GB2206751A

GB2206751A - Starting a variable speed constant frequency generating system

Info

Publication number: GB2206751A
Application number: GB08812390A
Authority: GB
Inventors: Yoshimi Okada; Masao Kimura; Kazuo Okubo
Original assignee: Shinko Electric Co Ltd
Current assignee: Shinko Electric Co Ltd
Priority date: 1987-05-29
Filing date: 1988-05-25
Publication date: 1989-01-11
Anticipated expiration: 2008-05-25
Also published as: GB2206751B; GB8812390D0; FR2616983B1; FR2616983A1

Abstract

The system includes a main generator 2 coupled to an engine 1, an AC exciter 9 for generator 2, a rectifier (17), (Fig 3B) and an inverter (18) for converting output power of the main generator. To start the engine 1, an external AC source (16) is connected to the rectifier (17) and the inverter (18) energises the generator armature 2b whereby the generator 2 is operated as a commutatorless motor. During starting, inverter (18) is commutated by a distributor (19) responsive to a rotor position sensor 14, and the field winding 9a of exciter 9 is supplied with A.C. from external source (16), the windings 9a, 9b acting as a transformer. When a predetermined speed is reached, a switch 21 is moved to position "H" and field winding 9a is then supplied with D.C. from source (16) via circuits 7C and 8A. When normal speed is reached, switches 15A, (15B) and 22 are moved to position "G" so that the output of armature 2b feeds the inverter (18) via rectifier (17), and field winding 9a is supplied with D.C. from a permanent magnet A.C. generator 12 via circuit 7 and a regulator 23 which controls the current in winding 9a to maintain a constant output voltage from generator 2. Switches 15A, (15B), 21, 22 may be operated manually, or automatically using generator 12, a F/V converter 13a and a comparator 13b or a speed sensor. <IMAGE>

Description

"A variable speed constant frequency generating system" The present invention relates to a variable speed constant frequency ("VSCF") generating system suitable for use as an electrical power generating system for aeroplanes.

Recently, with the progress in the practical use of a VSCF generating system which uses engine power as a driving source, the need for using a brushless generator as a brushless motor has increased.

In one known type of VSCF generating system, it is usual to include separately a starter for starting the engine, as shown in Fig. 1 of the accompanying drawings. As shown, such a system includes a starter 6 such as an air turbine or the like, for starting an engine 1, and an AC generator 2 which is coupled to the engine 1. The AC output from the AC generator 2 is converted to a desired AC supply, for example, of a three-phase supply of 115 V at a frequency of 400 Hz by means of a power rectifier 3, a power invertor 4, and a filter 5.

Furthermore, a generating system of the DC excitation type is known, for example, from an article entitled "Brushless Generator for Aircraft" by A.W. Ford, in the Institute of Electrical Engineers Paper No. 3812 U, 1962. As shown in Fig. 2A of the accompanying drawings, this system includes a main generator 2 having a field winding 2a and an armature winding 2b, an AC exciter 9 having a field winding 9a and a rotor winding 9b, a DC power source 71, a DC controller 81, and a rotary rectifier 10. A rotor assembly K1 includes the rotor winding 9b, the rotary rectifier 10, and the field winding 2a.

In addition, a generating system of the AC excitation type is known, for example, from an article entitled "Brushless Excitation with Rotating Transformer", in the SHINKO DENKI Technical Bulletin, Vol. 16, No. 2, 1971. As shown in Fig. 2B of the accompanying drawings, an AC power source 72, an AC controller 82, and a rotary transformer 11 are provided to excite a field winding 2a of a main generator 2 by AC power through the rotary transformer 11 and a rotary rectifier 10. In this case, a rotor assembly K2 includes a secondary winding of the rotary transformer 11, the rotary rectifier 10, and the field winding 2b.

It will be noted that the AC power supplied from the AC power source 72 is regulated by the AC controller 82 to an appropriate AC voltage according to a required torque at the time of starting, and that the AC voltage is applied to the rotary transformer 11, the output thereof being rectified by the rotary rectifier 10 to excite the field winding 2a. In the generation mode, AC power generated by a field magnet (not shown) is regulated by the AC controller 82 so that an AC voltage which enables the main generator 2 to generate a constant voltage is applied to a primary winding of the rotary transformer 11.

However, the following problems are liable to arise in the systems, disclosed in the prior art.

In the system shown in Fig. 1 in which the starter 6 constituted by an air turbine or the like is separately provided, it is necessary to provide such an additional starter device as compared to the system used in aeroplanes wherein the DC power is the primary electrical power and a generator for supplying power to various facilities in the aeroplane is used also as a DC motor serving as a starter for starting the engine. The necessity of such an additional device in particular poses a serious problem when the generating system is to be used on aeroplanes due to the increased weight.

In the DC excitation system shown in Fig. 2A, a problem has ocurred in that when the rotational speed of the rotor assembly K1 is zero, the electrical power is not generated in the exciter rotor winding 9b and therefore magnetic flux is not generated in the field winding 2a of the main generator 2.

On the other hand, in the AC excitation type system shown in Fig. 2B, since the rotary transformer 11 has no power amplifying capability, the stator and rotor require substantially equal capacity. As a result, although the magnetic field flux can be obtained at the time of starting, it is necessary to supply large electrical power to the rotary transformer 11 as compared to the exciter. Therefore a disadvantage arises in that the size and weight has to be large as compared with the DC excitation type system.

It is an object of the invention to provide a VSCF generating system which requires no particular starter, which is compact and light in weight as compared with the prior art generating systems of the AC excitation type, and which is capable of generating magnetic field flux at the time of starting.

Accordingly, there is provided a VSCF generating system which includes a main generator coupled to an engine, an AC exciter coupled to the engine for exciting the main generator, a power rectifier and a power invertor for converting output power of the main generator, a position sensor for detecting a position of a rotor of the main generator, and a distributor responsive to a signal of the position sensor for phase controlling the power invertor, wherein at the time of starting the engine, the main generator is operated as a commutatorless motor by using the position sensor and the distributor to obtain a starting torque, and a field winding (stator winding) of the AC exciter is selectively connected to an AC power source or a DC power source by a switch.

The present invention will now be described in greater detail by way of example with reference to the remaining figures of the accompanying drawings, wherein: Figs. 3A and 3B, together form a block diagram of a preferred form of a VSCF generating system according to the present invention; Figs. 4A and 4B, together form a circuit diagram of the distributor in Fig. 3B; and Figs. 5A and 5B, together form a circuit diagram of the DC field controller and the voltage regulator in Fig.

3A.

Referring to Figs. 3A and 3B, a permanent magnet generator 12 is coupled to a rotating shaft la of an engine 1, and it functions as an excitation power source for a field winding 9a of an AC exciter 9. AC output power from an output winding 12a of the permanent magnet generator 12 is converted by devices to be described later, and supplied to the field winding 9a for excitation by DC. The output of the permanent magnet generator 12 is also used to detect the rotational speed of the rotating shaft la of the engine 1, and for this purpose, the output is supplied to a speed detection circuit 13 having a frequency/voltage converter 13a and a comparator circuit 13b. The comparator circuit 13b includes, as shown in Fig. 5B, differential amplifiers Mll to M13, transistors Tr4 and Tr5, resistors R27 to R30, and a zener diode TZ3.

A position sensor 14 is mounted on the rotating shaft la in order to detect a rotational position of the rotating shaft la. The sensor 14 provides a control signal for commutation to a distributor 19 which will be described later. A first switch 15A performs switching of the output supply of a power invertor 18 (described later) between an armature winding 2b of a main generator 2 and a load side depending on whether the system is in a starter mode (including low speed running) or normal running mode (generator). On the other hand, a second switch 15b (Fig.

3B), is provided to switch between two sources of power supply to a power rectifier 17, the two sources being an AC output of the main generator 2 and an external AC power source 16, the switching depending on whether the system is in the starter mode or in the normal running mode. The power invertor 18 converts the DC output of the power rectifier 17 into an AC output. The distributor 19 performs phase control of the power invertor 18 so as to supply to the armature winding 2b an armature current having a phase corresponding to the signal from the position sensor 14.

The distributor 19 includes, for example, as shown in Figs.

4A and 4B, AND circuits Al and A2, NOT circuits N1 and N2, differential amplifiers M1 to M4, diodes dl to d3, capacitors C1 to C6, resistors R1 to Rll, a zener diode TZ1, and rectifiers S1. A filter 20 removes noise contained in the AC output of the power invertor 18.

A third switch 21 and a fourth switch 22 both responsive to a rotational speed signal from the speed detection circuit 13 perform switching of the current supply to the field winding 9a of the AC exciter 9 between a DC output from a DC field controller 8A and an AC output from an AC field controller 8B depending on whether the system is in the normal running mode or the starter mode (including a low speed of rotation). In each of the first, second, and fourth switches 15A, 15B and 22 shown in Figs. 3A and 3B, the character "S" designates a switching terminal of the start side, and "G" designates a switch terminal of the normal running (generating) side. In the third switch 21, "L" designates a low speed side terminal, and "H" designates a high speed terminal.

A DC power source 7 includes, for example, as shown in Figs. 5A and 5B, a full-wave rectifier 7a constituted by rectifier elements such as thyristors or the like which are adapted to be phase controlled. The AC output supplied from the output winding 12a of the permanent magnet generator 12 is rectified to obtain a DC output. In this case, the output of the full-wave rectifier 7a is phase controlled based on the output of the frequency/voltage converter 13a.

On the other hand, a second DC power source 7c supplies DC power by rectifying AC output of an external AC power source 16, and for example, as shown in Fig. 5B, the circuit including, a diode d4, transistors Trl to Tr3, and resistors R 10 to R12.

The DC field controller 8A includes, for example, as shown in Figs. 5A and 5B, differential amplifiers M4 to M7, resistors R13 to R20, and a capacitor C7. The DC power from the second DC power source 7C is regulated to provide DC power of a desired level.

The AC field controller 8B, as shown in Figs. 3 and 5, regulates the AC power (this power corresponding to the power of the AC power source 72 in Fig. 2B) supplied from the external AC power source 16 to a desired level, and as shown, this includes a transformer.

A voltage regulator 23 maintains the output voltage of the main generator 2 at a predetermined value regardless of the engine speed in the normal running (generator) mode, and it includes, for example, as shown in Figs. 5A and 5B, a diode d4' transistors Trl' to Tr3', resistors RlO'to R12', differential amplifiers M8 to M10, zener diodes TZ2 and TZ3, resistors R21 to R26, Capacitors C8 and C9, a rectifier S2, and a transformer T.

In the embodiment described above, the rotor winding 9b of the AC exciter 9 is shown as having a threephase winding. However, the winding is operable if it has not less than two phases. Also, the number of the phases of the rotary rectifier 10 may be applicable to half wave and full wave rectification. The switching operation of the first to fourth switches 15A, 15B, 21 and 22 are performed automatically by detecting that the output of the speed detection circuit 13 has reached a predetermined value as shown in Fig. 3A. However, this switching may be carried out manually.

With the arrangement described above, at the time of starting the engine 1, that is, when the rotor assembly K is initially stationary, by switching the second switch 15B to the side of the external AC power source 16, the VSCF generating system is driven as a commutatorless motor. In this mode, the AC power supplied from the external AC power source 16 is converted to DC power by the power rectifier 17, and the DC power is converted to AC power by the power invertor 18 in order to supply current to the armature winding 2b of the main generator 2. As a result, the main generator 2 is driven as a commutatorless motor and the engine 1 is driven and accelerated.In this case, the distributor 19 receives the position signal representative of a rotor position of the main generator 2 detected by the position sensor 14, and controls the power invertor 18 so that the commutation thereof is appropriate.

On the other hand, during the starting time of the engine 1 in which the generated voltage of the AC exciter 9 is low due to the low engine speed, this state is detected by the speed detecting circuit 13 and the speed signal is supplied to the third switch 21. As a result, the third switch 21 is switched to the side of the AC field controller 8B, and therefore to the external AC power source 16.

Accordingly, in this case, the field winding 9a of the AC exciter 9 is supplied with AC power, and a AC voltage is generated in the rotor winding 9b due to transformer action. On the other hand, when the rotor is rotating, the AC voltage is generated in the rotor winding 9b of the AC exciter 9 due to both a transformer action and a generator action. In either case, a DC current flows in the field winding 2a of the main generator 2, and desired the magnetic field flux is generated.

When the rotational speed of the engine 1 reaches a predetermined speed during the starter mode, the third switch 21, responsive to the signal from the speed detecting circuit 13, is automatically switched to the side of the DC field controller 8A. Consequently, the field winding 9a of the AC exciter 9 is supplied with DC power from the second DC power source 7C through the DC field controller 8A.

Thus, the field winding 2a of the main generator 2 is excited by the AC exciter 9 through the rotary rectifier 10, and a predetermined field flux is generated. In this case, the predetermined speed for switching from AC excitation to DC excitation is at a level sufficient to produce a required field current by the AC voltage generated in the AC exciter 9 even by the DC excitation thereof.

Next, when the speed of the engine 1 reaches a normal running speed or higher, the fourth switch 22, in response to a speed signal from the speed detection circuit 13, is automatically switched to the side ("G") of the voltage regulator 23. Furthermore, the second switch 15B is switched from the external AC power source 16 to the side of the main generator 2, and the first switch 15A is disconnected from the side of the filter 20. Consequently, the system is operated as a VSCF generating system. In this case, the switching operation of the first and second switches 15A and 15B is carried out based on the value of the speed signal from the speed detection circuit 13.In this mode, the main generator 2 generates AC power at a variable frequency corresponding to a variable speed of the engine 1, and after the AC power has been converted to DC power at a constant voltage by the power rectifier 17, the DC power is converted back to AC power at a low frequency.

The resultant AC power is wave shaped including removal of noise by the filter 20, and supplied to the load as 3-phase AC power, for example, 115 V, 400 Hz. The commutation of the power invertor 18 is controlled by a oscillator 25.

The voltage regulator 23 receives the output from the armature winding 2b of the main generator 2 and responsive to a signal supplied through the DC power source 7 from the speed detection circuit 13 representative of a speed variation of the rotating shaft la of the engine 1, regulates the voltage venerated by the main generator 2 to a predetermined constant voltage by controlling the current supplied through the fourth switch 22 to the field winding 9a of the AC exciter 9 by setting the zener voltage of the zener diode TZ2 included in the voltage regulator 23 to a predetermined voltage.

In the present invention, in order to operate the VSCF generating system as an engine starting apparatus, that is, as a commutatorless motor, a power rectifier and a power invertor are used at the time of starting the engine 1, and at the same time, an AC power source, a DC power source, and switches for supplying the power to the AC exciter are provided so as to perform the excitation by switching between AC excitation and DC excitation. Accordingly, the following advantages are obtained.

(a) A starter such as an air turbine driven by a high pressure air source which has previously been provided separately in the prior art systems becomes unnecessary.

Thus, the overall weight is reduced, the apparatus associated with the engine is simplified, and the maintenance of the system is improved. For this purpose, the equipment which is additionally required only includes two switches.

(b) As regard the AC exciter, since it is started by AC excitation to generate the magnetic field flux at the time of starting the engine, it is applicable to brushless starting. After the engine has been started, and when the engine is running normally in the generator mode, by switching the excitation of the AC exciter to DC excitation, the power required for the excitation of the AC exciter can be substantially reduced.

(c) Since a rotary transformer is not necessary as compared with the prior art AC excitation system, the size of the overall system can be made compact, and the weight can be substantially reduced, Accordingly, an exciter suitable for use in aeroplanes can be provided.

Claims

CLAIMS:-

1. A VSCF generating system for converting a variable speed shaft output of an engine to AC power having both a constant voltage and a constant frequency, said system including: an an AC exciter having a rotor winding and a field winding; (b) A rotary rectifier for rectifying the output of said AC exciter to direct current; (c) a main generator constituted by an AC generator having a rotary field winding and an armature winding, said rotary field winding being excited by the direct current from said rotary rectifier; (d) a power rectifier for converting an AC output of said main generator to DC power; (e) a power invertor connected to said power rectifier for converting the DC output of said power rectifier to an AC power;; (f) position sensor means mounted on the common shaft of said engine for detecting a rotational position of said rotary field winding of said main generator; (g) a filter connected to said power invertor for removing noise in AC output power thereof; (h) switching means for connecting the input of said power rectifier to an external AC power source, and for connecting the output of said power invertor to said armature winding of said main generator by disconnecting said filter thereby to drive said main generator as a commutatorless motor at the time of starting of said engine; and (i) a distributor connected to said position sensor means and said power invertor for controlling commutation of said power invertor based on a position detection signal from said position sensor means; said rotor winding of said AC exciter, said rotary rectifier, and said rotary field winding of said main generator all being mounted on a common shaft of said engine.

2. A VSCF generating system according to claim 1, further including an AC generator having a permanent field magnet mounted on said common shaft of said engine and having an output winding for supplying exciting current to said AC exciter in the generator mode.

3. A VSCF generating system according to claim 2, further including a speed detection circuit having a frequency/voltage converter and a comparator circuit, said speed detection circuit connected to receive an output signal from said permanent magnet type AC generator to detect the rotational speed of the rotating shaft of said engine.

4. A VSCF generating system including: (a) an AC exciter having a rotor winding and a field winding; (b) a rotary rectifier for rectifying the output of said AC exciter to direct current; (c) a main generator constituted by an AC generator having a rotary field winding and an armature winding, said rotary field winding being excited by the direct current from said rotary rectifier; (d) a power rectifier for converting the AC output of said main generator to DC power; (e) a power invertor connected to said power rectifier for converting the DC output of said power rectifier to an AC power; (f) a filter connected to said power invertor for removing noise in the AC output power thereof; (g) an external AC power source; (h) an AC field controller connected to said external AC power source for regulating an AC output of said AC power source to a predetermined level;; (i) a DC power source; (j) a voltage regulator connected to said DC power source for regulating a DC output of said DC power source to a predetermined level; and (k) switch means connected to said field winding of said AC exciter, said AC field controller, and said voltage regulator, wherein said switch means is switched to connect said AC exciter to said AC field controller to excite said AC exciter by AC current from said external AC power source at the time of starting of said engine and when said engine is running at low speed, and said switch means is switched to connect said AC exciter to said voltage regulator to excite said AC exciter by DC current from said DC power source when said engine is running normally;; said rotor winding of said AC exciter, said rotary rectifier, and said rotary field winding of said main generator being mounted on a common shaft of said engine.

5. A VSCF generating system according to claim 4, further including an AC generator having a permanent field magnet on said common shaft of said engine and having an output winding, and a speed detection circuit connected to said output winding for detecting whether said engine is starting, running at a low speed, and running at a normal speed.

6. A VSCF generating system according to claim 5, wherein said switch means receives a speed detection signal from said speed detection circuit to automatically switch the connection to said AC exciter from said AC field controller or said voltage regulator.

7. A VSCF generating system constructed substantially as herein described with reference to and as illustrated in Figs. 3 to 5 of the accompanying drawings.

8. An aircraft incorporating a VSCF generating system according to any one of the preceding claims.