What should I do if the amplitude of the modulation wave is too low to control the motor with SPWM

In order for the motor to rotate, the control department must turn on (or off) the power transistor in the inverter according to the position of the motor rotor sensed by the hall-sensor, and then according to the stator winding, so that the current flows through the motor coil in order to generate a forward (or reverse) rotating magnetic field, and interacts with the magnet of the rotor, so that the motor can rotate clockwise and counter-clock. When the motor rotor rotates to the position where the hall-sensor induces another set of signals, the control unit turns on the next set of power transistors, so that the circulating motor can continue to rotate in the same direction until the control department decides to stop the motor rotor and then turn off the power transistors (or only open the lower arm power transistor); If the motor rotor is reversed, the power transistor is turned on in the opposite order. If you want to know more about it, you can consult Yisheng (...).

Definition of modulation coefficient in SVPWM:

The modulation system is the carrier frequency modulation frequency, the modulation wave in SPWM = sine wave, carrier wave = triangle wave, the signal that needs to be modulated intersects with the fixed amplitude and carrier frequency, and the debugged waveform is obtained, and the area is equivalent to the signal that needs to be debugged.

If the modulation ratio is too small, the modulated signal is easy to distort, the waveform is difficult to sinusoidal, when our motor control is 4, the current waveform is more distorted, a bit like a triangle wave.

Formula: modulation system = modulation amplitude value carrier amplitude value; In general SPWM, modulated wave = sine wave, carrier wave = triangular wave; The magnitude of the output amplitude is proportional to the modulation.

The motor load is an inductive load, and the equivalent impedance of the high-frequency signal itself is very large, you can understand that although the high-frequency signal exists, the driving current generated is very small, so when generally considering, only the fundamental signal is concerned;

As for how to set the output voltage, just set the modulation index of your SPWM, the exact relationship is forgotten, but theoretically, the output 240 V voltage DC bus voltage must be at least 240* = 360 V or more, and the modulation system at this time is 1. As the modulation system decreases, so does the output voltage. I remember it should be linear.

In fact, since the voltage output by the inverter is a PWM signal, few people sample it (the sampling rate and oscilloscope bandwidth will affect the size of this value), on the contrary, the duty cycle is generally used to calculate the fundamental RMS value of the output voltage and display the value.

This needs to be analyzed on a case-by-case basis, but first of all, the header file used should be written, and then the main function of cavity disturbance, as for the latter problem, it should be divided into three parts, the first part: data entry; Part II: Ways to Solve the Problem of Missing ThingsPart III:

Result output.

I understand that the essence of single-phase motor speed control is to control the stator coil current and frequency, and it is more convenient to measure the current because it is close to the sine wave; In addition, the real speed also needs to be measured, such as using a vibration speedometer, etc., of course, the boost speed of about 1 second is very difficult to measure. I hope to communicate with you, my email.

The output of the inverter itself is the PWM SPWM SVPWM wave, which is determined by the principle of the inverter. The inverter outputs a pure sine wave, at present, the technology is not very mature, and it may be relatively high.

Modulation refers to the fact that the six-way trigger pulse to the IGBT three-phase bridge is compared with the sine wave and the triangle wave, and the frequency of the triangle wave is generally about 1000Hz, and the frequency is unchanged in the control process; By adjusting the amplitude, phase and frequency of the sine wave, you can adjust the size and frequency of the voltage input to the stator side of the motor, so as to achieve the purpose of frequency conversion speed regulation.

2.The final voltage input to the stator side of the motor is a series of unequal-amplitude unequal-width rectangular pulse waves.

3.Obviously, the pulse width is adjusted by adjusting the frequency of the sine wave.

4.The three-phase inverter circuit is composed of IGBT tubes, to achieve inverter, it is necessary to trigger the tube according to a certain law, and SPWM is the technology to get a certain law to trigger the pulse of the IGBT tube, and the trigger pulse obtained by SPWM modulation can be directly given to the base of the IGBT, and the interconnection of the two is realized.

You still don't know the concept, I suggest you first read the FOC motor control and three-phase bridge inverter circuit article, and then you will understand...

If you want the motor to run normally with load, there must be position feedback. However, the position data** can be measured using a sensor, or it can be calculated (estimated) by software using voltage, current, and some other known parameters. Position data is inevitably needed in control algorithms.

To put it simply, the sensor measurement is consistent with the actual rotation, so the controller knows the more accurate error (actual operation and expected operation state), and can stabilize to the desired operating state in a short time as long as it is not overloaded.

However, without a sensor, the actual position is replaced by the result of the software calculation, and in some cases, the error between the calculated value and the actual situation is large, so it cannot be stabilized to the desired state. It's like a blind person indirectly orients himself in space through other senses, and the error is large. Having a position sensor is like positioning directly through binocular vision, which is more accurate.

There's no location feedback on how do you know when to transpose.

With a fixed sine wave filter, the output waveform quality will vary when the output voltage or frequency of the inverter changes. Generally speaking, after installing a sine wave filter, the output waveform is a sine wave (harmonic distortion is less than a limited index) based on a certain frequency and amplitude range.

A sine wave filter filters the SPWM modulated wave into an approximate sinusoidal voltage waveform.

Sine wave filter features.

1.Extend motor life.

2.Protect the motor insulation.

3.Reduce motor bearing current.

4.Increase the transmission distance.

5.Improve system reliability.

6.After the application of this filter, the ordinary motor can replace the variable frequency motor.

SWF sine wave filter.

SWF sine wave filter.

7.It has a good suppression effect on electromagnetic interference.

8.Because the output of the inverter contains high-frequency harmonics, the loss of the power cable and the motor is increased; At the same time, extremely high DV DT can cause radiation interference of several MHz; If the motor needs to be transmitted over a long line (the motor cable exceeds 50 meters), the voltage at the motor end will be superimposed due to the traveling wave reflection, which will destroy the insulation of the motor and even burst the cable.

9.For harmonic currents, the harmonic components can be reduced but not completely eliminated by changing the modulation mode. For radio frequency interference caused by DV DT, a DV DT electromagnetic filter can be installed, but it can only be effective for a certain length of cable, and is not suitable for any length of cable.

10.The effective method to solve the above problems at the same time is to install a sine wave filter on the output side of the inverter, and filter the SPWM modulation wave into an approximate sinusoidal voltage waveform, and the sine wave filter is composed of a high-frequency phase reactor, RC loop, and a common-mode reactor. It can effectively suppress high-frequency loss and DV DT radio frequency interference, and extend the cable of the motor and inverter to 500 meters, or even 3 kilometers.