Paolo Mattavelli

Comparison of current control techniques for active filter applications

This paper presents the comparative evaluation of the performance of three state-of-the-art current control techniques for active filters. The linear rotating frame current controller, the fixed-frequency hysteresis controller, and the digital deadbeat controller are considered. The main control innovations, determined by industrial applications, are presented, suitable criteria for the comparison are identified, and the differences in the performance of the three controllers in a typical parallel active filter setup are investigated by simulations.

Repetitive-based control for selective harmonic compensation in active power filters

This paper proposes a repetitive-based controller for active power filters, which compensates selected current harmonics produced by distorting loads. The approach is based on the measurement of line currents and performs the compensation of selected harmonics using a closed-loop repetitive-based control scheme based on a finite-impulse response digital filter. Compared to conventional solutions based on stationary-frame current control, this approach allows full compensation of selected frequencies, even if the active filter has limited bandwidth. Compared to synchronous-frame harmonic regulations on line currents, the complexity of the proposed algorithm is independent of the number of compensated harmonics. Moreover, it is more appropriate for digital signal processor implementation and less sensitive to rounding and quantization errors when finite word length or fixed-point implementation is considered. Experimental results on a 5-kVA prototype confirm the theoretical expectations.

An improved deadbeat control for UPS using disturbance observers

A digital control technique for the inverter stage of uninterruptible power supplies is proposed, which is based on a predictive regulator on both output voltage and inductor current. Its aim is to achieve a deadbeat dynamic response for the controlled variables (output voltage and inverter current). Besides the linear state feedback which allocates system poles at the origin so as to achieve deadbeat response for all state variables, the use of a disturbance observer for the estimation of the load current and of any other source of errors (such as dead-times, parameter, and model mismatches) is investigated. The proposed solution is able to guarantee a fast dynamic response and also a precise compensation of any source of unpredictable disturbance. Moreover, with a proper design of observer parameters, it is possible to reduce control sensitivity to model uncertainties, parameter mismatches, and noise on sensed variables, which usually characterizes existing deadbeat control techniques. Finally, the control algorithm is quite simple and requires only the measurements of the output voltage and inductor current. Experimental results on a single-phase 2 kVA prototype show the effectiveness of the proposed approach.

Robust dead-beat current control for PWM rectifiers and active filters

The paper analyses the stability limitations of the digital dead-beat current control applied to voltage-source three-phase converters used as PWM rectifiers and/or active filters. In these applications the conventional control algorithm, as used in drive applications, is not sufficiently robust and stability problems may arise for the current control loop. The current loop is, indeed, particularly sensitive to any model mismatch and to the possibly incorrect identification of the model parameters. A detailed analysis of the stability limitations of the commonly adopted dead-beat algorithm, based on a discrete-time state space model of the controlled system, is presented. A modified line voltage estimation technique is proposed, which increases the controls robustness to parameter mismatches. The results of the theoretical analysis and the validity of the proposed modification to the control strategy are finally verified both by simulations and by experimental tests.

Simple digital control improving dynamic performance of power factor preregulators

This paper presents the practical implementation of a fully digital control for boost power factor preregulators (PFPs). The control algorithm, which is simple and fast, provides a significant improvement in the systems dynamic performance compared to the usual analog control techniques. The paper discusses the design criteria and the actions taken for the implementation of the digital control, which is performed by means of a standard microcontroller (Siemens 80C166). The effectiveness of the approach is assessed by experimental tests.

Repetitive-Based Controller for a UPS Inverter to Compensate Unbalance and Harmonic Distortion

This paper discusses a repetitive-based controller for an uninterruptible power supply (UPS) inverter. It is shown that a bank of resonant filters, used as a refinement term for harmonic compensation in earlier works, is equivalent to a repetitive scheme with a particular structure. The latter is implemented using a simple feedback array with a delay line, thus making the implementation relatively easy. More precisely, the repetitive scheme takes a negative feedback structure plus a feedforward path whenever the odd harmonics are considered for compensation only. The repetitive scheme, equivalent to the bank of resonant filters, acts as a refinement term to reject the harmonic distortion caused by the unbalanced and distorted load current, and thus, allowing the UPS inverter to deliver an almost pure sinusoidal balanced voltage. Experimental results in a 1.5 KVA three-phase inverter are included to show the performance of the proposed controller

Synchronous-frame harmonic control for high-performance AC power supplies

In order to achieve the reduction of voltage distortion in AC power supplies (ACPSs), this paper describes an implementation of synchronous-frame control for selected frequencies in the output voltage. The regulation of the fundamental output voltage, as well as that of some low-order harmonics, is achieved using a synchronous-frame controller for each selected frequency in addition to a conventional control. The conventional part conserves good dynamic performance under load changes, while rotating-frame controllers allow a slow, but very precise compensation of the residual errors within the assumption that the harmonics produced by distorting load are slowly varying. Moreover, motivated by a fixed-point implementation, a set of refinements and modifications of the original scheme is proposed, allowing a reduction of signal processing requirements and a new control algorithm structure less sensitive to quantization and rounding errors. This solution is particularly effective for high-power fully digitally controlled ACPSs, where the voltage loop bandwidth is usually not large enough to provide regulation at harmonic frequencies. The proposed control scheme has been implemented using a fixed-point single-chip digital signal processor (ADMC401 by Analog Devices). Experimental results on a 3-kVA three-phase converter prototype show the effectiveness of the proposed approach.

General-purpose fuzzy controller for DC-DC converters

In this paper, a general-purpose fuzzy controller for DC-DC converters is investigated. Based on a qualitative description of the system to be controlled, fuzzy controllers are capable of good performances, even for those systems where linear control techniques fail, e.g., when a mathematical description is not available or is in the presence of wide parameter variations. The presented approach is general and can be applied to any DC-DC converter topologies. Controller implementation is relatively simple and can guarantee a small-signal response as fast and stable as other standard regulators and an improved large-signal response. Simulation results of buck-boost and Sepic converters show control potentialities.

General-purpose sliding-mode controller for DC/DC converter applications

A general-purpose sliding-mode controller is described, which can be applied to most DC-DC power converter topologies. It has the same circuit complexity as standard current-mode controllers, but provides extreme robustness and speed of response against supply, load, and parameter variations. Moreover, contrary to other sliding-mode techniques, the proposed solution features constant switching frequency in the steady state, synchronization to external triggers, and absence of steady-state errors in the output voltage.<<ETX>>

Uninterruptible power supply multiloop control employing digital predictive voltage and current regulators

A digital control technique for the inverter stage of uninterruptible power supplies (UPSs) is described, which is based on voltage and current predictive regulators. Its aim is to achieve a deadbeat dynamic response for the controlled variables (output voltage and inverter current). The controller maintains the advantageous conventional multiloop structure and is capable of guaranteeing a high-quality dynamic performance. Moreover, its design is extremely simple and requires only a reasonably accurate knowledge of the output filter parameters. Finally, the only sensed variables are the output voltage and the converter output current. The validity of the proposed strategy is demonstrated by means of simulation and experimental results referring to a single-phase UPS laboratory prototype (1 kVA).