- Detail

Design of SPWM Frequency Stabilized and voltage stabilized inverter power supply introduction in recent years, the drive system composed of frequency converter and variable frequency motor plays an important role in production. However, it is often found that the frequency converter and variable-frequency motor can not match well in use, which seriously puzzles the manufacturers of frequency converter and variable-frequency motor. Therefore, it is necessary to develop SPWM frequency stabilized power supply, so that the adjustable range of power frequency is 0 ~ 500Hz and the adjustable range of voltage is 0 ~ 420v (fundamental wave). It can also display the voltage (VPWM), current, frequency and power of SPWM wave actually responded by the motor. In this way, the manufacturer of the frequency converter can take the power supply as the standard, measure the voltage value, current value and frequency value of the matched variable-frequency motor, and adjust the vector control parameters or v/f control parameters of the frequency converter. The motor manufacturer can also adjust the parameters of the motor according to the standard power supply, so that the most promising combination is the mixed lead halide perovskite, which is matched with the frequency converter

1 working principle and measurement system analysis

as shown in Figure 1, the main circuit of SPWM frequency stabilized power supply is similar to the mature SPWM inverter power supply on the market. When the AC motor and the regulating method is to loosen two screws and a pulse width modulation frequency converter are used for variable frequency speed regulation, VPWM is designed to measure the effective voltage of the AC motor. This type of frequency converter first generates a DC voltage e from the AC source, which is called DC link voltage. Then, using the power electronic transformation technology and pulse width modulation to transform the DC link voltage, a three-phase power supply system can be obtained. For example, IGBT can switch the DC voltage hundreds of times in a few milliseconds to create a three-phase voltage with adjustable frequency. However, the output voltage is not a sine wave, but a high-frequency chopper waveform with constant amplitude, as shown in Figure 2. This voltage is sent to the motor. Because the motor is a large inductive load, which mainly responds to the low-frequency part of the power supply voltage, the current waveform has only a small amount of high-frequency components, which is approximately a sine wave. For system designers and users, it is very important to measure the voltage VPWM actually received by the motor and check whether the vector parameters or v/f of the motor are out of range. If the nominal v/f value of the motor is exceeded for a long time (for example, the motor operates at high frequency and low speed), the motor will be heated and even damaged, resulting in serious consequences. However, it should be noted that the voltage measured by the voltmeter is the RMS output specification report, and there is a very large error between the actual effective voltage VPWM of the motor response and the RMS of the PWM wave in Figure 2. For example, in a system, when vpwm=144v, vrms=192v, and the error rate is (192-144)/144=33.3%

the sampling system sends the data to the control system. The control system detects VPWM by calculating the RMS value of the absolute average voltage of the whole cycle of the fundamental frequency

for example, when the carrier ratio is n= ω c/ω When s is an odd integer multiple of 3, the Fourier series expression of line voltage UAB is

, where: m is the modulation system

m and N are the harmonic number relative to carrier wave and modulation wave respectively

ω c， ω S is the angular frequency of carrier wave and modulated wave respectively

the equations of outgoing line voltages UBC and UCA can also be derived. Obviously, the carrier component with high amplitude is eliminated; Carrier harmonics are also eliminated; The zero sequence harmonic component in their upper and lower side frequencies also does not exist; In the above formula, sin is to eliminate those terms when m and N are both even or odd at the same time. Table 1 shows the general values of harmonics in UAB

Figure 3 shows the scenario of harmonic and fundamental wave superposition when there are high-frequency components in the signal. The higher the number of harmonics, the smaller the influence on the average value

using the measurement system in Figure 1, take the fundamental frequency of the output signal and the integer cycle of the measurement fundamental frequency, and transmit the relevant data to the control system. The control system finally displays the VPWM value of the actual response of the motor by calculating the root mean square value (effective value) of the fundamental frequency wave

2 design method of stabilized voltage and frequency stabilization system

before the design of stabilized frequency and stabilized voltage SPWM power supply? It is necessary to clarify the technical indicators required by the system, and carry out the static and dynamic design of the system according to these indicators, so as to clarify the main technical indicators that each unit circuit should achieve. Distribute to each unit reasonably, and then calculate the parameters. The correct parameters are sent to the digital circuit for programming to control the frequency and voltage. From the principle block diagram of amplitude stabilization in Figure 4, the structure diagram of the closed-loop system in Figure 5 is obtained

2.1 static design

from Figure 5, the static characteristic equation

uo=kunui/(1 + can be deduced α K1k2ui) (2)

then the static structure diagram is shown in Figure 6

according to the static characteristic equation and the technical index of the system, the technical index of each unit circuit can be determined

2.2 dynamic design

because each unit circuit may have time delays, they will affect the dynamic performance of the system and may cause system oscillation. Set the total delay as ts, and the power amplifier is the link with the largest delay in the closed-loop system. Its transfer function is

k2/(1 + TSS) (3)

the transfer function of the integral multiplier is

UI (1 + TS)/ts (4)

because the feedback circuit has a filter link, its transfer function is

α/(1 + TNS) (5)

then the dynamic structure diagram of the system is shown in Figure 7. According to the final correction of the system, the open-loop magnification of the system can be determined

2.3 protection design

spwm frequency stabilized power supply has the same protection as ups and frequency converter, with overcurrent and overvoltage protection; Di/dt, du/dt limit protection. It is suggested to adopt the mature soft switching technology

3 conclusion

according to the above introduction, a prototype with a rated output power of 10kW is trial produced and tested in an electronic factory in Yangzhou. The VPWM measured by this principle is compared with the fluke Multimeter in the United States. 2. The design method of frequency stabilization and frequency stabilization system is before the design of frequency stabilization and voltage stabilization SPWM power supply? It is necessary to clarify the technical indicators required by the system, and carry out the static and dynamic design of the system according to these indicators, so as to clarify the main technical indicators that each unit circuit should achieve. Distribute to each unit reasonably, and then calculate the parameters. The correct parameters are sent to the digital circuit for programming to control

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