High-voltage direct-current power generation system stability design method based on small signal model

Abstract

The invention belongs to the field of aviation electrical, and particularly relates to a high-voltage direct-current power generation system stability design method based on a small signal model. The method comprises the following steps: 1, constructing a three-stage synchronous generator simplified model, and obtaining a generator equivalent output impedance model; 2, acquiring equivalent output impedance stability characteristics of the synchronous generator; 3, according to the Nyquist stability criterion, providing a stability criterion of the high-voltage direct-current power generation system with a constant-power load; and 4, according to a stability criterion, restraining the amplitude of the load impedance to be greater than the amplitude of the equivalent output impedance of the generator by a certain stability margin as a load design input basis, and realizing stable operation of the high-voltage direct-current power generation system. The method can be used for analyzing the on-load stability of a typical aircraft high-voltage direct-current power generation system, reasonably constraining the load characteristics of airborne electric equipment, and ensuring the reliable operation of the airborne high-voltage direct-current power generation system.

Description

Technical Field

[0001] The present invention belongs to the field of aviation electrics, and particularly relates to a stability design method for a high-voltage DC power generation system based on a small-signal model. Background Art

[0002] The aircraft energy system is currently developing towards a more electric / all-electric direction. When the original secondary energy sources such as gas and liquid are gradually developed into electrical energy, the types of aircraft electrical loads will become more diverse, resulting in an impact on the stable and reliable operation of the aircraft power supply system. With the gradual increase in the power of airborne equipment, aviation electrical energy has evolved from low-voltage DC, constant-frequency AC / variable-frequency AC power supplies to high-voltage DC. The three-stage synchronous generator has been widely used as the main high-voltage DC power source in the power supply systems of model aircraft due to its reliable excitation adjustment ability and simple motor topology. When the aircraft airborne equipment is converted from a mechanical pump to an electric pump and mechanical actuation to electric actuation, its typical load characteristics are power electronic devices. Power electronic devices, due to their constant power output, exhibit non-energy dissipative devices with respect to the external impedance. Their different operating conditions will introduce problems such as renewable energy feedback and high-frequency pulse current modulation that affect the power supply stability of the airborne high-voltage DC power source. Summary of the Invention

[0003] The object of the present invention: to propose a stability design method for a high-voltage DC power generation system based on a small-signal model, establish an equivalent output impedance model of a three-stage synchronous generator, establish a stability determination criterion based on Nyquist impedance analysis, and formulate a stability design method applicable to constrained loads according to the stability criterion.

[0004] The technical solution of the present invention: To achieve the above object of the invention, the present invention proposes a stability design method for a high-voltage DC power generation system based on a small-signal model, including the following steps:

[0005] Step 1: Construct a simplified model of a three-stage synchronous generator to obtain an equivalent output impedance model of the generator;

[0006] Step 2: Obtain the stability characteristics of the equivalent output impedance of the synchronous generator;

[0007] Step 3: According to the Nyquist stability criterion, propose a stability criterion for the high-voltage DC power generation system with a constant power load;

[0008] Step 4: According to the stability criterion, by constraining the amplitude of the load impedance to be greater than the amplitude of the equivalent output impedance of the generator by a certain stability margin, as the input basis for load design, realize the stable operation of the high-voltage DC power generation system.

[0009] Furthermore, in the above Step 1, constructing the output impedance model of the generator includes:

[0010] Convert the electrical parameters of the rotor part of the main generator and the excitation motor to the stator side, and obtain the equivalent circuit diagrams of the main generator and the excitation motor in the rotating coordinate system;

[0011] Utilize the equivalent circuit diagrams of the main generator and the excitation motor to obtain the equivalent models of the main generator and the excitation motor;

[0012] Equivalent the permanent magnet machine to a constant voltage source;

[0013] Equivalent the generator voltage regulation circuit to a chopper circuit, and combine it with the equivalent constant voltage source of the permanent magnet machine to obtain the equivalent circuit at the front end of the exciter;

[0014] According to the equivalent circuit models of the permanent magnet machine, the exciter, the main generator, and the voltage regulation module, obtain the small-signal output impedance model of the three-stage synchronous generator.

[0015] Furthermore, in the second step, define the stability characteristic of the equivalent output impedance of the synchronous generator as that the phase angle of the output impedance is within [-90, 90] in the frequency range of [1, 10000], that is, its impedance characteristic shows a constant positive resistance characteristic.

[0016] Furthermore, in the third step, the stability criterion of the high-voltage DC power generation system with a constant power load obtained according to the Nyquist stability criterion: in the frequency range of [1, 10000], the equivalent output impedance of the three-stage synchronous motor shows a constant positive impedance, and the amplitude of the output impedance is less than the amplitude of the equivalent input impedance of the constant power load, then the high-voltage DC power generation system is stable.

[0017] Furthermore, in the fourth step, by restricting the magnitude of the load impedance, a general stability design method applicable to different load conditions is given, including:

[0018] Establish the equivalent output impedance model of the synchronous generator;

[0019] Calculate the amplitude of the equivalent output impedance of the synchronous generator at different frequencies;

[0020] Restrict the equivalent input impedance of the load and the equivalent output impedance of the generator to satisfy the following formula

[0021] |Z i |-Z o >GM(dB)

[0022] where GM is the amplitude margin of the impedance, generally selected as 6dB.

[0023] Furthermore, in the general stability design method: the amplitude of the load equivalent impedance should be greater than the power supply equivalent impedance and the amplitudes of both should exceed 6dB.

[0024] Positive effects:

[0025] a) The present invention establishes an equivalent impedance model for the output of a three - level synchronous generator, which can be used to evaluate the influence of different external conditions on the stability characteristics of a high - voltage DC generator;

[0026] b) The present invention defines the equivalent output impedance stability characteristics of a high - voltage DC generator and proposes a stability criterion for the matching of power supply and load

[0027] c) By restricting the matching relationship between the equivalent impedance of the load and the equivalent impedance of the three - level synchronous generator, the present invention can achieve the engineering application effect of stable operation of the high - voltage DC power supply system under different load access conditions

[0028] d) The present invention realizes a model - based design method, which participates in the design of the three - level synchronous generator and the matching design of the power supply and the constant - power load in advance, and fully releases the stability risks of different electrical equipment accessing the aircraft power grid.

[0029] e) The present invention can help professionals in the airborne power system deeply understand the stability concept of the high - voltage DC power generation system and the stability matching relationship between the load and the power supply

[0030] f) The present invention can be extended to the stability analysis of the airborne power system of more - electric and all - electric aircraft, providing a design reference for airborne power equipment. Brief Description of the Drawings

[0031] Figure 1 is a flow chart of the stability design method for a high - voltage DC power generation system based on a small - signal model;

[0032] Figure 2 is the equivalent circuit diagram of the exciter and the main motor stator side of a three - level synchronous generator in the rotating coordinate system.

[0033] In the figure, the superscript'represents the equivalent parameters of the rotor side referred to the stator side, r Fd is the resistance of the main generator field winding, L lfd is the leakage inductance of the field winding, r kd 、r kq 、L lkd 、L lkq are the resistance and inductance components of the damper winding in the d - q axes of the synchronous rotating coordinate system respectively, L md 、L mq are the magnetization inductances of the main generator in the d - q axes respectively, v d and v q are the voltage components of the main generator output AC voltage in the synchronous rotating coordinate system respectively, L ls and r m are the leakage inductance and resistance of the main generator stator winding respectively.

[0034] Figure 3This is the simplified circuit diagram of the voltage regulating chopper circuit for the permanent magnet machine and generator of the present invention;

[0035] In the figure, v PMG is the equivalent DC output voltage of the permanent magnet machine, S dc is the switch tube signal, L f is the inductance of the excitation coil of the exciter, R is the parasitic resistance of the excitation coil of the exciter, v dcref is the DC reference voltage, and d is the duty cycle of the chopper circuit;

[0036] Figure 4 This is the schematic diagram of the stability design method for the high-voltage DC power generation system with different power supplies and different loads of the present invention;

[0037] Figure 5 This is the schematic diagram of the stability design of the high-voltage DC power generation system with a 65kW high-voltage DC generator driving a 2kW buck circuit;

[0038] Figure 6 This is the stable simulation result of the high-voltage DC power generation system with a 65kW high-voltage DC generator driving a 2kW buck circuit. Specific implementation mode

[0039] To more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below in combination with the accompanying drawings of the specification or specific implementation cases. It should be noted that some (but not all) of the disclosed examples are shown in the drawings. In fact, many different examples can be described and these examples should not be understood as being limited to the examples set forth herein. On the contrary, these examples are described so that the positive effects of the present invention are more reflected, and the details not elaborated herein are regarded as well-known techniques or conventional technical means in the art.

[0040] To avoid problems such as grid impact and instability caused by constant power load electrical equipment, the present invention proposes a stability design method for a high-voltage DC power generation system based on a small-signal model, which is used to analyze the load-carrying stability of a typical aircraft high-voltage DC power generation system and reasonably restrict the load characteristics of airborne electrical equipment to ensure the reliable operation of the airborne high-voltage DC power generation system.

[0041] In this embodiment, as Figure 1 shown, a stability design method for a high-voltage DC power generation system based on a small-signal model is carried out according to the following steps:

[0042] Step 1: Construct a simplified model of a three-stage synchronous generator to obtain an equivalent output impedance model of the generator;

[0043] Specifically, according to Figure 2 the equivalent circuit diagram of the exciter and the main motor stator side of the three-stage synchronous generator shown in the rotating coordinate system, the small-signal model of the main generator stator and rotor circuits in the synchronous rotating coordinate system is obtained:

[0044]

[0045]

[0046] In the specific implementation process, according to Figure 2 the equivalent circuit diagram shown, the small-signal model of the exciter is analogously obtained as:

[0047]

[0048] where: the superscript ME represents the exciter parameters

[0049] In the specific implementation process, according to Figure 3 the permanent magnet machine and generator voltage regulation chopper circuit diagram shown, the small-signal models of the permanent magnet machine and the chopper circuit are obtained:

[0050]

[0051] where kpv and kiv are the proportional coefficient and differential coefficient of the PI link respectively

[0052] Based on the small-signal models of the permanent magnet machine, exciter, main generator and voltage regulation module, the small-signal impedance model of the generator can be solved as:

[0053]

[0054] where ZMG is the impedance of the three-stage synchronous generator, vdc and idc are the output DC voltage and DC current of the three-stage synchronous generator respectively, and Cf is the DC filter capacitor of the generator;

[0055] Step 2: Obtain the stability characteristics of the equivalent output impedance of the synchronous generator;

[0056] Specifically, the stability characteristic of the equivalent output impedance is that the phase angle of the output impedance within the time-frequency range is located in [-90, 90], that is, its impedance characteristic shows a constant positive resistance characteristic; if the impedance characteristic is a positive resistance characteristic, it indicates that the equivalent output impedance is stable by itself, proving that the synchronous generator can operate stably by itself.

[0057] Step 3: According to the Nyquist stability criterion, propose the stability criterion for the HVDC power generation system with a constant power load;

[0058] Specifically, the generalized Nyquist criterion defines that the system is stable when the Nyquist locus of the minimum loop gain composed of the closed-loop system does not enclose (-1, j0)

[0059] In the specific implementation process, according to the generalized Nyquist criterion, specifically for a high-voltage DC power generation system composed of a power supply and a load, its stability definition can be clearly stated as follows: If the equivalent output impedance of a three-level synchronous motor exhibits a constant positive impedance and the magnitude of the output impedance is less than the magnitude of the equivalent input impedance of a constant-power load, then the high-voltage DC power generation system is stable.

[0060] In the specific implementation process, according to the small-signal model described in Step 1, the small-signal impedance models of a 65kW DC generator and a DC / DC converter are obtained respectively and plotted as Bode plots, as Figure 4 shown; according to Figure 4 shown, it can be clearly seen that the stability characteristics of both the 65kW DC generator and the DC / DC satisfy the conditions described in Step 2 and Step 3. Therefore, the closed-loop system composed of the 65kW generator and the DC / DC converter is stable;

[0061] In the specific implementation process, a simulation analysis of the stability of a high-voltage DC power generation system composed of a 65kW DC generator and a DC / DC converter is carried out, as Figure 5 shown. By detecting the output voltage and current of the 65kW DC generator and the output voltage and current of the DC / DC converter, a consistency verification of the model is performed. The results prove that the closed-loop system is consistent with the model analysis conclusion, and the high-voltage DC power generation system can operate stably.

[0062] Step 4: According to the stability criterion, by restricting the magnitude of the load impedance, a general stability design method applicable to different load conditions is given.

[0063] Specifically, taking a 65kW DC generator as an example, an equivalent output impedance model of the synchronous generator is established

[0064] In the specific implementation process, as Figure 4 shown, it is proved that the stability characteristic of the output impedance of the 65kW generator is stable. The magnitude of the equivalent output impedance of the synchronous generator at different frequencies is obtained using the Bode plot

[0065] Restrict the equivalent input impedance of the load and the equivalent output impedance of the generator to satisfy the following formula

[0066] |Z i |-Z o >GM(dB)

[0067] where GM is the magnitude margin of the impedance. Generally, considering the safety threshold, the magnitude margin is selected as 6dB.

[0068] As Figure 6 shown, design the magnitude of the equivalent load impedance to fall within the Figure 6 area indicated by the frame line, and the system can operate stably.

[0069] In the specific implementation process, simulation analysis was carried out on a 65kW DC generator with 20kW constant power load, 30kW constant power load, and 40kW constant power load to verify the stability design method. As Figure 6 shown, it is proved that the high-voltage DC power supply system remains stable under different levels of constant power load conditions, and it is proved that when the load impedance is greater than the generator equivalent impedance by more than 6dB safety threshold, it can operate stably. The stability design method of the high-voltage DC power generation system based on the small-signal model proposed by the present invention is reasonable, correct, and feasible.

[0070] The above specific implementation manners or cases are only used to explain the technical solutions of the present invention, and do not limit this application. Those parts not described in detail are regarded as conventional technical means or common general knowledge in the art. It can be understood by those of ordinary skill in the art that: based on the design concept of this application, it should be possible to make adaptive modifications to the technical solutions recorded in the foregoing implementation manners, or make equivalent replacements for some or all of the technical features. These modified, equivalent replacement, and adaptively improved technical solutions do not depart from the technical essence of the present invention and should all be covered within the protection scope of this application.

Claims

1. A stability design method for a high voltage direct current power generation system based on a small signal model, characterized in that: The following steps are involved: Step 1: Construct a simplified model of a three-stage synchronous generator and obtain the equivalent output impedance model of the generator; Step 2: Obtain the stability characteristics of the equivalent output impedance of the synchronous generator; Step 3: Based on the Nyquist stability criterion, a stability criterion for the HVDC power generation system with constant power load is proposed; Step 4: According to the stability criterion, by constraining the amplitude of the load impedance to be greater than the amplitude of the equivalent output impedance of the generator by a certain stability margin, it is used as the basis for load design input to achieve stable operation of the high-voltage DC power generation system.

2. A high voltage direct current power generation system stability design method based on a small signal model as claimed in claim 1, characterized in that: In the step 1, constructing the generator output impedance model includes: Convert the electrical parameters of the rotor part of the main generator and the excitation motor to the stator side, and obtain the equivalent circuit diagram of the main generator and the excitation motor in the rotating coordinate system; Using the equivalent circuit diagram of the main generator and the excitation motor, the equivalent model of the main generator and the excitation motor is obtained; The permanent magnet machine is equivalent to a constant voltage source; The generator voltage regulating circuit is equivalent to a chopper circuit and combined with the permanent magnet machine equivalent constant voltage source to obtain the exciter front end equivalent circuit; According to the equivalent circuit model of permanent magnet machine, exciter, main generator and voltage regulating module, the small signal output impedance model of the three-stage synchronous generator is obtained.

3. A high voltage direct current power generation system stability design method based on a small signal model as claimed in claim 2, characterized in that: In step 1, according to the equivalent circuit diagram of the three-stage synchronous generator exciter and the main motor stator side rotating coordinate system, the small signal model of the main generator stator and rotor circuit in the synchronous rotating coordinate system is obtained:

4. A high voltage direct current power generation system stability design method based on a small signal model as claimed in claim 3, characterized in that: In step 1, based on the equivalent circuit diagram, the small signal model of the exciter is derived by analogy: Where: superscript ME represents exciter parameters.

5. A high-voltage direct current power generation system stability design method based on a small signal model as claimed in claim 4, in step 1, according to the permanent magnet machine and the generator voltage regulation chopper circuit diagram, a small signal model of the permanent magnet machine and the chopper circuit is obtained: Where kpv and kiv are the proportional coefficient and differential coefficient of the PI link respectively. According to the small signal models of the permanent magnet machine, exciter, main generator and voltage regulation module, the small signal impedance model of the generator is solved as follows: Where, ZMG is the impedance of the three-stage synchronous generator, vdc and idc are the output DC voltage and DC current of the three-stage synchronous generator respectively, and Cf is the DC filter capacitor of the generator.

6. A high-voltage direct current power generation system stability design method based on a small signal model as described in claim 1, wherein in the step 2, the stability characteristics of the equivalent output impedance of the synchronous generator are defined as that the phase angle of the output impedance in the frequency range of [1,10000] is located at [-90, 90], that is, its impedance characteristics exhibit a constant positive resistance characteristic.

7. A high-voltage direct current power generation system stability design method based on a small signal model as described in claim 1, wherein in said step 3, the stability criterion of the high-voltage direct current power generation system with a constant power load is obtained according to the Nyquist stability criterion: within the frequency range of [1,10000], the equivalent output impedance of the three-stage synchronous motor exhibits a constant positive impedance, and the output impedance amplitude is less than the equivalent input impedance amplitude of the constant power load, then the high-voltage direct current power generation system is stable.

8. The method for designing the stability of a high-voltage direct current power generation system based on a small signal model according to claim 1, wherein in step 4, by constraining the size of the load impedance, a general stability design method applicable to different load conditions is provided, comprising: Establish the equivalent output impedance model of synchronous generator; Calculate the equivalent output impedance amplitude of synchronous generator at different frequencies; The load equivalent input impedance and the generator equivalent output impedance satisfy the following equation: |Z i |-|Z o |>GM(dB) Among them, GM is the amplitude margin of impedance, which is selected as 6dB.

9. A high-voltage direct current power generation system stability design method based on a small signal model as described in claim 8, in which: the load equivalent impedance amplitude should be greater than the power source equivalent impedance and the amplitudes of both should exceed 6dB.

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