Application of ETD791 DC Regulator in Plasma Ignition

Abstract: The ETD791 series of DC current governors with current predictive control features excellent control performance, especially the performance of the current loop, which has been used successfully in the plasma ignition industry.
Key words: ETD 791 Plasma Ignition Cathode Anode Plasma Ignition and Steady Combustion technology has been successfully applied to boilers of various coal types, various combustion methods, and different milling systems in addition to anthracite coal. With the practical application level of plasma ignition and stable combustion technology and the further improvement of the reliability of equipment, it has laid a solid foundation for the implementation of demonstration projects for coal-fired power plants without fuel systems. Improvements in Plasma Ignition Technology In addition to the technical improvements in the cathode anode of plasma igniters, the stability of the power supply and the response speed are also critical.

I. Introduction of Plasma Ignition Device The plasma generator is a magnetically stable air carrier plasma generator, which consists of a coil, a cathode, and an anode, as shown in FIG. 1 . The cathode material is made of high-conductivity metal material or non-metal material; the anode is made of high conductivity, high thermal conductivity and anti-oxidation metal material. They are all water-cooled to withstand high temperature arc shock; the coil is at high temperature In the case of 50 °C, it has the ability to withstand the breakdown of kV DC voltage; the power supply uses a full-wave rectifier circuit, and has a constant current performance, and has high requirements for the power supply. Plasma generator firing principle is: first set the output current, when the cathode advances with the anode contact, the entire system has the ability to withstand short-circuit and the current is constant, when the cathode slowly leaves the anode, the arc in the magnetic force of the coil pull down Out of the nozzle. The air with a pressure of about 0.03 MPa is ionized into a high-temperature plasma under the action of an arc, and its energy density is as high as 105 to 106 W/cm, which creates good conditions for ignition of different types of coal.

Second, 791 all-digital driver in the plasma application of the case and its features 791 Governor is actually designed to drive the DC motor, with a rapid response of the speed and current loop, in the DC motor speed is very good However, plasma-ignition applications require a high-performance DC-stabilized current source, which places very high demands on the DC-governor current loop, while the 791 DC-DC converter current loop uses algorithmic advanced current-prediction control. Can meet the plasma ignition power requirements.
1: The practical application of plasma ignition work mode:
In practical application, the plasma ignition in this case works in two ways. One is to start contact with the cathode anode. At this time, the output of the driver is a short-circuit state, and the current limit of the driver is set. After startup, the cathode is activated. The electric motor drives the cathode to retreat. At this moment, the current keeps constant. When the external conditions are satisfied, an arc is drawn between the cathode and the anode. The other working method is: starting cathode anode does not contact, at this time set the current limit of the driver, and start the driver, then the cathode and anode are open circuit, the voltage is maintained at about 530V, then the cathode motor drives the cathode forward, so that the cathode In contact with the anode, at the moment of contact, the current between the anode and cathode rapidly rises to the set current, the voltage drop opportunity is zero volts, and then the cathode motor drives the cathode to retreat, and the current is maintained at the set current. The value of the voltage is based on the ohms. The law gets.
2: Setting of driver key parameters
The parameter setting of the 791 driver is very different from the parameter setting of the normal drive motor. The error output of the speed loop is the input of the current loop. The error of the speed loop is obtained by superposition of the speed setting and speed feedback and is used to stabilize the motor. The speed of rotation. However, in the application of plasma ignition, because there is no speed feedback, we set the speed loop to saturate the output, that is, the output of the speed loop is the maximum, so that the output of the given current loop is the largest, in order to limit the output current. We set the current limit in the current loop so that the current output is regulated by the current limit. This is the most important point of the 791 governor setup. Specific settings for important parameters are as follows:
Spd_fbk_selec = 92 , speed feedback select armature voltage feedback.
Arm_volt@1500rpm=500V When the 1500RPM is set, the armature output voltage is 500V, so that the output voltage is as high as possible when the cathode anode is disconnected, which is advantageous for the electrodes.
Current_lim_neg=300 Sets the current limit, which is controlled by plc, ie the ignition set current of the plasma igniter.
Max_Speed ​​= Motor_base_Spd = 1500, set the basic speed and maximum speed are 1500rpm, that is, when the armature voltage is 500V, the governor thinks the motor speed is 1500rpm
Spd_Prop_Gain=500, Spd_Integrl_Gain=40, set the proportional gain and integral gain of the speed loop. This parameter controls the speed of the saturated output of the speed loop.
C_ramp_ref_2= Internal_setpt6 , speed given value, at this time Internal_setpt6=8192 corresponds to armature voltage of 500V, that is, the speed given is the maximum, because the voltage between the cathode and the anode is generally about 300V, so the feedback speed is definitely higher than The speed is small, so the speed loop is saturated.
ANALOG_OUT_2= current_lim_pos Sets the analog output to the current limit output for displaying the set current.
Field_curr_ref = 0, this parameter sets the field current, because the field current is not used, the setting value is 0, that is, the magnetic field is turned off.
3: On-site control method:
791 drive communication can be powerful, built-in standard modbus protocol, simple communication with Siemens 200plc, can directly use 200plc internal MBUS_MSG module for communication.
The control is shown in the diagram. The Siemens PLC is used to control the drive. The reference to the current and the feedback of the variables are made using standard modbus communication. For the start and stop of the drive, the control is enabled, and the PLC I/O port is used. Control the digital quantity of the driver.

Three: feel after use:
ETD 791 series 400A DC speed control device is suitable for all kinds of plasma load, small current and voltage fluctuation, and good stability. The arc started successfully at 300A, the current is very stable, and the voltage fluctuation is not great. After the arc starts, the current does not drop when the current is slowly reduced to 200A. The running time is as long as 16 hours. There is no arc dropping, the stability is good, and the performance test passes.