Step Up Chopper

Choppers are widely employed in applications like battery charging, voltage regulation in power systems, motor drives, and renewable energy systems. Additionally, choppers can be integrated with filters, such as low-pass filters to reduce voltage ripples and harmonics in the output waveform, ensuring a stable and clean power supply. This feature is particularly important in sensitive electronic devices and applications where a constant and high-quality power source is essential for optimal performance. Overall, choppers play a crucial role in modern power electronics, enabling efficient and controlled power conversion in diverse electrical systems.

What is a Chopper ?

A chopper refers to an electronic device designed to control or convert the electrical power in a direct current system. It operates by interrupting or “chopping” the input DC voltage into pulses using semiconductor switches like thyristors or transistors . The key advantage of choppers lies un their ability to efficiently control the average output voltage by adjusting the duty cycle of the pulse-width modulation waveform.

Choppers are often classified based on their operating modes , such as :

• Step Up Chopper
• Step Down Chopper
• Step up/ down chopper

A step-up chopper increases the output voltage from the input , while a step-down chopper decreases it . Step-up/down chopper offer versatility by providing both higher and lower output voltages .

What is Step-Up Chopper ?

A step-up chopper , also known as a boost converter or a voltage amplifier , is a type of DC-DC converter used to increase the voltage level of a direct current (DC) power supply . It operates on the principle of energy storage and transfer through inductors and capacitors . The primary function of a step-up chopper is to boost a lower DC voltage to a higher level , making it valuable in applications such as power supplies , renewable energy systems and electrical vehicles .

The basic configuration of a step-up chopper includes a semiconductor switch , an inductor , a diode and a capacitor . During the operation , the switch is periodically turned on and off . When the switch is on , energy is stored in the inductor , and when it is off the stored energy is transferred to the capacitor resulting in an output voltage higher than the input voltage .

A step-up chopper is similar to step-up transformer whose output voltage is greater than the input voltage . Commonly employed , in power electronics ,renewable energy systems ,and electric vehicles , the step up choppers showcases versatility in voltage manipulation , making it an integral component for efficient energy conversion in diverse technological applications .

Step Up Chopper

Construction and Components of Step-Up Chopper

A step-up chopper is constructed with key components such as a power supply , power switch , a boost inductor to store and transfer energy , an output capacitor to filter the voltage , and a freewheeling diode to provide a path for inductor current during switch-off periods . The control circuit , which includes a feedback loop , regulates the output voltage by adjusting the power switch’s duty cycle. Optionally a snubber circuit may be added to dampen the voltage spikes .

During operation, the power switch controls the energy flow , allowing the step-up chopper to increase the input voltage , making it useful in applications where a higher voltage level is required than the input source .

• Power Supply : The input to the step-up chopper is a DC power source . This can be a battery , rectified AC power , or any other source of direct current .
• Power Switch : The heart of the step-up chopper is the power switch , typically a power semiconductor device such as an IGBT or a MOSFET .The power switch is responsible for turning the input voltage on and off in a controlled manner .
• Inductor : The inductor is a key component in the step-up chopper. It stores energy when the power switch is on and releases it when the switch is off . The inductor helps smooth out the output voltage and current .
• Capacitor : A capacitor often connected at the output of the chopper to filter the output voltage and reduce ripple . It helps maintain a more stable and continuous output voltage .
• Diode : A freewheeling diode is connected in parallel with the load . When the power switch is turned off, the freewheeling diode provides a path for the inductor current to circulate and prevent voltage spikes .
• Control circuit : The control circuit is responsible for regulating the output voltage of the step-up chopper. It typically includes a feedback loop that monitors the output voltage and adjusts the duty cycle of the power switch to maintain the desired output voltage.
• Snubber circuit (optional) : In some cases , a snubber circuit may be included to dampen voltage spikes and reduce stress on the power switch .

Working Principle of Step-Up Chopper

A step-up chopper also known as a boost chopper or DC-DC voltage multiplier , is an electronic device used in power electronics to increase the output voltage . It operates by chopping the input voltage into pulses and then transforming them to a higher voltage through an inductor and diode arrangement. This process involves storing energy in the inductor during the “on” state and releasing it during the “off” state , resulting in an output voltage higher than the input . Step-up choppers find applications in various fields , including power supply systems , renewable energy sources and electrical vehicles where elevating voltage levels id necessary for efficient operation .

A step-up chopper operates based on the principle of controlled switching to increase the output voltage . The fundamental principle involves the manipulation of duty cycle of a semiconductor switch , typically a transistor. The chopper circuit alternately connects and disconnects the input voltage source to an energy storage element , such as an inductor at a high frequency . During the on state of the switch, energy accumulates in the inductor, storing magnetic flux . When the switch turns off, the inductor discharges its stored energy through a diode , and the output voltage across the load is the sum of the input voltage and the induced voltage from the inductor .

By adjusting the duty-cycle is the ratio of the on-time to the total switching period is the average output voltage can be controlled. This process allows a step-up chopper to boost the input voltage to a higher level , making it valuable in applications where an elevated voltage is required, such as in DC-DC converters and renewable energy systems.

Efficient energy transfer and regulation are achieved by carefully modulating the switch’s on/off periods, ensuring that the output voltage meets the desired specifications. The energy stored in the inductor during on state is transferred to the load during off state, resulting in an increased output voltage . The relationship between the input and output voltages is influenced by the duty cycle of the PWM signal . A higher duty cycle leads to a higher output voltage and vice versa.

Step-Up Chopper With Low Pass Filter

A boost converter is a type of DC-DC converter that increases the voltage level of an input DC source . It operates on the principle of energy storage and transfer. The converter consists of an inductor , a diode ,capacitor and a switch . Initially the switch is closed allowing current to flow through the inductor ,storing energy in its magnetic field. When the switch opens the magnetic field collapses, inducing a voltage across the inductor . The diode conducts , transferring stored energy to the output capacitor effectively boosting the output voltage . By controlling duty cycle of the switch , the output voltage can be regulated .

Step-Up Chopper With Low Pass Filter

Case 1

When switch in a step up chopper is in the ON state , it acts as a closed circuit , offering ideally zero resistance to the flow of current . During this ON state , the DC input voltage is applied across the circuit , allowing current to flow through the switch and the inductor . The inductor stores energy in the form of a magnetic field. Let’s us consider that the switch is ON for a duration TON . As current flows through the inductor , it ramps up, and energy is stored in the magnetic field .

Simultaneously, the load connected to the circuit receives a fraction of this energy , leading to an increase in voltage across the load. After the ON state , the switch transitions to the OFF state , the switch is open, and the inductor discharges its stored energy through the load. The diode, typically connected in parallel with the load, allows the current to continue flowing in the same direction. By controlling the ratio of the ON time to the total switching period , the duty cycle , the average output voltage can be adjusted . This ability to regulate the duty cycle enables the step-up chopper to increase the output voltage level compared to the input voltage , making it a versatile component in DC- DC voltage conversion circuits .

When switch S is ON , inductor will starts charging .

V_L = V_s

I _c + I₀ = 0

I _c = -I₀

Step Up Chopper Waveform

Case 2

When switch in a step up chopper is in the OFF state, the polarity of the inductor is reversed. The energy stored in the inductor during the ON state is now released , and it acts as a source , helping to maintain the flow of current in the same direction through the load . This mode contributes to stepping up the output voltage. As the switch is off , the inductor discharges its stored energy, and the diode connected in parallel with the load allows the current to continue flowing in the same direction.

The load resistance plays a crucial role in dissipating the energy released by the inductor. The inductor ,now acting as a source , contributes to the overall output voltage , effectively boosting the voltage across the load. This process of releasing stored energy from the inductor during the off state is essential for achieving a higher output voltage compared to the input voltage . By carefully controlling the ON and OFF times of the switch, the step-up chopper efficiently regulates the energy transfer, making it a valuable component in various applications where voltage conversion and regulation are required .

When switch S is OFF , diode D is forward biased and inductor will starts discharging .

V _L = V_s – V₀

I _c = I_L – I₀

Since the average voltage across the inductor is zero

V₀ (DT_s) + (V_s – V₀) (1 – D)T_s = 0

V₀ = [1 /(1-D)] V_s

V_s * I_s = V₀ * I₀

I_s = I₀/(1 -D)

Ripple in the Inductor Current

During ON period -:

V_L = V_s

L (di _L /dt _on) = V_s

L (Δ i _L/DT_s) = V_s

Δ i _L = DV_s /L f

Ripple in the Output Voltage or Capacitor Voltage

During ON period , capacitor is feeding the load:

I _c = -I₀

C (d V _c /dt) = – I₀

C (Δ V _c / DT_s ) = – I₀

Δ V _c= DI ₀/ f C

Advantages of Step-Up Chopper

• The primary advantage of a step -up chopper is its ability to increase the output voltage . This is particularly useful in applications where a higher voltage is required than the input voltage .
• Step- up choppers can be designed to operate with high efficiency, especially when well – designed power electronic components are used . This efficiency is crucial in many power conversion applications to minimize energy losses .
• Step -up choppers provide flexibility in converting different DC voltage levels . They can be employed in various systems where a variable or adjustable output voltage is necessary.
• Step – up choppers find applications in renewable energy systems , such as solar and wind power , where the output voltage needs to be increased for efficient power transmission or storage .
• Step – up choppers can be utilized to improve the power factor of a system .
• Step – up choppers can help in regulating the output voltage , providing stability in applications that require a constant or regulated voltage level .

Disadvantages of Step-Up Chopper

• Step – up choppers typically operate at high switching frequencies to achieve voltage boosting . This can result in higher switching losses , reducing the overall efficiency of the system .
• The rapid switching of the chopper can generate electromagnetic interference , affecting nearby electronic devices and potentially causing signal distortions or malfunctions in sensitive equipment.
• The control system for a step -up chopper can be more complex compared to other voltage conversion systems . Precise control of the duty cycle and switching frequency is required to achieve the desired voltage boost.
• The output voltage may have more ripple compared to other voltage conversion techniques . This ripple can be problematic in applications where a stable output voltage is crucial .

Applications of Step-Up Chopper

• In solar power systems, photovoltaic panels generate a low voltage , which may not be sufficient for certain applications . Step-up choppers are used to increase the voltage to the required level for grid – tied inverters or battery charging .
• Battery powered devices , step-up choppers can be employed to boost the battery voltage to the level needed for the device , ensuring proper functionality .
• Electric vehicles rely on step-up choppers to increase the battery voltage to levels required for efficient motor operation .
• Step-up choppers are extensively used in industrial applications , particularly in motor drives and servo systems. They enable precise control of motor speed and torque by boosting the supply voltage to meet the motor’s operational requirements.
• In the telecommunications industry, step-up choppers are employed to power radio frequency amplifiers , which require higher voltage levels for effective signal transmission.

Conclusion

The step-up chopper or boost chopper plays a pivotal role in modern power electronics , offering a versatile solution for increasing DC voltage in various applications. Its ability to efficiently boost voltage levels makes it an essential component in technologies ranging from renewable energy systems , such as solar and wind power , to portable electronic devices and electric vehicles . The step-up chopper contributes significantly to power supplies , enabling the generation of higher output voltages critical for the operation of diverse electronic systems .

Moreover , the step-up chopper finds applications in power factor correction , telecommunication , LED lighting , and medical devices, showcasing its adaptability across industries. As the demand for energy – efficient and compact solutions continues to grow , the step-up chopper stands as a key enabler , addressing the need for voltage elevation in a wide array of technological advancements .

Its significance lies in optimizing power transfer , improving energy efficiency and facilitating the seamless integration of diverse electronic systems. As technology continues to advance , the step-up chopper remains a key player in modern power conversion , contributing to the evolution of efficient and adaptable electrical systems.

Solved Example

A step- up chopper has an input voltage of 240V and an output voltage of 680V . What is the pulse width of the output voltage if the non-conducting time of the thyristor is 100 microseconds.

Given input voltage V_s = 240V

output voltage V₀ = 680V

The output voltage of a step-up chopper is V₀ = V_s/(1 – D)

680 = 240/(1 – D)

D =0.64

The duty cycle (D) is :

D = T_ON/(T_ON + T_OFF )

0.64 = T_ON/(T_ON + 100)

T_ON = 177.7

FAQs on Step-Up Chopper

Can step-up choppers handle both DC and AC inputs ?

Step-up choppers are primarily designed for DC inputs , but they can be used in conjunction with AC – DC converters to handle AC inputs .

How does step-up choppers differ from a step-down chopper ?

While a step-up chopper boosts the input voltage , a step-down chopper reduces the voltage level .

Are step-up choppers suitable for high power applications ?

Yes , step-up choppers can be designed for high power applications by using appropriate switching devices and cooling methods.