The specific embodiment
The utility model is described in further detail below in conjunction with accompanying drawing and embodiment.
As shown in Figure 3, provided the schematic diagram that many motors of the present utility model drag the constant voltage and frequency ratio control system of band conveyor, shown AC asynchronous motor is used to order about the operation of band conveyor, and the specification of all electrical motors is identical; Each AC asynchronous motor is controlled it by a frequency converter.One is the main frame frequency converter in all frequency converters, and remaining is the slave frequency converter, and the main frame frequency converter is used to realize and the communicating by letter of upper computer.The power input of frequency converter is connected with electrical network, and power output end is connected with the stator input end of respective electrical motivation; Communicate by optical fiber between main frame frequency converter and all the slave frequency converters, frequency converter also can detect the active current size of respective electrical motivation operation simultaneously.
The frequency converter that the utility model uses is the voltage-source type frequency converter, and it is become by voltage transformer, ac-dc-ac inverter controller, control system and bypass group.It is AC asynchronous motor that controlled many motors drag band conveyor.Adopt ferry optics comunication between each frequency converter, improved communication efficiency and reliability.
The principle explanation: when induction motor drive, total hope keeps main flux
Be rated value.By the every emf phase effective value of asynchronous dynamo stator
As can be known, if omit stator impedance
Pressure drop has
Know by (2) formula, if stator terminal voltage is constant, along with
Raise,
To reduce.Again by the torque formula
As can be known, exist
Under the identical situation,
Reduce to cause the electrical motor output torque to descend, can make the electrical motor stall when serious.Therefore, in Control of Frequency Control Process, should change stator voltage and frequency simultaneously, to keep main flux constant.This is the theoretical foundation place of constant voltage and frequency ratio mode.
Many motors of the present utility model drag the control method of the constant voltage and frequency ratio control system of band conveyor, comprise start-up course, operational process and stopping process, as shown in Figure 5 and Figure 6, provided the program flow diagram of main frame frequency converter and slave frequency converter in the control method of the present utility model respectively;
Described start-up course may further comprise the steps:
A). receive starting-up signal and broadcasting, the main frame frequency converter receives the starting-up signal of this machine or upper computer, and through order wire starting-up signal is broadcast to all slave frequency converters, so that the start of slave frequency converter;
Before startup, the main frame frequency converter judges whether all frequency converters are ready in the system, if all frequency converters are ready, then the main frame frequency converter receives starting-up signal, and all frequency convertor systems start in the apprizing system; If the system failure or frequency converter failure are arranged, the main frame frequency converter does not respond starting-up signal, and system does not allow to start.
B). constant voltage and frequency ratio starts, and the main frame frequency converter is from 0Hz, and according to the pick-up time T1 that sets, gentle acceleration is to the frequency f of setting, according to constant voltage and frequency ratio mode output voltage, to control corresponding motor start-up; The main frame frequency converter is in the process that starts, and constantly running frequency and the active current with self is broadcast to all slave frequency converters by order wire;
In this step, if on the band conveyor load is arranged, main frame frequency converter and slave frequency converter all should increase certain torque magnification, as shown in Figure 1, provided the constant voltage and frequency ratio control VF curve synoptic diagram of band torque magnification, and the setting value of torque magnification want consistent.
As shown in Figure 4, provided constant voltage and frequency ratio frequency conversion speed-adjusting system schematic diagram.
C). the operation of slave frequency converter, the frequency that the slave frequency converter comes the transmission of main frame frequency converter is as the running frequency of self, according to the extremely corresponding electrical motor of the mode output voltage of constant voltage and frequency ratio, so that all AC asynchronous motor are according to the frequency operation of basically identical, execution in step d);
D). whether active current detects, and the slave frequency converter judges that the active current of self output sends and next active current with the main frame frequency converter, in allowed band; If two active currents are in allowed band, then the slave frequency converter keeps current frequency operation; If the difference of two active currents has exceeded allowed band, execution in step e then);
In this step, if the rated current of frequency converter is the M ampere, then described allowed band is meant 0~0.1M ampere, to guarantee the power unanimity or the basically identical of each electrical motor output.In this process, the speed speed that the active current that slave frequency converter response main frame frequency converter is sent is set needs to determine according to field condition; The slave frequency converter responds too fast or crosses and all will cause whole multimachine to drag the belt conveyor system instability slowly, causes the frequency converter protection.
E). by adjusting the frequency of self, the difference that reaches the active current of self output and the active current that main frame sends is in allowed band according to the mode of constant voltage and frequency ratio for the frequency control of slave frequency converter, slave frequency converter;
In the process that the slave frequency converter is regulated, if the active current that the active current of self sends less than the main frame frequency converter, the output that then increases active current by the frequency output that increases self; If the active current of self then reduces the output of active current greater than the active current that the main frame frequency converter sends by the frequency output that reduces self.
F). the main frame frequency converter reaches setpoint frequency f, and the slave frequency converter is followed running frequency, the active current operation of main frame frequency converter, and many motors drag the start-up course of band conveyor and finish;
Described operational process may further comprise the steps:
G). during main frame frequency converter smooth operation, constantly running frequency, the active current with self is broadcast to all slave frequency converters by order wire;
H). the frequency that the slave frequency converter comes the transmission of main frame frequency converter is as the running frequency of self, according to the mode operation of constant voltage and frequency ratio; And judge self active current and the main frame frequency converter send and the active current of coming whether in allowed band; If two active currents are in allowed band, then the slave frequency converter keeps current frequency operation; If the difference of two active currents has exceeded allowed band, execution in step i then);
I). by adjusting the frequency of self, the difference that reaches the active current of self output and the active current that main frame sends is in allowed band according to the mode of constant voltage and frequency ratio for the frequency control of slave frequency converter, slave frequency converter;
Described stopping process may further comprise the steps:
J). receive shutdown signal and broadcasting, the main frame frequency converter receives the shutdown signal of this machine or upper computer, and T2 deceleration time according to setting according to the constant voltage and frequency ratio mode, is decelerated to 0Hz gradually; The main frame frequency converter is in the process of slowing down, and constantly running frequency and the active current with self is broadcast to all slave frequency converters through order wire;
In stopping process, the frequency reducing time should not be provided with too short, and is too short if the frequency reducing time is provided with, and will cause motor to be in generating state, and energy charges to electric capacity by flywheel diode, causes the frequency converter unit overvoltage protection easily.
K). the operation of slave frequency converter, the frequency that the slave frequency converter comes the transmission of main frame frequency converter is as the running frequency of self, according to the extremely corresponding electrical motor of the mode output voltage of constant voltage and frequency ratio, so that all AC asynchronous motor are according to the frequency operation of basically identical, execution in step m);
M). whether active current detects, and the slave frequency converter judges that the active current of self output sends and next active current with the main frame frequency converter, in allowed band; If two active currents are in allowed band, then the slave frequency converter keeps current frequency operation; If the difference of two active currents has exceeded allowed band, execution in step n then);
N). by adjusting the frequency of self, the difference that reaches the active current of self output and the active current that main frame sends is in allowed band according to the mode of constant voltage and frequency ratio for the frequency control of slave frequency converter, slave frequency converter;
O). when main frame frequency converter output frequency arrives 0Hz, block output, and shutdown signal is issued all slave frequency converters by order wire broadcasting, the slave frequency converter blocks output; Many motors drag the band conveyor stopping process and finish.
The utility model adopts the constant voltage and frequency ratio mode, apply voltage according to predefined VF curve to the armature loop that multimachine drags the motor in the belt conveyor system, its characteristic can be equivalent to stable AC voltage source, its stability approaches common frequency power network most, thereby compare with the frequency converter of other mode and other type, have higher working stability and reliability.Simultaneously,, do not enter common frequency power network between the armature loop of motor and frequency converter, therefore reduced requirement, improved the input power factor of system net capacity because the reactive component of current that multimachine drags each motor in the belt feeder system only flows.
Also comprise the emergency protection process, it may further comprise the steps:
1). when running into the system failure or main frame frequency converter and detected communication failure, main frame frequency converter failure, slave frequency converter failure, electric network fault or electrical fault, the main frame frequency converter stops the armature loop power supply to respective motor immediately, notifies each slave frequency converter suddenly to stop simultaneously; After the slave frequency converter receives and suddenly stops order, stop armature loop power supply immediately to respective motor;
2). when the slave frequency converter has detected communication failure or faults itself, can stop armature loop power supply immediately, and inform the main frame frequency converter to respective motor; After the main frame frequency converter receives and informs, stop armature loop power supply immediately, notify all the other each slave frequency converters suddenly to stop simultaneously to respective motor; Remaining slave frequency converter stops the armature loop output voltage to corresponding motor after receiving and suddenly stopping order immediately.
This just makes multimachine drag between each frequency converter in the belt conveyor system is interlocking, as long as there is a frequency converter heavy fault to occur, then total system will be implemented urgency and stop, to avoid the generation of further fault.
Characteristics of the present utility model are: can use constant voltage and frequency ratio controllable type frequency converter to drive multimachine and drag band conveyor, start reposefully, shut down, with higher efficient converting operation; When being in an emergency, protect motor, frequency converter reliably.
The above is specific embodiment of the utility model and the know-why used, and is any based on the equivalent transformation on the technical solutions of the utility model basis, all belongs within the utility model protection domain.