A Z-source inverter is a type of

power inverter A power inverter, inverter or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the oppo ...

, a circuit that converts

direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or eve ...

alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in which ...

. The circuit functions as a buck-boost inverter without making use of DC-DC converter bridge due to its

topology In mathematics, topology (from the Greek words , and ) is concerned with the properties of a geometric object that are preserved under continuous deformations, such as stretching, twisting, crumpling, and bending; that is, without closing ho ...

. Impedance (Z) source networks efficiently convert power between source and load from DC to DC, DC to AC, and from AC to AC. The numbers of modifications and new Z-source topologies have grown rapidly since 2002. Improvements to the impedance networks by introducing coupled magnetics have also been lately proposed for achieving even higher voltage boosting, while using a shorter shoot-through time. They include the Γ-source, T-source, trans-Z-source, TZ-source, LCCT-Z-source that utilizes a high-frequency transformer connected in series with two DC-current-blocking capacitors, high-frequency transformer-isolated, and Y-source networks. Amongst them, the Y-source network is more versatile and can be viewed as the generic network, from which the Γ-source, T-source, and trans-Z-source networks are derived. The incommensurate properties of this network open a new horizon to researchers and engineers to explore, expand, and modify the circuit for a wide range of power conversion applications.

Types of inverters

Inverters A power inverter, inverter or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the oppo ...

can be classified by their structure as *Single-phase inverter: This type of

inverter A power inverter, inverter or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the oppo ...

consists of two legs or two poles. (A pole is connection of two switches where source of one and drain of other are connected and this common point is taken out). * Three-phase inverter: This type of

consists of three legs or poles or four legs (three legs for phases and one for neutral). Inverters are also classified based on the type of input source as follows: * Voltage-source inverter (VSI): In this type of inverter, a constant

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge t ...

source acts as input to the

bridge. The constant

source is obtained by connecting a large

capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of a ...

across the DC source. * Current-source inverter (CSI): In this type of inverter, a constant

current Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (stre ...

source acts as input to the

bridge. The constant

source is obtained by connecting a large

inductor An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a ...

in series the DC source.

Operation

Normally, three-phase inverters have 8 vector states (6 active states and 2 zero states). There is an additional state known as the shoot through state, during which the switches of one leg are short-circuited. In this state, energy is stored in the impedance network, and when the inverter is in its active state, the stored energy is transferred to the load, thus providing boost operation. This shoot through state is prohibited in VSI. Achieving the buck-boost facility in ZSI requires

pulse-width modulation Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a method of reducing the average power delivered by an electrical signal, by effectively chopping it up into discrete parts. The average value of voltage (and current) fed ...

. The normal sinusoidal pulse width modulation (SPWM) is generated by comparing carrier triangular wave with reference sine wave. For shoot through pulses, the carrier wave is compared with two complementary DC reference levels. These pulses are added in the SPWM. ZSI has two control freedoms:

modulation index The modulation index (or modulation depth) of a modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the '' carrier signal'', with a separate signal called ...

of the reference wave which is the ratio of amplitude of reference wave to amplitude of carrier wave and shoot through duty ratio which can be controlled by DC level.

Advantages

The advantages of Z-source inverter are: * The source can be either a voltage source or a current source. The DC source of a ZSI can be a battery, a diode rectifier or a thyristor converter, a

fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen fuel, hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most bat ...

stack or a combination of these. * The main circuit of a ZSI can either be the traditional VSI or the traditional CSI. * Works as a buck-boost inverter. * The load of a ZSC can be inductive or capacitive, or it can be another Z-source network.

Disadvantages

Typical inverters (VSI and CSI) have few disadvantages: * They behave in a boost or buck operation only. Thus the obtainable output voltage range is either smaller or greater than the input voltage. * They are vulnerable to

electromagnetic interference Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrost ...

and the devices get damaged in either open or short circuit conditions. * The combined system of DC-DC boost converter and the inverter has lower reliability. * The main switching devices of VSI and CSI are not interchangeable.

Applications

Renewable energy sources Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...

Electric vehicles An electric vehicle (EV) is a vehicle that uses one or more electric motors for propulsion. It can be powered by a collector system, with electricity from extravehicular sources, or it can be powered autonomously by a battery (sometimes ...

# Motor drives

References

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