Frequency synthesizers. Starikov O. basic circuit, building blocks and noise characteristics of PLL frequency synthesizers Reference frequency

Frequency synthesis - the formation of a discrete set of frequencies from one or more reference frequencies f on. The reference frequency is a highly stable frequency of a self-oscillator, usually quartz.

Frequency synthesizer (MF) is a device that implements the synthesis process. The synthesizer is used in radio receiving and radio transmitting devices of radio communication systems, radio navigation, radar and other purposes.

The main parameters of the synthesizer are: the frequency range of the output signal, the number N and the frequency grid step Df w, long-term and short-term frequency instability, the level of spurious components in the output signal and the transition time from one frequency to another. In modern synthesizers, the number of discrete frequencies it generates can reach tens of thousands, and the grid step can vary from tens of hertz to tens and hundreds of kilohertz. Long-term frequency instability, determined by a quartz self-oscillator, is 10 –6, and in special cases - 10 –8 ... 10 –9. The frequency range of a synthesizer varies widely depending on the purpose of the equipment in which it is used.

Practical frequency synthesizer designs are very diverse. Despite this diversity, it can be noted general principles, which form the basis for the construction of modern synthesizers:

All synthesizers are based on the use of one highly stable reference oscillation with a certain frequency f 0, the source of which is usually a reference crystal oscillator;

The synthesis of multiple frequencies is carried out by the extensive use of dividers, multipliers and frequency converters, ensuring the use of one reference oscillation to form a frequency grid;

Providing frequency synthesizers with a ten-day setting of the exciter frequency.

Based on the method of generating output oscillations, synthesizers are divided into two groups: those made using the direct (passive) synthesis method and those made using the indirect (active) synthesis method.

The first group includes synthesizers in which output oscillations are formed by dividing and multiplying the frequency of the reference oscillator, followed by adding and subtracting the frequencies obtained as a result of division and multiplication.

The second group includes synthesizers that generate output oscillations in a range self-oscillator of harmonic oscillations with parametric frequency stabilization, the instability of which is eliminated by an automatic frequency control (AFC) system based on reference (highly stable) frequencies.

Synthesizers of both groups can be made using analog or digital element base.

Synthesizers made using the direct synthesis method.

A highly stable quartz oscillator generates oscillations with a frequency f 0 , which are supplied to the frequency dividers and multipliers of the MF and HF frequencies.

Frequency dividers reduce the exhaust gas frequency f 0 by an integer number of times (d), and frequency multipliers increase it by an integer number of times (k). The frequencies obtained as a result of dividing and multiplying the frequency of the reference oscillator (f 0) are used to form reference frequencies in special devices called reference frequency sensors. Total reference frequency sensors in a midrange frequency synthesizer depends on the range of frequencies generated by the synthesizer and the interval between adjacent frequencies: the wider the midrange frequency range and the smaller the interval, the greater the number of frequency frequencies required. With a ten-day frequency setting, each DFC generates ten reference frequencies with a certain interval between adjacent frequencies. The total number of required sensors is determined by the number of digits (bits) in the record of the maximum frequency of the synthesizer.

The reference frequencies generated in the sensors are fed to the mixers. Bandpass switchable filters included at the output of the mixers highlight the total frequency in this example: at the output of the first f 1 + f 2 , at the output of the second f 1 + f 2 + f 3 , at the output of the third f 1 + f 2 + f 3 + f 4 .

The frequency at the exciter output with a ten-day setting is determined by the positions of the switches of each decade.

The relative frequency instability at the synthesizer output is equal to the instability of the exhaust gas. The disadvantage of this type of synthesizer is the presence of a large number of combination frequencies at its output, which is explained by the widespread use of mixers.

Frequency synthesizers built using the indirect synthesis method

In synthesizers made using the indirect synthesis method, the source of output oscillations is a range self-oscillator of harmonic oscillations, automatically adjusted to highly stable frequencies generated in the reference frequency block of the BOCH.

The essence of automatic frequency adjustment of the AFC is that the oscillator oscillations using highly stable frequencies are converted to a certain constant frequency f AFC, which is compared with the reference frequency value. If the compared frequencies do not match, a control voltage is generated, which is supplied to the controlled reactive element and changes the value of its reactivity (capacitance or inductance).

Controlled reactive elements are included in the circuit that determines the frequency of the AG. The AG frequency changes until f AFC approaches the reference frequency with a sufficiently small residual detuning.

Depending on the comparison device, all AFC systems can be divided into three types:

Frequency-controlled automatic control systems, in which frequency detectors of black holes are used as a comparison device;

Systems with phase-locked loop phase locking loop, using phase detectors PD as a comparing device;

Systems with pulse-phase automatic frequency control (IFAP), in which the comparing device is pulse-phase detectors IPD.

Synthesizers with phase-locked loop phase locking, unlike

synthesizers with CAP do not have residual detuning. In the FAP system, the comparing device is phase detector FD. The control voltage at the PD output is proportional to the phase difference between the two oscillations applied to it, the frequencies of which are equal in steady state.

Two oscillations of close frequencies are supplied to the PD: one of which is a reference with frequency f 0 generated in the barrel, the second is a product of converting the oscillations of the oscillator in the mixer using a frequency grid f 01 with the barrel

f PR = f UG – f 01.

If f PR and f 0 are close in value, then the control voltage from the PD output compensates for the detuning of the control unit and f PR = f 0, and a stationary mode is established in the system. However, the PLL system operates in a very narrow frequency band, not exceeding a few kHz. To ensure the tuning of the ultrasonic waveform throughout its entire frequency range, an auto-search system is used in a synthesizer with a phase-locking loop, which, by changing the frequency of the ultrasonic waveform throughout the entire frequency range, ensures that it falls within the coverage band of the phase-locking loop system. The auto-search system is a sawtooth voltage self-oscillator, which starts when there is no control voltage at the output of the low-pass filter. As soon as the frequencies of the UG fall into the capture band of the PLL system, the search generator is turned off, the system enters the auto-tuning mode with dynamic equilibrium f PR = f 0 .

The use of logic elements in the midrange led to the emergence of new types of synthesizers, which are called digital. They have significant advantages over analogue ones. They are simpler, more reliable in operation, and have smaller dimensions and weight.

Application of logical integrated circuits in the TsSCH made it possible to almost completely eliminate the frequency conversion of the UG, replacing the converters with a frequency divider with a variable division coefficient DPKD.

Structural scheme synthesizer with one phase-locked loop

In the DPKD diagram - a divider with a variable division coefficient - a K-bit programmable digital counter. The purpose of the other links of the circuit is clear from the inscriptions made on them. The control unit receives and stores programming data and generates a code signal, which sets the value of the division coefficient N depending on the command received by the synthesizer. As a result of the action of phase-locked frequency control, the equality of the frequencies of the signals arriving at the input of the pulse-phase discriminator is established: f 1 = f 2, which allows us to write the following relationship for the frequencies of the stabilized and reference self-oscillators, taking into account the values ​​of the division coefficients:

According to the frequency grid step Df w =f fl /M. By changing the controlled value N, the required frequency value of the stabilized generator is set, which, with the help of a control element, can be tuned in the required frequency range.

LECTURE 7

FREQUENCY SYNTHESIS IN TRANSMISSION DEVICES

Lecture outline:

Basic concepts of frequency synthesis

Parameters of frequency synthesis systems

Classification of frequency synthesis systems

Operating principles various types synthesizers

1 Basic concepts of frequency synthesis theory

To transfer a modulated signal to the required frequency for transmission, it is necessary to generate an oscillation with a frequency that lies in the operating range of the transmitter.

In transmitting devices, they can be used to generate the required frequencies. frequency synthesizers.

Modern frequency synthesis systems operate in the frequency range from fractions of hertz to tens of gigahertz. They are used in equipment for various purposes, replacing simple self-generators.

Frequency synthesis - is the process of obtaining one or more oscillations with the desired nominal frequency values ​​from a finite number of initial oscillations by converting frequencies, i.e. using such operations on vibrations in which addition, subtraction of frequencies and (or) multiplication and division by rational numbers occur.

A set of devices that perform frequency synthesis is called frequency synthesis system . If the frequency synthesis system is made in the form of a structurally independent device, then it is called frequency synthesizer .

2 Parameters of frequency synthesis systems

Indicators that allow one to evaluate the quality of the output oscillation formation (the purity of its spectral line, i.e., its difference from a monoharmonic). As a technical device, any SSC is characterized by a number of operational and technical characteristics.

The main operational and technical characteristics of SSCHs used in exciters of radio transmitters and as local oscillators of radio receivers are:

The set of nominal frequency values ​​that can be obtained at the output of a frequency synthesis system and follow each other at a given interval is called frequency grid .

The interval between adjacent nominal frequency values ​​included in the frequency grid is called frequency grid step. B currently, in frequency synthesis systems with grid spacing are widely used in radio transmitting and receiving equipment
Hz, where a is a positive or negative integer or zero. In addition, systems with grid spacing have become widespread
Hz

3 Classification of frequency synthesis systems

The oscillations that are the initial ones in the process of frequency synthesis are obtained from highly stable sources, which are called reference generators (OG 1, ΟΓ 2, ..., OG n in Fig. 1). The oscillation frequencies of these generators (f 01, f 02, ..., f on in Fig. B1) are called reference frequencies, more precisely, primary reference frequencies. Modern frequency synthesis systems operate, as a rule, from a single reference oscillator (Fig. B.2). Such systems are called single-support (coherent). With two or more reference oscillators, the system is called multi-support (incoherent).

In this case, we can talk about one oscillation, the frequency of which can take on any of these values ​​(see Fig. B.1a), or several simultaneously existing oscillations (see Fig. B.1 b). The first case occurs in exciters of radio transmitters and local oscillators of radio receivers, the second - in multi-channel equipment with frequency division of channels.

Typically, in single-reference frequency synthesis systems, first a device called a reference frequency transducer (RFS) or, more precisely, a secondary reference frequency transducer, generates auxiliary oscillations, the frequencies of which are called secondary reference frequencies. Then a device called a frequency grid transducer (FGS) produces from these auxiliary oscillations the desired output oscillations, the frequencies of which form a grid. Some oscillations are supplied to the output directly from the DOC (see Fig. B.2).

All types of SSCH are divided into two classes:

active frequency synthesis systems;

passive frequency synthesis systems.

Active frequency synthesis systems or, in short, active synthesis systems are called coherent frequency synthesis systems in which the oscillations of the synthesized frequency are filtered using an active filter in the form of a phase-locked loop (PLL).

Passive frequency synthesis systems or, in short, passive synthesis systems are systems of coherent frequency synthesis, in which the oscillation of the synthesized frequency is filtered without the use of a PLL.

Systems of both classes can be implemented entirely on analog elements or using digital element base.

4 An example of the operation of synthesizers based on analog passive frequency synthesis

Ha fig. Figure 1.4 shows a block diagram of the simplest passive synthesis system built on an analog element base. The oscillation of the reference oscillator (RO), having a frequency f 0 (primary reference frequency), is fed to the input of the reference frequency sensor. In the reference frequency sensor (RFS), using a multiplier and a frequency divider, two other oscillations with frequencies are generated
And
(secondary reference frequencies), which are fed to the inputs of two harmonic generators (ΓΓ 1 and ΓΓ 2).

Each of the harmonic generators consists of a pulse shaper (PI 1 and PI 2) and a tunable bandpass filter. The first converts the input quasi-harmonic oscillation into a sequence of very short (compared to the period of this oscillation) pulses of the same frequency (equal, respectively
And
). The spectrum of this sequence contains many higher harmonics; the filter is adjusted to the desired one and selected. As a result, quasi-harmonic oscillations with frequencies are obtained at the outputs of harmonic generators
And
.

Both of these oscillations are fed to a frequency adder consisting of a mixer (CM) and a tunable bandpass filter. The latter selects a quasi-harmonic oscillation with the required frequency from the spectrum of the mixer output product

The mixer is usually implemented as a balanced modulator.

Example. Let
,
, can take values ​​1, 2, 3, a - values ​​20, 21, 22, …, 39, then the system has a frequency range with a grid step
from

Passive digital frequency synthesis

In passive digital synthesis systems, the formation of the required frequency is carried out by digital signal processing, and only an analog filter is used at the system output.

The block diagram of the SSCH based on passive digital frequency synthesis is shown in Fig. 1.8.

Rice. 1.8. Block diagram of one of the options for a passive digital synthesis system

The reference oscillator generates a highly stable oscillation with a reference frequency that is used to obtain the desired frequency at the synthesizer output. This reference oscillation is converted into a sequence of rectangular pulses in a pulse shaper (PI) by limiting the level above and below the generated oscillation. At the output of a variable frequency divider (VFD), the sequence of input pulses is converted into a sequence of pulses that follows at a frequency determined by the division ratio. Division ratio N can be set to any integer value ranging from N1 to N2. Its value is determined by the counting device based on the frequency set on the frequency control panel. A trigger-based counter generates digital pulses with the required duty cycle. Bandpass filter(PF) restores a harmonic oscillation with the required frequency from this sequence of pulses.

Let's look at an example. Let, for example, you want to synthesize a frequency grid from 20 to 25 kHz with a step of 1 kHz. In this case, the frequency of the reference oscillator corresponds to 1 MHz.

In this case, you can use division factors N=25 (1,000,000/25 = 40,000) and N= 20 (1,000,000/20 = 50,000), at which frequencies of 40 kHz and 50 kHz will be generated with a step of 2 kHz. In the counter, based on these frequencies, a stream of rectangular pulses with a duty cycle of 2 and a frequency that can take on all the desired values ​​can be generated. Finally, you can use a bandpass filter with cutoff frequencies of 20 kHz (lower) and 30 kHz (upper) to isolate the desired vibrations by suppressing higher harmonics.

Purpose and principle of operation of frequency synthesizers

The frequency synthesizer is designed to control the VCO frequency (125..177.5) MHz with stability equal to the stability of the reference oscillator, and to form a grid of reference frequencies with a resolution of 25 kHz in the VHF and UHF range.

The frequency synthesizer performs the following functions:

It produces a control voltage in accordance with the channel dialed on the control panel (code of a given operating frequency) to set the VCO frequency with a given stability (1·10 -6), to configure the UHF receiver, to roughly set the frequencies of the exciter self-oscillators.

Based on the selected values ​​of intermediate frequencies and types of transformations, the frequency synthesizer ensures the formation of a VCO frequency grid:

MV: 125..174.975 MHz with an interval of 25 kHz;

UHF-1: 132.5..172.4875 MHz with an interval of 12.5 kHz;

UHF-2: 127.5..177.4875) MHz with an interval of 12.5 kHz;

Provides MV and DMV-1 signs to the switching unit.

Provides synchronization voltage to the control panel via three wires, which allows you to receive information about the dialed channel from the control panel via two wires.

The construction of a frequency synthesizer is based on the properties inherent in a PLL system with a frequency divider in the circuit feedback with preliminary conversion of harmonic oscillations of the VCO and reference oscillator using shaping devices into a sequence of video pulses. This made it possible to widely use elements and components of discrete technology when implementing synthesizer circuits and served as the basis for calling such systems digital synthesizers.

Thus, the synthesizer together with the VCO represents a PLL circuit.

To explain the digital method of generating and stabilizing a discrete set of frequencies, let’s consider a qualitative picture of the processes occurring in a digital synthesizer.

The harmonic signal of a highly stable reference oscillator with a frequency of 10 MHz (the stability of the reference oscillator frequency is no worse than ± 1·10 -6 under all operating conditions) is initially fed to a forming device, with the help of which it is converted into a sequence of unipolar pulses with a comparison frequency f cf = 781, 25 Hz, i.e. the frequency of the reference oscillator is divided to the comparison frequency f cf =781.25 Hz.

In this case, the frequency synthesizer together with the VCO, which is functionally part of the UHF, represents a closed PLL system. The auto-tuning ring operates at a low reference frequency of 781.25 Hz.

The nominal value of this frequency is determined by the frequency spacing between channels (25 kHz), the presence of a divider with a constant division factor (by 8 in the VChD and by 2 in the BUCH) and a doubler in the local oscillator.

The VCO frequency is successively reduced by constant and variable dividers.

The divided frequencies of the VCO and the reference oscillator are fed to the PD for comparison.

If the output frequency of the DPCD (f dpkd) is not equal to the comparison frequency (f cf), then the PD generates an error signal that controls the VCO frequency. In this case, the VCO frequency changes so that the output frequency of the DPCD becomes equal to the comparison frequency (f DPCD = f av = 781.25 Hz) accurate to the phase (fine tuning).

where f gun is the frequency of the VCO; 8 – ICP division coefficient; 2 – division coefficient of the divider included in the BUCH; N – DPKD division coefficient.

The required DPKD coefficient is set from the control panel through the system remote control The SDU allows you to set any communication frequency via five wires, connecting the control panel with the frequency synthesizer.

Frequency reference block (block 1-1)

The BOCH is designed to form a highly stable reference oscillator frequency of 10 MHz and lower it to the comparison frequency.

BOCH provides:

generation of a reference signal with a frequency of 20 MHz;

generation of a synchronization signal;

generation of gating pulses for SDS.

The composition of the BOCH includes:

Reference generator (subblock 1-1-1) GO-4A;

Shaper-doubler (subblock 1-1-2);

Reference frequency divider.

The reference oscillator is used to obtain a highly stable (stability no worse than ± 1·10 -6) voltage with a frequency of 10 MHz.

High frequency stability of the quartz oscillator is achieved by thermostatting the generator elements and stabilizing the supply voltage.

A sinusoidal voltage with a frequency of 10 MHz is amplified by an amplifier and supplied (Figure 3.1)

To the driver, where it generates a rectangular voltage to run the reference frequency divider;

To the doubler, where the voltage of the second local oscillator is formed f og = 20 MHz in the UHF range.

The doubler is assembled using a differential circuit and is activated in the UHF sub-bands by the “UHF SIGN” command from the switching unit.

The reference frequency divider generates:

For FD, the starting voltage of the saw generator with a frequency f av = 781.25 Hz;

For SDS, a synchronization signal with a frequency f cf;

Gating pulses with a frequency of 1562.5 Hz for the SDS decoder.

The DOC is a divider that provides a division coefficient N = 12800, which is ensured by sequentially connecting a divider by 25 and nine dividers by 2. The DOC generates signals (Figure 3.2):

- “saw start” to start the saw generator in the PD unit;

- “SDS synchronization” to start the SDS synchronizer;

- “gating pulse” to launch the SDS decoder.

Figure 3.1

According to the latest statistics, approximately 70% of all electricity generated in the world is consumed by electric drives. And every year this percentage is growing.

With a correctly selected method of controlling an electric motor, it is possible to obtain maximum efficiency, maximum torque on the shaft of the electric machine, and at the same time the overall performance of the mechanism will increase. Efficiently operating electric motors consume a minimum of electricity and provide maximum efficiency.

For electric motors powered by an inverter, the efficiency will largely depend on the chosen method of controlling the electrical machine. Only by understanding the merits of each method can engineers and drive system designers get the maximum performance from each control method.
Content:

Control methods

Many people working in the field of automation, but not closely involved in the development and implementation of electric drive systems, believe that electric motor control consists of a sequence of commands entered using an interface from a control panel or PC. Yes, from the point of view of the general hierarchy of control of an automated system, this is correct, but there are also ways to control the electric motor itself. It is these methods that will have the maximum impact on the performance of the entire system.

For asynchronous motors connected to a frequency converter, there are four main control methods:

• U/f – volts per hertz;
• U/f with encoder;
• Open-loop vector control;
• Closed loop vector control;

All four methods use PWM pulse width modulation, which changes the width of a fixed signal by varying the width of the pulses to create an analog signal.

Pulse width modulation is applied to the frequency converter by using a fixed DC bus voltage. by quick opening and closings (more correctly, switching) generate output pulses. By varying the width of these pulses at the output, a “sinusoid” of the desired frequency is obtained. Even if the shape of the output voltage of the transistors is pulsed, the current is still obtained in the form of a sinusoid, since the electric motor has an inductance that affects the shape of the current. All control methods are based on PWM modulation. The difference between control methods lies only in the method of calculating the voltage supplied to the electric motor.

In this case, the carrier frequency (shown in red) represents the maximum switching frequency of the transistors. The carrier frequency for inverters is usually in the range of 2 kHz - 15 kHz. The frequency reference (shown in blue) is the output frequency command signal. For inverters used in conventional electric drive systems, as a rule, it ranges from 0 Hz to 60 Hz. When signals of two frequencies are superimposed on each other, a signal will be issued to open the transistor (indicated in black), which supplies power voltage to the electric motor.

U/F control method

Volt-per-Hz control, most commonly referred to as U/F, is perhaps the simplest control method. It is often used in simple electric drive systems due to its simplicity and the minimum number of parameters required for operation. This control method does not require the mandatory installation of an encoder and mandatory settings for a variable-frequency electric drive (but is recommended). This leads to lower costs for auxiliary equipment (sensors, feedback wires, relays, etc.). U/F control is quite often used in high-frequency equipment, for example, it is often used in CNC machines to drive spindle rotation.

The constant torque model has constant torque over the entire speed range with the same U/F ratio. The variable torque ratio model has a lower supply voltage at low speeds. This is necessary to prevent saturation of the electrical machine.

U/F is the only way to regulate the speed of an asynchronous electric motor, which allows the control of several electric drives from one frequency converter. Accordingly, all machines start and stop simultaneously and operate at the same frequency.

But this method control has several limitations. For example, when using the U/F control method without an encoder, there is absolutely no certainty that the shaft of an asynchronous machine rotates. In addition, the starting torque of an electric machine at a frequency of 3 Hz is limited to 150%. Yes, the limited torque is more than enough to accommodate most existing equipment. For example, almost all fans and pumps use the U/F control method.

This method is relatively simple due to its looser specification. Speed ​​regulation is typically in the range of 2% - 3% of the maximum output frequency. The speed response is calculated for frequencies above 3 Hz. The response speed of the frequency converter is determined by the speed of its response to changes in the reference frequency. The higher the response speed, the faster the electric drive will respond to changes in the speed setting.

The speed control range when using the U/F method is 1:40. By multiplying this ratio by the maximum operating frequency of the electric drive, we obtain the value of the minimum frequency at which the electric machine can operate. For example, if the maximum frequency value is 60 Hz and the range is 1:40, then the minimum frequency value will be 1.5 Hz.

The U/F pattern determines the relationship between frequency and voltage during operation of a variable frequency drive. According to it, the rotation speed setting curve (motor frequency) will determine, in addition to the frequency value, also the voltage value supplied to the terminals of the electric machine.

Operators and technicians can select the desired U/F control pattern with one parameter in a modern frequency converter. Pre-installed templates are already optimized for specific applications. There are also opportunities to create your own templates that will be optimized for a specific variable frequency drive or electric motor system.

Devices such as fans or pumps have a load torque that depends on their rotation speed. The variable torque (picture above) of the U/F pattern prevents control errors and improves efficiency. This control model reduces magnetizing currents by low frequencies by reducing the voltage on the electrical machine.

Constant torque mechanisms such as conveyors, extruders and other equipment use a constant torque control method. With constant load, full magnetizing current is required at all speeds. Accordingly, the characteristic has a straight slope throughout the entire speed range.

U/F control method with encoder

If it is necessary to increase the accuracy of rotation speed control, an encoder is added to the control system. The introduction of speed feedback using an encoder allows you to increase the control accuracy to 0.03%. Output voltage will still be determined by the given U/F pattern.

This control method is not widely used, since the advantages it provides compared to standard U/F functions are minimal. Starting torque, response speed and speed control range are all identical to standard U/F. In addition, when operating frequencies increase, problems with the operation of the encoder may arise, since it has a limited number of revolutions.

Open-loop vector control

Open-loop vector control (VC) is used for broader and more dynamic speed control of an electrical machine. When starting from a frequency converter, electric motors can develop a starting torque of 200% of the rated torque at a frequency of only 0.3 Hz. This significantly expands the list of mechanisms where an asynchronous electric drive with vector control can be used. This method also allows you to control the machine's torque in all four quadrants.

The torque is limited by the motor. This is necessary to prevent damage to equipment, machinery or products. The value of torques is divided into four different quadrants, depending on the direction of rotation of the electric machine (forward or reverse) and depending on whether the electric motor implements . Limits can be set for each quadrant individually, or the user can set the overall torque in the frequency converter.

The motor mode of an asynchronous machine will be provided that the magnetic field of the rotor lags behind magnetic field stator. If the rotor magnetic field begins to outstrip the stator magnetic field, then the machine will enter regenerative braking mode with energy release; in other words, the asynchronous motor will switch to generator mode.

For example, a bottle capping machine may use torque limiting in quadrant 1 (forward direction with positive torque) to prevent overtightening of a bottle cap. The mechanism moves forward and uses the positive torque to tighten the bottle cap. But a device such as an elevator with a counterweight heavier than the empty car will use quadrant 2 (reverse rotation and positive torque). If the cabin rises to the top floor, then the torque will be opposite to the speed. This is necessary to limit the lifting speed and prevent the counterweight from free falling, since it is heavier than the cabin.

Current feedback in these frequency converters allows you to set limits on the torque and current of the electric motor, since as the current increases, the torque also increases. The output voltage of the inverter may increase if the mechanism requires more torque, or decrease if its maximum permissible value is reached. This makes the vector control principle of an asynchronous machine more flexible and dynamic compared to the U/F principle.

Also, frequency converters with vector control and open loop have a faster speed response of 10 Hz, which makes it possible to use it in mechanisms with shock loads. For example, in rock crushers, the load is constantly changing and depends on the volume and dimensions of the rock being processed.

Unlike the U/F control pattern, vector control uses a vector algorithm to determine the maximum effective operating voltage of the electric motor.

Vector control unit decides this task due to the presence of motor current feedback. As a rule, current feedback is generated by the internal current transformers of the frequency converter itself. Using the obtained current value, the frequency converter calculates the torque and flux of the electrical machine. The basic motor current vector is mathematically split into a vector of magnetizing current (I d) and torque (I q).

Using the data and parameters of the electrical machine, the inverter calculates the vectors of the magnetizing current (I d) and torque (I q). To achieve maximum performance, the frequency converter must keep I d and I q separated by an angle of 90 0. This is significant because sin 90 0 = 1 and a value of 1 represents the maximum torque value.

In general, vector control of an induction motor provides tighter control. The speed regulation is approximately ±0.2% of the maximum frequency, and the regulation range reaches 1:200, which can maintain torque when running at low speeds.

Vector feedback control

Feedback vector control uses the same control algorithm as open-loop VAC. The main difference is the presence of an encoder, which allows the variable frequency drive to develop 200% starting torque at 0 rpm. This point is simply necessary to create an initial moment when starting off elevators, cranes and other lifting machines to prevent cargo subsidence.

The presence of a speed feedback sensor allows you to increase the system response time to more than 50 Hz, as well as expand the speed control range to 1:1500. Also, the presence of feedback allows you to control not the speed of the electric machine, but the torque. In some mechanisms, it is the torque value that is of great importance. For example, winding machine, clogging mechanisms and others. In such devices it is necessary to regulate the torque of the machine.

3.1 Purpose and use of the control panel frequency converter

On the control panel frequency converter There are 2 indication displays (4 digits, 7 segments), control buttons, an analog potentiometer, operation indicators and block indicators. Using the buttons, you can set functional parameters, issue control commands and control the work frequency converter.

Control panel display

When setting (viewing) the functional parameters of the converter, the codes of the corresponding parameters are displayed on the upper display of the control panel, and their values ​​are displayed on the lower display.

In the operating mode of the converter, the current values ​​of the quantities are displayed on both screens, which are selected using functional parameters F 001 and F 002, when an error occurs - status error code frequency converter.

Function buttons

Indicators

Viewing and changing function parameter values frequency converter

IN frequency converters STA series C 5. CP/STA- C 3. CS there are more than two hundred functional parameters stored in the internal memory, the values ​​of which can be viewed and changed, thereby forming various operating modes and a general operating algorithm frequency converter. The values ​​of most parameters can be changed during operation frequency converter(for more details, see the table of functional parameters), and they are automatically saved when it is turned off.

For example, you need to change the carrier frequency of the inverter from 3 kHz (factory setting) to 6 kHz. Then you need to do the following:

3.2 Test run frequency converter

Control mode selection frequency converter

IN frequency converters STA series C 5. CP/STA- C 3. CS There are two main control modes frequency converter in operating mode: local (from the converter control panel) and remote (from the converter control terminals or via the interface R.S. -485). To determine the control mode of the frequency converter, a functional parameter is used F003.

Before the test run

Before the test run, check the correct connection of the power circuits, the tightness of the bolts, the routing of the wires, the integrity of the power cables, and the load.

During the test run

During the test run, make sure that the engine accelerates and stops smoothly, rotates in the specified direction, there are no unusual vibrations, unusual sounds, and the displays display accurate values.

Checking the direction of rotation of the motor

When power is applied to a frequency converter, the upper display of the control panel displays the inscription “C T.A. ", then both displays show the value "0.00" (if this value is greater than 0.00, turn the potentiometer to the leftmost position). The block indicators “Hz” and the operation indicator “M/D” begin to light up. This means that the reference frequency is indicated on the upper display, and the output frequency on the lower display.

Press and hold the REVERSE / STEP button, it starts frequency converter, the operation indicators “VOLTAGE” and “DIRECT” begin to light up. The upper display of the control panel displays the value of the reference frequency for the step mode - 5.00 Hz, the lower screen displays the output frequency (from 0.00 to 5.00 Hz), which, in accordance with the acceleration time in the step mode (functional parameter F032), increases to 5 Hz ( to the reference frequency). Release the REVERSE/STEP button. The display on the lower display of the control panel decreases to zero (the engine stops). The display value returns to its original value.

If the motor rotates in a direction different from the required one, then it is necessary to change the value of functional parameter F046. Change the order of connecting phases in a connection frequency converter and there is no need for an engine.

Using the control panel potentiometer during start-up

Apply power to a frequency converter, both control panel displays show the value “0.00”, if this value is greater than 0.00, be sure to turn the inverter control panel potentiometer to the extreme left position. The block indicators “Hz” and the operation indicator “M/D” begin to light up.

Press the START button, the “VOLTAGE” indicator lights up and the “DIRECT” indicator starts flashing. The inverter operates by producing an output frequency that is less than the minimum starting frequency. Turn the potentiometer clockwise to set the reference frequency of the converter. Now the upper display of the control panel displays the set reference frequency, and the lower display shows the output frequency, increasing from 0.00 Hz to the reference frequency value in accordance with the acceleration time of the converter (functional parameter F 019).

Also check other operating parameters of the inverter such as voltage, current using the ENTER/VD and CANCEL/ND function keys.

When the STOP/RESET function button is pressed, the inverter stops operating, reducing the output frequency from the reference (output if the reference has not yet been reached) to zero.

Setting/changing the converter reference frequency

Let's say it is necessary in local control mode frequency converter with constant acceleration and deceleration times, start the engine at a reference frequency of the supply voltage of 20 Hz in the forward direction, then accelerate it in the same direction to the rated speed at a reference frequency of the supply voltage of 50 Hz (the reference frequency setting mode is digital from the converter control panel), then carry out a reverse at a reference frequency of the supply voltage of 50 Hz and stop.