Variable Switching Frequency PWM Strategy of Two-Level Rectifier for DC-link Voltage Ripple Control

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The exchanging recurrence is an imperative control parameter of PWM rectifier to diminish exchanging misfortunes and EMI clamor. This paper proposed a variable exchanging recurrence PWM (VSFPWM) methodology for DC-connect voltage swell control in two-level rectifier. DC-connect voltage swell is controlled by the DC-interface current straightforwardly, and can be anticipated synchronously with PWM signals. An ongoing forecast model of DC-interface voltage swell is determined for a typical voltage arranged control (VOC) PWM rectifier. At that point, VSFPWM control is presented, which changes the changing recurrence cycle to cycle with a confinement of DC-connect voltage swell pinnacle esteem. Moreover, the dynamic conduct is additionally seen when the proposed VSFPWM control plot is received. Detail recreation and test correlations are done among VSFPWM and typical consistent exchanging recurrence PWM (CSFPWM), which exhibit the benefits of the proposed technique.



Fig.1 Control structure of AFE rectifier


Fig.2 Comparison between the prediction and the simulation results of the

DC-link voltage ripple in one line-cycle

Fig.3 DC-link voltage ripple comparison

Fig.4 Switching frequency comparison

Fig.5 AC-side current

Fig.6 Spectrum comparison (a) AC-side (2) DC-link

Fig.7 Step response (a) Step response of DC-link voltage (f) The change of

switching frequency with VSFPWM


The commitment of this paper is build up the VSFPWM procedure for DC-connect voltage swell control. Unique in relation to the past work on the AC-side current swell or torque swell, the DC-interface voltage swell is almost not influenced by the PWM current swell of AC-side. In a rectifier framework, the DC-connect voltage swell is dictated by the PWM technique and load current, and the pinnacle estimation of it is essential for DC-interface capacitor structure or choice. The proposed VSFPWM completely uses the opportunity of exchanging recurrence, which is regularly ignored in the PWM module. In any case, the proposed VSFPWM is unique in relation to the irregular PWM [24], which changes the exchanging recurrence dependent on the insights and no expectation show is utilized. It ought to be noticed that the proposed system can be connected to an alternate power factor than the unitary one and not can be connected direct to the rectifier with nonpartisan wire (four wire). Barely any ends can be determined as pursues:

(1) DC-interface voltage swell expectation model can be worked in the time sensitive area. With the three-stage obligation cycles, AC-side current and load current estimated by the present sensors, the DC-interface voltage swell pinnacle can be anticipated for refreshing the exchanging recurrence in next cycle. The forecast strategy additionally applies to other PWM strategies, and furthermore be utilized for structure and investigation of DC capacitors and DC battery dependability.

(2) In an entire line period, the exchanging recurrence of VSFPWM consistently changes beneath the planned steady exchanging recurrence, keeping the DC-interface voltage swell constantly under the prerequisite. Utilizing the proposed VSFPWM methodology, the exchanging misfortunes decline fundamentally, and EMI commotion decreases particularly.

(3) The dynamic property of VSFPWM is right off the bat explored in an ordinary shut circle control framework. Actually, VSFPWM still has a decent unique reaction, without about debilitating the following execution appeared normal CSFPWM. The open-circle Bode plot shows the VSFPWM strategies simply decline a tad of transfer speed of both voltage control circle and the current in CSFPWM as a result of the decrease of normal exchanging recurrence.

Comparison of DC/DC Converters in DCM for Reducing Low-Frequency Input Current Ripple of Single-Phase Two-Stage Inverters


DC/DC Converters  Single-phase two-stage inverters generally use an intermediate capacitor to buffer the power imbalance between DC input and AC output. However, the resultant low-frequency voltage ripple on this intermediate capacitor may produce low frequency ripple at the source side, especially when the front-end dc/dc converter operates in continuous conduction mode (CCM). Some common solutions to reducing this ripple are feed forward control and power decoupling circuits. Alternatively, this paper analyzes a two-stage inverter where the front-end is a dc/dc converter operating in discontinuous conduction mode (DCM). In general dc/dc converters operating in DCM have inherent natural capability to reduce this low-frequency input current ripple, without needing a sophisticated control or complex circuitry as compared with its CCM operation. Analysis with simulation verification is reported to demonstrate such capability.


  1. Dc/ac
  2. Low-frequency ripple
  3. Single-phase
  4. Two stage



dc/dc converters

Fig. 1. A simplified power-stage diagram of a single-phase two-stage inverter.


comparison dc dc converters

  • (a) CCM operation: _vin = 3:3V

  • comparison dc dc converters

(b) DCM operation: _vin = 0:88V

Fig. 2. DCM boost front-end converter has lower voltage ripple than CCM.

comparison dc dc converters

Fig. 3. DCM buck-boost front-end converter does not contain low-frequency ripple but only high-frequency ripple.

comparison dc dc converters                                               Fig. 4. SEPIC front-end converter operating in DCM+CCM contains negligible

low-frequency ripple but only high-frequency ripple.

comparison dc dc converters

Fig. 5. High-gain front-end converter operating in DCM does contains

significant low-frequency ripple.


This paper analyzes basic and several higher-order front-end dc/dc converters for single-phase two-stage inverter design. Through inspecting the instantaneous average input current of those converters in discontinuous conduction mode (DCM), it has confirmed that buck-boost converter and buck-boost derived converters such as ZETA are free of low-frequency (mainly double ac line frequency) input current ripple due to the lack of direct connection between input and output during switching actions. For boost converter based converters such as SEPIC and C´ uk converters, their input currents contain lower low-frequency content thanks to the cascaded design. For boost converter based high voltage gain converters, its input current may not necessarily reduce the low-frequency content effectively. It depends on how the high-gain sub circuit is constructed and interacts with the input inductor. Further research is necessary to identify suitable converter topologies which have both smooth input current and low frequency content.


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