Flexible gear shifting method and device based on hybrid power flow controller

Abstract

The invention relates to a flexible gear shifting method and device based on a hybrid power flow controller, and belongs to the technical field of power electronics. The method comprises the following steps: when a phase-shifting transformer needs gear shifting, controlling a cascaded H-bridge converter to work in a d-axis constant voltage control mode, and setting a d-axis voltage given value of the cascaded H-bridge converter; smoothly adjusting the d-axis voltage of the cascaded H-bridge converter to a d-axis voltage given value, and recording an output power value of the hybrid power flow controller when the d-axis voltage of the cascaded H-bridge converter reaches the d-axis voltage given value; the cascaded H-bridge converter is controlled to work in a constant power control mode, the cascaded H-bridge converter controls the output power value of the hybrid power flow controller to be unchanged, and gear shifting is carried out on the phase-shifting transformer at the same time; after gear shifting is completed, the power given value of the cascaded H-bridge converter is set according to the actual regulation and control requirement of a power grid. According to the invention, voltage and power jump in the gear shifting process of the phase-shifting transformer can be stabilized, the risk of harmonic generation of the hybrid power flow controller is reduced, and the electric energy quality is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and in particular relates to a flexible gear adjustment method and device based on a hybrid power flow controller. Background Art

[0002] With the rapid development of new energy, the proportion of new energy access to the power grid is increasing. However, due to the uneven distribution of power grid currents and the limitation of line thermal stability limits, the power grid has experienced transmission bottlenecks and idle power transmission capacity. Therefore, the use of safe, reliable and economical power flow controller equipment can improve the current power grid's power flow control capabilities. Improving the power grid's carrying capacity for new energy is an important direction for upgrading traditional AC power grids to flexible power grids.

[0003] The hybrid power flow controller is a topology that combines a passive phase-shifting transformer with an active cascaded H-bridge converter. Figure 1 As shown, the advantages of large adjustment capacity of the phase-shifting transformer and fast adjustment speed and high precision of the cascaded H-bridge converter are utilized to realize flexible and continuous control of the line flow over a large range. When the hybrid power flow controller topology is adjusted, voltage jumps may occur, resulting in poor power quality. Therefore, some existing technologies use the fast adjustment characteristics of the cascaded H-bridge converter to make the power change smoothly. However, this method requires the calculation of the corresponding power under the new gear in advance. The impedance characteristics of the power grid are also different when the power flow is different. Therefore, it is difficult to calculate the corresponding power under the new gear in real time. The corresponding power under the new gear may cause the power value controlled by the cascaded H-bridge converter to exceed the limit value. There may still be voltage jumps during the gear shifting process, affecting the power quality of the power grid. Summary of the invention

[0004] The purpose of the present invention is to provide a flexible gear shifting method and device based on a hybrid power flow controller to solve the problem that the existing gear shifting method has voltage jumps during the gear shifting process, which affects the power quality of the power grid.

[0005] The flexible gear adjustment method based on the hybrid power flow controller provided by the present invention to solve the above technical problems comprises the following steps: 1) When the phase-shifting transformer in the hybrid power flow controller needs to be adjusted, the working mode of the cascaded H-bridge converter is switched to the d-axis constant voltage control mode. d The shaft voltage setpoint is set according to the difference between the peak values ​​of the phase voltages of two adjacent gears of the phase-shifting transformer; 2) Cascade H-bridge converter d The shaft voltage is smoothly adjusted to d The axis voltage is set to the given value, and the axis voltage of the cascaded H-bridge converter is recorded. d Output power value of hybrid power flow controller when shaft voltage is given; 3) Switch the working mode of the cascaded H-bridge converter to the constant power control mode, use the output power value of the hybrid power flow controller as the power set value to perform constant power control, and adjust the gear of the phase-shifting transformer at the same time; 4) After the gear adjustment is completed, the power setpoint of the cascaded H-bridge converter is set according to the actual control requirements of the power grid.

[0006] Furthermore, the cascaded H-bridge converter d The formula for setting the shaft voltage given value is: in, u dref For cascaded H-bridge converters d Shaft voltage setpoint, Δ U gp is the difference between the peak values ​​of the phase voltages of two adjacent gears of the phase-shifting transformer, U dc is the rated DC voltage of the cascaded H-bridge converter submodule, and N is the number of cascaded H-bridge converter modules.

[0007] Furthermore, a smooth function relationship is used to smoothly adjust the d-axis voltage of the cascaded H-bridge converter to d Shaft voltage setpoint.

[0008] Furthermore, the smooth function relationship is a slope smooth function, an exponential smooth function or a triangular smooth function.

[0009] The beneficial effects of the method of the present invention are as follows: the prior art calculates the corresponding power under the new gear position when adjusting the gear position, and adjusts the phase shifter when the power of the hybrid power flow controller remains unchanged. This method requires the d-axis voltage amplitude of the cascaded H-bridge converter to increase or decrease by a voltage value of a gear difference, which may cause the d-axis voltage value of the cascaded H-bridge converter to exceed the limit value, thereby causing power jumps. The present invention controls the switching of the working mode of the cascaded H-bridge converter, first adjusts the d-axis voltage smoothly to the target gear voltage under the d-axis constant voltage control mode, and then switches to the constant power control mode to adjust the phase-shifting transformer when the output power value of the hybrid power flow controller remains unchanged. The flexible gear adjustment method of the present invention does not need to calculate the corresponding power under the new gear position in advance, and the power changes smoothly during the gear adjustment process, which can smooth the voltage and power jumps of the phase-shifting transformer during the gear adjustment process, reduce the risk of harmonics generated by the hybrid power flow controller, and improve the power quality.

[0010] The flexible gear adjustment device based on a hybrid power flow controller provided by the present invention to solve the above-mentioned technical problems includes a processor, a memory and a computer program stored in the memory, and the processor is used to execute the computer program to implement the steps of the flexible gear adjustment method based on a hybrid power flow controller described above.

[0011] The beneficial effects of the device of the present invention are: the flexible gear adjustment device of the present invention does not need to calculate the corresponding power under the new gear in advance, and the power changes smoothly during the gear adjustment process, which can smooth the voltage and power jumps in the gear adjustment process of the phase-shifting transformer, reduce the risk of harmonics generated by the hybrid power flow controller, and improve the power quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is the block diagram of the hybrid power flow controller; Figure 2 is the control diagram of the hybrid power flow controller; Figure 3 It is a flow chart of a flexible gear adjustment method based on a hybrid power flow controller according to an embodiment of the present invention. DETAILED DESCRIPTION

[0013] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.

[0014] The basic idea of ​​the present invention is that there is no need to calculate the corresponding power under the new gear in advance, and the power changes smoothly during the gear adjustment process. The voltage and power jumps in the gear adjustment process of the phase-shifting transformer are smoothed by cascading H-bridge converters, thereby reducing the risk of harmonics generated by the hybrid power flow controller and improving the power quality.

[0015] A flexible gear adjustment method based on hybrid power flow controller Based on the above basic ideas, Figure 3 As shown, the flexible gear shifting method based on the hybrid power flow controller of the present invention comprises the following steps: 1) When the phase-shifting transformer in the hybrid power flow controller needs to be adjusted, the working mode of the cascaded H-bridge converter is switched to the d-axis constant voltage control mode. d The shaft voltage setpoint is set according to the difference between the peak values ​​of the phase voltages of two adjacent gears of the phase-shifting transformer.

[0016] After the hybrid power flow controller is connected to the grid, the phase-shifting transformer operates in the appropriate gear, the phase-locking angle of the cascaded H-bridge converter is consistent with the secondary phase angle of the transformer parallel to the phase-shifting transformer, and the cascaded H-bridge converter operates at d Axis rated DC voltage and d Axis fixed power control mode, such as Figure 2 The output of the dq control of the cascaded H-bridge converter valve is added to the phase-to-phase and intra-phase voltage equalization control of the cascaded H-bridge converter valve after dq / abc conversion, thereby generating a modulation wave, which is then compared with the unipolar carrier phase-shift PWM to obtain the on / off signals of the four IGBTs in each submodule.

[0017] When the pole control command is received and the phase-shifting transformer needs to shift up or down, the d-axis constant power mode of the cascaded H-bridge converter is switched to dThe DC voltage control mode is set and the cascaded H-bridge converter is set d When the phase-shifting transformer needs to shift up, the cascaded H-bridge converter valve needs to generate a voltage value that is consistent with the secondary side of the parallel transformer of the phase-shifting transformer and equal to the gear difference. u dref When the phase-shifting transformer needs to downshift, the cascaded H-bridge converter valve needs to generate a voltage value that is opposite to the secondary side of the transformer parallel to the phase-shifting transformer and equal to the gear difference. u dref .

[0018] As a preferred implementation, the cascaded H-bridge converter d Shaft voltage setpoint u dref The setting is based on the difference between the peak values ​​of the phase voltages of two adjacent gears of the phase-shifting transformer. The specific setting formula is: in, u dref For cascaded H-bridge converters d Shaft voltage setpoint, Δ U gp is the difference between the peak values ​​of the phase voltages of two adjacent gears of the phase-shifting transformer, U dc is the rated DC voltage of the cascaded H-bridge converter submodule, and N is the number of cascaded H-bridge converter modules.

[0019] 2) Smoothly adjust the d-axis voltage of the cascaded H-bridge converter to d The axis voltage is set to the given value, and the axis voltage of the cascaded H-bridge converter is recorded. d The output power value of the hybrid power flow controller when the shaft voltage is given.

[0020] When the operation mode of the cascaded H-bridge converter is switched to the d-axis constant voltage control mode, the d-axis voltage at the current moment needs to be smoothly adjusted to d As a preferred implementation, the d-axis voltage of the cascaded H-bridge converter is smoothly adjusted to d The shaft voltage given value, the smoothing function relationship usually selects a ramp smoothing function, an exponential smoothing function or a triangular smoothing function.

[0021] 3) Switch the working mode of the cascaded H-bridge converter to the constant power control mode, use the output power value of the hybrid power flow controller as the power set value to perform constant power control, and adjust the gear of the phase-shifting transformer at the same time.

[0022] When the d-axis voltage of the cascaded H-bridge converter reaches dWhen the shaft voltage is set to a given value, the cascaded H-bridge converter switches the d-axis constant voltage control mode to the constant power control mode, the cascaded H-bridge converter controls the output power value of the hybrid power flow controller to remain unchanged, and the phase-shifting transformer is adjusted at the same time.

[0023] 4) After the gear adjustment is completed, the power setpoint of the cascaded H-bridge converter is set according to the actual control requirements of the power grid.

[0024] An embodiment of a flexible gear adjustment device based on a hybrid power flow controller The device of the present invention includes a processor, a memory, and a computer program stored in the memory. The processor is used to execute the computer program to implement a flexible gear adjustment method based on a hybrid power flow controller. The method refers to an embodiment of a flexible gear adjustment method based on a hybrid power flow controller and is not described in detail here.

Claims

1. A flexible gear adjustment method based on a hybrid power flow controller, characterized in that: The method comprises the following steps: 1) When the phase-shifting transformer in the hybrid power flow controller needs to be adjusted, the working mode of the cascaded H-bridge converter is switched to the d-axis constant voltage control mode. d The shaft voltage setpoint is set according to the difference between the peak values ​​of the phase voltages of two adjacent gears of the phase-shifting transformer; 2) Cascade H-bridge converter d The shaft voltage is smoothly adjusted to d The axis voltage is set to the given value, and the axis voltage of the cascaded H-bridge converter is recorded. d Output power value of hybrid power flow controller when shaft voltage is given; 3) Switch the working mode of the cascaded H-bridge converter to the constant power control mode, use the output power value of the hybrid power flow controller as the power set value to perform constant power control, and adjust the gear of the phase-shifting transformer at the same time; 4) After the gear adjustment is completed, the power setpoint of the cascaded H-bridge converter is set according to the actual control requirements of the power grid.

2. The flexible gear shifting method based on hybrid power flow controller according to claim 1 is characterized in that: For cascaded H-bridge converters d The formula for setting the shaft voltage given value is:

3. Among them, u dref For cascaded H-bridge converters d Shaft voltage setpoint, Δ U gp is the difference between the peak values ​​of the phase voltages of two adjacent gears of the phase-shifting transformer, U dc is the rated DC voltage of the cascaded H-bridge converter submodule, and N is the number of cascaded H-bridge converter modules.

4. The flexible gear shifting method based on hybrid power flow controller according to claim 1 is characterized in that: The smooth function relationship is used to smoothly adjust the d-axis voltage of the cascaded H-bridge converter to d Shaft voltage setpoint.

5. The flexible gear shifting method based on hybrid power flow controller according to claim 3 is characterized in that: The smoothing function relational expression is a slope smoothing function, an exponential smoothing function or a triangular smoothing function.

6. A flexible gear adjustment device based on a hybrid power flow controller, the device comprising a processor, a memory and a computer program stored in the memory, characterized in that: The processor is used to execute the computer program to implement the steps of the flexible gear adjustment method based on a hybrid power flow controller as described in any one of claims 1-4.

Images