of a metro traction power supply system, the system comprises a high-speed energy storage flywheel and a modular multi-level converter, the modular multi-level converter comprises a plurality of bridge arms, the bridge arms comprise a plurality of sub-modules, characterized in that, The method comprises: Real-time acquisition of DC traction network voltage, flywheel actual speed, sub-module capacitor voltage and bridge arm current direction, and preprocessing to obtain a modulation signal; Calculate the difference between the maximum sub-module capacitor voltage and the minimum sub-module capacitor voltage in each bridge arm; If the difference is less than a preset voltage difference, generate a PWM signal based on the modulation signal and a pre-generated carrier signal to control the turn-on and turn-off of the sub-module switching device using a preset carrier phase shift modulation method, otherwise, maintain the sub-module capacitor voltage balance using a bubble sort-carrier phase shift modulation method based on the modulation signal and the pre-generated carrier signal, and generate a PWM signal to control the turn-on and turn-off of the sub-module switching device. The process of maintaining the sub-module capacitor voltage balance and generating the PWM signal to control the turn-on and turn-off of the sub-module switching device using the bubble sort-carrier phase shift modulation method comprises: Based on the bubble sort algorithm, follow the sequence arrangement strategy, and sort the sub-module capacitors in each bridge arm according to the size of the sub-module capacitor voltage. Based on the bridge arm current direction, determine the charging and discharging mode of the corresponding bridge arm sub-module capacitor, and determine the turn-on priority of the sub-module capacitor according to the switching strategy to balance the sub-module capacitor voltage. Compare the instantaneous values of the modulation signal and the carrier signal, calculate the number of carrier signals with an amplitude greater than the modulation signal amplitude as the number of sub-modules that need to be turned on. Generate a PWM signal to control each sub-module based on the turn-on priority of each sub-module capacitor and the number of sub-modules that need to be turned on.

2. A high speed flywheel multi-level wide modulation ratio energy equalization cycling control method according to claim 1, characterized in that, Before use, the high-speed energy storage flywheel needs to preset the sub-module capacitor of the modular multilevel converter and the voltage difference.

3. A high speed flywheel multi-level wide modulation ratio energy equalization cycling control method according to claim 2, characterized in that, The preset value process of the sub-module capacitor of the modular multilevel converter comprises: Based on the high-speed energy storage flywheel topology of the subway traction power supply system, the modular multilevel converter is mathematically modeled, and the sub-module capacitor is calculated based on the actual acquisition of the bridge arm current and the bridge arm voltage.

4. A high speed flywheel multi-level wide modulation ratio energy equalization cycling control method according to claim 1, characterized in that, The preprocessing process comprises: According to the preset DC traction network voltage SOC curve relationship, the DC traction network voltage is converted into a flywheel output speed given value; Subtract the speed given value from the actual flywheel speed to obtain a speed error value, and process it through a PI regulator to generate a q-axis current given value; Subtract the preset d-axis current given value from the acquired d-axis feedback current to obtain a d-axis current error value, and subtract the q-axis current given value from the q-axis feedback current to obtain a q-axis current error value; Convert the d-axis current error value and the q-axis current error value through a PI regulator to obtain a modulation signal.

5. A high speed flywheel multi-level wide modulation ratio energy equalization cycling control method according to claim 1, characterized in that, The process of generating a PWM signal to control the turn-on and turn-off of the sub-module switching device using the preset carrier phase shift modulation method comprises: The carrier signal is paired with the sub-module one by one; Based on the bridge arm current direction, determine the charging and discharging mode of the corresponding bridge arm sub-module capacitor; The modulation signal is compared with a carrier signal in terms of instantaneous value, if the instantaneous value of the carrier signal is greater than that of the modulation signal, a low-level PWM signal is generated to control the sub-modules paired with the carrier signal based on the mode of the current sub-module capacitor, otherwise a high-level PWM signal is generated to control the sub-modules paired with the carrier signal based on the mode of the current sub-module capacitor.

6. A high speed flywheel multi-level wide modulation ratio energy balancing cyclo- conversion control method according to claim 1, characterized by, The specific sorting process of the bubble sorting algorithm comprises: From the voltage of the first sub-module capacitor, the voltages between adjacent sub-module capacitors are compared in sequence, if the voltage size relationship of adjacent sub-module capacitors does not conform to the descending order, the arrangement positions of the two are exchanged, if the order is met or the voltage values of the two are the same, the comparison is skipped and the next round of comparison is directly entered.

7. A high speed flywheel multi-level wide modulation ratio energy equalization cycling control method according to claim 1, characterized by, The process of judging the charging and discharging mode of the corresponding bridge arm sub-module capacitor and determining the turn-on priority of the sub-module capacitor according to the switching strategy comprises: When the bridge arm current direction is positive, i.e. the current flows from the DC side to the AC side, it is judged that the current sub-module capacitor is in a discharging state, the switching strategy is to preferentially input the sub-module with higher voltage, and the sub-module is given a descending turn-on priority according to the descending order of the capacitor voltage; When the bridge arm current direction is negative, i.e. the current flows from the AC side to the DC side, it is judged that the current sub-module capacitor is in a charging state, the switching strategy is to preferentially input the sub-module with lower voltage, and the sub-module is given an ascending turn-on priority according to the ascending order of the capacitor voltage.

8. A high speed flywheel multi-level wide modulation ratio energy equalization cycling control method according to claim 1, characterized by, When the train brakes and the regenerative braking energy is not absorbed by other metro trains, through PWM signal control, the modular multilevel converter makes the high-speed energy storage flywheel operate as a motor to store kinetic energy; when the train starts, through PWM signal control, the modular multilevel converter makes the high-speed energy storage flywheel operate as a generator to convert kinetic energy into electrical energy and transmit it to the DC traction network.

9. A high-speed flywheel multi-level wide modulation ratio energy balance circulating control device applied to the recycling of regenerative braking energy of a metro traction power supply system, the system comprising a high-speed energy storage flywheel and a modular multi-level converter, the modular multi-level converter comprising a plurality of bridge arms, the bridge arms comprising a plurality of sub-modules, characterized in that, The device comprises: a sampling module: real-time acquisition of DC traction network voltage, flywheel actual speed and bridge arm current direction, and data transmission to the main controller module; a main controller module: pre-processing of the data collected by the sampling module and the sub-module control module, obtaining a modulation signal; generating a carrier signal according to a preset strategy; calculating the difference between the maximum sub-module capacitor voltage and the minimum sub-module capacitor voltage in each bridge arm; if the difference is less than a preset voltage difference, generating a PWM signal for controlling the turn-on and turn-off of the sub-module switching device based on the modulation signal and the pre-generated carrier signal using a preset carrier phase shift modulation method, otherwise maintaining the sub-module capacitor voltage balance using a bubble sorting-carrier phase shift modulation method and generating a PWM signal for controlling the turn-on and turn-off of the sub-module switching device based on the modulation signal and the pre-generated carrier signal; a sub-module control module: collecting the capacitor voltage of the sub-module and sending it to the main controller module through an asynchronous transceiver transmission communication protocol, and receiving the PWM signal sent by the main controller module to control the turn-on and turn-off of the sub-module switching device; the process of maintaining the sub-module capacitor voltage balance using the bubble sorting-carrier phase shift modulation method and generating a PWM signal to control the turn-on and turn-off of the sub-module switching device comprises: Based on the bubble sort algorithm, follow the sequence arrangement strategy, according to the size of the sub module capacitor voltage, respectively to each bridge arm sub module capacitor sorting; Based on the bridge arm current direction, judge the charging and discharging mode of the corresponding bridge arm sub module capacitor, and determine the opening priority of the sub module capacitor according to the switching strategy, balance the sub module capacitor voltage; The instantaneous value of the modulation signal and the carrier signal is compared, and the number of carrier signals with an amplitude greater than the modulation signal is calculated as the number of sub modules that need to be turned on. Based on the opening priority of each sub module capacitor and the number of sub modules that need to be turned on, generate PWM signals to control each sub module.

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