Patent Description:
A form for implementing a variable speed pumped storage power generation device includes a system in which an inductive power generation motor is used to achieve a variable speed by secondary excitation of the inductive power generation motor, and a system in which a synchronous power generation motor device is connected to a power system via a parallel circuit of a power converter and a bypass line and a variable speed is achieved by adjusting a frequency in the power converter.

The present invention relates to a synchronous machine device of a system using a synchronous power generation motor device, a variable speed pumped storage power generation device, and a step-out estimation method. For example, PTL <NUM> discloses a variable speed operation control device and an operation method of a hydraulic power generation system that improve power generation efficiency by switching between a bypass operation mode in which a power generation device is operated in a manner of being directly connected to a power system through a bypass line and a converter operation mode in which the power generation device is operated via a power converter. In addition, in PTL <NUM>, equally a method to detect faults in a main circuit in case an electric motor has been already started is described. Herein, specifically, it is stipulated to detect a field current of a synchronous electric motor or a synchronous generation electric motor being a master machine and a second synchronous generation electric motor being used as a slave machine and determine a given circuit error in case the detected field current exceeds a predetermined range, leading further to the effect that additionally arranged circuit breakers may be opened so as to allow short-circuiting of the faulty circuit. Moreover, in NPTL <NUM>, a number of different strategies to further improve the reliability of speed pumped storage hydropower plants for balancing power fluctuations from wind power in an isolated grid are disclosed. Specifically, a topology based on a synchronous machine and a full scale back-to-back voltage source converter are suggested for obtaining variable speed operation of a pump-turbine unit.

In order to enable a variable speed pumped storage power generation device and a synchronous machine device of a system using a synchronous power generation motor device to contribute to stabilization of a power system, it is necessary to ensure operation continuity when there is a system fault. However, in a variable speed pumped storage power generation device that is switched between a bypass operation and a converter operation, for example, when troubleshooting of a system fault is delayed due to a main protection failure during the bypass operation, a synchronous speed of a power generation motor device may be greatly deviated and the power generation motor device steps out synchronization, which leads to the stop of the power generation motor device.

Here, an object of the present invention to provide a synchronous machine device, a variable speed pumped storage power generation device, and an operation method that can improve an operation tolerance when a system fault occurs during a bypass operation.

In order to solve the above-mentioned problems, a synchronous machine device according to independent claim <NUM> is proposed.

Dependent claims define preferable embodiments of the proposed invention.

It is possible to increase the degree of contribution to a stable operation of a power system of a device by improving an operation tolerance of the synchronous machine device and the variable speed pumped storage power generation device when there is a system fault.

<FIG> is a diagram showing a configuration example of a variable speed pumped storage power generation device <NUM> according to a first embodiment of the present invention. In the variable speed pumped storage power generation device <NUM>, a power generation motor device <NUM> is connected to a power system <NUM> via a parallel circuit of a power converter <NUM> and a bypass line <NUM> including a circuit breaker <NUM>, and a transformer <NUM>. The control device <NUM> receives signals from respective units of the variable speed pumped storage power generation device <NUM> so as to estimate whether the power system <NUM> steps out, thereby controlling the power converter <NUM>.

Although the power generation motor device <NUM> is shown in <FIG> in a simplified manner, the power generation motor device <NUM> includes a water wheel pump that converts potential energy of water into rotational energy (or converts rotational energy into potential energy), a synchronous power generation motor that converts the rotational energy into a power generation output Pg (or converts a pumping input Pg into rotational energy), a speed regulator (a governor) that controls a rotational speed of the water wheel pump, an automatic voltage regulator (AVR) that adjusts an excitation voltage of a rotor to control a terminal voltage of a power generator.

Here, the power generation motor device <NUM> in the present specification may be a synchronous power generator or a synchronous motor, in addition to a so-called power generation motor. In short, as long as the power generation motor device <NUM> has a configuration of a synchronous machine connected to a power system via a parallel circuit of the power converter <NUM> and the bypass line <NUM> including the circuit breaker <NUM>, the power generation motor device <NUM> may be a single machine such as a synchronous power generator and a synchronous motor, or may be a power generator motor that performs both power generation and pumping. In the present invention, such machines are collectively referred to as a power generation motor device (a power generation motor).

Although details will be described later, a step-out estimation control of the power system <NUM> according to the present invention can be applied to any mode of a power generation motor operation. In short, the step-out estimation control can be applied as long as the power generation motor device <NUM> is in a direct connection state in which the power generation motor device <NUM> is connected to a power system via the bypass line <NUM> including the circuit breaker <NUM>.

A power generation operation mode will be described as an example, and the power converter <NUM> includes a first converter that converts the power generation output Pg from AC to DC and a second converter that converts DC power to AC power of a commercial frequency. A two-level, three-level, or multi-level converter can be used for each converter. The power converter <NUM> has a frequency conversion function, and the frequency conversion function enables the power converter <NUM> to shift from a low-speed rotation range to a high-speed rotation range in a pumped storage power generation operation using a synchronous power generation motor.

The bypass line <NUM> is a line for directly connecting the power generation motor device <NUM> to the power system <NUM> via the transformer <NUM>. The bypass line is opened and closed by the circuit breaker <NUM>. After the synchronous power generation motor is started up, the synchronous power generation motor is disconnected from a power converter <NUM> side and shifted to a connection with a bypass line <NUM> side, and the synchronous power generation motor can be operated at high efficiency by using a direct connection operation.

The control device <NUM> includes a step-out estimation unit <NUM> that estimates whether the power generation motor device <NUM> steps out based on power of the power generation motor device <NUM> (the power generation output Pg during a power generation operation and the pumping input Pg during a motor operation) and an AC voltage Vac at an interconnection point where the variable speed pumped storage power generation device is interconnected to a power system or the like, and that calculates a start-up command Str of the power converter <NUM>, a bypass line opening determination unit <NUM> that calculates an opening or closing command SWoc of the circuit breaker <NUM> based on a current Ib of the bypass line <NUM> and the start-up command Str, and a converter control unit <NUM> that controls power Pc of the power converter <NUM>.

Next, a flow of a calculation process in the step-out estimation unit <NUM> will be described with reference to <FIG>. Here, it is assumed that the power generation motor device <NUM> shown in <FIG> is connected to a power system via the bypass line <NUM> and is in a so-called direct connection operation state. Since the following concept is exactly the same during a power generation operation and a motor operation, the power generation output Pg during the power generation operation will be described as a representative example of the power of the power generation motor device <NUM> in the following description.

In a process of step S1 shown in <FIG>, it is determined whether a system fault occurs based on whether the AC voltage Vac is lower than a first threshold Vac1. When it is detected that a system fault occurs, the calculation process proceeds to a process of step S2, and when it is detected that no system fault occurs, the calculation process is ended. In subsequent processes shown in <FIG>, when a system fault occurs and a voltage drop occurs, it is estimated whether this influence develops to a later stage in which the power system steps out. When the power system may step out, an early countermeasure will be taken using the power converter <NUM>.

In the process of step S2, a step-out determination threshold Eth is calculated in accordance with power Pg0 of the power generation motor device <NUM> and an AC voltage Vac0 immediately before the system fault, the step-out determination threshold Eth being a threshold for determining whether the power system steps out. A method of calculating the step-out determination threshold Eth will be described later with reference to <FIG>.

In a process of step S3, a step-out determination value E is calculated by integrating a difference between the AC voltage Vac0 immediately before the system fault and an AC voltage Vac at a current time. Here, the step-out determination value E can be regarded as a value obtained by integrating a difference between a mechanical input and output and an electrical input and output applied to the power generation motor device <NUM> during a fault continuation period after the occurrence of the fault. It can be said that the power system is likely to step out as the step-out determination value E increases.

In a process of step S4, the step-out determination value E is compared with the step-out determination threshold Eth, and when the step-out determination value E exceeds the step-out determination threshold Eth, it is determined that the power generation motor device <NUM> will step out later. In a process of step S5, the start-up command Str of the power converter is set to <NUM> to start up the power converter <NUM>. When the step-out determination value E is lower than the step-out determination threshold Eth, the calculation process proceeds to step S6.

In a process of step S6, it is determined whether the system fault is troubleshot based on whether the AC voltage Vac exceeds a second threshold Vac2. When it is determined that the system fault is not troubleshot, the calculation process returns to the process of step S3 and the step-out estimation process of the power generation motor device is continued. When it is determined that the system fault is troubleshot, the calculation process proceeds to a process of step S7, and the start-up command Str of the power converter is set to <NUM>, that is, the power converter is maintained in a stopped state, and the calculation process is ended. It is possible to prevent unnecessary operation switching between the bypass operation and the converter operation by using a step-out estimation method of the power generation motor device described above.

According to the series of processes described above, a comparison process between the step-out determination value E and the step-out determination threshold Eth is performed during the fault continuation period which is a period from when the fault occurs up to when the fault is troubleshot. As a result, it is possible to appropriately evaluate an influence on step-out according to the magnitude of the fault (the magnitude of a voltage drop) and the fault duration period.

A method of calculating the step-out determination threshold Eth in the process of step S2 will be described with reference to <FIG>.

In the process of step S2, the step-out determination threshold Eth is calculated using a table as shown in the drawing in accordance with the power Pg0 of the power generation motor device <NUM> and the AC voltage Vac0 immediately before the system fault. As the power Pg0 of the power generation motor device <NUM> decreases, the step-out determination threshold Eth is set to a larger value. In a case where the power Pg0 of the power generation motor device <NUM> is maintained at the same value, the step-out determination threshold Eth is set to a smaller value as the AC voltage Vac0 decreases.

<FIG> is a block diagram showing the bypass line opening determination unit <NUM>. A comparator 102a determines whether the current Ib of the bypass line is lower than a threshold Ibmin. The comparator 102a outputs <NUM> when the current Ib is lower than the threshold Ibmin, and outputs <NUM> when the current Ib is not lower than the threshold Ibmin.

An opening or closing command SWoc of the circuit breaker outputs <NUM> (a circuit breaker opening command) when the start-up command Str of the power converter described above in an AND logic circuit 102b is <NUM> (the power converter is in a start-up state) and the current Ib of the bypass line is lower than the threshold Ibmin. As a result, an operation of the power generation motor device <NUM> shifts from the bypass operation to the converter operation.

Next, a waveform example when a fault occurs in accordance with whether the present invention is applied will be described with reference to <FIG> and <FIG>. <FIG> is a waveform example when there is a system fault in a case where the bypass operation is continued without applying the present invention. <FIG> shows a case where the bypass operation is switched to the converter operation. The waveform indicates a system voltage Vac, the power Pg and a rotational speed N of the power generation motor device <NUM>, the power Pc and the start-up command Str of the power converter, the current Ib of the bypass line, and the opening or closing command SWoc of the circuit breaker from the top. A fault condition is a condition under which a three-phase equilibrium fault occurs in an AC system at a time t1 and the fault is troubleshot at a time t2 in both <FIG> and <FIG>.

When the bypass operation shown in <FIG> is continued, it is shown that the rotational speed N of the power generation motor device <NUM> greatly deviates from <NUM> [pu] of a synchronous speed after the system fault is troubleshot, the power generation motor device <NUM> steps out, and the device is stopped.

On the other hand, <FIG> shows a case where it is determined that the power generation motor device <NUM> steps out at a time t3 before the time t2 when the fault is troubleshot, the power converter <NUM> starts up, and the circuit breaker <NUM> of the bypass line <NUM> is opened at a time t4.

Since an electric torque of the power generation motor device <NUM> can be controlled by the power converter <NUM> by switching an operation mode from the bypass operation to the converter operation, an increase in the rotational speed of the power generation motor device <NUM> is prevented. A transiently increased rotational speed can be adjusted by a governor control of the power generation motor device <NUM> or a power control of the power converter <NUM>.

In this manner, it is possible to avoid step-out of the power generation motor device <NUM> when a system fault occurs during the bypass operation according to the first embodiment of the present invention. As a result, an operation tolerance of the variable speed pumped storage power generation device can be improved, and it is possible to increase the degree of contribution to a stable operation of a power system of the device.

Although the first embodiment exhibits an effect in the case of a power generation operation, the present invention can also be applied to a pumping operation.

In a second embodiment, another method of calculating the step-out determination threshold Eth will be described. In the first embodiment, the step-out determination threshold Eth is calculated based on the power Pg0 of the power generation motor device <NUM> and the AC voltage Vac0 immediately before the system fault, while in the second embodiment, an AC voltage VacO' immediately after the system fault may be used instead of the AC voltage Vac0 immediately before the system fault, as shown in <FIG>. In this case as well, as the power Pg0 of the power generation motor device <NUM> decreases, the step-out determination threshold Eth is set to a larger value.

Claim 1:
A synchronous machine device in which a power generation motor device (<NUM>) is connected to a power system (<NUM>) via a parallel circuit of a power converter (<NUM>) and a bypass line (<NUM>) including a circuit breaker (<NUM>), the synchronous machine device characterized by:
an estimation unit (<NUM>) configured to estimate whether the power generation motor device (<NUM>) steps out based on power of the power generation motor device (<NUM>) and a system voltage when a system fault occurs in a state in which the power generation motor device (<NUM>) is directly connected to the power system (<NUM>) via the parallel circuit and the power converter (<NUM>) is stopped; and
a control device (<NUM>) that includes a control unit (<NUM>) configured to control to start up the power converter (<NUM>) when it is estimated that the power generation motor device (<NUM>) steps out and to control the electric torque of the power generation motor device (<NUM>) based on the controlled power converter (<NUM>) in order to prevent the step out.