R. Mienski

A Power-Quality Management Algorithm for Low-Voltage Grids With Distributed Resources

As a result of many factors, including the European Unions aim to increase the share of electrical energy from renewable sources, the number of distributed-generation (DG) devices in Europe is significantly increasing. Increasing numbers of DG units may cause problems with power quality (PQ). In this paper, a PQ-management algorithm is presented that reduces or even solves this problem in low-voltage grids. This algorithm will be implemented as one of several software modules in a system for distributed power operation and PQ management in low-voltage grids. PQ management in this context means maintaining PQ within prescribed limits by optimizing the control of generators, storage units, and controllable loads. Significant advantages of the presented approach are that the algorithm is universal and that it adapts its control variables automatically. Therefore, a detailed analysis of the grid in advance is not necessary. Furthermore, local PQ control of distributed resources can work autonomously and continuously without triggering by external signals, which is advantageous in the case of loss of communications. Various simulations to validate the effectiveness and stable operation of the algorithm were performed and results presented that show a marked improvement in PQ.

Application of DSTATCOM compensators for mitigation of power quality disturbances in low voltage grid with distributed generation

The paper presents capabilities of DSTATCOM systems used to improve power quality (PQ) in low voltage (LV) grids with distributed energy resources (DERs). For the case study a typical rural network has been selected in which, on one hand DER installing is the most probable and on the other hand, integration process may cause the biggest problems. Selected single-phase DERs of varying power are connected into the network which introduce PQ disturbances such as voltage variations, harmonics and asymmetry. To mitigate deviations in power quality DSTATCOM compensator operating in current control mode has been applied. Models of the network together with the selected DERs and compensator system have been developed in the PSCAD/EMTDC environment. Simulation has been performed for the analysis of the network performance and the assessment of compensation effectiveness. The possibility of using the DSTATCOM operating in voltage control mode for reducing voltage dips coming from the supplying network has also been studied. Control circuits have been designed for these two modes of operation. Description of the study network, their element models and some selected results of simulation are presented in the paper.

Study on operation of energy storage in electrical power microgrid - Modeling and simulation

In the paper the application of energy storage for enhancing distributed energy sources penetration and contributing to better quality of energy delivery to customers was investigated. A simulation method was used to study the effectiveness of complex control algorithms of energy storage system enabling load leveling and simultaneous voltage stabilization effect in grid-connected microsystem. The energy storage ability of grid forming and local power balancing after transition to island operation of the microgrid has also been examined.

Energy management system as a mean for the integration of distributed energy sources with low voltage network

The paper concerns energy management in low voltage grid-connected microgrid integrating renewable and controllable energy sources, loads and storage systems. The central control system is presented which optimize the microgrid operation by minimizing the costs of energy in the time horizon. The system determines set-points for controllable sources and storage units. In formulating the objective function constraints regarding the network capacity are taken into account, i.e. voltage limits in the network nodes and load carrying capacity limits of lines and the supplying transformer. The management system enables the integration of energy sources into existing networks without re-designing the network itself and microgrid operation at minimum costs.

Voltage dip compensation in LV networks using distributed energy resources

The paper presents possibilities of using distributed generation (DG) sources to mitigate voltage dips in LV grids due to short circuits in the MV and HV network. DG sources based on voltage source inverters (VSI) with pulse width modulation (PWM) control were considered. The DG sources generate active power depending on the depth of voltage dips under faults conditions. The compensation effect is shown for different DG source capabilities and different coupling between the LV and MV networks, i.e. the short circuit power of the distribution transformer. The PSCADIEMTDC programme was used for analysis of system performance. Results of simulation for a study network are presented, which show the effectiveness of compensation.

Application of STATCOM controllers for power quality improvement - modeling and simulation

The paper deals with compensation of frequently time-varying loads by means of STATCOM controllers. As a varying load an arc furnace is considered. The 12-pulse STATCOM system was used for compensation to ensure good power quality in the point of common coupling. For analysis of the system performance the PSCAD/EMTPDC programme was applied. Models of the load and STATCOM controller useful for simulation are discussed. A PSCAD model of measurement blocks is also proposed for power quality assessment. Some results of simulation are presented in the paper, which show the effectiveness of compensation.

A simulation method for estimating supply voltage dips in electrical power networks

This paper describes the probabilistic approach for estimating voltage dips in electrical power networks. A method has been worked out which can estimate the typical magnitude and frequency of voltage dips, as well as momentary interruptions that may be expected at a given site. Evaluating such characteristics of voltage dips allows assessing compatibility between loads and the supply network. This methodology has been used to draw up a simulation tool by means of the LABVIEW program. The paper presents the results of simulation performed for a given electrical transmission and distribution network and discusses them.

Using energy storage for energy management and load compensation in LV microgrids

In the paper the application of energy storage for both energy management and ancillary services is investigated. A control algorithm is presented enabling storage unit to control active power and compensate current harmonics, unbalance and reactive power introduced to the network by disturbing loads. Thus, the storage unit participates in energy management according to the defined strategy and additionally contributes to power quality improvement. Effectiveness of compensation is examined by means of the simulation model of low voltage (LV) test microgrid. The results of real tests performed in the test microgrid in the laboratory of Distributed Generation of the Technical University of Lodz are also presented.

Power quality improvement in LV networks using distributed generation

The paper presents how power quality (PQ) can be improved in LV networks with distributed generation by using certain aspects of the sources, i.e. inverters and advanced controllers. This is demonstrated through simulation with PSCAD/EMTDC. PSCAD models of the loads, distributed sources and controllers are discussed. A model of measurement blocks is also proposed for power quality assessment. Some results of simulation are presented, which show the effectiveness of compensation.

Control algorithm for the 12-pulse SVC

A method is presented which became a basis for designing a control algorithm for the 12-pulse SVC system. The algorithm enables balancing of currents and powers drawn from the supplying network by unbalanced and time-varying load devices and at the same time effects in reduction supplying voltage fluctuations. The results of simulation are shown which illustrate the compensation effect and verifies correctness of the proposed algorithm.