WO2012055115A1 - Integrated excitation and turbine controller for synchronous generator and control method thereof - Google Patents
Integrated excitation and turbine controller for synchronous generator and control method thereof Download PDFInfo
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- WO2012055115A1 WO2012055115A1 PCT/CN2010/078244 CN2010078244W WO2012055115A1 WO 2012055115 A1 WO2012055115 A1 WO 2012055115A1 CN 2010078244 W CN2010078244 W CN 2010078244W WO 2012055115 A1 WO2012055115 A1 WO 2012055115A1
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- auxiliary
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- generator
- valve opening
- generator operation
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
- H02P9/04—Control effected upon non-electric prime mover and dependent upon electric output value of the generator
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
- H02P9/10—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load
- H02P9/105—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load for increasing the stability
Definitions
- This invention relates to the field of power system, and more particularly to an integrated excitation and turbine control method for synchronous generator.
- the transient behaviors are described in reference to the power-angle characteristics as shown in Figure 1A and 1 B.
- the generator is working at an equilibrium point, where the mechanical power is equal to the electromagnetic power.
- the electromagnetic power will decrease along with the depressed generator terminal voltage.
- the power mismatch which is the difference of the mechanical power and the electromagnetic power, will lead to rotor acceleration.
- the diagonal area represents generator acceleration area and the grid area represents generator deceleration area.
- the grid area becomes the same size of the diagonal area by taking valve closing control, and the generator stops acceleration and survives the first swing.
- the backward acceleration area is too large leading to rotor deflection towards negative power angle.
- the generator is still stable, it might take long time to damp out such synchronous power swings which are detrimental to system stability.
- the first swing is unstable and the generator starts asynchronous operation. It is obvious that without proper control, the total acceleration area is much bigger than the deceleration area, and the rotor can not return to the synchronous speed. Thus, the out-of-step protection will be activated and trip the generator off-line.
- the governor and exciter are two most important controllers used in the turbine-generator system for fulfilling secure, reliable and stable generator operation. Since generator frequency and voltage regulation are usually considered to be decoupled, these two controllers are always designed separately at present. However, separate excitation and turbine control might limit further improvement of generator's transient stability and dynamic performances. The fixed parameter settings might not be optimal in a wide range of operating conditions. And the independent controller design might not always provide consistent and complementary response to keep synchronization and sufficient damping to oscillations.
- US5547337A disclosed a method and a device for the closed-loop control of a turbine-generator configuration.
- a turbine control element is supplied with a first correcting variable and an exciter control element is supplied with a second correcting variable.
- the correcting variables in each case are formed from at least one reference value.
- the first correcting variable for the turbine control element is composed of at least two partial correcting variables.
- One of the partial correcting variables is derived from the reference value for forming the second correcting variable for the exciter control element, and vice versa.
- six transfer functions are needed to implement this multi-variable controller, which are sensitive to the displacements of operating points and system switchovers.
- a specially designed adaptive strategy needs to be built in the multi-variable controller, which further increases the complexity of the overall solution.
- the present invention provides an integrated excitation and turbine controller for synchronous generator and the control method thereof.
- an integrated excitation and turbine control method for synchronous generator comprises the following steps: categorizing the fault severity according to the accelerating energy caused by the power mismatch, detecting the generator operation mode according to the signs of the power angle derivation and the directions of the electromagnetic power, calculating the auxiliary excitation voltage according to the fault severity and the generator operation mode, calculating the auxiliary governor valve opening according to the fault severity and the generator operation mode; and calculating the intercept valve opening according to the fault severity and the generator operation mode.
- the fault severity can be categorized as large disturbance, moderate disturbance and smail disturbance.
- the large disturbance and moderate disturbance are aiso categorized as severe disturbance.
- the power mismatch is the difference of the mechanical power and the electromagnetic power.
- the operation modes of the generator are categorized as first swing, asynchronous swings and synchronous swings by detecting the signs of power angle derivation and the directions of electromagnetic power.
- the auxiliary excitation voltage is calculated as following: if the fault severity is categorized as large disturbance or moderate disturbance, and if the generator operation modes are categorized as first swing or asynchronous swings, the auxiliary excitation voltage shall be proportional to the electromagnetic power; else if the generator operation modes are categorized as the synchronous swings, the auxiliary excitation voltage shall be proportional to the power mismatch. Otherwise if the fault severity is categorized as small disturbance, regardless the generator operation modes, the auxiliary excitation voltage shall be proportional to the power mismatch.
- the auxiliary excitation voltage shall be proportional to the difference of the electromagnetic power and the mechanical power; the auxiliary excitation voltage further comprises a lead compensation to provide a phase lead I. Else if the generator operation modes are categorized as synchronous swings, the auxiliary excitation voltage shall be proportional to the difference of the electromagnetic power and the mechanical power; the auxiliary excitation voltage further comprises a lead compensation to provide a phase lead II which is smaller than said phase lead I.
- the auxiliary excitation voltage shall be proportional to the difference of the electromagnetic power and the mechanical power; the auxiliary excitation voltage further comprises a lead compensation to provide a phase lead II which is smaller than said phase lead I.
- the auxiliary governor valve opening is calculated as following: the auxiliary governor valve opening is proportional to the power angle derivation; the proportional parameter is negative to suppress the deviation.
- the auxiliary governor valve opening shall be proportional to the power angle derivation; the proportional parameter is negative to suppress the deviation. Else if the generator operation mode is categorized as synchronous swings, the auxiliary governor valve opening is proportional to the power angle derivation; the proportional parameter shall be negative to suppress the deviation; the auxiliary governor valve opening further comprises a lead compensator. Otherwise if the fault severity is categorized as small disturbance, regardless the generator operation modes, the auxiliary governor valve opening shall be proportionai to the power angle derivation; the auxiliary governor valve opening further comprises a lead compensator.
- the intercept valve opening is calculated as following: if the fault severity is categorized as large disturbance or moderate disturbance, and if the generator operation modes are categorized as first swing or asynchronous swings, the intercept valve opening shall be off to close the valve. Otherwise, the intercept valve opening shall be on to open the valve.
- the auxiliary excitation voltage is added to the Automatic Voltage Regulator to realize in-time response of excitation voltage for generator stabilization under disturbances.
- the auxiliary governor valve opening is added to the power/frequency droop regulator.
- the auxiliary excitation voltage and the auxiliary governor valve opening are all set to zero.
- an integrated excitation and turbine controller for synchronous generator.
- the integrated excitation and turbine controller comprises a categorizing module for categorizing the fault severity according to the accelerating energy caused by the power mismatch; an operation mode detecting module for detecting the generator operation mode according to the signs of power angle derivation and the directions electromagnetic power; an auxiliary excitation controller for calculating the auxiliary excitation voltage according to the fault severity and the generator operation mode; an auxiliary governor controller for calculating the auxiliary governor valve opening according to the fault severity and the generator operation mode; and an intercept valve controller for calculating the intercept valve opening according to the fault severity and the generator operation mode.
- the auxiliary excitation controller comprises an excitation signal module, two excitation compensation modules and an excitation logic module.
- the excitation signal module is to calculate the power mismatch of the mechanical power and the electromagnetic power.
- the excitation compensation modules are to provide two different phase lead compensations.
- the excitation logic module is to calculate the auxiliary excitation voltage based on the power mismatch and the phase lead compensations.
- the governor valve controller comprises a governor signal module, a governor compensation module and a governor logic module.
- the governor signal module is to calculate the power angle derivation.
- the governor compensation module is to provide phase lead compensation.
- the governor logic module is to calculate the auxiliary governor valve opening based on the power angle derivation and the phase lead compensation.
- Fig. 1A - 1 B shows the rotor acceleration led by the power mismatch; wherein, Fig. 1A shows the stable first swing followed by the deep synchronous swings; Fig. 1 B shows the asynchronous swings followed by the generator out of step tripping;
- Fig. 2 shows the basic concept of the integrated excitation and turbine controller for a steam-turbine synchronous generator system
- Fig. 3 is a schematic diagram which shows the structure of the integrated excitation and turbine controller
- Fig. 4 is the conceptual flowchart of auxiliary excitation voltage control method
- Fig. 5 is the conceptual flowchart of auxiliary governor valve opening control method.
- Fig. 2 shows the basic concept of the integrated excitation and turbine controller 23 for a steam-turbine synchronous generator 20, which is connected to the equivalent power grid 28 via step-up transformer 26 and transmission lines 27.
- AVR Automatic Voltage Regulator
- the high-level integrated excitation and turbine controller provides auxiliary excitation control signals 22 and turbine control signals 21 based on the measurements 29 and the built-in control strategies.
- the measurements 29 here Include mechanical power P m , electromagnetic power P e , and power angle ⁇ .
- the outputs here include auxiliary excitation voltage AE F * , auxiliary governor valve opening AUG , and intercept valve opening U
- the auxiliary excitation voltage AE F ' will be added to the Automatic Voltage Regulator to realize in-time response of excitation voltage for generator stabilization under disturbances.
- the auxiliary governor valve opening AU G * will be added to the power/frequency droop regulator.
- V * will be an on/off signal to limit large power mismatch of generator but wili not replace the over-speed protection logic.
- Fig. 3 is a schematic diagram which shows the structure of the integrated excitation and turbine controller.
- the integrated excitation and turbine controller 23 for synchronous generator comprises a categorizing module 31 for categorizing the fault severity according to the accelerating energy caused by the power mismatch; an operation mode detecting module 32 for determining the generator operation mode according to the signs of power angle derivation and the directions electromagnetic power; an auxiliary excitation controller 33 for calculating the auxiliary excitation voltage according to the fault severity and the generator operation mode; an auxiliary governor controller 34 for calculating the auxiliary governor valve opening according to the fault severity and the generator operation mode; and an intercept valve controller 35 for calculating the intercept valve opening according to the fault severity and the generator operation mode.
- the power-angle characteristics in Fig. 1A -1 B can be divided into four zones, according to the signs of power angle derivation and the directions electromagnetic power.
- the IETC controller quickly increases the excitation voltage and reduce the turbine valve opening to increase forward deceleration area, so as to ensure the first swing stability. If the first swing is stable, the IETC controller reduces the mismatch between the acceleration area and the deceleration area as much as possible to provide fast and effective damping to the synchronous power swings. For example in Zone-ll (backward swing and generator mode), the IETC controller reduces the excitation voltage and increase the turbine valve opening to reduce the backward acceleration area. In Zone-Ill (backward swing and motor mode), the IETC controller increases the excitation voltage and the turbine valve opening to increase the backward deceleration area.
- the generator will enter into Zone-IV as shown in Figure 1 B (forward swing and motor mode).
- the IETC controller reduces both the excitation voltage and the turbine valve opening to limit the forward acceleration area and help the generator to be re-synchronized after certain number of asynchronous swings.
- P e generator electromagnetic power
- ⁇ power angle
- E f excitation voltage reference
- U v turbine valve opening reference.
- the fault severity categorization is to ensure that the outputs of the integrated excitation and turbine controller are always sufficient under various system disturbances. Insufficient control may not effectively stabilize the generator under large disturbances while exaggerated control may adversely affect system stability under small disturbances. It is practical to use the integration of the difference between mechanical power and electromagnetic power as the criterion of fault severity categorization.
- the operation mode detecting module is to ensure that the outputs of the integrated excitation and turbine controller are sufficient to enhance generator transient stability and effective to damp out generator oscillations under disturbances.
- three typical generator operation modes after disturbances can be determined according to Table 3, including first S swing mode, asynchronous swing mode and synchronous swing mode.
- the calculation method for the auxiliary excitation voltage control is shown in Table 4. If the power angle keeps increasing, the auxiliary excitation voltage will increase proportionally to the electromagnetic power to maximally reduce the acceleration area. If the power angle starts decreasing, the auxiliary excitation voltage will decrease proportionally to the difference of the mechanical power and the electromagnetic power, which can provide effective damping to the power swings.
- the calculation method uses different functions and parameter settings according to the severity of disturbances and the operation mode of generator.
- algorithm design focuses on transient stability issue, considering the possibilities of both rotor deflections towards the negative power angle and the unstable first swing plus consequent asynchronous swings.
- the calculation method mainly focuses on dynamic performance issue, and only considers the generator operations in the first quadrant of power-angle characteristic. By setting the proportional parameter to zero for example under small disturbances, the output of auxiliary excitation voltage controller under this type of disturbance can be disabled accordingly.
- auxiliary turbine valve control The calculation method for auxiliary turbine valve control is shown in Table 5, which is in line with the working principle analysis given above.
- the output is proportional to the power angle derivation to reduce the power mismatch and damp out the oscillations.
- the proportional parameter is adjusted according to the severity of disturbances. By setting the proportional parameter to zero for example under small disturbances, the output of auxiliary governor controller will be disabled under this type of disturbance.
- Intercept valve control is only enabled under large disturbances.
- the intercept valve will be closed if the power angle keeps increasing so as to limit the mechanical power, and will be opened again if the rotor stops accelerating and starts to return to another equilibrium point. Under normal operation, the intercept valve control is kept open so as to avoid frequent change of the turbine valve which will lead to accelerated wear and tear.
- an improved calculation method for auxiliary excitation voltage is provided as shown in Table 6.
- the input signal is simplified to one signal P e -P m , instead of two signals P ei and P m -P e as shown in Table 4.
- the parameter setting is also simplified.
- Different compensators are designed to meet the requirements on stability enhancement and oscillation damping.
- Fig. 4 is the conceptual flowchart of the improved auxiliary excitation voltage control method.
- the auxiliary excitation controller 33 comprises an excitation signal module 331 , two excitation compensation modules 332 and an excitation logic module 333.
- the excitation signal module 331 is to calculate the power mismatch of the mechanical power and the electromagnetic power.
- the excitation compensation modules 332 are to provide two different phase lead compensations.
- the excitation logic module 333 is to calculate the auxiliary excitation voltage based on the power mismatch and the phase lead compensations.
- an improved calculation method for auxiliary governor valve is provided as shown in Table 7.
- the input signal is the same, d6/dt is adopted.
- a lead compensator is adopted to compensate the phase lag of turbine system so as to achieve better damping characteristics.
- Fig. 5 is the conceptual flowchart of the auxiliary governor valve control method.
- the auxiliary governor valve controller 34 comprises a governor signal module 341 , a governor compensation module 342 and a governor logic module 343.
- the governor signal module 341 is to calculate the power angle derivation.
- the governor compensation module 342 is to provide phase lead compensation.
- the governor logic module 343 is to calculate the auxiliary governor valve opening based on power angle derivation and the phase lead compensation.
- the proposed integrated excitation and turbine control method is beneficial to the generator transient stability enhancement and dynamic performance improvement.
- the possible economic advantages for power plants mainly include two aspects as follows:
- Integrated excitation and turbine control is a cost-effective way and no additional primary equipment is required. Compared with prior methods, the method also has the advantages that:
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Abstract
An integrated excitation and turbine controller (23) for a synchronous generator (20) and a control method thereof are provided. The method comprises following steps: categorizing the fault severity according to the accelerating energy caused by the power mismatch; detecting the generator operation mode according to the signs of power angle derivation and the directions of electromagnetic power; calculating the auxiliary excitation voltage according to the fault severity and the generator operation mode; calculating the auxiliary governor valve opening according to the fault severity and the generator operation mode; and calculating the intercept valve opening according to the fault severity and the generator operation mode. The disturbance severity categorization and the generator operation mode are both considered in the method based on the local measurements (29) so as to determine the best combination of the auxiliary excitation and the turbine control under various system disturbances and operation conditions. The outputs of the integrated excitation and turbine controller (23) will be added into the existing generator controllers for generator transient stability enhancement and dynamic performance improvement. When the disturbances disappear, the outputs of the integrated excitation and turbine controller (23) will be phased out automatically so as to minimize the impacts on the generator steady-state voltage and the frequency regulations.
Description
INTEGRATED EXCITATION AND TURBINE CONTROLLER FOR SYNCHRONOUS GENERATOR AND CONTROL
METHOD THEREOF
FIELD OF THE INVENTION
This invention relates to the field of power system, and more particularly to an integrated excitation and turbine control method for synchronous generator.
BACKGROUND OF THE INVENTION
The complicated grid structure and power flow raises higher requirements for stable operation of the generators. First, the long-distance bulk energy transmission becomes more and more popular today, which means the generators are usually located remote to the load center, and the transmission lines are often operated under heavy load conditions. Second, large-scale renewable energy generation gets rapid development. However the fluctuation and intermittent characteristics are usually detrimental to the system stability. Furthermore, Flexible AC Transmission Systems {FACTS) devices are widely used in power grid. FACTS is usually designed to improve the grid performance, but recent studies show that FACTS sometime might provide negative damping to oscillations. This may deteriorate the system stability.
There are typically two types of undesired generator transient behaviors under system disturbances. The transient behaviors are described in reference to the power-angle characteristics as shown in Figure 1A and 1 B. During the normal operation, the generator is working at an equilibrium point, where the mechanical power is equal to the electromagnetic power. When a short-circuit fault occurs on the power grid and close to the power plant, the electromagnetic power will decrease along with the depressed generator terminal voltage. The power mismatch, which is the difference of the mechanical power and the electromagnetic power, will lead to rotor acceleration. In Figure 1A and 1 B, the diagonal area represents generator acceleration area and the grid area represents generator deceleration area.
In the first case, as shown in Figure 1A, the grid area becomes the same size of the diagonal area by taking valve closing control, and the generator stops acceleration and survives the first swing. However, the backward acceleration area is too large leading to rotor deflection towards negative power angle. Although the generator is still stable, it might take long time to damp out such synchronous power swings which are detrimental to system stability.
In the second case, as shown in Figure 1 B, the first swing is unstable and the generator starts asynchronous operation. It is obvious that without proper control, the total acceleration area is much bigger than the deceleration area, and the rotor can not return to the synchronous speed. Thus, the out-of-step protection will be activated and trip the generator off-line.
The governor and exciter are two most important controllers used in the turbine-generator system for fulfilling secure, reliable and stable generator operation. Since generator frequency and voltage regulation are usually considered to be decoupled, these two controllers are always designed separately at present. However, separate excitation and turbine control might limit further improvement of generator's transient stability and dynamic performances. The fixed parameter settings might not be optimal in a wide range of operating conditions. And the independent controller design might not always provide consistent and complementary response to keep synchronization and sufficient damping to oscillations.
To improve the transient stability of the generator and avoid unplanned large-scale outage, several methods have been proposed such as the special protection systems, the fast valving technology, braking resistor, etc. However, these solutions have their own disadvantages. For example, special protection systems require selective tripping of critical generators or loads. Fast valving technology could result in second-swing instability problem. Braking resistor solution needs additional component that requires additional space and is subject to strong thermal strains.
US5547337A disclosed a method and a device for the closed-loop control of a turbine-generator configuration. A turbine control element is supplied with a first correcting variable and an exciter control element is supplied with a second correcting variable. The correcting variables in each case are formed from at least one reference value. In order to ensure reliable closed-loop control, the first correcting variable for the turbine control element is composed of at least two partial correcting variables. One of the partial correcting variables is derived from the reference value for forming the second correcting variable for the exciter control element, and vice versa. However, six transfer functions are needed to implement this multi-variable controller, which are sensitive to the displacements of operating points and system switchovers. To overcome these problems, a specially designed adaptive strategy needs to be built in the multi-variable controller, which further increases the complexity of the overall solution.
SUMMARY OF THE INVENTION
To overcome above mentioned shortcomings, the present invention provides an integrated excitation and turbine controller for synchronous generator and the control method thereof.
According to one aspect of the invention, an integrated excitation and turbine control method for synchronous generator is provided. The method comprises the following steps: categorizing the fault severity according to the accelerating energy caused by the power mismatch, detecting the generator operation mode according to the signs of the power angle derivation and the directions of the electromagnetic power, calculating the auxiliary excitation voltage according to the fault severity and the generator operation mode, calculating the auxiliary governor valve opening according to the fault severity and the generator operation
mode; and calculating the intercept valve opening according to the fault severity and the generator operation mode.
The fault severity can be categorized as large disturbance, moderate disturbance and smail disturbance. The large disturbance and moderate disturbance are aiso categorized as severe disturbance. The power mismatch is the difference of the mechanical power and the electromagnetic power.
The operation modes of the generator are categorized as first swing, asynchronous swings and synchronous swings by detecting the signs of power angle derivation and the directions of electromagnetic power.
According to one preferred embodiment of the present invention, the auxiliary excitation voltage is calculated as following: if the fault severity is categorized as large disturbance or moderate disturbance, and if the generator operation modes are categorized as first swing or asynchronous swings, the auxiliary excitation voltage shall be proportional to the electromagnetic power; else if the generator operation modes are categorized as the synchronous swings, the auxiliary excitation voltage shall be proportional to the power mismatch. Otherwise if the fault severity is categorized as small disturbance, regardless the generator operation modes, the auxiliary excitation voltage shall be proportional to the power mismatch.
According to another preferred embodiment, if the fault severity is categorized as large disturbance or moderate disturbance, and if the generator operation modes are categorized as first swing or asynchronous swings, the auxiliary excitation voltage shall be proportional to the difference of the electromagnetic power and the mechanical power; the auxiliary excitation voltage further comprises a lead compensation to provide a phase lead I. Else if the generator operation modes are categorized as synchronous swings, the auxiliary excitation voltage shall be proportional to the difference of the electromagnetic power and the mechanical power; the auxiliary excitation voltage further comprises a lead compensation to provide a phase lead II which is smaller than said phase lead I. Otherwise if the fault severity is categorized as small disturbance, regardless the generator operation modes, the auxiliary excitation voltage shall be proportional to the difference of the electromagnetic power and the mechanical power; the auxiliary excitation voltage further comprises a lead compensation to provide a phase lead II which is smaller than said phase lead I.
According to one preferred embodiment, the auxiliary governor valve opening is calculated as following: the auxiliary governor valve opening is proportional to the power angle derivation; the proportional parameter is negative to suppress the deviation.
According to another preferred embodiment, under severe disturbance, if the fault severity is categorized as large disturbance or moderate disturbance, and if the generator operation modes are categorized as first swing or asynchronous swings, the auxiliary governor valve
opening shall be proportional to the power angle derivation; the proportional parameter is negative to suppress the deviation. Else if the generator operation mode is categorized as synchronous swings, the auxiliary governor valve opening is proportional to the power angle derivation; the proportional parameter shall be negative to suppress the deviation; the auxiliary governor valve opening further comprises a lead compensator. Otherwise if the fault severity is categorized as small disturbance, regardless the generator operation modes, the auxiliary governor valve opening shall be proportionai to the power angle derivation; the auxiliary governor valve opening further comprises a lead compensator.
According to the preferred embodiments, the intercept valve opening is calculated as following: if the fault severity is categorized as large disturbance or moderate disturbance, and if the generator operation modes are categorized as first swing or asynchronous swings, the intercept valve opening shall be off to close the valve. Otherwise, the intercept valve opening shall be on to open the valve.
According to the preferred embodiments, the auxiliary excitation voltage is added to the Automatic Voltage Regulator to realize in-time response of excitation voltage for generator stabilization under disturbances. The auxiliary governor valve opening is added to the power/frequency droop regulator.
According to a preferred embodiment, under small disturbance, the auxiliary excitation voltage and the auxiliary governor valve opening are all set to zero.
According to another aspect of the present invention, an integrated excitation and turbine controller for synchronous generator is provided. The integrated excitation and turbine controller comprises a categorizing module for categorizing the fault severity according to the accelerating energy caused by the power mismatch; an operation mode detecting module for detecting the generator operation mode according to the signs of power angle derivation and the directions electromagnetic power; an auxiliary excitation controller for calculating the auxiliary excitation voltage according to the fault severity and the generator operation mode; an auxiliary governor controller for calculating the auxiliary governor valve opening according to the fault severity and the generator operation mode; and an intercept valve controller for calculating the intercept valve opening according to the fault severity and the generator operation mode.
According to one preferred embodiment, the auxiliary excitation controller comprises an excitation signal module, two excitation compensation modules and an excitation logic module. The excitation signal module is to calculate the power mismatch of the mechanical power and the electromagnetic power. The excitation compensation modules are to provide two different phase lead compensations. The excitation logic module is to calculate the auxiliary excitation voltage based on the power mismatch and the phase lead compensations.
According to one preferred embodiment, the governor valve controller comprises a
governor signal module, a governor compensation module and a governor logic module. The governor signal module is to calculate the power angle derivation. The governor compensation module is to provide phase lead compensation. The governor logic module is to calculate the auxiliary governor valve opening based on the power angle derivation and the phase lead compensation.
BRIEF DESCRIPTION OF THE DRAWINGS
The subject matter of the invention will be explained in more details in the following description with reference to preferred exemplary embodiments which are illustrated in the drawings, in which:
Fig. 1A - 1 B shows the rotor acceleration led by the power mismatch; wherein, Fig. 1A shows the stable first swing followed by the deep synchronous swings; Fig. 1 B shows the asynchronous swings followed by the generator out of step tripping;
Fig. 2 shows the basic concept of the integrated excitation and turbine controller for a steam-turbine synchronous generator system;
Fig. 3 is a schematic diagram which shows the structure of the integrated excitation and turbine controller;
Fig. 4 is the conceptual flowchart of auxiliary excitation voltage control method;
Fig. 5 is the conceptual flowchart of auxiliary governor valve opening control method.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS With reference to the above-mentioned figures, preferred embodiments of the present invention are provided.
Fig. 2 shows the basic concept of the integrated excitation and turbine controller 23 for a steam-turbine synchronous generator 20, which is connected to the equivalent power grid 28 via step-up transformer 26 and transmission lines 27. Besides the existing Automatic Voltage Regulator (AVR) 25 and Governor 24, the high-level integrated excitation and turbine controller provides auxiliary excitation control signals 22 and turbine control signals 21 based on the measurements 29 and the built-in control strategies. The measurements 29 here Include mechanical power Pm, electromagnetic power Pe, and power angle δ. The outputs here include auxiliary excitation voltage AEF *, auxiliary governor valve opening AUG , and intercept valve opening U|V *. The auxiliary excitation voltage AEF' will be added to the Automatic Voltage Regulator to realize in-time response of excitation voltage for generator stabilization under disturbances. The auxiliary governor valve opening AUG * will be added to the power/frequency droop regulator. The intercept valve opening U|V * will be an on/off signal to limit large power
mismatch of generator but wili not replace the over-speed protection logic.
Fig. 3 is a schematic diagram which shows the structure of the integrated excitation and turbine controller. According to the preferred embodiments, the integrated excitation and turbine controller 23 for synchronous generator comprises a categorizing module 31 for categorizing the fault severity according to the accelerating energy caused by the power mismatch; an operation mode detecting module 32 for determining the generator operation mode according to the signs of power angle derivation and the directions electromagnetic power; an auxiliary excitation controller 33 for calculating the auxiliary excitation voltage according to the fault severity and the generator operation mode; an auxiliary governor controller 34 for calculating the auxiliary governor valve opening according to the fault severity and the generator operation mode; and an intercept valve controller 35 for calculating the intercept valve opening according to the fault severity and the generator operation mode.
To explain the working principle of the Integrated Excitation and Turbine Control (IETC) method, the power-angle characteristics in Fig. 1A -1 B can be divided into four zones, according to the signs of power angle derivation and the directions electromagnetic power.
In the first case, as shown in Zone-I of Figure 1 A (forward swing and generator mode), the IETC controller quickly increases the excitation voltage and reduce the turbine valve opening to increase forward deceleration area, so as to ensure the first swing stability. If the first swing is stable, the IETC controller reduces the mismatch between the acceleration area and the deceleration area as much as possible to provide fast and effective damping to the synchronous power swings. For example in Zone-ll (backward swing and generator mode), the IETC controller reduces the excitation voltage and increase the turbine valve opening to reduce the backward acceleration area. In Zone-Ill (backward swing and motor mode), the IETC controller increases the excitation voltage and the turbine valve opening to increase the backward deceleration area.
In the second case, if the first swing is not stable, the generator will enter into Zone-IV as shown in Figure 1 B (forward swing and motor mode). Under this circumstance, the IETC controller reduces both the excitation voltage and the turbine valve opening to limit the forward acceleration area and help the generator to be re-synchronized after certain number of asynchronous swings.
The table below shows a summarization of the working principle of the integrated excitation and turbine control method provided by the present invention.
Table 1 : Working Principle of the Integrated Excitation and Turbine Control Method
IETC
NO. Operation Mode Criterion Remark
command
1 Generator mode Pe≥0 Ef† Uv J. Increase excitation voltage, reduce turbine valve
Forward swing d5/dt > 0 opening to increase forward deceleration area
Generator mode Pe≥0 Reduce excitation voltage, increase turbine valve
2
Backward swing d5/dt < 0 opening to decrease backward acceleration area
Motor mode Pe < 0 Reduce excitation voltage and turbine valve
3
Forward swing dSftJt≥ 0 opening to reduce forward acceleration area
Motor mode Pe < 0 Increase excitation voltage and turbine valve
4 E,†UV†
Backward swing dS dt < 0 opening to increase backward deceleration area
Wherein the variables in the Table 1 are defined as following:
Pe: generator electromagnetic power; δ: power angle; Ef: excitation voltage reference; Uv: turbine valve opening reference.
The fault severity categorization is to ensure that the outputs of the integrated excitation and turbine controller are always sufficient under various system disturbances. Insufficient control may not effectively stabilize the generator under large disturbances while exaggerated control may adversely affect system stability under small disturbances. It is practical to use the integration of the difference between mechanical power and electromagnetic power as the criterion of fault severity categorization.
During normal operation, mechanical power and electromagnetic power are balanced so that theoretically the difference should be zero. Whenever a disturbance occurs, this difference will be accumulated to a value depending on the degree of the unbalance and the lasting time of the disturbance. By comparing the value with pre-defined limits, disturbances can be divided into several types corresponding to different control modes of the integrated excitation and turbine control solution. Table 2 gives an example where disturbances are categorized into three types.
Table 2: Criteria for Fault Severity Categorization
The operation mode detecting module is to ensure that the outputs of the integrated excitation and turbine controller are sufficient to enhance generator transient stability and effective to damp out generator oscillations under disturbances. By detecting the signs of the power angle derivation and the directions of electromagnetic power, three typical generator operation modes after disturbances can be determined according to Table 3, including first
S swing mode, asynchronous swing mode and synchronous swing mode.
Table 3: Criteria for Generator Operation Mode Determination
According to one preferred embodiment, the calculation method for the auxiliary excitation voltage control is shown in Table 4. If the power angle keeps increasing, the auxiliary excitation voltage will increase proportionally to the electromagnetic power to maximally reduce the acceleration area. If the power angle starts decreasing, the auxiliary excitation voltage will decrease proportionally to the difference of the mechanical power and the electromagnetic power, which can provide effective damping to the power swings.
It can also be observed that, the calculation method uses different functions and parameter settings according to the severity of disturbances and the operation mode of generator. For the large and moderate disturbances, algorithm design focuses on transient stability issue, considering the possibilities of both rotor deflections towards the negative power angle and the unstable first swing plus consequent asynchronous swings. For the small disturbances, the calculation method mainly focuses on dynamic performance issue, and only considers the generator operations in the first quadrant of power-angle characteristic. By setting the proportional parameter to zero for example under small disturbances, the output of auxiliary excitation voltage controller under this type of disturbance can be disabled accordingly.
Table 4: Calculation Method for Auxiliary Excitation Voltage Controller
The calculation method for auxiliary turbine valve control is shown in Table 5, which is in line with the working principle analysis given above. For auxiliary governor valve control, the
output is proportional to the power angle derivation to reduce the power mismatch and damp out the oscillations. The proportional parameter is adjusted according to the severity of disturbances. By setting the proportional parameter to zero for example under small disturbances, the output of auxiliary governor controller will be disabled under this type of disturbance.
Intercept valve control is only enabled under large disturbances. The intercept valve will be closed if the power angle keeps increasing so as to limit the mechanical power, and will be opened again if the rotor stops accelerating and starts to return to another equilibrium point. Under normal operation, the intercept valve control is kept open so as to avoid frequent change of the turbine valve which will lead to accelerated wear and tear.
Table 5: Calculation Method for Auxiliary Turbine Valve Controller
According to one preferred embodiment, an improved calculation method for auxiliary excitation voltage is provided as shown in Table 6. Compared with previous calculation method for auxiliary excitation voltage, the input signal is simplified to one signal Pe-Pm, instead of two signals Pei and Pm-Pe as shown in Table 4. Moreover, the parameter setting is also simplified. Different compensators are designed to meet the requirements on stability enhancement and oscillation damping.
Table 6: Improved Calculation Method for Auxiliary Excitation Voltage Controller
Fig. 4 is the conceptual flowchart of the improved auxiliary excitation voltage control method. The auxiliary excitation controller 33 comprises an excitation signal module 331 , two excitation compensation modules 332 and an excitation logic module 333. The excitation signal module 331 is to calculate the power mismatch of the mechanical power and the
electromagnetic power. The excitation compensation modules 332 are to provide two different phase lead compensations. The excitation logic module 333 is to calculate the auxiliary excitation voltage based on the power mismatch and the phase lead compensations.
According to another preferred embodiment, an improved calculation method for auxiliary governor valve is provided as shown in Table 7. Compared with the previous calculation method for auxiliary governor opening, the input signal is the same, d6/dt is adopted. However, under severe disturbances and during generator synchronous swing mode, or under small disturbances, a lead compensator is adopted to compensate the phase lag of turbine system so as to achieve better damping characteristics.
Table 7: Improved Calculation Method for Auxiliary Governor Valve Controller
Fig. 5 is the conceptual flowchart of the auxiliary governor valve control method. The auxiliary governor valve controller 34 comprises a governor signal module 341 , a governor compensation module 342 and a governor logic module 343. The governor signal module 341 is to calculate the power angle derivation. The governor compensation module 342 is to provide phase lead compensation. The governor logic module 343 is to calculate the auxiliary governor valve opening based on power angle derivation and the phase lead compensation.
The proposed integrated excitation and turbine control method is beneficial to the generator transient stability enhancement and dynamic performance improvement. The possible economic advantages for power plants mainly include two aspects as follows:
- Improved power plant fault ride to mitigate the risk of unplanned outage of generator due to power grid disturbances. This will avoid undesired electricity production loss and boiler restart-up costs.
- There are cases that the output level of generator is limited by grid transient stability constraints under certain operation conditions. The improved power plant's dynamic performance can improve the overall power grid transient stability, and thus increase the revenue from unconstrained dispatch for power plant itself.
From power system point of view, the possible benefits of the proposed integrated excitation and turbine control solution mainly include two aspects as follows:
- Delay or even avoid building new transmission lines by improving the generator dynamic performances so as to fully utilize the existing transmission facilities.
- Reduce the risk of spread outages of generators under severe disturbances. This allows the grid operator to shed fewer loads and reduce the penalty for power supply interruption.
Integrated excitation and turbine control is a cost-effective way and no additional primary equipment is required. Compared with prior methods, the method also has the advantages that:
- Universal solution that can help to improve transient stability and dynamic performance of synchronous generator under different types of system disturbances;
- Self-adaptive characteristic to choose the control functions according to fault severity and generator operation conditions;
- No replacement of existing excitation and turbine control system (works with existing system) and minimum interactions with steady-state generator frequency/voltage regulations.
Though the present invention has been described on the basis of some preferred embodiments, those skilled in the art should appreciate that those embodiments should by no means limit the scope of the present invention. Without departing from the spirit and concept of the present invention, any variations and modifications to the embodiments should be within the apprehension of those with ordinary knowledge and skills in the art, and therefore fall in the scope of the present invention which is defined by the accompanied claims.
Claims
1. An integrated excitation and turbine control method for synchronous generator characterized in that it comprises:
categorizing the fault severity according to the accelerating energy caused by the power mismatch;
detecting the generator operation mode according to the signs of the power angle derivation and the directions electromagnetic power;
calculating the auxiliary excitation voltage according to the fault severity and the generator operation mode;
calculating the auxiliary governor valve opening according to the fault severity and the generator operation mode; and
calculating the intercept valve opening according to the fault severity and the generator operation mode.
2. The method according to claim 1 , characterized in that the fault severity can be categorized as large disturbance, moderate disturbance and small disturbance; said power mismatch is the difference of the mechanical power and the electromagnetic power.
3. The method according to claim 1 , characterized in that the generator operation modes are categorized as first swing, asynchronous swings and synchronous swings by detecting the signs of power angle derivation and the directions of electromagnetic power,
4. The method according to claim 2 or 3, characterized in that the auxiliary excitation voltage is calculated as following:
if the fault severity is categorized as large disturbance or moderate disturbance, and if
the generator operation modes are categorized as first swing or asynchronous swings, the auxiliary excitation voltage shall be proportional to the electromagnetic power, else if
the generator operation modes are categorized as the synchronous swings, the auxiliary excitation voltage shall be proportional to the power mismatch; otherwise if the fault severity is categorized as small disturbance, regardless the generator operation modes, the auxiliary excitation voltage shall be proportional to the power mismatch.
5. The method according to claim 2 or 3, characterized in that the auxiliary excitation voltage is calculated as following:
if the fault severity is categorized as large disturbance or moderate disturbance, and if
the generator operation modes are categorized as first swing or asynchronous swings, the auxiliary excitation voltage shall be proportional to the difference of the electromagnetic power and the mechanical power; the auxiliary excitation voltage further comprises a lead compensation to provide a phase lead I; else if
the generator operation modes are categorized as synchronous swings, the auxiliary excitation voltage shall be proportional to the difference of the electromagnetic power and the mechanical power; the auxiliary excitation voltage further comprises a lead compensation to provide a phase lead II which is smaller than said phase lead I; otherwise
if the fault severity is categorized as small disturbance, regardless the generator operation modes, the auxiliary excitation voltage shall be proportional to the difference of the electromagnetic power and the mechanical power; the auxiliary excitation voltage further comprises a lead compensation to provide a phase lead II which is smaller than said phase lead I.
6. The method according to claim 2 or 3, characterized in that the auxiliary governor vaive opening is calculated as following:
the auxiliary governor valve opening shall be proportional to the power angle derivation; the proportional parameter is negative to suppress the deviation.
7. The method according to claim 2 or 3, characterized in that the auxiliary governor valve opening is calculated as following:
if the fault severity is categorized as large disturbance or moderate disturbance, and if
the generator operation modes are categorized as first swing or asynchronous swings, the auxiliary governor valve opening shall be proportional to the power angle derivation; the proportional parameter is negative to suppress the deviation; else if the generator operation mode is categorized as synchronous swings, the auxiliary governor valve opening is proportional to the power angle derivation; the proportional parameter shall be negative to suppress the deviation; the auxiliary governor valve opening further comprises a lead compensator; otherwise
if the fault severity is categorized as small disturbance, regardless the generator operation modes, the auxiliary governor valve opening shall be proportional to the power angle derivation; the auxiliary governor valve opening further comprises a lead compensator.
8. The method according to claim 2 or 3, characterized in that the intercept valve opening is calculated as following:
if the fault severity is categorized as large disturbance or moderate disturbance, and if the generator operation modes are categorized as first swing or asynchronous swings, the intercept valve opening shall be off;
otherwise, the intercept valve opening shall be on.
9. The method according to any one of the claims above, characterized in that it further comprises the following step:
the auxiliary excitation voltage is added to the Automatic Voltage Regulator to realize in-time response of excitation voltage for generator stabilization under disturbances.
10. The method according to claim any one of the claims above, characterized in that it further comprises the following steps:
the auxiliary governor valve opening is added to the power/frequency droop regulator.
11. The method according to claim 4 or 5, characterized in that under small disturbance, the auxiliary excitation voltage is zero.
12. The method according to claim 6 or 7, characterized in that under small disturbance, the auxiliary governor valve opening is zero.
13. An integrated excitation and turbine controller for synchronous generator comprising:
a categorizing module (31) for categorizing the fault severity according to the accelerating energy caused by the power mismatch;
an operation mode detecting module (32) for detecting the generator operation mode according to the signs of power angle derivation and the directions electromagnetic power;
an auxiliary excitation controller (33) for calculating the auxiliary excitation voltage according to the fault severity and the generator operation mode;
an auxiliary governor controller (34) for calculating the auxiliary governor valve opening according to the fault severity and the generator operation mode; and
an intercept valve controller (35) for calculating the intercept valve opening according to the fault severity and the generator operation mode.
14. The controller according to claim 13, characterized in that
said auxiliary excitation controller (33) comprises an excitation signal module (331), two excitation compensation modules (332) and an excitation logic module (333);
the excitation signal module (331) is to calculate the difference of the mechanical power and the electromagnetic power;
the excitation compensation modules (332) are to provide two different phase lead compensations; and
the excitation logic module (333) is to calculate the auxiliary excitation voltage based on the power mismatch and the phase lead compensations.
15. The controller according to claim 13, characterized in that
the governor valve controller (34) comprises a governor signal module (341), a governor compensation module (342) and a governor logic module (343);
the governor signal module (341 ) is to calculate the power angle derivation;
the governor compensation module (342) is to provide phase lead compensation; and the governor logic module (343) is to calculate the auxiliary governor valve opening based on power angle derivation and the phase lead compensation.
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| PCT/CN2010/078244 WO2012055115A1 (en) | 2010-10-29 | 2010-10-29 | Integrated excitation and turbine controller for synchronous generator and control method thereof |
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| PCT/CN2010/078244 WO2012055115A1 (en) | 2010-10-29 | 2010-10-29 | Integrated excitation and turbine controller for synchronous generator and control method thereof |
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| CN103762579A (en) * | 2013-12-22 | 2014-04-30 | 南京南瑞集团公司 | Direct-current power emergency control performance index calculation method for improving transient power angle stability of power grid |
| CN104782043A (en) * | 2012-10-09 | 2015-07-15 | Abb研究有限公司 | Methods, systems, and computer readable media for adaptive out of step protection for power generators with load resynchronization capability |
| EP2936644A4 (en) * | 2012-12-20 | 2016-09-07 | Abb Technology Ltd | Method and apparatus for power plant dynamic var regulation and transient stability improvement |
| CN107301302A (en) * | 2017-07-12 | 2017-10-27 | 北京交通大学 | A kind of computational methods of Stator Coil added losses |
| CN110380410A (en) * | 2019-07-17 | 2019-10-25 | 国家电网有限公司 | A kind of dynamo governor dynamic state of parameters polymerization and its system |
| CN112039379A (en) * | 2020-07-15 | 2020-12-04 | 哈尔滨理工大学 | Excitation fault control for asynchronous steam turbine generator |
| CN113109688A (en) * | 2021-04-19 | 2021-07-13 | 东南大学 | Thyristor open-circuit fault diagnosis method for excitation system of synchronous phase modulator |
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| CN104782043A (en) * | 2012-10-09 | 2015-07-15 | Abb研究有限公司 | Methods, systems, and computer readable media for adaptive out of step protection for power generators with load resynchronization capability |
| EP2907235A4 (en) * | 2012-10-09 | 2016-07-06 | Abb Research Ltd | Methods, systems, and computer readable media for adaptive out of step protection for power generators with load resynchronization capability |
| EP2936644A4 (en) * | 2012-12-20 | 2016-09-07 | Abb Technology Ltd | Method and apparatus for power plant dynamic var regulation and transient stability improvement |
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| CN103762579A (en) * | 2013-12-22 | 2014-04-30 | 南京南瑞集团公司 | Direct-current power emergency control performance index calculation method for improving transient power angle stability of power grid |
| CN103762579B (en) * | 2013-12-22 | 2015-11-11 | 国家电网公司 | A kind of direct-current power emergency control performance index calculation method improving transient power angle stability of power grid |
| CN107301302A (en) * | 2017-07-12 | 2017-10-27 | 北京交通大学 | A kind of computational methods of Stator Coil added losses |
| CN107301302B (en) * | 2017-07-12 | 2019-10-25 | 北京交通大学 | A kind of calculation method of Stator Coil added losses |
| CN110380410A (en) * | 2019-07-17 | 2019-10-25 | 国家电网有限公司 | A kind of dynamo governor dynamic state of parameters polymerization and its system |
| CN110380410B (en) * | 2019-07-17 | 2023-02-10 | 国家电网有限公司 | Dynamic aggregation method and system for parameters of generator speed regulator |
| CN112039379A (en) * | 2020-07-15 | 2020-12-04 | 哈尔滨理工大学 | Excitation fault control for asynchronous steam turbine generator |
| CN113109688A (en) * | 2021-04-19 | 2021-07-13 | 东南大学 | Thyristor open-circuit fault diagnosis method for excitation system of synchronous phase modulator |
| CN113985775A (en) * | 2021-10-27 | 2022-01-28 | 中广核工程有限公司 | Nuclear power unit control method and system considering quick valve closing action |
| CN113985775B (en) * | 2021-10-27 | 2024-01-02 | 中广核工程有限公司 | Nuclear power unit control method and system considering fast closing valve action |
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