JPS6322135B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling 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. As devices for connecting these two power systems and controlling the amount of power between the systems, there have long been known rotary frequency converters using an induction machine or the like, or static frequency converters using a mercury rectifier. 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 perform alternating current → direct current → alternating current exchange are used. In particular, a device in which the length of the DC power line is increased is well known as a power converter for DC power transmission.

FIG. 1 shows a configuration diagram of a conventional power converter, in which a 50 Hz system and a 60 Hz system are connected and the amount of power flow between the two systems is controlled.

In the figure, 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 , TR ₂
is a power transformer, SS ₁ and SS ₂ are AC/DC power converters consisting of thyristor bridge circuits, L _p is a DC reactor, CAP ₁ and CAP ₂ are phase advance capacitors, SVC ₁ and
SVC ₂ is a reactive power compensator.

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 power receiving end from BUS ₁ to detect the instantaneous values of three-phase voltage and current. This is input to the 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 BUS ₂ , and together with the active reactive power calculation circuit PQC ₂ , the active power P ₂ and the reactive power Q ₂ are detected. P ₁ detects the incoming direction as positive, and P ₂ detects the outgoing direction as positive. Furthermore, Q ₁ and Q ₂ detect lagging reactive power as positive and detecting leading reactive power as negative.

Power command value P〓 by power flow setting device VRP
>0 is given. Schmitt circuit SH is P〓＞
When the output signal is 0, an output signal "1" is generated, and the switch SW ₁ is connected to the a side and the switch SW ₂ is connected to the b side. Therefore, the output voltage _{V 1} of the power converter SS 1 is controlled by the power control circuit APR so that the power flow rate P = (P ₁ + P ₂ )/2 is equal to the command value P〓, and The power converter SS ₂ is controlled by a constant voltage control circuit AVR so that its output voltage V ₂ becomes a constant value V . PH ₁ and PH ₂ are phase control circuits for SS ₁ and SS ₂ , respectively.

FIG. 2 is a voltage-current vector diagram for one phase on the AC input side of each power converter at this time. a is SS ₁
b is the voltage-current vector diagram of SS 2; b is the voltage-current vector diagram of SS ₂ ; In the figure, V _S1 and V _S2 are power supply voltages,
I _cap1 and I _cap2 are currents of phase advance capacitors CAP ₁ and CAP ₂ , I _ss1 and I _ss2 are input currents of power converters SS ₁ and SS ₂ , I _ss3 and I _ss4 are reactive power compensators SVC ₁ and SVC ₂
is the input current. When the current flowing through the DC reactor L _p is I _p , and the conversion constant is k, I _ss1 =
I _ss2 =k·I _p . If the above DC current I _p is in a steady state and the resistance of the DC reactor L _p is negligibly small, then the output voltage V ₁ of SS ₁ and the output voltage V ₂ of SS ₂ must be equally balanced. No. Let each ignition control angle be α ₁ and α ₂ , and the power supply voltage be
When V _s1 , V _s2 and the conversion constant are k _v , there is a relationship of V ₁ =k _v ·V _S1 ·cosα ₁ V ₂ =−k _v ·V _s2 ·cos α ₂ . When V _s1 =V _s2 , the relationship α ₂ =180°−α ₁ holds in the state of V ₁ =V ₂ .

When transmitting power from electric line BUS ₁ to electric line BUS ₂ , SS ₁ operates as a forward converter and SS ₂ operates as an inverse converter. The firing control angle α ₂ of the constant voltage controlled inverter SS ₂ is set to a certain value between 90° and 180°. When α ₂ = 180°, the power factor on the input side becomes |cosα ₂ |=1, but
The firing timing must be advanced by γ in order to allow the thyristor to naturally commutate. Generally, γ is said to be the commutation lead angle. Therefore, α ₂ =180°−γ=set to constant. In this state, the power flow rate is controlled by the forward converter _SS1 . The input voltages of SS ₁ and SS ₂ are V _s1 = V _s2 = constant, so the power is I _ss1 and I _ss2
are proportional to the respective effective current components I _p1 and I _p2 .
I _p1 and I _p2 can be expressed as follows.

I _p1 =k・I _p・cosα ₁ I _p2 =k・I _p・cosα ₂ α ₂ =180°−α In the state of ₁ , the relationship I _p1 = −I _p2 holds, and the signal enters the forward converter SS ₁ . It can be seen that the active power coming out is equal to the active power leaving the inverter SS ₂ .

The power flow rate is controlled by changing the magnitude of the DC current I _p . DC current I _p is DC reactor
It is controlled by varying the voltage V ₁ −V ₂ applied to L _p . Since V ₂ is controlled constant, V ₁
=k _v・V _s1・cosα ₁ is controlled by changing.
If you want to increase I _p , increase α ₁ so that V ₁ > V ₂
If you want to control and decrease I _p , then V ₁ <
Control α ₁ so that V ₂ . Near the stationary point, if the resistance of the DC reactor L _p is ignored, the relationship V ₁ ≒ V ₂ holds, and cosα ₁ ≒−cos α ₂ .

On the other hand, the reactive power at the receiving end of converters SS ₁ and SS ₂ is controlled as follows. In other words, in the vector diagram in Figure 2, the following relationship holds true:
Controls the values of I _ss3 and I _ss4 .

I _cap1 = I _q1 + I _ss3 = k・I _p・sin α ₁ + I _ss3 I _cap2 = I _q2 + I _ss4 = k・I _p・sin α ₂ + I _ss4 When the set value P of the power flow rate is changed, the DC current
I _p changes and I _ss3 and I _ss4 are also controlled accordingly.

If the above relational expression holds true, the current supplied from BUS ₁ will be I _AC1 = I _p1 , and the current supplied from BUS ₂ will be I _AC2 = I _p2 = ^- I _p1 , and the fundamental wave power at the receiving end will be With the rate held at 1, only the active power
Sent from BUS ₁ to BUS ₂ .

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

This conventional power conversion device has the following drawbacks. That is, in order to control the power flow rate, the DC current I _p is increased or decreased, but as the DC current changes, the reactive current component I _q1 = kI _p sin α on the input side of the converters SS ₁ and SS ₂ increases. ₁ and I _q2 =kI _p sinα ₂ also change, and it is necessary to control the currents I _ss3 and I _ss4 of the reactive power compensators SVC ₁ and SVC ₂ according to the changes.
The capacity of these reactive power compensators SVC ₁ and SVC ₂ is I _p (max.) when the maximum value of DC current I _p is I _ss3 = I _cap1 − I _q1 = k {I _p (max.) − I _p }・sinα ₁ I _ss4 = I _cap2 −I _q2 = k{I _p (max.) − I _p }・sin α ₂ , and considering the relationship α ₁ ≒ γ, α ₂ = 180° − γ, the above
Considering that I _p changes between 0 and I _p (max.), I _ss2 ≒ I _ss4 ≒ k·I _p (max.) sinγ 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 a converter arm short-circuit accident. Therefore, γ usually takes a value of 30° to 40°. Even if γ = 30°, sin γ = 0.5, and the capacity of reactive power compensators SVC ₁ and SVC ₂ is equal to that of the power converter.
The capacity becomes half the capacity of 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 it is possible to always maintain the fundamental wave power factor at the receiving end at 1 without using a conventional reactive power compensator, and to freely control the amount of power flow between two power systems. The purpose of the present invention is to provide a method for controlling a power conversion device that can be controlled.

FIG. 3 is a configuration diagram showing an embodiment of the power conversion device of the present invention. In the figure, BUS ₁ is the three-phase power line of the first power system (for example, 50Hz system), and BUS ₂ is the second
3-phase power line of the power system (e.g. 60Hz system),
CAP ₁ and CAP ₂ are phase advance capacitors, 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 _p is a DC reactor. Also, CT _p is a DC current detector, C ₁ ~ C ₃
is a comparator, A ₁ to _{A 8} are adders, K _O and K _I are operational amplifiers, M ₁ and M ₂ are multipliers, H _q (s) and H _p (s) are control compensation circuits, and SQ is 2 SQR is a square root calculation circuit, LM is a limiter circuit, and PH ₁ and PH ₂ are phase control circuits.

First, the control operation of the voltage on the DC side will be explained. To simplify the explanation, the DC current I _p is its command value I _p 〓
Consider a state that is controlled equally to .

The output υ〓 of the control compensation circuit H _p (s) is sent to the phase control circuit PH ₁ via the adder A ₁ and to the inverting amplifier K _I
(=-1) and the phase control circuit via adder A ₂
Each is input to PH ₂ . Since I _p =I _p 〓, the output ε ₂ =I _p 〓−I _p of comparator C ₂ is zero. Therefore PH ₁
And the input voltages υ〓 ₁ and υ〓 ₂ of PH ₂ are υ〓 ₁ = υ〓 υ〓 ₂ = −υ〓. Therefore, the firing phase α 2 of SS ₂ with respect to the firing phase α ₁ of power converter SS ₁ is _{α 2 =} 180° − _{α 1} ,
It will be operated in a state where each output voltage V ₁ and V ₂ are balanced. To increase V ₁ = V ₂ ,
What is necessary is to increase the output value υ〓 of the control compensation circuit H _p (s).

Next, the control operation of the DC current I _p will be explained.

DC current I _p detected by current detector CT _p
and its command value I _p 〓, and the deviation ε ₂ = I _p 〓−I _p
Take out. The deviation ε ₂ is amplified by an amplifier K _O and input to adders A ₁ and A ₂ . Therefore _, the input voltages υ〓 ₁ and _{υ〓 2 of the phase control} circuits PH ₁ and _{PH 2} are as follows. Therefore, the relationship α ₂ =180°−α ₁ breaks down, and V ₁ increases and V ₂ decreases by an amount proportional to K _O ·ε ₂ . The difference voltage V ₁ − V ₂ is the DC reactor
applied to L _p to increase the DC current I _p .

When I _p > I _p 〓, ε ₂ < 0, and V ₁ < V ₂
Therefore, the DC current I _p is decreased. Finally,
It settles down to I _p = I _p 〓, and in the steady state, V ₁ ≒ V ₂ and satisfies the relationship α ₂ ≒ 180° − _{α 1} .

Next, the active power control operation and reactive power control operation of this power converter will be explained.

It is known that the input voltages υ〓 ₁ and υ〓 ₂ of the phase control circuits PH ₁ and PH ₂ are proportional to the cosine values of the firing phase angles α ₁ and α ₂ , respectively.

The output voltage υ〓 of the control compensation circuit H _p (s) and the above PH ₁
and the input voltages υ〓 ₁ and υ〓 ₂ of PH ₂ have a relationship as shown in the following equation.

υ〓=(υ〓 ₁ + υ〓 ₂ )/2 = kα(cosα ₁ +cosα ₂ )/2 However, kα is a proportionality constant.

Therefore, by detecting the above υ〓 and multiplying it by the coefficient (1/kα), the average value of the cosine values of the firing phase angle cosα=(cosα ₁ +cosα ₂ )/2 can be found. The limiter circuit LM has the above-mentioned proportionality coefficient (1/kα) and serves to limit the range within a range that satisfies -1≦cosα≦+1.

The square calculation circuit SQ, the adder _A3 , and the square root calculation circuit SQR perform the calculation of ^√1-2 .
This value is equal to the sine value sinα of the phase angle α.

Multipliers M ₁ and M ₂ combine the DC current value I _p and the sinusoidal value
It multiplies sinα and cosine value cosα,
I _q = I _p ·sinα I _p = I _p ·cos α are obtained as each output value. The former I _q is the power converter SS ₁ and SS ₂
The latter I _p is the average value of the active current at the power receiving end.

The reactive current command value I _q 〓 and the reactive current detected value I _q are compared by the comparator C ₁ , and the deviation ε ₁ =I _q 〓−I _q is input to the next control compensation circuit H _q (s). In order to make the steady-state deviation ε ₁ zero, an integral element may be used for the above H _q (s). The output of H _q (s) is the DC current command value
I _p 〓. When I _q <I _q 〓, ε ₁ becomes a positive value and increases I _p 〓. Therefore, the output deviation of comparator C ₂ ε ₂
＝I _p 〓−I _p increases, V ₁ > V ₂ , and the DC current I _p
At this time, υ〓＝(υ〓 ₁ + υ〓 ₂ )／
2
does not change. Therefore, I _q = I _p・sinα increases,
It is controlled so that I _q = I _q 〓. Even when I _q > I _q 〓, control is performed in the same way, and finally I _q = I _q 〓.

Also, the effective current command value I _p 〓 and the effective current detection value I _p
are compared by a comparator _C3 , and the deviation ε ₃ =I _p 〓−I _p is input to the next control compensation circuit H _p (s). Steady-state deviation ε ₃
In order to make H _p (s) zero, an integral element is sometimes used. The output of H _p (s) becomes the signal υ〓 that determines the average value of the output voltages V ₁ and V ₂ of SS ₁ and SS ₂ .
When I _p <I _p 〓, ε ₃ >0 and υ〓 is increased.
Even if υ〓 is changed, the state of V ₁ = V ₂ is maintained, so
The direct current I _p remains unchanged. Since there is a relationship of υ〓=kα・cosα, I _p =I _p・cosα increases and control is made so that I _p =I _p 〓. When I _p > I _p 〓, ε ₃ <0 and υ〓 is decreased, and control is performed so that I _p =I _p 〓.

From the first power system BUS ₁ to the second power system
If you want to send power to BUS ₂ , you can control it by setting I _p 〓>0. On the other hand, when transmitting power from BUS ₂ to BUS ₁ , control may be performed such that I _p 〓<0.

Here, we will consider the mutual influence of the I _p control system and the I _q control system.

When I _p 〓 increases, I _p = I _p 〓.
cosα increases. Therefore, sinα= ^√1−2 decreases, and I _q =I _p・sinα decreases. Therefore, since I _q <I _q 〓, I _p is increased so that I _q = I _q 〓. As a result, I _p =I _p ·cosα also increases, and I _p >I _p 〓.
Therefore, this time cosα is decreased and the operation is reversed.
The above vibration phenomenon is repeated several times, and finally I _p =
It settles on I _p 〓, I _q = I _q 〓. How quickly this vibration phenomenon can be damped depends on the control compensation circuit H _q
It depends on how to choose the control constants for (s) and H _p (s). However, optimization can be easily achieved by using ordinary automatic control theory.

Similarly, when I _p 〓 is decreased and when I _q 〓 is increased/decreased, it is controlled so that it goes through an oscillation phenomenon and then settles down.

In other words, the cosine value cosα of the DC current I _p and phase angle α that constantly satisfies I _p = I _p 〓, I _q = I _q 〓
become.

FIG. 4 shows a voltage-current vector diagram for one phase on the AC input side of each power converter shown in FIG.
a is a voltage-current vector diagram of SS ₁ , and b is a voltage-current vector diagram of SS ₂ . V _s1 and V _s2 are power supply voltages,
I _cap1 and I _cap2 are currents of phase advance capacitors CAP ₁ and CAP ₂ , and I _ss1 and I _ss2 are input currents of power converters SS ₁ and SS ₂ . When the direct current is I _p and the conversion constant is k, there is a relationship of I _ss1 =I _ss2 =k·I _p .

Considering the steady state, V ₁ ≒ V ₂ ,
The firing phase angles of SS ₁ and SS ₂ have a relationship of α ₂ ≒180°−α ₁ . Separating I _ss1 into effective component I _p1 and reactive component I _q1 , and expressing it in relation to DC current I _p , I _p1 = I _ss1・cosα ₁ = kI _p cosα ₁ I _q1 = I _ss1・sinα ₁ = kI _p sinα ₁ . Furthermore, if I _ss2 is separated into an effective component I _p2 and a reactive component I _q2 and expressed as a relational expression with the DC current I _p , I _p2 = I _ss2・cosα ₂ = kI _p cosα ₂ I _q2 = I _ss2・cosα ₂ = kI _p cosα ₂ . If we include the relationship α ₂ ≒180°−α ₁ here, we get cosα ₁ ≒−cosα ₂ ≒cosα sinα ₁ ≒sinα ₂ ≒sinα, so the controlled amount I _p = I _p・cos α, I _q in Fig. 3 =
Substituting I _p · sin α into the above relational expression, I _p1 ≒kI _p I _q1 ≒kI _q I _p2 ≒−kI _p I _q2 ≒kI _q . If the reactive current setting value I _q 〓 is selected so that the leading reactive current I _cap1 = I _cap2 of the phase advance capacitors CAP ₁ and CAP ₂ is equal to the lagging reactive current I _q1 ≒ I _q2 , power converters SS ₁ and The reactive power at each power receiving end of SS ₂ becomes zero, and operation with a fundamental wave power factor of 1 is possible without providing a conventional reactive power compensator. On the other hand, if the effective current setting value I _p 〓 is chosen to be positive, I _p1 > 0, I _p2 <
0, the active power is sent from the first power system BUS ₁ to the second power system BUS ₂ , and if I _p 〓 is chosen negative, I _p1 < 0, I _p2 > 0 and the active power is sent from the first power system BUS 1 to the second power system BUS 2. from ₂
Sent to BUS ₁ . That is, by changing I _p 〓, the power flow amount can be selected to various values.

As described above, in the power converter of the present invention, the fundamental wave power factor at the receiving end is always maintained at 1 without using a conventional reactive power compensator, and the power flow rate between the two power systems can be freely controlled. can be controlled. Moreover, in controlling the reactive power at the receiving end, the DC current detection value I _p and the cosine value of the ignition phase angle are
Since the reactive current is directly calculated and controlled from cosα, there is no need for current transformers, transformers, etc. to detect the reactive power at the receiving end, which were required in the past, and the problem of detection delay is also eliminated, resulting in improved responsiveness. An extremely good control system can be achieved.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional power conversion device, Figure 2 is a voltage and current vector diagram at the receiving end of the device in Figure 1,
FIG. 3 is a block diagram showing one embodiment of the power conversion device of the present invention, and FIG. 4 is a voltage-current vector diagram at the power receiving end of the device shown in FIG. 3. BUS ₁ , BUS ₂ ... electric lines of the first and second power systems, CAP ₁ , CAP ₂ ... phase advance capacitors,
TR ₁ , TR ₂ ... Power transformer, SS ₁ , SS ₂ ... AC/DC power converter, L _p ... DC reactor, CT _p ...
DC current detector, C ₁ , C ₂ , C ₃ ... Comparator, A ₁ ,
A ₂ , A ₃ ... Adder, K _O , K _I ... Operational amplifier, H _q
(s), H _p (s)... Control compensation circuit, LM... Limiter circuit, SQ... Square calculation circuit, SQR... Square root calculation circuit, M ₁ , M ₂ ... Multiplier, PH ₁ , PH ₂ ...
...Phase control circuit.

Claims (1)

[Claims] 1 The AC side of the first AC/DC power converter is connected to the first power system, and the AC side of the second AC/DC power converter is connected to the second power system, and the two power converters In a power converter device in which the DC side of a DC reactor is connected so that a DC current I _p flows in a constant direction through a DC reactor, the cosine value of the firing control angle α is determined from the phase control input signals of the two power converters.
By calculating cosα and sine value sinα and multiplying the values by the detected value of the DC current I _p , the effective current is calculated.
Find I _p = I _p・cos α and reactive current I _q = I _p・sin α, compare the reactive current command value I _q 〓 and the above reactive current I _q , and control the above DC current I _p according to the deviation, And the power flow between the first and second power systems is controlled by comparing the active current command value I _p 〓 with the above active current I _p and controlling the DC side voltage of the two power converters according to the deviation. A method for controlling a power converter, characterized in that the amount of reactive power at the receiving end of the two power converters is controlled.