Abstract
This paper proposes a model predictive control scheme with a higher-level open-loop torque control and an underlying continuous-control-set model predictive current control (CCS-MPCC) combined with a space vector modulation and an integrated harmonic reference generator (HRG) for permanent magnet synchronous motors (PMSMs), which is able to utilize the DC-link voltage of a two-level inverter to its maximum during transient and steady-state conditions. By formulating the CCS-MPCC as a quadratic program with the voltage hexagon as inequality constraints, the MPCC's typical dynamic response can be achieved during transient operation. When the overmodulation region is reached, additional current harmonics are induced by the voltage constraints, causing a deterioration of the controller's performance. To overcome this problem a HRG is introduced, which calculates at each sampling instant a reference current that contains these harmonics by solving a boundary value problem, using an overmodulation method under the assumption of steady state.Hence, the HRG performs a model-based current reference trajectory prediction ensuring that the CCS-MPCC can enter the overmodulation region. This allows highest control dynamics even at the voltage constraint while ensuring a seamless transition from linear modulation to overmodulation and six-step operation. The method presented here is able to operate in the entire speed range including standstill. Thus, it is not necessary to switch between different controller frameworks for the constant-torque and constant-power regions. Extensive simulative and experimental investigations for a highly utilized PMSM with significant (cross-)saturation effects prove the viability of the proposed control methodology.
Highlights
For advanced drive applications, permanent magnet synchronous motors (PMSMs) are the preferred choice if highest torque and power density is required
In the context of optimal controllers, e.g. the linear-quadratic regulator (LQR) or the utilized CCS-MPCC, additional terms in the cost function can be used to penalize the deviation of the input to a reference input
ENSURING SIX-STEP OPERATION As seen in the previous section, even with exact knowledge of the motor parameters, errors in the solution of the boundary value problem (BVP) can occur due to a finite number of supporting points, the choice of the discretization method and the linearization of the magnetic motor model. In addition to these systematic errors, the solution of the BVP would deviate from the PMSM’s current trajectories due to inaccurate motor parameters based on various influences such as temperature, aging and further not modeled parasitic effects such as slot harmonics or the non-ideal inverter switching behavior
Summary
Permanent magnet synchronous motors (PMSMs) are the preferred choice if highest torque and power density is required. In this modulation region, additional torque and current harmonics are induced by the voltage constraints, causing a deterioration of the controller’s performance or even instability of the closed control loop [8]. Depenbrock’s direct self control (DSC) [28] or voltage angle controllers [2], [29], [30] are usually only applied in the constant-power region, whereby below the nominal speed in the constant-torque range a switchover to a current-based PI-FOC or another stateof-the-art controller is usually made This switching between different control strategies can lead to transition shocks, which is not desirable especially for highly dynamic applications such as servo or automotive traction drives
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