阅读说明：本技术 一种基于开环控制的发电机起励方法 (Generator excitation method based on open-loop control ) 是由 王波 余翔 赵先元 赵远 张敬 于 2021-07-19 设计创作，主要内容包括：一种基于开环控制的发电机起励方法,发电机起励过程步骤为：步骤一、发电机起励全过程励磁调节器在恒控制角运行方式；步骤二、以机端电压的目标电压设定值的50%和95%为界,分别采取最小控制角、插值控制角、额定空载角进行起励控制；步骤三、机端电压爬升到95%之后,励磁调节器以积分状态量设置为领偏差输入时的额定空载控制角作为闭环控制。通过在起励过程中采取恒控制角的开环控制方式,按照50%目标给定值和95%目标给定值设定励磁调节器输出控制角的控制策略,起励过程中发电机机端电压升值目标值时接近无超调,且能够显著减小振荡,适合在大型发电机的起励过程中实施。(A generator excitation method based on open loop control comprises the following steps: step one, the excitation regulator operates in a constant control angle mode in the whole process of generator excitation initiation; step two, taking 50% and 95% of a target voltage set value of the terminal voltage as boundaries, and respectively adopting a minimum control angle, an interpolation control angle and a rated no-load angle to carry out excitation control; and step three, after the terminal voltage climbs to 95%, setting the excitation regulator as a rated no-load control angle when the deviation is input by using the integral state quantity as closed-loop control. By adopting an open-loop control mode with a constant control angle in the excitation starting process and setting a control strategy of an output control angle of the excitation regulator according to a 50% target given value and a 95% target given value, the generator terminal voltage rise target value is close to without overshoot in the excitation starting process, the oscillation can be remarkably reduced, and the control strategy is suitable for being implemented in the excitation starting process of a large generator.)

1. A generator excitation method based on open-loop control is characterized in that the generator excitation process comprises the following steps:

step one, the excitation regulator regulates the output of the excitation current in a constant control angle operation mode in the whole excitation starting process of the generator;

step two, when the instantaneous value of the generator terminal voltage is lower than a target given value of 50%, setting the output control angle of the excitation regulator as an allowable minimum control angle; setting the output rated no-load angle of the excitation regulator after the generator terminal voltage rises to 95% of the target set value of the set value; when the generator terminal voltage is between 50% and 95% of the target given value, the excitation regulator outputs a rectification control angle which is subjected to interpolation calculation between the minimum control angle and the rated no-load angle range;

and step three, after the generator terminal voltage climbs to 95% of the target set value in the excitation starting process, neglecting a differential link, setting the PID control output integral state quantity of the excitation regulator to be a rated no-load control angle when zero deviation is input, converting the excitation regulator into closed-loop control based on a constant terminal voltage operation mode, setting the set value of the excitation regulator to be the target set value at the moment, and completing the excitation starting process.

2. The method for starting a generator based on open-loop control according to claim 1, wherein in the second step, when the generator-side voltage is between 50% and 95% of the target set values, a function curve difference method of voltage and angle is used to calculate the control angle corresponding to the output of the field regulator at the current voltage, and the specific interpolation formula is as follows:

wherein: α is the current field regulator control angle, α₀The generator rated no-load angle, the minimum control angle of the excitation regulator, the excitation set value and the current generator terminal voltage measured value are respectively alpha min and alpha min.

3. The method for starting a generator based on open-loop control according to claim 1, wherein in the second step, for a generator with unknown rated no-load control angle, when the generator terminal voltage rises to 95% of the target set value of the set value, the control angle is set to 80 °.

4. The method as claimed in claim 1, wherein in step three, after the generator terminal voltage climbs to 95% of the target set value during the excitation process, the rated no-load angle under the rated no-load condition of the generator is assumed to be α₀For parallel PID, the integral control quantity is set as:

U_I＝cosα₀

for series PID, the intermediate state quantity of an integral link is set:

Technical Field

The invention relates to the field of automatic control of a generator, in particular to a generator excitation method based on open-loop control.

Background

The generator excitation starting process is a process of establishing the voltage of a generator stator after a generator enters an idle state, and the national standard GBT7409.3-2007 requires that the adjusting time in the generator excitation starting process is not more than 10 seconds, the oscillation frequency is not more than 3 times, and the voltage overshoot is not more than 15% of the rated voltage.

The excitation process mostly raises the terminal voltage to the rated voltage, and a small part of the excitation process also raises the terminal voltage to the target value of the system voltage for quick grid connection. Under the excitation regulator test mode, excitation current control mode may be adopted to raise the excitation current to a preset value. The set value of the voltage mode excitation in the excitation regulator test mode may not be the rated generator terminal voltage value but set at any value within the rated voltage range of the generator, and the excitation process in the excitation regulator test mode does not examine performance indexes such as overshoot and oscillation frequency.

The rated working condition refers to the state of the generator set at the rated rotating speed, the rated frequency and the rated voltage when the generator set is not connected to a grid and is provided with a load. The control angle of the excitation system under the rated working condition is generally called a rated no-load angle. The rated no-load angle of most generators is between 74 degrees and 85 degrees.

PID control is a typical control mode of an excitation system and can be generally divided into a parallel PID and a series PID, which are transfer functions of the parallel PID and the series PID, respectively, as shown in fig. 1.

Fig. 1 shows the transfer function of a simplified excitation system PID control, where V is the instantaneous generator terminal voltage and Ref is a given value. K in FIG. 1-a_PIs a magnification factor, K_IIs the integral coefficient, K_DIs a differential coefficient. The implementation method in the program is as follows:

ΔV_k+1＝Ref_k+1-V_k+1

U_P＝K_P·ΔV_k+1

U_I＝U_I+K_I·ΔV_k+1

U_D＝K_D·(ΔV_k+1-ΔV_k)

U＝U_P+U_I+U_D

α＝arccos(U)

wherein Δ V_k+1Is the deviation of the present voltage from a given value, Δ V_kIs the deviation of the voltage of the previous control period from a given value, Ref_k+1Is the current voltage set value, U_PIs a proportional control quantity, U_IIs an integral control quantity, U_DIs a differential control quantity, U is a PID control quantity, and alpha is a rectifier bridge control angle.

T in FIG. 1-b₁₁、T₁₂As an integration element, T₁₃、T₁₄As a differential element, K is a gain, and is implemented by discretization in a control program.

Inputting a signal:

ΔV_k+1＝Ref_k+1-V_k+1

wherein Δ V_k+1Is the current voltage deviation value, V_k+1Is the present voltage measurement, Ref_k+1Is the current voltage set point.

And (3) an integration step:

where Δ t is the control period, Δ V_kIs the voltage deviation value of the previous control period; u. of_k+1Is the intermediate state quantity u of the integral link obtained by the current calculation_kIs the intermediate state quantity of the integral link obtained in the last control period; y is_k+1Is the output value of the integration element.

And (3) differentiation:

where Δ t is the control period, y_kIs an integrating loop of the last control periodSaving the output value; u'_k+1Is the currently calculated differential link intermediate state quantity, u'_kIs the intermediate state quantity of the differential link obtained in the previous control period; y'_k+1Is the derivative element output value.

Output control amount:

U＝K·y'_k+1

wherein U is a control amount calculated by PID control, and K is a PID control gain, y'_k+1Is the derivative element output value.

The control quantity is converted into a rectifier bridge control angle output by the excitation regulator:

α＝arccos(U)

the excitation methods of various excitation equipment manufacturers are different, for example, the generator terminal voltage can be raised to be close to a rated value through multiple steps, but in the excitation process, the rated voltage is required to be reached within a specified time, the oscillation frequency does not exceed 3 times, the voltage overshoot does not exceed 15% of the rated voltage, and a contradiction relationship exists among the standard parameters.

Disclosure of Invention

The invention aims to solve the technical problem of providing a generator excitation starting method based on open-loop control, wherein excitation starting adopts an open-loop set excitation starting strategy to reduce overshoot and oscillation generated by the terminal voltage in the excitation starting process of a generator.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

a generator excitation method based on open loop control comprises the following steps:

step one, the excitation regulator regulates the output of the excitation current in a constant control angle operation mode in the whole excitation starting process of the generator;

step two, when the instantaneous value of the generator terminal voltage is lower than a target given value of 50%, setting the output control angle of the excitation regulator as an allowable minimum control angle; setting the output rated no-load angle of the excitation regulator after the generator terminal voltage rises to 95% of the target set value of the set value; when the generator terminal voltage is between 50% and 95% of the target given value, the excitation regulator outputs a rectification control angle which is subjected to interpolation calculation between the minimum control angle and the rated no-load angle range;

and step three, after the generator terminal voltage climbs to 95% of the target set value in the excitation starting process, neglecting a differential link, setting the PID control output integral state quantity of the excitation regulator to be a rated no-load control angle when zero deviation is input, converting the excitation regulator into closed-loop control based on a constant terminal voltage operation mode, setting the set value of the excitation regulator to be the target set value at the moment, and completing the excitation starting process.

In the second step, when the generator terminal voltage is between 50% and 95% of the target given value, the control angle corresponding to the output of the excitation regulator under the current voltage is calculated by adopting a function curve difference method of the voltage and the angle, and a specific interpolation formula is as follows:

wherein: α is the current field regulator control angle, α₀The generator rated no-load angle, the minimum control angle of the excitation regulator, the excitation set value and the current generator terminal voltage measured value are respectively alpha min and alpha min.

In a preferred embodiment, in the second step, for a generator with an unknown rated no-load control angle, when the generator-side voltage rises to 95% of the target set value of the set value, the control angle is set to 80 °.

In the third step, after the generator terminal voltage climbs to 95% of the target given value in the excitation starting process, the rated no-load angle under the rated no-load condition of the generator is assumed to be alpha₀For parallel PID, the integral control quantity is set as:

U_I＝cosα₀

for series PID, the intermediate state quantity of an integral link is set:

according to the generator excitation method based on open-loop control, the open-loop control mode of a constant control angle is adopted in the excitation starting process, the control strategy of the output control angle of the excitation regulator is set according to the 50% target given value and the 95% target given value, overshoot does not exist when the generator terminal voltage rise target value is close to the target value in the excitation starting process, oscillation can be reduced remarkably, and the method is suitable for being implemented in the excitation starting process of a large generator.

Drawings

The invention is further illustrated by the following examples in conjunction with the accompanying drawings:

FIG. 1 is a graph of the transfer function of the parallel PID and series PID of the generator of the invention;

FIG. 2 is a graph of voltage versus angle during excitation;

FIG. 3 is a waveform of generator terminal voltage V and control angle when the generator is excited according to the excitation control strategy of the present invention;

fig. 4 is a full function waveform diagram of generator firing according to the firing control strategy of the present invention.

Detailed Description

The technical scheme of the invention is explained in detail in the following by combining the drawings and the embodiment.

A generator excitation method based on open loop control comprises the following steps:

step one, the excitation regulator regulates the output of the excitation current in a constant control angle operation mode in the whole excitation starting process of the generator;

step two, when the instantaneous value of the generator terminal voltage is lower than a target given value of 50%, setting the output control angle of the excitation regulator as an allowable minimum control angle; setting the output rated no-load angle of the excitation regulator after the generator terminal voltage rises to 95% of the target set value of the set value; when the generator terminal voltage is between 50% and 95% of the target given value, the excitation regulator outputs a rectification control angle which is subjected to interpolation calculation between the minimum control angle and the rated no-load angle range;

and step three, after the generator terminal voltage climbs to 95% of the target set value in the excitation starting process, neglecting a differential link, setting the PID control output integral state quantity of the excitation regulator to be a rated no-load control angle when zero deviation is input, converting the excitation regulator into closed-loop control based on a constant terminal voltage operation mode, setting the set value of the excitation regulator to be the target set value at the moment, and completing the excitation starting process.

In the second step, when the generator terminal voltage is between 50% and 95% of the target given value, the control angle corresponding to the output of the excitation regulator under the current voltage is calculated by adopting a function curve difference method of the voltage and the angle, and a specific interpolation formula is as follows:

wherein: α is the current field regulator control angle, α₀The generator rated no-load angle, the minimum control angle of the excitation regulator, the excitation set value and the current generator terminal voltage measured value are respectively alpha min and alpha min.

As shown in fig. 2, in the excitation process, when the voltage of the machine terminal is less than the target set value of 50%, the minimum control angle α min of the excitation regulator is adopted, and when the voltage of the machine terminal is at the target set value of 50% -95%, the control angle is a specific slope, and the slope value isWhen the voltage of the machine exceeds 95%, the control angle adopts the rated no-load angle alpha of the generator₀。

In a preferred embodiment, in the second step, for a generator with an unknown rated no-load control angle, when the generator-side voltage rises to 95% of the target set value of the set value, the control angle is set to 80 °.

The method comprises the steps that under the condition of counting rated no-load of a generator, a control angle output by an excitation regulator is 74-85 degrees, for a generator with an unknown rated no-load angle, 80 degrees can be set as the rated no-load angle of the generator, the excitation starting and voltage building of the generator can be successfully completed even if the rated no-load angle of the generator is uncertain and accurate, the excitation starting process of the generator is completed under the condition that the voltage at the machine end is slightly over-regulated by a small rated no-load angle of the generator, and the accurate rated no-load angle can be obtained after the generator is excited to the rated no-load voltage.

In the third step, after the generator terminal voltage climbs to 95% of the target given value in the excitation starting process, the rated no-load angle under the rated no-load condition of the generator is assumed to be alpha₀For parallel PID, the integral control quantity is set as:

U_I＝cosα₀

for series PID, the intermediate state quantity of an integral link is set:

after the excitation regulator is switched into closed-loop control of a constant machine end voltage operation mode, an integral link is matched with the control output of the current excitation regulator, the disturbance generated by the machine end voltage of the generator is very small, and the generator end voltage is close to the generator end voltage without overshoot and oscillation in the excitation starting process.

As shown in fig. 3, the excitation system does not output before the excitation process starts, and the control angle is 120 °; after the excitation starting process is started, the control angle is reduced to 15 degrees because the voltage of the generator terminal of the generator is lower than 0.5 Vn; 6S, when the voltage of the generator terminal of the front generator is lower than 0.5Vn, the voltage is maintained at the angle; in the excitation starting time of 6S-7.5S, the terminal voltage rises from 50% to 95%, the control angle rises according to a set curve, interpolation is carried out between the minimum angle and the no-load angle according to the voltage when the generator voltage is between 0.5Vn and 0.95Vn, and the change trend of the control angle is consistent with the terminal voltage of the generator; after the excitation starting time is 7.5S, the terminal voltage exceeds 95%, the control angle is 80 degrees of the rated no-load angle of the excitation regulator, the terminal voltage V is stabilized at 100 percent, the excitation starting process lasts for 8S in the whole process, and overshoot oscillation does not occur.

The method firstly accurately confirms the output control angle alpha of the excitation regulator when the terminal voltage reaches the rated value under the no-load operation condition of the current generator₀Passing voltage as a function of angleThe curve difference method calculates the corresponding control angle of the excitation regulator output under the current voltage, controls the generator end voltage to stably boost according to the set curve in the zero voltage boosting process, and when the generator end voltage reaches 0.95Vn, the regulator PID controls the output integral state quantity to be set as the rated no-load control angle alpha when zero deviation input is carried out₀The generator end voltage is increased to a rated voltage value, the excitation regulator completes the excitation starting process and transfers to a constant generator end voltage control mode, at the moment, the generator end voltage value V and the regulator control value ref have almost no deviation, and the integral state quantity in the regulator PID control corresponds to the rated no-load control angle alpha when zero deviation is input₀The regulator control angle maintains a nominal no-load control angle alpha₀In operation, the excitation regulator realizes the conversion from the stable transition of open-loop control to closed-loop control, and realizes no overshoot in the excitation starting process of the generator.