Motor-generator set parallel operation capacity increasing device based on small rotor angle difference method

Abstract

A motor-generator set parallel operation capacity increasing device based on a small rotor angle difference method is suitable for generator set parallel capacity increasing power generation equipment. The parallel capacity-increasing motor-generator set aims to solve the problems that an existing parallel capacity-increasing motor-generator set needs to be additionally provided with equipment, operation is complex, starting equipment is occupied, and the parallel capacity-increasing motor-generator set is prone to being affected by factors such as external control links and control equipment quality. Each motor-generator set comprises a motor and a generator; the specifications of the two motors are the same, and the specifications of the two generators are the same; in the same motor-generator set, the power supply input end of the motor is electrically connected with the power supply network; a power output shaft of the motor is in transmission connection with a power input shaft of the generator, and no-load rotor angles of the motor and the generator are the same; in the two motor-generator sets, the no-load rotor angles of the motors are the same.

Description

Technical Field

[0001] The utility model is suitable for generating sets connected in parallel to increase the capacity of generating equipment. Background Art

[0002] like Figure 1 As shown, a generator set consisting of two or more motors connected coaxially, usually two three-phase synchronous motors, one motor is connected to the power supply network to drive the other generator to be used as a voltage-regulated power supply of industrial frequency or other constant frequency, which is called a motor-generator set (set).

[0003] like Figure 2 As shown, the stator windings (armatures) of the two generators of the two sets of units are connected in parallel or in series to run in parallel, so that the capacities of the two generators are superimposed and output. When the two sets of units are of the same type or specification, they can be made into a parallel capacity increase or series capacity increase power supply with the sum of the capacities of the two generators.

[0004] like Figure 3 As shown, the existing parallel capacity increase motor-generator set adopts a master-slave control parallel capacity increase method in which one set is used as the main set and the other set is used as the slave set. The motor of the main set is connected to the power supply network for operation, and the motor of the slave set is powered by the inverter to track the synchronization of the motor of the main set. The generator is excited by the thyristor excitation device, and the generator of the slave set tracks the given output power of the generator of the main set.

[0005] However, the existing parallel capacity-increased motor-generator sets require additional equipment, are complex to operate, occupy starting equipment, and are easily affected by factors such as external control links and the quality of control equipment. Utility Model Content

[0006] The purpose of the utility model is to overcome the problems that the existing parallel capacity-increasing motor-generator sets need to add additional equipment, have complex operation and operation, occupy starting equipment, and are easily affected by factors such as external control links and the quality of control equipment. A motor-generator set parallel operation capacity-increasing device based on the small rotor angle difference method is provided.

[0007] The utility model discloses a motor-generator set parallel operation capacity increasing device based on a small rotor angle difference method, comprising two motor-generator sets;

[0008] Each motor-generator set includes a motor and a generator; the two motors have the same specifications, and the two generators have the same specifications;

[0009] In the same motor-generator set, the power input terminal of the motor is electrically connected to the power supply network; the power output shaft of the motor is drivingly connected to the power input shaft of the generator, and the no-load rotor angles of the motor and the generator are the same;

[0010] In both motor-generator sets, the no-load rotor angles of the motors are the same.

[0011] Furthermore, it also includes two sets of generator excitation devices;

[0012] Each generator excitation device includes an exciter field winding and an exciter armature;

[0013] In the two sets of excitation devices, one end of an excitation winding of an exciter is electrically connected to an excitation power supply, the other end of an excitation winding of an exciter is connected in series with one end of an excitation winding of another exciter, and the other end of an excitation winding of the other exciter is electrically connected to an excitation power supply; one end of an armature of an exciter is electrically connected to one end of an excitation winding of a generator, and the other end of an armature of an exciter is electrically connected to one end of an armature of another exciter; the other end of an excitation winding of a generator is electrically connected to the other end of an excitation winding of another generator, and the other end of an excitation winding of another generator is electrically connected to the other end of an armature of another exciter.

[0014] Furthermore, in all motor-generator sets, the motors are connected to the same node power supply of the power supply network;

[0015] The power supply at the same node is a three-phase power supply with the same phase sequence, phase and voltage.

[0016] Furthermore, the phases of the no-load potentials of the motor and the generator of the unit are the same.

[0017] The beneficial effects of the utility model are:

[0018] This motor-generator parallel operation capacity increasing device based on the small rotor angle difference method:

[0019] 1. No additional equipment is required, and the original engineering design, facilities and equipment installation status are not changed; saving project investment.

[0020] 2. Simple operation and no occupancy of starting equipment. The starting, running and operating procedures are the same as those of a single unit. The motors of the parallel units are started and connected to the grid and then run separately, and the starting device is exited. The excitation windings of the two parallel generators are excited in series (generators are excited in series). The output voltage of the parallel capacity increase can be controlled with one button.

[0021] 3. It is not affected by external control links and control equipment quality, has stable operation, and has a short implementation period through the transformation of existing motor-generator sets.

[0022] 4. Each of the two motor-generator sets can operate output separately or simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1It is a structural schematic diagram of an existing motor-generator set;

[0024] Figure 2 It is a structural schematic diagram of an existing parallel capacity-increased motor-generator set (industrial frequency);

[0025] Figure 3 It is a principle diagram of an existing parallel capacity-increasing motor-generator set;

[0026] Figure 4 It is the equivalent circuit diagram of the motor-generator parallel operation capacity increasing device based on the small rotor angle difference method;

[0027] Figure 5 It is a principle schematic diagram of the motor-generator parallel operation capacity increasing device based on the small rotor angle difference method of the utility model;

[0028] Figure 6 It is a structural schematic diagram of the generator no-load rotor angle lagging behind the motor no-load rotor angle θ0 when the motor is at the no-load rotor angle position;

[0029] Figure 7 It is a schematic diagram of the structure in which the no-load rotor angle between the motor and the generator is the same;

[0030] Figure 8 is a schematic diagram of the no-load rotor angle of the motor or generator;

[0031] Fig. 9 A schematic diagram showing the principle of adjusting the no-load rotor angles of the motors of the utility model to be the same;

[0032] Fig.10 It is a schematic diagram of the matching structure of the generator excitation device and the generator in the utility model;

[0033] Fig.11 This is a schematic diagram of the structure in which the motor and the generator in the utility model have the same no-load rotor angle;

[0034] Fig.12 This is a schematic diagram of the relationship between the motor, generator power angle and unit rotor angle in the utility model;

[0035] Fig.13 It is a schematic diagram of the magnetic potential and electromotive force of the parallel-operating generators of the utility model based on the small rotor angle difference method and the output voltage reference of the parallel-operating capacity increasing device of the motor-generator set;

[0036] Fig.14 It is a comparative schematic diagram of the motor-generator parallel operation capacity increasing device before and after adjustment based on the small rotor angle difference method in the fifth specific implementation mode. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0039] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0040] 1. Brief Introduction

[0041] 1.1 Parallel operation capacity expansion unit form

[0042] like Figure 1 As shown, a generator set consisting of two or more motors connected coaxially, usually two three-phase synchronous motors, one motor is connected to the power supply network to drive the other generator to be used as a voltage-regulated power supply of industrial frequency or other constant frequency, which is called a motor-generator set (set).

[0043] like Figure 2 As shown, the stator windings (armatures) of the two generators of the two sets of units are connected in parallel or in series to run in parallel, so that the capacities of the two generators are superimposed and output. When the two sets of units are of the same type or specification, they can be made into a parallel capacity increase or series capacity increase power supply with the sum of the capacities of the two generators.

[0044] The small rotor angle difference method of the utility model is a parallel capacity increasing method of the above-mentioned common unit form.

[0045] 1.2 Existing parallel capacity expansion methods in the industry

[0046] like Figure 3 As shown in the figure, the current industry adopts a master-slave control parallel capacity expansion method in which one set of units is used as the main unit and the other set of units is used as the slave unit. The motor of the main unit is connected to the power supply network for operation, and the motor of the slave unit is powered by the inverter to track the synchronization of the motor of the main unit. The generator is excited by the thyristor excitation device, and the generator of the slave unit tracks the given output power of the generator of the main unit. The output terminal voltage of the two motor-generator sets is the same.

[0047] 1.3 About the small rotor angle difference method:

[0048] By applying the structure and inherent characteristics of the motor itself, the load rotor angles of the two generators of the parallel capacity expansion unit are made close to the same, and the rotor angle difference between the two generators under different loads is kept small (small rotor angle difference), realizing a parallel capacity expansion method (called small rotor angle difference method or this method) that does not require high-power power electronic equipment and external control.

[0049] In addition to not adding additional equipment and saving project investment, this method also has the advantages of simple operation, no occupation of starting equipment, no influence from external control links and control equipment quality factors, stable operation and short project implementation period.

[0050] 2. Unit operation mode and operation:

[0051] 2.1 Small rotor angle difference method capacity increase operation mode:

[0052] 1) The main circuit diagram of parallel operation of the units is as follows Figure 5 As shown;

[0053] 2) Equipment and operation:

[0054] The original engineering design, facilities and equipment installation status shall not be changed;

[0055] The motors of the parallel units are started and connected to the grid and then run independently, and the starting device is exited;

[0056] The excitation windings 2-1 of the two parallel generators are excited in series (generator series excitation).

[0057] 3) Operation:

[0058] The startup, operation and operation procedures are the same as those of a normal single unit;

[0059] One-button control of parallel capacity increase output voltage.

[0060] 2.2 Independent operation of parallel units:

[0061] For parallel capacity expansion units, each unit can operate and output independently or simultaneously.

[0062] 3. Generator parallel operation and small rotor angle difference method circulating current:

[0063] 3.1 Load current and circulating current of generators running in parallel:

[0064] like Figure 4 As shown in the figure, due to the raw material performance deviation and processing error in the motor manufacturing process, it is inevitable that the electromagnetic parameters of the same type of machine are different. Even if the load (current) of the two parallel generators is equal, the internal potential of the two generators is The magnitude and phase of the potential difference will still be different. A circulating current I0 is generated between the generators.

[0065] 3.2 Circulation using small rotor angle difference method:

[0066] The circulating current between parallel-operating generators is the same as the circulating current of a single delta-connected motor winding, which is a zero-sequence additional current. The widely used three-phase delta-connected motor winding often has a circulating current of about 30% of the rated circulating current, but the effective value of the stator current is still close to the rated current, which has no actual effect on the motor heating and performance.

[0067]

[0068] Where:

[0069] I * —Stator current per unit value;

[0070] —Rated current per unit value;

[0071] —Per unit value of circulating current.

[0072] Small rotor angle difference method operating environment generator inter-circulation current I0 < 10% I N , which is smaller than the usual motor circulating current mentioned above.

[0073] 4. Establish the parallel operation conditions of the small rotor angle difference method:

[0074] 1) The no-load rotor angles of the motor and generator are the same;

[0075] 2) The no-load rotor angles of the motors in parallel units are the same.

[0076] 3) The parallel units are of the same type;

[0077] 4) Series excitation conditions of generators in parallel units;

[0078] 4.1 The no-load rotor angles of the motor and generator are the same:

[0079] Since the starting slot positions of the stator winding 2-2 are different during the motor manufacturing process, and the circumferential connection positions of the stator assembly and the unit shaft are also random, the no-load rotor angle between the motor and the generator of the unit is random. Figure 6 As shown, when the motor is in the no-load rotor angle position, the generator no-load rotor angle lags behind the motor no-load rotor angle θ0.

[0080] Adjustment method for the same no-load rotor angle between the motor and the generator:

[0081] Unlock the coupling, rotate the motor side and generator side shafts separately in a stationary state, adjust the motor and generator to their respective no-load rotor angle positions, and then connect the coupling to complete the adjustment of the no-load rotor angles of the unit motor and generator by changing the circumferential mechanical angle of the shaft connection. That is, the no-load potential of the unit motor and generator In phase or nearly in phase (this method allows for angle errors caused by rotor angle testing and adjustment).

[0082] like Figure 7 The following is a schematic diagram showing the same no-load rotor angle between the motor and generator of the adjusted unit:

[0083] Adjust unit 2 in the same way.

[0084] In addition, for the convenience of description, the present invention provides codes, restatements or conventions as follows:

[0085] 1) Motor 1: D;

[0086] 2) Generator 2: F;

[0087] 3) Unit 1: 1;

[0088] 4) Unit 2: 2;

[0089] 5) Same model: The design, process and raw materials are the same, the factory has the same work number (manufacturing number) or the same model of motors manufactured with the same work number;

[0090] 6) Same type of units: The motors and generators of the two units to be increased in parallel shall be of the same type;

[0091] 7) Described as units of the same type;

[0092] 8) Described in terms of a two-pole motor;

[0093] 9) Motor room: between motors of two sets of units running in parallel;

[0094] 10) Generator room: between the generators of two sets of units running in parallel;

[0095] 11) Internal potential: the resultant potential of the motor air gap;

[0096] 12) No-load rotor angle: The position of the magnetic pole axis and the axis of the stator phase winding (this method takes phase A as an example) when the motor is running at no-load, and the corresponding vector and vector state, such as Figure 8 As shown;

[0097] 13) Rotor angle: The rotor angle relative to the no-load rotor angle, the lagging direction is the positive angle;

[0098] 14) Same-node power supply: A three-phase power supply with the same phase sequence, phase and voltage, usually a same-node power supply, such as a set of wiring terminals at the load end of a transformer.

[0099] 4.2 The conditions for the same no-load rotor angle between motors in parallel units:

[0100] The motors running in parallel are powered by the same node power supply, that is, the no-load rotor angles of the motors running in parallel are adjusted in the same way driven by the power supply voltage. Fig. 9 As shown, where t0 = 0; e0 = E 0max :

[0101] After the unit shaft connection adjustment (mechanical connection adjustment) and the motor power supply voltage drive adjustment (electrical connection adjustment) between the units, the no-load rotor angles of the motors in parallel units are the same. As shown in the figure, at the instant of time t0=0, the no-load potential between the power supply side motor and the output side generator is the maximum value E 0max .

[0102] The above-mentioned parallel operation state with the same no-load rotor angle is the basic condition for capacity increase using the small rotor angle difference method.

[0103] The above-mentioned same-node power supply is a wiring having consistent phase sequence, motor and corresponding wiring terminals of the power supply.

[0104] 4.3 The conditions for parallel units to be of the same type are:

[0105] The parallel capacity increase units are of the same type, with the same capacity, similar electromagnetic parameters between motors and generators, easy to carry out load balancing control and superposition capacity close to the sum of the capacities of the two generators, and small internal potential difference and circulating current between parallel generators under balanced load. At present, the parallel capacity increase methods in the industry all use units of the same type or specification.

[0106] For newly purchased units that have been increased in capacity using the small rotor angle difference method, the generator and motor of the unit can be connected at the manufacturer so that their no-load rotor angles are the same.

[0107] 4.4 Series excitation conditions for parallel generators:

[0108] The standard stipulates that the rated excitation current of the same type of machine is the same, which is the excitation current test value obtained under the rated load of the type test. Under the same load, the output power of the same type of machine with the same excitation current is similar.

[0109] The load circuit of the parallel-connected capacity-increased generators is the same load. When the series excitation is constant and the same excitation current is used, the output power of the two generators is similar.

[0110] Series excitation will not cause failures or adjustment differences in the excitation system of a group of generators that are individually excited, resulting in a large load imbalance between parallel units.

[0111] like Fig.10 The following is the series excitation circuit diagram of the parallel generator:

[0112] In the two sets of excitation devices, two exciter field windings 3 are connected in series; two exciter armatures 4 are connected in series, and two generator field windings 2-1 are connected in series, and the two exciter armatures 4 connected in series and the two generator field windings 2-1 connected in series form a closed loop.

[0113] 5. The operating principle of the small rotor angle difference method is as follows:

[0114] 5.1 The diagram showing the same no-load rotor angle between the motors in parallel units drawn in a rotating rectangular coordinate system is used for illustration.

[0115] The rotating (time) rectangular coordinate system facilitates the explanation and direct comparison of the relationship between quantities.

[0116] The parallel unit motor no-load rotor angle is the same as shown in the figure, Fig.11 As shown, t = 0, e0 = E 0max .

[0117] 5.2 Unit motor load power angle and unit load rotor angle:

[0118] Since the power angle can be approximately considered as the angle between the main magnetic field and the air gap composite magnetic field (composite magnetic field) in space, the load rotor angle shared by the coaxial motor and generator can be approximately obtained from the motor load power angle - the unit load rotor angle. At this rotor angle position, the motor main magnetic field lags behind the composite magnetic field, and the generator main magnetic field leads the composite magnetic field.

[0119] like Fig.12 As shown:

[0120] 1) Unit-motor load power angle δ D1 And the unit-load rotor angle:

[0121] When the unit is running under load, the main magnetic field of the motor Hysteresis composite magnetic field Power angle. Generator main magnetic field With the motor power angle δ D1 The same angle lags the no-load rotor angle, and the unit rotor angle is at the corresponding δ D1 Load power angle position ( Fig.12 (the solid line filled part of the schematic diagram of unit 1 in the middle).

[0122] 2) Load power angle ∠δ of the second motor of the unit D2 And the load rotor angle of unit 2:

[0123] The relationship between the main magnetic field and power angle of unit 1 is the same as that of the main magnetic field of the generator of unit 2. With the motor load power angle δ D2 The same angle lags the no-load rotor angle, and the unit rotor angle is at the corresponding δ D2 Load power angle position ( Fig.12 (The solid line filled part of the schematic diagram of unit 2 in the middle).

[0124] 3) Power angle difference Δδ between motors in parallel units D and rotor angle difference Δδ 1,2 :

[0125] Due to the differences in electromagnetic parameters and load imbalance between the parallel units, the load power angles of the parallel motors are different, resulting in a load power angle difference Δδ between the motors. D .

[0126] Δδ D =δ D1 -δ D2

[0127] δ D1 -Unit-motor load power angle

[0128] δ D2 - For the convenience of comparison, the load power angle of the second motor of the unit is taken as δ D2 >δ D1 , δ D2 -δ D1 Is a positive value.

[0129] Similarly, the power angle difference of parallel units can be approximately regarded as the rotor angle difference of parallel units.

[0130] Δδ 1,2 =Δδ D

[0131] When the load is on, the rotor angles of the units are no longer the same. The phase difference is Δδ 1,2 It is called rotor angle difference (indicated by green in the figure). 5.3 Operation stability of small rotor angle difference method

[0132] The rotor angle stability is manifested as the unit operation stability. The rotor angle difference stability is manifested as the parallel operation stability. Under the small rotor angle difference method operation conditions, the unit rotor angle and rotor angle difference (corresponding to the unit power and the power balance between units) are only constrained by the mechanical fixed connection of the unit shaft and the stable grid power supply of the parallel motor. The operation is stable under the inherent characteristics of the unit and the unit motor structure and the motor.

[0133] 5.4 Parallel generator load power angle difference Δδ F :

[0134] Δδ F =δ F1 -δ F2

[0135] δ F1 —Unit-generator load power angle ( Fig.12 The part of the generator shown in the figure with the dashed and solid lines filled in between)

[0136] δ F2 —Unit 2 generator load power angle ( Fig.12 The part filled with virtual and real lines between the generators of unit 2 shown in the figure)

[0137] For the convenience of comparison, we take δ F2 >δ F1 , δ F2 -δ F1 Is a positive value.

[0138] 5.5 Synthetic magnetic field angle difference Δφ of parallel generator sets U and the internal potential angle difference Δδ U

[0139] Among them, the synthetic magnetic field angle difference of the parallel generator is Δφ U

[0140] ΔΦ U =Δδ D +Δδ F

[0141] Δδ D —Power angle difference of motors in parallel units

[0142] Δδ F —Power angle difference of parallel generator sets

[0143] Synthetic magnetic field angle difference ΔΦ between generators U , which is also the potential difference Δδ in the parallel generator U , and is always equal to the sum of the power angle difference between motors and the power angle difference between generators (shown in black in the figure).

[0144] Potential angle difference Δδ in parallel generators U

[0145]

[0146] 5.6 Small rotor angle difference method and test voltage regulating unit:

[0147] The generator of the voltage regulating unit used in the test is a low power factor generator whose apparent power is 5 to 10 times greater than the power of the unit motor. The power angle difference between the parallel generators can be ignored, and the circulating current is even smaller.

[0148] 6. Magnetic potential diagram and circulation calculation

[0149] 6.1 The magnetic potential and electromotive force diagram of parallel-operating generators is shown in Fig.13 As shown:

[0150] Fig.13 middle:

[0151] Φ—Increased output load power factor angle

[0152] Δδ U —Internal potential angle difference

[0153]

[0154] 6.2 Graphical explanation of internal potential difference and circulating current

[0155] The internal potential angle between generators is obtained by measuring the generator currents by the internal circuits of the parallel output nodes of the generators. (Electrical angle). Take Δδ U = 10° (adding the difference in parameters of the same type of machine, the increase in the influence of errors such as testing and measurement) and the known average value of the electromagnetic parameters of the motor, substitute it into the magnetic potential potential diagram of the parallel running generator to illustrate the potential difference between the generators

[0156] Circulation

[0157]

[0158] Where:

[0159] —0.09, zero-sequence reactance (take the smaller value)

[0160] VII. Industrial operation practice of small rotor angle difference method

[0161] 7.1 Phase-shifting units for enterprise capacity expansion:

[0162] Unit Specifications:

[0163] Electric Motor:

[0164] Capacity: 1.5MW (1.9MVA)

[0165] Voltage: 10kV;

[0166] Number of poles: 6

[0167] Speed: 1000r / min;

[0168] Power factor: 0.8;

[0169] dynamo:

[0170] Capacity: 60MVA

[0171] Voltage: 10kV;

[0172] Number of poles: 6

[0173] Speed: 1000r / min;

[0174] Power factor: 0;

[0175] The schematic diagram of the unit operation before and after adjustment by the small rotor angle difference method is as follows Fig.14 shown.

[0176] 7.2 Power Superposition and Safe Operation

[0177] The unit's operating capacity increased to the capacity of two motors and (61.9MVA).

[0178] Long-term safe operation demonstrates the feasibility of the application and implementation of the small rotor angle difference method.

[0179] 8. Operation reliability and advantages of small rotor angle difference method

[0180] 8.1 Reliability:

[0181] No need to add power electronic control equipment, reducing external influences on stable operation;

[0182] The generator series excitation does not occur in a separate excitation mode due to a large load imbalance caused by a group of unit excitation failure or adjustment differences;

[0183] Parallel operation is only related to the power supply of the power grid and the operation is stable;

[0184] The startup and operation procedures are simple, which is conducive to safe operation.

[0185] 8.2 Advantages:

[0186] Save project investment; the units are started and connected to the network for operation separately, without occupying the starting equipment; the original project design and installation facilities are not changed; the project design and implementation cycle is short; and it is easy to operate and maintain.

[0187] IX. Operation and maintenance: During operation, the utility model needs to maintain the mechanical and electrical connection relationship determined at the end of the construction. If modified, the operating conditions of the small rotor angle difference method for capacity increase need to be re-evaluated.

Claims

1. A motor-generator parallel operation capacity increasing device based on a small rotor angle difference method, characterized in that: It includes two motor-generator sets; Each of the motor-generator sets comprises a motor (1) and a generator (2); the two motors (1) have the same specifications, and the two generators (2) have the same specifications; In the same motor-generator set, the power input terminal of the motor (1) is electrically connected to the power supply network; the power output shaft of the motor (1) is drivingly connected to the power input shaft of the generator (2), and the no-load rotor angles of the motor (1) and the generator (2) are the same; In the two motor-generator sets, the no-load rotor angles of the motors (1) are the same; and the output terminal voltages of the two motor-generator sets are the same.

2. The motor-generator parallel operation capacity increasing device based on the small rotor angle difference method according to claim 1 is characterized in that: Also included are two sets of generator excitation devices; Each generator excitation device includes an exciter field winding (3) and an exciter armature (4); In the two sets of excitation devices, one end of an excitation winding (3) of an exciter is electrically connected to an excitation power supply, the other end of the excitation winding (3) of the exciter is connected in series with one end of an excitation winding (3) of another exciter, and the other end of the excitation winding (3) of the other exciter is electrically connected to the excitation power supply; one end of an exciter armature (4) is electrically connected to one end of an excitation winding (2-1) of a generator, and the other end of the excitation winding (4) of the exciter is electrically connected to one end of an armature (4) of another exciter; the other end of the excitation winding (2-1) of the generator is electrically connected to the other end of the excitation winding (2-1) of another generator, and the other end of the excitation winding (2-1) of another generator is electrically connected to the other end of the armature (4) of another exciter.

3. The motor-generator parallel operation capacity increasing device based on the small rotor angle difference method according to claim 1 or 2, characterized in that: In all motor-generator sets, the motors (1) are connected to the same node power supply of the power supply network; The same node power supply is a three-phase power supply with the same phase sequence, phase and voltage.

4. The motor-generator parallel operation capacity increasing device based on the small rotor angle difference method according to claim 3 is characterized in that: The phases of the no-load potentials of the motor (1) and the generator (2) of the unit are the same.

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