Three-Phase VSI with FPGA-Based Multisampled Space Vector Modulation

This paper describes a microprocessor-based digital control system for three-phase voltage source inverters (VSIs) with second-order LC filter for high- and variable-frequency applications. In order to economize computing time and for dynamic reasons, the innermost capacitor current control loop is realized as a simple but efficient hysteresis controller. An outer state controller-based on a continuous or discretized mathematical model-ensures sinusoidal load voltage and current.

A new switching scheme, which combines conventional space vector modulation (SVM) and carrier-based pulse width modulation (CBPWM), is proposed for a three-phase four-leg voltage source inverter (VSI). The proposed algorithm is simpler than conventional three-dimensional space vector modulation (3-D SVM) and easy in implementation in a real-time DSP system, it avoids the selection of a prism and tetrahedron in a 3-D SVM, therefore alleviates the computation burden of the DSP. Also, the concept of near-state pulse width modulation (NSPWM) method, which is used in a three-phase three-leg inverter to reduce the common mode voltage (CMV) noises, can be adopted in this algorithm so as to reduce the common mode voltage for a three-phase four-leg VSI. The feasibility of the proposed modulation technique is verified by both computer simulation and experimental results.

The proportional–integral (PI) control is usually applied in synchronous reference frame to regulate the output voltage of three-phase voltage source inverter (VSI). However, the PI controller is constrained by the capability of suppressing harmonic and negative sequence components; besides, its direct application in single-phase VSI is limited. While the proportional–resonant (PR) control can track ac reference and achieve harmonic suppression in stationary frame for both single-phase and three-phase VSI. Due to the high order of the resonant controller, lots of efforts are needed during the parameter design to get a satisfactory performance, such as trial-and-error. In this article, the way to approximately reduce the order of the resonant controller in the discrete time domain is presented, and then a method of selective pole placement and cancellation for the PR control design used in VSI is proposed. With the proposed method, the closed-loop pole-zero distribution of the PR control structure used in the VSI is well handled, and the parameters of the feedback controller and the reference feedforward controller are directly calculated by placing the selected poles and zeros in desired positions. The procedure of the parameter design is facilitated, and the performance of the VSI with PR control is improved.

In power electronics, the alleviation of the converter losses is the major target to accomplish higher efficiency and lower thermal stress that can pave the way to lifetime enhancement of devices. Hence, this paper intends to implement a novel variable switching frequency system for switching loss minimisation in a 3-phase Voltage Source Inverter (VSI). Here, the count of commutations is minimised by varying the switching frequency over the fundamental period. Here, the switching loss is reduced by optimising the modulation index and the reference angle of VSI with a novel hybrid optimisation model. The proposed novel hybrid optimisation model is constructed by hybridising the concept of Group search Algorithm (GSO) and Rider Optimisation Algorithm (ROA) and hence referred to as Bypass updated Group search Algorithm (BU-GSO). Finally, the performance of BU-GSO is evaluated over the traditional models in terms of convergence analysis, Total Harmonic Distortion (THD) as well. Moreover, the evaluation is accomplished with inductive load variation and restive load variation, respectively.

Bus-clamping Pulse Width Modulation (PWM) is an effective method to reduce the switching loss in a three-phase voltage source inverter (VSI). In bus-clamping PWM scheme, the phase legs are switched using high frequency PWM signals for two-third of the line cycle, while for the remaining duration of cycle, the pole voltage is clamped to either positive or negative rail of the DC bus. In PWM operation of a half bridge, a dead-time is applied between the gate signals of complementary switches to ensure safe and reliable operation. However, introduction of dead-time leads to poor power quality, increased Total Harmonic Distortion (THD) and variation in actual voltage compared to the intended pole voltage. Moreover, when the bus-clamping technique is used, the PWM has both high frequency switching region and clamped region in a line cycle, and consequently, the undesired effects of dead-time are further aggravated. Therefore, in order to enhance the quality of output voltage, this paper presents a dead-time compensation strategy for a VSI operating with bus-clamping PWM. The proposed method calculates the required compensation term to be added on the modulation signal considering wide range of operating conditions. Additionally, the compensation includes a new strategy for low current conditions near zero-crossing to avoid distortion. The proposed method is verified by simulation and experiments in a three-phase VSI with a switching frequency of 100 kHz and a fundamental frequency of 60Hz.

PWM control of inverters

The interest in multiphase drives has been steadily growing during the last decade due to the promising potentials offered by multiphase machines over conventional three-phase counterpart. In this context, six-phase induction machines are preferably used in many diversified high-power applications. Generally, thanks to its improved flux distribution, the asymmetrical six-phase winding topology fed from two three-phase voltage source inverters (VSIs) is commonly employed with isolated neutral points to prevent the flow of zero sequence currents and to limit the number of current controllers to four instead of five when neutral points are connected. In this paper, an innovative design of a six-phase dc-ac inverter is proposed for such type of six-phase ac machines based on the single-ended primary-inductance converter (SEPIC) topology. The proposed topology employs only four active-legs with eight switches with the same output voltage magnitudes as in conventional VSIs and without the mandatory dead-time between switches in the same-leg. Also, it naturally delivers a pure sinusoidal waveform at the output stage. The principle of operation of the proposed inverter topology is investigated in details and assessed through a detailed simulation study of an open-loop control system.

The sinusoidal pulse-width modulation (SPWM) technique is typically used for three-phase voltage source inverter (VSI) in low-voltage motor drives due to its simplicity and reliability. However, these VSI face increasing challenge to minimize electromagnetic interference (EMI) and increase power quality. This paper proposes a new SPWM switching based on a Bat-like reference signal that has the advantages of minimizing the output-voltage total harmonics distortion (THDv), lowering the switch rate of change in voltage (dv/dt), reducing the number of switching transitions, and increasing the peak and r.m.s. ac output voltage of the three-phase VSI. The proposed switching technique is verified using Matlab/Simulik on a 2-kW, 300-V three-phase VSI connected to an RL load. This technique shows improvement in reducing the output-voltage THDv by 36% and lowering the number of switching transition by 60% as compared to SPWM switching that is based on singlefrequency signal. Moreover, the dv/dt is low and the peak output voltage is increase by approximately 17%.

LLCL-filter is recently emerging into grid-connected inverters due to its high attenuation of high-frequency harmonics with a smaller size. Active damping methods have been proposed to reduce the resonance peak caused by the LLCL-filter to stabilize the whole system without extra losses. The active damping method with an extra feedback provides a high rejection of the resonance so that the dynamic is improved. In this paper, taking a Proportional-Resonant (PR) together with a harmonic compensator (HC), resonant-inductor-voltage-feedback active damping is applied on an LLCL-filter based three-phase grid-connected voltage source inverter (VSI). The design method is described through the analysis in the s-domain and the z-domain. Then the robustness and harmonic rejection of the grid voltage with the active damping method is analyzed considering the processing delay. Finally, the performance of the proposed method is investigated in simulation and by experimental results.

Two-level three-phase voltage source inverter (VSI) with resistive-inductive load has been widely applied in the real life and production. Precise control and fast response are essential for the performance of two-level three-phase VSI with the resistive-inductive load. In this paper, a novel controller design which consists of discrete-time model predictive control (DMPC) based on Laguerre functions and space vector pulse width modulation (SVPWM) is proposed to satisfy these requirements. The inputs of the three-phase are transformed into stationary α-β coordinate for reducing calculation. In addition, the parameters of DMPC based on Laguerre functions are calculated during the offline period, which can reduce the burden of online calculation. With the voltage detection of resistive-inductive load and the current compensation, required reference voltage can be predicted. The required reference voltage is later applied to SVPWM to get the switch sequences. A modified DMPC based on Laguerre functions-SVPWM can achieve a very low total harmonic distortion of output current. Extensive simulation results demonstrate that the proposed approach has a fast dynamic response and perfect steady-state performance.

The paper presents a new control scheme for voltage control of voltage source inverter (VSI) with LC output filter. Proposed high performance control scheme with use of stationary regulators can be used in UPS or standalone power generation where sine wave output voltage is to be maintained. The proposed controller is able to compensate voltage distortion from unbalanced and nonlinear loads, thus controlling negative and positive voltage sequence and its harmonics. For the control purpose only voltage measurement in required. Besides, the controller can be further used in distributed power generation where the parallel operation is desired. In order to improve the parallel operation and sharing any kind of distorting loads, the proposed controller allows adjusting the gain of selected harmonics required for proper harmonic sharing. The proposed scheme is fully appropriate for digital implementation of UPS systems where high quality AC output voltage is in importance. The diagram block of the proposed controller is shown together with some simulation and experimental results. Presented controller shows outstanding performance under nonlinear and unbalanced loads which uses selective harmonic compensators.

With rapid advancement in technologies used in solid-state electronics, nowadays, the conversion and control of electrical power has become easy due to inclusion of power electronics-based devices. With the help of these devices, accurate and smooth control of electrical power conversion can be consummated in three-phase voltage source inverters. But uses of power electronics devices also result in Total Harmonic Distortion (THD), which distorts overall system performance. Eliminating some selected harmonic in a system can quickly be done by using optimization techniques. This manuscript focuses on analysis of harmonics in a 3-phase voltage source inverter using Gravitational Search Algorithm (GSA) and Particle Swarm Optimization (PSO) technique.

Basically, the motor drive system comprises a voltage source inverter-fed induction motor (VSIM): namely a three-phase voltage source inverter and the induction motor. The squirrel-cage induction motor voltage equations are based on an orthogonal d-q reference-rotating frame where the coordinates rotate with the controlled source frequency. The paper presents a novel fuzzy logic controller for high performance induction motor drive system. The inputs to the fuzzy logic controller are the linguistic variables of speed error and change of speed error, while the output is change in switching control frequency of the voltage source inverter. In this paper a comparison between fuzzy logic controller and traditional PI controllers are presented. The results validate the robustness and effectiveness of the proposed fuzzy logic controller for high performance of induction motor drive. Simulink software that comes along with MATLAB was used to simulate the proposed model

In this paper, the fault detection and diagnosis in a three-phase voltage source inverter (VSI) is investigated. The open-circuit of power switches is considered as the faulty conditions. The proposed algorithm in this paper is the principle component analysis (PCA) that determines the failed switch and the fault starting time based on the inverter output currents. In order to validate the performance of the proposed fault detection method, one of the most commonly used methods presented in the literature entitled "3D Current Trajectory" is also implemented and its results are compared to those of PCA. Under the circumstances where the open-circuit fault occurs at a specific time or the fault time interval is very small, the conventional methods cannot detect the faults. Using the software simulations in MATLAB, it is demonstrated that the proposed method can detect any faults under any circumstances and identify the origin of them.

This paper proposes an event-triggered model predictive control (ET-MPC) method for the three-phase inverter with output LC filter. The proposed method is developed by combining the conventional finite-control-set MPC (FCS-MPC) method and the ET control strategy. The ET control strategy incorporates a preset triggering condition based on the requirement of the regulation performance for the three-phase inverter. When the state of the three-phase inverter activates the triggering condition, FCS-MPC is triggered with the updated state so that the optimal control actions can be generated when it is necessary. If the state of the inverter is within the preset triggering condition, FCS-MPC is suspended and the control actions are held as constant. Consequently, the unnecessary online prediction, online optimization, and the corresponding control actions can be avoided. Therefore, with the tolerate regulation performance, the proposed ET-MPC can reduce the computational burden of the conventional FCS-MPC. The various simulation studies of the three-phase inverter are conducted and discussed to demonstrate the effectiveness of the proposed ET-MPC method.