JPH06269173A - Frequency converter - Google Patents

Abstract

PURPOSE:To obtain a frequency converter having high conversion efficiency by performing frequency control utilizing a fact that the secondary frequency of an induction machine is the sum of primary frequency and a rotational frequency and controlling the rotational speed of the induction machine through power flow control using another induction machine and a power converter. CONSTITUTION:A power converter 10 detects power being fed to a power system (PP) 1 from an induction machine 3. A rotational speed detector 11 detects rotational speed of the induction machine 6. An adder 14 detects the difference between an output from the power converter 10 and a power command value 13 for providing a power flow control command from the PP1 to a PP2. An adder 17 detects the difference 1'7 between a synchronous speed reference value 16 for providing a rotational speed matching the primary and secondary frequency ratio of the induction machine 3 with the frequency ratio between the PP1 and PP2 and a rotational speed 11' of the induction machine 6 detected by a rotational speed detector 11. An adder 18 detects the difference between the outputs from the amplifier 15 and the adder 17. A power converter 9 controls the rotational speed of the induction machine 3 through the induction machine 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency converter including an induction machine and a power converter.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of an embodiment of a conventional rotary frequency converter. In the figure, 1 is the first power system,
2 is a power system of FIG. 2 having a frequency different from that of the first power system 1, 20 is a first synchronous machine connected to the first power system 1,
Reference numeral 21 is a slip ring that supplies current to the field of the first synchronous machine 20, 22 is an exciter that controls the field current of the first synchronous machine 20, and 23 is connected to the second power system 2 and rotates. A second synchronous machine, the child of which is mechanically coupled to the rotor of the first synchronous machine 20;
24 is a slip ring for supplying a current to the field of the second synchronous machine 23, 25 is an exciter for controlling the field current of the second synchronous machine 23, and 26 is an armature winding of the second synchronous machine 23. Is a rolling device that mechanically rotates. The number of poles of the first synchronous machine 20 and the second
The ratio of the number of poles of the synchronous machine 23 is assumed to be equal to the ratio of the frequency of the first power system 1 and the frequency of the second power system 2. In the above configuration, by rotating the armature winding of the second synchronous machine 23 by the rolling device 26, the phase difference angle of each synchronous machine with respect to the power system can be controlled. Therefore, if the rolling device 26 is operated to operate the second synchronous machine 23 as an electric motor and the first synchronous machine 20 as a generator,
Electric power is supplied from the second power system 2 to the first power system 1. Rotate the rolling device 26 in the opposite direction to move the first synchronous machine 20
Is operated as an electric motor and the second synchronous machine 23 is operated as a generator, electric power is supplied from the first electric power system 1 to the second electric power system 2.

FIG. 5 is a block diagram of a conventional static frequency converter. In the figure, 1 is a first power system, 2 is a second power system having a frequency different from that of the first power system 1, and 27 is a first power system.
Control rectifier, 28 is a power transformer that connects the first power supply system 1 and the first control rectifier 27, 29 is a second control rectifier, 30
Is a power transformer that connects the second power supply system 2 and the second controlled rectifier 29, and 31 is the first controlled rectifier 27 and the second controlled rectifier
A DC reactor for smoothing the DC current of 29, 32 a harmonic filter for absorbing harmonics generated by the first controlled rectifier 27, 33 a phase advance capacitor for absorbing reactive power generated by the first controlled rectifier 27, Reference numeral 34 is a harmonic filter that absorbs harmonics generated by the second controlled rectifier 29, and 35 is a phase advance capacitor that absorbs reactive power generated by the second controlled rectifier 29.

In the above structure, the control angle of the second control rectifier 29 is controlled to the advanced side (α operation range) from 90 °,
If the control angle of the controlled rectifier 27 is controlled to be delayed from 90 ° (β operating region), the electric power of the second power supply system 2 is forward-converted by the second controlled rectifier 29 and converted to DC electric power. This DC power is inversely converted by the first controlled rectifier 27 and supplied to the first power system 1. Therefore, power is supplied from the second power system 2 to the first power system 1. On the contrary, the control angle of the first controlled rectifier 27 is controlled to the leading side (α operating range) from 90 °, and the control angle of the second controlled rectifier 29 is controlled to the delayed side (β operating range) from 90 °. For example, the first power system 1
Is converted into DC power by the first controlled rectifier 27. This DC power is inversely converted by the second controlled rectifier 29 and supplied to the second power system 2. Therefore, power is supplied from the first power system 1 to the second power system 2.

[0005]

In the conventional configuration described above, in the configuration using the synchronous machine shown in FIG. 4, (1) there is a possibility that the synchronization may be lost due to the fluctuation of the power system. (2)
The frequency ratio between the two systems is strictly limited to the pole ratio of both synchronous machines and is not flexible. (3) The minimum capacity of the synchronous machine is limited in order to prevent loss of synchronization between the two systems. (4) The tidal current control needs to be performed by a mechanical rolling device, and the operation is considerably troublesome and cannot be performed quickly. (5) Since two synchronous machines are operated in series, there are disadvantages such as large loss and poor efficiency. In the configuration using the controlled rectifier of FIG. 5, (6)
In order to absorb the harmonics and reactive power generated by the controlled rectifier, a large-capacity harmonic filter and a phase-advancing capacitor are required, and the installation area becomes large. (7) There is a risk that the phase-advancing capacitor may generate an overvoltage in the event of a system failure, and if a static var compensator or the like is installed to prevent this, there is a drawback that the cost will be considerably high.

In order to eliminate the above-mentioned drawbacks of the conventional frequency conversion device, the present invention provides a frequency conversion device having a novel structure in which a rotating machine and a static power conversion device are combined to take advantage of each of them. The purpose is to do.

[0007]

In order to solve the above-mentioned problems, the present invention comprises a first induction machine, a second induction machine, and a power conversion device, and a rotor of the first induction machine. And a rotor of the second induction machine are mechanically coupled to each other, and the primary winding of the first induction machine and the primary winding of the second induction machine are first coupled to each other.
Connected to the electric power system, the secondary winding of the first induction machine is connected to the second electric power system, and the secondary winding of the secondary induction machine of the second induction machine is connected to the power conversion device. It is characterized in that it is connected to the second power system through

[0008]

The present invention performs frequency conversion by utilizing the fact that the secondary frequency of an induction machine is the sum of the primary frequency and the frequency due to rotation, and the rotation speed of the induction machine is converted to that of another induction machine. The device controls the power flow.

[0009]

Embodiments 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. In the figure, 1 is a first power system whose frequency is f ₁ [Hz], and 2 is a second power system whose frequency is f ₂ [Hz] different from that of the first power system 1.
The power system 3 is a first winding type induction machine. And 4
Is a primary winding of the first winding type induction machine 3 and is assumed to be connected to the first power system 1. Reference numeral 5 is a secondary winding of the first winding type induction machine 3, and is assumed to be connected to the second power system 2. 6 is a second winding-type induction machine mechanically coupled to the first winding-type induction machine, the primary winding 7 of which is connected to the first power system 1 and the secondary winding 8 of which is It is connected to a power conversion device 9 described later.

In the following description, the first and second wire wound induction machines are simply referred to as the first and second induction machines. Reference numeral 9 denotes a static power converter (hereinafter simply referred to as power converter) that controls the current of the secondary winding 8, and 10 is power that detects the power supplied from the first induction machine 3 to the first power system 1. Detector, 11
Is a rotation speed detector (TG) of the first induction machine 6, and 12 is a power flow control device (hereinafter simply referred to as a control device) for controlling the power flow of the frequency conversion device of the present invention. . Reference numeral 13 is a power command value that gives a command value for power flow control from the first power system 1 to the second power system 2. Reference numeral 14 is an adder that detects a deviation between the power command value 13 and the power detector 10, and reference numeral 15 is an amplifier (AMP) that amplifies the deviation obtained at the output of the adder 14. On the other hand, 16 is a synchronous speed reference value that gives a rotation speed such that the primary and secondary frequency ratio of the first induction machine 3 matches the frequency ratio of the first power system 1 and the second power system 2. is there. This speed reference value 16 is detected by an adder 17 as a deviation 17 'from the rotation speed 11' of the first induction machine 6 detected by the rotation speed detector 11. 18 is an amplifier (AM
P) An adder for detecting a deviation between the output of 15 and the output of the adder 17, and 19 is an amplitude limiter for the control signal.

FIG. 2 is a waveform diagram showing the operation of the embodiment of the present invention described with reference to FIG. In FIG. 2 (a), (V
_1U ) is the U-phase voltage of the first power system 1, and the frequency is 50Hz.
I am trying. (I _3-1U ) is the primary U-phase current of the first induction machine 3, (13) is the waveform of the power command value, and (P _3-11 ) is the first to the first of the induction machine 3. This is the power supplied to the power grid 1. In FIG. 2B, (V _2U ) is the second power system 2
And the frequency is 60 Hz. (I _3-2U )
Is the secondary U-phase current of the first induction machine 3, and (P _3-21 ) is the power supplied from the secondary of the first induction machine 3 to the second power system 2. In FIG. 2C, (I _6-1U ) is the primary U-phase current of the second induction machine 6, and (P _6-11 ) is the primary to first power of the second induction machine 6. This is the power supplied to the grid 1. Figure 2
In (d), (19 ') is a control signal given from the amplitude limiter 19 to the power converter 9, and (17') is a signal obtained as the output of the adder 17, which is the signal of the first induction machine 3. It shows the deviation between the rotation speed and the synchronous speed reference value 16. (Δ) is the phase difference angle of the secondary side internal induced voltage of the first induction machine 3 with respect to the voltage of the second power system 2, and this phase difference angle (δ) is set to zero in the initial state. At this time, the primary U-phase current (I _3-1U ) and the secondary U-phase current (I _3-2U ) of the first induction machine 3 shown in _FIGS . The exciting current is supplied from the first power system and the second power system 2 to the first induction machine 3. The exciting current of the second induction machine 6 is supplied from the power converter 9 and the primary U-phase current (I _6-1U ) is zero. When the power command value 13 is increased stepwise at time t ₁ , a control signal as shown by (19 ′) appears at the output of the amplitude controller 19, and this signal is given to the power converter 9. The power conversion device 9 uses the primary power (P
_6-11 ) according to the signal (19 '). Since the direction of power supply is positive from the induction machine to the power system, the positive power indicated by (P _6-11 ) is supplied from the second induction machine 6 to the first power system 1. It means that That is, the second induction machine 6 acts as a generator and reduces the rotation speed of the first induction machine 3. Therefore, the deviation signal (17 ') from the synchronous speed reference value 16 increases in the negative direction as shown in FIG. 2 (d). Further, in proportion to the integrated value of this deviation, the second-side internal induced voltage of the first induction machine 3 becomes the second
, The phase difference angle with respect to the voltage of the power system 2 increases in the negative direction as indicated by (δ). Therefore, the phase difference of the primary internal induced voltage of the first induction machine 3 with respect to the voltage of the first power system 1 Since the angle increases in the positive direction, the power (P _3-11 ) supplied from the primary of the first induction machine 3 to the first electric power system 1 increases as shown in the figure, and the first induction machine 3 The electric power (P _3-21 ) supplied from the secondary side to the second electric power system 2 increases in the negative direction as shown. At time t ₂ when the output (17 ′) of the adder 17 increases in the negative direction and becomes larger than the output of the amplifier 15,
The polarity of the output (19 ') of the amplitude limiter 19 is also inverted, and the polarity of the primary power ( _P6-11 ) of the second induction machine 6 is also inverted. At this time, the second induction machine 6 acts as an electric motor to increase the rotation speed of the first induction machine 3. Therefore, the synchronous speed reference value 16
The deviation signal (17 ') between and decreases as shown. In this way, the primary power (P _3-11 ) of the first induction machine 3 is controlled so as to match the power command value (13), and in proportion to this, the secondary power of the first induction machine 3 is controlled. The power (P _3-21 ) increases in the negative direction. Finally, the primary electric power (P
_3-11 ) and the sum of the primary electric power (P _6-11 ) of the second induction machine 6,
The secondary electric powers (P _3-21 ) of the first induction machine 3 are equal in magnitude. At this time, electric power is supplied from the second electric power system 2 to the first electric power system 1. That is, the electric power of 60 Hz is converted into the electric power of 50 Hz to act as a frequency conversion device.

FIG. 3 is another waveform diagram showing the operation of the embodiment of the present invention described in FIG. In the figure, (V _1U ) ~
(Δ) is the same as the same symbol in FIG. Figure 2 shows the initial state
Shows the final ballast state, the phase difference angle (δ) is negative, the power is supplied from the second power system 2 to the first power system 1, and the power of 60Hz is converted to the power of 50Hz. Is. At time t ₃ , when the power command value 13 is changed stepwise to negative as shown in FIG. 3A, FIG.
As shown in (19 '), the output of the amplitude limiter 19 increases in the negative direction, and this signal is given to the power converter 9. The power converter 9 increases the primary power (P _6-11 ) of the second induction machine 6 in the negative direction according to the signal (19 ′) as shown in FIG. Since the direction of electric power is positive in the direction of supply from the induction machine to the electric power system, an increase in the negative direction of the electric power shown in (P _6-11 ) causes the second induction machine 6 to operate as an electric motor. , The rotation speed of the first induction machine 3 is increased. Therefore, the rotational speed signal 11 'and the synchronous speed reference value 16
The deviation signal (17 ') between and increases as shown in FIG. 3 (d). Further, in proportion to the integrated value of this deviation, the phase difference angle (δ) of the internal induced voltage of the first induction machine 3 with respect to the voltage of the power system increases as shown in FIG. Power supplied from the primary of the machine 3 to the first power system 1 (P
_3-11 ), as shown in FIG. 3 (a), decreases and the power supplied from the secondary of the first induction machine 3 to the second power system 2 (P _3-21 ).
Decreases as shown in FIG. At time t ₄ when the output (17 ′) of the adder 17 increases and becomes larger than the output of the amplifier 15, the polarity of the output (19 ′) of the amplitude limiter 19 is inverted and the output of the second induction machine 6 The polarity of the primary power (P _6-11 ) is also inverted. At this time, the second induction machine 6 acts as a generator and reduces the rotation speed of the first induction machine 3. Therefore,
The deviation signal (17 ') from the sync speed reference value 16 decreases as shown. At time t _5, when the polarity of the phase difference angle (δ) is reversed, the primary power (P _3-11 ) and the secondary power (P _3-11 ) of the induction machine 3 are reversed.
The polarity of _3-21 ) is also reversed. In this way, the primary power (P _3-11 ) of the first induction machine 3 is controlled in the negative direction so as to match the power command value (13), and in proportion to this, the first induction machine 3 is controlled. The secondary power of ₃ (P _3-21 ) increases in the positive direction. Finally, the primary power (P _3-11 ) of the first induction machine 3 and the second
The sum of the primary power (P _6-11 ) of the induction machine 6 and the magnitude of the secondary power (P _3-21 ) of the first induction machine 3 become equal. At this time, electric power is supplied from the first electric power system 1 to the second electric power system 2. That is, the electric power of 50 Hz is converted into the electric power of 60 Hz to act as a frequency conversion device.

Next, another embodiment of the present invention will be described with reference to FIGS. 6 and 7A and 7B. FIG. 6 is a block diagram of another embodiment of the present invention. The difference from the embodiment of FIG. 1 is that the third induction unit 3 is directly connected to the same shaft by the same shaft.
The induction machine 43 is connected in cascade. In the drawing, the same symbols as those in FIG. 1 are components that are completely the same and that control the same operation, so detailed description thereof will be omitted, and portions different from FIG. 1 will be described below.

Reference numeral 43 is a third induction machine, and 44 is a primary winding (stator winding) of the third induction machine 43, which is connected to the second power system 2. Reference numeral 45 is a secondary winding (rotor winding) of the third induction machine 43. Reference numeral 46 is a shaft for directly connecting the rotors of the first induction machine 3 and the third induction machine 43, and the second induction machine 6 is shown in FIG.
Since it is directly connected to the first induction machine 3 as in the case of
The rotors of these three induction machines are directly connected by the same shaft and are configured to rotate in the same direction. Reference numeral 47 is a conductor that connects the secondary windings 5 and 45 of the first and third induction machines, and is arranged above or inside the direct coupling shaft 46 and connected so as to be in a reverse phase order. The power flow control device 12 is composed of elements 13 to 19 as described with reference to FIG. 1. However, the power flow control device 12 is exactly the same in FIG. 6 and has the same operation. Is omitted.

Next, the operation of the embodiment shown in FIG. 6 will be described. In the case of FIG. 1, assuming that the primary winding 4 of the first induction machine 3 is on the stator side, the secondary winding 5 is on the rotor side, and
It will be connected to the electric power system 2 via a slip ring and a brush. On the other hand, in the embodiment of FIG. 6, another induction machine third induction machine 43 is used instead of the slip ring and the brush, and the configuration described above is provided to provide a brushless frequency conversion device. . Therefore, it will be described below that the relationship between the first power system 1 and the second power system 2 having different frequencies works in exactly the same manner in FIGS. 1 and 6.

FIG. 7A shows the first induction machine 3 in FIG.
It is a figure explaining the relationship of the frequency of the primary and secondary winding. The frequency of the primary winding 4 or the first power system 1 is f
₁ and the frequency of the secondary winding 5, that is, the second power system 2 is f ₂ . The number of magnetic poles of the first induction machine 3 P, when the rotational speed is n, the rotation frequency f _r of the rotor

[0017]

[Equation 1] Becomes Therefore, if the slip is S

[0018]

[Equation 2] The frequency f ₂ of the secondary winding is

[0019]

[Formula 3] f ₂ = Sf ₁ (3) From the formulas (2) and (3),

[0020]

[Number 4] becomes the _{f 2 = f 1 -f r ......} (4). Next, FIG. 7 (B) is a diagram for explaining the relationship between the frequencies of the primary and secondary windings of the first induction machine 3 and the third induction machine 43, which are connected in cascade in FIG.

If the frequency of the first electric power system 1 is f ₁ and the frequency of the second electric power system 2 is f ₂ as in FIG. 7A, the frequency f ₁ is applied to the primary winding 4 of the induction machine. Power is applied, and power of frequency f ₂ is applied to the primary winding 44 of the third induction machine. Next, _assuming that the frequency of the secondary winding 5 of the first induction machine 3 is f _s , the frequency of the third induction machine secondary winding 45 also becomes f _s , which is the slip frequency of each induction machine. The number of magnetic poles of the first induction machine 3 is P ₁ , the number of magnetic poles of the third induction machine 43 is P ₂ , and the rotation speed of the rotor is n ′. First first
The rotation frequency f _r1 of the rotor of the induction machine 3 of

[0022]

[Equation 5] Therefore, if the slip is S ₁ ,

[0023]

[Equation 6] The frequency f _s of the secondary winding is

[0024]

[Equation 7] f _s = S ₁ f ₁ (7), and from equations (6) and (7)

[0025]

## _EQU8 ## f _s = f ₁ −f _r1 (8) On the other hand, the rotation frequency f _r2 of the rotor in the third induction machine 43 is

[0026]

[Equation 9] Therefore, if the slip based on the secondary winding is S ₂ ,

[0027]

[Equation 10] And the frequency f ₂ of the primary winding is

[0028]

[Equation 11] f ₂ = S ₂ f _s (11) From equations (10) and (11),

[0029]

[Number 12] _{f 2 = f s -f r2 ......} (12) Therefore, (8), from the equation (12)

[0030]

F ₂ = f ₁ − (f _r1 + f _r2 ) ... (13) From equation (4), in order to connect two power systems with different frequencies, the first induction in the configuration of FIG. Machine

[0031]

[Equation 14] That is, it is understood that the number of magnetic poles and the rotation speed should be selected so that the rotation frequency of the rotor becomes equal to the frequency difference between the two systems. On the other hand, in the case of the two induction machines 3 and 43 in cascade connection in Fig. 6, (13)
As you can see from the formula

[0032]

[Equation 15] That is, it suffices to design so that the rotation frequency of the rotor of a single induction machine having the same number of magnetic poles as the total number of magnetic poles of the two induction machines 3 and 43 becomes equal to the frequency difference between the two systems. . In other words, from equations (14) and (15),

[0033]

[Equation 16] f _r = f _r1 + f _r2 Therefore, if Pn = (P ₁ + P ₂ ) n ′ is satisfied, the first induction machine 3 in FIG.
The rotary machine connected in cascade of the third induction machine 43 is the first rotary machine of FIG.
It can be seen that the same action as in the case of the induction machine 3 is performed. Therefore, as described in FIGS. 2 and 3, by using the second induction machine 6, the first and third induction machines 3, 3 connected in cascade.
It is obvious that the power flow between the first power system 1 and the second power system 2 can be arbitrarily controlled by controlling the rotation speed of 43.

As described above, in the embodiment shown in FIG. 6, as in the embodiment shown in FIG. 2) No mechanical rolling device is required.

3) Power flow control with high responsiveness is possible. 4) Do not generate overvoltage in the event of a system fault. In addition to the effects such as the above, in addition to the effects peculiar to this embodiment, that is, since there is no brush that is the most burdensome in maintenance of the rotating machine,
It can be seen that there is an advantage that maintenance work such as inspection and replacement of the brush is unnecessary.

[0036]

As described above, according to the present invention, in order to obtain the secondary frequency frequency-converted to the secondary winding as the sum of the primary frequency of the first induction machine 3 and the frequency due to the rotation, the power consumption is reduced. It is characterized in that the rotation speed of the first induction machine 3 is controlled by using the second induction machine 6 which is subjected to the secondary excitation control by the conversion device 9, and the first induction machine 3 is controlled in accordance with the command value 13 of the electric power. It is possible to arbitrarily control the power flow between the first power system 1 and the second power system 2. According to the present invention, even if a fluctuation occurs in the power system, this fluctuation is detected by the power detector 10 as a change in the primary power of the first induction machine 3, and the first fluctuation is suppressed so as to suppress the change. Since the rotational speed of the induction machine 3 is controlled, there is no risk of loss of synchronization. Further, even if the frequency ratio between the two systems changes to some extent, it can be absorbed by changing the rotation speed of the first induction machine 3, so there is flexibility, and even if the two systems are connected by a small-capacity frequency conversion device. There is no risk of out of sync. Further, a mechanical rolling device for power flow control is not required, and fast power flow control can be performed electronically according to the command value. Further, in the prior art, when two synchronous machines are operated in series, the total electric power is once converted into mechanical energy and then converted into electric energy again, whereas according to the present invention, only the frequency difference part is converted. Converted to mechanical energy. That is, in FIG. 1, 50H of the first power system 1
When converting the electric power of z into the electric power of 60 Hz, the electric power of the primary winding 7 of the second induction machine 6 is 20 when the electric power of the primary winding 4 of the first induction machine 3 is 100. , This electric power is converted into mechanical energy and taken out from the secondary winding 5 as an increment of the secondary induced voltage of the first induction machine 3 due to rotation. Therefore, 120 electric power is extracted from the secondary winding 5 together with the inductive component 100 from the primary winding 4. As described above, the amount of energy that is once converted into mechanical energy is 17% of the whole, and a small induction machine with a small torque can be used, and the loss due to energy conversion is reduced and efficiency is increased. Also,
Since a large-capacity harmonic filter and a phase-advancing capacitor, which are required in the configuration using the controlled rectifier, are not required, the installation area can be reduced. Further, since a phase-advancing capacitor is not required, there is no risk of generating overvoltage in the event of a system fault.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a waveform chart showing the operation of the present invention.

FIG. 3 is another waveform diagram showing the operation of the present invention.

FIG. 4 is a configuration diagram of a conventional example.

FIG. 5 is a configuration diagram of another conventional example.

FIG. 6 is a configuration diagram of another embodiment of the present invention.

FIG. 7 is a diagram for explaining the operation of the embodiment shown in FIG.

[Explanation of symbols]

1 ... 1st electric power system, 2 ... 2nd electric power system, 3 ... 1st induction machine, 4 ... primary winding, 5 ... secondary winding, 6 ... 2nd induction machine, 7 ... primary Winding, 8 ... Secondary winding, 9 ... Power converter,
10 ... Power detector, 11 ... Rotation speed detector, 12 ... Control device,
13 ... Power command value, 14 ... Adder, 15 ... Amplifier, 16 ... Synchronous speed reference value, 17 ... Adder, 18 ... Adder, 19 ... Amplitude limiter,
43 ... Third induction machine.

Claims (3)

[Claims] 1. A first induction machine, a second induction machine, a power converter, a power detector of the first induction machine, a rotation speed detector of the first induction machine, and a power flow. And a rotor for the first induction machine and a rotor for the second induction machine mechanically coupled to each other, and a primary winding of the first induction machine and the second induction machine. A primary winding of the first induction machine is connected to a first power system, a secondary winding of the first induction machine is connected to a second power system, and a secondary winding of the second induction machine is connected to the power system. It connects to the 2nd electric power system via a converter, and the 2nd of the 2nd induction machine according to the electric power deviation signal of the command value of electric power and the electric power of the 1st induction machine by the electric power converter. A frequency conversion device, characterized in that a secondary current is controlled to control a rotation speed of the first induction machine. 2. A rotation speed detector for detecting the rotation speed of the first induction machine or the second induction machine is provided, and addition for obtaining a speed deviation signal between the output signal of this rotation speed detector and the synchronous speed reference value is added. The frequency converter according to claim 1, further comprising: a power flow controller that is provided with a power deviation signal, adds the speed deviation signal to the power deviation signal to obtain the deviation, and outputs the control signal to the power conversion apparatus based on the deviation signal. apparatus. 3. The rotors of the first induction machine and the third induction machine are mechanically coupled, and the rotor windings (secondary windings) of the two induction machines are mutually conductors. In a cascade connection, the rotor of the second induction machine is directly connected to the same shaft as the first and third induction machines, and the stator winding (primary winding) of the first induction machine is connected to the rotor. Connected to the first power system, the stator winding (primary winding) of the third induction machine to the second power system, and the primary winding of the second induction machine to the two power systems. The secondary winding of the second induction machine is connected to either one of them, and the secondary winding of the second induction machine is connected to the other power system via the power converter, and a power flow controller for controlling the power converter is provided. One of the output signal of the rotation speed detector driven by the induction machine and the stator winding of the first induction machine or the third induction machine An output signal of a power detector for detecting power is input, and the power converter is controlled by the output of the power flow controller calculated according to the deviation between the power command value of the power flow controller and the output of the power detector. A frequency conversion device, wherein the rotational speed of the cascade-connected induction machine is controlled.