JPH0618461B2 - Parallel operation method for power converters - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of operating a power converter that converts AC power of different frequencies, and sometimes uses two static power converters (rectifier and inverse converter). The present invention relates to a parallel operation method of power conversion devices, which is suitable for stable operation when a plurality of such power conversion devices are connected in parallel to a load system without a generator or the like.

[Background of the Invention]

Generally, when power is exchanged between two different frequency AC systems, it is necessary to match the voltage and frequency (and phase) of one AC system with the voltage and frequency (phase) of the other AC system. For this reason, the conventional MG
Using the device, the electric motor M converts electric energy into rotational energy, the generator G converts rotational energy into electric energy again, and the voltage and frequency (phase) of the AC system to be connected are adjusted (synchronized). The method has been taken. FIG. 4 is a configuration block diagram illustrating a conventional method for operating a power conversion device using this type of MG device. In FIG. 4, 1 is an AC system (60 Hz), 2 is an AC system 1
AC system (50 Hz) with a load of a voltage and frequency (phase) different from that, 3, 4 are electric motors M for converting the electric energy of the MG device into rotational energy, and 5, 6 are rotational energy of the MG device again into electrical energy. Synchronous generator G to convert,
Reference numerals 7 and 8 are field windings of the generators 5 and 6, 9 and 10 are field control devices for controlling currents flowing in the field windings 7 and 9, and 41 and 42 are output voltages of the generators 5 and 6, respectively. Is a voltage converter for detecting. With such a configuration, the magnitude of the AC voltage on the load side is adjusted to a specified value by controlling the field currents of the generators 5 and 6 in accordance with the operation command values P _{1 and} P ₂ , and the frequency (phase ) Is controlled by controlling the number of rotations of the electric motors 3 and 4 (control device is not shown), and operation is performed. Note that FIG. 4 shows the MG device 2
The figure shows the case where the units are operated in parallel.

In recent years, the realization of high-voltage and large-capacity semiconductor devices has led to, for example, "Tokyo Electric Power Co., Inc. Shin-Shinano Substation Control and Protection Device for Frequency Conversion Equipment", Hitachi Review Vol. 61, N
o. As shown in FIG. 2, a large-capacity static frequency conversion device has been put into practical use, and the conventional MG device has been replaced by this. As this replacement progresses, in the future, only a plurality of power converters including static power converters (rectifiers and inverse converters) will be connected to the load system, and the power converters will be operated in parallel. However, in this case, there is no technology for parallel operation before establishing the voltage and frequency (phase) in the power converter consisting of only the static power converter, and the voltage of the load system and its frequency (phase) during parallel operation are not available. And the load sharing among the power converters (static type) are problems.

[Object of the Invention]

The present invention relates to a generator or the like that has conventionally been used to establish the voltage and frequency (phase) of a power source in a load system when a plurality of power converters each including two static power converters are operated in parallel. An object of the present invention is to provide a parallel operation method of power conversion devices that can stably supply power to a load without using the power conversion device.

[Outline of Invention]

The present invention focuses on the fact that stable operation can be performed by determining the voltage and its frequency (phase) at one location in one electric power system and allowing the other to follow it, and has the following features. .

That is, a first static power converter that converts AC power of a first frequency into DC power, and DC power output from the first static power converter are received, and the DC power is converted into second power. A power converter configured to include a second static power converter that converts AC power of a frequency is applied to a power supply facility configured to be connected in parallel to a load, The second static power conversion device in one power conversion device does not take charge of load sharing,
After establishing the voltage / frequency / phase of the power supplied to the load, the second static power converters in the other power converters other than the one power converter are loaded into the respective power converters. By supplying electric power in accordance with the sharing, the other electric power conversion devices except the one electric power conversion device supply the total load electric power as a whole.

Further, generally, there are two types of static power converters, which are roughly classified into a self-excited power converter that has a commutation capability in commutation operation and a separately excited power converter that performs commutation by measuring the voltage of an AC system. Yes, the self-excited type is suitable for stable operation by specifying the voltage and frequency (phase) of the AC system, while the separately excited type is capable of maintaining the voltage and frequency (phase) in the connected AC system. Stable operation cannot be achieved without a generator or the like, but the circuit is simple and the capacity can be easily increased, which is suitable for converting a predetermined amount of power. According to the present invention, in consideration of having such characteristics, the second static power conversion device in the one power conversion device that does not bear the load sharing is configured by a self-excited power conversion device. , This self-excited power converter establishes the voltage of the load system and its frequency (phase), and the rest of the power converter (not only separately excited but also self-excited) may be used to supply the load power. A parallel operation method of power converters is provided.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a configuration block diagram showing an embodiment of a parallel operation method for power converters according to the present invention. In FIG. 1, 1 is an AC system on the power supply side, 2 is an AC system on the load side having a frequency or phase different from that of the AC system 1 (load system),
Reference numerals 11 and 12 denote static power converters (rectifiers) that convert AC to DC, and reference numerals 22 and 22 denote static power converters (inverter) that convert DC to AC. For example, one static power converter. The (inverter) 21 is preferably a GTO (Gato Turnoff Thyri) having a self-extinguishing function.
is a self-excited power converter in which the converter is composed of a converter, etc., and the other static power converter (inverse converter) 22 is a separately-excited power converter in which the converter is composed of a thyristor without self-extinguishing function The converter. Reference numerals 31 and 32 are control devices for the power converters (inverse converters) 21 and 22, respectively, 41 is a voltage transformer that detects the magnitude of the AC voltage of the load system, and 51 is a time current that detects the magnitude of the current of the DC circuit. Current transformer, 6
1 is a capacitor for lowering the impedance of the power source when using the self-excited power converter as a voltage source, and 71 is a direct current smoothing for increasing the impedance of the power source when using the separately excited power converter as a current source. It is a reactor for. P _{1 and} P ₂ are control devices 31 and 3, respectively.
The operation command value P ₁ has the magnitude of the voltage of the load system and its frequency (and phase) as its contents, and the operation command value P ₂ has the electric power required by the load as its contents. Although the control devices for the static power converters (rectifiers) 11 and 12 are not shown, the power converters (rectifiers) 11 are preferably used because of the operating characteristics of the power converters (inverse converters) connected to them. Constant voltage control operation with constant DC circuit voltage, power converter (rectifier)
Similarly, 12 may be constant voltage control operation, but preferably constant power (constant current) control operation in which the current flowing in the DC circuit is constant.

Next, the operation of each power conversion device in the power supply facility configured by connecting two static power conversion devices in parallel as described above will be described. First, the self-excited power converter (inverter) 21 is controlled by the controller 31 according to the load AC voltage and the operation command value P ₁ of the frequency (phase), and the AC voltage of its output is detected by the voltage transformer 41. Thus, when the magnitude of the output voltage is lower than the operation command value P ₁ , it is high, and when it is high, it is low. For example, the width of the conduction period of the GTO forming the self-excited power converter (inverse converter) 21 is wide. Controlled. On the other hand, the frequency (phase) thereof is controlled so as to have a constant phase difference from the operation command value P ₁ by changing the on / off time of the GTO. When the voltage and frequency (phase) of the load system 2 are thus determined (established), the separately-excited power converter (inverse converter) 22 operates the converter at an appropriate phase from the phase of the AC voltage of the load system. The ignition phase is controlled by turning on and off the constituent thyristors so as to output electric power according to the operation command value P ₂ of the electric power required by the load. The operation command value P ₂ of this electric power is made into the electric current command value I _dp from the electric power P required by the load and the voltage V _{d of the} DC circuit by the following equation, and this electric current command I _dp is the power converter (inverse converter) 22. Control device 3
2 becomes the current command value of the constant current control circuit, and the current of the DC circuit detected by the DC current transformer 51 becomes the current command value I _dp.
The control advance angle β is controlled (a kind of constant voltage control) so that the margin angle of the converter is minimized so as to be equal to.

I _dp = P / V _d ...... 1) Here, V _d 1.35e ₂ cos β ...... 2) e ₂ : AC voltage of load Note that when the power P of the load is rapidly changed due to disturbance or the like. In the separately-excited power converter (inverse converter) 22, the load follow-up control cannot be performed rapidly in accordance with the fluctuation of the power P, so at this time, the self-excited power converter (inverter) 21.
By smoothing excess and deficient electric power and supplying electric power to the load, stable operation of the load system is performed.

Such stable operation can be performed by one of the static power converters connected in parallel performing an operation to determine the voltage of the load system and its frequency (phase), and all the power converters use the power (or This cannot be done when operating with specified current. This is the case when the self-exciting power converter (inverse converter) 21 that specifies the voltage of the load system and its frequency (phase) in FIG. It is apparent that the case (21) is replaced with a separately excited power converter that is operating with specified power (or current).

FIG. 2 is a configuration block diagram showing another embodiment of the parallel operation method for the static power converters according to the present invention. In FIG. 2, the same reference numerals denote the same or corresponding parts throughout the drawings, 13 is a static power converter (rectifier) that converts alternating current to direct current, and 23 is a static power converter that converts direct current to alternating current ( In the reverse converter, for example, the static power converter (inverter) 23 is a separately excited power converter in which the converter is composed of a thyristor having no self-extinguishing function. Three
3 is a control device for the power converter (inverter) 23, 52 is a direct current transformer for detecting the magnitude of the current in the direct current circuit, 7
Reference numeral 2 is a DC smoothing reactor for increasing the impedance of the power source when using the separately excited type electric conversion control device as a current source. P ₃ is an operation command value of the control device 33, and the operation command values P _{2 and} P ₃ respectively have the shared power of the power required by the load. Although the control device of the static power converter (rectifier) 13 is not shown in the figure, a constant power (current) flowing in the direct current circuit is preferably constant because of the operating characteristics of the power converter (inverter) connected thereto. Constant current) control operation.

As described above, three static power converters in which the static power converter (rectifier) 13 and the separately excited power converter (inverse converter) 23 for designating the shared power of the load are further added to FIG. The operation of each power conversion device in the power supply facility configured by connecting in parallel will be described. First, the self-excited power converter (inverter) 21 is controlled according to the AC voltage of the load and the operation command value P ₁ of the frequency (phase) as in FIG. When the voltage and frequency (phase) of the load system 2 are determined (established) in this way, the separately-excited power converters (inverse converters) 22 and 23 respectively request the load in the same manner as in FIG. It is controlled to output electric power according to the operation command values P ₂ and P ₃ of the shared electric power of the electric power P. At this time, the operation command values P ₂ and P ₃ of the shared power of the separately-excited power converters are, for example, simply P
It is possible to set ₂ = P ₃ = P / 2, and generally P
_It may be specified so that ₂ + P ₃ = P. When the power P of the load suddenly changes due to a disturbance or the like, the self-excited power converter (inverter) 21 follows the load fluctuation and supplies power to the load, as in FIG. Stable operation of the system is performed.

FIG. 3 is a configuration block diagram showing still another embodiment of the parallel operation method for the static power converters according to the present invention. In FIG. 3, for example, the static power converter (inverter) 22 is a self-excited power converter in which the converter is composed of GT0 having a self-extinguishing function, unlike in FIG. Thus, two static power converters (inverse converters) 21 and 22
As a self-exciting power converter, the operation of each power converter in a power supply facility configured by connecting three static power converters in parallel as in FIG. 2 will be described. First, of the two self-excited power converters, for example, one self-excited power converter (inverter) 21 is shown in FIGS.
Similar to the figure, control is performed according to the AC voltage of the load and the operation command value P ₁ of the frequency (phase). When the voltage and frequency (phase) of the load system 2 are determined (established) in this way, another self-excited power converter (inverter) 22 and another excited power converter (inverter) are respectively provided. At 23, similarly to FIGS. 1 and 2, control is performed so as to output electric power corresponding to the operation command values P _{2 and} P ₃ of the shared electric power of the electric power P required by the load. In this way, one of the self-excited power converters operates to determine the voltage and frequency (phase) of the load system, and the other one (with the separately excited power converter) specifies power (or current). If operated, the load system is stably operated as in FIGS. 1 and 2.

In the above embodiment, one self-exciting power converter is made to determine the voltage of the load system and its frequency (phase), but the method according to the present invention is not limited to this one self-exciting type. Alternatively, a separately excited power converter may be used.

〔The invention's effect〕

According to the present invention, when a plurality of power conversion devices each including only two static power conversion devices (rectifier and inverse converter) are operated in parallel, the voltage, frequency, and phase of the load system can be easily established. Therefore, it is possible to stably supply electric power without a generator or the like.

[Brief description of drawings]

FIG. 1 is a structural block diagram showing an embodiment of a parallel operating method of a static power converter according to the present invention, FIG. 2 is a structural block diagram showing another embodiment of the same, and FIG. FIG. 4 is a block diagram showing the configuration of an example of a conventional MG.
It is a configuration block diagram which illustrates the operating method of the power converter by a device. 1 ... AC system, 2 ... Load system, 11-13 ... Stationary power converter (rectifier), 21-23 ... Stationary power converter (inverter), 31-33 ... Control device, 41
...... Voltage transformer, 51-52 ...... DC current transformer, 61
...... Capacitors 71 to 72 ...... DC reactor, P ₁
...... Operation command value (voltage and frequency (phase)), P ₂ ,
P ₃ ...... operation command value (power or current).

Claims (2)

[Claims] 1. A first static power converter that converts AC power of a first frequency into DC power, and DC power output from the first static power converter, and the DC power is received. In a power supply facility in which a plurality of power conversion devices configured to include a second static power conversion device that converts AC power of a second frequency are connected in parallel to a load, After the second static power converter in the power converter establishes the voltage / frequency / phase of the power to be supplied to the load without sharing the load, the one power converter is removed. The second static power conversion device in the power conversion device supplies the electric power according to the load sharing of each power conversion device, so that all the other power conversion devices except the one power conversion device are entirely operated. As full load power Parallel operation method of a power converting apparatus and supplying. 2. The parallel operation of the power converters according to claim 1, wherein the second static power converter in the one power converter is a self-excited power converter. Method.