**3. Classification of SMRs**

Basically, a SMR is formed by inserting a suited DC/DC converter between diode rectifier and capacitive output filter, under well regulated DC output voltage, the desired AC input line drawn power quality can be achieved. The existing SMRs can be categorized as:

#### **1. Schematics**


### **2. Control methods**

256 Electrical Generation and Distribution Systems and Power Quality Disturbances

The SMRs possess many categories in circuit topology and switching control approaches. A single-phase boost-type SMR is shown in Fig. 2(a), and the typical waveforms of *ac i* using low-frequency (LF) and high-frequency (HF) switchings are sketched in Figs. 2(b) and 2(c). The features of HF-SMR comparing to LF-SMR are: (i) more complicated in control; (ii) high control performances in line drawn current, power factor and output voltage; (iii) lower

*S*

(a)

*Cdc vi*

*iL iD*

*vdc*

Load

*ac i* \* *ac <sup>i</sup> vac*

ω*t*

(b) (c) Fig. 2. Boost-type SMR: (a) circuit; (b) sketched key waveforms for low-frequency switching;

Basically, a SMR is formed by inserting a suited DC/DC converter between diode rectifier and capacitive output filter, under well regulated DC output voltage, the desired AC input

a. Single-phase or three-phase: each category still possesses a lot of types of SMR schematics. The three-phase SMR will be a natural choice for larger power plants. b. Non-isolated or isolated: although the former SMR is simpler and more compact, the latter one should be used if the galvanic isolation from mains is required. See for example, the flyback SMR is gradually employed in communication distributed power architecture as a single-stage SMR front-end, or called silver box, to establish -48V DC-

c. Voltage buck, boost or buck/boost: depending on the input-output relative voltage levels, suited type of SMR and its control scheme should be chosen. Basically, the boosttype SMR possesses the best current control ability subject to having high DC output

d. Single-stage or multi-stage: generally speaking, the stage number should be kept as small as possible for achieving higher efficiency and system compactness. Hence,

line drawn power quality can be achieved. The existing SMRs can be categorized as:

ω*t*

efficiency. More detailed survey for SMRs will be presented in the latter paragraphs.

*<sup>L</sup> <sup>D</sup> ac <sup>i</sup>*

**2.2.4 Switch-mode rectifier** 

*vac*

(c) sketched waveforms for high-frequency switching

single-stage SMR is preferable if possible.

*ac i*

*vac*

**3. Classification of SMRs** 

θ *d* θ*on*

**1. Schematics** 

bus voltage.

voltage level.

