CN105226720A - Magneto alternator networking side converter improves droop control method - Google Patents

Abstract

The invention discloses an improved droop control method for a grid-side converter of a permanent magnet synchronous generator set, comprising: when the micro-grid operates in an island mode, the machine-side converter completes motor voltage control, and the grid-side converter calculates the output active power and reactive power and DC bus voltage changes, dynamically shift the droop characteristic curve of the grid-side converter to adjust the output frequency and voltage amplitude of the device, and calculate and obtain the command value of the active current loop of the grid-side converter according to the shifted curve and the command value of the reactive current loop, and obtain the feedback values of the active current loop and the reactive current loop according to the coordinate transformation at the same time, calculate the output voltage reference command, and control the work of the grid-side converter. In the method, by modifying the control method of the grid-side converter, the adjustment of the voltage at the user terminal can be realized, and the output voltage requirement can be met.

Description

Improved droop control method for grid-side converter of permanent magnet synchronous generator set

technical field

The invention belongs to the field of micro-grid systems, and in particular relates to an improved droop control method for a grid-side converter of a permanent magnet synchronous generator set in a micro-grid island operation state.

Background technique

Microgrid is an autonomous system capable of self-control, protection and management. It uses modern power electronics technology to combine wind power, photovoltaics, fuel cells and energy storage devices, and is directly connected to the user side. It can be connected to the external power grid and grid operation, and can also be disconnected from the external grid for island operation. When the microgrid is disconnected from the external grid and operates in island mode, the microgrid system is required to maintain the stability of the output voltage and frequency. When the microgrid is running in island mode, when the power supply load in the microgrid increases, the loss of the line increases and the voltage at the user end drops, resulting in a decrease in the quality of the power supply voltage. In order to ensure the quality of the power supply voltage of the microgrid, certain measures need to be taken to solve this problem. question.

According to the traditional generator control idea, it is usually chosen to add a dynamic reactive power compensation device in the system, and adjust the reactive current of the microgrid system through the dynamic reactive power compensation device, so as to increase the voltage amplitude of the grid and suppress the fluctuation of the grid voltage to achieve The purpose of improving the quality of the power supply voltage and increasing the stability of the system, but this solution requires the addition of new devices, which will bring additional costs to the microgrid system.

Through the analysis, it can be seen that when the user terminal voltage in the microgrid system decreases, the load distribution of the power generation units in the microgrid can be reasonably adjusted to increase the user terminal voltage. According to the composition and structure of the microgrid system, it can be realized by using the power electronic devices in the microgrid to simulate the frequency and voltage regulation characteristics of traditional generators, and the above requirements can be achieved by using the droop control strategy.

Due to the uncertain characteristics of wind energy, the power generated by wind turbines is determined by wind energy. When the microgrid is operating in an isolated island, the power generated by the side converter may not be equal to the output power of the grid side converter. Therefore, energy storage in the microgrid is required. In order to complete the coordinated control with the energy storage unit, on the basis of droop control, an improved control strategy of translational droop characteristic curve is adopted to adjust the droop control output power of the wind power converter, which improves the micro grid stability.

Contents of the invention

The purpose of the present invention is to solve the problems of voltage drop and voltage fluctuation in the above-mentioned microgrid, and propose an improved droop control method on the grid side of the permanent magnet synchronous generator set. According to the power imbalance change, the output frequency value is dynamically shifted The droop characteristic curve of the grid-side converter adjusts the output power of the grid-side converter, compensates the power difference, and ensures the power balance of the system. The method can realize system power balance coordination and user end power supply voltage quality assurance when the microgrid is running in an island mode.

In order to achieve the above object, the present invention adopts the following technical solutions:

A grid-side droop control method for a permanent magnet synchronous generator set, comprising:

When the microgrid operates in island mode, the grid-side converter of the permanent magnet synchronous generator set adopts the droop control mode, and at the same time, the machine-side converter completes the control of the DC bus voltage value and the motor stator voltage, and the grid-side converter obtains the DC bus voltage value through sampling , AC grid voltage value and grid current value; adjust the droop control strategy according to the variation range of the DC bus voltage, output voltage reference value command and output frequency command through droop control, and obtain the output voltage reference in the dq coordinate system according to the obtained voltage reference value command value, according to the output voltage reference value and the actual voltage in the dq coordinate system, calculate the command value of the active current current loop and the command value of the reactive current loop;

The collected AC grid current value is obtained according to the coordinate transformation to obtain the feedback value of the active current loop and the reactive current loop, and the output voltage command is calculated according to the command value and feedback value of the active current loop and the reactive current loop respectively, and after coordinate transformation Finally, the output voltage is obtained to control the work of the grid-side converter.

Obtain the active power P and reactive power Q output by the permanent magnet synchronous generator set according to the voltage value of the AC grid and the current value of the AC grid; process the active power P and the reactive power Q through low-pass filtering to obtain the average value of the power;

The frequency adjustment value is obtained according to the DC bus voltage fluctuation value, and the output voltage reference value command and the output frequency command are calculated according to the frequency adjustment value and the droop control principle.

The method for obtaining the active power P and reactive power Q output by the permanent magnet synchronous generator set is:

The sampled AC grid voltage and grid current values are subjected to Clarke transformation and park transformation to obtain the voltage and current values in the dq coordinate system, and the active power and reactive power values are calculated according to the obtained voltage and current values.

The specific method to obtain the frequency adjustment value according to the DC bus voltage fluctuation value is as follows:

Assume that A is the allowable fluctuation value of the DC bus voltage, and B is the limit setting value of the DC bus voltage;

When |u _dcref -u _dc |≤A, the system power is balanced and the frequency adjustment value is 0;

When |u _dcref -u _dc |>A, use P controller, the proportional link cuts into the control, shifts the droop characteristic curve in a small range, adjusts the output power, maintains the power balance, and the frequency adjustment value is the output value of the P controller;

When |u _dcref -u _dc |>B, the PI controller is used, and the proportional integral link plays a role at the same time. At this time, the frequency adjustment value is the output value of the PI regulator. At this time, the droop characteristic curve is greatly shifted according to the frequency adjustment value, and the power is adjusted. Balance, causing the DC voltage to return to the reference value;

In the formula, u _dcref is the DC reference value of the DC bus voltage, and u _dc is the actual value of the DC bus voltage;

When the DC voltage gradually approaches the reference value and the deviation is less than a, a is the set constant value; the input of the proportional integral link becomes 0, the output remains unchanged, the droop characteristic curve shifts to a new position, and the cycle works.

The output voltage reference value command and the output frequency command are respectively:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}^{<span\; class="notranslate">\; \&Center\; Dot;</span>}\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}}\\ {\mathrm{<span\; class="notranslate">\; u</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; Q</span>}}}^{<span\; class="notranslate">\; \&Center\; Dot;</span>}\mathrm{<span\; class="notranslate">\; Q</span>}\end{array}\right.$

Among them, ω ^* is the output frequency command value, ω ₀ is the no-load angular frequency, k _p is the active power droop coefficient, P is the output active power of the converter, ω _udc is the frequency adjustment value calculated and output by the DC voltage module, U ^* is the output voltage command value, U ₀ is the no-load operating voltage, k _Q is the reactive power droop coefficient, and Q is the output reactive power of the converter.

According to the obtained voltage reference value command, the output voltage reference value in the dq coordinate system is obtained, the voltage reference value of the d-axis is subtracted from the actual d-axis voltage value, and the d-axis current loop command value is obtained after passing through the PI regulator; the q-axis The voltage reference value is subtracted from the actual q-axis voltage value, and the q-axis current loop command value is obtained after passing through the PI regulator.

The output voltage reference value of the d-axis is the calculated output voltage command value U ^* ; the output voltage reference value of the q-axis is zero.

The collected AC grid current value is obtained according to the feedback value of the active current loop and the reactive current loop obtained by coordinate transformation, and the output voltage command is obtained. The specific method is as follows:

Subtract the active current value obtained through transformation from the active current command value, and obtain the d-axis output voltage command after passing through the PI regulator;

Subtract the reactive current value obtained through transformation from the command value of reactive current, and obtain the q-axis output voltage command after passing through the PI regulator.

The obtained output voltage command is calculated, and after ipark transformation, the obtained voltage command is sent to the SVPWM calculation module to obtain the output voltage for controlling the operation of the grid-side converter.

The beneficial effects of the present invention are:

The micro-grid system of the present invention does not require additional hardware, and is easy to implement and simple and effective. In the island operation state of the microgrid system, by adjusting the grid-side control scheme of the permanent magnet synchronous generator set, the grid-side converter adopts an improved droop control strategy to effectively improve the quality of the power supply voltage in the island operation state of the microgrid system.

When the microgrid operates in island mode, the grid-side converter of the permanent magnet synchronous generator adopts improved droop control. While completing the grid-side control of the permanent magnet synchronous generator, the power of the control system is kept balanced, and the AC of the power supply end can be improved. Voltage, using this method can effectively improve the quality of the user terminal voltage supply in the island state, and improve the quality and stability of the power supply voltage of the microgrid system.

Description of drawings

Fig. 1 is a schematic block diagram of the improved droop control strategy adopted by the grid-side converter of the permanent magnet synchronous generator set of the present invention;

Fig. 2 is a flowchart of a method for adopting an improved droop control strategy for the grid-side converter of a permanent magnet synchronous generator set according to the present invention.

detailed description:

Below in conjunction with accompanying drawing and embodiment the present invention will be further described:

An improved droop control method on the grid side of a permanent magnet synchronous generator set in an island operating state of a microgrid, comprising:

When the microgrid operates in island mode, the grid-side converter of the permanent magnet synchronous generator set adopts an improved droop control scheme. Obtain the command value of the active current loop and the command value of the reactive current loop of the grid-side converter; obtain the reference command of the output voltage according to the feedback values of the active current loop and the reactive current loop obtained through coordinate transformation, and finally obtain the output voltage control network work of the side converter.

The improved translational droop characteristic curve control scheme is as follows: according to the change of power unbalance, dynamically shift the droop characteristic curve of the grid-side converter by adjusting the output frequency value, adjust the output power of the grid-side converter, compensate the power difference, and ensure the power balance of the system .

Figure 1 shows the control principle block diagram of the improved droop control scheme for the grid-side converter of the permanent magnet synchronous generator set:

When it is detected that the microgrid system is running in the island mode, the grid-side converter of the permanent magnet synchronous generator set switches to the droop control mode:

The grid-side converter of the permanent magnet synchronous unit calculates the active power and reactive power of the grid-side converter through the detected output voltage Uabc and output current Iabc, and the calculated power value is passed through a low-pass filter to obtain the average power value; according to The DC bus voltage fluctuation value ΔUdc is calculated to obtain the frequency adjustment value;

The frequency adjustment value ω _udc is obtained by judging the DC bus voltage value:

1) When |u _dcref -u _dc |≤A, the system power is balanced, and the frequency adjustment value is 0;

2) When |u _dcref -u _dc |>A, use the P controller, the proportional link cuts into the control, shifts the droop characteristic curve in a small range, adjusts the output power, and maintains the power balance. The frequency adjustment value is the output value of the P controller;

3) When |u _dcref -u _dc |>B, the PI controller is used, and the proportional integral link plays a role at the same time. At this time, the frequency adjustment value is the output value of the PI regulator. At this time, the droop characteristic curve is greatly shifted according to the frequency adjustment value. Adjust the power balance to restore the DC voltage to the reference value; when the DC voltage gradually approaches the reference value and the deviation is less than a, the input of the proportional integral link becomes 0, the output remains unchanged, the droop characteristic curve shifts to a new position, and the cycle works.

In the formula, A is the allowable fluctuation value of the DC bus voltage, B is the limit setting value of the DC bus voltage, and a is the allowable DC voltage fluctuation value set for the normal operation of the system.

The average power value and frequency adjustment value are calculated by droop control to obtain the reference value and frequency reference value of the output voltage amplitude; specifically:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}^{<span\; class="notranslate">\; \&Center\; Dot;</span>}\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}\mathrm{<span\; class="notranslate">\; d</span>}}\\ {\mathrm{<span\; class="notranslate">\; u</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; Q</span>}}}^{<span\; class="notranslate">\; \&Center\; Dot;</span>}\mathrm{<span\; class="notranslate">\; Q</span>}\end{array}\right.$

Among them, ω _udc is the frequency adjustment value; ω ^* is the output frequency command value, ω ₀ is the no-load angular frequency, k _p is the active power droop coefficient, P is the output active power of the converter, and ω _udc is the calculated output of the DC voltage module The frequency adjustment value of , U ^* is the output voltage command value, U ₀ is the no-load operating voltage, k _Q is the reactive power droop coefficient, and Q is the output reactive power of the converter.

According to the voltage reference value, the output voltage reference value in the dq coordinate system is obtained; specifically:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}^{<span\; class="notranslate">\; *</span>}\\ {\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}\end{array}\right.$

Among them, U ^* is the output voltage command value;

After the detected AC grid voltage value is changed in coordinates, the d-axis and q-axis voltage components Ud and Uq are obtained, and the voltage components Ud and Uq are respectively compared with the obtained voltage reference value in the dq coordinate system to complete the closed-loop operation and output the result current Reference instructions id_ref and iq_ref;

The actually detected three-phase current of the power grid, after the coordinate change, obtains the d-axis and q-axis current components id and iq, and the current components id and iq are respectively connected with the d-axis active current loop id_ref and the q-axis reactive current loop iq_ref to complete the closed loop After the operation, output the result voltage instructions Udo and Uqo;

The voltage commands Udo and Uqo are transformed by ipark to obtain Uα and Uβ, and Uα and Uβ are sent to the SVPWM operation module for calculation, and the output results control the operation of the grid-side converter.

Figure 2 shows the flow chart of the improved droop control scheme for the grid-side converter of the permanent magnet synchronous generator set. The working process of the converter is as follows:

1) System state detection: When the permanent magnet synchronous generator set detects that the microgrid is in the island operation mode, it sets the island operation state flag;

2) Unit control mode setting: After the island operation status is confirmed, the grid-side converter is set to run in droop control mode;

3) The converter samples and obtains the DC bus voltage value, the AC grid voltage value, and the grid current value;

4) Clarke transformation and park transformation are performed on the grid voltage and grid current value to obtain the voltage and current values in the dq coordinate system;

5) Calculate and obtain the active power value and the reactive power value according to the transformed dq axis voltage and current values;

6) Calculation of the DC bus voltage loop: Subtract the sampled DC bus voltage value from the DC bus voltage value, and obtain the frequency adjustment value after being controlled by the corresponding regulator according to the magnitude of the voltage fluctuation value;

7) Obtaining an output voltage reference value and an output frequency reference value according to the droop control;

8) AC d-axis voltage loop calculation: subtract the calculated d-axis voltage value from the d-axis voltage command value; obtain the d-axis current loop command value after passing through the PI regulator;

9) AC q-axis voltage loop calculation: subtract the calculated q-axis voltage value from the q-axis voltage command value; obtain the q-axis current loop command value after passing through the PI regulator;

10) d-axis current loop calculation: subtract the d-axis current value obtained through transformation from the d-axis current command value, and obtain the d-axis output voltage command Ud0 after passing through the PI regulator;

11) Calculation of the q-axis current loop: subtract the q-axis current value obtained through transformation from the q-axis current command value, and obtain the q-axis output voltage command Uq0 after passing through the PI regulator;

12) Calculate the obtained Ud0 and Uq0 through ipark transformation to obtain Uα and Uβ;

13) Send Uα and Uβ to the SVPWM calculation module to complete the control.

When the microgrid operates in the island mode, the grid-side converter of the permanent magnet synchronous generator set adopts an improved droop control scheme, and the energy storage unit in the microgrid system is combined with the grid-side control scheme to ensure the microgrid under different wind speed conditions of the wind turbine. The power balance of the system can effectively improve the quality of the power supply voltage, and there is no need to add other hardware devices to the microgrid system. By adopting an improved droop control strategy, the quality of the microgrid power supply voltage is improved, and the stability and reliability of the microgrid system are improved. This scheme is easy to implement and economical.

Although the specific implementation of the present invention has been described above in conjunction with the accompanying drawings, it does not limit the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, those skilled in the art do not need to pay creative work Various modifications or variations that can be made are still within the protection scope of the present invention.

Claims (9)

1. magneto alternator networking side converter improves a droop control method, it is characterized in that, comprising:

When micro-capacitance sensor runs with island mode, magneto alternator networking side converter adopts droop control mode, machine-side converter completes d-c bus voltage value and motor stator voltage control simultaneously, and grid side converter obtains d-c bus voltage value, ac grid voltage value and power network current value by sampling; According to the excursion adjustment droop control strategy of DC bus-bar voltage, by the reference value instruction of droop control output voltage and output frequency instruction, output voltage reference value under dq coordinate system is obtained according to the voltage reference value instruction obtained, according to the virtual voltage under output voltage reference value and dq coordinate system, calculate command value and the reactive current ring command value of active current electric current loop;

The AC network current value collected is obtained the value of feedback of active current ring and reactive current ring according to coordinate transform, respectively according to command value and the value of feedback of active current electric current loop and reactive current ring, calculate output voltage instruction, finally obtain the work of output voltage control grid side converter through coordinate transform.

2. a kind of magneto alternator networking side converter as claimed in claim 1 improves droop control method, it is characterized in that, grid side converter obtains d-c bus voltage value, ac grid voltage value and power network current value by sampling; Active-power P and the reactive power Q of the output of magneto alternator group is obtained according to ac grid voltage value and AC network current value; By described active-power P and reactive power Q through low-pass filtering treatment, obtain the mean value of power;

Obtain frequency adjusted value according to DC bus-bar voltage undulating value, calculate the instruction of output voltage reference value and output frequency instruction according to frequency adjusted value and droop control principle.

3. a kind of magneto alternator networking side converter as claimed in claim 2 improves droop control method, it is characterized in that, the method for the active-power P that described acquisition magneto alternator group exports and reactive power Q is:

The ac grid voltage value obtained sampling and power network current value, through Clarke conversion and park conversion, obtain the electric current and voltage value under dq coordinate system, calculate active power value and reactive power value according to the electric current and voltage value obtained.

4. a kind of magneto alternator networking side converter as claimed in claim 2 improves droop control method, it is characterized in that, the concrete grammar obtaining frequency adjusted value according to DC bus-bar voltage undulating value is:

Suppose that A is that DC bus-bar voltage allows undulating value, B is DC bus-bar voltage limit setpoint;

When | u _dcref-u _dc| during≤A, system power balances, and frequency adjusted value is 0, does not need the output frequency of change system;

When | u _dcref-u _dc| during > A, adopt P controller, proportional component incision controls, by droop characteristic translation by a small margin, and regulation output power, keep power-balance, frequency adjusted value is P controller output valve;

When | u _dcref-u _dc| during > B, adopt PI controller, proportional integral link plays a role simultaneously, now frequency adjusted value is pi regulator output valve, now according to frequency adjusted value significantly translation droop characteristic, regulating power balances, and impels direct voltage to return to reference value;

U in formula _dcreffor DC bus-bar voltage DC reference value, u _dcfor DC bus-bar voltage actual value;

When direct voltage moves closer to reference value, when deviation is less than a, a is the DC voltage fluctuation value that the system set normally runs permission; The input of proportional integral link becomes 0, and export constant, droop characteristic moves to new position, periodic duty.

5. a kind of magneto alternator networking side converter as claimed in claim 2 improves droop control method, it is characterized in that, described output voltage reference value command value is the product that output voltage command value deducts the sagging coefficient of reactive power and current transformer output reactive power;

Described output frequency command value is the product that idler angular frequency deducts the sagging coefficient of active power and current transformer active power of output, then deducts the frequency adjusted value that direct voltage module calculates output.

6. a kind of magneto alternator networking side converter as claimed in claim 1 improves droop control method, it is characterized in that, output voltage reference value under dq coordinate system is obtained according to the voltage reference value instruction obtained, the voltage reference value of d axle and actual d shaft voltage value are subtracted each other, after pi regulator, obtains d shaft current ring command value; The voltage reference value of q axle and actual q shaft voltage value are subtracted each other, after pi regulator, obtains q shaft current ring command value.

7. a kind of magneto alternator networking side converter as claimed in claim 1 improves droop control method, and it is characterized in that, the output voltage reference value of d axle is output voltage command value U ^*; The output voltage reference value of q axle is zero.

8. a kind of magneto alternator networking side converter as claimed in claim 1 improves droop control method, it is characterized in that, the active current obtained according to coordinate transform and reactive current actual value, and obtain output voltage instruction, concrete grammar is:

The command value of the active current value obtained by conversion and active current electric current loop is subtracted each other, after pi regulator, obtains the instruction of d axle output voltage;

The command value of the reactive current value obtained by conversion and reactive current electric current loop is subtracted each other, after pi regulator, obtains the instruction of q axle output voltage.

9. a kind of magneto alternator networking side converter as claimed in claim 8 improves droop control method, it is characterized in that, the output voltage instruction just obtained calculates, after ipark conversion, the voltage instruction obtained is sent into SVPWM computing module, obtain the output voltage of Controling network side converter work.