JPH066000B2 - Variable speed power generation system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a variable speed power generation system in which low frequency AC excitation is performed by a current converter using a semiconductor switching element.

[Conventional technology]

Conventionally, this type of variable speed power generation system is disclosed in, for example, Japanese Patent Laid-Open No. 59-
No. 72998, which are shown in FIG. As shown in the figure, the wire wound induction generator 21
Is driven to rotate by a water wheel 22 directly connected to the rotor. The secondary winding 21b of the wound-rotor induction generator 21 is supplied with an AC exciting current adjusted to a predetermined phase by the cycloconverter 23 using a semiconductor switching element according to the rotation speed of the wound-rotor induction generator 21. , Primary winding 21a
The variable speed operation is performed so that AC power having a constant frequency equal to the rated frequency of the electric power system 24 is output. Rotational speed signal N detected by the rotational speed detector 26
And a generator output command P ₀ and a water level detection signal H given from the outside are input to a water wheel characteristic function generator 25, and the water wheel characteristic function generator 25 has a maximum rotation speed command N _a for operating at maximum efficiency. And an optimum guide valve opening command Y _a is generated. A slip phase detecting induction machine 27 in which the rotor is directly connected to the wound-rotor induction generator 21 has a primary winding 27a connected to the output side of the wound-rotor induction generator 21, and a slip phase signal S from the secondary winding 27b. Output _P. The slips phase signal S _P and the optimum rotational speed command N _a is provided to cycloconverter 23, the cycloconverter 23 controls the phase or the like of the secondary winding 21b to the supplying alternating excitation current wound-rotor induction generator 21. The optimum guide valve opening command Y _a is given to the guide valve driving apparatus 28, the guide valve driving apparatus 28 controls the opening of the guide valve 29 to hydraulic turbine output is the optimum value.

[Problems to be solved by the invention]

The cycloconverter 23 in the conventional variable speed power generation system as described above is composed of positive and negative semiconductor switching elements and is alternately energized, so that these elements are alternately cooled in the non-energized state. Therefore, if the heat capacity of the element is determined in consideration of this point, a more economical cycloconverter 23 can be obtained. However, in the variable speed power generation system, since the operating range is a certain range before and after the synchronous speed, for example, ± 10%, when the synchronous speed is passed, the DC excitation state or the extremely low frequency excitation state, that is, the operation prohibition zone is temporarily stopped. Therefore, the heat capacity of the element selected on the condition of excitation at a frequency higher than a certain frequency is exceeded.
For this reason, it is necessary to detect this state promptly and protect the element, but no measures have been taken in the conventional variable speed power generation system.

An object of the present invention is to provide a variable speed power generation system capable of protecting a semiconductor switching element from an abnormal temperature rise.

[Means for solving problems]

In order to achieve the above object, the present invention provides a heating element having a temperature rise characteristic same as that of the semiconductor switching element, as well as a current corresponding to the current flowing through the semiconductor switching element, and a temperature detecting element provided in the heating element. And a protection means for protecting the semiconductor switching element when the temperature of the heating element by the temperature detecting element reaches a predetermined value.

[Action]

Since the variable speed power generation system of the present invention has the above-mentioned configuration, when the temperature of the semiconductor switching element rises due to the inversion prohibition zone or the like, a similar temperature rise also occurs in the heating element corresponding to the temperature rise and the temperature detection element. Therefore, when the temperature rise exceeds a predetermined value, the protection means is operated to control the wire wound induction generator to a speed away from the target speed or disconnect from the power system, and the semiconductor switching The element can be protected.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a main part of a variable speed power generation system, in which a secondary winding 8 of a wound-rotor induction generator which is a variable speed machine is excited by a cycloconverter 9 via a secondary excitation circuit 10. Variable speed operation is performed, and the cycloconverter 9 has a semiconductor switching element. Secondary excitation circuit 1
A small current i ₂ corresponding to the current I ₂ is shunted to 0 through the current transformer 11 and is supplied to the heating element 12 described in detail later. The heating element 12 and the current transformer 11 show only one phase and the other phases are not shown. Heating element 12
Has the same temperature characteristics as the semiconductor switching element of the cycloconverter 9, and its temperature is detected by the temperature detecting element 6 and reaches a predetermined temperature determined in consideration of the heat capacity of the semiconductor switching element of the cycloconverter 9. When you do, protection measure 1
Reference numeral 4 performs a protection operation for the semiconductor switching element. For example, when the predetermined temperature is set in two stages and the predetermined temperature on the low temperature side is reached,
At the same time as changing the speed command to a speed away from the synchronous speed, the output command is also lowered. On the other hand, when the temperature reaches the predetermined temperature on the high temperature side, the field current is stopped at the same time as disconnection from the power system.

Here, the relationship between the semiconductor switching element of the cycloconverter 9 and the heating element 12 will be described.

The transient temperature characteristics of the heating element having a cooling effect due to a cooling fin or the like are as follows: the heat capacity of the heating element is m, the temperature rise of the heating element is U,
When t is time, electric resistance of heating element is R, current is i, heat transfer coefficient of cooling fins is α, and cooling area is S Becomes

From the equation (1), the temperature rise U of the heating element is expressed by the following equation assuming that the current i is constant.

Therefore, the semiconductor switching element of the cycloconverter 9 and the heating element 12 exhibit the same temperature rise characteristics under the same conditions below.

That is, the heat transfer coefficient α can be made to have the same temperature characteristic by adjusting R / S and S / m even if the semiconductor switching element and the heating element 12 cannot be made the same.

FIG. 2 shows the details of the heating element 12 of FIG. Generally, three-phase alternating current is used in the secondary excitation circuit 10 of FIG.
Since the current exchangers such as the cycloconverter 9 that produce this current also have three-phase outputs, different currents flow through the semiconductor switching elements of each phase, and they are independently cooled so that they do not receive temperature interference. Further, even if they are in the same phase, the semiconductor switching elements of the positive group and the negative group are constructed so as not to be interfered with each other by temperature, and the currents are momentarily different. In accordance with this, the heating element 12 is also configured as shown. That is, the heating element corresponding to the positive group semiconductor switching element of the cycloconverter 9 is composed of the diode 1 having the cooling fins 5 and the current limiting electric resistance 3 connected in series. The heating element corresponding to the negative group semiconductor switching element of the cycloconverter 9 is composed of a diode 2 having a cooling fin 5 and a current limiting electric resistance 4 connected in series. Moreover, the cooling fins 5 of the respective diodes 1 and 2 are provided with temperature detecting elements 6, respectively, and the protection means 14 of FIG. 1 is operated by the output of the temperature detecting elements 6.

Accordance connexion, secondary excitation current I ₂ current one phase that is proportional to i ₂
Is divided into currents i _2P and i _2m corresponding to the positive and negative semiconductor switching elements of the cycloconverter 9, and the internal loss of the diodes 1 and 2 generated by this current is transmitted to the cooling fin 5. . Since the diodes 1 and 2 correspond to the semiconductor switching elements of the cycloconverter 9, the temperature rise of the cooling fins 5 of the diodes 1 and 2 is detected by the temperature detecting element 6 as the temperature rise of the semiconductor switching elements.

FIG. 3 shows the waveform of the secondary exciting current. The U phase and V when the secondary exciting current passes through OH _Z with a constant magnitude.
It is the waveform of the phase. As in part A of the figure, if a very low frequency state has continued for a predetermined time or more, or when passing through the OH _Z repeatedly within a certain time, heat is accumulated in the semiconductor switching element of the cycloconverter 9. If this exceeds the heat resistance of the semiconductor switching element, it will be thermally destroyed.

This state is detected by the temperature detecting element 6 via the cooling fins 5 of the diodes 1 and 2 in FIG. The set value of the temperature relay 7 shown as a part of the protection means 14 is set to, for example, two stages, and when the temperature rises and reaches a predetermined temperature on the low temperature side, the speed command N _a is changed to a speed apart from the synchronous speed and output. The command _{Po is} also lowered. This prevents current from concentrating on a specific semiconductor switching element, and lowers the output to reduce the field current to prevent temperature rise of the semiconductor switching element. When the temperature reaches the high temperature side, disconnect from the system immediately. In this way, the semiconductor switching device is protected by the operation of the protection means 14.

FIG. 4 shows a heating element 12 according to another embodiment of the present invention. The same parts as those in FIG. 2 are designated by the same reference numerals, and only different parts will be described.

In this embodiment, the temperature detecting element 6 is attached to the current limiting electric resistances 3 and 4. Since the semiconductor switching element of the cycloconverter 9 is generally used at a high voltage, its temperature cannot be measured directly, but an equivalent heating element 12 is provided, and the current limiting electric resistances 3 and 4 of this heating element are used to control the temperature. Is being measured. According to this embodiment, as in the previous embodiment, the semiconductor switching device can be protected by operating the protection means 14 when the measured value by the temperature detecting element 6 exceeds the predetermined temperature.

In addition, the same effect can be obtained by operating the induction generator as an induction motor and the water turbine as a pump.

〔The invention's effect〕

As described above, the present invention provides a heating element having the same temperature characteristics as that of the semiconductor switching element while flowing a current corresponding to the current flowing through the semiconductor switching element of the current converter, and based on the temperature measured by this heating element. Since the protection operation is performed, the temperature can be easily detected even when the semiconductor switching element is a high voltage portion, and a corresponding current flows through the heating element, so that the protection operation can be performed before thermal destruction due to the operation prohibition zone.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a main part of a variable speed power generation system according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of a heating element of FIG. 1, and FIG. 3 is an OH of a secondary exciting current. FIG. 4 is a waveform diagram when passing through _Z, FIG. 4 is a circuit diagram of a main part according to another embodiment of the present invention,
FIG. 5 is a circuit diagram showing a conventional variable speed power generation system. 6 ... Temperature detecting element, 8 ... Secondary winding, 9 ... Cycloconverter, 10 ... Secondary excitation circuit, 12 ... Heating element,
14 …… Protective measures.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiro Yasaka 3-1-1, Saiwaicho, Hitachi City, Ibaraki Hitachi Ltd. Hitachi factory (72) Inventor Rie Nagura 3-chome, Saiwaicho, Hitachi City, Ibaraki Prefecture No. 1 Hitachi Ltd., Hitachi Plant (72) Inventor Shinsaku Shirata 3-1-1, Saiwaicho, Hitachi City, Ibaraki Prefecture Hitachi Ltd., Hitachi Plant (72) Inventor Eizo Kita Osaka City, Osaka Prefecture 3-3-22 Nakanoshima, Kita-ku, Kansai Electric Power Co., Inc. (72) Inventor Hiroto Nakagawa, Osaka City, Osaka City 3-3-22, Nakanoshima, Kita-ku, Kansai Electric Power Co., Ltd. 3-22 Nakanoshima, Kita-ku, Yokohama-shi Kansai Electric Power Co., Inc.

Claims (3)

[Claims] 1. A variable speed power generation system having a variable speed machine which is excited by a current converter using a semiconductor switching element, wherein a current corresponding to the current flowing through said semiconductor switching element is passed and said semiconductor switching element is connected. A heating element having the same temperature characteristics, a temperature detecting element provided on the heating element, and a protection means for protecting the semiconductor switching element when the temperature of the heating element by the temperature detecting element reaches a predetermined value are provided. A variable speed power generation system characterized in that 2. The heating element according to claim 1, wherein the heating element comprises a diode and a current limiting electric resistance connected in series, and the temperature detecting element is provided in a cooling fin of the diode. A variable speed power generation system characterized by 3. The device according to claim 1, wherein the heating element comprises a diode and a current limiting electric resistance connected in series, and the temperature detecting element is a current limiting electric resistance. A variable speed power generation system characterized by being provided.