Associate Professor Terrence Summers

The control of Cascaded H-Bridge (CHB) photovoltaic (PV) systems typically requires the power generated by the PV arrays to be measured. The power measurement is used to generate the reference current to inject power into the grid as well as for Maximum Power Point Tracking (MPPT). The number of current sensors required for high level number systems increases their cost and complexity. Power estimation can be used to eliminate current sensor requirements by inferring the PV power from other measurements. This paper presents a power estimation method for a CHB PV system with a Model Predictive Control (MPC) scheme. The performance is shown to be comparable to measurement via simulation results.

During a fault on the power grid, earthing systems operate to contain the energy keeping people and equipment safe. Unfortunately, these systems can fail and create hazards when the resistance is too high, as a result of improper design, installation or maintenance. Regular on-site testing of earthing grids is essential to prevent these situations. The most commonly used method to test earthing grids is accurate and reliable, but only for installations with low background noise, a limited number of feeders and a low system impedance. These limitations have motivated research into improvements in testing equipment. A robust current controlled inverter is introduced for use in high noise earthing system tests. This equipment was tested on-site, demonstrating improvements in noise rejection and stability. These improvements had little impact on the accurate measurement of small test signals elsewhere in the test. For this aspect, a current measurement strategy involving destructive interference, filtering and phase locked loops is also proposed and implemented.

Multilevel Cascaded H-Bridge (CHB) converters have attractive features for the implementation of large scale photovoltaic systems. They can be directly connected to high voltages and the multilevel voltage synthesis reduces the harmonic distortion introduced. In addition, they have individual DC links ideal for connecting photovoltaic arrays. Existing high performance voltage balancing techniques can also be adapted to integrate Maximum Power Point Tracking (MPPT). This paper considers the impact of Perturb and Observe Maximum Power Point Tracking on the performance of a 19 level three phase CHB converter and proposes the new method of Phase Shifted Perturb and Observe Maximum Power Point Tracking.

The Modular Multilevel Converter (MMC) is a relatively new converter topology which has been favoured for high voltage DC transmission due to its performance, flexibility in control and its modular and scalable design which allow it to be used over a wide variety of system voltage levels and power ratings. The converter consists of a number of cascaded half bridge cells with isolated capacitors to make up an upper and lower arm in each phase. A control requirement of these converters is to maintain voltage balance between all capacitors in the converter. This paper proposes a new arm voltage balancing method to maintain capacitor voltage balance with largely varying arm powers while maintaining AC and DC output performance. The proposed technique is confirmed in computer simulation.

Multilevel Cascaded H-Bridge (CHB) converters have attractive features for the implementation of large scale photovoltaic systems. They can be directly connected to high voltages and the multilevel voltage synthesis reduces the harmonic distortion introduced. In addition, they have individual DC links ideal for connecting photovoltaic arrays. Existing high performance voltage balancing techniques can also be adapted to integrate Maximum Power Point Tracking (MPPT). However, MPPT schemes typically require a measurement of the generated photovoltaic power to operate, leading to a significant number of current sensors in a multilevel system. This paper considers a 19 level three-phase CHB converter photovoltaic power system without sensing the photovoltaic array current for MPPT. The converter control strategy is used to infer the information necessary for the MPPT algorithms to operate. Simulation results are presented to demonstrate the performance of the proposed implementation of MPPT.

Cascaded H-Bridge (CHB) multilevel converters provide a number of attractive features for photovoltaic (PV) power systems. They have high quality output waveforms, high efficiency and the ability to incorporate multiple Maximum Power Point Tracking (MPPT) schemes. This paper investigates the ability of the CHB PV system to export maximum power for different configurations of PV arrays among the H-Bridges. It is shown that there is a minimum number of H-Bridges required to have PV arrays to ensure the maximum power is extracted without reactive power compensation. Reactive power must be injected or absorbed to extract maximum power when the minimum number is not reached. Simulation and experimental results are presented to validate the investigation.

Multilevel Cascaded H-Bridge (CHB) converters have attractive features for the implementation of large scale photovoltaic systems. They can be directly connected to high voltages and the multilevel voltage synthesis reduces the harmonic distortion introduced. In addition, they have individual DC links ideal for connecting photovoltaic arrays. Existing high performance voltage balancing techniques can also be adapted to integrate Maximum Power Point Tracking (MPPT). This paper considers a 19 level three-phase CHB converter with photovoltaic arrays supplying power. The structure and control of the system is presented, which shows that the DC link voltages can be individually controlled according to MPPT demands, negating the need for DC/DC converters. The system also maintains balanced output currents for power transfer to the grid. Simulation and experimental results are presented that validate the operation of the system.

Voltage and current harmonics can have various deleterious effects on the entire power system, from residential households to power utilities. The onus to correct these harmonic problems lies dually with the end user and the power utilities. Active harmonic filters (AHFs) are one solution that can ensure the supply of clean power to end users in a distributed system. Research into AHFs has become an area of growing interest in the recent years. This is due to the increased use of non-linear loads, coupled with greater demand for electricity in general. This paper outlines the development of simulations and low voltage modelling of a pure AHF. The filter is composed of a three-phase inverter direct-connected in shunt with the load and a microcontroller used to implement the control strategy. The control algorithm and filtering are performed in the dq rotating reference frame. This implementation attempts to improve the control scheme proposed by Akagi et al (2007a) for pure AHFs. The output stages ofAkagi's control scheme are replaced with a predictive current controller with space vector modulation. Simulation and experimental results are provided to support the findings of this paper. © Institution of Engineers Australia, 2009.