Grid-connected and islanding control method for a brushless doubly-fed power generation system

Abstract

The present invention relates to the technical field of motors, and specifically provides a grid-connected and off-grid control method for a brushless doubly-fed power generation system, including the following steps: when receiving a shaft-driven grid-connection command, obtain the amplitude and phase of the grid voltage and the power winding voltage, and use a synchronous control strategy to determine the voltage set value and the phase of the control winding rotation transformation; according to the voltage set value and the phase of the control winding rotation transformation, after controlling the power winding to output a voltage synchronized with the grid voltage, then control the corresponding execution unit to perform a parallel operation; according to the total active power of the load, and using a parallel operation control strategy, control the brushless doubly-fed power generation system to output the same power to the grid; use a load transfer strategy to perform load transfer, and after transferring the load to the brushless doubly-fed power generation system, complete the grid-connected to off-grid transition. The present invention is used to avoid current impact during grid-connected and off-grid switching.

Description

Technical Field

[0001] The present invention relates to the technical field of brushless doubly-fed power generation, and particularly to a grid-connected and off-grid control method for a brushless doubly-fed power generation system. Background Art

[0002] The brushless doubly-fed machine is a new type of AC motor. Since the brush and slip ring are eliminated, the maintenance cost is low and the reliability is higher, and the application prospect is very wide. Under the call of energy conservation and emission reduction in today's society, some existing ships are equipped with two sets of independent power systems, a main power generation system, that is, a diesel synchronous generator, and an auxiliary power generation system - a brushless doubly-fed shaft generator system. The prime mover (main engine) selected for the ship's propeller will have a certain redundancy. A speed increasing gear is installed at the end of the main engine shaft, and then the brushless doubly-fed motor is connected to the high-speed shaft of the gearbox. Then the high-speed shaft speed reaches the speed operation range of the brushless doubly-fed motor, and the redundant mechanical energy at the shaft end is converted into three-phase AC power. Generally, the shaft generator accounts for about 50% of the main generator.

[0003] When the ship is sailing normally, less power is used, and the shaft generator system is used. When entering and leaving the port, the speed is low, which cannot meet the speed requirements of the shaft generator, and the equipment requires a large amount of power. After the ship docks and the main engine stops, the ship still needs to be powered, so the main power generation system is used. The two systems are simultaneously connected to the busbar, that is, the AC bus, and are switched in and out of the busbar according to different working conditions. The prerequisite is that when switching the working mode, that is, when the load is transferred, no large electrical and mechanical shocks can be caused. Summary of the Invention

[0004] A grid-connected and off-grid control method for a brushless doubly-fed power generation system of the present invention can be applied to a field operation engineering vehicle with a wind turbine as the prime mover or a ship shaft generator system with a diesel engine as the prime mover, and can realize free switching between grid connection and off-grid, without inrush current, and realize smooth switching.

[0005] The present invention provides a grid-connected and off-grid control method for a brushless doubly-fed power generation system, including the following steps:

[0006] When receiving the shaft grid-connection instruction, obtain the grid voltage, the amplitudes and phases of the power winding voltages, and use the synchronous control strategy to determine the voltage set value of the control winding and the phase of the rotational transformation;

[0007] According to the voltage set value and the phase of the rotational transformation of the control winding, after controlling the power winding output voltage to synchronize with the grid voltage, then control the corresponding execution unit to perform the paralleling operation;

[0008] According to the total active power of the load, and using the paralleling control strategy, control the brushless doubly-fed power generation system to output the same power to the grid, and switch to the off-grid control of independent operation. Among them, during off-grid control, the shaft generator of the brushless doubly-fed power generation system synchronously disconnects from the grid;

[0009] Using a load transfer strategy, load transfer is performed. After transferring the load to the brushless doubly-fed power generation system, grid connection to off-grid transition is completed.

[0010] In an implementable manner, the amplitude and phase of the grid voltage and the power winding voltage are obtained by sampling the grid voltage and the power winding voltage respectively and using a phase-locked loop.

[0011] In an implementable manner, the synchronous control strategy includes:

[0012] The amplitude of the grid voltage and the amplitude of the power winding voltage are input into a voltage loop to obtain a first current reference value, where the first current reference value is the set value required for one of the current components; the voltage loop includes a first comparison element and a first PI controller;

[0013] The first current reference value and a second current reference value are respectively input into a current loop to obtain the voltage reference values of the control winding on the d-axis and q-axis; the current loop includes a second comparison element and a second PI controller;

[0014] The grid voltage angle, the rotor angle, and the initial phase compensation are compared to calculate the angle of the control winding;

[0015] The voltage reference values on the d-axis and q-axis and the rotation transformation angle of the control winding are subjected to inverse coordinate transformation to the three-phase coordinate system to obtain a first voltage command value, and then the output voltage of the inverter is controlled by SVPWM.

[0016] In an implementable manner, the phase of the control winding rotation transformation is:

[0017]

[0018] where, θ r is the rotor angle, θp is the phase of the power winding, f c is the excitation frequency of the control winding, θ r0 is the spatial position difference between the power winding and the control winding, obtained from the PI output of the phase loop. The reference value and the feedback value of the phase loop are the phase of the grid voltage and the phase of the power winding voltage respectively.

[0019] In an implementable manner, the parallel operation control strategy includes:

[0020] When the amplitude difference and phase difference between the power winding voltage and the grid voltage are within a preset range, automatic grid connection to off-grid transition is started, and the voltage loop and the phase loop are controlled to stop working;

[0021] Determine the total active power of the load; according to the total active power, and using the active power given value calculation formula, calculate the active power given value of the power winding. When calculating the active power, the given value of the reactive power is 0;

[0022] Take the active power given value and the reactive power given value as the inputs of the active power outer loop and the reactive power outer loop respectively. The output values of the voltage loop and the phase loop are the final PI output values when the call is stopped; and use the double closed-loop vector control strategy of the power outer loop and the current inner loop to obtain the voltage given values of the d-axis and the q-axis again, where the output value of the power outer loop current is the output value maintained after the voltage loop works;

[0023] After the obtained voltage given values of the d-axis and the q-axis and the rotation transformation angle of the control winding are inversely transformed to the three-phase coordinate system, obtain the second voltage command value, and then use SVPWM to control the output voltage of the inverter to output the same power to the power grid.

[0024] In an implementable manner, the active power given value calculation formula is:

[0025] P = Psum f p / (f p + f c )

[0026] In the formula, Psum is the total active power of the load, f p is the power winding frequency, and f c is the control winding excitation frequency.

[0027] In an implementable manner, the parallel operation control strategy includes:

[0028] Control the active power outer loop and the reactive power outer loop to stop working;

[0029] Convert the active power outer loop and the reactive power outer loop into a voltage loop. The output values of the two controllers of the active power loop and the reactive power loop are the final PI output values when the call is stopped; at the same time, use the given angular frequency of the power winding, and after integration and subtraction of the rotor phase, obtain the phase of the control winding again;

[0030] After the obtained voltage given values of the d-axis and the q-axis and the rotation transformation angle of the control winding are inversely transformed to the three-phase coordinate system, obtain the third voltage command value, and then use SVPWM to control the output voltage of the inverter to complete the load transfer.

[0031] In an implementable manner, the brushless doubly-fed power generation system includes a first actuator and a second actuator, where the first actuator is connected between the power grid and the load, and the second actuator is connected between the load and the brushless doubly-fed power generation system;

[0032] The first actuator is used to determine whether the grid voltage is within the output voltage range of the brushless doubly-fed power generation system when receiving the shaft-driven grid connection command;

[0033] When the grid voltage is within the real-time output voltage range of the brushless doubly-fed power generation system, the second actuator is triggered by the first signal, and the second actuator performs load transfer according to the load transfer strategy; the first signal is an off-grid control signal;

[0034] When the grid voltage is not within the output voltage range of the brushless doubly-fed power generation system, the second actuator is triggered by the second signal, and the second actuator reduces the excitation current of the brushless doubly-fed power generation system according to a preset gradient until the second actuator is triggered by the first signal, and the second actuator performs load transfer according to the load transfer strategy; the second signal is an output voltage overvoltage signal.

[0035] In an implementable manner, the control for the brushless doubly-fed power generation system to output the same power to the grid and switch to off-grid control for independent operation further includes:

[0036] Determine the optimal triggering angle of the thyristor through the thyristor preset between the brushless doubly-fed power generation system and the grid and based on the voltage given value and the phase of the control winding rotation transformation;

[0037] When the phase of the voltage output from the brushless doubly-fed power generation system to the grid and the voltage given value reach the optimal triggering angle, the thyristor conducts, and the brushless doubly-fed power generation system outputs the same power to the grid.

[0038] In an implementable manner, after the shaft generator synchronously disconnects from the grid, a disconnection signal is generated, wherein the disconnection signal and the load transfer signal after load transfer are synchronously generated and uploaded to the user terminal.

[0039] The beneficial effects that can be achieved by the present invention are:

[0040] The on-grid and off-grid control method of a brushless doubly-fed power generation system of the present invention can achieve free switching between on-grid and off-grid, without inrush current, and achieve smooth switching.

[0041] Other features and advantages of the present invention will be described in the subsequent description, and part of them will be obvious from the description, or understood by implementing the present invention. The objectives and other advantages of the present invention can be realized and obtained through the structures specifically pointed out in the written description, claims, and drawings.

[0042] The technical solutions of the present invention will be further described in detail below through the drawings and embodiments. Description of the Drawings

[0043] The accompanying drawings are used to provide a further understanding of the present invention and form a part of the specification. They are used in conjunction with the embodiments of the present invention to explain the present invention, but do not constitute a limitation to the present invention. In the accompanying drawings:

[0044] Figure 1 It is a flowchart of the grid connection and disconnection control method for the brushless doubly-fed power generation system in Embodiment 1 of the present invention;

[0045] Figure 2 It is a control strategy diagram for the no-load synchronization of the grid for the brushless doubly-fed wind power generation system in Embodiment 1 of the present invention;

[0046] Figure 3 It is an internal control block diagram of the phase-locked loop PLL in Embodiment 1 of the present invention;

[0047] Figure 4 It is a control strategy diagram for grid-connected power generation of the brushless doubly-fed wind power generation system in Embodiment 1 of the present invention;

[0048] Figure 5 It is a control strategy diagram for the load transfer of shaft-driven power generation in Embodiment 1 of the present invention;

[0049] Figure 6 It is a simulation structure diagram of the brushless doubly-fed shaft-driven power generation system in Embodiment 1 of the present invention. Detailed implementation manners

[0050] The following describes the preferred embodiments of the present invention in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0051] As Figure 1 shown, Embodiment 1 of the present invention provides a grid connection and disconnection control method for a brushless doubly-fed power generation system, including the following steps:

[0052] When receiving the shaft-driven grid connection command, obtain the voltage of the power grid (when the main power generation system of the brushless doubly-fed power generation system is connected to the power grid, the power grid voltage is equivalent to the voltage of the main power generation system), the amplitudes and phases of the power winding voltages, and use the synchronous control strategy to determine the voltage set value of the control winding and the phase of the rotation transformation;

[0053] According to the determined voltage set value of the control winding and the phase of the rotation transformation, after controlling the output voltage of the power winding to synchronize with the power grid voltage, then control the corresponding execution unit to perform the parallel operation;

[0054] According to the total active power of the load and using the parallel operation control strategy, the brushless doubly-fed power generation system is controlled to output the same power to the power grid and switched to the off-grid control of independent operation. During off-grid control, the shaft generator of the brushless doubly-fed power generation system is synchronously disconnected from the power grid. The brushless doubly-fed power generation system of the present invention includes a shaft generator and a main power generation system. During the process of off-grid control, when starting the off-grid control of independent operation, the shaft generator is in the off-grid operation process. After the shaft power generation system is synchronized with the main power generation system, load transfer is performed, and then the operation mode changes to the off-grid control of independent operation.

[0055] Using the load transfer strategy, load transfer is performed. After the load is transferred to the brushless doubly-fed power generation system, grid-connected to off-grid conversion is completed.

[0056] The working principle of the above technical solution: When receiving the shaft-driven grid-connection instruction, first obtain the amplitude and phase of the grid voltage and the amplitude and phase of the power winding voltage, and use the synchronization control strategy to obtain the voltage given value and the phase of the control winding rotation transformation. Then, according to the voltage given value and the phase of the control winding rotation transformation, control the power winding to output a voltage synchronized with the grid voltage. Next, control the corresponding execution unit to perform parallel operation to connect the brushless doubly-fed power generation system to the power grid. Then, first calculate the total active power of the load and use the parallel operation control strategy to output power to the power grid to meet the load demand. Finally, after the brushless doubly-fed power generation system operates stably and outputs power, prepare to start load transfer. Using the load transfer strategy, load transfer is performed. After the load is transferred to the brushless doubly-fed power generation system, grid-connected to off-grid conversion is completed.

[0057] The beneficial effects of the above technical solution: Through the control strategy of the present application, smooth switching between grid-connected and off-grid of the brushless doubly-fed power generation system is achieved, there is no impact current, and the electromagnetic torque is also very stable, extending the service life of the system. The smooth switching of the present invention is that after the shaft-driven power generation system is synchronized with the main power generation system, the power of the load is output to the power grid. At this time, the main power generation system has no power output, and the load power is completely borne by the shaft power generation system. Therefore, after removing the main power generation system, the power of the load is the output power of the shaft power generation system, and the two are exactly the same, there is no sudden change in power, and there is no impact current, realizing smooth switching.

[0058] On the basis of Embodiment 1, the amplitude and phase of the grid voltage and the power winding voltage are obtained by sampling the grid voltage and the power winding voltage respectively and using a phase-locked loop.

[0059] The working principle of the above technical solution: See Figure 3 and Figure 1, taking the power winding voltage phase-locked loop as an example, the principle of the phase-locked loop is described. The phase-locked loop includes a comparator and a PI controller. The command of the PI controller is 0, the feedback value is the q-axis component of the voltage, and the output result is that the d-axis voltage is the amplitude of the voltage and the q-axis component is 0. Here, the command value and the feedback value are added instead of subtracted, otherwise a negative angular frequency will be obtained. The feedback value can also be the d-axis component of the voltage, so that the q-axis component of the output voltage is the amplitude and the d-axis component is 0.

[0060] Beneficial effects of the above technical solution: The present application uses a phase-locked loop to be able to track the phase changes of the power grid and the power winding in real time and provide accurate phase information.

[0061] Based on Embodiment 1, the synchronization control strategy includes:

[0062] Input the amplitude of the grid voltage and the amplitude of the power winding voltage into the voltage loop to obtain a first current set value, which is the set value required for one of the components of the current; the voltage loop includes a first comparison element and a first PI controller;

[0063] Input the first current set value and the second current set value into a current loop respectively to obtain the voltage set values of the control winding on the d-axis and q-axis; the current loop includes a second comparison element and a second PI controller;

[0064] Compare the grid voltage angle, the rotor angle and the initial phase compensation, and calculate to obtain the angle of the control winding;

[0065] After performing coordinate inverse transformation of the voltage set values on the d-axis and q-axis and the rotation transformation angle of the control winding to the three-phase coordinate system, obtain a voltage command value, and then use SVPWM to control the output voltage of the inverter.

[0066] Working principle of the above technical solution:

[0067] See Figure 2 the no-load synchronization grid control strategy diagram of the brushless doubly-fed wind power generation system in Figure 2 , the strategy includes the following steps: First, input the amplitude of the grid voltage and the amplitude of the power winding voltage into the voltage loop composed of a first comparison element and a first PI controller, and then use the output of the voltage loop as the set value of the d-axis or q-axis current controller of the control winding. cq is 0 during synchronous grid connection, and i is during grid-connected power generationcq is the output of the active power loop. When operating independently, i cq is the output when the active power loop stops working. It is customized for the second current at different nodes.

[0068] The current loop includes a second comparison element and a second PI controller. It is also necessary to subtract the rotor angle from the grid voltage angle, and in addition, an initial phase compensation needs to be added to calculate the angle of the control winding.

[0069] The rotor angle is first obtained by an encoder from the BDFG to get the actual position and speed of the rotor, then the electrical angle is calculated, and after integrating the electrical angle, it is obtained. The initial phase compensation is the control space position difference between the power winding and the control winding, which is obtained through the phase loop. The phase loop includes a third comparison element, a third PI controller, and an integration element. Among them, the given value and the feedback value of the phase loop are the phase of the grid voltage and the phase of the power winding voltage respectively. Finally, the voltage command values of the d-axis and q-axis and the rotation transformation angle of the control winding are subjected to coordinate inverse transformation to the three-phase coordinate system to obtain the voltage command value, and then the output voltage of the inverter is controlled through SVPWM. When the output voltage of the inverter is synchronized with the grid voltage (i.e., the amplitude, frequency, and phase match), the brushless doubly-fed power generation system can be connected to the grid.

[0070] The beneficial effects of the above technical solutions:

[0071] Based on Example 1, the phase of the control winding rotation transformation is:

[0072]

[0073] Among them, θ r is the rotor angle, θp is the phase of the power winding, f c is the excitation frequency of the control winding.

[0074] In the above formula, according to the relationship between the rotational speed and the frequencies of the two sets of stator windings, if the power winding frequency is fixed and the rotational speed changes, the excitation frequency of the control winding is obtained.

[0075]

[0076] In the formula, p p is the number of pole pairs of the power winding, p c is the number of pole pairs of the control winding, f p ,, is the frequency of the power winding, p c is the pole frequency of the control winding, n r is the rotational speed of the generator. Voltage command value calculation:

[0077] Based on Example 1, the paralleling control strategy includes:

[0078] When the amplitude difference and phase difference between the power winding voltage and the grid voltage are within the preset range, start the automatic grid connection to off-grid transition, and control the voltage loop and phase loop to stop working;

[0079] Determine the total active power of the load; according to the total active power, and using the calculation formula for the given value of active power, calculate the given value of active power of the power winding. When calculating the active power, the given value of reactive power is 0;

[0080] Take the given value of active power and the given value of reactive power as the inputs of the outer active power loop and the outer reactive power loop respectively. The output values of the voltage loop and the phase loop are the final PI output values when the calls are stopped; and use the double closed-loop vector control strategy of the outer power loop and the inner current loop to obtain the given values of voltage on the d-axis and q-axis again. The output value of the outer power loop current is the output value maintained after the voltage loop works;

[0081] After performing coordinate inverse transformation of the obtained given values of voltage on the d-axis and q-axis and the rotation transformation angle of the control winding to the three-phase coordinate system, obtain the second voltage command value, and then use SVPWM to control the output voltage of the inverter to output the same power to the grid.

[0082] The working principle of the above technical solution:

[0083] See Figure 4 , when connecting to the grid, it is necessary to first control the voltage loop and the phase loop to stop working. Specifically, the grid connection command is issued by the processor according to the control strategy. If it is detected that the amplitude difference and phase difference between the power winding voltage and the grid voltage are within the allowable range for automatic grid connection to off-grid transition. The output values of the voltage loop and the phase loop are the final PI output values when the calls are stopped. Then, determine the total active power of the load; specifically, the total active power P sum of the load is calculated by sampling the voltage and current. After connecting to the grid, the double closed-loop vector control strategy of the outer power loop and the inner current loop is adopted, with the active and reactive powers of the power winding as the commands. The total active power P sum of the load is calculated according to the voltage and current at the load port. Then, take P = P sum fp / (fp + fc) as the given value of active power of the power winding. According to the total active power, and using the calculation formula for the given value of active power, calculate the given value of active power of the power winding.

[0084] Next, the active power reference value and the reactive power reference value are respectively used as the inputs of the outer loop of the active power and the outer loop of the reactive power. The outer loop of the active power and the outer loop of the reactive power respectively include a fourth comparison unit and a fourth PI controller. The outputs of the outer loop of the active power and the outer loop of the reactive power are respectively used as the second current reference value and the first current reference value of the current inner loop. The output of the current inner loop is the voltage reference value of the d-axis and the q-axis. Finally, the obtained voltage reference values of the d-axis and the q-axis and the rotation transformation angle of the control winding are subjected to inverse coordinate transformation to the three-phase coordinate system to obtain the second voltage command value, and then the output voltage of the inverter is controlled by SVPWM to output the same power to the power grid. In specific implementation, the output of the voltage loop is the output value maintained after it stops working, so as to avoid the impact generated when switching between the voltage loop and the power loop.

[0085] The beneficial effects of the above technical solution: It realizes the smooth switching between grid-connected and off-grid of the brushless doubly-fed power generation system, without inrush current, and the electromagnetic torque is also very stable, extending the service life of the system.

[0086] On the basis of Embodiment 1, the calculation formula for the active power reference value is:

[0087] P = Psum fp / (fp + fc)

[0088] Where P sum is the total active power of the load, f p is the frequency of the power winding, f c is the excitation frequency of the control winding.

[0089] On the basis of Embodiment 1, the parallel operation control strategy includes:

[0090] Control the outer loop of the active power and the outer loop of the reactive power to stop working;

[0091] Convert the outer loop of the active power and the outer loop of the reactive power into a voltage loop. The output values of the two controllers of the active power loop and the reactive power loop are the final PI output values when the calls are stopped; at the same time, using the given angular frequency of the power winding, and after integration and subtracting the rotor phase, the phase of the control winding is obtained again;

[0092] The obtained voltage reference values of the d-axis and the q-axis and the rotation transformation angle of the control winding are subjected to inverse coordinate transformation to the three-phase coordinate system to obtain the third voltage command value, and then the output voltage of the inverter is controlled by SVPWM to complete the load transfer.

[0093] The working principle of the above technical solution: Refer to Figure 5, after the shaft generator operates stably and outputs power, the load transfer is about to start. First, control the active power outer loop and the reactive power outer loop to stop working. The output values of the two controllers of the active power loop and the reactive power loop are the final PI output values when the call is stopped. Convert the active power outer loop and the reactive power outer loop into a voltage loop. At the same time, use the given angular frequency of the power winding, and after integration and subtraction of the rotor phase, obtain the phase of the control winding. After the d-axis and q-axis voltage given values obtained after converting into the voltage loop and the recalculated phase of the control winding are subjected to coordinate inverse transformation to the three-phase coordinate system, obtain the third voltage command value, and then control the output voltage of the inverter through SVPWM to complete the load transfer.

[0094] The beneficial effects of the above technical solution: It realizes the smooth switching between grid-connected and off-grid of the brushless doubly-fed power generation system, without inrush current, and the electromagnetic torque is also very stable, extending the service life of the system.

[0095] Embodiment 2, see Figure 6 , the structural schematic diagram of the brushless doubly-fed shaft generator system is as follows: The busbar / grid is the common AC bus, and the EMC is the electromagnetic compatibility filter. The complete working cycle of the shaft generator system is divided into two processes, the main generator system transfers to the shaft generator system and the shaft generator system switches back to the main generator system.

[0096] The main generator system transfers to the shaft generator system, and its logical timing is as follows: First, the main switch is closed, the shaft generator system takes power from the AC bus, and the rectifier cabinet and the inverter are turned on. When the amplitudes, phases, and frequencies of the three-phase power of the power winding and the three-phase power of the busbar are the same, the main contactor is attracted. Then, after the system calculates the load power, it outputs the same power to the busbar, and the main switch is disconnected, and it switches to the shaft generator working mode, as Figure 5 shown.

[0097] The load transfer from the main generator to the shaft generator is divided into three stages. The first step is that the inverter controls the power winding to output a voltage synchronized with the main generator voltage, that is, the busbar voltage. The second step is to generate power after direct parallel operation. The third step is the load transfer. The control strategies of the first step of synchronization control and the second step of parallel operation control are the same as the two processes of the previous grid-connected system, and the control strategies are the same. The load transfer control strategy in the third stage is as Figure 5 shown.

[0098] After the load is transferred to the shaft generator mode, the voltage / frequency mode, that is, the V / f mode, is adopted, with the goal of generating a constant three-phase AC voltage (including amplitude and frequency). Therefore, the power loop stops working, and the output values of the two controllers of the active power loop and the reactive power loop are the final PI output values when the call is stopped. Then the outer loop is converted into a voltage loop, and at the same time, the phase of the control winding is changed from the given angular frequency of the power winding after integration and subtraction of the rotor phase.

[0099] The timing sequence of the shaft generator and the main generator is as follows: The modulation inverter synchronizes the three-phase power grid of the power winding busbar, closes the main switch, the shaft generator and the main generator complete parallel operation, then the shaft generator system unloads to zero output and then shuts down the shaft generator system, and finally disconnects the main contactor and the main switch, the shaft generator and the main generator are separated, and the load is powered by the main generator.

[0100] Based on Embodiment 1, the brushless doubly-fed power generation system includes a first actuator and a second actuator, wherein the first actuator is connected between the power grid and the load, and the second actuator is connected between the load and the brushless doubly-fed power generation system;

[0101] The first actuator is configured to determine whether the grid voltage is within the output voltage range of the brushless doubly-fed power generation system when receiving the shaft-driven grid connection command;

[0102] When the grid voltage is within the real-time output voltage range of the brushless doubly-fed power generation system, the second actuator is triggered by a first signal, and the second actuator performs load transfer according to the load transfer strategy; the first signal is an off-grid control signal;

[0103] When the grid voltage is not within the output voltage range of the brushless doubly-fed power generation system, the second actuator is triggered by a second signal, and the second actuator reduces the excitation current of the brushless doubly-fed power generation system according to a preset gradient until the second actuator is triggered by the first signal, and the second actuator performs load transfer according to the load transfer strategy; the second signal is an output voltage overvoltage signal.

[0104] Working principle of the above technical solution: When receiving the shaft-driven grid connection command, the amplitude and phase of the grid voltage and the power winding voltage are obtained, and the synchronous control strategy is used to determine the voltage set value of the control winding and the phase of the rotation transformation. According to the voltage set value and the phase of the rotation transformation of the control winding, after controlling the power winding to output a voltage synchronous with the grid voltage, the corresponding execution unit is controlled to perform the parallel operation. During this process, the parallel operation control strategy can be used to ensure the smoothness and reliability of the parallel operation. According to the total active power of the load and using the parallel operation control strategy, the brushless doubly-fed power generation system is controlled to output the same power to the grid and switch to the off-grid control of independent operation. During this process, the shaft generator of the brushless doubly-fed power generation system will synchronously disconnect from the grid to avoid affecting the grid. Using the load transfer strategy, the load transfer is performed. After transferring the load to the brushless doubly-fed power generation system, the grid connection to off-grid conversion is completed. During this process, the load transfer can be achieved in a dynamically balanced manner to ensure the smoothness and rapidity of the load transfer. If it is detected that the grid voltage is not within the output voltage range of the brushless doubly-fed power generation system, a second signal, that is, the output voltage overvoltage signal, is sent. At this time, the second actuator will reduce the excitation current of the brushless doubly-fed power generation system according to the preset gradient until the second actuator is triggered by the first signal. Then, the second actuator performs the load transfer according to the load transfer strategy. The purpose of this is to prevent damage or affect the safety of grid connection caused by too high output voltage. When the second actuator is triggered by the first signal and after the load transfer is completed, the brushless doubly-fed power generation system will switch from the off-grid state back to the grid-connected state. At this time, the grid connection control can continue according to the previous steps.

[0105] The beneficial effects of the above technical solution are as follows: By precisely controlling the matching of the output voltage of the brushless doubly-fed power generation system and the grid voltage in the above manner, the stability and reliability of the system can be improved. The load can be intelligently transferred according to the grid state and the output of the power generation system, which can improve the energy utilization efficiency and the power supply quality of the load. When the grid voltage is not within the appropriate range, the overvoltage is prevented by reducing the excitation current to protect the safety of the power generation system and the load.

[0106] On the basis of Embodiment 1, the control of the brushless doubly-fed power generation system to output the same power to the grid and switch to the off-grid control of independent operation further includes:

[0107] By using the thyristor preset between the brushless doubly-fed power generation system and the grid and based on the voltage set value and the phase of the rotation transformation of the control winding, the optimal triggering angle of the thyristor is determined;

[0108] When the phase and voltage set value of the voltage output from the brushless doubly-fed power generation system to the grid reach the optimal triggering angle, the thyristor conducts, and the brushless doubly-fed power generation system outputs the same power to the grid.

[0109] The principle of the above technical solution is as follows:

[0110] When the present invention receives the shaft-driven grid connection command, it acquires the grid voltage, the amplitudes and phases of the power winding voltages, and uses a synchronous control strategy to determine the voltage set value of the control winding and the phase of the rotational transformation. According to the voltage set value and the phase of the rotational transformation of the control winding, the optimal triggering angle of the thyristor in the control winding is determined. This angle is achieved through the thyristor preset between the brushless doubly-fed power generation system and the grid. The triggering angle of the thyristor is determined according to the voltage set value and the phase of the rotational transformation of the control winding. When the phase of the voltage output from the brushless doubly-fed power generation system to the grid and the voltage set value reach the optimal triggering angle, the thyristor conducts, and the brushless doubly-fed power generation system outputs the same power to the grid.

[0111] The beneficial effects of the above technical solution are as follows:

[0112] Through the angle control of the thyristor, by precisely controlling the triggering angle, the present invention can ensure that the BLDC-DFIG outputs stable power to the grid. Thus, a soft start function is achieved, preventing abnormalities caused by the output voltage and phase of the brushless doubly-fed power generation system being different from those of the grid due to direct switching.

[0113] On the basis of Embodiment 1, after the shaft generator synchronously disconnects from the grid, a disconnection signal is generated, wherein the disconnection signal is synchronously generated with the load transfer signal after load transfer and uploaded to the user terminal.

[0114] In the above manner, users can understand the status of the power generation system and the load transfer situation, i.e., the grid connection and disconnection status in real time. The synchronously generated signals help to quickly locate and solve the abnormalities occurring during grid connection and disconnection.

[0115] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these changes and modifications.

Claims

1. A method for controlling a brushless double-fed power generation system in conjunction with or off the grid, characterized in that: The following steps are involved: When receiving the shaft-belt grid-connected instruction, the amplitude and phase of the grid voltage and the power winding voltage are obtained, and the voltage setpoint of the control winding and the phase of the rotation transformation are determined by using the synchronous control strategy; According to the voltage given value and the phase of the control winding rotation transformation, the power winding output voltage is controlled to synchronize with the grid voltage, and then the corresponding execution unit is controlled to perform the parallel operation; According to the total active power of the load and using the parallel control strategy, the brushless double-fed power generation system is controlled to output the same power to the power grid and switch to an independently operated off-grid control, wherein during the off-grid control, the shaft generator of the brushless double-fed power generation system is synchronously disconnected from the power grid; the brushless double-fed power generation system includes a first actuator and a second actuator, wherein the first actuator is connected between the power grid and the load, and the second actuator is connected between the load and the brushless double-fed power generation system; the first actuator is used to determine whether the grid voltage is within the output voltage range of the brushless double-fed power generation system when receiving the shaft-belt grid-connected instruction; when the grid voltage is within the real-time output voltage range of the brushless double-fed power generation system, the second actuator is triggered by the first signal, and the second actuator performs load transfer according to the load transfer strategy; the first signal is an off-grid control signal; when the grid voltage is not within the output voltage range of the brushless double-fed power generation system, the second actuator is triggered by the second signal, and the second actuator reduces the excitation current of the brushless double-fed power generation system according to a preset gradient until the second actuator is triggered by the first signal, and the second actuator performs load transfer according to the load transfer strategy; the second signal is an output voltage overvoltage signal; The load transfer strategy is used to execute load transfer, and after the load is transferred to the brushless double-fed power generation system, the grid-connected to off-grid transition is completed.

2. A method for controlling a brushless double-fed power generation system connected to or off-grid as claimed in claim 1, characterized in that: The amplitude and phase of the grid voltage and the power winding voltage are obtained by sampling the grid voltage and the power winding voltage respectively and using a phase-locked loop.

3. A method for controlling the on-grid and off-grid operation of a brushless double-fed power generation system according to claim 2, characterized in that: The synchronization control strategy includes: Inputting the amplitude of the grid voltage and the amplitude of the power winding voltage into the voltage loop to obtain a first current given value, the first current given value being a set value required for one of the components of the current; the voltage loop includes a first comparison element and a first PI controller; Inputting the first current given value and the second current given value into a current loop respectively to obtain the voltage given values ​​of the control winding voltage on the d-axis and the q-axis; the current loop includes a second comparison element and a second PI controller; Compare the grid voltage angle, rotor angle and initial phase compensation to calculate the angle of the control winding; The voltage given values ​​of the d-axis and q-axis and the rotation transformation angle of the control winding are inversely transformed into the three-phase coordinate system to obtain the first voltage command value, and then the output voltage of the inverter is controlled by SVPWM.

4. A method for controlling the on-grid and off-grid operation of a brushless double-fed power generation system according to claim 3, characterized in that: The phase of the control winding rotation transformation is: Among them, θ r is the rotor angle, θ p is the phase of the power winding, p p is the number of pole pairs of the power winding, p c is the number of pole pairs of the control winding, f p is the power winding frequency, f c Control winding excitation frequency, n r is the generator speed, θ r0 That is, it is the control space position difference between the power winding and the control winding, which is obtained by the PI output of the phase loop. The given value and feedback value of the phase loop are the phase of the grid voltage and the phase of the power winding voltage respectively.

5. The method for controlling the on-grid and off-grid operation of a brushless double-fed power generation system according to claim 1, characterized in that: The parallel control strategy includes: When the amplitude difference and phase difference between the power winding voltage and the grid voltage are within the preset range, the automatic grid-connection and grid-off switching is started, and the voltage loop and phase loop are controlled to stop working; Determine the total active power of the load; according to the total active power and using the active power given value calculation formula, calculate the active power given value of the power winding, wherein, when calculating the active power, the reactive power given value is 0; The active power given value and the reactive power given value are used as the input of the active power outer loop and the reactive power outer loop respectively, and the output values ​​of the voltage loop and the phase loop are the last PI output values ​​when the call is stopped; and the double closed-loop vector control strategy of the power outer loop and the current inner loop is used to re-obtain the voltage given values ​​of the d-axis and the q-axis, wherein the output value of the power outer loop current is the output value maintained after the voltage loop works; The obtained voltage given values ​​of the d-axis and q-axis and the rotation transformation angle of the control winding are transformed into the three-phase coordinate system to obtain the second voltage command value, which is then controlled by SVPWM to output the same power to the grid.

6. A method for controlling a brushless double-fed power generation system connected to or off-grid as claimed in claim 5, characterized in that: The active power given value calculation formula is: P=Psum f p / (f p +f c ) Where Psum is the total active power of the load, f p is the power winding frequency, f c To control the winding excitation frequency.

7. A method for controlling a brushless double-fed power generation system connected to or off-grid as claimed in claim 5, characterized in that: The parallel control strategy includes: Control the active power outer loop and the reactive power outer loop to stop working; The reactive power outer loop is converted into a voltage loop. The output values ​​of the two controllers, the active power outer loop and the reactive power outer loop, are the last PI output values ​​when the call is stopped. At the same time, the phase of the control winding is obtained again by using the given power winding angular frequency and subtracting the rotor phase after integration. The obtained voltage given values ​​of the d-axis and q-axis and the phase of the control winding are transformed into the three-phase coordinate system to obtain the third voltage command value, which is then controlled by SVPWM to control the output voltage of the inverter to complete the load transfer.

8. The method for controlling the on-grid and off-grid operation of a brushless double-fed power generation system according to claim 1, characterized in that: The control of the brushless double-fed power generation system to output the same power to the power grid and switch to independent off-grid control also includes: By pre-setting the thyristor between the brushless double-fed power generation system and the power grid, and based on the voltage set value and the phase of the control winding rotation transformation, the optimal trigger angle of the thyristor is determined; When the phase of the voltage output by the brushless double-fed power generation system to the power grid and the voltage set value reach the optimal trigger angle, the thyristor is turned on and the brushless double-fed power generation system outputs the same power to the power grid.

9. The method for controlling the on-grid and off-grid operation of a brushless double-fed power generation system according to claim 1, characterized in that: After the shaft generator is synchronously disconnected from the power grid, a disconnection signal is generated, wherein the disconnection signal and the load transfer signal after the load transfer are synchronously generated and uploaded to the user terminal.

Images