John Kim Pedersen

A review of single-phase grid-connected inverters for photovoltaic modules

This review focuses on inverter technologies for connecting photovoltaic (PV) modules to a single-phase grid. The inverters are categorized into four classifications: 1) the number of power processing stages in cascade; 2) the type of power decoupling between the PV module(s) and the single-phase grid; 3) whether they utilizes a transformer (either line or high frequency) or not; and 4) the type of grid-connected power stage. Various inverter topologies are presented, compared, and evaluated against demands, lifetime, component ratings, and cost. Finally, some of the topologies are pointed out as the best candidates for either single PV module or multiple PV module applications.

Power losses in PWM-VSI inverter using NPT or PT IGBT devices

This paper investigates the power losses for two different IGBT technologies (nonpunch through and punch through) for use in PWM-VSI inverters in order to choose the right device technology for a given application. A loss model of the inverter is developed based on experimental determination of the power losses. The loss model is used on two different modulation strategies which are a sine wave with a third harmonic added and a 60/spl deg/-PWM modulation where only two inverter legs are active at the same time. The two IGBT technologies are characterized on an advanced measurement system which is described. The total power losses in the inverter are estimated by simulation at different conditions and it is concluded that the nonpunch through (NPT) technology is most useful for higher switching frequencies, while the punch through (PT) technology is especially useful at lower switching frequencies and high load currents. It is also concluded that the 60/spl deg/-PWM modulation has the lowest power losses and the power losses are almost independent of phase angle cos(/spl phi/) for normal motor operation. >

Single current sensor technique in the DC-link of three-phase PWM-VS inverters. A review and the ultimate solution

This paper proposes an ultimate solution for reconstruction of three phase-currents in a PWM-voltage source inverter by one current sensor in the DC-link, and it gives a review of existing methods in literature and patents. The solution offers fully protection of the inverter including shoot-through of the DC-link, short-circuit of the output phases and earth faults with both low and high impedance. A special configuration in the DC-link can give such features. At the same time a new method to sample the DC-link current is proposed which both can eliminate disturbances from cables between an inverter and an induction motor, and it offers a true simultaneous sample value of all three phase-currents in the center of a switching period. The two methods are implemented in an experimental setup, and test results show that full protection is achieved and the three phase-currents are reconstructed precisely in the whole operating area.

Random pulse width modulation techniques for converter fed drive systems-a review

A review of the state of the art in RPWM (random pulse width modulation) theory and practice is presented. Topics covered include principles of RPWM, means of randomization, a review of the existing RPWM techniques, power spectra, implementation issues, and documented effects of RPWM on electric drive systems. A number of RWPM strategies have been reported, and a beneficial impact on acoustic noise and vibration has been unamiously agreed upon. Published studies have proven that significant improvement of the acoustic noise characteristics of the motors can be achieved at practically no extra expense in comparison with the systems with traditional, deterministic PWM strategies.<<ETX>>

Power inverter topologies for photovoltaic modules-a review

This review-paper focuses on the latest development of inverters for photovoltaic AC-modules. The power range for these inverters is usually within 90 Watt to 500 Watt, which covers the most commercial photovoltaic-modules. Self-commutated inverters have replaced the grid-commutated ones. The same is true for the bulky low-frequency transformers versus the high-frequency transformers, which are used to adapt the voltage level. The AC-module provides a modular design and a flexible behaviour in various grid conditions. It hereby opens the market for photovoltaic-power for everyone at a low cost due to the plug and play concept, which also makes a further enlargement of the system possible.

Adaptive SVM to compensate DC-link voltage ripple for four-switch three-phase voltage-source inverters

An adaptive space vector modulation (SVM) approach to compensate the DC-link voltage ripple in a B4 inverter is proposed and examined in detail. The theory, design, and performance of this pulsewidth modulation (PWM) method are presented, and the method effectiveness is demonstrated by extensive simulations and experiments. High-quality output currents are guaranteed by this approach even with substantial DC-voltage variations that might be caused by an unbalanced AC supply system, the diode rectification of the line voltages, and circulation of one output phase current through the split capacitor bank. The application of this approach to induction machine drives is also discussed. It is concluded that the DC-voltage ripple effect on the B4 inverter output can be minimized by an adaptive SVM algorithm with the advantage of improving the response of the DC-link filter and the output quality of the inverter becoming high.

On the energy optimized control of standard and high-efficiency induction motors in CT and HVAC applications

This paper contains an analysis of how the choice of energy optimal control of induction motors is influenced by motor construction, standard versus high-efficiency motor, and by application, constant torque (CT) and heating, ventilation, and air conditioning (HVAC) (interpreted as vector and scalar motor drives). The analysis is made with a 2.2 kW voltage-source-inverter-fed squirrel-cage motor drive as an example throughout the paper, but through statistics on the use of motors and their efficiencies, the conclusions are widened to a broader range (0-50 kW). Energy optimal control strategies are reviewed and cos(/spl thetav/) control, a model-based control, and a search control are implemented in the laboratory in a vector and a scalar motor drive. The convergence speed for the strategies and their ability to reject disturbances are investigated by experiments. It is also shown experimentally that, for both standard and high-efficiency motors, motor energy-efficiency improvement is achievable by energy optimal control below 60% load torque. The energy savings using energy optimal control strategies are measured on a pump system with a certain load cycle. Model-based control is recommended for CT applications and cos(/spl thetav/) control for HVAC applications.

Multilevel inverter by cascading industrial VSI

In this paper, the modularity concept applied to medium-voltage adjustable speed drives is addressed. First, the single-phase cascaded voltage-source inverter that uses series connection of insulated gate bipolar transistor (IGBT) H-bridge modules with isolated DC buses is presented. Next, a novel three-phase cascaded voltage-source inverter that uses three IGBT triphase inverter modules along with an output transformer to obtain a 3-p.u. multilevel output voltage is introduced. The system yields in high-quality multistep voltage with up to four levels and low dv/dt, balanced operation of the inverter modules, each supplying a third of the motor rated kVA. The concept of using cascaded inverters is further extended to a new modular motor-modular inverter system where the motor winding connections are reconnected into several three-phase groups, either six-lead or 12-lead connection according to the voltage level, each powered by a standard triphase IGBT inverter module. Thus, a high fault tolerance is being achieved and the output transformer requirement is eliminated. A staggered space-vector modulation technique applicable to three-phase cascaded voltage-source inverter topologies is also demonstrated. Both computer simulations and experimental tests demonstrate the feasibility of the systems.

New protection issues of a matrix converter: design considerations for adjustable-speed drives

Induction motors are traditionally controlled by standard pulsewidth modulation voltage-source inverters. An alternative is the matrix converter, which consists of nine bidirectional switches. This converter has benefits compared to a standard inverter, like sinusoidal input current and bidirectional power flow. The main disadvantage is the lack of a bidirectional switch, because such a switch may be done by two transistors and two diodes. An important topic is protection of the matrix converter, and this paper proposes two new protection circuits for matrix converters with a reduced number of components. The number of protection diodes is reduced by six. Design expressions of the protection circuit are calculated and validated by simulation. The standard protection circuit and the new circuits are demonstrated by simulation to have the same performance. Experimental results on an 8 kVA matrix converter show the design expressions are correct. It is concluded that it is possible to reduce the necessary power components in a matrix converter.

Space vector modulated matrix converter with minimized number of switchings and a feedforward compensation of input voltage unbalance

This paper presents a new double-sided modulation strategy for matrix power converters based upon an indirect conversion scheme which models the matrix converter as two independent stages performing rectification and inversion. The new modulation strategy keeps the number of switchings at a minimum. This paper shows that the indirect conversion scheme contains insufficient information to achieve the minimum. The new strategy establishes a link between the two modulations. Numerical simulations as well as analytical results show a reduction of more than 10% of the switchings compared to the conventional strategy. It is shown that the indirect conversion scheme is quite useful in the analysis of the input voltage unbalance. A feedforward compensation method based upon measurements of the instantaneous values of all three input voltages is presented. It is shown that, with a further restriction on the voltage transfer ratio, it is possible to operate the power converter with balanced output voltages, even when input voltages are unbalanced.