Abstract : This paper discusses in detail the relevant technologies of four-quadrant vector frequency converters in application, including application conditions, braking principle, braking characteristics, implementation conditions, working status, technical performance, circuit composition, application precautions, as well as the performance and technical parameters of high-voltage four-quadrant frequency converters and application scenarios.
1. Introduction - Overview of Four-Quadrant Vector Frequency Converters
When the motor power is large (≥100kW), the equipment's GD 2 is large, or when the equipment operates repeatedly for short periods of time, resulting in a large speed reduction from high to low speed and a short braking time, energy regenerative braking devices can be used to reduce energy loss during braking and convert kinetic energy into electrical energy to feed back to the grid, thereby achieving energy saving. Conditions for regenerative braking include:
(1) During the deceleration process of the motor from high speed ( fH ) to low speed ( fL ), the frequency suddenly decreases. Due to the mechanical inertia of the motor, the slip s < 0, and the motor is in the generating state. At this time, the back electromotive force E > U (terminal voltage).
(2) From the moment the motor starts running at a certain fN to the moment it stops at fN = 0, the motor enters a generating state during this process. At this time, the back electromotive force E > U (terminal voltage).
(3) Potential energy (or potential energy) load, such as when a crane lowers a heavy object, the actual speed n is greater than the synchronous speed n0 . At this time, the motor will also be in the state of generating electricity. Of course, E > U is inevitable.
2. Energy regenerative braking principle
As is well known, the bridge rectifier circuit of a general-purpose frequency converter is three-phase uncontrollable, so it cannot achieve bidirectional energy transfer between the DC circuit and the power supply. The most effective way to solve this problem is to use active inverter technology, as shown in Figure 1.
Figure 1. Connection circuit when the frequency converter and the power regenerative converter are combined.
The regenerated electricity is inverted into AC power with the same frequency and phase as the grid and fed back to the grid, as shown in Figure 2, thereby achieving braking.
Figure 2. Composition of a current tracking PWM rectifier
As shown in Figure 2, it employs a current-tracking PWM rectifier configuration, which facilitates bidirectional power flow and provides a fast dynamic response. This topology allows for complete control over the exchange of reactive and active power between the AC and DC sides, achieving an efficiency of up to 97%, resulting in significant economic benefits. Heat loss is only 1% of that in regenerative braking, and it does not pollute the power grid. Therefore, regenerative braking is particularly suitable for applications requiring frequent braking, especially when the motor power is relatively high. This leads to significant energy savings, averaging approximately 20% depending on operating conditions.
3. Characteristics of regenerative braking
(1) It can be widely used in energy-saving operation of PWM AC drive energy feedback braking.
(2) The feedback efficiency is high, reaching 97%, and the heat loss is small, only 1% of the energy consumption.
(3) The power factor is approximately 1.
(4) The harmonic current is small, and the pollution to the power grid is minimal, which is a green and environmentally friendly feature.
(5) Saves investment and makes it easy to control harmonics and reactive power on the power supply side.
(6) In multi-motor drive, the regenerative energy of each single machine can be fully utilized.
(7) It has a significant energy-saving effect (related to the power of the motor and its operating conditions).
(8) When multiple devices in the workshop are powered by a shared DC bus, the energy from the regenerative braking can be directly returned to the DC bus to supply other devices. Calculations show that this can save on the capacity of the regenerative inverter, and may even eliminate the need for a regenerative inverter altogether.
4. What are the conditions for implementing the four-quadrant model (Figure 3)?
Three necessary and sufficient conditions for achieving energy feedback
(1) The load must be a potential energy or potential energy load, such as elevators, conveyor belts, mine cages, cranes (moving up and down), etc.
(2) The feedback device must ensure three electrical parameters, namely, phase difference ±5°, voltage difference ±5V, and frequency difference ±0.5Hz, so that the electrical energy can be fed back into the power grid.
(3) The main circuit of the inverter is generally a voltage-type CSV AC-DC-AC topology circuit. Its rectifier AC/DC circuit must be composed of controllable rectifier, i.e. IGBT, which is the same as the PWM circuit of the inverter DC/AC, instead of diode, three-phase six-pulse uncontrolled rectifier.
5. Technical Performance Parameters
Braking method | Bidirectional automatic voltage tracking control mode |
reaction time | Less than 1ms, with multiple noise filters |
Permissible voltage grid | AC300~400V, 45~66Hz |
Operating voltage | DC700V, error 2V |
Hysteresis voltage | 20V |
Braking torque | 150% |
Feedback methods | Sine wave current mode |
Current distortion | Below 5% |
Built-in reactor | have |
Built-in noise filter | have |
Design work system | long |
Protect | Overheating, overcurrent, short circuit |
Protection level | IP00 |
6. Composition of a four-quadrant vector frequency converter
(1) Ordinary frequency converter + feedback device
Main circuit wiring method (Figure 4)
Figure 4 Main circuit wiring method
The main circuit wiring of the feedback device is very simple. When used with a frequency converter, simply connect the DC input terminals "DC(+)" and "DC(-)" of the feedback device to the positive and negative terminals of the DC bus of the frequency converter, and connect the AC feedback output terminals "A", "B" and "C" of the feedback device to the same power supply as the input terminal of the frequency converter.
Application Notes
(1) The feedback device is an external reactor structure, and an external reactor is required for use. When wiring, the terminals of the reactor must correspond one-to-one with the terminals on the feedback device. If the connection sequence is incorrect, it may damage the feedback device or even cause a fire.
(2) When wiring, pay attention to the polarity of the DC input terminals “DC (+)” and “DC (-)” of the feedback device. If the polarity is reversed, it may cause damage to the equipment or even cause a fire.
(3) In order to prevent the leakage current from harming the human body, the grounding terminal “PE” of the feedback device should be reliably grounded.
(4) The feedback device will automatically detect the phase of the power grid and work in sync with the power grid. Therefore, the AC feedback output terminals “A”, “B” and “C” of the feedback device are not polarity required to connect to the power grid.
(2) Composition of the main circuit of the four-quadrant vector frequency converter (Figure 5)
Figure 5. Main circuit composition of a four-quadrant frequency converter
7. Introduction to High-Voltage Four-Quadrant Vector Inverter
(1) Overview of high voltage four-quadrant vector frequency converter
The four-quadrant variable frequency speed control system is based on controllable rectification technology and consists of ordinary inverter technology. It does not require additional inverter units or separate braking units. It can send the electrical energy fed back by the motor during power generation back to the grid, realizing the four-quadrant operation of the motor.
High-frequency PWM technology is used to dynamically adjust the waveform and phase of the system's input current in real time, so that it closely follows the phase of the input voltage, in order to achieve the control target of COSφ=±1 and no harmonics.
Input voltage: 380VAC 660VAC 1140VAC
Power range: 380VAC: 75KW ~ 220KW
660VAC: 132KW~ 315KW
1140VAC: 132KW~ 500KW
Overload capacity: 150%~200%
(2) Performance overview of high voltage four-quadrant vector frequency converter
The input current is a sine wave.
In motor mode, the input current and input voltage are in phase, and COSφ=1.
In generator mode, the input current and input voltage are out of phase, and COSφ = -1.
The electrical energy fed back by the motor can be quickly fed back to the power grid.
Ideal for systems requiring frequent forward and reverse rotation, rapid braking, or potential energy loads.
200% (150%) overload for two minutes
The controllable rectifier section can operate independently and form a four-quadrant system with other models of ordinary frequency converters.
The controlled rectifier section can be used as a separate active filter.
(3) Technical parameters of high voltage four-quadrant vector frequency converter
660V Four-Quadrant Frequency Inverter | ||||||||
Rated power (KW) | 132 | 160 | 185 | 220 | 250 | 280 | 315 | 600 |
Rated output current (A) | 155 | 179 | 207 | 250 | 280 | 313 | 352 | 671 |
Rated input current (A) | 137 | 161 | 186 | 225 | 252 | 282 | 317 | 604 |
Input voltage (V) | 660VAC±20% | |||||||
Input frequency | 48~62Hz | |||||||
Input power factor | 1 | |||||||
1140V Four-Quadrant Frequency Inverter | ||||||||
Rated power (KW) | 500 | |||||||
Rated output current (A) | 330 | |||||||
Rated input current (A) | 290 | |||||||
Input voltage (V) | 1140VAC±20% | |||||||
Input frequency | 48~62Hz | |||||||
Input power factor | 1 | |||||||
Output voltage | 0~Rated input voltage | |||||||
Output frequency | 0~200Hz | |||||||
Overload capacity | 150%, lasting for 1 minute | |||||||
Control method | Both rectifier and inverter are sensorless vector control, using sinusoidal PWM. | |||||||
Frequency accuracy | 0.1Hz | |||||||
Frequency resolution | Maximum set frequency × 0.2% | |||||||
Communication function | RS-485 communication interface (optional), supports Modbus, Lonworks, Metasys | |||||||
Acceleration/deceleration time setting | Independent acceleration/deceleration curves (with S-curve) | |||||||
Rectifier section | Automatic operation mode; manual control mode can be used during debugging. | |||||||
Analog Input/Output | 0~5V, 0~10V, 0~20mA, 4~20mA | |||||||
Numeric input | 5 programmable digital input terminals | |||||||
Relay output | Two normally open/normally closed relays with programmable control | |||||||
Local/Remote Control | Includes functions such as start (forward/reverse), stop, reset, and speed setting. | |||||||
Display screen | 16-digit, 2-line number, automatic backlight and contrast adjustment | |||||||
Display variables | Output frequency, motor speed, load rate, output current, output power/voltage, temperature, I²t process variables | |||||||
Protection function | Current limiting protection, overvoltage/undervoltage protection, short circuit protection, ground fault protection, phase loss protection, motor overload protection, and overheat protection. | |||||||
Operating temperature | The temperature range is 0-40℃; when it reaches 50℃, the amount must be reduced. | |||||||
(4) Technical Specifications of High Voltage Four-Quadrant Vector Inverter
Most high- and medium-voltage frequency converters currently on the market are single-quadrant converters, suitable for loads such as fans and pumps, but unsuitable for applications with potential load characteristics, such as hoists. This is because these loads operate in four-quadrant mode, frequently in a regenerative braking state. The generated energy must be fed back to the grid or dissipated through a resistor; otherwise, the frequency converter will be damaged. Resistive braking reduces conversion efficiency and results in a very large frequency converter, hindering installation and maintenance. Grid-feedback braking is the most advanced method, offering advantages such as high frequency converter efficiency, small device size, and high power factor, but it is technically more challenging.
In light of the above, the following technical requirements are hereby proposed:
1. Power supply voltage levels: 3kV, 6kV, 10kV
2. Motor power range: 500~5000kW
3. Frequency conversion methods: AC-DC-AC
4. Frequency Conversion Structure: Unit series multi-level (or three-level, two-level)
5. Control method: High-performance vector control
6-frequency inverter output: 0~50Hz
7. Zero-speed torque: 120% of rated torque at 0Hz
8. Starting torque: 150% of rated torque at 0.1~50Hz
9. Input power factor: ≥0.97
10. Overall machine efficiency: ≥0.96
11 overload capacity; 200% Ie for one minute
12. Host Communication: RS485-Modbus Protocol
8. Main Application Scenarios
Energy feedback systems offer far superior performance compared to regenerative braking and DC braking. Therefore, in recent years, many organizations have requested energy feedback devices based on the characteristics of their equipment. However, previously, only a few foreign companies, such as ABB, Siemens, Fuji, Yaskawa, and Vacon, could provide these products, leaving the domestic market almost entirely untapped. Currently, Shenzhen Canon Electronics Co., Ltd., using Canadian technology, has begun specializing in the manufacturing and application of frequency converter braking devices. Shenzhen Invt Electric Co., Ltd. can also produce regenerative braking and regenerative braking products.
The use of regenerative braking is even more urgent in the following industries:
(1) A high-speed separator for glucose crystallization in a pharmaceutical factory.
(2) High-speed separator for civilian sugar-granulated sugar crystallization
(3) Paint mixers and agitators used in mixing plants
(4) Commonly used plastic dyeing machines, batching machines, and mixers
(5) Medium and large-sized washing machines, dewatering machines and spin dryers used in laundry plants
(6) Laundry and sheet washing machines used in hotels, guesthouses, and laundromats.
(7) Medium and high speed centrifuges and separators from various specialized centrifuge machinery plants
(8) Various tilting equipment such as converters, molten steel ladles, etc.
(9) The operating status of the main lifting hook of lifting machinery such as bridge cranes, tower cranes, and gantry cranes when the load is lowered.
(10) All high-load conveyor belts (e.g., conveying materials below)
(11) Mine hoist (for carrying people or loading materials), inclined shaft mine car
(12) Opening and closing devices for various gates
(13) Paper roller motors for papermaking and drawing machines for chemical fiber machinery
In conclusion , this article provides insights into the technical aspects of four-quadrant frequency converter applications. For certain loads, such as high-speed separators, elevators, cranes, material conveyors, mine cages, and gate opening and closing systems, only four-quadrant frequency converters can provide optimal electrical drive performance and significant energy savings. This concise yet insightful article offers valuable information; a preview is highly recommended.
