With the development of AC speed regulating technology, the AC frequency introduction AC frequency of the product of all digital frequency converter provides a broad space for the application of AC drive. Using AC variable frequency speed control can not only hoist pump application achieve hoist pump application the hoist pump application smooth start ABB of ABB the ABB pump, but also can make the pump flow rate is adjusted. After a survey of domestic and foreign VVVF, decided to use the ABB company's ACS504 digital AC frequency conversion device to implement the digital transformation of control system of hoist pumping station, the original open-loop control to achieve closed-loop control, level control, inhibition of pump frequent starting, overcoming the defects of the original system.
1 system composition and working principle
ACS504 full digital AC frequency conversion device of the main circuit rectifier bridge, the middle filter and inverter circuit 3 parts. The rectifier bridge adopts three-phase bridge half control rectifier circuit; the middle filter is composed of reactor L11 and capacitor C14-C16; the inverter circuit includes 6 insulated gate bipolar transistor IGBT.
System for the AC - DC - AC variable frequency speed control system. When the power supply is switched on, the capacitor is charged through the R14 and V14 charging circuit. Charging time is less than 1s, during the charging process, the rectifier bridge thyristor is not on the way.
When the voltage on the capacitor C14-C16 reaches 300V, the control power is switched on, and the control interface board, the motor control board and the main circuit interface board are connected. When the DC voltage of the rectifier bridge reaches to 80% of the nominal value, the processor on the motor control board can get electricity through the input protection board. After the rectifier thyristor is fully conduction, the nominal value of the DC voltage of the rectifier bridge is 1.35U1 (U1 is the actual line voltage value) by the middle filter.
The action of the 6 power switch of the inverter circuit is controlled by the motor control board through the main circuit interface board. The voltage on the output end U2, V2 and W2 is determined by the modulation and demodulation, and the waveform is pulse train. According to the basic control method of frequency conversion and speed regulation, the corresponding amplitude and frequency (F2) of the basic voltage waveform is generated according to the requirement of U2/f2= constant.
ACS504 full digital AC frequency conversion device is divided into starting data parameters, running data parameters, control connection parameters, transmission parameters, protection parameters. According to the different occasions of the frequency conversion device, the parameters are pre compiled into different application programs. Application macro program is a pre compiled set of parameters, stored in the motor control board EPROM, they are the lack of factory settings, manual / automatic control, PI control, constant torque control, sequential control, PFC control. They can be used to start the inverter faster and more easily. Through the control panel and computer to debug and monitor. In the application of hoisting winch pumping station pumping station, according to the needs of the process using a PFC control using the macro program.
In the coiler pit inside the collection tank in a static liquid level meter, liquid level meter is composed of pressure sensor, guide gas cable and transmitter. The pressure sensor to measure liquid level by level gauge in the actual value of the transmitter into 4-20mA current signal directly as reference signal of ACS504 AC frequency conversion device, when the coiler pit inflow is changed, the output frequency corresponding to the change of frequency converter, to achieve automatic control of variable speed pump. During normal production, the parameters of the frequency conversion device, can realize the coiler pit inside the collection tank water quantity and water balance, the pit level inside the collection tank are basically unchanged.
As the pump in the normal production, has been involved in the closed-loop control of the water level, so as to effectively prevent the frequent start of the pump, stop operation, to extend the pump life.
When the main rolling line stop rolling or maintenance, bus to coiler pit less water, in order to prevent water damage due to water idling in the PFC control using the macro program, set up a low water level through sleep, wake up the parameter settings, PFC will monitor the actual change of water level, and low water level in comparison, realize the automatic start and stop pump.
PFC control by the application of the parameters of the macro configuration configuration, you can achieve the water level indicator, high water level alarm, fault alarm, automatic switching of the two pumps and other functions.
ACS504 full digital AC frequency conversion device, the pump running smoothly, pump failure was significantly decreased, completely overcome the shortcomings of the original control system, the specific performance in the following aspects:
(1) the high precision of frequency conversion device, perfect protection function. The optimization of system parameters directly through the counter keyboard settings, system fault self diagnosis after directly displayed on the counter window, the system basically maintenance free, greatly improving the work efficiency.
(2) the level of liquid level detection, the detection signal as the reference input of the control system, the output frequency of the control system, to achieve the level of closed-loop control, improve the technical index of the system, improve the working condition of the pump, reduce the number of start and stop the pump, prolong the service life of the water pump.
(3) after the transformation, the control system is stable and reliable, and the economic operation of the motor can not only reduce the failure time, but also save a lot of energy.
(4) due to the maintenance free and low failure rate of digital converter, a lot of maintenance and repair cost is saved.