The load-controllable transformer-type adjustable reactor can realize fast and continuous adjustment of the inductance, and the control quantity and the linearity of the inductance are good, and the small harmonics are generated at the same time, so it is applied in many fields. However, the voltage on the DC side of the reactor inverter bridge has a great influence on its performance. If DC power is used on the DC side, it is beneficial to improve the performance of the reactor, but it will definitely increase the cost of the reactor system and also limit the reactor. The scope of application; the use of capacitors as the DC power supply of the inverter bridge will help to reduce the cost of the reactor and expand its application range, but it must effectively control its voltage and make the reactor work in a normal state. In the process of starting up, in order to make the reactor into the working fund project: the National Natural Science Foundation of China (50777066) research direction is the application of power electronics in the power system. State, the charging circuit of the capacitor is designed, but it does not involve how to control the charging circuit during operation to keep the voltage of the capacitor stable. Another characteristic of the reactor is that its primary equivalent reactance has a large dependence on the parameters of the transformer body. To effectively control the inductance, it is necessary to first determine the body parameters of the transformer. In the engineering practice, the transformer body parameters have a certain dispersion, and it will change with the change of the operating conditions of the transformer, which is not conducive to the development of the control system and the promotion of the reactor, and is not conducive to the precise control of the reactor.
Aiming at the above problems, a control system is designed, which does not depend on the parameters of the transformer body, and can effectively control the capacitor voltage on the DC side of the inverter bridge without special charging circuit, so that the reactor is in an effective working state.
2 On-line monitoring principle of reactance value When the transformer works in the state of the reactor, since its primary equivalent resistance is much smaller than the equivalent reactance, the ratio of the primary fundamental voltage to the current amplitude is the equivalent reactance of the reactor X. Due to the voltage or The current) contains harmonic components, so the fundamental component of the effective or real-time extraction of voltage or current is the key to achieving on-line monitoring of reactance values. For the fundamental component extraction model, the resonant link G1, the inertia G2, and the proportional link are respectively: show the amplitude and phase frequency characteristics of the medium subsystem Gb.
When Gb's input signal um1 frequency is 50Hz, Gb gain is 10dB), phase shift is zero; when Uin1 frequency is 49Hz, Gb gain is 0.95-0.446dB), phase shift is 3.44; when the centroid frequency is 51Hz The gain of Gb is 1.05. Even if the fundamental frequency of uin1 is shifted, the output signal u of Gb can track the fundamental component of Uin1.
And -157.83; if the frequency of um1 is further increased, the attenuation of Gin to Uin1 will be further enhanced. It can be seen that the subsystem Gb has a certain attenuation effect on the second harmonic, and has a good attenuation effect on the harmonics of three times or more.
In order to improve the system's ability to attenuate the second harmonic, and not adversely affect other harmonics, a delay link D with a delay time of 10 ms and a proportional link K with a proportional coefficient of 0.5 are added to the control system. Show. After the input signal um is delayed by 10ms and then subtracted from the signal itself, the 2nd harmonic and DC component in um can be effectively eliminated. Even if the frequency is shifted, the 2nd harmonic component in uw is much smaller than that in uin. The second harmonic component, and the other higher harmonic components in uin1 are not greater than the higher harmonic components corresponding to uin, which is more conducive to harmonic attenuation in the input signal. Subsystem Ga has little effect on the fundamental component of um.
It can be seen that the system shown has strong selectivity to frequency, which has a large attenuation effect on the DC component and the higher harmonic component, and the signal of the fundamental frequency can pass, so it can effectively extract um. The fundamental component of the wave. The system is used to extract the fundamental component of the primary winding voltage and current of the reactor, and then the amplitude of the fundamental component is obtained. The ratio of the fundamental component is the reactance value of the reactor in the current state, thus realizing the on-line monitoring of the reactance value. .
3 The control principle of the DC-side capacitor voltage of the inverter bridge shows the structural principle diagram of the transformer-type controllable reactor.
The current source is realized by a single-phase inverter bridge. According to the available: when /sinwt, the control kksinwt, where the real part is referred to as the in-phase component, the same below), then U1=R1+island+kM)di1/dt. When i2 is in phase or reverse phase with i1, the transformer works in the state of the reactor, and its reactance value is related.
It can be seen that only effective control of the transformer can work in the reactor state; and only effective control, the inverter can effectively control i2. Therefore, effective control of Ud is of great significance for the normal operation of the reactor.
During the power frequency cycle, the energy absorbed and released by the current source i determines the change of the capacitor voltage during the period, and the amount of change is: the average power active power); Uc0 is the capacitor voltage at the initial time of the cycle; C is the inverter The value of the bridge DC side capacitor.
If i2 has only the in-phase component, according to equation 2), the average power consumed in a T is the average power P1k12R2/72. In summary, due to the presence of R2, Ud will drop when the transformer operates in the reactor state. If this voltage is not controlled, it will eventually be unable to effectively control i2 due to the drop of Ud, which will affect the performance of the reactor, and the transformer will not even work in the reactor state. In the actual system, since R2 is small, the speed of Ud is also small.
-n/2), where 2 is a real number, the component is called a vertical component, the same below), then within T, the average power consumed by current source i is P2 = k22R2/2/2-k2wM/2/2. Control 0wM /R2, then P2 is always greater than zero. According to Equation 2), when i2 has only a vertical component, there is: according to the above, when i2 has only a vertical component, and k2 < 0 or k2 > WM / R2, Ud will decrease; when the control system of the 0 4 reactor shows The control system of the reactor, wherein the value of the reactance is monitored online by the method described in the second part, and the error formed by comparing it with the given value is taken as the input signal of the PI regulator, and the output signal of the PI regulator is ki, i and The product of the primary current fundamental component is the in-phase component of i2, the control ki will control the component to control the inductance value; 2 and the product of the primary current fundamental component after the delay constitute the vertical component of i2, and control k2 to control the vertical of i2 The component is controlled.
The system can better extract the fundamental component of the system.
The system for the reactor control system does not rely on the transformer's body parameters when controlling the reactor and can be controlled. The in-phase component and the vertical component of 2 are the fundamental current components, which eliminate the influence of the harmonic component of i1 on the performance of the reactor.
5 Simulation and fundamental component extraction model, and simulation analysis. When the input signal is a square wave signal of ~1000, the output signal is a fundamental signal of 50 Hz. Fourier analysis of the signal shows that the fundamental phasor in the input signal is 560.87e-10617, and the phasor of the output signal is 560.805e-20645. b is the primary voltage and current of the reactor after Ud enters the steady state, Before about 0.365 s, although Ud is decreasing, the reactor effectively tracks the given reactance value of 15 ft) because B is in an effective control state; at about 0.365 s, since Ud reaches the lower limit of the control voltage, A vertical current component is introduced into the secondary winding, which causes current distortion, but the process is very short. At about 0.4 s, the reactor again enters a stable operating state. It can be seen from b that during the adjustment process, the primary equivalent reactance of the reactor also effectively tracks the given reactance. If there is no R1, Ud will slow down more slowly, and the process of Ud adjusting from the lower limit to the upper limit will be shorter, and the Ud adjustment process will have less influence on the performance of the reactor.
The Ud is changed during operation to change the upper and lower limits of the DC voltage. The Ud's set value is adjusted from 550V to 560V and 540V, respectively, to 605V, and the upper and lower limits are 615V and 595V respectively. The adjustment starts at about 0.6s and the adjustment is completed at 0.65s.
d is the process of inductance adjustment.
In order to verify the effect of the proposed SVPWM subdivision optimization algorithm in practical applications, a voltage-type three-phase inverter with a 120W AC motor is controlled based on DSP-FPGA, and the amplitude of the oscilloscope waveform is 30 times of the actual waveform proportional compression.
The experimental waveform 5 conclusion proposes a SVPWM subdivision optimization method, and the algorithm is successfully applied to the AC motor speed control system through Matlab offline calculation and DSP-FPGA. Compared with the traditional SVPWM modulation method, the method is simple, takes up less hardware resources, and has strong real-time performance. The experiment proves that the control effect is good.
Aiming at the above problems, a control system is designed, which does not depend on the parameters of the transformer body, and can effectively control the capacitor voltage on the DC side of the inverter bridge without special charging circuit, so that the reactor is in an effective working state.
2 On-line monitoring principle of reactance value When the transformer works in the state of the reactor, since its primary equivalent resistance is much smaller than the equivalent reactance, the ratio of the primary fundamental voltage to the current amplitude is the equivalent reactance of the reactor X. Due to the voltage or The current) contains harmonic components, so the fundamental component of the effective or real-time extraction of voltage or current is the key to achieving on-line monitoring of reactance values. For the fundamental component extraction model, the resonant link G1, the inertia G2, and the proportional link are respectively: show the amplitude and phase frequency characteristics of the medium subsystem Gb.
When Gb's input signal um1 frequency is 50Hz, Gb gain is 10dB), phase shift is zero; when Uin1 frequency is 49Hz, Gb gain is 0.95-0.446dB), phase shift is 3.44; when the centroid frequency is 51Hz The gain of Gb is 1.05. Even if the fundamental frequency of uin1 is shifted, the output signal u of Gb can track the fundamental component of Uin1.
And -157.83; if the frequency of um1 is further increased, the attenuation of Gin to Uin1 will be further enhanced. It can be seen that the subsystem Gb has a certain attenuation effect on the second harmonic, and has a good attenuation effect on the harmonics of three times or more.
In order to improve the system's ability to attenuate the second harmonic, and not adversely affect other harmonics, a delay link D with a delay time of 10 ms and a proportional link K with a proportional coefficient of 0.5 are added to the control system. Show. After the input signal um is delayed by 10ms and then subtracted from the signal itself, the 2nd harmonic and DC component in um can be effectively eliminated. Even if the frequency is shifted, the 2nd harmonic component in uw is much smaller than that in uin. The second harmonic component, and the other higher harmonic components in uin1 are not greater than the higher harmonic components corresponding to uin, which is more conducive to harmonic attenuation in the input signal. Subsystem Ga has little effect on the fundamental component of um.
It can be seen that the system shown has strong selectivity to frequency, which has a large attenuation effect on the DC component and the higher harmonic component, and the signal of the fundamental frequency can pass, so it can effectively extract um. The fundamental component of the wave. The system is used to extract the fundamental component of the primary winding voltage and current of the reactor, and then the amplitude of the fundamental component is obtained. The ratio of the fundamental component is the reactance value of the reactor in the current state, thus realizing the on-line monitoring of the reactance value. .
3 The control principle of the DC-side capacitor voltage of the inverter bridge shows the structural principle diagram of the transformer-type controllable reactor.
The current source is realized by a single-phase inverter bridge. According to the available: when /sinwt, the control kksinwt, where the real part is referred to as the in-phase component, the same below), then U1=R1+island+kM)di1/dt. When i2 is in phase or reverse phase with i1, the transformer works in the state of the reactor, and its reactance value is related.
It can be seen that only effective control of the transformer can work in the reactor state; and only effective control, the inverter can effectively control i2. Therefore, effective control of Ud is of great significance for the normal operation of the reactor.
During the power frequency cycle, the energy absorbed and released by the current source i determines the change of the capacitor voltage during the period, and the amount of change is: the average power active power); Uc0 is the capacitor voltage at the initial time of the cycle; C is the inverter The value of the bridge DC side capacitor.
If i2 has only the in-phase component, according to equation 2), the average power consumed in a T is the average power P1k12R2/72. In summary, due to the presence of R2, Ud will drop when the transformer operates in the reactor state. If this voltage is not controlled, it will eventually be unable to effectively control i2 due to the drop of Ud, which will affect the performance of the reactor, and the transformer will not even work in the reactor state. In the actual system, since R2 is small, the speed of Ud is also small.
-n/2), where 2 is a real number, the component is called a vertical component, the same below), then within T, the average power consumed by current source i is P2 = k22R2/2/2-k2wM/2/2. Control 0wM /R2, then P2 is always greater than zero. According to Equation 2), when i2 has only a vertical component, there is: according to the above, when i2 has only a vertical component, and k2 < 0 or k2 > WM / R2, Ud will decrease; when the control system of the 0 4 reactor shows The control system of the reactor, wherein the value of the reactance is monitored online by the method described in the second part, and the error formed by comparing it with the given value is taken as the input signal of the PI regulator, and the output signal of the PI regulator is ki, i and The product of the primary current fundamental component is the in-phase component of i2, the control ki will control the component to control the inductance value; 2 and the product of the primary current fundamental component after the delay constitute the vertical component of i2, and control k2 to control the vertical of i2 The component is controlled.
The system can better extract the fundamental component of the system.
The system for the reactor control system does not rely on the transformer's body parameters when controlling the reactor and can be controlled. The in-phase component and the vertical component of 2 are the fundamental current components, which eliminate the influence of the harmonic component of i1 on the performance of the reactor.
5 Simulation and fundamental component extraction model, and simulation analysis. When the input signal is a square wave signal of ~1000, the output signal is a fundamental signal of 50 Hz. Fourier analysis of the signal shows that the fundamental phasor in the input signal is 560.87e-10617, and the phasor of the output signal is 560.805e-20645. b is the primary voltage and current of the reactor after Ud enters the steady state, Before about 0.365 s, although Ud is decreasing, the reactor effectively tracks the given reactance value of 15 ft) because B is in an effective control state; at about 0.365 s, since Ud reaches the lower limit of the control voltage, A vertical current component is introduced into the secondary winding, which causes current distortion, but the process is very short. At about 0.4 s, the reactor again enters a stable operating state. It can be seen from b that during the adjustment process, the primary equivalent reactance of the reactor also effectively tracks the given reactance. If there is no R1, Ud will slow down more slowly, and the process of Ud adjusting from the lower limit to the upper limit will be shorter, and the Ud adjustment process will have less influence on the performance of the reactor.
The Ud is changed during operation to change the upper and lower limits of the DC voltage. The Ud's set value is adjusted from 550V to 560V and 540V, respectively, to 605V, and the upper and lower limits are 615V and 595V respectively. The adjustment starts at about 0.6s and the adjustment is completed at 0.65s.
d is the process of inductance adjustment.
In order to verify the effect of the proposed SVPWM subdivision optimization algorithm in practical applications, a voltage-type three-phase inverter with a 120W AC motor is controlled based on DSP-FPGA, and the amplitude of the oscilloscope waveform is 30 times of the actual waveform proportional compression.
The experimental waveform 5 conclusion proposes a SVPWM subdivision optimization method, and the algorithm is successfully applied to the AC motor speed control system through Matlab offline calculation and DSP-FPGA. Compared with the traditional SVPWM modulation method, the method is simple, takes up less hardware resources, and has strong real-time performance. The experiment proves that the control effect is good.
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