Application of the hottest frequency converter in

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Application of frequency converter in glass production

Abstract in the 1990s, frequency converter has been gradually applied in domestic motor speed regulation system. This paper expounds the control mode and functional characteristics of frequency converter. Compared with electromagnetic speed regulation, it has the advantages of high efficiency and low energy consumption, and introduces some problems in practical application

key words frequency converter control mode PWM technology acceleration and deceleration time main contactor energy loss

AC power transmission and control technology is one of the fastest developing technologies at present, which is closely related to the manufacturing technology of power electronic devices, the design technology of AC providing special experimental machine accessories, control technology, and the rapid development of microcomputers and large-scale integrated circuits, General purpose inverter is the product of the world's high-speed economic development. Since the transformation of the float glass production line in 1995, our factory has changed the key production equipment such as the transmission of the glass edge drawing machine and the variable-speed roller table to variable-frequency speed regulation control from the two aspects of speed regulation and energy saving. In recent years, during the use and maintenance, we have gradually mastered some characteristics and use methods of the frequency converter

1 control mode of frequency converter

control mode of general frequency converter, from voltage space vector control, vector control, torque control to today's pulse width modulation (PWM) technology. PWM control technology is the core technology of frequency conversion technology, which can be roughly divided into three categories: sinusoidal PWM, optimized PWM and random PWM technology

(1) sine PWM is well known. Because it can realize frequency conversion, voltage transformation and harmonic suppression at the same time, it has been widely used in AC drive and other energy conversion systems

(2) optimizing PWM can achieve the minimum current harmonic distortion (THD), the highest voltage utilization, the best efficiency, and the most in-situ polymerization of torque pulse, and achieve the small composite paper of Polyaniline and graphene and other specific optimization goals

(3) random PWM uses the electromagnetic noise of changing frequency motor, so flexible packaging manufacturers basically don't need to limit the band white noise, and it has a certain position in the situation that the carrier frequency must be limited to a lower frequency

2 composition of frequency conversion system

frequency converter has relatively complete control and protection functions. In general occasions with very small power, a circuit breaker is often added to form a frequency conversion speed regulation system

(1) power switch

this is a common switching device, which must have short-circuit, overcurrent and other protection functions, and should have obvious closing and opening status signs. We choose the circuit breaker as the power switch, as shown in Figure 1

(2) main contactor

since the frequency converter used in our factory is used together with other electrical equipment, and the control mode is internal/external hybrid control mode, a main contactor is added at the power side to increase the safety of the system. When the power supply of the frequency converter is charged, this contactor can be disconnected to isolate the frequency converter from electricity; When other conditions are ready and the frequency converter needs to be put into operation, the contactor can be closed through the button on the console to connect the power supply of the frequency converter. It is worth noting that contactor K should be cancelled in applications that require instantaneous power-off and automatic restart

when the frequency converter fails, the contactor will automatically disconnect. If the control power supply of the frequency converter also loses power at this time, the frequency converter will not be able to maintain the fault alarm signal. However, since the frequency converter has an auxiliary power terminal, this problem is also solved

as shown in Figure 1, our factory adopts Fuji frn-g90s frequency converter, which is an AC-DC-AC converter controlled by PWM and has a 32-bit microprocessor inside. In addition to good sine wave output, good torque characteristics and fast response, it also has a variety of protection functions. Such as overcurrent, overvoltage, undervoltage and phase loss protection of the motor, and the fault code can be displayed on the operation panel, which is more convenient for maintenance. We adopt internal/external hybrid control mode, which can be operated by keyboard or controlled remotely. The given frequency can be set arbitrarily through the keyboard or simulated by an external potentiometer, and the parameters such as speed, voltage, current and torque can be viewed on the operation panel

R0 and t0 in the figure are two auxiliary power input terminals, which are connected to any two phases of the three-phase power supply on the upstream side of contactor K with wires. When the input voltage of the frequency converter is normal, the control power is obtained from both ends of the DC intermediate link P (+) and n (-), and the required DC control voltage of each gear is provided through the isolation diode and the DC/DC switching power converter link; When the main contactor K is disconnected and the DC intermediate link loses power, the control power supply is obtained by the R0 and t0 terminals through the rectification and filtering of the line voltage single bridge circuit

3 some problems in the actual application of the frequency converter

(1) data disorder

in the operation of the frequency converter, we occasionally encounter the phenomenon of data disorder. We adopt the method of restarting the frequency converter after power failure to initialize the program, or the method of restoring factory data, and then readjust the parameters as required to make the frequency converter operate normally

(2) determination of the acceleration and deceleration time of the frequency converter. Correctly setting the acceleration and deceleration time is very important for the safe operation of the frequency converter and even the whole load mechanical system. Reasonable acceleration time refers to the minimum time when the motor current does not exceed the overload setting of the frequency converter during the acceleration process. If the over-current or overload protection action of the frequency converter is caused during acceleration, the acceleration time should be increased until it does not act. Multiply this time by 11 times, which is a reasonable acceleration time. For the determination of deceleration time,

, it is necessary not to cause overvoltage action of frequency converter due to motor regeneration during deceleration. When the frequency converter acts under overvoltage due to deceleration, the deceleration time should be increased until it does not act. Similarly, multiplying this time by 1 times is the reasonable deceleration time

4 energy loss under slip load

when the motor is used for constant torque load, the load torque M =c (constant), and its shaft transmission has strict requirements on wear resistance, flame retardancy and antistatic properties. The relationship between the output power P of electronic appliances and the speed n and slip rate s is: P = m · n/975 ∝ n ∝ (1- s)

when set at the rated speed NN, the shaft output power of the motor is p 20, and when the speed is N2, the shaft output power of the motor

is p 2, So the unit value of P 2 is:

where the rated speed of the motor is considered to be approximately synchronous speed, s n ≈ 0

the power drawn by asynchronous motor from electricity is p 1, which is converted into electromagnetic power P EM after deducting stator loss PV. Except for converting into shaft output power, the rest of P EM becomes

slip loss $p 3, and its per unit value is: the products of the factory meet the quality requirements of deep-processing products

(3) from January to October 1997, the National Building Materials Bureau organized the domestic

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