Search

Direct current (dc) voltage sensor in each cell of the cascaded H-bridge rectifier (CHBR) is traditionally indispensable for capacitor voltage balancing control. The cost of dc sensors will increase with the number of cells. This letter proposes a strategy for dc-voltage digital sampling based on sliding window recursive least square (RLS), which employs only one voltage sensor. Sliding window RLS is used to decouple voltage information within one sampling interval. For the actual situation where the modulation waves of cells are different, this method owns faster updating rate and higher detection precision compared to the existing multisampling method. A downscale test platform of the single-phase CHBR is built to verify the correctness and effectiveness of the proposed method. The result shows that better current quality and steadier dc voltage are achieved. [ABSTRACT FROM AUTHOR]

For N-cells cascaded H-bridge (CHB) inverters based on unipolar double frequency phase-shifted pulsewidth modulation (PS-PWM), the output voltage is distorted and its harmonics are difficult to be suppressed under unbalanced conditions (different dc voltages and/or modulation indices). This article proposes a closed-loop harmonic suppression scheme based on the PS-PWM, and the scheme is easily implemented in the dq frame to adaptively adjust the displacement angles of the triangular carriers. The harmonic content can be suppressed to its possible minimum value without the limitation of the operational point by the proposed method. The adjustment rules of displacement angles and the harmonic suppression principle are presented in detail. This method can effectively restrain harmonic magnitudes without the limitation of the cells number and does not require complicated trigonometric function calculations or optimization algorithms. Moreover, the principle of symmetrical sideband harmonic suppression is also discussed. The effectiveness of the proposed method is verified by a downscale test platform of the single-phase CHB inverter. [ABSTRACT FROM AUTHOR]

• The proposed space vector modulation (SVM) method for active power decoupling quasi-Z-source inverter (APD-qZSI) is easy to implement. • Compared with the SPWM, the proposed SVM method has smaller storage capacitance and a wider normal operation range. • The APD method under the proposed SVM method is effective for suppressing the 2ω ripple power and reducing the qZS inductance and capacitance. The double-line frequency ripple power of the single-phase quasi-Z source inverter (qZSI) will result in a large designed qZS impedance on the dc side, which can be greatly reduced by the coupled-type active power decoupling (APD) method. However, the traditional sinusoidal pulse width modulation (SPWM) for the APD-qZSI needs extravagant APD storage capacitance and may cause abnormal operation under low load conditions. Classical space vector modulation (SVM) has higher flexibility and dc-link voltage utilization, but it cannot be directly applied to the APD-qZSI. In this paper, a simplified SVM method for the coupled-type APD-qZSI is proposed, where the switching time sequence is transformed to carrier-based pulse width modulation, so the shoot-through control of the qZSI is easy to implement. Next, the passive component parameters and normal operation range of the traditional SPWM and the proposed SVM are analyzed and compared. The proposed SVM has a smaller APD storage capacitance but a slightly larger ac side filter inductance. In addition, the decreased current of the APD branch under SVM can help suppress the abnormal operation of the inverter, so the APD-qZSI can operate at a lower load condition. Finally, experimental results validate the effectiveness and superiority of the proposed SVM method. [ABSTRACT FROM AUTHOR]

This article proposes a multisampling method for single-phase grid-connected cascaded H-bridge (CHB) multilevel inverters with the phase-shifted carrier pulsewidth modulation in order to reduce the time delay involved in the control loop and increase the control bandwidth. In this method, the controlled variables are sampled not only at the peak and the valley of all triangular carriers, but also at the intersection points of all phase-shifted carriers and inverted ones, which enables a minimum unity sampling interval without detecting the current ripple caused by the switching action and breaking the voltage-second balance in the modulation process. The bandwidth of the current control loop based on the proposed sampling method is illustrated and compared to other traditional sampling methods. The analysis shows that the system effectively reduces the time delay involved in the control loop and improves the bandwidth of the control loop. Finally, a downscale test platform of the single-phase grid-connected CHB multilevel inverter with an inductance (L)-filter is built to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Providing a sinusoidal line current with few low-order harmonics is important for power converters. First, the influence mechanisms of multifactors for the line current distortion in single-phase three-level neutral point clamped converters are analyzed in theory. Second, the corresponding compensation methods for various factors are discussed, respectively. Particularly, the phenomenon that deadtime effects on harmonics is revealed by the theoretical derivation of Fourier series, and a corresponding quantitative calculation method is proposed and used to solve the compensation component of the deadtime delay. The detailed and strict mathematical deduction provides an alternative theoretical system for the quantitative analysis and compensation of deadtime and forward voltage drops effects. As for the component to compensate the unsteady forward voltage drops, it is online computation with current variations. Then, a comprehensive distortion compensation method by injecting offset voltage in the modulated signal is proposed to improve the line current waveform quality. Finally, simulation results verify the correctness of the quantitative calculation of deadtime effect on harmonics, and experimental tests verify that the proposed method can effectively reduce total harmonic distortion and improve waveform quality of the line current. [ABSTRACT FROM PUBLISHER]

This paper presents a new model predictive direct power control (MP-DPC) to overcome the drawbacks of model predictive control (MPC) for single phase three-level rectifiers in the railway traction drive system, including huge online calculation, poor power control precision at the low switching frequency and variable switching frequency. To do so, an exact analytical solution of instantaneous power estimation is adopted to predict active and reactive powers in next duty cycle updating interval for achieving the deadbeat control and reducing the predictive error at the low switching frequency (below 1 kHz). The optimal d-axis and q-axis components of input voltage within next duty cycle updating interval of the adopted rectifier in rotating coordinate system are directly calculated by minimizing the cost function. And the optimal drive pulses are generated by pulse width modulation stage in the proposed MP-DPC, other than evaluating cost function for each voltage vector in traditional MP-DPC. Finally, the influence of inductance mismatch on control system is analyzed, and an inductance estimation method is shown to improve the control precision. An experimental comparison with other five different DPC schemes has verified the effectiveness of the proposed MP-DPC scheme. [ABSTRACT FROM AUTHOR]

This paper proposes a simple model predictive direct power control (MP-DPC) of single-phase pulsewidth-modulated rectifiers with constant switching frequency using modulation function optimization. The instantaneous active and reactive power theory for single-phase converters is discussed, on the basis of a second-order generalized integrator. The modulation function is resolved from the cost function of the MP-DPC scheme. The relationship between the instantaneous powers and ac-side inductance mismatch is discussed. The inductance mismatch has an effect on the reactive power, but not effect on active power. The quantitative expression of reactive power caused by inductance mismatch is shown and verified in the experimental test. An inductance parameter online estimation scheme is proposed to eliminate its effect on reactive power. Compared with the conventional proportional-integral-based instantaneous current control scheme and finite-control-set MP-DPC scheme, the proposed MP-DPC can provide these advantageous features: lower current harmonics and total harmonic distortion components, faster dynamic response, fewer adjusted parameters, and zero steady-state error. In addition, the proposed MP-DPC is free of the weighting factor selection in cost function. The effectiveness of the proposed MP-DPC scheme is verified by experimental results. [ABSTRACT FROM AUTHOR]

The converter with a single-phase rectifier, a dc-link circuit and a three-phase inverter is widely applied in high-speed railway electrical traction drive system. The fault frequency of single-phase rectifier is higher than that of three-phase inverter. Thus, this paper presents a new and fast model-based approach for open-switch fault diagnosis of the single-phase pulse width modulation rectifier, based on the mixed logical dynamic model and residual generation. It requires no additional hardware but only some measurements and command signals which are available in control system. This diagnosis method is quite suitable for electrical traction application due to the fast diagnosis time, simple structure and high reliability. Experimental results confirm the effectiveness and accuracy of the proposed algorithm. It is shown that such diagnosis method can locate the faulty switch in a few milliseconds which is important to avoid catastrophic consequences. [ABSTRACT FROM AUTHOR]