Application of the hottest high frequency chopper

Application of high-frequency chopper cascade speed regulation system in cement plant

preface

fans and pumps are applied in a large number of departments of the national economy, with extremely wide distribution and huge power consumption. According to the statistics of relevant departments, the power consumption of fans and water pump motors in the country accounts for about 40% of the total power consumption in the country. At present, there is still a great energy-saving potential in the operation of fans and pumps, and the focus of tapping its potential is to improve the operation efficiency of fans and pumps

we know that fans and water pumps are used to transport fluid substances such as gas and water. In many cases, the flow of these fluids needs to be adjusted and controlled. In China, the regulation of fluid flow is mostly achieved by valve or baffle control, that is, the so-called full throttle. Because there is throttling loss when adjusting with valves or baffles, and throttling increases the pipe resistance, pumps and fans often operate in low efficiency areas. Coupled with the energy consumption characteristics of pumps and fans, the efficiency of this adjustment method is very low. According to statistics, the average operating efficiency of full speed throttle regulation is less than 45%. Nearly half of the power generation in China is consumed by fans and pumps, with an annual power consumption of more than 20000 billion kwh. The average operating efficiency of the equipment is less than 45%, 20% lower than the international level, and there is a serious waste of energy. Therefore, it is imperative to adopt an efficient and energy-saving operation mode to benefit the country and the people

in September, 2005 and July, 2006, Sichuan Guang'an Tenghui Cement Co., Ltd. applied the high-frequency chopper cascade speed regulation system to the 1 and 2 kiln tail fans respectively. The application is introduced and analyzed below, so as to isolate and reduce seismic energy

I. principle and main functions of SEC high-frequency chopper cascade speed regulation system

1) principle of SEC series high-frequency chopper cascade speed regulation system

cascade speed regulation, that is, the additional electromotive force that can absorb slip power is cascaded into the rotor circuit, and the purpose of changing the rotor current and then changing the electromagnetic torque and speed is achieved by changing the size of the additional electromotive force. The speed is adjusted below the synchronous speed, and the slip power of the rotor circuit is recovered at the same time, so as to achieve the purpose of high efficiency and energy saving

when the additional electromotive force is introduced into the rotor circuit:

its rotor current is: ()

where: is the rotor induced electromotive force; Is the rotor resistance; Is the rotor reactance; S is the slip rate

electromagnetic torque of motor:

= ()

where: is torque constant; Is magnetic flux; Is rotor current; Is the rotor power factor

it can be seen that changing the size of the additional electromotive force EF can correspondingly change the size of the electromagnetic torque of the motor, and then change the speed of the motor

figure when the rotor is connected in series with the equivalent potential, the principle of the equivalent circuit

sec high frequency chopper cascade speed regulation system is shown in Figure 1-2. The system is composed of starting unit, rectifier unit, chopper unit and active inverter unit. The inverter angle of the inverter unit is fixed at the minimum value to produce a constant maximum additional DC back EMF, and the adjustment of the equivalent EMF is completed by the chopper

figure schematic diagram of SEC high frequency chopper cascade speed regulation system (external feedback)

starting unit: the starting unit is composed of frequency sensitive rheostat (PF), contactor 1km and contactor 2km. Large motors, especially wire wound motors, have large starting current, which will cause great impact on electricity when starting. In order to reduce the starting current and make the motor start smoothly, an automatic switching starting device is added to the high-frequency chopper cascade speed regulation device. When the motor starts, 1km is closed and 2km is opened, and the motor rotor is connected in series with the three-phase frequency sensitive rheostat PF. The resistance of the frequency sensitive rheostat is in direct proportion to the frequency of the current flowing. When the motor starts, the motor speed is zero, and the rotor current frequency is the highest, which is the power frequency. At this time, the resistance value of the frequency sensitive rheostat is also high, which limits the starting current. With the increase of motor speed, the frequency of rotor current decreases gradually, and the resistance of frequency sensitive rheostat also decreases gradually. When the motor stator current is lower than the set allowable value, the device will automatically close 2km, cut off the frequency sensitive rheostat, and complete the starting process

rectification unit: the rectification unit is three-phase full wave rectification, which converts the rotor current into DC current. SCR for protection is also installed in rectifier unit

chopper unit: the chopper control of the system is realized by IGBT components, which further improves the chopper frequency, makes the DC current more stable, and makes the system smaller and more compact. By adjusting the ratio of the chopper on time to the chopper cycle (i.e. duty cycle or PWM modulation pulse width), the magnitude of the equivalent potential cascaded into the rotor circuit can be changed, so as to change the rotor current and slip, so as to achieve the purpose of adjusting the motor speed. At the same time, the slip power is absorbed and fed back to the electricity through the inverter transformer, so that the power consumption of the system is minimized

fix the inverter angle at the minimum to obtain the maximum back EMF:

u1 = 1.35 U2 cos β Min

adjust the equivalent back EMF through PWM modulated chopper electronic switch:

u = U1 (1-k) = 1.35 (1-k) U2 cos β Min

where k - duty cycle

inverter unit: the inverter part is a three-phase full bridge active inverter. When the device works in the speed regulation state, the slip power after chopping control is inverted to the internal feedback winding or inverter transformer. The inverter trigger angle is the minimum fixed value, which overcomes the shortcomings of phase-shift trigger, such as strict requirements for trigger pulse and commutation, large pulse moving range, poor anti-interference ability, easy subversion, low power factor and so on. The synchronous signal is taken from the voltage signal of the internal feedback winding or inverter transformer, and has the functions of anti-interference, multiple digital phase locking, and automatic distribution

control unit: the control part is composed of control box, power supply and self inspection box. Its core is composed of single chip microcomputer and fast programmable logic device. The main functions include:

u pulse control and PWM modulation for IGBT, power battery supplier and corresponding positive and negative material supplier SCR and active inverter

u realize all automatic control and locking logic of the device

u measurement, setting, logic, alarm and outlet of all protections

u operation, display, alarm related to system operation, ensure that the power supply voltage meets the requirements of the tension machine, input voltage alarm and other information processing and instructions

u realize the communication management between the device and external systems

u auxiliary functions such as device parameter setting and experimental force sensor experiment

u the control box can realize local operation through the touch keyboard, including operation, stop, full speed, speed regulation, self inspection, automatic/manual, open-loop/closed-loop, remote/local and other operations related to operation. At the same time, the basic parameters and operation mode of the device can be set through the menu

u in order to meet the needs of centralized control in the control room, operations related to device operation can be carried out remotely

u the system retains the connection with the superior computer, P