An electric propulsion vessel safety braking system and control method

Abstract

The application provides a kind of electric propulsion ship safety braking system and control method, including direct current main network, frequency converter, anti-reverse diode, thyristor and frequency converter controller;Direct current end of frequency converter is provided with direct current support capacitor;Anti-reverse diode is connected between direct current main network and direct current end of frequency converter, forms one-way power supply circuit;Anode of thyristor is connected with frequency converter, cathode is connected with direct current main network, and forms reverse parallel structure with anti-reverse diode, for braking energy feedback to direct current main network under braking condition;Frequency converter controller is used to detect the running state of propulsion system and execute active torque support control and thyristor conduction control.

Description

Technical Field

[0001] This invention belongs to the field of marine power system technology, specifically relating to a safety braking system and control method for electrically propelled ships. Background Technology

[0002] With the deepening of the green and low-carbon transformation of the shipping industry, integrated electric propulsion systems are gradually becoming the mainstream direction of ship power system development due to their advantages such as high mobility, high overall energy efficiency, and flexible energy control. Compared with traditional mechanical propulsion systems, electric propulsion systems can better adapt to complex and ever-changing navigation conditions, enabling refined management and optimized allocation of ship power. However, in actual navigation, especially in inland waterway environments, ships face extremely complex hydrological conditions. Significant differences in current speed exist between different sections of the waterway, and the load characteristics of ships during upstream and downstream navigation are drastically different. Coupled with the influence of channel conditions and seasonal water level changes, this poses a severe challenge to the safe operation of the propulsion system.

[0003] Braking is a common scenario in propulsion system operation. When a ship needs to decelerate, turn, or respond to emergencies, the propulsion motor switches from electric to generator mode, and the resulting braking energy needs to be properly handled. Traditional solutions typically use braking resistors to absorb this energy and dissipate it as heat. While this method is technically mature and simple to control, it has significant drawbacks: firstly, braking energy is wasted, resulting in inefficient energy utilization; secondly, installing braking resistors requires additional space and cost, and their heat capacity limits the number of times they can operate per unit time and their continuous operating time, making it difficult to meet braking demands across the entire operating range.

[0004] Secondly, when the propulsion system operates at low speeds, the propulsion motor is prone to intermittent, high-frequency braking due to the impact of water flow. Under this condition, the electromagnetic torque delivered by the motor is less than the reverse mechanical torque generated by the water flow, causing the system to frequently switch between power supply and power generation states. This high-frequency state change not only generates significant electromagnetic interference, affecting the normal operation of other electrical equipment on board, but also causes switching devices to endure repeated commutation impacts, threatening the safe and stable operation of the propulsion system. Summary of the Invention

[0005] This invention proposes a safety braking system and control method for electrically propelled ships to solve the problems of wasted braking energy and system safety hazards caused by low-speed, high-frequency braking in the prior art.

[0006] To solve the above-mentioned technical problems, the present invention provides a safety braking system for electric propulsion ships, including a DC main grid, a frequency converter, a reverse protection diode, a thyristor, and a frequency converter controller;

[0007] The inverter is equipped with a DC support capacitor at its DC terminal.

[0008] The anti-reverse diode is connected between the DC main grid and the DC terminal of the inverter to form a unidirectional power supply circuit.

[0009] The anode of the thyristor is connected to the frequency converter, and the cathode is connected to the DC main grid. It forms an anti-parallel structure with the anti-reverse diode and is used to feed the braking energy back to the DC main grid under braking conditions.

[0010] The frequency converter controller is used to detect the operating status of the propulsion system and execute active torque support control and thyristor conduction control.

[0011] Preferably, the electric propulsion ship safety braking system further includes an energy storage system or load device connected to the DC main grid, used to absorb the braking energy fed back through the bypass branch formed by the thyristors.

[0012] This invention also provides a safety braking control method for electric propulsion ships, applicable to the aforementioned safety braking system for electric propulsion ships, comprising the following steps: acquiring the propulsion system speed, the output voltage of the anti-reverse diode, and the DC main grid voltage; when the active torque support triggering condition is met, switching the frequency converter to constant torque control mode; when the energy recovery triggering condition is met, turning on the bypass branch composed of thyristors to feed the braking energy back to the DC main grid.

[0013] Preferably, the constant torque control mode includes:

[0014] Given a constant d-axis current reference command for the frequency converter i dref and q-axis current constant reference command i qref ;

[0015] i dref and the d-axis component of the inverter output current i d The difference, after passing through the PI controller, is coupled with the cross-coupled term. ωL d i q The summation yields the d-axis modulation voltage command value. u d ;

[0016] i qref and the q-axis component of the inverter output current i q The difference, after passing through the PI controller, is coupled with the cross-coupled term. ωL qi d Subtracting the two values ​​yields the q-axis modulation voltage command value. u q ;

[0017] u q and u d The modulation signal for SVPWM control is then obtained through dq transformation.

[0018] in L d , L q These are the d-axis and q-axis components of the AC-side inductance. ω This refers to the mechanical angular velocity.

[0019] Preferably, the active torque support triggering condition includes: propulsion system rotational speed n ≤ first threshold n ref And the output voltage U of the anti-reverse diode dc ≥ the second threshold U1, and the output voltage U of the anti-reverse diode dc With DC main grid voltage U dc0 The difference U dc -U dc0 ≥ The third threshold U2; where the second threshold U1 is higher than the rated voltage of the DC main grid and lower than the voltage protection value of the frequency converter.

[0020] Preferably, the energy recovery triggering condition includes: the output voltage U of the anti-reverse diode. dc ≥ Fourth threshold U3, and the difference U between the output voltage of the reverse protection diode and the DC main grid voltage. dc -U dc0 ≥ Fifth threshold U4; where the fourth threshold U3 is greater than the second threshold U1, and the fifth threshold U4 is greater than the third threshold U2; after the braking energy recovery is completed, the voltage amplitude at the output terminal of the anti-reverse diode drops below the DC main grid voltage value, and the thyristor will automatically turn off due to its own characteristics.

[0021] Preferably, when the propulsion system rotational speed n is greater than the first threshold n ref Or the output voltage U of the anti-reverse diode dc Less than the second threshold U1, or the voltage difference U dc -U dc0 When the value is less than the third threshold U2, the frequency converter controller exits the constant torque control mode.

[0022] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0023] First, this invention, through a combination of a reverse-biased diode and a reverse-parallel thyristor, achieves the feedback utilization of braking energy to the DC main grid while meeting the safe power supply requirements of the frequency converter. The reverse-biased diode effectively isolates the frequency converter from high-frequency electromagnetic interference to the DC main grid and reduces the short-circuit current level of the DC main grid; the thyristor bypass branch provides an energy feedback channel when needed. Depending on the DC main grid load power requirements or the configuration of energy storage devices, the requirement for traditional braking resistors can be reduced or even completely eliminated, saving equipment investment and ship space.

[0024] Secondly, this invention addresses the problem of high-frequency braking under low-speed conditions by proposing an active torque support technology for the frequency converter. By actively providing a constant pulse torque at the software level to counteract the external water flow force, it fundamentally avoids the frequent switching between power supply and power generation states of the propulsion system, eliminates the resulting electromagnetic interference and equipment wear risks, and significantly improves the propulsion system's adaptability to extreme operating conditions.

[0025] Third, this invention employs a hardware and software collaborative braking control strategy, achieving a reasonable allocation of control priorities through differentiated trigger condition settings. Active torque support technology is the first to intervene under low-speed braking conditions, while thyristor energy recovery serves as a backup measure in case the former fails or during high-speed, high-power braking, forming a dual protection mechanism to comprehensively ensure the safe and reliable operation of the propulsion system under various operating conditions. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the optimized design of the DC-side power supply structure of the frequency converter of the present invention.

[0027] Figure 2 This is a flowchart illustrating the safety braking control method for electrically propelled ships according to the present invention.

[0028] Figure 3 This is a flowchart illustrating the trigger condition determination process for the active torque support technology of the frequency converter in this invention.

[0029] Figure 4 This is a control block diagram of the constant torque control strategy for the frequency converter of the present invention.

[0030] Figure 5 This is a flowchart illustrating the trigger condition determination for thyristor conduction recovery braking energy in this invention.

[0031] Figure 6 This is a schematic diagram of the topology and operating conditions of an example system in an embodiment of the present invention.

[0032] Figure 7 This is a DC voltage variation curve in an embodiment of the present invention when the inverter active torque support technology is not applied.

[0033] Figure 8 The curves showing the change in the input current of the frequency converter in an embodiment of the present invention when the active torque support technology of the frequency converter is not applied.

[0034] Figure 9 The DC voltage change curve is shown in the embodiment of the present invention after applying the active torque support technology of the frequency converter.

[0035] Figure 10 The curve showing the change in input current of the frequency converter after applying the active torque support technology in this embodiment of the invention. Detailed Implementation

[0036] 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 embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0037] Example 1

[0038] like Figure 1 As shown, this embodiment of the invention provides a safety braking system for an electric propulsion ship, including a DC main grid, a frequency converter, a reverse protection diode, a thyristor, and a frequency converter controller. The DC terminal of the frequency converter is equipped with a DC support capacitor to stabilize the DC-side voltage and provide instantaneous energy buffering. The reverse protection diode is connected between the DC main grid and the DC terminal of the frequency converter, forming a unidirectional power supply circuit. The anode of the thyristor is connected to the frequency converter, and the cathode is connected to the DC main grid, forming an anti-parallel structure with the reverse protection diode, used to feed braking energy back to the DC main grid during braking. The frequency converter controller is used to detect the operating status of the propulsion system and execute active torque support control and thyristor conduction control.

[0039] In this embodiment of the invention, the drive inverter adopts a three-phase two-level topology and includes six IGBT power switching transistors, numbered S1 to S6. The inverter output is connected to a filter resistor R and a filter capacitor C. f and filter inductor L f The drive motor M is powered via a disconnect switch. The inverter's DC terminal is equipped with a DC support capacitor C, which draws power from the main DC grid through a reverse protection diode.

[0040] The anode of the anti-reverse diode is connected to the DC main grid, and the cathode is connected to the DC support capacitor, ensuring that the current can only flow in one direction during power supply. This unidirectional power supply characteristic has several technical advantages: First, it can isolate the electrical energy at the load end, preventing the DC support capacitor of the frequency converter from discharging rapidly when a short circuit fault occurs in the DC main grid, thereby reducing the short circuit current level of the DC main grid and facilitating the selection of protection devices; Second, it has a certain effect on isolating the electromagnetic interference of the frequency converter's high-frequency switching noise on the DC main grid.

[0041] A reverse-biased thyristor bypass branch is connected in parallel across the anti-reverse diode. The anode of the thyristor is connected to the DC support capacitor, and the cathode is connected to the DC main grid. Under normal power supply conditions, the DC main grid voltage is higher than the DC support capacitor voltage of the inverter, so the anti-reverse diode is forward-biased and the thyristor remains off due to the reverse voltage. When the propulsion system enters braking mode, the back electromotive force generated by the propulsion motor is rectified by the inverter to charge the DC support capacitor, causing its voltage U to... dc Gradually rises and exceeds the DC main grid voltage U dc0 At this point, the anti-reverse diode is cut off due to reverse voltage. If not addressed promptly, the braking energy will continue to accumulate, leading to overvoltage at the inverter input. By triggering the bypass branch with a given thyristor pulse signal, the braking energy can be fed back to the DC main grid for absorption and utilization by connected energy storage systems, household loads, or other electrical equipment. Based on the configuration of load equipment or energy storage capacity that the DC main grid can absorb braking energy, and comparing it with the maximum braking power of the propulsion system, the system's braking load configuration can be reduced or even eliminated.

[0042] For example, the system in this embodiment also includes an energy storage system and a load device connected to the DC main grid, for absorbing the braking energy fed back through the bypass branch formed by the thyristors, and its charging and discharging power and capacity can be configured according to the maximum braking power of the propulsion system.

[0043] Example 2

[0044] like Figure 2 As shown, this embodiment provides a safety braking control method for electrically propelled ships, applicable to the aforementioned safety braking system. It employs a combined hardware and software braking control strategy, selecting appropriate processing methods based on the characteristics of different braking conditions. At the software control level, inverter active torque support technology is applied, using a constant pulse torque to offset external forces, primarily for handling low-speed, high-frequency braking conditions. At the hardware control level, a thyristor bypass branch is used to recover braking energy, suitable for conventional braking conditions and as a backup protection measure in case of software control failure. The two control methods are prioritized through differentiated trigger condition settings, ensuring that software control takes effect first when the conditions are met. This control method includes the following steps:

[0045] Step S1: Collect the propulsion system rotational speed n and the output voltage U of the anti-reverse diode. dc and DC main grid voltage U dc0 These parameters form the basis for judging braking status and switching control strategies.

[0046] Step S2: When the active torque support trigger condition is met, switch the frequency converter to constant torque control mode. Active torque support technology primarily addresses the problem of high-frequency braking under low-speed conditions. When the propulsion system operates at low speeds, the force of the water flow may exceed the electromagnetic torque output by the motor, causing the propulsion motor to passively enter a generator state. Without intervention, the system will frequently switch between power supply and generation, causing severe electromagnetic interference and equipment damage. By providing a constant electromagnetic torque slightly greater than the external braking torque, the reverse force of the water flow can be effectively counteracted, ensuring the propulsion system remains in a stable power supply state and preventing high-frequency braking.

[0047] like Figure 3 As shown, the triggering conditions for the inverter's active torque support technology include three aspects, all of which must be met simultaneously for triggering to occur: the propulsion system speed n is not greater than the first threshold n. ref The output voltage U of the anti-reverse diode dc Not less than the second threshold U1, the output voltage U of the anti-reverse diode dc With DC main grid voltage U dc0 The difference must be no less than the third threshold U2. All three conditions must be met simultaneously to trigger this control strategy. Set the speed threshold n. ref This is to limit the effective range of the active torque support technology to the low-speed range, because only at low speeds is the propulsion system susceptible to high-frequency braking due to water flow. Setting voltage thresholds U1 and differential pressure thresholds U2 is to accurately identify the braking state. U1 should be higher than the rated voltage of the DC mains to avoid false triggering during normal operation, while it should be lower than the inverter's voltage protection setting to provide a safety margin. By simultaneously detecting absolute voltage and relative differential pressure, braking conditions can be effectively distinguished from other conditions that cause voltage fluctuations, such as sudden load shedding.

[0048] like Figure 4 As shown, the constant torque control mode adopts a current inner loop control structure based on the dq coordinate system. First, a constant reference command for the d-axis current of the frequency converter is given. i dref and q-axis current constant reference command i qref In the inner loop of the d-axis current, i dref and the d-axis component of the inverter output current i d The difference, after passing through the PI controller, is coupled with the cross-coupled term. ωLd i q The summation yields the d-axis modulation voltage command value. u d In the q-axis current inner loop, i qref and the q-axis component of the inverter output current i q The difference, after passing through the PI controller, is coupled with the cross-coupled term. ωL q i d Subtracting the two values ​​yields the q-axis modulation voltage command value. u q .in L d , L q These are the d-axis and q-axis components of the AC-side inductance. ω This is the mechanical angular velocity. Ultimately, u q and u d The modulation signal for SVPWM control is then obtained through dq transformation. u a , u b and u c and convert S 1~ S The IGBT trigger signal of 6 drives the frequency converter to output the required electromagnetic torque.

[0049] Step S3: When the energy recovery trigger condition is met, the bypass branch formed by the conducting thyristors feeds the braking energy back to the DC main grid. This step mainly handles routine braking conditions and backup protection scenarios when the active torque support technology fails.

[0050] like Figure 5 As shown, the energy recovery triggering condition includes two conditions, both of which must be met simultaneously to trigger the thyristor to conduct: the output voltage U of the reverse protection diode. dc The difference between the output voltage of the reverse protection diode and the DC main grid voltage is not less than the fourth threshold U3. dc -U dc0The threshold value is not less than the fifth threshold U4. The fourth threshold U3 is greater than the second threshold U1, and the fifth threshold U4 is greater than the third threshold U2. This threshold gradient setting ensures that, under the same conditions, active torque support control always takes precedence over thyristor energy recovery control triggering. Only when the active torque support technology fails to effectively suppress the DC voltage rise will the thyristor bypass branch be activated as a backup measure, achieving complementary advantages and multiple protections between hardware and software. Furthermore, no speed limit is set in the energy recovery triggering conditions, meaning that energy recovery can be performed at any speed as long as the voltage condition is met, expanding the applicability of this function.

[0051] After the thyristor is turned on, the braking energy on the inverter side can flow in reverse into the DC main grid and be absorbed by the energy storage system or other load equipment. As energy continues to be fed back, the voltage at the output terminal of the reverse protection diode gradually decreases. When its amplitude is lower than the DC main grid voltage, the forward current flowing through the thyristor drops to zero, and the thyristor automatically turns off based on its own turn-off characteristics. The entire process does not require additional control signals, simplifying the system control logic.

[0052] When the propulsion system rotation speed n is greater than the first threshold n ref Or the output voltage U of the anti-reverse diode dc Less than the second threshold U1, or the voltage difference U dc -U dc0 When the torque is below the third threshold U2, the inverter controller exits the constant torque control mode and reverts to the original control strategy. This adaptive switching mechanism based on operating status ensures that the control system can flexibly adjust according to actual operating conditions, avoiding excessive intervention when no intervention is needed and slow response when protection is required.

[0053] Example 3

[0054] like Figure 6 As shown, this embodiment uses an inland waterway electric propulsion vessel as an example. It adopts a DC grid configuration with a rated DC main grid voltage of 1000V, connected to four 600kW generator sets and two 500kW / 500kWh lithium battery energy storage systems for power supply. Since the generator sets are connected in parallel with droop control, and the voltage regulation rate is set to 2%, the voltage adjusts from 1020V to 980V as the generators gradually increase power from no-load to full load. In actual operation, the two lithium battery energy storage systems are continuously connected to the grid. The system load includes one 200kW side thruster system, two 1000kW main thruster systems, and two 200kVA daytime inverters. In a certain navigation condition, two generator sets are engaged to power the two main thruster systems and the two daytime inverters. The speeds of main thruster systems #1 and #2 are 120rpm and 20rpm respectively. The difference in speed causes water flow, resulting in frequent braking of the low-speed #2 main thruster system.

[0055] Both the main-drive and side-drive inverters connect to the DC grid via a combination of anti-reverse diodes and reverse-parallel thyristors. Under normal power supply conditions, the thyristors are not conducting. Under braking conditions, a trigger signal is given to the reverse-parallel thyristors to feed energy back to the DC grid. Since the DC grid is equipped with two 500kW / 500kWh lithium-ion battery energy storage systems, which can charge and absorb braking energy during propulsion system braking, and whose capacity and power are sufficient to meet the maximum braking power and power generation requirements of the propulsion system, the braking load was eliminated in the system design.

[0056] During a certain voyage, two generator sets were put into operation to power two main propulsion systems and two daytime inverters. The No. 1 main propulsion system was set to operate at 120 rpm, and the No. 2 main propulsion system was set to operate at 20 rpm. Due to the significant difference in the operating speeds of the two propulsion systems and the uneven distribution of water currents around the hull, the No. 2 main propulsion system, operating at low speed, experienced frequent braking due to the impact of the water currents.

[0057] According to the control method of the present invention, the triggering condition parameters are set as follows: the triggering condition for the inverter active torque support technology is that the speed n is not greater than 60 rpm, i.e., the first threshold n. ref Set to 60rpm, anti-reverse diode output voltage U dc The second threshold U1 is set to 1040V, and the voltage difference U is not less than 1040V. dc Subtract U dc0 The third threshold U2 is set to 20V, meaning it should be no less than 20V; the trigger condition for the thyristor bypass branch is the output voltage U of the reverse protection diode. dc Not less than 1060V, i.e., the fourth threshold U3 is set to 1060V, and the voltage difference U dc Subtract U dc0 The fifth threshold, U4, is set to 40V, meaning it should be no less than 40V. Since the DC main grid voltage does not exceed 1020V during normal operation, the above voltage threshold setting can effectively prevent false triggering. At the same time, the fourth threshold, U3, is greater than the second threshold, U1, and the fifth threshold, U4, is greater than the third threshold, U2, ensuring that the active torque support technology takes effect first.

[0058] Figure 7 and Figure 8 The changes in DC voltage and inverter input current are shown when the inverter's active torque support technology is not applied. Since the No. 2 main propulsion system is operating at a low speed of 20 rpm, the speed triggering condition is met. However, without active torque support technology, the system can only rely on thyristors for energy recovery. The maximum applicable frequency of the phase-controlled thyristors is 50 Hz. Figure 7It can be seen that initially, the thyristor was able to limit the voltage within the normal range through frequent conduction. However, due to the excessively high braking frequency exceeding the thyristor's operating capacity, the inverter input eventually experienced overvoltage tripping due to accumulated braking energy. From Figure 8 It can be seen that the frequent switching of the thyristor causes the inverter input current to fluctuate drastically, generating large interference harmonic currents, which poses a serious safety hazard.

[0059] Figure 9 and Figure 10 The changes in DC voltage and inverter input current after applying the inverter's active torque support technology are shown. When the trigger condition is detected, the inverter controller switches to constant torque control mode, and adjusts the d-axis current reference command according to the braking situation under this condition. i dref It is set at approximately 5% of the rated propulsion power. i dref Maintaining the original control strategy and feed rate unchanged before triggering, sufficient electromagnetic torque is generated to counteract the reverse braking torque from the water flow, ensuring the frequency converter is in a relatively stable power supply state. It automatically exits and reverts to the original constant speed control once the propulsion system's operating state no longer meets the triggering conditions. Figure 9 It can be seen that after applying the active torque support technology, the output voltage of the anti-reverse diode remains at a normal level, with only small fluctuations triggered by low frequency at the condition boundary, and the propulsion system no longer experiences frequent braking. From Figure 10 It can be seen that the frequency converter continuously operates in a power supply state, and the DC side input current is stable, avoiding system disturbances caused by frequent commutation of switching devices. Under this condition, the thyristor bypass branch is not triggered, but it is always in a ready state as a backup protection measure, and can respond in a timely manner when the active torque support technology fails or other high-speed, high-power braking conditions occur.

[0060] According to the triggering conditions of this embodiment, the active torque support technology is preferentially triggered during low-speed braking and its effect is significant. The output voltage of the anti-reverse diode will drop to a normal level, thus preventing further triggering of the thyristor to open the bypass branch. The thyristor bypass branch can serve as a backup protection measure under this condition, and can also be activated in a timely manner to recover energy under other high-speed, high-power braking conditions, depending on the set triggering conditions.

[0061] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described; only preferred embodiments of the present invention are illustrated. The descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. As long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification.

[0062] It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of this invention. Therefore, the scope of protection of this invention should be determined by the appended claims.

Claims

1. A safety braking system for electrically propelled ships, characterized in that: This includes the DC main grid, frequency converter, anti-reverse diodes, thyristors, and frequency converter controller; The inverter is equipped with a DC support capacitor at its DC terminal. The anti-reverse diode is connected between the DC main grid and the DC terminal of the inverter to form a unidirectional power supply circuit. The anode of the thyristor is connected to the frequency converter, and the cathode is connected to the DC main grid. It forms an anti-parallel structure with the anti-reverse diode and is used to feed the braking energy back to the DC main grid under braking conditions. The frequency converter controller is used to detect the operating status of the propulsion system and execute active torque support control and thyristor conduction control; The active torque support triggering condition includes: propulsion system speed n ≤ first threshold n ref And the output voltage U of the anti-reverse diode dc ≥ the second threshold U1, and the output voltage U of the anti-reverse diode dc With DC main grid voltage U dc0 The difference U dc -U dc0 ≥ The third threshold U2; where the second threshold U1 is higher than the rated voltage of the DC main grid and lower than the voltage protection value of the frequency converter.

2. The safety braking system for an electric propulsion ship according to claim 1, characterized in that: The electric propulsion ship safety braking system also includes an energy storage system or load device connected to the DC main grid, used to absorb the braking energy fed back through the bypass branch formed by the thyristors.

3. A safety braking control method for electric propulsion ships, applicable to the safety braking system of electric propulsion ships as described in any one of claims 1 to 2, characterized in that: Includes the following steps: The system collects the propulsion system speed, the output voltage of the anti-reverse diode, and the DC main grid voltage; when the active torque support trigger condition is met, the frequency converter is switched to constant torque control mode; when the energy recovery trigger condition is met, the bypass branch formed by the conducting thyristors feeds the braking energy back to the DC main grid.

4. The safety braking control method for an electric propulsion ship according to claim 3, characterized in that: The constant torque control mode includes: Given a constant d-axis current reference command for the frequency converter i dref and q-axis current constant reference command i qref ; i dref and the d-axis component of the inverter output current i d The difference, after passing through the PI controller, is coupled with the cross-coupled term. ωL d i q The summation yields the d-axis modulation voltage command value. u d ; i qref and the q-axis component of the inverter output current i q The difference, after passing through the PI controller, is coupled with the cross-coupled term. ωL q i d Subtracting the two values ​​yields the q-axis modulation voltage command value. u q ; u q and u d The modulation signal for SVPWM control is then obtained through dq transformation. in L d , L q These are the d-axis and q-axis components of the AC-side inductance. ω This refers to the mechanical angular velocity.

5. A safety braking control method for an electric propulsion ship according to claim 3, characterized in that: The energy recovery triggering condition includes: the output voltage U of the anti-reverse diode. dc ≥ Fourth threshold U3, and the difference U between the output voltage of the reverse protection diode and the DC main grid voltage. dc -U dc0 ≥ Fifth threshold U4; where the fourth threshold U3 is greater than the second threshold U1, and the fifth threshold U4 is greater than the third threshold U2; after the braking energy recovery is completed, the voltage amplitude at the output terminal of the anti-reverse diode drops below the DC main grid voltage value, and the thyristor will automatically turn off due to its own characteristics.

6. A safety braking control method for an electric propulsion ship according to claim 3, characterized in that: When the propulsion system rotation speed n is greater than the first threshold n ref Or the output voltage U of the anti-reverse diode dc Less than the second threshold U1, or the voltage difference U dc -U dc0 When the value is less than the third threshold U2, the frequency converter controller exits the constant torque control mode.

Images