Current Regulated Voltage Source Inverter Research Articles

Precompensator for Disturbance Signal Elimination in Single-Phase Inverters With Virtual Vector Control

In virtual vector control schemes for single-phase current-regulated voltage source inverters, many methods are proposed to generate a virtual orthogonal feedback current from the real feedback current. However, the generation stage causes mismatch between feedback and command currents, which may deteriorate dynamic current-tracking capability and power quality. A precise scalar model is developed to analyze the phenomenon. Based on this model, the mismatch is presented as a current disturbance signal introduced into the control loop. The mathematical analysis establishes that the current disturbance cannot be eliminated by any orthogonal signal generation (OSG) method. To solve the problem, a current precompensator is mooted. In this paper, the effect of the current precompensator is studied in detail. Furthermore, a voltage precompensator is proposed, which better suits OSG methods than the current precompensator. Experimental results of both the current and voltage precompensator are compared with the conventional solution to substantiate enhanced dynamic performance.

Line-interactive Uninterruptible Power Supply System Eliminating the Inrush Current Phenomenon

Numerous critical load applications rely upon a line-interactive uninterruptible power supply system to maintain power during outages as well as during under- and over-voltage utility conditions. When any disturbance occurs at the utility side, the line-interactive uninterruptible power supply system takes over the load within a few milliseconds to avoid interruption. However, during this transition of load, a significant inrush current occurs due to the magnetic saturation of the load transformer. The inrush current phenomenon causes reduced line voltages and sometimes activates the over-current protection of the uninterruptible power supply system. This article proposes a new line-interactive uninterruptible power supply system that eliminates the inrush current phenomenon by connecting a standard current-regulated voltage source inverter to the secondary of the load transformer. During any transient condition at the utility side, the load current is monitored and regulated to achieve a seamless compensation or transition of load. Experimental results are obtained for a prototype during a number of possible irregular utility power conditions to endorse the performance of the proposed uninterruptible power supply system.

A Cost-Effective, Single-Phase Line-Interactive UPS System that Eliminates Inrush Current Phenomenon for Transformer-Coupled Loads

Sudden voltage drops and outages frequently disturb the operation of sensitive loads for domestic, commercial, and industrial use. In some cases, these events may even impair the functioning of relevant equipment. To maintain power under such conditions, a UPS system is usually installed. Once a disturbance happens at the grid side, the line-interactive UPS system takes over the load to prevent an interruption. But, due to magnetic saturation of the transformer, a significant inrush current may occur for the transformer-coupled loads during this transition. The generation of such transient currents may in turn decrease the line voltage and activates over-current protecting devices of the system. In this work, a cost-effective, line-interactive UPS system is proposed that eliminates the inrush current phenomenon associated with transformer-coupled loads. The strategy was implemented by connecting a standard current-regulated voltage source inverter (CRVSI) to the secondary winding of the load transformer. During any transient condition at the grid side, the load current is monitored and regulated to achieve either seamless compensation of the load current or complete transferal of load from grid to the inverter. Experimental results were obtained for a prototype under all possible operating conditions so as to validate the performance of the proposed topology.

Experimental verification of winding switching technique to enhance maximum speed operation of surface mounted permanent magnet machines

Flux weakening is an inevitable requirement in the operation of variable speed permanent magnet (PM) machines for high-speed applications due to inverter voltage limits. A new winding switching technique is experimentally validated in this study that can extend the speed range of such PM machines. A drive topology is proposed that utilises two current regulated voltage source inverters to control the machine in a dual inverter fed configuration before transitioning into an open winding configuration after winding switching. The proposed drive topology extends the constant torque region of the machine and boosts its maximum output power capability. Complete experimental results are provided to demonstrate the effectiveness of the proposed machine drive system for continuous operation over the entire speed range.

Virtual Admittance Loop for Voltage Harmonic Compensation in Microgrids

The use of the virtual admittance concept for harmonic and/or unbalance compensation in microgrids when multiple inverters operate in parallel is proposed in this paper. The virtual impedance concept has been traditionally used for these purposes. However, one drawback of the virtual impedance is that it can only be applied to distributed generation (DG) units operating in voltage control mode (VSI-VCM), but is not applicable to DG units working in current control mode (e.g., current-regulated voltage-source inverters, VSI-CCM). Contrary to this, the proposed method can be used in any converter topology and control mode, including VSI-CCM and VSI-VCM.

Asymmetrical Fault Correction for the Sensitive Loads Using a Current Regulated Voltage Source Inverter

Numerous industrial applications involve loads that are very sensitive to electrical supply instabilities. These instances involve various types of voltage imbalances as well as more serious disturbances such as symmetrical and asymmetrical faults. This paper proposes a cost-effective voltage imbalance and asymmetrical fault correction solution for the three phase sensitive loads utilizing an industry-standard current regulated voltage source inverter by connecting it in parallel to the grid mains powering to the sensitive load. The inverter regulates the current for the load and never permits it to go beyond a prescribed value under any type of asymmetrical fault condition, which ensures high power regulating and conditioning capacities. Experimental results are obtained from a small laboratory size prototype to validate the operation of the proposed technique.

Frequency-domain analysis of three-phase linear current regulators

Stationary frame proportional plus integral (PI) current-regulated voltage-source inverters are conventionally regarded as unsatisfactory for AC systems because they cannot eliminate steady-state errors. This paper presents a technique for interpreting the stationary/rotating frame transformations as modulation processes in the Laplace domain, which move the control function from one part of the frequency spectrum to another. The technique is used to compare stationary and synchronous frame PI regulators on a common basis to better understand the advantages of a synchronous frame regulator. A new form of stationary frame resonant regulator is then derived which achieves zero steady-state error without requiring the complex transformations of a synchronous frame regulator. The performance of this new regulator is evaluated and found to be similar to that of the synchronous frame PI regulator.