1 Introduction
The voltage stress of the power switch of the mixing multi-level inverter is different, so different power devices can be employed in the same topology, and the advantages of the power switches can be used. Asymmetric H bridges are the most basic, most typical type topologies in the mixed multi-level inverter, and the power switch of the half bridge can be operated in the fundamental frequency and high frequency PWM mode, and the traditional multi-level inverter phase, respectively. The ratio, in the case where the same level is output, the power device is reduced, and the switching loss is reduced [1, 2]. This paper first analyzes the asymmetric H-bridge five-level inverter, and uses its structural characteristics to propose a general modulation strategy. Finally, the test strategy was carried out by the experimental platform with the capacitance clamp type non-symmetrical H bridge topology.
2 non-symmetric H-bridge five-level inverter
Asymmetric H bridge topics is the most basic, most typical topology in the mixed multi-level topology, and the power switch of the half bridge can operate in the fundamental frequency and high frequency PWM mode, compared to the traditional multi-level inverter. In the case where the same level is output, the power device is reduced, and the switching loss is reduced. The most practical three kinds of five-level non-symmetrical H bridge are: two-way switch asymmetric H bridge, diode clamp type non-symmetrical H bridge and capacitor clamp type non-symmetrical H bridge, respectively, respectively (a), (B), (c) shown. Fig. 1 (a) two-way switch type five-level inverter outputs a five-level AC voltage by two DC power supplies by bidirectional switches (S5 and D1 to D4) and H bridges (S1 to S4); Figure 1 (b) is a diode clamp type five-level inverter, and the left half bridge is a diode clamp three-level half-bridge, and the right half bridge is two level half bridges, and Fig. 1 (c) is a capacitor. Clamp type five-level inverter, its left half bridge is a capacitance clamp three-level half-bridge.
Traditional multi-level inverters have three categories: diode clamp type, flying over capacitive type, H-bridge-level, scheduled to five-level inverter single-phase required power devices comparison table, three types with traditional Compared with the five-level inverter, the first three type topologies use the power switch of 1: 1, resulting in the highest power switch required for the topology; the non-symmetric H bridge five-level inverter mixed application voltage stress ratio Figure 1 It is 1: 2 power switch, with less power switch outputs five level voltage, from the perspective of the output voltage level and the number of power switchs, the top three topology have a greater advantage.
3 general modulation strategy
The unymmetric H-bridge five-level inverter in Figure 1 existing modulation strategies with a particular harmonic elimination method [3] and square wave-console PWM synthesis modulation strategy [4], the former is in motor driver During the frequency range of frequent wide speed, there is a certain deviation between the check-up time of the switch conversion time and the real value, the latter needs to separate the half bridge of the high and low frequency power switches, and calculate the high frequency power switch halfway. The modulation wave of the bridge adds the complexity of the modulation strategy. In response to these problems, this paper proposes a modulation strategy for the unusitorous H-bridge five-level inverter.
3.1 General modulation strategy principle
The currently used "half bridge" mainly has three types: two-level half-bridge HB1, diode clamp type N level half bridge HB2, capacitor clamp type N level half bridge HB3. These three types of "half bridges" are combined in order to constitute a universal non-symmetrical H bridge as shown in Figure 2. In the figure, HBX indicates that this "half bridge" is operated in step wave modulation mode with less high pressure power switch relative to HBX, while HBX operates in a PWM modulation state with more low voltage power switches, X is 1, 2, 3 , Even M is the coefficient of the DC power supply, and each level voltage of the output voltage is e. The non-symmetric H bridge is characterized by the power switch of the PWM modulated state, the power switch of the right half bridge HBX 'needs to reach ME when the power switch of the PWM modulation state is at the time of shutdown voltage stress. The power switch can only be low frequencies and high pressure resistors. The three non-niche H bridges five in Figure 1 topology is a general-purpose non-symmetrical H bridge of FIG. 2 when M = 1.
The right half bridge of the general non-symmetrical H bridge of FIG. 2 works in the baseband square wave modulation, and its drive signal is synchronized with the zero point of the modulated wave. Determine the distribution state of the carrier cycle in accordance with the position corresponding to the positive and negative region where the modulation wave is located and the left half bridge HBx output voltage level is determined. The three types of "semi-bridge" medium power switches are complementary, so the carrier number is the complementary pair of power switches of the left half bridge HBX, that is, the DC power supply marks M. Figure 3 is a general modulation strategy of a non-symmetrical H-bridge topor, carrier CM, and CM 'perform orderly laminated distribution based on the switching state corresponding to the output voltage level. And the position of the carrier laminated position is determined according to the switch state corresponding to the output level, and the modulation wave Vref is hierarchically, partition PWM modulation to obtain a PWM drive signal corresponding to the power switch Si complementary pair, The UO of the non-symmetrical H bridge is made to the PWM level layer corresponding to the carrier CI. In this time area, other power switches are in turn on / off.
3.2 General modulation strategy for non-symmetric H-bridge five-level inverter
The working mechanism of the asymmetric H bridge five-level inverter of Fig. 1 can be obtained, and the power switch of the right half bridge of the non-symmetric H bridge is operated in the base frequency, the left half bridge power switch drive signal is PWM complementary pair, for example Fig. 1 (a) The power switches S1, S5 (or S2, S5) are complementary; FIG. 1 (b) The power switches S1, S3 are complementary and S2, S4 complement; Fig. 1 (c) power switches S1, S4 complement each other and S2, S3 complementary. Universal modulation principle of the unsmailing of Figure 3 can be obtained by non-symmetrical H-bridge five-level inverter universal modulation principle as shown in FIG. Asymmetric H-bridge five-level inverter requires 2 vertical distribution carriers C1, C2, and modulation waves to perform SPWM modulation, corresponding to non-complementary power switches S1, respectively, corresponding to the two carriers. The drive signal of S2 such that the five level inverter outputs two PWM levels 1, 2 corresponding to carriers C1, C2. The drive signal of the right half bridge S5 is determined by the zero point of the modulated wave. During the negative half cycle of the modulated wave, the carrier interleaved distributed to the negative area of the modulated wave, complete the SPWM modulation of the negative half cycle, output the PWM level layer 1 ', 2'.
4 experimental results
In order to verify the general modulation strategy of the non-symmetric H-bridge five-level inverter, this paper is experimentally verified by a single-phase capacitor clamp type Five-level non-symmetrical H bridge topology as an experimental platform. DC bus voltage E = 20V, carrier frequency fc = 2 kHz, modulation wave frequency fm = 50Hz, adjustment MA = 0.95, RL load, R = 100Ω, L = 63ml.
Fig. 5 is a power switch S1, S5 drive signal experimental waveform, and both power switches S1 to S4 operate in high frequency PWM state, power switch S5, S6 operate in the fundamental frequency state. Fig. 6 is a pressure waveform of the inverter output voltage and the clamp capacitor voltage, UO is the five level voltage output from the inverter, and UO is the inverter clamp capacitor voltage, due to positive, negative half-periods to the clamp capacitor Charge, discharge, so that the capacitance voltage has a small fluctuation, but the general modulation strategy makes the clamp capacitor voltage reach a better balance. Figure 7 is a inverter output voltage and a load current experimental waveform, IL is a load current (resistance R-both end voltage), and the RL load makes the load current have a better sine degree.
5 Conclusion
This paper analyzes three non-symmetrical H-bridge five-level inverters. Based on this, a modulation strategy for uni-symmetric H-bridge is proposed, which is suitable for three non-true h-bridge five-level inverters. Finally, the correctness and effectiveness of the proposed method is verified by a single-phase capacitance clamp type five-level inverter experiment platform. , Reading the full text, the technology area
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