Theoretical Analysis and Control of DC Neutral-point Voltage Balance of Three-level Inverters in Active Power Filters

A novel carrier-based PWM (CBPWM) strategy of a three-level NPC converter is proposed in this paper. The novel strategy can eliminate the low-frequency neutral point (NP) voltage oscillation under the entire modulation index and full power factor. The basic principle of the novel strategy is introduced. The internal modulation wave relationship between the novel CBPWM strategy and traditional SPWM strategy is also studied. All 64 modulation wave solutions of the CBPWM strategy are derived. Furthermore, the proposed CBPWM strategy is compared with traditional SPWM strategy regarding the output phase voltage THD characteristics, DC voltage utilization ratio, and device switching losses. Comparison results show that the proposed strategy does not cause NP voltage oscillation. As a result, no low-frequency harmonics occur on output line-to-line voltage and phase current. The novel strategy also has higher DC voltage utilization ratio (15.47% higher than that of SPWM strategy), whereas it causes larger device switching losses (4/3 times of SPWM strategy). The effectiveness of the proposed modulation strategy is verified by simulation and experiment results.

Section: Modulation Wave Relationship Between the Novel Strategy mentioning

confidence: 99%

“…In Section II, the expressions of modulation wave of the novel strategy have been deduced. The final problem is to find available solutions to k shown in Equation (10). An infinite number of solutions can generally be found.…”

Section: Modulation Wave Solutions Of the Novel Pwm Strategymentioning

confidence: 99%

Novel Carrier-Based PWM Strategy of a Three-Level NPC Voltage Source Converter without Low-Frequency Voltage Oscillation in the Neutral Point

Li¹,

Wang

Liu

et al. 2014

“…An optimized modulation strategy that balances the neutral-point voltage is proposed in [5], [6], [23], which modifies the dwell time of the positive and negative small vectors by correctly selecting other vectors. Those do not have an impact on the neutral-point voltage when they the small vectors.…”

Section: Introductionmentioning

confidence: 99%

A Neutral-Point Voltage Balance Controller for the Equivalent SVPWM Strategy of NPC Three-Level Inverters

Lyu¹,

Hu²,

Wu³

et al. 2016

Based on the space vector pulse width modulation (SVPWM) theory, this paper realizes an easier SVPWM strategy, which is equivalently implemented by CBSPWM with zero-sequence voltage injection. The traditional SVPWM strategy has no effect on controlling the neutral-point voltage balance. In order to solve the neutral-point voltage unbalance problem for neutral-point-clamped (NPC) three-level inverters, this paper proposes a neutral-point voltage balance controller. The proposed controller realizes controlling the neutral-point voltage balance by dynamically calculating the offset superimposed to the three-phase modulation waves of an equivalent SVPWM strategy. Compared with the traditional SVPWM strategy, the proposed neutral-point voltage balance controller has a strong ability to balance the neutral-point voltage, has good steady-state performance, improves the output waveforms quality and is easy for digital implementation. An experiment has been carried out on a NPC three-level inverter prototype based on a digital signal processor-complex programmable logic device (DSP-CPLD). The obtained experimental results verify the effectiveness of the proposed neutral-point voltage balance controller.

“…Due to the wide application of power electronic loads such as switching mode power supplies, light controllers, interruptible power supplies, electric furnaces, ac voltage regulators and adjustable speed drives, a large amount of harmonic current or voltage is produced and reflected into distribution and transmission networks, which degrades the power quality [1], [2]. In order to mitigate harmonics, different configurations of active and passive filters have been proposed for different applications.…”

Section: Introductionmentioning

confidence: 99%

Control Strategy and Characteristic Analysis of Hybrid Active Power Filters with the Resonant Impedance Principle

Xu¹,

Luo²,

Li³

et al. 2012

A new kind of resonant impedance type hybrid active filter (RITHAF) is proposed for dynamic harmonic current suppression and high capacity reactive compensation in medium and high voltage systems. This paper analyzed the different performance of the RITHAF when the active part of the RITHAF is controlled as a current source and as a voltage source, respectively. The harmonic suppression function is defined in this paper. The influences of the changes caused by the grid impedance and the detuning of the passive power filter on the compensating characteristics of the RITHAF are studied by analyzing the suppression function. Simulation and industrial application results show that the RITHAF has excellent performances in harmonic suppression and reactive compensation, which is suitable for medium and high voltage systems.