The National Technical Committee on Standardization of Semiconductor Power Converters for Power Electronic Speed Control Electrical Drive Systems was established in 2000 amidst the rapid development of electrical drive speed control products both domestically and internationally. Its secretariat is affiliated with the Tianjin Electrical Drive Design Institute. The committee is responsible for organizing and managing standardization work in the field of electrical drive speed control systems, primarily covering AC/DC electrical drive equipment for the basic industries of the national economy. It has formulated six national and industry standards for electrical drive speed control systems : GB/ T3886.1-2002 , JB/T10251-2001, GB/ T12668.1-2003 , GB/ T12668.2-2003 , GB12668.3-2004 , and GB/T12668.4 .
To improve quality control throughout the entire product process, a number of supporting standards, such as test methods for speed control devices, environmental conditions for speed control devices, technical conditions for speed control devices, acceptance procedures for speed control devices, and safety procedures for speed control devices, will be gradually implemented between 2005 and 2007.
Currently, there is a great deal of attention focused on the National Compulsory Product Certification (3C certification), which is based on national standards and technical regulations. The first batch of products subject to compulsory product certification published by the state includes 19 categories and 132 types of products. Although electric drive speed control products are not included in the first batch of products, in order to accelerate the dissemination and implementation of the standard and the preparation for 3C certification, this introduction to the standard is presented as the first article in a series to communicate with everyone.
1. Scope of application of GB/ T12668.2 standard
GB/T 12668.2-2003, "Speed-Regulating Electrical Drive Systems Part 2: General Requirements – Specifications for Ratings of Low-Voltage AC Variable Frequency Electrical Drive Systems," applies to general-purpose AC speed-regulating drive systems (see Figure 1). These systems consist of electrical equipment (including converter sections, AC motors, and other equipment, but not limited to the power supply section) and control equipment (including switching controls—such as on/off controls, voltage, frequency, or current controls, triggering systems, protection, condition monitoring, communication, testing, diagnostics, process interfaces/ports, etc.). This standard does not apply to traction drives and electric vehicle drives; it applies to electrical drive systems connected to an AC power supply voltage below 1kV, 50Hz or 60Hz, with a load-side frequency up to 600Hz. This standard specifies requirements for inverter ratings, normal operating conditions, overload conditions, surge withstand capability, stability, protection, AC power supply grounding, and testing performance.
This article introduces the parameter ratings and test requirements of relevant low-voltage frequency converters.
2. Functional characteristics of frequency converters
The frequency converter should possess certain specified characteristics, which may include (but are not limited to) one or more of the following:
Timed acceleration;
Timed deceleration;
Inching;
Adjustable current limiting;
Energy-efficient braking;
Reverse;
Regeneration (braking);
Power grid filtering;
Input/output data processing (analog/digital);
Automatic restart;
(Torque) Boost;
DC braking;
Pre-charge circuit.
The frequency converter should be equipped with a specified fault indication, which may consist of two parts: a common alarm and/or trip signal provided by a dry-type relay or a solid-state relay. The fault indication typically activates in response to one or more faults, including (but not limited to) the following:
External failure;
Output power section fault;
Instantaneous overcurrent;
Overheating (inverter);
No cooling air;
Motor overload;
Auxiliary power supply failure;
Overvoltage/undervoltage of the power supply;
Power supply phase loss;
Internal control system malfunction;
Regulator/power circuit diagnostics.
The frequency converter should have a "drive engaged" status indication signal (whether rotating or stopped); it may also have a "drive ready" status indication signal.
3. Inverter operating conditions
3.1 Electrical operating conditions
It is necessary to consider factors such as frequency variation, voltage variation, voltage imbalance, power supply impedance, power supply harmonics, and some abnormal conditions: for example, the frequency is fLN±2%; the limit of the rated input voltage variation is ±10%; and the power supply voltage imbalance should not exceed 3% of the fundamental rated input voltage (ULN1).
3.2 Environmental Usage Conditions
This mainly includes climatic conditions and mechanical installation conditions: such as ambient temperature +5°C to +40°C; the frequency converter should be installed on a sturdy indoor base, and its installation area or additional housing should not seriously affect the ventilation or cooling system. Abnormal environmental operating conditions, such as exposure to excessive dust, altitude >1000m, etc., require specially selected structural or protective components.
3.3 Inverter Storage
If the shipping packaging is not suitable for outdoor or unprotected storage, the inverter should be placed in a location that meets the storage requirements immediately upon receipt.
Inverters should be stored away from rain, snow, freezing rain, and corrosive materials. They should not be stored in places more than 3,000 meters above sea level, and the total storage time should not exceed 6 months.
3.4 Transportation of Frequency Converters
The frequency converter should be able to be transported in the supplier's standard packaging box at an ambient temperature of -25°C to +70°C. Abnormal weather conditions...
If the transport temperature is below -25°C, heated transport or other methods should be used. Shock and vibration environments must not exceed the specified limits.
4. Inverter Ratings
4.1 Input rated value
Voltage; the manufacturer should specify the input ratings of the frequency converter, with the preferred values being:
a) 100, 110, 200, 220, 230, 240, 380, 400, 415, 440, 500, 660, 690V, for 50Hz;
b) 100, 115, 120, 200, 208, 220, 230, 240, 400, 440, 460, 480, 575, 600V for 60Hz.
Rated input current IVN value;
frequency;
number of phases;
Minimum power supply impedance (or maximum expected short-circuit current) and maximum power supply impedance.
4.2 Output Rated Value
Maximum rated output voltage;
Rated continuous current;
Overload capacity (overload capacity applies to the rated speed range);
Frequency range;
number of phases;
Rated power;
Output phase sequence.
4.3 Operating frequency range
The manufacturer should provide the following parameters to indicate the operating frequency range in which the frequency converter can maintain its specified steady-state output current:
fmin = minimum frequency;
f0 = fundamental frequency;
fmax = maximum frequency.
4.4 Efficiency and Losses
The manufacturer should provide the losses or efficiency at rated load and basic speed.
5. Inverter test
5.1 Test Type
Test types include type tests, factory tests, sampling tests, selection (special) tests, workshop tests, acceptance tests, on-site commissioning tests, and witnessed tests.
1) Type testing is a test conducted on one or more components manufactured according to a certain design to demonstrate that the design meets specific technical requirements.
2) Factory testing refers to tests conducted on individual components during or after manufacturing to determine whether they meet a certain criterion.
3) Sampling test: A test conducted on some parts randomly selected from a batch of products.
4) Select (specialized) tests, in addition to type tests and factory tests, tests conducted at the manufacturer's discretion or through consultation between the manufacturer and the user or their agent.
5) Workshop testing: Tests conducted on components or equipment in the manufacturer's laboratory to verify the design.
6) Acceptance testing, as specified in the contract, is a test used to demonstrate to the user that the component meets certain conditions in its technical specifications.
7) On-site commissioning tests: Tests conducted on components or equipment on-site to verify the correctness of installation and operation.
8) Witness test: Any of the above tests conducted in the presence of the customer, user or their agent.
5.2 Standard Tests for Frequency Converters
The standard test items for frequency converters are shown in the table below:
The purpose of the insulation test is to check the insulation condition of the frequency converter. To prevent unnecessary damage, the insulation resistance of the tested part can be measured with a 1000V megohmmeter before the test. Under the conditions of ambient temperature of 20±5°C and relative humidity of 90%, the value should not be less than 1MW. However, the measured insulation resistance is only used as a reference for the withstand voltage test and is not used for assessment.
The purpose of light load and functional tests is to verify that all parts of the inverter's electrical circuitry and cooling system are correctly connected, that it can operate normally with the main circuit, and that the static characteristics of the equipment meet the specified requirements. When this test is performed as a factory test, the inverter operates only at its rated input voltage. However, during type testing, the equipment's functionality should be verified at both the maximum and minimum values of the rated voltage.
The rated current test is to verify whether the frequency converter can operate satisfactorily under the rated current.
The overcurrent capacity test is part of the load test. Under rated operating conditions, a specified short-time overcurrent value is applied at specified time intervals, and the frequency converter can operate normally.
Ripple voltage and current measurements are performed only upon request by the user or their agent, and in accordance with the provisions of GB/ T3859.2 Electrical Test Methods and Product Classification Standards.
Power loss can be calculated based on measurements or directly determined. The power loss of an indirectly cooled converter can be calculated from the measured heat transferred by the heat transfer medium (using calorimetry) and the estimated heat flow through the converter housing.
The purpose of the temperature rise test is to determine whether the temperature rise of each component of the frequency converter exceeds the specified limit temperature rise when operating under rated conditions. The test should be conducted under the specified rated current and duty cycle, and under the most unfavorable cooling conditions.
Under normal circumstances, it is not necessary to measure the power factor. When measurement is required, the total power factor l should be determined.
The inherent voltage regulation rate is measured and calculated based on data obtained from light load tests and rated current tests when the inverter voltage is equal to the rated value (see GB/ T3859.2 ).
The inspection of auxiliary components mainly involves testing the performance of the inverter's electrical components, pumps, fans, and other auxiliary devices. However, as long as these components have factory certificates of conformity, only their operational functions within the inverter need to be tested, and it is not necessary to repeat the factory tests.
The performance test of control equipment is best performed using a motor with a similar rated power. Alternatively, a lower power motor can be used, provided the feedback is appropriately converted.
The inspection of protection devices mainly includes the overcurrent settings of various overcurrent protection devices; the correct operation of fast-acting fuses and fast-acting switches; the correct operation of various overvoltage protection facilities; the normal operation of the protection facilities of the device's cooling system; the correct setting of grounding devices and switches for safe operation; and the mutual coordination of various protection devices.
Electromagnetic interference (EMI) immunity is the performance of various sub-components of a frequency converter, such as power electronic circuits, drive circuits, protection circuits, control circuits, and display and control panels, tested to their immunity to electromagnetic interference. EMI can be categorized into low-frequency and high-frequency interference. Low-frequency interference includes harmonics and commutation gaps/voltage distortion; voltage variations, fluctuations, voltage dips, and short-term interruptions; voltage imbalances and frequency variations; and the effects of the power supply. High-frequency interference includes immunity to public and industrial environments and immunity to electromagnetic fields.
Electromagnetic emissions should be adapted to the actual operating environment conditions as much as possible. To ensure basic protection requirements, basic emission limits for low frequencies and high frequencies are specified for public and industrial environments, respectively.
Audio noise tests should be conducted in locations where there are no sound-reflecting surfaces within a 2m radius. During testing, interference from ambient noise should be minimized as much as possible.
Additional tests are required for other performance aspects not covered by the above tests. These should be requested when ordering and agreed upon.
5.3 Inverter-related tests
1) Steady-state performance
The steady-state performance of the inverter's transmission variables, such as output speed and torque, should be tested. The steady-state performance of the feedback control system should be illustrated using the selected deviation band (steady-state). The variable range of the specified operating and usage deviation band should be met.
2) Dynamic test
Current limit and current loop tests are used to characterize the dynamic performance of the frequency converter and are independent of the driven equipment. The following three tests can be performed at near 0, 50% of the basic speed, 100% of the basic speed, and the maximum field weakening speed (NM).
a) Current limit
Increasing the load requires the inverter to reach its preset current limit. (Another method is to increase the speed step to a sufficiently large moment of inertia, generating a transient load that causes the inverter to reach the set current limit.) At this point, the current rise time, overshoot and duration, and damping characteristics can be analyzed.
b) The bandwidth of the current loop can be determined by harmonic analysis of the response between the current setting and the current measurement (feedback). Amplitude and displacement must be checked. This test should be performed within the linear or quasi-linear region.
c) Step response to current setting
Speed ring
Provide and correctly select the speed increment for the following test. This test can be performed under no-load or light-load conditions.
a) The current limit is reached and an inspection is performed;
b) Measure the transmission output speed response without reaching any limits (typically at 50% of the basic speed, 100% of the basic speed, and the maximum speed NM of field weakening).
Torque pulsation
If a highly sensitive speed measuring device is coupled to the shaft, the relevant level of air gap torque pulsation can be measured by the change in speed under no-load conditions.
Automatic restart
If an automatic restart function is provided, it should be tested during the specified power outage period. This function should be coordinated with emergency shutdown and can be disabled if necessary.
3) Energy-efficient braking and energy-efficient deceleration
Regenerative braking and regenerative deceleration are two operational functions, and their characteristics should be agreed upon by the user and the manufacturer/supplier. Other performance requirements should be determined jointly by the buyer or manufacturer and the buyer.
6. Product Information
6.1 Mark
The following items should be marked on the nameplate of the frequency converter:
a) Manufacturer's name
b) Inverter model, serial number, and year of manufacture
c) Input the rated value
d) Output Rated Value
6.2 Items to be provided
The following information should be provided with the equipment:
Specify the information required for calibration elements, devices, and components to be adjusted by the user;
Select the appropriate information for input and output protection and grounding;
The instruction manual includes all the information needed to operate the equipment;
EMC information as specified in GB12668.3 ;
Security warning;
Output phase sequence.
The following information should be provided or made available to the user.
Maintenance and user manuals, including information on locating and replacing faulty components or electronic parts; the language should be the language of the country of origin, or a language agreed upon by the manufacturer and the customer;
Rated energy absorption values for energy-consumption braking deceleration and energy-consumption braking parking circuits.
