Modified digital current controller with reduced impact of transport delays

Abstract

In this paper, the authors discuss the means for reducing the negative effects of transport delays in digital current controllers. The signal acquisition path introduces delays due to anti-aliasing pre-filters and digital signal processing. The voltage actuators in digital current control systems are the pulse-width modulated (PWM) inverters. They introduce delays caused by the nature of the PWM process and by imperfections in the gating signal chain. A modified digital current controller is devised in this study, enhanced by derivative control action and suited to reduce the effects of transport delays. The controller is aided by a dedicated gain-setting procedure, suited to secure an improved bandwidth and robustness against the parameter changes. Analytical considerations and experimental results demonstrate the benefits of the devised solutions, which improve disturbance rejection and increase the closedloop bandwidth by 1.46 times. The main results are directly applicable to all stationary frame controllers, and also to PR controllers and d-q frame controllers, as they share the same basic control actions.

Discrete current control with improved disturbance rejection for surface‐mounted permanent magnet synchronous machine at high speed

“…which is proposed in [11] though no virtual resistance is employed there. The stability boundary for K is 0 < K<1, and the fastest command tracking without overshoots is achieved by [14]…”

“…However, both of these controllers are designed in the continuous domain and may not be able to consider the discrete behaviours of a digital controller properly, especially when the sampling-to-fundamental frequency ratio is low. Compared with discretisation of a continuous controller using Euler's or Tustin's method, designing a controller directly in the discrete domain can take the computational delay and the ZOH into account naturally and obtain better performance [11][12][13][14]. In [11], a discrete controller designed directly in z-domain for non-salient ac machines is developed based on their ZOH-equivalent model in the complex vector form.…”

“…The complex vector approach in s-domain is also generalised to the z-domain. Instead of the classical proportinal-integral (PI) controller, a discrete PI derivative controller is proposed in [14,16] in order to reduce the negative effects of the transport delays. The multisampling technique can increase the bandwidth of the controller and improve its disturbance rejection at the expense of a higher requirement for hardware [16][17][18].…”

Enhanced Control for Improving the Operation of Grid-Connected Power Converters under Faulty and Saturated Conditions

“…In the literature, many papers have been published about proportional-resonant controllers, addressing different topics such as different PR topologies, discretization/digital implementation [14][15][16] and parameters tuning [17][18][19][20][21][22], among others.…”

Impedance shaping method to improve grid-connected inverter under weak grid condition

“…Similarly, the model of time delay can be linearized as one and a half sampling time step. In [61], the effect of transport delays is discussed. Moreover, a modified digital controlled current controller is proposed to improve the performance of the derivative part.…”