Constant Switching Frequency Operation Research Articles

Voltage sensorless predictive direct power control of three‐phase PWM converters

This study develops a voltage sensorless predictive direct power control (PDPC) strategy for three-phase pulsewidth modulation (PWM) converters using accurate virtual flux (VF) estimation. This proposed PDPC can realise simultaneous control of the instantaneous active and reactive power, and achieve a constant switching frequency operation by adopting an on-line corrective space vector modulation modulator. AC voltage sensors are removed by using the following two techniques. One is that an accurate VF observer is employed to compensate the magnitude and phase errors introduced by the first-order low pass filter. The other is that grid voltages are estimated using the VF based estimation of instantaneous active and reactive power as intermediate variables. In addition, the time delay existing in a real system is taken into account in the proposed control model. Comparative results demonstrate the excellent performance of the proposed approach compared with the conventional look-up-table DPC and the conventional PDPC.

Direct Power Control of Three-phase Voltage Source Converters Using Feedback Linearization Technique

This paper describes the direct power control (DPC) of a three-phase voltage source converter (VSC) using feedback linearization technique. This technique transforms nonlinear model of the VSC into a linear one so that the controller design is easy and independent of the operating point. The problem is formulated in the DPC framework. The DPC with space-vector modulation (DPC-SVM) is adopted because of its constant switching frequency operation. The control scheme is implemented on a STM32F4DISCOVERY board. The validity of the scheme has been verified through experiment which shows that the proposed control strategy provides the VSC operation with wide operating range and fast transient responses.

Dual frequency inverter configuration for multiple‐load induction cooking application

Induction cooking application with multiple loads powered by suitable power converters and appropriate control technique needs attention. This study proposes dual frequency operated full-bridge inverter for multiple-load induction cooking. This inverter simultaneously powers two series resonant circuits. Each series resonant circuit is for one induction cooking load. This technique provides constant switching frequency operation for individual loads with asymmetrical duty cycle control. Output power of each load is independently controlled. The proposed inverter configuration and control technique is simulated and experimentally tested for two loads. Simulation and experimental results are in good agreement. This technique can be extended to more than two loads.

Direct Torque Control of Induction Motors Based on Discrete Space Vector Modulation Using Adaptive Sliding Mode Control

—Direct torque control (DTC) with space vector modulation (SVM) ensures constant switching frequency and high-performance operation, both in the steady state and under transient conditions. This article is devoted to the presentation of a comparison study between two DTC-SVM approaches for electric propulsion systems applications: (i) DTC-SVM with controllers, and (ii) DTC-SVM with sliding mode controllers. Following the formulation of both DTC-SVM approaches, their implementation in the Matlab-Simulink environment has been treated. The transient behavior as well as the steady state features of the drive system under both approaches are compared and commented. The robustness with respect to parameter variations of the induction motor drive is also tested. Simulation results show the effectiveness and the robustness of the proposed DTC-SVM adaptive sliding mode control against variations of induction motor parameters.

A Control Strategy and Design Method for Interleaved LLC Converters Operating at Variable Switching Frequency

LLC converters face challenges in high-current applications, where the high conduction loss limits the maximum load capacity and reduces efficiency. Interleaving technique can be used to solve this problem, but the component tolerances of the resonant tanks will cause severe load sharing problem. The SCC-LLC converter was proposed to solve the load sharing problem. However, due to its constant switching frequency operation, it has some limitations over complete line and load variation compared to conventional LLC converters. In this paper, a new control strategy is proposed for the SCC-LLC converter, which enables variable switching frequency operation; thus, it provides uncompromised performance while achieving interleaved operation. Analyses and a design method are provided, and a 600-W two-phase interleaved SCC-LLC prototype is built to verify the feasibility.

A Medium-Voltage Inverter-Fed IM Drive Using Multilevel 12-Sided Polygonal Vectors, With Nearly Constant Switching Frequency Current Hysteresis Controller

In this paper, a current error space vector (CESV)-based hysteresis current controller for a multilevel 12-sided voltage space vector-based inverter-fed induction motor (IM) drive is proposed. The proposed controller gives a nearly constant switching frequency operation throughout different speeds in the linear modulation region. It achieves the elimination of 6n ±1, n = odd harmonics from the phase voltages and currents in the entire modulation range, with an increase in the linear modulation range. It also exhibits fast dynamic behavior under different transient conditions and has a simple controller implementation. Nearly constant switching frequency is obtained by matching the steady-state CESV boundaries of the proposed controller with that of a constant switching frequency SVPWM-based drive. In the proposed controller, the CESV reference boundaries are computed online, using the switching dwell time and voltage error vector of each applied vector. These quantities are calculated from estimated sampled reference phase voltages. Vector change is decided by projecting the actual current error along the computed hysteresis space vector boundary of the presently applied vector. The estimated reference phase voltages are found from the stator current error ripple and the parameters of the IM.

Current Controlled PWM for Multilevel Voltage-Source Inverters with Variable and Constant Switching Frequency Regulation Techniques: A Review

Due to advancements in power electronics and inverter topologies, the current controlled multilevel voltage-source pulse width modulated (PWM) inverter is usually preferred for accurate control, quick response and high dynamic performance. A multilevel topology approach is found to be best suited for overcoming many problems arising from the use of high power converters. This paper presents a comprehensive review and comparative study of several current control (CC) techniques for multilevel inverters with a special emphasis on various approaches of the hysteresis current controller. Since the hysteresis CC technique poses a problem of variable switching frequency, a ramp-comparator controller and a predictive controller to attain constant switching frequency are described along with its quantitative comparison. Furthermore, various methods have been reviewed to achieve hysteresis current control PWM with constant switching frequency operation. This paper complies various guidelines to choose a particular method suitable for application at a given power level, switching frequency and dynamic response.

Modularized Bidirectional Grid-Connected Inverter With Constant-Frequency Asynchronous Sigma–Delta Modulation

The objective of this paper is to propose a modularized bidirectional single-phase grid-connected inverter (BGI) with constant-frequency asynchronous sigma-delta modulation (CF-ASDM) control for the renewable energy (RE)-supplied dc power system. The proposed BGI can be operated either in the inverter mode (IM) or rectified mode (RM); both are necessary features for the RE-supplied dc power system. By comparing to the conventional ASDM with variable switching frequency, the proposed CF-ASDM can simplify the filter design and can reduce the computational burden of the digital signal processor while maintaining the merit of quick dynamic response. Moreover, the proposed BGI has a redundant central controller which can increase the system reliability. The major contribution of this paper includes developing the modularized BGI with CF-ASDM control scheme for IM and RM operations thoroughly and applying it to the RE-supplied dc power system successfully. In this paper, the mathematical equations to achieve the constant switching frequency operation for the CF-ASDM will be derived. Computer simulations and hardware experiments are shown to verify the performance of the proposed modularized BGI with CF-ASDM control.

Modified stator flux estimation-based direct torque controlled induction motor drive with constant switching frequency operation

A space vector pulse width modulated (SV-PWM) direct torque controlled (DTC) induction motor drive, having reduced torque ripple even at low operating speeds and maintaining constant switching frequency has been studied and implemented with a modified stator flux estimation scheme. It utilises a compensator for the phase and magnitude error introduced by low pass filter, which is being used to avoid DC drift, problem of saturation and to enhance the transient response of the machine. Detailed simulation studies are carried out to verify the efficacy of the system. The viability of the scheme is confirmed by performing detailed experimental studies.

Single-stage high power factor step-up/step-down isolated AC/DC converter

This study presents a single-stage (S 2 ) isolated current rectifier with power factor correction, based on a full-bridge flyback converter. This converter is designed to operate with adjustable output voltage so that it can operate in two distinct operation modes, step-up or step-down, depending on the input and output voltages. The proposed converter presents some features that make it attractive for many applications, such as constant switching frequency, step-down and step-up operation, high power level capability and the absence of an auxiliary pre-loading circuit to control the inrush current. This study presents the theoretical analysis of the converter for continuous conduction mode as well as experimental results based on a 3 kW prototype.

Dynamic Programming Power Control for Doubly Fed Induction Generators

This paper presents a novel control strategy, dynamic programming power control (DPPC), to be applied to doubly fed induction generators most commonly used in wind energy applications. Although the technique can be implemented to control both rotor and grid converters, it will hereby be expounded the former, which regulates stator active and reactive powers. The results obtained are compared with those from other techniques, such as direct torque/power control (DTC/DPC) through the use of experimental tests, and indicate that DPPC achieves gains in dynamic response and considerable improvements in terms of ripple reduction and frequency spectrum as a result of constant switching frequency operation. The validation of results has been performed through experimental tests on a 6-kW generator.

Synthesis of power gyrators operating at constant switching frequency

A systematic procedure to synthesise power gyrators for constant switching frequency operation is presented. The equivalence between ideal sliding dynamics and PWM zero dynamics is used to derive the control law of the duty cycle. As a consequence, any power gyrator with stable behaviour in sliding-mode results in a stable equivalent gyrator at constant switching frequency with the same stability conditions. The design of a PWM G-gyrator with controlled output current based on a buck converter with input filter illustrates the procedure. Simulations and experiments are in good agreement with the theoretical predictions.

SYNERGETIC CONTROL FOR POWER ELECTRONICS APPLICATIONS: A COMPARISON WITH THE SLIDING MODE APPROACH

The theory of synergetic control was introduced in a power electronics context in a previous paper. In this paper we review the theory, then we focus on a comparison with the sliding mode approach. Common elements and main differences are underlined and illustrated through a comparative simulation example. The main advantages of synergetic control are that it is well-suited for digital implementation, it gives constant switching frequency operation, and it gives better control of the off-manifold dynamics. Finally, simulation and experimental results under transient conditions are compared. Advanced control laws with adaptation are presented and discussed to show how to better exploit the features of the synergetic control. The example used throughout the paper is the control of a boost converter operating in continuous conduction mode.

Unified constant-frequency integration control of active power filters-steady-state and dynamics

An active power filter (APF) is a device that is connected in parallel to and cancels the reactive and harmonic currents from a group of nonlinear loads so that the resulting total current drawn from the AC mains is sinusoidal. This paper presents a unified constant-frequency integration (UCI) APF control method based on one-cycle control. This method employs an integrator with reset as its core component to control the pulse width of an AC-DC converter so that its current draw is precisely opposite to the reactive and harmonic current draw of the nonlinear loads. In contrast to previously proposed methods, there is no need to generate a current reference for the control of the converter current, thus no need for a multiplier and no need to sense the AC line voltage, the APF current, or the nonlinear load current. Only one AC current sensor is used to sense the AC main current and one DC voltage sensor is used to sense the DC capacitor voltage. The control method features constant switching frequency operation, minimum reactive and harmonic current generation, and simple analog circuitry. It provides a low cost and high performance solution for power quality control. Steady-state and dynamic study is presented in this paper. Design example is given using a two-level AC-DC boost topology. A prototype was developed to demonstrate the performance of the proposed APF. This control method is generalized to control a family of converters that are suitable for APF applications. All findings are supported by experiments and simulation.

Field-oriented control of an induction motor using random pulsewidth modulation

The principle of field-oriented control (FOC) is a well-established means to obtain a high-performance drive, but the de facto standard FOC does not solve an important secondary problem for inverter-fed motors-the acoustic noise emitted from the motor is tonal due to the constant switching frequency operation. This may be very annoying, even if the exposure time is short. From this background, this paper proposes a classic FOC synchronized to a current-controlled pulsewidth modulation inverter operating with a random switching frequency. This implies that the sampling frequency of both the current controller and the flux estimator is nonuniform, but nevertheless, it is shown that the good dynamic response inherited from the FOC can be maintained while lowering the subjective acoustic annoyance to a great extent due to the random switching frequency operation. Besides laboratory test results documenting the dynamic and steady-state characteristics of the proposed system, design considerations are presented.

Soft-switched DC/DC converter with PWM control

In this paper, a new power converter with two variations is proposed. A novel asymmetrical pulse-width-modulation (PWM) control scheme is used to control the power converter under constant switching frequency operation. The modes of operation for both variations are discussed. The DC characteristics, which can be used in the design of the power converters, are also presented. Two 50 W power converters were built to verify the characteristics of the converters. Due to the zero-voltage-switching (ZVS) operation of the switches and low device voltage and current stresses, these power converters have high full- and partial-load efficiencies. They are, therefore, potential candidates for high-efficiency high-density power supply applications.

A high-power high-frequency ZCS-ZVS-PWM buck converter using a feedback resonant circuit

A buck DC-DC power converter using a novel lossless commutation cell for high switching frequency and high power operation is presented. The proposed cell consists of a main switch and an auxiliary switch, with ZVS (zero voltage switched) and ZCS (zero current switched) switching characteristics, respectively. The converter control using this cell is realized by the PWM technique, with constant switching frequency operation. The complete operation principles, theoretical analysis, relevant equations, state space phase, simulation, and experimental results for the buck converter are presented. >