JPH0515137B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is directed to converting alternating current power between a power plant consisting of a plurality of generators or an alternating current system including power plants into direct current power using an AC/DC converter. Synchronous combination when switching from a state in which direct current is being transmitted solely on the transmission line to AC/DC parallel power transmission by interconnecting the AC transmission line between the AC side ends of the AC/DC converter or interconnecting the AC transmission line via a disconnector. Regarding how to enter.

[Technical background of the invention and its problems]

The construction of large-capacity power plants is progressing in line with the expansion of electricity demand, but due to constraints such as location conditions, they must be constructed in areas far from the load side, and long-distance, high-power There is a need to transmit electricity. However, when such long-distance and high-power transmission is carried out using conventional AC transmission systems,
It is well known that system stability is a problem.

Therefore, as a power transmission method that solves this stability problem, high-power DC power transmission that applies high reliability, high voltage resistance, and large current thyristor elements using semiconductor technology, which has made remarkable progress in recent years, has been attracting attention. . By applying this DC power transmission technology, it becomes possible to transmit large amounts of power over long distances as described above, but the initial load control when a generator is connected to the grid becomes complicated when transmitting DC power alone. BACKGROUND OF THE INVENTION Due to various system configuration conditions such as eliminating the need for frequency control when generators are under low load, it has become necessary to install both a DC power transmission system and an AC power transmission system to transmit large amounts of power over long distances. When transmitting large amounts of power over long distances using such DC and AC transmission systems (hereinafter referred to as AC/DC parallel transmission systems), AC power from a power plant is converted to DC power at an AC/DC converter station, and then the DC power is transmitted. There is a process of transitioning from a state in which DC power is being transmitted solely through electric wires to AC/DC parallel power transmission by connecting AC power lines to the power plant side end of the AC/DC converter station using interconnections or disconnectors.

In the process of shifting to AC/DC/parallel power transmission, it is necessary to synchronize the frequency and voltage phase of the power plant with the frequency and voltage phase of the AC transmission line, and then turn on the interconnector or disconnector. in this case,
In a power plant consisting of multiple generators, even if the frequency and voltage phase of one generator are changed, the change in the frequency and voltage phase of the entire power plant is small, so the frequency on the AC transmission line side, It took a long time to synchronize to the voltage phase. In particular, if the power plant and the AC/DC converter station are installed far apart,
The time required for the synchronization was longer.

[Purpose of the invention]

The present invention was made based on the above circumstances, and
The purpose of this is to change the frequency and voltage phase period of the AC side of the AC/DC converter and the AC transmission line side in a short time in the state of DC single power transmission,
The object of the present invention is to provide a synchronous merging method that allows easy transition to AC/DC parallel power transmission.

[Summary of the invention]

In the synchronous joining method according to the present invention, the AC/DC converter is controlled so that the frequency at the AC side end of the AC/DC converter matches the frequency on the AC power transmission line side, and furthermore, a predetermined amount of electricity on the DC power transmission line side, that is, The above object is achieved by controlling the AC/DC converter so that the voltage phase at the AC side end of the AC/DC converter matches the voltage phase at the AC wire side due to minute changes in power, voltage, or current.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an example of a system configuration in which AC power generated by a power plant having a plurality of generators can be transmitted in AC/DC parallel to an AC load system. 1st
In the figure, PS is a plurality of generators G ₁ , G ₂ , ...,
It is a power plant with G _o . The output of each generator G ₁ , G ₂ , ..., G _o of this power plant PS is the output of the transformer T ₁ ,
The voltage is boosted by T ₂ , ..., T _o and the power plant AC bus
It is summarized in AB ₁ . AC power from the power station PS is transmitted from the power station AC bus line AB ₁ to the conversion station AC bus line AB ₂ of the AC/DC conversion station CS via the AC transmission line AL ₁ . At the AC/DC converter station CS, a part of the AC power from the power station PS is transmitted from the converter station's AC bus line AB ₂ to the substation SS via the interconnector, disconnector CB, and AC transmission line AL ₂ . The remainder of the above AC power is converted to DC power from the converter station AC bus AB ₂ by the AC/DC converter CONV, which is composed of a converter transformer T _cpov , an AC/DC converter V, and a DC reactor DCR, and is then transmitted via the DC transmission line DL. The power is being transmitted to the orthogonal converter station CR, which is in reverse conversion operation. In this orthogonal conversion station CR, the DC power is converted into AC power by the orthogonal conversion device INV, and is supplied to the AC load A together with the AC power from the AC power transmission line AL ₂ mentioned above.

In Figure 1, PT ₁ and PT ₂ are AC power transmission lines.
AL ₂ is a transformer installed on the AC bus line AB ₂ of the converter station, and outputs detection signals a and b, respectively. Also CT ₁ ,
CT ₂ is a current transformer installed on the AC side and DC side of the AC/DC converter CONV, and receives detection signals c and d, respectively.
Output.

Next, with reference to FIG. 2, the procedure for transitioning from DC independent power transmission to AC/DC parallel power transmission will be described. FIG. 2 shows a control device for the AC/DC converter V in a block diagram. In FIG. 2, Fref is a reference frequency setting circuit that outputs a reference frequency setting signal fref for setting the reference frequency of the AC/DC converter V. FC ₁ is based on the detection signal a from the transformer PT ₁ installed on the AC transmission line AL ₂ in FIG.
This is a frequency converter that outputs a frequency detection signal fc ₁ on the AC power transmission line AL ₂ side.

FC ₂ is a frequency converter that outputs a frequency detection signal fc ₂ on the converter station AC bus AB ₂ side based on the detection signal b from the transformer PT ₂ provided on the converter station AC bus AB ₂ in FIG. .

The reference frequency setting signal fref from the reference frequency setter Fref and the frequency detection signal fc ₁ from the frequency converter FC ₁ are switched and outputted by a switching mechanism S,
It is compared with the frequency detection signal fc ₂ from the frequency converter FC ₂ by the comparator COM1, and the deviation output Δf from the comparator COM1 is sent to the integrator I.

P is a power detector that outputs a power detection signal P on the converter station AC bus AB ₂ side based on the detection signal b from the transformer PT ₂ and the detection signal c from the current transformer CT ₁ .

In order to adjust the voltage phase on the conversion station AC bus AB ₂ side, BV is set on the condition that the switching mechanism S is operated to switch to the reference frequency setter Fref side.
This is a power control signal generation circuit that outputs a power control signal Δpdv to a constant power control circuit APR that adjusts power on the DL side of the DC transmission line. In the constant power control circuit APR, the power command signal PDP from the integrating circuit I is
Power detection signal p from power detector P via SW
and the power control signal Δpdv from the power control signal generation circuit BV in the comparator COM2, and outputs the power control signal idp for controlling the power on the DC transmission line DL side based on the deviation signal. This power control signal idp is sent to the constant current control circuit ACR. In this constant power flow control circuit ACR, the detection signal d from the current transformer _CT2 provided in the DC transmission line DL and the power control signal idp are combined with the comparator COM3.
A phase control signal phc for performing constant current control is sent to a phase control circuit (not shown) using the deviation signal.

Next, specific control during direct current power transmission will be explained with reference to FIG. 2. First, operate the switching mechanism S to compare the reference frequency setting signal fref and the frequency detection signal fc ₂ on the AC bus AB ₂ side of the converter.
Compare on COM1. At this time, the power control signal generation circuit BV does not operate due to the operation of the switching mechanism S. Deviation signal Δf ₁ = fc ₂ − at the above comparator COM1
fref is given to the integration circuit I to perform integration processing. From the integrating circuit I, the power command signal pdp ₁ =K∫Δf ₁ dt=
K∫(fc ₂ −fref)dt (K is a constant) is a constant power control circuit
APR and the power detection signal p from the power detector P controls a constant power control circuit APR, a constant current control circuit ACR, and a phase control circuit (not shown) to control the output frequency of the power station PS, that is, the AC bus line AB of the converter station. The output power of the power plant PS is controlled by matching the frequency on _{the second} side with the reference frequency. In order to simplify the explanation, the power loss in the AC power transmission line AL ₁ between the power station PS and the AC/DC converter station CS will be ignored. The switch SW is used to switch from the power command signal PDP during direct current transmission to the power command signal PDP' during AC/DC parallel power transmission.

Next, control at the time of transition from DC independent power transmission to AC/DC parallel power transmission will be explained with reference to FIG. 2. First, by operating the switching mechanism S, the frequency detection signal fc ₁ on the AC transmission line AL ₁ side and the frequency detection signal fc ₂ on the AC bus line AB ₂ side of the converter station are compared by the comparator COM1, and a deviation signal Δf ₂ is obtained. =fc ₂ -fc ₁ is sent to the integrating circuit I.
Based on this deviation signal Δf ₂ , the power command signal pdp ₂ =K∫Δf ₂ dt=K∫(fc ₂ −fc ₁ )dt (K is a constant) is given from the integrating circuit I to the constant power control circuit APR, and the power A constant power control circuit APR, a constant current control circuit ACR, and a phase control circuit (not shown) are controlled by the power detection signal p from the detector P, and the output frequency of the power station PS, that is, the frequency on the converter station AC bus AB ₂ side, is Control to match the frequency of AC power transmission line AL ₂ side.

Generally, the power receiving system capacity is larger than the capacity of the power station PS, so the frequency on the power station PS side is controlled to match the frequency on the AC power transmission line _AL2 side.

Next, by operating the switching mechanism S, the power control signal generating circuit BV is activated after a certain period of time. The power control signal Δpdv is output from the power control signal generation circuit BV and added to the input of the constant power control circuit APR. According to this power control signal Δpdv, the DC power in the DC power transmission line DL changes slightly, and the frequency on the converter station AC bus AB ₂ side changes very slightly and slowly. Therefore, the voltage phase on the converter AC bus line AB ₂ side and the voltage phase on the AC power transmission line AL ₂ side can be matched.

AC bus line AB ₂ side of the converter station mentioned above and AC transmission line
After synchronizing the frequency and voltage phase with the AL ₂ side,
A synchronization detection circuit as shown in Fig. 3 performs synchronization judgment, and the interconnector/disconnector CB shown in Fig. 1 is turned on to shift to AC/DC parallel power transmission.

In Fig. 3, ΔF is the detection signal a of transformer PT ₁ on the AC transmission line AL ₂ side and the AC bus line of the converter station.
Using the detection signal b of transformer P ₂ on the AB ₂ side as input,
This is a frequency deviation detector that detects the frequency deviation of the AC power transmission line AL ₂ and the converter station AC bus AB ₂ . LD1
is a level detector that outputs a signal when the frequency deviation output from the frequency deviation detector ΔF becomes equal to or less than a predetermined value. ΔPH is a voltage phase deviation detector that receives the detection signal a of the transformer PT ₁ and the detection signal b of the transformer PT ₂ as input and detects the voltage phase deviation of the AC power transmission line AL ₂ and the converter station AC bus AB ₂ . . LD2 is a level detector that outputs a signal when the voltage phase deviation output from the voltage phase deviation detector ΔPH becomes equal to or less than a predetermined value. The signal outputs of the level detectors LD1 and LD2 are combined with the operation signal s of the switching mechanism S in FIG.
Entered into AND. When the input signal satisfies the AND condition, the AND gate AND outputs a signal output m as a command to close the connection or disconnection CB in FIG. 1.

Next, referring to FIG. 4, the operating procedure shown in FIGS. 1 to 3 will be explained along with the passage of time t. In Figure 4, at time t ₁ , the DC transmission line DL
The DC power at the converter station will increase, and the AC bus
AB ₂ side frequency fc〓 ₂ is the frequency of AC transmission line AL ₂ side
fc〓 is in a state higher than ₁ . At this time, the switching mechanism S
When , the DC power increases and the frequency fc〓 ₂ on the AC bus line AB ₂ of the converter station gradually decreases. At time t ₂ , which has elapsed from time t ₁ to T ₁ hour, the frequency fc 〓 ₂ on the AC bus AB ₂ side of the converter station and the AC transmission line
The frequencies fc〓 ₁ on the AL ₂ side match, and at this time the level detector LD ₁ outputs a signal. Further time from time t ₂
At time t ₃ after T ₂ , the frequency fc 〓 ₂ on the converter station AC bus AB ₂ side changes slightly, but the voltage phase between the converter station AC bus AB ₂ side and the AC transmission line AL ₂ side changes slightly. match, and the level detector LD ₂ outputs a signal. At this time _t3 , the AND gate AND satisfies the AND condition, and the signal output m connects the connection or turns on the disconnector CB.

As described above, in this embodiment, after matching the frequencies of the AC power transmission line AL ₂ side on the AC bus line AB ₂ side of the converter station, the voltage phases are matched to establish synchronization conditions, and interconnection is established using this synchronization condition. or insert a disconnector CB,
It is possible to easily and quickly shift from DC single power transmission to AC/DC parallel power transmission.

Note that the present invention is not limited to the above embodiments. That is, even if the output of the power control signal generation circuit BV is added to the constant current control circuit ACR as shown in FIG. 5, the same effect as in the above embodiment can be obtained. The same effect can also be obtained by applying the output of the power control signal generation circuit BV to the voltage setting input of a converter operated under constant voltage control.

Furthermore, even if the output signal of the power control signal generation circuit BV is applied to the power detection amount feedback loop of the constant power control circuit APR or the current detection amount feedback loop of the constant current control circuit ACR,
Needless to say, similar effects can be obtained.

Moreover, in FIG. 1, a plurality of generators G ₁ , G ₂ ,
The power plant PS consisting of _... , _G It is applicable even if AL ₁ is the same as the converter station AC bus AB ₂ . Furthermore, it is also applicable to AC/DC parallel power transmission in a multi-terminal DC transmission system.

〔Effect of the invention〕

As described above, according to the present invention, the frequency of the AC side end of the AC/DC converter is matched to the frequency of the AC transmission line side between power plants having multiple generators or power systems including power plants. The AC/DC converter is controlled so that the voltage phase at the AC side end of the AC/DC converter matches the voltage phase at the AC power line side due to minute changes in a predetermined amount of electricity on the DC power line side. As a result, the frequency and voltage phase of the AC side of the AC/DC converter and the AC transmission line side can be synchronized in a short time in the state of single DC power transmission, making it easy to shift to AC/DC parallel power transmission. A method of synchronous merging that can be performed can be provided.

[Brief explanation of the drawing]

FIG. 1 is a system configuration diagram showing an example of the configuration of a power system to which the present invention is applied; FIGS. 2 and 3 are block diagrams for explaining an embodiment of the synchronous merging method according to the present invention; FIG. 4 is a diagram for explaining the operation of the same embodiment, and FIG. 5 is a diagram for explaining another embodiment of the present invention. G ₁ , G ₂ , ..., G _o ... Generator, PS ... Power plant, T ₁ , T ₂ , ..., T _o ... Transformer, AB ₁ ... Power plant AC bus, AL ₁ , AL ₂ ……AC transmission line, CS
...AC/DC converter station, AB ₂ ...Converter station AC bus, CB
...grid connection and disconnection, SS...substation, Tconv...
Converter transformer, V...AC/DC converter, DCR...
DC reactor, CONV……AC/DC converter, DL
...DC transmission line, CR...orthogonal converter station, INV...
Orthogonal transformation device, A...AC load, PT ₁ , PT ₂ ...
Transformer, CT ₁ , CT ₂ ... Current transformer, Fref ... Reference frequency setting circuit, FC ₁ ... Frequency converter, FC ₂ ...
Frequency converter, S...Switching mechanism, COM1, COM
2, COM3...Comparator, I...Integrator circuit, P...
...Power detector, BV...Power control signal generation circuit,
SW...Switch, APR...Constant current control circuit,
ACR: Constant current control circuit, AF: Frequency deviation detection circuit, ΔPH: Voltage phase difference detection circuit, LD1,
LD2...Level detection circuit, AND...And gate.

Claims (1)

[Scope of Claims] 1. From a state in which AC power in one power system including a power plant is converted to DC power by an AC/DC converter and solely transmitted as DC power to another power system via a DC transmission line, A method of synchronously joining the interconnector or disconnector at the AC side end of the converter when interconnecting the power systems with an AC transmission line and transitioning to AC/DC parallel power transmission. At that time, a value obtained by integrating the deviation value between the frequency of the AC side end of the AC/DC converter and the frequency of the AC power transmission line is added as a correction amount to the power command value of the AC/DC converter, and The frequency of the AC side end is controlled to match the frequency of the AC power transmission line, and then a minute power setting value is further added to the power command value, so that the voltage phase of the AC side end of the AC/DC converter and the AC Control is performed so that the phase difference with the voltage phase of the power transmission line is zero, and the frequency and voltage phase of the AC side end of the AC/DC converter are synchronized with the frequency and voltage potential of the AC power transmission line to achieve the interconnection. A synchronous merging method characterized by turning on a power cutter.