The Elevator Inverter
Elevators are an important means of transport, especially in high-rise buildings. They are a complex engineering solution that must meet increasing demands for reliability, safety and creation of comfortable conditions for passengers.
One way to achieve these goals is to use a frequency inverter. This helps control motor speed and energy usage, which ultimately saves money.
1. Load Sensorless Start Compensation Technology
The load sensorless start compensation technology used in Elevator inverters helps smooth start-ups. Compared with traditional methods that rely on the rotor position to start, this technology alleviates jitter and reverse slip at startup, ensuring stable lift startup and a comfortable ride quality.
The inverter is also equipped with a unique PWM dead zone compensating technology that improves energy efficiency. This technology allows the inverter to run at lower speed during startup and reduces switch losses. This inverter is also able to achieve a maximum junction temperature of 175°C, which results in less power loss and higher performance.
Moreover, this inverter is equipped with low-voltage, high-power technology that supports a variety of control modes and ensures accurate torque adjustment at zero speed without the need for load weighing equipment. This technology saves energy and costs while offering a smoother ride experience to the elevator passengers.
Further improvements of this inverter include a novel ABZ encoder for synchronous motors, low switching loss and a maximum junction temperature of 175°C. The inverter also offers a variety of features that help increase elevator safety.
For example, the inverter can be used to support a Elevator inverter positive pump flow rate when starting and stopping the car in an elevator system that may be adapted to compensate for pressure drop or loss due to a hydraulic pump leakage. This allows for a simplification of the hydraulic system by omitting complicated control valves, which can result in cost-efficiency.
In addition, this inverter can provide a smoother ride-quality by softening down travel speed of the elevator. This is achieved by running the inverter at a leakage speed, which is a speed where hydraulic pressures drops due to a pump leakage and/or a pressure drop inherent in the elevator system.
2. Zero-Speed Torque Compensation
Zero-speed torque compensation allows a motor to be adjusted at zero speed without the need for load weighing equipment, saving money and space. This feature also helps reduce power loss and energy consumption.
To achieve zero-speed torque compensation, the gain for the state feedforward torque command is based on the Physical inertia, viscous damping, and static friction parameter values. In addition, the state feedforward torque calculation uses filtered speed and acceleration from the state filter.
This type of control is a good choice for systems where the motor may become jammed or stalled. Having this function allows the motor to be set up so that it isn’t putting out an excess amount of torque when in its stall mode.
Unlike series resistance speed control, this type of motor speed control is completely independent of the battery and does not consume any additional energy. This feature makes it an excellent choice for elevator systems with a limited battery capacity.
Another advantage of this type of speed control is that it can be adjusted for the motor speed of a particular load. This can help prevent damage to the motor or the load when the motor reaches its maximum torque capability.
The Coil Driver(tm) optimizes the motor in real-time and seamlessly, under demand, allowing for efficiency optimization at each operating mode, resulting in smarter energy consumption, better performance, and lower system cost. It does this by calculating electrical losses and using tabulated data for low speeds and torques to provide accurate results.
3. Low Switch Loss
Elevator inverters typically consist of a series of high voltage switch devices, including IGBTs and MOSFETs. These switching devices are designed to rapidly change from on to off states in order to reduce power losses, improve inverter efficiency, and minimize the risk of exceeding their breakdown voltages. However, fast switch changes also introduce a high rate of dV/dt and dI/dt voltage and current transients into the system that can be detrimental to the performance of the device. In addition, these switching transients can lead to excessive heat generation in the switching circuit and the junction of the switch device itself.
In order to address these issues, some inverters are equipped with a device that is able to slow down a switch to prevent it from overshooting its maximum voltage. This solution increases the switch resistance in the circuit, which decreases the efficiency of the device and the inverter. Moreover, this solution is not always effective and may result in unnecessary costs and weight.
In a preferred implementation, a controller 215 is used to monitor one or more parameters indicative of a potential transitory voltage overshoot condition and dynamically adjust the default operation of a gate driver 210 to at least reduce the risk of occurrence of the potential transitory voltage overshoot. This operation may be accomplished by generating time-varying drive control signals for the gate driver and setting DC bias supply voltages (e.g., positive and negative rail voltages) for the switches in the gate driver responsive to the controller signals.
4. Maximum Junction Temperature 175°C
A key element to ensure long service life is junction temperature. A higher junction temperature means a lower maximum available power and a greater chance of failure. The maximum junction temperature is specified in the Absolute Maximum Ratings table of most Si, GaAs and AlGaAs PIN diode switches.
Generally, the maximum junction temperature of 175°C is considered to be a safe and robust level for most applications. However, some types of devices such as wideband-gap silicon devices are expected to exceed 150°C or even 200°C in the future. Therefore, new packaging and joining technologies are required to increase reliability of these devices.
A laboratory study tested the power cycling reliability of a 1200V, 150A IGBT module in an air-cooled fixture at both maximum junction temperatures of 150degC and 175degC. Each IGBT module was cycled for 2000 elapsed power cycles to obtain collector-emitter saturation voltage and junction-to-case thermal resistance data. Weibull analyses of this data showed shape parameters of 8.6 and 8.8 for the 150degC and 175degC maximum junction temperature tests, respectively. These results are significantly higher than those obtained with the current standard test of 1000 hours for a comparable IGBT. The results are encouraging for applications such as automotive, wind power and traction.
5. High Performance
The elevator inverter combines the advantages of different types of speed control. One common type is series resistance speed control which slows the motor down by lowering voltage inside the motor by connecting a resistor in series. It is more energy-efficient than frequency converter speed control, but it has a few disadvantages as well.
Other kinds of speed control, such as regenerative drive, convert braking force to useable energy and feed it back into the building Elevator inverter system. They improve the efficiency of a systems by up to 40 percent.
In addition, it is possible to install battery backup in a power failure situation. In this case, the lift inverter senses the power failure and automatically generates AC power from the batteries to keep the elevator running for a few seconds until the main supply is resumed.
Destination control also reduces travel time by allowing passengers to register their floor calls before boarding an elevator. Once they board, the system distributes adjacent stops among cars in the bank so that passengers are not always stranded between floors.
Another common feature of the modern elevator is a regenerative braking unit. It is a specialized device that takes the braking force from the counterweight during ascent and the load cab during descent and turns it into energy. This regenerated energy is then fed back into the system to power other equipment.
The inverter is a crucial part of an elevator. It controls the traction machine and ensures the smooth operation of the whole system. It is the key to ensuring safe and comfortable rides for both passengers and elevator workers.
