Power conversion circuit design The main switching element of the power conversion circuit adopts a fully-controlled power electronic device IGBT. The current sampling resistor is placed between the main switch tube of each phase arm and ground. For each phase winding, it can record the time of turn-on The current value can also record the current value during chopping. The current sampling is accurate and reliable, and the real-time performance is strong. The IGBT drive circuit adopts EXB840 of Fuji Corporation of Japan, which is equipped with a 2500V high isolation voltage photocoupler, has an overcurrent protection circuit and an overcurrent protection signal terminal, and is powered by a single power supply. Therefore, using EXB840 can easily realize the driving and protection of IGBT. Current detection circuit In the SRM speed control system, the inverter test controller needs to know the actual current in the winding in time and accurately in order to perform the necessary current feedback in the chopper control mode, so the current sampling must be accurate and reliable, and the real-time performance is strong . This article uses the resistance sampling method, the circuit has good anti-interference and isolation, stable and reliable operation, small temperature drift, high linearity of current detection, and simple circuit structure and low cost. The current detection signal is sent to TMS320F240 to form a current closed loop. Ningxia Elevator Maintenance TMS320F240 contains two 10-bit A / D converters with internal sample-and-hold circuits. There are a total of 16 analog input channels. The converter is provided to an ADC. To simplify the design, this article uses the SRM single-phase turn-on method, so only one ADC is needed. Position detection Position detection is a major feature of the operation of switched reluctance motors. It usually uses a corner-digital encoder (referred to as an encoding disk). It is a digital sensor that encodes directly by angle and is rigidly connected to the measured axis. This article uses an incremental encoder, selects the general-purpose timer GP2, is set to bidirectional up / down counting mode, and uses the quadrature encoding (QEP) circuit in the event manager of the TMS320F240DSP to pair the quadrature encoders on pins QEP1 and QEP2 Input pulses for decoding and counting. 3SRM control system software design the main program to initialize the entire system and coordinate the operation of each subprogram. Another important function of the main program is to track the rotor position and output switching signals to the power converter in the correct phase sequence. In order to protect the switching devices of the power converter circuit, it is also necessary to prevent overcurrent. The optimal operation of SRM requires both knowing the instantaneous position of the rotor and the optimal values ​​of the opening angle θon and the closing angle θoff under specific operating conditions. In this paper, θon and θoff are calculated offline, and stored in EPROM in the form of a table, and the corresponding switch signal is found according to the current operating state.
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Control system hardware and software detection
<p> 2SRM control system hardware block diagram Because the PWM pulse generation unit is integrated in the TMS320F240, as long as a few instructions can get a PWM trigger pulse of any pulse width and any frequency, so this article uses a constant chopping frequency variable pulse width based on the PWM technology Digital current closed-loop control. The basic strategy is to determine the duty cycle of the PWM pulse in the next cycle based on the difference between the current and the reference current in the previous sampling cycle. If the deviation of the current reference current and the sampling current is less than zero, the corresponding main switching device is turned off immediately; otherwise, the corresponding main switching device is turned on immediately, so it is also called Bang-Bang control. This control method can accurately approach the current target, and the chopping frequency is high and stable, which is conducive to the high efficiency and low noise of the motor.