Optimal inertia support control method based on propulsion motor frequency converter

Abstract

The application discloses an optimization inertia support control method based on a propulsion motor frequency converter, and is used for the ship propulsion system driven by the frequency converter, and the virtual inertia control is implemented in the frequency converter, the motor torque control inner ring is embedded, and the motor drive system speed closed loop small signal model is established, so that the motor speed is controlled in the steady state, and the transient power support is provided during the DC bus voltage fluctuation; the motor drive system DC voltage closed loop small signal model is established, the propulsion motor inertia support capability is evaluated, the inertia level is coordinated according to the system operation state, so that the optimization inertia support control scheme of the coordinated propulsion system and the power system is constructed, and then the application is applied to the suppression of the voltage fluctuation of the ship power grid system caused by the impact load switching, so as to realize the voltage safety and stability of the ship power system. According to the operation characteristics of the propulsion motor, the work state of the frequency converter is combined, the kinetic energy stored in the rotating load is utilized, the motor drive system is coordinately controlled, the voltage regulation of the DC grid is supported, and the stability and convenience of the ship power system are remarkably improved.

Description

Technical Field

[0001] This invention relates to a technology in the field of frequency converter control, specifically an optimized inertia support control method based on a propulsion motor frequency converter. Background Technology

[0002] The ship's electrical system is an independent power generation system, which is highly susceptible to impact loads. When high-power equipment on a ship is switched on or off, it causes instantaneous power surges. Due to the limitations of the gas turbine, the mechanical power response of the generator set is very slow, making the ship's electrical system less resistant to impact loads and unable to meet the requirements for stable operation. Summary of the Invention

[0003] This invention addresses the shortcomings of existing technologies that do not consider using rotor rotational inertia as an inertial support method, which cannot meet the power variation requirements in scenarios with high-power loads. It proposes an optimized inertial support control method based on a propulsion motor frequency converter. According to the operating characteristics of the propulsion motor and the working state of the frequency converter, the kinetic energy stored in the rotating load is used to coordinate the control of the motor drive system, providing support for DC grid voltage regulation and significantly improving the stability and convenience of the ship's power system.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to an optimized inertia support control method based on a propulsion motor frequency converter, comprising:

[0006] Step 1: For the ship propulsion system driven by frequency converter, implement virtual inertia control in the frequency converter, embed the inner loop of motor torque control, and establish a small-signal closed-loop speed model of the motor drive system to achieve steady-state control of motor speed and provide transient power support during DC bus voltage fluctuations.

[0007] Step 2: Based on the design scheme of DC bus voltage inertia support for propulsion motor frequency converter, establish a closed-loop small-signal model of DC voltage of motor drive system, evaluate propulsion motor inertia support capability, coordinate inertia level according to system operating status, and thus construct an optimized inertia support control scheme that coordinates propulsion system and power system.

[0008] Step 3: Apply the optimized inertia support control scheme suitable for motor drive systems to suppress voltage fluctuations in the ship's power grid system caused by impulsive load switching, so as to achieve safe and stable voltage in the ship's power system.

[0009] Technical effect

[0010] This invention employs a propulsion motor as a control technology to mitigate load fluctuations on ships. During transient DC voltage fluctuations in the ship's electrical grid, it utilizes the kinetic energy stored in the rotating load to provide significant DC voltage support to the ship's electrical grid. Compared to existing technologies, this invention offers flexible control, requires no dedicated energy storage system, incurs no additional costs, and can operate continuously under conditions of high current, high power, and high energy variation frequency, making it more suitable for mitigating situations with high power fluctuations in ship loads. Attached Figure Description

[0011] Figure 1 This is a flowchart of the present invention;

[0012] Figure 2 This is a schematic diagram of a ship propulsion system model;

[0013] Figure 3 This is a schematic diagram of DC voltage supporting torque;

[0014] Figure 4 This is a schematic diagram of a closed-loop small-signal model of DC voltage in a motor drive system.

[0015] Figure 5 Flowchart for optimizing inertia support control in frequency converter control;

[0016] Figure 6 and Figure 7 This is a schematic diagram illustrating the effect of an example. Detailed Implementation

[0017] like Figure 1 As shown in this embodiment, an optimized inertia support control method based on a propulsion motor frequency converter is provided, including:

[0018] Step 1: The structure of a variable frequency drive (VFD) driven marine propulsion system is as follows: Figure 2 The system model shown implements virtual inertia control in the inverter of the system model, embedding a virtual inertia control into the torque command output of the original speed outer loop, such as... Figure 3 The inner loop of motor torque control is shown, and a small-signal closed-loop model of the motor drive system speed is established, as follows. Figure 4 As shown.

[0019] like Figure 2 As shown, the system model includes: a propeller, a gearbox, a propulsion motor, and a frequency converter connected in sequence, as well as an impact load and a generator set connected to the output of the frequency converter.

[0020] like Figure 3 As shown, the virtual inertia control refers to the motor drive system providing supporting power to the ship's electrical grid when the grid load power fluctuates. It is used to improve the maximum voltage drop, maximum overshoot, and recovery oscillation during DC voltage dynamic processes, wherein: For the additional virtual inertial power, This is a virtual droop coefficient. For virtual capacitors, This is the equivalent DC voltage. This is the rated DC voltage.

[0021] The term "embedding" refers to: the original speed control torque generated based on the speed outer loop in the inverter control. Additional virtual torque command converted from virtual support power Add them together to get the total torque command. ,in: This refers to the actual operating speed of the propeller. To calculate the minimum rotational speed for propeller protection, in the specific implementation, a filtered differential is used to collect the voltage-time derivative, i.e. , It is a differential constant, and the voltage deviation soft dead zone Voltage change soft dead zone , The set voltage dead zone range, This is the set dead zone range for the rate of change of voltage.

[0022] The voltage deviation soft dead zone and voltage change soft dead zone are set simultaneously for voltage deviation and voltage change rate, so that the present invention only participates in grid voltage regulation when a deviation of 2% or greater is detected.

[0023] like Figure 4 As shown, the closed-loop small-signal model of the motor drive system speed is as follows: ,in: For load power disturbance, and To account for the virtual droop coefficient and the equivalent coefficient of the virtual capacitance in dead-zone control, the value range is as follows: , The total capacitance on the DC bus. Let be the inertial time constant of the inner current loop of the frequency converter. The power transient response on the grid side is represented by a first-order inertial approximation.

[0024] Step 2, as follows Figure 5 As shown, the inertia support capability of the propulsion motor is evaluated using the closed-loop small-signal model of the motor drive system speed obtained in step 1. The inertia level is coordinated according to the system operating state to achieve optimized inertia support control. Specifically, under the premise of ensuring the propulsion motor speed, torque, current, mechanical power, and ship propulsion conditions, a model predictive control algorithm is used to optimize the virtual droop coefficient and virtual capacitance, minimizing DC bus voltage fluctuations while avoiding excessive use of the propulsion motor's kinetic energy and preventing impact on long-term propulsion performance. This includes:

[0025] 2.1 Selecting State Variables ,in: DC voltage The derivative of DC voltage. This refers to the actual operating speed of the propeller. For electromagnetic torque, In the state of energy storage charge, For grid load power, To increase power, if there is no energy storage in the system, it can be removed. item.

[0026] 2.2 A prediction model is constructed based on the closed-loop small-signal model of the motor drive system speed. At each sampling time during the prediction phase, the parameters of the prediction model are updated according to the current operating point, thus obtaining a linear parameter variation model, specifically: ,in: , This indicates load disturbance or load power prediction.

[0027] 2.3 Based on the states of the power system and propulsion system, the support strength is dynamically configured using a linear parameter variation model, and a cost function is constructed, specifically as follows: ,in: To suppress bus voltage deviation, To suppress the rate of voltage change, To limit propulsion speed disturbances, To limit the impact of support torque, , The optimal virtual droop coefficient and virtual capacitance are calculated by minimizing the cost function to limit the rate of change of the parameters, and the relevant configurations in the control method are updated.

[0028] Through specific experiments, the above-mentioned optimized inertia support control scheme was applied to suppress DC voltage fluctuations in the ship's power grid system caused by the switching of impulsive loads. A ship power system model including generator set, impulsive load, frequency converter, propulsion motor, gearbox and propeller was established in MATLAB / Simulink for simulation. The simulation parameters are shown in Table 1.

[0029] Table 1 Simulation Parameters

[0030] Under simulated ship load power surge conditions, when using the traditional control scheme and the present invention, the DC voltage of the ship's power grid drops to 342V in 4 seconds, which is 54% less than the voltage drop of the traditional method. The DC voltage variation characteristics are referenced... Figure 6 The following diagram illustrates the changes in the internal state of the motor drive system after adopting this invention. Figure 7 As shown.

[0031] Simulation results show that this invention can immediately slow down the voltage deviation of the ship's power grid after a disturbance, thereby reducing the rate of voltage drop. Compared with the step increase in traditional systems, the generator power gradually increases under the proposed control system. This means that under the control action proposed in this invention, the motor drive system temporarily releases active power to suppress grid voltage fluctuations. Furthermore, it can be noted that in the initial instant after the disturbance, load sharing is achieved between the generator set in the ship's power grid and the motor drive system controlled by this invention according to the system's operational needs. Due to the deceleration of the propulsion motor, the kinetic energy stored in the propeller shaft is used for grid voltage regulation.

[0032] Compared with the prior art, the present invention enables the propulsion motor and motor drive system to exhibit a certain inertia to the ship's DC power grid. By utilizing the rotational kinetic energy of the propulsion motor and its load, it has the ability to participate in the DC voltage support of the ship's power grid and can be adjusted according to the system operation. It can more effectively suppress DC voltage deviation of the power grid and has lower sensitivity to power grid voltage distortion.

[0033] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. An optimized inertia support control method based on a propulsion motor frequency converter, characterized in that, include: Step 1: For the ship propulsion system driven by frequency converter, implement virtual inertia control in the frequency converter, embed the inner loop of motor torque control, and establish a small-signal closed-loop speed model of the motor drive system to achieve steady-state control of motor speed and provide transient power support during DC bus voltage fluctuations. Step 2: Based on the design scheme of DC bus voltage inertia support for propulsion motor frequency converter, establish a closed-loop small-signal model of DC voltage of motor drive system, evaluate propulsion motor inertia support capability, coordinate inertia level according to system operating status, and thus construct an optimized inertia support control scheme that coordinates propulsion system and power system. Step 3: Apply the optimized inertia support control scheme suitable for motor drive systems to suppress voltage fluctuations in the ship's power grid system caused by impulsive load switching, so as to achieve safe and stable voltage in the ship's power system.

2. The optimized inertia support control method based on a propulsion motor frequency converter according to claim 1, characterized in that, The system model includes: a propeller, a gearbox, a propulsion motor, and a frequency converter connected in sequence, as well as an impact load and a generator set connected to the output of the frequency converter.

3. The optimized inertia support control method based on a propulsion motor frequency converter according to claim 1 or 2, characterized in that, The aforementioned virtual inertia control refers to the motor drive system providing supporting power to the ship's electrical grid when the grid load power fluctuates. It is used to improve the maximum voltage drop, maximum overshoot, and recovery oscillation during DC voltage dynamic processes, wherein: For the additional virtual inertial power, This is a virtual droop coefficient. For virtual capacitors, This is the equivalent DC voltage. This is the rated DC voltage.

4. The optimized inertia support control method based on a propulsion motor frequency converter according to claim 3, characterized in that, The term "embedding" refers to: the original speed control torque generated based on the speed outer loop in the inverter control. Additional virtual torque command converted from virtual support power Add them together to get the total torque command. ,in: This refers to the actual operating speed of the propeller. To calculate the minimum rotational speed for propeller protection, in the specific implementation, a filtered differential is used to collect the voltage-time derivative, i.e. , It is a differential constant, and the voltage deviation soft dead zone Voltage change soft dead zone , The set voltage dead zone range, This is the set dead zone range for the rate of change of voltage.

5. The optimized inertia support control method based on a propulsion motor frequency converter according to claim 4, characterized in that, The closed-loop small-signal model of the motor drive system speed is as follows: ,in: For load power disturbance, and To account for the virtual droop coefficient and the equivalent coefficient of the virtual capacitance in dead-zone control, the value range is as follows: , The total capacitance on the DC bus. Let be the inertial time constant of the inner current loop of the frequency converter. The power transient response on the grid side is represented by a first-order inertial approximation.

6. The optimized inertia support control method based on a propulsion motor frequency converter according to claim 1, characterized in that, Step 2 specifically includes: 2.1 Selecting State Variables ,in: DC voltage The derivative of DC voltage. This refers to the actual operating speed of the propeller. For electromagnetic torque, In the state of energy storage charge, For grid load power, To increase power, if there is no energy storage in the system, it can be removed. item; 2.2 A prediction model is constructed based on the closed-loop small-signal model of the motor drive system speed. At each sampling time during the prediction phase, the parameters of the prediction model are updated according to the current operating point, thus obtaining a linear parameter variation model, specifically: ,in: , This indicates load disturbance or load power prediction; 2.3 Based on the states of the power system and propulsion system, the support strength is dynamically configured using a linear parameter variation model, and a cost function is constructed, specifically as follows: ,in: To suppress bus voltage deviation, To suppress the rate of voltage change, To limit propulsion speed disturbances, To limit the impact of support torque, , The optimal virtual droop coefficient and virtual capacitance are calculated by minimizing the cost function to limit the rate of change of the parameters, and the relevant configurations in the control method are updated.

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