FUTO Student Design And Constructs A UPS Inverter.

Hello! What do you think of a UPS Inverter that is designed and constructed by Okpala Sixtus Chidera, a student of Federal University of Technology, Owerri (FUTO) Nigeria constructing a rigid UPS Inverter? That’s amazing, right? We had an interesting discussion with him about his design and construction of the Uninterrupted power supply Inverter which he further said that it is the first of its kind.

The CEO of Sixotek Innovations focused his discussion mainly on Inverter. Now, what comes to your mind when you hear about the word Inverter? The inverter as the name implies simply means to invert. So Electrically, Inverter is an Electrical device(or interconnection of electronic circuits) that converts/changes a Direct Current(D.C) voltage into an Alternating current(A.C) voltage.

Similarly, the opposite of an Inverter is a Rectifier(a device that changes A.C to D.C). The electrical inverter is a high power electronic oscillator.

How do we come about the name Inverter?

The early mechanical A.C to D.C converters was made to work in reverse and thus was inverted to convert D.C to A.C. Between the late nineteenth century and mid-twentieth century, D.C to A.C power conversion was accomplished using rotary converters or motor-generator (M-G) sets.

The requirement to set up an Inverter

In the construction of a UPS Inverter, you will need to incorporate different circuits doing different jobs collectively into one big circuitry in order to work just fine. These are the circuits needed.

1. Oscillatory Circuit

This circuit uses a small voltage D.C from the inverter battery(s). It makes use of a chip which can either be programmed or not. This chip is an Integrated circuit(IC) which generates the A.C we need, with 50Hz oscillatory frequency. The voltage and current at this stage are considerably small.

Note: This is where the heart of the inverter lies and if anything goes wrong from this first stage, then your inverter is ruined for sure. You will get other circuitry incorporated into this one destroyed within seconds once the generated A.C has issues.

2. Pre-Amplifier And Driver Circuit

This circuit makes use of bipolar junction transistors (BJT) and Metallic oxide field-effect transistors (MOSFETs). The BJTs ensures amplification of the signals (mainly the currents) from the positive half cycle and the negative half cycle of the output from the oscillator circuit. These amplified signals are in the form of current and they are coupled to the gate of each MOSFET(s) in first and second channels respectively. Hence, the MOSFETs ensures that the inverter output can draw a high amount of current (100amps or more) from the inverter battery without causing damages to the whole inverter setup. But another problem needs to be solved (i.e voltage amplification), now this leads us to the third most important component/circuitry needed.

3. Voltage Amplification/Output Stage

Now the output signal at a 50Hz frequency that reached the two channels of the MOSFETs are now operating in a flip flop or alternating mode which is an A.C, thus a “Power Transformer ” comes into play. This power transformer will take the A.C signals (both current and voltage) from the drain pin of MOSFETs of the second circuitry and with the positive pin of the inverter battery, connected to it’s centre-tap will then transform the signals to 230volts or 120volts at 50Hz A.C and also allow loads to draw current according to its design.

Afterwards, a Polystyrene film capacitor or Fan capacitor (non- polarized) of well-calculated value is added in parallel to the inverter output to purify the A.C making. It has an almost perfect sine wave output for your household devices to use. The above three circuits are the fundamental inverter circuitry, but if we decide to use the inverter like this, there will be so many setbacks.

  • The Output will vary with respect to(w.r.t) applied loads
  • The battery will over drain when the output demands more than what the battery can offer
  • The battery will overcharge when left on the inverter in only constant voltage charge mode without control circuitry
  • There needs to be an auto change over circuitry so that the inverter output will not clash with mains supply

So to solve the above problems and make our inverter user-friendly. We need to incorporate about four more circuitry, so this leads us to the fourth circuit.

4. PWM Section Circuit

PWM stands for Pulse Width Modulation, this is simply a technology that ensures that loads do not have any effect on the inverter output. It makes use of sensing/monitor circuits that pulls the signal from the inverter output and feeds it to the main chip or IC of the oscillator circuit. This ensures that the load increase does not affect the inverter output.

5. Low Battery/Overload Shutdown Circuit

This is a protection circuitry that ensures your battery doesn’t get over drained.

6. Battery Charging Control Circuit

Once there is mains restoration, the inverter transformer works as a step-down transformer and outputs 12volts A.C at its secondary winding. During Charging, MOSFETs at pre-amplifier/driver section acts as a rectifier (due to internal diodes) and thus when the inverter receives A.C mains supply, the inverter transformer and MOSFETs together works as a charger and charge the battery bank. In order to protect the battery(s) from being overcharged and MOSFET(s) from sudden surge current at the start of charging when power is restored, two other circuits are incorporated.

  • The Soft Start Circuit makes use of IC, capacitors, and resistors mainly to delay for about five seconds before charging starts.
  • Charging Voltage Sensing Circuit ensures 3 stage battery charger for optimum battery maintenance and increased life cycle. Finally, there is another important circuit needed.

7. Change Over Circuit Section

This circuit makes use of one or more relays depending on the design. There is also a small transformer called the sensing transformer used here. This sensing transformer senses mains restoration and sends a signal to the Relay (auto electromagnetic switch) which then sends a signal to the oscillator part of the inverter to shut down and thus charge the inverter battery in a three-stage form (bulk, absorption, and float charge). Similarly, when the mains supply is out, the Relay(s) switches simultaneously back to the inverter backup mode within microseconds ensuring that the loads connected to the output of the inverter are kept “ON” steady.

This is how his Rigid UPS Prototype of modified sine wave A.C with full automation came to be. Below are more pictures of his design and construction of the UPS Inverter.

Hope you understood everything about this Uninterrupted Power Supply Inverter? Tell us what you think about this construction of UPS Inverter in the comment section. For more inquiries and sponsorship, you can call SIXO via +234 8160993963 (Nig.) or send an Email to Sixo4real@gmail.com.

Read our previous articles on solar systems and energy.

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