* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Variable Frequency Drive - UCF EECS
Power factor wikipedia , lookup
Immunity-aware programming wikipedia , lookup
Spark-gap transmitter wikipedia , lookup
Mercury-arc valve wikipedia , lookup
Solar micro-inverter wikipedia , lookup
Spectral density wikipedia , lookup
Ground loop (electricity) wikipedia , lookup
Ground (electricity) wikipedia , lookup
Audio power wikipedia , lookup
Current source wikipedia , lookup
Electrical ballast wikipedia , lookup
Utility frequency wikipedia , lookup
Brushless DC electric motor wikipedia , lookup
Electrical substation wikipedia , lookup
Electric power system wikipedia , lookup
Electrification wikipedia , lookup
Surge protector wikipedia , lookup
Power MOSFET wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Electric motor wikipedia , lookup
History of electric power transmission wikipedia , lookup
Stray voltage wikipedia , lookup
Voltage regulator wikipedia , lookup
Amtrak's 25 Hz traction power system wikipedia , lookup
Power engineering wikipedia , lookup
Three-phase electric power wikipedia , lookup
Brushed DC electric motor wikipedia , lookup
Power inverter wikipedia , lookup
Opto-isolator wikipedia , lookup
Distribution management system wikipedia , lookup
Buck converter wikipedia , lookup
Electric machine wikipedia , lookup
Voltage optimisation wikipedia , lookup
Power electronics wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Mains electricity wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Alternating current wikipedia , lookup
Stepper motor wikipedia , lookup
Variable Frequency Drive Merritt Robbins, Justin Barwick, Will Santos, and Chris Guido Dept. of Electrical Engineering and Computer Science, University of Central Florida, Orlando, Florida, 32816-2450 Abstract — A first of a kind at UCF; the Variable Frequency Drive designed and implemented by Group F is a simplified approach to the problem of vector motor control. Using open source software and original hardware design, the drive allows precisely variable speed and torque of a three phase AC induction motor of up to 1/2hp. The variable frequency drive designed by group F implements field oriented vector control to achieve the goal of variable speed and torque operation. The design focuses on efficiency and safety for the end user and his or her equipment being driven. Index Terms — Variable speed drives, Induction motors, Sensorless control, Machine vector control, Space vector pulse width modulation. I. OVERVIEW OF INDUCTION MACHINES Since Nikola Tesla patented the alternating current induction motor in 1896 [1], the simple action of a rotating magnetic field inducing an opposing field has been the driving force for the majority of heavy industry. The induction motor provides many distinct advantages over a DC motor of the same power; the induction motor is more efficient, more reliable, easier to manufacture, smaller, less costly to the environment, quieter, and can be more easily sealed for harsh environments. Due to these advantages, the induction motor has dominated industry and individual life for constant speed applications. The catch with induction motors is their lack of variable speed operation without varying both the current (or voltage) and frequency of the power signal sent to the motor. Varying the voltage or current of a signal is a trivial challenge, but varying frequency is not. The Variable Frequency Drive (VFD) designed by group F generates a 325V DC bus and then implements flux oriented vector control to synthesize an output waveform with variable voltage from 2.3V to 230V and power rated up to 500W input. II. VARIABLE FREQUENCY DRIVE APPLICATIONS Solving the problem of variable speed control for induction motors is massively useful. Without the limitation of constant speed, applications where an inefficient and heavy DC motor was used simply due to a requirement of variable speed can now implement AC motors and take advantage of their significant benefits. The primary target industry of the project is transportation; an innately variable speed drive system. Modern electric vehicle manufacturers use high performance VFDs which cost tens of thousands of dollars to drive hundreds of Kilowatts to their motors. Other key applications include machine tools, where the addition of a VFD to an existing tool allows for a massive performance improvement for the machine. Variable speed can be extremely useful on near 100% duty cycle motors in HVAC systems as well. Rarely does a building need the full capacity of its air conditioning system compressors, but the compressors can only be turned on or off because they are driven by induction motors. The problem can be partly solved by running fewer compressors, but controlling the speed of the compressor blades dynamically (thus avoiding excessive power cycling) to match the current load can have massive energy savings for the building owner. Beyond the current applications where variable speed is the only justifiable reason to use a VFD, if implemented on a large scale on large motors (over about 50hp), has the potential to increase grid efficiency by moving the load power factor to near unity. This can save money for the owner (if they get billed by the VA) and can save power for everyone but reducing reactive loading. III. MAJOR DESIGN GOALS AND SPECIFICATIONS The VFD design is focused on four major areas; operator and system safety, drive dynamic performance, simplicity of design, and efficiency. A. Operator and System Safety Safety is the number one priority of Group F for the VFD. Cartridge fuses are placed in every power path in the system, furthermore the motor has a fuse for each phase. The system is based around a differential positive and negative 162.5V DC link. The choice of a differential rail was made to reduce the high voltage potentials found on the board by a factor of two relative to ground. All microcontrollers are chassis grounded. The chassis and high voltage power board are both earth grounded. The DC link is not ground referred directly, it is indirectly ground referenced by earth grounding the center tap of the power transformer secondary. An array of nine NTC thermistors is implemented to monitor real time temperatures of all power switching and drive devices in the high voltage power system as well as the housing of the motor under test, In the case of over – temperature, the MSP430 that oversees the system will prevent catastrophic component failure by disconnecting the power to the power transformer. Further contributing to overall system safety is the large derating of all ceramic capacitors, integrated circuits, and power switches. All ceramic capacitors are voltage derated by a factor of at least 1.75. All drivers have carefully chosen current limiting resistors and are massively over – specified for drive current levels based on our switching frequency of 20kHz. B. Drive Dynamic Performance Due to the main target application for the VFD being the transportation sector, having an extremely wide dynamic range of control is essential. The VFD designed by group F achieves 1% to 110% operating speed range, ramping motor start up, 0.1% accurate speed and torque control, as well as the ability to shift the speed of the motor at a real time pace. C. Simplicity of Design Simplicity of design results in greater reliability, as well as easier troubleshooting and repair. To keep the design simple, group F elected to limit all resistor packages to 0603 package size minimum, disallow any integrated circuit packages without exposed leads, and use highly common packages for all permitting devices. One important step taken during prototyping phase was to leave all board vias un-tented thus allowing many convenient oscilloscope probe locations built into the signal path. C. Efficiency Efficiency is a major design goal of nearly all modern power systems. Group F’s VFD is no exception. The system achieves overall power efficiency of greater than 85% under full load. This efficiency is achieved by the selection of a highly efficiency rectifier design as well as a space vector modulation algorithm which minimizes switching cycles, thus minimizing switching losses. The switches themselves are selected for optimal conduction characteristics while maintaining reasonably low gate capacitance to reduce switching losses. The drive integrated circuits are selected specifically to optimize switching speed and minimize conduction losses due to long rise and fall times. III. POWER SYSTEM DESIGN The VFD power system will be broken into two sections for discussion; high voltage and low voltage. The high voltage section is the power path which supplies the motor itself. The low voltage section provides regulated DC busses to supply the various integrated circuits, sensors, and microcontrollers in contained in the system. A. High Voltage Power System The high voltage power system incorporates three main power blocks; The synchronous rectifier, the DC link, and the power inverter. The system takes mains power at 115VAC and steps up the voltage to 230VAC with a power transformer. The center tap of the power transformer secondary is grounded to chassis ground. The 230VAC is fed into a high efficiency MOSFET synchronous rectifier. The MOSFETs are configured such that their body diodes act as rectifier diodes when no gate drive is applied. A smart gate drive is used to switch the MOSFET on when the body diode starts conducting and switch it off just before the body diode stops conducting. This method results in a close approximation of the ideal diode rectifier, resulting in only a few hundred millivolts drop across the rectifier, and very low losses in the switching devices. The output of the synchronous rectifier is a nominal 325VDC, but because the center tap of the secondary on the power transformer was grounded, the output appears as positive and negative 162.5V relative to ground. The choice to use dual polarity rail was made for safety. This configuration allows the VFD to maintain half of the potentials to ground in its power system versus a single polarity, thus lowering the chance of electrocution or equipment damage. The choice has no impact on the drive system as the motor only responds to the differential voltage on the windings, they are not grounded. The output of the synchronous rectifier is fed into a capacitor bank which decouples the inductance of the power transformer from the inverter, providing the inverter with a large amount of reactive power, and smoothing switching noise on the DC link to maintain a predictable output signal. The DC link outputs power to the power inverter block. The power inverter consists of three identical phases which all consist of a pair of IGBTs driven by a gate driver PMIC and associated passive components. The gate drivers have built in isolation circuitry to allow one drive IC to manage one high-low pair of IGBT switches. The gate drivers receive their signals relative to the DC link negative rail. This requires that the drive signal be level shifted down to be a known PWM with respect to the DC link negative rail. To accomplish this there are six opt isolating bridges which level shift the signal from earth ground reference down to DC link negative reference while isolating the microcontroller from any high voltages. B. Low Voltage Power System The Low Voltage Power System provides proper supply and digital I/O voltages for the LCD Display, rotary encoder, and MCU interfaces. Mains 115VAC power is fed to another dual output toroidal transformer that provides two 15VAC isolated outputs: each as inputs to a Schottky Bridge Rectifier block. The Bridge Rectifier blocks have identical designs and follow the conventional diode bridge rectifier topology. The requirement for two bridge rectifier blocks comes from a ground reference consideration for certain integrated circuits in the system. The gate driver PMICs and opt isolating bridges require that their signals be referenced to the DC link negative reference, therefore the switch mode power supply for the ICs in these systems must also be referenced to the negative terminal of the DC Link. The Buck Regulators each receive their input voltages from the Schottky bridge rectifiers, so any power delivered to High Voltage Power System ICs must also be referenced to the negative terminal of the DC Link. On the low voltage power/control board all MCU interfaces and any LDO voltage regulators providing analog/digital supply voltages are referenced to chassis ground, so the bridge rectifier providing the input rail to the buck regulator engaged in the switch mode power supply for these blocks is also referenced to chassis ground. IV. SENSOR DATA ACQUISITION AND PROCESSING The term ‘sensorless’ in the context of a motor control system is somewhat of a misnomer. A sensorless motor controller is one which does not require any internal measurements of direct motor parameters such as flux density and rotor current. The critical measurements which the VFD uses to model the behavior of the motor are simply voltage and current delivered to the stator. We provide an optional third feedback to our controller in the form of a three channel rotary encoder which gives the controller a value for actual rotor speed, which can be estimated via mathematical modeling, but removes a significant computational load by measuring it directly. Further sensors include DC link voltage monitoring and an array of NTC thermistors which monitor real time system temperatures to protect from over – heating. A. Voltage Measurement Acquisition Probing of high voltages at the motor phase connections, as well as the DC link voltage, is accomplished with a resistor divider. The divider has one special feature, however, in that it includes a constant DC offset applied to the measurement. This is done so that none of the active filters to follow require negative power rails, and guarantees that the measurement voltage fed to the ADC will never be negative. This offset is accomplished by using a precision shunt voltage reference effectively raising the ground of the voltage divider up by a constant value. This value is fed to the ADC as well to reduce cost by allowing for lower precision shunt references since the actual offset can be measured and can therefore accept a higher tolerance shunt. B. Current Measurement Acquisition Measurement of phase current is accomplished via a current transformer which produces an output which has a highly linear relationship to the current flowing through the measured wire. The current transformers were specifically selected for appropriate bandwidth for the VFD application at hand as well as a high turns ratio to minimize power losses. The secondary of the current transformer is passed through a precision resistive shunt which is set at a constant offset to ground potential in the same manner as the voltage measurements described above. C. Current And Voltage Signal Processing Both current and voltage sensor signals are filtered through a second order Butterworth filter with its cutoff frequency set at approximately 200Hz. This gives a nominal -80dB attenuation to our 20kHz switching frequency and attenuates a 60Hz signal by less than 0.1%. The output of these filters will be the time average signals sent to the motor. This discrete analog filtering removes the need for filtering of the signals in software, reducing complexity of the code as well as computational load. D. Temperature Measurement Acquisition. The method of thermal measurement is achieved by using negative temperature coefficient resistor networks to provide a suitable voltage range for processor use. The effective temperature range for measurement is 20 to 100 degrees Celsius and, from a reference of 1.2V at 20 degrees Celsius, a 10 degree rise in temperature corresponds to a .1V increase in the output voltage of the thermistor network. The network receives power from a 3V regulated DC rail. A set of fixed resistors in series with the thermistor serve to limit current applied to the thermistor and set the top resistor value for a potential divider that sets the effective output voltage range of the network. The thermistors are thermally coupled to each gate drive IC, the motor housing, and the 15V regulator IC on the high voltage side of the power system. voltmeter and ammeter connections made to achieve the DC resistance. The Reliance Electric P56H5069G stator windings are configured in a 1Y topology in order to use the low voltage setting to drive the motor. Figure 1 -Wiring Diagram for determination of 𝑅𝐷𝐶 in the following equations E. Rotary Encoder Data Acquisition The rotary encoder chosen utilizes a novel technology reliant on magnetics for motion control and sensing, thereby eliminating any mechanical contact and consequently, wear and tear. Operating at a single supply voltage of 5V taken from the low voltage switch mode power supply, it has a three channel output: two that indicate direction of rotation. When channel A of the encoder leads channel B by 90 electrical degrees, the shaft of the motor is spinning in the clockwise direction, the opposite holding true for counterclockwise rotation. The third channel provides a pulse to indicate every full rotation of the shaft: thereby providing a suitable counter for use in software to determine the rotation speed of the shaft. The encoder is mounted such that the base will be attached to a quarter-inch shaft with a piece of 10-32 threaded bolt coupled to the motor shaft via matching threads. This connection is purely mechanical. F. Determination of Induction Motor Parameters A set of electrical tests determine the parameters used to characterize the motor and develop torque-speed characteristic curves. Among important considerations in the steady-state analysis of a three-phase induction motor are the variation of current, power, losses and torque associated with various operating conditions. Through completion of these tests, the equivalent circuit of the stator per phase can be modeled for development of torque-speed characteristics with multiple slip parameters to be generated. A set of simple DC tests determine the stator resistance of the motor. First, connection of any two stator leads to a variable voltage DC power supply, then adjustment of the power supply to provide the rated stator current for the motor. The series DC resistance is determined as the ratio of voltage to current from voltmeter and ammeter readings. In the case of this system, the motor will be utilizing a wyeconnected stator, so then the wye-connected stator resistance is determined as half the series DC resistance. The following figures illustrate this idea in addition to the 𝑅𝐷𝐶 = 𝑉𝐷𝐶 ⁄𝐼𝐷𝐶 (1) Figure 2-The wye connection configuration and illustration of stator resistances per phase 𝑹𝑫𝑪 = 𝟐𝑹𝟏,𝒘𝒚𝒆 (2) Consequently the stator resistance per phase is determined as 𝑅1,𝑤𝑦𝑒 = 𝑅𝐷𝐶 ⁄2 (3) i) The blocked rotor test The blocked rotor test determines each of the rotor and stator reactances referred to the line and load sides of the motor equivalent circuit. In addition, it determines the rotor resistance when combined with data from the DC test. The rotor is blocked so that it will not turn and a variable AC supply is connected to each phase of the motor to provide rated current. The following figures provides the wiring diagram for the blocked rotor and no load tests, and an illustration of the blocked rotor equivalent circuit [1]. Figure 3- Wiring diagram for no load and blocked rotor tests, V and A represent voltmeters and ammeters respectively [1] The blocked rotor impedance is then corrected to rated frequency of the motor via the scalar factor of 60/15 coupled to the blocked rotor reactance value calculated [1]. The blocked rotor reactance at rated frequency relates X1 and X2 as follows 𝑋1 + 𝑋2 = 𝑋𝐵𝑅 (9) Figure 4 - Simplified motor equivalent circuit for the blocked rotor test. R1 and R2 are the stator and rotor resistances of while X1 and X2 represent the stator and rotor reactances, respectively. [1] Per IEEE test standard 112-984 the blocked rotor test is performed using a quarter of the rated frequency with the test voltage adjusted The magnetizing inductance for the stator and to obtain approximately rated current. The 60 Hz Reliance Electric motor would use a 15 Hz test voltage. However, because the motor only provides a 0.5hp, rated frequency suits the needs of the test. The following presents the determination of R1 and R2. The blocked rotor resistance is calculated as [1]: 𝑅𝐵𝑅 = 𝑃𝐵𝑅𝑧 2 𝐼𝐵𝑅𝑧 (4) The numerator is the true power applied to the motor and can be obtained from the product of voltmeter and ammeter readings, and the blocked rotor current is determined as the ammeter reading [1]. Then it is known that R1 and R2 in series create the blocked rotor resistance The determination of X1 and X2 is achieved by dividing the blocked rotor reactance evenly among them per the NEMA design class of the motor. ii) The no load test The no load test allows for the determination of the magnetizing impedance, inductance and core, friction, and winding losses. The rotor is allowed to rotate freely and run unloaded at rated voltage and frequency, 230V@60Hz. In the no-load case, the speed of the rotor is very close to synchronous speed, equivalent to the speed of the magnetic fields, and hence the slip is very close to zero, causing the current in R2/s to be very small, and may be ignored in calculations [1]. The equivalent circuit becomes very simple as the core resistance and rotor resistance may be ignored. 𝑅1 + 𝑅2 = 𝑅𝐵𝑅 (5) R2 can now be determined as the difference between the blocked rotor resistance and R1 obtained from the DC test data [1]. The blocked rotor impedance is calculated as 𝑍𝐵𝑅 = 𝑉𝐵𝑅𝑧 𝐼𝐵𝑅𝑧 (6) The blocked rotor impedance relates the blocked rotor reactance and resistance as follows 2 2 𝑍𝐵𝑅 = √𝑅𝐵𝑅 + 𝑋𝐵𝑅 (7) The blocked rotor reactance can then be expressed as 2 2 𝑋𝐵𝑅 = √𝑍𝐵𝑅 − 𝑅𝐵𝑅 (8) Figure 5 - Simplified motor equivalent circuit for the no load test. [1] The no-load true power is determined as the product of no-load voltmeter and ammeter readings. The complex power is the product of the no-load voltage and current phasors. Its magnitude is related to the magnitudes of real and reactive power supplied to the motor as 2 2 𝑆𝑁𝐿 = √𝑃𝑁𝐿 + 𝑄𝑁𝐿 (10) Therefore the magnitude of no load reactive power becomes 2 2 𝑄𝑁𝐿 = √𝑆𝑁𝐿 − 𝑃𝑁𝐿 (11) The magnitude of no load reactive power is then related to the no load reactance and current as 2 𝑄𝑁𝐿 = 𝐼𝑁𝐿 𝑋𝑁𝐿 (12) Dividing the magnitude of the no load reactive power by the no load current yields the no load reactance and may be related to X1 obtained from the blocked rotor test and the magnetizing reactance XM. The magnetizing reactance is then calculated as the following [1]. 𝑋𝑀 = 𝑋𝑁𝐿 − 𝑋1 (13) rotor is equal and is calculated as [2] 𝐿𝑀 = 𝑋𝑀 2𝜋𝑓 (14) The combined friction, winding and core loss can be expressed as a function of no-load data 2 𝑃𝑁𝐿 − 𝐼𝑁𝐿 𝑅1,𝑤𝑦𝑒 = 𝑃𝑐𝑜𝑟𝑒 + 𝑃𝑓,𝑤 (15) V. VECTOR CONTROL ALGORITHM A. Clark and Park Transformation The Clarke transform projects the three abc-phases onto a new set of axes where one of the axes is the zerosequence component and the other two axes are the alpha and beta components of the new three phase system. The zero-sequence component is equidistant from the three abc-phase axes resulting in a phase that produces no effect onto the rotor. The alpha axis is aligned with the a-phase axis and the beta axis is aligned so that it is made up of only the b-phase and cphase components. This allows for the manipulation of two sinusoidal signals (alpha and beta) to control the three abc-phase signals sent to the stator The equations governing the Clarke transformation can be seen below. 1 𝛼 2 [𝛽 ] = √ [ 0 3 0 1/√2 −1/2 √3/2 1/√2 −1/2 𝑎 −√3/2] ∗ [𝑏 ] 𝑐 1/√2 signals. The zero component of the alpha-beta-zero phase system is equal to the zero component of the d-qzero phase system. The frequency and reference signal from the encoder allows for the Park transform to take place. The equations can be seen below where the dcomponent controls the flux and the q-component controls the torque. [d q 0 ]=[cos (θ) sin (θ) 0 -sin (θ) cos (θ) 0 0 0 1 ]*[α β 0] (17) This sampled signal is compared to the d- and qcomponents of a reference signal and the difference is sent through a proportional-integral (PI) controller. The two d-component values of the sampled and reference signals should have the same value but the q-component values will differ. This is due to the constant flux motor operating condition. Constant flux is accomplished using a volts-over-hertz (V/Hz) look-up table defined by the parameters of the motor. To maintain constant flux, the voltage of the stator signals must vary with respect to the frequency of signals sent to the stator (as defined by Faraday’s Law). As the frequency of the signal changes, the q-component of the reference signal will also change maintaining constant flux, also manipulating the output torque. The output signal from the PI controller passes through an inverse Park transform block converting the d and q components back into alpha and beta components. These waveforms then produce the new PWM signals using space vector modulation. B. Space Vector Pulse Width Modulation Space vector modulation projects the alpha and beta signals onto each of the inverter state vectors. These projections determine the duty cycle for each inverter state. (16) After the Clarke transformation, the alpha-beta-zero phases are passed through the Park transformation. This transformation rotates the three-dimensional plane of the alpha-beta-zero phases about the zero-sequence axis at the same frequency of the sampled signal, projecting the two alpha and beta phases onto the new set of rotating axes resulting in two dc quantities (the d- and q-components) that now control the three abc-phase For each of the sectors between the inverter states the calculations for the duty cycles of each of the abc-phase signals are shown below. The first set of duty cycle equations are for the a-phase duty cycles per sector. 1 2 𝑡𝑎 𝑡𝑚 [1 + 1 = 2 3𝑓𝑐 2𝑣𝑑𝑐 [1 + 1 𝑣𝑏𝑒𝑡𝑎 (−𝑣𝑎𝑙𝑝ℎ𝑎 − 3𝑓𝑐 2𝑣𝑑𝑐 (−2 √3 𝑣𝑎𝑙𝑝ℎ𝑎 √3 3𝑓𝑐 )]; 𝑠 = 1,4 )]; 𝑠 = 2,5 (18) 𝑣𝑏𝑒𝑡𝑎 {2 [1 + 2𝑣𝑑𝑐 (−𝑣𝑎𝑙𝑝ℎ𝑎 + √3 )]; 𝑠 = 3,6 The second set of calculations are for the b-phase duty cycles per sector. 1 2 𝑡𝑏 𝑡𝑚 [1 + 1 = 2 3𝑓𝑐 2𝑣𝑑𝑐 (𝑣𝑎𝑙𝑝ℎ𝑎 − √3𝑣𝑏𝑒𝑡𝑎 )]; 𝑠 = 1,4 3𝑓𝑐 [1 + 1 2𝑣𝑑𝑐 (−2 𝑣𝑏𝑒𝑡𝑎 √3 3𝑓𝑐 )]; 𝑠 = 2,5 (19) 𝑣𝑏𝑒𝑡𝑎 { 2 [1 + 2𝑣𝑑𝑐 (𝑣𝑎𝑙𝑝ℎ𝑎 − √3 )]; 𝑠 = 3,6 The third set of calculations are for the c-phase duty cycles per sector. 1 2 𝑡𝑐 𝑡𝑚 [1 + 1 = 2 1 3𝑓𝑐 2𝑣𝑑𝑐 [1 + (𝑣𝑎𝑙𝑝ℎ𝑎 + 𝑣𝑏𝑒𝑡𝑎 3𝑓𝑐 )]; 𝑠 = 2,5 2𝑣𝑑𝑐 (2 𝑣𝑏𝑒𝑡𝑎 √3 √3 )]; 𝑠 = 1,4 (20) 3𝑓 𝑐 {2 [1 + 2𝑣𝑑𝑐 (𝑣𝑎𝑙𝑝ℎ𝑎 + √3𝑣𝑏𝑒𝑡𝑎 )]; 𝑠 = 3,6 The variable fc is a compensation factor for when the amplitude of the signal approaches the maximum voltage. The variable tm is the period of each pulse. The duty cycles are then used to generate the PWM signals control the IGBTs. VI. EMBEDDED PROCESSING A. Microcontroller Selection In order to implement the control algorithm, we will need to have a microcontroller with high speed and precision when it comes to heavy computations. Based on these requirements, we have selected the TMS320f28027f microcontroller to drive the inverters. It has multiple 12-bit ADC channels for high precision in signal processing, a 60MHz clock for incredibly fast performance, and four enhanced PWM modules for generating the output signal to the inverter gates. We also wish to have an LCD display that gives the user information on the operations of the motor, such as speed the motor is outputting or the torque being produced. In order to drive this display, we have selected the MSP430f5529 microcontroller. It features 128KB of flash memory for storing a large amount of information, a 25MHz clock for the performance necessary to drive the display, and a large number of general purpose inputoutput pins for sending a large amounts of data to the LCD. While this is not as powerful as the TMS320f28027F, it is more than sufficient for the task at hand. B. Control Algorithm Implementation In order to implement the Space Vector PWM control algorithm, the TMS320f28027f will first receive various feedback signals as inputs. This feedback will provide us with information about the current state of the motor. We will also receive an input signal that will tell us at what frequency we want the motor to run at. Based off of that desired input, we can generate a reference signal to model what we want our output to be. All of these values will be generated through the various ADC pins on the microcontroller. Once we have all of our inputs collected, we generate the reference signal that we will compare our feedback with. We run these signals through the alpha-beta transformation to translate these signal values to their alpha-beta equivalent coordinates. We can then run these coordinates through the direct-quadrature-zero transformation for the equivalent values in the rotating reference frame. These values are run through a PI controller in order to properly match up the feedback signal to the reference signal, and then translated back from the direct-quadrature-zero system to the alpha-beta system using the inverse Park transformation. The next step is to map the alpha and beta values that we have onto the inverter-state map. This will determine the inverter-state signals that will be sent out, as well as the duration of the signals. Once we know the angle of the vector, as well as the magnitude, we will be able to calculate the inverter states and switching frequencies. The PWM is generated and sent as an output. The MSP430f5529 microcontroller will simply be receiving various analog signals as inputs and send those values to the LCD display. This will be done by reading in analog inputs and translating them into the appropriate values and units we wish to have on display. Those values will then be translated through a lookup table created so that each character will be able to be displayed on the 128x64 resolution display. The microcontrollers that we are using for this system will also be implementing SPI communication to send information to each other. Specifically, the TMS320f28027f will be gathering ADC inputs for the MSP430f5529, and will need to send that data to it so that it can be used on the LCD display. The MSP430f5529 will act as the Master, generating clock signals indicating the TMS320f28027f, acting as the Slave, to send the appropriate information. VII. CONCLUSION The variable frequency drive developed by Group F serves to provide an exploratory opportunity to develop a motor control algorithm to suit general purpose needs. With a battery management system and regenerative braking system the VFD can be incorporated into an inverter driven AC motor in a drive train to suit electric vehicle needs. The system incorporates robust power system, sensor interface, and signal processing blocks to achieve the proper signal conditioning required for the MCUs performing the many computations required to achieve vector control. With appropriate closed loop control, torque and speed is controlled effectively. ACKNOWLEDGEMENT The authors wish to acknowledge the assistance and support of Douglas Maukonen and Bobby Wong. REFERENCES [1] “Determination of Induction-Motor Parameters”. University of Massachusetts Dartmouth. ECE 441. www.faculty.umassd.edu/xtras/catls/resources/binarydoc/ 3581.ppt [2] Sinisa Jurkovic. “Induction Motor Parameters Extraction.” Massachusetts Institute of Technology. http://web.mit.edu/kirtley/binlustuff/literature/electric%2 0machine/motor-parameters.pdf [3] R. H. Park “Two-Reaction Theory of Synchronous Machines” NAPS, University of Waterloo, Canada, pp. 81-95, October 2000