5－5

55

Dynamic Braking

Introduction

The purpose of dynamic braking is to improve the ability of the inverter to stop

(decelerate) the motor and load. This becomes necessary when an application has some or all of the following characteristics:

ξHigh load inertia compared to the available motor torque

ξThe application requires frequent or sudden changes in speed

ξSystem losses are not great enough to slow the motor as needed

When the inverter reduces its output frequency to decelerate the load, the motor can temporarily become a generator. This occurs when the motor rotation frequency is higher than the inverter output frequency. This condition can cause the inverter DC bus voltage to rise, resulting in an over-voltage trip. In many applications, the over-voltage condition serves as a warning signal that we have exceeded the deceleration capabilities of the system. The X200 inverter can connect to an external braking unit, which sends the regenerative energy from the motor during deceleration to the optional braking resistor(s). The dynamic braking resistor serves as a load, developing heat to stop the motor just as brakes on an automobile develop heat during braking.

A switching circuit and power resistor are the main components of the dynamic braking unit that includes a fuse and thermally activated alarm relay for safety. However, be careful to avoid overheating its resistor. The fuse and thermal relay are safeguards for extreme conditions, but the inverter can maintain braking usage in a safe zone.

Dynamic Braking Usage

Dynamic braking usage must follow guidelines to avoid overheating. The timing diagram to the right shows the output frequency versus time. Dynamic braking is in effect during the deceleration ramp, and has the following constraints:

ξDynamic braking maximum duty cycle = 10%, where Tb/Tc ” 0.1 sec.

Output freq.

Dynamic braking

Tb t

Tc

Inverter Accessories

Dynamic braking maximum continuous ON time

Tb ” 10 sec.

Selecting Braking Resistors for External Braking Units

System

200V Class Inverters  The following tables specify the braking options for 200V class X200 inverters and the braking torque for each option. You can connect a single braking unit to the inverter, or two braking units for additional stopping torque.

Inverter

+



Braking

unit

Braking

unit

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Hitachi CP-X200 instruction manual Dynamic Braking Usage, Selecting Braking Resistors for External Braking Units
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CP-X200 specifications

The Hitachi CP-X200 is a versatile and robust projector designed to cater to the needs of educational and business environments. It combines affordability with high-quality performance, making it an attractive option for various presentations and multimedia applications.

At the heart of the CP-X200 is its high brightness capability, with a lumen output of 3,000 ANSI lumens. This feature enables the projector to deliver clear and vibrant images even in well-lit rooms. The resolution of XGA (1024 x 768 pixels) ensures that text and graphics are sharp, making it suitable for everything from classroom lectures to corporate presentations.

One of the standout characteristics of the Hitachi CP-X200 is its advanced lamp technology. The projector uses a long-lasting lamp that can provide up to 5,000 hours of usage in standard mode, allowing for extended intervals between lamp replacements. Additionally, the ECO mode can further enhance the lamp life, extending its longevity while reducing energy consumption.

The CP-X200 is equipped with a variety of connectivity options, including HDMI, VGA, and composite inputs, allowing users to easily connect it to various devices such as laptops, DVD players, and other multimedia systems. The inclusion of USB and RS-232 interfaces ensures compatibility with different control systems, making it a flexible choice for diverse setups.

Another significant feature is the projector's built-in 10-watt speaker, which provides decent audio output, eliminating the need for external speakers in smaller venues. The speaker system enhances presentations, ensuring that audio and visuals are cohesive, promoting better audience engagement.

Portability is another key aspect of the Hitachi CP-X200, which weighs just around 3.5 kg (approximately 7.7 lbs), allowing for easy transport between locations. Its compact design makes it suitable for both fixed installations and mobile use, catering to professionals who require a projector that adapts to various environments.

The user-friendly interface and robust remote control enhance the projector's operability, providing easy access to essential functions. Additionally, features such as auto keystone correction adjust the image to maintain consistent quality even when the projector is not perfectly aligned with the screen.

In summary, the Hitachi CP-X200 is a feature-rich projector that embodies reliability, performance, and ease of use. Its combination of high brightness, various connectivity options, long lamp life, portability, and integrated audio makes it an excellent choice for education and business professionals seeking a dependable presentation solution.
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