Energy feedback device suppliers remind you that due to the complex characteristics of electric power transmission, electric motors frequently operate in both forward and reverse directions, often in a state of overload operation and continuous switching between electric and braking; Its safety and reliability are also crucial. The frequency conversion technology of AC motors has become increasingly sophisticated, and the use of frequency converters for AC asynchronous motor speed regulation has become the most important energy-saving technology for motor speed regulation.
Communication speed regulation has evolved from stator voltage regulation speed regulation, wound rotor series pole speed regulation, electromagnetic slip clutch speed regulation in the 1970s to variable frequency speed regulation in the 1980s, and various technologies have reached the practical stage. With the increasing reliability and lower price of AC speed regulation, replacing DC speed regulation has become an inevitable trend.
1. Frequency converter and energy conservation
When regulating speed below the fundamental frequency of asynchronous motors, a control method with constant voltage frequency ratio and stator voltage drop compensation is usually adopted; If the speed is adjusted above the fundamental frequency, the control method of constant voltage and variable frequency is usually adopted. By combining the above two situations, the variable voltage and variable frequency speed control characteristics of asynchronous motors can be obtained. Corresponding to the DIT algorithm, according to the principle of symmetry, if x (n) is decomposed into two groups in the time domain, then in the frequency domain, X (k) will form odd even sampling groups, forming another commonly used FFT structure called the frequency-domain sampling FFT (DIF-FFT) algorithm. As it was first proposed by Sande and Turky, it is also commonly known as the Sande Turky algorithm.
The braking circuit in a universal frequency converter is designed to meet the braking needs of asynchronous motors. In the variable frequency drive system, in order to slow down and stop the asynchronous motor, the method of gradually reducing the output frequency of the universal frequency converter can be used to reduce the synchronous speed of the asynchronous motor, thereby achieving the purpose of slowing down the motor. During the deceleration process of the asynchronous motor, due to the synchronous speed being lower than the actual speed of the asynchronous motor, the phase of the rotor current will be reversed, causing the asynchronous motor to generate braking torque, that is, in a regenerative braking state. For large and medium capacity universal frequency converters, in order to save energy, a power regeneration unit is generally used to feed back the above energy to the power supply. For small capacity universal frequency converters, a braking circuit is usually used to consume the energy feedback from the asynchronous motor in the braking circuit. In engineering, the treatment of regenerative braking energy generally includes methods such as storage, feedback to the power grid, and resistance discharge, depending on the capacity and application scenarios of general frequency converters.
2. Application of Variable Frequency Speed Control Technology in Electrical Automation Control
2.1. Characteristics of Variable Frequency Speed Control
All Cyclone II devices use 300mm wafers and are manufactured based on TSMC 90nm, low-K processes to ensure high speed and low cost. Due to the use of minimized silicon regions, the Cyclone II series devices can support complex digital systems with only one chip, at a cost equivalent to a dedicated integrated circuit. High performance universal frequency converters have several hardware structures to meet different engineering needs: independent frequency converters, common DC bus frequency converters, and frequency converters with energy feedback units. Independent frequency converter is a type of frequency converter that places the rectifier unit and inverter unit in a single casing. It is currently the most widely used frequency converter and generally only drives one electric motor, used for general industrial loads. The configuration method used is a combination of JTAG and AS, so the configuration circuit must meet both AS and JTAG configuration requirements. The configuration chip adopts EPCS1. According to the specific connection method and pin characteristics of the configuration method mentioned above. When driving loads such as elevators, lifts, and reversible rolling mills with high-performance universal frequency converters, four quadrant operation is required, so an energy feedback unit must be configured. The function of the energy feedback unit is to feed back the regenerative energy generated during the braking of the electric motor to the power grid.
2.2. Application of Variable Frequency Speed Control Technology in Industrial Electrical Automation Control
(1) Adaptive motor model unit. The function of the adaptive motor model unit is to automatically identify the basic parameters of the motor by detecting the voltage and current input to the motor. This motor model is a key unit of direct torque control. For most industrial applications, if the speed control accuracy is greater than 0.5%, closed-loop speed feedback can be used.
(2) Torque comparator and magnetic flux comparator. The function of this type of comparator is to compare the feedback value with its reference value every 20ms, and output the state of torque or magnetic field by using a two-point hysteresis regulator.
(3) Pulse optimization selector. We selected the Cyclone II EP2C5Q208C8 chip to process information, and then designed the FPGA implementation of the signal source for OFDM modulation. We wrote a circuit consisting of five modules, mainly implementing constellation mapping FFT、 Inserting cyclic prefix, buffer module, and D/A functions, an OFDM signal source was designed, and the functions of each module were simulated and verified. Finally, the OFDM signal source was completed, including software simulation and FPGA hardware verification. Due to the significant variability in the capacity of electrolytic capacitors, they will experience unequal voltages. Therefore, a voltage equalizing resistor with equal resistance value is connected in parallel to each capacitor to eliminate the influence of variability. In order to prevent the charging current (surge current) flowing through the capacitor from burning out the rectifier circuit and causing other impacts when the power is turned on, measures to suppress surge current are also added to the storage circuit.
Energy conservation and consumption reduction are important means to reduce production costs, and cost reduction is an effective means to enhance product competitiveness. In addition to adding these functional modules, it is also necessary to continuously optimize the completed design during the design process, further improve performance and save resources, in order to achieve the entire system within one FPGA chip, achieve significant energy-saving effects, and improve process conditions.