Application of CHV190 Open-Loop Vector Control in Fixed Gantry Cranes

Abstract: Currently, crane hoisting motors all adopt closed-loop vector control, which has advantages such as high positioning accuracy, mechanical rigidity, fast dynamic response, and large starting torque. However, this requires the installation of a shaft encoder to collect the motor speed signal. In many old gantry crane retrofit sites, it is very difficult to install a shaft encoder, making it impossible to achieve closed-loop vector control. However, INVT CHV190 series crane hoisting dedicated frequency converters can also achieve smooth starting and braking of gantry cranes using open-loop vector control, ensuring good control and preventing hook slippage. This article is an example of the CHV190 used in the open-loop vector control retrofit of a fixed gantry crane.

Keywords: CHV190, switch vector control, gantry crane, shaft encoder

Abstract: Recently crane electric system adopt close-loop vector control mostly in lifting motor, that bring good mechanical properties, fast dynamic response and high start torque. All of these depend on shaft encoder collecting speed signal from motor, and there are so many problems for the shaft encoder's installation in most of the alteration projects with old portal crane electric system. However, INVT CHV190 series frequency converter could also realize smooth and steady control for portal crane motor by open-loop vector control, make sure no downwards sliding before starting, this article describes a successful using of open-loop vector control in fixed portal crane alteration projects by CHV190.

Keywords : CHV190, Open-loop vector control, Portal crane, Shaft encorder

I. System Overview

Fixed gantry cranes are a typical type of equipment in the lifting industry, widely used in warehouses, factories, docks, and open-air storage yards. The system has three mechanisms: lifting, slewing, and luffing. Because the turntable and supports are fixed to the civil engineering foundation of the workplace, there is no trolley traveling mechanism, and the entire machine cannot be moved horizontally.

The lifting mechanism of the fixed gantry crane is similar to that of the ordinary gantry crane. "Hook slippage" is not allowed during upward and downward movement. In terms of performance, it is required to output at least 150% of the rated torque when the speed is given at 4HZ. In terms of function, it needs to have reliable brake timing control.

This project involves a GZ1620 fixed crane with a rated lifting capacity of 16 tons, a maximum working radius of 20 meters, a minimum working radius of 7.5 meters, a lifting height of 7 meters, and a lifting speed of 33 meters per minute. The main modification is a dual lifting mechanism, consisting of two 55KW wound-rotor asynchronous motors. Before the modification, the crane used a traditional relay contactor control circuit without a PLC controller. The lifting motors employed series resistance speed regulation, achieving multi-speed switching and starting current limiting by gradually cutting off rotor resistance. This speed regulation method had low reliability, high noise, high energy consumption, and long downtime due to malfunctions. The mechanical brake was operated by a hydraulic brake; when the lifting handle returned to zero, the brake signal was immediately sent without any deceleration or stopping time, resulting in significant brake impact and damage to the metal structure, mechanical transmission device, and the brake itself. In view of these shortcomings, the port decided to cooperate with our company to use our CHV190 series frequency converters to perform frequency conversion speed regulation modification on the gantry crane's lifting mechanism.

II. Technical Solutions for Upgrading

Based on the site conditions, installing a shaft encoder is extremely difficult. However, this gantry crane is mainly used for loading and unloading general cargo such as steel coils and wire strips, and does not require high positioning accuracy. The customer requested that the original control circuit not be significantly altered, retaining the original control circuit and interlocking protection, with minimal changes to the wiring to facilitate future maintenance by the port staff. Therefore, we decided to adopt the following modification plan:

1. Two 55KW wound-rotor motors are driven by two CHV190-075G-4 motors with braking units and braking resistors;

2. No asynchronous PG card is configured; switch vector control is used directly.

3. Construct two frequency converter cabinets, equipped with circuit breakers, input and output reactors, isolation transformers, intermediate relays, current transformers, pointer ammeters, pointer voltmeters, operation/fault indicator lights, etc., and install them next to the original switch cabinet. Lead the power lines of the switch cabinet to the incoming line of the frequency converter cabinet as the main power supply, so that the original interlock protection can still function.

4. Remove the existing speed regulating resistor and install the braking resistor box;

5. Short-circuit the rotor of the wound-rotor motor to use it as a squirrel-cage motor;

6. Retain the original contactor with the cut-off resistor, and use it as the multi-speed setpoint signal and direction signal of the frequency converter through intermediate relay isolation.

7. Modify the brake control method by using the inverter output relay terminal as the coil control signal for the brake oil pump motor contactor. The inverter will realize deceleration and stopping, acceleration and starting, and brake release/holding, ensuring that the hook does not slip while avoiding impact on the metal structure.

III. System Diagram

Before the upgrade, speed regulation was achieved using series resistors, and forward and reverse rotation was achieved by switching contactors to engage. The brake would activate when the running signal disappeared.

After the upgrade, the inverter adopts multi-speed function for speed regulation, S-curve acceleration and deceleration operation, and the inverter output relay controls the brake.

IV. Debugging Process

1. Commissioning process of lifting frequency converter 1

Since the load cannot be separated from the site, the static self-learning function is used after setting the basic motor parameters. The parameters are shown in the table below:

Set other parameters as follows:

2. Parameter Adjustment of Lifting Inverter 2

Motor basic parameters and self-learning parameters

Set other parameters as follows:

After the parameters were set, both motors underwent no-load test runs. The no-load current of inverter #1 was 35A, and that of inverter #2 was 27A. After hoisting a 12-ton load, motor #2 experienced insufficient lifting torque and began to slip downwards at the start of lifting. Adjusting the parameters of inverter #2, P2.07 to 0.059 and P2.11 to 31.4, restored motor #2 to normal. After hoisting a 16-ton load, motor #1 occasionally slipped downwards during the lifting process. Although this did not happen every time, the customer found it unacceptable. Therefore, we adjusted the parameter of inverter #1, P2.08, to 0.039, and motor #1 returned to normal.

3. Record the waveform as follows:

Waveform of #1 frequency converter

Waveform of #2 frequency converter

V. Conclusion

The crane industry has high requirements for the performance and functions of frequency converters. Traditional closed-loop vector control is difficult to install encoders, involves many wiring modifications, and has a long modification cycle for retrofit projects. However, open-loop vector control often cannot meet the performance requirements of the retrofitted crane. Open-loop vector control of imported frequency converters such as ABB, Siemens, and Yaskawa has rarely been successful. The successful application of the open-loop vector control of INVT CHV190 series frequency converters in gantry cranes has created a technological breakthrough for domestic frequency converters in the lifting and hoisting industry, putting China at the forefront of the world.

VI. References

1. CHV190 Series Crane-Specific Frequency Converter Instruction Manual, INVT Electric Co., Ltd., 2007

2. National Standard GB/T3811-2004, "Code for Design of Cranes"