JPS6343973B2 - - Google Patents

Description

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

[Technical background of the invention and its problems]

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 converters 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 are in 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, a device with a long DC wire list is well known as a power converter 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 advance capacitors that also serve as harmonic 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 rate setting device VRP
>0 is given. The Schmitt circuit SH generates an output signal "1" when the power command P ^* >0, and connects the switch SW ₁ to the a side and the switch SW ₂ to the b side. In other words, the forward converter SS ₁ has a power flow rate P
Its output voltage V ₁ is controlled so that = (P ₁ + P ₂ )/2 is equal to its command value P ^* , and the inverter SS ₂
The output voltage V ₂ of is controlled to produce 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 V ₂ of the inverse converter SS ₂ to a constant value V ^* . PH ₁ and PH ₂ are each AC/DC power converter SS ₁
and SS ₂ phase control circuit.

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 ·cosα ₁ V ₂ =−k _V ·V _S2 ·cos _{α 2} . However, _kV 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 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 firing control angle α ₁ . Near the steady point, the DC reactor
If the resistance of 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.

If input current I _SS1 is divided into effective component I _p1 and reactive component I _q1 , I _p1 = I _SS1・cosα ₁ = k・I ₀・cosα ₁ I _q1 = I _SS1・sinα ₁ = k・I ₀・sinα ₁ Become. 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 electric 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・cosα ₂ = k・I ₀・cosα ₂ I _q2 = I _SS2・sinα ₂ = k・I ₀・sinα 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 power flow rate set value P ^* is increased, the ignition control angle α ₁ is transiently changed to increase the DC current I ₀ , but the DC current corresponding to P ^* = (P ₁ + P ₂ )/2 is increased. When the current approaches I′ ₀ , it settles down to α ₁ ≒ γ.
At this time, the invalid component on the input side is I _q ′ ₁ = k・I′ ₀・sinα ₁
So, if I _SS3 ′=I _cap1 −I _q ′ ₁ is decreased, I _AC1 =
I _p ′ ₁ =k·I′ ₀ ·cosα ₁ , and only the power flow amount can be increased. phase advance capacitor
The currents I _cap1 and I _cap2 of CAP ₁ and CAP ₂ should be prepared in amounts commensurate with the maximum power flowing.

If the power flow rate set 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 this time from the 60Hz power line BUS ₂ .
Power will now be 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.

This conventional power conversion device uses a phase advance capacitor
CAP ₁ , CAP ₂ and reactive power compensator SVC ₁ ,
Requires SVC ₂ . Phase advance capacitor CAP ₁ ,
The capacity of CAP ₂ requires the same capacity as converters SS ₁ and SS ₂ , and the capacity of reactive power compensators SVC ₁ and SVC ₂ is approximately 1/2 that of converters SS ₁ and SS ₂ , assuming γ = 30°. Requires. Therefore, the power conversion device as a whole has the drawback of being expensive and complicated.

In addition, the power conversion device described above is based on constant current power conversion, so even if a steep power request is made on the BUS ₂ side, it is often not possible to meet it due to the installed capacity of BUS ₁ on the supply side. .

[Purpose of the invention]

An object of the present invention is to provide a power conversion device that can maintain the basic power factor on the grid side at 1 without using a conventionally necessary reactive power compensator and can cope with steep power fluctuations.

[Summary of the invention]

The present invention connects power converters to a first system and a second system, connects the two power converters with a circuit with a higher frequency than the system frequency, and connects an energy storage device that operates at a high frequency to the two power systems. It is characterized by being configured by being connected between converters.

[Embodiments of the invention]

FIG. 3 shows a power conversion device showing an embodiment of the present invention, BUS _A represents the first power system A,
BUS _B indicates the second system B. A transformer T _A is connected to system A, and the primary winding is W ₁ ,
The secondary windings are W ₂ , W ₃ , and W ₄ . Similarly,
A transformer T _B is connected to the system B, and its primary winding is W ₁₁ and its secondary windings are W ₁₂ , W ₁₃ , and W ₁₄ . Cycloconverters CC _A and CC _B are connected to transformers T _A and T _B , respectively. A cycloconverter is generally used as a power conversion device that converts high frequency AC power to low frequency AC power, but in this embodiment, it converts to a higher frequency than the frequency of system A or B, and stores energy in a relatively small size. Care has been taken to ensure that the equipment can charge and discharge energy. Therefore, in the cycloconverter of this embodiment, the relationship between the input and output of a general cycloconverter is reversed. Since cycloconverters CC _A and CC _B have the same configuration and operating principle, CC _A will be explained below. Regarding the U phase, the positive group converter C _AU1 and the negative group converter C _AU2 are each composed of six thyristor arms, although detailed diagrams are omitted. Anode side terminal of positive group converter C _AU1 and negative group converter
Connect DC reactor _L1 with intermediate tap between the cathode side terminals of C _AU2 . Also, positive group converter
Reactor L ₂ with an intermediate tap is placed between the cathode terminal of C _AU1 and the anode terminal of negative group converter C _AU2 .
Connect. The intermediate tap of DC reactor _L1 is connected to one terminal of U-phase winding _W2 of the transformer via reactor _L7 , and the intermediate tap of DC reactor _L2 is connected to the other terminal of U-phase winding _W2 . do.
U of positive group converter C _AU1 and negative group converter C _AU2
Take out the common lead wire from each phase, V phase, and W phase arms, and connect it to the U phase output terminal of the cycloconverter CC _B. The positive group converter C _AV1 and the negative group converter C _AV2 form a V-phase cycloconverter, and similarly, the positive group converter C _AW1 and the negative group converter C _AW2 form a W-phase cycloconverter. The output terminals of the U-phase, V-phase, and W-phase cycloconverters are commonly connected to each phase and connected to the corresponding output terminal of the cycloconverter CC _B.

Note that cycloconverter CC _B also has the same configuration as CC _A , and a flywheel device as an energy storage device is connected between CC _A and CC _B. The flywheel device includes a synchronous motor SM as a motor generator, an inertial body FW, a rotor position detector PS of the synchronous motor, and a speed generator TG.
are directly connected.

The operation of the embodiment shown in FIG. 3 will be explained using FIGS. 4 and 5. The input of the cycloconverters CC _A and CC _B is 50 or 60 Hz, and the output, ie, the terminal voltage of the synchronous motor, is selected at a frequency about one order of magnitude higher than that. Regarding the phase angle of voltage and current, it is desirable that the input side be operated in the same phase, that is, with a power factor of 100%, so as not to adversely affect the grid. On the output side, on the other hand, in order to enable load commutation using a high-frequency output voltage, control is performed so that the current is leading when the motor is operating, and the current is lagging when the generator is operating.

FIG. 4 is a control block diagram. When it is desired to accelerate the synchronous motor, the deviation n _R −n ₀ between the speed command n _R and the actual speed n ₀ detected by the speed generator TG becomes positive. This deviation is converted into a current peak value command I _n via the speed controller G ₁ (S). Reference signal synchronized with the U-phase voltage of the grid in the next multiplier
Multiplying sinω ₁ t by the current peak value command I _n yields an input current command I ^* _CAU , which makes the input power factor 100%, that is, I _n
sinω ₁ t is obtained. Next, the input current command I ^* _CAU is compared with the actual input current detection value I ^* _CAU , and the current control circuit
Phase control circuit of positive group converter through G ₂ (S)
Give to PH _AU1 . Moreover, the polarity of the phase input signal obtained in the same manner is inverted and applied to the phase control circuit of the negative group converter. The phase control circuits PH _AU1 and PH _AU2 give gate signals to the corresponding positive group converter C _AU1 and negative group converter C _AU2 , respectively, and the commutation operation is performed as follows. The fifth position is detected by the position detection device PS.
The phase of the induced voltage as shown in Figure a is detected. If the angular frequency of the output is ω ₂ , e _u = E _n sin(ω ₂ t), e _v =
E _n sin (ω ₂ t−2π/3), e _w = E _n sin (ω ₂ t−4π/3)
It can be expressed as At this time, the phase reference signal
e _S1 and e _S2 are e _S1 (or e _S2 ) = sin (ω ₂ t−k・π/3+π
/6), six sine wave signals represented by k=1, 2, 3, 4, 5, 6. That is, in the positive group converter C _AU1 , as shown in FIG. 5b, commutation occurs sequentially at the intersection of the phase input signal and the downward slope of the reference signal e _S1 . In the negative group converter C _AU2 , commutation occurs at the intersection of the upward slope of the reference signal e _S2 and the phase input signal, as shown in Figure 5c, and the average voltage of both the positive and negative converters becomes U.
This is the output voltage of the phase cycloconverter.

When power is returned from the flywheel side to the grid side, the speed deviation n _R -n ₀ <0, and the phase and polarity of the phase input signal change accordingly, but the control block diagram does not require any changes. The same applies to the control of the V-phase cycloconverter and the operation of the W-phase cycloconverter. The operation of the cycloconverter CC _B connected to the system B is also the same as that of the cycloconverter CC _A. In the embodiment shown in FIG. 3, when system B requires large pulsed power, if the large power cannot be obtained due to the load condition of system A, the energy of the flywheel device, which is a storage device, is discharged to system B side. . As a result, the rotational speed of the flywheel device decreases, but in that case, the excess energy of system A or system B will be used for charging.

When directly transporting power from system A to system B,
Or vice versa, the flywheel device acts simply as a commutation element.

When actually operating the power converter shown in Figure 3,
The rotation speed of the flywheel body is the lowest rotation speed
Used between Nmin and maximum rotation speed Nmax.
The minimum rotation speed Nmin is determined from the efficiency of the motor generator, and the maximum rotation speed Nmax is determined by the mechanical strength of the inertial body. In the normal standby state, both the speed command n ^A _R for the cycloconverter CC _A and the speed command n ^B _R for the cycloconverter CC _B are set to No, and the flywheel is set to the rotation speed No (Nmin
<No<Nmax) and is rotating and accelerating (charging)
and deceleration (discharge) can both be selected. If power is currently required on the grid B side,
When the speed command n ^BR for the cycloconverter CC _B is decreased, the speed deviation n ^BR −n ₀ (n ₀ is the number of rotations of _the flywheel) becomes negative, and power is sent _from the flywheel side to the system B. At this time, since the rotational speed n ₀ of the flywheel decreases with discharge, the speed deviation n ^A _R −n ₀ with respect to the cycloconverter CC _A becomes >0, and power is sent from the system A to the flywheel side. Power is transferred to grid B from both grid A and the flywheel. When power from system B is no longer needed, the speed command for cycloconverter CC _B is set to n ^B _R = No again, and cycloconverter
Power is supplied from both CC _A and CC _B , and the flywheel waits while reaching the original rotation speed No.

When surplus power is generated in system B, increasing the speed command n ^B _R for the cycloconverter CC _B satisfies n ^B _R −n ₀ >0, and power is sent from system B to the flywheel side. Naturally, the rotational speed of the flywheel increases, so the speed deviation n ^A _R −n ₀ <0 with respect to the cycloconverter CC _A and the power is transmitted from the flywheel side to the system A. When the speed command of the cycloconverter CC _B is returned to its original value, the surplus energy of the flywheel is sent to the system A or B, and the rotation speed is reduced to No. and waits for the next operation.

In the above description, when sending power from power system A to system B, there are cases where there is no margin for sending power to system B considering the load condition of system A. In this case, most of the power will be supplied from the flywheel, which is an energy storage device. Conversely, from system B to system A
When transmitting power to grid A, a light load on grid A may cause a voltage rise. At this time, most of the electric power is stored as rotational energy of the flywheel by restricting the electric power of the cycloconverter CC _A.

Flywheel rotation speed is upper limit Nmax or lower limit
When in the Nmin state, only one direction of discharging or charging can be used, so operation is somewhat limited. Therefore, it is necessary to select the capacity of the energy storage device in consideration of the characteristics and operational duties of power systems A and B.

〔Effect of the invention〕

By placing a single buffer device called an energy storage device between system A and system B, the present invention is not only capable of simply transporting electric power, but also enables effective use of surplus energy. The rate can always be maintained at 100%.

[Brief explanation of the drawing]

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. The configuration diagram of one embodiment, FIGS. 4 and 5, are a control block diagram and an operation explanatory diagram of the phase control circuit for explaining the embodiment of FIG. 3. BUS _A , BUS _B ...Power system, T _A , T _B ...Power transformer, W ₁ , W ₁₁ ...Primary winding of power transformer,
W ₂ , W ₃ , W ₄ , W ₁₂ , W ₁₃ , W ₁₄ ... Secondary winding of power transformer, C _AU1 , C _AU2 , C _AV1 , C _AV2 , C _AW1 ,
C _AW2 ...Power converter, C _BU1 , C _BU2 , C _BV1 , C _BV2 ,
C _BW1 , C _BW2 ... Power converter, L ₁ , L ₂ ... L _G ... Reactor, L ₁₁ , L ₁₂ ... L _G ... Reactor, CC _A ,
CC _B ...cycloconverter, SM...synchronous motor,
FW...Flywheel device, PS...Position detector,
TG…Speed generator.

Claims (1)

[Claims] 1 It has a first system and a second system, the first and second power converters are connected to each system, and the two power converters are connected to a frequency higher than that of the first and second systems. A power conversion device characterized in that an energy storage device connected by a circuit and operating at a high frequency is connected between two power converters.