switched-quasi-Z-source

This paper presents a novel switched-quasi-Z-source bidirectional DC-DC converter for EVs with hybrid energy sources, which not only achieves a wide voltage gain range, but also has a common ground. The proposed converter is based on the traditional two-level quasi-Z-source bidirectional DC-DC converter: it simply changes the position of the main power switch. As well as a wide voltage gain range and a low voltage stress on power switches, this converter also has a simple structure. As a result, the proposed converter can select the power switches with the low rated voltage, and the low on-state resistance, which in turn can improve the conversion efficiency. Simultaneously, the voltage-gain of the proposed converter is just reduced a bit, which can still meet the requirement of the application of EVs with hybrid energy sources. The absolutely common ground also avoids the additional du/dt issue between the input and output grounds, which is beneficial for the operation of the proposed converter.

In this paper, a novel hybrid switched-capacitor/switched -quasi-Z-source bidirectional dc-dc converter with a wide voltage gain range for EVs with the hybrid energy sources has been proposed. The proposed converter has a simple structure and lower voltage stresses across the power switches, which are only one-third of the sum of the high-side and low-side voltages. Its control scheme is also relatively simple and easy to implement. Meanwhile, the operating principle, the voltage and current stresses across the power switches and the comparisons with other converters are analyzed in detail. Besides, the parameter design of the main components, the dynamic modelling analysis and the voltage control scheme are also given. The final experimental results validate the feasibility of the proposed converter. Therefore, for the application of the hybrid energy sources EVs described in the paper, the proposed converter is a viable solution and has a good dynamic and static performance, which provides a good balance among the voltage gain, the components counts and the voltage and current stresses.

By controlling the shoot through period, the duty cycle of Z-source converter can be controlled. The Z-source converter can produce any desired output ac voltage, even greater than the line voltage by controlling the shoot through period. Therefore Z-source inverters can be used to compensate the voltages when voltage sag occurs in power systems.

With the introduction and wide acceptance of Z Source Inverter(ZSI) as an alternative for traditional voltage source and current source inverters (VSI/CSI), the modified switching schemes from the traditional schemes has reached the point where the further improvements in firing the switches and inserting the shoot-through states bring crucial benefits. In addition to the active switching states of the VSI, a ZSI has shoot-through zero states, when the positive and negative switches of a same phase leg are simultaneously switched on. This shoot-through state is harmful in VSI/CSI and can result short circuiting and damaging of entire application. Due to the capability of buck-boost and wide range of operating points, ZSI are suitable for the applications with unstable power supply such as fuel cell, wind power, photovoltaic etc.

The circuit discusses about five level h type multilevel inverter using control freedom degree pulse generation technique. For renewable energy systems [10] the recent power conditioning system was developed using Quasi impedance source inverter with modeling and control. Development of reduced cost phase conversion converter using step up technology [11]. To develop photovoltaic applications embedded inverter are recent topologies that can perform both buck/boost functions are used [12]. To suggest [13] an impedance source inverter with different loads the simulation study was carried out and analysed its performance. For different loads the developed inverter has the additional step up capacity to increase the voltage [14]. With different configurations of voltage stress and low value of L, the inverter will have better performance [15]. A hardware is developed for ON/OFF configuration of inductor with Z network [16]. H-bridge inverter fed AC motor using SPWM technique is implemented [17]. A detailed study is made on various power circuits and control topologies of proposed inverters [18,19]. The single phase switched inductor switched capacitor type inverter is developed by [20]. The new type of cascaded Z source neutral point clamped inverter is developed [21]. For voltage step applications [22] new impedance source inverter was developed. Digital control is designed using MATLAB coding for new impedance source inverter.

The three-phase six-switch boost pulse width modulation (PWM) rectifier as shown in Fig. 1, due to its remarkable features of high power quality and low electromagnetic interference (EMI) emissions, is widely chosen for medium and high power industrial applications. However, during the commutation from diode to transistor, the antiparallel diodes of the rectifier experience reverse recovery process, which will cause severe switching losses and EMI problems due to high di/dt and dv/dt. Considering these problems, the switching frequency of PWM converters is usually confined, which may result in higher current total harmonic distortion, larger passive components, and high switching noise. The soft-switching technique can make switches be turned ON and OFF under zero-voltage or zero- current condition, which will resolve the diode reverse recovery problems and reduce switching losses. Meanwhile, the rising and falling edges of switch current and voltage waveforms can be shaped so the di/dt and dv/dt are reduced as well. Many soft-switching techniques for three-phase PWM converter have been investigated. The general methodology is to add auxiliary resonant circuit to decrease or eliminate the overlap between voltage and current at switching transitions. According to the placement of auxiliary circuit, the soft-switching threephase PWM converters can be divided into two classes: the dc-side soft-switching converter and the ac-side soft-switching converter. The dc- side soft-switching converter uses one group of auxiliary circuits placed on the dc-side of the converter to produce high-frequency pulsating voltage across the main switch bridge. The switches are commutated at the instants when the bridge Voltage is zero so the corresponding devices can be zero-voltage switching (ZVS) switched. Among the various dc-side soft-switching

ABSTRACT-Z-source inverters have become a research hotspot because of their single-stage buck-boost inversion ability, and better immunity to EMI noises. However, their boost gains are limited because of higher component-voltage stresses and poor output power quality, which results from the tradeoff between the shoot-through interval and the modulation index. To overcome these drawbacks, a new high-voltage boost impedance-source inverter called a switched-coupled-inductor quasi-Z-source inverter (SCL-qZSI) is proposed, which integrates a switched-capacitor (SC) and a three-winding switched- coupled-inductor (SCL) into a conventional qZSI. The proposed SCL-qZSI adds only one capacitor and two diodes to a classical qZSI, and even with a turns ratio of 1, it has a stronger voltage boost-inversion ability than existing high- voltage boost q-ZSI topologies. Therefore, compared with other (q)ZSIs for the same input and output voltages, the proposed SCL-qZSI utilizes higher modulation index with lower component-voltage stresses, has better spectral performance, and has a lower input inductor current ripple and flux density swing or, alternately, it can reduce the number of turns or size of the input inductor. The size of the coupled-inductor and the total number of turns required for three windings are comparable to those of a single inductor in (q)ZSIs. To validate its advantages, analytical, and experimental results are also presented.

In this paper, a new topology called "switched- inductor/capacitor quasi z-source inverter ( - )" from the qZSI family was proposed. This topology, in similar conditions to ESL-qZSI and EB-qZSI topologies, has a higher boost factor and higher voltage gain in the high modulation index and low duty cycle. According to simulation and experimental results, at = 0.2167 has a boost factor of 7.5 and 6.3, respectively. The low voltage stress on the capacitors, the relatively low current ripple, as well as, the higher efficiency due to the fewer diode than other structures were another advantages of this topology. This topology has the characteristics like, current and current ripple equal to all inductors. Also, the voltage stresses on capacitors , , were equal to their corresponding capacitor’s , , and , respectively. Therefore, the proposed topology has a symmetric structure. The experimental results and simulation results were confirmed the relations and performance of the proposed inverter.

In the shoot through mode, switches of the same phase in the inverter bridges are switched ON simultaneously for a very short duration. The source however does not get shortcircuited when attempted to do because of the presence LC filter, while boosting the output voltage. The DC link voltage during the shoot-through states is boosted by boost factor, whose value depends on the shoot through duty ratio for a given modulation index

Inverters are devices used to convert dc-ac. It can be of voltage source inverters (VSI) and current source inverters (CSI) among them voltage source inverters are commonly used. In conventional voltage source inverters ac output voltage is always less than dc input voltage, it produces buck voltage at the output side. To boost up output voltage, an additional dc-dc boost converter is required in between the input and output side. In practice ac output voltage is desirable to be higher than dc input. Furthermore an unbalanced midpoint voltage problem is also present in the conventional inverters which leads large ripples at the output side, and makes the system unstable. To solve the limited voltage problem we can add a dc-dc boost converter or a step up transformer in the circuit as explained in [8]. Adding a boost converter in the circuit will increase the cost and volume of the circuit. If a step up transformer is used in the circuit the output voltage will be fixed due to the fixed turns ratio of the transformer.

difficulties for commercialization of EVs such as short driving range. Charging battery pack is quite time consuming one and driving range is of only short distance are the major problems for EVs. Thus in order to overcome those shortages effective battery utilization and advanced motor control have become an important issue for EVs [4–6].There are three major parts in a Pure Electric Vehicle: they are 1. The power battery pack (usually series of energy-storage unit), 2. The driving motor [can be induction motor (IM) or brushless direct-current motor (BLDCM) or switched reluctance machine (SRM) [7], etc.], and 3. The power converter controller. Among all the driving motors, the brushless direct-current (BLDC) motor has many advantages over other motors such as brushed DC motors, induction motors and switch reluctance machines. It has the merits of simple construction, high efficiency, high starting torque, noiseless operation, high speed range last but not least electronic commutating device, etc. that’s why the brushless DC motor are widely used in EVs [8,9]. Conventional EVs use mechanical brakes to increase the friction of the wheel for fast and safe deceleration purposes. Thus, the kinetic energy of braking operation is wasted. With this problem in mind, this paper will discuss how to convert the kinetic energy wasted during braking into electrical energy that can be recharged to the battery pack. As a result, this regenerative braking can realize electric braking and energy saving applications as well.

Some papers have recently focused on improving the boost factor of the Z-source inverter by using a very high modulation index in order to achieve an improvement in the output waveform. A combination of the Z-source inverter and switched-inductor structure, called the switched-inductor Z-source inverter, provides strong step-up inversion to overcome the boost limitation of the classical Z-source inverter. In order to overcome inconvenience of inrush current suppression at start up of the switched inductor Z-source inverter, a switched inductor quasi-Z-source is proposed which provides continuous input current, reduced passive component count, reduced voltage stress on the capacitors, lower shoot-through current, and lower current stress on inductors and diodes, in comparison to the switched –inductor Z-source inverter for the same input and output voltages.

Fig. 3 shows the proposed tapped inductor quasi-Z-source inverter (TL-qZSI). The combination of Lt, D2, and D3 acts as a switched tapped inductor cell. Compared to the traditional quasi-Z-source inverter with continuous input current, only one tapped inductor and two diodes are added. This configuration allows the impedance network with different inductances under shoot-through state and non-shoot-through state. Only the inductance of winding N1 is effective during the shoot-through zero state, while both the inductances of winding N1 and N2 are effective during the non-shoot-through state. It is impossible for the tapped inductor to achieve a complete coupling effect, so leakage inductance exists in the real circuit as shown in Fig. 4. As the turns ratio can be defined as N=N2/N1. The leakage inductor Lk and magnetizing inductor Lm can be described as [18]-[19]

In [4] another Z source inverter technique known as Quasi Z source inverter (Fig. 2) is proposed. It has several advantages over ZSI. This inverter provides common ground between the Inverter Bridge and DC voltage source and thus produces continuous input current. This improves the input profile of inverter. It also reduces the voltage stress across the inverter bridge. Despite its advantages the boost ability of QZSI is similar to ZSI and not suitable for the application where high boost inversion is required. In 2010 Zhu [5] presents a developed inverter with high voltage inversion ability named as Switched inductor Z-source inverter. It exhibits the quality of high boost inversion at low input DC voltage.

Abstract— This paper explores Switched Inductor (SL) Quasi Z-source Inverter which has high boost factor and performance when compared to other Z-Source inverters along with three control methods: simple boost, maximum boost and maximum constant boost. The proposed inverter improves the input current, reduces the passive count and also the reliability. The simulations are done in MATLAB/Simulink environment by using same input voltage ratio and output load. From different control methods proposed, maximum constant boost provides the highest boost factor as well as reduces passive component requirement along with ripples.

ABSTRACT: This paper presents an extended switched inductor quasi Z-source inverter (ESL-qZSI) with the ability of high boost voltage inversion. This network combines the SL-qZSI with the boost converter hence improves the switched inductor cell performance and efficiency. The proposed system reduces the voltage stresses in a typical network caused by the capacitors, power devices and diodes when compared with the traditional qZSI without any variations in the output voltage. Further, the performance of the proposed topology is verified by simulations using MATLAB.

The quasi Z-source inverter (qZSI) is used in the proposed system to convert the dc output of the solar panel in to ac. It is a single stage power converter derived from the Z-source inverter topology, employing a unique impedance network. The conventional VSI and CSI suffer from the limitation that triggering two switches in the same leg or phase leads to a source short and in addition, the maximum obtainable output voltage cannot exceed the dc input, since they are buck converters and can produce a voltage lower than the dc input voltage. Both ZSI and qZSI overcome these drawbacks; by utilizing several shoot-through zero states. A zero state is produced when the upper three or lower three switches are fired simultaneously to boost the output voltage. But the qZSI has some drawbacks like the voltage stress across the passive components are high. This will affect the passive components used in the system and reduce the life of the components. The conversion efficiency of this system is low and the startup inrush current is high which will destroy the device. The boosting ability of the system is also low and the ripple control also less in this method. So we need an alternative system which increases

load range soft-switching technology applies this technology to three-phase inverter and proposes a modified modulation. A high-power threephase rectifier using six auxiliary switches to achieve full zero-current switching for all switches is proposed. the simplified three-phase ZCT inverter only uses three auxiliary switches and LC resonant tanks and it can achieve soft switching with normal PWM algorithms. All these technologies are only for singlestage rectifier. Since the Z-source converter was first proposed by Peng it has been widely used in three-phase rectifier and inverter. Many researchers have been done to solve the hard-switching of Z-source converter. presents a full soft- switching technology for a galvanically isolated quasi-Z-source converter. It only uses two snubber capacitors. But the high inductor current ripples increase the conduction losses. A new shoot-through control for qZSI is proposed. This control method makes the switching losses more balanced, but it can’t realize full soft switching. A switched coupled- inductor is used in unidirectional Z-source inverter. This configuration can make the transistors of inverter work with soft switching and the reverse-recovery of diodes is alleviated. A ZVS Z-source three-phase rectifier is proposed. This structure doesn’t use any additional circuit. It uses the freewheeling diode to clamp the voltage across the switch to zero in the shoot-through state. So the switches in the three-phase bridge can be turned on with ZVS. While the switch in the Zsource network will suffer high voltage and is in hard switching.

These inverters have advantages such as applying as a buck and boost converter in the form of one structure, there is no limitation like dead time and overlap time for VSI and CSI, respectively, suitable performance against noise. This structure is used in all ac-ac, dc-ac, dc-dc, ac-dc power stage with buck-boost capability [7]. With all the good advantages of ZSI, but this topology has major disadvantages such as the lack of share common ground between the input power source and the link-dc, the discontinuous input current due to the input diode. In 2008, the quasi impedance source inverters (qZSI) was introduced [8], which included advantages such as, common ground between the input power source and link-dc, the low voltage stress on capacitors and continuous input current. In 2010, diode-assisted qZSI (DA-qZSI) and capacitor-assisted qZSI(CA-qZSI) topologies were proposed [9], which have higher boost factor relative to previous structures. Another feature of these structures is their extensibility, that the boost factor can be increased by adding elements to the base structure. The CA-qZSI topology is shown in Figure 1(a). By replacing the switched-inductor (SL) cell instead of the inductors of ZSI and qZSI, the boost factor and voltage gain increase considerably [10], [11], [12]. The SL cell in these structures consists of a combination of three diodes and two inductors.

power quality, which are attributed to the use of a lower modulation index. The proposed topology is obtained by combining the switched-capacitor SC and a three-winding SCL into the classical qZSI. The charging of the SC through the SCL significantly enhances the boostability of the proposed inverter, without increasing the turn ratio of the SCL.The proposed inverter reduces the starting inrush current.