1 The accuracy of various dynamic calculations of the power system depends on the model of the generator, excitation system, speed control system and integrated load, and the accuracy of the parameters in the model. In recent years, the domestic power grid has a high voice for the above-mentioned parameter testing and dynamic modeling. A large number of analytical calculations show that the generator model and parameter problems are more complicated than the other links in the above parameters.
For the parameter problem of synchronous generator, the field method can be used to obtain the numerical calculation, or the system identification theory can be used for parameter identification. There are two main methods of identification: 1 frequency domain response method 2 time domain response method. Due to the limitations of the method itself, the former tends to decrease in recent years. The latter method has two practical difficulties when using online measurement technology. First, when the online identification is performed, the synchronous motor is in the normal running state, and the input disturbance signal cannot be too large, otherwise it will affect the normal operation. Most of the online identification in foreign countries is mainly the simulation results, and there are few field tests. Second, there is a problem of parameter identification instability, that is, when different calculation methods are used for different tests or even the same test, the obtained parameters vary greatly. For the same experiment, four calculation methods were used, and the d, q-axis transient and super-transient reactance were obtained, and the difference was (2.3-4.7) times. The d and q-axis transient open-time constants were different (1. 89 to 2.51) times, and the d and q axis super-transient open circuit time constants differ by several hundred times.
Using the generator to disassemble this normal operation, the recording terminal voltage transient process can be used to calculate the parameters of the synchronous generator, and the method is relatively simple. In this paper, the general expression of the terminal voltage after the synchronous generator is removed from the power grid is derived by the computational microproduct method. How to use this transient process to obtain the synchronous motor parameters is discussed. Tests on a small synchronous generator show that the parameter calculation is reproducible, and the results of the simulation calculation are close to the test results.
2 Synchronous generator suddenly cuts off the back-end voltage from the grid. In the following calculation process, it is assumed that: 1 does not count the saturation effect. 2 There is only one damper winding 3 in both the direct axis and the cross-axis due to the mechanical transient process compared to the electromagnetic transient process. It is slow, so when calculating the transient process after de-column, it is considered that the synchronous motor speed is still synchronous.
Since the magnetic linearity is assumed, the superposition principle can be applied, that is, the synchronous generator is cut off from the power grid as a current source that is suddenly connected in parallel with the opposite direction and the opposite direction before the cutting, so that the motor end is instantaneously cut off. The solution of the variable voltage is solved in the following two cases, namely: 1 the steady-state running current 2 before the motor is cut off from the grid, and the motor terminal voltage is suddenly connected in parallel with the current source of the same size and opposite direction before the cutting. The change.
2.1 Steady-state operation before reciprocation Steady-state symmetrical operation, the synchronous generator's speed is constant and equal to the synchronous speed, the excitation voltage and current are constant, the armature voltage and current are stable alternating voltage and current, damping The current in the winding is zero.
Let the instantaneous value of the excitation potential of each phase be δ to indicate the phase angle of the excitation potential before the terminal voltage, then the instantaneous value of the terminal voltage is converted from the Park equation to the d, q, 0 coordinate system. In the state operation, the d and q axis currents of the armature resistor R are respectively calculated as x in the direct axis and the cross axis synchronous reactance, respectively.
2.2 After the resection, the transient process is as shown in equation (6) (7). After the resection, it is equivalent to a sudden connection of a current source at the end of the motor to solve the transient voltage caused by this transient current. It is assumed that w = has the following The formal expression x(p) is the direct and cross-axis operational reactance of the motor, and its expression is as shown in equation (12)(23). G(p) is a direct-axis transfer function.
Since only the effects caused by the currents shown in the equations (4) and (5) are considered, the flux linkage equation is distinguished from the voltage before the ablation, and the cut-off transient voltage is referred to as uq, excluding the armature resistance. The voltage equation becomes symmetrical due to the three-phase voltage, and the zero-sequence component is zero. It can be seen from equation (11) that the solution of u and u becomes the solution of ψ and ψ.
From the equation, x is the direct-axis armature reaction reactance x and x, respectively, and the reactances R and R of the field winding and the damper winding are respectively the resistance of the field winding and the damper winding.
Then solve the original function of ψ, so that the time constant of the excitation winding is the time constant of the direct-axis damper winding, and the magnetic flux leakage coefficient between the excitation winding and the straight-axis damper winding is solved (15), and the equation (19) is obtained. Considering that the value of the damper winding resistance is much larger than the field winding, so that τ is much smaller than τ, so that τ is the open circuit of the stator winding and the field winding is shorted, that is, =0, the straight shaft damper winding The time constant is the case where the direct-axis armature winding and the straight-axis damper winding are both open, and the original function of the time constant of the field winding is where x and x are the direct-axis transient and the super-transient reactance in the x-axis. The armature reaction reactance is the cross-axis damper winding resistance, where τ is the open-axis armature winding open circuit, and the time constant of the cross-axis damper winding is the same as the above method, where x is the cross-axis super-transient reactance .
The transient voltage u obtained is where u and u are transformer potentials, and u and u are rotational potentials.
Since the transformer potential is much smaller than the rotating potential, if it is omitted, the expression of the terminal voltage after the cutoff of the 2.3 generator from the grid to the a, b, c coordinate system and u can be expressed according to u. Export.
It can be seen from equation (31) that after the synchronous generator is cut off from the grid, it undergoes a transient process with a steady-state value of E), and the value therein is related to the magnitude of the excitation current before the excision in the case where the excitation remains unchanged. Figure 4 shows an oscillogram of a kW, 400 V synchronous generator cutting back-end voltage and excitation current from the grid. The machine is i =0 before resection and operates in a under-excited state.
3 Using the transient process after cutting to obtain the motor parameters Since the above formula can be used to decompose the cut voltage into d and q-axis components, the parameters are obtained.
Therefore, since x is much smaller than τ, Δu is quickly attenuated, which is equivalent to the open circuit of the damper winding, u. From this equation and (4) and (33), we can see from equations (5) and (34) that we can find the transient components at t =0 when we find the parameters of (3) and (37). The value of the problem. The curve fitting method [3~5] can be used to obtain the time constant τ and the τ4 power angle δ in (39)(40) at the same time. The same black and white uniform mark (Figure 1). When the motor rotates, the rectangular position pulse emitted by the photoelectric speed sensor is connected to the light oscilloscope along with the voltage signal of any phase of the motor. Since this principle is used when no load is used, the black and white mark on the shaft is adjusted at no load to make the motor The voltage waveform coincides with the centerline of the rectangular wave (Figure 2). The δ angle at the time of motor load or after cutting can be determined by the following equation based on the phase difference of the above two waveforms (Fig. 3).
Transient process of terminal voltage at =0 瞬0 transient voltage process 5 Parameter calculation results and analysis Based on the above-mentioned method in the laboratory for repeated tests, a small synchronous generator produced by Shanghai Electric Machinery Factory was tested. Take the parameters. Table 1 gives the calculation results of the motor parameters. The design data and the d and q axis parameters obtained by the plant using the sudden short circuit method and the static measurement method are listed in the table. Nameplate data of the tested motor Remarks Design data Sudden short circuit method Shanghai Motor Factory test data static test method Shanghai Electric Machinery Factory test data test (1) δ test before resection (2) δ test before resection (3) δ utilization table test before resection The comparison between the results of the simulation calculations of the parameters obtained in (1) and (2) and the test results are shown in Fig. 6 and Fig. 7.
The traditional mathematical model is used in the simulation calculation, ie, i is the current in the excitation winding and the damper winding respectively.
The results of the simulation calculations are shown together in Figures 6 and 7. The parameters in equation (41) are obtained from the data in Table 1. The relationship is as follows.
It can be seen from Table 1 and Figure 6 and Figure 7: Time calculation and experimental curve (1) The calculation result of Figure 7 is close to the test result. The error of the maximum point in Figure 6 is about 7, and the error mainly comes from the following aspects: 1 model error, That is, it is assumed that the d and q axes have only one damper winding 2 measurement error 3 data processing error.
(2) Test (3) The obtained x differs greatly from other tests.
In addition to the above reasons, there may be a measurement error of the power angle δ and a fluctuation of the prime mover speed.
The calculation of the time and the d-axis parameter calculated by the terminal voltage transient process at the conclusion of the conclusion of the experimental curve 6 at 0 = 0, the results are satisfactory.
(2) The parameters obtained in test (2) are smaller than those in test (1), indicating that the method described in this paper can reflect the influence of magnetic saturation on the motor parameters according to the magnitude of the excitation current before the generator is cut off from the power grid.
At ≠0, the generator is disengaged from the grid, and the d and q axis parameters can be measured simultaneously, but the error needs further study.
Muping, etc. Simulation evolution method for synchronous generator parameter identification [J]. Electrical engineering Chen Wenchun. Motor transient process [M]. Beijing: Mechanical Industry Press, 1982.
The degree of change with I is small.
As the variation of I varies with I, it can be seen from Fig. 8. As the rotational speed increases, the efficiency η increases. This is because, in the case of the same power, the higher the rotational speed, the smaller the phase current, and the smaller the copper consumption, which is advantageous for the improvement of efficiency. Therefore, try to run at higher speeds.
The relationship between the change and the speed and output current. The increase in the rotational speed is beneficial to the decrease of ΔV, because the motor current will decrease after the rotational speed is increased, and the storage capacitor voltage pulsation ΔV caused by the current change will also decrease. The larger the output current, the larger ΔV, and thus the larger the ΔV.
The change with I 5 Conclusions (1) C dump bidirectional converter has a simple topology and high reliability, which is of great significance in the application of avionics systems.
(2) The brushless DC starter/generator based on the C dump bidirectional converter has the same external characteristics as the brushless DC generator when it is powered by the same brushless DC motor, and has a wide operating speed through closed-loop voltage control. There are flat external features in the range.
(3) The system is more efficient at high speeds, and the aeroengines are mostly under the working conditions of cruising speed and maximum speed (aircraft climb), so the application to the aviation brushless start/generator system has advantages in efficiency.
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