predictive current control of a 3-phase inverter
- 2. ABSTRACT INTRODUCTION MPC-MODEL PREDICTIVE CONTROL ILLUSTRATTION OF MODEL PREDICTIVE CONTROL MPC-CONTROLLER PREDICTIVE CURRENT CONTROL PREDICTIVE CURRENT CONTROLALGORIITHM ADVANTAGES PREDICTIVE CURRENT CONTROL COST FUNCTION CONVERTER MODEL LOAD MODEL CONCLUSION
- 3. A new predictive strategy for current control of a three-phase inverter is presented. The algorithm is based on a model of the system. From that model, the behaviour of the system is predicted for each possible switching state of the inverter. The state that minimizes a given quality function g is selected to be applied during the next sampling interval. Several compositions of g are proposed ,including terms dedicated to achieve reference tracking, balance in the dc link, and reduction of the switching frequency . In comparison to an established control method, the strategy presents a remarkable performance..
- 4. Current control is one of the most studied problems in power electronics , so it is very important to study the application of MPC in a current control scheme. In addition, the three-phase, two-level inverter is a very well-known topology that can be found in most drive applications.
- 5. MPC HAS RESPONSIBILITY TO COMPUTE THE PLANTS INPUT TO PREDICT THE FUTURE. MPC IS A FEEDBACK CONTROLLER ALGORITHM. MPC USES MODEL TO MAKE PREDICTIONS ABOUT FUTURE OUTPUTS OF A PROCESS. MPC CAN HANDLE MULTI INPUT AND MULTI OUTPUT (MIMO) SYSTEM. MPC CAN HANDLE CONTRAINTS. MPC HAS PREVIEW CAPABILITY(FEED FORWARD CONTROL).
- 7. MPC CONTROLLER USES MODELOF THE PLANT AND OPTIMIZER MODEL OF THE PLANT -TO MAKE PREDICTIONS ABOUT THE FUTURE PLANT OUTPUT BEHAVIOUR. OPTIMIZER -WHICH ENSURES THAT THE PREDICTED FUTURE PLANT OUTPUT TRACKS THE DESIRED REFERENCE. OPTIMIZER REDUCES THE ERROR BETWEEN THE REFERENCE AND THE PREDICTED VALUES.
- 8. Straightforward formulation, based on well understood concepts Explicitly handles constraints • Explicit use of a model Well understood tuning parameters –Prediction horizon – Optimization problem setup Development time much shorter than for competing advanced control methods Easier to maintain: changing model or specs does not require complete redesign, sometimes can be done on the fly
- 10. The proposed predictive control strategy is based on the fact that only a finite number of possible switching states can be generated by a static power converter and that models of the system can be used to predict the behaviour of the variables for each switching state.
- 11. The value of the reference current i∗(k) is obtained from an outer control loop, and the load current i(k) is measured. The model of the system is used to predict the value of the load current in the next sampling interval i(k+1) for each of the different voltage vectors. The cost function g evaluates the error between the reference and predicted currents in the next sampling interval for each voltage vector. The voltage that minimizes the current error is selected and the corresponding switching state signals are generated.
- 12. Define a cost function g. Build a model of the converter and its possible switching states. Build a model of the load for prediction.
- 13. The objective of the current control scheme is to minimize the error between the measured currents and the reference values. This requirement can be written in the form of a cost function. The cost function is expressed in orthogonal coordinates and measures the error between the references and the predicted currents: g =| i∗ α(k+1)−ip α(k+1)|+| i∗ β(k+1)−ip β(k+1)| where ip α(k+1) and ip β(k+1) are the real and imaginary parts of the predicted load current vector ip(k+1),. The reference currents i∗ α(k+1) and i∗ β(k+1) are the real and imaginary parts of the reference current vector i∗(k+1).
- 14. The power circuit of the three-phase inverter converts electrical power from DC to AC form using the electrical scheme shown in Figure. Considering that the two switches in each inverter phase operate in a complementary mode in order to avoid short-circuiting..
- 17. Taking into account the definitions of variables from the voltage source inverter circuit, the equations for load current dynamics for each phase can be written as
- 19. The predictive current control presented in this Letter does not require any current controller or modulator. It presents a very effective control of the load currents. In addition, this control strategy compares well with established control methods such as sub harmonic modulation (PWM). The dynamic response of this method is better than the classical PWM solution.