AN1958/D 56F800/E 56F800 56F805 56F8346 12VDC AM40V A2510 SG40N 56F803 56F807 - Datasheet Archive
Order by AN1958/D (Motorola Order Number) Rev. 0, 9/2003 Design of a Motor Control Application Based on Processor Expert 1.
Freescale Semiconductor, Inc. Order by AN1958/D AN1958/D (Motorola Order Number) Rev. 0, 9/2003 Design of a Motor Control Application Based on Processor Expert 1. Introduction 1. Introduction . 1 2. Motorola Hybrid Controller Advantages and Features . 1 3. Target Motor Theory . 3 3.1 3-phase AC Induction Motor Drives . 3 3.2 Volts per Hertz Control . 5 3.3 Speed Closed-Loop System. 6 4. System Design Concept . 7 This application note describes the design of a 3-phase AC induction motor drive with Volts per Hertz control in closed-loop (V/Hz CL). It is based on Motorola's 56F800/E 56F800/E hybrid microcontrollers, which are ideal for motor control applications. The system is designed as a motor control system for driving medium-power, 3-phase AC induction motors. The part is targeted toward applications in both the industrial and home appliance industries, such as washing machines, compressors, air conditioning units, pumps, or simple industrial drives. The drive introduced here is intended as an example of a 3-phase AC induction motor drive. The drive serves as an example of AC V/Hz motor control system design using Motorola hybrid controller with Processor ExpertTM (PE) support. This document includes the basic motor theory, system design concept, hardware implementation, and software design, including the PC master software visualization tool inclusion. 2. Contents Motorola Hybrid Controller Advantages and Features The Motorola 56F800/E 56F800/E families are ideal for digital motor control, combining the DSP's calculation capability with the MCU's controller features on a single chip. These controllers offer a rich dedicated peripherals set, such as Pulse Width Modulation (PWM) modules, Analog-to-Digital Converter 5. Hardware . 9 5.1 System Outline . 9 5.2 High-Voltage Hardware Set . 9 6. Software Design . 11 6.1 Data Flow . 11 6.1.1 Acceleration/Deceleration Ramp . 12 6.1.2 Speed Measurement . 12 6.1.3 PI Controller. 12 6.1.4 V/Hz Ramp. 12 6.1.5 DCBus Voltage Ripple Elimination . 13 6.1.6 PWM Generation . 15 6.1.7 Fault Control . 17 7. Software implementation . 18 7.1 Embedded Beans . 18 7.2 Bean Modules . 18 7.2.1 Initialization . 27 7.3 State Diagram . 27 7.3.1 Application State Machine . 29 7.3.2 Check Run/Stop Switch . 29 8. PC Master Software . 29 9. References . 31 © Motorola, Inc., 2002. All rights reserved. For More Information On This Product, Go to: www.freescale.com 3-Phase AC Motor Control with V/Hz Speed Closed Loop Freescale Semiconductor, Inc. 3-Phase AC Motor Control with V/Hz Speed Closed Loop Using the 56F800/E 56F800/E Freescale Semiconductor, Inc. Motorola Hybrid Controller Advantages and Features (ADC), timers, communication peripherals (SCI, SPI, CAN), on-board Flash and RAM. Several parts comprise the family: 56F80x with different peripherals and on-board memory configurations. Generally, all are suited for motor control. A typical member of the 56F800 56F800 family, the 56F805 56F805, provides the following peripheral blocks: Two Pulse Width Modulators (PWMA & PWMB), each with six PWM outputs, three current status inputs, and four fault inputs, fault-tolerant design with dead time insertion; supports both center- and edge- aligned modes · Two 12-bit, Analog-to-Digital Converters (ADCs), supporting two simultaneous conversions with dual 4-pin multiplexed inputs; can be synchronized by PWM modules · Two quadrature decoders (Quad Dec0 & Quad Dec1), each with four inputs, or two additional quad timers (A & B) · Two dedicated general-purpose quad timers totalling six pins: Timer C with two pins and Timer D with four pins · CAN 2.0 A/B module with 2-pin ports used to transmit and receive · Two Serial Communication Interfaces (SCI0 & SCI1), each with two pins, or four additional MPIO lines · Serial Peripheral Interface (SPI), with configurable 4-pin port, or four additional MPIO lines · Computer Operating Properly (COP) timer · Two dedicated external interrupt pins · Fourteen dedicated multiple purpose I/O (MPIO) pins and 18 multiplexed MPIO pins · External reset pin for hardware reset · JTAG/on-chip emulation (OnCETM) · Freescale Semiconductor, Inc. · Software-programmable, phase lock loop-based frequency synthesizer for the hybrid controller core clock The Pulse Width Modulation (PWM) block offers high freedom in its configuration, enabling efficient control of the AC induction motor. The PWM block has the following features: · Three complementary PWM signal pairs, or six independent PWM signals · Features of complementary channel operation · Dead time insertion · Separate top and bottom pulse width correction via current status inputs or software · Separate top and bottom polarity control · Edge-aligned or center-aligned PWM reference signals · 15 bits of resolution · Half-cycle reload capability · Integral reload rates from one to 16 · Individual software-controlled PWM outputs · Programmable fault protection · Polarity control · 20-mA current sink capability on PWM pins · Write-protectable registers The PWM outputs are configured in the complementary mode in this application. 2 3-Phase AC Motor Control with V/Hz Speed Closed Loop For More Information On This Product, Go to: www.freescale.com MOTOROLA Freescale Semiconductor, Inc. Target Motor Theory 3. Target Motor Theory 3.1 3-phase AC Induction Motor Drives The AC induction motor is a workhorse with adjustable speed drive systems. The most popular type is the 3-phase, squirrel-cage AC induction motor. It is a maintenance-free, less noisy and efficient motor. The stator is supplied by a balanced 3-phase AC power source. The synchronous speed ns of the motor is calculated by: Freescale Semiconductor, Inc. 120 × fs n s = -p [ rpm ] (EQ 3-1.) where fs is the synchronous stator frequency in Hz, and p is the number of stator poles. The load torque is produced by slip frequency. The motor speed is characterized by a slip sr: ( ns nr ) n sl s r = - = -ns ns [-] (EQ 3-2.) where nr is the rotor mechanical speed and nsl is the slip speed, both in rpm. Figure 3-1 illustrates the torque characteristics and corresponding slip. As can be seen from EQ 3-1 and EQ 3-2, the motor speed is controlled by variation of a stator frequency with the influence of the load torque. Figure 3-1. Torque-Speed Characteristic at Constant Voltage and Frequency MOTOROLA 3-Phase AC Motor Control with V/Hz Speech Closed Loop For More Information On This Product, Go to: www.freescale.com 3 Freescale Semiconductor, Inc. Target Motor Theory Freescale Semiconductor, Inc. In adjustable speed applications, the AC motors are powered by inverters. The inverter converts DC power to AC power at required frequency and amplitude. The typical 3-phase inverter is illustrated in Figure 3-2. Figure 3-2. 3- Phase Inverter The inverter consists of three half-bridge units; the upper and lower switches are controlled complementarily, which means that when the upper one is turned on, the lower one must be turned off and vice versa. As the power device's turn-off time is longer than its turn-on time, some dead time must be inserted between the turn-off of one transistor of the half-bridge and the turn-on of its complementary device. The output voltage is mostly created by a Pulse Width Modulation (PWM) technique, where an isosceles triangle carrier wave is compared with a fundamental-frequency sine modulating wave, and the natural points of intersection determine the switching points of the power devices of a half bridge inverter. This technique is shown in Figure 3-3. The 3-phase voltage waves are shifted 120o to each other and thus a 3-phase motor can be supplied. 4 3-Phase AC Motor Control with V/Hz Speed Closed Loop For More Information On This Product, Go to: www.freescale.com MOTOROLA Freescale Semiconductor, Inc. Freescale Semiconductor, Inc. Target Motor Theory Figure 3-3. Pulse Width Modulation The most popular power devices for motor control applications are Power MOSFETs and IGBTs. A Power MOSFET is a voltage-controlled transistor. It is designed for high-frequency operation and has a low voltage drop, resulting in low-power losses. However, the saturation temperature sensitivity limits the MOSFET application in high-power applications. An Insulated Gate Bipolar Transistor (IGBT) is a bipolar transistor controlled by a MOSFET on its base. The IGBT requires low-drive current, has fast switching time, and is suitable for high-switching frequencies. The disadvantage is the higher voltage drop of the bipolar transistor, causing higher conduction losses. 3.2 Volts per Hertz Control The Volts per Hertz control method, the most popular technique of Scalar Control, controls the magnitude of such variables as frequency, voltage or current. The command and feedback signals are DC quantities, and are proportional to the respective variables. The purpose of the Volts per Hertz control scheme is to maintain the air-gap flux of AC induction motor in constant, achieving higher run-time efficiency. In steady-state operation, the machine air-gap flux is approximately related to the ratio Vs/fs, where Vs is the amplitude of motor phase voltage and fs is the synchronous electrical frequency applied to the motor. The control system is illustrated in Figure 3-4. The characteristic is defined by the base point of the motor. Below the base point, the motor operates at optimum excitation due to the constant Vs/fs ratio. Above this point, the motor operates under-excited because of the DCBus voltage limit. A simple closed-loop Volts per Hertz speed control for an induction motor is the control technique targeted for low-performance drives. This basic scheme is unsatisfactory for more demanding applications, where speed precision is required. MOTOROLA 3-Phase AC Motor Control with V/Hz Speech Closed Loop For More Information On This Product, Go to: www.freescale.com 5 Freescale Semiconductor, Inc. Freescale Semiconductor, Inc. Target Motor Theory Figure 3-4. Volts per Hertz Control Method 3.3 Speed Closed-Loop System To improve system performance, a closed-loop Volts per Hertz control was introduced. In this method, a speed sensor measures the actual motor speed and the system takes this input into consideration. A number of applications use the closed-loop Volts per Hertz method because of its simple and relatively good speed accuracy, but it is not suitable for systems requiring servo performance or excellent response to highly dynamic torque/speed variations. Figure 3-5 illustrates the general principle of the speed PI control loop. Reference Speed (Omega_required) Speed Error PI Controller Corrected Speed (Omega_command) Controlled System Actual Motor Speed (Omega_actual) Figure 3-5. Closed Loop Control System The speed closed-loop control is characterized by the measurement of the actual motor speed. This information is compared with the reference speed while the error signal is generated. The magnitude and polarity of the error signal correspond to the difference between the actual and required speed. Based on the speed error, the PI controller generates the corrected motor stator frequency to compensate for the error. In an AC V/Hz closed-loop application, the feedback speed signal is derived from the incremental encoder using the Quadrature Decoder. The speed controller constants have been experimentally tuned according to the actual load. 6 3-Phase AC Motor Control with V/Hz Speed Closed Loop For More Information On This Product, Go to: www.freescale.com MOTOROLA Freescale Semiconductor, Inc. System Design Concept 4. System Design Concept The system is designed to drive a 3-phase AC induction motor. The application meets the following performance specifications: · Targeted for 56F800/E 56F800/E EVM platforms · Running on 3-phase ACIM motor control development platform at variable line voltage 115 230V AC · Control technique incorporates - motoring and generating mode - bi-directional rotation Freescale Semiconductor, Inc. - V/Hz speed closed-loop · Manual interface (Start/Stop switch, Up/Down push button speed control, LED indication) · PC master software interface (motor start/stop, speed set-up) · Power stage identification · Overvoltage, undervoltage, overcurrent, and overheating fault protection The AC drive introduced here is designed as a system that meets the general performance requirements in Table 4-1. Table 4-1. Motor / Drive Specification Motor Characteristics Motor Type Speed Range < 5000rpm Base Electrical Frequency 50Hz Max. Electrical Power 180 W Delta Voltage (rms) 200V (Star) Transducers IRC -1024 pulses per revolution Speed Range