JPH0641399U - Current detection circuit for marine shaft power generation system - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] A ship shaft that detects three-phase AC current in the main circuit accurately by converting it to a DC voltage accurately even if the current is small, without increasing the number of current transformers. A current detection circuit for a power generation system is provided. A three-phase main circuit is provided in current detection circuits 1 and 2 detected to suppress a main circuit current of a converter 6 or an inverter 8 which is a power conversion circuit of a shaft power generation system driven by a ship propulsion engine 21. Two current transformers 3 and 4 that detect two-phase currents of the circuit current, a resistor that converts the current on the secondary side of each current transformer into a voltage, and two-phase voltage waveforms of the resistors. Of an operational amplifier circuit that converts the voltage waveform of one phase into another one-phase voltage waveform, and when converting the three-phase AC voltage including the converted one-phase voltage into a DC voltage, the input / output characteristics are zero even in the low voltage region. Since it is composed of a rectifying circuit that linearly changes from, it can be accurately converted into a DC voltage.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a shaft power generation system for ships, and more particularly to a current detection circuit of the shaft power generation system for ships.

[0002]

[Prior art]

 FIG. 4 shows the configuration of a normal shaft power generation system for a ship, where 21 is a prime mover for propelling a ship, and 23 is a propeller for propulsion. An AC generator (shaft generator) 22 is mechanically connected to the propulsion shaft of this ship. Since the speed of the propulsion prime mover changes depending on the navigation state of the ship, the output frequency of the shaft generator 22 also changes. If the output frequency changes, it is not preferable as a power source for a general load, so it is converted to AC power of a constant frequency through the power converter 10.

Next, the outline thereof will be described. After the output of the shaft generator 22 is converted into direct current through the converter 6, it is reconverted into alternating current power of a constant frequency by using the separately excited inverter 8. A rotary synchronous phase shifter 24 is provided for the purpose of securing a commutation power source for the separately excited inverter 8 and supplying reactive power to the load. Reference numeral 5 is a power conversion control device for driving the thyristors of the converter 6 and the inverter 8 to fire. Reference numeral 25 is a main circuit breaker for cutting off the power bus. In the power conversion control device 5, current detection for knowing the current value is important for control. This current detection consists of a current transformer 3 for detecting the current on the converter side and a current detection circuit 1, and a current transformer 4 and a current detection circuit 2 for detecting the current on the inverter side. ing. As shown in FIGS. 5 and 6, in the conventional current detection, when three-phase currents are detected, two current transformers are used and used as a V connection.

FIG. 5 shows a configuration in which a rectifier circuit 31 is directly connected to the secondary side of a current transformer 3 having a V-connection. The rectifier circuit 31 converts an alternating current into a direct current, and a resistor 32 converts the current. The voltage is converted, smoothed by the resistor 34 and the capacitor 33, and the DC voltage output 36 is input to the control device 5 as a current detection signal. In the current detection circuit configured in this way, if an imbalance occurs in the current waveform of the three-phase alternating current, the secondary side terminal current will be in an unbalanced state, and the waveform will collapse and an error will occur.

Further, as shown in FIG. 6, three sets of resistors 19 are inserted on the secondary side of the current transformer 3 which is V-connected, current / voltage conversion is performed on the AC side, and the converted voltage is rectified by the rectifier circuit 31. Is converted into DC and smoothed by the resistor 34 and the capacitor 33, and the DC voltage output 36 is inputted to the control device as a current detection signal. In the current detection circuit configured as described above, the input voltage becomes low at the time of small current, and the forward voltage VF of the diode composing the rectifier circuit 31 appears as an amplitude error. There is a drawback that the detection error of is large.

[0006]

[Problems to be solved by the device]

 The present invention has been made to solve the above-mentioned drawbacks, and its purpose is to accurately perform main operation even when the main circuit current is small without increasing the number of current transformers of the conventional current detection circuit in the shaft power generation system. It is an object of the present invention to provide a current detection circuit for a marine shaft power generation system which converts a three-phase alternating current of the circuit into a direct current voltage and performs detection.

[0007]

[Means for Solving the Problems]

 In order to achieve the above object, the current detection circuit of the shaft power generation system for a ship of the present invention suppresses the main circuit current of a converter or an inverter which is a power conversion circuit of a shaft power generation system driven by a ship propulsion engine. In order to detect the current, two current transformers that detect the two-phase currents of the three-phase main circuit current and the currents on the secondary side of each of the above current transformers are converted into voltage. A resistor to be converted, an operational amplifier circuit for converting the voltage waveform of the resistor from two phases to a voltage waveform of another one phase, and an alternating current for three phases including the one phase converted by the operational amplifier circuit. It is characterized in that it is composed of a rectifier circuit whose input / output characteristics change linearly from zero even when the voltage is converted to a DC voltage even in the low voltage region.

[0008]

[Action]

 According to the present invention, it is possible to accurately convert a DC voltage into a DC voltage even when the current flowing through the main circuit is extremely small, without increasing the number of current transformers for detecting the current in the shaft power generation system.

[0009]

【Example】

 An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention. The same components as those of the conventional example shown in FIGS. In FIG. 1, reference numeral 20 denotes an input main circuit of the converter or an output main circuit of the inverter, which is a main circuit which is a target of the current detection circuit 1. The secondary side currents of the two current transformers 3 for detecting the currents flowing in the main circuit are voltage-converted with the current transformer 3 in a one-to-one manner by the voltage conversion resistor 19 to form a two-phase / three-phase conversion circuit. 11 can reproduce three-phase alternating current. These three-phase outputs are respectively input to the ideal diode circuit 14 and converted into direct current, input to the 3-input inverting amplification adder 15 via the resistor 18, and smoothed by the filter including the capacitor 16 and the resistor 17. A DC output 36 is obtained.

In the two-phase / three-phase conversion circuit 11, 12 is a non-inverting amplifier, and 13 is a two-phase input inverting amplification adder. The principle of the two-phase / three-phase conversion circuit 11 is, as shown in the vector diagram of FIG. 2, smoothing three-phase alternating current from U-phase (or R-phase) and W-phase (or T-phase) of two-phase alternating current by inverting amplification addition. It is a composite output of the V phase (or the S phase).

Further, in the present embodiment, as the ideal diode circuit 14, as shown in FIG. 3, a full-wave rectification type ideal diode circuit for performing a negative DC output by combining inverting amplifiers 141, 142 and diodes 143, 144. Is used.

[0012]

[Effect of device]

 As described above, according to the present invention, the main circuit current is detected by the two current transformers as the current for two phases and is converted into the voltage component by the resistor inserted in the secondary side of the current transformer. Since the operational amplifier circuit converts into three phases and the ideal diode circuit using the operational amplifier also performs AC / DC conversion, current detection is performed even when the main circuit current of the shaft power generation system is extremely small. The value error can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of current detection in a shaft power generation system of the present invention.

FIG. 2 is a vector diagram showing a principle of converting a detected current value of two phases into three phases.

FIG. 3 is a circuit diagram of an ideal diode circuit.

FIG. 4 is a circuit diagram of a shaft power generation system.

5 is a circuit diagram of a conventional current detection circuit of the shaft power generation system of FIG.

6 is a circuit diagram of another example of the conventional current detection circuit of the shaft power generation system of FIG.

[Explanation of symbols]

1, 2 ... Current detection circuit, 3, 4 ... Current transformer, 5 ... Power conversion control device, 6 ... Converter, 7 ... DC reactor, 8 ...
Inverter, 9 ... AC reactor, 10 ... Power converter,
11 ... Two-phase / three-phase conversion circuit, 12 ... Non-inverting amplifier, 13
... two-phase inverting amplification adder, 14 ... ideal diode rectifier circuit, 15 ... three input inverting amplification adder, 19 ... resistor, 2
0 ... Input main circuit of converter or output main circuit of inverter, 21 ... Propulsion motor, 22 ... Shaft generator, 23 ... Propeller for propeller, 24 ... Synchronous phaser, 25 ... Circuit breaker, 26
... onboard bus.

Claims (1)

[Scope of utility model registration request] 1. A current detection circuit detected to suppress a main circuit current of a converter or an inverter, which is a power conversion circuit of a shaft power generation system driven by a ship propulsion engine, among three-phase main circuit currents. Two current transformers for detecting currents of two phases, resistors for converting the current on the secondary side of each of the current transformers to a voltage, and one of the two phases of the voltage waveform of the resistors. Minute operational amplifier circuit for converting into a voltage waveform of three minutes, and when converting the three-phase AC voltage including one phase converted by the operational amplifier circuit into a DC voltage, the input / output characteristics are zero even in the low voltage region. And a rectifier circuit that linearly changes from the current detection circuit of the marine vessel shaft power generation system.