Traditional Three-phase Inverter Research Articles

A Three-Phase Five-Level Inverter With High DC Voltage Utilization and Self-Balancing Capacity of Floating Capacitor

Multilevel inverter are popular solutions in photovoltaic power station, wind farm, and other renewable energy generation. This article presents a three-phase five-level inverter with high dc voltage utilization. A significant feature of the inverter is that its maximum dc voltage utilization is twice that of the traditional three-phase inverters such as neutral point clamped, flying capacitor (FC), cascaded H-bridge, and active NPC. What is more, the inverter can realize the self-starting and self-balancing of the FC, and the self-balancing of the dc-link capacitors, so the complex FC voltage balancing strategy and bus midpoint voltage control method are not needed anymore. The voltage and current stresses analysis and the design guidelines of components are discussed in detail. A comparison with some existing topologies has also been made to highlight its performance. Taking one phase as an example, both the simulations and experiments are carried out to verify the validity of the proposed inverter and modulation strategy.

Predictive-Pulse-Injection-Based Dual-Inverter Complementary Sensorless Drive for 12/10 DC Vernier Reluctance Machine

A dc-excited Vernier reluctance machine (DC-VRM) using a 12-slot/10-pole-pair design exhibits the advantages of small torque ripple and a robust structure, which has good potential to be applied as an aerospace integrated starter/generator. By eliminating vulnerable position sensors, system reliability can be further improved by sensorless startup. However, driven by the traditional three-phase inverter, the phase inductance of the 12/10 DC-VRM becomes constant due to its complementary characteristic, which means the saliency effect in DC-VRM is obliterated, and thereby a sensorless operation using self-inductance detection cannot be applied. To release the machine saliency effect and further improve sensorless drive performance, a dual-inverter sensorless drive structure is introduced to reconstruct the machine saliency by using separated dual three-phase inverters. The released series inductance model with mutual inductance coupling is established through a piecewise function, and an accurate position estimation method without finite-element analysis or complex measurements is introduced. Moreover, by further analyzing the linearity of series inductance, the full-cycle inductance high-linearity range is composed of dual-inverter complementary features, and thus position estimation accuracy can be guaranteed. Through this feature, a predictive-position-based pulse injection sensorless drive method is proposed to improve acceleration performance with detection time reduction. Based on the predictive position, the detection pulses are only injected into one inverter whose corresponding phases are located at the inductance high-linearity range, thus decreasing the detection time and improving acceleration performance.

Reconstructing Saliency Effect in 12/10 DC Vernier Reluctance Machine for Position-Sensorless Drive Aerospace Starter Generator Application

DC-Excited vernier reluctance machine (DC-VRM) using a 12-slot/10-pole-pair design, exhibits the advantages of small torque ripple and low cogging torque due to the inherent commentary characteristic. However, the inherent saliency is canceled out by a 12/10 pole combination of machine design driven by a traditional three-phase inverter. As a result, the sensorless operation in zero/low-speed regions becomes difficult because the position estimation methods using self-inductance detection cannot be applied. To tackle this problem, we first analyzed the saliency annihilation phenomenon through Fourier analysis that the odd-order harmonics in self-inductance are canceled. Moreover, reconstructing saliency method is proposed by splitting a phase winding into two sub-phase coils and using parallel H-bridge converters to supply sub-phase coils and achieve sensorless drive. Through this method, the saliency effect is recovered in self-inductance, thereby pulse injection sensorless drive can be applied. The constructed 12/10 DC-VRM sensorless drive shows good fault-tolerant ability and can be applied in safety-critical industry applications such as aerospace propulsion. Analysis and experiments are performed in the initial position detection, start-up and free-running stages to verify the feasibility of the proposed solution. A sector estimation accurate to 6° can be achieved.

Comparative analysis of leakage current suppression capability of forward‐clamped and reverse‐clamped H10 three‐phase inverters

Non-isolated inverters have the disadvantage of large leakage current, which will damage the equipment and personal safety. In order to solve this problem, this paper proposes two H10 three-phase inverter topologies named forward-clamped and reverse-clamped H10 inverters. Each of the topologies is composed of two DC bus switches, a clamping circuit and a traditional three-phase inverter, but the clamping method of these two topologies is different. A general control strategy combining carrier modulation and logic operation for these two topologies are proposed. The control strategy allows the common-mode voltage of these two topologies to vary between one third and two thirds of the DC bus voltage, but the frequency of the common-mode voltage of the reverse-clamped inverter is three times that of the forward-clamped inverter. The loop impedance of the reverse-clamped inverter increases significantly at high frequency, so the leakage current suppression capability is better. Simulation and experiment platforms of the inverter systems are built. The obtained results verify the correctness of the theoretical analysis.

Non-isolated H10 three-phase inverter for leakage current suppression

In recent years, an increasing amount of attention has been paid to non-isolated photovoltaic power generation systems, where leakage current suppression is one of the key issues to be addressed. In view of this problem, this paper proposes a novel ten-switch three-phase circuit that is referred to as an H10 inverter. This circuit is obtained by adding two isolating switches and a clamping circuit to the traditional three-phase inverter (H6 inverter). The working principle of the proposed system is analyzed. On the basis of the logic relationship between the common-mode voltage (CMV) and the switching states, a control strategy combining carrier modulation and logic operation is proposed. With this proposed control strategy, the H10 inverter can effectively reduce the variation of the CMV and improve the leakage current suppression. Finally, simulation and experimental platforms are built for the inverter system, and the obtained results are compared with those of a traditional three-phase inverter to verify the correctness of the theoretical analysis.

A new hybrid multilevel converter for DFIG-based wind turbines fault ride-through and transient stability enhancement

The increasing participation of wind turbines based on doubly fed induction generator (DFIG) in the power system around the world is motivating the investigation of novel strategies to enhance the reliability of DFIG and power system connection. This paper proposes the use of a new hybrid multilevel back-to-back converter on DFIG wind turbine to improve its fault ride-through capability and power system transient stability. The proposed topology is built adding single-phase full-bridge inverters in series with each phase of traditional three-phase inverter. This converter is able to generate higher voltages in rotor circuit whenever it is required, which can effectively protect power converter and at the same time contribute with grid transient performance. Simulation results, using PSCAD®, are presented for a 2 MW DFIG machine submitted to symmetrical faults in single machine—infinite bus and three-bus system. Results show that the proposal is effective as a protection and works well as an alternative to traditional solutions, limiting currents and maintaining power control during voltage dips. It is also effective in contribution with the improvement of transient stability margin by the possibility of reactive power injection.

A Three-Phase Constant Common-Mode Voltage Inverter With Triple Voltage Boost for Transformerless Photovoltaic System

This paper introduces a new three-phase two-level inverter based on the switched-capacitor voltage multiplier. By adding a voltage multiplier network at the DC side of the traditional three-phase inverter topology, the DC-link voltage of the introduced inverter is stepped up to triple of the input voltage. Compared to the existing solutions, the common-mode voltage of the introduced topology is kept constant. Moreover, the voltage stress across additional semiconductor components is the same as one-third of DC-link voltage. Operating principles, mathematical analysis, circuit analysis, and pulse-width modulation (PWM) method based on the Boolean logic function for introduced inverter are presented. A comparison of the introduced inverter with other inverter topologies is also reported. The simulation results are shown to verify the introduced three-phase triple voltage boost inverter. Besides that, a laboratory-built prototype is developed based on a DSP F280049C microcontroller and the corresponding experimental tests are provided to prove the introduced inverter.

Admittance Reshaping Control Methods to Mitigate the Interactions between Inverters and Grid

With the increasing impedance coupling between inverters and grid caused by the phase-locked loop (PLL), traditional three-phase inverters suffer from the harmonic distortion or instability problems under weak grid conditions. Therefore, the admittance reshaping control methods are proposed to mitigate the interactions between inverters and grid. Firstly, a dynamics model of traditional inverter output admittance including main circuit and PLL is developed in the direct-quadrature (dq) frame. And the qq channel impedance of the inverter presents as a negative incremental resistance with the PLL effect. Secondly, two admittance reshaping control methods are proposed to improve the system damping. The first reshaping technique uses the feedforward point of common coupling (PCC) voltage to modify the inverter output admittance. The second reshaping technique adopts the active damping controller to reconstruct the PLL equivalent admittance. The proposed control methods not only increase the system phase margin, but also ensure the system dynamic response speed. And the total harmonic distortion of steady-state grid-connected current is reduced to less than 2%. Furthermore, a specific design method of control parameters is depicted. Finally, experimental results are provided to prove the validity of the proposed control methods.

Scheme based on buck‐converter with three‐phase H‐bridge combinations for high‐speed BLDC motors in aerospace applications

High reliability and safety are critical in aerospace applications. This study introduces a novel high-reliable inverter scheme based on buck-converter with three-phase H-bridge combinations and a high-accurate commutation instant shift correction method for high-speed brushless direct current (BLDC) motors. First, the traditional three-phase inverter and buck-converter-based BLDC motor drive system are analysed. Second, the zero-crossing points of back-electromotive force detection circuit are designed and the position detection error is analysed. Third, a speed measurement with enhanced detection frequency and accuracy is proposed. Then, a fast two-stage commutation instant shift compensation method is designed based on the unique speed measurement method. High-reliable and accurate commutations are achieved especially in the high-speed steady state, which improves the speed control precision and decreases the motor driving loss. Finally, the control system design process is proposed and a fault-tolerant-control strategy is presented to enhance the reliability of the system. Experimental results illustrate the effectiveness and practicability of the proposed inverter scheme and the position sensorless control method.

The Control System Method Design for the Three-Phase Inverter Parallel Using CANOpen Protocol

This paper proposed a new control system design scheme for three-phase inverter parallel. The scheme combined the distribute logic control method and the droop control method, which has been got from the talk about the traditional three-phase inverter parallel methods. The control system is based on TMS320F2812 DSP, and the interface implementation method is presented. As the data exchange method between the inverters, the communication protocol for this system based on CANopen protocol has been given and the parameters for communication map and object dictionary is also given. The method proposed in this paper has been used in the lab, and the successful use has proved that this method can meet the requirements for the processing speed, communication speed, and flexibility of three-phase inverter parallel control system.

Cascaded H-bridge inverter motor drives for hybrid electric vehicle applications

This paper presents the asymmetric cascaded H-bridge multilevel inverter for electric vehicles (EV) and hybrid electric vehicles (HEV) applications. Currently available power inverter systems for HEVs use a DC-DC boost converter to boost the battery voltage for a traditional three-phase inverter. The present HEV drive inverters have low power density, are expensive, and have low efficiency because they need a bulky inductor. Asymmetric cascaded H-bridge multilevel inverter design for EV and HEV applications without the use of inductors to output a boosted AC voltage is proposed in this paper. Traditionally, each H-bridge needs a DC power supply having equal values of DC power sources. The proposed design uses the asymmetric cascaded multilevel inverter using non-equal DC power sources based on specified ratios. A fundamental switching scheme is used to do modulation control and to produce a seven-level phase voltage.

DC–AC Cascaded H-Bridge Multilevel Boost Inverter With No Inductors for Electric/Hybrid Electric Vehicle Applications

This paper presents a cascaded H-bridge multilevel boost inverter for electric vehicle (EV) and hybrid EV (HEV) applications implemented without the use of inductors. Currently available power inverter systems for HEVs use a dc-dc boost converter to boost the battery voltage for a traditional three-phase inverter. The present HEV traction drive inverters have low power density, are expensive, and have low efficiency because they need a bulky inductor. A cascaded H-bridge multilevel boost inverter design for EV and HEV applications implemented without the use of inductors is proposed in this paper. Traditionally, each H-bridge needs a dc power supply. The proposed design uses a standard three-leg inverter (one leg for each phase) and an H-bridge in series with each inverter leg which uses a capacitor as the dc power source. A fundamental switching scheme is used to do modulation control and to produce a five-level phase voltage. Experiments show that the proposed dc-ac cascaded H-bridge multilevel boost inverter can output a boosted ac voltage without the use of inductors.

Elimination of common-mode voltage in three-phase sinusoidal power converters

This paper presents an active solution to a common-mode voltage created by typical three-phase inverters. It is shown that the addition of a fourth leg to the bridge of a three-phase inverter eliminates the common-mode voltage to ground created by the modulation of the inverter. An appropriate four-phase LC filter is inserted between the inverter and the load in order to create sinusoidal output line-to-line voltage. A simple modification of the modulation strategy is implemented for the four-phase inverter to achieve a three-phase wye-output neutral-to-ground voltage which is equal to zero at all times for an ideal inverter. The modulation strategy thereby completely eliminates the common-mode potential produced by traditional modulation techniques with traditional three-phase inverter topologies.