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Solid State Drives (DC Drives and AC Drives)

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Integrated Circuits
Is a complete electronic circuit put on a small piece of silicon.

Discrete Circuit
Are assembled circuits with individual components and wires.

The main difference between the above mentioned circuits is that the integrated circuits would be much less expensive to replace. If it's cheaper to replace a whole board, rather than rewire a whole system, chances are that a company looking at the bottom line will choose the cheapest way.

Types of Digital
IC's (Integrated Circuits)
TTL - Transistor / Transistor Logic ( Most Widely Used)
CMOS - Complementary Metal Oxide Semi-Conductor
FET - Field Effect Transistors

IC's are constructed by forming transistors, diodes, resistors, and small capacitors on a silicon chip. The styles vary and can be a T0-5, mini-dip, dual-in-line package, and flat pack. The most common being dual-in-line. There will be an indentifying mark and a gate type on the IC itself.
Dual In-Line-Package
To-5
8 pin mini-dip (dual-in-line)


Logic "Gate" - Digital

Is a device with high speed switching abilities. They are made of IC's, and can be connected in series or parallel. There are five basic logic gates.

Below are the five different logic gates. We put them together like this so you could see the similarities. The symbols are standards from USASI.




Now each are listed with the functions of each of the gates.

and (two switches in series)
A and B must be on for Y to turn on
nand A and B must be on for Y to turn off
or (two switches in parallel)
A or B could be on for Y to turn on
nor A or B could be on for Y to turn off
not (Inverter Gate)
Switch that turns off.


Terms for On and Off
* high - 1 - on - true - logic probe (green)
* low - 0 - off - false - logic probe (red)

Here is a view of combinations of gates on a Dual-In-Line Package, and what they would really look like below.






Truth Tables

In order for somebody to visually glance and see the functionality of a circuit the use of truth tables are important. It's a mathematical table that has a legitimate input value of either on, or off, or 1, or 0.

The following truth table is an "AND" gate. What each row is indicating is whether or not Y is on or off. For instance, the first column has A (off), and B (off). Since this is an "AND" gate then we know that both A and B must be ON in order for Y to be on. Since 1 equals on, and 0 equals off, then we know that only the last column is representative of the gate being in the "on" state.

A
B
Y
0
0
0
0
1
0
1
0
0
1
1
1




Operational Amplifiers - analog device




- Has two inputs, and one output
- Can operate in two modes. Open or closed loop.
- 9, 12, and 15V are typical. (35V maximum)
- Open loop is too unstable (too much gain) rarely used.
- Actual output cannot exceed saturation
- high gain amplifiers 200,000 (multiplying factor)
- low power, low voltage, low current
- closed loop, controls gains with use of resistors.

- inputs are inverting and non-inverting
- + is grounded (output is 180 degrees out of phase)
- - is grounded (output is in phase)




Differential Amplifiers


-The difference between the two outputs is the amplified output
- Several applications in solid state drives.




Comparator Amplifier



- Like a cruise control in a vehicle. The reference signal is the desired amount, and the feedback is the actual amount that is being produced.
- This amplifier is used as a speed controller for a drive system.
- That little pitchfork looking symbol is a chassis ground. A wire that runs from the motor to the machine's frame to absorb stray electric charge. Chassis ground is used when it is not possible to connect a grounding conductor into the earth.



DC Review

It is essential that you go back to the third year and review DC machines. This course has a lot of characteristics of DC machines (motors) and you will find it easier if you read over the course material for that year. Go to third year, dc machines, or just click here.

A few topics to hit are:
- Torque and characteristics
- Construction of a DC motor

- Speed Regulation
- Speed Control
- Efficiency
- Windings (Series, Compound, Shunt)



DC Drive


DC Drive System

The System
A Direct Current variable drive is made up of a control station that starts and stops the motor, a converter (or power supply) that converts the AC into DC, and the motor itself. This motor will be designated a power source code that suits the motor with the appropriate supply (A,C,D,E,or K).

The Converter
The very basic, first function of a DC drive, is to covert AC voltage into a variable DC voltage. An SCR is a commonly used device to convert AC to DC. This SCR is really just used as a switch. When current is applied from the gate, the SCR will activate. By timing the input to the gate at the beginning of the sine wave, this results in a higher voltage being applied to the motor. All SCR’s must be triggered in synchronization to the AC supply. One SCR is not smooth enough to control the voltage to a DC motor, so connecting six together in a three phase motor scenario, creates the best results. This is known as a bridge rectifier, or a DC drive converter.




Two Closed-Loop
The operation (closed-loop or open-loop) is determined by whether or not feedback is used. Using feedback actually forms a physical “closed” loop of reference that both inner and outer loops require in order to adjust for “the required operating condition”. The two loops are current (manipulating torque), and speed (voltage). The primary purpose of the control system is to provide speed control, so the 'input' to the system is the speed reference signal on the left, and the output is the speed of the motor (as measured by the tachometer ) “T” located on the armature, to the right. The closed-loop current controller, or current loop, is at the heart of the drive system. The purpose of the current loop is to make the actual motor current follow the current reference signal (Iref)


DC Compound Motor
Compound motors have a field connected in series with the armature and a separately excited shunt field. The series field provides better starting torque and the shunt field provides better speed regulation. There are two types of compound motor connections with these windings; the first is cumulative (additive), and the second is differential (subtractive). In the differential compound motor, the shunt field is connected so that its magnetic field opposes the magnetic fields in the armature and series field. This type of connection will tend to over speed the motor when the load is reduced, exactly like a series motor. Its speed will also drop more than the cumulative compound motor when the load increases at full rpm.

Armature versus Field Control
Drives which use field-weakening to above base speeds include automatic conditions for controlling both armature voltage and field current. Base speeds are when the motor reaches full rated armature voltage, and full rated field voltage. Base speeds can be controlled by the armature voltage, and above base speeds can be controlled by field voltages.

Speed/Torque Characteristics
Compound motors are commonly used in areas that require constant speed under varying load conditions. Speed is controlled by voltage, and torque is controlled by current. Therefore the usage of a two loop control, utilizing a feedback system for speed and current, is an essential component for output accuracy in above base speeds.

Speed Regulation
A motor's speed regulation is based on its design, and the components that are used to manipulate output under load conditions. There are many different designs, and combinations for several applications. A DC compound motor, utilizing a two loop control, has a steady speed regulation.

Braking Methods
The two most common methods of braking are dynamic braking, and regeneration. Dynamic braking is utilizing a bank of resistors to absorb the energy and "snuff" it out. Regeneration braking is taking the energy and returning it to the line. Of course, regeneration has the best reusable energy solution. The other methods for braking are coast to stop, deceleration (ramp to stop), and mechanical (disc & drum)

Protection
1) Overcurrent
2) Overload
3) Overvoltage
4) Field Loss Protection
5) Over Temperature Protection
6) Blower (for cooling motor) ie 60% below base speed.




AC Drive


AC Drives are rapidly replacing DC drives because of lower AC motor costs, and lower maintenance requirements. They are much smaller in size and considerably less noisy.

DC Power Section
Converts incoming AC supply into variable or fixed DC output. This is done by SCR's or rectifiers.

Filter Section
Reduces ripple voltage and increases ripple frequency.

AC Power Section
Provides adjustable frequency AC, from the DC bus, in the filter section.

Control Section
Provides circuitry which governs the range of frequency adjustments. 0-400Hz.

Inverter Types
(PWM) Pulse Width Modulation - The PWM is the most common of inverter types.
(VVI) Variable Voltage Inverter - Has a variable voltage converter. Boost required at low frequency.
(CSI) Current Source Inverter - A current regulator requiring large inductor filters. Poor power factor.

Speed
The speed of an AC motor depends on the frequency. Any change in the voltage or the frequency affects it's operating characteristics. AC motors usually operate on a fixed voltage and a fixed frequency.

Torque
In order to maintain constant stator flux, the applied voltage and frequency need to be adjusted. Once this balance is established, the torque-speed curve remains the same. If the frequency is changed after this balance, then the torque will shift downward (reduce).