Xuefang Lin-Shi

A Comparative Study of Predictive Current Control Schemes for a Permanent-Magnet Synchronous Machine Drive

This paper presents a comparative study of three predictive current control schemes for permanent-magnet synchronous machine (PMSM) drives. The first control scheme predicts the future evolution of the currents for each possible configuration of the inverter legs. Then, the switching state which minimizes a given cost function is selected and applied during the next sampling time. The second control scheme uses a modulator to apply two configurations of the inverter legs during a computation period. Among these configurations, one leads to null voltages. The duration of the other configuration is calculated in order to minimize the distance between the obtained state vector and the desired one. The third control scheme uses a model of the PMSM in order to predict the stator voltages which allows us to reach the desired currents after one modulation period. An algebraic method is presented to compute the duty cycle of each leg of the inverter in a direct manner. These control schemes are detailed and tested using the same switching frequency on the same test bench (1.6-kW PMSM drive). A simulation study is performed in order to compare sensitivity to parameters of each control scheme. Experiments confirm the simulation results.

Implementation of Hybrid Control for Motor Drives

This paper presents the implementation of a hybrid-control strategy applied to a permanent-magnet synchronous-motor (PMSM) drive. Hybrid control is a general approach for control of a switching-based hybrid system (HS). This class of HS includes a continuous process controlled by a discrete controller with a finite number of states. In the case of ac motor drives, in contrast to conventional vector control like proportional-integral control or predictive control, where the inverter is not taken into account by the controller, hybrid control integrates the inverter model and considers the state of the inverter as a control variable. It allows to obtain faster torque dynamics than vector-control algorithms. The hybrid control algorithm requires both computing velocity for real-time implementation and code flexibility for management of low-performance functions and analog-digital interfaces. Codesign appears as a promising methodology for partitioning hybrid-control algorithm between software (flexible) and hardware (velocity) while taking care of overall time constrains. In this paper, the implementation of hybrid-control algorithm for a PMSM drive is performed through a codesign approach on an Excalibur board, embedding a CPU-core (Nios-2 by Altera) inside an APEX20KE200EFC484-2X field-programmable gate array. The partitioning of software and hardware parts is explained. Experimental results show the effectiveness of the implementation. Performances, advantages, and limitations are discussed.

Permanent Magnet Synchronous Machine Hybrid Torque Control

This paper presents a control scheme suitable for systems composed of a continuous process modulated in energy by a power converter with a finite number of topologies. To track the continuous reference values, a topology of the power converter is determined from a criterion based on a process state variable model and taking into account the possible topologies of the power converter. The proposed hybrid control scheme is applied to an electrical motor drive composed of an inverter coupled to a permanent magnet synchronous machine. An evolution which insures a fixed modulation frequency is also proposed. Experimental results validate the feasibility and effectiveness of the proposed schemes.

An Integrated Sliding-Mode Buck Converter With Switching Frequency Control for Battery-Powered Applications

Mobile applications necessitate nowadays huge digital resources. Power management of a digital systems-on-chip is based on dynamic voltage scaling. DC/DC converters used to supply the digital system-on-a-chips are facing stringent constraints with respect to load transients, line transients, and reference tracking. Hysteretic control is known as the most convenient control scheme with a fair tradeoff between transient performances, analog implementation and power consumption. Fixed-switching frequency hysteretic control has been experimented as well as full sliding-mode control. Transient performances are reduced due to latencies introduced in the switching frequency control. A new analog implementation of the sliding-mode control is presented here with switching frequency control using a particular analog phase-locked loop but preserve transient performances. The dc/dc converter is implemented in CMOS 130 nm. The switching frequency range has been voluntarily limited and excludes the possible integration of passive components. A hybrid demonstrator is presented with peak efficiency of 89% at 2-W output power.

A Digital-Controller Parameter-Tuning Approach, Application to a Switch-Mode Power Supply

Analogue control of monolithic DC/DC converters is technologically coming to a limit due to high switching frequency and a request for large regulation bandwidth. Digital control is now experimented for low-power low-voltage switch-mode power supply. Digital implementation of analogue solutions does not prove real performances. This paper compares a classical digital controller to a candidate alternative strategy. Sensitivity functions are used to compare controller performances. An off-line approach using fuzzy logic to quantify controller performances and a genetic algorithm to obtain an optimal controller is presented. A so-called RST algorithm optimized with this approach shows better performances.

A predictive control for a matrix converter-fed permanent magnet synchronous machine

Many research efforts have been dedicated to matrix converters for several years. As major technological issues are now solved, this structure will widespread in industrial applications, in particular with AC motors. Current control is a key issue for AC motor drives, so many control schemes have been proposed. Some of them proposed at first for inverters, were applied to matrix converters. Among algorithms used with inverters, predictive control shows very good performances. In this paper a new control scheme is proposed for a matrix converter- fed permanent magnet synchronous machine. Literature about matrix converter technology and control and about predictive control for inverter-fed AC machines is reviewed. The proposed predictive control principle, the model of the whole machine - converter and the cost-function are detailed. The method offers a trade-off between the quality of motor currents and input power factor. Finally experimental results are reported. The feasibility and the effectiveness of the proposed method is assessed.

Hybrid control of a three-cell converter associated to an inductive load

This paper presents a control scheme for a multilevel multi-cell converter. For this type of converters, load current and capacitor voltages must be jointly controlled. Moreover the real-time constraint is important. This constraint leads us to propose a control based on a simplified state-space model. The model allows predicting the state vector evolution for every converter configuration. The control algorithm directly determines the converter switching state which minimizes a simple cost function. A normalization of the state variables is proposed for the cost function calculation in order to ensure a trade-off between the tracking of the load current and the tracking of the capacitor voltages. The proposed control scheme is detailed and compared with a classical control scheme with simulations. Finally, experimental results are presented to show the effectiveness of the proposed method.

Comparative study of two Predictive Current Controls for a Permanent Magnet Synchronous Machine drive

This paper presents the experimental results-based comparison of two predictive current controls (PCC) for permanent magnet synchronous machines (PMSM) drives. The first tested control scheme is based on a model including the inverter and the PMSM and taking into account the discrete nature of the inverter leg states. It predicts the future evolution of the currents for each possible configuration of the inverter. The switching state which minimizes a given cost function is selected. The selected inverter state is applied during the next sampling time. The second tested control scheme uses a model of the PMSM to predict the output voltages which allow to reach desired currents after one modulation period. A new algebraic method is presented to directly compute the duty cycle of each leg. Then a modulator generates the corresponding gate drive pulses of the inverter. These two control schemes are tested with a 1.6 kW PMSM drive at several operating points during steady state and transient operation. A detailed comparison of results is given. Advantages and drawbacks of each method are discussed.

Predictive Current Control for an Induction Motor

This paper presents a predictive current control (PCC) strategy applied to an induction motor (IM) drive. In contrast to conventional vector control, where the inverter is not taken into account by the controller, the PCC considers the state of the inverter as a discrete control variable. Based on a simplified state space model of the IM and the inverter, the proposed control scheme calculates the state vector evolution direction in the d- and q-reference frame for all possible switching states of the inverter. The switching state which minimizes a given cost function is selected and is applied during an adapted duration which is calculated for each computation cycle. As the control requires the knowledge of the instantaneous rotor fluxes and in order to improve the control robustness, a reduced-order extended high gain observer is proposed for estimation of rotor fluxes and inverse rotor time constant. The simulation results validate the observer. The controller is implemented on a 5.5 kW IM drive with a digital-signal-processor (DSP) on a DSpace1103 board. Experimental results show the effectiveness and the performances of the proposed control.

Design and Stability Analysis of a Frequency Controlled Sliding-Mode Buck Converter

Power management of mobile digital systems-on-chip necessitates large voltage regulation performances. DC/DC converters used to supply digital cores are facing stringent constraints with respect to load transients, reference tracking and accuracy. The fast transient response offered by sliding-mode control is well suited to DC/DC converters with fast varying load. Fixed switching-frequency is also mandatory for EMI and noise related issues. Fixed-switching frequency sliding-mode control has been experimented as a multi-loop system. There is a necessity to investigate the stability when multi-loops interact and the parameter set for each loop is quite large. The paper details a methodology for the stability analysis of a frequency-controlled sliding-mode DC/DC converter. The proposed stability analysis takes the possible cross-interactions into account and can be used to optimise the DC/DC controller without the limitations of a non-interaction criterion. As a verification a DC/DC converter is implemented in CMOS 130 nm. Experimental results agree with the analysis main recommendations.