JPS6353773B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power conversion device that controls the amount of power flow between two different power systems.

Japan's power system can be broadly divided into the 60Hz system in western Japan and the 50Hz system in eastern Japan.

Devices that connect these two power systems and control the amount of power between the systems include rotary frequency exchangers using induction motors and static frequency converters using mercury rectifiers. recently,
Static frequency converters using semiconductor-controlled rectifiers such as thyristors in place of mercury rectifiers have been put into practical use.

Furthermore, within the 50Hz system, there are various power systems managed by several power companies, and their voltage ratings and equipment capacities vary. In order to effectively connect these power systems and control the amount of power flow between the systems, power converters that convert from alternating current to direct current to alternating current are used. In particular, devices with long DC power lines are well known as power converters for DC power transmission.

FIG. 1 is a block diagram showing the configuration of a conventional power conversion device. This shows the case where a 50Hz system and a 60Hz system are connected and the power flow rate between the two systems is controlled.

In Figure 1, BUS ₁ is the 3-phase power line of the 50Hz power system, BUS ₂ is the 3-phase power line of the 60Hz power system,
TR ₁ and TR ₂ are power transformers, SS ₁ and SS ₂ are AC/DC power converters consisting of thyristor bridge circuits, and L ₀
is a DC reactor, CAP ₁ and CAP ₂ are phase advancing capacitors that also serve as high frequency filters, and SVC ₁ and SVC ₂ are reactive power compensators.

The reactive power compensator SVC ₁ is a power transformer TR ₃ ,
It is composed of a thyristor rectifier circuit SS ₃ and a DC reactor L ₁ , and a reactive power control circuit AQR ₁ controls the DC reactor L so that the reactive power Q ₁ at the receiving end becomes equal to the command value Q ₁ 〓 (=0). Current flowing through ₁
I _L1 is controlled. The reactive power compensator SVC ₂ is similarly configured, and the current I _L2 is controlled by the reactive power control circuit AQR ₂ so that the reactive power Q ₂ at the receiving end becomes equal to the command value Q ² 〓 (=0). be done.

First, the operation of this device will be explained using as an example the case where power is sent from the electric line BUS ₁ of the 50 Hz system to the electric line BUS ₂ of the 60 Hz system.

A current detector CT _s1 and a voltage detector PT _s1 are installed at the receiving end of the power line BUS ₁ to detect the instantaneous values of three-phase voltage and current. This is input to the next active reactive power calculation circuit PQC ₁ to obtain active power P ₁ and reactive power Q ₁ . Similarly, a current detector CT _s2 and a voltage detector PT _s2 are installed at the power receiving end from the electric line BUS ₂ , and together with the active reactive power calculation circuit PQC ₂ ,
Detect active power P ₂ and reactive power Q ₂ .

Active power P ₁ is positive in the incoming direction, active power
P ₂ detects the exit direction as positive. Also,
For reactive powers Q ₁ and Q ₂ , delayed reactive power is detected as positive, and advanced reactive power is detected as negative.

When transmitting power from the electric line BUS ₁ to the electric line BUS ₂ , the AC/DC power converter SS ₁ operates as a forward converter, and the AC/DC power converter SS ₂ operates as an inverse converter.

Power command value P〓 by power flow setting device VRP
>0 is given. The Schmitt circuit SH generates an output signal "1" when the power command value P>0, and connects the switch SW ₁ to the a side and the switch SW ₂ to the b side. That is, the output voltage V ₁ of the forward converter SS ₁ is controlled so that the power flow amount P = (P ₁ + P ₂ )/2 is equal to its command value P〓, and the output voltage of the inverse converter SS ₂ is V ₂ is controlled to generate a constant DC voltage V 〓.

CT ₀ is a DC current detector that detects current I ₀ flowing through DC reactor L ₀ . _The power control circuit APR calculates the average value _{(P 1 +}
The DC current I ₀ is controlled so that P ₂ )/2 becomes equal to the command value P〓.

Further, the constant voltage control circuit AVR controls the output voltage _V2 of the inverse converter _SS2 to a constant value V〓. PH ₁ and PH ₂ are each AC/DC power converters
This is a phase control circuit for SS ₁ and SS ₂ .

When the output voltages of the AC/DC power converters SS ₁ and SS ₂ are taken in the direction of the arrow in the figure, V ₁ = k _v · V _s1 · cos α ₁ V ₂ = −k _v · V _s2 · cos α ₂ . However, k _v is a conversion constant, and V _s1 and V _s2 are AC side input voltages of AC/DC power converters SS ₁ and SS ₂ , respectively.

The firing control angle α ₁ of the forward converter SS ₁ is controlled in the range from 0° to 90°, and the firing control angle α ₂ of the inverse converter SS ₂ is controlled in the range from 90° to
Set to a range of 180°. When the firing control angle α ₂ = 180°, the input power factor on the AC side of the inverter SS ₂ is 1, but it is necessary to shift the firing timing by the commutation advance angle γ to perform natural commutation. . Therefore, the firing control angle α ₂ =180°−γ, and V ₂ =−k _v・V _s2・cos
Generates an output voltage of (180°-γ). If the commutation advance angle γ is constant, the output voltage V ₂ will also be a constant DC voltage.

The DC current _I0 is controlled by changing the voltage _V1 - _V2 applied to the DC reactor _L0 . Since the output voltage V ₂ is controlled to be constant, V ₁ = k _v・
It is controlled by changing V _s1・cos α ₁ . If you want to increase the DC current I ₀ , control the ignition control angle α ₁ so that V ₁ > V ₂ , and if you want to decrease the DC current I ₀ , control the ignition control angle α 1 so that V ₁ < V ₂ . Control the ignition control angle α ₁ to Near the stationary point, if the resistance of the DC reactor L ₀ is ignored, the relationship V ₁ ≒ V ₂ holds true, and cos α ₁ ≒ −cos α ₂ makes α ₁ ≒ γ.

Figure 2 a and b are from the electric line BUS ₁ of the 50Hz system.
It is a voltage-current vector diagram for one phase on the AC input side of each AC/DC power converter when power is being sent to electric line BUS ₂ of the 60Hz system. FIG. 2a shows a voltage-current vector diagram of the converter SS ₁ , and FIG. 2b shows a voltage-current vector diagram of the converter SS ₂ .

Considering a steady state with a direct current I ₀ , V ₁ ≒V ₂ and the relationship α ₁ ≒γ holds. forward converter
The input current I _ss1 of SS ₁ lags the voltage V _s1 by a phase α ₁ and has a magnitude of I _SS1 =k·I ₀ .
In addition, the input current I _ss2 of the inverter SS ₂ lags the voltage V _s1 by a phase angle α ₂ = 180° − γ, and its magnitude is
I _ss2 =k·I ₀ .

I _Cap1 and I _cap2 are phase advance capacitors CAP ₁ and CAP ₂
The currents I _ss3 and I _ss4 flowing into the reactive power compensators SVC ₁ and SVC 2 are delayed currents flowing into the reactive power compensators SVC 1 and SVC ₂ , respectively.

Dividing the input current I _ss1 into an effective component I _p1 and a reactive component I _q1 , I _p1 = I _ss1・cos α ₁ = k・I ₀・cos α ₁ I _q1 = I _ss1 ×sin α ₁ = k・I ₀・sin α ₁ . If the lagging current I _ss3 is controlled so that the lagging current I _q1 + I _ss3 is equal to the leading current I _cap1 , the power line
The current I _AC1 that enters from BUS ₁ is only the effective component I _p1 , and operation can be performed with the fundamental wave power factor always being 1.

Similarly, if input current I _ss2 is divided into effective component I _p2 and reactive component I _q2 , I _p2 = I _ss2・cos α ₂・k・I ₀・cos α ₂ I _q2 = I _ss2・sin α ₂ =k・I ₀・sin α ₂ , and the lagging current I _ss4 so that I _q2 + I _ss4 = I _cap2
If we control the input current I _AC2 from the power line BUS ₂
is equal to the effective component I _p2 . Since the effective component I _p2 is out of phase with the voltage V _s2 by 180°, the fundamental wave power factor is 1, indicating that the power is returning in the direction of the electric line BUS ₂ .

When the set value P〓 of the power flow rate is increased, the ignition control angle α ₁ is changed transiently to increase the DC current I ₀ , but the DC current corresponding to P〓 = (P ₁ + P ₂ ) / 2 is increased. When the current I' approaches ₀ , it settles down to α ₁ =≒γ. At this time, the invalid part on the input side is I′ _q1 = k・I′ ₀・
sin α ₁ , and if I′ _ss3 = I _cap1 − I′ _q1 is decreased,
I _AC1 = I' _p1 = k·I ₁ '·cos α ₁ , and only the power flow amount can be increased. The currents I _cap1 and I _cap2 of the phase advance capacitors CAP ₁ and CAP ₂ should be prepared in amounts commensurate with the maximum power flowing.

When the power flow rate set value P〓 is set to a negative value, switch SW ₁ is connected to the b side, switch SW ₂ is connected to the a side, and this time the power line BUS ₂ of the 60Hz system is connected.
Power is then sent to the 50Hz power line BUS ₁ . At this time, SS ₁ is used as an inverse converter to perform constant output voltage control, and SS ₂ is used as a forward converter to perform DC current control.

This conventional power conversion device has the following drawbacks.

That is, in order to change the power flow rate, the DC current I ₀ is increased or decreased, but along with this change, the reactive components I _q1 , I _q2 on the input side of the converters SS ₁ and SS ₂ and, depending on the change, the currents of the reactive power compensators SVC ₁ and SVC ₂ I _ss3 ,
I need to control _ss4 .

As mentioned before, the capacity of the reactive power compensators SVC ₁ and SVC ₂ is _{I ss3 =} I _cap1 − I _q1 = k・(I _0(nax) −I ₀ )・sinα ₁ I _ss4 = I _cap2 −I _q2 = k・(I _0(nax) −I ₀ )・sinα ₂ , phase angle α ₁ ≒ γ, phase angle α ₂ = 180 Considering the relationship of °-γ and considering that the DC current I ₀ changes between 0 and I _{0 (nax)} , I _ss3 ≒ I _ss4 ≒ kI _{0 (nal)} sin γ is required.

As mentioned above, γ is the commutation advance angle required to naturally commutate the thyristor of the power converter, and is related to the inductance on the power supply side, the turn-off time of the thyristor, etc. In particular, the former value is quite large in order to prepare for short-circuiting of the converter arm. Therefore, the commutation advance angle γ usually takes a value of 30° to 40°. Even if the commutation advance angle γ=30°, sin γ=0.5, and the capacity of the reactive power compensators SVC ₁ and CVC ₂ becomes 1/2 of the capacity of the power converters SS ₁ and SS ₂ . Therefore, the device has the drawback of being expensive and complicated.

The present invention has been made in view of the above, and maintains the fundamental wave power factor at the power receiving end at 1 without using a reactive power compensator that was conventionally necessary.
An object of the present invention is to provide a power conversion device that can freely control the amount of power flow between two different power systems.

FIG. 3 is a block diagram showing the configuration of an embodiment of the power conversion device of the present invention.

In the drawings, the same reference numerals represent the same or corresponding parts.

CT ₃ is a three-phase AC current detector, PT _s is an AC voltage detector, PQC is an active reactive power calculation circuit, C ₁ to _{C 3}
is a comparator, A ₁ and A ₂ are adders, H _q (S), H _p (S)
is a control compensation circuit, and K ₀ and K _I are operational amplifiers.

Hereinafter, a case where power is sent from the electric line BUS ₁ to the electric line BUS ₂ will be explained as an example. In other words,
SS ₁ is operating as a forward converter and SS ₂ is operating as an inverse converter.

First, the DC current I ₀ is controlled as follows.

The DC current I ₀ is detected by the DC current detector CT ₀ and compared with the DC current command value I ₀ 〓 by the comparator C ₂ . The deviation ε ₂ =I ₀ 〓−I ₀ is amplified by the operational amplifier K ₀ and input to the phase control circuits PH ₁ and PH ₂ . Phase control circuits PH ₁ and PH ₂ transfer voltages proportional to their inputs ε ₅ and ε ₆ to converters SS ₁ and SS ₂
It is controlled so that it is generated from

Therefore, (command value) of DC current I ₀ 〓 > (detected value)
In the case of I ₀ , the deviation ε ₂ > 0, and ε ₅ = ε ₆ = ε ₂・K ₀
enters the phase control circuits PH ₁ and PH ₂ , the output voltage V ₁ of the converter SS ₁ moves in the direction of the arrow in Figure 3, and the output voltage V ₂ of the converter SS ₂ moves in the direction of the arrow in Figure 3. produces a voltage in the opposite direction with a magnitude proportional to the deviation ε ₂ .

Therefore, the voltage applied to the DC reactor L ₀ becomes V ₁ −V ₂ >0, increasing the DC current I ₀ .

Conversely, (command value) of DC current I ₀ 〓<(detected value)
When I becomes ₀ , the deviation ε ₂ < 0, and the output voltage V ₁ -
Since V ₂ <0, the DC current I ₀ decreases.

As a result, the DC current settles down to I ₀ =I ₀ 〓. At this time, if the resistance of the DC reactor L ₀ is sufficiently small, V ₁ ≈V ₂ .

Figures 4a and b show this embodiment (device in Figure 3)
FIG. 2 is a voltage and current vector diagram for one phase at the power receiving end of FIG.

Figure 4a is a vector diagram of the receiving end of converter SS ₁ ,
FIG. 4b is a vector diagram of the receiving end of converter SS ₂ .

Next, the power flow control operation and the reactive power control operation will be explained with reference to FIG. 3 and FIGS. 4a and 4b.

The instantaneous values of the voltage and current at the receiving end of the converter SS ₁ are detected by the three-phase AC current detector CT _s and the three-phase AC voltage detector PT _s . This is input to the active reactive power calculation circuit PQC to obtain active power P and reactive power Q. The active power P has a positive value in the power flow direction from the electric line BUS ₁ to the electric line BUS ₂ .
In addition, the reactive power Q assumes that delayed reactive power is positive.

The comparator C ₁ compares the reactive power Q with its command value Q〓, and its output deviation ε ₁ =Q〓−Q is integrated by the next control compensation circuit H _q (S). The output signal I ₀ 〓 of the control compensation circuit H _q (S) becomes the command value of the DC current I ₀ . Further, the comparator C ₃ compares the active power P and its command value P〓, and the deviation ε ₃ =P〓−P is determined by the following control control compensation circuit H _q (S)
integrated or amplified by control compensation circuit
One of the output signals ε _a of H _p (S) is input to the phase control circuit PH 1 via the adder A ₁ , and the other is input to the phase control circuit PH ₁ via the inverting amplifier K ₁ and the adder A ₂ .
Entered into PH ₂ .

Therefore, the input ε ₅ of the phase control circuit PH ₁ and the input ε ₆ of the phase control circuit PH ₂ can be expressed as follows.

ε ₅ = ε ₄ + ε ₂・K ₀ ε ₆ = −ε ₄ + ε ₂・K ₀ For convenience of explanation, if we consider the case where I ₀ = I ₀ , ε ₂ = 0, and the deviation ε ₅ = The relationship ε ₄ , ε ₆ =−ε ₄ holds, and the output voltage V ₁ =V ₂ . If the conversion constant is k _v and the AC side input voltage is V _s = V _s1 = V _s2 , then V ₁ = k _v・V _s・cos α ₁ ∝ε ₄ V ₂ = −k _v・V _s・cos α ₂ ∝−ε ₆ ∝ε ₄ , the cosine value of the firing control angle α _{1 of transducer SS 1 is} proportional to the deviation ε ₄ , and the cosine value of the firing control angle α ₂ of transducer SS ₂ is proportional to the deviation ε ₄ is proportional to the negative value of Therefore, the firing control angle α ₁ of the transducer SS ₁ and the firing control angle α ₂ of the transducer SS ₂ have a relationship of α ₂ =180°−α ₁ . direct current
When I ₀ ≠ I ₀ and the deviation ε ₂ ≠ 0, the above-mentioned ignition control angle α ₂ =180°−α ₁ relationship breaks down, and the output voltage V ₁ ≠ V ₂ and the DC current I ₀ Increase or decrease. As mentioned above, the output voltage V ₁ is approximately V ₂ in a steady state.

FIG. 4 shows a voltage-current vector diagram at the receiving end when the output voltage V ₁ ≈V ₂ . The input current I _ss1 of the converter SS ₁ has a magnitude kI ₀ and flows behind the voltage V _s1 by an angle α ₁ . In addition, the input current I _ss2 of the converter SS ₂ has a magnitude k・I ₀ and the angle α ₂ ≒ from the voltage V _s2
The flow is delayed by 180° _−α1 . Dividing the current I _ss1 into an effective component I _p1 and a reactive component I _q1 , I _p1 = I _ss1・cos α ₁ = k・I ₀・cos α ₁ I _q1 = I _ss1・sin α ₁ = k・I ₀・sin α ₁ , and dividing the current I _ss2 into an effective component I _p2 and a reactive component I _q2 , I _p2 = I _ss2・cos α ₂ = k・I ₀・cos α ₂ I _q2 = I _ss2・sin α ₂ = k・I ₀・sin α ₂ . When the relationship of phase control angle α ₂ ≒180°−α ₁ is included, I _p2 = −I _p1 I _q2 = I _q1 . Note that the lagging reactive current I _q1 = I _q2 is the leading reactive current of the phase advancing capacitors CAP ₁ and CAP ₂ .
I _cap1 and I _cap2 are controlled equally.

From this state, the command value of the power flow rate shown in Figure 3 is
Consider the case where P〓 is increased.

The deviation ε ₃ =P〓−P>0, and the control compensation circuit H _p
The output ε ₄ of (S) increases. Therefore converter SS ₁ and
The output voltage V ₁ ≈V ₂ of SS ₂ increases, and cos α ₁ and −cos α ₂ also increase. Therefore, I _p1 ≒ − I _p2 increases, the active power P increases, and finally P=
P〓 becomes.

In the process of becoming effective power P=P〓, the converter
Since the firing control angles α ₁ and α ₂ of SS ₁ and SS ₂ change, the reactive power control at the receiving end is also affected. That is, as cos α ₁ and −cos α ₂ increase, sin α ₁ and sin α ₂ decrease, and I _q1 = k・I ₀・sin α ₁ <I _cap1 I _q2 = k・I ₀・sin α ₂ < I _cap2 . Therefore, the reactive power Q at the power receiving end is leading and a negative value is detected. Therefore, the deviation ε ₁ =Q〓−Q
>0, and the DC current command value I ₀ 〓, which is the output of the next control compensation circuit H _q (S), is increased. The direct current I ₀ is controlled as described above, and is controlled so that I ₀ =I ₀ 〓. As a result, the invalid portions I _q1 and I _q2
increases, and is finally controlled so that the reactive power Q = Q = 0.

However, when the DC current I ₀ increases, the effective component I _p1 = −
I _p2 also increases, and the active power P becomes larger than its command value P〓. Therefore, now cos α ₁ and −cos α ₂
The direct current I ₀ also decreases slightly.

In other words, when the command value P〓 of power flow rate is increased, the output voltage of power converters SS ₁ and SS ₂
Active power control and reactive power control are performed simultaneously while V ₁ , V ₂ and DC current I ₀ are changed, and the output voltage V is such that finally active power P = P〓 and reactive power Q = Q〓. ₁ ≒ V ₂ and the value of DC current I ₀ . In the vector diagrams in Fig. 4a and b, as a result of increasing the command value P of the power flow rate, the input current of converter SS ₁ changes from I _ss1 to I' ss1, and the input current of converter SS ₂ changes from I ss1 to I' _ss1 . The input current changes from I _ss2 to I' _ss2 , showing that only the effective portion increases from I _p1 =-I _p2 to I' _p1 =-I' _p2 .

The same control is applied when the active power command value P〓 is decreased, and finally the effective part P=P〓, the reactive part Q
The direct current I ₀ and the output voltage V ₁ ≈V ₂ such that =Q=0.

In the above, we set the reactive power command value Q = 0 and controlled so that the reactive power Q at the receiving end becomes zero, that is, the input fundamental wave power factor becomes 1.
It goes without saying that the same control is achieved even if the setting is set to >0 or Q<0.

FIG. 5 is a block diagram showing the configuration of another embodiment of the present invention.

A ₃ and A ₄ are adders, K ₂ and K ₃ are operational amplifiers with a coefficient of 1/2, L ₀₁ and L ₀₂ are DC reactors, and R is a resistance of the DC line.

The other embodiment shown in FIG. 5 differs from the embodiment shown in FIG. 3 in that the resistance R of the DC line is taken into consideration. This is necessary in the case of a power conversion device for DC power transmission, when the distance of the DC power transmission line is long and the resistance R cannot be ignored.

In other words, the power of I ⁰ ₂ · R is consumed by the resistance R, and the effective power P ₁ from the electric line BUS ₁ and the electric power
A difference occurs in the active power P ₂ going out to BUS ₂ .
Therefore, =(P ₁ +P ₂ )/2 is detected and controlled. Considering the case where there is also a slight difference in the reactive powers Q ₁ and Q ₂ , = (Q ₁ +
Q ₂ )/2 is detected and controlled in the same way.

As described above, according to the power converter of the present invention, the fundamental wave power factor at the receiving end from both systems can be maintained at 1 at all times without using a conventionally required reactive power compensator. Moreover, it has the advantage of being able to freely control the amount of power flow between both systems. Therefore, it is possible to obtain a system that is economical and has a simple configuration not only as a frequency converter but also as a power converter for DC power transmission.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional power converter, Figures 2a and b are voltage and current vector diagrams at the receiving end to explain the operation of Figure 1, and Figure 3 is a diagram of the power converter of the present invention. A block diagram showing the configuration of one embodiment,
4a and 4b are vector diagrams of voltage and current at the power receiving end to explain the operation of the device shown in FIG. 3, and FIG. 5 is a block diagram showing the configuration of another embodiment of the present invention. BUS ₁ ...Electric line of the first power system, BUS ₂ ...Electric line of the second power system, TR ₁ , TR ₂ ...Power transformer, SS ₁ , SS ₂ ...Power converter, CAP ₁ , CAP ₂ ...Advanced Phase capacitor, L ₀ , L ₀₁ , L ₀₂ ...DC reactor,
R...Resistance, _CTs , _CTs2 , _CT0 ,...Current detector,
PT _s , PT _s1 , PT _s2 ...Voltage detector, PQC, PQC ₁ ,
PQC ₂ ...Active reactive power calculation circuit, H _q (S), H _p
(S)...Control compensation circuit, _C1 , _C2 , _C3 ...Comparator,
K ₀ , K ₁ , K ₂ , K ₃ … operational amplifier, A ₁ , A ₂ … adder, PH ₁ , PH ₂ … phase control circuit, SV ₁ , SV ₂ … reactive power compensator (TR ₃ , TR ₄ is transformer, SS ₃ ,
SS ₄ is a thyristor rectifier circuit, L ₁ and L ₂ are DC reactors, CT ₃ and CT ₂ are current detectors, VRQ ₁ and VRQ ₂
AQR ₁ , AQR ₂ ...reactive power control circuit, VRP...power flow setting device, APR...power control circuit, VRV...output voltage setting device, AVR...constant voltage control circuit, SH...Schmitt circuit.

Claims (1)

[Claims] 1. The AC side of the first AC/DC power converter is connected to the first power system, the AC side of the second AC/DC power exchanger is connected to the second power system, and the AC side of the first AC/DC power converter is connected to the second power system, and In a power conversion device in which the DC side of the AC/DC power exchanger is connected so that a DC current flows in a constant direction via a DC reactor, the power is exchanged between the first power system and the second power system. means for controlling the value of active power; means for simultaneously controlling the DC side output voltages of the two AC/DC power converters by means of an output signal from the means for controlling the value of the active power; A power conversion device comprising: means for controlling reactive power at a power receiving end; and means for controlling the direct current using an output signal from the means for controlling the reactive power.