Hitachi, Ltd.

Hiroo Konishi

Masahiro Watanabe

Masahiko Amano

Tomoharu Nakamura

Yasuo Matsuda

Shinya Tanifuji

Junzo Kawakami

Hisao Amano

Hironari Kawazoe

Tadao Kawai

Yukio Tokiwa

Tatsuhito Nakajima

Kiyoshi Goto

Takeichi Sakurai

Masashi Nishimura

In a power system wherein a plurality of power plants, load systems and power transmission components are connected to each other for increasing the power transmission capacity of the power system, the power system is stabilized and power swings are suppressed, by controlling a semiconductor switch used in a power system stabilizing apparatus which is provided at the power system in an applying manner adequately corresponding to its operation characteristics and function, in accordance with a stabilizing command signal generated by using state values (for example, voltage, current, power, frequency, phase angle) of the power system, detected by detecting circuits provided in the power system.

Apparatus for monitoring and stabilizing power swing in a power system

A system information input means takes in system information and a system state determining means determines states of the system. A component operation state determination means determines operation states of system stabilizing components. A control plan deciding means decides a control plan of the system in consideration of operation states of the system and the system stabilizing components. In deciding the control plan, a swing mode analyzing means firstly analyzes the swing mode at each place of the system on the basis of waveforms of time domain response simulations. Then, a control allotment setting means determines control allotment for each of the system stabilizing components based on the mode analysis and a control parameter setting means control sets the control parameters of each of the system stabilizing components. If plural control plans are obtained, the optimal one is selected based on eigenvalues of dynamics of the system or by evaluating time domain system responses by simulation method. The decided control plan is output to the system stabilizing components by a control plan output means.

Electric power system stabilization control apparatus and method thereof

A high voltage dc transmission system uses equipment of self-commutated converters each of which comprises switching devices with a self-commutating (gate-turn-off) function. A first control equipment associated with the rectifier comprises a constant reactive power (var) control circuit for holding constant the reactive power on the input side of the rectifier, and a constant dc voltage control circuit for holding constant the dc system voltage on the output side thereof. A second control equipment associated with the inverter comprises a constant reactive power control circuit for holding constant the reactive power on the output side of the inverter, and a constant active power control circuit for holding constant the active power on the output side thereof. The first control equipment and the second control equipment each have a current control circuit for making independent control of each component of a two-phase current resulted from transformation of a three-phase ac current.

Control equipment for high voltage direct current transmission system

A power conversion system for converting between a.c. and d.c. power has a pair of line commutated converters connected in series, and each is connected to a corresponding transformer, one of which transformers is YY connected and the other of which is Y.DELTA. connected. A pair of minimum voltage detectors generate minimum voltage signals, a first one of the minimum voltage signals being YY related and a second one of the minimum voltage signals being Y.DELTA. related. The power conversion system has a control circuit which generate two phase control signals for controlling the pair of line commutated converters respectively. When a fault occurs in a.c. or d.c. apparatus connected to the power conversion system, the control circuit generates the phase control signals on the basis of the first and second minimum voltage signals respectively. In this way, each of the line commutated converters are controlled by an independent signal, so that the power conversion of each is optimized.

Power conversion system, and a method of power conversion using such a

An AC system having, for example, a voltage source, an inductance and a load has connected thereto an apparatus for controlling the phase and amplitude of the voltage of the system. The instantaneous current and voltage in the AC electrical system are measured and power measurements derived therefrom. The power measurements may be instantaneous real and imaginary power, instantaneous active and reactive power, or active and reactive power averaged over less than one cycle. The power measurements are then used to derive phase related control values, on the basis of which control signals are generated to a converter. The action of the converter in accordance with the control signals thus controls the amplitude and phase of the voltage. By use of power measurements, it is not necessary to measure the phase of the voltage of the AC system.

Method and apparatus for controlling the output voltage of an AC

A reactive power compensator for an electric power system includes a voltage control circuit which amplifies a differential voltage between the potential command value and a potential signal corresponding to the voltage of the electric power system detected by a potential detector. The voltage control circuit outputs a reactive power compensation control signal. The control signal is fed to a reactive power output circuit which controls the voltage of the power system in order to compensate for reactive power in the power system. A gain calculation circuit is provided for setting the gain of the voltage control circuit to a value proportional to the level of short-circuit capacity of the system power on the system power supply side of the reactive power output circuit.

Reactive power compensator for electric power system

Two rectifiers and two inverters are operated under the state under which they are connected in parallel by common transmission lines. These rectifiers and inverters are controlled an independent control apparatus respectively which can selectively apply either the constant current control or the constant voltage control. The control apparatus of each converter has bestowed thereon the reference value of a current to flow through the particular converter and the reference value of a terminal voltage of the particular converter. A signal for lowering the current reference value is added to the control apparatus of one or all of the converters which are to be operated as the inverters. On the other hand, a signal for essentially rendering the terminal voltage of the converter smaller than the voltage reference value is added to the control apparatus of the converter which is to be operated as the converter for determining the voltage of a direct current system.

Converter control apparatus for parallel connected multi-terminal direct

A DC power transmission control system for a DC line inserted between a pair of converters comprises a transformer provided on the AC side of each of the converters for maintaining constant the no-load voltage on the converter side by tap position control. One of the converters is operated as an inverter for control of the DC voltage. The control angle of the converter operated as the inverter is controlled by a signal associated with, e.g., a DC current as a load. The DC terminal voltages of the converters are made variable, thus reducing the amount of increase in the reactive power of the rectifier under a small load condition.

DC Transmission control system

A pair of thyristor converters are connected by a DC power transmission line, and their AC terminals are connected through tapped transformers to AC systems respectively. The output signal of a constant-current circuit in a converter control unit associated with the forward converter is selected to control the gate of the forward converter, while the output signal of a constant-voltage circuit in a converter control unit associated with the reverse converter is selected to control the gate of the reverse converter. When the reactive power is to be controlled, a reactive power signal is applied for the gate control. A voltage limit indication circuit in each control unit receives the AC terminal voltage e.sub.2 of the transformer and the DC current I.sub.d so as to increase the control angle limit with a decrease in the values of e.sub.2 and I.sub.d. When the control advance angle or control delay angle determined by the output signals of the control circuits is larger than the control angle limit, this angle is limited to the control angle limit. When the reactive power is to be controlled, the tap position of either transformer is lowered to decrease e.sub.2 and to increase the control angle limit thereby widening the controllable range of the reactive power. During the start-stop stage or during the protective operation, the output of the voltage limit indication circuit in each control unit is inhibited to permit free variations of the control angle.

DC Power transmission control

A HVDC system has two converter stations, each of which has two converters connected in cascade to operate as a rectifier or an inverter and the stations are connected through a d.c. power transmission line to each other and are connected to respective a.c. power sources through the a.c. power transmission lines. Each converter is controlled depending on the difference between a current reference for the HVDC system and an actual current flowing in the HVDC system when the converter operates as a rectifier, and controlled depending on the output of the constant margin angle control circuit when the converter operates as an inverter. When the converter operation condition is changed, i.e. another converter operates in addition to the converters in operation or the direction of power transmission in the HVDC system is changed, the current reference for the HVDC system is reduced depending on the d.c. voltage during a predetermined period.

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Katsuta, Japan

Hiroo Konishi