JPS6032204B2 - Control device for DC-AC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a DC-AC converter that supplies DC power to an AC power system.

Since this type of DC-AC converter mainly uses a separately excited inverter to perform conversion, it has a capacity of about 70% of the converted power so as to absorb the non-power generated by phase control at the same time as supplying power. It was necessary to compensate for the power factor by using capacitor equipment, which inevitably made the equipment larger.

In consideration of this point, the present invention uses a visually energized inverter device and skillfully controls it, thereby making it possible to convert DC power to AC power without receiving reactive power from the grid. This is an attempt to solve all at once.

In addition, in the present invention, it is possible to effectively avoid the possibility of transient disturbance or abnormal operation of the self-excited inverter when starting or stopping AC power operation using the self-excited inverter. This paper attempts to propose a control device.

An example of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows the main circuit of the DC-AC converter according to the present invention, in which 1 is an AC power system, 2 is a DC power supply with an output voltage Ed whose one end is grounded, and 3 is a self-excited circuit connected to the DC power supply 2. In the inverter device, 4 is a transformer that sends out the output of the self-excited inverter device 3 as three-phase alternating current, and 5 is a switch that connects the transformer 4 and the AC power system 1, respectively. In this embodiment, the visually excited inverter device 3 includes three-phase inverter circuits 3A, 3B, and 3C having a McMurray bet board commutation circuit configuration.

Each phase inverter circuit 3A, 3B, 3C has two pairs of thyristors 6 and 7, 8 and 9 connected in series by reactors 10 and 11, respectively.
The midpoint of is derived as the switching output end. In addition, in each phase inverter circuit 3A, 3B, 3C,
Commutation capacitors 12 to 15 are connected in parallel to the thyristors 6 to 9, respectively, and bypass diodes 16 to 19 are similarly connected in parallel. However, the pairs of thyristors 6, 7, 8, and 9 of each phase inverter circuit 3A, 3B, 3C are alternately energized, and when one is energized, the other is extinguished.

In other words, if the thyristor 6 is currently energized,
At this time, the capacitor 13 is charged with the output voltage Ed of the DC power supply 2. When an ignition pulse is given to the thyristor 7 in this state, the charge on the capacitor 13 is transferred to the reactor 1.
0 and thyristor 7. At this time, the voltage of capacitor 3 is applied to commutation reactor 01, so
The cathode potential of the thyristor 6 is pushed up to twice the DC voltage. Since a reverse voltage is applied to the thyristor 6, the thyristor 6 is turned off. Similarly, when the thyristor 6 is ignited while the thyristor 7 is energized, the thyristor 7 is extinguished.

In FIG. 1, the thyristors of two parallel circuits of each phase inverter circuit 3A, 3B, 3C have output points a and b,
Potentials Va and Vb of c and d, e and f, Vc and Vd
, Ve and Vf are controlled so that they vary by 120 degrees from each other as shown in FIG.

However, if we focus on a one-phase inverter circuit, for example, the first phase inverter circuit 3A, the potential Va at the output point a becomes a DC voltage Ed when the thyristor 6 is suitable for conducting, and conversely, when the thyristor 7 is suitable for conducting. At this time, it becomes the ground potential, that is, 0 potential (Fig. 2c).

Similarly, the potential Vb at the output point 6 becomes a DC voltage Ed when the thyristor 8 is conducting, and conversely becomes 0 potential when the thyristor 9 is conducting properly (FIG. 2F). Therefore, although the values of potential changes at output points a and b are the same, there is a phase difference between them, and therefore the voltage difference between output points a and b is V
As shown in FIG. 2, the desk forms a rectangular wave voltage whose rise width is this phase difference of 0. Similarly, for the second and third phase inverter circuits 3B and 3C, the voltage between output points c and d is Vcd, and the voltage between output points e and f is Vef.
As shown in Figure 2 J and K, respectively, the phase width is ? This results in rectangular wave voltages with a phase shift of 120 degrees.

These first phase, second phase, and third phase inverter circuits 3A,
The output voltages Vab, Vq, and Vef of 3B and 3C are output from transformer 4.
In this way, step-like outputs as shown in FIG. T
-S phase-to-phase voltage VTs.

In this way, a three-phase system voltage as shown in FIG. 2A having a sinusoidal waveform of three-phase interphase voltage as shown in FIG. 2B is supplied to the AC power system 1.

Note that FIG. 2 shows a case where the output of the DC-AC converter is synchronized with the AC power system 1, and the voltage between a and b of the self-excited inverter 3 is small, the voltage between c and d is V,
The voltage Vef between f is the R phase voltage of the AC power system 1, and
It is synchronized with the S phase voltage and T phase voltage. The voltage of the AC power system 1 can be controlled by shifting the activation periods of the thyristors 6 and 7, and 8 and 9 of each phase inverter circuit 3A, 3B, 3C.

For example, when controlling the R-phase voltage of the AC power system 1 as shown in FIG. 3A, from a relatively large output state with a phase width ◇ as shown in FIG. 3BI, to a phase width ◇ as shown in FIG. By gradually narrowing the width, it is possible to control the change to a medium output state or a low output state. Note that in Figures 2 and 3, the case where there is no phase difference between the output of the DC-AC converter and the grid power is described, but when synchronizing with a phase difference of 6, the thyristor of the DC-AC converter The ignition control may be changed to obtain a state as shown in FIG.

Here, FIG. 4A is the phase voltage of the AC power system 1, FIG. 4B is the phase-to-phase voltage of the AC power system 1, and FIG. 4C is the voltage between a and b.
ab and FIG. 4D respectively show the RT phase voltage VRT.
The main circuit of the DC-AC converter has been described above, but in the present invention, a control system as shown in FIG. 5 is provided in order to convert reactive power to DC power without receiving supply of reactive power from the grid.

The main circuit has the same structure as in FIG. 1, with the same reference numerals attached to corresponding parts, and the symbol of each thyristor indicates that it is equipped with an arc extinguishing circuit. 21A-24
C is a trigger circuit, and inverter circuits 3A, 3B,
Firing pulses are given to the four thyristors 6, 7, 8, and 9 of 3C at the timings instructed by the trigger timing circuit 25, respectively.

This trigger timing circuit 25 includes a three-phase detection output of a grid voltage detection transformer 26 connected to the AC power system 1;
A phase difference calculation circuit 27 that calculates the phase 6 (FIG. 4) of the output voltage of the DC-AC converter with respect to the voltage of the AC power system 1
6 outputs and a small phase width of the DC-AC converter output voltage (
J output of the phase width arithmetic circuit 28 which calculates (FIG. 3) is received as a condition signal. The phase difference calculation circuit 27 receives the detection output of the system voltage detection transformer 26 and converts it into a reference circuit 29.
A phase difference 6 is calculated by comparing it with a conversion required power reference in the form of an analog signal coming from.

Further, the phase width calculation circuit 28 receives the output of the DC voltage detector 30 connected to the output end of the DC power supply 2, and the phase difference calculation circuit 27.
6 outputs and produce the corresponding 0 output.
In FIG. 5, reference numeral 31 denotes a start push button switch, which closes the switch of the main circuit and starts the calculation operation of the phase difference calculation circuit 27, thereby starting the DC-AC converter. In the control system having the configuration shown in FIG. 5, control is performed based on the following principle.

Generally, there is a relationship between the self-excited inverter device 3 and the AC power system 1 as shown in FIG. Here, Wataru S is the voltage vector of the AC power system 1, and Ec is the voltage vector of the inverter device 3.
, the fundamental wave voltage vector of the generated voltage, x indicates the AC reactance of the transformer 4 and the system, and 1 indicates the current vector flowing from the inverter device 3 to the system. However, the flowing current 1 is calculated by the following equation.

i=Shoji9...mjX Therefore, the current i is composed of an active component IR and an inactive component IL.

By the way, let the voltage amplitudes of ES and Wataru C be ES and Ec,
Also, assuming that the phase angle at which Es advances from Ec is 8, the active power and reactive power supplied to the AC power system 1 are P and Q, respectively.
Then, P and Q can be obtained by the following equations.

P=three demi in6. ．．・'2'Q=vine (E
S-ECCOS6) ---{31 From this equation, it can be seen that the powers P and Q can be controlled by controlling the phase angle 6 or the output voltage Ec of the eye-exciting inverter device 3.

On the other hand, in order to prevent the reactive power Q from being consumed by the grid, the effective control shown in FIG. 7 is performed.

That is, when the converted power is gradually increased from zero (FIG. 7A) (FIGS. 7B and C), the system voltage Es Control is performed to obtain a motion vector such that the in-phase component with respect to the system voltage Es becomes equal to this Es, and only the vertical component with respect to the system voltage Es is variable. In this way, only active power can be converted to the grid. In addition, in Figure 7,
Es is the voltage vector of the AC power system 1, Bc is the fundamental wave voltage vector of the voltage generated by the self-excited inverter, and × is the transformer 4
and the AC reactance of the system, 1 and 12 are the currents flowing into the system, and 6 and 62 are the leading phase angles between Ec and Es. By the way, if you use this kind of control, E.

= C poison too. ... [4] P = Supervisor 32
‐‐‐{5} Q=0...[61]

Here, the voltage amplitudes of ES and Bc are Es and Ec, and E
The phase angle at which c leads Es is 6, and the active power and reactive power supplied to the AC power system 1 are P and Q, respectively. Therefore, in the control system shown in FIG. 5, the conversion required power standard is supplied from the reference circuit 29 to the phase difference calculation circuit 27, and the system voltage Es is supplied from the system voltage detection transformer 26 to the phase difference calculation circuit 27. , which gives the following equation 6
Skin - (foundation). ...'7) The phase difference 6 is calculated in the circuit 27 based on the following.

The six outputs whose contents are the values determined by the formula {7} are given to the phase width calculation circuit 28, and this circuit 28 calculates the inverter output voltage Ec based on the formula (2).

At this time, the phase width calculation circuit 28 calculates the phase Z width based on the following equation using the DC voltage Ed coming from the DC voltage detector 30 and the output voltage Ec obtained by calculation.
E.

=2 Collar rate・Ed・Sin consideration ・・Side Naoko (8}
The formula is obtained by Fourier expansion of the phase-to-phase voltage waveform of the DC-AC converter described above with reference to FIGS. 2L to 2N. When the 8 signals and the J signal thus obtained in the phase difference calculation circuit 27 and the phase width calculation circuit 28 are input to the trigger timing circuit 25, this circuit 25 has a configuration as shown in FIG. Determine the point in time of occurrence.

In FIG. 8, 41 is a control transformer connected to the grid voltage detection transformer 26, and a rectangular wave generating circuit 42 connected to the output terminal of the control transformer 41 generates a rectangular signal periodically generated by the grid voltage (A in FIG. 9). A wave signal S is generated (FIG. 9B).

This rectangular wave output S, is generated by a phase discriminator 43, an oscillation circuit 44 that generates digital pulses according to its output, and a mirror-tooth wave output S2 (second 9C) and is fed to a PLL circuit (phase drop loop circuit) 46 comprising a counter circuit 45 which feeds it back to a phase discriminator 43. The chain tooth wave output S2 of the counter 45 is given to the adder 47 as an output of the PLL circuit 46, where it is added to the 6 signals.

As a result, the output S3 of the adder 47 is shifted in phase by a phase difference of 8, as shown in FIG. 9D. Incidentally, when the PLL output S2 and the 6th signal are added together and there is an overflow, it starts from zero, so the digital signal is generated earlier in time in accordance with the 6th signal. The output S3 of the adder 47 is sent to three triangular wave memories 4 in ROM configuration.
8A, 48B, and 48C, and generate two cycles of triangular wave outputs S4a, S4b, and S4c for one cycle of chain tooth wave output S3, as shown in FIG. 9E.

Here, these triangular wave outputs S4a, S4b, and S4c are shifted in phase by 1200 from each other to serve as a reference for each of the three phases, and in this way, the triangular wave memories 48A, 4
It is stored in advance in 8B and 48C. Triangular wave output S4a
, S4b, S4c are D/A conversion circuits 49A, 498, 4
After being converted into an analog signal at 9C, it is applied to comparators 50A, 50B, and 50C which receive the signal as a reference signal.

At this time, the comparators 50A, 50B, and 50C output triangular waves S
When 4a, S4b, and S4c match the ◇ signals (Fig. 9E), trigger pulses P,, P2, P3, P4, (Fig. 9 F1, F2.F3,
F4) is sent. Trigger pulses for the thyristors of each phase are sent to the thyristors 6, 7, 8, 9 through the distribution circuits 51A to 51C to the trigger circuits 21A, 22A,
23A, 24A to 21C, 22C, 23C, and 24C. Thus, as shown in FIG. 9G, the output voltage of the self-excited inverter device 3 has a phase that is ahead of the voltage of the AC power system 1 (FIG. 9A) by a phase difference of 6, and has a phase width ◇
It becomes a voltage waveform with . As described above, according to the configuration shown in FIG. 5 according to one example of the present invention, it is possible to obtain a control device for a DC-AC converter that can control the phase and voltage value of the output voltage, but other examples of the present invention In order to stably start and stop the visually excited inverter device 3 using such a control device, the following control is performed.

First, by controlling the phase width of the self-excited inverter device 3 during startup, the grid voltage and the self-excited inverter output voltage are completely matched, the phase difference 6 is also zero, and the switch 5 is closed, and then the transient The phase difference and magnitude of the output voltage of the self-excited inverter device 3 with respect to the system power supply voltage are controlled slowly so that disturbances do not occur. In this way, stable operation can be achieved. Next, when the power conversion is completed and stopped, the phase and magnitude of the output voltage of the self-excited inverter device 3 are made to match the voltage of the AC power system again, and the switch 5 is opened in this state.

In this way, it is effective to avoid abnormal operations such as transient disturbances and loss of commutation in the self-excited inverter device 3. As described above, according to the device of the present invention, the phase difference and voltage value of the output voltage of the self-excited inverter device with respect to the voltage of the AC power system can be arbitrarily controlled as necessary, and therefore, DC-AC conversion can be performed. This can be done without receiving reactive power from the grid. Furthermore, according to the device of the present invention, it is possible to prevent the possibility of transient disturbances occurring or failure of commutation during startup and shutdown, thereby ensuring stable operation.

Incidentally, since the self-excited inverter device 3 includes a bass-pass diode, if a switch is connected in parallel even when no trigger pulse is applied to the thyristor, an inrush current will flow into the DC power supply 2 through the diode, which is undesirable. Therefore, it is necessary to operate the visual inverter device 3 and connect it to the grid, but
A transient current according to the difference between the output voltage of the self-excited inverter device 3 and the grid voltage flows, and there is a possibility that the self-excited inverter device 3 may fail in commutation. According to the present invention, such a risk can be effectively avoided.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram showing the main circuit of a control device for a DC-AC converter according to the present invention, FIGS. 2 to 4 are signal waveform diagrams for explaining its operation, and FIG. A schematic connection diagram showing the control system, FIGS. 6 and 7 are signal waveform diagrams for explaining its operation, FIG. 8 is a block diagram showing the detailed configuration of a part of FIG. 5, and FIG. FIG. 3 is a signal waveform diagram for explaining its operation. 1... AC power system, 2... DC power supply, 3
...Self-excited inverter device, 3A to 3C...
Each phase inverter circuit, 4...Transformer, 5...
...Switch, 6-9...Thyristor, 10,11...
Reactor, 12-15...Commuting capacitor,
16~19... Bypass diode, 21A~
24C...Trigger circuit, 25...Trigger timing circuit, 26...Detection transformer, 27...Phase difference calculation circuit, 28...Phase width calculation circuit, 29
・・・・・・Reference circuit, 30...DC voltage detector,
31...Start push button switch, 41...
...Control transformer, 42...Square wave generation circuit, 46
...PLL, 47...Adder, 48A-4
8C...Triangle wave memory, 49A~49C...
・D/A converter, 50A to 50C... Comparator,
51A to 51C...Distribution circuit. Figure 1 Figure 2 Figure 3 Figure 6 Figure 7 Figure 4 Figure 5 Figure 8 Figure 9

Claims (1)

[Claims] 1. In a DC-AC converter that converts the output of a DC power source into AC using a self-excited inverter and supplies the converted AC to an AC power system, the voltage and phase of the AC power system are used as a reference. a phase adjustment device that adjusts the phase difference between the output voltage of the self-excited inverter device and the voltage of the AC power system; a voltage control device that adjusts the output voltage of the self-excited inverter device; and the self-excited inverter device and the AC power system. and a switch interposed between the DC power supply and the AC power system, and set the DC power supply to arbitrary reference values of active power and reactive power to be output from the DC power supply in order to supply predetermined power to the AC power system. On the other hand, while controlling the magnitude and phase difference of the output voltage of the self-excited inverter device,
When starting the self-excited inverter device, the magnitude and phase of the output voltage of the self-excited inverter device are made to match the magnitude and phase of the voltage of the AC power system with the switch open, and in this matched state, By closing the switch, the self-excited inverter starts supplying power to the AC power system, and when the self-excited inverter is stopped, the self-excited inverter starts supplying power to the AC power system. By matching the magnitude and phase of the output voltage of the self-excited inverter device with the magnitude and phase of the voltage of the AC power system, and opening the switch in this matched state, the self-excited inverter device is connected to the AC power system. A control device for a DC-AC converter, characterized in that an attempt is made to stop the supply of electric power.