challenge
At present, there are still many problems in the control strategies established by motor models at home and abroad, have many problems in low-speed pulsation, high-speed weakness, stability, and output torque consistency. In order to better solve the problem of low-speed torque ripple of the motor, this paper establishes a motor model introduced into the dead time of the inverter, and the inverter dead time is very short and there is still a problem of delay and lag in the switching process of IGBT. In order to accurately capture the voltage waveform distortion caused by the dead time, the data acquisition card is required to have a high sampling rate. In addition, in order to make the research result more accurate, it is necessary to have a high signal-to-noise ratio and effective Bit. In summary, in the study of voltage waveform distortion caused by dead time, a plate card that requires high sampling rate, high precision, and high signal-to-noise ratio, to meet the requirements of signal capture.
solution
First, the dead zone effect is analyzed, and a method of reducing the voltage waveform distortion of the dead zone is proposed for the simulation results, and data having a 16-bit high resolution A / D converter and synchronous sampling rate is as high as 16 ms / s. Collecting card PCI-9846H with current sensor, voltage sensor, torque, motor and its controller, dynamic machine and other equipment to complete the construction of the vehicle motor test platform, carry the host data through the LabVIEW related driver provided by Linghua Company The development design of the acquisition system verifies the method of deciding the output voltage waveform distortion on the reduction in dead zone proposed in this paper by the acquisition and analysis of the voltage, current, torque, and the speed information. The test results are based on PCI-9846H data. The acquisition system has high sample rate and high sampling accuracy, which can meet the requirements of the voltage waveform distortion signal caused by the dead time, and the improved method proposed herein can improve the output waveform of the voltage, and can reduce dead zones. The effect of time performance in the performance of the motor at low speed conditions
Introduction
The motor drive system is the core part of the electric vehicle [1-2]. According to the type of motor used, it can be divided into DC motor drive system and AC drive system [3], and in the AC motor drive system, the induction motor is easily accepted, widely used, and the permanent magnet synchronous motor is due to its own high energy density. With high efficiency, it has a relatively large competitive advantage, and the application range is increasing.
In order to meet the power performance requirements of the vehicle, the motor drive system has a high dynamic performance. The current relatively successful control strategy includes: a variable frequency transformer control (VVVF) based on steady-state model, magnetic field orientation control (FOC) based on dynamic model And Direct Torque Control - DTC. The direct torque control is developed on the basis of vector control. Its main advantage is to abandon the decoupling idea in vector control, directly control the magnetic chain and torque of the motor, and use the stator magnetic chain orientation to replace the vector. The rotor magnetic strand direction in the control avoids the identification of parameters (rotor resistance, etc.) that are not determined in the motor. At present, the mathematical model of the permanent magnet synchronous motor at home and abroad is only based on the mid-line non-receiving three-phase winding conditions, and the mutual inductance of each winding is introduced, and the bearing and other strand loss is ignored. And the impact of PWM waves and other factors on the motor, there is still many problems based on the control strategy established by the motor model in low speed pulsation, high-speed weakness, stability, and output torque consistency. [5]. In order to better solve the problem of low-speed torque ripple of the motor under direct torque, this paper establishes the motor model introduced into the dead time of the inverter, and analyzes the generation and action mechanism of dead time. Output voltage waveform distortion and key influence factor of phase change, a method for reducing a voltage waveform distortion of the dead zone is proposed for the simulation results, by applying PCI-9846H, current sensor, voltage sensor, torque, motor, and its control Equipment, dynamometer and other equipment to complete the construction of the vehicle motor test platform, the host computer writes the data acquisition system through the LabVIEW, and the reduced dead time proposed by the collection and analysis of the voltage, current, torque, and the speed information. The method of output voltage waveform distortion is verified.
1. Research on the dead time of the inverter
1.1 Inverter dead time generation mechanism
For the permanent magnet synchronous motor drive, the upper and lower bridge arms are alternately complementary when the IGBT is working properly. In the alternating process, there must be a state in which the upper and lower bridge arms are turned off, ensuring that the corresponding complementary / upper bridge arm is reliably turned off before the upper / next axle arm is turned on, and the time to turn off the two bridge arms at the same time. For the dead time. In response to the development of IGBT on the market, the inverter dead time is generally 3 to 7 μs [6]. When the motor operates above a certain speed, since the fundamental voltage is large enough, the dead zone effect has less affected by the fundamental voltage, so it does not pay attention to people; however, when the motor works at low speed, the fundamental voltage is small, dead zone effect The relatively large influence of the fundamental voltage, the longer the dead time, the larger the loss of the inverter output voltage, and the degree of distortion of the voltage waveform will also become large, and the dead time will affect the phase of the output voltage. The PWM waveform is no longer symmetrical, resulting in an increase in motor loss, low efficiency, output torque ripple, and the like. Figure 1 shows the mechanism of dead time generation and the influence on the output voltage, where V is the ideal PWM voltage output waveform, UA-a negative mobility
Pressure, UA + is a positive bus voltage, V is the error voltage, IA is the output current.
Be
Figure 1 dead zone effect
As shown in Figure 1, the error voltage can be found that the following features [7]:
1) There is an error voltage pulse in each switch cycle;
2) The magnitude of each error voltage pulse is UD;
3) The width of each error voltage pulse is Td;
4) The polarity of the error voltage pulse is opposite to the current polarity;
Although an error voltage pulse does not cause a change in the output voltage, the distortion of the voltage waveform caused by the total error voltage in one cycle is more serious, and the influence of the error voltage on the output voltage waveform is analyzed below. .
1.2 Analysis of Output Voltage Waveform Distortion
Using the concept of average voltage [8], it is assumed that the carrier frequency is very high, and no current is zero zero in a carrier cycle, the average value of the error voltage pulse sequence in half cycle is:, reading full text, technology area
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