JPS5943892B2 - Grid connection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a grid interconnection device for interconnecting different power systems.

2. Description of the Related Art Conventionally, a device as shown in a single line diagram in FIG. 1 has been used as an interconnection device for interconnecting different power systems, for example, a 50HZ system and a 60HZ system.

In FIG. 1, 1 indicates one power system (for example, 60H
Z system), 2 is another power system (for example, 50Hz system),
It is connected to power converters 4A and 4B via transformers 3A and 3B.

4A and 4B are thyristors 41 to 41 as shown in FIG.
It is probably a controlled rectifier consisting of 43 6-phase Gretz connections.

The DC terminals of the power converters 4A and 4B are connected to the DC reactor 5.
The 4A(7)P terminal is connected to the 4B(■!)N terminal via the reactor 5, and the 4B(7)P terminal is connected to the 4A(7)N terminal. 4A and 4B are
Depending on the state of power interchange between the two systems, one operates as a forward converter and the other operates as an inverse converter (inverter).

For example, when it is desired to send power from power system 1 to power system 2, 4A operates as a forward converter and 4B operates as an inverse converter. When power is supplied from system 2 to system 1, the operations of 4A and 4B are opposite to those described above. However, the conventional method had the following drawbacks.

4A and 4B operate as forward converters or separately commutated current inverse converters, and each of the thyristors 41 to 46 shown in FIG. Take the lagging reactive power from 6N+1st (N is 1, 2,
3...) harmonic currents will flow through the power system.

These reactive powers and harmonic currents are transferred to the power converter 4A
, 4B, which causes damage such as fluctuations in grid voltage and communication induction disturbances, and it is necessary to take measures against reactive power and harmonics for purposes other than grid connection. 6A and 6B in FIG. 1 are conventional reactive power compensators that also serve as harmonic filters.

The reactor 62 and the capacitor 61 are advanced reactive power equipment that also serves as a harmonic filter, and the equipment composed of the transformer 63, the reactor 64, and the thyristor 65 converts the lagging reactive power amount into the firing phase of the thyristor 65. This is a slow phase reactive power control device that performs control by controlling. 61,62
The lagging reactive power of the difference between the leading phase capacitance and the absolute value of the lagging reactive power consumed by the power converters 4A and 4B is expressed as 63, 64, 65.
The control angle of the thyristor 65 is controlled so that the delayed reactive power control device consisting of the following consumes it.

As a result, the reactive power flowing through the system 1 or 2 is reduced. On the other hand, the harmonic currents generated by the power converters 4A and 4B flow through the harmonic filters 62 and 61, and therefore do not flow out into the grid. As described above, conventional power converters have a major drawback in that in addition to the original purpose of interconnection between grids using power converters, a compensation device is required to suppress reactive power fluctuations and harmonic generation generated by grid interconnection equipment. had. The present invention has been made to eliminate the drawbacks of the conventional systems described above, and provides a novel system interconnection system that does not require reactive power compensation and a harmonic suppression device.

Now, FIG. 3 shows the configuration of an embodiment of the present invention.

In FIG. 3, numerals 1 and 2 indicate different power systems using single lines. 7A, 7B are multiplex transformers, 9A,
9B is a voltage source self-excited multiple inverter, 10A, 10
B is a DC capacitor, and 12 is a chopper circuit for DC voltage conversion.

The voltage type self-excited multiplex inverters 9A and 9B in FIG. 3 are composed of a plurality of sets of three-phase self-excited inverter units 90 shown in FIG.

The inverter unit basically consists of a thyristor switch 91U having a commutation circuit (not shown) as shown in FIG.
~91Z and feedback diodes 92U~92Z.

Thyristor switches 91U to 91Z are U, Z, V, X
, W, Y in the order of 600 and 1800, the amplitude of the AC output terminals U, V, W is equal to that of the DC capacitor 1.
With terminal voltage Ed of 0A or 10B, current carrying width is 1200
A three-phase rectangular wave AC voltage is generated. The output voltage of a voltage source inverter can be controlled using two methods: the amplitude modulation method (PAM method) that changes the amplitude Ed while keeping the conduction width 120i fixed, and the amplitude Ed
Pulse width modulation method (P) that changes the conduction width while keeping the
There are two types of inverters (WM method), and the inverter according to the present invention is characterized by using the former PAM method as a component. Next, in the multiplex inverter, as shown in FIG. 5, a plurality of three-phase inverter units 90 are installed in parallel at the DC power supply (DC capacitors 10A, 10B) terminals,
Controls multiple inverter units to have different phases.

In the case of Figure 5, two inverter units are used for simplicity.
Examples of 90A and 90B are shown. 90A AC output 3
For each phase, the AC output voltage of the 90B inverter unit is controlled so that it is generated with a 30 bar delay for each phase.

This relationship is illustrated in FIGS. 6a-f. Figure 6a
-c shows the output voltage waveform of the inverter unit 90A, which is a three-phase rectangular wave alternating current voltage with a conduction width of 120.
On the other hand, the output voltage waveform of inverter unit 90B is 9
Since the control is delayed by 30 points with respect to 0A, as shown in Figure 6 d-f, for each phase of the output voltage of 90A,
It is a three-phase rectangular wave AC voltage delayed by 90 steps. These three-phase voltages are applied to multiple monthly windings of a multiplex transformer consisting of 101, 102, etc.

The primary windings 103 and 107 of 101 and 102 are triangularly connected.

The secondary winding of transformer 101 is not a three-phase connection, but winding 1
At 04, 105, and 106, three-phase voltages U, Vl, and Wl are induced. The primary winding 107 of the transformer 102 is also triangularly connected. The secondary winding 107 has two windings for each phase, and U2, V2, and W2 are induced in the secondary winding in response to the three-phase voltage applied to the primary winding.

The mark written on the winding indicates the polarity of the induced voltage in the winding. Ul, vl, wlltc. On the other hand, U2,2
If the magnitude of W2 is chosen, the waveforms shown in FIGS. 6a-f will be induced in each secondary winding. If the secondary windings of each transformer are connected as shown in FIG. 5, the output terminal U of a multiplex transformer, for example. The voltage waveform between the neutral point M and the neutral point M becomes the waveform shown in FIG. 6g. That is, the voltage U. -M is a waveform synthesized by voltage U1 + U2 - V2, and is generated from 1 set of inverter units.
Compared to the wide rectangular AC voltage waveform, the waveform becomes closer to a sine waveform. By combining multiple sets of inverter units and multiple transformers, it is possible to obtain an output voltage close to a sine wave. For example, the harmonic components of the voltage generated from a combination of six three-phase inverter units and multiplex transformers are 35 times the grid frequency at the lowest frequency, and if 60Hz is the fundamental wave, harmonics higher than the harmonics of 2100Hz Contains only
Moreover, the amplitude is very small, 1/36 of the fundamental wave component, and a good voltage waveform can be obtained. Now, as shown in FIG. 7, an output voltage close to a sine wave is generated at the output of inverters 9A and 9B, and this voltage is boosted to the grid voltage level by transformers 7A and 7B, and impedances 15A and 15
A case in which the power grid is connected to the power system via B will be explained.

The system voltage is assumed to be 8, and the output terminal voltage of the transformer 7A or 7B output by the inverter is assumed to be M. In a state where the frequency of V1 matches the frequency of the system voltage Vs, Vs
A case will be described in which the amplitude and phase of V1 relative to V1 are maintained in the states shown in the vector diagrams of FIGS. 8a to 8d. FIG. 8a shows that V1 is delayed by an angle δ with respect to Vs, and
This is a case where the relationship between swing widths is maintained at 1V8 section and 1V11.

The voltage vector △V applied to the impedance element 15A or 15B is a vector directed from the lower right to the lower left as shown in the figure, and the current that is delayed by 900 with respect to the vector of △V flows into the system 1 or the 2 to inverter 9A, 9
Flows into B. This state means that active power flows from the grid to the inverter, and that the grid is supplying phase-advanced current. Next, as shown in Fig. 8b, if the phase of M with respect to Vs is delayed by δ and the amplitude relationship is maintained as 1Vs1>Vll, contrary to Fig. 8a, 15A or 15B
The vector of the voltage ΔV applied to is a vector pointing from the lower left to the upper right, and the current flowing from the grid is in a state of supplying active power to the inverter and lagging reactive power.

Next, as shown in FIG.
The voltage △V applied to A and 15B is a vector pointing from the upper right to the lower left, and the current with a delay of 900 is a state in which the grid side receives active power from the inverter and is supplied to the phase-advanced reactive power inverter. .

FIG. 8d shows a state in which the phase of V1 is advanced by δ with respect to Vs, and the amplitude relationship is maintained as 1Vs1>IVll.

The voltage ΔV applied to 15A and 15B becomes a vector directed from the upper left to the lower right, and the system is in a state where it is receiving active power from the inverter and supplying slow phase reactive power to the inverter.

As is clear from the above vector diagram, by controlling the inverter output voltage amplitude 1V11 for the grid voltage amplitude 1Vs1, the load state that consumes arbitrary reactive power from the slow phase to the advanced phase for the grid can be realized.

Of course, zero reactive power operation is also possible. On the other hand, by controlling the phase angle of the inverter output voltage V1 to be delayed or advanced with respect to the grid voltage Vs, the inverter can receive power supply or, conversely, can send out power. It is.

In the case of the interconnection device having the configuration shown in FIG. 3, when transmitting power from system 1 to system 2, inverter 9A operates with a phase angle delayed with respect to the voltage of system 1, and inverter 9B operates with a delay in phase angle with respect to the voltage of system 1. This can be achieved by operating in advance with respect to the voltage of .

Conversely, when transmitting power from grid 2 to grid 1, the phase of the output voltage of 9B is delayed with respect to the voltage of grid 2, and the phase of the output voltage of 9A is delayed relative to the voltage of grid 1. In contrast, it is better to say progress.

Now, when the difference between the active power flowing in from one power system and the power sent out to the other power system is zero, the change in energy within the device is zero, so the capacitors 10A and 10B
There is no change in the voltage. However, the incoming active power is
If it is greater than the active power flowing out, the capacitor voltage increases due to the differential power. On the other hand, if the power flowing out is larger, the capacitor voltage will decrease. 9A, 9B are P
Since it is an AM type inverter, a change in the capacitor voltage causes a change in the amplitude of the inverter's output voltage 1.
Leading or lagging reactive power flows from the grid into the inverter depending on the magnitude relationship with the grid voltage.

On the other hand, a small amount of loss occurs for the operation of the device.

Therefore, when the difference between the incoming power and the outgoing power of the interconnection device as a whole is equal to the loss of the device, the capacitor will maintain a stable state. Therefore, if you want to extract phase-advanced reactive power from the power grid, all you have to do is increase the capacitor voltage, so you can temporarily increase the power flowing in from the grid (or reduce the power flowing out). The phase of the output voltage of the inverter is controlled to be on the lagging side so that the output voltage is equal to or greater than the sum of the outflow power and the power consumed within the device. As a result, the capacitor voltage increases due to the increase in power flowing in from the grid, and the inverter output voltage increases.
Leading reactive power will flow in from the grid. Conversely, if you want to remove delayed phase reactive power from the grid, temporarily reduce the inflow power (or increase the outflow power) and make the sum of the outflow power and device power loss exceed the inflow power. , the voltage of the capacitor decreases, the output voltage of the inverter decreases, and the lagging reactive power from the grid increases.

When the inverters on both sides are configured as a grid interconnection device using the PAM method, the capacitor voltage is determined by the reactive power condition required by one power system, and it is not possible to take the reactive power required by the other power system. It disappears.

Therefore, as shown in Figure 3, 9A has 10A, 9
A combination of a 10B inverter and a capacitor is connected in series at B, and a chopper device 12 is placed in between.
By arranging the chopper device 12 in the middle, only the active power passes through the chopper device 12, and the voltage of the capacitors 10A and 10B on both sides can be maintained at that voltage regardless of the other inverter. Become. Now, assuming that there is no loss in the interconnection device, an example will be described.

When active power is sent from power system 1 to power system 2, and neither system currently requires a reactive power load, inverter 9A has the same voltage magnitude and phase angle as the system voltage of power system 1. generates an output voltage delayed by δ.

As a result of the above, only the active power is transferred from grid 1 to inverter 9A.
flows into. If the active power does not go out while it is in, the voltage of the capacitor 10A will continue to rise, so to prevent this, the chopper device 12 transfers the power to the capacitor so that the voltage of the capacitor 10A maintains a constant value. 10B
Send to. When the power flowing into the capacitor 10B increases, the terminal voltage of the capacitor 10B increases, so the inverter 9B advances the phase value by δ with respect to the system voltage of the system 2 so that the terminal voltage of the capacitor 10B is constant, and the vibration is reduced. This will generate an output voltage whose width is equal to the grid voltage. From this assumption, consider the case where a leading phase load is applied to system 1 and a lagging phase load is applied to system 2.

Since the inverter 9A takes the phase leading load from the system 1, it is necessary to increase the voltage of the capacitor 10A.

Therefore, while keeping the power passing through the chopper device 12 constant, the phase of the 9A output voltage is temporarily changed (until the voltage of the capacitor 10A reaches a state where it takes a predetermined phase-leading reactive power). ), the phase angle is delayed from the voltage of system 1, and when the value of the reactive power reaches a predetermined phase-advanced reactive power, the phase angle is returned to the original phase angle. On the other hand, since the inverter 9B needs to take the lagging phase reactive power, it is necessary to lower the voltage of the capacitor 10B to a value that takes the predetermined lagging reactive power. Therefore, the phase angle of the output voltage of inverter 9B with respect to the voltage of system 2 is temporarily advanced from the current position. Due to this,
Since the energy of the capacitor 10B is released to the power system 2, the voltage decreases, and the delayed phase reactive power taken from the system 2 increases, and when it reaches a predetermined reactive power value, the inverter 9
The phase of the output voltage of B is returned to the phase angle of the state in which only active power was being sent out. As described above, if it is possible to send active power from either power system to the other, and if it is possible to operate without drawing any reactive power from both systems, then it is possible to actively It becomes possible to obtain electricity as desired.

Here, FIG. 9, which is a specific embodiment of the capacitor and chopper device shown in FIG. 3, will be described.

In FIG. 9, 13 is a DC reactor, 14, 15
is a thyristor switch with an arc extinguishing circuit, and the current can be extinguished by external control.

16 and 17 are diodes.

FIG. 10a explains the operation of the switch 14 when power is sent from the capacitor 10A side to the capacitor 10B side. In this case, the switch 15 remains open. When the TA time switch 14 of FIG. 10a is closed, the capacitor 10A is short-circuited through the DC reactor 13, and the current passing through the DC reactor 13 increases linearly.

After time TA, when the switch 14 is extinguished by the operation of an unillustrated arc extinguishing circuit, the current flowing through the DC reactor 13 charges the capacitor 10B through the diode 17, and the voltage of the capacitor 10B increases by EdB. work. The current in this case is a current that gradually decreases, contrary to the previous case. After a period of T seconds, the switch 14 is closed again, the diode 17 is turned off due to the reverse voltage applied thereto, and the current in the series reactor 13 is transferred to the switch 14 and begins to increase again. Therefore, the current passing through the diode 17 and
The power equal to the product of the terminal voltage EdB of capacitor 10B is
It will be sent from capacitor 10A to 10B. Conversely, when power is sent from the capacitor 10B to the capacitor 10A, the switch 15 opens and closes, and the switch 14 remains open.

As shown in FIG. 10b, when the switch 15 is closed for a time T3 seconds out of the period T seconds, the capacitor 10B is short-circuited through the DC reactor 13 and the capacitor 10A, and the DC current in the DC reactor 13 increases. .

After a time TB seconds, the switch 15 is opened by the operation of an arc extinguishing circuit (not shown), and the current flowing through the DC reactor 13 circulates through the DC reactor 13, the capacitor 10A, and the diode 16. During this period, the current has a waveform that gradually decreases.

When the switch 15 is closed again, the current in the DC reactor 13 starts to increase. Therefore, power corresponding to the product of the current flowing through the DC reactor 13 and the voltage of the capacitor 10A is sent from the capacitor 10B to the capacitor 10A. Usually, in a chopper device having 12 configurations, the relationship between the voltage EdA of the capacitor 10A and the voltage EdB of the capacitor 10B is usually EdA minus EdB.

The present invention provides the following effects.

Since multiple inverters and multiple transformers are used, the output voltage of the inverter approaches a sine wave, and the harmonic current flowing through the grid is very small, making it unnecessary to install a harmonic suppression device. Even a very small capacity one is sufficient. Since this interconnection device can be operated without taking any lagging reactive power from the outside, a reactive power compensator is not required.

More than that, it is also possible to take any reactive power necessary for system operation while accommodating power, and it is possible to control reactive power independently of both systems. Since a reactive power compensator is not required, the installation space is small.

Since active power and reactive power are controlled by phase control using multiple inverters, control characteristics with quick response can be obtained. The capacitance of the capacitor installed in the interconnection device is only a fraction of the amount of reactive power handled.

[Brief Description of the Drawings] Fig. 1 is a schematic diagram of a conventional grid interconnection device, Fig. 2 is a schematic diagram of a rectifier used in the conventional grid interconnection device, and Fig. 3 is an embodiment of the present invention. A schematic configuration diagram of a grid interconnection device according to an example,
Figure 4 is a circuit diagram of a three-phase self-commutated inverter used in the present invention, Figure 5 is a circuit diagram of a multiplex inverter and multiple transformer, Figure 6 is an explanatory diagram of the output voltage waveform of the multiplex inverter, and Figure 7 is an illustration of the output voltage waveform of the multiplex inverter. A configuration diagram for explaining the principle of the grid interconnection device of the present invention, FIG. 8 is a vector diagram explaining the power and reactive power interchange state of the grid interconnection device according to the present invention, and FIG. 9 is a block diagram for explaining the principle of the interconnection device of the present invention. The configuration diagram of the device, FIG. 10 is an explanatory diagram of the operation of the chopper device. In the figure, 1 and 2 are power systems, 7A and 7B are multiplex transformers,
9A, 9B are amplitude modulation multiplex inverters, 10A, 10
B is a DC capacitor, and 12 is a chopper device.

Claims (1)

[Claims] 1. A first multiplex transformer whose primary winding is connected to a first power system and has a plurality of secondary windings having a predetermined phase difference from each other; this first multiplex transformer A first inverter device comprising a plurality of amplitude modulation type inverters connected to each secondary winding of and operated with a predetermined phase difference from each other;
a first capacitor connected between the DC terminals of the inverter device; a second multiple transformer having a primary winding connected to a second power system and having a plurality of secondary windings having a predetermined phase difference from each other; a second inverter device comprising a plurality of amplitude modulation inverters connected to each secondary winding of the second multiplex transformer and operated with a predetermined phase difference from each other; A grid interconnection device comprising a second capacitor connected between DC terminals, and a chopper device connected between the first and second capacitors and controlling the charging voltage of both capacitors. 2. The chopper device includes a first anti-parallel body formed by connecting a diode and a first switching element in anti-parallel, a reactor connected in series to the first anti-parallel body, and a diode and a second switching element. and a second anti-parallel body formed by connecting them in anti-parallel, and the first capacitor, the reactor, the first anti-parallel body, and the second capacitor are connected to form a series closed circuit, Claim 1, wherein the second anti-parallel body is connected between a connection point between the reactor and the first anti-parallel body and a connection point between the first and second capacitors. Grid connection equipment.