Control Of Induction Heating Process Research Articles

Two-channel time-optimal control of induction heating process with maximum temperature constraint

The formulation and method of solution of the problem of time-optimal control of induction heating process of an unlimited plate with two control actions on the value of internal heat sources with technological constraint in relation to a one-dimensional model of the temperature field are proposed. The problem is solved under the conditions of a given accuracy of uniform approximation of the final temperature distribution over the thickness of the plate to the required. The method of finite integral transformations is used to search for the input-output characteristics of an object with distributed parameters with two control actions. The preliminary parameterization of control actions based on analytical optimality conditions in the form of the Pontryagin maximum principle is used. At the next stage reduction is performed to the problem of semi-infinite optimization, the solution of which is found using the alternance method. The alternance properties of the final resulting temperature state at the end of the optimal process lead to a basic system of relations, which, if there is additional information about the shape of the temperature distribution curve, is reduced to a system of equations that can be solved. An example of solving the problem of time-optimal control of temperature field of an unlimited plate with two offices is carried out in two stages. At first stage the case of induction heating without maximum temperature constraints is considered, at the second stage is carried out on the basis of the results of the first stage to obtain the solution subject to the limitation on the maximum temperature of the heated billet.

Time constant measurement for control of induction heating processes for thixoforming

In controlling induction heating systems, several measurement methods exist for controlled heating of metal billets into the semi-solid state for thixoforming. The most common approach is to measure the billet temperature, which suffers from various drawbacks leading to difficulties in process stability. The main disadvantages are the small temperature range of the process window and the alloy composition dependency of the correlation between temperature and liquid fraction. An alternative is to determine the liquid fraction of the billet by measuring the time constant of the load. Although time constant measurement is not affected by the mentioned problems, it is difficult to use it as a controlled variable. This paper shows that disturbances affecting time constant measurement are mainly caused by semiconductor losses inside the inverter. A method is introduced to compensate these losses. This method was implemented and tested in the embedded system of an induction heating unit, thereby showing that it is possible to use time constant measurement to determine the liquid fraction of a billet during induction heating.

Technological practicability of the numericalmodeling of induction heating process in steel pieces

This paper presents the numerical modeling (using the Finite Difference Method-FDM, and Finite Element Method- FEM) of the electromagnetic and thermal fields in a steel piece heated up inside an induction crucible furnace, and the experimental validations. Both modelings have been validated experimentally, so they can be used in designing the equipments and in the numerical control of induction heating process. The program based on FDM can be used in the first stage of designing due to the reduced CPU time. In this stage the inductor parameters and heating time can be estimated, and a study of the influence of diverse factors upon the heating process can be achieved. The FLUX 2D program can be used in the optimization stage, because it allows a more thorough analysis of the phenomena.

Numerical investigation of optimal control of induction heating processes

We consider optimal control problems arising in induction heating processes. We are mainly concerned with two classes of these processes: uniform heating and metal hardening. The cost functions are chosen according to these classes. The control parameters are the inductor shape (assumed to be thin), the frequency, the current voltage and the heating duration. The induction heating model is a two-dimensional cartesian geometry. The numerical scheme is given as well as numerical experiments for practical applications.

Enhanced Control of Induction Heating Processes of Welded Tubes

This paper presents research results on improved low-cost automatic control of induction heating processes applied to seam-annealing and to preheatin for insulation of welded tubes. It has been done by introducing additional temperature loop at local control of medium -frequency generators and coordination by tracking a family of overal static characteristics, which define sets of local set-point commands. Local three-term controls are designet using the idea of extended frequency characteristics, while overal control is following the idea of direct coordination by penalty function tracking of commands. All models have been derivet and identified in plant environment, and family of overal characteristics also discretized into look-up tables. Benefits are estimated up to five percent energy savings and higher quality processing, while retaining simple control scheme.