三电平svpwm逆变器matlab仿真原理及介绍

A New SVPWM Method for Single-phase Three-level NPC Inverter and the Control Method of Neutral Point Voltage Balance
Zhang Zhi, Xie Yun-xiang, Huang Wei-ping, Le Jiang-yuan, Chen Lin
D3
iL
L
B
R
D4
Fig.1 Main circuit for diode-clamped single-phase three-level inverter
Each phase consists of four by-directional switches Sx1-Sx4 and two clamping diodes, where x=a,b, capacitors C1 and C2 are equal. Table I shows the switching states of a three-level inverter.
Sa
Sb
Ua
Ub
Uab STATE
P
P
E/2
E/2
0
1
P
O
E/2
0
E/2
2
P
NE/2-E/2E3OP
0
E/2
-E/2
4
O
O
0
0
0
5
O
N
0
-E/2
E/2
6
N
P
-E/2
E/2
-E
7
N
O
-E/2
0
-E/2
8
N
N
-E/2
-E/2
0
9
B. Dwelling-time Calculation
Time intervals T1 and T2 can be computed from the equilibrium of volt-seconds over sampling interval Ts.
Table I.
SWITCHING STATES OF A THREE-LEVEL INVERTER
Switching states
Sx1
Sx2
Sx3
Sx4
P(1)
ON
ON
OFF
OFF
O(0)
OFF
ON
ON
OFF
N(-1)
OFF
OFF
ON
ON
A. The Space Vector Diagram
Fig.2 shows the space voltage vector diagram for single-phase three-level inverter. The modulator input is represented as a reference vector with modulus V and phase ωt. The real part is the voltage Uab which is synthesized every switching period as a linear combination of the space vectors {-E, -E/2, 0, + E/2,E}.
Index Terms-- Single-phase three-level, capacitor voltage balance, redundant vectors, SVPWM.
I. INTRODUCTION
Multi-level neutral-point-clamped (NPC) voltage source inverter has been shown to provide significant advantages over the conventional two-level VSI , so it has been receiving increased attention recently, especially for high-power high-voltage applications. They can reduce harmonics in the output voltage and current due to the multi-level output voltage and the converter can offer the advantage of low voltage stresses on switches, reduced losses at reduced switching frequency for the same level of performance in terms of reduced harmonics, and the topology can be developed for a higher number of high-voltage and high-power applications[1-7].
Table II shows the voltage and the switch states of the NPC 3-level inverter. There are 9 possible switch operation states for the three-level converter. These space voltage vectors can be classified into 3 groups: large voltage vector(PN, NP), small voltage
In this paper, a SVPWM method for single-phase three-level inverter is proposed. The neutral-point voltage control by changing the dwelling-time of the small vectors is easy to implement, and the proposed scheme is able to deal with the voltage unbalancing problem effectively, which is inherent in the threelevel system. Finally, the feasibility and validity of the
vector(PO,PN,NO,OP), and zero voltage vector (PP,OO,NN). The vector diagram can be divided into 4 regions. Each small voltage vector and zero voltage vector have 2 and 3 redundant switching states, respectively. The redundancy will be used to balance the charge in the DC-link capacitors and reduce the number of commutations[7]. This will be analyzed in detail in Part D.
proposed control scheme and neutral-point voltage control scheme are verified by simulation and experiment results.
II. THE SVPWM METHOD OF SINGLE-PHASE THREELEVEL NPC INVERTER
A single-phase three-level inverter topology is presented in Fig.1, where switching functions of leg A and leg B are noted SA and SB, respectively.
A E
However, designing a proper PWM method for such a converter is generally a challenging task, and the threelevel converter has the problem of neutral point voltage fluctuations because of the irregular charging and discharging of output capacitors. A SHPWM method which use several triangular carrier signals with only one modulation wave per phase was proposed in Ref[2], but it is not easy to implement digitally. Ref[2]and [3] used different switch state to control the neutral-pointer voltage balance, but it did not solve the problem from the nature of the reason for the capacitor voltage imbalance.
South China University of Technology, Guangzhou 510640, Guangdong Province, China
Abstract-- A space vector PWM (SVPWM) algorithm is proposed for the single-phase three-level NPC inverter, and the cause of the imbalance of the capacitor voltage in DCside is analyzed. In order to lower the switching loss and avoid the abrupt change of output voltage vectors, an optimal SVPWM algorithm is proposed, it makes use of five-vectors modulation in which the positive(or negative) small vectors are used as the first output vector. The strategy of changing the voltage adjusting coefficient to adjust the effective time of the positive and the negative small vectors to control the neutral point potential balance is proposed, which is based on the detection of the direction of the load current and the capacitor voltage. The control of DC link neutral-point potential is easy to implement. The validity of the new SVPWM method is verified by simulation and experiment with a three-level MOSFET inverter.