[Show abstract][Hide abstract] ABSTRACT: The conventional back-to-back PWM converter, with lots of benefits over diode rectifier AC/DC/AC converter, do not have the advantage of efficiency. The proposed converter with novel topology remove the DC-link capacitor from inverter side of converter, decreasing the switching loss of inverter by synchronous operation between rectifier and inverter . The principle of operation and specified designed scheme for proposed topology is investigated, the loss comparison between conventional and proposed topology shows the advantage of proposed topology.
[Show abstract][Hide abstract] ABSTRACT: Cascaded H-bridge multilevel inverter has been receiving wide attention mainly due to its capability of high voltage operation without switching devices connected in series. In real applications, one or more cell may fail and the output voltage is unbalanced, causing damaging results to load. In this paper, three control schemes including NS 1 and NS 2 based on neutral shift (NS) with delta injection and space vector (SV) PWM way, are compared in terms of the output line-to-line voltages THDs and their difference ratio. The reason of the difference is given for the first time, which has not been fully understood before. Based on this, a modified SV method is proposed. The theoretical results are also given, which shows that the NS has better performance than SV in theory. However, NS 1 and NS 2 are only approximately way to implement NS and they cannot achieve the best performance of NS, while modified SV has much better performance in terms of voltage difference ratio, which plays the most important role in a system with faulty cells. Simulation and experimental results are given to verify the algorithm.
[Show abstract][Hide abstract] ABSTRACT: This paper presents a new topology of a three phase rectifier operating in the discontinuous conduction mode (DCM). It is based on the buck-boost converter and has the step-up and step-down characteristics of output voltage. The rectifier draws sinusoidal ac current from ac line with unity power factor, and needs only one switch and constant duty cycle of PWM control. The dynamic and steady equations of converter are analyzed. The results of the theoretical analysis are verified by digital simulation and the experiment results of laboratory prototype.
[Show abstract][Hide abstract] ABSTRACT: All switching converter topologies, operating from a grounded utility system and feeding a floating output system, create common mode voltages that are present on the load equipment. This paper develops a systematic analysis on the common mode voltage in various converter topologies typically used in AC drives, including two-level VSI (voltage source inverter), CSI (current source inverter) and multilevel inverters. The active front end rectifier used with each topology is also included in the analysis. The sources of common mode voltage are analyzed and the magnitudes of common mode voltages generated by different converter topologies are compared. The practical consequences of the common mode voltage and mitigation techniques are discussed. Simulation and experimental results are provided for verification.
[Show abstract][Hide abstract] ABSTRACT: Cascaded H-bridge inverters have been selected as one of the preferred power converter topologies for high-voltage, high-power applications. However, undesired oscillations could occur in the H-bridge inverter drive system particularly under light load conditions, which would cause high voltage or current stress on the motor and inverter. In this paper, the mechanism of the oscillations is analyzed and a novel mitigation method is proposed. The mitigation involves a simple inverter output voltage adjustment in the space vector PWM control in real time, such that the oscillation loop would be broken, leading to effective suppression of the oscillations. The proposed method features simple algorithm and easy implementation requiring only one voltage measurement per phase for any level H-bridge inverter. Simulation and experimental results are provided to demonstrate the efficiency of the method.
[Show abstract][Hide abstract] ABSTRACT: To solve the problem of computational complexity in multilevel inverters due to the large number of space vectors and redundant switching states, a simple and general space vector PWM algorithm is proposed. Based on this algorithm, the location of the reference voltage vector can be easily determined and the calculation of dwell times becomes very simple. More importantly, the proposed algorithm is general and can be directly applied to the cascaded H-bridge inverter of any voltage levels. In addition, a new switching sequence, large-small alternation (LSA), is proposed for the minimization of total harmonic distortion. To verify the algorithms, a 7-level cascaded H-bridge inverter drive system was constructed and experimental results are provided.
[Show abstract][Hide abstract] ABSTRACT: To increase the fault tolerance for cascaded H-bridge multilevel inverters, a novel control algorithm is proposed for the inverter operating under faulty conditions. The influence of various faults on space vectors is investigated and the maximum achievable output voltage of the inverter with faulty power cells is derived. Making use of the redundant switching states, the proposed algorithm is able to produce a three-phase balanced line-to-line voltage with minimum harmonic distortion for the inverter with disabled power cells. In addition, the control algorithm is suitable for use in the cascaded H-bridge inverters of any voltage levels. Simulation and experimental results are provided for verification.