阅读说明：本技术 功率系统 (Power system ) 是由 S.达斯古普塔 J.德姆哈特 M.克赖斯尔 S.杨 A.K.古普塔 于 2019-05-30 设计创作，主要内容包括：一种功率系统,包括：具有转子的同步电力发电机；角度计算单元,其被配置为：确定同步电力发电机的稳态周期内的转子角度,确定同步电力发电机的瞬态周期内转子角度的变化,并基于稳态转子角度和转子角度的变化来估算瞬态周期内的转子角度。(A power system, comprising: a synchronous power generator having a rotor; an angle calculation unit configured to: the method includes determining a rotor angle within a steady state period of the synchronous power generator, determining a change in the rotor angle within a transient period of the synchronous power generator, and estimating the rotor angle within the transient period based on the steady state rotor angle and the change in the rotor angle.)

1. A power system (10), comprising:

a synchronous power generator (11) having a rotor; and

An angle calculation unit (20, 40) configured to:

Determining a rotor angle (δ _e-pcc,ss ) within a steady state period of the synchronous power generator (11),

determining a change (∆δ) in rotor angle within a transient period of the synchronous power generator (11), and

estimating a rotor angle (δ) within the transient period based on the steady state rotor angle (δ _e-pcc,ss ) and the change in rotor angle (∆δ).

2. The power system (10) of claim 1, wherein the angle calculation unit (40) is configured to estimate the load angle (δ _LA ) within the transient period based on the estimated rotor angle (δ) and a difference between a voltage angle (θ _t ) at an output terminal (15) of the synchronous power generator (11) and a voltage angle (θ _pcc ) at a point of common coupling (17) to a load of the synchronous power generator (11).

3. The power system (10) of claim 2, comprising a PCC voltage sensor (22) configured to measure the voltage at the point of common coupling (17), wherein the angle calculation unit (40) is configured to receive a three-phase voltage from the PCC voltage sensor (22) and determine the voltage angle (θ _pcc ) at the point of common coupling (17).

4. The power system (10) of claim 1 wherein the angle calculation unit (20) includes a sample and hold circuit (66), the sample and hold circuit (66) configured to sample and hold the steady state rotor angle (δ _e-pcc,ss ) for a transient period.

5. The power system (10) of claim 4 wherein the angle calculation unit (20) includes a flip-flop circuit (63) configured to output a control signal (32) to the sample and hold circuit (66) based on a rate of change (|a|) of the angular velocity (ω _gen ) of the rotor.

6. a power system (10), comprising:

A synchronous power generator (11) having a rotor and an output terminal (15); and

An angle calculation unit (20, 40) configured for:

determining a load angle (δ _e-t,ss ) within a steady state period of the synchronous power generator (11),

Determining a change (∆δ) in rotor angle within a transient period of the synchronous power generator (11), and

Estimating a load angle (δ _LA ) within the transient period based on the change in rotor angle (∆δ), the steady state load angle (δ _e-t,ss ), and a voltage angle (θ _t ) at the output terminal (15).

7. the power system (10) of claim 6 wherein the angle calculation unit (40) is configured to estimate an internal voltage angle (θ _e ) of the synchronous power generator (11) during the transient period based on the steady state load angle (δ _e-t,ss ) and the voltage angle (θ _t ) at the output terminal (15), and to estimate the load angle (δ _LA ) during the transient period by determining a difference between the estimated internal voltage angle (θ _e ) and the voltage angle (θ _t ) at the output terminal (15).

8. The power system (10) of claim 7, wherein the angle calculation unit (40) is configured to estimate the internal voltage angle (θ _e ) based on a gradient from a held value of the internal voltage angle (θ _e ) when the transient period begins and a voltage angle (θ _t ) at the output terminal (15) when the transient period begins.

9. The power system (10) of claim 2 or 6, comprising a terminal voltage sensor (22) configured to measure the voltage at the output terminal (15), wherein the angle calculation unit (40) is configured to receive a three-phase voltage from the terminal voltage sensor (22) and to determine a voltage angle (θ _t ) at the output terminal (15).

10. The power system (10) of claim 1, wherein the angle calculation unit (20) is configured to determine the change (∆δ) in rotor angle by time integrating the difference (∆ω) between the angular velocity (ω _gen ) of the rotor and a reference angular velocity (ω _ref ).

11. The power system (10) of claim 5, comprising a prime mover (12) configured to drive the synchronous electrical generator (11), wherein the angle calculation unit (20) comprises a generator speed estimator (50), the generator speed estimator (50) configured to estimate an angular speed (ω _gen ) of the rotor based on the angular speed of the prime mover (12).

12. The power system (10) of claim 1 wherein the electrical power output from the synchronous electrical power generator (11) is less than 30 MW.

13. A method of determining a rotor angle (δ) in a power system (10) including a synchronous power generator (11), the method comprising:

Determining a rotor angle (δ _e-pcc,ss ) within a steady state period of the synchronous power generator (11),

determining a change (∆δ) in rotor angle within a transient period of the synchronous power generator (11), and

estimating a rotor angle (δ) within the transient period based on a steady state rotor angle (δ _e-pcc,ss ) and a change in the rotor angle (∆δ).

14. A method of determining a load angle (δ _LA ) in a power system (10) including a synchronous power generator (11), the method comprising:

Determining a load angle (δ _e-t,ss ) within a steady state period of the synchronous power generator (11),

Determining a change (∆δ) in rotor angle within a transient period of the synchronous power generator (11), and

estimating a load angle (δ _LA ) within the transient period based on the change in rotor angle (∆δ), a steady state load angle (δ _e-t,ss ), and a voltage angle (θ _t ) at output terminals (15) of the synchronous power generator (11).

15. the method of determining a rotor angle (δ) according to claim 13 or a load angle (δ _LA ) according to claim 14, wherein the power system is a power system (10) according to any one of claims 1 to 12.

16. A method of determining whether an out-of-sync condition has occurred, the method comprising:

Determining a rotor angle (δ) in a power system (10) according to claim 13 and/or determining a load angle (δ _LA ) in the power system (10) according to claim 14, and

Determining whether a out-of-step condition has occurred depending on the determined rotor angle (δ) and/or load angle (δ _LA ).

17. A computer program which, when executed by a computing device (20, 40), causes the computing device (20, 40) to determine a rotor angle (δ) in a power system (10) according to claim 13 and/or to determine a load angle (δ _LA ) in the power system (10) according to claim 14 and/or to determine an out-of-sync state according to the method of claim 16.

18. a computing device (20, 40) configured to determine a rotor angle (δ) and/or a load angle (δ _LA ) and/or an out-of-step condition in a power system (10) by executing the computer program of claim 17.

Technical Field

The present disclosure relates to the determination of load angle and/or rotor angle in electrical power generators driven by prime movers, such as reciprocating engines or gas/steam/wind turbines or motors for grid applications, and the like. The techniques disclosed herein provide for accurate determination of the load angle and/or rotor angle during high load conditions and also during transient periods when a fault has caused magnetic saturation of the generator. Thus, the techniques disclosed herein are particularly well suited for detecting when an out-of-step condition has occurred.

Background

There is a general need to improve known load angle and/or rotor angle determination techniques.

Disclosure of Invention

according to a first aspect of the invention, there is provided a power system comprising: a synchronous power generator having a rotor; and an angle calculation unit configured to: the method includes determining a rotor angle within a steady state period of the synchronous power generator, determining a change in the rotor angle within a transient period of the synchronous power generator, and estimating the rotor angle within the transient period based on the steady state rotor angle and the change in the rotor angle. This approach provides an inexpensive and reliable way to determine the rotor angle even during transient periods (e.g., after a fault).

The angle calculation unit can be configured to estimate the load angle within the transient period based on the estimated rotor angle and a difference between the voltage angle at the output terminal of the synchronous power generator and a voltage angle at a point of common coupling of a load attached to the synchronous power generator. The method provides an inexpensive and reliable way of determining the load angle even during transient periods.

The power system can include a PCC voltage sensor configured to measure a voltage at the point of common coupling. The angle calculation unit can be configured to receive the three-phase voltages from the PCC voltage sensor and determine a voltage angle at the point of common coupling.

The angle calculation unit can include a sample and hold circuit configured to sample the steady state rotor angle and hold its value for the transient period. The angle calculation unit can include a flip-flop circuit configured to output a control signal to the sample and hold circuit based on a rate of change of the angular velocity of the rotor.

According to a second aspect of the invention, there is provided a power system comprising: a synchronous power generator having a rotor and output terminals; and an angle calculation unit configured to: the method comprises determining a load angle within a steady-state period of the synchronous power generator, determining a change in rotor angle within a transient period of the synchronous power generator, and estimating the load angle within the transient period based on the change in rotor angle, the steady-state load angle, and a voltage angle at the output terminal. The method provides an inexpensive and reliable way of determining the load angle even during transient periods.

The angle calculation unit can be configured to: an internal voltage angle of the synchronous power generator during the transient period is estimated based on the steady-state load angle and the voltage angle at the output terminal, and the load angle during the transient period is estimated by determining a difference between the estimated internal voltage angle and the voltage angle at the output terminal. The angle calculation unit can be configured to estimate the internal voltage angle based on a gradient from a held value of the internal voltage angle when the transient period starts and the voltage angle at the output terminal when the transient period starts.

The power system can include: a terminal voltage sensor configured to measure a voltage at the output terminal, wherein the angle calculation unit is configured to receive the three-phase voltages from the terminal voltage sensor and determine a voltage angle at the output terminal.

The angle calculation unit can be configured to determine the change in the rotor angle by time integrating a difference between the angular velocity of the rotor and a reference angular velocity. The power system can include: a prime mover, e.g. a reciprocating engine or a gas/steam/wind turbine or a motor, etc., configured to drive the synchronous power generator, wherein the angle calculation unit comprises a generator speed estimator configured to estimate the angular speed of the rotor based on the angular speed of the prime mover.

The electrical power output from the synchronous electrical generator can be less than 30 MW. However, the applicability of the proposed method is not limited to this power range only.

According to a third aspect of the invention, there is provided a method of determining a rotor angle in a power system comprising a synchronous power generator, the method comprising: the method comprises determining a rotor angle within a steady state period of the synchronous power generator, determining a change in the rotor angle within a transient period of the synchronous power generator, and estimating the rotor angle within the transient period based on the steady state rotor angle and the change in the rotor angle.

According to a fourth aspect of the present invention, there is provided a method of determining a load angle in a power system comprising a synchronous power generator, the method comprising: the method comprises determining a load angle within a steady-state period of the synchronous power generator, determining a change in rotor angle within a transient period of the synchronous power generator, and estimating the load angle within the transient period based on the change in rotor angle, the steady-state load angle and a voltage angle at an output terminal of the synchronous power generator.

The power system in the third or fourth aspect can be a power system according to the first or second aspect.

according to a fifth aspect of the present invention, there is provided a method of determining whether an out-of-sync condition has occurred, the method comprising: determining a rotor angle or a load angle in the power system according to the method of the third or fourth aspect; and determining whether a loss of synchronism condition has occurred depending on the determined rotor angle and/or load angle.

according to a sixth aspect of the present invention there is provided a computer program which, when executed by a computing device, causes the computing device to determine a rotor angle or a load angle in a power system according to the method of the third or fourth aspect; and/or determining an out-of-sync status according to the method of the fifth aspect.

According to a seventh aspect of the present invention, there is provided a computing device configured to determine a rotor angle and/or a load angle and/or an out-of-step condition in a power system by executing the computer program of the sixth aspect.

Those skilled in the art will appreciate that features or parameters described in relation to any one of the above aspects may be applied to any other aspect unless mutually exclusive therein. Furthermore, any feature or parameter described herein may be applied to any aspect and/or in combination with any other feature or parameter described herein, unless mutually exclusive therein.

Drawings

Embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 illustrates components of a power system according to an embodiment;

FIG. 2 illustrates components of a power system according to an embodiment;

FIG. 3 illustrates how a rotor angle can be estimated according to an embodiment;

FIG. 4 illustrates how the angular velocity of a rotor can be estimated according to an embodiment;

FIG. 5 illustrates how a load angle can be estimated according to an embodiment;

FIG. 6 illustrates how the load angle can be estimated according to an alternative embodiment;

FIG. 7 is a flow diagram of a process according to an embodiment; and

FIG. 8 is a flow chart of a process according to an alternative embodiment.

Detailed Description

the present disclosure provides an improved method of determining load angle and/or rotor angle in an electrical power generator for an electrical grid.

In order to clearly present the background of the disclosure, details of the background art are provided below.

Electrical power systems are exposed to various abnormal operating conditions such as faults, generator losses, line trips and other disturbances that may cause power oscillations and consequent system instability. In these conditions, a suitable relay setting is necessary to ensure proper protection (i.e. disconnection of the generator out of synchronization and blocking of undesired operation of the distance relay associated with the high voltage, HV, line).

During normal operating conditions, the electrical power output from the generator produces an electrical torque that balances the mechanical torque applied to the generator rotor shaft. The rotor operates at a constant speed, with electrical and mechanical torque balanced. When a fault occurs and the amount of power transmitted is reduced, this thereby reduces the electrical torque against the mechanical torque. If the mechanical power is not reduced during a fault, the generator rotor will accelerate due to the unbalanced torque condition. In some cases, depending on the type and level of failure, the amount of power transmitted can be increased (rather than decreased).

During an unstable power condition, at least two generators providing power to the grid rotate at different speeds from each other and lose synchronization. This is referred to as an out-of-sync state (also referred to as an out-of-sync state or an out-of-sync state).

the out-of-step condition results in high currents and mechanical forces within the generator windings and results in high levels of instantaneous shaft torque. The torque can be large enough to damage the shaft of the generator. Pole slip events can also result in abnormally high stator core end iron flux, which can cause overheating and shorting of the stator core ends. The cell transformer will also be subjected to very high transient winding currents, which impose high mechanical stresses on the windings.

Thus, in the event of an out-of-sync condition, it is important that asynchronously operating generators or system areas be quickly isolated from each other using out-of-sync protection techniques.

Out-of-sync protection is described in detail in at least the following: IEEE Tutorial on the Protection of Synchronous Generators (second edition), published 29/8/2011, see http:// resource. ie-pes. org/pes/product/Tutorial/PESTP1001 (as seen on 14/3/2018).

For large power generation systems, it is standard for an out-of-step detector (e.g., an impedance relay) to be used to determine whether the generator is properly synchronized with the grid. However, a small synchronous generator (i.e. a generator with a power output of less than 30 MW) is typically not provided with a step-out detector.

A particularly suitable application for small synchronous generators is in smart grids. These are power grids with variable number of power sources and regulated power output from the power sources. Another particularly suitable application for small synchronous generators is in micro-grids. Therefore, it is desirable for small synchronous generators to provide out-of-step protection at a much lower cost than the out-of-step detection and prevention techniques currently used with large power generation systems.

The way to determine whether the generator is operating correctly or whether an out-of-step condition has occurred or is imminent is by determining and monitoring the rotor angle and/or the load angle of the generator. Accordingly, an accurate and low cost technique for determining the rotor angle and/or the load angle of a generator is desired.

A known and low cost technique for estimating Generator Load Angle is disclosed in "Synchronous Generator Load Angle Measurement and Estimation" by D.Sumina, AUTOMATIKA 45 (2004) 3-4, 179-186. This technique allows the load angle to be estimated from the measured output voltage and current. However, the estimation of the load angle depends on the reactance in the system. Therefore, this technique is not accurate at higher load conditions when high currents cause magnetic saturation in the generator core. Therefore, this technique is only applicable to the estimation of the load angle when the system is in steady state operation, and it cannot be used to estimate the load angle during the transient period of the out-of-sync protection. Furthermore, the accuracy of this technique may also be reduced when there is a change in saturation within the alternator core due to a change in the power required by the load.

Another known technique for estimating the Load Angle of a generator is disclosed in "Determination of Load Angle for salt-pole Synchronous Machine" of D.Sumina, MEASUREMENT SCIENCE REVIEW, Volume 10, No. 32010. The load angle is measured using an optical encoder and a digital control system.

Disadvantages of this technique include the need for additional components of the optical encoder and sensor. This adds cost and requires modification of the existing generator in order to have additional components to be installed. An idle angle calibration is also required after each synchronization.

The present disclosure provides a new method of determining load angle and/or rotor angle in a synchronous electric power generator for a power grid.

The disclosed technique differs from the known technique by continuously monitoring the change in the rotor angle. When the power system is in a steady state, the change in rotor angle is approximately zero. During a transient period (e.g., after a fault), the change in rotor angle can be combined with a hold value from another property (e.g., rotor angle or generator output voltage) at the beginning of the transient period in order to estimate the rotor angle and/or load angle.

Advantages include accurate determination of load angle and/or rotor angle, all during steady state operation, during transient periods of non-synchronous protection, and/or under high load conditions. In addition, the disclosed techniques can be implemented at low cost because there is no need for additional components such as optical encoders and sensors. In addition, the angle estimation can be seamlessly switched between steady state and transient state.

Fig. 1 illustrates a power system 10 according to one embodiment.

Power system 10 includes a prime mover 12, which may be, for example, a diesel engine. In the following description, an engine is provided as an example of the prime mover. Power system 10 also includes a synchronous power generator 11 having an output terminal 15, a cell transformer 16, and a Point of Common Coupling (PCC) terminal 17 at a point of common coupling. The cell transformer 16 is disposed between the output terminal 15 of the generator 11 and the PCC terminal 17. The engine 12 has a shaft arranged to drive the generator 11 such that the generator 11 produces electrical power that is output from the output terminals, through the cell transformer 16, through the PCC terminals 17 and out of the power system 10. Electrical power may be supplied to transmission line 18, transmission line 18 supplying electrical power to grid 19. These components of the power system 10 and the operation of the power system may be the same as known power systems.

As shown in fig. 2, the load angle δ _e-t (also referred to as a power angle) is defined herein as the angular difference between the open circuit voltage of the generator 11 (also referred to as the open armature voltage, no load voltage, electromotive force, back electromotive force, induced electromotive force, or internal voltage of the generator 11) and the voltage at the output terminal 15 of the generator 11.

The rotor angle (also referred to as the rotor internal angle) is defined herein as the angular difference between the open circuit voltage of the generator 11 (also referred to as the open armature voltage, no load voltage, electromotive force, back electromotive force, induced electromotive force, or the internal voltage of the generator 11) and the voltage at the PCC terminal 17.

By monitoring only the load angle, only the rotor angle, or both the load and rotor angles, the performance of the power system 10 can be determined and the out-of-step condition detected.

Power system 10 may also include one or more of a field current sensor 21 in generator 11 for measuring a field current, an output voltage sensor 22 for measuring a voltage at output terminal 15 of generator 11 (i.e., a generator output voltage), a terminal current sensor 23 for measuring a current at terminal 15 of generator 11 (i.e., a generator terminal current), and a PCC voltage sensor 24 for measuring a voltage at PCC17 (i.e., a PCC voltage).

also shown in fig. 1 are a resistor 14 and an inductor 13, these representing the internal resistance and reactance, respectively, of the generator 11.

The power system 10 includes an angle calculation unit 20 the angle calculation unit 20 is configured to determine the rotor angle δ _e-pcc,ss during a steady state period of the generator 11 in a steady state the rotor angle δ _e-pcc,ss can be determined using known methods for example, the rotor angle δ _e-pcc,ss can be calculated as the sum of the load angle δ _e-t,ss of the generator and the voltage angle difference δ _t-pcc,ss between the output terminal 15 and the PCC terminal 17.

The angle calculation unit 20 is configured to determine ∆δ a change in rotor angle during a transient period of the generator 11. in a steady state, the change in rotor angle ∆δ is approximately zero however, during the transient period, the change in rotor angle ∆δ can be non-zero due to the imbalance explained above. the angle calculation unit 20 is configured to estimate the rotor angle δ during the transient period based on the steady state rotor angle δ _e-pcc,ss and the change in rotor angle ∆δ.

When a fault occurs in the generator 11 or, more generally, in the power system 10, the parameters used to calculate the steady state rotor angle δ _e-pcc,ss are no longer valid, the steady state rotor angle δ _e-pcc,ss can be maintained (i.e., the rotor angle when the steady state period ends and the transient period begins) and the maintained value can remain constant throughout the transient period the rotor angle δ during the transient period can be calculated as the sum of the steady state rotor angle δ _e-pcc,ss and the change in rotor angle ∆δ.

During the steady state period, the change in rotor angle ∆δ is approximately zero, so that the change in rotor angle ∆δ is summed with the calculated steady state rotor angle δ _e-pcc,ss , simply resulting in the calculated steady state rotor angle δ _e-pcc,ss (i.e., in steady state, δ ≈ δ _e-pcc,ss ).

FIG. 3 is a schematic diagram illustrating the functionality of the angle calculation unit 20 As shown in FIG. 3, the angle calculation unit 20 can include a rotor angle change module 61 configured to determine ∆δ a change in rotor angle the rotor angle change module 61 is configured to determine ∆δ a change in rotor angle by time integrating the difference between ω _gen the angular velocity of the rotor and ω _ref . for example, the reference angular velocity ω _ref can be a previously calculated angular velocity ω _gen of the rotor, as shown in FIG. 3, the generator speed signal 21 is compared to a reference angular velocity ω _ref to determine a difference between ω _gen the angular velocity of the rotor and the reference angular velocity ω _ref , which can be referred to as a change in generator speed ∆ω.

The signal 37 of the change in generator speed is input to an integrator 64 of the rotor angle change module 61 the integrator 64 time integrates the signal 37 of the change in generator speed to determine ∆δ the change in rotor angle the rotor angle change module 61 is configured to output a corresponding rotor angle change signal 35.

As shown in FIG. 3, the angle calculation angle unit 20 may include a steady state angle module 62, the steady state angle module 62 configured to determine a steady state rotor angle δ _e-pcc,ss , a steady state rotor angle δ _e-pcc,ss determined as a sum of a steady state load angle δ _e-t,ss and a voltage angle difference δ _t-pcc,ss between the output terminal 15 and the PCC terminal 17.

Any method can be used to determine the steady state Load Angle δ _e-t,ss . for example, as shown in FIG. 3, the steady state Load Angle δ _e-t,ss can be estimated based on the Generator output voltage V _t and the Generator terminal current I _t . the steady state Load Angle δ _e-t,ss can be estimated using the formula described in "Synchronous Generator Load Angle Measurement and Estimation" by D. Sumina. in the equation shown in FIG. 3, X _q represents quadrature axis Synchronous reactance and R _s represents stator resistance. at the same time, in the PQ diagram of the Synchronous Generator 11, cosθ equals P and sinθ equals Q.

To determine the steady state load angle, the generator output voltage V _t and the generator terminal current I _t may be time-synchronized samples that are input to the angle calculation unit 20. the steady state load angle signal 38 is generated as an intermediate for determining the steady state rotor angle δ _e-pcc,ss .

The steady state angle module 62 is configured to determine a voltage angle difference δ _t-pcc,ss between the output terminal 15 and the PCC terminal 17 the generator output voltage V _t and the PCC voltage V _pcc may be time synchronized samples input to the angle calculation unit 20 As shown in FIG. 3, the steady state angle module 62 may include a phase locked loop 65 the phase locked loop 65 is configured to determine a voltage angle difference δ _t-pcc,ss between the output terminal 15 and the PCC terminal 17 based on the generator output voltage V _t and the PCC voltage V _pcc the phase locked loop 65 is configured to output a corresponding steady state voltage angle difference signal 34.

The steady state angle module 62 is configured to sum the steady state voltage angle difference signal 34 and the steady state load angle signal 38 to determine a steady state rotor angle. A corresponding steady-state rotor angle signal 33 is generated.

As shown in FIG. 3, the steady state angle module 62 can include a sample and hold circuit 66, the sample and hold circuit 66 is configured to sample and hold the steady state rotor angle δ _e-pcc,ss for the transient period.

As shown in fig. 3, the angle calculation unit 20 can include a flip-flop circuit 63, the flip-flop circuit 63 is configured to output the control signal 32 to the sample and hold circuit 66 based on a rate of change |a| of the angular velocity of the rotor.

The control of the sample and hold function is determined by the change in generator speed ω _gen (i.e., the angular velocity ω _gen of the rotor of the generator 11.) when a fault or disturbance occurs, unbalanced power causes acceleration of the rotor.

The angle calculation unit 20 is configured to combine the rotor angle change signal 35 with the preliminary rotor angle signal 31 in order to estimate the overall rotor angle δ the angle calculation unit 20 is configured to output a corresponding rotor angle signal 30 the preliminary rotor angle signal 31 is dependent on the trigger switch during steady state conditions, a continuously monitored steady state rotor angle δ _e-pcc,ss is used as the preliminary rotor angle signal 31 the change in rotor angle ∆δ is about zero such that the overall rotor angle δ is about the same as the continuously monitored steady state rotor angle δ _e-pcc,ss .

The sample and hold circuit 66 is controlled to hold the value of the steady state rotor angle δ _e-pcc,ss when a fault occurs such that a transient period begins, the held value is used as the preliminary rotor angle signal 31 during the transient period, the change in rotor angle ∆δ is non-zero and is used to estimate the total rotor angle δ during the transient period.

as depicted in FIG. 3, the rotor angle change module 61 can include a generator speed estimator 50, the generator speed estimator 50 is configured to estimate the angular speed ω _gen of the rotor of the generator 11. in the case of an engine power generation system, it may not be possible to measure the angular speed ω _gen of the rotor, however, the corresponding speed of the engine ω _eng may be measured, the generator speed estimator 50 is configured to estimate the angular speed ω _gen of the rotor based on the measured engine speed ω _eng , the generator speed estimator 15 receives the engine speed signal 210, as shown in FIGS. 1 and 2, the engine speed signal 210 is measured from the engine 12.

FIG. 4 is a schematic diagram showing how generator speed estimator 50 can estimate angular speed ω _gen of the rotor, as shown in FIG. 4, generator speed estimator 50 can use engine governor model 67. in the function shown in FIG. 4, T _eng represents engine torque, B _eng represents engine damping coefficient, θ _eng represents engine rotor angle, J _eng represents engine rotational inertia, T _elect represents electrical torque, B _gen represents alternator damping coefficient, θ _gen represents alternator rotor angle, J _gen represents alternator rotational inertia, and k represents torsional stiffness of the coupling.

The above description relates to the determination of rotor angle δ it may be desirable to determine load angle δ _LA for protection or monitoring purposes fig. 5 schematically depicts the functionality of the load angle calculation unit 40 fig. 40 may be combined with the angle calculation unit 20 as a single calculation device 20, 40.

The angle calculation unit 40 can be configured to estimate the load angle δ _LA within the transient period based on the estimated rotor angle δ and the difference between the voltage angle θ _t (t) at the output terminal 15 and the voltage angle θ _pcc (t) at the PCC terminal 17.

The terminal voltage sensor 22 is configured to measure a voltage at the output terminal 15, the PCC voltage sensor 22 is configured to measure a voltage at the PCC terminal 17, the generator output voltage V _t and the PCC voltage V _pcc may be time synchronized samples that are input to the angle calculation unit 40, the angle calculation unit 40 is configured to receive the three phase voltages from the terminal voltage sensor 22 and determine a voltage angle θ _t (t) at the output terminal 15, the angle calculation unit 40 is configured to receive the three phase voltages from the PCC voltage sensor 22 and determine a voltage angle θ _pcc (t) at the PCC terminal 17.

as depicted in FIG. 5, the angle calculation unit 40 can include one or more spatial vector angle calculation units 68 and one or more angle accumulation linearizing units 69 the three-phase voltages measured at the output terminal 15 and the PCC terminal 17 are fed into the spatial vector angle calculation unit 68 to calculate instantaneous voltage angles, then the instantaneous angles are linearized using the angle accumulation linearizing unit 69 to calculate a linearized instantaneous angle θ _t (t) _pcc (t), thereby generating the output voltage angle signal 42 and the PCC voltage angle signal 43. the angle calculation unit 40 is configured to output the load angle signal 41 based on the rotor angle signal 30, the output voltage angle signal 42, and the PCC voltage angle signal 43. the load angle δ _LA is calculated based on the equation δ _LA = δ - (θ _t (t) - θ _pcc (t)).

As described above, the angle calculation unit 20 can be configured to determine the steady state load angle δ _e-t,ss during a steady state period of the generator 11. the angle calculation unit 20 is also configured to determine a change in rotor angle ∆δ during a transient period As will be described in more detail with reference to FIG. 6 below, the angle calculation unit 40 can be configured to estimate the load angle δ _LA during a transient period based on the change in rotor angle ∆δ, the steady state load angle δ _e-t,ss , and the voltage angle θ _t (t) at the output terminal 15. in this method, the voltage measurement V _t at the generator output terminal 15 is used to estimate the load angle δ _LA , and there is no angle information from the voltage measurement at the PCC terminal.

as shown in FIG. 6, in steady state, the generator terminal voltage V _t is input to the spatial vector angle calculation unit 68 to calculate the instantaneous voltage angle, then the instantaneous voltage angle is linearized by the angle accumulation linearizer 69 to obtain the instantaneous voltage angle θ _t (t), thereby producing the output voltage angle signal 42 (similar to that shown in FIG. 5). The instantaneous voltage angle θ _t (t) is then summed with the estimated steady state load angle δ _e-t,ss to obtain the internal voltage instantaneous angle θ _e (t).

The angle calculation 40 can be configured to estimate an internal voltage angle θ _e (t) of the generator 11 during the transient period based on the steady state load angle δ _e-t,ss and the voltage angle θ _t (t) at the output terminal 15 the angle calculation unit 40 can be configured to estimate the load angle δ _LA during the transient period by determining a difference between the estimated internal voltage angle θ _e (t) and the voltage angle θ _t (t) at the output terminal 15.

As will be explained in more detail below, angle calculation unit 40 can be configured to estimate internal voltage angle θ _e (t) based on a gradient from a held value of internal voltage angle θ _e (t) when the transient period begins and voltage angle θ _t (t) at output terminal 15 when the transient period begins in the event of a fault, the gradient of voltage angle θ _t (t) at output terminal 15 is calculated, for example, as shown in FIG. 6, angle calculation unit 40 can include a gradient circuit 70 configured to calculate a gradient of voltage angle θ _t (t) at output terminal 15.

The load angle was calculated using the formula δ _LA = (θ _e (t) - θ _t (t)) + ∆δ.

At steady state, the change in rotor angle ∆δ is about zero, and θ _e (t) = δ _e-t,ss + θ _t (t), so the equation can be rewritten as δ _LA = (θ _e (t) - θ _t (t)) = δ _e-t,ss .

Using the voltage angle based approach, the rotor and/or load angle can still be accurately calculated during transient periods. At the same time, the rotor and/or load angle can be automatically calculated during the steady state period of the same system.

Fig. 7 is a flow chart of a process of determining a rotor angle and optionally also a load angle of the power system 10 according to the present disclosure. In step 701, the process begins.

In step 703, the rotor angle within the steady state period of the generator 11 is determined.

In step 705, a change in rotor angle within a transient period of the generator 11 is determined. The ordering of steps 703 and 705 is not important. Step 703 and step 705 may be performed consecutively.

In step 707, the sample and hold circuit 66 holds the value of the steady state rotor angle for the transient period. This is based on the control signal 32 received from the flip-flop circuit 63 (i.e. because the acceleration of the rotor is above a certain threshold).

In step 709, a rotor angle is estimated based on the steady state rotor angle and the change in the rotor angle.

in step 711, the load angle is estimated based on the estimated rotor angle and the difference between the voltage angle at the output terminal 15 of the generator 11 and the voltage angle at the PCC terminal 17.

In step 713, the process ends.

Fig. 8 is a flow chart of a process of an alternative method of determining a load angle of the power system 10 according to the present disclosure.

In step 801, the process begins.

In step 803, the load angle within the steady state period of the generator 11 is determined.

In step 805, a change in rotor angle within a transient period of the generator 11 is determined. The ordering of step 803 and step 805 is not important. Step 803 and step 805 may be performed continuously.

In step 807, the internal voltage angle of the generator 11 is estimated based on the steady-state load angle and the voltage angle at the output terminal 15.

In step 809, the load angle within the transient period is estimated based on the change in the rotor angle, the steady state load angle and the voltage angle at the output terminal by determining the difference between the estimated internal voltage angle and the voltage angle at the output terminal 15.

In step 811, the process ends.