Integrated coal mining production

In coal mines, most armoured face conveyors (AFCs), stage loaders, or hoists use either a direct start, a rare version of inverter, or a soft start drive. The drawbacks of a direct start are a high starting current, a high starting torque, a voltage drop, etc., all of which negatively impact electric motor performance. These disadvantages bring uncertainties for mining operations up to and including production breakdowns. Guaranteed reliability of motor performance is critical for profitable coal mine production. In recent years, with the progress and development of inverter technology, the technology of the integrated motor and drive (IMD) machine and other new innovations are becoming more mature. The coal mining industry has also begun to invest in IMD machines, permanent magnet motors, and other major equipment including emulsion pumps, belt tailpieces, and AFCs.

The explosion-proof and intrinsically safe IMD machine for mining is an innovative solution combining a motor with a drive and control technology for high risk, narrow longwall, or other working faces in coal mines. It integrates permanent magnetic motors and frequency inverters into a single compact system structure. With intelligent inverter topology, digital drive, diagnostic technology, higher control accuracy, fast response speed, smooth changes of torque, and motor magnetic chain, this IMD machine offers an improvement in power density. Moreover, by reducing harmonic content of the output, it improves the efficiency of the frequency inverter, extends the service life of the motor, and reduces interference with external equipment for increased system stability in coal mines.

The principle and construction of an integrated motor inverter machine

An IMD system mainly consists of an electric circuit system, control system, HMI system, driving system, and a three-phase asynchronous motor or three-phase permanent magnet synchronous motor, three-stage main control box, and other core components.

The motor portion of an IMD system has two optional configurations based on different load conditions in coal mines. The first configuration is a conventional three-phase 1500 RPM asynchronous motor. Other rotational speeds can be customised according to a user’s specification. The second option is a three-phase permanent magnet synchronous motor. For increased energy efficiency and power factor quality, the motor’s rotor consists of punched laminations inlaid with magnets. In recent years, international organisations and governments have been committing to net zero carbon emission initiatives, as well as working on decarbonisation policy and regulations. As a result, end-users globally are interested in more energy efficient technology, such as the IMD, to help evolve systems to meet future requirements.

In a practical setup, an AFC or belt conveyor load is mostly handled by several IMDs within one configured system. It is necessary to deploy a centralised main logic box for control and status monitoring for multiple IMD units. To accomplish this, IMDs and the main control box are equipped with a CAN communication control interface which also allows them to form a bus communication network for coordination. The control system sets a time for accelerating or decelerating IMD operation according to the production load. This level of control best meets requirements, allows for minimal mechanical impact, and prolongs the service life of underground system equipment. The centralised main control box can display the operating status, output current, torque, and speed of all IMD units in real time. It controls the output speed and torque of the IMDs to achieve the purpose of power and load balance.

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